KR20240161083A - Polarizing film and image display device - Google Patents

Abstract

A polarizing film in which a polarizing film and a resin film are directly bonded without interposing an adhesive layer or an adhesive layer, and the thickness of the polarizing film is 20 ㎛ or less and thinner than the thickness of the resin film. The polarizing film can suppress curling.

Description

Polarizing film and image display device

The present invention relates to a polarizing film and an image display device.

Conventionally, as polarizing films used in various image display devices such as liquid crystal displays and organic EL displays, dyed polyvinyl alcohol films (containing a dichroic substance such as iodine or a dichroic dye) have been used because they have both high transmittance and high polarization degree. The polarizing film is manufactured by subjecting a polyvinyl alcohol film to various treatments, such as swelling, dyeing, crosslinking, and stretching, in a bath, and then performing a washing treatment and then drying. In addition, the polarizing film is usually used as a polarizing film (polarizing plate) to which a transparent protective film such as triacetyl cellulose is bonded using an adhesive on one or both sides.

In addition, as the polarizing film (polarizing plate), a polarizing film in which a polarizing film and a transparent protective film are directly bonded without interposing an adhesive layer or pressure-sensitive adhesive layer is also known (Patent Document 1-4).

International Publication No. 2005/085918 Japanese Patent Publication No. 2002-303725 Japanese Patent Publication No. 2002-303726 Japanese Patent Publication No. 2002-303727

Polarizing films or polarizing films have a strong demand for thin film thinning, but when the polarizing film and the transparent protective film are bonded together with an adhesive layer as described above, the adhesive layer easily accumulates stress when the adhesive is cured, which has the problem of causing curling of the polarizing film. In addition, a polarizing film obtained by a manufacturing method specifically disclosed in Patent Document 1 has the problem that there is a concern that curling of the polarizing film may occur due to the relationship between the thicknesses of the polarizing film and the transparent protective film, and that the adhesive strength between the polarizing film and the transparent protective film is weak. In addition, a polarizing film obtained by a manufacturing method specifically disclosed in Patent Document 2-4 requires a pressing process at a high temperature of 135°C, and therefore has the problem of causing curling of the polarizing film.

In consideration of the above circumstances, the present invention aims to provide a polarizing film capable of suppressing curl.

In addition, the present invention aims to provide an image display device having the polarizing film.

That is, the present invention relates to a polarizing film in which a polarizing film and a resin film are directly bonded without interposing an adhesive layer or a pressure-sensitive adhesive layer, and the thickness of the polarizing film is 20 ㎛ or less and thinner than the thickness of the resin film.

In addition, the present invention relates to an image display device having the polarizing film.

The details of the mechanism of action of the effect in the polarizing film of the present invention are estimated as follows. However, the present invention is not interpreted as being limited to this mechanism of action.

In the polarizing film of the present invention, since the polarizing film and the resin film are directly bonded without interposing an adhesive layer or a pressure-sensitive adhesive layer, and the thickness of the polarizing film is 20 µm or less and thinner than the thickness of the resin film, interfacial stress due to shrinkage of the adhesive layer is suppressed, and since the shrinkage of the polarizing film can be maintained by the resin film, curling of the polarizing film can be suppressed.

In addition, since the polarizing film of the present invention can directly bond a polarizing film and a transparent protective film without interposing an adhesive layer or adhesive layer, diffusion of a dichroic substance such as iodine into the adhesive layer or adhesive layer is suppressed, and thus humidification reliability is also excellent.

<Polarizing film>

The polarizing film of the present invention is a polarizing film and a resin film that are directly bonded without interposing an adhesive layer or a pressure-sensitive adhesive layer, and the thickness of the polarizing film is 20 ㎛ or less and thinner than the thickness of the resin film.

<Polarizing film>

The above polarizing film is formed by adsorbing and aligning a dichroic material such as iodine or a dichroic dye on a polyvinyl alcohol-based film. From the viewpoint of the initial polarization performance of the polarizing film, the above polarizing film is preferably an iodine-based polarizing film containing iodine as the dichroic material.

The above polyvinyl alcohol (PVA) film has transparency in the visible light range, and can be used without particular limitation to disperse and adsorb a dichroic substance such as iodine or a dichroic dye. Examples of the material for the above polyvinyl alcohol film include polyvinyl alcohol or a derivative thereof. Examples of the derivative of the above polyvinyl alcohol include polyvinyl formal, polyvinyl acetal; olefins such as ethylene and propylene; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid, and those modified with alkyl esters thereof, acrylamide, and the like. The polyvinyl alcohol preferably has an average degree of polymerization of about 100 to 10,000, more preferably about 1,000 to 10,000, and still more preferably about 1,500 to 4,500. In addition, the polyvinyl alcohol preferably has a saponification degree of about 80 to 100 mol%, more preferably about 95 to 99.95 mol%. In addition, the average polymerization degree and the saponification degree can be obtained in accordance with JIS K 6726.

The above polarizing film is obtained by a conventional polarizing film manufacturing method, and is obtained, for example, by performing an arbitrary swelling process and a washing process on the above polyvinyl alcohol-based film, and at least a dyeing process, a crosslinking process, and a stretching process.

From the viewpoint of improving the initial polarization degree of the polarizing film, the above polarizing film is preferably 1 µm or more in thickness, more preferably 2 µm or more, and from the viewpoint of preventing warping of the panel, the above polarizing film is preferably 15 µm or less, more preferably 10 µm or less, and even more preferably 8 µm or less. In particular, in order to obtain a polarizing film having a thickness of about 8 µm or less, the following method for producing a thin polarizing film can be applied, which uses a laminate including a polyvinyl alcohol-based resin layer formed as a film on a thermoplastic resin substrate as the above polyvinyl alcohol-based film.

A polarizing film (thin polarizing film) is obtained by a conventional polarizing film manufacturing method, and for example, a step of preparing a laminate by forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a polyvinyl alcohol-based resin (PVA-based resin) on one side of a thermoplastic resin substrate having an elongated shape, and while returning the obtained laminate in the longitudinal direction, subjecting the laminate to an optional insolubilization treatment step, a crosslinking treatment step, and a washing treatment step, and at least an air-assisted stretching treatment step, a dyeing treatment step, and an underwater stretching treatment step.

<Suzy Film>

The above resin film is not particularly limited as long as its thickness is thicker than the thickness of the polarizing film, and for example, an organic substrate such as a transparent protective film or a phase difference film used in a polarizing film can be used.

The ratio of the thickness of the resin film to the thickness of the polarizing film (thickness of the resin film/thickness of the polarizing film) is preferably 1.2 or more, more preferably 2.0 or more, and even more preferably 3.0 or more, from the viewpoint of curl suppression, and is preferably 20.0 or less, more preferably 10.0 or less, and even more preferably 5.0 or less, from the viewpoint of curl/deformation of the polarizing plate caused by an excessively large thickness difference.

In addition, the thickness of the resin film can be appropriately determined, but generally, from the viewpoint of thinness, etc., it is preferable to be 500 ㎛ or less, more preferably 300 ㎛ or less, and even more preferably 100 ㎛ or less.

As the material constituting the transparent protective film, examples thereof include cellulose ester-based resins, polycarbonate-based resins, (meth)acrylic-based resins, cyclic polyolefin-based resins, and polyester-based resins. As the retardation film, examples thereof include a birefringent film formed by subjecting a polymer material to uniaxial or biaxial stretching, an orientation film of a liquid crystal polymer, and a film in which an orientation layer of a liquid crystal polymer is supported. In addition, the transparent protective film and the retardation film may further include one or more layers, such as a hard coat layer, an anti-reflection layer, an anti-sticking layer, a diffusion layer, or an anti-glare layer; and an optical layer used for forming an image display device, such as a reflector, a semi-transmissive plate, a retardation plate (including a wavelength plate such as 1/2 or 1/4), and a viewing angle compensation film.

When the above resin films are bonded to both sides of the above polarizing film, the resin films on both sides may be the same or different.

The above resin film may contain any appropriate additives such as an ultraviolet absorber, an antioxidant, an activator, a plasticizer, a release agent, an anti-coloring agent, a flame retardant, an antistatic agent, a pigment, a colorant, etc.

<Method for manufacturing polarizing film>

Methods for directly bonding the polarizing film and the resin film without interposing an adhesive layer or pressure-sensitive adhesive layer include a pressing method, a method of bonding by irradiating with energy rays such as ultraviolet rays or electron rays, etc., and in particular, from the viewpoint of suppressing curling of the polarizing film and increasing adhesiveness, a method of surface-treating one or both of the resin film and the polarizing film by irradiating with ultraviolet light, bonding via a volatile medium, and then bonding and drying the volatile medium is preferable. By the presence of the volatile medium, air bubbles or the like do not enter the bonding surfaces, so that close contact is possible, and further, by drying the volatile medium, the adhesive strength of the bonding surface (interface) is significantly increased. As the ultraviolet light, for example, one having a wavelength of 250-100 nm is preferable, more preferably 200-100 nm, and among these, a wavelength of 172 nm using a xenon excimer lamp (excimer UV) is particularly preferable from the viewpoint of mass productivity.

In addition, the ultraviolet light is preferably, from the viewpoint of processing capability, an illuminance of 1 mW/cm2 or more, more preferably 50 mW/cm2 or more. In addition, the accumulated light amount is preferably, from the viewpoint of adhesiveness, 1 mJ/cm2 or more, more preferably 50 mJ/cm2 or more, and from the viewpoint of damage to the film, it is preferably, 5000 mJ/cm2 or less, more preferably 2000 mJ/cm2 or less. In addition, the temperature at the time of ultraviolet light irradiation is not particularly limited, and from the viewpoint of stabilizing surface modification, it is preferably about 0 to 50 degrees Celsius, more preferably about 10 to 40 degrees Celsius, and it is convenient to use room temperature for the production of polarizing films. In addition, the atmosphere at the time of ultraviolet light irradiation may have an oxygen concentration of 21% or less, and from the viewpoint of processing efficiency, the oxygen concentration is preferably, 7.0% or less.

The above volatile medium is not particularly limited, and from the viewpoint of drying efficiency, solvents such as water, ethanol, toluene, cyclohexane, and acetone are preferable, and from the viewpoint of the environment, water is more preferable.

The temperature of the above heating may be any temperature that can appropriately dry the volatile medium, and for example, when the volatile medium is water, it is preferably about 40 to 80°C, and more preferably about 50 to 70°C. In addition, the time for the above drying cannot be uniformly determined because it is affected by the temperature of the polarizing film, but it is preferably about 1 to 60 minutes, and more preferably about 3 to 15 minutes. The above drying process may be performed only once, or may be performed multiple times as necessary.

The above bonding can be performed using a roll laminator or the like.

The bonding interface between the above polarizing film and the above resin film may have a modified layer or a high-elasticity layer derived from treatment during bonding.

In the above polarizing film, the adhesive strength (peeling strength) between the resin film and the polarizing film is preferably 0.5 N/15 mm or more, more preferably 1.0 N/15 mm or more, still more preferably 1.2 N/15 mm or more, and still more preferably 2.0 N/15 mm or more, as measured by peeling strength under the conditions of a peeling angle of 90° and a peeling speed of 1000 mm/min.

The above polarizing film can be applied to an image display device. Representative examples of the image display device include a liquid crystal display device and an organic electroluminescence (EL) display device. Since the image display device adopts a configuration well-known in the industry, a detailed description is omitted.

Example

The present invention is described in more detail below by way of examples, but the present invention is not limited to these examples.

<Example 1>

<Making polarizing films>

A laminate having a 9 ㎛ thick PVA layer formed on an amorphous PET substrate was formed into a stretched laminate by air-assisted stretching at a stretching temperature of 130°C, then the stretched laminate was dyed to form a colored laminate, and further, the colored laminate was stretched in boric acid water at a stretching temperature of 65°C to form an optical film laminate including a 5 ㎛ thick polarizing film stretched integrally with the amorphous PET substrate so that the total stretching ratio was 5.94 times. By this two-stage stretching, the PVA molecules of the PVA layer formed on the amorphous PET substrate were highly oriented, and an optical film laminate including a 5 ㎛ thick polarizing film in which iodine adsorbed by dyeing was highly oriented in one direction as a polyiodide ion complex was obtained.

<Production of polarizing film>

In a nitrogen-substituted atmosphere having an oxygen concentration of approximately 2.5%, the polarizing film surface of an optical film laminate including the polarizing film obtained above, and a cycloolefin-based resin film (ZF14, manufactured by Nippon Zeon Co., Ltd.) having a thickness of 13 µm as a resin film were irradiated with excimer UV light (wavelength 172 nm, peak illuminance 75 mW/cm2, accumulated light quantity 450 mJ/cm2) using an excimer UV treatment device (SVC342S-1N2-MN3-KWO1, manufactured by Ushio Denki Co., Ltd., xenon excimer lamp) to perform surface modification. Subsequently, water was applied to the surface-modified surface of each film, and before the water dried, the polarizing film and the resin film were laminated together using a laminator, and then dried in an oven at 60°C for 5 minutes and 30 seconds to obtain a polarizing film in which the polarizing film and the resin film were directly bonded.

<Evaluation of Curl>

After peeling off the PET substrate of the polarizing film to which the polarizing film and the transparent protective film are directly bonded, it is humidified for 72 hours in an environment of 23℃ and 55% relative humidity, cut to 100 mm x 100 mm, and the height from the horizontal plane of each of the four corners of the film is measured with the surface of the resin film facing upward, and the average value of the four points is taken as the curl of the film. In the table, a curl of less than 2 mm is indicated by ◎, 2 mm or more and less than 3 mm by ○, 3 mm or more and less than 5 mm by △, and 5 mm or more by ×.

<Evaluation of adhesive strength (peel strength)>

The PET substrate of the polarizing film, in which the polarizing film and the transparent protective film were directly bonded, was peeled off, and a double-sided tape (No. 500, manufactured by Nitto Denko Corporation) was attached to the peeling surface. In addition, a size of 200 mm parallel to the stretching direction of the polarizing film and 15 mm in the orthogonal direction was cut, and after making a cut between the polarizing film and the transparent protective film with a cutter knife, the peeling film of the double-sided tape was peeled off, and the adhesive side was attached to a glass plate. The polarizing film and the transparent protective film were peeled in the 90 degree direction at a peeling speed of 1000 mm/min using an angle material type adhesion/film peeling analysis device (VPA-2, manufactured by Kyowa Kaimen Chemical Co., Ltd.), and the peeling strength (N/15 mm) was measured.

<Evaluation of Humidification Reliability>

After peeling off the PET substrate of the above polarizing film, an adhesive layer (thickness 20 ㎛) was interposed on the polarizing film side, and a polarizing film (sample for evaluation of humidity durability test) was prepared by bonding it to one side of an alkali-free glass having a thickness of 0.7 mm. The transmittance Ts of the obtained polarizing film was measured using an ultraviolet-visible spectrophotometer (V-7100 manufactured by Nippon Bunko Co., Ltd.), and the single transmittance Ts, parallel transmittance Tp, and orthogonal transmittance Tc were defined as Ts, Tp, and Tc of the polarizing film, respectively. These Ts, Tp, and Tc are Y values measured with a 2-degree field of view (C light source) of JIS Z8701 and subjected to visibility correction. In an environment of 60℃ and 95%RH, the transmittance Ts of the polarizing film after exposure for 120 hours was measured in the same way, and the change in transmittance ΔT(%) = |(transmittance Ts(%) before exposure) - (transmittance Ts(%) after exposure)| was obtained. It was judged that the smaller the change in transmittance ΔT(%), the better the durability in a humid heat environment. ΔT(%) is preferably 0.4 or less, and more preferably 0.3 or less.

<Example 2>

A polarizing film in which a polarizing film and a resin film were directly bonded was obtained by the same operation as in Example 1, except that a cycloolefin resin film having a thickness of 23 ㎛ (ZF12, manufactured by Nippon Zeon Co., Ltd.) was used as the resin film.

<Example 3>

<Making polarizing films>

A 45 ㎛ thick polyvinyl alcohol film having an average degree of polymerization of 2400, a degree of saponification of 99.9 mol%, and was immersed in warm water at 30°C for 60 seconds to swell. Next, the film was immersed in a 0.3% aqueous solution of iodine/potassium iodide (weight ratio = 1/7) and dyed while being stretched up to 2.6 times. Thereafter, stretching was performed in a 4 wt% boric acid aqueous solution at 65°C so that the total stretching ratio became 6 times. After stretching, it was dried in an oven at 55°C for 1 minute to obtain a PVA-based polarizing film. This polarizing film had a thickness of 18 ㎛ and a moisture content of 15 wt%.

<Production of polarizing film>

Using the polarizing film obtained above, a polarizing film in which the polarizing film and the resin film were directly bonded was obtained through the same operation as in Example 2.

<Comparative Example 1>

As a resin film, the following active energy ray-curable adhesive was applied to a cycloolefin resin film (ZF14, manufactured by Nippon Zeon Co., Ltd.) having a thickness of 13 μm using a bar coater, and the polarizing film surface of an optical film laminate including a polarizing film having a thickness of 5 μm obtained in Example 1 was bonded using a laminator. In that state, active energy ray irradiation was performed from the resin film side to harden the adhesive, thereby obtaining a polarizing film in which the resin film is bonded to the polarizing film via the active energy ray adhesive.

[Active energy ray curing adhesive]

16.5 parts by weight of 2-hydroxyethyl acrylamide (manufactured by KJ Chemicals, trade name: HEAA), 1 part by weight of 4-vinylphenylboronic acid (manufactured by Tokyo Kasei Kogyo Co., Ltd., trade name: Aronix M-5700), 30.5 parts by weight of 2-hydroxy-3-phenoxypropyl acrylate (manufactured by Toagosei Co., Ltd., trade name: Aronix M-5700), 25 parts by weight of 1,9-nonanediol diacrylate (manufactured by Kyoei Chemical Co., Ltd., trade name: Light Acrylate 1,9ND-A), 13 parts by weight of hydroxypivalic acid diacrylate (manufactured by Kyoei Chemical Co., Ltd., trade name: Light Acrylate HPP-A), 15 parts by weight of an oligomer formed by polymerizing (meth)acrylate (manufactured by Toagosei Co., Ltd., trade name: ARFON UP-1190), 2-Methyl-1-[4-(methylthio)phenyl]-2-morphonylpropan-1-one (IGM resins, trade name: Omnirad 907) 3 parts by weight, 2,4-diethylthioxanthone (Nippon Kayakusha, trade name: KAYACURE-DETX-S) 3 parts by weight

[Active energy line]

As an active energy ray, a visible light (gallium-filled metal halide lamp) irradiation device: Heraeus Light HAMMER10 Valve: V valve Peak illuminance: 800 mW/cm2, accumulated irradiance 800/mJ/cm2 (wavelength 380–440 nm) was used. In addition, the illuminance of visible light was measured using the Sola-Check system from Solatell.

<Comparative Example 2>

A cycloolefin resin film (ZF14, manufactured by Nippon Zeon Corporation) having a thickness of 40 ㎛ was laminated by pressing it onto one side of a 30 ㎛ polarizing film (polyvinyl alcohol film) using a roll laminator at a temperature of 145°C to obtain a polarizing film in which the polarizing film and the resin film are directly bonded.

The polarizing films obtained in each of the above examples and comparative examples were used and the same evaluation as in Example 1 was performed. The results are shown in Table 1.

Claims (3)

The polarizing film and the resin film are directly bonded without intervening an adhesive layer or glue layer,
A polarizing film characterized in that the thickness of the polarizing film is 20㎛ or less and is thinner than the thickness of the resin film. In paragraph 1,
A polarizing film, characterized in that the ratio of the thickness of the resin film to the thickness of the polarizing film (thickness of the resin film/thickness of the polarizing film) is 1.2 to 10.0. An image display device characterized by having a polarizing film as described in claim 1 or claim 2.