Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-06-20
2002-07-16
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550EN, C428S3550AC, C428S041300, C428S041500, C428S041800, C524S800000, C524S804000, C524S833000, C516S127000
Reexamination Certificate
active
06420023
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to pressure sensitive adhesives (PSA's) based on aqueous latex emulsions and processes for the preparation of such adhesives.
Substrates (such as, for example, vinyl banners, vinyl binders, and vinyl containers) and face stocks (such as, for example, vinyl films and vinyl foams) contain plasticizers that make such products more pliable and less brittle. Often, these products are bonded with an adhesive (e.g., PSA's) onto similar substrates, metals, wood, and other materials. Unfortunately, the plasticizers in the substrates can migrate into the adhesive causing a loss of peel strength eventually leading to a product failure (residue, loss of peel strength). In particular, plasticizers used in the manufacture of vinyl foams (e.g., dioctylphthalate or DOP and dinonylphthalate or DINP) can migrate into a bonding PSA causing the adhesive peel strength to decrease, which eventually leads to product failure. In the case of automotive foams, manufacturers' specifications require minimum peel values over a range of environmental conditions for their PSA coated foam products. Traditional emulsion and solution PSA's fail to meet these specifications. Typical adhesives absorb the migrating plasticizers, which results in a loss of peel strength ending in adhesion failure.
The market would like a PSA, which can meet the automotive specifications and which would be resistant to plasticizer migration, thus extending the life of a product. The market also would prefer an emulsion adhesive having plasticizer resistance due to environmental and cost constraints, because emulsions are typically non-hazardous and less expensive than other technologies (e.g., solution, or UV prepared resinous adhesives). With an adhesive that has plasticizer resistant properties, the market could produce price competitive products (e.g., foam tapes, vinyl banner graphics, vinyl labels, and comfort mats), which would have extended usefulness and durability due to their resistance to plasticizer migration.
BRIEF SUMMARY OF THE INVENTION
An aqueous, pressure sensitive adhesive (PSA) resistant to plasticizer is made from an aqueous latex emulsion having an average particle size diameter of not substantially above about 100 nm and made from a mixture of ethylenically-unsaturated monomers and oligomers that include one or more of N-(iso-butoxymethyl) acrylamide, N-(n-butoxymethyl) acrylamide, and N-methylol acrylamide; and emulsified in the presence of an emulsifier consisting essentially of:
In structure I, R
1
is an alkyl, alkenyl, or aralkyl group containing between 6 and 18 carbon atoms, R
2
is H or R
1
, R
3
is H or a propenyl group; A is an alkylene group of 2 to 4 carbon atoms, n is an integer ranging from 1 to 200, X is H or SO
3
M, where M is an alkali metal, an ammonium ion, or an alkanolamine cation. Preferably, the ethylenically-unsaturated monomers includes 2-ethylhexyl acrylate, while 1,3-butanediol dimethacrylate can be added to increase cross-link density. Preferably, the emulsifier is:
The preferred aqueous latex emulsion is prepared from a monomer mixture consisting essentially of at least one alkylacrylate having at least 4 carbon atoms in the alkyl chain, at least one ethylenically unsaturated carboxylic acid or its corresponding anhydride, at least one styrenic monomer, and N-(iso-butoxymethyl) acrylamide, and has a mean particle size diameter of less than or equal to about 100 nm.
DETAILED DESCRIPTION OF THE INVENTION
The inventive PSA is designed to maintain peel performance when the PSA in use is subjected to plasticizers that migrate from the surfaces of substrates and face stocks. The inventive PSA is based on a polymer or resin, which is polymerized with special additives and a selection of monomers to give the final adhesive resistance to plasticizers, water, and other solvents. The inventive PSA further was designed using a polymerizable surfactant, which is incorporated into the polymer. Such surfactant incorporation into the cured polymer contributes to the reduction of the adverse effects (e.g., loss of peel, shear, and tack) caused by migration of and interaction with plasticizers from the substrate being adhered by such PSA.
PSA's also need to maintain their adhesion at elevated temperatures (typically up to about 80° C.). These elevated temperatures also increase the rate at which plasticizers migrate from the substrate or face into the PSA layer. These elevated temperatures cause prior art PSA's to fail. The inventive PSA, however, is formulated using specialty monomers (e.g., n-isobutoxymethyl acrylamide or IBMA, and 1,3-butanediol dimethacrylate or 1,3 BDDMA) to increase the cross-linking density of the PSA polymer and, therefore, the heat aged stability of the PSA.
The inventive PSA is significantly better than PSA's currently available, whether based on emulsion, solution, and/or UV curable technologies. The inventive PSA has excellent resistance to plasticizers. Based on the data reported herein, only small decreases (on the order of <25% of initial values) in peel values are observed when the adhesive is aged at 80° C. for 10 days. Currently available PSA's typically lose about 80%-90% of their initial values. All other aging and cycle testing typically shows no loss in peel resulting in foam destruction for the inventive PSA, whereas other adhesives usually display a loss of around 50%-90% of initial peel values.
Referring now to the preparation of the PSA emulsion polymer, the polymerization is carried out in the presence of a reactive emulsifier or surfactant as described below. A thermal free-radical initiator system (e.g., persulfate, peroxide, or azo compound initiators) is used in an amount sufficient to promote free radical polymerization of the monomers. A redox type free-radical cure can be used advantageously to finish off the polymerization step or can be used in place of the thermal system in preparing the PSA emulsion polymer. Once the polymerization is complete it may be desirable to adjust the pH of the latex emulsion in order to enhance its stability. Other ingredients commonly used in the preparation of aqueous latex emulsions such as buffering agents, chain transfer agents, and the like may be present. General latex technology is discussed in, Kirk-Othmer,
Encyclopedia of Technology, [
4thEd.], vol.15, p.51-65; which is hereby incorporated by reference. In addition to the aqueous latex emulsion, the pressure sensitive adhesive may also contain additional components such as, biocides, wetting agents, defoamers, tackifiers, rheology modifiers, etc.
The reactive surfactant or emulsifier consists essentially of a compound represented by the following general structure:
In structure I, R
1
is an alkyl, alkenyl, or aralkyl group containing between 6 and 18 carbon atoms, R
2
is H or R
1
, R
3
is H or a propenyl group; A is an alkylene group of 2 to 4 carbon atoms, n is an integer ranging from 1 to 200, X is H or SO
3
M, where M is an alkali metal, an ammonium ion, or an alkanolamine cation. This reactive emulsifier can be made in accordance with the procedure described in U.S. Pat. No. 5,332,854, the disclosure of which is expressly incorporated herein by reference.
Preferably, the emulsifier has the following general structure:
This preferred emulsifier is commercially available from Montello (Tulsa, OK) as Hitenol BC-10, poly(oxy-1,2-ethanediyl),&agr;-sulfo-&ohgr;-[4-nonyl-2-(1 -propenyl) phenyoxy]-branched ammonium salts; yellowish brownish viscous liquid, 97.0 % actives, combined sulfuric acid content of 8.70-9.70%, pH of 6.5-8.5 (1% aqueous solution). Typically, less than 4 wt-%, and desirably less than 1 wt-%, of the reactive surfactant based on the total weight of the latex (solids basis), is used.
The reactive emulsifier can be employed with a variety of latex emulsions for formulating the novel PSA's. The monomers used to prepare such aqueous lattices include
Harvey Raymond Scott
Richards Harvey Joseph
Rowley Tony Kyle
Ashland Chemical Company
Dawson Robert
Keehan Christopher M.
Mueller and Smith LPA
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