JPS59166551A - Light-diffusing acrylic resin sheet - Google Patents

Abstract

PURPOSE:The titled sheet that is obtained by adding a specific powder of calcium carbonate and subjecting to forming process, thus having high optical transparency and high optical diffusion to give bright feeling leading to energy saving. CONSTITUTION:A methyl methacrylate polymer is combined with an appropriate amount (usually 0.1-3.5pts.wt.) of a calcium carbonate powder which has a shape of substantially hexahedron and more than 80% of which have 1-15mu, preferably 2-8mu particle sizes and the composition is formed. The molecular weight of the methyl methacrylate polymer is 50,000-500,000, preferably 70,000- 300,000.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an acrylic resin sheet with excellent light diffusing properties. More specifically, it relates to a light-diffusing acrylic resin sheet with high light transmittance and excellent light-diffusing effect, which is formed by blending calcium carbonate powder having a specific particle shape with methyl methacrylate polymer and molding the mixture. It is. A light-diffusing sheet material made by adding a light-diffusing agent to a methyl methacrylate polymer can be used as a material for a variety of molded products that give a sense of elegance, including lighting covers, signboards, displays, and glazing (1). It is used. On the other hand, recently there has been a demand for the development of energy-saving materials that have both high light transmittance and light diffusivity, especially in the field of lighting.

Conventionally, various methods have been used as a means of imparting light diffusion performance, but if we limit ourselves to methods that involve the combination of inorganic fillers, barium sulfate, calcium carbonate, silicon dioxide, talc, titanium dioxide, hydroxide, etc. Al E =
(For example, in the case of calcium carbonate, see JP-A-57-155245). All of these utilize the difference in refractive index with the acrylic resin base material, and also select the average particle size and addition amount of the filler, and even create yarns with different refractive indexes that differ from the base material. Although the performance has been found by combining with organic light molecules, it has not always been possible to obtain a satisfactory balance between light transmittance and high light diffusivity.

In view of this situation, the present invention has been made through intensive studies to maximize the properties of conventional inorganic fillers, and as a result, we have developed an acrylic resin with high light transmittance and excellent weather resistance as the base thermoplastic resin. In addition to the refractive index, particle size, and addition amount of various factors considered to be effective as a light diffusing agent, the present invention was developed by paying particular attention to the particle shape, particle size, and particle size distribution of the filler. That is, the present invention provides an acrylic resin sheet containing an appropriate amount of calcium carbonate powder having a substantially hexahedral particle shape and containing 80% by weight or more of particles with a particle size of 1 to 15 μm, which is an extremely excellent total light beam. We have discovered that it is possible to obtain a sheet-like material that has good transmittance and light diffusivity, and also has a soft and bright appearance.

The methyl methacrylate polymer used in the present invention is a copolymer of methyl methacrylate monomer or this with other comonomers such as methyl acrylate, ethyl acrylate, butyl acrylate, etc., and has a methyl methacrylate component of 7
The molecular weight is not particularly limited in the present invention, but it is generally 50,000 to 500,000, preferably 70,000 to 800,000 in terms of ease of cross-wire, moldability, physical properties, etc. It is.

Calcium carbonate with a specific particle shape according to the present invention is calcium carbonate containing 80% by weight or more of particles having a substantially hexahedral shape and a particle size of 1 to 15 μm, and having a narrow particle size distribution (relatively uniform). The substantially hexahedral shape referred to here refers to hexahedrons such as rectangular parallelepipeds and rectangles, but the particle form has a shape in which the smallest short axis diameter is 1 μ or more and the largest long axis diameter is 15 μ or less. It may also include partially chamfered lines or uneven surfaces.

Calcium carbonate having a hexahedral shape according to the present invention has a particle size range of 1 to 15μ as a main component, but if the particle size is less than 1μ, the total light transmittance is insufficient to provide sufficient light diffusivity. On the other hand, if it exceeds 15μ, the light transmittance will improve, but the light diffusivity will be impaired and the transmission phenomenon of the light source image will easily appear, so it is preferable to use 2.
~8μ is used. In addition, in the present invention, calcium carbonate having a specific particle shape is uniformly dispersed and mixed into the methyl methacrylate polymer, and the amount of the calcium carbonate mixed varies depending on the thickness of the sheet, but is usually 0.1 to 3.5 parts by weight. 'It is the amount that can be applied. This is because if the airflow of the light diffusing agent to be dispersed is less than the lower limit, the light diffusivity will be insufficient, and if it exceeds the upper limit, the light transmittance will be significantly reduced.

The appearance of the light-diffusing acrylic resin sheet of the present invention is a bright translucent color with a glass-like surface, but in order to further increase the commercial value, it may be used as a coloring agent, particularly a fluorescent whitening agent or a fluorescent whitening agent. By using a bluing agent in combination, a warm and soft feel can be imparted. Various types of fluorescent brighteners are listed in the Dye Handbook, but oxazole-based and coumarin-based are preferred from the viewpoint of weather resistance. As the bluing agent, ultramarine blue is preferable from the viewpoint of stability of appearance quality (color blurring). Also, stabilizers such as weathering agents may be added as necessary.

Calcium carbonate in a specific particle shape used in the present invention is characterized by imparting high light transmittance and light diffusivity (5), but depending on its use and purpose, conventionally used silica, barium sulfate, titanium oxide,
It can be used in combination with ordinary light diffusing agents such as calcium carbonate.

The method for blending and kneading the methyl methacrylate polymer of the present invention and the light diffusing agent powder is not particularly stipulated, but in general, it is first mixed and stirred using a mixer such as a Henschel mixer or a tumbler, and then a conventional extruder is used. After pelletizing, the sheet is processed into a sheet with a smooth or matte surface using an extrusion device equipped with a Ben I or directly. The present invention will be described in more detail with reference to Examples below, but the present invention is not limited to these Examples.

Example-1 A methyl methacrylate copolymer containing 7.5 Mm% of ethyl acrylate with a molecular weight of 140,000 and a hexahedral particle shape and a particle diameter of 2 to 8 μm was prepared for 100 overlapping portions of beads. 1.5 parts by weight, 1.7 parts by weight, (6) 2.0 parts by weight, and 2.5 parts by weight of specific calcium carbonate powder containing 5% by weight or more and having a MW average particle size of 5μ, respectively, at high speed in a Henschel mixer. , mix and stir for 1 minute, then 65 wIIQ
J Extruder with vent Extruder extruder width is 600 mm 1-1 - Extrude into a sheet shape at 240°C using a hanger die, and use three rolls (smooth mirror finish) to form a sheet with a thickness of 2 mm.
It was processed into a tnm sheet. Regarding this sheet, the total light transmittance was measured and the invisible limit distance of a fluorescent lamp light source and FT (P (tungsten light hiding power)) were measured as a light diffusivity evaluation, and the results are shown in Table 1.

Each test item was evaluated using the following test method.

(1) The particle shape and particle size of the light spreader were observed (measured) using an electron microscope method, and the particle size distribution and average particle size were measured using a Shimadzu centrifugal sedimentation particle size distribution analyzer jl (S A-C]' 2).

(2) Total light transmittance according to A8TM D1008-61 T, integrating sphere type H'
Measured with an rtt meter.

(8) Invisibility Limit Distance Diagram-1 shows a schematic diagram of the measuring device.
When two 20W fluorescent light tubes 3 are set vertically in parallel at a distance of cm, and the distance 4 from the center of each of the two fluorescent light tubes is fixed in parallel at 10 at+ or 20 cm. The image of the light fJ”& is shown on the measurement sheet (30 (77
1X 80 cm) Visually determine the critical distance 6 that will no longer be recognized through FT.

(4) FIIP (filament light source @concealing power) 100
Using a W tungsten white light source, the distance from the light source is 1'JIl.
The strength of the filament light source image passing through the measurement sample from a position of 5 m was judged with the naked eye and expressed in four broad stages.

Grades 0 to 3: The luminescent filament image is clearly visible.

・Grades 1 to 6: Moderately blurred image.

7th to 10th grade Nio] I can barely see the image.

Level 10 and higher: I can't see it at all.

Comparative Example-1 An extruded sheet with a bleached thickness of 2 obtained in the same manner as in Example-1 except that barium sulfate and calcium carbonate shown in Table 1 were used in place of the specific shape calcium carbonate in Example-1. The results are shown in Table 1.

(9) As is clear from these results, by incorporating the light diffusing agent of the present invention, the balance between total light transmittance and light diffusing performance is extremely superior compared to the barium sulfate and calcium carbonate based comparative examples. It can be seen that L7 exhibits outstanding optical performance not seen in conventional light diffusion sheets.

[Brief explanation of drawings]

Figure 1 is a schematic top view of the device for measuring the invisible limit distance, in which 8 is a fluorescent lamp light source, 5 is a measurement sheet sample, and 6
is the invisible limit distance. (11 completed) Figure-1

Claims (1)

[Claims] It is characterized by being formed by blending an appropriate amount of calcium carbonate powder with a methyl methacrylate polymer having a substantially hexahedral particle shape and containing 80% by weight or more of particles with a particle size of 1 to 15μ. A light-diffusing acrylic resin sheet.