Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2001-11-09
2003-01-14
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S402210, C428S402220, C428S402240, C428S413000, C428S414000, C428S416000, C427S487000, C442S150000, C523S206000, C523S211000
Reexamination Certificate
active
06506494
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ambient-temperature-stable, one-part curable epoxy adhesive compositions, a method of curing the adhesive, a joint made with the cured adhesive and a method of making the joint.
2. Description of Related Art
Ambient-temperature-stable, one-part curable epoxy adhesive compositions that have a long shelf life over a broad range of storage conditions have long been the goal of the manufacturers of such products. Typically, storage conditions for such products would include temperatures which may range from well below 0° C. to 50° C. or higher.
Previous storage-stable, one-part, curable epoxy resin systems generally comprise two or more reactive or reaction-producing components stored in an intimately admixed, unreactive or slowly reactive state which, ideally, react rapidly when subjected to a suitable stimulus, such as application of heat or mechanical shear. Various attempts have been made to prepare one-part systems by utilizing as curatives latent chemical compounds which are stable at room temperature but will produce reactive curative material when heated to an appropriate temperature. Similarly, reactive curing agents and/or catalysts have been encapsulated into microcapsules typically having walls made of a polymeric material that is thermoset or cross-linked and, thus, are unaffected by heating but instead rely on shear forces to release the curing agent and/or catalyst to initiate the curing of the epoxy system.
Curable epoxy systems which contain curatives encapsulated in microcapsules having shell walls comprised of thermoplastic materials are known but the amount of the thermoplastic material in these compositions is generally limited to that just sufficient to provide a barrier between the curative and the curable epoxy systems and generally such amounts will have little or no effect in changing the physical properties of the resultant cured epoxy resin.
Curable epoxy systems which contain non-encapsulated curatives and thermoplastic particles are also known but such systems are not as storage stable as would be desired.
The use of engineering thermoplastic particulate to improve impact tolerance and delaminating resistance in composites is also known in the art as is the use of core-shell materials for use as tougheners in curable polymer.
A need exists for an ambient-temperature-stable, one-part curable epoxy adhesive composition which has excellent storage-stability under any of a wide variety of storage conditions, yet is easily cured by application of heat to produce a cured epoxy resin having excellent physical properties.
SUMMARY OF THE INVENTION
The present invention provides an ambient-temperature-stable, one-part curable epoxy adhesive composition which has excellent storage-stability under any of a wide variety of storage conditions, yet is easily cured by application of heat to produce a cured epoxy resin having excellent physical properties, including in some compositions a reduced modulus which makes it prone to cohesive failure which is desired in some applications. Compositions of the invention are useful in structural adhesive applications, either alone or in conjunction with conventional fastening techniques such as welding and/or mechanical fastening. The curable composition may be formed into sheets which provide a convenient way of introducing the adhesive composition between structural members to make a bonded joint. Preferred cured compositions according to the invention will fail cohesively before failing adhesively when adhered to a substrate.
Specifically, the present invention provides a one-part curable epoxy composition comprising a mixture of
A. epoxy resin capable of being cured to a cured epoxy resin when exposed to an activated latent curative system;
B. a latent curative system in an amount sufficient to cure said epoxy resin comprising (a) at least one epoxy-resin-miscible first curative contained substantially as a core within a multiplicity of ambient-temperature-stable, impermeable microcapsules having capsule walls comprised of a thermoplastic polymeric material and (b) at least one epoxy resin latent second curative admixed uniformly within said curable epoxy resin; and
C. sufficient particulate thermoplastic polymeric material having a melt flow temperature that exceeds ambient temperature and the ability to be at least partially melt blended into the epoxy resin to at least regionally plasticize the cured epoxy resin, wherein up to all of the total weight of the particulate thermoplastic polymeric material may be provided by the thermoplastic polymeric material of the capsule walls.
A preferred first curative comprises a solid epoxy resin hardener contained substantially as a core within the capsule walls of the microcapsules, and most preferably the curative also comprises a latent accelerator as the second curative which is not contained within the capsule walls with the first curative but may be contained in separate thermoplastic microcapsules.
The first curatives for use in curable compositions of this invention preferably are relatively non-acidic curing agents such as acid anhydrides of carboxylic acids, compounds containing the hydrazine function (—CO—NH—NH
2
) or an epoxide-curing derivative thereof, diaminediarylsulfones, and dicyandiamide compounds including analogs of dicyandiamide which are disclosed in Anderson et al. (U.S. Pat. No. 3,553,166), the disclosure of which is incorporated herein by reference.
Imidazoles or imidazole containing compounds, hereinafter termed “imidazoles” or “imidazolates,” are preferably present in the curable composition as the second curative together with the first curative in catalytic amounts, i.e., in amounts sufficient to catalyze the reaction between the epoxide resin, the hardeners, and other reactive materials with the epoxide resin on heating of the composition. Metal imidazolate curative materials and their derivatives are disclosed in Hill et al. (U.S. Pat. No. 3,792,016), the disclosure of which is incorporated by reference. Preferably, the amount of the imidazolate used is about 0.1 to about 10 weight percent, more preferably about 0.5 to about 3 weight percent based on the epoxide equivalent weight. Preferably, the imidazolate is a solid which is insoluble at the storage and processing temperatures in the epoxide resin to provide increased storage stability.
The imidazoles and imidazolates useful in the practice of the invention include imidazole compounds having a counter ion to balance the charge in the molecule. A suitable imidazolate is a metal imidazolate compound of the formula:
ML
m
wherein M is a metal selected from the group of Ag(I), Cu(I), Cu(II), Cd(II), Zn(II), Hg(II), Ni(II) and Co(II), and L is an imidazolate of the formula
wherein R
1
, R
2
, and R
3
are selected from a hydrogen atom, an alkyl radical or aryl radical and m is the valence of M.
An example of a suitable imidazole is diphenyl imidazole.
The most preferred metal imidazolate compound is a green colored copper (II) imidazolate made as described herein.
The compositions according to the invention include sufficient thermoplastic polymeric material in particulate form to improve physical properties of the cured composition. Additionally, the thermoplastic polymeric materials may be entirely provided by the thermoplastic material which provides capsule walls which enclose other reactive components of the epoxy resin. Materials that may be encapsulated by the thermoplastic material include an epoxy hardener and/or accelerator, and other reactive materials, such as catechol, that in the absence of encapsulation may prematurely cause the epoxy resin to harden.
The thermoplastic polymeric material from the capsule walls and, if present, the particulate material, is contained in the composition in an amount based on the total weight of the cured composition, such that, after melt blending the thermoplastic material with the composition during curing, the epoxy composition is at least partially regionally plasti
Brandys Frank A.
Irwin Michael J.
Tarbutton Kent S.
3M Innovative Properties Company
Jackson Monique R.
Knecht Harold C.
Little Douglas B.
Thibodeau Paul
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