Note: Descriptions are shown in the official language in which they were submitted.
2009291.
SPECIFICATION
TITLE OF THE INVENTION
Optical Recording Medium
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to an optical recording
medium on which recording is carried out by the irradiation
of light in near infrared region.
(ii) Description of the Prior Art
A heat-sensitive recording system is a direct recording
system which does not require any development and fixing,
and therefore it is excellent in operation and maintenace.
For this reason, the heat-sensitive recording system is
widely utilized in facsimiles, printers and the like.
In this system, however, the recording is thermally
made by bringing a thermal head or an exothermic IC pen into
direct contact with a heat-sensitive recording paper, and
hence melted colored substances adhere to the thermal head
or the exothermic IC pen, so that troubles such as dregs
adhesion and sticking take place, which brings about record
obstruction and impairs record quality inconveniently.
In particular, when a line is depicted continuously in
a recording direction as in the case of a plotter printer,
it is impossible to avoid the trouble of the dregs adhesion.
_ - 2 - 2009291.
Furthermore, when the recording is made by the thermal
head, it is difficult to more heighten an image resolution
of 8 dots/mm which is now employed.
Thus, as techniques by which troubles such as the dregs
adhesion and the sticking are solved and by which the
resolution is more improved, some non-contact recording
systems using light have been suggested.
Japanese Patent Laid-open Publication No. 209594/1983
discloses an optical recording medium prepared by laminating
at least one set of a near infrared absorbent layer having
an absorption wave length in a near infrared region of 0.8
to 2 ~m and a heat-sensitive color-developing material layer
onto a substrate, and Japanese Patent Laid-open Publication
No. 94494/1983 discloses a recording medium prepared by
superposing, on a base material, a layer containing one or
more kinds of heat-sensitive materials and a layer contain-
ing one or more kinds of near infrared absorbents comprising
compounds having a maximum absorption wave length in near
infrared rays of 0.7 to 3 ~m.
These publications disclose the procedure of laminating
or superposing the near infrared absorbent and the heat-
sensitive color-developing material on the substrate or the
base material. That is, the near infrared absorbent is
mixed with the heat-sensitive color-developing material and
the resulting mixture is then applied onto the substrate or
- _ 2009291.
the base material, or alternatively the heat-sensitive
color-developing material is first applied on the substrate
or the base material, and the near infrared absorbent is
then applied on the heat-sensitive color-developing material
layer.
In the above-mentioned publications, there are
disclosed dyestuffs such as cyanine dyestuffs, thiol nickel
complexes and squalilium as the near infrared absorbent.
In addition, as enumerated in "Near Infrared Absorption
Dyestuffs", Chemical Industry, Vol. 43, May 1986, other
dyestuffs are known which are, for example, nitroso
compounds and their metal complexes, polymethine dyestuffs
(cyanine dyestuffs), complexes of thiols and cobalt or
palladium, phthalocyanine dyestuffs, triallylmethane
dyestuffs, immonium dyestuffs, diimmonium dyestuffs and
naphthoquinone dyestuffs.
When these conventional near infrared absorbent and
heat-sensitive color-developing material are mixed and then
applied on the substrate as disclosed in the above-mentioned
publication, a desensitization phenomenon appears and a
color development performace deteriorates. Furthermore,
when the heat-sensitive color-developing material is first
applied on the substrate, and the near infrared absorbent is
then applied on this material layer, the deterioration in a
ground color occurs inconveniently. In addition, all the
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conventional near infrared absorbents have relatively strong
and wide absorption spectra in a visual region, and they are
also intensively colored. Therefore, it is difficult to
obtain the optical recording medium having a white ground
color, which obstructs putting the optical recording medium
into practice.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an
optical recording medium in which a ground color and a color
development performace are improved.
This object of the present invention can be achieved by
providing an optical recording medium which comprises a
substrate, a light-absorbing layer containing a near
infrared absorbent, and a heat-sensitive color-developing
layer, these layers being superposed upon the substrate, the
aforesaid near infrared absorbent being prepared by heating
a mixture of a thiourea derivative and a metallic compound.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a block diagram of an optical recording
device which is used when an optical recording medium of the
present invention is irradiated with a laser beam.
1: Laser diode collimator head
2: Shutter
3: Condenser
4: Optical recording paper
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-- 5 --
5: Power source
6: Paralleled laser beam
7: Condensed point
8: Operation distance
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to an optical
recording medium which comprises a substrate, a light-
absorbing layer containing a near infrared absorbent, and a
heat-sensitive color-developing layer containing a basic
colorless dye and an organic developer, these layers being
superposed upon the substrate, the aforesaid near infrared
absorbent being prepared by heating a mixture of a thiourea
derivative represented by the formulae (I)
R1 - NH
' C = S (I)
R2 - NR3
wherein each of R1, R2 and R3 is a monovalent
group selected from thè group consisting of
hydrogen, an alkyl group, an alkenyl group, a
cycloalkyl group, an aryl group, an aralkyl group
and a five-membered or six-membered heterocyclic
residue, a pair of R1 and R2 or a pair of R2 and
R3 may be linked together to form a ring, and each
group of R1, R2 and R3 may have one or more
substituents of an amino group, an alkyl group, an
- 6 - 2 O 0 9 Z 9l.
alkenyl group, an aryl group, an aralkyl group, a
nitro group, a halogen atom, a hydroxyl group, an
alkoxy group and an acyl group,
and a metallic compound represented by the formula (II)
(R-X)nM (II)
wherein R is hydrogen, an alkyl group, a cyclo-
alkyl group, an aryl group, an aralkyl group and a
heterocyclic residue, each group of R may have one
or more substituents, X is -COO, -SO4, -SO3, -PO4
or -O, n is an integer of 1 to 4, and M is a metal
having an atomic weight of 40 or more except
metals in the group IA and IIA of the periodic
table
or a metallic compound selected from the group of chloro-
phyll M, M chlorophyllin sodium and bisacetylacetonate M.
In particular, the light-absorbing layer containing the
near infrared absorbent prepared by heating a copper
compound and/or a lead compound and a thiourea derivative
may be used as an underlayer, and the heat-sensitive
color-developing layer containing the basic colorless dye
and the organic developer may be superposed upon the
above-mentioned layer, and in this case, a maximum effect
can be obtained.
Moreover, a transparent protective layer may be
disposed on the heat-sensitive color-developing layer, and a
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small amount of a conventional known near infrared absorbent
dye may be contained in the protective layer or the
underlayer, or on or under this layer, or alternatively a
synthetic resin pigment having a high near infrared
5 reflectivity is contained in the color-developing layer or
the light-absorbing layer. According to this constitution,
the more excellent optical recording medium can be obtained.
The feature of the present invention resides in that
the optical recording medium comprises the light-absorbing
10 layer containing the light absorbent and the heat-sensitive
color-developing layer, and the light absorbent is the near
infrared absorbent which can be prepared by heating the
mixture of the thiourea derivative and the metallic
`i compound.
This near infrared absorbent has relatively uniform and
strong absorption spectra all over the near infrared region
of 0.8 to 2.8 l~m, and has relatively weak absorption spectra
in a visible region. In addition, the near infrared
absorbent can convert the absorbed near infrared rays into
20 heat rapidly and effectively and then can release the heat.
Therefore, this absorbent is suitable for the present
invention.
The near infrared absorbent used in the present
invention can be prepared by the method disclosed in
Japanese Patent Application Nos. 145262/1988 and 232075/1988
- 8 - 2 0 0 9 2 9
filed by the same inventors as in the present application
and regarding the near infrared absorption material which
comprises the thiourea derivative and the copper compound or
lead compound. That is, the near infrared absorbent used in
the present invention can be prepared by mixing the thiourea
derivative and the metallic compound, and then heating the
resulting mixture. This preparation can be achieved by any
of the following processes: A process in which the thiourea
derivative is mixed with the metallic compound, and
immediately the resulting mixture is then heated; a process
in which both the materials are dispersed in a dispersant,
and the resulting dispersion is then heated; a process in
which each of the materials is separately dispersed in the
! dispersant, and the resulting dispersions are then mixed,
followed by heating; and a process in which the dispersant
is removed from the above-mentioned dispersion by drying or
the like, and heating is then carried out. In each of these
processes, the mixing and heating steps may be effected
simultaneously.
Other materials which do not impair the near infrared
absorbency of the absorbent, i.e., a binder, a dispersant, a
dispersing medium and the like may be added to the mixture
of the above-mentioned materials, if necessary.
In the heating treatment for generating the near
infrared absorbency, any means can be used, so long as it
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g
can supply a thermal energy by which the two components are
reacted to obtain a near infrared absorbing power. Examples
of such a means include an electric heater, induction
heating, melt molding of a film or the like, a thermal head,
a semiconductor laser and an infrared lamp. The heating
operation can be carried out under an optional atmosphere
such as the atmosphere or an inert atmospheric gas, but
usually under the atmosphere.
A heating temperature is usually in the range of 40 to
400C, preferably 50 to 350C. A heating time is usually in
the range of milliseconds to tens minutes. Furthermore, it
is preferred to add stirring, rotation or vibration so as to
increase the contact frequency of the materials, to uniform
the transmission of heat energy and to thereby accelerate
the reaction, and to uniform a mixing state.
In the present invention, a blend ratio of the thiourea
- derivative to the metallic compound depends upon kinds of
both materials themselves, but usually the amount of the
thiourea compound is 0.01 to 50 parts, preferably 0.1 to 10
parts with respect to 1 part of the metallic compound.
Typical examples of the thiourea derivative of the
formula (I) which is one of the constitutional components of
the near infrared absorbent used in the present invention
include 1,3-diphenylthoiurea, 1,3-dibenzylthiourea,
1,3-dilaurylthiourea, 1,3-diethylthiourea, 1,3-dimetha-
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chlorothiourea, 1-(2-thiazolyl)-3-phenylthiourea, 1-benzyl-
3-morpholinothiourea, and other compounds enumerated in
Japanese Patent Application No. 145262/1988.
Typical examples of the metallic compound which is the
other constitutional component of the near infrared
absorbent in the present invention include organic acid
salts, alkoxides and hydroxides of Y, Ti, Zr, V, Nb, Mn, Fe,
Co, Ni, Pd, Cu, Ag, Zn, Sn and Pb.
Examples of the organic acid include the following
compounds, but they are not limited.
Stearic acid, palmitic acid, oleic acid, behenic acid,
lauric acid, capric acid, caproic acid, valeric acid,
isobutyric acid, butyric acid, propionic acid, acetic acid,
formic acid, benzoic acid, orthotoluic acid, metatoluic
acid, paratoluic acid, paratertiary butylbenzoic acid,
orthochlorobenzoic acid, methachlorobenzoic acid, parachloro-
benzoic acid, dichlorobenzoic acid, trichlorobenzoic acid,
p-bromobenzoic acid, p-iodobenzoic acid, p-phenylbenzoic
acid, o-benzoylbezoic acid, p-nitrobenzoic acid, anthranyl
acid, p-aminobenzoic acid, oxalic acid, malonic acid,
succinic acid, glutaric acid, adipic acid, pimelic acid,
suberic acid, azelaic acid, sebacic acid, phthalic acid,
monoester phthalic acid, naphthenic acid, naphthalenecar-
boxylic acid, tartaric acid, diphenylamine-2-carboxylic
acid, 4-cyclohexylbutyric acid, diethyldithiocarbamic acid,
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gluconic acid, octylic acid, alkylbenzenesulfonic acid,
p-toluenesulfonic acid, naphthalinesulfonic acid, naphthylyl-
aminesulfonic acid, n-dodecylbenzenesulfonic acid, dodecyl-
sulfuric acid, 2,5-dimethylbenzenesulfonic acid, 2-carbo-
methoxy-5-methylbenzenesulfonic acid, ~-naphtylphosphoric
acid, stearylphosphoric acid, laurylphosphoric acid,
di-2-ethylhexylphosphoric acid and isodecylphophoric acid.
Examples of the alcohol include alcohols corresponding
to the above-mentoned organic acids.
Among others, the metallic compounds of V, Ni, Co, Fe,
Ag, Cu and Pb are preferable as the near infrared absorb-
ents, because they have uniform and intensive absorption
spectra all over the near infrared region. In particular,
the near infrared absorbent in which the copper compound or
lead compound is used is more preferable, because when such
a kind of absorbent is used, the light-absorbing layer
having a white ground color can be obtained.
The absorbency of the near infrared rays depends upon
kinds of the thiourea derivative and the metallic compound
and can be optionally regulated by adjusting a ratio of the
thiourea derivative to the metallic compound, the heating
temperature, the heating time and the like.
The thus obtained near infrared absorbent has weak
absorption spectra in the visible region, and therefore the
absorption spectra in the near infrared portion of 1 ~m or
2G09Zgl.
- - 12 _
less are weaker than in the other portions. This tendency
is noticeable, when a small amount of the near infrared
absorbent in the present invention is used. On the other
hand, most of the conventional known near infrared absorp-
tion dyestuffs have absorption peaks in the region of 1 ~m
or less. Accordingly, when the near infrared absorbent and
the known near infrared absorption dyestuff are used
together adjusting amounts of these absorbents, the
functionally balanced light-absorbing layer can be formed
which can absorb the near infrared rays uniformly in the
wide region.
The thus obtained near infrared absorbent is mixed with
and dispersed in the material constituting the light-
absorbing layer, and the light-absorbing layer containing
the absorbent is applied onto the substrate by means of
spray, coating or printing. Alternatively, the preparation
of the near infrared absorbent and the preparation of the
light-absorbing layer may be carried out simultaneously by
separately dispersing the thiourea compound or the metallic
compound with the material constituting the light-absorbing
layer to form slurries; mixing these sluries; applying the
mixture on the substrate by means of spray, coating or
printing; drying the applied material to remove a used
dispersing medium therefrom; and heating the same.
The material of the substrate is not limited at all,
2(~0!3291.
- 13 _
but papers, synthetic papers and plastic films are usually
used.
The material constituting the light-absorbing layer is
composed of auxiliaries such as a binder, a white pigment
and a near infrared absorption dyestuff.
The binder can be selected from conventional binders
for the heat-sensitive color-developing layer which will be
decribed.
The white pigment is effective to hide the color of the
near infrared absorbent and to whiten the whole optical
recording medium, and in addition, the pigment has functions
of scattering the incident near infrared rays so as to
increase the probability that the scattered near infrared
rays hit against the near infrared absorbent, and to thereby
heighten heat generation efficiency.
The white pigment works to reflect the visible rays
intensively on the average, and usually it reflects the near
infrared rays and visible rays similarly. Examples of the
usable white pigment include clay, calcium bicarbonate,
sedimentary calcium carbonate, titanium oxide, calcium
sulfate, barium sulfate, zinc sulfate, satin white, talc,
basic magnesium carbonate, zinc oxide, alumina, white
carbon, silica gel, colloidal silica and plastic pigments.
Preferable are white pigments having a porous state or a
large specific surface area, such as silica gel, colloidal
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silica, ultrafine alumina and plastic pigments.
In particular, the hollow plastic pigments are
preferable for the following reason: These hollow plastic
pigments are excellent in reflection properties of the near
infrared rays and insulating properties, and therefore they
can inhibit the diffusion of the heat generated from the
near infrared rays absorbed by the near infrared absorbent.
The near infrared absorption dyestuff which ensures the
effect of the near infrared absorbent used in the present
invention is relatively easily soluble in a solvent such as
water, an alcohol and toluene, and its solubility is
preferably 5% or more. Typical examples of such dyestuffs
include polymethine dyestuffs (cyanine dyestuffs), azulenium
dyestuffs, pyrylium dyestuffs and mercaptophenol dyestuffs
which are mentioned as soluble near infrared absorbents in
Japanese Patent Application No. 272702/1988 regarding an
optical recording medium using a solvent-insoluble dispers-
ible near infrared absorbent and filed by the same inventors
as in the present application.
This near infrared absorption dyestuff can be contained
in layers other than the heat-sensitive color-developing
layer of the optical recording medium, i.e., in the
light-absorbing layer and/or a protective layer or between
these layers.
The thus obtained light-absorbing layer is superposed
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- - 15 _
upon the heat-sensitive color-developing layer comprising a
basic colorless dye, an organic developer and a binder, and
if necessary, quality regulators such as a sensitizer and a
filler, thereby obtaining the optical recording medium.
The heat-sensitive color-developing layer is all the
same as a color-developing layer for a heat-sensitive
recording paper containing a known electron-donating
colorless dye and an electron-receiving organic developer by
way of color development components, and all the known
techniques regarding this color-developing layer for the
heat-sensitive recording paper can be applied hereto.
Examples of the basic colorless dye include a triphenyl-
methane leuco dye such as crystal violet lactone, a fluoran
leuco dye such as 3-diethylamino-6-methyl-7-anilinofluoran,
an azaphthalide leuco dye such as 3-(4-diethylamino-2-
ethoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4-azaphthalide
and a fluorhein leuco dye such as 3,6,6'-tris(dimethylamino)-
spiro[fluorhein-9,3'-phthalide].
Furthermore, examples of the organic developer include
bisphenol A's, 4-hydroxybenzoic acid esters, 4-hydroxy-
phthalic acid diesters, phthalic acid monoesters, bis-
(hydroxyphenyl) sulfides, 4-hydroxyphenylaryl sulfones,
4-hydroxyphenylarylsulfonates, 1,3-di[2-(hydroxyphenyl)-2-
propyl]-benzenes, 4-hydroxybenzoyloxybenzoic acid esters and
bisphenol sulfones.
ZC~09Z91.
- - 16 _
Examples of the binder include completely saponified
polyvinyl alcohol having a polymerization degree of 200 to
1900, a modified polyvinyl alcohol such as amide-modified
polyvinyl alcohol, hydroxyethyl cellulose and styrene-
butadiene copolymer.
Usually, fatty amide, montan wax and the like can be
used as sensitizers or quality regulators, and clay, calcium
carbonate, plastic pigments and the like which are generally
used in the paper coating field can also be used as fillers.
In particular, the hollow plastic pigments are preferable
because of excellent reflecting properties to the near
infrared rays and because of good heat retaining properties.
As these materials used in the heat-sensitive color-
developing layer, basic colorless dyes, organic developers,
binders, sensitizers, fillers and quality regulators
mentioned in Japanese Patent Application No. 272702/1988
filed by the same inventors as in the present case can also
be used in the present invention.
Kinds and amounts of the organic developer, the basic
colorless dye, the binder, the sensitizer, the filler and
other components in the color-developing layer used in the
present invention depend upon desired performace and
recording properties, and they are not particularly limited.
Usually, the suitable amount of the organic developer is
from 3 to 12 parts (weight parts of the solid~, that of the
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- 17 -
sensitizer is from 3 to 12 parts, that of the filler is 1 to
20 parts with respect to 1 part of the basic colorless dye,
and the suitable amount of the binder is from 10 to 25 parts
in the whole solids in the color-developing layer.
The organic developer, the basic colorless dye and the
sensitizer are ground separately or, if necessary and if
accepted, together with materials to be added, by means of a
mill such as a ball mill, an attritor, a sand grinder or a
suitable emulsifier until the particle diameter of each
component has been at a level of microns or less. After-
ward, the binder and, when desired, various quality
regulators are further added thereto in order to prepare a
coating solution.
The thus obtained coating solution is applied onto the
substrate or the optical recording layer, thereby preparing
the heat-sensitive color-developing layer.
When the heat-sensitive color-developing layer is
superposed upon the optical recording layer, the color of
the optical recording layer is further hidden, so that the
optical recording medium having a preferable appearance is
prepared.
It is a preferable way to dispose a protective layer on
the surface of the heat-sensitive color-developing layer so
as to diminish or inhibit the contamination by moisture,
gases, water, solvents, oily substances and the like.
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The protective layer must be permeable to the visible
rays and must not have a bad influence on the heat-sensitive
color-developing layer. Usually, the protective layer is
formed by coating with one or more selected from the binders
which are used in the heat-sensitive color-developing layer.
When the soluble near infrared absorbent is contained in the
protective layer or between the protective layer and the
heat-sensitive color-developing layer, the sensitivity of
the optical recording medium can be further heightened.
A light source necessary in an optical recording
operation must contain a wave length in the near infrared
region of 0.7 to 2.5 ~m, and examples of such a light source
include a semiconductor laser, a diode pumping YAG laser, a
Xe flashlamp, a quartz flashlamp and a halogen lamp, from
which preferable one can be selected in compliance with its
use purpose.
As discussed above, recording is performed by irradiat-
ing, with the near infrared rays, the optical recording
medium of the present invention which comprises the
substrate, the light-absorbing layer containing the near
infrared absorbent prepared by mixing and heating the
thiourea derivative and the metallic compound, the heat-
sensitive color-developing layer containing the basic
colorless dye and the organic developer, these layers being
superposed upon the substrate.
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The near infrared absorbent in the light-absorbing
layer absorbs the near infrared rays of any wave length
contained in the irradiation light and converts into heat
effectively. The generated heat rapidly transfers to the
heat-sensitive color-developing layer which lies on or under
the light-absorbing layer, and then causes a reaction
between the basic colorless dye and the organic developer in
the heat-sensitive color-developing layer. An image can be
recorded on the optical recording medium substantially
simultaneously with the irradiation of the light.
Since the near infrared absorbent has weak absorption
spectra in the visible region, the ground color of the
light-absorbing layer is good. In particular, when the
light-absorbing layer is disposed under the heat-sensitive
color-developing layer, the ground color is better, and in
addition, the near infrared absorbent is separated from the
heat-sensitive color-developing layer, so that any desensi-
tization does not occur in the color-developing layer.
Now, the present invention will be described in detail
in reference to examples, but the scope of the present
invention should not be limited to these examples. In the
examples, parts and percent are on weight.
Optical recording papers in the undermentioned examples
and comparative examples were evaluated in points of image
density and ground color. Measurements were carried out as
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follows, and the results are set forth in Table 1.
Density of developed color: An image density was
measured with a Macbeth densitometer by a light irradiation.
Ground color: A white paper portion was measured by
means of a Macbeth densitometer.
Examples 1 to 21
[Light-absorbing layer]
Each of a thiourea derivative and a metallic compound
shown in Table 1 was used in the form of the following
composition.
Solution A
Thiourea derivative 50 parts
10% Aqueous polyvinyl alcohol solution 25 parts
Water 125 parts
Total 200 parts
Solution B
Metallic compound 50 parts
10% Aqueous polyvinyl alcohol solution 25 parts
Water 125 parts
Total 200 parts
Each solution of the above-mentioned composition was
wet-ground by an attritor until the average particle
diameter of each component was about 3 ~m.
A filler was used in the form of the following
dispersion, i.e., solution C.
- 21 - 20~329~
Solution C: Filler-containing slurry
Silica 40 parts
Water 60 parts
Total 100 parts
Silica was dispersed in the solution C by a stirrer.
The solution A (thiourea derivative dispersion) was
mixed with the solution B (metallic compound dispersion) in
each blend ratio shown in Table 1, and the mixture was then
added to a filler-containing slurry prepared by adding 100
parts of a 10% aqueous polyvinyl alcohol solution to 250
parts of the solution C, the amount of the mixture being
described in the column of "amount of composition for near
infrared absorption" in Table 1, whereby a light-absorbing
layer coating solution was prepared.
A fine paper having a basis weight of 60 g/m2 was
coated with the thus prepared light-absorbing layer coating
solution by the use of a meyer bar so that a coating weight
might be 5 g/m2. After drying, a heat treatment was then
carried out at 150C to obtain a heat conversion under sheet
having the light-absorbing layer.
[Heat-sensitive color-developing layer]
Solution E (basic colorless dye dispersion)
Basic colorless dye shown in Table 1 2.0 parts
10% Aqueous polyvinyl alcohol solution 3.4 parts
Water 1.27 parts
20~9;~91.
- 22 -
Total 6.67 parts
In Table 1, ODB, S-205 and ODB-2 in the column of "Dye"
are indicative of the following compounds:
ODB: 3-Diethylamino-6-methyl-7-anilinofluoran
S-205: 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilino-
fluoran
ODB-2: Dibutylamino-6-methyl-7-anilinofluoran
Solution F (developer dispersion)
Developer shown in Table 1 6.0 parts
P-Benzylbiphenyl 4.0 parts
10% Aqueous polyvinyl alcohol solution 12.5 parts
Water 2.5 parts
Total 25.0 parts
In Table 1, BPA, BPS and POB in the column of "Devel-
oper" are indicative of the following compounds:
BPA: Bisphenol A
BPS: Bisphenol S
POB: p-Hydroxybenzoic acid benzyl ester
Solutions E and F having the above-mentioned composi-
tions were separately wet-ground for 1 hour by a sand
grinder for tests.
Next, 6.67 parts of the solution E (dye dispersion), 25
parts of the solution F (developer dispersion) and 11.76
parts of a 42.5% hollow pigment (trade name ROPAQUE OP-48J;
made by Rohm & Haas Co.) were mixed in order to prepare a
- 23 _ 200929~
heat-sensitive color-developing coating solution.
The light-absorbing heat conversion under sheet was
then coated with this coating solution by the use of a meyer
bar so that a coating weight might be 3.0 g/m2, followed by
drying, in order to obtain an optical recording paper.
(Protective layer)
10% Aqueous polyvinyl alcohol solution 100 parts
Glyoxal (40%) 5 parts
Total 105 parts
The above-mentioned optical recording paper was coated
with this protective layer coating solution by the use of a
meyer bar so that a coating weight might be 2 g/m2, followed
by drying, in order to obtain an optical recording paper
with the protective layer.
Comparative Examples 1, 7, 8 and 9
Each fine paper having a basis weight of 60 g/m2 was
coated with a filler-containing slurry prepared by mixing
250 parts of the solution C used in Examples 1 to 21 with
100 parts of a 10% aqueous polyvinyl alcohol solution by the
use of a meyer bar so that a coating weight might be 5 g/m2,
followed by drying. Next, a heat treatment was carried out
at 150C in order to obtain a filler-containing sheet
containing no near infrared absorbent. This sheet was then
coated with a coating material in which the dye and
developer in Table 1 were blended as in Examples 1 to 21, by
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the use of a meyer bar so that a coating weight might be
3.0 g/m2, followed by drying, in order to obtain recording
papers of Comparative Examples 1, 7, 8 and 9.
Comparative Examples 2, 3, 4, 5, 6 and 10
Solutions A and B were prepared from thiourea deriva-
tives or metallic compounds of Comparative Examples 2, 3, 4
and 5 in Table 1 in the same manner as in Example 1. Then,
20 parts of each of the solutions A and B was mixed with the
filler-containing slurry used in Comparative Example 1 in
order to form an undercoating solution. A fine paper having
a basis weight of 60 g/m2 was coated with this undercoating
solution by a meyer bar so that a coating weight might be
5 g/m2, followed by drying. A heat treatment was then
carried out at 150C in order to obtain under sheets
containing only one component of the near infrared absorbent
regarding Comparative Examples 2, 3, 4 and 5. Each sheet
was then coated with a coating material in which ODB and BPA
were blended as a dye and developer by the same procedure as
in Examples 1 to 21, by the use of a meyer bar so that a
coating weight might be 3.0 g/m2, followed by drying, in
order to obtain recording papers of Comparative Examples 2,
3, 4 and 5.
ODB and BPA were used as a dye and a developer in the
same manner as in Examples 1 to 21 in order to form a
heat-sensitive color-developing coating material. The thus
- 25 - 2~929~
prepared heat-sensitive color-developing coating material
was then mixed with 20 parts of 1,3-diphenylthiourea
dispersion formed by the same procedure as in the case of
the solution A in Examples 1 to 21. The filler-containing
sheet obtained in Comparative Example 1 was then coated with
the resulting mixture, followed by drying, whereby a
recording paper having the heat-sensitive color-developing
layer regarding Comparative Example 6 was obtained.
The heat-sensitive color-developing layer of this
recording paper regarding Comparative Example 1 was coated
with a coating material which had been prepared by mixing 20
parts of 1,3-diphenylthiourea dispersion formed in the same
manner as in the case of the solution A of Examples 1 to 21
with 105 parts of the protective layer coating solution used
in Examples 1 to 21, by the use of a meyer bar so that a
coating weight might be 2.0 g/m2, followed by drying, in
order to obtain a recording paper of Comparative Example 10.
The optical recording mediums thus obtained in Examples
1 to 12 and Comparative Examples 1 to 10 were then irradi-
ated with light from a strobo flash Auto 433D (made by SunPack Co., Ltd.) for cameras under conditions that an
emission window was stopped to 5% in order to perform
recording.
As is apparent from Table 1, in the comparative
examples regarding the optical recording mediums which do
-
2~9Z91.
- 26 -
not contain the near infrared absorbent used in the present
invention or which comprise the under layer containing
either of the thiourea compound or the metallic compound and
the heat-sensitive color-developing layer, any color is not
developed at all, when irradiated with the light. On the
contrary, with regard to the optical recording papers of the
examples in which the heat-sensitive color-developing layer
is superposed upon the light-absorbing layer containing the
near infrared absorbent of the present invention obtained by
mixing and then heating the thiourea derivative and the
metallic compound, a high image density and a white ground
color can be obtained, and therefore the optical recording
papers regarding the present invention are practical.
Furthermore, the optical recording medium in which the
protective layer is superposed upon the heat-sensitive
color-developing layer is substantially equal in the image
density and the ground color to the other medium in which no
protective layer is disposed. When the surface of the
optical recording medium having the protective layer was
rubbed with a wet finger of a man, it did not peel off,
which means that the optical recording medium of the present
invention is excellent in water resistance and wear
resistance.
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- 27 -
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Example 22
Optical recording was carried out by irradiating the
optical recording paper obtained in Example 1 with a laser
beam by the use of a device shown in Fig. 1 in which a
S semiconductor laser head (laser diode collimator head
LDC-8330-CINC; made by Applied Optic Co., Ltd., central wave
length 830 nm, output 30 nW) was used as a light source and
a condenser (MDPLAN 5 made by Olympus Optical Co., Ltd.,
0.1) was also used. An irradiation time was 1/500 second.
A colored spot was measured by the use of a densitometer
(PDM-5 made by Konishiroku Photo Industry Co., Ltd.), and
the measured value was converted into a Macbeth density,
whereby it was definite that the colored spot was an
extremely black color image having a Macbeth density of
1.35. On the contrary, when the optical recording papers of
Comparative Examples 1 to 10 were irradiated with the laser
beam under the same conditions, any image was not recorded
at all. Thus, the irradiation was further made for 10
minutes, but any color was not developed at all.
Example 23
Optical recording was carried out by irradiating the
optical recording paper obtained in Example 1 with a laser
beam for 1 second by the use of a device shown in Fig. 1 in
which an He-Ne laser head (Model 105-1 made by Spectra
Physics Co., Ltd., central weve length 632.8 nm, output
2~9;;~91.
- 32 -
5 mW) was used as a light source and a beam collimator (BC-5
made by Nippon Kagaku Engineering Co., Ltd.) was also used.
A colored spot was measured by the use of a densitometer
(PDM-5 made by Konishiroku Photo Industry Co., Ltd.), and
the measured value was converted into a Macbeth density,
whereby it was definite that the colored spot was a
completely colored image having a Macbeth density of 1.33.
On the contrary, when the optical recording papers of
Comparative Examples 1 to 10 were irradiated with the laser
beam under the same conditions, any image was not recorded
at all. Thus, the recording papers were further irradiated
for a long time of 10 minutes, but any color was not
developed at all.
As discussed above, on the optical recording medium of
the present invention, an image having a high resolution can
be directly obtained by the irradiation of near infrared
rays from a semiconductor laser or a strobo flash. When the
near infrared absobent of the present invention comprising a
less colored thiourea derivative and a metallic compound is
used, light sources such as a semiconductor laser having
optional near infrared wave lengths and a strobo flash
having continuous near infrared wave lengths can be utilized
effectively. In consequence, the near infrared absobent of
the present invention has led to a successful result in
putting a heat mode optical recording medium into practice.
