JPH1067829A - Microparticle suitable for light-diffusing plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide spherical microparticles which can give a light-diffusing plastic having a high frontal luminance and a high high-width diffusion angle. SOLUTION: The particles are substantially void-free, substantially spherical, and made of a crosslinked copolymer comprising methyl methacrylate, an alkyl acrylate, styrene and a polyfunctional (meth)acrylate, satisfying the formulas I, II and III: formula I: 6.66W2 -0.36<=W1 +W3 <=6.66W2 +0.31, formula II: 0.4<=W1 +W2 +W3 <=0.98, and formula III: 4W3 <=W1 (wherein W1 is the weight fraction of methyl methacrylate, W2 is that of styrene; and W3 is that of the alkyl acrylate), and having a mean particle diameter of 7-20μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fine particles suitable for light-diffusing plastics suitable for light-diffusing members such as lighting covers, lighting signs, glazing, various displays or screens for rear projection televisions. is there.

[0002]

2. Description of the Related Art Conventionally, as a light diffusing material for a lighting cover, a display screen, or the like, a material in which inorganic or organic transparent fine particles are dispersed in a transparent plastic such as an acrylic resin or a styrene resin, or a transparent plastic surface is used. Materials and the like that have been surfaced by some method are known, and their use in combination is also known. In recent years, many efforts have been made for higher performance materials, especially as the need for light-diffusing plastics, which require high performance such as screens for rear projection televisions, increases. The desired performance of these light diffusing materials is to (1) diffuse light uniformly and over a wide range as much as possible and (2) brightly. However, since the amount of light emitted from the light source is constant, these requirements (1) and (2) are mutually exclusive requirements. So, in practice, if needed,
It is selected and used so as to obtain the most preferable brightness and spread by a method such as changing the concentration of the diffusion material. In a method of obtaining a light diffusing material by dispersing a light diffusing material in a transparent plastic, as an index for obtaining a suitable combination of the light diffusing material and the transparent plastic, the particle diameter of the light diffusing material fine particles and the light diffusing material fine particles are mainly used. And the difference in the refractive index of transparent plastic has been used.

For example, Japanese Patent Publication No. 39-10515 discloses a cross-linked fine particle having a refractive index difference of 0.05 to 0.3 and an average diameter of 0.5 to 5 μ as a light diffusing material. A method is described, and JP-A-48-44
No. 333 discloses a method of blending a crystal powder having a refractive index larger than that of a base resin by 0.05 to 0.5 and a particle diameter of 10 μm or less.
No. 9758 discloses a refractive index difference of 0.02 to 0.1.
Japanese Patent Application Laid-Open No. Sho 60-184559 proposes a particle having a refractive index difference of 0.02 to 0.1 and a particle size of 4 to 10 μm. As disclosed in the publication, fine particles having a particle diameter of 4 to 50 μm and a refractive index of 0.02 to 0.1 larger than that of the base resin and fine particles having a particle diameter of 4 to 50 μm and a refractive index of 0.02 to 0.1 smaller are used together. A method is also described. In addition, Japanese Patent Publication No. 60-21662 or Japanese Patent Application Laid-Open No. Sho 62-174261 proposes a method of dispersing fine particles having a refractive index of 0.01 to 0.1 smaller than the base resin and an average particle size of 1 to 10 μm. ing.
In addition, there are a wide variety of combinations of the base resin and the light diffusing material with specific descriptions, and it is difficult to describe all of them. For example, methacrylic resin (refractive index 1.
492) as the base resin
(Refractive index 1.54), amorphous silica (refractive index 1.46)
, Calcium carbonate (refractive index 1.58), aluminum hydroxide (refractive index 1.57), glass beads GB-210
(Refractive index 1.521), glass sphere (refractive index 1.46),
Calcium fluoride (refractive index 1.43), lithium fluoride
(Refractive index: 1.39), barium sulfate (refractive index: 1.6)
4) Other than alumina powder (refractive index 1.7), the refractive index is unknown, but magnesium oxide, titanium oxide, talc, crosslinked polymer, etc. are used, and polystyrene resin (refractive index 1.59), polychlorinated Vinyl resin (refractive index 1.55)
Alternatively, various inorganic fine particles are used even when a polycarbonate resin (refractive index: 1.59) is used as the base resin. As described above, when the techniques that have been conventionally disclosed are arranged, a number of methods have been proposed for the refractive index difference and the particle size, but those having a very wide range have been proposed in various ways. At present, it is difficult to determine which combination is preferable. In fact, additional tests have shown that these existing technologies are still inadequate against the ever increasing demands for screens and the like for rear projection televisions in recent years.

[0004]

SUMMARY OF THE INVENTION The present invention has excellent light diffusion performance in such a cluttered flow of technology, that is, the maximum luminance Go is as large as possible and the half-value angle (luminance is 1/1). Spherical particles capable of providing a light-diffusing material whose transmitted light does not take on a reddish tint as much as possible, and which can provide good diffusion performance by being dispersed in methacrylic resin. The purpose is to provide.

[0005]

SUMMARY OF THE INVENTION In order to improve the light diffusion performance of a light-diffusing plastic comprising a methacrylic resin, the present invention provides a method for producing a methyl-methacrylate (hereinafter referred to as MMA), an alkyl acrylate, a styrene, and a polyfunctional resin. A) a cross-linked copolymer comprising meth) acrylate, satisfying the following general formulas (I) to (III), having an average particle size of 7 to 20 μm, and having substantially no pores inside; The object of the present invention is achieved by substantially spherical fine particles. 6.66W ₂ −0.36 ≦ W ₁ + W ₃ ≦ 6.66 W ₂ +0.31 (I) 0.4 ≦ W ₁ + W ₂ + W ₃ ≦ 0.98 (II) 4W ₃ ≦ W ₁ (III) ( Here, W ₁ represents the weight fraction of MMA, W ₂ represents the weight fraction of styrene, and W ₃ represents the weight fraction of alkyl acrylate.)

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have already comprehensively studied the relationship between the refractive index difference between a transparent resin substrate and transparent fine particles, the particle size of transparent fine particles, and diffusion performance (Japanese Patent Application No. 63-1460).
No. 28). That is, the difference Np-Ns between the refractive index Ns of the base transparent resin and the refractive index Np of the transparent fine particles is 0.01 or more,
It is important that it is less than 0.02 to obtain a light-diffusing plastic. Such a small difference in refractive index has been excluded in the conventional method on the assumption that the difference is too small and the diffusing ability is inferior. The present inventors have prepared various flat plates in which the refractive index difference between the base resin and the transparent fine particles and the particle size of the transparent fine particles are changed, and a parallel light beam is incident from the rear of the flat plate, and the angular distribution of the brightness of the light emitted forward. Was measured, and a gain G was calculated from the illuminance on the flat plate surface and each luminance by the following equation.

G = Luminance (Foot Lambert) / Illuminance (Foot Candle) (IV) The gain shows the highest value in front of the diffuser, and as the angle formed with the normal of the diffuser increases, as shown in FIG. , The value gradually decreases. If the maximum value of the gain is called a beak gain and expressed by Go, and the angle at which the gain becomes 1/2 of the peak gain is called a half-value angle and expressed by α, it is important to increase both Go and α. . However, in general, the light diffusion plate is not always used in the form of a simple flat plate.
In many cases, the purpose is achieved by using in combination with another light diffusibility imparting means such as surface treatment. Since Go and α vary depending on their type and degree, the values of Go and α by such measuring means are used. It is not appropriate to express with. However, when a large combination of Go and α measured with a flat light diffusing plate is employed in this way, it can be experimentally confirmed that excellent performance is exhibited in other shapes. A method using a flat plate, which makes it easy to compare and evaluate the light diffusion performance of the light diffusing material, was mainly adopted.
When the concentration of the light diffusing material is changed in a certain combination of the substrate resin and the light diffusing material, as shown in FIG. 2, Go decreases with increasing concentration and α increases. Therefore, as a means for selecting a good light diffusing material, the concentration of the light diffusing material is changed to select a concentration at which a constant Go is obtained, and a material having a large half-value angle α at that concentration is a preferable light diffusing plastic. Thought. As described above, another requirement is that the average particle size be in an appropriate range in order to obtain sufficient light diffusivity and large α with a small difference in refractive index. First of all, it is necessary that the average particle diameter does not fall below 7 μm.
When the average particle diameter does not reach 7 μm, when the concentration of fine particles is low, a large amount of light travels in a limited solid angle in the straight traveling direction,
And this light is reddish. As the concentration of fine particles is increased, straight-forward reddish light is reduced.
This extraordinary light does not go away until is very low. This light is perceived as so-called scale when observed by human eyes.

The human eye normally has a viewing angle of one minute (= 1/60).
In order to measure this phenomenon with an optical measuring device (luminance meter), it is necessary to use a device having a viewing angle comparable to that of the human eye. . Conventionally, there is no correlation between the data of the angular distribution of luminance and the scale in literatures, etc.,
This is probably due to the difference in viewing angle between the human eye and the luminance meter. The viewing angles of currently available luminance meters are 2, 1, and 1/3.
Degrees, 0.2 degrees, etc., all of which are larger than 1/60 degrees. Considering that the viewing angle is as small as possible and stable measurement can be performed, the present inventors performed the measurement using a Minolta luminance meter nt1 / 3 / p manufactured by Minolta and having a viewing angle of 1/3. As a result, it was found that intense light concentrated in an extremely narrow angle range could be measured corresponding to the phenomenon of invisibility, and that it was reflected to some extent on the values of Go and α. When the average particle diameter of the fine particles is less than 7 μm, it is necessary to increase the concentration of the light diffusing material until the maximum luminance becomes extremely low in order to prevent skein, and to obtain a light diffusion plate having no skein and a large gain. Not suitable for On the other hand, the degree of light diffusion generally decreases as the difference in refractive index decreases and as the average particle diameter increases. In particular, when the difference in refractive index from the base resin is small, unless the particle diameter is strictly controlled, sufficient diffusion performance cannot be provided within a practical range. In the present invention, the average particle size must be 20 μm or less. If the average particle size exceeds this range, the concentration of the fine particles used becomes too large,
Not only is it disadvantageous in terms of economy and production technology, but the half-value angle is smaller than in the case of a particle size within the range of the present invention.

Although there are various definitions for the average particle diameter, the average particle diameter in the present invention is represented by a weight median diameter, that is, a particle diameter at which the cumulative weight fraction becomes 50% in a weight cumulative curve. The particle size distribution can be measured by a Coulter counter method, a sedimentation method, a counting method using a micrograph or an electron micrograph, and any method may be used.

In the present invention, by specifying the shape of the light diffusing fine particles, it is possible to provide fine particles suitable for light diffusing plastics having better performance.
The first characteristic is that the proportion of hollow fine particles in all the fine particles is 3% by weight or less.
Second, the ratio of non-spherical fine particles in the total fine particles is 1%.
0% by weight or less.

Further, there are various crushed inorganic powders as fine particles substantially containing no hollow portion. By using these powders in a range satisfying the above conditions, an excellent light diffusing plastic can be obtained. Are more preferable, since the half-value angle α becomes larger in a diffusion plate having the same peak gain Go as compared with such amorphous particles. Non-spherical fine particles are preferably not more than 10%, most preferably not contained at all.

In order to satisfy the above conditions, it is advantageous and preferable to use a polymer, especially a crosslinked polymer, as the transparent fine particles. Spherical, non-hollow fine particles do not exist much other than the polymer, and in order to keep the refractive index difference within the above range, the refractive index of the beads is fixed, so that the refractive index of the base resin is suitable for the beads. It needs to be adjusted, which will affect the overall physical properties of the diffuser,
Not always advantageous.

On the other hand, when a polymer, particularly a crosslinked polymer, is used as the transparent fine particles, it is possible and advantageous to arbitrarily design it according to the refractive index of the substrate resin. In general, light-diffusing plastics are formed by melting and kneading light-diffusing fine particles and a substrate resin and extruding, or by a pressing method,
Alternatively, in some cases, it is produced by a method of dispersing light diffusing fine particles in a polymerizable monomer or a partially polymerized polymerizable monomer syrup and polymerizing. Therefore, it is necessary that the light diffusing fine particles do not change into an undesired shape due to melting, melting, etc. during the process of producing the light diffusing plastic. For this purpose, it is possible to use a method in which the molecular weight of the polymer is sufficiently high, but it is more preferable to provide appropriate crosslinking.

As the base resin of the light diffusing plastic, a resin having a high light transmittance, that is, a transparent resin, that is, a methacrylic resin is used. Methacrylic resin is a preferred resin because of its excellent durability and physical properties. Usually, methacrylic resin is used for improving heat resistance, moldability, durability, etc.
In addition to A, copolymerization of alkyl acrylate, lubricant,
Although an ultraviolet absorber is added, the methacrylic resin referred to herein refers to all such MMA-based resins. When the base resin is a methacrylic resin, it is preferable to use fine particles which are cross-linked resins containing MMA, styrene and polyfunctional (meth) acrylate as constituents. Since ordinary methacrylic resin has a refractive index of about 1.49, the refractive index of the light diffusing agent fine particles is 1.50 to 1.
It is preferably about 51. Of course, the refractive index may be slightly higher or lower depending on the type of methacrylic resin as the base resin.

The polyfunctional (meth) acrylate in the present invention is a compound having two or more acrylic or methacrylic groups in one molecule, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate (Poly) ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate such as tetraethylene glycol di (meth) acrylate and nonaethylene glycol di (meth) acrylate Glycol di (meth) acrylates such as tetramethylene glycol di (meth) acrylate, hexamethylene di (meth) acrylate, neopentyl glycol di (meth) acrylate, and trimethylolpropane tri (meth) Acrylate, polyhydric polyhydric alcohols such as pentaerythritol tetra (meth) acrylate (meth) acrylate. These polyfunctional (meth) acrylates serve to prevent the transparent fine particles from impairing the shape of the fine particles in the process of producing the light diffusing plastic, and 2% to 60% of the total monomers constituting the transparent fine particles. Is appropriately selected within the range.

In the present invention, the weight fraction of MMA is represented by W
_{1. When} the weight fraction of styrene is W ₂ , it is necessary to satisfy the following conditions (I) and (II). 6.66 W ₂ -0.36 ≦ W ₁ ≦ 6.66 W ₂ +0.31 (I) 0.4 ≦ W ₁ + W ₂ ≦ 0.98 (II) The copolymer of the present invention has improved thermal stability. For the purpose of the above, an alkyl acrylate such as methyl acrylate, ethyl acrylate or butyl acrylate may be copolymerized in addition to the monomer. In that case, the above formulas (I) and (II)
W ₁ and W ₁ tens W ₃ in (W _3: shows the weight fraction of alkyl acrylated Bok) and may be replaced. Alkyl acrylate is 1/4 or less of MMA.

When the weight fraction of MMA and the weight fraction of styrene are within the ranges satisfying the above formulas (I) and (II), they have excellent light diffusion performance, that is, Go
And α can be provided as large as possible, and fine particles for a light diffusing material can be provided in which transmitted light is not reddish.

When a copolymer of styrene and MMA is used as the base resin, the refractive index is increased, and the effect as a lens is enhanced, which may be advantageous. Even in such a case, it is desirable to use a crosslinked copolymer similar to the transparent fine particles used for the methacrylic resin. However, an appropriate refractive index may be adjusted according to the refractive index of the styrene-MMA resin. The polymer beads described above can be synthesized by a suspension polymerization method. For example, it can be produced by dispersing a monomer finely with a disperser or the like using polyvinyl alcohol as a dispersant, and then polymerizing, filtering, washing and drying.

[0019]

The present invention will now be described more specifically with reference to examples. Example 1 39 parts of MMA, 3 parts of ethyl acrylate, 8 parts of styrene,
50 parts of ethylene glycol dimethacrylate, 0.6 parts of lauroyl peroxide and 0.2 parts of lauryl mercaptan were mixed with polyvinyl alcohol (PVA manufactured by Kuraray Co., Ltd.).
-420) was mixed with 400 parts of water containing 0.4% and dispersed by a laboratory disperser. The solution was heated in a nitrogen atmosphere at 70 ° C. for 120 minutes and at 95 ° C. for 100 minutes with stirring. The resulting dispersion was repeatedly washed with water and water, and finally washed with methanol and dried.

When the particle size distribution of the thus obtained crosslinked fine particles was measured by a particle size distribution analyzer (Micron Photosizer SKA-5000, manufactured by Seishin Enterprise), the weight median diameter was 10.48 μm. As the specific gravity at this time, a value (1.2003) measured separately by preparing a polymer having the same composition was used. The refractive index was measured by a method of observing the movement behavior of the Becke line under a microscope, and was found to be 1.5078. Also, the beads were substantially all spherical and free of hollow particles. Using the crosslinked beads, methacrylic resin plates having a thickness of 1 mm and containing beads at various weight fractions were prepared by the following method.

11.9 parts by weight of ethyl acrylate, MMA
Acrylic resin beads containing 8.5% ethyl acrylate in a mixture of 128.1 parts (F-10 manufactured by Kyowa Gas Chemical Industry Co., Ltd.)
00B Refractive index 1.4920) 60 parts by weight
Acrylic resin syrup was made. The required amount of the crosslinked beads in this syrup, while being careful not to aggregate,
Dispersed. In this, azobisisobutyronitrile 0.1.
After dissolving 02 parts by weight, the mixture was put into two glass plates equipped with gaskets, degassed, and heated at 80 ° C. for 2 hours and further at 120 ° C. for 2 hours to carry out polymerization. The thickness is 1m
m. After the completion of the polymerization, an acrylic plate containing fine particle beads was taken out from the glass plate.

The light of the halogen lamp collimated into the fine particle-containing acrylic resin plate (light diffusion plate) thus obtained was incident from the rear. A luminance meter (Minolta luminance meter nt1 / 3 ゜ p) was placed 1.5 m ahead of the light diffusion plate, and the luminance was measured. The position of the luminance meter was shifted, the angle was changed, and the operation of measuring the same portion was repeated, and the angular distribution of luminance was measured. On the other hand, the illuminance at the position of the light diffusing plate is separately measured by an illuminometer, and the expression (I
V) was used to calculate the gain. Table 1 shows the values of the respective densities, where the front gain is Go and the angle at which the gain is 1/2 of Go is α.

[0023]

[Table 1]

The results are plotted on a log-logarithmic graph in which the vertical axis is Go and the horizontal axis is α, as shown in FIG. From this figure, at the concentration where Go is 20, α is 8.2 °. This value is larger than a value shown in a comparative example described later, and this light diffusion plate is an excellent material having a large diffusion half-value angle at a constant peak gain.

Example 2 In the same manner as in Example 1, MMA 41.3%, styrene 3.5%, ethylene glycol dimethacrylate 50
%, Ethyl acrylate 5.0%, lauryl mercaptan 0.2%, weight median diameter 8.55 microns,
Crosslinked beads having a refractive index of 1.5035 were obtained. Using the crosslinked beads, a 1 mm-thick acrylic resin light diffusion plate having various concentrations was prepared in the same manner as in Example 1, and the optical performance was measured. The results are shown in Table 2. These Go and α are plotted in FIG. From this figure, when the gain is 20, α is about 8.2 °, indicating good diffusion.

[0026]

[Table 2]

Comparative Examples 1-3 Light diffusing plates were prepared using various fine particles and a base resin as shown in Table 2, and the light diffusing performance was measured. Table 2 also shows the measurement results.

[0028]

According to the present invention, it is possible to obtain a light-diffusing plastic having a high front luminance and a large diffusion half-value angle.

[Brief description of the drawings]

FIG. 1 is a diagram showing an angular distribution of gain at each crosslinked bead concentration in Example 1. (The vertical axis is shown on a logarithmic scale, and the horizontal axis is shown on an equally spaced scale.)

FIG. 2 is a graph illustrating a peak gain and a half-value angle in an example and a comparative example. (The vertical and horizontal axes are shown on a logarithmic scale.)

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location C08L 101/00 C08L 101/00 F21V 1/14 F21V 1/14 Z G02B 5/02 G02B 5/02 B G03B 21/62 G03B 21/62 G09F 9/00 318 G09F 9/00 318B

Claims (3)

[Claims] 1. A crosslinked copolymer comprising methyl methacrylate, alkyl acrylate, styrene and a polyfunctional (meth) acrylate, which is represented by the following general formulas (I) to (I):
II), and the average particle size is 7 to 20 μm;
Substantially spherical fine particles having substantially no pores therein. 6.66W ₂ −0.36 ≦ W ₁ + W ₃ ≦ 6.66 W ₂ +0.31 (I) 0.4 ≦ W ₁ + W ₂ + W ₃ ≦ 0.98 (II) 4W ₃ ≦ W ₁ (III) ( Where W ₁ is the weight fraction of methyl methacrylate, W _1
2 represents the weight fraction of styrene, and W ₃ represents the weight fraction of alkyl acrylate. ) 2. The method according to claim 1, wherein the resin is used for a light-diffusing plastic having methacrylic resin as a base resin.
Fine particles as described. 3. The fine particles according to claim 1, which are used as a light diffusing material for a screen of a rear projection television.