Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-11-02
2001-10-09
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S217000, C525S218000, C525S232000, C525S240000, C525S241000
Reexamination Certificate
active
06300418
ABSTRACT:
RELATED APPLICATIONS
This is a continuation of International Application No. PCT/NL98/00232 filed Apr. 27,1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention deals with a thermoplastic elastomer composition having improved adhesion to polar materials, e.g. polar substrates, without requiring pre-treatment of such polar materials or the use of additional adhesives.
2. Description of Related Art
Thermoplastic elastomers are typically materials which exhibit properties between those of crystalline or glassy plastics and soft elastomers. To be considered thermoplastic they must soften upon heating, such that in the molten state they are capable of being shaped by plastic processing techniques, such as injection molding or extrusion.
Blends or alloys of plastic and rubber have become increasingly important in the production of high performance thermoplastic elastomers, particularly for the replacement of thermoset rubber in various applications. Among the more commercially relevant thermoplastic elastomers are those based on physical blends of polyolefins and rubbers.
Various blended products are described in U.S. Pat. Nos. 3,806,558, 3,835,201, 3,957,919, 4,130,535 and 4,311,628. These patent documents generally concern compositions which are comprised of polyolefin resins containing either uncured, partially cured, or fully cured polyolefin rubbers. According to these patent documents further improvements in physical properties such as tensile strength, elongation, and compression set are achieved when the rubber phase is well dispersed into small particles of fixed size. This occurs by curing the rubber in its dispersed state without curing the plastic phase so as to maintain its thermoplasticity.
Another type of thermoplastic elastomer which is frequently used is a thermo-elastomeric styrene based blockcopolymer, or its blend with a polyolefin.
These thermoplastic elastomer compositions are non-polar in nature. Consequently, ensuring that such materials adhere to a polar material presents a considerable challenge. The most common efforts focus on using substrate pre-treatments to improve adhesion or bonding. Industrially practiced pretreatment methods depend on the substrate and include solvent etching, sulfuric acid or chromic acid etching, sodium treatment, ozone treatment, flame treatment, UV irradiation, and plasma treatment. These procedures are costly, use hazardous materials, result in product degradation, and create environmental hazards.
Still other efforts include those described in U.S. Pat. No. 4,957,968, the complete disclosure of which is incorporated herein by reference, in which adhesive thermoplastic elastomer compositions comprised of blends of thermoplastic elastomer (TPE) containing about 15 to 40 wt. % of grafted maleic anhydride polypropylene are applied to substrates. The maleic anhydride (MAR) apparently functions as a means for introducing polarity into the formulation and to react with other reactable functional groups. In the case of bonding to a polyamide-based substrate, both such substrate and the TPE must be in the molten state to initiate the covalent bonds necessary for the adhesion. Adhering to a cold substrate using this so-called adhesive thermoplastic elastomer is generally unsuccessful. Little or no covalent bonds will form at the interface and the adhesion is therefore inadequate.
Another effort is detailed in the PCT International Patent publication WO 95/26380. According to this patent publication, adhesive thermoplastic elastomer compositions can be comprised of blends of thermoplastic elastomers with a reaction product of a functionalized polyolefin and a polyamide. These adhesive thermoplastic elastomers are said to provide improved surface properties and to adhere to engineering resins such as nylon (or polyamide). The improvement asserted over the U.S. Pat. No. 4,067,068 is that maleated polypropylene (PP) is grafted with low molecular weight polyamide to form an adhesion promoter (grafted nylon-MAH-PP). This grafted nylon-MAR-PP then is blended with the selected thermoplastic elastomer to yield the so-called adhesive product. In this case, the need for temperature-dependent covalent bonding across the interface between the composition and a polar material (engineering resin etc.) is eliminated and the polar segment of the dispersed adhesion promoter provides adhesion. Based on the Examples, the disclosed adhesive thermoplastic elastomer compositions would appear to be capable of bonding to Nylon 6.
However, the above-mentioned efforts suffer from some serious drawbacks. One deficiency is that blending the grafted nylon-MAH-PP with the selected thermoplastic elastomer results in a substantial increase in the overall hardness of the resulting thermoplastic elastomers which is, as can also be learned from the examples of the PCT-application, on the order of about 15 points (Shore A hardness). To maintain the starting hardness of the thermoplastic elastomer, common additives such as a block copolymer of styrene/conjugated diene/styrene are used. Compensating for the increase in hardness by starting from or adding amounts of a lower hardness thermoplastic elastomer results in a product exhibiting an inferior combination of physical properties.
Therefore a need remains for a composition which is capable of being adherent to a substrate, such as a polar substrate, without requiring pre-treatments while avoiding the disadvantages associated with the alternatives noted hereinabove.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermoplastic elastomer composition having improved adhesion to polar materials, e.g. polar substrates.
Another object of the present invention is provide a thermoplastic elastomer composition adapted for adhering to a polar substrate in which the addition of a adhesion promoter does not substantially increase the hardness of the thermoplastic elastomer composition.
An additional object of the present invention is to provide a thermoplastic elastomer composition in which the adhesion promoter has a lower hardness than the known adhesion promoters for use in thermoplastic elastomer applications.
A further object of the present invention is to provide a thermoplastic elastomer composition in which a higher hardness thermoplastic elastomer starting material can be used without unacceptably degrading the properties of the final adhesive composition.
Yet another object of the present invention is to provide a thermoplastic elastomer composition adapted for adhering to a polar material, e.g. substrate, which exhibits a better combination of properties than obtained with the heretofore known comparable compositions.
A still further object of the present invention is an article comprised of a substrate having at least one adhered segment formed from the present composition, like an overmolded or co-extruded article.
These and other objects are achieved with the present invention in which a thermoplastic elastomer composition having improved surface adhesion properties also comprises the reaction product of a functionalized thermoplastic rubber, such as a maleic anhydride graft functionalized thermoplastic rubber, with at least one polyamide. The resultant product has improved adhesion to polar materials.
REFERENCES:
patent: 3806558 (1974-04-01), Fischer
patent: 3835201 (1974-09-01), Fischer
patent: 3957919 (1976-05-01), Von Bodungen et al.
patent: 4067068 (1978-01-01), Bregstein et al.
patent: 4130535 (1978-12-01), Coran et al.
patent: 4311628 (1982-01-01), Abdou-Sabet et al.
patent: 4957968 (1990-09-01), Adur et al.
patent: 5420198 (1995-05-01), Papazoglou et al.
patent: 5506310 (1996-04-01), Vasselin et al.
patent: 90/03418 (1990-04-01), None
patent: 95/26380 (1995-10-01), None
Brzoskowski Ryszard
Sadeghi Mohammed R
DSM N.V.
Nutter Nathan M.
Pillsbury & Winthrop LLP
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