JP2000169658A - Light-dispersing resin composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light-dispersing resin composition that has excellent light dispersion and light transmission and occurs no color difference in the diffused light depending on the view angle, and obtain film and plate formed products from the resin composition or its fabricated products. SOLUTION: In a light-dispersing resin composition in which organic fine particles are dispersed in the base resin as a light disperser, the organic fine particles are made of a crosslinked vinyl copolymer prepared by copolymerizing 10-80 wt.% of a fluorine-containing alkyl (meth)acrylate monomer and 90-20 wt.% of vinyl monomer and has a difference in the Abbe's number of <=5 from that of the base resin and a lower refractive index than that of the base resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing plate and a light diffusing sheet which have excellent light diffusing properties and light transmissivity, and in which the difference in color generated in diffused light depending on the angle is suppressed. The present invention relates to a conductive resin composition. The light diffusing resin composition of the present invention can be suitably used as a raw material for molded articles such as light diffusing plates and light diffusing sheets used for TV screens, lighting covers, liquid crystal backlights and the like.

[Prior art]

Conventionally, there has been known a method of dispersing a light diffusing agent in a base resin in order to improve the light diffusing properties of a light diffusing plate and a light diffusing film. Inorganic fine particles such as titanium oxide and glass, and crosslinked organic fine particles such as polymethyl methacrylate and polystyrene are used. However, when inorganic fine particles are used as the light diffusing agent, there are various problems, such as a decrease in light transmittance, mechanical breakage during molding, and the inability to uniformly diffuse light. Further, when polymethyl methacrylate crosslinked fine particles as organic fine particles are added to methyl methacrylate resin, which is generally used as a base resin, although the light transmittance is improved, the difference in refractive index between the two is reduced. Satisfactory light diffusion cannot be obtained. On the other hand, when polystyrene crosslinked fine particles are used as the organic fine particles, although the light diffusivity increases because the refractive index difference between the organic fine particles and the methyl methacrylate resin as the base resin increases, the light emitted in the front direction And the luminance is reduced. Further, since the Abbe number of the crosslinked polystyrene particles is small, the difference in Abbe number between the crosslinked fine particles and the methyl methacrylate resin as the base resin becomes large, and the color of the diffused light varies depending on the viewing angle.

JP-A-10-67829 discloses that by dispersing crosslinked organic fine particles having a refractive index of about 1.50 to 1.53 in a methyl methacrylate resin, the resin has excellent light diffusion and high front luminance. Light diffusing resins have been proposed.

Such a light-diffusing resin has improved light-diffusing property and front luminance as compared with those obtained by dispersing polymethylmethacrylate or polystyrene crosslinked fine particles in a methyl methacrylate resin. The diffusivity was not always satisfactory.

To increase the light diffusivity, it is conceivable to increase the amount of organic fine particles proposed in the above publication. However, when the amount of fine particles is increased, the light emitted in the frontal direction decreases. When used as a projection television screen, there is a problem in that there is a difference in the fineness and brightness of an image when viewed from the front and when viewed from an oblique front.

Japanese Unexamined Patent Publication (Kokai) No. 54-155244 discloses fluorine-based inorganic fine particles having a refractive index whose difference from the refractive index of the base resin is 0.01 to 0.1 and a particle diameter of 1 to 10 μm. It is described that a light-diffusing resin having high light-diffusing property and high light-transmitting property can be obtained by dispersing a fluoride of polyacrylate in a base resin.

When a light-diffusing resin in which the above-mentioned fluorine-based inorganic fine particles are dispersed is used, for example, as a screen for a projection television, the light-diffusing property is high, but a satisfactory light-transmitting property is not obtained, and an image is formed. There is a problem of darkening. The difference in refractive index from the base resin is 0.0
The light-diffusing resin obtained by dispersing the fluoride of polyacrylic acid ester of 1 to 0.1 in the base resin can obtain satisfactory light-diffusing properties and light-transmitting properties, but is viewed from the front of the screen. There is a problem that the color differs between the case and the case when viewed from an oblique direction.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a light-diffusing resin composition which is excellent in light-diffusing property and light-transmitting property and does not cause a color difference in diffused light depending on a viewing angle. .

[0009]

In order to solve the above-mentioned problems, the present inventors have proposed an organic compound having a small difference from the Abbe number of the base resin and having a lower refractive index than the base resin. It has been found that it is effective to use fine particles as a light diffusing agent, and the present invention has been completed.

Thus, the present invention provides a light-diffusing resin composition in which organic fine particles as a light-diffusing agent are dispersed in a base resin, wherein the organic fine particles comprise 10 to 80% by weight of a fluorine-containing alkyl (meth) acrylate monomer. % And vinyl monomer 90-2
0% by weight and is a spherical fine particle of a crosslinked vinyl copolymer, and has an Abbe number whose difference from the Abbe number of the base resin is 5 or less, and is smaller than the refractive index of the base resin. An object of the present invention is to provide a light-diffusing resin composition having a low refractive index.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The base resin used in the present invention is not particularly limited as long as it is generally used as a base resin of a light diffusing resin. For example, methyl (meth) acrylate Resins, alkyl (meth) acrylate resins such as ethyl (meth) acrylate resin, and copolymers thereof, and alkyl (meth) acrylate-styrene copolymer resins. Of these, methyl methacrylate resin Is preferred.

The organic fine particles used in the present invention are spherical fine particles comprising a crosslinked vinyl copolymer obtained by copolymerizing a fluorine-containing alkyl (meth) acrylate with a vinyl monomer in the presence of a crosslinking agent. It is.

Examples of the fluorine-containing alkyl (meth) acrylate include trifluoroethyl methacrylate,
Examples thereof include fluorine-containing alkyl methacrylates such as tetrafluoropropyl methacrylate, and fluorine-containing alkyl acrylates such as perfluorooctylethyl acrylate.

The vinyl monomer copolymerizable with the fluorine-containing alkyl (meth) acrylate may be any vinyl monomer having a vinyl group. Specific examples thereof include alkyl methacrylates such as methyl methacrylate and butyl methacrylate. ,
Examples thereof include alkyl acrylates such as methyl acrylate and ethyl acrylate, and styrenes such as styrene and α-methylstyrene. These can be used alone or in combination. For example, when the base resin is a methyl methacrylate resin, it is preferable to use methyl methacrylate having an Abbe number close to that of the base resin as the vinyl monomer.

The content of the fluorine-containing alkyl (meth) acrylate is preferably from 10 to 80% by weight, more preferably from 20 to 80% by weight, based on the total amount of the monomers. When the content of the fluorine-containing alkyl (meth) acrylate is less than 10% by weight, the difference in the refractive index from the methyl methacrylate resin as the base resin becomes small, and satisfactory light diffusivity cannot be obtained. Therefore, when this is used for a projection TV screen, the front image looks bright, but the image seen obliquely becomes dark. When the fluorine-containing alkyl (meth) acrylate exceeds 80% by weight,
Methyl methacrylate resin (abbe number 5)
When 7) is used, the Abbe number difference between the two becomes large. Therefore, when this is used for a projection TV screen, a phenomenon occurs in which the color differs between when viewed from the front of the screen and when viewed obliquely, which is not preferable.

The crosslinking agent used in the polymerization reaction is not particularly limited, but it is preferable to use one having two or more unsaturated groups. For example, a crosslinking agent such as ethylene glycol dimethacrylate or polyethylene glycol dimethacrylate may be used. Functional dimethacrylate, trimethylolpropane trimethacrylate, divinylbenzene and the like can be mentioned. The polymerization reaction for producing the organic fine particles of the present invention may be either random copolymerization or block copolymerization.

The organic fine particles used in the present invention are spherical and have a weight average particle diameter of preferably 2 to 30 μm, more preferably 5 to 20 μm. When the weight average particle diameter is smaller than 2 μm, the methyl methacrylate resin composition obtained by dispersing the resin selectively scatters short-wavelength light, so that transmitted light is undesirably yellow. Further, when the weight average particle diameter exceeds 30 μm, the methyl methacrylate resin composition obtained by dispersing the resin has reduced light diffusivity, and when light passes through the resin, the particles are visually observed as foreign matter. Not preferred.

The organic fine particles used in the present invention are:
It has an Abbe number whose difference from the Abbe number of the base resin is 5 or less, and preferably has an Abbe number whose difference is 4.0 or less. If the Abbe number difference exceeds 5, for example, when used as a projection television screen, the color of the image changes depending on the position where the screen is viewed, which is not preferable. Therefore, the Abbe number of the organic fine particles varies depending on the Abbe number of the base resin, but generally, the organic fine particles preferably have an Abbe number of 58 to 62.

The Abbe number is a constant indicating the degree of dispersion of the optical glass. The smaller the refractive index difference due to a change in the wavelength of light, the higher the Abbe number, and the smaller the difference in color due to the light of the substance. The Abbe number is measured by using a refractometer capable of measuring the refractive index of a solid and using a light source (486n) having a different wavelength.
m, 589 nm, 656 nm) and is calculated by the following equation.

[0020]

(Equation 1)

For example, a fluorine-containing (meth) acrylic acid ester resin has a high Abbe number, and a homopolymer of 65 to 7
It is in the range of 0 (for example, the Abbe number of trifluoroethyl methacrylate is 67). In the case of a projection TV screen in which a light diffusing agent having a refractive index different from that of the base resin is dispersed in the base material, the smaller the difference in Abbe number between the base resin and the light diffusing agent, the smaller the difference in color depending on the viewing angle. Becomes smaller.

The organic fine particles used in the present invention may have a refractive index lower than that of the base resin. When the refractive index is larger than that of the base resin, the obtained light diffusion plate or light diffusion sheet has a low transmitted light amount,
In addition, a satisfactory viewing angle cannot be obtained with the obtained screen. Further, the difference in the refractive index between the base resin and the organic fine particles is preferably neither too small nor too large. For example, when the methyl methacrylate resin as the base resin has a refractive index of 1.495, the refractive index is 1.42.
When organic fine particles having a smaller refractive index or organic fine particles having a refractive index larger than 1.51 are used, the difference in refractive index from the base resin is too large, so that the light diffusion property is improved, but the light transmittance in the front direction is reduced. It is not preferable because it becomes low. In addition, when organic fine particles having a refractive index of 1.48 to 1.51 are used, the difference in refractive index from the methyl methacrylate resin as the base resin is too small, so that it is difficult to obtain a satisfactory light diffusing property.

From the above, it is preferable that the organic fine particles have a refractive index 0.015 to 0.075 lower than the refractive index of the base resin. Specifically, when the base resin is a methyl methacrylate resin having a refractive index of 1.495, the refractive index of the organic fine particles is preferably from 1.42 to 1.48.

The organic fine particles according to the present invention are added when the base resin is extruded or injection-molded, and once formed into a masterbatch, a plate comprising the light-diffusing resin composition or the light-diffusing resin composition obtained by casting. And films and their processed products. The addition ratio of the organic fine particles to the base resin is not particularly limited, but is usually preferably from 0.5 to 10.0% by weight, and more preferably from 1.0 to 7.0% by weight.

The temperature at which the organic fine particles are thermally decomposed (the temperature at which the resin is reduced by 3% by heat) is preferably equal to or higher than the molding temperature of the resin. For example, the molding temperature of methyl methacrylate resin is generally from 220 to 260 ° C. However, considering that the resin temperature rises to 280 ° C., the thermal decomposition start temperature of the organic fine particles is preferably higher than 280 ° C. When the thermal decomposition start temperature of the organic fine particles is low, molding defects such as silver streaks tend to occur during molding of the light diffusing resin composition, which is not preferable.

[0026]

EXAMPLES The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited thereto. In the following examples, "parts" means parts by weight.

Example 1 [Production of Organic Fine Particles] In a 2 liter container, 20 parts of tribasic calcium phosphate which is hardly soluble in water, 1200 parts of water and 1 part of sodium lauryl sulfate were placed.
Put the part. Separately, 260 parts of methyl methacrylate, 20 parts of ethylene glycol dimethacrylate, 120 parts of trifluoroethyl methacrylate
Parts, 2 parts of cumene peroxide and 2 parts of normal dodecyl mercaptan were added to prepare a monomer solution. This monomer solution was placed in the above-mentioned 2 liter container, mixed, and stirred at a high speed with a homomixer to be dispersed. Particle size is 10
At about μm, place in a 2-liter autoclave equipped with a stirrer and stir while stirring.
Polymerization was performed at 0 ° C. for 5 hours and at 100 ° C. for 5 hours. The obtained dispersion was filtered, washed, dehydrated and dried to obtain organic fine particles. The obtained organic fine particles have a weight average particle size of 8.7.
μm, and the thermal decomposition onset temperature was 292 ° C.

The weight average particle size is measured by a Coulter counter (manufactured by Coulter), and the thermal decomposition starting temperature is measured by using a thermal analyzer TG-40 (manufactured by Shimadzu Corporation) at a temperature at which the weight is reduced by 3% by heat. did.

Further, 100 parts of a monomer mixture (65 parts of methyl methacrylate, 5 parts of ethylene glycol dimethacrylate, 30 parts of trifluoroethyl methacrylate) having the same composition as the above-mentioned organic fine particles are added to 2,2-azobis-2,4
1 part of dimethylvaleronitrile was dissolved. This melt was poured into a glass mold of 100 mm × 50 mm, t = 1 mm, and was then polymerized while raising the temperature from 40 ° C. to 80 ° C. over 5 hours, and further polymerized at 100 ° C. for 1 hour. After cooling the obtained polymer, it was peeled from the glass mold to obtain a refractive index test piece. The refractive index is RX-2000 manufactured by Atago, and the Abbe number is Abbe refractometer 2 manufactured by Atago.
Measured using T. The refractive index is 1.465,
The Abbe number was 59.0.

[Production of Light-Diffusing Resin Composition and Light-Diffusing Plate] The organic fine particles obtained by the above-mentioned method were converted into a methyl methacrylate resin (manufactured by Sumitomo Chemical Co., Ltd .: MG-5, refractive index: 1.495, Abbe number) 57) to 3% by weight,
After blending, the mixture was supplied to an extruder to produce a pellet-shaped light diffusing resin composition. The pellets were supplied to an injection molding machine and injection molded to obtain a light diffusion plate of 100 mm × 50 mm, t = 2 mm. The projector was projected from the back side of the light diffusing plate, and the difference in color when viewed from the front and obliquely was examined.

The light diffusing property and light transmitting property of the obtained light diffusing plate were measured at 0 ° (front direction) using an automatic goniophotometer (GP-200, manufactured by Murakami Color Research Laboratory Co., Ltd.). ~ 90
For each angle of °, relative transmitted light intensity at each angle was measured with the transmitted light intensity in the 0 ° direction as 100.

The index of light diffusion is expressed as a degree of dispersion. The degree of dispersion indicates the angle at which the transmitted light intensity becomes 50 when the transmitted light intensity when the light is applied to the light diffusing plate from the front direction (0 °) is 100. Table 1 shows the refractive index, Abbe number, relative transmitted light intensity, and degree of dispersion measured as described above.

Since the light diffusing property and the light transmitting property change depending on the thickness of the light diffusing plate and the amount of the light diffusing agent, the thickness of the measuring piece of the light diffusing plate is 2 mm, and the amount of the organic fine particles added to the base resin. 3% by weight.

Examples 2 to 5 Except that the organic fine particles produced in Example 1 were added in an amount of 1.0, 2.0, 2.5 and 5.0% by weight to the methyl methacrylate resin, respectively. In the same manner as in Example 1, a light diffusing resin composition and a light diffusing plate were obtained. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number, and the degree of dispersion of the light diffusion plate obtained in each example.

Example 6 Organic fine particles were produced in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 180 parts and the amount of trifluoroethyl methacrylate was changed to 200 parts. The obtained organic fine particles had a weight average particle size of 7.9 μm and a thermal decomposition onset temperature of 293 ° C. Next, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number, and the degree of dispersion of the obtained light diffusion plate.

Comparative Example 1 Organic fine particles were produced in the same manner as in Example 1 except that styrene was used instead of trifluoroethyl methacrylate. The obtained organic fine particles had a weight average particle size of 8.5 μm and a thermal decomposition onset temperature of 293 ° C. Next, a light diffusing resin composition and a light diffusing plate were produced in the same manner as in Example 1, except that the obtained organic fine particles were added in an amount of 2% by weight based on the methyl methacrylate resin. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number, and the degree of dispersion of the obtained light diffusion plate.

COMPARATIVE EXAMPLES 2-5 Except that the organic fine particles produced in Comparative Example 1 were respectively added to the methyl methacrylate resin at 1.0, 2.5, 3.0 and 5.0% by weight, respectively. In the same manner as in Example 1, a light diffusing resin composition and a light diffusing plate were obtained. Table 1 shows the relative transmitted light intensity, refractive index, Abbe number, and degree of dispersion of the obtained light diffusion plate.
Shown in

Comparative Example 6 Organic fine particles were produced in the same manner as in Example 1 except that the amount of methyl methacrylate was 180 parts and styrene was used in place of trifluoroethyl methacrylate. The obtained organic fine particles have a weight average particle size of 8.6 μm.
m, thermal decomposition onset temperature was 291 ° C. Next, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number, and the degree of dispersion of the obtained light diffusion plate.

Comparative Example 7 Organic fine particles were produced in the same manner as in Example 1 except that the amount of methyl methacrylate was changed to 360 parts and the amount of trifluoroethyl methacrylate was changed to 20 parts. The obtained organic fine particles had a weight average particle size of 8.1 μm and a thermal decomposition start temperature of 290 ° C. Next, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number, and the degree of dispersion of the obtained light diffusion plate.

Comparative Example 8 Instead of the organic fine particles produced in Example 1, silicone fine particles (Tospearl 2000B: manufactured by Toshiba Silicone, average particle diameter 6.2 μm, refractive index 1.435, Abbe number 6)
A light diffusing plate was obtained in the same manner as in Example 1, except that 3) by weight of 7) was added to methyl methacrylate resin. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number, and the degree of dispersion of the obtained light diffusion plate.

Comparative Example 9 Example 1 was repeated except that the amount of methyl methacrylate was 0 parts and the amount of trifluoroethyl methacrylate was 380 parts.
Organic fine particles were produced in the same manner as described above. The obtained organic fine particles had a weight average particle size of 7.5 μm and a thermal decomposition onset temperature of 285 ° C. Next, a light diffusing resin composition and a light diffusing plate were manufactured in the same manner as in Example 1. Table 1 shows the relative transmitted light intensity, the refractive index, the Abbe number, and the degree of dispersion of the obtained light diffusion plate.

[0042]

[Table 1]

From Table 1 above, when the difference in Abbe number between the base resin and the organic fine particles is large, when projected from the back side of the light diffusing plate by the projector, the color viewed from the front and the angle (angle difference 60 °) °) It can be seen that there is a difference between the colors viewed from the direction. For example, in each of Comparative Examples 1, 6, 8, and 9, the difference in Abbe number exceeds 5, and the color difference depending on the viewing angle was confirmed. In addition, when the difference in the refractive index between the base resin and the organic fine particles is extremely small, it can be seen that the light diffusivity becomes small. For example, in Comparative Example 7 in which the difference in refractive index is 0.005, the amount of the organic fine particles added to the substrate is 3%, but the degree of dispersion is only 1 °.

From the results of Examples 1 to 5 and Comparative Examples 1 to 5, it can be seen that the one in which the refractive index of the organic fine particles is lower than the refractive index of the base resin is superior in light diffusivity. Table 2 and FIG. 1 show the addition amount of the organic fine particles and the front direction (0 °) based on the results obtained in Examples 1 to 5 and Comparative Examples 1 to 5.
With the transmitted light intensity.

[0045]

[Table 2]

From Table 2 and FIG. 1, it can be seen that the greater the amount of organic fine particles added, the lower the transmitted light intensity. Also, from FIG. 1, the refractive index of the base resin (1.495)
It can be seen that organic fine particles having a lower refractive index have higher transmitted light intensity than those having a higher refractive index than the base resin.

[0047]

The light diffusing plate manufactured from the light diffusing resin composition in which the organic fine particles of the present invention are dispersed includes a lighting cover,
It is effective in fields requiring high light diffusion and light transmission, such as light diffusion plates for liquid crystal backlights and screens for projection televisions, and has the advantage of appearing bright over a wide angle. There is also an effect that no color difference occurs in light.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of organic fine particles added and transmitted light intensity, and the relationship between the refractive index of organic fine particles and transmitted light intensity.

Claims (3)

[Claims] In a light-diffusing resin composition in which organic fine particles as a light-diffusing agent are dispersed in a base resin, the organic fine particles are composed of a fluorine-containing alkyl (meth) acrylate monomer.
-80% by weight and 90-20% by weight of a vinyl monomer are copolymerized fine particles of a crosslinked vinyl copolymer, and have a Abbe number whose difference from the Abbe number of the base resin is 5 or less. And a light diffusing resin composition having a lower refractive index than the refractive index of the base resin. 2. The organic fine particles have an Abbe number of 58 to 62 and a refractive index of 1.42 to 1.48.
3. The light diffusing resin composition according to item 1. 3. The light diffusing resin composition according to claim 1, wherein the base resin is a methyl methacrylate resin.