JPS5896593A - Optical recording medium - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical recording medium, and more particularly to an optical recording medium having a cover structure that improves recording sensitivity.

US Pat. No. 4,097,895 discloses an ablative optical recording medium for use in optical recording systems. A focused modulated light beam, such as a laser, having a predetermined output frequency is projected onto the recording medium. The "light" used in optical recording techniques includes near-infrared and ultraviolet regions. The recording medium of the above-mentioned US patent includes a layer of material that is reflective at the laser output frequency and an overlying layer of material that is absorbent at the output frequency. The thickness of the absorption layer is advantageously chosen such that as much as possible of the incoming optical energy M incident on the optical recording remains therein and is converted into thermal energy V. This thermal energy ablates the absorbing material in the areas where it absorbed the laser beam energy, exposing selected portions of the reflective layer. The recorded information is reproduced by sensing the light-absorbing pattern recorded on this medium.

In order to eliminate or reduce signal defects or omissions caused by surface dust deposited on the medium from the outside world, a thickness of approximately 0.05 mm is applied over the absorbing layer as described in U.S. Pat. No. 4,315,269. ~1 inch overcoat layer can be applied. Dust particles and other surface contaminants that settle on the top surface of this overcoat are far away from the focal plane of the recording lens, so their effect on the recorded or reproduced signal is significantly reduced.

No. 4,300,143 discloses providing a thin protective overcoat over the absorbent layer.

This protective layer must be hard and impermeable to atmospheric chemical components, such as oxygen and moisture, that may attack the absorbing layer. Advantageously, this thin protective overcoat can be cleaned to remove dust and other contaminants adhering to its surface.

U.S. Pat. No. 4,101,907 discloses an optical recording medium in which an absorbing layer is covered with a barrier layer, which is further covered with a thick overcoat layer. The barrier layer is generally comprised of the same type of material as in the above-mentioned US Pat. No. 41,300,143 when the protective overcoat is thin, i.e., impermeable to atmospheric components such as oxygen and moisture that could attack the undercoat. - The thick overcoat layer is similar to that of US Pat. No. 4,315,269.

These protective structures have drawbacks. A thin protective coating prevents dust particles from coming out of the focal plane, so it must be cleaned frequently, and when humidity is high, many of the dust particles adhere strongly to the surface, making normal cleaning difficult. It cannot be removed by law. Also, such a hard protective layer can reduce both the recording sensitivity of the optical recording medium and the signal-to-noise ratio of the information recorded thereon. The strength of a thin protective layer may interfere with the ablative recording medium and adversely affect the above properties.

The preferred material for the thick protective overcoat of U.S. Pat. No. 4,315,269 is silicone resin. Because materials such as silicone resins can be permeable to ambient components such as moisture and oxygen, such thick protective overcoats do not provide an adequate protective barrier and can degrade underlying layers such as absorbent layers. This may lead to a decrease in sensitivity or deterioration of the reproduced signal representing the recorded information. Moreover, the recommended material for this thick overcoat has a tendency to attract so much dust particles that it can actually render the overcoat opaque.

The solution in the above-mentioned US Pat. No. 4+315,269 to the problem of lack of impermeability of thick protective layers is to insert a barrier layer between this thick overcoat layer and the absorbent layer, but the absorbent layer is not coated. The above-mentioned disadvantages regarding the applied hard layer still remain.

Therefore, the optical recording medium has high sensitivity and a high signal-to-noise ratio of the reproduced signal representing the recorded information, has recording protection properties such as resistance to ambient components such as oxygen and moisture, dust and scratching action, and does not have the above-mentioned drawbacks. is desired.

The inventor of the present invention has discovered an optical recording medium in which an intermediate layer is provided between an absorbing layer and an outer transparent layer, which does not substantially inhibit the ability to record information in the absorbing layer and acts as a barrier layer against moisture, oxygen, etc. . The combined thickness of the intermediate layer and the outer cover layer is preferably selected such that dust particles, scratches, etc. on the outer cover layer do not impede the recording performance of the medium.

Next, this invention will be explained with reference to the drawings. FIG. 1 is a cross-sectional view of a first optical recording medium lO before recording, and this medium is made of a reflective material that is part of the optical recording system as described in the above-mentioned US Pat. No. 4.09'7.895. Contains 2. This reflective material 2 can be in the form of a layer or a substrate, for example a gold or aluminum layer on a plastic substrate. This reflective material 2 can also be an aluminum substrate. The reflective material 2 is covered with an absorption layer 4 which is absorbent at the output frequency of the laser. This absorbing layer number can be applied by sputtering, vacuum deposition, spin coating, or any other known method. Materials that can function as the absorption layer 4 include metals such as bismuth and tungsten.

Polymeric resins Electri, c mixed with various inorganic materials such as chalcogonia, organic materials such as 4-phenylazo-1-naphthylamine, and materials absorbing at the output frequency.
) RTV 615, RTV, ao2 and Dow Corning (DV
There are silicone resins such as A/Silguard. For example polyurethane or thio:I-tv
(Th1okol) Various acrylic resins such as Floo are also suitable. The thickness of the intermediate layer 6 is at least 5μ
is preferred. If this layer is too thin, the hard outer layer 8 may affect recording.

The outer layer 8 covers the intermediate layer 6 and acts as a barrier layer to exclude atmospheric components such as oxygen and moisture that could chemically degrade the underlying layer. The material of type 4 can be used as the outer covering layer 8, but for example, a hard and thin material such as S102 can be used as the intermediate layer 6.
It is better to have something that can be made thicker. However, the jacket layer 8 can also be made of a polymeric material that is relatively strong and can act as a barrier to atmospheric contaminants. Such polymeric materials include, for example, epoxy resins, polyurethane resins such as UV curable polyurethane commercially available as Thiokol 922, or vapor deposited polymers such as poly(p-xylylene). The total thickness of the outer layer 8 and the intermediate layer 6 is approximately 100 mm.
-1000μ is preferred. The outer layer 8 should adhere well to the intermediate layer 6 and should not substantially affect the recording sensitivity.

FIG. 2 is a cross-sectional view of the first optical recording medium 10 after recording. Pores 12 are created in the absorbing layer as a result of ablation during recording, exposing the underlying reflective material 2.

Although only one pore 12 is shown in FIG.

It should be understood that in reality, multiple such pores exist. The intermediate layer 6 must be sufficiently flexible to allow this pore formation.

The mechanism of ablation depends on the composition of the absorbent layer, but melting and evaporation are common. Optical recording media in which recording is performed by bleaching the areas exposed to the laser recording beam can also advantageously utilize this invention in which an intermediate layer and an overcoat layer are applied to the absorbing layer.

The recorded information can be reproduced using a laser with the same output frequency as the recording laser but with reduced power. Information is reproduced by converting the light-absorbing and light-reflecting patterns into electrical signals.

FIG. 3 is a sectional view of the second optical recording medium 20 of the present invention. In this second optical recording medium 2o, a number of component layers 14, 16, 18 serve as a composite jacket layer 22. Multilayers can thus be constructed of one or more layers. Solving the often difficult problem of obtaining a single material that is relatively non-adhesive to dust particles, easy to handle, and capable of acting as a barrier to oxygen, moisture, and other highly corrosive atmospheric components For this purpose, layer 14.16.18 may be used as composite jacket layer 22. For example, the first component layer 14 is selected to be an effective barrier to moisture, the second component layer 16 overlying the first component layer 14 is selected to be an effective barrier to oxygen, and the second component layer 14 is selected to be an effective barrier to oxygen. The third component layer 18 overlying the component layer 16 may be selected to be easy to handle and not to attract or retain dust particles. Although it is of course preferable to have a smaller number of component layers, this invention includes multi-component layers.

US Pat. No. 4,216,501 discloses an ablative three-layer optical recording medium in which an intervening layer is provided between a reflective layer 4 and an absorbing layer 20. This intervening layer is transparent at the output frequency of the laser. The feature is that the thickness of the absorbing layer is such that the thickness of the intervening layer and the optical constants, that is, the refractive index and absorbance of the reflective material 2, the intervening layer and the absorbing layer 4, reduce the light reflectance of the recording medium. It has become. Such an intervening layer is advantageously included in the present invention.

U.S. Pat. No. 4,097,895 discloses an ablative optical recording medium comprising a reflective material coated with an absorbing layer. Although in this patent the thickness of the absorbing layer is chosen so as to reduce the reflectivity of the recording medium.

Such a structure also has the advantage of being included in the present invention.

For example, the reflection prevention and other reflection reduction conditions under the above-mentioned U.S. Pat. FIG. 2 is a sectional view of the first optical recording medium after recording, and FIG. 3 is a sectional view of the second optical recording medium.

2... Reflective material, 4... Absorption layer, 6... Intermediate layer, 8.22... Outer layer.

Claims (1)

[Claims] (1) A material that is reflective at a certain output frequency of the recording laser, and an absorbing layer that is absorbent at the predetermined frequency, with a reed on top of the material, and the material is covered with the absorption layer and at the output frequency an intermediate layer that is essentially transparent and does not substantially affect the recording sensitivity of the absorbing layer; 1. An optical recording medium for a laser, comprising a coating layer.