U.S. patent application number 11/324559 was filed with the patent office on 2006-06-01 for photocuring of radiation-curable compositions under inert gas.
This patent application is currently assigned to BASF Akiengesellschaft. Invention is credited to Erich Beck, Oliver Deis, Peter Enenkel, Wolfgang Schrof.
Application Number | 20060115602 11/324559 |
Document ID | / |
Family ID | 7931041 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060115602 |
Kind Code |
A1 |
Beck; Erich ; et
al. |
June 1, 2006 |
Photocuring of radiation-curable compositions under inert gas
Abstract
A process is described for producing molding compounds and
coatings on substrates by curing radiation-curable compositions
under inert gas by exposure to light wherein said inert gas
comprises a gas heavier than air, and lateral escape of the inert
gas in the course of radiation curing is prevented by means of
appropriate apparatus or other measures.
Inventors: |
Beck; Erich; (Ladenburg,
DE) ; Deis; Oliver; (Rimbach, DE) ; Enenkel;
Peter; (Hessheim, DE) ; Schrof; Wolfgang;
(Neuleiningen, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
BASF Akiengesellschaft
Ludwigshafen
DE
|
Family ID: |
7931041 |
Appl. No.: |
11/324559 |
Filed: |
January 4, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10130599 |
May 21, 2002 |
|
|
|
PCT/EP00/11589 |
Nov 21, 2000 |
|
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11324559 |
Jan 4, 2006 |
|
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Current U.S.
Class: |
427/532 |
Current CPC
Class: |
B33Y 70/00 20141201;
F26B 2210/12 20130101; F26B 3/283 20130101; F26B 21/14 20130101;
B05D 3/067 20130101; B05D 3/0486 20130101 |
Class at
Publication: |
427/532 |
International
Class: |
B05D 3/00 20060101
B05D003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 1999 |
DE |
199 57 900.8 |
Claims
1-16. (canceled)
17. A process for coating a substrate with a radiation-curable
composition, comprising: coating the substrate with the
radiation-curable composition, introducing carbon dioxide gas into
a dip tank to force air upwardly out of the dip tank and form a
carbon dioxide-containing atmosphere in the dip tank, placing the
substrate coated with the radiation-curable composition in the
carbon dioxide gas-containing atmosphere in the dip tank, and
exposing the substrate in the dip tank to light to cure the
radiation-curable composition.
18. The process of claim 17, wherein the dip tank prevents lateral
escape of carbon dioxide gas.
19. The process of claim 17, wherein the carbon dioxide
gas-containing atmosphere surrounds the substrate at a distance of
up to 10 cm from the surface of the substrate and wherein the
carbon dioxide gas-containing atmosphere inside the dip tank
contains less than 15% by weight of oxygen gas based on the total
amount of gas.
20. The process as claimed in claim 17, wherein the carbon dioxide
gas-containing atmosphere in the dip tank comprises oxygen in an
amount of 1% by weight or less.
21. The process of claim 17, wherein the carbon dioxide
gas-containing atmosphere in the dip tank comprises oxygen in an
amount of 0.1% by weight or less.
22. The process of claim 17, wherein introducing carbon dioxide
into the dip tank includes: placing dry ice in the dip tank to
force air upwardly out of the dip tank, and evaporating the dry ice
to form the carbon dioxide gas-containing atmosphere in the dip
tank.
23. The process of claim 17, wherein the carbon dioxide gas is
introduced into the enclosed environment from gas bottles.
24. The process of claim 17, wherein the radiation-curable
composition comprises from 0.001 to 12 mol of radiation-curable
ethylenically unsaturated groups per 1,000 gm of one or more
radiation-curable compounds present in the radiation-curable
composition.
25. The process of claim 24, wherein at least 60 mol % of the
radiation-curable ethylenically unsaturated groups are (meth)
acrylic groups.
26. The process as claimed in claim 17, wherein the
radiation-curable composition comprises less than 10 parts by
weight of a photoinitiator per 100 parts by weight of the total
amount of the radiation-curable composition.
27. The process as claimed in claim 17, wherein the light has a
wavelength above 300 nm.
28. The process of claim 17, wherein the light is from one or more
selected from the group consisting of sunlight, a halogen lamp, an
incandescent lamp, a light emitting diode and a laser.
29. The process as claimed in claim 17, wherein the substrate is at
least one selected from the group consisting of a motor vehicle, a
road vehicle, a rail vehicle, an aircraft, a motor vehicle body and
a motor vehicle part.
30. The process as claimed in claim 17, wherein the substrate is
made of one or more selected from the group consisting of wood,
plastic, metal, a mineral material and ceramic.
31. The process as claimed in claim 17, wherein the substrate is at
least one of a composite material or a molding for
stereolithography.
32. The process as claimed in claim 17, wherein the substrate is
three-dimensional.
Description
[0001] The invention relates to a process for producing molding
compounds and coatings on substrates by curing radiation-curable
compositions under inert gas by exposure to light, wherein said
inert gas comprises a gas which is heavier than air, and lateral
escape of the inert gas in the course of radiation curing is
prevented by means of appropriate apparatus or other measures.
[0002] The radiation curing of free-radical polymerizable
compounds, e.g., (meth)acrylate compounds, may be accompanied by
severe oxygen inhibition of the polymerization or curing. This
inhibition results in incomplete curing at the surface and thus,
for example, in tacky coatings.
[0003] This oxygen inhibition effect may be lessened by using large
amounts of photoinitiator, by using coinitiators, such as amines,
by using high-dose high-energy UV radiation, with high-pressure
mercury lamps, for example, or by adding barrier-forming waxes.
[0004] It is also known to conduct radiation curing under an inert
gas, from, for example, EP-A-540 884 and from Joachim Jung, RadTech
Europe 99, Nov. 8 to 11, 1999, in Berlin (UV Applications in
Europe--Yesterday Today Tomorrow).
[0005] What is desired is a process of radiation curing in which
there is no need for high-energy UV light sources and the safety
measures they entail. At the same time, however, the process should
be extremely simple to implement.
[0006] Radiation-curable compositions may be processed without
water or organic solvents. The process of radiation curing is
therefore suitable for coatings which are implemented in small or
medium-sized workshops or in the domestic sphere. To date, however,
the complexity of the process and the equipment required,
especially the UV lamps, have prevented the use of radiation curing
within these segments.
[0007] It is an object of the invention to provide a simple process
of radiation curing which may be employed even in small workshops
or in the domestic sphere and which is generally suitable for
curing three-dimensionally coated articles.
[0008] We have found that this object is achieved by the process
defined at the outset.
[0009] Using the process of the invention it is possible to cure
coatings on planar surfaces (two-dimensional curing process) or
else coatings on three-dimensional moldings (three-dimensional
curing process) on all or a plurality of sides.
[0010] The process uses an inert gas heavier than air. The molar
weight of the gas is therefore greater than 28.8 g/mol
(corresponding to the molar weight of a gas mixture of 20% oxygen
and 80% nitrogen), preferably greater than 32 and, in particular,
greater than 35 g/mol. Suitable examples are noble gases such as
argon, hydrocarbons, and halogenated hydrocarbons. Carbon dioxide
is particularly preferred.
[0011] The carbon dioxide supply may be from pressurized
containers, filtered combustion gases, e.g., natural gas, or in the
form of dry ice. A dry ice supply is seen as advantageous,
especially for applications in the nonindustrial or small-scale
industrial segment, since dry ice may be transported and stored as
solid in simple, foam-insulated containers. The dry ice may be used
as it is; at the customary temperatures of use it is in gas
form.
[0012] The inert gas is heavier than air, and so air is forced
upward. It is necessary to prevent the lateral escape of the
gas.
[0013] A wide variety of apparatus or other measures may be
suitable for this purpose.
[0014] One possibility is to use one container as a dip tank. This
technique is particularly suitable for the three-dimensional
coating process.
[0015] The inert gas is introduced into the container and the air
is forced from it.
[0016] The container now contains an inert gas atmosphere into
which the substrate coated with the radiation-curable composition,
or molding, may be dipped. It is then possible to carry out
radiation curing, using sunlight or appropriately disposed lamps,
for example.
[0017] In the case of the radiation curing of coated areas,
especially floor areas, the area to be cured may be partitioned off
by means of appropriate devices, especially movable partitions, so
that the inert gas cannot escape during the period of
irradiation.
[0018] By means of the process it is also possible to carry out
coating and radiation curing of printable or printed substrates.
Examples of suitable substrates include paper, cardboard, films or
textiles. The radiation-curable coating in question may comprise
the printing ink or an overprint varnish. Radiation curing may take
place directly in the course of the printing process, e.g., in the
printing machine. Printing processes that may be mentioned include
offset, gravure, letterpress, flexographic, and pad printing
processes.
[0019] In the course of radiation curing, the amount of oxygen in
the inert gas atmosphere is preferably less than 15% by weight,
with particular preference less than 10% by weight, with very
particular preference less than 5% by weight, based on the total
amount of gas in the inert gas atmosphere; with the process of the
invention it is possible in particular and with ease to set oxygen
contents of less than 1%, even less than 0.1%, and in fact even
less than 0.01% by weight.
[0020] By inert gas atmosphere is meant the gas volume surrounding
the substrate at a distance of up to 10 cm from its surface.
[0021] Where dry ice is used as the inert gas, charging the dip
tanks--which may also be storage containers for dry ice--is simple.
The consumption of carbon dioxide is directly determinable from the
consumption of the solid dry ice. Dry ice evaporates directly at
-78.5.degree. C. to form gaseous carbon dioxide. As a result, in a
tank, atmospheric oxygen is displaced upward out of the tank with
little turbulence.
[0022] The residual oxygen may be measured using standard
commercial atmospheric oxygen meters. The tank may be covered in
order to minimize gas losses and also to counter any warming during
nonoperating periods. Owing to the oxygen-reduced atmosphere in the
dip tank and storage tank, and the associated risk of suffocation,
appropriate safety measures should be taken. In adjacent working
areas as well, sufficient ventilation and carbon dioxide
dissipation should be ensured.
[0023] The coated articles may be lowered into the dip tank for
exposure, individually using lifting and lowering apparatus or by
means of apparatus of the conveyor belt type in the case of mass
production coatings. In order to ensure that the article is flooded
as fully as possible, without entraining too much air into the
exposure zone, either slow lifting and lowering or the use of
upstream and downstream flooders is appropriate. The upstream and
downstream flooders are an extension of the inert gas tanks, in
order to separate air turbulence zones from the exposure zone. For
this purpose, starting from the exposure zone, the inert gas tank
may be extended both in terms of height and in terms of breadth on
both sides. The dimensions of the upstream flooders are dependent
primarily on the rate of immersion and emersion and on the geometry
of the article.
[0024] The duration of exposure depends on the desired degree of
cure of the coating or molding. The degree of cure may be
determined most simply from the detackification or from the
resistance to scratching with a fingernail, for example, or with
other articles such as pencil points, metal points or plastic
points. Likewise suitable are paint industry standard chemical
resistance tests, for example, toward solvents, inks, etc.
Particularly suitable without damaging the coated surfaces are
spectroscopic methods, especially Raman and infrared spectroscopy,
or measurements of the dielectric or acoustic properties, etc.
Radiation curing may take place by sunlight or by lamps which are
preferably arranged in the dip tank in such a way as to ensure the
desired curing of the coated substrates on all sides or a plurality
of sides.
[0025] For two-dimensional immovable substrates, e.g. floors or
articles fixed to the floor, it is possible to arrange simple
enclosures in order to prevent the dissipation of carbon dioxide.
Examples are the sealing of the door region in rooms, for example,
up to 40 cm in height from the floor, using, for example,
adhesively bonded films or erecting walls of wood, plastic,
stretched films or paper webs. The introduction of the carbon
dioxide gas may take place from gas bottles or in the form of dry
ice. It is also possible to hang-mount dry ice containers, from
which carbon dioxide is able to flow out onto the material to be
cured.
[0026] The radiation-curable composition comprises
radiation-curable compounds as binders. These are compounds
containing free-radically or cationically polymerizable and thus
radiation-curable ethylenically unsaturated groups. The
radiation-curable composition preferably contains from 0.001 to 12,
with particular preference from 0.1 to 8, with very particular
preference from 0.5 to 7 mol of radiation-curable ethylenically
unsaturated groups per 1000 g of radiation-curable compounds.
[0027] Examples of suitable radiation-curable compounds are
(meth)acrylic compounds, vinyl ethers, vinylamides, unsaturated
polyesters based, for example, on maleic acid or fumaric acid, with
or without styrene as reactive diluent, or maleimide/vinyl ether
systems.
[0028] Preference is given to (meth)acrylate compounds such as
polyester (meth)acrylates, polyether (meth)acrylates, urethane
(meth)acrylates, epoxy (meth)acrylates, silicone (meth)acrylates,
and acrylated polyacrylates.
[0029] Preferably, at least 40 mol %, with particular preference at
least 60 mol %, of the radiation-curable ethylenically unsaturated
groups are (meth)acrylic groups.
[0030] The radiation-curable compounds may further contain reactive
groups, e.g., melamine, isocyanate, epoxide, anhydride, alcohol,
carboxylic acid groups for additional heat curing, e.g., by
chemical reaction of alcohol, carboxylic acid, amine, epoxide,
anhydride, isocyanate, or melamine groups (dual cure).
[0031] The radiation-curable compounds may be present, for example,
as solutions, in an organic solvent or water, for example, as
aqueous dispersions, or as powders.
[0032] Preferably, the radiation-curable compounds and thus the
radiation-curable compositions as well are fluid at room
temperature. The radiation-curable compositions contain preferably
less than 20% by weight, in particular less than 30% by weight, of
organic solvents and/or water. They are preferably free from
solvent and free from water (100% solids).
[0033] As well as the radiation-curable compounds as binders, the
radiation-curable compositions may comprise further constituents.
Examples of suitable such constituents are pigments, leveling
agents, dyes, stabilizers, etc.
[0034] For curing with UV light, photoinitiators are generally
used.
[0035] Examples of suitable photoinitiators include benzophenone,
alkylbenzophenones, halomethylated benzophenones, Michler's ketone,
anthrone, and halogenated benzophenones. Benzoin and its
derivatives are also suitable. Likewise effective photoinitiators
are anthraquinone and many of its derivatives, examples being
.beta.-methylanthraquinone, tert-butylanthraquinone, and
anthraquinonecarboxylic esters, and--particularly
effective--photoinitiators containing an acylphosphine oxide group,
such as acylphosphine oxides or bisacylphosphine oxides, e.g.,
2,4,6-trimethylbenzoyldiphenylphosphine oxide (Lucirin.RTM.
TPO).
[0036] Where the radiation-curable compositions comprise
photoinitiators, these photoinitiators ought to have absorption
wavelengths in the range of the emitted light. Suitable
photoinitiators for visible light, which contains no UV components,
are in particular the abovementioned photoinitiators containing
acylphosphine oxide groups.
[0037] It is an advantage of the invention that the amount of
photoinitiators in the radiation-curable composition may be low or
that photoinitiators may be foregone entirely.
[0038] The radiation-curable compositions preferably contain less
than 10 parts by weight, in particular less than 4 parts by weight,
with particular preference less than 1.5 parts by weight, of
photoinitiator per 100 parts by weight of radiation-curable
compounds.
[0039] In particular, an amount of from 0 part by weight to 1.5
parts by weight, especially from 0.01 to 1 part by weight, of
photoinitiator is sufficient.
[0040] The radiation-curable composition may be applied to the
target substrate or brought into the appropriate shape by means of
customary techniques.
[0041] Radiation curing may then take place as soon as the
substrate is surrounded by the inert gas.
[0042] Radiation curing may be carried out with all lamps also used
to date for radiation curing. Radiation curing may be carried out
using electron beams, X-rays or gamma rays, UV radiation, or
visible light. It is an advantage of the process of the invention
that the radiation curing may be carried out using visible light
comprising little or no wavelengths below 300 nm.
[0043] In the process of the invention, therefore, radiation curing
may take place with sunlight or with lamps used as sunlight
substitutes. These lamps emit in the visible range above 400 nm and
comprise few or no UV light components below 300 nm.
[0044] In the process of the invention, in particular, the fraction
of radiation in the wavelength range below 300 nm is less than 20%,
preferably less than 10%, with particular preference less than 5%,
in particular less than 1 or 0.5%, or less than 0.1% of the
integral of the emitted intensity over the entire wavelength range
below 1000 nm.
[0045] The aforementioned radiation comprises the radiation which
is actually available for curing, i.e., when filters are used, the
radiation following passage through the filters.
[0046] Suitable lamps are those having a linear spectrum--that is,
lamps which emit only at certain wavelengths. Examples include
light emitting diodes and lasers.
[0047] Likewise suitable are lamps having a broadband
spectrum--that is, lamps where the light emitted is distributed
over a wavelength range. In this case the intensity maximum is
preferably in the visible range above 400 nm.
[0048] Examples that may be mentioned include incandescent lamps,
halogen lamps, xenon lamps. Mention may also be made of mercury
vapor lamps with filters to prevent or reduce radiation below 300
nm.
[0049] Likewise suitable are pulsed lamps, e.g., photographic
flashlamps, or high-performance flashlamps (from VISIT). A
particular advantage of the process is the capacity to use lamps
with a low energy consumption and low UV fraction, e.g., 500-watt
halogen lamps, as used for general lighting purposes. As a result
there is no need either for a high-voltage current supply unit (in
the case of mercury vapor lamps) or, possibly, for light protection
measures. Furthermore, with halogen lamps, even in air, there is no
risk posed by evolution of ozone, as with shortwave UV lamps. This
facilitates radiation curing using portable exposure units and
enables applications "in situ", i.e., independently of fixed
industrial curing installations.
[0050] For mobile use and for applications requiring a large number
of lamps to illuminate the substrate, particularly suitable sources
are lamps comprising lamp housings with reflector, possibly cooling
devices, radiation filters, and power supply connections, which
have a low weight of, for example, below 20 kg, preferably below 8
kg.
[0051] Particularly lightweight lamps, for example, are halogen
lamps, incandescent lamps, light emitting diodes, portable lasers,
photographic flashlamps, etc. A further feature of these lamps is
their particular ease of installation in container interiors or
container walls. There is also a reduction in the technical
complexity of power supply, especially in comparison with the
medium- and high-pressure mercury vapor lamps which have been the
industry standard to date. Preferred power sources for the lamps,
apart from mains power supply, comprise, in particular, standard
household alternating voltage, e.g., 220 V/50 Hz, or supply using
portable generators, batteries, accumulators, solar cells, etc.
[0052] The process of the invention is suitable for producing
coatings on substrates and for producing moldings.
[0053] Examples of suitable substrates include those of wood,
plastics, metal, mineral materials or ceramics.
[0054] Examples of moldings include composite materials, comprising
meshes or fiber materials impregnated with radiation-curable
composition, for example, or moldings for stereolithography.
[0055] A further advantage of the process is that the distances
between lamps and radiation-curable composition can be increased
relative to curing in air. Overall, it is possible to use lower
radiation doses, and one emitter unit may be used to cure
relatively large areas.
[0056] Consequently, in addition to customary applications of
radiation curing, the process also allows new applications in the
field of the curing of coatings and molding compounds of complex
three-dimensionally shaped articles, e.g., furniture, vehicle
bodies, in the construction of casings and instruments, for mobile
applications such as floor coating. Owing to the low level of
technical and material expenditure, the process is also suitable
for small and medium-sized workshops, homeworkers and the
do-it-yourself segment.
EXAMPLES
Example 1
[0057] A radiation-curable composition is prepared by mixing the
following constituents: TABLE-US-00001 35% by weight of Laromer
.RTM. LR 8987 (BASF Aktiengesellschaft), a urethane acrylate 20% by
weight of hexanediol diacrylate, 38.5% by weight of Laromer .RTM.
LR 8863, a polyether acrylate 3.5% by weight of Irgacure .RTM. 184
(Ciba Spezialitatenchemie), a photoinitiator 0.5% by weight of
Lucirin .RTM. TPO (BASF), a photoinitiator 2% by weight of Tinuvin
.RTM. 400 (Ciba Spezialitatenchemie), a UV absorber 1.5% by weight
of Tinuvin .RTM. 292, a UV absorber
[0058] This composition is used to coat (film thickness 50 .mu.m) a
pane of glass.
[0059] 500 g of dry ice are introduced into a container 60 cm deep
with a diameter of 40 cm. After about 60 minutes, the residual
oxygen content approximately 10 cm below the top edge of the
container is 3% by weight and at a depth of 45 cm is 0.01% by
weight. The pane of glass is inserted at the 45 cm level and
exposed for 2 minutes using a 500 watt halogen lamp at a distance
of 50 cm from the halogen lamp. The coating is high scratch
resistant and cannot be scratched under manual pressure and with
rubbing, either with a wooden spatula or with white typewriter
paper.
[0060] For comparison, exposure is carried out under the same
conditions but in air. The coating remained liquid. In comparison,
exposure was carried out twice on a conveyor belt at a belt speed
of 10 m/min under a 120 W/cm high-pressure mercury lamp (from IST)
at a distance of 15 cm from the lamp. The coating could not be
cured to a scratch resistant state.
Example 2
[0061] The radiation-curable composition was as in Example 1.
[0062] The radiation-curable composition was applied as clearcoat
to the housing of an exterior automobile mirror and cured in
accordance with the invention as described in Example 1. The
coating obtained was highly scratch resistant.
* * * * *