CA2037769A1

CA2037769A1 - Photoinitiator mixtures

Info

Publication number: CA2037769A1
Application number: CA 2037769
Authority: CA
Inventors: Manfred Kohler; Hermann F. Angerer; Andre Litzler
Original assignee: Ciba Geigy AG
Current assignee: Novartis AG
Priority date: 1990-03-09
Filing date: 1991-03-07
Publication date: 1991-09-10
Also published as: EP0446175A2; JPH04220404A; EP0446175A3

Abstract

Photoinitiator mixtures Abstract of the Disclosure Photoinitiator mixtures comprising a) 100 parts of a mono- or diacylphosphine oxide, b) 10-70 parts of an .alpha.-hydroxyacetophenone, and c) 10-70 parts of a benzophenone are effective initiators for photopolymerisations of ethylenically unsaturated compounds.
They are particularly suitable for photocuring white enamels.

Description

Photoinitiator mixtures The present invention relates to photoinitiato~ mixtures comprising three components and to photocurable mixtures containing such a photoinitiator mixture.

Acylphosphine oxides are disclosed as highly effective photoinitiators in EP-A-7086 und EP-A-7508. Recently, diacylphosphine oxides have been proposed for this utility (q.v.
(EP-A-184 095). As stated in EP-A-7508, page 13, the effectiveness of the acylphosphine oxides can be further enhanced by combining them with other photoinitiators, especially aromatic ketones. Typical examples of such co-initiators are benzil dimethylketal a-hydroxyisobutyrophenone, diethoxyacetophenone, benzophenone, 2-methyl-thioxanthone, 2-isopropylthioxanthone and 2-chlorothioxanthone. The addition of tertiary amines can effect a further acceleration. Mixtures of such phosphine oxides with aromatic ketones, aromatic disulfides or naphthalenesulfonyl chlorides, especially with benzil ketals, benzoin ethers or benzoin esters are cited in EP-A-7086, claims 6 and 7.
It has now been found that the etfectiveness of the mono- and diacylphosphine oxides can be further enhanced by combining them with two o~her different photoinitiators, one of which is an a-hydroxyacetophenone and the other is a benzophenone. Such a photoinitiator mixture is particularly suitable for photocuring pigmented rnatelials, " especially white enamels.

Accordingly, the invention relates to a photoinitiator mixture comprising ., ~.
a) 100 parts by weight of a compound of formula I, O O
,., 11 11 `i R~--P--C--R3 'il . R2 ., wherein Rl is Cl-C18alkyl, Cl-C4alkyl which is substituted by halogen or Cl-C6aLkoxy, or .j is Cs-C8cycloalkyl, C7-Cgphenylalkyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl ., ~ .: .... . .. ., .. ~.. . . . . . . . . . . .

,,: . . . . . . . . . . .

2~37~3 or biphenylyl which are each substituted by one or more identical ~r different members of the group consisting of halogen, Cl-Cl2alkyl and/or Cl-CI2aLtcoxy, or is a monovalent, 5-or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, R2 is phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one or more identical or different members of the group consisting of halogen, Cl-Cl2alkyl and/or Cl-Cl2alkoxy, or is a monovalent, 5- or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, or is Cl-Cl8alkoxy, phenoxy or phenoxy which is substituted by halogen, Cl-C4aLkyl or Cl-C4alkoxy, or is benzyloxy, cyclohexyloxy or a -CO-R4 group, or R2 and Rl, together with the phosphorus atom, form a ring, R3 is Cl-C18alkyl, Cl-C4aL~yl which is substiluted by halogen or Cl-C6alkoxy, or is .
Cs-C8-cycloalkyl, C7-Cgphenylalkyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one more identical or different members selected from the group consisting of halogen, Cl-CI2alkyl and/or Cl-Cl2aLkoxy, or is a monovalent, 5- or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, or is a group O O
. Il 11 --X--C~P--Rl wherein X is C2-C8alkylene, cyclohexylene, or phenylene or biphenylene which are each .
unsubstituted or substituted by halogen, Cl-C4alkyl or Cl-C4aL~coxy, and R4 is Cl-Cl8aLkyl, Cl-C4alkyl which is substituted by halogen or Cl-C4alkoxy, or is C5-C8cycloaLIcyl, C7-CgphenylaL~cyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one more identical or different members ; selected from the group consisting of halogen, Cl-Cl2alkyl and/or Cl-C12alkoxy, or is a monovalent, 5- or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, or R4 and R3, when taken together, are C2-Cl2aLtsylene, vinylene or o-phenylene, ..
b) lO-70 parts by weight of compound of formula II, R~ CllC_OH 11 , R7 R9 ., -... .
,. . . `. ,, : ..
." '' '~'` ,' ' "~ ", . - .'',' :'.

wherein R6 and R7 are each independently of the other hydrogen, Cl-CI8alkyl, phenyl9 Cl-C~8alkoxy, phenoxy, Cl-Cl8alkylthio, phenylthio, C2-C8diaLlcylamino, piperidino, morpholino or halogen, and R8 and Rg are each independently of the other Cl-C6alkyl, C3-C6alkenyl, C7-Cgphenylalkyl or cyclohexyl, or R8 and Rg, when taken together, are C4-C6alkylene, and c) 10-70 parts by weight of a compound of formula III, ~ ¦¦ ~R~ 3 wherein Rl 1, Rl2 and Rl3 are each independently of one another hydrogen, Cl-Cl2alkyl, Cl-C4-alkoxy, Cl-C4alkylthio, halogen or C2-C6alkoxycarbonyl, or a mixture of such benzophenone derivatives.

The substituents Rl, R3, R4, R6, R7, R8, Rg, Rl" Rl2 or Rl3 defined as alkyl may be unbranched or branched alkyl. Such aLkyl groups are typically methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, n-hexyl, 2-ethybutyl, n-octyl, isooctyl, 1,1,3,3-tetramethylbutyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, hexadecyl or octadecyl.
.
Rl, R3 or R4 as Cl-C4aLkyl which is substituted by halogen or Cl-C6alkoxy may bechlc)romethyl, trichloromethyl, trifluoromethyl, 2-chloroethyl, 2-me~hoxyethyl, - 2-ethoxypropyl, 2-butoxyethyl or 2-hexyloxyethyl.
:
Rl or R3 as Cs-C8cycloalkyl is preferably cyclohexyl. Rl, R3, R8 or Rg as C7-Cgphenylalkyl is preferably benzyl. R8 or R9 as C3-C6alkenyl is preferably allyl.

Rl, R2, R3 or R4 as phenyl, naphthyl or biphenylyl which are each substituted by one or more identica1 or different members selected from the group consisting of halogen, !'i Cl-CI2alkyl and/or Cl-Cl2alkoxy may be chlorophenyl, 2t4-dichlorophenyl, 2,6-dichlorophenyl, 2,4,6-trichlorophenyl, 4-tolyl, 2-tolyl, 2,4-xylyl, '', .
., -,, -, - .. . . : :: : .. : : . .
: : ~ : - : : . . , :: :
,. ~ : . ~ . . .
~ ~ , . . . . .

20377~9 . . .
2,4,6-trimethylphenyl, 4-isopropylphenyl, 4-tert-butylphenyl, 4-octylphenyl, 4-dodecylphenyl, 4-methoxyphenyl, 2,4-dimethoxyphenyl, 2,4,6-trimethoxyphenyl, 2-chloro-6-methoxyphenyl, 4-ethoxyphenyl, 4-isopropoxyphenyl, 4-hexyloxyphenyl, 1,3-dichloro-2-naphthyl, 1,3-dimethoxy-2-naphthyl, 2,8-dimethoxy-1-naphthyl, 2,8-di-- methyl-1-naphthyl, 4'-chloro-4-biphenylyl or 4'-ethoxy-4-biphenylyl. The preferred significance is a substituted phenyl radical.

Rl, R2, R3 or R4 as a a monovalent, 5- or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur may be a 2-, 3- or 4-pyridyl, 2,4-dimethyl-3-pyridyl, 2-furyl, 2,4-dimethoxy-3-furyl, 2-thienyl or 2,4-dimethoxy-3-thienyl.
: , Rll, Rl2 and R13 as Cl-C4alkoxy or Cl-C4alkylthio are preferably methoxy, ethoxy or methylthio. R2, R6 or R7 as Cl-C18aLlcoxy may be methoxy, ethoxy, isopropoxy, tert-butoxy, hexyloxy, octyloxy or dodecyloxy. R6 and R7 as Cl-CI8alkylthio preferably Cl-C4alkylthio.

R2 as subsdtuted phenoxy may be 4-chlorophenoxy, 2,4-dichlorphenoxy, 2,4,6-trichlorophenoxy~ 4-tolyloxy, 2,6-dimethylphenoxy, 2,4,6-trimethylphenoxy,3-methoxyphenoxy or 4-ethoxyphenoxy.

R6 or R7 as C2-C~dialkylamino may be dimethylatnino, diethylamino, dipropylamino or dibutylamino.

Rll, Rl2 or Rl3 as C2-C6alkoxycarbonyl may preferably be methoxycarbonyl or ethoxycarbonyl.
,.i :~j X as C2-C8alkylen may be 1,2-ethylene, trimethylene, tetramethylene, pentamethylene, ''Jj hexamethylene or octamethylene, or may also be a branched aLkylene group such as ;i 1,2-propylene, diethylmethylene or 2,2-dimethyl~rimethylene. R4 and R3 together as C2-C12alkylene may preferably be dimethylene or trimethylene which may be substituted ~; ~ by aL~cyl groups.
,'~
R8 and Rg together as C4-C6alkylene may preferably be tetramethylene or pentamethylene.

A ring formed by R2 and R1 together with the phosphorus atom is preferably a 5- or ~membered ring. The ring may contain oxygen and can be fused with benzene rings.

~:, :~ .. : : - , - . .. . . .- . ...
' - - ~ - ~
..
, . : , . .
.. . .
... .. . . .
... . . .

Preferred photoinitiator mixtures comprise a) 100 parts by weight of a compound of formula I, wherein Rl is phenyl, naphthyl or biphenylyl which are each unsubstituted or substituted by halogen, Cl-C4aLkyl or Cl-C4alkoxy, R2 is phenyl, naphthyl or biphenylyl which are each unsubstituted or substituted by halogen, Cl-C4aLIcyl or Cl-C4alkoxy or is a -CO-R4 group, R3 and R4 are each independently of the other Cl-CI2aLkyl, cyclohexyl, benzyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one more identical or different groups selected from the group consisting of halogen, Cl-C4alkyl and/or Cl-C4alkoxy, b) 20-70 parts by weight of a compound of formula II, wherein R6 and R7 are eachindependently of the other hydrogen, Cl-CI2alkyl, phenyl, Cl-CI2alkoxy, phenoxy or halogen, and R8 and Rg are each independently of the other Cl-C4alkyl, allyl or benzyl, or R8 and R9, when taken together, are C4-C6alkylene, and c) 10-60 parts by weight of a compound of folmula III, wherein Rll, Rl~ and Rl3 are each independently of one another hydrogen, Cl-C6alkyl, Cl-C4alkoxy or halogen, or a mixture of alkylated benzophenones.

Particularly preferred photoinitiator mixtures comprise -: ~ a) 100 parts by weight of a compound of formula I, wherein Rl is unsubstituted phenyl or phenyl which is substituted by halogen, Cl-C4aLkyl or Cl-C4aL~coxy, R2 is unsubstituted phenyl or phenyl which is substituted by halogen, Cl-C4aLkyl or Cl-C4alkoxy, or is a -CO-R4 group, ~' R3 and R4 are each independently of the other unsubstituted phenyl or phenyl which is substituted by halvgen, Cl-C4alkyl and/or Cl-C4alkoxy, b) 30-60 parts by weight of a compound of formula lI, wherein R6 and R7 are each independently of the other hydrogen, Cl-CI2aL'cyl, Cl-C4aL1coxy or halogen, R8 and R9 are each independently of the other Cl-C4alkyl, or R8 and R9, when taken :. together, are tetramethylene or pentamethylene, and c) 20-60 parts by weight of a compound of formula III, wherein Rll and Rl2 are hydrogen and Rl3 is hydrogen, Cl-C4alkyl, Cl-C4alkoxy or halogen, or a mixture of methylated benzophenones.

; :' ~ .
-- . . . , ",, . ; ,., - . - - . - . . . . . .
: .~, . . . - . . - . , ~ . . . - ~, . .. .
.: . :: .-: ~ : - : : . : :

2~377~

The following compounds are representative examples of compounds suitable for use as component (a):
isobu~royldiphenylphosphine oxide pivaloyldiphenylphosphine oxide benzoyldiphenylphosphine oxide p-toluyldiphenylphosphine oxide p-tert-butylbenzoyldiphenylphosphine oxide a-naphthoyldiphenylphosphine oxide 2,6-dimethylbenzoyldiphenylphosphine oxide 2,6-dimethoxybenzoyldiphenylphosphine oxide 2,4,6-trimethylbenzoyldiphenylphosphine oxide 2,6-dichlorobenzoyldiphenylphosphine oxide 1,3-dimethyl-2-naphthoyldiphenylphosphine oxide 1,3-dichloro-2-naphthoyldiphenylphosphine oxide 2,4-dimethylfuran-3-carbonyldiphenylphosphine oxide 2,4,6-trimethylpyridine-3-carbonyldiphenylphosphinje oxide 2,6-dimethoxybenzoyldiphenylenephosphine oxide 2,6-dichlorobenzoylditolylphosphine oxide methylpivaloylphenylphosphinate methyl-2,4-dimethylbenzoylphenylphosphinate bist2,6-dichlorobenzoyl)phenylphosphine oxide bis(2,6-dichlorobenzoyl)-4-chlorophenylphosphine oxide bis(2,6-dichlorobenzoyl~-4-t-butylphenylphosphine oxide bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide bis(2,6-dimethylbenzoyl)phenylphosphine oxide bis(2,6-dimethylbenzoyl)-4-tolylphosphine oxide bis(2,6-dimethoxybenzoyl)phenylphosphine oxide :
bis(2,6-dimethoxybenzoyl)-2-naphthylphosphine oxide bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide bis(2,4,6-~imethylbenzoyl)-4-methoxyphenylphosphine oxide ~is(2-methyl-1-naphthoyl)phenylphosphine oxide bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide.
Compounds especially prefe~ed for use as component a) are 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis(2,6-dichlorobenzoyl)-4-propyl-phenylphosphine oxide.

.
.

.

. .
- , . , . . - -.
, ,'- . . . .

2~37~69 The following compounds are representa~ive examples of compounds suitable for use as component (b):

a-hydroxyisobutyrophenone p-isopropyl-a-hydroxyisobutyrophenone p-t-butyl-c~-hydroxyisobutyrophenone p-octyl-o~-hydroxyisobutyrophenone p-dodecyl-~-hydroxyisobutyrophenone p-chloro-a-hydroxyisobutyrophenone p-bromo-a-hydroxyisobutyrophenone p-methoxy-a-hydroxyisobutyrophenone p-ethoxy-oc-hydroxyisobutyrophenone 3,4-dimethyl-~-hydroxyisobutyrophenone 3,4-dimethoxy-a-hydroxyisobutyrophenone 3-chloro-a-hydroxyisobutyrophenone a-hydroxy-o~-methylbutyrophenone a-hydroxy-a-ethylbutyrophenone l -benzoylcyclopentanol I -benzoylcyclohexanol 1-(4-chlorobenzoyl)cyclohexanol.
Component b) is most preferably 1-benzoylcyclohexanol.
, The following compounds are representative examples of compounds suitable for use as component (c):
benzophenone, 4-methylbenzophenone, 2,4-dime~hylbenzophenone, 4-isopropylbenzo-phenone, 2-chlorobenzophenone, 2,2'-dichlorobenzophenone, 2-methoxybenzophenone,4-methoxybenzophenone, 4-propoxybenzophenone or 4-butoxybenzophenone. Mixtures of benzophenone derivatives may also be used, technical alkylating mixtures of benzophenone or benzophenone derivatives which are position isomers. Component c) is most preferably benzophenone.

Especially preferred are mixtures of 100 parts by weight of 2,4,6-trimethylbenzoyl-di-phenylphosphine oxide, 30-60 parts by weight of l-benzoylcyclohexanol and 20-40 parts by weight of benzophenone. These mixtures are liquid or low melting, and are therefore particularly suitable for use in liquid photopolymerisable systems.
:, .

, .' ~ ..

. . . . . . . . . .

2037~

The photoinitiators may also contain organic solvents. It is possible to make the mixtures liquid and to regulate their viscosity by the addition of such solvents. Relatively small amounts of solvent suf~lce for this purpose, preferably 5-50 parts by weight per 100 parts by weight of photocurable mixture. Typical examples of suitable solvents are isopropanol, methyl ethyl ketone, butyl acetate or propylene carbonate.

The described mixtures can be used in the practice of this invention as photoinitiators for the photopolymerisation of ethylenically unsaturated compounds or mixtures whichcontain such compounds. The unsaturated compounds can contain one or more olefinic double bonds. They may be low molecular (monomeric) or high molecular (oligomeric) compounds. Monomers containing one double bond are, typically, alkylacrylates orhydroxyalkylacrylates or hydroxyalkylmethacrylates, for exarnple methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate or 2-hydroxyethyl acrylate, isobornyl acrylate, methyl acrylate or ethyl methacrylate. Further examples of such monomers are acrylonitrile, acrylamide, methacrylamide, N-substituted (meth)acrylamides9 vinyl esters such as vinyl acetate, vinyl ethers such as isobutyl vinyl ether, styrene, alkylstyrenes and halostyrenes, N-vinylpyrrolidone, vinyl chloride or vinylidene chloride.
.. . .
~ Monomers containing several double bonds are, typically, ethylene glycol, propylene '' -',!'j glycol, neopentyl glycol, hexamethylene glycol, or bisphenol A diacrylate, 4,4'-bis(2-acryloyloxyethoxy)diphenylpropane, trimethylolpropane triacrylate, pentaerythritol triacrylate or tetraacrylate, vinyl acrylate, divinyl benzene, divinyl succinate, diallyl ~tll phthalate, triallyl phosphate, triallyl isocyanurate or tris(2-acryloyloxyethyl)isocyanurate.

:~ Typical examples of high molecular (oligomeric) polyunsaturated compounds are acrylated epoxy resins, acrylated polyethers, acrylated polyurethanes or acrylated poly-esters. Further examples of unsaturated oligomers are unsaturated polyester resins, which are normally prepared from maleic acid, phthalic acid and one or more diols, and which have molecular weights of ca. 500 to 3000. Such unsaturated oligomers may also be refeIred to as prepolymers.
:~ ' `~1 Often two-component mixtures of a prepolymer with a polyunsaturated monomer, or three-component mixtures which additionally contain a mono-unsaturated monomer, are used. The prepolymer in this case chiefly determines the properties of the coating film. By va~ying it, the skilled person is able to influence the properties of the cured film. The polyunsaturated monomer acts as crosslinker which makes the coating film insoluble. The .
,, , . ,, . ~ , .. . . . . . . . .

~" 2~3~76~

mono-unsaturated monomer acts as reactive diluent with aid of which the viscosity is lowered without haYing to use a solvent.

Such two- and three-componellt systems based on a prepolymer are used for p~inting inks as well as for coating compositions, photoresists or other photocurable materials. Single component systems based on photocurable prepolymers are also often used as binders for printing inks.

Unsaturated polyester resins are normally used in two-component systems together with a mono-unsaturated monomer, preferably with styrene. Speci~lc single component systems are often used for photoresists, for example the polymaleimides, polychalcones or polyimides disclosed in DE-OS 2 308 830.

The unsaturated compounds can also be used in admixture with non-photopolymerisable film-forming components. These components may typically be physically drying polymers or their solutions in organic solvents, such as nitrocellulose or cellulose acetobutyrate.
'rhey may also, however, be chemically curable or therrnocurable resins such as polyisocyanates, polyepoxides or melamine resins. The concomitant use of thermocurable resins is important for use in so-called hybrid systems which are photopGlymerised in a first step and crosslinked by a a thermal aftertreatment in a second step.

The invention thus also relates to photocurable mixtures comprising at least oneethylenically unsaturated compound and, as photoinitiator, a rnixture of a) 100 parts by weight of a compound of formula I, b) 10-70 parts of a compound of formula II, and c) 10-70 parts by weight of a compound of foIrnula III.
." .
in addition to the photoinitiator, the photopolymerisable mixtures may further contain different additives. Such additives are typically thermal inhibitors for preventing a premature polymerisation, for example hydroquinone or sterically hindered phenols.
Copper compounds, phosphorus compounds, quaternary ammonium compounds or hydroxylamines may be used to increase storage stability in the dark. Paraffin or similar wax-like substances which, at the start of polymerisation, migrate to the surface, can be added to exclude atmospheric oxygen. Minor amounts of UV absorbers$ such as those of the benzotriazole, benzophenone, hydroxyphenyltriazine or oxalanilide type, may be added as light stabilisers. Better still is the addition of light stabilisers which do not absorb UV light, for example sterically hindered amines (HALS).
!

/

~ .

~ .
' ' , ~ ' ' 20377~ 9 ~o -Amines may be added to accelerate the photopolymerisation, for example triethanolamine, N-methyl-diethanolamine, p-dimethylaminobenzoate or Michler's ketone. The photopolymerisation can further be accelerated by the addition of photosensitisers which displace or broaden the specral sensitivity. These photosensitisers are preferably aromatic carbonyl compounds such as thioxanthone, anthraquinone and 3-acylcoumarin derivatives as well as 3-(aroylmethylene)thiazolines.

The photocurable compositions of the invention can be used for different purposes. Of primary importance is their use in pigmented coating materials. The mixtures areespecially useful in white enamels, by which are meant paints pigrnented with TiO2.
Further utilities are the radiation curing of photoresists and printed circuit boards, as w~
as the production of printing plates. Another utility is for exterior coats which undergo postcuring on the surface in daylight.

The photoinitiators are conveniently used for the indicated fields of application in amounts of 0.1 to 10 % by weight, prefeMbly ca. 0.5 to 5 % by weight, based on the photocurable mixture.

Photopolymerisation is effected by known techniques by irradiation with light which is rich in shortwave radiation. Suitable light sources are typically mercury medium-pressure, high-pressure and low-pressure lamps, superactinic fluorescent tubes, metal halide lamps or lasers, the maximum emissions of which are in the range from 250 to 450 nm. Where combinations with photosensitisers or ferrocene derivatives are used, it is also possible to use light of longer wavelength or laser beams of up to 600 nm.

A multistep irradiation with radiation sources of different intensity or of different spectral composition may in certain cases be useful. Thus, for example, the wipe resistance of the coating surface can be achieved by a primary exposure and the full cure of the coating composition by a second exposure.
i}
- The use of the photoinitiator mixtures of the invention is illustrated by fo310wing Examples, in which parts and percentages are by weight.
;~
xample 1 A white enamel formulation is prepared from : -i, ~ . .

i :. . . : .
. - . ~ : , . . : , . . .
-: ~ ~ . . - ~ .

- , 2~377~9 13.5 parts of Ebecryl~) 830 (polyester acrylate ex UCB, Belgium), 1.0 part of hexanediol diacrylate 0.5 part of trimethylolpropane trisacrylate, 5.0 parts of titanium dioxide (rutile).

The photoinitiator mixtures indicated in Table 1 are added to this formulation. Samples of the white enamel formulation are applied in a layer thickness of 200 ~lm to aluminium sheets which have been primed with a white coil coat.
.
- The enamel coats are irradiated in a PPG exposure apparatus with HG medium-pressure lamps (2 x 80 W/cm). The number of passes is determined which are necessary for effecting cure (wipe resistance) at a running speed of 10 mlrnin (column 1).
`' The full cure is assessed by means of the pendulum hardness test using the apparatus of Konig (DIN 53 157) and the results are reported in column 2. The samples are then irradiated for 16 hours with S 20 W lamps (Philips TL 05), and the pendulum hardness is again measured (column 3). A certain postcuring of all samples occurs.
.. ~, . . .
The yellowing which occurs during this 16 hours exposure is also determined by measuling the Yellowness Index (YI) in accordance with ASTM D 1925-70 before andafter this exposure (columns 4 and 5).

Finally, the 20 gloss (ASTM D 523) of the samples is measured using a multigloss device (column 6). The results are reported In the following Table.
:
~i! Table 1:

Initiator 1 2 3 4 5 6 ~; 1 % TPO + 0.5 % BCH + 0.5 % BZP 4 41 65 1.9 1.8 72 ;~ 1.20 % l E'O + 0.65 %BCH + 0.65 % BZP 4 53 91 1.9 1.6 75 1.5 % TPO + 0.5 % BCH + 0.5 % BZP 3 39 101 1.6 1.2 77 ;~ 1.5 % TPO + 0.75 % BCH + 0.75 ~o BZP 3 41 81 1.8 1.8 77 , .
'; 1: number of passes to effect wipe resistance ~;~t 2: pendulum hardness after wipe resistance (seconds) .
., . ~

. - . -- . . . . . .

2~37~

3: pendulum hardness after 16 h postcure (seconds) 4: Yellowness Index after wipe resistance 5: Yellowness Index aRer 16 h postcure 6: 20 gloss (%) TPO: 2,4,6-trimethylbenzoyldiphenylphosphine oxide BCH: l-benzoylcyclohexanol BZP: benzophenone Example 2:
A white enamel fo~nulation based on an unsaturated polyester resin and styrene, pigmented with TiO2, is blended with the amounts of photoinitiator indicated in Table 2 and applied to chip boards in a layer thickness of 150 ,um. The samples are precured for 2 minutes under four 40 watt lamps (Philips TL 03). The maximum running speed un~il the samples are wipe-resistant is determined using a 120 W/cm D lamp (ex Fusion Systems) in order to gauge the reactivity of the photoinitiator.

Immediately after the cure, the pendulum hardness is measured with the K~nig pendulum apparatus (DIN 53 157). The samples are then postcured for lS minutes with five 20 W
: lamps (Philips TL 05) and thereafter the pendulum hardness is measured once more.

Table 2 .i .~
r~ Photoinitiator Maxirnum Pendulum hardness (% by wt., based on white enamel runnlng speed immediate after postcure .. 1.5 % TPO 10 m/min 74 91 i 1.30 % TPO
. + 0.10 % BCH 10 m/min 91 112 ~ + 0.10 % BZP
'. .. __ . _ . 2.5 % TPO 30 m/min 66 90 :
.~ 1.30 % TPO
+ 0.60 % BCH 40 m/min 66 91 ,,jl! +0.60%BZP

Example 3:
The white enamel formulation of Example 1 is blended with the photoinitiators listed in Table 3 and applied in a layer thickness of 150 ,um to aluminium sheets which have been .

-. ~ . . . .
, ~ ~ , - ' ' ' :

2al~7769 primed with a white coil coating. The samples are irradiated first for 90 seconds with i~our 40 W-lamps (TL 03). The samples are then irradiated with a Fusion D lamp in two passes at a running speed of 3 m/min and finally irradiated in a further pass at 6 m/min with two 80 W/cm Hg medium pressure lamps (PPG apparatus).

The pendulum hardness of the samples is measured with the Konig pendulum apparatus (DIN 53 1~7) immediately after the cure, after 15 minutes and after 16 hours additional irradiation with four 40 W-lamps. The Yellowness Index is also measured immediately after the cure and after 16 hours further ilTadiation. Finally, the 20 and 60 gloss are measured immediately after the cure and after 16 'nours postcure. The results are reported in Table 3.

Table 3:
.
Initiator 1 2 3 4 5 6 7 _ __ _ 1.17 % TPO + 0.5 ~o BCH + 0.33 % BZP 146 158 195 2.1 0.6 65/87 65/86 1.33 % TPO + 0.33 %BCH + 0.33 % BZP 153 156 188 2.3 0.9 62/85 62/85 1.33 % P.DP + 0.33 ~o BClI + 0.33 % BZF 160 162 174 4.7 1.2 66/85 65/86 ` 1.17 % TPO + 0.5 % BCH + 0.33 % BZP
+ 0.42 % isopropan~l 147 167 190 2.0 0.6 66/86 65/87 1.17%TPO+0.5%BCH+0.33%BZP
+ 0.42 % propylene carbonate 147 156 186 2.4 0.6 76/90 76/90 1: pendulum hardness (sec) immediately after cure 2: pendulum hardness (sec) after 15 min postcure 3: pendulum hardness (sec) after 16 h postcure 4: Yellowness Index immediately after cure ; 5: Yellowness Index after 16 h postcure 6: 20/60 gloss immediately after cure (%) 7: 20/60 gloss after 16 h postcure (%) TPO: 2,4,6-trimethylbenzoyldiphenylphosphine oxide BDP: bis(2,6-dichlorobenzoyl~-4-propylphenylphosphine oxide ~, BCH: 1-benzoylcyclohexanol BZP: benzophenone :i :

.. . ' ! ' . . . . .

~03~6~

Example 4:
The white enamel formulation of Example 1 is blended with the photoinitiators listed in Table 3 and applied in a layer thickness of 200 llm to aluminium sheets which have been primed with a white coil coating. The samples are irradiated with a 80 W/em Hg medium-pressure lamp (Hanovia) in 8 passes at a running speed of 10 m/min.

The samples are subjected to the falling ball test according to Erichsen (D~ 53 156).
Table 4 shows the depth of the ball indentation at which the enamel finish remains undamaged. The deeper the indentation, the more elastic the finish.

Photoinitiators Erichsendepth . .
1.17%TPO+0.5%BCH+0.33%BZP 1.7mm 1.17%TPO+0.5%BCH+0.33%BZP
+ 0.42 % propylene carbonate l.S mm 1 %TPO+ 1 %BCH 1.2mm . .
.''' , ., , .
., "

, A

' . . ` ~ , : ' 1 ' ' ' ' ' , . . . . . . . .
.. , ' . ' , ; . ' ' ': . . , ' . ,

Claims

1. A photoinitiator comprising a) 100 parts by weight of a compound of formula I, I

wherein R1 is C1-C18alkyl, C1-C4alkyl which is substituted by halogen or C1-C6alkoxy, or is C5-C8cycloalkyl, C7-C9phenylalkyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one or more identical or different members of the group consisting of halogen, C1-C12alkyl and/or C1-C12alkoxy, or is a monovalent, 5-or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, R2 is phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one or more identical or different members of the group consisting of halogen, C1-C12alkyl and/or C1-C12alkoxy, or is a monovalent, 5- or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, or is C1-C18alkoxy, phenoxy or phenoxy which is substituted by halogen, C1-C4alkyl or C1-C4alkoxy, or is benzyloxy, cyclohexyloxy or a -CO-R4 group, or R2 and R1, together with the phosphorus atom, form a ring, R3 is C1-C18alkyl, C1-C4alkyl which is substituted by halogen or C1-C6alkoxy, or is C5-C8-cycloalkyl, C7-C9phenylalkyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one more identical or different members selected from the group consisting of halogen, C1-C12alkyl and/or C1-C12alkoxy, or is a monovalent, 5- or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, or is a group wherein X is C2-C8alkylene, cyclohexylene, or phenylene or biphenylene which are each unsubstituted or substituted by halogen, C1-C4alkyl or C1-C4alkoxy, and R4 is C1-C18alkyl, C1-C4alkyl which is substituted by halogen or C1-C4alkoxy, or is C5-C8cycloalkyl, C7-C9phenylalkyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one more identical or different members selected from the group consisting of halogen, C1-C12alkyl and/or C1-C12alkoxy, or is a monovalent, 5- or 6-membered heterocyclic radical which contains nitrogen, oxygen or sulfur, or R4 and R3, when taken together, are C2-C12alkylene, vinylene or o-phenylene, b) 10-70 parts by weight of compound of formula II, II

wherein R6 and R7 are each independently of the other hydrogen, C1-C18alkyl, phenyl, C1-C18alkoxy, phenoxy, C1-C18alkylthio, phenylthio, C2-C8dialkylamino, piperidino, morpholino or halogen, and R8 and R9 are each independently of the other C1-C6alkyl, C3-C6alkenyl, C7-C9phenylalkyl or cyclohexyl, or R8 and R9, when taken together, are C4-C6alkylene, and c) 10-70 parts by weight of a compound of formula III, III

wherein R11, R12 and R13 are each independently of one another hydrogen, C1-C12alkyl, C1-C4-alkoxy, C1-C4alkylthio, halogen or C2-C6alkoxycarbonyl, or a mixture of such benzophenone derivatives.

2. A photoinitiator mixture according to claim 1, comprising a) 100 parts by weight of a compound of formula I, wherein R1 is phenyl, naphthyl or biphenylyl which are each unsubstituted or substituted by halogen, C1-C4alkyl or C1-C4alkoxy, R2 is phenyl, naphthyl or biphenylyl which are each unsubstituted or substituted by halogen, C1-C4alkyl or C1-C4alkoxy or is a -CO-R4 group, R3 and R4 are each independently of the other C1-C12alkyl, cyclohexyl, benzyl, phenyl, naphthyl or biphenylyl, or phenyl, naphthyl or biphenylyl which are each substituted by one more identical or different groups selected from the group consisting of halogen, C1-C4alkyl and/or C1-C4alkoxy, b) 20-70 parts by weight of a compound of formula II, wherein R6 and R7 are eachindependently of the other hydrogen, C1-C12alkyl, phenyl, C1-C12alkoxy, phenoxy or halogen, and R8 and R9 are each independently of the other C1-C4alkyl, allyl or benzyl, or R8 and R9, when taken together, are C4-C6alkylene, and c) 10-60 parts by weight of a compound of formula III, wherein R11, R12 and R13 are each independently of one another hydrogen, C1-C6alkyl, C1-C4alkoxy or halogen, or a mixture of alkylated benzophenones.

3. A photoinitiator mixture according to claim 1, comprising a) 100 parts by weight of a compound of formula I, wherein R1 is unsubstituted phenyl or phenyl which is substituted by halogen, C1-C4alkyl or C1-C4alkoxy, R2 is unsubstituted phenyl or phenyl which is substituted by halogen, C1-C4alkyl or C1-C4alkoxy, or is a -CO-R4 group, R3 and R4 are each independently of the other unsubstituted phenyl or phenyl which is substituted by halogen, C1-C4alkyl and/or C1-C4alkoxy, b) 30-60 parts by weight of a compound of formula II, wherein R6 and R7 are each independently of the other hydrogen, C1-C12alkyl, C1-C4alkoxy or halogen, R8 and R9 are each independently of the other C1-C4alkyl, or R8 and R9, when taken together, are tetramethylene or pentamethylene, and c) 20-60 parts by weight of a compound of formula III, wherein R11 and R12 are hydrogen and R13 is hydrogen, C1-C4alkyl, C1-C4alkoxy or halogen, or a mixture of methylated benzophenones.

4. A photoinitiator mixture according to claim 1, wherein component a) is 2,4,6-trimethyl-benzoyldiphenylphosphine oxide.

5. A photoinitiator mixture according to claim 1, wherein component a) is bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide.

6. A photoinitiator mixture according to claim 1, wherein component b) is 1-benzoylcyclo-hexanol.

7. A photoinitiator mixture according to claim 1, wherein component c) is benzophenone.

8. A photoinitiator mixture according to claim 1, comprising 100 parts by weight of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 30-60 parts by weight of 1-benzoylcyclohexanol and 20-40 parts by weight of benzophenone.

9. A photoinitiator mixture according to claim 1, containing 5-50 parts by weight of an organic solvent per 100 parts by weight of the mixture of a), b) and c).

10. A photoinitiator mixture according to claim 1, comprising 100 parts by weight of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 35-50 parts by weight of 1-benzoylcyclohexanol, 25-35 parts by weight of benzophenone and 20-30 parts by weight of isopropanol.

11. A photocurable mixture comprising at least one ethylenically unsaturated photopolymerisable compound and, as photoinitiator, a mixture as claimed in claim 1.

12. A photocurable mixture according eo claim 11, which contains a pigment, preferably a white pigment.

13. A photocurable mixture according to claim 11, which contains 0.1 to 10 % by weight of a photoinitiator mixture as claimed in claim 1.

14. A photocurable mixture according to claim 11, which contains 0.5 to 5 % by weight of a photoinitiator mixture as claimed in claim 1.