JP3080454B2 - Card type optical recording medium and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal polymer (LCP)
The present invention relates to a card-type optical recording medium having a recording layer made of, and reversibly recording and erasing information by light irradiation, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a so-called heat mode recording system for applying information in the form of thermal energy and recording as a change in shape or a change in physical properties of a recording material has been put into practical use.
Such heat mode recording media include Te, B
Inorganic recording media using metal materials containing i, Se, Tb, In, etc. as main components, or polymethine dyes such as cyanine, macrocyclic azaannulene dyes such as phthalocyanine, naphthalocyanine and porphyrin, naphthoquinone and anthraquinone Recording media using organic dyes such as dyes and dithiol metal complex dyes are known.
In these recording media, heat energy is applied by irradiation of condensed laser light or the like to melt or evaporate the irradiated recording layer to form holes (pits) and record information. However, these recording media have no possibility of erasing the recorded information and recording new information again.

On the other hand, as a reversible recording medium capable of recording, reproducing and erasing, an optical thin film using an alloy thin film composed of a rare earth metal such as Gd, Tb and Dy and a transition metal such as Fe, Ni and Co is used. And a magnetic recording medium. However, this magneto-optical recording medium has a low sensitivity at the time of reproduction and has a low S / N ratio.
It has disadvantages such as a poor ratio, a deterioration in recording sensitivity due to the effects of oxidation and the like, and a problem in storage stability of recording.

On the other hand, as a reversible recording medium using an organic material, VP Shibaev et al., Polymer Communication
s, Vol. 24, pp. 363-365, 1983 and Japanese Patent Application Laid-Open No. 58-125247, which disclose reversible heat or electric fields using transparent and opaque non-aligned states of polymer liquid crystals. There is disclosed a recording medium that can be dynamically changed.

[0005] As one of the application examples of the optical recording medium, an optical card has recently attracted attention. This is a next-generation media featuring large capacity and high reliability, due to the social background that the number of light emitting cards, especially magnetic cards, has increased dramatically and is being used in a wide variety of fields. This is because one of them is in the spotlight. Various reports have been made on this optical card system so far, for example, USP 4,278,756 and USP 4,284,716, etc., report a so-called read-only or write-once optical card using a silver salt or the like as a recording layer. However, they have no possibility of reversible recording. As a card type recording medium using the above-mentioned polymer liquid crystal, for example, there is one disclosed in JP-A-63-51193. In this case, a polymer liquid crystal layer is used as a display portion. Not considered. Also, JP-A-63-284291 and JP-A-6-284291
No. 4,705,584 discloses a ferroelectric polymer liquid crystal (FL).
Although an application of an optical card using CP) is exemplified, there is no particular change as compared with an optical card using a low-molecular ferroelectric liquid crystal, and when an optical recording system is examined, an electric field or a magnetic field is applied. The mechanism is clearly disadvantageous in terms of system configuration and cost, and has not been put to practical use.

[0006]

The conventional reversible recording system using a polymer liquid crystal has various problems such as the recording and erasing transfer speeds and reliability. In particular, it is desired that the erasing speed be increased and the erasing be performed with high reliability without erasure. In the case of a recording medium using a polymer liquid crystal exhibiting the above ferroelectricity, the dielectric anisotropy is also high in response. In many cases, the orientation direction is positive, so that the orientation direction of the component (homeotropic orientation) which is perpendicular to the recording film surface becomes strong. However, it is known that the difference between the birefringence in the alignment and the non-alignment state is larger than the difference in the birefringence between the two states due to switching of the alignment direction of the liquid crystal part. Even when considering the fact that it is composed of an orthoscope composed of a light source and a pair of polarizers, it is easier to orient the recording layer material parallel to the recording film surface (homogeneous orientation). Obviously, However, when a ferroelectric polymer liquid crystal having a negative dielectric anisotropy is used, homogeneous orientation appears, but its response is not much different from that of a normal polymer liquid crystal, and its structure is special. Therefore, it was disadvantageous in terms of cost and was not practical.

In view of the above circumstances, the present invention provides a highly reliable erasing performance while maintaining a high S / N ratio by using a polymer liquid crystal reversible recording layer using a homogeneously oriented thermotropic polymer liquid crystal. It is an object of the present invention to provide a low-cost card-type optical recording medium.

[0008]

To achieve the above object, the present inventors reversibly change the polymer liquid crystal layer only by heat energy generated by light irradiation without the need for electric and magnetic fields. It has been found that the above object can be achieved by examining the recording and erasing conditions and appropriately selecting the light beam irradiation conditions during recording and erasing.

That is, according to the present invention, at least a heat-resistant resin layer on a plastic substrate, a photothermal conversion layer for absorbing irradiation light and converting it into heat, a polymer liquid crystal alignment layer, and a reversible change in alignment state or phase. It has a structure in which recording layers made of polymer liquid crystal that change and record and erase are sequentially laminated, and the recording layer changes its orientation state or phase state in a part of its thickness direction by short-time light irradiation. A card-type optical recording medium is provided.

Further, according to the present invention, the product (retardation) of the birefringence and the film thickness in the film thickness direction in the initial alignment state of the polymer liquid crystal constituting the recording layer in the above structure is 25-7.
The recording layer is formed such that the transmission or reflection polarization intensity Ib before the recording is smaller than the transmission or reflection polarization intensity Ia after the recording. A card type optical recording medium is provided. When using this recording medium, the recording is performed such that the change in the reproduction light amount due to the change in the retardation in the film thickness direction of the recording layer is greater after recording than before recording,
Further, it is possible to perform recording and erasing in which the recording pit is completely erased without applying an external force.

Further, according to the present invention, there is provided the method for manufacturing a card-type optical recording medium, wherein a heat-resistant resin layer is used as a primary substrate, and a photothermal conversion layer, a polymer liquid crystal alignment layer and a recording layer are sequentially formed thereon. After that, a method for manufacturing a card-type optical recording medium is provided, which comprises attaching the plastic substrate to a plastic substrate.

Further, according to the present invention, the above-mentioned manufacturing method further comprises a step of providing a separate plastic substrate or a protective layer after laminating the recording layer with a heat-resistant resin layer. A method for manufacturing an optical recording medium is provided.

Hereinafter, the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the basic structure of a card-type optical recording medium according to the present invention is a recording comprising a heat-resistant resin layer 2, a photothermal conversion layer 3, a polymer liquid crystal alignment layer 4, and a polymer liquid crystal on a plastic substrate 1. The layers 5 are sequentially laminated. The heat-resistant resin layer 2 is used as a primary substrate because a manufacturing process at a high temperature may be included when manufacturing the card-type optical recording medium. The light-to-heat conversion layer 3 absorbs irradiation light during recording and reproduction and converts it into heat,
At the time of reproduction, it also has a function of reflecting irradiation light. The polymer liquid crystal alignment layer 4 is for uniformly aligning the polymer liquid crystal as a constituent material of the recording layer 5. The recording layer 5 performs recording and erasing by causing a reversible change in the alignment state or phase change by light irradiation.

The card type optical recording medium of the present invention is not limited to the one shown in FIG. 1, and various modifications and changes are possible. For example, a structure in which a heat-resistant resin layer is formed again on the recording layer 5 of the medium shown in FIG. 1 and the entire recording medium is laminated to serve also as a protective layer, or a substrate material is newly pasted thereon A structure in which the protective layer 6 is formed (FIG. 2) can be used.

[0015] Recording is performed by irradiating the optical recording medium with the focused beam light. That is, the light absorbed by the photothermal conversion layer 3 is converted into heat, and this heat is
, And the temperature of a part of the recording layer 5 is heated to a temperature equal to or higher than an isotropic phase transition temperature (isotropic point),
Thereafter, the light irradiation is stopped and the film is rapidly cooled, so that an isotropic portion is formed in the recording layer 5. In order to achieve such recording, it is necessary that a temperature distribution as shown in FIG. If the light irradiation is stopped at this time, the portion heated above the isotropic point will maintain this isotropic state after cooling and will be in a polarization optically different state, forming a recording pit.

The control of the size of the recording pit in the present invention is to control the size of the recording pit according to the recording light irradiation condition, and more specifically, by controlling the recording light intensity difference as shown in FIG. This means that the two states (a) and (b) are formed. That is, when the intensity of the recording beam light is low, the recording pits are formed in the photothermal conversion layer 3 in the recording layer 5 as shown in FIG.
When the intensity is high, the recording pit is formed to be larger than that in (a) as shown in (b), and the optical path length of the polarized light in the film thickness direction is unrecorded part> ( a)> meaning shorter in the order of the part in the state of FIG. 1 (b). At this time, information can be reproduced by detecting a change in the amount of transmitted or reflected light of polarized light under crossed Nicols. According to the previous report, the relationship between the retardation R and the reproduction light amount I is expressed by the following equation (1). I = I ₀ sin ² (πR / λ) (1) where I ₀ is the irradiation light intensity and λ is the irradiation light wavelength. R = △ n · d, where Δn is the birefringence and d is the optical path length.

The present inventors have studied this point, and have set the retardation R of the recording layer 5 to 25 to 750.
By controlling to the range of nm, the above recording state is achieved,
Further, they have found that the recorded pits can be completely erased only by light irradiation in addition to having a higher polarization transmittance after recording than in the unrecorded state, and have completed the present invention. Although the thickness of the recording layer is related to the layer configuration of the present recording medium, it is preferably in the range of about 0.5 to 2.5 μm for a reflection type medium, and about twice as large for a transmission type medium. Is preferred. Further, the birefringence is hard to be specified unequivocally because the birefringence also depends on the structure and orientation state of the mesogen portion of the polymer liquid crystal, but a range of about 0.05 to 0.3 is preferable.

The term “recording by light irradiation for a short time” as used in the present invention means that the scanning of the light beam irradiating the recording medium is performed at such a speed that the exposure time per point is several ms or less. More specifically, it is desirable that the time be several tens μs or less. If the exposure time is extremely short, that is, several ns or less, the recording layer 5 is not heated above the isotropic phase transition temperature, and no recording pits are formed. If the time is extremely long, the part heated above the isotropic phase transition temperature will diffuse,
Since the entire film thickness is in an isotropic state, it cannot be easily erased.

Deletion of a record in the recording medium of the present invention
When the recording pit held in the isotropic state is reheated, the viscosity of the micro area containing the pit is reduced, and the molecules in the area are allowed to move, and the surrounding polymer liquid crystal is aligned. This is achieved by receiving the alignment regulating force from the molecules and the alignment layer and realigning the polymer liquid crystal molecules in a random state. The temperature at which this molecular reorientation occurs is preferably several degrees C. to several tens degrees C. below the isotropic point, but in order to perform complete erasure without erasure, at least the entire recording pit should fall within this temperature range. It needs to be heated. On the other hand, when recording, it is easier to erase if only a part of the recording layer is changed, so it is achieved by heating a part of the recording layer above the isotropic point by short-time exposure using strong laser light Therefore, it is desirable that the temperature distribution in the recording layer changes rapidly in the film thickness direction. However, it is preferable that a gradual temperature change occurs during erasing, and this is achieved by irradiating a laser beam of weak intensity for a relatively long time. At this time, for example, if only the intensity is weakened for the same irradiation time as during recording, the entire recording pit cannot be heated uniformly, and if only the irradiation time is increased, the deep portion in the film thickness direction is heated to a high temperature, and eventually. Will be re-recorded.

Next, the constituent materials of the substrate 1 of the recording medium according to the present invention will be described. Various known materials can be used for the substrate material. However, considering the portability of the card, various plastic substrates are most suitable. , Specifically, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyvinyl acetate, polyamide, polyimide, polyolefin, acrylic resin, phenol resin, epoxy resin,
It is possible to use fluororesins and the above-mentioned derivatives.

In the course of producing the recording medium of the present invention, there is a possibility that, during the alignment treatment of the polymer liquid crystal or the formation of the alignment layer, a step of performing the treatment at a temperature range of 100 ° C. or more for tens of minutes or more may appear. There is. In such a case,
Polyimide, epoxy resin,
Alternatively, only very limited materials such as fluororesins can be used.On the other hand, since these substrate materials do not have too high a birefringence or transmittance of irradiation light, it is difficult to use them at a film thickness at present. is there.

Therefore, the present inventors formed the heat-resistant resin layer 2 as a primary substrate, formed thereon a light-to-heat conversion layer 3, a polymer alignment layer 4, and a recording layer 5, and then bonded the plastic substrate 1 to the layer. By combining them, a method of producing the card type recording medium was adopted. Thereby, the manufactured card-type optical recording medium has high reliability.

The heat-resistant resin layer 2 can be made of a material such as polyimide, epoxy resin, fluororesin, etc.
５０50 μm is appropriate.

As the polymer liquid crystal used for the recording layer 5 in the present invention, known liquid crystals can be used, and those having a mesogen moiety in the main chain or side chain and having an average molecular weight of 500 or more can be used. Further, the polymer liquid crystal may be crosslinked, and more preferably a photocrosslinkable liquid crystal.

Hereinafter, specific examples of the polymer liquid crystal used in the present invention will be described. In the following, * indicates an asymmetric carbon atom.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

[Table 4]

[0030]

[Table 5]

[0031]

[Table 6]

[0032]

[Table 7]

[0033]

[Table 8]

[0034]

[Table 9]

[0035]

[Table 10]

[0036]

[Table 11]

[0037]

[Table 12]

Such high-molecular liquid crystals are usually used alone or as a mixture, and it is also possible to add other low-molecular liquid crystals. The low-molecular liquid crystal added here is intended to improve the recording and erasing characteristics by controlling the viscosity and phase transition temperature of the high-molecular liquid crystal, and those known as nematic, smectic or cholesteric liquid crystals are used. it can.

Using such a polymer liquid crystal, ketones such as methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, ester compounds such as butyl acetate, ethyl acetate, methyl acetate, carbitol acetate and butyl carbitol acetate, methyl It is dissolved in a solution such as an ether type such as cellosolve, ethyl cellosolve, and tetrahydrofuran, an aromatic type such as toluene and xylene, an alkyl type such as dichloroethane, N, N-dimethylformamide, NN-dimethylacetamide, and an alcohol type. For example, a solution coating method such as dip coating, spray coating, spinner coating, blade coating, roller coating, curtain coating, wire coating, etc. It can be formed by coating from the state.

As the material for forming the light-to-heat conversion layer 3 used in the present invention, known materials can be used. Specifically, for example, gold, platinum, silver, copper, lead, zinc, aluminum, nickel, tantalum , Cobalt, chromium, germanium,
Various metals such as niobium, palladium, tin and the like, and vapor deposition of metalloid, CVD, sputtering film and the like can be mentioned. The light-to-heat conversion layer 3 can also be used as a reflection layer that reflects part of the irradiation light during reproduction or the like.

Known materials can be used as the material of the alignment layer 4. Specifically, a material obtained by rubbing polyimide or a precursor thereof such as polyamic acid, or silicon oxide or the like is obliquely applied. Evaporated ones can be used.

[0042]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to only these examples.

Example 1 A polyimide film having a thickness of 30 .mu.m was W35 mm.times.D7
It was cut to 0 mm and used as the primary substrate 2. While patterning in the longitudinal direction on the primary substrate 5 as shown in FIG. 5, a chromium film was deposited to a thickness of 1000 ° to form the photothermal conversion layer 3. Since the photothermal conversion layer 3 also serves as a tracking and focusing group, the pitch is 20 μm.
m and a width of 10 μm. On this, silicon oxide was needle-evaporated at an angle of 60 ° with respect to the longitudinal direction of the substrate to form an orientation layer 4.
After the formation of No. A recording layer 5 having a thickness of 1.6 μm was formed on the alignment layer 4 using a solution obtained by dissolving about 10 wt% of the polymer liquid crystal of 33 (Table 5) in tetrahydrofuran. Place this sample in an oven at about 170 ° C for 30
After performing the alignment treatment for 5 minutes, observation with a polarization microscope confirmed that the recording layer 5 had good alignment. Next, the primary substrate of this sample and a polycarbonate substrate (W54 mm × D86 mm × t0.55 m
m) was bonded using an ultraviolet-curable resin, and the recording layer 5 was similarly W54 mm × D86 mm × t0.15 m
m of an acrylic resin plate was applied to form a protective layer 6, thereby producing a card-type optical recording medium according to the present invention.

Next, a semiconductor laser having a wavelength of 780 mm was used as a light source, and was condensed to φ5 μm.
The recording layer of the present recording medium was irradiated from the substrate side at 00 mm / s, an intensity of 13 mW, 10 kHz and a duty ratio of 50%, and recording was performed. Using this recording medium, a polarizing plate was provided on the optical path of the semiconductor laser and the φ5 μm condensing optical system before and after the recording layer was incident and after reflection, respectively. For the reflected light, a laser beam intensity was reduced to 3 mW on the sample surface using a system capable of measuring the amount of light by a pin photo dye auto after the second polarizing plate.
Reproduction of the preceding recording portion was performed at 0 mm / S. The obtained response was subjected to Fourier transform and its C / N was measured. As a result, it was confirmed that a C / N of at least 35 dB or more was obtained.

Next, the recording medium was exposed to CW (continuous lighting) at an intensity of 7 mW and a linear velocity of 1 mm / S by the same operation as during recording, and an erasing operation was performed. Observation with a microscope confirmed that the recording pits were completely erased.

[0046]

According to the present invention, recording is performed by changing the orientation of a part of the thickness of the polymer liquid crystal recording layer in the thickness direction. Since the changed portion easily returns to the original state at the time of erasing, there is no erasure left, the erasing speed is increased, and a new highly reliable card-type optical recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structural example of a card-type optical recording medium of the present invention.

FIG. 2 is a cross-sectional view showing another example of the structure of the card-type optical recording medium of the present invention.

FIG. 3 is a cross-sectional view showing a temperature distribution to be formed in a recording layer.

FIG. 4 is an explanatory diagram of control of the size of a recording pit.

FIG. 5 is an explanatory diagram of manufacturing a medium in an example.

[Explanation of symbols]

 Reference Signs List 1 plastic substrate 2 heat-resistant resin layer (primary substrate) 3 light-heat conversion layer 4 polymer liquid crystal alignment layer 5 recording layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B42D 15/10 511 B41M 5/26 G11B 7/24 522 G11B 7/24 571

Claims (4)

(57) [Claims] 1. A heat-resistant resin layer on at least a plastic substrate, a photothermal conversion layer that absorbs irradiation light and converts it into heat, a polymer liquid crystal alignment layer, and a reversible change in alignment state or phase change to record. It has a structure in which recording layers made of polymer liquid crystal for erasing are sequentially laminated, and the recording layer changes its orientation state or phase state in a part of its thickness direction by short-time light irradiation. Card type optical recording medium. 2. The product (retardation) of the birefringence in the film thickness direction and the film thickness in the initial orientation state of the polymer liquid crystal constituting the recording layer is in the range of 25 to 750 nm, and the recording layer is 2. The card type optical recording medium according to claim 1, wherein the recording is formed such that the transmitted or reflected polarized light intensity Ib before recording is smaller than the transmitted or reflected polarized light intensity Ia after recording. 3. The card-type optical recording medium according to claim 1, wherein a heat-resistant resin layer is used as a primary substrate, and a photothermal conversion layer, a polymer liquid crystal alignment layer, and a recording layer are sequentially formed thereon. And a method of manufacturing a card-type optical recording medium, which comprises attaching a plastic substrate. 4. The method of manufacturing a card-type optical recording medium according to claim 3, further comprising a step of providing a separate plastic substrate or a protective layer after laminating the recording layer with a heat-resistant resin layer. Method.