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
1999-02-04
2001-10-09
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...
C524S522000, C524S523000, C524S525000, C524S528000, C525S192000, C525S221000, C525S223000, C525S227000, C525S230000, C525S241000
Reexamination Certificate
active
06300407
ABSTRACT:
The present invention relates to elastomer compositions, a process for preparing the same and methods of plasticizing and/or enhancing processability of elastomers. These compositions have enhanced plasticity and processability with reduced loss of plasticizer from extraction or migration.
Elastomers are useful in many fields in a variety of applications. For instance, elastomers are used in the automobile, defense, space, oil drilling and oil recovery industries. Elastomers may be fabricated into tires, seals, gaskets, extruded goods, specialty parts, sheet stock, etc., for use in such industries. Consequently, in such applications, parts fabricated from elastomers may have to be resistant to, for example, fuel, lubricants, extreme temperatures, water, steam, or chemicals. Furthermore, depending on the application, such elastomers may be required to be plasticized to provide low temperature flexibility, as well as enhanced elongation and tensile properties. Also, such elastomers are preferred to have a certain amount of processability for efficient and economical fabrication into the required part.
Plasticizers are added to elastomers to provide or enhance the plasticity of the materials. Specifically, plasticizers are materials which when added to a polymeric material cause an increase in workability and flexibility brought about by a decrease in the glass transition temperature (Tg) of the polymer. Plasticizers are usually of two types, internal and external. Internal plasticizers are made by creating a plasticizing polymer in situ at the same time the polymer is formed. External plasticizers are fully prepared before they are added to the polymer. (Generally, see
Kirk
-
Othmer Encyclopedia of Chemical Technology,
Vol. 19. pages 258-273 for a discussion of plasticizers.)
Conventional plasticizers, at times, tend to migrate within the elastomer, “bloom” to the surface and “bleed” from the elastomer so that the effective lifetime of a part fabricated from the elastomer is shortened. This migration is excascerbated by the environments in which some of the elastomeric materials are required to operate. Such environments may caused the plasticizer to be extracted from the elastomer. Subsequently, the plasticization decreases and the environment may be polluted with the plasticizer. One conventional approach in overcoming plasticizer migration problems is by the use of plasticizers having a high molecular weight. However, use of such high molecular weight plasticizers results in elastomer compounding problems. That is, it was very difficult to compound and blend the components into a compatible elastomeric composition. Also, the processability of these elastomers suffer.
Conventionally, many chemical compositions have been utilized for the purpose of plasticizing polymers to improve the flexibility, low temperature performance, percent elongation before breaking, Shore A hardness, and resistance to tearing and cracking when impacted. Such physical tests are used as an actual indicator of actual performance in a finished product and are well known in the art. For instance, such physical tests are described in
Rubber Technology,
second edition, Chapters 4 and 5.
Short chain (meth)acrylates have been suggested as plasticizers in rubbers. For instance, hydroxyethyl and hydroxypropyl methacrylates, as well as their alkoxy derivatives, have been suggested as plasticizers in polychloroprene compositions. (See
UK Research Disclosures,
Vol.211, page 403 # 21122 ). Also, C
8
-C
13
alkyl methacrylates, as well as 2-ethoxy-ethyl methacrylates combined with powdered elastomers, i.e., natural rubber, styrene-butadiene, or acrylonitrile-butadiene have been suggested as soft acrylic elastomeric compositions for use in dental prosthesis. Such a combination is said to avoid the use of plasticizers. (See Parker, S. and Braden,
Biomaterials
1990, Vol. 11, September.) Vulcanized rubber was plasticized with C
7
-C
12
alkyl methacrylates. (See Panchenko et al Kauch,
I Rezina
(4), 24-26 (1979)). This reference suggests that lower chain methacrylates, i.e., heptyl methacrylate, have the highest plasticizing capacity. In U.S. Pat. No. 5,026,807 a methacrylic acid ester, having a repeating ester group within a long chain alkyl substituent, i.e., between a C
3-20
alkylene group and a C
1-20
hydrocarbon group, is used as an elastomer additive. The ester was compounded with a polymer having elasticity to provide a composition having enhanced oil, heat, and low temperature resistance.
Blends of polyacrylate copolymers and terpolymers of C
4
-C
8
alkyl acrylates, C
1
-C
3
alkyl acrylates and C
2
-C
12
alkoxyalkyl acrylates and partially hydrogenated nitrile rubbers are disclosed as useful in automobile engine belts, gaskets, seals, etc., in U.S. Pat. No. 5,612,418. However, the disclosed compositions also contain a plasticizer additive, which indicates that the polyacrylates were not considered to have plasticizer properties. Possible use of acrylate and methacrylate polymers as plasticizers is suggested in U.S. Pat. Nos. 4,158,736 and 4,103,093. However, these patents do not disclose specific elastomer compositions or use in elastomer compositions.
None of these references address the problem of plasticizer migration and plasticizer/elastomer compatibility discussed above. Suitable non-migrating plasticizers which are easily compounded with a variety of elastomers, including elastomers, such as fluoroelastomers which are known to be difficult to compound, have heretofore not been disclosed in the prior art. Accordingly, there is a need for a plasticizer for elastomers which has a substantial amount of permanence within the elastomer composition, but which is also compatible with the elastomer and effectively imparts “plastic” properties to the elastomer. An example of this need may be seen in the compounding of acrylic rubber (ACM) at line 1, paragraph 3 on page 930 of Kirk-Othmer, Volume 8 where lower concentrations of plasticizers must be used due to plasticizer loss from volatility at the higher typical ACM service temperatures and/or their partial extractibility by aggressive fluids where ACMs are employed. Other additives are therefor required to improve processibility due to decreased plasticizer levels.
The present inventors have discovered new elastomer compositions which are plasticized by polymeric materials prepared from at least one ethylenically unsaturated monomer and novel processes for preparing the same. The subject elastomer compositions have enhanced plasticity without attendant migration or compatibility problems associated with prior art elastomer compositions. This is true even in elastomeric materials, such as fluoroelastomers, which have heretofore had no or at best very few plasticizers available for use therein.
The polymeric compositions of the elastomer compositions of the present invention are present as interpenetrating networks of polymeric plasticizer and/or processing aids within the elastomer polymer matrix. The polymeric (meth)acrylate chains are trapped within the elastomer thereby having an enhanced permanence within the elastomer. This results in increased life to the plasticized elastomer and the ability to add more filler without bleed out of the filling material. This is accomplished without loss of compatibility between the plasticizer and the elastomer.
In a first aspect of the present invention, there is provided an elastomer composition, including: (A) at least one elastomer; (B) a plasticizer comprising at least one polymeric material, having a weighted average molecular weight (Mw) of 500 to 1,000,000, formed from at least one ethylenically unsaturated monomer, and (C) a curing agent, wherein the at least one polymeric material is substantially permanent within the elastomer.
In a second aspect of the present invention, there is provided a process for preparing an elastomer composition, including: (A) providing a mixture of an elastomer, at least one ethylenically unsaturated monomer or a polymeric material having a weighted average molecular
Bowe Michael Damian
Gore Robert Howard
Machleder Warren Harvey
Moorman David Sterett
Egwim Kelechi
Holler Alan
Rohm and Haas Company
Wu David W.
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