EP0390033B1 - Process and apparatus for roughening a support for photosensitive layers - Google Patents

Description

The invention relates to a method for roughening a support for light-sensitive layers, the surface of which is roughened mechanically and subsequently electrochemically in an aqueous electrolyte bath by applying a three-phase or alternating current to the electrodes opposite the support.

Such supports are used for the production of presensitized printing plates, the material of the supports which are processed in plate or tape form being a metal, in particular aluminum. For example, aluminum strips for the production of printing plates are roughened mechanically, electrochemically or in a combination of a mechanical and electrochemical roughening process. The aim is that the aluminum surface used for the water flow and the adhesion of the light-sensitive layer has a certain structure and uniformity. When mechanically roughened, the surface structures have pyramid-like shapes, while electrochemically roughened aluminum surfaces have a sponge-like structure with many cups and depressions.

Mechanical roughening has the advantage of a smaller specific energy consumption per square meter surface compared to purely electrochemical roughening of the support, but the disadvantage of a surface that is too coarse, on which crystalline structures are also present in addition to the pyramidal structures.

Mechanical roughening processes are generally grain processes, such as wire or brush grain, or emery grinding, while the electrochemical roughening is generally carried out by electrolytic etching in an aqueous electrolyte solution.

German patent 19 62 728 describes a process for the continuous production of a lithographic surface on a metal strip by wet grinding and electrochemical treatment in an electrolyte, in which the electrolyte is used to wet the metal surface during the grinding and the electrochemical treatment is carried out immediately afterwards the grinding is carried out. For this purpose, a fine-grained abrasive is suspended in the electrolyte, and the abrasive suspension is blasted onto the moving belt in a wide jet that extends over the entire width of the metal belt. The electrolyte is, for example, an aqueous acidic or aqueous alkaline bath.

In the graining process described in DE-OS 21 30 391, the aluminum plate is first roughened by grinding with a moist emery compound, and after rinsing and optionally cleaning the plate, the grained surface of the aluminum plate anodized in a sulfuric acid solution with direct current at a voltage in the range of approximately 10 to 20 V and a current density in the range of approximately 1 to 2.2 A / dm 2. Finally, the grained and anodized surface of the aluminum plate is treated with a primer to improve the bonding of the light-sensitive layer to be applied to the surface with the carrier material.

DE-AS 26 50 762 discloses a method for the electrolytic graining of aluminum substrates for lithography by means of alternating current in an electrolyte essentially containing hydrochloric acid or nitric acid, an alternating voltage being applied in this method, the anode voltage of which is greater than the cathode voltage and that Ratio of the cathodic coulombic input to the anodic coulombic input is less than 1. The anodic half period of the alternating current is set equal to or less than the cathodic half period. The diameter and the depth of the pores or holes in the surface of the aluminum substrate can be adjusted as desired by selecting a suitable ratio of the cathodic to the anodic coulombic input, determined by the voltage setting. The frequency of the regulated alternating current is not limited to the usual alternating current frequency range, ie 50 to 60 Hz. With higher frequencies, finer pores are obtained on the grained surface.

German patent 30 12 135 describes a method for producing a support for lithographic printing plates, in which the surface of an aluminum plate is mechanically roughened by wet grinding, aluminum is chemically etched from the surface of the plate and then an electric current with a waveform that by alternating polarity is applied to the plate in an acidic aqueous solution so that the ratio of the amount of charge formed with the plate as the anode to the amount of charge formed with the plate as the cathode is 0.5 / 1 to 1.0 / 1 lies. The electrolysis is carried out so that the current density, if the plate is the anode, is not less than 20 A / dm2 and the amount of charge formed with the plate as the anode is 200 coulombs / dm2 or less, and the anode and cathode voltages at 1 up to 50 V. Finally, the plate is subjected to anodic surface oxidation.

When combining mechanical and electrochemical roughening, the aim is to combine the advantages of both processes. It is expected that the mechanically roughened surface of the metal carrier will be finely overlaid by wells and depressions which are caused by the electrochemical roughening. However, it is shown in an undesirable manner that, in addition to the pyramidal structures of the mechanical roughening, relatively large holes occur which are caused by the electrochemical roughening. Around To achieve reasonably usable results, the mechanical roughening must be followed by a disproportionately high level of electrochemical roughening, as a result of which the power consumption increases very sharply, due to the holes that arise in the electrochemical roughening. The cause of the holes are too high and too long a current, which on the other hand is necessary to make the distribution of the holes very even. Equally problematic when superimposing the mechanically roughened surface of a metal carrier with electrochemical roughening by means of alternating current at a very high working speed of the metal carrier is the formation of so-called electrical cross-shocks in time with the alternating current voltage, these cross-shocks being visible in strip form on the surface of the metal carrier. In all likelihood, the cause of these disturbing cross-strikes is the constant change in polarity of the alternating current applied to the electrodes.

The object of the invention is to improve a method of the type described above in such a way that the surface of a carrier moving at high working speed for photosensitive layers is roughened mechanically and electrochemically in such a way that the electrochemical roughening superimposed on the mechanical pyramidal roughened surface of the carrier consists of uniformly and finely distributed wells and depressions, and has no holes or visible cross-cuts.

This object is achieved by a method according to the preamble of claim 1 in such a way that the frequency of the three-phase or alternating current is chosen to be greater than or equal to 50 Hz to 300 Hz and that the frequency is set higher with increasing transport speed of the carrier through the electrolytic bath.

According to the method, the carrier is moved through the electrolytic bath at a constant speed between 50 and 150 m / min, and the three-phase or alternating current frequency is chosen such that a distance t of the electrical cross-shocks on the carrier surface, which in time with the polarity changes of the rotational or Alternating current are formed, less than or equal to 15 mm.

In particular, the distance t of the electrical cross-shocks on the carrier surface according to the relationship t = v / f, with the carrier transport speed v in mm / sec and the three-phase or alternating current frequency f in Hz (1 / sec), is in the range from 3 to 15 mm chosen.

By using alternating or three-phase current with a frequency substantially higher than 50 Hz, the distance t between the cross-passages is reduced to such an extent that there is a uniform appearance on the surface of the carrier. For this purpose, the frequency of the current can be raised to 300 Hz, for example. At a speed of 100 m / min, the distance is t the electrical cross-cuts then on the carrier surface at a three-phase or alternating current frequency of 300 Hz less than or equal to 6 mm.

The current density of the electrodes which are immersed in the aqueous electrolyte bath is 5 to 50% of the current density of the electrodes which are operated at a three-phase or alternating current frequency of 50 Hz for the purely electrochemical roughening. In particular, the current density of the electrodes is 10 to 20% of the current density of the electrodes which are operated at a three-phase or alternating current frequency of 50 Hz for purely electrochemical roughening, and this first-mentioned current density is in the range from 250 to 1400 A / m 2.

Due to the high working speed, the duration of action of the electrical current for the electrochemical roughening on the metal surface is reduced, and since the specific power consumption is also reduced correspondingly compared to the purely electrochemical roughening, the undesirable hole formation does not occur. A very uniform roughening of the surface of the metal carrier is achieved even at very high working speeds, and with the increase in the current frequency, the duration of action per unit of time is simultaneously reduced, which also counteracts the formation of holes.

The device for carrying out the method comprises electrodes in the electrolyte bath, with the secondary side are connected to a first three-phase transformer, the primary side of which is connected to a regulating and a power transformer for three-phase current via a three-phase frequency converter.

In an embodiment of the invention, the three-phase frequency converter converts the mains frequency of the three-phase current in a range of greater than or equal to 50 to 300 Hz, at a voltage between 1 to 380 V for the individual phases of the three-phase current, which are fed in via lines. The three-phase transformer is connected in a star or delta connection. Furthermore, further electrodes in an electrolyte bath are connected to the secondary side of a second three-phase transformer, the primary side of which is connected to three-phase current via a three-phase control and a power transformer. The second three-phase transformer is also connected in a star or delta connection. The further electrodes are arranged at the beginning and / or at the end of the electrolyte bath, and the three-phase control transformer is fed with three-phase current at mains frequency via lines. In another embodiment of the invention, alternating current is used instead of three-phase current, and one pair of electrodes in an electrolyte bath is connected to the secondary side of an alternating current transformer, and the primary side of each alternating current transformer is connected to alternating current via an alternating current frequency converter. Each of the AC frequency converters works in a frequency range greater than or equal to 50 Hz to 300 Hz, at a voltage of 1 to 380 V of the AC current.

Fig. 1

schematisch eine erste Ausführungsform der erfindungsgemäßen Vorrichtung, deren Elektroden mit frequenzumgesetztem Drehstrom beaufschlagt sind,

Fig. 2

schematisch eine zweite Ausführungsform der Vorrichtung, bei der zusätzlich zu den Elektroden der ersten Ausführungsform weitere Elektroden vorhanden sind, die mit netzfrequentem Drehstrom arbeiten,

Fig. 3

schematisch eine dritte Ausführungsform der Vorrichtung, deren Elektrodenpaare mit frequenzumgesetztem Wechselstrom beaufschlagt sind
und

Fig. 4

schematisch eine vierte Ausführungsform der Vorrichtung, bei der zusätzlich zu den Elektrodenpaaren der dritten Ausführungsform weitere Elektrodenpaare vorhanden sind, an denen netzfrequenter Wechselstrom anliegt.

The invention is explained below with reference to the drawings of some embodiments. Show it:

Fig. 1

schematically a first embodiment of the device according to the invention, the electrodes of which are subjected to frequency-converted three-phase current,

Fig. 2

schematically a second embodiment of the device in which, in addition to the electrodes of the first embodiment, there are further electrodes which work with line-frequency three-phase current,

Fig. 3

schematically a third embodiment of the device, the electrode pairs are acted upon by frequency-converted alternating current
and

Fig. 4

schematically shows a fourth embodiment of the device in which, in addition to the electrode pairs of the third embodiment, further electrode pairs are present, to which mains-frequency alternating current is present.

The device shown schematically in FIG. 1 consists of an electrolyte bath 1, the electrolyte of which, for example dilute aqueous sulfuric, nitric or hydrochloric acid. A carrier 2 in the form of a tape moves in the running direction A through the electrolyte bath 1. Only the device for electrochemical roughening of the surface of the carrier 2 is shown in FIG. 1, but not the parts of the device or system in which the mechanical roughening of the carrier surface is carried out becomes. Such system or device parts are shown and described in detail in German Offenlegungsschrift 19 62 729 and German Patent 19 62 728.

At a distance from the carrier 2, electrodes 3, 4 and 5 are arranged in the electrolyte bath 1, which electrodes are connected to three windings of the secondary side of a first three-phase transformer 6, which are not described in more detail. The corresponding three windings on the primary side of the three-phase transformer 6 are connected to a three-phase frequency converter 7, which is connected via lines L1, L2 and L3 to regulating transformers, not shown, which are fed by a common power transformer for three-phase current. The three-phase frequency converter 7 makes it possible to convert the three-phase current fed in at the mains frequency of 50 Hz into a three-phase current in the frequency range greater than / equal to 50 Hz to 300 Hz. The frequency of the three-phase current is chosen to be greater than the mains frequency of 50 Hz, and with increasing transport speed of the carrier 2 through the electrolyte bath 1, the frequency converted is also set higher. The carrier 2 passes through the electrolyte bath 1 generally at a constant speed, which can be chosen between 50 to 150 m / min.

At a very high transport speed v of, for example, 100 m / min, at a frequency f = 50 Hz of the three-phase current applied to the electrodes 3, 4 and 5, corresponding to the relationship t = v / f, with the transport speed v in mm / sec, the current frequency in Hz or 1 / sec and the distance t in mm of the so-called cross-cuts on the surface of the carrier 2, distances t of 33.3 mm. These electrical cross-shocks are caused in accordance with the changes in polarity of the electrodes 3, 4 and 5 by the applied three-phase or alternating current.

The device according to the invention is operated to equalize these cross-cuts so that the freely selectable parameters, namely the transport speed of the carrier 2 and the frequency of the current applied to the electrodes 3, 4 and 5, are chosen so that the distance t of the cross-cuts is less than or equal to 15 mm, in particular 6 mm.

The current density of the electrodes 3, 4 and 5 is 5 to 50%, in particular 10 to 20% of the current density of the electrodes which are operated at a three-phase or alternating current frequency of 50 Hz for the purely electrochemical roughening. The current density of electrodes 3, 4 and 5 is in the range of 250 to 1400 A / m².

As soon as the electrochemical roughening in the electrolyte bath 1 has ended, the carrier 2 is rinsed, for example, without intermediate pickling and is electrochemically anodized.

The currents fed to the three-phase frequency converter 7 have voltages which are in the range from 1 to 380 V, and are transformed in terms of voltage such that the voltages applied to the electrodes 3, 4 and 5 are between 20 and 50 V, in particular 35 V.

The embodiment of the device according to FIG. 2 comprises an electrolyte bath 11 through which the carrier 2 is transported. In addition to the electrodes 3, 4 and 5 there are further electrodes 8, 9 and 10 in the electrolyte bath 11, which may contain an electrolyte of the same consistency as the electrolyte bath 1 of the embodiment according to FIG. 1. The running direction of the carrier 2 is not shown in FIG. 2, since it can move either from left to right or from right to left. This means that the electrodes 8, 9 and 10 are arranged at the end of the electrolyte bath in the direction of movement from left to right and the electrodes 8, 9, 10 are located at the beginning of the electrolyte bath 11 in the opposite direction of movement of the support 2.

The electrodes 8, 9 and 10 are connected to the corresponding windings of the secondary side of a second three-phase transformer 13, which are not described in more detail. The corresponding windings on the primary side of the second Three-phase transformers 13 are connected to three-phase current via a three-phase control transformer 12 and a power transformer, not shown. The second three-phase transformer 13 is connected in a star or delta connection. The three-phase control transformer 12 is connected to the power transformer (not shown) via lines L1, L2 and L3. The three-phase control transformer 12 is fed with three-phase current at mains frequency, ie at 50 Hz, via lines L1, L2 and L3; frequency conversion, as in the case of electrodes 3, 4 and 5, does not take place.

Although this is not shown in FIG. 2, analogously to electrodes 8, 9 and 10, a further three electrodes can be arranged in a correspondingly larger electrolyte bath 11 to the left of electrodes 3, 4 and 5. Such a construction boils down to the fact that both at the beginning and at the end of an extended electrolyte bath 11 there is a set of three electrodes which are supplied with three-phase current at the mains frequency, while the middle set of electrodes 3, 4 and 5 with three-phase current is higher Frequency is operated as the network frequency. Likewise, as already mentioned, it is preferably possible for the electrodes 3, 4 and 5 to be arranged at the beginning or at the end of the electrolyte bath and with the electrodes 8, 9 and 10, which then lie behind or in front of the electrodes 3, 4 and 5 are working together.

The third embodiment of the device according to the invention, as shown schematically in FIG. 3, differs from the first embodiment according to FIG. 1 in that instead of the individual electrodes, which are charged with three-phase current higher than the mains frequency, electrode pairs 14, 15; 16, 17 and 18, 19 are present in an electrolytic bath 20, through which the carrier 2 runs in the running direction A. The electrolyte in the electrolyte bath 20 has the same composition as was described with reference to FIG. 1. One of the electrode pairs 14, 15; 16, 17 and 18, 19 is connected to the secondary side of an associated AC transformer 21, 22 and 23, respectively. On the primary side, each alternating current transformer is connected to alternating current via an alternating current frequency converter 24, 25 and 26. The alternating current is fed in via lines L1, L2 of the frequency converter 24, lines L2, L1 of the frequency converter 25 and lines L1, L2 of the frequency converter 26. The symbols L1 and L2 stand for the two phase lines for alternating current. The electrochemical roughening takes place in accordance with the so-called center conductor method, ie the alternating current circuit of the one pair of electrodes 14, 15 is closed via the electrolyte of the electrolyte bath 20, the section of the carrier 2 located below the two electrodes 14, 15 and the secondary winding of the alternating current transformer 21. Each of the AC frequency converters 24, 25, 26 is operated in a frequency range greater than / equal to 50 Hz to 300 Hz, at a voltage of 1 to 380 V of the AC current.

The fourth embodiment of the device shown in FIG. 4 comprises an electrolyte bath 31 through which the carrier 2 is transported. Similar to the embodiment according to FIG. 2, the running direction of the carrier 2 is not shown in FIG. 4, since the carrier 2 can move through the electrolyte bath 31 either from left to right or from right to left. In this embodiment, in addition to the electrode pairs present in FIG. 3, further electrode pairs 27, 28 and 29, 30 are present in the electrolyte bath 31. These pairs of electrodes are connected to the windings on the secondary sides of alternating current transformers 32 and 33, which are fed on the primary side via alternating current regulating transformers 34 and 35 with mains frequency alternating current. The electrode pairs 14, 15; 16, 17; 18, 19 are arranged either at the beginning or at the end of the electrolyte bath 31. In this context, it should be pointed out that, for reasons of simplification, only one pair of electrodes 18, 19 according to the third embodiment according to FIG. 3 is shown in FIG. 4 and the electrode pairs 16, 17 and 14, 15 from FIG. 3 to the left of it have been omitted. Furthermore, although this is not shown in the drawing, an arrangement is possible in which two pairs of electrodes are arranged both at the beginning and at the end of an expanded electrolyte bath 31, which are operated with mains-frequency alternating current, which is controlled via alternating current regulating transformers and alternating current transformers with constant Gear ratio, as is the case with transformers 32 and 33, is applied to the electrode pairs. The fed AC currents, regardless of whether they are frequency-converted or have a mains frequency, have a voltage level in the range from 1 to 380 V. The frequency conversion of the mains frequency of the AC currents fed in is in the range from / greater than or equal to 50 Hz to 300 Hz Alternating current applied electrodes is 5 to 50%, in particular 10 to 20% of the current density at the electrodes for the purely electrochemical roughening.

With the devices according to the invention, a superimposition of the mechanically roughened surface of the carrier 2 is achieved, for example by wet brushing with a suspension of pumice and / or quartz powder, by means of electrochemical roughening, the current frequencies of the three-phase or alternating currents applied to the electrodes being im are generally much higher than 50 Hz. A roughening pattern that is optically free of transversal impact, a fine superimposition of the mechanically roughened surface of the carrier by the electrochemically generated roughening, lower specific power consumption and a very high working speed for the carrier, up to 150 m / min, are achieved. The roughness of the mechanically roughened surface of the carrier is considerably greater than the roughness that is obtained by the electrochemical roughening. The surface of the support is comparatively light, and the printing plate produced with such a support shows no color fog after development.

Claims (18)

1. A process for roughening a substrate for photosensitive layers, the surface of which substrate is roughened mechanically and subsequently electrochemically in an aqueous electrolyte bath by applying a three-phase or alternating current to the electrodes opposite the substrate, wherein the frequency of the three-phase or alternating current is chosen in the range of greater than/equal to 50 Hz up to 300 Hz and the frequency is adjusted higher with increasing rate of conveyance of the substrate through the electrolytic bath.
2. The process as claimed in claim 1, wherein the substrate is moved through the electrolytic bath at a constant rate of between 50 and 150 m/min, and the three-phase or alternating current frequency is chosen such that a spacing t of the electrical cross-strokes on the substrate surface, which are formed in step with the changes in polarity of the three-phase or alternating current, is less than/equal to 15 mm.
3. The process as claimed in claim 2, wherein the spacing t of the electrical cross-strokes on the substrate surface is chosen in the range from 3 to 15 mm in accordance with the relationship t = v/f, the rate of conveyance of the substrate v being in mm/sec and the three-phase or alternating current frequency f being in Hz (1/sec).
4. The process as claimed in claim 3, wherein the spacing t of the electrical cross-strokes on the substrate surface is chosen as less than/equal to 6 mm in the case of a three-phase or alternating current frequency of 300 Hz.
5. The process as claimed in claims 1 to 4, wherein the current density of the electrodes, which dip into the aqueous electrolytic bath, amounts to 5 to 50 % of the current density of the electrodes which are operated with a three-phase or alternating current frequency of 50 Hz for the purely electrochemical roughening.
6. The process as claimed in claim 5, wherein the current density of the electrodes, which dip into the aqueous electrolytic bath, amounts to 10 to 20 % of the current density of the electrodes which are operated with a three-phase or alternating current frequency of 50 Hz for the purely electrochemical roughening, and the first-mentioned current density amounts to 250 to 1400 A/m².
7. The process as claimed in claims 1 to 6, wherein after the electrochemical roughening without intermediate pickling the substrate is rinsed and electrochemically anodized.
8. The process as claimed in claims 1 to 7, wherein the voltages to be transformed in terms of frequency lie in the range from 1 to 380 volt in the case of frequencies in the range of greater than/equal to 50 and up to 300 Hz, and the voltages applied to the electrodes amount to 20 to 50 V, especially 35 V.
9. The process as claimed in claims 1 to 8, wherein at the start and/or at the end of the electrochemical roughening of the substrate an electrolytic treatment of the substrate is done with direct current.
10. An apparatus for carrying out the process as claimed in claims 1 to 9, wherein electrodes (3, 4, 5) in the electrolytic bath (1) are connected to the secondary side of a first three-phase transformer (6), whose primary side is connected via a three-phase frequency converter (7) via regulating transformers to a power transformer for three-phase current.
11. The apparatus as claimed in claim 10, wherein the three-phase frequency converter (7) transforms the line frequency of the three-phase current in a range from greater than/equal to 50 to 300 Hz, at a voltage between 1 to 380 V for the individual phases of the three-phase current, which are supplied via leads (L1, L2, L3).
12. The apparatus as claimed in claims 10 and 11, wherein the three-phase transformer (6) is wired up in a star or delta connection.
13. The apparatus as claimed in claims 10 to 12, wherein further electrodes (8, 9, 10) are connected in an electrolytic bath (11) to the secondary side of a second three-phase transformer (13), whose primary side is connected to three-phase current via a three-phase regulating transformer (12) and a power transformer, and the second three-phase transformer (13) is wired up in a star or delta connection.
14. The apparatus as claimed in claim 13, wherein the further electrodes (8, 9, 10) are arranged at the beginning and/or at the end of the electrolytic bath (11), and the three-phase regulating transformer (12) is supplied with three-phase current at line frequency via leads (L1, L2, L3).
15. An apparatus for carrying out the process as claimed in claims 1 to 9, wherein one pair each of electrodes (14, 15; 16, 17; 18, 19) is connected in an electrolytic bath (20) to the secondary side of an alternating-current transformer (21; 22; 23), and the primary side of each alternating-current transformer is connected to alternating current via an alternating-current frequency converter (24; 25; 26).
16. An apparatus as claimed in claim 15, wherein each of the alternating-current frequency converters (24; 25; 26) operates in a frequency range of greater than/euqal to 50 Hz up to 300 Hz at a voltage of from 1 to 380 volt of the alternating current.
17. The apparatus as claimed in claim 16, wherein further pairs of electrodes (27, 28; 29, 30) are connected in an electrolytic bath (31) to the secondary sides of alternating-current transformers (32, 33) whose primary sides are connected to alternating current via alternating-current regulating transformers (34; 35).
18. The apparatus as claimed in claim 17, wherein the further pairs of electrodes (27, 28; 29, 30) are arranged at the beginning and/or at the end of the electrolytic bath (31) and alternating current at line frequency is fed to the alternating-current regulating transformers (34; 35).

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