GB2293606A - Aqueous thixotropic polyester compositions - Google Patents

Abstract

A thixotropic composition comprises (i) water, and (ii) a water-dispersible or water-dilutable reactive polyester resin; thixotropy being imparted to the composition by the presence of a polyurea material prepared by reacting one or more (poly)amines with one or more (poly)isocycanates in the presence of at least a portion of the alkyd or modified polyester resin.

Description

THIXOTROPIC COMPOSITIONS This invention is concerned with thixotropic compositions and, more particularly, is concerned with thixotropic compositions comprising reactive polyesters as binder components.

It is known to provide reactive coating composition comprising a reactive polyester containing free hydroxyl groups together with a polyisocyanate which may react with the polyester under suitable conditions. It is also known to provide such coating composition in which the principal carrier/diluent is water and the polyester resin also contains free carboxyl groups in order to render it water-dilutable. The resultant compositions are, however, essentially non-thixotropic. Thixotropy is a most desirable characteristic in a coating composition, especially one intended to be applied by hand, e.g. for a composition to be supplied to the so-called "do-it-yourself" market.

It has now been found, in accordance with the present invention, that it is possible to provide a reactive polyester resin-based composition containing water as liquid carrier/diluent and which, at the same time, has thixotropic properties, by incorporating in the composition polyurea material as thixotropyimparting component.

According to the invention, therefore, there is provided a thixotropic coating composition comprising (i) water and (ii) a water-soluble or water-dilutable reactive polyester resin as a binder component; thixotropy being imparted to the composition by the presence of a polyurea material prepared by reacting one or more (poly)amines with one or more (poly)isocyanates in the presence of at least a portion of the polyester resin.

The polyester resins employed in the compositions of the invention contain both hydroxyl groups (for eventual reaction with a polyisocyanate cross-linking agent) and carboxyl groups (to render them water-dilutable, generally after neutralization with an amine or the like).

Basically, the polyester resins are prepared by polycondensation of one or more polycarboxylic acids (or anhydrides thereof) with one or more polyhydric alcohols, optionally together with one or more of monocarboxylic acids and/or polyhydric alcohols to serve as molecular weight control agents ("chain stoppers").

Suitably, the polyester have an average molecular weight of at least 500, preferably from 500 to 3,000 and more preferably from 800 to 1,000. The hydroxy value of the resins is suitably from 15 to 200 mgKOH/g, preferably 100 to 110 mgKOH/g; and the acid value is suitably from 30 to 80 mgKOH/g, preferably 50 to 60 mgKOH/g.

The polyesters are conveniently produced by a dry fusion process, typically involving reaction of the reactants at temperatures from 170 to 2200C. In order to provide polyesters having both hydroxyl and carboxyl functionality, the alcoholic component may be reacted with a less than stoichiometric amount of acid anhydride until substantially all the latter is consumed (as estimated by acid value) and then reacting the product with further acid until the desired acid value is obtained.

Suitable polycarboxylic acids or carboxylic acid anhydrides for use in the manufacture of the polyester of the invention include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, adipic acid and succinic anhydride; aromatic or saturated aliphatic monocarboxylic acids such as benzoic acid, hydrobenzoic acid, butylbenzoic acid, coconut oil acids, and ethylhexanoic acid; oleofinically unsaturated fatty acids and derivatives of olefinically unsaturated fatty acids such as fatty acids of linseed oil, soya oil, tung oil, safflower oil, dehydrated castor oil, cotton seed oil, groundnut oil, and tall oil; synthetic oleofinically unsaturated C12 to C22 fatty acids; and derivatives obtained by conjugation, isomerisation or dimerisation of these unsaturated fatty acids.

Suitable polyhydric alcohols include alcohols having 1 to 6, preferably 2 to 4 hydroxyl groups such as ethylene glycol, propylene glycol, butanediols, neopentyl glycols, cyclohexanedimethanols, 2-ethyl-1,3-propanediol, hexane diols, ether alcohols such as di- and triethylene glycols, ethoxylated bisphenols, hydrogenated bisphenols, trimethylolethane, trimethylolpropane, glycerol, pentaerythritol, dipentaerythritol, mannitol and sorbitol; and monohydric chain terminating alcohols such as methanol, propanol, butanol, cyclohexanol and benzyl alcohol.

Thixotropy is imparted to the compositions of the invention by the presence of polyurea material derived from the reaction of one or more (poly)amines with one or more (poly)isocyanates in the presence of at least a portion of the polyester resin and water. This general method of imparting thixotropy to a binder resin is described, using organic solvent systems, in GB-A-1454388 and GB-A-1454414. Basically the process involves the reaction of a polyisocyanate with a monoamine (optionally in the presence of monoisocyanate and/or polyamine) or of a monoisocyanate with a polyamine (optionally in the presence of monoamine and/or polyisocyanate). It is generally preferred, in accordance with the present invention, to prepare the polyurea material by reaction of a polyamine, especially a diprimary diamine, with a monofunctional isocyanate in the presence of some polyisocyanate.A variety of diamines may be used but preferred diamines include neopentane diamine, 2-methyl-1,5-pentamethylene diamine, 2-butyl-2-ethyl-1.5-pentane-diamine, ethylene diamine, isophorone diamine, meta-xylene diamine, hexamethylene diamine, 4.4- diaminocyclohexyl methane, N-benzyl dimethylamine, especially meta-xylene diamine (hereinafter simply referred to as "xylylene diamine".

Similarly, a variety of monofunctional isocyanate materials may be employed such as alkyl isocyanates with 1 to 22 carbon atoms, for example methyl isocyanate, ethyl isocyanate, propyl isocyanate, butyl isocyanate, stearyl isocyanate, and/or aromatic isocyanates such as phenyl isocyanate or cycloaliphatic isocyanates such as cyclohexyl isocyanate, the reaction products of monoalcohols with polyisocyanates, especially the reaction product of tridecanol with toluene diisocyanate (typically a 65:35 mixture of the 2,4- and 2,6-isomers), which product also contains unreacted toluene diisocyanate.

The (poly)amine and (poly)isocyanate are reacted together in the presence of at least a portion of the polyester resin, which is preferably neutralized with an amine. Typically, thus, the alkyl/polyurea material may be prepared by adding (poly)isocyanate to a mixture of polyester, water and (poly)amine, and then reacting (poly)isocyanate and (poly)amine. Alternatively, the product may be produced by reacting (poly)amine and (poly)isocyanate in the presence of the polyester, and then diluting the product with water. Suitably (poly)amine and (poly)isocyanate are reacted together in the presence of from 10 to 100% by weight of the total polyester resin to be employed in the composition; the remainder of the polyester resin being added during and/or after the reaction. The stoichiometric ratio of amine to isocyanate is suitably from 0.7 to 1.3: 1, preferably from 0.8 to 1.1: 1. The total amount of amine and isocyanate reacted together, to form the polyurea material, is suitably from 0.05 to 15% by weight, preferably 0.1 to 10% by weight of the total solid polyester resin present in the final coating composition.

Curable compositions in accordance with the water will also comprise a crosslinking agent, namely a polyisocyanate. Suitable such polyiocyanates are selected from isocyanates having aliphatically, cycloaliphatically, araliphatically and/or aromatically bound isocyanate groups which may optionally contain nonionic hydrophilic groups and/or cationic groups. The polyisocyanate is preferably liquid at room temperature. It is particularly preferred to use a polyisocyanate mixture having exclusively aliphatically and/or cycloaliphatically bound isocyanate groups, an average functionality of 2.2 to 5.0 and a viscosity at 230C of 50 to 5000 mPa.s.

Suitable polyisocyanates for use are polyisocyanate derivative having aromatically or (cyclo)aliphatically bound isocyanate groups, preferably (cyclo)aliphatically bound isocyanate groups.

Polyisocyanates derivatives prepared from hexamethylene diisocyanate, l-isocyanato-3,3,5trimethyl-5-isocyanatomethyl cyclohexane (IPDI) and/or 4,4-bis-(isocyanatocyclohexyl)-methane are very suitable, especially those prepared exclusively from hexamethylene diisocyanate. Polyisocyanate derivatives include polyisocyanates having biuret, urethane, uretedione and/or isocyanurate groups. These polyisocyanates are generally prepared from diisocyanates and are generally prepared from diisocyanates and are preferably subsequently treated to remove excess starting isocyanate in known manner, preferably by distillation, to a residual content of less than 0.5 wt.%.

Preferred polyisocyanate derivatives include polyisocyanates which contain biuret groups, are prepared from hexamethylene diisocyanate in accordance with the processes described eg. in US patents 3,124,605, 3,358,010, 3,903,126, 3,903,127, or 3,976,622 and contain mixtures of N,N,N-tris- (6-isocyanatohexyl biuret with minor amounts of its higher homologue; and polyisocyanates which contain isocyanurate groups, are prepared by the trimerisation of hexamethylene diisocyanate in accordance with the process described eg. in US Patent 4,324,879 and contain mixtures of N,N,N-tris- (6-isocyanato-hexyl) -isocyanurate with minor amounts of the higher homologue.Especially preferred are polyisocyanates which'contain uretedione and isocyanurate groups and are prepared by the catalytic oligomerisation of hexamethylene diisocyanate in the presence of trialkyl phosphines. Especially preferred are latter polyisocyanates having a viscosity of 50-500 mPa.s at 230C and an NCO functionality of 2.2 to 5.0.

The less preferred aromatic polyisocyanates include polyisocyanate derivatives prepared from 2,4-diisocyanatotoluene or mixtures thereof with its isomers and/or higher homologues. The aromatic polyisocyanate derivatives include those containing urethane groups which may be prepared by the reaction of excess amounts of 2,4-diisocyanatotoluene with polyhydric alcohols, such as trimethylolpropane, followed by removal by distillation of the unreacted diisocyanate. Other aromatic polyisocyanate derivatives include the trimers prepared from aromatic diisocyanates from which the excess monomeric isocyanates have preferably been removed by distillation following their production.

The use of hydrophilically modified polyisocyanates is particularly preferred and is generally advantageous due to the additional emulsifying effect. Such hydrophilic modification of the polyisocyanates can be carried out by reacting a portion of the isocyanate groups with monovalent polyether alcohols having ethylene oxide units, for example, the ethoxylation products of monomeric alkanols having 5 to 100 ethylene oxide units per molecule. These polyether alcohols and their production are described for example in DE-OS 3 521 618.

To produce the coating composition, the polyisocyanate component is emulsified into the aqueous solution or dispersion of the thixotropic polyester component.

The stoichiometric ratio of polyisocyanate to polyester (in terms of the hydroxyl content thereof) is suitably from 0.5:1.0 to 5.0:1.0, preferably 0.7:1.0 to 3.0:1.0.

The compositions of the invention may optionally comprise one or more pigment, as colorants, and suitable examples of those can be taken from any of the well known inorganic and organic pigments chemical types such as titanium dioxide, antimony oxide, calcium carbonates, barium sulphates, calcite, china clay, iron oxides, chromates, ferrocyanides,, carbon black, azo pigments, phthalocyanines, anthraquinones. The compositions may also contain antifoaming agents, levelling agents, dispersant aids for pigment distribution, thickeners, driers, extenders, catalysts for the isocyanate addition reaction, and less preferably solvents that are not incorporated in the film.

Pigments are suitably used in amounts of from 0.1 to 400% by weight, based on the weight of resin binder.

Further components which may be present in compositions in paints according to the invention include antiskinning agents such as methyl ethyl ketoxime (MEKO) cyclohexanone ketoxime, biocides such as Troysan Polyphosphates AF3, Acticide EP and Algon 100, and silicone oils.

In order that the invention may be well understood, the following Examples are given by way of illustration only.

Preparative Example A reactive polyester was prepared from the following: Octanoic acid 28.156 wt.6 Trimethylolpropane 34.424 wt.h Benzoic acid 6.708 wit.* Phthal ic anhydride 20.826 wt.k Phosphoric acid 0.019 wt.k Trimellitic anhydride 9.869 100.000 by the following procedure: 1. charge octanoic acid and trimethylolpropane and heat to melt at 100-1100C; sparge with nitrogen; 2. charge benzoic acid, phthalic anhydride and phosphoric acid and heat to 1700C, distilling off water of esterification via a packed column and keeping head temperature to 108 C maximum; 3. hold at 1700C for 2 hours; 4. heat to 1800C and hold for 3 hours; 5. heat to 2200C and hold for 1 hour; hold for acid value below 10mgKOH/g.

6. cool to 1600C and charge trimellitic anhydride; then heat to 170-1750C; 7. hold at 170-1750C until acid value is 52-56 mgKOH/g; 8. cool to 1600C and dilute to 80% solids content using Proglyde DMM(dimethylether of propylene glycol).

Example 1 An aqueous dispersion was prepared from the polyester in Proglyde DMM produced in the Preparative Example by blending 63.00 parts of the resin with 4.48 parts of 2-amine-2-methyl-l-propanol (as a 90t solution in water) and then reducing the blend with 29.60 parts of water. Xylylene diamine (0.39 parts) was added to the dispersion which was then stirred at 250C for 10 minutes. TDI-tridecanol adduct (2.53 parts) was added to the mixture and the whole held at 250C until complete reaction of the adduct was achieved. There was thus obtained a thixotropic dispersion of the polyester resin in water.

Coating Composition 1 t by weight Reaction product from Example 1 44.710 Byk 020 0.252 Byk 346 0.315 Efka 34, 10% in water 0.567 Water 14.743 LS2980 polyisocyanate 18.892 Water 19.521 100.00 The thixotropic dispersion of the polyester resin in water is blended with the optional auxiliary agents and additives by stirring, preferably before the addition of the polyisocyanate component. This mixture was then blended with the chosen polyisocyanate and the resulting product was reduced to application viscosity with water. This product was then coated (lOOm wet film thickness) onto glass plates. The plates are then left to cure at room temperature for 7 days and the coating properties such as hardness, water and chemical resistance were then determined.

The results indicate that the thixotropic dispersion of the polyester resin in water can be crosslinked by polyisocyanate at room temperature.

Example 1 Standard Non thixotropic system Tukon hardness 7.6 6.6 MEK runs 24s 21s Xylylene runs very soft. slight very soft. slight loss of gloss loss of gloss.

Water spot test slightly hazy slightly hazy 24 hours blisters very small blisters

Claims (6)

1. CLAIMS: 1. A thixotropic composition comprising (i) water, and (ii) a water-dispersible or water-dilutable reactive polyester resin; thixotropy being imparted to the composition by the presence of a polyurea material prepared by reacting one or more (poly)amines with one or more (poly)isocycanates in the presence of at least a portion of the alkyd or modified polyester resin.
2. 2. A composition as claimed in claim 1 in which the polyurea material is derived from the reaction of a polyamine with a monofunctional isocyanate in the presence of some polyisocyanate.
3. 3. A composition as claimed in claim 2 in which the polyamine is a diprimary diamine.
4. 4. A composition as claimed in any one of the preceding claims in which the polyurea material is present in an amount of from 0.05 to 15% by weight of the polyester resin.
5. 5. A composition as claimed in any one of the preceding claims also containing a polyisocyanate as a crosslinking agent.
6. 6. A composition as claimed in any one of the preceding claims substantially as hereinbefore described with reference to the Examples.