 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a recording sheet and a method for producing the
sheet. In particular, this invention relates to an improvement in a
recording sheet in which a phenol resin is used as a developer.
2. Description of the Prior Art
Recording sheets have been known in the past in which the coupling reaction
of an electron donating colorless organic compound (hereinafter referred
to as a color former) and an electron accepting solid acid (hereinafter
referred to as a developer) is utilized, for example, the
pressure-sensitive copying papers as described, e.g., 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 2,972,547; the heat-sensitive copying papers as described,
e.g., in U.S. Pat. No. 2,939,009; and the recording materials as
described, e.g., in German OLS No. 1,939,624.
Clays (such as terra alba, activated clay and attapulgite), organic acids
(such as succinic acid, tannic acid, gallic acid, salicylic acid and
phenols) and acid polymers (such as phenolformaldehyde resins) are known
as a developer. In particular, phenol resins are somewhat different from
other developers, probably due to their polymeric property, and are
particularly advantageous from the standpoint of practical use. Numerous
references in the prior art with respect to phenol resins are known, for
example, as disclosed in U.S. Pat. Nos. 3,501,331, 3,669,711, 3,427,180,
3,445,721, 3,516,845, 3,634,121, 3,672,935 and 3,732,120.
According to the prior art, a phenol resin is dissolved in an organic
solvent and, if necessary, after dispersion into an aqueous solution to
prepare an aqueous dispersion, coated on a support. However, conventional
developer sheets thus obtained do not have sufficient developability and
tend to yellow. In addition, the light resistance of the developed color
images formed on these sheets is not sufficient from a practical
standpoint.
SUMMARY OF THE INVENTION
A first object of this invention is to provide a recording sheet having
improved developability.
A second object of this invention is to provide a recording sheet capable
of developing a color image having improved light resistance.
A third object of this invention is to provide a recording sheet which
hardly yellows.
These objects can be attained with a developer composition containing a
phenol resin and an aqueous emulsion of an oily material on a support.
Accordingly, this invention provides a recording sheet comprising a support
having thereon a developer layer containing a phenol resin and an aqueous
emulsion of an oily material. In another embodiment of this invention,
this invention provides a method for producing this recording sheet
comprising coating a composition containing a phenol resin admixed with an
aqueous emulsion of an oily material on a support.
DETAILED DESCRIPTION OF THE INVENTION
It is already known to improve the developability of a recording sheet by
adding an aqueous emulsion of an oily material which is liquid at ordinary
temperature (e.g., 20.degree.-30.degree.C) to clays as a developer (for
example, as disclosed in British Pat. No. 1,290,369). In this case, it is
believed that the emulsion renders the active sites of the clays
hydrophobic, that is, it increases the affinity of clays to a developer
solution, whereby the developability of the recording sheet would be
improved. This phenomenon has been variously studied in an effort to
attain the above-described objects of this invention. As a result thereof,
it was found that a phenol resin and a water dispersible emulsion of an
oily material have an extremely specific relation.
Accordingly, the objects of this invention are attained by admixing a
phenol resin coating composition and an aqueous emulsion of an oily
material.
Phenol resins are described in detail in the above patents. In addition, a
brief explanation of phenol resins is given below.
Phenol resins which can be used in this invention are phenol resins capable
of donating hydrogen ions as is generally known in this technical field.
Phenol-aldehyde polymers (the so-called novolak type phenol resins) and
phenol-acetylene polymers are typical examples. Suitably the phenol
formaldehyde molar ratio is usually about 1:1 and the degree of
condensation ranges from about 2 to 50, preferably 5 to 20.
Representative examples of these phenol resins 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, p-carboxyphenol-formaldehyde
polymer, p-carboalkoxyphenol-formaldehyde polymer,
p-aroylphenol-formaldehyde polymer, p-lower alkoxyphenol-formaldehyde
polymer, p-alkyl(C.sub.1 -C.sub.12)-phenol-formaldehyde polymers, in which
the p-alkyl(C.sub.1 -C.sub.12)-phenol is 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, etc., and polymers of formaldehyde and isomers of these
p-alkyl-phenols where the alkyl groups have 1 to 12 carbon atoms, and
copolymers of formaldehyde and mixtures containing two or more of these
alkylphenols and the isomers thereof. Where these p-substituted phenols
are further substituted at the m-position, the resulting p- and m-
substituted phenols behave analogously to the p-substituted phenols, and
therefore, the addition of m-substituent(s) to the p-substituted phenols
does not provide any important advantage.
In the present invention, phenols are dissolved in a solvent (for example,
toluene, xylene, petroleum distillation fractions, perchloroethylene,
etc.) and then, if desired, dispersed in water. That is, the phenol resin
coating composition of this invention can be a dispersion of phenol resin
fine particles which is generally used, and the production of the coating
composition need not be specifically described in detail herein.
For example, the phenol resin coating composition of this invention can be
prepared as follows. Pulverized fine particles of a phenol resin are
dispersed in water, or a phenol resin is milled in a ball mill in the
presence of gum arabic or the like, and dispersed in water, and, if
desired, a conventional developer such as terra alba or activated clay for
increasing the developability and/or an inorganic pigment for increasing
the adsorbability is added thereto, and, if desired, a binder is further
added thereto, to form a phenol resin coating composition. The binder can
be any conventional binder which is well-known in this technical field.
Illustrative examples of binders are latexes such as styrene-butadiene
copolymer latex and synthetic or natural high molecular weight substances
such as polyvinyl alcohol, maleic acid anhydride-styrene copolymers,
starch, casein, gum arabic, gelatin, carboxymethyl cellulose and methyl
cellulose. The amount of a binder used can vary somewhat depending upon
the kind of the binder used or the amount and kind of other additives
used, but the binder is generally used in an amount of 5 parts by weight
or more, preferably 10 to 50 parts by weight, per 100 parts by weight of
the solid content in the coating composition. The amount of the binder to
be added is determined by balancing the developability and the film
surface strength of the developer layer formed and therefore, the smaller
the amount of the binder the better as long as a sufficient film surface
strength is obtained.
According to conventional techniques, a solution or an aqueous dispersion
of a phenol resin (or a phenol resin coating composition) is coated on a
support. However, in the present invention, it is to be noted that the
phenol resin coating composition is admixed with an aqueous emulsion of an
oily material. The term oily material as used herein designates a
hydrophobic material, including vegetable oils, animal oils, mineral oils,
synthetic oils and hydrophobic organic solvents. The oily material can be
a solid, but it is especially preferably a liquid (at normal temperature
of about 20.degree.-30.degree.C) since solids must be heated when
preparing an emulsion. If solids are used, they can be liquefied by
heating to about 30.degree. to 100.degree.C before and during
emulsification. Representative examples are vegetable oils such as olive
oil, castor oil, cotton seed oil, soybean oil, lemon oil, corn oil, sesame
oil and rice oil; animal oils such as fish oil and whale oil; mineral oils
such as those obtainable from petroleum, for example, various kinds of
paraffins, kerosene and petroleum naphtha; synthetic oils such as
alkylated naphthalenes, alkylated diphenyls, alkylated diphenylmethanes,
octyl diphthalate, tricresyl phosphate, silicone oil and
fluorine-containing oils; organic solvents such as benzene, toluene,
xylene and chlorobenzene. Vegetable oils and animal oils themselves tend
to yellow, and with oily materials having a low boiling point such as
benzene, toluene and xylene, safeguards against explosion need to be
observed. Accordingly, aliphatic hydrocarbons, halogenated hydrocarbons
and silicone oil are preferred. However, halogenated hydrocarbons and
silicone oil cause coated mottles to occur on a coated paper, since they
are highly repellant to water. Liquid paraffin is the most preferred oily
material, satisfying all the above conditions.
The preparation of an aqueous emulsion using the above-described oily
material can be carried out using conventional emulsifying and dispersing
processes. For example, an oily material is emulsified using a stirring
device with a high shearing power such as homomixer or an ultrasonic
emulsifying apparatus. In this case, if desired, a conventional
emulsifying agent can be used. Examples of emulsifying agents are
synthetic surface active agents such as soap, sodium salts of higher
alcohol sulfates and alkylbenzene sodium sulfonates; and gelatin, albumin,
casein, gum arabic, tragacanth gum, alginates, carboxymethyl cellulose,
saponin and polyvinyl alcohol. The emulsifying agent used in the present
invention can be any agent which can provide a stable emulsion of the oily
material used, and the kind thereof is not specifically limited. A
suitable particle size for the emulsified oily material can range from
about 0.0001 .mu. to about 10 .mu., preferably 0.001 to 1 .mu.. The amount
of the oily material emulsion admixed with the phenol resin coating
composition is about 0.1 part by weight or more, preferably 1 to 10 parts
by weight, calculated in terms of the oily material, per 100 parts by
weight of the solid content in the phenol resin coating composition.
The production of the recording sheet in the present invention can be
carried out as follows. A phenol resin coating composition containing an
aqueous emulsion of an oily material is coated on a support such as paper,
synthetic paper or a film, in an amount of about 0.1 g/m.sup.2 or more,
preferably 0.3-2 g/m.sup.2, calculated in terms of the phenol resin used.
Where the support has a color former layer thereon, this may be dealt with
in an analogous manner. Further, a developer layer can be coated on a
support having a color former layer on the surface opposite to that to be
coated with the developer layer, or a color former layer can be coated on
the developer layer formed. The upper limit of the amount of the developer
layer composition to be coated is determined mainly by economic reasons,
and therefore, the effect of the present invention is still effective even
outside the above-described range.
Phenol resins naturally have a high affinity for the color former
composition, and thus, the effect of the oily material emulsion to the
phenol resin is different from the case of clays. More precisely, it is
believed that an oily material emulsion would affect the adsorptive
surface area of a phenol resin to a color former composition. As a result
thereof, not only is the developability of the phenol resin improved but
also the yellowing thereof is markedly reduced, and further, the light
resistance of the developed color image formed on the phenol resin
developer layer is improved. This means that the effects of this invention
cannot be attained when an aqueous emulsion of an oily material is added
to clays.
It is especially to be noted that if a phenol resin coating composition and
an aqueous emulsion of an oily material are separately coated or if an
oily substance is directly added to a phenol resin coating composition and
coated, the above-described effects of this invention can not be attained.
A characteristic element of recording sheet of this invention is the
provision of a specific developer layer, and the above-described other
conditions such as the kind and form of a color former to be used and the
kind of a solvent to be used can be those conventionally employed. One
skilled in the art can easily select optimum color formers, solvents and
the like.
Color formers or couplers which are suitable for the recording sheet of
this invention include eall substances which accept electrons or donate
protons, or those capable of being colored when reacted with a developer.
These couplers are, for example, diarylmethane compounds (as described in
U.S. Pat. Nos. 2,828,342, and 2.983,756, etc.), triarylmethane compounds
(as described in U.S. Pat. Nos. 2,474,084 and 3,032,041, etc.), fluoran
compounds (as described in U.S. Pat. Nos. 3,514,310, 3,514,311, 3,531,331,
3,624,107, 3,627,787 and 3,637,757, etc.), spiro-pyran compounds (as
described in British Pat. No. 810,401, U.S. Pat. No. 3,293,060, etc.) and
leucoazine compounds (as described in British Pat. No. 791,426 and U.S.
Pat. No. 2,915,415). Representative examples of thesee 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-dimethylaminophthalide,
3,3-bis-(9-ethyl-carbazol-3-yl)-5-dimethylaminophthalide,
3,3-bis-(2-phenylindol-3-yl)-5-dimethylaminophthalide,
3-p-dimethylaminophenyl-3-(1-methyl-pyrol-2-yl)-6-dimethylaminophthalide;
diphenylmethane compounds such as
4,4'-bis-dimethylaminobenzhydrinbenzylether, N-halophenyl-leuco-Auramine,
N-2,4,5-trichlorophenyl-leuco-Auramine; xanthene compounds such as
Rhodamine B-anilinolactam, Rhodamine B-p-nitroanilinolactam, Rhodamine
B-p-chloroanilinolactam, 7-dimethyl-amino-2-methoxyfluoran,
7-diethylamino-2-methoxyfluoran, 7-diethylamino-3-methoxyfluoran,
7-diethylamino-3-chlorofluoran, 7-diethylamino-3-chloro-2-methylfluoran,
7-diethylamino-2,2-dimethylfluoran,
7-diethylamino-3-acetylmethylaminofluoran,
7-diethylamino-3'-methylaminofluoran, 3,7-diethylaminofluoran,
7-diethylamino-3-dibenzylaminofluoran,
7-diethylamino-3-methyl-benzylaminofluoran,
7-diethylamino-3-chloroethylmethylaminofluoran,
7-diethylamino-3-diethylaminofluoran; thiazine compounds such as
benzoyl-leuco-methylene blue, p-nitrobenzyl-leuco-methylene 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-methoxybenzo)-spiro-pyran,
3-propyl-spiro-dibenzopyran, etc., and mixtures of these compounds.
The color former can be encapsulated or can be dispersed in a binder
solution and coated on a support. A suitable coating amount of the color
former can range from about 0.01 to 2 g/m.sup.2 of the support. The binder
and support can be the same binders and supports as described above.
Suitable solvents which can be used are natural or synthetic oils, either
alone or in combination. Examples of solvents are cotton seed oil,
kerosene, paraffins, naphthene oils, chlorinated biphenyl, chlorinated
terphenyl, alkylated biphenyls, alkylated terphenyls, chlorinated
paraffins and alkylated naphthalenes. The productions of the capsules can
be carried out, for example, using a method where a coacervation of a
hydrophilic colloid sol is utilized, as described in U.S. Pat. Nos.
2,800,457 and 2,800,458, or using an interfacial polymerization method as
described in British Pat. Nos. 867,797, 950,443, 989,264 and 1,091,076.
The recording sheet of this invention can be produced and used in
accordance with prior techniques with respect to other factors than those
specifically indicated above.
The recording sheet of this invention has an extremely excellent
developability over other conventional recording sheets produced using
phenol resins, and the light resistance of the developed color image
formed thereon is markedly improved. Moreover, the recording sheet of the
present invention yellows less when exposed to air or light.
This invention will be explained in greater detail in the following
Examples where all parts and percents are by weight unless otherwise
specifically indicated.
The effect of this invention was confirmed using a combination of an upper
sheet produced by coating microcapsules on a support, the microcapsules
being prepared using the process as described below, and a lower sheet
produced by coating a developer of this invention on a support.
The microcapsules containing a coupler can be prepared using various
conventional methods, and those used herein were prepared as follows,
according to U.S. Pat. No. 2,800,457.
10 parts of an acid-treated pigskin 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 thereto as an emulsifying agent, and 40 parts of a color former
oil were emulsified and dispersed therein. The color former oil used was
prepared by dissolving 2% Crystal Violet Lactone or
3-N,N-dibenzylamino-7-N,N-diethylaminofluoran in diisopropylnaphthalene.
When the size of the oil droplets became about 5 .mu., on the average, the
emulsification was stopped. Water at 40.degree.C was added to the
resulting emulsion to make 900 parts in total and then the entire amount
was continuously stirred.
Next, a 10% acetic acid aqueous solution was added thereto to adjust the pH
of the emulsion to 4.0-4.2 and to cause coacervation.
While further continuously stirring, the emulsion was cooled with ice water
after 20 minutes whereby the coacervate films deposited around the oil
droplets were gelled. After the temperature of the solution became
20.degree.C, 7 parts of a 37% formaldehyde aqueous solution were added to
the solution. When the temperature became 10.degree.C, a sodium hydroxide
aqueous solution was added to the solution to adjust the pH thereof to 9.
Afterwards, the solution was heated for 20 minutes, while stirring, to
increase the temperature thereof to 50.degree.C.
After the thus prepared microcapsule dispersion was adjusted to a
temperature of 30.degree.C, this dispersion was coated on paper of a
weight of 40 g/m.sup.2 in an amount of 5 g/m.sup.2 (calculated in terms of
the solid content coated) and dried to form a microcapsule coated sheet to
be used for the following examples.
EXAMPLE 1
In a solution of 50 parts of water, 1 part of sodiumm caseinate and 1 part
of a 20% potassium hydroxide aqueous solution were emulsified 50 parts of
an oily material as described in the following Table 1 using an ultrasonic
emulsifying apparatus, until the particle size of the emulsified material
became 0.1-0.5 .mu., to prepare an O/W emulsion.
Next, 170 parts of p-phenylphenol and 70 parts of a 37% formaldehyde
aqueous solution were reacted for 10 hours, while stirring under reflux,
in the presence of 10 parts of a 37% hydrochloric acid aqueous solution
and 50 parts of water. After being cooled, the resulting phenol resin was
removed in the form of a powder.
40 parts of the above-obtained phenol resin and 6 parts of naphthalene
sulfonic acid-formaldehyde condensation product were milled in a ball mill
together with 54 parts of water for 1 day. Next, 100 parts of the
resulting phenol resin dispersion, 160 parts of kaolin and as a binder 40
parts of a styrene-butadiene latex were placed in 500 parts of water and
fully stirred and admixed, and then 8 parts or 16 parts of the
above-prepared oily material emulsion dispersed in water were added
thereto and stirred to prepare a coating composition. The thus prepared
coating composition was coated on a base paper of a weight of 50 g/m.sup.2
with a coating rod in an amount of 5 g/m.sup.2 (calculated in terms of the
solid content coated) and then dried.
COMPARATIVE EXAMPLE 1
A coating composition was prepared in the same manner as in Example 1, with
the exception of the addition of the oily substance material dispersed in
water, and coated on a base paper of a weight of 50 g/m.sup.2 with a
coating rod in an amount of 5 g/m.sup.2 (calculated in terms of the solid
content coated) and dried.
COMPARATIVE EVALUATION 1
On the developer sheets of Example 1 and Comparative Example 1 was
superposed a microcapsule sheet containing Crystal Violet Lactone or
3-N,N-dibenzylamino-7-N,N-diethylaminofluoran, and the resulting sheets
were typed on with a typewriter and the respective developed color density
was compared with each other. In addition, the developed color image
formed on each sheet was allowed to stand in a room where a fluorescent
lamp was kept lighted for 2 weeks to compare the degradation of the color
density of each color image.
On the other hand, the developer surface of each developer sheet was
irradiated with an Atlas Fade Meter (mercury-vapor lamp 500W) for 30
minutes. The degree of yellowing of the developer surface was measured
with a Hunter Whiteness Meter. The results obtained are shown in the
following Table 1.
Table 1
__________________________________________________________________________
Sample
Oily Added
Whiteness
Crystal Violet Lactone
3-N,N-Dibenzylamino-7-N,
No. Material
Amount
after N-diethylaminofluoran
Irradiation
Developed
Density
Developed
Density
with Color after Color after
Atlas Density Fluorescent
Density
Fluorescent
Fade Meter
with Light with Light
Typewriter.sup.(1)
Exposure
Typewriter
Exposure
__________________________________________________________________________
1 Liquid 0 65.0 2 1 2 1
Paraffin
2 " 8 67.5 4 3 4 3
3 " 16 68.9 5 4 5 4
4 Fluori-
8 65.5 3 2 3 2
nated-
chlorinat-
ed Ethylene
5 " 16 66.2 4 3 4 3
6 Silicone
8 67.8 3 2 3 2
Oil
7 " 16 69.0 4 3 4 2
8 Xylene 8 65.2 4 3 4 2
9 " 16 65.5 4 3 4 3
__________________________________________________________________________
.sup.(1) Note:
The higher the number, the higher the developed color density
EXAMPLE 2
194 parts of p-tert-butylphenol and 65 parts of a 37% formaldehyde aqueous
solution were heated under reflux for 12 hours in the presence of 10 parts
of a 37% hydrochloric acid aqueous solution, 1 part of oxalic acid and 50
parts of water. After being cooled, a phenol resin powder was obtained.
100 parts of the above prepared phenol resin, 350 parts of activated clay
and 20 parts of gum arabic were dispersed in 1500 parts of water, and
after the pH of the resulting dispersion was adjusted to 9 with a 10%
sodium hydroxide aqueous solution, the dispersion was milled in a ball
mill for 1 day, and after the milling, 140 parts of a
styrene-butadiene-latex("Dow Latex 636") were added thereto and the
mixture was fully stirred and admixed.
To this were added 10 parts or 20 parts of a water dispersed emulsion of an
oily material as shown in the following Table 2 which was prepared in the
same manner as in Example 1 with the exception that sodium oleate was used
in place of sodium caseinate, and stirred to form a coating composition.
The thus prepared coating composition was coated on a base paper of a
weight of 50 g/m.sup.2 with a coating rod in an amount of 5 g/m.sup.2
(calculated in terms of the solid content coated), and dried.
COMPARATIVE EXAMPLE 2
A coating composition was prepared in the same manner as in Example 2, with
the exception of the addition of the oily material emulsion dispersed in
water, and was coated on a base paper of a weight of 50 g/m.sup.2 with a
coating rod in an amount of 5 g/m.sup.2 (calculated in terms of solid
content coated) and dried.
COMPARATIVE EVALUATION 2
The developer sheets produced in the above Example 2 and Comparative
Example 2 were tested in the same manner as in Comparative Evaluation 1,
and the results obtained are given in the following Table 2.
Table 2
__________________________________________________________________________
Sample
Oily Added
Whiteness
Crystal Violet Lactone
3-N,N-Dibenzylamino-7-
No. Material
Amount
after N,N-diethylaminofluoran
Irradiation
Developed
Density
Developed
Density
with Color after Color after
Atlas Density Fluorescent
Density
Fluorescent
Fade Meter
with Light with Light
Typewriter.sup.(1)
Exposure
Typewriter
Exposure
__________________________________________________________________________
10 Liquid 0 64.2 3 2 3 2
Paraffin
11 " 10 66.9 5 4 5 4
12 " 20 68.4 6 5 6 5
13 Fluorinated-
10 65.0 4 3 4 3
chlorinated
Ethylene
14 " 20 65.8 5 4 5 4
15 Silicone
10 67.2 4 3 3 3
Oil
16 " 20 68.5 5 4 4 4
17 Xylene 10 65.0 4 3 3 3
18 " 20 65.3 5 4 4 4
__________________________________________________________________________
.sup.(1) Note:
The higher the number, the higher the developed color density
From the above results, the following conclusions can be drawn. The
addition of an aqueous emulsion of an oily material to a developer coating
composition containing a phenol resin brings about a marked improvement in
the developability of a developer sheet when typed upon with a typewriter,
and further brings about a marked reduction of the disadvantageous
yellowing of a developer sheet containing a phenol resin, when irradiated
with light.
While the invention has been described in detail and with reference to
specific embodiments thereof, it will be apparent to one skilled in the
art that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
* * * * *
|
|
 |
|
 |
Description |
|
