EP0098776B1 - Steel lithographic printing plate having multiple chromium layers - Google Patents

Abstract

1. Offset plates based on steel and having an aquaphilic layer of chromium comprising : - in contact with the steel, a protecting layer (A) of shiny chromium of thickness less than 0.4 mu m ; - above said protecting layer, a layer (B) of chromium with dull finish surface ; said plates being characterized in that said layer (B) is selected from : a) the layers of chromium comprising at least 400 micro-fissures per centimeter (known as micro-fissured layers) or comprising at least 40 cracks per centimeter (known as microcracked layers) ; b) the chromium layers obtained by successively depositing more than two layers of chromium, each of said layers having a thickness less than 0.5 mu m. c) or a superposition of layers a) and b) ; layer (B) having a thickness more than 1 mu m.

Description

The present invention relates to offset plates based on steel (or black iron) and with multiple layers of chromium.

Offset plates having a steel (or black iron) support, an aquaphile (and encrophobic) layer of chromium and an ink-absorbing printing layer of photosensitive material have already been described and marketed. For such plates, the aquaphile chromium layer must have very specific properties, in particular given that the surface of said layer must allow the attachment of the photosensitive material.

• - il est possible de limiter l'épaisseur des couches de chrome (couches aquaphiles, encrophobes et permettant l'accrochage) à condition que de telles couches soient déposées sur des couches métalliques dures et aquaphiles; on peut ainsi réaliser des plaques dans lesquelles la couche superficielle de chrome a une épaisseur inférieure à 1 micron et de préférence inférieure à 0,5 micron;
  • la couche superficielle de chrome peut se composer d'une couche de protection de chrome brilliant d'une épaisseur inférieure à 0,4 um et, au dessus de ladite couche de protection, d'une couche de chrome à surface mate;
• - il est possible d'utiliser des couches à base de chrome (donc dures et aquaphiles) pour la protection de la surface des supports en acier ou en fer noir; dans la recherche de la protection de ladite surface à l'aide de couches industrielles minces, on a décrit une couche de protection constituée de chrome-oxyde de chrome.

For many years, this chromium layer has been played the only role of aquaphile layer allowing the attachment of the photosensitive material. We therefore had to use an intermediate metal which protects the surface of the support (steel or black iron) against rust. This protective metal layer consisted of a generally encrophilic soft metal such as copper or tin or even nickel; the consequence of the presence considered to be necessary of this protective metallic layer in a covering encrophilic metal was the systematic use of thick chromium layers (from 1 to 3 microns for example) whose surface was made matt (to allow the attachment) by known techniques. In European patent No. 0 022 033, new offset plates have been proposed which have this same general structure by implementing two new ideas which can be expressed as follows:

• - It is possible to limit the thickness of the chromium layers (aquaphile, encrophobic layers and allowing attachment) provided that such layers are deposited on hard metallic and aquaphile layers; it is thus possible to produce plates in which the surface layer of chromium has a thickness of less than 1 micron and preferably less than 0.5 micron;
  • the surface layer of chromium may consist of a protective layer of shiny chrome with a thickness of less than 0.4 μm and, above said protective layer, of a layer of chromium with a mat surface;
• - it is possible to use chromium-based layers (therefore hard and aquaphiles) for the protection of the surface of steel or black iron supports; in the search for the protection of said surface using thin industrial layers, a protective layer has been described consisting of chromium-chromium oxide.

In both cases, the printer part was supplied by an ink-sensitive photosensitive resin (or a photopolymer).

If the offset plates obtained by implementing these two ideas having remarkable technical properties, it appeared that, for certain applications in particular, it could be advantageous to reinforce on the one hand the protection of the surface of the support and on the other hand the mechanical resistance (for example to abrasion) of the chromium layer, the surface of which is aquaphile, encrophobic and allows it to be attached.

• - comme couche de protection une couche de chrome brillant de faible épaisseur inférieure à 0,4 µm
• - comme couche aquaphile une couche de chrome d'épaisseur supérieure à 1 micron, de préférence d'épaisseur comprise entre 1 et 2 microns, à condition que cette couche de chrome soit
  • ou bien une couche de chrome microfissuré ou microcraqué
  • ou bien une couche de chrome obtenue par le dépôt successif de plus de deux couches de chrome présentant chacune une épaisseur inférieure à 0,5 micron,
  • ou bien une superposition de ces deux couches.

It has been found, and this is the object of the present invention, that offset plates with steel or black iron support and having improved properties could be produced using:

• - as a protective layer, a shiny chrome layer with a thickness of less than 0.4 µm
• - as an aquaphile layer a chromium layer with a thickness greater than 1 micron, preferably with a thickness of between 1 and 2 microns, provided that this chromium layer is
  • or a layer of microcracked or microcracked chromium
  • or a chromium layer obtained by the successive deposition of more than two chromium layers each having a thickness of less than 0.5 micron,
  • or a superposition of these two layers.

• - au contact de l'acier, une couche (A) de protection de chrome brillant d'épaisseur inférieure à 0,4 µm;
• - au dessus de ladite couche de protection, une couche (B) de chrome à surface mate; caractérisées en ce que ladite couche (B) est choisie parmi
  • a) les couches de chrome comportant au moins 400 microfissures au centimètre (dites microfissu- rées) ou comportant au moins 40 craquelures au centimètre (dites microcraquées);
  • b) les couches de chrome obtenues par le dépôt successif de plus de deux couches de chrome d'épaisseur inférieure à 0,5 pm chacune;
  • c) ou une superposition des couches a) et b), le couche (B) ayant une épaisseur supérieure à 1 um.

The present invention therefore relates to off-set plates based on steel and with an aquaphile layer of chromium, comprising

• - in contact with steel, a protective layer (A) of bright chrome with a thickness of less than 0.4 µm;
• - Above said protective layer, a layer (B) of chrome with a mat surface; characterized in that said layer (B) is chosen from
  • a) the chromium layers comprising at least 400 microcracks per centimeter (called microcracks) or comprising at least 40 cracks per centimeter (called microcracks);
  • b) the chromium layers obtained by the successive deposition of more than two chromium layers of thickness less than 0.5 μm each;
  • c) or a superposition of layers a) and b), the layer (B) having a thickness greater than 1 μm.

The protective layer is a thin layer of shiny chrome. Such layers are perfectly known and are used for the decoration and for the protection against corrosion of metallic surfaces susceptible to rusting in applications of the light fixture type, chromed chairs, etc. The known and described techniques for the production of such layers are obviously usable in the present invention; these techniques imply in particular that the industrial conditions for producing such layers are such that the layers adhere perfectly to the support and cover it as much as possible. In particular, electroplating with the use of baths working at relatively high temperatures (at least about 40 ° C.) and if possible with a highly conductive catalyst (addition of active fluorine) such as SiF _{s will be used} .

• ou bien d'utiliser une couche de chrome microfissuré ou microcraqué faite en une ou plusieurs fois
• ou bien d'utiliser une couche de chrome formée de couches élémentaires minces.

On this protective layer whose thickness will be less than 9.4 micron and preferably less than 0.2 micron, a layer will be deposited chrome aquaphile with a thickness greater than 1 micron. In order for such a chromium layer to have the desirable properties (both with regard to the properties of the surface of this layer, properties which have been described above, and with regard to the mechanical properties of the layer, in particular for avoid, during handling and bending of the plate, the formation of cracks or breaks) it has been found to be suitable:

• or use a layer of micro-cracked or micro-cracked chromium made in one or more stages
• or else to use a chromium layer formed of thin elementary layers.

A layer of chromium having a minimum of 400 microcracks per centimeter is called a layer of "microcracked chromium" and a layer of "microcracked chromium" a layer of chromium having at least 40 cracks per centimeter.

The definition and production of a chromium layer of this type are described in French patent 2,152,627 and 2,142,014.

According to the present invention, it has therefore been found that microcracked or microcracked chromium could be used as an aquaphile layer of offset plates, taking into account on the one hand its texture and on the other hand its surface properties since said surface can be rendered "mat" and sufficiently hang the photosensitive layers. The second technique for producing thick chromium surface layers consists in producing said layers by superimposing thin elementary layers of chromium. By thin elementary layer is meant a layer of chromium with a thickness of less than about 0.5 microns. This deposition of several successive elementary layers can be carried out in a chrome bath seal (by cutting the current several times) or in several successive baths; of course at least the last layer of chromium will be produced under known conditions leading to the production of a mat appearance layer allowing the adhesion of the photosensitive layers. When the technique of depositing several successive layers of chromium is thus used, it has been found that, in order to improve the protection of the underlying layers of steel via against corrosion, it was desirable to ensure that the first of said layers is made of shiny chrome and the other layers are all made so as to have a matt appearance.

• - dépôt sur la surface d'un flash de chrome brillant
• - dépôt sur la surface d'un inhibiteur de corrosion.

This chromium surface layer having a matt appearance is very important in the context of this invention; however, it has been found that the surface properties of this layer can be further improved by using at least one of the following two methods:

• - deposit on the surface of a bright chrome flash
• - deposit on the surface of a corrosion inhibitor.

The term "flash" deposition means the deposition of a very thin layer, generally less than 0.2 microns and preferably less than 0.1 microns. Here we call bright chrome a chrome which, if deposited directly on the smooth surface of steel, would have a shiny or semi-shiny appearance (that is to say which has the crystalline structure of a chromium brilliant). It is however eridly that the flash thus deposited will not profoundly modify the matt appearance of the chrome surface but this flash will have the function of at least partially closing the cracks or holes which appear on the surface of the matt chrome.

Corrosion inhibitors (steel and black iron) are known. The inhibitors used in the context of the present invention are preferably products of the anionic type.

Throughout the present application, the term "chromium" is understood to cover not only the chromium itself but also the chromium-based alloys which are harder than chromium (especially the Cr-Mo alloys) and which have the same aquaphile and encrophobic properties. In the context of the potential use of chromium alloys it has been found that it is sometimes desirable to use chromium alloys with a metal whose potential is strongly negative such as manganese for example. This lowers the negative potential of chromium by thereby modifying some of its properties advantageously. It is desirable that the metal alloyed with chromium is more electronegative than steel or iron.

The following nonlimiting examples illustrate the invention.

Example 1 A) Creation of the first protective layer (thin shiny chrome)

Portection (recto verso) of three steel supports was carried out (USINOR steel plate 0.3 mm thick) according to conventional electrolytic techniques.

After degreasing, rinsing, pickling and rinsing the steel plate, the electrolytic deposits of chromium were carried out according to one of the following methods:

1. plate A

The plate is immersed in a bath containing 250 g / I of Cr ₂ 0 ₃ and 2.5 g / I of S0 ₄ H ₂ ; the bath temperature is 45 ° C and the density of 30 A / dm ^2. The chromium layer has a thickness of 0.11 micron.

2.plate B

The plate is immersed in a bath giving rise to a deposit of microcracked chromium (bath sold under the reference 2300-WALBERG), the bath being at a temperature of 55 ° C. and using a current density of 30 A / dm ² . The chromium layer has a thickness of 0.39 microns.

3.plate C

The plate is immersed in a bath containing Cr ₂ 0 ₃ 247 g / I, S0 ₄ H ₂ 1; 1 g / l, SiF ₆ 2, 1 g / I (a bath of this type is described in US Patent 3,498 892); the temperature is 65 ° C, the current density used is 60 Aldm ^2. The chromium layer has a 0.11 micron thickener.

The deposit is shiny and very "covering", that is to say that it penetrates well into all the support pores.

B) Realization of the surface layer by microcracked chromium.

Plate B is used, which is again treated by an identical bath (2300 Walberg), but a temperature of 38 ° C. and a current density of 35 A / dm ^{2 are used} .

This produces a new layer (1, 1 micron) of microcracked chromium having a matt appearance and a surface that grips the photosensitive printing layers well; the micro-porosity of the deposit further improving the adhesion of the printing layer.

We could make the same layer of chromium micro-cracked with a mat appearance using plates A or C.

Example 2 Realization of a chromium layer by depositing thin elementary layers.

One of the plates A or C of Example 1 is used as starting material.

• -soit dans un bain à 35°C et à densité de courant de 45 A/dm²
• -soit dans un bain à 30°C et à densité de courant de 30 A/dm².

Using an electroplating bath identical to that used to obtain the plate A of Example 1, the deposition of three successive layers of chromium with a thickness of 0.4 micron each is carried out.

• - either in a bath at 35 ° C and a current density of 45 A / dm ²
• -or in a bath at 30 ° C and a current density of 30 A / dm ² .

In both cases, a plate is obtained which comprises, above the surface of the steel, four layers of chromium, the first of thickness 0.11 microns and the other three of thickness 0.4 microns each.

Example 3

The plates A and C of Example 1 are used. These three plates are deposited on three plates of chromium with a mat appearance and a thickness of 0.40 micron each, carrying out electrolysis at 35 A / dm ² and at 30 °. vs.

Then, on one of the two plates, a new layer of chromium is deposited under the same conditions as those used when the first layer of bright chromium was deposited. The plate having received this surface layer of "shiny chrome" (thickness 0.09 micron retains a matt appearance but has been shown to be particularly resistant to corrosion.

Example 4

A type B plate is used (cf. example 1) covered with two layers of matt chrome.

This plate is immersed for 20 seconds in a bath at 70 ° C. containing 19 g of monosodium phosphate and 19 g of sodium dichromate.

The plate was covered with a very slight deposit of these salts.

It has been shown that the plates according to the invention could, without deformation, undergo baking (10 minutes at 220 ° C. for example) intended to harden the exposed parts of the photosensitive surface layer deposited on the surface of the chromium.

Example 5

The technique described is used for the preparation of plate A, but by adding 50 g / l of manganese oxide to the bath.

Example 6

As starting material, a steel coil called T _FS (tin free steel), not oiled, 0.25 mm thick, 0.15 micron roughness, 22% elongation, 34 kg strength, quality calmed down, as produced for example by the SOLLAC Company. The thickness of the chromium is of the order of 0.005 microns.

This coil is degreased anodically at 40 ° C, 15 A / dm2 for 5 seconds, in a bath containing 40 g / I of sodium hydroxide. After rinsing and chromic immersion (temperature 20 ° C, duration 2.5 seconds) in a bath containing 50 g / I of chromium oxide, chromium plating is carried out in a so-called rapid chromium plating bath (containing fluorine) at 45 ° C and 52 A / dm2. This chrome plating is carried out by successive dipping of the coil in the bath (in fact, the coil takes place passing around cylinders located alternately in and out of the bath). Thus, the deposit is interrupted 5 times. Each interruption is approximately 2 to 3 seconds.

A deposit of chromium with a total thickness of approximately 1.2 microns is thus obtained.

Example 7

Example 6 was repeated, but treating the steel coil with cathodic degreasing instead of anodic degreasing. The degreasing bath contains soda, carbonate and phosphate; the temperature is 68 ° C, the intensity of 15 A / dm2 and the duration of 5 H. The coil thus degreased is treated as in Example 6.

The coils obtained in Examples 6 and 7 were cut into plates; each plate coated with an ink-absorbing photosensitive layer, then baked. The plates obtained were found to be excellent for printing.

It is possible to obtain results substantially equivalent to those obtained in Examples 6 and 7, by operating as in said examples, but by limiting the deposit of chromium to a total thickness of 0.5 to 0.6 microns.

Claims (5)

1. Offset plates based on steel and having an aquaphilic layer of chromium comprising:

-in contact with the steel, a protecting layer (A) of shiny chromium of thickness less than 0.4 um;

-above said protecting layer, a layer (B) of chromium with dull finish surface; said plates being characterized in that said layer (B) is selected from:

a) the layers of chromium comprising at least 400 mirco-fissures per centimeter (known as micro-fissured layers) or comprising at least 40 cracks per centimeter (known as microcracked layers);

b) the chromium layers obtained by sucessively depositing more than two layers of chromium, each of said layers having a thickness less than 0.5 um.

c) or a superposition of layers a) and b); layer (B) having a thickness more than 1 µm.

2. Plates according to claim 1, characterized in that said dull finish surface of the chromium layer or layers is coated with a layer of shiny chromium of thickness less than 0.2 pm.

3. Plates according to claim 1, characterized in that the dull finish surface is obtained by depositing a plurality of chromium layers each one of which is obtained by depositing a dull finish chromium.

4. Plates according to one of claims 1 to 3, characterized in that they have further received, on the dull finish chromium surface, a corrosion inhibiting agent.