JPH026557A - Light-diffusing plastic and fine particle suitable therefor - Google Patents

Abstract

PURPOSE:To form a light-diffusing plastic having excellent light diffusion properties by dispersing fine spherical transparent particles having a specified refractive index and a specified particle diameter in a transparent plastic base. CONSTITUTION:This light-diffusing plastic is formed in the following way. Namely, fine spherical, substantially transparent particles having a refractive index NP and a mean particle diameter d (mum) satisfying formula I: 0.02<=INPNSI<=0.04 and formula II: 7<=d<=30 and having a content of particles having voids in its inside <=3wt.% are dispersed in a substantially transparent plastic of a refractive index NS. It is desirable that the content of fine nonspherical particles in the fine transparent particles is at most 10wt.% based on the total fine particles. It is more desirable that fine particles of a polymer, especially, a crosslinked polymer are used as the fine transparent particles.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a light-diffusing plastic suitable for members intended to diffuse light, such as lighting covers, illuminated signboards, glazing, various displays, or transmission screens, and its use therein. It concerns fine particles suitable for.

(Prior art) Conventionally, light-diffusing materials for lighting covers, display gray screens, etc. have been made using materials in which inorganic or organic transparent fine particles are dispersed in transparent plastics such as acrylic resin or styrene resin, or on the surface of transparent plastics. Materials whose surfaces are roughened by some method are known, and it is also known to use these in combination. In recent years, with the increasing need for light-diffusing plastics that require high performance, particularly for screens for rear-view televisions, much effort has been made to find materials with higher performance.

The desired performance of these light-diffusing materials is to (1) diffuse light uniformly and brightly over as wide a range as possible. Since the amount of light emitted from a light source is constant,
These requirements (1) and (2) are mutually contradictory requirements. Therefore, in practice, the most preferable brightness and spread are selected and used by changing the concentration of the diffusing material as necessary. In the method of obtaining a light diffusing material by dispersing a light diffusing material in transparent plastic, the key points for obtaining a suitable combination of light diffusing material and transparent plastic are mainly the particle size of the light diffusing material fine particles and the light diffusing material. The difference in refractive index between microparticles and transparent plastics has been used.

For example, in Japanese Patent Publication No. 39-10515, the refractive index difference with the base transparent resin is 0.05 to 0.3, and the average diameter is 0.05 to 0.3.
A rack that is 5-5μ? ! A method of using fine particles as a light diffusing material is described, and in JP-A-48-44333, crystal powder with a particle size of 10 μm or less and having a refractive index 0.05 to 0.5 larger than that of the base resin is blended. Further, in JP-A-60-139758, the refractive index difference is 0.02-0.1 and the particle size is 10-50μ, and in JP-A-60-184559, the refractive index difference is 0. .02~0
．． 1 with a particle size of 4 to 10μ has been proposed, as well as
As disclosed in JP-A No. 61-4762, fine particles with a particle size of 4 to 50 μm and a refractive index of 0.02 to 0.1 larger than the base resin, and fine particles with a particle size of 4 to 50 μm and a refractive index of 0.02 to 0.1 μm are used. A method of using small microparticles in combination is also described.

Others JP-A-60-21662 or JP-A-62-1
In No. 74261, the refractive index is 0.0 than that of the base resin.
A method of dispersing fine particles with an average particle size of 1 to 10 microns has also been proposed.

In addition, there are a wide variety of combinations of base resins and light diffusing materials that have specific descriptions, and it is difficult to describe them all, but for example, methacrylic resin (refractive index 1.
492> as the base resin, crystalline silica (
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 spheres (refractive index 1.46), calcium fluoride (refractive index 1.43>, the bending refractive index of lithium fluoride (refractive index 1.39), barium sulfate (refractive index 1.64), and alumina powder (1,7) is unknown, but magnesium oxide, titanium oxide, talc, etc. Crosslinked polymers are used, including polystyrene resin (refractive index 1.59),
PVC v! Various am-free particles are also used when the base resin is 4 resin (refractive index 1.55>) or polycarbonate vJ resin (refractive index 1.59).

When we organize the technologies that have been disclosed so far, we find that
Although many methods have been proposed for refractive index difference and particle size, they range widely and are proposed in various ways, making it difficult to judge which combination is preferable. . In fact, additional tests have revealed that these existing technologies are still insufficient to meet the ever-increasing demands for screens for rear projection televisions in recent years.

(Problems to be Solved by the Invention) The present invention has excellent light diffusion performance in this chaotic flow of technology, that is, the maximum luminance G0 is as large as possible, and the half-value angle (luminance is up to μ). The object of the present invention is to provide a light diffusing material that has as large a reduction angle as possible and that does not give transmitted light a reddish tinge. Another object of the present invention is to provide spherical fine particles that can provide good diffusion performance when dispersed in a methacrylic resin.

(Means for Solving the Problems) The present invention provides a substantially transparent (hereinafter "substantially transparent" is simply abbreviated as "transparent") plastic made of a refractive index Ns, which contains the following formula (technique), and formula (I) 0.02≦|Np-Ns|≦0.04 ・----・
...-(I)7≦d≦30
...... Particles that have an average particle diameter d (microns) that satisfies (II), a refractive index NP, and have pores inside account for 3% by weight or less in the total fine particles This is preferably achieved by dispersing transparent spherical fine particles having the following properties, and by controlling the proportion of non-spherical particles among all the transparent fine particles to 10% by weight or less. In addition, in order to achieve the above conditions, the purpose can be preferably achieved by using a polymer, especially a crosslinked polymer, as the transparent fine particles. When using methacrylic resin as the transparent plastic, methyl methacrylate (hereinafter referred to as MMA), By using a crosslinked copolymer containing styrene and polyfunctional (meth)acrylate as constituent components, or when using a copolymer resin of MMA and styrene as a transparent plastic, MM
The above objective is achieved by using crosslinked copolymer fine particles containing A and a polyfunctional (meth)acrylate as constituent components, or crosslinked copolymer fine particles containing MMA, styrene, and a polyfunctional (meth)acrylate as constituent components. be able to. Furthermore, M
It is composed of a crosslinked copolymer consisting of MA, styrene, and polyfunctional (meth)acrylate, and satisfies the following formula (I[> and formula (IV)), and has a weight median diameter of 7 to 7.
The object of the present invention is achieved by substantially spherical transparent fine particles having a diameter of 30 μm and having substantially no internal pores.

4.54W2-0.94≦W+ <6.66W2+0.
36 (III) 0.98≦W, +W2≦0.4
(IV) (However, Wl represents the weight fraction of MMA, and W2 represents the weight fraction of styrene.) (Function) The present inventors have determined that the refractive index difference between the basic transparent resin and the transparent fine particles, the particle size of the transparent fine particles, After comprehensively considering the relationship between diffusion performance,
We have arrived at the present invention. That is, in the present invention, it is necessary that the absolute difference 1Np-Nsl between the refractive index Ns of the base transparent resin and the refractive index Np of the transparent fine particles is 0.02 or more and 0.04 or less. We created various flat plates with different refractive index differences between the base resin and the transparent fine particles and the particle diameter of the transparent fine particles, and parallel light rays were incident on the flat plates from the rear, and the angular distribution of the brightness of the light coming out in front of the flat plates was measured. The gain G was calculated from the illuminance on the surface and each brightness using the following formula.

The gain has a maximum value in front of the diffuser plate, and as the angle between the gain and the normal line of the diffuser plate increases, the value gradually decreases as shown in FIG. The highest value of the gain is called the peak gain and is expressed by Go, and the angle at which the gain sacrifices the peak gain is called the half-value angle and is expressed by α.The purpose of the present invention is to increase both Go and α. It is in. However, in general, light diffusing plates are not always used in the form of a simple flat plate; the purpose is often achieved by giving them various lens shapes or using them in combination with other means of imparting light diffusivity, such as surface treatment. , G0. Since α etc. vary depending on their type and degree, it is not appropriate to express the performance aimed at by the present invention by the values of G and α measured by such measuring means.

However, it has been experimentally confirmed that when a combination of large Go and α measured using a flat light diffusing plate is adopted, excellent performance is exhibited even in the shape of a song. We mainly adopted the flat plate method, which makes it easy to compare and evaluate the light diffusion performance of light diffusion materials. For a given combination of substrate resin and light diffusing material, if the concentration of the light diffusing material is changed, 00 decreases and α increases as the concentration increases, as shown in FIG. Therefore, as a means of selecting a good light-diffusing material, the concentration of the light-diffusing material is changed and a concentration that provides a constant Go is selected, and the one with a large half-value angle α at that concentration is a preferable light-diffusing plastic. Thought.

As a result of experiments, it has been found that a light-diffusing plastic with a significantly high α at a constant 00 can be obtained when the refractive index difference is 0.02 or more and 0.04 or less. Furthermore, in the present invention, it is necessary that the average particle diameter of the light-diffusing transparent fine particles is 7 to 30 μm.

When the average particle diameter is outside this range, α at a constant 00 becomes small. Especially when the average particle diameter is 7μmG″-
If the particle concentration is low, a lot of light travels in a limited solid angle in the straight direction, and this light has a reddish tinge. As the particle concentration increases, the reddish light that travels in a straight line is reduced, but this abnormal light does not disappear until Go reaches a very low value. It is recognized as a so-called sedge.

The human eye can normally distinguish one minute of viewing angle (= 1/60 degree), and measuring this sedge phenomenon with an optical measurement device (luminance meter) takes about the same amount of time as the human eye can distinguish. It is necessary to use equipment with a viewing angle of . Conventionally, there has been found in literature that there is no correlation between data on the angular distribution of luminance and sedge, but this is thought to be due to the difference in viewing angle between the human eye and the luminance meter. Currently, the viewing angle of commercially available luminance meters is 2 degrees, 1 degree, '/3 degrees, 0.2 degrees, etc. All of them are larger than 1/60 degree, and the viewing angle is as small as possible and stable measurement is required. In consideration of what could be done, the present inventors conducted measurements using a Minolta luminance meter tV3°P manufactured by Minolta, which has a viewing angle of 6°. As a result, it was found that it was possible to measure strong light concentrated in an extremely narrow angular range in response to the sedge phenomenon, and that this was reflected to some extent in the values of Go and α. The average particle diameter of fine particles is 7
Below μm, in order to prevent sedges, it is necessary to increase the concentration of the light diffusing material until the maximum brightness becomes extremely low.
It is not suitable for obtaining a light diffusing plate with no ridges and a large gain. If the average particle size exceeds 30 μm, the concentration of the fine particles used becomes too large, which is not only disadvantageous from an economic and production technology perspective, but also reduces the half-value angle compared to the case of a particle size within the range of the present invention. becomes smaller.

There are various definitions for the average particle size, but the average particle size as used in the present invention refers to the zero particle size distribution expressed by the weight and cyan diameter, that is, the particle size at which the cumulative weight fraction is 50% in the weight accumulation curve. For measurement, there are methods such as Coulter counter method, sedimentation method, counting method using micrographs or electron micrographs, and any method may be used.

In the present invention, factors related to the shape of the light-diffusing fine particles are very important. In other words, light-diffusing fine particles are
The proportion of hollow fine particles in the fine particles is 3% by weight or less,
Preferably, the particles need to be substantially spherical and not contain substantially hollow particles. Glass beads are generally well-known spherical transparent fine particles, but according to the present inventors, by applying the refractive index difference and particle size range as described above, glass beads can be used. It has been found that although the performance can be improved, the performance is inferior to that of cross-linked plastic beads of similar particle size and refractive index, such as those described below. In addition, there are various crushed inorganic powders as fine particles that do not substantially contain hollow parts, and if these are used within the range that satisfies the above conditions, they can be made into excellent light-diffusing plastics. has the same peak gain G compared to such irregularly shaped particles.

It is more preferable because the half-value angle α becomes large in a diffuser plate with a concentration that gives For this purpose, it is possible and in fact effective to improve the performance by mixing crushed fine particles into ordinary glass beads, but as mentioned above, it is preferable to have a high proportion of spherical fine particles, and non-spherical fine particles are It is preferably 30% or less, more preferably 10% or less, and most preferably substantially free.

In order to satisfy the conditions of refractive index difference, particle size, and shape mentioned above, 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, depending on the polymer composition. It is possible to adjust the refractive index, and by using an appropriate polymerization method, it is possible to obtain substantially spherical fine particles that are substantially free of hollow parts. In general, light-diffusing plastics are produced by melt-kneading light-diffusing fine particles and substrate 1 resin and extruding them, or by a pressing method, or in some cases, by adding light-diffusing fine particles to a polymerizable monomer or partially polymerized polymerizable monomer dilug. It is made by a method of dispersion and polymerization. Therefore, light-diffusing fine particles are used during the process of making light-diffusing plastic.
It is necessary that the material does not change into an undesirable shape due to melting, melting, etc. For this purpose, it is possible to make the molecular weight of the polymer sufficiently high, but it is more preferable to provide it with appropriate crosslinking.

As the base resin of the light-diffusing plastic, transparent resins with high light transmittance, such as methacrylic resin, polystyrene resin, polycarbonate resin, as well as epoxy resin and polyvinyl chloride resin, are used.

Among them, methacrylic VIJ resin is a preferred resin because it has excellent transparency, durability, and physical properties.Methacrylic resin is usually used to improve heat resistance, moldability, durability, etc.
In addition to MA, alkyl acrylate may be copolymerized, and lubricants and ultraviolet absorbers may be added, and the term methacrylic resin here refers to all resins that are mainly composed of MMA. When the base resin is a methacrylic resin, it is preferable to use fine particles of a crosslinked resin containing MMA, styrene, and polyfunctional (meth)acrylate as the light diffusing agent. Since the refractive index of ordinary methacrylic resin is around 1.49, the refractive index of the light diffusing agent particles is 1.51 to 1.49.
It is preferably about 53. Of course, the refractive index may be slightly higher or lower depending on the type of methacrylic resin that is the base resin. In the present invention, polyfunctionality (meta)
Acrylic resin is a compound having two or more acrylic or methacrylic groups in one molecule, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, nonaethylene (Poly)ethylene glycol di(meth)acrylate such as glycoldi(meth)acrylate, globylene glycol di(meth)acrylate, etc.
meth)acrylate, 1,3-butylene glycol di(
In addition to glycol di(meth)acrylates such as meth)acrylate, tetramethylene glycol di(meth)acrylate, hexamethylene di(meth)acrylate, and neopentylglycol di(meth)acrylate, trimethylolgropane tri(meth)acrylate, penta It plays a role in preventing damage to the shape of fine particles during the production process of polyhydric (meth) polyhydric alcohols such as erythritonyl tetra(meth)acrylate, and accounts for 2% of the total monomers that make up transparent fine particles. Appropriately selected within the range of ~60%. To illustrate the reference range for achieving the above refractive index using a terpolymer of ethylene glycol dimethacrylate, MMA, and styrene as an example, when the weight fraction of MMA is Wl and the t amount fraction of styrene is W2. , the following formula (I
II) and formula (IV).

4, 54W2 0. 94≦W+ <6. 66W
2+0. 36 (1) 0, 99≦W+ +W2≦0
．． 4 (IV) In addition to the above monomers, alkyl acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, etc. may be copolymerized with the copolymer of the present invention for the purpose of improving thermal stability.

In that case, in the above formulas (I[[) and (IV), W
It is sufficient to replace l with W+ +W3 (Wl: indicates the weight fraction of alkyl acrylate). The alkyl acrylate is usually less than MMA.

When a copolymer of styrene and MMA is used as the base resin, the refractive index increases, which increases the effectiveness of the lens.
It may be advantageous. Even in such cases, it is desirable to use a crosslinked copolymer similar to the transparent fine particles used in the methacrylic resin described above. However, styrene-M M
AV! The above-mentioned polymer beads can be synthesized by a suspension polymerization method. For example, it can be produced by using polyvinyl alcohol as a dispersant and finely dispersing monomers with a disperser or the like, followed by polymerization, filtering, washing, and drying.

(Example) Hereinafter, the present invention will be described in more detail with reference to Examples.

Example I MMA 34 parts, styrene 16 parts, ethylene glycol dimethacrylate 50 parts, lauroyl peroxide 0.
2 parts of polyvinyl alcohol (PVA-42 manufactured by Kuraray)
0) and 300 parts of water containing 0.4%, and dispersed using a lab body spazer. Do not stir this liquid and use N2
The mixture was heated in an atmosphere at 70°C for 20 minutes and at 95°C for 50 minutes. The resulting dispersion was passed through and washed repeatedly with water, finally washed with methanol, and then dried.

The particle size distribution of the crosslinked fine particles thus obtained was measured using a particle size distribution meter (Micron Photosizer 5KA-manufactured by Seishin Enterprises).
5000), the weight median diameter was 10.
It was 58 μm. In this case, the specific gravity was measured using a value (1,1891) obtained by separately preparing a polymer with the same composition, and the refractive index was measured using a method that observed the movement behavior of the Bessge line from 1°. It was 5174.

Also, the beads were substantially all spherical and did not contain hollow particles.

Using these crosslinked beads, methacrylic resin plates having a thickness of 1 mm and containing beads in various weight fractions were made by the following method.

Ethyl acrylate 11.9 parts by weight, MMA 128.1
Acrylic resin beads (Kyowa Gas Chemical Co., Ltd. F-1000) copolymerized with 8.5% ethyl acrylate in a mixed solution of
B refractive index: 1.4920) 60 fJ, and an acrylic resin sill was melted. The required amount of the cross-linked beads described above was dispersed in this sill, taking care not to aggregate them. In this, azobisisobutyronitrile 0.0
21 parts of 21E was dissolved, placed in two glass plates each equipped with a gas get, degassed, and then heated at 80° C. for 2 hours and then at 120° C. for 2 hours to polymerize. The thickness of the acrylic plate containing microbeads was adjusted to 1 mm, and the acrylic plate containing microbeads was taken out from the glass plate after zero weight. Collimated light from a halogen lamp was incident on the thus obtained fine particle-containing acrylic resin plate (light diffusion plate) from behind.

A brightness meter (Minolta brightness meter nth''P) was installed 1.5 m in front of the light diffusion plate to measure the brightness.The operation of measuring the same area was repeated by shifting the position of the brightness meter and changing the angle. , the angular distribution of brightness was measured.

On the other hand, the illuminance at the position of the light diffusing plate was separately measured using an illuminance meter, and the gain was calculated from the ratio of luminance and illuminance using equation (Vl). The values of each density are shown in Table 1, where the front gain is 00 and the angle when the gain is 00 is α.

Table 1 shows the results with the vertical axis being G0. When plotted on a logarithmic graph with α on the horizontal axis, it becomes as shown in Figure 2.

From this figure, at the concentration where 00 becomes 20, α is 7.
It becomes 8゛. This value is larger than the value shown in the comparative example described below, and this light diffusing plate is an excellent material with a large diffusion half-value angle when a constant peak gain is set.

Examples 2 to 4 and Comparative Example 1.2 Same as Example 1 (light diffusing plastics were created using various fine particles and base resin as shown in Table 2, and light diffusing performance was measured. .i1'!I constant results are also shown in Table 2.

Margin below.

Example 5 Same glass beads GB as used in Comparative Example 1
-210 (manufactured by Toshiba Barotini) at 1°1.2.2-
When the glass beads were immersed in a mixture of tetrapromoniethane and monochlorobenzene with a ratio of 12.424 and centrifuged, the glass beads were separated into those that floated to the top of the liquid and those that settled to the bottom. Each phase was separated, washed, dried, and placed in a liquid mixture of methylene iodide and carbon tetrachloride with a refractive index of approximately 1.521, and observed with an optical 5g1I microscope. For the peas, the boundary between the liquid and the beads was clearly visible, but the floating part of the glass peas had a black core that was clearly visible! The results were similar to those observed separately for hollow beads. The weight of the beads in the floating portion thus obtained was 4.7% of the weight of the beads before separation. Table 2 shows the results of a light diffusing plate obtained in the same manner as in Example 1 using the glass beads of the sedimented part obtained by this method as a light diffusing agent.In the case of Comparative Example 1, the relative peak gain was 20. The α of time was large, and the performance as a light diffusing agent was improved.

(Effects of the Invention) By combining a substantially transparent plastic that satisfies the conditions of the present invention and fine particles, it has become possible to obtain a light-diffusing plastic that has high front brightness and a large diffusion half-value angle.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the angular distribution of gain at each crosslinked bead concentration in Example 1, with the vertical axis shown on a logarithmic scale and the horizontal axis shown on an equally spaced scale. FIG. 2 is a graph showing the peak gain and half-value angle of Examples 1 to 5 and Comparative Examples 1 to 2, and both the vertical and horizontal axes are shown on a logarithmic scale. Patent applicant: Kyowa Gas Chemical Industry Co., Ltd. Figure 1 Figure 2 Half-value angle α (degrees) Angle (degrees) Procedural author's letter (spontaneous) September 7, 1988

Claims (7)

[Claims] (1) The following formula (I) and formula (II) 0.02≦|N
p-Ns｜≦0.04……(I) 7≦d≦30………………………………(II) Having a refractive index Np and an average particle diameter d (μm) that satisfy the following, and A light-diffusing plastic made of dispersed substantially transparent spherical fine particles having 3% by weight of particles having pores inside. (2) The light-diffusing plastic according to claim 1, wherein the fine particles are polymer fine particles. (3) The light-diffusing plastic according to claim 1, wherein the fine particles are crosslinked polymer fine particles. (4) The light-diffusing plastic according to any one of claims 1 to 3, wherein the proportion of non-spherical fine particles in the total fine particles is 10% by weight or less. (5) The light-diffusing plastic according to any one of claims 1 to 4, wherein the substantially transparent plastic is a methacrylic resin, and the fine particles are a copolymer of methyl methacrylate, styrene, and polyfunctional (meth)acrylate. (6) The substantially transparent plastic is a copolymer resin of methyl methacrylate and styrene, and the fine particles are a copolymer of methyl methacrylate and a polyfunctional (meth)acrylate or a copolymer of methyl methacrylate, styrene, and a polyfunctional (meth)acrylate. The light-diffusing plastic according to claims 1 to 4, which is a copolymer. (7) It is composed of a crosslinked copolymer consisting of methyl methacrylate, styrene, and polyfunctional (meth)acrylate, satisfies the following general formula (III) and formula (IV), and has a weight median diameter of 7 to 30 μm. , substantially transparent spherical fine particles having substantially no internal pores. 4, 54W
_2-0.94≦W_1≦6.66W_2-0.36(
III) 0.99≦W_1+W_2≦0.4 (IV) (where W_1 is the weight fraction of methyl methacrylate,
W_2 represents the weight fraction of styrene. )