Apparatus for UV exposure

Abstract

The invention relates to a device (100) for UV exposure of a radiation-cured polymer layer (11) on a component (1), in particular for UV exposure of a protective layer on a cover panel of a motor vehicle lighting device, comprising at least one exposure unit (2) for emitting UV radiation into an exposure zone (20) and a conveyor belt (3) for conveying the component (1) through the exposure zone (20). According to the invention, the device (100) has a conveying tunnel (4) in which the exposure zone (20) is arranged and through which the conveyor belt (3) runs, and an inerting system (5) for generating an inert gas atmosphere in the exposure zone (20).

Description

Technical Field

[0001] This invention relates to an apparatus for UV exposure of a radiation-cured polymer layer on a component, particularly an apparatus for curing a protective layer on a cover plate of a motor vehicle lighting device. Background Technology

[0002] Radiation curing of polymer surface coatings via UV (ultraviolet) exposure is a process used in numerous applications, with particular consideration currently given to curing protective layers on closures of automotive lighting systems or other external components of vehicles, such as fenders, side panels, or sensor windows. These protective layers are typically based on free-radical curing varnishes, such as acrylates, which are applied to the closures by spraying. A technical challenge in UV curing is the oxygen inhibition effect, where oxygen in the ambient air reacts with free radicals formed by photolysis, thereby interrupting the intended polymerization reaction of the coating. To minimize the effects of oxygen inhibition, existing techniques employ high radiation doses and long exposure times for UV exposure. This is disadvantageously accompanied by high energy consumption and high thermal loads on equipment and the irradiated components. Summary of the Invention

[0003] The objective of this invention is to provide an alternative embodiment of an apparatus for UV exposure, which is particularly capable of suppressing oxygen inhibition in free radical photopolymerization.

[0004] This task is accomplished by the apparatus according to claim 1. Advantageous improvements of the invention are given in the dependent claims.

[0005] The present invention discloses an apparatus for UV exposure, comprising: at least one exposure unit for emitting UV radiation into an exposure zone; and a conveyor belt for conveying a component to be exposed through the exposure zone; further comprising a conveyor tunnel in which the exposure zone is disposed and the conveyor belt passes through the conveyor tunnel, the apparatus having an inertization system for generating an inert gas atmosphere in the exposure zone.

[0006] This invention is based on the concept of providing a reaction space for UV curing that is substantially free of inhibitory oxygen by placing the exposure zone within a transport tunnel section filled with an inert gas (especially nitrogen). For this purpose, the apparatus has an inertization system capable of inertizing the exposure zone to a residual oxygen concentration preferably less than 100 ppm. The transport tunnel is specifically designed to allow the passage of, for example, a large-sized enclosed cover plate as a component. UV curing can be carried out as a continuous or quasi-continuous process via a conveyor belt extending through the transport tunnel.

[0007] Free radical polymerization in an inert gas atmosphere results in the formation of long polymer chains with a narrow molar mass distribution, thus producing a protective layer with exceptionally high hardness and abrasion resistance. Since no polymerization inhibition occurs, the varnish used can be supplied with lower concentrations of expensive photoinitiators. Furthermore, the UV radiation dose required for complete curing of the protective layer is up to 90% lower than that required for polymerization in ambient air, due not only to the absence of polymerization inhibition but also to the absence of radiation-induced ozone formation. Therefore, the exposure unit can operate at lower power, significantly reducing the thermal load on the equipment components and the irradiated parts, and lowering the process energy consumption.

[0008] In one embodiment, the walls of the conveyor tunnel are at least partially constructed of optical glass through which UV radiation emitted by the exposure unit is transmitted into the exposure area. The exposure unit is arranged adjacent to the section of optical glass outside the conveyor tunnel. For example, this section is formed by a quartz glass plate integrated into the top of the conveyor tunnel, allowing the exposure unit to irradiate the conveyor belt or the components conveyed thereon from above. The exposure unit is designed, for example, as a mercury vapor lamp or a UV-LED-based device.

[0009] In particular, the transport tunnel can be constructed almost entirely of optical glass in the section surrounding the exposure zone, allowing components transported through the exposure zone to be exposed at different angles. For example, the walls of the transport tunnel in the section surrounding the exposure zone have multiple polyhedral plates (e.g., quartz glass plates) made of optical glass. For example, the apparatus includes multiple exposure units arranged around the transport tunnel such that UV radiation from each exposure unit illuminates the exposure zone at its own different angle of incidence, thus enabling components with complex three-dimensional surfaces to be exposed substantially across their entire surface. As an alternative or supplement to using multiple exposure units, the apparatus may also include appropriately arranged reflectors that reflect UV radiation from at least one exposure unit into the exposure zone at their own different angles of incidence.

[0010] In particular, the transport tunnel has a height in the range of 300 mm to 1000 mm and / or a width in the range of 300 mm to 1000 mm. These dimensions can be used, for example, to transport conventional enclosed covers for motor vehicle lighting devices to be UV exposed to applied paint layers.

[0011] Preferably, the inerting system is configured to generate a substantially laminar flow of inert gas in the transport tunnel. The laminar flow profile produces a uniform inert gas distribution in the transport tunnel, even with minimal gas exchange between the equipment operating environment and the inert gas, particularly during the entry and exit of the components to be exposed. For this purpose, the inerting system may include multiple top nozzles to generate an inert gas flow directed onto the conveyor belt; these top nozzles are particularly in the form of slit nozzles and / or multi-channel circular nozzles. The slit nozzles, particularly in the entrance and exit regions of the transport tunnel, can create an "inert gas curtain," thus separating the interior of the transport tunnel from the operating environment. For example, the inert gas supply through the top nozzles within the tunnel can also be coupled to the exposure unit, thereby providing additional cooling to the light-emitting device. In another embodiment, the inerting system includes a large-area suction device at the bottom of the transport tunnel, such that the inert gas flow from the top nozzles is absorbed in the bottom region.

[0012] Preferably, an oxygen sensor for determining the oxygen content in the exposure zone is arranged in the transport tunnel.

[0013] In another embodiment, the transport tunnel has an entrance gate and / or an exit gate, each defined by a mechanical locking element. The gates are connected to an inerting system and, in particular, have slit nozzles arranged on the entrance and exit sides. The gates are sized to accommodate at least one component to be exposed. Attached Figure Description

[0014] The present invention will now be illustrated with reference to the accompanying drawings and related descriptions, using specific embodiments. The drawings are shown in schematic form: Figure 1 A first embodiment of the device of the present invention is shown; Figure 2 A second embodiment is shown; and Figure 3 The third embodiment is shown. Detailed Implementation

[0015] Figure 1 A schematic cross-sectional view of a first embodiment of an apparatus 100 for UV exposure according to the present invention is shown. UV exposure involves the radiation-cured polymer layer 11 forming a protective layer on a component 1 (in the form of a cover plate for a motor vehicle lighting device). The apparatus 100 includes an exposure unit 2 for emitting UV radiation into an exposure zone 20 disposed in a conveyor tunnel 4. The walls of the conveyor tunnel 4 are constructed of optical glass 40 in the top section above the exposure zone 20, through which UV radiation emitted by the exposure unit 2 disposed directly above it is transmitted and incident on the polymer layer 11 on the component 1 for radiation curing. A conveyor belt 3 conveys the component 1 through the conveyor tunnel 4 and across the exposure zone 20 in the direction of the arrow.

[0016] According to the present invention, the apparatus 100 has an inertization system 5 for generating an inert gas atmosphere with a substantially laminar inert gas flow in the exposure zone 20. In this embodiment, the inertization system 5 includes a plurality of top nozzles, in the form of two slit nozzles 51 arranged on the inlet and outlet sides of the conveyor tunnel 4, and a multi-channel circular nozzle 52 arranged in the conveyor tunnel 4, which are configured to generate an inert gas flow directed onto the conveyor belt 3. Nitrogen is used as the inert gas, exemplarily here. The slit nozzles 51 preferably extend across the entire width of the conveyor tunnel 4, such that the generated “curtain-like” inert gas flow isolates the interior of the conveyor tunnel 4 from the operating environment. Furthermore, the inertization system 5 includes a large-area suction device 53 at the bottom of the conveyor tunnel 4.

[0017] Because ambient air is exhausted from inside the transfer tunnel 4, UV exposure of the free radical-cured polymer layer 11 can be performed without oxygen inhibition. The dimensions of the transfer tunnel 4 and the capabilities of the inerting system 5 are designed to make the device 100 suitable for UV exposure of relatively large components (such as the enclosed cover shown here). To monitor the residual oxygen content in the exposure zone 20, an oxygen sensor 7 is arranged in the transfer tunnel 4.

[0018] Figure 2 The upper sub-figure shows a schematic cross-sectional view of a second embodiment of the device 100 of the present invention, which is based on the first embodiment by adding an inlet gate 4a and an outlet gate 4b. The inlet gate 4a and outlet gate 4b are sections of the conveyor tunnel 4 and are each limited by two mechanical locking members 6. During operation of the device 100, the opening and closing of the locking members 6 are synchronized with the conveying of the component 1 on the conveyor belt 3. Both gates 4a and 4b have slit nozzles 51 on the inlet and outlet sides, respectively, which serve as components of the inertization system 5. During operation, inert gas, in this case, nitrogen, is blown through these slit nozzles.

[0019] exist Figure 2 The lower subplot schematically illustrates the corresponding variation curves of residual oxygen content. In the regions of inlet gate 4a and outlet gate 4b, the oxygen content inside the transport tunnel 4 is significantly reduced compared to the operating environment, and the required inert gas atmosphere is present in the central section containing the exposure zone 20. The degree of polymerization of the exposed polymer layer 11 is initially strongly affected by the residual oxygen content; for example, when the oxygen content decreases from 5% to 3%, the double bond conversion of acrylate increases from 70% to 83%. To further improve the double bond conversion, particularly significant inertization is required, for example, achieving 0.05% O2 for a conversion rate of 89%.

[0020] Figure 3A schematic cross-sectional view of a third embodiment of the apparatus 100 of the present invention is shown, wherein the cutting plane extends transversely to the conveyor belt 3 through the exposure zone 20. In the section shown surrounding the exposure zone 20, the walls of the conveyor tunnel 4 have a plurality of plates 41 made of optical glass arranged in a polyhedral pattern. Each plate 41 is assigned a separate exposure unit 2, whose UV radiation is incident on the exposure zone 20 at its own different angle of incidence. Therefore, this embodiment is particularly suitable for exposing components with complex three-dimensional surfaces over the largest possible area.

[0021] List of reference numerals in the attached diagram: 1 component 11 Polymer Layer 2 Exposure Units 20 Exposure Zone 3 Conveyor Belt 4. Teleportation Tunnel 4a Entrance gate 4b Exit Gate 40 Optical Glass 41 boards 5. Inertized Systems 51 Slit Nozzle 52 Multi-channel circular nozzle 53 Suction Device 6 Locking components 7. Oxygen sensor 100 devices.

Claims

1. An apparatus (100) for UV exposure of a radiation-cured polymer layer (11) on a component (1), particularly for UV exposure of a protective layer on a cover plate of a motor vehicle lighting device, the apparatus comprising at least one exposure unit (2) for emitting UV radiation into an exposure zone (20) and a conveyor belt (3) for conveying the component (1) through the exposure zone (20). Its features are, The device (100) has a conveying tunnel (4), the exposure zone (20) is disposed in the conveying tunnel, and the conveyor belt (3) passes through the conveying tunnel. The device (100) has an inertization system (5) for generating an inert gas atmosphere in the exposure zone (20).

2. The device (100) according to claim 1, characterized in that, The walls of the transmission tunnel (4) are at least partially made of optical glass (40), through which UV radiation emitted by the exposure unit (2) is transmitted into the exposure area (20).

3. The device (100) according to claim 2, characterized in that, The walls of the transport tunnel (4) have multiple plates (41) made of optical glass in a polyhedral arrangement in the section surrounding the exposure area (20).

4. The device (100) according to any one of the preceding claims, characterized in that, The device (100) includes a plurality of exposure units (2) arranged around the transport tunnel (4) such that the UV radiation of the exposure units (2) irradiates the exposure area (20) at their respective different incident angles.

5. The device (100) according to any one of the preceding claims, characterized in that, The transport tunnel (4) has a height in the range of 300 mm to 1000 mm and / or a width in the range of 300 mm to 1000 mm.

6. The device (100) according to any one of the preceding claims, characterized in that, The inertization system (5) is configured to generate a substantially laminar flow of inert gas in the transport tunnel (4).

7. The device (100) according to any one of the preceding claims, characterized in that, The inertization system (5) includes multiple top nozzles, particularly slit nozzles (51) and / or multi-channel circular nozzles (52), for generating an inert gas flow directed onto the conveyor belt (3).

8. The device (100) according to any one of the preceding claims, characterized in that, The inertization system (5) includes a large-area suction device (53) at the bottom of the transport tunnel (4).

9. The device (100) according to any one of the preceding claims, characterized in that, An oxygen sensor (7) for determining the oxygen content in the exposure zone (20) is arranged in the transport tunnel (4).

10. The device (100) according to any one of the preceding claims, characterized in that, The transport tunnel (4) has an entrance gate (4a) and / or an exit gate (4b) respectively limited by a mechanical locking element (6).

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