U.S. patent application number 11/626729 was filed with the patent office on 2007-05-24 for uv-curing anti-fingerprinting coatings.
Invention is credited to Holger Endres, Karsten Hackbarth, Matthias Koch, Kerstin Motzkat, Joerg Sander, Wolfgang Schneider.
Application Number | 20070116947 11/626729 |
Document ID | / |
Family ID | 7698506 |
Filed Date | 2007-05-24 |
United States Patent
Application |
20070116947 |
Kind Code |
A1 |
Hackbarth; Karsten ; et
al. |
May 24, 2007 |
UV-Curing Anti-Fingerprinting Coatings
Abstract
Process for the production on metal or plastic surfaces of thin,
hydrolysis-resistant, scratch-resistant and stain-resistant
coatings, wherein the coating material can be applied directly to
the cleaned metal surface and subsequently cross-linked by
high-energy radiation, in particular UV radiation. The substrates
can be coated in the form of strip and only subsequently brought
into the required external shape. Coated substrates such as these
are no longer susceptible to staining by food, cleaning agents or
fingerprints and can also be rendered antibacterial. Objects coated
in this manner are thus suitable for use in architecture, for
interior fittings of buildings, in furniture-making as well as for
ornamental applications, and in particular in households, in
sanitary applications, in hospitals and in the food-processing and
pharmaceutical industries.
Inventors: |
Hackbarth; Karsten;
(Duesseldorf, DE) ; Koch; Matthias; (Duesseldorf,
DE) ; Motzkat; Kerstin; (Oberhausen, DE) ;
Sander; Joerg; (Velbert, DE) ; Endres; Holger;
(Neuss, DE) ; Schneider; Wolfgang; (Langenfeld,
DE) |
Correspondence
Address: |
HENKEL CORPORATION
THE TRIAD, SUITE 200
2200 RENAISSANCE BLVD.
GULPH MILLS
PA
19406
US
|
Family ID: |
7698506 |
Appl. No.: |
11/626729 |
Filed: |
January 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10796681 |
Mar 9, 2004 |
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11626729 |
Jan 24, 2007 |
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PCT/EP02/09967 |
Sep 6, 2002 |
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10796681 |
Mar 9, 2004 |
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Current U.S.
Class: |
428/336 ;
427/299; 427/487; 428/339; 428/458; 428/461 |
Current CPC
Class: |
C09D 167/07 20130101;
C08F 290/061 20130101; Y10T 428/31681 20150401; C08F 290/062
20130101; C08F 290/067 20130101; Y10T 428/269 20150115; Y10T
428/31692 20150401; C08F 290/064 20130101; Y10T 428/265 20150115;
C09D 175/16 20130101; C09D 163/10 20130101 |
Class at
Publication: |
428/336 ;
427/487; 427/299; 428/339; 428/458; 428/461 |
International
Class: |
G11B 5/64 20060101
G11B005/64; C08F 2/46 20060101 C08F002/46; B05D 3/00 20060101
B05D003/00; B32B 15/08 20060101 B32B015/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2001 |
DE |
101 44 531.8 |
Claims
1. A process for applying a fingerprint resistant coating on a
metal surface, said process comprising: applying to a metal surface
a layer of coating material, comprising: a. 40 to 90 wt. % of at
least one oligomeric substance selected from the group consisting
of epoxy (meth)acrylates, polyester (meth)acrylates, polyether
(meth)acrylates, and polyurethane (meth)acrylates, wherein said
oligomeric substance is linear or branched and contains at least
two unsaturated double bonds; b. 5 to 60 wt. % of at least one low
molecular weight (meth)acrylate selected from the group consisting
of monofunctional, difunctional, trifunctional and polyfunctional
(meth)acrylate compounds; c. 0.1 to 20 wt. % of at least one
(meth)acrylate compound containing one or more acidic groups; and
d. 0.1 to 20 wt. % of at least one auxiliary substance selected
from the group consisting of adhesion promoters different from c,
flow-control agents, defoaming agents, light stabilizers, dyes,
pigments, biocides, fillers and photoinitiators; wherein the
coating material has a viscosity of less than 1000 mPas within a
temperature range of 0 to 90.degree. C.; and crosslinking the layer
of coating material by means of high-energy radiation such that a
fingerprint resistant coating is formed.
2. The process according to claim 1 wherein cross-linking of said
layer is by means of high-energy radiation selected from UV
radiation, electron radiation or gamma-radiation.
3. The process according to claim 2 wherein the high-energy
radiation used is UV radiation.
4. The process according to claim 2 wherein said layer of coating
material is from 0.5 to 20 .mu.m in thickness.
5. The process according to claim 2 wherein said layer of coating
material is from 1 to 10 .mu.m in thickness.
6. The process according to claim 2 wherein no pretreatment or
primer is applied to the metal surface prior to said layer of
coating material.
7. The process according to claim 2 wherein the high-energy
radiation used has a wavelength of 200 to 450 nm.
8. The process according to claim 2 wherein the coating material
after cross-linking is transparent.
9. The process according to claim 2 wherein said metal surface is
in the form of a strip and is coated by roller application.
10. The process according to claim 2 wherein during the
cross-linking step the metal surface having the layer applied
thereon is in a low-oxygen or oxygen-free atmosphere.
11. The process according to claim 2 wherein after applying said
layer of coating material and before cross-linking said layer a
high-energy radiation permeable film is applied to said layer.
12. The process according to claim 11 wherein the film is comprised
of at least one polymer selected from the group consisting of
polyethylene, polypropylene, and PET and is separable from the
layer after cross-linking.
13. The process according to claim 2 additionally comprising the
step of forming the metal surface having the cross-linked layer
thereon.
14. The process according to claim 2 wherein said metal surface is
cleaned prior to applying said layer of coating material but does
not have a primer or pretreatment layer applied to the metal
surface.
15. A process for applying a fingerprint resistant coating on a
metal surface, said process comprising: optionally cleaning and
drying a metal surface; applying to the metal surface a layer of
coating material, comprising: a. 45 to 85 wt. % of at least one
oligomeric substance having at least two unsaturated double bonds
selected from the group consisting of aromatic epoxy
(meth)acrylates, and optionally, polyester (meth)acrylates,
polyether (meth)acrylates, and polyurethane (meth)acrylates,
wherein said oligomeric substance is linear or branched; b. 10 to
60 wt. % of at least one (meth)acrylate selected from the group
consisting of monofunctional, difunctional, trifunctional and
polyfunctional (meth)acrylate compounds; c. 0.5 to 10 wt. % of at
least one (meth)acrylate compound containing one or more phosphoric
or carboxyl acidic functional groups; d. 0.5 to 15 wt. % of at
least one radical photoinitiator; and e. up to 20 wt. % of at least
one silane selected from the group consisting of dialkoxysilanes
and trialkoxysilanes wherein said at least one silane contains an
amine functional group; wherein components a. through e. are
selected and homogenized together such that the coating material
has a viscosity of less than 300 mPas within a temperature range of
0 to 90.degree. C. in the absence of solvent; and crosslinking the
layer of coating material by means of high-energy radiation such
that a fingerprint resistant coating is formed.
16. An object comprising a metal substrate having a metal surface
and a layer of a cross-linked coating material deposited on the
metal surface by the process of claim 1, wherein said metal
substrate is a sheet or strip.
17. An object having a metal surface and a layer of a cross-linked
coating material up to 5 .mu.m in thickness deposited on the metal
surface by the process of claim 1.
18. The object according to claim 17 wherein said metal surface is
comprised of a material selected from the group consisting of
ferrous materials, steel, alloyed steel, light metals, non-ferrous
metals and precious metals.
19. The object according to claim 18 additionally comprising a film
comprising at least one polymer selected from the group consisting
of polyethylene, polypropylene, and PET on said layer of
cross-linked coating material.
20. A process for applying a fingerprint resistant coating on a
metal surface, said process comprising: optionally cleaning and
drying a metal surface; applying to the metal surface a layer of
coating material, comprising: a. 45 to 85 wt. % of at least one
oligomeric substance having at least two unsaturated double bonds
selected from the group consisting of epoxy (meth)acrylates,
polyester (meth)acrylates, polyether (meth)acrylates, and
polyurethane (meth)acrylates, wherein said oligomeric substance is
linear or branched; b. 10 to 60 wt. % of at least one
(meth)acrylate selected from the group consisting of
monofunctional, difunctional, trifunctional and polyfunctional
(meth)acrylate compounds; c. 0.5 to 10 wt. % of at least one
(meth)acrylate compound containing one or more phosphoric or
carboxyl acidic functional groups; d. 0.5 to 15 wt. % of at least
one radical photoinitiator; and e. up to 20 wt. % of at least one
silane selected from the group consisting of dialkoxysilanes and
trialkoxysilanes wherein said at least one silane contains at least
one functional group other than alkoxy groups; wherein 2.0 to 20
wt. %, based upon total coating material, of the monofunctional,
difunctional, trifunctional and polyfunctional (meth)acrylate
compounds are linear or branched; and crosslinking the layer of
coating material by means of UV radiation such that a formable,
fingerprint resistant coating is formed.
Description
CROSS-REFERENCE
[0001] This application is a divisional of U.S. application Ser.
No. 10/796,681, filed 9 Mar., 2004, which is a continuation under
35 USC Sections 365(c) and 120 of International Application No.
PCT/EP02/09967, filed 6 Sep. 2002 and published 20 Mar. 2003 as WO
03/022945, which claims priority from German Application No.
10144531.8, filed 11 Sep. 2001, each of which is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for producing
stain-resistant function coatings for metal surfaces, in particular
aluminum or high-grade steel surfaces, as well as suitable coating
materials for these.
DISCUSSION OF THE RELATED ART
[0003] A multitude of appliances, equipment and machines made of
metal, in particular high-grade steel or aluminum, are used in
households, in sanitary applications, in hospitals as well as in
the food-processing and pharmaceutical industries. Here, owing to
its high resistance to corrosion, e.g. high-grade steel is
preferably used. This is frequently used with a polished or brushed
surface and without additional coatings. Furthermore, a multitude
of metallic parts having very different compositions are also used
in architecture, for interior fittings of buildings, in
furniture-making as well as for ornamental applications. In these
cases, too, the surface of the metal is frequently polished,
brushed or otherwise provided with surface patterns and is used
without the application of further coatings.
[0004] In this form, the metal surface is highly susceptible to
soiling by dust, food or cleaning agents, or marking by
fingerprints. A number of methods of treating the surfaces of
metals in order to improve the scratch resistance of the surface or
to avoid soiling have already been proposed. These involve coating
processes using solvent-based and aqueous systems, for example,
aqueous electrophoretically precipitable dip coatings, or powder
coatings. These coatings are intended to improve the soiling
behavior and the scratch resistance of the surface. Disadvantages
of the processes are, for example, the curing conditions, such as
time, temperature, as well as the consequent plant dimensions.
Moreover, it is frequently impossible to form the objects without
destroying the surface coating.
[0005] DE 199 57 325 and DE 199 52 323 describe coating materials
for metals or plastics; there the coating materials are
heat-curable and based on aqueous sols consisting of organosilicon
compounds. EP 1 036 829 deals with UV-cross-linkable coating
materials for metals and conductive plastics, but describes only
aqueous systems, which are applied to electrically conducting
substrates by means of electrophoretic coating and are subsequently
first of all dried at elevated temperature, then post-cured under
UV light.
[0006] JP-A-07/171496 and JP-A-04/150976 (1992) describe
heat-curable coatings on high-grade steel which are produced from
polyester resins and silicate resin or melamine resin. JP 10/228446
and EP 0 789 065 describe special UV-cross-linking coating systems
substantially for coating wood, which are applied in layers of
above 20 or 30 .mu.m.
[0007] Although, therefore, there exists an extensive prior art
concerning UV-cross-linking coating materials, the problem of
coating with thin layer thicknesses in order to avoid soiling of
metal or even of plastics substrates has not yet been solved. In
this connection, the coated surface should have a good stain
resistance and be scratch resistant; in addition, the natural
appearance in particular of brushed or otherwise structured metal
surfaces should be preserved. No observations about these
requirements are made in prior art. Furthermore, an energy-saving,
rapid and environmentally mild coating process is required, in
order to be able to coat even large surfaces economically. A
further requirement is that it should be possible to form the
coated objects without impairing the coating. The object,
therefore, was to provide for these purposes a solvent-free, thin
coating system having a high scratch resistance and chemical
resistance to alkaline and acidic cleaning agents, such as are used
in households and in commerce or in the food-processing
industry.
BRIEF SUMMARY OF THE INVENTION
[0008] According to the invention, this object is achieved by the
provision of a solvent-free liquid coating material which is
cross-linked by means of high-energy radiation and, within a
temperature range of 0 to 90.degree. C., preferably 15 to
70.degree. C., has a viscosity of less than 1000 mPas, containing
[0009] a) 40 to 90 wt. % of at least one oligomeric, linear or
branched epoxy (meth)acrylate, polyester (meth)acrylate, polyether
(meth)acrylate and/or urethane (meth)acrylate, [0010] b) 5 to 60
wt. %, preferably 10 to 60 wt. %, of at least one monofunctional
liquid (meth)acrylate or di-, tri- or poly(meth)acrylate compound,
and [0011] c) 0.1 to 20 wt. % of methacrylate compounds containing
acidic groups, [0012] d) optionally 0 to 30 wt. % of a di- or
trialkoxysilane containing further functional groups, [0013] e) 0.1
to 20 wt. % of auxiliary substances used in coating technology,
such as adhesion promoters, flow-control agents, defoaming agents
and/or light stabilizers as well as photoinitiators.
[0014] The coating material according to the invention is used
preferably as coating material for metallic surfaces having thin
coatings which are resistant to hydrolysis and to cleaning agents
and are scratch resistant. The invention also provides the use of
the coating material according to the invention, where the coating
material is rendered antibacterial.
[0015] The invention also provides a process for coating metallic
surfaces, wherein the substrate is optionally first of all cleaned
and degreased, the coating material according to the invention is
then applied in a layer thickness of 0.5 to 20 .mu.m and finally
the coating is cross-linked by means of high-energy radiation. The
invention further provides a process for coating those surfaces
wherein, prior to the cross-linking step, the coated surface is
provided with a removable protective coating film.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE INVENTION
[0016] The process according to the invention and the coating
material according to the invention are particularly suitable for
use on surfaces consisting of ferrous materials, steel and alloyed
steel, light metals such as aluminum, magnesium, titanium,
non-ferrous metals such as copper, zinc, tin, or precious metals
such as gold, silver or alloys thereof. This surface may be ground,
brushed, polished, electrochemically treated or electrolytically
coated, for example, cadmium-plated, chromium-plated or
nickel-plated. Metallized plastics surfaces are also suitable. The
substrate may have any shape, but is preferably in the form of
sheets, strips or rolls.
[0017] The coating materials according to the invention contain
polymerizable oligomers containing unsaturated double bonds such
as, for example, polyester oligomers or polyether oligomers having
lateral or terminal (meth)acrylic groups, or preferably
(meth)acrylate functional aliphatic, cycloaliphatic and/or aromatic
epoxide compounds or polyurethane oligomers having reactive
(meth)acrylate groups. These oligomers are to have at least two
functional unsaturated double bonds and in general have a molecular
weight of between 500 and 15000. They are obtainable commercially.
The quantity is 40 to 90 wt. %, in particular 45 to 85 wt. %, and
mixtures of different oligomers are also possible.
[0018] The coating material is also to contain at least one mono-,
di-, tri- or polyfunctional unsaturated low-molecular
(meth)acrylate, with separate compounds or mixtures possibly being
present. Examples of such compounds are: optionally alkoxylated
alkanediol (meth)acrylates or alkanetriol (meth)acrylates, such as
1,3-butylene glycol di(meth)acrylate, 1,4-butanediol
di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trialkylene
glycol di(meth)acrylate, polyalkylene glycol di(meth)acrylate,
tetraalkylene glycol di(meth)acrylate, neopentyl glycol
di(meth)acrylate, glycerol alkoxytri(meth)acrylate, alkoxylated
neopentyl glycol di(meth)acrylate; (meth)acrylic epoxide compounds,
such as bisphenol A epoxide di(meth)acrylate; polyhydroxy
(meth)acrylates, such as pentaerythritol tri(meth)acrylate,
trimethylolpropane tri(meth)acrylate, trisalkoxy-trimethylolpropane
tri(meth)acrylate, di-trimethylolpropane tetra(meth)acrylate,
pentaerythritol tetra(meth)acrylate, tris(2-hydroxyalkyl)
isocyanurate tri(meth)acrylate, dipentaerythritol
tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate,
dipentaerythritol hexa(meth)acrylate, with alkylene denoting
ethylene, propylene or butylene and alkoxy denoting ethoxy, 1,2-or
1,3-propoxy or 1,4-butoxy.
[0019] The following (meth)acrylates are examples of monofunctional
acrylate compounds which can be used: linear, branched or cyclic
alkyl (meth)acrylates, such as n-/isoalkyl (meth)acrylate,
cyclohexyl (meth)acrylate,
[0020] 4-tert.-butyl cyclohexyl (meth)acrylate,
dihydrocyclopentadienyl (meth)acrylate, tetrahydrofurfuryl (meth)
acrylate, isobornyl (meth)acrylate, allyl (meth)acrylate,
mono(meth)acryloyl alkyl phthalate, succinate or maleate;
alkanediol mono(meth)acrylates, such as hydroxypropyl
(meth)acrylate, polyalkylene glycol (meth)acrylate,
monoalkoxytrialkylene glycol (meth)acrylate, 2,3-epoxypropyl
(meth)acrylate; aromatic (meth)acrylates, such as nonylphenol
(meth)acrylate,2-phenoxyalkyl (meth)acrylate; acrylamides, such as
N,N-dialkyl (meth)acrylamide, N,N-dialkylaminoalkyl
(meth)acrylamide. A proportion of vinyl ethers may also be used,
for example, vinyl ethyl ether, vinyl propyl ether, vinyl isobutyl
ether, vinyl dodecyl ether, butanediol-1,4-divinyl ether,
diethylene glycol divinyl ether, hydroxybutyl vinyl ether. The
monomeric acrylate compounds may be present separately or as a
mixture, the total quantity amounting to between 5 and 60 wt. %, in
particular between 15 and 50 wt. %.
[0021] The coating materials may also contain di- or
trialkoxysilanes having additional organofunctional groups.
Examples of these are aminopropyltrialkoxysilane,
bis(trialkoxysilylpropyl)amine, hydroxyethyl-trialkoxysilane,
carboxypropyltrialkoxysilane, vinyltrialkoxysilane, with alkoxy in
each case denoting methoxy, ethoxy, propoxy or butoxy. The quantity
is to be preferably between 0 and 15 wt. %.
[0022] Preferably, the coating materials are to contain
methacrylate compounds which have acidic groups and contain one,
two or more (meth)acrylic groups and in addition acidic functional
groups. The quantity of this component is to be between 0.1 and 20
wt. %, preferably between 0.5 and 10 wt. %. Examples of such acidic
functional groups are carboxyl groups, phosphoric or phosphonic
groups, sulfo groups and derivatives thereof, for example, esters.
Phosphoric groups are particularly preferred.
[0023] The known, preferably radical, initiators can be used as
photoinitiators, such as, for example,
2-benzyldimethylamino-1-(4-morpholinophenyl)butanone-1, benzil
dimethylketal or dimethoxyphenylacetophenone, .alpha.-hydroxybenzyl
phenyl ketone, 1-hydroxy-l-methylethyl phenyl ketone,
oligo-2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone,
benzophenone, methylorthobenzoyl benzoate, methyl benzoyl formate,
2,2-diethoxyacetophenone, 2,2-di-sec.-butoxyacetophenone,
p-phenylbenzophenone, 2-isopropylthioxanthone,
2-methylanthraquinone, 2-ethylanthraquinone, 2-chloroanthraquinone,
1,2-benzanthraquinone, benzil, benzoin, benzoin methyl ether,
benzoin isopropyl ether, .alpha.-phenylbenzoin, thioxanthone,
diethylthioxanthone, 1,5-acetonaphthalene, 1-hydroxycyclohexyl
phenyl ketone, ethyl p-dimethylaminobenzoate. These may be used
separately or as a mixture or combined with other radical
initiators of the peroxide type or with amine accelerators.
[0024] Besides the above-mentioned binders, the coating material
according to the invention contains small quantities of other
additives which have a beneficial influence on, for example, the
flow properties, film formation, adhesion or resistance of the
coating material. Examples of these are flow-control agents, such
as fluorinated polysilicone glycols, silicone glycols, polyether
polysiloxane copolymers. The known agents based on sterically
hindered amino compounds can be used as light stabilizers.
[0025] The coating material may also contain dyes, optical
brighteners and/or pigments as additives. Dyes are those based on
organic dyes, which are soluble in the coating material. These form
colored transparent coatings after the film has cured, and together
with the substrate surface can produce special visual effects.
Optical brighteners are compounds of the type which absorb UV
radiation and reradiate it in visible light; they may, for example,
be selected from among the triazine derivatives. By pigments are
meant organic or inorganic, colored or uncolored pigment
preparations, such as iron oxide pigments, titanium dioxide
pigments, carbon black, quinacridone or phthalocyanine pigments.
These have to be homogeneously distributed in the coating material.
In this connection, the particle size has to be appreciably less
than the intended layer thickness, preferably less than 1 .mu.m. It
may be advantageous to disperse these components in portions of the
liquid acrylate compounds prior to addition to the coating
material.
[0026] Micronised fillers such as, for example, silica, aluminum
oxide, titanium dioxide or barium sulfate, may also be used. These
are white, colorless or opaque/transparent and are used in finely
dispersed form. Depending on quantity and type, they can influence
the surface hardness, structure and scratch resistance of the
coating. The quantity of auxiliary substances is to be between 0.1
and 20 wt. %, preferably 0.5 to 15 wt. %.
[0027] Moreover, in a preferred embodiment the coating material may
contain antibacterial or biocidal compounds. These are, for
example, organic substances, such as bioguanidines, substituted
benzalkonium halides, alkyl polyvinylpyridines, betaine, or
inorganic compounds, such as silver salts or finely divided silver
particles within the particle-size range of a few nm. The quantity
is to be 0.1 to 5 wt. % and depends on the activity of the
substance used. These compounds are incorporated into the coating
material and are not destroyed during the cross-linking reaction.
They result in surfaces having long-term antibacterial action.
[0028] The components of the coating material according to the
invention can be mixed together by means of known methods. Here, it
may be useful to dissolve or, for example, in the case of pigments,
to disperse solid components in components of low viscosity. To
ensure stability in storage, in the case of particularly reactive
components it may be beneficial to premix these in components of
low viscosity prior to addition to the coating material and limit a
possible reaction.
[0029] The process according to the invention can be adapted for
the objects to be coated in the process. Depending on the condition
of its processing, the substrate is subjected to a cleaning step,
which can be carried out by dipping, spraying, high-pressure or
injection spraying or with the assistance of ultrasound or
electrolysis. In the course of this, dust particles, oxide layers,
adhering residues or fatty/oily substances are removed from the
production process. The known, preferably aqueous, cleaning agents
can be used for the cleaning process. After the cleaning process,
the surface is rinsed with water, dried and then immediately
further processed. Preferably, no further pretreatment is carried
out prior to the coating with the coating material according to the
invention; in particular, no primer is applied.
[0030] The substrate can be covered with the coating material by
means of the known methods of application. If formed or profiled
parts are to be coated, mainly the spraying systems commonly used
in coating technology, such as, for example, airless, air-assisted
or electrostatically assisted spraying processes, are suitable, or
even manual application by brush. Particularly preferably, the
coating material is applied to a level surface of a workpiece or of
a metal strip by flooding/squeezing off, spraying/squeezing off, or
by suitable squeegee or roller applications. Here, the viscosity of
the coating material during the application is to be below 1000
mPas, preferably below 300 mPas (measured in a cone/plate
viscometer).
[0031] The layer thickness of the coating material is generally 0.5
to 20 .mu.m, in particular 1 to 10 .mu.m, particularly preferably
up to 5 .mu.m.
[0032] The coating material is generally applied at temperatures of
between 0.degree. C. and 90.degree. C., preferably 15.degree. C.
and 70.degree. C. The coating is then cross-linked by high-energy
radiation such as, for example, UV radiation, electron radiation or
.UPSILON.-radiation. The electron radiation should have energy
values of between 150 and 350 keV. Preferably, cross-linking is
effected by UV radiation, in particular having a wavelength of 150
to 800 nm, particularly preferably of between 200 and 450 nm.
Suitable radiation sources are known to the person skilled in the
art. The intensity of radiation and the duration of the radiation
depend on the processing conditions, for example, distance of the
radiation source or relative movement between source and substrate.
The duration, however, is generally below 60 seconds, preferably
between 0.001 and 30 seconds. The respective variables for the
equipment can be determined by the person skilled in the art by
simple adjustment.
[0033] In a particular embodiment of the process, the oxygen
content may be decreased in the zone above the substrate to be
cross-linked. Here, it is to be in particular below 3000 ppm,
preferably below 1000 ppm. This can be effected, for example, by
partial or complete exchange of the ambient air present in the
cross-linking zone for inert gases, for example, argon, nitrogen,
CO.sub.2 or mixtures of these. An advantage of this embodiment of
the process is that the required concentration of photoinitiator in
the coating material can be decreased.
[0034] Another embodiment of the invention includes the additional
step wherein, after the application of the coating material, a film
which is permeable to the high-energy radiation used is first of
all applied to the substrate. It is possible to apply such a film
to three-dimensional substrates, but it is preferred that the
substrate be a sheet or strip. The application is carried out
preferably by a mechanical method; for example, the tear-resistant
film can be withdrawn from a delivery roll and applied, free from
voids, to the substrate surface by means of a roller. After this
processing step, the coating material under the film is
cross-linked by radiation. An advantage of this process is that the
curing takes place underneath the film under inert conditions, i.e.
in particular with the exclusion of oxygen.
[0035] The film consists, for example, of polyethylene,
polypropylene, PET or mixtures of these. It is colored or,
preferably, transparent. The film must not react with the coating
material. It is tear-resistant, so that in a subsequent processing
step it can be removed from the substrate surface by drawing off.
This can also be done at the premises of the end-user, so that the
film can serve as protection for the object during further
processing and/or transport.
[0036] The use of the coating material according to the invention
results in coated substrates, in particular of the metallic type,
having a thin surface coating. At the same time, special visual
effects can be achieved such as, for example, metallic lustre,
dulling, structures or colorations. Preferred uses of the objects
coated according to the invention are metal sheets, metal parts or
profiled metals used in architecture, for interior fittings of
buildings or in furniture-making, as well as metallic ornaments. In
particular, the metallic workpieces coated according to the
invention can be used in the manufacture of machines, articles or
equipment for households, sanitary applications, hospitals as well
as for the food-processing or pharmaceutical industries. For the
last-named fields, mainly high-grade steel is used.
[0037] The coatings according to the invention exhibit good
stability and resistance to soiling by a multitude of agents of the
type found, for example, in households or in the food industry,
such as black tea, black ink, condensed milk, fruit juices,
vinegar, mustard, ketchup, mayonnaise, onions, sugar and caramel.
The fingerprints which are left on uncoated metal surfaces do not
leave any permanent traces on metal coated according to the
invention, and can be easily removed. In particular, at
temperatures of up to 60.degree. C. the coatings are also resistant
to acidic and alkaline cleaning agents such as, for example,
rinsing agents, so-called "steel gloss" or all-purpose cleaning
agents. At the same time, the visual appearance of the surface is
completely preserved.
[0038] The invention is explained in more detail by means of the
following Examples, but the selection of the Examples does not
constitute a limitation to the scope of the invention. Unless
otherwise specified, all quantitative data in the following
Examples are per cent by weight or parts by weight, based on the
total composition.
EXAMPLES
[0039] In the following coatings according to the present
invention, brushed sheets of high-grade steel were used for
Examples 1 to 9. Prior to being coated, all substrates were
degreased by means of an aqueous, slightly alkaline cleaning agent
and then dried. The components of the coating material according to
the invention were homogenised by intensive mixing in high-speed
stirrers. The coating material was applied in a layer weight
of<5 g/m.sup.2 by means of a roll coater or coating knife and
cured in a standard atmosphere by means of UV radiation (emitter
type: Fusion VPS/1 600, H-emitter, 240 W/cm, 100% performance) in a
UV unit with a conveyor belt speed of 20 m/min.
[0040] The individual Examples and results are shown in Tables 1
and 2 below (quantities in parts by weight). TABLE-US-00001 TABLE 1
Example/RawMaterial 1 2 3 4 5 6 7 8 9 1 Aliphatic epoxy acrylate
61.9 -- -- -- -- -- -- -- -- 2 Aliphatic hexa-functional -- 56.9
56.9 56.9 -- 34.0 56.9 31.5 31.6 urethane acrylate Mw 1000 3
Aromatic epoxy -- -- -- -- 80.8 37.0 -- 34.3 34.5 diacrylate Mw 460
4 Isobornyl acrylate 30.6 35.1 35.1 35.1 -- 21.1 35.1 19.4 19.5 5
Neopentyl glycol propoxylate 20.0 20.0 -- -- 10.0 2.1 -- 2.0 2.0
diacrylate 6 Vinyltrimethoxy- -- -- 5.0 15.0 -- -- 5.0 -- -- silane
7 Bis(gamma-trimethoxysilylpropyl) 10.0 10.0 -- -- 4.2 1.0 -- 0.9
0.8 amine 8 Acid triacrylate 2.5 3.0 3.0 3.0 -- 1.8 3.0 1.7 1.7
(acid value 150) 9 Phosphoric acid acrylate (acid -- -- -- 3.0 --
-- 2.8 2.8 value 300) 10 Photoinitiator 5.0 5.0 5.0 5.0 5.0 3.0 4.5
4.6 4.7 11 Commercial biocide -- -- -- -- -- -- 0.5 -- -- 12
Hydrophobic silica -- -- -- -- -- -- -- 2.8 -- 13 Nanoparticulate
Al.sub.2O.sub.3 2.4 Photoinitiator is in the form of a 1.5:1
mixture of 1-hydroxy-1-methylethyl phenyl ketone and
1-hydroxycyclohexyl phenyl ketone.
Methods of measurement: [0041] 1. Fingerprint: a fingerprint was
made on the coated metal sheet and assessed visually. It was
optionally wiped off with a soft, dry cloth. [0042] 2. Cross cut in
accordance with DIN 53151: cross cuts were made using a cross-hatch
cutter (Erichsen Model 295) and glued over with an adhesive tape,
which was then torn off and the cuts assessed. The gluing and
tearing off were again carried out similarly after the cut had been
exposed to steam. The cross cut test results are reported on a
scale of from 0 (no additional damage except the cuts) to 5 (large
sections of the coating removed from the surface). [0043] 3.
Soiling: a 5 cm.sup.2 area of the surface of the coated metal sheet
was covered with the test agents (black tea, lemon juice, mustard,
ketchup, mayonnaise) and stored for 1 hour at 6.degree. C. The
metal sheet was then rinsed with water and dried with a soft cloth.
[0044] 4. Solvent resistance: a few drops of solvent were applied
to the coated metal sheet and, after about 5 seconds, removed with
a soft cloth. The swelling and dissolving behavior of the coating
were assessed. [0045] 5. Steam test: The metal sheet bent by
90.degree. was positioned at a small distance above a vessel filled
with boiling water and there exposed to steam for 2 hours.
[0046] The results of the examinations of the surface quality and
of the resistance of the coatings according to the invention are
summarized in Table 2 below. The surface qualities and the scratch
resistance are good; the sensitivity to fingerprints is likewise
good in all the coatings according to the invention.
[0047] In the following tables, a "+" signifies that a positive or
favorable result was obtained while "0" means that an intermediate
(medium) result was obtained. A negative or unfavorable result
(none of which were obtained in the testing reported herein) would
be signified by a "-" sign. TABLE-US-00002 TABLE 2 Resistance to
Surface quality Mild Strong Finger- Scratch cleaning cleaning
Example Prints.sup.1 Resistance.sup.6 Crosscut.sup.2 Foods.sup.3
agents.sup.3 agents.sup.7 Slovent.sup.4 Steam.sup.5 1 + + 0(0) 0 0
+ not + determined 2 0 + 0(0) + + + not + determined 3 + + 0(0) + +
+ not 0 determined 4 + + 0(0) + + 0 + 0 5 + + 0(0) + + + + + 6 + +
0(1) + + + + + 7 + + 0(0) + + + + 0 8 + + 0(0) + + + + + 9 + + 0(0)
+ + + + + .sup.1Visual assessment of fingerprints .sup.2Marking in
accordance with DIN 53151; results after exposure to steam are
shown in brackets. .sup.3Foods: mustard, tea, mayonnaise, ketchup,
lemon juice, et cetera; mild cleaning agents: all-purpose cleaning
agents, rinsing agents, et cetera .sup.4The tests were carried out
using acetone, naphtha and ethanol. .sup.5Sample metal sheets bent
by 90.degree. were treated with steam for 2 h and assessed
visually. .sup.6Determined using a hardness test rod 318, Erichsen
.sup.7Cleaning agents: oven cleaner, Ceran cleaner etc.
Examples 10-12
[0048] Additional substrates were coated and tested using the
coating material from Example 9: TABLE-US-00003 Substrate Layer
Cleaning Finger- Example (brushed) thickness Appearance agent print
10 brass 5 .mu.m in order + + (MS 39) 11 AlMg1 5 .mu.m in order + +
12 copper 5 .mu.m in order 0 +
* * * * *