Polarizer protective film, polarizing plate and image display device

Abstract

Provided is a polarizer protective film that is endowed with a light diffusion function without reducing the brightness viewing angle. The polarizer protective film of the present invention is composed of a resin film, the resin film includes a resin as a matrix and light diffusing particles dispersed in the matrix, the surface of the polarizer protective film has a concave-convex shape, and the ratio B / A of the cross-sectional area B of the concave part in the concave-convex part to the overall cross-sectional area A is 50% or more.

Description

Technical Field

[0001] The invention relates to a polarizer protective film, a polarizing plate and an image display device. Background Art

[0002] In recent years, there has been a strong desire for thinning of image display devices (such as liquid crystal display devices and organic EL display devices) and improving design (such as narrow frame). As a result, the desire for integration and / or functional merging of optical components and / or optical films used in image display devices is also increasing. As an example of such integration or functional merging, it has been proposed to directly affix a light diffusion film to the polarizer to give the polarizer a light diffusion function. However, the proposed technology has the problem of a reduced brightness field angle.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-118235

[0006] Patent Document 2: Japanese Patent Application Publication No. 2009-025774 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] The present invention has been made to solve the above-mentioned conventional problems, and a main object of the present invention is to provide a polarizer protective film that is provided with a light diffusion function without reducing the brightness viewing angle.

[0009] Solutions for solving problems

[0010] The polarizer protective film of the present invention is composed of a resin film, which contains a resin as a matrix and light diffusing particles dispersed in the matrix. The surface of the polarizer protective film has a concave-convex shape, and the ratio B / A of the cross-sectional area B of the concave part in the concave-convex part to the overall cross-sectional area A is greater than 50%.

[0011] In one embodiment, the refractive index n of the matrix is M The refractive index n of the light diffusing fine particles is P The following relationship is satisfied:

[0012] |n P -n M |≥0.05.

[0013] In one embodiment, a height H of a convex portion in the concavo-convex shape is 3 μm or more.

[0014] In one embodiment, the polarizer protective film includes the light diffusing fine particles in convex portions of the concavo-convex shape.

[0015] In one embodiment, in the polarizer protection film, the convex parts of the concavo-convex shape have intersections when viewed from above.

[0016] In one embodiment, the area ratio of the recessed portion to the entire area of ​​the polarizer protection film in a plan view is 50% or more.

[0017] According to another aspect of the present invention, a polarizing plate is provided. The polarizing plate comprises a polarizer and the polarizer protective film laminated on the polarizer via an adhesive layer. The polarizer protective film is arranged so that the surface having the concavo-convex shape is on the polarizer side.

[0018] In one embodiment, a substantially low refractive index portion generated by the concave portion of the concavo-convex shape is defined at the interface between the polarizer and the polarizer protective film. In one embodiment, the refractive index n of the low refractive index portion is L The refractive index n of the polarizer protective film is F The difference (n F -n L ) is greater than 0.2.

[0019] In one embodiment, a ratio T / H of a thickness T of the adhesive layer to a height H of a convex portion in the concavo-convex shape is 50% or less.

[0020] According to another aspect of the present invention, there is provided an image display device including the above-mentioned polarizing plate on the back side.

[0021] Effects of the Invention

[0022] According to the present invention, by dispersing light diffusing particles in a polarizer protective film and forming a concave-convex shape on at least one surface thereof, and further setting the cross-sectional area ratio of the concave portions in the concave-convex shape to be greater than a specified value, a polarizer protective film can be realized that is endowed with a light diffusing function without reducing the brightness viewing angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic cross-sectional view of a polarizer protective film according to one embodiment of the present invention.

[0024] Figure 2 This is a schematic plan view showing a typical example of the top view shape of the convex portion of the concavo-convex surface in the polarizer protective film according to the embodiment of the present invention.

[0025] Figure 3This is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. DETAILED DESCRIPTION

[0026] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited to these embodiments. It should be noted that the accompanying drawings are schematically shown for ease of observation, and the ratio of length, width and thickness, the shape and clarity of the concave and convex parts are different from the actual ones.

[0027] A. Polarizer protective film

[0028] A-1. Overall composition

[0029] Figure 1 Schematic cross-sectional view of a polarizer protective film according to an embodiment of the present invention. The polarizer protective film 100 shown in the figure is composed of a resin film, which includes a resin as a matrix 10 and light diffusing particles 20 dispersed in the matrix 10. With this structure, the polarizer protective film itself is endowed with light diffusing properties. As a result, the polarizer protective film can also serve as a light diffusing film, and the polarizer protective film becomes a part of the polarizing plate, so that the polarizing plate can be endowed with light diffusing properties and significantly thinned. The refractive index of the matrix n M The refractive index n of the light diffusing particles P The following relationship is preferably satisfied:

[0030] |n P -n M |≥0.05.

[0031] |n P -n M |It is more preferably 0.07 or more, and even more preferably 0.10 or more. |n P -n M The upper limit of | may be, for example, 0.20. With this configuration, better light diffusion performance can be achieved. It should be noted that the resin and light diffusing particles constituting the matrix will be described later in Item A-2 and Item A-3, respectively.

[0032] In an embodiment of the present invention, the surface 30 of the polarizer protective film 100 has a concave-convex shape. The concave-convex surface 30 has a convex portion 31 and a concave portion (air portion or gap portion) 32. The ratio B / A of the cross-sectional area B of the concave portion to the cross-sectional area A of the concave-convex surface as a whole is 50% or more, typically, more than 50%, preferably 60% or more, and more preferably 70% or more. The upper limit of the ratio B / A can be, for example, 90%. If the ratio B / A is in this range, sufficient brightness can be exhibited, the brightness viewing angle is maintained wide, good diffusion performance is given to the polarizer protective film, and when the polarizer protective film is stacked on the polarizer, the bonding strength between the polarizer protective film and the polarizer can be ensured. It should be noted that the cross-sectional area A of the concave-convex surface as a whole is the area of ​​the portion enclosed by the line segment connecting the surface of the convex portion and the line segment connecting the bottom of the concave portion and the line segment in the up and down directions at both ends of the film (for reference, the outside of this portion is enclosed by a dotted line and shown in FIG. Figure 1 ), the cross-sectional area B of the concave portion is the sum of the cross-sectional areas of each concave portion 32 (the area of ​​the portion surrounded by the line segment of the wall of the adjacent convex portion and the line segment connecting the surface of the convex portion and the line segment connecting the bottom of the concave portion). The ratio B / A may correspond to the porosity.

[0033] The height H of the convex portion 31 in the concave-convex surface is preferably 3 μm or more, more preferably 5 μm or more, and further preferably 10 μm or more. The upper limit of the height H of the convex portion can be, for example, 15 μm. If the height of the convex portion is in this range, when the polarizer protective film is laminated on the polarizer, only the convex portion (substantially the upper portion of the convex portion) of the polarizer protective film is bonded to the polarizer. It should be noted that in this specification, for convenience, the bonding of only the convex portion is sometimes referred to as "point bonding". By this point bonding, a substantially low refractive index portion generated by a concave portion (air portion or pore portion) is specified near the point bonding portion. As a result, good light diffusion performance can be achieved and the brightness viewing angle can be increased. In the past, in an image display device, a polarizer (polarizing plate) and a light diffusion film were separately provided, and as a result, an air layer was interspersed between the polarizer and the light diffusion film. The air layer will become an obstacle to thinning, and on the other hand, the brightness viewing angle is maintained larger due to the retro-reflection caused by the air layer. If the polarizing plate and the light diffusion film are integrated, thinning and functional integration can be achieved, and the brightness viewing angle can be reduced by excluding the above-mentioned air layer. By forming a low refractive index portion near the point bonding portion, light is efficiently retroreflected in the same way as when there is an air layer. Therefore, according to an embodiment of the present invention, the polarizer protective film can be given light diffusion performance, and the polarizer can be given the desired light diffusion performance by forming point bonding, and the brightness viewing angle can be maintained large (wide). Furthermore, according to an embodiment of the present invention, since the polarizer protective film itself has light diffusion performance and also serves as a light diffusion film, significant thinning can be achieved through a synergistic effect with the effect of excluding the air layer.

[0034] The top view shape of the convex portion 31 in the concavo-convex surface can adopt any appropriate shape. Figure 2 As shown in FIG. 1 , the convex portion 31 may be in a regular shape (e.g., a lattice shape) or an irregular shape. Figure 2 As shown, there is an intersection C when viewed from above. In other words, the convex portion extends in more than two directions. The spacing between the convex portions (the interval between the convex portions) is preferably less than 1000 μm, more preferably less than 500 μm, and further preferably less than 100 μm. When the top-view shape of the convex portion has regularity, an oblique angle of 1 to 90 degrees can be set. When the top-view shape of the convex portion is irregular, the spacing refers to the average spacing, and is preferably distributed in a manner that is more than 50% relative to the case where the average value of the spacing is within ±50%. If this is the structure, when the polarizer protective film is laminated on the polarizer, the bonding strength between the polarizer protective film and the polarizer can be ensured, and good display quality can be ensured.

[0035] The area ratio of the concave portion 32 relative to the overall area when looking down at the concave-convex surface is preferably 50% or more, preferably 60% or more, and more preferably 70% or more. The upper limit of the area ratio of the concave portion can be, for example, 90%. If the area ratio of the concave portion is within this range, the brightness viewing angle can be maintained wider and good diffusion performance can be given to the polarizer protective film, and when the polarizer protective film is laminated on the polarizer, the bonding strength between the polarizer protective film and the polarizer can be ensured.

[0036] In one embodiment, if Figure 1 As shown, the convex portion 31 includes the light diffusing fine particles 20. With this configuration, a better diffusion performance is imparted, and even with a uniform concavo-convex pattern, optical interference unevenness with pixels of a liquid crystal panel can be reduced.

[0037] The concavoconvex surface (concavoconvex shape) can be formed by any and appropriate method. The concavoconvex shape can be formed by, for example, roughening or using microparticles to impart concavoconvexity. As specific examples of the roughening method, embossing and sandblasting can be cited. Typically, the concavoconvex surface (concavoconvex shape) can be formed by shaping the surface of a melt-extruded film with an embossing roller.

[0038] A-2. Matrix

[0039] As the resin constituting the matrix, any and appropriate resin capable of forming a polarizer protective film can be used. As a specific example of this resin, (meth) acrylic resin, polyester resin (such as polyethylene terephthalate (PET)), cycloolefin resin (such as norbornene resin), cellulose resin (such as triacetyl cellulose (TAC)), polyvinyl alcohol resin, polycarbonate resin, polyamide resin, polyimide resin, polyether sulfone resin, polysulfone resin, polystyrene resin, polyolefin resin, acetate resin can be listed. These resins can be used alone or in combination of two or more. From the viewpoint of optical properties, transparency and versatility, preferably (meth) acrylic resin, polyester resin, cycloolefin resin, more preferably (meth) acrylic resin. It should be noted that in this specification, "(meth) acrylic acid" refers to acrylic acid and / or methacrylic acid.

[0040] As the (meth)acrylic resin, any and appropriate (meth)acrylic resin can be used. It should be noted that, in order to simplify the description, the (meth)acrylic resin will be referred to as acrylic resin below. In the acrylic resin, representatively, as a monomer unit, it contains (meth)acrylic acid alkyl ester as the main component. As the (meth)acrylic acid alkyl ester constituting the main skeleton of the acrylic resin, there can be exemplified (meth)acrylic acid alkyl esters having a linear or branched alkyl group with 1 to 18 carbon atoms. They can be used alone or in combination. Furthermore, any and appropriate comonomers can be introduced into the acrylic resin by copolymerization. The type, amount, copolymerization ratio, etc. of such comonomers can be appropriately set according to the purpose. The constituent components (monomer units) of the main skeleton of the acrylic resin are described below with reference to general formula (2).

[0041] The acrylic resin may preferably have at least one selected from the group consisting of a glutarimide unit, a lactone ring unit, a maleic anhydride unit, a maleimide unit and a glutaric anhydride unit. Acrylic resins having a lactone ring unit are described in, for example, Japanese Patent Publication No. 2008-181078, the contents of which are incorporated herein by reference. The glutarimide unit is preferably represented by the following general formula (1):

[0042]

[0043] In the general formula (1), R 1 and R 2 Each independently represents hydrogen or an alkyl group having 1 to 8 carbon atoms, R 3 represents an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aryl group having 6 to 10 carbon atoms. In the general formula (1), preferably: R 1 and R 2 are each independently hydrogen or methyl, R3 is hydrogen, methyl, butyl or cyclohexyl. More preferably: R 1 is methyl, R 2 is hydrogen, R 3 It is methyl.

[0044] Typically, the above-mentioned alkyl (meth)acrylate is represented by the following general formula (2):

[0045]

[0046] In the general formula (2), R 4 represents a hydrogen atom or a methyl group, R 5 represents a hydrogen atom, or an optionally substituted aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms. Examples of the substituent include halogen and hydroxyl. Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate, and 2,3,4,5-tetrahydroxypentyl (meth)acrylate. In the general formula (2), R 5 A hydrogen atom or a methyl group is preferred. Therefore, a particularly preferred alkyl (meth)acrylate is methyl acrylate or methyl methacrylate.

[0047] The acrylic resin may contain only one glutarimide unit, or may contain R 1 , R 2 and R 3 Different types of glutarimide units.

[0048] The content of the glutarimide unit in the acrylic resin is preferably 2 mol% to 50 mol%, more preferably 2 mol% to 45 mol%, further preferably 2 mol% to 40 mol%, particularly preferably 2 mol% to 35 mol%, and most preferably 3 mol% to 30 mol%. If the content is less than 2 mol%, the effects derived from the glutarimide unit (such as high optical properties, high mechanical strength, excellent adhesion to polarizers, and thinning) may not be fully exerted. If the content exceeds 50 mol%, for example, heat resistance and transparency may be insufficient.

[0049] The acrylic resin may contain only one type of alkyl (meth)acrylate unit, or may contain R 4 and R 5Different types of alkyl (meth)acrylate units.

[0050] The content of the (meth) alkyl acrylate unit in the acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, further preferably 60 mol% to 98 mol%, particularly preferably 65 mol% to 98 mol%, and most preferably 70 mol% to 97 mol%. If the content is less than 50 mol%, the effect (e.g., high heat resistance, high transparency) derived from the (meth) alkyl acrylate unit may not be fully exerted. If the above content is greater than 98 mol%, the resin is easily brittle and cracked, and high mechanical strength cannot be fully exerted, and productivity may be poor.

[0051] The acrylic resin may contain units other than the glutarimide unit and the alkyl (meth)acrylate unit.

[0052] In one embodiment, the acrylic resin may contain, for example, 0% to 10% by weight of an unsaturated carboxylic acid unit that does not participate in the intramolecular imidization reaction described below. The content of the unsaturated carboxylic acid unit is preferably 0% to 5% by weight, more preferably 0% to 1% by weight. If the content is within this range, transparency, retention stability, and moisture resistance can be maintained.

[0053] In one embodiment, acrylic resin can contain copolymerizable vinyl monomer units (other vinyl monomer units) except the above. As other vinyl monomers, for example acrylonitrile, methacrylonitrile, ethacrylonitrile, allyl glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, aminoethyl acrylate, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, cyclohexylaminoethyl methacrylate, N-vinyl diethylamine, N-acetyl vinylamine, allylamine, methylallylamine, N-methylallylamine, 2-isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acryloyl-oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, 2-styryl-oxazoline etc. can be listed. They can be used alone or in combination. Styrene monomers such as styrene and α-methylstyrene are preferred. The content of other vinyl monomer units is preferably 0 to 1% by weight, more preferably 0 to 0.1% by weight. Within this range, the expression of undesired phase difference and the reduction of transparency can be suppressed.

[0054] The imidization rate in the above-mentioned acrylic resin is preferably 2.5% to 20.0%. If the imidization rate is within this range, a resin having excellent heat resistance, transparency and molding processability can be obtained, and the occurrence of scorching during film forming and the reduction of mechanical strength can be prevented. In the above-mentioned acrylic resin, the imidization rate is expressed by the ratio of glutarimide units to (meth) alkyl acrylate units. This ratio can be obtained, for example, from the NMR spectrum, IR spectrum, etc. of the acrylic resin. In the present embodiment, the imidization rate can be expressed using 1 H NMR BRUKER AvanceIII (400 MHz), and through the resin 1 More specifically, the peak area of ​​O-CH3 protons derived from (meth) alkyl acrylate around 3.5 ppm to 3.8 ppm is defined as A, and the peak area of ​​N-CH3 protons derived from glutarimide around 3.0 ppm to 3.3 ppm is defined as B, and the result is determined by the following formula.

[0055] Imidization rate Im (%) = {B / (A+B)} × 100

[0056] The Tg (glass transition temperature) of the acrylic resin is preferably 110°C or more, more preferably 115°C or more, further preferably 120°C or more, particularly preferably 125°C or more, and most preferably 130°C or more. If Tg is 110°C or more, the durability of the polarizing plate including the polarizer protective film obtained from such a resin tends to be excellent. The upper limit of Tg is preferably 300°C or less, more preferably 290°C or less, further preferably 285°C or less, particularly preferably 200°C or less, and most preferably 160°C or less. If Tg is within this range, the formability is excellent.

[0057] The acrylic resin can be produced, for example, by the following method. The method comprises: (I) copolymerizing an alkyl (meth)acrylate monomer corresponding to the alkyl (meth)acrylate unit represented by the general formula (2) with an unsaturated carboxylic acid monomer and / or a precursor monomer thereof to obtain a copolymer (a); and (II) treating the copolymer (a) with an imidizing agent to carry out an intramolecular imidization reaction of the alkyl (meth)acrylate monomer unit and the unsaturated carboxylic acid monomer and / or a precursor monomer unit thereof in the copolymer (a), thereby introducing a glutarimide unit represented by the general formula (1) into the copolymer.

[0058] The details of the acrylic resin and its production method are described in, for example, Japanese Patent Application Laid-Open No. 2018-155812 and Japanese Patent Application Laid-Open No. 2018-155813. The descriptions of these publications are incorporated herein by reference.

[0059] A-3. Light diffusing microparticles

[0060] As light diffusing particles, any and appropriate particles can be used. As specific examples, inorganic particles and polymer particles can be listed. The light diffusing particles are preferably polymer particles. As the material of the polymer particles, for example, silicone resins, (meth) acrylic resins (for example, polymethyl methacrylate), polystyrene resins, polyurethane resins, and melamine resins can be listed. These resins have excellent dispersibility relative to the matrix and an appropriate refractive index difference with the matrix, so that a polarizer protective film with excellent light diffusion performance can be obtained. Preferably, silicone resins and polymethyl methacrylate are used. The shape of the light diffusing particles can be, for example, spherical, flat, or irregular. The light diffusing particles can be used alone or in combination of two or more.

[0061] The volume average particle size of the light diffusing fine particles is preferably 1 μm to 10 μm, more preferably 1.5 μm to 6 μm. By setting the volume average particle size to the above range, a polarizer protective film having excellent light diffusing performance can be obtained. The volume average particle size can be measured using, for example, an ultracentrifugal automatic particle size distribution measuring device.

[0062] The refractive index of the light diffusing fine particles is preferably 1.30 to 1.70, more preferably 1.40 to 1.65.

[0063] As mentioned above, the refractive index n of the light diffusing fine particles is P Refractive index n M The absolute value of the difference between |n P -n M | is 0.05 or more.

[0064] Light diffusible particles can be, for example, core-shell particles having a core and a shell and having different refractive indices between the core and the shell, or so-called GRIN (gradient index) particles whose refractive index continuously changes from the center of the particle toward the outside. Core-shell particles and GRIN particles are recorded in, for example, Japanese Patent Laid-Open No. 6-347617 Gazette, Japanese Patent Laid-Open No. 2003-262710 Gazette, Japanese Patent Laid-Open No. 2002-212245 Gazette, Japanese Patent Laid-Open No. 2002-214408 Gazette, Japanese Patent Laid-Open No. 2002-328207 Gazette, Japanese Patent Laid-Open No. 2010-077243 Gazette, and Japanese Patent Laid-Open No. 2010-107616 Gazette. The records of these gazettes are cited in this specification as a reference.

[0065] Light diffusing particles such as Figure 1As shown, a refractive index modulation region 22 with a substantially continuous change in refractive index can be formed near the surface of the light diffusible microparticle 21 outside. The refractive index modulation region can be formed by, for example, introducing a specific ultrafine particle component into the matrix. If this is the structure, backscattering can be suppressed, and as a result, more excellent light diffusion performance can be achieved. The details of the light diffusible microparticles formed with the refractive index modulation region are recorded in, for example, Japanese Patent Publication No. 2012-88692, Japanese Patent Publication No. 2012-83741, Japanese Patent Publication No. 2012-83743, and Japanese Patent Publication No. 2012-83744. The records of these publications are cited in this specification as a reference.

[0066] The content of the light diffusing fine particles in the polarizer protective film is preferably 0.3 wt % to 50 wt %, more preferably 1 wt % to 30 wt %, and further preferably 2.5 wt % to 20 wt %. If the content of the light diffusing fine particles is within this range, a polarizer protective film having excellent light diffusing performance can be obtained.

[0067] A-4. Characteristics of polarizer protective film

[0068] The polarizer protective film preferably has substantially optical isotropy. In this specification, "substantially optically isotropy" means that the in-plane phase difference Re(550) is 0nm to 10nm. The in-plane phase difference Re(550) is more preferably 0nm to 5nm, further preferably 0nm to 3nm, and particularly preferably 0nm to 2nm. If the Re(550) of the polarizer protective film is in this range, it is possible to prevent the adverse effects on the display characteristics when the polarizing plate containing the polarizer protective film is applied to an image display device. It should be noted that Re(550) is the in-plane phase difference of the film measured at 23°C using light of a wavelength of 550nm. Re(550) is calculated using the formula Re(550) = (nx-ny) × d. Here, nx is the refractive index in the direction where the in-plane refractive index reaches the maximum (i.e., the slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and d is the thickness of the film (nm).

[0069] When the thickness of the polarizer protective film is 40 μm, the higher the light transmittance at 380 nm, the more preferred. Specifically, the light transmittance is preferably 75% or more, more preferably 80% or more, and further preferably 85% or more. If the light transmittance is within this range, the desired optical properties can be ensured. The light transmittance is measured, for example, by a method based on ASTM-D-1003.

[0070] The haze of the polarizer protective film is preferably 50% to 99%, more preferably 70% to 95%.

[0071] The polarizer protective film preferably has the following properties: When the light transmittance at 550 nm is 100%, the difference between the light transmittance at 450 nm and 650 nm and the light transmittance at 550 nm is preferably within ±5%, more preferably within ±2%.

[0072] Regarding the brightness viewing angle of the polarizer protective film, the brightness half-value angle (the angle at which the brightness becomes 50% of the front) is preferably 56° (28° on one side) or more, and more preferably 60° to 70° (30° to 35° on one side). Furthermore, the angle at which the brightness becomes 25% of the front is preferably 90° (45° on one side) or more, and more preferably 96° to 120° (48° to 60° on one side). According to an embodiment of the present invention, the polarizer protective film can be endowed with excellent diffusion properties, and the brightness viewing angle can be maintained wider.

[0073] The refractive index n of the polarizer protective film as a whole F It is preferably 1.3 to 1.8, and more preferably 1.4 to 1.6. When the refractive index of the polarizer protective film is within such a range, the refractive index difference with the low refractive index portion defined by point bonding of the polarizer in the polarizing plate can be within a desired range.

[0074] The moisture permeability of the polarizer protective film is preferably 300 g / m 2 24 hr or less, more preferably 250 g / m 2 24 hr or less, more preferably 200 g / m 2 24 hr or less, particularly preferably 150 g / m 2 ·24hr or less, most preferably 100g / m 2 · 24 hr or less. When the water vapor permeability of the polarizer protective film is within such a range, a polarizing plate having excellent durability and moisture resistance can be obtained.

[0075] B.Polarizing plate

[0076] The polarizer protection film of the present invention described in the above-mentioned item A can be applied to a polarizing plate. Therefore, the present invention also includes a polarizing plate using such a polarizer protection film. Figure 3Schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 200 shown in the figure has a polarizer 130, and the polarizer protective film 100 described in the above-mentioned item A which is laminated on the polarizer 130 by means of an adhesive layer 120. The polarizer protective film 100 is configured in such a way that the surface having the above-mentioned concave-convex shape becomes the polarizer 130 side. The adhesive layer is composed of any and appropriate adhesive or adhesive. Typically, the adhesive layer is formed by a water-based adhesive (such as a vinyl alcohol-based adhesive) or an active energy ray-curable adhesive. Typically, the adhesive layer is formed by an acrylic adhesive. In practice, another protective film 140 is arranged on the side of the polarizer opposite to the protective film 100. In practice, an adhesive layer 150 is further provided as the outermost layer so that the polarizing plate can be attached to the image display unit. It should be noted that a separator (not shown) is temporarily bonded to the surface of the adhesive layer 150 in a removable manner to protect the adhesive layer and form a roll until the polarizing plate is actually used. Typically, the polarizing plate according to the embodiment of the present invention can be used as a back side polarizing plate of an image display device.

[0077] In the illustrated embodiment, a substantially low refractive index portion 110 (based on the above-mentioned point bonding) is defined at the interface between the polarizer 130 (substantially the adhesive layer 120) and the polarizer protective film 100, which is generated by the concave portion 32 of the concave-convex surface of the polarizer protective film. The refractive index n of the low refractive index portion is L It is preferably greater than 1.0 and less than 1.3, and more preferably greater than 1.0 and less than 1.2. The refractive index n of the low refractive index portion L The refractive index n of the polarizer protective film F The difference (n F -n L ) is preferably 0.2 or more, more preferably 0.25 or more. F -n L The upper limit of ) may be, for example, 0.4. It should be noted that the refractive index n of the low refractive index portion is L It is defined by the following formula.

[0078] n L =n M ×(100% - concave area ratio (%)) + air refractive index (1.0) × concave area ratio (%)

[0079] In one embodiment, the ratio T / H of the thickness T of the adhesive layer 120 to the height H of the convex portion in the concavo-convex shape is preferably 50% or less, and more preferably 30% or less. If the ratio T / H is within this range, good point bonding can be achieved. The lower limit of the ratio T / H can be, for example, 10%.

[0080] Any appropriate polarizer may be adopted as the polarizer. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

[0081] Specific examples of polarizers composed of a single-layer resin film include: polarizers obtained by dyeing and stretching hydrophilic polymer films such as polyvinyl alcohol (PVA) films, partially formalized PVA films, and partially saponified ethylene-vinyl acetate copolymer films with dichroic substances such as iodine and dichroic dyes; polyene-based oriented films such as dehydrated PVA and dehydrochlorinated polyvinyl chloride films, etc. From the perspective of excellent optical properties, it is preferred to use a polarizer obtained by dyeing a PVA film with iodine and uniaxially stretching it.

[0082] The above-mentioned iodine-based dyeing is carried out by, for example, immersing the PVA film in an iodine aqueous solution. The stretching ratio of the above-mentioned uniaxial stretching is preferably 3 to 7 times. The stretching can be carried out after the dyeing treatment, or it can be carried out while dyeing. In addition, it can also be dyed after stretching. As needed, the PVA film is subjected to swelling treatment, cross-linking treatment, cleaning treatment, drying treatment, etc. For example, by immersing the PVA film in water and washing it with water before dyeing, not only can the dirt and anti-blocking agent on the surface of the PVA film be washed away, but the PVA film can also be swollen to prevent uneven dyeing.

[0083] As a specific example of a polarizer obtained using a laminate, there can be cited a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate of a resin substrate and a PVA-based resin layer formed by coating the resin substrate. The polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by coating the resin substrate can be made by the following operations: for example, a PVA-based resin solution is applied to a resin substrate, dried to form a PVA-based resin layer on the resin substrate, and a laminate of the resin substrate and the PVA-based resin layer is obtained; the laminate is stretched and dyed to make the PVA-based resin layer into a polarizer. In the present embodiment, representatively, stretching includes immersing the laminate in an aqueous solution of boric acid and stretching it. Furthermore, stretching may also include, as needed, stretching the laminate in air at a high temperature (e.g., above 95°C) before stretching in an aqueous solution of boric acid. The obtained laminate of resin substrate / polarizer can be used directly (that is, the resin substrate can be used as a protective layer of polarizer), or the resin substrate can be peeled off from the laminate of resin substrate / polarizer, and any and appropriate protective layer consistent with the purpose can be laminated on the peeled surface for use. The details of the manufacturing method of such a polarizer are described in, for example, Japanese Patent Publication No. 2012-73580. All the records of the publication are cited in this specification as a reference.

[0084] The thickness of the polarizer is, for example, 1 μm to 80 μm. In one embodiment, the thickness of the polarizer is preferably 1 μm to 20 μm, and more preferably 3 μm to 15 μm.

[0085] C. Image display device

[0086] The polarizing plate described in item B above can be applied to an image display device. Therefore, the present invention also includes an image display device using such a polarizing plate. Typically, the image display device has the polarizing plate described in item B above on the back side. Typically, the polarizing plate is configured in such a way that the polarizer protective film described in item A above becomes the back side. As representative examples of image display devices, liquid crystal display devices and organic electroluminescent (EL) display devices can be listed. The image display device adopts a structure known in the industry, so the detailed description is omitted.

[0087] Example

[0088] The present invention is specifically described below by way of examples, but the present invention is not limited to these examples. The measuring methods of various properties are as follows. It should be noted that, unless otherwise specified, the "parts" and "%" in the examples are by weight.

[0089] (1) Cross-sectional area ratio of the concave portion

[0090] The cross-section of the polarizer protective film used in the examples and comparative examples was observed using a scanning electron microscope, and the overall cross-sectional area of ​​the concave and convex portions and the cross-sectional area of ​​the concave portions were measured from the image, and the ratio of the cross-sectional area of ​​the concave portions to the overall cross-sectional area of ​​the concave and convex portions was calculated. For the polarizer protective film without the concave and convex portions, the cross-sectional area ratio was set to zero (0).

[0091] (2) Brightness

[0092] The SJ8000 manufactured by LG was disassembled, and the liquid crystal panel with the polarizing plate was taken out. As the backlight side polarizing plate, the polarizing plate obtained in the embodiment and the comparative example was installed. In addition, for the light diffusion film provided in the backlight unit of the product, only the installation part was removed and reassembled. For the installed product obtained by the above operation, the brightness in the front direction was measured using Ezconstrast manufactured by ELDIM. The measured brightness is expressed as a ratio (%) when the front brightness when the polarizing plate and the light diffusion film are respectively provided is set to 100.

[0093] (3) Brightness viewing angle

[0094] The SJ8000 manufactured by LG was disassembled, and the liquid crystal panel with the polarizing plate was taken out. As the backlight side polarizing plate, the polarizing plate obtained in the embodiment and the comparative example was installed. In addition, for the light diffusion film provided in the backlight unit of the product, only the installation part was removed and reassembled. For the installed product obtained by the above operation, the brightness was measured using Ezconstrast manufactured by ELDIM. The angle at which the brightness of 25% is reached when the brightness in the front direction is set to 100% is measured on both sides of the diffusion, and the angle obtained by adding the angles on both sides is set as the brightness viewing angle. The measured brightness viewing angle is expressed as a ratio (%) when the brightness viewing angle when the polarizing plate and the light diffusion film are placed separately is set to 100.

[0095] <Example 1>

[0096] (Production of polarizer protective film)

[0097] 9 parts of silicone resin particles (volume average particle size of 4.5 μm) as light diffusing particles were added to 100 parts of methacrylic resin (manufactured by KURARAY Co., Ltd., product name "PARAPET HR-S") in a single screw extruder, melt-extruded at 260° C., and a concavo-convex shape was formed on one surface with an embossing roll to obtain a film with a thickness of 50 μm. The cross-sectional area ratio of the concave portion was 70%, and the height of the convex portion was 10 μm.

[0098] (Production of polarizing plate)

[0099] 1. Production of polarizer

[0100] As the resin substrate, a long amorphous polyethylene terephthalate film (thickness: 100 μm) having a water absorption of 0.60%, a Tg of 80° C., and an elastic modulus of 2.5 GPa was used.

[0101] One side of the resin substrate was subjected to corona treatment (treatment conditions: 55 W·min / m 2 ), and at room temperature, the corona treated surface is coated with an aqueous solution comprising 90 parts by weight of polyvinyl alcohol (degree of polymerization: 4200, degree of saponification: 99.2 mol %), 10 parts by weight of acetoacetyl-modified PVA (degree of polymerization: 1200, degree of acetoacetyl modification: about 5%, degree of saponification: 99.0 mol % or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name: "GOHSEFIMER Z200"), and 13 parts by weight of potassium iodide, and dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm to produce a laminate.

[0102] The obtained laminate was subjected to free-end uniaxial stretching to 2.4 times in the longitudinal direction (longitudinal direction) between rollers having different peripheral speeds in an oven at 140° C. (assisted stretching in air).

[0103] Next, the laminate was immersed in an insolubilization bath (boric acid aqueous solution prepared by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (insolubilization treatment).

[0104] Next, the sample was immersed in a dyeing bath (an iodine aqueous solution prepared by mixing 0.4 parts by weight of iodine and 3.0 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 30° C. for 60 seconds (dyeing treatment).

[0105] Next, the sample was immersed in a crosslinking bath (boric acid aqueous solution prepared by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (crosslinking treatment).

[0106] Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 3.0 wt %) at a liquid temperature of 70°C and uniaxially stretched (underwater stretching) along the longitudinal direction (length direction) between rollers having different circumferential speeds to a total stretching ratio of 5.5 times.

[0107] Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution prepared by mixing 4 parts by weight of potassium iodide with respect to 100 parts by weight of water) at a liquid temperature of 30° C. (cleaning treatment).

[0108] In this manner, a polarizer having a thickness of 5 μm was formed on the resin substrate.

[0109] 2. Production of polarizing plate

[0110] On the surface of the polarizer of the laminate of the resin substrate / polarizer obtained above, the concave-convex surface of the polarizer protective film is pasted by point bonding with the help of a polyvinyl alcohol-based adhesive (thickness 2 μm). Next, the resin substrate is peeled off, and a methacrylic resin film (thickness 40 μm) is pasted on the peeled surface with the help of a polyvinyl alcohol-based adhesive. It should be noted that the methacrylic resin film is made by putting a methacrylic resin (manufactured by KURARAY, product name "PARAPETHR-S") into a single screw extruder and melt-extruding it at 260°C.

[0111] In this manner, a polarizing plate was obtained. The refractive index of the substantially predetermined low refractive index portion of the polarizing plate was 1.15. The obtained polarizing plate was subjected to the evaluations of (2) and (3) above. The results are shown in Table 1.

[0112] <Example 2>

[0113] The same operation as in Example 1 was performed except that the embossing roller was changed to prepare a polarizer protective film having a cross-sectional area ratio of the concave portion of 55%. The same operation as in Example 1 was performed except that the polarizer protective film was used to prepare a polarizing plate. The refractive index of the low refractive index portion substantially defined in the polarizing plate was 1.22. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0114] <Comparative Example 1>

[0115] The same operation as in Example 1 was performed except that the embossing roller was changed to prepare a polarizer protective film having a cross-sectional area ratio of 30% of the concave portion. The same operation as in Example 1 was performed except that the polarizer protective film was used to prepare a polarizing plate. The refractive index of the low refractive index portion substantially defined in the polarizing plate was 1.34. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0116] <Comparative Example 2>

[0117] A polarizer protective film without a concavoconvex surface was prepared in the same manner as in Example 1 except that the embossing roller was not used. A polarizer protective film was prepared in the same manner as in Example 1 except that the polarizer protective film was used. The obtained polarizer was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

[0118] [Table 1]

[0119] Concave cross-sectional area ratio brightness(%) Brightness viewing angle (%) Benchmarks Place separately 100 100 Example 1 70％ 88 110 Example 2 55％ 84 108 Comparative Example 1 30％ 75 106 Comparative Example 2 zero 85 100

[0120] <Evaluation>

[0121] It is clear from Table 1 that the embodiments of the present invention can maintain the front brightness to an acceptable level and widen the brightness viewing angle when the polarizing plate and the light diffusion film are separately provided as a reference. That is, it can be seen that according to the embodiments of the present invention, a polarizer protective film that is endowed with a light diffusion function without reducing the brightness viewing angle can be realized.

[0122] Industrial Applicability

[0123] The polarizer protective film of the present invention can be applied to polarizing plates. The polarizing plates of the present invention can be applied to image display devices. The image display devices of the present invention can be used for portable devices such as portable information terminals (PDAs), smart phones, mobile phones, watches, digital cameras, portable game consoles, etc.; office automation equipment such as computer monitors, notebook computers, and copiers; household electrical appliances such as camcorders, televisions, and microwave ovens; vehicle-mounted equipment such as rear-view displays, displays for car navigation systems, and car audio systems; display equipment such as digital signage and store information displays; security equipment such as monitoring displays; nursing / medical equipment such as nursing displays and medical displays, etc., and various other uses.

[0124] Description of Reference Numerals

[0125] 10 Matrix

[0126] 20 Light diffusing particles

[0127] 30 Concave and convex surface

[0128] 31 convex part

[0129] 32 recess

[0130] 100 Polarizer protective film

[0131] 120 Adhesive layer

[0132] 130 polarizer

[0133] 200 polarizing plate

Claims

1. A polarizer protective film, comprising a resin film, the resin film comprising a resin as a matrix and light diffusing fine particles dispersed in the matrix, The surface of the polarizer protective film has a concavoconvex shape, The ratio B / A of the cross-sectional area B of the concave portion to the overall cross-sectional area A of the concave-convex portion is 50% or more, When viewed from above, the convex portions of the concavo-convex shape have intersections, The area ratio of the recessed portion to the entire area when viewed from above is 50% or more, The polarizer protective film has a brightness half-value angle of 56° or more.

2. The polarizer protective film according to claim 1, wherein: The refractive index n of the matrix M The refractive index n of the light diffusing fine particles P The following relationship is satisfied: |n P -n M |≥0.05。 3. The polarizer protective film according to claim 1 or 2, wherein: The height H of the convex portion in the concavo-convex shape is 3 μm or more.

4. The polarizer protective film according to claim 1 or 2, wherein: The convex parts of the concavo-convex shape contain the light diffusing fine particles.

5. A polarizing plate comprising: a polarizer, and the polarizer protective film according to any one of claims 1 to 4 laminated on the polarizer via an adhesive layer, The polarizer protection film is disposed so that the surface having the concavo-convex shape faces the polarizer side.

6. The polarizing plate according to claim 5, wherein: A low refractive index portion caused by the concave portion of the concavo-convex shape is defined at an interface between the polarizer and the polarizer protective film.

7. The polarizing plate according to claim 6, wherein: The refractive index n of the polarizer protective film is F The refractive index n of the low refractive index portion L The difference is n F -n L It is 0.2 or more.

8. The polarizing plate according to any one of claims 5 to 7, wherein A ratio T / H of a thickness T of the adhesive layer to a height H of a convex portion in the concavo-convex shape is 50% or less. 9 . An image display device comprising the polarizing plate according to claim 5 on a back side.

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