US2742833A - Optically sensitized prescreened photographic material - Google Patents

Description

April 4, 1956 R. M. EVANS ETAL 2,742,833

OPTICAL-LY SENSITIZED PRESCREENED PHOTOGRAPHIC MATERIAL Filed June 29, 1951 2 Sheets-Sheet 1 (CORNER OF DOT 1 n sENs/r/vE T0 SHORT WAVELENGTHS ONLY j CENTER OF DOT F1 1 SENSITIVE TO LONGER wAvELENeTHs 3 74/ g 20 1 coR/vER OF DOT/' \22\/\ 24 1 BLuE SENSITIVE j Fly 2 CENTER OF DOT p BL uE AND GREEN SENSITIVE 24 1 32/ v V' 4- CORNER OF DOT 32 BLUE SENSITIVE 9 3 CENTER OF DOT 33 BLUE AND RED SENSITIVE 46 CORNERS OF L/NE DOT SEMSIT/VE r0 BLUE BUT NOT RED CENTERS OF /20 L/NE D0T\/ 43'--- BLUE AND RED SENSITIVE j CORNERS OF 50 L/NE D0T- 45\ F1934 SENSITIVE TO BLUE BUT NOTGREEN CENTERS CF LINE DOT-\ 2"-- BLUE AND GREEN SENSITIVE 43 *1 Ral 12M Evans I RoberlE Slaaffer Henry C. Yaigy IN VEN TORS ATTURNEKS' April 1956 R. M. EVANS ETAL 2,742,833

OPTICALLY SENSITIZED PRESCREENED PHOTOGRAPHIC MATERIAL Filed June 29, 1951 2 Sheets-Sheet 2 Fig.5

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Raga/z M Evans RoberiE. Slaaffel' Henry C. Yuigy INVENTORS MQM ATTORNEYS United StatesPatent O lice I 2,742,833 7 OPTICALLYQSENSITIZED PRESCREENED v a PHOTOGRAPHIC MATERIAL Ralph M. Evans, Robert E. sauna, and Henry c. Yutzy,

Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application June 29,1951, Serial No, 234,332 llClaimsL (Cl. 95-8) a film or plate on which either halftone or non-halftone (e. g. continuous-tone or line) images can be made at will. In one embodiment this feature'permits either a halftone or a continuous tone record to be made from an original subject or continuous tone copy. In another embodiment it permits the combining of line copy and halftones such as is used in advertising illustrations.

Films, although they are sometimes rolled, are always exposed substantially flat and along with glass plates are herein referred to as flat supports. The sensitive layer in' the present invention is a silver halide emulsion layer usually of the so-called lith type with a gamma greater than four. This permits the making of good quality halftones or combinations of halftonesand line reproductions. gamma between 1.5 and 4 is used to permit either continuous tone or halftone records to be made. Halftone patterns have various forms; the term dot is used to refer to an element of the pattern, the centers being the points of maximum sensitivity or maximum ultimate density and the corners'being the points of minimum sensitivity whatever the shape of the dot. Heretofore,

prescreened materials were made by desensitization of the corners. of the dots-in the halftone pattern or by preexposure of the centers of the dots or by both of these steps, or fourthly, by pre-exposing a contact screen in a separate emulsion layer or the opposite side of the primary layer to be developed up with the main image. The present prescreened materials differ from all such former ones in many ways. In .the present materials there is no pre-exposure of the dot centers andno desensitizing of the corners; in fact, the sensitivity of the corners remains substantially unchanged although little harm is done if it inadvertently is increased slightly. The centers are optically sensitized to wavelengths to which the corners are not sensitive.

In general, blue sensitive films are used and the added sensitization is for green or red or both, butvthe film may be green sensitive with the added sensitization for red; The variation in spectral sensitivity from the corners to the centers is preferably a continuous one'but may include small areas of constant value right at the center or corner for special effects like drop out highlights or steps of substantially constant value for posterizmg.

When a blue sensitive film which has a halftone pattern of green sensitization according to the present invention' is exposed through a'blue filter, the prescreening In one embodiment, however, film with 21' 2,742,833 Patented Apr. 24, 1956 is quite ineffective and a continuous tone image of a continuous tone original or a line image of a line origi-.

nal results. In fact, a halftone original may be duplicated in this manner. If this same material is exposed to a continuous tone original through a green or yellow filter a halftone image results since the corners of the dots are insensitive to green light or at least havea very much lower sensitivity to green. than the centers have. The difierence in sensitivity from the corners to the centers is, in general, such that the ratio of blue sensitivity to green, or other longer wavelength sensitivityis lessat the centers (which have been optically sensitized to the longer Wavelength) than at the corners (which have received little or no optical sensitization).

When making halftone negatives for; newspaper repro-; duction, a line screen is desirable whereas magazine Matereproduction may require 120 or 150 line screen. rial prescreened according to the present invention with green sensitizer 50 lines per inch pattern and red sensitizer 120 lines per inch gives newspaper halftones when exposed through a green filter and magazine halftones when exposed through a red filter. With proper sensitizers conflict between them with respect to the individual silver halide grains does not produce any objectionable eflect'in'the end results. It is, of course, necessary to use sharp cutting filters so that neither vhalftone screen.

shows up when the other is the one intended.

The sensitizer may be applied from any form of printing plate, letterpress, intaglio or even litho, although sitizer is applied and also on the particular sensitizer used. The rate of drying after printing appears to have.

little effect.

The degree'of diifusionof sensitizer dyes is a ch arac'teristic well known to those working with such. dyes. 'U. S. Patents 2,282,116, Brooker, 2,239,698, Carroll,

2,239,699, Carroll, 2,331,660, Davey, 2,336,260, Knott,

2,358,060, Davey, 2,358,169, Kridel, 2,384,598, Carroll,

and 2,411,096, Knott are examples of discussions of this well known property. Reference is also made 'to the Annals of the New York Academy of Sciences, volume 36, pages 209-346, 1945; A. L. Geddes in Weissberger,

Physical Methods of Organic Chemistry, vol. 1, Interscience,"1945; Alexander, Colloid Chemistry, vol. IV,

Chemical Catalog Company Inc. 1932 pp. 194-234 and, Valko, Trans. Faraday Soc. 3], p. 230, 1935 for general. As pointed out discussions of the diffusion of dyestufis. above, optimum results require consideration of the dif fusion factor in selecting the dye to be used and the vehicle for the dye, but such consideration is no difierent from that usually given in the use of such dyes. The present invention is not concerned with the particular method used for controlling the diffusion; the examples given toward the end of this description present no dif-.

ficulty on this score. 7

Although the distribution of the sensitizer afiects the tone reproduction curve, it seems to be quite satisfac-.

tory merely to apply all of the sensitizer dye at or near the center of the dot and to let it spread in decreasing amounts to the corners. It is'theoretically desirable to have sensitizer barely reach the corners, but in practice, variations either way from this theoretical ideal still give satisfactory materials.

This invention works particularly well with the socalled lith emulsions which have the advantage of high contrast but for those embodiments requiring lower contrast, emulsion Examples 8, 9 and 10 described by A.

3 P. H. Trivelli and W. F. Smith on page 330 of the Photographic Journal, vol. 79, 1 939, are satisfactory. The preferred embodiments employ the lith emulsions however.

The invention and its advantages will be fully understood from the following description when read in connection with the accompanying drawings in which:

Figs. 1 to 4 are greatly enlarged cross sections of prescreen films according to different embodiments of the invention;

Figs. 5 and 6 illustrate the essential steps in one method of preparing such prescreened films;

Fig. 7 similarly illustrates an alternative method.

In Fig. l, a silver halide emulsion layer 10 on a fiat film (or glass) support 11 has a halftone pattern of varying sensitivity distributed over its surface. In this greatly enlarged view only a portion of one dot of the pattern is shown. The point 12 in the emulsion layer 10 constitutes a corner of a dot and is sensitive only to short wavelength light, e. g. blue or blue and green. The point 13 similarly constitutes a center and is sensitive to longer wavelengths e. g. green or red or both when point 12 is blue sensitive only and red when point 12 is green sensitive. Of course, the point 13 is also blue sensitive.

Fig. 2 similarly illustrates one of these embodiments in which the emulsion layer has corner points 22 sensitive only to blue (the term blue as used in this specification includes the usual violet and ultraviolet sensitivity common to photographic materials) and center points 23 sensitive to blue and green. The distribution of spectral sensitivity varies continuously from the corners to the centers as graphically represented by the curve 24 although its location in the layer 20 does not necessarily represent an actual boundary between optically sensitized and untreated emulsion. Probably the sensitization extends all the way to the base even near the corners 22 but the number of grains sensitized is greater near the centers 23. In Fig. 2 the film is any one of the blue sensitive lith types having a high gamma greater than 4 which insures good dot quality, good line reproduction and good halftone quality. Such a film is not intended for continuous tone reproduction but is used either for halftone reproduction or for line reproduction or, by successive exposure through a green or yellow filter for the halftone and through a blue filter for the line, for the combination of both.

Fig. 3 illustrates an embodiment of the invention using a lower contrast film such as process film with a gamma between 1.5 and 4 with a halftone pattern with blue sensitive corners 32 and blue and red sensitive centers 33. By

means of a blue filter such a film may be used wherever process film is used, e. g. for continuous tone copying, whereas when a red or dark yellow filter is used, this film produces a halftone negative of useful quality which may be contact printed to a lith film or used directly in the making of plates. In both embodiments as shown in Figs. 2 and 3, the dot centers may be either green or red sensitive or sensitive to both.

Fig. 4 differs from the other embodiments shown by having two different screen patterns, one 50 lines per inch for newspaper work and the other 120 lines per inch for magazine work. The emulsion 40 is normally a blue sensitive lith type emulsion which has been printed with a 50-line halftone dot pattern of green sensitizer and also with a 120-line halftone dot pattern of red sensitizer. The points 42 are the corners of the 120-line dots and thus have received minimum or no red sensitizer whereas the points 43 are the 120-line centers and have received a maximum of red sensitizer. The two patterns need not be registered in any way but are generally at an angle to avoid any possible moire. The points 45 (only one of which appears in this enlarged section) are the -line corners and have received no green sensitizer although they may or may not be red sensitive. The points 46 are the SO-line centers and have accordingly received the maxirnum amount of green sensitizer. Red and green sensitizers usable in aqueous solution are described below. The film is dried between the printings of the two dyes.

Through a blue filter such a film is not halftone sensitive and may be used for line reproduction. Through a green filter effectively removing both blue and red light, it produces a coarse SO-line per inch halftone. Through a red filter it produces a finer halftone of 120-line per inch quality.

In Figs. 5 and 6, a blue sensitive lith type emulsion layer 56 carried on a support 51 is passed between a pressure roll 57 and an intaglio printing roll 52 having small (almost highlight) cavities 53 filled with green sensitizer solution. The relative size of these cavities 53 compared to the area 55 between them is not too critical as long as the cavities are smaller than exact middle tones (checkerboard) but small cavities with a fairly high humidity surrounding the emulsion layer 56 or with a vehicle for the sensitizer which causes it to spread somewhat but not too much through the emulsion, appear preferable. The curve 54 graphically represents the distribution of the sensitizer after printing and drying, for example, by a blower 60 as shown in Fig. 6.

In Fig. 7 a lith type film having a blue sensitive emulsion layer 71 and film base 72 is laid emulsion side up on a flat support or table (not shown). A wash off relief film having a film base 73 and a pattern of raised dots 74 is placed in contact with the emulsion layer 71. This relief pattern of dots is prepared in any of the standard wash off or peroxide etch methods after exposure through a halftone screen. Either sharp small dots (made by exposure in contact with a ruled screen) or rounded dots of the type shown (made by exposure through a graded contact screen or through a ruled screen out of contact) may be used. The relief image is soaked in a bath of sensitizer solution which is thus in the dots 74. A squeegee or roller 75 (with handle 76) is pressed against and across the back of the relief film 73. The sensitizer dye transfers from the dots 74 and is distributed in the emulsion layer 71 according to the shape of the dots 74 and the wandering factor of the dye as discussed above.

Besides their versatility, films according to the present invention have several advantages over prior films. The keeping qualities of optically sensitized emulsions (e. g. ortho and pan films) is well known. Once the films are dry, there is little or no tendency for the sensitizer to Wander under normal storage conditions, so that the halftone pattern has unusual stability and, particularly, stability of scale or range. Also, the range may be selected at will by choice of filter, e. g. a primary green filter in one of the above-mentioned cases gives a maximum scale but a green filter letting through a little blue light compresses the scale accordingly. Optical sensitizers are, of course, well known and the one selected is not critical except with respect to the shape of the resultant dots, i. e. the distribution of sensitivity within each dot. Satisfactory quality prescreening is obtained by printing an ordinary blue sensitive lith film from a copper plate en' graying, lines per inch used as an intaglio plate by flooding with solution of:

0.05 g. dye, l-carboxymethyl-S-l(3-ethyl-2( l)-benzooxazolylidene)ethylidene]-3-phenyl-2-thiohydantoin 4 cc. triethylamine 96 cc. distilled water and wiping excess solution from the plate with a doctor blade in the usual way. The above dye is a known green sensitizer. Sensitizers in aqueous solutions have a relatively slow drying rate which is an advantage in the present process since faster drying materials have to be printed rapidly to prevent drying out on the printing plate itself.

With the resultant halftone sensitive material contact printing from a continuous tone record through a green filter (Wratten #63) over a low intensity lamp (60 watt tungsten about 18" away) gives adequate exposure in 18 or so seconds depending on the density of the record being copied. For projection copying, correspondingly A red sensitizer which can be used instead of the above 7 7 green sensitizer (or along with it in the double screen case) and which is water soluble isz' -[(3-ethyl-2(3)-benzothiazolylide)butenylidene] 3 fl-sulforhodanine. 7

Our invention is not limited to the examples given but is of the scope of the appended claims. I

We claim:

1. A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with a halftone pattern of square elemental areas juxtaposed with no intervening areas, said square elemental areas having a ratio of green to blue sensitivity greater at the centers than at the corners, and having substantially uniform sensitivity to blue light throughout.

2. A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with a halft-onetpattern of square elemental areas juxtaposed with no intervening areas, said square elemental areas having a ratio of red to blue sensitivity greater at the centers than at the corners, and having substantially uniform sensitivity to blue light throughout.

3. A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with a halftone pattern of square elemental areas juxtaposed with no intervening areas, said square elemental areas having a ratio of blue sensitivity to sensitivity to longer wavelengths less at the centers than at the corners, and having substantially uniform sensitivity to blue light throughout.

4. A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with two halftone patterns of difierent fineness of screen and continuously varying spectral sensitivity across the layer which is substantially uniformly sensitive to blue throughout, has a maximum and minimum sensitivity to green respectively at the centers and corners of the dots of one pattern and a maximum and minimum sensitivity to red respectively at the centers and corners of the dots of the other pattern, each dot pattern being made up of square dots juxtaposed with no intervening areas.

5. The method of prescr'eeninga photosensitive sheet having a silver halide emulsion layer which is sensitive only to relatively short wavelengths which comprises printing thereon from a uniform halftone printing plate of contiguous dots a halftone pattern of optical sensitize! solution which sensitizes the silver halide to longer wavelengths without desensitizing any areas and drying the sheet. a

6. A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with a halftone pattern of square elemental areasjuxtaposed'with no intervening areas, said square elemental areas being substantially uniformly sensitive to blue light from the corners to the centers thereof and the centers being more sensitive than the corners to longer wavelength light, thesensitivity tosaid longer wavelength light varying substantially continuously from the centers to the corners. I 7

7. A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with a gamma greater than four and with a halftone pattern of square elemental. areas juxtaposed with no intervening areas, said square elemental areas being substantially'uniformly sensitive to blue light from the corners to'the centers thereof and thecenters being more sensitive than the corners to longer wavelength light, the sensitivity to said longer wavelength light varying substantially continuously from the centers to the corners.

8. A photographic material for continuous tone or halftone reproduction comprising a flat support and a photosensitive silver halide emulsion on'the support with a gamma between 1.5 and 4 and with a halftone pattern of square elemental areas juxtaposed with no intervening areas, said square elemental areasbeing substantiallyuniformly sensitive to blue light from the corners to the' centers thereof and the centers being more sensitive than the corners to longer wavelength light, the sensitivity to said longer wavelength light varying substantially continuously from the centers to the corners. 1

9. ,A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with a halftone pattern of square elemental areas juxtaposed with no intervening areas, said square elemental areas being substantially uniformly sensitive to blue light from the corners to the centers thereof and the centers thereof being more sensitive than the corners to green light, the sensitivity to green light varying substantially continuously from the centers to the corners.

10. A photographic halftone material comprising a flat support and a photosensitive silver halide emulsion layer on the support with a halftone pattern of square elemental areas juxtaposed with no intervening areas, said square elemental areas being substantially uniformly sensitive to blue light from the corners to the centersthereof and the centers thereof being more sensitive'than the core ners to red light, the sensitivity to red light varying substantially continuously from the centers to the corners.

11. A photographic halftone material'cornprising a flat' support and a photosensitive silver halide emulsion layer on the support with a halftone pattern of square elemental areas juxtaposed with no intervening areas, said square elemental areas beingsubstantially uniformly sensitive to blue light from the corners to the centers thereof and the centers being more sensitive than the, corners to longer wavelength light, the sensitivity to said longer wavelength light varying substantially continuously from substantial- 1y zero at the corners to a maximum at the centers.

References Cited in the file of this. patent UNITED STATES PATENTS France Mar. 22, 1948

Claims (1)

1. A PHOTOGRAPHIC HALFTONE MATERIAL COMPRISING A FLAT SUPPORT AND A PHOTOSENSITIVE SILVER HALIDE EMULSION LAYER ON THE SUPPORT WITH A HALFTONE PATTERN OF SQUARE ELEMENTAL AREAS JUXTAPOSED WITH NO INTERVENING AREAS, SAID SQUARE ELEMENTAL AREAS HAVING A RATIO OF GREEN TO BLUE SENSITIVITY GREATER AT THE CENTERS THAN AT THE CORNERS, AND HAVING SUBSTANTIALLY UNIFORM SENSITIVITY TO BLUE LIGHT THROUGHOUT.

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