JPS60219028A - Thermoplastic resin sheet for compact disk - Google Patents

Abstract

PURPOSE:To manufacture the above stated resin sheet of less optical anisotropy and suitable to manufacture a compact disk with a press method of low cost by extruding together a thermoplastic resin and another thermoplastic resin which is non-adhesive to the former in a condition in which the both sides of the former are coated with the latter. CONSTITUTION:A thermoplastic resin (hereinafter called ''A'') for a compact disk substrate which is used as a core layer, and, further, another thermoplastic resin (hereinafter called ''B'') which is non-adhering to the resin ''A'' and used as an outer layer, are extruded together in a form in which both sides of the resin ''A'' is coated with the resin ''B'', and subsequently, under a normal condition, the layers of the resin ''B'' are stripped off, and an object sheet consisting of the resin ''A'' with a retardation value of less than 100mum is obtained. Additionally, the use of vinyl chloride resin composite etc. for the resin ''A'' is recommendable, and in such a case, the use of low density polyethylene for the resin ''B'' is recommended.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extruded thermoplastic resin sheet with low optical anisotropy for use in compact discs.

Compact discs have excellent features such as low noise, good sound reproduction, can be made compact, and can be used for long recording times, and have been used in place of conventional LP records and cassette tapes. Compact discs are made of polycarbonate, and are made by injection molding or injection combination molding, and there are problems such as deformation of the audio signal due to the molding stress at the time of injection molding, and the yield is low. , the cost is high.

Therefore, methods for manufacturing compact discs that are cheaper to manufacture are being considered, and a pressing method has been proposed as one of them, but there is no suitable thermoplastic resin sheet with low optical anisotropy. Development has been delayed.

In view of the above-mentioned circumstances, the inventors of the present invention have conducted intensive studies to produce a thermoplastic resin sheet with low optical anisotropy for use in compact discs, and have found that if thermoplastic resin is extruded using a specific manufacturing method, it can be used for the above-mentioned purposes. It has been discovered that a thermoplastic resin sheet with low optical anisotropy suitable for use can be produced, and the present invention has been achieved.

That is, the present invention provides a compact disk with a shear retardation value of 100 mμ or less, which is produced by co-extruding a thermoplastic resin and a non-adhesive thermoplastic resin in a state where both sides are coated. It is an extruded thermoplastic resin sheet.

The thermoplastic resin sheet for compact discs of the present invention is
It is an extruded thermoplastic resin sheet with low optical anisotropy.
Its retardation value (hereinafter referred to as R value) is 10
It is 0 mμ or less, more preferably 50 mμ or less. The R value is a unit expressing the birefringence of a film, and is expressed as the product of the thickness d of the film and the absolute value In, - nJ of the difference between two refractive indexes in the direction perpendicular to the film.

R=dln, -nLl where nl is a refractive index in an arbitrary direction, and n4 is a refractive index in a direction orthogonal to nl.

If the R value exceeds 100 mμ, the noise will increase when used as a base for a compact disc, which is undesirable.

This sheet is manufactured by using a thermoplastic resin for compact disc substrates (hereinafter referred to as resin A) as the core layer, and using resin A as the core layer.
This is achieved by co-extruding a non-adhesive thermoplastic resin (hereinafter referred to as resin B) as an outer layer, and a thermoplastic resin sheet with a desired small R value is obtained in the central core layer.

The thermoplastic resin used as resin A in the present invention is a thermoplastic resin with good transparency, such as vinyl chloride resin composition, polyamide, polyester, polycarbonate, polymethyl methacrylate, methyl hemp resin,
Examples include ionomer resin, polyether sulfone, polyphenylene sulfide, and the like. Among these, vinyl chloride resin compositions and polycarbonates are preferred.

In addition, resin B is a resin that can be easily peeled off after multilayer coextrusion with resin A. As a combination of resin A and resin B, for example, if resin A is a vinyl chloride resin composition, resin B is a resin that can be easily peeled off. low density polyethylene, high density polyethylene,
Examples include combinations with polypropylene, polystyrene, cellulose resins, etc. In this case, the combination with low-density polyethylene is particularly advantageous in obtaining the sheet of the present invention because the extrusion temperatures of both resins are close, making coextrusion easy. Other general combinations of resins can be found, for example, in the literature such as Plastic World, January 1980 issue, page 58.

The ratio of resin A layer to the total thickness in the coextruded sheet is 9
It is preferably 0% or less. If the ratio exceeds 90, optical anisotropy may occur in the resin sheet, which is not desirable.

It is not necessary to use only one type of resin B for both surface layers, and different resins may be selected for both surface layers.

Furthermore, the number of layers may be increased instead of three. For example, C.B.A.
A combination like B(C) or a combination like BABAI3 is also possible.

The core layer sheet of the present invention not only has the characteristic of not having optical anisotropy, but also has both surface layers that function as a protective film, so it can prevent the adhesion of dust, etc. This is advantageous for use with compact discs, which are disliked.

The thermoplastic resin notebook of the present invention is pressed with a press equipped with a stamper to transfer the fine pits of the stamper, and then undergoes the processes of reflection formation, protective film coating, and label printing, and is then pressed into a compact disc. It is said that

The present invention will be explained below with reference to Examples.

Example-1 Using a 65 mmφ, 4-layer mmφ extruder, a 2-type, 3-layer type feed block, a coat hanger type T-die, and a cooling rowope take-off machine, a vinyl chloride resin composition (Mitsui Vinicron 4000LL [Trademark]
Contains stabilizers. It is abbreviated as PVC under μ. ),
Low-density polyethylene (8 stones, Xuron F-41C trademark) from the 40 order φ extruder side. Hereinafter abbreviated as L D P E -1
゜）Wo supply, LDPE/PVC/LDPI layer 0.7
/ 1,1 / 0.7 Dragon multilayer sheet was extruded.

The conditions are that the resin temperature is 170°C for both PVC and Ll)l)E.
The sheet take-up speed is 0.5 m/mouth]in.

Next, the ILDPE notebook was peeled off from the multilayer sheet, and the adhesive strength of the obtained sheet was measured using a polarizing microscope equipped with a belenok convencator manufactured by Orinhas Optical Co., Ltd., and found to be 40 Illμ.

Next, a compact disc was made from this sheet using a conventional method, and its performance was evaluated, and it was confirmed that a compact disc with good performance and low noise could be made.

Comparative Example 1 The vinyl chloride resin composition of Example 1 was extruded from a 65 mrnφ extruder to obtain a sheet with a thickness of 1.1 strips. This material had a large turbulence value of 150 m.mu., and could not be used as a substrate for compact discs.

Example-2 LDPE/PC/LDPE=0,7 in the same manner as in Example-1 except that polycarbonate (hereinafter referred to as PC) was used instead of vinyl chloride resin in Example-1.
Extruding a multilayer sheet of /1.010.7mm, Example-
In the same manner as in 1, we measured the PC sorting adhesive strength value and produced a prototype compact disc, and evaluated its performance as 1-.The PC sheet adhesive strength value was 45 mμ, and we made it from the sheet. Compact disc performance was good.

Note that the PC extrusion temperature was 300°C.

patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] (1) Heat for compact discs with a tarpaulsion value of 100 mμ or less, characterized in that they are manufactured by coextruding a thermoplastic resin with both sides covered with a non-adhesive thermoplastic resin. Plastic resin extrusion sheet. (2) The sheet according to claim 1, wherein the thermoplastic resin is a hard vinyl chloride resin composition. (3) The sheet according to claim 1, wherein the thermoplastic resin is polycarbonate.