US2141813A - Zinc alloy engraving plate - Google Patents

Description

Patented Dec. 27, 1938 UNITED STATES PATENT OFFIQE ZINC ALLOY ENGRAVING PLATE setts No Drawing. Application September 18, 1936, Serial No. 101,530

Claims.

This invention relates to zinc sheets used in the graphic arts industry, such, for example, as rolled zinc plates used for photo-engraving.

'Zinc sheets in various thicknesses are used in 5 the graphic arts either as photo-engraving plates (zinc etchings), or as lithographers sheets. In the first instance the plates must have one surface carefully ground and polished on which the photo-engraver develops the desired image in relief by the well known processes of photography and etching. In the second instance, the sheets must have one surface grained and polished with hard, flint balls or marbles, and fine abrasives to render the surface porous, i. e., receptive to wetting by Water and ink and to the very slight absorption of these materials, since this property is an essential requirement for metal plates used in the lithographic process of printing. In both cases it is necessary to have a rolled zinc sheet or plate with sufficient hardness and toughness to resist wear and deformation. For example, in the case of zinc plates used for photo-engraving, theimage developed in relief may project above the etched surface of the metal from three to ten 5,, thousandths of an inch in half-tone cuts, and up to thirty thousandths of an inch in line cuts, and the small pin point dots in the highlights of a half-tone etching and the fine lines in a line out may be only a few thousandths of an inch in): in width.

Where the zinc etchings are used in newspaper work and similar types of printing, the raised surface of these plates are subjected to great pressure in the course of the stereotype mat molding operation wherein a sheet of specially prepared thick paper board, slightly dampened, is pressed into the surface of the zinc etching by means of a platen type or roller type press, in which pressures as high as 4000 pounds per square inch are sometimes reached. The paper mat after drying is removed from the zinc etching and then serves as a mold into which molten stereotype metal is cast. Since several mats are usually required from each zinc etching, this molding pressure is applied to the etching a number of times and in the case of zinc etchings for syndicated printed matter the number of mats required and the number of times the pressure is applied may run as high as 200 or 300. The zinc sheet therefore must possess sufficient hardness and strength to resist the repeated pressures of the molding operation, without the raised surfaces of the plate being crushed or distorted to any serious extent; otherwise loss of detail will result in the printed image.

Furthermore, the zinc plates are frequently heated to a temperature approximating 600 F. in the course of developing an acid-resisting top with the so-called hot top type of photosensitive enamel, and they must also be heated anywhere from 8 to 16 times to a temperature of approximately 300 F. to set or burn in the dragons blood powder used as an acid resist in the etching process. In the course of these Various heating operations, the zinc plate is softened somewhat, the drop in hardness depending upon the temperature to which the plate is heated and the number of times it is subjected to the heating operation. This softening or annealing of the plate makes it less resistant to crushing under the pressures used in mat molding and less resistant to wear also. For example, an ordinary grade of rolled zinc used for the production of photo-engraving will have an original Rockwell hardness of the order of 65, and a hardness of approximately 4.5 to 50 after being subjected to the various heating operations as described above.

Heretofore, in using the ordinary grade of photo-engraving zinc, photo-engravers have found it difficult, if not practically impossible, to maintain fine lines or dots in the zinc etching when the mats are subjected to the high molding pressures used in the so-called dry mat process, particularly if a number of mats had to be made from a given etching, as in the case of syndicated printed matter. To obviate this difficulty it is the practice either to make a number of zinc etchings of a given image so that a new zinc etching could be substituted for the old ones as they break down in the molding operation, or to resort to the use of the much more expensive engraving plates made of copper, brass, or other alloys, which possess greater resistance to de-v formation under the stresses imposed upon them by the molding operation.

Where printing is done directly from the zinc etchings, it is also necessary that the zinc possess suiiicient hardness and resistance to wear and deformation, so that the etched image does not crush down or wear off under the repeated application of pressure when the surface of the paper is brought in contact with the ink surface of the zinc etching in the action of the printing press, and also to withstand the abrasive or wearing action of the paper as it rubs against the zinc surface in the printing process.

The principal objects of the invention are to overcome the aforementioned difliculties; to provide a zinc base alloy capable of being rolled or otherwise formed into plates or sheets which possess a greater hardness and superior resistance to deformation and wear under the conditions to which they are subjected. in their use in the various branches of the printing industry; and to provide a zinc base alloy which will undergo a loss of hardness, after being subjected to the various heat treatments, which is materially less than that of the zinc plates heretofore used.

Further objects will be apparent from a consideration of the following description which discloses different examples illustrative of the invention.

I have found that a zinc plate or sheet possessing the aforementioned characteristics can be produced by alloying commercial zinc with a small percentage of one or more of the metals of the alkali metal group (sodium, potassium, lithium, etc.) and/or the alkaline earth group (magnesium, calcium, barium, etc.). For example, the zinc base may be alloyed with small percentages of magnesium or lithium to produce a plate or sheet having a greater hardness and superior resistance to deformation and wear than the ordinary zinc', regular commercial grade, photo-engravers plates, and if in addition to the magnesium or lithium small percentages of other alkali metals, such as sodium or potassium, or alkaline earth metals, such as calcium or barium, are incorporated, a further increase in hardness and resistance to deformation and wear is produced.

Although the relative percentages of the different alloying constituents may be varied, I have found that it is highly desirable, if not essential for the production of commercially satisfactory plates, that the relative amounts of certainof the alloying elements be carefully controlled and held below maximum limits, since amounts of the alloying elements in excess of such limits are quite apt to result either in the formation of inclusions which show up on the etched surface of the treated plate, or in the formation of defects which interfere with the etching and burning-in operations.

A satisfactory alloy is produced using a commercial zinc base (containing as impurities approximately 0.2 to 0.4% cadmium, 0.01 to 0.02% iron, and 0.2 to 0.3% or more lead), and alloying the zinc base, with sufficient lithium or magnesium to produce in the finished alloy from 0.002 to less than 0.005% lithium and/or similar amountsof magnesium; or by alloying the zinc base with either lithium or magnesium and sufficient barium or calcium to produce an alloy containing from 0.002 to 0.01% barium or calcium, or with sufficient sodium or potassium to produce an alloy which will contain from 0.002 to 0.01% sodium or potassium; or by alloying the zinc base with lithium or magnesium together with any one or more of the other elements, in amounts within the above specified limits.

In preparing a zinc alloy in accordance with the present invention, any of the usual methods of alloying may be used, it being understood that any suitable apparatus or procedure may be adopted as long as the composition or alloy produced possesses the characteristics herein set forth. In accordance with the preferred procedure, the zinc base is first melted in a crucible or other suitable apparatus, and is maintained at a temperature sufficient above its melting point (approximately 800 to 900 F.) to permit easy incorporation of the alloying ingredients, which may be in the form of a master alloy of predetermined composition, such, for 'example, as a calcium-zinc master alloy, a magnesium-zinc master alloy, etc. As the metals of both the alkali and alkaline earth groups possess a deoxidizing effect on the molten zinc, and as some of the more reactive metals may undergo volatilization, there are apt to be slight losses due to deoxidizing the molten zinc and volatilization, and hence it may be necessary or desirable either to add an excess sufficient to compensate for such losses, or to incorporate other metals of the same groups so as to insure the retention of a sufiicient amount of the alloying elements to effect the desired hardness. Since the percentage of the alloying elements are so low that in many cases they Would be reported by an ordinary analytical chemist as traces, it is necessary, in analyzing such alloys, to determine the alloying constituent by a spectroscop-e or other means capable of determining such small amounts.

The following example is illustrative of a preferred procedure for making a zinc-magnesiumcalcium alloy:

Example 1. Magnesium-caZcz'um-zinc alloy 1000 pounds of zinc, containing not more than approximately 0.60% cadmium, 0.025% iron, and 0.60% lead, but preferably having a composition within the range of cadmium 0.25-0.30%, iron 0.015-0.020%, lead 0.304135%, was first melted in a graphite crucible, and after the metal was entirely molten, the surface of the bath was skimmed to remove any accumulation of dross or oxide. While maintaining the bath at a temperature of between 800 and 900 F., 6 pounds and 1.1 ounces of a calcium zinc master alloy, containing 0.6% of calcium, was then added and throughly incorporated in the molten bath. After adding the calcium alloy, 9 ounces of a magnesium-zinc master alloy, containing 5.25% magnesium, was then added and thoroughly incorporated. A calculated analysis of the alloy showed 0.002 to 0.003% magnesium and 0.004% calcium. Rockwell hardness tests of the alloy showed an average. hardness of 86 before heating and an average hardness of 74 after heating four minutes at 600 F., as compared with an average hardness of 76 before heating and an average hardness of 55 after heating, for a regular commercial grade (soft) photo-engravers plate.

Further examples are as follows:

Example. 2. M agneszum-sodium-zmc alloy One thousand pounds of commercial zinc of the same composition as set forth in Example 1 was alloyed with 9 ounces of a magnesiurmzinc master alloy containing 5.25% magnesium and 2 pounds 8 ounces of a sodium-zinc master alloy containing 2.0% sodium. A calculated analysis of the resulting alloy gave a magnesium content of 0.003% in gnesium and 0.005% sodium. Rockwell hardness tests showed an average hardness of 86.5 before heating and an average hardness of '74 after heating.

Example 3. Magnesium-sodium-einc alloy Example 4. Magnesium-barium-zinc alloy One thousand pounds of commercial zinc of the same composition as set forth in Example 1 was alloyed with 9 ounces of a magnesium-zinc master alloy containing 5.25% magnesium and 5 pounds 9 ounces of a barium-zinc master alloy containing 0.9% barium. A calculated analysis of the resulting alloy showed a magnesium content of 0.003% and a barium content of 0.005%. Rockwell hardness tests showed an average hardness of 86 before heating and 73.5 after heating.

Example 5. M agnesium-barium-zinc alloy One thousand pounds of commercial zinc of the same composition as set forth in Example 1 was alloyed with 9 ounces of a magnesium-zinc master alloy containing 5.25% magnesium and 11 pounds 2 ounces of a barium-zinc master alloy containing 0.9% barium. A calculated analysis of the resulting alloy showed a magnesium content of 0.003% and a barium content of 0.01%. Rockwell hardness tests showed an average hardness of 85.5 before heating and 76 after heating.

Ermmple 6. M agnesium-barium-sodium-zinc alloy One thousand pounds of commercial zinc of the same composition as set forth in Example 1 was alloyed with 9 ounces of a magnesium-zinc master alloy containing 5.25% magnesium, 11 pounds 2 ounces of a barium-zinc master alloy containing 0.09% barium, and 5- pounds of a sodium-zinc master alloy containing 2.0% sodium. Analysis of the resulting alloy showed a magnesium content of 0.003%, a barium content of 0.01 and a sodium content of 0.01%. Rockwell hardness tests showed an average hardness of 86.5 before heating and 73.5 after heating.

Numerous other experiments have been conducted with zinc base alloys containing varying percentages of sodium, calcium and barium in amounts within the ranges above specified, and the resulting alloys showed a hardness before and after heating considerably greater than that of the regular commercial grade (soft) photo-engravers plate.

Alloys made in accordance with the present invention may be rolled or otherwise formed into sheets or plates for both photo-engraving and lithographic reproductions, and the sheets may be grained to produce a surface which can be easily wet with water and ink and which will retain a thin film of these materials, as required in lithographic printing processes. Although the graining operation produces a toothed surface in which the difference in elevation between the highest and lower points amounts to only four to five ten-thousandths of an inch, the fine tooth or grain is retained substantially intact during the entire run of the plate, due to the increased hardness and greater resistance to deformation and wear inherent to an alloy made in accordance with the present invention.

While I have described different desirable embodiments of the invention, it is to be understood that this disclosure is for the purpose of illustration, and that various changes and modifications of proportions, etc., may be made without departing from the spirit and scope of'the invention as set forth in the appended claims.

I claim:

1. A zinc base alloy having a high hardness and superior resistance to deformation and wear, said alloy containing 0.002 to 0.03% of a metal selected from a group consisting of magnesium and lithium, and 0.002 to 0.01% of a metal selected from a group consisting of sodium, calcium and barium, the remainder, except for minor impurities, being zinc.

2. A zinc base alloy having a high hardness and superior resistance to deformation and wear, said alloy containing 0.002 to 0.03% magnesium, and 0.002 to 0.01% of a metal selected from a group consisting of sodium, calcium and barium, the remainder, except for minor impurities, being zinc.

3. A zinc base alloy having a high hardness and superior resistance to deformation and wear, said alloy containing 0.002 to 0.03% of a metal selected from a group consisting of magnesium and lithium, and 0.002 to 0.01% of a binary alloy of metals selected from a group consisting of sodium, calcium and barium, the remainder, except for minor impurities, being zinc.

4. A zinc base alloy having a high hardness and superior resistance to deformation and wear, said alloy containing 0.002 to 0.03% magnesium,

and 0.002 to 0.01% of sodium, the remainder, .1

except for minor impurities, being zinc.

5. A zinc base alloy having a high hardness and superior resistance to deformation and wear, said alloy containing 0.002 to 0.03% magnesium, 0.002 to 0.01% sodium, and 0.002 to 0.01% barium, the remainder, except for minor impurities, being zinc.

WILLIAM H. FINKELDEY.