EP0737133B1 - Thermal process for applying hydrophilic layers on hydrophobic substrates and use of thus coated substrates as carriers for offset printing plates - Google Patents

Description

The invention relates to a thermal process for the application of hydrophilic Ceramic layers on substrates for printing plates. This hydrophilized Backing material is suitable due to the achievable surface topography particularly good for coating with photosensitive layers from which Printing plates can be made after exposure and development Printing forms with uniform topography, high print run stability and good Result in dampening solution guidance.

The most commonly used printing plates for offset printing exist usually from a carrier material to the one photosensitive Layer is applied firmly. This layer is exposed, after which the Non-image part must be removed from the surface without leaving any residue. Due to the remaining hydrophobic layer (part of the picture), color can move towards it printing product can be applied, but this is only guaranteed if there is water in the area of the non-image areas. For a qualitative high quality printed image is wettability with water (hydrophilic property) crucial in the area of non-image positions. It is known that Alumina has such properties.

It is therefore obvious to use aluminum substrates, these for to better roughen the printed image and to roughen the surfaces oxidize. Chemical or electrochemical processes, also in combination with Mechanical processes for roughening pure aluminum are, for example known from DE-A-34 13 899.

The multi-stage processes are based on a uniform aluminum composition bound to the support surface to ensure that when regulated chemical process control a uniform surface topography free of Scars develop. The disposal of the baths and the solids content are to be regarded as negative factors.

From DE-AS-13 00 579 a method is known in which by a electric arc between a heat-resistant electrode and a metallic carrier material in a protective gas jacket, a plasma is generated with whose help roughened printing plates with small amounts of waste, and by Addition of materials the surface can be modified so that it is a has improved hydrophilicity. However, this method can be used in practice difficult to realize as it is very much determined by several factors Intensities of the transmitted arcs is dependent.

DE-AS-23 48 717 is a further method for applying dampening solution layers on printing plates for the offset printing process known. They are layers of poorly or insoluble carbonates, Silicates or quartz are provided, which are based on the plasma spraying process roughened carrier applied, and then to produce the appropriate roughness be sanded. The image portion area is removed by partially removing the Get coating. However, this method is due to the mechanical Processing and the etching process to remove the layer, very complex.

The aim of the present invention was to provide a thermal coating process for To provide hydrophilization of surfaces in which not only aluminum supports but also other metals such as steels and other non-ferrous metals and Alloys or even plastics can be safely controlled and coated with adhesive can be. The residues are to be reduced to a minimum and should be so that recycling is easily possible.

The aim is achieved according to the invention by a method of the type mentioned at the outset, the characteristic features of which are that, in a first treatment step, a surface roughness R _a in the range from 0.2 to 1.5 μm is generated on the surface of the carrier film by mechanical micro-roughening, and in that the carrier film is then coated by thermal spraying of powdery oxides and / or oxidic mixtures and compounds with an average grain size in the range from -40 to + 1 μm with a permanently stable, hydrophilic coating.

Grain size information of the type -40 to + 1 µm mean within the scope of the present Invention that none in the powder with the corresponding grain size specification Particles with a grain size larger than 40 µm and no particles with a Grain size of less than 1 µm are available.

The hydrophilic layer applied according to the invention fulfills several functions, which when coating with photosensitive resins and used as Offset printing plates have a positive effect.

It was surprising for experts that particularly thin, flexible and abrasion-resistant coatings with low layer thickness tolerances without mechanical processing applied so that one in the core roughness (Term based on DIN 4776) creates a uniform surface. The surface is especially designed so that statistically well distributed punctiform Wells are created that are designed so that the applied on them photosensitive resin layer for producing the image portion firmly clipped can be. Another effect that is positively noticeable on exposure was achieved by statistically well distributed peaks from the Core roughness can be achieved. Other advantages of this procedure are to be seen in the fact that with the same machine arrangement the most different Carrier materials such as plastics or metals can be used, and on their chemical composition different coating materials can be used tailored to the respective application. The generated waste can be sorted and dry and sorted into the Material cycle can be returned.

The following description of preferred embodiments of the invention serves in connection with the drawing for further explanation.

Fig. 1 shows schematically a process flow with the enlarged Surface conditions.

A metal or plastic film 1 as a base support for offset printing plates is from a roll 2 is continuously wound at a constant belt speed, the base carrier preferably having a thickness in the range from 100 to 500 μm, particularly preferably from 120 to 350 microns, and should have a thickness tolerance of ± 2% with a scratch and scar-free surface that is free of coarse organic or mineral residues. As metallic materials can aluminum and its alloys of the preferred composition or Stainless steels or refined steels. Others can metallic materials that resist corrosion caused by the dampening solution and meet the mechanical properties, find use.

Thermoplastic polyesters can preferably be used as plastics be, with polyethylene terephthalate-containing homo- and copolymers and Mixtures thereof with other polyesters or polyamides are particularly suitable are. The plastics can also fillers in an amount of up to Contain 5 wt .-%, with inorganic fillers such as alumina, titanium dioxide and / or aluminum oxide are particularly suitable. Preferably located at least 1.5% by weight fillers in the plastic.

The basic carrier 1 is moved over a freely rotating, vertically guided movable roller 3 to accommodate speed compensation and to ensure one as large as possible wrap angle for the subsequently arranged Treatment roller 4 performed. On the treatment roller 4, the form fit adjacent body 1 according to the invention in a first step mechanically roughened so that a micro-rough surface is created without the Damage the base body by warping. Sandblasting process for derusting, for Removal of layers of paint or to solidify surfaces are indeed already known, but it was surprising that thin films with little distortion have particularly uniform micro-rough surface topographies provided.

According to the invention, a 'pressure jet method' is advantageously used, in which the jet pressure is in the range from 0.5 to 2 bar, preferably from 0.6 to 1.5 bar. The distance of the nozzle from the base body 1 is in the range from 50 to 150 mm, preferably from 50 to 80 mm. Sharp-edged blasting media are particularly suitable as blasting media, in particular mineral blasting media such as Al ₂ O ₃ or corundum with a grain size in the range from 10 to 100 μm, preferably from 20 to 50 μm. The amount of abrasive is 500 to 1000 g / m ^{2 of the base} carrier, which is metered consistently. The metering is advantageously carried out by rotating mechanical metering devices. The blasting device 5, which can optionally also comprise a plurality of nozzles, is moved parallel to the longitudinal axis 6 of the treatment roller 4 at a speed of 1000 to 2000 mm / s. After the blasting process, the surface of the base body is freed of dusts.

As a roller 3 can be a wear-resistant body with small masses flexible rubber pad can be provided.

After the roughening treatment according to the invention, the base body belt 1 has a micro-rough surface 7 with a roughness R _a of 0.2 to 1.5 μm, preferably 0.5 to 1.0 μm, and can be carried out continuously or in increments to the coating station, the plasma spraying, be performed.

The thermal spray process, plasma spraying with a plasma torch 10 in natural ambient atmosphere with a non-transmitted arc acc. DIN 32530, is known as technology for the application of thick layers. Oxidic layers, on rotationally symmetrical parts or a surface or Partial surface coating with robots by repeated painting, in thicknesses from 50 to 500 µm are state of the art.

The basic carrier 1, which can have a width of 500 to 2000 mm, becomes Coating by plasma spraying continuously or cyclically according to the Spray jet width, which can be 6 to 12 mm in the zenith, is form-fitting by a driven treatment roller 8 at a speed in the range from 5 to 50 mm / s under the hot gas jet of the plasma torch 10 moved through.

The use of several plasma spray guns is particularly advantageous and increases the coating speed many times over, depending on the number of guns. For example, with a particularly advantageous use of 10 plasma spray burners, an area in the range from 300 to 1000 m ² / h can be coated.

The roller body of the treatment roller 8, which is made of steel, aluminum or other metal alloys can also have the task of heat the thermal process with which the base support for printing plates inevitably is charged to record and derive. Additional cooling of the Roller body with heat-dissipating flow media, one Avoiding falling below the dew point causes a trouble-free Litigation.

In the hot gas jet of the plasma torch, which is parallel to the longitudinal axis 11 of the Treatment roller 8 over the base support 1 at a speed of 1000 up to 2000 mm / s is moved uniformly, undulating or oscillating ceramic powder added by a metering device 12, 13.

According to the invention, plasma spray layers with a thickness of 5 to 20 µm and with a layer thickness tolerance of ± 5%. The Layers have an adhesion that the "film test", as in electroplating is common to match. In doing so, adhesive strips are applied to the coated surface pressed and then suddenly again perpendicular to the coating plane deducted. The coating material on the adhesive layer must not stay attached. The layers can be bent by bending the body 1 Angles of 90 ° cannot be removed by chipping.

Argon and nitrogen can be used as the plasma-forming hot gases. Gas mixtures such as argon-nitrogen, nitrogen-hydrogen or are advantageous argon-hydrogen used particularly advantageously. The introduced electrical Power is advantageously 20 to 50 KW, particularly advantageously 25 to 35 KW.

According to the invention, a very fine powder with an average grain size of 20 20 μm is used to produce a layer with a roughness R _a of 1 to 2 μm. Powders with an average grain size of 5 to 12 μm could be used particularly advantageously. A second powder fraction with a grain size of 20 to 40 μm, which is expediently added separately, has the effect that from the basic roughness 14 it is possible to produce individual tips 15 which are controllable in terms of quantity and are distributed statistically uniformly over the surface. In this layer combination, the grains can have a different chemical composition, such as the base layer Al ₂ O ₃ - tips Al ₂ O ₃ + 3% TiO _2.

To achieve a hydrophilic wear-resistant layer can be preferred Aluminum oxides and mixtures or compounds with other oxides Find use that according to the invention on the layer surface Light absorption factor of 50 to 70%.

Surprisingly, in the plasma flame made of aluminum, Aluminum alloys such as B. AlSi, AlMg or Al-Si-Fe and perlet or sintered mixtures with these compositions by oxidation of fine Powders, the preferred grain sizes <20 microns, oxidic mixtures or Compounds with hydrophilic layer properties are generated.

According to the invention it is possible to use powdered oxides of the type described such, but optionally also powdered metals, in the plasma jet oxidize, or apply a combination of these.

The layer combination of base body and thermally applied hydrophilic Ceramic layer has a different hydrophilicity and increased wear resistance compared to oxide mixtures generated in the plasma gas jet Metals.

Within the scope of the invention it is also possible to use one with aluminum or Al alloy coated ceramic powder or from a grain agglomerate made of metal and ceramics and thus substrate for offset printing plates coat.

After the plasma spraying process, cleaning 16 is expediently carried out Blow off and suction of the non-sticky particles. these can analogous to the sandblasting process together with the dusts that are in the Plasma injection process occur, also be returned to the material cycle. The cleaned belts are then at a coating station 17 on the hydrophilized surface 19 coated with a photosensitive layer 18. The coated strips are then dried and, if necessary, tempering processes exposed.

After this process, the printing plates can be made to their final size band-shaped material can be cut. The actual formatting too Printing plates are made in the printing houses using known processes.

example 1

A rolled aluminum foil tape WSt. No. 3.0205 with a thickness of 300 µm and a width of 1600 mm was subjected to a sandblasting process in a first step. Two blasting nozzles with a diameter of 8 mm were moved at a distance of 60 mm parallel to the longitudinal axis of the sandblasting roller at a speed of 1.5 mm / s over the film strip. The sandblasting roller itself moved at a speed of 25 mm / s. A molten and broken sharp-edged aluminum oxide with 3% by weight of titanium oxide, which had an average grain size of 20 to 45 μm, was used as the abrasive. The abrasive was dosed through a rotating disc with a metering groove in such a way that an amount of 700 g / m ^{2 was} applied to the film. The amount of compressed air was 250 m ³ / h at a pressure of 1.2 bar. The blasting material used was conveyed into a dust screening system and there dusts with a particle diameter of <3 µm were removed from the blasting medium. The dust-free abrasive was then used again. This measure reduced the total abrasive consumption to 35 g / m ² .

After the blasting, the surface of the film strip was cleaned by blowing with dry compressed air and then with a rapidly evaporating commercially available solvent in a spraying process. The sheet had a roughness R _a of 0.92 µm measured in accordance with DIN 4768.

1.) Die 6 µm Linien waren im UGRA Test heil wiedergegeben

2.) Das Freilaufverhalten als Indiz für eine gute Feuchtmittelführung zeigte kein störendes Verhalten auf.

3.) Im Vergleich zu einem marktüblichen Korrekturmittel (KP 273) treten nach der Korrektur keine Farbunterschiede auf (= Farbschleierfreiheit)

4.) Die Druckauflage betrug 130 000 Drucke

5.) Die Druckauflage betrug bei einer nach dem Entwickeln 5 Minuten bei 230°C gehärteten Platte 500 000 Drucke.

The cleaned film strip was then coated with a powder combination of 99.5% aluminum oxide, aluminum titanium oxide 97: 3, and partially oxidized aluminum using the plasma spraying process. The grain size of the aluminum oxide was -12 µm +5 µm (designation powder A), the aluminum oxide with 3% titanium oxide had a grain size of -40 µm + 20 µm (designation powder B). A mixture with 95% powder A and 5% powder B was produced from these oxides (designation powder C). The grain size of the aluminum was -20 µm +5 µm (designation powder D). A gas mixture of 8% hydrogen and 92% argon was used to generate the hot gas jet (plasma flame), and the electrical power was 28 kW. Powder C and D were injected separately into the plasma flame. The plasma flame was moved over the film strip at a distance of 70 mm at a speed of 1800 mm / sec. The film strip was moved discontinuously by a water-cooled roller in steps of 12 mm, which are triggered by the guide unit of the plasma flame. The water temperature of the roll was 10 ° C, the wrap angle of 180 ° and the contact force of the film was 10 N. The layer thus prepared had a layer thickness of 10 .mu.m and a surface roughness R _a of 1.2 to 1.5 microns (DIN 4768 ). The adhesion of the layer was checked with an adhesive film and showed very good adhesion. The hydrophilized film strip was then coated with a light-sensitive layer, exposed and developed into a printing plate. The printing plate obtained had good quality in a printing test and has the following features:

1.) The 6 µm lines were clearly shown in the UGRA test

2.) The free-running behavior as an indication of good dampening solution management showed no disruptive behavior.

3.) In comparison to a standard correction medium (KP 273) there are no color differences after the correction (= freedom from color haze)

4.) The print run was 130,000 prints

5.) The print run was 500,000 prints for a plate which had been hardened for 5 minutes at 230 ° C.

Example 2

An aluminum foil strip as in Example 1 was moved with the same machine order as in Example 1. The hydrophilic layer was applied by the high speed flame spraying process. A powder C and D as in Example 1 was used in the burner. Powder C was injected directly into the center of the flame, using acetylene in an amount of 4,400 l / h and oxygen in an amount of 6,200 l / h as the fuel gas. Powder D was injected into the flame before the burner. 5 burners were mounted on the traverse unit so that a width of 75 mm could be coated at the same time. The burner distance was 200 mm. The layer produced in this way has a layer thickness of 10 to 12 μm and a roughness R _{a of} 1.2 to 1.5 μm. Examination of the adhesive strength of the applied layer with an adhesive strip showed very good adhesion. Processing into a printing plate was carried out analogously to Example 1.

Example 3

A biaxially stretch-oriented and heat-fixed sheet of polyethylene terephthalate with a thickness of 300 μm and a width of 1600 mm was subjected to micro-roughening as indicated in Example 1. The blasted surface was cleaned by blowing with dry compressed air, but without organic solvents, and had a non-grooved, fine-grained, micro-rough surface topography with a roughness R _a of 0.8 to 1.2 µm, measured according to DIN 4768.

The blasted film strip was then led to the plasma spray station. There was it with a force of 10 N to a temperature of one with water Pressed roll cooled from + 10 ° C. The role turned with one uniform speed of 25 mm / s under two plasma torches that even horizontally, i.e. parallel to the longitudinal axis of the roll, at one speed of 2000 mm / s were moved back and forth.

The distance between the burners and the film tape was 100 mm. To the Operating the plasma flame was a gas mixture of 10 vol .-% hydrogen and 90 vol .-% argon used, the electrical power was 28 KW. In the Plasma flame became a mixture of powder from two separate dosing systems D and powder C (name as in Example 1) in a mixing ratio of 30: 70 entered. The total amount of powder was adjusted so that at one Powder efficiency of 90% an even layer with a thickness of 5 µm arises. The thickness fluctuation of the layer produced in this way was ± 5%.

1.) Die 6 µm Linien waren im UGRA Test heil wiedergegeben

2.) Das Freilaufverhalten als Indiz für eine gute Feuchtmittelführung zeigte kein störendes Verhalten auf.

3.) Im Vergleich zu einem marktüblichen Korrekturmittel (KP 273) treten nach der Korrektur keine Farbunterschiede auf (= Farbschleierfreiheit)

4.) Die Druckauflage betrug 120 000 Drucke

5.) Die Druckauflage betrug bei einer nach dem Entwickeln 5 Minuten bei 230°C gehärteten Platte 450 000 Drucke.

The surface roughness R _{a of} the layer was 0.95 μm, measured in accordance with DIN 4768. The color location determination gave an L value of 75, measured with the Cielab system in accordance with DIN 5033. The number of peaks in the range between 3 to 10 μm was 1000 / m ² , determined by means of image analysis. The adhesion of the layer was checked with an adhesive film as in Example 1 and showed that it was not possible to peel off parts of the layer through the adhesive film perpendicular to the layer plane and starting from the outer edge, ie very good adhesion. The hydrophilized film tape was then coated with a positive diazo copy layer, exposed and developed into a printing plate. The printing plate obtained had a high quality in a printing test and has the following features:

1.) The 6 µm lines were clearly shown in the UGRA test

2.) The free-running behavior as an indication of good dampening solution management showed no disruptive behavior.

3.) In comparison to a standard correction medium (KP 273) there are no color differences after the correction (= freedom from color haze)

4.) The print run was 120,000 prints

5.) The print run was 450,000 prints for a plate cured for 5 minutes at 230 ° C. after development.

Comparative example

An aluminum foil strip as in Example 1 was coated with a conventional aluminum powder with a grain size - 80 + 40 μm and a conventional aluminum oxide powder with a grain size - 53 + 10 μm by the plasma spraying process. The two grits were mixed in a weight ratio of 1: 1 and injected into the plasma flame. Common parameters were used as they can be found in data sheets from plant manufacturers for coating oxides. An argon-hydrogen mixture with 75 vol.% Argon and 25 vol.% Hydrogen with an electrical output of 37 KW is recommended. The layer had a roughness R _a of 4 µm (DIN 4768) and an uneven composition, since the lightly melting aluminum adhered to the injector and detached in larger threads as melt material and was deposited as a peak-like elevation on the film strip. With the printing plate produced therefrom as in Example 1, only the 25 µm lines in the UGRA test were reproduced safely. Furthermore, punctiform portions of the image remained in the area of the non-image areas due to the high roughness. The printing plates produced in this way do not meet the quality standards of offset printers.

Claims (18)

1. A process for the production of printing plates, in which a hydrophilic layer is produced on a substrate film by thermal spraying processing, which comprises producing a surface roughness R_a in the range from 0.2 to 1.5 µm on the surface of the substrate film by mechanical microroughening in a first treatment step and then providing the substrate film with a durably firmly adhering hydrophilic coating by thermal spraying processing of pulverulent oxides and/or oxidic mixtures and compounds having a particle size in the range from -40 to +1 µm.
2. The process as claimed in claim 1, wherein the microroughening is effected by a pressure-blasting method in which a sharp-edged mineral blasting material having a particle size in the range from -100 to +10 µm is blasted onto the surface of the substrate film under a blasting pressure in the range from 0.5 to 2 bar.
3. The process as claimed in claim 1 or 2, wherein the substrate film is a metal foil having a thickness in the range from 100 to 500 µm, preferably from 120 to 350 µm, and having a scratch-fee and pit-free surface which is free from coarse organic or mineral residues.
4. The process as claimed in claim 3, wherein the metal foil comprises aluminum or its alloys, stainless steels or refined steels or metal hybrids.
5. The process as claimed in claim 1 or 2, wherein the substrate film is a biaxially draw oriented and heat-fixed plastics film having a thickness of 100 to 500 µm and comprising a thermoplastic, such as polyvinyl chloride, polyester, for example polyethylene terephthalate or polybutylene terephthalate, polyamide, polyphenylene sulfide or polypropylene.
6. The process as claimed in any of claims 1 to 5, wherein, after the microroughening, the substrate film is fed from a roll via a freely rotating, vertically guided roll to a downstream treatment roll and, while resting closely against the latter roll, is moved under the hot gas jet of a spraying means, the spraying means being moved parallel to the longitudinal axis of the treatment roll, in a straight line or in a wavy manner, above the substrate film.
7. The process as claimed in claim 6, wherein the spraying means comprises at least two spray burners.
8. The process as claimed in claim 6 or 7, wherein heat-removing flow media flow through the treatment roll.
9. The process as claimed in any of claims 1 to 8, wherein the oxide powder is alumina and/or mixtures and compounds with alumina and other oxides.
10. The process as claimed in claim 9, wherein the oxide powder has a particle size of -20 to +1 µm.
11. The process as claimed in claim 10, wherein a further oxide powder which has a particle size of -40 to +20 is mixed with the oxide powder having a particle size of -20 to +1 or is introduced separately into the plasma jet.
12. The process as claimed in claim 11, wherein the further oxide powder has a chemical composition which differs from that of the oxide powder having the particle size of -20 to +1.
13. The process as claimed in claim 12, wherein the further oxide powder is zirconium oxide or magnesium oxide.
14. The process as claimed in any of claims 1 to 13, wherein fine metal powder, preferably aluminum and its alloys and/or mixtures with other metals which are reacted in the plasma flame to give mixtures and/or compounds having hydrophilic properties, is also added to the oxide powder.
15. The process as claimed in any of claims 1 to 14, wherein the oxide powders used comprise mechanical mixtures, pelletized or sintered mixtures of metal and ceramic, or agglomerated particles of these or of oxides surrounded by metals, preferably aluminum and its alloys.
16. The process as claimed in claim 1, wherein plasma-spraying processing with the preferred plasma-forming gases argon, nitrogen, argon/nitrogen, nitrogen/hydrogen or argon/hydrogen or high-speed flame spraying with the preferred combustion gases hydrogen, acetylene, propane, propylene and oxygen is used as the thermal spraying processing process.
17. The use of a printing plate, produced by a process as claimed in any of claims 1 to 16, for offset printing.
18. The use of a printing plate, produced by a process as claimed in any of claims 1 to 16, as a relief printing plate in offset printing.

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