Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-01-05
2002-09-24
Seidleck, James J. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S041800, C428S041300, C428S041500, C526S338000
Reexamination Certificate
active
06455153
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to release coatings, and in particular to release coatings which can be used in conjunction with pressure-sensitive adhesives.
BACKGROUND OF THE INVENTION
Pressure sensitive adhesives (PSAs) have widespread uses a bonding agents for manufacturing tapes, labels, decals, and the like. PSAs adhere to many surfaces with no more than applied finger pressure, e.g., various tapes (office, packaging, masking, etc.) or labels (office, shipping, identification, etc.). The adhesive is typically coated onto a “backing,” which includes any suitable substrate, such as films, foil, and paper. The adhesive may be coated onto one or both sides of the backing. The side of the backing coated with adhesive is referred to as the “adhesive-coated backing side.”
In the case of tapes, the adhesive-coated backing is typically wound onto itself to form a roll, wherein the adhesive-coated backing side is in direct contact with the adhesive-free backing side of the continuous backing in the roll. As a result, tapes typically have two sides or surfaces: one side that is coated with a PSA, and the other side of the tape, which is free of adhesive. It is, therefore advantageous for the adhesive layer to have a different affinity for one side of the tape than that of the opposite side (e.g., for the two sides) of the tape. Such differential affinity is typically achieved by two methods: the primer coating method and the release coating method. In the primer coating method, an adhesive that has a low affinity for the backing is selected, and a primer coat is used to make the adhesive layer bond strongly to the backing. Upon rolling, the adhesive-coated backing side adheres therefore less strongly to the adhesive-free backing side. Non-limiting examples of this method include solvent-based natural rubber adhesives coated onto unplasticized polyvinylchloride film and aqueous-based acrylic adhesives coated onto oriented polypropylene film, wherein the coated backing side has been “primed” by corona discharge treatment.
In the release coating method, a release coating is applied to the adhesive-free side of the tape and an adhesive is applied to the other side of the tape to form the adhesive-coated backing side. The release coating has a strong affinity for the backing but a weak affinity for the adhesive. The adhesive-free side of the backing, which is coated with a releasing agent, is referred to herein as the “release-coated backing side.” In certain cases, both sides of the backing may be coated with adhesive and a separate backing containing the release-coating (release-coated paper) may be applied to one or both sides of the adhesive-coated backing sides. A backing having both sides coated with adhesive is referred to herein as “double adhesive-coated backing”, and the side or sides which contain the release-coated paper is referred to herein as the “release-coated paper side.” Such release coatings make it possible for the tape to be unwound from the roll (i) without using excessive force (low release peel force) and (ii) without causing the adhesive to adhere to the release-coated backing side.
Release coatings should also have the following characteristics. The low affinity of the release coating toward the adhesive should be maintained over prolonged exposure to wide variations of temperature and humidity. The release coating should also strongly bond to the backing side so that it does not delaminate when aggressive adhesives are used. Lastly, it is desired that components of the release coating do not migrate into the adhesive, thereby deteriorating the properties of the adhesive.
Conventional release coatings have been based on various polymers and copolymers prepared from monomers, such as alkylacrylates and alkylmethacrylates, vinylacetate, vinylchloride and acrylonitrile and combinations thereof. These monomers, however, are relatively expensive, and some of these monomers also require special and more expensive handling because of their toxicity. In addition, such conventional coatings often fail when the rolled tape is aged under heat and humidity.
It is, therefore, an object of the present invention to provide release coating compositions that provide release coatings with acceptable peel force values after prolonged exposure to heat and humidity. It is another object of the present invention to provide release coating compositions that include relatively inexpensive polymer components. These and other objects of this invention will become apparent in light of the following disclosure.
SUMMARY OF THE INVENTION
The present invention is directed to a release coating composition that includes (a) from about 20% to about 55% by weight of a copolymer having a T
g
from 0° C. to about 75° C., and (b) from about 45% to about 80% by weight of solvent. The copolymer has from 0% to about 50% by weight of acrylonitrile monomer, and from about 50% to about 100% by weight of butadiene and styrene monomers. The copolymer can further include one or more stability enhancing monomers. In one embodiment, the release coating composition can further include a release promoting additive. The present invention is also directed to release coatings obtained from applying and drying the release coating composition.
In another embodiment, the present invention is directed to a release coating that includes (a) from about 80% to 100% by weight of a copolymer having a T
g
from 0° C. to about 75° C., and (b) from 0% to about 20% by weight of a release promoting additive. The copolymer has from about 0% to about 50% by weight of acrylonitrile monomer, and from about 50% to about 100% by weight of butadiene and styrene monomers.
In still another embodiment, the present invention is directed to an article of manufacture, which includes (a) a backing having an adhesive-coated backing side, and (b) a release coating applied to the other side of the backing of (a) or a separate backing. The release coating is situated so that it is in contact with the adhesive-coated backing side. The release coating has from about 80% to about 100% by weight of a copolymer having a T
g
from 0° C. to about 75° C., wherein the copolymer comprising from 0% to about 50% by weight of acrylonitrile monomer, and from about 50% to about 100% by weight of butadiene and styrene monomers. The release coating of this article of manufacture can further include a release promoting additive.
DETAILED DESCRIPTION OF THE INVENTION
It has been surprisingly found that release coatings prepared from polymers of butadiene, styrene and acrylonitrile (BSA polymer) provide excellent, low release force even after prolonged exposure to heat and humidity. Until now it has been believed by those skilled in the adhesive/coatings arts that polymers of styrene and butadiene could not be successfully modified to form effective release coatings. This belief results from the well accepted chemical phenomenon that like materials tend to have a high affinity towards like materials. Since pressure-sensitive adhesives are typically produced from hydrocarbon based polymers of styrene and butadiene, e.g., triblock styrene-butadiene-styrene polymers, it was believed that effective release coatings could not contain styrene and butadiene monomers.
In line with this belief, conventional release coatings have contained various polymers, prepared from monomers which chemically differ from styrene and butadiene, such as alkylacrylates and alkylmethacrylates, vinylacetate, vinylchloride, acrylonitrile, and combinations thereof. Although effective, these conventional polymers used in release coatings are relatively expensive in comparison to the BSA polymers used in the present invention, and some also require special and more expensive handling because of their toxicity.
A. Release Coating Compositions
The release coating compositions of the present invention include: (i) a polymer of butadiene, styrene, and acrylonitrile, and (ii) a solvent. Preferably, the release coating compositions of the present invention further include one or
Lonc Gregory J.
Spitzer Jan J.
BASF AG
Bissett Melanie
Seidleck James J.
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