CN113495316A

CN113495316A - Polarizing plate and image display device using the same

Info

Publication number: CN113495316A
Application number: CN202110341359.5A
Authority: CN
Inventors: 武藤清; 斋藤邦智; 村上洋平; 竹内智康; 住田幸司
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-04-01
Filing date: 2021-03-30
Publication date: 2021-10-12
Also published as: TW202204986A

Abstract

The invention provides a polarizing plate which can inhibit the reduction of transmissivity even in the case of being used for an image display device with an interlayer filling structure, for example, even when being exposed to a high-temperature environment with the temperature of 105 ℃. The polarizing plate comprises a polarizing element formed by adsorbing and orienting a dichroic dye on a polyvinyl alcohol resin layer, and a transparent protective film, wherein the polyvinyl alcohol resin used for forming the polyvinyl alcohol resin layer has a boron adsorption rate of 5.70 mass% or more, and the water content of the polarizing element is equal to or higher than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

Description

Polarizing plate and image display device using the same

Technical Field

The present invention relates to a polarizing plate. The present invention also relates to an image display device in which one surface of the polarizing plate is bonded to an image display unit and the other surface is bonded to a transparent member such as a touch panel or a front panel.

Background

Liquid Crystal Displays (LCDs) are widely used not only in liquid crystal televisions, but also in mobile devices such as personal computers and mobile phones, in-vehicle applications such as car navigation, and the like. In general, a liquid crystal display device includes a liquid crystal panel member in which polarizing plates are bonded to both sides of a liquid crystal cell with an adhesive, and displays images by controlling light from a backlight member with the liquid crystal panel member. In recent years, organic EL display devices have been widely used in mobile devices such as televisions and cellular phones, and in vehicle-mounted applications such as car navigation, as well as liquid crystal display devices. In an organic EL display device, a circularly polarizing plate (a laminate including a polarizing element and a λ/4 plate) may be disposed on the visible-side surface of an image display panel in order to suppress external light from being reflected at a metal electrode (cathode) and observed as a mirror surface.

As described above, polarizing plates have been increasingly mounted in vehicles as a member of liquid crystal display devices and organic EL display devices. Polarizing plates used in image display devices for vehicles are often exposed to high-temperature environments as compared with other applications for mobile devices such as televisions and cellular phones, and therefore, are required to have less characteristic change at higher temperatures (high-temperature durability).

On the other hand, for the purpose of preventing damage to the image display panel due to impact from the outer surface, a front panel (also referred to as a "window layer") such as a transparent resin plate or a glass plate is provided on the visible side of the polarizing plate of the image display panel. In addition, in a display device including a touch panel, a configuration is widely adopted in which the touch panel is provided on the viewing side of a polarizing plate of an image display panel, and a front transparent plate is provided on the viewing side of the touch panel.

In such a configuration, if an air layer is present between the image display panel and a transparent member such as a front transparent plate or a touch panel, glare of reflection of external light (japanese character: external light reflection り Write み) due to reflection of light at an air layer interface is generated, and the visibility of the screen tends to be lowered. Therefore, a configuration (hereinafter, sometimes referred to as an "interlayer filling configuration") in which a space between the polarizing plate and the transparent member disposed on the viewing-side surface of the image display panel is filled with a layer (hereinafter, sometimes referred to as an "interlayer filler") which is usually a solid layer other than an air layer has been promoted, and a configuration in which the space is filled with a material having a refractive index close to that of the material is preferably used. As the interlayer filler, an adhesive or a UV curable adhesive is used for the purpose of suppressing a reduction in visibility due to reflection at an interface and bonding and fixing the members (for example, see patent document 1).

The above interlayer filling structure is being widely used in mobile devices such as cellular phones which are often used outdoors. In addition, in recent years, due to the increasing demand for visibility, in vehicle-mounted applications such as car navigation systems, the use of an interlayer filling structure in which a front transparent plate is disposed on the surface of an image display panel and the space between the panel and the front transparent plate is filled with an adhesive layer or the like has been studied.

However, it has been reported that when the image display device having such a configuration is left to stand at a temperature of 95 ℃ for, for example, 200 hours, a significant decrease in transmittance is observed in the central portion of the polarizing plate surface. On the other hand, it has been reported that, in the case of a polarizing plate alone, no significant decrease in transmittance is observed even when the polarizing plate is left to stand in an environment at a temperature of 95 ℃ for 1000 hours. From these results, it has been reported that a significant decrease in the transmittance of a polarizing plate in a high-temperature environment is a problem unique to the case where an image display device using an interlayer filling structure in which one surface of a polarizing plate is bonded to an image display unit and the other surface is bonded to a transparent member such as a touch panel or a front transparent plate is exposed to a high-temperature environment (patent document 2).

As a solution to this problem, patent document 2 proposes a method of suppressing a decrease in transmittance by setting the amount of water per unit area of the polarizing plate to a predetermined amount or less and setting the saturated water absorption amount of the transparent protective film adjacent to the polarizer to a predetermined amount or less.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 11-174417

Patent document 2: japanese patent laid-open publication No. 2014-102353

Disclosure of Invention

Problems to be solved by the invention

However, when the temperature of the test environment is increased to 105 ℃ and the test environment is exposed to the high temperature environment for a certain period of time, the conventional polarizing plates may not sufficiently suppress the decrease in transmittance. An object of the present invention is to provide a polarizing plate having an excellent effect of suppressing a decrease in transmittance even when used in an image display device configured by interlayer filling, even when exposed to a high temperature environment, for example, at a temperature of 105 ℃, and an image display device using the polarizing plate.

Means for solving the problems

The invention provides a polarizing plate, an image display device, and a method for manufacturing the polarizing plate.

A polarizing plate comprising a polarizing element obtained by adsorbing and orienting a dichroic dye onto a polyvinyl alcohol resin layer, and a transparent protective film,

the polyvinyl alcohol resin used for forming the polyvinyl alcohol resin layer has a boron adsorption rate of 5.70 mass% or more,

the water content of the polarizing element is not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30%, and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

the polarizing plate has a water content of not less than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

[ 3 ] the polarizing plate according to any one of [ 1] and [ 2], wherein the polarizing element has a boron content of 4.0 mass% or more and 8.0 mass% or less.

The polarizing plate according to any one of [ 1] to [ 3 ], further comprising an adhesive layer for bonding the polarizing element and the transparent protective film,

the adhesive layer is a coating layer of a water-based adhesive.

The polarizing plate according to [ 5 ] or [ 4 ], wherein the aqueous adhesive has a methanol concentration of 10 to 70 mass%.

The polarizing plate according to any one of [ 4 ] and [ 5 ], wherein the aqueous adhesive contains a polyvinyl alcohol resin.

The polarizing plate according to any one of [ 4 ] to [ 6 ], wherein the adhesive layer has a thickness of 0.01 μm or more and 7 μm or less.

The polarizing plate according to any one of [ 1] to [ 7 ], wherein the transparent protective film is a retardation film comprising a 1 st optical compensation layer and a 2 nd optical compensation layer in this order from the polarizing element side,

the absorption axis of the polarizing element is substantially orthogonal to the slow axis of the 1 st optical compensation layer,

the slow axis of the 1 st optical compensation layer is substantially parallel to the slow axis of the 2 nd optical compensation layer,

the 1 st optical compensation layer and the 2 nd optical compensation layer satisfy the following formulas (1) to (4):

80nm≤Re₁(590)≤120nm (1)

20nm＜Re₁(590)≤60nm (2)

1＜Nz₁＜2 (3)

－4＜Nz₂＜－1 (4)。

[ 9 ] the polarizing plate according to any one of [ 1] to [ 8 ], wherein the polarizing plate is used for an image display device,

in the image display device, a solid layer is provided in contact with both surfaces of the polarizing plate.

An image display device comprising an image display unit, a 1 st adhesive layer laminated on a viewing surface of the image display unit, and the polarizing plate according to any one of [ 1] to [ 9 ] laminated on the viewing surface of the 1 st adhesive layer.

The image display device according to [ 10 ] above, further comprising a 2 nd adhesive layer laminated on the viewing side surface of the polarizing plate, and a transparent member laminated on the viewing side surface of the 2 nd adhesive layer.

The image display device according to [ 11 ], wherein the transparent member is a glass plate or a transparent resin plate.

[ 13 ] the image display device according to [ 11 ], wherein the transparent member is a touch panel.

[ 14 ] A method for producing a polarizing plate according to [ 1],

a method for manufacturing a polarizing plate having a polarizing element and a transparent protective film,

the manufacturing method comprises:

a water content adjustment step of adjusting the water content of the polarizing element so that the water content is equal to or higher than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%; and

and a laminating step of laminating the polarizing element and the transparent protective film.

[ 15 ] A method for producing a polarizing plate according to [ 2],

the manufacturing method comprises:

a water content adjustment step of adjusting the water content of the polarizing plate so that the water content is equal to or higher than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%; and

Effects of the invention

According to the present invention, it is possible to provide a polarizing plate which can suppress a decrease in transmittance when exposed to a high temperature environment such as a temperature of 105 ℃ and is excellent in high temperature durability even when used in an image display device constituted by interlayer filling, and further, an image display device in which a decrease in transmittance in a high temperature environment is suppressed by using the polarizing plate of the present invention.

Detailed Description

The following description will explain embodiments of the present invention, but the present invention is not limited to the following embodiments.

[ polarizing plate ]

The polarizing plate according to the embodiment of the present invention includes a polarizing element in which a dichroic dye is adsorbed and oriented in a layer containing a polyvinyl alcohol resin, and a transparent protective film. The polarizing element is formed using a polyvinyl alcohol resin having a boron adsorption rate of 5.70 mass% or more. The polarizing plate of the present embodiment has at least one of the following features (a) and (b).

(a) The water content of the polarizing element is not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30%, and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

(b) The polarizing plate has a water content of not less than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than an equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%.

The polarizing plate of the present embodiment has at least one of the features (a) and (b) described above, and the polyvinyl alcohol resin used in the polarizing element has a boron adsorption rate within the above range, whereby the decrease in transmittance can be suppressed even when the constituent elements of the image display device configured as an interlayer filling are exposed to a high-temperature environment for a long time.

< polarizing element >

As the polarizing element of the present invention in which a layer containing a polyvinyl alcohol (hereinafter also referred to as "PVA") resin (hereinafter also referred to as "PVA-based resin layer") and a dichroic dye are adsorbed and oriented, a known polarizing element can be used. Examples of such a polarizing element include a polarizing element formed by using a PVA-based resin film, dyeing the PVA-based resin film with a dichroic dye, and uniaxially stretching the PVA-based resin film; the coating film is formed by using a laminated film obtained by applying a coating liquid containing a PVA-based resin to a base film, dyeing the PVA-based resin layer as a coating layer of the laminated film with a dichroic dye, and uniaxially stretching the laminated film.

The polarizing element is formed of a PVA resin obtained by saponifying a polyvinyl acetate resin. The polyvinyl acetate resin may be a copolymer of vinyl acetate and another monomer copolymerizable with vinyl acetate, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate. Examples of the other copolymerizable monomer include unsaturated carboxylic acids, olefins such as ethylene, vinyl ethers, and unsaturated sulfonic acids.

In the present invention, the PVA-based resin layer is formed of a PVA-based resin having a boron adsorption rate of 5.70 mass% or more. That is, the PVA-based resin at the stage of the raw material before dyeing and stretching has a boron adsorption rate of 5.70 mass% or more. By using such a PVA-based resin, the transmittance is less likely to decrease even when exposed to a high temperature environment, for example, at a temperature of 105 ℃. The polarizing element is preferably produced using a PVA-based resin having a boron adsorption rate of 5.72 mass% or more, more preferably 5.75 mass% or more, and most preferably 5.80 mass% or more. The PVA-based resin preferably has a boron adsorption rate of 10 mass% or less. By using such a PVA-based resin for the polarizing element, it is not necessary to set the boric acid concentration in the boric acid treatment tank to a high concentration, the treatment time of the boric acid treatment can be shortened, a desired polarizing element can be easily obtained, and the productivity of the polarizing element can be improved. When the boron adsorption rate of the PVA-based resin is 10 mass% or less, an appropriate amount of boron is introduced into the PVA-based resin layer, and the shrinkage force of the polarizing element is easily reduced. As a result, when incorporated into an image display device, problems such as peeling between the polarizing plate and other members such as the front panel are unlikely to occur. Further, when the boron adsorption rate of the PVA-based resin is less than 5.70%, the transmittance is liable to be lowered even when exposed to a high temperature environment having a temperature of, for example, 105 ℃. The boron adsorption rate of the PVA-based resin can be measured by the method described in the examples described later.

The boron adsorption rate of the PVA-based resin is a characteristic of the PVA-based resin in which the intervals between molecular chains and the crystal structure in the PVA-based resin are reflected. It is considered that the PVA-based resin having a boron adsorption rate of 5.70 mass% or more has an increased interval between molecular chains and fewer crystals than the PVA-based resin having a boron adsorption rate of less than 5.70 mass%. Therefore, it is presumed that boron is likely to enter the PVA based resin layer and that the polyene formation is likely to be prevented in a high temperature environment (Japanese text: ポリエン).

The boron adsorption rate of the PVA-based resin can be adjusted by, for example, subjecting the PVA-based resin to preliminary treatments such as hot water treatment, acid solution treatment, ultrasonic wave irradiation treatment, and radiation irradiation treatment in a stage before the production of the polarizing element. These treatments can widen the intervals between molecular chains in the PVA-based resin and destroy the crystal structure. The hot water treatment includes, for example, a treatment of immersing the substrate in pure water at 30 to 100 ℃ for 1 to 90 seconds and drying the substrate. The acidic solution treatment includes, for example, a treatment of immersing the substrate in a 10% to 20% aqueous solution of boric acid for 1 to 90 seconds and drying the substrate. The ultrasonic treatment may be, for example, a treatment in which ultrasonic waves having a frequency of 20kc to 29kc are irradiated at an output power of 200W to 500W for 30 seconds to 10 minutes. The ultrasonic treatment may be carried out in a solvent such as water.

The saponification degree of the PVA-based resin is preferably about 85 mol% or more, more preferably about 90 mol% or more, and still more preferably about 99 mol% to 100 mol%. The PVA-based resin has a polymerization degree of 1000 to 10000, preferably 1500 to 5000. The PVA-based resin may be modified, and examples thereof include polyvinyl formal, polyvinyl acetal, and polyvinyl butyral modified with aldehydes.

The thickness of the polarizer of the present embodiment is preferably 5 to 50 μm, more preferably 8 to 28 μm, still more preferably 12 to 22 μm, and most preferably 12 to 15 μm. By setting the thickness of the polarizing element to 50 μm or less, the influence of polyene formation of the PVA-based resin on the degradation of the optical properties in a high-temperature environment can be suppressed, and by setting the thickness of the polarizing element to 5 μm or more, the constitution for realizing desired optical properties can be easily formed.

The boron content of the polarizing element is preferably 4.0 mass% or more and 8.0 mass% or less, more preferably 4.2 mass% or more and 7.0 mass% or less, and still more preferably 4.4 mass% or more and 6.0 mass% or less. When the boron content of the polarizer is greater than 8.0 mass%, the shrinkage force of the polarizer is increased, and when the polarizer is incorporated into an image display device, problems such as peeling may occur between the polarizer and another member such as a front panel to be bonded. In addition, when the content of boron is less than 2.4% by mass, desired optical characteristics may not be achieved. The content of boron in the polarizer can be calculated as a mass percentage (mass%) of boron with respect to the mass of the polarizer by, for example, a high frequency Inductively Coupled Plasma (ICP) emission spectroscopy. Boron is considered to exist in the polarizing element in a state where boric acid or boric acid and a constituent of the polyvinyl alcohol resin form a crosslinked structure, but the content of boron referred to herein is a value as a boron atom (B).

In the polarizing element, the content of boron is set to 4.0 mass% or more and 8.0 mass% or less, whereby the reduction in transmittance can be suppressed even when the constituent elements of the image display device configured as an interlayer filling are exposed to a high-temperature environment. This is presumably because, when the content of boron in the polarizing element is 4.0 mass% or more and 8.0 mass% or less, the reduction in transmittance is suppressed because the polarizing element is less likely to be polymerized even in a high-temperature environment.

The content of potassium in the polarizing element is preferably 0.28% by mass or more, more preferably 0.32% by mass or more, and even more preferably 0.34% by mass or more, from the viewpoint of suppressing a decrease in optical characteristics of the polarizing element in a high-temperature environment, and is preferably 0.60% by mass or less, more preferably 0.55% by mass or less, and even more preferably 0.50% by mass or less, from the viewpoint of suppressing a change in color tone in a high-temperature environment.

Although the detailed mechanism is not clear, it is presumed that the hydroxyl group of the polyvinyl alcohol in the polarizer is protected (stabilized) by boric acid crosslinking because the content of boron is higher and the content of potassium is lower than those of the conventional polarizer, and the iodide ion which is a counter ion in the polarizer is stabilized by a proper potassium content, and the polyene formation can be suppressed.

The visibility correction monomer transmittance of the polarizing element is preferably 38.8% to 44.8%, more preferably 40.4% to 43.2%, and still more preferably 40.7% to 43.0%. When the transmittance of the visibility correcting element is more than 44.8%, deterioration of optical characteristics such as red discoloration may be large in a high-temperature environment, and when the transmittance of the visibility correcting element is less than 38.8%, polyene formation may be easily advanced in a high-temperature environment, and deterioration of optical characteristics may be large.

The visibility correction individual transmittance can be obtained by measuring a Y value obtained by correcting the visibility with a 2-degree field of view (C light source) prescribed in JIS Z8701-1982. The visibility correction monomer transmittance can be easily measured by, for example, a spectrophotometer (model V7100) manufactured by japan spectrophotometers.

The method for manufacturing the polarizing element is not particularly limited, but typical methods are: a method in which a polyvinyl alcohol resin film wound in a roll form in advance is fed out and then stretched, dyed, crosslinked, or the like is performed (hereinafter referred to as "production method 1"); a method including a step of stretching a laminate obtained by applying a coating liquid containing a polyvinyl alcohol resin to a base film and then forming a polyvinyl alcohol resin layer as a coating layer (hereinafter referred to as "production method 2").

The production method 1 can be produced through a step of uniaxially stretching a polyvinyl alcohol resin film, a step of adsorbing a dichroic dye such as iodine by dyeing the polyvinyl alcohol resin film with the dichroic dye, a step of treating the polyvinyl alcohol resin film adsorbed with the dichroic dye with an aqueous boric acid solution, and a step of washing with water after the treatment with the aqueous boric acid solution.

The content of boron and the content of potassium contained in the polarizing element can be controlled by the concentration of a boron component supplying substance such as boric acid, a boron compound such as borate or borax, or the concentration of a potassium component supplying substance such as potassium halide such as potassium iodide, or the treatment temperature and treatment time of each treatment bath in any of the treatment baths in the swelling step, dyeing step, crosslinking step, stretching step and washing step. In particular, in the crosslinking step and the stretching step, the boron content can be easily adjusted to a desired range by changing the treatment conditions such as the concentration of the boron component-supplying substance. In the water washing step, components such as boron and potassium can be eluted from the polyvinyl alcohol resin film or adsorbed to the polyvinyl alcohol resin film in consideration of the treatment conditions such as the amount of the boron component-supplying substance and the potassium component-supplying substance used in the dyeing step, the crosslinking step, the stretching step, or the like, and therefore the boron content and the potassium content can be easily adjusted to desired ranges.

The swelling step is a treatment step of immersing the polyvinyl alcohol resin film in a swelling bath, and can remove dirt, blocking agents, and the like on the surface of the polyvinyl alcohol resin film, and can suppress uneven dyeing by swelling the polyvinyl alcohol resin film. The swelling bath generally uses a medium containing water as a main component, such as water, distilled water, or pure water. The swelling bath may be added with a surfactant, an alcohol, or the like as appropriate according to a conventional method. In addition, from the viewpoint of controlling the content of potassium in the polarizing element, potassium iodide may be used in the swelling bath, and in this case, the concentration of potassium iodide in the swelling bath is preferably 1.5% by weight or less, more preferably 1.0% by weight or less, and still more preferably 0.5% by weight or less.

The temperature of the swelling bath is preferably about 10 to 60 ℃, more preferably about 15 to 45 ℃, and further preferably about 18 to 30 ℃. The immersion time in the swelling bath is not generally determined because the degree of swelling of the polyvinyl alcohol resin film is affected by the temperature of the swelling bath, but is preferably about 5 to 300 seconds, more preferably about 10 to 200 seconds, and still more preferably about 20 to 100 seconds. The swelling step may be performed only 1 time, or may be performed a plurality of times as needed.

The dyeing step is a treatment step of immersing the polyvinyl alcohol resin film in a dyeing bath (iodine solution), and may be performed by adsorbing a dichroic substance such as iodine or a dichroic dye to the polyvinyl alcohol resin film and aligning the same. The iodine solution is preferably an aqueous iodine solution containing iodine and an iodide as a dissolution aid. The iodide includes potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, and the like. Among them, potassium iodide is preferable from the viewpoint of controlling the content of potassium in the polarizing element.

The concentration of iodine in the dyeing bath is preferably about 0.01 to 1 wt%, more preferably about 0.02 to 0.5 wt%. The concentration of the iodide in the dyeing bath is preferably about 0.01 to 10 wt%, more preferably about 0.05 to 5 wt%, and still more preferably about 0.1 to 3 wt%.

The temperature of the dyeing bath is preferably about 10 to 50 ℃, more preferably about 15 to 45 ℃, and further preferably about 18 to 30 ℃. The immersion time in the dyeing bath is not generally determined because the degree of dyeing of the polyvinyl alcohol resin film is affected by the temperature of the dyeing bath, but is preferably about 10 to 300 seconds, and more preferably about 20 to 240 seconds. The dyeing step may be performed only 1 time, or may be performed a plurality of times as needed.

The crosslinking step is a treatment step of immersing the polyvinyl alcohol resin film dyed in the dyeing step in a treatment bath (crosslinking bath) containing a boron compound, and the polyvinyl alcohol resin film is crosslinked by the boron compound, and iodine molecules or dye molecules can be adsorbed to the crosslinked structure. Examples of the boron compound include boric acid, borate, and borax. The crosslinking bath is generally an aqueous solution, but may be a mixed solution of an organic solvent miscible with water and water, for example. In addition, from the viewpoint of controlling the content of potassium in the polarizing element, the crosslinking bath preferably contains potassium iodide.

The concentration of the boron compound in the crosslinking bath is preferably about 1 to 15 wt%, more preferably about 1.5 to 10 wt%, and still more preferably about 2 to 5 wt%. When potassium iodide is used in the crosslinking bath, the concentration of potassium iodide in the crosslinking bath is preferably about 1 to 15 wt%, more preferably about 1.5 to 10 wt%, and still more preferably about 2 to 5 wt%.

The temperature of the crosslinking bath is preferably about 20 to 70 ℃, and more preferably about 30 to 60 ℃. The immersion time in the crosslinking bath is not generally determined because the degree of crosslinking of the polyvinyl alcohol resin film is affected by the temperature of the crosslinking bath, but is preferably about 5 to 300 seconds, and more preferably about 10 to 200 seconds. The crosslinking step may be performed only 1 time, or may be performed a plurality of times as needed.

The stretching step is a treatment step of stretching the polyvinyl alcohol resin film at a predetermined magnification in at least one direction. In general, a polyvinyl alcohol resin film is uniaxially stretched in the transport direction (longitudinal direction). The stretching method is not particularly limited, and any of wet stretching and dry stretching may be employed. The stretching step may be performed only 1 time, or may be performed a plurality of times as needed. The stretching step may be performed at any stage in the production of the polarizing element.

In the wet stretching method, a solvent such as water or a mixed solution of an organic solvent miscible with water and water is usually used as the treatment bath (stretching bath). From the viewpoint of controlling the content of potassium in the polarizing element, the stretching bath preferably contains potassium iodide. When potassium iodide is used in the stretching bath, the concentration of potassium iodide in the stretching bath is preferably about 1 to 15 wt%, more preferably about 2 to 10 wt%, and still more preferably about 3 to 6 wt%. In addition, in the treatment bath (stretching bath), a boron compound may be contained from the viewpoint of suppressing film breakage during stretching, and in this case, the concentration of the boron compound in the stretching bath is preferably about 1 to 15% by weight, more preferably about 1.5 to 10% by weight, and further preferably about 2 to 5% by weight.

The temperature of the stretching bath is preferably about 25 to 80 ℃, more preferably about 40 to 75 ℃, and still more preferably about 50 to 70 ℃. The immersion time in the stretching bath is not generally determined because the degree of stretching of the polyvinyl alcohol resin film is affected by the temperature of the stretching bath, but is preferably about 10 to 800 seconds, and more preferably about 30 to 500 seconds. The stretching treatment in the wet stretching method may be performed together with any 1 or more treatment steps of the swelling step, the dyeing step, the crosslinking step, and the washing step.

Examples of the dry stretching method include an inter-roll stretching method, a hot-roll stretching method, and a compression-stretching method. The dry drawing method may be performed together with the drying step.

The total draw ratio (cumulative draw ratio) to be applied to the polyvinyl alcohol resin film may be appropriately set according to the purpose, but is preferably about 2 to 7 times, more preferably about 3 to 6.8 times, and still more preferably about 3.5 to 6.5 times.

The washing step is a treatment step of immersing the polyvinyl alcohol resin film in a washing bath, and can remove foreign matter remaining on the surface of the polyvinyl alcohol resin film or the like. The washing bath generally uses a medium containing water as a main component, such as water, distilled water, or pure water. In addition, from the viewpoint of controlling the content of potassium in the polarizing element, potassium iodide is preferably used in the washing bath, and in this case, the concentration of potassium iodide in the washing bath is preferably about 1 to 10% by weight, more preferably about 1.5 to 4% by weight, and further preferably about 1.8 to 3.8% by weight.

The temperature of the washing bath is preferably about 5 to 50 ℃, more preferably about 10 to 40 ℃, and further preferably about 15 to 30 ℃. The immersion time in the washing bath is not generally determined because the degree of washing of the polyvinyl alcohol resin film is affected by the temperature of the washing bath, but is preferably about 1 to 100 seconds, more preferably about 2 to 50 seconds, and still more preferably about 3 to 20 seconds. The washing step may be performed only 1 time, or may be performed a plurality of times as needed.

The drying step is a step of drying the polyvinyl alcohol resin film washed in the washing step to obtain a polarizing element. Drying may be carried out by any suitable method, and examples thereof include natural drying, forced air drying, and heat drying.

The production method 2 can be produced through a step of applying a coating liquid containing the above-mentioned polyvinyl alcohol resin onto a base film, a step of uniaxially stretching the obtained laminated film, a step of preparing a polarizing element by dyeing the polyvinyl alcohol resin layer of the uniaxially stretched laminated film with a dichroic dye and adsorbing the dichroic dye, a step of treating the film having the dichroic dye adsorbed thereon with an aqueous boric acid solution, and a step of washing with water after treatment with an aqueous boric acid solution. The base material film used for forming the polarizing element may be used as a protective layer of the polarizing element. The base material film may be peeled off from the polarizing element as needed.

< transparent protective film >

A transparent protective film (hereinafter also simply referred to as "protective film") used in the present embodiment is bonded to at least one surface of the polarizing element via an adhesive layer. The transparent protective film is attached to one surface or both surfaces of the polarizing element, but is more preferably attached to both surfaces.

The protective film may have other optical functions at the same time, or may be formed in a laminated structure in which a plurality of layers are laminated. From the viewpoint of optical characteristics, the protective film is preferably thin, but if it is too thin, the strength is reduced and the processability is poor. A suitable film thickness is 5 to 100 μm, preferably 10 to 80 μm, and more preferably 15 to 70 μm.

As the protective film, a cellulose acylate resin film, a polycarbonate resin film, a cycloolefin resin film such as norbornene, a (meth) acrylic polymer film, a polyester resin film such as polyethylene terephthalate, or the like can be used. In the case of a structure having protective films on both surfaces of the polarizing element, at least one of the protective films is preferably a cellulose acylate film or a (meth) acrylic polymer film, and among them, a cellulose acylate film is preferable. This is because these films have high moisture permeability and therefore can easily dry an aqueous adhesive such as a PVA adhesive.

At least one of the protective films may have a retardation function for the purpose of viewing angle compensation or the like. In this case, the film itself may have a retardation function, or a retardation layer may be separately provided, or a combination of both may be provided.

Although the structure in which the film having the retardation function is directly bonded to the polarizer via the adhesive has been described, the film having the retardation function may be bonded to the polarizer via another protective film bonded to the polarizer with an adhesive or an adhesive interposed therebetween.

For example, a viewing angle compensation film used for optical compensation of a liquid crystal cell (hereinafter referred to as an IPS mode liquid crystal cell) including a liquid crystal layer containing liquid crystal molecules aligned in a planar alignment in a state where an electric field is not present may be a retardation film including a 1 st optical compensation layer and a 2 nd optical compensation layer in this order from the polarizing element side. At this time, the surface of the 2 nd optical compensation layer is bonded to the liquid crystal cell using an adhesive or the like. The absorption axis of the polarizing element is substantially orthogonal to the slow axis of the 1 st optical compensation layer. The slow axis of the 1 st optical compensation layer is substantially parallel to the slow axis of the 2 nd optical compensation layer. The 1 st optical compensation layer and the 2 nd optical compensation layer may satisfy the following formulas (1) to (4).

80nm≤Re₁(590)≤120nm (1)

20nm＜Re₂(590)≤60nm (2)

1＜Nz₁＜2 (3)

－4＜Nz₂＜－1 (4)

Here, nx is a refractive index in the slow axis direction in each of the 1 st optical compensation layer and the 2 nd optical compensation layer₁、nx₂Ny is a refractive index in the fast axis direction in the plane₁、ny₂The refractive index in the thickness direction is nz₁、nz₂Then Re₁(λ)＝(nx₁－ny₁)×d₁，Re₂(λ)＝(nx₂－ny₂)×d₂，Nz₁＝(nx₁－nz₁)/(nx₁－ny₁)，Nz₂＝(nx₂－nz₂)/(nx₂－ny₂)，d₁、d₂The thicknesses of the 1 st and 2 nd optical compensation layers are shown, respectively, and λ represents the measurement wavelength.

The term "substantially parallel" includes not only complete parallelism but also substantial parallelism, and the angle thereof is generally within ± 2 °, preferably within ± 1 °, and more preferably within ± 0.5 °. The term "substantially orthogonal" includes not only a case of being completely orthogonal but also a case of being substantially orthogonal, and the angle thereof is generally in the range of 90 ± 2 °, preferably in the range of 90 ± 1 °, and more preferably in the range of 90 ± 0.5 °.

(1 st optical Compensation layer)

The 1 st optical compensation layer satisfies Nz as described above₁Layers > 1. Such a retardation film is sometimes called a "negative biaxial plate", a "negative double axis plate", or the like.

The 1 st optical compensation layer preferably satisfies the following formulae (1) and (3).

80nm≤Re₁(590)≤120nm (1)

1＜Nz₁＜2 (3)

Front retardation Re of the 1 st optical compensation layer₁(590) More preferably 81 to 119nm, still more preferably 85 to 115nm, and particularly preferably 90 to 110 nm.

In addition, Nz₁The value of (b) is more preferably 1.15 to 1.6, still more preferably 1.2 to 1.55, and particularly preferably 1.25 to 1.5.

The 1 st optical compensation layer preferably satisfies the following formula (5).

60nm≤Rth₁(590)≤100nm (5)

Here, Rth₁(590)＝Re₁(590)×(Nz₁-0.5) indicating a retardation in the thickness direction.

Retardation in the thickness direction of the 1 st optical compensation layer Rth₁(590) More preferably 61 to 99nm, still more preferably 65 to 95nm, and particularly preferably 70 to 90 nm.

The material, the production method, and the like of the 1 st optical compensation layer are not particularly limited as long as the above optical characteristics are satisfied. The 1 st optical compensation layer may be a single retardation film or a laminate of 2 or more retardation films. The 1 st optical compensation layer is preferably a separate retardation film. This is because the liquid crystal panel can be made thin while reducing the shrinkage stress of the polarizing element and the deviation and unevenness of retardation values due to heat of the light source. When the 1 st optical compensation layer is a laminate, it may contain an adhesive layer or an adhesive layer for bonding 2 or more retardation films. When the laminate includes 2 or more retardation films, the retardation films may be the same or different.

The optical characteristics of the retardation film used in the 1 st optical compensation layer can be appropriately selected depending on the number of retardation films used. For example, in the case where the 1 st optical compensation layer is composed of a single retardation film, the front retardation and the thickness direction retardation of the retardation film are preferably the same as the front retardation Re of the 1 st optical compensation layer₁(590) Thickness direction retardation Rth₁(590) Are equal. Therefore, the retardation values of the pressure-sensitive adhesive layer, the adhesive layer, and the like used when the 1 st optical compensation layer is laminated on the polarizing element and the 2 nd optical compensation layer are preferably as small as possible.

The 1 st optical compensation layer preferably has an overall thickness of 5 to 200 μm, more preferably 10 to 100 μm, and most preferably 15 to 50 μm, and by providing the 1 st optical compensation layer with a thickness in such a range, the workability in the production is excellent, and the optical uniformity such as a phase difference value can be improved.

The retardation film used for the 1 st optical compensation layer is preferably one which is excellent in transparency, mechanical strength, thermal stability, water resistance and the like and is less likely to cause optical unevenness due to strain. As the retardation film, a stretched film of a polymer film containing a thermoplastic resin as a main component is preferably used. In the present specification, the term "stretched film" refers to a plastic film in which molecular orientation is improved in a specific direction by applying a tension to an unstretched film at an appropriate temperature or by further applying a tension to a previously stretched film.

The transmittance of the retardation film, measured by light having a wavelength of 590nm, is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The theoretical upper limit of light transmission is 100%, however, since air and the film cause surface reflection due to the difference in refractive index, the achievable upper limit of light transmission is approximately 94%. It is preferable that the 1 st optical compensation layer as a whole has the same transmittance.

The absolute value of the photoelastic coefficient of the retardation film is preferably 1.0 × 10^－10m²A value of less than or equal to N, more preferably 5.0X 10^－11m²A value of less than or equal to N, more preferably 3.0X 10^－11m²A value of 1.0X 10 or less, particularly preferably 1.N^－11m²The ratio of the nitrogen to the nitrogen is less than N. By setting the value of the photoelastic coefficient within the above range, a liquid crystal display device having excellent optical uniformity, small change in optical characteristics even in an environment of high temperature and high humidity, and excellent durability can be obtained. The lower limit of the photoelastic coefficient is not particularly limited, but is generally 5.0X 10^－13m²A value of 1.0X 10 or more, preferably,/N^－12m²More than/N. If the photoelastic coefficient is too small, the retardation tends to be less reflected, and it is difficult to retard Re at the front₁(590) The range is as shown in the above formula (1). The photoelastic coefficient is a value specific to the chemical structure of a polymer or the like, and may be reduced by copolymerizing or mixing a plurality of components having different signs (positive and negative) of the photoelastic coefficient.

The thickness of the retardation film can be suitably selected depending on the material used for the retardation film and the laminated structure of the optical compensation layer, and when the 1 st optical compensation layer is composed of a single retardation film, the thickness is 5 to 300. mu.m, more preferably 10 to 200. mu.m, and most preferably 15 to 100. mu.m. When the amount is within the above range, a retardation film having excellent mechanical strength and display uniformity can be obtained.

As a method for obtaining a polymer film containing the thermoplastic resin as a main component, any suitable molding method can be used, and for example, a suitable method can be appropriately selected from compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, solvent casting, and the like. Among these methods, extrusion molding or solvent casting is preferably used. This is because a retardation film having high smoothness and good optical uniformity can be obtained. More specifically, the extrusion molding method is a method of producing a film by heating and melting a resin composition containing a thermoplastic resin as a main component, a plasticizer, an additive, and the like, extruding the melted resin composition in a thin film form onto the surface of a casting roll by a T-die or the like, and cooling the extruded resin composition. The solvent casting method is a method in which a resin composition containing a thermoplastic resin as a main component, a plasticizer, an additive, and the like is dissolved in a solvent, the obtained thick solution (dope (japanese text: ドープ)) is deaerated, and the solution is uniformly cast in a thin film form on the surface of a metal endless belt, a rotating drum, a plastic substrate, or the like, and the solvent is evaporated to produce a film. The molding conditions may be appropriately selected depending on the composition and type of the resin used, the molding method, and the like.

The material for forming the thermoplastic resin is not particularly limited, and Nz is satisfied by the formation₁For the purpose of negative biaxial plate with properties > 1, polymers with positive birefringence are preferably used.

Here, "having positive birefringence" means that when a polymer is oriented by stretching or the like, the refractive index in the orientation direction is relatively large, and most of the polymers correspond to this. Examples of the polymer having positive birefringence include polycarbonate-based resins, polyvinyl alcohol-based resins, cellulose fatty acid esters such as triacetylcellulose, diacetylcellulose, tripropylcellulose and dipropylcellulose, cellulose-based resins such as cellulose ether, polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate, polyarylate-based resins, polyimide-based resins, cyclic polyolefin-based (polynorbornene-based) resins, polysulfone-based resins, polyethersulfone-based resins, polyamide-based resins, and polyolefin-based resins such as polyethylene and polypropylene. These polymers may be used alone or in combination of two or more. Further, they may be modified by copolymerization, branching, crosslinking, molecular terminal modification (or end capping), stereomodification (Japanese text: stereovariable size), or the like.

The polymer film containing the thermoplastic resin as a main component may further contain any suitable additive as required. Specific examples of the additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, and thickeners. The kind and amount of the additive to be used may be appropriately set according to the purpose. The amount of the additive to be used is typically 10 parts by weight per 100 parts by weight of the total solid content of the polymer film. If the amount of the additive used is too large, the transparency of the film may be impaired, and the additive may bleed out from the film surface.

As a method of forming a stretched film of the polymer film, any suitable stretching method can be adopted. Specific examples thereof include a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method. As the stretching mechanism, any suitable stretching machine such as a roll stretcher, a tenter type stretching machine, a biaxial stretching machine of a pantograph (japanese text: パンタグラフ) type or a linear motor (japanese text: リニアモーター) type can be used. When the stretching is performed while heating, the temperature may be continuously changed or may be changed stepwise. The stretching step may be divided into 2 or more steps. From the viewpoint of obtaining a biaxial retardation film, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, and a longitudinal and transverse simultaneous biaxial stretching method can be suitably used.

In the polymer having positive birefringence, since the refractive index in the orientation direction is relatively large as described above, in the case of the transverse uniaxial stretching method, the slow axis is present in the direction orthogonal to the film conveyance direction, that is, in the width direction of the film (in other words, the refractive index in the width direction is nx 1). In the case of the longitudinal and transverse sequential biaxial stretching method or the longitudinal and transverse simultaneous biaxial stretching method, the slow axis may be set to either the transport direction or the width direction by the ratio of the longitudinal stretching magnification to the transverse stretching magnification. That is, if the stretch ratio in the vertical (transport) direction is relatively increased, the vertical (transport) direction becomes the slow axis, and if the stretch ratio in the lateral (width) direction is relatively increased, the lateral (width) direction becomes the slow axis.

The stretching is preferably performed so that either one of the film transport direction and the film width direction is the slow axis, and the stretching is different depending on the configuration of the liquid crystal panel, but from the viewpoint of making the slow axis of the 1 st optical compensation layer parallel to the slow axis of the 2 nd optical compensation layer, it is preferable to adjust the slow axis directions of both layers to be the same. That is, in the case where the 2 nd optical compensation layer has a slow axis in the film conveyance direction, the 1 st optical compensation layer preferably also has a slow axis in the film conveyance direction, and in the case where the 2 nd optical compensation layer has a slow axis in the film width direction, the 1 st optical compensation layer preferably also has a slow axis in the film width direction. By adjusting the direction of the slow axis in this manner, the two can be laminated in a roll-to-roll manner, and a laminate having parallel slow axes can be obtained, which is excellent in productivity.

The temperature in the stretching oven (also referred to as stretching temperature) when stretching the polymer film is preferably in the vicinity of the glass transition temperature (Tg) of the polymer film. Specifically, the Tg is preferably from-10 ℃ to Tg +30 ℃, more preferably from Tg to Tg +25 ℃, and still more preferably from Tg +5 ℃ to Tg +20 ℃. If the stretching temperature is too low, the retardation value and the slow axis direction tend to become nonuniform in the width direction, and the film tends to be crystallized (clouded). If the stretching temperature is too high, the film tends to melt, and the phase difference tends to be insufficiently developed. Typically, the stretching temperature is in the range of 110 to 200 ℃. The glass transition temperature can be determined by the DSC method in accordance with JIS K7121-1987.

The specific method for controlling the temperature in the stretching oven is not particularly limited, and may be appropriately selected from an air circulation type constant temperature oven in which hot air or cold air circulates, a heater using microwaves, far infrared rays, or the like, a heating method such as a roller heated for temperature adjustment, a heat pipe roller, or a metal belt, and a temperature control method.

The stretching ratio in stretching the polymer film is not particularly limited, and is determined according to the composition of the polymer film, the type of volatile components and the like, the residual amount of volatile components and the like, the designed retardation value and the like, but is preferably 1.05 to 5.00 times, for example. The feeding speed during stretching is not particularly limited, but is preferably 0.5 to 20 m/min from the viewpoint of mechanical accuracy, stability and the like of the stretching apparatus.

The retardation film used for the 1 st optical compensation layer may be any of the above-mentioned retardation films, and a commercially available optical film may be used as it is. Further, a commercially available optical film may be subjected to 2-pass processing such as stretching and/or relaxing.

(2 nd optical Compensation layer)

The 2 nd optical compensation layer satisfies Nz as described above₁A layer < -1. Such a retardation film is sometimes called a "positive biaxial plate", a "positive double axis plate", or the like.

The 2 nd optical compensation layer preferably satisfies the following formulae (2) and (4).

20nm＜Re₂(590)≤60nm (2)

－4＜Nz₂＜－1 (4)

Front retardation Re of the 2 nd optical compensation layer₂(590) More preferably 21 to 59nm, still more preferably 25 to 55nm, and particularly preferably 30 to 50 nm.

In addition, Nz₂The value of (b) is more preferably-3.5 to-1.5, still more preferably-3.3 to-1.8, and particularly preferably-3.0 to-2.0.

The 2 nd optical compensation layer preferably satisfies the following formula (6).

－150nm≤Rth₂(590)≤－60nm (6)

Here, Rth₂(590)＝Re₂(590)×(Nz₂-0.5) indicating a retardation in the thickness direction.

Retardation in thickness direction of the 2 nd optical compensation layer Rth₂More preferably from-140 to-70 nm, still more preferably from-130 to-80 nm, and particularly preferably from-120 to-85 nm.

Further, a front retardation Re of the 1 st optical compensation layer₂(590) And the front retardation Re of the 2 nd optical compensation layer₂(590) Preferably, the following formula (7) is satisfied.

110nm＜Re₁(590)+Re₂(590)＜150nm (7)

Re₁(590) And Re₂(590) And more preferably 115 to 145nm, still more preferably 120 to 140nm, and particularly preferably 125 to 135 nm.

The material, the production method, and the like of the 2 nd optical compensation layer are not particularly limited as long as the above optical characteristics are satisfied. The 2 nd optical compensation layer may be a single retardation film or a laminate of 2 or more retardation films. Preferably, the 2 nd optical compensation layer is a separate retardation film. This is because the shrinkage stress of the polarizing element and the deviation and unevenness of retardation values due to heat of the light source can be reduced, and the liquid crystal panel can be made thin. When the 2 nd optical compensation layer is a laminate, it may contain an adhesive layer or an adhesive layer for bonding 2 or more retardation films. When the laminate includes 2 or more retardation films, the retardation films may be the same or different.

The optical characteristics of the retardation film used in the 2 nd optical compensation layer can be appropriately selected depending on the number of retardation films used. For example, in the case where the 2 nd optical compensation layer is composed of a single retardation film, the front retardation and the thickness direction retardation of the retardation film are preferably the same as the front retardation Re of the 2 nd optical compensation layer₂Thickness direction retardation Rth₂Are equal. Therefore, the retardation values of the pressure-sensitive adhesive layer, the adhesive layer, and the like used when the 2 nd optical compensation layer is laminated on the polarizing element and the 2 nd optical compensation layer are preferably as high as possibleIs small.

As the retardation film used for the 2 nd optical compensation layer, similarly to the retardation film used for the 1 st optical compensation layer, a retardation film which is excellent in transparency, mechanical strength, thermal stability, water resistance and the like and is less likely to cause optical unevenness due to strain is preferably used. As the retardation film, a stretched film of a polymer film containing a thermoplastic resin as a main component is preferably used. The thickness, transmittance, photoelastic coefficient, molding method thereof, and the like of the film are not particularly limited, and the same ranges as described in the 1 st optical compensation layer are preferred.

The material for forming the above thermoplastic resin is not particularly limited, however, in order to obtain a resin satisfying Nz₂For the purpose of a positive biaxial plate with characteristics < -1, a polymer having negative birefringence is preferably used.

Here, "having negative birefringence" means that, when a polymer is oriented by stretching or the like, the refractive index in the orientation direction is relatively small, in other words, the refractive index in the direction perpendicular to the orientation direction is large. Examples of such polymers include polymers having a side chain to which a chemical bond or a functional group having a large polarization anisotropy, such as an aromatic group or a carbonyl group, is introduced. Specifically, an acrylic resin, a styrene resin, a maleimide resin, and the like can be given.

The above-mentioned acrylic resin, styrene resin and maleimide resin can be obtained by, for example, addition polymerization of an acrylic monomer, styrene monomer, maleimide monomer and the like. Further, after polymerization, the birefringence characteristics may be controlled by substitution of the side chain, maleimide reaction, graft reaction, or the like.

Examples of the acrylic resin include polymethyl methacrylate (PMMA), polybutyl methacrylate, and polycyclohexyl methacrylate.

Examples of the styrene-based monomer used as a raw material monomer for the styrene-based resin include styrene, α -methylstyrene, o-methylstyrene, p-chlorostyrene, p-nitrostyrene, p-aminostyrene, p-carboxystyrene, p-phenylstyrene, 2, 5-dichlorostyrene, and p-tert-butylstyrene.

Examples of the raw material monomer for the maleimide-based resin include N-ethylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-ethylphenyl) maleimide, N- (2-propylphenyl) maleimide, N- (2-isopropylphenyl) maleimide, N- (2, 6-dimethylphenyl) maleimide, N- (2, 6-dipropylphenyl) maleimide, N- (2, 6-diisopropylphenyl) maleimide, N- (2-methyl-6-ethylphenyl) maleimide, N- (2-chlorophenyl) maleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N- (2-methylphenyl) maleimide, N- (2-isopropylphenyl) maleimide, N- (2-methyl-6-ethylphenyl) maleimide, N- (2-chlorophenyl) maleimide, N- (2-isopropylphenyl) maleimide, N- (2-6-isopropylphenyl) maleimide, N- (2-isopropylphenyl) maleimide, N- (2-isopropylphenyl) maleimide, N, S, N- (2, 6-dichlorophenyl) maleimide, N- (2-bromophenyl) maleimide, N- (2, 6-dibromophenyl) maleimide, N- (2-biphenylyl) maleimide, N- (2-cyanophenyl) maleimide and the like. The maleimide monomer can be obtained from, for example, Tokyo chemical industry (Tokyo Co., Ltd.).

The polymer exhibiting negative birefringence may be a polymer obtained by copolymerizing another monomer for the purpose of improving brittleness, moldability, heat resistance, etc., and examples of the other monomer component used for such purpose include ethylene, propylene, 1-butene, 1, 3-butadiene, 2-methyl-1-butene, 2-methyl-1-pentene, 1-hexene, acrylonitrile, methyl acrylate, methyl methacrylate, maleic anhydride, vinyl acetate, etc.

When the polymer exhibiting negative birefringence is a copolymer of a styrene monomer and another monomer, the content of the styrene monomer component is preferably 50 to 80 mol%. When the polymer exhibiting negative birefringence is a copolymer of a maleimide monomer and another monomer, the content of the maleimide monomer component is preferably 2 to 50 mol%. When the content of the monomer component is in the above range, a film having excellent toughness and moldability can be obtained.

Among the above-mentioned polymers exhibiting negative birefringence, styrene-maleic anhydride copolymers, acrylonitrile copolymers, styrene- (meth) acrylate copolymers, styrene-maleimide copolymers, vinyl ester-maleimide copolymers, olefin-maleimide copolymers can be suitably used. These may be used alone or in combination of two or more. These polymers exhibit high negative birefringence and are excellent in heat resistance. These polymers are available from, for example, Nova Chemical Japan, Mikan Chemical industry (Ltd.) and the like.

Further, as the polymer exhibiting negative birefringence, a polymer having a repeating unit represented by the following general formula (I) can also be suitably used. Such a polymer can be obtained by using, as a starting material, a maleimide-based monomer obtained by using, as an N-substituted maleimide, an N-phenyl-substituted maleimide having, as an N-substituent, a phenyl group having a substituent at least at the ortho-position. The polymer has higher negative birefringence, and is more excellent in heat resistance and mechanical strength.

[ solution 1]

In the above general formula (I), R₁～R₅Each independently represents hydrogen, halogen atom, carboxylic acid, carboxylic ester, hydroxyl, nitro, or C1-8 linear or branched alkyl or alkoxy (wherein, R is₁And R₅Not simultaneously hydrogen atom), R₆And R₇Represents a hydrogen atom or a linear or branched alkyl or alkoxy group having 1 to 8 carbon atoms, and n represents an integer of 2 or more.

The polymer exhibiting negative birefringence is not limited to the above-mentioned polymer, and a cyclic olefin copolymer as disclosed in, for example, Japanese patent application laid-open No. 2005-350544 may be used. Further, a composition of a polymer and inorganic fine particles as disclosed in Japanese patent laid-open Nos. 2005-156862 and 2005-227427 may be suitably used. One kind of the polymer exhibiting negative birefringence may be used alone, or two or more kinds may be used in combination. Further, they may be modified by copolymerization, branching, crosslinking, molecular terminal modification (or capping), stereomodification, or the like, and then used.

The polymer film mainly composed of the thermoplastic resin may further contain any suitable additive as needed, similarly to the polymer film described for the 1 st optical compensation layer.

As a method for forming a stretched film of the polymer film, any suitable stretching method can be employed as in the method described for the 1 st optical compensation layer.

In the polymer having negative birefringence, since the refractive index in the orientation direction is relatively small as described above, the transverse uniaxial stretching method has a slow axis in the transport direction of the film (in other words, the refractive index in the transport direction is nx 1). In the case of the longitudinal and transverse sequential biaxial stretching method or the longitudinal and transverse simultaneous biaxial stretching method, the slow axis may be set to either the transport direction or the width direction by the ratio of the longitudinal stretching magnification to the transverse stretching magnification. That is, when the stretch ratio in the vertical (transport) direction is relatively increased, the horizontal (width) direction becomes the slow axis, and when the stretch ratio in the horizontal (width) direction is relatively increased, the vertical (transport) direction becomes the slow axis.

The stretching temperature, the method of controlling the temperature in the stretching oven, the stretching magnification and the like are not particularly limited, and the same stretching temperature, temperature control method and stretching magnification as described in the above 1 st optical compensation layer can be suitably used.

Although the method of obtaining the positive biaxial plate used for the 2 nd optical compensation layer using the polymer having negative birefringence has been described above, the positive biaxial plate may be produced using a polymer having positive birefringence.

As a method for obtaining a positive biaxial plate using a polymer having positive birefringence, for example, a stretching method for increasing the refractive index in the thickness direction as disclosed in Japanese patent laid-open Nos. 2000-231016, 2000-206328, 2002-207123, and the like can be used. That is, a heat-shrinkable film is bonded to one surface or both surfaces of a film having a polymer with positive birefringence, and the film having a polymer with positive birefringence is subjected to a shrinking force of the heat-shrinkable film by heat treatmentShrinkage is achieved by shrinking both the longitudinal and width directions of the film to increase the refractive index in the thickness direction, thereby obtaining a film satisfying Nz₂A positive biaxial plate of the characteristic of > -1.

As described above, the positive biaxial plate used as the 2 nd optical compensation layer can be produced using a polymer having both positive and negative birefringence, but in general, when a positive birefringent polymer is used, there is an advantage in that a large number of kinds of polymers can be selected, and when a negative birefringent polymer is used, there is an advantage in that a retardation film having high uniformity in the slow axis direction can be easily obtained due to the stretching method as compared with the case of using a positive birefringent polymer.

The retardation film used for the 2 nd optical compensation layer may be a commercially available optical film as it is, in addition to the above-described film. Further, a commercially available optical film may be subjected to 2-pass processing such as stretching and/or relaxing.

The polarizing element and the 1 st and 2 nd optical compensation layers are laminated using an adhesive or a pressure-sensitive adhesive described later. Further, an optically isotropic film described later may be disposed between the polarizing element and the 1 st optical compensation layer. The lamination of the polarizing element and the optically isotropic film, and the lamination of the optically isotropic film and the 1 st optical compensation layer are also performed using an adhesive or an adhesive to be described later.

When the polarizing plate provided with such an optical compensation film is applied to an O-mode IPS-mode liquid crystal cell, the polarizing plate of the present invention is preferably disposed on the viewing side of the liquid crystal display device. In addition, when the polarizing plate of the present invention is applied to an IPS mode liquid crystal cell of E-mode, the polarizing plate is preferably disposed on the light source side of the liquid crystal display device.

When the polarizing plate of the present invention is laminated on one surface of an IPS mode liquid crystal display device, the polarizing plate laminated on the other surface of the liquid crystal cell is a polarizing plate in which a polarizing element and an optically isotropic film are laminated, and is preferably laminated on the liquid crystal cell via an adhesive on the optically isotropic film side.

The optically isotropic film is a film satisfying the following formulae (8) and (9).

0nm≤|Re₃(590)|≤20nm (8)

0nm≤|Rth₃(590)|≤20nm (9)

Here, the refractive index in the slow axis direction in the plane of the optically isotropic film is nx₃Ny is a refractive index in the fast axis direction in the plane₃The refractive index in the thickness direction is nz₃，Re₃(λ)＝(nx₃－ny₃)×d₃，Rth₃(λ)＝{(nx₃+ny₃)/2-nz}×d₃，d₃The thickness of the optically isotropic film is indicated.

The material, the production method, and the like of the isotropic optical element are not particularly limited as long as the above optical properties are satisfied. The isotropic optical element may be a single optical film or a laminate of 2 or more optical films. Preferably the isotropic optical element is a separate film. This is because the shrinkage stress of the polarizing element and the generation and unevenness of birefringence due to heat of the light source can be reduced, and the liquid crystal panel can be made thin. When the isotropic optical element is a laminate, the isotropic optical element may include an adhesive layer or an adhesive layer for bonding 2 or more retardation films. When the laminate includes 2 or more retardation films, the retardation films may be the same or different. For example, when 2 retardation films are stacked, each retardation film is preferably arranged such that the slow axes thereof are orthogonal to each other. By configuring as described above, the in-plane retardation value can be reduced. In addition, each retardation film is preferably formed by laminating films in which the positive and negative retardation values in the thickness direction are opposite to each other. By stacking as described above, the retardation value in the thickness direction can be reduced.

As the optical film used for the isotropic optical element, similarly to the retardation film used for the 1 st and 2 nd optical compensation layers, a film which is excellent in transparency, mechanical strength, thermal stability, water resistance and the like and is less likely to cause optical unevenness due to strain is preferably used. As the film, a polymer film is preferably used. The thickness, transmittance, molding method thereof, and the like of the film are not particularly limited, but are preferably within the same ranges as described in the above 1 st optical compensation layer.

The absolute value of the photoelastic coefficient of the optical film used in the isotropic optical element is preferably 1.0 × 10^－10m²A value of less than or equal to N, more preferably 5.0X 10^－11m²A value of 1.0X 10 or less, more preferably,/N^－11m²A value of less than N, particularly preferably 5.0X 10^－12m²The ratio of the nitrogen to the nitrogen is less than N. By setting the value of the photoelastic coefficient within the above range, a liquid crystal display device having excellent optical uniformity, small change in optical characteristics even in an environment of high temperature and high humidity, and excellent durability can be obtained. The lower limit of the photoelastic coefficient is not particularly limited, but is generally 5.0X 10^－13m²More than/N. The value of the photoelastic coefficient can be suppressed by the same method as that described for the 1 st optical compensation layer.

Examples of the material constituting the optically isotropic film include polycarbonate-based resins, polyvinyl alcohol-based resins, cellulose-based resins, polyester-based resins, polyarylate-based resins, polyimide-based resins, cyclic polyolefin-based resins, polysulfone-based resins, polyethersulfone-based resins, polyolefin-based resins, polystyrene-based resins, polyvinyl alcohol-based resins, and mixtures thereof. In addition, a thermosetting resin or an ultraviolet curable resin such as a urethane-based, acrylic urethane-based, epoxy-based, or silicone-based resin may be used. The optically isotropic film may contain 1 or more kinds of any suitable additives as in the 1 st and 2 nd optical compensation layers.

As the cellulose-based resin, esters of cellulose and fatty acids are preferable. Specific examples of such cellulose ester resins include triacetylcellulose, diacetylcellulose, triacetylcellulose, and dipropylcellulose. Among them, triacetyl cellulose is particularly preferable. Triacetyl cellulose is available in many products, and is advantageous in terms of availability and cost. Triacetylcellulose often has a retardation in the thickness direction (Rth) of more than 10nm, and a cellulose-based resin film having not only a small front retardation but also a small retardation in the thickness direction can be obtained by using an additive for eliminating these retardations or by a film-forming method. Examples of the above-mentioned film forming method include: a method in which a base film such as polyethylene terephthalate, polypropylene, or stainless steel coated with a solvent such as cyclopentanone or methyl ethyl ketone is bonded to a general cellulose film, and the base film is peeled after heat drying (for example, heating at 80 to 150 ℃ for about 3 to 10 minutes); a method of applying a solution obtained by dissolving a norbornene resin, a (meth) acrylic resin, or the like in a solvent such as cyclopentanone or methyl ethyl ketone to a general cellulose resin film, drying the applied solution by heating (for example, heating at 80 to 150 ℃ for about 3 to 10 minutes), and then peeling the applied film.

As the cellulose resin film having a small retardation in the thickness direction, a fatty acid cellulose resin film having a controlled degree of substitution with fat can be used. In the commonly used triacetylcellulose, the degree of substitution with acetic acid is about 2.8, and the degree of substitution with acetic acid is preferably controlled to 1.8 to 2.7, whereby Rth can be reduced. By adding a plasticizer such as dibutyl phthalate, p-toluenesulfonanilide, acetyl triethyl citrate or the like to the fatty acid-substituted cellulose resin, Rth can be controlled to a small value. The amount of the plasticizer to be added is preferably 40 parts by weight or less, more preferably 1 to 20 parts by weight, and still more preferably 1 to 15 parts by weight, based on 100 parts by weight of the fatty cellulose resin.

Further, as the optically isotropic film, a polymer film containing a resin composition containing a thermoplastic resin having a substituted and/or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted and/or unsubstituted phenyl group and a nitrile group in a side chain, as described in Japanese patent laid-open No. 2001-343529 (WO01/37007) or the like; a polymer film containing an acrylic resin having a lactone ring structure as described in Japanese patent laid-open Nos. 2000-230016, 2001-151814, 2002-120326, 2002-254544, 2005-146084, 2006-171464; polymer films of acrylic resins containing a structural unit having an unsaturated carboxylic acid alkyl ester and a structural unit having glutaric anhydride, which are described in, for example, Japanese patent application laid-open Nos. 2004-70290, 2004-70296, 2004-163924, 2004-292812, 2005-314534, 2006-131898, 2006-206881, 2006-265532, 2006-283013, 2006-299005, and 2006-335902; and films containing a thermoplastic resin having a glutarimide structure described in, for example, Japanese patent application laid-open Nos. 2006-309033, 2006-317560, 2006-328329, 2006-328334, 2006-337491, 2006-337492, 2006-337493, and 2006-337569. These films are preferably low in both front retardation and retardation in the thickness direction and also low in photoelastic coefficient, and therefore, even when strain is generated in the polarizing plate by heating or the like, the films are less likely to cause inconveniences such as unevenness, and also have low moisture permeability and therefore excellent humidification durability.

In addition, a cyclic polyolefin resin is also preferably used as the optically isotropic film. As a specific example of the cyclic polyolefin resin, a norbornene resin is preferable. The cyclic polyolefin resin is a general term for resins obtained by polymerizing a cyclic olefin as a polymerization unit, and examples thereof include those described in Japanese patent application laid-open Nos. H1-240517, H3-14882, and H3-122137. Specific examples thereof include ring-opened (co) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers (typically random copolymers) of cyclic olefins with α -olefins such as ethylene and propylene, graft polymers obtained by modifying these with unsaturated carboxylic acids and derivatives thereof, and hydrogenated products thereof. Specific examples of the cyclic olefin include a norbornene-based monomer.

Various products are commercially available as cyclic polyolefin resins. Specific examples thereof include a trade name "Zeonor" manufactured by ZEON corporation, a trade name "Arton" manufactured by JSR corporation, a trade name "Topas" manufactured by TICONA corporation, and a trade name "Apel" manufactured by mitsui chemical corporation.

In the lamination of the polarizing element and the optically isotropic film, an adhesive or an adhesive described later may be used.

< adhesive layer >

Any suitable adhesive may be used as the adhesive constituting the adhesive layer for adhering the protective film to the polarizing element. As the adhesive, an aqueous adhesive, a solvent adhesive, an active energy ray-curable adhesive, or the like can be used, but an aqueous adhesive is preferable. From the viewpoint of improving heat resistance, the adhesive layer preferably contains at least one urea compound selected from urea, urea derivatives, thiourea and thiourea derivatives.

The thickness of the adhesive at the time of application may be set to any appropriate value. For example, the adhesive layer is set so as to have a desired thickness after curing or after heating (drying). The thickness of the adhesive layer is preferably 0.01 μm or more and 7 μm or less, more preferably 0.01 μm or more and 5 μm or less, still more preferably 0.01 μm or more and 2 μm or less, and most preferably 0.01 μm or more and 1 μm or less.

(aqueous adhesive)

As the aqueous adhesive, any suitable aqueous adhesive can be used. Among them, an aqueous adhesive (PVA-based adhesive) containing a PVA-based resin is preferably used. The average polymerization degree of the PVA resin contained in the aqueous adhesive is preferably about 100 to 5500, and more preferably 1000 to 4500 in view of adhesiveness. The average saponification degree is preferably about 85 mol% to 100 mol%, and more preferably 90 mol% to 100 mol%, from the viewpoint of adhesiveness.

The reason why the PVA-based resin contained in the aqueous adhesive preferably contains an acetoacetyl group is that the PVA-based resin layer has excellent adhesion to the protective film and excellent durability. The acetoacetyl group-containing PVA-based resin can be obtained by, for example, reacting a PVA-based resin with diketene by an arbitrary method. The acetoacetyl group modification degree of the acetoacetyl group-containing PVA resin is typically 0.1 mol% or more, and preferably about 0.1 mol% to 20 mol%.

The resin concentration of the aqueous adhesive is preferably 0.1 to 15% by mass, and more preferably 0.5 to 10% by mass.

The aqueous adhesive may contain a crosslinking agent. As the crosslinking agent, a known crosslinking agent can be used. Examples thereof include water-soluble epoxy compounds, dialdehydes, and isocyanates.

When the PVA-based resin is a PVA-based resin containing an acetoacetyl group, the crosslinking agent is preferably any one of glyoxal, glyoxylate, and methylolmelamine, more preferably any one of glyoxal and glyoxylate, and particularly preferably glyoxal.

The aqueous adhesive may contain an organic solvent. From the viewpoint of having miscibility with water, the organic solvent is preferably an alcohol, and methanol or ethanol is more preferable among alcohols. Some of the urea compounds have low solubility in water but sufficient solubility in alcohol. In this case, it is also one of preferable embodiments that the adhesive is prepared by dissolving the urea compound in an alcohol to prepare an alcohol solution of the urea compound, and then adding the alcohol solution of the urea compound to the PVA aqueous solution.

The concentration of methanol in the aqueous adhesive is preferably 10 mass% or more and 70 mass% or less, more preferably 15 mass% or more and 60 mass% or less, and still more preferably 20 mass% or more and 60 mass% or less. When the concentration of methanol is 10% by mass or more, the suppression of the polyene formation in a high-temperature environment is facilitated. Further, by setting the content of methanol to 70% by mass or less, deterioration of color tone can be suppressed.

(active energy ray-curable adhesive)

The active energy ray-curable adhesive is an adhesive which is cured by irradiation with an active energy ray such as ultraviolet ray, and examples thereof include an adhesive containing a polymerizable compound and a photopolymerization initiator, an adhesive containing a photoreactive resin, and an adhesive containing a binder resin and a photoreactive crosslinking agent. Examples of the polymerizable compound include photopolymerizable monomers such as a photocurable epoxy monomer, a photocurable acrylic monomer, and a photocurable urethane monomer, and oligomers derived from these monomers. Examples of the photopolymerization initiator include compounds containing active species that generate neutral radicals, anionic radicals, cationic radicals, and the like by irradiation with active energy rays such as ultraviolet rays.

(Urea-based Compound)

When the adhesive layer contains a urea compound, the urea compound is at least 1 selected from urea, urea derivatives, thiourea, and thiourea derivatives. As a method for containing a urea compound in the adhesive layer, it is preferable to contain a urea compound in the adhesive. In the process of forming the adhesive layer after the adhesive is subjected to a drying step or the like, a part of the urea compound may be allowed to move from the adhesive layer to the polarizing element or the like. That is, the polarizing element may contain a urea compound. The urea compound includes a water-soluble compound and a poorly-soluble compound, and any urea compound can be used in the adhesive of the present embodiment. When a sparingly soluble urea compound is used in an aqueous adhesive, it is preferable to study a dispersion method so as not to cause an increase in haze after the formation of an adhesive layer.

When the adhesive is an aqueous adhesive containing a PVA-based resin, the amount of the urea-based compound added is preferably 0.1 to 400 parts by mass, more preferably 1 to 200 parts by mass, and still more preferably 3 to 100 parts by mass, based on 100 parts by mass of the PVA resin.

(Urea derivative)

The urea derivative is a compound in which at least 1 of 4 hydrogen atoms of a urea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent containing a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of the urea derivative include mono-substituted urea, such as methyl urea, ethyl urea, propyl urea, butyl urea, isobutyl urea, N-octadecyl urea, 2-hydroxyethyl urea, hydroxyurea, acetyl urea, allyl urea, 2-propynyl urea, cyclohexyl urea, phenyl urea, 3-hydroxyphenyl urea, (4-methoxyphenyl) urea, benzyl urea, benzoyl urea, o-tolyl urea, and p-tolyl urea.

Examples of the di-substituted urea include 1, 1-dimethylurea, 1, 3-dimethylurea, 1-diethylurea, 1, 3-bis (hydroxymethyl) urea, 1, 3-di-tert-butylurea, 1, 3-dicyclohexylurea, 1, 3-diphenylurea, 1, 3-bis (4-methoxyphenyl) urea, 1-acetyl-3-methylurea, 2-imidazolidinone (vinylurea), and tetrahydro-2-pyrimidinone (propyleneurea).

Examples of the tetra-substituted urea include tetramethylurea, 1, 3, 3-tetraethylurea, 1, 3, 3-tetrabutylurea, 1, 3-dimethoxy-1, 3-dimethylurea, 1, 3-dimethyl-2-imidazolidinone, and 1, 3-dimethyl-3, 4, 5, 6-tetrahydro-2 (1H) -pyrimidinone.

(Thiourea derivatives)

The thiourea derivative is a compound in which at least 1 of 4 hydrogen atoms of a thiourea molecule is substituted with a substituent. In this case, the substituent is not particularly limited, but is preferably a substituent containing a carbon atom, a hydrogen atom and an oxygen atom.

Specific examples of the thiourea derivative include N-methylthiourea, ethylthiourea, propylthiourea, isopropylthiourea, 1-butylthiourea, cyclohexylthiourea, N-acetylthiourea, N-allylthiourea, (2-methoxyethyl) thiourea, N-phenylthiourea, (4-methoxyphenyl) thiourea, N- (2-methoxyphenyl) thiourea, N- (1-naphthyl) thiourea, (2-pyridyl) thiourea, o-tolylthiourea and p-tolylthiourea.

Examples of the di-substituted thiourea include 1, 1-dimethylthiourea, 1, 3-dimethylthiourea, 1-diethylthiourea, 1, 3-dibutylthiourea, 1, 3-diisopropylthiourea, 1, 3-dicyclohexylthiourea, N-diphenylthiourea, N '-diphenylthiourea, 1, 3-di (o-tolyl) thiourea, 1, 3-di (p-tolyl) thiourea, 1-benzyl-3-phenylthiourea, 1-methyl-3-phenylthiourea, N-allyl-N' - (2-hydroxyethyl) thiourea and ethylenethiourea.

Examples of the tri-substituted thiourea include trimethyl thiourea, and examples of the tetra-substituted thiourea include tetramethyl thiourea and 1, 1, 3, 3-tetraethyl thiourea.

Among the urea compounds, urea derivatives or thiourea derivatives are preferable, and urea derivatives are more preferable, from the viewpoint that the decrease in transmittance in a high-temperature environment can be further suppressed when the urea compounds are used in an image display device having an interlayer filling structure. Among the urea derivatives, a mono-substituted urea or di-substituted urea is preferable, and a mono-substituted urea is more preferable. Among the disubstituted ureas are 1, 1-substituted ureas and 1, 3-substituted ureas, however, 1, 3-substituted ureas are more preferred.

< layer containing Urea-based Compound >

The urea compound is not limited to the one contained in the adhesive layer as described above, and may be contained in a layer other than the adhesive layer from the viewpoint of improving the heat resistance of the polarizing plate. As described in the description of the transparent protective film as another layer, in recent years, in order to respond to a demand for a thinner polarizing plate, a polarizing plate having a protective film only on one surface of a polarizing element has been developed. In such a configuration, a cured layer may be laminated on the surface of the polarizing element not having the protective film for the purpose of improving physical strength or the like.

In the present embodiment, the solidified layer may contain a urea compound. Although such a cured layer is usually formed from a curable composition containing an organic solvent, a method of forming such a cured layer from an aqueous solution of an active energy ray-curable polymer composition is described in paragraphs [0020] to [0042] of japanese patent application laid-open No. 2017-075986. Since many of the urea compounds are water-soluble, the composition can contain a water-soluble urea compound.

< Water content >

(feature (a))

In the case of the feature (a), the water content of the polarizing element is equal to or higher than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%. More preferably, the equilibrium moisture content is 45% or less at a temperature of 20 ℃ and a relative humidity, still more preferably 42% or less at a temperature of 20 ℃, and most preferably 38% or less at a temperature of 20 ℃. If the equilibrium moisture content is less than 20 ℃ and 30% relative humidity, the polarizing element is likely to be broken due to reduced operability. If the moisture content of the polarizing element is greater than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 50%, the transmittance of the polarizing element tends to decrease. It is presumed that if the water content of the polarizing element is high, the polyene formation of the PVA-based resin is easily advanced. The water content of the polarizing element is the water content of the polarizing element in the polarizing plate.

As a method for confirming whether or not the water content of the polarizer is within a range of not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%, it can be confirmed by storing the polarizer in an environment adjusted to the ranges of the temperature and the relative humidity, and considering that the polarizer is in equilibrium with the environment when there is no change in mass for a certain period of time, or calculating the equilibrium water content of the polarizer in the environment adjusted to the ranges of the temperature and the relative humidity in advance, and comparing the water content of the polarizer with the equilibrium water content calculated in advance.

The method for producing the polarizing element having a water content of not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50% is not particularly limited, and examples thereof include a method in which the polarizing element is stored in an environment adjusted to the above temperature and relative humidity for 10 minutes to 3 hours, or a method in which the polarizing element is subjected to a heat treatment at 30 ℃ to 90 ℃.

Another preferable method for producing the polarizing element having the water content includes a method of storing a laminate in which a protective film is laminated on at least one surface of a polarizing element or a polarizing plate using a polarizing element in an environment adjusted to the temperature and the relative humidity for 10 minutes to 120 hours; or a method of performing heat treatment at 30 ℃ to 90 ℃. In the production of an image display device configured by interlayer filling, an image display panel in which a polarizing plate is laminated on an image display unit may be stored in an environment adjusted to the above temperature and relative humidity range for 10 minutes to 3 hours or less, or heated at 30 ℃ to 90 ℃ and then the front panel may be bonded.

The water content of the polarizer is preferably adjusted so that the water content falls within the above numerical range in the material stage used for forming the polarizing plate, which is a single polarizer or a laminate of a polarizer and a protective film. When the water content is adjusted after the polarizing plate is formed, the curl becomes too large, and a defect is likely to occur when the polarizing plate is bonded to an image display unit. By configuring the polarizing plate using the polarizing element adjusted so as to have the above water content in the material stage before the polarizing plate is configured, it is possible to easily configure a polarizing plate including the polarizing element having the water content satisfying the above numerical range. The water content of the polarizing element in the polarizing plate may be adjusted to the above numerical range in a state where the polarizing plate is bonded to the image display unit. In this case, since the polarizing plate is bonded to the image display unit, curling is less likely to occur.

(feature (b))

In the case of the feature (b), the moisture content of the polarizing plate is equal to or higher than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 50%. The moisture content of the polarizing plate is preferably an equilibrium moisture content of 45% or less at a temperature of 20 ℃ and a relative humidity, more preferably an equilibrium moisture content of 42% or less at a temperature of 20 ℃, and still more preferably an equilibrium moisture content of 38% or less at a temperature of 20 ℃. If the moisture content of the polarizing plate is less than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 30%, the workability of the polarizing plate is lowered and the polarizing plate is liable to crack. If the moisture content of the polarizing plate is greater than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 50%, the transmittance of the polarizing element is liable to decrease. It is presumed that if the water content of the polarizing plate is high, polyene formation of the PVA-based resin is facilitated.

As a method for confirming whether or not the water content of the polarizing plate is within a range of the equilibrium water content of the temperature 20 ℃ relative humidity 30% or more and the equilibrium water content of the temperature 20 ℃ relative humidity 50% or less, it can be confirmed by storing the polarizing plate in an environment adjusted to the temperature and the relative humidity and considering that the polarizing plate is in equilibrium with the environment when there is no change in mass for a certain period of time, or calculating the equilibrium water content of the polarizing plate in the environment adjusted to the temperature and the relative humidity in advance and comparing the water content of the polarizing plate with the equilibrium water content calculated in advance.

The method for producing the polarizing plate having a water content of not less than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and not more than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50% is not particularly limited, and examples thereof include a method in which the polarizing plate is stored in an environment adjusted to the above temperature and relative humidity for 10 minutes to 3 hours or less, and a method in which the polarizing plate is subjected to a heat treatment at 30 ℃ to 90 ℃.

In the production of an image display device configured by interlayer filling, an image display panel in which a polarizing plate is laminated on an image display unit may be stored in an environment adjusted to the above temperature and relative humidity ranges for 10 minutes to 3 hours or less, or 30 ℃ to 90 ℃ and then heated, and then the front panel may be bonded.

[ method for producing polarizing plate ]

The method for manufacturing a polarizing plate of the present embodiment includes a laminating step of laminating a polarizing element and a transparent protective film, and a water content adjusting step. In the moisture content adjustment step, in the case of manufacturing the polarizing plate having the characteristic (a), the moisture content of the polarizing element is adjusted so that the moisture content of the polarizing element is equal to or higher than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than the equilibrium moisture content at a temperature of 20 ℃ and a relative humidity of 50%. The water content of the polarizer can be adjusted in accordance with the description of the water content of the polarizer. In the water content adjusting step, in the case of manufacturing the polarizing plate having the characteristic (b), the water content of the polarizing plate is adjusted so that the water content of the polarizing plate is equal to or higher than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 30% and equal to or lower than the equilibrium water content at a temperature of 20 ℃ and a relative humidity of 50%. The water content of the polarizing plate can be adjusted in accordance with the above description of the water content of the polarizing plate. The order of the water content adjusting step and the laminating step is not limited, and the water content adjusting step and the laminating step may be performed simultaneously. The laminating step may be a step of bonding the polarizing element and the transparent protective film via the adhesive layer.

[ constitution of image display device ]

The polarizing plate of the present embodiment is used in various image display devices such as a liquid crystal display device and an organic EL display device. In the case where the image display device is configured to have an interlayer filling structure, that is, a structure in which both surfaces of the polarizing plate are in contact with a layer other than the air layer, specifically, a solid layer such as an adhesive layer, the transmittance tends to be lowered in a high-temperature environment. In the image display device using the polarizing plate of the present embodiment, even in the interlayer filling configuration, the decrease in transmittance of the polarizing plate in a high-temperature environment can be suppressed. As an example of the image display device, there is shown a configuration including an image display unit, a 1 st adhesive layer laminated on a visible-side surface of the image display unit, and a polarizing plate laminated on a visible-side surface of the 1 st adhesive layer. The image display device may further include a 2 nd adhesive layer laminated on the visible-side surface of the polarizing plate, and a transparent member laminated on a surface of the 2 nd adhesive layer. In particular, the polarizing plate of the present embodiment can be suitably used for an image display apparatus having an interlayer filling structure in which a transparent member is disposed on the viewing side of the image display apparatus, the polarizing plate is bonded to the image display unit with a 1 st adhesive layer, and the polarizing plate is bonded to the transparent member with a 2 nd adhesive layer. In the present specification, either or both of the 1 st adhesive layer and the 2 nd adhesive layer may be simply referred to as "adhesive layers". The member used for bonding the polarizing plate to the image display unit and the member used for bonding the polarizing plate to the transparent member are not limited to the adhesive layer, and may be an adhesive layer.

< image display Unit >

Examples of the image display unit include a liquid crystal unit and an organic EL unit. As the liquid crystal cell, any of a reflective liquid crystal cell using external light, a transmissive liquid crystal cell using light from a light source such as a backlight, and a transflective liquid crystal cell using both light from the outside and light from the light source can be used. In the case where the liquid crystal cell is a liquid crystal cell using light from a light source, the image display device (liquid crystal display device) is also provided with a polarizing plate on the side opposite to the visible side of the image display cell (liquid crystal cell) and a light source. The polarizing plate on the light source side and the liquid crystal cell are preferably bonded via an appropriate adhesive layer. As a driving method of the liquid crystal cell, any type of driving method such as a VA mode, an IPS mode, a TN mode, an STN mode, a bend alignment (pi-type) and the like can be used.

As the organic EL unit, an organic EL unit in which a transparent electrode, an organic light-emitting layer, and a metal electrode are sequentially stacked on a transparent substrate to form a light-emitting body (organic electroluminescence body) or the like can be suitably used. The organic light-emitting layer is a laminate of various organic thin films, and can be formed of various layers such as a laminate of a hole-injecting layer containing triphenylamine derivative or the like and a light-emitting layer containing a fluorescent organic solid such as anthracene, a laminate of these light-emitting layers and an electron-injecting layer containing perylene derivative or the like, or a laminate of a hole-injecting layer, a light-emitting layer, and an electron-injecting layer.

< bonding of image display Unit and polarizing plate >

In the bonding of the image display unit and the polarizing plate, an adhesive layer (adhesive sheet) can be suitably used. Among them, from the viewpoint of handling and the like, a method of bonding a polarizing plate with an adhesive layer in which an adhesive layer is provided on one surface of the polarizing plate to an image display unit is preferable. The adhesive layer may be attached to the polarizing plate in an appropriate manner. Examples thereof include a method of preparing a binder solution in which about 10 to 40 mass% of a base polymer or a composition thereof is dissolved or dispersed in a solvent of a single substance or a mixture containing an appropriate solvent such as toluene or ethyl acetate, and directly attaching the binder solution to a polarizing plate by an appropriate developing method such as a casting method or a coating method; or a method in which an adhesive layer is formed on a separator and then transferred to a polarizing plate.

< adhesive layer >

The adhesive layer may contain 1 layer, or may contain 2 or more layers, but preferably contains 1 layer. The pressure-sensitive adhesive layer may be formed from a pressure-sensitive adhesive composition containing, as a main component, (meth) acrylic resin, rubber-based resin, urethane-based resin, ester-based resin, silicone-based resin, or polyvinyl ether-based resin. Among them, the pressure-sensitive adhesive composition is suitable for use as a base polymer of a (meth) acrylic resin excellent in transparency, weather resistance, heat resistance and the like. The adhesive composition may be an active energy ray-curable type or a heat-curable type.

As the (meth) acrylic resin (base polymer) used in the adhesive composition, a polymer or copolymer containing 1 or 2 or more kinds of (meth) acrylic acid esters such as butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate as monomers can be suitably used. The base polymer is preferably copolymerized with a polar monomer. Examples of the polar monomer include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, and the like, such as a (meth) acrylic acid compound, a 2-hydroxypropyl (meth) acrylate compound, a hydroxyethyl (meth) acrylate compound, a (meth) acrylamide compound, an N, N-dimethylaminoethyl (meth) acrylate compound, and a glycidyl (meth) acrylate compound.

The adhesive composition may comprise only the above-mentioned base polymer, but usually also contains a crosslinking agent. Examples of the crosslinking agent include a metal ion having a valence of 2 or more, which forms a metal carboxylate with a carboxyl group, a polyamine compound which forms an amide bond with a carboxyl group, a polyepoxy compound or a polyol which forms an ester bond with a carboxyl group, and a polyisocyanate compound which forms an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferable.

The active energy ray-curable pressure-sensitive adhesive composition has a property of being cured after being irradiated with an active energy ray such as an ultraviolet ray or an electron beam, and also has a property of having adhesiveness before the irradiation with the active energy ray so as to be capable of being adhered to an adherend such as a film, and of being cured by the irradiation with the active energy ray so as to adjust the adhesion force. The active energy ray-curable adhesive composition is preferably an ultraviolet-curable adhesive composition. The active energy ray-curable adhesive composition contains a base polymer, a crosslinking agent, and an active energy ray-polymerizable compound. If necessary, a photopolymerization initiator, a photosensitizer, and the like may be contained.

The adhesive composition may contain additives such as fine particles, beads (resin beads, glass beads, and the like), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders, other inorganic powders, and the like), antioxidants, ultraviolet absorbers, dyes, pigments, colorants, defoamers, anticorrosive agents, and photopolymerization initiators for imparting light scattering properties.

The adhesive layer can be formed by applying a diluted organic solvent solution of the adhesive composition onto the surface of a base film, an image display unit, or a polarizing plate and drying the applied solution. The base film is usually a thermoplastic resin film, and a typical example thereof is a separator subjected to a mold release treatment. The separator may be a film obtained by subjecting a surface of a film containing a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarylate on which a pressure-sensitive adhesive layer is formed to a releasing treatment such as a silicone treatment.

For example, the pressure-sensitive adhesive composition may be directly applied to the release-treated surface of the separator to form a pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer with a separator may be laminated on the surface of the polarizing plate. The pressure-sensitive adhesive composition may be directly applied to the surface of the polarizing plate to form a pressure-sensitive adhesive layer, and a separator may be laminated on the outer surface of the pressure-sensitive adhesive layer.

When the adhesive layer is provided on the surface of the polarizing plate, the bonding surface of the polarizing plate and/or the bonding surface of the adhesive layer is preferably subjected to a surface activation treatment such as a plasma treatment or a corona treatment, and more preferably subjected to a corona treatment.

Alternatively, an adhesive sheet may be prepared in which an adhesive composition is applied to the 2 nd separator to form an adhesive layer, and a separator is laminated on the adhesive layer, and the separator-attached adhesive layer obtained by peeling the 2 nd separator from the adhesive sheet may be laminated on the polarizing plate. The release film 2 used was a film that had a lower adhesion force to the pressure-sensitive adhesive layer than the release film and was easily peeled off.

The thickness of the pressure-sensitive adhesive layer is not particularly limited, and is, for example, preferably 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

< transparent Member >

Examples of the transparent member disposed on the visible side of the image display device include a front panel (window layer), a touch panel, and the like. As the front panel, a front panel having appropriate mechanical strength and thickness is used. Examples of such a front panel include a transparent resin plate such as a polyimide resin, an acrylic resin, and a polycarbonate resin, a glass plate, and the like. A functional layer such as an antireflection layer may be laminated on the visible side of the front panel. In the case where the front panel is a transparent resin plate, a hard coat layer may be laminated to improve physical strength, and a low moisture-permeable layer may be laminated to reduce moisture permeability.

As the touch panel, various touch panels such as a resistive film type, a capacitive type, an optical type, and an ultrasonic type, a glass plate having a touch sensor function, a transparent resin plate, and the like can be used. When a capacitive touch panel is used as the transparent member, a front panel formed of glass or a transparent resin plate is preferably provided on the visible side of the touch panel.

< bonding of polarizing plate to transparent Member >

In the lamination of the polarizing plate and the transparent member, an adhesive or an active energy ray-curable adhesive can be suitably used. When an adhesive is used, the adhesive can be attached in an appropriate manner. As a specific method of attaching, for example, a method of attaching an adhesive layer used for bonding the image display unit and the polarizing plate is given.

In the case of using the active energy ray-curable adhesive, for the purpose of preventing the adhesive solution before curing from spreading, a method of providing a bank material so as to surround the peripheral edge portion on the image display panel, placing a transparent member on the bank material, and injecting the adhesive solution can be suitably used. After the adhesive solution is injected, alignment and defoaming are performed as necessary, and then curing is performed by irradiation with an active energy ray.

Examples

The present invention will be specifically described below based on examples. The materials, reagents, amounts of substances, ratios thereof, operations and the like shown in the following examples can be appropriately modified without departing from the gist of the present invention. Therefore, the present invention is not limited to the following examples.

(1) Measurement of thickness of polarizing element:

the measurement was carried out using a digital micrometer "MH-15M" manufactured by Nikon K.K.

(2) Visibility correction of polarizing element determination of monomer transmittance:

a spectrophotometer with an integrating sphere ("V7100" manufactured by japan spectrographic corporation, 2 degree field of view; c illuminant).

(3) Measurement of boron content in polarizing element:

0.2g of a polarizing element was dissolved in 200g of a 1.9 mass% aqueous mannitol solution. Then, the aqueous solution obtained was titrated with a 1 mol/l aqueous sodium hydroxide solution, and the boron content of the polarizer was calculated from the comparison of the amount of the aqueous sodium hydroxide solution required for neutralization with the standard curve.

(4) Determination of yellowness index (yellowness):

a spectrophotometer CM-3700A manufactured by Konica Minolta was used.

(5) Measurement of boron adsorption rate of PVA-based resin film:

the PVA-based resin film cut into a 100mm square was immersed in pure water at 30 ℃ for 60 seconds, and then immersed in an aqueous solution at 60 ℃ containing 5 parts of boric acid for 120 seconds. The PVA-based resin film taken out of the aqueous boric acid solution was dried in an oven at 80 ℃ for 11 minutes. The humidity was adjusted at 23 ℃ and 55%% RH for 24 hours to obtain a PVA film containing boron. 0.2g of the thus obtained boron-containing PVA based resin film was dissolved in 200g of a 1.9 mass% aqueous mannitol solution. Then, the aqueous solution obtained was titrated with a 1 mol/l aqueous sodium hydroxide solution, and the boron content of the PVA-based resin film was calculated from a comparison between the amount of the aqueous sodium hydroxide solution required for neutralization and a standard curve. The boron content of the PVA-based resin film obtained in this manner was used as the boron adsorption rate of the PVA-based resin film.

(preparation of polarizing element 1)

A polyvinyl alcohol resin film having a boron adsorption rate of 5.90 mass% and a thickness of 45 μm was immersed in pure water at 21.5 ℃ for 79 seconds, and then immersed in an aqueous solution containing 1.0mM iodine and a potassium iodide/boric acid/water weight ratio of 2/2/100 at 23 ℃ for 151 seconds. Thereafter, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 2.5/4/100 at 60.8 ℃ for 76 seconds. Next, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 3/5.5/100 at 45 ℃ for 11 seconds. Thereafter, the film was dried at 38 ℃ to obtain a polarizing element having a thickness of 18 μm in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was mainly performed in the steps of iodine dyeing and boric acid treatment, and the total stretching magnification was 5.85 times. The visibility correction monomer transmittance of the obtained polarizing element was 41.07%, and the boron content was 4.84 mass%.

(preparation of polarizing element 2)

A polyvinyl alcohol resin film having a boron adsorption rate of 5.73 mass% and a thickness of 45 μm was immersed in pure water at 21.5 ℃ for 79 seconds, and then immersed in an aqueous solution containing 1.0mM iodine and a potassium iodide/boric acid/water weight ratio of 2/2/100 at 23 ℃ for 151 seconds. Thereafter, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 2.5/4/100 at 60.8 ℃ for 76 seconds. Next, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 3/5.5/100 at 45 ℃ for 11 seconds. Thereafter, the film was dried at 38 ℃ to obtain a polarizing element having a thickness of 18 μm in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was mainly performed in the steps of iodine dyeing and boric acid treatment, and the total stretching magnification was 5.85 times. The visibility correction monomer transmittance of the obtained polarizing element was 41.06%, and the boron content was 4.62% by mass.

(preparation of polarizing element 3)

A polyvinyl alcohol resin film having a boron adsorption rate of 5.71 mass% and a thickness of 45 μm was immersed in pure water at 21.5 ℃ for 79 seconds, and then immersed in an aqueous solution containing 1.0mM iodine and a potassium iodide/boric acid/water weight ratio of 2/2/100 at 23 ℃ for 151 seconds. Thereafter, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 2.5/4/100 at 60.8 ℃ for 76 seconds. Next, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 3/5.5/100 at 45 ℃ for 11 seconds. Thereafter, the film was dried at 38 ℃ to obtain a polarizing element having a thickness of 18 μm in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was mainly performed in the steps of iodine dyeing and boric acid treatment, and the total stretching magnification was 5.85 times. The visibility correction monomer transmittance of the obtained polarizing element was 40.96%, and the boron content was 4.48% by mass.

(preparation of polarizing element 4)

A polyvinyl alcohol resin film having a boron adsorption rate of 5.68 mass% and a thickness of 45 μm was immersed in pure water at 21.5 ℃ for 79 seconds, and then immersed in an aqueous solution containing 1.0mM iodine and a potassium iodide/boric acid/water weight ratio of 2/2/100 at 23 ℃ for 151 seconds. Thereafter, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 2.5/4/100 at 60.8 ℃ for 76 seconds. Next, the plate was immersed in an aqueous solution of potassium iodide/boric acid/water at a weight ratio of 3/5.5/100 at 45 ℃ for 11 seconds. Thereafter, the film was dried at 38 ℃ to obtain a polarizing element having a thickness of 18 μm in which iodine was adsorbed and oriented on polyvinyl alcohol. The stretching was mainly performed in the steps of iodine dyeing and boric acid treatment, and the total stretching magnification was 5.85 times. The visibility correction monomer transmittance of the obtained polarizing element was 40.88%, and the boron content was 4.35% by mass.

(preparation of PVA solution for adhesive)

50g of a modified PVA-based resin containing an acetoacetyl group (Gohsenx Z-410, manufactured by Mitsubishi CHEMICAL corporation) was dissolved in 950g of pure water, heated at 90 ℃ for 2 hours, and then cooled to room temperature to obtain a PVA solution for adhesives.

(preparation of adhesive for polarizing plate 1)

The prepared PVA solution for adhesive, pure water, and methanol were mixed so that the PVA concentration was 3.0%, the methanol concentration was 35%, and the urea concentration was 0.5%, to obtain adhesive 1 for polarizing plate.

(preparation of adhesive for polarizing plate 2)

The prepared PVA solution for adhesive, pure water, and methanol were mixed so that the PVA concentration was 3.0%, the methanol concentration was 5%, and the urea concentration was 0.5%, to obtain adhesive 2 for polarizing plate.

(saponification of cellulose acylate film)

A commercially available cellulose acylate film KC4UYW (manufactured by Konica Minolta Co., Ltd.; film thickness: 40 μm) was immersed in a 1.5mol/L NaOH aqueous solution (saponification solution) maintained at 55 ℃ for 2 minutes, and then the film was washed with water, and thereafter, immersed in a 0.05mol/L sulfuric acid aqueous solution at 25 ℃ for 30 seconds, and then subjected to a water bath under running water for 30 seconds to make the film neutral. Thereafter, the membrane was dried by repeating 3 times the removal of water by the air knife, and then left in a drying zone at 70 ℃ for 15 seconds to produce a saponified membrane.

(preparation of polarizing plate 1)

The dried adhesive layers were adjusted to have a thickness of 100nm on both sides with the polarizing plate adhesive 1 interposed between both sides of the polarizing element 1, and the saponified cellulose acylate film prepared above was bonded to both sides with a roll bonding machine and then dried at 80 ℃ for 3 minutes to obtain a polarizing plate 1 having a cellulose acylate film on both sides.

(preparation of polarizing plate 2)

A polarizing plate 2 was produced in the same manner as the production of the polarizing plate 1, except that the polarizing element 1 of the polarizing plate 1 was replaced with the polarizing element 2.

(preparation of polarizing plate 3)

A polarizing plate 3 was produced in the same manner as the production of the polarizing plate 1, except that the polarizing element 1 of the polarizing plate 1 was replaced with the polarizing element 3.

(preparation of polarizing plate 4)

A polarizing plate 4 was produced in the same manner as the production of the polarizing plate 3, except that the polarizing plate adhesive 1 of the polarizing plate 3 was replaced with the polarizing plate adhesive 2.

(preparation of polarizing plate 5)

A polarizing plate 5 was produced in the same manner as the production of the polarizing plate 2, except that the polarizing plate adhesive 1 of the polarizing plate 2 was replaced with the polarizing plate adhesive 2.

(preparation of polarizing plate 6)

Polarizing plate 6 was produced in the same manner as in the production of polarizing plate 1, except that polarizing element 4 was replaced with polarizing element 1 of polarizing plate 1.

(production of optical laminate 1)

With reference to examples of jp 2018 a 025765, an optical laminate 1 having adhesive layers with a thickness of 25 μm on both sides was produced by applying an acrylic adhesive (manufacturer: linec (ltd)) to both sides of the polarizing plate 1 produced above.

(production of optical layered body 2 to 6)

Optical laminates 2 to 6 were produced in the same manner as the production of the optical laminate 1, except that the polarizing plate 1 was replaced with polarizing plates 2 to 6.

[ high temperature durability test (105 ℃ C.) ]

The optical laminates 1 to 6 produced above were cut into a size of 50mm × 100mm, and the surfaces of the pressure-sensitive adhesive layers on both sides were bonded to alkali-free glass (trade name "EAGLE XG", manufactured by Corning corporation), thereby producing evaluation samples. In order to adjust the water content of the polarizing element before the glass plate was bonded, the optical laminate was stored at 20 ℃ and 40% relative humidity for 72 hours. In all samples, the mass was measured and not changed after 66 hours, 69 hours, and 72 hours of storage. Therefore, the water content of the optical layered bodies 1 to 6 can be considered to be the same as the equilibrium water content in the storage environment for 72 hours used in the present experimental example. When the moisture content of the optical laminate is balanced in a certain storage environment, the moisture content of the polarizing plate in the optical laminate and the moisture content of the polarizing element in the polarizing plate can be similarly considered to be balanced in the storage environment. In addition, when the moisture content of the polarizing element in the polarizing plate is balanced in a certain storage environment, the moisture content of the polarizing plate can be similarly considered to be balanced in the storage environment.

The evaluation sample was subjected to a temperature of 50 ℃ and a pressure of 5kgf/cm²(490.3kPa) was autoclaved for 1 hour and then allowed to stand at 23 ℃ under a relative humidity of 55% for 24 hours. Thereafter, the transmittance (initial value) was measured, and the film was stored at a high temperature of 105 ℃ to measure the yellow index after 168 hours. The yellow index was measured using the value of the reflection color tone when the evaluation sample was placed on a mirror surface and incident light was emitted. The measured values of the yellow index are shown in tables 1 and 2.

[ TABLE 1]

[ TABLE 2]

It is found that the optical laminates 1 to 5 have a yellow index of 50 or less, and therefore can suppress a decrease in transmittance even when stored in a high-temperature environment.

Claims

1. A polarizing plate comprising a polarizing element obtained by adsorbing and orienting a dichroic dye onto a polyvinyl alcohol resin layer, and a transparent protective film,

2. A polarizing plate comprising a polarizing element obtained by adsorbing and orienting a dichroic dye onto a polyvinyl alcohol resin layer, and a transparent protective film,

3. The polarizing plate according to claim 1 or 2,

the content of boron in the polarizing element is 4.0 mass% or more and 8.0 mass% or less.

4. The polarizing plate according to any one of claims 1 to 3, further comprising an adhesive layer for bonding the polarizing element to the transparent protective film,

the adhesive layer is a coating layer of a water-based adhesive.

5. The polarizing plate of claim 4,

the aqueous adhesive has a methanol concentration of 10 to 70 mass%.

6. The polarizing plate of claim 4 or 5,

the aqueous adhesive contains a polyvinyl alcohol resin.

7. The polarizing plate according to any one of claims 4 to 6,

the adhesive layer has a thickness of 0.01 to 7 [ mu ] m.

8. The polarizing plate according to any one of claims 1 to 7,

the transparent protective film is a retardation film comprising a 1 st optical compensation layer and a 2 nd optical compensation layer in this order from the polarizing element side,

80nm≤Re₁(590)≤120nm (1)

20nm＜Re₁(590)≤60nm (2)

1＜Nz₁＜2 (3)

－4＜Nz₂＜－1 (4)。

9. the polarizing plate according to any one of claims 1 to 8,

the polarizing plate is used for an image display device,

10. An image display device, comprising:

an image display unit,

A 1 st adhesive layer laminated on a visible-side surface of the image display unit, and

the polarizing plate according to any one of claims 1 to 9 laminated on a viewing-side surface of the 1 st adhesive layer.

11. The image display device according to claim 10, further comprising:

a 2 nd adhesive layer laminated on the visible-side surface of the polarizing plate, and

and a transparent member laminated on a visible side surface of the 2 nd adhesive layer.

12. The image display apparatus according to claim 11,

the transparent member is a glass plate or a transparent resin plate.

13. The image display apparatus according to claim 11,

the transparent member is a touch panel.

14. A method for manufacturing a polarizing plate according to claim 1,

the manufacturing method comprises:

15. A method for manufacturing a polarizing plate according to claim 2,

the manufacturing method comprises: