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
2001-01-29
2003-02-25
Cain, Edward J. (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...
Reexamination Certificate
active
06525132
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a polychloroprene latex composition useful as an adhesive, and a method for its production and an adhesive composition employing it. More particularly, it relates to a chloroprene latex composition which is excellent in the initial adhesive performance and which is excellent in the balance of the heat resistance, water resistance, etc. with the adhesive properties, and a method for its production and an adhesive composition employing it.
BACKGROUND ART
Heretofore, adhesives using polychloroprene as a base were mainly of a solvent type. However, in recent years, demand for not employing a solvent has increased in view of problems such as toxicity, possible danger of fire and environmental pollution by an organic solvent during the production or use of solvent type adhesives. As a method for not employing a solvent, a method of substituting a latex adhesive for a solvent type adhesive is considered to be effective, and a study has been actively conducted on latex adhesives using various polymers.
Among them, a chloroprene latex adhesive is coated on both adherends to be bonded, such adhesive layers are dried and then bonded, whereby it exhibits high adhesiveness immediately after the bonding. From such a characteristic, it is expected to be useful as an aqueous contact type adhesive, but on the other hand, it is not necessarily satisfactory in the initial adhesive performance and in the balance of the heat resistance, water resistance, etc. with the adhesive properties, and improvements in this respect have been desired.
For example, JP-B-51-39262 discloses a method for producing a polychloroprene latex adhesive, wherein from 3 to 5 parts by weight of a long chain fatty acid or a rosinate is used as an emulsifier, per 100 parts by weight of chloroprene, and the monomer is polymerized at a temperature lower than 20° C. in an alkaline emulsion in the presence of from 0.09 to 0.15 part by weight of n-dodecyl mercaptan, and polymerization is terminated when the conversion of the monomer reaches from 90 to 98% to obtain a latex of polychloroprene containing from 40 to 90 wt % of a gel content, and a tackifier resin is blended thereto. However, latexes prepared in accordance with Examples of such publication lack in the contact property, and in order to make contact adhesion possible, a large amount of a tackifier resin is required to be added, and it takes time for the development of the strength, and the initial adhesive performance has not been necessarily satisfactory.
The present invention is intended to solve such problems of the prior art and to provide a chloroprene latex composition which is excellent in the initial adhesive performance and which is excellent also in the balance of the heat resistance and the water resistance, a method for its production and an adhesive composition employing it.
DISCLOSURE OF THE INVENTION
The present inventors have conducted extensive studies to solve the above problems, and as a result, have found it possible to obtain a chloroprene latex adhesive composition which is excellent in the initial adhesive performance and which is excellent also in the balance of the heat resistance, water resistance, etc. with the adhesive properties by a chloroprene latex composition having a certain specific amount of a gel content and a certain specific molecular weight of sol, and have accomplished the present invention.
Namely, the present invention provides a chloroprene latex composition comprising a chloroprene polymer containing from 3 to 40 wt % of a gel content and having a weight average molecular weight of sol of at least 400,000, and a method for its production and an adhesive composition employing it.
Further, the present invention provides the above-mentioned chloroprene latex composition wherein the chloroprene polymer is one obtained by polymerizing chloroprene, using a rosinate as an emulsifier, in the presence of a chain transfer agent at a temperature lower than 30° C. to a conversion of the monomer of from 80 to 95%, and the solid content concentration in the latex is from 45 to 65 wt %.
Further, the present invention provides the above-mentioned chloroprene latex composition wherein the emulsifier is potassium rosinate, and the polymerization is carried out in the presence of excess potassium hydroxide, a method for producing such a chloroprene latex composition, and an adhesive composition obtained by adding a tackifier resin to such a chloroprene latex composition.
Now, the present invention will be described in detail. The chloroprene polymer in the present invention is a homopolymer of 2-chloro-1,3-butadiene (hereinafter referred to as chloroprene), or a copolymer obtained by copolymerizing chloroprene with at least one monomer copolymerizable with chloroprene.
As the monomer copolymerizable with chloroprene in the present invention, 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, butadiene, isoprene, styrene, acrylonitrile, acrylic acid and its esters, methacrylic acid and its esters, may, for example, be mentioned, and if necessary, two or more types may be employed.
The gel content in the chloroprene polymer in the present invention is meant for the content of a component insoluble in a toluene solvent, and the sol is meant for a soluble component. In the chloroprene polymer in the present invention, the gel content is required to be within a range of from 3 to 40 wt %.
Further, the gel content was measured by the following method. The latex was freeze-dried (the weight was A) and dissolved in toluene at 23° C. for 20 hours (to adjust the concentration to 0.6 wt %), and using a centrifugal separator, and further using a 200 mesh metal net, the insoluble content i.e. the gel was separated. The gel content was dried in air and then dried in an atmosphere of 110° C. for one hour (the weight was B). The gel content was calculated by the following formula.
Gel content=
B/A
×100(%)
Further, in the present invention, the weight average molecular weight of the sol in the chloroprene polymer i.e. the toluene solvent-soluble component, plays an important role, and the weight average molecular weight of the chloroprene polymer of the present invention is required to be at least 400,000. A preferred range of the weight average molecular weight is from 400,000 to 1,200,000.
In the present invention, the gel content and the weight average molecular weight of the sol in the chloroprene polymer are defined as mentioned above, for the following reasons.
Development of the excellent initial adhesive performance in the present invention is attributable to the fact that the chloroprene polymer contains a large amount of sol excellent in molecular motion. Accordingly, fusion of chloroprene molecular chains at the adhesive interface takes place swiftly to instantaneously develop the adhesive strength, whereby it is possible to develop an excellent initial adhesive performance. If the gel content of the chloroprene polymer exceeds 40 wt %, this initial adhesive performance decreases substantially, such being undesirable.
On the other hand, in chloroprene latex adhesives which were commonly known, a chloroprene polymer having a low gel content tended to be poor in heat resistance, and the balance of the heat resistance with the initial adhesive property was poor. In the present invention, an excellent balance of the initial adhesive performance and the heat resistance has been made possible by adjusting the gel content of the chloroprene polymer to be from 3 to 40 wt % and adjusting the weight average molecular weight of the sol to be at least 400,000. If the gel content is less than 3 wt %, or the weight average molecular weight of the sol is less than 400,000, the heat resistance decreases substantially.
Further, when a still higher balance of the initial adhesive property and the heat resistance is required in the present invention, it is preferred that the gel content is from 5 to 30 wt %, and the weight average molecular weight of the sol is at least 500,000.
To obtain such a chloropr
Oba Hiroaki
Tsuji Tsuyoshi
Yamaguchi Mikio
Cain Edward J.
Denki Kagaku Kogyo Kabushiki Kaisha
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