Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1996-03-07
2001-08-07
Reddick, Judy M. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S503000, C524S515000, C524S516000, C524S517000, C524S522000, C524S523000, C524S524000, C524S525000, C524S526000, C524S527000, C524S528000, C524S167000, C524S291000, C524S323000
Reexamination Certificate
active
06271300
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a thermoreversible binder composition having a high chemical stability to factors other than heat. The thermoreversibly thickening binder composition of the invention produces an excellent gloss and printability when used as a component of coating materials in manufacturing coated paper and exhibits a rapid color development speed and an excellent color deepness, when used in manufacturing heat-sensitive recording sheets or pressure-sensitive recording sheets.
BACKGROUND ART
Description of the Prior Art
Recently, Ito et al. have disclosed in JP A 1-14276 a thermoreversible acrylamide polymer thickener, for example, a temperature-sensitive gelling composition comprising poly(N-isopropyl acrylamide) and a resin emulsion. Kimura et al. disclose in JP A 4-261453 a temperature-sensitive gelling composition comprising a resin latex having a chemical stability index of not more than 24, a polyvalent metal salt and an adduct of an alkylene oxide of an alkylphenol-formalin condensate, which adduct is a non-thermoreversible thickener. However, while disclosing, as a resin latex having a specific chemical stability index, a latex obtained by polymerizing vinyl monomers by using a smaller amount of a surface active agent or a self-emulsified latex obtained by using a polymerizable emulsifying agent, they make no mention of the amount of the emulsifier in the aqueous phase of the latex. The term “chemical stability index” means an index showing the chemical stability of a latex as expressed by the time required for the latex to coagulate and solidify after an aqueous solution of aluminum sulfate has been added thereinto. The actual method of measuring the index will be explained in the Reference Example 1.
By the way, in order that polymer particles be stably dispersed in an aqueous phase of a latex, emulsifier molecules need only to be chemically or physically bound to the polymer particles and need not exist in the aqueous phase. In order to impart a temperature-sensitive property to a latex and further strengthen the property, it is rather desirable that emulsifiers do not exist in the aqueous phase. In many applications of the binder compositions where a temperature-sensitive gelling property is required, a various kind of auxiliary agents which are water-soluble or water-dispersible and also ionic are frequently compounded therewith, thus the stability of the latex to factors other than heat tends to be impaired. This leads to a tendency to use a polymerizable or non-polymerizable emulsifier, in preparing the latex, in an amount larger than required, leaving an excessive amount of the emulsifier remaining in the aqueous phase. Accordingly, in the prior arts mentioned above, chemical stability to the factors other than heat and improvements in gloss, printability and color development property in the practical application remain insufficient. Thus, the conventional temperature-sensitive gelling compositions are not good enough in exhibiting a temperature-sensitive gelling property, and, therefore, the use thereof in coating paper gave problems that {circle around (1)} no excellent gloss was obtained, because pigments such as clay and calcium carbonate in the color coating composition could not be satisfactorily orientated by calendaring and {circle around (2)} no satisfactory printability was obtained, because the resin concentration on the surface of the coated layer became much higher than it was required. There was also a problem that no satisfactory color development was obtained when the compositions were applied to pressure-sensitive recording sheet or heat-sensitive recording sheet uses.
DISCLOSURE OF THE INVENTION
It is an object of the invention to provide a thermoreversibly thickening binder composition which has an excellent chemical stability to factors other than heat and sharp temperature-sensitive gelation properties and is suitable for use as a component of coating materials for coated paper, etc. without causing migration of latex resin particles onto the surface of coated layer even when dried by heating.
As the result of our researches on binder compositions to be used for coated paper, etc. to attain the object, we have found that, by using a vinyl polymer exhibiting a reversible transition from hydrophilicity to hydrophobicity at a certain transition temperature in combination with a resin latex containing an emulsifier in the aqueous phase only in a smaller amount, migration of the latex resin particles onto the coated surface can be suppressed. We have further found that such an improvement is also effective, in applications to pressure-sensitive recording sheet or heat-sensitive recording sheet, to suppress the decrease in color development by binder migration.
Thus, according to the present invention, a thermoreversibly thickening binder composition is disclosed, comprising (A) a resin latex wherein the amount of emulsifier in the aqueous phase is not larger than 0.01 mmol/g resin, and (B) a vinyl polymer which exhibits a reversible transition from hydrophilicity to hydrophobicity at a certain transition temperature. In order to attain the object of the present invention, it is required that the amount of emulsifier in the aqueous phase of the resin latex (A) used in the binder composition is not larger than 0.01 mmol/g resin, preferably not larger than 0.002 mmol/g resin. When the amount of emulsifier in the aqueous phase exceeds 0.01 mmol/g, the function of the vinyl polymer (B) exhibiting a reversible transition from hydrophilicity to hydrophobicity at a certain transition temperature will be inhibited, and the resulting binder composition does not provide a product having a satisfactory gloss, printability and color development. In the present invention, the amount of emulsifier in the aqueous phase is the value expressed based on the weight of the resin in the resin latex (A), which can be determined by quantitative analysis, such as liquid chromatography, of the aqueous phase of the resin latex (A) wherefrom the resin has been removed. To remove the resin from the resin latex, there may be used various methods, for example, those by freezing and then melting the resin latex to coagulate the resin component into solid followed by removing the solid, those by centrifuging the resin latex followed by removing the settled and solidified resin component, and those by adding an acid or an alkali to the resin latex followed by removing the settled and solidified resin component.
BEST MODE OF CARRYING OUT THE INVENTION
The thermoreversibly thickening binder composition of the invention, the constituent materials and the methods of preparation and application thereof, will be explained in more detail by way of examples.
First, the resin latex (A) in which the amount of emulsifier in the aqueous phase is not larger than 0.01 mmol/g, one of the constituents of the thermoreversibly thickening binder composition of the invention, will be explained. The resin constituting the resin latex (A) is a (co)polymer of various kinds of monomers. Examples of the monomers, which are not particularly limited, are (meth)acrylic esters such as methyl (meth)acrylates, ethyl (meth)acrylates, butyl (meth)acrylates, cyclohexyl (meth)acrylates, lauryl (meth)acrylates, octadecyl (meth)acrylates, glycidyl (meth)acrylates, trimethoxysilylpropyl (meth)acrylates, hydroxyethyl (meth)acrylates, diethylene glycol mono(meth)acrylates, polyethylene glycol mono(meth)acrylates, (meth)acryloyloxypolyglycerols, 2-cyanoethyl (meth)acrylates, N,N-dimethylaminoethyl (meth)acrylates, N,N-dimethylaminopropyl (meth)acrylates, N,N-diethylaminoethyl (meth)acrylates and N,N-diethylaminopropyl (meth)acrylates; (meth)acrylamides such as N,N-dibutyl (meth)acrylamides, N-cyclohexyl (meth)acrylamides, (meth)acrylamides. N-methyl (meth)acrylamides, N-methylol (meth)acrylamides and N,N-dimethylaminoethyl (meth)acrylamides; vinyl cyanides such as (meth)acrylonitriles; styrenes such as styrene, 1-methylstyrene and p-aminostyrene; vinyl carboxylates such as vinyl acetat
Kanzawa Toshihiro
Ohsumi Tatsuya
Kubovcik & Kubovcik
Reddick Judy M.
Sanyo Chemical Industries Ltd.
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