Aqueous Self-Dispersible Epoxy Resin Based on Epoxy-Amine Adducts

The present invention relates to aqueous epoxy resin dispersions based on epoxy-amine adducts. These dispersions are useful in preparing coating compositions comprising the same.

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 titled "Water-Reducible Coatings via Epoxy Resin Modification with Jeffamine (Reg. TM) ED-2001 and Jeffamine (Reg. TM) M-1000" available from Texaco Chemical Company, Bellaire, Tex. 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. TM) 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.sub.8 -C.sub.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.

According to the present invention, there is provided a self-dispersing curable epoxy resin composition comprising the addition product of reactants comprising (a) an epoxy resin, (b) from about 0.40 to 0.95 reactive equivalents of a polyhydric phenol per reactive equivalent of said epoxy resin, and (c) from about 0.005 to 0.5 reactive equivalents of an amine-epoxy adduct per reactive equivalent of said epoxy resin, said amine-epoxy adduct comprising the addition product of reactants comprising of a polyepoxide and from about 0.3 to 0.9 reactive equivalents of a polyoxyalkyleneamine per reactive equivalent of said polyepoxide, said polyoxyalkyleneamine having the structural formula:

wherein:

R.sub.1 represents a polyoxyalkylene chain having the structural formula:

wherein:

R.sub.3 is a monovalent organic radical selected from the group consisting of C.sub.1 to C.sub.4 aliphatic hydrocarbons,

`a` designates a number of ethoxy groups (CH.sub.2 --CH.sub.2 --O),

`b` designates a number of monosubstituted ethoxy groups (CH.sub.2 --CH(R.sub.3)O), the sum of `a` and `b` is equal to or greater than 10 but less than or equal to 300, and where the ratio of a to b is between 1:0 and 1:1. For any values of a and b the sequence of ethoxy and monosubstituted ethoxy groups within a polyoxyalkylene chain may be completely random and/or there may be blocks of ethoxy and/or monosubstituted ethoxy groups.

R.sub.2 designates hydrogen or a monovalent organic radical selected from the group consisting of C.sub.1 to C.sub.4 aliphatic hydrocarbons.

The self-dispersing curable epoxy resin of the invention is in the form of an aqueous dispersion. When cured, films of the self-dispersing curable epoxy resin dispersion are useful as a coating composition.

The self-dispersing curable epoxy resin used as a starting material herein can be any one of several self-dispersing curable epoxy resins that are based upon a polyoxyalkyleneamine.

In certain embodiments, the self-dispersing curable epoxy resin based on a polyoxyalkyleneamine is prepared by reacting (a) 1.0 reactive equivalents of an epoxy resin, (b) from about 0.01 to 1.0 reactive equivalents (e.g. from about 0.4 to about 0.6 reactive equivalents or from about 0.65 to about 0.95 reactive equivalents) of a polyhydric phenol, and (c) from about 0.005 to 0.5 reactive equivalents of an amine-epoxy adduct, wherein the amine-epoxy adduct is formed upon contacting 1.0 equivalents of a polyepoxide and from about 0.3 and 0.9 reactive equivalents of a polyoxyalkyleneamine. Such self-dispersing curable epoxy resins are described in detail in U.S. Ser. No. 08/255,732, filed Jun. 14, 1994 U.S. Pat. No. 5,565,505 (which is a continuation-in-part of U.S. Ser. No. 08/086,288, filed Jun. 30, 1993), U.S. Ser. No. 08/296,282, filed Aug. 25, 1994 U.S. Pat. No. 5,565,506 by J. Papalos et al., entitled "Self-Dispersing Curable Epoxy Resins, Dispersions Made Therewith, and Coating Compositions Made Therefrom (which is a continuation-in-part of U.S. Ser. No. 08/203,543, filed Mar. 1, 1994), and U.S. Ser. No. 366,343, filed Dec. 29, 1994 U.S. Pat. No. 5,648,409 entitled "Self-Dispersing Curable Epoxy Resins, Dispersions Made Therewith, and Coating Compositions Made Therefrom", the disclosures of which are incorporated herein by reference.

In other embodiments, the epoxy resin is prepared by reacting 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. Such self-dispersing curable epoxy resins are described in detail in U.S. Ser. No. 08/296,283, filed Aug. 25, 1994, abandoned by J. Papalos et al., entitled "Self-Dispersing Curable Epoxy Resins, Dispersions Made Therewith, and Coating Compositions Made Therefrom (which is a continuation-in-part of U.S. Ser. No. 08/173,455, filed Dec. 27, 1993) abandoned the disclosures of which are incorporated herein by reference.

In yet other embodiments, the epoxy resin composition is prepared by reacting (a) 1.0 reactive equivalents of an epoxy resin, (b) from about 0.005 to 0.5 reactive equivalents of an amine-epoxy adduct, and optionally (c) from about 0.01 to 1.0 reactive equivalents of a polyhydric phenol, wherein the amine-epoxy adduct is formed upon contacting 1.0 equivalents of a polyepoxide with from greater than about 1.0 equivalents (preferably from about 1.01 to about 2.5) reactive equivalents of a polyoxyalkyleneamine. Such self-dispersing curable epoxy resins are described in detail in U.S. Ser. No. 08/296,281, filed Aug. 25, 1994, U.S. Pat. No. 5,604,269 by J. Papalos et al., entitled "Self-Dispersing Curable Epoxy Resins, Dispersions Made Therewith, and Coating Compositions Made Therefrom (which is a continuation-in-part of U.S. Ser. No. 08/173,847, filed Dec.27, 1993), abandoned and U.S. Ser. No. 366,343, filed Dec. 29, 1994 U.S. Pat. No. 5,648,409 entitled "Self-Dispersing Curable Epoxy Resins, Dispersions Made Therewith, and Coating Compositions Made Therefrom", the disclosures of which are incorporated herein by reference.

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. Polyoxyalkyleneamines of this invention have the structural formula

wherein:

R.sub.1 represents a polyoxyalkylene chain having the structural formula:

wherein:

R.sub.3 is a monovalent organic radical selected from the group consisting of C.sub.1 to C.sub.4 aliphatic hydrocarbons,

`a` designates a number of ethoxy groups (CH.sub.2 --CH.sub.2 --O),

`b` designates a number of monosubstituted ethoxy groups (CH.sub.2 --CH(R.sub.4)O), the sum of `a` and `b` is equal to or greater than 10 but less than or equal to 300, and where the ratio of `a` to `b` is between 1:0 and 1:1. For any values of `a` and `b` the sequence of ethoxy and monosubstituted ethoxy groups within a polyoxyalkylene chain may be completely random and/or there may be blocks of ethoxy and/or monosubstituted ethoxy groups.

R.sub.2 designates hydrogen or a monovalent organic radical selected from the group consisting of C.sub.1 to C.sub.4 aliphatic hydrocarbons.

The techniques to prepare suitable polyoxyalkyleneamines are known in the art, and include reacting an initiator containing two hydroxyl groups with ethylene oxide and/or monosubstituted ethylene oxide followed by conversion of the resulting terminal hydroxyl groups to amines. Illustrative of the polyoxyalkyleneamine reactants employed in the invention are the Jeffamine.TM. brand of polyoxyalkyleneamines available from Huntsman Corporation, Bellaire, Tex. According to Huntsman Corporation, these polyoxyalkyleneamines are prepared from reactions of bifunctional initiators with ethylene oxide and propylene oxide followed by conversion of terminal hydroxyl groups to amines. The most preferred polyoxyalkyleneamines are the Jeffamine.TM. ED-series polyoxyalkyleneamines from Huntsman Chemical Company which have approximate molecular weight between 600 and 6,000, the value of `a` for these polyoxyalkyleneamines is between about 9 to 132 and the value of `b` is about 2.

The Polyepoxide

The polyepoxide reactant comprises one or more compounds each having a plurality of epoxide functional groups. The polyepoxide reactant has at least 2 epoxide groups present in the molecule, and may have as many as 6 epoxide groups present in the molecule. Techniques to prepare suitable polyepoxide compounds are known in the art, and include reacting compounds having a plurality of hydroxyl groups with epichlorohydrin in the presence of a suitable catalyst. Both aliphatic and aromatic polyepoxides can be used. Suitable aliphatic polyepoxide compounds are commercially available from Henkel Corporation, Ambler Pennsylvania under the trademarks "Capcures Reg. TM" or "Photomers Reg. TM". Suitable aromatic polyepoxides are glycidyl derivatives of polymeric aromatic alcohols or amines. Suitable aromatic alcohols and amines are those containing more than two hydrogen equivalents capable of reacting with epichlorohydrin. Examples of suitable aromatic alcohols are novolac phenolic resins and poly(vinyl phenol)s. Illustrative of suitable polyhydric phenols are 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3-bromo-4-hydroxyphenyl)propane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis (3-chloro-4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfide, resorcinol, hydroquinone, phenol-formaldehyde novolac resins, and the like. Examples of suitable aromatic amines are 4,4-diaminodiphenylenemethane, 4,4-diaminodiphenylenesulfone, 3-aminobenzylamine, 3-phenylenediamine, 4,4-diaminoazodiphenylene, and the like.

One representative class of polyepoxide reactant according to the invention has the structural formula: ##STR1## wherein R.sub.4 designates a linear, branched or cyclic aliphatic, alicyclic or aromatic organic radical having a valency equal to the sum of `c` and `d`, where the sum of `c` and `d` is equal to or greater than 2 but no more than or equal to 6 and where `d` is equal to or greater than 2 but less than or equal to 6. When the sum of `c` and `d` equals two (2).sub.1 R.sub.4 designates a linear, branched or cyclic aliphatic, alicyclic or aromatic divalent organic radical having from 2 to 14 carbon atoms, and specifically includes the hydrocarbon portions of the dihydric alcohols and phenols, ethylene glycol, butylene glycol, hexylene glycol, decanediol, dodecanediol and bis-phenol A which remain after the hydroxyl groups have been removed, and when the sum of `c` and `d` equals three (3), R.sub.4 designates a linear, branched or cyclic aliphatic, alicyclic or aromatic trivalent organic radical having from 3 to 14 carbon atoms, and specifically includes the hydrocarbon portions of the trihydric alcohols and phenols, glycerol, 1,1,1-tris(hydroxymethyl)ethane, and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol which remain after the hydroxyl groups have been removed, and when the sum of `c` and `d` equals four (4), R.sub.4 designates a linear, branched or cyclic aliphatic, alicyclic or aromatic tetravalent organic radical having from 5 to 30 carbon atoms, and specifically includes the hydrocarbon portion of the tetrahydric alcohol pentaerythritol which remains after the hydroxyl groups have been removed, and when the sum of `c` and `d` equals five (5), R.sub.4 designates a linear, branched or cyclic aliphatic, alicyclic or aromatic pentavalent organic radical having from 6 to 30 carbon atoms, and when the sum of `c` and `d` equals six (6), R.sub.4 designates a linear, branched or cyclic aliphatic, alicyclic or aromatic hexavalent organic radical having from 8 to 30 carbon atoms, and specifically includes the hydrocarbon portion of the hexahydric alcohol dipentaerythritol which remains after the hydroxyl groups have been removed. The term "aromatics" embraces groups such as phenyl, naphthyl, quinolyl, pyridyl, indoyl and the like in which the aromatic ring may be substituted by groups such as C1 to C6 alkyl, nitro, halo and the like.

R.sub.5 represents a divalent polyoxyalkylene chain having the structural formula:

wherein

R.sub.6 is a monovalent organic radical selected from the group consisting of C.sub.1 to C.sub.4 aliphatic hydrocarbons,

`e` designates a number of ethoxy groups (CH.sub.2 --CH.sub.2 --O),

`f` designates a number of monosubstituted ethoxy groups (CH.sub.2 --CH(R.sub.6)--O) where the substitution of one monosubstituted ethoxy group is independent from the substitution of any other monosubstituted ethoxy group in the polyoxyalkylene chain, the sum of `e` and `f` is equal to or greater than 0 but less than or equal to 10, and where the sequence of ethoxy and monosubstituted ethoxy groups within a polyoxyalkylene chain may be completely random and/or there may be blocks of ethoxy and/or monosubstituted ethoxy groups.

The most preferred aliphatic polyepoxide compound is the reaction product of pentaerythritol, propylene oxide and epichlorohydrin, having an epoxide equivalent weight (EEW) of about 230.

The most preferred aromatic polyepoxides are epoxy novolac resins such as Araldite.TM. EPN 1138 and 1139, epoxy cresol novolac resins such as Araldite.TM. ECN 1235, 1273, 1280 and 1299, epoxy phenol novolac resins such as Araldite.TM. PV 720, epoxy resin 0510, Araldite.TM. MY 720 and 721, and Araldite.TM. PT 810 all of which are available from Ciba-Geigy, Ardsley, N.Y. Tetrad C and Tetrad X resins available from Mitsubishi Gas Chemical Company are also suitable for use in this invention.

The Epoxy Resin

The epoxy resin used in the practice of this invention comprises one or more polyglycidyl ethers of polyhydric phenols having two (2) or more epoxide groups and one (1) or more six-carbon aromatized rings present in the molecule, as represented by the structural formula: ##STR2## wherein R.sub.7 represents a `g` valent C.sub.6 -C.sub.50 organic radical comprising at least one six-carbon aromatized ring (e.g. when g is 2, R.sub.7 can be --CH.sub.2 --O--.o slashed.--C(CH.sub.3).sub.2 --.o slashed.--O--CH.sub.2 -- or R.sub.7 can be --CH.sub.2 --O--.o slashed.--CH.sub.2 --.o slashed.--O--CH.sub.2 -- wherein .o slashed. represents a phenyl group), and `g` is equal to or greater than 2 but less than or equal to 6.

Techniques to prepare such epoxy resins are known in the art, and include reacting compounds having 2 or more hydroxyl groups with epichlorohydrin in the presence of a suitable catalyst. Suitable epoxy resins are commercially available from a variety of sources and include EPON (Reg. TM) epoxy resins from Shell Chemical Company, Houston, Tex., and DER (Reg. TM) or DEN (Reg. TM) epoxy resins from Dow Chemical Company, Midland, Mich.

Examples of suitable epoxy resins are:

I) Polyglycidyl and poly(beta-methylglycidyl) esters obtainable by reacting a compound having at least two carboxy groups in the molecule with epichlorohydrin or beta-methyl-epichlorohydrin, respectively. The reaction is advantageously carried out in the presence of bases. Examples of aromatic polycarboxylic acids which may be used include, for example, phthalic acid, isophthalic acid or terephthalic acid.

II) Polyglycidyl or poly(beta-methylglycidyl) ethers obtainable by reacting a compound having at least two free phenolic hydroxy groups with epichlorohydrin or beta-methyl-epichlorohydrin, respectively, under alkaline conditions, or in the presence of an acid catalyst and with subsequent alkali treatment.

The epoxy compounds of this type may be derived from mononuclear phenols, such as, for example, resorcinol or hydroquinone; or they are based on polynuclear phenols, such as, for example, bis(4-hydroxyphenyl)methane, 4,4'-dihydroxybiphenyl, bis(4-hydroxyphenyl)sulfone, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl) propane, and from novolacs obtainable by condensation of aldehydes, such as formaldehyde, acetaldehyde, chloral or furfuraldehyde, with phenols, such as phenol, or with phenols that are substituted in the nucleus by halide atoms or C.sub.1 -C.sub.18 (preferably C.sub.1 -C.sub.9) alkyl groups, such as, for example, 4-chlorophenol, 2-methylphenol or 4-tert-butylphenol, or by condensation with bisphenols, in the manner described above.

There are preferably used epoxy resins that have an epoxy content of from 2 to 10 equivalents/mole and that are glycidyl ethers or glycidyl esters of aromatic or alkylaromatic compounds. Especially preferred epoxy resins are polyglycidyl ethers of bisphenols, such as, for example, of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) or bis(4-hydroxyphenyl)methane (bisphenol F), or novolacs formed by reacting formaldehyde with a phenol. For reasons of cost and availability, the most preferred epoxy resins are polyglycidyl ethers based on bisphenol A.

Preferred epoxy resins have an epoxide equivalent weight of less than about 400 grams/equivalent, e.g. from about 100 grams/equivalent to about 350 grams/equivalent, more preferably from about 150 grams/equivalent to about 225 grams/equivalent, e.g. DER 331 available from Dow Chemical at about 182 grams/equivalent.

The Polyhydric Phenol

The polyhydric phenol reactant comprises one or more compounds each having a plurality of hydroxyl groups covalently bonded to one or more six-carbon aromatized rings. The polyhydric phenol reactant may contain substituents such as alkyl, aryl, sulfido, sulfonyl, halo, and the like. The polyhydric phenol is represented by the structural formula:

wherein

R.sub.8 represents an `h` valent C.sub.6 -C.sub.50 organic radical comprising at least one six-carbon aromatized ring, and `h` represents a number of phenolic hydroxyl groups where `h` is equal to or greater than 2 but less than or equal to 6.

Techniques to prepare suitable polyhydric phenol compounds are known in the art. Suitable polyhydric phenol compounds are commercially available from Dow Chemical Company, Midland Mich., and Shell Chemical Company, Houston, Tex.

Illustrative of suitable polyhydric phenols are 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3-bromo4-hydroxyphenyl)-propane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis(3-chloro-4-hydroxyphenyl)propane, bis(4-hydroxyphenyl)-methane, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfide, resorcinol, hydroquinone, phenol-formaldehyde novolac resins, and the like. The most preferred dihydric phenols are 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and bis(4-hydroxyphenyl)methane (bisphenol F) for reasons of cost and availability.

The Amine-Epoxy Adduct

The preparation of certain of the self-dispersing curable epoxy resins of the invention proceeds through an amine-epoxy adduct, where the amine-epoxy adduct is subsequently reacted with an epoxy resin and, optionally, a polyhydric phenol. The structure of the amine-epoxy adduct is dependent on the structures of the polyoxyalkyleneamine and the polyepoxide used in the preparation of the amine-epoxy adduct, as well as the relative ratio of the reactants. The amine-epoxy adducts are complex in nature due to the multifunctional nature of the polyoxyalkyleneamine and the polyepoxide.

The Self-Dispersing Curable Epoxy Resin

Certain of the self-dispersing curable epoxy resins of the invention can be prepared by reacting an amine-epoxy adduct with a polyhydric phenol and an epoxy resin. The structure and composition of the self-dispersing curable epoxy resin will depend on the identity of the amine-epoxy adduct, the identity of the epoxy resin, the identity of the polyhydric phenol and the relative ratio of the reactants. The products of the above reaction are envisioned to be an extremely complex mixture of polymeric materials.

Organic Cosolvents

The self-dispersing curable epoxy resin of the present invention may be combined with a non-reactive, organic cosolvent. The cosolvent serves to reduce the viscosity of the self-dispersible curable epoxy resin before its dispersion in water as well as that of the aqueous pre-emulsion of the epoxy resin and the aqueous emulsion that is formed by reduction of the particle size of the resin in the pre-emulsion. Another function that the organic cosolvent may perform is the prevention of agglomeration of dispersed resin particles which stabilizes the dispersion of the resin. A variety of organic cosolvents are considered suitable for use in this invention. Suitable cosolvents consist of non-solvents as well as solvents for the self-dispersible epoxy resins. The cosolvent may be miscible, partly miscible or immiscible with water. Mixtures of two or more organic cosolvents can also be employed in this invention. Examples of organic cosolvents include the lower fatty acid esters or alkyl ethers of monohydric and dihydric alcohols (or polyethers thereof), wherein the alkyl group comprises C.sub.1 -C.sub.8 linear or branched aliphatic or alicyclic chains and lower alkyl ketones, e.g. ketones having a total of from 3 to 6 carbon atoms, preferably methyl lower-alkyl ketones, wherein said lower alkyl group has from 1 to 3 carbon atoms. The choice of cosolvent can affect the pot-life of the self-dispersing curable epoxy resin. For example, for a given resin it may be possible to increase the pot-life by substituting for a cosolvent such as Ektasolve EP (Eastman Chemicals) with one of the following cosolvents (the greater increase being obtained in order): 1-methoxy-2-propyl acetate, methyl n-amyl ketone, or dipropylene glycol n-butyl ether.

Reactive Diluents

The preferred stable aqueous epoxy resin dispersions of the present invention are those which contain a water-immiscible C.sub.8 -C.sub.20 aliphatic monoepoxide reactive diluent. The said monoepoxide component can contain alicyclic and aromatic structures, as well as halogen, sulfur, phosphorus, and other such heteroatoms. Suitable reactive diluents are available from CVC Specialty Chemicals, Inc., Cherry Hill, N.J.

Illustrative of monoepoxide reactive diluents are epoxidized unsaturated hydrocarbons such as decene and cyclohexene; glycidyl ethers of monohydric alcohols such as 2-ethylhexanol, dodecanol and eicosanol; glycidyl esters of monocarboxylic acids such as hexanoic acid; acetals of glycidaldehyde; and the like. The preferred reactive diluent is glycidyl ether of monohydric C.sub.8 -C.sub.10 aliphatic alcohols.

The presence of a water-immiscible C.sub.8 -C.sub.20 aliphatic monoepoxide reactive diluent in an aqueous epoxy resin dispersion has significant beneficial effects in addition to modifying the viscosity of the dispersion. For example, the said water-immiscible reactive diluent appears to coat the particles of epoxy resin solids and thereby provide the aqueous dispersion with improved shear, freeze-thaw resistance, shelf viscosity stability, and paint gloss.

Also, since the reactive diluent is epoxy functional, it becomes chemically bonded into the film which is formed during the subsequent room temperature curing of the aqueous dispersion composition after it has been blended with a curing agent and coated on a surface. The total quantity of reactive diluent contributes to the calculated proportion of non-volatiles in the dispersion composition.

Preparation of the Self-Dispersing Curable Epoxy Resin

In preparing certain of the self-dispersing curable epoxy resins of this invention, an amine-epoxy adduct is first prepared by combining the polyoxyalkyleneamine reactant and the polyepoxide reactant, heating the mixture slowly to about 130.degree. C., holding the mixture at temperature for about 2.5 hours, and then discharging the amine-epoxy adduct from the reactor. The respective self-dispersing epoxy resin is prepared by combining the amine-epoxy adduct, the polyhydric phenol and the epoxy resin, and heating the mixture in the presence of a catalyst, e.g., potassium hydroxide, triphenyl phosphine, benzyl dimethylamine and the like, to a temperature of about 150.degree. C. with stirring. An exothermic reaction will then occur, and cooling is applied to maintain the reaction temperature at about 150.degree.-160.degree. C. The mixture is maintained at about 160.degree. C. for about one hour subsequent to the conclusion of the exothermic reaction. If the reaction has not proceeded to the desired degree of completion (as determined by the epoxide equivalent weight of the resin), the mixture is then heated to 190.degree. C. The mixture is then maintained at 190.degree. C. for about 15 minutes in order to drive the reaction to the desired degree of completion, then cooled to about 160.degree. C. whereupon a small amount of a water-soluble organic solvent is added prior to cooling and discharging the self-dispersing curable epoxy resin from the reactor.

In certain embodiments, the polyoxyalkyleneamine is reacted directly with the epoxy resin to prepare a self-dispersing curable epoxy resin. The conditions employed for such a reaction may be the similar to the conditions under which the amine-epoxy adduct is formed.

Preparation of an Aqueous Dispersion of the Self-Dispersing Curable Epoxy Resin

The aqueous epoxy dispersion of the invention can be prepared by charging the self-dispersing curable epoxy resin, as a mixture with an organic cosolvent, to a reaction vessel, then heating the resin to about 50.degree.-100.degree. C. with stirring. Water is then mixed with the mixture of organic cosolvent and self-dispersing curable epoxy resin to form an aqueous pre-emulsion which will typically be a disperse oil phase having a larger particle size. The relative amounts of the resin, water and organic cosolvent can vary broadly, but will typically be roughly equal, e.g. the amounts of each of resin, water and organic cosolvent will range between about 20% to about 50% each, more typically from about 35% to about 45% resin, and about 25% to about 35% each of water and organic cosolvent. One or more reactive diluents can be mixed into the pre-emulsion prior to reduction of particle size or they can be added to the aqueous dispersion after the reduction of the particle size.

The particle size of the oil phase in the aqueous dispersion can be modified by physical techniques to reduce the particle size. The particle size reduction is preferably accomplished by subjecting the aqueous dispersion to high shear, e.g. in a homogenizer such as that disclosed in U.S. Pat. No. 4,533,254 (Cook et al.), the disclosure of which is incorporated herein by reference, and commercially available as MICROFLUIDIZER.TM. from Microfluidics Corporation, Newton, Mass. Homogenizers as well as other equipment suitable for making aqueous dispersion of epoxy resins are discussed in W. C. Griffin, "Emulsions", Encyclopedia of Chemical Technology, Vol. 8, pp. 900-930 (Kirk-Othmer, eds., John Wiley & Sons, Inc., New York, N.Y., 3d ed., 1979), the disclosure of which is incorporated herein by reference. High shear mixers suitable for reducing particle size are further described in Wicks, Z. W., Jr., Jones, F. N., Pappas, S. P., Organic Coatings: Science and Technology, Volume II, Application, Properties and Performance, John Wiley & Sons, Inc., New York, 1994, pp. 42-45, the disclosure of which is incorporated herein by reference.

After reduction of the particle size, at least a portion of the organic cosolvent is removed. The organic cosolvent is removed by volatilizing the same from the mixture. This is an evaporative process that may be considered a distillation. Sufficient organic cosolvent should be removed so that the aqueous dispersion will be low in volatile organic compounds, and preferably essentially free of such compounds. Typically, less than 1%, more typically less than 0.1% by weight of organic cosolvent remains in the aqueous dispersion.

The removal of the organic cosolvent will be facilitated by subjecting an agitated dispersion to elevated temperatures and/or reduced pressures, e.g. a vacuum distillation. The precise temperature and pressure employed to effect removal of the organic cosolvent will, of course, depend upon the volatility of the organic cosolvent chosen, but temperatures that will cause degradation or polymerization of the resin should be avoided. Distillation is discussed in E. Hafslund, "Distillation", Encyclopedia of Chemical Technology, vol. 7, pp. 849-891 (Kirk-Othmer, eds. John Wiley & Sons, N.Y., 3d ed. 1979) and evaporation is discussed in F. Standiford, "Evaporation", Encyclopedia of Chemical Technology, vol. 9, pp. 472-493 (Kirk-Othmer, eds. John Wiley & Sons, N.Y., 3d ed. 1980), the disclosures of which are incorporated by reference.

The aqueous dispersion of self-dispersing resin will typically exhibit excellent chemical and physical stability over an extended shelf-life, e.g. of from five to six months. As an example of the chemical stability, the epoxide equivalent weight (EEW) of the aqueous dispersion of self-dispersing resin should remain essentially constant, e.g. should show no trend of increasing molecular weight, over a period of at least one month from the preparation of the aqueous dispersion.

Epoxide equivalent weight can be determined by differential titration with perchloric acid using crystal violet as an indicator (e.g. a first sample is titrated with 0.1N perchloric acid to an endpoint that shows the first sight of green color from the crystal violet indicator, the amine equivalent weight of the dispersion is calculated from this titration, a second sample is mixed with excess tetraethylammonium bromide and titrated with 0.1N perchloric acid to a green endpoint that persists for at least 30 seconds, total epoxide and amine equivalents are calculated from this titration, and the epoxide equivalent weight is calculated as the difference).

As an example of physical stability, the resin should not display layer formation for a period of at least one month from the preparation of the aqueous dispersion, i.e. there should be no formation of a macro-observable water phase as a layer separate from the dispersed resin phase.

Coating Compositions Comprising an Aqueous Dispersion of the Self-Dispersing Curable Epoxy Resin

The coating composition of the invention is prepared by combining the aqueous epoxy dispersion with a suitable hardening agent. The coatings are tack free after 45 minutes and have excellent film properties. An aqueous epoxy resin paint composition of the present invention may further contain additives conventionally employed in coating technology, such as organic pigments, inorganic pigments, surfactants, thickeners, and the like.

A room temperature curable water-borne coating composition is prepared by admixing a stable epoxy dispersion composition as described above with an epoxy-interacting curing vehicle, such as a polyamine curing agent. The ratio of active amino hydrogens to epoxy groups in the admixture is in the range of from 0.5:1 to 2:1 and, preferably, is in the range between about 0.8:1 to 1.5:1. For purposes of industrial maintenance paint compositions, the amino hydrogens must be sufficiently reactive to effect crosslinking interaction with the epoxy groups at ambient temperatures.

Suitable polyamine curing agents are those which are soluble or dispersible in water and which contain more than 2 active hydrogen atoms per molecule. Examples of such curing agents are alkylene polyamines represented by the formula:

wherein `T` is an alkylene radical containing 2 to 6 carbon atoms and `u` is equal to or greater than zero (0) but less than or equal to five (5). Such alkylene polyamines include ethylene diamine, diethylene triamine, triethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, propylene diamine, dibutylene triamine, hexamethylene diamine, and the like. Other polyamine curing agents that can be employed in the practice of this invention are the polyamido amines, which are reaction products of alkylene polyamines and fatty acids. Such polyamidoamines are well known in the art and are described in U.S. Pat. Nos. 2,705,223, 2,811,495 and 2,899,397, which patents are hereby incorporated by reference. Other polyamine curing agents are the adducts of polyamines and epoxy compounds such as those described in U.S. Pat. Nos. 2,651,589, 2,864,775 and 4,116,900, which patents are hereby incorporated by reference.

The epoxy curing agents can comprise the reaction product of reactants consisting essentially of an alkylene polyamine having less than about 12 carbon atoms, an aromatic mono-glycidyl ether having less than about 18 carbon atoms, and a diglycidyl ether of an aromatic diol having an average degree of oligomerization of less than about 3.5, wherein the ratio of primary amine equivalents of said alkylene polyamine to the total epoxide equivalents of said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol is not essentially less than one, and the ratio of epoxide equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is greater than one. Another useful curing agent is described in U.S. Ser. No. 08/279,587, filed Jul. 25, 1994, abandoned the disclosure of which is incorporated herein by reference. These epoxy curing agents comprise the reaction product of reactants consisting essentially of: (a) an amine component consisting essentially of a mono-alkylene polyamine having less than about 12 carbon atoms (preferably a member selected from the group consisting of lower alkylene diamines, said member having from 2 to 8 carbon atoms and, more preferably, only straight-chain alkylene groups) and an alicyclic polyamine, said alicyclic polyamine being present in an amount of greater than about 10% of the amine equivalents of said amine component; (b) an aromatic mono-glycidyl ether having less than about 18 carbon atoms (preferably selected from the group consisting of mono-alkylphenyl glycidyl ethers and di-alkyl phenyl glycidyl ethers having from 9 to 13 carbon atoms); and (c) a diglycidyl ether of an aromatic diol having an average degree of oligomerization of less than about 3.5 (preferably less than about 1.5, and preferably derived from an alkyl bis-phenol, e.g. bisphenol A), wherein (i) the ratio of primary amine equivalents of said alkylene polyamine to the total epoxide equivalents of said aromatic glycidyl ether and said diglycidyl ether of an aromatic diol are greater than essentially one (i.e. the molar equivalents of primary amine groups of said polyalkylene polyamine are in excess of the molar equivalents of glycidyl groups, e.g. a ratio of from about 1.5:1 to 2.5:1, preferably from about 1.75:1 to about 2.25:1), and (ii) the ratio of epoxide equivalents of said aromatic mono-glycidyl ether to epoxide equivalents of said diglycidyl ether of an aromatic diol is greater than one (preferably greater than 1.5, more preferably from about 2:1 to about 6:1, and most preferably from about 3:1 to 5:1).

In addition to the amine curing agent, a curing accelerator can be included in the coating composition. Such an accelerator will serve to reduce the time for the coating to become tack-free. Useful accelerators for amine curing agents include tertiary amines, e.g. N,N'-bis(dimethyl-amino-propyl) urea.

Other curing agents can be used in the composition of this invention, particularly when the coatings made from the compositions are heated to effect a cure. Examples of such additional curing agents are the aminoplast and phenolplast resins. Suitable aminoplast resins are the reaction products of ureas and melamines with aldehydes further etherified in some cases with an alcohol. Examples of aminoplast resin components are urea, ethylene urea, thiourea, melamine, benzoguanamine and acetoguanamine. Aldehydes include formaldehyde, acetaldehyde and propionaldehyde. The aminoplast resins can be used in the alkylol form but, preferably, are utilized in the ether form wherein the etherifying agent is a monohydric alcohol containing from 1 to 8 carbon atoms. Examples of suitable aminoplast resins are methylol urea, dimethoxymethylol urea, butylated polymeric urea-formaldehyde resins, hexamethoxymethyl melamine, methylated polymeric melamine-formaldehyde resins and butylated polymeric melamine-formaldehyde resins.

Phenolplast resins are the reaction products of phenols and aldehydes which contain reactive methylol groups. These compositions can be monomeric or polymeric in nature depending on the molar ratio of phenol to aldehyde used in the initial condensation reaction. Examples of suitable phenols are phenol, o, m or p-cresol, 2,4-xylenol, 3,4-xylenol, 2,5-xylenol, cardanol, p-tert-butyl phenol, and the like. Useful aldehydes are formaldehyde, acetaldehyde and propionaldehyde. Particularly useful phenolplast resins are polymethylol phenols wherein the phenolic group is etherified with an alkyl, e.g., methyl or ethyl, group.

Other epoxy resin curing agents may also be useful, e.g. catalytic curing agents: Lewis bases (such as tertiary amines), Lewis acids (such as boron trifluoride), cationic curing agents (such as aryldiazonium salts, diaryliodinium salts, onium salts of Group VIa elements, especially sulfur) and reactive curing agents: mercaptans, isocyanates, carboxylic acids, and acid anhydrides. Curing agents for epoxy resins in general are discussed in the Encyclopedia of Polymer Science and Engineering, vol. 6, pp. 340-361 (John Wiley & Sons, Inc., N.Y., N.Y., 1986), the disclosure of which is incorporated by reference.

The following examples are further illustrative of the present invention. The reactants and other specific ingredients are presented as being typical, and various modifications can be derived in view of the foregoing disclosure within the scope of the invention.

Self-Dispersible Epoxy Resin

A suitable apparatus for this reaction consists of a round-bottomed flask, condenser, means for heating and controlling temperature such as heating mantle, Jack-o-maticO, thermocouple, stirrer and means for maintaining inert (nitrogen) atmosphere. The reaction flask was charged with 55.2 g (0.24 equiv.) of Capcure 711 (available from Henkel Corporation) and 44.8 g (0.09 hydrogen equiv.) Jeffamine ED2001 (available from Texaco Chemical Co.). Contents of the flask were heated with stirring to 95.degree. C. After 1.5 h of reaction at this temperature epoxy equivalent weight (EEW) of the reaction mixture was found to be 487. In a separate reaction flask, 261.5 g (1.34 equiv.) of D.E.R. 331 (available from Dow Chemical Co.), 81.5 g (0.72 equiv.) of bis-phenol A (available from Shell Chemical Co.), 57.0 g of the amine-epoxy adduct prepared above and 0.7 g of triphenylphosphine catalyst were heated with stirring to 160.degree. C. Care was exercised to control the exotherm by stopping heat and/or application of cooling as necessary. The reaction mixture was held at 160.degree. C. for 1.5 h and then heating was stopped. It was again heated to 160.degree. C. and held at that temperature for 35 min. At that time EEW of the product was determined to be 533 (after correction for amine value) and addition of 54.5 g Ektasolve EP (available from Eastman Chemical Co.) was made with cooling. The reaction mixture was then allowed to cool to room temperature. The reaction mixture was again heated to 85.degree. C. and addition of 92 g de-ionized water was made with stirring in 1.5 h. It was then cooled to 44.degree. C. and addition of another 38 g de-ionized water was made. At that time a sample of the reaction mixture was found to be inverted from water-in-oil phase to oil-in-water phase as evident by its ready dispersion in water. After that 130 g of de-ionized water was added over 1 h. After complete addition of water the product was heated to 55.degree. C. and held at that temperature for 1 h. This gave 678 g of an aqueous dispersion of self-dispersible epoxy resin of 2.7 micron average particle size and 56% solids.

Self-Dispersible Epoxy Resin with Jeffamine ED2001

The amine-epoxy adduct for this example was prepared similar to that for Example 1 except 58.4 g (0.25 equiv.) of Capcure 711 was reacted with 41.6 g (0.08 hydrogen equiv.) of Jeffamine ED2001 at 95.degree. C. for 1.5 h. The uncorrected EEW of the product was 462. Self-dispersible epoxy resin for this example was prepared similar to Example 1 from 261.5 g (1.34 equiv.) D.E.R. 331, 81.5 g (0.72 equiv.) bis-phenol A, 61.0 g of the amine-epoxy adduct and 0.7 g ethyl triphenylphosphonium iodide. The corrected EEW of product was 556 prior to the addition of 55 g Ektasolve EP. The reaction product obtained was heated to 65.degree. C. and addition of 82.5 g deionized water was made in one hour. The reaction mixture was then cooled to 50.degree. C. and addition of 192 g deionized water was made in one hour. After cooling to room temperature addition of 150 g deionized water was made with stirring. Aqueous dispersion of the self-dispersible resin was obtained with 3.45 average particle size and 44.8% solids.