 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-erasable type information recording
medium (where information can be written only once) (for example, optical
disks) and an information recording method thereof.
2. Description of the Prior Arts
Optical disks, where a large capacity of information can be recorded in
high density, are widely used in an increasing number of fields. There are
two types of recording methods for optical disks: a non-erasable
(write-once) type where information can be written only once; and an
erasable type where information is erasable and rewritable. Of the above
two types, the non-erasable type optical disks are often used as sales
media for music, movies, etc., since the non-erasable type disks do not
allow the re-writing of information and the costs thereof are generally
restrained to be low.
Various kinds of information recording methods have been devised for
non-erasable optical disks. In all of the methods, information is recorded
by irradiating a narrowed laser beam on a recording layer of an optical
disk to change the physical/chemical characteristics of the recording
layer. The recording methods are roughly classified into two types where
the following two modes are used, respectively: a heat mode where a change
of the recording layer caused by a heating by laser beam is mainly used;
and a photon mode where a change of the recording layer caused by the
light (photon) of a laser beam is mainly used. In the heat mode recording
method, which includes a punch recording method where tiny holes (pits)
are made on the recording layer by a local heating by laser beam,
inorganic materials such as compounds of Bi, Re and Te, chalcogenide, etc.
whose melting and evaporating temperatures are low are mainly used.
Moreover, in the heat mode method and the photon mode method, a refractive
index/reflectance changing method is widely used where information is
recorded by causing a change in the refractive index and reflectance of
the recording layer. In this method, cyanic pigments are used as organic
pigments, and chalcogenide, TeO.sub.2 -Te, etc., as inorganic materials.
As described above, various kinds of materials have been developed as
materials for non-erasable optical disks. With respect to the inorganic
materials, since the spin coating, which can be easily conducted on the
organic materials, of the inorganic materials is difficult, an inefficient
process such as evaporation, etc. is required in many cases to form a
thin, uniform recording layer on the substrate of an optical disk.
Moreover, with respect to the organic pigments such as cyanic pigments,
etc., since the organic pigments tend to be decolored by light, it is
required to use an optical triplet quencher and to make the organic
pigments into metallic complexes to improve the stability, which
complicates the manufacturing process.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an information recording
medium which is excellent in both producibility and long-term
maintainability.
Another object of the present invention is to provide a method for
recording information onto the above-described information recording
medium.
A first feature of an information recording medium according to the present
invention is characterized in that, in an information recording medium for
recording information by adding heat or light to a recording layer on a
substrate, the recording layer includes a mixture of organic polysilane
and oxo metallic phthalocyanine pigment. Moreover, as a second feature, an
information recording medium may be provided a first layer including the
oxo metallic phthalocyanine pigment and a second layer consisting of the
organic polysilane.
As methods for recording information onto the recording layer of the
above-described two features, the following methods are effective: i) a
method where the decoloring reaction of the oxo metallic phthalocyanine
pigment is used which is caused by heating the recording layer to a
temperature equal to or higher than the pyrolyzing point of the organic
polysilane; and ii) a method where the decoloring reaction of the oxo
metallic phthalocyanine pigment is used which is caused by heating the
recording layer, on which ultraviolet rays are previously irradiated, to a
temperature equal to or higher than the glass transition point of the
organic polysilane.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of this invention will become clear
from the following description taken in conjunction with the preferred
embodiments with reference to the accompanied drawings in which:
FIG. 1A is a view where information is recorded on an information recording
medium which is the first feature of the present invention;
FIG. 1B is a view where information is recorded on an information recording
medium which is the second feature of the present invention;
FIG. 2 is a plan view showing recording pits of an optical disk;
FIGS. 3A and 3B respectively show the chemical formula of the organic
polysilane and that of the oxo metallic phthalocyanine pigment;
FIG. 4 is a graph showing a change in the light absorbance, by heating, of
the (PhMeSi)x/TiO-Pc lamination layer film which is an embodiment where a
quantity of ultraviolet irradiation is the parameter;
FIG. 5 is a graph showing the absorption spectra after an ultraviolet ray
irradiation where a quantity of ultraviolet irradiation on the
(PhMeSi)x/TiO-Pc lamination layer film is the parameter;
FIG. 6 is a graph showing a result of an FT-IR measurement before (the
upper) and after (the lower) ultraviolet rays are irradiated on
phenylmethylpolysilane which is an embodiment of the invention;
FIG. 7 is a graph showing a change in the absorption spectra when
ultraviolet rays are irradiated on a solution where titanylphthalocyanine
is dispersed in a toluene solution of phenylmethylpolysilane;
FIG. 8 shows the chemical formula showing a process of decomposition of
phenylmethylpolysilane by photon or heat;
FIG. 9 is a graph showing a result of the FT-IR measurement of each of (1)
only phenylmethylpolysilane (PhMeSi)x, (2) the (PhMeSi)x/TiO-Pc lamination
layer film, (3) after ultraviolet rays are irradiated on the
(PhMeSi)x/TiO-Pc lamination layer film for two hours, and (4) after the
lamination layer film is heated at 250.degree. C. and decolored; and
FIG. 10 is a graph showing a change in the light absorbance, by heating, of
the (PhMeSi)x/TiO-Pc lamination layer film when the first layer is an
evaporation film of the simple body of oxo metallic phthalocyanine
pigment, where a quantity of ultraviolet radiation is the parameter.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 3A and 3B respectively show the chemical formulae of organic
polysilane and oxo metallic phthalocyanine pigment which are included in a
recording layer of an information recording medium according to the
present invention. In FIG. 3A, R1 and R2 represent lower alkyl, aryl,
alkoxy, and acyl radicals, etc. In FIG. 3B, X represents a metallic atom;
R1, R2, R3 and R4 represent substituents of hydrogen atoms, halogen atoms,
alkyl radicals, alkoxy radicals, aryl radicals, aryloxy radicals, nitro
radicals, cyano radicals, hydroxyl radicals, benzyloxy radicals, and amino
radicals, etc; and k, l, m, and n represent integers from 0 to 4.
The recording layer is constituted by a mixture of organic polysilane and
oxo metallic phthalocyanine pigment (the feature will hereinafter be
referred to as a first feature). A first method for recording information
onto the recording layer of the first feature will be described. Firstly,
organic polysilane decomposes by heating the organic polysilane to a
temperature equal to or higher than its pyrolyzing point. Then, the
decomposition product decolors the oxo metallic phthalocyanine pigment by
reacting on the oxo metallic phthalocyanine pigment. Therefore, as shown
in FIG. 1A, by locally heating a recording layer 14 on a substrate 12 of
the information recording medium with a laser beam 10, etc., a heated
portion 16 is decolored (that is, the light absorbance is changed), so
that information where the heated portion 16 represents "1" and a
non-heated portion 18 represents "0" (or the reverse) can be recorded.
Next, a second method for recording information onto the recording layer of
the first feature will be described. Firstly, ultraviolet rays are
previously irradiated on the recording layer. Thereby, a photon
decomposition of the organic polysilane is caused. Then, by heating the
recording layer to a temperature equal to or higher than the glass
transition point of the organic polysilane, the decomposition product
produced by the photon decomposition contacts the oxo metallic
phthalocyanine pigment, which causes the decoloring reaction of the oxo
metallic phthalocyanine pigment. Therefore, in the case shown in FIG. 1A,
by locally irradiating ultraviolet rays 10 on the portion 16 in advance
and thereafter heating the entire surface of the recording layer 14, only
the portion 16 where the ultraviolet rays are irradiated is decolored, so
that information can be recorded. Or, by irradiating the ultraviolet rays
on the entire surface of the recording layer 14 in advance and thereafter
selectively conducting the local heating (with the laser beam 10, etc.),
information can also be recorded.
The recording layer may be constituted by a first layer including oxo
metallic phthalocyanine pigment and a second layer consisting of organic
polysilane (the feature will hereinafter be referred to as a second
feature) as well as by the above-described mixture (the first feature). In
this case, the first layer may be a layer consisting of only oxo metallic
phthalocyanine pigment produced by evaporation, etc. or may be a layer
consisting of a mixture of the oxo metallic phthalocyanine pigment and
some kind of binder polymer. When the binder polymer is used, however, it
is required that its glass transition point is lower than the pyrolyzing
point of a organic metallic polysilane.
In a case where information is recorded on a recording layer of the
above-described second feature by the above-described first method, the
operation therein is nearly the same as that when information is recorded
on a recording layer of the first feature by the first method.
That is, by heating the recording layer to a temperature equal to or higher
than the pyrolyzing point of the organic polysilane, the organic
polysilane in the second layer decomposes. Since the pyrolyzing point of
the organic polysilane is higher than its glass transition point, this
heating enables the contact of the organic polysilane in the second layer
with the oxo metallic phthalocyanine pigment in the first layer. Thereby,
the decomposition product of the organic polysilane reacts on the oxo
metallic phthalocyanine pigment, so that the oxo metallic phthalocyanine
pigment is decolored. Specifically, as shown in FIG. 1B, by locally
heating a recording layer 24 on a medium substrate 22 with a laser beam
20, the organic polysilane on a heated portion 26 of the second layer is
pyrolyzed. Since the pyrolyzing temperature of the organic polysilane is
higher than its glass transition point, the organic polysilane flows as
well as decomposes. Thereby, the second and first layers mix to promote
the contact of the organic polysilane with the oxo metallic phthalocyanine
pigment, so that only the portion 26 heated by the laser beam 20 is
decolored. Therefore, information where the heated portion 26 represents
"1" and a non-heated portion 28 represents " 0" (or the reverse) can be
recorded. As described above, the first layer may consist of only the oxo
metallic phthalocyanine pigment, or may consist of a mixed material of the
oxo metallic phthalocyanine pigment and binder polymer which softens and
flows at the time of the above heating.
When information is recorded on the information recording medium of the
second feature by the second method, the photon decomposition of the
organic polysilane in the second layer is caused by the previous
ultraviolet ray irradiation. However, since the heating is not conducted
at this point of time, the decomposition product remains within the second
layer. Thereafter, by heating the recording layer, the second and first
layers mix in a manner similar to the above-described case, and the
decoloring reaction of the oxo metallic phthalocyanine pigment is caused
by the contact of the organic polysilane with the oxo metallic
phthalocyanine pigment. In this case, there are also two kinds of methods
for recording information: a method where firstly the local ultraviolet
ray irradiation is selectively conducted and thereafter the entire surface
is heated; and a method where firstly the ultraviolet rays are irradiated
on the entire surface and thereafter the local heating is selectively
conducted.
In any of the above-described methods, as shown in, for example, FIG. 2,
various information can be recorded by forming with laser beam, etc. pits
32, which are decolored portions, in a base 30 colored by the oxo metallic
phthalocyanine pigment. The information can be read by detecting the
difference among the light absorbance of each portion (that is, bases 18,
28 and 30, and pits 16, 26 and 32) by scanning the recording layers 14 and
24 with low-energy laser beam.
A more detailed description of the embodiment of the present invention will
hereinafter be given with reference to the drawings.
Formation of a Lamination Layer Film
Firstly, phenylmethylpolysilane (PhMeSi)x was produced as an embodiment of
the organic polysilane. The following is the method. Under the existence
of 13 g metallic sodium, 50 g phenylmethyldichlorosilane (0.28 mol) was
heated to 135.degree. C. in 200 ml dry toluene, and was reacted for
approximately 11 hours while being agitated. After a cooling, ethanol was
added to the solution where dark violet precipitation had been deposited
to make the sodium which had not reached into ethoxide. After the
precipitation was filtered out, the solution was dried, and was dissolved
in toluene. The solution was dropped into ethanol and re-precipitated to
obtain phenylmethylpolysilane. The yield of the phenylmethylpolysilane was
10.2 g and 34%. In FIG. 3A showing the phenylmethylpolysilane, R1
represents the phenyl radical and R2 represents the methyl radical.
Next, titanylphthalocyanine TiO-Pc (shown in FIG. 3B) as an example of the
oxo metallic phthalocyanine pigment where Ti is a metal X. The
titanylphthalocyanine used was .alpha. type manufactured by Sanyo Shikiso
Co., Ltd. The lamination layer film consisting of the .alpha. type and
phenylmethylpolysilane was produced as hereinafter described. Ninety-mg
titanylphthalocyanine was added to 6 ml tetrahydrofuran (THF). After
kneading for a whole day and night in a ball mill, it was dispersed.
Ninety-mg polyvinyl butyral (S-LEC BM-2 manufactured by Sekisui Chemical
Co., Ltd. was used) was added thereto, and it was dispersed in a ball mill
for one more hour to be made into a coating liquid. This was spin-coated
on a transparent glass substrate (silica glass or slide glass) to form a
titanylphthalocyanine dispersion film. Next, 35 mg phenylmethylpolysilane
was dissolved in 0.35 ml benzene, and it was spin-coated on the
titanylphthalocyanine dispersion film to form a (PhMeSi)x/TiO-Pc
lamination layer film. In both of the titanylphthalocyanine dispersion
film and the phenylmethylpolysilane film, uniform layers were extremely
easily obtained by the spin-coating.
Recording characteristics of the Lamination Layer Film
FIG. 4 shows a change in the absorbance (at 25.degree. C.), to a 690 nm red
light, of the (PhMeSi)x/TiO-Pc lamination layer film formed as described
above when the lamination layer film was heated to 300.degree. C. after
ultraviolet rays having intensities of 0 J/cm.sup.2 to 39.2 J/cm.sup.2
were irradiated at room temperature. The ultraviolet light intensities
were 0.0, 4.9, 14.7, and 39.2 Joules per square centimeter. From the
figure, it is understood that, for example, when the lamination layer film
is heated to approximately 240.degree. C., there is a large difference in
absorbance between the portion where ultraviolet rays were irradiated
(39.2 J/cm.sup.2) and the portion where it was not irradiated (0
J/cm.sup.2). This means that pits of extremely high contrast are obtained
by using this lamination layer film for the recording layer of an optical
disk and by adopting the recording method of the ultraviolet ray
irradiation and heating to 240.degree. C.
Principle of the Recording
In order to search the cause of such a recording characteristic of the
(PhMeSi)x/Tio-Pc lamination layer film, firstly, the decomposition of
phenylmethylpolysilane by the irradiation of ultraviolet rays was
examined. After 300 nm to 400 nm ultraviolet rays having intensities of 0
J/cm.sup.2 to 5.1 J/cm.sup.2, respectively, were irradiated to a simple
component film of phenylmethylpolysilane, the absorbance of the film to
200 nm to 400 nm ultraviolet rays was measured. FIG. 5 shows the result at
intensities of 0.0, 0.6, 1.1, 2.3 and 5.1 Joules per square centimeter. A
peak of .lambda..sub.MAX =331 nm which appears when ultraviolet rays are
not irradiated (0 J/cm.sup.2) rapidly disappears after ultraviolet rays
are irradiated. Since the peak of .lambda..sub.MAX =331 nm corresponds to
an Si-Si compound which is the principal chain of phenylmethylpolysilane,
it is understood that the Si-Si compound which is the principal chain is
cut off by the irradiation of ultraviolet rays. Moreover, FIG. 6 shows an
FT-IR spectrum of phenylmethylpolysilane measured before and after the
irradiation of ultraviolet rays (the upper is before the irradiation, and
the lower is after the irradiation), where the existence of Si-OH compound
and Si-O-Si compound is confirmed. From the above, it is understood that
by irradiating ultraviolet rays on phenylmethylpolysilane, the Si-Si
compound which is the principal chain is cut off to form a polymer having
a bond in siloxane.
The formation of the siloxane chain (Si-O-Si) which is a loose compound by
the decomposition of phenylmethylpolysilane shows that the phenomenon that
the degree of freedom of polymer movement at the
ultraviolet-ray-irradiated portion is improved (that is, a glass
transition point Tg is decreased) is one of the causes of a shift (see
FIG. 4) of the decoloring reaction toward a low temperature side.
Next, in order to examine the decoloring reaction of titanylphthalocyanine
TiO-Pc, an examination was made with a dispersion solution of
titanylphthalocyanine. Titanylphthalocyanine was dispersed in a toluene
solution of phenylmethylpolysilane, and after ultraviolet rays were
irradiated thereon for 0 to 60 minutes, the absorption spectra of the
solution were measured. FIG. 7 shows the result after 0, 10, 30, and 60
minutes of irradiation. It is understood that in a dispersion solution
where a free contact of phenylmethylpolysilane and titanylphthalocyanine
is possible, the decoloring reaction is caused only by the irradiation of
ultraviolet rays.
As a result of the above research, it is considered that the decoloring
phenomenon of the (PhMeSi)x/TiO-Pc lamination layer film is caused in the
following process. Firstly, by the irradiation of ultraviolet rays, the
Si-Si compound of phenylmethylpolysilane is cut off as shown in FIG. 8, so
that decomposition products such as silyl radical, siloxane compound, Si-H
compound, etc. are produced. When the temperature is not high, however,
the decoloring reaction of titanylphthalocyanine pigment is not caused,
since these decomposition products cannot move from the
phenylmethylpolysilane layer to the titanylphthalocyanine layer. When the
lamination layer film is heated to a temperature equal to or higher than
the glass transition point temperature Tg of phenylmethylpolysilane,
phenylmethylpolysilane having the silyl radical and siloxane compound
moves to the titanylphthalocyanine layer, and decomposes a phthalocyanine
ring to decolor the titanylphthalocyanine pigment.
FIG. 9 shows the result of the FT-IR measurement in each of the following
conditions: (1) only phenylmethylpolysilane (PhMeSi)x; (2) the
(PhMeSi)x/TiO-Pc lamination layer film; (3) after ultraviolet rays are
irradiated on the (PhMeSi)x/TiO-Pc lamination layer film for two hours;
and (4) after, further to the condition (3), the lamination layer film is
heated at 250.degree. C. and decolored. By comparing (1) and (2), it is
confirmed that absorption peaks 1330, 1280, 1120, 1060 and 890 cm.sup.-1
shown by a mark .largecircle. in (2) are those of titanylphthalocyanine
pigment. These peaks still remain after the irradiation of ultraviolet
rays (3), although it is hidden in a large absorption band of 1000 to 1100
cm.sup.-1 showing the formation of the Si-O-Si compound by the photon
oxidation of the organic polysilane. After the heating (4), however, these
peaks shown by the mark .largecircle. disappear, and instead, the peak
(approximately 920 cm.sup.-1) of Si-O-Ti compound that is speculated to be
a reaction product of Si-OH compound, which is a decomposition product of
phenylmethylpolysilane after the irradiation of ultraviolet rays (3) and
titanylphthalocyanine pigment, is generated.
As described above, this embodiment showed that by heating the
(PhMeSi)x/TiO-Pc lamination layer film to an appropriate temperature after
the irradiation of ultraviolet rays, information can be recorded with an
extremely high contrast. Moreover, as its mechanism, it was clarified that
the Si-Si principal chain of the organic polysilane is decomposed by the
previous ultraviolet ray irradiation, and active species such as silyl
radical, etc. which is the decomposition product thereof reacts on the oxo
metallic phthalocyanine pigment to decolor the oxo metallic phthalocyanine
pigment.
Further, as shown by the solid line in FIG. 4, that the decoloring reaction
is caused even by only heating without previously irradiating ultraviolet
rays on the lamination layer film is substantiated by the data showing
that the absorbance of a lamination layer film on which ultraviolet rays
are not irradiated (0 J/cm.sup.2) largely decreases by heating the film to
approximately 300.degree. C.
FIG. 4 further shows that even after a large amount of ultraviolet rays
(39.2 J/cm.sup.2) are irradiated, the decoloring does not occur until the
temperature reaches 200.degree. C. Therefore, the recording layer where
information is once recorded is extremely stable in a normal condition (at
room temperature), so that a high contrast at the time of the recording is
maintained for a long period of time. The information recording medium
(optical disk) before the recording also has the characteristic of high
stability.
In the above-described embodiment, a mixture of oxo metallic phthalocyanine
pigment with a binder (phenylmethylpolysilane) whose glass transition
point is relatively low was used as the first layer of the lamination
layer film. FIG. 10 is a graph showing a change (the conditions are the
same as those in FIG. 4 of the above-described embodiment) in the light
absorbance according to the heating temperature when the first layer of
the lamination film is an evaporation layer consisting of only oxo
metallic phthalocyanine pigment and the second layer consists of
phenylmethylpolysilane, where a quantity of ultraviolet irradiation is the
parameter. The irradiation intensities in FIG. 10 are 0.0, 0.57 and 1.2
Joules per square centimeter. The relation nearly the same as that shown
in FIG. 4 is obtained, from which it is understood that quantitatively,
the above-described examination applies to this case. The temperature at
which the light absorbance decreases, however, is closer to the low
temperature side compared with the case in FIG. 4, so that the decoloring
reaction is caused at a lower temperature.
In the above description, a more detailed description of only the second
feature (the lamination layer construction) of the present invention was
given. From the results of the above-described various experiments,
however, it is clear that when a dispersion-type recording layer is formed
by mixing the organic polysilane and the oxo metallic phthalocyanine
pigment (the first feature), information can be recorded with a high
contrast by using the recording layer as an information recording medium
similarly to the above-described embodiment of the lamination layer
construction.
As understood from the above-described embodiment, according to the present
invention, since information pits with an extremely high contrast can be
recorded, the reading of information is trustworthy and the speed for the
reading can be increased. From the standpoint of the manufacturing, in the
case where any of the features (monolayer and lamination layer) of the
present invention is adopted, since the spin coating which is an extremely
efficient method can be used, the efficiency in manufacturing information
recording media is increased while its cost is decreased. Furthermore,
since the recording materials according to the present invention are
stable both thermally and chemically, the custody before and after the
recording is easy, and there is no possibility that errors of information
are made by the decolorization during the custody.
Obviously, many modifications and variations of the present invention are
possible in light of the above teachings. It is therefore to be understood
that within the scope of the appended claims, the invention may be
practiced other than as specifically described.
* * * * *
|
|
 |
|
 |
Description |
|
