Aqueous epoxy resin dispersions

Abstract

The invention relates to an aqueously dispersible epoxy resin E, comprising building blocks derived from an aliphatic polyether polyol A, an epoxy resin B having at least two epoxide groups per molecule, an epoxy resin B having at least two epoxide groups per molecule, which may be identical to B, or different from B, an epoxy-functional fatty acid ester D, and an aromatic polyol C, a process for the preparation thereof, and a method of use thereof.

Claims

1. A process of making an aqueous epoxy resin dispersion comprising an aqueously dispersible epoxy resin E, which process comprises reacting in the first step an aliphatic polyether polyol A and an epoxy resin B having at least two epoxide groups per molecule, wherein an adduct AB is formed, this adduct AB is then reacted in the second step in an advancement reaction with a further epoxy resin B, the epoxy functional fatty acid ester D, and an aromatic polyol C, wherein the amount of D is chosen such that a portion of at least 5% thereof remains unreacted.

2. The process of claim 1 wherein in the first step, the quantities of the aliphatic polyether polyol A and an epoxy resin B having at least two epoxide groups per molecule are chosen such that the ratio of the number of OH groups in the aliphatic polyol A to the number of epoxy groups of the epoxy compound B used in the condensation reaction is from being from 1:0.85 to 1:3.5, and the specific amount of substance of epoxy groups of said condensation product being between 0.002 mol/kg and 5 mol/kg.

3. The process of claim 1 wherein the adduct AB, further epoxy resin B and aromatic polyol C are first reacted in the second step in the presence of a catalyst until at least 90% of the epoxy groups present in the reaction mixture have been consumed, and then to add component D and optionally, further catalyst, and carry the reaction to completion.

4. An aqueous epoxy resin dispersion comprising an aqueously dispersible epoxy resin E, wherein the aqueously dispersible epoxy resin E comprises building blocks derived from an aliphatic polyether polyol A, an epoxy resin B having at least two epoxide groups per molecule, an epoxy resin B having at least two epoxide groups per molecule, which may be identical to B, or different from B, an epoxy-functional fatty acid ester D, an aromatic polyol C, and unreacted epoxy-functional fatty acid ester D in an amount to correspond to a mass fraction of from 0.5% to 20%, where the mass fraction is the ratio m.sub.D/m.sub.E of the mass m.sub.D of the component D to the mass m.sub.E of resin E in the composition; wherein the aqueous rpoxy resin dispersion is made by process according to claim 1.

5. The aqueous epoxy resin dispersion of claim 4 wherein the aliphatic polyether polyol A is a polyoxyalkylene ether glycol comprising a mass fraction of at least 20% of oxyethylene groups, and has a number average molar mass M.sub.n of from 0.2 kg/mol to 20 kg/mol.

6. The aqueous epoxy resin dispersion of claim 4 wherein the epoxy resin B having at least two epoxide groups per molecule, and which has a polyether structure which in turn has moieties derived from 1,2,3-trihydroxypropane and moieties derived from aromatic dihydroxy compounds.

7. The aqueous epoxy resin dispersion of claim 4 wherein the epoxy resin B has at least two epoxide groups per molecule, and may be identical to B, or different from B, and which has a polyether structure which in turn has moieties derived from 1,2,3-trihydroxypropane and moieties derived from aromatic dihydroxy compounds.

8. The aqueous epoxy resin dispersion of claim 4 wherein the epoxy-functional fatty acid ester D is an ester of an at least monovalent aliphatic alcohol D1 having from one to ten carbon atoms, and a monofunctional fatty acid D2 having from six to thirty carbon atoms, wherein at least one of the alcohol D1 and the fatty acid D2 has an epoxy group in its molecule.

9. The aqueous epoxy resin dispersion of claim 4 wherein the aromatic polyol C is an aromatic compound having from five to twenty carbon atoms and at least two hydroxyl groups.

10. The aqueous epoxy resin dispersion of claim 4 wherein the amount of epoxy functional fatty acid ester D is chosen to correspond to a mass fraction of from 1.5% to 15%, where the mass fraction is the ratio m.sub.D/m.sub.E of the mass m.sub.D of the component D to the mass m.sub.E of resin E in the composition.

11. A method of use of the aqueous epoxy resin dispersion of claim 4 comprising the steps of admixing one or more curing agents selected from the group consisting of the basic curing agents polyfunctional amines, adducts of amines and epoxy resins, Mannich bases, polyamidoamines, polycarboxylic acids and anhydrides thereof, polyfunctional phenols, and aminoplast and phenoplast resins, with the aqueous epoxy resin dispersion to form a mixture, depositing the mixture formed on substrates by methods selected from the group consisting of brushing, spraying, dipping, rolling on, and applying with a coating blade or wire, and curing the applied coating film by heating.

12. The method as claimed in claim 11, wherein the substrate is metal, wood, glass, concrete, plastic or ceramic.

Description

EXAMPLE 1

Preparation of an Emulsifier AB

EXAMPLE 1.1

(1) 1500 g of a polyethylene glycol having a weight average molar mass M.sub.w of 3 kg/mol and 185 g of a polyglycidyl ether based on bisphenol A having a specific amount of substance of epoxy groups of 5.41 mol/kg (corresponding to an epoxy equivalent of 185 g/mol) were heated together to 100 C. 9 g of BF.sub.3-diethyl etherate, diluted to 5% by weight with 1,4-dioxane, were added while stirring. The reaction mixture was then heated to 130 C. and kept at this temperature until the reaction had finished, which was indicated by the decrease of the specific amount of substance of epoxy groups to the specified value. The ratio of the number of OH groups to the number of epoxide groups was 1:1, and the specific amount of substance of epoxy groups of the reaction product was 2.8 mmol/kg (epoxy equivalent of approx. 360,000 g/mol).

EXAMPLE 1.2

(2) In another run, 300 g of polyethylene glycol having a weight average molar mass M.sub.w of 4 kg/mol and 34.4 g of a polyglycidyl ether based on polyoxypropylene glycol having specific amount of substance of epoxy groups of 5.03 mol/kg (corresponding to an epoxy equivalent of 199 g/mol) were heated together to 100 C., and 0.7 g of BF.sub.3-diethyl etherate, diluted with 10 ml of methyl isobutyl ketone, were added while stirring. The reaction mixture was then heated to 130 C. and kept at this temperature until the reaction had finished, which was indicated by the decrease of the specific amount of substance of epoxy groups to the specified value. The ratio of the number of OH groups to the number of epoxide groups was 1:1.15, and the specific amount of substance of epoxy groups was 6.7 mmol/kg (corresponding to an epoxy equivalent of approximately 150,000 g/mol).

EXAMPLE 2

Preparation of an Aquenusly Dispersed Epoxy Resin

(3) 2400 g of the diglycidyl ether of bisphenol A 400 g of an aqueous solution of the emulsifier of Example 1.1 (concentration of 50%), and 725 g of bisphenol A were mixed and heated to 85 C. Water was distilled off under reduced pressure, and then 1.6 g of triphenyl phosphine were added, and the mixture was heated to 150 C. under stirring. After one hour, 195 g of epoxidised soy bean oil were added together with another 1 g of triphenyl phosphine. The reaction was continued for two further hours, and then, 600 g of cold, fully deionised water were gradually added under vigourous stirring. The vessel temperature fell to 70 C., whereafter further three portions of 218 g of fully deionised water were added under stirring, at 60 C. The resulting whitish dispersion was then cooled to room temperature, and further 1400 g of fully deionised water were added.

(4) A resin dispersion having a mass fraction of solids of 57% was obtained, with an average particle size of 690 nm, and a viscosity of 790 mPa.Math.s at a shear rate of 100 s.sup.1, and 23 C.

EXAMPLE 3

Application Testing

(5) Clear coating compositions were prepared according to the following recipe:

(6) 50 g each of the resin dispersion of example 2, and for comparison, a resin dispersion prepared in accordance with example IV-1 of EP 0 272 595 B1 which contained 3% of benzyl alcohol and 7% of methoxypropanol, were mixed with 25.3 g, and 19.4 g, respectively, of a commercial adduct curing agent of an epoxy resin and an aliphatic amine (Beckopox VEH 2188/55WA, Cytec Austria GmbH). Viscosity was adapted by addition of fully deionised water to 830 MPa.Math.s for both systems. Potlife was determined to be 3 h in each case.

(7) These clear coating compositions (Paint 3.1 with the epoxy resin dispersion of example 2, and paint 3.2 with the comparative epoxy resin dispersion) were applied to glass plates and dried at 23 C. for seven days (approximately 70 m dry film thickness). Both coating films were tested for hardness (pendulum hardness measured according to the procedure of Knig, DIN EN ISO 1522, in ambient condition which is 23 C. and 50% of relative humidity, and 23 C. and at 100% relative humidity for the saturated steam test).

(8) Adhesion to the steel plates was on the same level for both, with a cross hatch test result of GT 0. Impact test in accordance with the Gardner method was conducted in accordance with ASTM D 2794-93 (1in.Math.lb=25.4 mm4.448 N=113.0 mJ) and measured on coated steel panels with a dry film thickness of approximately 55 m. The results are summarised in table 1:

(9) TABLE-US-00001 TABLE 1 Application results Paint of example Result for unit 3.1 3.2 Hardness after 24 h s 67 36 Hardness after 48 h s 81 46 Hardness after 7 d s 111 87 Hardness in saturated steam phase s 99 56 Gardner Impact in .Math. lb (J) 10 (1.13) 20 (2.26) Corrosion Test (EN ISO 9227) after blistering 1 (S3) 2 (S3) 840 h creep from scratch after 840 h mm 8 16

(10) It can easily be seen from the examples that the absence of benzyl alcohol and the presence of component D both provides faster development of hardness in the coating film, and better humidity resistance. The Gardner impact which is a measure for the elasticity of the film is also improved vis-a-vis the standard system which has benzyl alcohol as coalescent agent.

(11) As was expected, the VOC level is markedly reduced by the absence of benzyl alcohol, from a level of 188 g/L (resin dispersion for coating composition 3.2) to 4 g/L (resin dispersion for coating composition 3.1 according to the invention). The corrosion test was conducted in conformance with EN ISO 9227 (NSS Test), each sample having been tested with central scratch. Creep distance from the central scratch was markedly reduced which shows the excellent corrosion resistance achieved with a coating made from the resin composition of the present invention.