JPH0673296A - Light-diffusing resin composition excellent in optical transmission and its molding - Google Patents

Abstract

PURPOSE:To provide a material for a light diffuser having characteristics in that the image of a light source cannot be seen through it and the luminosity is uniform without reducing the brightness of the light source, the light diffuser being used as lighting covers and various displays. CONSTITUTION:Provided are fine solid silicone resin particles which satisfy simultaneously the following conditions: the particle size distribution range is 0.5-10mum; the number-average particle size is 2-5mum; the proportion of the particles of 1-6mum is 90% or more based on all the particles; and the half-value width of the particle size distribution is 2mum or less. The light-diffusing resin composition is prepared by dispersing 1-5 pts.wt. of the fine particles in 100 pts.wt. of a transparent resin. When its molding in the form of a 2-mm thick flat sheet is placed in front of a fluorescent tube light source illumination, it shows the characteristics of a luminance distribution ratio of 0.8 or more and a total light trnsmission of 60% or more. Thus, there can be obtained lighting commodities through which the image of a light source cannot be seen and which do not impair the brightness of the light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition having excellent light transmittance and a molded product suitable for a member for the purpose of diffusing light such as a lighting cover and various displays.

[0002]

2. Description of the Related Art Conventionally, a light diffusing member such as a lighting cover and various displays is generally formed by molding a material in which inorganic or organic fine particles are dispersed in a transparent synthetic resin. A method of widely diffusing light by diffusing or reflecting light rays at the interface between the base resin and the fine particles due to the difference in refractive index between the transparent base resin and the dispersed fine particles is widely used. As the transparent resin in this case, methacrylic resin, polycarbonate resin, polystyrene resin, polyvinyl chloride resin or the like is used.

It must be emphasized that products such as lighting covers and various displays are brighter and more uniform. Therefore, the light diffusing material used for these products is required to have a property of further transmitting and diffusing light. However, from the studies on conventional light diffusing materials, it is generally known that the light transmissivity decreases when the light diffusing property is increased.

As a method of obtaining a material having high light transmittance and high light diffusivity, which are contradictory to each other, a crosslinked polymer having a refractive index difference and a particle diameter within a specific range is added to a transparent resin such as methacrylic resin. A method of incorporating is known (JP-A-63-291001, JP-A-63-29).
No. 1002 publication). Further, a material containing a silicone resin having a specific structure and a particle size is also known (JP-A-1-172801, JP-A-3-207743, JP-A-3-294348).

The light diffusing materials disclosed by these prior arts are intended to improve the light transmittance. The illumination light sources used for lighting fixtures, various displays, signboards, etc. are becoming higher in brightness due to improved performance, and therefore, a light diffusing material that does not impair the brightness of the light sources as much as possible has been desired. Therefore, the study on the light diffusing material has been conducted with an emphasis on improving the light transmissivity rather than the light diffusing property.

[0006]

However, recently, there is a strong demand for further increasing the commercial value of light diffusing materials,
When used for lighting covers and various displays, it is becoming very important that the image of the light source cannot be seen through because the brightness of the light diffusion surface is not uneven. by the way,
It has been known from conventional studies that the light diffusibility may be improved in order to eliminate the image of the light source. That is, when the light diffusivity is increased, the direction of the image of the light source disappears, and the value of the luminance distribution ratio, which is a measure of the light diffusivity, also increases. However, under the present circumstances, if the light diffusivity of the material is increased to such an extent that the image of the light source is lost, the light transmittance is sharply reduced, and the brightness of the light source is extremely impaired. Therefore, it is a technical point to develop a light diffusing material that does not have an image of a light source when used as an actual product and has a light transmittance equivalent to that of conventional characteristics, that is, a total light transmittance of 60% or more. Has become.

The "luminance distribution ratio" in the present invention is defined by the following formula. Luminance distribution ratio = (luminance value at the darkest point) / (luminance value at the brightest point) That is, a light diffusing material is installed on the front surface of the illumination light source provided with two fluorescent tubes, and on that surface. This is a method of measuring the luminance distribution pattern and deriving the ratio of the maximum value and the minimum value within the measurement range. This light diffusing material is a flat sheet material molded from the light diffusing composition, or a flat sheet material molded from a molded product having any shape. The closer this value is to 1, the closer it is to a perfect diffuser, and the nonuniformity of the image and brightness of the light source disappears.

When the luminance distribution ratio is measured by the above method using the light diffusing material obtained according to the conventional technique, the light diffusing property can be quantitatively evaluated, and at the same time, the presence or absence of the image of the light source can be determined. . For example, Japanese Patent Laid-Open No. 3-2077
In the examples disclosed in Japanese Patent Application Laid-Open No. 43-43948 and Japanese Patent Application Laid-Open No. 3-294348, the total light transmittance is 60% or more, and there is no problem in brightness, but the brightness distribution ratio is 0.6 to
A value of about 0.7 was shown, and it was confirmed that the image of the light source did not disappear.

From the above results, the present inventors have made a detailed examination based on the above-mentioned evaluation method based on the luminance distribution ratio, and as a result, when a flat sheet having a thickness of 2 mm, the total light transmittance is 60. A molded product made of a resin composition that simultaneously satisfies the two properties of a brightness distribution ratio of 0.8 or more becomes a very bright light diffusing material in which the image of the light source disappears. Came to know.

[0010]

Under the present circumstances as described above, the present inventors have diligently studied a method of obtaining a light diffusing resin composition by incorporating fine particles having different refractive indexes into a transparent resin. As a result, it was found that there is an optimum particle size range, particle size distribution, and dispersion concentration in the balance of light diffusivity and light transmittance using solid silicone resin fine particles. In particular, the sharp and narrow structure of the particle size distribution is an important factor for satisfying the above properties, and it is very important that particles of various particle sizes are aligned within a certain range without being mixed. I found it important.

Further, the light diffusing resin composition obtained by selecting the optimum particle size range, particle size distribution and dispersion concentration can be processed by a practical method such as an injection molding method or an extrusion molding method. In addition, it succeeded in satisfying the above-mentioned two performances at the same time in the molded product after processing. That is, the present invention relates to 100 parts by weight of the transparent resin, (1) a particle size distribution range of 0.5 to 10 μm, (2) a number average particle size of 2 to 5 μm, and (3) particles of 1 to 6 μm based on all particles. Of 90%
As described above (4), the particles made of a solid silicone resin satisfying the half-value width of the particle size distribution of 2 μm or less are
A light diffusing resin composition characterized by being mixed and dispersed in an amount of 5% by weight, wherein the light diffusing resin composition is molded and has a wall thickness of 2 m under the condition of a temperature of 25 ° C.
A light-diffusing resin molded product having a total light transmittance of 60% or more in a state of m and a brightness distribution ratio of 0.8 or more when installed in front of an illumination light source.

The present invention will be described in detail below. Examples of the transparent resin used in the present invention include methacrylic resin, polycarbonate resin, polystyrene resin, polyvinyl chloride resin and the like. Particularly preferably adopted are
Methacrylic resin. The methacrylic resin that can be used in the present invention is a polymer whose main component is methyl methacrylate. In particular, methyl methacrylate homopolymer, or methyl methacrylate and methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate, acrylonitrile,
A copolymer with maleic anhydride, styrene or any one or more of α-methylstyrene, and a mixture of methylmethacrylate and the above copolymer are preferably used. In any case, the proportion of methyl methacrylate contained in the polymer is preferably 50% by weight or more.

The solid silicone resin used in the present invention is a polymer in which siloxane bonds in which silicon atoms directly bonded to organic groups and oxygen atoms are alternately repeated form a three-dimensional network structure. The organic group directly bonded to the silicon atom includes a methyl group, an ethyl group, a propyl group, an alkane group such as a butyl group, a carboxyl group, a carbonyl group, an ester group, an ether group, and the like, and the transparent resin or the monomer thereof used in the present invention. An organic group having an affinity for is used. A methyl group is mentioned as a typical organic group.

The form of the silicone resin is fine particles which are solid at room temperature or higher. Further, the shape of the fine particles is required to be non-uniform so as to obtain the desired optical characteristics. Above all, a shape ranging from an elliptical shape to a spherical shape is preferable. The particle size of the silicone resin particles is
It must be distributed in the range of 0.5 to 10 μm, preferably 0.8 to 8 μm.

The number average particle size of the silicone resin particles is 2
It is necessary to be ˜5 μm. Preferably 3-4μ
It is desirable that it is m. When the number average particle diameter is less than 2 μm, the light transmittance is poor, and the total light transmittance of the obtained molded product may not be 60% or more, which is not preferable. On the other hand, if it is 6 μm or more, the light diffusivity is poor, and the luminance distribution ratio is less than 0.8, and the image of the light source may be seen through, which is not preferable.

Further, it is desirable that various particle sizes are not mixed and are uniform within a certain range. That is, 0.
1 to 6 μm of all particles distributed in the range of 5 to 10 μm
Is required to be 90% or more, preferably 3 to 6 μm is 90% or more of all particles. When silicone resin particles in which the ratio of particles of 1 to 6 μm to all particles is 80% or less is used, the balance between the light diffusivity and the light transmittance is poor, and the brightness distribution ratio is caused by uneven brightness depending on the position of the molded body. Varies with a value of about 0.7, and the image of the light source may be seen through, which is not preferable.

Further, it is desirable that the structure of the particle size distribution is sharp and narrow, and the half width when the histogram is approximated to the normal distribution is preferably 2 μm or less. The histogram of the particle size distribution referred to here is a plot of the particle size on the horizontal axis and the number of particles corresponding to the particle size range on the vertical axis,
The range of the particle size having the number of particles which is ½ of the maximum number of particles is the half width. If this half-value width is larger than 2 μm, the structure of the distribution range of the particle size is widened, particles of various particle sizes are mixed, and the light distribution efficiency may be lowered, so that the luminance distribution ratio may be less than 0.8, which is not preferable. .

The amount of the silicone resin fine particles used is preferably 1 to 5% by weight, and particularly preferably 2 to 3% by weight, based on 100 parts by weight of the transparent resin such as the methacrylic resin. If it is less than 1% by weight, high light diffusion performance cannot be obtained, and if it exceeds 5% by weight, the desired light transmission performance in the present invention cannot be achieved. In order to enhance the commercial value of the obtained product, it is possible to add a small amount of an inorganic pigment, a fluorescent whitening agent, a light stabilizer, etc. within a range that achieves the object of the present invention. Further, an antistatic agent can be added for the purpose of reducing the adhesion of dust and the like.

The above-mentioned transparent resin such as methacrylic resin and fine particles of silicone resin can be mixed with a Henschel mixer or the like, and the desired product can be produced by injection molding or extrusion molding. The wall thickness of the product is preferably 2 mm, and if a deviation of 0.5 mm or more occurs, the performance of the present invention cannot be achieved, and there is a possibility of causing problems in rigidity and handling. The obtained product has a high light transmittance, that is, a total light transmittance of 60% or more, and a high light diffusion property, that is, a luminance distribution ratio of 0.8 or more when installed in front of an illumination light source. .

[0020]

The present invention will be described in detail below with reference to examples. The evaluations in the examples were carried out according to the following methods. (1) Number average particle diameter The number average particle diameter was measured by the following method.

Measuring apparatus: manufactured by Horiba, Ltd. Centrifugal automatic particle size distribution measuring apparatus CAPA-700 type Measuring method: Accumulation of particle size by light transmission type sedimentation particle size distribution measuring method adopting high speed centrifugal sedimentation method and natural sedimentation method A number histogram was created and the particle size corresponding to 50% of the total number was taken as the number average particle size.

Dispersion medium: Surfactant aqueous solution Dispersion condition: Ultrasonic dispersion (2) General optical properties The general optical property values of molded test pieces were measured by the following test methods. Total light transmittance (T): ASTM-D1003 Diffused light transmittance (DT): 〃 Parallel light transmittance (PT): 〃 Haze (H): 〃 (3) Luminance distribution ratio , Was derived by the following method.

Illumination light source: As shown in FIG. 1, two 20 W fluorescent tubes 11 (made by Matsushita Electric Works, Ltd.) installed in parallel were used. Measurement arrangement: As shown in FIG. 1, 30 mm from the surface of the fluorescent tube
A molded product 12 having a width of 250 mm was installed separately, and a luminance meter 13 was fixed at a position 2 m away from the surface of the molded product.

Measuring method: A luminance meter is rotated in a direction perpendicular to the tubes around a position (shown by a dotted line in FIG. 1) which is a half of the interval between the two fluorescent tubes arranged in parallel with each other as shown by an arrow. While scanning, the brightness values on the surface of the molded product were measured at equal angular intervals. The ratio of the maximum luminance value and the minimum luminance value within the measurement range was derived as the luminance distribution ratio.

[0025]

Examples 1 to 3 and Comparative Examples 1 to 3 As the solid silicone resin fine particles, silicone resin particles manufactured by Toshiba Silicone Co., Ltd. (trade name "TOSPEARL") were used. Since the particle size of the solid silicone resin “TOSPEARL” measured according to the above conditions is not within the desired range described above, it is essential to classify the particles. The classification of the solid silicone resin fine particles was performed by using a method in which a sedimentation classification method utilizing a difference in sedimentation speed of particles dispersed in a solvent and a centrifugal classification method utilizing a centrifugal force were combined.

The evaluation was carried out by forming a molded test piece according to the following method. (Extrusion method) Dell powder 70H (manufactured by Asahi Kasei Corporation)
And solid silicone resin fine particles were mixed at a predetermined concentration with a Henschel mixer, and extruded into pellets at a cylinder temperature of 200 to 250 ° C. using a twin-screw extruder. Use a single screw extruder with a sheet die to set the cylinder temperature to 190.
Extruded under the condition of ~ 250 ° C, the molten resin discharged from the die is passed between rolls and cooled to 600 × 300 × 2 m.
A sheet-shaped molded product of m was obtained.

(Pressing Method) The pellets produced in the same manner as in the above-mentioned extrusion method were used for 240
Pressed under the conditions of ℃ and 150kgf, 250 × 250
A 2 mm flat molded product was obtained. The experimental conditions and results of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1.

Examples 1 to 3 had a light transmittance of 60% and a brightness distribution ratio of 0.8 or more, and the preferable results were obtained without the image of the light source being seen through and the brightness being not impaired.
As in Comparative Example 1, the half-width of the particle size distribution curve of the solid silicone resin fine particles becomes larger than 2 μm, and
When the distribution structure of the particle diameter is wider than that of 2, the total light transmittance exceeds 60%, but the luminance distribution ratio becomes smaller than 0.8, which causes uneven brightness, which is not preferable.

As in Comparative Example 2, the particle size of the solid silicone resin fine particles was reduced as a whole, and the number average particle size was 2 μm.
When it is less than m, the brightness distribution ratio is 0.8 or more and the uniformity of brightness is not a problem, but the total light transmittance is 6 or less.
It is less than 0%, which is not preferable. As in Comparative Example 3, when the particle size of the solid silicone resin fine particles as a whole becomes large and the number average particle size becomes 12.0 μm, the total light transmittance is 81.
However, the brightness distribution ratio becomes very small, and the image of the light source can be seen through, resulting in non-uniform brightness.

In order to clarify the results of Table 1, FIG. 2 is a graph showing the luminance distribution ratio on the horizontal axis and the total light transmittance on the vertical axis. It can be understood that the hatched range in the drawing is the range that satisfies the required value, and that Examples 1 to 3 enter this region and satisfy the predetermined required characteristics.

[0031]

[Table 1]

[0032]

EFFECTS OF THE INVENTION The light diffusing resin composition and the molded article obtained by the present invention have a high light transmittance and thus are bright, and the light diffusing property is so high that the image of the light source cannot be seen through. It has unprecedented properties and is extremely useful industrially for lighting covers and various displays.

[Brief description of drawings]

FIG. 1 is a schematic view of a device for evaluating a luminance distribution ratio of a light diffusing resin molding according to the present invention.

FIG. 2 is a characteristic relationship diagram of Examples 1 to 3 and Comparative Examples 1 to 3 of the present invention.

[Explanation of symbols]

 11 20 W fluorescent tube 12 Light-diffusing resin molding 13 Luminance meter

Claims (2)

[Claims] 1. Particles having (1) a particle size distribution range of 0.5 to 10 μm, (2) a number average particle size of 2 to 5 μm, and (3) 1 to 6 μm based on 100 parts by weight of a transparent resin. Of 90%
Above (4) 1 to 5 particles made of a solid silicone resin satisfying the half-value width of the particle size distribution of 2 μm or less.
A light diffusing resin composition characterized by being mixed and dispersed by weight%. 2. The light according to claim 1, wherein a total light transmittance of a flat sheet having a thickness of 2 mm is 60% or more, and a luminance distribution ratio of the sheet is 0.8 or more. A molded body made of a diffusible resin composition.