JP7079857B2 - Polarizer protective film, polarizing plate and image display device - Google Patents

Description

The present invention relates to a polarizing element protective film, a polarizing plate, and an image display device.

In recent years, there has been an increasing demand for thinning and improving design (for example, narrowing the bezel) of image display devices (for example, liquid crystal display devices and organic EL display devices). Along with this, there is an increasing demand for integration of optical members and / or optical films used in image display devices and / or integration of functions. As an example of such integration or integration of functions, it has been proposed to directly attach a light diffusing film to a polarizing element to impart a light diffusing function to a polarizing plate. However, the proposed technique has a problem that the luminance viewing angle becomes small.

Japanese Unexamined Patent Publication No. 2012-118235 Japanese Unexamined Patent Publication No. 2009-025774

The present invention has been made to solve the above-mentioned conventional problems, and a main object thereof is to provide a polarizing element protective film to which a light diffusing function is imparted without narrowing a luminance viewing angle.

The polarizing element protective film of the present invention is composed of a resin film containing a resin as a matrix and light diffusible fine particles dispersed in the matrix, has an uneven surface, and has an uneven surface with respect to the entire cross-sectional area A in the uneven portion. The ratio B / A of the cross-sectional area B of the recess is 50% or more.
In one embodiment, the refractive index n _M of the matrix and the refractive index n _P of the light diffusible fine particles satisfy the following relationship:
| N _P -n _M | ≧ 0.05.
In one embodiment, the height H of the convex portion in the uneven shape is 3 μm or more.
In one embodiment, the polarizing element protective film contains the light diffusing fine particles in the convex portion in the concave-convex shape.
In one embodiment, in the polarizing element protective film, the convex portions in the concave-convex shape have intersections when viewed in a plan view.
In one embodiment, the polarizing element protective film has an area ratio of the recesses to the total area in a plan view of 50% or more.
According to another aspect of the invention, a polarizing plate is provided. The polarizing plate has a polarizing element and the above-mentioned polarizing element protective film laminated on the polarizing element via an adhesive layer. The polarizing element protective film is arranged so that the surface having the uneven shape is on the polarizing element side.
In one embodiment, a substantially low refractive index portion due to the concave-convex concave portion is defined at the interface between the polarizing element and the polarizing element 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 polarizing element 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 uneven shape is 50% or less.
According to yet another aspect of the present invention, an image display device is provided. This image display device includes the above-mentioned polarizing plate on the back side.

According to the present invention, the light diffusing fine particles are dispersed in the polarizing element protective film, an uneven shape is formed on at least one of the surfaces thereof, and the cross-sectional area ratio of the concave portions in the uneven shape is set to a predetermined value or more. This makes it possible to realize a polarizing element protective film to which a light diffusing function is imparted without narrowing the luminance viewing angle.

FIG. 3 is a schematic cross-sectional view of a polarizing element protective film according to one embodiment of the present invention. It is a schematic plan view which shows the typical example of the plan view shape of the convex part of the concavo-convex surface in the polarizing element protection film by embodiment of this invention. It is a schematic sectional drawing of the polarizing plate by one Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. It should be noted that the drawings are schematically shown for easy viewing, and the ratios of length, width and thickness, the shape and fineness of the unevenness, etc. are different from the actual ones.

A. Polarizer protective film A-1. Overall Configuration FIG. 1 is a schematic cross-sectional view of a polarizing element protective film according to one embodiment of the present invention. The polarizing element protective film 100 of the illustrated example is composed of a resin film as a matrix 10 and a resin film containing light diffusible fine particles 20 dispersed in the matrix 10. With such a configuration, the light diffusing performance is imparted to the polarizing element protective film itself. As a result, the polarizing element protective film can also serve as a light diffusing film, and the polarizing element protective film becomes a part of the polarizing plate, so that the light diffusing performance can be imparted to the polarizing plate and the thickness can be significantly reduced at the same time. can do. The refractive index n _M of the matrix and the refractive index n _P of the light diffusing fine particles preferably satisfy the following relationship:
| N _P -n _M | ≧ 0.05.
| N _P -n _M | is more preferably 0.07 or more, still more preferably 0.10 or more. The upper limit of | n _P -n _M | can be, for example, 0.20. With such a configuration, even better light diffusion performance can be realized. The resin and light diffusible fine particles constituting the matrix will be described later in Sections A-2 and A-3, respectively.

In the embodiment of the present invention, the surface 30 of the polarizing element protective film 100 has an uneven shape. The uneven surface 30 has a convex portion 31 and a concave portion (air portion or void portion) 32. The ratio B / A of the cross-sectional area B of the concave portion to the cross-sectional area A of the entire uneven surface is 50% or more, typically more than 50%, preferably 60% or more, and more preferably 70% or more. Is. The upper limit of the ratio B / A can be, for example, 90%. When the ratio B / A is in such a range, sufficient brightness can be exhibited, good diffusion performance is imparted to the polarizing element protective film while maintaining a wide luminance viewing angle, and the polarizing element protection film is provided. The adhesive strength between the stator protective film and the polarizing element can be ensured when the film is laminated on the polarizing element. The cross-sectional area A of the entire uneven surface is the area of the portion surrounded by the line connecting the surface of the convex portion, the line connecting the bottom of the concave portion, and the vertical line at both ends of the film (for reference, of the relevant portion). The cross-sectional area B of the recesses (shown in FIG. 1 surrounded by a broken line on the outside) is the cross-sectional area of each recess 32 (the line connecting the wall line of the adjacent convex portion and the surface of the convex portion and the line connecting the bottom of the concave portion). The area of the part surrounded by and). The ratio B / A can correspond to the porosity.

The height H of the convex portion 31 on the uneven 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 may be, for example, 15 μm. When the height of the convex portion is within such a range, when the polarizing element protective film is laminated on the polarizing element, only the convex portion (substantially the upper portion of the convex portion) of the polarizing element protective film is the polarizing element. Can be glued to. In the present specification, bonding of only the convex portion may be referred to as "point bonding" for convenience. By such point bonding, a substantially low refractive index portion due to a recess (air portion or void portion) is defined in the vicinity of the point bonding portion. As a result, good light diffusion performance can be realized and the luminance viewing angle can be increased. Conventionally, in an image display device, the polarizing element (polarizing plate) and the light diffusing film are separately placed, and as a result, an air layer is interposed between the polarizing plate and the light diffusing film. While the air layer becomes an obstacle to thinning, the luminance viewing angle is largely maintained by the retroreflection by the air layer. By integrating the polarizing plate and the light diffusing film, it is possible to reduce the thickness and integrate the functions, but the elimination of the air layer reduces the luminance viewing angle. By forming the low refractive index portion in the vicinity of the point bonding portion, the light is efficiently retroreflected as in the case where the air layer is present. Therefore, according to the embodiment of the present invention, the polarizing element protective film is imparted with light diffusing performance, and by forming point adhesion, the polarizing plate is imparted with desired light diffusing performance and the luminance viewing angle is increased. Can be kept large (wide). Further, according to the embodiment of the present invention, since the polarizing element protective film itself has a light diffusing performance and also serves as a light diffusing film, a remarkable reduction in thickness is realized by a synergistic effect with the effect of eliminating the air layer. can.

Any suitable shape can be adopted as the plan view shape of the convex portion 31 on the uneven surface. As shown in FIG. 2, for example, the shape of the convex portion in a plan view may be a shape having regularity (for example, a grid shape) or an irregular shape. The convex portion 31 preferably has an intersection C when viewed in a plan view, as shown in FIG. In other words, the convex portion extends in two or more directions. The pitch of the convex portions (distance between the convex portions) is preferably 1000 μm or less, more preferably 500 μm or less, and further preferably 100 μm or less. If the plan view shape of the convex portion has regularity, the angle may be biased by 1 degree to 90 degrees. When the shape of the convex portion in a plan view is irregular, the pitch means an average pitch, and it is preferable that the distribution is such that within ± 50% of the average value of the pitch is 50% or more. With such a configuration, when the polarizing element protective film is laminated on the polarizing element, the adhesive strength between the polarizing element protective film and the polarizing element can be ensured, and good display quality can be ensured.

The area ratio of the concave portion 32 to the total area when the uneven surface is viewed in a plan view is preferably 50% or more, preferably 60% or more, and more preferably 70% or more. The upper limit of the area ratio of the recesses can be, for example, 90%. When the area ratio of the concave portion is within such a range, good diffusion performance is imparted to the polarizing element protective film while maintaining a wide luminance viewing angle, and when the polarizing element protective film is laminated on the polarizing element, it is polarized. The adhesive strength between the child protective film and the stator can be ensured.

In one embodiment, as shown in FIG. 1, the convex portion 31 contains the light diffusing fine particles 20. With such a configuration, better diffusion performance is imparted, and it is possible to reduce optical interference unevenness with pixels of a liquid crystal panel even with a uniform uneven pattern.

The uneven surface (concave shape) can be formed by any suitable method. The uneven shape can be formed by, for example, a roughening method or a method of imparting unevenness with fine particles. Specific examples of the roughening method include embossing and sandblasting. The uneven surface (concave shape) can be typically formed by shaping the surface of the melt-extruded film with embossed rolls.

A-2. Matrix As the resin constituting the matrix, any suitable resin capable of forming a polarizing element protective film can be adopted. Specific examples of such resins include (meth) acrylic resins, polyester resins (eg, polyethylene terephthalate (PET)), cycloolefin resins (eg, norbornene resins), and cellulose resins (eg, triacetyl). Cellulose (TAC)), polyvinyl alcohol-based resin, polycarbonate-based resin, polyamide-based resin, polyimide-based resin, polyether sulfone-based resin, polysulfone-based resin, polystyrene-based resin, polyolefin-based resin, acetate-based resin can be mentioned. These resins may be used alone or in combination of two or more. From the viewpoint of optical properties, transparency and versatility, (meth) acrylic resin, polyester resin and cycloolefin resin are preferable, and (meth) acrylic resin is more preferable. In addition, in this specification, "(meth) acrylic" means acrylic and / or methacrylic.

As the (meth) acrylic resin, any suitable (meth) acrylic resin can be adopted. For the sake of simplification of the description, the (meth) acrylic resin is hereinafter simply referred to as an acrylic resin. 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 can be used alone or in combination. Further, any suitable copolymerization monomer may be introduced into the acrylic resin by copolymerization. The type, number, copolymerization ratio, etc. of such copolymerization monomers can be appropriately set according to the purpose. The constituent components (monomer unit) of the main skeleton of the acrylic resin will be described later with reference to the general formula (2).

The acrylic resin may preferably have at least one selected from glutarimide units, lactone ring units, maleic anhydride units, maleimide units and glutaric anhydride units. Acrylic resins having a lactone ring unit are described in, for example, Japanese Patent Application Laid-Open No. 2008-181078, and the description in this publication is incorporated herein by reference. The glutarimide unit is preferably represented by the following general formula (1):

In the general formula (1), R ¹ and R ² independently represent hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ is an alkyl group having 1 to 18 carbon atoms and 3 to 12 carbon atoms. The cycloalkyl group of the above, or an aryl group having 6 to 10 carbon atoms is shown. In the general formula (1), preferably R ¹ and R ² are independently hydrogen or methyl groups, and R ³ is a hydrogen, methyl group, butyl group or cyclohexyl group, respectively. More preferably, R ¹ is a methyl group, R ² is hydrogen and R ³ is a methyl group.

The alkyl (meth) acrylate is typically represented by the following general formula (2):

In the general formula (2), R ⁴ represents a hydrogen atom or a methyl group, and R ⁵ is a hydrogen atom or an aliphatic or alicyclic hydrocarbon group having 1 to 6 carbon atoms which may be substituted. show. Examples of the substituent include halogens and hydroxyl groups. Specific examples of alkyl (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, and t-butyl (meth) acrylate. Butyl, n-hexyl (meth) acrylate, cyclohexyl (meth) acrylate, chloromethyl (meth) acrylate, 2-chloroethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (meth) acrylate Examples include 3-hydroxypropyl, (meth) acrylic acid 2,3,4,5,6-pentahydroxyhexyl and (meth) acrylic acid 2,3,4,5-tetrahydroxypentyl. In the general formula ( ² ), R5 is preferably a hydrogen atom or a methyl group. Therefore, a particularly preferred alkyl (meth) acrylate is methyl acrylate or methyl methacrylate.

The acrylic resin may contain only a single glutarimide unit, or may contain a plurality of glutarimide units having different ^{R1 , R2} and R3 in the general formula (1).

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%, further preferably 2 mol% to 40 mol%, and particularly preferably 2 mol. % To 35 mol%, most preferably 3 mol% to 30 mol%. When the content ratio is less than 2 mol%, the effects exhibited from the glutarimide unit (for example, high optical properties, high mechanical strength, excellent adhesion to the modulator, thinning) are sufficiently exhibited. It may not be done. If the content ratio exceeds 50 mol%, for example, heat resistance and transparency may be insufficient.

The acrylic resin may contain only a single alkyl (meth) acrylate unit, or may contain a plurality of alkyl (meth) acrylate units having different ^R4 and R5 in the general formula ( ² ). May be good.

The content of the alkyl (meth) acrylate unit in the acrylic resin is preferably 50 mol% to 98 mol%, more preferably 55 mol% to 98 mol%, still more preferably 60 mol% to 98 mol%, and particularly preferably. Is 65 mol% to 98 mol%, most preferably 70 mol% to 97 mol%. If the content ratio is less than 50 mol%, the effects expressed from the alkyl (meth) acrylate unit (for example, high heat resistance and high transparency) may not be sufficiently exhibited. If the content ratio is more than 98 mol%, the resin is brittle and easily cracked, high mechanical strength cannot be sufficiently exhibited, and productivity may be inferior.

The acrylic resin may contain a unit other than the glutarimide unit and the alkyl (meth) acrylate unit.

In one embodiment, the acrylic resin can contain, for example, 0% by weight to 10% by weight of unsaturated carboxylic acid units that are not involved in the intramolecular imidization reaction 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. When the content is in such a range, transparency, retention stability and moisture resistance can be maintained.

In one embodiment, the acrylic resin can contain a copolymerizable vinyl-based monomer unit (another vinyl-based monomer unit) other than the above. Examples of other vinyl-based monomers include acrylonitrile, methacrylic acid, etacrylonitrile, allylglycidyl ether, maleic anhydride, itaconic anhydride, N-methylmaleimide, N-ethylmaleimide, N-cyclohexylmaleimide, and acrylic acid. Aminoethyl acid, propylaminoethyl acrylate, dimethylaminoethyl methacrylate, ethylaminopropyl methacrylate, cyclohexylaminoethyl methacrylate, N-vinyldiethylamine, N-acetylvinylamine, allylamine, methallylamine, N-methylallylamine, 2 -Isopropenyl-oxazoline, 2-vinyl-oxazoline, 2-acroyl-oxazoline, N-phenylmaleimide, phenylaminoethyl methacrylate, styrene, α-methylstyrene, p-glycidylstyrene, p-aminostyrene, 2-styryl- Examples include oxazoline. These may be used alone or in combination. Styrene-based monomers such as styrene and α-methylstyrene are preferable. The content ratio of the other vinyl-based monomer unit is preferably 0 to 1% by weight, more preferably 0 to 0.1% by weight. Within such a range, it is possible to suppress the appearance of an undesired phase difference and the decrease in transparency.

The imidization rate of the acrylic resin is preferably 2.5% to 20.0%. When the imidization ratio is within such a range, a resin having excellent heat resistance, transparency and molding processability can be obtained, and the generation of kogation and the decrease in mechanical strength during film molding can be prevented. In the acrylic resin, the imidization ratio is represented by the ratio of the glutarimide unit and the alkyl (meth) acrylate unit. This ratio can be obtained from, for example, an NMR spectrum, an IR spectrum, or the like of an acrylic resin. In this embodiment, the imidization ratio can be determined by ^{1 1} H-NMR measurement of the resin using ^{1 1} HNMR BRUKER Avance III (400 MHz). More specifically, the peak area derived from the O-CH ₃ proton of the alkyl (meth) acrylate around 3.5 ppm to 3.8 ppm is defined as A, and the peak area of glutarimide near 3.0 ppm to 3.3 ppm is N-CH ₃ . It is calculated by the following equation, where B is the area of the peak derived from the proton.
Imidization rate Im (%) = {B / (A + B)} × 100

The acrylic resin has a Tg (glass transition temperature) of preferably 110 ° C. or higher, more preferably 115 ° C. or higher, still more preferably 120 ° C. or higher, particularly preferably 125 ° C. or higher, and most preferably 130 ° C. or higher. When the Tg is 110 ° C. or higher, the polarizing plate containing the polarizing element protective film obtained from such a resin tends to have excellent durability. The upper limit of Tg is preferably 300 ° C. or lower, more preferably 290 ° C. or lower, still more preferably 285 ° C. or lower, particularly preferably 200 ° C. or lower, and most preferably 160 ° C. or lower. When Tg is in such a range, formability can be excellent.

The acrylic resin can be produced, for example, by the following method. In this method, (I) an alkyl (meth) acrylate monomer corresponding to an alkyl (meth) acrylate unit represented by the general formula (2), an unsaturated carboxylic acid monomer and / or a precursor thereof is used alone. The body and the copolymer are copolymerized to obtain the copolymer (a); and (II) the copolymer (a) is treated with an imidizing agent to obtain the copolymer (a) in the copolymer (a). An intramolecular imidization reaction is carried out between the alkyl (meth) acrylate monomer unit and the unsaturated carboxylic acid monomer and / or its precursor monomer unit, and the glutarimide unit represented by the general formula (1) is copolymerized. Introducing into the polymer;

Details of the acrylic resin and the method for producing the same are described in, for example, Japanese Patent Laid-Open No. 2018-155812 and Japanese Patent Application Laid-Open No. 2018-155813. The description of these publications is incorporated herein by reference.

A-3. As the light-diffusing fine particles, any suitable light-diffusing fine particles can be used. Specific examples include inorganic fine particles and polymer fine particles. The light diffusing fine particles are preferably polymer fine particles. Examples of the material of the polymer fine particles include silicone resin, (meth) acrylic resin (for example, polymethyl methacrylate), polystyrene resin, polyurethane resin, and melamine resin. Since these resins have excellent dispersibility with respect to the matrix and an appropriate refractive index difference with the matrix, a polarizing element protective film having excellent light diffusion performance can be obtained. Preferably, it is a silicone resin or polymethyl methacrylate. The shape of the light diffusing fine particles can be, for example, a true spherical shape, a flat shape, or an indefinite shape. The light diffusing fine particles may be used alone or in combination of two or more.

The volume average particle size of the light diffusing fine particles is preferably 1 μm to 10 μm, and more preferably 1.5 μm to 6 μm. By setting the volume average particle diameter in the above range, a polarizing element protective film having excellent light diffusion performance can be obtained. The volume average particle size can be measured by using, for example, an ultracentrifugation type automatic particle size distribution measuring device.

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

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

The light diffusing fine particles may be, for example, core-shell fine particles having a core and a shell and having different refractive indexes between the core and the shell, and the so-called refractive index changes continuously from the center of the fine particles to the outside. It may be GRIN (gradient index) fine particles. The core-shell fine particles and GRIN fine particles are, for example, JP-A-6-347617, JP-A-2003-262710, JP-A-2002-212245, JP-A-2002-214408, JP-A-2002-328207, and Japanese Patent Publication No. It is described in Japanese Patent Application Laid-Open No. 2010-077243 and Japanese Patent Application Laid-Open No. 2010-107616. The description of these publications is incorporated herein by reference.

As shown in FIG. 1, for example, the light-diffusing fine particles may have a refractive index modulation region 22 in which the refractive index changes substantially continuously outside the vicinity of the surface of the light-diffusing fine particles 21. The refractive index modulation region can be formed, for example, by introducing a specific ultrafine particle component into the matrix. With such a configuration, backscattering can be suppressed, and as a result, even better light diffusion performance can be realized. For details of the light diffusing fine particles in which the refractive index modulation region is formed, for example, Japanese Patent Application Laid-Open No. 2012-88692, Japanese Patent Application Laid-Open No. 2012-83741, Japanese Patent Application Laid-Open No. 2012-83743, JP-A-2012-83744. It is described in. The description of these publications is incorporated herein by reference.

The content of the light diffusing fine particles in the polarizing element protective film is preferably 0.3% by weight to 50% by weight, more preferably 1% by weight to 30% by weight, and further preferably 2.5% by weight to 25% by weight. 20% by weight. When the content of the light diffusing fine particles is in such a range, a polarizing element protective film having excellent light diffusing performance can be obtained.

A-4. Characteristics of the Polarizer Protective Film The polarizing element protective film is preferably substantially optically isotropic. As used herein, "substantially optically isotropic" means that the in-plane phase difference Re (550) is 0 nm to 10 nm. The in-plane retardation Re (550) is more preferably 0 nm to 5 nm, further preferably 0 nm to 3 nm, and particularly preferably 0 nm to 2 nm. When the Re (550) of the polarizing element protective film is in such a range, it is possible to prevent adverse effects on the display characteristics when the polarizing plate containing the polarizing element protective film is applied to an image display device. Re (550) is an in-plane phase difference of the film measured with light having a wavelength of 550 nm at 23 ° C. Re (550) is obtained by the formula: Re (550) = (nx-ny) × d. Here, nx is the refractive index in the direction in which the refractive index in the plane is maximized (that is, the slow phase axis direction), and ny is the direction orthogonal to the slow phase axis in the plane (that is, the phase advance axis direction). It is a refractive index, and d is the thickness (nm) of the film.

The higher the light transmittance at 380 nm of the polarizing element protective film at a thickness of 40 μm, the more preferable. Specifically, the light transmittance is preferably 75% or more. It is more preferably 80% or more, still more preferably 85% or more. When the light transmittance is in such a range, desired optical characteristics can be ensured. The light transmittance can be measured, for example, by a method according to ASTM-D-1003.

The haze of the polarizing element protective film is preferably 50% to 99%, more preferably 70% to 95%.

The polarizing element protective film preferably has the following characteristics. 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%, respectively. be.

Regarding the luminance viewing angle of the polarizing element protective film, the luminance half-value angle (angle at which the luminance is 50% of the front surface) is preferably 56 ° (28 ° on one side) or more, and more preferably 60 ° to 70 ° (30 on one side). ° -35 °). Further, the angle at which the brightness is 25% of the front surface is preferably 90 ° (45 ° on one side) or more, and more preferably 96 ° to 120 ° (48 ° to 60 ° on one side). According to the embodiment of the present invention, it is possible to impart excellent diffusion performance to the polarizing element protective film and maintain a wide luminance viewing angle.

The refractive index n _F of the polarizing element protective film as a whole is preferably 1.3 to 1.8, and more preferably 1.4 to 1.6. When the refractive index of the polarizing element protective film is in such a range, the difference in refractive index from the low refractive index portion defined by the point adhesion with the polarizing element in the polarizing plate can be set in a desired range.

The moisture permeability of the polarizing element protective film is preferably 300 g / m 2.24 hr or less, more preferably ²⁵⁰ g / ^m 2.24 hr or less, still more preferably ²⁰⁰ g / m 2.24 hr or less, and particularly preferably 150 g / ^m 2.24 hr or less. Below, it is most preferably 100 g / ^m 2.24 hr or less. When the moisture permeability of the polarizing element protective film is within such a range, a polarizing plate having excellent durability and moisture resistance can be obtained.

B. Polarizing plate The polarizing element protective film of the present invention according to the above item A can be applied to a polarizing plate. Therefore, the present invention also includes a polarizing plate using such a polarizing element protective film. FIG. 3 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention. The polarizing plate 200 of the illustrated example has a polarizing element 130 and the polarizing element protective film 100 according to the above item A, which is laminated on the polarizing element 130 via an adhesive layer 120. The polarizing element protective film 100 is arranged so that the surface having the uneven shape is on the polarizing element 130 side. The adhesive layer is composed of any suitable adhesive or adhesive. The adhesive layer is typically formed of a water-based adhesive (eg, vinyl alcohol-based adhesive) or an active energy ray-curable adhesive. The pressure-sensitive adhesive layer is typically formed of an acrylic pressure-sensitive adhesive. Practically, another protective film 140 is arranged on the opposite side of the protector from the protector 100. Practically, a pressure-sensitive adhesive layer 150 is further provided as the outermost layer, and the polarizing plate can be attached to the image display cell. A separator (not shown) is temporarily attached to the surface of the pressure-sensitive adhesive layer 150 so that it can be peeled off, protecting the pressure-sensitive adhesive layer until the polarizing plate is actually used, and enabling roll formation. The polarizing plate according to the embodiment of the present invention can be typically used as a back-side polarizing plate of an image display device.

In the embodiment of the illustrated example, the concave portion 32 on the uneven surface of the polarizing element protective film is formed at the interface between the polarizing element 130 (substantially the adhesive layer 120) and the polarizing element protective film 100 (due to the above-mentioned point adhesion). A substantially low refractive index portion 110 is defined. The refractive index n _L of the low refractive index portion is preferably more than 1.0 and 1.3 or less, and more preferably more than 1.0 and 1.2 or less. 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 polarizing element protective film is preferably 0.2 or more, and more preferably 0.25 or more. The upper limit of the difference (n _F − n _L ) can be, for example, 0.4. The refractive index n _L of the low refractive index portion is defined by the following equation.
n _L = n _M x (100% -recess area ratio (%)) + air refractive index (1.0) x 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 uneven shape is preferably 50% or less, more preferably 30% or less. When the ratio T / H is in such a range, good point adhesion can be realized. The lower limit of the ratio T / H can be, for example, 10%.

As the polarizing element, any suitable polarizing element may be adopted. For example, the resin film forming the polarizing element may be a single-layer resin film or a laminated body having two or more layers.

Specific examples of the polarizing element composed of a single-layer resin film include a hydrophilic polymer film such as a polyvinyl alcohol (PVA) -based film, a partially formalized PVA-based film, and an ethylene / vinyl acetate copolymer-based partially saponified film. Examples thereof include those which have been dyed and stretched with a bicolor substance such as iodine and a bicolor dye, and polyene-based oriented films such as a dehydrated product of PVA and a dehydrogenated product of polyvinyl chloride. Preferably, since the PVA-based film is excellent in optical properties, a polarizing element obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used.

The above-mentioned dyeing with iodine is performed, for example, by immersing a PVA-based film in an aqueous iodine solution. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after the dyeing treatment or may be performed while dyeing. Further, it may be dyed after being stretched. If necessary, the PVA-based film is subjected to a swelling treatment, a crosslinking treatment, a cleaning treatment, a drying treatment and the like. For example, by immersing the PVA-based film in water and washing it with water before dyeing, it is possible not only to clean the dirt and blocking inhibitor on the surface of the PVA-based film, but also to swell the PVA-based film to prevent uneven dyeing. Can be prevented.

Specific examples of the polarizing element obtained by using the laminate include a laminate of a resin base material and a PVA-based resin layer (PVA-based resin film) laminated on the resin base material, or a resin base material and the resin. Examples thereof include a polarizing element obtained by using a laminate with a PVA-based resin layer coated and formed on a base material. The ligand obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying the resin base material. It is produced by forming a PVA-based resin layer on top of the PVA-based resin layer to obtain a laminate of a resin base material and a PVA-based resin layer; obtain. In the present embodiment, stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further comprise, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution. The obtained resin base material / polarizing element laminate may be used as it is (that is, the resin base material may be used as a protective layer for the polarizing element), and the resin base material is peeled off from the resin base material / polarizing element laminate. Then, an arbitrary appropriate protective layer according to the purpose may be laminated on the peeled surface and used. Details of the method for producing such a polarizing element are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference.

The thickness of the splitter is, for example, 1 μm to 80 μm. In one embodiment, the thickness of the stator is preferably 1 μm to 20 μm, more preferably 3 μm to 15 μm.

C. Image display device The polarizing plate according to the above item B can be applied to an image display device. Therefore, the present invention also includes an image display device using such a polarizing plate. The image display device typically includes the polarizing plate according to the above item B on the back surface side. The polarizing plate is typically arranged so that the polarizing element protective film according to the above item A is on the back side. Typical examples of the image display device include a liquid crystal display device and an organic electroluminescence (EL) display device. Since the image display device adopts a configuration well known in the industry, detailed description thereof will be omitted.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. The measurement method of each characteristic is as follows. Unless otherwise specified, "parts" and "%" in the examples are based on weight.

(1) Cross-sectional area ratio of concave portion The cross-sectional area of the polarizing element protective film used in Examples and Comparative Examples is observed with a scanning electron microscope, and the total cross-sectional area of the uneven portion and the cross-sectional area of the concave portion are measured from the image to measure the unevenness. The cross-sectional area ratio of the recess to the total cross-sectional area of the portion was obtained. The cross-sectional area ratio of the polarizing element protective film that did not form the uneven portion was set to zero (0).
(2) Luminance LG's SJ8000 was disassembled, a liquid crystal panel with a polarizing plate was taken out, and the polarizing plates obtained in Examples and Comparative Examples were mounted as backlight-side polarizing plates. In addition, the light diffusion film provided in the backlight unit of the product was cut out and reassembled only at the mounting location. With respect to the mounted product thus obtained, the brightness in the front direction was measured using Ezconstrast manufactured by ELDIM. The measured luminance was expressed as a ratio (%) when the front luminance when the polarizing plate and the light diffusing film were placed separately was set to 100.
(3) Luminance viewing angle LG's SJ8000 was disassembled, a liquid crystal panel with a polarizing plate was taken out, and the polarizing plates obtained in Examples and Comparative Examples were mounted as backlight-side polarizing plates. In addition, the light diffusion film provided in the backlight unit of the product was cut out and reassembled only at the mounting location. The brightness of the mounted product thus obtained was measured using Ezconstrast manufactured by ELDIM. When the brightness in the front direction was 100%, the angle at which the brightness was 25% was measured on both sides of the diffusion, and the sum of the angles on both sides was defined as the brightness viewing angle. The measured luminance viewing angle was expressed as a ratio (%) when the luminance viewing angle was 100 when the polarizing plate and the light diffusing film were placed separately.

<Example 1>
(Making a polarizing element protective film)
For 100 parts of methacrylic resin (manufactured by Kuraray, product name "Parapet HR-S"), 9 parts of silicone resin fine particles (volume average particle diameter 4.5 μm) as light diffusible fine particles are put into a single-screw extruder. Then, while melt-extruding at 260 ° C., an uneven shape was formed on one surface with an embossing roll to obtain a film having 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.

(Manufacturing of polarizing plate)
1. 1. Preparation of Polarizer An amorphous polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption rate of 0.60%, a Tg of 80 ° C., and an elastic modulus of 2.5 GPa was used as a resin base material.
One side of the resin base material is subjected to corona treatment (treatment condition: 55 W · min / m ² ), and 90 parts by weight of polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%), aceto on this corona treated surface. 10 parts by weight of acetyl-modified PVA (polymerization degree 1200, acetoacetyl modification degree about 5%, saponification degree 99.0 mol% or more, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimer Z200"), and potassium iodide An aqueous solution containing 13 parts by weight was applied at room temperature and dried in an environment of 60 ° C. to form a PVA-based resin layer having a thickness of 13 μm to prepare a laminated body.
The obtained laminate was stretched 2.4 times in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 140 ° C. (aerial auxiliary stretching).
Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 30 ° C. (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) for 30 seconds (insolubilization treatment).
Next, it is immersed in a dyeing bath at a liquid temperature of 30 ° C. (an aqueous iodine solution obtained by blending 0.4 parts by weight of iodine and 3.0 parts by weight of potassium iodide with 100 parts by weight of water) for 60 seconds. (Staining treatment).
Then, it was immersed in a cross-linking bath at a liquid temperature of 30 ° C. (a boric acid aqueous solution obtained by blending 3 parts by weight of potassium iodide and 3 parts by weight of boric acid with respect to 100 parts by weight of water) for 30 seconds. (Bridge treatment).
Then, while immersing the laminate in a boric acid aqueous solution (boric acid concentration 3.0% by weight) having a liquid temperature of 70 ° C., the total draw ratio is 5.5 in the longitudinal direction (longitudinal direction) between rolls having different peripheral speeds. Uniaxial stretching was performed so as to double (stretching in water).
Then, the laminate was immersed in a washing bath having a liquid temperature of 30 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment).
In this way, a substituent having a thickness of 5 μm was formed on the resin substrate.

2. 2. Fabrication of Polarizing Plate The uneven surface of the polarizing element protective film is bonded to the surface of the polarizing element of the laminate of the resin base material / polarizing element obtained above by point bonding via a polyvinyl alcohol-based adhesive (thickness 2 μm). rice field. Next, the resin base material was peeled off, and a methacrylic resin film (thickness 40 μm) was attached to the peeled surface via a polyvinyl alcohol-based adhesive. The methacrylic resin film was produced by putting a methacrylic resin (manufactured by Kuraray Co., Ltd., product name "Parapet HR-S") into a single-screw extruder and melt-extruding it at 260 ° C.
In this way, a polarizing plate was obtained. The refractive index of the low refractive index portion substantially defined on the polarizing plate was 1.15. The obtained polarizing plate was used for the evaluation of (2) and (3) above. The results are shown in Table 1.

<Example 2>
A polarizing element protective film having a recessed cross-sectional area ratio of 55% was produced in the same manner as in Example 1 except that the embossing roll was changed. A polarizing plate was produced in the same manner as in Example 1 except that this polarizing element protective film was used. The refractive index of the low refractive index portion substantially defined on 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.

<Comparative Example 1>
A polarizing element protective film having a recessed cross-sectional area ratio of 30% was produced in the same manner as in Example 1 except that the embossing roll was changed. A polarizing plate was produced in the same manner as in Example 1 except that this polarizing element protective film was used. The refractive index of the low refractive index portion substantially defined on 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.

<Comparative Example 2>
A polarizing element protective film having no uneven surface was produced in the same manner as in Example 1 except that the embossed roll was not used. A polarizing plate was produced in the same manner as in Example 1 except that this polarizing element protective film was used. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.

<Evaluation>
As is clear from Table 1, in the embodiment of the present invention, when the polarizing plate and the light diffusing film are placed separately, the front luminance is maintained to an acceptable level and the luminance viewing angle is widened. can do. That is, according to the embodiment of the present invention, it can be seen that a polarizing element protective film to which a light diffusing function is imparted can be realized without narrowing the luminance viewing angle.

The polarizing element protective film of the present invention is suitably used for a polarizing plate. The polarizing plate of the present invention is suitably used for an image display device. The image display device of the present invention is a portable device such as a portable information terminal (PDA), a smartphone, a mobile phone, a clock, a digital camera, a portable game machine; an OA device such as a personal computer monitor, a laptop computer, a copy machine; a video camera, a television. , Home electrical equipment such as microwave ovens; In-vehicle equipment such as back monitors, car navigation system monitors, car audio; Exhibition equipment such as digital signage and information monitors for commercial stores; Security equipment such as monitoring monitors; Nursing care It can be used for various purposes such as nursing / medical equipment such as monitors and medical monitors.

10 Matrix 20 Light-diffusing fine particles 30 Concavo-convex surface 31 Convex part 32 Concave part 100 Polarizer protective film 120 Adhesive layer 130 Polarizer 200 Polarizing plate

Claims (9)

It is composed of a resin film containing a resin as a matrix and light diffusible fine particles dispersed in the matrix.
The surface has an uneven shape,
When viewed in a plan view, the convex portion in the uneven shape has an intersection, and the convex portion has an intersection.
The ratio B / A of the cross-sectional area B of the concave portion to the total cross-sectional area A of the uneven portion is 50% or more .
The area ratio of the recess to the total area when viewed in a plan view is 50% or more.
Luminance half-value angle is 56 ° or more,
Polarizer protective film. The polarizing element 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 fine particles satisfy the following relationship.
| N _P -n _M | ≧ 0.05. The polarizing element protective film according to claim 1 or 2, wherein the height H of the convex portion in the concave-convex shape is 3 μm or more. The polarizing element protective film according to any one of claims 1 to 3, wherein the convex portion in the concave-convex shape contains the light-diffusing fine particles. It has a polarizing element and the polarizing element protective film according to any one of claims 1 to 4 , which is laminated on the polarizing element via an adhesive layer.
The polarizing element protective film is arranged so that the surface having the uneven shape is on the polarizing element side.
Polarizer. The polarizing plate according to claim 5 , wherein a substantially low refractive index portion due to the concave-convex concave portion is defined at the interface between the polarizing element and the polarizing element protective film. The polarizing plate according to claim 6 , wherein the difference ( _nF −n _L ) between the refractive index n _L of the low refractive index portion and the refractive index n _F of the polarizing element 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 convex portion in the uneven shape is 50% or less. An image display device comprising the polarizing plate according to any one of claims 5 to 8 on the back surface side.

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