JPS60184821A - Optically non-anisotropic thermoplastic resin sheet - Google Patents

Abstract

PURPOSE:To obtain an optically non-anisotropic thermoplastic resin sheet by arranging a thermoplastic resin sheet extrusion molded to have a specified double refraction. CONSTITUTION:Three layers of thermoplastic resins non-adherent to each other are extruded together to obtain a core layer as a thermoplastic resin sheet with the double refraction of under 8X10<-5> in the final form. The resin A for the core layer herein used is preferably a vinyl chloride resin composition as a transparent resin. The thermoplastic resin B for the surface layer (protective layer) sandwitching the core layer herein used is preferably a low-density polyethylene. The use of the vinyl chloride resin component as the thermoplastic resin A facilitates the simultaneous extrusion in the combination with the low-density polyethylene because the extrusion temperature of both the resins are close to each other. As the sheet as the core layer is characterized by being optically non-anisotropic, addition to the non-adherent resins used in both the surface layers, there is no possibility of developing optical anisotropy due to peeling. Or as both the surface layers function as a protective film, this can prevent the attaching of dirts or the like thereby making it advantageous for the use in the field extremely vulnerable to dirts, for example, optical recording material.

Description

[Detailed description of the invention] Regarding

In recent years, optical recording has begun to be put into practical use due to its high recording density, fast recording and reading speeds, non-contact retrieval of records, and excellent durability. Therefore, a light-transmissive resin sheet is used. This resin sheet is required to have little optical anisotropy.

That is, since optical recording uses polarized light such as a laser, if the resin sheet has optical anisotropy, for example, the amount of light measured when reading the record will fluctuate, resulting in large noise and significantly reducing accuracy.

Therefore, it is desired to provide a light-transmitting resin sheet for use in optical recording that has less optical anisotropy. A method for manufacturing a sheet with low optical anisotropy is the so-called casting method, in which a thermoplastic resin is dissolved in a solvent and cast on a substrate. The anisotropy occurs irregularly, it is difficult to obtain a sheet with uniform optical anisotropy, and the manufacturing cost is high, so its uses are limited.

On the other hand, sheets obtained by calender molding or extrusion molding have large optical anisotropy, and are not currently used as optical recording materials.

The present inventors have arrived at the present invention as a result of intensive studies on thermoplastic resin sheets that are inexpensive and have little optical anisotropy.

That is, the present invention is an extrusion-molded thermoplastic resin sheet having a birefringence of 8X'10' or less and having no optical anisotropy.

In the present invention, it is necessary that the birefringence is 5xio' or less, preferably 5x10-5 or less, and 8x1
If it exceeds 0, the amount of light measured when reading the record will fluctuate, resulting in large noise, making it impossible to use it for optical recording because it will be difficult to match the direction of birefringence.

This molding method is based on Japanese Patent Application No. 58-148140, and its feature is that six layers of mutually non-adhesive thermoplastic resin are coextruded, and the final core layer has a birefringence of s x io". ”5
The point is that it can be obtained as a sheet of the following thermoplastic resin.

Thermoplastic resins that can be used in the present invention include vinyl chloride resin compositions, polymethyl methacrylate, polystyrene, ABS resins, cellulose resins, polyethylene, polypropylene, acetal resins, polyamides, polyesters, polycarbodies, polyphene, etc. Examples include thermoplastic resins such as nylene oxide, polysulfone, methylpentene resin, ionomer resin, polyether sulfone, polyphenylene sulfide, and high nitrile resin.

Among these, resin A for the core layer includes transparent resins such as vinyl chloride resin compositions, polymethyl methacrylate,
Preferred are polystyrene, polyester, polyamide, polycarbonate, cellulose resin, and the like.

Resin B for the surface layer (protective layer) sandwiching the core layer is also selected from the above thermoplastic resins, but the combination of thermoplastic resin A and thermoplastic resin B is a combination that can be easily peeled off after multilayer coextrusion. For example, if thermoplastic resin A is a vinyl chloride resin composition, thermoplastic resin B is low density polyethylene, high density polyethylene, polypropylene,
Examples include combinations with 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 publications such as Plastic World, January 1000 issue, page 58.

The ratio of A to the total thickness of the coextruded sheet is preferably 90% or less. If the ratio exceeds 9%, optical anisotropy may occur in the thermoplastic 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.

Combination is also possible.

The core layer sheet of the present invention not only has the characteristic of not having optical anisotropy, but also has non-adhesive resin on both surface layers, so there is no risk of optical anisotropy due to peeling ( Also, since both surface layers function as protective films, it is possible to prevent the adhesion of dust, etc., and it is advantageous for use in fields where dust is extremely averse, such as optical recording materials.

The sheet of the present invention takes advantage of its low optical anisotropy and can be advantageously used in various optical recording materials and other fields.

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

Example-1 Using a 65+++a, 40ia51 extruder, a 2-type 6-layer feed block, a coat hanger type T-die, a cooling roll, and a take-up machine, a 65+++ extruder was used to extrude the vinyl chloride resin composition (from the machine side). Mitsui Vinicron 4000LL (trademark) mixed with a stabilizer.Hereinafter abbreviated as PVC.)
, LDPE/PVC/LDPE-○, 3
/ 0.4 / 0.3 ms multilayer sheets were extruded. The conditions are that the resin temperature is 170'C for both PVC and LDPE.
, the sheet take-up speed is 1 m/-.

Next, the LDPE sheet was peeled off from the multilayer sheet, and the birefringence of the obtained sheet was measured using a polarizing microscope equipped with a Pelle and Kucompensator manufactured by Olympus Optical Co., Ltd.
It was X 10-5.

Actual example-2 In Example-1, the xenyl chloride resin composition was used in polystyrene (1-Boresox 555 (trademark), hereinafter abbreviated as PS), and the low-density polyethylene was used in polypropylene (Mitsui Norprene JS-G). Example-1 except for changing to (commercial)
In the same way as above, I created a 1) S sheet with a bet of 0.4. When the birefringence of this PS sheet was measured, it was 2 x 10-
It was 5.

Comparative Example-1 The vinyl chloride resin composition used in Example-1 was extruded under the same conditions as Example-1 using the 65mxl extruder, T-die, cooling roll, and take-off machine used in Example-1. ,0
．． A PVC single layer sheet with a thickness of 4 ms was obtained.

The birefringence index of the obtained PVC sheet was measured in the same manner as in Example 1, and was found to be 5XlO', and this sheet could not be used for optical purposes.

patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Scope of Claims] 1) A sheet of extruded thermoplastic resin having no optical anisotropy and having a birefringence of 8 x 10-5 or less. 2) A non-adhesive thermoplastic resin sheet with which the thermoplastic resin is bonded. 6) Sheet according to claim 1, which is coextruded into a sheet with both sides coated with resin and has protective layers on both sides; 6) The core layer is a vinyl chloride resin composition, and both sides are coated. The sheet according to claim 2, wherein the layer is made of low density polyethylene.