Self-dispersing curable epoxy resins, dispersions made...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

Reexamination Certificate

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C523S404000, C523S424000, C525S486000, C525S504000, C528S096000, C528S111000

Reexamination Certificate

active

06294596

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to coating compositions made from aqueous epoxy dispersions. More specifically, this invention relates to self-dispersing curable epoxy resins, and to aqueous dispersions and coating compositions comprising the same.
BACKGROUND OF THE INVENTION
Epoxy resins have come into widespread use as components in coating compositions. Coatings which comprise cured epoxy resins are valued for their durability, chemical resistance, and excellent adhesion to a broad range of substrates. Particularly desirable from an environmental point of view are epoxy resins which may be applied to a substrate with either minimal or no release of volatile organic components. Toward this end, there has been much research directed to the development of aqueous dispersions and emulsions of epoxy resins.
One class of aqueous epoxy dispersions employs one or more additives, also known as dispersants or emulsifiers or surfactants, which are necessary to stabilize the epoxy resin in the dispersion or emulsion form. Representative examples include an aqueous epoxy dispersion as described in U.S. Pat. No. 3,301,804 (employing the reaction product of a boric acid ester derived from boric acid with both an alkylene glycol and a beta-dialkyl-substituted aminoalkanol as an emulsifier), U.S. Pat. No. 3,634,348 (employing a phosphate ester as an emulsifying agent), U.S. Pat. No. 3,249,412 (employing in combination a cationic emulsifying agent selected from the group consisting of imidazolines and amides and a non-ionic emulsifying agent), and Specialty Chemicals Bulletin SC-021 entitled “Water-Reducible Coatings via Epoxy Resin Modification with Jeffamine (Reg. ™) ED-2001 and Jeffamine (Reg. ™) M-1000” available from Texaco Chemical Company, Bellaire, Tex. It should be noted that while the low molecular weight amines described in this Texaco bulletin may be adequate for emulsifying a low molecular weight epoxy resin (e.g. DER 331 from Dow Chemical), the low molecular weight amines are not alone effective for emulsifying a higher molecular weight resin (e.g. an epoxy resin such as DER 331 that has been advanced with a polyhydric phenol such as bisphenol A).
Another example comes from the technical literature of Synthron Inc., Morgantown, N.C., which discloses the use of PROX-E-141, a diglycidyl ether of Pluronic (Reg. ™) F88 diol (an ethylene oxide—propylene oxide—ethylene oxide block copolymer available from BASF Performance Chemicals, Parsippany, N.J.) as a reactive dispersant for epoxy resins. PROX-E-141 can act as a dispersant for epoxy resin in water, but then will react along with the epoxy resin when exposed to an amine functional curing agent.
The use of an additive to provide stability to an aqueous epoxy dispersion is preferably avoided as such additives add additional cost, formulation complexity, and may potentially interfere with the performance of a coating derived from the aqueous epoxy dispersion.
It is known to prepare aqueous epoxy dispersions from self-emulsifying epoxy resins. For example, U.S. Pat. No. 4,315,044 describes a stable epoxy dispersion composition comprising (1) an aqueous medium; and (2) between about 50-70 weight percent of self-emulsifying epoxy resin which is the addition product of reactants comprising (a) 40-90 parts by weight of diglycidyl ether of dihydric phenol, (b) 5-35 parts by weight of dihydric phenol, and (c) 2-15 parts by weight of diglycidyl ether of polyoxyalkylene glycol, wherein the molecular weight of the epoxy resin is in the range between about 500-20,000. The dispersion can also contain 1-25 weight percent based on resin solids of a water-immiscible C
8
-C
20
aliphatic monoepoxide reactive diluent.
U.S. Pat. No. 4,608,406 describes stable aqueous epoxy resin dispersions comprised of (1) an aqueous medium; and (2) between about 50 to about 70 weight percent of self-emulsifying epoxy resin which is the addition reaction product of (a) 40-90 parts by weight of a diglycidyl ether of a dihydric phenol; (b) 5-35 parts of a dihydric phenol; (c) 2-15 parts by weight of a diglycidyl ether of a polyoxyalkylene glycol; and (d) 2 to 15 parts by weight of an alkyl phenol-formaldehyde novolac resin wherein the molecular weight of the epoxy resin is in the range of about 1000 to about 20,000. The stable dispersions can be modified by the addition of about 1 to about 25 weight percent of an aliphatic monoepoxide reactive diluent. In an attempt to improve freeze-thaw stability, the stable aqueous epoxy resin dispersions can be modified by the addition of about 5-20 weight percent, based on resin solids weight, of a water-miscible solvent which, preferably, is a 2 to 8 carbon glycol or glycol ether.
There remains a need for further improvements in terms of the freeze-thaw resistance of aqueous epoxy resin dispersions, and in terms of the corrosion resistance and chemical resistance of coatings derived from aqueous epoxy resin dispersions which are adapted for application as industrial maintenance coating systems.
Accordingly, it is a primary object of this invention to provide a self-dispersing curable epoxy resin which may be dispersed in water without the necessity for an additive to stabilize the epoxy dispersion.
Another object of this invention is to provide aqueous dispersions of self-dispersing curable epoxy resins which exhibit long term stability under ambient storage conditions.
Yet another object of this invention is to provide coating compositions incorporating a self-dispersing curable epoxy resin, where the coating composition exhibits excellent properties when cured.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.
SUMMARY OF THE INVENTION
It has been found that a self-dispersing curable epoxy composition can be prepared upon contacting an epoxy resin with a polyoxyalkyleneamine having a molecular weight of from about 3,000 to about 15,000 in a ratio of about 0.001 to 0.060 reactive equivalents of polyoxyalkyleneamine to about 1.0 reactive equivalents of epoxy resin.
The self-dispersing curable epoxy resin of the invention forms an aqueous dispersion upon mixing with water. When cured, films of the self-dispersing curable epoxy resin are useful as a coating composition.
DETAILED DESCRIPTION OF THE INVENTION
The self-dispersing curable epoxy resin formulation of the invention is prepared upon contacting (a) 1.0 reactive equivalents of an epoxy resin with (b) from about 0.001 to 0.060 reactive equivalents, preferably from about 0.008 to about 0.015 reactive equivalents of a polyoxyalkyleneamine having a molecular weight of from about 3,000 to about 15,000.
The Polyoxyalkyleneamine
The polyoxyalkyleneamine reactant comprises one or more amino-compounds where the amino-compound comprises both an amine group and a substantially water-soluble polyether chain. The polyoxyalkyleneamine reactant is soluble or at least partially soluble in water. Techniques to prepare suitable polyoxyalkyleneamine reactants are known in the art, and include reacting a hydroxyl group containing initiator with ethylene oxide and/or propylene oxide, followed by conversion of the resulting terminal hydroxyl group(s) to amine(s). Illustrative of the polyoxyalkyleneamine reactants employed in the invention are the Jeffamine (Reg. ™) brand of polyoxyalkyleneamines available from Texaco Chemical Company, Bellaire, Tex.
The preferred polyoxyalkyleneamines of this invention have the structural formula:
R
1
—O—R
2
—CH
2
CH(R
3
)—NH
2
wherein:
R
1
designates a monovalent organic radical selected from the group consisting of C
1
to C
12
aliphatic, alicyclic or aromatic hydrocarbons, and
R
2
represents a polyoxyalkylene chain having the structural formula:
(CH
2
—CH
2
—O)
a
—(CH
2
—CH(R
4
)—O)
b
wherein:
R
4
is a monovalent organic radical selected from the group consisting of C
1
to C
4
aliphatic hydrocarbons, ‘a’ designates a number of ethoxy groups (CH
2
—CH
2
—O), ‘b’ designates a number of monosubstituted ethoxy groups (CH
2
—CH(R
4
)—O) where the substitution of one

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