Note: Descriptions are shown in the official language in which they were submitted.
1336091
Photoinitiator copolymers
The invention relates to photoinitiator copoly-
mers constructed from at least two different monomer
units, of which at least one carries a structural unit
with a photoinitiating effect. Polymeric compounds of
this type are used as free-radical-forming photo-
initiators in the photopolymerization of ethylenically
unsaturated compounds or systems containing such com-
pounds. Photoinitiator copolymers exhibit a number of
advantages, many of which are unexpected, compared with
conventional monomeric photoinitiators or also homopoly-
meric photoinitiators derived therefrom.
Photochemically induced polymerization reactions
have achieved great importance in industry, in particular
when rapid curing of thin layers is imPortant, such as,
for example, in the curing of paint coats and plastic
coatings on paper, wood, metal and plastic or in the
drying of printing inks. Here, radiation curing in the
presence of photoinitiators is distinguished by a saving
in raw materials and energy, a low thermal load of the
substrate, and, in particular, by high speed, compared
with conventional methods of drying or curing coatings.
However, the production of polymeric materials per se by
polymerization of corresponding unsaturated monomeric
starting materials is also frequently carried out photo-
chemically and using photoinitiators, with customary
processes, such as solution and emulsion polymerization,
being used.
In addition, photoinitiators are frequently used
in photopolymerizable compositions for photolithographic
processes, such as, in particular, in negative photo-
resists in semiconductor electronics and in
optoelectronics.
~ 2 i3360~1
Since none of the reactants is generally capable
of adequately absorbing the photochemically active
radiation in the reactions mentioned, photoinitiators
must be added which are capable either of absorbing
incident, high-energy radiation, usually W light, and at
the same time of forming active initiator free radicals
which in turn initiate the photopolymerization, or of
transmitting the energy absorbed for free-radical form-
ation to one of the polymerizable reactants. The init-
iators do not normally take part in the actual poly-
merization reaction.
Photoinitiators which are suitable for these
purposes are predominantly compounds of the aromatic
ketone type, such as benzophenones, benzoin ethers,
benzil monoketals, dialkoxyacetophenones, thioxanthones,
bisacylphosphine oxides or hydroxyalkylphenones, or
derivatives derived from these types of structure.
Hydroxyalkylphenone photoinitiators, as described in
German Patent 2,722,264 and European Patent 3,002, have
proven particularly advantageous, principally due to
their high reactivity, but also because of the excellent
shelf life in the dark of the radiation-curable systems
to which they are added, and the low tendency towards
yellowing of the layers cured using these systems.
The continuing diversification and specialization
of processes and products in the sector of coating
technology using polymeric materials and the increasing
demand for tailor-made problem solutions is accompanied
by the fact that greater and more specific d~m~ are
also being made on the photoinitiators. Frequently,
conventional photoinitiators do not satisfy the demands
made of them today, or at least do not do so in an
optimal manner. Increasingly, these demands are that
photoinitiators should be capable of more than merely
forming free radicals which initiate only the photopolym-
erization or photocrosslinking. Essential problem areas
here are, for example, the compatibility in a very wide
variety of systems, in particular also those which, in
order to achieve certain material properties, also
~ - 3 _ 133~091
21489-8453
contain non-photopolymerizable components (so-called
hybrid systems), and, in addition, the migration-resis-
tant incorporation of photoinitiator or photolysis
products thereof into the photopolymerized end product.
At the same time, the additional properties must not
influence the photoreactivity of the initiator; a long
shelf life in the dark of the systems provided therewith
is likewise of high importance for usability in practice.
Further developments in these directions have
already been carried out, principally starting from the
hydroxyalkylphenone photoinitiators, which have a par-
ticularly high performance with respect to photo-
reactivity. Thus, for example, the photoinitiators
described in German Offenlegungsschrift 3,512,179 are
particularly suitable for use in aqueous systems. The
photoinitiators of German Offenlegungsschrift 3,~34,645
and European Offenlegungsschrift 161,463, which are
provided with unsaturated functions, and the particularly
versatile, coreactive photoinitiators of European Patent
Application EP-A-281,491 enable migration-resistant
incorporation into the product by the photochemically and
non-photochemically induced coreaction with a very wide
variety of sys~em components, with themselves or with the
substrate, before, during or even after the actual
2S polymerization.
However, these further developments, which are
very promising as far as the principle is concerned, are
still in many cases in need of improvement. Thus, pre-
domin~ntly only individual specific additional properties
can be achieved in each of the modified photoinitiators
of the specifications cited above. For ~his reason,
various applications and uses require a large number of
appropriately modified photoinitiators to be synthesized
from first principles and kept ready, which requires high
expense and is therefore not very economical.
The invention therefore had the object of finding
and providing high-performance photoinitiators using
which, on the one hand, a large number of tailor-made
additional properties can be achieved and which, however,
~ - 4 - 133 6 0~1
are on the other hand easily accessible, for example
starting from a few universally applicable basic
components.
It has now been found that these requirements are
fulfilled in an excellent manner by photoinitiator
copolymers having molecular weights between 500 and
1,000,000, obtAin~hle by copolymerization of at least two
different monomer units of the formulae I and II in the
I/II ratio = 1-100
Ra
I
(I) CH2 = C-(X)0 l IN
1 0 ~,
(II) CH2 = C-(X)0 1 A
in which
R~ and Rb, independently of one another, are each H, Cl,
CN, C16-alkyl or phenyl
X is CO--, COO--, O-CO--, ( CH2 ) nY ~ COO ( CH2 ) I~Y,
CO(OCH2CH2)nY where n = 1-10 and Y is a single
bond, -O-, -S-, -CO-, -COO-, -OCO-, -NH- or
-N(Cl6-alkyl)-,
IN is one of the basic photoinitiator structures
~ -I-R 1l R
in whichO S
R is -CR3R~R5 or -P(R6) 2 ~ R2
and
R1 and R2 are H, halogen, Cll2-alkyl or Cll2-alkoxy,
R3 and R~ independently of one another, are each H, Cll2-
25alkyl, Cll2-alkenyl, Cll2-alkoxy or together are
C2 6-alkylene,
R5 is -OH, Cl6-alkoxy, Cl6-alkanoyloxy, -N(Cl6-
alkyl)2~
~ 5 - 1 33 6 09 1
26474-171
-N ~ , -N ~ , -N ~ -H -N 0
-So2R7 or -OS02R
R is Cl_6-alkyl, Cl_6-alkanoyl, phenyl or benzoyl, in
each case optionally substituted by halogen, Cl 6-alkyl or Cl 6-
alkoxy,
R7 is Cl 6-alkyl or phenyl,
A is one of the basic photoinitiator structures IN as
defined above, or H~ Cl 12-alkyl, Cl 12-alkenyl, phenyl, styryl,
halogen, NC0, NCS, N3, S03H, S02Cl,
CRC=CRdRe or CRC -\ CRdRe where RC, Rd and Re are each H or CH3,
or is SiR RgR where R , Rg and Rh are each Cl, Cl 12-alkyl,
Cl-12-alkXY or C1_12-alkanoyloxy.
The copolymers according to the invention are high-
performance, individually structurable photoinitiators for the
photopolymerization or photocrosslinking of ethylenically
unsaturated compounds or systems containing such compounds.
However, they can also be employed themselves as simultaneously
photoinitiating and film-forming components in radiation-curable
systems.
The invention thus relates to photoinitiator copolymers
having molecular weights of between 500 and 1,000,000, obtainable
by copolymerization of monomer units of the formulae I and II
defined above in the I/II ratio = 1-100.
The invention furthermore relates to the use of these
photoinitiator copolymers as photoinitiators for the photopolymeri-
` - 5a -
26474-171
13360~1
zation of ethylenically unsaturated compounds or systems contain-
ing such compounds.
The invention additionally relates to a process for the
preparation of photopolymerizable systems containing ethylenically
unsaturated compounds, at least one of these photoinitiator
copolymers being added to the mixture to be polymerized.
Finally/ the invention relates to polymerizable
~ 1336û~
systems contAini~g at least one ethylenically unsaturated
photopolymerizable compound and, optionally, further
known and customary additives cont~ining at least one of
these photoinitiator copolymers.
The photoinitiator copolymers according to the
invention are novel. They prove to be highly reactive
photoinitiators whose specific properties can be specifi-
cally modified and varied through the quan~titative and
qualitative choice of the monomer units I and II. They
are very simply accessible by thermal copolymerization of
the appropriate monomer components. Due to their polyme-
ric character, they have high migration resistance in the
photopolymerizable system and in the photopolymerized end
product.
The photoinitiator copolymers according to the
invention are built up from at least two different
monomer units of the formulae I and II.
The monomer unit I contains a polymerizable,
ethylenically unsaturated structural part in which the
radical R- can be hydrogen, chlorine, cyano, a Cl6-alkyl
group or a phenyl group. R~ is preferably hydrogen, and
the unsaturated structural part is thuc preferably a
vinylic groupc This unsaturated structural part is linked
to any basic photoinitiator structure IN, as is, in
principle, also present in conventional photoinitiators,
either directly via a single bond or via a bridging group
X.
The bridging group X can be a carbonyl, carboxyl
or alkylene group having 1-10 C atoms. It can alterna-
tively be a carbonyloxy alkylene or carbonylpolyoxy-
ethylene group, in each case having 1-10 methylene units
or oxyethylene units respectively. The linking to the
basic photoinitiator structure IN can take place via a
single bond or via an oxygen, sulphur, carbonyl, carboxyl
or amino group. Preferred linkings of unsaturated struc-
tural unit to basic photoinitiator structure IN are the
single bond, the carbonyl group, the carbonyloxymethyl-
enoxy group and the carbonyloxyethoxy group. In the case
of linking via a single bond, vinyl-substituted
~ 7 ~ 133~ 0~ 1
derivatives of customary photoinitiators result. In the
other cases of preferred linkings, acrylated photoinit-
iator derivatives result.
IN is essentially the aromatic ketone structural
unit or the thioxanthone structural unit 8
~ -C-R
Rl R2
as present in most classical photoinitiators, but can
alternatively be any other structures having photo-
initiator properties.
If R is the -CR3R4R5 group, the abovementioned
definitions for R3, R~ and R5 accordingly give the basic
photoinitiator structures of the acyloin ethers, the
dialkoxyacetophenones, the hydroxyalkylphenones and
aminoalkylphenones and the ~-sulphonyl ketones.
Copolymerizable hydroxyalkylphenone derivatives
are particularly preferred monomer units of the formula
I.
tol
If R is the -P(R6) 2 group, the resultant photo-
initiators belong to the class comprising the acylphos-
phine oxides.
Copolymerizable thioxanthone derivatives are
likewise preferred monomer units of the formula I.
Numerous unsaturated derivatives of a very wide
variety of photoinitiator groups, as represented by the
formula I, are known, and some are also commercially
svailable. This applies, in particular, to the hydroxy-
alkylphenone derivatives described in German Offenle-
gungsschrift 3,534,645 and European Offenlegungsschrift
161,463, and to the corresponding photoinitiators pro-
vided with unsaturated functions, of German Patent
Applications P 3,707,891 and P 3,738,567. In principle,
they can be prepared by st~n~Ard methods of organic
chemistry.
The reaction conditions here sre given in the
~ 13360~1
-- 8 --
st~ rd works of preparative organic chemistry, for
example HOUBEN-WEYL, Methoden der organischen Chemie
[Methods of Organic Chemistry], Georg-Thieme Verlag,
Stuttgart, or ORGANIC ~YNln~SIS, J. Wiley, New York,
London, Sydney.
In general, it i8 favourable to prepare the
comonomers of the formula I or corresponding precursors
by proven synthetic methods as customary for the basic
photoinitiators. It is advantageous here to start
directly from the known photoinitiators as starting
materials and to link the unsaturated structural unit to
these using customary reactions, such as substitution
reactions, in one or more steps. However, precursors of
the known photoinitiators which already have suitable
substituents can also be used and the actual photo-
initiator active structure only produced in these when
the unsaturated structural part is already present.
Particularly suitable precursors for photo-
initiators which have been provided with unsaturated
functions are the photoinitiator derivatives described in
German Patent Applications P 3,707,891 and P 3,738,567,
which carry substituents having reactive functional
groups.
Of these, the hydroxyethoxy- and hydroxyethyl-
thio-substituted photoinitiator derivatives are preferred
since they can easily be converted into the corresponding
(meth)acrylic acid esters. Typical photoinitiator deriv-
ative~ which have been provided with unsaturated func-
tions and can be used as monomer components of the
formula I for the photoinitiator copolymers according to
the invention are, for example,
4-vinylphenyl 2-hydroxy-2-propyl ketone (Ia)
4-allyloxyphenyl 2-hydroxy-2-propyl ketone (Ib)
4-2-allyloxyethoxyphenyl 2-hydroxy-2-propyl ketone (Ic)
vinyl 4-(2-hydroxy-2-methylpropionyl)phenoxyacetate
(Id)
4-acryloyloxyphenyl 2-hydroxy-2-propyl ketone (Ie)
4-methacryloyloxyphenyl 2-hydroxy-2-propyl ketone (If)
1336~1
~ g
4-2-acryloyloxyethoxyphenyl 2-hydroxy-2-propyl
ketone (Ig)
4-2-methacryloyloxyethoxyphenyl 2-hydroxy-2-propyl
ketone (Ih)
5 4-2-acryloyloxydiethoxyphenyl 2-hydroxy-2-propyl
ketone (Ii)
4-2-scryloyloxyethylthiophenyl 2-hydroxy-2-propyl
ketone (I~)
4-2-acryloyloxyethylthiophenyl 2-N-morpholino-2-propyl
ketone (Ik)
2-[2-(acryloyloxy)ethylthio]thioxanthone (Il)
2-t2-(acryloylamino)ethylthio]thioxanthone (Im)
2-t2-(allyloxyethylthio]thioxanthone (In)
2-t2-(allylamino)ethylthio]thioxanthone (Io)
4-t2-(methacryloyloxy)ethoxycarbonyl]thioxanthone (Ip)
The monomer unit of the formula II is built up
entirely analogously to the monomer unit of the formula
I. The group A linked in this unit to the unsaturated
structural unit, either directly or via the bridging
group X, can be a basic photoinitiator structure IN, as
defined above, or alternatively hydrogen, Cl ~,-alkyl,
-alkenyl, phenyl, styryl, halogen, such as, in particular, chlorine and
fluorine, the isocyanate, isothiocyanate, azide, sul-
phonic acid or sulphonyl chloride group, a vinyl or
oxiranyl group, which may also optionally be monosub-
stituted or polysubstituted by chlorine or methyl, or a
silyl group in which the radicals bonded to silicon are
chlorine and/or C1lz-alkyl and/or Cll2-alkoxy and/or Cll2-
alkanoyloxy.
A large number of unsaturated monomer units of
the formula II which contain no photoinitiating struc-
tural parts IN are known from the field of polymer
chemistry and are available. These are pre~omin~nt vinyl
and acrylic derivatives, i.e. customary, ea~ily and
inexpensively available, unsaturated monomer components.
Preferred monomer components of this type are, in
particular, those which contain functional groups which
are capable of further reactions, such as, in particular,
hydroxyl, carboxyl, carboxamide, sulphonic acid,
13~
-- 10 --
isocyanate, olefinically unsaturated and silyl groups.
Photoinitiator copolymers according to the invention
having specific properties which are tailor-made for the
particular use can be prepared through functionalized
monomer components of this type. Thus, compatibility with
a very wide variety of radiation-curable systems and, in
particular, also with hybrid binder systems can be
achieved. The functional groups impart the photoinitiator
copolymers according to the invention with coreactivity
as in P 3,707,891/P 3,738,567, i.e., in particular, with
the ability to react with components of the radiation-
curable systems or with the substrate.
Typical monomer units of the formula II of this
type are, for example, (meth)acrylic acid, (meth)acryl-
amide, alkyl (meth)acrylate, hydroxyethyl methacrylate,
alkenyl or epoxy (meth)acrylates, hexanediol diacrylate,
acrylonitrile, styrene, divinylbenzene, methyl vinyl
ketone, N-vinylpyrrolidone, 2-(N,N-dimethylamino)ethyl
methacrylate and 3-(trimethoxysilyl)propyl methacrylate.
In the case of monomer components of the formula
II cont~ining initiator groups, those are likewise
preferred which have been indicated above a4 being
preferred for the monomer units of the formula I. If the
photoinitiator copolymers according to the invention are
in each case built up only from initiator-cont~ining
monomers, the monomer units of the formula I and of the
formula II are different from one another.
The preparation of the photoinitiator copolymers
according to the invention from the monomer units of the
formulae I and II i8 carried out in a manner known per
se for the polymerization of olefinically unsaturated
compounds of this type, namely in solution using cus-
tomary thermally activatable free-radical initiators,
such as, for example, benzoyl peroxide or azobisiso-
butyronitrile, with exclusion of light. The monomer units
of the formulae I and II are employed here in amounts
such that the I:II ratio is between 1 and 100, preferably
between 2 and 10. Typical solvents of the polymerization
are, for example tetrahydrofuran and toluene. The reac-
11- 133~9~
tion is normally carried out at the reflux temperature of
the solvent. The photoinitiator copolymers are isolated
by precipitation using a non-solvent, for example n-
hexane. The photoinitiator copolymers can be purified by
re-precipitation, repeated if necessary. As is customary
for polymer products, the products obtained can be ade-
quately characterized by their average molecular weight
Mw, which can be determined by gel permeation chromato-
graphy and their glass transition temperature Tg, which
can be determined by differential thermoanalysis. A
random distribution of the various monomer units in the
copolymer is assumed. The average molecular weight can be
between 500 and 1,000,000 and is preferably between 1,000
and 10,000.
The photoinitiator copolymers according to the
invention can very advantageously be used for the photo-
polymerization of ethylenically unsaturated compounds or
systems contAining such compounds as photoinitiators
which have been provided with tailor-made additional
properties. They are principally used analogously to
conventional photoinitiators as W curing agents for
paint or polymer coatings, W-curable binder or hybrid
binder systems, printing inks and in the radiation curing
of aqueous prepolymer dispersions. They are used in a
customary manner, generally being added to the systems to
be polymerized in amounts of 0.1-20% by weight, prefer-
ably 0.5-12% by weight. They are generally added by
simply being stirred into the systems to be polymerized.
The photoinitiator copolymers according to the
invention can in many cases also be used even as the only
or the essential component of radiation-curable systems.
In this case, they simultsneously take on both the film-
forming and photoinitiating functions. Thus, for example,
copolymers of 4-(2-acryloyloxyethoxy)phenyl 2-hydroxy-2-
propyl ketone (Ig) with a 2-dimethylaminoethyl meth-
acrylate or 3-(trimethoxysilyl)propyl methacrylate,
applied as a layer to a substrate, can be photostructured
principally using W radiation. These materials are thus
suitable for use as negative photoresists.
` ~ - 12 - 1336091
21489-8453
Using the photoinitiator copolymers according to
the invention, polymer materials which cannot themselves
be photocrosslinked or photostructured since they do not
contain, for example, any ethylenically unsaturated
double bonds can also be rendered photoreactive.
It is known that the action of numerous conven-
tional photoinitiators can in some cases be considerably
increased by mixing with photoinitiators of a different
structure, i.e. coinitiators and/or sensitizers, such as,
in particular, organic amines. Typical mixtures are, for
example, mixtures of hydroxyalkylphenones with thioxan-
thones and, if appropriate, amino compounds, such as, for
example, N-methyldiethanolamine.
A particularly preferred aspect of the invention
is the combination of initiators with coinitiators or
sensitizers in the photoinitiator copolymers according to
the invention. This is because it has been shown, sur-
prisingly, that photoinitiator copolymers of this type
are more effective than mixtures of the basic conven-
tional photoinitiators, coinitiators and sensitizers.
Thus, for example, copolymers of the unsaturatedhydroxyalkylphenone derivative Ig and the unsaturated
thioxanthone derivative Im prove to be considerably more
effective than the corresponding mixture of the conven-
tional hydroxyalkylphenone and thioxanthone photo-
initiators. An explanation for this could be a direct,
coinitiating interaction of the various initiator groups,
caused by fixation in the copolymer structure.
Photoinitiator copolymers can very advantageously
also be applied to the substrate material as a discrete
photoinitiator layer and only then provided with a
photopolymerizable layer material. Use in the form of
two-layer systems of this type is carried out as in
German Offenlegungsschrift 3,702,897. Particularly
ad~antageous here are photoinitiator copolymers having
polar, optionally chelate-forming groups and having silyl
groups. Better fixation to metal, semiconductor, glass and
ceramic substrates is thereby achieved.
_ 13 - 13 3~9 1
Copolymers having amino-group-contAining monomer
components of the formula II, for example cont~ining
2-(N,N-dimethylamino)ethyl methacrylate, contain the
frequently advantageous amine accelerators and are more
reactive than the corresponding conventional systems.
Dyes which are capable of forming salts with
amino groups can be incorporated into amino-group-con-
t~ining photoinitiator copolymers of this type during
preparation. Examples of suitable dyes are xanthene dyes,
such as, for example, Bengal Pink. Surprisingly, the
absorption mAximllm is thereby shifted into the longer-
wave region, which means that photoinitiator copolymers
modified in this way can also be activated using longer-
wave radiation, for example between 500 and 600 nm.
In general, the photoinitiator copolymers accor-
ding to the invention have excellent migration resistance
due to their high-molecular character. This means that
they do not migrate into or out of the corresponding
radiation-curable systems, which is particularly impor-
tant for numerous applications.
A system to be polymerized is taken to mean a
mixture of monofunctional or polyfunctional, ethylenic-
ally unsaturated monomers which can be initiated by means
of free radicals, oligomers, prepolymers, polymers or
mixtures of ~hese oligomers, prepolymers and polymers
with unsaturated monomers, it also being possible, if
necessary or desired, for the mixture to contain further
additives, such as, for example, antioxidants, light
stabilizers, dyes, pigments, but also further known
photoinitiators and reaction accelerators. Suitable un-
saturated compounds are all those whose C=C double bonds
have been activated by, for example, halogen atoms,
carbonyl, cyano, carboxyl, ester, amide, ether or aryl
groups or by conjugated further double or triple bonds.
Examples of such compounds are vinyl chloride, vinylidene
chloride, acrylonitrile, methacrylonitrile, acrylamide,
methacrylamide, methyl, ethyl, n- or tert.-butyl, cyclo-
hexyl, 2-ethylhexyl, benzyl, phenyloxyethyl, hydroxy-
ethyl, hydroxypropyl, lower alkoxyethyl or tetrahydro-
~ l336asl
- 14 -
furfuryl acrylate or methacrylate, vinyl acetate,
propionate, acrylate or succinate, N-vinylpyrrolidone,
N-vinylcarbazole, styrene, divinylbenzene, substituted
styrenes, and the mixtures of unsaturated compounds of
this type. Polyunsaturated compounds, such as, for
example, ethylene diacrylate, 1,6-hexanediol diacrylate,
propoxylated bisphenol A diacrylate and dimethacrylate,
trimethylolpropane diacrylate and pentaerythritol tri-
acrylate can also be polymerized with the photoinitiators
used according to the invention. Suitable photopolymeriz-
able compounds are furthermore unsaturated oligomers,
prepolymers or polymer~ and mixtures thereof with un-
saturated monomers. These include, for example, un-
saturated polyesters, unsaturated acrylic materials,
epoxy materials, urethanes, silicones, aminopolyamide
resins and, in particular, acrylated resins, such as
acrylated silicone oil, acrylated polyesters, acrylated
urethanes, acrylated polyamides, acrylated soybean oil,
acrylated epoxy resin and acrylated acrylic resin,
expediently mixed with one or more acrylates of the mono-
di- or polyalcohol.
The expression "photopolymerization of ethylenic-
ally unsaturated compounds" should be understood in its
broadest sense. It includes, for example, the further
polymerization of or crosslinking between polymeric
materials, for example of prepolymers, the homopolymeriz-
ation, copolymerization and terpolymerization of simple
monomers and also the combination of the types of reac-
tion mentioned.
The photopolymerization can be initiated by the
action of high-energy radiation, preferably W light, on
the photopolymerizable systems containing the photo-
initiator copolymers according to the invention.
- The photopolymerization is carried out by methods
known per se by irradiation with light or W radiation of
the wavelength range from 250-500 nm, preferably
300-400 nm. Radiation sources which can be used are
sunlight or artificial-light lamps. For example, mercury
high-pressure, medium-pressure or low-pressure lamps and
1336091
- 15 -
xenon and tungsten lamps sre advantageous.
The photopolymerization using the photoinitiator
copolymers according to the invention can be carried out
both batchwise and continuously. The duration of irradi-
S ation depends on the way in which the polymerization iscarried out, on the type and amount of the polymerizable
materials employed, on the type and concentration of the
photoinitiators used, and on the intensity of the light
source, and can be in the range from a few seconds to
minutes, such as, for example, in the case of radiation-
curing of coatings, but also in the region of hours in
the case of large batches, such as, for example, in bulk
polymerization.
The photoinitiator copolymers according to the
invention are preferably used as photoinitiators in the
W curing of thin layers, such as, for example, paint
coats, on all materials and carriers which are customary
for this purpose. These can principally be paper, wood,
textile carriers, plastic and metal. An important area of
application is also the drying or curing of printing inks
and screen-printing materials, of which the latter are
preferably employed in surface coating or shaping of, for
example, cans, tubes and metallic sealing caps. Due to
the very substantial to complete absence of free in-
itiator radicals or free photolysis products when thephotopolymerization is complete in the systems to which
the photoinitiator copolymers according to the invention
have been added, they are particularly suitable in areas
of application where diffusion of such radicals into
media surrounding corresponding end products i~ to be
excluded, for example if packing provided with photo-
polymerizable coatings comes into contact with
foodstuffs.
ExamPles
A. Preparation of photoinitiator copolymers
General preparation procedure:
The monomeric starting materials in the approp-
riate molar amounts are dissolved in THF (150-300 ml/
batch up to 100 mmol), and azobisisobutyronitrile
~ - 16 - 1336~1
(150-300 mg/bstch up to 100 mmol) is added. The mixture
is refluxed for 12 hours. The solvent is then stripped
off, the residue is taken up in ethyl acetate, and the
solution is treated with activated charcoal and filtered.
The photoinitiator copolymer is obtained by precipitation
using n-hex~ne and re-precipitation from ethyl acetate/n-
hexane.
Photoinitiator monomers used:
4-(2-acryloyloxyethoxy)phenyl 2-hydroxy-2-propyl
ketone (Ig)
4-(2-methacryloyloxyethoxy)phenyl 2-hydroxy-2-propyl
ketone (Ih)
4-(2-acryloyloxyethylthio)phenyl 2-(N-morpholino)-2-
propyl ketone (Ik)
2-[2-(acryloyloxy)ethylthio]thioxanthone (Il)
4-[2-(methacryloyloxy)ethoxycarbonyl]thioxanthone (Ip)
Photoinitiator copolymers prepared:
Example Monomers/ Molar Mw Tg (C)
No. amount
1 ~g 10
Il 1 3000
2 Ig
Il 1 3200 37.7
3 Ik 5
Il 1 1900 47.4
4 Ik 10
Il 1 1900 47.9
Ik 15
Il 1 1950 40.8
6 Ik 10
Ip 1 4100 38.5
~ ~ 17 1336~1
Example Monomers/ Molar Mw Tg (C)
No. amount
7 Ik 10
Ip 1 3000 32.7
acrylic acid 2
8 Ik 10
Ip 1 3050 35.3
acrylic acid 5
9* Ig 3
2-dimethylamino- 1 3450 36.5
ethyl methacrylate
Bengal Pink (0.5 g/100 mmol batch)
Ih 6
methyl methacrylate 1 2200 107
11 Ih
methyl methacrylate 1 2300 90.2
12 Ig 10
n-dodecyl acrylate 1 3400 28.3
13 Ig 5
acrylic acid 1 3300 35.9
14 Ig 10
acrylamide 1 3000 45.3
Ig
acrylamide 1 2300 62.9
16 Ig 3
3-(trimethoxysilyl)- 1 3100 (oil)
propyl methacrylate
133~91
-18-
Example Monomers/ Molar Mw Tg (C)
No. amount
17 Ig 6
3-(~rimethoxysilyl)- 1 3100(oil)
propyl methacrylate
* Naximum absorption at ~ = 550 nm
B. Applicational comparison experiments
The photoinitiator copolymers according to the
invention to be tested and corresponding conventional
photoinitiators or photoinitiator mixtures for comparison
were stirred into samples of a pigmented, radiation-
curable binder system comprising
75 parts by weight of polyester acrylate (Laromer
EA 81, BASF)
25 parts by weight of heY~n~diol diacrylate
30 parts by weight of TiO2
The initiator-contA i n ing systems were applied to
glass plates (10 x 10 cm) in a film thickness of 24 ~m.
The W curing was then carried out by passing the
coated plates on a variable-speed col.ve~or belt under Hg
medium-pressure lamps (lamp power 2 x 80 W/cm; lamp
distance 10 cm).
As a measure of the respective curing result at
various belt speeds, the Konig pendulum hardness (DIN
53157) was determined after storage for 20 hours.
Belt speed (m/min)
Pendulum hardness (seconds) 5 10 15 20
Initiator/Content~
Ex. No. 1 / 3 ~ by weight 124 83 71 58
Ex. No. 2 / 3 ~ by weight 133 95 81 62
+
Comparison + / 3 % by weight 92 66 53 41
+ In all cases additionally 2% by weight of
13~6091
-19-
~'~ 2148g-8453
N-methyldiethanolamine
+
+ Mixture of phenyl 2-hydroxy-2-propyl ketone and 2-
isopropylthioxanthone/9:1 (Darocur~1664, E. Merck)
C. Application examples/photostructuring
The photoinitiator copolymers according to the inven~ion,
i.e , copolymers containing hydroxyalkyl phenone and thio-
xanthone units, furnish substantial better curing results,
~red with mlxtureso~ the respective basic photoinitiators
A 10~ solution of the copolymer as in Ex. No. 9
in diethylene glycol dimethyl ether was spin-coated (30
seconds, 4500 rpm) onto a glass plate (5 x 5 cm). The
coated plate was dried ~or 10 minutes at lS0~C. The plate,
half of which was covered, was irradiated for 4 minutes
using a W lamp (type TQ 180, Heraeus Original Hanau~ at
a distance of 5 cm. After the irradiation, the plate was
treated with acetone to dissolve off the unexposed part
of the coating. A highly adherent, cured, 0.4 ~m thick
coating which remained unchanged even after relatively
long storage in acetone remained in the exposed region.
An analogous result was achieved using the
copolymer as in Ex. No. 16.
An analogous result was achieved using a copoly-
mer comprising monomer Ig, 3-(trimethoxysilyl)propyl
methacrylate and methyl methacrylate in a molar ratio
3:1:5.
~' ~
~c: A
