US2738728A - Gravure printing plate - Google Patents

Description

March 20, 1956 SCHUHLER m Q m AVAV mm m J AVAVAV WW 00 mm w @000 0000 VMV .QA

R E m 0U H m V 8 W m W N VMU Y B ATTORNEYS United States Patent The, present invention relates to the art of printing iifromtplates engraved imintaglio; and 'more particularly eoncerns aanethod and apparatus- ="for engraving of 'itext matter froma photographic 'film. The photographic film or transparency from which the engraving is made may be prepared through the use of a photographic type composing machine, or by direct photography of the entire text after composition on any other form of type composing apparatus, or by any other method.

In current practice, the pictures and text to be impressed in intaglio are transferred to the printing plate by an intermediate medium, known in the art as carbon paper. The carbon paper is coated with a layer of photosensitive material, the printing plate being etched through the sensitive coating in such a manner as to obtaincavities or dots of different depths. These cavities are to receive ink for the impression.

The preparation of the carbon paper ordinarily involves two successive operations, first an exposure under a screen and second an exposure under the transparency comprising the text matter and the pictures. A third operation, called fogging, is sometimes necessary. This arises from the difficulty of balancing on the carbon paper the effect of the exposure under the pictures and under the text. The blacks of the texts are deeper than the blacks of the pictures. Fogging involves a third exposure of a few seconds in the section comprising only the text matter, which permits the required balance to be obtained.

A simplified procedure for preparation of the carbon paper involves combining the first two exposures; that is, the carbon paper is exposed simultaneously through the transparency and screen. But such a procedure is not suitable except for pictures; hence, where text matter is involved the preparation of the carbon paper requires two exposures, one under the screen and another under thetext. ,a

There are several defects in the above-described methods in addition to the balancing difliculty mentioned above. The most apparent defect is a lack of sharpness of the outlines of the characters due to the fact that the screen is not adapted to each character. A succession of portions of dots, whose sizes and pattern are determined by chance, form the edges of each of the characters. The effects resulting from. this are hereinafter more fully explained in connection with Fig. 1.

A principal object of the present invention is to provide means for improving the quality of text impressions in intaglio.

Another object is to provide means whereby the step of making a separate exposure of the carbon paper under a screen may be eliminated.

A principal feature of the present invention includes the provision of character matrices for preparation of the text transparency which carry their own screens. That is, a single exposure of the carbon paper through a transparency prepared with these special matrices is sufficient to prepare the carbon paper for use in etching the printing plate.

nt in-otherz featurexdireetly srela'te'tl with the. :aboye, 'zis that a' screienplan especially-adaptedtothe outline of-each -haracter:may""-tbe 'tusetl.

"invention, comprise certain novel arrangements and "methotlsavfvliich wvill becbmei-apparent {from-the description .and which"are more particularly ii'efineii by-the claim.

=lnjthe* drawings, *Fig. ilqslrowsthe relationship- :of "the screen and c'ha'racter exposures "uponthe #carbon ,pap'er *Re'ferringfirst to Fig." r-renew the "outlines; of :an imag e 1 of atypical screen,v as it,impingeson'the.carbonrpaper.

As is .eommonly-uniler'stood,'the :area "onihe screen within 'thet'c'l'ose'd 'ssquares is'opaque, iso that' light 'imp'inges "every- --wh'ere on the-carbon tpapen-exeept -witliin--the-squares Superimposedmpon tliisiimage is a part ofandmage-of'a charatcer 2, formed in a separate exposure through a text transparency. As is also commonly understood, the

, light strikes the carbon paper in this exposure everywhere except within the outlines of the characters, which are positives, i. e. opaque, on the transparency. These images are assumed to be formed by two successive exposures as already indicated.

The ideal pattern of engraved dots resulting from these exposures is represented at 3 by the criss-cross hatching. However, as it is well known'by those familiar with this art, there are at least two factors which work to prevent the ideal from being attained. First, the part of the gelatin that has been rendered insoluble by the action of the light tends to diffuse, causing the outlines of, the dots to take the shape represented at 4 by the horizontal hatching. The largest depth is found at the center of each dot. Secondly, the ink tends to spread when the impression is made because of the pressure exerted on the back of the paper by the cylinder of the printing press, which causes the outline of the printed letter to take substantially the shape of dotted lines 5.

Referring now to Fig. 2, I show a view representing a character matrix through which a text transparency can be exposed according to another method. The screen is formed of rectilinear lines upon the same matrix as the characters. It will be understood that this matrix is transparent only in the vertically hatched areas. Because of the simplicity of the screen form it may be made by any one of a number of mechanical methods such as diamond cutting which will suggest themselves to those familiar with this art.

For example, the matrix may be a rotating disk in a photographic type composing machine such as that described in the copending application of Higgonnet and Moyroud, Ser. No. 610,336, filed August 11, 1945. The disk may be cut by a lattice of lines 7 and the characters may be photographically imposed on the disk so that they are transparent on an opaque background. The characters may then be projected against a film in the machine which becomes the text transparency, wherein the areas corresponding to the areas 8 in Fig. 2 denoted by the vertical hatching will be opaque, these being the only areas struck by the light.

This film is then used to expose the carbon paper in a single exposure, with the result that only the areas 8 on the carbon paperv are excluded from the light. When the gelatin layer on the carbon paper is then transferred onto a printing plate or sheet of copper, for example, it is only these areas that will be etched by the etching compound.

It will be noted that the spacing of the lines in the screen is relatively large in proportion to the size of the character. The spacing is a function of the appearance of the printed character to the eye and must be adjusted so as to take this factor into account.

linear, but of curvilinear shapes.

The above embodiment is an example in which the screen is on the same matrix as the characters which are used in the composing of the type. Figs. 3 and 4 represent forms of the invention particularly useful in photographic composing machines, which not only have this characteristic but also involve the adaptation of the screen to the particular characters. Figs. 3 and 4 difier only in the sizes and shapes of the various dots of which the character is composed and may be considered together.

In these figures the screen is not composed of recti- The areas or dots 9, denoted by the diagonal hatching may represent, for example, the transparent areas on the character matrix in a photographic composing machine. The procedure for preparation of the printing plate in intaglio from this matrix may be similar to that already described in connection with Fig. 2.

In connection with the shapes of these areas 9, it will be noted that the periphery may be curved inwardly toward the center of each area and away from the desired outline denoted by the solid line 11, as shown in the figures. For reasons already indicated, the ink will not be confined within this periphery, but will spread toward the line 11. It is apparent that the sizes of the areas 9 as well as their shapes will depend upon the nature of the ink as well as the pressure applied.

Having thus described my invention, I claim:

A printing plate having text matter in intaglio, each character of said matter being formed in the generally fiat surface of said plate by a number of disconnected ink-receiving depressions therein arranged with substantially equal distances along said surface between the proxi mate boundaries of adjacent depressions, the surface of the plate at the boundary of each depression which is not proximate to an adjacent depression being convex toward said depression.

References Cited in the file of this patent UNITED STATES PATENTS 2,456,608 Alger Dec. 21, 1948 2,486,406 Higgonnet Nov. 1, 1949 2,662,455 Freund Dec. 15, 1953

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