DE10143039A1 - Preparation of a printing plate/cylinder, uses at least one point electrode to give an electrical field at the plate/cylinder with an effect on the base layer giving thermal distortion at the covering layer for the ink points of the image - Google Patents

Abstract

To prepare a printing plate, at least one point electrode (5) gives a selective action with a high frequency electrical field to give the points where ink is to be taken to print the required image. The printing plate blank (1) has a base layer (3) and a polymer and polar covering layer (4). To prepare a printing plate, at least one point electrode (5) gives a selective action with a high frequency electrical field to give the points where ink is to be taken to print the required image. The printing plate blank (1) has a base layer (3) and a polymer and polar covering layer (4). The covering layer has differing adhesions for the ink or with a wetting agent during printing. The effect of the electrical field on the base layer causes thermal distortions in the covering layer to give the printing image. To prepare a printing plate for wet offset printing, the base layer is hydrophilic and the covering layer is hydrophobic. The base layer is of anodized aluminum. The covering layer is a polar polymer, polyethylene terephthalate (PET), polyvinyl chloride (PVC), or polyvinylidene fluoride (PVDF).

Description

The invention relates to a method for producing a printing form, in particular one Lithographic printing plate.

Methods are known in which by spark discharge or by laser light the top layer of a printing form blank point by point in accordance with a printed image is thermally removed (US 5,237,923). The removal can be done directly with the pictures done by selectively burning off the top layer. As an example, let's take the picture Burn off a layer of silicone called. The removal can only be done in one subsequent development step, the cover layer being so during imaging is changed that the pixels when in contact with a developer solution be washed out (US 5,493,971). As a material for the top layer come here Polymers are used which, for. B. when exposed to laser light in the non-image areas network and harden and their pixels z. B. in wet offset printing by Wash out contact with the dampening solution.

All ablation processes have the disadvantage that the material removed Cover layer to avoid printing errors must be removed before printing. Furthermore, the geometry of a pixel is strongly dependent on the energy input and on the composition of the layers to be imaged. This can happen when printing an undesirable dot enlargement, resulting in the service life of the printing form reduced.

In order to avoid the above disadvantages, materials have been developed whose surface it is not broken up thermally or physically during and after imaging (DE 196 12 927 A1). Through energy input in the form of heat or light point by point the adhesion of a top layer with regard to printing ink or changed a fountain solution used in printing. The change in Adhesion is not satisfactory, so the pixels are not sharp to her Surroundings appear delimited. In addition, materials are such  Changes in properties cannot be very robust when printing, which reduces the service life. In US 3,972,715 is a system for generating a Image described, in which a static electric field for exposure is used for imaging comes, so that in the initial state non-aligned particles of an imaging layer be aligned according to the image. To ensure that the in the Imaging layer can align embedded particles, the imaging layer be softened by heating. By cooling the material of the imaging layer the picture is frozen. The system is used exclusively for image generation. On image-wise change in the adhesion with regard to printing ink or dampening solution not shown here.

The object of the invention is to provide a method for producing a printing form develop, which with little effort the production of printing plates with high Service life enabled.

The object is achieved with a method which has the features of claim 1 having.

Advantageous refinements result from the subclaims.

The fact that the generation of an ink-accepting pixel or Dampening point by a heat deformation in the top layer happens, there is no removal of the material of the cover layer. costly Cleaning devices and cleaning processes can be omitted. The material of one Pixel is displaced into the immediate vicinity of the pixel. To the Around the image point, a bulge is created from the displaced material. The minor Excess material of the top layer at the location of the beads does not interfere with the Printing process. Regarding the adhesive properties of the base layer and the top layer Printing ink or dampening solution are any combination between oleophobic / oleophilic and hydrophobic / hydrophilic conceivable. This allows printing forms for the Print with oil-based or water-based inks. Depending on,  whether the point exposed on the base layer is oleophilic or oleophobic can be positive or negative printing forms are generated. The procedure can be inside or outside be carried out on a printing press. The printing form blank can next to the Cover layer and the base layer have other layers that the handling of Promote printing form and the imaging process.

The invention will be explained in more detail using an exemplary embodiment demonstrate:

Fig. 1 is a diagram of an imaging device with a single electrode, and

Fig. 2 is a diagram of an imaging device with a multiple electrode head.

Fig. 1 shows the imaging in the scheme of a three layer printing form 1. In the raw state, the printing form 1 consists of a carrier layer 2 , an intermediate layer 3 and a cover layer 4 . The carrier layer 2 consists of aluminum or steel. Anodized aluminum or a gold-containing material serves as the hydrophilic intermediate layer 3 with a layer thickness of approximately 0.2 micrometers. The oleophilic cover layer 4 consists of a polar polymer, preferably of polyethylene terephthalate (PET), polyvinyl chloride (PVC) or polyvinylidene fluoride (PVDF) and has a layer thickness of approx. 1 micrometer. The dielectric loss factor of the material of the cover layer 4 is greater than 0.01. To generate the pixels, a tip electrode 5 is provided, the tip 6 of which is directed towards the cover layer 4 but does not touch it. The tip electrode 5 can be positioned along the surface of the cover layer 5 in the directions 7 , 8 shown , so that the entire surface of the printing form 1 to be imaged can be detected. The tip electrode 5 is connected to an AC voltage source 9 . The AC voltage 9 supplies voltages in the range of 500-1000 V in the frequency range around 30 MHz. The second pole of the AC voltage source 9 is connected to an electronic switch 10 which is controlled by a control device 11 . The switch 10 also has a connection to the electrically conductive carrier layer 2 .

If a negative pixel is to be generated, then the switch 10 is closed with the aid of the control device 11 . A strong alternating electrical field is formed at the tip 6 and penetrates the cover layer 4 . The dipoles in the cover layer 4 are excited to vibrate, so that the cover layer 4 is heated locally. In the area opposite the tip 6 , the material of the cover layer 4 becomes flowable. The material of the cover layer 4 is displaced so that the underlying hydrophilic intermediate layer 3 is exposed in a circular area with the diameter d. The displaced material of the hydrophobic cover layer 4 forms a bulge 13 around the area 12 with a slight elevation above the level of the non-imaging cover layer 4 . According to a print image, the tip electrode 5 is activated by the control device 11 when the surface of the printing form 1 to be imaged is passed over. The printing form 1 can be used for wet offset printing, with dampening agent accumulating on the exposed areas 12 and the areas of the surface of the cover layer 4 which have been retained after the imaging are color-guiding.

In FIG. 2, the application of the method is shown within a dry offset printing machine. A printing form blank 15 is clamped on a forme cylinder 14 . The printing form blank 15 is constructed in two layers. An oleophobic cover layer 17 made of a polar polymer lies over an oleophilic base layer 16 . The forme cylinder 14 is rotatably supported in bearings 18 , 19 . A motor 20 is used to drive the forme cylinder 14 . A multiple electrode head 23 can be positioned parallel to the axis of rotation 21 of the forme cylinder 14 by means of a screw drive 22 . The screw drive 22 is received in bearings 24 , 25 and coupled to a stepper motor 26 . The multiple electrode head 23 and the motors 20 , 26 are connected to a control device 27 . The control device 27 is connected to a computer 28 which carries out the image data processing.

For positive imaging of the printing form blank 15 , the raster image data of one of the partial colors of a multicolor image are supplied by the computer 28 to the control device 27 . According to the raster image data, when the forme cylinder 14 is rotated by means of the motor 20 in the direction 29 and translation of the multiple electrode head 23 by means of the motor 26 in the direction 30, the electrodes 31 of the multiple electrode head are activated. According to the partial image, areas 32 of the base layer 16 are exposed by thermal deformations in the cover layer 17 according to the same physical principle as described for FIG. 1.

The areas 32 form the pixels that guide the printing ink, which are colored in a conventional manner with printing ink and transferred to a printing material. With a high resolution, the diameters of the region 32 are in the micrometer range. By adjusting the amount and frequency of the AC voltage supplied to the electrodes 31 , it is ensured that only just enough electrical energy is coupled into the polar polymer material of the cover layer 17 that the cover layer 17 is melted and transported to the edge of the regions 32 .

LIST OF REFERENCE NUMBERS

1

printing form

2

backing

3

interlayer

4

topcoat

5

tip electrode

6

top

7

.

8th

direction

9

AC voltage source

10

switch

11

control device

12

Area

13

bead

14

form cylinder

15

Printing form blank

16

base layer

17

topcoat

18

.

19

camp

20

engine

21

axis of rotation

22

screw drive

23

Multiple electrode head

24

.

25

camp

26

stepper motor

27

control device

28

computer

29

.

30

direction

31

electrodes

32

Area

Claims (3)

1. A method for producing a printing form in which, by selective action of a high-frequency electric field emanating from at least one tip electrode, dots accepting printing ink are produced, characterized in that in the case of a printing form blank ( 1 , 15 ) consisting of a base layer ( 3 , 16 ) and a polymeric and polar cover layer ( 4 , 17 ) with different adhesiveness with regard to the printing ink or a dampening solution used in printing, by the action of the field ( 9 ) the base layer ( 3 , 16 ) by a point-by-point heat deformation in the cover layer ( 4 , 17 ) is exposed according to the image. 2. The method according to claim 1, characterized in that a hydrophilic base layer ( 3 ) and a hydrophobic cover layer ( 4 ) is used to produce a printing form ( 1 ) for wet offset printing. 3. The method according to claim 2, characterized in that anodized aluminum is used as the base layer ( 3 ) and a polar polymer, polyethylene terephthalate (PET) or polyvinylidene fluoride (PVDF) is used as the cover layer ( 4 ).