JP2002328207A - Optical diffusion body and display device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical diffusion body which exhibits only small absorption loss of incident light and small reflection loss to the incident direction, has excellent light utilization efficiency and in particular excellent optical diffusibility, and to provide a display device which can widen the viewing angle without loss of light and exhibits excellent visibility. SOLUTION: The optical diffusion body has transparent particles which has a refractive index n changing from the central part to the outer part according to the following formulae: n=n0 -(n0 -np )×r<m> /R<m> (1) r=(x<2> +y<2> )<1/2> (2), wherein x is the coordinate on the axis being parallel to the incident ray and having the center of the transparent particle as the origin, y is the coordinate on the axis being perpendicular to the incident ray and having the center of the transparent particle as the origin, n0 is the refractive index of the center of the transparent particle, np is the refractive index of the transparent particle surface, R is the radius of the transparent particle, r is the distance from the center of the transparent particle, and m is a real number larger than 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffuser, and more particularly, to a light diffuser used for a viewing angle expanding body such as a transmissive screen of a rear projection display, a liquid crystal display, a plasma display, and an electroluminescence display. The present invention relates to a body and a display device including the same.

[0002]

2. Description of the Related Art In recent years, light diffusers have been used for improving the display quality of display materials such as liquid crystal displays and improving viewing angle characteristics, and are used in various fields such as light modulating materials, optical elements and display elements. ing. As a configuration of a conventional light diffuser, for example, a method of forming fine irregularities on the surface, such as frosted glass, or a method of dispersing particles of several μm to about 10 μm in a resin film is generally used. . All of the conventional light diffusers using these methods refract light toward the front surface using a step in refractive index generated at the boundary between the transparent substance and the light diffusing agent. However, although these methods can certainly scatter light, a part of the light is reflected backward due to a step in the refractive index, and the backward scattering also increases. For this reason, the amount of transmitted light decreases, and the contrast of the display screen decreases.

On the other hand, JP-A-6-347616 and JP-A-6-347617 propose a light diffuser which prevents reflection of light in a reverse direction and is excellent in light control.
These light diffusers prevent reflection of light in the reverse direction and have a certain degree of light use efficiency, but are not sufficient in terms of light diffusivity.

[0004]

As described above, there is no light diffuser which has a small absorption loss of incident light and a small reflection loss in the incident direction, and which can sufficiently satisfy the light diffusivity and utilization efficiency. Is the current situation. Therefore, a first object of the present invention is to provide a light diffuser which has a small absorption loss of incident light and a small reflection loss in an incident direction, is excellent in light diffusivity and utilization efficiency, and is particularly excellent in light diffusivity. It is in. A second object of the present invention is to provide a display device which can increase a viewing angle without losing light and has excellent visibility.

[0005]

That is, the light diffuser of the present invention comprises: <1> a light diffuser having transparent particles whose refractive index n changes from the center to the outside according to the following equation (1). It is a diffuser. _{n = n 0 - (n 0} -n p) × r m / R m (1) r = (x 2 + y 2) 1/2 (2) x : Coordinate of an axis parallel to the incident ray with the center of the transparent particle as the origin y : Coordinates of an axis perpendicular to the incident light with the center of the transparent particle as the origin n ₀ : refractive index of the center of the transparent particle n _p : refractive index of the surface of the transparent particle R : Radius r of transparent particles ： Distance from center of transparent particle m : Real number greater than 2

According to the light diffusing body of the above <1>, the refractive index of the transparent particles increases from the center to the outside in the above formula (1).
, The step of the refractive index is small, and the reflection in the incident direction of light due to the step of the refractive index can be suppressed. Furthermore, since the transparent particles have a refractive index distribution structure that is distributed in a third-order or higher curve, light can be refracted greatly.

<2> Refractive index n from the center to the outside
Is a light diffuser having transparent particles that change according to the following formula (3). _{n = n 0 - (n 0} -n p) × r m / R 'm (3) r = (ax 2 + y 2) 1/2 (4) x : Coordinate of an axis parallel to the incident ray with the center of the transparent particle as the origin y : Coordinate of an axis perpendicular to the incident light with the center of the transparent particle as the origin n ₀ : Refractive index of the center of the transparent particle n _p : Refractive index of the surface of the transparent particle R ': Long axis radius of the transparent particle r ： Distance from center of transparent particle m : Real number greater than 2 a : 1 real number greater than

According to the light diffuser of the above <2>, the refractive index of the transparent particles is changed from the center to the outside by the above formula (3).
, The step of the refractive index is small, and the reflection in the incident direction of light due to the step of the refractive index can be suppressed. Further, since the transparent particles have a refractive index distribution structure in which the refractive index is distributed in a curve of a third order or more from the center toward the outside, light can be refracted greatly.

<3> The light diffuser according to <1> or <2>, wherein the transparent particles are dispersed in a transparent resin having a refractive index substantially equal to the refractive index of the surface of the transparent particles. is there.

According to the light diffuser of the above <3>, it is possible to suppress reflection of light in the incident direction due to a step in the refractive index at the boundary between the transparent particles and the transparent resin.

<4> A display device comprising the light diffusers of <1> to <3>.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the light diffuser and display device of the present invention will be described below.

<< Light Diffuser >> The light diffuser of the present invention is characterized by having transparent particles whose refractive index n changes from the center to the outside according to the following formula (1).

[0014] _{n = n 0 - (n 0} -n p) × r m / R m (1) r = (x 2 + y 2) 1/2 (2) x : Coordinate of an axis parallel to the incident ray with the center of the transparent particle as the origin y : Coordinates of an axis perpendicular to the incident light with the center of the transparent particle as the origin n ₀ : refractive index of the center of the transparent particle n _p : refractive index of the surface of the transparent particle R : Radius r of transparent particles ： Distance from center of transparent particle m : Real number greater than 2

The light diffuser of the present invention has the transparent particles whose refractive index n continuously changes from the center to the outside according to the above formula (1), so that the reflection due to the step of the refractive index in the transparent particles is prevented. Since it can be suppressed, the absorption loss of incident light and the reflection loss in the incident direction can be reduced, and the light use efficiency can be improved. Further, in the above equation (1),
Since m is a real number greater than 2, the refractive index of the transparent particles exhibits a third-order or higher curve distribution from the center toward the surface, and light diffusivity can be greatly improved.
If the refractive index changes according to the above equation (1), the central portion of the transparent particle may be at the maximum position or the minimum position of the refractive index.

The above equation (1) will be described with reference to FIG. FIG. 1 is a schematic view of a transparent particle for explaining the formula (1). In the above formula (1), n ₀ is the refractive index at the center of the transparent particle, and represents the refractive index at the origin O in FIG. In this case, the center of the sphere, which is the outer shape of the transparent particle, is defined as the center of the transparent particle. In FIG. 1, the incident light is indicated by an arrow I.
Incident on the transparent particles. In FIG. 1, an axis passing through the center of the transparent particle and parallel to the incident light is defined as an x-axis, and an axis perpendicular to the incident light is defined as ay-axis. X and y in the above formula (1) represent coordinates with respect to the x axis and the y axis at an arbitrary point A in the transparent particle. R in the above formula (1) is
This is the distance from the center of the transparent particle. That is, r is the distance from the origin O to an arbitrary point A in FIG. 1 and can be expressed by the above equation (2). R in the above formula (1) represents the radius of the transparent particles. The radius means an average radius from the center of the transparent particle to the surface. N _p in the above formula (1) represents the refractive index of the transparent particle surface. The refractive index of the surface of the transparent particles means the average refractive index of the surface of the transparent particles, and a measuring method thereof will be described later. In the above formula (1), m represents a real number larger than 2. The upper limit of m is not particularly limited, but is preferably 8 or less, more preferably 6 or less, from the viewpoint of preventing reflection in the light incident direction. In the present invention, the refractive index distribution of the transparent particles according to the above formula (1) can be measured by the method described in Upright Optics, Vol. As an apparatus used for the measurement, a differential interference microscope Interphako manufactured by Carl-Zeiss (Carl Zeiss) is used.
(Interfaco) and the like can be suitably used.

When the transparent particles are applied in a state of being dispersed in a solvent, when the solvent is evaporated and dried, the transparent particles are deformed in the thickness direction of the coating film, and the cross section of the transparent particles in the thickness direction of the light diffuser is elliptical. May be indicated. Even in such a case, the light diffuser of the present invention has a refractive index n according to the following equation (3).
Is continuously changed from the center to the outside, so that reflection due to the step of the refractive index in the transparent particles can be suppressed, so that the absorption loss of incident light and the reflection loss in the incident direction can be reduced, and the light utilization efficiency can be reduced. Can be improved. Further, in the following formula (3), since m is a real number larger than 2, the refractive index of the transparent particles exhibits a third-order or higher curved distribution from the center toward the surface, greatly improving the light diffusivity. Can be done. In addition, as long as the refractive index changes according to the following equation (3), the center of the transparent particle may be at the maximum position or the minimum position of the refractive index.

[0018] _{n = n 0 - (n 0} -n p) × r m / R 'm (3) r = (ax 2 + y 2) 1/2 (4) x : Coordinate of an axis parallel to the incident ray with the center of the transparent particle as the origin y : Coordinate of an axis perpendicular to the incident light with the center of the transparent particle as the origin n ₀ : Refractive index of the center of the transparent particle n _p : Refractive index of the surface of the transparent particle R ': Long axis radius of the transparent particle r ： Distance from center of transparent particle m : Real number greater than 2 a : 1 real number greater than

The above equation (3) will be described with reference to FIG. FIG. 2 is a schematic view of a transparent particle for explaining the equation (3). In the above formula (3), n ₀ , n _p , x and y are the same as those in the above formula (1), and thus description thereof is omitted. R in the above equation (3) is a distance from the center of the transparent particle. That is, r is the distance from the origin O to an arbitrary point in FIG. 2, and can be expressed by the above equation (4). In Expression (4), a is a real number greater than 1, and is a numerical value obtained from the ratio between the major axis and the minor axis of the ellipse. R ′ in the above formula (3) represents the major axis radius of the transparent particles. The major axis radius refers to the radius in the major axis direction from the center of the transparent particle, that is, the distance from the origin O to the contact point between the y axis and the boundary surface of the transparent particle in FIG. In the above formula (3), m represents a real number larger than 2. The upper limit of m is not particularly limited, but is preferably 8 or less, more preferably 6 or less, from the viewpoint of preventing reflection in the light incident direction.

(Transparent Particles) Next, the transparent particles used in the present invention will be described. The transparent particles of the present invention are particles having a refractive index distribution structure according to the above formula (1) or (3). The size of the particles can be appropriately selected depending on the desired thickness of the light diffuser and the like. However, considering the light diffusion effect, the volume average particle size is preferably 0.5 to 50 μm,
-20 μm is more preferable.

In order to form a transparent particle having a refractive index distribution structure according to the formula (1), a method of forming a core-shell latex by a usual emulsification degree may be used. However, in this case, the particle size of the obtained fine particles is 0.1. It is difficult to show the light diffusion property which is the object of the present invention because it is very small at 1 μm.
Is preferred. Therefore, such particles (0.5
It is preferable to apply various kinds of particles and a method for producing the same to form the particles having a thickness of about 20 μm.

For example, a so-called seed polymerization method in which fine particles (referred to as seed particles) are formed in advance and a new monomer is polymerized therein can be used. The seed particles are formed by polymerizing the first monomer by soap-free emulsion polymerization or the like. A second monomer is added to the particles, and polymerization is promoted while being absorbed by the seed particles, thereby forming a distribution in the polymer in the particles. The second monomer may be added at once, divided into several times, or added continuously. In this case, the polymer obtained from the first monomer is not always in the core and the polymer obtained from the second monomer is not always in the shell, but the hydrophilicity / hydrophobicity of each monomer and the addition rate of the second monomer are adjusted. For example, the desired morphology can be controlled, and the refractive index distribution inside the particle can be changed. ("Latest technology and application development of polymer fine particles" CMC (1997), "Polymer latex (New Polymer Bunko 26)" Soichi Muroi, Ikuo Morino Polymer Publishing Association (198
8) etc.)

Further, the first seed particles can be used after growing the particle diameter to a desired size by repeating absorption and polymerization of the first monomer. In this way, a combination of polymers obtained from the first monomer and polymers obtained from the second monomer having substantially different refractive indices can be used. The first monomer and the second monomer may each be of one type or the copolymers obtained from the first monomer group and the copolymer obtained from the second monomer group may have substantially different refractive indices. The types of monomers may be two or more as long as they are different from each other.

Further, microsuspension polymerization can also be used. This method is used in a usual suspension polymerization to obtain a so-called Gri.
Form n lenses. (Yasuhiro Koike et al. Apll. Op
t. 33 (16) 3394 (1994)) In this case, the monomer M1 is added to an aqueous PVA solution, and a monomer M2 which gives a polymer having a refractive index substantially different from that of the polymer obtained from the monomer M1 is slightly delayed while performing suspension polymerization.
Is added dropwise, or the monomer Ml
Is added to an aqueous PVA solution to form particles by suspension polymerization, and then the monomer M2 and an initiator are added to carry out polymerization again to continuously change the refractive index inside the particles. To form particles. However, in this document,
The particle size is about 0.5 to 1. It is as large as 1 mm. Therefore, in order to use the light diffuser of the present invention, a method of dispersing the particles for the Grin lens using a high-share disperser such as a homogenizer and then performing polymerization (microsuspension polymerization) is used.
It can be adjusted to a desired particle size (for example, 2 to 20 μm).

As an example of using microsuspension polymerization to form micron-sized particles having a polymer distribution within the particles, for example, first, a monomer Ml is first polymerized to about 20%, and the reaction solution is micro-suspended in an aqueous phase. It is also possible to use a method in which the polymerization is further carried out by turbidity, and the polymerization is carried out while dropping the monomer M2. (Michael F. et al. And J
Polym. Sci. Part A 38 345 (20
00)). However, in order to control the distribution of a desired refractive index, it is necessary to select a monomer, set polymerization conditions, and the like.

At this time, a polymer prepared by preliminarily polymerizing the monomer Ml is prepared, and the polymer is mixed with the monomer Ml and microsuspended in an aqueous phase. A method in which the polymerization is started in a turbid state, and then the polymerization is further performed while dropping the monomer M2, may be used. A method using a combination of monomers having substantially different refractive indices between the polymer obtained from the monomer M1 and the polymer obtained from the monomer M2 in these methods can also be used in the present invention. Also in this case, each of the monomers Ml and M2 may be one kind, or a copolymer obtained from the monomer Ml group,
As long as the copolymers obtained from the monomer M2 group have substantially different refractive indices, the types of the monomers may be two or more.

In particular, as the transparent particles in the present invention, those produced by the following method are preferred. That is, the transparent particles obtained from at least the first monomer group and the second monomer group, wherein the refractive index of the polymer obtained from the first monomer group is the refractive index of the polymer obtained from the second monomer group. Is a combination that is substantially higher than the first ratio, and at least the first and second monomers respectively selected from the first and second monomer groups correspond to the polymerization initiator.
Alternatively, after mixing a polymer obtained by polymerization of a monomer selected from the second monomer group, the mixture is dispersed in a medium, and then, before the polymerization is terminated in the process of forming transparent particles by a polymerization reaction. And furthermore,
This is a method of polymerizing while adding a monomer selected from the second or first monomer group to form transparent particles having an average particle size of 0.5 to 20 μm.

For the formation of the transparent particles, at least one monomer is selected from at least the first monomer group and the second monomer group and used. The first monomer group and the second monomer group are combinations in which the refractive index of the polymer obtained from the first monomer group is substantially higher than the refractive index of the polymer obtained from the second monomer group. If there is, the kind of the monomer is not particularly limited. In practice, the difference in refractive index is preferably 0.02 or more, more preferably 0.05 or more, and particularly preferably 0.1 or more. The refractive index of the polymer obtained from each monomer is, for example, PO
LYMER HANDBOOK (JOHN WILEY
& Sons).

In order to produce such a difference in refractive index, the first monomer group has at least one of an aromatic ring or a bromine atom, a chlorine atom and a sulfur atom in the molecule,
And compounds having at least one ethylenic double bond. More specifically, styrene, vinylnaphthalene, chlorostyrene, bromostyrene, chloromethylstyrene, methoxystyrene, methylstyrene, divinylbenzene, phenyl (meth) acrylate, benzyl (meth) acrylate, benzyl (meth) acrylamide, 2-phenyl Ethyl (meth) acrylate, 2-
(Tribromophenyl) ethyl (meth) acrylate,
2- (tribromophenyloxy) ethyl (meth) acrylate, 3- (m-methylbromophenoxy) -2-
Hydroxypropyl (meth) acrylate, 2,2-bis (4- (meth) acryloyloxyethoxy-3,5
-Dibromophenyl) propane, 3- (m-methylchlorophenoxy) -2-hydroxypropyl (meth) acrylate, bis (4-methacryloylthiophenenyl) sulfide, bis (4-vinylthiophenyl) sulfide, bis (β- (Meth) acryloyloxyethylthio) xylylene, diallyl phthalate, vinyl chloride, vinylidene chloride, vinyl benzoate, vinyl chlorobenzoate, vinyl bromobenzoate, allyl benzoate,
Allyl chlorobenzoate, allyl bromobenzoate and the like can be mentioned. The monomers used may be one of these or a combination of two or more thereof.

On the other hand, examples of the second monomer group include compounds having no aromatic ring, bromine atom, chlorine atom or sulfur atom in the molecule and having at least one ethylenic double bond. More specifically, an alkyl (meth) acrylate (as the alkyl group, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, hexyl, cyclohexyl, 2-ethyl Xyl, etc.), and fluorinated alkyl (meth) acrylates (as the fluorinated alkyl group are (CH ₂ ) _m C _n F
_{2n + 1} (m represents 0 to 3, n represents 1 to 10), hexafluoroisopropyl, trifluoroisopropyl and the like, (meth) acrylic acid, vinyl acetate, alkyl vinyl ether (the alkyl group is methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, hexyl, cyclohexyl, 2-ethylhexyl, etc.).

Among the combinations of these monomer groups,
The monomers selected from the first monomer group are styrene, substituted styrene, benzyl (meth) acrylate, and 2-phenylethyl (meth), particularly from the viewpoint of their polymerizability, solubility, supply property, and difference in refractive index. Acrylate,
2- (tribromophenyl) ethyl (meth) acrylate, 2- (tribromophenyloxy) ethyl (meth)
Acrylate, bis (4-methacryloylthiophenyl) sulfide, bis (4-vinylthiophenyl) sulfide, diallyl phthalate, wherein the monomers selected from the second monomer group are alkyl (meth) acrylates, alkyl fluoride Combinations of (meth) acrylates are preferred.

As the above-mentioned polymerization initiator, known thermal polymerization initiators and photopolymerization initiators can be used. Examples of the thermal polymerization initiator include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile), and peroxides such as benzoyl peroxide. System initiators and the like.

As the photopolymerization initiator, US Pat.
U.S. Pat. No. 2,672,512, a vicinal polyketaldonyl compound described in US Pat. No. 3,676,660, an acyloin ether compound described in U.S. Pat. No. 2,448,828.
Patent No. 3,049,127 and No. 2,951,758, polynuclear quinone compounds described in U.S. Pat. Nos. 3,046,127 and 2,951,758, and U.S. Pat. No. 3,549,367. Combination of triarylimidazole dimer and p-aminoketone, benzothiazole compound and trihalomethyl-s-triazine compound described in JP-B-51-48516, and trihalomethyl-s- described in U.S. Pat. No. 4,239,850. Triazine compounds, U.S. Pat.
No. 976, for example, a trihalomethyloxadiazole compound.

As the photopolymerization initiator, benzophenone, camphorquinone, 4,4-bis (dimethylamino) benzophenone, 4-methoxy-4'-dimethylaminobenzophenone, 4,4'-dimethoxybenzophenone, 4-dimethyl Aminobenzophenone, 4-dimethylaminoacetophenone, benzylanthraquinone,
Bis such as 2-tert-butylanthraquinone, 2-methylanthraquinone, xanthone, thioxanthone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, fluorenone, acridone, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide Acylphosphine oxides, Lucirin T
Aromatic ketones such as acylphosphine oxides such as PO, α-hydroxy or α-aminoacetophenones, α-hydroxycycloalkylphenyl ketones, and dialkoxyacetophenones;

Benzoin and benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoin phenyl ether; 2- (o-chlorophenyl) -4,5-
Diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di (m-methoxyphenyl) imidazole dimer, 2- (o-fluorophenyl) -4,5-
Diphenylimidazole dimer, 2- (o-methoxyphenyl) -4,5-diphenylimidazole dimer, 2
2,4,6-triarylimidazole dimer such as-(p-methoxyphenyl) -4,5-diphenylimidazole dimer, and others, U.S. Pat.
No. 252887, No. 4311783, No. 445934
No. 9, No. 4410621, No. 462286, etc .;

Polyhalogen compounds such as carbon tetrabromide, phenyltribromomethylsulfone and phenyltrichloromethylketone; JP-A-59-133428, JP-B-57
No.-1819, JP-B-57-6096, U.S. Pat.
A compound described in 615455;

2,4,6-tris (trichloromethyl)
-S-triazine, 2-methoxy-4,6-bis (trichloromethyl) -s-triazine, 2-amino-4,6
-Bis (trichloromethyl) -s-triazine, 2-
JP-A-58-29803 such as (P-methoxystyryl) -4,6-bis (trichloromethyl) -s-triazine
An s-triazine derivative having a trihalogen-substituted methyl group described in Item No.

Methyl ethyl ketone peroxide, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, benzoyl peroxide, di-tert-butyldiperoxyisophthalate, 2,5-dimethyl-2,5-di (benzoylperoxy) ) Hexane, tert-butylperoxybenzoate, a, a'-bis (tert-butylperoxyisopropyl) benzene, dicumyl peroxide, 3,3 ', 4,4'-tetra- (tert-butylperoxycarbonyl) ) Japanese Patent Application Laid-Open No.
Organic peroxides described in No. 9-189340;

Azinium salts described in US Pat. No. 4,743,530; organic boron compounds; phenylglyoxalic esters such as methyl phenylglyoxalate; bis (η ^{5, 2} -cyclopentadien-1-yl) ) -Bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium and the like; η ⁵ -cyclopentadienyl-η ⁶ -cumenyl-iron (1 +)-hexafluoro Iron allene complexes such as phosphate (1-); diaryliodonium salts such as diphenyliodonium salt; and triarylsulfonium salts such as triphenylsulfonium salt.

More detailed examples of the above-mentioned photopolymerization initiators,
Examples of other types of photopolymerization initiators include paragraphs [0067] to [0] of JP-A-10-45816.
132].

Further, as the photopolymerization initiator, a material composed of a combination of two or more compounds can be used. For example, a combination of 2,4,5-triarylimidazole dimer and mercaptobenzoxazole or the like,
4,4'- described in U.S. Pat. No. 3,427,161.
Combination of bis (dimethylamino) benzophenone, benzophenone and benzoin methyl ether, benzoyl-N-methylnaphthothiazoline and 2,4-bis (trichloromethyl) -6- (4'-) described in U.S. Pat. Methoxyphenyl) -triazole, a combination of a dialkylaminobenzoic acid ester and dimethylthioxanthone described in JP-A-57-23602, and a 4,4'-bis (-) bis described in JP-A-59-78339. Dimethylamino) benzophenone, benzophenone, and a polymethyl halide compound.

In the case of a photopolymerization initiator comprising two or more kinds, a combination of 4,4'-bis (diethylamino) benzophenone and benzophenone, a combination of 2,4-diethylthioxanthone and ethyl 4-dimethylaminobenzoate Or a combination of 4,4′-bis (diethylamino) benzophenone and 2,4,5-triarylimidazole dimer.

Further, a chain transfer agent can be used in combination. Examples of the chain transfer agent, for example, dodecyl mercaptan, octyl mercaptan, mercaptans such as mercaptoacetic acid, dibutyl sulfide, sulfides such as dibutyl disulfide, carbon tetrachloride, chloroform, carbon tetrabromide, butyl bromide and the like Halogen,
Examples thereof include amines such as triethylamine and butylamine. The chain transfer agent is used by mixing with a mixture of a monomer selected from the first or second monomer group, a polymerization initiator, and a polymer obtained by polymerization of the corresponding first or second monomer group. Or a mixture with a monomer selected from the second or first monomer group to be added later, or both. The amount of addition is not particularly limited, but is preferably 0.01 to 30 mol% relative to the total amount of the monomers,
More preferably, it is 0.1 to 15 mol%.
1% is particularly preferred. In addition, these solvents can be added to these monomer liquids or monomer / polymer mixed liquids as necessary.

As a medium for dispersing and polymerizing these monomers, polymers, initiators and the like, water or an aqueous medium is preferable. The aqueous medium is mainly composed of water, for example, methanol, ethanol, acetone, TH
A water-soluble solvent such as F, or polyvinyl alcohol,
An aqueous solution containing at least one or more of a water-soluble polymer such as poly (sodium acrylate), gelatin, methylhydroxycellulose, and polyethylene glycols, and a surfactant such as dodecylbenzenesulfonic acid is shown. These can be appropriately selected and used from the combination with the monomer to be used, particularly for imparting dispersion stability of particles and adjusting the particle diameter.

In the present invention, in the formation of transparent particles, a polymer obtained from the monomer group 1 or 2 is synthesized in advance,
This is preferably used in combination with a monomer and a polymerization initiator selected from the monomer group 1 or the second group, respectively. Weight average molecular weight of the polymer, polymer / monomer 1
The desired average particle size can be easily adjusted by the combined amount ratio of the group or the monomer 2 and the dispersion conditions (apparatus, rotation speed, dispersion time, etc.). That is, the particle diameter is determined by the combination of these respective conditions, and the respective conditions cannot be specified unconditionally. However, the weight average molecular weight of the polymer is approximately 2000 to 400,000, preferably 2,000.
100,000, the combined amount ratio of the polymer / monomer 1 group or 2 group is 5 to 80/95 to 20 mass ratio, preferably 5 to 50
/ 95 to 5 mass ratio. As the dispersing device, various types of known dispersing devices such as the present modifier and a bead mill can be used, and appropriate dispersing conditions can be selected and used for each device.

In this manner, a polymer obtained by previously synthesizing at least a monomer selected from the monomer group 1 or the monomer group 2, a monomer selected from the monomer group,
A dispersion of the mixture comprising the polymerization initiator is obtained. Since the average particle size of the dispersed particles at the time of this dispersion affects the particle size of the transparent particles finally obtained, it is preferably 0.1 to 40 μm,
More preferably, it is 0.8 to 20 μm.

Next, the polymerization of this dispersion is started. The polymerization is carried out by heating when a thermal polymerization initiator is used, and by light irradiation when a photopolymerization initiator is used. In this case, it is desirable to carry out the polymerization under a nitrogen stream in order to suppress the termination of the polymerization. In the course of this polymerization, a monomer selected from the other monomer group (if the monomer used in the first step is the first monomer group, the second monomer group, and conversely, the monomer used in the first step is the monomer Second
Group, monomer group 2) is added to the polymerization system.
The monomer may be added at once, or may be added in several portions, or may be continuously dropped, but a continuous dropping method is preferable.

Further, the start of the dropping of the monomer may be started at the same time as the start of the polymerization of the monomer in the first stage, or may be started after a certain period of time. It is preferable to start earlier than the time that ends. Here, whether or not the polymerization of the monomer is substantially terminated can be determined by the state of the dispersion, the viscosity, the amount of the remaining monomer, etc., in addition to the polymerization time. It can be approximately 2 to 6 hours, preferably 2 to 5 hours.
The speed of dropping the monomer is not particularly limited, but is preferably about 10 minutes to 3 hours. By such an operation, the refractive index changes from the particle center toward the outside, and the average particle diameter is 0.5 to 50 μm, preferably 1 to 30 μm,
More preferably, transparent particles of 2 to 20 μm are obtained. When the average particle size of the transparent particles is smaller than 0.5 μm, the light diffusion effect is small. When the average particle size is larger than 50 μm, the film thickness becomes too large or the surface is hardly flattened. And it is not preferable as light diffusing particles.

In the above-mentioned polymerization process, the outer periphery of the transparent particles is formed by polymerization of the monomer dropped.
Formula (1) wherein m of the transparent particles is a real number greater than 2.
Alternatively, as a method of controlling the distribution of the refractive index that changes according to (3), control by the addition polymerization method of the second monomer can be mentioned. As another method, for example, the refractive index distribution is adjusted by the reaction temperature. Method. Specifically, it is a method of adding a second monomer to the seed particles and changing the temperature at the time of polymerization. If the temperature is high, the diffusion of the second monomer into the seed particles increases, and the refractive index distribution changes gradually, resulting in a low-order curve distribution.
Conversely, when the temperature is low, the diffusion of the monomer into the seed particles decreases, and the refractive index distribution changes steeply, resulting in a higher-order curve distribution.

The transparent particles whose refractive index is changed according to the above formula (1) or (3) are converted into a transparent resin having a refractive index substantially equal to the refractive index of the surface of the transparent particles. By dispersing, a transparent polymer having a refractive index distribution can be obtained, and this can be molded to obtain a light diffuser having a desired shape.

The outermost (surface) refractive index of the transparent particles can be measured, for example, as follows. One is a method in which the particles in the immersion liquid are observed under a polarizing microscope. The magnitude of the refractive index between the particle outline and the immersion liquid is determined at the position of a bright line along the particle outline called the Becke line. Another method is Applied Optics Vol.25, No19 1 October19
86 (Applied Optics, Vol. 25, No. 19, October 1986 1
This is a method of measuring the change in the refractive index in the particles by the sharing interferometry described in JP-A-2002-176, and knowing the refractive index of the outermost particles.

Here, "a transparent resin having a refractive index substantially equal to the refractive index of the surface of the transparent particles" means that the difference between the refractive index of the transparent resin and the refractive index of the surface of the transparent particles is 0.01 or less.
Alternatively, it is a resin having a transparency of not more than 1/2 of the difference Δn between the maximum value and the minimum value of the refractive index in the transparent particles.
When the difference in the refractive index between the transparent particles and the transparent resin is greater than 0.01 or 1/2 of Δn, the refractive index step generated at the interface between the transparent resin and the transparent particles cannot be ignored,
It is not preferable because light reflection occurs and light diffusion toward the rear increases.

As a method of dispersing the transparent particles in the transparent resin, a known method may be used. For example, there is a method in which both are mechanically mixed with a Henschel mixer, a tumbler or the like, and then melt-kneaded with a Banbury mixer or a single-screw or twin-screw extruder. Alternatively, after mechanical kneading, injection molding or hot press molding may be performed. Further, there is a method in which the transparent particles are mixed with a syrup containing a monomer constituting the transparent resin and a partial polymer thereof, and the mixture is subjected to cast polymerization and suspension polymerization.

As the transparent resin having a refractive index substantially equal to the refractive index of the above-mentioned transparent particles, a polymer showing good transparency to the wavelength light to be used is preferable, and a UV-curable resin is particularly preferable. Examples of the transparent resin include acrylic monomers or oligomers, methacrylic monomers or oligomers, unsaturated polyester resins, vinyl group-containing compounds, epoxy resins, vinyl ethers, and cinnamic acid group-containing compounds.

(Light Diffuser) The production of the light diffuser of the present invention comprises:
For example, the method can be carried out by mixing the above-mentioned transparent particles and a transparent resin having a refractive index substantially equal to the refractive index of the surface of the transparent particles, and developing the mixed solution into a substrate form to solidify. . The transparent resin can be obtained as a solvent solution or a melt of a polymer. In such a case, particles having a refractive index distribution structure to be mixed are required to have solvent resistance and heat resistance. The substrate can be appropriately selected as long as it is a substance showing transparency, such as glass or a polymer, and a substance showing good transparency to the wavelength light used is preferable.

A preferred method for producing a light diffuser from the viewpoint of mass productivity is to use a liquid substance which can be polymerized by heat, ultraviolet rays or radiation as a transparent resin, and mix and disperse particles having a refractive index distribution structure in the liquid resin. This is a method of polymerizing a developing layer of a mixed solution. The development of the mixed liquid may be performed by an appropriate method such as a casting method, a coating method, a doctor blade method, a dipping method, a spin coating method, and a spray method.

The thickness of the light diffuser can be appropriately determined according to the purpose of use and the like. Generally, from the viewpoint that the transparent particles having a refractive index distribution structure are buried in the transparent resin, 0.5 μm to 0.1 mm is preferable, and 1 μm to 50 μm is preferable.
m is more preferable, and 2 to 20 μm is particularly preferable. The content of the transparent particles in the transparent resin can be appropriately determined depending on the size of the particles and the desired degree of light diffusion. Generally, the content is preferably 10 to 200 parts by mass, more preferably 20 to 100 parts by mass, per 100 parts by mass of the transparent resin. Parts by weight are more preferred.

In the present invention, the diffusion state of light can be changed by controlling the size, refractive index difference and the like of the transparent particles having a refractive index distribution structure dispersed and contained in the transparent resin. And so on can be effectively reduced.

A hard coat layer, an antifouling layer, an antireflection layer, an antiglare layer,
A flattening layer, an adhesive layer, an antistatic layer, and the like may be provided.

<< Display Device >> The light diffuser according to the present invention comprises:
It can be used as a viewing angle expanding body for various display devices such as a transmission screen of a rear projection display device, a liquid crystal display device, a plasma display device, and an electroluminescence display device. By using the light diffuser of the present invention for these various display devices, the viewing angle can be increased without losing light, and the visibility can be improved. Hereinafter, the display device of the present invention will be described using a liquid crystal display device including the light diffuser of the present invention as an example. However, the display device of the present invention is not limited to the following.

FIG. 3 is a schematic sectional view showing an example of a liquid crystal display device provided with the light diffuser of the present invention. In FIG. 3, the liquid crystal display device 10 includes a light diffuser 1 having transparent particles having a refractive index distribution structure that changes according to Expression (1);
Polarizing plate 2, retardation plate 3, liquid crystal cell 4, retardation plate 5
And a backlight system 6. The light diffuser 1 of the present invention is installed at least on the viewing surface side of the polarizing plate 2 of the light diffuser liquid crystal display device 10 and plays a role as a viewing angle widening body.

In FIG. 3, light emitted from the backlight 6 in the direction of the viewing surface is reflected by the retardation plate 5, the liquid crystal cell 4,
The light diffuser 1 passes through the phase difference plate 3 and the polarizing plate 2 in this order.
Incident on. The light incident on the light diffuser 1 is
And is emitted to the viewing surface side. The light diffuser 1 of the present invention has a small absorption loss and a small reflection loss in the incident direction, and is excellent in light use efficiency and light diffusivity. Therefore, the viewing angle of the light diffuser liquid crystal display device 10 is widened and visibility is improved. be able to.

[0063]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples. Unless otherwise specified, “parts” means “parts by mass”.

Example 1 <Preparation of Transparent Particle (a)> One part of a crosslinked polymer particle composed of 100 parts of styrene and 5 parts of divinylbenzene (dry mass: average particle size 5 μm, standard deviation of particle size distribution 0) .5 μm)
Then, 300 parts of an aqueous emulsion containing 0.05 parts of polyvinyl alcohol was placed in a separal flask equipped with a condenser, and heated to 71 ° C. in a water bath under stirring by a stirring blade. Thereafter, 3 parts of methyl methacrylate containing 0.015 part of benzoyl peroxide was added, and seed polymerization was carried out for 5 hours using the crosslinked polymer particles as seed particles. Then, by taking out the reaction system from the water bath, cooling, and terminating the polymerization,
Transparent particles (a) having a refractive index distribution structure in which the refractive index is distributed in a cubic curve from the center toward the surface and having an average particle size of about 5 μm were obtained. The average refractive index of the surface of the transparent particles (a) was 1.49, and the refractive index at the center was 1.6.

The refractive index distribution of the transparent particles obtained by the above method is referred to as “Applied Optics, Vol. 25, 19”.
Issue, the differential interference microscope In
terphako (Interfaco; Carl-Zei
As a result, the refractive index distribution showed a distribution represented by the above formula (1) [m = 3].

<Preparation of Light Diffuser> Transparent Particle (a) 5
0 parts are evenly dispersed in a liquid ultraviolet curable resin (phenoxydiethylene glycol acrylate), cast on a flat glass plate, and cured by ultraviolet light to a thickness of 5 μm.
Thus, a film-shaped light diffuser of m was obtained. Here, the UV-curable resin has an average refractive index (1.
This is prepared so as to form a transparent body having substantially the same refractive index as that of (49). The diffusion angle of the obtained light diffuser was measured using a goniometer (manufactured by Sigma Koki Co., Ltd.), and the diffusion angle was 21 °.

Comparative Example 1 <Preparation of Transparent Particle (b)> One part of crosslinked polymer particles composed of 100 parts of styrene and 5 parts of divinylbenzene (dry mass: average particle diameter 5 μm, standard deviation of particle diameter distribution 0) .5 μm)
Then, 300 parts of an aqueous emulsion containing 0.05 parts of polyvinyl alcohol was placed in a separal flask equipped with a condenser, and heated to 75 ° C. in a water bath under stirring by stirring blades. Thereafter, 3 parts of methyl methacrylate containing 0.015 part of benzoyl peroxide was added, and seed polymerization was carried out for 5 hours using the crosslinked polymer particles as seed particles. Then, the reaction system is taken out of the water bath and cooled, and the polymerization is terminated, whereby a transparent material having a refractive index distribution structure in which the refractive index is distributed in a quadratic curve from the center toward the surface and having an average particle size of about 5 μm. Particles (b) were obtained. The average refractive index of the surface of the transparent particles (b) was 1.49, and the refractive index of the central part was 1.6.

The refractive index distribution of the transparent particles obtained by the above method is referred to as “Applied Optics, Vol. 25, 19”.
Issue, the differential interference microscope In
terphako (Interfaco; Carl-Zei
As a result, the refractive index distribution showed a distribution of the above formula (1) [m = 2].

<Preparation of Light Diffuser> Transparent Particle (b) 5
0 parts are evenly dispersed in a liquid ultraviolet curable resin (phenoxydiethylene glycol acrylate), cast on a flat glass plate, and cured by ultraviolet light to a thickness of 5 μm.
Thus, a film-shaped light diffuser of m was obtained. Here, the UV-curable resin has an average refractive index (1.
This is prepared so as to form a transparent body having substantially the same refractive index as that of (49). When the diffusion angle of the obtained light diffuser was measured using a goniometer (manufactured by Sigma Koki), the diffusion angle was 17 °.

From the above, the light diffuser of Example 1 was obtained in Comparative Example 1
It can be seen that the diffusivity is superior to that of the light diffuser.
The display device provided with the light diffuser of Example 1 had a wide viewing angle and excellent visibility.

[0071]

According to the present invention, it is possible to provide a light diffuser which is small in absorption loss of incident light and reflection loss in the incident direction, is excellent in light use efficiency, and is particularly excellent in light diffusivity. Further, according to the present invention, it is possible to provide a display device having a wide viewing angle without loss of light and having excellent visibility.

[Brief description of the drawings]

FIG. 1 is a schematic view of a transparent particle for explaining the formula (1).

FIG. 2 is a schematic view of a transparent particle for explaining the formula (3).

FIG. 3 is a schematic sectional view showing an example of a liquid crystal display device provided with the light diffuser of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light diffuser 2 polarizing plate 3 retarder 4 liquid crystal cell 5 retarder 6 backlight system 10 liquid crystal display

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H042 BA02 BA20 5G435 AA01 BB12 BB15 DD11 EE26 FF06 HH04 KK07

Claims (4)

[Claims] 1. A light diffuser comprising transparent particles whose refractive index n changes from the center to the outside according to the following equation (1). _{n = n 0 - (n 0} -n p) × r m / R m (1) r = (x 2 + y 2) 1/2 (2) x : Coordinate of an axis parallel to the incident ray with the center of the transparent particle as the origin y : Coordinates of an axis perpendicular to the incident light with the center of the transparent particle as the origin n ₀ : refractive index of the center of the transparent particle n _p : refractive index of the surface of the transparent particle R : Radius r of transparent particles ： Distance from center of transparent particle m : Real number greater than 2 2. A light diffuser comprising transparent particles whose refractive index n changes from the center to the outside according to the following equation (3). _{n = n 0 - (n 0} -n p) × r m / R 'm (3) r = (ax 2 + y 2) 1/2 (4) x : Coordinate of an axis parallel to the incident ray with the center of the transparent particle as the origin y : Coordinate of an axis perpendicular to the incident light with the center of the transparent particle as the origin n ₀ : Refractive index of the center of the transparent particle n _p : Refractive index of the surface of the transparent particle R ': Long axis radius of the transparent particle r ： Distance from center of transparent particle m : Real number greater than 2 a : 1 real number greater than 3. The light diffuser according to claim 1, wherein the transparent particles are dispersed in a transparent resin having a refractive index substantially equal to the refractive index of the surface of the transparent particles. 4. A display device comprising the light diffuser according to claim 1.