EP0000342B1 - Photopolymerisable binders - Google Patents

Description

The invention relates to photopolymerizable binders for printing inks, coatings and printing plates based on at least one photopolymerizable olefinically unsaturated compound and optionally a polymeric binder component which contain an advantageous diaminobenzophenone compound as a photosensitizer.

Benzophenone derivatives containing amino groups are known. 4,4'-bis (N-dimethylamino) benzophenone (Michler's ketone) and its use in photoinitiator systems or as a photosensitizer for photopolymerizable systems has been described particularly frequently (cf. DT-OS 15 22 359). It is a disadvantage of Michler's ketone that its toxic properties are unsatisfactory for some applications, further that its limited solubility in many organic solvents and its limited compatibility with some polar photopolymerizable binders leave something to be desired, which, if higher concentrations of photosensitizers are required, can easily cause clouding in the corresponding mixtures occur that interfere with photopolymerization.

Since there is no general rule for improving the compatibility of polar organic compounds with one another, it was not possible for the person skilled in the art to predict how the compatibility of Michler's ketone, a very polar substance, with polar photopolymerizable compounds could be improved. US Pat. Nos. 3,933,682, 3,966,573 and 3,915,824 describe a large number of aromatic carbonyl compounds, including benzophenone derivatives, as photoinitiators for binder-containing photopolymerizable mixtures. From these copies, however, one can only learn that the effectiveness of the aromatic carbonyl compounds as photosensitizers can be increased by adding certain other substances, in particular halogenated carbons, as activators. There is no indication in these patents of how the compatibility of Michler's ketone with polar binders can be improved or whether or which substances from the large number of compounds suitable as photoinitiators have these properties.

The object of the present invention was to find a substitute for Michler's ketone for photopolymerizable binders, which has improved toxic properties, an improved compatibility with photopolymerizable mixtures and allows a versatile use as a photosensitizer or component in photoinitiator systems for photopolymerizable compositions.

enthalten, worin R¹ und R³ H-(OR⁵)_.-Reste mit R⁵=Alkylen mit 2 bis 3 C-Atomen, x=1, 2 oder 3, R² und R⁴ Alkylreste mit 1 bis 4 C-Atomen oder Reste der für R¹ und R³ genannten Art darstellen.It has now been found that photopolymerizable binders for printing inks, coatings and printing plates, consisting essentially of at least one photopolymerizable olefinically unsaturated compound and, if appropriate, a polymeric binder component which contain a diaminobenzophenone compound as photosensitizer, exhibit the desired improved properties when they contain a diaminobenzophenone Compound of formula (1)

contain, where R ¹ and R ^{3 are} H- (OR ⁵ ) _.- radicals with R ⁵ = alkylene with 2 to 3 C atoms, x = 1, 2 or 3, R ² and R ⁴ alkyl radicals with 1 to 4 C- Represent atoms or radicals of the type mentioned for R ¹ and R ³ .

ferner 4,4'-Bis(N,N-dihydroxyalkyl-amino)-benzophenone wie 4,4-Bis(N,N-di-ß-hydroxyäthyl-amino)-benzophenon, 4,4'-Bis(N,N-di-ß-hydroxypropyl-amino)benzophenon oder unsymmetrisch substituierte Benzophenone wie 4-(N,N-di-ß-hydroxyäthylamino)-4'-(N,N-di-ß-hydroxypropylamino)benzophenon der Formel (III)

Sehr geeignet sind die 4,4'-Bis(N-hydroxyäthyl-N-C₁-C₄-alkyl-amino)benzophenone.Examples of such compounds are 4,4'-bis (N-β-hydroxyethyl-N-methylamino) benzophenone, 4,4'-bis (N-β-hydroxyethyl-N-ethylamino) benzophenone, 4,4'- Bis (N-ß-hydroxyethyl-N-propylamino) benzophenone, 4,4'-bis (N-ß-hydroxypropyl-N-methylamino) benzophenone, 4,4'-bis (N-hydroxypropyl- N-methylamino) benzophenone, 4,4'-bis (N-hydroxyethoxyethyl-N-methylamino) benzophenone of the formula (11)

further 4,4'-bis (N, N-dihydroxyalkylamino) benzophenones such as 4,4-bis (N, N-di-β-hydroxyethylamino) benzophenone, 4,4'-bis (N, N -di-ß-hydroxypropylamino) benzophenone or asymmetrically substituted benzophenones such as 4- (N, N-di-ß-hydroxyethylamino) -4 '- (N, N-di-ß-hydroxypropylamino) benzophenone of the formula (III)

The 4,4'-bis (N-hydroxyethyl-NC ₁ -C ₄ -alkyl-amino) benzophenones are very suitable.

The following reaction represents a technically simple way of producing N-hydroxyalkylamino derivatives of benzophenone:

By using mixtures of different N-hydroxyalkyl-N-alkyl-anilines or N, N-dihydroxyalkylanilines, for the reaction with formaldehyde or paraformaldehyde in the presence of acid, asymmetrical derivatives of diaminobenzophenone can also be prepared, the correspondingly substituted ones always being intermediates Diaminophenylmethane arise, which then by oxidation with oxygen, for example can be converted into the correspondingly substituted diaminobenzophenones in the presence of chloranil and iron complexes of dihydrodibenzotetraaza annulene. The compounds used as photosensitizers according to the invention can then be easily isolated and purified as mostly acicular crystalline solid substances with melting points above 100 ° C.

The diaminobenzophenone compounds used according to the invention in photopolymerizable binders have, with activity comparable to Michler's ketone as photosensitizer, the advantages that they are less toxic than Michler's ketone, have better solubility in many organic solvents and have better compatibility with many polar photopolymerizable mixtures.

It is particularly advantageous to use, in addition to the diaminobenzophenone compound, a further known photoactivator in the binder according to the invention, such as benzoin, benzoin ether, anthraquinone, benzil, benzil monoalkyl ketals, fluorenone, fluorene, diacetyl and in particular benzophenone or a low absorbent in the range from 300 to 380 nm Benzophenone derivative, such as those with an extinction coefficient E360. _nm <200, whereby the molar ratios and amounts known for the combination with Michler's ketone can be used.

Suitable photopolymerizable olefinically unsaturated compounds are the known low molecular weight monomers and oligomers (in particular with a molecular weight below 2,000) which are known per se for photopolymerizable binders for printing inks, coating agents and for printing plates, the nature of the monomers, of course, depending on the intended use depends and, if necessary, also used polymeric binder with which they should be compatible. Monomers with two or more olefinically unsaturated photopolymerizable double bonds alone or mixtures thereof with monomers with only one olefinically unsaturated photopolymerizable double bond are preferred, the proportion of monomers with only one double bond generally only being about 5 to 50 and preferably 5 to 30 percent by weight of the total amount of monomers is.

Suitable olefinically unsaturated compounds are di- and polyacrylates and methacrylates, as can be prepared by esterification of diols or polyols with acrylic acid or methacrylic acid, such as the di- and tri (meth) acrylates of ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol with a molecular weight up to about 500, 1,2-propanediol, 1,3-propanediol, neopentyl glycol (2,2-dimethylpropanediol) 1,4-butanediol, 1,1,1-trimethylolpropane, glycerin or pentaerythritol; furthermore the monoacrylates and monomethacrylates of such diols and polyols, e.g. Ethylene glycol or di-, tri- or tetraethylene glycol monoacrylate, monomers with two or more olefinically unsaturated bonds which contain urethane groups and / or amide groups, such as those of low molecular weight prepared from aliphatic diols of the aforementioned type, organic diisocyanates and hydroxyalkyl (meth) acrylates Links. Also mentioned are acrylic acid, methacrylic acid and their derivatives such as (meth) acrylamide, N-hydroxymethyl (meth) acrylamide or (meth) acrylates of monoalcohols with 1 to 6 carbon atoms.

Binders according to the invention which contain polar monomers and / or polar polymeric binders, such as urethane acrylates or epoxy acrylates, have proven very useful. With regard to suitable binder components and the use of the systems according to the invention, reference is made to DT-OS 1 522 359, 2 200 478, 2 358 948, 2 441 148, the diaminobenzophenone compounds used according to the invention being able to replace the Michler ketone described there.

Suitable polymeric binder components are, for example, polyamides, polyurethanes, unsaturated polyesters and polyester urethanes. In a known manner, the inventive photopolymerizable binders can be mixed with the usual additives, such as thermal polymerization inhibitors, dyes, plasticizers, etc.

Of particular importance is the greater solubility of the photosensitizers used according to the invention when they are used for sufficient curing of highly pigmented photopolymerizable systems, in particular when using highly absorbent pigments, e.g. in UV-curing printing inks with opaque black. According to Examples 5 and 6, the prints achieved here show a greatly improved brilliance. The binders according to the invention are particularly suitable in layer thicknesses of less than 10 μm for UV-curing printing inks, but also for offset printing plate coatings and as a photoresist material.

The parts and percentages given in the examples and comparative tests below relate to the weight, unless stated otherwise.

Preparation of the substituted diaminobenzophenone compound

A mixture of 151 parts of N-methyl-N-hydroxyethylaniline, 16.5 parts of paraformaldehyde and 100 parts of glacial acetic acid is heated to 60 to 70 ° C for 1.5 hours. After adding 230 parts of methanol, 25 parts of chloranil and 2.5 parts of the iron complex of dihydrodibenzotetraazaannulene to the condensation solution, the latter is treated with air at 50 to 52 ° C. and 1 to 3 bar. The oxidation is stopped when almost no more oxygen is taken up. Colorless needles crystallize out of the reaction mixture, which has cooled to 10 ° C., and these are filtered off with suction and washed with 190 parts of methanol. After recrystallization from methanol, 885 parts of 4,4'-bis (N-methyl-N-hydroxyethylamino) benzophenone are obtained with a melting point of 153 ° C.

example 1

A UV-curable binder is produced by homogeneously mixing the components at 90 to 100 ° C, consisting of 20% of a urethane acrylate (produced by reacting an aliphatic biuret isocyanate with stoichiometric amounts of hydroxypropyl acrylate), 64% of a further urethane acrylate (produced by reacting hexamethylene diisocyanate) with stoichiometric amounts of hydroxypropyl acrylate), 10% butanediol diglycidyl ether diacrylate, 3% benzophenone and 3% 4,4'-bis (N-ß-hydroxyethyl-N-methylamino) benzophenone.

The UV-curable binder is clear even after 3 months of storage at room temperature.

Comparative experiment A

A UV-curable binder is produced exactly as stated in Example 1, but instead of 3% 4,4'-bis (N-β-hydroxyethyl-N-methylamino) benzophenone, 3% 4,4'-bis (N -dimethylamino) -benzophenone used. The binder is stored exactly like that of Example 1 for about 3 months at room temperature, but then shows a clear cloudiness due to fine crystals.

Example 2

A homogeneous mixture of 52% of an epoxy resin acrylate (produced by reacting a bisphenol A epichlorohydrin resin with an epoxy equivalent weight of 190 with 97 mol%, based on the epoxy groups, pure acrylic acid), 40% pentaerythritol tetraacrylate, 4% benzophenone and 4% 4,4'-bis (N-β-hydroxyethyl-N-methylamino) benzophenone is stored for 3 months at room temperature. The mixture remains clear and unclouded.

Comparative experiment B

Exactly as stated in Example 2, a homogeneous mixture is produced, but instead of 4% 4,4'-bis (N-β-hydroxyethyl-N-methylamino) benzophenone, 4% 4,4'-bis (N-dimethyl -amino) -benzophenone used. The mixture is stored exactly like that of Example 2 for 3 months at room temperature. At this point it shows a cloudiness due to fine crystals of 4,4'-bis (N-dimethylamino) benzophenone.

Example 2 and Comparative Experiment C

One UV-curing binder mixture each from 30% of a urethane acrylate (produced by reaction of an aliphatic biuret isocyanate with stoichiometric amounts of hydroxypropyl acrylate), 54% of a further urethane acrylate (produced by reaction of hexamethylene diisocyanate with stoichiometric amounts of hydroxypropyl acrylate), 10% N ', N' -Divinyl-2-oxo-hexahydropyrimidine, 3% benzophenone and 3% 4,4'-bis (N-β-hydroxyethyl-N-methylamino) benzophenone (Example 3) or 3% 4,4'- Bis (N-dimethylamino) benzophenone (comparative experiment C) is printed separately on a test paper in a layer thickness of about 1.3 μm on art paper. The printed layers produced from the various binder mixtures are irradiated on a commercially available UV curing system, containing 2 medium pressure mercury lamps, each with an output of 80 watts / cm arc length, and the maximum conveyor belt speed is determined, at which only one lamp has an immediate non-tacky one when switched on and abrasion-resistant curing of the printed layer can be achieved.

Result

Max. Belt speed: Example 3: 280 m / min

Comparative vers. C: 280 m / min

Example 4 and Comparative Experiment D

• In 2 getrennten Ansätzen werden aus
• 18% eines Blaupigments (C.I. Pigment Blue 15:3)
• 82% des Bindemittels einschließlich Initiatorsystem von Beispiel 3 (Ansatz=Beispiel 4) sowie aus
• 18% des vorgenannten Blaupigments und
• 82% des Bindemittels einschließlich Initiatorsystem von Vergleichsversuch C Ansatz = Vergleichsversuch D)

auf einem Dreiwalzwerk Druckfarben hergestellt. Diese werden getrennt auf Kunstdruckpapiere mittels eines Probedruckgerätes aufgedruckt. Die aufgedruckte Farbmenge wird so eingestellt, daß die Farbdrucke eine optische Dichte von 1,60 bis 1,65 (gemessen mit einem handelsüblichen Auflichtdensitometer) aufweisen. Die Farbdrucke werden wie in Beispiel 3 beschrieben (eine Lampe eingeschaltet) bestrahlt und die maximale Transportbandgeschwindigkeit bestimmt, die beträgt.

• In 2 separate approaches are made
• 18% of a blue pigment (CI Pigment Blue 15: 3)
• 82% of the binder including the initiator system from Example 3 (batch = Example 4) and from
• 18% of the aforementioned blue pigment and
• 82% of the binder including initiator system from comparative test C batch = comparative test D)

Printing inks produced on a three-roll mill. These are printed separately on art paper using a test printer. The amount of ink printed is adjusted so that the color prints have an optical density of 1.60 to 1.65 (measured with a commercially available incident light densitometer). The color prints are irradiated as described in Example 3 (a lamp switched on) and the maximum conveyor belt speed is determined, which is.

After 2 weeks of storage, the printing ink of comparative test D has a matt, granular surface. Fine crystals of 4,4'-bis (N-dimethylamino) benzophenone) can be seen under the microscope.

Example 5 and Comparative Experiment E

• 18% Ruß und
• 82% des Bindemittels einschließlich Initiatorsystem von Beispiel 3 (Ansatz=Beispiel 5) sowie aus 18% Ruß und
• 82% des Bindemittels einschließlich Initiatorsystem von Vergleichsversuch C

in 2 separate approaches are made

• 18% soot and
• 82% of the binder including the initiator system from Example 3 (batch = Example 5) and from 18% carbon black and
• 82% of the binder including initiator system from comparative experiment C

(Approach = comparative experiment E)

UV-curable printing inks and with them color prints on art paper with an optical density of 2.0 to 2.1. The color prints are irradiated as described in Example 3 (but both lamps are switched on) and the maximum conveyor belt speed is determined, which is.

Here, too, the sample from comparative experiment E showed a matt surface after 2 weeks' storage as a result of crystallization of 4,4'-bis (N-dimethylamino) benzophenone.

Claims (3)

1. A photopolymerizable binder for printing inks, coatings and printing plates, which consists essentially of at least one photopolymerizable olefinically unsaturated compound, with or without a polymeric binder component, and contains an N,N'-substituted diaminobenzophenone compound as photosensitizer, characterised in that it contains a diaminobenzophenone compound of the formula (I)

where R¹ and R³ are H(OR⁵)_x radicals, R⁵ being alkylene of 2 to 3 carbon atoms and x being 1, 2 or 3, and R² and R⁴ are each alkyl of 1 to 4 carbon atoms or are radicals of the type of R¹ and R³.

2. A photopolymerizable binder as claimed in claim 1, characterized in that it contains, in addition to a diaminobenzophenone compound of the formula (I), benzophenone or a benzophenone derivative which has a low absorption in the range from 300 to 380 nm.

3. A photopolymerizable binder as claimed in claim 1, characterized in that it contains 4,4'-bis-(N-hydroxyethyl-N-alkylamino)-benzophenone, where alkyl is of 1 to 4 carbon atoms, as the diaminobenzophenone compound of the formula (I).