US2214950A - Planographic printing plate - Google Patents

Description

Patented Sept. 11, 1940 PLANOGRAPHIO PRINTING PLATE Clues Barge Aller, Copenhagen, Denmark No Drawing. Application June 8, 1937, Serial No.

147,140. In Germany July 10, 1936 4 Gaims.

The invention relates to a planographic printing plate, more particularly a printing plate for offset printing, and a method of producing such a printing plate.

Planographic printing plates are produced, generally, by etching a stone plate or a zinc or aluminium plate. Printing by means of these plates is based in principle on the different cam pability of the etched and the non-etched areas ink in a moist condition.

Various drawbacks are connected to the employment of these printing plates, and this applies particularly to the plates made from aluminium or zinc, although the same are the only kinds of printing plates that can be employed for many kinds of printing work.

By way of example of these drawbacks it may be mentioned that the said printing plates are not so hard and so resistant against wear as it is desirable particularly for the purpose of producing greater issues.

Besides, the surface of the said plates must be provided with a grain previous to transferring the picture to the plate and etching the same, which limits naturally the fineness of the details in picture which can be transferred thereto, and in particular the fineness of the points of an autotype to be printed therewith.

Again, if it is desired to discontinue printing, even for a short period, the said plates must be coated with 8 11 arabic or some other protecting agent in order to prevent the chemical or physical differences between the ink-receiv- 35 ing and ink-refusing areas of the picture being destroyed by the oxidising influence of the atmospheric air.

Another planographic printing process has been proposed in which a thin coating of 40 chromium or some other metal that is not attacked by mercury is applied. to an under-layer consisting of copper or some other metal capable of being attacked by mercury. After having transferred the picture to the surface of the plate and covered the areas of chromium, which shall be retained, by enamel the plate is etched until the chromium layer has been removed from the areas not covered by the enamel and recesses have been formed in the copper. The recesses 50 are then filled by silver or gold amalgam. When printing with the finished plate from which the enamel has been removed a particular ink containing mercury is used which ink is refused by the amalgamated areas and received by the chromium areas. This printing method, howrespectively of retaining or receiving printer's ever, is expensive in use by reason of the precious metals employed and it' is detrimental to the health of the persons employed in carrying it out.

According to the present invention the abovenamed drawbacks of known methods are avoided by employing a printing plate in the manner known from printing with stone, aluminium and zinc, the water-retaining areas refusing the printer's ink in moist condition consisting of stainless steel, chromium, chromium alloys, metals related to chromium and possessing the same capability of refusing ink in moist condition' or alloyed steels containing such metals and having the said property.

The present invention comprises also the printing method in which a printing plate, the ink-refusingareas consist of stainless steel, chromium etc. is used, and in which the plate is moistened during the printing process, and printing is carried out in the same manner as printing by stone plates or aluminium or zinc plates.

The ink-receiving areas of the printing plate consist of metal capable of refusing water and retaining ink, when the printing method is carried out in the manner known from the stone printing method or from aluminotype or zincotype. Such metals are well known to printers. By way of examples of such metals may be mentioned copper, nickel and the like.

Preferably the ink-receiving areas consist of areas of the metals in question applied in a very thin layer to a supporting surface consisting of the ink-refusing material. The areas of ink-receiving material are preferably formedby the areas remaining on the support, when a thin coating of the ink-retaining metal on the same is locally etched through, so as to reveal the underlying surface of the supporting inkrefusing material.

The employment of the printing plate of the preferred form above described is advantageous on several points. Thus the surface of the stainless steel or chromium forms a firm and hard support of the printing points, which causes the plate to be very durable. By employing for the ink-receiving material a metal having wear-resisting properties the durability of the printing plate may be further improved. Moreover, printing with the new printing plate may be discontinued without necessity for coating the picture, the ink-refusing areas of the plate remaining unaltered, even if they are exposed to atmospheric air for ever so long, and, as it is Q well known, it is not dimcult choosing an inkreceiving material that is not altered in an undesirable way by exposure to air. After employment for printing purposes the plate of material having ink-refusing properties is made in condition for re-use simply by removing the ink-receiving metal by etching. The ink-refusing supporting surface may be brightly polished which permits the points, lines and areas of the picture to be as sharply limited as desired. The ink-refusing supporting surface is resistant against scratching during preparation of it and during erecting in the printing machine. Further the stainless steel or similar material possesses the greatest possible strength in the shape of plates, cylinders or the like.

In an embodiment of the invention the printmg plate consists of a plate of stainless steel or chromium which plate is plain or cylindrical or has the shape of a sector of a cylinder or any other shape suitable for graphical purposes. The plate is thick and self-supporting or thin like sheet metal in which case it is arranged during employment on a suitable support. Alternately the plate does not consist of stainless'steel or chromium but of a supporting plate or cylinder sector to which a thin plating of chromium or similar metal having the capability of refusing ink when used in a moist state is applied. The supporting plate or cylinder in this case may consist'of common steel. On the surface of the plate of stainless steel or chromium a thin layer of copper or another ink-receiving metal is applied in the localities corresponding the points or lines or areas of the picture. This layer is preferably applied galvanically. In order to secure proper adhering of the copper to the chromium-containing support the copper is applied galvanically by means of a bath the pH of which is at a very low value for instance 1.5 to 2.5 or still lower. In order to obtain still better adhering nickel is applied to the chromium-containing support in place of copper, the pH of the bath being at the low value mentioned above. Nickel is capable of receiving ink when moist but the capability of copper for this purpose is still better. Accordingly it is preferred to apply a layer of copper on the surface of the layer of nickel, the latter being in this case extremely thin.

In order to make the areas of copper, nickel or nickel and copper cover the localities of the supporting surface of thestainless steel or chromium corresponding the printing area of the picture and no other localities the surface of the plate is preferably completely covered by a thin layer of the said metal ormetals after which this layer is locally etched away at the. localities where the printing plate shall yield no print so that the stainless steel or chromium is exposed at these localities.

.In place of metals, other known ink-receiving thin layers of material may be used for forming the printing picture. When a metal is-used the same need not be applied galvanically but it may also be applied byspraying, cathode atomizing or by chemical precipitation.

I claim:

1. A planographic printing plate comprising areas of a metal capable of receiving printers ink and areas of an ungrained metal capable of refusing ink, said areas consisting of different metals, the ink refusing areas consisting of a substance selected from the group consisting of stainless steel, chromium, and chromium alloys.

2. A planographic printing plate, the surface of which comprises areas of chromium in an ungrained state and areas of an ink receptive metal selected from the group consisting of copper and nickel.

3. A planographic printing plate, the surface of which comprises areas of water receptive steel not sensitive to fatty drawings or transfer impressions in an ungrained state and areas .of an ink receptivemetal selected from the group consisting of copper and nickel.

4. A planographic printing plate comprising an unbroken layer of stainless steel not sensitive to fatty drawings or transfer impressions having an ungrained surface, parts of which are covered by areas of copper.

cmai'ts some ALLER.