U.S. patent application number 09/149662 was filed with the patent office on 2002-05-16 for radiation-curable formulations based on aliphatic, urethane-functional prepolymers having ethylenically unsaturated double bonds.
Invention is credited to BECK, ERICH, MENZEL, KLAUS, SCHWALM, REINHOLD, VOELLINGER, FRANK.
Application Number | 20020058146 09/149662 |
Document ID | / |
Family ID | 7842031 |
Filed Date | 2002-05-16 |
United States Patent
Application |
20020058146 |
Kind Code |
A1 |
SCHWALM, REINHOLD ; et
al. |
May 16, 2002 |
RADIATION-CURABLE FORMULATIONS BASED ON ALIPHATIC,
URETHANE-FUNCTIONAL PREPOLYMERS HAVING ETHYLENICALLY UNSATURATED
DOUBLE BONDS
Abstract
Radiation-curable formulations comprising i) at least one
aliphatic, urethane-functional prepolymer which on average has at
least two ethylenically unsaturated double bonds, ii) at least one
monofunctional ester of an .alpha.,.beta.-ethylenically unsaturated
carboxylic acid with a monofunctional alkanol which has a
saturated, carbocyclic or heterocyclic structural element, and iii)
if desired, a di- or polyfunctional ester of an
.alpha.,.beta.-ethylenically unsaturated carboxylic acid with an
aliphatic di- or polyol are used to coat substrates.
Inventors: |
SCHWALM, REINHOLD;
(WACHENHEIM, DE) ; VOELLINGER, FRANK; (EDENKOBEN,
DE) ; BECK, ERICH; (LADENBURG, DE) ; MENZEL,
KLAUS; (LUDWIGSHAFEN, DE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Family ID: |
7842031 |
Appl. No.: |
09/149662 |
Filed: |
September 9, 1998 |
Current U.S.
Class: |
428/423.1 ;
428/425.8; 428/458; 522/90; 522/96 |
Current CPC
Class: |
C08G 18/672 20130101;
C08G 18/8064 20130101; C08F 290/147 20130101; Y10T 428/31551
20150401; Y10T 428/31681 20150401; C08L 33/00 20130101; Y10T
428/31605 20150401; C09D 175/16 20130101; Y10T 428/31504 20150401;
C09D 175/16 20130101 |
Class at
Publication: |
428/423.1 ;
428/425.8; 428/458; 522/90; 522/96 |
International
Class: |
B32B 015/08; C08F
002/46; B32B 027/40; C08J 003/28 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 1997 |
DE |
19739970.3 |
Claims
We claim:
1. A radiation-curable formulation comprising i) at least one
aliphatic, urethane-functional prepolymer which on average has at
least two ethylenically unsaturated double bonds per molecule
(=component A), ii) at least one monofunctional ester of an
.alpha., .beta.-ethylenically unsaturated carboxylic acid with a
monofunctional alkanol which has as a structural element at least
one saturated 5- or 6-membered carbocycle or one saturated 5- or
6-membered heterocycle with one or two oxygens in the ring
(=component B), and iii) if desired, di- or polyfunctional esters
of an .alpha.,.beta.-ethylenically unsaturated carboxylic acid with
an aliphatic di- or polyol (=component C).
2. A formulation as claimed in claim 1, containing from 20 to 90%
by weight of component A, from 10 to 80% by weight of component B,
from 0 to 40% by weight of component C and up to 20% by weight,
based on the overall weight of components A, B and C, of customary
auxiliaries, with the proviso that the amounts by weight of
components A, B and C add up to 100% by weight.
3. A formulation as claimed in claim 1, in which the weight ratio
of components B and C is in the range from 20:1 to 1:1.
4. A formulation as claimed in claim 1, in which component B is a
compound of the formula I 2where R is H or CH.sub.3, k is from 0 to
4, and Y is a 5- or 6-membered saturated carbocycle or a 5- or
6-membered saturated heterocycle with one or two oxygens, the
heterocycle being unsubstituted or substituted by
C.sub.1-C.sub.4-alkyl.
5. A formulation as claimed in claim 4, in which component B is
selected from trimethylolpropane monoformal acrylate, glycerol
monoformal acrylate, cyclohexylmethyl acrylate, 4-tetrahydropyranyl
acrylate, 2-tetrahydropyranylmethyl acrylate and tetrahydrofurfuryl
acrylate.
6. A formulation as claimed in claim 1, in which component C is
selected from the diacrylates and dimethacrylates of aliphatic
diols.
7. A formulation as claimed in claim 6, comprising as component C
1,6-hexanediol diacrylate and/or 1,4-butanediol diacrylate.
8. A formulation as claimed in claim 1, in which the ethylenically
unsaturated double bonds of the aliphatic, urethane-functional
prepolymer are in the form of acrylate and/or methacrylate
groups.
9. A formulation as claimed in claim 1, in which the aliphatic,
urethane-functional prepolymer is obtainable by reacting i) at
least one aliphatic compound or one aliphatic prepolymer having at
least two isocyanate groups (component a1), ii) at least one
compound which has at least one reactive OH group and at least one
ethylenically unsaturated double bond (component a2) and, if
desired, iii) one or more aliphatic compounds having at least one
reactive OH group (component a3).
10. A formulation as claimed in claim 9, where component a1 is
selected from the biurets and the isocyanurates of aliphatic
diisocyanates and from the adducts of aliphatic diisocyanates with
polyfunctional, aliphatic alcohols having at least 3 reactive OH
groups.
11. A formulation as claimed in claim 10, where component a1 is the
isocyanurate of hexamethylene diisocyanate.
12. A formulation as claimed in claim 9, where component a2 is
selected from the esters of acrylic acid and/or methacrylic acid
with at least one aliphatic di- or polyol, where the residue still
has at least one free OH group.
13. A formulation as claimed in claim 12, where component a2 is
selected from 2-hydroxyethyl (meth)acrylate, hydroxypropyl
(meth)acrylate, 1,4-butanediol mono(meth)acrylate,
trimethylolpropane mono- and di(meth)acrylate and pentaerythritol
tri(meth)acrylate.
14. A formulation as claimed in claim 9, where component a3 is a
monofunctional alkanol having 1 to 10 carbons.
15. A method of coating substrates, which comprises applying a
formulation as claimed in claim 1 to the substrate which is to be
coated, removing any solvent and then curing the coating by
radiation with UV radiation or electron beams.
16. The method as claimed in claim 15, where the substrate is a
metal or a coated metal.
17. A coated substrate obtained by a method as claimed in claim 15.
Description
[0001] The present invention relates to radiation-curable
formulations which comprise at least one aliphatic,
urethane-functional prepolymer having at least two ethylenically
unsaturated double bonds and at least one monofunctional ester of
an .alpha.,.beta.-ethylenically unsaturated carboxylic acid with a
monofunctional alkanol, said prepolymer having as a structural
element at least one saturated 5- or 6-membered carbocycle or one
5- or 6-membered heterocycle with one or two oxygens in the
ring.
[0002] Radiation-curable compositions have acquired widespread
importance in the art, especially as high-grade surface coating
materials. By radiation-curable compositions are meant formulations
which include ethylenically unsaturated polymers or prepolymers and
which, directly or after a physical drying step, are cured by the
action of high-energy radiation, for example by irradiation with UV
light or by irradiation with high-energy electrons (electron
beams).
[0003] Particularly high-grade coatings are obtained if the
radiation-curable composition employed comprises formulations that
contain an ethylenically unsaturated, urethane-functional polymer
or prepolymer. Ethylenically unsaturated urethane-functional
polymers and prepolymers are known, for example, from P. K. T.
Oldring (ed.), Chemistry and Technology of UV- and EB-Formulations
for Coatings, Inks and Paints, Vol. II, SITA Technology, London
1991, pp. 73-123. Because of the high viscosity of ethylenically
unsaturated, urethane-functional polymers and prepolymers, such
compositions are often admixed with ethylenically unsaturated
compounds of low molecular mass in order to reduce the viscosity.
These compounds, like the ethylenically unsaturated polymers and
prepolymers, are polymerized in the course of curing and so
incorporated into the coating. They are therefore referred to as
reactive diluents. Hence the properties of the resulting coatings
are determined both by the ethylenically unsaturated polymer or
prepolymer employed and by the reactive diluent. For optimum
coating properties, furthermore, it is necessary to harmonize the
ethylenically unsaturated polymers or prepolymers with the reactive
diluents.
[0004] DE-A-27 260 41 discloses radiation-curable compositions
comprising at least one polyetherurethane which is modified at the
ends with acrylate and/or methacrylate groups, a low molecular mass
polyfunctional acrylate with ether groups, and hydroxyalkyl
acrylates. Radiation-curable compositions of this kind lead to
coatings having increased flexibility.
[0005] EP-A-508 409 discloses radiation-curable compositions which
comprise at least one ethylenically unsaturated polyesterurethane
and at least one nonaromatic, low molecular mass substance having
at least one, preferably at least two, (meth)acryloyl groups, as
crosslinker (=reactive diluent). Radiation-curable compositions of
this kind lead to coatings having improved weathering
stability.
[0006] A fundamental problem with the radiation-curable
compositions of the prior art is that, although it is possible by
selecting and harmonizing the components (prepolymer and reactive
diluent) to improve individual in-use properties such as coating
hardness, flexibility and weathering resistance, this is always at
the expense of other properties.
[0007] It is an object of the present invention to provide
radiation-curable compositions which lead to coatings having
balanced profiles of properties, with great hardness, high
flexibility and high weathering resistance, and which at the same
time feature low application viscosity and a high curing rate.
[0008] We have found that this object is achieved, surprisingly, by
a radiation-curable composition which comprises at least one
aliphatic, urethane-functional prepolymer and at least one
monofunctional ester of an .alpha.,.beta.-ethylenically unsaturated
carboxylic acid with a monofunctional alkanol which has as a
structural element at least one saturated 5- or 6-membered
carbocycle or one corresponding heterocycle having one or two
oxygens in the ring.
[0009] The present invention consequently provides
radiation-curable formulations which comprise
[0010] i) at least one aliphatic, urethane-functional prepolymer
which on average has at least two ethylenically unsaturated double
bonds per molecule (=component A),
[0011] ii) at least one monofunctional ester of an
.alpha.,.beta.-ethyleni- cally unsaturated carboxylic acid with a
monofunctional alkanol which has as a structural element at least
one saturated 5- or 6-membered carbocycle or one saturated 5- or
6-membered heterocycle with one or two oxygens in the ring
(=component B), and
[0012] iii) if desired, di- or polyfunctional esters of an
.alpha.,.beta.-ethylenically unsaturated carboxylic acid with an
aliphatic di- or polyol (=component C).
[0013] In accordance with the invention, the aliphatic,
urethane-functional prepolymer is free from aromatic structural
elements such as phenylene or naphthylene or substituted
derivatives thereof. Component B contains no nitrogens.
[0014] In general, the compositions of the invention contain from
20 to 90% by weight, preferably from 30 to 80% by weight, and in
particular from 40 to 70% by weight, of component A, from 10 to 80%
by weight, preferably from 20 to 60% by weight, and in particular
from 30 to 50% by weight, of component B, from 0 to 40% by weight
and, preferably, from 0 to 30% by weight, of component C and up to
20% by weight, based on the overall weight of components A, B and
C, of customary auxiliaries, with the proviso that the amounts by
weight of components A, B and C add up to 100% by weight. In
general, the weight of components B and C is in the range from 10
to 80% by weight, preferably from 20 to 70% by weight and, in
particular, from 30 to 60% by weight, based in each case on the
overall weight A+B+C.
[0015] Depending on the desired profile of properties the
compositions of the invention comprise component B and component C
or exclusively component B. Where high coating hardness is desired
the formulation of the invention preferably comprises component B
and component C. If instead greater value is placed on high
flexibility, component C may be omitted. In addition, as the amount
of component C increases, the viscosity of the formulations of the
invention is improved. In the first case the ratio of component B
to component C is preferably in the range from 20:1 to 1:1 and, in
particular, in the range 10:1 to 1.5:1.
[0016] In general, component A is composed essentially of one or
more aliphatic structural elements, urethane groups and at least
two ethylenically unsaturated structural units. Aliphatic
structural elements include both alkylene groups, preferably with 4
to 10 carbons, and cycloalkylene groups, preferably with 6 to 20
carbons. Both the alkylene and cycloalkylene groups can be
substituted one or more times by C.sub.1-C.sub.4-alkyl, especially
by methyl, and may include one or more nonadjacent oxygens. The
aliphatic structural elements may be connected to one another by
way of quaternary or tertiary carbons, by way of urea groups,
biuret, uretdione, allophanate, cyanurate, urethane, ester or amide
groups or by way of ether oxygen or amine nitrogen. Component A is
preferably free from uretdione or allophanate groups and from amine
nitrogen. Furthermore, component A in accordance with the invention
has at least two ethylenically unsaturated structural elements.
These are preferably vinyl or allyl groups, which can also be
substituted by C.sub.1-C.sub.4-alkyl, especially methyl, and which
are derived in particular from .alpha.,.beta.-ethylenically
unsaturated carboxylic acids and/or their amides. Particularly
preferred ethylenically unsaturated structural units are acryloyl
and methacryloyl groups, such as acrylamido and methacrylamido and,
in particular, acryloxy and methacryloxy. With particular
preference, component A has at least three ethylenically
unsaturated structural elements per molecule.
[0017] Very particular preference is given to components A in which
the aliphatic structural elements are linked by way of cyanurate,
biuret and/or urethane groups and whose ethylenically unsaturated
structural elements are acryloxy groups.
[0018] The number-average molecular weight M.sub.n of the
urethane-functional prepolymers of component A is preferably
.ltoreq.2000 and is in particular in the range from 400 to 1500.
The double bond density in such prepolymers is preferably above 1.5
mol/kg of prepolymer and, in particular, is in the range from 2 to
6 mol/kg of prepolymer.
[0019] Ethylenically unsaturated, urethane-functional prepolymers
of this kind are fundamentally known to the skilled worker.
Preferred aliphatic urethanes that are free of urea groups are
obtainable, for example, by reacting
[0020] i) at least one aliphatic compound or one aliphatic
prepolymer having at least two and preferably three or 4 isocyanate
groups (component a1) with
[0021] ii) at least one compound which has at least one reactive OH
group and at least one ethylenically unsaturated double bond
(component a2) and, if desired,
[0022] iii) one or more aliphatic compounds having at least one
reactive OH group (component a3).
[0023] In this case the ratio of the OH groups of components a2 and
a3 to the NCO groups of component a1, OH/NCO, is .gtoreq.1, so that
the resulting prepolymer contains no NCO groups. Component a2 is
preferably employed in an amount such that the OH groups it
contains (OH.sub.a2) are in a ratio to the NCO groups of component
a1, OH.sub.a2/NCO, which is in the range from 0.4 to 0.95 and,
preferably, from 0.6 to 0.9.
[0024] Compounds suitable as component a1 are aliphatic
diisocyanates, oligomeric adducts of aliphatic diisocyanates with
polyfunctional alcohols having preferably 2 to 20 carbons, and the
uretdiones, isocyanurates, biurets and allophanates of aliphatic
diisocyanates. Examples of suitable aliphatic diisocyanates are
tetramethylene diisocyanate, hexamethylene diisocyanate,
octamethylene diisocyanate, decamethylene diisocyanate,
dodecamethylene diisocyanate, tetradecamethylene diisocyanate,
1,6-diisocyanato-2,2,4-trimethylhexane,
1,6-diisocyanato-2,2,4,4-tetramethylhexane, 1,2-, 1,3- or
1,4-diisocyanatocyclohexane, 4,4'-di(isocyanatocyclohexyl)methane,
1-isocyanato-3,3,5-trimethyl-5-(isocyanatomethyl)cyclohexane
(=isophorone diisocyanate) and 2,4- or
2,6-diisocyanato-1-methylcyclohexane. Suitable polyfunctional
alcohols include aliphatic di- or polyols having preferably 2 to 20
carbons, such as ethylene glycol, diethylene glycol, triethylene
glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene
glycol, tripropylene glycol, 1,4-butanediol, 1,5-pentanediol,
neopentyl glycol, 1,6-hexanediol, 2-methyl-1,5-pentanediol,
2-ethyl-1,4-butanediol, dimethylolcyclohexane, glycerol,
trimethylolethane, trimethylolpropane, trimethylolbutane,
pentaerythritol, ditrimethylolpropane, erythritol and sorbitol.
Component a1 is preferably selected from the trimerization products
of the abovementioned aliphatic diisocyanates, in other words the
biurets and the isocyanurates, and the adducts of the
abovementioned aliphatic diisocyanates with one of the
abovementioned polyfunctional aliphatic alcohols having at least
three reactive OH groups. It is particularly preferred to employ as
component a1 the isocyanurate and/or the biuret of hexamethylene
diisocyanate and, with very particular preference, its
isocyanurate.
[0025] Examples of suitable components a2 are the esters of
ethylenically unsaturated carboxylic acids with one of the
abovementioned aliphatic polyols and also the vinyl, allyl and
methallyl ethers of these polyols, provided they also have one
isocyanate-reactive OH group. It is also possible to employ the
amides of ethylenically unsaturated carboxylic acids with amino
alcohols. Preference as component a2 is given to the esters of
acrylic and methacrylic acid, such as 2-hydroxyethyl
(meth)acrylate, hydroxypropyl (meth)acrylate, 1,4-butanediol
mono(meth)acrylate, neopentyl glycol mono(meth)acrylate,
trimethylolpropane di(meth)acrylate, pentaerythritol di- and
-tri(meth)acrylate. With particular preference component a2 is
selected from hydroxypropyl acrylate and butanediol monoacrylate,
and in particular a2 is 2-hydroxyethyl acrylate.
[0026] Examples of suitable aliphatic compounds having at least one
reactive OH group (component a3) are alkanols having preferably 1
to 10 carbons, cycloalkanols having preferably 5 to 10 carbons, and
monoalkyl ethers of polyalkylene glycols. Examples of suitable
alkanols are methanol, ethanol, n- and isopropanol, n-, 2-, iso-
and tert-butanol, amyl alcohol, isoamyl alcohol, n-hexanol,
n-octanol, 2-ethylhexanol and decanol. Suitable cycloalkanols
include, for example, cyclopentanol and cyclohexanol, which are
unsubstituted or substituted one or more times by
C.sub.1-C.sub.4-alkyl, for example methyl, ethyl, n-propyl,
isopropyl, n-butyl, 2-butyl, isobutyl or tert-butyl, especially by
methyl. Examples of monoalkyl ethers of polyalkylene glycols are
the mono-C.sub.1-C.sub.4-alkyl ethers and, in particular, the
methyl ethers of ethylene glycol, diethylene glycol or triethylene
glycol.
[0027] Component A is prepared in a known manner by reacting
component a1 with components a2 and, if used, a3 at from 0 to
100.degree. C. and, in particular, at from 20 to 70.degree. C. It
is preferred to react component a1 and a2 first of all. Component
a3 is added subsequently under reaction conditions.
[0028] To accelerate the reaction it is possible to employ
catalysts as are described, for example, in Houben-Weyl, Methoden
der Organischen Chemie, Vol. XIV/2, Thieme-Verlag, Stuttgart 1963,
p. 60f. and Ullmanns Enzyklopdie der Technischen Chemie, 4th ed.,
Vol. 19 (1981), p. 306. Tin-containing catalysts are preferred,
such as dibutyltin dilaurate, tin(II) octoate or dibutyltin
dimethoxide. Such catalysts are generally employed in an amount of
from 0.001 to 2.5% by weight, preferably from 0.005 to 1.5% by
weight, based on the overall amount of the reactants.
[0029] To stabilize the free-radically polymerizable compounds
(component a2) it is preferred to add to the reaction from 0.001 to
2% by weight, in particular from 0.005 to 1.0% by weight, of
polymerization inhibitors. These are the usual compounds suitable
for hindering free-radical polymerization, examples being
hydroquinones or hydroquinone monoalkyl ethers,
2,6-di-tert-butylphenols, such as 2,6-di-tert-butylcresole,
nitrosamines, phenothiazines or phosphorous esters. The reaction
can be carried out either without solvent or with the addition of
solvents. Suitable solvents are inert solvents such as acetone,
methyl ethyl ketone, tetrahydrofuran, dichloromethane, toluene,
C.sub.1-C.sub.4-alkyl esters of acetic acid, such as ethyl acetate
or butyl acetate. The reaction is preferably carried out without
solvent.
[0030] As component B it is possible in principle to employ all
monofunctional esters of .alpha.,.beta.-ethylenically unsaturated
carboxylic acids with a monofunctional alcohol which has as a
structural element at least one saturated 5- or 6-membered
heterocycle with one or two oxygens in the ring. Component B is
preferably derived from acrylic or methacrylic acid. Examples of
suitable compounds of component B embrace compounds of the formula
I 1
[0031] where
[0032] R is H or CH.sub.3, especially H,
[0033] k is from 0 to 4, especially 0 or 1, and
[0034] Y is a 5- or 6-membered saturated carbocycle or a 5- or
6-membered saturated heterocycle with one or two oxygens, the
heterocycle being unsubstituted or substituted by
C.sub.1-C.sub.4-alkyl, such as by methyl, ethyl, n-propyl,
isopropyl, n-butyl, 2-butyl, isobutyl or tert-butyl.
[0035] The 5- or 6-membered saturated heterocycle is preferably
derived from tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,3-
or 1,4-dioxane.
[0036] With particular preference, component B is selected from
trimethylolpropane monoformal acrylate, glycerol monoformal
acrylate, cyclohexylmethyl acrylate, 4-tetrahydropyranyl acrylate,
2-tetrahydropyranylmethyl acrylate and tetrahydrofurfuryl acrylate.
Very particular preference is given to the use as component B of
trimethylolpropane monoformal acrylate.
[0037] In addition, the radiation-curable formulations may
comprise, in the amounts indicated above, a di- or polyfunctional
ester of an .alpha.,.beta.-ethylenically unsaturated carboxylic
acid with an aliphatic di- or polyol. Suitable examples are the
esterification products of the di- or polyols set out above in
connection with component a1. Preference is given to the esters of
acrylic and methacrylic acid, especially the diesters of diols.
Preferably, the diols and/or polyols contain no heteroatoms other
than in OH functions. Examples of suitable components B include
ethylene glycol di(meth)acrylate, propylene glycol
di(meth)acrylate, butylene glycol di(meth)acrylate, 1,6-hexanediol
di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene
glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate,
tripropylene glycol di(meth)acrylate, 1,4-cyclohexanediol
di(meth)acrylate and 1,4-bis(hydroxymethyl)cyclohexane
di(meth)acrylate, and also trimethylolethane tri(meth)acrylate,
trimethylolpropane tri(meth)acrylate and pentaerythritol
tetra(meth)acrylate. Particularly preferred components B are
butanediol diacrylate, hexanediol diacrylate, 1,4-cyclohexanediol
diacrylate and 1,4-bis(hydroxymethyl)cyclohexane diacrylate.
Hexanediol diacrylate is especially preferred.
[0038] The radiation-curable formulations of the invention may also
include, depending on their intended use, up to 20% by weight of
customary auxiliaries, such as thickeners, leveling assistants,
defoamers, UV stabilizers, lubricants and fillers. Suitable
auxiliaries are sufficiently well known to the skilled worker from
paints and coatings technology. Suitable fillers include silicates,
for example silicates obtainable by hydrolysis of silicon
tetrachloride such as Aerosil.RTM. from Degussa, silica, talc,
aluminum silicates, magnesium silicates, calcium carbonates, etc.
Suitable stabilizers include UV absorbers, such as oxanilides,
triazines and benzotriazole (the latter obtainable as Tinuvin.RTM.
grades from Ciba-Spezialittenchemie) and benzophenones. These can
be used alone or together with suitable free-radical scavengers,
examples being sterically hindered amines, such as
2,2,6,6-tetramethylpiperidine, 2,6-di-tert-butylpiperidine or
derivatives thereof, such as bis(2,2,6,6-tetramethyl-4-piperidyl)
sebacate. Stabilizers are normally employed in amounts of from 0.1
to 5.0% by weight and preferably from 0.5 to 3.5% by weight, based
on the components A to C present in the formulation.
[0039] Insofar as curing takes place by means of UV radiation, the
formulations of the invention comprise at least one photoinitiator
which is able to initiate the polymerization of ethylenically
unsaturated double bonds. Such photoinitiators include benzophenone
and benzophenone derivatives such as 4-phenylbenzophenone and
4-chlorobenzophenone, Michler's ketone, anthrone, acetophenone
derivatives, such as 1-benzoylcyclohexan-1-ol,
2-hydroxy-2,2-dimethylacetophenone and
2,2-dimethoxy-2-phenylacetophenone, benzoin and benzoin ethers,
such as benzoin methyl, ethyl and butyl ethers, benzil ketals, such
as benzil dimethyl ketal,
2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-on- e,
anthraquinone and its derivatives, such as
.beta.-methylanthraquinone and tert-butylanthraquinone,
acylphosphine oxides, such as
2,4,6-trimethylbenzoyldiphenylphosphine oxide,
ethyl-2,4,6-trimethylbenzo- ylphenylphosphinate and
bisacylphosphine oxides. These photoinitiators are, where
necessary, employed in amounts of from 0.05 to 20% by weight,
preferably from 0.1 to 10% by weight, and in particular from 0.1 to
5% by weight, based on the polymerizable components A, B and C of
the formulations of the invention. If the formulation of the
invention is cured by means of electron beams, the use of
photoinitiators can be omitted. When electron beam curing is
employed, the formulations of the invention may additionally
contain colored pigments.
[0040] Preferably, the formulations of the invention contain no
pigments or fillers. In addition, the formulations of the invention
are preferably free from inert, nonpolymerizable solvents.
[0041] The formulations of the invention are prepared by blending
the components in a conventional manner. Blending may take place at
room temperature or at up to 100.degree. C. and is effected, for
example, by means of customary mixing equipment such as stirring
vessels or static mixers.
[0042] The formulations of the invention are found to be
particularly appropriate for the coating of substrates such as
wood, paper, plastic surfaces, mineral construction materials, such
as shaped cement blocks and cement fiber slabs, and especially for
metals or coated metals.
[0043] Accordingly, the present invention also provides a method of
coating substrates, especially metals or coated metals, and the
coated substrates obtainable by this method. The substrate is
generally coated by applying at least one radiation-curable
formulation of the invention in the desired thickness to the
substrate which is to be coated, removing any solvent and then
curing the coating by the action of high-energy radiation such as
UV radiation or electron beams. This operation may, if desired, be
repeated one or more times. The radiation-curable formulations are
applied to the substrate conventionally, for example by spraying,
brushing, rolling or flow-coating or by coating with a filler knife
or doctor blade. The coating add-on is generally in the range from
3 to 500 g/m.sup.2 and preferably from 10 to 200 g/m.sup.2,
corresponding to wet film thicknesses of from about 3 to 500 .mu.m,
preferably from 10 to 200 .mu.m. Application can be made either at
room temperature or above, but preferably not above 100.degree. C.
The coatings are subsequently cured through the action of
high-energy radiation, preferably UV radiation with a wavelength of
from 250 to 400 nm, or by irradiation with high-energy electrons
(electron beams; from 150 to 300 keV). Examples of UV sources used
are high-pressure mercury vapor lamps, for example the CK or CK1
lamps from IST. The radiation dose which is usually sufficient for
crosslinking is within the range from 80 to 3000 mJ/cm.sup.2.
[0044] In one preferred procedure curing takes place continuously
by passing the substrate that has been treated with the formulation
of the invention at a constant speed in front of a radiation
source. This requires the curing rate of the formulation of the
invention to be sufficiently high.
[0045] The formulations of the invention feature low viscosity,
preferably .ltoreq.10 Pas (determined at 23.degree. C. using an ICI
cone-plate viscometer) and high reactivity, represented by a value
of .gtoreq.10 m/min (corresponding to the rate at which the
substrate, treated with a radiation-curable formulation in a wet
film thickness of 100 .mu.m, can be passed at a distance of 10 cm
in front of a UV source having an output of 120 W/cm so that full
cure still takes place). It is possible at the same time to realize
high hardnesses, characterized by a pendulum attenuation (in
analogy to DIN 53157, see below) .gtoreq.80 sec., and high
flexibilities, characterized by Erichsen indentations .gtoreq.5 mm
(see below), without the systems receiving low grades for viscosity
and reactivity. Moreover, the coatings obtainable from the
formulations of the invention feature enhanced weathering
resistance as can be determined, for example, by sun tests.
[0046] The examples below are intended to illustrate the present
invention without, however, limiting it.
EXAMPLES
I Preparing the Formulation of the Invention
1. Examples 1 to 10
[0047] A stirred vessel was charged with 1000 parts.sup.1) of the
cyanurate of hexamethylene diisocyanate, 1.44 parts of
2,6-di-tert-butyl-4-methylphenol and 0.72 part of hydroquinone
monomethyl ether. This initial charge was heated to 50.degree. C.,
0.3 part of dibutyltin dilaurate was added, and then, at a
temperature of 50 to 60.degree. C., x parts of hydroxyethyl
acrylate (ATA, see Table 1) were added dropwise. The mixture was
subsequently heated to 70.degree. C. and this temperature was
maintained for 3 hours. Then, while still retaining the
temperature, y parts of methanol (MeOH, see Table 1) were added and
the temperature was maintained for 2 hours more until the NCO value
had fallen to 0.05%. The mixture was then cooled and the colorless
product was discharged at 60.degree. C.
[0048] 1) All amounts (parts) hereinbelow are to be understood as
parts by weight.
[0049] Subsequently, the resulting urethane acrylates were blended
in the amounts indicated in Table 1 with trimethylolpropane
monoformal acrylate (TMPMFA), with or without 1,6-hexanediol
diacrylate and 4% by weight of photoinitiator
(2-hydroxy-2-methyl-1-phenylpropan-1-one=Darocure.RTM. 1173 from
Ciba-Spezialittenchemie), based on the overall weight of components
A to C. Table 1 indicates the viscosities and reactivities found
for the formulations of Examples 1 to 10.
1 TABLE 1 Urethane prepolymer HDDA TMPMFA Viscosity.sup.3)
Reactivity.sup.4) Ex. x HEA.sup.1 y MeOH.sup.1 [% by wt.].sup.2 [%
by wt.].sup.2 [% by wt.].sup.2 [Pas] m/min 1 362 76.3 70 0 30 9.9
20 2 453 50.8 62.5 0 37.5 6.0 20 3 453 50.8 60 5 35 2.6 20 4 453
50.8 60 6 34 2.5 20 5 453 50.8 60 0 40 3.1 20 6 513 33.9 61.4 0
38.6 3.8 20 7 513 33.9 60 5 35 4.0 20 8 513 33.9 60 6 34 4.0 25 9
513 33.9 60 0 40 6.0 25 10 453 50.8 40 20 40 0.33 20 .sup.1parts by
weight of hydroxymethyl acrylate (HEA) and methanol per 1000 parts
by weight of the cyanurate of hexamethylene diisocyanate .sup.2% by
weight of components A to C in the radiation-curable formulation
.sup.3)determined at 23.degree. C. using an ICI cone-plate
viscometer .sup.4)determined on coatings with a wet film thickness
of 100 .mu.m on glass in the manner described above
Examples 11 to 14, Comparative Examples V1, V2
[0050] Following the procedure of Examples 1 to 10, a urethane
acrylate was prepared from 1000 parts by weight of the isocyanurate
of hexamethylene diisocyanate, 453 parts of hydroxyethyl acrylate
and 50.8 parts of methanol. 70 parts of the urethane acrylate thus
prepared were then blended with 30 parts of the monoacrylate
indicated in Table 2 (component B) and 4 parts of the
photoinitiator Darocure.RTM. 1173.
[0051] The viscosity and reactivity of the resulting formulations
are indicated in Table 2.
2TABLE 2 Examples 11 to 15, Comparative Examples V1, V2 Reactivity
Example Component B Viscosity [Pas] [m/min] 11 Glycerol mono- 4.6
15 formal acrylate 12 Tetrahydrofur- 1.8 15 furyl acrylate 13
Tetrahydro- 3.6 15 pyran-4-yl acrylate 14 Cyclohexyl- 2.8 15 methyl
acrylate 15 Tetrahydropyra- 3.6 15 nyl-2-methyl acrylate V1
Tripropylene 3.6 20 glycol mono- methyl ether acrylate V2
Dipropylene 2.4 30 glycol mono- methyl ether acrylate
II. Determining the Mechanical Properties of the Cured Coatings of
Examples 1 to 14 and Comparative Examples V1 and V2
[0052] 1. Coating Hardness
[0053] The coating hardness was characterized by determining the
pendulum attenuation in analogy to DIN 53157. To this end the
radation-curable compositions of the Examples and Comparative
Examples were applied with a wet film thickness of 100 .mu.m to
glass. The resulting sample was cured by being passed at a belt
speed of 10 m/min and at a distance of 10 cm twice in front of a
high-pressure mercury vapor lamp (120 W/cm). The pendulum
attenuation was then determined using a pendulum device in
accordance with DIN 53157 (Konig). The results are stated in
seconds and are summarized in Table 3.
[0054] 2. Flexibility
[0055] The flexibility of the coating was determined by measuring
the Erichsen indentation in analogy to DIN 53156. To this end, the
respective formulation was applied using a spiral-wound coating bar
in a wet film thickness of 50 .mu.m to a BONDER 132 metal panel.
Curing was carried out in the manner described above by exposure
with a high-pressure mercury vapor lamp (120 W/cm). The Erichsen
indentation was then measured by pressing a metal ball into the
uncoated side of the panel (DIN 53156). The results are summarized
in Table 3.
3 TABLE 3 Pendulum attenuation Erichsen indentation Example [sec]
[mm] 1 80 7.0 2 98 6.5 3 86 6.8 4 89 6.6 5 88 6.9 6 85 5.7 7 102
5.3 8 122 5.7 9 130 5.5 10 105 5.5 11 120 6.3 12 90 6.6 13 130 5.8
14 110 6.0 15 80 6.3 V1 21 7.0 V2 25 7.0
III.Determining the Weathering Stability of the Coatings of the
Invention
[0056] The test systems used were formulations of 70 parts by
weight of urethane acrylate from Example 2, 30 parts of reactive
diluent as per Table 4 and the photoinitiator Darocure.RTM. 1173
(Example 16, Comparative Example V3 and V4). The formulations were
then applied to a glass plate with a wet film thickness of 100
.mu.m using a box-type coating bar, the films were cured by UV
radiation in the manner described for the pendulum test, and then
the coatings were irradiated in a Heraeus Sun Test apparatus CPS+
with an output of 750 W/m.sup.2 at 37.degree. C. After various
periods the yellowing--as b values of the L*a*b system (determined
using a Minolta Remission Colorimeter), and the degree of gloss, in
accordance with DIN 67530 at 60.degree. geometry, were recorded.
The b values are summarized in Table 4 for different times. The
gloss values of all formulations were within the range from 170 to
178 and remain at approximately the same level throughout the
1000-hour exposure time.
4 TABLE 4 b values Example Reactive diluent 0 h 160 h 700 h 1000 h
V3 HDDA.sup.1) 0.45 0.7 0.7 0.82 16 TMPMFA.sup.2) 0.29 0.47 0.5
0.55 V4 LR8945.sup.3) 0.3 1.79 3.0 3.6 .sup.1)1,6-hexanediol
diacrylate .sup.2)trimethylolpropane monoformal acrylate
.sup.3)Laromer .RTM. LR8945 from BASF; polyether acrylate modified
with bisphenol A units
[0057] The increase in the b values corresponds to increasing
yellowing. The increase in yellowing is least pronounced for the
formulation of Example 16 according to the invention.
[0058] In addition, the thermal stability of the formulations of
Example 16 and of the Comparative Examples V3 and V4 were
determined by measuring the b value after thermal conditioning at
100.degree. C. for 24 hours. In parallel with this a formulation
was examined in which the HDDA from Example V3 had been replaced by
N-vinylcaprolactam (Comparative Example V5). For Example 15 and
Comparative Examples V3 and V4, no notable increase in the b value
was observed. In contrast, the b value for the sample from V5 shows
a dramatic increase, corresponding to marked yellowing under
thermal exposure.
* * * * *