DETAILED DESCRIPTION OF THE
imperceptible thickness in relation to the thicknesses of graphic object pattern typically consists of a plastic the support media and the graphic object patterns. sheet with a photographic emulsion on one face.
There is no FIG. 7 in the application. In FIG. 2, a coating layer of water-soluble photosen
sitive stencil material of type A 20 is formed on at least 5 a portion of a support medium 21. The support medium 21 may be any suitable sheet of paper, card, plastic, Reference will now be made in detail to the presently metal or the like which will support the photosensitive preferred embodiments of the invention, examples of stencil material 20 and the final image-defining color which are illustrated in the accompanying drawings. medium 25.
For the sake of clarity, it is desirable to make a dis- 10 Preferred materials for the type A water-soluble photinction between the definition of a "photostencil", as tosensitive stencil material 20 includes well-known phodefined herein, and a "photoresist," as commonly de- tohardenable materials with ethylenically unsaturated fined. A "photoresist" as used in the manufacture of a groups in the molecule. The molecular weight of these letterpress printing plate is defined as a photosensitive materials is increased by exposure to actinic radiation, coating material which, when coated on an etchable 15 Also useful are the various combinations of an organic support, exposed imagewise through a photomask to colloid or synthetic resin with a diazonium compound actinic light and treated in a development step, retains that are described in Kosar, Light Sensitive Systems, an imagewise protective layer on the support represent- Chapter 7 (Wiley, 1965).
ing the exposed areas. This imagewise protective layer An unmodified Type A photoresist insolubilized by is resistant to the dissolving action of an etchant. The 20 actinic light may also be suitable for use as photosensiphotoresist coated areas thus become the images or tive stencil material if the length of exposure to actinic printing areas when the printing plate thus produced is radiation is reduced so that the exposed areas, although inked and the ink transferred to the support. rendered insoluble, are not so insoluble that they cannot
In the present invention, however, the photosensitive subsequently be removed, coating material will be designated as "photostencil" 25 To achieve easily removable photostencils, however, and defined as a photosensitive coating material which, type A photoresist formulas can be modified by adding when coated on at least a portion of a support medium, radiation-insensitive materials such as methyl cellulose, exposed imagewise through a graphic object pattern polyamides, or polyvinylpyrrolidones. These com(photomask) to actinic light and treated in a develop- pounds reduce the resistance to removal during the ment step with water or an aqueous solution, produces 30 stripping step of the photosensitive stencil material ex
(1) an image on the support representing either the posed to the actinic radiation. Further, casein-dichroexposed or the masked areas, depending on the type of mate Type A photoresist, in which ammonium carbonphotostencil material used, as explained hereafter, and ate is used in place of ammonium hydroxide to provide
(2) areas having no photostencil material which are the necessary alkalinity to dissolve the casein, is desirdefined by the image. A color medium is subsequently 35 able because the exposed regions of this material puff up applied to the image and the defined areas. A stripping in the stripping solution, thus facilitating removal of the procedure thereafter removes the photostencil image photostencil.
along with the overlying color layer. The color image Aqueous pigment dispersions are also desirable addiremains on the support as a monolayer in those defined tives to either Type A photosensitive stencil material or areas not protected by the photostencil material after 40 to Type A photoresist materials. The pigments provide the development step. a visual aid for inspecting the stencil after the water or
There are at least two basic types of photosensitive aqueous solution development step and also aid penetramaterials useful as photostencils in the present inven- tion of the photosensitive stencil material layer by the tion. Type A is a water-soluble material which reacts to water or aqueous solution during the stripping step, light, particularly actinic light, by becoming insoluble 45 Another desirable additive is at least one dyestuff seto water in the exposed areas. lected from the group consisting of amino fluorines,
Type A materials, as used in photoetching processes, hydroxy fluorines and hydroxy fluorones. for example, are described as negative-working photo- Surfactants such as the alkyl sulfates or the polar resists, i.e., a negative photomask is required to form a ethoxylated alkyl phenols are also advantageous as adpositive image. Type A materials as used in the present 50 ditives to the photosensitive stencil material because process, however, are described as positive-working they assist in achieving rapid water penetration and photostencils, i.e., a positive photomask is required to evenness of flow when the material is applied as a coatform a positive image. ing.
Type B photosensitive material is water-insoluble but As further shown in FIG. 2, graphic object pattern 23 reacts to actinic light by becoming soluble to water or 55 is laid emulsion side down on the stencil coating layer aqueous solutions in the exposed areas. Type B materi- 20. The stencil layer 20 on the support 21 is exposed als as used in photoetching processes, for example, are imagewise to actinic rays 22 passing through the transdescribed as positive-working photoresists, i.e, a posi- parent areas of graphic object pattern 23 to photographtive photomask is required to form a positive image. ically produce an imagewise pattern of water-insoluble
Type B materials as used in the present process, how- 60 and water soluble regions on the support medium 21. ever, are described as negative-working photostencils, FIG. 3 represents the step of developing the exposed i.e., a negative photomask is required to form a positive stencil material by washing out the unexposed and thus color image. still water-soluble regions of the stencil material with
FIG. 1 shows a graphic object pattern or photomask water or an aqueous solution and leaving the exposed, 23 which includes a clear area defining an opaque emul- 65 water-insoluble material regions 20 on the support mesion surface or mask represented by the character A. dium 21. The regions 20 form a stencil image which also Although the graphic object pattern 23 is representative defines areas 50 on the support medium 21 having no of any intermediate of which reproduction is desired, a stencil material.