JPS58224449A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain an optical recording medium having improved vanishing performance, improved sensitivity to rewriting and an improved S-N ratio in readout and reducing the deterioration of the vanishing performance, by forming a recording layer contg. a low mol. wt. thermoplastic resin and a light absorber on a reflective substrate. CONSTITUTION:A recording layer having <=70% light transmittance is formed on a reflective substrate. The recording layer contains a thermoplastic resin having <=30,000 number average mol. wt. such as polystyrene and a light adsorber selected from dyes, carbon black, pigments, etc. in accordance with the wavelengths of light for recording. A heat insulating intermediate layer made of a thermoplastic resin, a thermosetting resin, SiO2, MgF2 or the like may be interposed between the substrate and the recording layer to improve the sensitivity to writing. Thus, an optical recording medium enabling heat-mode writing and vanishing by being irradiated with light for recording is obtd. The recording medium has high sensitivity to rewriting after vanishing and a high S-N ratio in readout.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION Technical Field The present invention relates to optical recording media, and particularly to erasable and rewritable heat mode optical recording media.

Prior art optical recording media have the characteristic that the recording medium does not deteriorate due to wear and tear because there is no contact between the medium and the writing or reading head, and for this reason, a lot of research and development is being carried out on optical recording media.

Among such optical recording media, heat mode optical recording media are being actively developed because they do not require image processing in a darkroom.

Such a heat mode optical recording medium is an optical recording medium that uses recording light as heat, and a part of the medium is melted or removed using laser recording light to form small holes called pits. However, there are devices that record information using these pits and detect the presence or absence of these pits using readout light.

An example of such a pit-forming heat mode medium is one in which a recording layer made of a thermoplastic resin and a light absorber is coated on a reflective substrate, and pits are formed by melting the resin. known (for example, Japanese Patent Application Laid-Open No. 55-16169)
No. 0).

According to research conducted by the present inventors, it has been confirmed that in such a medium, the pits once formed can be erased using erasing light or heat to flatten the surface of the recording layer and rewrite can be performed again.

However, such media do not have sufficient erasing performance.

Further, even when erasing is possible, repeated erasing causes significant erasure degradation in which write sensitivity and read S/N ratio deteriorate.

Furthermore, the writing sensitivity and reading S/N ratio are still not fully satisfactory.

■ Purpose of the Invention The present invention was made in view of the above-mentioned circumstances, and its main purpose is to provide an erasable and replayable recording medium having a recording layer made of a thermoplastic resin and a light absorber on a reflective substrate. The purpose of the present invention is to improve erasing performance, reduce erasing deterioration, and improve writing sensitivity and read S/N ratio in a writable heat mode optical recording medium.

The present inventors have conducted intensive research for such purposes,
The present invention has been accomplished.

The first invention of this application is an optical recording medium characterized by having a recording layer containing a low molecular weight thermoplastic resin and a light absorber on a reflective substrate. In a second aspect of the invention, an intermediate layer is provided between the substrate and the recording layer.

■Specific structure of the invention Hereinafter, a specific configuration of the present invention will be explained in detail.

The optical recording medium of the present invention is formed by disposing a recording layer on a reflective substrate.

The recording layer contains a predetermined thermoplastic resin.

This resin is a thermoplastic resin that softens or melts and deforms as the temperature rises in the area irradiated with the recording light, thereby forming recording pits on the surface.

The thermoplastic resin used in the present invention has a low molecular weight, and particularly preferably has a number average molecular weight of 3 or less, more preferably 20,000 or less.

By setting the average molecular weight of the low-molecular lid to such a value, the writing sensitivity is improved and the reading S/N ratio is improved.

Further, when erasing pits once formed, the erasing temperature can be lowered or the intensity of the erasing light can be reduced, improving erasing performance. Furthermore, when line erasing is performed by scanning with erasing light, the line width for line erasing can be narrowed.

Then, erasure degradation becomes extremely small.

In addition, there is a clear threshold value in the optical energy or temperature required to form pits in the recording layer, and the region of light intensity where pit formation becomes unstable becomes narrower, resulting in a decrease in the S/N ratio due to fluctuations in the output of the recording light. Fluctuations will also be smaller.

The molecular weight distribution of the resin may vary, but in particular, 50% or more of the total number is within ±5 of the number average molecular weight.
It is preferable that the molecular weight is within 0%.

This improves erasing performance, sensitivity, S/N ratio, erasing performance, unstable region of pit formation, and heat resistance.On the other hand, the thermoplastic resin used may be of various types, but among these,
Examples of those that can be particularly suitably used include the following.

i) Polyolefin/polyethylene In this case, the number average molecular weight is 10,000 or less, especially 350-
io and o oo are preferred.

Polypropylene in this case has a number average molecular weight in particular of 400 to 10,000
is more preferable.

Polyolefins having 4 to 6 carbon atoms, such as polybutene, polyisobutyne, poly4-methylpentene-1, and the like.

it) polyolefin copolymers such as ethylene-vinyl acetate copolymers, ethylene-acrylate copolymers, ethylene-acrylic acid copolymers,
Ethylene-propylene copolymer, ethylene-butene-1
copolymers, ethylene-maleic anhydride copolymers, ethylene propylene terpolymers (EPT), etc. In this case, the polymerization ratio of the comonomers can be arbitrary.

ii) Polyolefin halides such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymer, CFQ=CF2.
CF2=CFCl, CH2=cHFcI4:CF
Fluororesins which are homopolymers or copolymers such as CF2=CFCF3, chlorinated polyethylene, chlorinated polypropylene, copolymers of propylene and halogenated olefins, etc.

■) Vinyl chloride copolymer For example, vinyl acetate-vinyl chloride copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-maleic anhydride copolymer, acrylic ester or methacrylic ester and vinyl chloride copolymers, acrylonitrile-vinyl chloride copolymers, vinyl chloride-vinyl ether copolymers, ethylene nipropylene-vinyl chloride copolymers, ethylene-vinyl acetate copolymers grafted with vinyl chloride, etc.

In this case, the copolymerization ratio can be arbitrary.

(2) Vinylidene chloride copolymer Vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl chloride-acrylonitrile copolymer, vinylinae chloride-butadiene-vinyl halide copolymer, etc.

In this case, the copolymerization ratio can be arbitrary.

vi) Polystyrene number average molecular weight is 10,000 or less, especially 350 to 10,000
It is preferable that

vi) Styrene copolymers, such as styrene-acrylonitrile copolymer (AS resin), styrene-acrylonitrile-butadiene copolymer (ABS), styrene-maleic anhydride copolymer (SMA resin), styrene- Acrylic ester-acrylamide copolymer, styrene-butadiene copolymer (S
BR), styrene-vinylidene chloride copolymer, styrene-methyl methacrylate copolymer, etc.

In this case, the copolymerization ratio can be arbitrary.

vii) Styrene type polymers such as p-methylstyrene, α-methylstyrene, 2. ．． 5-dichlorostyrene, α, β-vinylnaphthalene, α-vinylhyricine, acenaphthene, vinylanthracene, etc., or copolymers thereof.

■) Chroman-indene resin Chroman-indene homopolymer or copolymer.

The number average molecular weight is preferably 2,000 or less.

X) Terpene resin or picolite For example, terpene resin which is a polymer of limonene obtained from α-pinene, or picolite obtained from β-pinene.

The molecular weight is preferably 1,200 or less.

xi) Acrylic resin 1 Particularly preferred are those containing an atomic group represented by the following formula.

-011-〇- -Oa 1 In the above formula, R□ represents a hydrogen atom or an alkyl group, and 曵 represents a substituted or unsubstituted argyl group. In this case, in the above formula, 1 (□) is preferably a hydrogen atom or a lower alkyl group having 1 to 4 carbon atoms, particularly a hydrogen atom or a methyl group. It may be a base, but
The number of carbon atoms in the argyl group is preferably 1 to 4, and when RQ is a substituted alkyl group, the substituent substituting the alkyl group is a hydroxyl group, ), a rogen atom, or an amino group (especially a dialkylamino group). It is preferable that

Such an atomic group represented by the above formula may form a copolymer with other repeating atomic groups to constitute various acrylic resins, but usually - one of the atomic groups represented by the above formula The acrylic resin is formed by forming a glaze or a homopolymer or copolymer having two or more repeating units.

xii) Polyacrylonitrile-)acrylonitrile copolymer, such as acrylonitrile-vinyl acetate copolymer, acrylnitrile-vinyl chloride copolymer, acrylonitrile-styrene copolymer, acrylonitrile-vinylidene chloride copolymer, acrylic Nitrile-vinylpyridine copolymer, acrylonitrile-methyl methacrylate copolymer,
Acrylonitrile-butadiene copolymer, acrylonitrile-butyl acrylate copolymer, etc.

In this case, the copolymerization ratio can be arbitrary.

i-ripolyacrylamide or dia-neptone acrylamide polymer A dia-neptone acrylamide polymer obtained by reacting polyacrylamide or acrylonitrile with acetone.

xy) Polyvinyl acetate xvi) Examples of vinyl acetate copolymers Copolymers with Eva, acrylic ester, vinyl ether, ethylene, vinyl chloride, etc.

The copolymerization ratio may be arbitrary.

New) Polyvinyl ethers such as polyvinyl methyl ether, polyvinyl ethyl ether, polyvinyl butyl ether, etc.

xvii) Polyamide In this case, the polyamide includes nylon 6, nylon 66, nylon 610. Nylon 612, nylon 9
, nylon 11. In addition to normal homonylons such as nylon 13 and nylon 13, copolymers such as nylon 6/66/610, nylon 6/66/12, nylon 6/66/11, and even modified nylon in some cases. good.

xix) Polyesters For example, various dibasic acids such as aliphatic dibasic acids such as oxalic acid, succinic acid, maleic acid, adipic acid, and sebastenic acid, or aromatic dibasic acids such as inphthalic acid and terephthalic acid, and ethylene chloride. Condensates and co-condensates with glycols such as recall, tetramethylene glycol and hegisamethylene glycol are suitable.

Among these, particularly preferred are condensates of aliphatic dibasic acids and glycols, and cocondensates of glycols, aliphatic dibasic acids, and aromatic dibasic acids.
Furthermore, modified daligtal resin, which is obtained by esterifying and modifying glyptal resin, which is a condensate of retalic anhydride and glycerin, with fat e, natural resin, etc., is also suitably used.

Xx) Polyvinyl alcohol or polyvinyl acetal resin In addition to polyvinyl alcohol, polyvinyl acetal resins such as polyvinyl formal, polyvinyl acetoacetal, and polyvinyl butyral obtained by acetalizing polyvinyl alcohol are preferably used.

In this case, the degree of acetalization of the polyvinyl acetal resin can be arbitrary.

xxi) Polyurethane resin Thermoplastic polyurethane resin with urethane bonds.

Particularly suitable are polyurethane resins obtained by condensation of glycols and diisocyanates, particularly polyurethane resins obtained by condensation of alkylene glycol and alkylene diisocyanate.

xxii) Nitrogen-containing vinyl polymers For example, more preferably polyvinylcarbazole with a number average molecular weight of 6 or less, OOO or less, polyvinylcarbazole co-It combination of vinylcarbasol and ethylene, styrene, etc., more preferably polyvinyl with a number average molecular weight of 10,000 or less Polyvinylpyrrolidone copolymer with pyridine, polyvinylvinylacetate, etc., polyvinylpyridine, etc.

xxii) Diene polymers, such as polybutadiene, butadiene-styrene copolymer (SBR), nitrile rubber (NBI), chloroprene rubber, isoprene rubber, inbrene-isobutylene copolymer, etc.

xxiv) Polyethers, such as, more preferably, polyoxymethylene with a number average molecular weight of 10,000 or less, styrene-pormarine resin, ring-opened heavy metals of cyclic acetals, polyethylene oxide and glycol, more preferably polypropylene with a number average molecular weight of 10,000 or less Oxides and glycols, propylene oxide
Ethylene oxide copolymer, polyphenylene oxide, more preferably hydrin rubber with a number average molecular weight of 10,000 or less,
Tetramethylene oxide, polystyrene oxide, chlorinated polyether resin, more preferably ring-opened tetrahydrofuran with a number average molecular weight of 10,000 or less, thermoplastic bisphenol epoxide obtained by a combination of bisphenol A and epichlorohydrin, etc. .

xxv) polycarbonates such as polydioxydiphenylmethane carbonate,
Polydioxydiphenylethane carbonate, dipropane carbonate, etc. are manufactured in each building.

xxvi) Polyethyleneimines xxvii) Cellulose resins Examples include original or mixed organic acid esters such as acetylcellulose, acetylbutyrylcellulose, acetylpropionylcellulose. In this case, the degree of esterification is preferably 01 to 90%.

Alternatively, for example, cellulose ethers of methylcellulose, ethylcellulose, hydroxyethylcellulose, carbogyzomethylcellulose, methylhydroxyenalcellulose, ethylhydroxyethylcellulose, methylhydroxypropionylcellulose, cyanoethylcellulose, and benzylcellulose.

In this case, the degree of etherification is preferably 03 to 60%.

Such a cellulose conductor may be a mixed conductor having two or more types of ester groups or ether groups, or may have other substituents. 8 xxvii) A blend of two or more of the above i) to xxvii), or a blend with other thermoplastic resins.

These various resins are manufactured by ordinary known methods,
This is used after being separated by molecular weight as necessary. Alternatively, commercially available products may be separated and used as necessary.

On the other hand, in the recording layer, along with such thermoplastic resin,
A light absorber is contained.

This light absorber exhibits a large light absorption rate with respect to recording light, and is intended to enable temperature rise in the irradiation section.

Therefore, depending on the wavelength of recording light, generally 400 to 850
Various known dyes, carbon black, various known inorganic or organic pigments such as lake pigments, ultrafine powders of metals or oxides, complexes, etc. that absorb wavelength light of nm can be used. .

It is preferable that such a recording JWir has a transmittance of 25%, more preferably 65% or less for the reading light.

Further, the thickness thereof is preferably 0.007 to 7 μS, more preferably 0.01 to 4 μS.

This improves the writing sensitivity and the read S/N ratio, improves the erasing performance, reduces erasing deterioration, and improves the film formation properties of the recording layer.

In addition, the content ratio of the thermoplastic resin contained in the recording layer and the light absorber is generally 0.0 with respect to the resin single-layer lid part.
It can be selected from a wide range of about 0.02 to about 200 parts by weight.

Such a recording layer is usually coated onto a substrate using various known methods such as a spinner or a coater.

Note that such a recording layer may contain other additives in addition to the above-mentioned thermoplastic resin and light absorber.

Examples of such additives include various oligomers and polymers. In this case, the polymer or oligomer is contained in the thermoplastic resin in an amount of approximately 30 wt. You can also do so.

In addition, various plasticizers, surfactants, antistatic agents, lubricants,
Flame retardant, stabilizer, dispersant, leveling agent, bleed prevention agent, ultraviolet absorber, dye migration inhibitor, water repellent, solubility improver, emulsifier, antifoaming agent, polishing agent, antiblocking agent, softener , a slip improver, a pinhole prevention agent, an orange peel prevention agent, etc. may be contained.

On the other hand, the substrate on which such recordings J- are layered and supported is reflective.

In order to impart reflectivity to the substrate, the substrate itself may be made reflective, but it is particularly preferable to provide a reflective layer on the surface of the substrate and form a recording layer on this reflective layer.

In this preferred embodiment, the reflective substrate having a reflective layer on its surface preferably has a surface reflectance of 90% or more with respect to readout light.

Such a reflective layer may be formed from a reflective material such as metal by, for example, a vapor phase deposition method such as vacuum deposition, sputtering, or ion blasting, or plating. The thickness can be arbitrary as long as it has reflective properties.

In this case, there are no particular restrictions on the substrate material on which the reflective layer is formed, but thermal conductivity, surface properties, mechanical strength, hygroscopicity,
In terms of warpage, we usually use various types of glass, various types of tempered glass, various ceramics, or polymethacrylic resin, polyacrylic resin, polycarbonate resin, phenol resin, epoxy resin, diallyl phthalate resin, polyester resin, polyimide resin, polyether ketone resin, etc. It is preferable to use various resins such as polyetherketone, methylpentene polymer, polyalate resin, polyolenoin, polyphenylene sulfide, nylon, and fluororesin.

Further, the shape and dimensions of the base body can be varied depending on the intended use, such as a disk, tape, bell, drum, etc.

In this case, in the first invention, a recording layer is provided on the reflective substrate as described above.

Moreover, in the second invention, an intermediate layer is interposed between the reflective substrate and the recording layer.

The intervening intermediate layer has a heat insulating effect when the temperature of the recording layer increases, and this heat insulating effect particularly improves the writing sensitivity.

Such a heat insulating intermediate layer may be made of a variety of materials as long as it has lower thermal conductivity than the above-described reflective layer or the entire reflective substrate.

For this reason, coating layers, plasma polymerized layers, etc. that are made of various thermoplastic resins, thermosetting resins, ultraviolet ray or electron beam curable resins, etc., or that have these as their main components,
Any of them can be suitably used.

Alternatively, it may be a vapor phase deposited film of silicon oxide, magnesium fluoride, tin oxide, indium oxide, or the like.

Such a heat insulating intermediate layer protects read light and recording light from
It may be transparent or absorbent.

The thickness thereof is usually about 0.001 to 20 μm, particularly about 0.005 to 5 μm.

At such a layer thickness, a heat insulating effect occurs and the writing sensitivity improves.

In the first and second inventions configured in this way,
The recording layer is provided directly on the reflective substrate or via the above-mentioned intermediate layer, but in the first and second inventions, the recording layer is provided on one surface of the reflective substrate. The recording layer may have a recording layer on both sides. In addition, two reflective substrates with a recording mark coated on one side are used, and the recording layers are placed facing each other with a predetermined gap between them, and they are sealed to prevent dust and scratches. You can also set it to 5.

Moreover, various protective layers, a -7-mirror layer, etc. can also be provided on the recording layer.

Furthermore, it may have a non-reflective structure.

(2) Specific Effects of the Invention In general, the medium of the present invention is irradiated with predetermined recording light in a pulsed manner from the recording layer side while running. At this time, the thermoplastic resin is melted by the heat generated by the light absorber in the recording layer, and a bit is formed.

The bits formed in this manner are read by detecting the reflected light of the read light while the medium is running.

On the other hand, erasing may be performed by heating the whole or a part of the medium, or by irradiating the whole or a part of the medium with erasing light.

It is also possible to perform line erasing by scanning the erasing light while the medium is running.

By such heating or irradiation with erasing light, the recording j- in the bit forming area is flattened, and writing and reading can be performed again.
− becomes μ ■ ability.

(2) Specific Effects of the Invention Furthermore, when rewriting is performed after erasing once formed bits, the thermal erasing temperature can be lowered or the erasing light intensity can be reduced, and erasing performance is improved. Furthermore, when line erasing is performed by scanning with erasing light, the line width for line erasing can be narrowed.

Then, the deterioration of erasing due to repeated erasing becomes extremely small.

In addition, there is no clear threshold value for the optical energy or temperature required to form bits in the recording layer, and the region of light intensity where bit formation becomes unstable becomes narrow, and the S/N ratio due to fluctuations in the output of the recording light increases. Fluctuations in the ratio will also be reduced.

The inventors conducted various experiments to confirm the effects of the present invention. An example is shown below.

Experimental Example 1 Polystyrene (
psB was obtained by molecular weight fractionation.

In this case, the molecular weight distribution of each polystyrene is 50
% or more was within ±30% of the number average molecular weight.

On the other hand, as a light absorber, Kayaset Blue 814 (manufactured by Nippon Kayaku Co., Ltd.), an anthraquinone dye, was used.

These were dissolved in toluene so that the weight ratio of polystyrene to dye was 5:1, and a recording layer with the thickness shown in Table 1 was formed on a 30 cInφ acrylic substrate with a 100 OA At reflective layer on the surface. Painted.

The transmittance of each sample to He-Ne light is 70%.
It was below.

Then, 8 mW of He-Ne was applied while rotating each sample.
The laser beam was focused on a 1μ beam and pulsed. The duration of the pulse was changed, and the duration of the pulse during which bits were formed on the surface of the recording layer was measured, and the value was determined as the reciprocal of the writing sensitivity (μ5ec).

The results are shown in Table 1.

Next, writing was performed by fixing 1 μSee Ic in the pulse of the laser.

After that, a 1 mW lie-Ne laser was focused to 1 μm diameter using the same optical system as above, and irradiated for 0.5 μsec at a repetition frequency of 50 Hz. The reflected light was detected by a photodiode and read out. and the S/N ratio (
dB) was calculated. In this case, the amplifier system is 10M
Hz band was used, and for noise, 1MS value (effective value) was used. The results are shown in Table 1.

Furthermore, an infrared heater heated each medium to 120°C, 2
Erasing was performed by heating for 0 seconds.

Whether the erasure was successful or not is indicated by O and X in il.

From the results shown in Table 1, the effects of the present invention are clear.

Experimental Example 2 In the medium/Vi1 to Vi4 of Experimental Example 1, an ultraviolet curing resin (photoresist,
AZ 1350J (manufactured by Shipley) was layered at a thickness of 07 μm to prepare media/169 to 12, and the reciprocal of the writing sensitivity was measured. °The results are shown in Table 2.

Note that the readout S/N ratio is approximately the same, and
Good erasing was possible with each medium.

Table 2 9 0.01 0.1 10 0.6 0.1 11 1.2 0.2 12 3 0.2 From the results shown in Table 2, the effect of the second invention of this application is clear.

Experimental Example 3 In Experimental Example 1, the type and number average molecular weight of the thermoplastic resin were changed as shown in Table 3 below, and the dye was changed to 1.
: Type 2 metal complex dye Eizenspiron Black RLH
Mediums 413 to 18 were produced in the same manner except that Special (manufactured by Hodogaya Chemical Co., Ltd.) was used.

In this case, the recording layer thickness was 08 μm. Further, the molecular weight distribution of each resin was such that 50% or more of the total number was within ±50% of the average molecular weight, and the weight ratio of resin to dye was 3 nia.

In addition, in Table 3, VA is vinyl acetate.

The polyester (PEs) was obtained by condensation of cono-phosphoric acid and tetramethylene glycol and the molecular weight was fractionated.
used had a degree of acetylation of 2%, a degree of butyrylation of 53%, and a degree of hydroxylation of 1.5%.

Furthermore, for medium A13.15.17, the intermediate layer in Experimental Example 2 was interposed to produce a medium of %19 to 21.

The characteristics of these media/1613 to 21 were measured in the same manner as in Experimental Example 1.

The results are shown in Table 3.

From the results shown in Table 3, the effects of the first and second inventions of this application are obvious.

Note that it has been confirmed that this uneven effect can be equally reproduced even when other thermoplastic resins or other light absorbers are used.

Applicant: Tokyo Denki Kagaku Kogyo Co., Ltd. Agent Masu Burier Yo Ishii -

Claims (1)

[Scope of Claims] 10. An optical recording medium comprising a recording layer containing a low molecular weight thermoplastic resin and a light absorber on a reflective substrate. 2. The optical recording medium according to claim 1, wherein the low molecular weight thermoplastic resin has a number average molecular weight of 30,000 or less. 3. The optical recording medium according to claim 1 or 2, wherein the transmittance of the recording light to the reading light is 70% or less. 5. The optical recording medium according to any one of claims 1 to 4, wherein the substrate has a reflective layer on its surface. 6. The light according to any one of claims 1 to 5, which performs recording by deforming the recording layer by irradiating the recording light to form pits that can be erased by heat or light. recoding media. 7. An optical recording medium comprising an intermediate layer on a reflective substrate, and a recording layer containing a low molecular weight thermoplastic resin and a light absorber on the intermediate layer. 8. The optical recording medium according to claim 7, wherein the low molecular weight thermoplastic resin has a number average molecular weight of 30,000 or less. 9. The optical recording medium according to claim 7 or 8, when the transmittance of the recording layer to the protruding light is 70% or less. 10. The optical recording medium according to any one of claims 7 to 9, wherein the recording layer has a thickness of 0.007 to 7 μm. 11. The optical recording medium according to any one of claims 7 to 10, wherein the substrate has a reflective layer on its surface. 12. The optical recording medium according to any one of claims 7 to 11, wherein the thickness of the intermediate layer is 0.001 to 20 μm and the Al% is allowed. 13. The light according to any one of claims 7 to 12, which performs recording by deforming the recording layer by irradiating the recording light to form pits that can be erased by heat or light. recoding media.