CA2482325A1 - Process and apparatus for curing a radiation-curable coating, and an irradiation chamber - Google Patents
Process and apparatus for curing a radiation-curable coating, and an irradiation chamber Download PDFInfo
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- CA2482325A1 CA2482325A1 CA002482325A CA2482325A CA2482325A1 CA 2482325 A1 CA2482325 A1 CA 2482325A1 CA 002482325 A CA002482325 A CA 002482325A CA 2482325 A CA2482325 A CA 2482325A CA 2482325 A1 CA2482325 A1 CA 2482325A1
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- irradiation
- inert gas
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
- B05D3/061—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation using U.V.
- B05D3/065—After-treatment
- B05D3/066—After-treatment involving also the use of a gas
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
- B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
- B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D2252/00—Sheets
- B05D2252/04—Sheets of definite length in a continuous process
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/06—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation
- B05D3/061—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by exposure to radiation using U.V.
- B05D3/065—After-treatment
- B05D3/067—Curing or cross-linking the coating
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
- B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
- B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
- B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
- B29C2035/0827—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using UV radiation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C2791/00—Shaping characteristics in general
- B29C2791/004—Shaping under special conditions
- B29C2791/005—Using a particular environment, e.g. sterile fluids other than air
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Electromagnetism (AREA)
- Toxicology (AREA)
- Oral & Maxillofacial Surgery (AREA)
- Thermal Sciences (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
- Coating Apparatus (AREA)
Abstract
The present invention relates to a process for curing a radiation-curable coating on a substrate in an irradiation chamber (20) provided with at least one or more UV radiation sources (18). It is provided according to the invention that the substrate is guided through a closed channel that is formed by an inlet chamber (30), the irradiation chamber (20) and an outlet chamber (40) , and that an inert gas is fed into the irradiation chamber (20) in such a way that an at least slight inert gas overpressure is produced in irradiation chamber. The present invention also relates to an apparatus for carrying out this process.
Description
Process and apparatus for curing a radiation-curable coating, and an irradiation chamber Description The present invention relates to a process for curing a radiation-curable coating according to the preamble of claim 1 as well as to an apparatus for carrying out this process according to the preamble of claim 12 and to an irradiation chamber provided in such an apparatus.
Such irradiation chambers are part of an apparatus for curing radiation-curable coatings. The irradiation chamber is provided with one or more W radiation sources. It is possible thereby, in particular to treat two-dimensional or three-dimensional substrates by providing them with a radiation-curable coating that is then cured by means of W radiation.
It is known to cure radiation-curable coatings by means of high-energy W radiation, for example by using medium-pressure mercury radiators or W Excimer radiators (R. Mehnert et al., W & EB Technology and Application, SITA-Valley, London 1998). The specific electric power of these radiators is typically between 50 and 240 W per cm radiator length. For a radiator length of 1 m, the converted electric power is thus between 5 and 24 kW. These powerful radiators are used chiefly for curing coatings on planar substrates.
Typical illuminances of 100 to 1000 mW/cm2 are measured on the layer to be cured. It is possible thereby to achieve curing times of 100 ms and less . Such a system is known, for example, from DE 24 25 217 Al. A
comparable apparatus is also known, for example, from WO 96/34700 A1 and FR 2 230 831 A1.
Such irradiation chambers are part of an apparatus for curing radiation-curable coatings. The irradiation chamber is provided with one or more W radiation sources. It is possible thereby, in particular to treat two-dimensional or three-dimensional substrates by providing them with a radiation-curable coating that is then cured by means of W radiation.
It is known to cure radiation-curable coatings by means of high-energy W radiation, for example by using medium-pressure mercury radiators or W Excimer radiators (R. Mehnert et al., W & EB Technology and Application, SITA-Valley, London 1998). The specific electric power of these radiators is typically between 50 and 240 W per cm radiator length. For a radiator length of 1 m, the converted electric power is thus between 5 and 24 kW. These powerful radiators are used chiefly for curing coatings on planar substrates.
Typical illuminances of 100 to 1000 mW/cm2 are measured on the layer to be cured. It is possible thereby to achieve curing times of 100 ms and less . Such a system is known, for example, from DE 24 25 217 Al. A
comparable apparatus is also known, for example, from WO 96/34700 A1 and FR 2 230 831 A1.
It is to be borne in mind when applying medium-pressure mercury radiators that approximately 50% of the electric power is converted into heat. An arrangement 5 in which radiators of this type are situated close to one another fails not only for reasons of overheating, but also because of the high-voltage supply required at the ends (electrodes) of the radiators. Admittedly, in the case of W Excimer radiators the heat is dissipated 10 by cooling the lamp surface, but the distance between neighboring tubes and their geometric arrangement is likewise limited by the required high-voltage supply.
Because of the biological effects of W rays, extensive 15 screening measures and other protective measures are required when use is made of these W radiators. In order to cure coatings on three-dimensional objects, individual W radiators are, for example, fitted in closed spaces such that it is possible to ensure 20 adequate radiation protection. An adequate homogeneous irradiation of the coatings to be cured on three-dimensional substrates is, however, impossible in practice. The energy outlay for curing is therefore determined by the outlay for curing layer regions, that 25 can be achieved only by obliquely incident radiation or scattered radiation.
A further problem arises, in particular, with the polymerization and crosslinking of radically curing 3o compounds such as, for example, monomers and oligomers of acrylates or methacrylates. Radical polymerizations are inhibited by oxygen due to the action of oxygen as a radical interceptor. Oxygen can prevent both the initiation and the chain propagation, and also the 35 crosslinking. This takes place principally at the interface between air and coating at the region of a depth of a few Vim. Here, during the irradiation operation the consumption of oxygen that takes place in the layer owing to the reaction of radicals with oxygen 5 can be balanced by rapid rediffusion from the air. The consequence of this process is incomplete curing at the surface which leads to sticky, completely useless coatings.
10 This inhibition effect can be reduced or avoided by measures such as covering the surface to be cured with waxes or films, by using very high dosing powers (>2000 mW/cm2) during irradiation, by raising the photo initiator concentration, and by using special amines as 15 co initiators (R. Mehnert et a.: UV&EB Curing Technology, SITA-Wiley, London 1998).
The most frequently applied measure for avoiding inhibition is, however, to carry out the radiation 20 curing in an oxygen-reduced protective gas atmosphere.
The literature describes apparatuses and processes in which nitrogen (for example EP 540 884 A1) or carbon dioxide (DE 199 57 900 A1) are used as protective gas.
The reduction of the residual oxygen concentration in 25 the irradiation chamber is decisive for the avoidance of inhibition of the radiation curing by oxygen.
Inhibition of the surface of the coating is reliably avoided during radiation curing whenever the number of the initiator radicals, produced by the irradiation, 30 for polymerization and crosslinking during the entire irradiation operation clearly exceeds the number of the radicals deactivated by the reaction with oxygen.
Since the concentration of the initiator radicals in 35 the coating is directly proportional to the dosing power (in mW/cmz) of the radiation source, the upper boundary of the oxygen concentration required in the inert gas to avoid inhibition reliably is determined by the dosing power of the radiation source.
Because of the biological effects of W rays, extensive 15 screening measures and other protective measures are required when use is made of these W radiators. In order to cure coatings on three-dimensional objects, individual W radiators are, for example, fitted in closed spaces such that it is possible to ensure 20 adequate radiation protection. An adequate homogeneous irradiation of the coatings to be cured on three-dimensional substrates is, however, impossible in practice. The energy outlay for curing is therefore determined by the outlay for curing layer regions, that 25 can be achieved only by obliquely incident radiation or scattered radiation.
A further problem arises, in particular, with the polymerization and crosslinking of radically curing 3o compounds such as, for example, monomers and oligomers of acrylates or methacrylates. Radical polymerizations are inhibited by oxygen due to the action of oxygen as a radical interceptor. Oxygen can prevent both the initiation and the chain propagation, and also the 35 crosslinking. This takes place principally at the interface between air and coating at the region of a depth of a few Vim. Here, during the irradiation operation the consumption of oxygen that takes place in the layer owing to the reaction of radicals with oxygen 5 can be balanced by rapid rediffusion from the air. The consequence of this process is incomplete curing at the surface which leads to sticky, completely useless coatings.
10 This inhibition effect can be reduced or avoided by measures such as covering the surface to be cured with waxes or films, by using very high dosing powers (>2000 mW/cm2) during irradiation, by raising the photo initiator concentration, and by using special amines as 15 co initiators (R. Mehnert et a.: UV&EB Curing Technology, SITA-Wiley, London 1998).
The most frequently applied measure for avoiding inhibition is, however, to carry out the radiation 20 curing in an oxygen-reduced protective gas atmosphere.
The literature describes apparatuses and processes in which nitrogen (for example EP 540 884 A1) or carbon dioxide (DE 199 57 900 A1) are used as protective gas.
The reduction of the residual oxygen concentration in 25 the irradiation chamber is decisive for the avoidance of inhibition of the radiation curing by oxygen.
Inhibition of the surface of the coating is reliably avoided during radiation curing whenever the number of the initiator radicals, produced by the irradiation, 30 for polymerization and crosslinking during the entire irradiation operation clearly exceeds the number of the radicals deactivated by the reaction with oxygen.
Since the concentration of the initiator radicals in 35 the coating is directly proportional to the dosing power (in mW/cmz) of the radiation source, the upper boundary of the oxygen concentration required in the inert gas to avoid inhibition reliably is determined by the dosing power of the radiation source.
German patent application DE 102 42 719.4 discloses an apparatus in the case of which a plurality of W
radiation sources are arranged close to one another and S interconnected to form one or more irradiation modules, the illuminance inside an irradiation module and/or between at least two irradiation modules being spatially variable. This apparatus is therefore built up from geometrically suitable arrangements of a 10 plurality of radiation sources situated close to one another. Each of these arrangements is denoted as an irradiation module. Thus, an irradiation module is understood here as a planar arrangement of radiation sources arranged close next to one another (for example 15 with a common electric supply) . The enveloping surface of the radiation sources of each module can be flat or curved. It is possible to construct irradiation modules that focus light into a selected, including curved, irradiation plane, and which permit the substrate 20 surfaces to be irradiated in a geometrically largely homogeneous fashion.
The construction is therefore performed in such a way that a spatially variable illuminance is set up in the 25 interior of the irradiation chamber, in which the radiation-curable coatings are cured, such that the coating to be cured is cured homogeneously without there being a disturbing input of heat into the coating and/or substrate. The variation can be performed, on 30 the one hand, by setting the enveloping surfaces of the radiation sources of a single module and, on the other hand, by the spatial arrangement of the irradiation modules relative to one another in the apparatus, it being possible to realize a multiplicity of geometric 35 arrangements. Owing to the modular construction, the apparatus can thus be adapted to the geometry of the substrate to be treated such that the energy outlay is reduced. The radiation modules can therefore have fluorescent tubes with a specific electric power of, for example, 1 W/cm. The dosing power of these irradiation units is therefore only between 10 and 100 mW/cmz. This also has the consequence that biological radiation protection is simplified, that is to say may be limited, for example to measures which apply to the use of tanning lamps.
In order, however, to be able to use the advantages, named in this patent application, of these irradiation modules for radiation curing of coatings such as, for example, reduced energy outlay for curing, low thermal input into the substrate and the coating, as well as simple radiation protection, it is necessary to provide apparatuses that produce a residual oxygen concentration of preferably below 500 ppm in the corresponding irradiation chamber during the irradiation operation.
This concentration is also to be maintained during the continuous passage of substrates to be coated, which are fed at short spaces over lengthy times by means of a conveyor unit. However, during continuous conveyance of the substrates air is continuously entrained into the inert gas by turbulence. The tolerable oxygen concentration in the inert gas can thereby be exceeded rapidly.
It is therefore the object of the present invention to provide an apparatus that permits an adequate inertization of irradiation chambers which are, for example, equipped - although not necessarily - with fluorescent tube modules even if coated substrates are continuously conveyed through the irradiation chamber at short spaces.
radiation sources are arranged close to one another and S interconnected to form one or more irradiation modules, the illuminance inside an irradiation module and/or between at least two irradiation modules being spatially variable. This apparatus is therefore built up from geometrically suitable arrangements of a 10 plurality of radiation sources situated close to one another. Each of these arrangements is denoted as an irradiation module. Thus, an irradiation module is understood here as a planar arrangement of radiation sources arranged close next to one another (for example 15 with a common electric supply) . The enveloping surface of the radiation sources of each module can be flat or curved. It is possible to construct irradiation modules that focus light into a selected, including curved, irradiation plane, and which permit the substrate 20 surfaces to be irradiated in a geometrically largely homogeneous fashion.
The construction is therefore performed in such a way that a spatially variable illuminance is set up in the 25 interior of the irradiation chamber, in which the radiation-curable coatings are cured, such that the coating to be cured is cured homogeneously without there being a disturbing input of heat into the coating and/or substrate. The variation can be performed, on 30 the one hand, by setting the enveloping surfaces of the radiation sources of a single module and, on the other hand, by the spatial arrangement of the irradiation modules relative to one another in the apparatus, it being possible to realize a multiplicity of geometric 35 arrangements. Owing to the modular construction, the apparatus can thus be adapted to the geometry of the substrate to be treated such that the energy outlay is reduced. The radiation modules can therefore have fluorescent tubes with a specific electric power of, for example, 1 W/cm. The dosing power of these irradiation units is therefore only between 10 and 100 mW/cmz. This also has the consequence that biological radiation protection is simplified, that is to say may be limited, for example to measures which apply to the use of tanning lamps.
In order, however, to be able to use the advantages, named in this patent application, of these irradiation modules for radiation curing of coatings such as, for example, reduced energy outlay for curing, low thermal input into the substrate and the coating, as well as simple radiation protection, it is necessary to provide apparatuses that produce a residual oxygen concentration of preferably below 500 ppm in the corresponding irradiation chamber during the irradiation operation.
This concentration is also to be maintained during the continuous passage of substrates to be coated, which are fed at short spaces over lengthy times by means of a conveyor unit. However, during continuous conveyance of the substrates air is continuously entrained into the inert gas by turbulence. The tolerable oxygen concentration in the inert gas can thereby be exceeded rapidly.
It is therefore the object of the present invention to provide an apparatus that permits an adequate inertization of irradiation chambers which are, for example, equipped - although not necessarily - with fluorescent tube modules even if coated substrates are continuously conveyed through the irradiation chamber at short spaces.
The solution consists of a method having the features of claim 1, and of an apparatus having the features of claim 12, and of an irradiation chamber having the features of claim 8.
Thus, it is provided according to the invention that the substrate is guided through a closed channel that is formed by an inlet chamber, the irradiation chamber and an outlet chamber, and that an inert gas is fed 10 into the irradiation chamber in such a way that an at least slight inert gas overpressure is produced in the irradiation chamber.
The apparatus according to the invention is distinguished in that the irradiation chamber is assigned an inlet chamber and an outlet chamber, the irradiation chamber, inlet chamber and outlet chamber forming a closed channel, and wherein the irradiation chamber has an apparatus for feeding in inert gas which 20 produces an at least slight inert gas overpressure in the irradiation chamber.
The subject matter of the present invention is also an irradiation chamber having a frame inside which an 25 irradiation space is arranged whose walls are transparent to W light and in which an apparatus for feeding in inert gas is provided.
The apparatus for feeding in inert gas serves for 30 filling the volume of the chambers with inert gas by displacing air. The substrates can pass continuously in this case through the irradiation chamber at short spaces. The low concentration of residual oxygen required for radiation curing is achieved by 35 continuously feeding inert gas into the irradiation chamber such that an inert gas volumetric flow is produced in the direction of the inlet chamber and/or of the outlet chamber. The inert gas must be fed in such that the required minimum oxygen concentration in _ 7 _ the irradiation chamber is maintained during the process of conveying the substrates_ No undesired suction of air may be allowed to happen. For this purpose, an at least slight overpressure is set up in 5 the irradiation chamber by appropriately feeding in inert gas. The effect of this is that the inert gas flows out continuously in the direction of the inlet chamber and of the outlet chamber. The outflowing inert gas therefore removes from the closed channel the atmospheric oxygen entrained by the conveyance of a substrate.
Advantageous developments follow from the subclaims.
15 It is possible for the irradiation chamber to be composed of a plurality of elements interconnected in an airtight fashion, that is to say to be of modular configuration. The apparatus according to the invention can therefore be designed for different capacities. If 20 the capacity is to be increased, the transit time of a substrate through the irradiation chamber is usually shortened in conjunction with a given length of the irradiation chamber with increasing quantity of the substrate to be coated. In order then to ensure the 25 required irradiation time for curing the substrate surfaces, it is possible to use a longer irradiation chamber with additional W light sources. By contrast, it is advantageous to lengthen a modularly configured irradiation chamber by one or more elements with W
30 light sources. This allows an improved flexibility for the apparatus according to the invention with regard to its capacity and permits a particularly economical operation.
35 The same holds mutatis mutandis for the inlet chamber and the outlet chamber.
A particularly preferred development provides that inert gas is also fed either into the inlet chamber or _ g _ into the outlet chamber, or into both in such a way that an inert gas pressure is produced that is lower than the inert gas pressure in the irradiation chamber.
The inflow of oxygen during the conveying operation of the substrates is thereby additionally impeded.
Furthermore, the inert gas in the irradiation chamber can be fed in as a volumetric flow running in the conveying direction, and maintained. The orientation in the conveying direction effects an additional orientation of the inert gas in the direction of the inlet or outlet chamber, in order to impede the entrance of oxygen into the irradiation chamber.
In this case, the inert gas is preferably fed into the irradiation chamber via an arrangement of one or more tubes that are arranged parallel to the conveying direction of the substrate and have outlet openings which can, for example, be configured such that the inert gas can flow out essentially with a low level of turbulence. This is achieved, for example, by suitable rows of nozzles and/or bores that are narrow and/or arranged close to one another. Instead of tubes, however, it is also possible, for example, to use plates made from a porous material, such as sintered plates, for example. The porous material is intended to be permeable to the inert gas and preferably to have small pores situated close to one another so that the inert gas can flow out essentially without turbulence.
Another development provides also that the inlet chamber or the outlet chamber, preferably however every chamber has a dedicated apparatus for feeding in inert gas. The flow rate of the feeding of inert gas is advantageously set such that the inert gas pressure is highest in the irradiation chamber. This ensures that the inert gas flows continuously in the direction of the inlet chamber and outlet chamber, that is to say in the direction of both outlets of the closed channel.
_ g _ The volumetric inertization thus implemented can be supplemented by feeding inert gas into the inlet chamber and/or outlet chamber, the inert gas flow thereof being overlaid at the side on the volumetric flow running in the conveying direction. Consequently, further apparatuses for feeding in inert gas can be fitted on the walls of the inlet chamber and/or outlet chamber perpendicular to the conveying direction of the substrate. The flow rate of the inert gas, here flowing out perpendicular to the conveying direction, is preferably set such that an inert gas flow that removes entrained air and displaces it into the outgoing volumetric flow is applied to the substrate (which is being let in or out) obliquely to the conveying direction. In the outlet chamber, this way of feeding in inert gas advantageously additionally prevents air from being back-mixed into the irradiation chamber.
Use is made in general of inert gas volumetric flows of 15 to 1000 Nm3/h, preferably between 30 and 400 Nm3/h.
The flow rate of the inert gas volumetric flow fed in perpendicular to the conveying direction is preferably approximately 10 to 80% by volume of the entire inert gas volumetric flow, preferably 15 to 60% by volume of the volumetric flow. In a closed channel with a cross section of 500 x 500 mm, for example, the flow rate for the volumetric flow can typically be 200 Nm3/h, while the flow rate of the inert gas fed in perpendicular to the conveying direction is preferably approximately 25-50% by volume of the volumetric flow.
In order to keep the consumption of inert gas as low as possible, it is not only possible to adapt the cross section of the closed channel to the cross section of the substrate to be coated, but the inlet and outlet of the closed channel can be sealed, for example via fitted plates, baffles or doors to such an extent that the substrate can pass and yet inert gas can still flow out with a low level of turbulence.
As radiation sources, consideration is given to lamps, preferably fluorescent tubes, of low electric power, for example from 0,1 to 10 W per cm radiator length, which have, for example, a continuous emission spectrum between 200 and 450 nm, preferably between 300 and 450 nm. Since the development of heat is lower than in the case of high-power UV radiators, it is sufficient to cool merely the surface thereof, for example with the aid of an air current.
Such lamps are known per se and are used, for example, as tanning lamps in solaria. With a specific power of, for example, 1 W per cm radiator length and the low illuminance resulting therefrom, these lamps are not suitable as such in and of themselves for technical applications for curing radiation-curable coatings.
Such lamps, which are typically provided with reflectors with emission angles of, for example, approximately 160°, generally have standardized dimensions (diameter of the tubes approximately 25 to 45 cm, luminance length up to approximately 200 cm) and are operated at an operating voltage of 220 V, are very well suited as radiation sources for the irradiation modules mentioned. This relates, in particular, to the reflectors that simplify focusing into the desired irradiation plane. Also advantageous is their high photon yield of approximately 30% of the electric power.
At a distance of, for example, 10 cm from the radiation source, irradiation modules of this design yield illuminances of typically approximately 20 mW/cm2.
Admittedly, these illuminances are smaller by a factor of to 50 than those that can be achieved with conventional W radiators, but they suffice to cure coatings given radiation times of approximately 30 to 300 s.
A further advantageous development consists in that at least one irradiation module is arranged in the apparatus in a fashion capable of movement about at least one of its three spatial axes. This facilitates the geometric adaptation to the substrate and the focusing of the rays in the desired radiation plane.
In order to improve the adhesion of radiation-cured coatings on some substrates such as, for example, 15 polypropylene, polycarbonate and polyamide, it is advantageous also to vary the illuminance temporally.
If the irradiation is begun with a low illuminance, for example, the layer, which always shrinks during curing, can relax more effectively than in the case of immediate 20 irradiation with a high illuminance. Stresses between the layer to be cured and the substrate can be balanced out more effectively. The consequence is a better adhesion of the cured layer on the substrate. A temporal control of the power of the individual irradiation modules is 25 possible in a simple way, and so it is possible to exploit this advantageous irradiation regime.
Exemplary embodiments of the present invention are explained in more detail below with the aid of the 30 attached drawings, in which:
figure la shows a schematic illustration, not true to scale, of an embodiment of the irradiation module according to the invention in the view 35 from below;
figure lb shows the irradiation module from figure la in a side view in accordance with arrow B;
5 figure lc shows the irradiation module from figure la in a side view in accordance with arrow C;
figure 2 shows a section along the line II - II in figure la;
figure 3 shows a schematic side view, not true to scale, of an exemplary embodiment of the apparatus according to the invention for discontinuous irradiation;
figure 4 shows a schematic side view, not true to scale, of an exemplary embodiment of the apparatus according to the invention for continuous irradiation;
figure 5 shows a longitudinal section through an exemplary embodiment of an apparatus according to the invention in a schematic illustration, not true to scale;
figure 6 shows a longitudinal section through an irradiation chamber of an apparatus according to the invention;
30 figure 7 shows a section along the line vII-VII in figure 6; and figure 8 shows a longitudinal section through an inlet or outlet chamber in an illustration as in 35 figure 7.
The first step is to describe the structure of an irradiation module 10 by way of example with the aid of the exemplary embodiment illustrated in figures la, b, c and 2. The components are mounted on a baseplate 11.
The baseplate 11 preferably consists of a metal such as aluminum or steel, or of a metal alloy, and has on its rear side the required electric terminals 13 and, if appropriate, a holder 12. Furthermore, devices can be provided there for installing the irradiation module 10 in irradiation systems and devices for moving the irradiation module 10. Also mounted on the baseplate are the starters and terminals for W radiation sources 18. Inlet and outlet for a ventilation system 16 of the radiation sources 18 are also located here. Cross-flow fans, for example, are suitable for this purpose Also provided on the front side of the baseplate 11 is a frame 14 inside which the ventilation system 16 and the W radiation sources 18 are installed. Suitable W
radiation sources 18 are, for example, fluorescent tubes such as are used as tanning lamps in solaria.
Such fluorescent tubes generally have standardized dimensions, for example a luminance length of 2 m in conjunction with a diameter of 25 to 45 cm. They can, furthermore, be provided with reflectors that have an emission angle of approximately 160°, for example.
These fluorescent tubes are operated at an operating voltage of 220 V.
The frame 14 with the ventilation system 16 and the W
radiation sources 18 is surrounded on three sides in an airtight fashion by a W-transparent plate 15, for example made from plastic, such as, for example, polymethyl methacrylate or polycarbonate. The surface of the plate 15 forms the front side of the irradiation module 10, as illustrated by the arrow A symbolizing the direction of radiation.
5 One or more irradiation modules 10 are installed in a sealed irradiation vessel. The irradiation vessel surrounds an irradiation chamber that is illuminated by at least one irradiation module.
Figure 3 shows schematically an exemplary embodiment of 10 an apparatus 20 for discontinuous irradiation of substrates. A rectangular container, provided with supporting feet 21, of length 2.10 m, width 80 cm and height 80 cm was equipped with four irradiation modules 10 of length 1.50 m and equipped with 10 fluorescent 15 tubes 18 arranged in a planar fashion. The irradiation modules 10 were fastened to the frame of the container on the base, the sides and the cover. The upper irradiation module can be raised with the cover of the container. The fluorescent tubes 18 in the irradiation 20 modules 10 were cooled by means of cross-flow fans.
The upper sides of the plates 15 of the irradiation modules define and surround a rectangular irradiation space 22 of length 1.60 m, width 60 cm and height 25 40 cm. Furthermore, four laterally arranged tubes 23 each having 40 bores for letting in nitrogen are located in the irradiation space 22.
Such a device 20 can be operated as follows. The coated 30 substrates are introduced into the irradiation space 22. Thereafter, the irradiation space 22 is flooded with inert gas. When an oxygen concentration of 5%, preferably 1%, with particular preference 0.1%, is reached, the irradiation is started, and it is 35 terminated after curing of the layer. The duration of the irradiation is typically approximately 30 to 300 s.
In this embodiment, the apparatus according to the invention is particularly suitable for curing coatings on substrates. It renders possible the application of radiation curing, for example in the handicraft sector for production and repair. The moderate electric supply power of the modules, which is typically 1 to 2 kW, is advantageous in this case.
In a test, a motor vehicle wheel rim as substrate was coated on all sides with a radiation-curing spray lacquer. The wheel rim was provided with a holder at the valve hole and suspended in the irradiation space 22. After closure of the irradiation space 22, the latter was flooded with nitrogen. The concentration of the oxygen was measured with the aid of a sensor in the irradiation space 22, and displayed. An oxygen concentration of below 0.1% was achieved after flooding for 2 minutes given a nitrogen current of 60 m3/h. Once this value was reached, the nitrogen current was reduced to 10 m3/h and irradiation was started. After an irradiation time of 2 minutes, the nitrogen was switched off and the apparatus 20 was opened. The lacquer on the wheel rim was cured at all points and could also not be damaged by manual pressure.
However, the irradiation modules 10 described can also be used to construct an irradiation tunnel 30 as it is illustrated diagrammatically in figure 4. In such an irradiation tunnel 30, the irradiation modules 10 are arranged on the sides and on the top side such that they define and surround a tunnel-shaped irradiation chamber 32. Coated substrates passing through via conveying appliances, for example, can be cured therein during the transit. If, for example, two irradiation modules are arranged in a row, the luminance length of the irradiation chamber 32 can be up to 4 m. If the curing is performed within approximately 30 to 300 s, transit speeds of 0.8 to 8 m/min are possible. It is to 5 be borne in mind in this case that the residual oxygen concentration should be sufficiently low during the transit and the irradiation. The atmospheric oxygen introduced into the irradiation zone by the movement of the molded part to be irradiated should not exceed the 10 limiting value of 5%. Consequently, locks and/or suitable nozzles are advantageously provided, chiefly upstream of the irradiation zone, as seen in the conveying direction, for the purpose of feeding in inert gas, preferably nitrogen, which prevents the 15 entrainment of air.
In a continuation of this exemplary embodiment, the subject matter of the present invention will be explained below with the aid of figures 5 to 8.
Figure 5 shows schematically an exemplary embodiment of an apparatus 40 according to the invention. This apparatus comprises an irradiation chamber 50 that is assigned an inlet chamber 60 and an outlet chamber 70.
25 The substrate to be coated is transported in a direction of the arrow A by means of a conveying device, for example a conveyor belt, firstly through the inlet chamber 60, then through the irradiation chamber 50 and, finally, through the outlet chamber 70.
30 The actual curing of the coating of the substrate by W
rays takes place in the irradiation chamber 50. The inlet chamber 60, the irradiation chamber 50 and the outlet chamber 70 form a channel closed to the outside.
The inlet and the outlet of the closed channel, that is 35 to say the end of the inlet chamber 60 and of the outlet chamber 70 averted in each case from the irradiation chamber 50, can be sealed, for example, via fitted flaps, doors or plates to such an extent that the substrate can pass. It is thereby possible for less inert gas to emerge to the outside, and so the consumption of inert gas is reduced.
Figures 6 and 7 show schematically the structure of the irradiation chamber 50. Just like the inlet chamber 60 and/or the outlet chamber 70, the irradiation chamber 50 can also be of modular configuration, that is to say be composed of two or more elements that are preferably of the same design, are interconnected in an airtight fashion and form a closed channel. Proceeding from figure 4, the frame of the irradiation chamber 50 is now denoted by 51. Fitted inside the frame 51 is a second frame 52 that is constructed, for example, from plates that are preferably sealed from one another in an airtight fashion and are transparent to W light. W
radiators 53 are arranged between the frames 51 and 52.
These radiators can, but need not necessarily, consist of the irradiation modules described. The frame 52 stands, for example, inside the frame 51 on stilts 52' that are reinforced with cross-struts 52 " .
The frame 52 surrounds an irradiation space 54. The substrate is conveyed through the irradiation space 54 by means of a conveying device, for example by means of a conveyor belt. In this process, the substrate is firstly transported at the start of the apparatus 40 into the inlet chamber 60, and it moves further through the irradiation chamber 50 and the outlet chamber 70 until it leaves the apparatus 40 at the end of the outlet chamber 70. Fitted inside the irradiation space 54 is an apparatus 55 for feeding in inert gas, for example nitrogen or carbon dioxide. This apparatus 55 has, for example, two tubes 56a, 56b running along the inner longitudinal sides of the irradiation space 54.
Of course, it is also possible for a plurality of such tubes to be arranged under or next to one another, or to be combined otherwise with one another in any desired way, for example whenever the irradiation space has particularly long or high dimensions. Those tube sections that run parallel to the conveying direction (arrow A) of the substrate have outflow openings 57, situated close to one another, for an inert gas, for example nitrogen or carbon dioxide. The outlet openings can be configured, for example, as nozzles or bores.
Provided on the underside of the tubes 56a, 56b, outside the irradiation space 54 but inside the irradiation chamber 50 are valves 58 for controlling manually or electronically the volumetric flow of the inert gas fed through them.
Instead of tubes with outflow openings, it is also possible to use porous materials, for example, the inert gas entering the irradiation space 54 through the pores. It would also be conceivable, for example, for the inner walls of the irradiation space 54 to be partially clad with plates made from porous material, for example sintered material, ceramic, etc, and for the inert gas to be introduced into the interspace between the irradiation space 54 and the plates.
Particularly suitable are porous materials in which the pores are small and arranged regularly close to one another. The effect of this is that the inert gas flows out essentially without turbulence.
One or more apparatuses 55 of identical design can also be provided in the inlet chamber 60 or in the outlet chamber 70, or in both chambers, in order to further reduce the entrance of air into the closed channel during the entrance and/or exit of the substrate.
Instead of this, or in addition, it is also possible to provide an apparatus 65 such as is illustrated in figure 8 with reference to the example of an inlet chamber 60, the following statements being valid correspondingly for the outlet chamber 70. The inlet chamber 60 (or the outlet chamber 70) also has a frame 61 inside which there is fitted a second frame 62 that surrounds a conveying space 63. This frame 62 can be made from any desired material; all that is important is for it to be configured such that the conveying space 64 of the inlet chamber 60 (or the outlet chamber 70) and the irradiation space 54 of the irradiation chamber can be combined to form a closed channel. The frame 62 stands, for example, inside the frame 61 on stilts 62' that are reinforced with cross-struts 62 " .
The substrate is conveyed by means of a conveying device through the conveying space 64 and the irradiation space 54, for example by means of a conveyor belt. In the process, the substrate is firstly transported at the start of the apparatus 40 into the conveying space 64 of the inlet chamber 60, and it moves further through the irradiation space 54 of the irradiation chamber 50 and the conveying space of the outlet chamber 70 until it leaves the apparatus 40 at the end of the outlet chamber 70. Fitted inside the conveying space 64 is either an apparatus 55 for feeding in inert gas, for example nitrogen or carbon dioxide, as has already been described with reference to the example of the irradiation space 54. Instead of or in addition to this, an apparatus 65 for feeding in inert gas can be provided. This apparatus 65 has a tube 66 running along the cross section of the conveying space 64. Of course, it is also possible for a plurality of such tubes to be arranged next to one another or otherwise combined with one another in any desired way, for example whenever the conveying space 64 has particularly long or high dimensions. The tube 64 has outflow openings 67 situated close to one another for an inert gas, for example nitrogen or carbon dioxide. The outflow openings 67 can be configured, for example, as nozzles or bores. Provided on the underside of the tube 66, outside the conveying space 64 but inside the inlet chamber 60 are valves 68 for manually or electronically controlling the volumetric flow of the inert gas fed through them.
Instead of tubes with outflow openings, it is also possible to use porous materials, for example, the inert gas entering the conveying space 64 through the pores. It would also be conceivable, for example, for the inner walls of the conveying space 64 to be wholly or partially clad with plates made from porous material, for example sintered material, ceramic, etc, and for the inert gas to be introduced into the interspace between the conveying space 64 and the plates. Particularly suitable are porous materials in which the pores are small and arranged regularly close to one another. The effect of this is that the inert gas flows out essentially without turbulence.
The apparatus 40 according to the invention operates as follows:
The substrates transit the closed channel individually or continuously. The low concentration of residual oxygen required for radiation curing is achieved by continuously feeding inert gas into the irradiation space 54 of the irradiation chamber 50, the inert gas flowing out of the tubes 56, 66 essentially with a low level of turbulence. This produces an inert gas 5 volumetric flow in the direction of the conveying space 64 of the inlet chamber 60 or the outlet chamber 70.
For this purpose, an at least slight overpressure is set in the irradiation space 54 by appropriately feeding in inert gas. The effect of this is that the inert gas flows out continuously in the direction of the conveying spaces 64. In addition, the inert gas is fed into the irradiation space 54 as a volumetric flow running in the conveying direction, and maintained. The orientation in the conveying direction effects an 15 additional orientation of the inert gas in the direction of the conveying spaces 64 in order to impede the entrance of atmospheric oxygen into the irradiation space . The inert gas f lowing out thus removes f rom the closed channel the atmospheric oxygen entrained by the conveyance of the substrate.
Apparatuses 65 for feeding in inert gas are additionally provided in the exemplary embodiment, both in the conveying space 64 of the inlet chamber 60 and 25 in the conveying space of the outlet chamber 70. The inert gas pressure in the conveying spaces is, for example, set such that it is lower than the inert gas pressure in the irradiation space 54. In this way, the inert gas flow from the irradiation space 54 is 30 maintained in the direction of the conveying spaces 64, but the inlet and outlet of the closed channel are additionally shielded against the penetration of atmospheric oxygen.
In the exemplary embodiment, the apparatuses 65 for feeding inert gas into the conveying spaces 64 from the inlet chamber 60 and outlet chamber 70 are designed such that their inert gas flow is overlaid at the side 5 on the volumetric flow running in the conveying direction. This is achieved by virtue of the fact that the tubes 66 are arranged with their outflow openings 67 perpendicular to the conveying direction of the substrate. Furthermore, in the exemplary embodiment the 10 outflow openings are set such that an inert gas flow that removes entrained air and displaces it into the outgoing volumetric flow is applied to the substrate (which is being let in or out) obliquely to the conveying direction. In the conveying chamber of the 15 outlet chamber 70, this way of feeding in inert gas advantageously additionally prevents air from being back-mixed into the irradiation space 54 of the irradiation chamber 50.
20 Use is made in general of inert gas volumetric flows of 15 to 1000 Nm3/h, preferably between 30 and 400 Nm3/h.
The f low rate of the inert gas volumetric f low fed in perpendicular to the conveying direction is preferably approximately 10 to 80% by volume of the entire inert 25 gas volumetric flow, preferably 15 to 60% by volume of the volumetric flow. In a closed channel with a cross section of 500 x 500 mm, for example, the flow rate for the volumetric flow can typically be 200 Nm'/h, while the flow rate of the inert gas fed in perpendicular to 30 the conveying direction is preferably approximately 25-50% by volume of the volumetric flow.
Thus, it is provided according to the invention that the substrate is guided through a closed channel that is formed by an inlet chamber, the irradiation chamber and an outlet chamber, and that an inert gas is fed 10 into the irradiation chamber in such a way that an at least slight inert gas overpressure is produced in the irradiation chamber.
The apparatus according to the invention is distinguished in that the irradiation chamber is assigned an inlet chamber and an outlet chamber, the irradiation chamber, inlet chamber and outlet chamber forming a closed channel, and wherein the irradiation chamber has an apparatus for feeding in inert gas which 20 produces an at least slight inert gas overpressure in the irradiation chamber.
The subject matter of the present invention is also an irradiation chamber having a frame inside which an 25 irradiation space is arranged whose walls are transparent to W light and in which an apparatus for feeding in inert gas is provided.
The apparatus for feeding in inert gas serves for 30 filling the volume of the chambers with inert gas by displacing air. The substrates can pass continuously in this case through the irradiation chamber at short spaces. The low concentration of residual oxygen required for radiation curing is achieved by 35 continuously feeding inert gas into the irradiation chamber such that an inert gas volumetric flow is produced in the direction of the inlet chamber and/or of the outlet chamber. The inert gas must be fed in such that the required minimum oxygen concentration in _ 7 _ the irradiation chamber is maintained during the process of conveying the substrates_ No undesired suction of air may be allowed to happen. For this purpose, an at least slight overpressure is set up in 5 the irradiation chamber by appropriately feeding in inert gas. The effect of this is that the inert gas flows out continuously in the direction of the inlet chamber and of the outlet chamber. The outflowing inert gas therefore removes from the closed channel the atmospheric oxygen entrained by the conveyance of a substrate.
Advantageous developments follow from the subclaims.
15 It is possible for the irradiation chamber to be composed of a plurality of elements interconnected in an airtight fashion, that is to say to be of modular configuration. The apparatus according to the invention can therefore be designed for different capacities. If 20 the capacity is to be increased, the transit time of a substrate through the irradiation chamber is usually shortened in conjunction with a given length of the irradiation chamber with increasing quantity of the substrate to be coated. In order then to ensure the 25 required irradiation time for curing the substrate surfaces, it is possible to use a longer irradiation chamber with additional W light sources. By contrast, it is advantageous to lengthen a modularly configured irradiation chamber by one or more elements with W
30 light sources. This allows an improved flexibility for the apparatus according to the invention with regard to its capacity and permits a particularly economical operation.
35 The same holds mutatis mutandis for the inlet chamber and the outlet chamber.
A particularly preferred development provides that inert gas is also fed either into the inlet chamber or _ g _ into the outlet chamber, or into both in such a way that an inert gas pressure is produced that is lower than the inert gas pressure in the irradiation chamber.
The inflow of oxygen during the conveying operation of the substrates is thereby additionally impeded.
Furthermore, the inert gas in the irradiation chamber can be fed in as a volumetric flow running in the conveying direction, and maintained. The orientation in the conveying direction effects an additional orientation of the inert gas in the direction of the inlet or outlet chamber, in order to impede the entrance of oxygen into the irradiation chamber.
In this case, the inert gas is preferably fed into the irradiation chamber via an arrangement of one or more tubes that are arranged parallel to the conveying direction of the substrate and have outlet openings which can, for example, be configured such that the inert gas can flow out essentially with a low level of turbulence. This is achieved, for example, by suitable rows of nozzles and/or bores that are narrow and/or arranged close to one another. Instead of tubes, however, it is also possible, for example, to use plates made from a porous material, such as sintered plates, for example. The porous material is intended to be permeable to the inert gas and preferably to have small pores situated close to one another so that the inert gas can flow out essentially without turbulence.
Another development provides also that the inlet chamber or the outlet chamber, preferably however every chamber has a dedicated apparatus for feeding in inert gas. The flow rate of the feeding of inert gas is advantageously set such that the inert gas pressure is highest in the irradiation chamber. This ensures that the inert gas flows continuously in the direction of the inlet chamber and outlet chamber, that is to say in the direction of both outlets of the closed channel.
_ g _ The volumetric inertization thus implemented can be supplemented by feeding inert gas into the inlet chamber and/or outlet chamber, the inert gas flow thereof being overlaid at the side on the volumetric flow running in the conveying direction. Consequently, further apparatuses for feeding in inert gas can be fitted on the walls of the inlet chamber and/or outlet chamber perpendicular to the conveying direction of the substrate. The flow rate of the inert gas, here flowing out perpendicular to the conveying direction, is preferably set such that an inert gas flow that removes entrained air and displaces it into the outgoing volumetric flow is applied to the substrate (which is being let in or out) obliquely to the conveying direction. In the outlet chamber, this way of feeding in inert gas advantageously additionally prevents air from being back-mixed into the irradiation chamber.
Use is made in general of inert gas volumetric flows of 15 to 1000 Nm3/h, preferably between 30 and 400 Nm3/h.
The flow rate of the inert gas volumetric flow fed in perpendicular to the conveying direction is preferably approximately 10 to 80% by volume of the entire inert gas volumetric flow, preferably 15 to 60% by volume of the volumetric flow. In a closed channel with a cross section of 500 x 500 mm, for example, the flow rate for the volumetric flow can typically be 200 Nm3/h, while the flow rate of the inert gas fed in perpendicular to the conveying direction is preferably approximately 25-50% by volume of the volumetric flow.
In order to keep the consumption of inert gas as low as possible, it is not only possible to adapt the cross section of the closed channel to the cross section of the substrate to be coated, but the inlet and outlet of the closed channel can be sealed, for example via fitted plates, baffles or doors to such an extent that the substrate can pass and yet inert gas can still flow out with a low level of turbulence.
As radiation sources, consideration is given to lamps, preferably fluorescent tubes, of low electric power, for example from 0,1 to 10 W per cm radiator length, which have, for example, a continuous emission spectrum between 200 and 450 nm, preferably between 300 and 450 nm. Since the development of heat is lower than in the case of high-power UV radiators, it is sufficient to cool merely the surface thereof, for example with the aid of an air current.
Such lamps are known per se and are used, for example, as tanning lamps in solaria. With a specific power of, for example, 1 W per cm radiator length and the low illuminance resulting therefrom, these lamps are not suitable as such in and of themselves for technical applications for curing radiation-curable coatings.
Such lamps, which are typically provided with reflectors with emission angles of, for example, approximately 160°, generally have standardized dimensions (diameter of the tubes approximately 25 to 45 cm, luminance length up to approximately 200 cm) and are operated at an operating voltage of 220 V, are very well suited as radiation sources for the irradiation modules mentioned. This relates, in particular, to the reflectors that simplify focusing into the desired irradiation plane. Also advantageous is their high photon yield of approximately 30% of the electric power.
At a distance of, for example, 10 cm from the radiation source, irradiation modules of this design yield illuminances of typically approximately 20 mW/cm2.
Admittedly, these illuminances are smaller by a factor of to 50 than those that can be achieved with conventional W radiators, but they suffice to cure coatings given radiation times of approximately 30 to 300 s.
A further advantageous development consists in that at least one irradiation module is arranged in the apparatus in a fashion capable of movement about at least one of its three spatial axes. This facilitates the geometric adaptation to the substrate and the focusing of the rays in the desired radiation plane.
In order to improve the adhesion of radiation-cured coatings on some substrates such as, for example, 15 polypropylene, polycarbonate and polyamide, it is advantageous also to vary the illuminance temporally.
If the irradiation is begun with a low illuminance, for example, the layer, which always shrinks during curing, can relax more effectively than in the case of immediate 20 irradiation with a high illuminance. Stresses between the layer to be cured and the substrate can be balanced out more effectively. The consequence is a better adhesion of the cured layer on the substrate. A temporal control of the power of the individual irradiation modules is 25 possible in a simple way, and so it is possible to exploit this advantageous irradiation regime.
Exemplary embodiments of the present invention are explained in more detail below with the aid of the 30 attached drawings, in which:
figure la shows a schematic illustration, not true to scale, of an embodiment of the irradiation module according to the invention in the view 35 from below;
figure lb shows the irradiation module from figure la in a side view in accordance with arrow B;
5 figure lc shows the irradiation module from figure la in a side view in accordance with arrow C;
figure 2 shows a section along the line II - II in figure la;
figure 3 shows a schematic side view, not true to scale, of an exemplary embodiment of the apparatus according to the invention for discontinuous irradiation;
figure 4 shows a schematic side view, not true to scale, of an exemplary embodiment of the apparatus according to the invention for continuous irradiation;
figure 5 shows a longitudinal section through an exemplary embodiment of an apparatus according to the invention in a schematic illustration, not true to scale;
figure 6 shows a longitudinal section through an irradiation chamber of an apparatus according to the invention;
30 figure 7 shows a section along the line vII-VII in figure 6; and figure 8 shows a longitudinal section through an inlet or outlet chamber in an illustration as in 35 figure 7.
The first step is to describe the structure of an irradiation module 10 by way of example with the aid of the exemplary embodiment illustrated in figures la, b, c and 2. The components are mounted on a baseplate 11.
The baseplate 11 preferably consists of a metal such as aluminum or steel, or of a metal alloy, and has on its rear side the required electric terminals 13 and, if appropriate, a holder 12. Furthermore, devices can be provided there for installing the irradiation module 10 in irradiation systems and devices for moving the irradiation module 10. Also mounted on the baseplate are the starters and terminals for W radiation sources 18. Inlet and outlet for a ventilation system 16 of the radiation sources 18 are also located here. Cross-flow fans, for example, are suitable for this purpose Also provided on the front side of the baseplate 11 is a frame 14 inside which the ventilation system 16 and the W radiation sources 18 are installed. Suitable W
radiation sources 18 are, for example, fluorescent tubes such as are used as tanning lamps in solaria.
Such fluorescent tubes generally have standardized dimensions, for example a luminance length of 2 m in conjunction with a diameter of 25 to 45 cm. They can, furthermore, be provided with reflectors that have an emission angle of approximately 160°, for example.
These fluorescent tubes are operated at an operating voltage of 220 V.
The frame 14 with the ventilation system 16 and the W
radiation sources 18 is surrounded on three sides in an airtight fashion by a W-transparent plate 15, for example made from plastic, such as, for example, polymethyl methacrylate or polycarbonate. The surface of the plate 15 forms the front side of the irradiation module 10, as illustrated by the arrow A symbolizing the direction of radiation.
5 One or more irradiation modules 10 are installed in a sealed irradiation vessel. The irradiation vessel surrounds an irradiation chamber that is illuminated by at least one irradiation module.
Figure 3 shows schematically an exemplary embodiment of 10 an apparatus 20 for discontinuous irradiation of substrates. A rectangular container, provided with supporting feet 21, of length 2.10 m, width 80 cm and height 80 cm was equipped with four irradiation modules 10 of length 1.50 m and equipped with 10 fluorescent 15 tubes 18 arranged in a planar fashion. The irradiation modules 10 were fastened to the frame of the container on the base, the sides and the cover. The upper irradiation module can be raised with the cover of the container. The fluorescent tubes 18 in the irradiation 20 modules 10 were cooled by means of cross-flow fans.
The upper sides of the plates 15 of the irradiation modules define and surround a rectangular irradiation space 22 of length 1.60 m, width 60 cm and height 25 40 cm. Furthermore, four laterally arranged tubes 23 each having 40 bores for letting in nitrogen are located in the irradiation space 22.
Such a device 20 can be operated as follows. The coated 30 substrates are introduced into the irradiation space 22. Thereafter, the irradiation space 22 is flooded with inert gas. When an oxygen concentration of 5%, preferably 1%, with particular preference 0.1%, is reached, the irradiation is started, and it is 35 terminated after curing of the layer. The duration of the irradiation is typically approximately 30 to 300 s.
In this embodiment, the apparatus according to the invention is particularly suitable for curing coatings on substrates. It renders possible the application of radiation curing, for example in the handicraft sector for production and repair. The moderate electric supply power of the modules, which is typically 1 to 2 kW, is advantageous in this case.
In a test, a motor vehicle wheel rim as substrate was coated on all sides with a radiation-curing spray lacquer. The wheel rim was provided with a holder at the valve hole and suspended in the irradiation space 22. After closure of the irradiation space 22, the latter was flooded with nitrogen. The concentration of the oxygen was measured with the aid of a sensor in the irradiation space 22, and displayed. An oxygen concentration of below 0.1% was achieved after flooding for 2 minutes given a nitrogen current of 60 m3/h. Once this value was reached, the nitrogen current was reduced to 10 m3/h and irradiation was started. After an irradiation time of 2 minutes, the nitrogen was switched off and the apparatus 20 was opened. The lacquer on the wheel rim was cured at all points and could also not be damaged by manual pressure.
However, the irradiation modules 10 described can also be used to construct an irradiation tunnel 30 as it is illustrated diagrammatically in figure 4. In such an irradiation tunnel 30, the irradiation modules 10 are arranged on the sides and on the top side such that they define and surround a tunnel-shaped irradiation chamber 32. Coated substrates passing through via conveying appliances, for example, can be cured therein during the transit. If, for example, two irradiation modules are arranged in a row, the luminance length of the irradiation chamber 32 can be up to 4 m. If the curing is performed within approximately 30 to 300 s, transit speeds of 0.8 to 8 m/min are possible. It is to 5 be borne in mind in this case that the residual oxygen concentration should be sufficiently low during the transit and the irradiation. The atmospheric oxygen introduced into the irradiation zone by the movement of the molded part to be irradiated should not exceed the 10 limiting value of 5%. Consequently, locks and/or suitable nozzles are advantageously provided, chiefly upstream of the irradiation zone, as seen in the conveying direction, for the purpose of feeding in inert gas, preferably nitrogen, which prevents the 15 entrainment of air.
In a continuation of this exemplary embodiment, the subject matter of the present invention will be explained below with the aid of figures 5 to 8.
Figure 5 shows schematically an exemplary embodiment of an apparatus 40 according to the invention. This apparatus comprises an irradiation chamber 50 that is assigned an inlet chamber 60 and an outlet chamber 70.
25 The substrate to be coated is transported in a direction of the arrow A by means of a conveying device, for example a conveyor belt, firstly through the inlet chamber 60, then through the irradiation chamber 50 and, finally, through the outlet chamber 70.
30 The actual curing of the coating of the substrate by W
rays takes place in the irradiation chamber 50. The inlet chamber 60, the irradiation chamber 50 and the outlet chamber 70 form a channel closed to the outside.
The inlet and the outlet of the closed channel, that is 35 to say the end of the inlet chamber 60 and of the outlet chamber 70 averted in each case from the irradiation chamber 50, can be sealed, for example, via fitted flaps, doors or plates to such an extent that the substrate can pass. It is thereby possible for less inert gas to emerge to the outside, and so the consumption of inert gas is reduced.
Figures 6 and 7 show schematically the structure of the irradiation chamber 50. Just like the inlet chamber 60 and/or the outlet chamber 70, the irradiation chamber 50 can also be of modular configuration, that is to say be composed of two or more elements that are preferably of the same design, are interconnected in an airtight fashion and form a closed channel. Proceeding from figure 4, the frame of the irradiation chamber 50 is now denoted by 51. Fitted inside the frame 51 is a second frame 52 that is constructed, for example, from plates that are preferably sealed from one another in an airtight fashion and are transparent to W light. W
radiators 53 are arranged between the frames 51 and 52.
These radiators can, but need not necessarily, consist of the irradiation modules described. The frame 52 stands, for example, inside the frame 51 on stilts 52' that are reinforced with cross-struts 52 " .
The frame 52 surrounds an irradiation space 54. The substrate is conveyed through the irradiation space 54 by means of a conveying device, for example by means of a conveyor belt. In this process, the substrate is firstly transported at the start of the apparatus 40 into the inlet chamber 60, and it moves further through the irradiation chamber 50 and the outlet chamber 70 until it leaves the apparatus 40 at the end of the outlet chamber 70. Fitted inside the irradiation space 54 is an apparatus 55 for feeding in inert gas, for example nitrogen or carbon dioxide. This apparatus 55 has, for example, two tubes 56a, 56b running along the inner longitudinal sides of the irradiation space 54.
Of course, it is also possible for a plurality of such tubes to be arranged under or next to one another, or to be combined otherwise with one another in any desired way, for example whenever the irradiation space has particularly long or high dimensions. Those tube sections that run parallel to the conveying direction (arrow A) of the substrate have outflow openings 57, situated close to one another, for an inert gas, for example nitrogen or carbon dioxide. The outlet openings can be configured, for example, as nozzles or bores.
Provided on the underside of the tubes 56a, 56b, outside the irradiation space 54 but inside the irradiation chamber 50 are valves 58 for controlling manually or electronically the volumetric flow of the inert gas fed through them.
Instead of tubes with outflow openings, it is also possible to use porous materials, for example, the inert gas entering the irradiation space 54 through the pores. It would also be conceivable, for example, for the inner walls of the irradiation space 54 to be partially clad with plates made from porous material, for example sintered material, ceramic, etc, and for the inert gas to be introduced into the interspace between the irradiation space 54 and the plates.
Particularly suitable are porous materials in which the pores are small and arranged regularly close to one another. The effect of this is that the inert gas flows out essentially without turbulence.
One or more apparatuses 55 of identical design can also be provided in the inlet chamber 60 or in the outlet chamber 70, or in both chambers, in order to further reduce the entrance of air into the closed channel during the entrance and/or exit of the substrate.
Instead of this, or in addition, it is also possible to provide an apparatus 65 such as is illustrated in figure 8 with reference to the example of an inlet chamber 60, the following statements being valid correspondingly for the outlet chamber 70. The inlet chamber 60 (or the outlet chamber 70) also has a frame 61 inside which there is fitted a second frame 62 that surrounds a conveying space 63. This frame 62 can be made from any desired material; all that is important is for it to be configured such that the conveying space 64 of the inlet chamber 60 (or the outlet chamber 70) and the irradiation space 54 of the irradiation chamber can be combined to form a closed channel. The frame 62 stands, for example, inside the frame 61 on stilts 62' that are reinforced with cross-struts 62 " .
The substrate is conveyed by means of a conveying device through the conveying space 64 and the irradiation space 54, for example by means of a conveyor belt. In the process, the substrate is firstly transported at the start of the apparatus 40 into the conveying space 64 of the inlet chamber 60, and it moves further through the irradiation space 54 of the irradiation chamber 50 and the conveying space of the outlet chamber 70 until it leaves the apparatus 40 at the end of the outlet chamber 70. Fitted inside the conveying space 64 is either an apparatus 55 for feeding in inert gas, for example nitrogen or carbon dioxide, as has already been described with reference to the example of the irradiation space 54. Instead of or in addition to this, an apparatus 65 for feeding in inert gas can be provided. This apparatus 65 has a tube 66 running along the cross section of the conveying space 64. Of course, it is also possible for a plurality of such tubes to be arranged next to one another or otherwise combined with one another in any desired way, for example whenever the conveying space 64 has particularly long or high dimensions. The tube 64 has outflow openings 67 situated close to one another for an inert gas, for example nitrogen or carbon dioxide. The outflow openings 67 can be configured, for example, as nozzles or bores. Provided on the underside of the tube 66, outside the conveying space 64 but inside the inlet chamber 60 are valves 68 for manually or electronically controlling the volumetric flow of the inert gas fed through them.
Instead of tubes with outflow openings, it is also possible to use porous materials, for example, the inert gas entering the conveying space 64 through the pores. It would also be conceivable, for example, for the inner walls of the conveying space 64 to be wholly or partially clad with plates made from porous material, for example sintered material, ceramic, etc, and for the inert gas to be introduced into the interspace between the conveying space 64 and the plates. Particularly suitable are porous materials in which the pores are small and arranged regularly close to one another. The effect of this is that the inert gas flows out essentially without turbulence.
The apparatus 40 according to the invention operates as follows:
The substrates transit the closed channel individually or continuously. The low concentration of residual oxygen required for radiation curing is achieved by continuously feeding inert gas into the irradiation space 54 of the irradiation chamber 50, the inert gas flowing out of the tubes 56, 66 essentially with a low level of turbulence. This produces an inert gas 5 volumetric flow in the direction of the conveying space 64 of the inlet chamber 60 or the outlet chamber 70.
For this purpose, an at least slight overpressure is set in the irradiation space 54 by appropriately feeding in inert gas. The effect of this is that the inert gas flows out continuously in the direction of the conveying spaces 64. In addition, the inert gas is fed into the irradiation space 54 as a volumetric flow running in the conveying direction, and maintained. The orientation in the conveying direction effects an 15 additional orientation of the inert gas in the direction of the conveying spaces 64 in order to impede the entrance of atmospheric oxygen into the irradiation space . The inert gas f lowing out thus removes f rom the closed channel the atmospheric oxygen entrained by the conveyance of the substrate.
Apparatuses 65 for feeding in inert gas are additionally provided in the exemplary embodiment, both in the conveying space 64 of the inlet chamber 60 and 25 in the conveying space of the outlet chamber 70. The inert gas pressure in the conveying spaces is, for example, set such that it is lower than the inert gas pressure in the irradiation space 54. In this way, the inert gas flow from the irradiation space 54 is 30 maintained in the direction of the conveying spaces 64, but the inlet and outlet of the closed channel are additionally shielded against the penetration of atmospheric oxygen.
In the exemplary embodiment, the apparatuses 65 for feeding inert gas into the conveying spaces 64 from the inlet chamber 60 and outlet chamber 70 are designed such that their inert gas flow is overlaid at the side 5 on the volumetric flow running in the conveying direction. This is achieved by virtue of the fact that the tubes 66 are arranged with their outflow openings 67 perpendicular to the conveying direction of the substrate. Furthermore, in the exemplary embodiment the 10 outflow openings are set such that an inert gas flow that removes entrained air and displaces it into the outgoing volumetric flow is applied to the substrate (which is being let in or out) obliquely to the conveying direction. In the conveying chamber of the 15 outlet chamber 70, this way of feeding in inert gas advantageously additionally prevents air from being back-mixed into the irradiation space 54 of the irradiation chamber 50.
20 Use is made in general of inert gas volumetric flows of 15 to 1000 Nm3/h, preferably between 30 and 400 Nm3/h.
The f low rate of the inert gas volumetric f low fed in perpendicular to the conveying direction is preferably approximately 10 to 80% by volume of the entire inert 25 gas volumetric flow, preferably 15 to 60% by volume of the volumetric flow. In a closed channel with a cross section of 500 x 500 mm, for example, the flow rate for the volumetric flow can typically be 200 Nm'/h, while the flow rate of the inert gas fed in perpendicular to 30 the conveying direction is preferably approximately 25-50% by volume of the volumetric flow.
Claims (25)
1. A process for curing a radiation-curable coating on a substrate in an irradiation chamber (50) provided with at least one or more UV radiation sources (18, 53), wherein the substrate is guided through a closed channel that is formed by an inlet chamber (60), the irradiation chamber (50) and an outlet chamber (70), and wherein an inert gas is fed into the irradiation chamber (50) in such a way that an at least slight inert gas overpressure is produced in the irradiation chamber.
2. The process as claimed in claim 1, wherein inert gas is also fed either into the inlet chamber (60) or into the outlet chamber (70), or into both in such a way that an inert gas pressure is produced that is lower than the inert gas pressure in the irradiation chamber (50).
3. The process as claimed in one of the preceding claims, wherein the inert gas in the irradiation chamber (50) is fed in as a volumetric flow running in the conveying direction, and is maintained.
4. The process as claimed in one of the preceding claims, wherein the inert gas is fed into the irradiation chamber (50) and/or the inlet chamber (60) and/or the outlet chamber (70) in such a way that the volumetric flow from the irradiation chamber (50) flows out in the direction of the inlet chamber (60) and of the outlet chamber (70) essentially with a low level of turbulence.
5. The process as claimed in one of claims 3 to 4, wherein the inert gas volumetric flow from the irradiation chamber (50) either in the inlet chamber (60) or in the outlet chamber (70) or in both chambers is overlaid by inert gas flowing out obliquely to the conveying direction.
6. The process as claimed in claim 5, wherein the overlaid inert gas volumetric flow is 10 to 50% by volume of the total inert gas volumetric flow, preferably 15 to 30% by volume of the volumetric flow.
7. The process as claimed in one of the preceding claims, wherein inert gas volumetric flows of 15 to 1000 Nm3/h, preferably between 30 and 400 Nm3/h are used.
8. An irradiation chamber (50), in particular for carrying out the method as claimed in one of claims 1 to 7, wherein it has a frame (51) inside which there is provided an irradiation space (54) with walls transparent to UV light and in which an apparatus (55) is provided for feeding in inert gas.
9. The irradiation chamber as claimed in claim 8, wherein the apparatus (55) has bundled cavities that are provided with closely set nozzle-shaped and/or porous openings.
10. The irradiation chamber as claimed in one of claims 8 to 9, wherein the apparatus (55) has tubes (56, 56a, 56b) that are arranged parallel to the conveying direction of the substrate.
11. The irradiation chamber as claimed in one of claims 8 to 10, wherein it is composed of two or more elements interconnected in an airtight fashion.
12. An apparatus (20, 30, 40) for curing a radiation-curable coating, which has an irradiation chamber (50) provided with one or more W radiation sources (18, 53), wherein the irradiation chamber (50) is assigned an inlet chamber (60) and an outlet chamber (70), the irradiation chamber (50), inlet chamber (60) and outlet chamber (70) forming a closed channel, and wherein the irradiation chamber (50) has an apparatus (55, 65) for feeding in inert gas which produces an at least slight inert gas overpressure in the irradiation chamber (50).
13. The apparatus as claimed in claim 12, wherein the irradiation chamber (50) and/or the inlet chamber (60) and/or the outlet chamber (70) is composed of two or more elements interconnected in an airtight fashion.
14. The apparatus as claimed in one of claims 12 to 13, wherein the inlet chamber (60) or the outlet chamber (70) or both likewise have an apparatus (55, 65) for feeding in inert gas, which produce an inert gas pressure that is less than the inert gas pressure in the irradiation chamber (50).
15. The apparatus as claimed in claim 14, wherein the apparatus (55, 65) for feeding in inert gas is arranged either in the inlet chamber (60) or in the outlet chamber (70) or in both chambers in such a way that inert gas flows out obliquely to the conveying direction.
16. The apparatus as claimed in one of claims 12 to 15, wherein the apparatus (55, 65) has bundled cavities that are provided with closely set nozzle-shaped and/or porous openings.
17. The apparatus as claimed in one of claims 12 to 16, wherein a plurality of UV radiation sources (18) are arranged close to one another and interconnected to form one or more irradiation modules (10), the illuminance inside an irradiation module (10) and/or between at least two irradiation modules (10) being spatially variable.
18. The apparatus as claimed in one of claims 12 to 17, wherein the irradiation chamber (20) has a frame (21) in which surfaces (22) transparent to UV light are fitted.
19. The apparatus as claimed in claim 18, wherein the surfaces (22) transparent to UV light are sealed off from one another in an airtight fashion.
20. The apparatus as claimed in one of claims 12 to 19, wherein lamps, preferably fluorescent tubes (18) with a power of 0,1 to 10 UV per cm radiator length, preferably 1 UV per cm radiator length are provided as UV radiation sources.
21. The apparatus as claimed in one of claims 12 to 20, wherein the UV radiation sources (18) have a continuous emission spectrum between 200 and 450 nm, preferably between 300 and 450 nm.
22. The apparatus as claimed in one of claims 12 to 21, wherein a ventilation system (16) is provided for cooling the surface of the UV radiation sources (18).
23. The apparatus as claimed in one of claims 12 to 22, wherein at least a plurality of radiation sources (18) have reflectors, preferably with emission angles of 160°.
24. The apparatus as claimed in one of claims 12 to 23, wherein at least one irradiation module (10) is arranged in the apparatus (1) in a fashion capable of movement about at least one of its axes.
25. The apparatus as claimed in one of claims 12 to 24, wherein the illuminance of at least one irradiation module (10) can be set in a temporally variable fashion.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE10341208 | 2003-09-04 | ||
| DE10341208.5-11 | 2003-09-04 | ||
| EP2004009714 | 2004-09-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2482325A1 true CA2482325A1 (en) | 2005-03-04 |
Family
ID=34129680
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002482325A Abandoned CA2482325A1 (en) | 2003-09-04 | 2004-09-01 | Process and apparatus for curing a radiation-curable coating, and an irradiation chamber |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP1512467A1 (en) |
| CA (1) | CA2482325A1 (en) |
| DE (1) | DE102004029667A1 (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102004028727A1 (en) * | 2004-06-14 | 2006-01-05 | Basf Coatings Ag | A method for curing free-radically curable compositions under a protective gas atmosphere and apparatus for its implementation |
| DE102007053543B4 (en) * | 2007-11-09 | 2012-11-22 | Sturm Maschinenbau Gmbh | Device for irradiating elements with UV light and method for their operation |
| DE102007060104A1 (en) * | 2007-12-13 | 2009-06-18 | Eisenmann Anlagenbau Gmbh & Co. Kg | Device for drying objects, in particular painted vehicle bodies |
| CN115071012B (en) * | 2022-07-22 | 2023-08-15 | 四川智研科技有限公司 | Plate electron beam curing method and device |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2230831A1 (en) | 1973-05-25 | 1974-12-20 | Union Carbide Corp | Floor tiles with photocured coatings - using selective irradiation for high speed curing |
| US4143468A (en) * | 1974-04-22 | 1979-03-13 | Novotny Jerome L | Inert atmosphere chamber |
| DE4133290A1 (en) | 1991-10-08 | 1993-04-15 | Herberts Gmbh | METHOD FOR PRODUCING MULTILAYER LACQUERING USING RADICALLY AND / OR CATIONICALLY POLYMERIZABLE CLEAR VARNISHES |
| DE59603722D1 (en) | 1995-05-04 | 1999-12-30 | Noelle Gmbh | DEVICE FOR HARDENING A LAYER ON A SUBSTRATE |
| US5644135A (en) * | 1996-02-20 | 1997-07-01 | Matheson; Derek S. | Ultraviolet curing chamber with improved sealing device and tool |
| DE19907681A1 (en) * | 1999-02-23 | 2000-08-24 | Juergen Wahrmund | Continuous treatment of bands with UV light to cross-link coatings, is accompanied by flows of gas to control temperature ideally, preventing excessive heating, with optional local control of moisture and oxygen |
| DE19957900A1 (en) | 1999-12-01 | 2001-06-07 | Basf Ag | Light curing of radiation-curable compositions under protective gas |
| DE10051109C1 (en) * | 2000-10-14 | 2002-04-25 | Messer Griesheim Gmbh | Hardening of coatings in an inert atmosphere using radiation, comprises using a tower construction with low parts entrance and exit, and a high irradiation source |
| DE10242719A1 (en) | 2002-09-13 | 2004-03-18 | Cetelon Lackfabrik Walter Stier Gmbh & Co.Kg | Method for radiation hardening of suitable sheet materials has multiple narrow close fitting UV tubes on a plate with reflectors and ventilation |
-
2004
- 2004-06-18 DE DE102004029667A patent/DE102004029667A1/en not_active Withdrawn
- 2004-09-01 CA CA002482325A patent/CA2482325A1/en not_active Abandoned
- 2004-09-01 EP EP04020703A patent/EP1512467A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| DE102004029667A1 (en) | 2005-04-07 |
| EP1512467A1 (en) | 2005-03-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |