JPH02122984A - Optical information recording medium and recording method - Google Patents

Abstract

PURPOSE:To contrive a single-plate structure with a smaller thickness while maintaining high sensitivity and high C/N by causing a light-reflecting layer to comprise a coloring matter film having a peak of light reflectance in the vicinity of the wavelengths of recording and reproducing lights, and specifying the film thickness of the light-reflecting layer at a value at which the film thickness-dependent reflectance at the wavelengths of recording and reproducing lights is maximized. CONSTITUTION:Upon irradiation with laser light, heat is generated more strongly, and mixing or dissolution of materials occurs at the interface between a light-absorbing layer 6 and a light-reflecting layer (coloring matter film) 3, whereby the clear interface is lost, snd an interference structure is broken. This causes a partial lowering in reflectance, resulting in recording. The light-reflecting layer, which reflects the laser light and is capable of recording information therein through some optical change effected by intense irradiation with laser light, comprises a croconium-type dye or the like as a main constituent. The film thickness of the light-reflecting layer is set at such a value that the reflectance of the layer is maximized at the wavelength of the light used. The value is determined depending on the birefringence of the light-reflecting layer, and is not determined unconditionally, but is preferably about 100Angstrom to 10mum. The light-absorbing layer is provided by use of a material which is of substantially the same kind as the material for the light-reflecting layer but which is superior to the material for the light-reflecting layer in light-absorbing capability at the wavelength of a recording light.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improved optical information recording medium and recording method that can be used in the optical recording field.

[Problems to be solved by conventional techniques and inventions] In recent years,
Optical information recording media such as optical disks are attracting attention because of their large capacity, high density storage, non-contact recording and playback, and ease of access.
It is applied to various information devices such as backup memory, still image/video files, etc.

The following types of optical information recording media have been proposed so far:

(a) A low melting point metal thin film is used for the recording layer. (b) A two-layer structure recording layer consisting of a reflective film and an organic light absorption layer is used. (c) A high reflectance organic dye film is used for the recording layer. The recording medium of the above (,) type is made of low melting point metal T.

The recording layer is composed of a thin film mainly composed of
There are a hole-drilling type and a phase change type that utilizes the change in reflectance associated with the phase transition between delivery and amorphous. This type of recording medium has disadvantages such as poor storage stability, hole-punched type media with low resolution and low recording density, and phase change type media with difficult manufacturing conditions and high cost.

In the recording medium of type (b) above, an organic light absorbing layer is provided by coating on a metal reflective film, and information is recorded by irradiating the organic light absorbing layer with a laser beam to create depressions. This type of recording medium is difficult to manufacture because the recording layer has a 2,11 structure in which an organic absorption layer is laminated on a metal reflective film, and the metal reflective layer is not deformed or altered by light or heat. The disadvantage is that recording and reproducing from the board side is difficult because it is held in place.

The recording medium of type (c) above has an organic dye thin film with high reflectance provided on a substrate as a recording layer. Organic dye thin films have high melting points, high decomposition temperatures, and low thermal conductivity, so they can be expected to have high sensitivity, high C/N ratio, and high reliability.Also, since thin films can be formed by coating, they are suitable for mass production and are low cost. It has the advantage of being expected to increase However, if this type of recording medium does not have an air sandwich structure, the sensitivity and C/N will drop significantly. For this reason, it is difficult to reduce the thickness of the medium, making it difficult to create a single-plate structure or apply it to optical floppies. This also applies to the perforated recording medium of type (a) above and the recording medium of type (b) above.

On the other hand, optical disk files were first commercialized using optical disks with a diameter of 30 mm, and later on 20 mm.

The diameter gradually becomes smaller with the 13-inch type, and there are signs that it will eventually shift to the 9-inch type. This is an attempt to make drives smaller and expand the market for personal use. Despite this trend toward miniaturization, the conventional air sandwich structure has a disk substrate thickness of 1.
In the case of 2n+m, it is very difficult to reduce the overall thickness to 3cm or less.

This is because the conventional punch-type optical disc has a configuration of l, l + substrate/recording/air, and the air acts as a heat insulator, increasing thermal efficiency and preventing evaporation of the recording layer during recording. , does not suppress decomposition and scattering,
High sensitivity and high C were able to be maintained.

If a protective layer or the like is provided in place of this air layer, the sensitivity and C/N will immediately drop.

In view of the above-mentioned problems of the prior art, the present invention provides high sensitivity, high C.
An object of the present invention is to provide an optical information recording medium that can be made into a single-layer structure and thinner while maintaining the /N.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an optical information recording medium in which a light reflecting layer containing an organic dye as a main component is provided on a substrate directly or via an undercoat layer, and further a light absorbing layer is provided. The light reflecting layer is made of a dye film having a peak of spectral reflectance near the recording and reproducing wavelength, and the film thickness is defined to be such that the film thickness dependence of the reflectance at the recording and reproducing wavelength is maximum. An optical information recording medium is provided.

Further, according to the present invention, light having a wavelength near the peak of the spectral reflectance of the light reflection layer of the optical information recording medium is focused on the recording medium to destroy the interference structure of the light reflection layer. A recording method is provided which is characterized in that information is recorded by.

The present invention will be described in detail below with reference to the drawings.

In a conventional optical information recording medium having an organic dye film J (V) recording layer, as illustrated in FIG. Dyes that have spectral absorption/reflection characteristics such that the reflectance peak is around 870 nm are often used. That is, dyes that exhibit a spectral absorption peak near the recording/reproducing wavelength are used.

This is based on the idea of increasing the absorption efficiency of light energy, decomposing and sublimating the dye, and obtaining a highly sensitive recording medium. The recording method of the present invention differs from this in that information is recorded and reproduced using light having a wavelength near the peak of the spectral reflectance of the dye film. Therefore, the first
As shown in the figure, a dye that exhibits a peak in spectral reflectance near the recording/reproducing wavelength is used in the recording layer (light reflecting layer), and the recording layer (light reflecting layer) is made such that the film thickness dependence of the reflectance is maximum at the recording/reproducing wavelength. Specify the film thickness of the light reflecting layer). FIG. 3 illustrates the film thickness dependence of the reflectance and transmittance of the dye film used in the Examples described below. In the present invention, the dependence of the reflectance on the film thickness is 1 where the reflectance is maximum
Use something vaguely thick. As is clear from FIGS. 1 and 3, a recording medium using such a dye film has high reflectance and low absorption.

The reason for this is that, as shown in Figure 4, when the complex refractive index of a dye is 6=n-ik, for organic dyes, the consumption coefficient is generally at its maximum near the absorption peak, and n is at its minimum, and n is further below the absorption peak. This is because it increases rapidly on the long wavelength side. That is, in a simple example, plastic (會=1.5-i
・Considering the interface with 0), the reflectance 1( is expressed by the following equation, (n+1.5)''+2) This is because the term n becomes dominant on the long wavelength side.

Another means of increasing the reflectance can be achieved by setting the thickness of the dye film so that the reflections from the front and back surfaces strengthen each other across -F.

When using a recording medium whose recording layer (light reflection IC'J) is an organic dye film with the optical properties and film thickness as described above, light absorption becomes small and rapid decomposition or sublimation of the dye film does not occur. Although it becomes difficult, even if the dye film is slightly deformed, the interference structure of the film is destroyed and the reflectance is significantly lowered, making it possible to record. FIG. 5 shows the principle by which information is recorded by destroying the interference structure of the film. In the figure, 1 is a recording medium, 2 is a substrate, 3 is a recording layer (light reflecting layer), 4 is an incident beam, and 5 is a focus. Further, FIG. 6 shows how recording is performed using the recording medium according to the present invention. In the figure, elements similar to those in FIG. 5 are given the same reference numerals, and 6 indicates a light absorption layer. The recording medium 1 of the present invention is constructed by providing a light absorbing layer 6 containing a material that strongly absorbs light irradiated during recording on a light reflecting layer 3. In this way, more heat is generated by laser irradiation, and the light is reflected by the light absorbing layer 6! Mixing and dissolution of materials occur at the interface of the IC dye film 3, resulting in the disappearance of a clean interface and the destruction of the interference structure. This causes a partial decrease in reflectance and recording is performed. In this case, by appropriately selecting the material and film thickness of the dye film, the light absorption ability of the light absorption layer 6, and the thermal and chemical properties, it is possible to create a recording medium with better sensitivity and Cc. It is possible.

When an optical information recording medium is configured as described above, for example, when reading by irradiating weak light (approximately 1/10 the power of writing) and reproducing, there is little light absorbed by the light reflecting layer: ++j Deterioration caused by raw light is reduced. Also, by providing the light absorption layer 6, oxygen and dyes in the air are blocked, so deterioration of the light reflection layer 3 caused by reproduction light is further reduced.

Further, according to the present invention, as shown in FIG. 7, it is also possible to have a structure in which a protective JM7 is provided on the light absorbing Jf 8, and in this way, a single-plate structure or a laminated structure is possible. It can also be used for optical carts and optical floppies.

Next, the materials constituting the optical information recording medium of the present invention and the necessary characteristics of each layer will be specifically explained.

(1) No.j: As a necessary characteristic of the plate substrate, it must be transparent to the laser beam used only when recording and reproducing is performed from the substrate side, and it does not need to be transparent when recording and reproducing is performed from the recording layer side. As the substrate material, for example, plastics such as polyester, acrylic resin, polyamide, polycarbonate resin, polyolefin resin, phenol resin, epoxy resin, polyimide, glass, ceramic, or metal can be used.

Furthermore, on the surface of the board, there are guide grooves and pits for racking, as well as brake forms such as address signals.
may be formed.

(2) Undercoat Jv The undercoat layer (a) improves adhesion, (b) serves as a barrier against water or gas, (C) improves storage stability of t'J, and (d) improves reflectance. (c) protection of the substrate from solvents;
(f) Used for forming guide grooves, guide pits, preformats, etc. For the purpose of (a), polymeric materials such as ionomer resins, polyamide resins,
Various polymer substances such as vinyl resins, natural resins, natural polymers, silicones, liquid rubbers, silane coupling agents, etc. can be used, and for the purposes (b) and (c), the above polymers can be used. In addition to materials, inorganic compounds such as 5in.
2. M[CFz, 5iO1TLO□, ZnO1Ti
N, SiN, etc., gold or semimetal such as Zn,
Cu, S, Ni, Cr, Ge, Se, Au, A
l^Q etc. can be used. Furthermore, for the purpose of (d), metals such as AQ, Aε, Te, etc., and organic thin films having metallic light σ, such as methine dyes, xanthine dyes, etc., can be used; and (f)
For this purpose, ultraviolet curing resin IN, thermosetting resin, thermoplastic resin, etc. can be used.

(3) Light-reflecting layer Light-reflecting layer Iυ is a layer that reflects laser light and causes some kind of optical change by intense irradiation with laser light, and can record information based on that change. Its main components are, for example, croconium-type dyes and azulene. type dyes CM'l materials), 1-lifted thiazine compounds, phenanthrene derivatives, phthalocyanine compounds, tetrahydrochlorin compounds, dioxane compounds or derivatives thereof, anthraquinone derivatives, xanthine dyes, triphenylmethane type dyes, squarylium type dyes, polymethine dyes (Pyrylium-type pigments.

Cyanine dyes, merocyanine dyes, etc.), croconium dyes bonded with polymethine, azulene-type dyes bonded with polymethine, etc.

In order to improve recording characteristics and stability, the light-reflecting layer in the present invention may contain other dyes, such as phthalocyanine-based, naphthalocyanine-based, tetrahydrocholine-based dyes, etc., as necessary.
Dioxazine-based, 1-rifetchazine-based, phenanthrene-based, anthraquinone (indanthrene)-based, cyanine (merocyanine)-based, croconium-based, xanthine-based, triphenylmethane-based, pyrylium-based, squarylium-based, azulene-based dyes, and metals. or metal compounds such as In, Sn, Te, Bi, AQ, Se,
'reo2.5nO1^s, Cd, etc. may be dispersed and contained, or may be laminated.

In addition, the light-reflecting layer may be made of a polymeric material, an organic compound (aminium, immonium, diimmonium compounds, etc.) that has an absorption ability in a wavelength range longer than the cyanine dye, or an organometallic complex compound (bisdithiodicene, bisphthalene, etc.). A low-molecular compound such as enyldithiol-based forceps, etc.) may be mixed and dispersed. Furthermore, the light-reflecting layer can also contain storage stabilizers (metal complexes, phenolic compounds), dispersants, flame retardants, lubricants, plasticizers, and the like. As described above, the thickness of the light reflecting layer is set to a value that maximizes the reflectance at the wavelength used. The value depends on the birefringence of the light reflecting layer and is not uniquely determined, but it is approximately 100 to 1
0 μm, preferably 200 to 2 μm. As a method for forming the light-reflecting layer, vapor deposition, CVO method, sputtering method, and solvent coating methods such as dip coating, spray coating, spinner coating, blade coating, roller coating, curtain coating, etc. can be used.

(4) Light absorption layer The light absorption layer absorbs the light irradiated during recording and generates heat.
It functions to transform the light-reflecting layer or the interface of the light-reflecting layer.

For this purpose, almost the same type of material as the light absorption layer is used, but it is necessary to select a material that has a higher light absorption ability than the light reflection layer at the wavelength of the recording light. Additives similar to those used in the light-reflecting layer can be added to improve stability and the like. The thickness of the light absorption layer is determined based on light absorption ability, thermal conductivity, etc., and a thickness of approximately 100A or more is used. If this light absorption layer also serves as a protection film, it can be set to a thickness of 100 μm or more.

(5) Protective layer The protective layer (a) protects the light reflector Wl from scratches, dust, tears, etc., (b) improves the storage stability of the light reflector 114, and (,) improves reflectance. used for this purpose. For these 1-J targets, the materials shown above for the undercoat waste can be used, but in the present invention, in order to maintain sensitivity and C/N as described above, polymethyl acrylate is used. , polycarbonate, epoxy resin, polystyrene, polyester resin, vinyl resin, cellulose,
Heat softening properties of aliphatic hydrocarbon resins, aromatic hydrocarbon resins, natural rubber, styrene-butadiene resins, chloroprene rubber, waxes, alkyd resins, drying oils, rosins, etc.
It is more preferable to use a hot-melt resin.

In the present invention, the undercoat layer and protective JPJ contain stabilizers, dispersants, flame retardants, lubricants, etc., as in the case of the recording layer.
A 4W antistatic agent, a surfactant, a plasticizer, etc. can be contained.

〔Example〕

The present invention will be further explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 The compound of structural formula (1) was dissolved in 1,2-dichloroethane at about I
A solution was prepared by dissolving wL%. Add this solution to another 100
When the absorption spectrum was diluted twice and determined to 1lllJ (the absorption peak was found at i90nm), a spin code was applied to an acrylic plate hard-coated with JS liquid, and the reflection spectrum from the substrate side and the absorption spectrum were measured. As a result, the spectrum shown in Figure 1 was obtained. Dye film samples with various film thicknesses were prepared by changing the rotation speed during the spin code. The reflectance and transmittance of this dye film at a wavelength of 790 r+m We plotted the corresponding reflectance and transmittance with the transmittance as the optical density and the film thickness as the horizontal axis, and obtained the result shown in Figure 3.From now on, we will get a film with an absorbance of 0.4. It was found that the reflection was maximized.

Made of acrylic photopolymer on a polymethyl methacrylate (PMMA) board with a thickness of 1.2+nn+ and a diameter of 130+nm, it has a depth of 900 people, a half width of 0.4 homes, and a pitch of 1.
．． The stock solution was spin-coated onto a substrate with 6μ... helical groups under conditions such that the optical density was 0.4, and the following structural formula (1) whose absorption spectrum was shown in Figure 8 was added.
A film of the dye was formed by vapor deposition.

This recording medium has a linear velocity of 2. The semiconductor laser beam with a wavelength of 790 nm was irradiated from the substrate side at jK (JK).The beam diameter at the writing point of the laser beam used at this time was approximately 1.3 μI. Recording frequency is 0.5
M117. Recordings were made using the fundamental frequency as the fundamental frequency.

At this time, a C/N of 57 dB was obtained with a recording power of 3 mW, indicating that sufficient recording was being performed. When this recorded portion was read 1 million times at a reproduction power of 0.31, the amplitude decreased by about 10%.

Comparative Example 1 In Example 1, the optical density after spin coding was 0.6.
A recording film was formed and a recording medium was obtained in the same manner except that the C/N was 40.
dB, and the decrease in amplitude for 1 million readings is 25
%Met.

Comparative Example 2 In Example 1, the optical density after spin-to-1 was 0.
A recording medium was produced and evaluated in the same manner, except that the recording film was adjusted so that the particle diameter was 25. A C of 55 dB was obtained, but the amplitude reduction after 1 million readings was 30%.

Example 2 In Example 1, a protective layer was further provided on the recording film to produce a recording medium. The protective layer was prepared by dissolving 2 wt % of an aromatic hydrocarbon resin (trade name Vetrozin #L30, manufactured by Mitsui Ishiura Chemical) in cyclohexane and spin coating at 400 rpm. As a result of evaluation in the same manner as in Example 1, C was 53 dB and amplitude deterioration after 1 million plays was 7.
%Met.

Example 3 A recording medium was prepared and evaluated in the same manner as in Example 1, except that the following compound (2) was used instead of compound (1), and similar results were obtained.

(Ie Examples 4 to 11 In Example 1, compounds 3 to 10 in Table 1 were used instead of compound (1) to form a recording film with a thickness that maximized the reflectance, and a recording medium was obtained. Note that a protective layer was provided as appropriate.The evaluation results of these recording media are shown in Table 2.

table table One is without a protective layer. I'm sure I'll never know 〔Effect of the invention〕 As described in detail above, according to the present invention.

Recording is performed using light at a wavelength near the peak of the spectral reflectance of the recording layer, making it possible to create a single-layer structure and reduce the thickness while maintaining high sensitivity and high C/N. It becomes possible to provide information recording media.

Furthermore, the present invention can be used not only for optical discs but also for optical cards and optical floppies. Also, CD
It is also possible to replace it with a CD-ROM or the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the spectral reflectance and absorption of the organic dye film according to the present invention, FIG. 2 is a diagram showing the spectral reflectance and absorption of the organic dye film used in conventional recording media, and FIG. The figure shows the relationship between the reflectance and transmittance of the dye film in Figure 1 and the film thickness. Figure 4 shows the relationship between the refractive index and extinction coefficient of a general organic pigment film and the wavelength. Figures 5 and 6 are diagrams showing how the interference structure of the organic dye film is destroyed and information is recorded.
The figure is a cross-sectional view of a recording medium provided with a protective layer, and Figure 8 is (11
) is a graph showing the absorption spectrum 1 Her of the dye expressed by the formula. 1... Recording medium 2... Substrate 3... Recording layer (light reflecting layer) 4... Incident beam 5 Pit 6... Light absorption layer Patent applicant Rico Co., Ltd. Patent attorney Ike? lft Toshiaki (first name) Sensei ← Mejo) Retirement￥＼鼾i1Me 3rd figure 0.4 0.6 0.8 Pi/1t- (Ei 几草 A0) 1.0 〕亙荍- (nm)

Claims (2)

[Claims] (1) In an optical information recording medium in which a light-reflecting layer containing an organic dye as a main component is provided directly or via an undercoat layer on a substrate, and a light-absorbing layer is further provided, the light-reflecting layer has a wavelength close to the recording/reproducing wavelength. 1. An optical information recording medium comprising a dye film having a peak in spectral reflectance, the film thickness being defined to a film thickness that maximizes the film thickness dependence of the reflectance at the recording/reproducing wavelength. (2) Destroying the interference structure of the light reflection layer by focusing light at a wavelength near the peak of the spectral reflectance of the light reflection layer of the optical information recording medium according to claim 1 on the recording medium. A recording method characterized by recording information by.