JP6968531B2 - Manufacturing method of polarizing plate with protective film - Google Patents

Description

The present invention relates to a method for manufacturing a polarizing plate with a protective film, which is formed by laminating a protective film on the surface of the polarizing plate.

In recent years, mobile terminals such as smartphones are rapidly becoming larger and slimmer in terms of design and portability. In order to realize long-time driving with a limited thickness, there is a demand for high brightness, thinness and light weight of the polarizing plate used.

As the polarizing plate, conventionally, a polarizing film made of a polyvinyl alcohol-based resin and a protective film made of triacetyl cellulose (TAC) bonded to the polarizing film with an adhesive are generally used. However, in recent years, protective films made of resins other than TAC have also come to be used from the viewpoints of thinning, durability, cost, productivity and the like (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2004-245925

The polarizing plate is sensitive to the environment in which it is placed, and depending on the environmental conditions, it is likely to be deformed in a bow shape. In the present specification, this variation is also referred to as "curl". There are two types of curls, "normal curl" and "reverse curl". Where the polarizing plate has a first main surface on the side to be bonded to an image display element such as a liquid crystal cell and a second main surface on the opposite side, the "positive curl" is the first main surface. The curl is convex on the surface side, and the "reverse curl" is a curl on the second main surface side. If the polarizing plate has reverse curl, when it is bonded to the image display element via the pressure-sensitive adhesive layer, a bonding error may occur or air bubbles may be mixed in the interface between the pressure-sensitive adhesive layer and the image display element. It is easy to cause problems such as.

Therefore, the present invention is to provide a method capable of manufacturing an optical member including a polarizing plate structure and in which reverse curl is sufficiently suppressed.

The present inventor 1) the polarizing plate is usually marketed as a polarizing plate with a protective film to which a peelable protective film (also referred to as a surface protective film) for protecting the surface thereof is attached, and is used as an image display element. In many cases, they are bonded in the form of a polarizing plate with a protective film, and 2) Therefore, in order to solve the above problems, reverse curl is sufficiently suppressed as a polarizing plate with a protective film. Based on the idea that it should be done, the present invention was reached after further diligent studies. That is, the present invention provides the following method for manufacturing a polarizing plate with a protective film.

[1] A method for manufacturing a polarizing plate with a protective film, which comprises a step of stacking a protective film on one side of the polarizing plate and passing it between a pair of bonding rolls to press the polarizing film.
The thickness of the protective film is T ₁ [μm], the tensile elastic modulus in MD is E ₁ [MPa], and the film tension in MD before being passed through the pair of laminating rolls is F ₁ [N / m]. When the thickness of the plate is T ₂ [μm], the tensile elastic modulus in the MD direction is E ₂ [MPa], and the film tension in the MD before being passed through the pair of laminating rolls is F ₂ [N / m]. The pressing process is described by the following formula (I):

A manufacturing method performed under the conditions that satisfy the conditions.
[2] The pressing step is described by the following formula (II):

The production method according to [1], which is carried out under the conditions satisfying the above conditions.
[3] The production method according to [1] or [2], wherein the polarizing plate produces curls with the side on which the protective film is stacked convex when the polarizing plate is made into a single-wafered body.

[4] The polarizing plate includes a polarizing film, a first thermoplastic resin film laminated on one surface thereof, and a second thermoplastic resin film laminated on the other surface [1] to [ 3] The manufacturing method according to any one of.

[5] The production method according to [4], wherein the first thermoplastic resin film has a higher equilibrium moisture content at a temperature of 23 ° C. and a relative humidity of 55% than the second thermoplastic resin film.

[6] The production method according to [5], wherein the difference between the first thermoplastic resin film and the second thermoplastic resin film is 0.5% by weight or more.

[7] The production method according to any one of [4] to [6], wherein the protect film is arranged on the side of the first thermoplastic resin film.

[8] The production method according to any one of [4] to [7], wherein the first thermoplastic resin film has an equilibrium moisture content of 1.5% by weight or more.

[9] The production method according to any one of [1] to [8], wherein the thickness of the polarizing plate is 100 μm or less.

According to the present invention, it is possible to manufacture a polarizing plate with a protective film in which reverse curl is sufficiently suppressed. According to this polarizing plate with a protective film, it is possible to suppress the above-mentioned problems and carry out bonding to an image display element with good productivity.

It is a side view schematically showing an example of the manufacturing method of the polarizing plate with a protective film which concerns on this invention. It is a schematic diagram explaining MD curl, (a) is a side view, (b) is a top view. It is a schematic sectional drawing which shows an example of the layer structure of a polarizing plate. It is the schematic sectional drawing which shows the other example of the layer structure of a polarizing plate. It is the schematic sectional drawing which shows the other example of the layer structure of a polarizing plate.

(1) Pressing Step With reference to FIG. 1, in the method for manufacturing a polarizing plate with a protective film according to the present invention, the protective film 1 is placed on one side of the polarizing plate 2 and between a pair of bonding rolls 5 and 5. A step of pressing the laminated body of the protective film 1 and the polarizing plate 2 from above and below by passing the polarizing film 1 is included, and the polarizing plate 3 with a protective film is manufactured by the step. Normally, the protect film 1 and the polarizing plate 2 used in the pressing step are continuously fed from a feeding roll (not shown) and continuously conveyed, and introduced between the pair of bonding rolls 5 and 5. Will be done. The transport direction of the protect film 1 and the polarizing plate 2 is the longitudinal direction of the film, and the transport directions of both are usually parallel.

In the pressing step, the thickness of the protective film 1 is T ₁ [μm], the tensile elastic modulus in MD is E ₁ [MPa], and the film tension in MD before being passed through the pair of bonding rolls 5 and 5 is F ₁ [. N / m], the thickness of the polarizing plate 2 is T ₂ [μm], the tensile modulus in the MD direction is E ₂ [MPa], and the film tension in the MD before being passed through the pair of bonding rolls 5 and 5 is F _2. When [N / m] is set, the following formula (I):

Perform under the conditions that satisfy the conditions. As used herein, MD means the mechanical flow direction of the film, that is, the longitudinal direction of the film. The direction orthogonal to the MD, that is, the film width direction is also referred to as TD in the present specification.

_{The tensile elastic moduli E 1} and E ₂ in the MD of the protective film 1 and the polarizing plate 2 are the tensile elastic moduli in an environment of 55% relative humidity at 23 ° C., and are measured according to the description in the section of Examples described later. .. _{The film tensions F 1} and F ₂ in the MD of the protective film 1 and the polarizing plate 2 are the film tensions before being passed through the pair of bonding rolls 5 and 5, and are on the pair of bonding rolls 5 and 5 and on the upstream side thereof. It refers to the tension of the film running between the drive rolls (pair of nip rolls) closest to the bonded rolls 5 and 5.

By bonding the protect film 1 to the polarizing plate 2 under the condition satisfying the above formula (I), the shape of the polarizing plate 2 is changed in the direction in which the main surface on which the protect film 1 is stacked becomes concave (that is, the normal curl direction). ) Can be corrected (curl correction). Therefore, for example, when the polarizing plate 2 used in the pressing step produces reverse curl (curl with the main surface side on which the protect film 1 is overlapped is convex) when formed into a single-wafer body, the present invention. According to the report, this reverse curl can be corrected in the forward curl direction, and as a result, the reverse curl is sufficiently suppressed when the single-wafer body is formed, the reverse curl is flat without curl, or the positive curl is positive. A polarizing plate with a protective film 3 having a curl can be obtained. The obtained polarizing plate 3 with a protective film is preferably flat without curling or has positive curl when made into a single-wafered body.

According to the study of the present inventor, the left side and the right side of the above formula (I) are indexes indicating the distorted state of the protective film 1 and the polarizing plate 2 when they are bonded to each other, respectively. By bonding the protective film 1 to the polarizing plate 2 under the condition satisfying the above formula (I), the polarizing plate 2 can be corrected in the positive curl direction because of the force for eliminating the strain acting after the bonding. It is considered that this is because the protective film 1 becomes larger.

The relationship of the above formula (I) is selected from 1 or the thickness of the protective film 1 and / or the polarizing plate 2, the tensile modulus in MD, and the film tension in MD before being passed through the pair of bonded rolls 5, 5. This can be achieved by adjusting two or more elements. The element to be adjusted preferably includes the film tension of the protect film 1 and / or the polarizing plate 2.

Here, curl will be described. Curl refers to deformation in which an optical member (optical film) such as a polarizing plate 2 or a polarizing plate with a protective film 3 warps in a bow shape, and this deformation usually occurs in a single-wafer of the optical member. Curling tends to occur as the optical member becomes thinner.

The curl can be classified into two types, "normal curl" and "reverse curl", depending on which side of the two opposing main surfaces of the optical member is convex and curled. When the main surface on the side to be bonded to an image display element such as a liquid crystal cell is the first main surface and the main surface on the opposite side is the second main surface, the "normal curl" is the first main surface. The curl has a convex side, and the "reverse curl" is a curl having a convex side on the second main surface. The polarizing plate 2 used in the manufacturing method according to the present invention typically produces reverse curl (curl with the main surface side on which the protect film 1 is laminated) when it is made into a single frond. be.

Further, the curl can be classified into two types, "MD curl" and "TD curl", depending on which end (side) of the optical member which is a frond. With reference to FIG. 2, when the single-wafer of the curled optical member is placed on a flat table with the convex side down, the "MD curl" is the end (typically both ends) in the MD. The curl is such that the portions) are lifted, and the "TD curl" is a curl in which the ends (typically both ends) in the TD are lifted. The manufacturing method according to the present invention is particularly advantageous for correcting MD curls.

The evaluation of the curl that an optical member such as the polarizing plate 2 or the polarizing plate with a protective film 3 can have (certification of the type of normal curl, reverse curl, MD curl, TD curl, and the amount of the curl) is obtained by the obtained optical member. This is done for the sheet-fed body cut from. This single-wafer is a square single-wafer with a pair of opposing sides parallel to the MD and the remaining pair of opposite sides parallel to the TD, with an MD length of 300 mm and a TD length of 200 mm. And.

According to the present invention, it is possible to obtain a polarizing plate 3 with a protective film, which is sufficiently suppressed in reverse curl when formed into a single frond, preferably flat without curl, or has positive curl. can. According to the polarizing plate 3 with a protective film, when the polarizing plate 3 with a protective film is bonded to the image display element via the pressure-sensitive adhesive layer, a bonding error may occur or air bubbles may be mixed at the interface between the pressure-sensitive adhesive layer and the image display element. Defects can be effectively suppressed, and the polarizing plate 3 with a protective film and the image display element can be bonded with good productivity. Since the curl generated in the polarizing plate 3 with a protective film is a positive curl, even if the curl amount is relatively large, there is no particular problem in terms of the above-mentioned defects and productivity. The polarizing plate with a protective film 3 obtained by the present invention may have a reverse curl to the extent that the above-mentioned defects can be suppressed (preferably, the above-mentioned defects do not occur).

The amount of correction in the positive curl direction according to the present invention depends on the difference between the left side and the right side of the above formula (I), which is an index of strain, and the larger the difference, the larger the correction amount tends to be. Although it depends on how much the polarizing plate 2 used in the pressing step is curled when made into a single-wafered body, the obtained polarizing plate 3 with a protective film does not have reverse curl. In order to be flat or have a positive curl, the pressing step is performed by the following formula (II):

It is preferable to carry out under the conditions satisfying. When the polarizing plate 2 used in the pressing step has a large reverse curl, the above formula (II) is used to make the obtained polarizing plate with a protective film 3 flat or have a positive curl. The left side of the may have to be greater than 55 (eg, 60 or greater, 70 or greater, 80 or greater, 100 or greater, 130 or greater, 160 or greater, or 180 or greater). The left side of the above equation (II) may be, for example, 1000 or less.

The left side and the right side of the above formula (I) are usually 1 × 10 ^{-5 to} 1000 × 10 ^-5 , respectively, and may be 5 × 10 ^{-5 to} 500 × 10 ^-5 , respectively.

When the protect film 1 is laminated on one side of the polarizing plate 2 and passed between the pair of bonding rolls 5 and 5, the adhesive layer of the protect film 1 is laminated so as to be in contact with the one side of the polarizing plate 2. Prior to laminating the protective film 1 and the polarizing plate 2, plasma treatment, corona treatment, ultraviolet irradiation treatment, frame (flame) treatment, on the bonded surface of at least one of the adhesive layer of the protective film 1 and the polarizing plate 2 are performed. A surface activation treatment such as a saponification treatment may be performed.

In the step of pressing with the pair of bonding rolls 5 and 5, the pressure (nip pressure) applied to the laminate of the protective film 1 and the polarizing plate 2 is, for example, 0.01 to 0.5 MPa, and 0.05 to 0.05 MPa. It may be 0.3 MPa. The nip pressure usually does not significantly affect the curl of the obtained polarizing plate 3 with a protective film. As the bonding rolls 5 and 5, conventionally known ones such as those having a surface made of metal (including an alloy such as SUS) or rubber can be used.

(2) Protect film The protect film 1 is usually composed of a base film and an adhesive layer laminated on the base film. The protective film 1 is a film for protecting the surface of the polarizing plate 2, and is usually peeled off together with the pressure-sensitive adhesive layer that the polarizing plate 3 with a protective film has after being bonded to, for example, an image display element. .. The base film is a thermoplastic resin, for example, a polyolefin resin such as a polyethylene resin, a polypropylene resin, or a cyclic polyolefin resin; a polyester resin such as polyethylene terephthalate or polyethylene naphthalate; a polycarbonate resin; (meth) acrylic resin. It can be made of resin or the like. The pressure-sensitive adhesive layer can be composed of an acrylic pressure-sensitive adhesive, an epoxy-based pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, or the like. Further, it can also be composed of a resin layer having self-adhesiveness such as polypropylene-based resin and polyethylene-based resin. _{The tensile elastic modulus E 1} in the MD direction can be adjusted mainly by selecting the material of the base film.

In addition, in this specification, "(meth) acrylic resin" represents at least one kind selected from the group consisting of an acrylic resin and a methacrylic resin. The same applies to other terms with "(meta)".

The thickness T ₁ of the protective film 1 can be, for example, 5 to 200 μm, preferably 10 to 150 μm, more preferably 20 to 120 μm, still more preferably 25 to 100 μm (for example, 90 μm or less, further 75 μm). Below). If the thickness T ₁ is less than 5 μm, the polarizing plate 2 may be insufficiently protected, which is disadvantageous in terms of handleability. If the thickness T ₁ exceeds 200 μm, it is disadvantageous in terms of cost and reworkability of the protective film 1. Further, when the thickness T ₁ exceeds 200 μm, it tends to be difficult to satisfy the relational expressions of the above equations (I) and / or equations (II).

(3) Polarizing plate The polarizing plate 2 is a polarizing element including at least a polarizing film, and further includes a thermoplastic resin film such as a protective film usually laminated on at least one surface of the polarizing film. The protective film is an optical film that protects the polarizing film.

(3-1) Example of Configuration of Polarizing Plate The polarizing plate 2 may include a layer or film other than a polarizing film and a protective film, for example, an optical layer or an optical film having an optical function other than the polarizing film. Examples of the optical layer or optical film having the other optical function are a retardation film (or a retardation layer), a luminance improving film, and the like. Various optical films including a protective film can be laminated and bonded on a polarizing film via an adhesive layer or an adhesive layer. Further, the polarizing plate 2 may have a surface treatment layer (coating layer) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer.

The thickness T _{2 of the} polarizing plate 2 is usually 200 μm or less, and is preferably 125 μm or less, more preferably 100 μm or less, and further preferably 75 μm or less from the viewpoint of thinning. Although more polarizing plate 2 thickness T ₂ is small it becomes prone to curl at its sheet material, according to the present invention, a small thickness T ₂ of the polarizing plate 2, opposite when the polarizing plate 2 has a sheet body Even if curl is generated, this reverse curl can be effectively corrected in the forward curl direction. From the viewpoint of thinning and optical characteristics, it is difficult to adjust the mechanical properties of the polarizing film and the protective film in order to make the curl when the polarizing plate 2 is a single-wafered body flat or positive, but the protective film. Is usually peeled off after the polarizing plate 3 with a protective film is attached to, for example, an image display element, so that the mechanical properties can be adjusted for the purpose of curl correction.

Examples of the layer structure of the polarizing plate 2 will be described with reference to FIGS. 3 to 5, but the layer structure is not limited to these examples. The polarizing plate 2a shown in FIG. 3 is a polarizing film 10; a first thermoplastic resin film 20 bonded to one surface of the polarizing film 10; a second thermoplastic bonded to the other surface of the polarizing film 10. The resin film 30; the pressure-sensitive adhesive layer 40 laminated on the outer surface of the second thermoplastic resin film 30; the separate film 50 laminated on the outer surface of the pressure-sensitive adhesive layer 40 is included. The separate film 50 is a peelable film for protecting the surface (outer surface) of the pressure-sensitive adhesive layer 40. The first and second thermoplastic resin films 20 and 30 are, for example, protective films.

As in the polarizing plate 2b shown in FIG. 4, one of the first and second thermoplastic resin films 20 and 30 may be omitted. In the polarizing plate 2b, the second thermoplastic resin film 30 is omitted, and the pressure-sensitive adhesive layer 40 is directly applied to the outer surface of the polarizing film 10 (the surface opposite to the surface on which the first thermoplastic resin film 20 is laminated). Is pasted together. Such a polarizing plate having a thermoplastic resin film on only one surface of the polarizing film 10 is advantageous for thinning the polarizing plate. When the thermoplastic resin film is laminated on only one surface of the polarizing film 10, the polarizing plate 2 tends to cause curl on the single-wafered body, but according to the present invention, only one surface of the polarizing film 10 is laminated. Even if the polarizing plate 2 causes reverse curl when the polarizing plate 2 is made into a single-wafered body by laminating and laminating a thermoplastic resin film on the surface, this reverse curl can be effectively corrected in the forward curl direction. ..

Further, the pressure-sensitive adhesive layer 40 and the separate film 50 may be omitted as in the polarizing plate 2c shown in FIG. The polarizing plate 2 may have a protective film on one surface in advance, which is different from the protective film 1 used in the pressing step. In this case, the obtained polarizing plate with a protective film 3 is a polarizing plate having a protective film on both sides.

Although not shown in FIGS. 3 to 5, the polarizing film 10 and the first and second thermoplastic resin films 20 and 30 can be bonded to each other, preferably using an adhesive.

(3-2) Polarizing film The polarizing film 10 can be a uniaxially stretched polyvinyl alcohol-based resin film in which a dichroic dye is adsorbed and oriented. As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and a copolymer of vinyl acetate and another monomer copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth) acrylamides having an ammonium group.

The degree of saponification of the polyvinyl alcohol-based resin can be in the range of 80.0 to 100.0 mol%, preferably in the range of 90.0 to 100.0 mol%, and more preferably 98.0. It is in the range of 100.0 mol%. When the degree of saponification is less than 80.0 mol%, the water resistance and moisture heat resistance of the obtained polarizing plate 2 may decrease.

_{The degree of saponification is the ratio of the acetic acid group (acetoxy group: −OCOCH 3} ) contained in the polyvinyl acetate resin, which is the raw material of the polyvinyl alcohol resin, changed to a hydroxyl group by the saponification step in terms of unit ratio (mol%). It is expressed by the following formula:
Degree of saponification (mol%) = 100 x (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic acid groups)
Defined in. The degree of saponification can be determined in accordance with JIS K 6726 (1994). The higher the degree of saponification, the higher the proportion of hydroxyl groups, and therefore the lower the proportion of acetic acid groups that inhibit crystallization.

The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10000, more preferably 1500 to 8000, and further preferably 2000 to 5000. The average degree of polymerization of the polyvinyl alcohol-based resin can also be determined in accordance with JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain preferable polarization performance, and if it exceeds 10,000, the solubility in a solvent deteriorates, and it may be difficult to form a polyvinyl alcohol-based resin film.

The dichroic dye contained (adsorption orientation) in the polarizing film 10 can be iodine or a dichroic organic dye. Specific examples of the bicolor organic dyes are Red BR, Red LR, Red R, Pink LB, Rubin BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Includes Sky Blue, Direct First Orange S, and First Black. As the dichroic dye, only one kind may be used alone, or two or more kinds may be used in combination. The dichroic dye is preferably iodine.

The polarizing film 10 is a step of uniaxially stretching a polyvinyl alcohol-based resin film; a step of adsorbing a bicolor dye by dyeing the polyvinyl alcohol-based resin film with a bicolor dye; polyvinyl adsorbed with a bicolor dye. It can be produced through a step of cross-linking the alcohol-based resin film; and a step of washing with water after the cross-linking treatment.

The polyvinyl alcohol-based resin film is a film formed by forming the above-mentioned polyvinyl alcohol-based resin. The film forming method is not particularly limited, and a known method such as a melt extrusion method or a solvent casting method can be adopted. The thickness of the polyvinyl alcohol-based resin film is, for example, about 10 to 150 μm, preferably 50 μm or less, and more preferably 35 μm or less.

The uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before, simultaneously with, or after dyeing the dichroic dye. If the uniaxial stretching is performed after staining, the uniaxial stretching may be performed before or during the crosslinking treatment. Further, uniaxial stretching may be performed at these a plurality of steps.

In uniaxial stretching, rolls having different peripheral speeds may be uniaxially stretched, or thermal rolls may be used to uniaxially stretch the rolls. Further, the uniaxial stretching may be a dry stretching in which stretching is performed in the atmosphere, or a wet stretching in which the polyvinyl alcohol-based resin film is stretched in a solution. The draw ratio is usually about 3 to 8 times.

As a method of dyeing the polyvinyl alcohol-based resin film with a dichroic dye, for example, a method of immersing the polyvinyl alcohol-based resin film in an aqueous solution (dyeing solution) containing the dichroic dye is adopted. The polyvinyl alcohol-based resin film is preferably subjected to a dipping treatment (swelling treatment) in water before the dyeing treatment.

When iodine is used as the dichroic dye, a method of immersing a polyvinyl alcohol-based resin film in an aqueous solution containing iodine and potassium iodide for dyeing is usually adopted. The iodine content in this dyeing aqueous solution is usually 0.01 to 1 part by weight per 100 parts by weight of water. The content of potassium iodide is usually 0.5 to 20 parts by weight per 100 parts by weight of water. The temperature of the dyeing aqueous solution is usually about 20 to 40 ° C.

On the other hand, when a dichroic organic dye is used as the dichroic dye, a method of immersing a polyvinyl alcohol-based resin film in a dyeing aqueous solution containing a water-soluble dichroic organic dye and dyeing is usually adopted. The content of the dichroic organic dye in the dyeing aqueous solution is usually 1 × 10 ^-4 to 10 parts by weight, preferably 1 × 10 ^-3 to 1 part by weight per 100 parts by weight of water. This dyeing aqueous solution may contain an inorganic salt such as sodium sulfate as a dyeing aid. The temperature of the dyeing aqueous solution is usually about 20 to 80 ° C.

The cross-linking treatment after dyeing with a dichroic dye can be performed by immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing a cross-linking agent. A preferred example of the cross-linking agent is boric acid, but other cross-linking agents such as boron compounds such as borax, glyoxal and glutaraldehyde can also be used. Only one type of cross-linking agent may be used, or two or more types may be used in combination.

The amount of the cross-linking agent in the cross-linking agent-containing aqueous solution is usually 2 to 15 parts by weight, preferably 5 to 12 parts by weight per 100 parts by weight of water. When iodine is used as the dichroic dye, the cross-linking agent-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the cross-linking agent-containing aqueous solution is usually 0.1 to 15 parts by weight, preferably 5 to 12 parts by weight per 100 parts by weight of water. The temperature of the cross-linking agent-containing aqueous solution is usually 50 ° C. or higher, preferably 50 to 85 ° C.

The polyvinyl alcohol-based resin film after the cross-linking treatment is usually washed with water. The water washing treatment can be performed, for example, by immersing the crosslinked polyvinyl alcohol-based resin film in water. The temperature of water in the washing treatment is usually about 1 to 40 ° C.

After washing with water, a drying treatment is performed to obtain a polarizing film 10. The drying treatment can be drying with a hot air dryer, drying by contacting with a hot roll, drying with a far-infrared heater, or the like. The temperature of the drying treatment is usually about 30 to 100 ° C, preferably 50 to 90 ° C.

The thickness of the polarizing film 10 is usually about 2 to 40 μm. From the viewpoint of thinning the polarizing plate 2, the thickness of the polarizing film 10 is preferably 20 μm or less, more preferably 15 μm or less, and further preferably 10 μm or less. The smaller the thickness of the polarizing film 10, the more likely the polarizing plate 2 is to curl in its single-wafer body. Even if curl is generated, this reverse curl can be effectively corrected in the forward curl direction.

(3-3) First and Second Thermoplastic Resin Films The first and second thermoplastic resin films 20 and 30 are independently translucent thermoplastic resins, preferably optically transparent heat. It is a film made of a plastic resin. The thermoplastic resins constituting the first and second thermoplastic resin films 20 and 30 are, for example, polyolefin resins such as chain polyolefin resins (polypropylene resins and the like) and cyclic polyolefin resins (norbornen resins and the like). Cellular resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate resins; (meth) acrylic resins such as methyl methacrylate resin; polystyrene resins; Polyvinyl chloride resin; Acrylonitrile / butadiene / styrene resin; Acrylonitrile / styrene resin; Polyvinyl acetate resin; Polyvinylidene chloride resin; Polyamide resin; Polyacetal resin; Modified polyphenylene ether resin; Polysulfone resin; Polyether sulfone-based resin; polyallylate-based resin; polyamideimide-based resin; polyimide-based resin and the like can be used.

Examples of the chain polyolefin resin include homopolymers of chain olefins such as polyethylene resin and polypropylene resin, and copolymers composed of two or more kinds of chain olefins. More specific examples are polypropylene-based resins (polypropylene resin which is a homopolymer of propylene and copolymers mainly composed of propylene), polyethylene-based resins (polyethylene resin which is a homopolymer of ethylene, and ethylene as a main component). Containing a copolymer).

Cyclic polyolefin resin is a general term for resins that are polymerized with cyclic olefin as a polymerization unit. Specific examples of the cyclic polyolefin resin include a ring-opened (co) polymer of a cyclic olefin, an addition polymer of a cyclic olefin, and a copolymer of a cyclic olefin and a chain olefin such as ethylene or propylene (typically). Is a random copolymer), a graft polymer obtained by modifying these with an unsaturated carboxylic acid or a derivative thereof, and a hydride thereof. Among them, a norbornene-based resin using a norbornene-based monomer such as norbornene or a polycyclic norbornene-based monomer is preferably used as the cyclic olefin.

The cellulosic resin is obtained by substituting a part or all of hydrogen atoms in the hydroxyl group of cellulose obtained from raw material cellulose such as cotton linter and wood pulp (broadwood pulp, coniferous pulp) with an acetyl group, a propionyl group and / or a butyryl group. Also, it refers to a cellulose organic acid ester or a cellulose mixed organic acid ester. For example, those composed of acetic acid ester of cellulose, propionic acid ester, butyric acid ester, mixed ester thereof and the like can be mentioned. Of these, triacetyl cellulose, diacetyl cellulose, cellulose acetate propionate, and cellulose acetate butyrate are preferable.

The polyester-based resin is a resin other than the above-mentioned cellulose-based resin having an ester bond, and is generally composed of a polyvalent carboxylic acid or a polycondensate of a derivative thereof and a polyhydric alcohol. As the polyvalent carboxylic acid or a derivative thereof, a divalent dicarboxylic acid or a derivative thereof can be used, and examples thereof include terephthalic acid, isophthalic acid, dimethyl terephthalate, and dimethyl naphthalenedicarboxylate. As the polyhydric alcohol, a divalent diol can be used, and examples thereof include ethylene glycol, propanediol, butanediol, neopentyl glycol, cyclohexanedimethanol and the like. Examples of suitable polyester-based resins include polyethylene terephthalate.

The polycarbonate-based resin is an engineering plastic made of a polymer in which a monomer unit is bonded via a carbonate group, and is a resin having high impact resistance, heat resistance, flame retardancy, and transparency. The polycarbonate-based resin may be a resin called modified polycarbonate having a polymer skeleton modified in order to lower the photoelastic coefficient, or a copolymerized polycarbonate having improved wavelength dependence.

The (meth) acrylic resin is a polymer containing a structural unit derived from the (meth) acrylic monomer. The polymer is typically a polymer containing a methacrylic acid ester. The polymer preferably contains 50% by weight or more of the structural units derived from the methacrylic acid ester with respect to all the structural units. The (meth) acrylic resin may be a homopolymer of a methacrylic acid ester, or may be a copolymer containing a structural unit derived from another polymerizable monomer. In this case, the ratio of the structural units derived from other polymerizable monomers is preferably 50% by weight or less with respect to the total structural units.

As the methacrylic acid ester that can constitute the (meth) acrylic resin, an alkyl methacrylic acid ester is preferable. Examples of the alkyl methacrylate ester include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate. , Methacrylic acid alkyl ester having 1 to 8 carbon atoms of an alkyl group such as 2-hydroxyethyl methacrylate. The number of carbon atoms of the alkyl group contained in the methacrylic acid alkyl ester is preferably 1 to 4. In the (meth) acrylic resin, only one type of methacrylic acid ester may be used alone, or two or more types may be used in combination.

Examples of the other polymerizable monomer constituting the (meth) acrylic resin include acrylic acid esters and other compounds having a polymerizable carbon-carbon double bond in the molecule. As the other polymerizable monomer, only one kind may be used alone, or two or more kinds may be used in combination. As the acrylic acid ester, an acrylic acid alkyl ester is preferable. Examples of the acrylic acid alkyl ester include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate. , Acrylic acid alkyl ester having 1 to 8 carbon atoms of an alkyl group such as 2-hydroxyethyl acrylate. The number of carbon atoms of the alkyl group contained in the acrylic acid alkyl ester is preferably 1 to 4. In the (meth) acrylic resin, only one kind of acrylic acid ester may be used alone, or two or more kinds may be used in combination.

Examples of the compound having a polymerizable carbon-carbon double bond in other molecules include vinyl compounds such as ethylene, propylene and styrene, and vinyl cyan compounds such as acrylonitrile. As the other compounds having a polymerizable carbon-carbon double bond in the molecule, only one kind may be used alone, or two or more kinds may be used in combination.

The first and second thermoplastic resin films 20 and 30 can be protective films for protecting the polarizing film 10 which are laminated and bonded to one surface of the polarizing film 10. The first or second thermoplastic resin films 20 and 30 can also be protective films having optical functions such as a retardation film and a luminance improving film. For example, by stretching a thermoplastic resin film made of the above material (uniaxial stretching or biaxial stretching, etc.) or forming a liquid crystal layer or the like on the film, a phase difference to which an arbitrary retardation value is given is given. It can be a film. The first and / or second thermoplastic resin films 20 and 30 are surface-treated layers (coatings) such as a hard coat layer, an antiglare layer, an antireflection layer, an antistatic layer, and an antifouling layer laminated on the surface thereof. It may have a layer).

The thicknesses of the first and second thermoplastic resin films 20 and 30 are usually 1 to 100 μm, but are preferably 5 to 60 μm, more preferably 5 to 50 μm from the viewpoint of strength, handleability, and the like. If the thickness is within this range, the polarizing film 10 can be mechanically protected, and the shrinkage of the polarizing film 10 when the polarizing plate 2 is exposed to a moist heat environment can be suppressed. The smaller the thickness of the first thermoplastic resin film 20 and the second thermoplastic resin film 30, the more likely the polarizing plate 2 is to curl in its single-wafer, but according to the present invention, the first thermoplastic resin film 20 and the like. Even if the thickness of the second thermoplastic resin film 30 is as thin as 40 μm or less, further 30 μm or less, and reverse curl occurs when the polarizing plate 2 is made into a single-wafer, this reverse curl is directed in the forward curl direction. It can be corrected effectively.

When the first thermoplastic resin film 20 is provided on one surface of the polarizing film 10 and the second thermoplastic resin film 30 is provided on the other surface, as in the polarizing plates 2a and 2c shown in FIGS. 3 and 5. The first thermoplastic resin film 20 and the second thermoplastic resin film 30 may be made of the same kind of thermoplastic resin or different kinds of thermoplastic resin, but different kinds of heat. When the equilibrium moisture content and moisture permeability of the thermoplastic resin films bonded on both sides are different from each other, such as when the film is made of plastic resin, curl is particularly likely to occur on the single-wafer body of the polarizing plate 2. The present invention is particularly advantageous in such cases.

For example, as the first thermoplastic resin film 20, a film having a higher equilibrium moisture content than the second thermoplastic resin film 30 can be used. The larger the difference in the equilibrium moisture content between the first thermoplastic resin film 20 and the second thermoplastic resin film 30 bonded to both sides of the polarizing film 10, the more likely the polarizing plate 2 is to curl in its single-wafer. According to the present invention, when the difference in equilibrium moisture content is 0.5% by weight or more, further 1% by weight or more, further 1.5% by weight or more, and the polarizing plate 2 is a single-wafered body. Even if a reverse curl is generated, the reverse curl can be effectively corrected in the forward curl direction.

In the present specification, the equilibrium moisture content of the film is measured by the dry gravimetric method, and specifically, the following formula:
Equilibrium moisture content (% by weight) = {(film weight before drying treatment-film weight after drying treatment) / film weight before drying treatment} x 100
Asked according to. Here, the weight of the film before the drying treatment is the weight after the film is stored for 24 hours in an environment of a temperature of 23 ° C. and a relative humidity of 55%, and the drying means a treatment of drying the film at 105 ° C. for 2 hours. Examples of the combination of the thermoplastic resin films having a difference in equilibrium moisture content of 0.5% by weight or more include a combination of a cellulose-based resin film (TAC film or the like) and a cyclic polyolefin-based resin film, and a cellulose-based resin film (TAC). A combination of a film, etc.) and a (meth) acrylic resin film, a combination of a cellulose-based resin film (TAC film, etc.) and a polyester-based resin film, a cellulose-based resin film (TAC film, etc.) and a chain polyolefin-based resin film. , A combination of a (meth) acrylic resin film and a cyclic polyolefin resin, a combination of a (meth) acrylic resin film and a polyester resin film, and the like. The difference in the equilibrium moisture content between the first thermoplastic resin film 10 and the second thermoplastic resin film 20 is usually 5% by weight or less, preferably 2.5% by weight or less.

The equilibrium moisture content of the first thermoplastic resin film 20 is, for example, 1.5% by weight or more, and may be 2% by weight or more. The equilibrium moisture content of the first thermoplastic resin film 20 is usually 5% by weight or less.

When a film having a higher equilibrium moisture content than the second thermoplastic resin film 30 is used as the first thermoplastic resin film 20, the equilibrium moisture content of the second thermoplastic resin film 20 is usually 0.1 to 1.5. It is% by weight, preferably 0.1 to 1% by weight. Examples of the thermoplastic resin constituting the second thermoplastic resin film 20 capable of achieving such an equilibrium moisture content are a cyclic polyolefin resin, a (meth) acrylic resin, a polyester resin, a chain polyolefin resin and the like.

The equilibrium moisture content of a thermoplastic resin film is determined by the material (type of thermoplastic resin constituting the film), the thickness of the film, the presence or absence of a surface treatment layer (coating layer) that can be attached to the film surface, and the material. Can also be adjusted by.

When a film having a higher equilibrium moisture content than the second thermoplastic resin film 30 is used as the first thermoplastic resin film 20, the reverse curl that tends to occur in the polarizing plate 2 is usually corrected in the positive curl direction. In the pressing step, the protect film 1 is arranged on the first thermoplastic resin film 20 side of the polarizing plate 2.

Further, for example, as the first thermoplastic resin film 20, a film having a higher moisture permeability than the second thermoplastic resin film 30 can be used. The larger the difference in moisture permeability between the first thermoplastic resin film 20 and the second thermoplastic resin film 30 bonded to both sides of the polarizing film 10, the more likely the polarizing plate 2 is to curl in its single-wafer. According to the present invention, the difference in moisture permeability 30g / (m ² · 24hr) or more, still more 50g / (m ² · 24hr) or more, still further is a 100g / (m ² · 24hr) or more, the polarization Even if the plate 2 causes reverse curl when it is made into a single-wafer body, this reverse curl can be effectively corrected in the forward curl direction.

In the present specification, the moisture permeability of the film is the moisture permeability at a temperature of 40 ° C. and a relative humidity of 90% measured by the cup method specified in JIS Z 0208. The combination as the combination of the difference in moisture permeability is 30g / (m ² · 24hr) or more thermoplastic resin film, for example, cellulose-based resin film (TAC film) and the cyclic polyolefin resin film, a cellulose-based resin film Combination of (TAC film, etc.) and (meth) acrylic resin film, combination of cellulose-based resin film (TAC film, etc.) and polyester-based resin film, cellulose-based resin film (TAC film, etc.) and chain polyolefin-based resin Examples thereof include a combination with a film, a combination of a (meth) acrylic resin film and a cyclic polyolefin resin, a combination of a (meth) acrylic resin film and a polyester resin film, and the like. The first thermoplastic resin film 10 is the difference between the moisture permeability of the second thermoplastic resin film 20 is usually 5000g / (m ² · 24hr) or less.

Moisture permeability of the first thermoplastic resin film 20 is, for example, 300g / (m ² · 24hr) or more, may be 400g / (m ² · 24hr) or more. Moisture permeability is 300g / (m ² · 24hr) or more, in the case of laminating a first thermoplastic resin film 20 and the polarizing film 10 with a water-based adhesive, efficiency layer consisting of water-based adhesive It is also advantageous in that it can be dried well and productivity can be increased. Moisture permeability of the first thermoplastic resin film 20 is usually 5000g / (m ² · 24hr) or less.

As the first thermoplastic resin film 20, when the moisture permeability than the second thermoplastic resin film 30 having a high film, moisture permeability of the second thermoplastic resin film 20 is usually 1~350g / (m ² · 24hr ), and preferably ^{5~200g / (m 2 · 24hr)} . Examples of the thermoplastic resin constituting the second thermoplastic resin film 20 capable of achieving such moisture permeability are a cyclic polyolefin resin, a (meth) acrylic resin, a polyester resin, a chain polyolefin resin and the like.

The moisture permeability of a thermoplastic resin film depends on the material (type of thermoplastic resin constituting the film), the thickness of the film, the presence or absence of a surface treatment layer (coating layer) that can be attached to the film surface, and the material. Can also be adjusted.

When a film having a higher moisture permeability than the second thermoplastic resin film 30 is used as the first thermoplastic resin film 20, the above is usually used from the viewpoint of correcting the reverse curl that tends to occur in the polarizing plate 2 in the positive curl direction. In the pressing step, the protect film 1 is arranged on the first thermoplastic resin film 20 side of the polarizing plate 2.

As described above, the polarizing film 10 and the first and second thermoplastic resin films 20 and 30 can be bonded to each other by using an adhesive. Prior to laminating and laminating the first and second thermoplastic resin films 20 and 30 on the polarizing film 10, plasma is applied to the laminating surface of the polarizing film 10 and / or the first and second thermoplastic resin films 20 and 30. Surface activation treatments such as treatment, corona treatment, ultraviolet irradiation treatment, frame (flame) treatment, and saponification treatment may be performed. By this surface activation treatment, the adhesiveness between the polarizing film 10 and the first and second thermoplastic resin films 20 and 30 can be enhanced.

As the adhesive, a water-based adhesive, an active energy ray-curable adhesive or a thermosetting adhesive can be used, and a water-based adhesive or an active energy ray-curable adhesive is preferable. When the thermoplastic resin film is laminated and bonded on both sides of the polarizing film 10, the adhesives on both sides may be the same type of adhesive or different types of adhesives. When a different type of adhesive is used, the polarizing plate 2 tends to curl in its single-wafered body, but according to the present invention, when the polarizing plate 2 is made into a single-wafered body by using a different type of adhesive. Even if a reverse curl is generated, this reverse curl can be effectively corrected in the forward curl direction.

The water-based adhesive is one in which the adhesive component is dissolved in water or one in which the adhesive component is dispersed in water. The water-based adhesive preferably used is, for example, an adhesive composition using a polyvinyl alcohol-based resin or a urethane resin as a main component.

When a polyvinyl alcohol-based resin is used as the main component of the adhesive, the polyvinyl alcohol-based resin can be a polyvinyl alcohol resin such as partially saponified polyvinyl alcohol and fully saponified polyvinyl alcohol, as well as carboxyl group-modified polyvinyl alcohol. , Acetacetyl group-modified polyvinyl alcohol, methylol group-modified polyvinyl alcohol, amino group-modified polyvinyl alcohol, and other modified polyvinyl alcohol-based resins may be used. The polyvinyl alcohol-based resin is a vinyl alcohol homopolymer obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as the co-weight of vinyl acetate and other monomers copolymerizable therewith. It may be a polyvinyl alcohol-based copolymer obtained by saponifying the coalescence.

The water-based adhesive containing a polyvinyl alcohol-based resin as an adhesive component is usually an aqueous solution of the polyvinyl alcohol-based resin. The concentration of the polyvinyl alcohol-based resin in the adhesive is usually 1 to 10 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of water.

Adhesives consisting of an aqueous solution of polyvinyl alcohol-based resin have curable components such as polyhydric aldehydes, melamine-based compounds, zirconia compounds, zinc compounds, glioxal, glioxal derivatives, and water-soluble epoxy resins in order to improve adhesiveness. It is preferable to contain a cross-linking agent. The water-soluble epoxy resin is a polyamide polyamine epoxy resin obtained by reacting a polyamide amine obtained by reacting a polyalkylene polyamine such as diethylenetriamine or triethylenetetramine with a dicarboxylic acid such as adipic acid with epichlorohydrin. Can be preferably used. Commercially available products of such polyamide polyamine epoxy resin include "Smiley's Resin 650" (manufactured by Taoka Chemical Industry Co., Ltd.), "Smiley's Resin 675" (manufactured by Taoka Chemical Industry Co., Ltd.), and "WS-525" (Japan). (Manufactured by PMC Co., Ltd.) and the like. The amount of the curable component and the cross-linking agent added (the total amount when both the curable component and the cross-linking agent are added) is usually 1 to 100 parts by weight, preferably 1 to 100 parts by weight, based on 100 parts by weight of the polyvinyl alcohol-based resin. 1 to 50 parts by weight. When the amount of the curable component or the cross-linking agent added is less than 1 part by weight with respect to 100 parts by weight of the polyvinyl alcohol-based resin, the effect of improving the adhesiveness tends to be small, and the amount of the addition is polyvinyl. If it exceeds 100 parts by weight with respect to 100 parts by weight of the alcohol-based resin, the adhesive layer tends to be brittle.

Further, as a preferable example when the urethane resin is used as the main component of the adhesive, a mixture of a polyester ionomer type urethane resin and a compound having a glycidyloxy group can be mentioned. The polyester-based ionomer type urethane resin is a urethane resin having a polyester skeleton, in which a small amount of an ionic component (hydrophilic component) is introduced. Such an ionomer type urethane resin is suitable as a water-based adhesive because it is directly emulsified in water to form an emulsion without using an emulsifier.

When a water-based adhesive is used, after the polarizing film 10 and the first and / or second thermoplastic resin films 20 and 30 are bonded together, a drying step for removing water contained in the water-based adhesive is performed. It is preferable to carry out. After the drying step, a curing step of curing at a temperature of, for example, 20 to 45 ° C. may be provided.

The active energy ray-curable adhesive is an adhesive that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays. When an active energy ray-curable adhesive is used, the adhesive layer of the polarizing plate 2 is a cured product layer of the adhesive.

The active energy ray-curable adhesive can be an adhesive containing an epoxy-based compound that is cured by cationic polymerization as a curable component, and preferably an ultraviolet curable adhesive containing such an epoxy-based compound as a curable component. It is an agent. The epoxy compound referred to here means a compound having an average of one or more, preferably two or more epoxy groups in the molecule. Only one type of epoxy compound may be used, or two or more types may be used in combination.

Specific examples of an epoxy-based compound that can be preferably used are hydrided epoxy-based compounds obtained by reacting an alicyclic polyol obtained by subjecting an aromatic ring of an aromatic polyol with an alicyclic polyol (epichlorohydrin). Glycidyl ether of a polyol having an alicyclic ring); an aliphatic epoxy compound such as an aliphatic polyhydric alcohol or a polyglycidyl ether of an alkylene oxide adduct thereof; an epoxy group bonded to the alicyclic ring is 1 in the molecule. It contains an alicyclic epoxy compound which is an epoxy compound having more than one.

The active energy ray-curable adhesive can contain, as a curable component, a (meth) acrylic compound which is radically polymerizable in place of or together with the epoxy-based compound. The (meth) acrylic compound is a (meth) acrylate monomer having at least one (meth) acryloyloxy group in the molecule; obtained by reacting two or more kinds of functional group-containing compounds, and at least two in the molecule. Examples thereof include (meth) acryloyloxy group-containing compounds such as (meth) acrylate oligomers having a (meth) acryloyloxy group.

When the active energy ray-curable adhesive contains an epoxy-based compound that is cured by cationic polymerization as a curable component, it preferably contains a photocationic polymerization initiator. Examples of the photocationic polymerization initiator include aromatic diazonium salts; onium salts such as aromatic iodonium salts and aromatic sulfonium salts; and iron-allene complexes. When the active energy ray-curable adhesive contains a radically polymerizable curable component such as a (meth) acrylic compound, it is preferable to contain a photoradical polymerization initiator. Examples of the photoradical polymerization initiator include an acetophenone-based initiator, a benzophenone-based initiator, a benzoin ether-based initiator, a thioxanthone-based initiator, xanthone, fluorenone, camphorquinone, benzaldehyde, anthraquinone and the like.

When an active energy ray-curable adhesive is used for laminating and bonding the polarizing film 10 and the first and / or second thermoplastic resin films 20 and 30, a drying step is performed as necessary after laminating and bonding. Then, a curing step of curing the active energy ray-curable adhesive is performed by irradiating the active energy ray. The light source of the active energy ray is not particularly limited, but ultraviolet rays having a emission distribution having a wavelength of 400 nm or less are preferable, and specifically, a low pressure mercury lamp, a medium pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a chemical lamp, a black light lamp, and a micro. A wave-excited mercury lamp, a metal halide lamp, or the like can be used.

The intensity of the active energy ray irradiation to the adhesive layer made of the active energy ray-curable adhesive is appropriately determined by the composition of the adhesive, but the irradiation intensity in the wavelength region effective for activating the polymerization initiator is 0.1. It is preferably set to be ~ 6000 mW / cm ^2. When the irradiation intensity is 0.1 mW / cm ² or more, the reaction time does not become too long, and when it is 6000 mW / cm ² or less, the heat radiated from the light source and the heat generated when the adhesive is cured causes the adhesive layer to grow. There is little risk of yellowing or deterioration of the polarizing film 10.

The irradiation time of the active energy rays is also appropriately determined by the composition of the adhesive, but the integrated light amount expressed as the product of the irradiation intensity and the irradiation time shall be set to be ^{10 to 10,000 mJ / cm 2.} Is preferable. If the integrated light quantity is 10 mJ / cm ² or more to generate a sufficient amount of the active species derived from the polymerization initiator can proceed more reliably the curing reaction, if it is 10000 mJ / cm ² or less, longer irradiation time Good productivity of the polarizing plate 2 can be maintained without becoming too much.

(3-4) Adhesive Layer and Separate Film As shown in FIGS. 3 and 4, the polarizing plate 2 can include the adhesive layer 40. The pressure-sensitive adhesive layer 40 can be directly laminated on the surface of the first or second thermoplastic resin films 20, 30 or the polarizing film 10, and the polarizing plate 3 with a protective film is attached to an image display element (for example, a liquid crystal cell). Can be used to fit.

The pressure-sensitive adhesive layer 40 for bonding the polarizing plate 3 with a protective film to an image display element (for example, a liquid crystal cell) is the main surface (first main surface) of the polarizing plate on the side to be bonded to the image display element such as a liquid crystal cell. It is placed on the surface) side. For example, the polarizing plate 2 contains the first and second thermoplastic resin films 20 and 30, and the first thermoplastic resin film 20 is a film having a higher equilibrium moisture content and / or moisture permeability than the second thermoplastic resin film 30. When used, the pressure-sensitive adhesive layer 40 can be arranged on the side of the second thermoplastic resin film 30.

The pressure-sensitive adhesive layer 40 can be composed of a pressure-sensitive adhesive composition containing a resin such as (meth) acrylic, rubber, urethane, ester, silicone, or polyvinyl ether as a main component (base polymer). .. Among them, a pressure-sensitive adhesive composition using a (meth) acrylic resin having excellent transparency, weather resistance, heat resistance and the like as a base polymer is preferable. The pressure-sensitive adhesive composition may be an active energy ray-curable type or a thermosetting type.

Examples of the (meth) acrylic resin used in the pressure-sensitive adhesive composition include butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2-ethylhexyl (meth) acrylate. A polymer or copolymer containing one or more of (meth) acrylic acid esters as a monomer is preferably used. It is preferable to copolymerize the (meth) acrylic resin with a polar monomer. Examples of the polar monomer include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylic acid, hydroxyethyl (meth) acrylate, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, and glycidyl ( Examples thereof include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group and the like, such as meth) acrylate.

The pressure-sensitive adhesive composition may contain only the above-mentioned base polymer, but usually further contains a cross-linking agent. The cross-linking agent is a divalent or higher metal ion that forms a carboxylic acid metal salt with a carboxyl group; a polyamine compound that forms an amide bond with a carboxyl group; poly. Examples thereof include epoxy compounds and polyols that form an ester bond with a carboxyl group; polyisocyanate compounds that form an amide bond with a carboxyl group. Of these, polyisocyanate compounds are preferable.

The active energy ray-curable pressure-sensitive adhesive composition has a property of being cured by being irradiated with active energy rays such as ultraviolet rays and electron beams, and has adhesiveness even before irradiation with active energy rays. It is a pressure-sensitive adhesive composition having a property that it can be brought into close contact with an adherend such as, etc., and can be cured by irradiation with active energy rays to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably an ultraviolet-curable type. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. Further, if necessary, a photopolymerization initiator, a photosensitizer, or the like may be contained.

The pressure-sensitive adhesive composition includes fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, pressure-sensitive adhesives, fillers (metal powders and other inorganic powders). Etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoaming agents, corrosion inhibitors, photopolymerization initiators and other additives can be included.

In the pressure-sensitive adhesive layer 40, the organic solvent diluted solution of the pressure-sensitive adhesive composition is applied onto the pressure-sensitive adhesive layer forming surface of the polarizing plate 2 (that is, the polarizing film 10 or the first or second thermoplastic resin films 20, 30). It can be formed by drying. Alternatively, an organic solvent diluted solution of the pressure-sensitive adhesive composition is applied onto a separate film (for example, separate film 50) and dried to form a pressure-sensitive adhesive layer, which is then transferred to the pressure-sensitive adhesive layer-forming surface of the polarizing plate 2. You may. In either method, it is preferable to attach a separate film to the outer surface of the pressure-sensitive adhesive layer 40 to protect the pressure-sensitive adhesive layer 40 until use. When the active energy ray-curable pressure-sensitive adhesive composition is used, the formed pressure-sensitive adhesive layer can be irradiated with active energy rays to obtain a cured product having a desired degree of curing. The thickness of the pressure-sensitive adhesive layer 40 is usually 1 to 40 μm, but is preferably 3 to 25 μm from the viewpoint of thinning the polarizing plate 2.

The separate film 50 is a film that is attached to protect the surface of the pressure-sensitive adhesive layer 40 until it is attached to an image display element (for example, a liquid crystal cell). The separate film 50 is usually made of a thermoplastic resin film having a mold release treatment on one side, and the mold release treatment surface is bonded to the pressure-sensitive adhesive layer 40. The thermoplastic resin constituting the separate film 50 can be, for example, a polyethylene resin such as polyethylene, a polypropylene resin such as polypropylene, a polyester resin such as polyethylene terephthalate or polyethylene naphthalate, or the like. The thickness of the separate film 50 is, for example, 10 to 100 μm.

(3-5) Other Components of Polarizing Plate The polarizing plate 2 can include other components other than the above. Examples of other components include an optical layer or an optical film having an optical function other than the polarizing film 10, and specific examples thereof are optical films such as a retardation film and a brightness improving film. Other optical films can be laminated and bonded via an adhesive layer or an adhesive layer.

Further, the polarizing plate 2 can include a protective film different from the protect film 1 used in the pressing step. This protective film is arranged on one surface of the polarizing plate 2. Regarding the configuration of this protect film, the above-mentioned description about the protect film 1 is quoted.

(3-6) Curling of polarizing plate As described above, according to the present invention, the polarizing plate 2 can be corrected in the forward curl direction, whereby the reverse curl is sufficiently suppressed when a single-wafered body is formed. It is possible to obtain a polarizing plate 3 with a protective film which is flat, preferably has no curl, or has a positive curl. The manufacturing method according to the present invention is a case where reverse curl (curl with the main surface side on which the protect film 1 is overlapped is convex) occurs when the polarizing plate 2 is made into a single-wafered body (further, with reverse curl). It is particularly advantageous when it is present and causes MD curl).

In the above, as one of the forms of the polarizing plate 2 in which reverse curl is likely to occur when a single-wafered body is formed, the first thermoplastic resin film 20 and the second thermoplastic resin film 30 have different equilibrium moisture rates and / or different from each other. The case of having moisture permeability is mentioned, but the case is not limited to this, and reverse curl is likely to occur when the polarizing plate 2 has an asymmetric layer structure with respect to the polarizing film 10.

An example of the configuration of the polarizing plate 2 that easily causes reverse curl is as follows.
(A) A structure in which a thermoplastic resin film (protective film, etc.) is bonded to only one side of the polarizing film 10.
(B) A configuration in which a protective film is bonded to one surface of the polarizing film 10 and an optical film (such as a brightness improving film) other than the protective film is bonded to the other surface.
(C) The configurations (resin type, thickness, equilibrium moisture content, moisture permeability, presence / absence of surface treatment layer, etc.) of the thermoplastic resin film (protective film, etc.) bonded to both sides of the polarizing film 10 are different from each other. d) A structure in which an adhesive layer for adhering a thermoplastic resin film (protective film or the like) to both sides of the polarizing film 10 is formed of adhesives of different types from each other.
(E) A structure in which a thermoplastic resin film (protective film or the like) is bonded to both sides of the polarizing film 10, and another optical film is bonded to one of the thermoplastic resin films.
(F) In addition, the total number of films and layers on one side and the total number of films and layers on the other side are different from each other with respect to the polarizing film 10.

(4) Other Steps The manufacturing method according to the present invention may further include a step of cutting the polarizing plate with a protective film 3 obtained by the pressing step to obtain a single-wafer of the polarizing plate with a protective film 3. can. For cutting, a commonly used cutting device such as a shear cutter can be used.

The shape of the single-wafer is not particularly limited, but it is usually a square shape, preferably a square shape having a long side and a short side, and more preferably a rectangular shape. This single-wafer is usually cut so that the pair of opposite sides is parallel to the MD and the remaining pair of opposite sides are parallel to the TD, but the direction in which each side is tilted from the MD or TD. It may be cut so as to be. The lengths of the long side and the short side of the frond are not particularly limited, but usually the long side is 50 mm or more and the short side is 30 mm or more. Curls are more likely to occur as the size of the fronds increases. If the size (long and / or short sides) is too small, the curl problem itself is less likely to occur.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these examples. In the following examples, the equilibrium moisture content, moisture permeability, thickness and tensile elastic modulus, and the film tension and curl amount were measured according to the following methods.

(1) Equilibrium moisture content of film A test piece having an MD length of 150 mm and a TD length of 100 mm was cut out. The film weight was measured after storage for 24 hours in an environment of a temperature of 23 ° C. and a relative humidity of 55%. Then, the film was dried at 105 ° C. for 2 hours, and the weight of the film after the drying was measured. Based on the film weight before and after drying, the following formula:
Equilibrium moisture content (% by weight) = {(film weight before drying treatment-film weight after drying treatment) / film weight before drying treatment} x 100
The equilibrium moisture content was determined based on the above.

(2) by a cup method as defined in moisture permeability JIS Z 0208 of the film, temperature of 40 ° C., was measured moisture permeability at 90% relative humidity [g / (m ² · 24hr)].

(3) Thickness of polarizing plate and film Measured using a digital micrometer "MH-15M" manufactured by Nikon Corporation.

(4) Tension elastic modulus of polarizing plate and protective film in MD A rectangular test piece having an MD length of 100 mm and a TD length of 25 mm was cut out. Next, with the upper and lower grippers of the tensile tester [AUTOGRAPH AG-1S tester manufactured by Shimadzu Corporation], sandwich both ends of the test piece in the long side direction so that the distance between the grippers is 5 cm, and the temperature is 23 ° C., relative to each other. In an environment of 55% humidity, the test piece is pulled in the MD (length direction of the test piece) at a tensile speed of 1 mm / min, and from the slope of the initial straight line in the obtained stress-strain curve, at 23 ° C. and 55% relative humidity. The tensile elastic modulus [MPa] in MD was calculated.

(5) Film tension in MD of polarizing plate and protect film Between a pair of bonding rolls for bonding the polarizing plate and the protective film and a pair of nip rolls on the upstream side thereof and closest to the bonding roll. The film tension [N / m] of the polarizing plate and the protective film traveling on the plate was measured using a tension detection roll installed between the bonding roll and the pair of nip rolls closest to the bonding roll.

(6) Polarizing plate with protective film and curl amount of polarizing plate A rectangular test piece having an MD length of 300 mm and a TD length of 200 mm was cut out from the obtained polarizing plate with a protective film, and had a temperature of 23 ° C. and a relative humidity of 55%. It was left in the environment for 24 hours. The test piece was placed on a reference plane (horizontal table) with its concave side facing up, that is, with the four ends raised. In this state, the heights from the reference planes were measured for each of the four corners of the test piece, and the curl amount [mm] was calculated as the average of the heights of the four corners. If the curl amount is a positive value, it means that the first thermoplastic resin film side is concave (positive curl), and if it is a negative value, the second thermoplastic resin film side is concave. It means that it is (reverse curl). The polarizing plate with a protective film of Example 2 did not curl regardless of whether the first thermoplastic resin film side or the second thermoplastic resin film side was on top.

<Example 1>
(A) Preparation of polarizing film While continuously transporting a long polyvinyl alcohol film (average degree of polymerization: about 2400, degree of polymerization: 99.9 mol% or more, thickness: 30 μm), it is about four times as dry. After uniaxially stretching and immersing in pure water at 40 ° C. for 1 minute while maintaining a tense state, the mixture was immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.1 / 5/100 at 28 ° C. for 60 seconds. Soaked. Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 10.5 / 7.5 / 100 at 68 ° C. for 300 seconds. Subsequently, the film was washed with pure water at 5 ° C. for 5 seconds and then dried at 70 ° C. for 180 seconds to obtain a long polarizing film in which iodine was adsorbed and oriented on a uniaxially stretched polyvinyl alcohol film. The thickness of the polarizing film was 11.1 μm.

(B) Preparation of polarizing plate While continuously transporting the polarizing film obtained in (A) above, it is hard on a long first thermoplastic resin film [TAC film "KC2UAW" manufactured by Konica Minolta Opto Co., Ltd. film coating layer is formed, the thickness: 32.4Myuemu, equilibrium moisture content: 1.9 wt%, moisture ^{permeability: 455g / (m 2 · 24hr} ) ] and a second thermoplastic resin film [JSR long (strain ) made of cyclic polyolefin trade name of a resin film "FEKB015D3", thickness: 15.1Myuemu, equilibrium moisture content: 0.8 wt%, moisture ^{permeability: 115g / (m 2 · 24hr} ) ] continuously conveying the The first thermoplastic resin film / A laminated film composed of a water-based adhesive layer / polarizing film / water-based adhesive layer / second thermoplastic resin film was obtained. Subsequently, the obtained laminated film was conveyed and passed through a hot air dryer for heat treatment at 80 ° C. for 300 seconds to dry the aqueous adhesive layer to obtain a polarizing plate. The above water-based adhesive has a concentration of 3 weight obtained by dissolving polyvinyl alcohol powder [trade name "Gosefimer" manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average degree of polymerization 1100] in hot water at 95 ° C. An aqueous solution prepared by mixing a cross-linking agent [sodium glyoxylate manufactured by Nippon Synthetic Chemical Industry Co., Ltd.] with 10 parts by weight of polyvinyl alcohol powder at a ratio of 1 part by weight to 10 parts by weight of polyvinyl alcohol powder was used.

The thickness T ₂ of the polarizing plate was 58.6 μm, and the tensile elastic modulus E ₂ in MD was 6540 MPa. When the curl amount of the polarizing plate was measured according to the above method, it was -10 mm (reverse curl).

(C) Preparation of polarizing plate with protective film While continuously transporting the polarizing film obtained in (B) above, a long protective film [the base film is made of polyethylene terephthalate, and (meth) acrylic is placed on it. A protective film having a pressure-sensitive adhesive layer, total thickness T ₁ : 57.3 μm, tensile elasticity in MD E ₁ : 2521 MPa] is continuously conveyed, and these are stacked and passed between the laminating rolls to form a protective film. A polarizing plate with a protective film was produced by pressing the laminate with the polarizing plate from above and below. The protective film is attached to the surface of the first thermoplastic resin film (TAC film) of the polarizing plate via the pressure-sensitive adhesive layer. The pressure (nip pressure) applied to the laminate of the protective film and the polarizing plate by the bonding roll is 0.1 MPa, and this value is approximately the same in the following Examples and Comparative Examples.

Film tension in MD of the polarizing plate and protective film, multiplied by 10 ⁵ to the left side of the formula (I), the table multiplied by 10 ⁵ to the right side, and the difference between them, the curl amount of the polarizing plate with the protective film Shown in 1. "Δ" in Table 1, the difference between multiplied by 10 ⁵ to one side and the right side multiplied by 10 ⁵ to the left side of the formula (I), i.e., represents the left side of the formula (II).

<Examples 2 to 5>
A polarizing plate with a protective film was produced in the same manner as in Example 1 except that the film tensions of the polarizing plate and the protective film in the MD were as shown in Table 1. Multiplied by 10 ⁵ to the left side of the formula (I), shown multiplied by 10 ⁵ to the right side, and the difference between them, the curl amount of the polarizing plate with the protective film in Table 1.

<Example 6>
A long protective film in which the base film is made of polyethylene terephthalate, has a (meth) acrylic pressure-sensitive adhesive layer on it, has a total thickness T _{1 of 69.3 μm, and has a tensile modulus E 1} in MD of 2743 MPa. A polarizing plate with a protective film was produced in the same manner as in Example 1 except that the film tensions of the polarizing plate and the protective film in the MD were as shown in Table 1. Multiplied by 10 ⁵ to the left side of the formula (I), shown multiplied by 10 ⁵ to the right side, and the difference between them, the curl amount of the polarizing plate with the protective film in Table 1.

<Example 7>
Second thermoplastic resin film [trade name "ZF14-023", which is a cyclic polyolefin resin film manufactured by Nippon Zeon Corporation, thickness: 22.9 μm, equilibrium moisture content: 0.1% by weight, moisture permeability: 17 g / but using (m ² · 24hr)] in the same manner as in example 1, the thickness T ₂ is 66.8Myuemu, elastic modulus E ₂ tensile in MD is a polarizing plate was prepared is 6080MPa. When the curl amount of the polarizing plate was measured according to the above method, it was -6 mm (reverse curl).

Next, polarized light with a protective film was used in the same manner as in Example 1 except that the polarizing plate obtained above was used and the film tension of the polarizing plate and the protective film in the MD was as shown in Table 1. A plate was made. Multiplied by 10 ⁵ to the left side of the formula (I), shown multiplied by 10 ⁵ to the right side, and the difference between them, the curl amount of the polarizing plate with the protective film in Table 1.

<Comparative Example 1>
As the first thermoplastic resin film, Konica Minolta Opto Co., Ltd. TAC film "KC2UAW" [Thickness: 25.5, equilibrium moisture content: 3.0 wt%, moisture ^{permeability: 1207g / (m 2 · 24hr} ) ] _{A polarizing plate having a thickness T 2} of 51.7 μm and a tensile elastic modulus E ₂ in MD of 6839 MPa was produced in the same manner as in Example 1 except that the above was used. When the curl amount of the polarizing plate was measured according to the above method, it was -13 mm (reverse curl).

Next, polarized light with a protective film was used in the same manner as in Example 1 except that the polarizing plate obtained above was used and the film tension of the polarizing plate and the protective film in the MD was as shown in Table 1. A plate was made. Multiplied by 10 ⁵ to the left side of the formula (I), shown multiplied by 10 ⁵ to the right side, and the difference between them, the curl amount of the polarizing plate with the protective film in Table 1.

1 Protect film, 2,2a, 2b, 2c polarizing plate, 3 Protect film plated plate, 5 bonded roll, 10 polarizing film, 20 1st thermoplastic resin film, 30 2nd thermoplastic resin film, 40 adhesive layer , 50 separate film.

Claims (5)

A method for manufacturing a polarizing plate with a protective film, which comprises a step of stacking a protective film on one side of the polarizing plate and passing it between a pair of bonding rolls to press the polarizing film.
The polarizing plate includes a polarizing film, a first thermoplastic resin film laminated on one surface thereof, and a second thermoplastic resin film laminated on the other surface.
The first thermoplastic resin film has a higher equilibrium moisture content at a temperature of 23 ° C. and a relative humidity of 55% than the second thermoplastic resin film.
The difference in the equilibrium moisture content between the first thermoplastic resin film and the second thermoplastic resin film is 0.5% by weight or more and 1.8% by weight or less.
The protect film is arranged on the side of the first thermoplastic resin film.
The thickness of the protective film is T ₁ [μm], the tensile elastic modulus in MD is E ₁ [MPa], and the film tension in MD before being passed through the pair of laminating rolls is F ₁ [N / m]. When the thickness of the plate is T ₂ [μm], the tensile elastic modulus in the MD direction is E ₂ [MPa], and the film tension in the MD before being passed through the pair of laminating rolls is F ₂ [N / m]. The pressing process is described by the following formula (I):

A manufacturing method performed under the conditions that satisfy the conditions. The pressing step is described by the following formula (II):

The manufacturing method according to claim 1, wherein the production method is carried out under the conditions satisfying the above conditions. The manufacturing method according to claim 1 or 2, wherein when the polarizing plate is made into a single-wafered body, a curl is generated so that the side on which the protective film is overlapped is convex. The production method according to any one of claims 1 to 3 , wherein the first thermoplastic resin film has an equilibrium moisture content of 1.5% by weight or more at a temperature of 23 ° C. and a relative humidity of 55%. The production method according to any one of claims 1 to 4 , wherein the thickness of the polarizing plate is 100 μm or less.

Images