GB2117382A - Epoxy resin derivatives, their production, and their use in the production of surface coatings - Google Patents

Abstract

By blocking the epoxy groups in an epoxy resin and grafting side chains, for example lactone chains, onto the resin by reaction with resin secondary hydroxyl groups, which may be generated by the choice of a suitable blocking compound such as an organic secondary amine or an organic carboxylic acid, epoxy resin derivatives which crosslink readily are produced. The derivatives formed by using amines to block the epoxy groups with subsequent conversion to the salt form may be suitable for use in water-based cationic surface coating compositions. The derivatives formed by using organic acids to block the epoxy groups may be suitable for use in organic-based surface coatings or, if a semi-ester is formed by reaction between the side chains and a dicarboxylic acid anhydride with subsequent conversion to the salt by reaction with, for example, a secondary amine the derivatives maybe suitable for use in water-based anionic surface coating compositions.

Description

SPECIFICATION Epoxy resin derivatives their production and their use in the production of surface coatings This invention relates to the production and use in surface coatings of novel epoxy resin derivatives. Epoxy resins are understood to be chain materials based on the use of an epoxide, which may be a mono, di or poly-epoxide, although in the final resins the epoxy groups may, or may not, have been destroyed by reaction with other materials. Epoxy resins usually, although not invariably, contain a plurality of secondary hydroxyl groups.

Epoxy resins are commonly used in surface coating compositions. In some such compositions an epoxy resin may be compounded, together with a cross-linking resin, in an organic liquid diluent for application as metal primers, equipment coatings, appliance finishes, can, drum, tank and wire coatings, stoved finishes and the like. In other compositions an epoxy resin may be converted to a cationic water dispersible form. The resulting cationic resin may be applied to substrates, such as for example suitably charged motor car bodies, by electrodeposition from an aqueous dispersion as described in US Patent No. 4,104,147.

To improve the characteristics of the surface coatings obtained using epoxy resins it has been the practice, as exemplified in US Patent No. 4104147 and European Patent Application No 2075021, to "flexibilise" the resins by chain extending them by causing reaction between the epoxy groups of the epoxy resin and terminal hydroxyl groups on a polyester chain, thereby linking together epoxy resin chains by means of a polyester chain. The effect of chain extension is to produce coatings of greater flexibility, and therefore more resistant to bending, whether intended as part of a manufacturing process or accidentally.

To provide suitable surface coatings it is the practice to cross-link epoxy resins which may be achieved primarily by reaction between the secondary hydroxyl groups on the epoxy resin and reactive groups on the cross-linking resin.

According to the broadest aspect of the invention a new range of epoxy resin derivatives has been produced which have been "flexibilised", not by the above described chain extension technique but by grafting one or more primary hydroxyl containing side chains, for example polyester side chains, onto secondary hydroxyl groups on epoxy resins which contain such groups either as a result of their manufacture or as a result of the subsequent reaction of the epoxy resins so as to generate such groups. It has been found that the resulting epoxy resin derivatives may be cross-linked particularly efficiently by a cross-linking reaction involving these primary hydroxyl groups. The side chains bearing the primarily hydroxyl groups are preferably polymeric.

The present invention is preferably put into effect by grafting lactone onto the epoxy resin by a ring opening reaction between the lactone and the epoxy resin secondary hydroxyl groups thereby grafting lactone or polylactone chains onto the epoxy resin.

The epoxy resin used in accordance with the present invention may be a polyglycidyl ether, particularly preferably a diglycidyl ether. Such ethers may be produced by the reaction under alkaline conditions and usually at a temperature of from about 750C to 1 750C between an epihalohydrin, preferably epichlorohydrin, and a polyol, preferably a diol. Suitably the polyol is a polyphenol such as, for example, resorcinol, pyrocatechol, hydroquinone,1,4-dihydroxy naphthalene, bis-(4-hydroxyphenyl) tolyl methane, 4,4' dihydroxy diphenyl, bis-(4-hydroxy phenyl) sulphone or, particularly preferably, 4,4' dihydroxy diphenyl dimethylmethane (Bisphenol "A").Another group of epoxy resins suitable for use according to the present invention are the cycloaliphatic epoxides such as for example 3,4epoxycyclohexylmethyl-3,4-epoxy cyclohexane carboxylate, vinyl cyclohexene dioxide or bis-(3,4epoxycyclohexyl)adipate. Alternatively the cycloaliphatic epoxide may be based on cyclopentadiene or derivatives thereof.

A further group of epoxy resins which are, particularly, suitable for use according to the present invention are the epoxidised polydienes. We mean, by polydienes, polymers corresponding to monomeric dienes. Preferably the diene has a main chain of 4 to 8 carbon atoms for example, particularly preferably, butadiene or isoprene or substituted derivatives thereof such as 2-methyl 1,4 butadiene. Preferably each substituent group is an aikyl group and contains not more than 5 carbon atoms. Alternatively the polydiene may be a copolymer with an unsaturated monomer such as styrene, vinyl toluene, alpha-methyl styrene, acrylonitrile, or acrylic or methacrylic ester's. Preferably the polydiene or copolymer thereof has a weight mean average molecular weight of from 500 to 5000.

Polydiene epoxides may be obtained commercially or may be produced by techniques known in the art by the action of a peracid on the polydiene in a suitable solvent system.

Yet a further group of epoxy resins particularly suitable for use according to the present invention are the unsaturated natural oil epoxides for example epoxides of soya oil.

The "epoxy equivalent" of a polymer, that is the weight in g of the polymer containing an equivalent of epoxide functionality, is an indication of chain length the lower the epoxy equivalent the shorter the chain length. The epoxy resin used according to the present invention may preferably have an epoxy equivalent within the broad range of from about 1 60 to 9000 preferably within the range of from 450 to 4000.

In the shortest chain polyglycidyl ether polyepoxides or in the cycloaliphatic or polydiene polyepoxides or in the natural oil polyepoxides there may be few, if any, secondary hydroxyl groups although such groups may be formed for the purposes of the present invention as hereafter described.

In order to graft lactone onto the epoxy resin it has been envisaged above that, preferably, polymerisation of the lactone monomer may be initiated by reaction with the secondary hydroxyl groups. Certain epoxides, for example the polyglycidyl ethers, contain very reactive epoxy groups and, to direct the polymerisation initiation to the secondary hydroxyl groups, it is necessary to first block the epoxy groups by reaction with a suitable reagent. Any material which reacts with epoxy groups but does not interfere with lactone polymerisation reactions is suitable for use as a reagent to block the epoxy groups. If the epoxide is of a type containing relatively less reactive epoxy groups, for example a polydiene epoxide, it may not be necessary to block these groups to achieve the desired reaction between the secondary hydroxyl groups and the lactone.However it may be necessary to react the epoxy with a blocking compound to generate the secondary hydroxyl groups in the first place to generate a functional group capable of reaction to give cationicity to the epoxy resin to render it useable for electrodeposition. Both of these features are described hereafter and apply, particularly to polybutadiene epoxides.

Reagents which may be used to block the epoxy groups are water or monoalcohols such as for example, pentanol or other chain alcohols having a suitable boiling point to allow their use. Where the epoxy resin has few or no secondary hydroxyl groups it is preferred to use a blocking compound which will generate such groups, such as for example, organic secondary amines or organic carboxylic acids.

Preferably the organic secondary amine, where used, is a monoamine, particularly preferably one containing not more than 10 carbon atoms such as dimethylamine, diethylamine or dipropylamine.

Preferably the organic carboxylic acids, where used, are monocarboxylic acids. Organic acid blocking agents are particularly suitable where organic diluent compoundable epoxy resins are desired. Suitable organic carboxylic acids are aliphatic straight chain acids such as acetic acid, propionic acid or higher homologous acids up to, for example 10 carbon atoms in chain length, or aliphatic branched chain carboxylic acids, such as the Versatic (Trade Mark) acids produced by Shell Chemical Co., up to for example, 1 5 or more carbon atoms in total chain length. The reaction to block the epoxy groups may be conducted by mixing the epoxy resin and the blocking compound, preferably together with a proportion of processing aid such as a suitable organic diluent, for example xylene, and heating to encourage reaction to, for example, 800C to 1 500C.

The lactones reacted with the epoxy resin secondary hydroxyl groups according to the invention are preferably those having the formula

wherein R may be hydrogen or an organic substituent and x is a number from 5 to 10. Preferably in at least the majority of occurrences, R is hydrogen. Preferably, the total number of carbon atoms in all the occurrences of R within each lactone monomer is not more than 12 and R has no more than 6 carbon atoms in any occurrence. Particularly preferably, the lactone is unsubstituted epsilon caprolactone (hereafter called caprolactone) which corresponds to the above general formula where every occurrence of R is hydrogen and x has the value 5.

The ring opening of the lactone, may be accomplished at temperatures of from about 200C to 2000C preferably in the presence of a catalyst. Preferably the ring opening is conducted at a temperature of from 1 200C to 2000C and, particularly preferably, at from 1 250C to 1 850C. When using the last mentioned range of temperatures the catalyst may, suitably, be an alkyl tin or an alkyl titanium compound, for example stannous octoate or dibutyl tin dithiooctyl glycolate. Alternatively, when somewhat lower polymerisation temperatures are used, the catalyst may suitably be a Lewis acid for example, boron trifluoride, or a suitable organic acid.The quantity of catalyst is preferably from 0.00019/0 to 1.0% particularly preferably from 0.005% to 0.2% by weight of the lactone.

The present invention results in novel epoxy resin derivatives having primary hydroxyl-containing side chains having the general formulaOA wherein A in at least some of the occurrences is an entity containing one or more units each having the general formula ACO(CR2)xp' H wherein R, and x have the values hereinbefore ascribed to them and n' is the number of units in the side chain, for example from 1 to 10 and, in the remainder of its occurrences, is a hydrogen atom.

Preferably the side chains A are present on the epoxy resin in from 5% to 80%, particularly preferably from 10% to 60% based on their combined weights. Where the epoxy groups have been blocked the novel expoy resin derivatives also contain chain terminating groups B representing the residues of the blocking reagent and having the formula

when the blocking reagent is an organic acid

when the blocking reagent is a secondary amine -OA or -OH when the blocking reagent is water, since some or all of the primary hydroxyl groups initially formed may provide a site for the attachment of a side chain -OR when the blocking reagent is a primary alcohol where R is an organic radical preferably having from 2 to 20 carbon atoms.

The particular character of the epoxy resin derivatives produced according to this invention is due at least in part to the presence of a number of side chains anchored at one end on the epoxy resin chain.

The cross-linking agent used in accordance with the present invention may be selected as known in the art, and depending on the type of surface coating required from, for example, blocked isocyanates, isocyanates where a room temperature cure is required, amino resins or aldehyde condensation products. Some epoxy resins for example polydiene epoxides, may be self cross-linkable.

Nevertheless, we believe the use of the cross-linking system of the present invention to be advantageous even when using such epoxides.

Where the cross-linking agent is a blocked isocyanate it may be, for example, blocked aromatic or aliphatic di- or tri- isocyanate such as a blocked toluene di-isocyanate or a blocked hexamethylene diisocyanate. The blocking agent in contrast to those used to block the epoxy groups is, preferably, selected for its ability to unblock at the curing temperature to be used. Where the curing temperature is to be, for example, above 1 700C the blocking agent may, suitably be diphenyl amine, phenol, isooctyl phenol, p-phenyl phenol (hydroxy biphenyl) or pyrrolidone. The composition of suitable blocked isocyanate cross-linking agents is fully dealt with in "The development and use of polyurethane products" byE. N. Doyle, published by McGraw Hill 1971.

Alternatively, where the cross-linking agent is an aldehyde condensation product, it may be, for example, a phenol/formaldehyde resin, a urea/formaldehyde resin, a melamine/formaldehyde resin, a benzoguanamine/formaldehyde resin or an etherified methylol melamine. A urea/formaldehyde crosslinking agent is suitable for primer coatings. A melamine/formaldehyde cross-linking agent is suitable for stoved finishes although a urea/formaldehyde cross-linking agent may be used as an alternative.

Phenol/formaldehyde cross-linking agents are suitable for industrial applications such as can coatings.

Benzoguanamine-formaldehyde or melamine-formaldehyde cross-linking agents are suitable for appliance finishes.

The cross-linking agent is preferably present in coating compositions containing epoxy resin derivatives according to the invention in from 5% to 40%, particularly preferably from 10% to 35% by weight of the resin components thereof that is, of the epoxy resin derivative and the cross-linking agent itself. A cross-linking catalyst may be present in the compositions according to the invention in, preferably, from 0.1% to 5%, particularly preferably, from 1 O/o to 3% by weight of the resin components thereof, and may be an acid such as, for example, hydrochloric acid, sulphuric acid, para-toluene sulphonic acid, salts of para-toluene sulphonic acid, such as the dimethyl ethanolamine salt, sulphonic acid, dodecylbenzene sulphonic acid, phosphoric acid, maleic acid, succinic acid or phthalic acid.

However, since the cross-linking reaction proceeds readily when the epoxy resin derivatives according to the present invention are used a cross-linking catalyst may not be essential in every instance.

The epoxy resin derivatives of the present invention may be compounded with the desired crosslinking agents and with an organic diluent such as for example a mixture of xylene and 2-ethoxyethyl acetate for application directly to a surface and curing thereon either at room temperature if the crosslinking agent is suitable, or by heating to, for example, from 1 500C to 2500C.

Alternatively, the epoxy resin derivatives produced using secondary amines to block the epoxy groups may be made suitable for inclusion in cationic water-based coating compositions in the manner known in the art by converting the resulting epoxy resin terminal tertiary amine groups to the salt form by treatment with a water dispersible organic acid, such as acetic acid or formic acid, or inorganic acid such as phosphoric acid, in an aqueous medium.

Additionally however, the epoxy resin derivatives of the present invention when produced using an organic acid blocking agent, may be made suitable for inclusion in anionic water-based coating compositions. This may be achieved by reacting a proportion of the primary hydroxyl groups on the grafted on side chains with an acid anhydride to form a partial ester of the corresponding acid and reacting the free carboxyl groups of the partial ester with an amine to give an amine salt of which the epoxy resin portion is anionic. The acid anhydride may be based on any suitable anionic acid, preferably containing no more than 12 carbon atoms and is suitably phthalic anhydride. Preferably not more than 50% of the terminal primary hydroxyl groups are reacted with the anhydride the remainder being reserved for the cross-linking reaction.

To form suitable surface coatings the epoxy resin derivatives according to the invention subject to any overriding requirements such as, for example, the need for a clear coating or to produce a water dispersed rather than an organic-dispersed coating, may, besides crosslinking agents contain other organic or inorganic ingredients commonly used in the art such as, for example, fillers, extenders or pigments.

Suitable fillers may be, for example, mica, asbestos fines, silica, magnesium carbonate, ground chalk, asphalt, bitumen, cellulose, or glass fibres. Suitable pigments may be for example, inorganic pigment, such as titanium dioxide or lead carbonate or organic pigments, such as a diarylamine yellow or phthalocyanine blue. Other additives such as, for example, corrosion inhibitors such as zinc chromate or zinc phosphate may also be included.

The invention will now be illustrated by means of the following examples.

Examples 1,3, 5 and 6 are according to the invention and involve the preparation of novel epoxy resin derivatives, the inclusion of the derivatives in surface coating compositions and the testing of coatings made using the surface coating compositions for flexibility by the Reverse Impact and T-Bend tests described hereafter and/or for solvent resistance after a given cure time and hardness. Examples 2 and 4 are not according to the invention and involve in Example 2 (comparative with Example 1) the preparation and testing of an epoxy resin surface coating not containing any lactone flexibiliser and, in Example 4, (comparative with Example 3) the preparation and testing of an epoxy resin surface coating in which the epoxy resin has been flexibilised by chain extension by reaction between epoxy groups and terminal hydroxyl groups of a prepolymerised polylactone diol.

The surface coating composition prepared according to each of the examples was applied to a Bonderized (Trade Mark) 0.9 mm aluminium panel or a steel panel as indicated, to a dried coating thickness of 12 microns, unless otherwise stated, using a wire-wound bar coater. The coated panels were heated at 1 950C and for the time indicated hereafter, uniess otherwise stated, were allowed to stand at room temperature for 24 hours and were subject to tests for film hardness (by attempting to scratch the film with Staedtler pencil leads of increasing hardness until the hardest lead which did not penetrate the film was determined) reverse impact resistance (by using a Sheen Tester to allow a 4 Ib (1.8 kg) weight to fall onto the back of the panel the force, expressed in kg cm units, required to cause flaking of the coating being noted) solvent resistance (by rubbing with a methyl ethyl ketone-soaked cloth for a given number of double rubs), and flexibility (by the 1 800 T bend test recognised by the European Coil Coaters Association-the lower the value given the greater the flexibility). The results of the tests are set out in the tables included with the examples.

Example 1 554.7 parts by weight of a bisphenol A/epichlorohydrin polyether epoxy resin (Epikote 1004 from the Shell Company), having an epoxy equivalent weight of 895.7 and 50 parts by weight of xylene were heated to 600C in a stirred reaction vessel fitted with a nitrogen purge, heat control means and a reflux condenser. To block the epoxy groups 45.3 parts by weight of diethylene amine was added and the temperature of the reaction mixture was raised to 800C over 45 minutes and then quickly to 1000C and was maintained for one hour at that level. The xylene was then removed using a Dean a Stark condenser under vacuum.

The resulting tertiary amine-terminated polyether resin was cooled to 80"C and 1 50 parts by weight of caprolactone and 0.015 parts by weight of stannous octoate were added. The temperature was then raised to 1 550C and maintained for 6 hours at that level after which a further 0.1 5 parts by weight of stannous octoate was added. After a further 4 hours at 1 500C the free caprolactone level, determined by gas chromatography, was less than 0.1% the caprolactone having grafted onto the polyether resin by reaction with the resin secondary hydroxyl groups. The resulting caprolactonemodified tertiary amine-terminated polyether was cooled to 800C and thinned with 125 parts by weight xylene and 125 parts by weight methyl isobutyl ketone.

To produce an aqueous surface coating composition containing the caprolactone-modified polyether resin in cationic form 1 00 parts by weight of the caprolactone-modified polyether resin was blended with 33.3 parts by weight of a solution of a blocked isophoronediisocyanate adduct (B1065 from the Huls Company containing 25% by weight of a xylene/methyl isobutyl ketone 1:1 mixture. 37.2 gms of a 10% aqueous acetic acid solution was then added and the mixture was dispersed in 79.5 parts by weight of deionised water using a high speed mixer. 0.1 gms of flow additive (FC 1 35 from 3 M's Company) was then added.

Example 2 554.7 parts by weight of the same epoxy resin as used in Example 1 and 50 parts by weight of xylene were heated to 600C in a stirred reaction vessel fitted with a nitrogen purge, heat control means and a reflux condenser. 45.3 parts by weight of diethylene amine were added and the temperature of the reaction mixture was raised to 800C over 45 minutes. The temperature was raised quickly to 1 OO"C and maintained for one hour. The resulting tertiary amine-terminated polyether resin was cooled to 800C and thinned with 50 parts by weight xylene and 100 parts by weight of methyl isobutyl ketone.

1 00 parts by weight of the polyether resin was blended with 33.3 parts by weight of the same blocked isocyanate solution as used in Example 1, 46.5 gms of a 10% aqueous acetic acid solution was then added and the mixture was dispersed in 70.2 parts by weight of deionised water using a high speed mixer. 0.1 gms of the same flow additive was added.

The resulting aqueous dispersion contained the amine-terminated resin in cationic form.

Table 1 Solvent resistance vs. cure time for the cationic coatings of Examples 1 b 2 Cure time (minutes) 10 20 30 Number of MEK double rubs 10 47 70 Example 1-(lactone graft) Number of MEK double rubs 0 11 1 5 Example 2-(no lactone present) Table 2 Physical properties of coatings in Examples 1 a 2 (30 mins cure) Cationic coating containing Cationic coating without caprolactone caprolactone Property (Example 1) (Example 2) Pencil hardness 3H 3H Reverse impact 190 143 Flexibility (1800T bend 1.5 3 test-number of bends) Example 3 1791.4 parts by weight of the same epoxy resin as used in Example 1 together with 350 parts by weight of Versatic Acid 10 and 70 parts by weight of xylene were heated to 1 400C in a stirred reaction vessel fitted with heat control means, a nitrogen purge and a reflux condenser. This temperature was maintained for 2 hours and the xylene was then removed using a Dean 8 Stark condenser under vacuum.

The resulting ester-terminated polyether was cooled to 1000C and 455.3 parts by weight of caprolactone and 0.05 parts by weight of stannous octoate were added. The temperature was then raised to 1 550C and maintained at that level for 6 hours after which time 0.05 parts by weight of stannous octoate was added. After a further 4 hours reaction time at 1 550C, the free caprolactone level, determined by gas chromatography, was below 0.10/0 the remainder of the caprolactone being grafted onto the polyether. The resulting caprolactone-modified ester-terminated polyether resin was cooled to 1000C and then was thinned with 865.6 parts of xylene and 865.6 parts of 2-ethoxy ethyl acetate.

To form an organic-based surface coating composition 100 parts by weight of the thinned caprolactone-modified polyether resin was blended with 33.3 parts by weight of a blocked isophoronediisocyanate adduct (B1065 from Huls Company) containing 40% by weight of a xylene:2 ethoxy ethyl acetate 1:1 mixture.

Example 4 2008 parts by weight of a bisphenol A/epichlorohydrin polyether epoxy resin (Epikote 1001 from Shell Company) having an epoxy equivalent weight of 502 together with 536.4 gms of a 536.4 molecular weight polycaprolactone diol (Capa 200 (Trade Mark) from Laporte Industries Limited) and 2.54 parts by weight of benzyl dimethyl amine were heated to 1 400C in a stirred reaction vessel fitted with heat control means a nitrogen purge and a reflux condenser. This temperature was maintained for 2.5 hours and the resulting chain-extended polyether resin was then cooled to 800C and thinned with 848 parts by weight of xylene and 848 parts by weight of 2-ethoxy ethyl acetate. In order to achieve the same tin content as the resin in Example 3, 0.10 parts by weight of Stannous octoate was added.

To form an organic-based surface coating composition 100 parts by weight of the polycaprolactone-chain-extended polyether epoxy resin still containing its secondary hydroxyl groups was blended with 33.3 parts by weight of a solution of the same blocked isocyanate as used in Example 3.

Table 3 Solvent resistance vs. cure time for coating Examples 3 & 4 Cure time 10 20 30 MEK double rubs (Example 3-(lactone graft)) 9 60 > 100 MEK double rubs Example 4-(polylactone 0 3 6 chain extension) Table 4 Physical properties of coatings in Examples 3 Et 4 Coating containing Coating containing grafted caprolactone Capa 200 Property (Example 3) (Example 4) Pencil hardness 3H 3H Reverse impact > 190 95 Flexibility 1800 T bends 1.5 3 Example 5 880.3 parts by weight of a bisphenol A/epichlorohydrin polyether epoxy resin (Epikote 1007 from Shell Company having an epoxy equivalent weight of 1933), 79.7 parts by weight of Versatic Acid 10 and 50 parts by weight of xylene were heated to 1 400C in a stirred reaction vessel fitted with heat control means, a nitrogen purge and a reflux condenser. This temperature was maintained for 2 hours and the xylene was then removed using a Dean a Stark condenser under vacuum. The resulting esterterminated polyether was cooled to 1000C and 640.0 parts by weight of caprolactone and 0.032 parts by weight of Stannous octoate were added. The temperature was then raised to 1 550C and maintained at that level for 6 hours, whereupon a further 0.032 parts by weight stannous octoate was added.After a further 4 hours reaction time at the same temperature the free caprolactone level, determined by GLC, was below 0.1%. The resulting caprolactone-modified ester-terminated polyether resin was cooled to 750C and 193.6 parts by weight of phthalic anhydride was added. The mixture exothermed to 1050C indicating reaction between the phthalic anhydride and the primary hydroxyl groups terminating the grafted-on caprolactone chains and this temperature was maintained for 2 hours. The resulting carboxyl-containing caprolactone-modified polyether resin was cooled to 800C and thinned with 448.4 parts by weight of 2-butoxy ethanol.

100.0 parts by weight of the carboxyl-containing resin was blended with 5.1 parts by weight of 2-dimethyl ethanolamine, 20 parts by weight hexamethoxy methyl melamine, 10 parts by weight of 2butoxy ethanol and 87.1 parts by weight of deionised water. 0.4 parts by weight of a solution made from 25 parts by weight of para-toluene sulphonic acid, 11.6 parts by weight of 2-dimethyl ethanolamine and 63.4 parts by weight of n-butanol was added.

The water-based coating composition so made, containing the caproiactone-modified polyether resin in anionic form was applied by bar coater to give a 20 micron film on the same aluminium panels.

The panels were stoved for 30 minutes at 1 6000 and the following properties were obtained: Table 5 Pencil hardness 3H MEK double rubs 100 Reverse impact 167 Flexibility (1800 T bend) 1.5 From the above results it can be seen that by modifying a Bisphenol A polyether with caprolactone according to the invention the curing rate measured by solvent resistance may be greatly improved. This is evidence that secondary hydroxyl groups in the polyether resin are converted into primary hydroxyl groups facilitating more rapid reaction with isocyanates. Furthermore, flexibility and impact resistance may be greatly improved whilst maintaining good hardness.

Example 6 339 parts by weight of an epoxidised polybutadiene resin having an oxirane content of 4.72% and a weight mean average molecular weight of 1 500 available from Chemische Werke Huls under the trade name Poiyoil 110 together with 65.3 parts by weight morpholine and 0.4 parts by weight hydroquinone were heated to 1750C in a stirred reaction vessel fitted with reflux condenser and heat control means. This reaction temperature was maintained for 6 hours before raising it to 1 800C. After a further 2 hours the unreacted morpholine present was distilled off under vacuum at 1 800C. The resulting tertiary amine functional resin had an amine nitrogen content of 1.5% by weight.

100 parts by weight of this resin, 25 parts by weight epsilon-caprolactone and 0.025 parts by weight of stannous octoate were heated to 1 550C in a stirred reaction vessel fitted with heat control means and dry nitrogen purge. This temperature was maintained for 10 hours when a caprolactone level determined by gas chromatography was found to be below 0.1% by weight.

A water based coating was prepared by blending 50 g of the resulting caprolactone modified polybutadiene derivative with glacial acetic acid, butoxy ethanol cosolvent, a blocked isocyanate available under the tradename Desmodur KL52544 and a flow additive available from 3M Company under the Trade Name FC430. These were dispersed in deionised water using a high speed mixer. The flow agent was added to the dispersion and thoroughly mixed in. The following quantities in grams were used.

2n butoxy ethanol 10.00 Glacial acetic acid 2.57 Desmodur KL52544 19.30 Deionized water 79.31 FC430 0.06 Coatings were applied to 0.9 mm steel panels and stoved at 1 800C to give 1 5 micron thick dry films. The coating properties obtained after 1 5, 20 and 30 minutes curing at 1 800C are given below.

Solvent resistance Duration mins MEK double rubs Pencil hardness 15 28 HB 20 150 H 30 greater than 300 4H These properties compare favourably with those of coatings based on epsilon caprolactonemodified polyglycidyl ethers and with coatings based on the same epoxidised morpholine adduct which had not been modified with epsilon caprolactone. In particular, the 1 5 minute tests show an improved cure rate in comparison with a similar coating in which the unmodified epoxy resin-morpholine adduct had been used.

Claims (14)

Claims

1. A process for the production of a chain extended epoxy resin derivative characterised by grafting onto secondary hydroxyl groups on the epoxy resin primary hydroxyl bearing side chains.

2. A process as claimed in claim 1 wherein the side chains are polyester side chains.

3. A process as claimed in claim 2 wherein the polyester side chains are polylactone side chains the polymerisation of which is initiated by a ring opening reaction between the lactone and the secondary hydroxyl groups.

4. A process as claimed in claim 3 wherein the lactone is selected from those having the formula

wherein R in the majority of occurrences in the formula is hydrogen the total number of carbon atoms in all occurrences of R in the formula being no more than 12 and in any one of the occurrences in the formula being no more than 6.

5. A process as claimed in claim 4 wherein the lactone is caprolactone, the value of x in the formula being 5 and every occurrence of R therein being hydrogen.

6. A process as claimed in any one of claims 3 to 5 wherein the epoxy resin is selected from polyglycidyl ethers, and cycloaliphatic epoxides.

7. A process as claimed in any one of claims 3 to 5 wherein the epoxy resin is selected from epoxidised polydienes and epoxidised unsaturated natural oils.

8. A process as claimed in any preceding claim wherein substantially all of the epoxy groups of the epoxy resin to be chain extended have first been blocked by reaction with a suitable reagent before the secondary hydroxyl groups have been allowed to react with the lactone.

9. A process as claimed in claim 8 wherein the reagent is selected from secondary amines, carboxylic acids, primary alcohols and water.

1 0. A composition comprising a chain extended epoxy resin derivative bearing primary hydroxyl containing side chains the said chains borne on the resin being grafted onto secondary hydroxyl sites thereon.

11. A composition as claimed in claim 10 also containing a cross linking agent and an organic diluent.

12. A composition as claimed in claim 10 in the form of a cationic water based coating composition wherein the epoxy resin epoxy groups have first been blocked by reaction with a secondary amine and the resulting tertiary amine containing chain-extended epoxy resin has then been converted to cationic form by reaction with a water dispersible acid.

1 3. A composition as claimed in claim 10 in the form of an anionic water based coating composition wherein the epoxy resin epoxy groups heave first been blocked by reaction with a carboxylic acid and wherein the chain extended epoxy resin has then been converted to anionic form by reaction with an acid anhydride to form a partial ester the partial ester being reacted with an amine to give an amine salt of which the epoxy resin portion is anionic.

14. A composition as claimed in claim 10 and substantially as described herein.

1 5. A process as claimed in claim 1 and substantially as described herein.