GB2160534A - Cross-linkable polymeric coating compositions - Google Patents

Abstract

A polymer composition comprises (1) an olefinic polymer having hydroxyl- or carboxyl-reactive groups, for example an epoxy group, an alkylolated amide group, or an isocyanate group which may be blocked if required, and (2) a flexibilising cross-linking agent comprising a lactone polyester chain compound, for example polycaprolactone, bearing at least two carboxyl or hydroxyl groups. The composition may be cross-linked to give flexible tough coatings.

Description

SPECIFICATION Polyolefins This invention relates to olefinic polymers and surface-coatings made therefrom.

The olefinic polymers contemplated herein particularly include vinyl, vinylidene, styrene, allyl and acrylic polymers. For the avoidance of doubt the term "olefinic" is used herein in relation to polymers to denote their derivation by the addition polymerisation of olefinic monomers, not to denote any residual olefinic functionality in the polymer itself.

Olefinic polymers may be cross-linked, for example, to increase the toughness of surface-coatings made from them. This may be accomplished by including in the polymer a monomer or copolymer containing one or more active hydrogen-containing groups, such as hydroxyl or amine, which group or groups remain in the polymer backbone and may be reacted with cross-linking agents. Depending on whether a one component or a two component composition is required the cross-linking agent may be selected accordingly. For example, one component heat-cured surface coating compositions may include amino formaldehyde or phenol formaldehyde resins as cross-linking agents and two component low temperature cured surface coating compositions may include polyisocyanates as cross-linking agents.

The production of satisfactory compositions based on cross-linked polyolefins has been beset by difficulty. Polyfunctional cross-linking agents are commonly used to impart the necessary toughness required, for example, in surface coatings. Conventional polyfunctional cross-linking agents have disadvantages. Particularly, amino formaldehyde or phenol formaldehyde cross-linking agents tend to self-condense during the coating or curing processes leading to coating embrittlement. It is particularly difficult to build-in flexibility by resin modification of these cross-linking agents. Isocyanate cross-linking agents also have drawbacks since free isocyanate groups are likely to be unstable to moisture.

The present invention provides a process for the preparation of a composition for example a surface coating composition comprising a cross-linked olefinic polymer characterised by reacting an olefinic polymer bearing a plurality of hydroxyl-reactive or carboxyl-reactive functional groups with a cross-linking agent consisting essentially of a lactone polyester chain compound bearing two or more chain terminating hydroxyl or carboxyl groups.

The present invention may, however, be modified by the use of lactone polyesters containing chain terminating groups, other than hydroxyl or carboxyl, with the use of olefinic polymers containing appropriate functional groups to react with such other chain terminating groups.

It has been proposed, in United States Patent No. Re 30234, to polymerise a lactone using a hydroxy functional acrylic polymer as initiator and cross-linking the resulting lactone polyester-modified acrylic polymer by means of urea formaldehyde, melamine formaldehyde or benzoquanimine formaldehyde resins using the terminal hydroxyl groups of the lactone polyester chains as cross-linking reactive sites. The lactone polyester is present in the role of a chain extending flexibiliser and the disadvantages inherent in the use of amine formaldehyde or phenol formaldehyde resins are present. The concept of the present invention, to use a lactone polyester in the primary cross-linking role, preferably in the absence of any other cross-linking agent, is absent from US Patent Re 30234.

The use of a hydroxy functional acrylic resin as an initiator for lactone polymerisation as described in US Patent RE 30234 does not of itself result in cross-linking since hydroxy terminated chains are produced pendant from the resin which cannot react with the resin to give cross-linking.

According to the present invention the preformed lactone polyester chain compound may be produced with any desired functionality by the suitable choice of initiators as hereafter described thus enabling any desired degree of cross-linking to be obtained in use.

The lactone may be polymerised using a suitable initiator molecule containing two active hydrogen containing groups or more depending on the functionality required in the lactone polyester which, particularly preferably, are hydroxyl groups. Given suitable reaction conditions substantially equal proportions of the lactone may be polymerised onto each of the active hydrogen sites on the initiator to give a controllable chain length depending on the quantity of lactone used.

Where a polyester containing two terminal hydroxyl groups is required the initiator may suitably be a glycol such as, preferably, butane diol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, polypropylene glycol or polyethylene glycol. Where a polyester containing three terminal hydroxyl groups is required the initiator may suitably be a triol such as, preferably, glycerol, trimethylol propane, triethanclamine, triisopropanolamine or 1,2,6-hexane triol.Initiators suitable for the production of polyesters containing a greater number of terminal hydroxyl groups are tetrols such as, for example, erythritol or pentaerythritol, or hexols such as, for example, sorbitol or a suitably multi-functional polyacrylates or polymethacrylates for example hydroxy functional polyacrylates or polymethacrylates which may be used to initiate lactone polymerisation either in monomeric or polymeric form and which may contain non-functional comonomer or copolymer sections or suitably multifunctional, for example multi-hydroxy, functional polyesters.

The lactone utilised may contain from 5 to 8 carbon atoms in the lactone ring each of which carbon atoms save that satisfied by the oxygen atom is satisfied either by hydrogen atoms or lower alkyl radicals with the proviso that the lactone may not contain more than 12 carbon atoms in total nor any alkyl radical itself containing more than three carbon atoms. Particularly preferably, however, the lactone contains 6 carbon atoms in the lactone ring said carbon atoms being satisfied solely by hydrogen atoms that is epsilon caprolactone.

One preferred range of lactone polyesters are those based on epsilon caprolactone and 2 to 6 functional polyol initiators in a molar ratio of epsilon caprolactone to polyol, of from 0.25 to 1 to 10 to 1 particularly preferably from 1 to 1 to 4 to 1. Another preferred range of lactone polyesters are those based on epsilon-caprolactone and hydroxy functional polyolefins.

The characteristics of surface coatings resulting from the practice of the invention may be varied by suitable control of the particular initiator and lactone used and by their relative quantities. In general terms the balance between hardness and flexibility in the coatings depends on the combination of the chain length of the lactone polyester chain compound used as a cross-linking agent and its functionality.

By using an initiator containing one or more aromatic rings such as, for example, benzene rings surface coatings may be made more resistant to hydrolysis. An example of such a diol initiator is an aromatic polyester containing the recurring unit - C6H4-CO-OR-. On the other hand the use of purely aliphatic initiators produces softer surface coatings which are not so resistant to hydrolysis but which may be preferred for certain applications such as, for example, flexible coatings on plastic substrates and on metal where a high degree of flexibility is required as, for example, in coil coatings.

It is understood that the use of initiator molecules containing other active hydrogen containing groups together with or in place of hydroxyl groups not excluded from the present invention.

The lactone polyester is preferably produced in the presence of a catalyst at a temperature, preferably, of from 20"C to 2000C. At lower temperatures within the given range, for example below 125"C the catalyst may be a Lewis acid such as boron trifluoride. Preferably the temperature is at least 1250C particularly preferably from 140"C to 180"C and the catalyst is an alkyl tin compound such as dibutyl tin dilaurate. The quantity of catalyst is suitably from 0.0001% to 0.2% by weight of the remaining constituents of the polyester.The polymerisation reaction is preferably conducted under efficient stirring conditions so that substantially the whole of the reactants are maintained in motion during the duration of the polymerisation which may be, for example, from 0.5 hours to 10 hours depending on the other reaction conditions and the requirements for practical processing. Preferably the reactants are subjected to an initial sparging with inert gas or nitrogen under reduced pressure, preferably at a slightly elevated temperature. Suitable conditions are a temperature of from 50"C to 80"C a duration of from 0.5 to 5.0 hours and a pressure less than 3 x 104 Nm-2.

A wide range of epsilon polycaprolactone di-or polyols are available from Interox Chemicals Limited under the Trade Name CAPA. The above detail is given, however, to enable particular lactone polyesters which may not be available commercially, to be prepared for the purposes of this invention. The production of carboxyl functional lactone polyester derivatives is described hereafter.

The present invention may be applied to a variety of olefinic polymers containing segments derived from a suitably functional monomer the quantity of polyester being selected according to the stoichiometry of the reaction between the hydroxyl or carboxyl groups on the polyester and the functional groups on the olefinic polymer and whether it is desired to leave a proportion say up to 50% of said groups unreacted. Such segments suitably may be included by copolymerisation of an olefinic monomer with a suitable quantity of the functional monomer. The particular quantity of the functional monomer selected will depend on the degree of cross-linking required but is suitably from 0.5% to 99% particularly preferably from 5% to 50% by weight of the olefinic polymer.The copolymerisation may be conducted using well understood principles utilising free radical initiators such as peroxides or azonitriles and a suitable polymerisation medium, which may be an organic medium or an aqueous medium, depending on the technique used, which may be bulk, solution, suspension or emulsion polymerisation.

Preferably, the olefinic polymer bearing functional groups is a copolymer of an acrylic or methacrylic acid derivative with an acrylic or methacrylic acid derivative or a vinyl derivative bearing a functional group reactive with the terminal hydroxyl groups of the lactone polyester. Alternatively, a proportion or all of the acrylic monomer not bearing the functional group may be replaced by other compounds bearing vinyl, vinylidene or allyl unsaturation or such other compounds may be present in addition depend ing on the particular olefinic "backbone" polymer required.

The olefinic polymer may suitably be prepared by the usual technique of solution polymerisation. An organic solvent such as, for example, benzene, xylene, or methyl propionate may be used and the polymerisation may be initiated by an organic peroxidic compound preferably a peroxydicarbonate, a diacyl peroxide or a hydroperoxide, such as, for example, benzoyl peroxide or an azo compound such as, for example, 2,2'azobisisobutyronitrile. Alternatively, the olefinic polymer may be prepared by emulsion polymerisation in an aqueous medium containing a surfactant to assist in the emulsification of the mono mers. In this case a water-soluble vinyl polymerisation catalyst such as, for example, alkali metal or ammonium persulphate is preferably used. The manner of polymerising olefinic monomers is well known in the art and is described in "Application of Synthetic Resin Emulsions" (1972) by H. Warson.

Preferably the functional monomer included in the olefinic polymer is an acrylate, methacrylate, or a vinyl compound containing an isocyanate group, (with the proviso that it may require to be blocked if an aqueous medium is to be used), an epoxy group, or an amide e.g. a methylylolated amide group. The blocking of isocyanate groups is well understood in the art and is described for example in "The Development and use of Polyurethane Products" by E.N. Doyle (McGraw Hill) 1971. The blocking agent may be, for example, diphenyl amine, phenol, isooctyl phenol, hydroxy biphenyl, pyrrolidone, or a lactam such as epsilon caprolactam.Examples of suitable monomers containing an isocyanate group are 2-isocyanatoethyl methacrylate (IEM) available from the Dow Chemical Company, or benzene, 1-(1-isocyanato1-methyl ethyl)-4-(1-methyl ethenyl) (m-TMI) available from the Cyanamid Company. An Example of a suitable monomer containing an epoxy group is glycidyl methacrylate. An example of a suitable monomer containing an amide group is N-methylol acrylamide.

Suitably, the olefinic polymer is included in a two component coating composition in which it is maintained separate from the lactone polyester cross-linking agent until required for use. However, if a heat activatable one component composition is required this may be achieved on the basis of a polymer containing a blocked isocyanate group using a blocking group which will 'unblock' at or below the desired activation temperature.

It may be desired to produce anionic or cationic water-based polymer surface coating composition. In this case it is preferred that the functionality of the lactone polyester is at least in part and preferably in a major proportion carboxy functionality. This may be achieved by reacting the lactone polyester polyol with an acid an hydride resulting in the formation of an ester linkage with the polyester and generating a free carboxyl group which is neutralised with a base to give an anionic character if such is required. If desired, aromatic character may also be built into the polyester by selecting an aromatic anhydride such as, for example, phthalic anhydride. Other suitable acid anhydrides are maleic, sebacic or trimellitic anhydrides.

If desired tertiary nitrogen atoms may be incorporated in the lactone polyester and treated with a water-soluble acid in an aqueous medium to give cationicity. Suitable acids are, for example, formic acid, acetic acid, or phosphoric acid. The incorporation of the tertiary nitrogen atom in the lactone polyester may preferably be achieved by selecting a lactone polymerisation initiator containing one or more tertiary nitrogen atoms. Examples of such initiators are the di-or tri-alkanolamines, preferably containing alkyl chains of no more than 10 carbon atoms, such as, N-methyl-, N-ethyl-, N-butyl-, N-propyl-, N-hexyl, N-cyclohexyl-, or N-phenyl diethanolamine or the corresponding di-propanolamines. A suitable trialkanolamine is triethanolamine although its higher homologues such as the tripropanolamines may also be used.

If an organic surface coating composition is required the olefinic polymer is preferably produced by solution polymerisation in a suitable organic solvent which is preferably present in a suitable quantity for direct inclusion in the coating composition and the lactone polyester may be directly included with it either as a one component storable mix or to produce a directly curable composition.

If a water-based surface coating composition is required the olefinic polymer is preferably produced by emulsion polymerisation. In this event the functional groups to be included in the polymer should be selected to be non-reactive with water and are, preferably, blocked isocyanate groups. The lactone polyester, produced in water dispersible form as described above may be directly included with the aqueous emulsion of the resulting polymer.

The coating compositions may include other ingredients usual in the art such as pigments, fillers, opacifiers, flow enhancers or catalysts and may be applied to suitable surfaces and cured. Depending on the reactivity of the polymer functional groups low temperature curing may be used to produce appliance or vehicle coatings, or even coatings on plastic substrates. Such temperatures are preferably above ambient temperature and may be, for example, up to 120 C. However, for a one component system where the reactivity is lower, for example where an epoxy or blocked isocyanate curing system, where the blocking mechanism is relatively temperature stable, higher temperatures, for example up to 1500C or even 200"C or more may be required.

The invention will now be illustrated by means of Examples 1 and 2(a) to (h) of which Examples 1 and Examples 2(a), 2(d), 2(f) and 2(g) are according to the invention and Examples 2(b), 2(c), 2(e) and 2(h) are not according to the invention and are present for comparative purposes.

The abbreviations used in the Examples are: m-TMI Benzene, 1 -(1 -isocyanato-1 -methylethyl)-4- (1-methyl ethenyl) MMA Methyl methacrylate BA Butyl acrylate MEKO Methyl ethyl ketoxime DBTL Dibutyl tin dilaurate AZBN Azobisisobutyl nitrile ME Mercapto ethanol DBTL Dibutyl tin laurate BCTM Bromo trichloro methane Example Stager Preparation of a hydroxy functional olefin copolymer To a 500 ml stirred reaction vessel fitted with reflux condenser, nitrogen purge and heat control means was added the following.

Dry Xylene 100.00 gms Dry 2 ethoxy ethyl acetate 100.0 gms ME 0.15 gms BTCM 0,45 gms AZBN 1.50 gms In a separate beaker a monomer feed was prepared by mixing the following : Styrene 193.60 gms 2 Hydroxyethyl acrylate 106.40 gms AZBN 1.50 gms ME 0,15 gms BCTM 0.45 gms The temperature of the contents of the reaction vessel was raised to 80 C and the monomer feed was started. A constant rate was maintained throughout. The temperature of the reactants in the vessel was raised gradually to 105"C over a 30 minute period. 40 minutes after the start of the monomer feed, AZBN (0.75 gms) and mercapto ethanol (0.15 gms) were added to the reaction vessel. The monomer feed took 1 hour 55 minutes to complete at a constant rate.

A sample taken immediately after the feed was over showed a monomer conversion of 38% (determined by weight solids content).

At three half hourly intervals after the monomer feed was over, additions of AZBN (0.75 gms) and mercapto ethanol (0.15 gms) were made to the reaction vessel. After 30 minutes after the last initiator and chain transfer agent addition, monomer conversion was found to be greater than 99%. The temperature of the resin was quickly raised to 1400C and held at this temperature for 15 minutes before the heat was switched off and the resin allowed to cool to room temperature.

The resulting 61.2% solids resin product had a water white colour and a viscosity of 7,250 centipoise at 24"C.

Stage II Preparation of a Blocked Isocyanate functional derivative of the copolymer of Stage I To a 500 ml reaction stirred fitted with reflux condenser nitrogen purge, heat control and cooling means was added the following : epsilon caprolactam 235.00 gms Dry xylene 60.00 gms Dry 2 ethoxy ethyl acetate 60.00 gms The temperature of the vessel contents was raised to 50"C to bring about solution of the epsilon caprolactam. 111.75 gms of isophorone diisocyanate and 0.72 gms of a 10% solution in xylene of DTBL was added. An exothermic reaction was controlled with cooling. A temperature of 50"C was maintained for 3 hours 45 minutes. At this point 235.00 gms of the product of Stage I was added. A temperature of 50"C was maintained for a further 4 hours until free isocyanate was not detectable by butylamine/acid back titration.

The resulting 60% solution of blocked isocyanate functional styrene acrylic resin had a water white colour and a viscosity of 18,000 centipoise at 24"C.

Stage Ill Preparation of a coating composition containing the blocked isocyanate functional copolymer of Stage 11 and a polyester polyol.

To a 1 litre sized ball mill was charged the following paint ingredients : Rutile titanium dioxide 250.00 gms Blocked isocyanate resin 180.00 gms (Stage II) Xylene 100.00 gms 2 ethoxy ethyl acetate 100.00 gms The ball mill contents were allowed to grind for 18 hours after which a Hegman dispersion rating of 7 1/2 was recorded.The liquid paint dispersion base was then drained and utilised in the following formulation : To an 8 oz sample bottle was added the following paint ingredients Paint base 80.00 gms Blocked isocyanate resin (Stage li) 25.05 gms Polycaprolactone tetra-ol 10.93 gms CAPA 316 (Trademark) DBTL (10% in xylene) 1.31 gms Bayer silicone fluid OL 0.21 gms (50% in xylene 2 ethoxy ethyl acetate) Xylene 3.65 gms 2 Ethoxy ethyl acetate 3.65 gms The sample bottle was sealed and the contents intimately mixed by rolling for two hours to produce a paint.

Stage IV Coating application and testing The paint product of Stage Ill was applied to 0.9 mm Bonderised (Trademark) mild steel and Alochromed (Trademark) aluminium panels using a number 5 wire wound bar coater.

The coated panels were then stoves for 30 minutes in an oven at 218"C.

The panels were allowed to cool before physical and chemical testing was carried out.

The tests were as follows: Tests on the coated steel panels Pencil Hardness: The hardest Staedtler Mars (Trademark) pencil lead which did not penetrate the coating.

Reverse Impact: Impact of a falling weight onto the back of the panel from various heights - the minimum weightiheight product which caused flaking in kg/cm units.

Methyl ethyl ketone The number of double rubs with double rub a ketone soaked cloth to remove the coating.

Tests on the coated aluminium panels T. bend flexibility European Coil Coaters Association 1800 T-bend test the lower the figure the greater the flexibility.

45 Gloss % of light reflected at angle of 45" to normal to the panel.

Test results Pencil hardness 3H Reverse impact > 140 T-bend flexibility 1/2 T 45" gloss 81% MEK double rubs 100 From the results it can be seen that the polycaprolactone tetra-ol functioned as a flexibilising crosslinking agent. Allround coatings properties were excellent.

Examples 2(a) to 2(h) These Examples consist of the following sections of experimental work.

Stage / Preparation of a half blocked isocyanate.

Stage lI Preparation of an isocyanate functional olefinic resin copolymer utilising the product of Stage Stage 111 The preparation of paint surface coating compositions containing the resin product of Stage II and a polyol cross-linking agent either according to the invention - cross-linking agents (a), (d), (f) or (g) or outside the invention and included to enable comparisons with alternative cross-linking agents to be made - (b), (c), (e) (h), and the application and testing of the compositions.

Stage I Preparation of a blocked isocyanate functional polyolefin (Resin A) Apparatus: 500 ml stirred reaction vessel fitted with dry air purge heating and cooling means.

Reagents (gms) m-TMI 210.50 MEKO 95.68 DBTL (10% in xylene) 1.53 Hydroquinone 0.06 Procedure: The m-TMI and hydroquinone were charged to vessel and the MEKO and DBTL mixture added dropwise over 15 minutes whilst applying cooling. The temperature was kept at 40"C for 4 hours. Resulting light amber viscous liquid was cooled and stored in a refrigerator at 5"C prior to its use. It had a theoretical blocked NCO equivalent weight of 292.75 gms Stage 11 Preparation of the MMAlBAlMEKO-m-TMI copolymer Apparatus 750 ml stirred reaction vessel fitted with dry nitrogen purge and heating means.

Reagents (gms) Initial vessel charge: Xylene 240.00 AZBN 1.80 Mercapto ethanol 0.18 Monomer Feed: MMA 129.48 BA 90.00 MEKO-m TMI adduct 140.52 AZBN 1.80 Mercapto ethanol 0.18 Catalyst additions: 5 additions of: AZBN 1.80 Mercapto ethanol 0.35 Procdure: The solvent, initiator and chain transfer agent mixture were charged to the vessel and heated to 950C. The monomers were fed over a 2 hour period.

At hourly intervals after the monomer feed was completed additions of AZBN and ME were made until conversion determined by non-volatile matter at 1500C indicated a conversion of greater than 95%. The resulting clear, colourless resin had a viscosity of 1138 centipoise at 25"C measured by means of a Brookfield Viscometer, an approximate solids content of 60% and an approximate blocked NCO equivalent weight of 750gms on resin solids.

Stage III Paint Preparation, application and testing A white pigmented mill-base made from the blocked isocyanate functional resin (Resin A) was used to prepare a number of stoving paints cross-linked~with polyols a)-g) listed below.

Preparation of mill base B Apparatus: 1.5 litre ceramic ball mill Ball mill Tiona 472 (SCM Corp) 240.00 charge: Sylosiv A4 (Grace) 10.00 Blocked NCO acrylic (Resin A) 200.00 Xylene 75.00 2 ethoxy ethyl acetate 75.00 ("TIONA" and "SYLOSIV" are Trade Marks) Procedure: The above ingredients were charged to the ball mill and ground to a Hegman Gauge reading of 7 1/2 over a 24 hour period.

Preparation of polyol cross-linked stoving paints Table 1 gives formulation details of the compositions of the stoving paint compositions. The polyol cross-linking agents used in coatings (a) to (h) were as follows : (a) Polylactone tetra-ol - molecular weight approx 1000. This was an epsilon polycaprolactone available under the Trade Name "CAPA 316" from Interox Chemicals Limited.

(b) Polyester tetra-ol - molecular weight approx. 1000. This was a reaction product of hexane diol, adipic acid and pentaerythritol adipate.

(c) Linear polyester - molecular weight approx. 400 available from Bayer under the Trade Name Desmophen 850.

(d) Linear polylactone - molecular weight approx 400. This was an epsilon polycaprolactone diol available from Interox Chemicals Limited under the Trade Name CAPA 203.

(e) Branched polyether - hydroxy equivalent weight approx 148, available from Bayer under the Trade Name Desmophen 550U.

(f) Polylactone modified polyolefin.

This was a styrene/hydroxyacrylate copolymer modified with 15% of n-butyl acrylate and 25% wt epsilon polycaprolactone based on total solids and having a hydroxy equivalent weight of approx 912.

(g) This was a methyl methacrylate/hydroxy acrylate copolymer modified with 50% by weight on total solids of epsilon polycaprolactone and having a hydroxy equivalent weight of approx 450.

(h) This was a styrene/hydroxy acrylate copolymer modified with 40% of n-butyl acrylate and having a hydroxy equivalent weight of approx 912.

The ingredients in each case were weighed into 4oz sample bottles and allowed to mix by gently rolling over a 24 hour period.

The paints were applied to 0.9mm steel and aluminium panels using a No. 7 "K-Bar" coater (R.K. Print Coat Instruments Ltd) and stoved for 30 minutes at 175"C. "K-Bar" is a Trade Mark.

The properties of the coatings are summarised in Table 2.

TABLE 1 Formulations of Stoving Paints Polyol Crosslinker Grams a b c d e f g h Mill Base B 30.00 30.00 30.00 30.00 30.00 30.00 30.00 30.00 Resin A 9.47 9.47 10.57 10.60 11.76 1.76 6.28 1.76 Polyol a)-h) 3.95 3.95 3.29 3.27 2.57 15.59 10.66 15.59 DBTL(10% in Xylene) 0.31 0.31 0.31 0.31 0.31 0.31 0.31 0.31 2 ethoxy ethyl acetate - - - - - - 3.00 All the paints were formulated to a pigment-binder ratio of 0.80:1.00. A theoretical blocked NCO:OH ratio of 1.00:1.00 was used. DBTL at 0.20% on binder was used as catalyst.

TABLE 2 Properties of Stoving Paints Property a b c d e f g h Solvent Resis tance. > 100 > 100 90 60 > 100 > 100 > 100- > 100 Pencil Hardness. 3H 3H 3H 3H 3H 4H 4H 3H Reverse Impact. > 160 > 160 < 5 > 160 < 5 35 > 160 8 Flexi bility. 1T 11/2T * 1/2T * 11/2T 1T 2T Gloss (%). 65 33 48 40 58 78 10 85 Solids Content. 61.8 59.5 59.9 - - - - - *Impossible to bend through a 90" angle.

Properties of Stoved Polyol Crosslinked Paints The Examples fall into two separate groups depending on the molecular weight of the cured systems.

Group (1) are low molecular weight polyol cured systems represented by Examples a) toe). Group (2) are higher molecular weight hydroxy polyolefin cured systems represented by Examples f) to g).

It is evident from the data in Table 2 that the polylactone based coatings possess the best overall combination of hardness and flexibility within group (a)-(e). Coating (a) shows improved gloss and flexibility compared to the coating (b). A superior T-Bend flexibility was obtained by switching to a lower molecular weight and functionality polylactone as the crosslinker for coating (d) but there was an accompanying loss in solvent resistance. The polyethers and polyesters used respectively in coatings (e) and (c) appear to give inadequate flexibility and these coatings lose their integrity with very minor amounts of flexing or impact.

All of the paints which are cured with hydroxy polyolefins (coatings (f) to (h)) are tough in character as both the base resin A and the crosslinker are high molecular weight film-forming polymers. Paint f) cured with a 25% Epsilon-caprolactone modified styrene hydroxy acrylate is both tougher and more flexible than the equivalent paint cured with a butyl acrylate flexibilised resin.

The advantages in terms of flexibility are clearly seen by building a larger quantity of polylactone into the hydroxy polyolefin crosslinker. Paint g) is highly flexible and impact resistant compared to both f) and h).

There appear to be additional advantages in using polylactone based polyols as crosslinkers. These materials are generally lower in viscosity compared to conventional polyesters. This is reflected by the solids/viscosity relationship shown by paints a), (b) and c).

Claims (17)

1. A process for the preparation of a composition comprising an olefinic polymer characterised by reacting the olefinic polymer bearing a plurality of hydroxyl-reactive or carboxyl-reactive functional groups with a cross-linking agent consisting essentially of a lactone polyester chain compound bearing two or more chain terminating hydroxyl or carboxyl groups.

2. A process as claimed in claim 1 wherein the olefinic polymer bearing functional groups is a copolymer of an olefinic monomer with an acrylic, methacrylic or vinyl monomer containing isocyanate, blocked isocyanate, epoxy or amide functional groups.

3. A process as claimed in claim 1 wherein the monomer containing functional groups is present in the olefinic polymer in from 5% to 50% by weight thereof.

4. A process as claimed in any preceding claim wherein the lactone polyester is derived from the polymerisation of a lactone initiated by a compound containing 2 or more hydroxyl groups.

5. A process as claimed in claim 4 wherein the polymerisation of the lactone has been initiated by a compound containing from 2 to 6 hydroxyl groups or by a multi hydroxy functional polymer.

6. A process as claimed in any preceding claim wherein the lactone polyester is poly (epsilon) caprolactone.

7. A process as claimed in claim 6 wherein the lactone polyester is poly (epsilon) caprolactone the polymerisation of which has been initiated by a polyol containing from 2 to 6 hydroxyl groups used in a quantity corresponding to a molar ratio of epsilon caprolactoneto polyol of from 0.25:1 to 10:1.

8. A process as claimed in any preceding claim wherein the cross-linking reaction is carried out by mixing a component containing the olefinic polymer with a component containing the lactone polyester and if required heating the mixture.

9. A process as claimed in any one of claims 1 to 7 wherein the cross-linking reaction is carried out by forming a single component containing the olefinic polymer, the olefinic polymer containing blocked isocyanate functional groups, and the lactone polyester and if required heating the component.

10. A process as claimed in claim 9 wherein the component is included in anionic form in an aqueous composition and the lactone polyester contains carboxy functionality which has been neutralised with a base.

11. A process as claimed in claim 9 wherein the component is included in cationic form in an aqueous composition and the lactone polyester contains tertiary nitrogen atoms which have been treated with a water-soluble acid in an aqueous medium.

12. A process as claimed in any one of claims 1 to 9 where the component or components are included in an organic composition comprising the olefinic polymer solution polymerisation reaction medium.

13. A process as claimed in any one of claims 9 to 11 wherein the component or components are included in an aqueous medium comprising the olefinic polymer emulsion polymerisation reaction medium.

14. A process as claimed in any one of claims 1 to 13 for the preparation of a surface coating.

15. A surface coating composition, comprising one or more components containing the olefinic polymer and a cross-linking agent therefor comprising the lactone polyester, suitable for use in the process claimed in any one of claims 1 to 14.

16. A process substantially as described herein and as claimed in any one of claims 1 to 14.

17. A surface coating composition substantially as described herein and as claimed in claim 15.