JP2010107616A - Light diffusing particle and method of manufacturing the same, light diffusing resin composition and application thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusing particle which provides an optical molding having high total light transmittance and an excellent light scattering property, to provide a method of manufacturing the light diffusing particle, and to provide a light diffusing resin composition and application thereof. <P>SOLUTION: The light diffusing particle includes a central part with a refractive index of n1 and a surface layer covering the central part. The surface layer includes polymer particles in which the refractive index continuously or gradually changes from n1 to n2, (wherein n2≠n1), toward a surface from an interface with the central part. A gel fraction of the polymer particle is 90% or more. A ratio of a radius of the central part and thickness of the surface layer in the polymer particle is 1:1 to 20:1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light diffusing particle comprising polymer particles, a method for producing the same, a light diffusing resin composition containing the light diffusing particle, and applications thereof.

  As an optical film having light diffusibility, an optical film containing polymer particles as a light diffusing agent is known. An optical film obtained by depositing composite particles having different shell parts (see Patent Document 1), (2) polymer particles whose refractive index changes from the central part toward the surface part. Optical films (see Patent Documents 2 to 4) have been proposed.

JP-A-4-98201 Japanese Patent No. 2657536 JP 2002-328207 A Japanese Patent Laid-Open No. 2004-354892

However, the optical film of (1) has a problem that the total light transmittance is reduced because backscattering of light occurs at the interface between the core portion and the shell portion.
Further, the optical film (2) has a problem that sufficient light scattering properties cannot be obtained. This is because the monomer penetrates into the central part when forming the surface layer part in the production of polymer particles, or the polymer particles swell into the resin forming the film in the production of the optical film. it is conceivable that.

  The present invention has been made on the basis of the circumstances as described above, and the object thereof is light diffusion capable of obtaining an optical material molded article having high total light transmittance and excellent light scattering properties. It is providing a diffusible particle, its manufacturing method, a light diffusable resin composition, and its application.

  The light diffusing particle of the present invention comprises a central part having a refractive index of n1 and a surface layer part covering the central part, and the surface layer part has a refractive index of n1 to n2 (from the interface with the central part toward the surface). However, it is composed of polymer particles that continuously or stepwise change to n2 ≠ n1), the gel fraction of the polymer particles is 90% or more, and the ratio between the radius of the central portion and the thickness of the surface layer portion of the polymer particles Is 1: 1 to 20: 1.

In the light diffusing particles of the present invention, the central part of the polymer particles is preferably made of a polymer obtained from a monomer containing 10 to 100% by mass of a polyfunctional monomer.
Moreover, it is preferable that a volume average particle diameter is 0.5-10 micrometers.

The method for producing a light diffusing particle of the present invention includes a step of producing seed particles from a monomer containing 10 to 100% by mass of a polyfunctional monomer,
The aromatic vinyl monomer and the (meth) acrylate monomer are used in a mass ratio of 10:90 to 90:10, and these monomers are used in the presence of the seed particles in the presence of the aromatic. A step of producing polymer particles by adding and polymerizing the group vinyl monomer and the (meth) acrylate monomer while increasing or decreasing the ratio continuously or stepwise It is characterized by including.

The light diffusing resin composition of the present invention comprises the above light diffusing particles and a binder resin,
The absolute value | n1-n0 | of the difference between the refractive index n1 of the central portion of the light diffusing particles and the refractive index n0 of the binder resin is 0.03 or more.

Further, the light diffusing resin composition of the present invention comprises the above light diffusing particles and a binder resin,
The absolute value | n2-n0 | of the difference between the refractive index n2 of the surface layer portion of the light diffusing particles and the refractive index n0 of the binder resin is 0.02 or more.

  The optical material molded article of the present invention is characterized by containing a resin component and the light diffusing particles.

  In the optical material molded article of the present invention, an antiglare film, a light diffusion film, a light diffusion plate, a prism sheet, a polarizing plate, or a light guide plate is preferable.

  The film laminate of the present invention comprises a base material layer and a light diffusion layer formed on at least one surface of the base material layer and made of the light diffusing resin composition described above. To do.

According to the light diffusing particles of the present invention, an optical material molded article having a high total light transmittance and excellent light scattering properties can be obtained.
According to the method for producing light diffusing particles of the present invention, it is possible to produce light diffusing particles capable of obtaining an optical material molded article having high total light transmittance and excellent light scattering properties. According to the light diffusing resin composition of the present invention, an optical material molded article having a high total light transmittance and excellent light scattering properties can be obtained.

Hereinafter, embodiments of the present invention will be described in detail.
(Light diffusing particles)
The light diffusing particles of the present invention are composed of polymer particles comprising a central part and a surface layer part covering the central part.
The polymer particles have a gel fraction of 90% or more. When the gel fraction is less than 90%, the polymer particles may swell in the binder resin that forms a film. Here, the gel fraction means the mass of the gel with respect to the mass of the polymer particles before being dissolved in toluene when the polymer particles are dissolved in toluene and the remaining portion without being dissolved is used as a gel. The ratio is expressed as a percentage.

The central part of the polymer particles is preferably made of a polymer obtained from a monomer containing a polyfunctional monomer.
Specific examples of the polyfunctional monomer include polyfunctional aromatic vinyl monomers such as divinylbenzene, polyethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-hexane glycol diacrylate, and polypropylene glycol. Diacrylate compounds such as diacrylate, triacrylates such as trimethylolpropane triacrylate, tetramethylolmethane triacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butylene Glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexane glycol dimethacrylate, neopentyl Dimethacrylates such as recall dimethacrylate, trimethylol propane trimethacrylate, and the like trimethacrylate such as trimethylolpropane trimethacrylate. These compounds can be used individually by 1 type or in combination of 2 or more types.
Specific examples of other monomers (monofunctional monomers) include styrene, α-methylstyrene, vinyltoluene, p-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4- Ethylstyrene, 4-tert-butylstyrene, 3,4-dimethylstyrene, 4-methoxystyrene, 4-ethoxystyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 2,4-dichlorostyrene, 2 , 6-dichlorostyrene, 4-chloro-3-methylstyrene, 1-vinylnaphthalene, 2-vinylpyridine, 4-vinylpyridine and other aromatic vinyl monomers, methyl (meth) acrylate, ethyl (meth) acrylate , Propyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) ) (Cyclo) alkyl (meth) acrylates such as acrylate and cyclohexyl (meth) acrylate; alkoxy (cyclo) alkyl (meth) acrylates such as 2-methoxyethyl (meth) acrylate and p-methoxycyclohexyl (meth) acrylate (Meth) acrylic acid ester monomers, (meth) acrylic acid, crotonic acid, cinnamic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, monomethyl maleate, monoethyl maleate, Carboxyl group-containing unsaturated monomers such as monomethyl itaconate, monoethyl itaconate, mono-2- (meth) acryloyloxyethyl hexahydrophthalate, and anhydrides thereof, (meth) acrylonitrile, crotonnitrile, cinnamon Vinyl cyanide such as acid nitrile Monomers: Cyano group-containing monomers such as 2-cyanoethyl (meth) acrylate, 2-cyanopropyl (meth) acrylate, 3-cyanopropyl (meth) acrylate, hydroxymethyl (meth) acrylate, 2-hydroxyethyl Hydroxy (cyclo) alkyl mono (meth) acrylates such as (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 4-hydroxycyclohexyl (meth) acrylate, neopentyl glycol mono (meth) acrylate; 3-chloro-2 Hydroxyl-containing monomers such as substituted hydroxy (cyclo) alkyl mono (meth) acrylates such as hydroxypropyl (meth) acrylate and 3-amino-2-hydroxypropyl (meth) acrylate, allyl glycidyl ether, glycidyl (meta Acrylate, and the like glycidyl group-containing monomers such as methyl glycidyl methyl acrylate, epoxidized cyclohexyl (meth) acrylate. These compounds can be used individually by 1 type or in combination of 2 or more types.

  In the monomer for obtaining the central part of the polymer particles, the proportion of the polyfunctional monomer is preferably 10 to 100% by mass, more preferably 20 to 100% by mass. If this ratio is too small, the monomer for obtaining the surface layer portion may be impregnated in the center portion when the surface layer portion is formed. Therefore, the center portion having the desired refractive index is not formed. It may be difficult to obtain.

  The surface layer portion of the polymer particle has a refractive index continuously from n1 to n2 (where n2 ≠ n1) from the interface with the center portion to the surface, where n1 is the refractive index of the center portion of the polymer particle. Or it changes gradually. Such a surface layer portion uses a monomer from which a polymer having a refractive index n1 equivalent to that of the central portion is obtained and a monomer from which a polymer having a refractive index n2 different from that of the central portion is obtained. It can be formed by changing the polymerization ratio of the two continuously or stepwise from the interface toward the surface and polymerizing so that the polymerization conversion rate is always 60% or more.

The surface layer of the polymer particles is preferably made of a polymer obtained from a monomer comprising an aromatic vinyl monomer and a (meth) acrylate monomer.
Specific examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, p-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-ethylstyrene, 4- tert-butylstyrene, 3,4-dimethylstyrene, 4-methoxystyrene, 4-ethoxystyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 2,4-dichlorostyrene, 2,6-dichlorostyrene Monofunctional aromatic vinyl monomers such as 4-chloro-3-methylstyrene, 1-vinylnaphthalene, 2-vinylpyridine and 4-vinylpyridine, polyfunctional aromatic vinyl monomers such as divinylbenzene, etc. Can be mentioned. These compounds can be used alone or in combination of two or more.
Specific examples of the (meth) acrylate monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and cyclohexyl. (Cyclo) alkyl (meth) acrylates such as (meth) acrylate; monofunctional compounds such as alkoxy (cyclo) alkyl (meth) acrylates such as 2-methoxyethyl (meth) acrylate and p-methoxycyclohexyl (meth) acrylate ( Dimethacrylate compounds such as (meth) acrylate monomers, polyethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,6-hexane glycol diacrylate, polypropylene glycol diacrylate, and trimethylo Triacrylates such as propane triacrylate and tetramethylol methane triacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4 butylene glycol di Polyfunctional (meth) acrylate monomers such as methacrylates, 1,6-hexane glycol dimethacrylate, dimethacrylates such as neopentyl glycol dimethacrylate, trimethacrylates such as trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate And so on. These compounds can be used alone or in combination of two or more.

  Moreover, in the monomer for obtaining the surface layer part of the polymer particles, the ratio of the polyfunctional monomer is preferably 5 to 80% by mass, more preferably 10 to 50% by mass. If this ratio is too small, the polymer particles may swell in the binder resin forming the film. On the other hand, when this ratio is excessive, when the surface layer portion is formed, the monomer for obtaining the surface layer portion is not adsorbed by the seed particles as the central portion, and is polymerized alone outside the seed particles. There is a risk.

  The absolute value | n1-n2 | of the difference between the refractive index n1 of the central part and the refractive index n2 of the surface of the surface layer part is preferably 0.03 to 0.20, more preferably 0.05 to 0.00. 18. When the absolute value | n1-n2 | of this difference is too small, sufficient light diffusibility may not be obtained. On the other hand, when the absolute value | n1-n2 | of this difference is excessive, the forward luminance may be reduced.

In the light diffusing particles of the present invention, the volume average particle diameter is preferably 0.5 to 10 μm, more preferably 1.0 to 5.0 μm. When the volume average particle diameter is less than 0.5 μm, sufficient light diffusibility may not be obtained. On the other hand, when the volume average particle diameter exceeds 10 μm, when the thin film is formed with the obtained light diffusing resin composition, the light diffusing particles are present non-uniformly throughout the binder resin forming the thin film. In other words, light that is not scattered by the light diffusing particles may be generated.
Moreover, the ratio of the radius of the central part and the thickness of the surface layer part in the polymer particles is 1: 1 to 20: 1, preferably 2: 1 to 10: 1. When the thickness of the surface layer portion is too small, the amount of change in the refractive index per unit thickness increases from the surface layer portion to the center portion, which may cause back scattering. On the other hand, when the thickness of the surface layer portion is excessive, sufficient light diffusibility cannot be obtained.

  Such light diffusing particles produce seed particles as a central part from a monomer containing a polyfunctional monomer, and an aqueous dispersion containing the seed particles is mixed with an aromatic vinyl monomer and ( The surface layer part is formed on the surface of the central part made of seed particles by adding a meth) acrylate monomer while continuously or stepwise changing so that the proportion of either one increases or decreases, and seed polymerization. Is obtained.

  The method for producing seed particles is not particularly limited, but in order to obtain seed particles having a uniform particle diameter, a part of the monomer used is subjected to emulsion polymerization under appropriate conditions, thereby being monodispersed. A method of preparing particles and subjecting the remainder of the monomer to emulsion polymerization in the presence of the monodispersed particles can be used.

In the formation of the surface layer portion, the ratio of the aromatic vinyl monomer and the (meth) acrylate monomer used is 10:90 to 90:10 by mass ratio, preferably 30:70 to 70:30. It is. When the ratio of the aromatic vinyl monomer is too small, or when the ratio of the aromatic vinyl monomer is excessive, the amount of change in the refractive index per unit thickness is large from the surface layer to the center. And may cause backscattering.
In addition, as a method of adding a monomer to an aqueous dispersion, two containers are prepared, for example, an aromatic vinyl monomer is placed in one container, and a (meth) acrylate monomer in the other container. It is possible to use a method of adding a monomer from one container to an aqueous dispersion while putting the body into the container and supplying the monomer from the other container. Each container may contain a mixture of an aromatic vinyl monomer and a (meth) acrylate monomer having different composition ratios.

  According to the light diffusing particles obtained in this manner, the refractive index of the surface layer portion changes continuously or stepwise from the interface with the central portion toward the surface, so that when it is contained in the resin Therefore, it is possible to obtain an optical material molded article having a low backscattering property and a high total light transmittance. Moreover, when the surface layer portion of the polymer particle is formed, since the monomer is prevented from penetrating into the seed particle that is the central portion, the central portion having the desired refractive index can be reliably obtained, and the optical In the production of a material molded product, the polymer particles are prevented from swelling in the resin forming the optical material molded product, so that the desired refractive index is maintained in the surface layer portion, and as a result, has excellent light scattering properties. An optical material molded product can be obtained.

[Light diffusing resin composition]
The light diffusing resin composition of the present invention comprises a binder resin and the above light diffusing particles.
As the binder resin, thermoplastics such as polyethylene terephthalate, polymethyl (meth) acrylate, polycarbonate, cycloolefin polymer, polyarylate, polyethersulfone, polystyrene, methyl (meth) acrylate-styrene copolymer, styrene-acrylonitrile copolymer, etc. Resin; Epoxy resin, vinyl ether resin, curable resin curable with heat or active energy rays such as (meth) acrylate having two or more (meth) acryl groups, oxetane resin, vinyl ester resin, etc. can be used. .

In the light diffusing resin composition of the present invention, the absolute value | n1-n0 | of the difference between the refractive index n1 of the central portion of the light diffusing particles and the refractive index n0 of the binder resin is 0.03 or more, preferably Is 0.03 to 0.20. If the absolute value | n1-n0 | is too small, sufficient light diffusibility cannot be obtained. On the other hand, if the absolute value | n1-n0 | is excessive, the forward luminance may be reduced.
In addition, the absolute value | n2-n0 | of the difference between the refractive index n2 of the surface of the light diffusing particles and the refractive index n0 of the binder resin is preferably 0.03 or less, more preferably 0.02 or less. . If this absolute value | n2-n0 | is excessive, there is a risk of causing backscattering.

  In the light diffusing resin composition of the present invention, the ratio of the binder resin to the light diffusing particles is preferably 100: 50 to 100: 1 by mass ratio, more preferably 100: 30 to 100: 3. is there. If the ratio of the light diffusing particles is too small, sufficient light diffusibility may not be obtained. On the other hand, when the ratio of the light diffusing particles is excessive, the forward luminance may be lowered.

  The light diffusing resin composition of the present invention may contain an additive such as a solvent and inorganic fine particles such as silica fine particles.

In the present invention, for example, the above light diffusing resin composition is dissolved in an organic solvent to prepare a slurry, and a light diffusing layer having a desired thickness is obtained by a known coater. A target optical material molded article can be produced by a method of coating on one surface of the material layer and then drying the coating layer (hereinafter also referred to as “solvent casting method”).
The optical material molded article thus obtained has a high light diffusibility and a high total light transmittance. By using such an optical material molded article for a display device, sufficient Viewing angle and brightness can be obtained. Moreover, this optical material molded product can also be suitably used for a lighting device.

[Optical material moldings]
The optical material molded article of the present invention contains a resin component and the light diffusing particles. Such an optical material molded article has an extremely excellent balance between light transmittance and light diffusibility. Specific examples of the optical material molded product applied to the present invention include an antiglare film, a prism sheet, a light diffusion film, a light diffusion plate, a polarizing plate, and a light guide plate. In addition, since the optical material molded article of this embodiment has a very excellent balance between light transmittance and light diffusibility, it can be suitably used as a light diffusing plate or a light diffusing film.

  The resin component is not particularly limited, and various types can be used, but a transparent one having high transparency to visible light is preferable. In the present specification, “transparent” conceptually includes colored and translucent in addition to colorless and transparent.

  In the case where the resin component is formed into a sheet having a thickness of 200 μm, the light transmittance of the sheet at a wavelength of 550 nm is preferably 80% or more, and 85% or more. More preferred is 90% or more. By using such a resin component, there is an advantage that the light transmittance of the obtained optical material molded article is further improved. The glass transition temperature of the resin component is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and particularly preferably 150 ° C. or higher. When the glass transition temperature of the resin component is in the above range, there is an advantage that an optical material molded product having heat resistance to the extent that it can be put into practical use can be obtained.

  As a resin component, what was illustrated as binder resin in said light diffusable resin composition can be used. Among these, a curable resin that is curable with heat or active energy rays is preferable from the viewpoint of being easily compounded with glass fiber or glass fiber cloth and being thermally stable. More preferred are (meth) acrylates having two or more (meth) acryl groups.

  As a method for producing an optical material molded article of the present invention, for example, (1) a resin component and light diffusing particles are mixed, the mixture is kneaded and granulated by an extruder, and the granulated material is injected. A method of molding by a molding machine, (2) a method of applying a liquid material comprising a resin component, light diffusing particles and a solvent to a transparent substrate, then evaporating the solvent, and performing a heat treatment if necessary, (3) A method of applying a liquid material composed of a monomer curable with active energy rays and light diffusing particles to a transparent substrate and then irradiating and curing with active energy rays can be used. In the method, a master batch in which a high concentration of light diffusing particles is contained in the resin component is granulated by an extruder, and a mixture of the master batch and the granular resin component is molded by an injection molding machine. Good.

[Film laminate]
The film laminated body of this invention is equipped with a base material layer and the light-diffusion layer which consists of said light diffusable resin composition formed on the at least one surface of this base material layer. In such a film laminate, since the light diffusing layer is formed by the light diffusing resin composition of the present invention containing light diffusing particles having good dispersibility in the resin component, in the light diffusing layer, The light diffusing particles are uniformly dispersed. Therefore, the balance between light transmittance and light diffusibility is very excellent.

Base material layer:
The substrate layer is preferably a layer made of a transparent (that is, colorless, transparent, colored, or translucent) resin, and those exemplified as the binder resin in the light diffusing resin composition can be used. .
Although the thickness of a base material layer is not specifically limited, It is preferable that it is 0.03-0.3 mm, and it is still more preferable that it is 0.05-0.2 mm.

Light diffusion layer:
The thickness of the light diffusing layer is not particularly limited as long as it is layered, but the thickness is preferably 0.005 to 0.1 mm, and more preferably 0.008 to 0.08 mm. If the thickness of the light diffusion layer is less than 0.005 mm, sufficient light diffusibility may not be obtained. On the other hand, if it exceeds 0.1 mm, the total light transmittance may decrease.
When the light diffusing layer is used as an antiglare layer, it may be formed on one surface of the base material layer or on both surfaces, but it is disposed on the surface of a television or the like. It is sufficient to form on one surface of the substrate.

Specific examples of the present invention will be described below, but the present invention is not limited to these examples. In the following examples and comparative examples, “parts” are based on mass unless otherwise specified.
Moreover, the measuring method of various physical-property values and the evaluation method of various characteristics are shown below.

[Volume average particle diameter]
Using a scanning electron microscope (trade name “JSM-6030LA”) manufactured by JEOL Ltd., the particles were observed at an imaging magnification of 5000 times or 10,000 times, and the volume average particle diameter was determined by image analysis of 10 particles. It was measured.
(Refractive index)
particle:
Based on the refractive index of the homopolymer measured with an Abbe refractometer, the refractive index of the particle center portion and the particle surface layer portion was calculated from the monomer composition ratio. In addition, the particles were cut with a microtome, and the cross section was stained with ruthenium. When observed with a transmission electron microscope, the color density gradually increased from the interface with the center of the surface layer toward the surface. I confirmed that it would change.
Binder resin:
A transparent film was prepared with a binder resin and measured with an Abbe refractometer.
[Gel fraction]
0.5 g of polymer particles were weighed, placed in 30 cc of toluene and shaken for 3 hours, and then the supernatant was filtered by centrifugation, and the remaining solid was dried at 130 ° C. for 1 hour. And the mass of the solid substance after a drying process was measured, and the gel fraction was calculated | required by (mass of the solid substance after a drying process / 0.5) x100.
[Total light transmittance]
Using a turbidimeter manufactured by Nippon Denshoku Co., Ltd. (trade name “NDH-5000”), the measurement was carried out in accordance with JIS K7105, assuming that no sample (air) was 100%.
[Haze value]
Using a turbidimeter manufactured by Nippon Denshoku Co., Ltd. (trade name “NDH-5000”), the measurement was performed according to JIS K7105.
[Half angle of transmitted scattered light]
Using a variable angle photometer (trade name “GP-200”) manufactured by Murakami Color Co., Ltd., the transmitted scattered light angle distribution of the film was observed. At this time, the range of the angle which becomes 1/2 of the transmitted light intensity of 0 ° was defined as the half-value angle.
In addition, this half value angle of the transmitted scattered light indicates that the higher the value, the higher the light scattering property.

<Example 1>
(1) Preparation of seed particles:
95 parts of styrene (hereinafter referred to as “ST”), 3 parts of methacrylic acid (hereinafter referred to as “MA”), 2 parts of t-dodecyl mercaptan as a chain transfer agent, and 2 parts of sodium persulfate as a water-soluble initiator Was used to produce monodisperse particles having a number average molecular weight of 50,000 and a volume average particle size of 1.0 μm.
Next, 3,5,5-trimethylhexanoyl peroxyside (trade name “Perroyl 355”, manufactured by NOF Corporation, water solubility: 0.01%) as a polymerization initiator, 2 parts, sodium lauryl sulfate as an emulsifier 0.1 And 20 parts of water were stirred and emulsified, and then further finely divided with an ultrasonic homogenizer to prepare an aqueous dispersion of a polymerization initiator. To the obtained aqueous dispersion, 30 parts of the above monodispersed particles were added and stirred for 16 hours. Next, a monomer composed of 80 parts of styrene and 20 parts of divinylbenzene was added to the aqueous dispersion, and the monomer was absorbed into the monodisperse particles by slowly stirring at 40 ° C. for 3 hours. Thereafter, 5 parts of a styrene-α-methylstyrene-acrylic acid copolymer composition (manufactured by Johnson Polymer Co., Ltd., “Jonkrill 6030”, hereinafter referred to as “J6030”) is added to the aqueous dispersion at 75 ° C. The seed particles were obtained by raising the temperature to 3 hours and conducting a polymerization reaction for 3 hours. The obtained seed particles had a volume average particle diameter of 1.5 μm, and almost no coagulum was generated.

(2) Production of light diffusing particles:
An aqueous dispersion of a polymerization initiator was prepared in the same manner as in the above (1), 60 parts of the seed particles were added to the obtained aqueous dispersion, stirred for 12 hours, and then 5 parts of J6030 was added. . On the other hand, a mixed monomer consisting of 40 parts of ST and 10 parts of divinylbenzene (hereinafter referred to as “DVB”) is prepared in a container (hereinafter referred to as “container X”), and another container (hereinafter referred to as “container”). Y ”) and 40 parts of methyl methacrylate (hereinafter referred to as“ MMA ”) and trimethylolpropane tri (meth) acrylate (trade name“ Light Ester TMP ”manufactured by Kyoeisha Chemical Co., Ltd.), hereinafter referred to as“ TMP ”. ) A mixed monomer consisting of 10 parts was prepared. Then, the mixed monomer in the container Y is continuously added to the mixed monomer in the container X, and at the same time, the mixed particles in the container X are heated to 75 ° C. Polymerization was carried out while continuously adding to the aqueous dispersion contained. At this time, the addition rate was adjusted so that the mixed monomer in the container X and the mixed monomer in the container Y were completely added in 2 hours. After the addition was completed, the system was heated to 80 ° C. Time polymerization was performed. And by making it dry with a spray dryer (manufactured by Nihon Büch, model number “B-290 type”), the refractive index continuously changes from the interface with the central part toward the surface at the central part made of seed particles. Light diffusing particles (hereinafter referred to as “particle A”) made of polymer particles having a surface layer portion were produced. Almost no coagulum was generated.
The volume average particle diameter of the obtained particle A, the gel fraction of the particle A, the central part of the particle A, the interface with the central part in the surface layer part (hereinafter referred to as “interface”) and the refractive index of the surface are shown in Table 1 below. Shown in
Further, the particle A was cut with a microtome, and the cross section was stained with ruthenium. When observed with a transmission electron microscope, the color gradually faded from the interface in the surface layer to the surface. confirmed.

<Examples 2-5 and Comparative Examples 1-3>
(1) In preparation of seed particles, the amount of monodispersed particles and the composition of the monomer were changed according to the formulation shown in Table 1, and (2) in the production of light diffusing particles, the amount of seed particles used and the container Except that the composition of each mixed monomer of X and container Y was changed according to the formulation shown in Table 1 below, light diffusing particles (hereinafter referred to as “particle B” to “ Particles H ”).
The following table shows the volume average particle size of seed particles, the volume average particle size of particles B to H, the gel fraction of particles B to H, the refractive index of the interface and the surface in the central part and surface layer part of particles B to H. It is shown in 1.

<Comparative example 4>
(1) Monodisperse particles having a volume average particle diameter of 1.0 μm produced in the preparation of seed particles are used as seed particles. (2) In the production of light diffusing particles, the amount of seed particles used, as well as container X and container Except that the composition of each mixed monomer of Y was changed according to the formulation shown in Table 1 below, light diffusing particles (hereinafter referred to as “Particle I”) were obtained in the same manner as in Example 1. Manufactured.
Table 1 below shows the volume average particle size of the obtained particles I, the gel fraction of the particles I, and the refractive index of the interface and the surface in the center portion and surface layer portion of the particles I.
In the above, about the particle F which concerns on the comparative example 1, when ruthenium dyeing | staining is performed with respect to the cross section and this is observed with the transmission electron microscope, the dyeing | staining state of a surface layer part is non-uniform | heterogenous, Changes in the composition of structural units derived from aromatic vinyl monomers and structural units derived from (meth) acrylate monomers were not observed toward the surface. This is presumably because the seed particles that became the central part were impregnated in forming the surface layer part.

<Example 6>
100 parts of a mixture of dipentaerystol penta and dipentaerythritol hexaacrylate (trade name “Aronix M402”, hereinafter referred to as “DPHA”) as a photosensitive binder resin, and 90 parts of toluene as an organic solvent; A light diffusing resin composition was prepared by mixing 10 parts of cyclohexanone and adding and dispersing 10 parts of particles A in the resulting mixture.
The obtained light diffusing resin composition was coated on a polyethylene terephthalate substrate having a thickness of 0.25 mm by using a Mayer bar and dried to form a coating film having a thickness of 20 μm. Next, an optical film was produced by irradiating the coating film with ultraviolet rays (irradiation amount: 500 mJ / cm ² ) and curing with a high-pressure mercury lamp. Here, the refractive index of the binder resin after curing was 1.51.
Table 2 below shows the total light transmittance, haze value, and transmitted scattered light half-value angle of the obtained optical film (including the base material).

<Examples 7 to 10 and Comparative Examples 5 to 8>
A light diffusing resin composition was prepared in the same manner as in Example 6 except that the type of the light diffusing particles was changed according to Table 2, and an optical film was produced.
Table 2 below shows the total light transmittance, haze value, and transmitted scattered light half-value angle of the obtained optical film.

  As is clear from the results in Table 2, according to the light diffusing resin composition according to Examples 6 to 10, the haze value is high and the transmitted scattered light half-value angle is high while the total light transmittance is high. It was confirmed that an optical material molded article having excellent light scattering properties can be obtained.

Claims (9)

  It consists of a central part having a refractive index of n1 and a surface layer part covering the central part, and the surface layer part has a refractive index continuously from n1 to n2 (where n2 ≠ n1) from the interface with the central part to the surface. Or the polymer particles have a gel fraction of 90% or more, and the ratio of the radius of the central portion to the thickness of the surface layer portion of the polymer particles is 1: 1 to 20: 1. A light diffusing particle characterized by being.   2. The light diffusing particle according to claim 1, wherein the central part of the polymer particle is made of a polymer obtained from a monomer containing 10 to 100% by mass of a polyfunctional monomer.   3. The light diffusing particle according to claim 1, wherein the volume average particle diameter is 0.5 to 10 [mu] m. Producing seed particles from a monomer containing 10 to 100% by mass of a polyfunctional monomer;
The aromatic vinyl monomer and the (meth) acrylate monomer are used in a mass ratio of 10:90 to 90:10, and these monomers are used in the presence of the seed particles in the presence of the aromatic. A step of producing polymer particles by adding and polymerizing the group vinyl monomer and the (meth) acrylate monomer while increasing or decreasing the ratio continuously or stepwise A process for producing light diffusing particles. It contains the light diffusing particles according to any one of claims 1 to 3 and a binder resin,
The light diffusing resin composition is characterized in that the absolute value | n1-n0 | of the difference between the refractive index n1 at the center of the light diffusing particles and the refractive index n0 of the binder resin is 0.03 or more. It contains the light diffusing particles according to any one of claims 1 to 3 and a binder resin,
A light diffusing resin composition, wherein an absolute value | n2-n0 | of a difference between a refractive index n2 of a surface layer portion in the light diffusing particles and a refractive index n0 of the binder resin is 0.02 or more.   An optical material molded article comprising a resin component and the light diffusing particles according to any one of claims 1 to 3.   The optical material molded article according to claim 7, which is an antiglare film, a light diffusion film, a light diffusion plate, a prism sheet, a polarizing plate, or a light guide plate.   A base material layer and a light diffusion layer formed on at least one surface of the base material layer and comprising the light diffusing resin composition according to claim 5 or 6, Film laminate.