JPH04151623A - Information memory medium and information memory device - Google Patents

Abstract

PURPOSE:To obtain a good contrast and C/N by using a simple recording, reproducing and erasing device by using the information memory medium having the recording layer contg. a uniaxially oriented high-polymer liquid crystal compd. CONSTITUTION:The recording layer 3 contg. the high-polymer liquid crystal compd. is uniaxially oriented and the ¦DELTAnd¦ (DELTA=n -nrt. angle, d: denotes the film thickness (mum) of the recording layer 3 and n denotes a refractive index) to reproducing light 16 is lambda(m+ or -1/4) (m: 0 to 3 integer, lambda: the wavelength (mum) of the reproducing light). The high reflectivity and the good contrast are obtd. by using the information memory medium having the recording layer 3 contg. the uniaxially oriented high-polymer liquid crystal compd. in such a manner.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an information storage medium that reversibly and optically stores an extremely large amount of data, and an information storage device using the same, and in particular to an information storage device using the same. The present invention relates to an information storage medium and an information storage device used in a recording layer.

[Prior Art] Optical storage systems are currently in practical use as they have a large capacity and are excellent in random access. There are many different ways to do this, and for playback only, digital audio discs (C
D) and laser video discs (LD) have been put into practical use. Write-once optical discs (
WO), optical cards (OC) are known, and some use phase change of a metal thin film and others use a bit format of organic dye.

Furthermore, research on rewritable optical disks is progressing, and efforts are being made to put those using the magneto-optical effect and those using phase change into practical use. Among these, polymer liquid crystals have also been proposed as information storage media.
Publication No. 0, JP-A-59-35989, JP-A-62
-154340). Among them, a recording method has been proposed in which the helical pitch length of cholesteric polymer liquid crystal is changed or the light reflectance is multi-valued by forming bits in a non-oriented state (Japanese Unexamined Patent Application Publication No. 1983-1982-1). 107448, JP-A-62-12937).

In addition, since polymer liquid crystals have birefringence, alignment treatment is performed, and a method using the birefringence has also been proposed.
Publication No. 0, Japanese Patent Application Publication No. 63-266647, Japanese Patent Application Publication No. 1999
-162245 Publication) Information storage media using such polymeric liquid crystals are easier to create than magneto-optical media or inorganic phase change media manufactured by vapor deposition, etc., and have excellent optical properties. ing.

[Problems to be Solved by the Invention] However, in the conventional example described above, the one using reflection uses a polarizing beam splitter and a quarter-wave plate to separate and detect the reflected light, and the recording layer This method detects changes in the amount of reflected light due to absorption, scattering, diffraction, etc., and the utilization efficiency of irradiated light tends to be low, and alignment of the polarization plane of the device is complicated.

Furthermore, in media and devices using the magneto-optical effect, linearly polarized light is irradiated, but since the rotation of the plane of polarization is negligible, the configuration of the medium and the device are complicated and the efficiency is low.

The present invention has been made to improve the shortcomings of the prior art, and aims to provide an information storage medium that can obtain high reflectance and good contrast, and an information storage device using the same. This is the purpose.

[Means for Solving the Problems] That is, the present invention provides an information storage medium having a recording layer containing a polymeric liquid crystal compound and a reflective layer on a substrate, in which the recording layer containing the polymeric liquid crystal compound is uniaxially aligned. and
and 1Δndl (Δn = nl −n
l, d: represents the film thickness (gm) of the recording layer. n represents the refractive index. ) is λ(mfl/4) (m: an integer of 0 to 3, λ: wavelength (μm) of reproduction light).

Further, the present invention has a recording layer containing a polymeric liquid crystal compound and a reflective layer on a substrate, the recording layer containing the polymeric liquid crystal compound is uniaxially oriented, and 1Δn with respect to reproduction light.
dl (Δn=nI-n↓, d: represents the film thickness (gm) of the recording layer. n represents the refractive index) is λ (1/4 above m)
(m: integer from 0 to 3, λ: wavelength of reproduction light (#Lm)
represents. ), a means for irradiating the information storage medium with linearly polarized light tilted by 35° to 55° with respect to the uniaxial orientation direction of the information storage medium, a means for separating the linearly polarized light, and a means for separating the linearly polarized light; An information storage device characterized by having means for detecting intensity.

The present invention will be explained in detail below.

The present invention provides an information storage medium having a recording layer containing a -axis aligned polymer liquid crystal and a reflective layer on a substrate, in which linearly polarized light is recorded at an angle of 35° to 55° with respect to the -axis alignment axis. An information storage medium in which light is transmitted through the recording layer, and reflected light from the reflective layer is transmitted through the recording layer again, and the recording layer has a glue tarp.
John (1Δnd1) (Δn:nI-nt, d: Represents the film thickness (μm) of the recording layer.) Replacement (1/4 above m)
(m: integer of O40, λ: reproduction light wavelength (μm)
), this eliminates the need for a 1/4 wavelength plate and achieves high reflectance and good contrast.

In the present invention, the polymeric liquid crystal compound used in the recording layer has a high birefringence (Δn), which is compared to the thickness required to obtain λ/4 retardation with conventional stretched polymers, etc. Therefore, a thickness of 1/10 to 1/1000 has sufficient advantages. Furthermore, by using the glass transition point or viscosity effect, it is possible to change and fix the orientation state or birefringence.

The birefringence of the polymeric liquid crystal compound used in the present invention is usually 0. O1-2.0, preferably 0.05-1.0
Desirably, if it is less than 0.01, the thickness of the recording layer necessary to obtain the necessary turpitude becomes too large, causing difficulties in manufacturing the recording layer, and recording sensitivity also decreases.

If it exceeds 2.0, the thickness of the recording layer that provides the lowest order turbulence becomes too small, making it difficult to form it uniformly and making it impossible to obtain good optical properties.

Examples of polymeric liquid crystal compounds that can be used in the recording layer of the information storage medium of the present invention include the following.

(In the following formulas (1) to (13), p=5 to 1000.
1≦<15.

(lO) (In the following formulas (14) to (17), p=5~1000° 1)l+1)2= S~1000° q = 1-16 ql: 1~16° qz= 1-16 It is.

CH3 −+ CH2-C → “ -(-CH2-C→“ (In the formula, R”-CH3゜ -H or -Cp shows.

(In the following formulas (18) to (47), * indicates optically active carbon atom shows, n=5 to 1000.

(m,=2~10) (m1=2~10) (m2 2~15) (l112=2~15) →CH2−C→r (Il+2=2~15) H3 (mz=2~15) ( J) (mz=2~15) (m2=2~15) (x+y=1 q=l~10 =1~1O) (x+y=1 q=1~10 p2=1~15) (x+y=1, p4 p, = 1 to 15, q3 q4 = 1 to 10) (R = C) 43 ■ or P 1 to 10) H3 (p+ = 1 to 15) (m, = 2 to 15 x + y = 1) (x + y = 1.1112:2~15) (x + y = 1, 12 = 2~15) (x + y
=11m2=2-15) (+os=1-5) (x+y=1) (+++s=0-5) (m,=0-5) r (q3=1-10 x+y=1) The polymer liquid crystal compound They can be used alone, or two or more kinds can be mixed or copolymerized.

Further, in order to control the refractive index, it is preferable to mix it with a low-molecular liquid crystal within a range that does not impair memory stability.

The polymeric liquid crystal compound or composition described above preferably has a glass transition point in order to stably retain its memory content. It is particularly preferable for the storage stability of the memory to retain the written content below the glass transition point.

The thickness of the recording layer is usually 0.05 to 10 μm, preferably 0.05 to 10 μm.
．． A thickness of 1 to 5 μm is desirable. Further, the recording layer can be easily formed on the substrate by a dipping method, a bar code method, a spin code method, or the like.

For the initial orientation of the polymer liquid crystal of the information storage medium of the present invention, a horizontally oriented polymer film such as PVA, P■ polyamide, or polyamideimide, or an obliquely vapor-deposited film of an inorganic material such as 5i02 may be used as the alignment film. It is possible. It is also possible to process these alignment films by uniaxial alignment treatment such as rubbing. Similarly, uniaxial orientation processing can also be performed by shearing.

In the present invention, the reflective layer includes Af, Au, A
It is possible to use a metal film or dielectric mirror such as Gm, and the film thickness is 0.01 to 100 gm, preferably 0.
A pot size of 805 to 10 m is desirable.

Further, as the substrate, a glass substrate, a plastic substrate, etc. can be used.

The shape of the substrate may be a sheet, card, disk, tape, etc., as long as it is suitable for writing and reproduction by an information storage device.

Light sources used for recording, reproducing, and erasing in the information storage device of the present invention include gas lasers such as He-Ne gas laser, Ar'' gas laser, N! gas laser, and solid state lasers such as ruby laser and glass laser YAG laser. It is desirable to use a laser, a semiconductor laser, or the like.

Further, a semiconductor laser having a wavelength range of 600 nm to 1600 nm is preferably used. Particularly preferably 600
A semiconductor laser with a wavelength range of ~900 nm is used. Further, by using the second and third harmonics of these laser beams, it is possible to shorten the wavelength.

When writing with a laser beam or the like and performing /A erasure, the sensitivity can be improved by providing a laser beam absorbing layer or adding a laser beam absorbing compound to the recording layer containing a polymeric liquid crystal compound. I can do it.

Examples of laser light absorbing compounds added to the polymer liquid crystal layer include azo compounds, bisazo compounds, trisazo compounds, anthraquinone compounds, naphthoquinone compounds, phthalocyanine compounds, naphthalocyanine compounds, and tetrabenzoporphyrin compounds. compounds, aminium salt compounds, diimonium salt compounds, metal chelate compounds, etc.

Among the above laser light absorbing compounds, compounds for semiconductor lasers have absorption in the near infrared region, are useful as stable light absorbing dyes, and have good compatibility or dispersibility with polymeric liquid crystal compounds. In addition, some compounds have dichroism, and if these dichroism compounds are mixed into polymer liquid crystals, thermally stable host-guest memory and display media can be obtained. .

Further, the polymeric liquid crystal compound may contain two or more types of the above-mentioned compounds.

Further, the above compound may be combined with other near-infrared absorbing dyes or dichroic dyes. Representative examples of near-infrared absorbing dyes that can be suitably combined include cyanine, merocyanine, phthalocyanine, tetrahydrocholine, dioxazine, anthraquinone, triphuedithiazine, xanthine, triphenylmethane, pyrylium, croconium, azulene, and triphenylamine. Examples include dyes such as.

The amount of the above compound added to the polymeric liquid crystal compound is about 0.1 to 20% by weight, preferably 0.5 to 20%.
lO% is good. The polymeric liquid crystal compound used in the present invention is a polymeric thermotropic liquid crystal, and uses a nematic, smectic, chiral smectic, or cholesteric phase as an intermediate phase.

More specific light-absorbing dyes include: The following can be used.

Direct Red 2g Direct Violet 12 Direct Blue 1 Direct Blue 15 Direct Blue 98 Direct Blue 151 1M Direct Red 81 Direct Yellow 44 Direct Yellow 12 Direct Orange 39 th 　NH2 II　　　　　　　1’:n 　NH2 II I Cn Disperse Blue 214 Disperse Red 60 0H 0H Disperse Yellow 56AsFs.

(J’0.

As the orientation control film, for example - silicon oxide, silicon dioxide,
aluminum oxide, zirconia, magnesium fluoride,
Cerium oxide, cerium fluoride.

Inorganic insulating materials such as silicon nitride, silicon carbide, boron nitride, polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylerin, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, An alignment control film formed by using an organic insulating material such as melamine resin, urea resin, or acrylic resin can be provided.

This orientation control film is obtained by forming a film of an inorganic insulating material or an organic insulating material as described above, and then rubbing the surface in one direction with velvet, cloth, or paper.

In another preferred embodiment of the present invention, the orientation control film can be obtained by forming a film of an inorganic insulating material such as SiO or SiO□ on a substrate by oblique vapor deposition.

In another specific example, after forming a film of the above-mentioned inorganic insulating material or organic insulating material on the surface of a substrate made of glass or plastic or on the substrate, the surface of the film is etched by an oblique etching method. An orientation control effect can be imparted to the surface.

The above-mentioned alignment control film preferably functions as an insulating film at the same time, and for this purpose, the thickness of this alignment control film is generally 100 to 1 μm, preferably 500 to 500 μm.
It can be set to a range of 0 people.

Further, in the present invention, to ensure molecular alignment of the polymeric liquid crystal compound in the recording layer, it is preferable to use stretching methods such as axial stretching, biaxial stretching, and inflation stretching, or rearrangement by shearing. Those that do not have film properties and are difficult to stretch when used alone can be co-stretched by sandwiching them into a film to obtain a desired orientation.

As other orientation methods, orientation using an electric field or magnetic field, orientation using shearing, etc. can be used.

Further, it is preferable that the information storage medium of the present invention has groups for tracking.

4 of the recording layer containing a polymeric liquid crystal compound provided on the substrate
An example of the shape of No. 13 is shown in FIGS. 3(a) to 3(d). or,
From the experimental results, the sizes of the grooves illustrated in FIG. 4, that is, the groove depth a, the groove width, and the groove land width C, are as follows. , the groove width is 0.
5μm~5. Oμm, the width C of the land part of the groove is 0.5 to 5
．． 0 μm, especially the groove depth a is 0.1 μm to 0.3
μm, the width of the groove is 0.5m to 2.0m, and the width C of the land part of the groove is 1.0m. Oμm~3. It was confirmed that Oμm is preferable.

However, even if all three of the above conditions are not met, the effect can still be obtained as long as the groove depth is set within the above conditions at least within the above range.

It was also confirmed that the shape of the groove did not have much of an effect.

When an information storage medium is obtained using the above-mentioned specific disk substrate, the polymer liquid crystal layer sandwiched between the substrates is heated to a temperature higher than the isotropic liquid temperature and slowly cooled to become oriented, resulting in a spiral or outlet shape. An information storage medium that is uniformly oriented in the direction of the rick-shaped grooves can be obtained.

Also used is a disk configuration that allows the application of an electric field, as shown in FIG. As one example,
In FIG. 5, a conductive film 14 such as an ITO vapor-deposited film is provided on a substrate l, a substrate with a groove-structured film 15 formed thereon, and another substrate with a conductive film (reflective layer 2) provided thereon. It has a cross-sectional structure in which a recording layer 3 containing a polymeric liquid crystal compound is disposed between one substrate 5.

FIG. 1 is a sectional view showing an example of an information storage medium of the present invention, FIG. 2(a) is a schematic diagram showing an example of an information storage device of the invention, and FIG. FIG. 3 is an explanatory diagram showing a relative relationship with an orientation axis.

In FIG. 1, the information storage medium of the present invention has a reflective layer 2 on a lower substrate l, an alignment control film 4 on an upper substrate 5, and a polymeric liquid crystal compound containing a liquid crystal compound between the two substrates. The polymeric liquid crystal compound of the recording layer is uniaxially aligned concentrically or radially by an alignment control film 4 to show an alignment axis 11. (Figure 2 (
b) As shown in Figure 2 (al), the laser beam irradiated from the semiconductor laser 6 to the alignment axis 11 is converted into linearly polarized light in the incident linear polarization direction 10 by the polarizing beam splitter 7, and the alignment axis The light is incident on the information recording medium at an angle θ with respect to 11. At this time, the angle θ
is used in a range of 35 to 55'', more preferably 45''.

At this time, the film thickness of the recording layer of the information recording medium is d (μm), thickness (Δnd), thickness (m+1/4) (m:
An integer from 0 to 3, where ``e'' represents the wavelength (gm) of the reproduction light. )
It is created so that Actually ((m±l/4)
It is used with a film thickness in the range of ±1/16). In addition, Δ
n''n/-n, where n represents the refractive index.

When m>3, the film thickness of the recording layer becomes too thick, which deteriorates the orientation and sensitivity of the recording layer, which is not preferable. More preferably, m=o or 1 is used.

In FIG. 2(a), when linearly polarized light is incident on the recording layer 3 at an angle θ, it becomes elliptically polarized light due to its birefringence, and becomes circularly polarized light when the retardation is λ (m±l/4). When this circularly polarized light is reflected by the reflective layer 2, the rotation direction of the circularly polarized light is reversed. When this counter-rotating circularly polarized light enters the recording layer 3 again, it is emitted as linearly polarized light in the reflected linearly polarized direction 12 orthogonal to the incident linearly polarized direction 10 through the reverse process. This is incident on a detector 8 by a polarizing beam splitter 7.

At this time, in the recording layer containing the polymeric liquid crystal compound,
By changing the direction of the alignment axis or the birefringence at the same time, the state of the emitted light changes, the amount of light separated by the polarizing beam splitter 7 changes, and a signal is detected by the detector 8.

In the present invention, the recording and non-recording portions of the recording layer are in the following states: ■ Isotropic phase ■ Nematic phase vertical alignment ■ Nematic phase horizontal alignment ■ Smectic synergistic orthogonal alignment ■ Smectic phase horizontal alignment ■ Chiral smectic synergistic orthogonal alignment ■ By selecting from chiral smectic phase horizontal orientation and selecting writing conditions such as heating directly or by laser irradiation, application of electric field, etc., each state can be identified as having a different orientation axis direction and birefringence index. be able to.

[Example] Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A polymeric liquid crystal compound represented by the following structural formula (I) was dissolved in cyclohexanone to prepare a 20 wt % solution. next,
1.5 wt % of the IR absorbing dye represented by structural formula (n) was added to the polymeric liquid crystal compound.

-+(: H-CH2+- <c mountain) 2 NiV% N <c 2H5) 2C
Af was evaporated to a thickness of 1,000 mm on a disk-shaped glass substrate with a thickness of 1.2 mm on which I2.4° (II) groups were formed, and a polyimide alignment film (manufactured by Nissan Chemical Industries, Ltd., high-purity polyimide alignment film) was deposited on top of it. A film, Sunever 100) was formed.

Uniaxial orientation was imparted in the group direction by the rubbing method.

A solution of the above polymeric liquid crystal compound was applied to this substrate at 2000 rpm.
It was coated with a spinner to give a thickness of 1.2 μm after drying. Heat treatment was performed at 105° C. for 3 hours to achieve -axis orientation. The retardation (Δnd) is measured using a polarized light microscope tli 'f
r-light wavelength 50 by Berek compensator using
When measured from 0 to 600 nm, it was 205 nm.

An 830 nm semiconductor laser and a polarizing beam splitter are connected at an angle of 45° to the orientation axis of this storage medium.
211. by the lens. gathered at mφ. 0
．． When a 5 mW reproduction laser beam was incident, a reflectance of 48% of the total reflection configuration when only an AR reflector using a 1/4 wavelength plate was detected was detected. When a recording portion was formed by applying a pulse of 10 mW and 10 psec, the reflectance at 0.5 mW was 5%, and good contrast was obtained.

Furthermore, when the disk was rotated at 150 Orμm and recording and playback was performed under the same conditions as above while applying autofocus and autotracking, the playback C/N was
(resolution bandwidth 3 KHz) was 51 dB.

Next, when the recording section was irradiated with a defocused 5 mW laser beam for 100 msec, the data could be almost erased.

Note that n/ is the refractive index due to extraordinary rays, n is the refractive index due to ordinary rays, and Δn=birefringence.

Comparative Examples 1 and 2 The results are shown in Table 1 below, except that only the thickness of the recording layer was changed in the same manner as in Example 1.

Table 1 Comparative Example 3 In Example 1, the angle/degree between the linearly polarized light and the alignment axis was changed to 3 degrees.
When the angle was set to 0°, the reflectance of the unrecorded area was 33%, and the reflectance of the recorded area was 4%.

Example 2 0.63 g and 0.67 g of the monomers of the following structural formulas (In) and (rv), respectively, were dissolved in dry toluene, 3 mo1% AIBN was added, and the mixture was frozen and degassed at 60°C for 24 hours. Allowed time to react. The reprecipitation was repeated in methanol to obtain 0.68 g of a copolymer. (Yield 52%)C
H=CH2 (III) CH=CH2 (rV) Number average molecular weight Weight average molecular weight Phase transition temperature ('C) Optical rotation [α]2'=+8.9° (CH(J'S) Same as above polymer liquid crystal Dissolve the polymer in chloroform and add 20w
t% binding, and near-infrared absorbing dye (manufactured by Sansui Kasei ■, NI
R-13) was added to the polymer liquid crystal in an amount of 1.5 wt%.

Next, a polyimide alignment film (high purity polyimide varnish Sunever 100, manufactured by Nikkei Kagaku Kogyo ■) was formed on a card-shaped glass substrate on which AP was deposited to a thickness of 3000 mm, and uniaxial alignment was imparted by a rubbing method. 1000 ITO
A similar process was applied to a glass substrate deposited to a human thickness. The polymer liquid crystal copolymer solution described above on the ITO-attached glass substrate was coated with a spinner, and after drying, the film thickness was 1.1 m.

Next, the AI! An information storage medium was obtained by attaching a glass substrate and heating and cooling it for orientation.

Next, +40V was applied between the upper and lower substrates, and uniaxial orientation was achieved by cooling from 90°C. Retardation (Δnd) by polarizing microscope (measured light wavelength 500-600 nm)
was 200 nm.

When this information storage medium was measured using the storage device of Example 1, with the angle θ between the incident linearly polarized light and the alignment axis being Oo, the reflectance was 3%. Next, apply -40V between the upper and lower boards at room temperature.
Apply 5mW of 8301 semiconductor laser to l 0m
When condensed light was irradiated as a 5 ec pulse, the orientation axis of the irradiated portion was tilted by 40°. The reflectance was 42%, and good contrast was obtained.

[Effects of the Invention] As explained above, according to the present invention, by using an information storage medium having a recording layer containing a -axis oriented polymeric liquid crystal compound, a simple recording/reproducing/erasing device can be used. Good contrast and C/N can be obtained.

In addition, it is possible to achieve a high reflectance, which has the effect of simplifying the reproduction signal processing system.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of an information storage medium of the present invention, FIG. 2(a) is a schematic diagram showing an example of an information storage device of the invention, and FIG. An explanatory diagram showing the relative relationship with the orientation axis, FIGS. 3(a) to 3(d) are cross-sectional schematic diagrams showing the shape of the tracking group of the recording layer, and FIG. 4 shows the size of the shape of the tracking group of the recording layer. FIG. 5 is a partial schematic diagram showing another example of the information storage medium of the present invention. 1... Lower substrate 2... Reflective layer 3... Recording layer 4... Orientation control film 5... Upper substrate
6... Semiconductor laser 7... Polarizing beam splitter 8... Detector 9... Condensing lens 10...
・Incoming linear polarization direction 11...Orientation axis 2...Reflection linear polarization direction 3...Groove 4...Conductive film 5...Film with groove structure 6...Recording/erasing/reproduction destination

Claims (4)

[Claims] (1) In an information storage medium having a recording layer containing a polymeric liquid crystal compound and a reflective layer on a substrate, the recording layer containing the polymeric liquid crystal compound is uniaxially oriented, and with respect to reproduction light |Δnd |(Δn=n■-n■, d: represents the film thickness (μm) of the recording layer. n represents the refractive index) is λ(m±
1/4) (m: integer from 0 to 3, λ: wavelength of reproduction light (μm
) represents. ). (2) The information storage medium according to claim 1, wherein the reproduction light is linearly polarized light. (3) The information storage medium according to claim 1, wherein the regenerating light is semiconductor laser light with a wavelength of 600 to 900 nm. (4) A recording layer containing a polymeric liquid crystal compound and a reflective layer are provided on the substrate, the recording layer containing the polymeric liquid crystal compound is uniaxially oriented, and |Δnd|(Δn
=n■-n■, d: represents the film thickness (μm) of the recording layer. n represents the refractive index. ) is λ(m±1/4) (m: an integer of 0 to 3, λ: wavelength of reproduction light (μm)), and an information storage medium whose angle is 35° with respect to the uniaxial orientation direction of the information storage medium. ~5
An information storage device comprising means for irradiating the information storage medium with linearly polarized light tilted by 5 degrees, means for separating the linearly polarized light, and means for detecting the intensity of reflected light.