Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Reexamination Certificate
1999-06-16
2001-09-25
Berman, Susan W. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
C522S153000, C522S129000, C522S130000, C522S904000, C522S905000, C526S283000, C526S328000, C526S328500
Reexamination Certificate
active
06294591
ABSTRACT:
The invention relates to a process for preparing radiation-crosslinkable polymers based on polymeric acrylates or methacrylates, generally referred to below for short as (meth)acrylates. Polymers of this kind are known and are used to produce radiation-curable coatings, paints, adhesives or impregnating compositions.
These polymers are copolymers comprising units of (meth)acrylates, especially the alkyl esters, and possibly (meth)acrylic acid, and units having polymerizable or crosslinkable groups. Polymerization or crosslinking takes place either thermally, ie. at elevated temperature, or—preferably—by exposure to actinic radiation, especially ultraviolet radiation. Crosslinking by radiation requires the presence of initiators which can be activated by radiation, especially free-radical initiators. Such compounds are often not very compatible with the polymers, and tend to separate out. Coating of the substrate that is to be treated is therefore generally carried out from a solution in a common solvent for both of the components.
Because of the environmentally polluting solvent vapors produced in this operation, attempts have been made more recently to employ solvent-free coating compositions, which are either liquid and comprise low molecular polymerizable constituents or which can be applied from the melt or as a powder coating. Compositions comprising liquid monomers have an unpleasant odor, are often allergenic and are of only limited storage life. To prepare compositions consisting essentially of solid constituents it is necessary, for the reasons given above, to incorporate photoinitiator units into the reactive polymers.
EP-A 458 164 describes radiation-crosslinkable polymers containing copolymerized units having phenone radicals, especially benzophenone radicals, in side groups.
EP-A 395 990 describes UV-crosslinkable copolymers which contain units of compounds capable of hydrogen abstraction and photoreactive units.
The preparation of these known polymers and the introduction of the reactive radicals takes place in each case by polymerizing a mixture of the starting materials. To prepare the individual end products, therefore, it is necessary in each case to prepare the monomers substituted by the functional groups, especially the photo-reactive groups, these monomers generally being (meth)acrylates, and to isolate these monomers in the purity required for polymerization. This technique requires the handling of aggressive monomers up to the final stage and is laborious on account of additional purification steps.
It is an object of the present invention to propose a process for preparing radiation-crosslinkable, polymeric (meth)acrylates having different reactive substituents, especially photoactive substituents, with or without further, crosslinkable, substituents, in which it is possible, for individual products, to start from a common, nonaggressive product which is, if appropriate, available on the industrial scale as well and to obtain, by reaction with readily available co-reactants, a large number of different desired end products.
We have found that this object is achieved by a process for preparing radiation-crosslinkable, polymeric (meth)acrylates that consists in reacting an acrylate or methacrylate copolymer containing units having a reactive side group with a compound that contains a group which is capable of reacting with the reactive side group and also a group which is capable of forming free radicals under the action of actinic radiation.
The term “radiation-crosslinkable” is intended for the purposes of this description to refer to a layer or mixture that can be permanently altered in its properties, in particular in its solubility, by actinic, ie. chemically active radiation. Short-wave visible or long-wave ultraviolet light is preferably employed as such radiation. Any relatively high-energy radiation is of course also suitable, such as short-wave UV light, electron beams, X-rays or gamma radiation, or—given appropriate sensitization—relatively long-wave light as well. Laser radiation can likewise be employed.
As (meth)acrylate copolymers it is preferred to employ those which in addition to (meth)acrylate units also comprise units having hydrogens which can be eliminated by the action of free radicals. Particularly suitable such units are those having tertiary hydrogens or hydrogens a to a double bond. Units of other copolymerizable monomers, for example maleic or flmaric acid compounds, can also be present in the copolymers.
Reactive side groups in the (meth)acrylate copolymers employed are especially isocyanate, hydroxyl, carboxyl, carboxylic anhydride, amino or oxirane groups. These groups have generally been introduced by copolymerization with appropriate monomers, for example with hydroxyalkyl (meth)acrylates, (meth)acrylic acid, aminoalkyl (meth)acrylates, isocyanatoalkyl (meth)acrylates or glycidyl (meth)acrylate.
The groups, in the generally low molecular mass co-reactants of the copolymers, that have the capacity to react with the reactive side groups of said copolymers are preferably hydroxyl, carboxyl, carboxylic anhydride, isocyanate or amino groups. Examples of such low molecular mass co-reactants are hydroxy-, hydroxyalkyl- or hydroxyalkoxybenzophenones, -anthraquinones or -thioxanthones. These compounds are preferably reacted with oxirane, isocyanate, carboxyl or carboxylic anhyride groups in the polymer.
For the polymer-analogous introduction of radicals having groups which can be induced to form free radicals by radiation, as is to be undertaken here, it is appropriate in principle to use any combination of reactive side groups in the polymer having corresponding groups, suitable as co-reactants, in the low molecular mass reaction component. Groups capable of inter-reacting in this way are required merely to be of such kind that they do not disrupt the preparation of the components, for example the polymerization of the corresponding monomers to give the reactive polymer, and do not react with themselves under the conditions of processing. Appropriate combinations of reactive groups are known and are customary in the modification of polymers by means of polymer-analogous reactions.
Groups which are capable of forming free radicals under actinic irradiation are, preferably, the radicals of aromatic ketones or of quinones, for example of xanthone, thioxanthone, 9,10-anthraquinone, benzil, acetophenone, benzophenone and substituted benzophenones. Particularly preferred parent structures are phenones of the formula
R
1
—CO—Ph(—R
2
)n
where Ph is a phenylene group with n-1 additional free valences
R
1
is alkyl or aryl or a radical R
2
,
R
2
is OH, R
3
OH, N(R
3
)
2
, NHR
4
, NHR
3
OH, COOH, COOR
3
OH, R
3
NCO or NCO, where R
3
is alkyl or alkylene of 1 to 6 carbons and R
4
is alkyl of 1 to 6 carbons or cycloalkyl, and
n is 1 to 3
and where two or more radicals R
2
can be identical to or different from one another.
The alkyl or alkylene groups R
1
or R
2
generally have 1 to 6, preferably 1 to 3, alkylene groups, in general of at least 2 carbons.
The above-described polymer-analogous reaction produces modified polymers having side groups which under actinic radiation form free radicals. The modified, radiation-sensitive polymers preferably also include groups which have hydrogens that can be eliminated or abstracted under the action of free radicals, especially tertiary hydrogens or hydrogens &agr; to a double bond. They may also contain other crosslinkable side groups, for example free-radically polymerizable double bonds, and especially (meth)acryloyloxy groups.
Such groups are preferably introduced in the course of copolymerization, for example by using isopropyl (meth)acrylate, isobutyl (meth)acrylate, ethylhexyl (meth)acrylate, phenoxyethyl (meth)acrylate, tetrahydrourfiryl (meth)acrylate, furfuryl (meth)acrylate, isobornyl (meth)acrylate or adamantyl (meth)acrylate, alone or in any desired mixture, as comonomers in the preparation of the acrylate or methacrylate copolymers.
Particularly high radiation sensitivity is had by
Blum Rainer
Keller Peter
BASF Coatings AG
Berman Susan W.
Keil & Weinkauf
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