US2387048A - Photoengraving or the like - Google Patents

Description

@d. 16, i 4fi, c ALGER 2,387,048

I PHOTO ENGRAVING OR THE LIKE Filed July 18, 1942 Patented Oct. 16, 1945 r 4 orric 2,387,048 PHOTOENGKAVING on THE LIKE Harley C. Alger, Chicago, Ill.

Application July 18, 1942, Serial No. 451,478

3 Claims.

Thi invention relates to the art of photo-engraving. and more particularly to the screens which are used to make half-tone dot positives by what is commonly -known as the Contact Method" and to the use of such screens to produce a positive suitable for use in making intaglio, photogravure printing plates or cylinders.

One of the objects of this invention is to produce a screen for use in making a. positive which will have a half-tone clot formation in the lighter tone areas and a gravure clot formation in the denser tone areas.

Another object of the invention is the production of a screen adapted to produce such a positive by contact with the photographic material from which the positive is to be made.

A further object is the production of a screen which may be used to produce a positive having so-called gravure screen lines therein which eliminates the step known as Carbon tissue screening, in making gravure plates or cylinders.

Another object is to produce a screen which may be used to make such a positive which in turn may be used to produce an intaglio image on the surface of a plate or cylinder of such character that the image will not easily wear away during the operation of printing, thus giving long life to such plate or cylinder.

Another object of the invention is to provide an improved method in the art of photo-engraving nectlon with the accompanying drawin in which Fig. 1 is a fragmentary view of one form of screen made in accordance with this invention and adapted for carrying out my improved method; 1

Fig. 2 is a fragmentary view of a modified form of screen made in accordance with this invention;

Fig. 3 is an illustration showing a positive in the form of a tone scale extending from light to dark tones made in accordance with this invention, using the screen shown in Fig. 1; r

Fig. 4 is a view similar to Fig. 3 showing a positive also in the form of a tone scale extending from light to dark tones made in accordance with this invention, using the screen shown in Fig. 2.

In gravure printing, many attempts have been made to produce a positive which could be used to make an intaglio printing plate or cylinder which would have a half-tone image in which the various tones are brought out by virtue of varying the size of the dots or wells etched into the surface and making them of substantial uniform depth, instead of the conventional gravure dot formation in which the various tones are brought out by virtue of dots of varying depth but of substantially uniform area. 1

One of the disadvantages encountered-in so doing has been that the half-tone clot formation cannot be carried further than asemi-tone or the well known checkerboard formation when considering a tone scale extending from light to dark tones, it being necessaryto leave the remaining areas unetched or surface high throughout the darker tone areas in order to support the doctor blade. This blade is used to remove surplus ink from the printing plate or cylinder during the process of printing. This results in the lowering of the quality well recognized in the art of gravure printing because the tone gradation of such an image does not extend completely to a dark solid but stops far short of this point.

In accordance with this invention, I have eliminated this disadvantage by producing a screen with resultant positive which may be used for making a plate or cylinder printing surface having a half-tone dot image in the highlight areas and also having a gravure dot image in the denser tones, thus extending the tone range of the image completel to a solid dark tone as is common in ordinary gravure printing.

In the attempts heretofore made to produce such a positive, it has been the practice to do the work in a camera using theLevy half-tone screen which is well known in the art. This operation takes considerable time and the useof a camera adds to the cost of positives made by such a method.

In accordance with my invention, considerable time is saved and the cost of the positives is reduced for the reason that the positives can be made quickly in a simple vacuum printing frame by the contact method.

Ordinarily in making a gravure plate or cylinder a transparent positive image is made in continuous tone uninterrupted by any dot formation. A gravure screen having transparent screen lines and opaque square dots is printed by light in a vacuum printing frame on a sheet of carbon tissue paper which has been sensitized with potassium dichrornate; next the continuous tone positive is printed by light in a vacuum printing frame on the same sheet of screened carbon tissue paper. Subsequently the carbon tissue is laid on a copper plate or cylinder which receives the image printed from the screen and positive and which is finally etched to produce a gravure printing as is'welii known: in. the: art;

'me ordinary gravure screen: isrone having; clear .1. a u lines surrounding-: opaque dots? or.- gnnreogzwhilesthewgrainedi" gravureiiscreen is: one having irregular" transparent; li'nessubstantially surrounding irregular: opaque dots: or areas. In: eithenficase, the? clear. lines permit the surface of.

the; carbomtissueto beshardenedand; these. screen.

lines. correspond; to; the: surf ace-high. lines of 1' the: finishedv gravure; plate; or cylinder which support;

the: doctor: bladeduning: theoperatiorroi printing,

at ther center offithe-areasi-defihedi byany four dots. Dense tone: lines: or" bands: of. solid color 8?. are; formed; running: through. each rowof dots atleastzin one direction.v

Figure 2; showsa modified" form. of the inven tionainrwhi'ch the.- screengfii is providedwith dots ill formedjandiarrangedina similar-manner to the dotsshowneinltig: 1.. Denselinesql l or solid lines. of? definite: tormation' and substantially uniform widthapasszthrough: the dots.- in; one direction as 7 shown: andiothersimilardines-It: pass through the dots ahrightzanglestox the lines I L.

Thezsereen may hezmad'e: by preparing a suitable drawing-for? larger" scale: than the finished. screenaand; photographing. the drawing on a dry plate orr'fllrn'atthezsametime reducing so that therezwiiLbe approximately one hundred and fifty totwo hundred dots per" linear inch; Coarser on finer-dot: spacing may be made if desired.

Onthe screen may be. made in the camera by using the: Kerry-"screen set close to the dry plate or: film: upon: which the dots and lines are to be. formed; I'rrthiscase; the-dotsare formed firstby setting the distance of the Levy screen from the: plate-or; film so'that small dots the size of thecorezdesired', wilibe formedion. the plate and: thempartially exposing. by reflected light to form the coresof; each: dot. Next the screen distance is altered: a: small. amountiso that. arger dots areiormedi, each: having an. area a trifle larger than the; size of. the corefirstformedagain by partial exposure: process is repeated several times until. the-dots; are increased in sizeuntil they overlaprand. th'e: unexposed areas are only small clear: spotsatthe: points where the diagonal lines from-the; centers ofi' each fourdots: cross each other: Then the-lines are formed by placing a suitable; aperture in the lens; chamber of. the cameraaandagain; makingra partial'exposure. In

the; casesotithesingleset of. parallel lines on the screen: as; shown in Fig. 1, the aperture is in the formofj a narrow slit: while in the screen shown in Fig. 2.1 whichhasi-two sets of parallel lines at: right: angles; to.l each other; the aperture is in the formv of. a: thinline Maltese cross; After these. exposures, the plate is: developed, fixed and. washedyand ascreen having dense tone lines with dots: positioned thereon,v each. dot having a. dense, center; or core: with the. tone gradually decreasing: density outwardly from: its; center, is"

produced;

It would. be-ioundth'at operators skilledin the use of the; Levy ha lfi toner screen; can-readily produce'a screenzlike: therone'shownimEigZ. 1 ortl'iea one:- shown: in Fig; method,

Aiterz'thescreen. is made,..it; is to: noted; that the. image dot I3, thatiis-theportiorr off the: screen:

that: makesthe. image dot; of; the positive, is spacerhaving a. clear; center: at; the.- crossing point" of." the diagonalsaextending; from each. set of. four dense: tone dots; this: image dot" of the screen having; acenter; with a density offpractically zero. and? with: gradually" increasing-density" extending outwardly from its center. untilit rneetsitheadense tone-lines: of thescreen.

The; use: of the? screen: inmaking positives. now becomes; a relatively simple; matter; The nega-- tive'; made.- fromlth'er. copy; which it: is desired to. reproduce; is. placed; against: the-:- glass: of. a vacuumprinting" frame, the screen is;placed in con-- tact with the negative, a: suitable: dry plate or. film. is placed; incontacti with. the screen, the frame is. closed and the plate is exposed to. suitable light, usually an arc light, through the; negative and screen. to produce: an image on. the dry: plate which-11's brought out bysubsequent developmentrin.the-iormofiatpositive.

Figure: 3 shows-such a positive I4 which would result by usi'ngthe screen of; Fig. 1 with a negative made with. atone scale as copy, with. tones extending from a very light tone at: the. left,v to ;.fu1l dense tone at: the; right. The. angle. of'the' lines ofthe positiveewhena single: set of. parallel lines. are used;. should be; such. that the corresponding lines which are formed on theprinting cylinder: are at: an. angle of 20 to. with the line'of contact oi the doctorbla'de with the cylinder.

The positive l5" shown inEig. 4 is similar to that shown in Fig. 3 when. made with. a screen such as shown in- Fig; 2; In accordance. with this invention, it will be. seen that I. have produced a. screen which carries a vignetted' clot formation which forms half. tone dotsinthe positive when printed from a negative by the contact method and that the screen also carries gravure type screen lines running through thevignetted dot formation which gives a. gravure dot formation in the darker tones of the positive. From this it is seen that the positive carries all the: necessary screen. lines and that the operation; 0i screeningthe' carbon tissue is not necessary as; the lines will be formed in thecarbon tissue from the positive in a single printing of the positive only.

Further, it will be seen that by the use of this screen. with itsresultantpositive having halftonedots in the lighter: tones, a. printing plateor cylinder will be made; which will. have intaglio half-tones dots representing the lighter tones formed in its surface. Thesedots are" relatively smaller than the conventional. gravure: dots and: the area of surface-high metalv aroundv the dots. is proportionately larger; thus providing alarger surface to support "the doctor blade during the operation. of printing which. gives the image in. the surface of the cylinder longer life, all of which is brought about by the: use of my improved screen.

While the accompanying drawing is intended. to illustrate the invention as fully as possible, it will be noted that the figures are drawn on an enlarged scale as the wells or inkrecesses in intaglio printing are usually of exceedingly small dimensions.

While I have shown and describedv a preferred form. of my improved screen, and my improved method in the art of photoengraving, it will be aasaou tone practice and the circular figures extendin beyond the bands and intersecting at substan-- tially midway between the bands.

2. A screen adapted to produce a half-tone image by the contact method, having a transparent base and having a set of substantially continuous parallel dense tone lines of substantially uniform width spaced on the order 0! to per inch and dots formed at uniform intervals on each line, also spaced at approximately100 to 1'75 per inch, the dots on one line being tangent to the dots of theadJacent lines. each dot having a dense tone center with the tone gradually decreasing in density outwardly from its center.

3. A screen for the purposes set forth, having a transparent base with parallel dense tone stripes of substantially uniform width and having vignetted dots intersected by said lines, said dots having dense tone centers with the tone gradually decreasing in density toward the outer periphery with the outer peripheries of adjacent dots substantially intersecting each other, said dots and stripes being spaced substantially in accordance with the usual half-tone practice.

HARLEY- C. ALGER.

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