Note: Descriptions are shown in the official language in which they were submitted.
. ~ 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.
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~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
1062839
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_
106Z839
` 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-
106Z839
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 -
1062839
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
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106Z839
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.
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106Z839
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.
EXAMPLE 2
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 $or
component (B) hardening hardening
m/min mrad
~ 4 : 6 1,4-butane diol 30 approx. 2.3
bis-acrylate
5 : 5 1~4-butane diol 25 approx. 2.8
bis-acrylate
6 : 4 1,4-butane diol 20 approx 3.5
bis-acrylate
7 : 3 1,4-butane diol 15 approx. 4.6
bis-acrylate
4 : 6 trimethylolpropane 40 approx. 1.7
tris-acrylate
5 : 5 trimethylolpropane 30 approx. 2.3
tris-acrylate
6 : 4 trimethylolpropane 25 approx. 2.8
tris-acrylate
7 : 3 trimethylolpropane 15 approx. 4.6
tris-acrylate
The coatings are glossy~ extremely hard and completely
scratch-proof.
EXAMPLE 3
A clear lacquer consisting of 50 parts, by weight, of
unsatur~ted polyester according to Exa~ple 1, 50 parts, by
weight~ of 1~4-butane diol bis-acrylate~ 50 parts, by weight,
oi butyl acetate and 15 parts, by weight, of~ elustrant
~elustrant 0~ 412, a product of Degussa, Frankfurt), is
prepared by grinding for 2 hours in an edge-runner mill. The
lacquer is applied in the same way as described in Example 1
and hardened, again in the same way as in Example 1, after
an evaporation time of 30 seconds (in warm recirculating air
at 100C). Complete hardening is carried out in an inert
gas atmosphere at a belt speed of 25 metres per minute. The
coat$ng is matt, extremely hard and completely scratch-proof.
Le A 1 613 -10-
10628~9
EXAMPLE 4
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 ~
106Z839
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.
EXAMPLE 6
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
- 12 -
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.
EXAMPLE 7
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~
