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
1997-12-31
2001-01-30
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S423000, C525S430000, C525S438000, C525S449000, C525S533000, C525S934000
Reexamination Certificate
active
06180727
ABSTRACT:
1. FIELD OF THE INVENTION
This invention is related to curing agent composition for epoxy resins, to two component solvent borne or solventless systems having enhanced compatibility between the epoxy resin and the curing agent, which are rapidly heat curable at ambient and sub-ambient temperatures in the absence of external catalysts/accelarators. The invention is also directed to methods of application and manufacture, as well as to the cured products made thereby.
2. BACKGROUND OF THE ART
There has long been a desire to formulate a curing agent which is immediately compatible with conventional epoxy resins, especially at low curing temperatures, and which is sufficiently reactive with epoxy resins that the system will cure in a wide range of temperatures, even as low as 4.4° C., within a 24 hour period in the absence of external accelarators if possible.
Typical amine curing agents, whether aliphatic, aromatic, or adducts with epoxy resins, have terminated with at least one primary amine group. The primary amines are notorious for producing the undesired side effect of blooming or hazing in the cured product. This phenomena is thought to result from the reaction between the highly reactive primary amine groups in the curing agent with atmospheric carbon dioxide and moisture to produce carbamates, resulting in scission of the curing agent polymer chain. Blooming or hazing is more likely to be encountered when the curing agent is stored for a lengthy period of time, and applied in low temperature or high humidity environments.
To some extent, this problem can be ameliorated by reacting out many of the primary amine hydrogens. The drawback to this approach in the past has been that the reactivity of the curing agent was impaired because secondary amines are less reactive than the primary amines, such that accelerators had to be used to obtain adequate cure times, especially at low curing temperatures. Furthermore, many of the amine curing agent adducts whose primary amine groups were converted to secondary amine groups are poorly compatible with epoxy resin.
It would be desirable to have a curing agent composition for curing epoxy resins whose primary amine groups are converted to secondary amine groups, yet is reactive enough to cure epoxy resins without external catalysts/accelerators in a wide range of curing temperatures and which is immediately compatible with a standard diglycidyl ether of Bisphenol-A.
3. SUMMARY OF THE INVENTION
There is provided a curing agent composition, a method for making a curing agent composition, two component curable epoxy resin compositions, methods of their manufacture, and the different cured products thereof. The curing agent comprises the reaction product of an a) a phenolic acid substituted with at least one carboxyl group and at least one hydrocarbyl group having at least 1 carbon atom; b) a polyepoxide compound; c) a polyamine compound having at least two primary amine groups; and d) a monoglycidyl capping agent. The compounds produced by this reaction can be characterized by having a &bgr;-hydroxy ester group and a &bgr;-hydroxy secondary amine group, terminated with moieties unreactive towards epoxide groups at room temperature in the absence of catalysts, and having one or more secondary amine sites throughout the compound.
Preferably, the phenolic acid compound is reacted with the polyepoxide compound to produce a substituted aromatic glycidyl ester compound, which is combined and reacted with the polyamine compound and the monoglycidyl capping agent. Preferable phenolic acid compounds are those having an 8 to 36 carbon branched or unbranched alkyl group.
There is also provided a two component epoxy resin composition using this curing agent composition, methods for their manufacture, and the cured products made thereby.
4. DETAILED DESCRIPTION OF THE INVENTION
The curing agents of the invention exhibit a good overall balance of mechanical and chemical properties. The curing agents of the invention can cure epoxy resins neat or modified within 24 hours at temperatures as low as 4.4° C. in the absence of external accelarators or catalysts. The curing agents can cure epoxy resins at 4.4° in as short a time as within 15 hours in the absence of external accelarators. While not being limited to a theory, it is believed that the compositions can self cure without external accelarators, even at low temperatures, because the curing agent adduct contains phenolic hydroxyl groups which catalyze a reaction between the epoxide groups of the epoxy resin and the amine nitrogens of the curing agent. The curing agents also have the advantage of enhanced compatibility with epoxy resins as evidenced by the clarity of the epoxy resin/curing agent mixtures almost immediately upon mixing. This enhanced compatibility makes it unnecessary to have an induction time, improves the curing rate, and ultimately improves the mechanical properties of the cured product as compared to similar products made with conventional curing agents and given little or no induction time.
The curing agent is made by reacting a a) phenolic acid substituted with at least one carboxyl group and at least one hydrocarbyl group having at least 1, and preferably 8 or more, more preferably 14 or more carbon atoms, b) a polyepoxide compound c) a polyamine compound having at least two primary amine groups and d) a monoglycidyl capping agent. The ingredients a)-d) should be reacted in a sequence which will produce a compound characterized by having a &bgr;-hydroxy ester group and a &bgr;-hydroxy secondary amine group, terminated with moieties unreactive towards epoxide groups at room temperature in the absence of catalysts, and having one or more epoxide reactive secondary amine sites throughout the compound. Preferably, the phenolic acid compound is reacted with a polyepoxide compound to make a substituted aromatic glycidyl ester, which ester is combined with the polyamine compound and monoglycidyl capping agent. More preferably, the substituted aromatic glycidyl ester is reacted first with the total amount of the polyamine compound used in the manufacture of the curing agent, to make a glycidyl ester-amine adduct, followed by addition of the monoglycidyl capping agent with the adduct.
In another embodiment, however, one may first react the monoglycidyl capping agent with the polyamine compound to convert one of the primary amine groups to a secondary amine group, followed by reaction of the polyepoxide compound onto the free primary amine group, and finishing the reaction with addition of the phenolic acid compound onto the free epoxide linkage.
Whichever approach is used, the sequences of addition and reaction should be such to produce compounds having the above described features, that is, a &bgr;-hydroxy ester group and a &bgr;-hydroxy secondary amine group, terminated with moieties unreactive towards epoxide groups at room temperature in the absence of catalysts, and having one or more epoxide reactive secondary amine sites throughout the compound. The preferred method is the former described method, where the polyepoxide compound is reacted with the phenolic acid to make a substituted aromatic glycidyl ester composition, followed by combing and reacting onto the substituted aromatic glycidyl ester composition the polyamine and monoglycidyl capping agent in the stated sequence or as a mixture, more preferably in the stated sequence.
In one embodiment, the curing agent compound is characterized by the following structure:
wherein R
1
is a branched or unbranched, substituted or unsubstituted, monovalent hydrocarbyl group having at least one carbon atom, preferably an alkyl group having at least an average of at least 14 carbon atoms; R
2
and R
4
each independently represent a branched or unbranched, substituted or unsubstituted, divalent hydrocarbyl group having 2-24 carbon atoms, preferably 2-6 carbon atoms, or
wherein R
6
represents a branched or unbranched, substituted or unsubstituted, divalent hydrocarbyl group having 2-24 carbon atoms; R
3
is a branched or unbranched, subs
Carmen Dennis V.
Dawson Robert
Robertson Jeffrey B.
Shell Oil Company
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