JP7367756B2 - Polarizer - Google Patents

Description

The present invention relates to a polarizing plate.

A polarizing plate used in a display device such as a liquid crystal display device includes a polarizer and protective films disposed on both sides of the polarizer. As the protective film, a film containing a (meth)acrylic resin such as polymethyl methacrylate as a main component is used because it has excellent transparency, dimensional stability, and low moisture absorption.

On the other hand, since (meth)acrylic resin films are brittle, elastic particles such as rubber particles are further added thereto in order to eliminate the brittleness.

A polarizing plate using such a (meth)acrylic resin film includes a polarizer and two protective films arranged on both sides of the polarizer, and the two protective films are polymethyl methacrylate containing elastic particles. A polarizing plate is known that is a coextruded film having a core layer of 1, and two skin layers of polymethyl methacrylate that do not contain elastic particles arranged on both sides of the core layer (for example, Patent Document 1). The same film is used as the two protective films.

When manufacturing a display device as a product, such a polarizing plate is punched out into a predetermined size and shape according to the product.

Japanese Patent Application Publication No. 2008-40275

In recent years, from the viewpoint of improving production yields, there has been a demand for narrower margins than ever before when punching polarizing plates with a blade. Although the protective film used in the polarizing plate of Patent Document 1 contains elastic particles, cracks cannot be suppressed completely when the polarizing plate is punched out, and the margins between the polarizing plates cannot be narrowed. There wasn't.

Furthermore, in the process of punching out a polarizing plate, when the blade is pulled out from the polarizing plate, peeling tends to occur between the (meth)acrylic resin film and the polarizer, and interlayer adhesion tends to decrease. As described above, a display device having a polarizing plate with reduced interlayer adhesion is likely to cause display unevenness due to keystrokes when used for a long time in a high humidity environment.

The present invention has been made in view of the above circumstances, and provides a polarizing plate that can suppress cracks and delamination during punching, and can reduce display unevenness due to keystrokes when used for a long time in a high humidity environment. The purpose is to

The above problem can be solved by the following configuration.

The polarizing plate of the present invention includes a polarizer, a protective film A disposed on one surface of the polarizer, a protective film B disposed on the other surface of the polarizer, and the polarized light of the protective film B. A polarizing plate including an adhesive layer disposed on the opposite side of the polarizing plate, the protective film A includes a (meth)acrylic resin and rubber particles a, and the protective film B includes: In the cross section along the thickness direction of the protective film A, which includes (meth)acrylic resin and rubber particles b, the average aspect ratio of the rubber particles a is 1.0 to 1.1, and the In the cross section along the thickness direction of film B, the average aspect ratio of the rubber particles b is 1.2 to 3.0, and the (meth)acrylic resin contained in the protective film B is ) 50 to 95% by mass of structural units derived from methyl methacrylate, 1 to 25% by mass of structural units derived from phenylmaleimide, and 1 to 25% by mass of all structural units constituting the acrylic resin. It is a copolymer containing a structural unit derived from an acrylic acid alkyl ester.

According to the present invention, it is possible to provide a polarizing plate that can suppress cracks and delamination during punching and can reduce display unevenness due to keystrokes when used for a long time in a high humidity environment.

FIG. 1 is a sectional view showing a polarizing plate according to an embodiment of the present invention. FIG. 2 is a sectional view illustrating an estimated mechanism in the process of punching out a polarizing plate. FIGS. 3A and 3B are diagrams showing a punching process of a polarizing plate in an example.

Embodiments of the present invention will be described in detail below with reference to the drawings.

1. Polarizing Plate FIG. 1 is a sectional view showing a polarizing plate 100 according to the present embodiment.

As shown in FIG. 1, a polarizing plate 100 according to the present embodiment includes a polarizer 110 (polarizer) and a protective film 120A disposed on one surface thereof and containing rubber particles 150a (rubber particles a). (protective film A), a protective film 120B (protective film B) disposed on the other surface and containing rubber particles 150b (rubber particles b), and an adhesive disposed between the protective film 120A and the polarizer 110. It has an adhesive layer 130A (adhesive layer A) and an adhesive layer 130B (adhesive layer B) disposed between the protective film 120B and the polarizer 110.

Furthermore, the polarizing plate 100 further includes an adhesive layer 140 disposed on the surface of the protective film 120B opposite to the polarizer 110. The adhesive layer 140 is a layer for attaching the polarizing plate 100 to a display element (not shown) such as a liquid crystal cell. The surface of the adhesive layer 140 is usually protected with a release film (not shown).

The present inventors speculated as follows about the mechanism by which cracks and delamination occur during the punching process of a polarizing plate.

FIG. 2 is a cross-sectional view illustrating the estimated mechanism in the punching process of the polarizing plate 100. Among these, FIG. 2A is a cross-sectional view when pushing the blade 160 into the polarizing plate 100, and FIG. 2B is a cross-sectional view when the blade 160 is pulled out from the polarizing plate 100.

As shown in FIG. 2A, when pushing the blade 160 into the polarizing plate 100, the protective film 120A does not push in the adjacent layer due to the pushing of the blade 160, so the stress caused by pushing the blade is reduced. Although it is small (dotted arrow in FIG. 2A), the protective film 120B is pushed in by the blade because the adjacent layers (adhesive layer 130B, polarizer 110, adhesive layer 130A, and protective film 120A) are pushed in by the blade. The resulting stress tends to become large (solid arrow in FIG. 2A). As a result, the protective film 120B is more likely to undergo physical deformation over a wide range than the protective film 120A due to the pushing of the blade. Therefore, when the blade 160 is pushed in, cracks are likely to occur in the protective film 120B, and when the blade 160 is pulled out, delamination is likely to occur between the protective film 120B and the adhesive layer 130B.

On the other hand, as in Patent Document 1, the present inventors have determined that the average aspect ratio of rubber particles included in a protective film disposed on one surface of a polarizer and the average aspect ratio of rubber particles included in a protective film disposed on one surface of a polarizer, Rather than making the average aspect ratio of the rubber particles contained in the protective film the same as the average aspect ratio of the rubber particles 150b contained in the protective film 120B; It has been found that by increasing the height, cracks and delamination can be suppressed (see FIG. 2A).

Specifically, the average aspect ratio of the rubber particles 150b included in the protective film 120B is adjusted to 1.2 to 3.0. As a result, the rubber particles 150b included in the protective film 120B can better follow the deformation of the protective film 120B caused by the pushing of the blade 160, so stress can be alleviated and cracks etc. can be made less likely to occur. . In particular, the hardness of the rubber particles 150b is relatively high (the amount of styrene is relatively large), and by setting the hardness of the rubber particles 150b (amount of styrene)>hardness of the rubber particles 150a (amount of styrene), stress is applied to the protective film B. When the rubber particles 150b are stretched, interfacial peeling between the rubber particles 150b and the (meth)acrylic resin can be made more difficult to occur, so setting the average aspect ratio within the above range is more effective. It's easy to get caught. Furthermore, since the stress generated when the blade is pushed in the protective film 120B can be reduced, delamination between the protective film 120B and the adhesive layer 130B can be made less likely to occur when the pushed blade is pulled out (see FIG. 2B).

Furthermore, the present inventors have determined that the (meth)acrylic resin contained in the protective film 120B includes a structural unit (U1) derived from methyl methacrylate, a structural unit (U2) derived from phenylmaleimide, and an alkyl acrylate. It has been found that by using a copolymer containing a structural unit (U3) derived from ester in a predetermined ratio, delamination when the blade 160 is pulled out can be further suppressed without worsening brittleness (Fig. (See 2B). In particular, the structural unit (U2) derived from phenylmaleimide has high planarity and moderate polarity, so it has a moderately high average aspect ratio and tends to increase the affinity with the rubber particles 150b having planarity. Thereby, interfacial peeling with the rubber particles 150b can be suppressed, and thereby interlayer peeling between the protective film 120B and the adhesive layer 130B can be suppressed.

Each component of the polarizing plate according to this embodiment will be explained below.

1-1. Polarizer A polarizer is an element that passes only light with a plane of polarization in a certain direction. The polarizer can typically be a polyvinyl alcohol-based polarizing film. Examples of polyvinyl alcohol polarizing films include polyvinyl alcohol films dyed with iodine and dichroic dyes.

The polyvinyl alcohol polarizing film may be a film obtained by uniaxially stretching a polyvinyl alcohol film and then dyeing it with iodine or a dichroic dye (preferably a film further subjected to durability treatment with a boron compound); It may be a film obtained by dyeing an alcoholic film with iodine or a dichroic dye and then uniaxially stretching the film (preferably, a film further subjected to durability treatment with a boron compound). The absorption axis of polarizer 110 is typically parallel to the direction of maximum stretch.

Examples of polyvinyl alcohol-based polarizing films include those described in JP-A-2003-248123, JP-A-2003-342322, etc. with an ethylene unit content of 1 to 4 mol%, a degree of polymerization of 2000 to 4000, and a degree of saponification of 99. 0 to 99.99 mol% of ethylene-modified polyvinyl alcohol is used.

The thickness of the polarizer is preferably 5 to 30 μm, and more preferably 5 to 20 μm from the viewpoint of making the polarizing plate thinner.

1-2. Protective film A
Protective film A contains (meth)acrylic resin and rubber particles a.

1-2-1. (Meth)acrylic resin The (meth)acrylic resin contained in the protective film A may be a homopolymer containing a structural unit derived from methyl methacrylate, or a structural unit derived from methyl methacrylate, It may also be a copolymer containing a structural unit derived from a copolymerizable monomer other than methyl methacrylate.

The copolymerizable monomer is not particularly limited, and the alkyl group other than methyl methacrylate has 1 to 1 carbon atoms, such as ethyl (meth)acrylate, propyl (meth)acrylate, and six-membered ring lactone (meth)acrylate. 18 (meth)acrylic acid esters; α, β-unsaturated acids such as (meth)acrylic acid; unsaturated group-containing dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid; styrene, α-methylstyrene α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile; maleimides such as maleimide and N-substituted maleimide; maleic anhydride and glutaric anhydride. One type of copolymerizable monomer may be used, or two or more types may be used in combination.

Among these, from the viewpoint of easy adjustment of the tensile modulus of the film within the range described below, we use a homopolymer containing a structural unit derived from methyl methacrylate (polymethyl methacrylate) or a structural unit derived from methyl methacrylate and glutaric acid. Imide structural units (for example, structural units derived from (meth)acrylic esters reacted with imidizing agents such as amines), structural units derived from glutaric anhydride, or six-membered ring lactones (meth) A copolymer containing a structural unit derived from an acrylic acid ester (lactone ring structural unit) is preferred, and a homopolymer containing a structural unit derived from methyl methacrylate (polymethyl methacrylate) is more preferred.

The content of structural units derived from methyl methacrylate is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, based on the total structural units constituting the (meth)acrylic resin. . The type and composition of the monomer of the (meth)acrylic resin can be identified by ¹ H-NMR.

The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 90°C or higher, more preferably 100 to 150°C. The protective film A in which the (meth)acrylic resin has a Tg of 90° C. or higher can have good heat resistance.

The glass transition temperature (Tg) of a (meth)acrylic resin can be measured using DSC (Differential Scanning Colorimetry) in accordance with JIS K 7121-2012 or ASTM D 3418-82. .

The weight average molecular weight (Mw) of the (meth)acrylic resin is not particularly limited and can be appropriately set depending on the film forming method. For example, when the protective film A is formed by a melt method, the weight average molecular weight of the (meth)acrylic resin is preferably 100,000 to 300,000. When the protective film A is formed by a casting method, the weight average molecular weight of the (meth)acrylic resin is preferably from 500,000 to 3,000,000, more preferably from 600,000 to 2,000,000. . When the weight average molecular weight of the (meth)acrylic resin is within the above range, sufficient mechanical strength (toughness) can be imparted to the film without impairing film formability.

The weight average molecular weight (Mw) of the (meth)acrylic resin can be measured in terms of polystyrene by gel permeation chromatography (GPC). Specifically, it can be measured using a column (TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series, manufactured by Tosoh Corporation). The measurement conditions may be the same as in the examples described later.

The content of the (meth)acrylic resin is preferably 60% by mass or more, more preferably 70% by mass or more, based on the protective film A.

1-2-2. rubber particles a
The rubber particles a contained in the protective film A can impart toughness and flexibility to the protective film A.

In a cross section along the thickness direction of the protective film A, the average aspect ratio of the rubber particles a is preferably 1.0 to 1.1. In the process of punching out a polarizing plate, the stress generated in protective film A by pushing in the blade is smaller than the stress generated in protective film B by pushing in the blade, so the followability of rubber particle a needs to be adjusted as much as rubber particle b. That's because there isn't. Further, when the blade is pushed into the protective film A, stress is likely to be applied isotropically to the rubber particles 150a, so the stress is likely to be released by the rubber particles 150a themselves.

The average aspect ratio means the average value of the aspect ratios of a plurality of rubber particles a. Aspect ratio means the ratio of the longer axis to the shorter axis (longer axis/breadth axis) of a rubber particle.

In the cross section along the thickness direction of the protective film A, the long axis of the rubber particle a can be measured as the length in the longitudinal direction (length of the long side) of the rectangle circumscribed by the rubber particle a; The short axis can be measured as the length in the short direction (length of the short side) of the rectangle circumscribed by the rubber particle a.

Specifically, the cross section along the thickness direction of the protective film A refers to a cross section parallel to the in-plane slow axis among the cross sections of the protective film A along the thickness direction. The in-plane slow axis refers to the axis where the refractive index is maximum in the film plane. When the in-plane slow axis of the protective film A cannot be specified, it refers to a cross section parallel to the width direction (TD direction) of the protective film A among the cross sections along the thickness direction of the protective film A.

The average major axis of the rubber particles a is preferably 100 to 400 nm. When the average major axis of the rubber particles a is 100 nm or more, it is easy to impart sufficient toughness to the film, and when it is 400 nm or less, the transparency of the film is unlikely to decrease. The average major axis of the rubber particles a is more preferably 150 to 300 nm. The average length of the rubber particles is the average value of the lengths of the rubber particles.

The average aspect ratio and average major axis of the rubber particles a can be calculated by the following method.
1) Observe the cross section of protective film A using a TEM. The observation area may be an area corresponding to the thickness of the protective film A, or may be an area of 5 μm x 5 μm. When the observation area is a region corresponding to the thickness of the protective film A, the number of measurement points can be one. When the observation area is a 5 μm×5 μm area, the number of measurement points can be four.
2) Measure the major axis and minor axis of each rubber particle in the obtained TEM image, and calculate the aspect ratio. The average value of the aspect ratios obtained from the plurality of rubber particles is defined as the "average aspect ratio", and the average value of the major diameters obtained from the plurality of rubber particles is defined as the "average major axis".

The average aspect ratio and average major axis of the rubber particles a can be adjusted by the film forming conditions and stretching conditions of the protective film A. In order to reduce the average aspect ratio of the rubber particles a, it is preferable, for example, to lower the stretching ratio at the time of forming the protective film (preferably to not stretch it).

Such rubber particles a are particles containing a rubbery polymer (crosslinked polymer). Examples of rubbery polymers include butadiene-based crosslinked polymers, (meth)acrylic-based crosslinked polymers, and organosiloxane-based crosslinked polymers. Among these, (meth)acrylic crosslinked polymers are preferred from the viewpoint of having a small refractive index difference with methacrylic resins and the transparency of the protective film is less likely to be impaired, and acrylic crosslinked polymers (acrylic rubber-like polymers) are preferred. More preferred.

That is, the rubber particles are preferably particles containing the acrylic rubbery polymer (a1).

(Acrylic rubber-like polymer (a1))
The acrylic rubbery polymer (a1) is a crosslinked polymer containing acrylic ester as a main component. That is, the acrylic rubber-like polymer (a1) contains a structural unit derived from an acrylic ester, a structural unit derived from a monomer copolymerizable with the acrylic ester, and two or more radically polymerizable groups (non-conjugated) in one molecule. A crosslinked polymer containing a structural unit derived from a polyfunctional monomer having a reactive double bond) is preferable.

The acrylic ester is preferably an acrylic alkyl ester having an alkyl group of 1 to 12 carbon atoms, such as methyl acrylate or butyl acrylate. The number of acrylic esters may be one type or two or more types. From the viewpoint of lowering the glass transition temperature of the rubber particles to −15° C. or lower, the acrylic ester preferably contains at least an alkyl acrylic ester having 4 to 10 carbon atoms.

The content of structural units derived from acrylic ester is preferably 40 to 80% by mass, and preferably 45 to 65% by mass, based on the total structural units constituting the acrylic rubbery polymer (a). is more preferable. When the content of acrylic ester is 45% by weight or more, sufficient toughness can be easily imparted to the film.

The copolymerizable monomers are monomers copolymerizable with acrylic esters other than polyfunctional monomers. That is, the copolymerizable monomer does not have two or more radically polymerizable groups. Examples of copolymerizable monomers include methacrylic acid esters such as methyl methacrylate; styrenes such as styrene and methylstyrene; unsaturated nitrites such as acrylonitrile and methacrylonitrile. Among these, the copolymerizable monomer preferably contains styrenes, from the viewpoint of easily making the tensile modulus of the protective film A lower than that of the protective film B.

When the copolymerizable monomer contains styrenes, the content of structural units derived from styrenes in rubber particles a contained in protective film A is equal to the structure derived from styrenes in rubber particles b contained in protective film B. It is preferable that the amount is less than the unit content. That is, the content of structural units derived from styrenes in the acrylic rubbery polymer (a1) is preferably lower than the content of structural units derived from styrenes in the acrylic rubbery polymer (b1). . Specifically, the content of structural units derived from styrene in the acrylic rubbery polymer (a1) is 5 to 55% by mass based on the total structural units constituting the acrylic rubbery polymer (a1). It is preferably 30 to 50% by mass, and more preferably 30 to 50% by mass. When the content of structural units derived from styrenes is within the above range, it is easy to adjust the rubber particles a to appropriate hardness.

The content of structural units derived from styrenes in rubber particles can be measured from the area ratio of peaks detected by pyrolysis GC/MS. Specifically, it can be measured by the following procedure.
1) First, prepare several known samples with different contents of styrenes, perform pyrolysis GC/MS measurement, and create a calibration curve based on the obtained peak area ratios.
2) Next, the sample to be measured is subjected to pyrolysis GC/MS measurement, and the peak area ratio is calculated.
3) The peak area ratio obtained in 2) above is compared with the calibration curve in 1) above to identify the content of styrenes in the sample to be measured.
The measurement conditions for GCMS may be as follows.
Measuring device: SHIMAZU GCMS QP2010
Column type: Ultra Alloy-5 (size 30m x diameter 0.25mm)
Carrier gas type: He
Flow rate conditions: 1.8mL/min Column oven temperature conditions: 40℃-10℃/min-320℃
Interface temperature: 300℃
Ion source temperature: 200℃
Detection mode: SIM (target ion: m/z104, confirmation ion: m/z78)

Examples of polyfunctional monomers include allyl (meth)acrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl maleate, divinyl adipate, divinylbenzene, ethylene glycol di(meth)acrylate, diethylene glycol (meth) Acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethanetetra(meth)acrylate, dipropylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate.

The content of the structural unit derived from the polyfunctional monomer is preferably 0.05 to 10% by mass, and 0.1 to 5% by mass based on the total structural units constituting the acrylic rubbery polymer (a1). It is more preferable that it is mass %. When the content of the polyfunctional monomer is 0.05% by mass or more, it is easy to increase the degree of crosslinking of the obtained acrylic rubber-like polymer (a), so that the hardness and rigidity of the obtained film are not excessively impaired. When the content is 10% by mass or less, the toughness of the film is less likely to be impaired.

The particles containing the acrylic rubbery polymer (a1) may be particles made of the acrylic rubbery polymer (a1); in the presence of the acrylic rubbery polymer (a1), methacrylic acid ester Particles made of an acrylic graft copolymer obtained by polymerizing a monomer mixture of It may be a type particle.

The core portion constituting the core-shell type particle contains the acrylic rubbery polymer (a1). The shell portion constituting the core-shell type particle contains a polymer (a2) (graft component) containing a structural unit derived from a methacrylic acid ester.

The methacrylic acid ester is preferably an alkyl methacrylic ester having an alkyl group of 1 to 12 carbon atoms, such as methyl methacrylate. The number of methacrylic esters may be one, or two or more.

The content of the methacrylic acid ester is preferably 50% by mass or more based on the total structural units constituting the polymer (a2). When the content of methacrylic acid ester is 50% by mass or more, the hardness and rigidity of the obtained film can be made difficult to decrease. Further, from the viewpoint of increasing the affinity with solvents such as methylene chloride, the content of methacrylic acid ester is more preferably 70% by mass or more based on the total structural units constituting the polymer.

The polymer (a2) may further contain structural units derived from other copolymerizable monomers. Examples of other monomers include acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate; benzyl (meth)acrylate, dicyclopentanyl (meth)acrylate, phenoxy (meth)acrylate Includes (meth)acrylic monomers (ring structure-containing (meth)acrylic monomers) having an alicyclic structure such as ethyl, a heterocyclic structure, or an aromatic group.

The weight ratio (grafting ratio) of the graft component in the rubber particles is preferably 10 to 250%, more preferably 25 to 200%, more preferably 40 to 200%, and 60 to 150%. It is more preferable that When the mass ratio is 10% or more, the proportion of the shell portion does not become too small, so that the hardness and rigidity of the film are less likely to be impaired. When the mass ratio is 250% or less, the proportion of the core portion does not become too small, so that the effect of improving the toughness and brittleness of the film is less likely to be impaired.

The mass ratio of grafting rate is measured by the following method.
1) Dissolve 2 g of core-shell type particles in 50 ml of methyl ethyl ketone and centrifuge for 1 hour at 30,000 rpm and 12°C using a centrifuge (manufactured by Hitachi Koki Co., Ltd., CP60E) to separate insoluble and possible components. Separate into soluble components (centrifugation is performed 3 times in total).
2) The weight of the obtained insoluble matter is applied to the following formula to calculate the grafting ratio.
Grafting rate (%) = [{(Weight of methyl ethyl ketone insoluble matter) - (Weight of acrylic rubbery polymer (a))}/(Weight of acrylic rubbery polymer (a))] x 100

(About physical properties)
The glass transition temperature (Tg) of the rubber particles can be below room temperature (25° C. or below). Further, the glass transition temperature of the rubber particles a is preferably lower than the glass transition temperature of the rubber particles b. When the glass transition temperature (Tg) of the rubber particles satisfies the above range, it is easy to impart sufficient toughness to the film. The glass transition temperature (Tg) of the rubber particles is measured in the same manner as described above.

The glass transition temperature (Tg) of the rubber particles a can be adjusted, for example, by adjusting the composition and grafting rate of the polymers constituting the core and shell parts. In order to lower the glass transition temperature (Tg) of the rubber particles, for example, an acrylic ester with an alkyl group having 4 or more carbon atoms in the acrylic rubber-like polymer (a1) of the core part, as described later. It is preferable to increase the mass ratio of /copolymerizable monomer (for example, 3 or more, preferably 4 or more and 10 or less).

The content of rubber particles a in the protective film A is not particularly limited, but is preferably higher than the content of rubber particles b in the protective film B. Specifically, the content of rubber particles a in the protective film A is preferably 12 to 25% by mass, more preferably 15 to 22% by mass. When the rubber particle content is 12% by mass or more, sufficient toughness or flexibility can be easily imparted to the protective film A, and when it is 25% by mass or less, increase in internal haze can be easily suppressed.

1-2-3. Other Components The protective film A may further contain other components other than those mentioned above, if necessary. Examples of other ingredients include matting agents and the like. Examples of matting agents include inorganic fine particles such as silica particles, organic fine particles having a glass transition temperature of 80° C. or higher, and the like.

1-2-4. Physical properties (tensile modulus)
The tensile modulus of the protective film A is not particularly limited, but is preferably lower than the tensile modulus of the protective film B from the viewpoint of easily suppressing cracks and delamination during punching of the polarizing plate. As mentioned above, in the punching process of the polarizing plate, the stress generated in the protective film A by pushing the blade is smaller than the stress generated in the protective film B, so the adjustment of the load applied to the rubber particles a of the protective film A is This is because it is not as necessary as B. Furthermore, when the tensile modulus of the protective film A is relatively low, it is possible to reduce the "stress caused by the tip of the blade" and the "stress caused by the protective film A being pushed in" that the protective film B receives. Specifically, the tensile modulus of the protective film A at 25° C. is preferably 1.6 to 2.6 GPa.

The tensile modulus of protective film A can be measured in accordance with JIS K7127. Specifically, it can be measured by the following procedure.
1) Cut the protective film A into a 1 cm (TD direction) x 10 cm (MD direction) piece to use as a sample piece, and condition the sample piece in an environment of 25° C. and 60% RH for 24 hours.
2) The tensile modulus of the obtained sample piece is measured by the tensile test method described in JIS K7127. That is, the sample piece is set in a tensile testing device Tensilon manufactured by Orientech Co., Ltd., and a tensile modulus is measured when a tensile test is conducted under the conditions of a distance between chucks of 50.0 mm and a tensile speed of 50 mm/min. Measurements are performed at 25° C. and 60% RH.

The tensile modulus of the protective film A can be adjusted by the composition of the (meth)acrylic resin, the content and composition of the rubber particles a, and the like. From the viewpoint of lowering the tensile modulus of protective film A, it is possible to lower the ratio of structural units derived from the ring-containing monomer of the (meth)acrylic resin, increase the content of rubber particles a, or increase the content of styrene in rubber particles a. It is preferable to reduce the content of structural units derived from the same group.

(Haze)
It is preferable that the protective film A has high transparency. The haze of the protective film A is preferably 2.0% or less, more preferably 1.0% or less. Haze can be measured using a haze meter (HGM-2DP, Suga Test Instruments) using a 40 mm x 80 nm sample at 25° C. and 60% RH according to JISK-6714.

(thickness)
Although the thickness of the protective film A is not particularly limited, it is preferably thicker than the thickness of the protective film B. If the thickness of the protective film A is relatively thick, the rigidity of the protective film A increases, so it is easier to reduce deformation of not only the protective film A but the entire polarizing plate when cutting out the blade in the punching process of the polarizing plate. . Specifically, the thickness of the protective film A is preferably 40 to 100 μm, more preferably 50 to 80 μm.

1-3. Protective film B
The protective film B can function as a retardation film disposed between a polarizer and a display element such as a liquid crystal cell when used as a display device. Protective film B contains (meth)acrylic resin and rubber particles b.

1-3-1. (Meth)acrylic resin The (meth)acrylic resin contained in the protective film B consists of a structural unit (U1) derived from methyl methacrylate, a structural unit (U2) derived from phenylmaleimide, and an alkyl acrylate. It is a copolymer containing the structural unit (U3) derived from

The content of the structural unit (U1) derived from methyl methacrylate is preferably 50 to 95% by mass, and preferably 70 to 90% by mass, based on the total structural units constituting the (meth)acrylic resin. is more preferable.

The structural unit (U2) derived from phenylmaleimide has a highly planar structure and has appropriate polarity. As a result, it is easy to suppress the formation of voids between the rubber particles and the resin due to the interaction between the structure and the rubber particles against deformation in the plane of the film that occurs during punching. As a result, interfacial peeling between the (meth)acrylic resin and the rubber particles can be easily suppressed, and thereby interlayer peeling between the protective film B and the adhesive layer can also be suppressed.

The content of the structural unit (U2) derived from phenylmaleimide is preferably 1 to 25% by mass based on the total structural units constituting the (meth)acrylic resin. When the content of the structural unit (U2) derived from phenylmaleimide is 1% by mass or more, interfacial peeling between the rubber particles B and the (meth)acrylic resin can be easily suppressed, and thereby the protective film B and the adhesive It is easy to suppress delamination between layers. When the content of the structural unit (U2) derived from phenylmaleimide is 25% by mass or less, the brittleness of the protective film B is less likely to be impaired. From the above viewpoint, the content of the structural unit (U2) derived from phenylmaleimide is more preferably 7 to 15% by mass.

The structural unit (U3) derived from acrylic acid alkyl ester can suppress interfacial peeling between the (meth)acrylic resin and the rubber particles b. Specifically, as described below, when the polymer (b2) constituting the shell portion of rubber particle b has a structural unit derived from an acrylic ester such as butyl acrylate, a structural unit derived from an alkyl acrylate ester. Since (U3) has a high affinity with the structural unit derived from acrylic ester, it can increase the affinity between the (meth)acrylic resin and the rubber particles b. Thereby, in the punchability of the polarizing plate, interfacial peeling between the (meth)acrylic resin and the rubber particles can be suppressed, thereby suppressing a decrease in interlayer adhesion between the protective film B and the adhesive layer. The acrylic acid alkyl ester is preferably an acrylic acid alkyl ester in which the alkyl moiety has 1 to 7 carbon atoms, preferably 1 to 5 carbon atoms. Examples of acrylic acid alkyl esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, and the like.

The content of the structural unit (U3) derived from acrylic acid alkyl ester is preferably 1 to 25% by mass based on the total structural units constituting the (meth)acrylic resin. When the content of the structural unit (U3) derived from acrylic acid alkyl ester is 1% by mass or more, it is easy to suppress interfacial peeling between the (meth)acrylic resin and the rubber particles, and when it is 25% by mass or less, Heat resistance is less likely to be impaired. From the above viewpoint, the content of structural units derived from acrylic acid alkyl ester is more preferably 5 to 15% by mass.

The ratio of the structural unit (U2) derived from phenylmaleimide to the total amount of the structural unit (U2) derived from phenylmaleimide and the structural unit (U3) derived from acrylic acid alkyl ester shall be 20 to 70% by mass. is preferred. When the ratio is 20% by mass or more, the heat resistance and tensile modulus of the protective film B are appropriately increased, while interfacial peeling between the rubber particles b and the resin and the resulting interlayer peeling between the protective film B and the adhesive layer are prevented. If the amount is 70% by mass or less, the protective film B will not become too brittle.

The (meth)acrylic resin may further contain structural units derived from monomers other than those mentioned above, if necessary. Examples of such other monomers include those similar to those listed as copolymerizable monomers constituting the (meth)acrylic resin used in the protective film A.

The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 105°C or higher, more preferably 110 to 150°C. When the Tg of the (meth)acrylic resin is within the above range, not only the heat resistance of the protective film B can be easily increased, but also the drying efficiency during cast film formation can be easily increased. In order to increase the Tg of the (meth)acrylic resin, it is preferable to appropriately increase the content of the structural unit (U2) derived from phenylmaleimide or the structural unit (U3) derived from acrylic acid alkyl ester, for example.

The weight average molecular weight (Mw) of the (meth)acrylic resin is preferably 500,000 to 3,000,000. When the weight average molecular weight of the (meth)acrylic resin is within the above range, sufficient mechanical strength (toughness) can be imparted to the film. From the above viewpoint, the weight average molecular weight of the (meth)acrylic resin is more preferably from 600,000 to 2,000,000.

The content of the (meth)acrylic resin is preferably 60% by mass or more, more preferably 70% by mass or more, based on the protective film B.

1-3-2. rubber particles b
The rubber particles b contained in the protective film B can impart toughness to the protective film B, as described above.

In a cross section along the thickness direction of the protective film B, the average aspect ratio of the rubber particles b is preferably 1.2 to 3.0. When the average aspect ratio of the rubber particles b is 1.2 or more, the rubber particles b easily follow the deformation of the protective film B when a blade is pushed in during the polarizing plate punching process. Therefore, the stress applied to the protective film B can be alleviated, and cracks etc. during punching of the polarizing plate can be suppressed. When the average aspect ratio of the rubber particles b is 3.0 or less, interfacial peeling between the rubber particles b and the (meth)acrylic resin can be made difficult to occur. In other words, if the average aspect ratio of the rubber particles b is too high, the residual stress due to the stretching of the rubber particles b is also large, which tends to cause a misalignment between the plastic deformation of the (meth)acrylic resin and the plastic deformation of the rubber particles b. Voids are likely to be formed at the interface between the meth)acrylic resin and the rubber particles b. When the average aspect ratio of the rubber particles b is 3.0 or less, the residual stress caused by such stretching can be reduced, so that interfacial peeling between the rubber particles b and the (meth)acrylic resin can be made less likely to occur. Thereby, delamination between the adhesive layer and the protective film B can be suppressed when the blade pushed in in the process of punching out the polarizing plate is pulled out. From the same viewpoint, the average aspect ratio of the rubber particles b is more preferably 1.5 to 2.9.

The average major axis of the rubber particles b is preferably 250 to 400 nm. When the average major axis of the rubber particles a is 250 nm or more, not only sufficient toughness and flexibility can be imparted to the protective film B, but also the effect of relieving stress can be easily obtained. When the average major axis of the rubber particles a is 400 nm or less, the effect of dispersing stress is less likely to be impaired. The average major axis of the rubber particles b is the average value of the major axis of the rubber particles.

The average aspect ratio of rubber particles b is defined similarly to the average aspect ratio of rubber particles a, and can be measured in the same manner. The average length of the rubber particles b is also defined in the same manner as the average length of the rubber particles a, and can be measured in the same manner.

The average aspect ratio and average major axis of the rubber particles b can be adjusted by adjusting the stretching conditions of the protective film B, as described above. In order to increase the average aspect ratio of the rubber particles b, it is preferable to increase the stretching ratio when forming the protective film B, for example. Further, in order to increase the average major axis of the rubber particles b, it is preferable to use rubber particles having a large average particle diameter as a raw material or to increase the stretching ratio, for example.

The monomer components and structure of rubber particles b may be the same as those of rubber particles a. For example, the rubber particles b are core-shell particles having a core portion containing an acrylic rubber-like polymer (b1) and a shell portion containing a polymer (b2) containing a structural unit derived from a methacrylic acid ester. sell. The acrylic rubbery polymer (b1) is similar to the acrylic rubbery polymer (a1), and the composition may be the same or different. Polymer (b2) is similar to polymer (a2), and the composition may be the same or different.

However, if the acrylic rubbery polymer (b1) constituting rubber particles b contains structural units derived from styrenes, the content of structural units derived from styrenes in rubber particles b contained in protective film B is , is preferably larger than the content of structural units derived from styrenes in the rubber particles a contained in the protective film A. That is, the content of structural units derived from styrenes in the acrylic rubbery polymer (b1) is preferably higher than the content of structural units derived from styrenes in the acrylic rubbery polymer (a1). . Specifically, the content of structural units derived from styrenes in the rubber particles b is preferably 5 to 60% by mass based on the total structural units constituting the acrylic rubbery polymer (b1), More preferably, it is 40 to 60% by mass. The higher the content of structural units derived from styrenes, the higher the hardness of the rubber particles b usually becomes. When the content of the structural unit derived from styrene is within the above range, the rubber particles b can be appropriately hardened, so that the tensile modulus can be easily adjusted within the above range.

The glass transition temperature of the rubber particles b may be below room temperature (25° C. or below), as described above. Further, the glass transition temperature of the rubber particles b is preferably higher than the glass transition temperature of the rubber particles a.

The content of rubber particles b in protective film B is not particularly limited, but from the viewpoint of making the tensile modulus of protective film B higher than that of protective film A, it should be lower than the content of rubber particles a in protective film A. is preferred. Specifically, the content of rubber particles b in the protective film B is preferably 2 to 15% by mass, more preferably 5 to 12% by mass.

1-3-3. Other Components The protective film B may further contain other components other than those mentioned above, if necessary. For other components, the same components as those for the protective film A can be used.

1-3-4. Physical properties (tensile modulus)
The tensile modulus of the protective film B is not particularly limited, but it is preferably higher than the tensile modulus of the protective film A from the viewpoint of easily suppressing cracks and delamination during punching of the polarizing plate. This is because, in the process of punching out the polarizing plate, the stress generated in the protective film B due to the pushing of the blade is greater than the stress generated in the protective film A, and it is highly necessary to adjust the load applied to the rubber particles b in the protective film B. In other words, if the rubber particle b is surrounded by soft resin, the force received from the blade will be easily dispersed into the resin; whereas if the rubber particle b is surrounded by hard resin, the force received from the blade will be easily dispersed into the resin. The rubber particles b are easily subjected to force without being dispersed too much. In other words, by appropriately increasing the tensile modulus of the protective film B, it becomes easier to apply an appropriate load to the rubber particles b, which makes it easier for the rubber particles b to absorb the stress applied during punching of the polarizing plate, and the resin This can help prevent cracks from forming. Thereby, it is possible to easily suppress cracks and interlayer peeling when punching out the polarizing plate. The difference in tensile modulus at 25° C. between the protective film B and the protective film A can be, for example, 0.3 GPa or more. The tensile modulus of the protective film B at 25° C. is preferably 2.4 to 3.4 GPa. The tensile modulus of the protective film B can be measured in the same manner as described above.

The tensile modulus of the protective film B can be adjusted by the composition of the (meth)acrylic resin, the content and composition of the rubber particles b, and the like. From the viewpoint of increasing the tensile modulus of the protective film B, the structural unit (U2) derived from phenylmaleimide in the (meth)acrylic resin/(derived from the structural unit (U2) derived from phenylmaleimide and an acrylic acid alkyl ester) It is preferable to increase the ratio of structural units (U3) (total of structural units (U3)), decrease the content of rubber particles b, or increase the content of structural units derived from styrenes in rubber particles b.

(Haze)
As described above, the haze of the protective film B is preferably 2.0% or less, more preferably 1.0% or less.

(Phase difference Ro and Rt)
For example, from the viewpoint of using the protective film B as a retardation film for IPS mode, the in-plane retardation Ro measured at a measurement wavelength of 550 nm and in an environment of 23° C. and 55% RH is 0 to 10 nm. It is preferably 0 to 5 nm, more preferably 0 to 5 nm. The retardation Rt of the protective film B in the thickness direction is preferably -20 to 20 nm, more preferably -10 to 10 nm.

Ro and Rt are each defined by the following formula.
Formula (2a): Ro=(nx-ny)×d
Formula (2b): Rt=((nx+ny)/2-nz)×d
(In the formula,
nx represents the refractive index in the in-plane slow axis direction (direction where the refractive index is maximum) of the film,
ny represents the refractive index in the direction perpendicular to the in-plane slow axis of the film,
nz represents the refractive index in the thickness direction of the film,
d represents the thickness (nm) of the film. )

The in-plane slow axis of the protective film B can be confirmed using an automatic birefringence meter Axo Scan Mueller Matrix Polarimeter (manufactured by Axometrics).

Ro and Rt can be measured by the following method.
1) Humidify the protective film in an environment of 23° C. and 55% RH for 24 hours. The average refractive index of this film is measured using an Abbe refractometer, and the thickness d is measured using a commercially available micrometer.
2) The retardation Ro and Rt of the film after humidity conditioning at a measurement wavelength of 550 nm were measured at 23° C. and 55% RH using an automatic birefringence meter Axo Scan Mueller Matrix Polarimeter (manufactured by Axometrix). Measure under environmental conditions.

The retardation Ro and Rt of the protective film B can be adjusted by, for example, the monomer composition of the (meth)acrylic resin and the stretching conditions. In order to lower the retardation Ro and Rt of the protective film B, a (meth)acrylic resin that does not easily produce a retardation upon stretching is used (for example, a structural unit derived from a monomer with negative birefringence and a monomer with positive birefringence) is used. It is preferable to set the monomer ratio so that the phase difference can be canceled out by the structural unit derived from the monomer having the following.

(Residual solvent amount)
Since the protective film B is preferably formed by a casting method, it may further contain a residual solvent. The amount of residual solvent is preferably 700 ppm or less, more preferably 30 to 700 ppm, based on the protective film B. The content of the residual solvent can be adjusted by the drying conditions of the dope cast on the support in the process of manufacturing the protective film.

The amount of residual solvent in the protective film B can be measured by headspace gas chromatography. In the headspace gas chromatography method, a sample is sealed in a container, heated, and while the container is filled with volatile components, the gas in the container is immediately injected into a gas chromatograph and mass spectrometry is performed to identify the compound. The volatile components are quantified while the test is being carried out. In the headspace method, it is possible to observe all peaks of volatile components using a gas chromatograph, and by using an analysis method that utilizes electromagnetic interaction, it is also possible to quantify volatile substances and monomers with high precision. It can be done at the same time.

(thickness)
The thickness of the protective film B is not particularly limited, but is preferably thinner than the thickness of the protective film A. When the thickness of the protective film B is relatively thin, not only can the blade be less likely to be caught when the blade is pulled out in the process of punching out the polarizing plate, but also physical deformation when the blade is pushed can be reduced. Thereby, cracks when punching out the polarizing plate can be further suppressed. For example, the thickness of the protective film B can be 20 to 77% of the thickness of the protective film A. Specifically, the thickness of the protective film B is preferably 10 to 60 μm, more preferably 10 to 40 μm.

1-3-5. Method for manufacturing protective films A and B Protective films A and B may be manufactured by any method, and may be manufactured by a solution casting method (casting method) or by a melt casting method (melt method). It's okay.

The protective film A can be manufactured, for example, by a melt casting method. The melt casting method (melt) involves a process of melt-extruding a resin composition containing a (meth)acrylic resin and rubber particles, a process of cooling and solidifying the extruded resin composition, and cooling as necessary. A protective film can be obtained through a step of stretching the film-like material obtained by solidification. The stretching ratio when manufacturing the protective film A is not particularly limited, but from the viewpoint of making the average aspect ratio of the rubber particles a smaller than that of the rubber particles b, it should be lower than the stretching ratio when manufacturing the protective film B, e.g. It is preferably 10% or less, and more preferably unstretched.

The protective film B is preferably manufactured by a casting method from the viewpoint of reducing restrictions on the materials that can be used. That is, the protective film A includes at least 1) a step of obtaining a dope containing the above-mentioned (meth)acrylic resin, rubber particles, and a solvent, and 2) a step of casting the obtained dope onto a support. , drying and peeling to obtain a film-like product; and 3) drying the obtained film-like product while stretching as necessary.

Regarding the step 1), a dope is prepared by dissolving or dispersing a (meth)acrylic resin and rubber particles a or b (hereinafter also collectively referred to as "rubber particles") in a solvent.

The solvent used for the dope contains at least an organic solvent (good solvent) that can dissolve the (meth)acrylic resin. Examples of good solvents include chlorinated organic solvents such as methylene chloride; non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran. Among these, methylene chloride is preferred.

The solvent used for the dope may further contain a poor solvent. Examples of poor solvents include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. When the ratio of alcohol in the dope becomes high, the film-like material tends to gel and easily peel off from the metal support. Examples of straight-chain or branched aliphatic alcohols having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Among these, ethanol is preferred because of its dope stability, relatively low boiling point, and good drying properties.

Regarding the step 2), the obtained dope is cast onto a support. The dope can be cast by being discharged from a casting die.

Next, the solvent in the dope cast onto the support is evaporated and dried. The dried dope is peeled off from the support to obtain a film-like product.

The amount of residual solvent in the dope when it is peeled off from the support (the amount of residual solvent in the film-like material when it is peeled off) is preferably, for example, 25% by mass or more, and more preferably 30 to 37% by mass. When the amount of residual solvent at the time of peeling is 37% by mass or less, it is easy to prevent the film-like material from stretching too much due to peeling.

The amount of residual solvent in the dope at the time of peeling is defined by the following formula. The same applies to the following.
Amount of residual solvent in dope (mass%) = (mass of dope before heat treatment - mass of dope after heat treatment) / mass of dope after heat treatment x 100
Note that the heat treatment when measuring the amount of residual solvent refers to heat treatment at 140° C. for 30 minutes.

The amount of residual solvent at the time of peeling can be adjusted by adjusting the drying temperature and drying time of the dope on the support, the temperature of the support, and the like.

Regarding step 3): Dry the obtained film-like material. Drying may be performed in one step or in multiple steps. Moreover, drying may be performed while stretching as necessary.

For example, the process of drying a film-like material includes a step of pre-drying the film-like material (pre-drying step), a step of stretching the film-like material (stretching step), and a step of drying the film-like material after stretching (main drying step). drying step).

(Pre-drying process)
The pre-drying temperature (drying temperature before stretching) can be higher than the stretching temperature. Specifically, when the glass transition temperature of the (meth)acrylic resin is Tg, it is preferably equal to or higher than Tg (°C), and more preferably from (Tg+10) to (Tg+50)°C. When the pre-drying temperature is Tg (°C) or higher, preferably (Tg + 10)°C or higher, the solvent is easily volatilized to an appropriate extent, which facilitates improving transportability (handling properties); does not volatilize too much, so the stretchability in the subsequent stretching process is less likely to be impaired. In the case of (a) drying using a non-contact heating type while conveying with a tenter stretching machine or rollers, the initial drying temperature can be measured as the temperature inside the stretching machine or the ambient temperature such as the hot air temperature.

(Stretching process)
Stretching may be carried out according to the required optical properties, and it is preferable to stretch in at least one direction, and in two directions perpendicular to each other (for example, in the width direction (TD direction) of the film-like material and in the direction perpendicular thereto). Biaxial stretching in the transport direction (MD direction) may also be performed.

From the viewpoint of easily adjusting the average aspect ratio of the rubber particles b contained in the protective film B to the above range, the stretching ratio when manufacturing the protective film B may be higher than the stretching ratio when manufacturing the protective film A. preferable. Specifically, the stretching ratio when producing the protective film B is preferably 40 to 100%, more preferably 60 to 100%. In the case of biaxial stretching, the stretching ratio in each direction is preferably within the above range.

The stretching ratio (%) is defined as (stretching direction size of the film after stretching−stretching direction size of the film before stretching)/(stretching direction size of the film before stretching)×100. In addition, when performing biaxial stretching, it is preferable to set it as the said stretching magnification about each of TD direction and MD direction.

As described above, the stretching temperature (drying temperature during stretching) is preferably Tg (°C) or higher, where Tg is the glass transition temperature of the (meth)acrylic resin, and (Tg + 10) to (Tg + 50). It is more preferable that the temperature is ℃. When the stretching temperature is Tg (°C) or higher, preferably (Tg + 10)°C or higher, the solvent is easily volatilized to an appropriate extent, making it easy to adjust the stretching tension to an appropriate range; does not volatilize too much, so stretchability is less likely to be impaired. The stretching temperature during production of the protective film B can be, for example, 115° C. or higher. As for the stretching temperature, it is preferable to measure the ambient temperature such as (a) the temperature inside the stretching machine, as described above.

The amount of residual solvent in the film-like material at the start of stretching is preferably about the same as the amount of residual solvent in the film-like material at the time of peeling, for example, preferably 20 to 30% by mass, and 25 to 30% by mass. % is more preferable.

Stretching of the film-like material in the TD direction (width direction) can be carried out, for example, by fixing both ends of the film-like material with clips or pins and widening the interval between the clips or pins in the traveling direction (tenter method). Stretching of the film-like material in the MD direction can be carried out, for example, by a method (roll method) in which a plurality of rolls are provided with a difference in peripheral speed and the difference in peripheral speed between the rolls is utilized.

(Main drying process)
From the viewpoint of further reducing the amount of residual solvent, it is preferable to further dry the film-like material obtained after stretching. For example, it is preferable to further dry the film-like material obtained after stretching while conveying it with a roll or the like.

The main drying temperature (drying temperature in the case of unstretched) is preferably (Tg-50) to (Tg-30)°C, where Tg is the glass transition temperature of the (meth)acrylic resin; -40) to (Tg-30)°C is more preferable. If the post-drying temperature is (Tg-50)°C or higher, the solvent can be sufficiently volatilized and removed from the stretched film, and if it is below (Tg-30)°C, the deformation of the film can be seriously prevented. can be suppressed. As for the main drying temperature, it is preferable to measure the atmospheric temperature such as (a) hot air temperature, as described above.

1-4. Adhesive layer A and B
Adhesive layer A is placed between the protective film A and the polarizer and bonds them together. Similarly, the adhesive layer B is placed between the protective film B and the polarizer to bond them together.

Adhesive layers A and B may be layers obtained from a completely saponified polyvinyl alcohol aqueous solution (water paste), or may be layers of a cured product of an active energy ray-curable adhesive. From the viewpoint of having high affinity with the protective films A and B containing (meth)acrylic resin and facilitating good adhesion, adhesive layers A and B should be cured layers of an active energy ray-curable adhesive. is preferred.

The active energy ray-curable adhesive may be a photo-radical polymerizable composition or a photo-cationic polymerizable composition. Among these, photocationic polymerizable compositions are preferred.

The cationic photopolymerizable composition includes an epoxy compound and a cationic photopolymerization initiator.

An epoxy compound is a compound having one or more, preferably two or more, epoxy groups in the molecule. Examples of epoxy compounds include hydrogenated epoxy compounds obtained by reacting alicyclic polyols with epichlorohydrin (glycidyl ether of polyols having an alicyclic ring); aliphatic polyhydric alcohols or their alkylenes; Aliphatic epoxy compounds such as oxide adduct polyglycidyl ether; alicyclic epoxy compounds having one or more epoxy groups bonded to an alicyclic ring in the molecule are included. The epoxy compounds may be used alone or in combination of two or more.

The photocationic polymerization initiator may be, for example, an aromatic diazonium salt; an onium salt such as an aromatic iodonium salt or an aromatic sulfonium salt; or an iron-arene complex.

The cationic photopolymerization initiator may be a cationic polymerization accelerator such as oxetane or polyol, a photosensitizer, an ion trapping agent, an antioxidant, a chain transfer agent, a tackifier, a thermoplastic resin, a filler, or a fluid. It may further contain additives such as regulators, plasticizers, antifoaming agents, antistatic agents, leveling agents, and solvents.

The thickness of the adhesive layers A and B is not particularly limited, but may be, for example, about 0.01 to 10 μm, preferably about 0.01 to 5 μm.

1-5. Adhesive Layer The adhesive layer is arranged on the surface of the protective film B of the polarizing plate opposite to the polarizer. The polarizing plate of the present invention is bonded to a display element such as a liquid crystal cell via the adhesive layer.

The adhesive constituting the adhesive layer is not particularly limited, and may be, for example, an acrylic adhesive, a silicone adhesive, a rubber adhesive, or the like. From the viewpoints of transparency, weather resistance, heat resistance, and processability, acrylic adhesives are preferred.

Adhesives include tackifiers, plasticizers, glass fibers, glass beads, metal powder, other fillers, pigments, colorants, fillers, antioxidants, ultraviolet absorbers, silane coupling agents, etc. as required. , may further contain various additives.

The thickness of the adhesive layer is usually about 3 to 100 μm, preferably 5 to 50 μm.

The surface of the adhesive layer is protected by a release film that has been subjected to release treatment. Examples of release films include plastic films such as acrylic films, polycarbonate films, polyester films, and fluororesin films.

2. Method for manufacturing a polarizing plate The polarizing plate of the present invention includes the steps of 1) laminating and bonding the protective film A on one surface of the polarizer via an adhesive, and 2) adhering the protective film A to the other surface of the polarizer. 3) a step of laminating and bonding the protective film B via an adhesive; and 3) a step of pasting the adhesive layer and its protective film on the protective film B of the bonded laminate to obtain a polarizing plate. can get. An example in which an active energy ray-curable adhesive is used as the adhesive will be described below.

Regarding the step 1), the surface of the protective film A is subjected to surface treatment such as corona treatment, if necessary. Next, protective film A is applied to one side of the polarizer via a layer of active energy ray-curable adhesive (if surface-treated, the surface-treated side of protective film A faces the polarizer side). (b) After lamination, the active energy ray-curable adhesive is cured by irradiation with active energy rays. Thereby, the polarizer and the protective film A are bonded together via the cured layer of the active energy ray-curable adhesive.

Regarding the step 2) Similarly, the surface of the protective film B is subjected to surface treatment such as corona treatment, if necessary. Next, apply the protective film B to the other side of the polarizer via a layer of active energy ray-curable adhesive (if the surface has been surface-treated, apply the protective film B so that the surface-treated side of the protective film B faces the polarizer). (b) After lamination, the active energy ray-curable adhesive is cured by irradiation with active energy rays. Thereby, the polarizer and the protective film B are bonded together via the cured layer of the active energy ray-curable adhesive.

Steps 1) and 2) may be performed simultaneously or sequentially. From the viewpoint of increasing manufacturing efficiency, it is preferable to perform the steps 1) and 2) simultaneously.

When the steps 1) and 2) are performed simultaneously, the lamination of the protective film A, the polarizer, and the protective film B is preferably performed in a roll-to-roll manner. Then, the obtained laminate may be irradiated with active energy rays to cure the active energy ray-curable adhesive.

Regarding step 3) Next, an adhesive layer and its release film are attached on the protective film B of the obtained polarizing plate. Specifically, the adhesive layer can be formed on the protective film B by a method such as transferring a release film provided with an adhesive layer.

The obtained polarizing plate may be a long polarizing plate. The elongated polarizing plate is wound up into a roll to form a roll of polarizing plate. Then, the roll of the polarizing plate is unrolled during use (for example, when manufacturing a display device), and then punched out into a desired size and shape, and used for manufacturing the display device. Punching of the polarizing plate is performed by pushing a blade into the protective film A side (see FIG. 2A).

3. Display Device The display device of the present invention includes the polarizing plate of the present invention. The display device of the present invention may be a liquid crystal display device, an organic EL display device, or the like, and preferably a liquid crystal display device.

That is, the liquid crystal display device of the present invention includes a liquid crystal cell, a first polarizing plate disposed on one surface of the liquid crystal cell, and a second polarizing plate disposed on the other surface of the liquid crystal cell.

Display modes of liquid crystal cells include, for example, STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybridaligned Nematic), VA (Vertical Alignment), MVA (Multi-domain Vertical Alignment), and PVA. (Patterned Vertical Alignment), IPS (In-Plane-Switching), etc. For example, in a liquid crystal display device for portable equipment, the IPS mode is preferable.

One or both of the first polarizing plate and the second polarizing plate may be the polarizing plate of the present invention. The polarizing plate of the present invention is arranged such that the adhesive layer is in close contact with the liquid crystal cell.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

1. Materials for Protective Film (1) (Meth) Acrylic Resin (Meth) Acrylic Resins 1 to 9 shown in Table 1 were prepared.

The glass transition temperature and weight average molecular weight of (meth)acrylic resins 1 to 9 were measured by the following methods.

(Glass-transition temperature)
The glass transition temperature (Tg) of the (meth)acrylic resin was measured using DSC (Differential Scanning Colorimetry) in accordance with JIS K 7121-2012.

(Weight average molecular weight)
The weight average molecular weight (Mw) of the (meth)acrylic resin was measured using gel permeation chromatography (HLC8220GPC manufactured by Tosoh Corporation) and a column (TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL series manufactured by Tosoh Corporation). . 20 mg±0.5 mg of the sample was dissolved in 10 ml of tetrahydrofuran and filtered through a 0.45 mm filter. 100 ml of this solution was injected into a column (temperature: 40°C), measured with a detector RI temperature of 40°C, and the value converted to styrene was used.

(2) Rubber particles <Preparation of rubber particles R1>
The following compounds were charged into an 8L polymerization apparatus equipped with a stirrer.
Deionized water: 175 parts by mass Polyoxyethylene lauryl ether phosphoric acid: 0.104 parts by mass Boric acid: 0.4725 parts by mass Sodium carbonate: 0.04725 parts by mass

After sufficiently purging the inside of the polymerization machine with nitrogen gas, the internal temperature was raised to 80°C, and 27 parts by mass of monomer mixture (1-1) (70.9% by mass of methyl methacrylate, 12.5% by mass of butyl acrylate, 16% by mass of styrene) was added. 26% by mass of a mixture consisting of 0.6% by mass) and 0.135 parts by mass of allyl methacrylate was added to the polymerization machine all at once, and then 0.0645 parts by mass of sodium formaldehyde sulfoxylate, 2-ethylenediaminetetraacetic acid 0.0056 parts by mass of sodium, 0.0014 parts by mass of ferrous sulfate, and 0.0207 parts by mass of t-butyl hydroperoxide were added, and 15 minutes later, 0.0345 parts by mass of t-butyl hydroperoxide was added. , and polymerization was continued for an additional 15 minutes.
Next, 0.0098 parts by mass of sodium hydroxide in the form of a 2% by mass aqueous solution, 0.0852 parts by mass of polyoxyethylene lauryl ether phosphoric acid were added as they were, and the remaining 74% by mass of the above mixture was continuously added over 60 minutes. added. Thirty minutes after the completion of the addition, 0.069 parts by mass of t-butyl hydroperoxide was added and polymerization was continued for an additional 30 minutes to obtain a polymer.

Thereafter, 0.0267 parts by mass of sodium hydroxide in the form of a 2% by mass aqueous solution and 0.08 parts by mass of potassium persulfate in the form of a 2% by mass aqueous solution were added, and then monomer mixture (1-2) (acrylic acid A mixture consisting of 50 parts by mass (47.0% by mass of butyl, 53.0% by mass of styrene) and 0.75 parts by mass of allyl methacrylate was continuously added over 150 minutes. After the addition was completed, 0.015 parts by mass of potassium persulfate was added in the form of a 2% by mass aqueous solution, and polymerization was continued for 120 minutes to obtain an acrylic rubber-like polymer. The content (mass%) of structural units derived from styrene with respect to all structural units (total of monomer mixtures (1-1) and (1-2)) of the obtained acrylic rubber-like polymer was 40% by mass. Met.

Thereafter, 0.023 parts by mass of potassium persulfate was added in the form of a 2% by mass aqueous solution, and 15 parts by mass of monomer mixture (2-1) (95% by mass of methyl methacrylate, 5% by mass of butyl acrylate) was added over 45 minutes. The polymerization was continued for an additional 30 minutes.

Thereafter, 8 parts by mass of monomer mixture (2-2) (52% by mass of methyl methacrylate, 48% by mass of butyl acrylate) was continuously added over 25 minutes, and the polymerization was continued for an additional 60 minutes to form a graft mixture. A polymer latex was obtained.

The obtained latex was salted out with magnesium chloride, coagulated, washed with water, and dried to obtain a white powdery graft copolymer (rubber particles R1). The graft ratio of the rubber particles R1 was 24.2%, the amount of styrene was 40% by mass, the glass transition temperature (Tg) was 5° C., and the average particle diameter was 200 nm.

<Preparation of rubber particles R2 to R5>
The monomer mixture (1-1) and (1-2 Graft copolymers (rubber particles) were obtained in the same manner as rubber particles R1 except that the monomer composition of ) was changed.

Table 2 shows the composition of rubber particles R1 to R5.

The average particle diameter of rubber particles R1 to R5 was measured by the following method.

(Average particle size)
The dispersed particle size of the rubber particles in the obtained dispersion was measured using a zeta potential/particle size measuring system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.).

(Amount of styrene)
The content of structural units derived from styrenes in the rubber particles was measured by the method of calculating from the area ratio of peaks detected by pyrolysis GC/MS described above. Note that the measurement conditions for GCMS were as follows.
Measuring device: SHIMAZU GCMS QP2010
Column type: Ultra Alloy-5 (size 30m x diameter 0.25mm)
Carrier gas type: He
Flow rate conditions: 1.8mL/min Column oven temperature conditions: 40℃-10℃/min-320℃
Interface temperature: 300℃
Ion source temperature: 200℃
Detection mode: SIM (target ion: m/z104, confirmation ion: m/z78)

2. Preparation of protective film 2-1. Production of protective film A <Production of protective film 101>
The pellets of (meth)acrylic resin 1 and rubber particles R1 were dried in a dryer at 80° C. for 4 hours, and then supplied to a φ65 mm single-screw extruder. The resin was melted by heating to a temperature of 270° C. at the exit of the extruder, and the molten resin was extruded from a T-die. The resin temperature at the T-die outlet immediately after the third discharge was 270°C. The discharged molten resin was sandwiched between a cast roll adjusted to 70°C and a touch roll adjusted to 70°C, and cooled and solidified. Thereafter, both ends of the obtained film were continuously slit, and then wound up while being taken up with a take-up roll to obtain a protective film 101 with a thickness of 55 μm.

<Production of protective film 102>
A protective film 102 was obtained in the same manner as the protective film 101 except that the film obtained after cooling and solidifying was stretched under the conditions shown in Table 3.

<Production of protective film 103>
Protective film 103 was obtained in the same manner as protective film 101 except that rubber particles R1 were not added and stretching was performed under the conditions shown in Table 3.

<Production of protective film 104>
(Preparation of rubber particle dispersion)
11.3 parts by mass of rubber particles R2 and 200 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then dispersed using a Milder dispersion machine (manufactured by Pacific Kiko Co., Ltd.) at 1500 rpm, A rubber particle dispersion was obtained.

(Preparation of dope)
Next, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. Next, the (meth)acrylic resin 2 was charged into the pressurized dissolution tank while being stirred. Next, the rubber particle dispersion prepared above was added and completely dissolved while stirring. This was filtered using SHP150 manufactured by Loki Techno Co., Ltd. to obtain a dope.
(Meth)acrylic resin 2: 100 parts by mass Methylene chloride: 200 parts by mass Ethanol: 100 parts by mass Rubber particle dispersion: 500 parts by mass

(Film forming)
Using an endless belt casting device, the dope was uniformly cast onto a stainless steel belt support at a temperature of 30° C. and a width of 1800 mm. The temperature of the stainless steel belt was controlled at 28°C. The conveyance speed of the stainless steel belt was 20 m/min.

The solvent was evaporated on a stainless steel belt support until the amount of residual solvent in the cast dope became 30% by mass. Next, it was peeled off from the stainless steel belt support with a peeling tension of 128 N/m to obtain a film-like material. In other words, the amount of residual solvent in the film-like material at the time of peeling was 30% by mass. The peeled film was further dried while being conveyed by a number of rollers to obtain a protective film 104 having a thickness of 55 μm.

<Production of protective films 105 and 106>
Protective films 105 and 106 were obtained in the same manner as protective film 101 except that the content of rubber particles R1 was changed as shown in Table 3.

<Production of protective films 107 and 108>
Protective films 107 and 108 were obtained in the same manner as protective film 101 except that the discharge amount was adjusted so that the thickness of the protective film became the value shown in Table 3.

<Evaluation>
The average aspect ratio and tensile modulus of rubber particles in the obtained protective films 101 to 108 were measured by the following method.

(Average aspect ratio, average major axis)
The average aspect ratio and average major axis of the rubber particles were calculated using the following procedure.
1) Among the cross sections along the thickness direction of the protective film, a cross section parallel to the TD direction of the protective film was observed using a TEM. The observation area was 5 μm×5 μm.
2) The major axis and minor axis of each rubber particle in the obtained TEM image were measured, and the aspect ratio was calculated.
3) The operations 1) and 2) above were performed at a total of four locations, changing the observation areas. The average value of the measured aspect ratios was defined as the "average aspect ratio", and the average value of the measured major axes was defined as the "average major axis".

(Tensile modulus)
The obtained protective film was cut out into a 1 cm (TD direction) x 10 cm (MD direction) piece to prepare a sample piece, and the humidity was conditioned in an environment of 25° C. and 60% RH for 24 hours. The tensile modulus of the obtained sample piece was measured by the tensile test method described in JIS K7127. Specifically, the sample piece was set in a tensile testing device, Tensilon manufactured by Orientech Co., Ltd., and a tensile modulus was measured when a tensile test was conducted at a distance between chucks of 50.0 mm and a tensile speed of 50 mm/min. The measurement was performed at 25° C. and 60% RH.

Table 3 shows the evaluation results for the protective films 101 to 108. Note that the content of rubber particles in Table 3 indicates the amount relative to the protective film. The same applies to Tables 4 and 5.

2-2. Production of protective film B <Production of protective film 201>
(Preparation of rubber particle dispersion)
11 parts by mass of rubber particles R3 and 200 parts by mass of methylene chloride were stirred and mixed with a dissolver for 50 minutes, and then dispersed at 1500 rpm using a Milder disperser (manufactured by Pacific Kiko Co., Ltd.). , a rubber particle dispersion was obtained.

(Preparation of dope)
Next, a dope having the following composition was prepared. First, methylene chloride and ethanol were added to a pressurized dissolution tank. Next, the (meth)acrylic resin was charged into a pressurized dissolution tank while being stirred. Next, the rubber particle dispersion prepared above was added and completely dissolved while stirring. This was filtered using SHP150 manufactured by Loki Techno Co., Ltd. to obtain a dope.
(Meth)acrylic resin 3: 100 parts by mass Methylene chloride: 400 parts by mass Ethanol: 90 parts by mass Rubber particle dispersion: 220 parts by mass

(Film forming)
Using an endless belt casting device, the dope was uniformly cast onto a stainless steel belt support at a temperature of 30° C. and a width of 1800 mm. The temperature of the stainless steel belt was controlled at 28°C. The conveyance speed of the stainless steel belt was 20 m/min.

The solvent was evaporated on a stainless steel belt support until the amount of residual solvent in the cast dope became 30% by mass. Next, it was peeled off from the stainless steel belt support with a peeling tension of 128 N/m to obtain a film-like material. The amount of residual solvent in the film-like material at the time of peeling was 30% by mass.

Next, while the peeled film was conveyed by a number of rollers, the obtained film-like material was stretched by 70% in the width direction (TD direction) using a tenter at 60° C. (Tg-60° C.). Thereafter, it was further dried at 140° C. (Tg+40° C.) while being transported by rolls, and the ends sandwiched between tenter clips were slit with a laser cutter and wound up to obtain a protective film 201 with a thickness of 20 μm.

<Production of protective films 202 to 205>
Protective films 202 to 205 were obtained in the same manner as protective film 201 except that the stretching conditions were changed as shown in Table 4.

<Production of protective film 206>
A protective film 206 was obtained in the same manner as the protective film 201 except that rubber particles R3 were not added and the stretching conditions were changed as shown in Table 4.

<Production of protective films 207 to 212>
Protective films 207 to 212 were obtained in the same manner as protective film 201 except that the type of (meth)acrylic resin was changed as shown in Table 4. Note that for the protective film 207, the stretching conditions were also changed as shown in Table 4.

<Production of protective films 213 and 214>
Protective films 213 and 214 were obtained in the same manner as protective film 201 except that the types of rubber particles were changed as shown in Table 4.

<Production of protective films 215 and 216>
Protective films 215 and 216 were obtained in the same manner as protective film 201, except that the casting amount was adjusted so that the thickness of the resulting protective film became the value shown in Table 4.

<Evaluation>
The average aspect ratio and tensile modulus of rubber particles in the obtained protective films 201 to 216 were measured in the same manner as described above. Table 4 shows the evaluation results for the protective films 201 to 216. Note that the average major axis of the rubber particles contained in the protective film 201 was 360 nm.

3. Preparation and evaluation of polarizing plate <Preparation of polarizing plate 301>
(Preparation of polarizer)
A polyvinyl alcohol film with a thickness of 25 μm was swollen with water at 35°C. The obtained film was immersed for 60 seconds in an aqueous solution consisting of 0.075 g of iodine, 5 g of potassium iodide and 100 g of water, and further immersed in an aqueous solution at 45°C consisting of 3 g of potassium iodide, 7.5 g of boric acid and 100 g of water. . The obtained film was uniaxially stretched at a stretching temperature of 55°C and a stretching ratio of 5 times. This uniaxially stretched film was washed with water and then dried to obtain a polarizer with a thickness of 12 μm.

(Preparation of ultraviolet curable adhesive composition)
After mixing the following components, defoaming was performed to prepare an ultraviolet curable adhesive composition.
3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate: 45 parts by mass Epolead GT-301 (alicyclic epoxy resin manufactured by Daicel): 40 parts by mass 1,4-butanediol diglycidyl ether: 15 Parts by mass Triarylsulfonium hexafluorophosphate: 2.3 parts by mass (solid content)
9,10-dibutoxyanthracene: 0.1 part by mass 1,4-diethoxynaphthalene: 2.0 parts by mass The triarylsulfonium hexafluorophosphate was blended as a 50% propylene carbonate solution.

(Preparation of polarizing plate)
The surface of the protective film 101 produced above was subjected to corona discharge treatment at a corona output strength of 2.0 kW and a line speed of 18 m/min. Next, the ultraviolet curable adhesive composition prepared above is coated on the corona discharge treated surface of the protective film 101 using a bar coater so that the film thickness after curing is about 3 μm to form an ultraviolet curable adhesive layer. Formed.
Similarly, after corona discharge treatment was applied to the surface of the protective film 201 prepared above, the UV curable adhesive composition prepared above was applied so that the film thickness after curing was 3 μm. An adhesive layer was formed.

Next, a protective film 101 is placed on one surface of the polarizer produced above via an ultraviolet curable adhesive layer, and a protective film 201 is placed on the other surface via an ultraviolet curable adhesive layer. , a laminate was obtained. Lamination was performed so that the absorption axis of the polarizer and the slow axis of the protective film were perpendicular to each other.

Next, the obtained laminate was irradiated with ultraviolet rays using an ultraviolet irradiation device with a belt conveyor (the lamp used was a D bulb manufactured by Fusion UV Systems) so that the cumulative light amount was 750 mJ/cm ² , The UV curable adhesive layer was cured.

Then, on the obtained laminated protective film B, an adhesive layer (thickness: 20 μm) of the following adhesive layer-attached PET film was laminated. Thereby, a polarizing plate 301 having a laminated structure of protective film 101 (protective film A)/adhesive layer/polarizer/adhesive layer/protective film 201 (protective film B)/adhesive layer/PET film was obtained. Note that the adhesive layer is obtained by applying an acrylic adhesive composition containing a (meth)acrylic polymer and a crosslinking agent onto a PET film, and then heating and drying (partially crosslinking).

<Production of polarizing plates 302 to 323>
Polarizing plates 302 to 323 were obtained in the same manner as polarizing plate 301 except that the protective films A and B were changed as shown in Table 5.

<Evaluation>
The punchability and display unevenness (after the keystroke test) of the obtained polarizing plate were measured by the following methods.

(Punching property)
FIGS. 3A and 3B are diagrams showing the punching process of the polarizing plate 100 in the example. 3A is a perspective view of the polarizing plate 100, and FIG. 3B is a partial cross-sectional view taken along the line AA.

As shown in FIGS. 3A and 3B, the obtained polarizing plate 100 was bonded onto a PET film 170 via an adhesive layer 140. Then, from the polarizing plate 100 bonded to the PET film 170, as shown in FIG. 3A, nine 1 m square polarizing plates 100 (W in FIG. 3A is 1 m) were punched into 10 cm squares. The gap p between adjacent polarizing plates was 1 cm.

The nine punched polarizing plates were observed with an optical microscope, and the number of cracks and peeling that occurred were counted and the average was calculated. Then, punching properties were evaluated based on the following evaluation criteria.
◎: Neither cracks nor peeling are observed ○: Cracks or peeling occur in 2 or less places ○△: Cracks or peeling occur in 3 to 5 places △: Cracks and peeling occur in 3 to 5 places each ×: Cracks and peeling ○△, ○, and ◎ occur in six or more locations, respectively. ○△, ○, and ◎ are at practically acceptable levels.

(Display unevenness)
(1) Production of a liquid crystal display device having a touch panel member Two polarizing plates that had been bonded together in advance were peeled off from a 21.5-inch VAIOTap21 (SVT21219DJB) manufactured by SONY, which is a liquid crystal display device having a touch panel member, and the above production was carried out. The polarizing plates obtained were bonded together to obtain a liquid crystal display device having a touch panel member. The polarizing plates were bonded together by peeling off the PET film so that the exposed adhesive layer was in close contact with the liquid crystal cell.

(2) Keystroke test The obtained liquid crystal display device was left for 300 hours in a variable air conditioning room (AES-200 manufactured by Asahi Scientific Co., Ltd.) controlled at 40° C. and 95% RH. After that, under the same environment, using a keystroke testing machine 202 type-950-2 (manufactured by Touch Panel Research Institute Co., Ltd.), the input pen was pressed from above the cover glass side at 15,000 m I pressed it twice. The nib material of the input pen is a measuring board placed under the rubber, which is a glass substrate, placed on top of it with the conductive mesh facing the glass side, and the input pen is pressed from above with a load of 300 g to make it slide. Sliding was repeated at a distance of 5 cm and a reciprocating time of 1 second (5 cm reciprocating in 1 second). Note that the nib material of the input pen is polyacetal, and R is 0.8 mm.

(3) Display unevenness
After the keystroke test, the liquid crystal display device was left for 300 hours in an environment of 40° C. and 95% RH. Next, it was placed in a dry environment at 40°C for 2 hours, and then turned on for 24 hours in an environment at 23°C and 55% RH, after which display unevenness was observed from the front of the display panel. Display unevenness was evaluated based on the following criteria.
◎: Unrecognizable unevenness on the display panel ○: Very slight unevenness can be seen on the display panel, but it does not affect the quality ○△: Localized unevenness can be seen on the display panel, but there is a boundary between the uneven part and the non-mura part is not visible. △: Local unevenness is seen on the display panel, and the boundary between the uneven part and the non-mura is visible. can
○△, ○ and ◎ are practically acceptable levels.

Table 5 shows the configurations and evaluation results of the polarizing plates 301 to 323 obtained.

As shown in Table 5, it can be seen that all of the polarizing plates 301 to 303, 310 to 312, and 315 to 323 (Examples) had good punching properties and little display unevenness.

In particular, it can be seen that by making the tensile modulus of protective film B higher than that of protective film A, the punching performance is further improved and display unevenness can be further suppressed (comparison between polarizing plate 320 and 322 or 317). ). This is thought to be because the protective film B has an appropriate hardness, so that the deformation due to the pushing of the blade is small, and the stress generated thereby can be reduced.

Furthermore, it can be seen that by making the thickness of the protective film B thinner than the thickness of the protective film A, punching performance is further improved and display unevenness can be further suppressed (comparison between polarizing plates 301 and 323). This is because the protective film B is appropriately thin, making it difficult for the blade to get caught when pulling it out, which makes it easier to suppress cracks; This is thought to be due to less deformation (strain) and less stress generated.

On the other hand, it can be seen that polarizing plates 305 to 309 and 313 to 314 (comparative examples) all have poor punching properties and display unevenness. Furthermore, it can be seen that the polarizing plate 304 (comparative example) causes display unevenness. Specifically, it is thought that this is because the polarizing plate 305 was unable to sufficiently relieve stress because the average aspect ratio of the rubber particles b in the protective film B was low. The reason why the display unevenness of the polarizing plate 304 is poor is because the average aspect ratio of the rubber particles b in the protective film B is high, so the residual stress is also high, and this is due to the plastic deformation of the rubber particles b and the plastic deformation of the (meth)acrylic resin. It is thought that this is because a shift occurs between the rubber particles B and the (meth)acrylic resin, which tends to cause interfacial peeling, and as a result, interlayer peeling occurs between the protective film B and the adhesive layer. It is considered that the polarizing plate 307 was too brittle and could not withstand deformation during punching because the protective film B did not contain the rubber particles b, resulting in cracks and chips.

Furthermore, in the polarizing plate 308, since the protective film A does not contain the rubber particles a, it is thought that cracks were likely to occur in the protective film A during punching. In the polarizing plate 306, the punchability and display unevenness are low because the average aspect ratio of the rubber particles a in the protective film A is too high, so the rubber particles a easily follow the deformation of the protective film A, and the protective film B This is thought to be due to an increase in the stress applied to the In the polarizing plates 313 and 314, the reason why the punchability and display unevenness are low is because the ratio of PMI in the protective film B is too high, which increases the brittleness of the film and makes it easy to apply an excessive load to the rubber particles B, which causes damage to the resin. It is thought that this is because the load has become easier to apply.

It can also be seen that the polarizing plate 309 has lower display unevenness than the polarizing plate 306. This is because the (meth)acrylic resin contained in the protective film B used for the polarizing plate 309 does not contain a structural unit derived from phenylmaleimide, so the interface between the rubber particles B and the (meth)acrylic resin This is thought to be due to peeling.

According to the present invention, it is possible to provide a polarizing plate that can suppress cracks and delamination during punching and can reduce display unevenness due to keystrokes when used for a long time in a high humidity environment.

100 Polarizing plate 110 Polarizer 120A Protective film (Protective film A)
120B Protective film (Protective film B)
130A, 130B Adhesive layer 140 Adhesive layer 150a Rubber particles (rubber particles a)
150b Rubber particles (Rubber particles b)

Claims (6)

A polarizer, a protective film A disposed on one surface of the polarizer, a protective film B disposed on the other surface of the polarizer, and a surface of the protective film B opposite to the polarizer. A polarizing plate comprising an adhesive layer disposed on the
The protective film A includes a (meth)acrylic resin and rubber particles a,
The protective film B includes a (meth)acrylic resin and rubber particles b,
In the cross section along the thickness direction of the protective film A, the average aspect ratio of the rubber particles a is 1.0 to 1.1, and the average major axis of the rubber particles a is 100 to 400 nm,
In the cross section along the thickness direction of the protective film B, the average aspect ratio of the rubber particles b is 1.4 to 3.0, and the average major axis of the rubber particles b is 250 to 400 nm,
The (meth)acrylic resin contained in the protective film B contains 50 to 95% by mass of structural units derived from methyl methacrylate, and 1 A copolymer containing ~25% by mass of structural units derived from phenylmaleimide and 1~25% by mass of structural units derived from acrylic acid alkyl ester ,
The tensile modulus of the protective film B at 25° C. is higher than the tensile modulus of the protective film A at 25° C.
Polarizer. The tensile modulus of the protective film A at 25° C. is 1.6 to 2.6 GPa,
The tensile modulus of the protective film B at 25° C. is 2.4 to 3.4 GPa.
The polarizing plate according to claim 1 . The content of the rubber particles b in the protective film B is lower than the content of the rubber particles a in the protective film A.
The polarizing plate according to claim 1 or 2 . A polarizer, a protective film A disposed on one surface of the polarizer, a protective film B disposed on the other surface of the polarizer, and a surface of the protective film B opposite to the polarizer. A polarizing plate comprising an adhesive layer disposed on the
The protective film A includes a (meth)acrylic resin and rubber particles a,
The protective film B includes a (meth)acrylic resin and rubber particles b,
In the cross section along the thickness direction of the protective film A, the average aspect ratio of the rubber particles a is 1.0 to 1.1, and the average major axis of the rubber particles a is 100 to 400 nm,
In the cross section along the thickness direction of the protective film B, the average aspect ratio of the rubber particles b is 1.4 to 3.0, and the average major axis of the rubber particles b is 250 to 400 nm,
The (meth)acrylic resin contained in the protective film B contains 50 to 95% by mass of structural units derived from methyl methacrylate, and 1 A copolymer containing ~25% by mass of structural units derived from phenylmaleimide and 1~25% by mass of structural units derived from acrylic acid alkyl ester,
The rubber particles a include an acrylic rubbery polymer (a1) containing a structural unit derived from styrenes,
The rubber particles b include an acrylic rubbery polymer (b1) containing a structural unit derived from styrenes,
The content of structural units derived from styrenes in the acrylic rubber strip polymer (b1) is greater than the content of structural units derived from styrenes in the acrylic rubbery polymer (a1).
Polarizing plate . A polarizer, a protective film A disposed on one surface of the polarizer, a protective film B disposed on the other surface of the polarizer, and a surface of the protective film B opposite to the polarizer. A polarizing plate comprising an adhesive layer disposed on the
The protective film A includes a (meth)acrylic resin and rubber particles a,
The protective film B includes a (meth)acrylic resin and rubber particles b,
In the cross section along the thickness direction of the protective film A, the average aspect ratio of the rubber particles a is 1.0 to 1.1, and the average major axis of the rubber particles a is 100 to 400 nm,
In the cross section along the thickness direction of the protective film B, the average aspect ratio of the rubber particles b is 1.4 to 3.0, and the average major axis of the rubber particles b is 250 to 400 nm,
The (meth)acrylic resin contained in the protective film B contains 50 to 95% by mass of structural units derived from methyl methacrylate, and 1 A copolymer containing ~25% by mass of structural units derived from phenylmaleimide and 1~25% by mass of structural units derived from acrylic acid alkyl ester,
The thickness of the protective film B is thinner than the thickness of the protective film A.
Polarizing plate . A polarizer, a protective film A disposed on one surface of the polarizer, a protective film B disposed on the other surface of the polarizer, and a surface of the protective film B opposite to the polarizer. A polarizing plate comprising an adhesive layer disposed on the
The protective film A includes a (meth)acrylic resin and rubber particles a,
The protective film B includes a (meth)acrylic resin and rubber particles b,
In the cross section along the thickness direction of the protective film A, the average aspect ratio of the rubber particles a is 1.0 to 1.1, and the average major axis of the rubber particles a is 100 to 400 nm,
In the cross section along the thickness direction of the protective film B, the average aspect ratio of the rubber particles b is 1.4 to 3.0, and the average major axis of the rubber particles b is 250 to 400 nm,
The (meth)acrylic resin contained in the protective film B contains 50 to 95% by mass of structural units derived from methyl methacrylate, and 1 A copolymer containing ~25% by mass of structural units derived from phenylmaleimide and 1~25% by mass of structural units derived from acrylic acid alkyl ester,
The protective film A is polymethyl methacrylate.
Polarizing plate .

Images