Color screens for diffusion transfer processes containing color formers

Abstract

Abstract avoid this defect or hazard. The net effect of this defect or hazard on the completed three color positive image is a deterioration in hue image quality known to the art as ''''cross talk'''' or ''''dye drop-off.'''' This defect or hazard in subtractive depthwise stacking is usually minimized by a number of secondary techniques outlined in numerous supporting patents (see for example U.S. pat. Nos. 3,230,082; 3,265,498; 3,069,263; 3,208,991; etc.) which may be classified in their collective sense as '''' Cross Talk Technology.'''' A subtractive lateral stacking mode in which the color elements yield color or color forming streams which progress in a side-byside or lateral manner out of a two dimensional planar negative towards a receiving sheet or layer would obviate a reaction between any color or color forming stream and a photosensitive element not proper to its modulation and would not exhibit the defect or hazard known as ''''cross talk'''' or ''''dye drop-off'''' common to diffusion transfer systems based on subtractive depthwise stacking modes. Such lateral modes are thus the natural choice for proper use in color diffusion transfer photography. Such modes have previously been proposed for diffusion transfer color systems (see for example British Pat. No. 926,462) in the form known to the art as ''''mixed grain screens,'''' or ''''photosensitive screens.'''' In such approaches a two dimensional array is coated, printed, or formed in diverse ways in random or structured patterns as a mixture of a multitude of three classes of micro areas normal to the direction of exposure. The first class consists of silver halide grains sensitive to blue light only and accompanied by a yellow color precursor; the second class consists of silver halid grains sensitive to green light, accompanied by a magneta color precursor and a yellow filter dye; the third class consists of silver halide grains sensitive to red light, accompanied by a cyan color precursor and a yellow filter dye. The exposing actinic radiation is thus analyzed and registered in the three different areas of the photo sensitive screen containing color forming agents proper to its reproduction. In the development step the color precursor reacts with oxidized color developer to form an insoluble dye which remains in the screen; left over color former transfers to a receiving sheet to form a pre-color positive image which upon treatment yields a full color reproduction. Size, proportion, and location of the differential areas may be chosen such that the result duplicates the reproduction available from subtractive depthwise stacking modes. Area overlap upon diffusion removes the pattern of the original screen. This is an unsophisticated and direct approach to the problem of subtractive lateral stacking and amounts in principle to mere r A dual-nature screen process wherein a panchromatic emulsion is exposed through the screen, then brought into intimate contact with a receiving element with a fast acting color developer of pH 10.0 to 11.0 interposed. The color formers from the screen, modulated by the exposed panchromatic emulsion, diffuse to the receiving layer of the receiving element where they are converted to azomethine or indoaniline dyes. The receiving element may be of a nature wherein it is peeled off of the joined configuration for viewing or it may be of the type wherein the finished image may be viewed in the joined configuration. This invention relates to the making of positive color reproductions of faithful to the hue, saturation and density variations fo the original image using a novel stutractive lateral stacking mode. Additive lateral stacking modes are well known to the prior art (see for example U.S. Pat. Nos. 411,186; 471,187; 822,532; 877,351; 1,429,430; etc.) under the generic name of ''''Screen Plates'''' and represented the main stream of inventive effort for three color photography before their sudden eclipse following the introduction of practical tripacks to the marketplace. In these schemes, a so called ''''Screen'''' was interposed permanently between, on the one hand, a panchromatic emulsion and the screne to be imaged; and, on the other hand in the postreversal-development stage, between the resulting silver image and the observer. The screen thus served a dual purpose; that of color analysis in the imaging stage and color provider in the viewing stage. THE SCREEN WAS COMPOSED OF A MULTITUDE OF RED, GREEN, AND BLUE MICORFILTERS OF SUCH SIZE AND DISTRIBUTION LATERALLY IN A TWO DIMENSIONAL ARRAY AS TO GIVE A TOTAL IMPRESSION OF WHITE LIGHT TO THE EYE AT A GIVEN VIEWING DISTANCE AND PROJECTION MAGNIFICATION BELOW THE RESOLVING POWER OF THE RETINA; YET MAINTAINING THE ABILITY OF THE ADJACENT PANCHROMATIC EMULSION TO RESOLVE SUCH MINUTE AREAS BELOW THE THRESHOLD OF RETINAL RESOLUTION INTO THEIR DIFFERENTIAL COMPONENTS OF RED, GREEN, AND BLUE, ONLY, BY REGISTERING AS LATENT IMAGE RED LIGHT ONLY IN THOSE EMULSION GRAINS COVERED BY RED MICROFILTERS; BLUE LIGHT ONLY IN THOSE EMULSION GRAINS COVERED BY BLUE MIRCROFILTERS; AND GREEN LIGHT ONLY IN THOSE EMULSION GRAINS COVERED BY THE GREEN MICROFILTERS. It will become apparent to the careful reader that the selective blockage of light via reversal development of the panchromatic emulsion to yield a positive silver record of that imaged pattern, viewed through the still intact filter screen will be seen as a reverse analysis of the tricolor imaging and, under the conditions presented, appear as one color sensation to the eye, that color being the color of the original point in the object. Such principles are well known to those versed in the history of the art and are presented here to emphasize the differences between these early additive lateral stacking modes and our novel subtractive lateral stacking modes. The defects inherent in such additive lateral stacking modes are manifold and let to their quick replacement by subtractive depthwise stacking modes known bY the generic name as ''''tripacks.'''' For instance, screen systems prove practical for projection purposes only; they discard two thirds of the light in the projection beam and project dimly; further reproduction of the picture proves practically impossible since the new screen would require a point-to-point coincidence with the old screen to avoid moire patterns; since the screen remains for viewing one must accept the superimposition of the screen pattern on the picture, etc. The above gross defects are itemized because of an unfortunate accident of history. Subtractive as opposed to additive lateral stacking modes developed much later have used the nomenclature ''''screen'''' - ours included. Such ''''screens,'''' to be discussed later, are not to become confused with these old ''''screen systems'''' and have none of the defects itemized above, even though at some times in the process they bear what is only a superficial resemblance to these early screens. The tripack utilized reactions of the latent image bearing silver halide to form cyan, magneta, and yellow dye images in different red sensitized, green sensitized, and blue sensitive layers respectively (see for example U.S. Pat. Nos. 1,954,452; 2,010,459; English Pat. No. 481,501; etc.). The imaging, color providing multilayers were stacked, or coated vertically to the direction of imaging or viewing forming a depthwise arrangement of the color elements as opposed to the previous side-by-side or lateral arrangement of color elements in the additive scheme. The color forming reaction of latent images took place with immediately after imaging as in negative-positive systems, or after a second exposure or fogging following black and white development of the image registered latent image as in reversal development. These subtractive depthwise stacking packages obviated all of the above defects of the additive lateral stacking modes and provided the basis for so-called ''''conventional'''' color films to this day. Of course additive depthwise color modes never entered the picture since any two primary colors stacked depthwise for viewing yield black. Given the ease with which multilayer subtractive depthwise stacking modes are coated by modern techniques, and given the pleasing results they yield for conventional color photography, no serious efforts have been made to perfect the fourth permutation; namely subtractive lateral stacking modes. It is only with the advent of practical diffusion transfer color photography that the need for subtractive lateral stacking modes become apparent and indeed imperative. Aside from early attempts to utilize the old additive lateral stacking modes described above in a color transfer scheme (see for example U.S. Pat. No. 2,707,150) via the transfer both of positive silver and additive screen to a receiving sheet, the main thrust of diffusion transfer schemes have used the subtractive depthwise stacking modes of more conventional color photography (see for example U.S. Pat. No. 2,983,606). In most of these schemes a dye developer is coated immediately behind a photosensitive layer sensitive to that due of light complementary to the hue of the dye developer. The dye developer solubilizes during processing and passes through the image bearing layer on its way to a receiving sheet or layer. While in the image bearing layer the dye stream is modulated imagewise by reaction between dye developer and latent image to form nondiffusible deposits. The dye stream now continues towards the receiving sheet now bearing a positive dye image record of that primary color. Three such pairs of photosensitive layers and their companion dye developer layers are coated or stacked depthwise in a complete package to yield three color reproductions of the original image on the receiving sheet or layer which has a mordanting ability to hold each of the three modulated dye streaMs which reach it. Analogous schemes involving color formers have also been disclosed (see for example U.S. Pat. No. 3,359,104). The careful observer will note that subtractive depthwise stacking modes while eminently suitable for more conventional three color photography are not directly suitable without extensive modification and painstaking effort for diffusion transfer three color photography. By the very nature of depthwise stacking of color elements, the already properly modulated dye or color former stream of at least some color element must pass through the modulating photosensitive layer of another, noncomplementary, improper color and be subject to the defect or hazard of further, undesirable, improper modulation by another image bearing layer interdicting its path to the receiving sheet or layer; there being no way to stack depthwise elements in three color photography to

Inventors

• 👤 Burton Harvey Waxman
• 👤 Robert Thomas Shannahan
• 👤 Felix Viro

Bibliographic Details