Card – picture – or sign exhibiting – Check – label – or tag – Adhesive-backed label
Reexamination Certificate
1999-09-22
2001-09-25
Dawson, Robert (Department: 1712)
Card, picture, or sign exhibiting
Check, label, or tag
Adhesive-backed label
C428S483000, C428S511000, C428S517000
Reexamination Certificate
active
06293037
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to unique pressure sensitive adhesives and self-adhesive postage stamps made with these adhesives.
BACKGROUND OF THE INVENTION
Pressure-sensitive adhesives (PSAs) are now widely used in many consumer products, including labels, tapes, and similar constructions. Both acrylic and rubber-based PSAs are known. Many PSAs adhere well to only certain types of substrates and do not adhere or perform well when applied to other substrates. For example, Kraton® rubber-based hot-melt PSAs adhere extremely well to low-energy surfaces like polyolefins, but do not adhere as well to paper or corrugated board. Many acrylic-based PSAs exhibit good adhesion to paper, but do not adhere well to low-energy, non-polar surfaces. Although a tackifier can be added to acrylic adhesives to improve their adhesion to non-polar substrates, often this results in a lowering of shear, convertibility, and other performance characteristics.
As PSAs continue to be used in a growing number of applications, a need has emerged for a truly “broad spectrum” PSA that performs well on a variety of surfaces and substrates. Such an adhesive would be useful in both the prime label business (e.g., labels for consumer products—bottles, cans, etc.) and the information processing (IP) business (e.g., EDP, laser printer labels, price marking labels, inventory labels, etc.). A broad spectrum PSA would also be useful in self-adhesive postage stamps and in other applications.
Since their introduction a few years ago, self-adhesive postage stamps have enjoyed tremendous popularity. In a typical construction, a sheetlet of self-adhesive postage stamps includes a laminate of an array of postage stamps made of a die-cut face stock, printed on one side with postage indicia, adhered to a release liner by a pressure-sensitive adhesive (PSA). U.S. Pat. No. 5,296,279 (Birnbaum et al.), assigned to Avery Dennison Corporation, is representative. ATM-dispensable, self-adhesive postage stamps are also known, and are disclosed in U.S. Pat. No. 5,503,436 (Alpaugh et al.), also assigned to Avery Dennison Corporation. Both patents are incorporated herein by reference.
The United States Postal Service (USPS) sets standards for United States-issued postage stamps. Government specification USPS-P-1238C (Jan. 24, 1996), which is attached hereto as Appendix 1 and incorporated by reference herein, identifies and describes certain “required,” “target,” and to-be-“monitored” properties of face stocks, adhesive layers (PSAs) and release liner backings (as well as linerless release coatings) to be used in self-adhesive postage stamps.
An important property of self-adhesive postage stamps is the ability to form a permanent adhesive bond, after a short dwell time, to a variety of substrates, including woven paper, regular Kraft, corrugated board, polyethylene based envelope stock (e.g., Tyvek®, sold by DuPont de Nemours, E.I., Co. of Wilmington Del.), and other materials commonly used in envelopes and parcels. To deter theft and re-use of stamps, it is desirable that the adhesive leave a telltale fiber tear mark on the paper envelope or package if attempts are made to remove the stamp.
SUMMARY OF THE INVENTION
According to the present invention, there are provided pressure-sensitive adhesives that exhibit excellent adhesion to a variety of surfaces, including paper; non-polar, low-energy surfaces such as polyethylene; and difficult-to-bond-to surfaces such as corrugated board. In one embodiment, the inherently tacky PSA comprises an acrylic emulsion polymer formed from (a) a plurality of monomers, comprising, based on the total weight of monomers, (i) about 9 to 40 percent by weight of an ethylenically unsaturated monomer containing an isobornyl group, such as isobornyl acrylate, and (ii) about 50 to 91 percent by weight of one or more alkyl acrylates, the alkyl group of each alkyl acrylate having about 4 to 8 carbon atoms; (b) at least one emulsifier; and (c) at least one polymerization initiator. Minor amounts of additional monomers may also be included in the monomer mixture. Alternatively, the polymer is prepared by bulk or by solvent polymerization.
When dried and laminated to a facestock, such as paper or a polymeric material, the polymers exhibit pressure-sensitive adhesive behavior and adhere well to paper, corrugated board, and low-energy surfaces. In particular, when applied to a low-energy surface, such as polyethylene, adhesive constructions prepared in accordance with the present invention exhibit 180° peel adhesion to polyethylene of at least 3.5 N/in—preferably at least 5.0 N/in; more preferably at least 8.0 N/in. When applied to a corrugated board substrate, the adhesive constructions exhibit a corrugated fiber tear of at least about 90%—more preferably at least about 95%. The adhesives are useful for a variety of label applications, including self-adhesive postage stamps and other PSA constructions.
In one embodiment, the PSAs are made by forming a synthetic latex by emulsion polymerization of the plurality of monomers, in the presence of at least one emulsifier and at least one polymerization initiator. Preferably, the initiators are added to the reaction mixture in a stepped, or ramped feed, beginning slowly and then doubling the rate of addition. In another embodiment, an acrylic PSA is made by solvent polymerization using, for example, ethyl acetate or any suitable organic solvent. In still another embodiment, a PSA is made by bulk polymerization.
The present invention also provides self-adhesive postage stamps made With these unique PSAs. Postage stamp constructions are conveniently prepared by coating or otherwise applying the PSA to a protective release liner and laminating the coated release liner to a suitable face stock having opposed first and second faces, at least one of which is imprinted with—or imprintable with—postage indicia. Alternatively, the PSA is applied directly to a face stock and then protected with a release liner. When applied to an envelope substrate, such as a woven paper substrate, the self-adhesive postage stamp constructions leave a fiber tear mark on the envelope even after only very short dwell times (as little as 5 minutes or less).
DETAILED DESCRIPTION
The present invention provides pressure-sensitive adhesives (PSAs) that exhibit good adhesion to a variety of substrates, including paper, corrugated board, and low-energy surfaces, such as polyethylene. In one embodiment, a PSA comprises an inherently tacky polymer formed by emulsion polymerization of (a) a plurality of monomers comprising, based on the total weight of monomers, (i) about 9 to 40 percent by weight of isobomyl acrylate and (ii) about 50 to 91 percent by weight of one or more alkyl acrylates, the alkyl group of each alkyl acrylate having about 4 to 8 carbon atoms; (b) at least one emulsifier; and (c) at least one polymerization initiator. In an alternative embodiment, an inherently tacky polymer is formed by solvent (solution) polymerization, using an organic solvent (for example, ethyl acetate) and no emulsifier. In another embodiment, an adhesive polymer is made by bulk polymerization.
Isobomyl acrylate (IBOA) is a high boiling, low odor, low toxicity, ethylenically unsaturated monomer containing an isobomyl group, a large (C
10
H
17
) cycloalkyl group that is believed to have a profound effect on the adhesive and rheologic properties of the resulting PSA. IBOA forms a homopolymer having a high glass transition temperature (T
g
=94° C.). Preferred PSAs are made using between about 20 and 30% by weight of IBOA, based on the total weight of monomers.
Useful alkyl acrylates having from 4 to 8 carbon atoms in the alkyl group include, but are not limited to, butyl acrylate (BA), ethylhexyl acrylate (EHA), and isooctyl acrylate (IOA).
Preferably, the plurality of monomers further comprises a minor amount of one or more additional monomers, the presence of which yields a PSA having improved adhesive, processing, and/or converting properties. Nonlimiting examples include polar monomers, such as
Alpaugh Kathleen M.
Koch Carol A.
Spada Lon T.
Avery Dennison Corporation
Aylward D.
Christie Parker & Hale LLP
Dawson Robert
LandOfFree
Pressure-sensitive adhesives and self-adhesive postage... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pressure-sensitive adhesives and self-adhesive postage..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressure-sensitive adhesives and self-adhesive postage... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2437740