| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 18.07.2000 |
| PATENT TITLE |
Aqueous secondary amine functional acrylic polymer |
| PATENT ABSTRACT |
A two-component thermosetting coating composition is disclosed wherein the binder components comprise: (a) an amino component comprising an aqueous solution and/or dispersion of at least one polyacrylate containing amino groups in a quantity sufficient to make said polyacrylate soluble and/or dispersible in water; and (b) a polyisocyanate component containing free isocyanate groups. Also disclosed is the method of emulsifying component (b) into component (a). -------------------------------------------------------------------------------- |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | April 3, 1997 |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A polymer of olefinically unsaturated monomers consisting of: (a) olefinically unsaturated monomer which contains at least one secondary amino group; and (b) olefinically unsaturated monomer which contains neither amino nor hydroxyl groups and which consists of a mixture of at least one ester of acrylic or methacrylic acid containing from 1 to 18 carbon atoms in the alcohol radical and at least one member selected from the group consisting of styrene and alkyl substituted styrene; wherein: (c) the olefinically unsaturated monomer which contains at least one secondary amino group constitutes from 10 to 50 percent by weight, based on the total weight of the monomers used; (d) the olefinically unsaturated monomer which contains neither amino nor hydroxyl groups constitutes from 50 to 90 percent by weight, based on the total weight of the monomers used; (e) the amine content of the polymer is in the range of from 0.05 to 2.70 milliequivalents per gram; and (f) the number average molecular weight of the polymer is in the range of from 500 to 50,000. 2. The polymer of claim 1 wherein the ester of acrylic or methacrylic acid contains from 1 to 8 carbon atoms in the alcohol radical. 3. The polymer of claim 1 wherein the ester of acrylic or methacrylic acid is selected from the group consisting of methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-stearyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, n-stearyl methacrylate, and mixtures thereof. 4. The polymer of claim 1 wherein the amino groups of the polymer have been at least partially neutralized with acid. 5. The polymer of claim 4 wherein the acid is mineral acid. 6. The polymer of claim 4 wherein the acid is organic acid. 7. The polymer of claim 4 wherein the acid is selected from the group consisting of acetic acid, propionic acid, lactic acid, and trifluoroacetic acid. 8. The polymer of claims 4 wherein: (a) the olefinically unsaturated monomer which contains at least one secondary amino group is tert-butylaminoethyl methacrylate; (b) the olefinically unsaturated monomer which contains neither amino nor hydroxyl groups is a mixture of n-butyl acrylate, methyl methacrylate, and styrene; and (c) the acid is acetic acid. 9. The polymer of claim 8 wherein the olefinically unsaturated monomers consist of 364.5 parts by weight tert-butylaminoethyl methacrylate, 783.5 parts by weight methyl methacrylate, 273.5 parts by weight n-butyl acrylate, and 401.0 parts by weight styrene. 10. An aqueous solution comprising the polymer of claim 4 dissolved in an aqueous medium. 11. The aqueous solution of claim 10 wherein the polymer constitutes from 10 to 50 percent by weight of the aqueous solution. 12. An aqueous dispersion comprising the polymer of claim 4 dispersed in an aqueous medium. 13. The aqueous dispersion of claim 12 wherein the polymer constitutes from 10 to 50 percent by weight of the aqueous dispersion. 14. An aqueous dispersion comprising the polymer of claim 8 dispersed in an aqueous medium. 15. The aqueous dispersion of claim 14 wherein the polymer constitutes from 10 to 50 percent by weight of the aqueous dispersion. 16. An aqueous dispersion comprising the polymer of claim 9 dispersed in an aqueous medium. 17. The aqueous dispersion of claim 16 wherein the polymer constitutes from 10 to 50 percent by weight of the aqueous dispersion. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION This invention relates to aqueous coating compositions based on two-component polyureas and to a process for their production. It is generally desirable to use water based coatings instead of organic solvent based coatings for the sake of environmental considerations. However, the use of water instead of organic solvents in two-component isocyanate reactive coating compositions based on polyisocyanates containing free isocyanate groups has been hampered by the fact that isocyanate groups react not only with isocyanate reactive groups in the intended crosslinking reaction, but also with the water. Therefore, in a composition including a polyisocyanate, isocyanate reactive groups, and water, the isocyanate/water reaction takes place with formation of urea and carbon dioxide. This reaction not only fails to achieve the intended crosslinking of the isocyanate reactive groups, but also results in gassing or foaming of the composition due to the formation of carbon dioxide. It was disclosed in U.S. Pat. No. 5,075,370 that it is possible to produce aqueous, two-component polyurethane coating compositions by using neutralized, acid group-containing polyhydroxy polymers, i.e. polyhydroxypolyacrylates, as dispersing agents for polyisocyanates containing free isocyanate groups. The polyisocyanates containing free isocyanate groups are emulsified in the aqueous, anionic polymer solution or dispersion. The coating compositions according to that patent are said to have a pot life of several hours and cure by way of isocyanate/hydroxyl group reaction to form polyurethane linkages. SUMMARY OF THE INVENTION The present invention is directed to aqueous, two-component coating compositions that contain as binder components: (a) a polymeric component containing at least one polymer based on olefinically unsaturated compounds and containing isocyanate reactive primary or secondary amino groups and, optionally, hydroxyl groups; and (b) a polyisocyanate component containing polyisocyanate groups in amounts sufficient to provide an NCO/NH equivalent ratio of about 0.5:1 to 5:1. If the amino group-containing component includes hydroxyl groups as is optionally permitted, these ratios relate to the NCO/(NH+OH) equivalent ratio. For the purposes of the present invention, a primary amino group is considered as an equivalent of two, and a secondary amino group is considered an equivalent of one. Thus, NH in the ratios above represents equivalents of amine hydrogen. Component (a) is solubilized in water by acid neutralization of the amino groups, and the polyisocyanate component (b) is emulsified in component (a), optionally with the aid of a surfactant. Although acid has heretofore been considered a retardant to isocyanate curing reactions, the acid solubilized system of the present invention has surprisingly been found to provide rapid cure. Furthermore, the present invention exhibits reduced gassing from reaction with water and yields films having good water resistance. The present invention also relates to a process for the production of this coating composition which is characterized in that the polyisocyanate component (b) is emulsified in an aqueous solution or dispersion of component (a) in a quantity which makes component (b) dispersible in water, the quantitative ratios between the two components corresponding to an NCO/NH equivalent ratio, or NCO/(NH+OH) if hydroxy groups are present, of 0.5:1 to 5:1 based on the isocyanate groups of the polyisocyanate component (b) and the incorporated primary or secondary amino groups and any hydroxy groups of the polymer component (a). DETAILED DESCRIPTION Component (a) is based on polymers of olefinically unsaturated monomers containing primary or secondary amino groups. These amino groups serve both as sites for partial neutralization by an acid to form cationic aqueous dispersions as well as curing sites for reaction with isocyanate groups of component (b) to form urea linkages. Optionally, the polymers of component (a) may also include hydroxyl groups, which upon curing with the isocyanate groups of component (b) form urethane linkages. The amino group-containing polymers of component (a) have a number average molecular weight (M.sub.n), as determined by gel permeation chromatography, of about 500 to 50,000, preferably about 1,000 to 10,000. The amine content of component (a) is preferably 0.05 to 2.70 milliequivalents per gram, most preferably 0.25 to 1.62 milliequivalents per gram. In a particularly preferred embodiment, these cationic groups are acetic acid neutralized secondary amino groups. The polymer resins are present in the aqueous medium in amounts of 10 to 50 percent by weight resin solids, preferably 20 to 40 percent by weight, and have a pH value of 4 to 6, preferably 5 to 5.5. Depending upon the molecular weight of the polymers and their content of cationic groups, the aqueous systems containing the polymers may be either colloidal dispersions or molecular solutions. The polymers containing amino groups are produced in the known manner by copolymerization of olefinically unsaturated monomers with monomers containing amino groups. The amino group containing polymer may optionally contain hydroxyl groups. After copolymerization, the amino groups are at least partially neutralized with an acid for inversion into the aqueous medium. The amino groups contained in the copolymer are used for the purpose of salt formation by acid groups that either fully or partially neutralize the amino groups. In general, the amino comonomers are used in quantities of about 1 to 50 percent by weight, preferably in quantities of about 5 to 30 percent by weight, based on the total weight of the monomers used. In principle, suitable amino comonomers are any olefinically unsaturated, polymerizable compounds which contain at least one primary or secondary amino group, e.g.: amino acrylates and amino methacrylates such as tert-butylaminoethyl methacrylate or meta-isopropenyl-.alpha.,.alpha.-dimethylbenzylamine. Amino groups can also be obtained by the reaction of acid polymers with aziridines such as ethylene imine, or by the reaction of epoxy and blocked ketimines, as well as other techniques known for adding amine functionality to polymers. Monomers containing hydroxyl groups are not required in the present invention, but when used, may be included in the monomer mixture in such quantities that the amino group-containing polymers have a hydroxyl group content of 0 to 10 percent, preferably 0 to 5 percent by weight. In general, the hydroxy functional comonomers are used in quantities of about 0 to 50 percent by weight, preferably 0 to 30 percent by weight based on the total weight of monomers used to copolymerize the amino group-containing polymer of component (a). Suitable monomers containing hydroxyl groups include, in particular, hydroxyalkyl esters of acrylic acid or methacrylic acid preferably containing 2 to 4 carbon atoms in the alkyl radical such as 2-hydroxyethyl acrylate or methacrylate, 2-or 3-hydroxypropyl acrylate or methacrylate, the isomeric hydroxybutyl acrylates or methacrylates and mixtures of such monomers. The third group of olefinically unsaturated monomers which may be used for the production of the copolymers of component (a) are olefinically unsaturated compounds which contain neither amino nor hydroxyl groups. These compounds include esters of acrylic acid or methacrylic acid containing from 1 to 18, preferably from 1 to 8, carbon atoms in the alcohol radical, such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, n-stearyl acrylate, and tertiary amine containing acrylates or methacrylates, and the methacrylates corresponding to these acrylates. Also included are styrene, alkyl substituted styrenes, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl stearate and mixtures of such monomers. The monomers of this third group are used in quantities of 50 to 90 percent by weight, preferably about 40 to 80 percent by weight, based on the total weight of the monomers used. The polymers may be produced by standard polymerization processes. The polymers are preferably produced in organic solution. The polymerization reaction is free radically initiated when the monomer mixture is added together with an initiator mixture over a period of about 1 to 10 hours, preferably about 3 to 6 hours, at reaction temperature. Thereafter more activator may optionally be added to take the polymerization to a conversion of at least 99 percent. Suitable solvents for the amino group-containing polymer are characterized by their solubility toward the polymer and their ability to be azeotropically distilled off the inversion to the aqueous medium. These may include alcohols such as ethanol, propanol, and butanol; aromatic hydrocarbons such as benzene, toluene, xylene and chlorobenzene; esters such as ethyl acetate, butyl acetate, methyl glycol acetate, ethyl glycol acetate and methoxypropyl acetate; ethers such as butyl glycol, tetrahydrofuran, dioxane and ethyl glycol ether; ketones such as acetone and methyl ethyl ketone; halogen-containing solvents such as methylene chloride and trichloromonofluoroethane; and mixtures of these solvents. The polymerization may be initiated by initiators commercially available for this purpose. In general, the copolymerization reaction takes place at temperatures in the range previously set forth, preferably at a temperature of about 50.degree. to 160.degree. C. under atmospheric pressure. The exact polymerization temperature is determined by the type of initiator and solvent used. The initiators are used in quantities of about 0.05 to 10 percent by weight, based on the total quantity of monomers. Suitable initiators include aliphatic azo compounds such as azoisobutyronitrile and peroxides such as dibenzoyl peroxide, t-butyl perpivalate, t-butyl per-2-ethylhexanoate, t-butyl perbenzoate, t-butyl hydroperoxide, di-t-butyl peroxide, cumene hydroperoxide and dicyclohexyl and dibenzyl peroxydicarbonate. The molecular weight of the polymers may be regulated by standard regulators such as n-dodecylmercaptan, diisopropyl xanthogene disulfide, di-(methylene-trimethylolpropane)-xanthogene disulfide and thioglycol. They are added in quantities of up to about 3 percent by weight, based on the monomer mixture. On completion of polymerization, the copolymers are converted into an aqueous solution or dispersion. The acid is introduced into the polymerization solution, followed by addition of water. Then the organic solvent is removed by azeotropic distillation. Fugitive acids are preferred for the neutralization, i.e., those that will escape from the coating as it cures, thereby avoiding interference with the cure. Fugitive acids are generally organic acids, preferred among which are acetic acid, propionic acid, lactic acid, and trifluoroacetic acid. However, within the broad aspects of the invention, mineral acids could also be employed, such as carbonic acid, phosphoric acid and sulfuric acid, of which fugitive carbonic acid is preferred. Other organic and mineral acids are well known in the art and may be used for neutralization in the present invention. The polyisocyanate component (b) may be any polyisocyanate containing aliphatically, cycloaliphatically, araliphatically and/or aromatically bound isocyanate groups which are liquid at room temperature. The polyisocyanate component is preferably not modified to be water dispersible or soluble, although it may be so modified in a less preferred embodiment. The polyisocyanate component (b) is preferably a polyisocyanate or polyisocyanate mixture exclusively containing aliphatically and/or cycloaliphatically bound isocyanate groups and having an average NCO functionality of about 2.0 to 5.0. If necessary, the polyisocyanates may be used in admixture with small quantities of inert solvents to reduce the viscosity. However, the maximum quantity in which such a solvent is used is such that the coating compositions contain at most 20 percent by weight of solvent, based on the quantity of water and any solvent that may still present in the polymer dispersions or solutions. Suitable solvents for the polyisocyanates include aromatic hydrocarbons such as solvent naphtha, acetates, or the solvents set forth as suitable for the polymerization of component (a). Suitable polyisocyanates include those containing aromatically or (cyclo)aliphatically bound isocyanate groups, (cyclo)aliphatic polyisocyanates being particularly preferred. Particularly suitable are polyisocyanates based on hexamethylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (IPDI) and/or bis-(isocyanatocyclohexyl)-methane, particularly those based on hexamethylene diisocyanate. Other suitable polyisocyanates based on these diisocyanates may include the biuret, urethane, uretdione and/or isocyanurate derivatives of these diisocyanates which, after their production, have been freed in the known manner, preferably by distillation, from excess starting diisocyanate to a residual content of less than 0.5 percent by weight. Aliphatic polyisocyanates for use in accordance with the invention include biuret polyisocyanates based on hexamethylene which are based on mixtures of N,N',N"-tris-(6-isocyanatohexyl)biuret with small quantities of its higher homologs. These polyisocyanates may be obtained by the processes according to U.S. Pat. Nos. 3,124,605; 3,358,010; 3,903,126; 3,903,127 or 3,976,622. Also preferred are the cyclic trimers of hexamethylene diisocyanate corresponding to the criteria mentioned above which may be obtained in accordance with U.S. Pat. No. 4,324,879 and which are based on N,N'N"-tris-(6-isocyanatohexyl)-isocyanurate in admixture with small quantities of its higher homologs. The aromatic polyisocyanates which may also be used in accordance with the invention, but are less preferred, are based on 2,4-diisocyanatotoluene or commercial mixtures thereof with 2,6-diisocyanatotoluene or based on 4,4'-diisocyanatodiphenylmethane or mixtures thereof with its isomers and/or higher homologs. Aromatic polyisocyanates of this type include the urethane isocyanates obtained by the reaction of excess quantities of 2,4-diisocyanatotoluene with polyhydric alcohols such as trimethylolpropane and subsequent removal of the unreacted diisocyanate excess by distillation. Other aromatic polyisocyanates include the trimers of the previously mentioned monomeric diisocyanates which have also been freed from excess monomeric diisocyanates, preferably by distillation, after their production. To prepare the ready-to-use coating compositions, polyisocyanate component (b) is emulsified in an aqueous dispersion of amino group-containing polymer component (a). The dissolved or dispersed polymer simultaneously serves as an emulsifier for the polyisocyanate added. Optionally, dispersing component (b) may be assisted by a separate surfactant. Mixing may be carried out by simple stirring at room temperature. The quantity of the polyisocyanate component is selected to provide an NCO:NH equivalent ratio {or NCO:(NH+OH) equivalent ratio if hydroxyl functionality is present}, based on the isocyanate groups of component (b) and the primary and secondary amino groups and hydroxyl groups of component (a) of about 0.5:1 to 5:1, preferably about 0.8:1 to 2:1. Before polyisocyanate component (b) is added, additives typically used in coating technology may be incorporated into polymer component (a). The additives include foam inhibitors, leveling aids, pigments, dispersion aids for pigments, etc. The coating compositions according to the invention thus obtained are suitable for virtually any applications where high performance is desired. They are particularly useful for coating of metal surfaces and various plastic surfaces. The invention is further illustrated but is not intended to be limited by the following examples in which all parts and percentages are by weight unless otherwise specified. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
|
Want more information ? Interested in the hidden information ? Click here and do your request. |