JP2009237342A - Light diffusion film, and method for manufacturing light diffusion film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion film and a method for manufacturing the light diffusion film attaining excellent light diffusibility without reducing total light transmittance, and hardly causing deformation of hollow particles to obtain desired light diffusing performance. <P>SOLUTION: The diffusion film has a light diffusion layer containing the hollow particles of single-pore structure and a binder resin and laminated on a transparent base material layer. The hollow particles of single-pore structure have an average particle diameter of 0.5-30 μm, and a shell of the hollow particle of single hole structure is formed of resin containing at least 30 wt.% of a component derived from a cross-linking monomer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention is a light diffusion film capable of realizing excellent light diffusivity without reducing the total light transmittance, and the hollow fine particles are hardly swelled or deformed, and have a desired light diffusion performance. The present invention relates to a method for producing a light diffusion film capable of obtaining a light diffusion film.

Light diffusion films are widely used in backlight units such as liquid crystal displays and liquid crystal televisions equipped in mobile phones, digital cameras, and the like. The light diffusing film is used to obtain surface illumination that is uniform and has high front luminance by diffusing the light of a point light source or a linear light source or adjusting the angle of outgoing light.
Currently, such light diffusion sheets are required to have high light diffusibility. Conventionally, as a method for improving the light diffusibility of the light diffusing sheet, a method of forming irregularities on the surface of the light diffusing sheet has been used.
However, there is a limit to improving the light diffusibility only by forming irregularities on the surface, and there is a problem that it is difficult to exhibit the high light diffusivity as required for liquid crystal display devices in recent years. there were.

On the other hand, Patent Document 1 discloses a light diffusion sheet including a light diffusion layer in which substantially spherical transparent fine particles having hollow portions are dispersed and a transparent base material layer.
In such a light diffusion sheet, while light passes through one transparent fine particle, in addition to refraction at the entrance and exit points on the surface of the transparent fine particle, it is also refracted at the boundary between the skeleton and the hollow portion of the transparent fine particle. Happens. For this reason, since the number of times of refraction of light rays in the transparent fine particles increases, it is said that high light diffusibility is exhibited.
Patent Document 1 also discloses a light diffusion sheet including a light diffusion layer in which transparent fine particles having a large number of concave portions on the surface are dispersed and a transparent base material layer.
In such a light diffusing sheet, it is said that the number of refractions of light rays while passing through transparent fine particles having a large number of recessed portions on the surface increases, and similarly exhibits high light diffusibility.

However, even with such a light diffusion sheet, there is a problem that the light diffusibility is not sufficient, and it is still insufficient to exhibit the high level of light diffusivity required in a liquid crystal display device or the like. .
Further, in the light diffusing sheet of Patent Document 1, it is necessary to add a large amount of transparent fine particles in order to improve the light diffusibility, but the light transmittance of the light diffusing sheet is reduced by adding a large amount of transparent fine particles. There was a problem that.
Further, when such a light diffusing sheet is produced by the method of the example of Patent Document 1, the transparent fine particles are swollen by the binder resin or organic solvent to be used, or are crushed into the transparent fine particles in the process of forming the light diffusing layer. There has been a problem that desired light diffusion performance cannot be obtained due to the occurrence of slack.
Japanese Patent No. 3384983

In view of the above-mentioned present situation, the present invention provides a light diffusion film capable of realizing excellent light diffusivity without reducing the total light transmittance, and the hollow fine particles are less prone to swelling, deformation, etc. It aims at providing the manufacturing method of the light-diffusion film which can obtain the light-diffusion film which has the light-diffusion performance of this.

The present invention is a light diffusion film in which a hollow fine particle having a single pore structure and a light diffusion layer containing a binder resin are laminated on a transparent substrate layer, and the hollow fine particles having the single pore structure are average particles. The shell of hollow fine particles having a diameter of 0.5 to 30 μm and having the single pore structure is a light diffusion film made of a resin containing 30% by weight or more of a component derived from a crosslinkable monomer.
The present invention is described in detail below.

The light diffusion film of the present invention has a light diffusion layer containing hollow fine particles having a single pore structure and a binder resin.

The shell constituting the hollow fine particles has a single-hole structure.
By having the single-hole structure, the void formed inside the shell is excellent in hermeticity, and the binder component and other components intrude into the void, resulting in a decrease in light diffusibility. Can be prevented.
In the present specification, the “single pore structure” refers to a structure having only one closed void, not including a plurality of voids such as a porous shape.

The shell is made of a resin containing 30% by weight or more of a component derived from a crosslinkable monomer.
By comprising such a resin, the shell is not softened and deformed by the monomer component of the binder resin or the organic solvent, and the light diffusion performance of the light diffusion film can be prevented from being lowered. Moreover, since it does not swell or whiten by the monomer component or organic solvent of binder resin, it can prevent that a total light transmittance falls.

Examples of the crosslinkable monomer include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, trimethylolpropane di ( Di (meth) acrylates such as (meth) acrylate; Tri (meth) acrylates such as trimethylolpropane tri (meth) acrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate; pentaerythritol tetra (Meth) acrylate, dipentaerythritol hexa (meth) acrylate, diallyl phthalate, diallyl malate, diallyl fumarate, diallyl succinate, triary Diallyl compounds such as isocyanurates or triallyl compounds; divinyl benzene, divinyl compounds such as butadiene and the like. These crosslinkable monomers may be used alone or in combination of two or more.

In the resin constituting the shell, the lower limit of the content of components derived from the crosslinkable monomer is 30% by weight. When it is less than 30% by weight, softening deformation, swelling, and whitening due to the monomer component of the binder resin and the organic solvent occur, and light diffusibility and total light transmittance decrease. A preferred lower limit is 30% by weight and a preferred upper limit is 95% by weight.

The resin constituting the shell is not particularly limited as long as it has 30% by weight or more of the component derived from the crosslinkable monomer, and has a component derived from the crosslinkable monomer and a component derived from the polymerizable monomer. A copolymer or the like can be used.

Examples of the polymerizable monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, cumyl (meth) acrylate, cyclohexyl (meth) acrylate, and myristyl (meth) acrylate. , Alkyl (meth) acrylates such as palmityl (meth) acrylate, stearyl (meth) acrylate, isobornyl (meth) acrylate; (meth) acrylonitrile, (meth) acrylamide, (meth) acrylic acid, glycidyl (meth) acrylate, 2- Polar group-containing (meth) acrylic monomers such as hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate; styrene, α-methylstyrene, p-methylstyrene, p-chlorostyrene, etc. Vinyl monomers; vinyl esters such as vinyl acetate and vinyl propionate; halogen-containing monomers such as vinyl chloride and vinylidene chloride; vinyl pyridine, ethylene, propylene, polydimethylsiloxane macromonomer, polyoxyethylene glycol (meth) acrylate, polyoxy Examples include propylene glycol (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and N-vinylpyrrolidone. Of these, alkyl (meth) acrylate monomers, polydimethylsiloxane macromonomers, and the like are preferable because of their relatively low refractive index. These polymerizable monomers may be used alone or in combination of two or more.

The hollow part of the hollow fine particles may contain a transparent liquid having a refractive index different from that of the shell of the hollow fine particles. Thereby, even if the ratio of the hollow part of the hollow fine particles is increased, it is possible to prevent deterioration of mechanical properties and the like.
The transparent liquid having a refractive index different from that of the hollow fine particle shell may be included in a part of the hollow part of the hollow fine particle or may be included in the entire hollow part.

Examples of the transparent liquid having a refractive index different from that of the hollow fine particle shell include n-pentane, n-hexane, cyclohexane, n-heptane, n-octane, isooctane, benzene, toluene, xylene, water, dichloromethane, chloroform, Methanol, ethanol, n-propanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, t-butyl alcohol, n-pentanol, isopentyl alcohol, neopentyl alcohol, octanol, diethyl ether, dioxane, tetrahydrofuran, acetone , Methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, nitromethane, nitroethane, acetonitrile, aniline, 2 Pyrrolidone, an organic solvent such as wax, water, as the polymer and various oligomers such as gelatin swells in a solvent and the like.

The lower limit of the average particle diameter of the hollow fine particles is 0.5 μm, and the upper limit is 30 μm. If the thickness is less than 0.5 μm, the light diffusion intensity is insufficient, and if it exceeds 30 μm, the surface roughness is conspicuous and not suitable for practical use. A preferred lower limit is 0.8 μm, a preferred upper limit is 20 μm, a more preferred lower limit is 1 μm, and a more preferred upper limit is 10 μm. Further, a more preferable lower limit is 1.5 μm, and a more preferable upper limit is 5 μm.

The hollow fine particles have a preferable lower limit of the porosity of 30% by volume and a preferable upper limit of 95% by volume. If the porosity is less than 30% by volume, light diffusibility may not be sufficiently imparted. If it exceeds 95% by volume, the shape of the hollow fine particles may not be maintained or the strength may not be ensured. A more preferred lower limit is 50% by volume.
In the present specification, the porosity refers to the volume ratio of the void portion excluding the core agent in the total volume of the hollow fine particles, for example, based on a photograph taken with a transmission electron microscope. It can be measured by measuring the average particle diameter (outer diameter) and the average inner pore diameter, and calculating the ratio of the volume of the void portion to the volume of the hollow fine particles.

In the light diffusion layer, the preferable lower limit of the content of the hollow fine particles is 5% by weight, and the preferable upper limit is 90% by weight. If it is less than 5% by weight, the light diffusibility of the resulting light diffusion layer may be extremely low, and if it exceeds 90% by weight, the durability of the light diffusion layer may be reduced.

The method for producing the hollow fine particles is not particularly limited. For example, a step of preparing a reactive monomer containing a crosslinking monomer at 30% by weight or more and a reactive solution containing a liquid that does not react with the reactive monomer, By a method comprising the steps of suspending oil droplets comprising the reactive solution in a polar solvent, polymerizing the reactive monomer to cause phase separation from the liquid, and producing microcapsule-type polymer particles containing the liquid. Can be manufactured.

The minimum with preferable content of the crosslinkable monomer in the said reactive monomer is 30 weight%. If it is less than 30% by weight, the resulting hollow fine particle shell is insufficiently crosslinked, resulting in insufficient strength, heat resistance and solvent resistance. The minimum with more preferable content of the said crosslinkable monomer is 50 weight%, and a still more preferable minimum is 70 weight%.

Examples of the monomer other than the crosslinkable monomer in the reactive monomer include the above-described polymerizable monomer and hydrophilic monomer.

The liquid is not particularly limited as long as it does not react with the reactive monomer and is liquid at the polymerization temperature of the reactive monomer. For example, n-pentane, n-hexane, cyclohexane, n-heptane. , N-octane, isooctane, benzene, toluene, xylene, water, methylene chloride, dichloromethane, chloroform, carbon tetrachloride, methanol, ethanol, n-propanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, t- Butyl alcohol, n-pentanol, isopentyl alcohol, neopentyl alcohol, octanol, diethyl ether, dioxane, tetrahydrofuran, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexa Organic solvents such as styrene, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, nitromethane, nitroethane, acetonitrile, aniline, 2-pyrrolidone, wax, polymers such as water, gelatin, and various oligomers swollen in the solvent Is mentioned.

The polar solvent used in the step of suspending the oil droplets composed of the reactive solution in a polar solvent is not particularly limited, and is used in, for example, a normal suspension polymerization method such as water, ethanol, methanol, isopropyl alcohol, or the like. Things can be used.
Further, for example, an emulsifier such as sodium dodecylbenzenesulfonate or a dispersion aid such as cetyl alcohol may be used in combination.

In the step of polymerizing the reactive monomer to cause phase separation from the liquid and producing microcapsule polymer particles enclosing the liquid, for example, when a polymerization initiator is added to the reactive solution, By heating the reactive solution dispersed in oil droplets to the reaction start temperature of the polymerization initiator, the reactive monomer in the reactive solution reacts to form a shell. As a result, microcapsule-type polymer particles in which the liquid is encapsulated in the generated shell are produced.

Thereafter, if necessary, the liquid encapsulated in the obtained microcapsule type polymer particles may be removed, or the liquid may be used as it is without being removed.
The method for removing the liquid is not particularly limited, and examples thereof include a method of blowing a gas such as nitrogen or air into the obtained dispersion of microcapsule polymer particles; a method of reducing the pressure, and the like.

The hollow fine particles obtained by using the production method of the present invention may be used as a dispersion dispersed in a solvent, or may be used in the form of particles after drying.

The binder resin constituting the light diffusion layer is not particularly limited as long as it has a particularly high transparency. For example, acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamideimide, epoxy resin, etc. Is mentioned.

The minimum with preferable content of binder resin in the said light-diffusion layer is 0.1 weight%, and a preferable upper limit is 50 weight%. If it is less than 0.1% by weight, the durability of the light diffusion layer may be lowered, and if it exceeds 50% by weight, the light diffusion property of the light diffusion layer may be lowered.

Moreover, the preferable minimum of the thickness of the said light-diffusion layer is 1 micrometer, and a preferable upper limit is 300 micrometers. If it is less than 1 μm, the light diffusibility may be insufficient, and if it exceeds 300 μm, the total light transmittance of the film may be reduced.

The transparent substrate layer is not particularly limited as long as it is transparent and has an appropriate strength. Examples thereof include films made of acrylic resin, polyolefin, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, cellulose acetate, and the like. It is done. In the present invention, the term “transparent” means that the total light transmittance in the wavelength region of 400 to 800 nm is 60% or more.

Moreover, the preferable minimum of the thickness of the said transparent base material layer is 70 micrometers, and a preferable upper limit is 200 micrometers. If it is less than 70 μm, the strength may be insufficient and deformation may occur, and if it exceeds 200 μm, the total light transmittance of the film may be reduced.

The method for producing the light diffusing film of the present invention is not particularly limited, but the step of preparing a light diffusing layer forming resin composition containing hollow fine particles having a single pore structure, a binder resin and a solvent, A method of forming a light diffusing layer by applying a predetermined curing treatment after drying the coated resin composition for forming a light diffusing layer, after coating the resin composition for a transparent substrate film As the hollow fine particles having a single-pore structure, those having an average particle diameter of 0.5 to 30 μm are used, and a component derived from a crosslinkable monomer is added to the shell of the hollow fine particles having the single-pore structure. A method using a resin containing at least wt% is preferred. Such a method for producing a light diffusion film is also one aspect of the present invention.

In the method for producing a light diffusion film of the present invention, first, a step of preparing a resin composition for forming a light diffusion layer containing hollow fine particles, a binder resin, and a solvent is performed.

In the method for producing a light diffusing film of the present invention, the hollow fine particles having a single pore structure have an average particle diameter of 0.5 to 30 μm, and the shell of the hollow fine particles having the single pore structure is a crosslinkable monomer. It is made of a resin containing 30% by weight or more of components derived from the above.
As a result, the hollow resin does not swell, whiten, or soften and deform due to the monomer component or solvent of the binder resin, enabling a low refractive index and improving the total light transmittance of the light diffusion film. can do.
In addition, as the material for the hollow fine particles, the same materials as described above can be used.

The hollow fine particles preferably have a volume change rate of 100 to 110% by volume after being immersed in an organic solvent for 24 hours.
By using such hollow fine particles, it is possible to prevent a decrease in total light transmittance.
As the organic solvent, methanol, ethanol, n-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, N, N-dimethylformamide, tetrahydrofuran, and toluene are used. Moreover, the volume change rate after being immersed in the organic solvent for 24 hours is the volume immediately after the dried hollow fine particles and the organic solvent are mixed, put in a graduated cylinder and settled, and is 24 in the organic solvent. The volume of the hollow fine particles in the graduated cylinder after being immersed for a period of time is defined as V2, and (V2 / V1) × 100 is calculated.

As the material of the binder resin, the same ones as described above can be used, and ionizing radiation curable resins are particularly preferable. By using the ionizing radiation curable resin, the bond with the hollow fine particles can be further strengthened. In particular, when the shell of the hollow fine particles is made of a copolymer having a segment derived from a crosslinkable monomer, the residual polymerizable group of the shell and the ionizing radiation curable resin are copolymerized at the time of curing. A strong light diffusion layer can be formed.

Next, a step of applying the light diffusion layer forming resin composition to the transparent substrate film is performed.
The coating method in the step of coating the light diffusion layer forming resin composition on the transparent substrate film is not particularly limited. For example, spin coating, slitting & spinning, slit coating, spray coating, dip coating, bar Conventionally known coating methods such as coating can be used.

Then, after drying the applied resin composition for forming a light diffusion layer, a predetermined curing treatment is performed to form a light diffusion layer.
In the step of drying the coated resin composition for forming a light diffusion layer, for example, the solvent is removed by heating.

The predetermined curing treatment is not particularly limited, and when a curable resin is used as the binder resin, the binder resin is cured using heat, light, electron beam, ionizing radiation, or the like.

According to the present invention, the light diffusion film capable of realizing excellent light diffusivity without reducing the total light transmittance, and the hollow light particles are less likely to swell and deform, and the desired light diffusion performance. The manufacturing method of the light-diffusion film which can obtain the light-diffusion film which has can be provided.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

Example 1
(1) Preparation of hollow fine particles 25 parts by weight of acrylonitrile and 25 parts by weight of polyoxyethylene dimethacrylate (polyoxyethylene unit number = 1; manufactured by NOF Corporation, Blenmer PDE-50R) as a polyfunctional acrylic monomer, trimethylol A monomer solution was prepared by mixing and stirring 50 parts by weight of propane triacrylate, 100 parts by weight of normal hexane as a hollowing agent, and 0.3 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator.
The total amount of the obtained monomer solution was added to an aqueous solution of 1% by weight polyvinyl alcohol (PVA) and 0.02% by weight sodium nitrite and stirred using a stirring and dispersing device to obtain an emulsified suspension.
Next, using a 20 liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized, and after deoxidizing the vessel, the pressure was returned to atmospheric pressure with nitrogen gas. The inside of the polymerization vessel was set to a nitrogen atmosphere. The entire amount of the emulsified suspension obtained above was charged all at once into this polymerization vessel, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 4 hours, the polymerization vessel was cooled to room temperature to obtain a dispersion of microcapsule polymer particles containing the liquid. The obtained dispersion was dried using a spray dryer to obtain hollow microparticles that did not enclose the liquid.

(2) Preparation of light diffusion layer forming resin composition 20 parts by weight of hollow fine particles obtained, 15 parts by weight of acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd .: copolymer of methacrylic acid and acrylic monomer) as a binder resin, solvent Then, 20 parts by weight of toluene was mixed and stirred to prepare a resin composition for forming a light diffusion layer.

(3) Production of light diffusing film The obtained light diffusing layer-forming resin composition was applied onto a 150 μm thick polyester resin sheet using a spin coater, dried at 120 ° C. for 3 minutes, and a thickness of 80 μm. A light diffusion layer was formed to obtain a light diffusion film.

(Example 2)
(1) Preparation of hollow fine particles 20 parts by weight of methyl methacrylate, 40 parts by weight of methacrylonitrile, 40 parts by weight of trimethylolpropane triacrylate as a crosslinkable monomer, 150 parts by weight of cyclohexane as a non-polymerizable substance and a polymerization initiator A cyclohexane-dispersed primary emulsion was prepared by mixing and stirring 0.3 parts by weight of azobisisobutyronitrile (AIBN).
Thereafter, the obtained primary emulsion was added to 370 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersant and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor. By stirring using a stirring and dispersing device, a secondary emulsion composed of a composite emulsion in which oil droplets encapsulating cyclohexane was dispersed in an aqueous medium was obtained.
Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 4 hours, the polymerization vessel was cooled to room temperature to obtain a dispersion containing microcapsule-type polymer particles containing the liquid. The solvent of the obtained dispersion was replaced with isopropanol using a centrifuge to obtain a hollow fine particle isopropanol dispersion containing cyclohexane.

(2) Preparation of light diffusion layer forming resin composition Isopropanol dispersion of cyclohexane-containing hollow fine particles obtained (250 parts by weight in terms of dry powder), UV curable resin (urethane acrylic monomer) as binder resin ), 30 parts by weight of a benzophenone photopolymerization initiator, and 10 parts by weight of toluene as a solvent were mixed and stirred to prepare a resin composition for forming a light diffusion layer.

(3) Preparation of light diffusing film The obtained light diffusing layer forming resin composition was applied onto a 80 μm thick triacetylcellulose sheet using a spin coater, dried at 80 ° C. for 5 minutes, and then irradiated with ultraviolet rays. Then, a light diffusion layer having a thickness of 40 μm was formed to obtain a light diffusion film.

(Comparative Example 1)
(1) Preparation of hollow fine particles As a monomer component, polypropylene glycol dimethacrylate (polyoxypropylene unit number = about 7; manufactured by NOF Corporation, Blenmer PDP-400) 50 parts by weight, methyl methacrylate 30 parts by weight, trimethylolpropane tri 20 parts by weight of methacrylate, 100 parts by weight of heptane as a non-polymerizable substance, and 0.3 part by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator were mixed and stirred to prepare a heptane-dispersed primary emulsion.
Thereafter, the obtained primary emulsion was added to 400 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersant and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor. By stirring using a stirring and dispersing device, a secondary emulsion composed of a composite emulsion in which oil droplets containing heptane were dispersed in an aqueous medium was obtained.
Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 8 hours, the polymerization vessel was cooled to room temperature to obtain a dispersion containing solvent-containing porous fine particles. The obtained dispersion was dried using a spray dryer to obtain porous fine particles.

(2) Preparation of light diffusion layer forming resin composition 20 parts by weight of the obtained porous fine particles, 15 parts by weight of acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd .: copolymer of methacrylic acid and acrylic monomer) as a binder resin, A resin composition for forming a light diffusion layer was prepared by mixing and stirring 20 parts by weight of toluene as a solvent.

(3) Production of light diffusing film The obtained light diffusing layer-forming resin composition was applied onto a 150 μm thick polyester resin sheet using a spin coater, dried at 120 ° C. for 3 minutes, and 70 μm thick. A light diffusion layer was formed to obtain a light diffusion film.

(Comparative Example 2)
(1) Preparation of hollow fine particles 45 parts by weight of methyl methacrylate, 50 parts by weight of methacrylonitrile, 5 parts by weight of trimethylolpropane triacrylate as a crosslinkable monomer, 140 parts by weight of heptane as a non-polymerizable substance, and as a polymerization initiator A heptane-dispersed primary emulsion was prepared by mixing and stirring 0.3 parts by weight of azobisisobutyronitrile (AIBN).
Thereafter, the obtained primary emulsion was added to 370 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersant and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor. By stirring using a stirring and dispersing device, a secondary emulsion composed of a composite emulsion in which oil droplets containing heptane were dispersed in an aqueous medium was obtained.
Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 4 hours, the polymerization vessel was cooled to room temperature to obtain a dispersion containing microcapsule-type polymer particles containing the liquid. The obtained dispersion was dried using a spray dryer to obtain hollow microparticles that did not enclose the liquid.

(2) Preparation of light diffusion layer forming resin composition 45 parts by weight of hollow fine particles obtained, 30 parts by weight of UV curable resin (urethane acrylic monomer) as binder resin, 5 parts by weight of benzophenone photopolymerization initiator, solvent As a mixture, 50 parts by weight of toluene was mixed and stirred to prepare a resin composition for forming a light diffusion layer.

(3) Preparation of light diffusing film The obtained light diffusing layer-forming resin composition was applied onto a 80 μm thick triacetylcellulose sheet using a spin coater, dried at 120 ° C. for 5 minutes, and then irradiated with ultraviolet light. Then, a light diffusion layer having a thickness of 30 μm was formed to obtain a light diffusion film.

(Comparative Example 3)
(1) Preparation of hollow fine particles 10 parts by weight of acrylonitrile and 10 parts by weight of a polyfunctional acrylic monomer, such as polypropylene glycol dimethacrylate (polyoxypropylene unit number = approximately 7; manufactured by Nippon Oil & Fats Co., Ltd., Blemmer PDP-400), polyoxy 10 parts by weight of ethylene dimethacrylate (polyoxyethylene units = 1; manufactured by NOF Corporation, BLEMMER PDE-50R), 70 parts by weight of trimethylolpropane triacrylate, 100 parts by weight of normal hexane as a hollowing agent, and as a polymerization initiator A monomer solution was prepared by mixing and stirring 0.3 parts by weight of azobisisobutyronitrile (AIBN).
The total amount of the obtained monomer solution was added to an aqueous solution of 1% by weight polyvinyl alcohol (PVA) and 0.02% by weight sodium nitrite and stirred using a stirring and dispersing device to obtain an emulsified suspension.
Next, using a 20 liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized, and after deoxidizing the vessel, the pressure was returned to atmospheric pressure with nitrogen gas. The inside of the polymerization vessel was set to a nitrogen atmosphere. The entire amount of the emulsified suspension obtained above was charged all at once into this polymerization vessel, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 4 hours, the polymerization vessel was cooled to room temperature to obtain a solvent-encapsulated microcapsule dispersion. The obtained dispersion was dried using a spray dryer to obtain hollow microparticles that did not enclose the liquid.

(2) Preparation of light diffusion layer forming resin composition 18 parts by weight of the obtained hollow fine particles, 15 parts by weight of acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd .: copolymer of methacrylic acid and acrylic monomer) as a binder resin, solvent As a result, 25 parts by weight of toluene was mixed and stirred to prepare a resin composition for forming a light diffusion layer.

(3) Production of light diffusing film The obtained light diffusing layer forming resin composition was applied onto a 150 μm thick polyester resin sheet using a spin coater, dried at 120 ° C. for 3 minutes, and 100 μm thick. The antireflection film was formed.

(Evaluation)
(1) Average particle diameter The hollow fine particles obtained in each Example and Comparative Example, and the hollow fine particles after heating the sample for 10 minutes in an oven at an internal temperature of 200 ° C. were photographed with a drop-type electron microscope, and obtained. 350 photographs were randomly extracted from the obtained photographs, and the major axis and minor axis were measured.
The major axis was taken as the particle diameter, and the number average was taken as the average particle diameter.

(2) Porosity The hollow microparticles produced in each Example and Comparative Example were photographed with a transmission electron microscope, 350 photographs were randomly extracted from the obtained photographs, and the pore diameters in the particles were measured. The number average was obtained.
Then, assuming that the obtained hollow fine particles are true spheres, and determining the volume from the average particle diameter (outer diameter) and the average inner pore diameter, respectively, {(hole volume / volume of hollow fine particles) × 100} By calculating, the porosity was obtained.

(3) Volume change rate (swelling rate) after immersion in organic solvent
10 parts by weight of the hollow fine particles obtained in Examples and Comparative Examples and 100 parts by weight of toluene are mixed, and the volume immediately after settling in a graduated cylinder is set to V1, in a graduated cylinder after being immersed in toluene for 24 hours. The volume of the hollow fine particles at V is defined as V2, and (V2 / V1) × 100 is calculated.
In addition, about the isopropanol dispersion of the hollow microparticles encapsulating cyclohexane obtained in Example 2, the dispersion was dried using a spray dryer to obtain hollow microparticles not encapsulating the liquid, and then the above method. The swelling rate was determined.

(4) Internal state of light diffusing layer The cross section of the light diffusing layer of the light diffusing film obtained in Example and Comparative Example was observed using a scanning electron microscope (SEM), and the state of the hollow fine particles in the light diffusing layer was observed. evaluated.

(5) Total light transmittance and haze value measurement of light diffusion sheet The total light transmittance and haze value of the light diffusion film were measured using a haze meter (NDH-2000, manufactured by Nippon Denshoku Industries Co., Ltd.).

According to the present invention, the light diffusion film capable of realizing excellent light diffusivity without reducing the total light transmittance, and the hollow light particles are less likely to swell and deform, and the desired light diffusion performance. The manufacturing method of the light-diffusion film which can obtain the light-diffusion film which has this can be provided.

Claims (6)

A light diffusion film in which a light diffusion layer containing a hollow fine particle having a single pore structure and a binder resin is laminated on a transparent substrate layer,
The hollow fine particles having the single-pore structure have an average particle diameter of 0.5 to 30 μm, and
The shell of hollow fine particles having a single pore structure is made of a resin containing 30% by weight or more of a component derived from a crosslinkable monomer. 2. The light diffusion film according to claim 1, wherein the hollow fine particles having a single pore structure have a porosity of 30 to 95% by volume. 3. The light diffusing film according to claim 1, wherein a transparent liquid having a refractive index different from that of the shell of the hollow fine particles having a single pore structure is included in a hollow portion of the hollow fine particles having a single pore structure. . A step of preparing a resin composition for forming a light diffusion layer, comprising hollow fine particles having a single pore structure, a binder resin and a solvent;
Applying the light diffusing layer forming resin composition to a transparent substrate film;
After drying the coated resin composition for forming a light diffusion layer, a method for producing a light diffusion film having a step of forming a light diffusion layer by performing a predetermined curing treatment,
The hollow fine particles having the single-pore structure have an average particle diameter of 0.5 to 30 μm, and
The shell of hollow fine particles having a single pore structure is made of a resin containing at least 30% by weight of a component derived from a crosslinkable monomer. The method for producing a light diffusing film according to claim 4, wherein the hollow fine particles having a single pore structure have an expansion rate of 100 to 110% by volume with an organic solvent. 6. The method for producing a light diffusion film according to claim 4, wherein the binder resin contains an ionizing radiation curable resin.