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
2000-10-03
2002-12-17
Yoon, Tae H. (Department: 1714)
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...
C524S458000, C524S503000
Reexamination Certificate
active
06495628
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for producing a vinyl acetate polymer based emulsion and to a water based adhesive including the vinyl acetate polymer based emulsion. The vinyl acetate polymer based emulsion is useful as, for example, a paint base and a coating agent, in addition to an adhesive. The water based adhesive is advantageous as a plasticizer-free water based adhesive.
BACKGROUND ART
Vinyl acetate polymer based emulsions have been widely used as, for example, adhesives and paints for woodworking, paper processing, and fiber processing. However, such vinyl acetate polymer based emulsions as intact have high minimum film-forming temperatures, and must be incorporated with film-forming auxiliaries such as volatile plasticizers and organic solvents in many cases. As such plasticizers, phthalic esters and the like are employed. However, these pthalic esters are pointed out that they are environmentally undesired through increasing environmental sensitivities in recent years. The replacement of the ophthalmic esters with, for example, safer plasticizers is therefore examined. However, plasticizers are essentially VOC components (Volatile Organic Compounds), and such VOC components particularly in adhesives for use in housing are suspected to be causative substances for “New House Syndrome” (“Sick House Syndrome”). Thus, VOC problems due to plasticizers have been pointed out even in water based adhesives which apply less loads on environment. Plasticizer-free vinyl acetate polymer based emulsion adhesives have therefore been proposed, but there is no technology which can exhibit such a high adhesive strength as to be used for woodworking, and can form films even at low temperatures for example in winter.
The present applicants proposed a woodworking adhesive including a vinyl acetate polymer based emulsion, which emulsion is obtained by subjecting an ethylene-vinyl acetate copolymer based emulsion having an ethylene content of 15 to 35% by weight to seed polymerization with vinyl acetate, in the specification of Japanese Patent Application No. 9-270358. This technique can yield previously unseen excellent performances, i.e., the technique can exhibit a high adhesive strength and can form films even at low temperatures for example during wintertime without adding a plasticizer. However, even this technique has a disadvantage that a low-temperature adhesive strength when cured at low temperatures such as in winter is low. If a desired adhesive strength cannot be obtained even under such daily conditions that an adhesive is applied on an adherend and is cured at low temperatures as in winter or in cold climates, the reliability of the adhesive will be greatly lost.
As thus described, under present circumstances, there is no technique that can provide a plasticizer-free water based adhesive that has a high film-forming property at low temperatures and can positively perform adhesion operations at low temperatures. Accordingly, demands have been made to provide techniques to solve these problems, also from public viewpoints.
DISCLOSURE OF INVENTION
Accordingly, it is an object of the present invention to provide a process for producing a vinyl acetate polymer based emulsion which has satisfactory film-forming property at low temperatures and adhesive strength, even containing no plasticizer, and that can exhibit a high adhesive strength (low-temperature adhesive strength) even when cured at low temperatures, and to provide a water based adhesive including the vinyl acetate polymer based emulsion having the satisfactory performances.
After multiphasic investigations on, for example, polymerization, processing, and modification (improvement) techniques of vinyl acetate polymer based emulsions to achieve the above objects, the present inventors found the following findings. Specifically, they found that in the production of a vinyl acetate polymer based emulsion by subjecting vinyl acetate to seed polymerization in an ethylene-vinyl acetate copolymer based emulsion, the addition of a small amount of butyl acrylate (BA) to a system prior to a step of performing seed polymerization while adding vinyl acetate to the ethylene-vinyl acetate copolymer based emulsion resolves the phenomenon that adhesive strengths when cured at low temperatures are markedly decreased as seen in conventional vinyl acetate polymer based emulsions.
In addition, the same operations and advantages as above were obtained when butyl acrylate was added to a system subsequent to the step of performing seed polymerization while adding vinyl acetate to the ethylene-vinyl acetate copolymer based emulsion. The operations and advantages were supposed to be due to the action of a butyl acrylate homopolymer as a polymer plasticizer. A similar test was then performed using butyl methacrylate (BMA) instead of the butyl acrylate, and the present applicants found that low-temperature adhesive strength when cured at low temperatures was maintained at a high level also in this case. The butyl methacrylate has relatively high film-forming temperature and glass transition temperature of its homopolymer, and is not expected to serve or act as a polymer plasticizer.
In contrast, the aforementioned operations and advantages were not obtained when seed polymerization was performed while adding a mixture containing vinyl acetate and BA or BMA to a system (i.e., a conventional copolymerization procedure). In these results, a first wonder is that the aforementioned operations and advantages are obtained not when a mixture of vinyl acetate and BA or the like is added to the system but when BA or the like is, independently from vinyl acetate, added and incorporated into the system and is subjected to polymerization prior to or subsequent to the step of performing seed polymerization while adding vinyl acetate to the system. A second wonder is that similar operations and advantages can be obtained both in BA which is a soft monomer whose polymer is capable of forming a film at low temperatures, and in BMA which is a hard monomer whose polymer is not capable of forming a film at low temperatures.
The present invention has been accomplished based on these findings and further investigations on the type and amount of a polymerizable unsaturated monomer added to the system.
Specifically, the present invention provides a process for producing a vinyl acetate polymer based emulsion by seed polymerization of vinyl acetate in an ethylene-vinyl acetate copolymer based emulsion to yield a vinyl acetate polymer based emulsion. This process includes a step of performing seed polymerization while adding vinyl acetate to a system, and, prior to or subsequent to the step, a step of adding a polymerizable unsaturated monomer other than vinyl acetate to the system.
According to this production process, when the obtained emulsion is used as an adhesive, the resulting adhesive can yield satisfactory low-temperature film-forming property, adhesion, adhesive strength and adhesion workability even containing no plasticizer, and can prevent a problem of conventional technologies, i.e., the phenomenon that low-temperature adhesive strength when cured at low temperatures is remarkably decreased.
In the above production process, decrease in low-temperature adhesive strength when cured at low temperatures can be especially minimized when the step of adding a polymerizable unsaturated monomer other than vinyl acetate to the system is performed prior to the step of performing seed polymerization while adding vinyl acetate to the system.
The amount of the polymerizable unsaturated monomer other than vinyl acetate for use in the production process may be in a range from 0.0 5 to 10 parts by weight relative to 100 parts by weight of vinyl acetate. When the amount of the polymerizable unsaturated monomer other than vinyl acetate is within the above range, especially satisfactory low-temperature film-forming property, adhesion, adhesive strength, and adhesion workability can be obtained while minimizing or preventing the low-temperature adhesiv
Ogawa Shintaro
Origuchi Toshiki
Birch & Stewart Kolasch & Birch, LLP
Konishi Co. Ltd.
Yoon Tae H.
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