JPH1067828A - 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 transparent, and made of a crosslinked copolymer comprising methyl methacrylate, styrene and a polyfunctional (meth)acrylate and satisfying the formulas I, II and III: formula I: 4.54W2 -0.94<=W1 <6.66W2 -0.36, formula II: 0.4<=W1 +W2 <=0.98, and formula III: 7<=d<30 (wherein W1 is the weight fraction of methyl methacrylate, W2 is that of styrene; and d is the mean particle diameter (μm)).

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 as follows:
(1) To diffuse light uniformly and as widely as possible, and (2) to emit light. However, since the amount of light emitted from the light source is constant, these requirements (1) and (2) are mutually exclusive requirements. Therefore, in practice, the brightness is selected and used so as to obtain the most preferable brightness by, for example, changing the concentration of the diffusing material as necessary.
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 difference in refractive index from a transparent resin of the substrate 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.
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.

[0005] As described above, when the techniques disclosed in the prior art are summarized, although many methods have been proposed for the refractive index difference and the particle diameter, they have a very wide range.
Various proposals have been made, and it is currently difficult to determine what combination is preferable. In fact, additional tests have shown that these existing technologies are still inadequate for the ever increasing demands for screens for rear projection televisions in recent years.

[0006]

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). 2), which can provide a light-diffusing material that has as large an angle as possible and that does not cause the transmitted light to have a reddish tinge, and can provide good light-diffusing performance by being dispersed in methacrylic resin. It is intended to provide fine particles.

[0007]

DISCLOSURE OF THE INVENTION The present invention relates to a method for improving the light diffusion performance of a light-diffusing plastic comprising a methacrylic resin, wherein methyl methacrylate (hereinafter, methyl methacrylate is referred to as MMA), styrene and polyfunctional ( A substantially spherical, substantially void-free, substantially spherical interior material which is composed of a crosslinked copolymer comprising meth) acrylate and satisfies the following general formulas (I), (II) and (III). The object of the present invention is achieved by the transparent fine particles. 4.54 W ₂ -0.94 ≦ W ₁ <6.66 W ₂ −0.36 (I) 0.4 ≦ W ₁ + W ₂ ≦ 0.98 (II) 7 ≦ d <30 (III) (W ₁ is the weight fraction of methyl methacrylate, W
₂ represents the weight fraction of styrene, and d represents the average particle size (μm). )

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have comprehensively studied the relationship between the refractive index difference between a transparent resin and transparent fine particles and the particle size of transparent fine particles and diffusion performance (Japanese Patent Application No. 63-1563).
No. 97). That is, the absolute difference | Np−Ns | of the refractive index Ns of the base transparent resin and the refractive index Np of the transparent fine particles is 0.02.
As described above, the value of 0.04 or less is important for obtaining a light-diffusing plastic. 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 has the highest value in front of the diffuser, and as the angle between the diffuser and the normal increases, as shown in FIG. , The value gradually decreases. If the highest value of the gain is called peak gain and expressed by Go, and the angle at which the gain becomes 1/2 of the peak gain is called half-value angle and expressed by α, the object of the present invention is to make both Go and α large. Is to do. However, in general, the light diffusion plate is not always used in the form of a simple flat plate, and often achieves its purpose by giving various lens shapes or by using another light diffusion imparting means such as surface treatment. , Go, α, etc. also vary depending on their type and degree, and it is not appropriate to represent the values of Go and α by such measuring means. 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.

In the present invention, it is necessary that the average particle size of the light-diffusing transparent fine particles is not less than 7 μm and less than 30 μm. If the average particle size is outside this range, a constant G
α at o becomes smaller. Especially the average particle size is 7μm
When the concentration does not reach, 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. Increasing the concentration of the fine particles reduces the straight-forward reddish light, but does not eliminate this extraordinary light until Go has a very low value. This light is perceived as so-called scale when observed by human eyes.

The human eye normally has a viewing angle of 1 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 skewing. Not suitable for obtaining boards. When the average particle size is 30 μm or more, the concentration of the fine particles to be used becomes too large, so that not only is it economically disadvantageous in terms of production technology, but also the half-value angle is smaller than in the case of a particle size within the range of the present invention. Become smaller.

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

In the present invention, factors relating to the shape of the light diffusing fine particles are very important. That is, the ratio of the hollow fine particles to the fine particles is 3 or less.
It is important that the fine particles are substantially spherical particles containing no fine particles by weight, preferably containing no hollow fine particles at all.

There are various types of crushed inorganic powder as fine particles substantially free of a 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. It is preferable that the ratio of the spherical fine particles is high as described above. The non-spherical fine particles are preferably not more than 30%, more preferably not more than 10%, most preferably not containing any.

In order to satisfy the above-mentioned conditions of the difference in refractive index, particle size and shape, it is advantageous and preferable to use a polymer, especially a crosslinked polymer, as the transparent fine particles. In the case of crosslinked polymer fine particles, the refractive index can be adjusted by the polymer composition, and by an appropriate polymerization method, substantially no hollow portion can be obtained, and substantially spherical fine particles can be obtained. .

In general, the light-diffusing plastic is prepared by melt-kneading the light-diffusing fine particles and the substrate resin and extruding them, or by pressing, or, in some cases, in a polymerizable monomer syrup obtained by polymerizing the light-diffusing fine particles or a partially polymerized monomer. It is made by a method of dispersing 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 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 1.51 to 1.
It is preferably about 53. 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 acryl groups or methacryl groups in one molecule, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, (Poly) ethylene glycol di (meth) acrylates such as tetraethylene glycol di (meth) acrylate and nonaethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, 1,3-butylene 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, there 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 , the following formula (I)
And (II) must be satisfied. _{4.54W 2 -0.94 ≦ W 1 <6.66W} 2 -0.36 (I) 0.4 ≦ W 1 + W 2 ≦ 0.98 (II)

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, G
It is possible to provide fine particles for a light diffusing material in which o and α are as large as possible and the transmitted light does not take on a reddish tint.

The copolymer of the present invention may be copolymerized with an alkyl acrylate such as methyl acrylate, ethynoleacrylate or butyl acrylate in addition to the above-mentioned monomers for the purpose of improving the thermal stability. In that case, the above formula (I)
And Formula (II) with W ₁ W ₁ tens W ₃ in (W _3: shows the weight fraction of alkyl acrylated Bok) and may be replaced. Alkyl acrylate can usually be 1/4 or less of MMA.

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, polyvinyl alcohol is used as a dispersant, and the monomer is produced using a disperser or the like.
After finely dispersing, it can be produced by polymerization, filtration, washing and drying.

[0024]

The present invention will now be described more specifically with reference to examples. Example 1 34 parts of MMA, 16 parts of styrene, 50 parts of ethylene glycol dimethacrylate, lauroyl peroxide 0.1 part
2 parts of polyvinyl alcohol (PVA-4 manufactured by Kuraray Co., Ltd.)
20) The mixture was mixed with 300 parts of water containing 0.4%, and dispersed with a laboratory disperser. This liquid was heated with stirring in a nitrogen atmosphere at 70 ° C. for 20 minutes and at 95 ° C. for 50 minutes.
The resulting dispersion was filtered and washed repeatedly with water, and finally washed with methanol and dried. The particle size distribution of the crosslinked fine particles thus obtained was measured using a particle size distribution analyzer (Micron Photosizer SKA-500 manufactured by Seishin Enterprise).
0), the weight median diameter was 10.58 μm
m. As the specific gravity at this time, a value (1.1891) measured separately by preparing a polymer having the same composition was used. The refractive index is measured by observing the movement behavior of the Becke line under a microscope.
5174. 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.

Ethyl acrylate 11.9 parts by weight, MMA
Acrylic resin beads prepared by copolymerizing 8.5% of ethyl acrylate in a mixture of 128.1 parts (F Kyowa Gas Chemical Industry Co., Ltd.)
An acrylic resin syrup was prepared by dissolving 60 parts by weight of -1000B refractive index 1.4920). The required amount of the crosslinked beads was dispersed in this syrup while taking care not to aggregate. 0.02 parts by weight of azobisisobutyronitrile was dissolved therein, and a gasket was attached.
After putting in a glass plate and degassing, at 80 ° C for 2 hours,
Further, the mixture was heated at 120 ° C. for 2 hours to carry out polymerization. The thickness was adjusted so as to be 1 mm. 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.

[0027]

[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 7.8 °. 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.

Examples 2 and 3 and Comparative Examples 1 to 4 In the same manner as in Example 1, a light-diffusing plastic was prepared using various fine particles and a base resin as shown in Table 2, and the light-diffusing performance was measured. did. Table 2 also shows the measurement results.

[0030]

[Table 2]

[0031]

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, styrene and a polyfunctional (meth) acrylate, having the following general formulas (I), (II) and (III)
Substantially transparent particles having substantially no pores therein. 4.54 W ₂ -0.94 ≦ W ₁ <6.66 W ₂ −0.36 (I) 0.4 ≦ W ₁ + W ₂ ≦ 0.98 (II) 7 ≦ d <30 (III) (W ₁ is the weight fraction of methyl methacrylate, W
₂ represents the weight fraction of styrene, and d represents the average particle size (μm). ) 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.