US2261554A - Method of preparing printing plates - Google Patents

Description

Patented Nov. 4, 1941 I METHOD or PREPARING PRINTING PLATES Albert L. Lengel, Berkeley, Calif., assignor to The Tribune Publishing 00., trustee, a corporation of California No Drawing. Application June 6, 1938, Serial No. 212,131v

2 Claims.

The present invention relates to printing plates, and particularly to a novel photo process plate especially adapted for use in high speed rotary web perfecting presses of the type used cidentalto successive reproductions of illustrative material in mat and stereotype before printing.

A further object of the invention is the elimsecond acting cylinder of a rotary web perfecting press, of illustrative matter printed by the first acting cylinder.

A further object of the invention is the proin newspaper production. 5 vision of means for securing increased accuracy The incorporation of illustrative matter in of register in color printing by means of rotary newspaper material has heretofore required, not web perfecting presses. only the preparation of half-tones or line en- The novel features of the invention are set gravings which must be mounted on blocks, forth with particularity in the appended claims. set into the form with accompanying textual The inve n itself, however, together With admatter, and subjected to the usual make-' ditional objects a a tages thereof, will be ready, as for printing on fiat bed presses, but best understood from' the following description has also required mats to be made and formed of the preferred manner in which the novel plate to the proper curvature so that stereotype plates is P p and usedfitted to the press cylinders may be molded The printing plate of the present invention is therefrom, substantially planographic, the entire surface Such procedure not only requires much more i g m de up f printing elements, p era y time and labor'than the novel plate and methformed in the same manner as the dots of the 0d of preparing and using the same,. contemconventional half-tone photo-engraving. These plated by the present invention, but also pro-" dots are dispersed throughout the entire surduces a printed sheet distinctly inferior in qualface of the printing area of the plate in densiity to that hi h an b produced upon a flat ties comparable to the density of dispersion of bed type of press. The molding of the mats, the dots in a conventional half-tone, but the the forming thereof to the proper curvature, minimum e s y in y P Of the P t and t h k g of t stereotype t l i areaof the plate is not less than would be prothe casting process inevitably introduce irregduced in making a half-tone of a clear white ularities and distortion into the illustrative matsurface. The plate therefore differs from what ter, and the successive reproduction of the halfis known as a deep-etch dry Plate Ofi in tones, first in the mat and then in stereotype that the heig t o e highest pointsbf the plate, inevitably results in loss of detail. printing elements, do above e interven- Stereotype plates are, furthermore, of the reins l w r p i ts, is f t order of nly bout lief type, in that the recessed areas must have .005 to .007 of an inch, and in that the entire a substantial depth, depending upon their area, surface of the printing area of the plate is prein order to prevent them from being inked and sented to the web upon the impression cylinder printed, and it has been found that when such and the inking rollers, the dots in the lightest relief type plates are run on the press cylinders printing areasserving merely as mechanical supwhich print last on the web, illustrative matter ports for the inking rollers and web, and being theretofore printed on the opposite side of the designed to retain and transfer to the web as little Web is distorted. ink as possible.

H v in mi he foregoing and oth r de- 40 In preparing a plate of this character, a plate iiciencies of previous methods h devicas lfsed film somewhat larger than the final size of the in work of the class concerned, it is a prln lp plate to be made in order to allow for trimming, ob-lect of the Present 'F f to iq is first prepared by photographing a plain white nieans meuzod frhiutihzmgdsubitantlany background through a half-tone screen of any p 't 10 es gh spee My web desired fineness. The standard half-tone screen perfecting presses of the type used in newspaper f r k t th production, without recourse to offsetting or simnewspaper W con ams y mes to e ilar processes requiring extreme care and skill. m but for thls plate screenalt usually It is a further important object of the sirable to use a less fine screen of fifty lines per vention to avoid loss of detail and distortion ineven less, because as explained above,

the purpose of forming half-tone dots throughout the area of the plate in which no printed ination of distortion by relief type plates on the 55 matter appears, is merely to support the inking rollers and the web so that as little ink is re-. tained and transferred to the web as possible,

although this portion of the surface of the plate is substantially planographic.

Next, half tone films of the illustrative matter in the form of one or more photographs or the like, are prepared by photographing such illustrative matter with such enlargement or reduction of the size thereof as may be desired through a half-tone screen of any desired fineness. Due to thefact'that tonal films and detail are reproduced much more perfectly by the use of a plate prepared according to the present invention, it is not necessary to use a screen as coarse as sixty lines to the inch in preparing these films. Screens as fine as eighty-five lines to the inch have actually been used successfully in commercial newspaper production, and even finer screens may be used. It is important to note that the screen used in thus preparing the illustrative matter does not need to have any relationship whatever to the screen used in preparing the plate film.

The plate film described above is then, for convenience, placed upon a transparent working plate of glass or the like, and the films of the illustrative matter are inset into the first film by stripping, which consists of cutting the illustrative matter films to the desired dimensions and cutting an aperture in the plate film of the same size as the trimmed film of the illustrative matter, after which the film of the illustrative matter is set into the aperture of the plate film.

After the plate film with the illustrative matter inset has been prepared, a transparent sheet is placed over it andtext matter, large type, and any desired line drawings on an opaque medium, are placed on the transparent sheet in proper register with the illustrative matter on the main plate film, and a separate film is made from the transparent sheet by photographing it from the rear .50 that the lettering thereon will be reversed before the camera. It is not necessary to use any screen whatever in preparing this film, it being desired to provide a film in which th lettering and line drawing is represented by transparent areas and the remainder of the film is opaque.

The two films, one containing the illustrative matter and dotted field, and the other containing the textual matter, are then printed successively on a fiexible sheet of sensitized metal, each such printing being effected in the well known manner in which half-tones are produced. This sheet may be of zinc, jem metal, or the like, and should be thin enough to be capable of being readily sprung around a printing cylinder. Sheets as thin as .020 to .027 of an inch have been successfully used, and since these are much thinner than any printing plates commonly used in newspaper presses or the like, it is possible to effect substantial economies in metal used, as well as to render the plates much easier to handle.

- It will be apparent that, since all portions of the film containing the textual matter made from the transparent sheet, except those occupied by lettering or drawing, are opaque, the sensitized metal surface underlying the opaque portion will not be exposed or reexposed during the printing of this negative. Only the lettering and drawing appearing on this negative will be printed on the sensitized metal, but if the negative of the main layout sheet has been printed first, the lettering and drawing will be overprinted thereon. It'makes no difference which negative is printed first, or whether the screen lines register on the two negatives.

As is well known in the art of producing halftones, the sensitized coating of the metal plate is rendered insoluble where it is exposed to light, and this insoluble material receives a well known roll up treatment, rendering it sufliciently strong to resist acid, after which the plate-ls exposed to the action of acid which etches the bare portions thereof to a depth of the order of .005 to .007 of an inch. All methods of photoengraving are in essentials done in this way, differing merely in detail, and any well known method may be used in this step of the preparation of the plate.

Opposite edges of the completed plate are preferably bent to provide 'an angular flange which may be perforated at several points to adapt the plate for direct attachment to the dummy supports or printing cylinders of any well known type of rotary web perfecting press commonly used in newspaper production.

Such presses include first and second printing cylinders which successively print upon opposite sides of the web and it has been found to be advantageous, where relief type plates are to be used to print one side and the plate of the present invention is to be used to print the other side of the web, to dispose the relief type plates on the printing cylinder printing first. This is desirable because relief type Plates deform the web sufiiclently to distort any illustrative matter previously printed on the opposite side thereof. The plate of the present invention, being substantially planographic, however, does not deform the web and will not distort illustrative matter printed on the opposite side of the web by printing cylinders carrying relief type plates, disposed in advance thereof.

It will be seen that plates produced in the manner described fulfill the objects of the invention set forth above, and have other obvious advantages. Because of the clear printing obtainable it is possible to use finer screens than have heretofore been practicable for newspaper half-tones, and to thereby obtain better tonal values and detail in the illustrative matter. It is also apparent that the planographic surface of the plates practically eliminates shocks and vibration incidental to the passage of relief type plates under the inking rollers and impression cylinders, thus making possible higher press speeds without undue wear and tear on the printing surfaces and press mechanism.

In color printing where a plurality of plates are used to successively print different colors, the preservation of perfect alignment, or register, is of the greatest importance and the plate of the present invention possesses outstanding advantages. The separate color plates required for the well known color printing processes are each made in the same way as has been described above in-connection with a single-color plate, except that each pair of half-tone films for a given plate is sensitized for a different color as is well known. In printing the negatives upon the sensitized metal plates, perfect alignment of the negatives and plates can be maintained quite easily and since the plates are used directly in the'press, there is no possibility for misalignment arising from mat deformation or stereotype shrinkage.

While the plates of the present invention are intended for direct use in the press and the best results will be obtained by so using them, it is of course possible to take mats from such plates and make stereotype cylinder plates from such mats. Certain of the ad antages of the invention can be obtained by use of such plates, and

it is usually desirable to take a mat impression of a new plate for use in case the original is damaged.

It will be apparent that no additional equipment is necessary in a' well equipped photo-engraving plant in order to prepare plates according to the present invention, and that the plates are not only interchangeable with the stereotype cylinder plates in common use, but may be mixed with such stereotype plates in the same press and even on the same printing cylinder, in multicolor work, as well as in single-color work. In color work, for instance, stereotype plates may be used for certain colors, and overprinting efiected by a plate of the present type.

Since modifications in the application of the invention will necessarily be required under various circumstances, and will be obvious to those skilled in the art, it is to be understood that the invention is not to be considered as restricted by the foregoing description except as required by the prior art and the spirit of the appended claims.

What is claimed is:

1. A method of preparing a letterpress printing plate of substantially planographic character which comprises the steps of integrating a plurality of separate halftone films prepared from photographic illustrations, with a principal halftone film prepared from a surface of uniform tone, which principal film is at least as large as the desired plate; and photoengraving a metal plate from the integrated film thus produced.

2. The method set forth in claim 1 in which one or more of the halftone films prepared from photographic illustrations are prepared by means of a finer halftone screen than that used in preparing the principal film.

ALBERT L. LENGEL,