JPS632129A - Protection film for optical information recording medium - Google Patents

Abstract

PURPOSE:To suppress the write/read error of information to a degree as long as it suits for practical use by using the titled film having a surface smoothness in which the Hays value is <=0.7%, the average surface coarseness of a face provided with a metallic thin film layer is <=0.006mu, and the height of multiple interference projections on the surface being >=0.6mu is susbstantially zero. CONSTITUTION:The Hays value of the protection film for an optical information recording medium is <=0.75, the average coarseness of a face provided with the metallic thin film layer is <=0.006mu and the film has the smoothness in which the height of the multiple interference projections on the surface >=0.6mu is substantially zero. In the optical information recording medium formed by using the said film, a light such as a laser beam reaches the recording spot correctly to attain write and the light for read is returned to a read head without being reflected irregularly. Thus, the error rate in case of information read/write is suppressed in the order of 10<-5>, and the medium is sufficient for practical use.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention [Field of Industrial Application] The present invention relates to a protective film for an optical information recording medium in which necessary information is written and read by optical recording and reproducing means.

[Prior art] For example, a thin film of a low-melting point metal such as tellurium or bismuth is provided on a base material, and a part of the thin film is changed by irradiation with a laser beam to record the information. There is an optical recording and reproducing technology that performs optical reproduction. The advantage of optical recording and reproducing technology is that the recorded information density and therefore the amount of information that can be handled is higher than that of conventional magnetic recording and reproducing technology, and
This is dramatically larger than that using C.

Therefore, attempts are being made to apply optical recording and reproducing technology to various types of cards in addition to optical discs.

Of course, when using optical information recording media such as optical discs and optical cards, it is necessary to avoid errors in writing and reading information. There are various causes of errors, one of which is the unevenness of the metal thin film layer that serves as the optical recording medium.

The smoothness of the metal thin film layer depends on the smoothness of the substrate or protective film to which it adheres, especially in the case of reflectively readable types. If we try to produce 1 q of protective film with the smoothest possible surface, various restrictions on the material and processing method are inevitable, and the cost will be high. This will put a brake on the spread of information recording media.

Therefore, the inventors conducted repeated research in an attempt to manufacture optical recording media at a low cost by controlling the error rate to an acceptable limit. -Generally, the error rate in optical recording is 10-
It is said that if the number of units is kept to five, there will be no practical problem. The present invention was achieved by establishing the limits of permissible unevenness from a different perspective and the smoothness of the protective film that provides this.

[Problems to be Solved by the Invention] An object of the present invention is to provide an optical information recording medium, such as an optical disk or an optical card, in which errors in writing and reading information can be suppressed to a practical limit. Our goal is to provide protective films for

Structure of the Invention [Means for Solving the Problems] The protective film for optical information recording media of the present invention is provided with a metal thin film layer for recording optical information on one side of a transparent plastic film. The protective film for optical information recording media that constitutes the medium has a haze value of 0.7% or less and an average roughness of 0.006μ on the surface on which the metal thin film layer is provided.
or less, and the height of the multiple interference protrusions on the surface is 0.6
It is characterized by having such smoothness that the value of μ or more is substantially zero.

A polyimide film formed by a solution casting method is optimal as a protective film that ensures the characteristic values under the above conditions. A suitable thickness is approximately several microns to 800 microns. Other preferred examples of protective films include films of polyimide resin such as polyether sulfon formed by extrusion, stretched polyamide films formed by stretching after extrusion, and acrylic resins and polycarbonate formed by polymer casting. There are films made of resin, etc.

The haze value is measured by the method specified in JIS-6714.

Average aging is measured using an aging meter.

For multiple interference protrusions, optical unevenness in the thickness direction is measured using an interference microscope.

[Function] Since the protective film for an optical information recording medium of the present invention has the smoothness of the characteristic value described above, an optical information recording medium formed using the same can be used to ensure that light such as a laser beam correctly reaches the recording spot. The reading light returns to the reading head with almost no diffused reflection.

Therefore, the error rate when writing or reading information can be reduced to 1
It can be kept to 0-5 units, and there is no practical problem.

(Example 1) Polyimide resin was dissolved in dimethylacetamide and 1
A 5% solution was cast on a glass plate with good flatness, and after drying at a temperature of 150° C., the cast layer was peeled off to obtain a polyimide film with a thickness of 25 μm.

The haze value of this polyimide film is 0.5%, the average roughness of the surface in contact with the glass plate is 0.006μ, and the height of multiple interference protrusions exceeding 0.6μ is within a 1m” area. was zero.

A tellurium layer having a thickness of 0.3 μm was formed on the polyimide film in contact with the glass plate by vacuum deposition.

On the other hand, a sheet was prepared in which the front surface of a 300 μm thick white rigid polyvinyl chloride sheet was printed by offset printing, and a magnetic stripe was provided on the back surface by a transfer method.

The surface of this sheet and the tellurium layer of the polyimide film were bonded together via an acrylic resin heat-sensitive adhesive so as to face each other, and the sheet was pressed using a hot roll with a surface temperature of 110°C to obtain an optical card material. Ta.

This material was punched using a punching mold to produce an optical card.

Next, when 1 Mbyte of information was written on this optical card, read, and compared with the original information, the error rate was 5×10 −5 .

[Example 2] A polyamide resin was extruded and stretched to prepare a stretched polyamide film having a thickness of 50 μm.

The haze value of this film is 0.6%, the average roughness of the - side is 0.006μ, and the height of the multiple interference protrusions is 0.6%.
There were zero cases of μ or more in 1 and 2 cases.

Thereafter, an optical card was manufactured in the same manner as in Example 1, and when 1 Mbyte of information was written and read on it, the error rate was 8×10'.

Effects of the Invention If an optical information recording medium such as an optical disk or an optical card is formed using the protective film for an optical information recording medium of the present invention, errors in writing or reading information will be within a limit that does not pose a practical problem. Because this protective film can be provided at a low price,
The uses of optical recording media can be greatly expanded and popularized.

Claims (1)

[Claims] In a protective film for an optical information recording medium that constitutes an optical information recording medium by providing a metal thin film layer for recording optical information on one side of a transparent plastic film, the metal thin film layer has a haze value of 0.7% or less. 1. A protective film for an optical information recording medium, characterized in that the average roughness of the surface provided with is 0.006 μm or less, and the number of multiple interference protrusions on the surface having a height of 0.6 μm or more is substantially zero.