WO1996035735A1

WO1996035735A1 - Alkoxylated dimethylolpropionic acid modifier

Info

Publication number: WO1996035735A1
Application number: PCT/US1996/006443
Authority: WO
Inventors: Michel J. Hourani; Thomas H. Marman
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-05-08
Filing date: 1996-05-08
Publication date: 1996-11-14
Anticipated expiration: 1997-11-08
Also published as: AU5919096A

Abstract

The present invention is a modifier for use in preparing a prepolymer having free acid groups, a prepolymer, a coating composition containing the prepolymer, and methods for preparing the prepolymer and the coating composition. The modifier is a mixture of compounds prepared by reacting dimethylolpropionic acid with at least one alkylene oxide. The prepolymer is prepared by reacting a modifier with at least one organic compound which is terminated with at least two groups independently chosen from the group consisting of isocyanate, hydroxyl, carboxyl, and epoxy. The free acid groups on the prepolymer are neutralized to form a water-borne prepolymer useful in coating compositions.

Description

ALKOXYLATED DIMETHYLOLPROPIONIC ACID MODIFIER

Field of the Invention

The present invention relates to coating compositions, to prepolymers used in preparing coating compositions, and to modifiers used to add free acid groups to the prepolymers. Background of the Invention

Coatings are used extensively in commerce and industry to protect the exterior walls of buildings, industrial machinery, military equipment and vehicles, commercial and passenger vehicles, and other surfaces. They are also used as sealants and adhesives. Coatings protect surfaces from destructive environmental conditions such as exposure to ultraviolet radiation (UV), acid rain, salt, chipping agents such as stones and hail, and extremes in temperature and humidity. Protection of surfaces is particularly important in geographical areas with harsh environmental conditions. For example, in arid regions, surfaces are exposed to high amounts of UV radiation. In other geographical regions, surfaces are exposed to ocean spray, road salt, or acid rain.

Many coatings are prepared by reacting organic compounds with modifiers to form prepolymers having free acid groups or "water-reducible" prepolymers. The free acid groups make the water-reducible prepolymers soluble or dispersible in water, and thus amenable to use in a coating formulation. The water-reducible prepolymers may then be treated with agents to neutralize the free acid groups in water and to form neutralized or "water-borne" prepolymers. The water-borne prepolymers may then be chain-extended to form higher molecular weight polymers. The water-borne prepolymers or the higher molecular weight polymers are then used in coating formulations.

Introducing free acid groups to a prepolymer has been done by reacting dimethylolpropionic acid with at least one organic compound to form a water- reducible prepolymer having free acid groups. Dimethylolpropionic acid ("DMPA") is a trifunctional compound incorporating a hindered, tertiary carboxylic acid group and two reactive, primary hydroxyls. The hindered carboxylic acid group is less reactive than most acid groups, and, therefore, DMPA reacts as a diol, leaving the carboxyl group to provide the water-reducible prepolymer with free acid groups.

An object of the instant invention is to provide a modifier to be used as an alternative to DMPA in preparing a prepolymer having free acid groups. Other objects of the invention are to provide a prepolymer having free acid groups, a method of preparing the prepolymer, a coating composition comprising a water- borne prepolymer prepared from the prepolymer having free acid groups, and a method of preparing the coating composition. Summary of the Invention The present invention is a modifier for use in preparing a prepolymer having free acid groups. The modifier is prepared by reacting dimethylolpropiomc acid with at least one alkylene oxide, thereby alkoxylating the hydroxyl groups on dimethylolpropionic acid to produce a mixture of compounds. Examples of alkylene oxides are ethylene oxide and propylene oxide. The present invention also encompasses a method of preparing a prepolymer having free acid groups, a "water-reducible" prepolymer. The water- reducible prepolymer is prepared by reacting the modifier with at least one organic compound. Suitable organic compounds are those terminated with at least two groups independently chosen from the group consisting of isocyanate, hydroxyl, carboxyl, and epoxy.

Further aspects of the present invention are a coating composition prepared using the water-reducible prepolymer and a method of preparing a coating composition. Detailed Description of the Invention The modifier of the instant invention is prepared by the process of alkoxylating the hydroxyl groups on dimethylolpropionic acid. The essential feature, the hindered carboxylic acid group, is still present in the product modifier; the carboxylic acid group of the modifier is sterically hindered by hydroxyalkyl or hydroxyalkyl ether groups. The modifier comprises a mixture of two or more different compounds, each compound having the general structure: OH I O= C I

HOR j O CH₂ C CH₂ O R₂ OH

CH₃ wherein for each compound R_j and R are independently chosen from the group consisting of alkyls and alkyl ethers. Examples of alkyls are ethyl and propyl; examples of alkyl ethers are ethylether and propylether. The distribution of compounds in the mixture will depend upon the alkylene oxide(s) used to synthesize the modifier. For example, where the alkylene oxide used is ethylene oxide, R_j and R2 will be ethyl, ethoxyethyl, or a polyether of the form -(CH2- CH2-O)_n-CH2-CH2, wherein n is an integer and wherein the n for R_j may differ

The alkoxylation reaction is carried out by reacting dimethylolpropionic acid with at least one alkylene oxide. Examples of alkylene oxides are ethylene oxide and propylene oxide.

The modifiers of the instant invention which are liquids will be further beneficial in that where they are used to prepare prepolymers for coatings, more homogeneous prepolymer solutions will be possible. Preferred modifiers have a melting point of less than about 50°C, most preferably less than about 40°C. In addition, ether linkages in the modifiers may provide better solubility of the modifier also providing more homogeneous polymer solutions. The modifier of the instant invention is intended to include modifier mixtures which are purified or subjected to separation procedures so that the modifier used comprises at least a portion of the mixture produced by the alkoxylation reaction, i.e. , at least two different products or compounds which result from reacting the dimethylolpropionic acid with at least one alkylene oxide. Purification or separation may be useful in making the modifiers more amenable to use in reaction with an organic compound to form a prepolymer.

Many coatings are prepared using prepolymers having free acid groups or water-reducible prepolymers. The water-reducible prepolymers may be prepared by reacting the modifier with at least one organic compound to form a prepolymer having free acid groups. The free acid groups on the water-reducible prepolymer may be used to make the water-reducible prepolymer soluble in water or dispersible in water after neutralization with a base. Adding free acid groups is also a way in which a polar group may be introduced to improve the adhesion of coatings or adhesives made from the prepolymer or to improve the dye receptivity of synthetic fibers made from the prepolymer. Free acid groups may also be added to increase the alkali solubility of deposited films in applications such as photoprint plates or photoresists.

Organic compounds with which the modifier of the present invention may be reacted are those which are terminated with at least two groups independently chosen from the group consisting of isocyanate, hydroxyl, carboxyl, and epoxy. For example, a polyurethane prepolymer is formed by reacting the modifier with two organic compounds, an organic compound terminated with at least two isocyanate groups and an organic compound terminated with at least two hydroxyl groups (a polyol); polyesters or alkyds are formed by reacting a polyol with the modifier in the presence of a dibasic acid.

Examples of isocyanate-terminated organic compounds which may be used to form a urethane prepolymer are toluene diisocyanate, diphenylmethane-4,4'- diisocyanate, bis(4-isocyanatocyclohexyl)methane, and isopherone diisocyanate. Polyols which may be used to form the urethane prepolymer are glycerol, trimethylol propane, neopentyl glycol, pentaerythritol, 1,4-butanediol, poly(butylene glycol), poly (ethylene glycol), wherein the poly (ethylene glycol) may be either monofunctional (terminating in an alkyl group) or difunctional (terminating in a hydroxyl group).

Examples of polyols which may be used to form a polyester or an alkyd prepolymer are glycerol, ethylene glycol, neopentyl glycol, trimethylol propane, pentaerythritol, and propylene glycol. Examples of dibasic acids are oleic acid, linoleic acid, linolenic acid, eleostearic acid, ricinoleic acid, phthalic anhydride, trimellitic anhydride, isophthalic acid, aliphatic dicarboxylic acids (e.g. , ethyl, butyl, and octyl), terephthalic acid, and maleic anhydride. After formation, the water-reducible prepolymer is treated with an agent to partially or totally neutralize the free acid groups, and the neutralized or water- borne prepolymer may then be chain-extended to form a higher molecular weight polymer. Examples of solvents which may be used in the reaction of at least one organic compound with the modifier to form the prepolymer are water, ketones, aldehydes, acetates, N-methylpyrilodone, and nitroparaffins.

Uses for the prepolymers prepared using the modifier of the instant invention are coatings such as aqueous urethane dispersions, water soluble alkyd and polyester resins, electrodeposition coatings, epoxy ester coatings, rosin-free paper sizes, adhesive tackifiers, urethane elastomers, elastomeric coatings, nylon fibers, powder coatings, photoprint plates/photo resists, dye receptivity modifiers for polyester fibers, amino and phenolic resins, surfactants, and lubricating oil additives. Components which may be added to the water-borne prepolymer to prepare the coating composition include surfactants, wetting agents, defoamers, solvents, pigments, and crosslinkers.

The following examples are presented to describe embodiments and utility of the present invention and are not meant to limit the present invention unless otherwise stated in the claims appended hereto.

EXAMPLE 1 A polyurethane dispersion is prepared by mixing a polyol prepolymer (poly (ethylene glycol), HO-(-CH2-CH2-O-)_n-H) with a diisocyanate (toluene diisocyanate) and a modifier of the present invention. An isocyanate-terminated water-reducible prepolymer is formed. The free acid groups on the water- reducible prepolymer is then neutralized with a tertiary amine (triethylamine) to form a water-borne prepolymer and then optionally chain-extended by treating with a diamine (emylenediamine) to produce a high molecular weight polyurethane dispersion useful for coating applications. EXAMPLE 2

The polyurethane dispersion prepared in Example 1 is incorporated into a coating formulation. One such formulation is a topcoat for wood which is prepared by mixing 70-75 wt. % of the urethane dispersion, 15-20 wt. % of a polyol, 0.5-1 wt. % of a surfactant, 0.5-1.0 wt. % of one or more wetting agents, 0.01-0.1 wt. % of a defoamer, and 3-5 wt. % of a solvent.

EXAMPLE 3 A polyurethane dispersion incorporated into a sealer for wood is prepared as was the topcoat for wood in Example 2 with 70-75 wt. % of the urethane dispersion, 15-20 wt. % of a polyol, 0.5-1.0 wt. % of a surfactant, 0.5-1.0 wt. % of one or more wetting agents, 0.01-0.1 wt. % of a defoamer, 3-5 wt. % of a solvent, and an additional component, 1-2 wt. % zinc oxide.

EXAMPLE 4 An alkyd water-reducible prepolymer (or alkyd resin) is prepared by mixing 800 parts by weight of a fatty acid with 202 parts by weight of monopenta- erythritol, 244 parts by weight of trimethylolethane, 714 parts by weight of phthalic anhydride, and 206 parts by weight of a modifier of the present invention.

The alkyd water-reducible prepolymer is then heated to a temperature in the range of from about 390°F to about 400°F, and holding for an acid value 45- 50 and cure of 25". The mixture is then cooled to 300 °F and 80/20 butyl cellosolve/isobutyl alcohol to 75% solids. The free acid groups on the water- reducible prepolymer is then neutralized with an amine to produce an alkyd dispersion or water-borne prepolymer useful for coating applications.

EXAMPLE S

The alkyd dispersion prepared in Example 4 is incorporated into an enamel coating formulation. One such formulation contains 100.0 parts by weight of a wetting agent, 200.0 parts by weight of titanium dioxide, 8.0 parts by weight of ammonium hydroxide, 50.0 parts by weight of butyl cellosolve, 1.5 parts by weight of a defoamer, and 150 parts by weight water. The formulation is ground to 7.5+ Hegman. Then 255 parts by weight of the ground formulation is let down by mixing with 2.6 parts by weight of 12% cobalt naphthenate, 3.5 parts by weight of 9% manganese naphthenate, 2.4 parts by weight of Active 8 (R.T.

Vanderbilt), 20.0 parts by weight butyl cellosolve, 8.5 parts by weight ammonium hydroxide, 1.0 parts by weight wetting agent, 287 parts by weight water, and 0.6 parts by weight mar-resistant agent.

EXAMPLE 6 An alkyd prepolymer and dispersion may also be prepared by preparing a first mixture of a fatty acid with trimethylolethane, isophthalic acid, benzoic acid, and pentaerythritol. The mixture may then be cooked to an acid value of 10 under nitrogen at 230°C and then cooled to 205 °C.

A second mixture is prepared by mixing a modifier of the present invention with phthalic anhydride and an additional amount of the fatty acid. The second mixture may then be mixed with the first, cooked at 205 °C to an acid value of 52 and an ICI cone and plate viscosity of 16-18 poise at 125 °C. The total mixture is then cooled to at least 150°C and let down to 75% NVM in 4:1 by volume butoxyethanol/s-butyl alcohol. The alkyd dispersion so prepared is useful for coating applications.

EXAMPLE 7 The alkyd dispersion prepared in Example 4 is incorporated into a enamel coating formulation. One such formulation contains the alkyd dispersion, deionized water, ammonia (28%), and titanium dioxide. This mixture is then dispersed to NS 6+, and then the following components are added: additional alkyd dispersion, additional ammonia (28%), s-butyl alcohol, a wetting agent, deionized water, and a drier premix. EXAMPLE 8

An urethane/polyester resin water-reducible prepolymer and dispersion (containing the water-borne prepolymer) is prepared by mixing a fatty acid with a modifier of the present invention, trimethylolethane, pentaerythritol, and dibutyltin oxide, heating the mixture to 385-395 °C, holding for an acid value of 65-70 (about 1 1/4 hours), then cooling to 300°C, and sealing the container. Butyl cellosolve acetate is then added while cooling to 115-120°F. Toluene diisocyanate is then added over a one hour period; the exotherm is allowed to raise the temperature to 215 °F. The mixture is then processed at 180-200°F to complete reaction of toluene diisocyanate. Additional toluene diisocyanate is then added to obtain the desired viscosity. Finally butyl cellusolve and isobutyl alcohol are added. The dispersion is useful for coating applications.

EXAMPLE 9 The urethane/polyester resin dispersion prepared in Example 8 is incorporated into a varnish coating formulation. One such formulation contains the dispersion prepared in Example 8, butyl cellusolve, 1-butanol, 12% cobalt- based drier, 9% manganese-based drier, ammonium hydroxide, and water. The pH of the formulation is between 7.5 and 8.5.

Claims

Claims:

1. A water-reducible prepolymer, said water-reducible prepolymer which is prepared by the process comprising reacting a modifier with at least one organic compound; said modifier which comprises a mixture prepared by the process comprising reacting dimethylolpropionic acid with at least one alkylene oxide, and said organic compound which is terminated with at least two groups independently chosen from the group consisting of isocyanate, hydroxyl, carboxyl, and epoxy.

2. The water-reducible prepolymer of claim 1, wherein said modifier comprises at least two different products which result from reacting the dimethylolpropionic acid with at least one alkylene oxide.

3. The water-reducible prepolymer of claim 1, wherein said alkylene oxide is ethylene oxide.

4. The water-reducible prepolymer of claim 1, wherein said alkylene oxide is propylene oxide.

5. The water-reducible prepolymer of claim 1, wherein said modifier has a melting point of less than about 50 °C.

6. The water-reducible prepolymer of claim 5, wherein said modifier has a melting point of less than about 40°C.

7. The water-reducible prepolymer of claim 1, wherein the water- reducible prepolymer is prepared by the process comprising reacting the modifier with an organic compound terminated with at least two isocyanate groups and an organic compound terminated with at least two hydroxyl groups.

8. The water-reducible prepolymer of claim 1 wherein the water- reducible prepolymer is prepared by the process comprising reacting the modifier with an organic compound terminated with at least two hydroxyl groups.

9. A method of preparing a water-reducible prepolymer, comprising reacting a modifier with at least one organic compound; said modifier which comprises a mixture prepared by the process comprising reacting dimethylolpropionic acid with at least one alkylene oxide, and said organic compound which is terminated with at least two groups independently chosen from the group consisting of isocyanate, hydroxyl, carboxyl, and epoxy.

10. The method of claim 1, wherein said modifier comprises at least two different products which result from reacting the dimethylolpropionic acid with at least one alkylene oxide.

11. The method of claim 9, wherein said alkylene oxide is ethylene oxide.

12. The method of claim 9, wherein said alkylene oxide is propylene oxide.

13. The method of claim 9, wherein said modifier has a melting point of less than about 50°C.

14. The method of claim 13, wherein said modifier has a melting point of less than about 40°C.

15. The method of claim 9, wherein the modifier is reacted with an organic compound terminated with at least two isocyanate groups and an organic compound terminated with at least two hydroxyl groups.

16. The method of claim 9, wherein the modifier is reacted with an organic compound terminated with at least two hydroxyl groups.

17. A coating composition comprising a water-reducible prepolymer; wherein said water-reducible prepolymer is prepared by the process comprising:

(i) reacting a modifier with at least one organic compound terminated with at least two groups independently chosen from the group consisting of isocyanate, hydroxyl, carboxyl, and epoxy to form a water-reducible prepolymer having free acid groups; (ii) neutralizing the free acid groups on the water-reducible prepolymer to form a water-borne prepolymer; and

(iii) chain-extending the water-borne prepolymer; and wherein said modifier comprises a mixture prepared by the process comprising reacting dimethylolpropionic acid with at least one alkylene oxide.

18. The composition of claim 17, wherein said modifier comprises at least two different products which result from reacting the dimethylolpropionic acid with at least one alkylene oxide.

19. The composition of claim 17, wherein the modifier is reacted with an organic compound terminated with at least two isocyanate groups and an organic compound terminated with at least two hydroxyl groups.

20. The composition of claim 17, wherein the modifier is reacted with an organic compound terminated with at least two hydroxyl groups.

21. The composition of claim 17, wherein said alkylene oxide is ethylene oxide.

22. The composition of claim 17, wherein said alkylene oxide is propylene oxide.

23. The composition of claim 17, wherein said modifier has a melting point of less than about 50°C.

24. The composition of claim 23, wherein said modifier has a melting point of less than about 40°C.

25. The composition of claim 17 further comprising at least one component chosen from the group consisting of a surfactant, a wetting agent, a pigment, a defoamer, a solvent, and a crosslinker.