WO1988002381A1

WO1988002381A1 - Pigment dispersant resin with s-containing acid

Info

Publication number: WO1988002381A1
Application number: PCT/US1987/002386
Authority: WO
Inventors: Jozef Theresia Huybrechts; Guido Richard Van Den Bosch; Landriette Rudolf Felix Verhaegan
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1986-09-30
Filing date: 1987-09-25
Publication date: 1988-04-07

Abstract

Acrylic polymers with carboxylic acid and small amounts of sulfur-containing strong acids are good pigment dispersants for use in water-based coating compositions.

Description

Pigment Dispersant Resin with S-Containing Acid

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part application of U.S. Serial No. 913,400 filed September 30, 1986.

Background The present invention comprises a pigment dispersant. More particularly, it comprises such a dispersant having an acrylic resin containing organic acid and strong acid sulfur-containing monomers. Sulfur-containing monomers, including 2-acrylamide-2-methylpropane sulfonic acid (AMPS), have been polymerized with acrylics and other monomers in various proportions for a variety of purposes, including for use in dispersing sediments in water. However, an optimum dispersant resin for use in water-based coating compositions has remained an elusive desideratum.

U.S. Patent 4,450,013 - Hirsch et al. (1984) teaches a pigment grinding or dispersing resin of, for instance, 40-90% by weight acrylic acid, 10-60% AMPS, and 0-10% acrylonitrile, or equivalent monomers. (Parts, percentages and proportions herein are by weight except where indicated otherwise).

U.S. Patent 3,711,449 - Brendley (1973) teaches interpolymers of 0.2-1.0% AMPS with other acrylates or methacrylates.

U.S. Patent 3,898,037 - Lange et al. (1975) teaches acrylamido-sulfonic acid polymers such as AMPS which may be copolymerized with other acrylics, and their use in corrosion inhibition. U.S. Patent 4,177,178 - Das et al. (1979) teaches the use of AMPS copolymerized with other acrylics including long chain acrylics such as stearyl methacrylate, with a molecular weight of 15,000 to 100,000. These are said to be used to make thermosetting automotive topcoat paints.

U.S. Patent 4,001,150 - June et al. (1977) teaches the use of phosphoric or sulfonic esters, including AMPS, copolymerized with acrylics such as methacrylic acid, for use as an electroconductive resin.

U.S. 2,914,499 - Sheetz (1959) teaches the use of various acrylic esters of sulfonic acid in emulsion polymerization. U.S. Patent 4,008,293 - Maska et al. (1977) teaches the preparation of crosslinkable coating compositions containing, for instance, AMPS, as an internal crosslinking catalyst.

European Patent Publication 129,329 - Farrar et al. (1984) teaches pigment dispersions using copolymers of acrylic acid with 1-50% AMPS having molecular weights in the range of 1,000 to 5,000, or up to 5700, with a low polydispersity.

European Patent Publication 58,865-Perrey et al. (1982) teaches pigment dispersants with 1-10% pigment, using various acrylic sulfonic acid polymers.

European Patent Publication 170,474 - Backhouse (1986) teaches the use of phosphorus-containing compounds in water-based polymers to reducing gasing from metal pigments.

Summary of the Invention

The present invention provides a pigment dispersant resin comprising copolymerized units of the iallowing monomers in weight percent based on the polymer solids:

(a) 1.5-4% of at least one unsaturated strong-acid functional acrylic monomer having the structure C^H2 O

" "

R - C - R¹ - S - OH

wherein R is H or CH₃ R¹ is an ester, amido, alkyl, or ether linkage having 1-4 carbon atoms,

(b) 1-10% of at least one organic-acid- functional acrylic monomer selected from acrylic acid, methacrylic acid, and maleic, fumaric and itaconic acids and esters,

(c) 86-96% of at least one ethylenically unsaturated monomer selected from the group consisting of acrylate and methacrylate esters of alcohols having 1-12 carbon atoms, styrene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, vinyl chloride, dialkyl esters with 1-12 carbon atoms of maleic, fumaric and itaconic acids, and hydroxy-functional acrylates and methacrylates from alcohols or esters having 1-4 carbon atoms, said resin having a weight average molecular weight in the range of about 5,500-30,000 and an acid number in the range of about 30-120. Preferably, the sulfur-containing monomer is one of 2-acrylamide-2-methylpropane sulfonic acid, 2-sulfoethylmethhacrylate, and styrene sulfonic acid.

The invention also includes water-based dispersions of the resin of the invention (including more or less of the resin in solution), with 50-150% of the amount of tertiary amine needed for neutralization. Pigment dispersions are also included.

Detailed Description

It has been found that 1% AMPS is too little in polymers of the invention to obtain desirable dispersant effects, and 5% is too much in that it causes major viscosity increases and instability in paints. Molecular weightr of the polymer is important. Measured as the weight average, 4,000 is too small to obtain the advantages of the invention, 5,500 or 6,000-15,000 seems preferred, although 15,000-30,000 or 40,000 is acceptable.

The preferred sulfur-containing monomer for the invention is

AMPS, 2-Acrylamide-2-methylpropanesulfonic acid

Water based coating composition technology is based on a higher molecular weight or crosslinked latex giving rheology control with a water dispersible or soluble crosslinker such as a methylated melamine resin. The amount of inorganic acid in the dispersing resin is important for the stability, of and the compatibility with the latex. With larger amounts than in this invention, one could expect real problems in film properties and compatibility, at least with certain resins. It is also known that reactive melamine resins are sensitive to self condensation and hydrolysis in presence of strong acids giving unstable products in the can. Too high acid values in general do give cured films which are sensitive to humidity. The rest of the copolymer composition can be based on any unsaturated monomer such as acrylate, methacrylate, styrene, vinyl maleate, acrylamides or methacrylamides, or acrylonitrile or methacrylonitrile. Certain preferred compositions contain MMA (methylmethacrylate) and BA (butylacrylate). The copolymers should also have preferably hydroxy functionality to become an integral part of the cured polymer network. HEMA (hydroxyethyl methacrylate) is preferred but one could also use HEA (hydroxyethylacrylate) or less reactive HPA (hydroxy-propylacrylate) or HPMA

(hydroxypropylmethacrylate). HEMA is preferred over HEA because of its better hydrolysis resistance and over HPA, HPMA, HBA (hydroxybutyl acrylate) because it renders the copolymer more water soluble. Too low a molecular weight will not give a polymeric dispersant, resulting in poor film properties, and too high molecular weight can give compatibility problems with the other film constituents and too high viscosities with the dispersions.

The copolymers are made by radical polymerization using solvents as diluents which are preferably water soluble. Isopropanol (IP) is in this technology a good candidate since it forms a low boiling azeotrope with water. Chain transfer agents (e.g. mercaptans) can be used to control the molecular weight. Example 1 - Resin Preparation

IP : 785.73

MMA : 385

BA : 712.26

HEMA : 154

AA : 48.4

Mercaptoethanol : 8.25

IP . 79.75

Heat up to reflux at 83°C

IP : 1571.46

MMA . 1155

BA : 712.26

HEMA . 462

AA : 144.10

AMPS 77 g. dissolved in 88 g water (deionized) VAZO 64 : 38.5 Azobisisobutyronitrile initiator from Du Pont IP : 102.14 Rinsing Step Feed I

Mercaptoethanol : 27.5 IP : 220

IP : 27.5 Rinsing step

Feed II

Add Feed 1 and II simultaneously over 90 min. followed by rinsing steps Triganox 25C75 : 5.5 TP : 77

Add over 60 min. Hold 1 hour at reflux, solids : 56% Viscosity: Y - 1/3

(Gardner Holdt) MN : 3500 acid no. (AN): 51 MW : 12300 polydispersity (d) : 3.5 Examples 2-4 In variations on example 1, the following resin solutions were prepared.

MMA BA HEMA AA AMPS

Example 1 37.5 50.4 5.1 5.1 2.1

Example 2 37.5 50.4 5.1 2.1 5.1

Example 3 40 37 16 5 2

Example 4 40 37 16 2 5

Test results:

Solids- -% MN MW D AN vise

1 49.6 3700 13500 3.7 50 R+1/2

2 49.1 2200 5800 2.7 38 T+1/2

3 56 3500 12300 3.5 51 Y-1/3

4 55.1 1700 13000 7.6 38.6 Y-1/4

All resin solutions were neutralized with AMP (aminomethylpropanol) to pH 8.4 - 8.7 and diluted to 50% solids with deionized water (where relevant). Example 6 - Pigment Dispersion

Sicotrans L 2817 transparent iron oxide red from BASF

Following blends made with a Cowless mixer blade and afterwards ground in suitable equipment such as Dynomill, ball mill, etc. Constraints:

10% < Sicotrans L 2817 < 30%

15% < Neutralized resin solution < 80%

50% solids 10% < Deionized water/Propyleneglycol < 75% blend All dispersions were tested for gloss, transparency, rheology. Example 1 gave the best results. Example 2 was found to be unstable when formulated in the finished product. Example 7 - Pigment Dispersion Ti-pure 902 titanium dioxide from Du Pont

The same tests were run as above with following constraints: 40 < TiO₂ 4.85%

10 < Neutralized resin solution < 55% 5 < Deionized water < 50%

Resin examples 1 and 3 gave excellent results. However, examples 2 and 4 with 5% AMPS resulted in a strong viscosity increase when formulated in the finished product.

Claims

1. A pigment-dispersant resin comprising copolymerized units of the following monomers in weigh percent based on the polymer solids:

(a) 1.5-4% of at least one unsaturated strong-acid functional acrylic monomer having the structure CH₂ O

" "

R - C - R¹ - S - OH

"

O wherein R is H or CH₃

R¹ is an ester, amido, alkyl, or ether linkage having 1-4 carbon atoms,

(c) 86-96% of at least one ethylenically unsaturated monomer selected from the group consisting of acrylate and methacrylate esters of alcohols having 1-12 carbon atoms, stryene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, vinyl chloride, dialkyl esters with 1-12 carbon atoms of maleic, fumaric and itaconic acids, and hydroxy-functional acrylates and methacrylate from alcohols or esters having 1-4 carbon atoms, said resin having a weight average molecular weight in the range of about 5,500-30,000 and an acid number in the range of about 30-120.

2. The resin of claim 1 wherein

(a) is 2-acrylamide-2-methylproprane sulfonic acid.

3. The resin of claim 1 wherein

(a) is 2-sulfoethymethacrylate.

4. The resin of claim 1 wherein

(a) is styrene sulfonic acid.

5. The resin of claim 1 wherein

(b) is acrylic acid.

6. The resin of claim 1 wherein (b) is methacrylic acid,

7. The resin of claim 1 wherein

(c) is hydroxyethyl methacrylate

8. The resin of cliam 1 wherein

(b) is methyl methacrylate and butyl acrylate and

(c) is hydroxyethyl methacrylate

9. The resin of claim 8 having a weight averagemolecular weight in the range of 6,000-15,000.

10. An aqueous dispersion of the resin of claim 9 containing tertiary amine in an amount from 50% to 150% of the amount needed for stoichiometric neutralization of said resin.

11. A pigment dispersion comprising the dispersion of claim 10 and a pigment.

12. The pigment dispersion of claim 11 wherein the pigment comprises TiO₂.

13. The pigment dispersion of claim 11 wherein the pigment comprises aluminum flake.

14. The pigment dispersion of claim 11 wherein the pigment comprises iron oxide.