Stock material or miscellaneous articles – Composite – Including interfacial reaction product of adjacent layers
Reexamination Certificate
1999-08-05
2002-09-10
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Composite
Including interfacial reaction product of adjacent layers
C428S421000, C428S446000, C428S447000, C428S451000, C156S297000, C156S307100
Reexamination Certificate
active
06447916
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to multi-layered composites of fluorinated polymers and silicon-containing polymers.
BACKGROUND OF THE INVENTION
Fluoropolymers are a commercially important class of materials that include, for example, crosslinked and uncrosslinked fluorocarbon elastomers and semi-crystalline or glassy fluorocarbon plastics.
Fluorocarbon elastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated and non-halogenated monomers, such as hexafluoropropene, have particular utility in high temperature applications, such as seals, gaskets, and linings. See, for example, R. A. Brullo, “Fluoroelastomer Rubber for Automotive Applications,”
Automotive Elastomer
&
Design
, June 1985, “Fluoroelastomer Seal Up Automotive Future,”
Materials Engineering
, October 1988, and W. M. Grootaert, et al., “Fluorocarbon Elastomers,” Kirk-Othmer,
Encyclopedia of Chemical Technology
, Vol. 8, pp. 990-1005 (4
th
ed., John Wiley & Sons, 1993).
Fluorocarbon plastics (or fluoroplastics) are generally of high thermal stability and are particularly useful at high temperatures. They also exhibit extreme toughness and flexibility at very low temperatures. Many of these fluoroplastics are almost totally insoluble in a wide variety of solvents and are generally chemically resistant. Some have extremely low dielectric loss and high dielectric strength, and many have unique nonadhesive and low-friction properties. See, for example, F. W. Billmeyer,
Textbook of Polymer Science,
3
rd
ed., pp. 398-403, John Wiley & Sons, New York (1984).
Silicone-containing polymers are also a commercially important class of material. These polymers are known for their wide useful temperature range. See, for example, “Elastomers, Synthetic,” Kirk-Othmer,
Encyclopedia of Chemical Technology
, Vol. 7, pp. 698-699 (2nd ed., John Wiley & Sons, 1967) and “Silicones,” Kirk-Othmer,
Encyclopedia of Chemical Technology
, Vol. 18, pp. 221-260 (2nd ed., John Wiley & Sons, 1969). Silicone-containing polymers, such as silicone-containing elastomers, are also known for their non-stick nature. This feature is a problem when it is desired to use silicone-containing elastomers in combination with other materials.
There are a number of product applications where the advantages of these two polymers are very beneficial. For example many automotive applications require higher performance standards for high and low temperature capabilities, as well as better chemical resistance. One example of these higher performance standards is the new requirements for turbo-charger hose used on some automotive or truck engines. These requirements may be met by the unique combination of properties available from composite structures containing both fluoropolymers and silicone-containing polymers. However, the techniques used to make these composites have not been entirely satisfactory. These techniques include grafting a silicone-containing layer onto an existing cured fluoropolymer substrate (European Pat. No. 0 492 416); grafting unsaturated fluorocarbons onto organosiloxanes (U.S. Pat. No. 4,492,786); and employing a tie layer to adhere a peroxide curable fluoroelastomers to a silicone-containing polymer. These techniques require the use of several processing steps. Often the processes are complicated and time consuming.
There is still a need for an easily manufactured composite of a fluoropolymer directly bonded to a silicone-containing polymer. The bond strength of the resulting composite structures is preferably at least as high as that of the prior art composite structures. More preferably the bond strengths are higher. Additionally the method of making the composite should eliminate the complex and time consuming techniques presently used. Such techniques and materials are preferably useful with bisphenol curable as well as peroxide curable fluoroelastomers and preferable do not require a tie-layer. Single step or in-line processing are particularly desirable.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a novel composite structure comprising a fluoropolymer adhered directly to a silicone-containing polymer. The composite article comprises
a) a layer of a fluoropolymer selected from the group consisting of fluorothermoplastic polymers and fluoroelastomer polymers, or mixtures thereof, the fluoropolymer having first and second surfaces; and
b) a layer of a cured silicone-containing polymer adhered directly to the first surface of the fluoropolymer.
The two polymers are joined to one another through a transition zone that comprises the reaction product of a peroxide and (i) the fluoropolymer and (ii) the silicone-containing polymer. The peroxide comprises an amount effective to cure the silicone-containing component and to provide the transition zone. The fluoropolymers are selected from melt processable thermoplastic fluoropolymers, fluoroelastomeric fluoropolymers and mixtures thereof.
Also provided is a novel method of bonding a fluoropolymer to a silicone-containing polymer. The method comprises the steps of:
a) providing (i) a fluoropolymer composition comprising a fluoropolymer that is capable of providing a reactive site, and (ii) a curable silicone-containing polymer composition comprising the curable silicone-containing polymer and a peroxide;
b) contacting the fluoropolymer composition with the silicone-containing polymer composition to provide interfacial contact between the two and form a composite structure;
c) exposing the composite structure to conditions sufficient to (i) create the reactive site on the fluoropolymer, (ii) form a transition zone between the fluoropolymer composition and the silicone-containing polymer composition that comprises the reaction product of the peroxide and each of the fluoropolymer composition and the silicone-containing polymer composition, and (iii) bond the fluoropolymer to the silicone-containing polymer.
The composite article demonstrates good bonding between the fluoropolymer and the silicone-containing polymer. These bonds are achieved without the use of a third or tie layer, are preferably at least as good as those achieved with prior art composites. Often they are better. A preferred aspect of the method comprises the addition of a peroxide to both the fluoropolymer composition and the silicone-containing polymer composition.
The method of bonding the fluoropolymer to the silicone-containing polymer eliminates the need for complicated and time consuming processing techniques. It also eliminates the need to use separate tie layers and scrims.
DETAILED DESCRIPTION
Fluoropolymers
Fluoropolymers used in the invention are capable of providing a reactive site. The reactive site may be provided through dehydrofluorination or by incorporating a reactive comonomer in the polymer. Additionally, the fluoropolymers useful in the invention are capable of interacting with a peroxide to bond to the silicone-containing polymer.
The fluoropolymers may either be vinylidene fluoride containing or substantially non-vinylidene fluoride containing fluoropolymers or mixtures thereof. Additionally, they may be either fluoroplastics (also known as fluorothermoplastics) or fluororubbers (also known as fluoroelastomers) or mixtures thereof. See, for example, American Society for Testing and Materials (ASTM) D 1566 for elastomer and rubber definitions. Preferably, the fluoropolymers are fluoroelastomers. Fluoroplastics are distinguished from fluoroelastomers by their properties. Fluoroplastic materials are melt-processable and have either a melt point and are semi-crystalline, or have a glass transition temperature above ambient temperature. In contrast, fluororubbers are generally amorphous and do not exhibit a melt point. Fluoroplastics and fluororubbers may be used if desired. Additionally, blends of different fluoroplastics or different fluororubbers may be used.
The fluoropolymer used as a starting material in this invention may be provided either in a neat form (i.e., free from other additives) or as
Chen Vivian
Dyneon LLC
Lilly James V.
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