Metal salt modifiers for bonding compositions

Details Metal salt modifiers for bonding compositions Metal salt modifiers for bonding compositions

2001-12-31

2004-05-11

Zalukaeva, Tatyana (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S134000, C526S183000, C526S195000, C526S197000, C526S198000, C526S328000, C526S329100, C526S217000, C526S346000, C428S500000, C156S325000, C156S326000

Reexamination Certificate

active

06734268

ABSTRACT:

FIELD
The invention relates to bonding compositions, particularly bonding compositions for low surface energy substrates and reactive two-part bonding compositions. The bonding compositions are particularly useful to prepare bonded composites, particularly of low surface energy substrates.
BACKGROUND
An efficient, effective means for adhesively bonding low surface energy substrates such as polyethylene, polypropylene and polytetrafluoroethylene (e.g., TEFLON) has long been sought. The difficulties in adhesively bonding these materials are well known. See, for example, “Adhesion Problems at Polymer Surfaces” by D. M. Brewis that appeared in Progress in Rubber and Plastic Technology, volume 1, page 1 (1985).
The conventional approaches often use complex and costly substrate surface preparation techniques such as flame treatment, corona discharge, plasma treatment, oxidation by ozone or oxidizing acids and sputter etching. Alternatively, the substrate surface may be primed by coating it with a high surface energy material. However, to achieve adequate adhesion of the primer, it may be necessary to first use the surface preparation techniques described above. All of these techniques are well known, as reported in Treatis on Adhesion and Adhesives (J. D. Minford, editor, Marcel Dekker, 1991, New York, volume 7, pages 333-435). The known approaches are frequently customized for use with specific substrates. As a result, they may not be useful for bonding low surface energy substrates generally.
Moreover, the complexity and cost of the presently known approaches do not render them particularly suitable for use by the retail consumer (e.g., home repairs, do-it-yourselfers, etc.) or in low volume operations. One persistent problem is the repair of many inexpensive common household articles that are made of polyethylene, polypropylene or polystyrene such as trash baskets, laundry baskets and toys.
A series of patents issued to Zharov et al. (U.S. Pat. Nos. 5,539,070, 5,690,780 and 5,691,065) report a polymerizable acrylic bonding composition that comprises at least one acrylic monomer, an effective amount of certain organoborane amine complexes, and an effective amount of an acid for initiating polymerization of the acrylic monomer. The acrylic composition is especially useful as an acrylic adhesive for bonding low surface energy polymers.
Another series of patents issued to Pocius et al. (U.S. Pat. Nos. 5,616,796, 5,684,102 and 5,795,657) report polymerizable acrylic bonding compositions that comprise acrylic monomer, organoborane polyamine complex and a material reactive with amine. Polymerizable acrylic monomer compositions useful as adhesives for bonding low surface energy polymers can be prepared. The polyamine is the reaction product of a diprimary amine-terminated material, and a material having at least two groups reactive with a primary amine.
With increasingly demanding end-user requirements, bonding composition formulators are constantly being challenged to improve both application performance (e.g., worklife, rate of strength increase and cure time) and physical property performance (e.g., T-peel strength) of bonding, compositions. It is very often times the case that a formulation change that enhances one property of a bonding composition deleteriously affects a second property of the bonding composition. Because of this, the formulator may have to accept less than a desirable balance between the competing properties. For this reason, adhesive formulators are constantly seeking new materials that provide a more favorable overall balance of properties in bonding compositions.
In many industrial and consumer applications for bonding compositions a long worklife is very desirable feature. Worklife refers generally to the maximum time period available for bringing the bonding composition into contact with the substrate(s) to be bonded (i.e., closing the bond) after the initiation of the cure of the bonding composition. If the substrates are brought into contact with the bonding composition after the worklife has expired, the ultimate strength of the bond formed between the substrates is compromised.
Several techniques have been reported for increasing the worklife of bonding compositions. In one known technique, worklife is increased by slowing the cure rate of the bonding composition, for example, by reducing the amount of polymerization initiator in the bonding composition and/or the chemical reactivity of the initiator. This technique, however, may typically lengthen the overall cure time and may slow the rate of strength increase of the bonding composition. The addition of certain polymerizable monomers to bonding compositions has also been reported to increase worklife. U.S. Pat. No. 5,859,160 (Righettini et al.) reports a free radical curable composition, useful as a two part adhesive, that includes a free radical curable compound and a vinyl aromatic compound that is chemically different than the free radical curable compound. Another known technique for increasing worklife is disclosed in U.S. Pat. No. 6,291,593 (Cheng) by the addition of a retarding additive selected from the group consisting of non-protic Lewis acids, zinc salts and mixtures thereof. Worklife extension was not demonstrated for these retarding additives for organoborane based systems.
Although the above reported techniques may be used to increase the worklife of bonding compositions, other properties of the bonding composition such as rate of strength build, cure time and T-peel strength may be sacrificed as a result of the increased worklife. In view of the foregoing, improved compositions having a favorable balance of long bonding composition worklife and fast rate of strength build are desirable.
SUMMARY
The present invention provides bonding compositions that are particularly useful in bonding low surface energy substrates (e.g., polyethylene, polypropylene and polytetrafluoroethylene) to one another. Bonding compositions of the present invention include an organoborane, a polymerizable monomer, and a metal salt which functions to modify the cure kinetics of the bonding composition to provide a favorable balance of long bonding composition worklife and fast rate of strength build.
In one embodiment the present invention provides a bonding composition comprising:
(i) an organoborane;
(ii) a polymerizable monomer; and
(iii) a metal salt according to formula (1):
[
M
a+
L
n
][X
−m
]
a/m
  (1)
 wherein:
M is a metal cation having two chemically accessible oxidation states and having positive charge a, where a is an integer ranging from 1 to 6;
X is a counterion having charge -m, where m is an integer ranging from 1 to 3;
L is a covalently bonded ligand; and
n is an integer ranging from 0 to 10 representing the number of ligands covalently bonded to the metal cation.
Representative examples of metal cation M having two chemically accessible oxidation states include vanadium, chromium, manganese, iron, cobalt, nickel, copper, molybdenum, ruthenium, rhodium, palladium, antimony, platinum, and cerium. In a preferred embodiment of the invention, the two chemically accessible oxidation states of are separated by one unit of charge.
Representative examples of counterion X include halides, borates, sulfonates, and carboxylates, more preferably chloride, bromide, tetrafluoroborate, trifluoromethanesulfonate, naphthenate, and 2-ethylhexanoate.
Representative examples of ligand L include ammonia, amine, carbonyl, isonitriles, phosphines, phosphites, arsines, nitrosyl, ethylene and alkenes.
Examples of metal salts suitable for use in the present invention include copper (II) bromide, copper (II) chloride, copper (II) 2-ethylhexanoate, iron (III) bromide, vanadium (III) bromide, chromium (III) bromide, ruthenium (III) bromide, copper (II) tetrafluoroborate, copper (II) trifluoromethanesulfonate, copper (II) naphthenate, copper (I) bromide, iron (II) bromide, manganese (II) bromide, cobalt (II) bromide, nickel (II) bromide, antimony (III) bromide, and palladium (II) bro

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