Self-associating low adhesion backsize material

Details Self-associating low adhesion backsize material Self-associating low adhesion backsize material

1999-04-09

2002-03-05

Truong, Duc (Department: 1711)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

C428S343000, C428S349000, C428S3550RA

Reexamination Certificate

active

06352766

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a low adhesion backsize and release coatings of the type employed in connection with normally tacky and pressure-sensitive adhesive coated articles and more particularly to self-associating low adhesive backsize coatings.
BACKGROUND OF INVENTION
Normally tacky and pressure-sensitive adhesive (PSA) materials have been used for well over half a century. Products of this type, which take the form of tapes, labels, and other types of adhesive coated articles, must be protected from unintended adhesion to other surfaces. Hence, tapes are typically wound into a roll on their own backing and labels and sheets are typically laminated to a release sheet or one on top of another to prevent their accidental adhesion to other surfaces and also to prevent their contamination with air-borne dust and other contaminants. In order to allow the roll to be unwound without the undesirable transfer of adhesive to the tape backing, or to permit an adhesive-coated sheet to be removed from a stack of similarly coated sheets, it is customary to provide the tape backing or the surface of a successive sheet with a low adhesion backsize (LAB). Similarly, the release sheet or liner to which the adhesive coated article is typically laminated is supplied with a release coating to permit the easy removal of the liner from the coated article.
This LAB or release coating is 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 relatively stable with time. In recent years, as competition has expanded in the PSA industry, a need to differentiate product performance as well as more demanding product requirements has led to recognition of the importance of release level. D. Satas, Chapt. 23 “Release Coatings”, Handbook of Pressure Sensitive Adhesive Technology, Second Edition, D. Satas, ed., Van Nostrand Reinhold, 1989, defines seven distinct levels of release, ranging from “super low release” (0.15-0.30 N/dm) to “very tight release” (20-80 N/dm). In many circumstances it is important for the LAB to possess other properties besides functioning as a release agent. For example, the release coating on masking tape must possess good solvent resistance in addition to providing a surface to which paint can adhere.
Release coatings and LABs are typically applied to substrates at coating weights around 1 g/m
2
. In order to obtain such thin coatings, dilute solutions (2 to 5% solids) of the coating compositions in organic solvents have traditionally been used. Recent efforts have been directed to delivering such coatings at high or 100% solids or from aqueous media, thus reducing the environmentally damaging hydrocarbon emissions, conserving precious natural resources, and lowering economic cost. Despite the numerous efforts to produce release coatings at high or 100% solids or from aqueous media, such coatings have still required a complex combination of components and involved polymerization processes in order to insure adequate release levels, as well as minimizing release coating transfer.
For example, a release coating is described comprising a hydrocolloid stabilized aqueous emulsion of a crosslinkable film forming vinyl polymer having a glass transition temperature of from 0° to 60° C. and from 0.5 to 20% by weight on emulsion polymer solids of a release promoting compound including silicone copolyols, hydrocarbon or fluorocarbon Werner complexes, or organofunctional siloxanes. Unfortunately, this coating requires cross-linking.
Another example discloses a substrate coated with a release coating composition consisting essentially of polyvinyl alcohol, a migratable release-promoting agent, a water-soluble salt of a coordinating metal, and a water soluble boron compound. The release-promoting agent is functionally defined as a surfactant that gives a release value less than about 162.5 grams per centimeter for masking tape when formulated at 5% loading into polyvinyl alcohol. Not only does this example require cross-linking, but uses salts of a coordinating metal, which can be toxic.
One conventional method improves the releasability of a backing layer by applying a mixture comprising a polymer, preferably having acid functionality, and an aqueous solution or dispersion of an organic compound having at least one fatty acid ester and at least one quaternary amine, such as lecithin. However, the use of an ionic interaction to develop anchorage to a substrate lends itself to moisture sensitivity.
Yet another aqueous release coating for pressure sensitive adhesive tapes attempts to provide a release coating comprising a latex film forming polymeric material, a release promoting additive, and a microdispersed polyamide resin having a softening point greater than 70° C. As described, preferred release promoting additives include N-alkyl sulfosuccinamates, alkyl sulfosuccinates, alkylaryl polyalkylene oxides, salts of long chain alkyl sulfates, and amine polyglycol condensates. It has been observed that initially there is transfer of the release coating to the adhesive and such observation is supported by heat aging data that reveals loss of tack (using a rolling ball test).
Another example of an aqueous based release coating composition suitable for a repositionable adhesive that comprises about 10 to about 80 parts by wet weight of a sulfosuccinamate surfactant and about 20 to about 90 parts by wet weight of an acrylic copolymer. These compositions appear to rely solely on ionic interactions, which tend to be sensitive to humidity.
Therefore, what is needed is an aqueous release coating composition that can be prepared by blending commercially available materials, hence does not require a polymerization process; that can provide a wide range of release levels for both permanent and repositionable pressure sensitive adhesives with the level of release determined by the amount and nature of the components; that does not require post-coating crosslinking reactions to provide stable release performance and minimal loss in readhesion values; and that is not sensitive to humid environments. A further need is a release coating prepared from water based materials that does not require organic cosolvents to provide acceptable release performance on coating and drying. A still further need is a release coating delivered from water with the above attributes that is capable of being written on with water based pens and which securely anchors paint and ink.
SUMMARY OF THE INVENTION
Briefly, in one aspect of the present invention, a low adhesion backsize coating is provided comprising:
(1) 25% to 75% by weight on a solids basis of a functional polymer wherein the functional polymer has
(a) a functional moiety,
(b) is non-tacky at room temperature,
(c) is water dispersible or water-based or a latex emulsion,
(d) optionally, may be a copolymer,
(e) optionally, may be crosslinked and
(2) 75% to 25% by weight on a solids basis of a release-promoting additive having a molecular weight of 10,000 or less, wherein the release-promoting additive is
(a) a bifunctional material, wherein such bifunctional material has
(i) a release moiety at one end, and
(ii) an anchoring moiety at the other end has a complementary function to the functional moiety of the functional polymer, and
(b) is water dispersible or water miscible.
The functional polymer in combination with the release-promoting additive advantageously minimizes surface energy and cohesive failure. The functionality of the functional polymer is selected in such way as to promote ionic interactions, acid-base interactions, and/or hydrogen bonding. It is preferable that the combination of the functional polymer and the release promoting additive work in such a fashion as to provide more than one interaction per molecule of each component, for example multiple hydrogen bonds or acid-base interactions. Although some covalent bonding may be tolerated between the functional polymer and the release promo

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