FR2480677A1 - Offset plate supports made from black iron - has satin finish and coated with rust preventative before use - Google Patents

Abstract

The offset plate supports are made from black iron and have a thickness of less than 0.3 mm. The surface of the plates supports are polished to a satin finish and are protected against rusting by any appropriate method before use. The rust preventative is removed prior to fitting of the support plates. The surface roughness is controlled to between 0.45 to 0.55 microns and the plate may be degreased before the application of an appropriate coating.

Description

New black iron offset plate supports.

 The present invention relates to new offset plate supports these supports being of black iron.

 The offset plates consist of a support, a hydrophilic surface and an encrophilic surface. The surface of the support can constitute - after possible modifications - said hydrophilic surface.

 As an offset plate support, up to now, either aluminum plates, steel plates or stainless steel plates or brass plates have been used. Each of these materials has, in its offset application, technical and economic advantages and disadvantages.

However, the offset plate supports must have very specific properties and in particular a constant thickness, a surface free from defects and perfect flatness.

 The present invention relates to a new support for offset plates having, compared to known supports, advantageous characteristics, characterized in that this support consists of black iron.

 According to EURONORM, black iron means a t81e made of mild steel with a low carbon content and having undergone no tinning (we would call it tinplate), oiling or other treatment. This black iron is recommended as a support for the manufacture of metal packaging such as canned boots for example.

 However, the untreated black iron supports cannot be used in the raw state because this material rusts extremely quickly even when an attempt is made to protect it by depositing, on its surface, oil films.

 Consequently, various treatments of the surfaces of the black iron plates have been described and used in order to protect said plates against rust. These treatments include tinning and chrome plating. Black iron plates, the surface of which has been suitably protected from rust, in particular by tinning or chromium plating, will therefore be used as starting material for carrying out the present invention.

 Various techniques of tinning or chromium plating are known; these techniques are either of the conventional type in which the protection of the surface of the support is carried out by the offset of a relatively thick layer (0.38 to 25 microns for example) of the protective metal (tin for example) or of the modern type in which protection of the support surface is achieved using the properties of thin layers of chromium oxide optionally combined with at least one layer of tin-tin, tin or chromium. These modern protection techniques are for example described in French patents 1,575,515, 77/25,340, 77/25,886, 78/09,425, 74/19,235 and 78/25,140; in the present invention, preferably the black iron plates, the surface of which has been protected according to modern techniques.

 One of the considerable advantages of black iron plates is that it is possible to industrially manufacture plates which can be used for offset (that is to say having the properties mentioned above) even with very small thicknesses. It is known that the current technique practically does not allow the preparation of steel plates with a thickness of less than about 0.3 mm; indeed for lower thicknesses, the flatness and / or the state of the surface of the plates prove to be insufficient, in general for their use in offset. Now, we know today the industrial techniques allowing the preparation of black iron plates with a thickness less than 0 × 3 mm, for example plates with a thickness of 0, 15 or 0.2 mm; it has been found that such thin plates are particularly advantageous for the implementation of the invention.

It is also known that certain properties of industrial black iron plates depend on the surface condition of these plates; in fact, the industrial conditions for manufacturing the plates sometimes imply obtaining plates having particular surface properties.

 I1 was found that the black iron plates according to the invention could advantageously have satin surfaces because such plates also have particular advantages with regard to their flatness and the absence of surface defects.

 By satin surfaces is meant surfaces having "roughness" of less than 2.5 microns, preferably between 0.3 and 1.6 microns and more precisely between 0.4 and 0.7 microns.

From the plates of black iron whose surfaces have been protected by tinning or chromium plating techniques, offset plates can be produced according to two methods, one consisting in first removing the protective coating so as to obtain the black iron plate with a bare and clean surface which will be immediately coated with the necessary metal layer (s), the other consisting, when possible, in degreasing the plate to reveal a metallic surface (metal and all oxide ) directly usable either as an aquaphile surface or as a surface capable of receiving an aquaphile metallic deposit.

The following nonlimiting examples illustrate the invention.

Example 1.

 We use a "SOLCHROME" plate made in France by the company SOLLAC - finished reference r4eulé. This plate is made of black iron (thickness 25/100) cold rolled and having a roughness between 0.45 and 0.5su; it is coated with 3 13 / cm2 2 of chromium oxide and Q, 3 to 4 Zglcm of chromium and is supplied under oil.

 This plate is degreased and a photosensitive commercial printer layer is deposited there on a spinning wheel (thickness of the layer approximately 1.8 microns).

 After drying at 450C for 3 minutes and then at 850C for 5 minutes, the plate is exposed with a positive film.

 We develop, rinse and eraser.

The plate is then baked for 3 minutes at 2300 C.

 The plaque thus produced easily allowed the printing of more than 500 proofs.

Example 2.

 We use a plate '1SOLCHR0ME'1 made in France by the company SOLIAC - reference gloss finish - that is to say having a roughness between 0.20 and 0.30 micron.

 This plate is immersed for a few seconds in an anodic chromium plating bath containing caustic soda.

 The plate emerging from this bath is apparently freed from the chromium oxide and chromium with which it had been covered and the surface of the black iron appears bare, perfectly clean.

 After rinsing, a thickness of 4 microns of copper (alkaline bath) is placed on the surface of this plate, followed by a thickness of 1.9 microns of chromium (the surface of which has been made matt by the known process of cutting the current by deposit course).

A polymetallic offset plate with black iron support is thus obtained.

Example 3.

We start from the same plate as that described in Example 1 and after degreasing, rinsing, a layer of 1.9 micron of chromium is deposited on its surface, the surface of which appears "mat".

 The plate obtained can be used after deposition, on the chromium layer, of a suitable layer of photosensitive material.

Example 4.

Take a plate covered with an iron-tin and chromium oxide layer (iron-tin with a thickness equal to or less than 0.12 micron) and treat the plate as in Examples 1, 2 and 3.

Claims (5)

1. Offset plate supports characterized in that said supports are black iron plates. 2. Supports according to claim 1, characterized in that said supports have a thickness of less than 0.3 mm. 3. Supports according to one of claims 1 and 2, characterized in that said supports have a satin surface. 4. Method for producing offset plates with a support according to one of claims 1 to 3, characterized in that a starting material is used a black iron support protected from rust by an appropriate surface treatment. 5. Method according to claim 4, characterized in that the protected support used as starting material is, in a first operation, stripped of its protective layer,