WO2000042452A1

WO2000042452A1 - Light reflector

Info

Publication number: WO2000042452A1
Application number: PCT/JP2000/000127
Authority: WO
Inventors: Yoshihisa Ishihara; Satoshi Iwasaki; Yoshiaki Momose; Takeshi Aoki; Seiji Takahashi
Original assignee: Jsp Corporation
Priority date: 1999-01-13
Filing date: 2000-01-13
Publication date: 2000-07-20
Also published as: AU2003500A

Abstract

A shaped body having a light reflecting surface of a composition containing (a) at least 50 % by weight of an aromatic polycarbonate resin and (b) an auxiliary ingredient in such an amount that the light reflecting surface has a total reflectance of at least 80 % and a diffuse reflectance of at least 75 %. The shaped body is useful as a light reflector.

Description

SPECIFICATION

LIGHT REFLECTOR

Technical Field

This invention relates to a shaped body suitable for use as a light reflector for, for example, an electric sign, a light box for observing photographs, or lighting equipment such as a fluorescent lamp.

Background Art

A light reflector is used in various lighting or illuminating devices. In the case of a light box for observing an X-ray photograph of a patient, for example, a light reflecting plate is disposed opposite to a translucent white display plate made of an acrylic resin with one or more fluorescent lamps being interposed therebetween. In use, the photograph is fixed onto the acrylic resin display plate and is illuminated through the display plate with light directly emitted from the lamps as well as light reflected on the reflecting plate.

One conventionally used reflecting plate is a metal plate having a mirror surface film of aluminum deposits. While such a mirror surface reflecting plate has a high reflectance, a problem is caused because of its low diffuse reflectance. Thus, since the reflected light is not uniform, an image of the light source (fluorescent lamps) unavoidably appears on the display plate. It is, therefore, necessary to provide a large distance between the light source and the illuminating surface (display plate) , in order to prevent the light source from appearing on the illuminating surface.

WO97/01117 discloses a light reflecting plate made of a polyester foam containing fine cells and having a high diffuse reflectance. The polyester foam is prepared by a method in which a polyester sheet and a separating sheet are stacked on each other and wound to form a roll. The roll is impregnated with an organic solvent to improve the crystallinity thereof and is then with an inert gas such as C0₂ in a high pressure vessel. The roll is unwound and the polyester sheet is heated at a 240°C to foam the sheet.

The foamed sheet is heated at 150°C or more and then cooled.

Thus, the preparation of the light reflecting plate requires a complicated process. The present invention has been made in view of the above-described problems of the conventional reflecting plates .

Disclosure of the Invention In accordance with the present invention, there is provided a shaped body having a light reflecting surface of a composition comprising (a) at least 50 % by weight of an aromatic polycarbonate resin, and (b) an auxiliary ingredient in such an amount that said light reflecting surface has a total reflectance of at least 80 % and a diffuse reflectance of at least 75 %.

The shaped body is suitably used as a light reflector, Thus, the following description will be made with reference to the light reflector. The light reflector according to the present invention is light in weight, exhibits high total reflectance and high diffuse reflectance and has excellent heat resistance. Further, the reflector is obtainable by a simple method.

The aromatic polycarbonate resin is a polycarbonate containing (a) diol components including aromatic diol components and (b) carbonate components and is preferably of a type which is obtained from a bisphenol such as 2,2- bis (4-oxyphenyl) propane, 2, 2-bis (4-oxyphenyl) butane, 1,1- bis (4-oxyphenyl) cyclohexane, 1, 1-bis (4-oxyphenyl) isobutane or 1, 1-bis (4-oxyphenyl) ethane . It is preferred that the polycarbonate resins obtained from these bisphenols have a heat deformation temperature (in accordance with ASTM D- 648; load: 18.24 MPa (18.6 kgf/cm²)) of at least 120°C, more preferably at least 125°C, most preferably 130-170°C, for reasons of high resistance to heat, acid, weather and mechanical shocks and of excellent processability such as in cutting. The diol components of the aromatic polycarbonate resin may contain 0-25 mole % of aliphatic diol components, though the presence of such aliphatic diol components does not provide any significant merit.

Because of its good transparency, the aromatic polycarbonate resin has poor total reflectance and diffuse reflectance to visible light. When used in conjunction with an auxiliary ingredient, however, the aromatic polycarbonate resin unexpectedly exhibits excellent total reflectance and diffuse reflectance to visible light.

As the auxiliary ingredient, a synthetic resin or a synthetic rubber having a refractive index Da greater or smaller by 0.03 or more than the refractive index Dp of the aromatic polycarbonate resin is suitably used (Da Dp +

0.03 or Da ≤ DP - 0.03) . The refractive index herein is as measured in accordance with the method described in JIS K 7105. A typical polycarbonate obtained from bisphenol A has a refractive index of about 1.59. A white pigment may also be suitably used as the auxiliary ingredient.

It is preferred that the auxiliary ingredient be at least one member selected from acrylic resins, polyolefin resins, white pigments and mixtures thereof, for reasons of providing high total reflectance and diffuse reflectance of visible light even with a small amount without adversely affecting the excellent properties inherent to the polycarbonate resin such as high heat resistance, high impact resistance, high resistance to cracking and good self-extinguishing property. The acrylic resin to be used as the auxiliary ingredient is a polymer or copolymer obtained from an unsaturated compound having an acrylic group of the formula CH₂=C(R)- where R is a lower alkyl group having 1-4 carbon atoms. Illustrative of suitable unsaturated compounds are acrylic acid, acrylic acid esters, acrylamide, acrylonitrile, methacrylic acid and methacrylic acid esters. Typical examples of the acrylic resins include polymethyl methacrylate resins and polymethyl acrylate resins. The use of polymethyl methacrylate resin is particularly preferred because a tearing strength of the light reflector is prevented from being lowered so that the resistance to cracking is high. The use of the acrylic resin as the auxiliary ingredient has a merit that the amount of a relatively expensive white pigment may be saved or reduced to zero.

The polyolefin resin to be used as the auxiliary ingredient is a polymer or a copolymer of an olefin such as et ylene, propylene or butene . Illustrative of suitable polyolefin resins are polyethylene, ethylene-butene-1 random copolymers, ethylene-octene-1 random copolymers, ethylene-pentene-1 random copolymers, polypropylene, propylene-ethylene random copolymers, propylene-ethylene block copolymers, propylene-butene-1 random copolymers, propylene-ethylene-butene-1 random copolymers and polybutene. The polyolefin resin is desirably used in conjunction with a white pigment. However, when a polyethylene resin is used as the polyolefin resin, the amount of the white pigment may be saved or reduced to zero. The white pigment to be used as the auxiliary ingredient is preferably a white inorganic pigment such as titanium dioxide, calcium carbonate or silica. Titanium dioxide is particularly preferably used because even a small amount thereof can impart high total reflectance and diffuse reflectance to the light reflector. The amount of the white pigment is generally 0-20 % by weight, preferably 3-15 % by weight, based on the total weight of the composition. It is preferred that the white pigment be used in conjunction with the above-described acrylic resin and/or polyolefin resin, because the functions and effects of respective ingredients can be obtained simultaneously.

The amount of the aromatic polycarbonate resin in the composition of which the light reflecting surface of the light reflector is formed should be at least 50 % by weight, generally 50-99 % by weight, based on the total weight of the composition in order that the light reflector retain the desired properties of the aromatic polycarbonate resin such as those previously described. However, the aromatic polycarbonate resin should be used in conjunction with a quantity of the auxiliary ingredient so that the light reflecting surface of the light reflector has a total reflectance of at least 80 % and a diffuse reflectance of at least 75 % . Preferably, the aromatic polycarbonate resin is used in an amount of 55-95 % by weight. The amount of the auxiliary ingredient is generally 1-50 % by weight, preferably 5-45 % by weight, based on the total weight of the composition.

It is important that the light reflecting surface of the light reflector should exhibit a total reflectance of at least 80 % and a diffuse reflectance of at least 75 %, in order to obtain homogeneous and high reflecting light. Significantly homogeneous and high reflecting light can be obtained when the reflecting surface shows a total reflectance of at least 93 % and a diffuse reflectance of at least 90 % . The use of such a light reflector can effectively reduce consumption of electrical energy for illuminators with which the light reflector is used. Further, when the light reflector is applied to an electric sign or a light box, the distance between a light source and an illuminating surface can be reduced. This permits a reduction of the size (thickness) of the device. The light reflector according to the present invention may be a single layer body of the above composition containing the aromatic polycarbonate resin and the auxiliary ingredient. The single layer body may be prepared by kneading the aromatic polycarbonate resin and the auxiliary ingredient. The kneaded mass is then subjected to extrusion molding or injection molding to obtain a molded body in the form of a sheet, a film, a plate, a concaved plate or any other desired shape. A sheet-like molded body may be further subjected to thermoforming to obtain a desired shape. The single layer body has generally has a thickness of 0.1 mm or more, preferably 0.1-20 mm.

The light reflector of the present invention may also be a composite body having a surface layer formed of the above composition and provided on a substrate. The substrate is suitably used for improving the mechanical strengths, shape retentivity and design of the light reflector and for reducing the thickness of the surface layer. The substrate may be made of any desired material such as a plastic, a ceramic or a metal. For reasons of easiness in manufacture and lightness in weight, the substrate is preferably made of a synthetic resin, more preferably a synthetic resin foam, such as an aromatic polycarbonate resin foam. The surface layer generally has a thickness of 0.1 mm or more, preferably 0.1-5 mm, while the substrate generally has a thickness of 0.1 mm or more, preferably 0.1-20 mm. The substrate in the form of a resin foam has a thickness of generally 0.2 mm or more, preferably 0.2-10 mm.

A surface of the substrate on which the surface layer is provided is desired to be white, so that the thickness of the surface layer can be reduced while maintaining high total reflectance and diffuse reflectance of the surface layer. The use of a synthetic resin foam as the substrate is thus also preferred, because the foam is generally white when no coloring agent is incorporated therein.

The surface layer and the substrate may be composited with each other by fuse-bonding or by using an adhesive. The surface layer to be bonded to the substrate with an adhesive may be produced in the same manner as described above with reference to the single layer body. The fuse- bonding may be carried out by extruding the surface layer on the substrate. When the substrate is made of a resin or resin foam, the fuse-bonding may be performed by extruding the substrate on the surface layer or by coextruding the surface layer and the substrate. The composite body may also be produced in a mold cavity in which the surface layer is disposed and in which expanded resin particles are heated and molded to form a substrate on which the surface layer is provided.

The above-described single layer body and the surface layer of the composite body, which provide the light reflecting surface, may be a foam layer having a density of 0.05 g/cm 3 or more, preferably 0.07-1.0 g/cm3. Too small a density below 0.05 g/cm is undesirable because of low mechanical strengths.

It is preferred that the above-described single layer body and the surface layer of the composite body contain a UV-absorbing agent and/or an antistatic agent. The UV- absorbing agent can prevent the light reflecting surface from being deteriorated by UV-rays from a light source. The antistatic agent can prevent deposition of dusts on the light reflecting surface, so that the light reflector can maintain its reflectance for a long period of time. The single layer body and the surface layer of the composite body may additionally contain one or more additives such as an oxidation preventing agent, a flame retardant (with or without a synergist therefor) , and a fluorescent whitening agent . The following examples will further illustrate the present invention. Parts and percentages are by weight except otherwise indicated. Example 1 A composition containing 70 parts of an aromatic polycarbonate resin (IUPILON HR3001NR manufactured by Mitsubishi Engineering Plastics Inc.; compound of 90 % of an aromatic polycarbonate having a refractive index of 1.59 with 10 % of titanium dioxide) and 30 parts of a polymethyl methacrylate resin (ACRYPET IR-G504 manufactured by

Mitsubishi Rayon Co., Ltd.; refractive index of 1.49) was melted and kneaded in an extruder and extruded through a T- die. The extrudate was sheeted and cut to obtain a flat plate having a thickness of 1 mm.

Example 2

Example 1 was repeated in the same manner as described except that a high density polyethylene resin (IDEMITSU HD 520MB manufactured by Idemitsu Petrochemical Inc.; refractive index of 1.54) was substituted for the polymethyl methacrylate resin to obtain a flat plate having a thickness of 1 mm.

Example 3 Example 1 was repeated in the same manner as described except that a low density polyethylene resin (NUC POLYETHYLENE NS-1 manufactured by Nippon Unicar Co., Ltd.; refractive index of 1.51) was substituted for the polymethyl methacrylate resin to obtain a flat plate having a thickness of 1 mm.

Example 4

Example 1 was repeated in the same manner as described except that the sheeting condition was changed to obtain a flat plate having a thickness of 0.6 mm. Example 5

The kneaded composition of Example 1 was extruded and laminated on a previously prepared foam sheet of an aromatic polycarbonate resin (thickness: 1 mm, density: 0.28 g/cm ) at a line speed so that a surface layer having a thickness of 0.25 mm was formed on the foam sheet.

Example 6 A composition containing 70 parts of an aromatic polycarbonate resin (IUPILON H3000 manufactured by Mitsubishi Engineering Plastics Inc.; a refractive index of 1.54) and 30 parts of a high density polyethylene resin (IDEMITSU HD 520MB manufactured by Idemitsu Petrochemical Inc.; refractive index of 1.54) was melted and kneaded in an extruder and extruded through a T-die, sheeted and cut to obtain a flat plate having a thickness of 3 mm.

Example 7 Example 1 was repeated in the same manner as described except that the aromatic polycarbonate resin (IUPILON HR3001NR manufactured by Mitsubishi Engineering

Plastics Inc.; compound of 90 % of an aromatic polycarbonate having a refractive index of 1.59 with 10 % of titanium dioxide) was processed by itself to obtain a flat plate having a thickness of 1 mm.

Example 8

A composition containing 63 parts of an aromatic polycarbonate resin (IUPILON H3000 manufactured by

Mitsubishi Engineering Plastic Inc.; a refractive index of 1.54), 30 parts of a high density polyethylene resin (IDEMITSU HD 520MB manufactured by Idemitsu Petrochemical Inc.; refractive index of 1.54), 7 parts of a master batch (RE-120-80K manufactured by Polycol Color Industries Co., Ltd.; composed of 20 % of polyethylene wax and 80 % of titanium dioxide) and 0.1 part of a fluorescent whitening agent (UVITEX OB manufactured by Ciba Geigy Inc.) was melted and kneaded in an extruder and extruded through a T- die. The extrudate was sheeted and cut to obtain a flat plate having a thickness of 0.6 mm.

Example 9

Example 8 was repeated in the same manner as described except that 1 part of an antistatic agent (PC-3 manufactured by Kao Coporation) was additionally incorporated into the composition, thereby obtaining a flat plate having a thickness of 0.5 mm.

Example 10

Example 9 was repeated in the same manner as described except that 3.75 parts of a flame retardant (decabromodiphenyl ether) and 1.5 parts of a synergist for the flame retardant (antimony trioxide) were additionally incorporated into the composition, thereby obtaining a flat plate having a thickness of 0.6 mm.

Comparative Example 1

A composition containing 70 parts of an aromatic polycarbonate resin (IUPILON H3000 manufactured by

Mitsubishi Engineering Plastics Inc.; a refractive index of 1.54) and 30 parts of a polystyrene resin (IDEMITSU STYROL HH32 manufactured by Idemitsu Petrochemical Inc.; refractive index of 1.58) was melted and kneaded in an extruder and extruded through a T-die, sheeted and cut to obtain a flat plate having a thickness of 1 mm.

Each of the plates thus obtained was measured for total reflectance, diffuse reflectance, gloss and illuminance in the manner described below. The results are summarized in Table 1. Total Reflectance and Diffuse Reflectance

Reflectance is measured with a recording spectrophotometer (UV-2200 manufactured by Shimadzu Corporation) equipped with an integrating sphere attachment (ISR-2200 manufactured by Shimadzu Corporation) at a wavelength of 550 n . The total reflectance is measured with an incident angle of 8°, while the diffuse reflectance is measured with an incident angle of 0°. The reflectance of each sample is indicated in terms of a percentage based on the reflectance of a standard plate (white plate of barium sulfate powder) mounted on the integrating sphere attachment. The standard plate is prepared by filling and pressing barium sulfate powder (Product No. 022-00425, Lot No. PAR2142; manufactured by Wako Pure Chemical Industries Ltd.) in a cavity of a sample holder of the attachment using a glass rod. Gloss

Gloss is measured for "60° mirror surface gloss" in accordance with Japanese Industrial Standard JIS K7105 using a gloss meter (GLOSSMETER PG-3D manufactured by

Nippon Denshoku Industries Co., Ltd.) . Each value shown in Table 1 is an arithmetical mean of measured values at 6 different points on the sample including 3 arbitrary points aligned in the extrusion direction and 3 arbitrary points aligned in the direction normal to the extrusion direction. Illuminance

A light box for observing an X-ray photograph (SHAUKASUTEN KSA211 manufactured by Kihara Medical Industry Co., Ltd.) is used. The light box includes a steel casing (size: length: 625 mm, width: 495 mm, depth: 110 mm) having inside bottom and side walls (painted white) . The front top of the casing is provided with a translucent milky white display plate made of an acrylic resin (size: 565 mm x 425 mm) . Four (4) elongated fluorescent lamps (each 15 W) are accommodated in the light box for illuminating the display plate.

In measurement, sample plate is fixed with an adhesive tape on the bottom of the light box and lamps are put on. Illuminance at 35 points on the surface of the display plate is measured with an illuminance meter (ANA-F9 LUX METER) . The 35 measured points include 20 points just above the lamps (5 equally spaced apart points on each of the 4 lamps) and 15 points above the center of two lamps (5 equally spaced apart points above the centerline between each of the two adjacent lamps) . An average of the illuminance of the 35 points is calculated (average illuminance) . The difference R between the maximum illuminance and the minimum illuminance among the 35 measured values is also calculated.

Comparative Example 2

A mirror was measured for total reflectance, diffuse reflectance, gloss and illuminance in the manner described above. The results are summarized in Table 1.

*1 unable to measure

Claims

1. A shaped body having a light reflecting surface of a composition comprising (a) at least 50 % by weight of an aromatic polycarbonate resin, and (b) an auxiliary ingredient in such an amount that said light reflecting surface has a total reflectance of at least 80 % and a diffuse reflectance of at least 75 % .

2. A shaped body as set forth in claim 1, wherein said auxiliary ingredient is at least one member selected from acrylic resins, polyolefin resins, white pigments and mixtures thereof.

3. A shaped body as set forth in claim 2, wherein said polyolefin resins are polyethylene resins.

4. A shaped body as set forth in claim 1, wherein said auxiliary ingredient is present in an amount of 5-50 % by weight .

5. A shaped body as set forth in claim 1, comprising a substrate and a surface layer provided on said substrate, said surface layer being formed of said composition and providing said light reflecting surface.

6. A shaped body as set forth in claim 5, wherein said substrate is a foam layer of an aromatic polycarbonate resin.

7. A shaped body as set forth in claim 1, wherein said light reflecting surface has a total reflectance of at least 93 % and a diffuse reflectance of at least 90 % .

8. The use of a shaped body according to any one of preceding claim as a light reflector.