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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a recording sheet, more precisely, to a
novel recording sheet having a color developer layer capable of reacting
with a color former to form a developed color image.
2. Description of the Prior Art
Recording sheets are, in general, well known where a developed color image
is formed by a so-called color forming reaction of a substantially
colorless electron donating organic compound capable of forming a color
(hereinafter referred to as a "color former") on contact with an electron
accepting solid acid (hereinafter referred to as a "color developer").
Examples of color developers are clay substances such as terra alba,
activated clay, attapulgite, zeolite, bentonite and kaolin; organic acids
such as succinic acid, tannic acid, gallic acid, alkyl substituted phenols
and bisphenol A; metal salts of aromatic carboxylic acids such as zinc
salts and aluminum salts of alkyl substituted salicylic acids; and acid
polymers such as p-phenylphenol/formaldehyde resins. The term "color
former" as used hereinafter means an electron donating or proton (for
example, from an acid) accepting material capable of forming a color
image, and the term "color developer" as used hereinafter means an
electron accepting or proton donating material.
Recording sheets where these phenomena are specifically used include
pressure-sensitive copying papers (for example, as disclosed in U.S. Pat.
Nos. 2,505,470, 2,505,489, 2,550,471, 2,548,366, 2,712,507, 2,730,456,
2,730,457 and 3,418,250) and heat-sensitive recording papers (for example,
as disclosed in Japanese Patent Publication No. 4160/68 and U.S. Pat. No.
2,939,009). Heat-sensitive recording papers are obtained by coating a
color former and a color developer on a support together with a heat
fusible substance such as acetanilide. A heat fusible substance means a
substance capable of melting on heating to dissolve a color former. Color
developers having a low melting point themselves may be used without a
heat fusible substance.
Another printing method is known where an ink containing a color former is
supplied to a color developer coated sheet through a medium such as
stencil to obtain a developed color image (for example, as disclosed in
German Patent Application (OLS) No. 1,939,624).
The recording using above-described phenomena requires a physical stimulus
such as application of a pressure with a ball-point pen or a typewriter or
heating with a heating element or an electric current, etc.
The most typical embodiment of a recording sheet is a pressure-sensitive
copying paper, which is prepared by dissolving a color former in a solvent
such as an alkylated naphthalene, alkylated diphenylmethane, alkylated
diphenyl, terphenyl or chlorinated paraffin, dispersing the resulting
solution in a binder or encapsulating the resulting solution in
microcapsules, and then coating such on a support such as paper, a plastic
sheet or a resin coated paper. On the other hand, where a color developer
is dissolved in a solvent such as an organic solvent, the color developer
solution in situ penetrates into a support, or after being dissolved or
dispersed in a medium together with a binder, this is coated on a support.
In general, color former and color developer are coated on the same
surface or opposite surfaces of a support or on different supports.
Some problems which occur with these conventional color developer coated
sheets need to be improved. More precisely, where clay substances such as
activated clay are used as a color developer, the developed color image
(for example, Crystal Violet formed from crystal violet lactone as a color
former) fades away on contact with polar solvents such as water or
glycols, which is a disadvantage.
In addition, where phenol resins such as p-phenylphenolformaldehyde resin
are used as a color developer, a yellowing of the surface to be developed
easily occurs due to the effects of light, which is also a defect.
Moreover, aldehydes such as formaldehyde are used in the synthesis of
phenol resins and the use of highly toxic formaldehyde results in various
difficulties occurring during the synthesis steps and is not preferred.
Where phenol compounds such as alkyl substituted phenols and bisphenol A
are used as a color developer, these compounds tend to sublime or diffuse
in a support with the lapse of time, and as a result, the color
developability gradually decreases, which is a disadvantage. In addition,
the use of alkyl substituted phenols and bisphenol A is not preferred
because the initial color developability is low. These defects greatly
affect the product value and it is desired to improve these problems.
It was previously found that dimers of compounds of the following formula
(I) (hereinafter referred to as alkenyl phenols) were effective as a color
developer for recording sheets:
##STR2##
wherein R.sub.1, R.sub.2 and R.sub.3 each represents a hydrogen atom, an
alkyl group, an aryl group or an aralkyl group, and n is an integer of 1
to 4. The use of the above-described alkenyl phenol dimers results in a
substantial improvement in various properties of the color developer.
However, the color developability of the coated layer and the film surface
strength are still not sufficient, and improvements must further be made.
SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to provide recording sheets
having improved color developability and film surface strength.
Another object of this invention is to improve the coating properties of
coating solutions in the preparation of recording sheets having improved
color developability and film surface strength.
It has now been found that the incorporation of an oil adsorptive inorganic
pigment in a color developer layer of a recording sheet containing a dimer
of an alkenyl phenol of the above formula (I) satisfies the above objects.
Accordingly, this invention provides a recording sheet comprising a support
having thereon a layer of a color developer capable of forming a developed
color image in the presence of a color former wherein the layer of the
color developer contains (1) a dimer of a compound of the formula (I):
##STR3##
wherein R.sub.1, R.sub.2 and R.sub.3, which may be the same or different,
each represents a hydrogen atom, an alkyl group, an aryl group or an
aralkyl group, and n is an integer of 1 to 4, as a color developer; and
(2) an oil adsorptive inorganic pigment.
DETAILED DESCRIPTION OF THE INVENTION
In the above formula (I), R.sub.1, R.sub.2 and R.sub.3 each represents a
hydrogen atom, an alkyl group (preferably C.sub.1 to C.sub.18, more
preferably C.sub.1 to C.sub.12), an aryl group or an aralkyl group
(wherein the alkyl moiety is preferably C.sub.1 to C.sub.18, more
preferably C.sub.1 to C.sub.12), and n is an integer of 1 to 4, and the
hydroxyl group may be in the m- or p-position to the
##STR4##
moiety and is most preferably in the p-position.
Compounds of the above formula (I) can be synthesized, for example, in
accordance with the following reaction schematic:
##STR5##
The pyrolysis can be carried out as follows: The starting compound of the
formula (II) is subjected to a pyrolysis at a temperature of about
80.degree. C. to about 150.degree. C., preferably 110.degree. C. to
140.degree. C., in the presence of a basic catalyst such as an oxide,
hydroxide, alcoholate or phenolate of an alkali metal (e.g., Na, Ka, Li,
etc.) or alkaline earth metal (e.g., Mg, Ca, etc.) and in the absence of
water to obtain the compound of the formula (I). Suitable examples of
these materials include oxides such as magnesium oxide and calcium oxide,
hydroxides such as magnesium hydroxide and calcium hydroxide, alcoholates
such as sodium ethoxide, sodium methoxide, potassium ethoxide, potassium
methoxide, lithium ethoxide, and lithium methoxide, and phenolates such as
sodium phenolates, potassium phenolates and lithium phenolates. The
dimerization can be carried out by heating at least one compound of the
formula (I) at about 15.degree. to about 130.degree. C. These procedures
are described in detail in Japanese Patent Application (OPI) No. 30852/75
and British Pat. No. 903,062.
In the synthesis as described above, the dimer of the alkenyl phenol of the
formula (I) above is predominantly formed, however, some amount of trimer
or higher oligomers are also formed and some amount of monomer, i.e.,
alkenyl phenol per se, remains. The color developer can be a dimer of the
alkenyl phenol or a composition containing such along with unreacted
monomer and trimer or higher oligomers and such is suitable as a color
developer for use in this invention if the amount of dimer present is
about 70 to 90% by weight, the amount of monomer is about 15% by weight or
less, (i.e., about 0 to 15% by weight) and the amount of trimer or higher
oligomers is about 25% weight or less generally ranging from about 5 to
about 25% by weight.
As described above, alkenyl phenol dimers as used in the present invention
can be synthesized more safely and easily than phenol resins.
Examples of alkenyl phenols of the formula (I) which can be used to form
the dimers used in this invention include p-isopropenyl-phenol,
2-(p-hydroxyphenyl)-2-butene, 2-(p-hydroxyphenyl)-2-pentene,
.alpha.-(p-hydroxyphenyl)styrene, 1-(p-hydroxyphenyl)-1-isobutene,
p-cyclohexenylphenol, 2-(p-hydroxyphenyl)-3-methyl-2-butene,
2-(p-hydroxyphenyl)-2-hexene, 2-(p-hydroxyphenyl)-2-hexadecene,
m-methyl-p-isopropenyl-phenol, 2-(o-isopropyl-p-hydroxyphenyl)-2-butene,
2-(o-phenyl-p-hydroxyphenyl)-2-pentene,
2-(o-tert-butyl-p-hydroxyphenyl)-2-pentene, m-isopropenylphenol and
1-(p-hydroxyphenyl)-1-propylene.
Oil adsorptive inorganic pigments, e.g., those capable of adsorbing an oil
as used in the present invention include clay minerals such as kaolin,
talc, bentonite, terra alba, activated clay, agalmatolite, mica and
zeolite; and metal oxides such as zinc oxide, titanium oxide and alumina;
and silicates other than clay substances such as silicic acid anhydride,
aluminum silicate and zinc silicate. Of these inorganic pigments, clay
minerals are more effective in the present invention since they have a
higher oil adsorptivity, and in particular, kaolin, talc, agalmatolite and
activated clay are most effective.
The particle size of the oil adsorptive inorganic pigments to be used in
the present invention preferably can be that of pigments having an average
particle diameter of about 40.mu. or less, particularly 1 to 20.mu., more
particularly 2 to 10.mu., are preferable. In this preferred range, the
evenness of the color developer coated surface is excellent and recording
sheets having a high product value can be obtained.
The amount of oil adsorptive inorganic pigment to be used is preferably
about 10 to 100,000 parts by weight, particularly 50 to 10,000 parts by
weight, more particularly 100 to 5,000 parts by weight, per 100 parts by
weight of alkenyl phenol dimer.
The essential elements of the recording sheets of the present invention are
a support and a color developer layer which is coated on the support and
which contains at least one alkenyl phenol dimer and at least one oil
adsorptive inorganic pigment, and therefore, any and all techniques known
in this field can be adopted and used in the present invention. More
precisely, the color developer of the present invention can be provided on
the same surface on which a color former is provided or on opposite
surfaces of a support, or the color developer and the color former can be
provided on different supports. In addition, the color developer of this
invention can be stored in the form of an ink and can be coated or printed
on a support when needed.
It is particularly preferred, because of the effects obtained, to
incorporate a phenol resin (novolak type) and/or a metal salt of an
aromatic carboxylic acid in a color developer layer of this invention,
which is specifically illustrated in the Examples which follow.
Any conventional proton donating phenol resin can be used, and, for
example, phenol-aldehyde polymers (so-called novolak type) and
phenol-acetylene polymers can be used.
Examples of these phenol polymers are as follows:
p-phenylphenol-formaldehyde polymer, p-fluorophenol-formaldehyde polymer,
p-chlorophenol-formaldehyde polymer, p-bromophenol-formaldehyde polymer,
p-iodophenol-formaldehyde polymer, p-nitrophenol-formaldehyde polymer,
p-carboxyphenol-formaldehyde polymer, o-carboxyphenol-formaldehyde
polymer, p-carboalkoxyphenol-formaldehyde polymer,
p-aroylphenol-formaldehyde polymer, p-lower alkoxyphenol-formaldehyde
polymer; copolymers of p-alkyl(C.sub.1 to C.sub.12)phenols (such as
p-methylphenol, p-ethylphenol, p-n-propylphenol, p-isopropylphenol,
p-n-amylphenol, p-isoamylphenol, p-cyclohexylphenol,
p-1,1-dimethyl-n-propylphenol, p-n-hexylphenol, p-isohexylphenol,
p-1,1-dimethyl-n-butylphenol, p-1,2-dimethyl-n-butylphenol,
p-n-heptylphenol, p-isoheptylphenol, p-5,5-dimethyl-n-amylphenol,
p-1,1-dimethyl-n-amylphenol, p-n-octylphenol,
p-1,1,3,3-tetramethylbutylphenol, p-isooctylphenol, p-n-nonylphenol,
p-isononylphenol, p-1,1,3,3-tetramethylamylphenol, p-n-decylphenol,
p-isodecylphenol, p-n-undecylphenol, p-isoundecylphenol,
p-n-dodecylphenol) with formaldehyde; copolymers of isomers of these
p-alkyl(C.sub.1 to C.sub.12)phenols with formaldehyde; and copolymers of
mixtures containing two or more of these alkyl phenols and isomers thereof
with formaldehyde. A suitable polymerization degree is about 2 to about
20, preferably 3 to 10. These p-substituted phenols can be additionally
substituted with a substituent in the meta position, and such m- and
p-substituted phenols behave in a similar way to the above-described
p-substituted phenols. In any event, m-substituents are not very
significant. Where phenol resins are used in the present invention, the
amount of the phenol resin to be added is about 0.001 to about 30 parts by
weight, preferably 0.05 to 2 parts by weight, to 1 part by weight of an
alkenyl phenol dimer.
Examples of metal salts of aromatic carboxylic acids include copper, lead,
magnesium, calcium, zinc, aluminum, tin and nickel salts of aromatic
carboxylic acids. Typical examples of aromatic carboxylic acids are
benzoic acid, chloro-benzoic acid (o-, m-, p-), nitro-benzoic acid (o-,
m-, p-), toluic acid (o-, m-, p-), 4-methyl-3-nitro-benzoic acid,
2-chloro-4-nitro-benzoic acid, 2,3-dichloro-benzoic acid,
2,4-dichloro-benzoic acid, p-isopropyl-benzoic acid, 2,5-dinitro-benzoic
acid, p-tert-butyl-benzoic acid, N-phenyl-anthranilic acid,
4-methyl-3-nitro-benzoic acid, salicylic acid, m-hydroxy-benzoic acid,
p-hydroxy-benzoic acid, 3,5-dinitro-salicylic acid, 5-tert-butyl-salicylic
acid, 3-phenyl-salicylic acid, 3-methyl-5-tert-butyl-salicylic acid,
3,5-di-tert-butyl-salicylic acid, 3,5-di-tert-amyl-salicylic acid,
3-cyclohexyl-salicylic acid, 5-cyclohexyl-salicylic acid,
3-methyl-5-isoamyl-salicylic acid, 5-isoamyl-salicylic acid,
3,5-di-sec-butyl-salicylic acid, 5-nonyl-salicylic acid,
2-hydroxy-3-methyl-benzoic acid, 2-hydroxy-5-tert-butyl-benzoic acid,
2,4-cresotinic acid, 5,5-methylene-disaicylic acid, acetoamino-benzoic
acid (o-, m-, p-), 2,4-dihydroxy-benzoic acid, 2,5-dihydroxy-benzoic acid,
anacardic acid, 1-naphthoic acid, 2-naphthoic acid, 1-hydroxy-2-naphthoic
acid, 2-hydroxy-3-naphthoic acid, 2-hydroxy-1-naphthoic acid,
3-phenyl-5-(.alpha.,.alpha.-dimethylbenzyl)salicylic acid,
3,5-di(.alpha.-methylbenzyl)salicylic acid, thiosalicylic acid and
2-carboxybenzaldehyde.
Where metal salts of aromatic carboxylic acids are used in the present
invention, the amount of the metal salt to be added is about 0.01 to about
30 parts by weight, preferably 0.05 to 2 parts by weight, to 1 part by
weight of the alkenyl phenol dimer. Preferred metal salts of aromatic
carboxylic acids are those having a hydroxy group in the ortho position.
The alkenyl phenol dimers as used in this invention can also be used with
basic compounds in order to achieve a further advantageous result.
Examples of suitable basic compounds are alkali metal compounds such as
sodium hydroxide and potassium hydroxide, and alkaline earth metal
compounds such as magnesium hydroxide, magnesium oxide, magnesium
carbonate, calcium hydroxide and calcium carbonate. Of these basic
compounds, sodium, potassium and magnesium compounds, particularly
magnesium compounds, are more effective. In particular, magnesium oxide is
the most effective. The amount of the basic compound to be added is
preferably about 1 to about 5,000 parts by weight, particularly 2 to 1,000
parts by weight, more particularly 5 to 500 parts by weight, to 100 parts
by weight of the alkenyl phenol dimer.
It has also been found that certain types of metal salts function in the
color developer layer of this invention in a manner similar to that of the
aromatic carboxylic acid salts described above and addition thereof to the
color developer layer results in an increase in the light resistance of
the developed color image. Examples of these metal salts are copper,
aluminum, manganese, nickel, zinc, cobalt and iron salts, for instance,
inorganic acid salts such as the sulfates, hydrochlorides, nitrates and
phosphates and organic acid salts such as the acetates and oxalates. The
amount of these metal salts to be added is about 0.1 part by weight or
more, preferably 0.5 to 100 parts by weight, to 100 parts by weight of the
alkenyl phenol dimer.
The color developer sheets of this invention can be prepared by coating a
dimer of a compound of the above-described formula (I) (this may contain
monomer and trimer or higher oligomers as described previously) and an oil
adsorptive inorganic pigment and, if desired, a phenol resin, a metal salt
of an aromatic carboxylic acid and/or a basic compound, on a support, if
desired, together with a binder, with the coating components being
dissolved or dispersed in an organic solvent before coating. An
appropriate amount of additives which are generally used in this field,
for example, an anti-foaming agent such as silicone oil and octyl alcohol
can be used in the preparation of color developer sheets of this invention
without decreasing the effect of this invention, generally up to about 10%
by weight based on the weight of the color developer layer composition.
Examples of organic solvents which can be used for dissolving the
components of color developer layer of this invention include alcohols
such as methanol, ethanol and butanol; esters such as ethyl acetate, butyl
acetate, ethyl lactate, n-butyl lactate, ethyl hydroxyacetate,
n-butyl-.beta.-oxypropionate, isobutyl-.beta.-oxypropionate,
n-propyl-.beta.-oxypropionate, methyl-.alpha.-hydroxy-isobutyrate, and
ethyl-.alpha.-hydroxy-n-butyrate; ketones such as acetone, methyl ethyl
ketone and methyl isobutyl ketone; and hydrocarbons such as benzene,
toluene and xylene.
Binders which can be used in this invention include methyl
polymethacrylate, polyacrylates, polyvinyl acetate, vinyl acetate-vinyl
chloride copolymers, polyvinyl butyral, polystyrene, linear saturated
polyester resins, ethyl cellulose, cellulose acetate and nitrocellulose.
The thus prepared color developer solution or dispersion is coated on a
support such as paper, a plastic sheet such as polyethylene terephthalate
or a resin coated sheet such as polyethylene coated paper.
On the other hand, the color developer components of this invention can be
processed in an aqueous system as follows: An alkenyl phenol dimer and, if
desired, a phenol resin and/or a metal salt of an aromatic carboxylic acid
are pulverized to fine powders and dispersed in water or dissolved in an
organic solvent which is not compatible with water selected from the
above-described organic solvents (such as ethyl acetate or benzene) and
then emulsified in water, or an aromatic carboxylic acid and an alkenyl
phenol dimer are dissolved in an alkali metal hydroxide aqueous solution
and then a metal compound such as a copper, aluminum, zinc, tin or nickel
compound is added thereto and reacted. In this aqueous system, the joint
use of a water dispersed emulsion of an oily substance brings about an
improvement of developability and developing speed of the resultant
recording sheet. The oily substance which is used is a hydrophobic
substance which is liquid at normal temperature (e.g., about
20.degree.-30.degree. C.) including vegetable oils, animal oils, mineral
oils, synthetic oils and hydrophobic organic solvents. Examples of these
oily substances are vegetable oils such as olive oil, castor oil, cotton
seed oil, soybean oil, lemon oil, corn oil, sesame oil and rice bran oil;
animal oils such as fish oil and whale oil; mineral oils obtained mainly
from petroleum such as paraffins, kerosene and petroleum naphtha;
synthetic oils such as alkylated naphthalenes, alkylated diphenyls,
alkylated diphenylmethanes, octyl diphthalate, silicone oil, fluorine oil
and octyl p-hydroxybenzoate; and hydrocarbons and chlorinated derivatives
thereof such as benzene, toluene, xylene and chlorobenzene. Paraffins and
synthetic oils are preferred.
A water-soluble natural high molecular weight compound such as a protein
(e.g., gelatin, albumin and casein, etc.), a cellulose (e.g.,
carboxymethyl cellulose and hydroxyethyl cellulose, etc.) or a saccharose
(e.g., agar, sodium alginate, carboxymethyl starch and gum arabic, etc.);
a water-soluble synthetic high molecular weight compound such as polyvinyl
alcohol, polyvinyl pyrrolidone, polyacrylic acid or polyacrylamide, etc.;
or a latex such as an acrylate copolymer latex, a vinyl acetate latex or a
styrene-butadiene copolymer latex is added to the thus prepared color
developer aqueous dispersion as a binder. The amount of the
above-described binder to be used is preferably about 1 to about 50 parts
by weight, more preferably 5 to 40 parts by weight, most preferably 10 to
30 parts by weight, to 100 parts by weight of the solid components (color
developer and inorganic pigment). If the amount of the binder used is too
small, sufficient film surface strength cannot be obtained, and if the
amount of the binder is too large, the developability decreases and the
manufacturing cost is high.
In the preparation of a coating solution containing an alkenyl phenol
dimer, if the viscosity of the coating solution increases too much or
flocculation of the alkenyl phenol dimer occurs to form agglomerates and,
as a result, the developability and the film surface strength of the color
developer layer ultimately formed are not sufficient, it is desirable to
add a surface active agent to the color developer coating solution.
Examples of suitable surface active agents which can be used in this
invention are anionic surface active agents such as Turkey red oil, alkyl
sulfoacetate salts, higher alcohol sulfate salts, alkylbenzene sulfonate
salts, alkylsulfonate salts, soaps, alkylaryl sulfonic acid salts, dialkyl
sulfosuccinic acid salts, alkyl naphthalene sulfonic acid salts, higher
alcohol phosphate salts, naphthalene sulfonic acid salt-formaldehyde
condensation products, polyoxyethylene-alkyl sulfonic acid salts, dialkyl
sulfuric acid salts, sulfated olefin salts and sulfated fatty acid ester
salts; cationic surface active agents such as tertiary amines and
ethanolamine ester salts; nonionic surface active agents such as glycerin
mono-fatty acid esters and saccharide fatty acid esters; and mixtures of
these compounds. Anionic surface active agents are especially effective,
and in particular, alkylenbenzene sulfonic acid salts, higher alcohol
sulfate salts, naphthalene sulfonic acid salt-formaldehyde condensation
products and alkylnaphthalene sulfonic acid salts are preferred. The
actual chemical structures of the above-described surface active agents
are not generally well-known, but these are easily commercially available.
A suitable amount of the surface active agent to be used is about 0.5 part
by weight or more preferably 1 to 20 parts by weight, to 100 parts by
weight of the alkenyl phenol dimer.
The thus prepared coating solution can be coated on a support as follows:
Where an organic solvent is used as a medium, a printing coating method
such as a flexographic printing or gravure printing method is suitable. In
an aqueous system coating solution where water is used as a medium, and
and all conventional methods which are well known in this field can be
used including air-knife coating, roll coating, blade coating or
size-press coating. The amount of the coating solution to be coated on a
support is about 0.1 to about 10 g/m.sup.2 (on a solids basis), preferably
0.2 to 8 g/m.sup.2, more preferably 0.3 to 7 g/m.sup.2. If the coating
amount is lower than about 0.1 g/m.sup.2, the developability is not
sufficient, and the upper limit is determined mainly by economic reasons
rather than the properties of the products obtained.
The color formers which react with color developers used in the recording
sheets of this invention are not specifically limited. Suitable examples
of color formers are described in U.S. Pat. Nos. 2,548,365, 2,548,366,
3,293,060, 3,551,181, 3,506,471, 3,514,530, 3,501,331, 3,631,064,
3,097,540, 3,681,392, 3,663,571, etc. Specific examples of suitable color
formers are triarylmethane compounds such as
3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (or Crystal Violet
Lactone), 3,3-bis(p-dimethylaminophenyl)phthalide,
3-(p-dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide,
3-(p-dimethylaminophenyl)-3-(2-methylindol-3-yl)phthalide,
3-(p-dimethylaminophenyl)-3-(2-phenylindol-3-yl)phthalide,
3,3-bis(1,2-dimethylindol-3-yl)-5-dimethylaminophthalide,
3,3-bis(1,2-dimethylindol-3-yl)-6-dimethyaminophthalide,
3,3-bis(9-ethylcarbazol-3-yl)-5-dimethylaminophthalide,
3,3-bis(2-phenylindol-3-yl)-5-dimethylaminophthalide and
3-p-dimethylaminophenyl-3-(1-methylpyrrol-2-yl)-6-dimethylaminophthalide;
diphenylmethane compounds such as 4,4'-bis-dimethylaminobenzhydrin
benzylether, N-halophenylleucoauramine and
N-2,4,5-trichlorophenyl-leucoauramine; xanthene compounds such as
Rhodamine B-anilinolactam, Rhodamine B-p-nitroanilinolactam, Rhodamine
B-p-chloroanilinolactam, 3-dimethylamino-7-methoxyfluoran,
3-diethylamino-7-methoxyfluoran, 3-diethylamino-6-methoxyfluoran,
3-diethylamino-7-chlorofluoran, 3-diethylamino-7-chloro-6-methylfluoran,
3-diethylamino-6,8-dimethylfluoran,
3-diethylamino-7-acetylmethylaminofluoran,
3-diethylamino-7-methylaminofluoran, 3,7-diethylaminofluoran,
3-diethylamino-7-dibenzylaminofluoran,
3-diethylamino-7-methylbenzylaminofluoran,
3-diethylamino-7-phenylamino-6-methylfluoran,
3-diethylamino-7-chloroethylmethylaminofluoran and
3-diethylamino-7-dichloroethylaminofluoran; thiazine compounds such as
benzoyl leucomethylene blue and p-nitrobenzyl leucomethylene blue; spiro
compounds such as 3-methyl-spiro-dinaphthopyran,
3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran,
3-benzyl-spiro-dinaphthopyran,
3-methyl-naphtho-(3-methoxy-benzo)-spiro-pyran and
3-propyl-spiro-dibenzopyran; and mixtures of these compounds.
The color former is dissolved in a solvent and encapsulated or dispersed in
a binder solution and coated on a support. Suitable color former solvents
are natural or synthetic oils which can be used individually or as
combinations. Examples of specific solvents which can be used in this
invention are cotton seed oil, kerosene, paraffins, naphthalene oils,
alkylated biphenyls, alkylated terphenyls, chlorinated paraffins and
alkylated naphthalenes. The encapsulation can be carried out according to
conventional methods such as a method utilizing coacervation of a
hydrophilic colloid sol as described, for example, in U.S. Pat. Nos.
2,800,457 and 2,800,458, or an interfacial polymerization method as
described, for example, in British Pat. Nos. 867,797, 950,443, 989,264 and
1,091,076. A suitable concentration of the color former in the solvent can
range from about 0.1 to about 50% by weight and a suitable coating amount
for the microcapsules is about 0.5 to about 20 g/m.sup.2.
The effect of recording sheets of this invention was demonstrated using the
following color former sheet.
Color former containing microcapsules were prepared in a conventional
method, for example, as described in U.S. Pat. No. 2,800,457, according to
the procedures described below. All parts, percents ratios and the like
are by weight, unless otherwise indicated.
10 parts of acid treated pig skin gelatin and 10 parts of gum arabic were
dissolved in 400 parts of water at 40.degree. C., 0.2 part of Turkey red
oil was added as an emulsifier, and 40 parts of color developer oil were
emulsified and dispersed. The color developer oil was prepared by
dissolving 2% of Crystal Violet Lactone in diisopropyl naphthalene.
When the size of the oil droplets reached 5.mu. on the average, the
emulsification was stopped, and water at 40.degree. C. was added to make
the total volume 900 parts and the total amount was continuously stirred.
While stirring, the temperature of the liquid was not allowed to decrease
below 40.degree. C. Next, 10% acetic acid was added to adjust the pH of
the liquid to 4.0 to 4.2 whereby coacervation occurred.
The stirring was further continued, and after 20 minutes, the entire system
was cooled with ice water to gel the coacervate film deposited around the
oil droplets.
When the temperature of the liquid was 20.degree. C., 7 parts of a 37%
formaldehyde aqueous solution was added. At 10.degree. C., a 15% sodium
hydroxide aqueous solution was tested to make the pH 9. Afterwards, the
liquid was heated for 20 minutes with stirring, to increase the
temperature thereof to 50.degree. C. After the thus prepared microcapsule
dispersion was cooled to 30.degree. C., the dispersion was coated on paper
(weighing 40 g/m.sup.2) in an amount of 6 g/m.sup.2 (coated solids) and
dried. In this way, a microcapsule sheet containing Crystal Violet Lactone
as a color former was obtained.
The following Examples are given to illustrate the invention in greater
detail but the invention is not to be construed as being limited to these
Examples.
EXAMPLE 1
10 parts of p-isopropenyl phenol dimer synthesized using the method
described in Japanese patent Application (OPI) No. 30852/75 and 3 parts of
ethyl cellulose were dissolved in 50 parts of ethanol and 20 parts of
kaolin were dispersed in the resulting solution. Then, this dispersion was
coated on a paper (weighing 50 g/m.sup.2) with a coating rod and dried,
the amount of coated solids being 5 g/m.sup.2, to obtain a coated paper
according to this invention.
COMPARATIVE EXAMPLE 1
Another coated paper for comparison was prepared in a similar manner to
Example 1, except that kaolin was not used, 1 part of ethyl cellulose was
used and the coated amount was 2 g/m.sup.2.
EXAMPLE 2
40 Parts of 2-(p-hydroxyphenyl)-2-butene dimer obtained in a manner similar
to Example 1 and 6 parts of naphthalene sulfonic acid-formaldehyde
condensation product were milled in a ball-mill for one day together with
54 parts of water. Next, 100 parts of the resulting dimer dispersion and
160 parts of kaolin and, as a binder, 80 parts of a styrene-butadiene
copolymer latex (solids content 50%) were mixed with 500 parts of water
and well stirred and admixed to obtain a coating solution for use in this
invention. This was coated on a paper (weighing 50 g/m.sup.2) with a
coating rod and dried, the amount of coated solids being 6 g/m.sup.2.
COMPARATIVE EXAMPLE 2
Another coated paper for comparison was prepared in a manner similar to
Example 2, except that kaolin was not used, 16 parts of a
styrene-butadiene copolymer latex were used and the coated amount was 2
g/m.sup.2.
EXAMPLE 3
40 Parts of p-isopropenyl phenol dimer as described in Example 1, 5 parts
of sodium caseinate and 1 part of Turkey red oil were milled in a
ball-mill for one day together with 54 parts of water. Next, 100 parts of
the thus prepared dimer dispersion, 160 parts of kaolin and 10 parts of
magnesium oxide and, as a binder, 80 parts of a styrene-butadiene
copolymer latex were mixed with 500 parts of water and well stirred and
admixed to obtain a coating solution for use in this invention. This was
coated on a paper (weighing 50 g/m.sup.2) with a coating rod and dried,
the amount of coated solids being 6 g/m.sup.2.
COMPARATIVE EXAMPLE 3
To 100 parts of p-isopropenyl phenol dimer dispersion obtained as in
Example 3, 16 parts of a styrene-butadiene copolymer latex and 50 parts of
water were added and well stirred and admixed to obtain another coating
solution for comparison. This was coated on a paper (weighing 50
g/m.sup.2) with a coating rod and dried, the amount of coated solids being
2 g/m.sup.2.
EXAMPLE 4
2 g of sodium hydroxide was dissolved in 500 parts of water and 200 parts
of terra alba and 50 parts of kaolin were added and well stirred, and then
10 parts of magnesium oxide, 100 parts of p-isopropenyl phenol dimer
dispersion obtained as in Example 3 and 100 parts of a styrene-butadiene
copolymer latex were added to obtain a coating solution for use in this
invention. This solution was coated on a paper (weighing 50 g/m.sup.2)
with a coating rod and dried, the amount of coated solids being 6
g/m.sup.2.
EXAMPLE 5
To 100 parts of p-isopropenyl phenol dimer dispersion obtained as in
Example 3, 5 parts of magnesium oxide and, as a binder, 20 parts of a
styrene-butadiene copolymer latex and 50 parts of water were added and
well stirred and admixed to obtain a coating solution for use in this
invention. This solution was coated on a paper (weighing 50 g/m.sup.2)
with a coating rod and dried, the amount of coated solids being 2
g/m.sup.2.
COMPARATIVE TESTING
The Crystal Violet Lactone containing capsule coated sheet produced as
described above was placed on each coated paper prepared in the above
Examples and Comparative Examples, and pressed using a pressure of 600
kg/cm.sup.2 for coloration. After one day, the developed color density was
measured with a spectrophotometer. This is the fresh density. Next, the
developed color image was exposed to sunlight for one hour, and
afterwards, the density thereof was measured with a spectrophotometer. The
wavelength for the measurement was 610 m.mu..
The results obtained are shown in the Table 1 below.
TABLE 1
______________________________________
Density after
One Hour
Example No. Fresh Density
Sunlight Exposure
______________________________________
Example 1 0.72 0.65
Comparative Example 1
0.58 0.44
Example 2 0.78 0.69
Comparative Example 2
0.61 0.43
Example 3 0.85 0.79
Comparative Example 3
0.63 0.47
Example 4 0.92 0.87
Example 5 0.76 0.69
______________________________________
The above results show that excellent color developer sheets can be
obtained according to the present invention.
EXAMPLE 6
10 Parts of the color developer shown in the Table 2 below and 3 parts of
ethyl cellulose were dissolved in 50 parts of ethanol, and 20 parts of
kaolin were dispersed in the resulting solution. The thus prepared coating
solution was coated on a paper of high quality (weighing 50 g/m.sup.2)
with a coating rod and dried, the amount of coated solids being 5
g/m.sup.2, to obtain a color developer sheet of this invention.
EXAMPLE 7
40 Parts of a color developer shown in the Table 2 below and 6 parts of a
naphthalene sulfonic acid-formaldehyde condensation product were milled in
ball-mill for one day together with 54 parts of water. Next, 100 parts of
the thus prepared dimer dispersion and 160 parts of kaolin and, as a
binder, 80 parts of a styrene-butadiene copolymer latex (solids content
50%) were mixed with 500 parts of water and well stirred and admixed to
obtain a coating solution for use in this invention. This was coated on a
paper (weighing 50 g/m.sup.2) with a coating rod and dried, the amount of
coated solids being 6 g/m.sup.2, to obtain a color developer sheet of this
invention.
EXAMPLE 4A AND COMPARATIVE EXAMPLE 5
Color developer sheets were prepared in a manner similar to Example 6,
except that different compounds shown in Table 2 below were used.
COMPARATIVE EXAMPLES 6 AND 7
Comparative color developer sheets were prepared in a manner similar to
Example 7, except that different compounds shown in Table 2 below were
used.
The physical data for the color developer sheets prepared in the above
Examples and Comparative Examples are shown in Table 2 below.
TESTING METHOD
The properties of color developer sheets prepared in the above Examples and
Comparative Examples were tested as follows:
Developability
Each color developer sheet was placed on the Crystal Violet Lactone
containing capsule sheet prepared as described above and pressed at a
pressure of 600 kg/cm.sup.2 for coloration. After the paper was left for
one day in a dark place, the density at 610 m.mu. was measured with a
Toshiba Beckman DB-type Spectrophotometer.
Light Resistance
After the developed color image obtained as described above was exposed to
ultraviolet light for one hour with an Atlas Fade-O-Meter, the density of
the image was measured and the light resistance was calculated according
to the following formula:
##EQU1##
Moisture Resistance
After each recording sheet was left in an atmosphere of relative humidity
(RH) = 90% and temperature = 50.degree. C. for 24 hours, the sheet was
treated in the same way as described above to obtain a developed color
image and the density of the image was measured in a similar manner. The
moisture resistance is calculated according to the following formula:
##EQU2##
TABLE 2
__________________________________________________________________________
Developed
Light Moisture
Color Resistance
Resistance
Example No.
Color Developer Density
(%) (%)
__________________________________________________________________________
Example 6
6:4 Mixture of 2-(p-hydroxyphenyl)-2-pentene
0.80 82.9 81.2
dimer and p-phenylphenol-formaldehyde
polymer (polymerization degree: about 3)
Example 7
5:4 Mixture of 2-(o-isopropyl-p-hydroxy-
0.81 80.1 82.6
phenyl)-2-butene dimer and p-chlorophenol-
formaldehyde polymer (polymerization degree:
about 4)
Example 4A
2-(p-Hydroxyphenyl)-2-pentene dimer
0.71 65.2 60.9
Comparative | | |
