CA2239379A1 - Radiation-hardenable coating compound and its use in coating - Google Patents

Abstract

The invention concerns a radiation-hardenable coating compound containing between 50 and 85, preferably between 60 and 75, wt % polyetheracrylate, between 15 and 40, preferably between 20 and 30, wt % fillers, between 0 and 10, preferably between 0 and 5, wt % water and in UV formulations between 0 and 6, preferably between 3 and 5, wt % UV initiator.

Description

CA 02239379 l998-06-03 tlLC, r~ AR~IC(~
~3~T TF~A~!~~LAT,~N
'~ FI/Br PAT95573 BASF Lacke I Farben Aktiengesellschaft, Munster 26.09.1996 Radiation-curable coating composition and its use for coating The present invention relates to radiation-curable coating compositions and to the use of radiation-curable coating compositions for coating wood, woodbasematerials and paper.
It is known to cure compositions based on acry-lates by radiation, especially UV radiation. A problem which occurs here, however, is that the presence of air is disruptive to the curing of surfaces.
DE-C 26 25 538 discloses photopolymerizable coating compositions which comprise amines as reducing agents and/or chain-transferring compounds. The use of a free amine of this kind has the disadvantage that it may act as a plasticizer and leads to an unwanted covering on the surface and to instances of odour nuisance.
By incorporating the amino group into a molecule which comprises groups which are still polymerizable an amine is obtained which is incorporated by polymerization in the course of curing and does not have the above-mentioned disadvantages. A known method of incorporation is the addition of amines onto double bond-rich mole-cules, which takes place in the manner of a Michael addition and is described, for example, in F. Moller, Houben-Weyl, Vol. 11/1 (1957), pp. 277-280. US-A

2,759,913 teaches the addition of amines onto activated, olefinically unsaturated compounds, such as acrylates, in equimolar amounts, leading to the complete reaction of the activated ethylenic double bonds. Systematic investi-gations into the addition of amino alcohols onto acry-lates have been carried out by N. Ogata and T. Asahara, Bull. Chem. Soc. Jap. 39, pages 1486-1490, 1966.
DE-C 2 346 424 describes the preparation of radiation-curable compositions starting from acrylic esters of polyhydric alcohols and secondary, aliphatic monofunctional amines. These compositions have the disadvantage of reduced stability on storage. The addi-tion reaction of a secondary amine, moreover, leads to a reduction in the acrylic ester functionality of the molecule and hence also to a reduction in the cross-5 linking possibilities for the radiation-induced polymerization.
EP-A-280 222 discloses adducts of esters of acrylic or methacrylic acid and polyhydric alcohols with primary monoamines, the molar ratio of monoamine to (meth)acrylic double bond of the ester being from 0. 05: 1 to 0.4:1. The adducts of EP-A-280 222 are employed in radiation-curable compositions which cure in the air. The storage stability of the products known from EP-A-280 222, however, is inadequate. Thus when the adducts 15 are stored there is a marked increase in viscosity. In addition, problems of compatibility arise in the case of adducts of tetrahydric polyols with the primary mono-amines. Products of this kind are cloudy and/or have a milky white appearance. A further disadvantage of the 20 amine-modified compositions described in the European application is that a relatively high proportion of monoamine is necessary to ensure that the resulting adducts have sufficiently high nitrogen contents for systems, for example, which are initiated with benzo-25 phenone. Sufficiently high nitrogen contents are neces-sary in order to provide for a photopolymerization which proceeds to completion and is sufficient in actual practice at the customary radiation dose.
EP-A-2457 describes plastics for shaped plastics 30 parts, the plastics curing under elevated temperatures.
The plastics are Michael adducts of acrylate monomers and amines having an amine hydrogen functionality of at least 3. The components are reacted in a ratio of equivalents of acrylate to amin-e hydrogen of from 0. 5 to 2Ø
US Patents Nos. 4,547,562 and 4,675,374 disclose radiation-curable solvent-free compositions based on polyacrylates and mono-, di- or polyamines. Di- and polyamines specified as being suitable are ~pecies having more than one primary amino group. When used, these polyamines give highly crosslinked coating compositions of relatively high molecular mass and hence relatively high viscosity, which without the addition of reactive diluents and solvents have too high an application viscosity or even lead to solid products.
US-A 4,045,416 and US-A 3,845,056, finally, relate to radiation-curable coating compositions based on amine acrylates which are obtained by reacting poly-acrylates with amines having at least one amine hydrogen.
Amines specified as being suitable are primary and secondary monoamines and also polyamines. According to the US patents, the polyamine components specified are polyamines having more than one primary amino group, polyamines having exclusively secondary amino groups or polyamines having secondary and tertiary amino groups.
When polyamines having more than one primary amino group are used, non-homogeneous adducts of low stability on storage are obtained, while the use of polyamines having exclusively secondary amino groups, such as piperazine, for example, leads to non-homogenous mixtures owing to inadequate reactivities or to instances of incompatibil-ity. The use of polyamines having secondary and tertiary amino groups leads only to a reduction in the acrylate or methacrylate functionality of the molecule.
Formulations employed to date on the bases of customary commercial binders exhibit good adhesion to the usual wood substrates (e.g. walnut, oak, cheery) only in the case of relatively small proportions of so-called fillers and additives such as waxes, talc, silicates or else calcium carbonate, calcium sulphate and barium sulphate. Substrates regarded as particularly critical for adhesion are compressed woods coated with melamine resin (film), and plastics such as PVC, polypropylene.
On the other-hand, especially in the case of primary coatings, a high proportion of filler is essen-tial to ensure the good sandability which is required in woodworking. Customary commercial formulations based on polyether acrylates have filler contents of not more than about 15~. A higher proportion of filler in such formula-tions leads, for example, to intolerable losses in adhesion.
Furthermore, if their filler contents are too high such formulations tend to settle.
One option of avoiding this is to add binders of relatively high molecular weight. The increases in viscosity of the formulations which this entails must then, however, be compensated with additions of monomers (reactive diluents). For environmental reasons associated with the product, however, this is undesirable.
The object on which the present invention is based was therefore to eliminate the disadvantages described above; in other words, to provide radiation-curable coating compositions which have sufficient stability on storage and are homogeneous even using tetrafunctional (meth)acrylic esters as precursor. They should be radiation-curable without the use of external synergists such as amines, for example. The coating compositions of the invention should be oligomers combining low viscosity with comparatively good radiation-curability and comparatively good resulting film properties, especially hardness. They should be of low viscosity so that it is possible to dispense with the use of reactive diluents and organic solvents. Finally, good sandability with good adhesion should be ensured even on critical substrates.
The object on which the present invention is based is achieved by a radiation-curable coating composi-tion comprising from 50 to 85, preferably from 60 to 75 by weight of polyether acrylate, from 15 to 40, preferably from 20 to 30~ by weight of fillers, from 0 to 10, preferably from 0 to 5% by weight of water and, in W
applications, from 0 to 6, preferably from 3 to 5~ by weight of W initiators.
The polyether acrylate employed in accordance with the invention is an adduct of oligomers having at least two acrylate and/or methacrylate groups per mole-cule and polyamines.
Suitable acrylates and methacrylates are con-structed, for example, with dihydric aliphatic alcohols, such as ethylene glycol, propylene 1,2- and 1,3-glycol, 1,4-butanediol, 1,2-pentanediol, neopentyl glycol, 1,6-hexanediol,2-methyl-1,5-pentanediol,2-ethyl-1,4-butane-diol, dimethylolcyclohexane and diethylene glycol, withtrihydric alcohols, such as glycerol, trimethylolethane, trimethylolpropane and trimethylolbutane, with tetra-hydric alcohols, such as pentaerythritol, and with higher polyhydric alcohols, such as di(trimethylolpropane), di(pentaerythritol) and sorbitol.
Also suitable are cycloaliphatic alcohols, such as cyclohexanols and 1,4-bis(hydroxymethyl)cyclohexane, araliphatic alcohols, such as 1,3-xylylenediol, and phenols, such as 2,2-bis(4-hydroxyphenyl)propane (bis-phenol A).
It is preferred as oligomers to use esters ofacrylic acid and/or methacrylic acid with tri- to tetra-hydric alcohols.
The polyhydric alcohols set out above will preferably have been converted into ether alcohols of relatively high molecular mass by alkoxylation with, for example, ethylene oxide or propylene oxide prior to the esterification with acrylic acid or methacrylic acid.
Polyether acrylates or polyether methacrylates are the result of this. Such polyether (meth)acrylates are used with particular preference in the adducts of the inven-tion.
The hydroxyl-containing polyethers which are esterified with acrylic acid and/or methacrylic acid are obtained by reacting di- and/or polyhydric alcohols with various amounts of ethylene oxide and/or propylene oxide in accordance with well-known methods (cf. e.g. Houben-Weyl, Volume XIV, 2, Makromolekulare Stoffe II, (1963)).
The invent-ion -gives particular preference to polyether acrylates which are prepared from acrylic acid and a propoxylated trimethylolpropane polyol with subse-quent reaction with 4-dimethylaminopropylamine.
It is also possible to employ polymerization products of tetrahydrofuran or of butylene oxide.

Further suitable oligomers are polyester acry-lates and/or polyester methacrylates. The polyester (meth)acrylates are prepared using hydroxyl-containing polyesters (polyesterpolyols) as polyhydric alcohols.
These can be prepared by esterification of dicarboxylic acids with diols and triols in accordance with well-known methods (cf. e.g. P.J. Flory, J. Am. Chem. Soc. 58, 1877 (1936) and J. Am. Chem. Soc. 63, 3083 (1953)).
The preparation of polyether acrylates and polyester acrylates is described, for example, in DE-A-38 36 370.
The polyamines are diamines having a primary and a tertiary amino group, and the ratio of primary amino groups to (meth)acrylic double bonds is from 0.01:1 to 0.2:1, preferably from 0.03:1 to 0.1:1.
Suitable diamines having a primary and a tertiary amino group are N,N-dialkyldiaminoalkanes, such as, for example, N,N-dimethyl-1,3-diaminopropane, which is obtainable by catalytic hydrogenation of dimethylamino-propionitrile. The preparation of this polyamine isdescribed, for example, in Houben Weyl, Vol. 11/1, 1957, p. 565, in EP-A-316 761 or in P. Lappe, H. Springer and J. Weber, Chem.-Ztg. 111 (4), pp. 117-125 (1987).
Further suitable dialkylaminopropanes are N,N-diethyl-1,3-diaminopropane, N,N-di-n-propyl-1,3-diamino-propane, 4-morpholinopropylamine, 3-(N-piperidine)-propylamine, N,N-diphenyl-1,3-diaminopropane.
Further compounds suitable as the polyamine component of the adducts of the invention are: N,N-dialkyl-1,2-diaminoethanes, such as dimethylaminoethyl-amine, diethylaminoethylamine, N-~-aminoethylmorpholine (for preparation see e.g. Houben Weyl, Vol. 11/1, 1957, p. 563), N,N-dialkyl-1,5-diaminopentanes, which can be prepared by 1,4-ad-diti-on of secondary amines onto 1-cyano-1,3-butadiene to form the nitriles, with subsequent catalytic hydrogenation (for preparation see Houben-Weyl, Vol. 11/1, 1957, p. 276). Examples of suitable N,N-dialkyl-1,5-diaminopentanesaredimethylaminopentylamine, diethylaminopentylamine, 4-morpholinopentylamine.

Particularly good results are obtained if the amine component used is N,N-dimethyl-1,3-diaminopropane.
The adducts of the invention are liquid at room temperature. They are prepared by adding the diamines onto an acrylate or methacrylate or onto a mixture of these esters in a Michael reaction. The resulting amine-modified oligomers comprise still unreacted acrylate and/or methacrylate groups and also tertiary amino groups.
The addition reaction is carried out in liquid phase at moderate temperature in the absence of a cata-lyst. The diamine in an appropriate amount is added to the ester at room temperature with stirring. The tempera-ture may rise to about 40~C in the course of this addi-tion. The reaction can be accelerated by raising the temperature; at 60~C it has subsided after about 12 hours. The viscosity of the resulting mixture is then constant over time.
For reproducibility the reaction should progress as completely as possible, which is achieved at reaction temperatures above 40~C.
The reaction is generally conducted without solvent, although solvents may also be employed especial-ly in order to allow solid amines to be metered in as a solution. The solvent is then removed after Michael addition has taken place.
So that no unwanted polymerization takes place in the course of the addition reaction, polymerization inhibitors are generally added to the reaction mixture.
Suitable polymerization inhibitors include known prod-ucts, such as substituted phenols, such as 2,6-di-tert-butyl-p-cresol, hydroquinones, such as methylhydro-quinones, and thioethers, such as thiodiglycol or phenothiazine. -- ~
The amine-modified adducts described are used as film-forming components in radiation-curable coating compositions of the invention. In addition to the amino-modified oligomers of the invention, these radiation-curable coating compositions may, depending on the visco-sity of the esters, comprise further copolymerizable compounds known for use in radiation-curable coating compositions, examples being (meth)acrylates, especially methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, 3,5,5-trimethylhexyl (meth)acrylate, decyl (meth)acrylate,dodecyl (meth)acrylate, hexadecyl (meth)acrylate, octyldecyl (meth)acrylate, octadecenyl (meth)acrylate and also the corresponding esters of maleic, fumaric, tetrahydrophthalic, crotonic, isocrotonic, vinylacetic and itaconic acid. Preference is given to the use of monomers having more than 1 double bond per molecule, examples being ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, trimethylene glycol diacrylate, neopentyl glycol diacrylate, 1,3-butylene glycol diacrylate, 1/4-butylene glycol diacrylate, 1,6-hexamethylene glycol diacrylate, 1,10-decamethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol tetraacrylate and penta-erythritol triacrylate and also the corresponding meth-acrylates. Very particular preference is given to the useof trimethylolpropane triacrylate and acrylates of propoxylated trimethylolpropane.
The addition of these monomeric copolymerizable compounds (often also called reactive diluents), however, is generally unnecessary, since the amine-modified esters of the invention are of low viscosity.
The advantage of the adducts described is also to be seen in particular in the fact that by virtue of the tertiary amino groups they comprise they are dispersible in water; in other words, it is possible to dispense entirely with the use of organic solvents. The tertiary amino groups can be converted into the charged groups by at least partial reaction with acids. Acids suitable for neutralizing the basic groups are, for example, lactic acid, acetic acid, formic acid, phosphoric acid and hydrochloric acid.
For W applications, the radiation-curable coating compositions also comprise photoinitiators which are normally employed in radiation-curable coating compositions, examples being benzophenones, benzoins or benzoin ethers. The use of synergists can be dispensed with, since the esters present in the coating compositions have been amine-modified and hence exhibit a synergistic effect.
The coating materials of the invention can also be cured with electron beams. In the corresponding formulations it is possible to dispense with the addition of W initiators.
In addition to the amine-modified reaction products of the esters and the diamines, the radiation-curable compositions of the invention can additionally comprise further photopolymerizable binders, which may likewise have been amine-modified. Examples of suitable such further, amine-modified binders are the radiation-curable binders known from EP-A-280 222 and those known from US Patents Nos. 4,045,416, 4,547,562 and 4,675,374.
Suitable further binders which have not been amine modified are the epoxy acrylates and epoxy meth-acrylates, urethane methacrylates, urethane acrylates,polyester methacrylates, polyester acrylates, polyether methacrylates and polyether acrylates described above by way of example of the oligomer component.
The radiation-curable coating compositions of the invention comprise customary auxiliaries and additives, examples being extenders, defoamers, levelling agents and film-forming auxiliaries, lubricants, adhesion promoters.
Suitable fillers are in accordance with the invention silicates, carbonates and sulphates. The former include in particular kaolins, talc, siliceous chalk, micas, e.g. micaceous iron ore, silicon carbide and quartz flour.
Suitable carbonate fillers are calcium carbonates and calcium magnesium carbonates (dolomite).

Barium sulphates (heavy spar) and potassium sulphates (light spars) are employed as sulphate fillers.
In addition to the substances mentioned it is also possible to use wood flour and cellulose deriva-tives.
Substances which impart colour are also suitable in accordance with the invention. These include both inorganic pigments, e.g. carbon black, TiO2 and organic pigments.
Filler contents of from 20 to more than 30~ by weight have been realised in the formulations of the invention. In the prior art, such high filler contents were considered impossible.
It is surprising according to the invention that there are no losses in adhesion in a range of more than 15% by weight filler content. Moreover, the coating compositions of the invention show no tendency whatsoever towards irreversible settling. Further surprisingly advantageous properties are the good sandability and very good adhesion even on critical substrates, such as plastics or woodbase materials coated with melamine resins, for example.
In one variant of the invention the viscosity and reactivity can be established within certain limits by simple addition of amine prior to application. If about 48 h elapse between the addition of amine and the appli-cation of the coating composition, the amine is no longer present in free form but is bonded physically or chemi-cally to the remaining constituents of the coating composition. In this case the reactivity of the mixture produced with addition of amine increases relative to the base formulation described above. Experiments have shown that, depending on amounts, an approximately double rate of reaction is found under W radiation. The viscosity can also be very nearly doubled.
In a preferred embodiment of the invention the coating composition consists accordingly of from 95 to 100~ by weight, preferably from 98 to 100% by weight of the above-described coating material and from 0 to 5, preferably from 0 to 2~ by weight of polyamine added prior to application.
Suitable polyamines are the compounds already described above. In other words, mention should be made here primarily of diamines having a primary and tertiary amino group. Particular preference is given in this context to the addition of dimethylaminopropylamine.
Lubricants can be present in a proportion of from 0.8 to 1.2~ and levelling agents in a proportion from 0.2 to 0.8~ by weight in the coating composition. In this case the remaining amount of filler is reduced according-ly .
It is surprising that the good adhesion mentioned on the various substrates is obtained without the use of typical adhesion promoters. In specific cases, however, additional adhesion promoters can be employed. Examples are alkoxysilanes, such as, for example, N-~-aminoethyl-, -aminopropyltrimethoxysilane, -N-methyl-~-aminopropyl-trimethoxysilane or triamino-modified propyltrimethoxy-silane (e.g. adhesion promoter DYNASYLAN type "TRIAMO",commercial product of Dynamit Nobel Chemie).
The coating films are cured by means of radi-ation, preferably by means of W or electronic radiation.
Accordingly, the W-cured coating compositions of the invention comprise W initiators. These are preferably benzophenone, benzoin alkyl ethers, benzil ketals, hydroxyalkylphenones, thioxanthones and also phosphine oxide derivatives and bisacylphosphine oxide derivatives.
The curing of the coating films takes place directly following application or following the evapor-ation of any water present by means of W or electron beams. The equipment and conditions for these curing methods are known from the literature (cf. e.g. R.
Holmes, U.V. and E-.B. ~uring Formulations for Printing Inks, Coatings and Paints, SITA Technology, Academic Press, London, United Kingdom 1984, pp. 79 to 111) and require no further description.
The coating compositions can be applied to the substrate, preferably to wood, to woodbase materials or to paper, by spraying, rolling, flowcoating, dipping, knifecoating, spreading, by casting or by Vakumat appli-cation.
The radiation-curable coating compositions of the invention exhibit an excellent stability on storage, have a transparent appearance and good radiation-curability, and following radiation curing lead to films having excellent properties. The films obtained are notable for excellent transparency.
In the text below the invention is illustrated further with reference to working examples. Parts are by weight unless stated otherwise:

Example 1 Base formulation:

15 1. Polyether acrylate 68.5%
prepared from propoxylated trimethylolpropane polyol (Desmophen550U from Bayer), acrylic acid and subsequent reaction with 4%
of dimethylaminopropylamine 2. Phyllosilicate 2.0%
3. Talc 10.0%

4. Calcium carbonate 10.0 25 5. Lubricant (Lanco wax) 1.0%
6. Levelling agent (Byk 306) 0.5%
7. Water 4-0%
8. Benzophenone 4.0%

Total 100%

Viscosity 42-45 seconds flow viscosity in accordance with DIN6/20~C.

Example 2 Adjusting viscosity, adjusting reactivity 1. Base formulation see above 99.5%
2. Dimethylaminopropylamine 0.5%

5 Total 100%

1. and 2. are mixed with one another and then left for 48 h.

Result: The reactivity of the mixture has risen to 15 m/min relative to the base formulation of 9 m/min per 80 W mercury W radiator. The viscosity has risen from 44 to 72 seconds (flow in accordance with DIN6/20~C).

ExamPle 3 1. 70.30 parts of binder as in Ex. 1 2. 4.10 parts of benzophenone 3. 8.30 parts of talc 4. 10.30 parts of chalk (CaCO3) (5. 3.00 parts of phyllosilicate for matting) (6. 3.50 parts of phyllosilicate) 5. 6.50 parts of phyllosilicate 6. 0.50 parts of levelling agent 100 . O

In addition to the advantages referred to, the formulation also meets the chemicals test of DIN68861 B.

Comparative examples with customary commercial binders For Example 1 - -1) Item 1: 68.50 parts of Laromer PO84F (obtainable from BASF AG) Phyllosilicate 2.0 Talc 10.0 Calcium carbonate 10.0 Lubricant (Lanco wax) 1.0 Levelling agent (Byk 306) 0 .5%
Water 4.0 Benzophenone 4.0g6 Result: Viscosity too high, DIN6>120 sec., hence cannot be processed in practice.

2) Item 2: 68. 50 parts of Laromer PO83F

Result: Viscosity acceptable but coating material not stable on storage, severe irreversible tendency towards settling.

Claims (10)

Patent claims

1. Radiation-curable coating composition comprising 50-85, preferably from 60 to 75% by weight of polyether acrylate, from 15 to 40, preferably from 20 to 30% by weight of filler, from 0 to 10, preferably from 0 to 5 by weight of water and, in W formulations, from 0 to 6, preferably from 3 to 5% by weight of W initiator.

2. Radiation-curable coating composition according to Claim 1, characterized in that the polyether acrylate is an adduct of oligomers having at least two acrylate and/or methacrylate groups per molecule and polyamines.

3. Radiation-curable coating composition according to one of Claims 1 or 2, characterized in that the polyamines are diamines having a primary and a tertiary amino group and the ratio of primary amino groups of the polyamines to (meth)acrylic double bonds of the oligomers is from 0.01:1 to 0.2:1, preferably from 0.03:1 to 0.1:1.

4. Radiation-curable coating composition according to Claim 3, characterized in that the oligomer is an ester of acrylic acid and/or methacrylic acid and tri-and/or tetrahydric alcohols.

5. Radiation-curable coating composition according to Claim 3, characterized in that polyether acrylates and/or polyether methacrylates are used as oligomer.

6. Radiation-curable coating composition according to Claim 3, characterized in that the polyamine is N, N-dimethyl-1,3-diaminopropane.

7. Radiation-curable coating composition according to Claim 3, characterized in that from 95 to 100%, preferably from 98 to 100% of coating material according to one of Claims 1 to 7 and from 0 to 5%, preferably from 0 to 2% of polyamine are employed.

8. Radiation-curable coating composition according to Claim 6 or 7, characterized in that the polyamines are diamines having a primary and a tertiary amino group.

9. Radiation-curable coating composition according to Claim 8, characterized in that the polyamine is dimethylaminopropylamine.

10. Use of the radiation-curable coating composition according to one of Claims 1 to 9 for coating wood, wood-base materials, paper and plastics.