Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-06-30
2001-03-27
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S479000, C428S451000, C428S447000, C524S114000, C524S261000, C528S032000, C528S041000, C528S015000, C556S451000
Reexamination Certificate
active
06207769
ABSTRACT:
The present invention relates to a polymer composition which comprises a polymer matrix and a siloxane-containing additive, which composition is capable of forming plastics articles to which cured silicone elastomers can adhere, in particular silicone elastomers cured by a hydrosilylation reaction, to a method for preparing a plastics article from said polymer composition, and to use of a siloxane-containing additive in the preparation of said polymer composition.
In many applications silicone elastomers are desirably applied to plastics substrates. For example, in the field of sealing and gasketing a gasket made from a silicone elastomer may be formed onto a plastics substrate. However, adhesion of the silicone elastomer to the plastics substrate can be poor and modification of the silicone elastomer and/or plastics substrate surface is often necessary for adhesion of the silicone elastomer to the plastics substrate. Modification of the silicone elastomer and/or plastics substrate surface is commonly achieved by the use of adhesion promoters, and silanes have been used for this purpose. Modification of a plastics substrate surface may be achieved, for example, by coating the surface with an adhesion promoter, or more conveniently by adding the adhesion promoter to the polymer melt prior to forming the plastics substrate. If the adhesion promoter is added to the polymer melt it is essential that adhesion promoter migrates to the surface of the polymer substrate if adhesion with an applied silicone elastomer is to be promoted. We have found that this migration does not always occur to a satisfactory extent when silane adhesion promoters are used, resulting in poor adhesion of an applied silicone elastomer.
U.S. Pat. Nos. 4,814,231 and 4,686,124 disclose thermosplastic resin-silicone composites wherein the resin may contain an organohydrogenpolysiloxane, e.g. vinyl-terminated organohydrogenpolysiloxane, for facilitating adhession of the resin to an addition curing silicone composition.
In a first aspect, according to the present invention there is provided a polymer composition which comprises a polymer matrix and a siloxane-containing additive which is substantially incompatible with the polymer matrix, wherein the siloxane of the additive has hydroxy, alkoxy or epoxy functionality and a functionality which is capable of bonding with a silicone elastomer-forming composition which is curable by a hydrosilylation reaction.
The present invention thus provides a polymer composition from which plastics articles can be formed, which composition may be prepared by simply mixing the additive with the polymer matrix melt and subsequently shaping the polymer composition to form the plastics substrate to which a silicone elastomer can adhere. The polymer composition according to the present invention has the further advantage of easing demolding of plastics substrates prepared therefrom compared to plastics substrates prepared from polymer melt not containing siloxane-containing additive used in the present invention.
The siloxane-containing additive used in the present invention is substantially incompatible with the polymer matrix. Herein “substantially incompatible” means that the additive will migrate to the surface of the polymer composition to allow bonding of the additive with the silicone elastomer-forming composition which is curable by a hydrosilylation reaction, but some compatibility between additive and polymer matrix is required so that complete separation of the additive from the polymer matrix does not occur as the additive might then bond only with the silicone elastomer and not the plastics substrate thus resulting in poor adhesion. The additive should act as a link between the molecules of the plastics substrate and the silicone elastomer.
Polymer matrices suitable for use in the polymer composition according to the present invention are well known in the art and include polysulphones, polyphenylenes, polyphenylenesulphide polyetherketones, polyimides, polyesters, polyethylene, polypropylene and phenolic and epoxy resins, with polyphenylenesulphide being preferred. As mentioned hereinbefore, the polymer matrix should be substantially incompatible with the siloxane-containing additive, but should not be totally incompatible therewith so as not to result in complete separation of the additive from the polymer matrix. The polymer matrix must melt to allow mixing of the additive therein and shape the polymer composition according to the present invention into a desired article, for example by molding. Mixing of the additive with the polymer matrix may be facilitated if the additive is a liquid at the melt temperature of the polymer matrix (i.e. the melt temperature of the polymer matrix is equal to or greater than the melt temperature of the additive). An example of a suitable polymer matrix is polyphenylenesulphide having a molecular weight of from 150,000 to 1,000,000.
The siloxane-containing additive for use in the present invention has a hydroxy, alkoxy or epoxy functionality and a functionality which is capable of bonding with a functional group of a silicone elastomer-forming composition which is curable by hydrosilylation reaction. Examples of functional groups which are capable of bonding with a functional group of a silicone elastomer-forming composition which is curable by hydrosilylation reaction include alkenyl (e.g. vinyl, hexen-1-yl) alkynyl, allyl, acrylate, methacrylate and silicon-bonded hydrogen groups. Preferably, the siloxane comprises units of the formula R
a
X
b
SiO
(4−a−b)/2
wherein R represents an alkyl group, most preferably a methyl group, X represents hydrogen, an alkenyl (e.g. vinyl, 5-hexenyl) alkynyl, allyl, acrylate, or methacrylate group, &agr; is 1, 2 or 3 and b is 0, 1, or 2, and &agr;+b≦3, with the proviso that the siloxane molecule contains at least one group X. The siloxane may be either linear or cyclic. Examples of suitable additives having these functionalities are trimethylsilyl end-blocked methylvinylsiloxane, trimethylsilyl end-blocked methylhydrogensiloxane and trimethylsilyl end-blocked dimethylmethyl(5-hexenyl)siloxane. Lower molecular weight siloxanes, such as those having a viscosity of 1000 mm
2
/s or less at 25° C., for example 10 to 100 mm
2
/s, tend to have higher mobility in polymer matrices than siloxanes having a higher molecular weight, and this may be a determining factor in the ability of the siloxane additive to migrate to the surface of the polymer matrix. However, the molecular weight of the siloxane additive is not crucial provided the additive can migrate to the surface of the polymer matrix and is substantially incompatible therewith, as discussed hereinabove. There is no lower limit to the molecular weight of the siloxane, e.g. disiloxanes may be used as additives.
The additive used in the polymer composition according to the present invention should act as a link between the polymer matrix and the silicone elastomer to provide adhesion therebetween, and must not completely separate from the polymer matrix but must maintain a degree of bonding therewith. This additive-polymer matrix bonding may be a physical or chemical bond, and the additives thus comprise a siloxane which has a hydroxy, alkoxy or epoxy functionality for chemically bonding with the polymer matrix, in addition to the functionality for bonding with a silicone elastomer-forming composition which is curable by a hydrosilylation reaction. Suitable alkoxy groups include methoxy and ethoxy groups. The preferred functionality for bonding with the polymer matrix used in the present invention is hydroxy. Thus, a preferred additive for use in the polymer composition of the present invention is hydroxy-terminated methylvinylsiloxane, in particular hydroxy-terminated methylvinylsiloxane having a viscosity from 20 to 40 mm
2
/s at 25° C.
Bonding of the siloxane-containing additive to the polymer matrix can also be aided using a silane having appropriate finctionalities to allow bonding of the silane to both the additive and the po
Gerlach Ernst
Joseph Edouard
Kunz Klaus
Zaulig Dieter
Boley William F.
Dawson Robert
Dow Corning GmbH
Peng Kuo-Liang
Warren Jennifer S.
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