Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-10-11
2003-04-22
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S515000, C524S528000, C524S236000
Reexamination Certificate
active
06552108
ABSTRACT:
FIELD
The present invention relates generally to rubber compositions having improved thermal stability and green strength. These rubber compositions comprise blends of a first rubber component, an isoolefin/para-alkylstyrene copolymer rubber component and an amine.
BACKGROUND
Most conventional rubbers must be crosslinked, i.e., cured or vulcanized, in order to obtain suitably strong, shaped articles. However, crosslinking introduces relatively permanent bonds among the rubber's polymer molecules. Once these bonds are formed, they prevent adequate flowability for subsequent processing or molding. Thus, it is often desirable to process and mold rubber articles prior to curing.
Prior to being crosslinked, however, these rubbers often lack sufficient strength, also known as green strength, for easy handling and processing. Green strength refers to the cohesiveness and dimensional stability under relatively low stress of a rubber compound before it is vulcanized or cured. Green strength is important in such industries as tire manufacturing, where the innerlining and other layers of the tire may be formed in one stage, while curing takes place in a later stage. Green strength is important in allowing the manufacturer to shape and stretch the uncured rubber, while maintaining other favorable properties such as low air permeability.
Ionomerization (i.e., ionomer formation) provides a means for modifying green strength without chemical crosslinking through a cure process. Ionomerization of amines is also known in the art as quaternization, due to the formation of a quaternary amine. Since it is a reversible process, ionomerization provides green strength at lower temperature as well as good processability at higher temperatures. A typical method of ionomerization is the addition of tertiary amines to the rubber compositions, the basic amine functionality interacting with a more acidic functional group on the polymer in order to form stable interactions that increase green strength. U.S. Pat. Nos. 3,898,253 and 4,256,857 generally describe the use of tertiary amines to directly modify halobutyl rubber compositions to improve their green strength. Halobutyl rubber, such as bromobutyl rubber, however, is not very reactive with these amines. Therefore, the mixture must be heated for a substantial period of time in order to obtain sufficient green strength.
The present inventors have found that rubber green strength and/or thermal stability is greatly improved by blending the rubber with an amine and an isoolefin/para-alkylstyrene copolymer. The amine preferentially reacts with the isoolefin/paralkylstyrene to form a quaternary amine ionomer which results in improved green strength. The ionomerization can be performed in situ and with little or no heating. It has also been discovered that these compositions, when cured, exhibit improved thermal and aging stabilization. Alternatively, depending on the type of amine used, stability may be improved without the formation of ionomers.
SUMMARY
The present invention is a composition and a method of forming a composition blend, the composition blend comprising at least two components. A third rubber component may additionally be present in the blend of the invention. The first component is a halogenated isoolefin/para-alkylstyrene copolymer, hereinafter referred to as “component A”. Component A is present in the blend from about 95% to about 5% by weight of the blend.
In one embodiment, the isoolefin has between 4 and 7 carbon atoms and said copolymer containing from about 0.5% to about 20% by weight para-alkylstyrene, wherein from about 0.01 mole % to about 60 mole % of the methyl groups present on the benzene ring of the para-alkylstyrene contain a halogen atom. In a preferred embodiment, component A is an EXXPRO™ Elastomer (ExxonMobil Chemical).
The second component is an amine compound represented by the formula (R
1
R
2
R
3
)N, wherein R
1
is either hydrogen or a C
4
to C
30
hydrocarbyl group, R
2
is either hydrogen or a C
1
to C
30
hydrocarbyl group; and R
3
is either hydrogen or a C
1
to C
30
hydrocarbyl group provided that at least one of R
1
, R
2
and R
3
is not hydrogen. The amine is present from about 0.1 to about 5% by weight of the blend. In another embodiment, the blend contains the amine from about 0.1 mole % to about 60 mole % relative to the mole % of halogen atom present in the blend. Further, the amine compound is selected from the group consisting of N,N-dimethyl hexadecylamine, N,N-dimethyl hexylamine, N,N-dimethyl dodecylamine, N,N-dimethyl octadecylamine and N,N-diethyl decylamine, N,N-dimethylbenzylamine, N,N-methyl propyl hexadecylamine, and morpholine.
When present, a third component is a rubber component (hereinafter referred to as a “rubber” or “rubber component”) comprising from about 5% to about 95% by weight of the blend. The rubber is selected from the group consisting of butyl rubber, halogenated butyl rubber, isobutylene homopolymers, neoprene, nitrile rubbers, ethylene/propylene/diene terpolymers, ethylene/propylene copolymers, an isoolefin/para-alkylstyrene, a halogenated isoolefin/para-alkylstyrene, and natural rubbers.
In another embodiment, the rubber component is a halogenated butyl rubber, wherein the halogenated butyl rubber contains from about 85% to about 99.5% by weight repeat units derived from isobutylene, from about 0.1 to about 15% by weight repeat units derived from conjugated diene and from about 0.1% to about 15% by weight halogen. In a preferred embodiment, the conjugated diene is derived from isoprene. In another preferred embodiment, the rubber component is a halogenated isoolefin/para-alkylstyrene.
DETAILED DESCRIPTION
The blends of the present invention comprise at least two components: a first halogenated isobutylene/paralkylstyrene component and an amine component. In another embodiment, another rubber may be present as a third component. The invention also includes a method of forming the blend with the amine and other components. The blend is initially uncured (or unvulcanized) when combined, but may also be cured to form a cured blend.
The rubber component is the constituent for which improved green strength is desired. The term “rubber” or “rubber component” as used herein may include, but is not in any way limited to, the following polymers: butyl rubber, halogenated butyl rubber, isobutylene homopolymer, neoprene, nitrile rubbers, ethylene/propylene/diene terpolymers, ethylene/propylene copolymers, styrene butadiene rubbers, polybutadiene, polyisoprene, isoolefin/paralkylstyrene copolymer, halogenated isoolefin/paralkylstyrene copolymer, natural rubber, and mixtures thereof.
As used herein the term “butyl rubber” is defined to mean a polymer predominately comprised of repeat units of isobutylene but including a few repeat units of a conjugated diene. Preferably from about 85% to about 99.5% by weight of the butyl rubber are repeat units derived from the polymerization of isobutylene, while from about 0.1% to about 15% by weight of the repeat units are derived from a conjugated diene having from 4 to 8 carbon atoms such as butadiene, isoprene, hexadiene, etc., with isoprene being preferred.
“Halogenated butyl rubber” is defined to mean butyl rubber that contains at least 0.05% by weight halogen such as chlorine or bromine, preferably bromine.
Preferred halogenated butyl rubbers are those that contain from about 0.1% to about 15% by weight halogen, more preferably from about 0.5% to about to about 10.0% by weight halogen based on the total weight of the halogenated polymer.
Numerous patents disclose halogenated butyl rubber containing various amounts of chemically bound halogen, see for example, U.S. Pat. Nos. 2,631,984; 2,732,354; 3,099,644; 2,732,354; 2,944,578; 3,943,664; 2,964,489; and 4,130,534 (each fully incorporated herein by reference).
As used herein “nitrile rubbers” are copolymers of acrylonitrile with a conjugated diene having from 4 to 8 carbon atoms, with butadiene being preferred.
As used herein, “ethylene/propylene copolymers” are defined to mean those
Agarwal Pawan Kumar
Duvdevani Ilan
Qian Connie R.
Wang Hsien Chang
Arechederra Leandro
ExxonMobil Chemical Patents Inc.
Faulkner Kevin M.
Mulcahy Peter D.
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