JPS6212938A - Optical information recording element - Google Patents

Abstract

PURPOSE:To obtain an optical recording element having high information recording sensitivity and C/N and excellent heat resistance and durability as a substrate by incorporating 4-4'-(dihydroxyl diphenyl)-1-1-cyclohexane into a resin compsn. of the transparent plastic substrate. CONSTITUTION:The transparent resin compsn. having the excellent heat resistance and durability includes bisphenol A polycarbonate. The bulky molecular groups such as cyclohexyl groups which induce a steric hindrance are added to the isopropyl group among the isopropyl groups and carbonate groups in the chemical structure thereof. The increase of the specific heat near about 140 deg.C, i.e., sensible heat of melting specific to the bisphenol A polycarbonate is eliminated by using such resin compsn., by which the recording and C/N are eventually improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical recording Φ reproducing/erasing element, and in particular, an element having recording characteristics suitable as a substrate of an information recording medium and having heat resistance. , relates to an optical information recording element with excellent durability.

[Background of the invention]

An optical information recording element is formed by forming on a substrate a recording medium whose optical properties such as reflectance change depending on the source beam of a laser source, for example. For example, in the above, the recording medium is the third
As shown in the figure, a recording material whose reflectance changes with heat (such as a chalcogen compound) is placed on an optically transparent substrate 1 (such as glass, acrylic resin, polycarbonate, etc.) having information tracks and pits (not shown). , an amorphous thin film such as tellurium, etc.) 2 is formed.

5 is a protective film.

As an example of a detailed description of the structure of such an optical information recording element, see "Optical Technology" Contact J 1) 2.
6-55. vo122. There is No. 4 ('84).

However, in the optical information recording element configured as described above, the physical characteristics of the substrate material are
Properties such as regeneration and erasure, and durability effects may be exhibited.

In other words, when glass is used as a substrate, it is difficult to directly form information tracks or focal points on the glass surface, and it is difficult to form information tracks or focal points directly on the glass surface, so it is difficult to form information tracks or focal points directly on the glass surface.
It must be formed by a photo polymerization method, which poses a problem in productivity.

In addition, when using acrylic resin as a substrate material, injection molding method (Japanese Patent Application Laid-open No. 127940/1983) etc.
Information tracks, bits, etc. can be formed simultaneously, resulting in high productivity (and a photoelastic constant of 3 x 10-@II6”/
Since it is as small as glass (kg), it can be used as a substrate with low birefringence, and it is suitable for preventing the generation of laser noise, so it is used. However, this acrylic resin has a low heat resistance of less than 90°C, and a moisture absorption rate of Q,
It had the disadvantage of being large at 44.

On the other hand, compared to acrylic resin, bisphenol A polycarbonate is attracting attention as a transparent plastic material that has a low moisture absorption rate of Q, 1% and a heat resistance of about 140°C. This material has a photoelastic constant of 55 x 10-w
IP/kg, and is approximately 20 times thicker than acrylic resin (a great deal of effort has been spent on reducing or improving birefringence during substrate molding).

According to our studies, we have achieved birefringence comparable to that of acrylic resin by using bisphenol A polycarbonate, which has a low molecular weight and low resin melt viscosity, and by reducing molding strain.

On the other hand, the bisphenol A polycarbonate substrate obtained in this way has the same characteristics as the substrate made of acrylic resin.
As a result of comparing the recording characteristics, as shown in Table 1, the recording sensitivity was approximately 25 coefficients, and the carrier signal-to-noise ratio (C/'N) was 5 d.
Is B low? Q) This is because bisphenol A polycarbonate did not take into account the following points, even though its birefringence was as small as that of acrylic resin.

In other words, as noted in Table 1, the thermal conductivity of bisphenol A polycarbonate is 1% higher than that of acrylic resin.
In addition, bisphenol A polycarbonate has a crystallinity of about 0.3 to α5, and these grain boundaries cause light scattering, causing energy loss in the writing source, and furthermore, the specific heat It has a change point, that is, a latent heat of crystal fusion, and this change point is around 1406 C, which is the threshold temperature (~1
70° C.), the original energy required to raise the temperature of the information recording medium is lost due to latent heat of fusion.

[Purpose of the invention]

The purpose of the present invention is to achieve high speed recording sensitivity and high C/N (
Another object of the present invention is to provide an optical recording element having excellent heat resistance and durability as a substrate.

[Summary of the invention]

Bisphenol A polycarbonate is a resin composition that is transparent and has excellent heat resistance and durability, but as described above, it causes a decrease in recording sensitivity and a deterioration in C/N. This is due to not only high thermal conductivity but also high crystallinity.

That is, in the chemical structure of bisphenol A polycarbonate, isopropyl group CH.

(-C-) and carbonate group blasphemy This is because it greatly contributes to crystallization.

In the present invention, a bulky molecular group that causes steric hindrance, such as a cyclohexyl group, is added to the isopropyl group to inhibit the crystallization.

By using such a resin composition, the characteristic temperature of bispheno-A/A polycarbonate lc% is about 140°C.
It was possible to increase the specific heat in the vicinity, that is, to eliminate the latent heat of fusion, and as a result, it was possible to improve recording sensitivity and speed.

[Embodiments of the invention]

The configuration of an embodiment of the present invention is shown in FIGS. 1 and 2.

In FIG. 1, 1 is a transparent plastic substrate on which information tracks and pits are formed by injection molding, which is the object of the present invention;
Reference numeral 2 is a recording member provided on the substrate 1 and whose reflectance changes with laser irradiation, and 3 is a protective layer for the recording member made of an organic material such as an ultraviolet curing acrylic resin.

In the following examples of the present invention, the recording material is Sb,
A recording member with a two-layer structure in which a Bi thin film was formed on a Se thin film was used. In addition, the comparison of recording sensitivity in the examples was conducted by forming the optical recording element into a disk shape like the one made of acrylic resin,
Rotating at 1800 RPM and using a semiconductor laser with a wavelength of 850 nm, the laser power CP) and reflectance change ΔR are compared.

Here, the change in reflectance for a laser power of 1 oaJ/rn (
After recording/before recording) was defined as the recording sensitivity. In addition, the carrier signal-to-noise ratio (C/N) was compared at a recording frequency of 5 MI (z) and a sensor power of 5 mW @Example 1 As the substrate material, bisphenol A polycarbonate (4 −
4-dio-oxydiphenyl-2-2propane), and the substrate was molded at a molding temperature of 380°C and a substrate molding mold temperature of 110°C. The birefringence of the substrate 1a obtained in this way is about 5 in a single pass, which is equivalent to that of acrylic resin.
The recording film was formed on this substrate 1 and used as an optical recording element, and the recording sensitivity was evaluated. Compared to 5 times/(6oOttJ/n), the sensitivity was reduced by about 25 mm, and the C/N comparison was about 5 dB lower.

In addition, the specific heat measurement of this substrate 1 and the differential scanning calorimeter (
As a result of measuring the heat of transition with DSC), as shown in Figures 4 and 5, there was a clear change in specific heat around 1506C,
and endothermy was observed.

In an embodiment of the present invention, the substrate material has a melt viscosity of 4-4'-(dihydroxyldiphenyl)-1-1-cyclohexane with a number average molecular weight of about 9,500, which causes steric hindrance to the inglovir group. Using low-temperature materials, molding temperature: 380°C, substrate mold temperature: 110°C
It was molded under the following conditions.

The birefringence of the substrate 1b thus obtained was about 7°. The sensitivity of the recording film formed on this substrate is 5 times / (6
00ATA) and acrylic resin, and almost the same as that of potato.

As a result of examining this substrate by DSC, it was confirmed that there was no clear endothermic change around 150°C, and that it was not crystallized.

Example 2 4-4-(dihydroxyldiphenyl)-1-t cyclohexane is used as A, bisphenol A polycarbonate is used as B and copolymerized as (-A-B-A-B),
Using a copolymer composition having a number average molecular weight of about 9,500 and having a low melt viscosity, a substrate 1C was molded at a molding temperature of 380°C and a substrate molding mold temperature of 110°C. The birefringence of the substrate thus obtained was approximately 7°.

The sensitivity of the recording film formed on this substrate is 24 times / (6
0rJttJ/m ), and a slight decrease in sensitivity was observed, but no difference was seen in the C/N ratio compared to Banmaton. The results of measuring this substrate using DSC were also similar to those obtained in Example 2.

Example 3 Example 2. The optical information recording device made of the substrates obtained in Steps 3 and 3 was bonded together with adhesive 4 as shown in FIG. 5, so that it could be used on both sides. By doing so, it is possible to obtain the same recording sensitivity as that obtained in the above embodiment, and to obtain an 80°
It was confirmed that the substrate did not deform even if it was left at a high temperature of C for 1000 hours. On the other hand, in the case of acrylic resin, 7
00C, 6 hours, obvious deformation is seen.

As can be seen from the above examples, the reason for the decrease in recording sensitivity is that the crystal transition temperature of the substrate is close to the phase transition temperature of the recording film, and the latent heat of fusion associated with the transition is large. In this example, an example was described in which a molecular group that inhibits crystallization (cyclohexane) was introduced into the resin composition. By suitably introducing atomic groups, the wavelength of light is 6.
It is clear that similar effects will be exhibited if the light transmittance is 87' or higher in the range of 30 to 830 nm.

where at least one of X and Y is a molecular group that contributes to more steric hindrance than a methyl group, such as an ethyl group, a propyl group, or an isopropyl group.

Pentyl group, hexyl group, cyclohexyl group.

and/or by introducing bulky substituents such as halogens (C1, F, Br), etc., which inhibit crystallization and provide an optical information recording element with high sensitivity, excellent heat resistance, and durability. I can do it.

Similarly, as can be easily seen from the examples and objects of the present invention, in addition to the substitution of bulk molecular groups, a copolymerized polycarbonate having a polyester bond or a urethane bond is used, resulting in a substantially crystalline polycarbonate. or,
This can also be achieved by setting the transition temperature at which the endothermic reaction occurs to a temperature higher than the temperature at which the photothermal properties of the recording film occur.

〔Effect of the invention〕

The optical information recording element according to the present invention has high recording sensitivity,
In addition, it has excellent heat resistance, durability, and productivity.

[Brief explanation of drawings]

1 and 2 are a perspective view and a partial sectional view used to show an embodiment according to the present invention, and FIG. 3 is a diagram showing the structure of an optical information recording element to which the present invention is applied. The partial cross-sectional views, FIGS. 4 and 5, are diagrams used to explain changes in specific heat and endothermic changes of bisphenol A polycarbonate used in conventional substrates. 2... Recording medium, 3... Protective film, 4... Adhesive.

Claims (1)

[Claims] 1. In an optical information recording element that utilizes the fact that a transparent plastic substrate is heated by writing light and its optical properties change before and after heating, the resin composition of the transparent plastic substrate is 4 An optical information recording element comprising -4'-(dihydroxyldiphenyl)-1-1-cyclohexane.