JPH07234304A - Light diffusion plate - Google Patents

Abstract

PURPOSE:To provide a light diffusion plate which is capable of contriving compatibility of excellent light diffusiveness with excellent light transmissivity and has good appearance. CONSTITUTION:This light diffusion plate is formed of a substantially transparent resin and light diffusive resin particles dispersed into this resin. The light diffusive resin particles are substantially spherical and the average grain size thereof is 3 to 20mum. The CV value of their particle size distribution is <=20%. The particles of >=75wt.% of the polymer particles constituting these light diffusive resin particles have the particle size of the average particle size of + or -10%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission screen for a projection television, a light diffusing plate for a liquid crystal backlight, a light diffusing plate used for an illumination shade and the like.

[0002]

BACKGROUND OF THE INVENTION Projection television,
A liquid diffuser is used in a liquid crystal display device or the like in order to uniformly diffuse light from a light source. This light diffusing plate is composed of a transparent resin and light diffusing particles dispersed in this resin.

As the light diffusing particles contained in such a light diffusing plate, inorganic powders such as barium sulfate, calcium carbonate, titanium oxide, silica, alumina and glass powder have been conventionally used. However, the particle shape of the inorganic powder is not spherical, and the particle size is generally large, which makes uniform light diffusion difficult, and the surface of the light diffusing plate itself is rough due to the inorganic powder. There are various problems such as the surface being flattened and the light transmittance being low.

Under these circumstances, it has been proposed to use resin particles instead of inorganic particles. Such resin particles are disclosed, for example, in JP-A Nos. 63-147911 and 1-292064.
Nos. 3-207743 and 3-294348.

By using the resin particles as disclosed in the above publication, the light diffusing property tends to be improved as compared with the case of using the inorganic particles, but the light diffusing characteristics of these resin particles are not always required. I'm not satisfied.

In particular, there is a problem that the color and brightness of the light from the light source change depending on the angle at which the light diffusing plate is viewed and the light diffusing plate. For example, when such a light diffusing plate is used in a projection television, using resin particles known in the related art, the projection television screen can be seen from the front and the diagonal front. There is a problem that the colors and brightness of the screen look different.

[0007]

An object of the present invention is to provide a light diffusing plate which is particularly excellent in light diffusing performance.

Another object of the present invention is to provide a light diffusing plate having good light diffusibility and containing light diffusing resin particles having further improved light transmissivity and having good light transmissivity.

[0009]

SUMMARY OF THE INVENTION A light diffusing plate of the present invention comprises a substantially transparent resin and light diffusing resin particles dispersed in the resin, wherein the light diffusing resin particles are substantially The polymer particles are spherical and have an average particle diameter in the range of 3 to 20 μm, and the CV value of the particle diameter distribution of the light diffusing resin particles is 20% or less, and the light diffusing resin particles have a CV value of 20% or less. It is characterized in that 75% by weight or more of the particles have an average particle diameter of the light diffusing resin particles of ± 10%.

The light diffusing plate of the present invention is a light diffusing plate comprising a substantially transparent resin and light diffusing resin particles dispersed in the resin, and scattered light was observed from any position. Even in such a case, good light diffusivity and total light transmittance can both be achieved, and a good appearance is exhibited. For this reason, when this light diffusing plate is used in, for example, a projection television, the light diffusing property and the light transmitting property are good, and the color and brightness of the screen change little from any position. Furthermore, the appearance becomes beautiful.

[0011]

DETAILED DESCRIPTION OF THE INVENTION Next, the light diffusing plate of the present invention will be specifically described. The light diffusing plate of the present invention comprises a substantially transparent resin and light diffusing resin particles dispersed in the resin.

The "substantially transparent resin" forming the light diffusing plate of the present invention has a total light transmittance of usually 80 to 93% in a flat resin molding having a thickness of 2 mm molded from this resin. The resin is within the range.

The total light transmittance can be controlled within the above range by changing the composition of the monomers used in preparing the resin. The D-line refractive index (n ²⁵ _D ) measured at 25 ° C. of the plate-shaped resin molded body molded from this substantially transparent resin is usually within the range of 1.40 to 1.60, and The Abbe number is usually in the range of 30-65.

The Abbe number is a number indicating the degree of dependence of the refractive index of the resin on the wavelength of light. The smaller the Abbe number, the greater the difference between the refractive index for light of short wavelength and the refractive index for light of long wavelength. It is shown that.

The refractive index and the Abbe number can be controlled within the above ranges by changing the composition of the monomers used in preparing the substantially transparent resin forming the light diffusing plate of the present invention.

Examples of such substantially transparent resins include polymethylmethacrylate, polycarbonate, polystyrene, methylmethacrylate / styrene copolymer (MS resin) and styrene / acrylonitrile copolymer (AS resin). You can As the substantially transparent resin, for example, the above resins can be used alone or in combination. However, when a plurality of resins are used in combination, the total light transmittance often decreases, so that it is preferable to use the above resins alone in the present invention.

The light diffusing resin particles constituting the light diffusing plate of the present invention are substantially spherical polymer particles. The light diffusing resin particles have an average particle diameter of 3 to 20 μm, and it is preferable that the average particle diameter is in the range of 10 to 15 μm.

Resin particles having an average particle diameter within the range of 3 to 20 μm have already been known, but if the known particles are mixed with the above-mentioned substantially transparent resin, good light diffusivity is obtained. Not shown.

The present invention has been completed by finding particularly excellent characteristics of resin particles by blending the resin particles in the light diffusing plate. That is, the light diffusing resin particles forming the light diffusing plate of the present invention are substantially spherical polymer particles. Here, “substantially spherical” means polymer particles obtained by reacting a monomer using a known polymerization method such as emulsion polymerization, suspension polymerization, precipitation polymerization, and seed polymerization. Therefore, particles having irregularities on the surface, such as fine particles obtained by crushing a polymer produced by bulk polymerization, are included in the light diffusing resin particles composed of substantially spherical polymer particles used in the present invention. Absent.

Whether or not the polymer particles are spherical is quantitatively represented by the sphericity. The polymer particles of the present invention usually have an average sphericity in the range of 0.80 to 0.99.
Further, it is preferable that the sphericity is in the range of 0.90 to 0.99. In this way, the particles having a high average sphericity can diffuse light uniformly because each particle is a sphere that is extremely close to a perfect sphere.

This sphericity can be calculated by measuring the diameter of the particles using an enlarged photograph of the polymer particles. That is, a 500 to 1000 times magnified image of a polymer particle is photographed with an optical microscope or a scanning electron microscope, and 50 particles randomly selected have a diameter of 2 directions perpendicular to each particle of 2 particles. The average value of 50 particles is calculated by measuring the number of times and dividing the minor axis by the major axis as the sphericity. The minor axis and the major axis are measured with a loupe with a scale.

Furthermore, in the light diffusing resin particles constituting the light diffusing plate of the present invention, 75% by weight or more of the particles have an average particle diameter of the light diffusing resin particles ± 10%. Need to be present. In addition, 85% by weight of this particle
The above preferably has a particle diameter of 10% of the average particle diameter of the particles. This means that the light-diffusing resin particles of the present invention have a very narrow particle size distribution. Therefore, the light transmittance and the light diffusing property of the light diffusing plate become uniform in all parts of the light diffusing plate, and good light diffusing characteristics can be formed.

In the present invention, this particle size distribution is measured by a laser diffraction type particle size distribution measuring device (MASTER SIZE manufactured by MALVERN).
R) is the value measured using. Further, the CV value of the particle size distribution of the light diffusing resin particles of the present invention needs to be 20% or less, and further, the CV value is preferably 10% or less, and further 2 to 10%. Within the range, it is particularly preferable. The CV value is a value indicating the dispersed state of the particle size distribution, and in the present invention, the CV value indicates the distributed state of the particle size of the polymer particles forming the light diffusion plate. That is, it means that the particle size distribution of the light diffusing resin particles constituting the light diffusing plate of the present invention has a very narrow particle size distribution.

When resin particles are produced by suspension polymerization, the CV value is often 40% or more, and it is extremely difficult to achieve a uniform light diffusion state by using particles having such a CV value. Have difficulty. From the viewpoint of light diffusion performance, it is preferable that the CV value is low, but the CV value of 0 means that all the particles are spherical and all have the same particle diameter. It is extremely difficult to form such a state. Therefore, the lower limit of the CV value in the present invention is usually 2%. When the light diffusing resin particles used in the present invention are produced by a suspension polymerization method or the like, for example, by classifying 1 to 5 times using an air classifier, or by a seed polymerization method. For this purpose, seed particles having a uniform particle size are used, and the blending amount of the (mixed) monomer with respect to the seed particles in one seed polymerization operation is 3 with respect to 100 parts by weight of the seed particles.
The CV value as described above can be achieved by taking measures such as 000 parts by weight or less.

In the present invention, the CV value is a value calculated from the standard deviation and the average particle diameter measured by a laser diffraction type particle size distribution measuring device (MASTER SIZER manufactured by MALVERN).

As described above, the light diffusing resin particles used in the present invention are substantially spherical polymer particles having an average particle diameter in the range of 3 to 20 μm, a narrow particle size distribution, and a CV. The value is below a certain value and the particle size distribution of the particles is extremely narrow. By satisfying these requirements, the light diffusing resin particles exhibit excellent light diffusing property and light transmitting property. Specifically, the content of particles of 2 μm or less is preferably 5% by weight or less, and more preferably the content is in the range of 0.5 to 3% by weight.
When the content of particles having a relatively small particle diameter in the light diffusing resin particles deviates from the above value and is large, the light reflecting surface is relatively increased, and as a result, all light rays of the light diffusing plate are obtained. Permeability tends to be low.

The light-diffusing resin particles constituting the light-diffusing plate of the present invention as described above have a refractive index (n ²⁵ ) of D line measured at 25 ° C. measured as a flat bulk polymer having the same composition as the particles. It is preferable that _D ) is usually in the range of 1.350 to 1.650, and this n ²⁵ _D is in the range of 1.400 to 1.600. This refractive index can be adjusted to the above range by adjusting the polymer composition constituting the particles.

The difference between the refractive index (n ₁ ²⁵ _D ) of the particles and the above-mentioned refractive index (n ₂ ²⁵ _D ) of the substantially transparent resin forming the light diffusion plate is (±) 0. 0.005-0.060
It is preferably within the range. Furthermore, this difference is
It is particularly preferable that it is within the range of (±) 0.010 to 0.055.

If the difference in refractive index is smaller than (±) 0.005, the light passing through the light diffusion plate may not be sufficiently refracted, and the incident light tends to be emitted as it is. For example, when such a light diffusion plate is used as a light diffusion plate for a projection television,
The texture of the image tends to be rough, and the texture and brightness of the image may differ when the screen is viewed from the front and diagonally from the front. On the other hand, when it is larger than 0.060, the refraction of light inside the light diffusing plate is large, and the emitted light tends to decrease with respect to the incident light.
That is, the total light transmittance may be low. For example, when this light diffusing plate is used as a light diffusing plate for a projection television, the brightness of the entire screen may decrease.

As described above, in the light diffusing plate of the present invention, by selecting the substantially transparent resin and the refractive index of the light diffusing resin particles as described above, the light diffusing property having particularly good light diffusing property is obtained. Plates can be formed.

Further, in the light diffusing plate of the present invention, the Abbe's number measured for the flat bulk polymer having the same composition as the light diffusing resin particles is in the range of 30 to 65. The difference between this Abbe number and the Abbe number of the substantially transparent resin is preferably within the range of -10 to +10, and this difference is also within the range of -7.5 to +7.5. Is particularly preferable. If the difference in Abbe number deviates from −10 to +10, for example, when such a light diffusing plate is used as a light diffusing plate for a projection television, the color of the image varies depending on the position where the screen is viewed. May occur, and the reproducibility of the original image may deteriorate.

In the present invention, the difference in Abbe number between the substantially transparent resin forming the light diffusing plate and the light diffusing resin particles is set within the above range, so that the light diffusing characteristic is particularly excellent. Plates can be formed.

The light-diffusing resin particles have a light transmittance of 2 mm.
The total light transmittance measured as a flat bulk polymer having a thickness of 8
It is preferable to have the same composition as the monomer composition of the resin in the range of 0 to 93%. The total light transmittance of the light diffusing plate varies depending on the thickness of the light diffusing plate, the average particle size of the particles, the particle size distribution, the light transmittance of the particles, the compounding amount of the particles with respect to the resin forming the light diffusing plate, and the like.

Therefore, in order to form a light diffusion plate having a higher light transmittance, it is desirable that the individual particles contained in the light diffusion plate have a high light transmittance. In order to improve the total light transmittance of the particles, the resin composition forming the particles is adjusted, and the total light transmittance of the particles is made extremely high as described above, and the dispersion stability contained in the production process of the particles is stable. It is preferable to adopt a method of improving the light transmittance of individual particles by removing impurities such as agents by careful washing.

The polymer particles are resin particles obtained by reacting a bifunctional or higher polyfunctional monomer in an amount within the range of 1 to 20% by weight. Soxhlet extraction using acetone as a solvent. The undissolved fraction by the method is 9
It is preferably formed from a resin that is 8% or more. Examples of such resins include (meth) cross-linked with bifunctional or higher polyfunctional monomers.
Acrylic polymers are preferred. Here, the acrylic polymer is usually formed from a (meth) acrylic acid ester (co) polymer or a (meth) acrylic acid ester / styrene copolymer.

Here, examples of the (meth) acrylic acid ester include methyl (meth) acrylate and ethyl (meth) acrylate.
Acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth)
Acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, chloro-2-hydroxypropyl (meth) acrylate, diethylene glycol Mono (meth) acrylate, methoxyethyl (meth) acrylate, ethoxyethyl (meth)
Mention may be made of acrylates, dimethylaminoethyl (meth) acrylates and glycidyl (meth) acrylates.

Further, as an example of the styrene-based monomer,
Alkyl styrenes such as styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene and octyl styrene; fluorostyrene, chlorostyrene, bromostyrene, dibromostyrene And halogenated styrenes such as iodostyrene;
Mention may be made of nitrostyrene, acetylstyrene and methoxystyrene.

In the present invention, the polymer particles include (meth) acrylic acid ester obtained by copolymerizing one or more kinds of the above-mentioned (meth) acrylic acid ester with a bifunctional or higher polyfunctional monomer. Copolymers are preferred.

Here, examples of the bifunctional or higher polyfunctional monomer include ethylene glycol di (meth) acrylate and triethylene glycol di (meth).
Acrylate, tetraethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol trimethacrylate,
1,1,1-trihydroxymethylethane triacrylate,
Examples include 1,1,1-trishydroxymethylethanetrimethacrylate, 1,1,1-trishydroxymethylpropanetriacrylate, divinylbenzene and the like.

Furthermore, a (meth) acrylic acid ester / styrene copolymer, which is a copolymer of the above-mentioned (meth) acrylic acid ester and a styrene-based monomer, can also be preferably used.

The acrylic polymer may be a copolymer obtained by copolymerizing a vinyl monomer and / or an unsaturated carboxylic acid monomer in addition to the (meth) acrylic acid ester and the styrene monomer.

Here, as an example of the vinyl-based monomer,
Vinylpyridine, vinylpyrrolidone, vinylcarbazole, divinylbenzene, vinyl acetate and acrylonitrile; conjugated diene monomers such as butadiene, isoprene and chloroprene; vinyl halides such as vinyl chloride and vinyl bromide; vinylidene halide such as vinylidene chloride. You can

Examples of unsaturated carboxylic acid monomers include acrylic acid, methacrylic acid, α-ethyl acrylic acid, crotonic acid, α-methyl crotonic acid, α-ethyl crotonic acid, isocrotonic acid, tiglic acid and ungeric acid. And addition-polymerizable unsaturated aliphatic monocarboxylic acids; addition-polymerizable unsaturated aliphatic dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid and dihydromuconic acid.

The polymer particles used in the present invention include:
The (meth) acrylic acid ester is usually 20 to 89 parts by weight, preferably 40 to 75 parts by weight, and the styrene-based monomer is usually 10 to 79 parts by weight, preferably 20 to 55 parts by weight, and bifunctional or higher. The polyfunctional monomer is usually used in an amount of 1 to 20 parts by weight, preferably 5 to 15 parts by weight, the vinyl monomer is usually used in an amount of 0 to 50 parts by weight, and the unsaturated carboxylic acid monomer is usually used in an amount of 0 to 50 parts by weight. Polymerized.

The polymer particles used in the present invention may further be copolymerized with a component copolymerizable with the above-mentioned monomer within a range not impairing the characteristics of the polymer particles.

In order to produce highly uniform spherical polymer particles from the above-mentioned monomers, an arbitrary monomer selected from the above-mentioned monomer group is mixed within a range not impairing the characteristics of the polymer particles, and a polymerization initiator is added. A suspension polymerization method, in which a solution is dispersed in an aqueous medium to form fine droplets and then polymerized, and an arbitrary monomer selected from the above monomer group is mixed within a range not impairing the properties of the polymer particles, and an aqueous medium Polymerization by finely dispersing in, emulsion polymerization method, using polymer particles obtained by using a known polymerization method such as soap-free emulsion polymerization method, as a seed, the seed particles swell with any monomer selected from the above monomer group A seed polymerization method can be employed in which the particles are allowed to grow, and the particles are grown to form particles and polymerized.

When polymer particles are obtained by suspension polymerization, a polymerization initiator is used. Examples of the polymerization initiator used here include organic peroxides such as benzoyl peroxide and lauryl peroxide. The polymerization initiator used in the suspension polymerization is usually used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the monomer.

In suspension polymerization, metal phosphate, inorganic substances such as magnesium hydroxide and aluminum hydroxide,
Alternatively, natural water-soluble polymers such as starch and gelatin, semi-synthetic or synthetic water-soluble polymers such as celluloses, polyacrylates, polymethacrylates, polyvinyl alcohol, and vinyl acetate / maleic acid copolymers can be used as monomer droplets. Is added for the purpose of stable dispersion. These monomer droplet stabilizers are usually used in an amount of 0.1 to 30 parts by weight based on 100 parts by weight of the monomer.

The monomer droplet stabilizer can be used by dissolving or dispersing it in an aqueous medium at the time of polymerization, or by dissolving or dispersing it in a monomer mixture in which a polymerization initiator is dissolved. it can.

The seed polymerization is carried out by polymerizing a mixed monomer prepared by mixing an arbitrary monomer selected from the above-mentioned monomer group within a range not impairing the characteristics of the polymer particle to prepare a suspension containing the seed particle. Is swollen with a mixed monomer composed of an arbitrary monomer selected from the above-mentioned monomer group within a range that does not impair the characteristics of the obtained polymer particle, and is polymerized to grow the particle. To produce polymer particles by seed polymerization, first, a suspension containing seed particles is prepared. This suspension is
It can be prepared by a method such as emulsion polymerization, soap-free emulsion polymerization, or precipitation polymerization. Furthermore, in this seed polymerization, particles obtained by other polymerization methods can be used as seed particles, but it is preferable that such seed particles have a particle diameter as uniform as possible.

When a suspension containing seed particles is prepared by emulsion polymerization, an arbitrary monomer selected from the above-mentioned monomer group is mixed within a range that does not impair the characteristics of the polymer particles to be obtained, and polymerization is preliminarily initiated. The agent is mixed with an emulsifier in an aqueous medium in which the agent is dissolved and polymerized.

When seed particles are prepared by this emulsion polymerization, a polymerization initiator is used. Examples of the polymerization initiator used here include potassium persulfate and persulfate salts such as ammonium persulfate, but the polymerization initiator is not limited to this as long as it is a polymerization initiator soluble in the aqueous medium used at the time of polymerization. It is not something that can be done. The polymerization initiator is usually used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the monomer.

An emulsifier is used when preparing seed particles by this emulsion polymerization. Examples of emulsifiers used here include alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, polyethylene glycol alkyl ethers such as polyethylene glycol nonyl phenyl ether, and the like.
The emulsifier is usually used in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the monomer.

A polymerization initiator is used when preparing a suspension containing seed particles by soap-free emulsion polymerization. Examples of the polymerization initiator used here include potassium persulfate, persulfate salts such as ammonium persulfate, and the like, as long as the polymerization initiator is soluble in the aqueous medium used at the time of polymerization. It is not limited to. It is usually used in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the monomers used in the soap-free emulsion polymerization.
However, when seed particles are obtained by this soap-free emulsion polymerization, a monomer whose solubility in an aqueous medium is not 0 is selected from the above monomer group and used.

When a suspension containing seed particles is prepared by precipitation polymerization, a polymerization initiator is used. Examples of the polymerization initiator used here include benzoyl peroxide, peroxides such as lauryl peroxide, and azo compounds such as azobisisobutyronitrile. If it is a soluble polymerization initiator, it is not limited to this. Here, the polymerization initiator is a monomer 100.
It is usually used in an amount of 0.1 to 10 parts by weight based on parts by weight.

After the suspension containing the seed particles is prepared in this manner, the suspension is sampled and newly introduced into an aqueous medium, and the (mixed) monomer and the polymerization initiator are further added to the seed particles. Swell and polymerize to grow particles.

Examples of the polymerization initiator used in this operation include organic peroxides such as benzoyl peroxide and lauryl peroxide, and azo compounds such as azobisisobutyronitrile. During this operation, the polymerization initiator is
Usually, 0.1 to 5 parts by weight is used with respect to 100 parts by weight of the monomer.

Examples of emulsifiers used here include alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, polyethylene glycol alkyl ethers such as polyethylene glycol nonyl phenyl ether, and the like. In the seed polymerization, this emulsifier is usually used in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the monomer.

In this operation, the (mixed) monomer is blended in an amount of 100 to 10,000 parts by weight with respect to 100 parts by weight of seed particles usually contained in the suspension. By repeating this operation 3 to 10 times, spherical polymer particles having a predetermined particle diameter can be produced.

Particles produced by suspension polymerization as described above,
When compared to particles produced by seed polymerization, particles produced by suspension polymerization tend to have a broader particle size distribution, and therefore particles produced by suspension polymerization are more likely to be classified by, for example, a wind classifier. It is preferable to classify using such as. On the other hand, the particles produced by seed polymerization are
Since the particle diameters are relatively uniform, it is often unnecessary to perform the classification operation as described above.

The light diffusing plate of the present invention can be manufactured by various methods in which the above-mentioned light diffusing resin particles are uniformly dispersed in a substantially transparent resin. For example, the light-diffusing resin particles and the substantially transparent resin are mixed using a mixing device such as a Henschel mixer, pelletized to produce pellets, and the pellets thus obtained are supplied to an injection molding machine. Then, a method of melting a substantially transparent resin and injecting it into a mold can be mentioned. During this injection molding, the temperature condition is set so that the substantially transparent resin is in a molten state but the light diffusing resin particles are not in a molten state.

The compounding amount of the light-diffusing resin particles with respect to the substantially transparent resin cannot be generally determined because the characteristics required of the light-diffusing plate differ depending on the use of the light-diffusing plate, but it is usually impossible.
The light-diffusing resin particles are mixed in an amount of 5 to 20 parts by weight, preferably 6 to 20 parts by weight, based on 100 parts by weight of the substantially transparent resin.

Here, the characteristics of the substantially transparent resin (total light transmittance, refractive index, Abbe number, etc.) and the characteristics of light diffusing resin particles (total light transmittance, refractive index, Abbe number, CV value, average) Particle size, sphericity, particle size distribution, etc.), for example, when the difference in refractive index between the two is small, a relatively large amount of light diffusing resin particles should be added to a substantially transparent resin. If it is not good light diffusing characteristics cannot be obtained, and if the average particle size of the light diffusing resin particles is relatively small, the blending amount of the light diffusing resin particles with respect to the substantially transparent resin should be adjusted. Good light transmission cannot be obtained unless the amount is relatively small, and when the average particle size of the light diffusing resin particles is relatively large, the light diffusing resin particles are If the blending amount is too large, a phenomenon such that good smoothness of the light diffusing plate surface cannot be obtained occurs.

Therefore, depending on the combination of the properties of the substantially transparent resin used and the properties of the light diffusing resin particles, and the use of the light diffusing plate, the light diffusing property can be improved with respect to 100 parts by weight of the substantially transparent resin. In some cases, the light diffusion plate may be molded with a compounding amount of 100 parts by weight of the light-diffusing resin particles with respect to 0.5 parts by weight of the resin particles or 100 parts by weight of the substantially transparent resin.

The light diffusing plate of the present invention comprises, in addition to the above-described method for producing a light diffusing plate, a substantially transparent resin in which the above-mentioned light diffusing resin particles are dispersed in a flat plate shape or a film shape. It is also possible to manufacture the light diffusing plate by a method of uniformly coating one or both of the resins.

The light diffusing plate of the present invention is usually 0.5 to 5 mm.
Has a thickness of. This light diffusing plate has a good light diffusing property, and the light transmitting property is, as described above, the thickness of the light diffusing plate, the average particle size of the light diffusing resin particles, the particle size distribution, and the individual particles. Of the light diffusing plate, the content of light diffusing resin particles in the light diffusing plate, etc., but measured using an integrating sphere light transmittance measuring device according to the method specified in JIS-K-7105 The light transmittance of the light diffusion plate having a thickness of 2 mm is usually 60% or more, preferably 70 to 90%.

The light diffusing plate of the present invention may contain the transparent resin and the light diffusing resin particles as described above.
Additives such as an antioxidant and a plasticizer which are usually added to the resin plate may be contained within a range that does not impair the characteristics of the light diffusing plate of the present invention.

Further, the substantially transparent resin and the light diffusing resin particles constituting the light diffusing plate of the present invention may be used in any combination as long as the characteristics of the light diffusing plate are not impaired.

Such a light diffusing plate is used in a wide range of applications requiring light diffusing properties, such as a transmission screen of a projection television, a light diffusing plate for a liquid crystal backlight, a lighting shade, a signboard having a built-in light, and the like. be able to.

[0070]

The light-diffusing resin particles constituting the light-diffusing plate of the present invention are substantially spherical polymer particles, the average particles of which are in the range of 3 to 20 μm, and the sphericity is high. , The particle size distribution is narrow, and the CV value is extremely low. Furthermore, it has a structure in which the number of fine particles that decrease the light transmittance is extremely small.

The light diffusing plate of the present invention having such a constitution is a light diffusing plate even if a large amount of the light diffusing resin particles as described above is mixed in a substantially transparent resin. The light transmissivity of (3) does not easily decrease, and even in this state, good light diffusivity is exhibited. Furthermore, the light diffusing plate of the present invention has a very uniform particle diameter of the light diffusing resin particles contained therein, and therefore, even if a large amount of this light diffusing resin particles of a substantially transparent resin is blended, It has an advantage that the appearance of the light diffusing plate is not roughened by roughening the surface.

[0072]

The present invention will now be described in more detail with reference to examples of the present invention, but the present invention is not limited thereto.

[0073]

Example 1 40 parts by weight of methyl methacrylate, 20 parts by weight of normal butyl methacrylate, 20 parts by weight of styrene, and 20 parts by weight of divinylbenzene were placed in a glass reaction vessel and mixed, and then 1.5 parts by weight of benzoyl peroxide was added. And allowed to dissolve.

Separately, 2 parts by weight of polyvinyl alcohol was added and dissolved in 300 parts by weight of ion-exchanged water to prepare a solution, which was added to the above glass reaction vessel and dispersed by vigorous stirring with a homomixer. . A nitrogen gas introduction tube, a thermometer and a condenser were attached to this reactor, nitrogen gas was introduced and purged, and then the dispersion was heated to 80 ° C. while stirring.

After maintaining this temperature for 8 hours, the obtained suspension was cooled to room temperature and filtered to separate the polymer particles and the polyvinyl alcohol aqueous solution as the dispersion medium.

The obtained polymer particles were redispersed in 100 parts by weight of methyl alcohol, stirred for 1 hour, and then separated by filtration. 8 polymer particles obtained
It was crushed after being dried for 8 hours using a dryer kept at 0 ° C.

The average particle size and CV value of the polymer particles (non-classified particles) thus obtained were determined. As a result, the average particle size was 22.4 μm and the CV value was 47.2%. The average sphericity of the unclassified particles was 0.91, and the content of particles having a particle size of 20.4 to 24.6 μm in the polymer particles was 24.4% by weight. The content of particles having a particle diameter of 2 μm or less in this particle was 4.3% by weight.

Further, a flat bulk polymer having a thickness of 2 mm and having the same composition as the particles had an n ²⁵ _D of 1.532, an Abbe number of 50.2 and a total light transmittance of 90.1%. Met. The non-elution ratio of the particles by Soxhlet method using acetone as a solvent was 98.5%, and the decomposition temperature was 238 ° C.

The particles were air-classified to have an average particle size of 13.
Particles having 7 μm and a CV value of 13.3% (classified particles) were obtained.
The average sphericity of the particles was 0.92, and the content of particles having a particle diameter of 12.3 to 15.1 μm was 7.
It was 7.9% by weight. In addition, 2μ in this particle
The content of particles having a particle diameter of m or less was 0.9% by weight.

Further, a tabular polymer having a thickness of 2 mm and having the same composition as the particles had a n ²⁵ _D of 1.532, an Abbe number of 50.2 and a total light transmittance of 90.1%. Met. The non-elution ratio of the particles by Soxhlet method using acetone as a solvent was 98.5%, and the decomposition temperature was 238 ° C.

In the present invention, the average particle size and CV value are values measured as follows. Average particle size ; Laser diffraction particle size distribution measuring device (MALVER
This is the value of the volume-based cumulative 50% diameter as a result of measurement by using N: MASTER SIZER).

CV value : the result of measurement using a laser diffraction type particle size distribution measuring device (MALVERN: MASTER SIZER)

[0083]

[Equation 1]

[0084]

[Example 2] 33 parts by weight of cyclohexyl methacrylate and 66 parts of isopropyl methacrylate were placed in a glass reaction container.
By weight, 1 part by weight of ethylene glycol dimethacrylate was added and mixed, and then 900 parts by weight of ion-exchanged water in which 1 part by weight of sodium dodecylbenzenesulfonate was dissolved in advance was added and emulsified by vigorous stirring using a homomixer. .

A nitrogen gas introducing tube, a thermometer and a condenser were attached to this reactor, nitrogen gas was introduced and purged, and then the emulsion was heated to 75 ° C. with stirring. When the temperature of this emulsion reached 75 ° C, potassium persulfate 1
By weight, the emulsion was added with stirring, and the temperature of the emulsion was maintained at 75 ° C. for 8 hours to obtain a suspension.

In this suspension, the average particle size is 0.2 μm,
It contains polymer particles having a CV value of 8.8%. Seed polymerization was carried out using the polymer particles contained in this suspension as seeds.

That is, 100 parts by weight of the above suspension was added to 900 parts by weight of ion-exchanged water in which 1 part by weight of sodium dodecylbenzenesulfonate was previously dissolved, and cyclohexylmethacrylate in which 1 part by weight of azobisisobutyronitrile was further dissolved. A mixture of 33 parts by weight, 66 parts by weight of isopropyl methacrylate, and 1 part by weight of ethylene glycol dimethacrylate was added and heated to 75 ° C. with vigorous stirring, and the temperature was maintained for 4 hours to perform seed polymerization.
A suspension was obtained.

The same seed polymerization as above was performed 5 times in total to obtain a suspension containing polymer particles having an average particle size of 8.19 μm and a CV value of 11.8%. Furthermore, this suspension 100
1 part by weight of sodium dodecylbenzenesulfonate
In addition to 900 parts by weight of ion-exchanged water in which 1 part by weight was dissolved, 1 part by weight of azobisisobutyronitrile was further dissolved.
A mixture of 20 parts by weight of cyclohexyl methacrylate, 40 parts by weight of isopropyl methacrylate, and 40 parts by weight of trimethylolpropane triacrylate was added and heated to 75 ° C. with vigorous stirring, and this temperature was maintained for 4 hours to perform seed polymerization. A suspension containing polymer particles having a particle size of 12.9 μm and a CV value of 11.6% was obtained.

The obtained suspension was filtered to separate the particles from the dispersion medium. The obtained polymer particles were redispersed in 330 parts by weight of 55% by weight methyl alcohol aqueous solution and stirred for 1 hour, then the polymer particles were separated by filtration, further dispersed in 330 parts by weight of ion-exchanged water and stirred for 1 hour. rear,
The polymer particles were separated by filtration.

The obtained polymer particles were dried for 8 hours using a drier kept at 80 ° C. and then crushed. When the average particle size and CV value of the polymer particles thus obtained were determined, the average particle size was 12.9 μm and the CV value was 11.6%.

The average sphericity of this non-classified particle is 0.95.
And the particle size in this polymer particle is 16.6 ~
The content of particles having a size of 14.2 μm was 79.5% by weight.
The content of particles having a particle diameter of 2 μm or less in the particles was 0.3% by weight.

Further, a flat bulk polymer having a thickness of 2 mm and having the same composition as the particles had an n ²⁵ _D of 1.515, an Abbe number of 56.2 and a total light transmittance of 87.8%. Met. The undissolved fraction of the particles by Soxhlet method using acetone as a solvent was 99.1%, and the decomposition temperature was 243 ° C.

[0093]

Example 3 Polymethylmethacrylate resin (Asahi Kasei Kogyo KK, Delpet 60N, n ²⁵ _D : 1.494, Abbe number: 57, total light transmittance of a plate having a thickness of 2 mm: 93%) 1
To 100 parts by weight, the average particle size prepared in Example 1 was 13.7.
After adding 10 parts by weight of particles (classified particles) having a μm and a CV value of 16% and stirring and mixing with a Henschel mixer, pellets were produced by melting the polymethylmethacrylate resin with an extruder. The pellets were supplied to an injection molding machine and injection-molded at a molding temperature of 200 ° C. and a mold temperature of 50 ° C. to obtain a flat resin molded product (light diffusion plate) having a thickness of 2 mm.

The appearance, light transmittance and light diffusivity of this flat plate resin molded product were evaluated as follows. -Appearance: A fluorescent lamp was reflected indoors on the surface of the obtained flat resin molded product, and visual observation was performed to evaluate the surface condition of the sample. Meanings of symbols used for evaluation in the table are as follows.

AA: The contour of the fluorescent lamp is not recognized, and the surface condition is uniform. BB: The outline of the fluorescent lamp is not recognized, but the surface condition is not uniform. CC: The outline of the fluorescent lamp is partially or entirely recognized, and the surface has a feeling of roughness.

Light transmittance: According to JIS-K-7105, integrating sphere type light transmittance measuring device (Murakami Color Research Laboratory Co., Ltd .; MR-1)
5) was measured. Meanings of symbols used for evaluation in the table are as follows.

AA ... A transmittance of 60% or more. BB: Transmittance of 30% or more and less than 60%. CC: a transmittance of less than 30%.

Light diffusivity: 0 using the goniophotometer (Murakami Color Research Laboratory; GP-1R) under the following optical conditions.
The transmitted light intensity of the light diffusion plate was measured at each angle of °, 10 °, 30 °, 45 °, 75 °, 90 °, and the transmitted light intensity in the 0 ° direction was set to 100, and the relative transmitted light intensity at each angle was measured. The area of the portion surrounded by the curve and the horizontal axis and the vertical axis is plotted when a graph is plotted in a coordinate system where the horizontal axis is the angle and the vertical axis is the relative intensity.

Further, the same operation was performed for a flat plate resin molded product (molded product containing no particles = blank) which was molded only from the substantially transparent resin used for the light diffusing plate. The ratio was used as an evaluation target.

Regarding the relative transmitted light intensity at an angle of 45 ° obtained by the above measurement, a flat plate-shaped molded product (blank) formed only of a substantially transparent resin used for a light diffusing plate.
The ratio was calculated and this value was also evaluated.

The optical conditions for the light diffusing property are as follows. Optical conditions Luminous flux: 12 m / mφ Parallelism: ± 0.5 or less Condenser lens: Effective aperture 16 m / mφ Light receiving viewing angle: 0.86 ° Light receiving slit diameter: 3 m / mφ Spectral condition: CIE relative luminous efficiency for C light Approximation Further, the meanings of the symbols used for evaluation in the table are as follows.

AA: The area ratio of the graph is 200% or more, and the relative intensity ratio at 45 ° is 500% or more. BB: The area ratio of the graph is 200% or more, or the relative intensity ratio at 45 ° is 500% or more, but both conditions are not satisfied at the same time.

CC: The ratio of the graph areas is less than 200%, and the ratio of the relative intensities at 45 ° is less than 500%.

[0104]

Example 4 Instead of the particles (classified particles) having the average particle size of 13.7 μm and the CV value of 13.3% prepared in Example 1, the average particle size of 12.
A light diffusing plate was manufactured in the same manner except that polymer particles having 9 μm and a CV value of 11.6% (seed polymerized particles) were used.

The resulting light diffusing plate was evaluated for light diffusing property, light transmitting property and its appearance. The results are shown in Table 1.

[0106]

Comparative Example 1 Instead of the particles (classified particles) having an average particle size of 13.7 μm and a CV value of 13.3% prepared in Example 1, the classified particles were separated before classification. Non-classified particles having an average particle size of 22.4 μm and a CV value of 47.
A light diffusing plate was manufactured in the same manner except that 2% of particles (non-classified particles) were used.

The light diffusing property, light transmitting property and appearance of the obtained light diffusing plate were evaluated. The results are shown in Table 1.

[0108]

[Table 1]

[0109]

Comparative Examples 2 to 7 Light diffusing plates were manufactured in the same manner as in Example 3, except that the type of particles used and the amount added were changed as shown in Table 2 below.

The obtained light diffusing plate was evaluated for light diffusing property, light transmitting property and appearance in the same manner as in Example 3.
The results are shown in Table 2. In addition, in Table 2 below, the evaluations of the light diffusing properties, the light transmitting properties, and the appearances of the light diffusing plates manufactured in Examples 3 and 4 and Comparative Example 1 are also described.

[0111]

[Table 2]

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location G03B 21/62

Claims (12)

[Claims] 1. A light diffusing plate comprising a substantially transparent resin and light diffusing resin particles dispersed in the resin, wherein the light diffusing resin particles are substantially spherical and have an average particle diameter. Is in the range of 3 to 20 μm, the CV value of the particle size distribution of the light diffusing resin particles is 20% or less, and 75% by weight of the polymer particles constituting the light diffusing resin particles. The above particles have an average particle diameter of the light-diffusing resin particles of ± 1.
A light diffusing plate having a particle size of 0%. 2. The refractive index of the D-line at 25 ° C. measured on the plate-shaped molded product molded from the substantially transparent resin is in the range of 1.400 to 1.600. The light diffusion plate according to claim 1. 3. The light diffusing plate according to claim 1, wherein the Abbe number measured for the plate-shaped molded product molded from the substantially transparent resin is in the range of 30 to 65. . 4. The total light transmittance measured with respect to a plate-shaped molded product having a thickness of 2 mm molded from the substantially transparent resin is in the range of 80 to 93%. The light diffusing plate according to item 1. 5. The polymer particles of the same composition as the resin, wherein the light-diffusing resin particles have a D-line refractive index in the range of 1.350 to 1.650 at 25 ° C. when measured on a plate-shaped molded article. The light diffusing plate according to claim 1, characterized in that 6. The light-diffusing resin particles are composed of polymer particles having the same composition as the resin having an Abbe's number in the range of 30 to 65 when measured as a plate-shaped molded body. The light diffusing plate according to item 1. 7. The light-diffusing resin particles have a total light transmittance of 80 to 9 when measured as a plate-shaped molded product having a thickness of 2 mm.
The light diffusing plate according to claim 1, wherein the light diffusing plate is composed of polymer particles having the same composition as the resin in the range of 3%. 8. The light diffusing plate according to claim 1, wherein the light diffusing resin particles are made of a copolymer containing (meth) acrylic acid ester as a main component. 9. The light diffusing plate according to claim 1, wherein the light diffusing resin particles are a copolymer containing a bifunctional or trifunctional or more polyfunctional monomer. 10. The light diffusing plate according to claim 1, wherein the decomposition temperature of the light diffusing resin particles in the air is in the range of 220 ° C. to 280 ° C. 11. A plate-shaped molded product made of a resin having the same composition as that of the light-diffusing resin particles, and a D-line refractive index measured at 25 ° C. of the plate-shaped molded product molded from the substantially transparent resin. The difference in the refractive index of the D line at 25 ° C. measured for the molded body is within the range of (±) 0.005 to 0.060. The light diffusing plate according to any one of 1. 12. The difference between the Abbe number measured for the plate-shaped molded product molded from the substantially transparent resin and the Abbe number measured for the plate-shaped molded product having the same composition as the light diffusing resin particles. , -10 to +10, The light diffusing plate according to any one of claims 1, 3 or 6, wherein the light diffusing plate is in the range of -10 to +10.