Acylphosphinesulfide compounds, process for their preparation and their use.

The present invention relates to new acylphophinsulfide compounds, a process for their preparation and their use as photoinitiators in photopolymerizable compositions, such as coating agents, lacquers, printing inks, unsaturated polyester molding compositions and recording materials.

A number of photoinitiators of different structures are already known, for example benzil dimethyl ketal (DE-AS 22 61 383), benzoin ether (DE-AS 16 94 149), thioxanthones (DE-OS 20 03 132). However, photopolymerizable compositions which are cured with such initiator systems show undesirable yellowing, which renders use of these systems on light (or white) surfaces or for curing translucent moldings unusable. Another disadvantage is the often inadequate storage stability of the fully sensitized resin mixtures, which can often only be kept for a few days despite being stored in the dark. There is also a need for photoinitiators that outperform the known systems mentioned above in their curing rate.

From DE-OS 28 30 927 acylphosphine oxide compounds and inre use as photoinitiators are already known.

The aim of the present invention is to show compounds which absorb even longer waves and are suitable as photoinitiators, by means of which the use of less dangerous light sources or curing with sunlight is made possible. Ls / BL The present invention relates to acylp_HOsphine sulfide compounds of the general formula (I)<chemistry id="chem0001" num="0001"><img file="EP0047902A2_D0001.tif" /></chemistry>where R¹ for a straight-chain or branched alkyl radical having 1 to 6 carbon atoms, a cyclohexyl, cyclopentyl, phenyl or naphthyl radical, a 0-, S- or N-containing five- or six-membered heterocyclic radical or a fluorine, chlorine, bromine , C₁- to C₄-alkyl- or C₁- to C₄-alkoxyl-substituted phenyl, naphthyl, 0-, S- or N-containing five- or six-membered heterocyclic radical;<ul id="ul0001" list-style="none"><li>R² the meaning of R¹ has, where R¹and R² may be the same or different from one another, or for an alkoxyl radical having 1 to 6 carbon atoms, a phenoxy radical which may contain chlorine, C.₁- to C₆-alkyl- or C₁- to C₆-alkoxyl-substituted, or a phenoxyalkyl radical having 1 to 4 carbon atoms in the alkyl group or R¹ and R² are linked to one another to form a ring which contains 4 to 10 carbon atoms and may optionally have 1 to 6 further alkyl radicals each having 1 to 4 carbon atoms and 1 or 2 fused-on benzene rings as substituents;</li><li>R³ for a straight-chain or branched alkyl radical having 2 to 18 carbon atoms, a cycloaliphatic radical containing 3 to 12 carbon atoms, a 1 to 4-fold substituted phenyl, an optionally 1 to 4-fold substituted naphthyl, 0, S or N -containing five- or six-membered heterocyclic radical, these substituents being identical or different from one another and containing 1 to 6 carbon atoms, alkyl, alkylthio or alkoxy groups and chlorine, Bromine or fluorine atoms can be, or for grouping<chemistry id="chem0002" num="0002"><img file="EP0047902A2_D0002.tif" /></chemistry>where R¹ and R have the meaning given above and X is an optionally up to 4-fold substituted phenylene radical, the substituents of which may be the same or different and may be alkyl, alkylthio or alkoxy groups containing 1 to 6 carbon atoms and halogen atoms with an atomic weight of up to 80, .or X represents an aliphatic or cycloaliphatic divalent radical containing 2 to 6 carbon atoms; and where appropriate at least one of the residues_R¹to R³ can be olefinically unsaturated.</li></ul>

The present invention also relates to a process for the preparation of these acylphosphine sulfides, acylphosphines of the general formula (II)<chemistry id="chem0003" num="0003"><img file="EP0047902A2_D0003.tif" /></chemistry>where R¹ to R³ have the meaning given above, at temperatures between 20 and 200 ° C, preferably 60 to 120 ° C, optionally in the presence of an inert solvent in an inert gas atmosphere with elemental sulfur.

The present invention furthermore relates to the use of the acylphosphine sulfides of the general formula (I), where R³ can additionally be a methyl or a phenyl radical, as photoinitiators in photopolymerizable compositions, for example for coating compositions, lacquers, printing inks and for the production of plastic moldings based on unsaturated polyester resins, these acylphosphine sulfides optionally also in combination with secondary or tertiary amines, other photoinitiators or initiators for thermal polymerization can be used.

Acylphosphine sulfide compounds of the general formula (I) in which R³ is a tertiary aliphatic residue. Compounds in which

R³ represents an at least doubly substituted phenyl, pyridyl, pyrrolyl, furyl or thienyl radical which bears the substituents A and B at least on the two carbon atoms adjacent to the point of attachment to the carbonyl group, which substituents can be the same as each other and for 1 to Alkyl, alkoxy or alkylthio residues containing 6 carbon atoms, cycloalkyl residues containing 3 to 7 carbon atoms, phenyl residues or halogen residues, preferably chlorine or bromine atoms, or R³ for an α-naphthyl radical substituted at least in the 2,8 positions by A and B, a β-naphthyl radical substituted by A and B at least in the 1,3 positions or for the grouping<chemistry id="chem0004" num="0004"><img file="EP0047902A2_D0004.tif" /></chemistry>is, where the radicals A, B, C and D are the same or different from one another, C and D have the same meaning as A and B and R, R have the meaning given above or are optionally olefinically unsaturated.

With regard to the general formula (I) of the acylphosphine oxide compounds according to the invention, the following must be carried out in detail:<ul id="ul0002" list-style="none"><li>R¹ can be a straight-chain or branched alkyl radical having 1 to 6 carbon atoms, such as, for example, methyl, ethyl, i-propyl, n-propyl, n-butyl, sec.-butyl, iso-butyl, t -Bu_- tyl, amyl, n-hexyl; a cyclopentyl, cyclohexyl radical; a phenyl or naphthyl radical; a fluorine, chlorine or bromine-substituted phenyl or naphthyl radical, such as mono- or dichlorophenyl, a C₁- to C₄-alkyl-substituted phenyl or naphthyl, such as a methylphenyl, ethylphenyl, isopropylphenyl, tert-butylphenyl, dimethylphenyl, trimethylphenyl, C₁- to C₄alk alkoxy-substituted phenyl or naphthyl radical such as, for example, a methoxyphenyl, ethoxyphenyl, dimethoxyphenyl radical, 0-, S- or N-containing five- or six-membered heterocyclic radicals, such as furyl, thienyl, pyridyl, pyrrolyl radical, which are also Fluorine, chlorine, bromine, C₁- to C₄--alkyl- or C₁- to C₄-alkoxyl-substituted, such as a methylfuryl or chloropyridyl radical.</li><li>R has the meaning of R, where R¹ and R can be the same or different from one another. Furthermore, R² stand for an alkoxyl radical with 1 to 6 carbon atoms, a phenoxy radical, which optionally chlorine, C₁- to C₆-alkyl- or C₁- to C₆-alkoxyl-substituted, or a phenoxyalkyl radical having 1 to 4 carbon atoms in the alkyl group. Finally, R¹ and R² be linked together to form a phosphorus-containing ring which contains 4 to 10 carbon atoms and may optionally have 1 to 6 further alkyl radicals each having 1 to 4 carbon atoms and 1 or 2 fused-on benzene rings as substituents;</li><li>R³ can be a straight-chain or branched alkyl radical having 2 to 18 carbon atoms, such as, for example, ethyl, i-propyl, n-propyl, n-butyl, i-butyl, i-amyl, n-hexyl, heptyl -, n-Octyl, 2-ethylhexyl, i-nonyl, dimethylheptyl, dimethyloctyl, dimethylnonyl, dimethyldecyl, lauryl, stearyl radical, a cycloaliphatic radical containing 3 to 12 carbon atoms, such as, for example a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, norbornenyl, adamantyl radical; an alkyl, alkylthio or alkoxy group which may contain 1 to 6 carbon atoms or a phenyl, naphthyl, 0-, S- or N-containing radical which is 1- to 4-fold substituted with chlorine, bromine or fluorine, such as a methylphenyl, dimethylphenyl, trimethylphenyl, tert-butylphenyl, isopropylphenyl, methoxyphenyl, dimethoxyphenyl, i-propyloxyphenyl, methylthiophenyl, α and β-naphthyl, thienyl, pyridyl radical.</li></ul>

R can preferably³ be a t-butyl, a 1-methylcylcohexyl, 1-methylcyclopentyl, 1,1-dimethyloctyl radical.

R is particularly preferred³ a 2,6-dimethylphenyl-, 2,6-dimethoxyphenyl-, 2,6-dichlorophenyl-, 2,6-dibromophenyl-, 2-chloro-6-methoxyphenyl-, 2-chloro-6-methylthio-phenyl-, 2,4,6-trimethylphenyl-, 2,4,6-trimethoxyphenyl-, 2,3,4,6-tetramethylphenyl, 2,6-dimethyl-4-tert-butylphenyl-, 1,3-dimethylnaphthalene-2- , 2,8-dimethylnaphthalene-1-, 1,3-dimethoxy-naphthalene-2-, 1,3-dichloronaphthalene-2-, 2,8-dimethoxynaphthalene-1-, 2,4,6-trimethylpyridine-3-, 2,4-dimethoxy-furan-3 or a 2,4,5-trimethylthiophene-3 radical.

R¹, R²and R³ can also contain CC double bonds, which allow the photoinitiator to be polymerized into the binder.

Examples of the acylphosphine sulfide compounds according to the invention are:<ul id="ul0003" list-style="none"><li>Isobutyroyl-diphenylphosphine sulfide, 2-ethylhexanoyl-diphenylphosphine sulfide, p-toluene-diphenylphosphine sulfide, o-toluyl-diphenylphosphine sulfide, p-tert.-butylbenzoyl-diphenylphosphine sulfide, 3-pyridylcarbonyl-diphenylphosphide bis-diphenylphosphine sulfide and preferably pivaloyl diphenylphosphine sulfide, 1-methyl-l-cyclohexane carbonyl bis (p-tolyl) phosphine sulfide, 2,2-dimethylheptanoyl diphenylphosphine sulfide and preferably</li><li>2,6-dimethylbenzoyl-diphenylphosphine sulfide, 2,6-dimethoxybenzoyl-diphenylphosphine sulfide, 2,4,6-trimethylbenzoyl diphenylphosphine sulfide,</li><li>2,3,6-trimethylbenzoyldiphenylphosphine sulfide, 2,4,6-trimethoxybenzoyldiphenylphosphine sulfide, 2,6-dichlorobenzoyldiphenylphosphine sulfide, 2-chloro-6-methylthio-benzoyldiphenylphosphine sulfide, 2,6-bis (methylthio) benzoyl diphenylphosphine sulfide 4,6-tetramethylbenzoyldiphenylphosphine sulfide, 2-phenyl-6-methylbenzoyldiphenylphosphine sulfide, 1,3-dimethylnaphthalene-2-carbonyl-diphenylphosphine sulfide, 2,8-dimethylnaphthalene-1-carbonyl-diphenylphosphine sulfide, 1,3-dimethoxynaphthalene-2-carbonyl-diphenylphosphine sulfide, 1,3-dichloronaphthalene-2-carbonyl-diphenylphosphine sulfide, 2,4,6-trimethylpyridine-3-carbonyl-diphenylphosphine sulfide, 2,4-dimethylfuran-3-carbonyl-diphenylphosphine sulfide, 2,4-dimethoxyfuran-3-carbonyl-di (n-butyl) phosphine sulfide, 2,4,5-trimethylthiophene-3-carbonyldiphenylphosphine sulfide, 2,4,5-trimethylthiophene-3-carbonyl diphenylphosphine sulfide, 2, 6-dimethoxybenzoyl-bis- (o-tolyl) phosphine sulfide, 2,4,6-trimethoxybenzoyl-bis (p-tolyl) phosphine sulfide, 2,6-dimethoxybenzoyl-bis (p-chlorophenyl) phosphine sulfide, 2,4,6-trimethoxybenzoyl-bis- (p-chlorophenyl) - phosphine sulfide, 2,6-dimethoxybenzoyl-di-tert-butylphosphine sulfide, 2,4,6-trimethoxybenzoyl-di-tert-butylphosphine sulfide, 2,3,5,6-tetrachloroterephthaloyl-bis-diphenylphosphine sulfide.</li></ul>

The compounds according to the invention can preferably be prepared in such a way that an acylphosphine of the formula (II)<chemistry id="chem0005" num="0005"><img file="EP0047902A2_D0005.tif" /></chemistry>is reacted in bulk or in the presence of a suitable inert organic solvent in an inert gas atmosphere of preferably nitrogen, argon or carbon dioxide at a temperature of from 20 to 200 ° C., preferably from 60 to 120 ° C., with approximately equimolar amounts of elemental sulfur. Preferred solvents are hydrocarbons such as toluene, cyclohexane, chlorobenzene and aliphatic and aromatic ethers such as dibutyl ether, dioxane, diethylene glycol dimethyl ether or diphenyl ether. The resulting acylphosphine solution is separated by filtration from any sulfur still present. After the solvent has been evaporated off, the acylphosphine sulfide remains, which can be further purified by distillation or recrystallization. The manufacturing process can be described as an example:<chemistry id="chem0006" num="0006"><img file="EP0047902A2_D0006.tif" /></chemistry>

Acylphosphines are obtained by methods which are known to the person skilled in the art from the literature (see, for example, H. Kunzek, J. Organometallic Chemistry, 49, 149 (1973) and K. Issleib and 0. Löw, Journal of Inorganic and Analytical Chemistry 346, 241 (1966 ».

The particularly preferred acylphosphine sulfide compounds can also be prepared in the manner described above from the corresponding acylphosphine compounds. The preparation of the acylphosphine compounds required for this, in which R³ represents an at least doubly substituted phenyl, pyridyl, pyrrolyl, furyl or thienyl radical which bears the substituents A and B at least in the two carbon atoms adjacent to the point of attachment to the carbonyl group, which have the meaning given above or in which R represents an α-naphthyl radical which is substituted by A and B at least in the 2,8 positions or a β-naphthyl radical which is substituted by A and B at least in the 1,3 positions or for the group<chemistry id="chem0007" num="0007"><img file="EP0047902A2_D0007.tif" /></chemistry>, with identical or different radicals A, B, C, D, which have the meaning given above for A, B, is described, for example, in German patent application P 30 20 092.1.

Suitable acylphosphines include:<ul id="ul0004" list-style="none"><li>Benzoyldiphenylphosphine</li><li>p-toluyldiphenylphosphine</li><li>o-toluyl diphenylphosphine</li><li>p-dimethylaminobenzoyldiphenylphosphine.</li></ul>

Suitable acylphosphines for the preparation of the preferred acylphosphine sulfide compounds are, for example:<ul id="ul0005" list-style="none"><li>Pivaloyldiphenylphosphine,</li><li>2,2-dimethylheptanoylditolylphosphine,</li><li>2-methyl-2-ethylhexanoyldiphenylphosphine.</li></ul>

Suitable acylphosphines for the production of the particularly preferred acylphosphine sulfide compounds are, for example:<ul id="ul0006" list-style="none"><li>2,6-dimethylbenzoyldiphenylphosphine,</li><li>2,4,6-trimethylbenzoyldiphenylphosphine,</li><li>2,6-dimethoxybenzoyldiphenylphosphine,</li><li>2,6-dichlorobenzoyldiphenylphosphine.</li></ul>

Examples of the compounds according to the invention are, without seeing this as a limitation, in particular the following:<tables id="tabl0001" num="0001"><img file="EP0047902A2_D0008.tif" /></tables>

The acylphosphine sulfide compounds according to the invention show a very good reactivity as photoinitiators for photopolymerizable monomers with at least one CC multiple bond and mixtures thereof with one another and with known additives. The acylphosphine sulfide compounds according to the invention are particularly suitable as photoinitiators in photopolymerizable compositions for coatings, lacquers, printing inks and recording materials. They are far superior to known photoinitiators, for example the benzil dimethyl ketal known from DE-AS 22 61 383, with regard to the yellowing of the paints or coatings obtained in this way. The acylphosphine sulfide compounds according to the invention can also be used very advantageously as photoinitiators for the light curing of styrenic polyester resins, which may optionally contain glass fibers and other auxiliaries.

Suitable photopolymerizable monomers are the customary compounds and substances with polymerizable CC double bonds, which are, for example, aryl, carbonyl, amino, amide, amido, ester, carboxy or cyanide groups, halogen atoms or additional CC double bonds - or CC triple bonds are activated. Examples include vinyl ethers and vinyl esters with 3 to 10, preferably 4 to 8, carbon atoms, vinyl aromatics, such as styrene, vinyl toluene, acrylic acid and methacrylic acid, and their esters with mono- or polyhydric alcohols with up to 20, preferably 1 to 8, carbon atoms, for example Methyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, butane-1,4-diol diacrylate, hexane-1,6-diol diacrylate, nitriles or amides of acrylic acid or Methacrylic acid, maleic and fumaric esters of alcohols having 1 to 20, preferably 1 to 8 carbon atoms, such as fumaric acid diethyl ester and N-vinyl compounds, such as N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylcarbazole and allyl esters such as diallyl phthalate.

Suitable photopolymerizable higher molecular compounds are, for example: unsaturated polyesters made from α, β-unsaturated dicarboxylic acids, such as maleic acid, fumaric acid or itaconic acid, optionally in a mixture with saturated or aromatic dicarboxylic acids such as adipic acid, phthalic acid or terephthalic acid, by reaction with alkanediols such as ethylene glycol, propylene glycol, butanediol, neopentyl glycol or oxyalkylated bisphenol A; Epoxy acrylates, made from acrylic or methacrylic acid and aromatic or aliphatic diglycidyl ethers and urethane acrylates (e.g. made from hydroxyalkyl acrylates and polyisocyanates) as well as polyester acrylates (e.g. prepared from saturated polyesters containing hydroxyl groups and acrylic or methacrylic acid).

The photopolymerizable compounds, the composition of which is known to the person skilled in the art for the respective intended use, can be saturated and / or unsaturated polymers and other additives such as inhibitors against thermal polymerization, paraffin, pigments, dyes, peroxides, leveling agents, fillers and glass fibers and stabilizers in a known manner against thermal or photochemical degradation.

Such mixtures are known to the person skilled in the art. The type and amount of additives depend on the intended use.

The acylphosphine sulfide compounds according to the invention are generally used in a concentration of 0.01 to 15% by weight, preferably 0.05 to 5% by weight, based on the photopolymerizable composition. If necessary, they can be combined with accelerators which remove the inhibiting influence of atmospheric oxygen on the photopolymerization.

Such accelerators or synergists are, for example, secondary and / or tert. Amines, such as methyldiethanolamine, dimethylethanolamine, triethylamine, triethanolamine, ethyl p-dimethylaminobenzoate, benzyldimethylamine, dimethylaminoethyl acrylate, N-phenylglycine, N-methyl-N-phenylglycine and analogous compounds known to the person skilled in the art. To accelerate the curing, aliphatic and aromatic halides such as 2-chloromethylnaphthalene, 1-chloro-2-chloromethyl-naphthalene and optionally radical formers, such as are generally used as initiators for thermal polymerization, for example peroxides, azo compounds and CC, can also be used labile compounds which can be added in amounts of up to 15% by weight, based on the photopolymerizable composition, and are known to the person skilled in the art.

Furthermore, the acylphosphine sulfide compounds, _bif necessary in the presence of the synergists and accelerators described above, in combination with other photoinitiators for light curing coatings, varnishes, printing inks, photosensitive recording materials, such as photopolymerizable printing plates and styrenic polyester resins. Such photoinitiators are, for example, aromatic ketones such as benzil ketals, benzoin ethers, benzoin esters, C.₁- to C₃-alkyl, chlorine- or chloromethyl-substituted thioxanthones, the acylphosphines described in German patent application P 30 20 092.1 and the acylphosphine oxides and acylphosphinic esters known from DE-OS 28 30 927 and DE-OS 29 09 994. These also include aromatic disulfides and naphthalenesulfochlorides. These and optionally other suitable compounds are known to the person skilled in the art.

Radiation sources for the light which triggers the polymerization of such mixtures are generally those which preferably emit light in the absorption range of the compounds according to the invention, ie between 230 and 450 nm. Mercury low-pressure lamps, medium-pressure and high-pressure lamps and superactinic fluorescent tubes or pulse lamps are particularly suitable . The lamps mentioned can optionally be doped.

A particular advantage of the acylphosphine sulfides according to the invention is that they are suitable as photoinitiators with which photopolymerization with longer-wave and thus less dangerous light sources such as fluorescent tubes or curing with sunlight is possible.

Unless otherwise stated, the parts and percentages given in the examples below relate to the weight. Parts by volume are related to parts like liters_LKilogram.

example 1

7.0 parts of 2,6-dimethoxy-benzoyl-diphenylphosphine (cf. Example 1 of German patent application P 30 20 092.1) are dissolved in 60 parts by volume of toluene and the solution is flushed with nitrogen for 30 minutes. Then 0.64 parts of sulfur are added. This solution is stirred in a nitrogen atmosphere at 60 ° C. for 4 hours. The mixture is then cooled and the solvent is stripped off in vacuo. The residue is recrystallized from toluene.

Yield: 3.4 parts of 2,6-dimethoxybenzoyldiphenylphosphine sulfide (44.5% of theory), mp. 109-111 ° C .; NMR (CDCl₃, δ):<ul id="ul0007" list-style="none"><li>3.56 (s, 6H); 6.52 (d. 2H); 7.2-8.2 (m, 11 h)</li><li>Analysis C₂₁^H₁₉⁰₃^PS (3⁸²)</li><li>calc .: C 65.97 H 4.97 P 8.12 S 8.38</li><li>found: C 65.9 H 5.0 P 8.4 S 7.9</li></ul>

Example 2

6.6 parts of 2,4,6-trimethylbenzoyldiphenylphosphine (cf. Example 2 of German patent application P 30 20 092.1) are dissolved in 60 parts by volume of toluene and the solution is flushed with nitrogen for 30 minutes. Then 0.64 parts of sulfur are added. This solution is stirred in a nitrogen atmosphere at 60 ° C for 2 hours. The mixture is then cooled and the solvent is stripped off in vacuo. The residue is recrystallized from diethyl ether.

Yield: 3.6 parts (52.5% of theory), mp. 108-110 ° C; NMR (CDCl₃, δ): 1.98 (s, 6H); 2.28 (s, 3H); 6.81 (s, 2H); 7.2-7.8 (m, 6H); 7.8-8.4 (m, 4H). analysis^C.22^H₂₁^0PS (364) calc .: C 72.53 H 5.77 P 8.52 S 8.79 found: C 72.7 H 5.9 P 8.7 S 9.0

Example 3

To measure the curing activity of the compounds according to the invention, the temperature profile was recorded in unsaturated polyester resin (UP resin) during the UV exposure; For this purpose, a thermal sensor coated with a wax layer, which is connected to a temperature recorder (Tastotherm Script-3 N, standard sensor T 300 from Deutsche Gulton GmbH), is immersed in a tinplate lid with a diameter of 5 cm filled with 10 g UP resin (layer thickness of the UP resin 4.8 mm). To avoid heat loss during UV exposure, the lid is embedded in rigid polyurethane foam. A UV field consisting of 5 fluorescent tubes (TLAK 40 W / 05, Philips) side by side serves as the radiation source. The distance emitter / UP - resin surface was 8.5 cm.

From the registered temperature-time curves, the hardening time HZ becomes characteristic parameters for the hardening activity_{25 ° C}-T_Max and the maximum curing temperature T reached_Max contained. As curing time HZ_{25 ° C}-T_Max applies the time span in which the sample temperature changes from 25 ° C to T_Max increases.

The examples and comparative examples were carried out with the following unsaturated polyester resins:<ul id="ul0008" list-style="none"><li>Resin A is a 65% styrenic solution of an unsaturated polyester made from maleic acid, o-phthalic acid, stabilized with 0.01% hydroquinone. Ethylene glycol and 1,2-propylene glycol in a molar ratio of 1: 2: 2.3: 0.70. Of the. unsaturated polyester has an acid number of 50.</li><li>Resin B is a 66% styrenic solution of an unsaturated polyester made from maleic acid, o-phthalic acid and 1,2-propylene glycol stabilized with 0.01% hydroquinone in a molar ratio of 1: 0.5: 1.5. The unsaturated polyester has an acid number of 50.</li><li>Resin C is a 65% styrenic solution of an unsaturated polyester, stabilized with 0.012% hydroquinone, of an unsaturated polyester composed of maleic acid, o-phthalic acid, 1,2-propylene glycol and diethylene glycol in a molar ratio of 1: 0.25: 1: 0.25. The unsaturated poly. ester has an acid number of 43.</li><li>Resin D is a 67% styrenic solution of an unsaturated polyester made from maleic acid, tetrahydrophthalic acid and diethylene glycol in a molar ratio of 1: 0.5: 1.5, stabilized with 0.01% hydroquinone. The unsaturated polyester has an acid number of 43.</li><li>Resin E is a 65% styrenic solution of an unsaturated polyester made from maleic acid, isophthalic acid, propylene glycol 1,2 and diethylene glycol in a molar ratio of 1: 0.67: 0.72: 1 stabilized with 0.01% hydroquinone. The unsaturated polyester has one Acid number of 26.</li></ul>

The following compounds belonging to the prior art were used as UV sensitizers for comparative examples:<ul id="ul0009" list-style="none"><li>I benzil dimethyl ketal</li><li>II benzoin methyl ether</li><li>III benzoin isopropyl ether</li><li>IV methylolbenzoin methyl ether.</li></ul>

These were with the two photoinitiators according to the invention<ul id="ul0010" list-style="none"><li>V 2,6-dimethoxybenzoyldiphenylphosphine sulfide and</li><li>VI 2,4,6-trimethylbenzoyldiphenylphosphine sulfide compared. The results are shown in Table 2.<img file="EP0047902A2_D0009.tif" /></li></ul>

The photoinitiators according to the invention have a significantly higher activity than the commercially available (I-IV); in addition, the yellowing of the molding material is less.

Example 4

3 parts of photoinitiator are dissolved in a binder composed of 65 parts of a reaction product of bisphenol A glycidyl ether and acrylic acid and 35 parts of hexane-1,6-diol diacrylate. The finished mixture is placed on glass plates in a layer of 60_/u The thickness is raked up and passed at a distance of 10 cm under a high pressure mercury lamp (power 80 W / cm - arc length). The reactivity is given as the maximum possible conveyor belt speed at which a nail-hard, scratch-resistant curing of the coating is achieved. The results are summarized in Table 3.

Example 5

3% methyldiethanolamine are added to a lacquer produced according to Example 4. Then, as in Example 4, it is mounted on glass plates and exposed. The results are summarized in Table 3. The curing rate of the compounds according to the invention can then be increased by adding an amine accelerator.<tables id="tabl0002" num="0002"><img file="EP0047902A2_D0010.tif" /></tables>