WO1997027253A1

WO1997027253A1 - Radiation-curable powder paint binder composition

Info

Publication number: WO1997027253A1
Application number: PCT/NL1997/000014
Authority: WO
Inventors: Johan Franz Gradus Antonius Jansen; Dirk Armand Wim Stanssens; Evert Sjoerd De Jong; Saskia Udding-Louwrier
Original assignee: Dsm N.V.
Priority date: 1996-01-23
Filing date: 1997-01-15
Publication date: 1997-07-31
Also published as: AU1321197A; NL1002153C2

Abstract

The invention relates to a radiation-curable powder paint binder composition comprising a resin and optionally a crosslinker in which more than 0,5 mol % of the total amount of polymerizable unsaturation of the binder composition results from itaconic acid ester units. The polymer can be a polyester, a polyacrylate, a polyolefin or an addition product of epoxy resins and itaconic acid. The binder composition can result in matte powder coatings.

Description

RADIATION-CURABLE POWDER PAINT BINDER COMPOSITION

The invention relates to a radiation-curable powder paint binder composition. The invention also relates to powder paints which can be converted to (semi)-matte powder coatings.

As shown by the article "Overview of the powder coatings market worldwide" by G. Maggiore in Pitture e Vernice Europe 1/92, pp. 15-22 and by the lecture by D. Richart "Powder Coating: Current Developments, Future Trends" (Waterborne, High-Solids and Powder Coatings Symposium, February 22-24, 1995), the search is still continuing for powder paint formulations which can be cured with little thermal stress of the substrate and which conseguently are suitable for use on heat-sensitive substrates such as, for example, wood and plastic.

As is further shown by the lecture "Radiation curing of powder coating" by Dr. Wittig at the Radtech Europe 1993 Conference (2-6 May 1993), no commercial radiation-curable binder compositions are available as yet. The reguirements include, on the one hand, good storage stability at relatively high temperatures (for example at 40°C) and, on the other hand, a viscosity which is sufficiently low to allow for good flow at a relatively low curing temperature.

A vital component in a powder paint composition is the binder composition which is generally based on a polymer optionally with a crosslinker. In general, the composition contains at least about 50 wt% of polymer and at most about 50 wt% of crosslinker. It is the object of the present invention to provide a powder paint binder composition which is radiation-curable, which is storage-stable at temperatures of, for example, 40°C and below, which shows good flow behaviour at temperatures between, for example, 60°C and 200°C, and which results in a powder paint formulation (which typically comprises the binder composition, and optionally the photoinitiator and optionally other additives) to be used on heat- sensitive substrates such as wood (wood substrates include substrates comprising chipboard, MDF (medium density fibre board) and any substrate in which wood is an important constituent).

The invention is characterized in that more than 0,5 mol% of the total amount of polymerizable ethylenic unsaturation of the binder composition results from itaconic acid ester units.

The powder paint composition according to the invention is curable at relatively low temperature, is storage-stable at 30°C, is radiation-curable and exhibits good flow at temperatures between 60°C and 200°C. The powder paint formulations on the basis of this composition are very suitable for application to heat-sensitive substrates. The itaconic acid or itaconic acid derivative used to prepare the itaconic acid functional unit can be represented by:

CO - R¹ /

H₂0 = C

\

CH, - CO - R²

wherein R¹ and R², independently of each other, allow the polymer, the crosslinking agent, or both to be functionally adapted to include the itaconic acid functional units by a covalent linkage through at least one of the R¹ or R². Hence, R¹, R², or both can serve as a linking or bridge site. If R¹ or R² is not a linking site, it can be a terminal site which is not covalently bound and does not link the itaconic acid functional unit to the composition.

By methods known in the art, one or both of the carboxylic acid groups of the itaconic acid structure can be functionalized with R¹ and R² groups such as, for example, -OH, -F, -Cl, -Br, -I, -OR³ or OP which allow for covalent binding of the itaconic acid functional units to a composition ingredient by customary coupling methods. R³ can be, for example a (Ci-Cjo) alkyl derivative and P is a polymer such as, for example, a polyester or a polyacrylate.

Alternatively, itaconic acid can be derivatized to the anhydride structure and then linked to the composition via the polymer, the crosslinker, or both, which allows for radiation polymerization to occur in the mixed formulation and generate desirable properties in both the pre-cure paint and post-cure coating compositions.

Exemplary itaconic acid derivatives include, for example, itaconic anhydride, itaconyl dichloride and mono- or diitaconic acid esters such as, for example, (C_-C_B )-alkyl mono- or diitaconates. Examples of suitable (mono- or di-)alkyl itaconates include mono- or dimethyl itaconate, mono- or diethyl itaconate, mono- or dibutyl itaconate, mono- or dioctyl itaconate and mono- or diperfluorooctyl itaconate.

Preferred examples include itaconic acid or itaconic anhydride.

In addition to the above noted advantages, another important practical advantage of the radiation- curable binder composition according to the invention is that the coated substrate can be immediately stacked after radiation curing. Physically-dried coatings are often used for the coating of wood and in practice the dying times can be as long as 24 hours. With use of the present radiation-curable compositions storage delay can be avoided, which results in considerable savings. According to a preferred embodiment of the invention, more than 40 mol% of the total amount of radiation-polymerizable ethylenic unsaturation in the binder composition results from the itaconic acid ester unit.

The amount of unsaturation of the binder composition can be determined by means of NMR. This determination is described, for example, in Journal of Applied Polymer Science, Vol. 23, 1979. pp 25-38, the complete disclosure of which is hereby incorporated by reference.

According to further preferred embodiment of the invention, more than 80 mol% and more particularly more than 90 mol% of the total amount of polymerizable unsaturation of the binder composition results from itaconic acid ester units. It is also possible that substantially all of the total amount of radiation polymerizable ethylenic unsaturation of the binder composition results from itaconic acid ester units. The present powder paint formulation can be used on substrates which comprise for example, wood, metal, plastic, paper and cardboard. Suitable plastics include, for example, unsaturated polyester based compositions, ABS, mela ine-formaldehyde resins, polyethylene, polypropylene and polyethyleneterephthalate. Suitable metals include for example alumina and steel.

The binder composition can be formed by a combination of at least one resin and at least one crosslinker or optionally can substantially or totally comprise just the resin. The polymer, the crosslinker or both can contain itaconic acid functional units.

In a preferred embodiment of the invention, the polymer in the binder composition contains itaconic acid ester units. Suitable examples of the polymers and oligomers include polyesters, polyacrylates, polyolefins, polyurethanes, addition products of epoxy resins and itaconic acid and polystyrenes. Preferably, the polymer is a polyester

In general, the amount of unsaturation in the polymer is in the range between 145 and 3000 grams per mole of unsaturated group (WPU) , preferably in the range between 200 and 2000 and more preferably in the range between 400 and 1000 grams per mole of unsaturated group. The number average molecular weight (M_n) can be, for example, between about 1000 and about 10,000 and may be chosen as a function of the crosslinker to be used.

The polymer can be either amorphous or (semi)- crystalline. In general, the glass transition temperature (Tg) of amorphous compounds is higher than 35°C and the melting point of crystalline is higher than 50°C.

The polymer can be a polyester and polyesters are generally polycondensation products of aliphatic polyalcohols and polycarboxylic acids. The polyester can contain as the acidic component, the itaconic acid units or itaconic acid derivative units and other polycarboxylic acids such as, for example, isophthalic acid, terephthalic acid, hexahydroterephthalic acid,

2,6-naphthalenedicarboxylic acid and 4,4 '-oxybisbenzoic acid, 3,6-dichlorophthalic acid, tetrachlorophthalic acid, tetrahydrophthalic acid, hexahydroterephthalic acid, hexachloroendomethylenetetrahydrophthalic acid, phthalic acid, azelaic acid, sebacic acid, decanedi- carboxylic acid, adipic acid, succinic acid. trimellitic acid and maleic acid, fumaric acid, citraconic acid and mesaconic acid. These illustrative acids can be used in their acid form or where avail¬ able, in the form of their anhydrides, acyl chlorides or lower alkyl esters. Mixtures of acids can be used. In addition hydroxycarboxylic acids and lactones can be used. Examples include 12-hydroxystearic acid, hydroxypivalic acid and ε-caprolactone.

Polyalcohols, in particular diols, can be reacted with the carboxylic acids to prepare the polyester. Examples include aliphatic diols, for example, ethylene glycol, propane-l,2-diol, propane- 1,3-diol, butane-l,2-diol, butane-l,4-diol, butane- 1,3-diol, 2,2-dimethylpropane-l,3-diol (= neopentyl glycol), hexane-2,5-diol, hexane-1,6-diol, 2,2-bis-

(4-hydroxycyclohexyl)-propane (hydrogenated bisphenol- A) , 1,4-dimethylolcyclohexane, diethylene glycol, dipropylene glycol and 2,2-bis[4-(2-hydroxyethoxy)- phenyl]propane, the hydroxypivalic ester of neopentylglycol and 4,8-bis-

(hydroxymethyl)tricyclo[5,2,1,0]decane (= tricyclodecane dimethylol)

Small amounts, such as less than about 4 wt% but preferably less than 2 wt%, of trifunctional alcohols or acids can be used to obtain branched polyesters. Examples of suitable polyols and polyacids are glycerol, hexanetriol, t imethylolethane, trimethylolpropane, tris-(2-hydroxyethyl) isocyanurate and trimellitic acid. The polyesters can be prepared via customary, generally known polymerisation methods by esterification or transesterification. For example, if needed, customary esterification catalysts such as, for example, butylchlorotindihydroxide, dibutyltin oxide or tetrabutyl titanate can be used. The conditions of preparation and the COOH/OH ratio can be chosen such that end products are obtained which have an acid value or hydroxyl value which is within the intended range of values.

Preferably, the polymer used is a polymer which has hydroxyl functionality, such as, for example, a polyester which has hydroxyl functionality. The polymer, for example a polyester, can be reacted at temperatures between, for example, about 70°C and about 200°C optionally in the presence of a catalyst such as, for example, dibutyltin laurate, with itaconic anhydride to give an itaconic acid-based polymer having acid functionality. This reaction can be carried out, for example, in an extruder or a static mixer. This reaction provides a simple synthesis, in which no side reactions occur, for a polymer containing itaconic acid units. Surprisingly, the resultant polymer after radiation cure on metal yields coating having good mechanical properties.

The polymer containing itaconic acid units can also be a polyacrylate. Generally, the acrylate polymer is based on alkyl esters of (meth)acrylic acid such as, for example, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, n-propyl (meth)acrylate, isobutyl (meth)acrylate, ethylhexyl acrylate and/or cyclohexyl (meth)acrylate, vinyl compounds such as, for example, styrene and vinyl acetate, maleate, fumarate and itaconate.

The acrylate resin can have carboxyl, glycidyl or hydroxyl functionality. Preferably, the acrylate polymer has hydroxyl functionality.

Acrylate resins having hydroxyl functionality are generally based on hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate and methyl (meth)acrylate. Acrylate resins can be prepared by a polymerization which involves the reactor being initially charged with solvent, for example toluene, xylene or butyl acetate. Then, heating takes place to the desired reaction temperature, for example the reflux temperature of the solvent used. This is followed, over a period of, for example, between 2 and 4 hours, by the addition of monomers, initiator and optionally mercaptan. Then, for example, the temperature is kept for two hours at reflux temperature and the solution is refluxed for 1 to 4 hours. The solvent is then distilled off by increasing the temperature, after which a vacuum distillation can be carried out over a period of, for example, one to two hours. Then the product is drawn off and cooled. Subsequently the product obtained, for example a polyacrylate having hydroxyl functionality, can be mixed with itaconic anhydride, an itaconic acid-based acrylate resin having acid functionality being obtained as a result.

Additional suitable acrylate polymers include, for example, glycidyl acrylate polymers. The glycidyl groups of these polymers can react with the acid group of a monoester of itaconic acid, for example monoethyl itaconate, an itaconic-acid based acrylate resin being obtained as a result.

Depending, on such factors as the type and functionality of the itaconic acid-based polymer a crosslinker can be selected.

The crosslinkers can be, for example, solid or liquid compounds which comprise functional groups such as for example vinyl ether, vinyl ester or (meth)acrylate functionalities. Such compounds are described, for example, in EP-A-636669, the complete disclosure of which is hereby incorporated by reference. Illustrative examples include tripropylene glycol divinyl ether, di- or triethylene glycol divinyl ether and di-, tri- and tetraacrylates. Other examples include divinyl ether-functionalized urethanes based on, for example, a diisocyanate and hydroxybutyl or hydroxyethyl vinyl ether and di(meth)acrylate- functionalized urethanes based on, for example, diisocyanate and hydroxyethyl methacrylate. It is also possible to apply crosslinkers containing allyl groups, for example, allyl ethers, allyl esters and allylamines. Suitable examples include diallylphtalate, diallyurea and diallylmelamine.

Preferably, solid crosslinkers are used. Like the polymer the crosslinker can also contain the itaconic acid functional unit. For example, it can be triethylene glycol diitaconate or pentaerythritol tetraitaconate.

In a further preferred embodiment of the invention the binder composition comprises a crosslinker which contains itaconic acid functional groups and a polymer containing unsaturated groups.

Suitable examples of such polymers include polymers having acrylate functionality, polymers having vinyl ether functionality, polymers having allylfunctionality or polymers, as already described in the above, having itaconic acid functionality.

According to a further preferred embodiment of the invention, a compound having polymerizable unsaturation resulting from itaconic acid ester units is processed as such into a powder paint.

The radiation-curable system generally comprises a resin and optionally a crosslinker, a photoinitiator or an inhibitor. According to another embodiment of the invention, the radiation-curable system comprises additives which are able to co-react with, for example, the double bond of the itaconate groups during radiation curing. Examples of such reactive additives include monoacrylates, monoitaconates and monovinyl ethers. These additives can be added in amounts between, for example, about 0.1 and about 15 wt% based on the total amount of the binder composition.

Radiation curing of the binder composition according to the invention preferably takes place by means of UV and EB curing. These methods are described in more detail in the article "UV and EB curing" by S.J. Bett et al. in JOCCA 1990 (11), pp. 446-453, the complete disclosure of which is hereby incorporated by reference. If necessary, curing can also take place thermally, by means, for example, of thermally latent catalysts.

The UV curing of the binder composition can occur from free radical-initiated polymerization and cationically-initiated polymerization.

For UV radiation curing of the powder paint formulation, a photoinitiator can be mixed, at a temperature between, for example about 70°C and about 150°C, with a binder composition according to the invention. Mixing can take place either in a solvent or in the melt in an extruder, which is preferred. It is also possible to add pigments and the desired adjuvants such as, for example, flow control agents, fillers, triboadditives, degassing agents and stabilizers. Then the paint can be applied to the substrate or be sprayed electrostatically. The powder paint can be placed in an oven, exposed to IR radiation or a combination of both, so as to effect a softening or melting of the paint at temperatures between, for example, 80°C and 200°C to give a continuous smooth coating film having a layer thickness between, for example, 50 and 200 μm. The still warm panel can be cured under a UV light source. Subsequently a post-heating operation can take place. Suitable light sources include, for example, an UV-lamp, a microwave powered UV-lamp and an excimer lamp. The excimer lamps are described in, for example, - li ¬

the conference proceedings of RADTECHEUROPE 95 (pages 48-52).

Examples of suitable photoinitiators are described in Volume 3 "Photoinitiators for free radical and cationic polymerization" of "Chemistry and

Technology of UV and EB formulations" by K. Dietliker (1991; SITA Technology Ltd. London).

Photoinitiators initiate curing of the compositions according to the invention upon exposure to light having wavelengths in the range between 200 and 600 nm. Suitable initiators are ketonic and may be aromatic, such as, for example, benzophenone. Darocur 1173® (Merck) is a suitable benzylketal-based photo- initiator and contains 2-hydroxy-2-methyl- 1-phenylpropan-l-one as the active component. Irgacure 184® (Ciba) is an aryl ketone containing hydroxycyclohexyl phenyl ketone as the active component and, like Irgacure 369® (active component 2-benzyl- 2-dimethylamino-l-(4-morpholinophenyl)-butan-l-one) , is a suitable photoinitiator. Acyl phosphine such as 2,4, 6-trimethylbenzoyl diphenyl phosphine oxide (Lucerine TPO®, BASF) can also be used, as can Quantacure CPTX® (Octel Chemicals) containing, as the active component, l-chloro-4-propoxythioxanthone. Chemical derivatives of these photoinitiators are also suitable, as are combinations of these initiators. A suitable combination of photoinitiators is formed by Irgacure 1800® (Ciba) which consists of 75 wt% of Irgacure 184® and 25 wt% of (bis(2,6-dimethoxybenzoyl)- 2,4,4-trimethylpentyl phosphine oxide).

Besides it is possible to apply a compound which forms a strong exciplex with one of the components of the binder composition according to the invention as a photoinitiator. A very important advantage which results from radiation-curing is that the heat-induced flow of the powder paint is substantially or entirely uncoupled from the curing reaction (by UV or EB radiation). Therefore powder coatings can be provided which exhibit extremely good flow. When the above-described method of heating and curing is employed, the coating reaches a higher temperature than the substrate, as a result of which lower thermal stress of the substrate occurs, which is of great importance for e.g. wood as a substrate. The processing of powder paints is described by Misev in "Powder Coatings, Chemistry and Technology" (pp. 224-300; 1991, John Wiley) the complete disclosure of which is hereby incorporated by reference.

A particularly import aspect of the present invention is the use of these binder comopsitions in powder paints to make matte powder coatings.

Matte powder coatings which also have other desired properties are very difficult to obtain as disclosed in for example "Powder Paints" in Paintindia (February 1992, p. 50), "New developments in powder coatings" in Polymer Paint Colours Journal (December 1993, vol. 183, pp. 590-591) and the lecture "Factors affecting the gloss reducing efficiency of ionomeric flatting agents for powder coatings" by Donald F. Loar at the Waterborne, Higher Solids and

Powder Coatings Symposium of 22-24 February 1995, It is further disclosed in "Grenzen und Mβglichkeiten in Sachen Pulverlack" in Metalloberflache (43 (1989) 3, pp. 99-101) that powder coatings are generally flatted with the aid of compounds containing polyolefins and silicon groups. These additives, however, have a negative effect on the mechanical properties and adhesion.

The powder paint composition comprising a binder composition according to the invention can result, after curing on various substrates, in (semi)matte powder coatings. These powder coatings also exhibit the other desired properties such as, for example, mechanical properties, outdoor durability, hardness, flow, colour stability, scratch resistance, and flow.

This binder composition generally contains, as the resin, a mixture of polymers.

Preferably, this mixture contains more than 0,5 mol % (relative to the total amount of polymerisable unsaturation) of the itaconic acid-based polymer or itaconic acid derivative-based polymer, the polymer preferably being a polyester. This polymer can be mixed with a polymer containing unsaturated groups, such as, for example an unsaturated polyester or an unsaturated polyacrylate.

The polymer can also be used in conjunction with a crystalline polymer such as, for example, a crystalline polyester.

The crosslinkers can be, for example, solid or liquid compounds which comprise functional groups such as for example vinyl ether, vinyl ester or (meth)acrylate functionalities. Such compounds are described, for example, in EP-A-636669, the complete disclosure of which is hereby incorporated by reference. Illustrative examples include tripropylene glycol divinyl ether, di- or triethylene glycol divinyl ether and di-, tri- and tetraacrylates. Other examples include divinyl ether-functionalized urethanes based on, for example, a diisocyanate and hydroxybutyl or hydroxyethyl vinyl ether and di(meth)acrylate- functionalized urethanes based on, for example, diisocyanate and hydroxyethyl methacrylate.

It is also possible to apply crosslinkers containing allyl groups, for example, allyl ethers, allyl esters and allylamines. Suitable examples include diallylphtalate, diallyurea and diallylmelamine. Preferably, solid crosslinkers are used. Like the polymer the crosslinker can also contain the itaconic acid. For example, it can be triethylene glycol diitaconate or pentaerythritol tetraitaconate.

Preferably, the binder composition comprises, as the resin, a mixture comprising a polyester containing itaconic acid functional units and an unsaturated polyester which is not based on itaconic acid functional units, and, as a crosslinker, a vinyl ether derivative.

Preferably, to obtain a (semi) matte powder coating the weight ratio polymer: crosslinker is in the range between 95:5 and 40:60. Generally, powder coatings have a high gloss, and the reflection (gloss) at 60° is generally higher than 95. By means of the known fillers as a flatting agent it is possible to obtain a gloss of approximately 50 at 60°. The gloss is generally measured according to

ASTM-D-523 at 60° and/or 20°.

Unexpectedly, however, the binder composition according to the invention allows powder coatings to have a gloss of between about 1 and about 50 at 60°. The desired gloss can be adjusted by selecting depending on the temperature the ratio between the polymer components on the one hand and the ratio between the resin and the crosslinker on the other hand. According to a preferred embodiment the invention relates to a process for imparting excellent matte finish characteristics to a powder coating with use of a powder paint binder composition comprising the combination of steps of: preparing a radiation-curable powder paint compositions from a binder composition, wherein said binder composition comprises as ingredients (i) a functionally useful amount of at least one polymer having a molecular weight between about 1,000 and about 10,000 and having an amount of unsaturation between about 145 and about 3,000 grams per mol of unsaturation, and (ii) optionally, a functionally useful amount of at least one crosslinking agent for said polymer, wherein said polymer, said crosslinking agent, or both comprise itaconic acid functional units in an amount of more than 0,5 mol% to impart said excellent matte finish to said powder coating, applying said radiation-curable powder paint to a substrate, and radiation-curing said radiation-curable powder paint to obtain a powder coating on said substrate. EP-A-0636669 discloses radiation-curable binder compositions for powder paint formulations but does not disclose or suggest how to formulate the paint to achieve matte finish powder coatings. The binders are based on unsaturated polyester. It is generically disclosed that one of the di- or poly-functional carboxylic acids which can be used to prepare the polyester can be itaconic acid. However, this publication does not teach or suggest that any of the carboxylic acids in general, or itaconic acid functional units in particular, can impart excellent matte finishes to the powder coatings when used in functionally sufficient amounts in the compositions. In addition, this publication does not suggest the particular use of itaconic acid functional units in the crosslinking agent.

Surprisingly the binder composition comprising itaconic acid units is more reactive than for example binder compositions based on maleate- or fumaric acid units. This results in faster curing compositions.

The invention is explained in more detail with reference to the following non-limiting experiments and examples.

Experiment 1 Preparation of an itaconate-containinα polyester

A 3-litre round bottomed flask provided with a thermometer, a stirrer and distillation head was charged with 98.3 grammes of trimethylolpropane, 113.6 grammes of neopentylglycol and 1.1 gramme of butylchlorotin dihydroxide.

With a constant flow of nitrogen, the temperature was increased to 150°C. 1203.8 grammes of terephthalic acid were added in two portions. The temperature was then increased to 220°C over a period of approximately 10 hours, water being distilled off in the process. When an acid value of less than approximately 10 mg KOH/g resin was reached, the reaction mixture was cooled to 165°C. Then 286.6 grammes of itaconic acid, 1.1 gramme of butylchlorotin dihydroxide and 0.3 gramme of mono-tert- butylhydroquinone were added, and the temperature was then raised to approximately 220°C until the acid value was smaller than approximately 12 mg KOH/g resin. The reaction mixture was cooled to approximately 180°C and placed under vacuum for approximately one hour.

The resultant polyester had an M_n (theor.) of 3000, a WPU of 1000 g/mol of unsaturated group, an acid value of 7.6 mg KOH/g resin, a hydroxyl value of 61 mg KOH/g resin, a T_g of 40°C (Mettler, TA 3000 at 5°C/min) and a viscosity of 105 dPas (Emila at 165°C).

Experiment 2

Preparation of an itaconic acid-terminated polyester A glass reactor having a volume of 1 litre was charged with 400 grammes of a polyester having hydroxyl functionality (Uralac P 2115®, OH value of 40 mg KOH/gram resin, DSM Resins), 32 grammes of itaconic anhydride and 800 mg of dibutyltin dilaurate. The reactor was heated to 160°C over a period of 2 hours, after which a polyester containing itaconic acid groups was drawn off.

The itaconic acid-terminated polyester had the following characteristics: acid value: 42 mg KOH/g resin - WPU: 1500 grammes per mole of unsaturated group and

T_g: 49°C

Experiment 3

Preparation of itaconic acid-terminated polyester Experiment 2 was repeated, the polyester having hydroxyl functionality used being Uralac P 1580® (DSM Resins) having an OH value of 75 mg KOH/gramme resin.

The product obtained had the following characteristics: - acid value: 73 mg KOH/gramme resin

WPU: 800 grammes per mole of unsaturated group and T_g: 52°C

Experiment 4 Preparation of an itaconate-containinσ polyester

A 3-litre round bottomed flask provided with a thermometer, a stirrer and distillation head was charged with 98.6 grammes of trimethylolpropane, 1398 grammes of 4,β-bis-(hydroxymethyl) tricyclo[5.2.1.0]decane and 1.1 gramme of butylchlorotin dihydroxide.

With a constant flow of nitrogen, the temperature was increased to 100°C. 418.1 grammes of terephthalic acid were aded in two portions. The temperature was then increased to 220°C over a period of approximately

2 hours, water being distilled off in the process. When an acid value of less than approximately 10 mg KOH/g resin was reached, the reaction mixture was cooled to 140°C. Then 573.1 grammes of itaconic acid, 1.1 gramme of butylchlorotin dihydroxide and 0.3 gramme of mono- tert-butylhydroquinone were added. The temperature was then raised to approximately 190°C until the acid value was smaller than approximately 12 mg KOH/g resin. The reaction mixture as cooled to approximately 170°C and placed under vacuum for approximately 40 minutes. The resultant polyester had an M_n (theor.) of

3000, a WPU of 500 g/mol of unsaturated group, an acid value fo 7.6 mg KOH/g resin, a hydroxyl value of 57 mg KOH/g resin, a T_g of 40°C (Mettler, TA 3000 at 5°C/min) and a viscosity of 50 dPas (Emila at 165°C).

Example I

Preparation of a powder coating

170 parts by weight of the resin according to Experiment 1, 30 parts by weight of vinyl ether co- crosslinker (Uralac ZW 3307P, DSM Resins), 2 parts by weight of Irgacure 184® (Ciba) and 1.3 parts by weight of flow control agent (BYK 361®) were homogenously blended in a Prism extruder at 70°C and 200 rpm. After cooling, the paint was ground and seeved, and the fraction having a particle size of less than 90 μm was then applied, with the aid of an electrostatic spray apparatus, to MDF panels in layers having a thickness of approximately 100 μm.

The powder coating obtained was heated for 60 seconds with IR lamps, which resulted in the panel at its surface reaching a temperature of approximately 120°C, whereupon the panel, which was still warm, was cured by UV radiation (1 J/cm², measured with an IL 390 light bug). The coating obtained had good flow

(determined visually), very good acetone resistance (no damage to the coating after 100 acetone double rubs) and a gloss (in accordance with ASTM-D-523/70) of 7 at 20° and of 1 at 60°.

Example II

Preparation of a powder coating

Example I was repeated, 125 parts by weight of the resin according to Experiment 1, 41 parts by weight of an unsaturated polyester not based on itaconic acid units (URALAC XP3125, DSM Resins) and 34 parts by weight of crosslinker being blended.

The resultant coating had good flow, very good acetone resistance and a gloss of 7 at 20° and of 1 at 60°.

Example III

Preparation of a powder coating

Example II was repeated, 41 parts by weight of resin according to Experiment 1 being used instead of 125 parts by weight of resin, and 125 parts by weight of Uralac XP3125 being used instead of 41 parts by weight of Uralac XP3125.

Example IV

Example II was repeated 4.1 parts by weight of resin according to Experiment 1, 161.9 parts by weight of unsaturated polyester (Uralac XP 3125), 34 parts by polyester weight of a vinylether crosslinker

(Uralac ZW 3307), 2 parts by weight flow control agent

(Resiflow PV 5™) and 2 parts by weight photoinitiator

(Irgacure 184™) being mixed. The coating obtained had good flow, very good acetone resistance and a gloss of 7 at 20° and of 1 at 60 ° .

Comparative Example A

Example IV was repeated with the exception that the itaconic acid based polyester according to Experiment I was replaced by the same amount of Uralac XP 3125, which does not comprise itaconic acid units.

The coating obtained had a good flow, very good acetone resistance and a gloss of 58 at 20° and 83 at 60°.

These examples show that the binder compositions according to the invention can provide matte finished powder coatings.

Example V

Preparation of a powder coating

A powder coating was prepared starting from 200 grammes of polyester according to Experiment 2, with 2 grammes of Irgacure 184® added thereto. After application to an aluminium Q panel, the powder was softened, with the aid of an IR oven, at 120°C and then cured for 30 seconds with the aid of a mercury lamp by UV radiation.

The soft, flexible, high gloss powder coating obtained had the following characteristics: acetone resistance (determined visually): very good, hardness in accordance with Kδnig: 85 seconds, and impact resistance (reversed impact, test ASTM- 2794/69) > 80 inch pound.

Example VI

Preparation of a powder coating

Example V was repeated, the polyester according to Experiment 3 being used. The hard, brittle, high gloss, powder coating obtained had the following characteristics: acetone resistance: very good, hardness in accordance with Kδnig: 140 seconds, and - impact resistance (reversed impact, test ASTM- 2794/69) > 20 inch pound.

Example VII

Preparation of a powder coating 200 parts by weight of the resin according to

Experiment 4, 2 parts by weight of Irgacure 184® (Ciba) and 1.3 parts by weight or flow control agent (Resiflow PV™) were homogeneously blended in a Prism extruder at 70°C and 200 rpm. After cooling, the paint was ground and screened, and the fraction having a particle size of less than 90 μm was then applied, with the aid of an electrostatic spray apparatus, to MDF panels in layers having a thickness of approximately 100 μm.

The powder coating obtained was heated for 80 seconds with an IR lamp whereupon the powder layer was liquified. After that, the panel, which was still warm, was cured by UV radiation (2 J/cm², measured with an IL 390 light bug).

The coating obtained had good flow (determined visually), very good acetone resistance (no damage to the coating after 100 acetone double rubs) and a gloss (in accordance with ASTM-D-523/70) of 68 at 20° and 92 at 60°.

These examples show that a binder composition having substantially all of the total amount of radiation-polymerisable ethylenic unsaturation resulting from itaconic acid ester units results in coatings having desired characteristics. Moreover these examples show that the reactivity of the itaconic acid ester units is high enough for homopolymerisation. If substantially 100% of the polymerizable unsaturations are based on itaconic acid units, high gloss powder coatings will be obtained.

Claims

C L A I M S

1. Radiation-curable powder paint binder composition comprising a polymer having unsaturated groups and optionally a crosslinker, characterized in that more than 0,5 mol % of the total amount of polymerizable ethylenic unsaturation of the binder composition results from itaconic acid ester units.

2. Composition according to Claim 1, characterized in that more than 40 mol% of the total amount of polymerizable unsaturation of the binder composition results from itaconic acid ester units.

3. Composition according to any one of Claims 1-2, characterized in that more than 90 mol% of the total amount of polymerizable unsaturation of the binder composition results from itaconic acid ester units.

4. Composition according to any one of Claims 1-3, characterized in that the the polymer is a polyester, a polyacrylate, a polyolefin or an epoxy resin which comprises itaconic acid ester units.

5. Composition according to any one of Claims 1-3, characterized in that the crosslinker comprises itaconic acid ester units and the polymer is a polymer containing unsaturated groups.

6. Powder paint composition comprising a binder composition according any one of Claims 1-5.

7. Powder coating based on a powder paint composition according to Claim 6.

8. Matte powder coatings based on a powder paint composition according to Claim 6.

9. Entirely or partially coated substrate, characterized in that the coating material used is a powder coating according to any one of Claims 7 or 8.

10. A process for imparting excellent matte finish characteristics to a powder paint coating with use of a powder paint binder composition comprising the combination of steps of: preparing a radiation-curable powder paint composition from a binder composition, wherein said binder composition comprises as ingredients (i) a functionally useful amount of at least one polymer having a molecular weight between about 1,000 and about 10,000 and having an amount of unsaturation between about 145 and about 3,000 grams per mol of unsaturation, and (ii) optionally, a functionally useful amount of at least one crosslinking agent for said polymer, wherein said polymer, said crosslinking agent, or both comprise itaconic acid functional units in an amount of more than 0,5 mol% to impart said excellent matte finish to said powder coating, applying said radiation-curable powder paint to a substrate, and radiation-curing said radiation-curable powder paint to obtain a powder coating on said substrate.

11. Method for the preparation of an itaconic acid based polymer having acid functionality characterized in that a polymer having hydroxyl functionality reacts, at temperatures between 70°C and 200°C, with itaconic anhydride in an extruder or in a static mixer.