Fluoropolymer laminate

Details Fluoropolymer laminate Fluoropolymer laminate

1998-07-13

2001-11-06

Chen, Vivian (Department: 1773)

Stock material or miscellaneous articles

Composite

Of fluorinated addition polymer from unsaturated monomers

C428S422000, C428S461000, C428S463000, C525S199000, C525S200000, C526S242000, C526S243000, C526S248000

Reexamination Certificate

active

06312814

ABSTRACT:

FIELD OF THE INVENTION
This invention is in the field of melt-fabricable fluoropolymers, and is specifically concerned with laminates of melt-fabricable fluoropolymer compositions and metal.
BACKGROUND OF THE INVENTION
Fluoropolymer resins, and especially perfluoropolymer resins, are known for their low surface energy and antistick properties, and thermal and chemical resistance. These copolymers do not stick to other materials, especially dissimilar materials, with any practical degree of bond strength.
Some high temperature resistant thermoplastics (HTRP), such as polyamide imide, polyarylene sulfide and polyether sulfone, have found use as adhesion promoters in fluoropolymer coating formulations. See, for example U.S. Pat. No. 5,230,961 (Tannenbaum) and U.S. Pat. No. 5,093,403 (Rau et al). However, such adhesion promoters are typically used in relatively high proportions which can detract from the properties of the fluoropolymer. For example, U.S. Pat. No. 5,230,961 claims (claim 7) a coated substrate wherein the primer contains 15-30% of polyamide imide and 25-55% of perfluoropolymer, and TABLE 14 of U.S. Pat. No. 5,093,403 gives primer formulations containing 15-20 wt % of polyphenylene sulfide or polyetheretherketone.
There remains a need for laminates of melt-flowable fluoropolymer to dissimilar materials, notably metals, in which the fluoropolymer component has good adhesion to the metal at high fluoropolymer content, so that the fluoropolymer component of the laminate substantially retains the thermal and chemical resistance of fluoropolymer.
SUMMARY OF THE INVENTION
This invention provides a laminate of metal and melt-fabricable fluoropolymer composition adhered thereto, said composition comprising functionalized fluoropolymer resin and high temperature resistant thermoplastic resin adhesion promoter. Preferably, the composition contains minor portions of functionalized fluoropolymer and high temperature resistant thermoplastic resin adhesion promoter, and a major portion of non-functional fluoropolymer. The composition exhibits synergistic enhanced adhesion to metal, so that a laminate having good adhesion between components is obtained with a fluoropolymer composition having a relatively low concentration of high temperature resistant thermoplastic (adhesion promoter) and, thus, predominantly fluoropolymer character.
DETAILED DESCRIPTION
It has been discovered that a combination of functionalized fluoropolymer and high temperature resistant thermoplastic (HTRP) results in a synergistic increase in the adhesion of the composition to metal. When both components are present, the adhesion result is better than would be predicted from adhesion results when only one of these components is present. In one aspect, notably, the presence of the functionalized fluoropolymer enhances rather than interferes with the adhesion promotion of the HTRP. As a result, relatively low concentrations of HTRP can be used to achieve good adhesion, so that the composition has a relatively high proportion of fluoropolymer and, therefore, predominantly fluoropolymer characteristics.
As used herein, “functionalized fluoropolymer” means fluoropolymer having functional side groups or functional groups attached to side groups. Usually, but not necessarily, such functional units are at the ends of the pendant side groups. Functional groups, in the context of the present invention, are groups capable of enhancing the effect of HTRP adhesion promoter, when functional groups and HTRP adhesion promoter are both present in a fluoropolymer composition, to achieve an adhesive bond between the fluoropolymer composition and a metal surface to form a laminate. Such functional groups can be introduced, for example, by incorporating into the fluoropolymer, during polymerization, monomer units having such functional groups, i.e., functional monomers.
Functional groups that can enhance the effect of HTRP adhesion promoter include ester, alcohol, acid (including carbon-, sulfur-, and phosphorus-based acid) and salt and halide thereof. Other functionalities include cyanate carbamate, nitrile, and the like. Specific functional groups that can be used include —SO
2
F, —CN, —COOH and —CH
2
—Z wherein —Z is —OH, —OCN, —O—(CO)—NH
2
, or —OP(O)(OH)
2
. Preferred functional groups include —SO
2
F and —CH
2
—Z wherein —Z is —OH, —O(CO)—NH
2
, or —OP(O)(OH)
2
. The functional groups —CH
2
—Z wherein —Z is —OH, —O—(CO)—NH
2
, or —OP(O)(OH)
2
are especially preferred. As one skilled in the art will recognize, more than one type of functional group can be present. Normally, however, a single type of functional group is used.
The concentration of functional groups in the fluoropolymer resin component, i.e., in the functionalized fluoropolymer or in functionalized fluoropolymer plus non-functional fluoropolymer, if non-functional fluoropolymer is present, of the melt-fabricable fluoropolymer composition used in the laminate of this invention is effective to enhance the effect of HTRP adhesion promoter and thereby to enable good adhesion to metal even at low HTRP concentration. As will be recognized by one skilled in the art, the concentration of functional groups that is effective to enhance the effect of HTRP adhesion promoter can vary at least with the type of functional group and with the type of HTRP. The concentration of functional groups present can be expressed relative to the number of main chain carbon atoms in the fluoropolymer resin. Generally, the concentration of functional groups present is at least about 25/10
6
main chain C atoms, based on total fluoropolymer in the composition. The concentration of functional groups is usually in the range of 25-2500 per 10
6
main chain C atoms, preferably in the range of 50-2000 per 10
6
main chain C atoms, based on total fluoropolymer present.
The desired concentration of functional groups in the functionalized fluoropolymer resin can be achieved with a single fluoropolymer having functional groups, or a mixture of such fluoropolymers. The desired concentration of functional groups can also be achieved by blending functionalized fluoropolymer (or mixture of) having a higher concentration of functional groups with non-functional fluoropolymer (or mixture of), i.e., fluoropolymer having essentially no functional groups. In this embodiment, functionalized fluoropolymer acts as a functional group concentrate that can be let down (diluted) with non-functional fluoropolymer. This approach has the advantage of permitting one to achieve a variety of functional group concentrations with a single functionalized fluoropolymer by varying the blending ratio with non-functional fluoropolymer, and is a preferred embodiment of the invention. Preferably, in a functionalized fluoropolymer that is a blend, the functionalized fluoropolymer component is in minor (lesser) amount relative to non-functional fluoropolymer component.
Thus, in a preferred embodiment of the present invention, the melt-fabricable fluoropolymer composition contains minor amounts of functionalized fluoropolymer and high temperature resistant thermoplastic resin, and a major amount of non-functional fluoropolymer. By “major amount” is meant at least 50 wt %, preferably at least 70 wt %, of non-functional fluoropolymer based on combined weight of non-functional fluoropolymer, functional fluoropolymer, and HTRP adhesion promoter. In this embodiment, the composition preferably contains 1-30 wt %, more preferably 1-20 wt %, most preferably 3-15 wt %, of functionalized fluoropolymer and 0.5-10 wt %, more preferably 1-5 wt %, of HTRP adhesion promoter, based on combined weight of non-functional fluoropolymer, functionalized fluoropolymer, and HTRP. In this embodiment of the invention, then, the concentration of functional groups in the functionalized fluoropolymer will be higher than recited above for total fluoropolymer according to the amount of non-functional fluoropolymer present in the blend.
Fluoropolymer resins that can be used include copolymers of TFE with one or more copolymerizable monomers chosen from perfluorool

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