Method for Baking Coated Printing Plates

Abstract

The invention relates to a method for burning in a coating of an aluminium or an aluminium alloy printing plate support, in the case of which the printing plate is heated to a burning in temperature, maintained at this temperature for a predefined duration and subsequently cooled. Deformations can be minimised even further after the burning in process if at least in a temperature range between 150 C. and the burning in temperature, preferably 100 C. and the burning in temperature, the temperature differences of the metal temperature of the printing plate measured along a line in the longitudinal direction of the printing plate during the heating and cooling are maximum 40 C. over a length of 40 cm and the temperature differences of the metal temperature of the printing plate measured along a line perpendicular to the longitudinal direction are less than 10 C. during the heating and cooling.

Claims

1. A method for burning in a coating of a printing plate support, wherein the printing plate comprises aluminium or an aluminium alloy as the support material, in the case of which the printing plate is heated to a burning in temperature, maintained at this temperature for a predefined duration and subsequently cooled, characterised in that at least in a temperature range between 150 C. and the burning in temperature, preferably 100 C. and the burning in temperature, the temperature differences of the metal temperature of the printing plate measured along a line in the longitudinal direction of the printing plate during the heating and during the cooling are maximum 40 C. over a length of 40 cm and the temperature differences of the metal temperature of the printing plate measured along a line perpendicular to the longitudinal direction are less than 10 C. during the heating and during the cooling.

2. The method according to claim 1, characterised in that the burning in takes place in a furnace in a discontinuous manner, preferably in a batch furnace or in a continuous furnace operating in a discontinuous manner.

3. The method according to claim 1, characterised in that at least in a temperature range between 150 C. and the burning in temperature, preferably 100 C. and the burning in temperature, the temperature differences of the metal temperature of the printing plate during the heating and during the cooling measured along a line perpendicular to the longitudinal direction are maximum 5 C., preferably maximum 2 C.

4. The method according to claim 1, characterised in that printing plate supports with a width of at least 400 mm and a length of at least 600 mm, preferably with a width of at least 1000 mm and a length of at least 2000 mm are subjected to the burning in process.

5. The method according to claim 1, characterised in that the burning in temperature of the metal of the printing plate is between 220 C. and 320 C. with a burning in duration of between 1 and 15 minutes, preferably 240 C. to 300 C. with a burning in duration of 2 to 10 minutes.

6. The method according to claim 1, characterised in that the printing plates are transported using transport means which prevent or sharply reduce heat dissipation from the printing plate support via the transport means.

7. The method according to claim 1, characterised in that the cooling is carried out using cooling means, in particular convective cooling media such that the entire printing plate support is simultaneously cooled in a controlled manner during the cooling.

8. A continuous furnace for carrying out a method according to claim 1 having a burning in area for heating and maintaining a printing plate at a burning in temperature and means for transporting the printing plate to be burned in into the burning in area and means for transporting the printing plate out of the burning in area, characterised in that the burning in area of the continuous furnace is at least the size of the printing plate, the means for transporting the printing plate into the burning in area and the means for transporting the printing plate out of the burning in area are designed for the discontinuous transport of the printing plate into the burning in area and out of the burning in area.

9. The continuous furnace according to claim 8, characterised in that wire belt conveyors that can operate in a discontinuous manner are provided as the means for transporting the printing plate into the burning in area and out of the burning in area of the continuous furnace.

10. The continuous furnace according to claim 8, characterised in that the means for transporting the printing plate into and out of the burning in area have very low heat conductivity in the contact regions with the printing plates due to the geometry and/or the materials of the contact regions used.

11. The continuous furnace according to claim 8, characterised in that an inlet area is provided in which the printing plates can be heated from room temperature to maximum 150 C., preferably maximum 100 C. and out of which the printing plates can be transported into the burning in area.

12. The continuous furnace according to claim 8, characterised in that an outlet area is provided in which the printing plates are cooled from the burning in temperature to less than 100 C., preferably less than 50 C. or less than 30 C.

13. The continuous furnace according to claim 8, characterised in that the inlet area and the outlet area are designed as a buffer or store and can receive a plurality of printing plates to be heated or to be cooled.

14. The continuous furnace according to claim 8, characterised in that a rinsing device is provided which is provided on the outlet side of the outlet area and in which the printing plates are rinsed with a fluid rinsing medium and further cooled.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0024] Furthermore, the invention will be explained in more detail based on exemplary embodiments in connection with the drawing. The drawing shows in:

[0025] FIG. 1 depicts a printing plate support in a schematic perspective view;

[0026] FIG. 2 depicts a schematic sectional view of an exemplary embodiment of a continuous furnace operating in a discontinuous manner;

[0027] FIG. 3 likewise depicts a schematic view of a second exemplary embodiment of the method according to the invention with a batch furnace; and

[0028] FIG. 4 depicts a continuous furnace operating in a discontinuous manner with an inlet and outlet area in a schematic sectional view.

DETAILED DESCRIPTION OF THE INVENTION

[0029] In FIG. 1, a printing plate 1, which usually has a rectangular form, is depicted in a schematic perspective view. The formats used are generally at least 300 mm in width and at least 1000 mm in length. Large-format printing plates 1 preferably comprise a width of at least 1000 mm and a length of at least 2000 mm. Common large-format printing plates have for example the following width to length ratios: 1350 mm2800 mm or 1600 mm2900 mm. The printing plate 1 consists in this regard of an aluminium or aluminium alloy sheet metal as the printing plate support having a thickness of 0.1 mm to 0.5 mm. The printing plate 1 comprises a coating, for example a light-sensitive coating, on the support which should be burned in.

[0030] In order to examine the phenomenon, printing plates 1 are firstly examined that are burned in with conventional methods, wherein the printing plate was firstly divided into a plurality of measuring surfaces on which the temperature of the metal of the printing plate was measured for example via a pyrometer. The temperatures were measured during the burning in process, during the heating process and also during the cooling process. The elastic and plastic deformation of the corresponding regions of the printing plate was then simulated based on the temperature curves and the stresses arising in the sheet metal distributed over the surface of the printing plate were determined therefrom. The deformations calculated therefrom were compared with the deformations that actually occurred so that conclusions could be drawn regarding the temperature profile to be set of the printing plate.

[0031] It was determined that the temperature distribution of the metal temperature of the printing plate in the longitudinal direction L may comprise temperature differences of a maximum of 40 C. over a distance of 40 cm both during the heating and also during the cooling in order to limit deformations. Exceeding this temperature difference leads to greater prestresses in the printing plate after the burning in process and thus to an irreversible deformation of the printing plate. The deformation leads to undesirably large wave formation and rejection of printing plates.

[0032] At the same time, it was determined that the printing plate reacts significantly more sensitively to temperature differences in the transverse direction Q, thus perpendicular to the longitudinal direction and temperature differences of less than 10 C. perpendicular to the longitudinal direction have to be maintained in order not to lead to undesirably strong wave formation. The maximum temperature difference transverse to the longitudinal direction during the burning in or cooling process is 5 C., particularly preferably maximum 2 C. such that the wave formation can be reduced.

[0033] In order to achieve this, the burning in can be carried out in a discontinuous manner in a continuous furnace. FIG. 2 for this purpose shows for example a continuous furnace 3 operating in a discontinuous manner. The printing plate 1 is for this purpose transported on transport means 2 into the burning in area 4 and the heating thereof only commences there. The transport means 2 can be designed for example as a wire belt conveyor that can be operated in a discontinuous manner in order to transport the printing plate into the burning in area. The burning in area 4 of the continuous furnace is at least as large as the printing plate 1 itself. When the printing plate is arranged in the burning in area of the continuous furnace 3, the wire belt conveyor 2 stops the transport process until the printing plate 1 is burned in. The wire belt conveyor 2 can also comprise materials which have a particularly low heat conductivity at least in the contact regions with the printing plate 1 in order to avoid heat dissipation or an uneven heating of the printing plate 1. In particular, the contact surfaces of the transport means 2 with the printing plate 1 comprise corresponding materials. The contact surfaces can for example consist of temperature-resistant epoxide resin with a heat conductivity of less than 1 W/Km. The contact surfaces of the transport means 2 can in the cross section also comprise radii such that only one tangential contact point with the printing plate 1 is provided. The contact to the printing plate 1 which is very small in terms of surface area also has a positive effect on reducing the heat dissipation from the printing plate 1.

[0034] Wire belt conveyors 2 are preferably used as transport means which ensure particularly small contact surfaces to the printing plate 1 via the wire mesh. The wire belt conveyor 2 conveys the printing plate 1 into the burning in area 4 of the burning in furnace 3. As soon as the printing plate is arranged in the burning in area 4, the speed of the wire belt conveyor 2 is reduced to zero and the printing plate 1 is then burned in in a virtually stationary manner in the burning in area 4. After the virtually stationary burning in of the printing plate, the printing plate is removed via the wire belt conveyor out of the burning in area 4 with high speed and cooled over its whole surface. A discontinuous operation of the continuous furnace 3 or burning in furnace 3 is thus ensured by wire belt conveyors 2 that can be operated in a corresponding manner.

[0035] However, it is also conceivable to use other transport means that can be operated in a discontinuous manner.

[0036] As already mentioned, heating of the printing plate 1 via the heating means 4 preferably only takes place when the printing plate 1 is positioned in the burning in area 4 of the continuous furnace 3. For example, a combination of radiation and convective heating can heat the printing plate particularly effective, but also homogenously. Since only particularly small temperature differences can be tolerated in the transverse direction, good temperature control of the burning in process plays an important role. The positioning of the printing plate 1 in the burning in area 4 of the continuous furnace 3 preferably takes place within a maximum of one minute, maximum 30 s or preferably within a maximum of 20 s, particularly preferably within a maximum of 10 s or 5 s. The transport means must ensure transport speeds adapted to the geometry or to the size of the printing plate 1. The continuous furnace 3 is operated in a discontinuous manner due to the printing plate 1 remaining in the continuous furnace for the duration of the burning in.

[0037] The burning in temperature of 210 C. to 320 C. or 220 C. to 300 C. is maintained for 1 to 15 minutes, preferably 2 to 10 minutes and the printing plate 1 is subsequently cooled. For this purpose, the printing plate 1 preferably remains on the transport means, here the wire belt conveyor. The transport means is then simultaneously cooled in a convective manner via a cooling medium 5 with the printing plate 1. This cooling process is also carried out in a controlled manner such that the entire printing plate is simultaneously homogenously cooled. It was found that the temperature differences to be maintained in the longitudinal direction L are a maximum 40 C. over 40 cm or in the transverse direction Q, perpendicular to the longitudinal direction 10 C., preferably 5 C. particularly preferably 2 C., otherwise undesirably strong wave formation may occur. The wave height can be reduced by these measures after the burning in of the printing plate 1 to significantly below 6 mm. The rejection of printing plates after burning in is hereby significantly reduced and to some extent use of the printing plates is hereby only enabled.

[0038] In order to maintain the specifications according to the invention for the temperature on the printing plate, the temperature of the printing plate has to be measured at least once in the process over the entire surface in order to adjust the burning in device. For this purpose, a temperature measurement with pyrometers takes place in the process. The temperature of the printing plate has to be measured already during inserting of the printing plate into the burning in furnace or continuous furnace 3. The heating means 4 are then to be adjusted with regard to their heat output such that the temperature differences required according to the invention are maintained during the heating and burning in. The same is also carried out for the cooling process and the adjustment for example of the throughput rates of the cooling media. The adjustment of the heating means and optionally also the cooling means with regard to the heating output/cooling output per surface element is very specific and must therefore be individually adapted to the conditions present. Independent of the parameters of the respective system for burning in the printing plates, the method according to the invention ensures a notable reduction of undesired deformations of the printing plate.

[0039] FIG. 3 schematically shows a further exemplary embodiment of the method according to the invention using a batch furnace 6 into which a plurality of printing plates 1 can be inserted. By using the batch furnace 6, the capacity of the burning in process can be increased and therefore all printing plates 1, which are arranged in the batch furnace 6, can be heated very homogenously and evenly. Usually, the printing plates 1 are arranged for this purpose perpendicular in the batch furnace 6. The cooling process subsequently takes place with cooling medium 5. Preferably, a plurality of printing plates 1, arranged in transport means 2 are simultaneously cooled via a cooling medium 5.

[0040] If the heating process and the cooling process of the printing plate for burning in the coating takes place in a batch furnace while maintaining the temperature differences according to the invention, the prestresses of the printing plate can be significantly reduced after the burning in process and the size of the undesired deformations substantially reduced.

[0041] FIG. 4 shows a device with a continuous furnace 3 that can be operated in a discontinuous manner which in each case comprises an inlet area 7 and an outlet area 9. The printing plates 1 are heated to a temperature of maximum 150 C. in the inlet area 7 designed as a store or buffer and are conveyed out of the inlet area using wire belt conveyors 2 into the burning in area 4. Stockpiling in the inlet area 7 allows the heating process to take place slowly. In addition, a preheated printing plate 1 is already available as soon as a printing plate leaves the burning in area 4 of the continuous furnace 3 and is transported into the outlet area 8. The printing plates 1 can be carefully cooled in the outlet area 9, which is likewise designed as a buffer or store and can receive a plurality of printing plates 1, without the temperature differences being exceeded. The printing plate 1 is subsequently transported into a rinsing device 9 in which the printing plate is cleaned and further cooled at the same time.

[0042] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0043] The use of the terms a and an and the and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms comprising, having, including, and containing are to be construed as open-ended terms (i.e., meaning including, but not limited to,) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., such as) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0044] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.