IE61121B1

IE61121B1 - Process for the production of coatings by radiation crosslinking

Info

Publication number: IE61121B1
Application number: IE255887A
Authority: IE
Inventors: Francois Chevallier; Sammy Chevalier
Original assignee: Poudres & Explosifs Ste Nale
Priority date: 1986-10-02
Filing date: 1987-09-22
Publication date: 1994-10-05
Also published as: ATE63937T1; FR2604715A1; DK515687D0; DE3770399D1; FI86882B; NO874051L; NO874051D0; EP0263749B1; PT85847A; FI86882C; AU7902287A; PT85847B; JPS63284272A; AU590976B2; FI874299A0; ES2022409B3; DK515687A; FR2604715B1; EP0263749A1; IE872558L

Abstract

Radiocrosslinking of compositions containing a resin capable of being cured by polymerisation of double bonds SIGMA C=CH2 and a reactive diluent system containing at least one reactive diluent corresponding to the general formula (I) <IMAGE> in which - R1 = H, CH3 - R2 and R3 = H, C1-C4 alkyl chain or form an alkylene ring containing 5 or 6 carbon atoms - R4 = H, C1-C4 alkyl chain, phenyl - R5 = C1-C10 aliphatic chain, C5-C6 cycloaliphatic chain, or a C1-C4 alkyl chain substituted by an aryl group or an aromatic heterocyclic ring - or R4 and R5 form a 5- or 6-membered ring. The invention also relates to isopropyl beta-hydroxyethylcarbamate acrylate, a new compound corresponding to the general formula (I).

Description

The subject of the invention is a process for -the production of coatings by radiation crosslinking of compositions containing a resin which, can be cured by the polymerisation of the double bonds 2XXC = Cn2 and a reactive diluent system. It also relates to the acrylate of isopropyl beta-hydroxyethylcarbamate, a new compound which may especially be employed in the production of coatings by radiation crosslinking.

Coating means a polymerised film coating a 10 support such as wood, paper, a metal, a plastic or inorganic substance.

Resin which can be cured by the polymerisation of the double bonds = CH2 means an oligomer or a mixture of oligomers generally having at least one"~"^:C = CH2 end group or side group, and which crosslinks through these groups by suitable radiation crosslinking means, especially photocrosslinking.

The compositions employed for the production of coatings combine such a curable resin with a reactive diluent system which enables, in a first stage, the viscosity of the composition to be reduced, the abovementioned resin being too viscous to be applied properly as a film on the support. In a second stage, the reactive diluent system takes part in the polymerisation of the resin (copolymerisation), which enables the desired mechanical properties to be obtained.

These reactive diluent systems, which are miscible with the resin, contain at least ©ne diluent containing one or more unsaturations, which react with the double bonds of the resin.

The choice of th© reactive diluent determines the physical and mechanical properties of the coating. For obvious reasons, this diluent must be of low volatility and non~toxic. Its reactivity with the resin must be high, especially for reasons which will be specified 1 ~ later.

: Many reactive diluent systems have already been described in the literature. Reactive diluents may be classified into two groupss vinyl monomers and acrylic monomers .

The advantage of vinyl monomers such as N-vinylpyrrolidone is that they enable very reactive mixtures to .be obtained. However, they are volatile and very often toxic. Additionally, with N-vinylpyrrolidone, which is the vinyl monomer most frequently employed, coatings which are relatively hygroscopic,, which modifies their mechanical properties, are obtained.

Acrylic monomers do not have this disadvantage5 however, they lead, to less reactive mixtures than with Nvinyl-pyrrolidone.

For example, EP-147,172 describes a composition for the production of coatings by radiation crosslinking, containing, as reactive diluent, a carbamoyloxyalkyl acrylate which corresponds to the general formula Monoacrylates such as E.D.G.A. of formula O C2H5° (CH2 }2° (CH2) 2~°~C~CH"CH2 or, in order to increase the reactivity, multifunctional acrylates such as hexanedediol diacrylate (HDDA) or trimethylol-propan® triacrylate (TMPTA), are also very frequently employed.

Moreover,?. SP-A-0,2.68,226 describes compositions which ar® UV-crosslinkable to obtain abrasion-resistant products. These compositions contain a polymerization shrinkage modifier permitting elimination of the internal stresses induced in the polymer by shrinkage- This modifier may be a polyacrylic carbamic ester of formula rc in which c is an integer between 2 and 15, R3 is H or CH3, R6 is a C\-C6 alkylene group and Rs is a linear polyvalent structure. These compositions also contain, as reactive diluents, acrylic monomers such as acrylic acid, TMPTA, 2-phe.no xysthyl acrylate and 2-carbamoyloxyethyl acrylate or vinyl monomers such as styrene, vinyl chloride and vinyl acetate.

In the field of processes for the production of coatings by radiation crosslinking, the person skilled in the art seeks reactive diluents which enable, on the one hand, the properties of use such as flexibility, adhesion and abrasion resistance to be improved and, on the other hand, the reactivity of the resin-diluent system to be increased.

The Applicant Company has discovered in an unexpected way that the acrylates of hydroxyalkylcarbamate corresponding to the general formula (I) 0 / // # CH2 = C-C -0 —CH - CH — N—C —0 —Rs I III Rl R2 Ra in which R3 represents a hydrogen atom or a methyl group, R2 and R3 represent a hydrogen atom, or an alkyl chain containing 1 to 4 carbon atoms, R4. represents a hydrogen atom, or an alkyl chain containing 1 to 4 carbon atoms, Rg represents an optionally substituted aliphatic chain, containing I to 10 carbon atoms, or alternatively, R* and R, form, with the carbamate group to which they are attached, a 5- or 6-membered ring, 1 may be employed as react ive diluents in the compositions for the production of coatings by radiation crosslinking and/that, in comparison with similar acrylic esters or with the corresponding carbamoyloxyalkyl acrylates described in SP-147,172 they make It possible to achieve, on the one hand, a very significant increase in reactivity and, on the other hand, a better compromise between flexibility and hardness of the coating obtained, i.e. an increased flexibility at a given surface hardness or a greater hardness at a given flexibility. The increased reactivity results either in a decrease in the time of exposure to radiations required to achieve crosslinking, which is very significant, or, at a given exposure time, in a saving of initiator, which enables, in the case of use of systems such as bensophanone/tertiary amine or thioxanthone/tertiary amine, the amine content required to be reduced significantly. Now, it is well known that the presence of an amine causes a yellowing or a significant decrease In hardness of the coating, in addition to the fact that its odour is unpleasant.

The process according to the invention, for the production of coatings by radiation crosslinking of compositions containing a resin which can be cured by the polymerisation of the double bonds ~~~~~ C = CH2 and a reactive diluent system is characterised in that the said system contains at least one reactive diluent corresponding to the general formula (I) o o « C - c~ 0 - CH - ra - N - C < 0 - R5 in „hich »1 R2 *3 Rj represents a hydrogen atom or a methyl group, Rg and Rg represent a hydrogen atom, or an alkyl chain containing 1 to 4 carbon atoms, represents a hydrogen atom, or an alkyl chain containing 1 to 4 carbon atoms, R3 represents an optionally substituted aliphatic,, chain containing 1 to 10 carbon atoms, or alternatively, R* and Rj form, with the carbamate group to which they are attached, a 5- or S-membered ring..

According to a variant of the invention, when represents an aliphatic chain, the latter contains at least one acrylic or methacrylic group.

According to a preferred variant, and represent a hydrogen atom.

According to other preferred variants, r4 represents a hydrogen atom, or alternatively, R. forms, with Rs and the carbamate group, an ox&solidone ring, It is especially preferable that the reactive diluent is the acrylate of beta-hydroxyethyloxazolidone of formula CHn = CH -(CHO)O-N - CH„ 2 , | 2 C CH_ Il\ / 2 0 0 or the acrylate of isopropyl beta-hydroxyethylcarbamate of TO formula CH β CH - C - 0 "(CH2)2 NH zCH3 CH 'CH.

The latter compound is new, whereas, for example, GB-980,393 describes, inter alia, the use of the acrylate of beta-hydroxyethyloxazolidone in lubricating oils and FR-1,090,805 describes that of the methacrylate of ethyl beta-hvdroxyethylcarbamate as intermediate of synthesis of isocyanate esters which can be polymerised.

The reactive diluents corresponding to the abovementioned general formula (I), which can be used for Implementing the process according to th® invention for th® production of coatings by radiation crosslinking, may be synthesised, for example, according to methods described in FSL-1,090,805 and GB-980,393- Example 1 below illustrates such a synthesis.

The process according to the invention is implemented by operating according to conventional working procedure for the production ox coatings by radiation crosslinking of compositions containing a resin which can be .cured by the polymerisation of the double bonds = ¢3¾ and a reactive diluent system.

Th© proportion of constituents in the compositions may vary depending on the mechanical properties sought for the coating.

According to one variant of the invention, a reactive diluent corresponding to the general formula (I) mentioned above Is employed as the only reactive diluent.

According to other variants, it may be employed mixed with at least one other reactive diluent, for example with an acrylic reactive diluent, or mixed with a non-reactive diluent.

A mixture of reactive diluents corresponding to the general formula (I) may also be employed.

The proportion of the different constituents per 100 parts by weight of the composition is generally within the following limitss Resins 30 to 80% Reactive diluent system; 70 to 20% The resins which can be cured by the polymerization of the double bonds C = GH2 which can be employed, for implementing the process according to the invention may have one or more unsaturations, preferably 0.2 to 5 equivalents of unsaturations per kg of resin. More precisely, the resins which are suitable for implementing the invention include polyester/acrylic resins, pο 1yether/acry1ic resins and polycarbonate/acrylic resins which are obtained by the reaction of acrylic or methacrylic acid with a polyhydric alcohol, unsaturated urethane resins resulting from the reaction of a polyhydric alcohol with an unsaturated ester- containing an active hydrogen via an aliphatic or aromatic poly-isocyanate and epoxy/acrylic resins which may be obtained by the reaction of acrylic or methacrylic acid with epoxide compounds.

As examples of unsaturated esters containing an active hydrogen, there may he mentioned hydroxyalkyl acrylates or methacrylates and, in particular, 2~hydroxyefchyl acrylate or methacrylate and 2-hydroxypropyl acrylate or methacrylate.

Among suitable polyisocyanates,, there may be mentioned, by way of indication, the following compounds s 2,4- and 2, S-diisocyanntotoluene, 2,4- and 2, β-diisocyanato-l-methylcyclohexane, 4,4'-diisocyanatodicvclohexylmethane, diisoeyanatoisophorone, hexamethvlene diisocyanate, diisocyanato-2,2,4-trimethylhexamethylen®, biurets based, for example, on hexamethylene diisocyanate and their mixture.

Among polyhydric alcohols which are suitable for the present invention, there may be mentioneds hydroxvlated polyepichlorohydrins, hydroxvlated polybutadienes, hydroxytelechelic polycarbonates obtained by the phosgenation or th® transesterification of aliphatic, alicyclic or aromatic diols or triols, either alone or as mixtures, polycaprolactones, hydroarytelechelic polyesters obtained by the reaction of a polyhydric alcohol (such as ethylene glycol, diethylene glycol, glycerol, butane-1,3-diol, propoxylafed bisphenol A, sorbitol and the like) with a polycarboxylic acid or its anhydride or its ester (such as adipic acid and maleic, succinic or terephthalic anhydride), polyether polyols obtained by the addition of an alkylene oxide (such as ethylene oxide, propylene oxide or tetrahydrofuran) with the polyhydric alcohol as mentioned above, polyether esters such as polydiethylene glycol adipate and polytriethylene glycol adipate in which the polyether replaces a part of th® glycol, and hydroxytelechelic polyurethanes formed starting with polyhydric alcohols as mentioned above and polyisocyanates as those mentioned’above.

Among suitable epoxide compounds, there may be mentioned, for example, diglyoidyl ether of bisphenol A (DGBBA).

For isaplementing reasons, it is preferable to choose linear resins» It is also preferable that these resins have a molecular weight of between 600 and 10,000., In order to implement the process according to I· the invention, the composition containing the resin and the reactive diluent system is radiation crosslinked after it is applied to the support to be coated in the form of a thin film, by a means known per se. The thickness is preferably less than 0.2 mm.

As radiation, an electromagnetic radiation, an electron bombardment or a nuclear radiation may, for example, be employed.

A UV radiation is preferably employed, in the presence of a photoinitiator.

As non-limiting examples of photoinitiators, there may be mentioned benzoin ethers and phenone derivatives such as benzophenone or diethoxyacetophenone, alone (for example the photoinitiator marketed by CIBA under the trade mark IRGAGURE 551" or the photoinitiator marketed by MERCK under the registered trade mark DAROCUR 1115) or in combination with a tertiary amine, for example methyldiethanolamine.

A preferred method of implementing the invention consists in passing the support coated with the composition under a UV lamp, at a desired speed.

The composition employed for implementing the process according to the invention may contain all the additives which are commonly used in coating compositions which can be radiation crosslinked, especially agents for adjusting the gloss of the coating surface, surfactants, fillers or colours.

Th® examples below illustrate the invention without, however, limiting it.

Example Is Synthesis of the acrylate of isopropyl betahydro»? ethylcarbamate.

This synthesis is carried out in 2 stages; Stage 1: o cr2ci2 ch3 o \ v \ e C&-O-C * (ΟΪ-3) ?OR*K->CO-> -CR-O-C-NH/ \ ' / CH3 Ci ch3 (CH2)2"OS * KC1 * XSCO3 .0 ch2 + η2ο Stage 1; The following are mixed with a 50-1 reactor carrying a jacket through which ethylene glycol at -lO’C is circulated: 1 of methylene chloride 6900 g (50 moles) of potassium carbonate 5 1 of water 3202 g (52.5 moles) of ethanolamine.

The mixing temperature is of the order of 0°G. 6125 g (50 moles) of isopropyl chloroformate are then added gradually.

After filtering and decanting the phases, the organic phase is recovered and neutralized with water in order to remove therefrom the traces of potassium salts formed. After evaporating off the methylene chloride, 6300 g of isopropyl beta-hydroxyethylcarhamate, which corresponds to a yield of 86% are obtained» The product was identified by IR spectrometry and NMR spectrometry and its purity (97%) was determined chemically (hydroxyl content and nitrogen content).

Stage 2s The following are mixed, at ambient temperature and with stirring, in a, 20-1 reactor carrying a jacket through which oil is circulated: 3381 g (23 moles) of isopropyl beta-hydroxyethyl· carbamate 1740 g (24.15 moles) of acrylic acid 1 of toluene 2.3 g of para~methoxyphenol.

The temperature is raised to 75 G by circulating hot oil in the Jacket of the reactor. 360 g (3.6® moles) ί 1 of 98% sulphuric acid are then added. A partial vacuum is created within the reactor so as to recover aseotropically the water formed during the esterification reaction.

After approximately 4 h of reaction,, 450 g (4.6 moles) of sodium carbonate are added in order to remove any residual acidity from the medium.

The reaction medium is then washed in order to solubilise the salts formed during the reaction with sodium carbonate.

The toluene and volatile products are evaporated off under reduced pressure. 3136 g of acrylate of isopropyl beta-hydroxyethylcarbamate, identified by IR spectrometry and NMR spectrometry, are thus obtained, which corresponds to a yield of 68% relative to the isopropyl bete-hydroxyethylcarbamate.

The purity of the product, which is greater than 90%, was determined by potentiometry and elemental analysis .

It is a clear liquid with the following physical properties: density: 1.11 refractive index at 25 C: 1,455 boiling point: 115°C at 2 mm Hg viscosity at 25°C: 70 xaPa.s.

Examples 2 to 20s Production of coatings with compositions containing th® acrylate of isopropyl beta-hydroxyethylcarbamate as reactive diluent. Comparisons with coatings obtained according to known processes.

A/ Examples 2 to 7 - comparison of reactivity Tests are carried out with th® diacrylic urethane resin marketed by SNPS under the registered trade mark ACTIIANS 20" (Act. 20) of molecular weight approximately 1300,[ obtained starting with: 2 n moles of 2-hydroxyethyi acrylate n moles of isophorone diisocyanate (IPDI) n moles of polyethylene glycol adipate.

The photoinitiator employed is that marketed by under th® ' trade mark IRGACURE 651 CIB& (Irg. 651) .

Xn Example 2, the reactive diluent is a bifunctional acrylic compound, hexanediol diacrylate (HDDA) .

In Example 3, the reactive diluent is a monofunc5 tional acrylate of the abovementioned formula (EDGA).

In Example 4, the reactive diluent is N-isopropyl carbamoyloxyethylacrylate of formula o CHj - CH - C -O-ICH-jH ch3 C3s \ C3t3 (diluent no. 1) In Example 5, the reactive diluent is, according 10 to the invention, the acrylate of ispropyl beta-hydroxyethylcarbamate (diluent no. 2).

In Example 6, the reactive diluent is, according to the invention, a mixture of acrylate of isopropyl beta-hydroxyethylcarbamate (diluent no. 2) and HDDA.

In Example 7, the reactive diluent is a monofunctional acrylate, phenoxyethyl acrylate (P.E.A.).

After mixing the resin, the reactive diluent system and the photoinitiator, a film of the composition thus obtained is deposited on a support which is then fo passed at different speeds under a UV lamp which has a linear power of 80 W/em, along a direction perpendicular to the direction formed by the length of the lamp.

The proportion of th© various constituents in the compositions, expressed In parts by weight, and the speed of passing under the ϋν lamp required for the coating to be dried to touch are given in Table 1 belows Example no. Constituents 2 3 4 5 6 7 Act. 20 50 50 50 50 50 50 HDDA 50 - - - 25 EDGA - 50 - - - PEA - - - - - 50 Diluent no. 1 - - 50 - - - Diluent no. 2 - - - 50 25 - Irg. 651 5 5 5 5 5 5 1 Speed in m/min 10 1.25 3.3 10 10 5 TABLE 1 Although the reactive diluent employed in the present invention (diluent no. 2) is monofunctional, it has a reactivity similar to that of the bifunctional monomers used until now.

The reversal of the carbamate unit relative to the known reactive diluent (diluent no. l) described In EP-147,172 causes, in an unexpected way, a very significant increase in reactivity. 3/ Examples 8 to 11 - Comparison of mechanical properties of the coatings obtained.

The tests are carried out as in Examples 2 to 7.

Table 2 below specifies the nature and the proportion by weight of the constituents in the composi25 tions employed as well as the results obtained in each test.

Determinations of mechanical properties were carried out using standardized H3 test-pieces, in the I 4 form of a 150 film which is dried and stabilised for 3 days .

The photoinitiator employed is that marketed by MERCK under the registered trade mark DAROCUR 1116".

TPGDA means tripropyleneglycol diacrylate, it is a known reactive diluent which is frequently used.

Example no. Constituents 8 9 10 11 Act. 20 70 70 70 70 EDGA 30 «β - - PEA - 30 - - TPGDA - - 30 J Diluent no. 2 - - 30 Darocur 1116 4 4 4 4 . Breaking stress (in MPa) 5 20 35 15 Breaking elongation (in %) 27 79 22 93 -. .. - - - --- - - _ _ f TABLE 2 Th© reactive diluent (diluent no. 2) employed within the scope of the present invention enables films with a higher breaking elongation to be obtained, which results, in practice, in a greater flexibility.

C/ Examples 12 to 19 - Comparison of viscosity of the compositions.

Table 3 below specifies the nature and the proportion by weight of the constituents in the composition studied as well as the results obtained-for viscosity (rotating spindle method at 25eC).

Example no. Constituents 12 13 14 15 lo 17 18 IS Act. 20 80 80 80 - - 50 50 TPGDA 20 = 100 - - - - TMPTA 20 . - 100 - 50 - Diluent no. 2 - - 20 - - 100 - 50 Viscosity (in mPa.s) 105 106 130000 15 80 70 12000 5700 _ TABLE 3 These results demonstrate the excellent and surprising diluting power of ths reactive diluent no. 2 according to the invention. In fact, it is observed in an unexpected way that on the one hand, a mixture with the resin Act. 20 (Example 14) which has a viscosity of the same order of magnitude (slightly greater) as that of the mixture In Example 12 is obtained, whereas the viscosity of the reactor diluent no. 2 is 5 times greater than that of TPGDA and, on the other hand, mixtures with the resin Act. 20 (Examples 14 and 19) with a viscosity which is very significantly less than those for the corresponding mixtures (Examples 13 and 18) with THPTA are obtained, whereas the viscosity of the reactive diluent no. 2 is of the same order of magnitude as that of TMPTA.

D/ Example-20 - Study of th© light stability of a composition employed in the process according to the invention.

A 50/50 mixture of Act. 20 and diluent no. 2 has a yellowing Index of less than 1 after 500 hours under a QUV panel.

Examples 21 to 32 Production of coatings with compositions containing the acrylate of beta-hydroxyethyloxazolidone as reactive diluent (diluent no. 3). Comparison with coatings obtained according to known processes.

A/ Examples 21 to 25 - Comparison of reactivity of the compositions and the hardness of coatings.

These tests were carried out as in Examples 2 to 7.

Table 4 below gives the data and the results relating to each example.

Example no. Constituents 21 22 23 24 25 Act. 20 50 50 50 50 50 HDDA - 50 - 25 25 EDGA 50 - 25 - Diluent no. 3 - - 50 - 25 Irg. 651 5 5 5 5 5 Speed m/min 1.25 10 10 10 20 Persos hardness40. 80 - 200 —L~J TABLE 4 Although the reactive diluent employed as the only monomer in the present invention (diluent no. 3) is monofunctional, it has a reactivity similar to that of I the bifunctional monomers used until now.

Moreover, an unexpected synergistic effect is ϊ 7 observed when diluent 3 is mixed with HDDA, the reactivity under these conditions being greater than that obtained with each of the 2 reagents used separately.

With regard to hardness, the replacement of EDGA, which is the commonly used monofunctional reagent, with the monofunctional reactive diluent no. 3 according to the invention enables the hardness to be doubled, at a given flexibility.

B/ Examples 26 to 29 - Comparisons of mechanical properties of the coatings obtained.

The tests are carried out as in Examples 8 to 11. Table 5 below gives the data and the results relating to each example. i ' Ί Example no. Constituents 26 27 28 29 Act. 20 70 70 70 70 EDGA 30 - - PEA - 30 - - TPGDA - - 30 Diluent no. 3 - - - 30 Darocur 1116 4 4 4 4 Breaking stress (in MPa) '5 20 35 28 Breaking elongation (in %) 27 79 | 22 82 I TABLE 5 It Is observed that the diluent no. 3 according to the invention enables the best compromise between breaking stress and breaking elongation to be obtained. C/ Example 30 and 31 - Comparison of viscosity of the compositions .

Table 6 below specifies the nature and the proportion by weight of the constituents in the compositions studied as well as the results obtained for viscosity (rotary spindle method at 25°C), in comparison with the Examples 11, 12, 14 and 15 mentioned above.

Example no. Constituents 30 31 12 13 15 16 Act. 20 80 - 80 80 - - TPGDA = - 20 - 100 - TMPTA - - - 20 100 Diluent no. 3 20 100 viscosity (in mPa.s) 135000 50 100000 1000000 15 80 TABLE 6 These results demonstrate the excellent and surprising diluting power of the reactive diluent no. 3 according to the invention. In fact, it is observed, in a surprising way, that a mixture with the resin Act. 20 (Example 30) which has, on the one hand, a viscosity of the same order of magnitude (slightly greater) as that for the mixture In Example 12 to be obtained whereas the viscosity of the reactive diluent no. 3 is more than 3 times greater than that of TPGDA and, on the other hand, a viscosity which is 6 times lower than that of the corresponding mixture (Example 13) with TMPTA to be obtained, whereas the viscosity of the reactive diluent no. 3 is only about half that of TMPTAϊ 9 D/ Example 32 - Study of light stability of a composition employed in the process according to the invention.

A 50s25 mixture of Act. 20 and diluent no. 3 has a yellowing index of less than 2 after 500 h under a Quiz panel.

Examples 33 and 34 Production of a coating with a composition containing the methacrylate of isopropyl beta-hydroxyethyl -carbamate (diluent no. 4) as reactive diluent. Comparison of reactivity with a composition containing Nisopropyl carbamoyloxyethyl methacrylate (diluent no. 5).

These tests were carried out as in Examples 2 to 7.

Table 7 below gives the data and the results relating to each example.

Example no. Constituents 33 - - 1 34 Act. 20 50 50 Diluent no. 4 50 - Diluent no. 5 - 50 Irg. 651 5 5 ’ · ' Speed m/min _ 3.0 2.2 L.

TABLE 7 The reversal of the carbamate unit relative to the known reactive diluent no. 5 results In. an Increase ia reactivity.

Claims

1., Process for the production of coatings by radiation crosslinking of compositions containing a resin which can be cured by the polymerisation of the double bonds /C = CH 2 and a reactive diluent system which is characterised in that the said system contains at least one reactive diluent corresponding to th© general formula (I) I) CH.2 = c - c - o - ch - ch I I I Rl R2 R3 ί Ά '1 R4 Rs in which R x represents a hydrogen atom or a methyl group, R 2 and R 3 represent a hydrogen atom, or an alkyl chain containing 1 to 4 carbon atoms, R,i represents a hydrogen atom, or an alkyl chain containing 1 to 4 carbon atoms , R 3 represents an optionally substituted aliphatic chain containing 1 to 10 carbon atoms,· or alternatively, R 4 and R 3 form, with the carbamate group to which they are attached, a 5- or 6-membered ring.

2. Process according to Claim 1, characterised in that R 2 and R 3 represent a hydrogen atom.

3. Process according to any one of the preceding claims, characterised in that R 6 represents a hydrogen atom.

4. Process according to any on® of the preceding claims, characterised in that R 3 forms, with R* and the carbamate group, an oxazolidone ring.

5. Process according to either ox Claims 1 and 2, characterised In that the reactive diluent corresponding to the general formula (1 Ji is chosen fro®, the group consisting of the acrylate of beta-hydroxyethyloxazolidone and the acrylate of Isopropyl beta-hydroxyethylcarbamate .

6. Process according to any one of the preceding claxsts, characterised In that the reactive diluent system contains at least one reactive diluent other than that V 2 fl corresponding to the general formula (I).

7. Process according to any one of the preceding claims, characterised in that the reactive diluent system contains a mixture of reactive diluents of general j 5 formula (I). «

8. Process according to any one of the preceding claims, characterised in that the composition contains between 30 and 80% by weight of resin which can be cured and between 70 and 20% by weight of reactive diluent 10 system.

9. Process according to Claim 1, characterised in that the resin which can be cured is chosen from the group consisting of polyester/acrylic resins, epoxy/acrylic resins, polycarbonate/acrylic resins, polyether/aery15 lie resins and unsaturated urethane resins.

10. Process according to any one of Claims 1 to 9, characterised in that the resin which can be cured is linear and is of molecular weight between 600 and 10,000.

11. Process according to any one of the preceding 20 claims, characterised in that the radiation crosslinking is carried out by UV radiation, in the presence of a photo-initiator.

12. The acrylate of isopropyl beta-hydroxyethylcarbamate. 25

13. A process according to claim 1 for the production of coatings by radiation cross-linking, substantially as hereinbefore described and exemplified.

14. A coating whenever produced by a process claimed in a preceding claim.