Device and method for curing a polymer layer on a cylinder

Abstract

The invention relates to a curing device (20) for curing a polymer layer on a cylindrical substrate (1), comprising a UV lighting device (21) for generating UV light and providing the UV light at a light opening (21a); a curing gap (27) which is arranged in front of the light opening (21a); an inert gas supply device (22) for supplying inert gas to the curing gap (27) upstream of the light opening (21a); a flow of inert gas through the curing gap (27); and an oxygen measuring device (37) for measuring the oxygen content in the inert gas downstream of the light opening (21a).

Description

[0001] The invention relates to a hardening device for hardening a polymer layer on a cylindrical substrate.

[0002] Coating substrates with a polymer layer and subsequent curing is known. This applies particularly to plastic films that are to be coated with a polymer layer which is then cured. Examples of this application are known from US 2002 / 0057999 A1 and US 2006 / 0204671 A1.

[0003] However, such plastic films are not cylindrical substrates, but flat or planar substrates that may be guided over a cylinder. The invention, however, relates to the curing of a polymer layer on a cylindrical substrate.

[0004] Such a substrate could, for example, be a printing plate that can be coated with a polymeric coating material. The term substrate or printing plate will be used below primarily as a generic term for gravure printing plates, relief printing plates, or structural plates for embossing, but also for coating rollers or inking rollers.

[0005] WO 2021 / 052641 A1 discloses a printing form and a polymeric coating material for it. The coating material is a polymeric nanocomposite that can be applied as a single layer to printing forms. The polymeric nanocomposite is applied in a flowable form to the cylindrical outer surface of the printing form and subsequently cured by irradiation with UV light. The resulting polymer layer can be structured, for example, using infrared lasers to create a surface structure with features such as cells or structures for ink retention or embossing, as also described in WO 2021 / 052641 A1.

[0006] Applying and curing a still-flowable polymer, such as the aforementioned nanocomposite, is a complex process. Curing is primarily achieved using UV light. To achieve efficient and low-emission, i.e., ozone-free, curing, UV LEDs are increasingly being used. Due to the prevailing oxygen inhibition at the surface of the radical polymerization, these LEDs require surface inerting.

[0007] Since the polymer coating is to be applied to substrates with different dimensions, especially different lengths and diameters, UV radiation curing should be provided that is independent of format and size, with minimal inert gas consumption.

[0008] The invention is therefore based on the objective of providing a hardening tool that can be used flexibly for different circumferences and format widths of cylindrical substrates.

[0009] The problem is solved according to the invention by a hardening device having the features of claim 1. Advantageous embodiments are specified in the dependent claims.

[0010] A curing device is described for curing a polymer layer on a cylindrical substrate, comprising a UV light device for generating UV light and supplying the UV light to a light aperture; a curing gap arranged in front of the light aperture; an inert gas supply device for supplying inert gas to the curing gap upstream of the light aperture; an inert gas flow through the curing gap; and an oxygen measuring device for measuring the oxygen content in the inert gas downstream of the light aperture.

[0011] The coated substrates can be rollers of all kinds, such as printing forms, gravure printing forms or cylinders, structural forms or cylinders, embossing forms or cylinders, as well as letterpress forms or cylinders or coating rollers and inking rollers, e.g. for flexographic printing.

[0012] The polymer material was applied to the outer surface of the substrate in a suitable manner before the curing process, but is still fluid in this state, i.e., before curing.

[0013] The polymeric coating material can be, for example, the material described in WO 2021 / 052641 A1. In particular, the polymer can be a coating material for coating a printing form, comprising a liquid starting material that is polymerizable by UV light to form a polymer matrix, a filler having a sub-microscale size, wherein the coating material contains, in addition to the sub-microscale filler, a further filler, wherein the sub-microscale filler is in particle form and its size is in the range between 100 nm and 999 nm, wherein the further filler is a nanoscale filler such that the further filler has filler particles with a nanoscale size in the range between 1 nm and 99 nm, wherein the sub-microscale filler consists of at least one metal oxide and / or a semi-metal oxide selected from metal oxide-coated mica.TiO₂ or (Sn, Sb)O₂, wherein the nanoscale filler is metal and / or semimetal oxides selected from Al₂O₃, SiO₂, TiO₂, ZrO₂ or organometallic particles, wherein the sub-microscale filler is covalently embeddable in a polymer matrix of the starting material, wherein the nanoscale filler is included to increase wear resistance and is covalently embeddable in the polymer matrix of the starting material, and wherein the sub-microscale filler in the starting material can effect an absorption of IR radiation that is higher than an absorption without filler.

[0014] The UV light device generates UV light that exits through the light aperture and from there can directly reach the polymer layer on the substrate to be cured. For this purpose, the curing gap is positioned in front of the light aperture and forms a narrow inerting and irradiation channel. The formation of the curing gap, or channel, can be ensured by precisely positioning the curing device relative to the polymer surface (and thus the substrate surface), as will be explained later.

[0015] The curing gap is at least partially open to the polymer layer to be cured. In particular, the curing gap is at least partially open on its side facing the substrate. The curing gap may have a gas inlet for introducing the inert gas and a gas outlet for removing the inert gas. Within the curing gap itself, the light aperture is positioned opposite the polymer layer to enable curing of the polymer layer by irradiation with UV light.

[0016] The oxygen measuring device measures the oxygen content in the inert gas discharged from the light aperture. Specifically, it measures the residual oxygen content in the inert gas. To achieve the desired protective effect of the inert gas on the polymer layer, the inert gas must have a specific concentration, which can be indirectly determined by measuring the residual oxygen content in the inert gas stream. For this purpose, the oxygen measuring device can incorporate a lambda probe (λ probe). Based on the residual oxygen measurement results, the required amount of inert gas can be set and supplied at the upstream end via the inert gas supply device. This ensures a consistently sufficient supply of inert gas in the curing gap during UV irradiation. Conversely, it also prevents excessive inert gas consumption, thus enabling the curing process to be carried out economically and with minimal resource consumption.

[0017] Nitrogen is particularly suitable as an inert gas, as it provides a sufficient inerting effect.

[0018] The curing device allows a polymer layer to be cured on a cylindrical substrate, regardless of the shape or format of the substrate.

[0019] The light aperture on the UV light unit can be covered with UV-transmitting quartz glass. This quartz glass cover in front of the UV light unit seals the gas flow in the curing gap, preventing inert gas from escaping into the rest of the working space.

[0020] The UV light device can in particular be an LED-based light device in which UV light is generated using LEDs.

[0021] A positioning device may be provided for positioning the UV light unit. In this case, positioning means holding and / or moving the curing device or the UV light unit relative to the polymer layer or substrate to be cured. The desired curing gap should be maintained as precisely as possible to ensure a reliable supply of inert gas.

[0022] For this purpose, a distance measurement system can be provided, utilizing, for example, an inductive, capacitive, or laser-based measuring principle. The distance can be variably controlled or mechanically precisely set. This depends on the specific conditions regarding the positioning of the curing device relative to the substrate.

[0023] The positioning device may include a distance control device, wherein the distance control device comprises a distance measuring device for measuring the distance between the UV light device and a surface of the polymer layer and / or a surface of the substrate. The distance control device may include a distance adjusting device for setting the distance of the UV light device to the surface of the polymer layer and / or the surface of the substrate such that the distance corresponds to a predetermined value.

[0024] A gas supply device may be provided to generate the inert gas flow through the curing gap. The gas supply device may be arranged downstream of the curing gap, and may also be arranged downstream of the oxygen measuring device. The inert gas flow can be guided through the curing gap and the oxygen measuring device by the action of the gas supply device, starting from the inert gas supply device. The gas supply device may, in particular, include a fan with which a corresponding flow effect can be generated by drawing in air and the inert gas.

[0025] The inert gas supply device can be configured to deliver inert gas from an inert gas source to a gas inlet of the curing gap. The inert gas supply device may include an injection nozzle for introducing the inert gas into the curing gap, and may also include a calming section upstream of the gas inlet to reduce turbulent flow in the supplied inert gas. The inert gas source may be, for example, a tank or a gas cylinder.

[0026] The inert gas should be introduced across as much of the curing gap as possible to achieve a uniform, ideally laminar, flow of inert gas through the curing gap. This is made possible by the injection nozzle, which fans out the inert gas accordingly. Furthermore, a calming section can be incorporated into the inert gas supply system or injection nozzle immediately before the inert gas enters the curing gap. This section calms the flow and makes it largely laminar. The injection nozzle can be designed as a type of slot nozzle.

[0027] The inert gas supply device may include a mass flow controller to regulate the flow of inert gas from the inert gas source. The mass flow controller allows precise adjustment of the amount of inert gas supplied to the curing gap per unit of time.

[0028] Downstream of the hardening gap, a gas outlet can be provided through which inert gas escapes from the hardening gap, wherein downstream of the gas outlet a gas discharge device can be provided, wherein the gas discharge device can have a measuring chamber feed which is arranged at the gas outlet and through which inert gas escaping from the hardening gap can be directed to a measuring chamber, and wherein the oxygen measuring device is designed to measure the oxygen content in the measuring device.

[0029] The gas outlet defines the end of the curing gap. Immediately afterward, a portion of the inert gas can be captured and vented by the gas extraction system. The remaining inert gas escapes into the environment. The portion of inert gas captured and vented by the gas extraction system is fed into the measuring chamber, where the oxygen measuring device can measure the (residual) oxygen content in the inert gas. This enables the inert gas supply control described above, ensuring that a sufficient quantity of inert gas is always supplied to the curing gap so that the polymer surface is exposed to a gas with a sufficiently low oxygen content to prevent oxidation processes during UV curing of the polymer.

[0030] A residual oxygen control device may be provided, which includes the oxygen measuring device and is designed to maintain the oxygen content measured by the oxygen measuring device within a predetermined range. In this way, the inert gas content in the gas stream is also indirectly determined.

[0031] In practice, it has been found that a residual oxygen content of 0.1% to 10%, in particular 0.5% to 5%, should be set, depending on the curing behavior of the polymer mixture.

[0032] The residual oxygen control device can be coupled with the mass flow controller to regulate the supply of inert gas.

[0033] The gas conveying device (e.g. the fan) can be located at the downstream end of the gas discharge device.

[0034] The curing gap, gas inlet, and gas outlet can be at least partially sealed to the environment by a non-contact seal. This non-contact seal can, for example, consist of one or more layered sheet metal or plastic elements. Alternatively, the non-contact seal can be implemented using a doctor blade. In this case, the doctor blade and its associated sheet metal or plastic elements generate turbulent flow to prevent the escape of inert gas. This allows for an almost laminar flow of inert gas between the gas inlet and outlet. The turbulent flow in the area of ​​the non-contact seal acts as a flow obstruction, thus limiting the amount of inert gas that can escape to the environment.

[0035] A curing system for curing a polymer layer on a cylindrical substrate is described, comprising a curing device according to one of the preceding claims; a substrate receptacle for supporting the cylindrical substrate; a translation device for moving the curing device in a translational direction; a rotation device for moving the substrate supported by the substrate receptacle in a rotational direction; and a motion control configured to coordinate the movement by the translation device with the movement of the rotation device such that the curing device performs a spiral movement relative to the substrate.

[0036] In this way, the curing device can be moved relative to the rotating substrate to harden the polymer. The direction of translation can be, in particular, the longitudinal direction of the substrate, i.e., its central axis, while the substrate itself is rotated around its main or central axis. The desired relative spiral motion is achieved through the superimposed movement of the substrate's rotation and the translation of the curing device. This allows the polymer to be cured uniformly on the substrate's surface. In particular, the resulting spiral path of UV irradiation ensures complete and effective curing of the polymer.

[0037] A method for hardening a polymer layer on a cylindrical substrate is described, comprising the following steps: Generating and supplying UV light to a light aperture; supplying inert gas to a curing gap located upstream of the light aperture; generating an inert gas flow through the curing gap; and measuring the oxygen content in the inert gas downstream of the light aperture.

[0038] These and other features and advantages of the invention are explained in more detail below with the aid of examples and the accompanying figures. They show: Fig. 1 a coating system for applying a polymer layer to a cylindrical substrate; Fig. 2 a coating device as part of the coating system of Fig. 1 , for coating a cylindrical substrate with a polymer; Fig. 3 a sectional side view of the device of Fig. 2 ; Fig. 4 a close-up "C" from Fig. 2 ; Fig. 5 a hardening system for hardening a polymer layer on a cylindrical substrate; Fig. 6 a hardening device as part of the hardening system of Fig. 5 ; Fig. 7 a close-up of the hardening device from Fig. 6 ; and Fig. 8 a cutaway side view of the hardening device of Fig. 6 .

[0039] Fig. 1 Figure 1 shows a perspective view of a coating system as part of a layer generation system for producing a polymer layer on a cylindrical substrate.

[0040] In the example shown, substrate 1 is a printing form, specifically a gravure cylinder for use in gravure printing. The gravure cylinder is to be coated with a flowable polymer. This could, for example, be the nanocomposite known from WO 2021 / 052641 A1. The polymer coating of the gravure cylinder is suitable for creating small depressions, so-called cells, by laser treatment, particularly with a near-field infrared (NIR) laser. These cells can then hold the printing ink and transfer it to the object to be printed. For this purpose, the polymer layer must have a relatively small thickness (layer thickness), for example, 10 mm. µ m to 500 µ m, in particular 10 µ m to 250 µ exhibit m.

[0041] The substrate 1 or the gravure cylinder is held rotatably in a rotational direction R in a photograph not shown.

[0042] A coating device 2 is provided on the outer surface of the substrate 1 and can be moved in a translational direction X along the outer surface of the substrate 1. The coating device 2 serves to apply the still-flowable polymer material to the cylindrical surface of the substrate 1.

[0043] When the translational movement of the coating device 2 in translational direction X and the rotation of the substrate 1 in rotational direction R are superimposed, the coating device 2 performs a helical movement relative to the outside of the substrate 1, as shown in Fig. 1 This is indicated by an arrow S. Using the coating device 2, flowable polymer material with a width of, for example, a few millimeters, e.g., 5 mm to 30 mm, can be applied to the outside of the substrate 1. The spiral relative movement allows one polymer layer to be applied next to another in a spiral or helical pattern, so that ultimately the entire surface of the substrate or a portion thereof is uniformly covered with a polymer layer. With the aid of smoothing elements, which will be explained later, any gap that arises between the adjacent polymer layers can be uniformly closed, resulting in a smooth, homogeneous polymer layer.

[0044] For the application of the polymer material, it is necessary that the coating device 2 maintains a uniform, very close distance to the substrate surface. For this purpose, the coating device 2 can be moved in the radial direction Z of the substrate 1 by a coating positioning device (not shown). The coating positioning device can include a distance control device with a distance measuring device 3 for this purpose. Depending on the embodiment, the distance measuring device 3 can operate inductively, capacitively, or using a laser as a distance sensor and support the distance control.

[0045] The Fig. 2 bis 4 show the coating device 2 in detail, wherein Fig. 2 represents a main section Fig. 3 a cutaway side view of Fig. 2 and Fig. 4 a section enlargement C of Fig. 2 .

[0046] The coating device 2 has a carrier body 5. A feed nozzle 6 is held in the carrier body 5, to which coating material 7 in the form of a flowable polymer material is fed. The coating material 7 can be fed by continuous, pulsation-free and precise material delivery, e.g. by means of syringe pumps or progressive cavity pumps (dispensers).

[0047] The feed nozzle 6 has a cylindrical material feed 8 that tapers conically towards an outlet opening 9. The outlet opening 9 can have a depth T of, for example, 1 to 3 mm and a width B of 5 to 30 mm, although other dimensions are also possible.

[0048] Furthermore, the feed nozzle 6 can taper towards the outlet opening 9 (material outlet) with a tapering angle. A tapering angle α of, for example, 1° to 7° ensures laminar flow and an increasing fluid velocity of the coating material 7 shortly before the material exits.

[0049] It has been found that at distances between the feed nozzle 6, and in particular the outlet opening 9 of the feed nozzle 6, and the substrate 1 in the range of 1xS to 4xS, where S is the desired layer thickness on the substrate 1, a sufficiently large meniscus or heel is generated at the nozzle outlet, thus ensuring complete wetting across the entire nozzle width. A constant distance therefore also results in a constant layer thickness.

[0050] Viewed downstream of the feed nozzle 6 in the direction of rotation, a smoothing blade 10 is attached to the carrier body 5 to smooth the surface of the polymer material applied to the substrate 1. The smoothing blade 10 can, for example, be a plastic sheet. The plastic surface of the smoothing blade 10 is well suited to achieving the desired surface quality on the smoothed polymer.

[0051] A support blade 11 is arranged across the entire back surface of the smoothing blade 10 on its rear side. The support blade 11 can be made of spring steel. The support blade 11 thus supports the shape of the smoothing blade 10 and ensures sufficient pressure of the smoothing blade 10 on the polymer to be smoothed or spread.

[0052] Fig. 4 shows the smoothing squeegee 10 and the support squeegee 11 in enlarged view.

[0053] A reset blade 12, also made of steel or spring steel, is provided on the front of the smoothing blade 10 and extends over a partial surface of the smoothing blade 10 ( Fig. 4 ). For example, the reset squeegee 12 can extend over half or a third of the area of ​​the smoothing squeegee 10.

[0054] The squeegees 10, 11, 12 are attached together laterally to a squeegee attachment 13 on the carrier body 5.

[0055] On the rear side of the smoothing blade 10 is a pressure piston 14, which is actuated and moved by a pneumatic cylinder 15. The pneumatic cylinder 15 is in turn controlled by compressed air via a pneumatic supply 16. The compressed air in the pneumatic cylinder 15 allows the pressure piston 14 to be pressed downwards against the support blade 11 and thus against the smoothing blade 10, thereby pressing the support blade 11 and the smoothing blade 10 against the return blade 12. The return blade 12 exerts a counterforce against the action of the pressure piston 14, so that a force equilibrium is established depending on the applied air pressure. This allows the contact force of the smoothing blade 10 against the polymer material to be smoothed to be precisely adjusted.

[0056] The contact pressure of the smoothing tool 10 on the applied polymer layer can be adjusted using a control system. Excessive contact pressure leads to significant changes in the layer distribution, while insufficient contact pressure prevents the transition gap between the individual spiral coatings from closing. It has been shown that, due to varying viscosities, surface tensions, and other material variables, a range of surface pressures of the smoothing tool 10 on the polymer material must be achievable.

[0057] The width of the smoothing squeegee 10 can be two to three times, or up to five times, or up to ten times the width of a spiral layer to ensure a large contact area and uniform layer homogenization.

[0058] Fig. 5 shows a curing system as a further part of the layer production system for producing a polymer layer on a cylindrical substrate. The in Fig. 5 The components shown can in particular complement those in Fig. 1 The components shown represent the entire layer generation system, such that the components of the Fig. 1 and 5 In summary, this involves first applying a layer of a flowable polymer to substrate 1 and then curing the polymer layer on substrate 1.

[0059] In the hardening system of Fig. 5 It is therefore assumed that substrate 1 is already covered with a flowable polymer layer, which now needs to be hardened to become dimensionally stable and to be able to serve its actual purpose, e.g. as a gravure printing roller.

[0060] The substrate 1, e.g. the gravure printing roller, is – as in the system of Fig. 1 - continued to be held in the unseen position and rotated in the direction of rotation R.

[0061] A curing device 20 is arranged around the circumference of the substrate 1, which cures the polymer layer using UV light.

[0062] The entire, with components of the Fig. 1 and 5 The formed layer generation system can thus be used in Fig. 1 The illustrated coating device 2 and the curing device 20 comprise this system. This allows a polymer layer to first be applied to the surface of the substrate 1 by the coating device 2 and subsequently cured by the curing device 20 using UV light irradiation. During both process steps, the substrate 1 can be rotated about its main or longitudinal axis while the coating device 2 and the curing device 2 are moved along its surface.

[0063] When UV curing polymers using LEDs, there is a risk that the free radicals of the photoinitiator released by the LED's UVA radiation will be bound by atmospheric oxygen, thus preventing complete surface curing. Therefore, UV irradiation must take place under an inert gas atmosphere. To achieve this, the curing device 20 includes not only a UV light unit 21 but also an inert gas supply unit 22.

[0064] Analogous to the coating device 2 in Fig. 1 The curing device 20 also includes a curing translation device (not shown) with which the curing device 20 can be moved in a translational direction X along the longitudinal axis of the substrate 1. Simultaneously, the substrate rotates in the direction of rotation R, resulting in a spiral movement S. In this way, the curing device 20, together with the UV light device 21, can cover the entire surface of the polymer layer applied to the lateral surface of the substrate 1 and thus cure the polymer.

[0065] Analogous to the coating device 2 described above, the curing device 20 also has a curing positioning device (not shown) with a distance control device to adjust the distance of the curing device 20 in the Z direction, i.e., in the direction of the surface of the substrate 1 (radial direction of the substrate 1). A distance measuring device 23 is provided for this purpose. Precise maintenance of the distance is important to achieve a satisfactory curing result.

[0066] Fig. 6 Figure 1 shows the curing device 20 in an enlarged sectional view. The curing device 20 is shown in relation to two substrates 1a, 1b of different sizes to illustrate that the curing device 20 can be used for substrates 1 with significantly different diameters.

[0067] Approximately in the middle of the curing device 20 is the UV light device 21, which in the example shown is arranged vertically and at the underside of which the UV light passes through a light aperture 21a ( Fig. 7 ) can exit, as will be explained later.

[0068] The in Fig. 6 The inert gas supply device 22, located to the right of the UV light device 21, has a gas supply line 24 through which inert gas is supplied from a storage source, e.g., a gas cylinder or a gas tank. Nitrogen is particularly well suited as an inert gas. The flow of the inert gas to the light aperture 21a of the UV light device 21 is regulated by a mass flow controller 25. This will be explained in more detail later.

[0069] Fig. 7 shows the area below the UV light device 21 in a view opposite the Fig. 6 enlarged illustration. The light aperture 21a, which serves as the exit aperture of the UV light device 21 and through which the UV light exits to irradiate the polymer material, is covered by a UV-transmitting quartz glass cover 26.

[0070] A curing gap 27 is formed between the UV light device 21 or the quartz glass cover 26 on the one hand and the surface of the substrate 1 covered with the polymer layer, which is spaced apart from it, on the other hand. Upstream of the quartz glass cover 26 and the curing gap 27, the inert gas supply device 22 has an injection nozzle 28 through which the inert gas can be introduced into the curing gap 27 via a gas inlet 29. The injection nozzle 28 is arranged at the end of an injection hopper 30, to which an injection channel 31 is connected, as shown. Fig. 8 shows.

[0071] Fig. 8 shows a cross-section through the inlet channel 31 of Fig. 7It is clearly visible that the inert gas supplied via a gas line 32 from the mass flow controller 25 is fanned out in the injection hopper 30 and subsequently calmed in the narrow injection channel 31. In the injection channel 31, which also serves as a calming section, a substantially laminar flow of the inert gas can be achieved, allowing the inert gas to be discharged across the entire width of the injection nozzle 28 and thereby cover polymer material on the substrates 1a, 1b before this area of ​​the polymer material, now protected by inert gas, reaches the light aperture 21a on the quartz glass cover 26 in the curing gap 27, where UV irradiation takes place.

[0072] After exiting the injector nozzle 28, it is to be expected that the inert gas will partially mix with atmospheric oxygen, since the area of ​​the gas inlet 29 into the curing gap 27 cannot be completely sealed off from the environment.

[0073] The curing gap 27 is therefore not filled with pure inert gas, but with a gas mixture that contains residual oxygen in addition to inert gas. The sealing measures intended to reduce the ingress of ambient air, as well as the measures for achieving a specified proportion of inert gas in the gas mixture, will be explained later.

[0074] Downstream of the quartz glass cover 26 or the curing gap 27, i.e., after UV irradiation, the curing gap 27 ends at a gas outlet 33. A gas discharge device 34 with a downstream measuring chamber 35 is provided there. The gas discharge device 34 can, in particular, be designed as a gap and provide a connecting channel from the end of the curing gap 27 (gas outlet 33) to the measuring chamber 35. A portion of the inert gas is thus discharged via the gas discharge device 34 to the measuring chamber 35, while another portion of the inert gas, not captured by the gas discharge device 34, can escape into the environment.

[0075] To reduce inert gas leakage or losses into the environment, the curing gap 27 is sealed on all four sides by non-contact seals, which are primarily designed as doctor blade seals 36. The doctor blade seals 36 have one or more sheet metal elements arranged in a staggered pattern, creating flow obstructions so that the inert gas cannot escape freely. This, in conjunction with a gas conveying device described later, ensures that only a relatively small portion of the inert gas escapes into the environment, while the remainder is extracted via the measuring chamber.

[0076] A lambda probe (λ probe) 37 is provided in measuring chamber 35 as part of an oxygen measuring device. Using this oxygen measuring device, the (residual) oxygen content in the inert gas downstream of the UV irradiation point at the light aperture 21a can be measured. This allows the inert gas flow rate and the ratio of inert gas to oxygen to be controlled by the mass flow controller 25. This ensures that the residual oxygen content, and consequently the inert gas content, remains within a predetermined range, thus guaranteeing effective protection of the polymer surface from oxidation during UV irradiation. A residual oxygen content of 0.1% to 10%, and in particular 0.5% to 5%, has proven suitable, depending on the curing behavior of the polymer mixture.

[0077] The inert gas flow is generated by a gas conveying device 38, which includes an exhaust fan 39. The exhaust fan 39 creates a negative pressure, which draws the gas mixture from the inert gas supply device 22 through the curing gap 27. The gas flow thus proceeds via the gas supply line 24, the mass flow controller 25, the gas line 32, the injector 30, the injector nozzle 28, the curing gap 27, the gas discharge device 34, the measuring chamber 35, and the exhaust fan 39.

Claims

1. A curing system for curing a polymer layer on a cylindrical substrate (1), comprising: - a curing device (20); - a substrate receptacle for holding the cylindrical substrate; - a translation device for moving the curing device in a translational direction (X); - a rotation device for moving the substrate borne by the substrate receptacle in a rotational direction (R); and comprising: - a motion control unit which is designed to coordinate the movement carried out by the translation device with the movement of the rotation device such that the curing device performs a spiral movement (S) relative to the substrate; wherein - the cylindrical substrate (1) is a roller; and wherein - the curing device (20) is provided, comprising: - a UV lighting device (21) for producing UV light and providing the UV light at a light aperture (21a); - a curing gap (27) which is arranged in front of the light aperture (21a); - an inert gas supply device (22) for supplying inert gas to the curing gap (27) upstream of the light aperture (21a); - an inert gas flow through the curing gap (27); and comprising: - an oxygen measuring device (37) for measuring the oxygen content in the inert gas downstream of the light aperture (21a).

2. The curing system according to claim 1, wherein the light aperture (21a) is covered with a UV-light transmissive quartz glass (26).

3. The curing system according to any one of the preceding claims, wherein a positioning device is provided for positioning the UV lighting device (21a).

4. The curing system according to any one of the preceding claims, wherein - the positioning device includes a distance adjusting device; - the distance adjusting device includes a distance measuring device (23) for measuring the distance between the UV lighting device (21) and a surface of the polymer layer and / or a surface of the substrate (1); and wherein - the distance adjusting device includes a distance setting device for setting the distance of the UV lighting device (21) to the surface of the polymer layer and / or the surface of the substrate (1) such that the distance corresponds to a predetermined value.

5. The curing system according to any one of the preceding claims, wherein a gas conveying device (38) is provided for generating the inert gas flow through the curing gap (27).

6. The curing system according to any one of the preceding claims, wherein - the inert gas supply device (22) is designed to supply inert gas from an inert gas source to a gas inlet (29) of the curing gap (27); - the inert gas supply device (22) has a flushing nozzle (28) for introducing the inert gas into the curing gap (27); and wherein - the inert gas supply device (22) has a calming section (31) upstream of the gas inlet (29) to minimize turbulent flows in the inert gas supplied.

7. The curing system according to any one of the preceding claims, wherein the inert gas supply device (22) includes a mass flow adjusting unit (25) for adjusting the inflow of inert gas from the inert gas source.

8. The curing system according to any one of the preceding claims, wherein - a gas outlet (33) is provided downstream of the curing gap (27), via which inert gas escapes from the curing gap (27); - a gas discharge device (34) is provided downstream of the gas outlet (33); - the gas discharge device (34) has a measuring chamber supply which is arranged at the gas outlet (34) and via which inert gas escaping from the curing gap (27) can be supplied to a measuring chamber (35); and wherein - the oxygen measuring device (37) is designed to measure the oxygen content in the measuring chamber.

9. The curing system according to any one of the preceding claims, wherein a residual oxygen adjusting device is provided, which includes the oxygen measuring device (37) and is designed to keep the oxygen content measured by the oxygen measuring device (37) within a predetermined range.

10. The curing system according to any one of the preceding claims, wherein the gas conveying device (38) is provided on the downstream end of the gas discharge device (34).

11. The curing system according to any one of the preceding claims, wherein the curing gap (27), the gas inlet (29) and the gas outlet (33) are at least partially sealed from the environment by a non-contact seal (36).

12. A method for curing a polymer layer on a cylindrical substrate (1), wherein the cylindrical substrate (1) is a roller, comprising the steps of: - producing UV light and providing the UV light at a light aperture (21a); - supplying inert gas to a curing gap (27) which is arranged in front of the light aperture (21a) upstream of the light aperture (21a); - generating an inert gas flow through the curing gap (27); and - measuring the oxygen content in the inert gas downstream of the light aperture (21a).

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