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
1999-08-18
2002-12-17
Wu, David W. (Department: 1713)
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...
C524S296000, C524S297000, C524S523000, C525S227000, C525S228000
Reexamination Certificate
active
06495626
ABSTRACT:
This application is the national phase of international application PCT/GB96/03246 filed Dec. 31, 1996 which designated the U.S.
The present invention relates to an acrylic polymer—containing plastisol composition.
Plastisols are well known in the art. They are understood to be non-aqueous fluid compositions ranging in viscosity from pourable liquids to heavy pastes which contain a particulate polymer (polyvinyl chloride being historically and commercially the most important example) dispersed in a non-volatile liquid organic plasticiser material which for practical utility should be compatible with the polymer. Under ordinary conditions of storage (ambient temperatures) the polymer does not dissolve to any extent in the plasticiser but on heating the plastisol composition at an appropriate evaluated temperature, after forming the plastisol into a desired shape (e.g. by moulding or coating), the plastisol composition gels to form a homogeneous coalesced mass which retains its homogenous character permanently on cooling. The presence of the plasticiser provides desirable properties to the polymer of the plastisol, particularly workability prior to gelling and flexibility after gelling. Similar types of composition are obtained with volatile organic liquid solvents, known as organosols, and the term “plastisol” herein is intended to embrace both plastisols and organosols. The plastisols may (and usually do) contain other materials, particularly inorganic or carbonaceous fillers.
Historically, polyvinyl chloride has been the prime example of the polymer to be used for plastisol compositions because of its particular suitability for this type of composition, and indeed the art of plastisol technology has been largely built up around the use of this particular polymer. Nevertheless polyvinyl chloride does have certain disadvantages, such as a tendency to be rather sensitive to light (leading to yellowing) and to release hydrogen chloride on aggressive heating (leading to corrosion effects on substrate such as metals).
Alternatives to the use of polyvinyl chloride as the particulate polymer in plastisol compositions have therefore been sought by the industry, and in particular acrylic polymers have been proposed and used for this purpose.
For example, it is disclosed in U.S. Pat. No. 4,210,567 to employ as the polymeric component for plastisols acrylic polymers based principally either on homopolymers of methyl methacrylate or copolymers of methyl methacrylate with methacrylates of aliphatic C
2
to C
10
(preferably C
2
to C
4
) alcohols or acrylates of C
1
to C
10
(preferably C
1
to C
4
) alcohols.
It is appreciated by those skilled in the art that the acrylic polymer should be acceptably compatible with the plasticiser used for the plastisol composition, i.e. form a homogenous gelled mass or film on heating which is stable on cooling and does not later (e.g. after 7 days storage at ambient temperature after gelling) exude liquid plasticiser, as shown by a completely dry surface. For this purpose it is known that acrylic polymers based on methyl methacrylate (the favoured monomer for this purpose) often require the presence of copolymerised units of a suitable comonomer, such as an alkyl acrylate or a higher alkyl methacrylate, depending on the type and amount of plasticiser in the final s formulation. [N.B. The formal test herein to determine whether or not a polymer is acceptably compatible with a plasticiser in a plastisol composition is as follows: for compatibility the plastisol should form a homogeneous gelled mass or film when heated at temperature(s) within the range of from 140 to 200° C. (usually ca 160° C.) for a period within the range of from 1 to 30 minutes, usually ca. 20 minutes, which on cooling to ambient temperature (which herein is considered as ranging from about 15 to 30° C., and is usually taken as ca 23° C.), does not exclude plasticiser after 28 days storage at ambient temperature as shown by a completely dry surface of the cooled mass or film].
Another problem encountered with acrylic polymer plastisols concerns their viscosity storage stability. Thus such plastisols may tend to undergo an unacceptable increase in viscosity on standing without any application of heat, and may even gel on storage at ambient temperature.
Plastisol viscosity stability can be considered as sufficient for many industrial applications if the viscosity does not increase to exceed an upper usable limit of e.g. 100 Pas after 21 days storage at ambient temperature (23° C.) and/or in an accelerated test at 30° C. does not exceed for example 100 Pas after 1 day.
Unfortunately, in many cases there is a problem in achieving both acceptable polymer/plasticiser compatibility and acceptable plastisol viscosity stability in a given acrylic polymer plastisol composition.
Thus in many cases while the acrylic polymer is compatible with the plasticiser employed, the plastisol is not viscosity stable and quickly gels even at ambient temperature. Conversely, in many other cases the acrylic polymer plastisol is viscosity stable but unfortunately the polymer is not compatible with the plasticiser being used and either will not form a gelled mass on heating, or if it does form one, after the plastisol has been gelled and cooled to ambient temperature, the plasticiser exudes from the gelled mass as a liquid.
This problem is addressed in U.S. Pat. No. 4,199,486 and is solved therein by employing a plastisol composition comprising emulsion particles of a methyl methacrylate copolymer and an organic plasticiser, the particles having a size of from 0.05 to 5 &mgr;m and having a core/shell construction, with the shell portion surrounding the core being an acrylic polymer which is compatible which the plasticiser used, and the core portion being a methyl methacrylate homo- or copolymer which is incompatible with the plasticiser used, the overall core/shell copolymer comprising >80 weight % of methyl methacrylate and having Tg≧50° C.
The drawback with the solution proposed in U.S. Pat. No. 4,199,486 is that the core/shell construction must be achieved by a sequential polymerisation process, i.e. the polymerisation of the monomers for forming the shell part are polymerised in the presence of the core polymer, usually both polymerisations being carried out without isolating the product of the first polymerisation. Since the core/shell polymer particles contain both the plasticiser compatible and plasticiser incompatible polymers, this inevitably places limitations on a formulator desiring to modify the plastisol formulation for each particular application. (Furthermore, such sequential polymerisation does not in many cases provide the desired core/shell structure for the particles). By contrast, if a plastisol formulation could be made using a combination of plasticiser compatible and plasticiser incompatible polymers, both of which have been preformed, then the formulator would have the freedom to make adjustments to the compatible/incompatible polymer ratio and thus optimise the formulation for each application.
It would therefore be far more convenient if a viscosity (storage) stable plastisol based on a compatibly formulated acrylic polymer system could be derived from a combination of plasticiser compatible and plasticiser incompatible polymer components, both of which have been preformed (i.e. separately prepared prior to combination for the plastisol composition) and have not had to be combined by the formation of one polymer in the presence of the other.
Unfortunately, according to the teaching of U.S. Pat. No. 4,199,486, such an advance is not feasible because while the overall polymer system may be compatible with the plasticiser, the plastisol formed is highly unstable from a viscosity viewpoint. Thus the core/shell invention compositions of U.S. Pat. No. 4,199,486 are compared in that specification with compositions based on simple mixtures of plasticiser compatible and plasticiser incompatible polymers, having the same monomer compositions as the core and shell polymers and
Cooper David Henry
Overend Andrew Stuart
Padget John Christopher
Egwim Kelechi C.
Pillsbury & Winthrop LLP
Wu David W.
Zeneca Limited
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