US2290719A - Typographical plate - Google Patents

Description

Patented July 21, 1942 TYPOGRAPHICAL PLATE Jeptha H. Todd, City, M0.

N Drawing.

Application June 5, 1941,

Serial No. 396,777

3 Claims.

This invention relates to improvements in typographical or printing plates and refers more particularly to. printing plates produced from an improved plastic composition which has satisfactory structural strength, a proper aiilnity for ink, and which will withstand heat necessary to transfer typographical forms, cuts and halftones from matrices and will accept and reproduce exceedingly fine detail.

Heretofore, attempts have been made to produce printing plates of plastic material.- As early as 1892, the use of vulcanized clay, shellac and wood pulp was suggested by Steele in Patent No.- 486,572. In 1901, stereotypes of Celluloid were produced according to the invention of the Danish patentee, Madsen, as described in Patent No. 672,534. Novotny, in 1921, advocated the use of Bakelite, in Patent No. 1,377,516. Reinforced acetyl cellulose was recommended by Richter in 1 according to Patent No. 1,794,322. A cellulosic plastic, combined with a metal compound such a lead carbonate and iron oxide was described by Boutwell in Patent No. 2,219,587, issued in 1940. I

All of these attempted improvements, in so far as the printing industry is concerned, were of doubtful success. For one reason or another, the typographical forms or plates did not meet the requirements of' the printer. Hardness and structural strength, with a certain amount of flexibility, are necessary, as well as the ability of the composition to receive and reproduce the fine details of half-tone plates and stereotypes. The affinity of the composition for ink has been another difilculty that was not overcome in some instances.

The process of thepresent invention comprises a series of steps in the production of a printing plate, that has been found to meet the requirements of the trade. The steps of the process willfrom which the plastic printing plate is made is by use of a powerful rolling machine constructed on a heavy base with two parallel rollers 30 inches in length and 12 inches in diameter,

rolling in opposite directions which causes a One roller is heated to 200 F.

and the other is cooled with circulating water. A mixture of 2 pounds 5 ounces shellac, 1 pound 14 ounces wool flock, 12 pounds basic lead sulphate and a small quantityofblack dye'to add color is mixed thoroughly and run between the rollers. The moisture in the shellac and high pressure forces the powder into the shellac and the mixture becomes moist and kneads itself in the revolving machine. After being thoroughly mixed, it is removed from the. hot roller in the form of a slab about inch in thickness, 26

inches wide and 36 inches long. When removed,

it is placed on a flat surface and within a few minute is in a hardened plastic state. It is from this material that the plastic printing plate is made.

In order to make a negative plastic printing plate, it is necessary to mould this by using a positive matrix. This matrix is made from the a piece is cut to the size of the piece to be reproduced. It is placed on a steam-heated table of 200 F. and allowed to soften. It is then placed over the indented matrix and together the matrix and plastic plate are placed in a hydraulic press and the press is closed under pressure of from 25 to tons, depending upon the size of the plate being reproduced. When the press is closed so that the plastic doughis thoroughly pressed into the intaglio mould and of the proper thickness, the closing process is discontinued but the pressure is held. Through a cooling process-of circulating refrigerated water through the top and bottom platens of the hydraulic-press, the plastic is cooled and when removed from the press is easily separated from'the matrix leaving a negative perfect reproduction of the matrix. Through the action of intense pressure while in a warm and flexible state and the cooling process, the plastic plate assumes a hardness greater than lead, zinc or a nickel stereotype, but will route and tool as metal.

The time required for reproductionof a plastic printing plate from the original metal half-tone or electrotype is approximately 2 minutes to complete the matrix and minutes to make the first plastic plate. However after this is 000mplished, additional plastic printing pla can be produced identical with the first at the rate of one for each 5-minute period and it has been demonstrated that as many as or more identical plates may be produced from the matrix.

After the negative impression is taken from the Bakelite matrix, it is sawed to size and mounted and planed to type-high or to a proper thickness for incorporating into the conventional type of printing bases in general use. Composition typographical forms or plates of this material can be drilled for tacking to a base or can be glued to a base, depending upon the manner in which the printer intends to use the plate for reproduction purposes. The composition has a very high afiinity for ink and will withstand considerably more use and abuse than the average printing plate in general use.

In place of the wool flock suggested as a constituent of the mix above, cotton, rayon or other types of fibre flock which have a sumcient degree of fineness and strength may be used. Instead of lead sulphate, lithopone, consisting chiefly of a mixture of zinc sulphide and barium sulphate, has been usedwith satisfaction. On occasions, a small amount of ethyl cellulose has been found to give the plastic added toughness, but care must,

be taken to restrict the amount to avoid any likelihood of ignition. Particularly during the mixing process and from the heat of the press when the impression is made from the positive matrix, care must be taken to avoid excess temperatures. In the example of a typical mix described heretofore, from 2 to 4 ounces of ethyl cellulose to 2 pounds 5 ounces of shellac, 1 pound 14 ounces of wool flock and 12 pounds of lead sulphate proved satisfactory.

Plates made according to this .method have;

pressures and wear from operations in the press, plates which are not easily defaced due to handling and storage and plates which give a perfect reproduction of fine lines and images from copper plates and zinc etchings.

In addition to the fine reproductions obtained by using this plastic printing plate, it affords the printer a great saving in both time and money. In case the printer desires to complete a large runand is required to mount several copies on his press so that they may all be printed in one operation, it is possible to obtain these cuts at the rate of speed previously mentioned and at a great saving over metal cuts previously used. I

The general custom followed by a printer is that he does not use the original cut supplied from a photograph or artists drawing but uses electrotypes reproduced from the original: The

plastic printing plate afiords this reproduction at a saving of time and expense;

It will be understood that certain feature and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without shellac, a fibre fiock and a filler selectedfrom the group of materials consisting of basic lead sulfate and lithopone.

3. A printing plate 'composed or a mixture of a binder, a fibre fiock and a filler selected from the group consisting of basic lead sulfate and lithopone and a minor portion of ethyl cellulose.

- JEPmA K. Tool).