JPS5853490A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a heat-mode optical recording medium permitting the erasing and rewriting of recorded information and having a high writing sensibility by using a polyurethane resin as a thermoplastic resin to be contained in the recording layer of the optical recording medium. CONSTITUTION:A recording layer of a thickness of 0.05mum-1mm., containing 1pt.wt. a thermoplastic polyurethane resin having urethane bonds (e.g., one obtained from condensation of a glycol and a diisocyanate) and 0.002-10pts.wt. a pigment (e.g., carbon black) or a light-absorptive dye, together with various oligomers or polymers and an additive (e.g., plasticizer, etc.), is formed on a base material (e.g., a glass or ceramic, etc.). Also, as needed, a metallic reflection layer and an undercoat of a resin are provided. In such an optical recording material thus obtained, uneven pits recorded by irradiation of lasers can be fused and flattened by reheating for restoration.

Description

[Detailed Description of the Invention] ■ Technical Field The invention of this application relates to optical recording media in more detail.
The present invention relates to a heat mode optical recording medium capable of erasing and rewriting recorded information.

l Conventional optical recording media have the feature 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.For this reason, research and development of various optical recording media have been carried out.
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Among such optical recording media, heat mode optical recording media are being actively developed because they require image processing in a dark room.

This 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 light to form small holes called pits. This is to record information.

However, conventional heat mode optical recording media have drawbacks in that information recorded as pits cannot be erased, and written information cannot be corrected or rewritten, or it is difficult.

To explain this situation more specifically, one of the conventionally known heat mode optical recording media is:
Some have a recording layer consisting of nitrocellulose and a light absorber.

When such a medium is irradiated with a laser beam as recording light in the form of a minute spot of, for example, about 1 μιφ, the irradiated area becomes extremely hot in a short time, and the nitrocellulose ignites and disappears, forming minute holes. One bit of information is recorded. However, recorded information cannot be erased from such media.

On the other hand, heat mode optical recording media having a recording layer made of tellurium or tellurium selenium-arsenic are also known. However, even in this case, since the bits are formed by melting metalloids with a high melting point, it is extremely difficult to restore the recorded bits.

Further, JP-A-55-161690 describes a heat mode optical recording medium having a recording layer made of a light-absorbing dye and a thermoplastic resin on a reflective substrate. In this medium, the recording layer is thinned to about 0.01 to 0.2μK, and by irradiation with laser light, the resin in the irradiated area is melted and moved, or the light-absorbing dye in the irradiated area is moved in a lateral direction. The reflective substrate is moved to form a diagonal surface to form a bit.

However, even in this case, it is difficult to return the light-absorbing dye that has once moved or to backfill and flatten the small holes that have once reached the layered layer. Therefore, the publication does not disclose or suggest that this medium is capable of erasing and rewriting recorded information.

In contrast, using a medium in which thermoplastic is coated on a conductive substrate, a charge is uniformly applied to the thermoplastic layer, a part of the thermoplastic is melted by laser light irradiation, and the volume change causes electrical A recording method is known in which a change in suction force is generated and bits are obtained from surface irregularities corresponding to laser beam irradiation. In this method, by reheating the medium, the surface unevenness returns to a flat surface and the recorded information can be erased, but it requires a corona discharger, etc., complicates the mechanism of the writing device, and consumes the device. There are disadvantages such as increased power consumption.

■ Purpose of the invention The invention of this application was made in view of the above circumstances.

The first object of the invention of this application is to provide a heat mode optical recording medium that is erasable and rewriteable, and to enable information to be written and erased using the medium.

The second purpose is to reduce the optical energy used to form pits in the recording layer in such erasable optical recording media.
A region of manual light energy or temperature in which a clear threshold value appears in temperature, bits are always formed with good reproducibility at input energy above a predetermined input energy, bits are not formed at energy below a predetermined value, and the reproducibility of bit formation varies. At the same time, the heat resistance is controlled.
S/N of information signal written to bits under high temperature storage
There is little deterioration in the ratio, and the readout light does not deform the surface of the focus or surrounding areas, the S/N ratio of the write information signal does not deteriorate, and the write sensitivity is good, and in addition, the readout S The purpose of this invention is to provide a medium with an extremely high /N ratio.

Other objects of the invention of this application will become clear from the following description.

The inventors of the present invention have extensively studied this purpose and found that when a recording layer is formed by incorporating a light-absorbing dye or pigment into a polyurethane resin, an erasable and rewritable medium can be realized. Moreover, the inventors have found that the second object described above can be effectively achieved, and have come up with the invention of this application.

That is, the invention of this application provides that a layer containing both a thermoplastic resin and a light-absorbing dye or pigment remains on the substrate at the bottom of the recording pit formed in the recording layer, and the recording pit is formed. The optical recording medium is configured such that the surface of the recording layer becomes flat by heating the recording layer, wherein the thermoplastic resin is made of a polyurethane resin.

■Specific structure of the invention Below, the specific structure of the invention of this application will be explained in detail.

In the optical recording medium in this application, the urethane resin on the substrate is a thermoplastic resin that softens or melts and deforms as the temperature rises in the area irradiated with recording light, forming erasable recording pits on the surface. be.

In this case, as the polyurethane resin, any thermoplastic polyurethane resin having urethane bonds can be used, but in particular, polyurethane obtained by condensation of glycols and diisocyanates [fats, especially alkylene glycols and alkylene Polyurethane resins obtained by condensation with diisocyanates are preferred.

The number average molecular weight of such a polyurethane resin is preferably 30,000 or less as long as it can be obtained as a solid.

This is because when the value is 30.000 or less, the broadening of the above-mentioned threshold value is further reduced, and both the writing sensitivity and the reading S/N ratio are further increased.

Such a polyurethane resin is produced by a conventionally known method, and is used after molecular weight fractionation or purification, if necessary. Alternatively, commercially available products may be used as they are, or after fractionation, purification, etc.

On the other hand, the recording layer contains a light-absorbing dye or pigment along with such a polyurethane resin. This light-absorbing dye or pigment exhibits a large light absorption rate for the recording light and causes a temperature rise in the irradiated area. It is intended to make it possible.

Therefore, depending on the wavelength of the recording light, it is possible to use various known dyes and various known inorganic or organic pigments such as carbon black, ultrafine metal powder, and lake pigments that absorb wavelength light of 400 to 800 nm. can.

On the other hand, the content ratio of the polyurethane resin and the light-absorbing dye or pigment contained in the recording layer is as follows:
Generally, it can be selected from a wide range of about 0.002 to 10 parts by weight.

Such a recording layer is coated on a substrate using various known methods such as a spinner or a coater. The thickness is generally 0.05 μS to 1 μS.

Note that such a recording layer may contain other additives in addition to the above-mentioned polyurethane resin and light-absorbing dye or pigment.

Examples of such additives include various oligomers and polymers. In this case, the polymer or oligomer is contained in an amount of approximately 30% by weight or less based on the polyurethane resin to improve adhesion to the support,
It is possible to improve the coating properties and change the softening temperature.

In addition, various plasticizers, surfactants, antistatic agents, lubricants,
Flame retardants, ultraviolet absorbers, antioxidants, stabilizers, dispersants, etc. can be included.

On the other hand, the substrate for supporting such a recording layer is not particularly limited, and any material can be used. However, in terms of thermal conductivity, various types of glasses, ceramics, polymethacrylic resins, polyacrylic resins, polycarbonate resins, phenol resins, engineered boxy resins, diallyl phthalate resins, unsaturated polyester resins, polyimide resins, etc. are usually used. It is preferable to use resin or the like. or,
The shape and dimensions vary depending on the application, such as disk, tape,
It can be a belt, a drum, etc.

In this case, the medium of this application may have the above-mentioned recording layer on one side of such a sand body, or may have recording layers on both sides. In addition, two substrates each having a recording layer coated on one side are used, and the recording layers are placed facing each other with a predetermined gap between them, and the substrate is sealed to prevent dust and scratches. You can also do it like this.

Note that the above-mentioned medium may be provided with a subbing layer such as a metal reflective layer or various resin layers, if necessary, and a recording layer may be provided on the subbing layer.

M. Specific Effects of the Invention Information can be written and erased in the following manner using the optical recording medium of this application configured as described above.

First, recording light is irradiated. Recording light can be used for various racers,
For example, He-Ne, He-Cd, Ar.

This is carried out by condensing various lasers such as semiconductors with wavelengths of about 400 to 850 nm, and various outputs can be used. Furthermore, the scanning conditions, pulse width, focusing conditions, etc. of the laser beam can be varied widely.

Then, by irradiating recording light with such a laser,
The polyurethane resin in the recording layer is melted and softened, and minute recording bits corresponding to the irradiated light are formed on the surface of the recording layer in the irradiated portions.

In this case, under normal recording light irradiation conditions, the recorded bits are
The stratification of the recording layer is not reached, and a layer containing polyurethane resin and light-absorbing dye or pigment remains at the bottom of the bit.

As a result of bits being formed in this manner, erasing, which will be described later, becomes possible. The medium of this application provides bits with extremely high sensitivity and a good shape. Furthermore, the broadening of the national value of the recording light energy required for bit formation is extremely small.

Furthermore, even when stored at high temperatures, the S/N ratio of the read light from the bits deteriorates very little.

On the other hand, in order to read out the information written on the medium from the bits formed in this way, a reading laser beam with lower power than the recording beam is used, which is focused and scanned.
Detects the output of either transmitted or reflected light.

At this time, as described above, the bits formed on the medium of this application have a good shape, and a high S/N ratio can be obtained during reading.

Also, the S of information recorded on the medium by the readout light is
There is no possibility that the /N ratio will deteriorate or that unnecessary information will be recorded in areas other than the bit part.

On the other hand, to erase information recorded in this way,
All you have to do is reheat the medium. At this time, the surface that has been recorded and has become an uneven bit is remelted and returns to a flat surface. As heating for erasing, any of laser light irradiation, heating with various heaters, infrared lamp irradiation, etc. may be used.

Then, when such erasing and writing are repeated, the writing sensitivity is always good, the bit always shows a good shape, reading with a high S/N ratio is performed, and further reading causes the S/N ratio to decrease. Since the surface does not deteriorate and always returns to a flat surface after erasing, erasing and writing can always be performed reliably and satisfactorily even if erasing is repeated many times.

■ Specific effects of the invention Information is written using the optical recording medium of this application,
When the information is subsequently erased, the information once written can be easily and reliably erased.

Further, the broadening of the dark value of the optical energy or temperature required for bit formation in the recording layer is extremely small, and the range of input optical energy or temperature that balances the reproducibility of bit formation is extremely narrow.

Moreover, it has high heat resistance, and even if it is stored at a high temperature of about 50 to 60° C., there is very little deterioration in the S/N ratio of the information signal recorded in the pits.

Further, there is very little change in the shape of the bit or the shape around the bit due to the readout light, and there is very little deterioration in the S/N ratio due to repeated irradiation with the readout light.

In addition, the writing sensitivity is good, and a high S/N ratio can be obtained whether transmitted light or reflected light is used for reading.

Moreover, since the erasure is always stable.

Even if erasing and rewriting are repeated many times, information can be written in a sufficiently stable manner.

In this case, the number average molecular weight of the polyurethane resin is 30.0
When using 00 or less, these effects become even more excellent.

The present inventors carried out Tokkutsu fruit cultivation in order to confirm the young fruits of the present invention. One example is shown below.

Experimental Example 1 As a polyurethane resin, condensation polymerization of tetramethylene diisocyanate and hexamethylene glycol was carried out in Kizilor, and the molecular weight was fractionated to determine the number average molecule! 8,
000 polyurethane was obtained.

This polyurethane and lake pigment (C・■・Pigme
nt Blue l, color index number 42595-Lake; Fanal manufactured by BASF
Blue BSupra) at a weight ratio of 3:1.
・After mixing and dispersing with a sand grind mill,
Particles of 0.5μ or more were removed with a filter, and coated with a bar code on a 150μφ, 1.2m thick Pyrex glass plate with a thickness of 30μ and a thickness of 1μ.
Separately from this application, for comparison purposes, the fat was replaced with polystyrene, polyethylene, and polypropylene, each having a number average molecular weight of 10,000, to obtain three comparative media.

Among these 4aI media, the relationship between the deformation of the recording layer surface and the temperature was measured for one having a recording layer with a thickness of 30 μm. That is, the medium is placed in a constant temperature bath, and 0.0% is applied to the surface of the recording layer.
An enclosure of 64 mφ and 50 f was placed, and while the temperature was raised at 5° C./min, the relationship between the degree of penetration of the enclosure into the layer was measured. Then, the temperature was measured from when the sealing material began to penetrate into the layer until it reached a certain penetration depth, and the broadening of the bit formation value was evaluated. The results are shown in Table IK″ below., 83.4..5sczt1, .

The following experiment was carried out on a device with a thick recording layer.

First, a 10 mW He-Ne v-laser was focused for 1/4 s using an objective lens with an AN (numerical aperture) of 0.55.40 times, and pulse irradiation was performed. The pulse width was changed, and the pulse width at which pits were formed on the surface of the recording layer was measured, and was taken as the reciprocal of the writing sensitivity (μsec). The results are shown in Table 1. At that time, we lowered the ambient temperature by 20°C and irradiated a pulse with the previously obtained frequency to evaluate the broadening of one value of the input energy. was performed, whereas no bit formation was performed in the medium of the invention of this application.

Next, the pulse width of the laser was fixed to 0.5 μsec and writing was performed, and then a 1 mW He-Ne laser was focused on a 1 μ φ with the same optical system as above for 3.1 μs.
ec at a repetition frequency of 10 Hz, the reflected light was detected by a photodiode, and the S/N ratio was calculated.

In this case, the amplifier system used was one with a 10 MHz band, and the RMS value (effective value) was used for the noise. The results are shown in Table 1.

In addition, each medium was stored at 70° C. for 100 hours, and the deterioration (%) of the S/N ratio thereafter was measured to evaluate heat resistance.

The results are shown in Table 1.

Further, the pulse repetition frequency of the extrusion laser was changed, irradiation was performed for 10 seconds, and the reading light frequency at which pits were formed on the surface of the recording layer was measured. The results are shown in Table 1.

From the results shown in Table 1, it can be seen that polyurethane resin has extremely superior properties compared to other resins.

Solid Line Example 2 In the medium of this application in Experimental Example 1, the number average molecular cap of the polyurethane resin is 3,000, l(
,000, 30,000, and 100,000, and the organic pigment (referred to as OP) was replaced with copper-phthalocyanine dye oleosol fast blue EL (
Various media were prepared in the same manner as in Experimental Example 1, except that Sumitomo Chemical Co., Ltd. (referred to as D), 13 μm carbon black (referred to as CB), and 10 nm Ni ultrafine powder (manufactured by Shinku Yakiniku Co., Ltd., referred to as Ni) were used. An experiment was conducted.

The results are shown in Table 2.

Table 2 Molecular weight (℃) (μsec) Ratio 3.000
D 41 0.7 48” CB 40 0.8
46 I/ OF 4 (10,845 8,000D 42 0.8 46 tt Ni 41 0.9 44 /l OP 40 0.9 43 30.000 D 42 0.9 42# CB
42 1.0 40 tt Ni 42 1.0 40 100.000 D 44 2.6 17" CB4
3 2.7 15 ” OP 43 2.8 14 The heat resistance of all media is 6% or less,
Regarding the generation of noise due to readout light, it can be seen from the results of frequency table 2 at 300 Hz for all media that more favorable results can be obtained when the number average molecular weight of the polyurethane resin is 30,000 or less.

It should be noted that it has not been possible to achieve this effect by using dyes or pigments for semiconductor lasers, or by using other thermoplastic polyurethane resins. Patent attorney Yo Ishii −

Claims (1)

[Claims] A recording layer containing a thermoplastic resin and a light-absorbing dye or pigment is formed on a substrate, and upon irradiation with recording light, the recording layer melts and softens to form recording pits, which are formed in the recording layer. A layer containing both a thermoplastic resin and a light-absorbing dye or pigment remains at the bottom of the recording pit, and by heating the recording layer in which the recording pit is formed, the surface of the recording layer becomes flat. An optical recording medium configured as follows, wherein the thermoplastic resin is a polyurethane resin.