Apparatus and method for exposure of relief precursors

Abstract

To provide an apparatus and a method for exposure of relief precursors.SOLUTION: Provided is an apparatus for exposure of a relief precursor (P) which comprises a substrate layer and at least one photosensitive layer, the apparatus comprising: a first light source (1) configured to illuminate a first side of the relief precursor, a movable second light source (2) configured to illuminate a second side of the relief precursor opposite the first side, a movable shield (3) located between the first light source and the second light source (2) and configured to capture at least a portion of the light of the second light source transmitted through the relief precursor (P), and moving means configured to move the movable shield simultaneously with the second light source.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The field of the invention relates to apparatus and methods for exposing relief precursors, in particular printing plate precursors, more in particular for exposing the front and back sides of printing plate precursors.

[0002] background

[0003] The relief structure can be made by transferring image information onto an imageable layer and removing parts of the imageable layer. The formed relief can then be used to transfer information onto a substrate in a printing step. An example of a relief precursor is a printing plate precursor. Digitally imageable flexible printing plate precursors are known and typically include at least a dimensionally stable support layer, a photosensitive layer and a digitally imageable layer. The digitally imageable layer can be, for example, a laser ablation layer. In the case of conventional printing plate precursors, the digitally imageable layer is replaced by a mask attached to the photosensitive layer.

[0004] To generate 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. Following writing of the mask, the plate is exposed to radiation through the mask so that the photosensitive layer undergoes polymerization or crosslinking, or a reaction that changes the solubility or flowability of the photosensitive layer in the areas not covered by the mask. After exposure, the mask and the residues of the non-exposed parts of the photosensitive layer are removed. This can be done with one or more liquids in a washing device or by thermal development, where the non-exposed material of the photosensitive layer is liquefied and removed by increasing the temperature.

[0005] An exposure device for printing plate precursors is known. The exposure device may comprise a first light source for back exposure and a second light source for front exposure. The back exposure can be performed with a set of UV light tubes. The back exposure creates a solid layer (floor) that creates the relief structure. The front exposure can be performed with a set of UV light tubes or with a movable UV light source such as a movable laser or LED bar. Some exposure devices perform only pre-exposure or only post-exposure, depending on the requirements. In some cases, the exposure device can expose from both sides, and embodiments of the present invention relate to such cases.

[0006] US 2016 / 0368260 A1 discloses an autonomous apparatus for photopolymerization of a flexographic printing plate, the plate comprising a major surface and a base opposite to the major surface. The apparatus comprises an exposure chamber in which at least a first photopolymerization means of the base of the plate is located. The apparatus further comprises a moving means configured to pull the plate along a feed direction. The first photopolymerization means comprises an array of LEDs aligned along a direction substantially perpendicular to the feed direction.

[0007] US 2018 / 0210345 A1 discloses a method for exposing a photosensitive printing plate with a predetermined radiation density from the main (top) side and with a predetermined radiation density from the back (bottom) side, which includes performing a main exposure with a time delay after the back exposure.

[0008] overview

[0009] It is an object of embodiments of the present invention to provide an apparatus and method for exposing a relief precursor comprising a substrate layer and at least one photosensitive layer using a first light source illuminating a first side of the relief precursor and a second light source illuminating a second side of the relief precursor, while avoiding ghost images and limiting heating of the first light source by the second light source.

[0010] According to a first aspect of the invention, an apparatus comprises a first light source, a movable second light source, a movable shield and a moving means. The first light source is configured to illuminate a first side of the relief precursor. The movable second light source is configured to illuminate a second side of the relief precursor opposite the first side. The movable shield is located between the first light source and the second light source and configured to capture at least a portion of the light from the second light source that has been transmitted through the relief precursor. The moving means is configured to move the movable shield simultaneously with the second light source.

[0011] Thus, according to an embodiment of the invention, a shield is used, which moves with the second light source to limit the amount of light going from the second light source to the first light source, and thus the amount of reflection by components of the first light source, such as the support on which the light elements are mounted, or components in the vicinity of the first light source, such as a shutter arranged above the first light source. This prevents or reduces the presence of ghost images created by reflected light. Furthermore, heating of components of the first light source and components in the vicinity of the first light is reduced. In particular, if a shutter is present above the first light source, its heating can be reduced to avoid its burning.

[0012] Preferably, the first light source extends substantially in a plane intended to be oriented parallel to the relief precursor, and the second light source is movable in a plane parallel to the plane of the first light source. The first light source can comprise a plurality of first light emitting elements, such as light tubes or LEDs, and the plane is the plane on which the plurality of first light emitting elements are placed. Similarly, the second light source can comprise a plurality of second light emitting elements, and the plane is the plane on which the plurality of second light emitting elements are placed.

[0013] Preferably, the first light source is stationary, however in other embodiments, for example when an LED array is used for the first light source, the first light source may be movable as well.

[0014] Preferably, the first light source is configured to illuminate a first illumination area of ​​the surface and the second light source is configured to illuminate a second illumination area of ​​the surface, the surface being placed between the shield and the second light source and corresponding to the surface on which the first side of the relief precursor is intended to be placed, the term illumination area of ​​the surface being defined by an area with an intensity higher than 10% of the maximum light intensity at said surface. If a carrier structure is present, the surface corresponds to the support surface of the carrier structure. It is preferred that the second illumination area is at least two times, more preferably at least three times, most preferably at least five times smaller than the first illumination area. In a typical embodiment, the first light source is used to illuminate substantially the entire first side of the relief precursor and the second light source illuminates a smaller area of ​​the second side of the relief precursor, typically with a higher light intensity.

[0015] As mentioned above, the shield is configured to capture at least a portion of the electromagnetic radiation emitted from the second light source that is transmitted through the relief precursor. The term "capture" should be interpreted to include absorbing a portion of the radiation and / or directing a portion of the radiation away from the first light source or an area nearby.

[0016] Preferably, the shield is impermeable to the electromagnetic radiation emitted by the second light source.

[0017] Preferably, the surface of the shield facing the second light source is configured to absorb at least 80%, preferably at least 95%, of the electromagnetic radiation received at that surface, which can be easily achieved by having a black surface.

[0018] Preferably, the shield is a plate-like element, but other shapes are possible: for example, the shield may be a rod with a black outer surface, or it may be a sheet mounted in a frame.

[0019] According to a possible embodiment, the movable shield is mechanically coupled to the second light source so that they can be easily moved simultaneously. According to another embodiment, the shield and the second light source can be moved independently, the moving means comprising a moving means for moving the second light source and a moving means for moving the shield. In the latter case, the control means can control the two moving means to obtain a synchronous movement of the second light source and the shield.

[0020] According to a preferred embodiment, the vertical projection of the shield on the surface intended to correspond to the operation with the first side of the relief precursor is 1-10% larger, preferably 5-10% larger, than the illumination area of ​​the second light source on said surface, the illumination area being defined by an area with an intensity higher than 10% of the maximum light intensity on said surface.

[0021] Preferably, the apparatus further comprises a support structure configured to support the relief precursor. The support structure may be placed between the second light source and the shield. Preferably, the support structure is transparent to the electromagnetic radiation emitted by the first light source. The support structure may be, for example, a transparent glass plate, a screen of a transparent material or a transparent plastic.

[0022] Preferably, the distance between the carrier structure and the movable shield is less than 50 mm, preferably less than 20 mm, more preferably less than 10 mm. In this way, the shielding capacity of the shield can be increased while limiting the size of the shield.

[0023] Preferably, the carrier structure is a plate and the thickness of the carrier plate is between 2mm and 20mm. Preferably, the distance between the second light source and the carrier structure is 10mm-100mm.

[0024] Preferably, the second light source comprises a support, e.g. a printed circuit board (PCB), on which a plurality of light emitting elements, e.g. an array of LEDs, are mounted. Preferably, the support has a width of less than 500 mm, e.g. between 100 mm and 400 mm.

[0025] Optionally, a plurality of second light sources and a plurality of shields may be provided, for example two second light sources and two associated shields may be provided, each second light source intended to move along the relief precursor and to illuminate a portion, for example half of the relief precursor.

[0026] Optionally, the apparatus further comprises cooling means configured to cool the moveable shield. For example, the moveable shield may be cooled by gas or fluid. In an exemplary embodiment, the moveable shield may comprise cooling channels through which a cooling medium is routed. Alternatively, a cooling gas flow may be generated around the shield.

[0027] According to typical embodiments, the first light source is selected from the group including a plurality of LEDs, a set of fluorescent lamps, a flash lamp, a set of light tubes, an LCD screen, a light projection system (with a movable mirror), a solar collection system, and combinations thereof. Preferably, the first light source takes the form of an LED array including a plurality of LEDs.

[0028] Preferably, the apparatus further comprises control means operatively controlling the first light source depending on the location of the moveable shield.

[0029] According to a typical embodiment, if the first light source comprises a set of light tubes or an LED array, the control means can be configured to power the first light source for a first period of time and power and move the second light source for a subsequent period of time. In other words, the first and second light sources operate alternately. In this way, the back exposure is not hindered by the light emitted by the shield or the second light source. The UV tubes have the advantage that substantially the entire first side, i.e. the entire back side of the relief precursor, can be exposed simultaneously, which is often referred to as flood exposure. The intensity output of the UV tubes is axially homogeneous, and by tightly packing the tubes the homogeneity was sufficient to produce a printing plate.

[0030] According to another exemplary embodiment, in which the first light source comprises an LED array, the control means may be configured to simultaneously power the first and second light sources, the first light source being controlled such that a group of light emitting elements of the LED array facing the shield is switched off while other light emitting elements of the LED array are switched on, said group changing as the shield moves. In this way, the amount of light emitted by the first light source towards the shield can be kept very low, avoiding or reducing undesirable reflections on the side of the shield facing the first light source. This also limits any heating of the shield by the light from the first light source. LEDs are advantageous for the first light source due to their narrow emission spectrum and low energy consumption.

[0031] Preferably, the first light source comprises a support having a light absorbing surface, e.g. a black surface, facing the second light source. For example, if the first light source is an LED array, the LEDs may be mounted on a PCB, and the PCB may have a black exterior surface. In this way, any light reflected or transmitted in the direction of the first light source may be at least partially absorbed by the light absorbing surface of the support.

[0032] According to an exemplary embodiment, the first light source is an array of LEDs comprising a plurality of subsets of one or more LEDs, each subset being individually controllable. Preferably, the first light source is configured to simultaneously illuminate a predetermined surface area. The surface area can be adjusted for different relief precursor sizes. The control unit may be configured to individually control the plurality of subsets, such that the variation in illumination intensity in the predetermined surface area is within a predetermined range. By using an LED array with individually controllable subsets of LEDs, the illumination intensity of the subsets can be adjusted to obtain an approximately homogeneous illumination of the illuminated surface area. In this way, a floor with a substantially constant thickness can be achieved. Furthermore, by having a control unit configured to individually control the subsets, in case of failure of an LED, the subsets may be controlled to compensate for the failed LED, so that the homogeneity is not significantly affected, while it may not be necessary to replace the failed LED. A more detailed description of such an exemplary embodiment can be found in patent application NL2023537 in the name of the applicant, which is hereby incorporated by reference.

[0033] Preferably, the first light source is configured to be movable in a direction perpendicular to the plane of the relief precursor, typically perpendicular to a transparent carrier plate supporting the relief precursor. It should be noted that the LED array and / or the carrier structure may be moved. By using such adjustment means, the homogeneity of the illumination in the desired plane can be further improved. For example, the distance between the carrier structure and the LED array can be adjusted depending on the thickness of the relief precursor.

[0034] The first light source is preferably configured to provide a lower intensity than the second light source. For example, the first light source may provide an intensity of less than 100 mW / cm 2 The first light source can be configured to deliver an intensity of 100 mW / cm 2 Intensity of more than 350 mW / cm 2The optical fiber can be configured to deliver an intensity greater than 100 Hz.

[0035] In a typical embodiment, the second light source is selected from the group including an LED array, a set of fluorescent lamps, a flash lamp, a set of linearly arranged light tubes, a (scanning) laser, an LCD screen, a light projection system (with a moveable mirror), and combinations thereof. Preferably, the second light source is an array of LEDs including multiple subsets of one or more LEDs, each subset being individually controllable. Individual LEDs of the second light source may be controlled to illuminate an area with a substantially homogenous intensity. Preferably, the second light source has a power of 100 mW / cm or more. 2 More preferably, 350 mW / cm 2 Sends out strength that exceeds

[0036] Preferably, the first light source and / or the second light source emits wavelength radiation between 200-2000 nm, more preferably between 250-500 nm, even more preferably between 300-450 nm, most preferably between 270-410 nm, for example mainly at 365 nm.

[0037] According to yet another embodiment, the apparatus comprises a shutter placed between the first light source and the movable shield. If fluorescent lamps are used, the shutter may be required to be pre-adjusted before the start of the exposure in order to produce a stable light output. The shutter is made of a material that is non-transparent to the electromagnetic radiation emitted by the first light source. The shutter may be a rigid flat sheet, a combination of several flat sheets, a foldable structure, a curtain, or a flexible material that can be rolled up on a roll.

[0038] According to an exemplary embodiment, the means for moving the second light source and / or the moveable shield is one or more linear motors, one or more chains, cables or belts, one or more lead screws, creep drives, one or more toothed wheels, timing wheels, belts, or combinations thereof.

[0039] Optionally, one or more sensors may be provided, such as light sensors, magnetic sensors, proximity sensors, temperature sensors, overheat sensors, flow sensors, intensity sensors, pressure sensors, thickness sensors, etc. The movement of the second light source and / or the shield, and the actuation of the first and / or second light sources may then be further controlled as a function of sensor data measured by the one or more sensors.

[0040] Optionally, the apparatus may include additional light sources, additional cooling means, heating or cooling means, transport means, feeding means, unloading means, positioning means, identification means, and combinations thereof. Optionally, the apparatus further comprises a controller for controlling various components of the apparatus and / or a housing having one or more openings (for loading and unloading the relief precursor). Optionally, the apparatus may comprise one or more additional processing units selected from the group including a loading and unloading unit, an imaging unit, a liquid developing unit, a thermal developing unit, a drying unit, a post-processing unit, a pre-processing unit, a storage unit, and combinations thereof.

[0041] According to another aspect of the invention there is provided a method for exposing a relief precursor, preferably using an apparatus according to any one of the above embodiments, comprising the steps of: a. placing a relief precursor between a first light source and a second light source; b. exposing the relief precursor to a first light source; c. moving the second light source while exposing the relief precursor to the second light source; d. absorbing at least a portion of the light emitted by the second light source and transmitted through the relief precursor in a space between the first light source and the relief precursor; e. removing the relief precursor and performing any further steps; Includes.

[0042] Preferably, the absorption is performed by moving a shield in the space between the first light source and the relief precursor during exposure by the second light source. The shield may have any one of the characteristics described above in relation to the apparatus.

[0043] Steps b) and c) may be performed sequentially, simultaneously, or in the opposite order. If performed simultaneously, step b) may be completed while step c) is still in progress, or vice versa. For example, for thin plates, step b) may be completed before step c), and for thick plates, step c) may be completed before step b). For example, as described above, when the first light source comprises a set of light tubes, the first light source and the second light source may be powered sequentially. In another embodiment where the first light source includes multiple LEDs, the powering of the first and second light sources may be performed simultaneously.

[0044] Furthermore, step b) may comprise multiple exposure cycles and / or step c) may comprise multiple exposure and movement cycles, where the exposure cycles of steps b) and c) may be performed simultaneously or successively in any order, where, optionally, an exposure cycle of step b) may be performed between two exposure cycles of step c) and / or an exposure cycle of step c) may be performed between two exposure cycles of step b). For example, step c) may consist of performing one or more first cycles in which the second light source is moved back and forth and controlled to emit light at a first intensity, and one or more second cycles in which the second light source is moved back and forth and controlled to emit light at a second different intensity, preferably a second lower intensity. More generally, the timing and intensity of the exposure and movement in steps b) and c) may be controlled in any possible way, for example functionally adjusted depending on the type of relief precursor. For example, when steps b) and c) are performed simultaneously, it is possible to time the second light source to move back and forth multiple times while the first light source is exposed at a high power level, so that each portion of the relief precursor receives the same dose at the end of the exposure by the first light source. It is also possible to perform steps b) and c) according to two or more cycles, where these cycles may be periodic or aperiodic. For example, a first exposure by the first light source and a first exposure by the second light source may be followed by a second or subsequent exposure by the first light source and a second or subsequent exposure by the second light source. The second or subsequent exposure by the first light source may be performed after or during the retraction of the second light source.

[0045] Step c) can be performed by moving the second light source over the relief precursor several times in one or several cycles. Furthermore, in step c) the second light source can be moved forwards or backwards over the relief precursor or both, and the second light source can be controlled to emit light during the forward movement, the backward movement or both movements.

[0046] In step c), the moving speed of the second light source may be the same or different for the forward and backward movements. Furthermore, in step d), the speed of the forward movement may be faster than the speed of the backward movement or vice versa. Optionally, in step c), the movement of the second light source may be performed periodically or with increasing or decreasing speed for the forward and / or backward movements.

[0047] According to further developed embodiments, in step b) and / or in step c), the intensity distribution of the light output by the first light source and / or the second light source may be varied during the movement. For example, in step c), the intensity of the light output may be different for the forward and backward movements and / or may be different in different cycles. Also, in step b) and / or in step c), the intensity of the light output may be varied over time.

[0048] Furthermore, if the first light source comprises an LED array, in step b) the intensity of the light output of a subset of the LED array can be varied. In a typical embodiment, steps b) and c) are performed simultaneously, and in step b) the intensity distribution of the light output by the first light source is correlated to the movement of the second light source in step c). For example, if the first light source comprises an LED array, the first light source and the second light source can be powered simultaneously, and the first light source is controlled such that a group of light-emitting elements of the LED array facing the shield is switched off while other light-emitting elements of the LED array are switched on, said group changing as the shield moves. Thus, the intensity distribution of the first light source changes as the shield moves. In this way, the amount of light emitted by the first light source towards the shield can be kept very low, avoiding or reducing undesirable reflections on the side of the shield facing the first light source. This also limits any heating of the shield by the light from the first light source.

[0049] Preferably, the relief precursor is a precursor for an element selected from the group comprising flexographic printing plates, relief printing plates, letterpress plates, intaglio printing plates, (flexible) printed circuit boards, electronic elements, microfluidic elements, microreactors, photovoltaic cells, photonic crystals and optical elements, Fresnel lenses.

[0050] The optional further steps may be selected from the group of removing uncured material, washing, drying, heating, post-exposing, polishing, cutting, and combinations thereof. [Brief description of the drawings]

[0051] The accompanying drawings are used to illustrate 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 invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings. [Figure 1]FIG. 1 is a schematic cross-sectional view of an exemplary embodiment of an apparatus for exposing a relief precursor. [Diagram 2] FIG. 2 is a schematic cross-sectional view of an exemplary embodiment of an apparatus for exposing a relief precursor. [Diagram 3] FIG. 3 is a schematic cross-sectional view of an exemplary embodiment of an apparatus for exposing a relief precursor. [Figure 4] FIG. 4 is a perspective view of another exemplary embodiment of an apparatus for exposing a relief precursor.

[0052] Detailed Description of the Embodiments

[0053] Fig. 1 illustrates diagrammatically an apparatus for exposure of a relief precursor P comprising a substrate layer and at least one photosensitive layer. The apparatus comprises a first light source 1, a movable second light source 2, a carrier structure 4 and a movable shield 3. The first light source 1 is configured to illuminate a first side of the relief precursor P, here the underside also called the back side. The movable second light source 2 is configured to illuminate a second side of the relief precursor P opposite to the first side. The second side is typically the top side of the relief precursor P. The movable shield 3 is arranged between the first light source and the second light source 2, in particular between the first light source 1 and the carrier structure 4.

[0054] The shield 3 is configured to capture at least a portion of the light of the second light source 2 that has been transmitted through the relief precursor P (see arrow L). The shield 3 is non-transparent to the electromagnetic radiation emitted by the second light source. The shield has a surface 32, here a top surface, facing the second light source 2 and configured to absorb more than 80% of the light received at said surface, preferably more than 95%. This top surface 32 may be a black surface. In an exemplary embodiment, the shield 3 is a plate with a flat top surface 32, but the skilled person will understand that the shield may have any suitable shape, for example a rod with a black outer surface. The shield 3 may be mechanically coupled to the second light source 2 or may be independently movable. Optionally, the device may further comprise cooling means (not shown) configured to cool the movable shield 3.

[0055] The first light source 1 extends substantially in a plane parallel to the relief precursor P. The first light source 1 is stationary. The second light source 2 is movable back and forth in a plane parallel to the plane of the first light source 1, as indicated by the arrow A1. Also, the shield 3 is movable back and forth in a plane parallel to the plane of the first light source 1, as indicated by the arrow A2.

[0056] Preferably, the first light source 1 is configured to illuminate a first illumination area of ​​a surface (having a width w1' in FIG. 1) and the second light source is configured to illuminate a second illumination area of ​​said surface (having a width w2' in FIG. 1), said surface being placed between the shield and the second light source and corresponding to the surface on which the first side of the relief precursor is intended to be placed. The illumination area of ​​a surface refers to an area that is greater than 10% of the maximum light intensity on said surface. If a carrier structure 4 is present, the surface corresponds to the support surface of the carrier structure 4. Preferably, the second illumination area (having a width w2' in FIG. 1) is at least two times smaller than the first illumination area (having a width w1' in FIG. 1), more preferably at least three times smaller, most preferably at least five times smaller. In a typical embodiment, a first light source 1 is used to illuminate substantially the entire first side (i.e. the entire back side) of the relief precursor, while a second light source 2 illuminates a smaller area of ​​the second side (i.e. the top side) of the relief precursor, typically with a higher light intensity.

[0057] The vertical projection of the shield 3 on the surface is 1-10% larger, preferably 5-10% larger, than the second illumination area (having a width w2' in FIG. 1) of the second light source 2 on said surface. For example, the width w3 of the shield 3 may be 5 mm or more larger than the width w2' of the second illumination area. Preferably, the widths w2, w2' and w3 are between 100 mm and 600 mm, for example between 200 mm and 400 mm. Preferably, the width w1' is between 1500 mm and 3000 mm, for example between 1800 mm and 2500 mm.

[0058] A carrier structure 4, for example a glass plate, is configured to support the relief precursor and is placed between the second light source 2 and the shield 3. The carrier structure 4 may be transparent to the electromagnetic radiation emitted by the first light source 1. Preferably, the distance d between the carrier structure 4 and the movable shield is less than 50 mm, preferably less than 20 mm, more preferably less than 10 mm. Preferably, the carrier structure is a plate with a thickness tc of 0.5-20 mm (preferably 1-15 mm). Preferably, the distance d2 between the second light source 2 and the carrier structure 4 is 10 mm-100 mm, for example 20 mm-50 mm. Preferably, the distance d1 between the first light source 1 and the support surface of the carrier structure 4 is 10 mm-150 mm, for example 20 mm-100 mm. The thickness tp of the relief precursor P is preferably 0.5-10 mm (preferably 1-7 mm).

[0059] The first light source 1 may be selected from the group consisting of a plurality of LEDs, a set of fluorescent lamps, a flash lamp, a set of light tubes, an LCD screen, a light projection system (with a moving mirror), a solar collection system, and combinations thereof. The second light source 2 may be selected from the group consisting of an LED array, a set of fluorescent lamps, a flash lamp, a set of linearly arranged light tubes, a (scanning) laser, an LCD screen, a light projection system (with a moving mirror), and combinations thereof.

[0060] In the embodiment of FIG. 2, the first light source 1 comprises a set of UV light tubes. The driving of the first light source 1 and the second light source 2 is performed by a control means 5. The control means 5 may be configured to power the first light source 1 during a first time period and to power and move the second light source 2 during a next time period after said first time period when the first light source is off. It is also possible to perform the powering of the first light source 1 and the second light source 2 according to two or more cycles, which may be periodic or aperiodic. For example, after a first exposure by the first light source 1 and a first exposure by the second light source 2, a second or subsequent exposure by the first light source 1 and a second or subsequent exposure by the second light source 2 may be performed. The second or subsequent exposure by the first light source 1 may be performed after or during the retraction of the second light source 2.

[0061] 2 shows a moving means M1 configured to move the movable shield 3 and a moving means M2 configured to move the second light source 2. A control means 5 may control the moving means M1, M2 such that the second light source 2 and the shield 3 move synchronously, so that the shield 3 performs an optimal shielding function. An openable and closable shutter 6 may be used to shield the UV light tube 1 during preconditioning.

[0062] In the embodiment of Fig. 3, the first light source 1 comprises an LED array and the control means 5 are configured to simultaneously power the first light source 1 and the second light source 2, the first light source being controlled such that a group of light emitting elements 1a of the LED array facing the shield is switched off while other light emitting elements 1b of the LED array are switched on, said group 1a changing as the shield 3 moves. The first light source 1 comprises a support 10, typically a PCB, having a light absorbing surface 12 (e.g. a black surface) facing the second light source 2.

[0063] 3 shows a moving means M configured to move a movable shield 3 simultaneously with a second light source 2. A control means 5 may control the moving means M such that the second light source 2 and the shield 3 move together, and may control the driving of the first light source 1 such that the light distribution of the first light source 1 is functionally adjusted depending on the position of the shield 3.

[0064] The exposure of the relief precursor with the first light source 1 may be completed before the exposure of the relief precursor with the second light source 2, or vice versa. For example, for a thin relief precursor, the back exposure with the first light source 1 may be completed before the main exposure with the second light source 1, and for a thick plate, the main exposure with the second light source 2 may be completed before the back exposure with the first light source 1. Also, the exposure with the first light source 1 and the second light source 2 may be performed in multiple cycles. For example, the main exposure may include multiple first fast cycles and one or more second slow cycles, where the fast cycles are controlled such that the second light source 2 is moved back and forth and emits light at a first intensity, and the second slow cycles are controlled such that the second light source 2 is moved back and forth and emits light at a second different intensity, preferably a second lower intensity. The first fast cycles with high intensity can be used to remove oxygen from the system, while the second slow cycles can slow down the polymerization. At the same time, a back exposure with the first light source may be performed. More generally, the timing and intensity of the exposure and movement steps by the first and second light sources can be controlled in any possible manner, for example functionally tailored depending on the type of relief precursor, for example, the second light source can be timed to be moved back and forth multiple times while the first light source is exposed at a high power level, so that each portion of the relief precursor receives the same dose at the end of the exposure by the first light source.

[0065] Figure 4 shows in detail an exemplary embodiment using the same main components as the embodiment of figures 1-3, which will not be described again. The device comprises a housing 100 having a lower housing part 130 with a first light source and an upper housing part 110, optionally with an additional light source. A relief precursor P may be brought manually or automatically on a carrier structure 4 so as to be placed between the first light source in the lower housing part 130 and the upper housing part 110. The device comprises a second light source 2 with a movable LED bar. The movable LED bar structure 2 is movable from right to left and backwards.

[0066] In embodiments not shown, a post-treatment unit may be provided to perform a post-treatment on the relief precursor, such as washing, drying, post-treatment exposure, heating, cooling, removing material, etc. Furthermore, in embodiments not shown, a pre-treatment unit may be provided to perform a pre-treatment on the relief precursor, said pre-treatment being selected from the group comprising cutting, ablation, exposure to electromagnetic radiation, and combinations thereof.

[0067] The relief precursor generally comprises a support layer and at least one photosensitive layer. The support layer may 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 flexible metal, the support layer may comprise a thin film, a sieve-like structure, a mesh-like structure, a woven or non-woven structure, or a combination thereof. Steel, copper, nickel or aluminum sheets are preferred and may have a thickness of about 50-1000 μm. In the case of polymer films, the film is dimensionally stable but flexible and can be made, for example, from polyalkylenes, polyesters, polyethylene terephthalate, polybutylene terephthalate, polyamides and polycarbonates, polymers reinforced with woven, non-woven or layered fibers (e.g. glass fibers, carbon fibers, polymer fibers) or combinations thereof. Preferably, polyethylene and polyester foils are used, their thicknesses ranging from about 100-300 μm, preferably 100-200 μm.

[0068] In addition to the photosensitive layer and the support layer, the relief precursor may comprise one or more further additional layers. For example, the further additional layers may be any of the following: a directly engravable layer (e.g. by a laser), a solvent or water developable layer, a thermally developable layer, a mask layer, a cover layer, a barrier layer, etc. Between the different layers mentioned above, one or more adhesive layers may be placed which ensure proper adhesion of the different layers.

[0069] While the principles of the present invention have been described above with reference to specific embodiments, it should be understood that this description is made merely 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 (P) comprising a substrate layer and at least one photosensitive layer, comprising: - a first light source (1) configured to illuminate a first side of the relief precursor; a movable second light source (2) configured to illuminate a second side of the relief precursor opposite to the first side; a movable shield (3) placed between the first light source and the second light source (2) and configured to capture at least a portion of the light of the second light source transmitted through the relief precursor (P); a moving means configured to move the movable shield simultaneously with the second light source; An exposure apparatus comprising:

2. 2. The apparatus of claim 1, wherein the first light source extends substantially in a plane intended to be parallel to the relief precursor, and the second light source is movable in a plane parallel to the plane of the first light source.

3. The apparatus of any one of claims 1 to 2, wherein the first light source is stationary.

4. 4. The device according to claim 1, wherein the first light source is configured to illuminate a first illumination area of ​​a surface and the second light source is configured to illuminate a second illumination area of ​​the surface, the surface being placed between the shield and the second light source and corresponding to a surface on which the first side of the relief precursor is intended to be placed, and the second illumination area is at least two times smaller than the first illumination area, more preferably at least three times smaller and most preferably at least five times smaller.

5. The apparatus of any one of claims 1 to 4, wherein the shield is impermeable to electromagnetic radiation emitted by the second light source.

6. Apparatus according to any one of the preceding claims, wherein a surface of the shield facing the second light source is configured to absorb more than 80%, preferably more than 95% of the electromagnetic radiation received at said surface.

7. The apparatus of any one of claims 1 to 6, wherein the movable shield is mechanically coupled to the second light source or is independently movable.

8. 8. Apparatus according to any one of claims 1 to 7, wherein the vertical projection of the shield, placed between the shield and the second light source, on a surface corresponding to a surface on which the first side of the relief precursor is intended to be placed, is 1-10% larger, preferably 5-10% larger, than the illuminated area of ​​the second light source on said surface, the illuminated area being defined by an area whose intensity exceeds 10% of the maximum light intensity in said area.

9. The apparatus according to any one of the preceding claims, further comprising a support structure (4) configured to support the relief precursor, the support structure being placed between the second light source and the shield.

10. The apparatus of claim 9 , wherein the support structure is transparent to electromagnetic radiation emitted from the first light source.

11. 11. Apparatus according to claim 9 or 10, wherein the distance (d) between the support structure and the movable shield is less than 50 mm, preferably less than 20 mm, more preferably less than 10 mm.

12. An apparatus according to any one of the preceding claims, further comprising cooling means arranged to cool the moveable shield.

13. 13. The apparatus of any one of claims 1 to 12, wherein the first light source is selected from the group comprising a plurality of LEDs, a fluorescent lamp, a flash lamp, a set of light tubes, an LCD screen, a light projection system (having a movable mirror), a solar collection system, and combinations thereof.

14. Apparatus according to any one of the preceding claims, further comprising control means operatively controlling said first light source depending on the location of said movable shield.

15. 15. Apparatus according to any preceding claim, wherein the first light source comprises a set of light tubes and the control means is configured to power the first light source for a first period of time and to power and move the second light source for a later period of time.

16. 16. The apparatus of any one of claims 1 to 15, wherein the first light source comprises an LED array, the control means being configured to power the first light source and the second light source simultaneously, and the first light source being controlled such that groups of light emitting elements of the LED array facing the shield are turned off and other light emitting elements of the LED array are turned on, the groups changing as the shield moves.

17. An apparatus according to any preceding claim, wherein the first light source comprises a support having a light absorbing surface facing the second light source.

18. An apparatus according to any preceding claim, wherein the first light source is configured to deliver a lower intensity than the second light source.

19. 19. The apparatus of any one of claims 1 to 18, wherein the second light source is selected from the group consisting of an LED array, a set of fluorescent lamps, a flash lamp, a set of linearly arranged light tubes, a (scanning) laser, an LCD screen, an optical projection system (with a moving mirror), and combinations thereof.

20. Apparatus according to any one of the preceding claims, comprising a shutter (6) located between said first light source and said movable shield.

21. A method for exposing a relief precursor, preferably using an apparatus according to any one of claims 1 to 20, comprising the steps of: a. placing a relief precursor between a first light source and a second light source; b. exposing the relief precursor to the first light source; c) moving the second light source while exposing the relief precursor to the second light source; d. absorbing at least a portion of the light emitted by the second light source and transmitted through the relief precursor in a space between the first light source and the relief precursor; e. removing said relief precursor and performing any further steps; A method comprising:

22. 22. The method of claim 21, wherein the absorbing step is performed by moving a shield into the space between the first light source and the relief precursor during exposure by the second light source.

23. 23. The method according to claim 21 or 22, wherein steps b) and c) are carried out sequentially in any order or simultaneously, where step b) can be completed before, after or simultaneously with step c).

24. 24. The method according to any one of claims 21 to 23, wherein step b) comprises a plurality of exposure cycles and / or step c) comprises a plurality of exposure and movement cycles, and wherein the exposure cycles of step b) and step c) can be performed simultaneously or successively in any order, or an exposure cycle of step b) can occur between two exposure cycles of step c) and / or an exposure cycle of step c) can occur between two exposure cycles of step b).

25. Method according to any one of claims 21 to 24, wherein step c) is performed by moving the second light source over the relief precursor once or several times in a cycle.

26. 26. The method according to any one of claims 21 to 25, wherein in step c) the second light source is moved forwards or backwards or both over the relief precursor, and the second light source is emitting light during said forward movement, said backward movement or during both movements.

27. The method according to any one of claims 21 to 26, wherein in step c) the intensity of the light output by the second light source is varied during the movement.

28. 28. The method according to any one of claims 21 to 27, wherein steps b) and c) are performed simultaneously, and wherein in step b) the intensity distribution of light output by the first light source is correlated with a movement of the second light source in step c).

29. 29. The method according to any one of claims 21 to 28, wherein the relief precursor is a precursor for an element selected from the group comprising flexographic printing plates, relief printing plates, letterpress plates, intaglio plates, (flexible) printed circuit boards, electronic elements, microfluidic elements, microreactors, electrophoretic cells, photonic crystals and optical elements, Fresnel lenses.

30. A printing plate obtainable by exposing a relief precursor according to the method of any one of claims 21 to 29.

Images