TWI801688B - Polarizer protective film, polarizing plate, and image display device - Google Patents

Abstract

The invention provides a protective film for a polarizer with light diffusion function without narrowing the viewing angle of brightness. The polarizer protective film of the present invention is composed of a resin film, and the resin film includes a resin as a matrix and light-diffusing fine particles dispersed in the matrix; The ratio B/A of the area B to the overall cross-sectional area A is 50% or more.

Description

Polarizer protective film, polarizing plate, and image display device

The invention relates to a polarizer protective film, a polarizer and an image display device.

Background of the invention In recent years, there has been a strong demand for thinning and design (eg, narrower frame) of image display devices (eg, liquid crystal display devices, organic EL display devices). Accordingly, the requirements for the integration and/or functional integration of optical components and/or optical films used in image display devices have also increased. As an example of the above-mentioned integration or functional integration, there is a proposal to attach a light-diffusing film directly to the polarizer to give the polarizer a light-diffusing function. However, the proposed technique suffers from a problem of reduced brightness viewing angle.

prior art literature patent documents Patent Document 1: Japanese Patent Laid-Open No. 2012-118235 Patent Document 2: Japanese Patent Laid-Open No. 2009-025774

Summary of the invention The problem to be solved by the invention The present invention is made to solve the above-mentioned conventional problems, and its main purpose is to provide a polarizer protective film having a light-diffusing function without narrowing the viewing angle of brightness.

Means for Solving the Problems The polarizer protective film of the present invention is composed of a resin film, and the resin film includes a resin as a matrix and light-diffusing fine 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 to the cross-sectional area A of the whole in the concave-convex part is 50% or more. In one embodiment, the refractive index n _M of the matrix and the refractive index n _P of the light-diffusing fine particles satisfy the following relationship: |n _P −n _M |≧0.05. In one embodiment, the height H of the convex portion in the above-mentioned concavo-convex shape is 3 µm or more. In one embodiment, the convex portion of the polarizer protective film in the concave-convex shape contains the light-diffusing fine particles. In one embodiment, when the polarizer protective film is viewed in plan, the protrusions in the uneven shape have intersections. In one embodiment, the polarizer protective film has an area ratio of 50% or more of the concave portion with respect to the entire area of the polarizer protective film in plan view. According to another aspect of the present invention, a polarizer can be provided. The polarizing plate has a polarizing element and the above-mentioned polarizing element protective film that passes through and is laminated on the polarizing element. The polarizer protective film is arranged such that the surface having the above-mentioned concavo-convex shape becomes the polarizer side. In one embodiment, a substantial low-refractive-index portion derived from the concave portion of the concave-convex shape is defined at the interface between the polarizer and the polarizer protective film. In one embodiment, the difference ₍ n _F −n L ) between the refractive index n _L of the low refractive index portion and the refractive index n _F of the polarizer protective film is 0.2 or more. In one embodiment, the ratio T/H of the thickness T of the adhesive layer to the height H of the convex portion in the concave-convex shape is 50% or less. According to another aspect of the present invention, an image display device can be provided. This image display device includes the above-mentioned polarizing plate on the back side.

Invention effect According to the present invention, the light-diffusing fine particles are dispersed in the polarizer protective film, and an uneven shape is formed on at least one surface thereof, and the cross-sectional area ratio of the concave portion in the uneven shape is set to be more than a predetermined value, thereby realizing a non-polarizing film. A polarizer protective film that narrows the viewing angle of brightness and has a light-diffusing function.

form for carrying out the invention Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited by these embodiments. In addition, the drawings are schematically shown for easy recognition, and the ratio of length, width, and thickness, unevenness, and fineness are different from actual ones.

A. Polarizer Protective Film A-1. Overall Structure FIG. 1 is a schematic cross-sectional view of a polarizer protective film according to an embodiment of the present invention. The polarizer protective film 100 of the illustrated example is composed of a resin film including a resin as a matrix 10 and light-diffusing fine particles 20 dispersed in the matrix 10 . According to such a structure, light-diffusion performance can be imparted to the polarizer protective film itself. As a result, the polarizer protective film can also serve as a light-diffusing film, and since the polarizer protective film becomes a part of the polarizer, it is possible to simultaneously impart light-diffusing performance to the polarizer and significantly reduce thickness. The refractive index n _M of the matrix and the refractive index n _P of the light-diffusing microparticles satisfy the following relationship: |n _P -n _M |≧0.05. |n _P -n _M | is preferably at least 0.07, more preferably at least 0.10. The upper limit of |n _P -n _M | may be 0.20, for example. As long as it is the said structure, favorable light-diffusion performance can be realizable. In addition, the resin constituting the matrix and light-diffusing fine particles will be described later in A-2 and A-3, respectively.

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 convex portions 31 and concave portions (air portions or void portions) 32 . The ratio B/A of the cross-sectional area B of the concave portion to the cross-sectional area A of the entire concave-convex surface is 50% or more, typically more than 50%, preferably 60% or more, preferably 70% or more. The upper limit of the ratio B/A may be 90%, for example. If the ratio B/A is in the above range, sufficient brightness can be exhibited, and a wide brightness viewing angle can be maintained, and good diffusion performance can be imparted to the polarizer protective film, and at the same time, polarization can be ensured when the polarizer protective film is laminated on the polarizer. Adhesion strength between protective film and polarizer. In addition, the overall cross-sectional area A of the concave-convex surface is the partial area surrounded by the line connecting the surface of the convex part, the line connecting the bottom of the concave part, and the line in the up-down direction of both ends of the film (for reference, the outside of this part is surrounded by a dotted line and As shown in Figure 1), the cross-sectional area B of the concave portion is the sum of the cross-sectional area of each concave portion 32 (the area surrounded by the line adjacent to the wall of the convex portion, the line connecting the surface of the convex portion, and the line connecting the bottom of the concave portion) . The ratio B/A may correspond to void ratio.

The height H of the convex portion 31 in the uneven surface is preferably 3 µm or more, preferably 5 µm or more, more preferably 10 µm or more. The upper limit of the height H of the convex part may be 15 µm, for example. As long as the height of the convex portion is within the above 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 can be attached to the polarizer. In addition, in this specification, only the bonding of convex parts may be called "point bonding" expediently. By the spot bonding, a substantial low-refractive index portion originating from a concave portion (air portion or void portion) can be defined in the vicinity of the spot bonding portion. As a result, good light-diffusing performance can be achieved, and at the same time, the luminance viewing angle can be increased. Conventionally, in an image display device, a polarizer (polarizer) and a light-diffusing film are disposed separately, and as a result, an air layer is sandwiched between the polarizer and the light-diffusing film. The air layer will become an obstacle to thinning, but on the other hand, the retroreflection of the air layer can greatly maintain the brightness viewing angle. Integrating the polarizing plate and the light-diffusing film can achieve thinning and functional integration, but the removal of the above-mentioned air layer will reduce the brightness and viewing angle. By forming the low-refractive-index portion in the vicinity of the point bonding portion, light can be efficiently retroreflected similarly to the case where an air layer exists. Therefore, according to the embodiment of the present invention, the polarizer protective film can be endowed with light diffusion performance, and the required light diffusion performance can be provided to the polarizing plate by forming dots, while maintaining a large (wide) brightness viewing angle. In addition, according to the embodiment of the present invention, the polarizer protective film itself has light diffusing properties and doubles as a light diffusing film, so that significant thinning can be achieved by synergistic effect with the effect of excluding the air layer.

Arbitrary and appropriate shapes can be adopted for the plan view shape of the convex portion 31 of the concave-convex surface. The plan view shape of the convex part is shown in FIG. 2, for example, and it may be a regular shape (for example, grid shape), or it may be an irregular shape. The convex portion 31 preferably has an intersection C in plan view as shown in FIG. 2 . In other words, the convex portion extends in two or more directions. The pitch between the convex parts (the distance between the convex parts) is preferably 1000 µm or less, preferably 500 µm or less, more preferably 100 µm or less. When the plan view shape of the convex part is regular, it is also possible to set a deviation of 1 degree to 90 degrees in the angle. When the top view shape of the convex portion is irregular, the pitch means the average pitch, and it is preferable to have a distribution of more than 50% within ±50% of the average pitch. According to the above structure, when the polarizer protective film is laminated on the polarizer, the adhesive strength between the polarizer protective film and the polarizer can be ensured, and a good display quality can be ensured.

The area ratio of the concave portion 32 is preferably 50% or more, preferably 60% or more, more preferably 70% or more, relative to the overall area of the concave-convex surface when viewed from above. The upper limit of the area ratio of the concave portion may be, for example, 90%. As long as the area ratio of the concave portion is within the above range, a wide viewing angle of brightness can be maintained, good diffusion performance can be given to the polarizer protective film, and the gap between the polarizer protective film and the polarizer can be ensured when the polarizer protective film is laminated on the polarizer. Then intensity.

In one embodiment, as shown in FIG. 1 , the light-diffusing fine particles 20 are included in the convex portion 31 . With such a configuration, more excellent diffusion performance can be imparted, and even with a uniform concave-convex pattern, optical interference unevenness with pixels of a liquid crystal panel and the like can be reduced.

The concave-convex surface (concave-convex shape) can be formed by any appropriate method. The concavo-convex shape can be formed by, for example, roughening or a method of imparting concavo-convexity with fine particles. Specific examples of the roughening method include embossing and sandblasting. The concave-convex surface (concave-convex shape) can be formed by giving shape to the surface of the melt-extruded film with an embossing roll.

A-2. Matrix As the resin constituting the matrix, any appropriate resin that can form a polarizer protective film can be used. Specific examples of the resin include (meth)acrylic resins, polyester resins (such as polyethylene terephthalate (PET)), cycloolefin-based resins (such as norbornene-based resins), cellulose resins (such as triacetyl cellulose (TAC)), polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether resins, polycarbonate resins, Polystyrene resin, polyolefin resin, acetate resin. These resins may be used alone or in combination of two or more. From the viewpoint of optical properties, transparency, and versatility, (meth)acrylic resins, polyester resins, and cycloolefin resins are preferable, and (meth)acrylic resins are more preferable. In addition, in this specification, "(meth)acryl" means acryl and/or methacryl.

Arbitrary and appropriate (meth)acrylic resin can be used for (meth)acrylic resin. In addition, for simplification, only (meth)acrylic resin is called an acrylic resin below. Acrylic resins typically contain an alkyl (meth)acrylate as a main component as a monomer unit. Examples of the alkyl (meth)acrylate constituting the main skeleton of the acrylic resin include linear or branched alkyl groups having 1 to 18 carbon atoms. These may be used alone or in combination. In addition, arbitrary and appropriate comonomers can also be introduced by copolymerization in an acrylic resin. The kind, quantity, copolymerization ratio, etc. of the said comonomer can be set suitably according to the objective. The constituents (monomer units) of the main skeleton of the acrylic resin will be described in detail later with reference to the general formula (2).

The acrylic resin preferably has at least one selected from glutarimide units, lactone ring units, maleic anhydride units, maleimide units, and glutaric anhydride units. The acrylic resin having a lactone ring unit has been described in, for example, Japanese Patent Application Laid-Open No. 2008-181078, and this specification uses the description of this publication as a reference. The glutarimine unit is preferably shown in the following general formula (1):

[chemical formula 1]

In the general formula (1), R ¹ and R ² independently represent hydrogen or an alkyl group with 1 to 8 carbons, and R ³ represents an alkyl group with 1 to 18 carbons, a cycloalkyl group with 3 to 12 carbons, or an alkyl group with 1 to 8 carbons. Aryl group of 6~10. In the general formula (1), ideally, ^R1 and ^R2 are independently hydrogen or methyl, and ^R3 is hydrogen, methyl, butyl or cyclohexyl. More desirably ^R1 is methyl, ^R2 is hydrogen and ^R3 is methyl.

The above-mentioned alkyl (meth)acrylate can be represented by the following general formula (2):

[chemical formula 2]

In the general formula (2), R ⁴ represents a hydrogen atom or a methyl group, and R ⁵ represents a hydrogen atom or an aliphatic or alicyclic hydrocarbon group with 1 to 6 carbon atoms that may be substituted. Examples of substituents 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, (meth)acrylate Base) tert-butyl acrylate, n-hexyl (meth)acrylate, cyclohexyl (meth)acrylate, chloromethyl (meth)acrylate, 2-chloroethyl (meth)acrylate, (meth)acrylic acid 2-Hydroxyethyl ester, 3-hydroxypropyl (meth)acrylate, 2,3,4,5,6-pentahydroxyhexyl (meth)acrylate and 2,3,4,5-(meth)acrylate tetrahydroxypentyl ester. In the general formula (2), R ⁵ is preferably a hydrogen atom or a methyl group. Therefore, the alkyl (meth)acrylate is particularly preferably methyl acrylate or methyl methacrylate.

The above-mentioned acrylic resin may contain only a single glutarimide unit, or may contain multiple glutarimide units in which R ¹ , R ² and R ³ in the above general formula (1) are different from each other.

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

The above-mentioned acrylic resin may contain only a single alkyl (meth)acrylate unit, or may contain a plurality of alkyl (meth)acrylate units in which R ⁴ and R ⁵ in the above general formula (2) are different from each other.

The content ratio of the alkyl (meth)acrylate unit in the acrylic resin is preferably 50 mol % to 98 mol %, more preferably 55 mol % to 98 mol %, more preferably 60 mol % ~98 mol%, especially 65 mol%~98 mol%, most preferably 70 mol%~97 mol%. If the content ratio is less than 50 mol%, the effects derived from the alkyl (meth)acrylate unit (for example, high heat resistance, high transparency) may not be fully exhibited. If the above-mentioned content ratio exceeds 98 mol %, the resin may become brittle and easily cracked, and the high mechanical strength may not be fully exerted, thereby deteriorating productivity.

The above-mentioned acrylic resin may contain units other than glutarimide units and alkyl (meth)acrylate units.

In one embodiment, the acrylic resin may contain, for example, 0% to 10% by weight of unsaturated carboxylic acid units that do not involve intramolecular imidization described later. The content ratio of the unsaturated carboxylic acid unit is preferably 0% by weight to 5% by weight, more preferably 0% by weight to 1% by weight. Transparency, retention stability, and moisture resistance can be maintained as long as the content is within the above range.

唑啉、2-乙烯基-

唑啉、2-丙烯醯基-

唑啉、N-苯基馬來醯亞胺、甲基丙烯酸苯基胺乙酯、苯乙烯、α-甲基苯乙烯、對環氧丙基苯乙烯、對胺基苯乙烯、2-苯乙烯基-

唑啉等。該等可單獨使用亦可併用。宜為苯乙烯、α-甲基苯乙烯等苯乙烯系單體。其他乙烯基系單體單元的含有比率宜為0~1重量%，較宜為0~0.1重量%。只要在所述範圍內，即可抑制展現非預期之相位差及透明性降低。In one embodiment, the acrylic resin may contain a copolymerizable vinyl monomer unit (other vinyl monomer unit) other than the above. Other vinyl monomers include: acrylonitrile, methacrylonitrile, ethacrylonitrile (Ethacrylonitrile), allyl glycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleic acid imine, N-ethylmaleimide, N-cyclohexylmaleimide, aminoethyl acrylate, propylamineethyl acrylate, dimethylaminoethyl methacrylate, ethyl methacrylate Aminopropyl, Cyclohexylaminoethyl Methacrylate, N-Vinyldiethylamine, N-Acetylvinylamine, Allylamine, Methallylamine, N-Methallylamine Amine, 2-isopropenyl-

Azoline, 2-vinyl-

Azoline, 2-acryloyl-

Azoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, 2-styrene base-

oxazoline etc. These may be used alone or in combination. Styrenic monomers such as styrene and α-methylstyrene are preferred. The content ratio of other vinyl monomer units is preferably 0 to 1% by weight, more preferably 0 to 0.1% by weight. As long as it is within the range, it is possible to suppress development of an unexpected phase difference and decrease in transparency.

The imidization rate in the above-mentioned acrylic resin is preferably 2.5%-20.0%. As long as the imidization rate is within the above range, a resin excellent in heat resistance, transparency, and moldability can be obtained, and sintering or lowering of mechanical strength during film formation can be prevented. In the above-mentioned acrylic resin, the imidization rate is expressed by the ratio of glutarimide units to alkyl (meth)acrylate units. This ratio can be obtained, for example, from NMR mass spectrum, IR spectrum, etc. of an acrylic resin. In the present embodiment, the imidization ratio can be obtained by ¹ H-NMR measurement of the resin using ¹ HNMR BRUKER Avance III (400 MHz). More specifically, the peak area of the alkyl (meth)acrylate derived from O- _CH3 protons around 3.5ppm to 3.8ppm can be set to be A, and the glutarimide around 3.0ppm to 3.3ppm can be set to The peak area derived from the N—CH ₃ proton is B, and is obtained by the following formula. Imidization rate Im(%)＝{B/(A+B)}×100

The Tg (glass transition temperature) of the acrylic resin is preferably above 110°C, more preferably above 115°C, more preferably above 120°C, especially preferably above 125°C, most preferably above 130°C. When Tg is 110° C. or higher, a polarizing plate including a polarizer protective film made of the resin tends to be excellent in durability. The upper limit of Tg is preferably below 300°C, more preferably below 290°C, more preferably below 285°C, especially preferably below 200°C, most preferably below 160°C. As long as Tg is within the above range, formability is good.

The above-mentioned acrylic resin can be produced, for example, by the following method. The method comprises: (1) combining an alkyl (meth)acrylate monomer corresponding to an alkyl (meth)acrylate unit represented by general formula (2), and an unsaturated carboxylic acid monomer and/or its precursor copolymerization of monomers to obtain copolymer (a); and (II) by treating the copolymer (a) with an imidization agent, the alkyl (meth)acrylate monomer in the copolymer (a) Intramolecular imidization reaction between the unit and the unsaturated carboxylic acid monomer and/or its precursor monomer unit, and the glutarimide unit represented by the general formula (1) is introduced into the copolymer.

The details of the acrylic resin and its production method are described in, for example, Japanese Patent Laid-Open No. 2018-155812 and Japanese Patent Laid-Open No. 2018-155813. This manual refers to the records of these publications as a reference.

A-3. Light-diffusing fine particles Arbitrary and appropriate ones can be used for the light-diffusing fine particles. Specific examples include inorganic fine particles and polymer fine particles. The light-diffusing fine particles are preferably polymer fine particles. The material of the polymer microparticles can be, for example, polysiloxane resin, (meth)acrylic resin (such as polymethyl methacrylate), polystyrene resin, polyurethane resin, and melamine resin. These resins have excellent dispersibility to the matrix and have an appropriate refractive index difference with the matrix, so a polarizer protective film with excellent light diffusion performance can be produced. Ideal for silicone resin, polymethyl methacrylate. The shape of the light-diffusing fine particles may be, for example, spherical, flat, or irregular. The light-diffusing fine particles may be used alone or in combination of two or more.

The volume average particle diameter of the light-diffusing microparticles is preferably 1 µm to 10 µm, more preferably 1.5 µm to 6 µm. By setting the volume average particle diameter within the above range, a polarizer protective film having excellent light diffusing performance can be obtained. The volume average particle size can be measured, for example, using an ultracentrifugal automatic particle size distribution analyzer.

The refractive index of the light-diffusing fine particles is preferably 1.30-1.70, more preferably 1.40-1.65.

The absolute value |n _P -n _M | of the difference between the refractive index n _P of the light-diffusing fine particle and the refractive index n _M of the matrix is 0.05 or more as described above.

The light-diffusing microparticles may be, for example, core-shell microparticles having an inner core and an outer shell in which the refractive indices of the inner core and the outer shell are different, or GRIN (gradient index: progressive refractive index) in which the refractive index continuously changes from the center of the microparticle toward the outside. microparticles. Core-shell particles and GRIN particles have been described in, for example, Japanese Patent Laid-Open No. 6-347617, Japanese Patent Laid-Open No. 2003-262710, Japanese Patent Laid-Open No. 2002-212245, and Japanese Patent Laid-Open No. 2002-214408 , Japanese Patent Laid-Open No. 2002-328207, Japanese Patent Laid-Open No. 2010-077243, and Japanese Patent Laid-Open No. 2010-107616. This manual refers to the records of these publications as a reference.

As shown in FIG. 1 , the light-diffusing fine particles may have a refractive index modulation region 22 in which the refractive index changes substantially continuously outside the surface vicinity of the light-diffusing fine particles 21 . The refractive index modulation region can be formed, for example, by introducing specific ultrafine particle components into the matrix. With such a configuration, backscattering can be suppressed, and as a result, more excellent light diffusion performance can be realized. The details of the light-diffusing fine particles having the refractive index modulation region are described in, for example, Japanese Patent Laid-Open No. 2012-88692, Japanese Patent Laid-Open No. 2012-83741, and Japanese Patent Laid-Open No. 2012-83743. , Japanese Patent Application Laid-Open No. 2012-83744. This manual refers to the records of these publications as a reference.

The content of the light-diffusing fine particles in the polarizer protective film is preferably 0.3% by weight to 50% by weight, more preferably 1% by weight to 30% by weight, more preferably 2.5% by weight to 20% by weight. As long as the content of the light-diffusing fine particles is within the above range, a polarizer protective film having excellent light-diffusing performance can be produced.

A-4. Characteristics of Polarizer Protective Film The polarizer protective film is preferably substantially optically isotropic. In this specification, "being substantially optically isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm. The in-plane retardation Re(550) is preferably 0 nm to 5 nm, more preferably 0 nm to 3 nm, especially preferably 0 nm to 2 nm. As long as the Re(550) of the polarizer protective film is within the above range, when a polarizing plate including the polarizer protective film is applied to an image display device, adverse effects on display characteristics can be prevented. In addition, Re(550) is the in-plane retardation of the film measured at 23°C with light having a wavelength of 550nm. Re(550) can be obtained by the formula: Re(550)=(nx-ny)×d. Here, nx is the refractive index in the direction where the in-plane refractive index is the largest (that is, the direction of the slow axis), ny is the refractive index in the direction that is perpendicular to the slow axis in the plane (that is, the direction of the fast axis), and d is Film thickness (nm).

The thickness of the polarizer protective film is 40µm, and the higher the light transmittance at 380nm, the better. Specifically, the light transmittance should be above 75%, more preferably above 80%, more preferably above 85%. As long as the light transmittance is within the range, desired optical characteristics can be ensured. The light transmittance can be measured, for example, according to the method of ASTM-D-1003.

The haze of the polarizer protective film should be 50%~99%, more preferably 70%~95%.

The polarizer protective film preferably has the following characteristics. When the transmittance at 550nm is 100%, the difference between the transmittance at 450nm and 650nm and the transmittance at 550nm should be within ±5%, more preferably within ±2%.

Regarding the brightness viewing angle of the polarizer protective film, the brightness half-value angle (the angle at which the brightness is 50% of the front side) should be above 56° (28° on one side), preferably 60°~70° (30°~35° on one side) °). In addition, the angle at which the brightness is 25% of the front surface should be more than 90° (45° on one side), more preferably 96°~120° (48°~60° on one side). According to the embodiment of the present invention, excellent diffusion performance can be imparted to the polarizer protective film, and a wide brightness viewing angle can be maintained.

The overall refractive index n _F of the polarizer protective film is preferably 1.3-1.8, more preferably 1.4-1.6. As long as the refractive index of the polarizer protective film is within the above-mentioned range, the difference in refractive index between the polarizer and the polarizer can be made within the required range in the low refractive index portion defined next to the polarizer.

The moisture permeability of the polarizer protective film should be below 300g/m ² ·24hr, more preferably below 250g/ ^m2 ·24hr, more preferably below 200g/ ^m2 ·24hr, especially below 150g/ ^m2 ·24hr, The optimum is below 100g/m ² · 24hr. A polarizing plate excellent in durability and moisture resistance can be obtained as long as the moisture permeability of the polarizer protective film is within the above range.

B. Polarizer The polarizer protective film of the present invention described in the above item A can be applied to a polarizing plate. Therefore, the present invention also includes a polarizing plate using the polarizer protective film. Fig. 3 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention. The polarizing plate 200 shown in the illustration has a polarizer 130 and the polarizer protective film 100 laminated on the polarizer 130 through the adhesive layer 120 in item A above. The polarizer protective film 100 is arranged such that the surface having the aforementioned concavo-convex shape is on the polarizer 130 side. The adhesive layer may be composed of any and appropriate adhesive or adhesive. Typically, the adhesive layer can be formed with a water-based adhesive (such as a vinyl alcohol-based adhesive) or an active energy ray-curable adhesive. The adhesive layer represents that the top is formed with an acrylic adhesive. Practically, another protective film 140 is disposed on the opposite side of the polarizer to the protective film 100 . Practically, an adhesive layer 150 is provided as the outermost layer, so that it can be attached to the image display unit of the polarizer. In addition, a separator (not shown) is temporarily adhered on the surface of the adhesive layer 150 in a detachable state, which can protect the adhesive layer until the polarizer is actually used, and can be formed into a roll. 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.

In the embodiment shown in the drawing, the interface between the polarizer 130 (essentially the adhesive layer 120) and the polarizer protective film 100 is defined to be formed by the concave portion 32 on the concave-convex surface of the polarizer protective film (formed by the above point bonding) Substantial low refractive index portion 110 . The refractive index n _L of the low refractive index portion is preferably greater than 1.0 and not greater than 1.3, more preferably greater than 1.0 and not greater than 1.2. The difference (n _F −n _L ) between the refractive index n _L of the low refractive index portion and the refractive index n _F of the polarizer protective film is preferably 0.2 or more, more preferably 0.25 or more. The upper limit of the difference (n _F -n _L ) can be 0.4, for example. In addition, the refractive index n _L of the low refractive index portion can be defined by the following formula. n _L =n _M ×(100%-recess area ratio (%))+air refractive index (1.0)×recess area ratio (%)

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, more preferably 30% or less. If the ratio T/H is within the above-mentioned range, good dot adhesion can be realized. The lower limit of the ratio T/H may be, for example, 10%.

Any suitable polarizer can be used 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.

Specific examples of polarizers composed of a single-layer resin film include polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, ethylene vinyl acetate, etc. Hydrophilic polymer films such as partially saponified ester copolymer films are dyed and stretched, and polyene-based oriented films such as dehydration-treated products of PVA or dehydrochloridized products of polyvinyl chloride, etc. From the viewpoint of excellent optical properties, it is preferable to use a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching it.

The above-mentioned dyeing with iodine can be carried out, for example, by immersing a PVA-based film in an iodine aqueous solution. The elongation ratio of the above-mentioned uniaxial stretching is preferably 3 to 7 times. The elongation may be performed after the dyeing treatment or simultaneously with the dyeing. In addition, dyeing after stretching is also possible. Swelling treatment, cross-linking treatment, cleaning treatment, drying treatment, etc. can be performed on PVA-based films according to requirements. For example, immersing the PVA-based film in water for washing before dyeing can not only clean the dirt and anti-adhesive agent on the surface of the PVA-based film, but also make the PVA-based film swell, thereby preventing uneven dyeing.

Specific examples of polarizers obtained by using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a laminate formed using a resin substrate and coating. A polarizer obtained from a laminate of PVA-based resin layers on the resin substrate. A polarizer obtained by using a laminate of a resin base material and a PVA-based resin layer coated on the resin base material can be produced, for example, by the following procedure: apply a PVA-based resin solution to the resin base material, and use It is dried to form a PVA-based resin layer on the resin substrate to obtain a laminate of the resin substrate and the PVA-based resin layer; the laminate is stretched and dyed to make the PVA-based resin layer into a polarizer. In this embodiment, stretching typically includes stretching by immersing the laminate in an aqueous solution of boric acid. In addition, if necessary, the stretching may further include stretching the laminate in air at a high temperature (for example, 95° C. or higher) before stretching in a boric acid aqueous solution. The obtained resin substrate/polarizer laminate can be used directly (that is, the resin substrate can be used as a protective layer of the polarizer), or the resin substrate can be peeled off from the resin substrate/polarizer laminate and placed on the peeled surface Depending on the purpose, an arbitrary and appropriate protective layer is laminated for later use. The details of the manufacturing method of the polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. In this specification, the entire description of this publication is incorporated by reference.

The thickness of the polarizer is, for example, 1 μm˜80 μm. In one embodiment, the thickness of the polarizer is preferably 1 µm-20 µm, more preferably 3 µm-15 µm.

C. Image display device The polarizing plate described in the above item B can be applied to an image display device. Therefore, the present invention also includes an image display device using the polarizing plate. The image display device typically has the polarizing plate described in item B above on the back side. This polarizing plate is representatively placed on the upper side so that the polarizer protective film described in the above item A is on the back side. Representative examples of image display devices include liquid crystal display devices and organic electroluminescence (EL) display devices. The image display device can adopt a well-known structure in the industry, so detailed description is omitted. Example

Hereinafter, the present invention will be specifically described with examples, but the present invention is not limited by these examples. The measuring method of each characteristic is as follows. In addition, unless otherwise noted, "parts" and "%" in the examples are based on weight.

(1) The cross-sectional area ratio of the concave part The cross-section of the polarizer protective film used in Examples and Comparative Examples was observed with a scanning electron microscope, and the overall cross-sectional area of the concave-convex portion and the cross-sectional area of the concave portion were measured from the image, and the ratio of the overall cross-sectional area of the concave-convex portion to the total cross-sectional area of the concave-convex portion was obtained. The cross-sectional area ratio of the recess. The cross-sectional area ratio was set to zero (0) for the polarizer protective film in which the concavo-convex portion was not formed. (2) Brightness SJ8000 manufactured by LG Corporation was disassembled to take out a liquid crystal panel with a polarizing plate, and the polarizing plates obtained in Examples and Comparative Examples were attached as backlight side polarizing plates. Also, with regard to the light-diffusing film provided on the backlight unit of this product, only the mounting part is removed and reassembled. The luminance in the frontal direction was measured using Ezconstrast manufactured by ELDIM Corporation about the mounting object produced in the above-mentioned manner. The measured luminance is expressed as a ratio (%) when the front luminance of the case where the polarizing plate and the light-diffusing film are arranged separately is 100. (3) Brightness viewing angle SJ8000 manufactured by LG Corporation was disassembled to take out a liquid crystal panel with a polarizing plate, and the polarizing plates obtained in Examples and Comparative Examples were attached as backlight side polarizing plates. Also, with regard to the light-diffusing film provided on the backlight unit of this product, only the mounting part is removed and reassembled. The luminance was measured using Ezconstrast manufactured by ELDIM Corporation about the mounting object produced in this way. When the brightness in the front direction is 100%, the angle at which the brightness becomes 25% is measured on both sides of the diffusion, and the sum of the angles on both sides is used as the brightness viewing angle. The measured luminance viewing angle is expressed as a ratio (%) when the luminance viewing angle of the case where the polarizing plate and the light-diffusing film are arranged separately is 100.

>Example 1> (Making polarizer protective film) Into a uniaxial extruder, 9 parts of silicone resin fine particles (volume average particle diameter 4.5µm), while performing melt extrusion at 260°C, one surface was given a concave-convex shape with an embossing roll to obtain a film with a thickness of 50µm. The cross-sectional area ratio of the concave portion was 70%, and the height of the convex portion was 10 µm.

(Production of Polarizing Plate) 1. Production of Polarizer Resin base material used long strip-shaped amorphous polyethylene terephthalate film (thickness: 100 μm) with water absorption rate of 0.60%, Tg80°C, elastic modulus of 2.5GPa. Apply corona treatment to one side of the resin substrate (treatment condition: 55W·min/m ² ), and coat 90 parts by weight of polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%), 10 parts by weight of acetyl acetyl modified PVA (polymerization degree 1200, acetyl acetyl modification degree of about 5%, saponification degree of 99.0 mol % or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd. Product name "GOHSEFIMER Z200") and an aqueous solution of 13 parts by weight of potassium iodide were dried at 60°C to form a PVA-based resin layer with a thickness of 13 μm, thereby producing a laminate. In an oven at 140°C, the obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different circumferential speeds (assisted stretching in the air). Next, the laminated body was immersed in an insoluble bath (an aqueous solution of boric acid obtained by mixing 4 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (insoluble treatment). Next, it was immersed in a dyeing bath (an iodine aqueous solution obtained 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) of a liquid temperature of 30° C. for 60 seconds (dyeing treatment). Next, it was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water) at a liquid temperature of 30° C. for 30 seconds (crosslinking treatment). ). Then, while the laminate was immersed in a boric acid aqueous solution (boric acid concentration: 3.0% by weight) at a liquid temperature of 70°C, it was uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds so that the total stretching ratio Up to 5.5 times (extended in water). Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained 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. (washing treatment). A polarizer with a thickness of 5 µm was formed on the resin substrate as described above.

2. Make polarizer On the surface of the polarizer of the resin substrate/polarizer laminate obtained above, a polyvinyl alcohol-based adhesive (thickness 2 µm) was used to spot-bond the concave-convex surface of the polarizer protective film. Next, the resin substrate was peeled off, and a methacrylic resin film (thickness 40 µm) was attached to the peeled surface through a polyvinyl alcohol-based adhesive. In addition, the methacrylic resin film was produced by putting a methacrylic resin (manufactured by Kuraray, product name "Parapet HR-S") into a single-screw extruder and performing melt extrusion at 260°C. A polarizing plate was prepared in the above manner. The refractive index of the low refractive index portion substantially defined in the polarizing plate is 1.15. The obtained polarizing plate was used for the evaluation of (2) and (3) above. List the results in Table 1.

>Example 2> Except having changed the embossing roll, it carried out similarly to Example 1, and produced the polarizer protective film whose cross-sectional area ratio of a recessed part was 55%. A polarizing plate was produced in the same manner as in Example 1 except for using this polarizer protective film. The refractive index of the low refractive index portion substantially defined by the polarizing plate is 1.22. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

>Comparative example 1> Except having changed the embossing roll, it carried out similarly to Example 1, and produced the polarizer protective film whose cross-sectional area ratio of a recessed part was 30%. A polarizing plate was produced in the same manner as in Example 1 except for using this polarizer protective film. The refractive index of the low refractive index portion substantially defined by the polarizing plate is 1.34. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

>Comparative example 2> A polarizer protective film having no uneven surface was produced in the same manner as in Example 1 except that the embossing roll was not used. A polarizing plate was produced in the same manner as in Example 1 except for using this polarizer protective film. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are listed in Table 1.

[Table 1]

>Evaluation> It is evident from Table 1 that, when the polarizing plate and the light-diffusing film are separately arranged as a reference, the embodiment of the present invention can maintain the front brightness at an allowable level and at the same time widen the brightness viewing angle. That is to say, according to the embodiments of the present invention, a polarizer protective film with a light diffusion function can be realized without narrowing the brightness viewing angle.

Industrial availability The polarizer protective film of the present invention is suitable for polarizing plates. The polarizing plate of the present invention can be suitably used in image display devices. The image display device of the present invention can be used in portable machines such as portable information terminals (PDA), smart phones, mobile phones, clocks, digital cameras, portable game machines; OA machines such as computer monitors, notebook computers, copiers, etc. Household electrical appliances such as video cameras, TVs, and microwave ovens; automotive equipment such as rear monitors, car navigation system monitors, and car audio equipment; display equipment such as digital signage and information guide screens for commercial stores; monitor screens, etc. Security equipment; Nursing monitors, medical monitors and other nursing medical equipment and other uses.

10: matrix 20, 21: Light-diffusing fine particles 22:Refractive index modulation area 30: concave and convex surface 31: convex part 32: Concave 100: Polarizer protective film 110: low refractive index part 120: Then layer 130: Polarizer 140: another protective film 150: Adhesive layer 200: polarizer C: intersection point H: Height of convex part T: The thickness of the bonding layer

FIG. 1 is a schematic cross-sectional view of a polarizer protective film according to an embodiment of the present invention. Fig. 2 is a schematic plan view showing a representative example of the planar shape of the convex portion of the concave-convex surface in the polarizer protective film according to the embodiment of the present invention. Fig. 3 is a schematic cross-sectional view of a polarizing plate according to an embodiment of the present invention.

10: matrix

20, 21: Light-diffusing fine particles

22:Refractive index modulation area

30: concave and convex surface

31: convex part

32: Concave

100: Polarizer protective film

H: Height of convex part

Claims (9)

A protective film for a polarizer, which is composed of a resin film, the resin film contains a resin as a matrix and light-diffusing fine particles dispersed in the matrix; the surface has a concave-convex shape; when viewed from above, the convex parts in the concave-convex shape have cross Point; the ratio B/A of the cross-sectional area B of the concave part to the overall cross-sectional area A in the concave-convex shape is more than 50%; when viewed from above, the area ratio of the concave part is more than 50% relative to the overall area; and the half-value angle of brightness It is more than 56°. The polarizer protective film according to claim 1, wherein the refractive index n _M of the matrix and the refractive index n _P of the light diffusing microparticles satisfy the following relationship: |n _P -n _M |≧0.05. The polarizer protective film according to claim 1 or 2, wherein the height H of the protrusions in the concave-convex shape is 3 μm or more. The polarizer protective film according to claim 1 or 2, wherein the light-diffusing fine particles are contained in the convex portions of the concave-convex shape. A polarizer, comprising a polarizer and a polarizer protective film according to any one of Claims 1 to 4 that is laminated on the polarizer; the polarizer protective film is configured so that the surface with the aforementioned concave-convex shape becomes the polarizer piece side. The polarizing plate according to claim 5, wherein substantially low-refractive index portions originating from concave portions of the concave-convex shape are defined at the interface between the polarizer and the protective film for the polarizer. The polarizing plate according to claim 6, wherein the difference (n _F -n _L ) between the refractive index n _L of the low refractive index portion and the refractive index n _F of the polarizer protective film is 0.2 or more. The polarizing plate according to any one of claims 5 to 7, wherein the ratio T/H of the thickness T of the adhesive layer to the height H of the protrusions in the uneven shape is 50% or less. An image display device having the polarizing plate according to any one of Claims 5 to 8 on the back side.

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