GB2259513A - Autoxidisable coating composition - Google Patents

Abstract

An autoxidisable coating composition (especially a paint, varnish or woodstain) comprises an autoxidisable film- forming polymer and a cobalt drier dispersed or dissolved in an organic or preferably aqueous volatile carrier liquid where the activity of the drier is promoted by the presence of a halogenated (preferably fluorinated) ( beta -keto ester either added as a complex with the cobalt or which forms such a complex in situ. The esterifying moiety of the beta -keto ester is aliphatic (including cycloaliphatic). The autoxidisable groups of the polymer may be derived from the condensation of allyl glycidyl ether or one of its analogues with a carboxylic acid moiety e.g. acrylic or methacrylic acids. The polymer preferably also comprises hydrophobic non-acid monomers e.g. alkyl acrylates, vinyl acetate and styrene. Alternatively the polymer may be an alkyd resin. The promoter is preferably (2,2,2-trifluoroethyl 3-oxobutanoate) or (ethyl,4,4,4-trifluoro-3-oxobutanoate). The invention also relates to a bis cobalt (II) ion complex, wherein the complexing moiety is a promoter as defined above, particularly, bis (ethyl 4,4,4-trifluoro-3-oxobutanato) cobalt (II). <IMAGE>

Description

AUTOXIDISABLE COATING COMPOSITION HAVING AN ACCELERATED RATE OF AUTOXIDATION This invention relates to an autoxidisable coating colnposition having an accelerated rate of autoxidation. The composition will generally be an air-drying paint, varnish, woodstain or timber preservative applicable (usually at ambient temperatures) by for example brush, roller, pad or spray to architectural surfaces, fittings or furnishings, that is to say surfaces usually found in buildings or on furniture.

An autoxidisable coating composition comprises at least an autoxidisable film-forming polqnler (including copolymer), a volatile carrier liquid (for example water or white spirit! in which the film-forming polymer is dispersed and/or dissolved and cobalt ions which accelerate autoxidation of the polymer. When the coating composition is applied as a coating to a surface, the coating dries by evaporation of the carrier liquid leaving a dried film of the composition in which in the presence of air the autoxidisable polymer crosslinks by autoxidation of its autoxidisable moieties. Somewhat confusingly, the paint trade also calls this crosslinking "drying" ad the cobalt compounds which provide the cobalt ions to accelerate autoxidation are likewise called "driers".

Crosslinking is important because it creates macromolecular structures which are stronger and more water-resistant than the uncrosslinked polymer. It is important that crosslinking occurs quickly so as to develop adequate strength and water-resistance within say 48 hours (and preferably within 16 hours) of the application of the composition and it is for this reason that cobalt ions are used to accelerate the rate of autoxidation. The cobalt ions should be used in association with some moiety such as the naphthenate or so-called "octoate" anions which ensure their dissolution or at least their thorough dispersion in the carrier liquid. (The so-called "octoate" anions are more correctly called ethylhexanoate anions).Cobalt naphthenate and cobalt octoate both work well in paints based on organic solvents, but cobalt ions can be less active in aqueous paints even when used with anions which ensure good dissolution. This reduced activity is probably caused in part by a partial poisoning of the cobalt ions by certain basic species used to render the film-forming polymer water-soluble. It has been suggested that the accelerating effect of cobalt ions can be promoted by forming complexes with ethyl acetoacetate or l,10-phenanthroline either by pre-forming the complex or by adding the promoter to a solution of cobalt salt in paint whereupon the complex forms spontaneously in situ. In either case, the improvement achievable in aqueous paints is still minimal.

Cobalt ions also have an unwelcome tendency to impart a slight bluish tint to aqueous paint when used in larger concentrations.

An object of this invention is to provide better promoters for use with cobalt ions in autoxidisable coating compositions.

Accordingly this invention provides an autoxidisable coating composition which comprises an autoxidisable film-forming polymer, a volatile carrier liquid in which the film-forming polymer is dispersed and/or dissolved, cobalt ions which accelerate autoxidation of the polymer and a promoter for the cobalt ions wherein the promoter comprises a halogenated B-keto ester in which the esterifying moiety is aliphatic (including cyclo aliphatic) and preferably contains from 1 to 10 carbon atoms. The promoter accelerates the rate of autoxidation of autoxidisable polymers in coating compositions and especially in aqueous compositions.

The promoter may be provided in the foim of a pre-formed complex of cobalt(II) ions and halogenated ss-keto ester. The complex is easily made by adding the B-keto ester to an aqueous solution of cobalt(II) ions (for example aqueous cobalt acetate) whereupon spontaneous precipitation of the complex occurs.

Sometimes it may be necessary to cause the complex to precipitate by adding organic base, for example methanolic triethylamine. Pre-formation of the complex leads to less wastage of the ss-keto ester which is an expensive compound. Alternatively the promoter may be added directly to a coating composition or precursor for the composition containing dissolved cobalt ions whereupon the cobalt complex forms in situ. Direct addition has the advantage of simplicity and it can be used with existing formulations containing cobalt naphthenate or cobalt octoate but it usually requires use of more B-keto ester than would be needed to achieve the same acceleration using a pre-formed complex.

It is believed that the halogen groups in the halogenated B-keto ester serve to increase the ability of the complex to co-ordinate with hydroperoxides formed during the autoxidation reaction and this helps to accelerate the rate of autoxidation. Fluorine groups are best at this and so are preferred. Chlorine groups create a risk of liberation of hydrochloric acid whilst bromine and iodine are unattractive for steric reasons in addition to being liable to form hydrogen halide acids. It is preferred that the ester contain at least three halogen groups and possibly as many as 12. Preferably at least three halogen groups should be attached to a single carbon atom and trihalomethyl and 2,2,2-trihaloethyl groups are especially preferred.

The esterifying moiety of the ss-keto ester preferably comprises from 1 to 10 carbon atoms ana especially preferred groups are methyl, ethyl, trifluoromethyl and 2,2,2-trifluoroethyl. In addition to the carbon atoms in the esterifying moiety, the ester preferably also comprises from 4 to 12 (preferably aliphatic or cycloaliphatic) carbon atoms and most preferably 4 to 6. Preferred fluorinated ss-keto esters include (2,2,2-trifluoroethyl 3-oxobutanoate) and (ethyl 4,4,4-trifluoro-3-oxobutanoate) which latter is commercially available.

The ratio of moles of promoter to gram ions of cobalt used in the composition is preferably 1.8 to 2.2 when the promoter forms a bis complex with the cobalt ions. However if the promoter is added to the composition to form a complex in situ the ratio should be preferably 2:4. Usually the amount of cobalt ion present in a coating composition is from 0.08 to 2 wt% based on the weight of autoxidisable polymer present in the composition.

The promoters produce accelerated rates of autoxidation both in compositions where the carrier liquid is an organic solvent and in compositions where it is an aqueous liquid. Autoxidisable coating compositions based on organic solvents are well kno*m and are described for example in the second edition of the book "Introduction to Paint Chemistry and Principles of Paint Teclmology" by G P A Turner published in London by Chapman and Hall. in 1980, see Chapter 12, the contents of which are herein incorporated by reference. The promoters are particularly suitable for use with compositions comprising alkyd resins. However the promoters are of most benefit in aqueous autoxidisable coating compositions such as those described in European Patent Specifications EP 0 425 Os5A and EP 0 435 428A, the contents of which are herein incorporated by reference.These aqueous autoxidisable compositions typically comprise copolymers including copolymerised unsaturated carboxylic acids such as acrylic or methacrylic acids some of whose acid groups have been neutralised with monovalent cat ions to render the polymer soluble in water and some have been condensed with allyl glycidyl ether or its analogues to introduce the autoxidisable moieties. Allyl glycidyl ether and its analogues have respectively the formulae:

and

where R, R1 and Rill are independently H or C1 to C8 alkyl and m and n are independently 1 or 2.

The autoxidisable polymer preferably comprises non-acid monomers predominantly derived from hydrophobic unsaturated monomers which have solubilities of less than 6 t in pure water.

Preferably hydrophobic non-acid monomers are of the type conventionally used in making resins for the paint trade. The polymer may comprise just one such non-acid monomer such as methyl, ethyl or butyl acrylate but in general it has been found easier to obtain a better balance of properties when a combination of at least two non-acid monomers is used, one of which would give a homopolymer of high glass transition temperature (Tg), for example Tg above 30"C and one which would give a homopolymer of low Tg, for example Tg below -10 C. Monomers should be chosen which copolymerise at similar rates.

Examples of non-acid monomers which give homopolymers of high Tg include methyl methacrylate, vinyl acetate and styrene. Examples of non-acid monomers which give homopolymers of low Tg include ethyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, butyl acrylate and the material commercially available from the Shell Chemical Company under the trade name "Vinyl Versatate" which is believed to be the vinyl ester of a mixture of branched chain acids which acids contain around 10 carbon atoms. 2-ethylhexyl acrylate has the advantage of being less maloderous if present in residual trace amounts in the final coating composition.

Preferably the polymer comprises from 0 to 55 (preferably at least 15) mol 7c of the copolymerised non-acid monomer of the high Tg type and from 10 or more preferably 20 to 70 wtX of the non-acid monomer of the low Tg type. Too much copolymerised monomer of the high Tg type or too little of the low Tg type leads to poorer lapping whereas too much of the low Tg type increases the time needed to achieve touch dryness. The polymer itself before neutralisation should preferably have a Tg of from -10 C to 15"C.

The theoretical Tg (i.e. the Tg as calculated by te Fox equation) of the polymer should preferably be much higher than what would normally be found in film-forming polymers selected for use in paints intended for application at ambient temperatures.

For example the theoretical Tg will generally be at least 70"C and preferably from 90 to 1300C. It should be cautioned that in view of the presence of carboxylic acid moieties in the copolymer, the theoretical Tg will differ somewhat from an observed Tg, but nevertheless the theoretical Tg has been found to be useful in identifying suitable prepolymers for this invention.

In addition to water, the aqueous liquid may also contain organic cosolvent. The organic cosolvent assists the neutralised polymer to dissolve and it helps to control the viscosity of the coating composition as it dries in air which leads to better application including better lapping. The cosolvent can also improve gloss. The coating composition should contain an effective amount of cosolvent which means as little as possible. Usually at least 0.1 wt% (based on the weight of water and cosolvent) of organic cosolvent will be necessary. The improvements become less worthwhile with amounts of cosolvent beyond 25 wt%. The preferred range of cosolvent concentrations is from 5 to 15 wt%.

The organic cosolvent should be a water-miscible liquid which plasticises the autoxidisable film-forming polymer and/or otherwise increases its solubility in water when neutralised. The cosolvent preferably has a boiling point of from 75 to 200"C at 1 bar absolute. An ideal cosolvent should also be odourless and non-toxic and it should have a high flash point (preferably at least 300C). Examples of useful cosolvents included alcohols, glycols, ester alcohols, ether alcohols and the esters of ether alcohols for example: n-butanol, 2-pentancl, ethylene or propylene glycol, benzyl alcohol, 2,2,4 trimethylpentane 1,3 diolmonoisobutyrate, diethylene glycol, dipropylene glycol, dipropylene glycol methyl ether, diethylene glycol ethyl ether, and most preferably propylene glycol monomethyl ether (ie l-methoxy-2-hydroxy propane (MHP)).

The coating compositions usually have a total non-volatile content of from 10 to 70 wt% of the composition. Non-volatile content is determined according to the procedure of ASTM Test D 1210-9 performed at 150"C or 210 C if the cosclvent has a boiling point above 1500C. The contents of this Test are herein incorporated by reference. The total non-volatile content is generally 30 to 60 wt%, for gloss paints, 30 to 70 wt% for partial gloss paints, 10 to 50 wt% for varnishes and 10 to 30 wt% for woodstains and timber preservatives. Depending on the type of coating composition required, from 10 to 100 wt% of the total non-volatile content may consist of the au-toxidisable film-forming polymer (weighed before neutralisation).Preferably for gloss paints, from 20 to 75 wt% of the total non-volatile content of the composition is partially esterified carboxylic acid copolymer and the corresponding preferred ranges for partial gloss paints, varnishes and woodstain or timber preservative are 10 to 60 wt%, 20 to 100 wt and 20 to 100 wt% respectively.

The coating compositions may additionally contain components conventionally used in making for example paints, varnishes, woodstains or timber preservatives. Such components include pigments, dyes, extenders, thickeners, fungicides, anti-skinning agents, flow improvers and drying agents. The coating compositions have also been found to have a good ability to soak into wood and so they are useful as woodstains and timber preservatives.

The invention is further illustrated by the following Examples of which A to F are Comparative.

EXAMPLE 1 Preparation of 2,2,2-trifluoroethyl 3-oxobutanoate fluorinated ss-keto ester: 80 m mol of freshly distilled diketene dissolved in 10 ml diethyl ether were added dropwise to a solution of 80 m mol 2,2,2-trifluoroethanol and 0.1 ml triethylamine in 10 mls of ether. The mixture was refluxed for 2 hours, then cooled to room temperature and washed firstly with 10 mls of dilute hydrochloric acid and secondly with two 10 ml volumes of demineralised water. The mixture partitioned into aqueous and ether layers with most of the ester being in the ether layer. The layers were separated and the aqueous layer was extracted with ether. The ether layer obtained from the extraction was combined with the ether layer obtained from the initial separation and the combined ether layers were dried.

The solvents were evaporated off under reduced pressure from the combined layers and the organic residue was fractionated to give an oil which was 2,2,2-trifluoroethyl 3-oxobutanoate.

EXAMPLE 2 Preparation of Bis-Chelated Cobalt II Complexes: The fluorinated B-keto ester made according to Example 2 and also ethyl 4,4,4-trifluoro-3oxobutanoate (available commercially from the Aldrich Chemical Company Ltd of Gillingham, Dorset, England) were both used to make bis-chelated cobalt(II) complexes as follows: 20 m mol of cobalt(II) acetate tetrahydrate dissolved in 20 ml demineralised water were mixed with 40 m mol of the ss-keto ester dissolved in 10 ml methanol. A precipitate of the complex formed and was washed twice with 10 ml methanol.The complexes after re-crystallisations had the following melting points: Bis(ethyl 4,4,4-trifluoro-3-oxobutanato)cobaltII: 112 to 1140C Bis (2,2,2-trifluoroethyl 3-oxobutanato)cobaltll: 160 to 1640C EXM!PLES 3 END 4 AND COMPARATIVE EXAMPLES A TO E Evaluation of the Cobalt Complexes in an Aqueous Autoxidisable Coating Composition:: Seven coating compositions containing an aqueous solution of a film-forming polymer made autoxidisable by the condensation of allyl glycidyl ether with carboxylic acid moieties in the polymer were made up according to Example 2 of European Patent Specification EP 0 425 085A except that in six of them, the cobalt octoate drier (i.e. bis (2-ethyl hexanato)cobalt(II)) was replaced by a equimolar amounts of cobalt(II) complexes as specified in Table 1. The coating compositions were then subjected to the Through Dry Test as hereinafter described. The Through Dry Test indicates the time taken for a coating to autoxidise and crosslink to a non-fluid state which extends from the exposed surface of the coating through to its surface which contacts the substrate.Through Dry is important in creating water-resistance and the ability to receive further coats of coating composition.

TABLE 1

Example Complexing Moiety in the Complex Through Dry Time Hours A 2-ethylhexanoato (i.e. "octoate") 15 B ethyl 3-oxobutanoato 14 3 ethyl 4,4,4-trifluoro-3-oxobutanoato 9 4 2,2,2-trifluoroethyl 3-oxobutanoato 12 C trifluoroacetoato (i.e. trifluoroacetate) 15 D heptafluorobutanoato (i.e. heptafluorobutyrate) 15 E 4-ethylphnyl-3-oxobutanoato 21 F 2-ehtylhexanoato (i.e. "octoate") 14 5 ethyl 4,4,4-trifluoro-3-oxobutanato 11 Table 1 shows that cobalt complexes of trifluorinated Th-keto esters have superior Through Dry times as compared with both those of the conventional octoate (i.e. 2-ethylhexanoato) and those of the unfluorinated 3-oxobutanoato complex.

Comparative Examples C and D show that mere fluorination of the carboxylic acid moiety is ineffective and comparative Example E shows that the introduction of an aromatic moiety actually suppresses the ability of the complex to promote the acceleration autoxidation.

It was also found that the complexes of Examples 3 to 4 imparted less of a bluish tint to the coating compositions.

EXAMPLE 5 AND COMPARATIVE EXAMPLE F Evaluation of the Cobalt complexes in an Autoxidisable Coating Composition based on Organic Solvent.

A commercial gloss paint formulation based on white spirit as -the volatile carrier liquid and available as "Dulux" Brilliant White Gloss from Imperial Chemical Industries PLC of Slough, England was made up but with its conventional cobalt octoate drier replaced by an equimolar amount of the cobalt complex of Example 4. The paint was then subject to the Through Dry Test and the results are showy in Table 1.

Complexes containing two or more carbon atoms each attached to at least three halogen groups are expected to be even better promoters of the acceleration of autoxidation.

THROUGH DRY TEST A coat of coating composition 300mm long by 15mm wide and lOOm deep is applied to a clean glass plate. A vertical blunt needle is biassed onto the freshly applied coat by a ig load and then dragged through the coat at a speed of 25.4 mm/h in a direction parallel to the length of the coat.

Initially the coat is wet and fluid so the blunt end of the needle penetrates through to the glass and scores the coat. The score is soon erased by fluid composition flowing into it. As the coat dries, it becomes less fluid and so the needle is forced up towards and eventually onto the surface where it initially scores the surface and the score is no longer erased because the composition has lost its fluidity. As soon as the surface has autoxidised and crosslinked enough to become hard, it is no longer scored by the needle. The time taken for scoring to cease is recorded as the Through Dry Time.

Claims (10)

1. An autoxidisable coating composition which comprises an autoxidisable film-forming polymer, a volatile carrier liquid in which the film-forming polymer is dispersed dissolved, cobalt ions which accelerate autoxidation of the polymer and a promoter for the cobalt ions wherein the promoter comprises a halogenated B-keto ester in which the esterifying moiety is aliphatic (including cyclo aliphatic) and preferably contains from 1 to 10 carbon atoms.

2. A coating composition according to Claim 1 wherein the carrier liquid is aqueous.

3. A coating composition according to Claim 1 or Claim 2 wherein the promoter is fluorinated.

4. A coating composition according to any one of claims 1 to 3 wherein the promoter comprises at least three halogen groups

5. A coating composition according to any one of Claims 1 to 4 wherein the promoter comprises three halogen groups on a single carbon atom.

6. A coating composition according to Claim 5 wherein the promoter comprises ethyl 4,4,4-trifluoro-3-oxobutanoato.

7. A coating composition according to any one of the preceding Claims where the film-forming polymer comprises autoxidisable groups derived from the condensation of allyl glycidyl ether or one of its analogues with a carboxylic acid moiety.

8. A coating composition according to any one of the preceding Claims wherein the promoter has been added as a bis complex of cobalt(II) ions.

9. A bis cobalt(II) ion complex wherein the complexing moiety is a promoter as defined in one of claims 1 or 3 to 6.

10. Bis(ethyl 4,4,4-trifluoro-3oxobutanato)cobalt(II).