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EP-4264374-B1 - METHOD FOR EXPOSURE OF RELIEF PRECURSORS WITH MULTIPLE PROFILES

EP4264374B1EP 4264374 B1EP4264374 B1EP 4264374B1EP-4264374-B1

Inventors

  • THATE, MAXIMILIAN
  • BEYER, MATTHIAS

Dates

Publication Date
20260506
Application Date
20211217

Claims (16)

  1. A method for exposing a relief precursor (P) with a light source (2), the illumination area of the light source (2) covering part of the area of the precursor, wherein exposing the total area of the precursor is performed during an exposure pass by moving relatively to each other the light source and the precursor, the method comprising: - a step (20) of providing a mask (4) on a photosensitive layer of the precursor (P); - a first exposing step (ES1) comprising exposing during one or more exposure passes the precursor through the mask according to a first intensity profile (IP1) and a first speed profile (SP1); - a second exposing step (ES2) comprising exposing during one or more exposure passes the precursor through the mask according to a second intensity profile (IP2) different from the first intensity profile (IP1) and a second speed profile (SP2) different from the first speed profile (SP1), wherein the average intensity (I1) during an exposure pass of the first exposing step (ES1) is higher than the average intensity (I2) during an exposure pass of the second exposing step (ES2).
  2. The method according to claim 1, wherein the first speed profile (SP1) is such that the speed during the one or more exposure passes of the first exposing step (ES1) is substantially constant and/or wherein the second speed profile (SP2) is such that the speed during the one or more exposure passes of the second exposing step (ES2) is substantially constant.
  3. The method according to any of the above claims, wherein the average speed (S1) during an exposure pass of the first exposing step (ES1) is higher than the average speed (S2) during an exposure pass of the second exposing step (ES2).
  4. The method according to any of the above claims, wherein the first intensity profile (IP1), is such that the intensity during the one or more exposure passes of the first exposing step (ES1) is substantially constant, and/or wherein the second first intensity profile (IP2) is such that the intensity during the one or more exposure passes of the second exposing step (ES2) is substantially constant.
  5. The method according to any of the above claims, wherein the first exposing step (ES1) comprises a first number of exposure passes (n1), and/or wherein the second exposing step (ES2) comprises a second number of exposure passes (n2).
  6. The method according to any of the above claims, wherein a first dose applied during an exposure pass of the first exposing step (ES1) is lower than a dose applied during an exposure pass of the second exposing step (ES2); wherein preferably the first and second dose are between 0.2 to 30 J/cm 2 each; wherein more preferably the first dose is between 0,2 and 20 J/cm 2 and the second dose is between 2 and 28 J/cm 2 .
  7. The method according to any one of the claims 5-6, wherein the first number of exposure passes (n1) is different from the second number of exposure passes (n2); wherein preferably the first number of exposure passes (n1) is higher than the second number of exposure passes (n2); wherein more preferably the first number of exposure passes (n1) is two or more and wherein the second number of exposure passes (n2) is one.
  8. The method according to any one of the above claims, wherein the light source (2) is moved in exposure cycles with a first movement in a first direction and a second movement in a second opposite direction, and wherein each exposure cycle comprises one or two exposure passes.
  9. The method according to any of the above claims, wherein the one or more first exposure passes of the first exposing step and one or more exposure passes of the second exposing step are performed during movements in the same direction or wherein one or more exposure passes of the first exposing step and/or one or more exposure passes of the second exposing step are performed during movements in both directions.
  10. The method according to any of the above claims, wherein the ratio between the average speed (S1) during an exposure pass of the first exposing step and the average speed (S2) during an exposure pass of the second exposing step is higher than 1.5 preferably higher than 2, or wherein the ratio between the second and the first average speed is higher than 0,05 preferably higher than 0,08; and/or wherein the ratio between the average intensity (I1) during an exposure pass of the first exposing step and the average intensity (I2) during an exposure pass of the second exposing step is higher than 0.15, preferably higher than 0.5, more preferably higher than 1 or wherein the ratio between the second and the first average intensity is higher than 0,5, preferably higher than 0.7, more preferably higher than 1.
  11. The method according to any of the above claims, further comprising back-exposing the precursor to electromagnetic radiation from a side of the precursor opposite to the relief forming side exposed before, after or during the first and second exposing step; wherein optionally the back-exposing is performed during the first (ES1) and/or the second exposing step (ES2).
  12. The method of claim 11, further comprising prior to the first (ES1) and second exposing step (ES2), receiving (21) the first intensity profile (IP1), the first speed profile (SP1), the second intensity profile (IP2) and the second speed profile (SP2) through an operator interface (7), and, based on the input first and second speed profile (SP1,SP2), whether or not to perform the step of back-exposing during the first and/or the second exposing step (ES1, ES2).
  13. A control means (5) configured for controlling the exposing of a relief precursor (P) with a light source (2), the illumination area of the light source (2) covering part of the area of the precursor, wherein exposing the total area of the precursor is performed during an exposure pass by moving relatively to each other the light source and the precursor, the control means (5) being configured to control an intensity at a surface of the precursor and a movement speed of the light source (2), such that the following steps are performed: - a first exposing step (ES1) comprising exposing during one or more exposure passes the precursor through a mask (4) according to a first intensity profile (IP1) and a first speed profile (SP1); - a second exposing step (ES2) comprising exposing during one or more exposure passes the precursor through the mask (4) according to a second intensity profile (IP2) different from the first intensity profile (IP1) and a second speed profile (SP2) different from the first speed profile (SP1), wherein the average intensity (I1) during an exposure pass of the first exposing step (ES1) is higher than the average intensity (I2) during an exposure pass of the second exposing step (ES2).
  14. The control means according to claim 13, configured to control a movement speed of the light source (2) such that the speed the one or more exposure passes of the first exposing step is substantially constant and/or such that the speed during the one or more exposure passes of the second exposing step is substantially constant; wherein optionally the average speed (S1) during an exposure pass of the first exposing step is higher than the average speed (S2) during an exposure pass of the second exposing step; and/or configured to control an intensity at a surface of the precursor such that the intensity during the one or more exposure passes of the first exposing step is substantially constant, and/or such that the intensity during the one or more exposure passes of the second exposing step is substantially constant.
  15. The control means according to claim 13 or 14, wherein the first exposing step comprises a first number of exposure passes, and/or wherein the second exposing step comprises a second number of exposure passes, wherein preferably the first number of passes is different from the second number of passes, wherein more preferably the first number of passes is higher than the second number of passes; and/or wherein a first dose applied during an exposure pass of the first exposing step is lower than a dose applied during an exposure pass of the second exposing step; and/or wherein the light source is moved in cycles with a first movement in a first direction and a second movement in a second opposite direction, and wherein each cycle comprises one or two exposure passes.
  16. An exposure apparatus comprising a first light source (1) configured to expose a first side of a relief precursor, a movable second light source (2) configured to expose a second side of the relief precursor opposite the first side during one or more exposure passes, a moving means configured to move the second light source, and a control means according to any one of the claims 13-15; wherein optionally the control means is configured for back-exposing the precursor to electromagnetic radiation from a side of the precursor opposite to the relief forming side exposed before, after or during the first and second exposing step.

Description

Field of invention The field of the invention relates to apparatus and methods for exposure of relief precursors, in particular printing plate precursors. Background Relief structures can be made by transfer of image information onto an imageable layer and removing parts of the imageable layer. The formed relief may then be used to transfer the information in a printing step onto a substrate. An example of a relief precursor is a printing plate precursor. Digitally imageable flexible printing plate precursors are known, and typically comprise at least a dimensionally stable support layer, a photosensitive layer and a digitally imageable mask layer. The digitally imageable mask layer may be e.g. a laser-ablatable layer. In case of conventional printing plate precursors, the digitally imageable mask layer is replaced by a separate mask which is attached to a photosensitive layer. To produce a printing plate from a printing plate relief precursor, according to existing methods, first a mask is written into the digitally imageable layer based on image data to be printed. Following the writing of the mask, the plate is exposed through the mask with radiation such that the photosensitive layer undergoes polymerization or crosslinking or a reaction changing the solubility or fluidity of the photosensitive layer in the regions which are not covered by the mask. Following the exposure, the residues of the mask and of the non-exposed portions of the photosensitive layer are removed. This may be done with one or more liquids in a washer apparatus or by thermal development wherein non-exposed material of the photosensitive layer is liquefied by temperature increase and removed. Exposure apparatus for printing plate precursors are known. An exposure apparatus may comprise a first light source for back exposure and a second light source for front exposure. Back exposure may be done using a set of UV light tubes. The back exposure creates a solid layer (floor) onto which the relief structures are generated. Front exposure may also be done using a set of UV light tubes or may be done using a movable UV light source, such as a movable laser or a LED bar or using stationary light source e.g. an arrangement of tubular light sources. Some exposure apparatus only do front exposure or only do back exposure, depending on the requirements. In some cases the exposure apparatus is capable to expose from both sides and embodiments of the invention relate to such cases. As prior art are known US2018/0004093, US2018/0126721 and US2013/0242276 disclosing known methods for producing flexographic plates. Summary The object of embodiments of the invention is to provide apparatus and methods to expose a relief precursor according to a plurality of profiles with an increased efficiency and/or printing quality. According to a first aspect of the invention, a method according to claim 1 is provided for exposing a relief precursor with a light source, the illumination area of the light source covering part of the area of the precursor, wherein exposing the total area of the precursor is performed during an exposure pass by moving relatively to each other the light source and the precursor. The method comprises a step of providing a mask on a photosensitive layer of the precursor, a first exposing step comprising exposing during one or more exposure passes the precursor through the mask according to a first intensity profile and a first speed profile and a second exposing step comprising exposing during one or more exposure passes the precursor through the mask according to a second intensity profile different from the first intensity profile and a second speed profile different from the first speed profile. Thus, according to embodiments of the invention, both an intensity profile and a speed profile may be changed between two exposing steps. In this way, both the print quality and the power consumption may be controlled in a multi-variable manner depending on circumstances. Intensity and speed affecting both the printing quality and the efficiency (power consumption), a finer and more versatile control is achieved by controlling the first and the second exposing step according to different profiles for both intensity and speed. In this way, a wider range of relief precursors may produced while reaching for each the best printing quality at the best efficiency. Depending on the characteristics of the relief precursor (reactivity, thickness among others) to be exposed, typically one or more fast exposure passes at a high intensity may be followed by one or more slow exposure passes at a low intensity, to mitigate heat accumulation while achieving high curing quality. According to a preferred embodiment, the first speed profile is such that the speed during the one or more exposure passes of the first exposing step is substantially constant and/or the second speed profile is such that the speed during the one or more exposure passes of the second