JP2014134735A - Light diffusion film and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusion film which is easy to manufacture.SOLUTION: In one embodiment of the present invention, a light diffusion film is manufactured by coating one or both surfaces of a transparent film with an emulsion (A) obtained by emulsion-polymerizing an unsaturated monomer (I) in the presence of an addition-fragmentation chain transfer agent and then adding an unsaturated monomer (II) to the resultant emulsion-polymerized unsaturated monomer to thereby polymerize the monomer. A polymer of the unsaturated monomer (I) has a theoretical glass-transition temperature of 80 to 150°C, inclusive, and a polymer of the unsaturated monomer (II) has a theoretical glass-transition temperature of -70 to 50°C, inclusive. An absolute value of a difference in refractive index between the unsaturated monomer (I) and the unsaturated monomer (II) is in the range of 0.020 to 0.100, inclusive.

Description

  One embodiment of the present invention relates to a light diffusion film, a method for producing a light diffusion film, a backlight unit, and a liquid crystal display device.

  Conventionally, in a liquid crystal display device used for a television, a personal computer, a mobile phone, a digital camera, etc., in order to make a display image easy to see, a backlight unit is arranged behind the liquid crystal display panel, and light from the backlight unit is liquid crystal. Generally, an image is displayed by supplying it to a display panel. As a component of the backlight unit, a light diffusion film that supplies as much light as possible to the liquid crystal display panel is used.

  As a method for producing a light diffusion film, a method of applying a binder resin and a coating liquid containing resin particles on a transparent film is known.

  Patent Document 1 discloses a light diffusing film having a base film and a light diffusing layer thereon, the light diffusing layer comprising resin particles for light diffusing film and a binder resin layer in which the light diffusing film is dispersed. It is disclosed. Also, in Cited Document 1, as a method for producing resin particles for a light diffusion film, a step of polymerizing a non-fluorinated vinyl monomer in the presence of a chain transfer agent to obtain seed particles, A monomer mixture containing 5% to 50% by weight of a vinyl fluoride monomer and 5 to 50% by weight of a crosslinkable vinyl monomer is absorbed or absorbed until the seed particles swell 35 to 120 times, and then the monomer mixture is polymerized. And a step of obtaining resin particles for a light diffusion film having an average particle diameter of 10 to 50 μm.

  However, since it is necessary to uniformly apply the coating liquid in which the resin particles are uniformly dispersed in the binder resin solution on the transparent film, a great amount of labor is required to maintain the quality regarding the dispersibility of the resin particles. .

JP 2011-137096 A

  An object of one embodiment of the present invention is to provide a light diffusing film that can be easily manufactured in view of the problems of the conventional techniques.

(1) The emulsion (A) obtained by emulsion polymerization of the unsaturated monomer (I) in the presence of an addition-cleavage chain transfer agent and then adding the unsaturated monomer (II) to the polymerization is transparent. The unsaturated monomer (I) is produced by coating on one or both sides of the film, and the theoretical glass transition temperature of the polymer is 80 ° C. or higher and 150 ° C. or lower, and the unsaturated monomer (II) is a polymer having a theoretical glass transition temperature of −70 ° C. or more and 50 ° C. or less, and an absolute difference in refractive index between the unsaturated monomer (I) and the unsaturated monomer (II). A light diffusion film having a value of 0.020 or more and 0.100 or less.
(2) The light diffusion film according to (1), wherein the addition-cleavage chain transfer agent is 2,4-diphenyl-4-methyl-1-pentene.
(3) The mass ratio of the addition-cleavage chain transfer agent to the unsaturated monomer (I) is 5 × 10 ⁻³ or more and 5 × 10 ⁻² or less (1) or (2) The light diffusing film described in 1.
(4) The mass ratio of the unsaturated monomer (I) to the unsaturated monomer (I) and the unsaturated monomer (II) is from 0.1 to 0.5. The light diffusing film according to any one of (1) to (3).
(5) The light diffusing film according to any one of (1) to (4), wherein the unsaturated monomer (I) contains methyl methacrylate.
(6) The light diffusing film according to any one of (1) to (5), wherein the unsaturated monomer (II) includes cyclohexyl methacrylate.
(7) The light diffusing film according to any one of (1) to (6), wherein the total light transmittance is from 80% to 100% and the haze is from 20% to 80%. .
(8) a step of emulsion-polymerizing the unsaturated monomer (I) in the presence of an addition-cleavage chain transfer agent and then polymerizing the unsaturated monomer (II) to produce an emulsion (A); A step of applying the emulsion (A) to one or both sides of a transparent film, wherein the unsaturated monomer (I) has a theoretical glass transition temperature of 80 ° C. or higher and 150 ° C. or lower; Monomer (II) has a theoretical glass transition temperature of the polymer of −70 ° C. or more and 50 ° C. or less, and a difference in refractive index between the unsaturated monomer (I) and the unsaturated monomer (II). The manufacturing method of the light-diffusion film characterized by the absolute value of being 0.020 or more and 0.100 or less.
(9) A backlight unit comprising the light diffusing film according to any one of (1) to (7).
(10) A liquid crystal display device comprising the backlight unit according to (9).

  According to one embodiment of the present invention, a light diffusion film that can be easily manufactured can be provided.

  Next, the form for implementing this invention is demonstrated.

  The light diffusing film is an emulsion (A) obtained by emulsion polymerization of the unsaturated monomer (I) in the presence of an addition-cleavage type chain transfer agent and then adding the unsaturated monomer (II) for polymerization. Is applied to one or both sides of a transparent film.

  Here, when the unsaturated monomer (I) is emulsion-polymerized in the presence of an addition-cleavage type chain transfer agent, a polymer having a double bond at the terminal is generated. Next, when the unsaturated monomer (II) is polymerized in the presence of a polymer having a double bond at the terminal, a block copolymer or a graft copolymer is formed.

  Since the emulsion (A) contains a block copolymer or a graft copolymer, when the emulsion (A) is applied to a transparent film and then dried, a light diffusion layer having a fine concavo-convex structure on the surface Is formed.

  The unsaturated monomer (I) may be one type of monomer or a mixture of a plurality of monomers. When unsaturated monomer (I) is a mixture of a plurality of monomers, the refractive index of unsaturated monomer (I) means the refractive index in the state of the mixture. Moreover, the theoretical glass transition temperature of unsaturated monomer (I) is a calculated value calculated | required by the formula mentioned later.

  The same applies to the unsaturated monomer (II).

  The theoretical glass transition temperature of the polymer of the unsaturated monomer (I) is 80 to 150 ° C, and preferably 90 to 140 ° C. When the theoretical glass transition temperature of the polymer of the unsaturated monomer (I) is lower than 80 ° C., the block copolymer or the graft copolymer becomes too soft, and the fine uneven structure on the surface of the light diffusion layer is present. It becomes difficult to form and light diffusibility falls. On the other hand, when the theoretical glass transition temperature of the polymer of the unsaturated monomer (I) is higher than 150 ° C., the block copolymer or the graft copolymer becomes too hard to form a light diffusion layer.

Here, the theoretical glass transition temperature Tg [K] of the polymer of the unsaturated monomer (I) is a homopolymer of each unsaturated monomer constituting the unsaturated monomer (I). Based on the theoretical glass transition temperature Tg _n [K] and the mass fraction (copolymerization ratio) W _n of each unsaturated monomer, the formula of Fox (FOX) 1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ + ... + W _n / Tg _n
It can be calculated from

_{Incidentally, W 1, W 2, ···} , W n is the weight ratio of the unsaturated monomer to the total weight of the unsaturated monomer.

  Moreover, the theoretical glass transition temperature of the homopolymer of the unsaturated monomer is described in the adhesion technology handbook (manufactured by Nikkan Kogyo Shimbun) or the polymer handbook (manufactured by Wiley-Interscience). Yes. Here, the theoretical glass transition temperature of a homopolymer of an unsaturated monomer not described in the above-mentioned material can be obtained by the following method. First, a test sample is prepared by casting and drying a solution of a homopolymer (homopolymer) obtained by solution polymerization of an unsaturated monomer on a release liner. Next, using a differential scanning calorimeter (DSC), the temperature was changed from −80 ° C. to 280 ° C. at a rate of temperature increase of 10 ° C./min. The temperature is defined as the theoretical glass transition temperature of the homopolymer of the unsaturated monomer.

  The unsaturated monomer constituting the unsaturated monomer (I) is not particularly limited, but is an aromatic unsaturated monomer such as styrene, α-methylstyrene, vinyltoluene, divinylbenzene; (meth) acrylic (Meth) acrylic acid esters such as methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate; vinyl esters such as vinyl acetate and vinyl propionate; (meth) acrylic acid Carboxyl group-containing unsaturated monomers such as itaconic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid half ester, maleic acid half ester; styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfone Sulfonic acid group-containing unsaturated monomers such as sodium acid salt; Hydroxyethyl methacrylate, etc. Hydroxyl group-containing unsaturated monomers; Cyano group-containing unsaturated monomers such as acrylonitrile and methacrylonitrile; Epoxy group-containing unsaturated monomers such as glycidyl (meth) acrylate and glycidyl allyl ether; (meth) acrylamide, Amide group-containing monomers such as diacetone (meth) acrylamide; silicone-modified unsaturated monomers; amino group-containing unsaturated monomers such as (meth) acrylic acid N, N-dimethylaminoethyl, and the like, Two or more kinds may be used in combination.

  The unsaturated monomer (I) preferably contains methyl methacrylate.

  In the present invention, (meth) acrylic acid means acrylic acid or methacrylic acid, and (meth) acrylamide means acrylamide or methacrylamide.

  The theoretical glass transition temperature of the polymer of the unsaturated monomer (II) is −70 to 50 ° C., and preferably −50 to 40 ° C. When the theoretical glass transition temperature of the polymer of the unsaturated monomer (II) is lower than −70 ° C., the block copolymer or graft copolymer becomes too soft, and the fine uneven structure on the surface of the light diffusion layer Is difficult to form, and the light diffusibility decreases. On the other hand, when the theoretical glass transition temperature of the polymer of the unsaturated monomer (II) is higher than 50 ° C., the block copolymer or the graft copolymer becomes too hard to form a light diffusion layer.

  The unsaturated monomer constituting the unsaturated monomer (II) is not particularly limited, but is an aromatic unsaturated monomer such as styrene, α-methylstyrene, vinyltoluene, divinylbenzene; (meth) acrylic (Meth) acrylic acid esters such as methyl acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate; vinyl esters such as vinyl acetate and vinyl propionate; (meth) acrylic acid Carboxyl group-containing unsaturated monomers such as itaconic acid, maleic acid, fumaric acid, crotonic acid, itaconic acid half ester, maleic acid half ester; styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, styrene sulfone Sulfonic acid group-containing unsaturated monomers such as sodium acrylate; hydroxyethyl methacrylate Hydroxyl group-containing unsaturated monomers; cyano group-containing unsaturated monomers such as acrylonitrile and methacrylonitrile; epoxy group-containing unsaturated monomers such as glycidyl (meth) acrylate and glycidyl allyl ether; (meth) acrylamide Amide group-containing monomers such as diacetone (meth) acrylamide; silicone-modified unsaturated monomers; amino group-containing unsaturated monomers such as (meth) acrylic acid N, N-dimethylaminoethyl, etc. Two or more kinds may be used in combination.

  The unsaturated monomer (II) preferably contains cyclohexyl methacrylate.

  The ratio of the mass of unsaturated monomer (I) to the total mass of unsaturated monomer (I) and unsaturated monomer (II) is usually 0.1 to 0.5, 0.12 It is preferable that it is -0.4, and it is more preferable that it is 0.15-0.3. When the ratio of the mass of the unsaturated monomer (I) to the total mass of the unsaturated monomer (I) and the unsaturated monomer (II) is less than 0.1, the fineness on the surface of the light diffusion layer It is difficult to form a concavo-convex structure, and the light diffusibility of the light diffusion film may be lowered. On the other hand, when the ratio of the weight of unsaturated monomer (I) to the total weight of unsaturated monomer (I) and unsaturated monomer (II) is greater than 0.5, a light diffusion layer is formed. It may not be possible.

  The absolute value of the difference between the refractive index of the unsaturated monomer (I) and the refractive index of the unsaturated monomer (II) is 0.020 to 0.100, and 0.030 to 0.080. Is preferred. When the absolute value of the difference between the refractive index of the unsaturated monomer (I) and the refractive index of the unsaturated monomer (II) is smaller than 0.020, the light diffusibility of the light diffusing film is lowered. On the other hand, when the absolute value of the difference between the refractive index of the unsaturated monomer (I) and the refractive index of the unsaturated monomer (II) is larger than 0.100, the appearance of the light diffusion film is deteriorated.

The refractive index is meant a refractive index for the D line of Fraunhofer at ²⁵ ℃ ⁽ⁿ 25 _D).

  The addition-cleavage type chain transfer agent is not particularly limited, but α-bromomethylstyrene, α-phenoxymethylstyrene, α-alkylthiomethylstyrene, α-t-butylperoxymethylstyrene, α-benzyloxystyrene, methyl-α. -Phenoxymethyl acrylate, methyl-α-alkylthiomethyl acrylate, 2,4-diphenyl-4-methyl-1-pentene and the like may be mentioned, and two or more may be used in combination. Among them, 2,4-diphenyl-4-methyl-1-pentene is preferable because it is easy to handle due to low odor and is relatively inexpensive and easily available industrially.

The mass ratio of the addition cleavage chain transfer agent to the unsaturated monomer (I) is usually 5 × 10 ^{−3 to} 5 × 10 ⁻² and 6 × 10 ⁻³ to 4 × 10 ^−2. Is preferable, and it is more preferable that it is 7 * 10 ^{< -3} > ^-2 * 10 ^<-2 >. When the mass ratio of the addition-cleavage chain transfer agent to the unsaturated monomer (I) is smaller than 5 × 10 ⁻³ or larger than 5 × 10 ⁻² , fine irregularities on the surface of the light diffusion layer It becomes difficult to form a structure, and the light diffusibility of the light diffusing film may be lowered.

  The addition-cleavage type chain transfer agent may be charged into the reactor before dropping the unsaturated monomer (I), or may be dropped together with the unsaturated monomer (I) into the reactor.

  When the unsaturated monomer (I) is emulsion-polymerized and when the unsaturated monomer (II) is polymerized, a polymerization initiator may be used as necessary. The polymerization initiator is a compound that generates radicals for initiating radical polymerization.

  The polymerization initiator is not particularly limited, but persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate; hydroperoxides such as hydrogen peroxide, benzoyl peroxide, and t-butyl hydroperoxide; azobis Examples include azo compounds such as isobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 4,4′-azobis (4-cyanovaleric acid), etc. Also good. Further, a redox polymerization initiator using a reducing agent such as sodium thiosulfate, sodium hydrogen sulfite, and sodium formaldehyde sulfoxylate together with a peroxide polymerization initiator may be used.

The ratio of the mass of the polymerization initiator to the total mass of the unsaturated monomer (I) and the unsaturated monomer (II) is usually 1 × 10 ^{−4 to} 5 × 10 ⁻² .

  When the unsaturated monomer (I) is emulsion-polymerized and when the unsaturated monomer (II) is polymerized, an emulsifier may be used as necessary.

  The emulsifier is not particularly limited, but alkyl sulfate salts such as sodium lauryl sulfate and sodium myristyl sulfate; alkyl aryl sulfonates such as sodium dodecylbenzenesulfonate and potassium dodecylbenzenesulfonate; sodium dioctylsulfosuccinate and dihexyl Sulfosuccinic acid ester salts such as sodium sulfosuccinate; fatty acid salts such as ammonium laurate and potassium stearate; anionic surfactants such as polyoxyethylene alkylsulfuric acid ester salts; polyoxyethylene alkylaryl sulfuric acid ester salts; sorbitan monooleate Sorbitan esters such as polyoxyethylene sorbitan monostearate; polyoxyethylene alkyl ethers; Hydrophilic nonionic emulsifiers such as polyoxyethylene alkyl esters; alkylphenyl ethers cetylpyridinium chloride, cationic emulsifiers such as cetyltrimethylammonium bromide and the like, may be used in combination.

The ratio of the mass of the emulsifier to the total mass of the unsaturated monomer (I) and the unsaturated monomer (II) is usually 5 × 10 ^{−3 to} 5 × 10 ⁻² . When the ratio of the mass of the emulsifier to the total mass of the unsaturated monomer (I) and the unsaturated monomer (II) is smaller than 5 × 10 ^−3, there is a possibility that the emulsion polymerization cannot be stably performed. There is. On the other hand, when the ratio of the mass of the emulsifier to the total mass of the unsaturated monomer (I) and the unsaturated monomer (II) is greater than 5 × 10 ⁻² , the water resistance of the light diffusion film may be reduced. There is sex.

  A conventionally well-known emulsion and water-soluble resin may be suitably added to an emulsion (A) as another coating-film formation component as needed.

  Further, when the block copolymer or graft copolymer contained in the emulsion (A) has a crosslinkable functional group, the emulsion (A) has a crosslinker capable of reacting with the crosslinkable functional group. You may mix | blend.

  Although it does not specifically limit as a crosslinking agent, The compound which has an isocyanate group, a dihydrazide compound, etc. are mentioned.

  In the emulsion (A), a film forming aid such as a plasticizer and an organic solvent, a coloring pigment, a pigment dispersant, a curing catalyst, an antifoaming agent, a thickening agent, an antiseptic, an antifreezing agent, and a leveling are added as necessary. Agents, softeners, antioxidants, anti-aging agents, light stabilizers, UV absorbers, polymerization inhibitors, light stabilizers such as benzotriazoles, phosphate esters and other flame retardants, surfactants, etc. You may mix | blend additives, such as an antistatic agent, suitably.

  Furthermore, resin particles or / and inorganic particles can be added to the emulsion (A) for the purpose of adjusting haze.

  Although it does not specifically limit as a transparent film, A plastic film etc. are mentioned.

  Although it does not specifically limit as resin which comprises a plastic film, Polyesters, such as a polyethylene terephthalate (PET) and a polyethylene naphthalate (PEN); Acrylic resins, such as a polymethylmethacrylate (PMMA); Polyethylene (PE), Polypropylene (PP) Such as polyolefin; polycycloolefin; polyimide; polycarbonate; polyurethane; triacetate cellulose (TAC); polylactic acid (PLA), and the like. Among these, polyester, polycarbonate, or a mixture thereof is preferable, and polyethylene terephthalate is more preferable.

  The thickness of the transparent film is usually 15 to 300 μm.

  The application device used when applying the emulsion (A) on the transparent film is not particularly limited, but is a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, A comma coater, a direct coater or the like is used.

The coating amount of the emulsion (A) is usually ² to 50 g / m ² and preferably 5 to 30 g / m ² in terms of mass after drying.

  The total light transmittance of the light diffusion film is usually 80 to 100%. When the total light transmittance of the light diffusion film is less than 80%, the light extraction efficiency may be reduced.

  The haze of the light diffusion film is usually 20 to 80%. If the haze of the light diffusing film is less than 20%, the light diffusibility may be reduced, and if it is greater than 80%, the light extraction efficiency may be reduced.

  In addition, the total light transmittance and haze of a light-diffusion film can be measured by the measuring method based on JISK7105 using a turbidimeter (for example, NM-150 (made by Murakami Color Research Laboratory)).

  In addition, light diffusing films are easy-adhesion layers, hard coat layers, antistatic layers, wear-resistant layers, antireflection layers, color correction layers, ultraviolet absorption layers, printed layers, metal layers, transparent conductive layers, gas barrier layers, holograms. Functional layers such as a layer, a release layer, an adhesive layer, an emboss layer, and an adhesive layer may be further formed.

  The light diffusion film can be applied to a known light diffusion unit for a liquid crystal display device.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, this invention is not limited by an Example. Moreover, a part and% mean a mass part and mass%, respectively.

[Example 1]
To a 1 L four-necked flask equipped with a stirrer, thermometer, dropping funnel and reflux condenser, 520 parts of deionized water, 8 parts of sodium dodecylbenzenesulfonate, 0.5 part of potassium persulfate and NOFMER MSD (2, 4 -Diphenyl-4-methyl-1-pentene) (manufactured by NOF Corporation) was charged, and the internal temperature was raised to 85 ° C while stirring.

  Using a separate container, after dissolving 2 parts of sodium dodecylbenzenesulfonate in 50 parts of deionized water, an unsaturated unit consisting of 100 parts of methyl methacrylate, 2 parts of methacrylic acid and 2 parts of 2-hydroxyethyl methacrylate Body (I) was added and stirred to prepare an emulsion. The unsaturated monomer (I) has a refractive index of 1.412, and the polymer has a theoretical glass transition temperature of 105 ° C.

  With the internal temperature maintained at 85 ° C., the emulsion was continuously dropped into a four-necked flask over 1 hour and stirred for 1 hour. Next, in a state where the internal temperature of the four-necked flask is maintained at 85 ° C., the unsaturated is composed of 200 parts of cyclohexyl methacrylate, 200 parts of 2-ethylhexyl acrylate, 8 parts of methacrylic acid and 8 parts of 2-hydroxyethyl methacrylate. Monomer (II) was added dropwise over 3 hours, followed by stirring for 2 hours. The unsaturated monomer (II) has a refractive index of 1.447, and the theoretical glass transition temperature of the polymer is 7 ° C. Further, after cooling, 14 parts of a 10% aqueous sodium hydroxide solution was added to adjust the pH to obtain an emulsion. The emulsion had a solid content concentration of 48.2%.

Using a bar coater, the emulsion was applied on one side of a polyethylene terephthalate (PET) film A4300 (manufactured by Toyobo Co., Ltd.) having a thickness of 100 μm so that the mass after drying was 20 g / m ^2, and then 1 at 105 ° C. It dried for minutes and obtained the light-diffusion film.

[Example 2]
Except for using unsaturated monomer (II) consisting of 50 parts of methyl methacrylate, 50 parts of cyclohexyl methacrylate, 300 parts of 2-ethylhexyl acrylate, 8 parts of methacrylic acid and 8 parts of 2-hydroxyethyl methacrylate In the same manner as in Example 1, an emulsion was obtained. The emulsion had a solid content concentration of 48.1%. The unsaturated monomer (II) has a refractive index of 1.436, and the theoretical glass transition temperature of the polymer is -25 ° C.

  A light diffusion film was obtained in the same manner as in Example 1 except that the obtained emulsion was used.

[Example 3]
Except for using unsaturated monomer (II) consisting of 50 parts of cyclohexyl methacrylate, 50 parts of 2-ethylhexyl acrylate, 300 parts of benzyl acrylate, 8 parts of methacrylic acid and 8 parts of 2-hydroxyethyl methacrylate In the same manner as in Example 1, an emulsion was obtained. The emulsion had a solid content concentration of 48.0%. The unsaturated monomer (II) has a refractive index of 1.497, and the theoretical glass transition temperature of the polymer is 8 ° C.

  A light diffusion film was obtained in the same manner as in Example 1 except that the obtained emulsion was used.

[Comparative Example 1]
An emulsion was obtained in the same manner as in Example 1 except that 2,4-diphenyl-4-methyl-1-pentene was not used. The emulsion had a solid content concentration of 47.3%.

  A light diffusion film was obtained in the same manner as in Example 1 except that the obtained emulsion was used.

[Comparative Example 2]
Except for using unsaturated monomer (II) consisting of 160 parts of methyl methacrylate, 240 parts of 2-ethylhexyl acrylate, 8 parts of methacrylic acid and 8 parts of 2-hydroxyethyl methacrylate, the same as in Example 1. An emulsion was obtained. The emulsion had a solid content concentration of 48.3%. The unsaturated monomer (II) has a refractive index of 1.427, and the polymer has a theoretical glass transition temperature of −20 ° C.

  A light diffusion film was obtained in the same manner as in Example 1 except that the obtained emulsion was used.

[Comparative Example 3]
Unsaturated monomer (I) consisting of 100 parts of styrene, 2 parts of methacrylic acid and 2 parts of 2-hydroxyethyl methacrylate and 160 parts of methyl methacrylate, 240 parts of 2-ethylhexyl acrylate, 8 parts of methacrylic acid and 2 of methacrylic acid -An emulsion was obtained in the same manner as in Example 1 except that the unsaturated monomer (II) consisting of 8 parts of hydroxyethyl was used. The emulsion had a solid content concentration of 48.2%. The unsaturated monomer (I) has a refractive index of 1.540, and the theoretical glass transition temperature of the polymer is 105 ° C. The unsaturated monomer (II) has a refractive index of 1.427, and the theoretical glass transition temperature of the polymer is -20 ° C.

  A light diffusion film was obtained in the same manner as in Example 1 except that the obtained emulsion was used.

[Comparative Example 4]
80 parts of methyl methacrylate, 20 parts of 2-ethylhexyl acrylate, 2 parts of methacrylic acid and 2 parts of 2-hydroxyethyl methacrylate and 100 parts of cyclohexyl methacrylate, 2-ethylhexyl acrylate 300 An emulsion was obtained in the same manner as in Example 1, except that the unsaturated monomer (II) consisting of 8 parts of methacrylic acid and 8 parts of 2-hydroxyethyl methacrylate was used. The emulsion had a solid content concentration of 48.4%. The unsaturated monomer (I) has a refractive index of 1.417, and the polymer has a theoretical glass transition temperature of 58 ° C. The unsaturated monomer (II) has a refractive index of 1.441, and the polymer has a theoretical glass transition temperature of −25 ° C.

  A light diffusion film was obtained in the same manner as in Example 1 except that the obtained emulsion was used.

  Table 1 shows the production conditions for the emulsions of Examples and Comparative Examples.

［不飽和単量体の屈折率］
デジタルアッベ屈折計ＤＲ−Ａ１（アタゴ社製）を用いて、不飽和単量体の２５℃におけるＤ線の屈折率を測定した。

[Refractive index of unsaturated monomer]
Using a digital Abbe refractometer DR-A1 (manufactured by Atago Co., Ltd.), the refractive index of the D-line at 25 ° C. of the unsaturated monomer was measured.

  Next, the total light transmittance, haze, and appearance of the light diffusion films of Examples and Comparative Examples were evaluated.

[Total light transmittance of light diffusion film, haze]
Using a haze meter NM-150 (Murakami Color Research Laboratory Co., Ltd.), the total light transmittance and haze of the light diffusion film were measured. The haze was calculated by dividing the diffuse transmittance by the total light transmittance and then multiplying by 100. In addition, n number was made into 3 times and the average value was employ | adopted.

[Appearance of light diffusion film]
The appearance of the light diffusion film was visually observed. In addition, the case where the state of the surface of a light-diffusion film was uniform was evaluated as (circle), and the case where defects, such as a crack and a sink, were recognized on the surface of a light-diffusion film was evaluated as x.

  In Table 2, the evaluation result of the total light transmittance, haze, and external appearance of the light-diffusion film of an Example and a comparative example is shown.

表１及び表２から、実施例１〜３の光拡散フィルムは、全光線透過率が８３〜９１％であり、ヘイズが３３〜７１％であり、外観が優れることがわかる。

From Table 1 and Table 2, it can be seen that the light diffusion films of Examples 1 to 3 have a total light transmittance of 83 to 91%, a haze of 33 to 71%, and an excellent appearance.

  On the other hand, since the light-diffusion film of Comparative Example 1 does not use an addition-cleavage chain transfer agent during the production of the emulsion, the haze is lowered.

  Since the light diffusion film of Comparative Example 2 has | X−Y | of 0.015, the haze is lowered.

  Since the light diffusion film of Comparative Example 3 has | X−Y | of 0.113, the total light transmittance decreases.

  Since the theoretical glass transition temperature of unsaturated monomer (I) is 58 degreeC, the light-diffusion film of the comparative example 4 has a haze fall.

Claims (10)

The emulsion (A) obtained by emulsion polymerization of the unsaturated monomer (I) in the presence of the addition-cleavage type chain transfer agent and then adding the unsaturated monomer (II) to the emulsion (A) is obtained on one side of the transparent film. Or it is manufactured by applying to both sides,
The unsaturated monomer (I) has a theoretical glass transition temperature of the polymer of 80 ° C. or higher and 150 ° C. or lower,
The unsaturated monomer (II) has a theoretical glass transition temperature of the polymer of −70 ° C. or higher and 50 ° C. or lower,
A light diffusion film, wherein an absolute value of a difference in refractive index between the unsaturated monomer (I) and the unsaturated monomer (II) is 0.020 or more and 0.100 or less.   The light diffusion film according to claim 1, wherein the addition-cleavage type chain transfer agent is 2,4-diphenyl-4-methyl-1-pentene. 3. The light diffusion according to claim 1, wherein a mass ratio of the addition-cleavage chain transfer agent to the unsaturated monomer (I) is 5 × 10 ⁻³ or more and 5 × 10 ⁻² or less. the film.   The ratio of the mass of the unsaturated monomer (I) to the total mass of the unsaturated monomer (I) and the unsaturated monomer (II) is from 0.1 to 0.5. The light diffusion film according to any one of claims 1 to 3.   The light diffusing film according to any one of claims 1 to 4, wherein the unsaturated monomer (I) contains methyl methacrylate.   The light diffusion film according to any one of claims 1 to 5, wherein the unsaturated monomer (II) contains cyclohexyl methacrylate. The total light transmittance is 80% or more and 100% or less,
The light diffusion film according to claim 1, wherein the haze is 20% or more and 80% or less. A step of emulsion-polymerizing the unsaturated monomer (I) in the presence of an addition-cleavage type chain transfer agent and then polymerizing the unsaturated monomer (II) to produce an emulsion (A);
A step of applying the emulsion (A) to one or both sides of the transparent film;
The unsaturated monomer (I) has a polymer theoretical glass transition temperature of 80 ° C. or higher and 150 ° C. or lower,
The unsaturated monomer (II) has a theoretical glass transition temperature of the polymer of −70 ° C. or higher and 50 ° C. or lower,
The method for producing a light diffusing film, wherein an absolute value of a difference in refractive index between the unsaturated monomer (I) and the unsaturated monomer (II) is 0.020 or more and 0.100 or less.   A backlight unit comprising the light diffusion film according to claim 1.   A liquid crystal display device comprising the backlight unit according to claim 9.