Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-05-09
2002-03-19
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C524S547000, C524S558000, C524S560000, C524S561000, C524S577000, C524S817000, C524S833000, C526S318000, C526S318400, C526S318450, C526S911000, C428S3550AC
Reexamination Certificate
active
06359092
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
None
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to pressure sensitive adhesives based on aqueous latex emulsions and processes for the preparation of the adhesives. Pressure sensitive adhesives prepared according to the present invention have mean particle diameter sizes of less than or equal to about 100 nm and narrow particle size distributions. These pressure sensitive adhesives are particularly suitable for applications that require that the pressure sensitive adhesive maintain adhesion between the substrate and facestock when subjected to hot water spraying or immersion. In addition, the adhesives exhibit resistance to water-whitening or “blush”, often determined by a cold or ice water immersion test. Hot water adhesion is required in applications such as bottle labels where the bottles are subjected to hot water spraying in washing operations. In general, resistance to water-whitening is desirable anywhere a pressure sensitive adhesive with transparent facestock or substrate is subjected to water or high humidity. Examples include labels on the sides of trucks, signs, and bottles.
Methods of providing water-whitening resistant latex emulsions for use in pressure sensitive adhesives are disclosed in the art. U.S. Pat. Nos. 5,286,843 and 5,536,811 disclose a process for improving the water-whitening resistance of pressure sensitive adhesives containing an aqueous latex emulsion and water soluble ions by removing the water soluble ions and adjusting the pH to at least about 6. The patents disclose that water-soluble ions may be removed by a number of techniques including centrifugation, dialysis, precipitation and deionization with ion exchange resins. The preferred method of removing the water-soluble ions is to contact the aqueous latex emulsion, the formulated pressure sensitive adhesive containing the aqueous emulsion or both with an ion exchange resin.
International Application WO 97/11996 discloses a process for preparing hot water-whitening resistant latex emulsions useful in pressure sensitive adhesive compositions. The process involves copolymerizing a monomer mixture containing at least one alkyl acrylate ester of an alcohol containing at least 4 carbon atoms, at least one polar co-monomer and at least one partially soluble co-monomer present in an amount of at least about 7 weight-%. Polymerization is carried out in the presence of at least one nonionic surfactant containing at least 8 moles of ethylene oxide and at least one anionic surfactant containing up to about 10 moles of ethylene oxide. The polymerization product is neutralized to produce an emulsion having a pH greater than 7 and containing particles having a volume average particle size diameter up to about 165 nm. An electrolyte may be added subsequent to polymerization to stabilize opacity of a film cast from the emulsion.
International Application WO 98/44064 discloses inherently tacky pressure sensitive adhesives prepared by emulsion polymerization of at least one monomer mixture comprising; at least one alkyl acrylate, the alkyl group of which has from 4 to 12 carbon atoms; at least one unsaturated carboxylic acid containing from about 3 to 5 carbon atoms and one styrenic monomer; wherein the particles have a mean diameter of 300 nm or less. The publication discloses a single stage preparation of aqueous acrylic emulsions in examples 4D, 4E, 4F, 4G and 4H with average particle sizes ranging from 245 nm to 139 nm. Each of the examples discloses the use of silane crosslinkers to improve blush resistance. The publication discloses a preferred method of preparation, which yields adhesives resistant to water-whitening and involves a sequential polymerization of a first and second monomer charge. None of the above references disclose a pressure sensitive adhesive that maintains adhesion in hot water environments and is resistant to water-whitening.
BRIEF SUMMARY OF THE INVENTION
An aqueous, blush-retardant pressure sensitive adhesive (PSA) is made from an aqueous latex emulsion having an average particle size diameter of not substantially above about 100 nm 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, and M is an alkali metal, an ammonium ion, or an alkanolamine cation. 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, and at least one styrenic monomer, and has a mean particle size diameter of less than or equal to about 100 nm.
Pressure sensitive adhesives of the present invention are useful in clear label applications, marking films, etc. The inventive pressure sensitive adhesives maintain adhesion and transparency (water-whitening resistance) when immersed in boiling water for 10 minutes. The inventive PSA's also possess good wet-out.
DETAILED DESCRIPTION OF THE INVENTION
The polymerization is carried out in the presence of a reactive emulsifier or surfactant as described below. A redox type free radical initiator system is used in an amount sufficient to promote free radical polymerization of the monomers. 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, [
4th Ed.], 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, 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, and 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, Okla.) as Hitenol BC-10, poly(oxy-1,2-ethanediyl),&agr;-sulfo-&ohgr;-[4-nonyl-2-(1-propenyl)phenyoxyl]-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). The pendant double bond is reactive in the latex emulsion preparation if a slightly higher temperature is used, higher amounts of redox catalyst are employed, and a hydrophilic monomer is included in the monomer mix. Typically, less than 4 wt-% of the reactive surfactant based on the total weight of the latex, is used.
While use of a reactive emulsifier can be employed with a variety of latex emulsions for formulating the novel PSA's, a preferred latex emulsion is disclosed in commonly-assigned application Ser. No. 09/290,159, filed on Apr. 12, 1999. The monomers used to prepare such aqueous lattices include alkyl acrylates, ethylenically unsaturated carboxylic acids and their corresponding anhydrides and styrenic monomers.
Alkyl acrylates are alkyl esters of acrylic or methacrylic acid having at least 4 carbon atoms in the alkyl portion of the mol
Harvey Raymond Scott
Richard Harvey Joseph
Ashland Chemical, Inc.
Egwin Kelechi C.
Mueller and Smith LPA
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