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
1998-06-10
2001-08-21
Sellers, Robert E. L. (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...
C523S404000, C523S414000
Reexamination Certificate
active
06277928
ABSTRACT:
FIELD OF INVENTION
This invention relates to curing agents for epoxy resins. In one aspect, the invention relates to curing agents suitable for use in waterborne applications.
BACKGROUND OF THE INVENTION
Epoxy coating systems cured with polyamine-based curing agents are used for the preparation of industrial maintenance coatings and other types of protective coatings for a variety of substrates. Epoxy resins have excellent resistance to chemicals also have good adhesion to most substrates, e.g. various woods, wall-boards, metals and masonry surface.
There has long been a desire to formulate a curing agent which is essentially free of volatile organic compounds (VOC's), which are self emulsifiable and curable at a wide range of temperatures in the absence of external accelerators if possible.
Many of the current waterborne epoxy resins and curing agents are plagued with the problem of poor film properties because the surfactants tend to migrate to the surface during the cure of the resin system. Thus, it would be desirable to provide a curing agent system containing a surfactant which does not migrate during cure, that is, a self emulsifiable system which does not require salting the surfactant, e.g. with acids, or using plasticizers to stably disperse the curing agent in water.
In addition to providing a self emulsifiable waterborne curing agent, the curing agent should be readily compatible with a waterborne epoxy resin in order to make a coating having good mechanical properties and weatherability. A waterborne curing agent that does not have good compatibility with the epoxy resin will not coalesce well when applied onto a substrate. The problem of compatibility is more acute where the curing agent primary amine groups have been converted to secondary amine groups to reduce the blooming or hazing phenomena.
Due to more stringent environmental regulations particularly with respect to reduced volatile organic compounds (VOC), toxicity, etc. aqueous based coating systems (waterborne epoxy resin systems) are receiving significant attention in terms of research and development efforts.
These curing agents for waterborne epoxy resins are typically water-dilutable polyamines that are either inherently water soluble or whose water solubility is enhanced by means of reaction with an organic acid such as acetic acid. Those that are highly water compatible provide for coatings which exhibit water sensitivity and poor protection from corrosion.
For example, in U.S. Pat. No. 5,489,630 describes a waterborne curing agent based on low molecular weight polyetheramine are water soluble. These low molecular weight polyetheramine have high levels of water-soluble polyethers which may lower the aqueous chemical resistance of paints.
It is desirable to obtain curing agents that are incompatible with water but dispersible in water and further can be water dispersible without the aid of an acid.
SUMMARY OF THE INVENTION
According to the invention, a curing agent for epoxy resins is provided, comprising a reaction product having an amine equivalent weight of at least 50 prepared by the steps comprising reacting (a) an epoxy-functional compound prepared by reacting an amidoamine having the formula:
wherein R
1
is an alkyl aryl, or arylalkyl group having 1 to 15 carbon atoms, preferably C
1
-C
4
alkyl or nonylphenyl, most preferably methyl, R
2
is aliphatic, cycloaliphatic, or aromatic group having 2 to 18 carbon atoms optionally containing non-reactive oxygen or at most an average of 4 secondary and/or tertiary nitrogen atoms per structure in the backbone, X and Y are independently a hydrogen, methyl or ethyl group with the provision that if X is methyl or ethyl, Y is hydrogen or if Y is methyl or ethyl, X is hydrogen, and n+m+o is a real number from 65 to 200, and n, m, and o are each a real number such as to provide a number average molecular weight of the amidoamine from 3000 to 10,000, and n+o is within the range of from 80 percent to 100 percent of n+m+o, in a ratio of (I) to (II) by weight in the range of 100:0 to 0:100, in a ratio of (I) to (III) by weight in the range of 100:0 to 0:100, and in a ratio of (II) to (III) by weight in the range of 100:0 to 0:100, and at least one epoxy resin having a functionality of from 1.5 to 2.5 epoxide group per molecule in an active amine hydrogen atoms to epoxy groups ratio of from 1:350 to 1:15; and
(b) at least one polyamine in an active amine hydrogen atoms to epoxy groups ratio of 2:1 to 30:1 thereby producing an amine-terminated product having a amine equivalent weight of at least 50.
DETAILED DESCRIPTION OF THE INVENTION
There has been found that a certain amidoamine-based curing agent is dispersible in water without an acid, thus providing a superior curing agent for waterborne epoxy coatings formulations. Further, the curing agent of the invention requires only small amounts of surfactant based on solids. The curing agents of this invention when combined with a solid epoxy dispersion give coatings with good impact resistance, high gloss and gloss retention.
The waterborne curing agent composition of the invention is a solid phase dispersed in a continuous phase, the continuous phase comprising water, the solid phase comprising a curing agent composition and a surfactant composition. The dispersion can be a suspension, emulsion, or a colloidal dispersion. The aqueous continuous phase can contain other liquids in admixture, but is preferably free of any VOC's and free of any cosolvents. By an continuous phase that is essentially free of VOC's is meant that 5 wt. % or less of the waterborne curing agent composition is a VOC.
The curing agent of the invention can be produced by reacting a certain epoxy-functional component (a) and at least one certain polyamine component (b). The epoxy-functional component (a) can be prepared by reacting an amidoamine having the formula:
wherein R
1
, R
2
, n, m, and o are as described above, and X and Y are independently a hydrogen, methyl or ethyl group with the provision that if X is methyl or ethyl, Y is hydrogen or if Y is methyl or ethyl, X is hydrogen. Particularly, n, m, and o are each a real number such as to provide a number average molecular weight of the amidoamine from 3000, preferably from 4000, to 10,000, preferably to 6000, n+o is preferably in the range of from 80 percent, more preferably from 90 percent, to 100 percent of n+m+o. In a preferred embodiment, the ratio of n+o to m is in the range of 100:1 to 55:45.
In formula (I), preferably m is a real number from 0 to 70 and n and o are independently a real number from 5 to 395. In formula (II), preferably m is a real number from 0 to 70, n is a real number from 0 to 395, and o is a real number from 0 to 400, more preferably from 20 to 380. In formula (III), preferably m is a real number from 0 to 70, n is a real number from 0 to 395, and o is a real number from 0 to 400, more preferably from 20 to 380. In all of the above formulae (I), (II), and (III), n+o must be a real number in an amount effective to provide resin emulsification which is typically at least 15, preferably at least 35. In one preferred embodiment, m is 0.
In one embodiment, the epoxy-functional component (a) can be prepared by reacting amidoamine of structures (I) and (II) in a ratio of (I) to (II) by weight in the range of 99:1 to 1:99, preferably in the range of 20:80 to 80:20, and at least one epoxy resin. In another embodiment, the epoxy functional component can be prepared by reacting amidoamine of structures (II) and (III) in a ratio of (II) to (III) by weight in the range of 99:1 to 1:99, preferably in the range of 20:80 to 80:20, and at least one epoxy resin. In yet another embodiment, the epoxy functional component can be prepared by reacting amidoamine of structures (I) and (III) in a ratio of (I) to (III) by weight in the range of 99:1 to 1:99, preferably in the range of 20:80 to 80:20, and at least one epoxy resin. Further, the epoxy functional component can be prepared by reacting amidoamine of struc
Back Gayle Edward
Dangayach Kailash
Elmore Jimmy D.
Ghosh Kalyan
Stark Charles J.
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