Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-09-20
2004-11-23
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S259000, C525S302000, C525S309000, C525S310000, C524S850000
Reexamination Certificate
active
06822052
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed generally to toughening copolymer additives such as alkene-(meth)acrylate ester copolymer additives which when incorporated into adhesive compositions, such as cyanoacrylate adhesive compositions, increase the toughness of the adhesive upon cure.
BRIEF DESCRIPTION OF RELATED TECHNOLOGY
Cyanoacrylates are highly reactive monomers that undergo rapid anionic polymerization reactions initiated by minute amounts of basic or nucleophillic species. It is generally known that small amounts of acidic or electrophilic species will retard or inhibit this reaction. As a consequence of their extreme anionic reactivity, commercial formulations of cyanoacrylate monomers usually contain small amounts of acidic stabilizers that are intended to be sufficient to ensure a reasonable shelf-life for the product, but not so excessive as to render the product inactive when it is applied to the surface of a substrate. If too little stabilizer is added, the product will be prone to premature polymerization and if too much is added it will be less active and function less effectively as an adhesive. The commercially available ethylene/methyl acrylate toughening additives, are also problematic in this respect because they often contain small amounts of materials, e.g. acids, that result in the over- or under-stabilization of the total adhesive composition.
While cyanoacrylate adhesives are useful for many applications, they inherently lack sufficient toughness and are often too brittle for certain applications. Attempts have been made to eliminate post-cure embrittlement, through the addition of various types of additives, and particularly toughening additives, which generally have elastomeric properties. For example, copolymers formed from the copolymerization of acrylate esters with olefins have been added as modifiers to cyanoacrylate adhesive compositions to impart toughening properties and lower brittleness of the cured product. In particular, ethylene-methyl acrylate copolymers are sold commercially by DuPont under the trademark Vamac and have been used as toughening additives for cyanoacrylate adhesives.
Loctite Corporation's U.S. Pat. No. 4,440,910 discloses a cyanoacrylate adhesive composition which contains a monomeric ester of 2-cyanoacrylic acid and about 0.5% to about 20% by weight of an elastomeric polymer selected from the group consisting of elastomeric copolymers of a lower alkene monomer and (i) acrylic acid esters, (ii) methacrylic acid esters or (iii) vinyl acetate. Acrylic rubbers disclosed in this patent include ethylene-methyl acrylates under the trade name Vamac N-123 and Vamac B-124. These rubbers, as well as other Vamac products, for example, Vamac-G and Vamac-D, either contain free carboxylic acid functionalities and/or impurities which cause a slowing of the cure rate of cyanoacrylate adhesive compositions or a decrease in shelf-life when incorporated therein.
It is generally accepted in the reactive adhesive art that increased toughness and lower brittleness is achievable if toughening additives can be solvated by the uncured reactive monomer and subsequently undergo a phase separation from the adhesive matrix during the curing process.. The ability of these additives to be solvated by the cyanoacrylate monomer results in a demonstrable phase separation of the additive during polymerization of the cyanoacrylate monomer. Phase separation is generally accepted as a necessary condition for increased adhesive toughness. One problem with some commercially available ethylene-methyl acrylate copolymers is that they are only partially solvated by cyanoacrylate monomers. Thus, when cyanoacrylate adhesives which incorporate these commercially available toughening additives are cured, polymerization-induced phase separation, and hence toughening, is not optimized.
Compatibility of the toughening additive with the cyanoacrylate monomer is an important feature. For example, as noted above the toughening agent itself should not be so acidic that it significantly slows down the cure rate, and not so basic or nucleophilic that it cures prematurely. Known commercially available ethylene-acrylate copolymers are also problematic in this respect because they often contain trace amounts of carboxylic functional groups, which are known to cause a slowing of the cure rate of the adhesive In addition, these functionalities contribute to reduced activity upon storage.
Commercially available toughening copolymers used in cyanoacrylate adhesive formulations are generally prepared from olefin monomers having three carbons or less. In general, for formation of the copolymers, olefins with greater than three carbons are difficult to polymerize with alkyl acrylate esters by free radical polymerization due to their low reactivity toward free radicals and their increased tendency to undergo a chain transfer rather than a propagation reaction.
U.S. Pat. No. 3,183,217 discloses a process for copolymerizing an alkene with a (meth)acrylic acid ester. The '217 patent discloses higher alkenes such as 1-hexene, as well as lower alkenes, as being useful materials for copolymerization with (meth)acrylic acid esters. This patent discloses admixing the alkenes with (meth)acrylic acid esters with equimolar amounts of a Lewis acid per mole of the polar vinyl monomer, i.e., (meth)acrylic acid ester, and copolymerizing the resulting admixture in the presence of a free radical initiator, under anhydrous conditions and at a temperature of about −78° to about 175° C. Using this method and the ratio of reactants disclosed therein, however, limits the amount of olefin which can be incorporated into the final copolymer product.
It is generally desired to have higher levels of olefin relative to (meth)acrylic acid ester incorporated into the copolymer product in order to avoid an unwanted plasticization of the cured adhesive. If the olefin incorporated into the copolymer product is too low, a plasticization rather than toughening of the cured adhesive occurs, which would be manifested by an incomplete or absence of phase separation of the copolymer from the adhesive matrix during cure. Moreover, the optimal amount of olefin for incorporation into the copolymer for adhesive toughening may change depending on the cyanoacrylate monomer used in the adhesive composition.
It would therefore be desirable to have a means of varying the olefin content in the olefin/(meth)acrylate ester copolymers in accordance with the cyanoacrylate monomer chosen in order to control the balance between toughening and plasticization. Thus, there is a need for a process of polymerization of an alkene (olefin) with a (meth)acrylate ester wherein the reaction conditions can be varied in order to increase the olefin content and vary the molecular weight of the resulting copolymer to achieve adhesive toughening.
It would also be beneficial to achieve toughening without the reactivity and stabilization difficulties associated with commercial toughening copolymer additives. Therefore, there is a need for curable adhesives containing toughening copolymer additives with improved solubility in cyanoacrylate monomers, as well as copolymers which do not contain trace amounts of interfering functional groups, additives, or stabilizers that can shorten the shelf life of the adhesive monomer or reduce its activity.
It would therefore be desirable to provide toughening copolymers which have been synthesized de novo from olefin and (meth)acrylate ester monomers by a method wherein the resulting copolymer products are free of interfering functional groups, additives or stabilizers. Moreover, it would be desirable to provide a method for modifying existing commercial olefin (meth)acrylate and olefin/alkenoic acid copolymers in order to eliminate acidic functional groups which are known to affect the cure rate of cyanoacrylate monomers, and by so doing make them suitable for use as toughening additives of cyanoacrylate adhesives.
SUMMARY OF THE INVENTION
The present invention provides new copolymer tou
Morrill Susanne
Woods John
Asinovsky Olga
Bauman Steven C.
Henkel Corporation
Seidleck James J.
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