Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
1999-10-08
2003-04-01
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C106S287110, C106S287130, C428S447000, C428S500000, C525S100000, C525S101000, C525S431000, C525S446000, C525S464000
Reexamination Certificate
active
06541109
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to release coatings and coatable formulations used to form release coatings. More specifically, the present invention relates to release coatings and corresponding, coatable formulations incorporating a silicone-vinyl copolymer and a second polymer, wherein the combination provides the release coating with water compatibility, ink receptivity, stability, and the improved ability to preserve and maintain characteristics (e.g., readhesion characteristics in the case of adhesive tape) of the surfaces being protected by the coating and the like.
BACKGROUND OF THE INVENTION
Many different kinds of products are backed with surfaces formed from pressure sensitive adhesives so that such products can be permanently or releasably attached to other items. There are numerous embodiments of these adhesive-backed products, including bandages, adhesive tapes (masking tape, gaffer's tape, transfer tape, Scotch® brand tape, duct tape, electrical tape, packaging tape, construction tape, medical tape, cloth tape, and the like), floor tiles, labels, mounting brackets, transdermal drug delivery devices, electrode pads for attaching medical devices to patients, retroreflectors, signage, pathway and roadway markings, vehicle emblems, and the like.
Prior to use, the adhesive surfaces of such products must be protected against the environment and against accidental adhesion to other items. Accordingly, adhesive-backed surfaces of these products typically are stored on a release coating that can be easily separated from the adhesive surface when desired. For example, labels are often stored on a sheet-shaped release liner from which the labels can be peeled when ready to be used. Likewise, a release surface is formed on the backing of adhesive tape rolls so that the tape can be unwound and removed from the roll when desired.
Release coatings are expected to reproducibly provide an appropriate level of release from the adhesive of interest, to not deleteriously affect the adhesive, and to be resistant to aging so that the release level remains stable over time. One way of assessing the release qualities of a particular release coating involves comparing the immediate and aged readhesion characteristics of the adhesive surface being protected by the coating. Desirably, the aged readhesion values and the immediate readhesion value are substantially the same. A large change in peel strength upon aging indicates a poorly performing release coating. To evaluate immediate readhesion, an adhesive backed sample is adhered to the release coating. The sample is then immediately peeled off the release coating and applied to clean glass. The force required to peel the sample from the glass is measured. To evaluate aged readhesion, the sample is left on the coating for an extended period, e.g., three days, before being peeled off the coating and tested for peel strength from the clean glass.
Another way of assessing the quality of a release coating involves comparing the immediate peel force and the aged peel force of the protected adhesive surface. To evaluate immediate peel force, a test tape sample is positioned on a coating and immediately peeled off. The force to accomplish this is measured. To evaluate the aged peel force, the test tape sample is left on the release coating for an extended period, e.g., three days. As was the case with the readhesion test, the aged and immediate peel force measurements are desirable substantially the same. A large change in peel force upon aging indicates a poorly performing release coating.
In addition to providing stable, appropriate release over time, release coatings often must satisfy other performance criteria as well. In many applications, a release coating must be solvent resistant, receptive to marking with pencil, ink, and/or paint, and characterized by an appropriate level of gloss or even low gloss. For example, gloss reducing agents are often used to lower gloss in products such as gaffer's tape. However, such agents must be compatible with the formulations from which release coatings are formed. This is particularly challenging for formulations in the form of water-based solutions, dispersions, latex materials, and the like. Such agents also should not unduly compromise the performance of the release coating.
One common approach for forming release coatings involves dissolving or dispersing, as the case may be, polymer materials having good release properties in a suitable solvent. The solution or dispersion is then coated onto a suitable substrate and dried. The resultant coating can then be used to releasably store the desired adhesive-backed item(s). Many polymeric materials with good, inherent release characteristics have been used to form such release coatings. For example, silicone-vinyl copolymers have excellent release characteristics, and release liners incorporating silicone-vinyl copolymers have been described in U.S. Pat. Nos. 5,202,190; 5,200,436; 5,154,962; 5,057,619; 5,089,336; and 5,032,460; as well as in documents cited in the background sections of these patents. Silicone-vinyl copolymers generally include at least one silicone block and at least one vinyl copolymeric block. These copolymers offer many advantages. The silicone blocks form surfaces with good release quality while the vinyl copolymeric blocks help to anchor the release coating to an underlying substrate. The level of release can be easily adjusted by varying the silicone content of the copolymer. The use of more expensive, 100% silicone polymers is avoided. The vinyl copolymeric blocks independently of the silicone blocks can be formed with a wide variety of functionality to enhance performance characteristics without unduly affecting the release quality of the silicone blocks.
Unfortunately, the use of silicone-vinyl copolymers in release coatings does have some drawbacks. When such release coatings are used to protect aggressive adhesives, the integrity of such adhesives can be compromised in some instances due to transfer of the silicone-vinyl copolymer to the adhesive.
The manufacture of release coatings from water-based formulations containing silicone vinyl copolymers has been described, for example, in U.S. Pat. Nos. 5,032,460 and 5,089,336. Water-based formulations advantageously eliminate the environmental concerns, flammability, handling issues, and expense associated with nonaqueous solvents. However, notwithstanding the promise offered by such water-based formulations, obtaining high performance release coatings from water-based formulations has remained a challenge, particularly when the formulation incorporates one or more other polymers blended with the silicone-vinyl copolymer. Often, the blend provides release coating performance that is no better than that provided by the use of a silicone-vinyl copolymer by itself. In some aspects, the release coating performance of blends of the silicone-vinyl copolymer with one or more other polymers has even been worse.
What is needed, therefore, is a way to incorporate silicone-vinyl copolymers into release coatings in a manner effective to maintain the integrity of the pressure sensitive adhesive to be protected by the coating. It would also be desirable to form the coatings from water-based formulations.
SUMMARY OF THE INVENTION
The present invention provides release coating formulations and release coatings derived therefrom that incorporate a blend of a silicone vinyl copolymer and a second polymer for which the release qualities are extremely stable over time. This indicates that the release coating does not unduly compromise the integrity of the pressure sensitive adhesive that is being protected by the release coating. For instance, readhesion force values and peel force values obtained in tests involving the release coatings of the present invention remain substantially stable, even after aging. Significantly, preferred embodiments of the silicone-vinyl copolymer and the second polymer are not only very compatible with each other, but are also very compa
Bloemendal Elda T. G.
Kumar Ramesh C.
Schmidt Bruce C.
3M Innovative Properties Company
Dawson Robert
Fagan Lisa
Zimmer Marc S
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