GB2039912A - Air drying aqueous epoxyacrylic copolymer coating compositions - Google Patents

Abstract

An aqueous coating composition comprises (I) an acid-neutralized organic solvent soluble copolymer comprising at least 60% of non reactive monoethylenic monomer, and from 15- 40% of monoethylenic tertiary amine monomer, the copolymer being in solution in a water miscible organic solvent; and (II) a resinous polyepoxide in solution in an organic solvent which is at least partially water miscible. The composition may be supplied as a "two- component pack" comprising I and II.

Description

SPECIFICATION Air drying thermosetting aqueous epoxy-acrylic copolymer coating compositions The present invention relates to thermosetting aqueous epoxy-acrylic copolymer coating compositions which are adapted to cure on air drying. Such compositions are intended for use in coating systems comprising two packages which cure upon admixture with one another and are particularly adapted for the painting of porches and floors, including cementitious substrates.

Aqueous coating systems of this general nature are known for example from United States Patent 3,719,629. However these known systems tend not only to be expensive, but also to exhibit poor chalking resistance, and poor tint retention. Furthermore they tend to be unsatisfactory from the standpoints of (1) applicability to porches; (2) film hardness; and (3) cracking resistance.

In the aqueous coating systems of US Patent 3,719,629, an apoxy resin is combined in an aqueous medium with an aminoethylated vinyl polymer having pendant aminoethyl groups, these groups having the formula:

and the cure is between the oxirane (epoxy) group in the epoxy resin and the amino hydrogen atoms in the aminoethyl group pictured. The production of the pendantaminoethyl groups requires the use of ethylene imine which is expensive and hazardous.

It is an object of the present invention to avoid the use of such expensive and hazardous materials.

Other resin systems have been proposed to provide air drying porch and floor paints, for example, two aqueous systems, one based on an alkyd resin and another based on an aqueous copolymer latex, and also an organic solvent-based epoxy system.

It is a further object of the invention to provide a coating having superior properties to those of these three systems.

According to the present invention a thermosetting aqueous epoxy resin-acrylic copolymer coating composition comprises water having dissolved therein an acid-neutralised organic solvent soluble tertiary amine copolymer of copolymerized monomers substantially free of any hydroxy functional monomer and comprising at least about 60% of a nonreactive monoethylenic monomer, and from 15-40% of a monoethylenic tertiary ethylenic monomer, selected from the group consisting of esters and amides of monoethylenic carboxylic acids, the water further including a resinous polyepoxide.

The copolymer is preferably in solution in a water-miscible inert organic solvent and may also be partially in solution in water. The resinous polyepoxide may be in solution in an inert organic solvent which is at least partially water-miscible.

A two package system is preferably employed in the present invention. One may include the acid-neutralised tertiary amine copolymer in solution in a water-miscible alcoholic solvent. The other may contain the epoxy resin, preferably together with a catalyst for the epoxy-tertiary amine reaction, in solution in an organic solvent which may be at least partially water-miscible, and which is preferably alcoholic. Before applying the coating, the two separately stable solution components may be mixed together to form an aqueous mixture of limited pot life, and this aqueous mixture may be coated upon the surface to be painted.

The water which is present in the aqueous mixture is preferably added to the first component prior to admixture of the two components, but all or a portion of the water can be added to the first component prior to admixture of the two components, but all or a portion of the water can be added after the mixture is formed. The first component also desirably includes a surfactant for maintaining the epoxy resin in a relatively stable emulsion in the aqueous mixture which is provided.

Typical coatings produced by the present invention may have a pot life of at least about 8 hours, usually about 12-14 hours, and can be applied by roller, brush, or air spray. The applied aqueous coatings may dry to the touch in air at room temperature in about 6-7 hours and become water and solvent resistant in about 8-12 days. Recoat properties may be comparable to that of conventional porch and floor paints. Polymer solubility may be obtained using acids like lactic or acetic acid which are less toxic than anionic systems solubilised with amines, and generally less than 10% of nonobectionable alcoholic solvents are needed which is advantageous from the point of view of cost, hazard, pollution, and the like.

The tertiary amine copolymers are preferably organic solvent-soluble copolymers comprising two copolemerized monoethylenically unsaturated components, namely: (1) nonreactive monomer; and (2) tertiary amine monomer. While small amounts of other monomers may be present, such as monoethylenic carboxylic acids, monoethylenic am ides or N-methylol derivatives thereof, or polyethylenic hydroxyfunctional materials such as polyesters, these are not essential.

The nonreactive monoethylenically unsaturated (monoethylenic) monomer preferably constitutes at least about 60% of the copolymer in order to provide the desired physical characteristics. Styrene is the preferred nonreactive monoethylenic monomer, but vinyl toluene may also be used. Methyl methacrylate, acrylonitrile, and vinyl acetate are further examples of suitable nonreactive monomers. A portion of a flexibilising nonreactive monomer may also be present, such as ethyl acrylate or methacrylate or butyl acrylate or methacrylate. These flexibilising monomers can be more generally defined as C2 - C18 alkanol esters of monoethylenic carboxylic acids.

Preferably the nonreactive monomer component will constitute from about 60% to about 85% of the weight of the tertiary amine copolymer, typically about 73%.

An important component of the tertiary amine copolymer is the monoethylenic tertiary amine monomer.

Typical tertiary amine monomers may be dimethyl aminoethyl acrylate or methacrylate, dimethyl aminopropyl acrylate or methacrylate, diethyl aminomethyl acrylate or methacrylate, and diethyl aminoethyl or aminopropyl acrylate or methacrylate. The corresponding crotonates and tertiary amino esters of other monoethylenic carboxylic acids are also suitable. Additionally, the corresponding amides such as dimethyl aminoethyl methacrylamide are suitable.

The proportion of the tertiary amine monomer can vary in the same way as the hydroxy monomer, namely, from 15-40% by weight of the copolymer, preferably from 20-30% by weight.

Water miscible organic solvents which may be used in this invention are preferably alcoholic for example ethanol, propanol, isopropanol, n-butanol, isobutanol, 2-ethoxy ethanol and 2-butoxy ethanol.

The specific nature of the solubilising acid used to disperse the amine copolymer in water may be of secondary significance. Inorganic acids, such as hydrochloric acid or sulphuric acid, may be used, though these are not preferred. It is preferred to employ phosphoric acid, glycolic acid (hydroxy acetic acid), or acetic acid, but other acids can be used, such as formic acid, carbonic acid, or propionic acid.

The solubilising acid is used in an amount to provide a colliodal dispersion having a preferred pH in the range of pH 6.0 - 7.0, though a pH in the range of pH 3 - 8 may be employed.

The epoxy resins which are used in this invention can be broadly referred to as resinous polyepoxides, and those which possess a 1, 2-epoxy equivalency in the range of about 1.4 to about 2.0 are preferred.

Polyepoxides which are diglycidyl ethers of bisphenols are particularly preferred, especially those having an average molecular weight in the range of about 350 to 4000. A diglycidyl ether of bisphenol A having an average molecular weight of about 390 will be used to illustrate the invention.

The polyepoxide component is itself conventional, as discussed in U.S. Patent No.3,719,629 referred to above.

The polyepoxide is desirably used in an amount providing approximate stoichiometry between epoxy groups in the polyepoxide and tertiary nitrogen atoms in the amine copolymer, + 50%, more preferably + 20%.

The organic solvent component of the package containing the polyepoxide is intended to provide a desirable liquidity, particularly since the polyepoxide is normaily a viscous liquid or a solid at room temperature. Since it is desired that the polyepoxide be stably dispersed in the aqueous mixture which is ultimately produced, the organic solvent is preferably at least partially water miscible, but the partial miscibility which is intended need merely be that which is consistent with the ultimate stable dispersion which is contemplated, and it is most accurate to refer to the form of the dispersion as an emulsion since the presence of the polyepoxide component in the aqueous mixture which is formed is such as to induce considerable opacity to the liquid mixture.

A su rfactant may be included in the polyepoxide solution in order to stabilize the aqueous emulsions which are formed. Appropriate surfactants may be nonionic or anionic and the selection of surfactants appropriate for the emulsification of epoxy resins in water is well known and is not a feature of this invention. Surfactants, though preferable, are not essential, however, since the cationic copolymer itself functions to help to maintain the epoxy resin in a relatively stable emulsion.

Catalysts may also be included for the tertiary amine-epoxy curing reaction. This reaction is itself well known, and thus the selection of catalysts for the reaction is not a feature of the invention. Appropriate catalysts are Lewis acids, such as dibutyl tin dilaurate, though, no catalyst is essential, and none is used in the preferred form of the invention.

The systems of this invention can be applied clear or pigmented, but pigmented systems containing titanium dioxide rutile at a pigment to binder ratio of 0.3:1.0 are preferred.

The invention may be carried into practice in various ways and some embodiments will be illustrated in the following examples.

EXAMPLE I Preparation of solvent soluble tertiary amine copolymer in solution in water miscible organic solvent 450 parts of 2-butoxy ethanol are heated to 1200C in a reactor equipped with an agitator, a reflux condenser, a thermometer, and a nitrogen inlet tube for sparging the reaction mixture.

Monomers and catalysts are premixed in an addition tank. 900 parts of styrene, 630 parts of butyl acrylate, 560 parts of dimethyl aminoethyl methacrylate and 30 parts of azobisisobutyronitrile are thus premixed and slowly added to the reactor over a period of 3 hours. The temperature in the reactor is maintained at 120"C during the period of addition and for one hour thereafter.

To complete the monomer conversion, 2 parts of azobisisobutyronitrile are added and the reaction is continued for one hour at 120"C. 2 more parts of the same catalyst are then added and the reaction continued for 2 additional hours at the same temperature.

The product is then cooled to about 70"C and 250 parts of 2-butoxy ethanol are added together with 700 parts of 2-ethoxy ethanol and the final copolymer solution is filtered to provide a solution having a Gardner viscosity of Z1, a Gardner-Holdt colour of 1-2 and a nonvoiatile solids content of 58.4%.

EXAMPLE II Preparation of pigmented acidified copolymer aqueous solution.

Parts Component 223.6 - solution of Example I 3 surfactant (note 1) 150 titanium dioxide rutile 50 amorphous silica 4 Attapulgus clay Note 1 - The surfactant utilized is the American Cyanamide product Aerosol C-61 which is a cationic surfactant. Surfactant selection is not critical.

The above mixture is ground at high speed and then, with slow agitation, 12 parts of acetic acid are slowly added. After continuing the agitation for 3 minutes, 558.11 parts of water containing 1 part of 37% aqueous formaldehyde and 1.5 parts of a biocide are added. The formaldehyde and the biocide prevent the growth of mould and are optional. 1.0 part of defoamer (Drew Chemical Company L-475) may also be used, but is not essential.

EXAMPLE Ill Preparation ofpolyepoxide curing solution Parts Component 3.04 Diglycidyl ether of bisphenol A having an average molecular weight of 390.

10.1 2-butoxy ethanol.

EXAMPLE IV Upon admixture of the solutions of Example II and Ill, an aqueous emulsion which has a pot life of about 8 hours is obtained. Coating this emulsion by brushing on a concrete surface followed by air drying at room temperature for 8 hours provided a painted surface which was hard enough to be walked upon without being marred.

The advantages of the invention will be apparent from the tabulated data presented below in which X indicates a positive feature, 0 indicates a negative feature, and 1 indicates neither.

TABLE Competitive materials in commerce US Patent Example Two-Component 3,719,629 Property IV Latex Alkyd Epoxy (Dow) Water based X X X Solvent based O 0 Price X X X O 0 One Package X X Two Package O 0 0 Ease of Clean Up X X O O X Use on Previous Paints X X X O X Flammable X X O O X Use on Interior X X O O X Hazardous 1 0 Use on Porches X X X O ? One Coat Hide X O O X X Alkali Resistance X X O X X Abrasion Resistance X 1 1 X X Chemical Resistance X 1 O X X Hardness X O 0 1 1 Good Adhesion X X X X X Tire Track Adhesion X O 1 X X Tint Retention 1 X 1 0 0 Chalking Resistance 1 X 1 0 0 Cracking Resistance 1 1 1 ?

Claims (12)

1. A thermosetting aqueous epoxy resin-acrylic copolymer coating composition comprising water having dissolved therein an acid-neutralized organic solvent soluble tertiary amine copolymer of copolymerized monomers substantially free of any hydroxy functional monomer and comprising at least about 60% of a non-reactive monoethylenic monomer, and from 15-40% of a monoethylenic tertiary amine monomer selected from the group consisting of esters and amides of monoethylenic carboxylic acids, the water further including a resinous polyepoxide.

2. A thermosetting aqueous coating system as claimed in Claim 1 in which the copolymer is in solution in a water-miscible inert organic solvent.

3. A thermosetting aqueous coating system as claimed in Claim 1 in which the copolymer is in solution in a mixture of water and a water-miscible inert organic solvent.

4. A thermosetting aqueous coating system as claimed in any preceding claim which is curable upon drying in air.

5. A thermosetting aqueous coating system as claimed in any preceding claim in which the resinous polyepoxide is in solution in an organic solvent which is at least partially water-miscible.

6. A thermosetting aqueous composition as claimed in any preceding claim in which the resinous polyepoxide is a diglycidyl ether of a bisphenol having an average molecular weight in the range 350-4000.

7. A thermosetting aqueous coating system as claimed in any preceding claim in which the polyepoxide is used in an amount providing approximate stoichiometry between epoxy groups in the polyepoxide and tertiary nitrogen atoms in the amine copolymer + 50%.

8. A thermosetting aqueous coating system as claimed in any preceding claim in which the water miscible organic solvent is alcoholic.

9. Athermosetting aqueous coating system as claimed in any preceding claim in which the amine copolymer consists essentially of from about 60% to about 85% of the nonreactive monomer, and from 20-30% of the tertiary amine monomer.

10. A thermosetting aqueous coating system as claimed in any preceding claim in which the tertiary amine monomer is a dimethyl or diethyl amino alkyl acrylate, methacrylate, acrylamide or methacrylamide.

11. A thermosetting aqueous coating system as claimed in any preceding claim in which the component containing the polyepoxide includes a surfactant for emulsifying the polyepoxide in water.

12. A thermosetting aqueous epoxy resin-acrylic copolymer coating composition substantially as herein specifically described with reference to Example VI in the accompanying Examples.