Apparatus and method for exposing relief precursors

Abstract

The invention discloses a device for exposing a relief precursor (P), the relief precursor comprising a substrate layer and at least one photosensitive layer, the device comprising: a supporting structure (10) for supporting the relief precursor; an LED array (20) configured to illuminate the photosensitive layer of the relief precursor supported by the supporting structure, the LED array being configured to illuminate at least 900 cm 2 A predetermined surface area of ​​the LED array, the LED array comprising a plurality of subsets (25) of one or more LEDs (21), each subset being individually controllable; and a control unit (40) which individually controls the plurality of subsets (25) and makes the illumination intensity difference in the predetermined surface area within a predetermined range.

Description

Technical Field

[0001] The field of the invention relates to an apparatus and a method for exposing relief precursors, in particular printing plate precursors and more in particular for backside exposure of printing plate precursors. Background Art

[0002] The relief structure can be made by transferring the image information to the imageable layer and removing part of the imageable layer. The relief formed can then be used to transfer the information to the substrate in the printing step. An example of a relief precursor is a printing plate precursor. Digitally imageable flexographic printing plate precursors are known and typically include at least a dimensionally stable support layer, a photopolymerizable layer and a digitally imageable layer. The digitally imageable layer can be, for example, a laser ablatable layer. In the case of a conventional printing plate precursor, the digitally imageable layer is replaced by a mask attached to the photopolymerizable layer.

[0003] To produce a printing plate from a printing plate relief precursor, according to existing methods, a mask is first written into the digitally imageable layer based on the image data to be printed. After writing the mask, the plate is exposed to radiation through the mask so that the photopolymerizable layer undergoes polymerization in the areas not covered by the mask. After exposure, the mask and the residues of the unpolymerized parts must be removed. This can be done in a washing device with one or more liquids.

[0004] Exposure devices for printing plate precursors are known. The exposure device may include an irradiation device for front exposure and an irradiation device for back exposure. Back exposure is usually performed using a set of UV (ultraviolet) lamps. Back exposure produces a solid layer (bottom layer) on which the relief structure is generated. Front exposure can also be performed using a set of UV lamps, or a movable UV light source (such as a movable laser or LED (light emitting diode) strip) can be used. Depending on the needs, some exposure devices only perform front exposure or only perform back exposure. In some cases, the exposure device is capable of exposing from both sides, wherein the plate is flipped, or one side is exposed through a transparent support. When a UV tube is used, the entire precursor is exposed at the same time, which is usually called full-sheet exposure. An important feature of this type of exposure is the uniformity of the light output over the entire exposure area. The intensity output of the UV tube is quite uniform along its axis, and with the dense stacking of the tubes, the uniformity is sufficient to produce printing plates.

[0005] LEDs are used due to their high energy output, narrow emission spectrum and low energy consumption. Due to the high intensity of LEDs, in existing solutions, the LEDs are mounted in a linear manner into so-called LED strips that span the width of the printing plate. The strips are then moved across the plate, whereby the movement results in a homogenization of the light output in the scanning direction. Due to the different intensity outputs of individual LEDs, attempts to use LEDs for full sheet exposure have so far failed. In order to improve uniformity, relative motion is applied between the LED array and the substrate (see, for example, WO2016160301A1), or the intensity distribution is changed using optics and / or reflectors (see, for example, WO2017192499A1). These methods are complex, error-prone and expensive.

[0006] US 2018 / 0210345 A1 discloses a method and apparatus for exposing a photosensitive printing plate with a predetermined radiation density from the main side (top) and from the back side (bottom). The method includes performing the main exposure with a certain time delay after the back exposure. The time delay between the back exposure and the main exposure is optimized to produce smaller stable single dot elements on the photosensitive printing plate after processing and to produce smaller single element dot sizes printed on the printing substrate. The bottom layer of the plate can be adjusted by performing only the back exposure before performing the combined back and main exposure with this time delay. Summary of the invention

[0007] It is an object of embodiments of the present invention to provide an apparatus and a method for exposing a relief precursor which allows for improved control of the area to be exposed when using LEDs.

[0008] According to a first aspect of the present invention, there is provided an apparatus for exposing a relief precursor (P), the relief precursor comprising a substrate layer and at least one photosensitive layer. The apparatus comprises a carrying structure for carrying the relief precursor, an LED array and a control unit. The LED array is configured to illuminate the photosensitive layer of the relief precursor carried by the carrying structure, preferably through the substrate layer of the relief precursor. The LED array is configured to illuminate at least 900 cm 2 , preferably at least 1000cm 2 , more preferably at least 2000cm 2 , most preferably at least 5000cm 2 The LED array includes a plurality of subsets of one or more LEDs, each subset being individually controllable. The control unit is configured to individually control the plurality of subsets and cause the illumination intensity in the predetermined surface area to vary within a predetermined range.

[0009] By using an LED array with individually controllable subsets of LEDs, the illumination intensity of the subsets can be adjusted to obtain a more or less uniform illumination of the surface area to be illuminated. In this way, a base layer with a substantially constant thickness can be achieved. Further, when an LED fails, by having a control unit configured to individually control a subset, the subset can be controlled to compensate for the failed LED, so that the uniformity is not significantly affected, and at the same time the failed LED may not need to be replaced.

[0010] Moreover, by having an LED array covering a large area, the device can be designed so that the relief precursor can be subjected to back or front exposure in a single step by activating the LED array. Note that the device can be designed for the largest relief precursors and when smaller relief precursors have to be exposed (e.g. back exposure), only a portion of the LEDs of the LED array can be activated. Although the device is preferably intended for back exposure through a transparent substrate layer of the relief precursor, embodiments of the present invention also cover devices in which the LED array is used for direct front exposure without light passing through the relief precursor and the supporting structure.

[0011] By performing control so that the irradiation intensity in a predetermined surface area varies within a certain range, accurate control of the thickness variation of the underlying layer can be achieved.

[0012] Further, by using an LED array, the energy consumption and cost of embodiments of the present invention can be lower than existing solutions using, for example, backside exposure with UV lamps. Also, since no preheating is required as with UV lamps, the method can be faster. Also, since subsets of the LED array can be activated individually depending on the size of the relief precursor, smaller plates will consume less energy than existing solutions where all UV lamps are activated regardless of size.

[0013] The illumination intensity at a point in a predetermined surface area may be the light intensity measured at that point at one moment in time and is expressed in W / cm 2 Preferably, the illumination intensity is the UV light intensity measured within a predetermined wavelength range, for example using a sensor as described below. When the illumination intensity variation in the predetermined surface area is within a predetermined range, this means that the difference between any two points of the predetermined surface area is within a predetermined range.

[0014] The predetermined surface area is a surface area at a certain distance from the LED array and parallel to the plane of the LED array. Preferably, the distance between the LED array and the predetermined surface area is at least 35 mm. The size of the predetermined surface area is approximately the same as the size of the LED array. However, if only a portion of the LEDs of the LED array are used, the shape and size of the predetermined surface area will roughly correspond to the shape and size of the used portion of the LED array. The relief precursor to be exposed can be arranged so that the predetermined surface area is located in the relief precursor, and in particular in at least one photosensitive layer, but the predetermined surface area can also be located at a smaller distance from the relief precursor, because for multiple parallel surface areas within a specific distance range of the LED array, the illumination intensity variation will be almost the same.

[0015] Preferably, the condition that the illumination intensity variation in a predetermined surface area is within a predetermined range is valid for any surface area parallel to the plane of the LED array, which is at a distance between a first distance (d1) and a second distance (d2) of the LED array, wherein the difference (d2-d1) between the second distance and the first distance is at least 1 mm, more preferably at least 2 mm, even more preferably at least 5 mm, and most preferably 7 mm.

[0016] Preferably, each subset of the plurality of subsets of one or more LEDs comprises at least four LEDs, more preferably comprises an array of at least two rows and at least two columns of LEDs. Preferably, each subset comprises less than seventeen LEDs, more preferably less than thirteen LEDs, even more preferably less than ten LEDs. For example, each subset may comprise an array of 2×2 LEDs connected in series so that the intensity delivered by the four LEDs together is controlled. By keeping the subsets relatively small and by using an array of LEDs, good uniformity can be obtained. In a possible embodiment, the distance between two adjacent LEDs of the same subset is smaller than the distance between two adjacent LEDs from different subsets.

[0017] Preferably, the control unit is configured to control the plurality of subsets such that the difference in illumination intensity in predetermined surface areas is less than 10%, preferably less than 5%, more preferably less than 4%, most preferably less than 1.5% of the nominal value.

[0018] By performing control so that the difference in illumination intensity in a predetermined surface area is less than 10%, it is possible to achieve a thickness variation of the underlying layer of the exposed and developed relief precursor of less than 10% of the average underlying layer thickness, more preferably less than 4%, and most preferably less than 1.5%.

[0019] According to a second aspect of the invention, there is provided a device for exposing a relief precursor, the relief precursor comprising at least one photosensitive layer. The device comprises a supporting structure for carrying the relief precursor, an LED array, at least one sensor and a control unit. The LED array is configured to illuminate the photosensitive layer of the relief precursor carried by the supporting structure. The LED array comprises a plurality of subsets of one or more LEDs, each subset being individually controllable. At least one sensor is configured to measure a value representing the intensity of illumination at a plurality of locations of a surface area illuminated by the LED array. The control unit is configured to individually control the plurality of subsets based on the values ​​measured by the at least one sensor.

[0020] By using one or more sensors to measure the illumination intensity, the subset can be controlled in an improved manner to obtain a predetermined illumination pattern, typically a uniform illumination pattern. For example, when at least one sensor detects that one of the LEDs is damaged, the driving of the adjacent LEDs can be controlled to compensate for the damaged LED. Also, for example, the LEDs may age in different ways, and such aging differences can be compensated based on the values ​​measured by at least one sensor.

[0021] At least one sensor is configured to measure a value representing the intensity of the irradiation. The value may be, for example, the UV light intensity (in mW / cm 2 ) and / or the total amount of UV radiation (i.e. radiation dose) (in mJ / cm 2 ). Optionally, the at least one sensor may be configured to measure the 3D distribution covering a plurality of parallel predetermined surface areas. Additionally or alternatively, the at least one sensor may be mounted such that the distance between the LED array and the at least one sensor is adjustable.

[0022] In a preferred embodiment, the LED array and the supporting structure are fixed so that the relief precursor does not move relative to the LED array during exposure by the LED array.

[0023] In a preferred embodiment, each subset consists of one, two, three, four or five LEDs. By keeping the subsets small enough, accurate control of uniformity can be achieved. One or more LEDs of a subset can be the same or different.

[0024] In a preferred embodiment, the LED array is configured to expose the relief precursor through its substrate layer. However, in other embodiments, the device can be used for direct front exposure without light passing through the relief precursor or the supporting structure.

[0025] Preferably, the device further comprises a moving means configured to move the at least one sensor so as to perform measurements in a plurality of locations. The moving means may comprise, for example, a belt, a track, a lead screw, a slow drive, a linear motor or the like.

[0026] Preferably, the moving means comprises a drive configured to move at least one sensor in a surface parallel to the relief precursor carried by the carrying structure.

[0027] Preferably, the control unit is configured to control the LED based on the measurement values ​​of the at least one sensor in the plurality of locations so that the difference in illumination intensity in the plurality of locations is within a predetermined range.

[0028] The plurality of locations may be arranged along a grid, which may be selected independently of the position of the LEDs. Alternatively, there may be a correlation between the position of the LEDs and the plurality of locations. Preferably, the number of the plurality of locations is equal to or greater than the number of the plurality of subsets. For example, each subset may include one LED, and sensor measurements may be performed for each LED. However, depending on the pattern according to which the LEDs are arranged, the number of locations may be less than the number of the plurality of subsets.

[0029] According to an exemplary embodiment, the control unit is configured to associate one or more LEDs with one of the multiple locations. Typically, one or more LEDs near the measurement location will affect the measured illumination intensity, and the control unit will be able to use the association between the multiple locations and the LEDs of the LED array to adjust the illumination intensity of the LEDs that need to be adjusted to achieve the desired illumination. For example, three or more LEDs may be closest to one of the multiple locations, and these three or more LEDs may be associated with the location. The controller is able to adjust the illumination intensity of the LEDs near the first location to be similar to the illumination intensity measured at another location. Moreover, the controller is able to adjust the illumination intensity of the LEDs so that the illumination intensity in the multiple locations is similar to the value measured in the first location.

[0030] According to an exemplary embodiment, the controller is configured to control the subset such that the difference in illumination intensity between the plurality of locations is less than 10%, preferably less than 5%, more preferably less than 4%, most preferably less than 1.5%.

[0031] According to an exemplary embodiment, at least one sensor includes a camera, a light sensor, a temperature-sensitive sensor, or a combination thereof. Such sensors may include, for example, photodiodes, including avalanche photodiodes, phototransistors, photoconductivity detectors, linear sensor arrays, CCD (charge coupled device) detectors, CMOS (complementary metal oxide semiconductor) optical detectors (including CMOS array detectors), photomultipliers, and photomultiplier arrays. According to certain embodiments, the sensor (e.g., a photodiode or a photomultiplier) may include additional signal conditioning or processing electronics. For example, the sensor may include at least one preamplifier, an electronic filter, or an integrated circuit. Suitable preamplifiers include integral, mutual impedance, and current gain (current mirror) preamplifiers.

[0032] Preferably, the device further comprises a distance adjustment device, which is configured to adjust the distance between the supporting structure and the LED array. Note that the LED array and / or the supporting structure may be movable.

[0033] Using such an adjustment device, the illumination uniformity in a desired plane can be further improved.For example, depending on the thickness of the transparent layer of the relief precursor, the distance between the support structure and the LED array can be adjusted.

[0034] Preferably, the LEDs of the LED array are configured to emit electromagnetic radiation having a wavelength in the range of 200 to 2000 nm, more preferably from 250 to 500 nm, even more preferably from 300 to 450 nm, most preferably from 270 to 410 nm (e.g. predominantly at 365 nm). The at least one sensor may then be sensitive to the corresponding wavelength region (e.g. 200 nm to 2000 nm).

[0035] Preferably, the intensity of the illumination delivered by the LED in the predetermined surface area is between 0.1 and 2000 mW / cm 2 For back exposure, preferably, the irradiation intensity delivered by the LED in the predetermined surface area is between 5 and 100 mW / cm 2 between 8 and 60 mW / cm 2 between 10 and 50 mW / cm 2 For front exposure, preferably, the irradiation intensity delivered by the LED in the predetermined surface area is between 30 and 500 mW / cm 2 between 50 and 450 mW / cm 2 between 100mW / cm2 and above, most preferably above 100mW / cm2 2 Preferably, the distance between the LED array and the predetermined surface area is at least 35 mm. The predetermined surface area may be a surface area in the relief precursor when mounted on / in the carrier structure or a surface area at a smaller distance from the relief precursor.

[0036] Preferably, the radiation dose delivered by the LED in the predetermined surface area is between 0.01 and 200 J / cm 2 For back exposure, preferably, the dose delivered by the LED in the predetermined surface area is in the range of 0.1 to 100 J / cm 2 In the range of 0.5 to 50 J / cm 2 In the range of 0.5 to 30 J / cm 2 For front exposure, preferably, the dose delivered by the LED in the predetermined surface area is higher than 10 J / cm 2, more preferably higher than 20 J / cm 2 .

[0037] The LED array may be arranged on one or more carriers, such as PCBs (printed circuit boards). For example, the LED array may consist of multiple groups of smaller arrays arranged on multiple LED PCBs, which are arranged adjacent to each other in the same plane. The driver circuit for driving the LED array may be arranged on one or more separate driver PCBs. The one or more driver PCBs may be arranged in a plane parallel to the plane in which the multiple LED PCBs are arranged and at a certain distance from the plane. When the relief precursor faces a first side of the multiple LED PCBs, the one or more driver PCBs may face the other side of the multiple LED PCBs.

[0038] Preferably, the distance between individual LEDs of the LED array is at least 5 mm, more preferably at least 7 mm, and preferably less than 100 mm, more preferably less than 30 mm. Such a distance allows obtaining sufficiently uniform illumination intensity in a predetermined plane parallel to the plane in which the LED array is arranged.

[0039] Preferably, the device further comprises a cooling device configured to cool the LED array. The cooling device may be, for example, a cooling device configured to generate a gas flow, typically an air flow. Additionally or alternatively, a cooling device with a liquid coolant may be used.

[0040] Preferably, the device further comprises a driver device configured to drive the LED array preferably by a pulse width modulation (PWM) signal. As described above, the driver device may include a driver circuit arranged on one or more separate driver PCBs, and the one or more driver PCBs may be arranged in a plane parallel to and at a distance from a plane in which a plurality of LED PCBs are arranged. More particularly, the control unit may be configured to change the duty cycle of the PWM signal so as to change the illumination intensity generated by a subset of the one or more LEDs. The driver device may drive the subset using a current or a voltage.

[0041] Preferably, the carrier structure comprises a support structure on which the relief precursor can be supported and which is at least partially transparent to light generated by the LED array.

[0042] Preferably, the carrying structure comprises any one of the following structures: a glass plate, a polymer plate, a mesh, a set of rollers, a drum, a structure configured for suspending the relief precursor, a structure configured for tensioning the relief precursor.

[0043] In an exemplary embodiment, the apparatus may include a housing having an inlet and an outlet, and optionally, the relief precursor may be automatically delivered through the inlet to a position on a support structure, irradiated, and subsequently removed from the apparatus through the outlet. In other words, embodiments of the present invention allow for construction of a fully automated in-line system.

[0044] The inlet and outlet can be on the same side or on opposite sides. The inlet and outlet can be configured to connect to other units.

[0045] The apparatus may include a conveyor system for automatically conveying the relief precursor through the apparatus.

[0046] The conveying system may include a conveying device selected from the group consisting of an endless belt, a pair of chains or belts (with push blocks), a pair of lead screws, a retarder drive, a friction drive, and combinations thereof.

[0047] The conveying system may further comprise at least one attachment device to attach the relief precursor to the conveying device. The attachment device may be a conveying rod having a plurality of pins extending through the edge of the relief precursor. Alternatively, a clamping device for clamping the relief precursor may be used. The conveying rod may be configured to be coupled to the leading edge of the relief precursor, wherein the conveying system is configured to pull the conveying rod with the coupled relief precursor through the housing. When the conveying system comprises two lead screws, the end of the conveying rod may be provided with a recess adapted to be coupled to the lead screws.

[0048] Additional components may be part of the device. These additional components may be selected from the group comprising a power supply, an additional light source for front exposure, an additional conveying device, a motor, a sensor, and combinations thereof. The additional light source may be selected from the group comprising an LED, a fluorescent lamp, a flash lamp, a set of lamps arranged in a linear manner, a (scanning) laser, an LCD (liquid crystal display) screen, a projection system (e.g. with a movable mirror), a laser, and combinations thereof (these components may be fixed and / or movable).

[0049] In a possible embodiment, the additional light source may be a further LED array, preferably a further LED array as defined above. In other words, the invention covers embodiments in which the LED array as defined above is used for back exposure, embodiments in which the LED array as defined above is used for front exposure, and embodiments in which the first LED array as defined above is used for back exposure and the second LED array as defined above is used for front exposure.

[0050] In a preferred embodiment, the back exposure is performed simultaneously with the front exposure. For example, the back exposure can be performed using an LED array according to any of the above embodiments, and the front exposure can be performed using an LED array or other suitable light source at the same time as the back exposure, that is, the same point of the relief precursor can be exposed from both the back and the front.

[0051] Optionally, the control unit controls components of the apparatus as well as components of other units in the process chain. In this way, various operations that need to be performed on the relief precursor can be coordinated by a single control unit. Note that the control unit can also be a distributed control device with multiple control modules that perform control in an independent or subordinate manner.

[0052] The control unit can also be configured to control the timing of the front exposure and the back exposure, so that the back exposure is performed using the LED array according to any of the above-mentioned embodiments, and the front exposure is performed using the LED array or other suitable light source at the same time as the back exposure, that is, the same point of the relief precursor can be exposed from both the back and the front.

[0053] According to an exemplary embodiment, the irradiated surface area is divided into at least two areas, which are irradiated with different irradiation intensities, and wherein, preferably, the difference in irradiation intensity at different positions within each area is less than 10%, preferably less than 5%, more preferably less than 4%, and most preferably less than 1.5%; or wherein the difference in thickness of the underlying layer of the exposed and developed relief precursor is less than 10% of the thickness of the underlying layer, preferably less than 5%, more preferably less than 4%, and most preferably less than 1.5%.

[0054] By dividing the irradiated surface area into at least two areas, different irradiation intensities can be used in these areas, so that at least two bottom layers with different thicknesses can be obtained.

[0055] According to another aspect of the present invention, there is provided a method for exposing a relief precursor comprising a substrate layer (preferably a transparent substrate layer) and at least one photosensitive layer. The method comprises the following steps: using an LED array (optionally an LED array of an apparatus according to any of the preceding embodiments) to emit radiation, preferably through the substrate layer of the relief precursor, to the photosensitive layer of the relief precursor, so that at least 900 cm 2 A predetermined surface area of ​​a photosensitive layer is illuminated, the LED array includes multiple subsets of one or more LEDs, each subset is individually controllable; the multiple subsets are individually controlled, and the illumination intensity in the predetermined surface area varies within a predetermined range, and preferably the illumination intensity difference is less than 10%, preferably less than 5%, more preferably less than 4%, and most preferably less than 1.5%.

[0056] According to another aspect of the present invention, a calibration method for calibrating an exposure device including an LED array (e.g., an exposure device according to any of the above embodiments) is provided. The method comprises the following steps: using an LED array to emit radiation in a predetermined surface area; the LED array comprises a plurality of subsets of one or more LEDs, each subset being individually controllable; measuring values ​​representing the illumination intensity at a plurality of locations in the predetermined surface area; determining a control scheme for controlling the plurality of subsets based on the values ​​measured by at least one sensor to obtain a desired illumination pattern in the predetermined surface area.

[0057] The calibration method can be repeated from time to time and can compensate for aging or failed LEDs of the LED array. Preferably, the illumination intensity settings for the individual LEDs are saved and / or applied to the exposure of further relief precursors, wherein preferably a large number of relief precursors are exposed before performing the calibration process again.

[0058] Preferably, the desired illumination pattern is a substantially uniform illumination pattern.

[0059] Preferably, the measurements in the plurality of locations are performed by moving the at least one sensor such that the at least one sensor performs measurements in the plurality of locations. The plurality of locations may be selected as explained above in connection with another aspect of the invention.

[0060] In an exemplary embodiment, measuring and controlling includes the following steps:

[0061] 1. Positioning at least one sensor at a first position in a plane parallel to the LED array, the first position being associated with one or more first adjacent LEDs of the LED array;

[0062] 2. measuring the illumination at a first location associated with a first position of at least one sensor;

[0063] 3. Positioning at least one sensor at an additional location in the plane, the additional location being associated with one or more additional adjacent LEDs of the LED array;

[0064] 4. measuring the illumination intensity at a further location associated with a further position of at least one sensor;

[0065] 5. adjusting the illumination of one or more of the first and / or further adjacent LEDs such that the difference between the illumination intensity in the first location and the further location is reduced;

[0066] 6. Optionally, the above steps are repeated for the same and / or other locations.

[0067] Alternatively, the illumination area may be covered with a grid, wherein the distance of the grid lines is equal to or greater than the minimum distance between LEDs of the LED array, and at least one sensor may be positioned at an intersection of the grid lines.

[0068] Preferably, the first position and the further position of the at least one sensor are selected such that at least one neighbouring LED of the first position is a neighbouring LED of the further position.

[0069] According to an exemplary embodiment, measured radiation values ​​in multiple locations are collected and stored, and an algorithm is used to adjust the intensity of each LED to a target value so that the difference between different locations is less than 10% of the illumination intensity at the first location, preferably less than 5%, more preferably less than 4%, and most preferably less than 1.5%.

[0070] The present invention also relates to a method for exposing a relief precursor comprising a substrate layer and at least one photosensitive layer, the method comprising the calibration method of any one of the above embodiments, and a step of irradiating the photosensitive layer of the relief precursor with a desired irradiation pattern using a determined control scheme.

[0071] According to another aspect of the present invention, there is provided a calibration method for calibrating an exposure device including an LED array (e.g., an exposure device according to any of the above embodiments). The method comprises the following steps: using the LED array to emit radiation in a predetermined area of ​​a photosensitive layer of a relief precursor so that the predetermined area is cured; the LED array comprises a plurality of subsets of one or more LEDs, each subset being individually controllable; removing an uncured portion of the relief precursor; measuring a thickness variation of the cured area; and determining a control scheme for controlling the plurality of subsets based on the measured thickness variation to obtain a desired irradiation pattern in the predetermined area.

[0072] The calibration process may be repeated from time to time and can compensate for aging or failed LEDs of the LED array.Preferably, the illumination intensity settings for the individual LEDs are saved and / or applied to the exposure of further relief precursors.

[0073] Removal of the uncured portions of the relief precursor may be performed by a solvent or by thermal development.

[0074] Alternatively, the illuminated area may be covered with a grid, wherein the distance of the grid lines is equal to or greater than the minimum distance between the LEDs, and the thickness may be measured at the intersection of the grid lines. The locations of the thickness measurements may be selected so that at least one adjacent LED associated with a first location is also an adjacent LED to another location.

[0075] According to an exemplary embodiment, the measured thickness values ​​are collected and stored, and an algorithm is used to adjust the intensity of each LED to a target value so that in future relief precursors, the difference between different thicknesses is less than 10% of the thickness at the first position, preferably less than 5%, more preferably less than 4%, and most preferably less than 1.5%.

[0076] The present invention also relates to a method for exposing a relief precursor comprising a substrate layer and at least one photosensitive layer, the method comprising the calibration method of any one of the above-mentioned embodiments, and a step of irradiating the photosensitive layer of another relief precursor with a desired irradiation pattern using the determined control scheme.

[0077] According to a further aspect of the invention there is provided a method for exposing a relief precursor, comprising the steps of:

[0078] a) providing a device according to any one of the above embodiments;

[0079] b) performing a calibration process according to any one of the above embodiments;

[0080] c) providing a relief precursor comprising a substrate layer and at least one photosensitive layer;

[0081] d) optionally performing a pre-exposure with an additional light source;

[0082] e) optionally positioning the relief precursor on an at least partially transparent support;

[0083] f) performing an exposure of the relief precursor with the intensity setting obtained in step b);

[0084] g) optionally performing the exposure with an additional light source;

[0085] h) Optional additional steps.

[0086] Step b) may be performed after step c), d) or e).

[0087] Step f) may be performed through the substrate layer of the relief precursor. Step f) and step g) may be performed simultaneously or consecutively. Step f) may be a backside exposure and step g) may be a frontside exposure, or vice versa.

[0088] The pre-exposure of step d) can be performed using a light source selected from the group consisting of LEDs, fluorescent lamps, flash lamps, a set of lamps arranged in a linear manner, (scanning) lasers, LCD screens, light projection systems (e.g. with movable mirrors), and combinations thereof. During the pre-exposure step, the transmittance of the relief precursor layer is changed in an image-wise manner (including ablation and transmittance change).

[0089] The optional further steps of step h) may be selected from the group of removal of uncured material, washing, drying, heating, post-exposure, grinding, and combinations thereof.

[0090] According to a further aspect of the invention there is provided a method for exposing a relief precursor comprising the steps of:

[0091] a) providing a relief precursor having a substrate layer and at least one photosensitive layer;

[0092] b) exposing the relief precursor with uniform radiation emitted by the LED array through the substrate layer;

[0093] c) optional additional steps,

[0094] Wherein no mask or imaging device is used in step b), and wherein the difference in illumination intensity at different locations in the relief precursor is less than 10%.

[0095] Any of the above features may be combined with the method where possible. Preferably, the uniform irradiation intensity is between 0.1 and 2000 mW / cm 2 Preferably, the radiation dose delivered in step b) is between 0.01 and 200 J / cm 2 within the range.

[0096] Optionally, pre-exposure can be performed before step b) using a light source selected from the group consisting of LEDs, fluorescent lamps, flash lamps, a set of lamps arranged in a linear manner, (scanning) lasers, LCD screens, light projection systems (e.g. with movable mirrors), and combinations thereof. Optionally, additional steps (e.g. selected from the group consisting of removal of uncured material, removal of uncured material, cleaning, drying, heating, post-exposure, grinding, and combinations thereof) can be performed.

[0097] The relief precursor may be a precursor for an element selected from the group comprising flexographic printing plates, relief printing plates, movable type plates, intaglio plates, (flexible) printed circuit boards, electronic components, microfluidic components, microreactors, moving cells, photonic crystals and optical components, Fresnel lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0098] The accompanying drawings are used to illustrate the presently preferred non-limiting exemplary embodiments of the apparatus and method of the present invention. The above and other advantages of the features and objects of the present invention will become more apparent and the present invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

[0099] Figure 1 is a schematic perspective view of an exemplary embodiment of an apparatus for exposing a relief precursor;

[0100] Figure 1A is a cross section of a relief precursor;

[0101] Figure 1B is a view of an LED array illustrating the location of a predetermined surface area at a certain distance of the LED array;

[0102] Figure 2A is a top view of an exemplary embodiment of an LED array;

[0103] Figure 2B is a top view of another exemplary embodiment of an LED array;

[0104] Figure 3 is a perspective view of an exemplary embodiment of an apparatus for exposing a relief precursor;

[0105] Figure 4 yes Figure 3 Detailed perspective view of an exemplary embodiment of the invention;

[0106] Figure 5 yes Figure 3 A detailed perspective view of a sensor device of an exemplary embodiment of the present invention;

[0107] Figure 6 yes Figure 3 A detailed perspective view of an exemplary embodiment of an LED and a driver PCB; and

[0108] Fig. 7A and Figure 7B Two further exemplary embodiments of the invention are illustrated in schematic cross-section. DETAILED DESCRIPTION

[0109] Figure 1 The apparatus for exposing the relief precursor P is schematically illustrated. Figure 1A is shown in cross section and includes a substrate layer L s (here a substrate layer which is transparent to the illumination of the LED, see further content) and at least one photosensitive layer L p The device includes a supporting structure 10 for supporting a relief precursor P, an LED array 20, a driving device 30 for driving the LED array 20, a control unit 40 for controlling the driving device 30, and at least one sensor 50. The LED array 20 is configured to illuminate the photosensitive layer L of the relief precursor P supported by the supporting structure 10. p .

[0110] The supporting structure 10 provides horizontal support for the relief precursor and can be, for example, a transparent plate. However, in other embodiments, the supporting structure 10 can be configured to provide tilted support or to vertically suspend the relief precursor or to tension the relief precursor so that the relief precursor extends in a plane. The supporting structure 10 is arranged so that the relief precursor supported by the supporting structure extends substantially parallel to the plane in which the LED array 20 is arranged.

[0111] The LED array 20 is configured to simultaneously illuminate at least 900 cm 2 The predetermined surface area S, see also Figure 1B The LED array 20 includes a plurality of subsets 25 of one or more LEDs 21, each subset 25 being individually controllable in the sense that the intensity of illumination delivered by a first subset 25 can be controlled independently of the intensity of another subset 25. Figure 1 and Figure 2A In the exemplary embodiment of FIG. 1 , each subset 25 includes an individually controllable LED 21. However, if Figure 2B For example, the plurality of LEDs 21 may be grouped into subsets 25 (e.g., a plurality of LEDs 21 connected in series), wherein the subsets 25 are individually controllable. Figure 2B In the example of , each subset 25 includes four LEDs 21, and the intensity delivered by the four LEDs together can be controlled.

[0112] The LED array 20 is arranged to pass through the substrate layer L of the relief precursor P. s Irradiating the photosensitive layer L of the relief precursor P p , i.e., the device is intended for backside exposure. Fig. 7A As shown in the schematic diagram of FIG. 1 , an LED array 20 ′ having LEDs 21 ′ for front exposure can also be implemented, or as Figure 7B As shown, two LED arrays 20, 20' are implemented for front exposure and back exposure. The LEDs 21 may be arranged on one or more LED PCBs.

[0113] The control unit 40 is configured to control the plurality of subsets 25 individually and such that the illumination intensity in a predetermined surface area varies within a predetermined range. The predetermined surface area may correspond, for example, to a support plane of the relief precursor or to a plane at a small distance above the support plane. Ideally, the predetermined surface area corresponds to the photosensitive layer L to be illuminated. p The plane on which it is located.

[0114] The LED array 20 with individually controllable subsets 25 of LEDs 21 allows adjusting the illumination intensity of the subset 21 to obtain a controlled illumination and, in particular, to obtain a more or less uniform illumination of a predetermined surface area S to be illuminated. In this way, a substrate with a controlled thickness, in particular a substrate with a substantially constant thickness, can be achieved. Further, when an LED 21 fails, by having a control unit 40 configured to individually control a subset 21, the subset 21 can be controlled to compensate for the failed LED, such that the uniformity is not significantly affected.

[0115] like Figure 1B As shown, the predetermined surface area S is a surface area at a certain distance from the LED array 20 and parallel to the plane of the LED array. Preferably, the distance ds between the LED array 20 and the predetermined surface area S is at least 35 mm. The size of the predetermined surface area S is substantially the same as the size of the LED array 20. However, if only a portion of the LEDs 21 of the LED array 20 is used, the shape and size of the predetermined surface area S will substantially correspond to the shape and size of the used portion of the LED array 20. The relief precursor P to be exposed can be arranged so that the predetermined surface area S is located in the relief precursor P, and in particular in at least one photosensitive layer L p , but the predetermined surface area can also be located at a smaller distance from the relief precursor, because the illumination intensity variation will be more or less the same for a plurality of parallel surface areas within a certain distance range of the LED array. Preferably, the condition that the illumination intensity variation in the predetermined surface area S is within the predetermined range is valid for any surface area parallel to the plane of the LED array 20, which is at a distance between the first distance d1 and the second distance d2 of the LED array, wherein the difference between the second distance and the first distance (d2-d1) is at least 1 mm, more preferably at least 2 mm, even more preferably at least 5 mm, and most preferably 7 mm. This is in Figure 1B As shown in the example, this condition is valid for all surface areas S between S1 and S2. p This condition can be easily satisfied in .

[0116] At least one sensor 50 is configured to be located at a plurality of locations L1, L2, L3, L1', L2', L3', etc. (see Figure 2A ) in the plurality of locations L1, L2, L3, L1', L2', L3'. This surface area may be the same as the predetermined surface area described above, or may be located in another plane parallel to the plane of the LED array 20. The control unit 40 may then be configured to control the plurality of subsets 25 individually based on the values ​​measured by the at least one sensor. The plurality of locations may correspond to Figure 2AThe positions above the plurality of LEDs 21 are shown as an example, but the measurement can also be performed at positions such as Figure 2B The other locations L1, L2, L3 illustrated are carried out. More generally, any location pattern that allows a representative image of the illumination in the relevant surface area to be obtained can be used. The device includes a moving device (not shown) configured to move at least one sensor 50 in the X direction and the Y direction in a plane parallel to the LED array 20 so as to perform measurements in multiple locations. The moving device may include a driver configured to move at least one sensor 50 in a plane parallel to the relief precursor P carried by the bearing structure 10. The plane in which at least one sensor 50 moves can be the plane of the relief precursor P, a plane at a certain distance above the relief precursor P, or a plane at a certain distance below the relief precursor P. Optionally, at least one sensor 50 can be configured to measure the 3D distribution of multiple parallel predetermined surface areas S covering between S1 and S2. Additionally or alternatively, at least one sensor 50 can be installed so that the distance between the LED array 20 and at least one sensor 50 in the Z direction is adjustable.

[0117] The control unit 40 may be configured to control the LEDs 21 based on the measurements of the at least one sensor 50 in a plurality of locations so that when it is desired to obtain a substantially uniform illumination and thus a polymerized photosensitive layer L p When the layer thickness is substantially constant, the difference in irradiation intensity at a plurality of locations is within a predetermined range.

[0118] Optionally, the apparatus further comprises a distance adjustment device (not shown) configured to adjust the distance d between the support structure 10 and the LED array 20. In this way, the distance d can be optimized so that the illumination is maximized in the area to be exposed.

[0119] Preferably, the LEDs 21 of the LED array 20 are configured to emit electromagnetic radiation having a wavelength in the range of 270 to 410 nm. Preferably, the LEDs 21 emit UV light. Preferably, the intensity of the illumination delivered by the LEDs in the predetermined surface area is in the range of 1 to 200 mW / cm 2 and / or the radiation dose delivered by LED 21 is in the range of 1 to 100 J / cm 2 Between. See Figure 2A , the distance d1 between each LED 21 of the LED array 20 may be at least 5 mm, preferably at least 7 mm, and preferably less than 100 mm.

[0120] The apparatus further comprises a cooling device 60 configured to cool the LED array 20. The cooling device 60 may be configured to send airflow under the LED array 20, in particular under one or more LED PCBs on which the LEDs 21 are mounted.

[0121] The driver device 30 is configured to drive the LED array 20 preferably by a pulse width modulated signal. The driver device 30 may include one or more driver PCBs, on which the driver circuit is mounted. The driver PCB may be positioned in a plane parallel to the LED PCB, below the LED PCB.

[0122] By using an LED array with individually controllable subsets of LEDs, the illumination intensity of the subsets can be adjusted to obtain a more or less uniform illumination of the surface area to be illuminated. In this way, a base layer with a substantially constant thickness can be achieved. Further, when an LED fails, by having a control unit configured to individually control a subset, the subset can be controlled to compensate for the failed LED, so that the uniformity is not significantly affected, and at the same time the failed LED may not need to be replaced.

[0123] Furthermore, by having an LED array covering a large area, the device can be designed so that the relief precursor can be subjected to back exposure in a single step by activating the LED array. Note that the device can be designed for the largest relief precursors, and when a smaller relief precursor has to be exposed (e.g. back exposure), only a portion of the LEDs of the LED array (enough to cover the size of the smaller plate) can be activated. Although the device is preferably intended for back exposure through a transparent substrate layer of a relief precursor, embodiments of the invention also cover devices in which the LED array is used for front exposure.

[0124] By performing control so that the irradiation intensity in a predetermined surface area varies within a certain range, accurate control of the thickness variation of the underlying layer can be achieved.

[0125] Further, by using an LED array, the energy consumption and cost of embodiments of the present invention can be lower than existing solutions using, for example, backside exposure with UV lamps. Also, since no preheating is required as with UV lamps, the method can be faster. Also, since subsets of the LED array can be activated individually depending on the size of the relief precursor, smaller plates will consume less energy than existing solutions where all UV lamps are activated regardless of size.

[0126] According to an exemplary embodiment, Figure 1 The device can be used as follows: The LED array 20 is controlled to emit radiation to the photosensitive layer of the relief precursor P through the substrate layer of the relief precursor so that predetermined surface areas are irradiated simultaneously, wherein multiple subsets are controlled individually and so that the radiation intensity in the predetermined surface areas varies within a predetermined range.

[0127] Before using the device, the device may be calibrated using any of the following methods. According to a first possible embodiment, the calibration method comprises: emitting radiation in a predetermined surface area using the LED array 20; measuring values ​​representing the illumination intensity in a plurality of locations L1, L2, L3, etc. of the predetermined surface area using at least one sensor 50; determining a control scheme for controlling the plurality of subsets 21 based on the measured values ​​to obtain a desired illumination pattern in the predetermined surface area. The desired illumination pattern may be a substantially uniform illumination pattern in order to obtain a bottom layer having a substantially constant thickness, but may also be a pattern with different illumination areas in order to obtain different bottom layer thicknesses.

[0128] The measurements in the multiple locations L1, L2, L3, etc. can be performed by moving at least one sensor 50 so that the at least one sensor performs measurements in the multiple locations. For example, the measurements and controls may include:

[0129] positioning at least one sensor 50 at a first position in a plane parallel to the LED array, the first position being associated with one or more first adjacent LEDs of the LED array;

[0130] measuring an illumination intensity at a first location L1 associated with a first position of at least one sensor 50;

[0131] positioning at least one sensor 50 at an additional location in the plane, the additional location being associated with one or more additional adjacent LEDs of the LED array;

[0132] measuring the illumination intensity at a further location L2 associated with the further position of the at least one sensor;

[0133] adjusting the illumination intensity of one or more of the first and / or further adjacent LEDs such that the difference between the illumination intensity in the first location L1 and the further location L2 is reduced;

[0134] The above steps may be repeated for the same locations L1 , L2 and / or other locations L3 and so on until the desired illumination pattern is achieved.

[0135] According to another possible embodiment, the calibration method includes:

[0136] emitting radiation in predetermined areas of the photosensitive layer of the relief precursor using the LED array 20 so that the predetermined areas are cured;

[0137] removing uncured portions of the relief precursor;

[0138] Measure thickness variation in the cured area;

[0139] A control scheme for controlling the plurality of subsets is determined based on the measured thickness variations to obtain a desired illumination pattern in a predetermined area.

[0140] Figures 3 to 6 Detailed examples of using Figure 1 The exemplary embodiment of the embodiment of the present invention has the same main components as those of the embodiment of the present invention, and these components will not be described again. The device includes a housing 100, which has a lower housing part 130 including a back exposure device and an upper housing part 110 including a front exposure device. The relief precursor P can be brought to the supporting structure 10 manually or automatically so that the relief precursor is located between the back exposure device in the lower housing part 130 and the front exposure device in the upper housing part 110. Optionally, the device can include an additional front exposure device 120, which includes a movable LED strip. The movable LED strip structure 120 can be moved from right to left and backward.

[0141] Figure 4 The cross section of the lower housing portion 130 is illustrated. The LED array 20 is arranged in the lower housing portion 130 and includes a plurality of LED PCBs 22 (here, 3×6 LED PCBs 22 ) arranged adjacent to each other in a plane parallel to the glass plate 10 supporting the relief precursor P. Figure 4 and Figure 6 Also shown is a driver device 30 including a plurality of driver PCBs 32 carrying driver circuits. The driver PCBs 32 are arranged in a plane below the LED PCBs 22. A plurality of cables 31 connect the driver circuits on the driver PCBs 32 to connectors on the upper LED PCBs 22 to connect the LEDs 21 arranged on the LED PCBs 22. The LED PCBs 22 and the driver PCBs 32 are mounted on opposite sides of a support structure 65 (preferably made of a thermally conductive material). A cooling device (not shown) may be configured to generate an airflow through the channels 61 of the support structure 65 to cool the LED PCBs 22 and the associated LEDs 21.

[0142] The upper housing portion 130 houses a plurality of primary UV tubes 112 for front-side exposure of the relief precursor P in a manner known to those skilled in the art.

[0143] Figure 5 The sensor device 50 is shown in detail. The sensor device 50 comprises a movable support structure 51 carrying a sensor support plate 52 on which a plurality of sensors, typically UV sensors, such as diodes (in Figure 5The support structure 51 is movable in the X-direction and the Y-direction in a plane parallel to the LED array 20. Optionally, the support structure 51 may be movably attached to a front exposure device 120 movable in the X-direction, wherein the support structure is movable relative to the front exposure device 120 in the Y-direction.

[0144] The method explained above in conjunction with the previous embodiment can also be used Figures 3 to 6 device to execute.

[0145] In non-illustrated embodiments, a post-treatment may be provided to perform post-processing on the relief precursor, such as cleaning, drying, post-exposure, heating, cooling, removal of material, etc. Further, in non-illustrated embodiments, a pre-treatment may be provided to perform pre-processing on the relief precursor, the pre-treatment being selected from the group consisting of cutting, ablation, exposure to electromagnetic radiation, and combinations thereof.

[0146] The relief precursor generally includes a support layer and at least one photosensitive layer. The support layer can be a flexible metal, a natural or artificial polymer, paper, or a combination thereof. Preferably, the support layer is a flexible metal or polymer film or sheet. In the case of a flexible metal, the support layer can include a film, a sieve structure, a mesh structure, a woven or nonwoven structure, or a combination thereof. Steel, copper, nickel, or aluminum plate is preferred, and can be about 50 to 1000 μm thick. In the case of a polymer film, the film is dimensionally stable but flexible, and can be, for example, made of a polymer reinforced by a woven, nonwoven, or layered fiber (e.g., glass fiber, carbon fiber, polymer fiber), or a combination thereof. Preferably, polyethylene and polyester foil are used, and their thickness can be in the range of about 100 to 300 μm, preferably in the range of 100 to 200 μm.

[0147] In addition to the photosensitive layer and the support layer, the relief precursor may also include one or more further additional layers. For example, the further additional layer may be any of the following layers: a layer that can be directly engraved (e.g. by laser), a solvent or water developable layer, a heat developable layer, a mask layer, a cover layer, a barrier layer, etc. One or more bonding layers may be positioned between the above-mentioned different layers, which ensure proper bonding of the different layers.

[0148] Although the principles of the present invention have been described above in conjunction with specific embodiments, it should be understood that this description is intended only as an example and not as a limitation on the scope of protection determined by the appended claims.

Claims

1. An apparatus for exposing a relief precursor comprising at least one photosensitive layer, the apparatus comprising: A housing (100) having a lower housing portion (130) including a backside exposure device and an upper housing portion (110) including a frontside exposure device (120); A supporting structure (10) for supporting a relief precursor; The backside exposure device comprises an LED array (20) configured to illuminate the photosensitive layer of the relief precursor carried by the carrying structure, the LED array comprising a plurality of subsets of one or more LEDs, each subset being individually controllable; at least one sensor (50) configured to measure values ​​representative of illumination intensity at a plurality of locations (L1, L2, L3) of a predetermined surface area illuminated by the LED array; a control unit (40) for individually controlling the plurality of subsets based on a value measured by the at least one sensor; as well as a moving device configured to move the at least one sensor in order to perform measurements in the plurality of locations, wherein the bearing structure comprises a support structure which is at least partially transparent to the light generated by the LED array, The at least one sensor is located in the upper housing portion (110), and the supporting structure (10) is located between the upper housing portion (110) and the lower housing portion (120).

2. The device according to claim 1, characterized in that The moving means comprises a drive configured to move the at least one sensor in a surface parallel to the relief precursor carried by the carrying structure.

3. The device according to claim 1 or 2, characterized in that: It also includes a support structure (51) that carries a sensor support plate (52) on which at least one sensor is mounted, wherein the support structure (51) is movable in an X direction and a Y direction in a plane parallel to the LED array (20).

4. The device according to claim 3, characterized in that The front exposure device (120) is movable in the X direction, and the support structure (51) is movably attached to the front exposure device (120), wherein the support structure (51) is movable relative to the front exposure device (120) in the Y direction.

5. The device according to any one of claims 1 to 4, characterized in that The control unit is configured to control the LED based on the measurement values ​​of the at least one sensor in the plurality of locations so that the difference in illumination intensity in the plurality of locations is within a predetermined range.

6. The device according to any one of claims 1 to 5, characterized in that The number of the plurality of locations is equal to or greater than the number of the plurality of subsets.

7. A device according to any one of the preceding claims, characterised in that Also included is a distance adjustment device configured to adjust the distance (d) between the supporting structure and the LED array.

8. A device according to any one of the preceding claims, characterised in that The LEDs of the LED array are configured to emit wavelengths in the range of 200 nm to 2000 nm.

9. A device according to any one of the preceding claims, characterised in that The irradiation intensity delivered by the LED in the predetermined surface area is between 0.1 and 2000 mW / cm 2 within the range.

10. The device according to any one of the preceding claims, characterized in that The distance (ds) between the predetermined surface area (S) and the LED array 20 is at least 35 mm.

11. The device according to any one of the preceding claims, characterized in that For any predetermined surface area (S) at a distance between a first distance (d1) and a second distance (d2) of the LED array, the illumination intensity variation in the predetermined surface area (S) is within a predetermined range, wherein the difference (d2-d1) between the second distance and the first distance is at least 1 mm.

12. A device according to any one of the preceding claims, characterised in that The distance between each LED of the LED array is at least 5 mm.

13. A device according to any one of the preceding claims, characterised in that Also included is a cooling device (60) configured to cool the LED array.

14. A device according to any one of the preceding claims, characterised in that Also included is a driving device configured to drive the LED array.

15. A device according to any one of the preceding claims, characterised in that The supporting structure comprises any one of the following structures: a glass plate, a polymer plate, a mesh, a set of rollers, a drum, a structure configured for suspending the relief precursor, a structure configured for tensioning the relief precursor.

16. A method for exposing a relief precursor comprising a transparent substrate layer and at least one photosensitive layer, the method comprising: emitting radiation to the photosensitive layer of the relief precursor using an apparatus according to any one of claims 1 to 15, such that a predetermined surface area of ​​at least 900 cm2 of the photosensitive layer is irradiated simultaneously, the LED array of the apparatus comprising a plurality of subsets of one or more LEDs, each subset being individually controllable; as well as The plurality of subsets are controlled individually and the illumination intensity in the predetermined surface area is made to vary within a predetermined range.

17. A calibration method for calibrating an exposure apparatus according to any one of claims 1 to 15, the method comprising: Using the LED array to emit radiation in a predetermined surface area; the LED array includes a plurality of subsets of one or more LEDs, each subset being individually controllable; measuring values ​​representing the intensity of the illumination in a plurality of locations of the predetermined surface area by moving at least one sensor so that the at least one sensor performs measurements in the plurality of locations; as well as A control scheme for controlling the plurality of subsets is determined based on the measured values ​​to obtain a desired illumination pattern in the predetermined surface area.

18. The calibration method according to claim 17, characterized in that: A desired illumination pattern is a substantially uniform illumination pattern.

19. The calibration method according to claim 17 or 18, characterized in that: The measurements in the plurality of locations are performed by moving at least one sensor so that the at least one sensor performs measurements in the plurality of locations.

20. The calibration method according to any one of claims 17 to 19, characterized in that: Measurement and control include: positioning at least one sensor at a first position in a plane parallel to the LED array, the first position being associated with one or more first adjacent LEDs of the LED array; measuring the illumination intensity at a first location associated with the first position of the at least one sensor; positioning the at least one sensor at an additional location in the plane, the additional location being associated with one or more additional adjacent LEDs of the LED array; measuring the illumination intensity at a further location associated with the further position of the at least one sensor; and The illumination intensity of one or more of the first and / or further adjacent LEDs is adjusted such that a difference between the illumination intensity in the first location and the further location is reduced.

21. The calibration method according to claim 20, characterized in that: The first position and the further position of the at least one sensor are selected such that at least one adjacent LED of the first position is an adjacent LED of the further position.

22. A method for exposing a relief precursor comprising a substrate layer and at least one photosensitive layer, the method comprising the calibration method according to any one of claims 17 to 21 and the step of irradiating the photosensitive layer of the relief precursor with the obtained desired illumination pattern.

23. A calibration method for calibrating an exposure device according to any one of claims 1 to 15, the exposure device comprising an LED array, the method comprising: emitting radiation in predetermined areas of the photosensitive layer of the relief precursor using the LED array so that the predetermined areas are cured; The LED array includes a plurality of subsets of one or more LEDs, each subset being individually controllable; removing an uncured portion of the relief precursor; Measure thickness variation in the cured area; as well as A control scheme for controlling the plurality of subsets is determined based on the measured thickness variation to obtain a desired illumination pattern in the predetermined area.

24. A method for exposing a relief precursor comprising a substrate layer and at least one photosensitive layer, the method comprising the calibration method according to claim 23 and the step of irradiating the photosensitive layer of another relief precursor with the obtained desired illumination pattern.

25. The method according to any one of claims 17 to 24, characterized in that The relief precursor is a precursor for an element selected from the group consisting of flexographic printing plates, relief printing plates, movable type plates, intaglio plates, (flexible) printed circuit boards, electronic components, microfluidic components, microreactors, moving cells, photonic crystals and optical components, Fresnel lenses.

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