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
1998-06-09
2001-04-24
Le, Hoa Van (Department: 1752)
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...
C524S459000, C524S167000, C526S330000, C526S331000, C525S056000, C525S057000, C525S058000, C525S060000
Reexamination Certificate
active
06221952
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aqueous emulsion composition, an adhesive, and a method for thickening an aqueous emulsion.
2. Discussion of the Background
An aqueous emulsion having as the dispersant, a polyvinyl alcohol polymer (hereinafter referred to as PVA polymer) has extremely high mechanical stability, chemical stability and miscibility with pigment, as the PVA polymer acts as protective colloid. In addition, films formed from these aqueous emulsions are extremely stiff. Aqueous emulsions have many applications in various fields of coating compositions, adhesives, fiber processing agents, paper processing agents, etc.
An aqueous emulsion having a PVA polymer as the dispersant is characterized by so-called shear thinning (hereinafter referred to as thixotropy), which generally indicates the decrease in the apparent viscosity of a fluid with the increase in the shear rate. In practical uses of such aqueous emulsions, shear-thinning is often preferred.
Recently, it is desirable to speed up production of products e.g., wood bonded products, paper bonded products, fiber products, etc. made from an aqueous emulsion having a PVA polymer as the dispersant. This is typically accomplished, for example, by accelerating the speed of roll rotation in the line. In this situation, the conventional, shear-thinning aqueous emulsion has problems because it is difficult to control the amount of emulsion applied to the rolls and, after it has been applied, the emulsion scatters around the rolls.
To solve these problems, an aqueous emulsion is often processed into a Newtonian one wherein the apparent viscosity does not depend on the shear rate, or into a shear-thickening one wherein the apparent viscosity increases with an increase in shear rate (the latter may be hereinafter referred to as dilatant fluid).
To convert a thixotropic, aqueous emulsion having a PVA polymer as the dispersant into a Newtonian one, for example, the emulsion polymerization method for producing the emulsion may be improved by controlling the amount of the initiator and the dispersant, or the PVA polymer may be defined with respect to the degree of hydrolysis and molecular weight.
Where such a Newtonian, aqueous emulsion is desired to be further converted into a dilatant one, it is generally difficult to convert the viscosity or fluidity of the emulsion by merely improving the emulsion polymerization method or specifically defining the PVA polymer to be used as the dispersant in the manner as above while the dispersion stability of the aqueous emulsion is still kept stable. For this, therefore, to convert the thixotropic emulsion into a dilatant one, it may be possible to employ a method of adding to an aqueous emulsion having a thixotropic PVA polymer as the dispersant, a gelling agent for the PVA polymer in the step of post-processing the emulsion. However, this method has problems because the gelling agent is not safe and would unfavorably color the emulsion. In addition, the use of the emulsion produced would be limited.
Japanese Patent Application Laid-Open (JP-A) No. Hei-6-211911 discloses an aqueous copolymer emulsion for processing paper, which is obtained by emulsion polymerization using a naphthalenesulfonate-formaldehyde condensate and a polyoxyethylene alkylphenyl ether sulfate, and is characterized by its high-speed coatability. The laid-open patent application discloses that PVA may be optionally added to the emulsion, but is silent regarding the meaning of the combination of PVA and the naphthalenesulfonate-formaldehyde condensate, the compositional ratio of the two in the emulsion, and the amount of PVA being larger than that of the condensate in the emulsion.
SUMMARY OF THE INVENTION
Accordingly, the first object of the present invention is to provide an aqueous emulsion composition which is free from the problems noted above and in which the apparent viscosity relative to the shear rate is prevented from being lowered or is increased.
The second object of the invention is to provide an adhesive that contains the aqueous emulsion composition, which has excellent initial adhesiveness.
The third object of the invention is to provide a method for thickening an aqueous emulsion.
The first embodiment of the invention relates to an aqueous emulsion composition, including: a dispersoid, containing a (co)polymer polymerized from at least one monomer unit selected from the group consisting of ethylenic unsaturated monomers, dienic monomers, and mixtures thereof; a dispersant, containing: (A) a polyvinyl alcohol (co)polymer, and (B) a condensate of an alkali metal salt of an aromatic sulfonic acid with formaldehyde; wherein a weight ratio of the solid content of (A)/(B) is 100/0.05 to 100/100.
The second embodiment of the invention relates to an adhesive, including the aqueous emulsion composition described above.
The third embodiment of the invention relates to a method for thickening an aqueous emulsion, including: adding to an aqueous emulsion a condensate (B) of an alkali metal salt of an aromatic sulfonic acid with formaldehyde.
The fourth embodiment of the invention relates to a method of preparing the above-described aqueous emulsion composition, including: in the presence of a dispersant containing (A) a polyvinyl alcohol, preparing a (co)polymer dispersoid by emulsion (co)polymerizing at least one monomer unit selected from the group consisting of ethylenic unsaturated monomers, dienic monomers, and mixtures thereof; and adding (B) a condensate of an alkali metal salt of an aromatic sulfonic acid with formaldehyde; wherein a weight ratio of the solid content of (A)/(B) is 100/0.05 to 100/100.
DESCRIPTION OF PREFERRED EMBODIMENTS
Other features of the invention will become apparent in the course of the following description of preferred embodiments, which are not intended to be limiting.
The aqueous emulsion composition of the invention comprises, a dispersed (co)polymer (hereinafter dispersoid) that comprises at least one monomer unit selected from ethylenic unsaturated monomers and dienic monomers.
The ethylenic unsaturated monomers and dienic monomers for the dispersoid are not particularly limiting. As preferred examples of ethylenic unsaturated monomers for use in the invention, mentioned are olefins such as ethylene, propylene, isobutylene, etc.; halogenated olefins such as vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride, etc.; vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl versatate, etc.; acrylic acid, methacrylic acid; acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, 2-hydroxyethyl acrylate, etc.; methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, 2-hydroxyethyl methacrylate, etc.; dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate and their quaternary derivatives; acrylamide-type monomers such as acrylamide, methacrylamide, N-methylolacrylamide, N,N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid and its sodium salt, etc.; styrenic monomers such as styrene, &agr;-methylstyrene, p-styrenesulfonic acid and its sodium and potassium salts, etc.; N-vinylpyrrolidone, etc. Preferred examples of dienic monomers for use in the invention include butadiene, isoprene, chloroprene, etc. Those monomers may be used either singly or combined. Preferred examples of (co)polymers comprising at least one of those monomers for use in the invention are vinyl ester-based (co)polymers such as ethylene-vinyl acetate copolymer and polyvinyl acetate, as well as (meth)acrylate-based (co)polymers, styrene-diene-based copolymers, etc.
The aqueous emulsion composition of the invention comprises a PVA polymer as the dispersant.
The types of PVA polymer suitable for the dispersant are not particularly limiting. Preferably, the PVA polymer is prepared by polymerizing a vinyl ester monomer such as vinyl acetate followed by hydrolyzing the resulting polymer
Kuraray Co. Ltd.
Le Hoa Van
Lee Sin J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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