WO2007074333A2

WO2007074333A2 - Coating compositions and reactive diluents therefor

Info

Publication number: WO2007074333A2
Application number: PCT/GB2006/004839
Authority: WO
Inventors: Hanamanthsa Shankarsa Bevinakatti; Alan Geoffrey Waite
Original assignee: Croda International Plc
Priority date: 2005-12-24
Filing date: 2006-12-21
Publication date: 2007-07-05
Also published as: GB0526457D0; WO2007074333A3

Abstract

A coating compositions are disclosed which have at least one binder, for example an alkyd resin, and a reactive diluent. The reactive diluent is obtained by reacting a polyunsaturated fatty acid with a dicarboxylic acid and a polyol. A particularly preferred reactive diluent is obtainable by reacting glycerol, a saturated C5 to C8 dicarboxylic acid, more especially adipic acid, and linoleic acid. In preferred embodiments, the polyunsaturated acids are derived from natural oils.

Description

Coating Compositions and Reactive Diluents Therefor

The present invention relates to coating compositions and reactive diluents therefor. In particular, the present invention relates to coating compositions such as paints, varnishes and wood stains containing reactive diluents prepared from polyols, di- carboxylic acids and polyunsaturated fatty acids and to such reactive diluents per se.

Coating compositions based on alkyd resins are in very wide spread use owing to the ease of applicability of such compositions to various substrates and to subsequent adhesion, protective properties and aesthetic appearance of the polymeric film formed from such compositions on drying. In many applications, the compositions air dry as the alkyd resins are auto-oxidisable in air.

For safety and environmental reasons, there is a significant drive to reduce or eliminate the use of volatile organic solvents in such coating compositions, which solvents evaporate off during the drying (auto-oxidation) process. Accordingly, attempts have been made to increase the solids content of such compositions, ie to reduce the solvent content, or to reduce or eliminate the volatile organic solvent component by introducing water-based formulations. An alternative approach has been to consider the use of reactive diluents. Such reactive diluents act as solvents for the alkyd resins but are subsequently incorporated into the polymeric network formed as the composition dries, ie the reactive diluent is essentially non-volatile or at most of low volatility thus enabling the presence of volatile organic solvents in the composition to be at least significantly reduced if not eliminated entirely. Examples of the use of such reactive diluents in alkyd resin coating compositions may be found in GB-A-815179, EP-A-0685543, US 4689266, US 4798859, US 5064892, US 2006/0240194 and WO 03/064548. As can be seen from these disclosures of coating compositions incorporating reactive diluents, there are strong environmental reasons for preparing such reactive diluents from materials derived from renewable resources.

Clearly, an important factor in selecting suitable reactive diluents is the ability of the diluent to function as a solvent for the alkyd resin components, ie to have a suitable viscosity to impart the correct viscosity range to the coating composition for its subsequent use, whilst having a low volatility. A factor that affects the viscosity of reactive diluents based on fatty acid esters of polyols as described in the aforementioned prior disclosures is the number of free OH groups remaining in the molecules following esterification. It is an object of the present invention to provide coating compositions containing reactive diluents and to provide reactive diluents for use in such compositions in which the number of free OH groups is minimised. More especially, it is an object to provide such reactive diluents from renewable resources. According to a first aspect of the present invention, a coating composition comprises at least one binder and a reactive diluent therefor, said reactive diluent being obtainable by the reaction of at least one polyol with at least one dicarboxylic acid or alkyl ester or anhydride thereof and at least one polyunsaturated fatty acid or alkyl ester thereof, said reactive diluent having a viscosity of less than 0.5 Pa s at 25°C. According to a second aspect of the present invention, the use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester compound obtainable by the reaction of at least one polyol with at least one dicarboxylic acid or alkyl ester or anhydride thereof and at least one polyunsaturated fatty acid or alkyl ester thereof, said reactive diluent having a viscosity of less than 0.5 Pa s at 25⁰C. A third aspect of the invention comprises a polyunsaturated fatty acid polyester of a polyol which is obtainable by the reaction of at least one polyol with at least one dicarboxylic acid or alkyl ester or anhydride thereof and at least one polyunsaturated fatty acid or alkyl ester thereof, said polyester having a viscosity of less than 0.5 Pa s at 25°C. The Applicants have found that the reaction of the polyunsaturated fatty acid, the polyol and the dicarboxylic acid (or derivatives thereof) results primarily in the formation of polyunsaturated fatty acid esters of oligomers of the polyol and the dicarboxylic acid, although it will be appreciated that other monomeric and oligomeric species may be present. Such esters of the oligomers are particularly useful as reactive diluents in accordance with the invention.

Although it is preferred to obtain the reactive diluents of the present invention using a "one pot" reaction in which all three components are introduced at the start of the reaction process, it is possible to obtain the reactive diluents using a two stage reaction scheme. In the two stage reaction scheme, the polyol and the dicarboxylic acid components are subjected to an initial reaction following which the polyunsaturated fatty acid is added to the reaction mixture.

In particularly preferred embodiments of the present invention, the reactive diluent has a free OH group hydroxyl value of not more than 25 mgKOH/g, more preferably not more than 20 mgKOH/g and more especially not more than 15 mgKOH/g. In typical examples, the reactive diluent has a free OH group hydroxyl value of around Wθ ₂θ 7/»74333

3 10 mgKOH/g or less. It is to be noted that, in measuring hydroxyl values, the resultant figure is a combination of residual acid OH groups and residual alcohol OH groups. Accordingly, in this specification, the expression "free OH group hydroxyl value" is the difference between the total hydroxyl value and the acid value (which is also expressed in mgKOH/g).

Preferably, the polyols used to form the polyester according to the invention are selected from C₃ to C₁₀ polyols, preferably aliphatic, and having a minimum of three hydroxyl groups. Preferably, the polyols have at least two primary hydroxyl groups and, optionally, at least one secondary hydroxyl group. Preferred polyols are selected from C₃ to C₈ polyols, more especially C₃ to C₆ polyols. Suitable polyols may be selected from: a) alditols, etherified derivatives thereof and cyclitols preferably selected from C₃ to C₆ alditols but may include dimeric and higher anhydrides thereof, for example glycerol and diglycerol and partial esters thereof, or any triglycerides containing multiple hydroxyl groups, C₄ polyols such as threitol and erythritol, C₅ polyols such as ribitol, arabitol and xylitol and hexitols, especially sorbitol or mannitol, but including sorbitan and inositols; b) alkyl, especially Ci to C₄ alkyl, glycosides, more particularly glycosides of mono- and disaccharides; and c) polymethylol alkanes such as neopentyl glycol, trimethylol ethane, trimethylol propane, pentaerythritol and dimers and trimers thereof and partial esters thereof.

Mixtures of polyols may be used to form the polyester according to the invention.

Preferred polyols are C₃ to C₆ polyols, especially such polyols having not more than four hydroxyl groups on average.

In a preferred embodiment of the present invention, the polyol is an alditol; especially glycerol or diglycerol or mixtures of glycerol and diglycerol. More particularly, the polyol is glycerol.

Preferably, the dicarboxylic acids or alkyl esters or anhydrides thereof used to form the polyester according to the present invention are selected from C₂ to C₃₆ dicarboxylic acids which can be saturated or unsaturated, linear or branched and may include dimer acids.

The term dimer acid is well known in the art and refers to the dimerisation product of mono- or polyunsaturated fatty acids and/or esters thereof. Dimer acids are typically dimer fatty acids of Ci₀ to C₃₀, more typically C₁₂ to C₂₄ unsaturated fatty acids. Preferred examples are dimer fatty acids of C₁₄ to C₂₂, especially C₁₈ unsaturated fatty acids. Specific examples of suitable dimer fatty acids are the dimerisation products of oleic acid, linoleic acid, linolenic acid, palmitoleic acid and elaidic acid and mixtures thereof. The dimerisation products of the unsaturated fatty acid mixtures obtained in the hydrolysis of natural fats and oils may also be used. Examples of such fats and oils include but are not limited to safflower, tall oil, calendula oil, corn oil, rapeseed oil, peanut oil, soya bean oil, tung oil, linseed oil, sardine oil, herring oil, sesame oil, olive oil, dehydrated castor oil, tallow oil, sunflower oil, cottonseed oil and mixtures thereof. Hydrogenated dimer fatty acids may also be used; hydrogenation of the dimer fatty acids being undertaken using a nickel catalyst for example.

The dimer fatty acids, as a result of the dimerisation process, usually contain varying amounts of oligomeric fatty acids (so called "trimer" acids) and residues of monomeric fatty acids ("monomer") or esters thereof. The amount of monomer present in the dimer acid may be reduced by distillation. Preferred dimer fatty acids have a dimer content of greater than 50%, more preferably greater than 70%, particularly greater than 85% and especially greater than 94% by weight. The trimer acid content is preferably less than 50%, more preferably in the range 1 to 20%, particularly 2 to 10% and especially 3 to 6% by weight. The monomer content is preferably less than 5%, more preferably in the range 0.1 to 3%, particularly 0.3 to 2% and especially 0.5 to 1% by weight.

Preferably, the dicarboxylic acids are aliphatic or aromatic dicarboxylic acids having C₂ to C₂₀ carbon atoms, more preferably C₄ to C₁₂ carbon atoms. Preferred acids are straight chain aliphatic dicarboxylic acids having C₄ to C₁₂ carbon atoms, more especially C₄ to C₈ carbon atoms or aromatic acids having C₈ carbon atoms. Typically, the acids include malonic acid, maleic acid, fumaric acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecane dicarboxylic acid, and dodecane dicarboxylic acid. Examples of aromatic acids include phthalic acid, isophthalic acid and terephthalic acid.

The acids may also be alkyl- or alkenyl-substituted acids wherein the substituent group may be C₆ to C₂₂ linear or branched alkyl or alkenyl group. More particularly, the substituent group is suitably a C₈ to C₂₂, preferably a C₁₀ to C₂₂, more preferably a C₁₂ to C₂₀, particularly a C₁₄ to C₁₈ alkyl or alkenyl, and especially alkenyl, group. The alkenyl group preferably comprises a single double bond. Preferably, the alkyl or alkenyl group is linear but, when it is not, it preferably has at most a total of two, and more preferably not more than one, branches on average.

Esters and anhydrides of such acids may also be used. If alkyl esters of the polyunsaturated fatty acids are used, preferably it is a C₁ to C₆ alkyl ester, more preferably it is a C₁ to C₄ alkyl ester and even more preferably is a C₁ to C₂ alkyl ester. Examples of suitable anhydride are maleic anhydride, succinic anhydride, alkenyl succinic anhydride, and phthalic anhydride.

Mixtures of such acids, and their derivates, may be used, if desired.

Preferred acids are straight chain aliphatic or aromatic dicarboxylic acids having C₄ to C₈ carbon atoms, more especially such acids having C₅ to C₈ carbon atoms, and C₈ aromatic acids, and especially preferred are adipic acid and/or phthalic acid.

Suitable polyunsaturated fatty acids used to form the polyester of the present invention are the semi-drying or drying polyunsaturated fatty acids or mixtures thereof that are ethylenically unsaturated, whether conjugated or non-conjugated. More particularly, the acids are selected from C₁₈ to C₂₂ polyunsaturated fatty acids and may be linoleic, linolenic, arachindonic, eicosatetraenoic, eicosapentaenoic and docasahexaenoic acids or mixtures thereof. More especially, the acids are selected from C₁₈ to C₂₀ polyunsaturated fatty acids or mixtures thereof. In a particularly preferred embodiment, the polyunsaturated fatty acid is linoleic acid. Although pure forms of the polyunsaturated acids may be used, in a preferred form of the invention, the polyunsaturated fatty acids are derived from natural or synthetic oils in which the preferred acids are a major component, other acids being present in minor amounts. The raw oils themselves may be used; preferably, however, the polyunsaturated acids are the distilled fractions obtained from the raw oils. Examples of suitable natural oils include but are not limited to safflower oil, tall oil, calendula oil, corn oil, rapeseed oil, peanut oil, soya bean oil, tung oil, linseed oil, sardine oil, herring oil, sesame oil, olive oil, dehydrated castor oil, tallow oil, sunflower oil, cottonseed oil and mixtures thereof. In the preferred embodiment when the polyunsaturated fatty acid is linoleic acid, the linoleic acid is preferably derived from sunflower oil or soya bean oil.

In preferred embodiments of the invention, distilled fatty acid fractions derived from such oils are used to make the reactive diluent of the present invention, such distilled fractions having at least 50 wt% polyunsaturated fatty acids, the majority of the remaining balance being long chain saturated acids, preferably no more than about 20 wt%, and mono-unsaturated fatty acids, preferably no more than about 30 wt%. Typically, the long chain saturated fatty acids are C₁₄ to C₂o or greater fatty acids and the mono-unsaturated fatty acid is Ci₈ mono-unsaturated fatty acid.

Such polyunsaturated fatty acids are auto-oxidisable similarly to alkyd resins and the distilled fatty acid fractions used in the reactive diluent of the present invention preferably have an iodine number of at least 100, more preferably of at least 120 and preferably up to around 140 expressed in terms of the number of centigrams of iodine per gram of fatty acids (eg ASTM test method D-1959).

If alkyl esters of the polyunsaturated fatty acids are used, preferably it is a C₁ to C₆ alkyl ester, more preferably it is a C₁ to C₄ alkyl ester and even more preferably is a Ci to C₂ alkyl ester. Mixtures esters may also be used.

In the polyunsaturated fatty acid polyesters of the present invention, the molar ratio of polyol : dicarboxylic acid : polyunsaturated fatty acid used in the reaction is preferably in the range 1 : 0.5 to 0.75 ; 1.5 to 2, more preferably is in the range 1 : 0.5 to 0.7 : 1.6 to 2, more particularly is in the range 1 : 0.5 to 0.7 : 1.7 to 2, and more especially is in the range 1 : 0.5 to 0.67 : 1.7 to 1.9.

In preferred embodiments of the invention, the polyol is a C₃ to Ce polyol, especially such a polyol having not more than four hydroxyl groups on average, and is preferably glycerol and/or diglycerol; the dicarboxylic acid or derivative thereof is an aliphatic acid having C₄ to Cs carbon atoms, and is preferably adipic acid, or an aromatic acids having C₈ carbon atoms, especially isophthalic acid or anhydride thereof; and the polyunsaturated acid is derived from sun flower oil or soya bean oil.

In an especially preferred embodiment of the present invention, the reactive diluent, ie the polyunsaturated fatty acid polyester, is obtained by reacting glycerol, a saturated C₅ to C₈ dicarboxylic acid, more especially adipic acid, and linoleic acid. It will be appreciated that, when the linoleic acid is derived from natural oils, other acid esters may also be present in the final product. A particularly preferred ratio of polyol : dicarboxylic acid : polyunsaturated fatty acid reactants is 1 : 0.5 : 1.8.

It will be appreciated also that, whilst the amounts of starting materials may be selected to obtain particular oligomers, eg polyunsaturated fatty acid/ residue/polyol residue/dicarboxylic acid residue/polyol residue/polyunsaturated fatty acid residue, it will be a statistical mixture of other higher and lower oligomers.

Preferably, reactive diluents of the present invention have a weight average molecular weight, measured as described in relation to the Example below, in the range 1000 to 4200, more particularly in the range 1000 to 4000, even more preferably in the range 1500 to 4000 and especially in the range 2000 to 4000.

Preferably, reactive diluents of the present invention have viscosity of less than 0.5 Pa s at 25°C, more particularly less than 0.25 Pa s at 25°C and more especially less than 0.2 Pa s at 25°C.

Preferably, the reactive diluent according to the invention is made by reacting polyol(s) with the dicarboxylic acid(s) and polyunsaturated fatty acid(s) without any catalysts or in the presence of acid and/or base catalysts, eg phosphorous acid, sodium hydroxide, in a "one pot" reaction wherein the reaction components are all added at the start of the reaction process. The reaction mixture is heated to a temperature of about 17O⁰C to 240⁰C, more preferably 180⁰C to 240⁰C, and typically about 220⁰C, preferably under vacuum. Depending on the composition of the starting materials, the esterification reaction may be direct, inter- or trans- esterification or a combination thereof. The reaction is terminated after the acid value of the reaction mixture has dropped to a suitable level, typically less than 25 mgKOH/g, more particularly less than 20 mgKOH/g and more especially less than 10 mgKOH/g.

Using similar conditions, it is possible to use a two stage reaction process in which the polyol and the dicarboxylic acid components are subjected to an initial reaction period following which the polyunsaturated fatty acid component is added.

The binders of the coating compositions of the present invention are preferably auto- oxidisable alkyd resins. As is well known in the art, alkyd resins are in general the reaction product of the esterification of polyhydric alcohols with polybasic acids (or their anhydrides) and fatty acids (or glycerol esters thereof) and need not to be further described herein. The properties of the alkyd resins are primarily determined by the nature and the ratios of the alcohols and acids used and by the degree of condensation. Suitable alkyd resins include long oil and medium oil resins eg derived from 45 to 70 wt. % of fatty acids. The binder may also be selected from (meth)acrylic-modified alkyd resins, vinylated alkyd resins, styrene alkyd resins, polyurethane alkyd resins, silicone alkyd resins, polyamide modified alkyds and epoxy esters.

The coating composition according to the present invention preferably has a binder to reactive diluent ratio in the range from 98 to 50 : 2 to 50 parts by weight, more preferably from 95 to 50 : 5 to 40 and more especially from 90 to 70 : 10 to 30 parts by weight. The coating compositions according to the present invention may be formulated by any conventional mixing techniques including, as appropriate, dispersing and grinding with a liquid carrier and at least one drier and optionally pigments, filler/extenders and other conventional additives. Although the aim of using reactive diluents in coating compositions is to reduce or eliminate the use of organic solvents as liquid carriers, it may be necessary in some formulations of the coating compositions to include some organic solvent. Examples of suitable solvents include aliphatic, cycloaliphatic and aromatic hydrocarbons, alcohol ethers, alcohol ether esters, alcohol esters and mixtures thereof. Typical examples of such solvents are: butyl glycol butyl diglycol isoparafins propylene glycol mono methyl ether - dipropylene glycol mono methyl ether white spirits including de-aromatised and higher flash point white spirits.

Mixtures of solvents may also be used. The solvent is typically present at about 10 to about 20 wt% and preferably about 10 to about 15 wt%.

The auto-oxidation process that polymerises the alkyd resin compositions may be accelerated by the inclusion of driers, for example the commercial material available under the trade name Nuodex, preferably incorporated in the range 1% to 10% by weight based on the binder. Examples of suitable driers are salts of (cyclo)aliphatic, natural or synthetic acids, such as, for example, linoleic acid, naphthenic acid, 2-ethyl-hexanoic acid and neodecanoic acid of various metal like cobalt, manganese, iron, lead, zirconium, strontium, aluminium, calcium, barium, bismuth, zinc, lithium and potassium. To control the catalytic activity of the driers and to preclude untimely oxidation of the alkyd resin and reactive diluent, an anti- skinning agent such as a ketpxime, typically methyl ethyl ketoxime, n-butyl ketoxime or cyclohexane ketoxime, may be present in the coating composition. Other additives to the coating composition according to the present invention may include rheology modifiers, wetting and compability agents, flow and levelling agents, extenders, anti-sagging agents, anti-oxidants, bactericides, fungicides, insecticides, UV absorbers, flame retardants and other additives that are well known in the art.

Coating compositions according to the present invention will optionally comprise one or more inorganic or organic, transparent or non-transparent pigments. Typically, such pigments may be selected from titanium dioxide, iron oxides, carbon black, mixed metal oxides, mono- and di- azo pigments, copper phthalocyanines and anthraquinones.

These coating compositions according to the present invention are typically used, for coating substrates such as wood, plastics, leather, textiles, glass, ceramic or metals. The coating compositions according to the present invention may be applied to such substrates by any known methods, such as spraying, brushing, flooding, casting, dipping and rolling.

The present invention will now be further described by way of illustration only with reference to the following examples. In this specification, the following test methods have been used.

Acid Value

The acid value was determined using ASTM D1980-87.

Hvdroxyl Value

The hydroxyl value was determined using ASTM D1957-86. Colour

Colour was determined using ASTM D1544-89.

Viscosity

The viscosity was determined using ISO 2555.

Molecular Weight Molecular weight was determined by gel permeation chromatography (GPC) using a Viscotek Evolution system consisting of a solvent pump, vacuum degasser, autosampler, column oven and refractive index detector. Tetrahydrofuran (THF) was used as the mobile phase at a flow rate of 1ml/min, along with a set of two ViscoGel (TSK GMHHR) columns. Column and detector temperature was maintained at 40⁰C. Polystyrene standards were used for determination of molecular weight information. Drying Time

The drying time was determined using a drying time recorder from Byk-Gardner. Kδnig Hardness

The Kδnig hardness was determined using DIN/ISO 1522. Yellowing Index

The yellowing Index was determined using ASTM E313 96.

Gloss

Gloss was determined using DIN/ISO 2813.

Example 1 Samples 1 to 3 were made by charging polyol, dicarboxylic acid and potassium carbonate in the proportions shown in Table 1 to a 1000ml round bottomed flask fitted with a propeller stirrer, side-arm water condenser and collection flask, vacuum pump, nitrogen sparge and thermometer (thermocouple), the flask being mounted on an isomantle. The reaction mixture was heated using the isomantle under stirring (300 rpm), with a nitrogen sparge under the conditions shown in

Table 1 and held for [until the acid value of the reaction mixture was < 5mgKOH/g.] Polyunsaturated fatty acid was then added to the reaction mixture and the reaction was continued until the acid value of the reaction mixture was again less than < 20mgKOH/g. The reaction was then stopped by switching off the isomantle to allow the product to cool, following which it was discharged.

Samples 4 to 12 were made by charging polyol, dicarboxylic acid (or anhydride in the case of Sample 10), polyunsaturated fatty acid and phosphorous acid in the proportions shown in Table 1 to a 1000ml round bottomed flask fitted with a propeller stirrer, side-arm water condenser and collection flask, vacuum pump, nitrogen sparge and thermometer (thermocouple), the flask being mounted on an isomantle. The reaction mixture was heated under stirring (300 rpm), with a nitrogen sparge under the conditions shown in Table 1 and held until the acid value of the reaction mix was < 20 mgKOH/g or < 10 mgKOH/g, as shown in Table 2. The reaction was then stopped by switching off the isomantle to allow the product to cool, following which it was discharged.

Notes relating to Table 1 : The polyol used in Sample 1 was sorbitol and the polyol used in

Samples 2 to 12 was glycerol available from Uniqema under the trade mark PRICERINE 9091.

The dicarboxylic acid used in Samples 1, 2, 4 and 9 was a C36 dimer acid available from Uniqema under the trade mark PRIPOL 1017. and the dicarboxylic acid used in Samples 3, 5 to δ, 11 and 12 was adipic acid. Phthalic anhydride was used in Sample 10.

The polyunsaturated fatty acid used in Samples 1 to 7, 9 and 11 was a distilled sunflower fatty acid fraction available from Uniqema under the trade name PRIFAC 8960 and the polyunsaturated fatty acid used in Sample 8, 10 and 12 was a distilled soya bean fatty acid fraction available from Uniqema under the trade name of PRIFAC 8953.

4. The moles of dicarboxylic acid, anhydride, polyunsaturated fatty acid and catalyst used were based on 1 mole of polyol.

Table 1

Samples 1 , 2, 4 and 5 are comparative examples. The Samples had the properties shown in Table 2 above.

Comparative Samples 1 , 2, 4 and 5 were too viscous to be of use as reactive diluents.

Sample 3 was formulated into a paint composition. Samples 6 to 12 are particularly useful in formulating paint compositions. Table 2

* Measured hydroxyl value - measured acid value. ** Samples 1, 2, 4 and 5 are comparative examples.

Example 2

Long oil alkyd resin formulation (Formulations 1 and 2) based on Samples 10 and 12 as described in Example 1 were made using the components shown in Table 3. The long oil alkyd resin has the composition shown in Table 4.

Table 3

The formulations were tested for drying time, Kδnig hardness, yellowing and gloss retention as described above. The results for Formulations 1 and 2 are shown in Tables 5 and 6, respectively.

Table 5

Table 6

The above results show that the reactive diluents can be used to formulate an alkyd based coating which give comparable results to traditional based solvent alkyd formulations.

Claims

1. A coating composition comprises at least one binder and a reactive diluent therefor, said reactive diluent being obtainable by the reaction of at least one polyol with at least one dicarboxylic acid or alkyl ester or anhydride thereof and at least one polyunsaturated fatty acid or alkyl ester thereof, said reactive diluent having a viscosity of less than 0.5 Pa s at 25⁰C.

2. A coating composition according to claim 1 in which said at least one polyol is selected from C₃ to C₁₀ polyols having a minimum of three hydroxyl groups.

3. A coating composition according to claim 1 or claim 2 in which said at least one polyol is selected from aliphatic C₃ to Ce polyols and more especially from aliphatic C₃ to C₆ polyols.

4. A coating composition according to any one of the preceding claims in which said at least one polyol has at least two primary hydroxyl groups and, optionally, at least one secondary hydroxyl group.

5. A coating composition according to any one of claims in which said at least one polyol is selected from alditols.

6. A coating composition according to claim 5 in which said at least one polyol is glycerol or diglycerol or mixtures of glycerol and diglycerol.

7. A coating composition according to claim 5 or claim 6 in which said at least one polyol is glycerol.

8. A coating composition according to any one of the preceding claims in which said at least one polyunsaturated fatty acid is a semi-drying or drying polyunsaturated fatty acids or mixtures thereof that are ethylenically unsaturated, whether conjugated or non-conjugated.

9. A coating composition according to any one of the preceding claims in which said at least one polyunsaturated fatty acid is selected from C₁₈ to C₂₂ polyunsaturated fatty acids.

10. A coating composition according to any one of the preceding claims in which said at least one polyunsaturated fatty acid is selected from linoleic, linolenic, arachindonic, eicosatetraenoic, eicosapentaenoic and docasahexaenoic acids or mixtures thereof.

11. A coating composition according to any one of the preceding claims in which said at least one polyunsaturated fatty acid is selected from C₁₈ to C₂₀ polyunsaturated fatty acids or mixtures thereof.

12. A coating composition according to any one of the preceding claims in which said at least one polyunsaturated fatty acid is linoleic acid.

13. A coating composition according to any one of the preceding claims in which said at least one polyunsaturated fatty acid, or mixtures of such acids, is derived from natural or synthetic oils in which the acid or acids are a major component.

14. A coating composition according to claim 13 in which the natural oil is selected from safflower, tall oil, calendula oil, corn oil, rapeseed oil, peanut oil, soya bean oil, tung oil, linseed oil, sardine oil, herring oil, sesame oil, olive oil, dehydrated castor oil, tallow oil, sunflower oil, cottonseed oil and mixtures thereof.

15. A coating composition according to claim 13 or claim 14 in which the natural oil is sunflower oil or soya bean oil.

16. A coating composition according to any one of the preceding claims in which said at least one dicarboxylic acid is selected from dicarboxylic acids having C₂ to C₂₀ carbon atoms, more preferably C₄ to Ci₂ carbon atoms.

17. A coating composition according to claim 16 in which said at least one dicarboxylic acid is selected from straight chain aliphatic dicarboxylic acids having C₄ to Ci₂ carbon atoms, more especially C₅ to C₈ carbon atoms, or aromatic acids having C₈ carbon atoms.

18. A coating composition according to claim 16 or claim 17 in which said at least one dicarboxylic acid is adipic acid or phthalic acid.

19. A coating composition according to any one of the preceding claims in which, in the reactive diluent, the molar ratio of polyol : dicarboxylic acid : polyunsaturated fatty acid used in the reaction is preferably in the range 1 : 0.5 to 0.75 ; 1.5 to 2, more preferably is in the range 1 : 0.5 to 0.7 : 1.6 to 2, more particularly is in the range 1 : 0.5 to 0.7 : 1.7 to 2, and more especially is in the range 1 : 0.5 to 0.67 : 1.7 to 1.9.

20. A coating composition according to any one of the preceding claims in which the reactive diluent is obtainable by reacting glycerol, a saturated C₅ to C₈ dicarboxylic acid, more especially adipic acid and/or phthalic acid or anhydride, and linoleic acid.

21. A coating composition according to any one of the preceding claims in which the reactive diluent has a free OH group hydroxy! value of not more than 25 mgKOH/g, more preferably not more than 20 mgKOH/g and more especially not more than 15 mgKOH/g.

22. A coating composition according to claim 20 in which the reactive diluent has a free OH group hydroxyl value of around 10 mgKOH/g or less.

23. A coating composition according to any one of the preceding claims in which the reactive diluent has a weight average molecular weight in the range 1000 to 4200, more particularly in the range 1000 to 4000, even more particularly in the range 1500 to 4000 and especially in the range 2000 to 4000.

24. A coating composition according to any one of the preceding claims in which the reactive diluent has a viscosity of less than 0.25 Pa.s at 25°C.

25. A coating composition according to any one of claims 1 to 23 in which the reactive diluent has a viscosity of less than 0.2 Pa.s at 25°C.

26. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester compound obtainable by the reaction of at least one polyol with at least one dicarboxylic acid or alkyl ester or anhydride thereof and at least one polyunsaturated fatty acid or alkyl ester thereof, said reactive diluent having a viscosity of less than 0.5 Pa s at 25°C.

27. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to claim 26 in which said at least one polyol is selected from C₃ to C₁₀ polyols having a minimum of three hydroxyl groups.

28. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid ester according to claim 27 in which said at least one polyol is selected from aliphatic C₃ to C₈ polyols and more especially from aliphatic C₃ to C₆ polyols.

29. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid ester according to claim 27 or claims 28 in which said at least one polyol has at least two primary hydroxyl groups and, optionally, at least one secondary hydroxyl group.

30. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 29 in which said at least one polyol is selected from alditols.

31. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to claim 30 in which said at least one polyol is glycerol or diglycerol or mixtures of glycerol and diglycerol.

32. A coating composition according to claim 30 or claim 31 in which said at least one polyol is glycerol.

33. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 32 in which said at least one polyunsaturated fatty acid is a semi-drying or drying polyunsaturated fatty acid,, or mixtures of such acids, that is ethylenically unsaturated, whether conjugated or non-conjugated.

34. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 33 in which said at least one polyunsaturated fatty acid is selected from Ci₈ to C₂₂ polyunsaturated fatty acids.

35. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 34 in which said at least one polyunsaturated fatty acid is selected from linoleic, linolenic, arachindonic, eicosatetraenoic, eicosapentaenoic and docasahexaenoic acids or mixtures thereof.

36. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 35 in which said at least one polyunsaturated fatty acid is selected from Ci₈ to C₂₀ polyunsaturated fatty acids or mixtures thereof.

37. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 36 in which said at least one polyunsaturated fatty acid is linoleic acid.

38. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 37 in which said at least one polyunsaturated fatty acid, or mixtures of such acids, is derived from natural or synthetic oils in which the acid or acids are a major component.

39. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to claim 38 in which the natural oil is selected from safflower, tall oil, calendula oil, corn oil, rapeseed oil, peanut oil, soya bean oil, tung oil, linseed oil, sardine oil, herring oil, sesame oil, olive oil, dehydrated castor oil, tallow oil, sunflower oil, cottonseed oil and mixtures thereof.

40. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to claim 38 or claim 39 in which the natural oil is sunflower oil or soya bean oil.

41. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 40 in which said at least one dicarboxylic acid is selected from dicarboxylic acids having C₂ to C₂₀ carbon atoms, more preferably C₄ to C₁₂ carbon atoms.

42. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to claim 41 in which said at least one dicarboxylic acid is selected from straight chain aliphatic dicarboxylic acids having C₄ to C₁₂ carbon atoms, more especially C₅ to Ce carbon atoms, or aromatic acids having C₈ carbon atoms.

43. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to claim 41 or claim 42 in which said at least one dicarboxylic acid is adipic acid or phthalic acid.

44. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 13 in which, in the polyester, the molar ratio of polyol : dicarboxylic acid : polyunsaturated fatty acid used in the reaction is preferably in the range 1 : 0.5 to 0.75 ; 1.5 to 2, more preferably is in the range 1 : 0.5 to 0.7 : 1.6 to 2, more particularly is in the range 1 : 0.5 to 0.7 : 1.7 to 2, and more especially is in the range 1 : 0.5 to 0.67 : 1.7 to 1.9.

45. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 44 in which said polyester is obtainable by reacting glycerol, a saturated C₅ to C₈ dicarboxylic acid, more especially adipic acid and/or phthalic acid or anhydride, and linoleic acid.

46. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 45 in which the reactive diluent has a free OH group hydroxyl value of not more than 25 mgKOH/g, more preferably not more than 20 mgKOH/g and more especially not more than 15 mgKOH/g.

47. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to claim 46 in which the reactive diluent has a free OH group hydroxyl value of around 10 mgKOH/g or less.

48. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 47 in which said ester has a weight average molecular weight in the range 1000 to 4200, more particularly in the range 1000 to 4000, even more particularly in the range 1500 to 4000 and especially in the range 2000 to 4000.

49. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 48 in which the reactive diluent has a viscosity of less than 0.25 Pa s at 25°C.

50. The use as a reactive diluent in a coating composition of a polyunsaturated fatty acid polyester according to any one of claims 26 to 48 in which the reactive diluent has a viscosity of less than 0.2 Pa.s at 25°C.

51. A polyunsaturated fatty acid polyester of a polyol which is obtainable by the reaction of at least one polyol with at least one dicarboxylic acid or alkyl ester or anhydride thereof and at least one polyunsaturated fatty acid or alkyl ester thereof, said polyester having a viscosity of less than 0.5 Pa s at 25⁰C.

52. A polyunsaturated fatty acid ester according to claim 51 in which said at least one polyol is selected from C₃ to Ci₀ polyols having a minimum of three hydroxyl groups.

53. A polyunsaturated fatty acid ester according to claim 52 in which said at least one polyol is selected from aliphatic C₃ to C₈ polyols and more especially from aliphatic C₃ to Ce polyols.

54. A polyunsaturated fatty acid ester according to claim 51 or claim 52 in which said at least one polyol has at least two primary hydroxyl groups and, optionally, at least one secondary hydroxyl group.

55. A polyunsaturated fatty acid ester according to any one of claims 51 to 54 in which said at least one polyol is selected from alditols.

56. A polyunsaturated fatty acid ester according to claims 55 in which said at least one polyol is glycerol or diglycerol or mixtures of glycerol and diglycerol.

57. A polyunsaturated fatty acid ester according to claim 55 or claim 56 in which said at least one polyol is glycerol.

58. A polyunsaturated fatty acid ester according to any one of claims 51 to 57 in which said at least one polyunsaturated fatty acid is a semi-drying or drying polyunsaturated fatty acid, or mixtures of such acids, that is ethylenically unsaturated, whether conjugated or non-conjugated.

59. A polyunsaturated fatty acid ester according to any one of claims 51 to 58 in which said at least one polyunsaturated fatty acid is selected from Ci₈ to C₂₂ polyunsaturated fatty acids.

60. A polyunsaturated fatty acid ester according to any one of claims 51 to 59 in which said at least one polyunsaturated fatty acid is selected from linoleic, linolenic, arachindonic, eicosatetraenoic, eicosapentaenoic and docasa- hexaenoic acids or mixtures thereof.

61. A polyunsaturated fatty acid ester according to any one of claims 51 to 60 in which said at least one polyunsaturated fatty acid is selected from C₁₈ to C₂₀ polyunsaturated fatty acids or mixtures thereof.

62. A polyunsaturated fatty acid ester according to any one of claims 51 to 61 in which said at least one polyunsaturated fatty acid is linoleic acid.

63. A polyunsaturated fatty acid ester according to any one of claims 51 to 62 in which said at least one polyunsaturated fatty acid, or mixtures of such acids, is derived from natural or synthetic oils in which the acid or acids are a major component.

64. A polyunsaturated fatty acid ester according to claim 63 in which the natural oil is selected from safflower, tall oil, calendula oil, corn oil, rapeseed oil, peanut oil, soya bean oil, tung oil, linseed oil, sardine oil, herring oil, sesame oil, olive oil, dehydrated castor oil, tallow oil, sunflower oil, cottonseed oil and mixtures thereof.

65. A polyunsaturated fatty acid ester according to claim 63 or claim 64 in which the natural oil is sunflower oil or soya bean oil.

66. A polyunsaturated fatty acid ester according to any one of claims 51 to 65 in which said at least one dicarboxylic acid is selected from dicarboxylic acids having C₂ to C₂₀ carbon atoms, more preferably C₄ to C₁₂ carbon atoms.

67. A polyunsaturated fatty acid ester according to claim 66 in which said at least one dicarboxylic acid is selected from straight chain aliphatic dicarboxylic acids having C₄ to C₁₂ carbon atoms, more especially C₅ to Ce carbon atoms, or aromatic acids having C₈ carbon atoms.

68. A polyunsaturated fatty acid ester according to claim 66 or claim 67 in which said at least one dicarboxylic acid is adipic acid or phthalic acid.

69. A polyunsaturated fatty acid polyester according to any one of claims 51 to 68 in which, in the polyester, the molar ratio of polyol : dicarboxylic acid : polyunsaturated fatty acid used in the reaction is preferably in the range 1 : 0.5 to 0.75 ; 1.5 to 2, more preferably is in the range 1 : 0.5 to 0.7 : 1.6 to 2, more particularly is in the range 1 : 0.5 to 0.7 : 1.7 to 2, and more especially is in the range 1 : 0.5 to 0.67 : 1.7 to 1.9.

70. A polyunsaturated fatty acid polyester according to any one of claims 51 to 69 in which said polyester is obtainable by reacting glycerol, a saturated C₅ to C₈ dicarboxylic acid, more especially adipic acid and/or phthalic acid or anhydride, and linoleic acid.

71. A polyunsaturated fatty acid polyester according to any one of claims 51 to 70 in which the reactive diluent has a free OH group hydroxyl value of not more than 25 mgKOH/g, more preferably not more than 20 mgKOH/g and more especially not more than 15 mgKOH/g.

72. A polyunsaturated fatty acid polyester according to claim 71 in which the reactive diluent has a free OH group hydroxyl value of around 10 mgKOH/g or less.

73. A polyunsaturated fatty acid ester according to any one of claim 51 to 72 in which said ester has a weight average molecular weight in the range 1000 to 4200, more particularly in the range 1000 to 4000, even more particularly in the range 1500 to 4000 and especially in the range 2000 to 4000.

74. A polyunsaturated fatty acid polyester according to any one of claims 51 to 73 in which the reactive diluent has a viscosity of less than 0.25 Pa.s at 25°C. A polyunsaturated fatty acid polyester according to any one of claims 51 to 73 in which the reactive diluent has a viscosity of less than less than 0.2 Pa.s at 25°C.