Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-03-15
2002-11-12
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...
C526S346000, C526S328000, C526S328500, C502S103000
Reexamination Certificate
active
06479602
ABSTRACT:
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 highly desirable feature. Worklife refers 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 may be 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. The vinyl aromatic compound is present in an amount that is reportedly sufficient to decelerate the cure rate of the free radical composition without adversely effecting completion of cure and the properties of the curable composition after it has cured. In general, the amount of vinyl aromatic compound is less than 5 weight percent, preferably less than 2 weight percent, based on the total weight of the part of the composition that includes the free radical curable component. 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 increase, cure time and T-peel strength may be sacrificed as a result of the increased worklife.
In addition to the foregoing, when formulating two-part bonding compositions it is very often desirable to formulate the parts such that they can be mixed with one another in a convenient mix ratio, for example, 1:1, 1:4, 1:10, and the like. To this end, materials are desired that may be added to one or more of the parts of the bonding composition to modify the mix ratio, wherein the addition of the materials does not deleteriously affect the performance characteristics and storage stability of the resulting bonding composition.
SUMMARY
In one embodiment, the present invention provides polymerization initiator systems that are particularly useful in providing two-part curable bonding compositions, particularly those that cure (i.e., polymerize) to acrylic adhesives, more particularly those that cure to acrylic adhesives capable of bonding low surface energy substrates. The polymerization initiator systems of the present invention may be conveniently used to formulate two-part bonding compositions having a convenient whole number mix ratio. In addition, the polymerization initiator systems of the present invention enable the formulation of bonding compositions having a long worklife without substantially affecting other important properties such as rate of strength increase, cure time and T-peel strength. In preferred embodiments, the worklife of the bonding composition is increased and the T-peel strength of the cured bonding composition is also increased. Broadly, the polymerization initiator systems include an organoborane and at least one vinyl aromatic compound according to general formula (1) or general formula (2):
In formula (1), n represents an integer having a value of 1 or greater, preferably 2 or greater. In formula (1) and formula (2), Ar represents a substituted aryl group. Examples of Ar include a substituted benzene group or a substituted napthalene group. Most preferably, Ar is a substituted benzene group.
In formula (1) and (2), subscript x, which represents an integer having a value of 1 or greater, represents the number of unsaturated groups bonded to each Ar group in the vinyl aromatic compound.
In formulas (1) and (2), R
31
, R
32
and R
33
are independently selected from the group consisting of hydrogen, alkyl, aryl and halogen. Preferably, R
31
is selected from the group consisting of hydrogen and methyl and R
32
and R
33
are hydrogen.
In formulas (1) and (2), R
34
represents a non-hydrogen substituent bonded to the aryl group (Ar). Subscript y is an integer having a value of 0 or greater which represents the number of individual substituents bonded to the aryl group Ar. Whe
3M Innovative Properties
Cheung William K
Pribnow Scott R.
Wu David W.
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