Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-06-21
2002-12-10
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C525S523000, C528S119000, C528S120000, C528S123000, C528S125000, C528S407000, C528S418000
Reexamination Certificate
active
06492437
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to novel solvent-based processes for making curable epoxy resin compositions.
BACKGROUND OF THE INVENTION
Articles prepared from an epoxy resin have excellent adhesion, mechanical properties, thermal properties, chemical resistance and electrical properties. These properties have led to the widespread commercial use of the articles in such items as paints, adhesives, and electrical and electronic insulation. Epoxy resin formulations used for such applications can be either a one-component system or a two-component system.
One-component systems are highly desirable for numerous reasons. For example, one-component systems allow manufacturers and consumers to avoid the complex packaging required of two-component systems, to avoid the additional mixing step of a two-component system and to avoid the possibility of an inaccurate mixing step. Further benefits of a one-component system include a reduction in variation of properties via incomplete mixing and, frequently, a longer pot life.
Amine compounds, and in particular imidazoles, are widely used as curing agents for epoxy resins because products cured with imidazoles generally exhibit highly desirable chemical and physical properties. Like most tertiary-nitrogen-containing curing agents, imidazoles react very rapidly with epoxy resin systems, even at room temperature. The resulting catalyst is generally a thermoplastic solid which has a melting point between about 70° C. and 140° C. The catalyst may be repeatedly melted and allowed to cool and resolidify. These catalysts are not subjected to cure or cross-linking when heated. Most conveniently, the catalysts are provided as finely divided powders, such as those capable of passing through a 200-mesh screen. Further, the resulting catalyst provides a synergistic effect when combined with an additional curing agent, such as a dicyandiamid.
The use of phenolic novolac resins as a reactant with the epoxy resin and the imidazole compound is highly advantageous. The composition resulting from the addition of the phenolic resin has a shelf life of up to five times longer than without the phenolic resin. This improvement is believed to be achieved by the formation of an acid-base complex or polysalt between the novolac phenolic resin and the product of the addition reaction between the oxirane group and the imino nitrogen. The epoxy resins which are most advantageous for the reaction with imidazole those with an epoxide equivalent weight of from about 170 to about 2000 and preferably a melting point below about 140° C. Sufficient epoxy resin should be utilized in order to provide a ratio of oxirane groups to imidazole compound molecules between 1:1 and 2:1. Larger relative quantities of oxirane groups will result in a thermosetting or high melting reaction product which is excessively difficult to activate with heat. Smaller relative quantities of oxirane groups will result in a reaction product which melts at a temperature below 70° C. or which contains a high proportion of residual imidazole, thus resulting in a shorter shelf life of the catalyst.
The amount of phenolic novolac resin to be included with the epoxy resin may be as much as 1.5 equivalent per molecule of the imidazole. More preferably, the ratio of phenolic novolac resin to imidazole is in the range of about 0.7-1.5 with an optimum ratio of approximately 1:1.
U.S. Pat. No. 4,066,625 discloses a unitary catalyst comprising epoxy, an imidazole and phenolic resin. The processes for the reactions between the ingredients of the catalyst, along with the various ingredients and mechanisms of reaction, are set forth in that patent and U.S. Pat. No. 4,066,625 is incorporated herein by reference as if set forth in full. No solvents are used in these disclosed processes. The solvent-free process of that patent of combining the epoxy and the imidazole produces an extremely high exotherm within minutes. Consequently, the process for manufacturing the catalyst is quite dangerous and requires extreme caution during the period in which the imidazole is added to the epoxy. Thus, it would be desirable to provide a process for manufacturing the catalyst which utilizes a solvent and eliminates the risk of the high exotherm during the addition of the imidazole to the epoxy.
SUMMARY OF THE INVENTION
The present invention provides a process for producing a catalyst without causing an extreme exotherm. The process of the present invention includes combining an amine compound curing agent with a solvent, heating the mixture, adding an epoxy/solvent mixture via slow addition, removing the solvent and then heating the remaining composition. Following the heating, a phenolic resin is added to produce the final catalyst. The final catalyst comprises an amine compound, an epoxy, phenolic resin and a residual solvent. The process may also be reversed such that the amine compound is added to the epoxy. Alternatively, epoxy resin may be added via slow addition to an initial charge solution of solvent and imidazole. Phenolic resin may be added either to the initial charge solution or via slow-addition along with the epoxy resin.
DETAILED DESCRIPTION OF THE INVENTION
A catalyst for use with epoxy resins may be produced via a method which eliminates the exotherm upon the combination of imidazole and epoxy resin. The imidazole and epoxy components which are to be selected as the starting materials for the preparation of the catalyst are chosen for the desired properties of the resulting adduct as a catalyst. Properties which are generally important and should be considered include the catalyst's chemical structure which promotes the curing reaction by anionic polymerization, the catalyst's melting point, the catalyst's compatibility with the epoxy resin which will be cured in a molten state, its quick curability and its effect of addition (high curing reactivity with the smallest amount of addition).
The starting point for the process of manufacturing the adduct is combining either an amine compound or an epoxy with a solvent. While a wide range of ratios of amine to solvent may be employed, it is most preferable to combine the amine and the solvent in a ratio of about 1:1. Preferably, the amine compound is used as the starting material. While any amine compound may be utilized for the present invention, the selection of the particular amine compound is determined by the type of epoxy compound to be combined. While it is possible to use any type of amine compound which have at least one active amino-hydrogen in their molecule with monofunctional epoxy compounds, the amine which can be combined with polyfunctional epoxy compounds is an amine compound which has only one active amino-hydrogen, i.e., having a secondary amino group, in its molecule which contributes to the addition reaction with the epoxy group. Use of compounds having at least one tertiary amino group, i.e., having no active hydrogen, is also permitted, since the presence of the tertiary amino group is desirable for increasing the concentration of the amino groups which contribute to the curing reaction of the adduct, or in other words to increase the effect of the curing agent. If this condition for combination is met, any combinations of one, two or more kinds of amine compounds may be employed.
Exemplary amines which may be utilized include imidazoles such as 2-methylimidazole; 2,4-dimethylimidazole; 2-ethyl, 4-methylimidazole; 4,5 dimethylimidazole; 2,4,5 trimethylimidazole; 2 propyl, 4,5-dimethylimidazole; 2-cyclohexyl, 4-methylimidazole; 2-butoxy, 4-allylimidazole; 2-octyl, 4-hexylimidazole; 2-ethyl, 4-phenylimidazole; 2-butyl, 5-methylimidazole; 2,5 chloro, 4-ethylimidazole; 4-methyl-2-phenylimidazole; imidazolines such as 2-methylimidazoline; piperazines such as N-methyl piperazine; anabasines such as anabisine; pyrazoles such as 3,5-dimethyl pyrazole; purines such as tetramethyl quinidine and purine; and triazoles such as 1,2,4-triazole.
Once the amine compound is chosen, a solvent is added to that amine compound. The s
Cipullo Michael J.
Musa Osama M.
Almer Charles W.
Aylward D.
Dawson Robert
National Starch and Chemical Investment Holding Corporation
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