JP2010150491A - Resin composition for light diffusion film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin composition for light diffusion film which can stably manufacture a light diffusion film high in luminance and excellent in physical properties such as surface transparency. <P>SOLUTION: The resin composition for light diffusion film essentially consists of particulates and a resin component. The particulates comprises at least two kinds of particulates having different volume average grain size. The particulate having larger volume average grain size has larger degree of swelling in the resin components than that of the particulate having smaller volume average grain size. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a resin composition for a light diffusion film, a light diffusion film using the same, and a method for producing the same. More specifically, a resin composition for a light diffusing film that is suitably used for producing a light diffusing film used in liquid crystal displays such as televisions and computer displays, a light diffusing film using the same, and a production thereof Regarding the method.

A light diffusing film is a film having a function of uniformly diffusing light from a light source, and must be a member constituting a liquid crystal display device widely used in televisions, computer displays, digital cameras, mobile phones, and the like. It will not be. The liquid crystal display device has a liquid crystal display panel and a backlight unit, and the backlight unit is arranged behind the liquid crystal display panel, and light supplied from the backlight unit is transmitted through the liquid crystal display panel. Display an image. The backlight unit basically has a reflective film, light source, light diffusing plate, light diffusing film, prism sheet and brightness enhancement film in order from the rear when the liquid crystal display panel side is the front and the opposite side is the rear. The light diffusing film further diffuses the light that has passed through the light diffusing plate and collects the light in the direction of the liquid crystal display panel to improve the luminance.

As such a light diffusing film, a film in which a light diffusing layer is formed by applying a resin composition comprising a transparent resin bead as a light diffusing material and a transparent resin binder to the surface of a transparent film substrate is known. As an example of the light diffusing film, it comprises a light diffusing material containing acryl urethane resin fine particles and a resin binder obtained by crosslinking an acrylic resin containing an acrylic monomer having a hydroxyl group as a copolymerization component with polyisocyanate. A light diffusion film having a light diffusion layer is disclosed (for example, see Patent Document 1).
Moreover, the improvement of the performance of a light-diffusion film is tried by various methods. For example, a method of using two or more kinds of monodispersed particles having different average particle diameters as light diffusing agent particles as a light diffusing material for the purpose of improving luminance uniformity without reducing light transmittance is disclosed. (See, for example, Patent Documents 2, 3, 4, and 5).

Each of these resin compositions for light diffusion films is obtained by dispersing resin fine particles in a resin solution comprising a resin component and a solvent. When two or more kinds of resin fine particles having different particle diameters are used in the resin composition for light diffusion film, generally, a plurality of kinds of fine particles differing only in terms of the particle diameter are used. A situation occurs in which fine particles having a smaller particle diameter are more likely to settle, and the fine particles having a smaller particle diameter are less likely to settle. As a result, the concentration of resin fine particles is uneven in the resin solution over time.
When the application process of the light diffusion film is performed using the resin solution having such uneven density, a light diffusion film containing a large amount of fine particles having a relatively small particle diameter can be obtained by using the upper part of the resin solution. On the other hand, when the bottom part of the resin solution is used, a light diffusion film containing many fine particles having a large particle diameter can be obtained. In a light diffusion film containing a large number of fine particles having a small particle diameter, the fine particles are buried in the resin component, so that the lens effect is reduced and the luminance cannot be increased. On the other hand, a light diffusion film containing a large amount of fine particles having a large particle diameter has a large lens effect because the number of fine particles embedded in the resin component is small. The scale becomes uneven.
As described above, the conventional resin composition for light diffusing film has a problem that the physical properties of the obtained light diffusing film can vary due to the unevenness of the concentration of resin fine particles. There is a demand for a resin composition for a light diffusion film that can stably produce a uniform light diffusion film.
JP 2006-126822 A (page 1-2) Japanese translation of PCT publication No. 2004-533656 (page 1-2) JP-A-9-127313 (page 1-2) JP-A-10-160909 (page 1-2) JP-A-9-113708 (page 1-2)

The present invention has been made in view of the above situation, and provides a resin composition for a light diffusing film that can stably produce a light diffusing film having high luminance and excellent physical properties such as surface scaling. The purpose is to provide.

The present inventors have conducted various studies on resin compositions for light diffusing films that can be suitably used to stably produce a light diffusing film with uniform physical properties, in which unevenness in the concentration of fine particles in the composition is suppressed. Focusing on the fact that the density of fine particles is a factor affecting the sedimentation rate. Then, among the fine particles contained in the composition, when the swelling degree of the fine particles having a large volume average particle diameter is larger than the swelling degree of the particles having a small volume average particle diameter, the density of the fine particles having a large volume average particle diameter decreases. As a result of the slowing of the sedimentation rate of the fine particles, it was found that the difference in the sedimentation rate with the fine particles having a small volume average particle diameter becomes small, and it is difficult to cause uneven density. In order to exhibit the performance required for light diffusion films such as uniformity of light diffusion, it is necessary to use fine particles with the same refractive index of light, usually when using multiple types of fine particles However, the fine particles often use the same material, but the degree of swelling can be changed by changing the degree of crosslinking of the fine particles. It is possible to produce fine particles with different density, and it is possible to obtain a composition that is difficult to cause density unevenness while sufficiently exhibiting the performance required for a light diffusion film, and to solve the above-mentioned problems wonderfully. The present invention has been reached.

That is, the present invention is a resin composition for a light diffusing film comprising fine particles and a resin component as essential components, wherein the fine particles include at least two kinds of fine particles having different volume average particle diameters, and the volume average particle among the fine particles. The fine particle having a large diameter is a resin composition for a light diffusion film characterized in that the degree of swelling in the resin component is larger than that of the fine particle having a small volume average particle diameter.
The present invention is described in detail below.

The resin composition for light diffusion films of the present invention contains at least two kinds of fine particles having different volume average particle diameters. Here, including at least two types of fine particles means containing at least two types of fine particles that differ in at least one of the composition and physical properties of the fine particles in addition to the volume average particle diameter. As long as they are different from each other, fine particles having no difference in other points may be used. Further, the resin composition for a light diffusing film of the present invention may contain three or more kinds of fine particles as long as it contains at least two kinds of fine particles, as long as the light diffusibility and luminance of the light diffusing film are not inhibited. In addition, other components may be included.

Since the fine particles are a collection of individual particles having various particle sizes, fine particles having a large volume average particle size include particles having a small particle size, and fine particles having a small volume average particle size are also included. Large particles are included. The particle size distribution of the fine particles having a large volume average particle size and the fine particles having a small volume average particle size may include an overlapping range, but the overlapping range is preferably smaller, and the overlapping range is preferably a resin composition for a light diffusion film. It is preferably 20% or less with respect to the entire fine particles contained in the product. More preferably, it is 10% or less.
When the particle size distribution of the fine particles includes an overlapping range, the entire fine particles contained in the resin composition for a light diffusing film of the present invention are divided into fine particles having a particle size larger and smaller than the volume average particle size of the entire fine particles. The average swelling degree of the fine particles contained in the large fine particles should be larger than the average swelling degree of the fine particles contained in the small fine particles. Such a resin composition for a light diffusing film, which contains fine particles and a resin component as essential components, wherein the fine particles include at least two kinds of fine particles having different volume average particle diameters and are contained in the resin composition. When fine particles are divided into fine particles having a particle size larger than the volume average particle size of the entire fine particles and small particles, the average swelling degree of the fine particles contained in the large fine particles is the average swelling degree of the fine particles contained in the small fine particles. A resin composition for a light diffusion film larger than that is also one aspect of the present invention.
The volume average particle diameter of the fine particles can be calculated by measuring the particle size distribution of the fine particles. The particle size distribution of the fine particles can be measured by a precision particle size distribution measuring apparatus using a pore electrical resistance method. For example, the method used in the examples is preferably used.
Further, the degree of swelling of the fine particles referred to here represents the degree of swelling of the fine particles when using the solvent used for coating the film, and the average of the degree of swelling of the fine particles can be obtained, for example, by the following method. .
Measurement method of average degree of swelling: 1 g of fine particles are put into Gardner viscosity tube (outer diameter × inner diameter × full length (mm) = 11.9 × 10.7 × 114) manufactured by Fuji Science Industry Co., Ltd., and butyl acetate is used as Gardner viscosity tube. Insert the line below. Then, shake by hand until the fine particles are uniformly dispersed in the solvent, and let X be the height of the fine particle layer after standing at 25 ° C. for 1 hour. Furthermore, the height of the fine particle layer after standing at 25 ° C. for 24 hours is defined as Y. The fine particles are measured three times, and the average value of Y / X is taken as the average of the degree of swelling.

In the resin composition for a light diffusion film of the present invention, fine particles having a large volume average particle diameter have a higher degree of swelling in the resin solution than fine particles having a small volume average particle diameter. When the resin composition for light diffusing films of the present invention contains three or more kinds of fine particles having different volume average particle diameters, the volume average particle diameter of at least one of a combination of two kinds of fine particles selected from these fine particles It is sufficient that the large fine particles have a higher degree of swelling in the resin solution than the fine particles having a small volume average particle size, but in many combinations, the fine particles having a large volume average particle size are smaller than the fine particles having a small volume average particle size. Also, it is preferable that the degree of swelling in the resin solution is high. Most preferably, in any combination of two kinds of fine particles selected from the fine particles contained in the composition, fine particles having a large volume average particle diameter have a higher degree of swelling in the resin solution than fine particles having a small volume average particle diameter. In other words, the larger the volume average particle diameter of the fine particles contained in the composition, the greater the degree of swelling.
In the specification of the present application, any description of the size of the volume average particle size of the fine particles expresses the relative size of the volume average particle size among a plurality of types of fine particles.
As a method for measuring the degree of swelling of the fine particles, for example, the method used in the examples is preferably used.

In the fine particles, the degree of swelling can be changed by various methods, but is preferably changed by adjusting the degree of crosslinking of the fine particles. If the degree of swelling is changed by changing the degree of crosslinking, it is possible to change the degree of swelling while using fine particles of a homogeneous material having the same refractive index when two or more types of fine particles are used. Therefore, the degree of swelling of the fine particles can be changed without deteriorating the physical properties required for the light diffusion film, such as light diffusibility and high luminance.

The fine particles preferably have a cross-linking degree of fine particles having a large volume average particle diameter of 1 to 20% by mass, and a fine particle having a small volume average particle diameter of 15 to 60% by mass. Fine particles having a low degree of cross-linking tend to swell by sucking the solvent in the resin composition. When the degree of cross-linking of the fine particles having a large volume average particle diameter and the fine particles having a small volume average particle diameter is in such a range, the physical properties such as high luminance and surface scaling required for the light diffusion film and the concentration of the composition It becomes possible to more effectively achieve the effect of suppressing unevenness. More preferably, the degree of crosslinking of the fine particles having a large volume average particle size is 1 to 15% by mass, and the degree of crosslinking of the fine particles having a small volume average particle size is 15 to 55% by mass. The degree of crosslinking of fine particles having a large volume average particle size is 5 to 15% by mass, and the degree of crosslinking of fine particles having a small volume average particle size is 15 to 50% by mass.
The fine particles contained in the resin composition for a light diffusion film of the present invention may contain fine particles not containing a crosslinked structure as long as at least two kinds of fine particles having a crosslinked structure and different volume average particle diameters are contained.
The degree of crosslinking of the fine particles is defined by the mass ratio of the crosslinkable monomer contained in the entire monomer component that is a raw material for producing fine particles that are polymers.

The volume average particle diameter of the fine particles contained in the resin composition for light diffusion film of the present invention is preferably in the range of 0.5 to 40 μm. When the volume average particle diameter is less than 0.5 μm, the lens effect is reduced and the luminance is lowered. On the other hand, when the volume average particle diameter exceeds 40 μm, it is difficult to uniformly coat the fine particles, and the luminance is lowered. More preferably, it is the range of 1-30 micrometers, More preferably, it is the range of 2-25 micrometers.

The fine particles preferably have a volume average particle size ratio of 1.05 to 20 between the fine particles having the largest volume average particle size and the fine particles having the smallest volume average particle size. When the volume average particle size ratio is in such a range, the surface scale becomes small, the luminance unevenness becomes small, and the luminance becomes high. More preferably, the volume average particle size ratio is 1.1 to 15, and still more preferably, the volume average particle size ratio is 1.2 to 10.
The volume average particle size ratio is a value obtained by dividing the volume average particle size of the fine particles having the largest volume average particle size by the volume average particle size of the fine particles having the smallest volume average particle size.

The fine particles preferably have a difference in refractive index of 0.1 or less between fine particles having a large volume average particle size and fine particles having a small volume average particle size. When the difference in refractive index is such, the physical properties such as light diffusivity are excellent. More preferably, it is 0.05 or less.
When the resin composition for a light diffusing film of the present invention contains three or more kinds of fine particles, the difference in refractive index between at least two kinds of fine particles may be 0.1 or less. It is preferable that this difference in refractive index is satisfied among the fine particles.
The refractive index of the fine particles can be measured with an Abbe refractometer.

In the resin composition for a light diffusion film of the present invention, the absolute value of the difference in refractive index between the contained fine particles and the resin component is preferably 0.1 or less. When the difference in refractive index is within this range, light loss due to reflection or refraction is small and the luminance is high. The absolute value of the refractive index difference is more preferably 0.07 or less, and still more preferably 0.05 or less. The resin composition for a light diffusing film of the present invention contains at least two kinds of fine particles having different volume average particle diameters, and among these fine particles, the refractive index difference between the fine particles and the resin component is larger. The absolute value is preferably in the above range, and the absolute value of the refractive index difference between the fine particles and the resin component is most preferably in the above range for all fine particles.

As long as the resin composition for light diffusing film of the present invention contains at least two kinds of fine particles having different volume average particle diameters, the particle size distribution of the contained fine particles is not particularly limited, but at least one kind of the fine particles is included. The fine particles are preferably monodisperse fine particles. As the monodisperse fine particles, the coefficient of variation represented by the following formula is preferably 20% or less, more preferably 10% or less, and further preferably 5% or less.
Coefficient of variation of particle diameter (%) = (σ /) × 100
In the formula, σ represents the standard deviation of the particle diameter, and represents the average particle diameter.
Since the monodispersed fine particles are fine particles having a small variation in particle size distribution, if the resin composition for the light diffusing film contains the monodispersed fine particles, the amount of fine particles embedded in the binder is reduced and the lens effect is increased. Rises. More preferably, two or more kinds of fine particles contained in the resin composition for light diffusing film are monodispersed fine particles, and most preferably, the fine particles contained in the resin composition for light diffusing film. All are monodisperse fine particles.

The fine particles preferably include two types of fine particles having different volume average particle diameters. When two kinds of fine particles having different volume average particle diameters are contained, a difference in swelling degree is provided to prevent unevenness in concentration, and the composition can exhibit physical properties required for light diffusion film applications. Thus, it becomes easy to design the resin composition. Further, when the number of fine particles to be used is reduced, it is advantageous from the viewpoint of manufacturing cost.

When the resin composition for a light diffusion film of the present invention contains two types of fine particles having different volume average particle diameters, the mass ratio of the fine particles having a large volume average particle diameter and the fine particles having a small volume average particle diameter is The ratio of the mass of the fine particles having a small volume average particle diameter to the mass is preferably 0.005 to 0.5. When the mass ratio is in such a range, the light diffusion film obtained from the resin composition exhibits excellent light diffusion performance. More preferably, it is 0.01-0.3, More preferably, it is 0.03-0.2.
The mass ratio is a value obtained by dividing the mass of all fine particles by the mass of fine particles having a small volume average particle diameter.

In the light diffusion film resin composition, the weight ratio of the fine particles to the resin component (fine particles / resin component) is preferably 0.5 to 5. When the ratio of the constituent components of the resin composition is in such a range, the effect of suppressing the occurrence of uneven density in the resin composition and the light diffusing film obtained from the resin composition exhibit excellent light diffusibility and the like It becomes the thing which was excellent by both of the effect to become.
The weight ratio of the fine particles to the resin component (fine particles / resin component) is more preferably 1 to 4.5, and still more preferably 1.5 to 4.
Here, the fine particles are the whole fine particles contained in the resin composition.

The fine particles contained in the resin composition for light diffusing film of the present invention are not particularly limited as long as they can transmit light, but acrylic resins, acrylic urethane resins, styrene resins, organic inorganic composites, amino formalin crosslinks It is preferably at least one selected from the group consisting of resins and inorganic compounds. As the organic / inorganic composite fine particles, for example, those produced by the method described in JP-A-8-81561 or JP-A-2003-183337 can be used.

The acrylic resin is not particularly limited as long as it is obtained by polymerizing a monomer component containing an acrylic monomer. As the acrylic monomer to be polymerized, acrylic acid, methacrylic acid and derivatives thereof can be used. Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n- Butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, Dodecyl (meth) acrylate, glycidyl (meth) acrylate, methoxyethyl (meth) acrylate, propoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, methoxydiethylene glycol (meth) acrylate, ethoxydi Tylene glycol (meth) acrylate, methoxyethylene glycol (meth) acrylate, butoxytriethylene glycol (meth) acrylate, methoxydipropylene glycol (meth) acrylate, cyclohexyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, hydroxyethyl ( Examples include meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, acrylonitrile, acrylamide, and N-methylolacrylamide. 1 type may be used for these monomers and 2 or more types may be used for them.
Among these, it is preferable to use at least one selected from the group consisting of methyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, and cyclohexyl (meth) acrylate. More preferably, methyl (meth) acrylate and / or n-butyl (meth) acrylate is used.

The acrylic urethane resin is preferably obtained by reacting an acrylic monomer having a hydroxyl group, an acrylic monomer having no hydroxyl group, and an isocyanate compound. More preferably, one or more selected from the group consisting of hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate and isobutyl It is a resin obtained by reacting at least one selected from the group consisting of (meth) acrylates with a modified polyisocyanate compound. The modified polyisocyanate compound is preferably an isocyanurate type trimerized based on hexamethylene diisocyanate or an adduct obtained by adding a polyhydric alcohol to hexamethylene diisocyanate.

The styrene resin is not particularly limited as long as it is obtained by polymerizing a monomer containing a styrene monomer, but styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methyl. It is preferable to use at least one selected from the group consisting of styrene, ethylstyrene, dimethylstyrene, and butylstyrene. 1 type may be used for these monomers and 2 or more types may be used for them. Further, as the fine particles, a resin obtained by copolymerizing the acrylic monomer and the styrene monomer may be used.
Examples of the amino formalin crosslinked resin include benzoguanamine / melamine / formaldehyde condensate and melamine / formaldehyde condensate.

Among the fine particles in the present invention, fine particles having a crosslinked structure in the molecule are synthesized by using a monomer component containing a polyfunctional unsaturated monomer (crosslinkable monomer) capable of forming a crosslinked structure as a raw material. Can be obtained at As polyfunctional unsaturated monomers, divinylbenzene, trimethylolpropane triacrylate, trimethylolpropane tri (meth) acrylate, dipentaerythritol hexaacrylate, dipentaerythritol hexa (meth) acrylate, ethylene glycol di (meth) acrylate , Diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,4- Butanediol di (meth) acrylate, 1,5-pentanediol (meth) acrylate, 1,6-hexanediol diacrylate, neopentyl glycol di (meth) At least one member selected from the group consisting of acrylate is preferably used. These crosslinking agents may be used alone or in combination of two or more.
The content of the polyfunctional unsaturated monomer can be appropriately set so that the degree of cross-linking of the fine particles having a large volume average particle diameter and the fine particles having a small volume average particle diameter are within the above-mentioned preferable ranges. it can.

The method for synthesizing the fine particles is not particularly limited, but can be synthesized by radical polymerization of monomer components. For radical polymerization, general radical polymerization initiators such as peroxide-based initiators and azo compound-based initiators can be used.
Examples of peroxide initiators include benzoyl peroxide, tert-butyl peroxide, di-tert-butyl peroxide, tert-butyl peroxy-2-ethylhexanoate, and tert-butyl peroxyisobutyrate. , Tert-butylperoxyneodecanoate, isobutyryl peroxide, di-3-methoxybutylperoxydicarbonate, methyl ethyl ketone peroxide, methylisobutyl peroxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, lauroyl peroxide Etc. Examples of the azo compound-based initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2-methylpropio). Nitrile), 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), dimethyl 2,2′-azobis (2-methylpropionate), 2 , 2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) and the like. These radical polymerization initiators may be used alone or in combination of two or more.

Examples of the inorganic compound that can be used as the fine particles contained in the resin composition for light diffusion film of the present invention include compounds containing Si atoms such as silica, silica alumina, silicone resin, and glass particles; compounds containing Ti atoms such as titania; Compounds containing Al atoms such as alumina; compounds containing Zn atoms such as zinc oxide; alkali metal salts such as calcium carbonate and barium carbonate, alkaline earth metal salts, and the like, and one or more of these are used. be able to. Among these compounds, compounds containing Si atoms are preferable, and silica and silicone resins are more preferable.

The silicone resin is not limited to a group such as an organic group bonded to the main chain as long as the main chain is a polymer formed by a siloxane bond, but is preferably a condensate of organosilane, and is a carbon-carbon dimer. In order for the organic component and the inorganic component to be integrated by chemical bonding by being polymerized after absorbing monomers having a double bond as an organic component, it is a condensate of an organosilane compound having a heavy bond. Further preferred. As specific examples of the silicone resin, dimethyl silicone, methylphenyl silicone, methyl hydrogen silicone, polyalkylsilsesquioxane or a modified product thereof is preferably used. The polyalkylsilsesquioxane is the following formula (1);

(In the above formula (1), R represents an alkyl group) and can be expressed as a hydrolysis condensate.
[RSiO _3/2 ]
(In the formula, R represents an alkyl group).
Examples of the silica fine particles include amorphous silica, porous silica, and hollow silica.

The silicone resin can be obtained by hydrolyzing and then condensing organotrialkoxysilane. As the organotrialkoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxysilane having a carbon-carbon double bond are preferably used. Trialkoxysilane may be used. The particulate silicone resin can be produced, for example, by various methods described in JP-A-2001-294670.

The shape of the fine particles contained in the resin composition for a light diffusing film of the present invention is not particularly limited, and may be any of spherical, plate-like, ellipsoidal, bowl-shaped, disk-shaped, surface wrinkled, hollow, crushed, etc. Although it may be shaped, it is preferably spherical from the viewpoint of light collection. Note that fine particles having one type of shape may be used, and fine particles having two or more types of shapes may be used.

In the resin composition for light diffusion film of the present invention, examples of the binder resin used as the resin component include (meth) acrylic resins, (meth) acrylurethane resins, polyvinyl chloride resins, polyvinylidene chloride resins, Melamine resin, urethane resin, styrene resin, alkyd resin, phenol resin, epoxy resin, polyester resin, (meth) acryl silicone resin, alkylpolysiloxane resin, silicone resin, silicone alkyd resin, Examples thereof include modified silicone resins such as silicone urethane resins, silicone polyester resins, and silicone acrylic resins, and fluorine resins such as polyvinylidene fluoride and fluoroolefin vinyl ether polymers. The resin component may be a thermoplastic resin or a curable resin such as a thermosetting resin, a moisture curable resin, an ultraviolet curable resin, or an electron beam curable resin. Examples of other resin components include organic binder resins such as synthetic rubber and natural rubber, and inorganic binders. Examples of organic binder resins for synthetic rubber include ethylene-propylene copolymer rubber, polybutadiene rubber, styrene-butadiene rubber, and acrylonitrile-butadiene rubber. Examples of the binder resin for the inorganic binder include silica sol, alkali silicate, silicon alkoxide, and their (hydrolyzed) condensates and phosphates. These may be used independently and may use 2 or more types together. Among these, as the resin component, a (meth) acrylic resin is preferable.

Examples of the (meth) acrylic resin include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, cyclohexyl (meth) acrylate, Methyl cyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, lauryl (meth) acrylate, isobornyl (meth) acrylate, Examples thereof include resins containing structural units derived from stearyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. Among these, a resin containing a structural unit derived from methyl (meth) acrylate, t-butyl (meth) acrylate, isobutyl (meth) acrylate, or cyclohexyl (meth) acrylate is preferable.

The binder resin may be obtained by polymerizing a monomer component containing a monomer having a functional group. Monomers having a functional group include unsaturated monomers having a carboxyl group such as (meth) acrylic acid, itaconic acid and maleic anhydride; acidic phosphoric acid such as 2- (meth) acryloyloxyethyl acid phosphate Ester unsaturated monomer; 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, caprolactone-modified hydroxy (meth) acrylate (for example, trade name “manufactured by Daicel Chemical Industries, Ltd. Unsaturated monomer having a group having active hydrogen such as PLACCEL FM "); (meth) acrylic acid ester; unsaturated monomer having an epoxy group such as glycidyl (meth) acrylate; (meth) acrylamide, N, N′-dimethylaminoethyl (meth) acrylate, N, N-diethylamino Unsaturated monomers having nitrogen atoms such as ethyl (meth) acrylate and imide (meth) acrylate; ethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tri Unsaturated monomers having two or more polymerizable double bonds such as methylolpropane tri (meth) acrylate and pentaerythritol tetra (meth) acrylate; unsaturated monomers having a halogen atom such as vinyl chloride; styrene, Aromatic unsaturated monomers such as α-methylstyrene; vinyl esters such as vinyl acetate; vinyl ethers and the like. These may be used alone or in combination of two or more.

The binder resin may contain organic-inorganic composite ultrafine particles. When the resin composition contains inorganic fine particles, the heat resistance of the resin composition is improved. The organic-inorganic composite ultrafine particles are preferably composite fine particles in which an organic polymer is fixed on the surface of the inorganic fine particles. When the organic polymer is fixed on the surface of the inorganic fine particles, the light diffusion obtained from the resin composition due to the improved dispersibility of the inorganic fine particles in the binder and the affinity between the binder and the inorganic fine particles. The light transmittance of the film is improved. Here, “fixing” does not mean mere adhesion and adhesion, but means that a chemical bond is formed between the organic polymer and the inorganic fine particles. Therefore, when the inorganic fine particles are washed with the washing liquid, the organic polymer is not substantially detected in the washing liquid. The inorganic fine particles may include an organic polymer in the fine particles. Thereby, moderate softness and toughness can be imparted to the core of the inorganic fine particles.

Although the inorganic substance which comprises the inorganic fine particle contained in the said organic-inorganic composite ultrafine particle is not specifically limited, It is preferable that it is an inorganic oxide. Here, the “inorganic oxide” means an oxygen-containing metal compound in which metal elements are bonded in a three-dimensional network mainly through oxygen atoms. Further, in the present application, “metal element” includes silicon. As the metal element constituting the inorganic oxide, a metal element selected from Group 2 to Group 16 is preferable. More preferably, it is a metal element selected from Group 3 to Group 5, more preferably at least one metal element selected from the group consisting of Si, Al, Ti, and Zr. Most preferred is colloidal silica in which the metal element is Si. Colloidal silica can be produced relatively easily and is inexpensive. Moreover, you may use the inorganic fine particle marketed as an inorganic fine particle.

The shape of the inorganic fine particles contained in the organic-inorganic composite ultrafine particles is not particularly limited, and may be any of a spherical shape, a needle shape, a plate shape, a scale shape, a crushed shape, and the like. Two or more kinds of inorganic fine particles may be used in combination, and in that case, the shape of the inorganic fine particles may be the same or different.

As an organic polymer contained in the organic-inorganic composite ultrafine particles, the molecular weight, shape, composition, presence / absence of a functional group, etc. are not particularly limited as long as it is a polymer composed of organic components. Examples of the resin constituting the organic polymer include (meth) acrylic resins; polystyrene; polyvinyl acetate; polyolefins such as polyethylene and polypropylene; polyesters such as polyvinyl chloride, polyvinylidene chloride and polyethylene terephthalate, and copolymers thereof. It is done. These organic polymers may be partially modified with functional groups such as amino groups, epoxy groups, hydroxyl groups, and carboxyl groups.

The volume average particle diameter of the organic-inorganic composite ultrafine particles is preferably 5 to 200 nm. More preferably, it is 5 to 100 nm. If the volume average particle size is too small, the surface energy of the organic-inorganic composite ultrafine particles becomes high, and aggregation and the like are likely to occur. On the other hand, if this volume average particle size is too large, the transparency is lowered.

The binder resin may or may not be crosslinked, but is preferably crosslinked from the viewpoint of improving durability. Crosslinking may be performed by the polymer itself or by a crosslinking agent. The resin may be cured under any curing condition such as room temperature curing type, heat curing type, ultraviolet ray or electron beam curing type. The amount of addition, addition, and dispersion method of the crosslinking agent (curing agent) are not particularly limited. For example, when the resin is a polyol, the use amount, addition, and dispersion method that are usually used for the polyol can be used.

From the viewpoint of enabling curing (crosslinking) with a polyfunctional isocyanate or the like, the binder resin is preferably one having two or more hydroxyl groups in one molecule, that is, a polyol, and a monomer component having a hydroxyl group. It is preferable to polymerize a monomer containing. More preferably, it is a (meth) acrylic resin having two or more hydroxyl groups in one molecule, that is, a (meth) acrylic polyol. As the unsaturated monomer having a hydroxyl group, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, caprolactone-modified hydroxy (meth) acrylate (for example, manufactured by Daicel Chemical Industries, Ltd.) , Trade name “PLAXEL FM”) and the like.

As said crosslinking agent (curing agent), when resin is a polyol, polyfunctional isocyanates, such as (block) polyisocyanate compound, aminoplast resin, etc. are mentioned, for example. These may be used alone or in combination of two or more.

The (block) polyisocyanate compound means a polyisocyanate compound and / or a block polyisocyanate compound. The polyisocyanate compound is not particularly limited as long as it is a compound having at least two isocyanate groups in the molecule. For example, tolylene diisocyanate xylylene diisocyanate, diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, isophorosidiisocyanate, Polyisocyanates such as 4,4'-methylenebis (cyclohexyl isocyanate), lysine diisocyanate, trimethylhexamethylene diisocyanate, 1,3- (isocyanatomethyl) cyclohexane, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate; Polyisocyanate derivatives (modified products) such as isocyanate adducts, burettes, and isocyanurates are listed.

The block polyisocyanate compound is obtained by blocking an isocyanate group of a polyisocyanate compound with a blocking agent. With this block polyisocyanate compound, the binder resin can be cross-linked during heating and drying, and the storage stability at room temperature is enhanced. It does not specifically limit as a blocking agent, For example, compounds, such as (epsilon) -caprolactam, phenol, cresol, oxime, alcohol, etc. are mentioned. Examples of commercially available (block) polyisocyanate compounds include Sumidur N3300, Sumidur BL3175, Death Module N3200, Death Module N3400, Death Module N3600 and Death Module VPLS2102 (trade name, manufactured by Sumika Bayer Urethane Co., Ltd.); HK, Coronate HL and Coronate HX (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.); Duranate E-402-90T (trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.) and the like. From the viewpoint of preventing yellowing of the binder resin, a non-yellowing polyisocyanate compound having no isocyanate group directly bonded to the aromatic ring is preferable.

Although it does not specifically limit as the usage-amount of the said (block) polyisocyanate compound, It is the quantity from which the isocyanate group of a (block) polyisocyanate compound will be 0.6-1.4 mol with respect to 1 mol of hydroxyl groups in resin. It is preferable. More preferably, the amount is 0.8 to 1.2 mol. When the number of isocyanate groups of the (block) polyisocyanate compound is less than 0.6 moles relative to 1 mole of hydroxyl groups in the binder resin, many unreacted hydroxyl groups remain in the binder resin, so the weather resistance of the resulting binder May decrease.
When the amount exceeds 1.4 mol, many unreacted isocyanate groups remain in the binder, which reacts with moisture in the air, and foaming or whitening may occur in the binder.

The glass transition temperature (Tg) of the binder resin is preferably -80 to 160 ° C. More preferably, it is -50-130 degreeC, More preferably, it is 0-110 degreeC, Most preferably, it is 20-100 degreeC. By using a binder resin having such a glass transition temperature, the light resistance of the light diffusion film obtained from the resin composition can be improved.
The glass transition temperature can be calculated by the following Fox equation.
1 / Tg = Σ (Wn / Tgn) / 100
In the formula, Wn represents the mass% of the monomer n present in 100% by mass of the copolymer, and Tgn represents the glass transition temperature (absolute temperature) of the homopolymer composed of the monomer n.

The polymer constituting the binder resin preferably has a weight average molecular weight of 1000 to 100,000. More preferably, it is 2000-80000, More preferably, it is 4000-60000.
The weight average molecular weight can be determined, for example, by GPC (gel permeation chromatography) measurement under the following measurement conditions.
Measuring instrument: HLC-8120GPC (trade name, manufactured by Tosoh Corporation)
Molecular weight column: TSK-GEL GMHXL-L and TSK-GELG5000HXL (both manufactured by Tosoh Corporation) are connected in series. Eluent: Tetrahydrofuran (THF)
Standard material for calibration curve: Polystyrene (manufactured by Tosoh Corporation)
Measurement method: The measurement object is dissolved in THF so that the solid content is about 0.2% by mass, and the molecular weight is measured using an object obtained by filtration through a filter as a measurement sample.

As a polymerization method for producing the binder resin, a polymerization method such as solution polymerization, dispersion polymerization, suspension polymerization, emulsion polymerization or the like can be used. The solvent for performing the solution polymerization is not particularly limited, and examples thereof include aromatic solvents such as toluene and xylene; alcohols such as iso-propyl alcohol, n-butyl alcohol, propylene glycol methyl ether, and dipropylene glycol methyl ether. Solvent; ester solvent such as butyl acetate, ethyl acetate, cellosolve acetate; ketone solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and one or more solvents selected from the group consisting of dimethylformamide, etc. it can.
The usage-amount of a solvent can be suitably set with polymerization conditions, the mass ratio of the polymer in binder resin, etc.

In the polymerization of the binder resin, a polymerization initiator can be used. The polymerization initiator is not particularly limited, and general radical polymerization initiators such as peroxides and azo compounds can be used. As the peroxide-based initiator and the azo compound-based initiator, those similar to those used for the above-described fine particle synthesis can be used.
Although the usage-amount of a polymerization initiator should just be suitably set from the characteristic value etc. of a desired polymer, it is preferable to set it as 0.01-50 mass% with respect to the whole monomer. More preferably, it is 0.05-20 mass%.

The polymerization conditions for producing the binder resin may be appropriately set depending on the polymerization method used, and are not particularly limited. For example, the polymerization temperature is preferably room temperature to 200 ° C., more Preferably, it is 40-140 degreeC. The polymerization reaction time may be appropriately set so that the polymerization reaction is completed according to the composition of the monomer component, the type of the polymerization initiator, and the like.

As a solvent which the resin composition for light diffusion films of this invention contains, what is used in the polymerization reaction for manufacturing the binder resin mentioned above can be used.
As a quantity of the solvent contained in the said resin composition, the quantity suitable for coating the base material with this resin composition mentioned later can be used.

The method for producing the resin composition for light diffusing film of the present invention is not particularly limited, and after mixing at least two kinds of fine particles having different volume average particle diameters in advance, the fine particles obtained by mixing are mixed with a binder resin. May be obtained by mixing with a binder resin in order without mixing at least two kinds of fine particles having different volume average particle diameters in advance. Are mixed with the binder resin in order without mixing them in advance. By setting it as such a manufacturing method, a resin composition can be manufactured cheaply and stably.

A light diffusing film can be formed by applying the resin composition for a light diffusing film of the present invention to a substrate. Such a method for producing a light diffusion film including the step of applying the resin composition for a light diffusion film of the present invention to a film substrate is also one aspect of the present invention. Furthermore, the light diffusion film manufactured by such a method of manufacturing a light diffusion film is also one aspect of the present invention.
The light diffusing film of the present invention is produced by applying and drying a resin composition on the above film substrate, and the resin composition contains at least two kinds of fine particles having different volume average particle diameters of the present invention. Therefore, it has sufficient light diffusibility and high brightness.

The light diffusion film preferably has a three-dimensional average surface roughness Ra of the surface of the light diffusion layer made of the resin composition of 1 μm to 5 μm. When the three-dimensional average surface roughness Ra of the surface of the light diffusion layer is less than 1 μm, the lens effect is not exhibited so much that sufficient luminance cannot be obtained. Further, when the three-dimensional average surface roughness Ra of the surface of the light diffusion layer exceeds 5 μm, the uniformity of light is weakened and the fine particles may fall off the light diffusion layer. More preferably, Ra is 1.5 μm to 4.5 μm, and still more preferably Ra is 2 μm to 4 μm.
The three-dimensional average surface roughness Ra can be measured using a non-contact type surface roughness meter or a laser confocal microscope in accordance with JIS B0601-2001.

The thickness of the film substrate is preferably 10 μm to 300 μm. If the thickness of the film is less than 10 μm, sufficient strength as a substrate cannot be exhibited, and if the thickness is 300 μm or more, the transmission of visible light is deteriorated and sufficient front luminance cannot be obtained. End up.

The said film base material is not restrict | limited especially unless the optical characteristic of a light-diffusion film is inhibited, The material generally used as an optical material can be used. Examples of film substrates include glass; polyesters such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate); triacetyl cellulose; olefin polymers such as cyclopolyolefin and amorphous polyolefin; polymethyl methacrylate and lactone ring structure Examples include (meth) acrylic resins such as (meth) acrylates having polystyrene; polystyrenes; polycarbonates; polyvinyl acetals such as bratilles resins; polyaryl ether resins. Particularly preferred substrates include polyethylene terephthalate (PET) films and (meth) acrylate films having a lactone ring structure. Among these, a PET film is preferably used because of excellent surface smoothness and mechanical strength.

The light-diffusion film of this invention is manufactured by the manufacturing method including the process of apply | coating the resin composition for light-diffusion films to a film base material, and the process of drying the apply | coated resin composition.
Examples of the method for applying the resin composition to the film substrate include air knife coating, gravure coating, reverse roll coating, spray coating, and blade coating. Moreover, the method of drying the apply | coated resin composition can use a well-known drying method, and there is no restriction | limiting in particular.

The coating amount of the resin composition on the film base material in the method for producing a light diffusing film is preferably in the range of 2 to 20 g. If the coating amount is less than 2 g, the thickness of the produced light diffusion film becomes too thin, so that a sufficient light diffusion effect cannot be exhibited. On the other hand, when the coating amount exceeds 20 g, the light transmittance of the light diffusing film decreases, and sufficient luminance cannot be obtained.

The resin composition for a light diffusing film of the present invention has the above-described configuration, and by increasing the degree of swelling of the fine particles having a large volume average particle diameter among the fine particles to be larger than that of the fine particles having a small volume average particle diameter, The difference in the sedimentation rate in the resin solution of fine particles having different particle diameters can be reduced, thereby suppressing the change in the composition of the resin composition when the resin composition is applied to the film substrate. It is a resin composition for a light diffusion film capable of producing a uniform and stable light diffusion film.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” means “part by weight” and “%” means “mass%”.

In the following examples and comparative examples, various physical properties of the fine particles, the binder resin, and the light diffusion film were measured as follows.
<Analysis of fine particles>
[Swelling degree]
1 g of fine particles were placed in a Gardner viscosity tube (outer diameter × inner diameter × full length (mm) = 11.9 × 10.7 × 114) manufactured by Fuji Science Industry Co., Ltd., and butyl acetate was added to the line below the Gardner viscosity tube. Thereafter, the mixture was shaken by hand until the fine particles were uniformly dispersed in the solvent. Let X be the height of the fine particle layer when left at 25 ° C. for 1 hour. Further, Y is the height of the fine particle layer when left at 25 ° C. for 24 hours. The fine particles were measured three times, and the average value of Y / X was taken as the degree of swelling.
[Particle size distribution]
The average particle diameter of the inorganic particles and the polymer particles and the coefficient of variation of the particle diameter were measured by the following measuring method. The particle diameter of 30000 particles was measured with a Coulter Multisizer (manufactured by Beckman Coulter) to determine the average particle diameter. The variation coefficient of the particle diameter was determined according to the following formula.
Coefficient of variation of particle diameter (%) = (σ /) × 100
In the formula, σ represents the standard deviation of the particle diameter, and represents the average particle diameter.
In addition, the 5 μm fine particle ratio (5 μm fine particle%) is the volume% of the volume average particle diameter of the 5 μm fine particles (fine particles b) and the volume% of the volume average particle diameter of the entire fine particles (fine particles a−1 + fine particles b or fine particles a−2 + fine particles b). ) Divided by.
Aperture diameter: 30 μm
Measurement range: full mode Measurement method: 1 g of 1% hytenol NF-08 aqueous solution is added to 1 g of the particles to be measured, and the particles are dispersed for 5 minutes using an ultrasonic cleaning device. The resulting dispersion is “Coulter Multisizer ”.

<Analysis of binder resin>
[Solid content]
1.0 g of the binder resin solution was collected on an aluminum dish and diluted with 3.0 g of ethyl acetate to obtain a uniform solution. After this solution was dried at 120 ° C. for 1 hour, the mass was measured, and the solid content was determined according to the following formula.
(Solid content) = (mass of resin after drying) / (mass of binder resin solution)
[Number average molecular weight and weight average molecular weight]
The number average molecular weight and the weight average molecular weight were determined by GPC (gel permeation chromatography) measurement under the following measurement conditions.
Measuring instrument: HLC-8120GPC (trade name, manufactured by Tosoh Corporation)
Molecular weight column: TSK-GEL GMHXL-L and TSK-GELG5000HXL (both manufactured by Tosoh Corporation) are used in series.
Eluent: Tetrahydrofuran (THF)
Standard material for calibration curve: Polystyrene (manufactured by Tosoh Corporation)
Measurement method: The molecular weight was measured using a measurement sample dissolved in THF so that the solid content was about 0.2% by mass and filtered through a filter.
[Glass-transition temperature]
The glass transition temperature was calculated by the following Fox formula.
1 / Tg = Σ (Wn / Tgn) / 100
In the formula, Wn represents the mass% of the monomer n present in 100% by mass of the copolymer, and Tgn represents the glass transition temperature (absolute temperature) of the homopolymer composed of the monomer n.

<Analysis of light diffusion film>
[Brightness measurement]
A liquid crystal television AQUAS LC-37AD5 manufactured by Sharp Corporation was used as the backlight unit and the light diffusion plate. A spectroradiometer (SR-3 manufactured by Topcon Co., Ltd.) was fixed at a position 50 cm away from the light diffusion plate, the light diffusion film prepared was placed on the light diffusion plate, and the luminance of the light diffusion film was measured.

<Synthesis of binder resin A>
In a four-necked flask equipped with a stirrer, a thermometer, a cooling tube, a dropping funnel and a nitrogen gas introduction tube, 100 parts of butyl acetate was added as a solvent, and the temperature was raised to the reflux temperature. Then, while introducing nitrogen gas, 40 parts of cyclohexyl methacrylate as monomer, 37.7 parts of butyl methacrylate, 7.3 parts of butyl acrylate, 13.9 parts of 2-hydroxyethyl methacrylate, and 1. 1 part of methacrylic acid. A monomer mixture consisting of 1 part and 3.0 parts of t-butylperoxy-2-ethylhexanoate (trade name, Perbutyl O, manufactured by NOF Corporation) as a polymerization initiator is taken over 3 hours. It dropped from the dropping funnel. Further, 0.2 part of 1,1-di (t-hexylperoxy) cyclohexane (trade name: Perhexa HC, manufactured by NOF Corporation) was added three times at 30 minute intervals, and the reflux temperature was 2 times. Held for hours. Thereafter, the reaction solution was cooled to room temperature to obtain a solution of copolymer A. The resulting copolymer had a solid content of 50.3%. The molecular weight of the copolymer A was number average molecular weight (Mn) / weight average molecular weight (Mw) = 5300/10500. The theoretical glass transition temperature calculated from the Fox formula was 40 ° C., and the theoretical hydroxyl value was 60.

<Synthesis of Fine Particle (a-1)>
A solution prepared by mixing 250 parts of water and 5 parts of 25% ammonia water is placed in a four-necked flask equipped with a condenser, a thermometer, and a dropping funnel, and γ-methacryloxypropyltrimethoxysilane 40 is added to this solution while stirring. A solution in which 125 parts of methanol and 125 parts of methanol were mixed was added from a dropping port, and γ-methacryloxypropyltrimethoxysilane was hydrolyzed and condensed to prepare inorganic particles. One hour after the start of the reaction, 250 parts of water was added from the dropping port to dilute the inorganic particle dispersion. After stirring for 2 hours and 30 minutes from the start of the reaction, 1.5 parts of an anionic emulsifier (LA-10, manufactured by Daiichi Kogyo Seiyaku), 150 parts of water, 135 parts of methyl methacrylate, 15 parts of ethylene glycol dimethacrylate, 2, An emulsion was prepared by emulsifying and dispersing 1 part of 2′-azobis (2,4-dimethylvaleronitrile) (trade name V-65, manufactured by Wako Pure Chemical Industries, Ltd.) for 5 minutes using a homogenizer. It added to the inorganic particle dispersion from the dropping port in 15 seconds. After stirring for 30 minutes after the addition of the monomer emulsion, the inorganic particles were observed with a microscope. As a result, it was confirmed that the particle diameter had increased from before the addition of the monomer emulsion and the inorganic particles had absorbed the monomer. One hour after the addition of the monomer emulsion, 1 kg of water was added to the inorganic particle dispersion that had absorbed the monomer, and the reaction solution was heated to 75 ° C. under a nitrogen atmosphere and held at 75 ° C. for 30 minutes for radical polymerization.
After radical polymerization, the obtained emulsion was subjected to solid-liquid separation by natural sedimentation (decantation), and the resulting cake was washed with methanol, and further vacuum dried at 120 ° C. for 2 hours to obtain polymer particles (a-1 ) When the particle diameter of the polymer particles (a-1) was measured with a Coulter Multisizer (manufactured by Beckman Coulter, Inc.), the volume average particle diameter was 10.8 μm and the variation coefficient was 2.58%.

<Synthesis of fine particles (a-2)>
Except for using 105 parts of methyl methacrylate and 45 parts of ethylene glycol dimethacrylate, the synthesis was performed in the same manner as the fine particles (a-1). As a result, the volume average particle diameter was 10.5 μm, and the coefficient of variation was 2.38%. Fine particles (a-2) were obtained.

<Synthesis of fine particles (b)>
Synthesis was performed in the same manner as the fine particles (a-2) except that 25 parts of ammonia water was changed to 20 parts. As a result, fine particles (b) having a volume average particle size of 5.2 μm and a variation coefficient of 2.87% were obtained. It was.

The results of measuring the degree of swelling of the fine particles (a-1), (a-2) and (b) were as shown in Table 1 below.

<Example 1>
To 100 parts of copolymer A solution, 120 parts of fine particles (a-1), 30 parts of fine particles (b), and 150 parts of butyl acetate were added. Thereafter, a polyfunctional isocyanate compound (Desmodur N3200, manufactured by Sumika Bayer Urethane Co., Ltd.) was added to this mixture as much as OH / NCO = 1 (equal ratio), and mixing and dispersion were performed with a disper. Thereafter, the amount of the composition obtained was moved to a height of 9 cm into a 110 ml screw tube (manufactured by Maruemu Co., Ltd., screw tube No. 8) and allowed to stand for 5 minutes. An 8 cm portion of liquid from the bottom of this composition was collected with a dropper (this is the top), and a polyethylene terephthalate film (Cosmo Shine A-4300, manufactured by Toyobo Co., Ltd.) as a transparent film using a bar coater; The film was allowed to stand at room temperature for 3 minutes and then dried at 100 ° C. for 3 minutes and at 80 ° C. for 2 hours to obtain a light diffusion sheet. Similarly, a 1 cm portion of the liquid from the bottom was collected with a dropper (this is the lower part) to prepare a light diffusion sheet. The upper and lower portions of the composition were sampled, filtered on a membrane filter, washed with acetone, and the particle size distribution was measured with a Coulter counter.
Further, after 1 hour from the dispersion, the liquid of 8 cm part (upper part) and 1 cm part (lower part) was collected in the same manner to prepare a light diffusion sheet, and the particle size distribution was measured with a Coulter counter.
In addition, when the screw pipe | tube containing the said composition solution is represented typically, it is as FIG.

<Comparative Example 1>
The same operation as in Example 1 was carried out except that 120 parts of the fine particles (a-2), 30 parts of the fine particles (b) and 150 parts of butyl acetate were added to 100 parts of the copolymer A solution.

The results of measuring the luminance of the light diffusing sheets prepared in Example 1 and Comparative Example 1 are as shown in Table 2 below.

The results of measuring the particle size distribution of the compositions prepared in Example 1 and Comparative Example 1 are as shown in Table 3 below.

The following was found from Tables 1-3 above. In Example 1, since the (a-1) particle having a large particle size swells, the (a-1) particle having a large particle size (volume average particle size: 10.8 μm, 10 μm fine particle) and a small particle size (b) Particles (volume average particle diameter; 5.2 μm) settle at approximately the same speed. Therefore, even if 1 hour passes after dispersion, the balance of (a-1) particles and (b) particles does not collapse at the upper part and the lower part. The brightness is 5 minutes and 1 hour after dispersion, and the brightness does not change at the top and bottom. Thus, in Example 1, a stable light diffusion film could be created regardless of the passage of time or the location of the coating liquid.
On the other hand, in Comparative Example 1, (a-2) particles having a large particle diameter (volume average particle diameter; 10.5 μm, 10 μm fine particles) do not swell, and thus settle faster than (b) particles having a small particle diameter. Therefore, the number of (a-2) particles having a large particle size is reduced in the upper part, and the number of (a-2) particles is increased in the lower part. As a result, the brightness of the sample after 1 hour is relatively small when the upper part is used, so that the lens effect is reduced and the brightness is lowered. As described above, in Comparative Example 1, the composition of the composition liquid changed with time, so that the light diffusion sheet could not be stably formed.

In Example 1 and Comparative Example 1, it is a schematic diagram of a screw tube in which the composition is put and allowed to stand. In the figure, circles represent sampling points.

Claims (8)

A resin composition for a light diffusing film comprising fine particles and a resin component as essential components,
The fine particles include at least two kinds of fine particles having different volume average particle diameters. Among the fine particles, fine particles having a large volume average particle diameter have a higher degree of swelling in the resin component than fine particles having a small volume average particle diameter. A resin composition for a light diffusing film, characterized in that The fine particles have a degree of crosslinking of fine particles having a large volume average particle diameter of 1 to 20% by mass,
The resin composition for a light diffusing film according to claim 1, wherein the degree of crosslinking of the fine particles having a small volume average particle diameter is 15 to 60% by mass. 3. The light according to claim 1, wherein the fine particles have a volume average particle size ratio of 1.05 to 20 between the fine particles having the largest volume average particle size and the fine particles having the smallest volume average particle size. A resin composition for a diffusion film. The resin composition for a light diffusion film according to any one of claims 1 to 3, wherein the fine particles include at least one kind of monodispersed fine particles. The resin composition for a light diffusion film according to any one of claims 1 to 4, wherein the fine particles include two types of fine particles having different volume average particle diameters. The resin composition for a light diffusing film according to any one of claims 1 to 5, wherein the resin composition has a weight ratio of fine particles to a resin component (fine particles / resin component) of 0.5 to 5. . A process for producing a light diffusing film, comprising a step of applying the resin composition for a light diffusing film according to claim 1 to a film substrate. A light diffusion film produced by the production method according to claim 7.