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
1999-10-08
2002-07-16
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...
C525S481000
Reexamination Certificate
active
06420496
ABSTRACT:
BACKGROUND OF THE INVENTION
Amine-functional epoxy curing agents for coatings and related applications have been known and described in the art. These have included reaction products of diamines and/or polyamines with: (1), epoxy resins or other epoxy-functional materials to produce the commonly designated amine adducts; (2) phenol or various substituted phenols and formaldehyde or other aldehydes to produce the commonly designated Mannich bases; and (3) various acidic hydrogen donors such as phenols or various substituted phenols to produce designated amine salts. See, e.g.,
Encyclopedia of Polymer Science and Engineering
6:322-82 (1986) and references cited therein. Nevertheless, there exists still in the art a need for low temperature epoxy curing agents having improved properties and handling characteristics.
BRIEF SUMMARY OF THE INVENTION
It was discovered that by completely blocking or “salting” most or all of the primary amine groups of an amine-functional epoxy curing agent with an acidic hydrogen donor group, it was possible to produce amine-functional epoxy curing agents that do not exhibit reaction with atmospheric carbon dioxide and moisture to produce the bicarbonates or carbamates characterized as amine “blush.” It was further discovered that such curing agents exhibited very rapid cure response when reacted with epoxy resins and other epoxy-functional materials, and that by judicious choice of ingredients, such systems exhibited excellent cure characteristics at significantly lower temperatures than previously attainable. It was further discovered that if an amine adduct produced by the reaction of diamines and/or polyamines with an epoxy resin or other epoxy functional material was further reacted with sufficient acidic hydrogen donor groups to block or “salt” most or all of the remaining primary amine groups, the curing agent thus produced also did not exhibit reaction with atmospheric carbon dioxide and moisture, and also exhibited excellent low temperature cure characteristics. It was further discovered that if a Mannich base, produced by the reaction of diamines and/or polyamines or polyamine-epoxy adducts with the reaction product of a phenolic compound and formaldehyde or other aldehyde, was further reacted with sufficient acidic hydrogen donor groups to block or “salt” most or all of the remaining primary amine groups, the curing agent thus produced also did not exhibit reaction with atmospheric carbon dioxide and moisture, and also exhibited excellent low temperature cure characteristics. It was further discovered that all the curing agents described in the foregoing exhibited the positive attributes of their respective classes, such as hardness, toughness, chemical resistance and corrosion resistance.
DETAILED DESCRIPTION OF THE INVENTION
Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term “about”.
In one important embodiment of the invention epoxy curing agents are formed by (1) reacting at least one phenol with at least one aldehyde in the presence of a basic catalyst, (2) reacting the resulting product with at least one polyamine or a polyamine-epoxy adduct, and finally (3) reacting the product of the preceding step with at least one proton donor compound having a pK
a
of 11 or less to form the epoxy curing agent. The amine-functional epoxy curing agents thus formed exhibit the performance properties of known epoxy curing agents, with the additional benefits of extraordinarily rapid ambient temperature cure response and excellent cure response at very low temperatures, together with complete resistance to formation of amine bicarbonates or carbamates.
The phenol used in the first step to prepare the curing agents of the invention can be any compound which contains at least one hydroxyl group attached to at least one aromatic ring. The aromatic ring(s) may have one or more substituents such as alkyl groups, so long as at least one carbon atom located at the 1, 4 or 6 positions relative to the hydroxyl bearing carbon atom is unsubstituted. Preferably the phenolic compounds are represented by the formula:
wherein R
1
and R
2
are independently hydrogens or hydrocarbyl groups having from 1 to 16 carbon atoms. R
1
and R
2
can be linear, branched or aromatic. Examples of suitable phenolic compounds include, but are not limited to, phenol; nonylphenol; resorcinol; butylphenol; ortho; meta and para cresols; hydroquinone; paraphenylphenol; dodecylphenol; 4,4′-dihydroxy-2,2-diphenylpropane (Bisphenol A); p-t-butyl phenol; and 2-hydroxybenzoic acid (salicylic acid).
The aldehyde used in step (1) can be any aldehyde that will react with a phenol to form a methylol phenol. Such aldehydes include, but are not limited to, formaldehyde paraformaldehyde; acetaldehyde; butyraldehyde; and other aliphatic aldehydes; with formaldehyde and paraformaldehyde being preferred.
The basic catalyst used in the reaction between the phenol and the aldehyde in step (1) can be any base known to those skilled in the art typically used in the reaction of a phenol and an aldehyde. Preferably, the catalyst is an amine, more preferably N,N-dimethylbenzyl amine (BDMA).
Step (1) can be carried out at a temperature of from 20° to 120° C., preferably at about 100° C. The reaction is conveniently carried out in aqueous solution. The mole ratio of phenol to aldehyde can range from 1:1 to 6:1, preferably from 1.5:1 to 3:1.
The polyamines used in step (2) can be any amine having two or more primary amine functionalities, including those compounds having secondary amine functionalities in addition to the two or more primary amine groups. Diamines and polyamines that can be employed in step (2) are preferably those represented by the formula
H
2
N—(—R
3
—NH—)
m
—(R
4
—)
n
—NH
2
wherein R
3
and R
4
are divalent hydrocarbyl groups, preferably having 2 to 20 carbon atoms, and m and n are integers ranging from 0 to 5, with the condition that m and n may not both be simultaneously 0 (m+n is at least 1). The hydrocarbyl groups may be branched or linear alkylene groups, cycloaliphatic groups or contain aromatic groups so long as the attached amines are primary or secondary aliphatic amines.
Examples of diamines and polyamines that can be used herein include, but are not limited to: 1,3-benzenedimethanamine (MXDA); metaxylylene diamine; 1,3-cyclohexanedimethanamine (1,3-BAC); 1,2-diaminocyclohexane (DACH); norbornanediamine; isophorone diamine; 5-amino-1,3,3-trimethylcyclo-hexanemethanamine (IPDA); trimethylhexamethylenediamine (TMD); 1,3-pentanediamine (DYTEK™ EP); 2-methyl-1,5-pentanediamine (DYTEK™ A); 1,6-hexanediamine (HMDA); 4,4′-diaminodicyclohexylmethane (PACM); and ethyleneamines such as 1,2-ethanediamine (EDA), N-(2-aminoethyl)-1,2-ethanediamine (DETA), N,N-bis(2-amino-ethyl)-1,2-ethanediamine (TETA), N-(2-aminoethyl)-N′-[(2-amino-ethyl)amino-ethyl]-1,2-ethanediamine (TEPA), aminoethylpiperazine, and higher polyethylenepolyamines.
Epoxy functional materials useful in preparing the polyamine-epoxy adducts that can be used in step (2) include, but are not limited to: Bisphenol A epoxy resins, such as the common diglycidyl ether of Bisphenol EA with epoxy equivalent weights ranging from 170-525; Bisphenol F epoxy resins, such as the common diglycidyl ether of Bisphenol F with epoxy equivalent weights ranging from 156-190; Bisphenol F epoxy novolac resins; cresol epoxy novolac resins; and various mono-, di- and tri-functional reactive epoxy “diluents,” such as butyl glycidyl ether, C
8
-C
10
alkyl glycidyl ethers, C
12
-C
13
alkyl glycidyl ethers, C
12
-C
14
alkyl glycidyl ethers, cresyl glycidyl ether, 1,4-butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, resorcinol diglycidyl ether, and other glycidyl ethers.
The above epoxy functional materials are reacted with a diamine or polyamine, such as those described above, to form the polyamine-epoxy adduct that can be used in step (2)
Cash, Jr. Ronald T.
DeAngelis Gaetano D.
Moon Robert M.
Mulvey Joseph L.
Natesh Anbazhagan
Cognis Corporation
Drach John E.
Millson, Jr. Henry E.
Sellers Robert E. L.
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