Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
2001-02-07
2003-06-17
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S213000, C428S220000, C428S343000, C428S354000, C428S500000, C428S515000, C428S516000, C264S464000, C264S472000
Reexamination Certificate
active
06579601
ABSTRACT:
TECHNICAL FIELD
This invention relates to conformable films, and more particularly, to multilayer films having alternating layers of a stiff polymeric material and flexible polymeric material.
BACKGROUND OF THE INVENTION
There is an ongoing need for conformable, non-yielding films, which may be bonded to uneven and/or irregular surfaces and having a variety of new properties not possessed by current products.
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.
Multilayer films have also been described. For example, constructions having up to several thousand layers of alternating polymers with different refractive indices have been shown to have mirror-like properties. Also, films that are severable or have puncture resistance have been made by using alternating layers of stiff and ductile polymers as described in U.S. Pat. Nos. 4,908,278 and 5,427,842 (Bland et al.). Pressure sensitive adhesive tapes are also known that have multilayered films as the backings on which the pressure sensitive adhesive is coated.
Although a variety of properties have been accomplished with such multilayered constructions, there is still a need for conformable, non-yielding film products to replace poly(vinyl chloride) films.
SUMMARY OF THE INVENTION
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 graphics applications, where stress relaxation and strain recovery properties are important and in auto paint masking tapes, where, in addition, minimal ghosting is also desired.
For graphics film and paint masking applications, it is desirable to have an easy to apply, conformable, non-yielding film that has good stress relaxation and low strain recovery to enable the film to be applied over irregular surfaces without delaminating or releasing from the substrate surface (“popping up”). In addition the graphics films should be printable (i.e. to have a receptive surface for printing and/or graphics) and exhibit good weathering for outdoor applications. A disadvantage of PVC and flexible polyolefin films is that they have poor stress relaxation, strain recovery properties and/or ghosting.
The present invention provides unified multilayer films having alternating layers of stiff and flexible polymeric materials. Preferably, multilayer films of the present invention are no greater than about 250 micrometers (em) thick. In one embodiment, multilayer films have a construction of alternating layers of different stiff materials or different flexible materials.
In any one construction of the alternating layers of stiff material and a flexible material, each of the stiff layers typically includes the same material or combination of materials, although they may include different materials or combinations of materials. Similarly, each of the layers that is flexible typically includes the same material or combination of materials, although they may include different materials or combinations of materials.
Preferably, multilayer films of the present invention have a unified construction of at least 10 substantially contiguous layers of organic polymeric material, more preferably, at least 13 layers, even more preferably, at least 29 layers, although as few as 5 layers are possible or two layers with certain materials. In certain embodiments, there are at least three layers of the same stiff material and often, at least three layers of the same material that is a flexible material.
The two outermost layers of multilayer films of the present invention can include one or more stiff materials, which may be the same or different in each of the two outermost layers. Alternatively, the two outermost layers can include one or more materials that are flexible materials, which may be the same or different in each of the two outermost layers. Furthermore, the inventive films include embodiments in which only one of the outermost layers includes a stiff material.
Multilayer films of the present invention can also be oriented, either in one or two directions, if so desired. In addition, the films can be annealed by running the film over hot rolls, through an oven or heating the film with an infrared heater. In certain embodiments of the present invention, the multilayer films can include a layer that is flexible, a stiff material layer, and a tie layer therebetween.
The present invention also provides a process of preparing a multilayer film. The process includes melt processing organic polymeric material to form a unified construction of at least 2, preferably at least 5, substantially contiguous layers of organic polymeric material, the construction comprising layers of stiff organic polymeric materials alternating with layers of flexible organic polymeric material. Preferably, all the layers are substantially simultaneously melt processed, and more preferably, all the layers are substantially simultaneously coextruded.
Another aspect of the present invention provides a multilayer film having a unified construction and a total thickness of no greater than about 250 micrometers; the construction comprising layers comprising a stiff material alternating with layers comprising a material that is flexible.
In another aspect, the present invention provides a multilayer film having alternating layers of stiff and flexible materials and further having a layer of pressure sensitive adhesive.
In another aspect, the present invention provides a multilayer film having alternating layers of stiff and flexible materials and further having a layer of a material, such as a thermoplastic layer or primer layer, to improve the ink receptivity of the surface.
A further aspect of the present invention provides a process of preparing a multilayer film, the process comprising melt processing organic polymeric material to form a unified construction of at least 2, preferably at least 5, substantially contiguous layers of organic polymeric material, the construction comprises layers comprising a stiff material alternating with layers comprising a material that is flexible.
Herein, the following definitions are used:
“Stiff materials” comprises thermoplastic polymers and blends of polymers having a Young's modulus 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).
“Flexible materials” comprises thermoplastic polymers and blends of polymers having a Young's modulus less than about 172.4 MPa (25,000 psi), more preferably less than about 68.9 MPa (10,000 psi) and most preferably from about 0.69 to 68.9 MPa (100 to 10,000 psi).
“Unified” means that the layers are not designed to be separated or delaminated as would a pressure sensitive adhesive tape in roll form.
“Melt viscosity” means the viscosity of molten material at the processing temperatures and shear rates employed.
“Conformability” means that the film accommodates curves, depressions or projections on a substrate surface so that the film may be stretched around curves or
Kollaja Richard A.
Nguyen David D.
Radovanovic Philip D.
Ree Buren R.
Solomonson Steven D.
3M Innovative Properties Company
Jackson Monique R.
Kokko Kent S.
Thibodeau Paul
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