WO2001044377A1

WO2001044377A1 - Coating composition and novel thiol included therein

Info

Publication number: WO2001044377A1
Application number: PCT/SE2000/002437
Authority: WO
Inventors: Nicola Rehnberg; Ulf Annby; Carl-Axel SJÖGREEN; Robert S. Davidsson
Original assignee: Perstorp Specialty Chemicals Ab
Priority date: 1999-12-16
Filing date: 2000-12-06
Publication date: 2001-06-21
Also published as: SE9904609L; AU2241601A; SE9904609D0

Abstract

A radiation curable coating composition based on thiol-ene chemistry is disclosed. The coating composition comprises at least one novel thiol having a mercapto functionality of at least two and at least one compound having an alkenyl functionality of at least two. Said novel thiol is a reaction product between at least one alkoxylated di, tri or polyhydric alcohol and at least one mercapto carboxylic acid and said alkenyl functional compound is preferably an allyl or methallyl ether of a di, tri or polyhydric alcohol and/or an ester of an unsaturated carboxylic acid, such as a cycloalkene or a bicycloalkene carboxylic acid, and a di, tri or polyhydric alcohol. In a further aspect the present invention refers to the novel thiol included in said coating composition.

Description

COATING COMPOSITION AND NOVEL THIOL INCLUDED THEREIN

The present invention relates to a radiation curable coating composition and a novel thiol included therein. The coating composition is based on thiol-ene chemistry and comprises at least one thiol having a mercapto functionality of at least two and at least one compound having an alkenyl functionality of at least two. Said thiol is a reaction product between at least one alkoxylated di, tri or polyhydric alcohol and at least one mercaptocarboxylic acid and said alkenyl functional compound is preferably an allyl or methallyl ether of a di, tri or polyhydric alcohol or an ester of an unsaturated carboxylic acid and a di, tri or polyhydric alcohol.

A main use for thiols, especially aliphatic thiols, is as polymerisation modifiers in for instance emulsion polymerisation. Low molecular weight alkanethiols, such as methanethiol, ethanetiol and propanethiol, are for example used as intermediates in the manufacture of substances such as insectisides and herbicides and as odorants in petroleum based gases and liquids. Furthermore, polythiol compounds find a use in for instance epoxy curing agents. Polysulphide polymers having terminal thiol groups are normally prepared from dihalo compounds and used inter alia in sealant and adhesive applications. Mercaptoacid esters and alkanethiols are inter alia known as intermediates in the manufacture of sulphides used for polymer resin stabilisation. Thiocarboxylic acid or anhydride substituted unsaturated α-olefine polymers are useful as oil-soluble lubricating oil additives as disclosed in for instance US patent 5,225,091. The manufacture, physical properties and use of thiols are thoroughly disclosed in a number of handbooks and encyclopaedias such as Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd. ed., 1978, vol. 22, pp. 846-964.

Radiation curable compositions comprising unsaturated and thiol monomers were developed in the early 1970s. The thiol-ene reaction, the photoinitiated 1 ,2-addition of thiols to unsaturated olefins, is thus known to produce resistant and durable surface coatings. The thiol-ene reaction does not suffer from oxygen inhibition which is a very valuable property, particularly when curing very thin films. The cure is normally rapid enabling for instance high line speeds in coating equipment. A major drawback for the utilisation of the thiol-ene chemistry in applications such as coatings is the presence of low molecular weight thiols. These thiols are known to have a very unpleasant odour which can be detected by the human nose at very low concentrations. The thiol-ene chemistry and its use in various polymer and polymer producing compositions is by now well-known in the art and inter alia disclosed in a number of patents and patent applications, including:

- US patent 4,234,676 disclosing a composition which primarily is used in the production of printing plates and which composition comprises an unsaturated polymer, a cross linkable monomer, a polythiol and a curing agent, - US patent 4,808,638 disclosing a composition comprising a norborene resin, a polythiol and a free radical initiator,

- US patent 4,139,385 disclosing a composition comprising a polyolefme, a polythiol and an onium salt photoinitiator, and

- US patent 5,876,805 disclosing a thiol-ene composition comprising a monomer or oligomer having a plurality of alkenyl groups, a compound having a plurality of thiol groups and an acyl phosphine oxide photoinitiator.

The present invention quite surprisingly provides a coating composition based on thiol-ene chemistry and comprising a thiol of a novel molecular structure, which thiol exhibits reduced and even eliminated odour. The coating composition comprises at least one thiol having a mercapto functionality of at least two, at least one unsaturated compound having an alkenyl functionality of at least two, whereby said composition has an average mercapto and/or alkenyl functionality of more than two, and at least one curing agent and/or free radical initiator.

The novel thiol of the present invention is a compound of Formula (I)

wherein R¹ and R² independently are alkyl, aryl, aralkyl or alkaryl, whereby R¹ is derived from an alcohol having a hydroxyl functionality (f) of 2 to 12, n and p are independent integers and at least 1 , (m + q) gives an integer between 1 and 24, whereby m and q independently are

0 or an integer being at least 1, y is an integer and at least 2 and x is (f - y). The novel thiol is a reaction (esterification) product between at least one di, tri or polyhydric alcohol, having at least one alkoxy group, and at least one mercapto carboxylic acid. The reaction product is obtained in a synthesis employing a molar ratio said alcohol to said mercapto carboxylic acid yielding an ester (a thiol) having said mercapto functionality of at least two and being a compound of said Formula (I). Said alkyl is suitably and independently a linear or branched alkanyl, alkenyl, alkynyl, cycloalkanyl, cycloalkenyl or cycloalkynyl.

Said di, tri or polyhydric alcohol having at least one alkoxy group is preferably a reaction product between at least one alkylene oxide or corresponding glycol and at least one 2-substituted or 2,2-substituted 1,3-propanediol or a reaction product between at least one alkylene oxide or corresponding glycol and at least one dimer, trimer or polymer of at least one 2-substituted or 2,2-substituted 1,3-propanediol. Said at least one alkylene oxide is suitably selected from the group consisting of ethylene oxide, propylene oxide, butylene oxide and/or phenylethylene oxide. Suitable 2-substituted and 2,2-substituted 1 ,3-propanediols are for instance found among 2-alkyl- 1 ,3-propanediols, 2, 2-dialkyl- 1,3-propanediols, 2-hydroxy- alkyl- 1,3-propanediols, 2-alkyl-i -hydroxyalkyl-l,3-propanediols and 2,2-dihydroxyalkyl- - 1,3-propanediols.

The di, tri or polyhydric alcohol having at least one alkoxy group is in especially preferred embodiments a reaction product between at least one alkylene oxide, such as said ethylene oxide, propylene oxide, butylene oxide and/or phenylethylene oxide, or a to said alkylene oxide corresponding glycol and neopentyl glycol, glycerol, diglycerol, trimethylolethane, trimethylolpropane, ditrimethylolethane, ditrimethylolpropane, pentaerythritol or dipentaerythritol.

The mercaptocarboxylic acid is, in preferred embodiments of the novel thiol, an aliphatic or aromatic acid, such as mercaptoacetic acid, mercaptopropionic acid, mercaptobenzoic acid and mercaptosuccinic acid or anhydride.

The unsaturated compound having an alkenyl functionality of at least two, and being included in the coating composition of the present invention, is in preferred embodiments an allyl or methallyl ether of a di, tri or polyhydric alcohol, whereby said alkenyl functionality is an allyl functionality, or an ester of an unsaturated carboxylic acid and a di, tri or polyhydric alcohol, which ester has an alkenyl functionality of said at least two.

Said allyl and methallyl ether is suitably found among allyl and methallyl ethers of 2-substituted and 2,2-substituted 1,3-propanediols or among allyl and methallyl ethers of dimers, trimers and polymers of 2-substituted and 2,2-substituted 1 ,3-propanediols. Suitable 2-substituted and 2,2-substituted 1,3-propanediols are for instance 2-alkyl- 1,3-propanediols, 2,2-dialkyl- 1 ,3-propanediols, 2-hydroxyalkyl- 1 ,3-propanediols, 2-alkyl-2-hydroxyalkyl- -1,3-propanediols, 2,2-dihydroxyalkyl- 1,3-propanediols, 2-hydroxyalkoxy- 1,3-propanediols, 2-alkyl-2-hydroxyalkoxy- 1,3-propanediols and 2,2-dihydroxyalkoxy- 1,3-propanediols.

Said allyl or methallyl ether is in especially preferred embodiments a diallyl and/or dimethallyl ether of neopentyl glycol, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol, a triallyl and/or trimethallyl ether of glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol, and/or a tetraallyl and/or tetramethallyl ether of pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol.

The unsaturated ester (ester of said unsaturated carboxylic acids) is suitably an ester of a cycloalkene or bicycloalkene carboxylic acid, such as cyclohexene or bicycloheptene carboxylic acid, and a di, tri or polyhydric alcohol as disclosed above for allyl ethers. The ester is accordingly and preferably selected among esters of said carboxylic acids and 2-substituted and 2,2-substituted 1,3-propanediols or among said esters of said carboxylic acids and dimers, trimers and polymers of 2-substituted and 2,2-substituted 1,3-propanediols. Suitable 2-substituted and 2,2-substituted 1,3-propanediols are for instance 2-alkyl- 1,3-propanediols, 2,2-dialkyl-l ,3-propanediols, 2-hydroxyalkyl-l ,3-propanediols, 2-alkyl-2-hydroxyalkyl- - 1,3-propanediols, 2,2-dihydroxyalkyl-l,3-propanediols, 2-hydroxyalkoxy- 1,3-propanediols, 2-alkyl-2-hydroxyalkoxy- 1,3-propanediols and 2,2-dihydroxyalkoxy- 1,3-propanediols.

Said unsaturated ester is in especially preferred embodiments a diester of neopentyl glycol, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol, a triester of glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol, and/or a tetraester of pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol.

Said at least one curing agent and/or free radical initiator, included in the coating composition of the invention, is preferably a photoinitiator and/or accelerator selected from the group consisting of phenone derivatives, such as benzophenone, bezoine derivatives, bezil ketals and acylphosphine oxides. Further embodiments of the curing agent and/or free radical initiator include oniumsalts such as iodonium and sulphonium salts.

In a further aspect, the present invention refers to a novel thiol as herein disclosed. The thiol is a reaction product between at least one di, tri or polyhydric alcohol, having at least one alkoxy group, and at least one mercapto carboxylic acid. The reaction (esterification) product is obtained at a molar ratio said alcohol to said mercaptocarboxylic acid yielding an ester (a thiol) having a mercapto functionality of at least two. Preferred embodiments of the novel thiol and the alcohol as well as the mercaptocarboxylic acid from which it is derived are as disclosed above for the thiol included in the coating composition of the present invention.

When coating formulations containing thiols based on di, tri and polyhydric alcohols having at least one alkoxy group, such as ethoxylated and/or propoxylated pentaerythritol and trimethylolpropane, were being made up, the lack of smell was very noticeable. In addition, cured coatings were free from the odour of thiols. The cured films exhibited good gloss. What is most surprising is the high hardness values of films obtained from coating formulations comprising thiols in accordance with the present invention. The films were not, as could be anticipated, softened by the polyether component of these compounds. The present invention discloses that alkoxylated di, tri and polyohydric alcohols can be esterified with mercaptocarboxylic acids to give thiols of very low or even no odour that can be used with benefit in the thiol-ene reaction.

These and other objects and the attendant advantages will be more fully understood from the following detailed description, taken in conjunction with appended Examples 1-51, wherein: Examples 1-3 refer to syntheses of thiols according to embodiments of the present invention, Examples 4-19 refer to coating formulations comprising the thiols of Examples 1-3 as well as pentaerythritol tetrakis(3-mercaptopropionate) for comparative reasons and wherein Examples 20-51 refer to evaluations of films obtained from the coating formulations of Examples 4-19.

While particular embodiments of the invention are shown, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

EXAMPLE 1-3

Mercaptopropionates were in a process as substantially disclosed in

- Canadian Journal of Chemistry, June 1, 1967, vol. 45, no. 1 1, "Allene Chemistry. VIII. Diaddition of thiol compounds to allene" ppl 173-1 184 - "Expertimental" page 1169, and

- Synthesis, March 1995, "Synthesis of 12- and 13 Membered Sulur-Containing Lactones by Homolytic Macrocyclization of Mercaptoacetic Esters with alkynes", pp 307ff, "Esterifi cation of 1,2- and 1.3-Diols With Mercapto Acid; General Procedure:" page 308, produced from 3-mercaptopropionic acid and

Example 1 : Ethoxylated pentaerythritol (Polyol PP50, Perstorp Chemicals AB, Sweden) having an ethoxylation degree of 5 moles of ethylene oxide on 1 mole of pentaerythritol, Example 2: Ethoxylated pentaerythritol (Polyol PP150, Perstorp Chemicals AB, Sweden) having an ethoxylation degree of 15 moles of ethylene oxide on 1 mole of pentaerythritol, and Example 3: Ethoxylated trimethylolpropane (Polyol TP70, Perstorp Chemicals AB, Sweden) having an ethoxylation degree of 7 moles of ethylene oxide on 1 mole of trimethylolpropane.

The following products were yielded: Example 1 : Polyol PP50 tetrakis(3-mercaptopropionate), Example 2: Polyol PP150 tetrakis(3-mercaptopropionate), and Example 3: Polyol TP70 tris(3-mercaptopropionate). EXAMPLES 4-19

Coating formulations were made up using the following raw materials: Thiols: Pentaerythritol tetrakis(3-mercaptopropionate) * ' Mercapto funct. 4 Polyol PP50 tetrakis(3-mercaptopropionate) *² Mercapto funct. 4 Polyol PP150 tetrakis(3-mercaptopropionate) *³ Mercapto funct. 4 Polyol TP70 tris(3-mercaptopropionate) *⁴ Mercapto funct. 3

Alkenyl compounds: Pentaerythritol triallyl ether *⁵ Allyl funct. 3

Trimethylolpropane diallyl ether *⁵ Allyl funct. 2

Photoinitiators: (2-methyl-2-hydroxy)propiophenone *⁶

Benzophenone *⁷

*' Commercially available product (Aldrich-Chemie, Germany).

*² As obtained in Example 1.

*³ As obtained in Example 2.

*⁴ As obtained in Example 3.

*⁵ Commercially available product (Perstorp Chemicals AB, Sweden).

*⁶ Commercially available product (Darocure^® 1173 - Ciba, Switzerland)

*⁷ Commercially available product (Aldrich-Chemie, Germany).

The thiol-ene reaction is a stoicheometric reaction and formulations were therefore made up in which the concentration of thiol groups matched the concentration of the alkenyl (allyl) groups. The thiol groups were titrated to obtain the molecular weight of the thiols. From these molecular weights, the amount of mercapto groups in 100 g of respective thiol was calculated and hence the corresponding weight of respective allyl compound necessary to match the thiol groups. The formulations were made up by mixing respective thiol with respective allyl compound and subsequently adding the photoinitiator. The formulations were, in order to avoid unnecessary parameters in the evaluation, not surface optimised by addition of for instance wetting, flow, levelling and similar additives. In order to ascertain the addition level of the photoinitiator, a coating formulation comprising pentaerythritol tetrakis(3-mercapto- propionate) and pentaerythritol triallyl ether was used. (2-methyl-2-hydroxy)propiophenone was incorporated into the mixture at 0.5, 1, 2, 3 and 4% levels (by weight) and films were cured using a conveyor belt system in which the sample was passed under a 300 Watt H-bulb (equivalent to a medium pressure mercury lamp) and the infrared spectra recorded on a Digilab FTS-60 FTIR spectrometer equipped with a UMA300A microscope. Cure was observed at the lowest conveyor belt speed with 0.5% (by weight) initiator, but in order to ensure complete cure 4% (by weight) of initiator was incorporated in all formulations but one.

Viscosities were measured using a Brookfield (DV III programmable Rheometer) cone and plate viscometer at a constant shear rate and the result is given in table 1.

Table 1.

Compound key:

PTM = Pentaerythritol tetrakis(3-mercaptopropionate). TP70 = Polyol TP70 tris(3-mercaptopropionate). PP50 = Polyol PP50 tetrakis(3-mercaptopropionate). PP150 = Polyol PP150 tetrakis(3-mercaptopropionate). PETE = Pentaerythritol triallyl ether. TMPDE = Trimethylolpropane diallyl ether. MHPP = (2-methyl-2-hydroxy)propiophenone. BP = Benzophenone. EXAMPLES 20-35

Films of 50 and 100 μm were produced from the coating formulations of Examples 4-11 using K Bars to lay down said films on aluminium slides. Curing was carried out with a UV Products Ltd. curing tunnel equipped with a Fusion System Ltd. 300 Watts H-bulb and at a belt speed of 12.8-13.0 m/min. Obtained films were subjected to a hardness test using a Kόnig pendulum and to a methyl ethyl ketone solvent rub test. The result is given in Table 2.

Table 2

* Comparative Example. Compound key: See Table 1.

EXAMPLES 36-51

Films of 50 and 100 μm were produced from the coating formulations of Examples 12-19 using K Bars to lay down said films on aluminium slides. Curing was carried out with a UV Products Ltd. curing tunnel equipped with a Fusion System Ltd. 300 Watts H-bulb and at a belt speed of 12.8-13.0 m/min. Obtained films were subjected to a hardness test using a Kόnig pendulum and to a methyl ethyl ketone solvent rub test. The result is given in Table 3.

Table 3

* Comparative Example. Compound key: See Table 1.

Claims

A radiation curable coating composition having an average mercapto and/or alkenyl functionality of more than two characterised in, that it comprises i) at least one thiol having a mercapto functionality of at least two and a general formula of

O

H-(O-CnH₂n)m-0 -Rl- -O— (C_pH _p— O)_q— C-R2— SH

wherein R¹ and R² independently are alkyl, aryl, aralkyl or alkaryl, whereby R¹ is derived from an alcohol having a hydroxyl functionality (f) of 2 to 12, n and p are independent integers and at least 1, (m + q) gives an integer between 1 and 24 whereby m and q independently are 0 or an integer being at least 1 , y is an integer and at least 2 and x is (f - y), ϋ) at least one compound, having an alkenyl functionality of at least two, and iii) at least one curing agent and/or free radical initiator.

A coating composition according to Claim 1 characterised in, that said alkyl independently is a linear or branched alkanyl, alkenyl, alkynyl, cycloalkanyl, cycloalkenyl or cycloalkynyl.

A coating composition according to Claim 1 or 2 characterised in, that said thiol is a reaction product between at least one di, tri or polyhydric alcohol, having at least one alkoxy group, and at least one mercapto carboxylic acid, said reaction product being obtained at a molar ratio yielding a thiol having said mercapto functionality of at least 2.

A coating composition according to Claim 3 characterised in, that said di, tri or polyhydric alcohol having at least one alkoxy group is a reaction product between at least one alkylene oxide or corresponding glycol and at least one 2-substituted or 2,2-substituted 1,3-propanediol.

A coating composition according to Claim 3 characterised in, that said di, tri or polyhydric alcohol having at least one alkoxy group is a reaction product between at least one alkylene oxide or corresponding glycol and at least one dimer, trimer or polymer of at least one 2-substituted or 2,2-substituted 1,3-propanediol.

A coating composition according to Claim 4 or 5 characterised in, that said 2-substituted or 2,2-substituted 1,3-propanediol is a 2-alkyl- 1,3-propanediol, a 2,2-dialkyl-l,3-propanediol, a 2-hydroxyalkyl- 1,3-propanediol, a 2-alkyl-2-hydroxy- alkyl- 1,3-propanediol or a 2,2-dihydroxyalkyl- 1,3-propanediol.

7. A coating composition according to any of the Claims 4-6 characterised in, that said 2-substituted or 2,2-substituted 1,3-propanediol is 2-methyl- 1,3-propanediol, 2,2-dimethyl-l ,3-propanediol, 2-ethyl-2-butyl-l ,3-propanediol, 2-methyl-2-propyl- -1 ,3-propanediol, 2-methyl-2-hydroxymethyl, 2-ethyl-2-hydroxym ethyl- 1 ,3-propanediol or 2,2-dihydroxymethyl- -1,3-propanediol.

8. A coating composition according to Claim 3 characterised in, that said di, tri or polyhydric alcohol having at least one alkoxy group is a reaction product between at least one alkylene oxide or corresponding glycol and neopentyl glycol, glycerol, diglycerol, trimethylolethane, trimethylolpropane, ditrimethylolethane, ditrimethylolpropane, pentaerythritol or dipentaerythritol.

9. A coating composition according to any of the Claims 3-8 characterised in, that said at least one alkylene oxide is ethylene oxide, propylene oxide, butylene oxide or phenylethylene oxide.

10. A coating composition according to any of the Claims 1-9 characterised in, that said mercapto carboxylic acid is mercaptoacetic acid, mercaptopropionic acid, mercaptobenzoic acid or mercaptosuccinic acid or anhydride.

11. A coating composition according to any of the Claims 1-10 characterised in, that said compound having an alkenyl functionality of at least two is an allyl or methallyl ether of a di, tri or polyhydric alcohol and/or an ester of a cycloalkene or biclycloalkene carboxylic acid.

12. A coating composition according to Claim 11 characterised in, that said allyl or methallyl ether is an allyl or methallyl ether of a 2-substituted or 2,2-substituted 1,3-propanediol.

13. A coating composition according to Claim 11 characterised in, that said allyl or methallyl ether is an allyl or methallyl ether of a dimer, trimer or polymer of a 2-substituted or 2,2-substituted 1,3-propanediol.

14. A coating composition according to Claim 11 characterised in, that said ester is an ester of a cyclohexene or bicycloheptene carboxylic acid and a 2-substituted or 2,2-substituted 1,3-propanediol.

15. A coating composition according to Claim 11 characterised in, that said ester is an ester of a cyclohexene or bicycloheptene carboxylic acid and a dimer, trimer or polymer of a 2-substituted or 2,2-substituted 1,3-propanediol.

16. A coating composition according to any of the Claims 12-15 characterised in, that said 2-substituted or 2,2-substituted 1,3-propanediol is a 2-alkyl- 1,3-propanediol, a 2,2-dialkyl- 1,3-propanediol, a 2-hydroxyalkyl- 1,3-propanediol, a 2-alkyl-2-hydroxy- alkyl- 1,3-propanediol, a 2,2-dihydroxyalkyl- 1,3-propanediol, 2-hydroxyalkoxy- - 1,3-propanediol, a 2-alkyl-2-hydroxyalkoxy- 1,3-propanediol or a 2,2-dihydroxy- alkoxy- 1,3-propanediol.

17. A coating composition according to Claim 11 characterised i n, that said allyl or methallyl ether is a diallyl or dimethallyl ether of neopentyl glycol, glycerol, trimethylol ethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol or dipentaerythritol, a triallyl or trimethallyl ether of glycerol, trimethylol ethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol or dipentaerythritol and/or a tetraallyl or tetramethallyl ether of pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol or dipentaerythritol.

18. A coating composition according to Claim 11 characterised in, that said ester is a diester of neopentyl glycol, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol, a triester of glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol, and/or a tetraester of pentaerythritol, diglycerol, ditrimethylolethane, ditrimethylolpropane, pentaerythritol and/or dipentaerythritol.

19. A coating composition according to any of the Claims 1-18 characterised in, that said at least one curing agent and/or free radical initiator is a photoinitiator and/or accelerator selected from the group consisting of phenone derivatives, such as benzophenone, bezoine derivatives, bezil ketals and acylphosphine oxides.

20. A coating composition according to any of the Claims 1-18 characterised in, that said at least one curing agent and/or free radical initiator is an onium salt, such as a iodonium or sulphonium salt.

21. A novel thiol characterised in, that it is a reaction product between at least one di, tri or polyhydric alcohol, having at least one alkoxy group, and at least one mercapto carboxylic acid, said reaction product being obtained at a molar ratio said alchohol to said mercaptocarboxylic acid yielding an ester having a mercapto functionality of at least two.

22. A novel thiol according to Claim 21 characterised in, that said di, tri or polyhydric alcohol having at least one alkoxy group is a reaction product between at least one alkylene oxide or corresponding glycol and at least one 2-substituted or 2,2-substituted 1,3-propanediol.

23. A novel thiol according to Claim 21 characterised in, that said di, tri or polyhydric alcohol having at least one alkoxy group is a reaction product between at least one alkylene oxide or corresponding glycol and at least one dimer, trimer or polymer of at least one 2-substituted or 2,2-substituted 1,3-propanediol.

24. A novel thiol according to Claim 22 or 23 c haract eri s ed i n, that said 2-subsituted or 2,2-substituted 1,3-propanediol is a 2-alkyl-l,3-propanediol, a 2,2-dialkyl- 1,3-propanediol, a 2-hydroxyalkyl- 1,3-propanediol, a 2-alkyl-2-hydroxy- alkyl- 1,3-propanediol or a 2,2-dihydroxyalkyl- 1,3-propanediol.

25. A novel thiol according to Claim 22 or 23 ch aract eri s ed i n, that said 2-substituted or 2,2-substituted 1,3-propanediol is 2-methyl- 1,3-propanediol, 2,2-dimethyl- 1,3-propanediol, 2-ethyl-2-butyl- 1,3-propanediol, 2-methyl-2-propyl- - 1,3-propanediol, 2-methyl-2-hydroxymethyl, 2-ethyl-2-hydroxymethyl- 1,3-propanediol or 2,2-dihydroxymethyl- 1,3-propanediol.

26. A novel thiol according to Claim 21 ch aracteri sed i n, that said di, tri or polyhydric alcohol having at least one alkoxy group is a reaction product between at least one alkylene oxide or corresponding glycol and neopentyl glycol, glycerol, diglycerol, trimethylolethane, trimethylolpropane, ditrimethylolethane, ditrimethylolpropane, pentaerythritol or dipentaerythritol.

27. A novel thiol according to any of the Claims 22-26 characterised in, that said at least one alkylene oxide is ethylene oxide, propylene oxide, butylene oxide or phenylethylene oxide.

28. A novel thiol according to any of the Claims 21-27 characterised in, that said mercapto carboxylic acid is mercaptoacetic acid, mercaptopropionic acid, mercaptobenzoic acid or mercaptosuccinic acid or anhydride.