BINDER COMPOSITION COMPRISING A STRONGLY ACTIVATED CARBANION-FUNCTIONAL POLYMER AND A CROSS-LINKER

Abstract: The invention relates to a binder composition comprising a strongly activated carbanion-functional polymer and a cross-linker. The cross-linker contains aldehyde groups and the polymer is an alkyd resin or a polyester resin. The carbon-functional groups are acetoacetate groups, malonate groups, acetonate groups or mixtures thereof. Preferably, the polymer is an alkyd resin having said carbanion-functional groups and having a hydroxyl number between 40 and 70 mg of KOH/gram of resin and an acid number between 15 and 25 mg of KOH/gram of resin.

Description: BINDER COMPOSITION COMPRISING A STRONGLY ACTIVATED CARBANION-FUNCTIONAL POLYMER AND A CROSSLINKER The invention relates to a binder composition 10 comprising a strongly activated carbanion-functional polymer and a crosslinker. A binder composition of this type is disclosed in EP-A-227454. In this disclosure an acetoacetate-modified polymer is crosslinked with use 15 of a Michael addition reaction with poly-α,β- unsaturated esters. Binder compositions which are cured by means of Michael addition reactions generally yields, coatings that are slow drying and unacceptably yellow. One object of the invention is to provide 20 binder compositions comprising a strongly activated carbanion-functional polymer, especially an alkyd resin or a polyester resin, and a crosslinker that quickly dry. The invention is characterized in that the 25 crosslinker contains aldehyde groups. In this way quicker drying of binder compositions comprising a strongly activated carbanion- functional polymer is achieved. It is another advantage of the present 30 invention that coatings based on binder compositions according to the invention show less yellowing. Preferably, the aldehydes have (1-20) carbon atoms. Generally the crosslinker contains aldehydes t 35 having (1-4) aldehyde groups, more preferably (1-2) » aldehyde groups. Examples of suitable aldehydes include formaldehyde, cinnamaldehyde and polyaldehydes, such as for instance, glutardialdehyde. Preferably, a mixture of formaldehyde and glutardialdehyde is used. The molar ratio of formaldehyde to glutardialdehyde can be, for example, between about 70:30 and about 30:70 and preferably, between about 55:45 and about 45:55. A strongly activated carbanion-functional polymer is understood to be a polymer backbone modified with one or more strongly, for example, doubly, activated carbanion groups. In theory, many polymers can serve as polymer backbone. Examples of suitable polymer matrices include alkyd resins, polyesters, polyethers and epoxy- functional resins or mixtures hereof. Preferably, the polymer backbone comprises a polyester resin or an alkyd resin. These polymer matrices can comprise mixtures of polymers. Preferably they contain more than 50% by weight of a polyester or an alkyd resin. Preferably, the alkyd resin has, after transesterification with the strongly activated carbanion groups, a hydroxyl number between about 40 and about 70 mg of KOH/gram of resin and an acid number of between 15 and 25 mg of KOH/gram of resin. Alkyd resins can be obtained from polyols, dicarboxylic acids or dicarboxylic acid derivatives and fatty acids, as described in, for example, EP-A-227454, the complete disclosure of which is incorporated by reference. Preferably, unsaturated fatty acids, such as for example, tall oil fatty acid (TOFA) and soy oil fatty acid (SOFA) , are incorporated into the alkyd resin. Examples of suitable dicarboxylic acids or dicarboxylic acid derivatives include phthalic anhydride, maleic anhydride and corresponding dicarboxylic acids thereof. Examples of suitable polyols include trimethylol propane, trimethylol ethane, cyclohexane dimethanol, 1,6-hexanediol, hexane-2,5-diol, neopentyl glycol, ethylene glycol, diethylene glycol, propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, mono- or disorbitol, mono- or dipentaerythritol, trishydroxyethylisocyanurate, glycerol, polypropylene glycol, polyethylene glycol and polytetrahydrofuran. Preferred suitable strongly activated carbanion groups include acetoacetate groups, malonate groups and acetonate groups. Preferably, acetoacetate groups are used such as methyl acetoacetate, ethyl acetoacetate, isopropyl acetoacetate, butyl acetoacetate, t-butyl acetoacetate, methyl benzyl acetoacetate and/or dodecyl acetoacetate. The transesterification reaction of the acetoacetate groups on the polymer can take place under usual conditions as described in, for example, EP-A- 227454. The catalyst for this reaction can be for example p-toluene sulphonic acid. The amount of strongly activated carbanion groups incorporated into the polymer can be for example between about 5 and about 15 wt.%, relative to the modified polymer. In general, the molar ratio of the carbanion groups to the aldehyde groups is between about 1:5 and about 5:1, and preferably between about 1:1 and about 3:1 and more preferably between about 1:1 and about 2:1. The binder composition according to the invention is preferably used in an aqueous emulsion because binder compositions comprising a strongly activated carbanion-functional polymer and a crosslinker may form a gel in an organic solution. Moreover, the presence of solvents is undesirable in view of current environmental requirements. The strongly activated carbanion-functional polymer can be emulsified in water by addition of an emulsifier and/or by neutralization of the acid groups in the alkyd resin. In general, the polymer is emulsified at temperatures of between about 0°C and about 100°C, preferably at a temperature of between about 25°C and about 75°C. According to a further preferred embodiment of the invention the emulsifying temperature is between about 58°C and about 62°C. In general the particle size of the emulsion is between 100 and 1000 nm, preferably between 200 and 600 nm. An aldehyde compound can subsequently be added to the strongly activated carbanion-functional polymer at for example room temperature as a crosslinker. The binder compositions according to the present invention can be used, for example, as a one- component system for coatings that cure at temperatures between about 0°C and about 100°C, preferably for coatings that cure at about 25°C or room temperature. The binder compositions according to the present invention can be mixed with the usual additives to obtain coatings. Examples of these additives include pigments, colorants, fillers, thickeners, flow- promoting agents, matting agents, stabilizers and/or siccatives. The substrate material to be coated is not particularly limited but exemplary substrates include glass, plastic, wood and metal substrates. The invention will be explained further by reference to the following, non-limiting experiments and examples. Examples Experiment I Preparation of an alkyd resin with incorporated acetoacetate groups 1399 parts by weight of tall oil fatty acid, 857 parts by weight of phthalic anhydride and 744 parts by weight of pentaerythritol were mixed and reacted at 240 °C until a resin with an acid number of about 20 mg of KOH/gram of resin was obtained. The mixture was cooled to 160°C 530 parts by weight of methylacetoacetate were added and methanol was distilled off for 2 hours. After the transesterification had been finished all volatile components were distilled off in a vacuum. The characteristics of this resin are given in Table 1. Comparative Experiment A Preparation of an alkyd resin without acetoacetate groups 1238 parts by weight of tall oil fatty acid, 1107 parts by weight of phthalic anhydride and 655 parts by weight of glycerol were reacted at 220°C until the acid number was 20 mg KOH/gram resin. The characterization of this resin is given in Table 1. TABLE 1 Alkyd resin according Alkyd resin according to Experiment I to Experiment A Acid number 1) 22.6 20.4 Viscosity 2) 0.7 dPa.s 2.7 dPa.s Alkyd constant 0.981 0.9Θ1 % Acetoacetate groups 11.2 - Oil length 46.5% 46.5% OH number 62 60 1) mg KOH/gram resin 2) Resin diluted 1:1 in Xylene, 23°C. Experiment II-III and Comparative Experiment B Preparation of resin emulsions The resin emulsions are obtained by adding water very slowly to the resin/emulsifier/neutralizer mixture at a temperature of about 60°C in a ratio as illustrated in Table 2. Table 2 II B III based on alkyd based on alkyd based on a 1:1 mixture resin according resin according of alkyd resins - to Exp. I to Exp. A according to Exp. I and A Resin 1) 1000 1000 1000 Nonylphenol-20- 150 150 150 ethylene oxide 1) NaOH, 10% χ) 71 120 96 water 1) 650 606 628 Physical characteristics d 90 (nm) 326 388 377 pH 5.6 5.6 5.9 % sc 2) 54.6 54.6 54.6 1) Parts by weight 2) % SC = solids content The particle size (d 90 ) of the emulsion was measured with the aid of a Coulter LS-130 apparatus. Examples Preparation of a binder composition comprising formaldehyde 2.5% by weight of a drier (Siccatol 938™ from Acros), and 5% by weight of a thickener (RM 1020™, Rohm & Haas) were added to the emulsions II, III and B. Next formaldehyde solutions were added to the emulsion as indicated in the following. All emulsions used had a solids content of 54.6% by weight. The coating composition were applied to a glass plate at room temperature at a thickness of lOOμm. After evaporation of water and solvents a 20-50 μm dry coating layer was obtained. Figure 1 shows the hardness buildup (in terms of the number of pendulum oscillations) as a function of time (the number of days) for seven coatings based on the following compositions: 1) emulsion B (alkyd resin without acetoacetate groups) without formaldehyde (-AC-F) 2) emulsion B (alkyd resin without acetoacetate groups) with 1.6 g of 37% formaldehyde solution (-AC+F) 3) emulsion II (alkyd resin with 11.2% acetoacetate groups) without formaldehyde (+AC-F) 4) emulsion II (alkyd resin with 11.2% by weight acetoacetate groups) with 1.6 g of 37% formaldehyde solution (+AC+F) 5) emulsion III (alkyd resin with 5.6% by weight acetoacetate groups) without formaldehyde (0.5AC-F) 6) emulsion III (alkyd resin with 5.6% by weight acetoacetate groups) with 0.8 g of 37% formaldehyde solution (0.5AC+0.5F) 7) emulsion III (alkyd resin with 5.6% acetoacetate groups) with 1.6 g of 37% formaldehyde solution (0.5AC+F) The hardness build-up was monitored by a measurement according to the Konig pendulum hardness test (DIN 53157). These examples show that the coatings 4), 6) and 7) which are based on binder compositions comprising a polymer having acetoacetate groups and formaldehyde are immediately tackfree after evaporation of water. Furthermore, the combination of formaldehyde and an acetoacetate-functional alkyd resin in emulsion results in a more rapid hardness buildup in the first stage of the drying process. All publications referred to herein are hereby incorporated by reference. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to those of ordinary skill in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims: C L A I M S 1. A binder composition comprising a strongly activated carbanion-functional polymer and a crosslinker, characterized in that the crosslinker contains aldehyde groups and the polymer is an alkyd resin or a polyester resin. 2. A binder composition according to claim 1, characterized in that, said carbonion-functional groups are acetoacetate groups, malonate groups, acetonate groups or mixtures thereof. 3. A binder composition according to claim 1, characterized in that the polymer is an alkyd resin having said carbonion-functional groups and having a hydroxyl number between 40 and 70 mg of KOH/gram of resin and an acid number between 15 and 25 mg of KOH/gram of resin. 4. A binder composition according to any one of claims 1-3 characterized in that crosslinker contains aldehydes having (1-20) carbon atoms. 5. A binder composition according to any one of claims 1-4, characterized in that the crosslinker is formaldehyde, glutardialdehyde or a mixture thereof. 6. A binder composition according to any one of claims 1-5, characterized in that the binder composition is used in an aqueous emulsion. 7. A process for preparing a binder composition comprising the combination of steps of providing an alkyd resin having carbanion group, dispersing said alkyd resin in water to obtain an emulsion, and adding an aldehyde compound to said emulsion and wherein the emulsion has a particle size between 200 and 600 nm and the molar ratio of carbanion groups to said aldehyde groups is between 1:1 and 3:1. 8. Use of a binder composition according to any one of the claims 1-6 or of a binder composition obtained using the process according to claim 7 in the preparation of coating compositions. 9. Coating based on a binder composition according to any one of the claims 1-6 or coating based on a binder composition obtained using the process according to claim 7. 9. Wholly or partially coated substrate wherein the coating according to claim 9 is applied.

Inventors: HENDRIKS JOHANNES WILHELMUS MA, HENDRIKS, JOHANNES, WILHELMUS, MARIA
Applicants: DSM NV, HENDRIKS JOHANNES WILHELMUS MA, DSM N.V., HENDRIKS, JOHANNES, WILHELMUS, MARIA
Application year: 1996
Main classification: C08K5
IPC codes: C08K5, C09D167