HK1075224B - Method and device for hardening a coating - Google Patents
Method and device for hardening a coating Download PDFInfo
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- HK1075224B HK1075224B HK05107547.8A HK05107547A HK1075224B HK 1075224 B HK1075224 B HK 1075224B HK 05107547 A HK05107547 A HK 05107547A HK 1075224 B HK1075224 B HK 1075224B
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Description
Technical Field
The present invention relates to a method and apparatus for curing a coating on a workpiece, in particular for curing a radiation-curable coating.
Background
It is known in the prior art to coat workpieces with a material coating, which is cured when irradiated with ultraviolet light, and subsequently the coated workpiece is irradiated with ultraviolet light.
In particular, it is known to paint workpieces, for example vehicle bodies, with a UV-curable bright lacquer and to cure the coating by irradiating the workpiece with UV light.
The UV-curable gloss lacquer is characterized by a high scratch resistance.
In the known method and apparatus for uv-curable coating, the coated workpiece is irradiated with uv light from a uv lamp.
If the complex solid geometry of the coated workpiece has recesses and shaded areas, it is necessary to mount uv lamps on the curing apparatus, which are movable relative to the workpiece so that all the coated surfaces of the workpiece can be covered by the uv lamps. Since the uv lamp is bulky, even if such curing apparatus is used, the uv light cannot reach all of the recessed portions or other shielded areas. Areas of the coating not exposed to the ultraviolet light are not cured, which results in no volatilization of the cured coating components after a period of operation of the workpiece, thus resulting in the long-term presence of odor contaminants that are detrimental to health.
To avoid this problem, hybrid paint systems are generally used, which can be cured both by ultraviolet light and by heat. Such a hybrid paint spray system may allow for areas of the workpiece that are readily accessible to the ultraviolet lamps to be cured by ultraviolet light, while areas of the workpiece that are not readily accessible to the ultraviolet lamps are cured by thermal convection. The disadvantage is that, for complete curing, such hybrid paint systems have to carry out two different complete operating steps, i.e. uv irradiation and thermal convection curing, one after the other, which leads to high expenditure in terms of time and equipment costs, since uv lamps and suitable heating devices have to be available during the curing process.
Disclosure of Invention
It is therefore an object of the present invention to provide a method for curing coatings, in particular radiation-curable coatings, which enables the coating on less accessible areas of a three-dimensional workpiece to be cured in a simple manner.
The object of the invention is achieved by a method in which the workpiece is arranged in a plasma generation zone, in which a plasma is generated, by means of which the coating is at least partially cured.
The solution of the invention is based on the knowledge that plasma can be used to cure coatings. Since the workpiece itself is disposed in the plasma generation zone and the workpiece is located within the generated plasma, the coating of all surfaces of the workpiece, even the interior surfaces that are not readily accessible, can be cured.
Since the coating is radiation curable and the radiation suitable for curing the coating is generated in a plasma, the plasma is particularly easy to cure the coating.
Since the workpiece itself is arranged in the plasma generation region and the workpiece is located in the generated plasma, the radiation emitted by the plasma can reach the workpiece from all sides. In particular, a plasma may also be generated inside the cavities of the workpiece, so that the boundary surfaces of these cavities can receive suitable radiation for curing the coating from the cavities themselves. In this way, radiation suitable for curing the coating can reach any desired coating surface of the workpiece, particularly recessed portions or masked areas of the workpiece, so that the radiation-curable coating on the workpiece can be cured satisfactorily without the need for complex and expensive processing equipment.
Preferably, the coating is substantially completely cured, mainly by means of plasma, in which case the method according to the invention requires only one single step, the plasma curing step, so that the curing method according to the invention saves time and equipment costs.
Furthermore, it is sufficient that the coating is cured with radiation; in particular, the coating does not have to be cured simultaneously with heating, so that complex hybrid paint systems are not required.
The coating is made of radiation-curable materials of high quality, in particular high scratch resistance, without the need for thermal curing.
Since in the method according to the invention the plasma occupies the space of the plasma generation zone not occupied by the workpiece, changes in the geometry of the workpiece have little or no effect on the process.
Since the curing of the coating is effected by radiation and not, at least not completely, by thermal convection, it is not necessary to heat the entire workpiece to cure the coating. As a result, the energy costs required to effect curing are significantly reduced.
A separate thermal curing process may be performed before, during or after the plasma curing process, for example by convection and/or infrared radiation.
In a preferred embodiment of the invention, electromagnetic radiation comprising at least the ultraviolet component is generated in the plasma.
The term "ultraviolet" in the description and claims refers to electromagnetic radiation having a wavelength in the range of 1nm to 400 nm.
By appropriate selection of the composition of the working gas from which the plasma is generated, and the type of energy input to the plasma, as well as the working pressure of the plasma, the wavelength range and dose of the electromagnetic radiation generated in the plasma can be influenced.
The composition of the ultra-short wavelength radiation with a wavelength of less than 100nm is made as small as possible to avoid damage to the cured coating.
Furthermore, it has been shown that limiting the time that the coating is exposed to plasma radiation, which radiation time is at most about 120 seconds, preferably at most about 90 seconds, is beneficial for the quality of the cured coating.
Preferably, the generated plasma emits electromagnetic radiation having a wavelength in the range from about 50nm to about 850nm, in particular in the range from about 50nm to about 700nm, preferably in the range from about 150nm to about 700nm, particularly preferably in the range from about 200nm to about 600 nm.
It is particularly advantageous if the radiation emitted by the plasma emits at least a portion of ultraviolet radiation having a wavelength preferably in the range from about 200nm to about 400 nm.
It is advantageous for the workpiece to have a radiation-curable coating which is cured by radiation emitted by the plasma.
It is particularly advantageous if the workpiece has a coating which can be cured by electromagnetic radiation which contains at least a UV component, preferably in the range from about 200nm to about 400 nm.
It is particularly advantageous to generate a high radiation dose emitting plasma suitable for curing the coating if the pressure value in the plasma generation zone is set to a maximum of about 100Pa, preferably to a maximum of about 1Pa, particularly preferably to a maximum of about 0.1 Pa.
Furthermore, operating at such low pressures has the advantage that the curing of the coating is substantially isolated from oxygen. Since oxygen acts as a suppressor of the coating crosslinking reaction, the power delivered to the plasma and/or under vacuum is less than the power of the crosslinking reaction under an oxygen atmosphere, and the coating curing can proceed more rapidly.
The gas used as the working gas for generating the plasma should be a chemically inert and easily ionizable gas.
It is particularly advantageous if the plasma-generating region contains nitrogen and/or an inert gas, preferably argon, as the working gas.
In addition, in order to increase the generation of effective radiation, if a metal, such as mercury, or a metal halide, such as OsF, is added to the working gas7Or IrF6It would be advantageous.
In principle, the plasma can be generated by applying an electrostatic field to the plasma generation zone and/or by inputting an electromagnetic alternating field to the plasma generation zone.
Preferably, the plasma is generated by means of electromagnetic radiation input into the plasma generation zone by at least one input device.
The frequency of the electromagnetic radiation input to the plasma generation zone may be in the microwave range or in the high frequency range.
In the description and in the appended claims, microwave radiation is to be understood as electromagnetic radiation whose frequency is in the range from 300MHz to 300GHz, while high-frequency radiation is to be understood as electromagnetic radiation whose frequency is from 3kHz to 300 MHz.
The use of microwave radiation has proven particularly suitable for generating high doses of ultraviolet radiation.
Thus, in a preferred embodiment of the invention, the plasma is generated by input microwave radiation, the frequency of which is preferably in the range from about 1GHz to 10GHz, particularly preferably in the range from about 2GHz to 3 GHz.
The input electromagnetic radiation is generated in particular by a magnetron.
In order to increase the ionizing effect of the input electromagnetic radiation, the generated magnetic field is used to generate an ECR (electron cyclotron resonance) effect. In this case, for example, a static magnetic field oriented substantially parallel to the axis of an alternating electromagnetic field input into the plasma radiation region is generated in the plasma radiation region by an exciting coil device. The magnetic field strength is set such that the cyclotron frequency of the electrons in the magnetic field corresponds to the frequency of the incoming electromagnetic radiation. In the case of resonance, the free electrons in the plasma generation zone absorb a large amount of energy from the alternating electromagnetic field, which leads to a particularly efficient ionization of the working gas.
In order to be able to generate as high an ionization density as possible in the different regions of the plasma, the electromagnetic radiation is supplied to the plasma generation region by means of a plurality of supply devices, which are preferably arranged on different sides with respect to the workpiece.
If the workpiece to be treated comprises a cavity with an entrance, electromagnetic radiation is advantageously input into the plasma-generating region with at least one input device, so that the electromagnetic radiation enters the cavity of the workpiece through the entrance. This ensures that a plasma with a high ionization density and correspondingly high uv radiation is generated in the workpiece cavity, so that the coating on the cavity boundary surfaces can be cured quickly.
If the workpiece is a vehicle body, it is particularly important to cure paint that is oversprayed into the interior of the vehicle body during painting. This is expedient in the method according to the invention, in particular, by arranging the input device for inputting electromagnetic radiation against a window of the vehicle body, i.e. in such a way that the axis of the radiation field generated by the input device passes through the window into the interior of the vehicle body.
In a preferred embodiment of the invention, the gas to be ionized is supplied to the plasma generation zone during the curing process.
The gas to be ionized is in particular nitrogen or an inert gas, such as argon.
Since the gas to be ionized is continuously supplied to the plasma generation zone during the curing process, as a result of which a flow is generated in the plasma generation zone, ionized gas particles and/or gas particles excited by collisions with the ionized particles can reach, due to the flow, shadow areas of the workpiece where the input electromagnetic radiation cannot reach and thus cannot activate the plasma.
Furthermore, the gas flow generated in the plasma-generating zone results in a plasma which is as homogeneous and isotropic as possible and thus in a dose of radiation which is suitable for curing the coating and which is as independent of direction and position as possible.
It is particularly advantageous if the gas to be ionized is conveyed to the plasma generation zone by means of a conveying device close to the feed device, whereby electromagnetic radiation is fed into the plasma generation zone. Particularly high ion densities are produced in the introduced gas if the gas is guided through the location of the electromagnetic radiation input as intensively as possible in the plasma generation region before distribution, which is then distributed over the entire plasma generation region by the gas flow.
In order to be able to carry out the method according to the invention in a particularly time-saving manner, the workpiece can be pre-treated before the curing process is carried out in a prechamber and can be conveyed from the prechamber to the plasma generation zone in which the curing process is carried out.
In particular, after the workpiece is placed in the antechamber, the antechamber is evacuated, and the chamber is used as an input chamber, wherein the ambient pressure of the workpiece is reduced from atmospheric pressure to the operating pressure of the plasma generation zone.
The evacuation of the antechamber first causes the solvent in the coating to evaporate in advance, so that the coating to be cured is already pre-dried in the antechamber.
Alternatively or in addition, the workpiece may be subjected to electromagnetic radiation, in particular microwave radiation, in the front chamber. In this case, the coating to be cured can be pre-dried, in particular by absorbing energy in the electromagnetic radiation. Alternatively or in addition, a plasma may be activated in the pre-chamber, which emits radiation suitable for curing the coating which has undergone a first curing process on the coating.
In addition, after the curing process, the workpiece may be transferred from the plasma generation zone to the output chamber.
In particular, the output chamber is pumped to the operating pressure of the plasma generation zone before the workpiece is transferred to the output chamber.
After the transfer of the workpiece to the outlet chamber, the latter is charged, i.e. the pressure of the outlet chamber is increased to atmospheric pressure, and the workpiece is subsequently removed from the outlet chamber.
According to another aspect, the invention relates to a workpiece having a coating cured by the method of the invention.
The workpiece comprises any desired material, in particular a metallic and/or non-metallic material.
In particular, the workpiece is made of steel, plastic or wood material, for example.
The method according to the invention is particularly suitable for curing coatings on workpieces whose structure is non-planar and/or three-dimensional.
A non-planar workpiece is a workpiece whose coated surfaces are not in the same plane but in different planes, in particular in planes that are not parallel to each other and/or out of plane.
In particular, the non-planar workpiece has coated surfaces that are perpendicular to each other.
In particular, the method according to the invention is suitable for curing coatings on workpieces which have a coating depression and/or a coating shadow region.
In this case, the shaded area of the workpiece is an area which cannot be directly reached by light emitted from a point light source or a planar light source when the workpiece is irradiated with the light source.
The method according to the invention is suitable for curing coatings on workpieces comprising electrically conductive materials, and preferably workpieces made entirely of one or more electrically conductive materials.
In particular, the workpiece comprises a metallic material and is preferably made entirely of one or more electrically conductive materials.
Alternatively or in addition, the workpiece also comprises a plastic and/or wood material, and is preferably made entirely of a plastic material or entirely of a wood material.
The plasma-generating region may contain a gas or a mixture of several gases as the working gas in which the plasma is generated by ionization.
It has proven to be particularly advantageous if the plasma generation zone contains nitrogen, helium and/or argon as working gas.
Argon is particularly suitable for activating and stabilizing the plasma.
Helium causes a single density peak, particularly in the ultraviolet spectral long wavelength range.
Nitrogen forms a high density medium over a wide range of the ultraviolet spectrum.
In particular, the plasma generation zone contains a working gas whose composition changes during the curing process.
Thus, for example, the variation in the composition of the working gas is such that, in a first stage of the curing process, the density centre of the electromagnetic radiation generated in the plasma is at a first wavelength, and in a subsequent second stage of the curing process at a second wavelength, which is different from the first wavelength.
It is particularly advantageous if the second wavelength is smaller than the first wavelength.
As a result, electromagnetic radiation having a density centered in the long-wave range is generated in the first stage of the curing process, which is particularly suitable for curing coatings over the entire thickness of the workpiece.
In the second stage of the curing process, electromagnetic radiation is generated whose density centers are in the short-wave range and is therefore particularly suitable for curing coating overlays close to the free surface.
In a preferred variant of the method according to the invention, the change in the composition of the working gas during the curing process causes the density center of the electromagnetic radiation generated in the plasma to shift to shorter wavelengths with increasing curing time during the curing process.
Thus, for example, the gas supply can be controlled accordingly in the first stage of the curing process for about 60 seconds so that the working gas composition contains about 20% by volume of argon, the remainder being helium. This working gas composition causes the density center of the electromagnetic radiation spectrum generated in the plasma to be in the long-wave ultraviolet range.
In the second stage of the subsequent curing process of about 30 seconds, for example, nitrogen gas may be added to the mixed gas so that the density center of the electromagnetic radiation spectrum generated in the plasma is shifted to a shorter wavelength.
In addition, it has proven to be particularly advantageous if the plasma generation zone contains argon when the plasma is activated. Argon is particularly suitable as an activating gas for forming and stabilizing the plasma.
In a particularly preferred variant of the method according to the invention, the plasma-generating zone therefore contains predominantly only argon when the plasma is activated.
One or more gases and/or mixtures of gases are delivered to the plasma generation zone via one or more delivery devices in order to form the desired working gas composition.
In order to adapt the distribution of the radiation in the plasma-generating zone to complex, non-planar workpiece geometries, the plasma is generated by inputting electromagnetic radiation into the plasma-generating zone by means of a plurality of input devices, which are arranged such that, during the curing process, the plasma-generating zone is divided into two parts by a horizontal plane passing through the center of density of the workpiece, at least one input device is located in one of the two parts thereof.
Alternatively or additionally, the at least one input device is in one of its two parts when the plasma-generating region is divided into two parts by a vertical plane passing through the density center of the workpiece during curing.
In order to adapt the radiation distribution in the plasma generation zone to complex non-planar workpiece geometries and spatially varying coating thicknesses, the plasma is generated by inputting electromagnetic radiation into the plasma generation zone by means of a plurality of input devices, wherein at least two input devices have mutually different input powers.
Thus, in particular, an input device with a high input power can be arranged in the vicinity of a region of the workpiece with a coating of large thickness, whereas an input device with a low input power can be arranged in the vicinity of a region of the workpiece with a coating of small thickness.
Furthermore, the plasma may be generated by inputting electromagnetic radiation into the plasma generation region through a plurality of input devices, wherein at least two of the input devices are configured differently.
Thus, one input device may be configured, for example, as an ECR (electron cyclotron resonance) plasma source, while the other input device may be configured as a high frequency parallel plate plasma device.
In order to be able to distribute the radiation uniformly in the plasma generation region and/or to adapt it as well as possible to workpieces of a particular geometry, at least one reflector is arranged in the plasma generation region, reflecting the electromagnetic radiation generated in the plasma.
Specifically, at least one mirror film is provided in the plasma generation region as a reflector.
Alternatively or in addition, at least a sub-region of the plasma generation region boundary wall constitutes a reflector.
It has proven to be particularly advantageous if the at least one reflector comprises aluminum and/or stainless steel as the reflective material.
In order to exchange the reflector for another reflector having a different geometry or made of a different material, it is advantageous if the at least one reflector is detachable from the plasma generation zone.
In order to obtain the desired working gas flow shape in the plasma generation zone, gas is withdrawn from the plasma generation zone via one or more suction devices.
If the pressure in the plasma-generating region is varied by means of at least one suction device with a throttle valve arranged therein, while the gas supply is kept constant, the pressure in the plasma-generating region can be varied in a simple manner.
Depending on the material and geometry of the workpiece to be coated, it may be advantageous to connect the workpiece to a potential that is different from or the same as the potential of the boundary wall of the plasma-generating region.
In a particular embodiment of the method according to the invention, the workpiece is electrically isolated from the boundary wall of the plasma generation zone by means of at least one locally electrically insulating holder.
According to a variant of this method, the workpiece is connected to a potential different from the potential of the boundary wall of the plasma generation zone.
Alternatively, the workpiece is electrically connected to the boundary wall of the plasma generation region by means of an electrically conductive holder.
As a result, the workpiece can be connected in a simple manner to the same potential as the potential of the boundary wall of the plasma-generating region. Furthermore, the workpiece and/or the plasma-generating region boundary wall may be connected to ground potential.
The generated plasma is stabilized by locally selecting the potential of the workpiece relative to the plasma generation zone boundary wall.
In a particular embodiment according to the invention, the workpiece is additionally provided with a coating which can be cured by electromagnetic radiation comprising at least the ultraviolet component or by heating, or by a combination of electromagnetic radiation and heating comprising at least the ultraviolet part.
Such known coatings are known, for example, as "binary process paints".
By using such a coating, areas of the workpiece coating that are inaccessible or not easily accessible to the treatment with electromagnetic radiation generated in the plasma can be cured with a heat source. In this case, the thermal energy is provided, for example, by infrared radiation or convection. Furthermore, thermal energy may also be provided before, during and/or after curing by means of electromagnetic radiation generated in the plasma.
In particular for the purpose of preliminary drying or subsequent curing, the workpiece is subjected to electromagnetic radiation which is not generated in the plasma before, during and/or after the generation of the plasma.
Such radiation may in particular be microwave radiation and/or infrared radiation.
To prevent the generation of bubbles when curing the solvent-containing coating, the workpiece may be dried before, during and/or after the generation of the plasma.
Such drying can be achieved, for example, by irradiating the coating with microwave radiation and/or infrared radiation.
Alternatively or in addition thereto, the workpiece is at a pressure below atmospheric pressure prior to generating the plasma, preferably in the range of about 2000Pa to about 50000 Pa.
By subjecting the workpiece to low pressure, the solvent can evaporate from the coating being cured.
In order to reduce the equipment cost for the formation of the vacuum for the preliminary drying, it is preferable that the workpiece is under a pressure lower than atmospheric pressure before the plasma is generated, which is higher than the pressure to which the workpiece is subjected when the plasma is generated.
Furthermore, a magnetic field is generated in the plasma generation zone during the curing process, which can be used in particular to influence the local ionization degree of the plasma and thus the radiation distribution of the plasma generation zone.
The magnetic field influencing the radiation distribution of the plasma generation region is generated independently or may be added to the magnetic field serving to utilize the ECR (electron cyclotron resonance) effect and generate plasma.
In order to be able to vary the degree of local ionization and the radiation distribution in the plasma radiation zone during the curing process, in a particular variant of the method according to the invention the magnetic field strength which influences the radiation distribution during the curing process is varied.
In particular, the magnetic field is generated in the plasma generation region only after the curing process has started.
Due to such a magnetic field generated at a later stage of the curing process, the effective curing time of the workpiece at a particularly exposed location can be shortened compared to other locations of the workpiece.
This is particularly advantageous for preventing the paint used, in particular the white paint, from yellowing under the light.
In order to be able to adapt the local ionization degree and the radiation distribution in the plasma generation region as advantageously as possible to the geometry of the workpiece and to the local coating thickness on the workpiece, the magnetic field strength which influences the radiation distribution varies spatially in the plasma generation region.
In particular for heavy workpieces, it is advantageous to provide a transport device by means of which the workpiece is transported to the plasma generation zone and removed therefrom after the curing process.
It is a further object of the present invention to provide an apparatus for curing a coating on a workpiece, in particular a radiation-curable coating on a workpiece, which enables a coating in a position which is not easily accessible to the workpiece to be cured in a simple manner.
The apparatus includes a plasma generating region, means for feeding a workpiece into the plasma generating region, and means for generating a plasma in the plasma generating region. Wherein radiation for curing the radiation-curable coating is generated in the plasma and by means of this radiation the radiation-curable coating is at least partially cured.
In particular, the plasma generated in the plasma generating region may emit the radiation required for curing the radiation curable coating.
Drawings
Further features and advantages of the invention are given below by way of embodiments described with reference to the drawings. Wherein:
FIG. 1 is a basic schematic of curing a radiation-curable coating on a workpiece in a plasma;
FIG. 2 is a schematic cross-sectional view of a first embodiment of an apparatus for curing a radiation-curable coating on a workpiece;
FIG. 3 is a schematic cross-sectional view of a second embodiment of an apparatus for curing a radiation-curable coating on a workpiece;
FIG. 4 is a schematic longitudinal cross-sectional view of a third embodiment of a radiation curable coating apparatus for curing a radiation curable coating on a vehicle body and including an input chamber, a plasma chamber, and an output chamber;
FIG. 5 is a schematic cross-sectional view of the device of FIG. 4 taken along line 5-5 of FIG. 4;
FIGS. 6-10 are schematic side views of successive stages of the duty cycle of the apparatus of FIGS. 4 and 15;
FIG. 11 is a schematic longitudinal cross-sectional view of a fourth embodiment of a radiation curable coating apparatus for curing a radiation curable coating on a vehicle body and including an input chamber, a plasma chamber, and an output chamber;
FIG. 12 shows a schematic cross-sectional view of the device of FIG. 11 taken along line 12-12 of FIG. 11;
FIG. 13 is a schematic cross-sectional view of a fifth embodiment of a radiation curable coating apparatus for curing a radiation curable coating on a vehicle body and including a reflector;
FIG. 14 is a schematic cross-sectional view of a sixth embodiment of a radiation curable coating apparatus for curing a radiation curable coating on a vehicle body including a plasma chamber having reflective chamber walls;
FIG. 15 is a schematic cross-sectional view of a seventh embodiment of a radiation curable coating apparatus for curing a radiation curable coating on a vehicle body, including several delivery devices and working gas suction devices;
FIG. 16 is a schematic cross-sectional view of an eighth embodiment of a curing radiation curable coating apparatus for curing a radiation curable coating on a vehicle body and having a magnet that affects the degree of ionization of the generated plasma;
FIG. 17 is a schematic cross-sectional view of a vehicle body having a radiation curable coating held on a carriage by a work holder including an electrical insulator;
fig. 18 is a schematic cross-sectional view of a vehicle body with a radiation-curable coating, which is held on a carriage by means of a workpiece holder, said vehicle body being connected to the carriage in an electrically conductive manner with the workpiece holder.
Detailed Description
The same reference numbers are used throughout the drawings to refer to identical or functionally identical parts.
Fig. 1 illustrates the operating principle of a method for curing a radiation curable coating 100 on a workpiece 102, the workpiece 102 being disposed in a plasma generation zone 104.
The coating is cured by radiation that can be provided with ultraviolet radiation.
The formulation of these radiation curable materials is well known and widely disclosed in the art. These formulations contain, for example, components to be polymerized such as mono-, oligo-and/or polymers, possibly binders, one or more photoinitiators, and also, in general, other possible lacquer additives, such as solvents, flow regulators, adhesion improvers, stabilizers, such as photo-protectants, UV absorbers.
Examples of suitable mono-mers are acrylates, possible acrylates containing hydroxyl or epoxy groups. Unsaturated, possibly functional, amides, polyesters, polyurethanes and polyethers can be used as the polymeric component.
Such radiation curable formulations can be prepared, for example, by mixing the following components:
89.0 parts of 75% epoxy acrylate in hexanediol diacrylate (referred to on the market asEbecry 604, manufactured by UCB corporation of Belgium)
Polyethylene glycol-400-diacrylate 10.0 parts (referred to as "PEG-diacrylate" on the market)Sartomer SR344, available from Sartomer corporation)
1.0 part of silicon diacrylate (referred to as silicon diacrylate on the market)Ebecryl 350, manufactured by UCB corporation of Belgium)
Phenyl-1-hydroxycyclohexyl-ketone 2.0 parts (referred to on the market asIrgacure, produced by Ciba specialty Chemicals, Sweden)
The material may be crosslinked and thus cured by irradiation with visible light and ultraviolet light having a wavelength of about 200nm to about 600 nm.
The workpiece 102, which may be made of a desired metallic or non-metallic material, has a coating of a radiation curable material that is not initially cured in a suitable manner, such as by dipping, painting or spraying.
The coated workpiece 102 is placed in a plasma generation zone 104 that is filled with a working gas, such as argon or nitrogen, having a working pressure of about 0.1Pa to about 100 Pa.
After the workpiece 102 is placed in the plasma generation region 104 and the low pressure is established in its working gas, or as shown in fig. 1, plasma is generated in the plasma generation region 104 by applying an electrostatic field to the plasma generation region 104 and/or an alternating electromagnetic field to the plasma generation region via electrodes 106, 108.
In particular, electromagnetic radiation may be applied to plasma generation region 104. The electromagnetic radiation frequency may be in the microwave range (from about 300MHz to about 300 GHz) or in the high frequency range (from about 3kHz to about 300 MHz).
Neutral particles (atoms or molecules) 110 of the working gas ionize due to collisions of electrons absorbing energy in the applied electrostatic field or the input alternating electromagnetic field, thus forming additional free electrons 112 and gas ions 114.
Radicals 116 and excited gas particles (atoms and molecules) 118 are formed as a result of collisions of free electrons 112 and gas ions 114 with other neutral gas particles.
These excited particles of the plasma release a portion of the energy that is converted into energy in the form of electromagnetic radiation 120, at least a portion of which has a wavelength in the visible and ultraviolet ranges (from about 200nm to about 600 nm).
A portion of the radiated ultraviolet radiation exits the plasma to the coating 100 of the workpiece 102 disposed within the plasma and is absorbed and causes a crosslinking reaction, such as a polymerization, polycondensation, or polyaddition reaction, to cure the coating 100.
After the coating 100 has received a sufficient dose of ultraviolet radiation to achieve a sufficiently cured coating, the supply of plasma energy is discontinued so that a neutral working gas atmosphere is created, the pressure in the plasma generation zone 104 is at atmospheric pressure, and the workpiece 102 with the cured coating 100 is removed from the plasma generation zone 104.
An apparatus, schematically illustrated in fig. 2 and generally designated by reference numeral 122, for curing a radiation-curable coating 100 on a workpiece 102 includes a gas-tight plasma chamber 124 within which a plasma-generating region 104 is formed.
The internal volume of the plasma chamber 124 is, for example, about 100 liters.
The plasma chamber 124 is evacuated by means of an evacuation tube 126,to a pressure of about 10-3Pa which is connected to a vacuum pump system 128 and closed by a check valve 130.
The workpiece 102, which is held on a workpiece holder 131, for example in the form of a silicon disc, has a coating 100 of the above-mentioned radiation-curable material on its upper side remote from the workpiece holder 131, is placed in the operating position shown in fig. 2 by means of an access door (not shown) of the plasma chamber 124.
A microwave radiation input device, generally indicated by reference numeral 132, comprising an antenna 134 is provided in a wave guiding portion 136 and an excitation coil arrangement 138, the input device being provided centrally above the workpiece 102 in the operative position.
The antenna 134 is connected to a magnetron 140 through a wave guide portion 136, which generates microwaves having a frequency of, for example, 2.45GHz, which enter the antenna 134 through the wave guide portion 136 and are input therefrom into the plasma generation region 104.
The waveguide portion 136 is separated from the plasma generation region 104 by a quartz window 141.
The excitation coil arrangement 138 serves to amplify the ionizing effect of the microwave radiation by the ECR (electron cyclotron resonance) effect.
The excitation coil arrangement generates a static magnetic field that is oriented within plasma generation region 104 substantially parallel to an axis 142 of the beam of microwave radiation that is propagated by antenna 134. The magnetic field strength is set so that the electron cyclotron frequency in the magnetic field corresponds to the frequency of the radiated microwaves. In the case of resonance, the free electrons absorb particularly large amounts of energy from the alternating electromagnetic field, which leads to the ionization of the working gas particularly effectively.
If microwave radiation with a frequency of 2.45GHz is used, a magnetic field with a magnetic field strength of 875 gauss must be used to obtain the ECR effect.
Several delivery devices 144 for delivering the working gas are arranged symmetrically with respect to the axis 142 of the beam of microwave radiation generated by the input device 132, which delivery devices each comprise a delivery nozzle 146 which enters the plasma chamber 124 in a sealed manner, which delivery nozzles 146 are each connected to a gas storage tank 150 by a delivery pipe 148 having a flow regulator 149. Of course, several delivery devices 144 may be connected to the same gas storage tank 150.
Each flow regulator 149 is connected to a control unit 153 via control lines 151, respectively, to control the total amount of working gas delivered to the plasma generation zone 104 in accordance with the radiation requirements.
An ECR (Electron cyclotron resonance) plasma source sold under the name RR 250, manufactured by Roth & Rau surface technology, Inc. (D-09337 Hohenstein-erntsthal, Germany), may be used in particular as the input device 132.
The above-described device 122 operates as follows:
after the workpiece 102, which has the uncured coating 100 and is held on the workpiece holder 131, is placed in the plasma chamber 124, the plasma chamber 124 is evacuated by means of the vacuum pump system 128 after the check valve 130 has been opened, so that its base pressure is about 10-3Pa。
The working gas from the gas storage tank then enters the plasma generation region 104 by means of the delivery device 144 until its working pressure is, for example, about 0.3 Pa.
In this case, the gas flowing into the plasma chamber 124 is controlled by the flow regulator 149 such that the total flow rate of the gas flowing into the plasma chamber 124 is about 10sccm (standard cubic centimeters per minute) to about 200 sccm.
The working gas may be, for example, argon or nitrogen.
Upon reaching the desired operating pressure, microwave radiation generated by magnetron 140 is input into plasma generation region 104 and excites a plasma in plasma generation region 104.
The input microwave power is, for example, between about 400 watts and about 1000 watts, and preferably up to about 600 watts.
If several input devices 132 are used, the microwave input power to each input device is preferably between about 400 watts and about 1000 watts, respectively, with a maximum of about 600 watts being particularly preferred.
The gas particles introduced into plasma chamber 124 are ionized in the microwave radiation beam and then drift through plasma generation region 104 such that the plasma substantially fills the entire plasma chamber 124.
As the charged particles collide with gas particles excited in the plasma, ultraviolet-level radiation is released, which is absorbed by the coating 100 and causes a crosslinking reaction, thereby curing the coating.
After a 90 second irradiation time, the plasma treatment was interrupted and the plasma chamber was vented.
The workpiece 102 with the cured coating 100 is removed.
Two practical examples of curing methods implemented with the above-described apparatus 122 are illustrated below:
example 1:
a photocurable composition was prepared by mixing the following components:
44.5 parts of aliphatic urethane acrylate (Ebecryl 284; 88 parts of aliphatic urethane acrylate/12 parts of hexanediol diacrylate; Bayer AG)
Aliphatic urethane tri/tetra-acrylate (Roskydal UA VP LS 2308; Bayer AG) 32.2 parts
50.0 parts of isopropanol
Flow regulator (Byk 306; Byk Chemic)1.5 parts
The following components were added to the composition specified in the list and stirred in a water tank at 40 ℃: 1-hydroxy-cyclohexyl-benzophenone (Irgacure 184; Ciba specialty Chemicals) 2.7%, bis (2, 4, 6-trimethylbenzoyl) (Irgacure 819; Ciba specialty Chemicals) phenylphosphine oxide 0.5%, and tinuvin (bis(2, 2, 6, 6-tetramethyl-4-piperidinyl) sebacate) 400(═ mixture, which comprises 2- [4- [ (2-hydroxy-3-dodecylpropoxy) oxy ] oxy]-2-hydroxyphenyl]4, 6-bis (2, 4-diethylphenyl) -1, 3, 5-triazine and 2- [4- [ (2-hydroxy-3-tridecylpropoxy) oxy ] oxy]-2-hydroxyphenyl]-4, 6-bis (2, 4-diethylphenyl) -1, 3, 5-triazine; ciba specialty chemistry) 1.5% and tinuvin 292(═ mixture, which includes bis (1, 2, 2, 6, 6-pentamethyl-4-piperidinyl) -sebacate and 1- (methyl) -8- (1, 2, 2, 6, 6-pentamethyl-4-piperidinyl) -sebacate; ciba specialty chemistry) 1% (calculated as solids). The aluminized coil rack is in an inverted U shape. The paint was sprayed by a spray device to a final dry layer thickness of 30 μm. The lacquer on the three-dimensional substrate was vented at room temperature for 5 minutes, then vented at 80 ℃ for 10 minutes in a vented oven chamber and then cured in plasma chamber 124. Curing was carried out under an N2/He atmosphere at a gas ratio of 135/65sccm with a microwave power of 500w input through a microwave antenna for 90 seconds. The sample was spaced 150mm from the microwave antenna to obtain a well cured coating that did not peel off. Degree of cure is formed byPendulum hardness (DIN 53157). The greater the pendulum hardness value, the stronger the coating. The pendulum hardness of the U-shaped metal plate was 67 on the left side and 91 on the right side. The pendulum hardness value of the top of the U-shaped plate is 126.
Example 2
Compositions a and B were prepared by mixing the following compositions:
composition A:
11.38 parts of polyacrylate containing hydroxyl groups; 70% butyl acetate (DesmophenA870, Bayer AG)
21.23 parts of 75% polyester polyol in butyl acetate (Desmophen VP LS 2089, Bayer AG)
Flow regulator (Byk 306; Byk Chemie)0.55 part
32.03 parts of methanol
The following photoinitiator and photo-protecting agent were stirred into composition a:
0.17 part of bis (2, 4, 6-trimethylbenzoyl) phenylphosphine oxide (Irgacure 184; Ciba specialty Chemicals)
1.52 parts of 1-hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184; Ciba specialty Chemicals)
tinuvin 400(═ mixture, which comprises 2- [4- [ (2-hydroxy-3-dodecylpropoxy) oxy ] -2-hydroxyphenyl ] -4, 6-bis (2, 4-diethylphenyl) -1, 3, 5-triazine and 2- [4- [ (2-hydroxy-3-tridecylpropoxy) oxy ] -2-hydroxyphenyl ] -4, 6-bis (2, 4-diethylphenyl) -1, 3, 5-triazine; Ciba specialty Chemicals) 0.85 part
tinuvin 292(═ mixture, which includes bis (1, 2, 2, 6, 6-pentamethyl-4-piperidinyl) -sebacate and 1- (methyl) -8- (1, 2, 2, 6, 6-pentamethyl-4-piperidinyl) -sebacate; Ciba specialty chemistry) 0.56 parts
Then, 32.09 parts of hexyl carbamate acrylate containing isocyanate groups (Roskydal UA VP LS 2337; Bayer AG) was added to composition B and distributed homogeneously.
Thus, a binary treatment paint was prepared.
The paint was sprayed onto the coated aluminum of the flat coil support with a 100 μm slotted spray-painting blade to obtain a dry layer thickness of 30 μm. The lacquer was vented for 5 minutes at room temperature, then thermally crosslinked for 15 minutes at 120 ℃ in a vented oven chamber, and then cured in plasma chamber 124. Cured at N at a gas ratio of 160/40sccm2The reaction was carried out in an Ar atmosphere at a microwave power of 800w for 90 seconds. The sample was spaced 150mm from the microwave antenna to obtain a well cured coating that did not peel off. The degree of curing is determined by the Kaenig pendulum hardness (DIN 53157). The greater the pendulum hardness value, the stronger the coating. A pendulum hardness value of 118 was obtained.
A high frequency parallel plate plasma device including a parallel plate electrode assembly at a distance from the workpiece in the plasma generation region may be used in device 122 in place of the ECR plasma source described above. In this case, the plasma is excited by a high-frequency alternating voltage of, for example, about 13.6MHz, applied between the parallel-plate electrode device and the workpiece holding device. The power provided is, for example, about 10 watts to about 200 watts. The preferred operating pressure is about 1Pa and is set by delivering an ionized gas, preferably argon, with a flow regulator in the delivery line.
The other aspects of the structure and function of the device operated by high frequency are the same as those of the device operated by microwaves, for which reference is made to the above description.
The second embodiment of the apparatus 122 for curing the radiation curable coating 100 on the workpiece 102, schematically illustrated in fig. 3, differs from the first embodiment described above in that, in addition to the first input device 132 above the operating position of the workpiece 102, a second input device 132' is provided on the opposite side of the plasma chamber 124 with respect to the first input device 132.
The second input device 132 'is of the same construction as the first input device 132 and comprises in particular an antenna 134 in a wave guiding portion 136 leading to a magnetron 140 and separated from the plasma generating region 104 by a quartz glass plate 141, the second input device 132' further comprising an excitation coil arrangement 138 for generating the ECR effect.
Furthermore, several delivery devices 144 'of the working gas are arranged symmetrically with respect to the axis 142 of the beam of microwave radiation generated by the second input device 132', which delivery devices each comprise a delivery nozzle 146 entering the plasma chamber 124 in a sealed manner, which delivery nozzles 146 are each connected to a gas storage tank 150 by a delivery pipe 148 having a flow regulator 149.
Each flow regulator 149 is connected via a control line 151 to a control unit 153 which controls the total amount of working gas delivered to the plasma generation region 104 in accordance with the radiation requirements.
The second embodiment of the apparatus 122 shown in fig. 3 can cure a coating 100 on a complex-shaped three-dimensional workpiece 102, such as the workpiece 102 shown in fig. 3, for example, having a cavity 152 with an entrance 154, wherein the cavity boundary surface has the coating 100 to be cured.
The workpiece 102 is positioned in the plasma generation region 104 such that the entrance 154 of the cavity 152 is opposite the second input device 132 ' and the axis 142 ' of the input device 132 ' enters the cavity 152 through the entrance 154.
This ensures that microwave radiation from the second input device 132' passes into the cavity 152 of the workpiece 102 to generate a plasma in the cavity 152.
Excited gas particles that have collided with the charged particles of the plasma diffuse through the shadow region 156 of the cavity 152 and emit visible and ultraviolet radiation there, which is absorbed by the coating on the inner wall of the shadow region 156 of the cavity 152, whereas visible or ultraviolet radiation cannot enter the cavity from the region of the plasma generation region 104 located outside the workpiece 102. In this way, the coating in the masked areas 156 is completely cured.
The structure and function of the second embodiment of the apparatus 122 for curing the radiation curable coating 100 shown in fig. 3 is the same as the first embodiment shown in fig. 2, for which reference is made to the above description.
The third embodiment of the apparatus shown in fig. 4 and 5 for curing a radiation curable coating 100 on a workpiece 102 includes three chambers, evacuated and arranged in sequence in the direction of conveyance, with the three chambers being a pre-chamber or input chamber 160, a plasma chamber 124, and an output chamber 162.
Each chamber is about 2.5 metres in diameter and about 6 metres in length, so that each chamber receives a workpiece in the form of a car body 164, which is held on a carriage 166.
Each carriage comprises two slide rails 168 parallel to the conveying direction 158, by means of which their respective carriage 166 is supported on the conveying rollers of a roller conveyor 170 arranged in each chamber 160, 124 and 162, respectively.
The inlet of the input chamber 160 and the outlet of the output chamber 162 are sealed by vacuum-tight outer lift gates 172, respectively. The path from input chamber 160 to plasma chamber 124 and the path from plasma chamber 124 to output chamber 162 are sealed by vacuum-tight inner lift gate 172', respectively.
Fig. 4 and 5 show the upper open position of the lift gates 172, 172' in which the passageway is open and the vehicle body 164 can pass.
Each chamber 160, 124 and 162 is pumped by a respective front pump 174 and a roots blower 176 to a working pressure of about 1 Pa.
The plasma chamber 124 is provided with a plurality of microwave radiation input devices 132, one of which is disposed directly above a body 164 placed in the plasma chamber 124, and the other two of which are disposed on side walls of the plasma chamber 124, which face windows 178 of the body 164, so that axes 142 of the beams of microwave radiation generated by these input devices pass through the windows into the interior of the body 164.
Each of the input devices 132 is connected to a magnetron 140 through a waveguide portion 136, respectively, for generating microwaves having a frequency of 2.45 GHz.
In addition, a gas injection system (not shown) is provided adjacent each input 132, and is connected to the gas storage tank via a delivery line that delivers a working gas, such as argon or nitrogen, into plasma chamber 124 during the curing process.
The input device 132 for microwave radiation connected to the magnetron 140 via the waveguide portion 136 is disposed in the input chamber 160 directly above the vehicle body 164, i.e., in the input chamber 160.
The input devices 132 are detachable inside the plasma chamber 124 or the input chamber 160, so that they can be arranged immediately in an optimal manner, in particular as close as possible to the window, depending on the geometry of the vehicle body.
The above-described apparatus 122 for curing a radiation curable coating on a vehicle body 164 functions as follows:
the device is operated in a defined cycle, wherein the first working cycle, the first conveying cycle, the second working cycle and the second conveying cycle are each carried out successively one after the other, forming an operating cycle of the device.
The total cycle time, i.e. the total time of two work cycles and two delivery cycles, is about 90 seconds.
During the first work cycle, schematically shown in fig. 6, all lift gates 172, 172' are closed. One body 164 is disposed in the output chamber 162 and the other body 164' is disposed in the plasma chamber 124.
In a first duty cycle, the output chamber 162 is inflated until ambient pressure is reached.
In a first working cycle, the body 164' in the plasma chamber 124 undergoes plasma curing, wherein a working gas is delivered to the interior of the plasma chamber 124, which serves as the plasma generation zone 104, by means of a gas injection system, and the plasma is activated by microwave radiation from the magnetron 140.
Those areas of the coating 100 of the vehicle body 164' that are immediately adjacent to the plasma generation zone 104 of the activated plasma are radiated from that area by the visible radiation and the ultraviolet radiation.
Further, the gas particles excited by the collision with the plasma charged particles are diffused to the shielded area inside the vehicle body 164' and generate visible light and ultraviolet rays, so that the coating 100 in the shielded area 156 is also cured.
The microwave power delivered to the plasma chamber 124 during curing is about 10kw in total.
The empty inlet chamber is charged during the first working cycle until the ambient pressure is reached.
In a first delivery cycle, shown in fig. 7, following the first duty cycle, the outer lift gate 172 is opened. A new vehicle body 164 "is transported out of the paint shop area, for example into the input booth 160, which is located in front of the input booth 160 in the transport direction 158, wherein the new vehicle body 164" already has a coating of radiation-curable material with the above-mentioned components, and the vehicle body 164 located in the output booth 162 is transported in a first operating cycle to the paint shop behind the output booth 162 by means of the roller conveyor 170.
During the first conveying cycle, the body 164' thereof remains in the plasma chamber 124, and plasma curing is continued during the first conveying cycle.
After the first conveying cycle, a second working cycle of the device shown in fig. 8 is carried out, for which all lifting gates 172, 172' are closed again.
In the second work cycle, the plasma curing of the vehicle body 164' continues in the plasma chamber 124.
In addition, in the second working cycle, the inlet chamber 160 and the outlet chamber 162 are evacuated by means of a respective front pump 174 and a respective rough exhaust blower 176 from their atmospheric pressure to their working pressure of approximately 100 Pa. The suction results in a pre-drying of the coating 100 in the form of a paint layer on the vehicle body 164 entering the chamber 160.
In addition, microwave radiation from the magnetron 140 can be input to the input 160 by means of the input device 132, directly drying the coating 100 with microwaves, if necessary activating a plasma, which is now in the input chamber 160, which emits visible radiation and ultraviolet radiation into the coating, thus producing a first curing process for the coating.
After the irradiation of the body 164' in the plasma chamber for about 60 seconds is completed, the power supply to the plasma is interrupted and the gas supply is regulated.
In the second delivery cycle shown in fig. 9 after the second duty cycle, the inner lift gate 172' is opened while the outer lift gate 172 remains closed.
In a second transport cycle, the vehicle bodies 164' are transported out of the plasma chamber 124 into the output chamber 162 by means of the roller transport devices in the input chamber 160 and the plasma chamber 124.
At the same time, during the second conveying cycle, the vehicle bodies 164 "are conveyed out of their conveying chambers 160 into the plasma chamber 124 by means of the roller conveying devices in the conveying chambers 160 and the plasma chamber 124.
The inner lift gate 172' is then closed and the first duty cycle of the device 122 operating cycle (fig. 10) is restarted, wherein the body 164 "in the plasma chamber 124 undergoes the plasma curing process, and the output chamber 162 and input chamber 160 are again charged until ambient pressure is reached therein.
For plasma curing in the plasma chamber 124, the body may also be thermally pretreated in the input chamber 160 and/or thermally post-treated in the output chamber 162.
The thermal pre-or post-treatment may in particular comprise a separate thermal curing process, wherein the coating is heated, for example with a heat source, for example with infrared light by thermal convection and/or thermal radiation, for example to a temperature of about 50 ℃ to about 250 ℃ and is thus cured.
Furthermore, the body can also be subjected to a heat treatment before, during and/or after the plasma curing process, for example by heating the lacquer coating with infrared radiation.
The fourth embodiment of the apparatus for curing a radiation curable coating 100 on a workpiece 102 shown in fig. 11 and 12 differs from the third embodiment shown in fig. 4 and 5 in that in addition to the input device 132 for microwave radiation, which is arranged above the horizontal longitudinal center of the plane of the vehicle body 164 with the radiation curable coating 100, an additional input device 132' is arranged below the horizontal longitudinal center of the plane of the vehicle body 164, as can be seen clearly from fig. 12.
Each additional input device 132' is connected to the magnetron 140 through a respective waveguide section for generating microwaves having a frequency of 2.45 GHz.
The different input devices 132, 132' may have the same structure.
Alternatively, however, at least two such input devices 132, 132' may be provided, having different configurations and/or different microwave powers input to the plasma generation zone 104.
In particular, the input devices 132, 132 'disposed near the region of the body 164 having the thicker coating 100 may be made to have greater input power, while the input devices 132, 132' disposed near the region of the body 164 having the thinner coating 100 may be made to have less input power.
Furthermore, in the fourth exemplary embodiment, on the one hand, a throttle valve 200 can be provided on the suction line 126 between the plasma chamber 124, the inlet chamber 160 and the outlet chamber 162, respectively, and, on the other hand, a vacuum pump 128 is provided, by means of which the respective chamber 124 can be evacuated.
Since the throttle valve 200 is disposed at the suction side, the pressure in the plasma chamber 124 or the input chamber 160 or the output chamber 162 can be changed even if the gas supplied to the respective chambers is constant. In this way, a desired pressure distribution can be generated in each chamber which changes in time, without the gas supply to the respective chamber having to be controlled or regulated.
The plasma state in the plasma chamber 124 can be homogenized by increasing the number of input devices 132, 132 'and/or due to the input power of the input devices 132, 132' adapted to the thickness of the respective partial coating.
The other structures and functions of the fourth embodiment of the apparatus for curing radiation curable coatings are the same as the third embodiment, as described above.
The fifth embodiment of the radiation-curable coating apparatus shown in fig. 13 for curing a radiation-curable coating on a workpiece 102 differs from the third embodiment described above only in that the reflector 202 within the plasma chamber 124 has a corresponding reflective surface 204 facing the vehicle body 164.
The reflector 202 serves to reflect electromagnetic radiation generated in the plasma towards the body 164 and to homogenize the radiation distribution in the plasma chamber 124.
Furthermore, a sufficient amount of electromagnetic radiation can be made to reach the shaded areas of the body 164 that are not readily accessible by means of the reflector 202.
The reflecting surface 204 may be made of, for example, aluminum or stainless steel or have a mirror film made of one of these materials.
Reflector 202 is preferably removably retained on a wall of plasma chamber 124 such that reflector 202 can be removed from plasma chamber 124 and replaced with another reflector 202.
The other structures and functions of the fifth embodiment of the cured coating device are the same as those of the third embodiment, for which reference is made to the above description.
The sixth embodiment of the radiation-curable coating apparatus on a curing body 164 shown in fig. 14 differs from the fifth embodiment described above only in that the boundary wall of the plasma chamber 124 (including the wall surface of the inner lift gate 172' facing the interior of the plasma chamber 124) has a reflective layer 206 so that the boundary wall of the plasma chamber 124 itself acts as a reflector 202 in this embodiment to reflect electromagnetic radiation generated at the plasma generation zone 104 toward the workpiece 102.
The reflective coating 206 may be made of, for example, aluminum or stainless steel.
Furthermore, it is also possible to make the boundary walls of the plasma chamber 124 without a reflective layer, but entirely of a reflective material.
The reflector provided separately from the boundary wall of the plasma chamber 124 in the fifth embodiment may be omitted in the sixth embodiment. It is also conceivable, however, to provide an additional reflector 202 in connection with the fifth exemplary embodiment inside the plasma chamber 124 with reflective boundary walls in order to influence the radiation distribution in the plasma chamber 124 in a targeted manner if required.
The other structures and functions of the sixth embodiment of the apparatus for curing radiation curable coatings are the same as the fifth embodiment, for which reference is made to the above description.
The seventh embodiment of the apparatus for curing the radiation curable coating 100 on the workpiece 102 shown in fig. 15 has several input devices 144 that deliver working gas into the plasma chamber 124 and several pumping devices 208 that draw gas from the plasma chamber 124.
Each suction device 208 includes a suction tube 126 on which a check valve 130 and a vacuum pump 128 are disposed.
As can be seen in fig. 15, the conveying device 144 is arranged in a region below the horizontal longitudinal center plane of the vehicle body 164, while the suction device 208 is arranged in a region above the horizontal longitudinal center plane of the vehicle body 164.
In this way, the flow formed by the working gas in which the plasma is generated can pass through the plasma chamber 124, in particular through the body 164, from below upwards.
The flow of working gas through the plasma chamber 124 thus created proves advantageous for producing a stable plasma with a uniform radiation distribution.
The other structures and functions of the seventh embodiment of the cured radiation curable coating device are the same as the third embodiment, for which reference is made to the above description.
The eighth embodiment of the apparatus for curing a radiation-curable coating shown in fig. 16 differs from the above embodiments in that at least one magnet member 210 is additionally provided for generating a magnetic field in the plasma generation region 104.
The local ionization level and radiation distribution of the plasma in the plasma chamber 124 can be influenced by the magnetic field generated by the magnet piece 210.
The magnet piece 210 may be formed of a permanent magnet or an electromagnet.
The configuration using magnet piece 210 as an electromagnet is particularly suitable for generating a time-varying magnetic field.
Specifically, after the curing process of the coating 100 begins, e.g., after about half of the curing time has elapsed, the magnetic field is generated only by the magnet pieces 210 to reduce the radiation intensity, particularly at the exposed locations of the workpiece 102.
In particular, yellowing can be prevented during photocuring, in particular for white paints.
The other structures and functions of the eighth embodiment of the apparatus for curing a radiation curable coating on a workpiece thereof are the same as the third embodiment, for which reference is made to the above description.
Especially in the case of a workpiece 102 made of an electrically conductive material, it is advantageous to stabilize the generated plasma if the workpiece 102 is provided with a coating 100 and the boundary walls of the plasma chamber 124 are connected to the same potential.
This can be achieved in particular by electrically conductively connecting the workpiece 102 to a boundary wall of the plasma chamber 124 by means of an electrically conductive workpiece holder.
By way of example, the body 164 shown in fig. 18 is connected via an electrically conductive workpiece holder 212 to a carriage 166, which is itself connected in an electrically conductive manner to a boundary wall of the plasma chamber 124. This ensures that the workpiece (body 164) is at potential φ1Connection, potential phi1And a potential phi provided on a boundary wall of the carriage 166 and the plasma chamber 1242The same is true.
And in particular, the boundary walls of workpiece 102 and plasma chamber 124 may be grounded.
But alternatively it may be advantageous in some cases to connect workpiece 102 at a potential different from the boundary wall potential of plasma chamber 124.
In this case, it is desirable to electrically insulate the workpiece 102 from the boundary walls of the plasma chamber 124.
To this end, the vehicle body 164 shown in fig. 17 is mechanically connected to the carriage 166 by means of a workpiece holder 212, for example, but in this case the workpiece holder 212 comprises an electrical insulation 214 which electrically isolates the workpiece holder 212 portion on the workpiece side from the carriage-side workpiece holder 212 portion.
In this case, the potential φ of the workpiece (the vehicle body 164)1Potential phi at the boundary wall with the carriage 166 and plasma chamber 1242Different.
Potential phi of the workpiece 1021It may be set at a certain level, for example ground potential or a potential different from ground potential.
Alternatively, the workpiece 102 may not be connected to an external predetermined potential, but may be changed.
The electrical insulator 214 may be made of any desired material having sufficient electrical insulation, such as a suitable plastic material or a suitable ceramic material.
The electrical insulation 214 thereof is preferably made of a vacuum resistant material.
Claims (133)
1. A method of curing a coating (100) on a workpiece (102), characterized in that the workpiece (102) has a coating (100) which can be cured by means of electromagnetic radiation,
the workpiece (102) with the coating thereon is arranged in a plasma generation zone (104), and
generating a plasma in the plasma generation zone (104),
wherein a plasma is generated by inputting electromagnetic radiation into the plasma generation zone (104) by at least one input device (132, 132'), thereby generating electromagnetic radiation in the plasma suitable for curing the coating (100), and at least partially curing the coating (100) with said electromagnetic radiation.
2. The method of claim 1, wherein: the wavelength of the electromagnetic radiation generated in the plasma is in the range of 50nm to 850 nm.
3. The method of claim 2, wherein: the wavelength of the electromagnetic radiation generated in the plasma is in the range of 50nm to 700 nm.
4. The method of claim 2, wherein: the wavelength of the electromagnetic radiation generated in the plasma is in the range of 150nm to 700 nm.
5. The method of claim 2, wherein: the wavelength of the electromagnetic radiation generated in the plasma is in the range of 200nm to 600 nm.
6. The method of claim 2, wherein: the workpiece has a coating (100) that is curable by electromagnetic radiation that includes at least an ultraviolet component.
7. The method of any of claims 1-6, wherein: the pressure value in the plasma generation region (104) is set at 100Pa at maximum.
8. The method of claim 7, wherein: the pressure value in the plasma generation region (104) is set at 1Pa at maximum.
9. The method of claim 7, wherein: the pressure value in the plasma generation region (104) is set at 0.1Pa at maximum.
10. The method of claim 1, wherein: the plasma generation zone (104) contains nitrogen and/or an inert gas as a working gas.
11. The method of claim 10, wherein: the inert gas is argon.
12. The method of claim 1, wherein: the plasma generation zone (104) contains a working gas with an additive added thereto.
13. The method of claim 12, wherein: the additive is a metal and/or a metal halide.
14. The method of claim 13, wherein: the plasma is generated by input microwave radiation.
15. The method of claim 14, wherein: the frequency of the microwave radiation is in the range of 1GHz to 10 GHz.
16. The method of claim 14, wherein: the frequency of the microwave radiation is in the range of 2GHz to 3 GHz.
17. The method of any of claims 14-16, wherein: the electromagnetic radiation is generated by a magnetron (140).
18. The method of claim 1, wherein: the generated magnetic field is used to generate an electron cyclotron resonance effect.
19. The method of claim 1, wherein: the electromagnetic radiation is input into the plasma generation zone (104) by means of a plurality of input devices (132, 132').
20. The method of claim 1, wherein: the workpiece (102) has a cavity (152) with an inlet (154), and electromagnetic radiation is input into the plasma generation region (104) by means of at least one input device (132) such that the electromagnetic radiation enters the cavity (152) of the workpiece (102) through the inlet (154).
21. The method of claim 1, wherein: during the curing process, the gas to be ionized is delivered to the plasma generation zone (104).
22. The method of claim 21, wherein: the gas to be ionized is conveyed to the plasma generation region (104) by means of a conveying device (144) close to the input device (132, 132'), whereby electromagnetic radiation is input into the plasma generation region (104).
23. The method of claim 1, wherein: the workpiece (102) is placed in a pre-chamber (160) and transported from the pre-chamber (160) to a plasma generation zone (104) for a curing process.
24. The method of claim 23, wherein: the antechamber (160) is evacuated after the workpiece (102) is placed therein.
25. The method of claim 23 or 24, wherein: the workpiece (102) is subjected to electromagnetic radiation in a front chamber (160).
26. The method of claim 25, wherein: the electromagnetic radiation is microwave radiation.
27. The method of claim 1, wherein: after the curing process, the workpiece (102) is transferred from the plasma generation zone (104) into an output chamber (162).
28. The method of claim 27, wherein: the output chamber (162) is evacuated before the workpiece (102) is transferred to the output chamber (162).
29. The method of claim 1, wherein: the structure of the workpiece (102) is non-planar.
30. The method of claim 1, wherein: the workpiece (102) has at least one recess and/or at least one masked area.
31. The method of claim 1, wherein: the workpiece (102) includes an electrically conductive material.
32. The method of claim 1, wherein: the workpiece (102) comprises a metallic material.
33. The method of claim 1, wherein: the workpiece (102) comprises a plastic and/or wood material.
34. The method of claim 1, wherein: the plasma generation zone (104) contains nitrogen, helium and/or argon as the working gas.
35. The method of claim 1, wherein: the plasma generation region (104) contains a working gas whose composition changes during the curing process.
36. The method of claim 35, wherein: the variation in the composition of the working gas causes the electromagnetic radiation generated in the plasma to be centered at a first wavelength during a first stage of the curing process and to be centered at a second wavelength, different from the first wavelength, during a subsequent second stage of the curing process.
37. The method of claim 36, wherein: the second wavelength is less than the first wavelength.
38. The method of any one of claims 35-37, wherein: the variation in the composition of the working gas shifts the center of the intensity of the electromagnetic radiation generated in the plasma during the curing process towards shorter wavelengths as the curing time increases.
39. The method of claim 1, wherein: the plasma generation zone (104) contains argon gas when the plasma is activated.
40. The method of claim 39, wherein: the plasma generation zone (104) contains substantially only argon gas when the plasma is activated.
41. The method of claim 1, wherein: one or more gases and/or mixtures of gases are delivered to the plasma generation region (104) by one or more delivery devices (144).
42. The method of claim 1, wherein: plasma is generated by inputting electromagnetic radiation into a plasma generation zone (104) by a plurality of input devices (132, 132 '), wherein at least two of the input devices (132, 132') have different input powers from each other.
43. The method of claim 1, wherein: plasma is generated by inputting electromagnetic radiation into a plasma generation region (104) by a plurality of input devices (132, 132 '), wherein at least two of the input devices (132, 132') differ in structure.
44. The method of claim 1, wherein: at least one reflector (202) is disposed in the plasma generation region (104) to reflect electromagnetic radiation generated in the plasma.
45. The method of claim 44, wherein: at least one mirror film is disposed in the plasma generation region (104) as a reflector (202).
46. The method of claim 44 or 45, wherein: at least a partial region of the boundary wall of the plasma generation region (104) forms a reflector (202).
47. The method of claim 44, wherein: the at least one reflector (202) comprises aluminum and/or stainless steel as a reflective material.
48. The method of claim 44, wherein: the at least one reflector (202) is detachable from the plasma generation region (104).
49. The method of claim 1, wherein: gas is withdrawn from the plasma generation zone (104) by means of one or more pumping devices (208).
50. The method of claim 1, wherein: the pressure in the plasma generation zone (104) is varied by means of at least one suction device (208) having a throttle valve (200).
51. The method of claim 1, wherein: the workpiece (102) is electrically isolated from the boundary wall of the plasma generation region (104) at least by means of a locally electrically insulating holder (212).
52. The method of claim 1, wherein: the workpiece (102) is connected to a potential different from a boundary wall potential of the plasma generation region (104).
53. The method of claim 1, wherein: the workpiece (102) is connected in an electrically conductive manner to a boundary wall of the plasma generation region (104) by means of an electrically conductive holder.
54. The method of claim 1, wherein: the workpiece (102) is connected to the same potential as the plasma-generating region (104) boundary wall.
55. The method of claim 1, wherein: the workpiece (102) is connected to ground potential.
56. The method of claim 1, wherein: the workpiece (102) has a coating (100) that is curable by electromagnetic radiation including at least an ultraviolet component, or by heat or a combination of electromagnetic radiation including at least an ultraviolet component and heat.
57. The method of claim 1, wherein: the workpiece (102) is subjected to electromagnetic radiation that is not generated in the plasma before, during and/or after the plasma is generated.
58. The method of claim 57, wherein: the workpiece (102) is subjected to microwave radiation and/or infrared radiation that is not generated in the plasma before, during and/or after the plasma is generated.
59. The method of claim 1, wherein: the workpiece (102) is dried before, during and/or after the plasma is generated.
60. The method of claim 1, wherein: the workpiece (102) is at a pressure below atmospheric pressure prior to generating the plasma.
61. The method of claim 60, wherein: the workpiece (102) is at a pressure in the range of 2000Pa to 50000Pa prior to generating the plasma.
62. The method of claim 1, wherein: prior to generating the plasma, the workpiece (102) is at a pressure below atmospheric pressure, which is higher than the pressure to which the workpiece (102) is subjected when the plasma is generated.
63. The method of claim 1, wherein: a magnetic field is generated in the plasma generation zone (104).
64. The method of claim 63, wherein: during the curing process, the magnetic field strength is varied.
65. The method of claim 63 or 64, wherein: only after the curing process has started, its magnetic field is generated in the plasma-generating zone (104).
66. The method of claim 63, wherein: the magnetic field strength varies spatially in the plasma generation zone (104).
67. An apparatus for curing a coating (100) curable by electromagnetic radiation on a workpiece (102), characterized by: the device (122) comprises a plasma generation zone (104), means (170) for introducing the workpiece (102) with the coating thereon into the plasma generation zone (104), and at least one input device (132, 132') for inputting electromagnetic radiation into the plasma generation zone (104) for generating a plasma in the plasma generation zone (104),
wherein electromagnetic radiation for curing the coating (100) on the workpiece (102) is generated in the plasma and the coating (100) is at least partially cured by the electromagnetic radiation.
68. The apparatus of claim 67, wherein: a plasma can be generated in the plasma generation zone (104) that emits electromagnetic radiation having a wavelength in the range of 50nm to 850 nm.
69. The apparatus of claim 68, wherein: a plasma can be generated in the plasma generation zone (104) that emits electromagnetic radiation having a wavelength in the range of 50nm to 700 nm.
70. The apparatus of claim 68, wherein: a plasma can be generated in the plasma generation zone (104) that emits electromagnetic radiation having a wavelength in the range of 150nm to 700 nm.
71. The apparatus of claim 68, wherein: a plasma can be generated in the plasma generation zone (104) that emits electromagnetic radiation having a wavelength in the range of 200nm to 600 nm.
72. The apparatus of any one of claims 67-71, wherein: the pressure value of the working gas in the plasma generation region (104) is set at 100Pa at maximum.
73. The apparatus of claim 72, wherein: the pressure value of the working gas in the plasma generation region (104) is set at 1Pa at maximum.
74. The apparatus of claim 72, wherein: the pressure value of the working gas in the plasma generation region (104) is set at 0.1Pa at maximum.
75. The apparatus of claim 67, wherein: the plasma generation zone (104) contains nitrogen and/or an inert gas as a working gas.
76. The apparatus of claim 75, wherein: the inert gas is argon.
77. The apparatus of claim 67, wherein: microwave radiation can be input into the plasma generation region (104) by means of an input device (132, 132').
78. The apparatus of claim 77, wherein: the frequency of the microwave radiation is in the range of 1GHz to 10 GHz.
79. The apparatus of claim 78, wherein: the frequency of the microwave radiation is in the range of 2GHz to 3 GHz.
80. The apparatus of any one of claims 77-79, wherein: the apparatus (122) comprises means (140) for generating electromagnetic radiation.
81. The apparatus of claim 67, wherein: the apparatus (122) includes means (138) for generating a magnetic field in the plasma generation region (104).
82. The apparatus of claim 67, wherein: the device (122) comprises a plurality of input means (132, 132') for inputting electromagnetic radiation into the plasma generation zone (104).
83. The apparatus of claim 67, wherein: at least one input device (132 ') is positioned and oriented such that electromagnetic radiation input into the plasma generation region (104) by the input device (132') passes through an inlet (154) on a cavity (152) of a workpiece (102) disposed in the plasma generation region (104).
84. The apparatus of claim 67, wherein: the apparatus (122) comprises at least one delivery device (144) for delivering the gas to be ionized to the plasma generation region (104).
85. The apparatus of claim 84, wherein: the conveying device (144) is arranged close to the input device (132, 132 '), by means of which electromagnetic radiation can be input into the plasma generation region (104) by means of the input device (132, 132').
86. The apparatus of claim 67, wherein: the apparatus (122) includes a pre-chamber (160) that receives the workpiece (102) prior to a curing process.
87. The apparatus of claim 86, wherein: the antechamber (160) can be evacuated.
88. The apparatus of claim 86 or 87, wherein: the antechamber (160) is provided with means (132, 136, 140) for electromagnetic radiation of the workpiece (102) in the antechamber (160).
89. The apparatus of claim 88, wherein: the electromagnetic radiation is microwave radiation.
90. The apparatus of claim 86, wherein: the device (122) comprises a transport device (170) for transporting the workpiece (102) from the antechamber (160) into the plasma generation zone (104).
91. The apparatus of claim 90, wherein: the transmission device (170) is a roller transmission device,
92. the apparatus of claim 67, wherein: the apparatus (122) includes an output chamber (162) for receiving the workpiece (102) after a curing process.
93. The apparatus of claim 92, wherein: the output chamber (162) may be evacuated.
94. The apparatus of claim 92 or 93, wherein: the apparatus (122) includes a transport device (170) to transport the workpiece (102) out of the plasma generation region (104) into the output chamber (162).
95. The apparatus of claim 94, wherein: the transfer device (170) is a wheel transfer device.
96. The apparatus of claim 67, wherein: the apparatus is configured for curing a coating (100) on a non-planar workpiece (102).
97. The apparatus of claim 67, wherein: the apparatus is configured for curing a coating (100) on a workpiece (102) having at least one recess and/or at least one masked area.
98. The apparatus of claim 67, wherein: the apparatus is configured for curing a coating (100) on a workpiece (102) comprising an electrically conductive material.
99. The apparatus of claim 67, wherein: the apparatus is configured for curing a coating (100) on a workpiece (102) comprising a metallic material.
100. The apparatus of claim 67, wherein: the apparatus is configured for curing a coating (100) on a workpiece (102) comprising a plastic and/or wood material.
The apparatus of claim 67, wherein: nitrogen, helium and/or argon can be delivered to the plasma generation zone (104) as a working gas.
The apparatus of claim 67, wherein: the plasma generation zone (104) contains a working gas whose composition changes during the curing process.
The apparatus of claim 102, wherein: the change in the composition of the working gas causes the electromagnetic radiation generated in the plasma to be centered at a first wavelength during a first stage of the curing process and to be centered at a second wavelength, different from the first wavelength, during a subsequent second stage of the curing process.
The apparatus of claim 103, wherein: the second wavelength is less than the first wavelength.
The apparatus as set forth in one of claims 102-104, wherein: the change in the composition of the working gas in the plasma generation zone (104) causes the center of intensity of the electromagnetic radiation generated in the plasma to shift toward shorter wavelengths as the curing time increases during the curing process.
The apparatus of claim 67, wherein: the plasma generation zone (104) contains argon gas when the plasma is activated.
The apparatus of claim 106, wherein: the plasma generation zone (104) contains substantially only argon gas when the plasma is activated.
The apparatus of claim 67, wherein: the apparatus comprises one or more delivery devices (144) by means of which one or more gases and/or gas mixtures are delivered to the plasma generation zone (104).
The apparatus of claim 67, wherein: the apparatus comprises a plurality of input devices (132, 132 ') for generating a plasma by inputting electromagnetic radiation into the plasma generation zone (104), wherein the input power of at least two input devices (132, 132') are different from each other.
110. The apparatus of claim 67, wherein: the device comprises a plurality of input devices (132, 132 ') for generating a plasma by inputting electromagnetic radiation into the plasma generation zone (104), wherein the structure of at least two input devices (132, 132') is different.
111. The apparatus of claim 67, wherein: at least one reflector (202) is disposed in the plasma generation region (104) to reflect electromagnetic radiation generated in the plasma.
112. The apparatus of claim 111, wherein: at least one mirror film is disposed in the plasma generation region (104) as a reflector (202).
113. The apparatus of claim 111 or 112, wherein: at least a partial region of the boundary wall of the plasma generation region (104) forms a reflector (202).
114. The apparatus of claim 111, wherein: the at least one reflector (202) comprises aluminum and/or stainless steel as a reflective material.
115. The apparatus of claim 111, wherein: the at least one reflector (202) is detachable from the plasma generation region (104).
116. The apparatus of claim 67, wherein: the apparatus includes one or more pumping devices (208) that draw gas from the plasma generation zone (104).
117. The apparatus of claim 67, wherein: the device comprises at least one pumping device (208) with at least one throttle valve (200) for changing the pressure of the plasma generation zone (104).
118. The apparatus of claim 67, wherein: the device comprises at least one partially electrically insulating holder (212), by means of which the workpiece (102) is electrically isolated from the boundary wall of the plasma generation zone (104).
119. The apparatus of claim 67, wherein: the workpiece (102) can be connected to a potential different from a boundary wall potential of the plasma generation region (104).
120. The apparatus of claim 67, wherein: the device comprises an electrically conductive holder (212), by means of which the workpiece (102) is electrically conductively connected to a boundary wall of the plasma generation region (104).
121. The apparatus of claim 67, wherein: the workpiece (102) can be connected to the same potential as the plasma generation zone (104) boundary wall.
122. The apparatus of claim 67, wherein: the workpiece (102) is connected to ground potential.
123. The apparatus of claim 67, wherein: the apparatus is configured to cure a coating (100) on a workpiece (102), the coating being curable by electromagnetic radiation including at least an ultraviolet component, or by heat, or by a combination of electromagnetic radiation including at least an ultraviolet component and heat.
124. The apparatus of claim 67, wherein: the apparatus includes means for the workpiece (102) to receive electromagnetic radiation that is not generated in the plasma before, while and/or after the plasma is generated.
125. The apparatus of claim 124, wherein: the electromagnetic radiation is microwave radiation and/or infrared radiation.
126. The apparatus of claim 67, wherein: the apparatus includes means for drying the workpiece (102) before, during and/or after the plasma is generated.
128. The apparatus of claim 67, wherein: the apparatus includes means for subjecting the workpiece (102) to a sub-atmospheric pressure prior to generating the plasma.
128. The apparatus of claim 127, wherein: the apparatus comprises means for subjecting the workpiece (102) to a pressure in the range 2000Pa to 50000Pa prior to generating the plasma.
129. The apparatus of claim 67, wherein: the apparatus includes means for exposing the workpiece (102) to a sub-atmospheric pressure prior to generating the plasma, the pressure being higher than a pressure to which the workpiece (102) is exposed while the plasma is generated.
130. The apparatus of claim 67, wherein: the apparatus includes means for generating a magnetic field in a plasma generation region (104).
131. The apparatus of claim 130, wherein: during the curing process, the strength of the magnetic field generated by the means for generating a magnetic field is varied.
132. The apparatus of claim 130 or 131, wherein: the generation of the magnetic field in the plasma generation zone (104) can lag the beginning of the curing process.
133. The apparatus of claim 130, wherein: the strength of the magnetic field generated by the magnetic field generating means varies spatially in the plasma generation region (104).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP02008255.8 | 2002-04-19 | ||
| EP02008255A EP1354640A1 (en) | 2002-04-19 | 2002-04-19 | Process and apparatus for hardening a coating |
| PCT/EP2003/004018 WO2003089155A2 (en) | 2002-04-19 | 2003-04-17 | Method and device for hardening a coating |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| HK1075224A1 HK1075224A1 (en) | 2005-12-09 |
| HK1075224B true HK1075224B (en) | 2009-12-18 |
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