JPH01209402A - Fire retardant light diffusion plate - Google Patents

Abstract

PURPOSE:To obtain a light diffusion plate suitable for the back light of a liquid crystal display by using a polycarbonate plate in which specific ratios of short glass fiber and fine particulate calcium carbonate are uniformly dispersed. CONSTITUTION:The polycarbonate plate formed by dispersing and incorporating the short glass fiber and the fine particulate calcium carbonate is used. Formulas I, II are satisfied when the thickness of the polycarbonate plate is designated as tmm, the content of the short glass fiber as (x)wt.%, and the content of the fine particulate calcium carbonate as (y)wt.%. The polycarbonate used in this embodiment is the polymer obtd. by reaction of bisphenol A and carbonate precursor such as phosgene or diphenyl carbonate. The fire retardant light diffusion plate suitable for the backlight of the liquid crystal display is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light diffusing plate, and more particularly to a flame-retardant light diffusing plate suitable for use in the lighting of special liquid crystal displays.

<Prior Art> Conventionally, an acrylic resin plate containing a light diffusing agent has been used as a light diffusing plate for a bank light of a liquid crystal display. however,! As light diffusion plates used in near future applications are required to have improved heat resistance and flame retardancy, the acrylic resin plates manufactured by Urarai are unable to meet these demands. In other words, such a light diffusing plate has 0) heat resistance that can withstand temperatures approximately 10°C or more higher than conventional acrylic light diffusing plates;
2) Flame retardancy that passes UL standard V-2, Q) Total light transmittance of approximately 45% or more and half-angle of approximately 55° or more, and (4) Must not contain highly corrosive halogen. Must be.

On the other hand, polycarbonate is used for optical applications such as optical disk substrates and lighting lenses due to its excellent heat resistance, transparency, and non-corrosion properties, but it is not often used as a light diffusing plate.

<Purpose of the Invention> The purpose of the present invention is to have superior heat resistance than acrylic light diffusing plates, flame retardancy that passes UL standard V-2K, total light transmittance of about 45 degrees or more, and half reduction of about 55 degrees or more. It is an object of the present invention to provide a light diffusing plate having corners and containing no corrosive halogen, particularly a light diffusing plate suitable for backlights of liquid crystal displays.

As a result of intensive research and efforts to solve this problem, the inventor of the present invention has discovered that a polycarbonate plate in which a specific amount of short glass fibers and finely powdered calcium carbonate are uniformly dispersed satisfies all of the above requirements.
The present invention has been achieved based on these findings.

<Structure of the Invention> The present invention uses a polycarbonate board containing short glass fibers and finely powdered calcium carbonate dispersed therein.The thickness of the polycarbonate board is tm, the content of short glass fibers is When the content of is y weight ik%, the following formula fil and tlly
yl≦t
This relates to a flame-retardant light diffusing plate that satisfies (■).

A typical example of the polycarbonate used in the present invention is a polymer obtained by reacting bisphenol A with a carbonate precursor such as phosgene or diphenyl carbonate, in which part or all of the bisphenol A is formed by other dihydric phenols, e.g. ★Hydroquinone', dihydroxydiphenyl.

Bis(hydroxyphenyl)alkane, bis(hydroxyphenyl)cycloalkane, bis(hydroxyphenyl)ether, bis(hydroxyphenyl)ketone, bis(hydroxyphenyl)sulfide, bis(hydroxyphenyl)sulfone or lower alkyl substituted products thereof, etc. Furthermore, some of the carbonate residues may be substituted with residues of other dibasic acids, such as terephthalic acid and inphthalic acid. These polycarbonates may be mixed with other polycarbonates, polynisder, polystyrene, polyphenyl ether, etc., within a range that does not impair transparency. Among them, those with a refractive index of 1.57 to 1.60! It can be preferably used for.

Short glass fibers are glass fibers with a diameter of 5 to 15μ and a length of 1
The glass is preferably alkali-free glass, such as E glass, which is cut or crushed into pieces of 00μ or less.
The refractive index is the refractive index of the polycarbonate used and 0.01
A difference of ~0.04 is desirable. Such short glass fibers can be easily obtained from the market as milled fibers or glass powder.

Although commercially available fine powder calcium carbonate can be used as is, it is preferable to have an average particle size of about 4 to 6 μm and an angular shape.

The flame-retardant light diffusing plate of the present invention is a polycarbonate plate having a thickness of lf1 or more in which the short glass fibers and finely powdered calcium carbonate are uniformly dispersed, and the short glass fiber content is
Heavy! %, the content of finely divided calcium carbonate is X% by weight
, K when the thickness of the polycarbonate plate is tl, Formula 1
11. If the formula fil is not satisfied, the performance of total light transmittance of about 45% or more and half-reduction angle of about 55° cannot be satisfied at the same time, and the thickness is 12 UL standard 94 V-2 without LTX groove. become dissatisfied. Furthermore, from the viewpoint of the appearance of the molded plate, the content of short glass fibers is 1.
2% by weight ungrooved is preferred, and when a high degree of flame retardance is required, for example, an alkali metal salt of an organic sulfonic acid.

Non-logenic flame retardants such as imide alkali metal salts may be added.

The light diffusing plate of the present invention can be prepared by mixing the short glass eIi fibers, finely powdered calcium carbonate, and polycarbonate by any method, molding the mixture by injection molding, extrusion molding, injection compression molding, or the like, and cutting it as necessary. Manufactured by Stabilizers, release agents, ultraviolet absorbers, dyes, etc. that are usually added to polycarbonate during production may be added.

<Effects of the Invention> The light diffusion plate of the present invention has superior heat resistance than acrylic light diffusion plates, and has a flame retardance of UL standard 94 V-2 or higher, approximately 45%.
It has a total light transmittance of about 55° or more and a half-ray angle of about 55° or more,
Since it does not contain corrosive halogen, it is suitable for various optical applications, and in particular, a light diffusing plate with a thickness of 2 to 3 nm is suitable for backlights of liquid crystal displays.

<Example> The present invention will be described in detail with reference to Examples below.

The total light transmittance and half-life angle were measured by the following method.

Total light P4 transmittance: Based on JIS K-6735.

Half-angle: Using a gloss meter VGS-ID manufactured by Nippon Heavy Industries ■, place the molded plate 1 on the sample stage as shown in the figure, and place the light source 2 of a 5V-1, 25A halogen lamp directly above the light receiver. 3, and measure the intensity of the transmitted light hanging down on the sample surface, and define this as A. Move the light receiver in the circumferential direction as shown in the figure on the right, and find the angle γ0 at which the intensity of transmitted light becomes V2.

Examples 1 to 4 Polycarbonate (Kinjin Kasei ■: Panlite L-125
0 refractive index 1.58) (indicated by pc in the table) Glass short fiber (Nitto Boseki: PFBIO1 refractive index 1.55 average diameter 9 μ, average length 50 μ) and fine powder calcium carbonate (Cipro Kasei Nijipron A average particle size 5μ) was mixed in a planer with the composition shown in Table 1, and then extruded into pellets at a cylinder temperature of 280°C using a 30+nφ vented extruder (Nakatani ■: VSK-30). After drying the pellets at 120°C for 6 hours, they were molded using an injection molding machine (Sumitomo Cycamp 8480/150) at a cylinder temperature of 290°C and a mold temperature of 100°C.
Test pieces of l2.7yX2*y and 127ryuX12.7yx3+n were molded and subjected to a UL standard 94 combustion test. The results are shown in Table-1. Also under the same conditions I
50mX 150muX 2ho and 150silkX150
*A square plate of mX3 Tomomi was molded, and the total light transmittance and half-angle were measured. The results are shown in Table-1.

[Brief explanation of the drawing]

The figure is a diagram for explaining a method of measuring the half-reduction angle of transmitted light, and in the figure, 1 is a sample, 2 is a light source, and 3 is a light receiver. Procedural amendment dated March 1988

Claims (1)

[Claims] From a polycarbonate plate containing short glass fibers and finely powdered calcium carbonate dispersed therein, the thickness of the polycarbonate plate is tmm, the content of short glass fibers is x% by weight, and the content of finely powdered calcium carbonate is tmm. When is y weight%, the following formulas (I) and (II) (11.3x)/y+1.9≦xt≦45.7logx
/y+22...(I) A flame-retardant light diffusing plate that satisfies 1≦t...(II)