CZ50094A3 - Enhanced photochemically hardened composition and a coating based thereon - Google Patents

Abstract

An aqueous, actinic radiation-curable coating composition containing a latex polymer emulsion and a multifunctional (meth)acrylate is disclosed. The critical aspect of the invention is that the actinic radiation-curable composition does not contain more than 5% by weight of the AOPAte ester of the multifunctional acrylate and 20% by weight of the ether resulting from a Michael addition of a multifunctional acrylate with the hydroxyl group of another multifunctional acrylate. This limitation on the maximum concentration of these components, which are typically the by-products formed in the manufacture of multifunctional (meth)acrylates, results in the improved appearance of the final cured coating.

Description

Object of the invention!

The present invention relates to an improved photochemically cured composition and a coating based thereon. In particular, the present invention relates to a water-dilutable photochemically cured composition capable of forming surface defect-free coatings.

BACKGROUND OF THE INVENTION

There is a need for quality coatings which can be formed at low concentrations of polluting solvents. Water-dilutable thermoplastic coatings can be formed at low concentrations of polluting solvents, but these coatings do not have thermal and chemical resistance sufficient for many applications, especially if the articles on which the coatings are formed must be stacked shortly after application of the coatings and in those cases where the material of the articles on which the coatings are formed cannot be heated to high temperatures. For chemically cured coatings that are characterized by good thermal and chemical resistance, there are problems with pot life and cure speed.

Photochemically cured coatings provide a solution to both of the above problems. However, current coating techniques remain expensive and it is difficult to apply thin coatings. Conventional photochemically cured coatings must be diluted with solvents in order to be spray applied.

The photochemically cured coatings may be composed of polymer latex and polyfunctional monomers. The coating composition can be prepared either directly by mixing the polymer latex with the polyfunctional monomer or by first emulsifying the polyfunctional monomer and then mixing the emulsified

9286 with polymer latex. The presence of water-insoluble impurities interferes with the mixing of the coating composition.

polyfunctional monomer not identified in these two components at

This leads to defect formation and loss of clarity of the final photochemically cured coating.

US-A-4 101 493 discloses a crosslinkable emulsion. The emulsion consists of an oil-in-water polymer emulsion and at least one (meth) acrylate ester with a polyol with at least two (meth) acryloyl groups per molecule, with a molecular weight of less than 1000 per (meth) acryloy group and a boiling point at normal pressure of at least 200 ° C.

The object of EP-0 320 472 is a water-based ultraviolet curing coating comprising a polymer latex and a polyfunctional (meth) acrylate in which the polymer latex contains more than 47 mole percent acrylate and has a glass transition point lower than 28 ° C.

The aforementioned patents are examples of attempts to form crosslinkable photochemically cured coatings from blends of polymer emulsions with polyfunctional compounds. The presence of unidentified water-insoluble compounds causes these coatings to be defective and lose their clarity.

The object of the present invention is to overcome the drawbacks of the known coatings.

9286

The essence of the invention

According to the present invention there is provided a composition consisting of (a) a polymer latex, (b) a polyfunctional (meth) acrylate, (c) a polyfunctional triol ester and an acrylic acid of the general formula

STEED'

CH ₂

CHj

OR ¹ where

R 1 = CH 3, -CH 2 CH 2, r 2, R 3 = - (CO) CH = CH ₂ , and

R <= - (CO) CH ₂ CH 2 O (CO) CH = CH 2, az (d) a polyfunctional acrylic ester which is the product of the Michael addition of a hydroxy group and has the general formula

OR ² • ch ₂ . ^:

OR ³

R ¹ - CH ₂ CH ₂

OR ⁴ .

9286 kd ©

R 1 = -CH 3, -CH 2 CHa;

R 2, R 3 = - (CO) CH = CH 2; and

R 4 = -CH ₂ CH 2 (CO) -OCH ₂ CH (R 1) [CH 2 O (CO) CH = CH 2] ₂ , wherein component (c) is present at a concentration of less than 5 wt. X, b preferably less than 3 wt. X and component (d) is present at a concentration of less than 20 wt. X, preferably less than 10 wt. X, based on the total weight of components (b), (c) and (d).

It has been found that if the concentration of components (c) and (d), which are previously unidentified water-insoluble impurities, is less than 5% and 5%, respectively.

coating with excellent properties, the property is excellent clarity, properties of coatings of various substrates and wood and plastics.

the polyfunctional (meth) acrylate whose molecule contains at least two functional groups, has a molecular weight per functional group of less than 1000 and a boiling point of at least 200 ° C normally. Polyfunctional (meth) acrylates may be

20 Oct, can gain cured Once of these excellent which Yippee particularly significant

composites including e.g.

As used herein, a (meth) acryloylic substance is a single pressure used alone or in combination. The molecular weight per one (meth) acrylic acid group is less than 1000, preferably from 95 to 300 and even more preferably from 95 to 150.

Suitable polyfunctional (meth) acrylates are polyfunctional compounds containing (meth) acrylic acid, (meth) acrylic acid alkyd resins (meth) acrylates obtained by reaction of a methacryloyl group such as (meth) acrylooylhaloerenide or ester with various compounds such as containing hydroxyl groups with polyesters polycondensates or polyether polycondensates. These compound (meth) acrylated compounds are in some sense polymeric compounds because the (meth) acryloyloxy groups can be attached to either the polycondensate, e.g., polyester or an addition polymer, e.g., a polyether, a polymer, e.g., a glycidyl (meth) polymer. acrylate. Examples of such compounds are:

to polyurethane, or to vinyl

9286 (A) Urethane (meth) acrylates obtained by reacting isocyanate groups of polyisocyanates such as hexamethylene diisocyanate with hydroxyalkyl (meth) acrylates, for example, with hydroxyethyl (meth) acrylate. These polyurethane poles of (meth) acrylate monomers are described in U.S. Pat. No. 3,279,745.

(B) Polyether (meth) acrylates obtained by esterification of hydroxyl-terminated polyethers described in U.S. Pat. No. 3,380,831.

(C) Polyesters with at least two (meth) acrylate groups obtained by reacting hydroxyl groups with a (meth) acrylic carboxylic acid described in U.S. Pat. No. 3,935,173.

(D) The polyfunctional (meth) acrylates disclosed in US-A 3,560,237, obtained by reacting a hydroxyalkyl (meth) acrylate, for example, hydroxyethyl (meth) acrylate with any of the following compounds:

(a) di-carboxylic acid having 4 to 15 carbon atoms; (b) polyepoxides with terminal glycidyl groups; (c) polyisocyanates with reactive terminal isocyanate groups.

(E) Polyesters with terminal (meth) acrylate groups prepared from (meth) acrylic acid, a polyol with at least three hydroxyl groups, and a dicarboxylic acid as described in U.S. Pat. No. 3,567,494.

(F) Polyfunctional (meth) acrylates obtained by reacting (meth) acrylic acid with at least two epoxy groups of epoxidized oils containing double bonds, such as soybean oil and linseed oil, for example the respective epoxidized unsaturated fatty acids, their esters or amides, or the corresponding alcohols, containing at least two epoxy groups. Such polyfunctional (meth) acrylates are described in US-A 3 125 592.

(G) Polyfunctional (meth) acrylates which are urethane derivatives or amino derivatives of (meth) acrylated epoxidized oil containing double bonds> fatty acids and the like described in (F) and in the patent mentioned in point F, obtained by reaction of isocyanate (isocyanates) ) or amine (s) with (meth) acrylated epoxy oils containing double bonds, fatty acids and the like described in US-A 3 125 592. Urethane derivatives or amino derivatives, in

9286 which retain some or all of the methacrylate groups are disclosed in U.S. Pat. No. 3,976,518 or U.S. Pat. No. 3,876,077.

(H) polyfunctional, (meth) acrylates obtained by the addition of (meth) acrylic acid to the epoxy groups of the bisphenol-based aromatic epoxy resins described in US-A 3 373 075.

(I) Polyfunctional (meth) acrylates obtained by adding (meth) acrylic acid to a linear vinylic polymer with pendant glycidyl groups, for example polymers of glycidyl methacrylate, vinyl glycidyl ether or vinyl glycidyl sulfide, described in US-A 3,530,100.

(J) Polyfunctional (meth) acrylates derived from (meth) acrylic anhydride and polyepoxides, described in US-A 3,676,398.

(K) Polyfunctional (meth) acrylates-urethanes-polyesters obtained by the combination of hydroxyalkyl (meth) acrylates, diisocyanate and hydroxy functionalized alkyd, described in US-A 3,676,398.

(L) Methacrylate end-urethane polyesters obtained by reacting a polyol-caprolactone diol or triol with a polyisocyanate, for example a diisocyanate, and a hydroxyalkyl (meth) acrylate. These products are described in US-A 3,700,643.

(M) Polyfunctional (meth) acrylate-urethanes, obtained by reaction of a hydroxyl group ester formed by the reaction of a polyol with (meth) acrylic acid and a polyisocyanate, as described, for example, in U.S. Pat.

The patents mentioned in paragraphs (A) to (M) above describe polyfunctional compounds containing (meth) acryloyloxy groups and a process for their preparation. Thus, those skilled in the art can obtain information from these documents.

. Preferred polyfunctional (meth) acrylates are trimethylol propane triacrylate and trimethylol propane trimethacrylate, with trimethylol propane triacrylate being more preferred.

Although there is no theoretical justification here, it is believed that the occurrence of water-insoluble impurities is related to the mixing of the latex with the (meth) acrylate monomer. Polyfunctional (meth) acrylate is generally sufficiently soluble in water to rapidly penetrate into the latex particles. The water-insoluble impurities do not pass into the latex particles, but form discrete particles which cause defects and consequently reduced

9286

Clarity of the final cured coating.

The polyfunctional ester of triol and acrylic acid has the general formula: - OR ² ----------------------- CH 2 OR ³ -CH ₂ ch ₂

OR ⁴

where

R 1 = -CHa, -CH ₂ CHa.

R 2, R 3 = - (CO) CH = CH ₂ , and

- (CO) CH ₂ CH ₂ O (CO) CH = CH ₂ .

The polyfunctional acrylic ester, which is the product of the Michael addition of the hydroxy group, has the general formula. OR ²

CH, i X ^R - ^C - CH,

STEED

CH,

OR where

R 1 -CH ₂ , -CH ₂ CHa,

R2, R3 = - <CO) CH = CH ₂ and

R 4 = -CH ₂ CH ₂ (CO) -OCH ₂ CH (R ₁ ) [CH ₂ O (CO) CH = CH ₂ ] ₂ .

9236

The clarity of the final cured coating and the ease of its preparation are improved when the water-dilutable photochemically cured composition of the present invention contains less than 5 wt. X of a polyfunctional ether of triol and acrylic acid and less than 20 wt. % of polyfunctional acrylic acid ester formed by Michael addition of hydroxy group, based on the total weight of polyfunctional (meth) acrylate, polyfunctional ester of triol and acrylic acid, and polyfunctional acrylic acid ester formed by Michael addition of hydroxy group. Preferably, the water-dilutable photochemically cured composition of the present invention comprises less than 3 wt. X of a polyfunctional triol-acrylic acid ester and less than 10 wt. % of polyfunctional acrylic acid ester formed by Michael addition of hydroxy group, based on the total weight of polyfunctional (meth) acrylate, polyfunctional ester of triol and acrylic acid, and polyfunctional acrylic acid ester formed by Michael addition of hydroxy group.

The concentration of the water-insoluble impurities contained in the polyfunctional (meth) acrylate may be reduced or eliminated by modifying the process for preparing the polyfunctional (meth) acrylate, such as by changing the ratio of reactants, temperature or catalyst, or distillation, chromatographic purification and the like.

The term latex as used herein refers to a water insoluble polymer prepared by a conventional polymerization technique, such as emulsion polymerization. The glass transition temperature or Te * used herein has the meaning of the glass transition temperature of the polymer calculated on the basis of the Fox equation [Bulletin of the American Physics Society 1, (3), 123 (1956) 3:

wi w ₂

Values wi a and Tet i>, Tet 2> homopolymers. referred to as j

Te T » ₍ 2)

W 2 are the mass fractions of comonomers in the copolymer are the glass transition temperatures of two corresponding In this document, acrylates and methacrylates (meth) acrylates, acryloyl and methacryloyl as

9286 (meth) acryloyl and acrylic acid and methacrylic acid such as (meth) acrylic acid.

The latex used in the photochemically cured composition is prepared in a conventional manner by emulsion polymerization. The latex-forming polymer is formed from any monomer or monomer mixture that is capable of forming water-insoluble polymer latex particles.

A variety of monomers or mixtures thereof may be used to prepare the latex-forming polymer. For example, they may be acrylates including methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, pentylacrylate, neopentyl acrylate, ethyl acrylate, hexylacrylate, hexylacrylate, hexylacrylate, hexylacrylate, isodecylacrylate, lauryl acrylate, boric lacquers, and saber lacquers, myristy, acrylate, pentadecyl acrylate, stearyl acrylate and the like; methacrylic acid esters inclusive, methyl methacrylate, ethyl methacrylate, propylmethakrylátu, isopropylmethakrylátu, butyl methacrylate, isobutylmethakkrylátu, hexyl methacrylate, octyl methacrylate, isooctane methacrylate, decylmethakrylátu, isodecyl methacrylate, lauryl methacrylate, Born methacrylate, isoborny methacrylate, mirystylmethakrylátu, pentadecyl methacrylate, stearyl methacrylate, and under.; acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, styrene, substituted styrenes, butadiene, acrylonitrile, ethylene and vinyl acetate.

The particle size of the latex is relatively small, between about 70 nm to 225 nm, preferably between 70 nm and 120 nm. It is known that the particle size of the same polymer is primarily controlled by the type and concentration of the emulsifier.

The dry weight of the polymer emulsion is from 30% to 50%, preferably from 35% to 50%.

The weight ratio of the latex-forming polymer to the polyfunctional (meth) acrylate is from 30: 70 to 95: 5, preferably from 60: 40 to 80: 20, most preferably from 65: 35 to 75: 25.

The coating composition may be prepared either by direct blending of latex and polyfunctional (meth) acrylate or

9286, first emulsifying polyfunctional (meth) acrylate and then mixing it in this form with latex. Polyfunctional (meth) acrylate can be converted to an oil-in-water emulsion by adding a surfactant in a concentration of 2 to 5%. Suitable surfactants are, for example, sulphates of higher fatty alcohols such as sodium lauryl sulfate; alkyl aryl sulfonates such as isopropylbenzenesulfonates or alkali salts of higher alkyl alkyl sulfosuccinates such as sodium octylsulfuccinate, sodium salt of N-methyl or sodium or potassium salts of isopropyl naphthalene sulfonates;

alkyl aryl aryl polyols are, for example, oxyethylene

N-palmitoyl 2-amino acid derivatives, and oleyl isothionate; and alkali salts of ethoxyethanolsulphates or sulionates, such as octylphenoxypolyethoxyethylsulfate of 1 to 5 units.

Appropriate. nonionic surfactants are alkylene oxypolyethoxyethanols having alkyl groups of 7 to 18 carbon atoms and 6 to 60 oxyethylene units such as heptyl enoxy polyethoxy ethanols and methyloctylene oxypolyethoxyethanols; polyethoxyethanol derivatives of alkylphenols connected by methylene bridges; sulfur-containing substances such as those prepared by polycondensation of 6 to 60 moles of ethylene oxide with nonyl mercaptan and dodecyl mercaptan or with an alkylthiophenol having an alkyl group of 6 to 16 carbon atoms; long chain ethylene oxide derivatives of carboxylic acids such as lauric, myristic, palmitic and oleic acids or acids found in tall oil containing 6 to 60 oxyethylene units per molecule; similar ethylene oxide condensates with long-chain alcohols such as octyl alcohol, decyl alcohol, lauryl alcohol or cetyl alcohol, ethylene oxide derivatives of etherified or esterified polyhydroxy compounds with a hydrophobic hydrocarbon chain such as sorbitol stearic ester with 6 to 60 oxyethylene units; also ethylene oxide blocks combined with one or more hydrophobic propylene oxide blocks. Mixtures of alkylbenzene sulfonates and ethoxylated alkylphenols can be used.

A susceptible photoinitiator may be included in the composition

9286 such as iluorenones, d-halogenated chlorine-sulphated δ-halogenated alkyl derivatives, and dithiocarbamate initiators, which have ultraviolet radiation. A small amount of this optional iotoinitiator present in the composition is another advantage of the present invention. The photoinitiator may be added to the composition in an amount of from 0.1 wt. % to 0.5 wt. Ss, based on the total weight of the nonvolatiles, preferably in an amount of from 0.2 wt. SS · up to 0.3 wt. %, based on the total weight of the non-volatile substances. Suitable photoinitiators are the cleavable iotoinitiators, halogenated polynuclear ketones, benzanthrones, chlorosulfonated alkyl benzanthrone and fluorenone alkyl derivatives described in US-A-3,827,957 and US-A-3,827,959; benzoin, ethers thereof such as methyl ether, ethyl ether, isopropyl ether, butyl ether and octyl ether; carbonyl compounds such as diacetyl and benzil; sulfur-containing compounds such as diphenyl sulfide, chloromethyl carbamate and anthracene. Further, the alkylphenols described in US-A-3,759,807 may be used. Photoinitiators suitable for pigmented coatings are disclosed in US-A-3,915,824 and US-A-3,847,771. The most suitable are cleavable photoinitiators.

If the coating is heat cured, the composition may comprise a thermal initiator. The thermal initiator is added to the composition in an amount of about 0.5 wt. ss, based on the total weight of the non-volatile substances. Suitable thermal initiators are azo compounds such as azo-bis-isobutyronitrile, organic peroxides such as ketoperoxides, hydroperoxides, alkylperoxides, acylperoxides and peroxyesters and inorganic peroxides such as ammonium persulfate, potassium persulfate and hydrogen peroxide.

In addition, conventional coating components such as pigments, dispersants, surfactants, coalescing agents, wetting agents, flow modifiers, thickeners, drying retardants, defoamers, colorants, waxes, preservatives, heat and UV stabilizers can be used in the present invention.

These photochemically cured compositions are rolled-in, apertured and sprayed.

The coating may be cured or crosslinked either by photochemically active radiation or by heating after most stabilizers have been applied.

9286 water or all the water from the mixture has evaporated. Suitable photochemically active radiation is ionizing radiation, electron beams and ultraviolet radiation. The source of ultraviolet radiation may be sunlight, a mercury lamp, an electric arc, and a xenon lamp. Medium pressure mercury lamps are particularly suitable.

The photochemically cured compositions can be used as topcoats, interlayers or bases. The compositions are suitable for use in which ease of processing and excellent clarity are required, such as paints including wood lacquers, adhesives, paints and inks including screen printing, intaglio printing and lexography ii, plastics including foils and floor coverings. of PVC, for fibers, for paper, including printing varnishes for paper and paperboard, for leather, for photoresist solder masks on electrical circuits, for printing plates and for other photochemically cured compositions. The compositions are particularly suitable for coating wood such as cabinets, furniture and floors.

The invention is further described by way of example.

PrXKlariy, prgyede.ni vy nal ftav.

Example 1

Preparation of polymer latex

Polymeric latex is a single-stage latex prepared by emulsion polymerization initiated by a redox system with sequential addition of initiator. To reaction deionized water and 26.8 g (SLS). The mixture in the reaction vessel was charged with 1450 g of 28% sodium lauryl sulphate solution and the vessel was heated to 59-61 ° C.

A monomer emulsion was prepared by mixing 1485 <3 methyl acrylate and 15 g acrylic acid with 600 g deionized water and 27 g of 28% lauryl sodium sulphate solution. When the temperature of the mixture in the reaction vessel reached 59-61 <3, 160 grams of monomer emulsion was added,

1.5 g of ammonium persulfate and 0.3 g of sodium bisulfite. After two minutes, several milligrams of ferric sulfate were added.

9286

The reaction mixture was heated to 67 ° C to 69 ° C with the released reaction heat. Fifteen minutes after initiation, simultaneous dosing of the monomer emulsion, ammonium persulfate solution (1.6 g ammonium persulfate dissolved in 60 g deionized water) was started. The monomer emulsion was added over 3 hours and the ammonium persulfate solutions were dosed for the same time and then for 20 minutes. After completion of the monomer addition, 40 g of deionized water was added twice in succession. After all the components were added, the contents of the reaction vessel were maintained at 63 ° C for 20 minutes and then cooled to 35 ° C. When the temperature reached 35 ° C, a mixture of 14.3 g of a 28% aqueous ammonium hydroxide solution in 25.7 g of deionized water and 0.2 g of Proxel ^R CRS was added. The contents of the reaction vessel were further cooled to ambient temperature and then filtered. The dry weight of the latex thus obtained was 37.5 ss.

Example 2

Preparation of polyfunctional (meth) acrylate

The polyfunctional (meth) acrylate was converted into an emulsion. A 1.2 liter metal cylindrical vessel with an inner diameter of 12.5 cm was equipped with a disperser with a Cowles gear propeller of 6? 7 cm. 125.8 g of deionized water were metered into this vessel. 8.6 g of non-ionic surfactant (Triton ^R X-15) and 2.2 g of other non-ionic surfactant (Triton ^R X-102). 360 g of trimethylolpropane triacrylate (TMPTA) was metered in over 20 minutes using a 3 mm plastic dropper, and the dispersant speed, which was initially from 1000 to 1200 rpm, was gradually increased depending on how the foam allowed the mixture to to 2000 rpm After all trimethylolpropane trimethacrylate was added, the speed was further increased to 3000 rpm. and stirred at this speed for 10 min.

9286

Example 3

Preparation of the composition

In a 2 L container of 30 <3 polymer emulsion (Darocur * 1173). Thereafter, 0.03 g was added with a 5 cm stirrer, and a 3 mm dropper was added dropwise over a period of 3 minutes using a TMTPA emulsion (6.6 g) with stirring, the intensity of which was noticeably small on the surface of the mixture. vortex. After complete addition of TMPTA, the mixture was stirred for an additional 30 min. and then 2.8 g deionized water was added. 2a, 0.8 g of a thickener (Acryeol ® QR-708, dry solids content in water 2 &lt; &gt;) was added to the agitation to form a small vortex on the surface of the mixture. The mixture was stirred for an additional 15 min. The mixture was allowed to stand for at least 16 hours prior to use. The viscosity of the composition measured by a Brookfield viscometer was about 90 cP.

Example 4

Preparation of coated articles and evaluation of coating quality

The prepared composition was coated onto phosphated steel plates using a liquid film applicator with a slot width of 0.0254 mm. The coating was allowed to dry for 10 min. at normal temperature and then at 70 ° C in a forced air oven. The coated plate was then passed through a type 1202 remote controlled ultraviolet irradiation device with two 8.7 W / cm mercury vapor lamps at a strip speed of 6 m / min (corresponding to a total energy of approximately 2 J / cm ² ). The thickness of the cured coating thus obtained was about 0.0254 mm.

The composition of composition 1 with a reduced content of water-insoluble impurities after curing had no surface defects. A comparative composition of composition 2 having a higher content of water-insoluble impurities had a large number of surface defects which caused the resulting coating to be opaque.

Claims (10)

PATENT CLAIMS A composition consisting of (a) a polymer latex, (b) a polyfunctional (meth) acrylate, (c) a polyfunctional triol ester and an acrylic acid of the general formula C H, CH, STEED OR ³ CH, OR ⁴ where R1 = -CHg, -CHa CHa, R2, R3 = - (CO) CH = CH3, and R 4 = - (CO) CH ₂ CH ₂ O (CO) CH = CH 2 and az (d) a polyfunctional acrylic ester, which is the product of the Michael addition of the hydroxy group and has the general formula STEED* R ¹ CH ₂ OR ³ • Cc.h ₂ . ch ₂ OR ¹ 9286 where R 1 = -CH ₂ , -CH ₂ CHa, r ₂ , r 3 = - (CO) CH = CH ₂ and -R 4 --- = -CH ₂ CH ₂ (CO) -OCH ₂ CH (R 1) [CH ₂ O (CO) CH = CH 2) ₂ . characterized in that component (c) is present in a concentration of less than 5 wt. 96, preferably less than 3 wt. and component (d) is present at a concentration of less than 20 wt. preferably, less than 10 wt. 96, based on the total weight of the components < b), (c) and (d). 2. The composition of claim 1 wherein said polyfunctional (meth) acrylate is trimethylol propane triacrylate or trimethylol propane trimethacrylate. Composition according to claim 1, characterized in that the weight ratio of said polymer latex to polyfunctional (meth) acrylate is from 30: 70 to 95: 5, preferably from 65: 35 to 75: 25. The composition of claim 1, further comprising a photoinitiator, wherein the photoinitiator is preferably a cleavable type photoinitiator. Composition according to claim 9, characterized in that the initiator is present in a concentration lower than the weight of the non-volatile substances. by 0.5 wt. 96, The composition of claim 1, further comprising a thermal initiator. A method of obtaining a cured coating with improved clarity, comprising (a) preparing a composition according to any preceding claim, (b) applying the composition to a substrate and (c) exposing the substrate to which the composition is exposed to radiation. 9286 Use of the compositions defined in claims 1, coating of substrates. Method and use according to claims 7 and 8, the substrate being wood. 10. The cured polymer coating obtained by Method 9. 2,3,4 and 6 for wherein said according to claims 7 a