Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1998-07-20
2002-08-20
Morris, Terrel (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S343000
Reexamination Certificate
active
06436531
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to polymer blends that exhibit properties useful in tape backing compositions. The tape backing compositions are useful in forming films, such as tape backings in auto paint masking tape.
BACKGROUND OF THE INVENTION
Polyvinyl chloride (PVC) films and tapes are conventionally used for a wide variety of applications. One prevalent use is for auto paint masking applications. PVC has many properties that are advantageous for such applications. For example, PVC films are known to be conformable to the varying topographies present on an automobile's exterior.
One disadvantage of PVC films, however, is the accompanying use of plasticizers in PVC films. Plasticizers are typically needed in PVC films in order to make the films more flexible, lower the glass transition temperature of the films, and make the films more conformable. However, plasticizers can migrate to the substrate on which PVC films are adhered, leaving a residue or “ghosting” when removed. The ghosting is not removable with solvent wipes. Thus, the exterior appearance of the automobile may be detrimentally affected when PVC films are used as the tape backing in auto paint masking tapes. Furthermore, such plasticizers may degrade adjacent adhesive layers, reducing the adherence of the tape to the automobile.
It is desired to have alternative compositions for use in tape backings and films. It is particularly desired to have alternative compositions for use in auto paint masking tapes, where ghosting is often associated with conventional tapes.
SUMMARY OF THE INVENTION
Tape backing compositions of the present invention comprise a blend of a first and second polymer, the two polymers having a melting temperature of at least about 93° C. (200° F.), more preferably at least about 149° C. (300° F.), even more preferably at least about 154° C. (310° F.). Generally, one of the two polymers is more flexible than the other polymer. For example, in one embodiment, the first polymer has an elastic modulus of about 103 MPa or less and the second polymer has an elastic modulus of about 207 MPa or more. Typically, each of the first and second polymers comprises at least about 20 weight %, more preferably at least about 40 weight %, of the blend. It is preferred that each of the polymers in the blend is compatible. Thus, for example, preferably the blend exhibits a single melting temperature.
Accordingly, in one embodiment, the two polymers are polypropylene polymers. Typically, at least one of the polypropylene polymers is more flexible than the other polypropylene polymer. Thus, for example, a first polypropylene polymer can be at least about 20% atactic, more preferably about 25% atactic to about 50% atactic, and a second polypropylene polymer can be at least about 80% syndiotactic and/or isotactic. In another embodiment, the two polymers are polyester polymers. In yet another embodiment, the two polymers are polyamide polymers.
Tape backing compositions of the present invention are especially useful for making flexible films. Such films advantageously possess properties particularly useful for applications involving elevated temperatures, such as auto paint masking tape applications. For example, certain flexible films of the present invention exhibit less than about 5%, more preferably less than about 2%, shrinkage when tested according to ASTM D1204 at 93° C. (200° F.) and 149° C. (300° F.). Furthermore, certain flexible films of the present invention preferably exhibit greater than about 20% stress relaxation when tested at 10% elongation and/or greater than about 40% stress relaxation when tested at 57% elongation. Another preferred property is where the flexible films exhibit less than about 5% necking and/or where the films exhibit essentially no yield point when tested according to ASTM D882-95a. Also preferred are certain flexible films that are hand-tearable. In order to accomplish certain of the above properties, preferably the flexible films are heat-treated.
Typically, flexible films according to the present invention possess more than one of the above-described properties. For example, one particularly preferred flexible film of the present invention comprises a first polymer having a melting temperature of at least about 149° C. (300° F.); and a second polymer having a melting temperature of at least about 149° C. (300° F.), wherein the film exhibits less than about 5% shrinkage when tested according to ASTM D1204 at 149° C. (300° F.), the film exhibits greater than about 40% stress relaxation when tested at 10% elongation, the film exhibits greater than about 55% stress relaxation when tested at 57% elongation, and the film exhibits essentially no yield point when tested according to ASTM D882-95a.
Tapes comprising the flexible films include a backing of the flexible film; and an adhesive coated on at least a portion of one side of the backing for adherence to a substrate. Tapes of the present invention, like flexible films, may optionally be heat-treated. As compared to conventional polyvinyl chloride-containing tapes, tapes of the present invention can be prepared such that they exhibit essentially no ghosting when used, for example, as paint masking tapes on substrates exposed to elevated temperatures.
In one application, an auto paint masking tape comprises a chloride-free backing comprising a blend comprising at least one relatively inflexible polymer and at least one relatively flexible polymer and an adhesive coated on at least a portion of one side of the backing for adherence to an automobile. In another embodiment, an auto paint masking tape comprises a backing comprising a blend comprising at least one relatively inflexible polymer and at least one relatively flexible polymer; and an adhesive coated on at least a portion of one side of the backing for adherence to an automobile, wherein the backing is essentially free of plasticizers.
Auto paint masking tapes of the present invention can be effectively used on automobiles for masking paint thereon. For example, selected portions of an automobile can be protected from paint during painting of the automobile by adhering such an auto paint masking tape to the selected portions of the automobile, painting the automobile, and removing the auto paint masking tape from the selected portions of the automobile.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Tape backing compositions of the present invention comprise a polymer blend that includes at least two polymers. Preferably, at least one of the polymers is relatively flexible and at least one of the polymers is relatively inflexible. It is to be understood, however, that outside of the context of the present invention, all polymers in the blend may be considered flexible.
A polymer's flexibility, as used herein, is measured in relation to the other polymer(s) in the blend. Any suitable method can be utilized for measuring the flexibility of a polymer. For example, the modulus (e.g., Young's modulus) of a polymer has been found to correlate to a polymer's flexibility.
As used herein, “relatively flexible polymers” generally have a relatively low Young's modulus as compared to other polymer(s) in the blend. For example, preferably, the Young's modulus of relatively flexible polymers herein is less than about 207 MPa (30,000 psi), more preferably less than about 103 MPa (15,000 psi), even more preferably less than about 34 MPa (5,000 psi).
As used herein, “relatively inflexible polymers” generally have a relatively high Young's modulus as compared to other polymer(s) in the blend. For example, preferably, the Young's modulus of relatively inflexible polymers herein is greater than about 207 MPa (30,000 psi), more preferably greater than about 345 MPa (50,000 psi), even more preferably greater than about 517 MPa (75,000 psi).
While a wide variety of polymers can be used in the blend, at least one polymer being relatively flexible as compared to the other polymer (preferably such that the Young's moduli of the two
Franzwa Sarah A.
Kollaja Richard A.
Solomonson Steven D.
3M Innovative Properties Company
Morris Terrel
Singh Arti R.
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