JPH02179790A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide high reflectivity and to enhance recording sensitivity by containing a substance mainly absorbing laser beam and a substance mainly deteriorated and decomposed by heating in a recording layer. CONSTITUTION:In a recording layer, an org. dye material is used as a recording material and two kinds of substances are also used in a mixed state. The first substance (component 1) is one mainly absorbing laser beam and, concretely, there are a cyannine dye, a metal complex dye, a phthalocyanine dye and a naphthalocyanine dye. The second substance (component 2) absorbs almost no laser wavelength and is deteriorated and decomposed with a sudden temp. rise due to laser irradiation to generate gas. As a substance usable in the component 2, a cyanine dye (absorbing no laser wavelength) and a cumarine dye are designated. Herein, the mixing ratio of two kinds of the substances compounded with the recording layer is regulated to easily set reflectivity to 70% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an optical information recording medium using an organic dye as a recording material, and particularly to improving the reflectance thereof.

[Summary of the invention]

The present invention provides an optical information recording medium in which a recording layer and a metal reflective layer are sequentially formed on a substrate. The purpose of this invention is to provide an optical information recording medium that has a high reflectance in the semiconductor laser wavelength region used for signal reading and also has excellent recording sensitivity.

[Conventional technology]

In recent years, in the field of information recording, research on optical information recording methods has been progressing in various places. This optical information recording method is capable of recording and reproducing without contact, can achieve a recording density that is more than an order of magnitude higher than that of magnetic recording methods, is a read-only type, and is a write-once type.

It has many advantages such as being compatible with various rewritable memory formats, and is considered to have a wide range of uses, from industrial to consumer use, as a method that makes it possible to create large-capacity files at low cost.

Among the above-mentioned memory types, the write-once type allows the end user to record and play back data, and cannot be erased, so it is mainly used as a file for long-term storage of data. During recording, local irreversible physical changes in the recording layer are used when the recording material absorbs light energy and converts it into thermal energy. As this irreversible physical change, changes in the shape of the recording layer (formation of bits), changes in surface properties, changes in crystal state, etc. are known.

Most write-once optical information recording media currently in practical use use tellurium alloys or tellurium compounds as recording materials. However, in recent years, organic dyes have been attracting attention in place of these tellurium-based materials from the viewpoint of further improving the mass productivity and economic efficiency of media. The above-mentioned organic dyes must exhibit large absorption in the near-infrared region, which is the wavelength range of semiconductor lasers used for recording and reproduction.
Metal phthalocyanine dyes, naphthoquinone dyes, etc. are known.

[Problems to be Solved by the Invention] Incidentally, in order to achieve desirable recording/reproduction characteristics in an optical information recording medium, it is necessary that the physical properties of the recording material satisfy the following conditions. In order to obtain high recording sensitivity, it is necessary to have a high light absorption rate, a small heat capacity, a low thermal conductivity, and the thermal change for recording to occur at a relatively low temperature. In order to obtain high sensitivity, the change in reflectance before and after recording must be large, and the shape of the formed focus must be smooth.
It is necessary that there is little noise generation. As mentioned above, there are various desirable conditions, but the most basic optical properties are high absorption and high reflectance.

However, conventionally known organic dyes have a low reflectance of 30 to 40% at most when formed into a film, making it impossible to achieve sufficient reproduction sensitivity. When considering reproducing an optical information recording medium that uses an organic dye as a recording material using a reproducing device that reproduces an optical disc (so-called compact disc) that has an aluminum reflective film on a substrate with a focal point formed on it, at least the reflectance needs to be as high as the value of current compact discs (more than 70% at 780 nm). However, unlike read-only compact discs, write-once optical information recording media have
If only high reflectance is pursued, there is a problem that recording sensitivity will be impaired. In other words, in order to achieve high reflectance at a certain wavelength, the light absorption rate at that wavelength must be low, but if the light absorption rate is low, it will not be possible to effectively cause irreversible physical changes. It is. To solve this problem, it is necessary to search for organic dyes that can efficiently convert even a small amount of absorbed light energy into thermal energy and cause irreversible physical changes.

Among these, it is extremely difficult to find a dye that has good properties as a recording material, such as being resistant to photodeterioration, having excellent weather resistance, and having high solubility in general-purpose solvents.

In addition, for dye materials being considered as recording materials, such as cyanine dyes, the laser wavelength range is at the tail of the dye absorption band, so the absorbance becomes thicker with a slight change in wavelength (and of course the reflectance also changes significantly). For example, with cyanine dyes, the reflectance differs by about 10% between 780 nm and 770 nm, and the wavelength of normal laser diodes has an allowable range of about 780 ± 10 nm.
It is difficult to obtain the same reflectance for all laser diodes, and there is a possibility that the signal strength will vary greatly depending on the reproduction device.

Therefore, the present invention was proposed in view of the conventional situation, and the present invention not only has a high reflectance in the wavelength range of a semiconductor laser, but also has small fluctuations in reflectance near the wavelength range.
Furthermore, the purpose of the present invention is to develop a recording layer that undergoes physical changes due to a small amount of light energy, and to provide an optical recording medium with excellent recording and reproduction characteristics.

[Means to solve the problem]

As a result of intensive studies to achieve the above-mentioned object, the present inventors found that it was possible to relax the optical conditions of materials that can be used as recording materials by mixing two or more kinds of materials with different optical constants. We have found that recording and reproducing characteristics can be improved by selecting materials with better characteristics.

The present invention was completed based on such findings, and provides an optical recording medium in which a recording layer and a metal reflective layer are sequentially formed on a substrate, in which the recording layer mainly absorbs laser light. It is characterized by containing a substance and a substance that changes and decomposes mainly by heating.

As shown in FIG. 1, the structure of the optical recording medium of the present invention is a transparent substrate (
In 1-1 of 1), a recording layer (2) that absorbs semiconductor laser light and performs photothermal conversion, and a metal reflective layer (3) for increasing reflectance are sequentially laminated. A protective film (4) made of ultraviolet curing resin, thermosetting resin, etc. may be further provided on the metal reflective layer (3), if necessary.

The material of the substrate (1) is not particularly limited as long as it is used in ordinary optical recording media, and suitable materials include, for example, plastics such as polycarbonate and acrylic, and glass.

The metal reflective layer (3) provided on the -F recording layer (2) is made by depositing a metal with high reflectance at 780 nm using a vacuum thin film forming technique such as vacuum evaporation or sputtering. . Usable metals include Au, C
Examples thereof include u, Affi, Ag, and the like. This metal reflective layer (
The layer thickness for 3) is selected to be approximately 300 to 2,000 people. If the layer thickness is less than 300 layers, the effect of increasing the reflectance of the optical recording medium will be insufficient, and if it exceeds 2000 layers, it will take a long time to form a film, which is disadvantageous in terms of productivity, and the recording layer (2 ) There is also a risk that the light energy reaching the target may become insufficient.

On the other hand, the recording layer (2) uses an organic dye material as a recording material, and here, in order to achieve both high reflectance and high recording sensitivity, two types of substances described below are mixed and used. do.

First, the first substance (hereinafter referred to as component 1 for convenience).

), but this is a substance that mainly absorbs laser light. That is, component 1 has absorption at the laser wavelength, and has a 1M elementary refractive index n″″=n+k i (n
is the real part, so-called refractive index, is the extinction coefficient, and 1 is the imaginary unit), and the value of k is 0.3 or more, preferably 0.3 to
2. Those having a value of n of 1.5 to 3.2 are selectively used. This component 1 is desirable because the closer the absorption peak is to the laser wavelength, the smaller the fluctuation of k in the Rede wavelength range, and the reflection spectrum becomes 1,120. That's fine. In addition, component 1 needs to effectively absorb laser light during recording,
Therefore, it is desirable to use a material whose absorption does not change due to light irradiation or temperature rise (approximately 300° C.).

Specific examples of substances that satisfy these conditions include cyanine dyes, metal complex dyes, phthalocyanine dyes, and naphthalocyanine dyes. Among them, phthalocyanine dyes and naphthalocyanine dyes are preferred.
Especially heat resistance and sensitivity.

In consideration of solubility in general-purpose solvents, substituted aminophthalocyanines such as hexylaminophthalocyanine, propylaminophthalocyanine, dodecylaminophthalocyanine, and hendylaminophthalocyanine are preferred.

The second substance (hereinafter referred to as component 2) has almost no absorption at the laser wavelength (k≦0.05, preferably ≦0.019, n ~1.5-3.2). but,
As the temperature rises rapidly due to laser irradiation, the recording layer must be deformed significantly due to deterioration and decomposition, generating gas. Therefore, it is desirable to use a material that generates gas by decomposition or vaporization in the range of 100 to 300°C. Of course, it is desirable that the recording material has excellent weather resistance like the -C recording material.

Substances that satisfy these conditions and can be used as component 2 include cyanine dyes (those with no absorption at the laser wavelength), coumarin dyes, and the following substances.

(Margin below) i) Allantoin pigment ■Antread 88 (minute 8 temperature 280'C.

λ,,, 505nm) ■7 Sidopurafuku 48 (decomposition temperature 275°C1 λ□-663nm) H mountain) Thiazine dye ■Azure 8 (decomposition temperature 205°C) ■Oil Blue N (decomposition temperature 210°C) ■Methylene diamide 1 C1θ ii) Azo dye iv) Triphenylmethane dye ■7 Sidoi Io-29 (decomposition temperature 238°C1λ, -
, 407nm) ■Brilliant Green (Decomposition temperature 210'Cλ,
,, 625nm) NG(C)12cL) Z・H3O4"U3Na ■Thymol blue (decomposition temperature 221-224'C λ,, lI 594nm) ■11) Bisuzu dye ■Sudan■ (decomposition temperature 199℃.

λ,,,507nm) ■Tyleft Red 21 (minj1 degree 240°C1 λ, □508nm) ■) Acridine dye ■7 Chrysin Oreshishi (minute MKi'fX165°C1 λ,,, 488nm) ■Acridine yellow ( λ,...442nm) 輔] Xanthine dye ■Rose Bengal (decomposition temperature 184°C1 λ,...559nm) vi) Oxazine dye t■Totamine 6G (λ-1l 524nm) Ingredients 1. The recording layer (2) containing component 2 is -
1G is formed on the substrate (1) by applying a solution dissolved in an appropriate organic solvent.

In this case, it is preferable to select the N thickness of recording N(2) such that the reflectance is 70% or more due to the interference effect.
When the wavelength of the laser beam to be used is λ, it may be selected around λ/2n or an integral multiple thereof.

Furthermore, the mixing ratio of component 1 and component 2 varies depending on the type of material selected, and may be set appropriately taking into account reflectance, recording sensitivity, etc. For example, n in the complex refractive index The values of 1.5≦n≦3.2, respectively.
, O<k≦0.2. As the organic solvent, one that can dissolve component 1 and component 2 and does not damage the substrate (1) is appropriately selected and used.

The optical recording medium of the present invention configured as described above has the same overall thickness as the current compact disc etc.<1.
It is possible to set it to 5 mm or less. Conventionally, for example, in an optical recording medium in which a protective film is formed on an organic dye layer, a gap is provided between the organic dye layer and the protective film in order to prevent the formation of pits from being physically suppressed. was proposed. However, this makes the medium too thick as a whole and cannot be played by current playback devices such as compact discs and CD-ROMs, resulting in a narrowing of the medium compatibility of playback devices. On the other hand, in the present invention, even with the configuration shown in FIG.
The excellent characteristics of the material enable good recording and reproduction, and as a result, a thinner device can be achieved.

[Function] In the optical recording medium of the present invention, the recording layer is mainly composed of 2IIg substances (component 1 and component 2), and component 1 mainly absorbs laser light and performs photothermal conversion, reducing the amount of light energy. This also effectively induces alteration and decomposition of component 2, and the gas generated at this time causes thermal deformation. Therefore, it is possible to achieve high recording sensitivity.

By adjusting the mixing ratio of the two types of substances added to the recording layer, the complex refractive index in the laser wavelength range can be controlled quite freely, and a reflectance of 70% or more can be easily obtained. . In addition, the reflection spectrum in the laser wavelength range is also flattened, so even if there is a slight wavelength fluctuation in the laser diode (within the tolerance range (approximately ±10%)), the reflectance will not change significantly. High reflectance can be obtained stably.

〔Example] The present invention will be explained below based on specific experimental results.

In the Fudan-Tsuchimoto experiment, first, the relationship between the value of n and the reflectance of the recording layer was investigated.

The medium used performs recording and reproduction from the substrate side, and has a structure in which a recording layer, a high reflection layer, and a protective layer are successively laminated on a transparent substrate.

The transparent substrate is polycarbonate (n=1.58),
The high reflective layer is a vapor-deposited gold film (n”=0.15-4.5i, I
In order to obtain a reflectance of 70% or more, the complex refractive index of the recording layer had to be within the shaded area to the left of curve A in FIG.

However, this range varies somewhat depending on the material of the transparent substrate and the material and thickness of the high-reflection layer, and tends to widen as the refractive index of the transparent substrate is low, the reflectance of the high-reflection layer is high, and 12r\ is thicker. It was there.

For example, the refractive index of the transparent substrate is 1.33 (this value is considered to be the lowest for a transparent solid), and the high reflective layer has a refractive index of 1.33.
When using a silver vapor deposited film of 100n or more (the silver vapor deposited film has the highest reflectance), the complex refractive index is determined by curve B in Figure 2.
If it falls within the shaded area on the left side, the reflectance of the recording layer is 70.
% or more.

Actual 1 All the media actually created were disk media with a diameter of 12 cm and compatible with a laser diode with a wavelength of 780 nm.

The recording layer was formed by applying a mixed solution of the composition shown in Table 1 on a polycarbonate substrate by a spin coat method, and then gold was deposited to a film thickness of 50 to 100 nm using a vacuum evaporator.
A thickness of about 100n was formed.

Table 1 The structural formula of each dye in the table is as follows.

Cyanine dye A: manufactured by Nippon Kanko Shokuryo Co., Ltd., NK125 Cyanine dye B: manufactured by Nippon Kanko Shokuryo Co., Ltd., 529 to N Sample disks (Example 1 to Example 3) were produced in place of Samples 1 to 3 shown in Table 1. Table 2 shows the recording layer thickness 6 and the reflective layer thickness of each of the sample disks produced.

Table 2 results are shown in Table 3. Note that Table 3 also lists the results of examining the film uniformity of the recording layer on each sample disk.

Table 3 Among the sample disks prepared, the reflection spectrum of Example 1 is shown in FIG.

Looking at this FIG. 3, the reflectance is 70% or more in the wavelength range of 770 to 790 nm, and its fluctuation is 5% or less. Similar trends were confirmed for other sample disks (Example 2, Example 3).

Next, we investigated the recording characteristics of each sample disk.

The recording characteristics are a wavelength of 780 nm and a laser power of 10.
Evaluation was made by recording a single signal of 500 kHz at a linear velocity of 1.2 m/sec using a 5 mW near-infrared semiconductor laser beam, and then measuring the CN ratio of the reproduced output signal when this was read out using the laser beam. did.

It can be seen that good recording characteristics are maintained in all sample disks.

Note that the CN ratio in Example 1 and Example 2 was almost the same under the above conditions (laser power 10.5 mW), but when the laser power was lower (e.g. 8 mW), in Example 1 it was 30 dB. Whereas there was
In Example 2, it was 54 dB, suggesting that the latter is more advantageous.

〔Effect of the invention〕

As is clear from the above explanation, if the present invention is applied, even if the absorbed light energy is small, the component 1 in the recording layer
(a substance that mainly absorbs the laser beam) efficiently converts this into thermal energy, and component 2 (a substance that mainly changes and decomposes when heated) gasifies, creating a sufficient space between the exposed and non-exposed areas. A deformation is created in the substrate or metal reflective layer that causes a difference in reflectance in magnitude. Moreover, since the reflectance of the recording layer is maintained sufficiently high, improvements in recording sensitivity and reproduction sensitivity can be achieved at the same time without sacrificing either, resulting in reliability suitable for high-speed recording and high-density recording. A highly writeable optical recording medium is provided.

Furthermore, since good recording and reproducing characteristics can be obtained even if a metal reflective layer is directly laminated on the recording layer, the thickness of the optical information recording medium can be reduced to the current so-called "complex" thickness. ...It can be made equivalent to a disc, etc., and it can also be played back using a playback device that is common to these.

It is a characteristic diagram which shows the relationship between the value of k and the reflectance at that time.

FIG. 3 is a characteristic diagram showing a reflection spectrum of an example of an optical recording medium to which the present invention is applied.

substrate recording layer metal reflective layer Protective film

Claims (1)

[Claims] An optical recording medium in which a recording layer and a metal reflective layer are sequentially formed on a substrate, wherein the recording layer contains a substance that mainly absorbs laser light and a substance that mainly changes or decomposes when heated. An optical recording medium characterized by containing: