CA1062839A - Coating compositions hardenable by electron beams and suitable for coating wood and wood-like materials - Google Patents

Abstract

COATING COMPOSITIONS HARDENABLE BY ELECTRON
BEAMS AND SUITABLE FOR COATING WOOD AND WOOD-LIKE MATERIALS
Abstract of the Disclosure:

A coating composition hardenable by an electron beam comprising at least one unsaturated poly-ester and at least one polyfunctional acrylate.

Description

. ~ 1062839 This invention relates to highly reactive coating compositions, hardenable by electron beAms and suitable for coating wood and wood-like materials, baeed on unsaturated ~ polyesters and certain polymerisable acrylic acid esters.
The hardening of polymerisable resin compositions by electron beams takes only a matter of seconds and, above all, i~ an economic method of hardening in cases where shaped artlcles of the same kind are coated in large numbers.
Essential requirements for the economy of this particular method Or hardening are the availability of the components and the reactivity of the binders used which determines the throughput of the shaped articles to be coated and, hence, ;~ the amount of energy to be expended.
~ Resin compositions hardenable by electron beams are known from numerous publications (for example, German Offenlegungsschrirt Nos. 1,644,796; 1,644,799; 1,957,358;
- . 2,031,476; 2,038,6~1; 2,038,652 and 2,038,677; Belgian Patent Specification Nos 632,795 and 718,388; and US Patent Specification Nos. ~,660,~71; 3,697,317 and 3,723,166).
These conventional products are mixtures of a variety of different unsaturated resins with known polymerisable monomers, such as acrylic and methacrylic acid esters, allyl and vinyl e0ters and aromatic vinyl compounds~ such as - styrene.
Unfortunately, the coating of wood and wood-like materials with binders of this kind which are hardenable by electron beams generally leads to products Wit}l inadequate reactivity, defective levelling, inade~ ate adhesion andpoor stability, all disadvantages wbi~h preclude rational practical application.
Le A 15 61~ -l-~062839 It is known from DOS(German Published Specification) No. 2,038,676 that the adhesion of an unsaturated polyester or of a coating of binder of unsaturated polyester resin and monovinyl monomers to a polyolefin substrate is improved when the binder contains from 10 to 45 %, by weight, of diacrylates or dimethacrylates of a diol or triacrylates or trimethacrylates of a triol, and the film is polymerised by electron beams onto the surface of the polyolefin.
Although resins of this kind are also basically suitable for coat-ing wood and wood-like materials, reactivity is still not satis-factory because economic processing involves the use of very small doses of radiation, i.e. necessitates extremely high rates of travel of the substrate for the same radiation intensi~y.
Although in conventional hardening processes for un-saturated polyester resins Cwhether carried out in the presence of peroxides and accelerators or by W -irradiation in the presence of photoinitiators) the combinations with styrene as co nomer are by far the most reactive, and although under these conditions systems of this kind form excellent coatings even on wood and wood-like materials, they still do not show the reactivity required for hardening by electron beams, even in cases where they contain phosphines, arsines or stibines (cf. DOS ~German Published Specification) No. 1,769,952).
It has now been found that resin compositions based on unsaturated polyesters which are known to be readily available, may also be used as highly reactive coating materials harden-able by electron beams, for coating wood and wood-like materials, providing di- or trifunctional esterification products of acrylic acid with di-, tri- or tetra-hydric alcohols are used as comonomer rather than styrene, allyl or vinyl esters, meth-acrylic acid esters or esters or acrylic acid with monohydric alcohols, which have always been used in the past. This is all the more surprising insofar as it is those very comonomers which, in conventional hardening processes~ are greatly in-~erior to styrene-containing resin compositions on account of their slow hardening, which give formulations with the highest level of reactivity for hardening by electron be~ms.
Accordingly, the present invention relates to highly reactive coating compositions, h~rdenable by electron beams and suitable for coating wood and wood-like materials, based . on a~-unsaturated polyesters and polymerisable acrylic esters, distingui~hed by the fact that, apart from non-polymerisable solvents, pigments and particulate mineral fillers, they con-tain A) from 20 to 55 ~, by weight, based on ~he sum of (A) + (B) and preferably from 30 to 50 %, by weight, ofo~,B-unsaturated ~5 polye8ters; and ~) from 45 to 80 %, by weight~ based on the sum of (A) + (B) and preferably from 50 to 70 %, by weight of diacrylat~ of alkane diolq with from 2 to 6 carbon atoms and/or di- or tri-acrylat~ of triols or tetraols with from 3 to 6 carbon atoms.
By virtue of the low vapour pressure of their components, the coating compositions according to the invention give off hardly any volatile fractions to the atmosphere under processing conditions and are also physiologically acceptable in contrast to systems containing for example~ styrene or esters of acrylic or methacrylic acid with monohydric alcohols.
In the context of the invention, wood and wood-like materials are, above all, the various types of natural wood, chipboard, hardboard, paste board and paper.
Depending upon the viscosity of the resin compositions used which is primarily determined by the molecular weight of components (A) and (B), the ratio in which they are mixed and the proportion of non-polymerisable solvents~ it is possible to use different coating techniques, for example roll coating, ke A 1~ 61~ _3_ ` ca~t~ng~ spray coating~ brush coating~ spread coating or p~l~ting. The coatings normally ha~e layer t~lcknes~es o~ ~rom 0.01 to 0.5 mm preferably from 0.02 to 0.1 mm. In some cases, it may be advisable to add non-polymerisable diluents, such as normal lacquer-grade solvents, for example monocarboxylic acid alkyl esters or dialkyl ketones, to the coating compositions according to the invention in order to enable particular viscosity conditions to be maintained during application of the lacquer film.
For hardening, the coating compositions are irradiated with electrons preferably with an energy in the range from 50,000 to ~ ,000,000 eV. The acceler~tlon voltage has to be adapted to the layer thickness of the coatings.
Acceleration voltages of from 50 to 1000 kV, preferably from 250 to 500 kV, are required for layer thicknesses in the range irom 5 to 900 g per square metre, preferably from 5 to 150 g per square metre. The cathode current intensity is generally ~rom 10 to 300 mA, and preferably from 50 to 150 mA.
The unsaturated polyesters used in accordance with the invention are obtained by known methods by polycondensing at least one a,~-etllylenically unsaturated dicarboxylic acid or its ester-forming derivatives~ optionally in admixture with up to 90 mol ~ based on the unsaturated acid component~ of at least one saturated dicarboxylic acid or its ester-forming derivatives with at least one dihydric alcohol (see Bj~rksten et al., "Polyester and their Applications", Reinhold Publishing Corp., New York 1956). Examples of preierred unsaturated dicarboxylic acids or their derivatives are: maleic acid or maleic acid anhydride and fumaric acid.
~owever, it is also possible to use, for example, mesaconic acid, citraconic acid and itaconic acid. Examples of the saturated dicarboxylic acids used, or their derivatives, are:
phthalic acid or phthalic acid anhydride, isophthalic acid, terephthalic acid, hexahydrophthalic or tetrahydrophthalic Le A 1~ 61~ -4-id or their anhydrides~ endomethylene tetrahydrophthalic acid or its anhydride, succinic acid or succinic acid anhydride and succinic acid esters and chlorides, glutaric acid, adipic acid sebacic acid and trimellitic acid. In order to produce substantially non-inflammable resins~ it is possible to use, for example, hexachloroendomethylene tetrahydrophthalic acid (~ET acid), tetrachlorophthalic acid or tetrabromophthalic acid.
Non-inilammability may also be obtained by adding halogen-containing compounds which are not co-condensed with the poly-ester, such as a chloroparaffin. Preferred polyesters containmalelc acid radicals,oi~ which up to 25 mol ~ may be replaced phthalic acid and/or isophthalic acidOradicals.Suitable dihydi~
alcohols include:ethylene glycol,1,2-propane diol,1,3-propane diol, diethylene glycol~ dipropylene glycol, 1,3-butane diol, }5 1,4-butane diol, neopentyl glycol, 1,6-hexane diol, trimethylol-propane ahd pe~taerythritol. It is preferred to use 1,2-propane diol, diethylene glycol and dipropylene glycol.
- Further modifications may be made by incorporating mono-hydric alcohols, such as butanol, benzyl alcohol, cyclohexanol and tetrahydrofurruryl alcohol, and also by incorporating monobasic acids, such as benzoic acid, oleic acid, linseed oil fatty acid and ricinene fatty acid.
Unsaturated polyesters containing ~,~-unsaturated ether radicals in co-condensed form in accordance with DAS No. 1,024,654 to make them air-drying, may also be used with advantage.
The polyesters should have acid numbers of from 1 to 50, preferably from 5 to 25, OE-numbers from 10 to 100, preferably from 20 to 50, and molecular weights Mn from 500 to 10,000, preferably from 700 to 3000 (molecular weights up to 5000 are measured by vapour pressure osmosis in dioxane and acetone, and if both value~ differ from one another the lower value is considered to be the correcter one; molecular weights above 5000 are destined by membrane osmosis).

Acrylic acid esters suitable for use in accordance with the invention are, for example, diacrylates of 1,2-propane diol, Le A 15 613 - 5 -1,3-propane diol, 1,3-butane diol~ 1~4-butane diol~ l~6-hexane diol, diethylene glycol, triethylene glycol, or di-acrylates and triacrylates o~ trimethylolpropane, penta-erythritol~ neopentyl glycol, which may be obtained in known manner, for example by azeotropic esterification~ trans-esterification reactions or by reacting the aforementioned polyhydric alcohols with acrylic acid halides in known manner.
In order to protect the polymerisable coating compositions against undesirable premature polymerisation~ polymerisation inhibitors or antioxidants may be added to them during preparation in quantities of from O.OOl to O.l ~O~ by weight, based on the sum total of components (A) and (B). Suitable additives of this kind are, for e~ample, phenols and phenol derivatives~ preferably sterically hindered phenols containing alkyl substituents with from 1 to 6 carbon atoms in both o-positions to the phenolic hydroxy group~ amines, preferably secondary aryl amines and their derivatives, quinones~ copper salts o~ organic acids, addition compounds of copper(I)halides with phosphites, such as 4,4'-bis-(2,6-di-tert.-butyl phenol), 1,3,5-trimethyl-~ 2,4~6-tris-(3,5-di-tert.-butyl-4-hydroxy benz~l)-benzene, 4~4'-butylidene-bis-(6-tert.-butyl-m-cresol), 3,5-di-tert.-butyl-4-hydroxy benzyl phosphonic acid diethyl ester, N,N'-bis-(~-naphthyl)-p-phenylene diamine, N,N'-bis-(l-methyl heptyl)-~-phenylene diamine, phenyl-~-naphthyl amine, 4,4'-bis-(a~-dimethyl benzyl)-diphenyl amine, 1,3,5-tris-(3,5-di-tert.-butyl-4-hydroxy hydrocinnamoyl)-hexahydro-s-triazine, hydroquinone, p-benzoquinone, 2,5-di-tert.-butyl quinone, toluhydroquinone, ~-tert.-butyl pyrocatechlo, 3-methyl pyrocatechol, 4-ethyl pyrocatechol, chloranil, naphthoquinone, copper naphthenate, copper octoate, Cu(I)Cl/triphenyl phosphite, Cu(I)Cl/trimethyl phosphite~ Cu(I)Cl/tris-chloroethyl phosphite~ Cu(I)Cl/tripropyl phosphite~ ~-nitrosodimethyl aniline~ Other suitable stabilisers are described in "Methoden der organischen Chemie" (Houben-Weyl), 4th Edition, Vol. XIV/l, pages 433-452~ 756, Georg Thieme Le A 15 613 -6-Verlag, Stuttgart, 1961. For example~ ~-benzoquinone and/or hydroquinone monomethyl ether is/are particularly suitable in a concentration of from 0.01 to 0.05 ~, by weight, based on the sum total of components (A) and (B).
The coating compositions according to the invention may optionally contain polymerisation initiators in the usual quantities, preierably in quantities o~ ~rom 0.1 to 5 %, by weight~ based on the sum total of components (~) and (B). Examples of suitable polymerisation initiators are: diacyl peroxides, such as diacetyl peroxide, dibenzoyl peroxide~ di-~-chlorobenzoyl peroxide, dilauroyl peroxide, peroxy esters~ such as tert.-butyl peroxy acetate, tert.-butyl peroxy ben~oate, dicyclohexyl peroxy dicarbonate, alkyl peroxides, such as bis-(tert.-butyl peroxy butane), dicumyl peroxide, tert.-butyl cumyl peroxide, hydroperoxides~ ~uch as cumene hydroperoxide, tert.-butyl hydroperoxide, ketone peroxides~ such as cyclohexanone hydro-peroxide~ methyl ethyl ketone hydroperoxide, acetyl acetone peroxide or azoisobutyrodinitrile.
Heavy metal salts of carboxylic acids such as cobalt~ zirconium and vanadium naphthenate, or chelates of these metals~ such as cobalt and zirconium acetyl acetonate~
may be added in e~feGtive quantities as accelerators together with the polymerisation initiators.
The phosphlnos, arsines and ~tibinos descrlbed ~ initiators in DO~German Publi~hed Specification)No.1 ,769,952 are al~o ef~ect-ive a8 accelerator~.The quantity in whlch the accelerators ~F~n ally added are used is from 0.1 to 3 %,by weight,based on the8u~
total o~ ¢omponent~(A)and O.~he requisite dose oi~ radiation may be appreciably reduced by adding these compounds.
In addition, the coating compositions according to the invention may contain up to 300 ~, by weight~ and preferably ~rom 50 to 200 %, by weight, of ~illers, pigments andthixotropsing Le A 15 613 -7- ~

1~6283~
~gents. Additives of this kind include such inorganic materials as silica~ talcum~ chalk~ heavy spar~ light spar, titanium dioxide, iron oxide, calcium carbonates~ silicates~ aluminas~
lime, carbon, asbestos, glass metals, primarily in the form of fibres~ woven fabrics or mats, and organic fillers, such as cotton~ sisal~ jute, polyester~ polyamide, again in the form of iibres or woven fabrics. These materials may be present during electron-beam hardening.
In order to protect light-sensitive substrates, for example light woods, the usual UV-absorbers may be added to the coating compositions in small quantities. Examples of suitable UV-absorbers include: 2-hydroxy-4-methoxy ben~ophenone and the cinnamic acid and benzotriazine derivatives normally used.
The percentages of the following examples are percentages by welght.
~XAMPLE 1 An unsaturated polyester with an acid number of 20 and a viscosity of 1350 cP~ as measured on a 65 ~ solution in styrene at 20C in accordance with DIN 53 015, prepared by condensing 152 parts, by weight, of maleic acid anhydride, 141 parts, by weight, of phthalic acid anhydride and 195 parts, by weight~ of 1,2-propane diol, has 0.045 part, by weight, of hydroquinone added to it, followed by dissolution in various polyfunctional acrylic acid esters to form 50 ~ solutions.
The thus-obtained mixtures are applied with a film coater (120 ~u) to a non-porous substrate, for example to chipboard panels provided with a hardened surfacing composition.
Immediately afterwards~ the coated panels are delivered on a conveyor belt to the electron beam issuing from the scanner of an electron beam installation (accelerator volatage 320 kVj cathode current 50 mA). Hardening of the polyester/polyacrylate mixture is completed at the belt speeds shown in Table 1 in an inert gas atmosphere to avoid oxygen inhibition. The radiation dose required in each case is also shown in Table 1.
Le A 15 61~ -8-Table 1 Belt speed Aadiation dose Component (~) required ior required for hardening hardening m/min mrad 1,2-ethane diol bis-acrylate 25 approx. 2.8 1,2-propane diol bis-acrylate 25 approx. 2,8 1,4-butane diol bis-acrylate 30 approx. 2 3 trimethylolpropane tris-acrylate 35 approx 2.0 The coatings are glossy, extremely hard and completely scratch-prooi.
When, ior comparison, the above unsaturated polyester is dissolved to iorm a 50 ~ solution in an acrylic ester oi a monohydric alcohol, for example ethyl acrylate or butyl acrylate, or in styrene~ iollowed by hardening under the same conditions as described above~ the coating remains wet and tacky, even at belt ~peeds oi 10 metres per minute.

The unsaturated polyester according to Example 1 is mixed in diiierent ratios with 1~4-butane diol bis-acrylate and trimethylol propane tris-acrylate. 50 parts, by weight~ oi butyl acetate are added to 100 parts, by weight~ oi the respective mixtures. The thus-obtained solutions are applied as in Example 1 and hardened in the same way as described in Example 1 aiter an evaporation time oi 30 seconds (in warm recirculating air at 100C). The mixing ratios, the requisite belt speeds and the particular radiation dose required are set out in Table 2.

Le ~ 15 613 -9-. 1062839 ~able 2 M$xing ratio Component (B) Belt speed Radiation dose component (A) required for required $or component (B) hardening hardening m/min mrad ~ 4 : 6 1,4-butane diol 30 approx. 2.3 bis-acrylate 5 : 5 1~4-butane diol 25 approx. 2.8 bis-acrylate 6 : 4 1,4-butane diol 20 approx 3.5 bis-acrylate 7 : 3 1,4-butane diol 15 approx. 4.6 bis-acrylate 4 : 6 trimethylolpropane 40 approx. 1.7 tris-acrylate 5 : 5 trimethylolpropane 30 approx. 2.3 tris-acrylate 6 : 4 trimethylolpropane 25 approx. 2.8 tris-acrylate 7 : 3 trimethylolpropane 15 approx. 4.6 tris-acrylate The coatings are glossy~ extremely hard and completely scratch-proof.

A clear lacquer consisting of 50 parts, by weight, of unsatur~ted polyester according to Exa~ple 1, 50 parts, by weight~ of 1~4-butane diol bis-acrylate~ 50 parts, by weight, oi butyl acetate and 15 parts, by weight, of~ elustrant ~elustrant 0~ 412, a product of Degussa, Frankfurt), is prepared by grinding for 2 hours in an edge-runner mill. The lacquer is applied in the same way as described in Example 1 and hardened, again in the same way as in Example 1, after an evaporation time of 30 seconds (in warm recirculating air at 100C). Complete hardening is carried out in an inert gas atmosphere at a belt speed of 25 metres per minute. The coat$ng is matt, extremely hard and completely scratch-proof.
Le A 1 613 -10-10628~9 A pigmented lacquer consisting of 50 part~, by weight, of unsaturated polyester according to Example 1, 50 parts, by weight, of trimethylolpropane tris-acrylate, 50 parts, by weight~ of butyl acetate and 50 parts, by weight, of titanium dioxide, i8 prepared by grinding for 15 hours in an edge-runner mill.
The lacquer is applied in the same way as Example 1 and hardened, again as described in Example 1, after an evaporation time of 30 seconds (in warm recirculating air at 100C), Complete hardening is carried out in an inert gas atmosphere at a belt speed of 30 metres per minute. The coating is glossy, extremely hard and completely scratch-proof.
EXAMPLE ~
A clear lacquer consisting of 50 parts, by weight, of unsaturated polyester according to Example 1, 50 parts, by weight, of 1,4-butane diol biq-acrylate, 60 parts, by weight, of a 5 nitrocellulose solution (Standard type 4 E) in butyl acetate ~e/~rtr~ el~str~n~
9 parts of a delustr~n* (delu~rant OK 412, a product of Degussa, Frankfurt), 0.025 parts, by weight, of a silicone oil ( Baysilon~oil PL, a product of Bayer AG~ Leverkusen) and 150 parts, by weight, of butyl acetate, is prepared by grinding for 2 hours in an edge-runner mill. After the viscosity of the lacquer has been adjusted with butyl acetate to 25 seconds, as measured at 20C using a DIN-4 mm cup in accordance with DIN 53 211, it is applied by means of a casting machine (layer thickness 80 g/m2) to a closed-pore, ground polyester substrate and hardened in the same way as described in ExampIe 1 after an evaporation time of 30 seconds ( in warm recirculating air at 100C). Complete hardening takes place in an inert gas atmosphere at a belt speed of 25 metres per minute.
The coating is matt, extremely hard and completely scratch-proof.
If the above lacquer is cast directly onto veneer in a layer thickness of 80 g per s~uare metre, followed by ~e ~ 15 61~ -11-7 r~Je ~

evaporation and hardening as described aboveJ and if, after gentle grinding, another coating of lacquer is applied, followed by hardening, good-quality matt, com~etely scratch-proof so-called "open-pored" lacquer finishes completely resistant to chemicals are obtained.

A pigmented lacquer, consisting of 50 parts, by weight, of unsaturated polyester according to Example 1, 50 parts, by weight, of 1,4-butane diol bis-acrylate (or 50 parts, by weight, of trimethylolpropane tris-acrylate), 100 parts, by weight, of titanium dioxide, 6Q parts, by weight, of barium sul-phate, 12 parts, by weight, of a Delustrant* (Delustrant* OK
412, a product of DegussaJ Frankfurt), 0.5 parts, by weightl of a highly disperse silica CAerosil* 300, a product of Degussa, Frankfurt), 0.025 part, by weight, of a silicone oil ~Baysilon*_ oil PL, a product of Bayer AG, Leverkusen), 0.15 part, by weight, of a polybutadiene oil ~Polyol 130, a product of Chem. Werke Huls, Marl), 60 parts, by weight, of ethyl acetate (lOQ parts, by weight, of ethyl acetate where trimethylolpropane tris-acrylate is used), is prepared by grinding for 15 hours in an edge-runner mill, the delustrant only being added in the last 2 hours. After the vis-cosity of the lacquer has been adjusted with ethyl acetate to 30 seconds, as measured using a DIN-4 mm cup at 20C in accordance with DIN 53 211, the lacquer is applied by means of a casting machine in a layer thickness of 100 g per square metre to primed, non-absorbent chipboard or hardboard panels and hardened in the same way as described in Example 1 after an evaporation time of 30 seconds (in warm recirculating air at 100C). Complete hardening takes place in an inert gas atmosphere at a belt speed of 25 metres per minutes. The coatings are matt, hard and completely scratch-proof.

*Trademark 1~6Z839 If 0.1 part, by weight, of tr:Lphenyl phosphine is added to the above lacquer~ complete hardening takes place at a belt speed of 35 m per mînute where 1,4-butane diol bis-acrylate is used.

A surfacing composition~ consisting of 50 parts, by weight, of unsaturated polyester according to Example 1, 50 parts, by weight, of 1,4-butane diol bis-acrylate, 80 parts~
by weight, of fine to medium-fine talcums, 40 parts, by weight, of barium sulphate, 20 parts, by weight, of titanium dioxide and 1 part~ by weight, of a highly disperse silica~ is pre-pared by stirring. The thus-prepared composition is applied by a coating machine to typical chipboard panels in a layer thickness of 120 g per square metre.
The thus-coated panels are hardened immediately afterwards in the same way as described in Example 1.
Complete hardening takes place in an inert gas atmosphere at a belt speed of 25 metres per minute. The coating is bubble-free, completely hard and may be readily sanded to form an excellent substrate for surface coats.

Le A 15 61~

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Highly reactive coating compositions, hardenable by electron beams and suitable for coating wood and wood-like materials, based on .alpha.,.beta.-unsaturated polyesters and polymerisable acrylic esters, wherein, apart from non-polymerisable solvents, pigments and particulate mineral fillers, it contains: (A) from 20 to 55%, by weight, based on the sum of (A)+(B), of .alpha.,.beta. -unsaturated polyesters; and (B) from 45 to 80 %, by weight, based on the sum of (A)+(B), of diacrylates of alkane diols with from 2 to 6 carbon atoms and/or di- or tri-acrylates of triols or tetraols with from 3 to 6 carbon atoms.

2. Coating compositions as claimed in Claim 1, wherein they contain from 0.1 to 3 %, by weight, based on the sum total of components (A) and (B), of phosphines, arsines and/or stibines.as accelerators.

3. A method of coating wood and wood-like materials which compriese applying to the wood or wood-like material a coating composition as claimed in claim 1 and hardening the composition by an electron beam.