Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-09-08
2003-01-28
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S375000, C524S504000, C524S925000, C524S926000, C524S575500
Reexamination Certificate
active
06512034
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cationic graft-modified natural rubber latex. More particularly, it relates to a cationic graft-modified natural rubber latex which contains a cationic surfactant and a specific nonionic surfactant and is also superior in adhesion to papers and fibers.
Heretofore, a natural rubber latex whose cohesive force is enhanced by modifying a graft has been used in applications such as adhesive. For example, Japanese Published Unexamined Patent (Kokai Tokkyo Koho Hei) No. 10-259360 discloses a primer composition comprising a methyl methacrylate graft copolymer containing a natural rubber as a main polymer, an ultraviolet absorber and an antioxidant, and describes that the primer composition itself is used for forming a primer layer of an applying structure made of polyvinyl chloride. This prior art aims at preventing an adhesive force from lowering by forming a primer layer thereby to prevent ultraviolet light, which has passed through a base material, from reaching an adhesive layer and suppressing oxidative deterioration of these layers.
With regard to a cationic latex, in page 94 of “Natural Rubber Science and Technology” (edited by A. D. Roberts, published by Oxford University Publication, 1988), it is described that a cationic natural rubber latex obtained by adding a cationic surfactant to a natural rubber latex is superior in adhesion to fibers. That is, a latex comprising positively charged particles is obtained by adding a sufficient amount of a cationic surfactant to a natural rubber latex diluted to about 30%. The cationic latex has such a feature that the adhesion to fibers is improved because the fibers are negatively charged when treated in water.
A conventional cationic rubber latex has the features described above, but has various problems in view of practicality. For example, the cationic latex described above has limited applications because of low concentration of the rubber, and its applicability to printing is not sufficient. Furthermore, a conventional cationic graft-modified natural rubber latex is inferior in workability on coating papers or fibers because of high increase in viscosity with a lapse of time and large thixotropy.
SUMMARY OF THE INVENTION
Under these circumstances, the present inventors have intensively studied about cationic modification of a graft-modified natural rubber latex and found that the viscosity of the latex is lowered by cationically modifying a graft-modified natural rubber latex in the presence of a nonionic surfactant (non-ionic surfactant) and also the resulting cationic graft-modified natural rubber latex is stable with a lapse of time. The present inventors have further studied based on this knowledge, thus completing the present invention.
The present invention provides:
1) A cationic graft-modified natural rubber latex comprising a graft-modified natural rubber latex, a cationic surfactant, and one or more nonionic surfactants selected from the group consisting of polyoxyalkylene alkyl phenyl ether, polyoxyalkylene monostyryl phenyl ether, polyoxyalkylene distyryl phenyl ether and polyoxyalkylene tristyryl phenyl ether;
2) The cationic graft-modified natural rubber latex according to the term 1), wherein the cationic surfactant is a quaternary ammonium salt;
3) The cationic graft-modified natural rubber latex according to the term 1), wherein HLB of the nonionic surfactant is within a range from 14 to 19;
4) The cationic graft-modified natural rubber latex according to the term 1), which contains 0.5 to 20% by weight of the cationic surfactant and 0.2 to 5.0% by weight of the nonionic surfactant based on the graft-modified natural rubber component; and
5) The cationic graft-modified natural rubber latex according to the term 1), wherein a protein in the natural rubber latex is subjected to a decomposition treatment.
The cationic graft-modified natural rubber latex of the present invention can be employed as an adhesive in various applications because of low density and stability. The cationic deproteinized natural rubber latex is particularly superior in adhesion to fibers and papers and therefore suited for use as an adhesive for them.
MODE FOR CARRYING OUT THE INVENTION
The cationic graft-modified natural rubber latex of the present invention is obtained by cationically modifying the graft-modified natural rubber latex using the cationic surfactant in the presence of the specific nonionic surfactant described above.
As the graft-modified natural rubber latex as the raw material, for example, those prepared by a conventional method can be used. That is, a radical polymerizable monomer is added to the natural rubber latex, and then the rubber is graft-polymerized in the latex by adding a radical initiator or irradiating with light such as ultraviolet light or radiation such as &ggr;-ray.
The radical polymerizable monomer includes, but is not limited to, acrylic monomer such as methyl methacrylate, methyl acrylate, butyl methacrylate, butyl acrylate, or 2-ethylhexyl acrulate; or styrene monomer. For applications such as adhesive, methyl methacrylate, methyl acrylate or styrene monomer which has a high effect of enhancing a cohesive force is preferable.
The radical initiator includes, for example, redox initiator of hydroperoxide and polyamine, or persulfate. Among these radical initiators, the redox initiator of hydroperoxide and polyamine is preferable because it has a high graft efficiency and is not influenced by ammonia. The radical polymerizable monomer to be grafted is added in the amount within a range from about 10 to 50% by weight based on the rubber component.
The cationic graft-modified natural rubber latex can be obtained by adding the cationic surfactant to the graft-modified natural rubber latex thereby to cationically charge rubber particles. In the present invention, the total solid content in the graft-modified natural rubber latex is preferably within a range from 35 to 60% by weight.
The cationic surfactant is derived from a higher amine, but a quaternary ammonium salt or an alkylamine salt is preferably used in the present invention. The quaternary ammonium salt includes, for example, chlorides such as lauryltrimethylammonium chloride, cetyltrimethylammonium chloride, stearyltrimethylammonium chloride, distearyltrimethylammonium chloride and alkylbenzyldimethylammonium chloride; and bromides corresponding to them. The alkylamine salt includes, for example, coconutamine acetate or stearylamine acetate. Among these, a quaternary ammonium salt is preferable in view of the effect of stabilizing the latex, and cetyltrimethylammonium chloride or its corresponding bromide and stearyltrimethylammonium chloride or its corresponding bromide are particularly preferable.
The amount of the cationic surfactant is appropriately selected and preferably within a range from about 0.5 to 20% by weight, and more preferably from 1 to 10% by weight, based on the graft-modified rubber component of the latex. When the amount of the cationic surfactant is less than 0.5% by weight, the cationic surfactant is not sufficiently adsorbed in the rubber particles of the latex. On the other hand, when the amount exceeds 20% by weight, the moisture-absorption properties of the solid rubber obtained by drying the latex are enhanced and the cost increases, which is not preferable.
The method of adding the cationic surfactant is not specifically limited, but a predetermined amount of an aqueous 10-20 wt % solution of the cationic surfactant is preferably added to the graft-modified natural rubber latex.
The cationic graft-modified natural rubber latex of the present invention is characterized by enabling a specific nonionic surfactant to coexist. As described above, an object of cationically modifying the latex can be attained by adding the cationic surfactant to the graft-modified natural rubber latex. However, the viscosity of the latex is drastically increased by only adding the cationic surfactant to cause gelation sometimes, thereby making it impossible to obtain a latex of pra
Hamada Akihiko
Ichikawa Naoya
Birch & Stewart Kolasch & Birch, LLP
Sumitomo Rubber Industries, Ltd
Szekely Peter
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