CN102681039A - Polarizer protective film - Google Patents

Abstract

The present invention provides a polarizer protective film having a total value T _c (%) of the transmitted image clarity C _n (%) in a transmission image clarity measurement test satisfying the following formula (1): Relation and the light-diffusion layer which satisfy|fills the relation of following formula (2) with total haze (haze) value H(%). The total value T _c is the total value of the transmitted image sharpness C _0.125 , C 0.5 , C 1 , and C 2 when the width n (mm) of the optical comb is 0.125, _0.5 , ₁ , and _2, respectively. 0≤T _c ≤125 Formula (1) 0≤H≤10 Formula (2).

Description

Polarizer protective film

technical field

The present invention relates to a polarizer protective film having a light-diffusing layer.

Background technique

On the display surface of image display devices such as liquid crystal displays or plasma display panels, Braun tube (cathode ray tube: CRT) displays, organic electroluminescent (EL) displays, in order to prevent scratches on the surface, it is generally provided with high hardness performance protective film. In addition, since external light is reflected on the display surface of the image display device, visibility is impaired, so TVs and personal computers that value image quality, video cameras or digital cameras used outdoors where external light is strong, and those that use reflected light to display In mobile phones, etc., the function of preventing external light from being reflected is sometimes added to the protective film, and the non-reflection processing technology that utilizes the interference caused by the optical multilayer film is used, or the incident light is scattered by forming fine unevenness on the surface. Image vignetting anti-glare processing technology. In particular, the latter anti-glare treatment technology is relatively inexpensive, so it is preferably used in applications such as large monitors and personal computers.

In addition, in the application of large-screen image display devices, such as wall-mounted TV sets, the demand for further thinning and lightening of image display devices continues to emerge. In order to cope with the thinning and large-screen image display components, the protective film also requires reinforcement The function of the strength of the image display element requires thinning of the protective film itself. As a protective film meeting these requirements, a film formed of, for example, a polyester resin is used as a base film in view of excellent mechanical strength, durability, and cost (refer to Japanese Patent Laid-Open No. 2008-3541 (Patent Document 1)) .

Contents of the invention

When a film made of a polyester resin is used as a base film, it is usually stretched and used because it can be adjusted to a desired strength and thickness and is advantageous in cost. Since the stretched resin film has birefringence, there is a problem of poor visibility due to the occurrence of rainbow spots caused by retardation.

Patent Document 1 describes that rainbow spots due to the birefringence of the base film can be prevented by setting the total haze value of the polarizer protective film in the range of 10 to 80%. However, elimination of rainbow spots is not only related to the total haze value, and even a protective film having a total haze within the above-mentioned range sometimes produces rainbow spots. In addition, if the total haze is set to a high value, the occurrence of rainbow spots is suppressed, but in this case, there is a so-called "fading and whitening" that easily causes the entire display surface to become white due to diffused light and display indistinct colors. "The problem.

An object of the present invention is to provide a polarizer protective film that suppresses the occurrence of discoloration and whitening, and further suppresses the occurrence of rainbow spots caused by transmitted light mainly due to the birefringence of the base film.

The present invention was accomplished by discovering that the occurrence of rainbow spots caused by transmitted light also correlates with the sharpness of transmitted images. The present invention includes the following contents.

[1] A polarizer protective film having a light diffusion layer,

The total value T _c (%) of the transmission image sharpness C _n (%) in the transmission image sharpness measurement test satisfies the relationship of the following formula (1), and the total haze value H (%) satisfies the following formula (2) relationship,

In the test for the measurement of the clarity of the transmitted image, the light quantity of the transmitted light of the test piece is measured by an optical comb with a width n (mm) moving at a speed of 10 mm/min, which is perpendicular to the beam axis of the transmitted light.

The above-mentioned transmitted image sharpness C _n (%) in the above-mentioned transmitted image sharpness measurement test assumes that the maximum value of the transmitted light amount when there is the transmission portion of the above-mentioned optical comb on the ray axis is M _n , and the light beam on the ray axis is When the minimum value of the amount of transmitted light at the time of the light-shielding portion of the above-mentioned optical comb is _mn , it is calculated by the following formula (3):

The total value T _c is the total value of the transmitted image sharpness C _0.125 , C 0.5 , C 1 , and C ₂ when the width n (mm) of the optical comb is 0.125, _0.5 , ₁ , and 2, respectively.

0≤T _c ≤125 Formula (1)

0≤H≤10 Formula (2)

C _n ＝{(M _n -m _n )/(M _n +m _n )}×100 Formula (3)

[2] The polarizer protective film according to [1], wherein a base film and the light diffusion layer are laminated, and the base film has birefringence.

[3] The polarizer protective film according to [2], wherein the base film has an in-plane retardation value of 400 nm or more.

[4] The polarizer protective film according to [2] or [3], wherein the base film contains a polyester resin as a main component.

[5] The polarizer protective film according to any one of [2] to [4], wherein the base film has a thickness of 50 μm or less.

[6] The polarizer protective film according to any one of [1] to [5], wherein the light diffusion layer contains a translucent resin and translucent fine particles.

[7] The polarizer protective film according to [6], wherein the translucent fine particles include amorphous fine particles.

With the polarizer protective film of the present invention, it is possible to constitute an image display device that suppresses occurrence of rainbow spots and discoloration and whitening due to transmitted light, and has good appearance quality and display quality.

Description of drawings

FIG. 1 is a schematic cross-sectional view showing a preferred example of the polarizer protective film of the present invention.

2 is a graph showing the relationship between the total haze value H of the polarizer protective film of Example 1 and the optical films of Comparative Examples 1 to 5, and the total value T _c of transmitted image clarity.

Detailed ways

[Polarizer Protective Film]

The polarizer protective film of this invention has a light-diffusion layer. The light-diffusing layer is laminated on, for example, a base film. A polarizer protective film may have other layers other than the said light-diffusion layer and a base film.

Fig. 1 is a schematic cross-sectional view showing a preferred example of the protective film of the present invention. The polarizer protective film 100 shown in FIG. 1 according to the present invention has a base film 101 and a light-diffusing layer 102 laminated on the base film 101 . The light-diffusing layer 102 is a layer based on a translucent resin 103 , and translucent fine particles 104 are dispersed in the translucent resin 103 . Hereinafter, the polarizer protective film of this invention is demonstrated in more detail.

<Optical properties of polarizer protective film>

The total value T c (%) of the transmission image clarity _{C n} (%) of the polarizer protective film of the present invention in the transmission image clarity measurement test satisfies the relationship of the following formula (1), and the total haze value H(%) satisfies the relationship of the following formula (2).

0≤T _c ≤125 Formula (1)

0≤H≤10 Formula (2)

In the test for measuring the sharpness of the transmitted image, the light intensity of the transmitted light of the test piece (polarizer protective film) passes through the light of a width n (mm) that is perpendicular to the ray axis of the transmitted light and moves at a speed of 10 mm/min. Comb to measure. Specifically, measurement was performed using a mapping property measuring device (manufactured by Suga Test Instrument Co., Ltd.). The mappability measuring instrument consists of an optical device that makes the light transmitted through the slit incident on the test piece as parallel rays perpendicularly, and detects the transmitted light through a moving optical comb, and a measurement that records the change of the detected light amount as a waveform. Department of device composition. The width ratio of the light part and the dark part of the optical comb is 1:1, the width n (mm) is 0.125, 0.5, 1, 2, and the moving speed is 10mm/min.

Regarding the transmitted image sharpness C _n (%), in the transmission image sharpness measurement test, the maximum value of the transmitted light amount when the light beam axis has a transmission portion (bright portion) of the comb is set to M _n , The minimum value of the amount of transmitted light when there is a light-shielding portion (dark portion) of the comb on the ray axis is calculated by the following formula (3) when m _n is used.

C _n ＝{(M _n -m _n )/(M _n +m _n )}×100 Formula (3)

The total value T _c (%) is the clarity of four transmission images C _0.125 (%), C 0.5 (%), C ₁ (%) when the width n (mm) of the optical comb is 0.125, _0.5 , 1, and 2 respectively. ), C ₂ (%), therefore, the maximum value that can be obtained is 400%.

By making the total value T _c (%) satisfy the relationship of the above-mentioned formula (1), the total haze value H (%) satisfies the relationship of the above-mentioned formula (2), so that the occurrence of fading and whitishness can be suppressed, and it is possible to suppress the occurrence of haze caused by transmission. A polarizer protective film that prevents the occurrence of rainbow spots caused by light.

Here, the "total haze value" is determined by the total light transmittance Tt representing the total amount of light transmitted through the polarizer protective film and the diffused light transmitted through the polarizer protective film. The ratio of the rate Td was calculated|required by the following formula (4).

Total haze (%) = (Td/Tt) × 100 Formula (4)

The total light transmittance Tt is the sum of the parallel light transmittance Tp transmitted coaxially with the incident light and the diffuse light transmittance Td. The total light transmittance Tt and the diffuse light transmittance Td are values measured based on JIS K 7361.

The total haze value of a polarizer protective film is specifically measured as follows. That is, first, in order to prevent warping of the film, the base film 101 side of the polarizer protective film was bonded to the glass substrate with an optically transparent adhesive so that the light-diffusing layer 102 became the surface, and a test was prepared. The total haze value of the test piece was measured. The total haze value is measured using a haze transmittance meter based on JIS K 7136 (for example, Haze Meter "HM-150" manufactured by Murakami Color Technology Research Institute Co., Ltd.), to measure the total light transmittance Tt and diffuse light transmission. The ratio (Td) is calculated according to the above formula (4).

<Light diffusion layer>

The polarizer protective film 100 shown in FIG. 1 has the light-diffusion layer 102 laminated|stacked on the base film 101. As shown in FIG. The light-diffusing layer 102 is a layer based on the translucent resin 103 , and the translucent fine particles 104 are dispersed in the translucent resin 103 . It should be noted that there may be other layers (including an adhesive layer) between the base film 101 and the light diffusion layer 102 .

The light-transmitting resin 103 is not particularly limited as long as it is a light-transmitting resin. Thermoplastic resins, cured products of metal alkoxides, etc. When ionizing radiation curable resin, thermosetting resin, or metal alkoxide is used, the resin is cured by irradiation with ionizing radiation or by heating to form the translucent resin 103 . Among these resins, ionizing radiation-curable resins are preferable because they have high hardness and can impart high scratch resistance when used as a polarizer protective film provided on the surface of a liquid crystal display device.

Examples of ionizing radiation-curable resins include polyfunctional acrylates such as polyol acrylates or methacrylates, polyfunctional polyurethanes synthesized from diisocyanates, polyols, and hydroxy esters of acrylic or methacrylic acid. Acrylic etc. In addition, in addition to these resins, polyether resins, polyester resins, epoxy resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiol-polyene resins, etc. having acrylate functional groups can also be used. .

Examples of the thermosetting resin include phenolic resin, urea melamine resin, epoxy resin, unsaturated polyester resin, and silicone resin, in addition to thermosetting polyurethane resin composed of acrylic polyol and isocyanate prepolymer.

Examples of thermoplastic resins include cellulose derivatives such as cellulose acetate, nitrocellulose, acetylbutyl cellulose, ethyl cellulose, methyl cellulose, vinyl acetate and its copolymers, vinyl chloride and its Vinyl resins such as copolymers, vinylidene chloride and its copolymers, acetal resins such as polyvinyl formal and polyvinyl butyral, acrylic resins such as acrylic resins and their copolymers, methacrylic resins and their copolymers, etc. resins, polystyrene resins, polyamide resins, polyester resins, polycarbonate resins, etc.

As the metal alkoxide, a silicon oxide-based substrate or the like made of a silicon alkoxide-based material can be used. Specifically, tetramethoxysilane, tetraethoxysilane, etc., can be made into an inorganic or organic-inorganic composite matrix (light-transmitting resin) by hydrolysis or dehydration condensation.

In addition, as the translucent microparticles 104 used in the present invention, organic microparticles or inorganic microparticles having translucency can be used. For example, organic fine particles made of acrylic resin, melamine resin, polyethylene, polystyrene, silicone resin, acrylic-styrene copolymer, etc., or organic particles made of calcium carbonate, silicon dioxide, aluminum oxide, barium carbonate , barium sulfate, titanium oxide, inorganic particles formed by glass, etc. In addition, organic polymer balls or hollow glass beads can also be used. The translucent fine particles 104 may be composed of one kind of fine particles, or may contain two or more kinds of fine particles. The shape of the light-transmitting fine particles 104 may be spherical, flat, plate-like, needle-like, or indeterminate. The interface of the light-transmitting fine particles 104 provides a slight deviation, and it is easy to form a polarizer protective film in which the total value T _c of the clarity of the transmitted image satisfies the relationship of the above-mentioned formula (1). Examples of the amorphous translucent fine particles include amorphous silica.

Here, the weight-average particle diameter of the translucent fine particles 104 is preferably 0.1 μm to 30 μm, more preferably 0.1 μm to 5 μm. When the weight-average particle diameter of the translucent fine particles 104 is less than 0.1 μm, they may hardly contribute to internal scattering of visible light. In addition, if the weight-average particle diameter exceeds 5 μm, it may be difficult to form a polarizer protective film so that the total haze value H satisfies the relationship of the above-mentioned formula (2), and further, the thickness of the light diffusion layer 102 as a whole becomes thicker, and sometimes Thinning of the display is hindered. The weight-average particle diameter of the light-transmitting fine particles 104 was measured using a Coulter Multisizer (manufactured by BECKMAN COULTER) using the Coulter principle (pore resistance method). The light-transmitting fine particles 104 may contain two or more kinds of fine particles having different weight-average particle diameters.

The refractive index of the translucent fine particles 104 is preferably larger than the refractive index of the translucent resin 103, and the difference is preferably in the range of 0.04 to 0.15. By setting the difference in refractive index between the light-transmitting fine particles 104 and the light-transmitting resin 103 within the above-mentioned range, moderate internal scattering due to the difference in refractive index between the light-transmitting fine particles 104 and the light-transmitting resin 103 occurs, and it is easy to cause The total value T _c of the transmitted image sharpness of the polarizer protective film is controlled so as to satisfy the relationship of the above-mentioned formula (1).

In addition, it is preferable that the surface of the light scattering layer (the surface on the opposite side to the base film 101 ) be formed of only the translucent resin 103 . That is, it is preferable that the light-transmitting fine particles 104 are completely buried in the light-diffusing layer 102 without protruding from the surface of the light-diffusing layer 102 . When the translucent fine particle 104 protrudes from the surface of the light-diffusion layer 102, it may become difficult to make a polarizer protective film so that total haze value H may satisfy the relationship of said Formula (2).

The layer thickness of the light-diffusing layer 102 is preferably 10 μm to 20 μm. When it is less than 10 μm, the light-transmitting fine particles 104 may protrude from the surface of the light-diffusing layer 102 . On the other hand, if it exceeds 20 μm, the overall thickness of the polarizer protective film becomes thick, and it tends to curl or crack easily, which is disadvantageous in handling.

In addition, the polarizer protective film of this invention may be provided with the antireflection layer laminated|stacked on the light-diffusion layer 102 shown in FIG. 1 (surface opposite to the base film 101). The anti-reflection layer is provided to reduce the reflectance infinitely, and the reflection on the display screen can be prevented by forming the anti-reflection layer. As the antireflection layer, a low-refractive-index layer made of a material with a lower refractive index than the light-diffusing layer 102, a high-refractive-index layer made of a material with a higher refractive index than the light-diffusing layer 102, and a layer made of a material with a higher refractive index than the light-diffusing layer 102 can be cited. A laminated structure of low-refractive-index layers made of low-refractive-index materials.

<Base film>

The base film 101 is a film having birefringence. The in-plane retardation value R for light having a wavelength of 590 nm is preferably 100 to 2500 nm, more preferably 400 to 1500 nm. When the in-plane retardation value of the base film 11 is less than 100 nm, rainbow spots due to birefringence are less likely to occur, and even if they occur, they are less likely to affect image quality degradation. The in-plane retardation value R of the base film 11 is a value defined by the following formula (5).

R＝(n _{x -ny} )×d Formula (5)

In formula (5),

n _x : Refractive index in the direction of the in-plane slow axis of the substrate film,

n _y : Refractive index in the in-plane advancing axis direction (direction perpendicular to the slow axis direction) of the substrate film,

d: Average thickness of the base film.

The material of the base film 101 is not particularly limited, and known materials can be used. For example, polyester-based resins such as polyethylene terephthalate, polyolefin-based resins such as polyethylene or polypropylene, ethylene-vinyl acetate-based resins, polymethyl methacrylate, etc. Synthetic polymers such as cyclic olefin-based resins such as acrylic resins and norbornene-based resins, and natural polymers including cellulose-based resins such as cellulose diacetate or cellulose triacetate. The base film 101 is preferably colorless and transparent, but it may be colored or translucent as long as it does not affect defect detectability for the purpose of surface recognition or the like.

The method of manufacturing the base film 101 using the above materials is not particularly limited, and it can be manufactured by a known method such as a solvent casting method or an extrusion method. In addition, the base film 101 subjected to a stretching treatment such as uniaxial stretching or biaxial stretching after film molding can be used. As the base film 101 whose in-plane retardation value R is in the said range, it is preferable to use the base film 101 which consists of the polyester resin which performed the stretching process. For example, the base film 101 which consists of stretched polyethylene terephthalate is mentioned.

Stretching is usually performed continuously while unwinding the film roll, and is stretched in a heating furnace in the direction in which the roll advances, in a direction perpendicular to the advance direction, or in both directions. The temperature of the heating furnace is generally in the range from the vicinity of the glass transition temperature of the resin constituting the base film 101 to the glass transition temperature +100°C.

The polyester film used as the base film 101 is a film mainly composed of polyester, and may be a single-layer film mainly composed of polyester or a multilayer film having a layer mainly composed of polyester. In addition, surface treatment can also be carried out on both sides or one side of these single-layer films or multi-layer films, and the surface treatment can be surface modification by corona treatment, saponification treatment, heat treatment, ultraviolet irradiation, electron beam irradiation, etc., Thin film formation by coating, vapor deposition, etc. of polymers or metals may also be used. The weight ratio of polyester to the entire polyester film is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more.

Examples of polyester include polyethylene terephthalate, polyethylene isophthalate, polyethylene 2,6-naphthalate, and polybutylene terephthalate. , 1,4-cyclohexanedimethanol terephthalate, two or more of these can be used as needed. Among them, polyethylene terephthalate is preferably used.

Polyethylene terephthalate is a polyester having a structural unit derived from terephthalic acid as a dicarboxylic acid component and a structural unit derived from ethylene glycol as a diol component, and preferably 80 mol% or more of all repeating units are Ethylene terephthalate may contain structural units derived from other copolymerization components. Other copolymerization components include isophthalic acid, p-β-hydroxyethoxybenzoic acid, 4,4'-dicarboxybiphenyl, 4,4'-dicarboxybenzophenone, bis(4-carboxy Dicarboxylic acid components such as phenyl)ethane, adipic acid, sebacic acid, sodium isophthalic acid-5-sulfonate, 1,4-dicarboxycyclohexane, or propylene glycol, butylene glycol, neopentyl diol Diol components such as alcohol, diethylene glycol, cyclohexanediol, ethylene oxide adduct of bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

These dicarboxylic acid components or diol components can be used in combination of 2 or more types as needed. In addition, hydroxycarboxylic acids such as p-hydroxybenzoic acid may be used together with the above-mentioned carboxylic acid component or diol component. As other copolymerization components, dicarboxylic acid components and/or diol components containing small amounts of amide bonds, urethane bonds, ether bonds, carbonate bonds, etc. can be used. As a method for producing polyethylene terephthalate, the following method can be used: the so-called direct polymerization method of directly reacting terephthalic acid, ethylene glycol, and other dicarboxylic acids and/or other glycols used as needed , an arbitrary production method such as a so-called transesterification method in which dimethyl terephthalic acid and ethylene glycol, and dimethyl ester of other dicarboxylic acids and/or other diols are subjected to a transesterification reaction if necessary.

Known additives can be added to polyester as needed, and examples thereof include lubricants, antiblocking agents, heat stabilizers, antioxidants, antistatic agents, light stabilizers, impact resistance modifiers, and the like. However, since transparency is generally required when using a polyester film as a base film of an antiglare film, it is preferable to limit the additive amount to a minimum.

The polyester film is preferably uniaxially stretched or biaxially stretched (the polyester film thus uniaxially stretched or biaxially stretched is also abbreviated as "stretched polyester film" hereinafter). A stretched polyester film is excellent in mechanical properties, solvent resistance, scratch resistance, cost, and the like, and an optical film using such a polyester film has excellent mechanical strength and can be reduced in thickness.

A stretched polyester film can be obtained by molding polyester into a film and performing a uniaxial stretching treatment or a biaxial stretching treatment. By stretching, a polyester film with high mechanical strength can be obtained. The production method of the stretched polyester film is arbitrary and is not particularly limited. For example, as a uniaxially stretched polyester film, polyester is melted and extruded into a sheet to obtain a non-oriented film. A method in which the non-oriented film is stretched transversely with a tenter at a temperature equal to or higher than the glass transition temperature, and then subjected to a heat-fixing treatment. In addition, for the biaxially stretched polyester film, polyester is melted and extruded into a sheet to obtain a non-oriented film, and the non-oriented film is longitudinally stretched at a temperature above the glass transition temperature by a tenter. After that, heat-fixing treatment is carried out, and after transverse stretching, heat-fixing treatment is carried out. In this case, the stretching temperature is usually 80 to 130°C, preferably 90 to 120°C, and the draw ratio is usually 2.5 to 6 times, preferably 3 to 5.5 times. When the draw ratio is low, the polyester film tends not to exhibit sufficient transparency.

In addition, in order to reduce the deviation of the main axis of orientation, it is preferable to perform a relaxation treatment on the polyester film before heat-fixing treatment after stretching. The temperature during the relaxation treatment is usually 90 to 200°C, preferably 120 to 180°C. The amount of relaxation varies depending on stretching conditions, but it is preferable to set the amount of relaxation and the temperature during the relaxation treatment so that the thermal shrinkage rate at 150° C. of the polyester film after the relaxation treatment is 2% or less.

The heat fixing treatment temperature can be set at 180 to 250°C, preferably 200 to 245°C. In the heat setting treatment, first, after performing the heat setting treatment at a fixed length, it is preferable to perform a relaxation treatment in the width direction in order to reduce the deflection of the main axis of orientation and improve the strength such as heat resistance. The amount of slack at this time is preferably adjusted so that the thermal shrinkage rate at 150° C. of the polyester film after the slack treatment is 1 to 10%, more preferably 2 to 5%. The maximum value of the deflection of the main axis of orientation of the stretched polyester film used in the present invention is usually 10 degrees or less, preferably 8 degrees or less, more preferably 5 degrees or less. When the maximum value of the orientation main axis is larger than 10 degrees, coloring defects tend to increase when bonded to a liquid crystal display screen. In addition, "the maximum value of the deflection of an orientation main axis" of a stretched polyester film can be measured, for example with the retardation film detection apparatus RETS system by Otsuka Electronics Co., Ltd..

The thickness of the base film 101 is preferably 20 to 100 μm, more preferably 30 to 50 μm. If the thickness of the base film 101 is less than 20 μm, it tends to be difficult to handle, and if the thickness exceeds 100 μm, the advantage of thinning tends to be weakened.

<Manufacturing method of polarizer protective film>

Next, the method for manufacturing the polarizer protective film shown in FIG. 1 is demonstrated. The polarizer protective film 100 is preferably produced by a method including the following steps (A) and (B).

(A) a coating process of forming a coating layer by coating a coating liquid containing a translucent resin in which translucent fine particles 104 are dispersed on the base film 101, and

(B) A curing step of curing the above-mentioned coating layer.

二唑系光聚合引发剂等。另外，作为光聚合引发剂，例如，可以使用2，4，6-三甲基苯甲酰基二苯基氧化膦、2，2′-双(邻氯苯基)-4，4′，5，5′-四苯基-1，2′-二咪唑、10-丁基-2-氯吖啶酮、2-乙基蒽醌、苯偶酰、9，10-菲醌、樟脑醌、苯乙醛酸甲酯、二茂钛化合物等。光聚合引发剂的用量通常相对于涂装液中含有的树脂100重量份为0.5～20重量份，优选为1～5重量份。应予说明，为了使光扩散膜的光学特性和表面形状均质化，涂装液中的透光性微粒104的分散优选为各向同性分散。The coating solution used in the above step (A) contains translucent fine particles 104, translucent resin 103 constituting the light diffusion layer 102, or a resin forming the translucent resin 103 (for example, ionizing radiation curable resin, thermosetting resin, etc.). resin or metal alkoxide), and other components such as solvents used as needed. When an ultraviolet curable resin is used as the resin forming the translucent resin 103 , the above-mentioned coating liquid contains a photopolymerization initiator (radical polymerization initiator). As the photopolymerization initiator, for example, acetophenone-based photopolymerization initiators, benzoin-based photopolymerization initiators, benzophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, triazine-based photopolymerization initiators, photopolymerization initiator,

Oxadiazole-based photopolymerization initiators, etc. In addition, as a photopolymerization initiator, for example, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,2'-bis(o-chlorophenyl)-4,4',5, 5′-Tetraphenyl-1,2′-diimidazole, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, benzil, 9,10-phenanthrenequinone, camphorquinone, phenethyl Methyl alkydate, titanocene compound, etc. The usage-amount of a photoinitiator is 0.5-20 weight part normally with respect to 100 weight part of resin contained in a coating liquid, Preferably it is 1-5 weight part. In addition, in order to homogenize the optical characteristics and surface shape of a light-diffusion film, it is preferable that the dispersion|distribution of the translucent fine particle 104 in a coating liquid is an isotropic dispersion.

The above-mentioned coating liquid can be applied to the substrate film by, for example, a gravure coating method, a micro gravure coating method, a bar coating method, a knife coating method, an air knife coating method, a kiss coating method, or a die coating method. Law and so on. When performing coating of a coating liquid, as mentioned above, the coating layer thickness is adjusted so that the layer thickness of the light-diffusion layer 102 after hardening may become 10 micrometers - 20 micrometers.

Various surface treatments can be given to the surface (light-diffusion layer side surface) of the base film 101 for the purpose of the improvement of the coatability of a coating liquid, or the improvement of the adhesiveness with the light-diffusion layer 102. Examples of the surface treatment include corona discharge treatment, glow discharge treatment, acid surface treatment, alkali surface treatment, ultraviolet irradiation treatment, and the like. In addition, other layers such as an undercoat layer may be formed on the base film, and a coating liquid may be applied to the other layers.

In addition, in order to improve the adhesiveness of the polarizer protective film of the present invention and the polarizer, it is preferable to make the surface of the base film 101 (surface opposite to the light diffusion layer) various surface treatments to make it hydrophilic. change.

In the above step (B), the coating layer is cured. When ionizing radiation-curable resin, thermosetting resin, or metal alkoxide is used as the resin forming the light-transmitting resin 103, the above-mentioned coating layer is formed, dried (removal of solvent) as necessary, and irradiated with ionizing radiation (using ionizing radiation Curing resin) or heat (when using thermosetting resin or metal alkoxide) to cure the coating layer. The ionizing radiation can be appropriately selected from ultraviolet rays, electron beams, near ultraviolet rays, visible light, near infrared rays, infrared rays, X-rays, etc. according to the type of resin contained in the coating liquid. Among these ionizing radiations, ultraviolet rays and electron beams are preferred. Ultraviolet rays are particularly preferred from the viewpoint of ease of handling and obtaining high energy.

As a light source of ultraviolet light, for example, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, or the like can be used. In addition, an ArF excimer laser, a KrF excimer laser, an excimer lamp, synchrotron radiation light, or the like can be used. Among these light sources, ultra-high pressure mercury lamps, high pressure mercury lamps, low pressure mercury lamps, xenon lamps, and metal halide lamps are preferably used.

In addition, examples of electron beams include Cockcroft-Walton type, Van de Graff type, resonant transformer type, insulating core transformer type, and linear type. An electron beam having an energy of 50 to 1000 keV, preferably 100 to 300 keV, emitted from various electron beam accelerators such as Dynamitron type and high frequency type.

_Tc and H of the polarizer protective film can be adjusted within the ranges prescribed by the present invention by, for example, the method shown below. First, a polarizer protective film was produced using the above-mentioned materials and methods, and _Tc and H were measured. As a result, when the value of T _c is too high, by any treatment such as increasing the number of translucent fine particles added, greatly increasing the particle diameter of the translucent fine particles, thickening the layer thickness of the light diffusion layer, or combining these treatments 2 or more, thereby re-manufacturing the polarizer protective film, and measuring its _Tc and H; treatment, or a combination of these treatments, to manufacture a polarizer protective film again, and measure its _Tc and H. The above-mentioned production of the polarizer protective film and the measurement of its T _c and H are repeated until the target T _c value and H value are reached.

[Polarizer]

The polarizer protective film of this invention is bonded to the surface of a polarizer, and the polarizing plate which consists of a polarizer and a polarizer protective film is comprised. Utilize the protective film of the polarizer of the present invention, suppress the occurrence of discoloration and whitishness, and suppress the generation of the rainbow spot caused by transmitted light, mechanical strength is also excellent, so the polarizing plate that has used this protective film of the polarizer becomes and this A polarizing plate that suppresses the occurrence of fading and whitening as well as the polarizer protective film, suppresses the occurrence of rainbow spots, and has excellent mechanical strength. As the polarizer, known polarizers can be used. The polarizer is generally formed of a polyvinyl alcohol-based resin film in which iodine or a dichroic dye is adsorbed and aligned. The polarizer protective film of the present invention is bonded to at least one surface of a polarizer to constitute a polarizing plate. Either of the polarizing plate used on the visible side of the image display element and the polarizing plate used on the rear side can be configured. For example, the polarizing plate on the visible side can be configured by arranging the polarizer protective film and the polarizer so that the light-diffusing layer 102 , the base film 101 , and the polarizer are stacked in this order from the visible side. For example, a polarizer protective film and a polarizer can be arranged so that the polarizer, the base film 101, and the light-diffusion layer 102 are laminated|stacked in this order from a visible side, and the polarizing plate of a back side can be comprised. The polarizer protective film of this invention can be bonded on both surfaces of one polarizer, and a polarizing plate can be comprised.

[Image display device]

A polarizing plate using the polarizer protective film of the present invention is used together with an image display element to constitute an image display device. Here, a typical image display element is a liquid crystal panel that includes a liquid crystal cell in which liquid crystal is sealed between upper and lower substrates, and displays an image by changing the alignment state of the liquid crystal by applying a voltage. The image display device provided with the polarizer protective film of the present invention suppresses discoloration and whitening of the display screen and occurrence of rainbow spots caused by transmitted light, and is excellent in mechanical strength.

Example

Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these Examples. In addition, the measuring method of the optical characteristic of the polarizer protective film in the following example, and the weight average particle diameter of a light-transmitting fine particle is as follows.

(a) The total value T _c of the clarity of the light-transmitting image C _n

The above-mentioned transmission image sharpness measurement test was carried out using a mapping tester (manufactured by Suga Testing Instrument Co., Ltd.), and the transmission images when the widths of the optical combs were 0.125mm, 0.5mm, 1mm, and 2mm were calculated according to the formula (3) Sharpness C _0.125 , C _0.5 , C ₁ , C ₂ . And calculate the total value T _c of C _0.125 , C _0.5 , C ₁ , and C ₂ .

(b) Total haze value H

Using a haze transmittance meter based on JIS K 7136 (Haze Meter "HM-150" manufactured by Murakami Color Technology Research Institute Co., Ltd.), the total light transmittance Tt and the light transmitted through the polarizer protective film were measured. Diffuse light transmittance Td, calculate total haze value H according to formula (4).

(c) Weight-average particle diameter of light-transmitting fine particles

Measurement was performed using a Coulter Multisizer (manufactured by Beckman Coulter) utilizing the Coulter principle (pore resistance method).

<Example 1>

92 parts by weight of an acrylic ultraviolet curable resin (solid content 100%, trade name LIGHT ACRYLATE DPE-6A, manufactured by Kyoeisha Chemical Co., Ltd.) and amorphous silica 8 with an average particle diameter of 1.3 μm (Coulter principle) Parts by weight (trade name: AZ-204, manufactured by TosohSilica Co., Ltd.), 0.24 parts by weight of dispersant (trade name: DISPERBYK102, manufactured by BYK-Chemie Japan Co., Ltd.), 0.16 parts by weight of anti-settling agent (trade name: BYK411, BYK-Chemie Japan Co., Ltd.) was mixed with a disperser to obtain a dispersion (A). 2.4 parts by weight of photoinitiator (trade name: IRGACURE184, manufactured by Ciba Specialty Chemicals), 25 parts by weight of toluene, and 25 parts by weight of isobutanol are mixed into 47.6 parts by weight of the above-mentioned compounded dispersion with a disperser, and stirred to obtain Coating solution (B). Coating solution (B) was coated on a 38 μm polyethylene terephthalate (PET) film (trade name: Lumirror, manufactured by TORAY Co., Ltd., in-plane retardation value 1000 nm) with a #10 bar coater On, cured with 300mJ/cm ² ultraviolet rays to obtain a polarizer protective film.

<Comparative example 1>

As the optical film of Comparative Example 1, the following optical film was used: On a biaxially stretched polyethylene terephthalate (PET) film (substrate film) (trade name: Lumirror, manufactured by TORAY Co., Ltd.) , has an anti-glare layer mainly formed of pentaerythritol tetraacrylate (PETA) and trimethylol hexyl lactone (HDI), and does not contain light-transmitting particles in the anti-glare layer.

<Comparative example 2>

As the optical film of Comparative Example 2, the following optical film was used: On a biaxially stretched polyethylene terephthalate (PET) film (substrate film) (trade name: Lumirror, manufactured by TORAY Co., Ltd.) , having a hard coat mainly formed of pentaerythritol tetraacrylate (PETA), triallyl isocyanurate (trade name: TAIC (registered trademark)), and isophorone diisocyanate (IPDI), on hard The coating contains perfluoropolyether (antifouling agent), light-transmitting particles with a weight average particle size of 6 μm (copolymerization of styrene, ethylene glycol dimethacrylate (EDMA) and methyl methacrylate (MMA) things).

<Comparative example 3>

As the optical film of Comparative Example 3, the following optical film was used: On a biaxially stretched polyethylene terephthalate (PET) film (substrate film) (trade name: Lumirror, manufactured by TORAY Co., Ltd.) , has a hard coat mainly formed of pentaerythritol tetraacrylate (PETA) and isophorone diisocyanate (IPDI), and contains light-transmitting fine particles (styrene, diisocyanate) with a weight average particle diameter of 6.5 μm in the hard coat Copolymer of ethylene glycol methacrylate (EDMA) and methyl methacrylate (MMA), Al particles with a weight average particle diameter of 100 nm, and Mg aggregates.

<Comparative example 4>

As the optical film of Comparative Example 4, the following optical film was used: on a biaxially stretched polyethylene terephthalate (PET) film (substrate film) (trade name: Lumirror, manufactured by TORAY Corporation), A hard coat mainly composed of pentaerythritol tetraacrylate (PETA) and isophorone diisocyanate (IPDI). Copolymers of glycol esters).

<Comparative example 5>

As the optical film of Comparative Example 5, the following optical film was used: on a biaxially stretched polyethylene terephthalate (PET) film (substrate film) (trade name: Lumirror, manufactured by TORAY Corporation), with A hard coat mainly composed of pentaerythritol tetraacrylate (PETA) containing amorphous silica particles.

(Manufacture of liquid crystal display devices)

Moreover, liquid crystal display devices were produced using the obtained polarizer protective film of Example 1 and the optical films of Comparative Examples 1 to 4, and rainbow unevenness and discoloration due to transmitted light were evaluated according to the following method. First, the visible-side polarizing plate was peeled off from the liquid crystal display device "AQUOS (registered trademark) LC-20AX5" manufactured by Sharp Co., Ltd. The polarizer protective film of 1 and the optical films of Comparative Examples 1 to 4 were bonded together as a visible side protective film to produce a liquid crystal display device.

(Rainbow spot evaluation)

The obtained liquid crystal display device was made to perform white display, and the occurrence of rainbow unevenness due to transmitted light was visually evaluated according to the following criteria. The results are shown in Table 1.

A: Almost no rainbow spots can be seen

C: Rainbow spots are clearly seen

(evaluation of fading and whitishness)

The obtained liquid crystal display device performed black display, and the fading and whitishness of the black display image were visually evaluated in accordance with the following criteria in a room where a fluorescent lamp was lit. The results are shown in Table 1.

A: The black is tight, less fading and whitish

C: Black appears faded and whitish

Table 1

It can be seen from Table 1 that the polarizer protective film of Example 1 whose total haze value _Tc satisfies the relationship of formula (1) and the total haze value H satisfies the relationship of formula (2) can suppress the transmission The occurrence of rainbow spots of light suppresses the occurrence of fading and whitishness.

(Analysis of test results)

2 shows a graph plotting the relationship between the total haze value H of the polarizer protective film of Example 1 and the optical films of Comparative Examples 1 to 5 in Table 1, and the total value _Tc of the clarity of the transmitted image.

As shown in FIG. 2 , the relationship of the straight line 200 was derived from the plotted points of the relationship between the total haze value H of the optical films (general optical films) of Comparative Examples 1 to 5 and the total value T _c of the transmitted image clarity. On the other hand, the plotted points of Example 1 deviate greatly from the straight line 200 . In the relationship with the straight line 200, if the plot point of the relationship between the total haze value H and the total value _Tc of the transmitted image sharpness is located in the peripheral region 201 of Example 1, it is expected to be the same as that of Example 1. It is possible to construct an image display device that suppresses the occurrence of rainbow spots caused by transmitted light and suppresses the occurrence of discoloration and whitening, and derives the relationship between formula (1) and formula (2).

Claims (7)

1. A polarizer protective film having a light diffusion layer, The total value T _c of the transmission image sharpness C _n in the transmission image sharpness measurement test satisfies the relationship of the following formula (1), and the total haze value H satisfies the relationship of the following formula (2). _n , T _c and H are all in %, In the test for the measurement of the clarity of the transmitted image, the light quantity of the transmitted light of the test piece is measured by an optical comb of width n moving at a speed of 10 mm/min, which is perpendicular to the ray axis of the transmitted light. The unit is mm, In the test for the measurement of the sharpness of the transmitted image, the maximum value of the transmitted light amount when the transmitted portion of the optical comb exists on the ray axis is M _n , and the maximum value of the transmitted light amount when the light-shielding portion of the optical comb is present on the ray axis is M n . When the minimum value of the excess light is m _n , the clarity of the transmitted image C _n is calculated by the following formula (3), and the C _n is expressed in %, The total value T _c is the total value of the transmission image sharpness C _0.125 , C 0.5 , C 1 , and C 2 when the width n of the optical comb is 0.125, _0.5 , ₁ , and _2, respectively, and the unit of n is is mm, 0≤T _c ≤125 Formula (1) 0≤H≤10 Formula (2) Cn={(M _n -m _n )/(M _n +m _n )}×100 Formula (3). 2. The polarizer protective film according to claim 1, wherein a base film and the light diffusion layer are laminated, and the base film has birefringence. 3. The polarizer protective film according to claim 2, wherein the in-plane retardation value of the base film is 400 nm or more. 4. The polarizer protective film according to claim 2, wherein the base film contains a polyester-based resin as a main component. 5. The polarizer protective film according to claim 2, wherein the base film has a thickness of 50 μm or less. 6. The polarizer protective film according to claim 1, wherein the light-diffusing layer contains a translucent resin and translucent fine particles. 7. The polarizer protective film according to claim 6, wherein the translucent fine particles contain amorphous fine particles.

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