Polarizing plate and method for producing same, liquid crystal display device, and protection film and method for producing same

Abstract

by mass of an acrylic acid alkyl ester unit. In a cross section of the protection film which is taken along an in-plane slow axis, the requirement represented by the formula: Rs2 ≥ Ra is satisfied wherein Ra represents an average shorter diameter of the rubber particles and Rs2 represents an average secondary particle diameter of the silica particles. The YI of the protection film is

Description

[Technical Field]

[0001] This invention relates to polarizing plates and their manufacturing methods, liquid crystal display devices, protective films and their manufacturing methods. [Previous Technology]

[0002] A polarizing plate used in a display device such as a liquid crystal display device includes a polarizer and a protective film disposed on both sides thereon. As a protective film, a (meth)acrylic resin film is used because it has low moisture absorption, dimensional stability and excellent transparency.

[0003] However, polarizing plates often bend or their dimensions change due to temperature or humidity in the environment. If stress is generated due to the bending of the polarizing plate or the dimensional changes of the components, optical non-uniformity can easily occur in the display device. In order to suppress optical non-uniformity caused by stress due to bending or dimensional changes of such polarizing plates, it is required that the components of the polarizing plate be thin films with low photoelastic modulus.

[0004] The proposal includes, for example, a polarizing plate having a polarizer and an optical film as a protective film, wherein the optical film is made of a (meth)acrylic resin composition having (meth)acrylate units, (meth)benzyl acrylate units, and (meth)acrylic acid units (e.g., Patent Document 1). Thus, by using an optical film with a low coefficient of linear expansion, the curling of the polarizing plate can be suppressed. [Prior Art Documents] [Patent Documents]

[0005] Patent Document 1: Japanese Patent Application Publication No. 2014-506683 [Summary of the Invention]

[0006] [The problem the invention aims to solve]

[0007] However, polarizing plates are usually manufactured by bonding the polarizer to a protective film using an adhesive. Adhesives include water-based adhesives such as polyvinyl alcohol-based adhesives, or active energy line curing adhesives. Among these, active energy line curing adhesives have been considered for use due to their good affinity with hydrophobic (meth)acrylic resin films and the ability to bond quickly, thus improving the manufacturing efficiency of polarizing plates.

[0008] However, when an active energy line curing adhesive is applied to a (meth)acrylic resin film as shown in Patent Document 1, the (meth)acrylic resin film is prone to surface unevenness or wrinkling due to the curing shrinkage of the adhesive. Surface unevenness refers to wavy deformation extending in the film transport direction; wrinkling refers to wavy unevenness generated in random directions. These surface unevenness or wrinkling deformations are particularly noticeable when the protective film is thinner. Polarizing plates containing protective films that produce surface unevenness or wrinkling deformations are prone to light leakage in display devices, easily degrading display performance.

[0009] This invention was made in view of the above circumstances, and its object is to provide a polarizing plate that, when manufacturing a polarizer by using an active energy line curing adhesive to bond a protective film containing a (meth)acrylic resin to a polarizer, can suppress deformation such as surface unevenness or wrinkling of the protective film accompanying curing shrinkage, thereby suppressing optical non-uniformity; a method for manufacturing a polarizing plate; and a liquid crystal display device using the same. [Means for solving the problem]

[0010] The above problem can be solved by the following structure.

[0011] The polarizing plate of the present invention includes a polarizer, a protective film disposed on the surface of the polarizer, an adhesive layer disposed between the protective film and the polarizer and formed of a cured material of an active energy line curing adhesive, and an adhesive layer disposed on the side of the protective film opposite to the polarizer. The protective film includes (meth)acrylic resin, rubber particles, and silicon oxide particles. The (meth)acrylic resin comprises 50~ units relative to all the structural units constituting the (meth)acrylic resin. The protective film comprises a copolymer of 95% by mass of methyl methacrylate building blocks, 1-25% by mass of phenylmaleimide building blocks, and 1-25% by mass of alkyl acrylate building blocks. In the cross-section along the slow axis of the in-plane of the aforementioned protective film, the aforementioned rubber particles have a flat shape with a major axis and a minor axis. When the average minor axis of the aforementioned rubber particles is set as Ra, and the average secondary particle size of the aforementioned silicon oxide particles is set as Rs2, Rs2≧Ra, and the yellow index (YI) of the aforementioned protective film is 1.2-1.8.

[0012] The method for manufacturing a polarizing plate according to the present invention includes the following steps: 1) preparing a protective film; 2) depositing a protective film on the surface of a polarizer by means of a layer formed by an active energy line curing adhesive, thereby obtaining a laminate; 3) irradiating the laminate with active energy lines to cure the active energy line curing adhesive; and 4) forming an adhesive layer on the surface of the protective film opposite to the polarizer. Step 1) above comprises: obtaining a concentrate containing 50-95% by mass of a (meth)acrylic resin derived from methyl methacrylate, 1-25% by mass of a (meth)acrylic acid resin derived from phenylmaleimide, and 1-25% by mass of a (meth)acrylic acid resin derived from alkyl acrylate, rubber particles, silica particles, and a solvent, wherein the average primary particle size of the rubber particles is defined as R, and the average primary particle size of the silica particles is defined as Rs1, satisfying the following relationship: 5 < R / Rs1 ≤ 80; casting the concentrate onto a support, drying and peeling it to obtain a film; and extending the film to obtain the protective film.

[0013] The liquid crystal display device of the present invention includes: a liquid crystal unit, a first polarizing plate disposed on one side of the liquid crystal unit, and a second polarizing plate disposed on the other side of the liquid crystal unit, wherein at least one of the first polarizing plate and the second polarizing plate is the polarizing plate of the present invention, and the adhesive layer of the polarizing plate is attached to the liquid crystal unit.

[0014] The protective film of the present invention is a protective film bonded to a polarizer using an active energy line curing adhesive. The protective film comprises (meth)acrylic resin, rubber particles, and silicon oxide particles. The (meth)acrylic resin is a copolymer comprising 50-95% by mass of methyl methacrylate-derived structural units, 1-25% by mass of phenylmaleimide-derived structural units, and 1-25% by mass of alkyl acrylate-derived structural units relative to all structural units constituting the (meth)acrylic resin. In the cross-section along the slow axis of the in-plane of the protective film, the rubber particles have a flat shape with a major axis and a minor axis. When the average minor axis of the rubber particles is set as Ra, and the average secondary particle size of the silicon oxide particles is set as Rs2, Rs2 ≥ Ra is satisfied, and the yellow index (YI) of the protective film is 1.2-1.8.

[0015] The method for manufacturing the protective film of the present invention comprises the following steps: obtaining a concentrated liquid comprising a (meth)acrylic resin containing 50-95% by mass of methyl methacrylate-derived building blocks, 1-25% by mass of phenylmaleimide-derived building blocks, and 1-25% by mass of alkyl acrylate-derived building blocks, rubber particles, silica particles, and a solvent, wherein the average primary particle size of the aforementioned rubber particles is defined as R, and the average primary particle size of the aforementioned silica particles is defined as Rs1, satisfying the following relationship: 5 < R / Rs1 ≤ 80; casting the aforementioned concentrated liquid onto a support, drying and peeling it off to obtain a film; and extending the aforementioned film to obtain the aforementioned protective film. [Effects of the Invention]

[0016] According to the present invention, a polarizing plate, a method for manufacturing a polarizing plate, and a liquid crystal display device using the present invention can suppress deformation such as unevenness or wrinkling of the surface of the protective film accompanying the curing shrinkage when a protective film containing a (meth)acrylic resin and a polarizer are manufactured using an active energy line curing adhesive.

Implementation Method

[0017] The inventors have discovered for the first time that by moderately increasing the YI of the protective film, the deformation of the protective film that accompanies hardening shrinkage can be reduced.

[0018] Although the mechanism is not yet clear, it is speculated as follows: A thin protective film with a moderately high YI content will moderately absorb the active energy lines, thus moderately reducing the amount of the active energy line-curing adhesive reaching the active energy line (to the point where poor adhesion does not occur). In particular, the active energy line-curing adhesive moderately penetrates into the protective film, causing those with the same light absorption to cure simultaneously, thereby facilitating improved adhesion. This reduces the curing shrinkage of the active energy line-curing adhesive.

[0019] Furthermore, the inventors have discovered that by including both rubber particles and silicon oxide particles in the protective film, and by making the average secondary particle size Rs2 of the silicon oxide particles the same as or larger than the average minor diameter Ra of the rubber particles, the deformation of the protective film accompanying hardening shrinkage can be significantly suppressed.

[0020] Although the mechanism is not yet clear, it is speculated as follows: Rubber particles exhibit a stress-relieving effect (reducing the stress on the protective film caused by the hardening shrinkage of the active energy line hardening adhesive), while the aggregation of appropriately sized silicon oxide particles increases the mechanical strength (elastic modulus) of the protective film. Through these effects, the stress caused by the hardening shrinkage of the active energy line hardening adhesive is alleviated, and deformation such as unevenness or wrinkling of the protective film surface is less likely to occur.

[0021] That is, by 1) appropriately increasing the YI of the protective film, and 2) the protective film contains both rubber particles and silicon oxide particles, and by adjusting the average secondary particle size Rs2 of the silicon oxide particles to be the same as or larger than the average minor diameter Ra of the rubber particles, the deformation of the protective film accompanied by hardening shrinkage can be reduced.

[0022] The YI of the protective film can be adjusted by, for example, the monomer composition of the (meth)acrylic resin in the protective film (especially the content of building units derived from phenylmaleimide) or the thickness of the protective film. The relationship between the average secondary particle size Rs2 of the silica particles in the protective film and the average minor diameter Ra of the rubber particles can be adjusted by, for example, the average primary particle size Rs1 of the silica particles used as raw materials or the average primary particle size R of the rubber particles, the ratio of these (R / Rs1), the type of resin, and the elongation of the film.

[0023] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings.

[0024] 1. Polarizing plate The polarizing plate of the present invention includes a polarizer, a protective film disposed on its surface, and an adhesive layer disposed between the protective film and the polarizer.

[0025] Figure 1 is a cross-sectional view showing the polarizer 100 of this embodiment.

[0026] As shown in FIG1, the polarizing plate 100 of this embodiment has a polarizer 110, a protective film 120 disposed on one side, a counter film 130 disposed on the other side, an adhesive layer 140 disposed between the protective film 120 and the polarizer 110, and an adhesive layer 150 disposed between the counter film 130 and the polarizer 110.

[0027] Furthermore, the polarizing plate 100 further includes an adhesive layer 160 disposed on the side of the protective film 120 opposite to the polarizer 110. The adhesive layer 160 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 160 is typically protected with a release film (not shown).

[0028] 1-1. Polarizer 110 A polarizer is a component that allows light from a polarized surface in a specific direction to pass through. Polarizers are typically polyvinyl alcohol (PVA) polarizing films. Examples of PVA polarizing films include those dyed with iodine and those dyed with dichroic dyes.

[0029] The polyvinyl alcohol-based polarizing film may be a film formed by uniaxially stretching a polyvinyl alcohol-based film and then dyeing it with iodine or dichroic dyes (preferably a film further subjected to a durability treatment with boron compounds); or it may be a film formed by uniaxially stretching a polyvinyl alcohol-based film after dyeing it with iodine or dichroic dyes (preferably a film further subjected to a durability treatment with boron compounds). The absorption axis of the polarizer 110 is generally parallel to the direction of maximum stretching.

[0030] As a polyvinyl alcohol-based polarizing film, ethylene-modified polyvinyl alcohol 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% can be used, for example, as described in Japanese Patent Application Publication No. 2003-248123 and Japanese Patent Application Publication No. 2003-342322.

[0031] The thickness of the polarizer is preferably 5~30μm, and based on the viewpoint of making the polarizer plate thinner, it is more preferably 5~20μm.

[0032] 1-2. Protective Film 120 When a protective film is provided in a display device, it is disposed between a polarizer and display elements such as a liquid crystal cell, and functions as a phase difference film for adjusting the phase difference. Specifically, as described later, the protective film is bonded to the polarizer using, for example, an active energy line curing adhesive to form a polarizing plate. These protective films contain (meth)acrylic resin, rubber particles, and silicon oxide particles.

[0033] 1-2-1. The (meth)acrylic resin contained in the (meth)acrylic resin protective film preferably includes structural units (U1) derived from methyl methacrylate, structural units (U2) derived from phenylmaleimide, and structural units (U3) derived from alkyl acrylate, based on the viewpoint of adjusting the yellow index (YI) of the protective film to the range described below and improving brittleness.

[0034] The content of the building units (U1) derived from methyl methacrylate is preferably 50 to 95% by mass, and more preferably 70 to 90% by mass, relative to all the building units constituting the (meth)acrylic resin.

[0035] The building unit (U2) derived from phenylmaleimine has a maleimine skeleton that can easily and moderately absorb active energy lines (preferably ultraviolet light), thus imparting moderate light absorption to the protective film.

[0036] The content of the phenylmaleimide-derived building units (U2) is preferably 1 to 25% by mass relative to all the building units constituting the (meth)acrylic resin. If the content of the phenylmaleimide-derived building units (U2) is 1% by mass or more, it is easy to impart moderate light absorption to the protective film. If the content of the phenylmaleimide-derived building units (U2) is 25% by mass or less, it is less likely to impair the brittleness of the protective film. Based on the above viewpoint, the content of the phenylmaleimide-derived building units (U2) is more preferably 7 to 15% by mass.

[0037] The alkyl acrylate-derived building units (U3) impart flexibility to the film, thus suppressing the reduction in film brittleness caused by the inclusion of phenylmaleimide-derived building units (U2). Furthermore, the alkyl acrylate-derived building units (U3) have good affinity with rubber particles, such as those constituting the shell polymer (b), which contain butyl acrylate-derived building units, thereby improving the dispersibility of the rubber particles.

[0038] Alkyl acrylates preferably have 1 to 7 carbon atoms in the alkyl portion, preferably 1 to 5. Examples of alkyl acrylates include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-hydroxyethyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, etc.

[0039] The content of the alkyl acrylate-derived building units (U3) is preferably 1 to 25% by mass relative to all the building units constituting the (meth)acrylic resin. If the content of the alkyl acrylate-derived building units (U3) is 1% by mass or more, the film will not become too brittle and will not easily break because it imparts appropriate flexibility to the (meth)acrylic resin. If the content of the alkyl acrylate-derived building units (U3) is 25% by mass or less, the Tg of the (meth)acrylic resin will not be excessively reduced, so it will not easily impair the heat resistance or mechanical strength of the protective film. Based on the above, the content of the alkyl acrylate-derived building units is more preferably 5 to 15% by mass.

[0040] The ratio of the building unit (U2) derived from phenylmaleimide to the total amount of building units (U2) derived from phenylmaleimide and building units (U3) derived from alkyl acrylate is preferably 20 to 70% by mass. If the ratio is 20% by mass or more, the heat resistance of the protective film is easily improved, and if it is 70% by mass or less, the protective film will not become too brittle.

[0041] The monomer types or composition of (meth)acrylic resins can be identified by 1H-NMR.

[0042] The glass transition temperature (Tg) of the (meth)acrylic resin is preferably 110°C or higher, more preferably 120~150°C. When the Tg of the (meth)acrylic resin is within the above range, the heat resistance of the protective film is easily improved. In order to adjust the Tg of the (meth)acrylic resin, it is preferable to adjust, for example, the content of structural units (U2) derived from phenylmaleimide or structural units (U3) derived from alkyl acrylate.

[0043] The glass transition temperature (Tg) of (meth)acrylic resins can be determined using DSC (Differential Scanning Colorimetry) according to JIS K 7121-2012 or ASTM D 3418-82.

[0044] The weight-average molecular weight (Mw) of the (meth)acrylic resin is preferably 500,000 or higher. If the weight-average molecular weight of the (meth)acrylic resin is 500,000 or higher, the viscosity of the concentrated solution used for solution casting will not be too low, thus easily inhibiting the aggregation of rubber particles. Furthermore, if the weight-average molecular weight of the (meth)acrylic resin is 500,000 or higher, sufficient mechanical strength (toughness) can be imparted to the protective film. Based on the above points, the weight-average molecular weight of the (meth)acrylic resin is more preferably 500,000 to 3,000,000, and even more preferably 600,000 to 2,000,000.

[0045] The weight-average molecular weight (Mw) of (meth)acrylic resins can be determined by gel chromatography (GPC) using polystyrene conversion. Specifically, it can be determined using a TOSOH HLC8220 GPC and a column (TOSOH TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series). The determination conditions are the same as in the examples described later.

[0046] The content of (meth)acrylic resin is preferably 60% by mass or more, and more preferably 70% by mass or more, relative to the protective film.

[0047] 1-2-2. Rubber Particles Rubber particles possess the function of imparting toughness (extensibility) to the protective film. Rubber particles are particles comprising rubber-like polymers. The rubber-like polymers are soft cross-linked polymers with a glass transition temperature below 20°C. Examples of such cross-linked polymers include butadiene-based cross-linked polymers, (meth)acrylic acid-based cross-linked polymers, and organosiloxane-based cross-linked polymers. From the viewpoint that the refractive index difference with (meth)acrylic acid resins is smaller and less likely to impair the transparency of the protective film, (meth)acrylic acid-based cross-linked polymers are preferred, and acrylic acid-based cross-linked polymers (acrylic acid rubber-like polymers) are even more preferred.

[0048] That is, the rubber particles are preferably particles containing an acrylic rubber-like polymer (a).

[0049] Regarding the acrylic rubber-like polymer (a): The acrylic rubber-like polymer (a) is a crosslinked polymer comprising building units derived from acrylates as the main component. "Comprising as the main component" means that the content of building units derived from acrylates is within the range described below. Preferably, the acrylic rubber-like polymer (a) is a crosslinked polymer comprising building units derived from acrylates, building units derived from other monomers that can copolymerize with acrylates, and building units derived from multifunctional monomers having two or more free radical polymerizable groups (non-conjugated reactive double bonds) in one molecule.

[0050] The acrylate is preferably an alkyl acrylate with 1 to 12 carbon atoms, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, dibutyl acrylate, isobutyl acrylate, benzyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, or n-octyl acrylate. There may be one or more types of acrylate.

[0051] The content of the acrylate building blocks is preferably 40 to 80% by mass, more preferably 50 to 80% by mass, relative to all the building blocks constituting the acrylic rubber polymer (a1). If the content of the acrylate is within the above range, it is easy to impart sufficient toughness to the protective film.

[0052] Other copolymerizable monomers that are not multifunctional monomers among those copolymerizable with acrylates. That is, the copolymerizable monomer does not have more than two free radical polymerizable groups. Examples of copolymerizable monomers include methacrylates such as methyl methacrylate; styrene-based monomers such as styrene and methylstyrene; (meth)acrylonitrile derivatives; (meth)acrylamide derivatives; and (meth)acrylic acid. Among these, styrene-based monomers are preferred. The other copolymerizable monomers may be one type or two or more types.

[0053] The content of building units derived from other copolymerizable monomers is preferably 5 to 55% by mass, more preferably 10 to 45% by mass, relative to all building units constituting the acrylic rubber polymer (a).

[0054] Examples of multifunctional monomers include allyl methacrylate, triallyl cyanurate, triallyl isocyanurate, diallyl phthalate, diallyl malate, divinyl adipate, divinylbenzene, ethylene glycol di(meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, dipropylene glycol di(meth)acrylate, and polyethylene glycol di(meth)acrylate.

[0055] The content of the building units derived from the multifunctional monomers is preferably 0.05 to 10% by mass, more preferably 0.1 to 5% by mass, relative to all the building units constituting the acrylic rubber polymer (a). If the content of the multifunctional monomers is 0.05% by mass or more, the degree of crosslinking of the obtained acrylic rubber polymer (a) is easily increased, so the hardness and rigidity of the obtained film are not excessively damaged. If it is less than 10% by mass, the toughness of the film is not easily damaged.

[0056] The composition of the monomers constituting the acrylic rubber polymer (a) can be determined by, for example, the peak area ratio detected by thermal decomposition GC-MS.

[0057] The glass transition temperature (Tg) of the rubber-like polymer is preferably below 0°C, and more preferably below -10°C. If the glass transition temperature (Tg) of the rubber-like polymer is below 0°C, it imparts appropriate toughness to the film. The glass transition temperature (Tg) of the rubber-like polymer is determined by the same method as described above.

[0058] The glass transition temperature (Tg) of the rubber-like polymer can be adjusted by the composition of the rubber-like polymer. For example, in order to lower the glass transition temperature (Tg) of the acrylic rubber-like polymer (a), it is preferable to increase the mass ratio of acrylates with 4 or more carbon atoms in the alkyl group to other copolymerizable monomers in the acrylic rubber-like polymer (a) (for example, 3 or more, preferably 4 to 10).

[0059] The particles containing the acrylic rubber-like polymer (a) may be particles formed of the acrylic rubber-like polymer (a), or particles formed of a hard layer of a hard crosslinked polymer (c) with a glass transition temperature of 20°C or higher and a soft layer of the acrylic rubber-like polymer (a) disposed therearound (these are also referred to as "elastomers"); or particles formed of an acrylic graft copolymer obtained by polymerizing at least one stage of a mixture of monomers such as methacrylate in the presence of the acrylic rubber-like polymer (a). The particles formed of the acrylic graft copolymer may also be core-shell type particles having a core containing the acrylic rubber-like polymer (a) and a shell covering it.

[0060] Regarding core-shell rubber particles containing acrylic rubber-like polymers: (Core) The core contains an acrylic rubber-like polymer (a), and may further contain a hard cross-linked polymer (c) if necessary. That is, the core may have a soft layer made of an acrylic rubber-like polymer and a hard layer made of a hard cross-linked polymer (c) disposed inside it.

[0061] The crosslinking polymer (c) is a crosslinking polymer with methacrylate as the main component. That is, the crosslinking polymer (c) is preferably a crosslinking polymer containing building units derived from alkyl methacrylate, building units derived from other monomers that can copolymerize with it, and building units derived from multifunctional monomers.

[0062] The alkyl methacrylate may be the aforementioned alkyl methacrylate; other monomers that can be copolymerized may be the aforementioned styrene and acrylate, etc.; examples of multifunctional monomers are the same as those used as examples of multifunctional monomers mentioned above.

[0063] The content of building units derived from alkyl methacrylate is 40 to 100% by mass relative to all building units constituting crosslinked polymer (c). The content of building units derived from other copolymerizable monomers is 60 to 0% by mass relative to all building units constituting other crosslinked polymers (c). The content of building units derived from polyfunctional monomers is 0.01 to 10% by mass relative to all building units constituting other crosslinked polymers.

[0064] (Shell portion) The shell portion includes a methacrylate polymer (b) (other polymers) comprising mainly methacrylate-derived building units grafted onto an acrylic rubber-like polymer (a). "Main component" refers to the content of methacrylate-derived building units, as described below.

[0065] The methacrylate constituting the methacrylate polymer (b) is preferably an alkyl methacrylate, such as methyl methacrylate, in which the alkyl group has 1 to 12 carbon atoms. There may be one or more types of methacrylate.

[0066] The content of methacrylate is preferably 50% by mass or more relative to all the building units constituting the methacrylate polymer (b). If the content of methacrylate is 50% by mass or more, it is easy to obtain compatibility with methacrylate resins that mainly contain building units derived from methyl methacrylate. Based on the above viewpoint, the content of methacrylate is preferably 70% by mass or more relative to all the building units constituting the methacrylate polymer (b).

[0067] The methacrylate polymer (b) may further include building units derived from other monomers that can copolymerize with methacrylates. Examples of other copolymerizable monomers include acrylates such as methyl acrylate, ethyl acrylate, and n-butyl acrylate; and (meth)acrylate monomers having alicyclic, heterocyclic, or aromatic rings such as (meth)acrylate, (meth)acrylate, dicyclopentyl acrylate, and (meth)acrylate phenoxyethyl ester (meth)acrylate (monomers containing rings).

[0068] The content of building units derived from copolymerizable monomers is preferably 50% by mass or less, and more preferably 30% by mass or less, relative to all building units constituting the methacrylic polymer (b).

[0069] The grafting ratio (grafting rate) of the grafted component in the rubber particles is preferably 10-250% by mass, more preferably 15-150% by mass. If the grafting rate is above a certain level, the proportion of the grafted component, that is, the methacrylic polymer (b) whose main component is derived from the building blocks of methacrylate, is moderately high, thus easily improving the compatibility between the rubber particles and the methacrylic resin, and making it less likely for the rubber particles to aggregate. Furthermore, it is less likely to damage the rigidity of the film. If the grafting rate is below a certain level, the proportion of the acrylic rubber-like polymer (a) will not be too low, and the effect of improving the toughness and brittleness of the film is less likely to be compromised.

[0070] The grafting rate was determined by the following method: 1) 2g of core-shell particles were dissolved in 50ml of methyl ethyl ketone. The mixture was centrifuged (Hitachi Koki Co., Ltd., CP60E) at 30,000 rpm and 12°C for 1 hour to separate the insoluble and soluble components (the centrifugation operation was set to be repeated 3 times). 2) The weight of the obtained insoluble component was substituted into the following formula to calculate the grafting rate. Grafting rate (mass%) = [{(mass of insoluble methyl ethyl ketone) - (mass of acrylic rubber polymer (a))} / (mass of acrylic rubber polymer (a))] × 100

[0071] Regarding the shape of the rubber particles: In the cross-section of the protective film parallel to the in-plane slow axis, the rubber particles have a flat shape with a major axis and a minor axis.

[0072] Specifically, the (meth)acrylic resin has an in-plane slow axis in a direction orthogonal to the extension direction. On the other hand, the rubber particles have a major axis in a direction parallel to the extension direction and a minor axis in a direction orthogonal to the extension direction. Therefore, in a cross-section of the protective film parallel to the in-plane slow axis, the minor axis of the rubber particles is preferably approximately parallel to the in-plane slow axis (specifically, ±10° or less), and the major axis is preferably orthogonal to the in-plane slow axis.

[0073] The average minor diameter Ra of the rubber particles is not particularly limited as long as it satisfies Rs2 ≥ Ra as described later, and more preferably Rs2 / Ra as described later. It is preferably, for example, 300 nm or less, and more preferably 200 nm or less. If the average minor diameter Ra of the rubber particles is 300 nm or less, the difference between the curing shrinkage of the active energy line-curing adhesive and the shrinkage of the protective film (caused by the rubber particles) will not be too large, so deformation caused by this is not likely to occur. The lower limit of the average minor diameter Ra of the rubber particles is not particularly limited, but it is preferably, for example, 50 nm, and more preferably 100 nm. If the average minor diameter Ra of the rubber particles is 50 nm or more, the stress (shrinkage force) of the rubber particles under the tensile stress is easily applied to the protective film, so it is easy to exhibit a stress mitigation effect, that is, the stress on the protective film caused by the curing shrinkage force of the active energy line-curing adhesive can be reduced.

[0074] The ratio of the average major diameter Rb to the average minor diameter Ra of the rubber particles, i.e., the aspect ratio Rb / Ra of the rubber particles, is preferably 1.1 to 4.0. If the aspect ratio of the rubber particles is 1.1 or higher, stress relief of the rubber particles is easier to occur, thus easing the stress caused by the curing shrinkage of the active energy linear curing adhesive. If the aspect ratio of the rubber particles is 4.0 or lower, it is easier to suppress the formation of voids between the rubber particles and the surrounding resin matrix due to stress relief of the rubber particles. The aspect ratio of the rubber particles is more preferably 1.3 to 2.5.

[0075] The average minor axis Ra, average major axis Rb, and aspect ratio Rb / Ra of the rubber particles can be determined by the following methods: 1) Observe a cross-section of the protective film parallel to the in-plane slow axis using TEM. The observation area can be a region with a thickness equivalent to that of the protective film, or a 5μm × 5μm region. When a region with a thickness equivalent to that of the protective film is used as the observation area, the measurement location is location 1. When a 5μm × 5μm region is used as the observation area, the measurement location is location 4. 2) Measure the minor axis and major axis of each rubber particle in the obtained TEM image, and take the average value of these values ​​as the average minor axis Ra and the average major axis Rb. Then, the ratio Rb / Ra of the obtained average major axis Rb to the average minor axis Ra is set as the aspect ratio. Furthermore, the minor axis of each rubber particle is measured in the TEM image as the length (short side length) of the short side of the rectangle circumscribed by the rubber particle. The major axis of the rubber particle is determined in the TEM image described later, as the length of the long side of the rectangle circumscribed by the rubber particle (long side length).

[0076] The average minor diameter Ra or aspect ratio Rb / Ra of the rubber particles can be adjusted by, for example, the average primary diameter R of the rubber particles used as raw materials or the elongation conditions of the protective film. In order to reduce the average minor diameter Ra of the rubber particles, it is preferable to use rubber particles with, for example, a smaller average primary diameter R as raw materials, or to increase the elongation ratio of the protective film.

[0077] The content of rubber particles Mr is not particularly limited, but it is preferably 5 to 25% by mass relative to the protective film, and more preferably 5 to 20% by mass.

[0078] 1-2-3. Silicon oxide particles: Silicon oxide particles roughen the surface of the protective film and impart sliding properties.

[0079] Based on the viewpoint of adjusting the turbidity of the thin film, it is preferable to treat the silicon oxide particles with a hydrophobic agent. The so-called surface treatment with a hydrophobic agent refers to replacing the hydrogen atoms of the hydroxyl groups on the surface of the silicon oxide particles with silyl groups such as dimethylsilyl, trimethylsilyl, octylsilyl, and dimethylpolysiloxane.

[0080] Examples of hydrophobic agents used in surface treatment include chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, tributyldimethylchlorosilane, and vinyltrichlorosilane; tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, methylphenyltrimethoxysilane, and butyltrimethoxysilane. Alkoxysilanes such as alkylsilane, hexyltrimethoxysilane, octyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, and dimethylaminotrimethylsilane; alkylsilanes such as triethylsilane and octylsilane; hexamethyldimethylsilane... Silazanes, including silazane, hexaethyldiazane, hexapropyldiazane, hexabutyldiazane, hexapentyldiazane, hexahexyldiazane, hexacyclohexyldiazane, hexaphenyldiazane, divinyltetramethyldiazane, dimethyltetravinyldiazane, etc.; linear silica oils, including dimethyl silica oil, methyl hydrosiloxane, methylphenyl silica oil, etc.; alkyl-modified silica oil, chloroalkyl-modified silica oil, chlorophenyl-modified silica oil. Modified silicone oils, including oils, fatty acid modified silicone oils, polyether modified silicone oils, alkoxy modified silicone oils, carbitol modified silicone oils, amino modified silicone oils, epoxy modified silicone oils, carboxyl modified silicone oils, fluorine modified silicone oils, methacrylic acid modified silicone oils, and mercapto modified silicone oils; and silicone oils such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, and octamethyltricyclosiloxane.

[0081] Examples of silicon oxide particles include commercially available products such as AEROSIL R972, R972V, R974, and R812 (all manufactured by AEROSIL Corporation of Japan, AEROSIL (registered trademark)). Among them, AEROSIL R812V is preferred.

[0082] (Relationship between Rs2 and Ra) The average secondary particle size Rs2 of silicon oxide particles is preferably the same as or larger than the average minor diameter Ra of rubber particles, that is, Rs2≧Ra.

[0083] Specifically, Rs2 / Ra is preferably 1.1 to 4.0. If Rs2 / Ra is 1.1 or higher, the average secondary particle size Rs2 of the silicon oxide particles is sufficiently large relative to the average minor diameter Ra of the rubber particles, thus imparting sufficient strength to the protective film and making it less prone to surface unevenness or wrinkling caused by the hardening shrinkage of the active energy line hardening adhesive. If Rs2 / Ra is 4.0 or lower, it is not only easy to suppress the increase of turbidity of the protective film, but also to prevent the average minor diameter Ra of the rubber particles from being too small, thus making it less likely to impair the stress relief effect. In this way, it is less likely to cause surface unevenness or wrinkling caused by the hardening shrinkage of the active energy line hardening adhesive. Based on the same viewpoint, Rs2 / Ra is preferably 1.5 to 3.0.

[0084] Rs2 / Ra can be adjusted by, for example, the average primary particle size Rs1 of the silica particles used as raw materials or the average primary particle size R of the rubber particles, the ratio of these (R / Rs1), the content ratio of silica particles to rubber particles (Mr / Ms), the type of resin, the elongation of the film, etc.

[0085] That is, in order to satisfy Rs2 ≥ Ra (preferably Rs2 / Ra is a certain value or higher), it is preferable to make the average primary particle size R of the rubber particles in the raw material stage smaller, to make Mr / Ms moderately reduced, to make the rubber particles easier to disperse (less prone to agglomeration), and to improve the elongation ratio of the film. This is because when the average primary particle size R or R / Rs1 of the rubber particles in the raw material is moderately reduced, the specific surface area of ​​the silicon oxide particles increases, making them easier to agglomerate. Resins containing more structural units derived from phenylmaleimide have lower affinity for, for example, hydrophobically treated silicon oxide particles due to moderately increased polarity, thus making it less likely for the silicon oxide particles to agglomerate. If the elongation ratio of the film is high (the average minor diameter Ra of the rubber particles is smaller), the stress-relieving effect of the rubber particles is more easily exhibited.

[0086] (Average Primary Particle Size Rs2) The average secondary particle size Rs2 of silicon oxide particles only needs to satisfy Rs2 ≥ Ra (preferably Rs2 / Ra is a certain value or higher). Specifically, the average secondary particle size Rs2 of silicon oxide particles is preferably 150~400 nm. If the average secondary particle size Rs2 of silicon oxide particles is 150 nm or higher, it is not only easy to satisfy Rs2 ≥ Ra (preferably Rs2 / Ra is a certain value or higher), but also, due to the large aggregation of silicon oxide particles, the protective film is less prone to surface unevenness or wrinkling caused by the hardening shrinkage of the active energy line hardening adhesive. If the average secondary particle size Rs2 of silicon oxide particles is less than 400 nm, it will suppress the increase of turbidity of the protective film. Based on the same point of view, the average secondary particle size Rs2 of silicon oxide particles is more preferably 200~350 nm.

[0087] (Average primary particle size Rs1) The average primary particle size Rs1 of silicon oxide particles is not particularly limited to the degree to which aggregates satisfying Rs2 ≥ Ra (preferably Rs2 / Ra is a certain value or higher), but is preferably, for example, 5 to 100 nm. If the average primary particle size Rs1 of silicon oxide particles is within the above range, it is easy to moderately aggregate, thus easily forming aggregates of a suitable size (aggregates satisfying Rs2 ≥ Ra, preferably Rs2 / Ra is a certain value or higher). This imparts appropriate strength to the protective film and makes it less prone to surface unevenness or wrinkling deformation of the protective film. Based on the same viewpoint, the average primary particle size Rs1 of silicon oxide particles is more preferably 10 to 50 nm.

[0088] The average primary particle size Rs1 and average secondary particle size Rs2 of silicon oxide particles can be determined using the same method as for rubber particles. That is, 1) Observe the cross-section of the protective film parallel to the in-plane slow axis using TEM. The observation area is the same as described above. 2) Measure the particle size of any 10 aggregates in the obtained TEM image, and set the average value of these as the "average secondary particle size Rs2". The particle size of each aggregate is determined by TEM image. Furthermore, measure the primary particle size of any 10 silicon oxide particles, and set the average value of these as the "average primary particle size Rs1".

[0089] (Specific Surface Area) The specific surface area of ​​silicon oxide particles, as determined by the BET method, is preferably 50~800 m² / g. This is because silicon oxide particles with this specific surface area tend to have an average primary particle size within the aforementioned range, and are prone to moderate aggregation. The specific surface area of ​​silicon oxide particles can be determined by the BET method after separating the silicon oxide particles, for example, from other components of a protective film.

[0090] The content of silicon oxide microparticles, Ms, is preferably 0.1 to 1.0% by mass relative to the (meth)acrylic resin contained in the protective film. If the content of silicon oxide microparticles is 0.1% by mass or more, it is easy to form sufficiently large aggregates on the film surface, thus improving the slip properties. If it is less than 1.0% by mass, it will inhibit the increase of film turbidity. Based on the same point of view, the content of silicon oxide particles is preferably 0.3 to 0.7% by mass relative to the (meth)acrylic resin.

[0091] The mass ratio of rubber particle content Mr to silica microparticle content Ms, Mr / Ms, is preferably 5 to 100, more preferably 10 to 100. If Mr / Ms is 5 or higher, the average secondary particle size Rs2 of silica particles will not be too large, making it easy to keep Rs2 / Ra below a certain value. Furthermore, since the amount of rubber particles is sufficient, stress mitigation is easily achieved. If Mr / Ms is 100 or lower, the average secondary particle size Rs2 of silica particles will not be too small, making it easy to adjust Rs2 ≥ Ra (preferably Rs2 / Ra above a certain value), and a sufficient amount of secondary silica particles will be formed. This allows for the easy imparting of appropriate strength to the protective film, further suppressing surface unevenness or wrinkling of the protective film.

[0092] 1-2-4. Physical Properties (YI) The yellowness index (YI) of the protective film is preferably 1.2 to 1.8. When the YI of the protective film is 1.2 or higher, when bonding with a polarizer using an active energy line curing adhesive, the protective film will moderately absorb active energy lines (e.g., ultraviolet light), thus moderately reducing the amount of active energy lines reaching the active energy line curing adhesive. This reduces the curing shrinkage of the active energy line curing adhesive, thereby reducing surface unevenness or wrinkling of the protective film caused by this. When the YI of the protective film is 1.8 or lower, poor bonding caused by excessive absorption of active energy lines can be suppressed. For the same reason, the YI of the protective film is more preferably 1.4 to 1.6.

[0093] The YI of the protective film can be determined according to the YI (yellow index: the index of yellow hue) of the film specified in JIS K 7103. Specifically, for the protective film, the tristimulus values ​​X, Y, and Z of the light source color specified in JIS Z8701 are calculated using a Hitachi High Technology (U-3300) spectrophotometer and its accompanying chroma calculation program. Then, the following formula is used to calculate YI: YI = 100(1.28X - 1.06Z) / Y

[0094] The YI of the protective film can be adjusted by, for example, the composition of the (meth)acrylic resin (especially the content of building units (U2) derived from phenylmaleimide) or the film thickness. To increase the YI of the protective film, it is preferable to increase the content of building units (U2) derived from phenylmaleimide in the (meth)acrylic resin. On the other hand, to suppress poor adhesion caused by excessively high YI of the protective film, it is preferable, for example, to reduce the thickness of the protective film.

[0095] (Phase Difference Ro and Rt) The protective film preferably has a phase difference corresponding to the required optical characteristics. From the viewpoint of using the protective film as a phase difference film for IPS mode, the in-plane phase difference Ro and the thickness-direction phase difference Rt, measured at a wavelength of 550 nm, 23°C, and 55%RH, preferably satisfy the following formulas respectively: |Ro|≦10nm |Rt|≦10nm

[0096] Ro and Rt are defined by the following formulas respectively. Formula (I): Ro=(nx-ny)×d Formula (II): Rt=((nx+ny) / 2-nz)×d (where nx represents the refractive index of the thin film in the slow axis direction (the direction with the maximum refractive index), ny represents the refractive index of the thin film in the direction orthogonal to the slow axis, nz represents the refractive index of the thin film in the thickness direction, and d represents the thickness of the thin film (nm)).

[0097] The in-plane slow axis of the protective film can be confirmed by an automatic birefringence meter AXOSCAN (AxoScan Mueller Matrix Polarimeter: manufactured by Axometrics).

[0098] Ro and Rt can be determined by the following methods: 1) The protective film is conditioned for 24 hours at 23°C and 55%RH. The average refractive index of the film is measured using an Abbe refractometer, and the thickness d is measured using a commercially available micrometer. 2) The conditioned film is then conditioned using an automatic birefringence meter AXOSCAN (AxoScan Mueller Matrix Polarimeter: manufactured by Axometrics) at 23°C and 55%RH, with the hysteresis Ro and Rt measured at a measurement wavelength of 550 nm.

[0099] The phase difference Ro and Rt of the protective film can be adjusted by, for example, the monomer composition of (meth)acrylic resin or the stretching conditions.

[0100] (Photoelasticity coefficient) The photoelasticity coefficient of the protective film at 23°C and 55%RH is preferably -4.0×10⁻¹² to 4.0×10⁻¹² Pa⁻¹. If the photoelasticity coefficient is within the above range, even if stress occurs on the protective film due to polarizer warping under high temperature and high humidity conditions, the phase difference caused by the stress is not easily displayed, thus reducing the likelihood of circular optical non-uniformity, such as that produced in the center of the screen of a liquid crystal display device. Based on the above viewpoint, the photoelasticity coefficient of the protective film is more preferably -1.0×10⁻¹² to 1.0×10⁻¹² Pa⁻¹.

[0101] The photoelastic coefficient of the protective film can be determined by the following method. Specifically, using a KOBRA-31PRW (manufactured by Oji Measurement Equipment Co., Ltd.), a tensile load (stress) is applied to the in-plane slow axis direction of the protective film, and a tensile test is performed. The phase difference exhibited at this time is measured at a wavelength of 589 nm. Specifically, the phase difference (nm) under 589 nm light is plotted against a tensile load (stress) of 1~15 N at 10 points, and the slope of the plot when it approximates a straight line is calculated and defined as the photoelastic coefficient. The measurement can be performed at 23°C and 55% RH. When the in-plane slow axis direction is not specified, it is assumed that a tensile load is applied to the width direction of the protective film.

[0102] The photoelasticity of the protective film can be adjusted by the monomer composition of the (meth)acrylic resin. In order to reduce the absolute value of the photoelasticity of the protective film, it is preferable to adjust the ratio of the content of the building units derived from methyl methacrylate, which have a negative photoelasticity when the film is a homopolymer, to the content of the building units derived from phenylmaleimide, which have a positive photoelasticity when the film is a homopolymer, to a range that cancels out the overall photoelasticity.

[0103] (Internal Turbidity) The internal turbidity of the protective film is preferably 1.0% or less, more preferably 0.1% or less, and even more preferably 0.05% or less. The internal turbidity of the protective film can be measured using the same method as described above. The internal turbidity of the protective film can be adjusted by factors such as the content of rubber particles.

[0104] (Residual Solvent Content) Since the protective film is preferably manufactured using a casting method, it contains residual solvent. The residual solvent content is preferably below 700 ppm relative to the protective film, and more preferably 30 to 700 ppm. The residual solvent content is adjusted by the drying conditions of the concentrated liquid cast onto the support during the manufacturing process of the protective film.

[0105] The residual solvent content of the protective film can be determined by headspace gas chromatography. Headspace gas chromatography involves sealing the sample in a container and heating it. The gas in the container is then rapidly injected into a gas chromatograph to perform mass analysis, identify the compounds, and simultaneously quantify the volatile components. In headspace chromatography, all peaks of the volatile components can be observed using a gas chromatograph. Furthermore, by using analytical methods utilizing electromagnetic interaction, the quantification of volatile substances and monomers can be performed with high precision.

[0106] (Thickness) The thickness of the protective film should be set in a manner that allows YI to meet the above-mentioned range, preferably 5 μm or more but not exceeding 60 μm. If the thickness of the protective film is 5 μm or more, it is easy to adjust YI to a certain level, thus appropriately reducing the amount of active energy lines reaching the active energy line curing adhesive. If the thickness of the protective film is 60 μm or less, it is possible to prevent excessively high YI from causing an excessively low amount of active energy lines reaching the active energy line curing adhesive, thus reducing the likelihood of decreased adhesion. Furthermore, if the thickness of the protective film is 60 μm or less, the distance between the polarizer, which becomes the driving force for bending, and the panel is shorter, thus reducing the likelihood of panel warping. Based on the same viewpoint, the thickness of the protective film is more preferably 5 to 50 μm, and more preferably 30 to 50 μm.

[0107] 1-3. Opposite film 130 The opposite film is any transparent resin film and is not particularly limited. From the point of view of improving damp heat durability, a resin film with low moisture permeability is preferred.

[0108] Examples of resins constituting opposing films include (meth)acrylic resins, polyester resins, and cellulose ester resins.

[0109] ((Meth)Acrylic resin) The (meth)acrylic resin contained in the opposed film may be a homopolymer containing building units derived from methyl methacrylate, or a copolymer containing building units derived from methyl methacrylate and building units derived from comonomers other than methyl methacrylate that can be copolymerized with it.

[0110] The copolymer monomer is not particularly limited and may include methyl methacrylates other than methyl methacrylates such as ethyl methacrylate, propyl methacrylate, and six-membered lactone methacrylates; maleic anhydride and glutaric anhydride. One copolymer monomer may be used, or two or more monomers may be used in combination.

[0111] Among them, based on the view that the moisture permeability of the film can be easily adjusted to the above range, it is preferable to be a homopolymer (polymethyl methacrylate) containing building units derived from methyl methacrylate, or a copolymer containing building units derived from methyl methacrylate, glutaramide building units (e.g., those derived from (meth)acrylate building units reacted with amides or the like), building units derived from glutaric anhydride, or building units derived from six-membered lactone (meth)acrylate (lactone ring building units), and more preferably a homopolymer (polymethyl methacrylate) containing building units derived from methyl methacrylate.

[0112] The content of the building units derived from methyl methacrylate is preferably 80 to 100% by mass, more preferably 90 to 100% by mass, relative to all the building units constituting (meth)acrylic resins.

[0113] The glass transition temperature (Tg) of (meth)acrylic resin is preferably 90°C or higher, and more preferably 100-150°C. Opposite films of (meth)acrylic resin with a Tg of 90°C or higher will exhibit good heat resistance. The glass transition temperature can be determined using the same method described above.

[0114] The weight-average molecular weight (Mw) of (meth)acrylic resins is not particularly limited and can be appropriately set according to the film-forming method. For example, the weight-average molecular weight of (meth)acrylic resins is preferably 100,000 to 300,000 when forming films by melt casting, and preferably 400,000 to 3,000,000, more preferably 500,000 to 2,000,000 when forming films by solution casting. The weight-average molecular weight can be determined by the same method as described above.

[0115] (Polyester resin) Examples of polyester resins include polyethylene terephthalate, polyethylene terephthalate, polyethylene terephthalate, and polyethylene naphthalate. Polyethylene terephthalate (PET) is preferred.

[0116] (Cellulose ester resin) Examples of cellulose ester resins include triacetyl cellulose, etc.

[0117] The opposite film is preferably one with low moisture permeability, and more preferably contains (meth)acrylic resin.

[0118] The thickness of the opposing film is not particularly limited, but it is preferable to be thicker than the protective film, based on the viewpoint that it is easier to reduce moisture permeability. Specifically, the thickness of the opposing film is preferably 40~100μm, more preferably 50~80μm.

[0119] 1-3-5. Manufacturing method of protective film 120 and opposing film 130 The protective film and opposing film can be manufactured by any method, including melt casting and solution casting.

[0120] From the viewpoint that high molecular weight (meth)acrylic resins can be used, it is preferable that the protective film of the present invention is manufactured by solution casting. That is, the protective film is manufactured by at least the following steps: 1) obtaining a concentrated solution containing the aforementioned (meth)acrylic resin, rubber particles, silicon oxide particles and solvent; 2) casting the obtained concentrated solution onto a support, drying and peeling it off to obtain a film; 3) stretching the obtained film.

[0121] Regarding step 1), the (meth)acrylic resin, rubber particles, and silicon oxide particles are dissolved or dispersed in a solvent to prepare a concentrated solution.

[0122] When the average primary particle size of the rubber particles used as raw material is set as R, and the average primary particle size of the silicon oxide particles used as raw material is set as Rs1, it is preferable to satisfy 5 < R / Rs1 ≤ 80. The reason is that if R / Rs1 is within the above range, the Rs2 / Ra of the resulting protective film can be easily adjusted to the above range. Based on the same viewpoint, R / Rs1 is preferably 10 to 60, and more preferably 20 to 50.

[0123] The average primary particle size R of the rubber particles is not particularly limited as long as R / Rs1 meets the above-mentioned range, but it is preferably, for example, 400 nm or less, and more preferably 220 nm or less. If the average primary particle size R of the rubber particles is 400 nm or less, the Rs2 / Ra of the resulting protective film can be easily adjusted to a certain value or higher. The lower limit of the average primary particle size R of the rubber particles is not particularly limited, but it is preferably, for example, 100 nm. If the average primary particle size R of the rubber particles is 100 nm or more, the Rs2 / Ra of the resulting protective film can be easily adjusted to a certain value or lower. The average primary particle size Rs1 of silicon oxide particles is the same as described above.

[0124] The average primary particle size of the rubber particles or silicon oxide particles in the raw material can be determined by using a zeta potential and particle size measurement system (ELSZ-2000ZS manufactured by Otsuka Electronics Co., Ltd.) to measure the dispersed particle size of the rubber particles or silicon oxide particles in the dispersion.

[0125] The solvent used for the concentrated solution shall at least include an organic solvent (good solvent) capable of dissolving (meth)acrylic resins. Examples of good solvents include chlorinated organic solvents such as dichloromethane, or non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran. Dichloromethane is preferred.

[0126] The solvent used in the concentrated solution may further contain a weak solvent. Examples of weak solvents include aliphatic alcohols with 1 to 4 carbon atoms that are either straight-chain or branched-chain. If the alcohol ratio in the concentrated solution increases, the film is more likely to gel, and peeling from the metal support becomes easier. Examples of aliphatic alcohols with 1 to 4 carbon atoms that are either straight-chain or branched-chain include methanol, ethanol, n-propanol, isopropanol, n-butanol, dibutanol, and terbutanol. Among these, ethanol is preferred due to its stability, lower boiling point, and better drying properties.

[0127] Regarding step 2), the obtained concentrate is cast onto the support. The casting of the concentrate can be carried out by spraying it from the casting nozzle.

[0128] Next, the solvent in the concentrated liquid cast onto the support is evaporated and dried. The dried concentrated liquid is peeled off from the support to obtain a film.

[0129] The amount of residual solvent in the concentrate during self-supporting peeling (the amount of residual solvent in the film during peeling) is preferably 25% by mass or more, and more preferably 30 to 37% by mass. If the amount of residual solvent during peeling is less than 37% by mass, it is easier to suppress excessive stretching of the film caused by peeling.

[0130] The amount of residual solvent in the concentrate during stripping is defined by the following formula. The same applies below. Residual solvent amount (mass%) of concentrate = (mass of concentrate before heat treatment - mass of concentrate after heat treatment) / mass of concentrate after heat treatment × 100. And, the heat treatment when measuring the amount of residual solvent means heat treatment at 140°C for 30 minutes.

[0131] The amount of residual solvent during peeling can be adjusted by the drying temperature or drying time of the concentrated liquid on the support, the temperature of the support, etc.

[0132] Regarding step 3), the resulting film is dried. Drying can be carried out in one stage or in multiple stages. Alternatively, drying can be carried out gradually as needed.

[0133] For example, the drying step of the film also includes a step of preparing the film for drying (preparation drying step), a step of stretching the film (stretching step), and a step of drying the stretched film (formal drying step).

[0134] (Preparatory Drying Step) The preparatory drying temperature (drying temperature before stretching) is a temperature higher than the stretching temperature. Specifically, when the glass transition temperature of the (meth)acrylic resin is set to Tg, it is preferably (Tg-50)~(Tg+50)℃. If the preparatory drying temperature is above (Tg-50)℃, the solvent is more likely to evaporate moderately, thus improving the workability. If it is below (Tg+50)℃, the solvent will not evaporate excessively, thus not easily impairing the stretchability of the subsequent stretching step. The initial drying temperature is measured as the ambient temperature, such as the temperature inside the stretching machine or the hot air temperature, when drying by (a) a stretching machine or by non-contact heating while being conveyed by rollers.

[0135] (Extension Step) The extension can be carried out according to the required optical characteristics. It is preferred to extend in at least one direction, but it can also extend in two mutually orthogonal directions (e.g., biaxial extension in the width direction of the film (TD direction) and the transport direction orthogonal to it (MD direction).

[0136] The elongation ratio during the manufacture of the protective film is preferably 5 to 100%, and more preferably 20 to 100%. In the case of biaxial elongation, the elongation ratio in each direction is preferably within the above range.

[0137] The elongation ratio (%) is defined as (length of the elongation direction of the film after elongation - length of the film before elongation) / (length of the film before elongation) × 100. When performing biaxial elongation, the above elongation ratio is preferably set for both the TD direction and the MD direction.

[0138] The stretching temperature (drying temperature during stretching) is the same as described above. When the glass transfer temperature of the (meth)acrylic resin is set to Tg, it is preferably above Tg (°C), and more preferably (Tg+10) to (Tg+50)°C. If the stretching temperature is above Tg (°C), preferably above (Tg+10)°C, the solvent is easily volatilized to a suitable extent, thus making it easier to adjust the stretching tension within an appropriate range. If it is below (Tg+50)°C, the solvent will not volatilize excessively, thus minimizing damage to the stretchability. The stretching temperature during the manufacture of the protective film is set to, for example, 115°C or above. As described above, the stretching temperature is preferably the ambient temperature, such as the temperature inside the stretching machine, which is measured (a).

[0139] The amount of residual solvent in the film at the start of the extension is preferably the same as the amount of residual solvent in the film at the time of peeling, for example, preferably 20-30% by mass, more preferably 25-30% by mass.

[0140] The extension of the film in the TD direction (width direction) can be achieved, for example, by fixing both ends of the film with clamps and pins and expanding the spacing between the clamps and pins in the direction of travel (stretching method). The extension of the film in the MD direction can be achieved, for example, by generating a difference in circumferential speed among multiple rollers and utilizing the difference in circumferential speed among the rollers (roller method).

[0141] (Formal drying step) From the viewpoint of further reducing the amount of residual solvent, it is preferable to further dry the film obtained after stretching. For example, it is preferable to dry the film obtained after stretching by conveying it on an equal side with rollers.

[0142] The final drying temperature (the drying temperature before extension) is preferably (Tg-50) to (Tg-30) °C, and more preferably (Tg-40) to (Tg-30) °C, when the glass transition temperature of the (meth)acrylic resin is set as Tg. If the subsequent drying temperature is above (Tg-50) °C, the solvent can be easily and fully evaporated and removed from the extended film; if it is below (Tg-30) °C, deformation of the film can be highly suppressed. The final drying temperature is the same as described above, and preferably the ambient temperature at which (a) the hot air temperature is measured.

[0143] 1-4. Adhesive layers 140, 150 Adhesive layer 140 is disposed between the protective film and the polarizer, and bonds them together. Similarly, adhesive layer 150 is disposed between the opposing film and the polarizer, and bonds them together.

[0144] The adhesive layer 140 is a layer formed by the curing of an active energy line curing adhesive.

[0145] The active energy line curing adhesive can be a photoradical polymer or a photocationic polymer. Preferably, it is a photocationic polymer.

[0146] The photocationic polymerizable composition includes an epoxy compound and a photocationic polymerization initiator.

[0147] Epoxy compounds are compounds having one or more, preferably two or more, epoxy groups within their molecule. Examples of epoxy compounds include hydrogenated epoxy compounds (glycidyl ethers of polyols having an alicyclic ring) obtained by reacting an alicyclic polyol with epichlorohydrin; aliphatic epoxy compounds such as polyglycidyl ethers of aliphatic polyols or their epoxy alkyl adducts; and alicyclic epoxy compounds having one or more epoxy groups bonded to an aliphatic ring within their molecule. Only one type of epoxy compound may be used, or two or more may be used in combination.

[0148] The photocationic polymerization initiator is, for example, an aromatic diazonium salt; an aromatic monium salt and an aromatic strontium salt; an iron aromatic complex, etc.

[0149] The photocationic polymerization initiator may also be further supplemented with cationic polymerization promoters such as cyclobutane and polyols, photosensitizers, ion scavengers, antioxidants, chain transfer agents, tackifiers, thermoplastic resins, fillers, flow modifiers, plasticizers, defoamers, antistatic agents, leveling agents, solvents, etc., as needed.

[0150] The adhesive layer 150 may be a layer formed by a cured product of an active energy line curing adhesive, or it may be a layer formed by an adhesive other than that (e.g., a fully saponified polyvinyl alcohol aqueous solution (water paste)). That is, the adhesive layer 150 can be selected only in relation to the opposing film. When the opposing film 130 contains (meth)acrylic resin or polyester resin, the adhesive layer 150 is preferably a layer formed by a cured product of an active energy line curing adhesive.

[0151] The thickness of the adhesive layers 140 and 150 is not particularly limited, but for example, it is 0.01~10μm, preferably about 0.01~5μm.

[0152] 1-5. Adhesive layer 160 The adhesive layer is disposed on the side of the protective film opposite to the polarizer. The adhesive layer is a layer for bonding the polarizer of the present invention to display elements such as liquid crystal cells.

[0153] The adhesive layer is preferably a dried and partially cross-linked adhesive composition comprising a base polymer, a prepolymer and / or a cross-linking monomer, a cross-linking agent and a solvent. That is, at least a portion of the adhesive composition is cross-linked.

[0154] Examples of adhesive compositions include acrylic adhesive compositions using (meth)acrylic polymers as the base polymer, silicone adhesive compositions using silicone polymers as the base polymer, and rubber adhesive compositions using rubber as the base polymer. Among these, acrylic adhesive compositions are preferred from the viewpoints of transparency, weather resistance, heat resistance, and processability.

[0155] The (meth)acrylic polymer contained in the acrylic adhesive composition is a copolymer of (meth)acrylic alkyl ester and monomers containing functional groups that can crosslink with crosslinking agents.

[0156] (Meth)acrylate alkyl esters are preferably alkyl acrylates with 2 to 14 carbon atoms in the alkyl group.

[0157] Examples of monomers containing functional groups that can crosslink with crosslinking agents include monomers containing amide groups, monomers containing carboxyl groups (such as acrylic acid), and monomers containing hydroxyl groups (such as hydroxyethyl acrylate).

[0158] Examples of crosslinking agents contained in acrylic adhesive compositions include epoxy crosslinking agents, isocyanate crosslinking agents, and peroxide crosslinking agents. The content of crosslinking agents in the adhesive composition is typically 0.01 to 10 parts by mass relative to 100 parts by mass of the base polymer (solids).

[0159] The adhesive composition may further contain various additives such as adhesive agents, plasticizers, glass fibers, glass beads, metal powders, other fillers, pigments, colorants, antioxidants, ultraviolet absorbers, and silane coupling agents as needed.

[0160] The thickness of the adhesive layer is usually around 3~100μm, preferably 5~50μm.

[0161] The surface of the adhesive layer is protected by a release film that has undergone a demolding process. Examples of release films include plastic films such as acrylic films, polycarbonate films, polyester films, and fluoropolymer films.

[0162] 2. Method for manufacturing polarizing plate The polarizing plate of the present invention is manufactured by the following steps: a step of depositing a protective film on the surface of a polarizer by means of a layer formed by an active energy line curing adhesive; a step of irradiating the deposited material with active energy lines to cure the active energy line curing adhesive; and a step of forming an adhesive layer on the surface of the protective film opposite to the polarizer.

[0163] For example, as shown in FIG1, 1) a step of depositing a protective film on one side of the polarizer by separating a layer formed of an active energy line curing adhesive; 2) a step of depositing a counter film on the other side of the polarizer by separating an adhesive layer; 3) a step of irradiating the laminate with active energy lines to cure the active energy line curing adhesive; and 4) a step of attaching an adhesive layer and peeling off the film on the protective film of the laminate. The adhesive used for bonding the counter film to the polarizer will be described below using an active energy line curing adhesive as an example.

[0164] Regarding step 1), surface treatment such as corona treatment is performed on the surface of the protective film as needed. Next, a protective film is deposited on one side of the polarizer by means of a layer of active energy line curing adhesive.

[0165] Similar to step 2), a surface treatment such as corona treatment is performed on the surface of the opposing film as needed. Next, an opposing film is deposited on the other side of the polarizer by means of a layer of active energy line curing adhesive.

[0166] Regarding step 3), the laminate is irradiated with active energy lines to cure the active energy line curing adhesive. In this way, cured layers of the active energy line curing adhesive are separated between the polarizer and the protective film, and between the polarizer and the opposing film, respectively, for bonding.

[0167] The active energy rays used for irradiation can be any of visible light, ultraviolet light, X-rays, and electron beams. Ultraviolet light is generally preferred due to its ease of processing and sufficient curing speed. The irradiation conditions for ultraviolet light only need to meet the requirements for curing the adhesive. The cumulative irradiation dose of ultraviolet light is preferably 50~1500 mJ / cm², more preferably 100~500 mJ / cm².

[0168] Furthermore, steps 1) and 2) can be performed simultaneously or sequentially. From the perspective of improving manufacturing efficiency, steps 1) and 2) are preferably performed simultaneously.

[0169] Regarding step 4), next, an adhesive layer and a release film are then attached to the protective film of the obtained polarizing plate. Specifically, an adhesive layer can be formed by transferring a release film with a release agent layer onto the protective film.

[0170] In the polarizing plate of the present invention, at least the YI of the protective film is adjusted to be moderately high. Therefore, since the protective film moderately absorbs the active energy lines, the amount of active energy lines reaching the active energy line-curing adhesive can be reduced to a level that does not cause poor adhesion. This reduces the curing shrinkage of the active energy line-curing adhesive. Furthermore, the protective film contains rubber particles and silicon oxide particles, and the average secondary particle size Rs2 of the silicon oxide particles is moderately larger than the average minor axis Ra of the rubber particles. This provides stress relief from the rubber particles and increases the mechanical strength (elastic modulus) of the protective film through the aggregation effect of the silicon oxide particles. Through these effects, good adhesion to the polarizer is achieved, and deformation of the protective film such as surface unevenness or wrinkling caused by the curing shrinkage of the active energy line-curing adhesive can be suppressed.

[0171] 3. Liquid Crystal Display Device The liquid crystal display device of the present invention includes a liquid crystal unit, a first polarizing plate disposed on one side of the liquid crystal unit, and a second polarizing plate disposed on the other side of the liquid crystal unit. Furthermore, at least one of the first polarizing plate and the second polarizing plate is the polarizing plate of the present invention.

[0172] FIG2 is a cross-sectional view showing a liquid crystal display device according to an embodiment of the present invention. As shown in FIG2, the liquid crystal display device 200 of the present invention includes a liquid crystal unit 210, a first polarizing plate 220 and a second polarizing plate 230 holding therebetween, and a backlight unit 240.

[0173] The display mode of the liquid crystal cell 210 is, for example, STN (Super-Twisted Nematic), TN (Twisted Nematic), OCB (Optically Compensated Bend), HAN (Hybrid Aligned Nematic), VA (Vertical Alignment), MVA (Multidomain Vertical Alignment), PVA (Patterned Vertical Alignment), IPS (In-Plane-Switching), etc. For example, an IPS mode is preferred for liquid crystal display devices used in portable devices.

[0174] The first polarizing plate 220 is disposed on the visual recognition side of the liquid crystal cell 210 through an adhesive layer 224. The first polarizing plate 220 includes a first polarizer 221, a counter-film 222 (F1) disposed on the visual recognition side of the first polarizer 221, a protective film 223 (F2) disposed on the liquid crystal cell side of the first polarizer 221, and two adhesive layers 225 disposed between the first polarizer 221 and the counter-film 222 (F1) and between the first polarizer 221 and the protective film 223 (F2).

[0175] The second polarizing plate 230 is disposed on the side of the backlight unit 240 of the liquid crystal unit 210, which is separated by an adhesive layer 234. The second polarizing plate 230 includes a second polarizer 231, a protective film 232 (F3) disposed on the side of the second polarizer 231 on the side of the liquid crystal unit 210, a counter-film 233 (F4) disposed on the side of the second polarizer 231 on the side of the backlight unit 240, and two adhesive layers 235 disposed between the second polarizer 231 and the protective film 232 (F3) and between the second polarizer 231 and the counter-film 233 (F4).

[0176] The absorption axis of the first polarizer 221 and the absorption axis of the second polarizer 231 are preferably orthogonal (becoming orthogonal chords). Furthermore, the unit composed of the liquid crystal cell 210, the first polarizer 220 and the second polarizer 230 is also called the liquid crystal display panel 250.

[0177] Moreover, at least one of the first polarizing plate 220 and the second polarizing plate 230 is the polarizing plate of the present invention. That is, when the first polarizing plate 220 is the polarizing plate of the present invention, the opposing film 222 (F1) is the opposing film in the polarizing plate of the present invention (opposing film 130 in FIG. 1), the protective film 223 (F2) is the protective film in the polarizing plate of the present invention (protective film 120 in FIG. 1), and the adhesive layer 224 is the adhesive layer in the polarizing plate of the present invention (adhesive layer 160 in FIG. 1). Similarly, when the second polarizing plate 230 is the polarizing plate of the present invention, the opposing film 233 (F4) is the opposing film in the polarizing plate of the present invention (opposing film 130 in FIG. 1), the protective film 232 (F3) is the protective film in the polarizing plate of the present invention (protective film 120 in FIG. 1), and the adhesive layer 234 is the adhesive layer in the polarizing plate of the present invention (adhesive layer 160 in FIG. 1). [Example]

[0178] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

[0179] 1. Materials for the protective film (1) Resin preparation: Resins 1-8 as shown in Table 1. MMA: Methyl methacrylate PMI: Phenylamimide MA: Methyl acrylate BA: Butyl acrylate BzMA: Benzyl methacrylate MAA: Methacrylate PMMA: Polymethyl methacrylate MR1000 (manufactured by Nippon Shokubai Co., Ltd., lactone acrylic resin)

[0180] The glass transfer temperature and weight-average molecular weight of resins 1 to 8 were determined by the following method.

[0181] (Glass transition temperature) The glass transition temperature (Tg) of the resin was determined using DSC (Differential Scanning Colorimetry) according to JIS K 7121-2012.

[0182] (Weight Average Molecular Weight) The weight average molecular weight (Mw) of the resin was determined using a gel chromatography system (TOSOH HLC8220GPC) and a column (TOSOH TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series). 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 the column (temperature 40°C), and the value was measured using the detector RI at 40°C, with values ​​converted to styrene.

[0183] (2) Rubber particles Rubber particles R1 (KANEKA M210 manufactured by KANEKA Corporation, average primary particle size R: 200nm) Rubber particles R2 (METABLEN W450A manufactured by Mitsubishi Chemical Corporation, average primary particle size R: 400nm) Rubber particles R3 (MX-80H3wT acrylic particles manufactured by Soken Chemical Corporation, average primary particle size R: 800nm) Rubber particles R4 (METABLEN W300A manufactured by Mitsubishi Chemical Corporation, average primary particle size R: 100nm)

[0184] (3) Silicon oxide particles S1 (AEROSIL (registered trademark) R812, manufactured by AEROSIL Corporation of Japan, hydrophobic fuming silicon oxide, average primary particle size Rs1: 7nm, specific surface area: 260±30m2 / g) S2 (AEROSIL (registered trademark) OX50, manufactured by AEROSIL Corporation of Japan, average primary particle size Rs1: 40nm, hydrophilic fuming silicon oxide, specific surface area: 50±15m2 / g) S3 (AEROSIL (registered trademark) R972V, manufactured by AEROSIL Corporation of Japan, average primary particle size Rs1: 16nm, hydrophobic fuming silicon oxide, specific surface area: 110±20m2 / g)

[0185] The average primary particle size of rubber particles and silicon oxide particles was determined by the following method.

[0186] (Average primary particle size) The average primary particle size of rubber particles and silicon oxide particles was determined by transmission electron microscopy.

[0187] 2. Preparation of protective film <Preparation of protective film 101> (Preparation of rubber particle dispersion) After stirring and mixing a solution containing 10 parts by mass of rubber particles R1 and 90 parts by mass of ME16 (a mixed solvent of dichloromethane and ethanol in a mass ratio of 84:16) for 50 minutes in a dissolver, the solution is dispersed at 1500 rpm using a Milder disperser (manufactured by Pacific Machinery Co., Ltd.) to obtain a rubber particle dispersion.

[0188] (Preparation of Silicon Oxide Particle Dispersion) 20 parts by weight of silicon oxide particles S1 (AEROSIL (registered trademark) R812, manufactured by AEROSIL Corporation, Japan) were mixed with 80 parts by weight of ME50 solution in a dissolving tank and stirred for 50 minutes. The mixture was then dispersed using a Manton Gaulin homogenizer to obtain an additive solution. Next, 10 parts by weight of the above additive solution were slowly added to 90 parts by weight of ME16 that had been thoroughly stirred in a dissolving tank, and the mixture was dispersed using a mill. The mixture was then filtered through a FineMet NF filter manufactured by Nippon Seiki Co., Ltd. to obtain a silicon oxide particle dispersion.

[0189] (Concentrate Preparation) Next, a concentrate with the following composition is prepared. First, dichloromethane and ethanol are added to a pressure dissolving tank. Then, resin 1 is added to the pressure dissolving tank while stirring. Next, the rubber particle dispersion prepared above is added and stirred until completely dissolved. The concentrate is filtered using a SHP150 filter manufactured by ROKITECHNO (stock). Resin 1: 80 parts by mass Dichloromethane: 90 parts by mass Ethanol: 10 parts by mass Rubber particle dispersion: 200 parts by mass Silicon oxide particle dispersion: 30 parts by mass

[0190] (Membrane Formation) Next, a membrane is formed using the above-mentioned preserved concentrate. Specifically, an annular casting apparatus is used to uniformly cast the concentrate at a temperature of 30°C and a width of 1800 mm onto a stainless steel strip support. The temperature of the stainless steel strip is controlled at 28°C.

[0191] On a stainless steel strip support, the solvent is evaporated until the residual solvent in the cast concentrate is 30% by mass. Then, it is peeled off from the stainless steel strip support with a peel tension of 128 N / m to obtain a film. The residual solvent in the film at the time of peeling is 30% by mass.

[0192] Next, while conveying the peeled film with multiple rollers, the resulting film is stretched by 50% in the width direction (TD direction) at 140°C (Tg+15°C) using a tenter frame. Subsequently, while conveying with rollers, it is dried at 105°C (Tg-20°C), and the end clamped by the tenter frame fixture is cut open and wound into a roll to obtain a protective film 101 (roll body) with a film thickness of 40μm.

[0193] <Preparation of Protective Films 102~123> Except for changing at least one of the film composition, stretching conditions and thickness as shown in Table 2, protective films 102~120 are obtained in the same manner as protective film 101. The film thickness is adjusted by the casting amount.

[0194] <Production of Protective Film 124> Except for adjusting the casting amount and changing the film thickness as shown in Table 2, the protective film 124 is obtained in the same way as the protective film 108.

[0195] <Evaluation> The cross-sectional observation and optical properties of the obtained protective films 102~124 were measured by the following methods.

[0196] (Thin Film Cross-Sectional Observation) (1) Average Short Axis Ra and Average Long Axis Rb of Rubber Particles The average short axis Ra, average long axis Rb, and Rb / Ra (aspect ratio) of the rubber particles in the obtained protective film are calculated in the following order. 1) Observe the cross-section of the protective film with TEM (the cross-section parallel to the TD direction in the thickness direction). The observation area is set to a region of 5μm×5μm. 2) Measure the short axis and long axis of each rubber particle in the obtained TEM image. 3) Perform the above operations 1) and 2) on a total of 4 parts by changing the observation area. Then, calculate the average short axis Ra and average long axis Rb from the average values ​​of the 4 parts, and calculate the aspect ratio Rb / Ra.

[0197] (2) Average primary particle size Rs1 and average secondary particle size Rs2 of silicon oxide particles. Similar to (1)1) above, the particle size of any 10 primary silicon oxide particles was measured when a cross-section of the protective film (a cross-section parallel to the TD direction along the thickness direction) was observed by TEM in an observation area of ​​5 μm × 5 μm. The average value of these was then set as the average primary particle size Rs1. Similarly, the particle size of 10 secondary silicon oxide particles (agglomerates) was measured, and the average value of these was set as the average secondary particle size Rs2. The secondary particle size Rs2 was measured by TEM image analysis, the same as that of rubber particles.

[0198] (Measurement of optical properties) (1) The yellow index (YI) of the protective film was measured using a Hitachi High Technology (Group) Co., Ltd. spectrophotometer U-3300 and its associated chroma calculation program. The measurement was performed at 10 points, and the average value of these points was calculated.

[0199] (2) Phase difference (Ro, Rt) The Ro and Rt of the protective film were measured by the following methods. 1) The protective film was conditioned for 24 hours at 23°C and 55%RH. The average refractive index of the film was measured by an Abbe refractometer, and the thickness d was measured by a commercially available micrometer. 2) The hysteresis Ro and Rt of the conditioned film were measured at a measurement wavelength of 550 nm using an automatic birefringence meter AXOSCAN (AxoScan Mueller Matrix Polarimeter: manufactured by Axometrics) at 23°C and 55%RH.

[0200] (3) The photoelasticity coefficient was measured using a KOBRA-31PRW (manufactured by Oji Measurement Equipment Co., Ltd.). A tensile load (stress) was applied to the optical film along its maximum elongation direction (the direction with the greatest elongation), and a tensile test was performed. The phase difference observed at this point was measured at a wavelength of 589 nm. Specifically, the phase difference (nm) was plotted against the tensile load (stress) at 10 points with a range of 1 to 15 N. The slope of the plot when it approximates a straight line was calculated and set as the photoelasticity coefficient. The measurement was performed at 23°C and 55% RH.

[0201] The composition and elongation conditions of the protective films 101~124 are shown in Table 2, and the evaluation results are shown in Table 3.

[0202]

[0203]

[0204] 3. Preparation of PET film with adhesive layer (preparation of adhesive composition) For 100 parts by weight of solid fraction of (meth)acrylic polymer solution, add 0.1 parts by weight of isocyanate crosslinking agent (trade name: TAKENATE D110N, trimethylolpropane xylene diisocyanate, manufactured by Mitsui Chemicals Co., Ltd.) and 0.4 parts by weight of peroxide crosslinking agent benzoyl peroxide (trade name: NAYPER BMT, manufactured by Nippon Yushi Co., Ltd.) and stir to obtain adhesive composition (acrylic adhesive composition).

[0205] (Preparation of Adhesive Layer) The obtained adhesive composition is uniformly coated onto a 38 μm thick polyethylene terephthalate film (PET film, release film) treated with a silicone-based release agent using a spray-type doctor blade coater. The film is then dried in an air-circulating constant-temperature oven at 155°C for 2 minutes to form a 20 μm thick adhesive layer. This yields a PET film with an adhesive layer attached.

[0206] 4. Fabrication and Evaluation of Polarizing Plate <Fabrication of Polarizing Plate 201> (Fabrication of Polarizer) A 25μm thick polyvinyl alcohol film was swelled in water at 35°C. The resulting film was immersed in an aqueous solution of 0.075g iodine, 5g potassium iodide, and 100g water for 60 seconds, and then immersed in an aqueous solution of 3g potassium iodide, 7.5g boric acid, and 100g water at 45°C. The resulting film was uniaxially stretched at a stretching temperature of 55°C and a stretch ratio of 5. The uniaxially stretched film was washed with water and dried to obtain a polarizer with a thickness of 12μm.

[0207] <Preparation of Active Energy Line Curing Adhesive A1> After mixing the following components, degas and prepare Active Energy Line Curing Adhesive A1. 3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate: 45 parts by weight EPOLEAD GT-301 (Daicelyl epoxy resin): 40 parts by weight 1,4-Butanediol diglycidyl ether: 15 parts by weight Triarylsulfuron hexafluorophosphate: 2.3 parts by weight (solids) 9,10-Dibutoxyanthracene: 0.1 parts by weight 1,4-Diethoxynaphthalene: 2.0 parts by weight The triarylsulfuron hexafluorophosphate is prepared as a 50% propyl carbonate solution.

[0208] (Fabrication of Polarizing Plate) Next, corona discharge treatment is performed on the surface of the aforementioned protective film 101, which serves as a protective film, with a corona output intensity of 2.0 kW and a linear velocity of 18 m / min. Then, the aforementioned modified active energy line-curing adhesive A1 is applied to the corona discharge treated surface of the protective film 101 using a rod coater to achieve a cured film thickness of approximately 3 μm, forming a layer composed of the active energy line-curing adhesive A1. Similarly, after corona discharge treatment is performed on the surface of a widely used PMMA film (ACRYPET manufactured by Mitsubishi Chemical Corporation, 60 μm thick), which is a counter-film, the aforementioned modified active energy line-curing adhesive A1 is applied to achieve a cured film thickness of approximately 3 μm, forming a layer composed of the active energy line-curing adhesive A1.

[0209] Next, on one side of the polarizer fabricated above, a protective film 101 is disposed with a layer formed by an active energy line curing adhesive A1 as a separator, and on the other side, a widely used PMMA film is disposed with a layer formed by an active energy line curing adhesive A1 as a separator, thereby obtaining a laminate. The lamination is performed in a manner in which the absorption axis of the polarizer and the slow axis of the protective film are orthogonal.

[0210] Next, the obtained laminate is subjected to ultraviolet irradiation using a conveyor belt-equipped device (using a D bulb manufactured by Fusion UV System Co., Ltd.) with a metal halide lamp source, and the cumulative light intensity is 400mJ / cm2 to irradiate the ultraviolet light, thereby curing the active energy line curing adhesive A1.

[0211] Next, a PET film with an adhesive layer prepared above is bonded to the protective film 201 of the obtained laminate to obtain a polarizing plate 301 having a laminated structure of protective film 101 (opposite film) / adhesive layer / polarizer / adhesive layer / widely used PMMA film (protective film) / adhesive layer / PET film.

[0212] <Fabrication of polarizing plates 202~226> Except for changing the combination of the protective film and the opposing film as shown in Table 2, polarizing plates 202~226 are obtained in the same way as polarizing plate 201.

[0213] <Evaluation> The following methods were used to determine the presence or absence of deformation (surface unevenness and wrinkling) and (2) adhesion of the obtained polarizing plate.

[0214] (1) Deformation of the polarizing plate (presence or absence of surface unevenness and wrinkling) The surface of the thin film was measured by the reflection of the fluorescent lamp. Then, the surface unevenness and wrinkling of the polarizing plate were evaluated based on the following criteria. ○: No fluorescent lamp skew was observed. △: Slight skew was observed in some areas. ×: Severe skew was observed. If it is △ or above, it is judged as good.

[0215] (2) Adhesion of the polarizing plate The peel strength (adhesion) of the optical film of the polarizing plate when peeled from the interface with the polarizer is determined by a 90° peel test at 23°C and 55%RH (according to JIS Z0237:2009) using a 90° peel test fixture (P90-200N) manufactured by IMADA Co., Ltd. ○: Peel strength is 2.0 (N / 25mm) or more △: Peel strength is 1.0 (N / 25mm) or more but less than 2.0 (N / 25mm) ×: Peel strength is less than 1.0 (N / 25mm) If it is △ or more, it is judged as good.

[0216] The obtained polarizing plate was used to make a liquid crystal display device, and the display characteristics (3) were evaluated (bending unevenness, optical unevenness, light leakage).

[0217] (3) Display characteristics (manufacturing of liquid crystal display device) Two pre-laminated polarizing plates were peeled off from the LG 50V LCD TV 50UK6400EJC of the IPS type liquid crystal display device, and the polarizing plates manufactured above were laminated to obtain a liquid crystal display device with a touch panel component. The polarizing plates were laminated with a protective film to become the liquid crystal cell side.

[0218] (3-1) Uneven Bending: The liquid crystal display device manufactured above was placed in an environment of 40°C and 80%RH for 80 hours. Next, in a dry environment at 60°C, the liquid crystal display device was brought to a black display state, and the difference in brightness between the area near the four vertex points of the display screen and the area near the center of the display screen was visually observed (image unevenness between the center and the periphery). Then, the uneven bending was evaluated based on the following evaluation criteria: ○: No uneven bending was observed at all. △: Slight uneven bending was observed, but it was not a problem for practical use. ×: Obvious uneven bending was observed, and there were problems for practical use. Furthermore, uneven bending is caused by panel bending, which is easily caused by, for example, when the protective film is thicker. It is seen as a circular unevenness in the center of the screen. If it is △ or above, it is judged as good.

[0219] (3-2) Optical Inhomogeneity: The liquid crystal display device manufactured above was placed in a dry environment at 80°C for 80 hours. Next, the liquid crystal display device was set to a black display state, and the difference in brightness between the area near the four vertex points of the display screen and the area near the center of the display screen was visually observed (image inhomogeneity between the center and the periphery). Then, the optical inhomogeneity was evaluated based on the following evaluation criteria: ○: No optical inhomogeneity was observed at all. △: Slight optical inhomogeneity was observed, but it was not a problem for practical use. ×: Obvious optical inhomogeneity was observed, and there were problems for practical use. Furthermore, optical inhomogeneity is an inhomogeneity caused by photoelasticity, and white areas are observed near the four vertex points. If it is △ or above, it is judged as good.

[0220] (3-3) Light leakage causes the liquid crystal display device manufactured above to display in black. Light leakage is evaluated based on the following criteria: ◎: No light leakage observed at all ○: Slight light leakage is observed, but it is not a problem for practical use. △: Light leakage is observed, but it is acceptable for practical use. ×: Light leakage is clearly observed, and there are problems for practical use. Furthermore, light leakage is caused by unevenness or wrinkling of the polarizing plate surface, adhesion, and phase difference (Ro, Rt), resulting in a white appearance in the form of lines or waves. If it is △ or above, it is judged as good.

[0221] The structure of the obtained polarizing plates 201~226 is shown in Table 4, and the evaluation results are shown in Table 5.

[0222]

[0223]

[0224] As shown in Table 5, polarizing plates 201-206, 208, 210, 212, 221-224, and 226 (examples) all exhibit suppressed surface unevenness or wrinkling and good adhesion. Furthermore, it is evident that in display devices using these polarizing plates, light leakage caused by surface unevenness or wrinkling is also suppressed. Moreover, it is clear that the display device does not exhibit uneven bending or optical unevenness.

[0225] In particular, it can be seen that the thinner the protective film, the more the adhesion, bending or optical unevenness is reduced (comparison of polarizers 201, 202 and 206, comparison of polarizers 210 and 226).

[0226] It can also be seen that if Rs2 / Ra is less than 4, it can better suppress unevenness or wrinkling of the protective surface and light leakage (comparison of polarizers 202 and 224).

[0227] It can also be seen that if Ra is below 200nm, it can better suppress unevenness or wrinkling of the protective surface and light leakage (comparison of polarizers 202 and 222).

[0228] In contrast, it can be seen that polarizing plates 207, 211, 213-217, 219, 220 and 225 (comparative examples) all have uneven or wrinkled surfaces. It can be seen that the display device also produces light leakage caused by uneven or wrinkled surfaces.

[0229] The polarizing plates 209 and 218 (comparative examples) both exhibited significantly low adhesion, indicating light leakage in the display device. [Industrial Applicability]

[0230] According to the present invention, a polarizing plate, a method for manufacturing a polarizing plate, and a liquid crystal display device using the present invention can suppress the deformation of the surface of the protective film, such as unevenness or wrinkling, which is accompanied by curing shrinkage, when a protective film containing (meth)acrylic resin and a polarizer are manufactured using an active energy line curing adhesive. [Simplified Explanation of the Diagram]

[0232] [Figure 1] is a cross-sectional view showing a polarizing plate according to an embodiment of the present invention. [Figure 2] is a cross-sectional view showing a liquid crystal display device according to an embodiment of the present invention.

Claims

1. A polarizing plate comprising a polarizer, a protective film disposed on the surface of the polarizer, an adhesive layer disposed between the protective film and the polarizer and formed of a cured product of an active energy line curing adhesive, and an adhesive layer disposed on the side of the protective film opposite to the polarizer, wherein the protective film comprises a (meth)acrylic resin, rubber particles, and silicon oxide particles, the (meth)acrylic resin being a copolymer comprising 50-95% by mass of methyl methacrylate-derived structural units, 1-25% by mass of phenylmaleimide-derived structural units, and 1-25% by mass of alkyl acrylate-derived structural units relative to all the structural units constituting the (meth)acrylic resin, wherein in a cross-section along the slow axis of the in-plane of the protective film, the rubber particles have a flat shape having a major axis and a minor axis, wherein when the average minor axis of the rubber particles is defined as Ra, and the average secondary particle size of the silicon oxide particles is defined as Rs2, Rs2 ≥ Ra. The yellow index (YI) of the aforementioned protective film is 1.2 to 1.

8.

2. The polarizing plate of claim 1, wherein the phase difference Ro of the aforementioned protective film at a wavelength of 550 nm, expressed by formula (I), and the Rt at a wavelength of 550 nm, expressed by formula (II), satisfy the following relationships respectively: |Ro|≦10nm |Rt|≦10nm Formula (I): Ro=(nx-ny)×d Formula (II): Rt=((nx+ny) / 2-nz)×d (where nx represents the refractive index of the film in the slow axis direction (the direction of maximum refractive index), ny represents the refractive index of the film in the direction orthogonal to the slow axis, nz represents the refractive index of the film in the thickness direction, and d represents the thickness of the film (nm)).

3. The polarizing plate as requested in item 1 or 2, wherein Rs2 / Ra is 1.1 to 4.

0.

4. A polarizing plate as requested in any of items 1 to 3, wherein Ra is below 200 nm.

5. The polarizing plate of any one of claims 1 to 4, wherein the thickness of the aforementioned protective film is 5 to 50 μm.

6. The polarizing plate of any one of claims 1 to 5, wherein the mass ratio of the aforementioned rubber particle content Mr to the aforementioned silicon oxide particle content Ms, Mr / Ms, is 5 to 100.

7. The polarizing plate of any one of claims 1 to 6, wherein the aforementioned active energy line curing adhesive is a photocationic polymeric composition.

8. A method for manufacturing a polarizing plate, comprising the following steps: 1) preparing a protective film; 2) depositing a protective film on the surface of a polarizer, with a layer of an active energy line curing adhesive as a separator, to obtain a laminate; 3) irradiating the laminate with active energy lines to cure the active energy line curing adhesive; and 4) forming an adhesive layer on the surface of the protective film opposite to the polarizer, wherein step 1) comprises: obtaining a dope, the dope comprising a (meth)acrylic resin containing 50-95% by mass of methyl methacrylate-derived building blocks, 1-25% by mass of phenylmaleimide-derived building blocks and 1-25% by mass of alkyl acrylate-derived building blocks, rubber particles, silicon oxide particles and a solvent, wherein when the average primary particle size of the rubber particles is set to R and the average primary particle size of the silicon oxide particles is set to Rs1, the following relationship is satisfied: 5 < R / Rs1 ≦ 80; The steps of casting the aforementioned concentrated liquid onto the support, drying and peeling it off to obtain a film; and the steps of extending the aforementioned film to obtain the aforementioned protective film.

9. The method for manufacturing a polarizing plate as described in claim 8, wherein R is 220 nm or less.

10. The method for manufacturing a polarizing plate as claimed in claim 8 or 9, wherein the aforementioned active energy line curing adhesive is a photocationic polymeric composition.

11. A liquid crystal display device comprising: a liquid crystal cell, a first polarizing plate disposed on one side of the liquid crystal cell, and a second polarizing plate disposed on the other side of the liquid crystal cell, wherein at least one of the first polarizing plate and the second polarizing plate is a polarizing plate as described in any one of claims 1 to 7, and the aforementioned adhesive layer of the polarizing plate is bonded to the liquid crystal cell.

12. The liquid crystal display device of claim 11, wherein the aforementioned liquid crystal cell is an IPS-type liquid crystal cell.

13. A protective film bonded to a polarizer using an active energy line curing adhesive, the protective film comprising a (meth)acrylic resin, rubber particles, and silicon oxide particles, wherein the (meth)acrylic resin is a copolymer comprising 50-95% by mass of methyl methacrylate-derived structural units, 1-25% by mass of phenylmaleimide-derived structural units, and 1-25% by mass of alkyl acrylate-derived structural units relative to all structural units constituting the (meth)acrylic resin, wherein in a cross-section along the slow axis of the in-plane of the protective film, the rubber particles have a flat shape having a major axis and a minor axis, wherein when the average minor axis of the rubber particles is Ra and the average secondary particle size of the silicon oxide particles is Rs2, Rs2 ≥ Ra, and the yellowness index (YI) of the protective film is 1.2-1.

8.

14. A method for manufacturing a protective film, comprising a method for bonding a protective film to a polarizer using an active energy line curing adhesive, and comprising the following steps: obtaining a concentrated liquid comprising a (meth)acrylic resin containing 50-95% by mass of methyl methacrylate-derived building blocks, 1-25% by mass of phenylmaleimide-derived building blocks, and 1-25% by mass of alkyl acrylate-derived building blocks, rubber particles, silicon oxide particles, and a solvent, wherein the average primary particle size of the aforementioned rubber particles is defined as R, and the average primary particle size of the aforementioned silicon oxide particles is defined as Rs1, satisfying the following relationship: 5 < R / Rs1 ≤ 80; casting the aforementioned concentrated liquid onto a support, drying and peeling it to obtain a film; and extending the aforementioned film to obtain the aforementioned protective film.

Images