Stereotypy

Stereotypy 

the process of preparing stereotypes— duplicates of relief printing surfaces. The process consists of ma-trixing, preparing the stereotype from the matrix, and trimming the stereotype. Stereotypy is used in printing large numbers of copies, printing newspapers simultaneously at several locations, reprinting, and printing on rotary presses. Stereotypes may be prepared by casting, electrotyping, or molding.

In the casting process, the cardboard matrix is placed on the bottom of a built-up casting form, and molten type metal at a temperature of 300°-320°C is poured into the form. The matrix can produce 15–17 castings; the thickness of the stereotype depends on the type of printing press to be used. After casting, the stereotypes undergo mechanical finishing: the thickness is reduced by removing excess metal on the reverse side of the stereotype, the side edges are trimmed, and large blank areas are recessed by milling. The majority of flat and curved stereotypes are cast by semiautomatic equipment with an output of one piece every 2–3 min or by automatic equipment with an output of 2–3 pieces per min. Major newspaper printing plants use production lines equipped with facilities for the automatic, high-speed casting and mechanical finishing of stereotypes. Because type metal is not very strong, special measures are taken if the quantity of copies to be printed exceeds 40,000. In this case, the printing surface of the stereotypes is electroplated with a layer of stronger metal, such as iron, nickel, or chromium, having a thickness of 0.01–0.03 mm.

In electrotyping, the stereotype is produced by depositing a layer of metal, usually copper, on the matrix. After separation from the matrix, this layer is strengthened on the nonprinting side with type metal or plastic. The mechanical finishing of such a stereotype is similar to that of cast stereotypes.

In the molding process, the matrix is used as a die to mold a ductile material, such as plastic or rubber, into the required relief form. The matrices are usually made of a thermosetting plastic, and the stereotypes, of some thermoplastic, reusable material. The matrices are mounted in a special press in which the lower plate is heated, to 170°-190°C, and the upper plate is cooled. Several stereotypes can be made from a single matrix; they require very little mechanical finishing. Unvulcanized rubber is used as the raw material for rubber stereotypes. After molding, the material is vulcanized under pressure. A process for producing polymer stereotypes by casting molten plastic materials has also been developed; the process is several times more productive than the molding process.

The choice of process is determined mainly by publication deadlines, by the required quality of printing, and by economic considerations. Cast metal stereotypes, which can be produced quickly and simply, are the most widely used. However, they do not print as clearly as other stereotypes. Cast stereotypes with supplementary electroplating are particularly prone to severe distortion. They are used to print newspapers, books, journals with few illustrations, and tear-off calendars. Electroplated stereotypes are much more expensive because their labor costs are higher. However, they withstand long printing runs (up to 300,000 copies) and very accurately reproduce all details of the original. They are widely used for printing long runs of illustrated publications, including those with multicolored illustrations, such as encyclopedias, reproductions of oil paintings, and multicolored inserts in books and journals. Plastic stereotypes can be used for printing large numbers of copies (approximately 200,000). They are also used for printing various texts and publications with monochromatic illustrations. Rubber stereotypes yield the lowest accuracy of reproduction but have high wear-resistance. For this reason they are used for printing large quantities of packaging materials, wrappers, and forms. They can also be used to print long runs of books without illustrations.

REFERENCES

Shaposhnikov, S. I. Slereottpiia. Moscow, 1966.
Valershtein, I. Ia., I. A. Davydov, and O. P. Trofimova. Polimernyestereolipy. Moscow, 1972.

N. N. POLIANSKII