U.S. patent application number 10/454690 was filed with the patent office on 2004-02-12 for photo-responsive high-molecular compound, photo-responsive high-molecular composition, dicarboxylic acid monomer, polyester, optical recording medium and optical record reproducing device.
This patent application is currently assigned to FUJI XEROX CO., LTD.. Invention is credited to Kawano, Katsunori, Maruyama, Tatsuya, Minabe, Jiro, Yasuda, Shin.
Application Number | 20040029038 10/454690 |
Document ID | / |
Family ID | 31497571 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040029038 |
Kind Code |
A1 |
Minabe, Jiro ; et
al. |
February 12, 2004 |
Photo-responsive high-molecular compound, photo-responsive
high-molecular composition, dicarboxylic acid monomer, polyester,
optical recording medium and optical record reproducing device
Abstract
In the present invention, a photosensitive layer of an optical
recording medium includes a photo-responsive high-molecular
compound comprising a photo-responsive group (e.g., an azobenzene
derivative) which is geometrically isomerized by light radiation,
and a liquid crystal linear mesogen group (e.g., a biphenyl
derivative), wherein the photo-responsive group and the linear
mesogen group are respectively bonded as side chains. The invention
provides an optical recording medium enabling large scale recording
by making the photosensitive layer thick without impairing
recording characteristics. The photo-responsive high-molecular
compound preferably comprises an aromatic ring on a main chain.
Further, the photo-responsive high-molecular compound preferably
comprises a structural unit which is capable of forming a
liquid-crystalline or crystalline polymer and a structural unit
which is capable of forming an amorphous polymer.
Inventors: |
Minabe, Jiro;
(Ashigarakami-gun, JP) ; Maruyama, Tatsuya;
(Ashigarakami-gun, JP) ; Kawano, Katsunori;
(Ashigarakami-gun, JP) ; Yasuda, Shin;
(Ashigarakami-gun, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
31497571 |
Appl. No.: |
10/454690 |
Filed: |
June 5, 2003 |
Current U.S.
Class: |
430/270.1 ;
G9B/7.169 |
Current CPC
Class: |
G11B 7/25 20130101 |
Class at
Publication: |
430/270.1 |
International
Class: |
G03C 001/492 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2002 |
JP |
2002-167796 |
May 1, 2003 |
JP |
2003-126692 |
Claims
What is claimed is:
1. A photo-responsive high-molecular compound comprising a
photo-responsive group which is geometrically isomerized by light
radiation, and a liquid crystal linear mesogen group, wherein the
photo-responsive group and the linear mesogen group are
respectively bonded as side chains.
2. A photo-responsive high-molecular compound comprising an
aromatic ring on a main chain, a photo-responsive group which is
geometrically isomerized by light radiation, and a liquid crystal
linear mesogen group, wherein the photo-responsive group and the
liquid crystal linear mesogen group are respectively bonded with
the aromatic ring as side chains.
3. A photo-responsive high-molecular compound according to claim 1,
wherein the main chain comprises a structural unit which is capable
of forming a liquid-crystalline or crystalline polymer and a
structural unit which is capable of forming an amorphous
polymer.
4. A photo-responsive high-molecular compound according to claim 1,
wherein the photo-responsive group contains an azobenzene
skeleton.
5. A photo-responsive high-molecular compound according to claim 1,
wherein the liquid crystal linear mesogen group contains a biphenyl
skeleton.
6. A photo-responsive high-molecular composition comprising: a
photo-responsive high-molecular compound in which a
photo-responsive group to be geometrically isomerized by light
radiation is bonded as a side chain; and a photo-unresponsive
high-molecular compound in which a liquid crystal linear mesogen
group is bond as a side chain.
7. A photo-responsive high-molecular composition comprising: a
photo-responsive high-molecular compound containing an aromatic
ring on a main chain and a photo-responsive group which is
geometrically isomerized by light radiation and bonded with the
aromatic ring as side chains; and a photo-unresponsive
high-molecular compound containing an aromatic ring on a main chain
and a liquid crystal linear mesogen group bonded with the aromatic
ring as side chains.
8. A photo-responsive high-molecular composition according to claim
6, wherein the main chain comprises a structural unit which is
capable of forming a liquid-crystalline or crystalline polymer and
a structural unit which is capable of forming an amorphous
polymer.
9. A photo-responsive high-molecular composition according to claim
6, wherein the photo-responsive group contains an azobenzene
skeleton.
10. A photo-responsive high-molecular composition according to
claim 6, wherein the liquid crystal linear mesogen group contains a
biphenyl skeleton.
11. A dicarboxylic acid monomer represented by the following
general formula (1): General formula (1) 23wherein X represents a
lower alkyloxy group, a substituted or unsubstituted benzyloxy
group, a substituted or unsubstituted phenyloxy group, an acid
residue of a lower fatty acid, an acid residue of a substituted or
unsubstituted benzoic acid, or a halogen atom; Y represents a
hydrogen atom or a lower alkyl group; Z represents a hydrogen atom,
a methyl group, a methoxy group, a cyano group, or a nitro group; m
denotes an integer from 1 to 3; and n denotes an integer from 2 to
18.
12. A polyester represented by the following general formula (4):
24wherein Y represents a hydrogen atom or a lower alkyl group; Z
represents a hydrogen atom, a methyl group, a methoxy group, a
cyano group, or a nitro group; R represents a hydrocarbon chain
which may contain at least one of a substituted or unsubstituted
aromatic group and a substituted or unsubstituted aliphatic group;
m denotes an integer from 1 to 3; n denotes an integer from 2 to
18; and p denotes an integer from 5 to 2000.
13. A polyester according to claim 12, wherein R in the general
formula (4) comprises a structural unit which is capable of forming
a liquid-crystalline or crystalline polymer and a structural unit
which is capable of forming an amorphous polymer.
14. A polyester according to claim 12, wherein R in the general
formula (4) is a functional group represented by the following
general formula (5): 25wherein U represents a hydrogen atom, a
halogen atom, a substituted or unsubstituted lower alkyl group, a
substituted or unsubstituted lower alkenyl group, or a substituted
or unsubstituted lower alkinyl group; T represents a direct bond, a
sulfone bond, a sulfoxide bond, an ether bond, a thioether bond, a
substituted imino bond, or a ketone bond; q denotes an integer from
1 to 4; and 1 denotes an integer from 2 to 18.
15. A polyester comprising a repeat unit represented by the
following general formula (6): 26wherein Y and Y' each
independently represent a hydrogen atom or a lower alkyl group; Z
and Z' each independently represent a hydrogen atom, a methyl
group, a methoxy group, a cyano group or a nitro group; R
represents a hydrocarbon chain containing a substituted or
unsubstituted aromatic group, a substituted or unsubstituted
aliphatic group; m and m' each independently denote an integer from
1 to 3; n and n' respectively denote an integer from 2 to 18; p
denotes an integer from 5 to 2000; and x and y respectively
represent abundance ratios of the repeat unit and fulfill the
following relationships: 0<x.ltoreq.1, 0.ltoreq.y<1 and
x+y=1.
16. A polyester according to claim 15, wherein R in the general
formula (6) is a functional group represented by the following
general formula (5): 27wherein U represents a hydrogen atom, a
halogen atom, a substituted or unsubstituted lower alkyl group, a
substituted or unsubstituted lower alkenyl group, or a substituted
or unsubstituted lower alkinyl group; T represents a direct bond, a
sulfone bond, a sulfoxide bond, an ether bond, a thioether bond, a
substituted imino bond, or a ketone bond; q denotes an integer from
1 to 4; and 1 denotes an integer from 2 to 18.
17. A polyester comprising a repeat unit represented by the
following general formula (10): 28wherein R.sub.1 represents a
structural unit capable of forming a liquid-crystalline or
crystalline polymer; R.sub.2 represents a structural unit capable
of forming an amorphous polymer; Y and Y' respectively represent a
hydrogen atom or a lower alkyl group; Z and Z' each independently
represent a hydrogen atom, a methyl group, a methoxy group, a cyano
group or a nitro group; R represents a hydrocarbon chain including
a substituted or unsubstituted aromatic group, a substituted or
unsubstituted aliphatic group or both of a substituted or
unsubstituted aromatic group and a substituted or unsubstituted
aliphatic group; m and m' each independently represent an integer
from 1 to 3; n and n' each independently represent an integer from
2 to 18; p represents an integer from 5 to 2000; and x, y, r and s
each independently represent the abundance ratio of the repeat unit
wherein x, y, r and s satisfy the following relations:
0<x.ltoreq.1, 0.ltoreq.y<1, x+y=1, 0.ltoreq.r.ltoreq.1,
0.ltoreq.s.ltoreq.1 and r+s=1.
18. An optical recording medium provided with a photosensitive
layer containing a photo-responsive high-molecular compound
comprising a photo-responsive group which is geometrically
isomerized by light radiation and a liquid crystal linear mesogen
group, the photo-responsive group and the liquid crystal linear
mesogen group being respectively bonded therewith as side chains,
wherein information is recorded in the photosensitive layer by
utilizing at least one of a change in absorption, a change in
refractive index, and a change in shape, due to light
radiation.
19. An optical recording medium provided with a photosensitive
layer containing a photo-responsive high-molecular composition
comprising: a photo-responsive high-molecular compound in which a
photo-responsive group to be geometrically isomerized by light
radiation is bonded as a side chain; and a photo-unresponsive
high-molecular compound in which a liquid crystal linear mesogen
group is bond as a side chain, wherein information is recorded in
the photosensitive layer by utilizing at least one of a change in
absorption, a change in refractive index, and a change in shape,
due to light radiation.
20. An optical recording medium provided with a photosensitive
layer containing a polyester, the recording medium recording
information in the photosensitive layer by utilizing at least one
of a change in absorption, a change in refractive index, and a
change in shape, due to light radiation, wherein the polyester is
represented by the following general formula (4): 29wherein Y
represents a hydrogen atom or a lower alkyl group; Z represents a
hydrogen atom, a methyl group, a methoxy group, a cyano group or a
nitro group; R represents a hydrocarbon chain which may contain at
least one of a substituted or unsubstituted aromatic group and a
substituted or unsubstituted aliphatic group; m denotes an integer
from 1 to 3; n denotes an integer from 2 to 18; and p denotes an
integer from 5 to 2000.
21. An optical recording medium according to claim 18, wherein the
photosensitive layer has a thickness of 50 .mu.m or more.
22. An optical recording medium according to claim 18, wherein
recording of a hologram is possible.
23. An optical recording medium according to claim 18, wherein
recording of a hologram is independently possible in each of a case
where a polarization direction of light that is incident on an
object and a polarization direction of reference light are parallel
to each other, and a case where polarization direction of light
that is incident on an object and a polarization direction of
reference light are perpendicular to each other.
24. An optical recording medium according to claim 18, wherein
recording of a hologram by the amplitude, phase and direction of
polarization of object light is possible.
25. An optical recording reproducing device for recording and/or
reproducing information by using an optical recording medium
provided with a photosensitive layer containing a photo-responsive
high-molecular compound comprising a photo-responsive group which
is geometrically isomerized by light radiation, and a liquid
crystal linear mesogen group, the photo-responsive group and the
linear mesogen group being respectively bonded as side chains,
wherein information is recorded in the photosensitive layer by
utilizing at least one of a change in absorption, a change in
refractive index, and a change in shape, due to light radiation.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of and priority to Japanese
Patent Applications Nos. 2002-167796 filed on Jun. 7, 2002 and
2003-126692 filed on May 1, 2003, which are incorporated herein by
reference in its entirety for all purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical recording
material, an optical recording medium and an optical record
reproducing device, and, particularly, to a large scale volume type
optical recording medium, optical recording materials and raw
materials thereof, such as a photo-responsive high-molecular
compound, a photo-responsive high-molecular composition, a
dicarboxylic acid monomer and a polyester, which are used in the
optical recording medium and an optical record reproducing device
which records and reproduces information by using the optical
recording medium.
[0004] 2. Description of the Related Art
[0005] Rewritable optical disk recording devices such as phase
change types and photomagnetic types have been widely spread
already. However, these optical disks are not admitted to have
performances coping with future demands for large scale recording
to deal with an increase in scale along with a development of
highly functional operating systems (OS) and application software,
a trend to a huge scale on account of the spread of multimedia for
various documents and data for presentation and digital recording
of video signals of a long time animated cartoon with high
precision and high density. In such a high density and large scale
optical disk recording device, in order to increase recording
density the ideas that, for example, the diameter of a beam spot is
decreased to shorten an interval between neighboring trucks or
neighboring bits are exploited.
[0006] DVD-ROMs are among those put to practical use by the
development of such technologies. These DVD-ROMs store 4.7 Gbyte
data on one surface of a disk 12 cm in size. Rewritable and
erasable DVD-RAMs enables recording with a density as high as 5.2
Gbyte on both surfaces of a disk 12 cm in diameter by a phase
change system. Namely, the DVD-RAM enables writing and reading of
information with a capacity four times that of a CD-ROM or with a
capacity corresponding to 1900 or more disks in the case of floppy
disks. Like this, the optical disks are progressing in
densification every year. However, on the other hand, because the
aforementioned optical disks record data in a plane, the
diffraction limit of light limits the recording, leading to the
physical limit of high density recording. In order to develop a
larger scale disk, three-dimensional (volume type) recording
including recording in the direction of the depth is required.
[0007] As a volume type optical recording medium as mentioned
above, a photorefractive material medium enabling volume recording
of a holographic grating and the like are regarded as promising
ones. Among photorefractive materials (hereinafter called "PR
material"), those are known which have high sensitivity and
therefore absorb relatively weak light on the same level as that of
a solid laser with changing in refractive index. These
photorefractive materials are expected to be applied to volume
multiple hologram recording with the possibility that super-high
density and super-large scale can be attained.
[0008] To state the principle of the photorefractive effect, two
coherent light waves are applied to a PR material to form
interference. An electron at a dobor level is excited to a
conductive band in a place where light intensity is strong, moved
by diffusion or drift and caught in a place where light intensity
is weak. A positive charge remains in the place where light
intensity is strong and a negative charge remains in the place
where light intensity is weak. This allows a charge distribution to
be formed, producing static electric field. A change in refractive
index is caused as a result of the electro-optical effect of the
static electric field. The period of the change in refractive index
is the same as that of the interference fringe and the index
modulation functions as a holographic grating.
[0009] As the PR material, inorganic ferroelectric crystals such as
barium titanate, lithium niobate and bismuth silicate (BSO) have
been frequently used. These materials produce a highly sensitive
and highly efficient photo-induced index changing effect
(photorefractive effect), but on the other hand, have drawbacks
that many of them have a difficulty in crystal growth and are so
hard and fragile that they are not processed into desired shapes
and also have a difficulty in controlling their sensitive
wavelengths.
[0010] In recent years, PR materials comprising organic materials
have been proposed as those which overcome these drawbacks.
Generally, organic PR materials comprise i) a charge generating
material which receives light to produce a charge, ii) a charge
transfer material which promotes the transfer of the generated
charge in a medium, iii) a dichroic organic dye sensitive to the
induced electric field by the charge transfer, iv) a high-molecular
base material (binder) which supports these materials and v)
additives (e.g., a plasticizer and a compatibility-improving agent)
which change the physical properties of base materials. Also, there
is the case where one component combines plural functions as, for
example, a material doubling as a charge transfer material and a
high-molecular base material and a material doubling as a charge
transfer material and a plasticizer. The effects of these organic
PR materials cause a positive and a negative charge to generate
from the charge generating material which has absorbed light. These
charges are separated into a positive charge and a negative charge
by the charge transfer material when existing external electric
field is effected, whereby an internal electric field is created.
The internal electric field causes a change in the orientation of
the dichroic dye, which causes a change in the distribution of
refractive index in the base material. If such an organic PR
material is applied, volume hologram recording with high recording
density is considered to be possible in theory.
[0011] The organic PR material, however, has the problem that it is
essential to apply an external electric field in substance. The
electric field is as remarkably large as several hundreds
V.multidot.mm.sup.-1 which imposes a large restriction on devices
when using the system as a recording device. Moreover, few
different materials such as the charge generating material, the
charge transfer material and the high-molecular base material are
mixed and used in the material system, giving rise to a large
problem concerning a reduction in stability caused by phase
separation during recording or storage.
[0012] To avoid the foregoing problem, for instance, S. Hvilsted et
al., proposes that using a polymer having cyanoazobenzene at a side
chain, an index modulation is written therein to record holograms
[Opt, Lett., 17 [17], 12 (1992)]. It has been clarified that in the
material, an index modulation with 2500 high and low refractive
indexes can be written in a space of 1 mm and it is expected that
high recording density will be attained.
[0013] A holographic memory of a layer of a polymer having
azobenzene at a side chain utilizes the photo-induced anisotropy of
the polymer layer. Azobenzene in an amorphous azo polymer layer
takes a random orientation state. When linearly polarized and
excited light having a wavelength which corresponds to the
absorption band belonging to the .pi.-.pi.* transition of an azo
group is applied to the azo polymer layer, azobenzene as a trans
isomer is excited in such a high probability that the transition
dipole moment accords to the direction of the polarized light,
namely, selectively, and is eventually photo-isomerized to a cis
isomer. The excited cis isomer is isomerized again to a trans
isomer by light or heat.
[0014] A change in the orientation of azobenzene is caused in a
direction stable to the excited light, namelya direction
perpendicular to the direction of the polarization through such an
angle-selective trans-cis-trans isomerization cycle caused by the
application of polarized light. Because azobenzene has an optical
anisotropy, it exhibits birefringence and dichroism as a result of
a change in orientation. Utilizing the photo-induced anisotropy
makes it possible to record a hologram by the distribution of
intensity and the distribution of polarization. Because the
recording is based on a change in the orientation of the polymer,
it is carried out stably for a long period of time and a hologram
can be recorded repeatedly by erasing the recorded hologram by
applying circularly polarized light or by applying heat to an
isotropic phase. As a material for a rewritable type holographic
memory, a layer of the polymer having azobenzene at a side chain is
a most promising material type.
[0015] For instance, the inventors of the invention have proposed
polyesters having azobenzene, which is useful as an optical
recording material, at the side chain in Japanese Patent
Application Laid-Open (JP-A) Nos. 2000-109719, 2000-264962 and
2001-294652. In JP-A No. 2000-109719, a monomer and a polyester in
which a methyl group is introduced into azobenzene to control the
absorption band to within a range suitable for optical recording
and optical recording media using these monomer and polyester are
disclosed. Also, in JP-A No. 2000-264962, a polyester which is made
suitable to optical recording by defining a methylene chain as a
main chain and by controlling the glass transition temperature of a
polymer and optical recording media using the polyester are
proposed. In addition, in JP-A No. 2001-294652, it is disclosed
that optical recording characteristics is improved using a
polyester in which a methylene chain as a side chain is
defined.
[0016] "A development of thick recording media" is most important
to attain the development of a large scale volume type holographic
memory. Generally, the condition of incident angle necessary for
diffraction becomes more strict with an increase in the thickness
of a hologram. Namely, diffracted light diminishes only by a small
deviation of the incident condition from the Bragg's condition. The
angle multiplex system in the volume type holographic memory makes
use of the angular selectivity. Namely, plural holograms are formed
in the same volume and the incident angle of reading light is
controlled whereby a desired hologram can be read out without any
crosstalk. If the angle selectivity is improved by increasing the
thickness of a recording medium in this manner, multiplicity can be
raised and recording capacity can be increased accordingly.
[0017] Also, the magnitude of modulation of refractive index for
forming a hologram is limited by the capability of a medium
material. For this, the formation of plural holograms in the same
volume corresponds to the fact that the capability of modulation of
refractive index which a material possesses is divided by plural
holograms upon use. Because the square of the amplitude of
refractive index acts on diffraction efficiency, a rise in
multiplicity reduces the diffraction efficiency of a hologram in
inverse proportion to the square of the multiplicity. Accordingly,
it is desired to develop recording media which can obtain a high
diffraction efficiency raised to some extent also in the case of
raising the multiplicity.
[0018] On the other hand, in the case of the layer of a polymer
having azobenzene at a side chain, it is necessary to record using
a wavelength enough to excite the .pi.-.pi.* transition of
azobenzene. Although it is effective to select wavelengths which
can be highly absorbed to improve recording sensitivity, this gives
rise to another problem at the same time. Namely, if a material
which highly absorbs light with a recording wavelength is used,
incident recording light is absorbed by molecules in the vicinity
of the surface, with the result that an effective hologram cannot
be formed over a whole region extending in the direction of the
thickness of a medium. Further, the absorption loss of the medium
makes it difficult to attain high diffraction efficiency.
Accordingly, in order to accomplish a rise in thickness with
maintaining high recording sensitivity and high diffraction
efficiency, it is important to control the absorbance of a medium
(the amount of light to be absorbed) for recording wavelengths.
[0019] Also, the magnitude and stability of the photo-induced
anisotropy (birefringence) of the layer of a polymer having, at a
side chain, azobenzene to be a source of the formation of a
hologram are largely affected by the thermal properties of the
polymer. In general, the photo-induced birefringence of an
amorphous polymer is relatively small and has inferior record
retentivity. On the contrary, the photo-induced birefringence of a
crystalline or liquid crystalline polymer is relatively large, is
stable to heat and has superb record retentivity. However, these
crystalline and liquid crystalline polymer layers are increased in
thickness, noises due to scattering caused by the crystal are
increased, posing the problem that errors are produced when reading
out data. From such a problem, the thickness of the film of a
polymer having azobenzene at a side chain has been limited to about
the order of 20 .mu.m to 40 .mu.m when applying it to a holographic
memory. Accordingly, it is important to control the crystallinity
of the polymer to attain an increase in layer thickness while
maintaining high record retentivity and preventing the generation
of noises.
[0020] The invention has been made in view of the aforementioned
prior art problem and it is an object of the invention to provide
an optical recording material (e.g., a photo-responsive
high-molecular compound, a photo-responsive high-molecular
composition or a polyester) which can be increased in layer
thickness while maintaining high recording sensitivity and high
diffraction efficiency by controlling the absorbance of a medium
and also to provide its raw material (dicarboxylic acid monomer).
Another object of the invention is to provide an optical recording
material which can be increased in the layer thickness while
maintaining high record retentivity and preventing the generation
of noises by controlling the crystallinity of the material and also
to provide its raw material. Also, a further object of the
invention is to provide an optical recording medium enabling large
scale recording by accomplishing an increase in layer thickness
without damaging recording characteristics. A still further object
of the invention is to provide an optical record reproducing device
enabling recording and reproduction of large scale data.
SUMMARY OF THE INVENTION
[0021] Optical Recording Material
[0022] The above object can be attained by the following invention.
As a first aspect of a photo-responsive high-molecular compound and
a first aspect of a photo-responsive high-molecular composition of
the present invention, a photo-responsive high-molecular compound
comprising a photo-responsive group which is geometrically
isomerized by light radiation, and a liquid crystal linear mesogen
group, wherein the photo-responsive group and the linear mesogen
group are respectively bonded as side chains, is provided. Also, as
a first aspect of a photo-responsive high-molecular composition of
the present invention, a photo-responsive high-molecular
composition which comprises a photo-responsive high-molecular
compound comprising a photo-responsive group which is geometrically
isomerized by light radiation, and a liquid crystal linear mesogen
group, wherein the photo-responsive group and the linear mesogen
group are respectively bonded as side chains, is provided.
[0023] As examples of the photo-responsive group which is
geometrically isomerized by light radiation in the above compound
and composition according to the first aspects, those containing an
azobenzene skeleton, a stilbene skeleton or an azomethine skeleton
are given. The photo-responsive group preferably contains an
azobenzene skeleton. The liquid crystal linear mesogen group may be
those used as a mesogen group of usual low molecular liquid
crystals such as a biphenyl type, terphenyl group, benzoate type,
cyclohexylcarboxylate type, phenylcyclohexane type, pyrimidine
type, dioxane type and cyclohexylcyclohexane type containing a p
(para)-substituted aromatic ring. The linear mesogen group
preferably contains a biphenyl skeleton.
[0024] The photo-responsive high-molecular compound and the
photo-responsive composition according to the first aspects of the
invention have the following characteristics (1): (1) The
introduction of the "liquid crystal linear mesogen group" such as a
biphenyl derivative makes it possible to reinforce and to fix a
change in the orientation of the "photo-responsive group which is
geometrically isomerized by light radiation" by light. Namely, the
introduction of the "liquid crystal linear mesogen group" which is
not geometrically isomerized makes it possible to control the
absorbance of a medium to thereby decrease absorption loss and also
to maintain high recording sensitivity and high diffraction
efficiency owing to its orientation characteristics. This makes it
possible to attain an increase in thickness. It is to be noted that
in the case of the photo-responsive high-molecular compound, the
"liquid crystal linear mesogen group" can be introduced into the
same molecule by copolymerization or the like. Also, in the case of
the photo-responsive high-molecular composition, the "liquid
crystal linear mesogen group" can be introduced into the
composition by blending a photo-unresponsive high-molecular
compound having the "liquid crystal linear mesogen group".
[0025] For example, biphenyl derivatives bonded by a flexible
methylene chain function as a mesogen in a liquid crystal state.
Accordingly, it is possible to induce a change in the orientation
of the biphenyl derivative followed in a change of the orientation
of azobenzene. Although it is necessary to decrease the absorbance
of a medium in order to attain a thick medium, the decrease in the
absorbance of a medium directly implies that the magnitude of
photo-induced anisotropy and sensitivity are sacrificed. However,
the introduction of the biphenyl derivative into the side chain
makes it possible to enforce and to fix a change in the orientation
of azobenzene.
[0026] Also, the above object can be attained by the following
invention. As a second aspect of the invention, a photo-responsive
high-molecular compound comprising an aromatic ring on a main
chain, a photo-responsive group which is geometrically isomerized
by light radiation, and a liquid crystal linear mesogen group,
wherein the photo-responsive group and the liquid crystal linear
mesogen group are respectively bonded with the aromatic ring as
side chains, is provided. Also, As a photo-responsive
high-molecular composition of the second aspect of the invention, a
photo-responsive high-molecular composition comprising a
photo-responsive high-molecular compound which contains an aromatic
ring on a main chain and a photo-responsive group, which is
geometrically isomerized by light radiation, as a side chain of the
aromatic ring, and a photo-unresponsive high-molecular compound
which contains an aromatic ring on a main chain and a liquid
crystal linear mesogen group as a side chain of the aromatic ring,
is provided.
[0027] As examples of each of the photo-responsive group which is
geometrically isomerized by light radiation and the liquid crystal
linear mesogen group in the above photo-responsive compound and the
photo-responsive composition of the second aspects, the same groups
as those exemplified as the photo-responsive compound and the
photo-responsive composition of the first aspects may be given.
Also, examples of the high-molecular compound containing an
aromatic ring on its main chain include polyesters obtained by a
polycondensation between a dicarboxylic acid such as phthalic acid
or isophthalic acid and a diol.
[0028] The photo-responsive high-molecular compound and the
photo-responsive high-molecular composition according to the second
aspects of the invention are provided with the following
characteristics (2) in addition to the above characteristics (1):
(2) The side chain is bonded with the "aromatic ring", such as
isophthalic acid derivatives, which is fixed to the main chain, so
that the crystallinity of the polymer is easily controlled by the
presence of the "aromatic ring" at the bonded part. Namely, the
crystallinity is controlled by the "aromatic ring" present at the
bonded part of the side chain to thereby maintain high record
retentivity and to prevent the generation of noises, whereby an
increase in layer thickness can be attained.
[0029] Generally, many polymers having azobenzene at the side chain
exhibit a liquid crystal phase such as a nematic phase or a smectic
phase because the azobenzene side chain functions as a mesogen. As
aforementioned, it is difficult to increase the layer thickness of
the liquid crystal polymers because of the noises caused by
scattering. The crystallinity of a polyesters having side chains
bonded with aromatic rings can be easily controlled between a
liquid crystal state and an amorphous state according to the
structure of its main chain. This is assumed to be because of a
structure in which the mobility of the side chain is limited by the
presence of the "aromatic ring" such as an isophthalic acid
derivative and therefore the polyester group takes a liquid crystal
phase with more difficulty than the polymer in which no aromatic
ring is present at the bonded part (even if the polyester group has
a liquid crystal phase, the range of the temperature at which it
takes a crystal state is narrow).
[0030] In addition to the foregoing characteristics (1) and (2),
the photo-responsive high-molecular compound and photo-responsive
high-molecular composition of the third aspects of the invention
have the following useful characteristic (3) to control
crystallinity. (3) It is possible to control continuous
crystallinity easily by introducing a structural unit capable of
forming a liquid-crystalline or crystalline polymer and a
structural unit capable of forming an amorphous polymer
simultaneously into the main chain of the same molecule and by
changing the ratio of the both structural units. Moreover, as will
be described in examples in detail, it has been found that there is
a copolymerization ratio to increase photo-induced birefringence
with decreasing scattering caused by crystallinity exists.
Therefore, by obtaining of the characteristics (3), it becomes
possible to achieve both a reduction in scattering and an
improvement in photo-induced anisotropy which have been considered
to be in a tradeoff relation with each other. This enables the
production of a thick film medium superior in record
retentivity.
[0031] As the raw monomer for introducing the liquid crystal linear
mesogen group, a dicarboxylic acid monomer represented by the
following general formula (1) may be used. The dicarboxylic acid
monomer is useful to control the amount of absorption of a compound
or a composition without impairing the optical recording
characteristics of an optical recording material. 1
[0032] wherein X represents a lower alkyloxy group, a substituted
or unsubstituted benzyloxy group, a substituted or unsubstituted
phenyloxy group, an acid residue of a lower fatty acid, an acid
residue of a substituted or unsubstituted benzoic acid or a halogen
atom, Y represents a hydrogen atom or a lower alkyl group, Z
represents a hydrogen atom, a methyl group, a methoxy group, a
cyano group or a nitro group, m denotes an integer from 1 to 3 and
n denotes an integer from 2 to 18.
[0033] The dicarboxylic acid monomer represented by the above
general formula (1) can be produced by reacting a dicarboxylic acid
derivative represented by the following general formula (2) with a
biphenyl derivative represented by the following general formula
(3) in the presence of a condensing agent. 2
[0034] In the above general formula (2), X represents a lower
alkyloxy group, a substituted or unsubstituted benzyloxy group, a
substituted or unsubstituted phenyloxy group, an acid residue of a
lower fatty acid, an acid residue of a substituted or unsubstituted
benzoic acid or a halogen atom, Y represents a hydrogen atom or a
lower alkyl group and m denotes an integer from 1 to 3.
[0035] In the above general formula (3), Q represents an atomic
group which is easily dissociable by the effect of a nucleophilic
substitution reaction in the condition of the Williamson's ether
synthetic reaction, Z represents a hydrogen atom, a methyl group, a
methoxy group, a cyano group or a nitro group and n denotes an
integer from 2 to 18.
[0036] As the aforementioned photo-unresponsive high-molecular
compound, a polyester represented by the following general formula
(4) may be used. The polyester is useful as a binder polymer which
controls the amount of absorption of a dye (dye concentration)
without impairing optical recording characteristics.
[0037] General Formula (4) 3
[0038] In the above general formula (4), Y represents a hydrogen
atom or a lower alkyl group; Z represents a hydrogen atom, a methyl
group, a methoxy group, a cyano group, or a nitro group; R
represents a hydrocarbon chain which may contain at least one of a
substituted or unsubstituted aromatic group and a substituted or
unsubstituted aliphatic group; m denotes an integer from 1 to 3; n
denotes an integer from 2 to 18; and p denotes an integer from 5 to
2000. Also, R in the above general formula (4) preferably includes
a structural unit which is capable of forming a liquid-crystalline
or crystalline polymer and a structural unit which is capable of
forming an amorphous polymer. More preferably, R in the above
general formula (4) is a functional group represented by the
following general formula (5). 4
[0039] In the above general formula (5), U represents a hydrogen
atom, a halogen atom, a substituted or unsubstituted lower alkyl
group, a substituted or unsubstituted lower alkenyl group or a
substituted or unsubstituted lower alkinyl group; T represents a
direct bond, a sulfone bond, a sulfoxide bond, an ether bond, a
thioether bond, a substituted imino bond or a ketone bond; q
denotes an integer from 1 to 4; and 1 denotes an integer from 2 to
18.
[0040] As the aforementioned photo-responsive high-molecular
compound, a polyester comprising a repeat unit represented by the
following general formula (6) may be used. The copolymer obtained
by copolymerization with the azobenzene derivative is very useful
as an optical recording material constituting a photosensitive
layer with high layer thickness in the optical recording medium.
5
[0041] In the above general formula (6), Y and Y' each
independently represent a hydrogen atom or a lower alkyl group, Z
and Z' each independently represent a hydrogen atom, a methyl
group, a methoxy group, a cyano group or a nitro group, R
represents a hydrocarbon chain containing a substituted or
unsubstituted aromatic group, a substituted or unsubstituted
aliphatic group or both, m and m' each independently denote an
integer from 1 to 3, n and n' each independently denote an integer
from 2 to 18, p denotes an integer from 5 to 2000 and x and y
respectively represent abundance ratios of the repeat unit and
fulfill the following relationships: 0<x.ltoreq.1,
0.ltoreq.y<1 and x+y=1. Also, R in the above general formula (6)
preferably includes a structural unit which is capable of forming a
liquid-crystalline or crystalline polymer and a structural unit
which is capable of forming an amorphous polymer. More preferably,
R in the above general formula (6) is represented by the above
general formula (5).
[0042] The polyester represented by the above general formula (6)
may be obtained by reacting a dicarboxylic acid monomer represented
by the above general formula (1) with a photo-responsive
dicarboxylic acid monomer represented by the following general
formula (7) and with a diol compound represented by the following
general formula (8) in the presence of a proper catalyst. 6
[0043] In the general formula (7), X represents a lower alkyloxy
group, a substituted or unsubstituted benzyloxy group, a
substituted or unsubstituted phenyloxy group, an acid residue of a
lower fatty acid, an acid residue of a substituted or unsubstituted
benzoic acid or a halogen atom, Y represents a hydrogen atom or a
lower alkyl group, Z represents a hydrogen atom, a methyl group, a
methoxy group, a cyano group, or a nitro group, m denotes an
integer from 1 to 3 and n denotes an integer from 2 to 18.
[0044] In the general formula (8), U represents a hydrogen atom, a
halogen atom, a substituted or unsubstituted lower alkyl group, a
substituted or unsubstituted lower alkenyl group, or a substituted
or unsubstituted lower alkinyl group, T represents a sulfone bond,
a sulfoxide bond, an ether bond, a thioether bond, a substituted
imino bond, or a ketone bond, q denotes an integer from 1 to 4 and
1 denotes an integer from 2 to 18.
[0045] As the aforementioned photo-responsive high-molecular
compound, it is particularly preferable to use a polyester composed
of a repeat unit represented by the following general formula (10).
The crystallinity of a copolymer of this compound and an azobenzene
derivative is easily controlled by the ratio between the structural
units R.sub.1 and R.sub.2 of the main chain and is therefore useful
as an optical recording material constituting a thick
light-sensitive layer of the optical recording medium. 7
[0046] In the general formula (10), R.sub.1 represents a structural
unit capable of forming a liquid-crystalline or crystalline
polymer; R.sub.2 represents a structural unit capable of forming an
amorphous polymer; Y and Y' respectively represent a hydrogen atom
or a lower alkyl group; Z and Z' each independently represent a
hydrogen atom, a methyl group, a methoxy group, a cyano group or a
nitro group; R represents a hydrocarbon chain including a
substituted or unsubstituted aromatic group, a substituted or
unsubstituted aliphatic group or both of a substituted or
unsubstituted aromatic group and a substituted or unsubstituted
aliphatic group; m and m' each independently represent an integer
from 1 to 3; n and n' each independently represent an integer from
2 to 18; and p represents an integer from 5 to 2000; x, y, r and s
each independently represent the abundance ratio of the repeat unit
wherein x, y, r and s satisfy the following relations:
0<x.ltoreq.1, 0.ltoreq.y<1, x+y=1, 0.ltoreq.r.ltoreq.1,
0.ltoreq.s.ltoreq.1 and r+s=1.
[0047] The polyester represented by the general formula (10) may be
obtained by reacting the dicarboxylic acid monomer represented by
the general formula (1), the photo-responsive dicarboxylic acid
monomer represented by the general formula (7) and two types of
diol compounds represented by the general formula (8) in the
presence of an adequate catalyst.
[0048] Optical Recording Medium
[0049] The above object can be attained by the following invention.
According to a third aspect of the invention, an optical recording
medium provided with a photosensitive layer comprising the
photo-responsive high-molecular compound or the photo-responsive
high-molecular composition of the invention, wherein information is
recorded in the photosensitive layer by utilizing at least one of a
change in absorption, a change in refractive index, and a change in
shape, due to light radiation, is provided. Also, the invention
provides an optical recording medium having a photosensitive layer
comprising the polyester according to the invention, wherein
information is recorded in the photosensitive layer by utilizing at
least one of a change in absorption, a change in refractive index,
and a change in shape, due to light radiation.
[0050] In the optical recording medium of the invention, the
foregoing optical recording material (the photo-responsive
high-molecular compound, the photo-responsive high-molecular
composition and the polyester) is used to control the absorbance of
a medium and crystallinity, whereby a thick photosensitive layer
can be formed without impairing recording characteristics. It is
possible to form a layer as thick as, for example, 50 .mu.m. This
enables large scale recording. It is undesirable that the
photosensitive layer constituted of the above optical recording
material exhibit a thermotropic liquid crystal phase.
[0051] A hologram can be recorded in the optical recording medium
of the invention. For example, recording of a hologram is
independently possible in each of a case where a polarization
direction of light that is incident on an object and a polarization
direction of reference light are parallel to each other, and a case
where polarization direction of light that is incident on an object
and a polarization direction of reference light are perpendicular
to each other. Also, recording of a hologram by the amplitude,
phase and direction of polarization of object light is
possible.
[0052] Optical Record Reproducing Device
[0053] The above object can be attained by the following invention.
According to a fourth aspect of the invention, there is provided an
optical record reproducing device recording and/or reproducing
information by using an optical recording medium according to the
invention. The optical record reproducing device makes it possible
to record and reproduce large scale data because an optical
recording medium enabling large scale recording according to the
invention is used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 is a diagram showing a change in the absorption
coefficient of a photo-responsive polyester carrying a biphenyl
derivative for light with a wavelength of 515 nm as a function of
the copolymerization ratio of a side chain of a biphenyl derivative
in the present invention.
[0055] FIG. 2 is a diagram showing a change in the transmittance of
an optical recording medium using a photo-responsive polyester
carrying a biphenyl derivative for light with a wavelength of 515
nm as a function of the copolymerization ratio of a side chain of a
biphenyl derivative in the invention.
[0056] FIG. 3 is a schematic view showing the structure of an
optical system which records optical anisotropy.
[0057] FIG. 4 is a diagram for explaining the effect of a biphenyl
derivative in a binder polymer according to the invention.
[0058] FIG. 5 is a schematic view showing the structure of an
optical system recording a hologram.
[0059] FIG. 6 is a diagram for comparing the diffraction efficiency
of an optical recording medium according to the invention using an
optical recording material according to the invention with that of
an optical recording medium of prior art technologies.
[0060] FIG. 7 is a diagram for comparing the sensitivity of an
optical recording medium according to the invention using an
optical recording material according to the invention with that of
an optical recording medium of prior art technologies.
[0061] FIG. 8 is a diagram showing a change in the diffraction
efficiency of an intensity modulation or polarization modulation
hologram in an optical recording medium according to the invention
using an optical recording material according to the invention.
[0062] FIG. 9 is a schematic view showing the structure of an
optical system which materializes a digital holographic memory.
[0063] FIG. 10 is a diagram showing the medium shift selectivity of
diffraction light in a spherical reference wave shift multiple
system using an optical recording medium according to the invention
using an optical recording material according to the invention.
[0064] FIG. 11 is a diagram showing the condition of a change in
birefringence .DELTA.n with time with respect to the
copolymerization ratio of the main chain-consisting monomer having
an ether bond.
[0065] FIG. 12 is a diagram showing the condition of a change in
birefringence .DELTA.n and a change in medium transmittance with
respect to the copolymerization ratio of the main chain-consisting
monomer having an ether bond.
[0066] FIG. 13 is a diagram showing that the sensitivity of
hologram recording is improved by controlling crystallinity by
means of the copolymerization of the main chain-consisting
monomer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] Embodiments of the present invention will be explained in
detail.
[0068] Optical Recording Material
[0069] Dicarboxylic Acid Monomer
[0070] A dicarboxylic acid monomer according to the invention and
represented by the following general formula (1) will be
exemplified. 8
[0071] In the general formula (1), X represents a lower alkyloxy
group, a substituted or unsubstituted benzyloxy group, a
substituted or unsubstituted phenyloxy group, an acid residue of a
lower fatty acid, an acid residue of a substituted or unsubstituted
benzoic acid, or a halogen atom. Among these groups, a lower
alkyloxy group, a substituted or unsubstituted phenyloxy group, an
acid residue of a lower fatty acid and a halogen atom are
preferable. Examples of the substituent include a methyl group,
ethyl group, halogen atom and cyano group.
[0072] Examples of the lower alkyloxy group include a hydroxy
group, methyloxy group and ethyloxy group. Examples of the
benzyloxy group include a benzyloxy group, methylbenzyloxy group,
ethylbenzyloxy group and chlorobenzyloxy group. Examples of the
phenyloxy group include a phenyloxy group, methylphenyloxy group,
ethylphenyloxy group and chlorophenyloxy group. Examples of the
acid residue of a lower fatty acid include an acetyloxy group,
chloroacetyloxy group, fluoroacetyloxy group, trifluoroacetyloxy
group and cyanoacetyloxy group. Examples of the acid residue of
benzoic acid include a benzoyloxy group, chlorobenzoyloxy group,
fluorobenzoyloxy group and cyanobenzoyloxy group. Examples of the
halogen atom include a chlorine atom and bromine atom.
[0073] In the general formula (1), Y represents a hydrogen atom or
a lower alkyl group. Examples of the lower alkyl group include a
methyl group, ethyl group and propyl group. Z represents a hydrogen
atom, a methyl group, a methoxy group, a cyano group or a nitro
group. m denotes an integer from 1 to 3 and preferably 1. n denotes
an integer from 2 to 18 and preferably 4 to 12.
[0074] The dicarboxylic acid monomer represented by the above
general formula (1) can be produced by reacting a dicarboxylic acid
derivative represented by the following general formula (2) with a
biphenyl derivative represented by the following general formula
(3) in the presence of a condensing agent. 9
[0075] X, Y and m in the general formula (2) are respectively the
same as X, Y and m in the general formula (1). 10
[0076] In the general formula (3), Q represents an atomic group
which is easily dissociable by the effect of a nucleophilic
substitution reaction in the condition of an ether synthetic
reaction. Examples of the atomic group which is easily dissociable
by the effect of a nucleophilic substitution reaction in the
condition of an ether synthetic reaction include a halogen atom, a
tosyl group and a trifluoroacetyloxy group. Among these groups, a
bromine atom and tosyl group are preferable. In the general formula
(3), Z represents a hydrogen atom, a methyl group, a methoxy group,
a cyano group or a nitro group and n denotes an integer from 2 to
18 and preferably 4 to 12.
[0077] Examples of the aforementioned condensing agent include
sodium hydroxide, potassium hydroxide, sodium carbonate, sodium
bicarbonate, potassium carbonate, potassium bicarbonate,
triethylamine, tributylamine, pyridine and
1,8-diaza[5,40]bicyclo-undecene-7. Among these groups, potassium
bicarbonate, triethylamine and 1,8-diaza[5,40]bicyclo-undecene-- 7
are preferable.
[0078] Binder Polymer
[0079] Next, the polyester of the invention represented by the
following general formula (4) will be explained. The polyester is a
novel compound and may be used as a binder polymer for controlling
the concentration of a dye.
[0080] General Formula (4) 11
[0081] In the general formula (4), Y, Z, m and n are each
independently represent the same as Y, Z, m and n in the general
formula (1), p denotes an integer from 5 to 2000, preferably 5 to
500 and more preferably 10 to 100. R represents a hydrocarbon chain
which may contain at least one of a substituted or unsubstituted
aromatic group and a substituted or unsubstituted aliphatic group.
The structure of R of the main chain portion decides the
crystallinity of the polymer. Examples of the substituent include a
methyl group, ethyl group, hydroxy group, methoxy group, ethoxy
group and chlorine atom. Examples of the aforementioned hydrocarbon
chain containing a substituted or unsubstituted aromatic group or
aliphatic group or the both include the following structures.
12
[0082] The hydrocarbon chain containing a substituted or
unsubstituted aromatic group or aliphatic group or the both may
include a difunctional atomic group containing a hetero atom
(hereinafter referred to as a difunctional atomic group containing
a hetero atomic group) such as a sulfone bond, sulfoxide bond,
ether bond, thioether bond, substituted imino bond and ketone
bond.
[0083] As examples of the hydrocarbon chain containing a
substituted or unsubstituted aromatic group or aliphatic group or
the both and containing a difunctional atomic group containing a
hetero atom group, functional groups represented by the following
formulae (5) and (5-a) to (5-d) are given. Among these groups,
functional groups represented by the following general formula (5)
are preferable. As the functional group represented by the
following general formula (5), functional groups represented by the
following general formula (5-d) are preferable. 13
[0084] In the general formula (5), U represents a hydrogen atom, a
halogen atom, a substituted or unsubstituted lower alkyl group, a
substituted or unsubstituted lower alkenyl group or a substituted
or unsubstituted lower alkinyl group. Among these groups, a lower
alkyl group is preferable. Examples of the substituent include a
hydrogen atom, fluorine atom, chlorine atom and alkyl group.
Examples of the aforementioned halogen atom and lower alkyl group
are the same as those exemplified above. Examples of the lower
alkenyl group include a vinyl group. Examples of the lower alkinyl
group include a propargyl group.
[0085] In the formulae (5) and (5-a) to (5-d), T represents a
direct bond, a sulfone bond, a sulfoxide bond, an ether bond, a
thioether bond, a substituted imino bond or a ketone bond. Among
these bonds, a sulfon bond, ether bond and ketone bond are
preferable. In the general formula (5), q denotes an integer from 1
to 4 and preferably 1 or 2. In the general formula (5), 1 denotes
an integer from 2 to 18 and preferably 4 to 10. Also, 1 in the
formulae (5-b) to (5-d) are the same.
[0086] The polyester represented by the general formula (4) may be
synthesized in the following manner. Isophthalic acid derivatives
represented by the following compound (1) which is a kind of
dicarboxylic acid represented by the general formula (1) is led to
a polyester provided with a biphenyl derivative bonded with the
side chain thereof by condensing with various aliphatic diols,
diols containing an aromatic ring and bisphenol in an appropriate
condition in the same manner as in the case of a usual diester of
an aromatic dicarboxylic acid. For example, the isophthalic acid
derivative is reacted with diols derived from a bisphenol compound
represented by the following general formula (8) by a
high-temperature polycondensation method based on ester exchange to
thereby synthesize a polyester compound represented by the
following general formula (9) which is a kind of polyester
represented by the general formula (4). In this case, if a known
reaction catalyst, such as calcium acetate, zinc acetate or
antimony oxide, is used which is regarded as an effective one in a
high-temperature polycondensation reaction based on ester exchange,
a better result is obtained. 14
[0087] In the formulae (8) and (9), U, T, q and l are each
independently the same as U, T, q and l in the general formula (5).
Also, p in the general formula (9) is the same as p in the general
formula (4).
[0088] Photo-Responsive Polymer
[0089] Next, the polyester of the invention which is represented by
the following general formula (6) will be explained. The polyester
is a novel compound and may be used as a photo-responsive polymer.
15
[0090] In the general formula (6), Y and Y', which may be the same
or different and are each independently the same as Y in the
general formula (4), Z and Z', which may be the same or different
and are each independently the same as Z in the general formula
(4), R is the same as R in the general formula (4) and the
structure of R of the main chain decides the crystallinity of the
polymer, m and m', which may be the same or different and are each
independently the same as m in the general formula (4), n and n',
which may be the same or different and are each independently the
same as n in the general formula (4), p is the same as p in the
general formula (4) and x and y represent abundance ratios of the
repeat unit and fulfill the following relationships:
0<x.ltoreq.1, 0.ltoreq.y<1 and x+y=1.
[0091] The polyester represented by the above general formula (6)
may be led to a polyester provided with a biphenyl derivative and
an azobenzene derivative bonded with the side chain thereof by
mixing an isophthalic acid derivative represented by the
aforementioned compound (1) which is a kind of dicarboxylic acid
monomer represented by the aforementioned general formula (1), an
isophthalic acid derivative represented by the compound (2)
containing azobenzene which is a kind of dicarboxylic acid monomer
represented by the aforementioned general formula (7) and diols
derived from a bisphenol compound represented by the aforementioned
general formula (8) in each appropriate amount and by reacting the
mixture by the aforementioned high-temperature polycondensation
method based on ester exchange. Here, the ratio of the
aforementioned two monomers is adjusted corresponding to the design
of a medium, whereby the absorbance of the photo-responsive
polyester can be controlled. 16
[0092] Here, the absorption coefficient of this photo-responsive
polyester may be controlled by adjusting the ratio between the
aforementioned two dicarboxylic acid monomers corresponding to the
design of a medium. It is desirable to design the ratio x from the
viewpoint of the influence of an azobenzene derivative capable of
inducing a change in the orientation of a biphenyl derivative and
the number of azobenzene units contained in one molecule.
Specifically, the ratio x is preferably 0.0005 (1/p) to 0.5
(azobenzene: biphenyl derivative=1:1) and more preferably 0.05 to
0.5.
[0093] Next, the polyester represented by the following general
formula (10) will be explained. This polyester is also a novel
compound and may be used as a photo-responsive polymer. 17
[0094] In the general formula (10), R.sub.1 represents a structural
unit capable of forming a liquid-crystalline or crystalline polymer
among R in the general formula (4). Also, R.sub.2 represents a
structural unit capable of forming an amorphous polymer among R in
the general formula (4). The crystallinity of the polymer is
defined by the structure of the main chain part. Specifically, the
crystallinity of the polymer is dependent on structures of the
structural units R.sub.1 and R.sub.2 and constituting ratio thereof
in the main chain. The structural unit capable of forming a
liquid-crystalline or crystalline polymer provides a
liquid-crystalline or crystalline polymer which is a polymer
polymerized using one type of main chain structural unit and
exhibits a liquid crystal phase or has a melting point. Examples of
this structural unit include 6,6'-(4,4'-carbonyldiphenylenedioxy)
dihexanol which is represented by the general formula (8) in which
T is a ketone bond and 6,6'-(4,4'-oxydiphenylenedioxy) dihexanol in
which T is an ether bond. The aforementioned structural unit
capable of forming an amorphous polymer provides an amorphous
polymer which is a polymer polymerized using one type of main chain
structural unit and has no melting point. Examples of this
structural unit include 6,6'-(4,4'-sulfonyldiphenylenedi-
oxy)dihexanol which is represented by the general formula (8) in
which T is a sulfone bond.
[0095] Y and Y' may be the same or different and are similar with Y
in the general formula (4). Z and Z' may be the same or different
and are similar with Z in the general formula (4). m and m' may be
the same or different and are similar with m in the general formula
(4). n and n' maybe the same or different and are similar with n in
the general formula (4). P represents an integer from 5 to 2000. x,
y, r and s represent the abundance ratio of the repeat unit wherein
x, y, r and s satisfy the following relations: 0<x.ltoreq.1,
0.ltoreq.y<1, x+y=1, 0.ltoreq.r.ltoreq.1, 0.ltoreq.s.ltoreq.1
and r+s=1.
[0096] As to the polyester represented by the general formula (10),
a derivative of isophthalic acid represented by the compound (1)
which is one of dicarboxylic acid monomers represented by the
general formula (1), a derivative of isophthalic acid represented
by the compound (2) containing azobenzene which is one of
dicarboxylic acid monomers represented by the general formula (7)
and two types of diols derived from a bisphenol compound
represented by the general formula (8) are mixed in an proper ratio
and reacted by the high-temperature polycondensation method based
on ester exchange, which can be led to the production of a
polyester with a biphenyl derivative and an azobenzene derivative
bound with the side chain thereof.
[0097] Here, the crystallinity of this photo-responsive polyester
can be controlled by adjusting the ratio between the structural
units of the foregoing two types of main chain parts corresponding
to the design of a medium. The ratio r is preferably in a range
from 0.2 to 0.95, and more preferably in a range from 0.5 to 0.9,
from the viewpoint of recording characteristics and scattering.
[0098] Synthetic Example of a Binder Polymer
[0099] Dicarboxylic acid monomer: diethyl
5-[6-[4-(4-cyanophenyl)phenoxy]h- exyloxy]isophthalate
[0100] (1) Synthesis of 4-(6-bromohexyloxy)-4'-cyanobiphenyl
[0101] 0.2 mol (39 g) of 4-hydroxy-4'-cyanobiphenyl, 2 mol (487.5
g) of 1,6-dibromohexane, 1.45 mol (200 g) of potassium carbonate
anhydride and 800 ml of acetone were placed in a 2 l three-neck
flask equipped with a mechanical stirrer and the mixture was
reacted under reflux for 20 hours by using a water bath. The
reaction mixture was cooled to ambient temperature and then
undissolved salts were removed by filtration. The resulting
reaction solution was concentrated to a volume of about 1/2 by
using a rotary evaporator, to which was then added 500 ml of
hexane, followed by heating with stirring. Then, the resulting
solution was cooled gradually to ambient temperature and then
allowed to stand in a freezing chamber to crystallize. After the
crystallized product was subjected to vacuum filtration, it was
washed with n-hexane and dried under reduced pressure to obtain a
crude target product (yield: 85% (61.3 g)), which was then
recrystallized from ethanol to obtain a purified target product
4-(6-bromohexyloxy)-4'-cyanobiphenyl (yield: 58% (41.8 g)).
[0102] (2) Synthesis of diethyl 5-hydroxyisophthalate
[0103] 1 mol (182.4 g) of 5-hydroxyisophthalic acid, 1500 ml of
ethanol and 10 ml of concentrated sulfuric acid were placed in a 2
l three-neck flask and the mixture were reacted under reflux for 24
hours by using a water bath. After the reaction was completed, the
system was concentrated to a volume of about 1/2 by using a rotary
evaporator. The resulting solution was poured into a cooled aqueous
solution containing about 20% of sodium bicarbonate to precipitate
a crude target product as a white flock, which was then separated
by filtration and dried under reduced pressure (yield: 96% (229
g)). The crude product was recrystallized from ethanol to obtain
diethyl 5-hydroxyisophthalate (yield: 80% (190 g)).
[0104] (3) Synthesis of (Diethyl Isophthalate Carrying
Cyanobiphenyl: diethly
5-{6-[4-(4-cyanophenyl)phenoxy]hexyloxy}isophthalate)
[0105] 0.08 mol (28.8 g) of 4-(6-bromohexyloxy)-4'-cyanobiphenyl,
0.08 mol (16.6 g) of diethyl 5-hydroxyisophthalate, 0.12 mol (19.2
g) of potassium carbonate anhydride and 400 ml of acetone were
placed in a 1 l three-neck flask and the mixture was reacted under
reflux for 24 hours by using a water bath. After the reaction
solution was allowed to cool, it was poured into about 4 l of
purified water to take out a precipitate, which was to be a crude
subject product, by filtration and the precipitate was dried under
reduced pressure (yield: 90% (37 g)). The resulting precipitate was
recrystallized from acetone to obtain diethyl isophthalate carrying
cyanobiphenyl through a hexyl group as a target product (yield: 73%
(30 g)). The resulting compound was subjected to nuclear magnetic
resonance (NMR) measurement. The results of measurement are shown
below. Also, the compound was subjected to mass spectrometry, with
the result that a peak corresponding to a molecular weight of 515.6
was confirmed.
1 18 Position of hydrogen a b c d e f g h i j k .delta.in ppm 1.41
4.40 4.05 1.86 1.58 8.26 7.74 7.00 7.71 7.62 7.74
[0106] Main chain monomer: Synthesis of
6,6'-(4,4-sulfonyldiphenylenedioxy- )dihexanol
[0107] 0.3 mol (82.3 g) of 4,4'-sulfonyldiphenol, 0.66 mol (90.2 g)
of 6-chloro-1-hexanol and 0.7 mol (97 g) of potassium carbonate
anhydride were weighed and mixed and 250 ml of
N,N-dimethylformamide was added to the mixture, followed by
stirring to suspend. The system was heated to 160.degree. C. using
an oil bath and reacted for 24 hours. After that, the reaction
solution was poured into water containing a small amount of
hydrochloric acid. The generated white powder material was
separated by filtration and dried to obtain a crude target product,
which was then recrystallized from a water-N,N-dimethylformamide
system to obtain purified
6,6'-(4,4'-sulfonyldiphenylenedioxy)dihexanol (yield: 89% (120 g)).
The resulting compound was subjected to measurements of infrared
absorption spectrum (IR) and nuclear magnetic resonance (NMR). The
results are shown in the following.
[0108] IR: 2937 cm.sup.-1 (CH expansion), 1594 cm.sup.-1 (C.dbd.C),
1252 cm.sup.-1 (C--O--C) 1149 cm.sup.-1 (S.dbd.O)
2 19 Position of hydrogen a, b, e b c f g .delta.in ppm 1.40-1.81
3.65 3.98 6.91 7.82
[0109] Binder polymer (1) for controlling the concentration of a
dye: synthesis of a polyester having cyanobiphenyl at a side
chain
[0110] 0.005 mol (2.58 g) of diethyl
5-{6-[4-(4-cyanophenyl)phenoxy]hexylo- xy}isophthalate, 0.005 mol
(2.25 g) of 6,6'-(4,4'-sulfonyldiphenylenedioxy- )dihexanol and
0.05 g of zinc acetate anhydride were taken in a 300 ml three-neck
flask equipped with a vacuum device and a stirring device and the
mixture was reacted at 160.degree. C. for 2 hours and then for 20
minutes under a vacuum of about 10 Torr with heating and stirring.
Next, the temperature was raised to 180.degree. C. with dropping
the pressure of the system gradually to 2 Torr over 30 minutes.
After the reaction was completed, the reaction solution was
dissolved in chloroform and the resulting solution was poured into
methanol to taken out a crude polymer. This crude polymer was
reprecipitated and then subjected to boiling-washing using hot
methanol and then hot water. The precipitate was separated by
filtration and dried under reduced pressure to obtain a target
polyester (yield: 82% (3.96 g). The resulting polyester was a
transparent amorphous polymer having a number average molecular
weight of 8244 and a glass transition temperature of 53.degree.
C.
[0111] Synthesis of a Photo-Responsive Polymer
[0112] Photo-Responsive Dicarboxylic Acid Monomer Carrying
Methylazobenzene: Synthesis of Diethyl
5-{6-[4-(4-methylphenylazo)phenoxy- ]hexyloxy}isophthalate
[0113] (1) (Synthesis of 4-hydroxy-4'-methylazobenzene)
[0114] A 3 l beaker was charged with 750 ml of 6 N hydrochloric
acid and then with 107 g (1 mol) of finely pulverized p-anisidine
(4-methylaniline). The mixture was sufficiently suspended by
stirring and about 300 g of ice was added to the suspension,
followed by cooling the system. In the meantime, 80 g (1.16 mol) of
sodium nitrite was dissolved in 500 ml of water. 400 ml of the
sodium sulfite solution was poured into the suspension over 20
minutes. After completion of the dripping, the solution was stirred
at about 5.degree. C. for one hour. To the solution was gradually
added a solution obtained by dissolving 94 g (1 mol) of phenol in 1
l of a 2N potassium hydroxide solution, followed by mixing and the
mixture was reacted overnight. After the reaction was completed,
the generated precipitate was separated by filtration and dried
under reduced pressure to obtain 210 g (almost quantitative) of
crude 4-hydroxy-4'-methylazobenzene. The product was subjected to
the next reaction without purifying the same. The maximum
absorption wavelength (.lambda.max) of the compound was 345 nm.
[0115] (2) Synthesis of
(4-(6-bromohexyloxy)-4'-methylazobenzene
[0116] A 2 l three-neck flask equipped with a mechanical stirrer
was charged with 42.4 g (0.2 mol) of 4-hydroxy-4'-methylazobenzene
synthesized in the same manner as in the Example, 448 g (2 mol) of
1, 6-dibromohexane and 212 g (1.5 mol) of potassium carbonate
anhydride. To the mixture was added 800 ml of acetone and the
resulting mixture was suspended by stirring. The reaction system
was heated until acetone was refluxed to react hydroxybenzene with
bromoalkane. After the reaction was continued for 20 hours,
insoluble salts were separated by filtration and removed. The
system was concentrated to a volume of about 1/3 by using a rotary
evaporator. When the system was cooled in a freezing chamber,
4-(6-bromohexyloxy)-4'-methylazobenzene was produced as a crystal.
After the generated product was subjected to filtration, it was
washed with a small amount of cool acetone, cool ether and n-hexane
in this order and then dried under reduced pressure to obtain 38.1
g of crude 4-(6-bromohexyloxy)-4'-methylazobenzene (yield: 50.8%).
The resulting product was recrystallized from ethanol to obtain 32
g (yield: 42%) of 4-(6-bromohexyloxy)-4'-methylazobenzene. It was
found from an analysis using high performance liquid chromatography
that the purity of the product was 98.6% or more.
[0117] (3) Synthesis of Diethyl
(5-{6-[4-(4-methylphenylazo)phenoxy]hexylo- xy}isophthalate
[0118] A 1 l three-neck flask was charged with 16.6 g (0.07 mol) of
diethyl 5-hydroxyisophthalate, 26.1 g (0.07 mol) of
4-(6-bromohexyloxy)-4'-methylazobenzene and 15.1 g (0.11 mol) of
potassium carbonate anhydride. To the mixture was added 300 ml of
acetone and the system was refluxed under heating to react for 24
hours. After the reaction was completed, the system was poured into
1500 ml of cool water to obtain diethyl
{6-[4-(4-methylphenylazo)phenoxy]hexyloxy}isophth- alate, which was
then separated by filtration and dried under reduced pressure
(yield: 83% (35.1 g)). The product was recrystallized from acetone
twice to obtain 30.1 g (80.1%) of a target product, diethyl
(5-{6-[4-(4-methylphenylazo)phenoxy]hexyloxy}isophthalate. It was
found from an analysis using high performance liquid chromatography
that the purity of the product was 98.5% or more. The resulting
compound was subjected to measurements of infrared absorption
spectrum (IR) and nuclear magnetic resonance (NMR). The results are
shown in the following. IR: 2938 cm.sup.-1 (CH expansion), 1716
cm.sup.-1 (ester C.dbd.O), 1601 cm.sup.-1 (C.dbd.C), 1580 cm.sup.-1
(N.dbd.N), 1246 cm.sup.-1 (C--O--C)
3 20 Position of hydrogen a b c d e f g h, k i, j l .delta.in ppm
1.41 4.41 4.05 1.87 1.58 8.27 7.75 6.98-7.01 7.85-7.88 3.88
[0119] Photo-Responsive Polymer: Synthesis of a Polyester Having
Cyanobiphenyl and Methylazobenzene at a Side Chains
[0120] Diethyl
(5-{6-[4-(4-cyanophenyl)phenoxy]hexyloxy}isophthalate as a
dicarboxylic acid monomer carrying cyanobiphenyl, diethyl
5-{6-[4-(4-methylphenylazo)phenoxy]hexyloxy}isophthalate as a
photo-responsive dicarboxylic acid monomer carrying
methylazobenzene and 6,6'-(4,4-sulfonyldiphenylenedioxy)dihexanol
as a main chain portion monomer were used to synthesize four types
of polymer different in the copolymerization ratio of the dye
(methylazobenzene) side chain by using the same method as in the
case of the polyester synthesis as mentioned above. The mixing
ratios of the materials in each synthesis are found in Table 1.
Also, the structure of the synthesized polyester is shown as
[Compound 28]. The yield, number average molecular weight and glass
transition temperature of each resulting polymer are shown in Table
2. These polymers were transparent amorphous polymers free from
scattering.
4TABLE 1 Side chain portion Side chain portion Copolymerization
ratio of monomer carrying monomer carrying Main chain portion the
dye side chain cyanobiphenyl methylazobenzene monomer Zinc acetate
Polymer 1 0 g 2.66 g 2.25 g 0.05 g (100%: x = 1, y = ) Polymer 2
1.29 g 1.33 g 2.25 g 0.05 g (50%: x = 0.5, y = 0.5) Polymer 3 1.72
g 0.89 g 2.25 g 0.05 g (33%: x = 0.33, y = 0.67) Polymer 4 2.06 g
0.53 g 2.25 g 0.05 g (20%: x = 0.2, y = 0.8) 21
[0121]
5TABLE 2 Number Glass Copolymerization average transition ratio of
molecular tempera- the dye side chain Yield (amount) weight ture
Polymer 1 (100%:x = 1, y = 0) 75.8% (3.73 g) 8540 53.degree. C.
Polymer 2 (50%:x = 0.5, y = 0.5) 82.1% (4.00 g) 8462 53.degree. C.
Polymer 3 (33%:x = 0.33, y = 0.67) 76.0% (3.70 g) 8561 51.degree.
C. Polymer 4 (20%:x = 0.2, y = 0.8) 81.5% (3.95 g) 7957 52.degree.
C.
[0122] Photo-Responsive Polymer: Synthesis of a Polyester
Containing Two Types of Main Chain Structure Parts and Having
Cyanobiphenyl and Methylazobenzene as Side Chains
[0123] Six types of polymers varing in the copolymerization ratio
of main chain part monomers are produced in the same manner as in
the above example of the synthesis of a polyester by using diethyl
5-{6-[4-(4-cyanophenyl)phenoxy]hexyloxy}isophthalate as a
dicarboxylic acid monomer carrying cyanobiphenyl, diethyl
5-{6-[4-(4-methylphenylazo)p- henoxy]hexyloxy}isophthalate as a
photo-responsive dicarboxylic acid monomer carrying
methylazobenzene, 6,6'-(4,4-sulfonyldiphenylenedioxy)dih- exanol as
a main chain part monomer and 6,6'-(4,4'-oxydiphenylenedioxy)dih-
exanol synthesized in the same manner as the above dihexanol. The
structural general formula of each synthesized polymer is shown
below. The ratio x of the photo-responsive side chain is 0.1, and
each ratio r of the main chain part monomer having an ether bond is
0, 0.1, 0.5, 0.8, 0.9 and 1.0. 22
[0124] Optical Recording Medium
[0125] Structural Materials of the Photosensitive Layer
[0126] The optical recording medium of the invention is provided
with a photosensitive layer structured of prefixed optical
recording materials.
[0127] As the optical recording material, a photo-responsive
high-molecular compound may be used which is provided with a
photo-responsive group to be geometrically isomerized by light
radiation and a liquid crystal linear mesogen group, these both
groups being bonded therewith as side chains. An introduction of
the liquid crystal linear mesogen group, which is not geometrically
isomerized, into the compound makes it possible to control the
absorbance of a medium and also to reinforce and fix a change in
the orientation of the photo-responsive group which change is
caused by light radiation. This therefore ensures that a thick
layer can be attained with maintaining good recording sensitivity.
Among these compounds, a photo-responsive high-molecular compound
which contains an aromatic ring on its main chain and is provided
with a photo-responsive group to be geometrically isomerized by
light radiation and a liquid crystal linear mesogen group, these
both groups being bonded with the aromatic ring as a side chains.
In the compound, the side chains are bonded with the aromatic ring
fixed to the main chain, rendering it easy to control the
crystallinity of the polymer. Accordingly, the layer can be made
thick while maintaining high record retentivity.
[0128] Additionally, as the optical recording material, a
photo-responsive high-molecular compound into which a structural
unit capable of forming a liquid-crystalline or crystalline polymer
and a structural unit capable of forming an amorphous polymer are
introduced into the main chain of the same molecule simultaneously
is preferable. Using the compound, continuous crystallinity can be
controlled easily by changing the structural ratio of the main
chain part thereof. Further, there is a copolymerization ratio to
increase photo-induced birefringence with decreasing scattering
caused by crystallinity. Therefore, it is possible to attain both a
reduction in scattering and an improvement in photo-induced
anisotropy, making it possible to maintain higher record
retentivity and to attain a thick film at the same time.
[0129] Here, as examples of the high-molecular compound containing
an aromatic ring on its main chain, polyesters obtained by reacting
a dicarboxylic acid such as phthalic acid or isophthalic acid with
a diol by polymerization condensation are given. Also, examples of
the photo-responsive group which is geometrically isomerized by
light radiation include isomerizing groups containing an azobenzene
skeleton. Examples of the liquid crystal linear mesogen group
include mesogen groups containing a biphenyl skeleton and having a
geometrically bar-like form.
[0130] As the photo-responsive polymer having controlled dye
concentration, photo-responsive polyesters (copolymers) obtained by
copolymerizing, for example, a dicarboxylic acid monomer having a
biphenyl skeleton and a dicarboxylic acid monomer having an
azobenzene skeleton and represented by the aforementioned general
formula (6) may be preferably used.
[0131] Also, as the optical recording material, a photo-responsive
high-molecular composition may be used which comprises a
photo-responsive high-molecular compound provided with a
photo-responsive group which is geometrically isomerized by light
radiation and bonded therewith as a side chain and a
photo-unresponsive high-molecular compound provided with a liquid
crystal linear mesogen group bonded therewith as a side chain. The
absorption amount of a composition can also be controlled by
blending a photo-unresponsive high-molecular compound having a
liquid crystal linear mesogen group which is not geometrically
isomerized as a binder polymer with a polymer containing a low
molecular dye or an azobenzene derivative as a structural part.
Also, the composition can reinforce and fix a change in the
orientation of the photo-responsive group which change is caused by
light radiation.
[0132] Also, a photo-responsive high-molecular composition may be
used, the composition comprising a photo-responsive high-molecular
compound which contains an aromatic ring on its main chain and is
provided with a photo-responsive group which is geometrically
isomerized by light radiation and bonded with the aromatic ring as
a side chain and a photo-unresponsive high-molecular compound which
contains an aromatic ring on its main chain and is provided with a
liquid crystal linear mesogen group bonded with the aromatic ring
as a side chain. In the high-molecular compound contained in the
composition, the side chain is bonded with the aromatic ring fixed
to the main chain and it is therefore easy to control the
crystallinity of the polymer. Accordingly, the layer can be made
thick while maintaining high record retentivity.
[0133] The crystallinity of the respective high-molecular compounds
can be controlled more easily by introducing a structural unit
capable of forming a liquid-crystalline or crystalline polymer and
a structural unit capable of forming an amorphous polymer
simultaneously into the main chain of the same molecule, making it
possible to attain a reduction in scattering and promotion of a
change in the orientation of a photo-responsive group at the same
time.
[0134] For example, a polyester represented by the general formula
(4) is preferable as the binder polymer. It is also possible to
control the concentration of a dye by blending a polyester
represented by the general formula (4) with a photo-responsive
polyester represented by the general formula (6).
[0135] It is also possible to add additives such as phthalates to
the aforementioned optical recording material with the intention of
improving filming characteristics and adhesion to a substrate.
[0136] Structure of the Optical Recording Medium
[0137] The optical recording medium of the invention may be
constituted of a substrate and a photosensitive layer comprising
the aforementioned optical recording material or may be constituted
only of the aforementioned optical recording material provided that
the whole of the optical recording medium is formed as the
photosensitive layer. No particular limitation is imposed on a
material used for the substrate as far as it is transparent and
firm in the range of wavelengths to be used and is not
significantly changed in qualities and dimension in a usual
temperature and humidity range. Examples of the material used for
the substrate include soda glass, boro-silicated glass, potash
glass, acryl plates, polycarbonate and polyethylene terephthalate
(PET) sheets.
[0138] The optical recording medium of the invention allows the
photosensitive layer to be made thick by using the aforementioned
optical recording material, though the thickening of the
photosensitive layer has been difficult. The thickness of the
photosensitive layer can be varied within a range from 10 .mu.m to
10000 .mu.m without impairing optical recording characteristics.
With an increase in thickness, the multiplicity of recording can be
more raised. However, the diffraction efficiency of a multiplexed
hologram decreases in inverse proportion to almost the square of
the multiplicity and it is therefore preferable that the thickness
of the photosensitive layer be within the range where several
thousands multiples are allowed, namely the range from 50 .mu.m to
1000 .mu.m.
[0139] The optical recording medium of the invention may be formed
into a two-dimensional or three-dimensional shape such as a sheet
form, tape form, film form and disk form. As to specific methods,
the optical recording material is dissolved in an aliphatic or
aromatic halogen type solvent or an ether type solvent such as
chloroform, methylene chloride, o-dichlorobenzene, tetrahydrofuran,
anisole and acetophenone and the resulting solution is applied to a
substrate such as glass, whereby a transparent and tough film-like
optical recording medium can be formed. Also, the optical recording
medium can also be formed in the form of a film by compressing a
powdery, pellet or flake solid of the optical recording material by
means of a hot press method or the like.
[0140] Preferable examples of the form of the optical recording
media of the invention include the following optical recording
media (1) to (5): (1) optical recording media which have a disk
form and are rotated with moving a record reproducing head along
the radius vector thereon to scan, whereby recording and
reproduction can be carried out; (2) optical recording media which
have a sheet form and on which a record reproducing head is moved
in a two-dimensional direction to scan, whereby recording and
reproduction can be carried out; (3) optical recording media which
have a tape form, on a fixed part of which a record reproducing
head is moved with rolling it to scan, whereby recording and
reproduction can be carried out; (4) optical recording media which
have a three-dimensional bulk form and are fixed to a fixed or
movable stage and the surface or inside of which is scanned by a
movable or fixed record reproducing head, whereby recording and
reproduction can be carried out; and (5) optical recording media
which have a two-dimensional form such as a disk form, sheet form
or card form or other three-dimensional forms obtained by
laminating film-like media appropriately and which are scanned by a
record reproducing head by using each of the methods described in
(1) to (4), whereby recording and reproduction can be carried
out.
[0141] Applicable Recording Method
[0142] The optical recording medium of the invention is used for
optical recording utilizing a change in the absorption, refractive
index or shape of an optical recording material which change is
associated with application of light or heat to the optical
recording material. Examples of optical recording methods include
hologram recording, light absorbance modulation recording, light
reflectance modulation recording and photo-induced relief
formation. Among these methods, hologram recording is a preferable
optical recording method suitable for the optical recording medium
of the invention. The optical recording medium of the invention
enables independent recording in the case where the direction of
polarization of incident object light and the direction of
polarization of reference light are parallel to each other and in
the case where these both directions are perpendicular to each
other. The arrangement of the polarization of two light waves when
recording a hologram is not limited to these cases and an optional
one can be selected as far as it is an arrangement by which the
distribution of light intensity due to interference or the
distribution of polarization is formed.
[0143] Production of an Optical Recording Medium
[0144] Optical recording media are produced using 13 types of
optical recording materials. 4 types of the optical recording
materials were photo-responsive polymers 1 to 4 shown in Tables 1
and 2. 3 types of the optical recording materials were blend
polymers obtained by blending polymers 1 prepared so that the
contents of methylazobenzene are the same as those of the polymers
2 to 4 with the aforementioned binder polymer (1) shown in the
synthetic example. And 6 types of the optical recording materials
were photo-responsive polymers obtained by introducing two
different structural parts into the main chain part and by changing
the ratio between these structural parts according to the following
two methods.
[0145] (1) Spin Coat Film
[0146] Each polymer as an optical recording material was dissolved
in a ratio of 0.1 g/ml in chloroform and each solution was applied
to a cleaned glass substrate by spin coating in the condition of
1000 rpm and 10 sec to form 13 types of thin films. After dried,
the film thickness of each film was measured by a tracer type
surface roughness tester, to find that it was a thin film 1 to 1.5
.mu.m in thickness. Each film had a uniform surface and transparent
amorphous films free from scattering were obtained except for some
films using 6,6'-(4,4'-oxydiphenylenedioxy)dihex- anol as the main
chain part monomer. Films in which scattering was found was made
into transparent amorphous films by heating and quenching
treatment.
[0147] (2) Sandwich Type Glass Cell Medium
[0148] A flake-form polymer was put on a cleaned glass substrate
and a glass substrate was further put on the polymer. The glass
substrates were heat-pressed under reduced pressure to produce a
sandwich type glass cell medium having a structure in which an
optical recording material was sandwiched between two glass
substrates.
[0149] As to each of the above 4 types of photo-responsive polymers
obtained as the polymers 1 to 4 shown in Tables 1 and 2 and the
above 3 types of polymer blends obtained by blending polymers 1
prepared such that the contents of methylazobenzene were the same
as those of the polymers 2 to 4 with the aforementioned binder
polymer (1) shown in the synthetic example, 4 types of cell media
differing in the film thickness of the optical recording material
layer, specifically cell media in which the thicknesses of the
optical recording material layers were 50 .mu.m, 100 .mu.m, 180
.mu.m and 500 .mu.m were produced. The film thickness was
controlled using a spacer having the same thickness of the film
thickness. The cell media produced in this manner was transparent
and uniform films free from scattering and air bubbles.
[0150] Also, as to each of the above 6 types of photo-responsive
polymers obtained by introducing two different structural parts
into the main chain part and by changing the copolymerization ratio
between these structural parts, a cell medium in which the
thickness of the optical recording material layer was 250 .mu.m was
produced. In the case of media in which the ratio of the principal
part monomer, 6,6'-(4,4'-oxydiphenyle- nedioxy)dihexanol was high,
a reduction in transparency caused by scattering was confirmed
visually.
[0151] FIG. 1 shows the absorption coefficient of the thin film
obtained from each of the 4 types photo-responsive polymers of the
polymers 1 to 4 at a wavelength of 515 nm. It is found from FIG. 1
that the absorption coefficient .alpha. of each polymer can be
controlled by changing the copolymerization ratio y of the monomers
carried on the side chain of cyanobiphenyl. In short, the
absorption coefficient .alpha. is more decreased with increased
copolymerization ratio y.
[0152] Also, FIG. 2 shows the transmittance of the 100-.mu.m-thick
cell medium obtained from each of these photo-responsive polymers
at a wavelength of 515 nm. As shown in FIG. 2, the transmittance of
a thick film medium can be increased by raising the
copolymerization ratio y of the monomers carried on the side chain
of cyanobiphenyl. Particularly, when the copolymerization ratio y
is 0.6 or more, the transmittance of the thick film medium is
greatly increased.
[0153] Optical Anisotropy (Birefringence) Recording by Irradiation
with Polarized Light
[0154] Next, an example in which using the optical recording medium
of the invention, linearly polarized light is applied to carry out
birefringence recording will be explained. The optical system used
is shown in FIG. 3.
[0155] As shown in FIG. 3, linearly polarized light (7.9 mW) with a
wavelength of 515 nm which is sensitive to a polymer constituting
an optical recording medium 18 was made to be incident on the
polymer as recording light from an argon ion laser 10 through a 1/2
wavelength plate 12, a pinhole 14 and a half mirror 16. Also,
linearly polarized light with a wavelength of 633 nm was made to be
incident at an angle of 45.degree. to the axis of the polarized
light as pumping light from a He--Ne laser 20 through a mirror 22,
a 1/2 wavelength plate 24, a lens 26 and a half mirror 16. The
laser light penetrating the optical recording medium 18 passes
through an interference filter 28 and is divided into polarized
light components traveling in polarized directions perpendicular to
each other by a polarizing beam splitter 30. The light out put of
each polarized light component were measured by two power meters 32
and 34 respectively. A change in birefringence was calculated from
the condition of polarization of the transmitted light by using the
values measured by the two power meters 32 and 34.
[0156] A spin-coated layer of each of the aforementioned thirteen
types of polymer was used as an optical recording medium to carry
out birefringence recording and as a result, it was confirmed that
in all media, birefringence was induced and stored. Accordingly,
the optical recording medium of the invention can be used for the
recording and reproduction of optical anisotropy by irradiation
with polarized light.
[0157] Here, to confirm the effect obtained by introducing the
dicarboxylic monomer carrying a biphenyl derivative according to
the invention, a spin-coated layer made of a blend material
comprising the aforementioned polymer 1 having methylazobenzene at
a side chain and the binder polymer (1) having cyanobiphenyl at a
side chain was compared in photo-induced anisotropy with a
spin-coated layer made of a blend material comprising the above
polymer 1 and a binder polymer having no side chain. The binder
polymer having no side chain was synthesized using diethyl
isophthalate as a monomer. The contents of the polymer 1 in both
spin-coated films were made to be equal to each other.
[0158] FIG. 4 shows the condition of a change with time as to a
change of birefringence .DELTA.n. Here, a medium was exposed in the
condition of 1 W/cm.sup.2 and 1800 sec to carry out birefringence
recording. In the medium using the binder polymer (1) according to
the invention, birefringence is induced once polarized light was
applied and a change in the birefringence was stored after the
polarized light was shut out. In the medium using a binder polymer
having no side chain, on the other hand, birefringence could be
neither induced nor stored.
[0159] The difference directly reflects the effect obtained by
introducing dicarboxylic acid monomer carrying a biphenyl
derivative in the invention. Namely, it is considered that the
cyanobiphenyl group bonded with the side chain of the binder
polymer (1) appropriately restricts the mobility of
methylazobenzene to thereby contribute to the retention of records
caused by a change in the orientation of methylazobenzene. As
aforementioned, the introduction of the dicarboxylic acid monomer
carrying a biphenyl derivative into the layer makes it possible to
control the concentration of a dye in the thin layer and also to
retain optical recording characteristics based on a change in the
orientation of azobenzene.
[0160] Further, in order to confirm the effect of controlling
crystallinity in the high-molecular compound according to the
invention, a spin coat film is produced using 6 types of
photo-responsive polymers differing in the copolymerization ratio
of the main chain part, to record photo-induced birefringence. Each
copolymerization ratio r of the main chain monomer having an ether
bond is 0, 0.1, 0.5, 0.8, 0.9 and 1.0. The condition of a change in
birefringence .DELTA.n with time with respect to copolymerization
ratio is shown. When measuring the change in birefringence
.DELTA.n, exposure is carried out in the condition of 2 W/cm.sup.2
and 900 sec to record birefringence. Also, in FIG. 12, the recorded
birefringence and the transmittance measured using a cell medium
provided with a light-sensitive layer having a thickness of 250
.mu.m are plotted against copolymerization ratio. The transmittance
is measured using 633 nm He--Ne laser light.
[0161] Firstly, explanations will be furnished as to the control of
crystallinity by a difference in the structure of the main chain
part on the basis of the results of measurement made when the
copolymerization ratios of the main chain part is 0 and 1.0. When
the ratio is 0, namely the structure of the main chain part having
a sulfone bond gives an amorphous polymer having no melting point.
As shown in FIGS. 11 and 12, this polymer brings about high medium
transmittance because it can form a thick film free from scattering
though recordable birefringence is relatively low. On the other
hand, when the ratio is 1.0, namely the structure of the main chain
part having a ether bond forms a crystalline polymer. In the case
of a medium having a film thickness of 250 .mu.m, the transmittance
is dropped even to 0.36% because of large scattering caused by
crystallinity. However, recordable birefringence is larger than
that of an amorphous polymer, there is no relaxation after
recording light is cut off and the medium exhibits high record
retentivity. As aforementioned, the high molecular compound in the
invention has a structure in which the side chain is bound with an
aromatic ring fixed to the main chain and it is therefore possible
to control the crystallinity of the polymer by using different main
chain part monomers.
[0162] Next, explanations will be furnished as to the control of
crystallinity by the copolymerization ratio of the main chain part.
It is possible to suppress a reduction in transmittance caused by
scattering and to increase the recorded birefringence continuously
by increasing the ratio of the monomer having an ether bond forming
a crystalline polymer as shown in FIG. 12. Furthermore, it is
amazing that in the case of a polymer in which the copolymerization
ratio of the main chain having an ether bond is designed to be 0.9,
a reduction in transmittance caused by the scattering of a
crystalline polymer having a copolymerization ratio of 1.0 can be
remarkably improved and also recordable birefringence can be
increased. As shown in FIG. 11, the increase in recorded
birefringence also directly contributes to an improvement in
recording sensitivity. FIG. 13 shows diffraction efficiency with
respect to exposure energy when carrying out hologram recording
according to the recording method which will be explained later.
The results of a medium (film thickness: 250 .mu.m) using a polymer
in which the copolymerization ratio of the main chain having an
ether bond is 0.9 and which exhibited the highest sensitivity in
the recording of birefringence are shown in comparison with those
of a medium using an amorphous polymer in which the
copolymerization ratio of the main chain is 0. Exposure energy
reaching the maximum value can be reduced to about 1/6 in the
condition that the maximum diffraction efficiency is maintained and
it is understood that the invention enables a thick film medium to
be highly sensitized. As aforementioned, a thick film medium having
the characteristics that its crystallinity can be easily controlled
by changing the copolymerization ratio of the main chain part, and
it has low scattering and high record retentivity and is also
superior in recording sensitivity can be produced.
[0163] Hologram Recording
[0164] Next, an example in which hologram recording was carried out
using the optical recording medium of the invention will be
explained. The optical system used is shown in FIG. 5.
[0165] As shown in FIG. 5, a 515 nm oscillation line of an argon
ion laser 36 was used for recording and reproduction. The linearly
polarized light emitted from the laser 36 is rotated as to
polarization by a 1/2 wavelength plate 38 and is then divided into
two light waves, namely, signal light and reference light by a
polarizing beam splitter 40. At this time, a balance in intensity
between the two light waves can be adjusted by controlling the
angle of rotation of polarization. In the structure of the
invention, these two light waves intersect with each other in an
optical recording medium 42 and induces optical anisotropy in the
medium corresponding to the distribution of intensity due to the
interference of the two light waves or the distribution of
polarization. A 1/2 wavelength plate 44 disposed in a signal light
optical path controls the polarization of the signal light, whereby
an intensity modulation hologram in which the directions of
polarization of the signal light and reference light are parallel
to each other or a polarization modulation hologram in which the
directions of polarization of the both are perpendicular to each
other can be recorded. When reproducing a hologram, diffracted
light of the recorded hologram is obtained by applying only the
reference light to the optical recording medium 42 and the light
output can be measured by a power meter 45. The diffraction
efficiency of the optical recording medium was calculated by
finding the ratio of the intensity of the diffracted light to the
light intensity of the reference light.
[0166] FIG. 6 is a chart in which the diffraction efficiency of the
optical recording medium using the photo-responsive polymer of the
invention is plotted against the layer thickness of a
photosensitive layer (shown as an "optical recording layer" in FIG.
6) as compared with an optical recording medium using a
conventional polymer. Here, the obtained diffraction efficiency is
effected by the polarization hologram recorded when signal light
and reference light are respectively the light polarized in a
direction horizontal to the space and when the both lights are
respectively the light polarized in a direction perpendicular to
the space.
[0167] In the figure, (a) corresponds to a polyester having
cyanobenzene at a side chain. It is to be noted that there is a
description concerning a polyester having cyanobenzene at a side
chain in (MINABE Jiro et al., "Holographic Recording and
Reconstruction of Polarized light with Azo polymer (II)", the 59th
Meeting, Japan Society of Applied Physics, Preprints, p. 1015
(1998)). Also, in the figure, (b) shows the results concerning a
polyester having methylazobenzene at a side chain as disclosed in
JP-A No. 2000-109719. It is found that the both are decreased
rapidly in diffraction efficiency with an increase in layer
thickness.
[0168] On the other hand, (c), (d) and (e) in the figure relate to
the photo-responsive polymer of the invention and correspond to the
aforementioned polymer 2, polymer 3 and polymer 4 respectively. As
this result shows, the optical recording medium of the invention
can give a diffraction efficiency more than 100 times that of an
optical recording medium according to prior art technologies when
the layer thickness is 100 .mu.m and more than 10000 times that of
an optical recording medium according to prior art technologies
when the layer thickness is 150 .mu.m. These effects are considered
to be obtained by the reasons that the absorption loss of the
medium is decreased and the scattering is decreased by increased
amorphousness.
[0169] Also, FIG. 7 shows the relationship between a change in
diffraction efficiency and exposure time in the case of a
100-.mu.m-thick optical recording medium using the polymer 2
according to the invention and in the case of a 50-.mu.m-thick
optical recording medium using a conventional polymer (polyester
having cyanobenzene at a side chain). Namely, exposure energy
increases in proportion to exposure time. It is found that an
optical recording medium using the photo-responsive polymer of the
invention has a higher thickness and sensitivity than an optical
recording media according to prior art technologies. The use of the
photo-responsive polymer of the invention ensures that high
diffraction efficiency can be attained and the sensitivity of an
optical recording medium can be improved even if layer thickness is
increased.
[0170] FIG. 8 shows the relation between a change in diffraction
efficiency and exposure energy in the behavior of the intensity
modulation hologram and polarization modulation hologram recorded
in a 100-.mu.m-thick optical recording medium using the polymer 2
according to the invention. The optical recording medium of the
invention can record both types of hologram. In the polarization
holograms recorded by horizontal polarization and vertical
polarization, the direction of polarization of reference light is
rotated at 90.degree. when the hologram is reproduced. Accordingly,
when these both types of hologram are multiple-exposed in the same
volume and then read out by the same reference light, the both
holograms can be independently reproduced by a polarizing beam
splitter and a polarizing plate because the polarizations of the
diffracted lights of the both are different by 90.degree. from each
other.
[0171] In this manner, the optical recording medium using the
photo-responsive polymer of the invention enables polarization
multiple recording. Also, as shown in FIG. 8, the diffraction
efficiencies of the both of the intensity modulation hologram and
the polarization modulation hologram are almost the same. The
utilization of the characteristics makes it possible to use the
optical recording medium of the invention as an optical recording
medium enabling polarization recording. Namely, the optical
recording medium of the invention may be utilized in methods as
described in JP-A No. 10-340479, in a recording and reproduction
method in which information is encoded as the distribution of
polarization and as a vector holographic memory medium enabling
optical calculation of polarization multiple recorded data
pages.
[0172] Digital Holographic Memory
[0173] Next, an example in which the optical recording medium using
the photo-responsive polymer according to the invention is applied
to a digital holographic memory will be explained. The memory
system used is shown in FIG. 9.
[0174] The memory system has the following structure. Namely, an
oscillation line with a wavelength of 532 nm from a solid laser 46
excited by a laser diode was used to record. The laser beam emitted
from the solid laser 46 is incident on a polarizing beam splitter
50 through a 1/2 wavelength plate 48 where it is divided into two
light waves, namely signal light and reference light. The signal
light is expanded and collimated by a lens system 52 and passed
through a spatial light modulator 54. At this time, data encoded
corresponding to information is expressed by light and shade on a
liquid crystal display which is the spatial light modulator 54 and
imparted to the signal light. In succession, the signal light is
processed by Fourier transformation using a lens 56 and then
applied to the optical recording medium 58. On the other hand, the
reference light is changed to a sphere wave by a lens 60 disposed
just before the optical recording medium 58 and applied to the
optical recording medium 58 such that it is superimposed on the
signal light in the optical recording medium 58.
[0175] An interference fringe or a polarization distribution is
formed in the optical recording medium 58 by the signal light and
the reference light. In response to this, optical anisotropy is
induced and a hologram is recorded. When reproducing the hologram,
the light diffracted by the spherical wave is processed by Fourier
transformation using a lens 62 and a desired polarized angle
component is selected by a polarizing plate 64 to form an image on
a CCD camera 66. The distribution of intensity reproduced by the
CCD camera 66 is binary-coded by a proper threshold value and then
decoded by a proper means, whereby the recorded information is
reproduced.
[0176] A digital data was recorded and reproduced using a
100-.mu.m-thick glass cell type optical recording medium using the
polymer 2 according to the invention. Setting 160.times.120 pixels
as one page, 19.2 kbits text data was recorded and reproduced
together. The reproduced two-dimensional digital data was
binary-coded using a proper threshold value and decoded, whereby
the text data could be reproduced without any error. Here, although
in the example, binary digital data was recorded and reproduced
using the distribution of intensity of a signal light, the encoding
method is not limited to this, but multilevel digital data using
the distribution of intensity may be used. Also, in the optical
recording medium of the invention, the direction of polarization of
signal light can be recorded. Accordingly, the data may be
expresses by the binary or multilevel distribution of polarization
direction.
[0177] Also, the reason why spherical reference wave is used in the
example is that it is intended to attain volume multiple recording
by using a simple method. It is previously mentioned that in the
case of a thick hologram, volume multiple recording is possible by
utilizing hologram selectivity based on the angle of incidence of
reference light. That spherical reference wave is used to record
and the recorded medium is moved in a horizontal direction
corresponds to the fact that the angle of incidence of the
reference light on the effectively recorded hologram is made to be
changed. Accordingly, by recording with shifting the medium in the
condition that optical paths of the signal light and reference
light are fixed, volume multiple recording can be attained with
ease.
[0178] FIG. 10 shows the medium shift selectivity of a recorded
hologram. A 500 .mu.m-thick glass cell medium obtained using a
material prepared by blending the polymer 2 according to the
invention with the binder polymer according to the invention in a
ratio of 2:9 was used. It was found that the hologram recorded by
spherical reference wave was made to disappear by shifting the
medium by a distance of 50 .mu.m. From the value, the effective
thickness of the recorded hologram was calculated, to find that it
almost accorded to the layer thickness of the photosensitive layer.
This shows that an effective hologram is formed in all the
direction of the thickness of the photosensitive layer.
[0179] Also, from experimental results, a multiplexed hologram can
be reproduced without any crosstalk by moving the medium by a
distance of 100 .mu.m to record the next hologram. A recording
region corresponding to one page of the example has a diameter of
about 10 mm. 100 multiples can be attained by recording a hologram
by moving at intervals of 100 .mu.m. Here, although a spherical
reference wave shift multiplexing is used, the multiplexing is not
limited to this. The optical recording medium may be applied to a
phase multiplexing provided with a phase distribution and a
correlation multiplexing. Also, because the optical recording
medium of the invention can record the direction of polarization of
signal light, a polarization angle multiplexing can be
attained.
[0180] As explained above, the optical recording material of the
invention decreases dye concentration to thereby reduce absorption
loss by introducing the "liquid crystal linear mesogen group", such
as a biphenyl derivative, which is not geometrically isomerized,
whereby information can be recorded extensively in the direction of
the layer thickness even if it is made thick. At the same time, the
"liquid crystal linear mesogen group" can reinforce and fix a
change in the orientation of the "photo-responsive group which is
geometrically isomerized by light radiation" such as azobenzene due
to its orientation characteristics. Accordingly, it is possible to
maintain high recording sensitivity and high diffraction efficiency
even if the optical recording material is made thick.
[0181] Also, in the case where a side chain is bonded with the
"aromatic ring", such as an isophthalic acid derivative, which is
fixed to a main chain, the presence the "aromatic ring" at the
bonded part restricts the mobility of the side chain and it is
therefore difficult for the medium to take a liquid crystal phase.
Accordingly, it is possible to control its crystallinity from a
liquid crystal state to an amorphous state corresponding to the
structure of the main chain. Namely, the degree of freedom for
material designing is large. Accordingly, it is possible to control
crystallinity to prevent the generation of noises, to thereby
maintain high record retentivity even if the thickness of the
optical recording material is increased.
[0182] Moreover, crystallinity can be continuously controlled
easily by introducing a structural unit capable of forming a
liquid-crystalline or crystalline polymer and a structural unit
capable of forming an amorphous polymer simultaneously and by
changing the ratio of these units into the main chain of the same
molecule. Also, such a copolymerization ratio as to increase
photo-induced birefringence with decreasing scattering caused by
crystallinity exists. Therefore, it is possible to attain both a
reduction in scattering and an improvement in photo-induced
anisotropy, making it possible to produce a thick film medium
having higher record retentivity.
[0183] Also, a novel dicarboxylic acid monomer and a novel
polyester for an optical recording material which embodies the
invention can be provided. The polyester synthesized using the
dicarboxylic acid monomer is useful as a binder polymer for
controlling dye concentration. Also, a photo-responsive polyester
synthesized using the dicarboxylic acid monomer is suitable for
optical recording materials, particularly, optical recording
materials for hologram recording.
[0184] Using the aforementioned optical recording material, a
highly sensitive and thick medium which attains high diffraction
efficiency can be provided. Accordingly, it is possible to improve
volume multiplicity outstandingly in, particularly, hologram
recording and the optical recording medium of the invention may be
used as a large scale optical recording medium Also, the optical
recording medium of the invention can record the direction of
polarization of signal light. This ensures that the optical
recording medium of the invention can be used as media used in a
large scale recording system and an optical processing utilizing
polarization recording. It is also possible to provide a large
scale optical recording reproducing device using this these optical
recording media.
[0185] According to the invention, a novel dicarboxylic acid
monomer and a novel polyester are provided. Also, according to the
invention, optical recording materials (e.g., a photo-responsive
high-molecular compound, a photo-responsive high-molecular
composition and a polyester) which can control the absorbance of a
medium, can maintain high recording sensitivity and high
diffraction efficiency and can also be made to be thick by the
control of the absorption amount of a recording material, and the
starting materials (a dicaboxylic acid monomer) of these optical
recording materials can be provided. Further, according to the
invention, optical recording materials which can control
crystallinity, can maintain high record retentivity and prevent the
generation of noises by the control of crystallinity to thereby
enable the layer thickness to be thickened, and the starting
materials (a dicaboxylic acid monomer) of these optical recording
materials can be provided.
[0186] Also, according to the optical recording medium of the
invention, a photosensitive layer can be made thick without
impairing recording characteristics, whereby such an effect that
large scale recording is attained can be obtained.
[0187] Further, according to the optical recording and
reproducinging device of the invention, such an effect can be
obtained that it is possible to record and reproduce large scale
data.
* * * * *