EP0683248B1 - Process for the after-treatment of plates, foils or strips and its application as substrate for offset printing plates - Google Patents

Abstract

Plates which have been chemically, mechanically or electrochemically roughened are anodised and then treated in an aqueous solution of a pure and crystalline alkali metal silicate followed by rinsing in an ion-containing water.

Description

The invention relates to a process for the aftertreatment of plate, film or tape material based on chemically, mechanically and / or electrochemically roughened and anodically oxidized aluminum or one of its alloys, the aluminum oxide layers of which are treated with an alkali metal silicate in aqueous solution, and one Carrier made of such a material, in which the aluminum oxide layer is coated with an alkali metal silicate layer, and the use of such a carrier as a carrier for offset printing plates.

Carrier materials for offset printing plates are either equipped directly by the consumer or by the manufacturer of precoated printing plates or equipped on one or both sides with a radiation or light-sensitive layer, a so-called reproduction layer, with the help of which an image to be printed is created for submission in a photomechanical way. After the radiation-sensitive layer has been exposed and developed, the support carries the image-bearing areas which later lead to color printing and, at the same time, forms the hydrophilic background for the lithographic printing process at the non-image areas during later printing, the so-called non-image areas.

The following requirements must therefore be placed on a layer support for reproduction layers for the production of offset printing plates:

The parts of the radiation-sensitive layer which have become relatively more soluble after exposure must be easy to remove from the support without residue by development in order to produce the hydrophilic non-image areas.

The carrier exposed in the non-image areas must have a high affinity for water, i.e. be highly hydrophilic in order to absorb water quickly and permanently during the lithographic printing process and to be sufficiently repellent to the bold printing ink.

The adhesion of the radiation-sensitive layer before or the printing parts of the layer after the irradiation must be sufficient.

Aluminum, which is roughened on the surface by known methods by dry, wet brushing, sandblasting, chemical and / or electrochemical treatment, is used in particular as the base material for such layer supports. To increase the abrasion resistance, the roughened substrate is subjected to an anodization step to build up a thin oxide layer.

In practice, the carrier materials, in particular anodically oxidized carrier materials based on aluminum, are often used to improve the Layer adhesion, to increase the hydrophilicity and / or to facilitate the developability of the radiation-sensitive layers prior to the application of a radiation-sensitive layer, undergo a further treatment step, as described for example in EP-B 0 105 170 and EP 0 154 201.

EP-B 0 105 170 discloses a process for the aftertreatment of aluminum oxide layers with an aqueous alkali silicate solution, in which after the treatment a) is carried out with an aqueous alkali silicate solution, a treatment b) is also carried out with a solution containing aqueous alkaline earth metal salts. The alkali silicate solution is an aqueous solution containing Na ₂ SiO ₃ .5 H ₂ O. It is then rinsed with distilled water, this intermediate cleaning can also be omitted, and then, or immediately after the silicatization, treatment is carried out in an aqueous solution of an alkaline earth metal nitrate, such as calcium, strontium or barium nitrate. The intermediate rinses with distilled water show a certain influence on the alkali resistance, which is generally better for pores that have not been rinsed after the silicatization step than for rinsed pores.

EP-B 0 154 201 describes a process for the aftertreatment of aluminum oxide layers in a solution which contains an alkali metal silicate and alkaline earth metal cations. Calcium or strontium salts are used as alkaline earth metal salts, in particular nitrates or hydroxides used. The aqueous solution in the aftertreatment additionally contains at least one complexing agent for alkaline earth metal ions. The materials are electrochemically roughened in an aqueous solution containing nitric acid. The materials are further anodically oxidized in one or two stages in aqueous solutions containing H ₂ SO ₄ and / or H ₃ PO ₄ . The aftertreatment is carried out electrochemically or by immersion treatment.

In the case of the layer supports which were treated by the known processes, it can be seen that the sodium metasilicates frequently used for silicating, such as Na ₂ SiO ₃ . 5 H ₂ O, at a higher pH of 12.2, of the aftertreatment solution very quickly degrade the aluminum oxide in an undesirable manner.

The object of the invention is therefore to improve a process for the aftertreatment of flat aluminum layer supports which have an aluminum oxide layer in such a way that the degradation of the oxide layer by the silicating can be avoided or at least kept very slight.

This object is achieved according to the invention by a process of the type described in the introduction that a) the aftertreatment is carried out in an aqueous solution of the ϑ modification of sodium phyllosilicate Na ₂ Si ₂ O ₅ and b) subsequently rinsed with water containing alkali metal or alkaline earth metal ions being, the Alkali or alkaline earth metal ions can be selected from the group Ca, Mg, Na, K, Sr.

In an embodiment of the process, the SiO ₂ / Na ₂ O molar ratio of the crystalline layered sodium silicate is preferably in the range from 1.9 to 3.5 to 1. In a further development of the invention, the solution in the after-treatment stage a) contains 0.1 to 10% by weight. % of ϑ-Na ₂ Si ₂ O ₅ .

The aftertreatment can be carried out as an immersion treatment or else electrochemically, the latter procedure bringing about a certain increase in the alkali resistance and / or improvement in the adsorption behavior of the material. It is assumed that a firmly adhering silicate top layer forms in the pores of the aluminum oxide layer, which protects the aluminum oxide from attacks, the surface topography previously generated, such as roughness and oxide pores, being changed practically or only insignificantly.

The post-treatment stage a) is carried out electrochemically and / or by an immersion treatment for a time of 10 to 120 seconds and at a temperature of 40 ° C. to 80 ° C. The electrochemical aftertreatment is carried out in particular with direct or alternating current, trapezoidal, rectangular or triangular current or overlapping forms of these types of current. The current density is generally 0.1 to 10 A / dm ² and / or the voltage is 3 to 100 volts. Post-treatment stage b) with ionic Water generally follows an immersion treatment in a 0.1 to 10% by weight salt solution, this salt solution containing, for example, individually or in combination NaF, NaHCO ₃ , CaSO ₄ , polyvinyl phosphoric acid and MgSO ₄ .

In addition to aluminum, suitable base materials for the layer supports are also alloys of aluminum which, for example, have a content of more than 98.5% by weight of Al and proportions of Si, Fe, Ti, Cu and Zn.

All process stages can be carried out discontinuously with plates or foils, but they are preferably carried out continuously with belts in belt systems.

Regarding the process parameters for continuous process control in the electrochemical roughening stage, the pre-cleaning and the anodic oxidation of the layer support material, in particular of aluminum, reference is made to the statements in EP-B 0 154 201, column 5, lines 5 to 39, 47 to column 6 , Line 36 including and in EP-B 0 105 170, page 4, lines 11 to 60. These statements also apply to the layer supports described here, in which the same process parameters are used for electrochemical roughening, pre-cleaning and anodic oxidation. The disclosure content of these two European patents with regard to the process parameters in the continuous process control also applies in full to the layer support materials of the present invention.

Fig. 1

die Struktur des Natriumschichtsilikats, das für die Silikatisierung in der Nachbehandlungsstufe eingesetzt wird,

Fig. 2

das Si/Al-Verhältnis in der Oberfläche eines Schichtträgers in Abhängigkeit von der Konzentration des Natriumschichtsilikats bei vorgegebener Temperatur des Tauchbades und vorgegebener Tauchzeit,

Fig. 3

den Abbau des Oxidgewichts in der Oberfläche eines Schichtträgers in Abhängigkeit von der Eintauchzeit und der Temperatur des Eintauchbades,

Fig. 4

die Alkaliresistenz nachbehandelter Schichtträger in Abhängigkeit von der Eintauchzeit, und

Fig.en 5 und 6

das Si/Al-Verhältnis in der Oberfläche nachbehandelter Schichtträger und den Naund Ca-Gehalt der Oberfläche nach der Spülung mit voll entionisiertem Wasser und mit Stadtwasser.

The invention is explained in more detail below with reference to drawings. Show it:

Fig. 1

the structure of the layered sodium silicate used for the silicatization in the aftertreatment stage,

Fig. 2

the Si / Al ratio in the surface of a layer support as a function of the concentration of the layered sodium silicate at a given temperature of the immersion bath and a given immersion time,

Fig. 3

the reduction of the oxide weight in the surface of a substrate depending on the immersion time and the temperature of the immersion bath,

Fig. 4

the alkali resistance of post-treated substrates depending on the immersion time, and

Figures 5 and 6

the Si / Al ratio in the surface of the aftertreated layer support and the Na and Ca content of the surface after rinsing with fully deionized water and with city water.

FIG. 1 shows the structure of layered sodium silicate, which is a pure sodium silicate, ie it is composed exclusively of sodium, silicon and oxygen. It is the ϑ phase of the crystalline disilicate Na ₂ Si ₂ O ₅ . It is similar to the common water glass, but is anhydrous and crystalline. The structure shown in FIG. 1 was determined by X-ray diffraction on single crystals. It shows the polymeric wavy layer structure of the silicate framework made of sodium ions, which are represented in the figure by large bright spheres, oxygen by large black spheres and silicon by small black spheres. The sodium ions are almost in one plane. The crystalline layered sodium silicate, which is a layered silica, has a SiO ₂ / Na ₂ O molar ratio of 1.9 to 3.5 to 1. The structure of this compound is almost identical to that of the mineral natrosilite, in which it is a β modification of Na ₂ Si ₂ O ₅ . Very pure sand and soda or sodium hydroxide solution are used as the base material in the production of layered sodium silicate, from which a water glass solution is produced. This solution is then dewatered and crystallized at high temperature into the delta modification of the disilicate. The product obtained can be ground and, if necessary, compacted into granules. In aqueous solution, water penetrates between two layers and widens the distance. The sodium ions can then be exchanged with other ions. The calcium and magnesium ions of the rinse water, for example tap water, are bound by the crystalline layered silicate in an ion exchange process, ie the sodium ions of the layered silicate are quickly replaced, thereby stabilizing the silicate structure. This exchange process takes place faster than the dissolution of the layered sodium silicate - with the effect that the particles are much smaller than when the amorphous silicate. The layered sodium silicate provides the desired alkalinity and stabilizes the pH. Hoechst AG offers the product as a builder or builder for detergents.

Under the name of layer silicates (SKS systems from Hoechst AG, corresponding to S chicht k iesel s äure) are known a variety of compounds of the very komplexten Na-layer silicate system (types SKS 1-21), with the type according to the invention SKS-6 as the most important with regard to builder properties in detergents (binding capacity of Mg, Ca ions); it is also advantageously water-soluble for silicating and processing.

Thus, trioctahedral layered silicates, such as SKS 20 (mineralogical name "Saponit") and SKS 21 ("Hectorite"), have water solubility and a good cation exchange capacity of the intermediate Na ions.

Furthermore, the anhydrous layered Na silicate with Kanemite structure (SKS-9) and the synthetic Kanemite (SKS 10) have a very good Ca binding capacity.

Radiation-sensitive coatings are applied to the aftertreated layer supports, and the offset printing plates thus obtained are converted into the desired printing form in a known manner by imagewise exposure and washing out of the non-image areas with a developer, preferably an aqueous developer solution. Surprisingly, offset printing plates stand out, their layer support materials using the two-stage process were treated compared to those plates in which the same layer support material was aftertreated with aqueous solutions containing silicates, such as water glass or α- or β-Na ₂ Si ₂ O ₅ , by improved alkali resistance, a lower tendency to form color and great resistance to a rubber coating of the offset printing plate.

In the description and the examples below, the% data always mean% by weight, unless stated otherwise. The following method for determining the resistance to alkali is given in the examples:

Alkali resistance measurement

To measure the alkali resistance of an oxidized aluminum surface, a defined area of 7.5 cm x 7.5 cm at room temperature is immersed in a 0.1 N NaOH solution with an electrolyte concentration of 4 g NaOH per liter of fully deionized water and the alkali resistance is determined electrochemically . For this purpose, the time course of the potential of an Al / Al ³⁺ half cell against a reference electrode is measured without current. The potential curve provides information about the resistance that the aluminum oxide layer opposes to its dissolution.

The time in seconds, which is determined in the voltage-time diagram after passing through a minimum until a maximum occurs, serves as a measure of the alkali resistance. An average value is formed from the measured values of two samples.

For the non-post-treated substrate, the alkali resistance with an oxide weight of 3.21 g / m ^{2 is} 112 ± 10 seconds, this value being an average of 5 double measurements.

FIG. 2 shows the silicatization or the covering with silicate on an aluminum surface of a printing plate, in which the aftertreatment with layered sodium silicate of different concentrations in aqueous solution takes place at an immersion bath temperature of 60 ° C. for different lengths of time. The surface silicatization is investigated according to the ESCA method, which is "Electron Spectroscopy for Chemical Analyzes", with which the atomic layers on a surface up to approx. 5 nm thick, due to their binding energy position and the intensity of the peak values, the surface atoms, if applicable theirs Binding state, can be determined. Furthermore, the intensity ratio of the different peak values compared to the peak value of aluminum allows an assessment of the atomic occupancy on the aluminum oxide surface. FIG. 2 shows the Si / Al and the Na / Al ratio or the coating with Si and Na on the aluminum oxide surface.

The support with the highest Si / Al ratio is rinsed with fully deionized water and dried and then gummed with an aqueous solution of dextrin, H ₃ PO ₄ , glycerin, which has a pH of 5.0, and after 16 hours Washed off with fully deionized water. The Si / Al ratio does not change after this procedure and is 0.56, and the Na / Al ratio goes to 0.07 back. The silication with layered sodium silicate is not attacked by the rubber coating, ie the silicate coating is not removed. Phosphorus from the rubber coating can only be detected in the ESCA spectrum, which is proof that the rubber coating does not attack the silicate coating.

As can be seen from FIG. 2, the silicatisation of the aluminum oxide surface increases with increasing concentration of the layered sodium silicate in the aftertreatment solution, with increasing temperature of the immersion bath (see FIG. 5) and with a longer immersion time. This is expressed in particular in an increase in the Si / Al ratio. The concentration of the layered sodium silicate was increased from 1 g / l to 10 g / l of fully deionized water, furthermore demineralized water, the immersion temperature of the aftertreatment solution was raised from 60 to 80 ° C. (see FIG. 5) and the immersion time was 10 s increased to 120 s.

Furthermore, the ESCA measurements show that the applied layered sodium silicate retains its ion exchange capacity, ie when sodium is rinsed with tap or city water, the sodium ions are exchanged for calcium ions. After silicating and rinsing with demineralized water, there is always a high sodium content in addition to silicon, which is greatly reduced after rinsing with city or tap water and instead an increase in the calcium content is found. While the magnesium content after such a rinse is poor due to its peak value It can be demonstrated that the exchange of sodium for strontium could also be determined using a strontium solution (see also Table 2).

Figure 3 shows the oxide degradation in the aluminum oxide layer of a layer or printing plate support. The substrate is roughened electrochemically in hydrochloric acid and anodized in sulfuric acid. Its total thickness is 0.3 mm, the oxide weight is 3.21 g / m ² , the thickness of the oxide layer is about 1 µm. The aftertreatment is carried out in accordance with the process according to the invention in an aqueous solution with a 1% concentration of the layered sodium silicate, deionized water being used. The solution had a pH of 11.4. In the post-treatment step, the printing plate carrier was immersed in the immersion bath at a temperature of 60 ° C. The diving times were 10 to 120 s. As can be seen from Figure 3, the aluminum oxide is attacked only slightly. The surfaces of the substrate, which were treated for 10 s, 30 s, and 120 s in the 1% sodium layer silicate solution at 60 ° C, show little change in SEM images compared to the starting material, only that Porosity of the surface, ie the refinement of the pore structure increases slightly. In comparison, the surfaces of substrates were also investigated, in which sodium metasilicates Na ₂ SiO ₃ x 5 H ₂ O were used for the silicatization, under otherwise identical immersion conditions. These investigations were carried out for the diving temperatures of 25 ° C and 60 ° C. A very strong oxide degradation is found, which is still at a low diving temperature of 25 ° C is significantly higher than when silicating with layered sodium silicate. The 1% sodium metasilicate solution (10 g / l Na ₂ SiO ₃ x 5 H ₂ O, whereby the water of crystallization is not taken into account) has a pH of 12.2.

The oxide degradation is determined gravimetrically in a chrome / phosphoric acid bath at a higher temperature of approx. 70 ° C by differential weighing; the starting oxide weight of the support is 3.21 g / m ² at an immersion temperature of 60 ° C.

The basis weight of aluminum oxide layers is determined by chemical detachment in accordance with DIN standard 30944 (March 1969 edition) in conjunction with an internal operating regulation of the applicant from 1973.

The alkali resistance measurements of substrates after treatment with sodium silicate and rinsing with water with different compositions are explained with reference to FIG. 4. In the tests, aluminum substrates were immersed in a 1% sodium layer silicate solution (10 g / l sodium layer silicate in demineralized water) at different immersion temperatures in the range from 40 to 80 ° C, the immersion times being 10, 30 and 120 s. After squeezing off the solution, the sample was treated with either demineralized water or city water at room temperature for about 20 s in the rinsing step. The results of these tests are shown in FIG. 4.

In addition, further tests were carried out in which a post-treated carrier (1% sodium phyllosilicate solution / demineralized water, immersion bath temperature 60 ° C., immersion time varied) was carried out (see Table 1). Table 1 ϑ-Na ₂ Si ₂ O ₅ post-treatment Rinse Alkali resistance ESCA: X / A1 (X = Si, Na, Ca) 1% layered sodium silicate solution, immersion temperature 60 ° C Dive time / s (20s) Max after s Si N / A Approx 20th VE-H ₂ O 80/82 0.33 0.18 - 120 VE-H ₂ O 99/61 0.44 0.22 - 20th City water 206/127/188 0.34 0.04 0.06 120 City water 447/244/209 0.47 0.06 0.07 120 VE-H ₂ O 78 0.46 0.20 - 120 VE-H ₂ O 119 0.51 0.15 - 120 VE-H ₂ O 118 0.43 0.22 - 120 VE-H ₂ O 86 0.43 0.21 - 120 City water 60 ° C / 20s 307 0.43 0.03 0.06 10th VE-H ₂ O 100 0.27 0.14 0.02 30th VE-H ₂ O 95 0.36 0.18 0.01 120 VE-H ₂ O 150 0.43 0.16 0.02

The city water used for rinsing has the following composition:
pH = 7.7, 16 ° DH (German hardness), 10.5 ° HCO ₃ carbonate hardness; Ca ions 85 mg / l Cl ions 102 mg / l Mg ions 15 mg / l SO ₄ ions 75 mg / l Na ions 61 mg / l NO ₃ ions 6 mg / l K ions 5.8 mg / l SiO ₂ ions 5.9 mg / l DOC 0.8 mgC / l with DOC = dissolved, organically bound carbon

In addition to NaCl, mainly Ca ⁺⁺ and SO ₄ ^- , but relatively little Mg are detectable in the city water.

As shown in FIG. 4, rinsing with demineralized water at most provides a slightly increased alkali resistance, which is only slightly dependent on the immersion temperature. The aftertreatment with city water results in an alkali resistance of the oxidized aluminum surface, which is significantly higher than with the aftertreatment with demineralized water. This resistance to alkali rises sharply with increasing immersion bath temperature of the layered sodium silicate solution.

In the course of these experiments (see Table 1), for comparison, an aluminum layer support was also rinsed with a 1% sodium layer silicate solution at 60 ° C. for two minutes and then rinsed with demineralized water. The mean value of the measured alkali resistance from six double measurements of plates treated in this way is 106 ± 19 s until the maximum is reached. In contrast, the alkali resistance of a standard silicate coating, which is rinsed with city water, is significantly increased. In parallel to increasing the alkali resistance when flushing with city water, the Na ions are largely exchanged for Ca ions.

The significantly increased resistance to alkali demonstrated by rinsing with city water is presumably due to the fact that when treated with layered sodium silicate ϑ-Na ₂ Si ₂ O ₅ , aluminosilicates (Na salts) initially form, which in the rinsing step with city water form further alkali-resistant bonds, for example with Ca. , K, Mg and possibly with the anions.

Investigations were also carried out to improve the surface properties, in particular to increase and stabilize the alkali resistance, by rinsing the layer supports treated with layered sodium silicate with various salt solutions. Alkali resistance measurements were also carried out on standard-pretreated substrate boards, which were then rinsed with anionic salt solutions. The support plates were silicated with 1% sodium phyllosilicate solution, the immersion temperature was 60 ° C and the immersion time was 120 s, then rinsed with demineralized water and then rinsed soaking wet in the salt solutions listed below, the immersion time being 20 s at room temperature. For rinsing, mostly 0.1 to 0.4% salt solutions were used, only in one case a 1% salt solution for comparison purposes.

Alkali resistance values were determined for the following rinse solutions: Rinse solutions: Alkali resistance: 0.4% NaHCO ₃ in VE-H ₂ O 210/204 s to the maximum 1.0% NaHCO ₃ in VE-H ₂ O 350 " 0.4% Na ₂ CO ₃ in VE-H ₂ O 258 " 0.4% Na ₂ SiO ₃ in VE-H ₂ O 413 " 0.4% Na ₃ PO ₄ in VE-H ₂ O 278 " , PO ₄ ^3-, SiO ₃ ^2-, CO ₃ ^2- anions can be significantly enhanced by rinsing with the appropriate salt solutions ^- in addition to the alkaline earth metal cations and anions decisive influence on the size of the alkali resistance, for example, by HCO ₃ have. The table also shows that in the case of a rinsing solution in NaHCO ₃ , the alkali resistance also increases with increasing concentration.

Table 2 below shows alkali resistance values for further rinsing solutions, together with the X / Al ratios of various alkaline earth metals X in the rinsing solutions to aluminum Al, measured by the ESCA method.

For these measurements, the samples were prepared as standard, that is, siliconized with 1% sodium phyllosilicate solution in demineralized water, at an immersion temperature of 60 ° C and an immersion time of 120 s. It was rinsed with demineralized water and with solutions in which 0.4% strength CaCl ₂ , MgCl ₂ , SrCl ₂ and dextrin were dissolved. Further Solutions were CaSO ₄ , Na ₂ SO ₄ , MgSO ₄ , NaF, polyvinyl phosphoric acid NaHCO ₃ . After drying, the alkali resistance value and the X / Al ratios were determined by ESCA measurements in order to determine the surface coverage by Si, Na, Ca, Sr and the like. TABLE 2 Layered sodium silicate Rinse Alkali resistance in s up to the maximum ESCA: X / Al X = Ca, Mg, Sr, F, P Si / Al Well / Al X / Al default VE water 80-120 0.46 0.20 - " 0.4% igCaCl ₂ / VE 145 0.47 0.02 0.07 / approx " "MgCl ₂ / VE 118 0.48 0.04 ? / Mg " "SrCl ₂ / VE 126 0.49 0.02 0.07 / Sr " City water DH = 16 ° 200-250 0.47 0.06 0.07 / approx " 0.4% Dextrin / VE 130 0.49 0.16 - default 0.4% igCaCl ₂ / city water 217 0.49 0.04 0.06 / approx " 0.4% igCaCl _2/60 ° C 254 0.42 0.03 0.08 / approx City water " 0.1% igCaSO ₄ / VE 212/242 0.42 0.03 0.10 / approx 0.06 / P " 0.4% igNa ₂ SO ₄ / VE 90/115 0.46 0.29 - " 0.2% MgSO ₄ / VE 144 0.42 0.09 0.05 / P default 0.4% igNaF / VE 182 ** / 255 0.47 0.33 0.13 / F " 0.4% igNaF / * city water 362 0.46 0.29 0.21 / F 0.06 / approx " 0.4% igNaF / 60 ° C * 246 0.39 0.41 0.35 / F 0.09 / approx " 0.4% igNaF / 60 ° C 128 ** 0.40 0.43 0.19 / F default 0.22% igLC1 / VE 110/135 0.31 0.01 0.58 / P " 0.4% nigHCO ₃ / VE 210/204 0.42 0.31 - " 0.4% igNaHCO _3/60 ° C 168 ** 0.45 0.31 - ** 2. Max./ mean LC1 = polyvinylphosphonic acid * rinsed with city water before rinsing

The results on the temperature dependence of the silication are shown in FIGS. 5 and 6:
According to FIG. 5, the Si / Al ratio is independent of the rinsing and increases sharply with increasing temperature and with increasing immersion time.

It can be seen from FIG. 6 that the Ca / Al and Na / Al ratios in the case of rinsing with city water are in the same range of about 0.05 ± 0.02, while the rinsing with demineralized water also contains the Na / Al ratio increasing temperature increases, similar to the Si / Al ratio.

The layered sodium silicate on the Al / AlOOH surface largely retains its ion exchange function; the alkaline earth ions replace the Na ions in the silicated Al / AlOOH surface.

• Unter Standardbedingungen für die Silikatisierung der Oberflächen der Schichtträgerplatten wird durch die Erhöhung der Natriumschichtsilikatkonzentration, der Tauchtemperatur auf 80 °C sowie eventueller Verlängerung der Eintauchzeit und Alterung der Al/AlOOH-Trägeroberfläche eine stärkere Silikatbelegung erreicht.
• Das aufgebrachte Natriumschichtsilikat mit einem Si/Al-Verhältnis von 0,4 bis 0,5 und einem Na/Al-Verhältnis von ca. 0,2 erhöht nicht die Alkaliresistenz bei Nachspülung mit VE-Wasser.
• Das Natriumschichtsilikat behält auf der Schichtträgeroberfläche seine Ioneraustausch-Eigenschaften, d.h. es erfolgt ein Austausch der Na- gegen Ca-Ionen, wenn mit Stadtwasser nachgespült wird.
• Durch die Nachspülung mit Stadtwasser, in dem verschiedene Ionen, insbesondere Ca, Mg, vorhanden sind, wird die Alkali- resistenz deutlich erhöht, die Meßwerte liegen oberhalb von 200 s. Dieser Effekt wird verstärkt, wenn das Stadtwasser erhitzt wird, beispielsweise die Tauchtemperatur 60 °C beträgt. Der Wet der Alkaliresistenz liegt dann bei etwa 300 s. Nach Fig. 4 beträgt der Alkaliresistenzwert mehr als 400 s bei 60 °C Tauchbadtemperatur.
     Die Nachspülung mit verschiedenen Salzlösungen in VE-Wasser steigert die Alkaliresistenz nicht wesentlich, nur mit Salzlösungen auf der Basis von beispielsweise NaHCO₃, CaSO₄, MgSO₄ läßt sich die Alkaliresistenz erhöhen.
• Die Nachspülung mit 0,4 %iger NaF-Lösung in VE-Wasser bzw. in Stadtwasser bringt eine sehr hohe Alkaliresistenz. Es wird vermutet, daß das schwer lösliche CaF₂ im Schichtsilikat aufgrund einer vorangegangenen Stadtwasserspülung entsteht, das dann die Alkaliresistenz erheblich steigert.
• Die Vorteile von Natriumschichtsilikat gegenüber anderen Silikaten, wie beispielsweise Na₂SiO₃, liegt in seiner geringeren Alkalität und dem stark reduzierten Oxidangriff, wie anhand von Figur 3 schon beschrieben wurde.
• Die Silikatschicht bleibt auch nach erfolgter Gummierung erhalten. Bei den ESCA-Messungen wird die Gummierung durch das andeutungsweise Vorhandensein von Phosphor nachgewiesen, während das gleichbleibende Si/Al-Verhältnis anzeigt, daß die Gummierung die Silikatisierung nicht beeinträchtigt.

The results of the rinse tests from Table 2 and the illustration in FIGS. 4 to 6 allow the following statements:

• Under standard conditions for the silicatization of the surfaces of the substrate plates, a higher silicate coating is achieved by increasing the sodium layer silicate concentration, the immersion temperature to 80 ° C and possibly extending the immersion time and aging of the Al / AlOOH substrate surface.
• The applied layered sodium silicate with a Si / Al ratio of 0.4 to 0.5 and a Na / Al ratio of approx. 0.2 does not increase the alkali resistance when rinsed with demineralized water.
• The layered sodium silicate retains its ion exchange properties on the surface of the substrate, ie the Na ions are exchanged for Ca ions when rinsed with city water.
• The rinsing with city water, in which various ions, in particular Ca, Mg, are present, significantly increases the alkali resistance; the measured values are above 200 s. This effect is intensified when the city water is heated, for example the diving temperature is 60 ° C. The alkali resistance is then around 300 s. 4, the alkali resistance value is more than 400 s at 60 ° C immersion bath temperature.
  Rinsing with various salt solutions in demineralized water does not significantly increase the alkali resistance; only with salt solutions based on, for example, NaHCO ₃ , CaSO ₄ , MgSO ₄ can the alkali resistance be increased.
• Rinsing with 0.4% NaF solution in demineralized water or in city water results in a very high resistance to alkali. It is believed that the poorly soluble CaF ₂ in Layered silicate arises due to a previous city water rinse, which then increases the resistance to alkali considerably.
• The advantages of layered sodium silicate over other silicates, such as Na ₂ SiO ₃ , lie in its lower alkalinity and the greatly reduced oxide attack, as has already been described with reference to FIG. 3.
• The silicate layer is retained even after gumming. In the ESCA measurements, the gumming is demonstrated by the hint of the presence of phosphorus, while the constant Si / Al ratio indicates that the gumming does not affect the silication.

To investigate the formation of color fog, layered substrates of type P51 in the 32 x 27 cm format, which were coated with sodium silicate and rinsed with city water, were produced as standard and hand-coated with a positive printing plate formulation (P61 solution) and a negative printing plate formulation (N50 solution). For comparison purposes, an untreated P51 substrate, which was also not treated with polyvinylphosphonic acid solution, was coated with the same printing plate formulations and then dried.

After exposure, the positive layer supports P51 were developed for 60 s with an EP26 developer and then consumed. The negative layer supports N50 were treated by hand with 30 ml of DN-5 developer for 60 s without exposure and then brewed.

The essential components of the EP-26 developer are Na silicate, hydroxide, tetraborate, Sr levolinate, polyglycol and water. The DN-5 developer contains benzyl alcohol, mono-, di- and triethanolamine, nitrogen and has a pH of 10.9.

According to visual assessment, the formation of blue haze is more pronounced in the case of the positive layer supports than the formation of green haze in the case of the negative layer supports, the fog formation being the least noticeable on the layer supports in which the silicate coating has been rinsed with city water.

The values for the brightness L and the color shift a / b of the substrates listed in Table 3 below are measured in accordance with DIN standard 6171 (version from January 1979). The values entered in Table 3 are mean values from three measurements. TABLE 3 P51 carrier / aftercare Plate type Development time / developer L a b without LC1 / untreated uncoated - 77.7 -0.26 0.65 "" + (P61) 60s / EP26 74.7 -0.82 -0.10 "" - (N50) 60s / DN-5 74.7 -1.82 0.48 SKS-6 standard / city water careless - 77.0 0.08 0.64 "" + (P61) 60s / EP26 74.1 -0.64 -1.39 "" - (N50) 60s / DN-5 75.7 -0.96 -0.06 SKS-6 standard / demineralized water careless - 77.4 0.04 0.55 "" + (P61) 60s / EP26 71.6 -1.57 -4.3 "" - (N50) 60s / DN-5 73.9 -1.92 -1.62 LC1 = polyvinylphosphonic acid SKS-6 = layered sodium silicate ϑ-Na ₂ Si ₂ O ₅

Claims (13)

1. Process for post-treating material in plate, sheet or strip form based on chemically, mechanically and/or electrochemically roughened and anodically oxidised aluminium or an alloy thereof, the aluminium oxide layers of which are treated with an alkali metal silicate in an aqueous solution, characterised in that

   a) post-treatment proceeds in an aqueous solution of the δ modification of sodium phyllosilicate Na₂Si₂O₅ and

   b) post-rinsing is then performed with water containing alkali metal or alkaline earth metal ions, wherein the alkali metal or alkaline earth metal ions are selected from the group Ca, Mg, Na, K, Sr.
2. Process according to claim 1, characterised in that the SiO₂/Na₂O molar ratio of the crystalline sodium phyllosilicate is in the range from 1.9-3.5 to 1.
3. Process according to claims 1 and 2, characterised in that the solution in post-treatment stage a) contains 0.1 to 10 wt.% of ϑ-Na₂Si₂O₅.
4. Process according to one or more of claims 1 to 3, characterised in that post-treatment stage a) is performed electrochemically and/or by immersion for 10 to 120 seconds and at a temperature of 25°C to 80°C.
5. Process according to claim 1, characterised in that post-treatment stage b) with water containing ions is followed by immersion in a 0.1 to 10 wt.% salt solution.
6. Process according to claim 5, characterised in that electrochemical post-treatment is performed at a current density of 0.1 to 10 A/dm² and/or a voltage of 3 to 100 V.
7. Process according to claim 5, characterised in that the salt solution contains NaF, NaHCO₃, CaSO₄, polyvinylphosphonic acid and MgSO₄ individually or in combination.
8. Process according to claim 7, characterised in that rinsing with the salt solution is preceded by spraying with water containing ions.
9. Support made from material in plate, sheet or strip form based on chemically, mechanically and/or electrochemically roughened and anodically oxidised aluminium or an alloy thereof, the aluminium oxide layer of which is coated with an alkali metal phyllosilicate layer, characterised in that the alkali metal silicate layer consists of pure, crystalline sodium phyllosilicate.
10. Support according to claim 9, characterised in that the sodium phyllosilicate has a lamellar, polymeric structure.
11. Support according to claim 9, characterised in that the sodium silicate has the composition ϑ-Na₂Si₂O₅ and that the SiO₂:Na₂O molar ratio of the crystalline sodium phyllosilicate is in the range from 1.9-3.5 to 1.
12. Support according to claim 11, characterised in that, at the Al/AlOOH surface, the Si/Al ratio is 0.10-0.8 and the Ca/Al ratio is 0.01-0.15.
13. Use of the material post-treated according to one or more of claims 1 to 8 as a support of offset printing plates.

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