|||||||||||||| s USOOS28354A United States Patent (19) 11 Patent Number: 5,283,154 Stein (45) Date of Patent: Feb. 1, 1994 (54) RANDOM SCREEN WATERLESS PRINTING 56) References Cited PROCESS U.S. PATENT DOCUMENTS 75 Inventor: Richard E. Stein, Denver, Colo. 4,037,533 7/1977 Rapoport et al. ................... 430/30 4,259,905 4/1981 Abiko et al. ........................ 10/467 73) Assignee: National Printing and Packaging Company, Denver, Colo. Primary Examiner-John Kight, III Assistant Examiner-John M. Cooney, Jr. 21) Appl. No.: 861,226 Attorney, Agent, or Firm-Beaton & Swanson 57 ABSTRACT 22 Filed: Apr. 1, 1992 An improved method of making lithographic reproduc tions is disclosed. The method involves several im Related U.S. Application Data provements over prior processes, including (a) the com (63) continuation-in-part of ser. No. 602,676, Oct. 24, 1990, bination of random plates and a waterless, dry press for abandoned. halftone, duotone, tritone and four color separation halftone printing, and (b) the use, in duotone, tritone 51) Int. Cl. ................................................ G03F 7/00 and four color separation halftone printing of random 52 U.S.C. .................................... 430/301; 430/303; plates exclusively for all the plates involved in the mul 101/456; 101/467; 101/450.1; 101/469 ti-step printing process. 58) Field of Search ................ 430/301, 303; 101/456, 101/467, 450.1, 469 10 Claims, No Drawings 5,283,154 1. 2 Both line art reproductions and continuous tone art RANDOM SCREEN WATERLESS PRINTING reproductions may be multi-colored, by the superimpo PROCESS sition of additional monotone colors over the substrate in the case of multi-colored line art, and by the superim This is a continuation-in-part of copending applica position of additional halftone colors over the substrate tion Ser. No. 07/602,676 filed on Oct. 24, 1990, now in the case of multi-colored continuous tone art. Be abandoned. cause both line art and continuous tone art may, there fore, be single-colored or multicolored, it should be BACKGROUND OF THE INVENTION understood that the two styles are not distinguished This invention pertains to the photolithographic re O from one another by the number of colors rendered, but production of original copy, and more particularly to by the presence or absence of graduated tone values in processes including (a) the new combination of a half the colors, whether one color or many. As used in this tone, random screen printing method and a waterless application, "monotone' and "halftone' will always printing press, and also including (b) an improved refer to line art and continuous tone art, respectively, method of enhanced halftone printing using random 15 distinguishing them by the characteristic presence or screens for all plates. absence of graduated tone values in the original copy. The photolithographic reproduction process of this As used in this application, "monochrome' and "multi invention is an improvement in offset printing. To better color' will refer to single color and more than a single understand the invention, the following description will color, respectively, applied over a substrate, and either 20 term may pertain to monotone or halftone originals. first discuss the offset printing of original copy using Other terms that will be introduced later in this applica printing plates formed from conventional halftone grid tion, such such as duotone, tritone, and the like, will screens and using conventional water and ink emulsion have their own meanings as set forth in the context in press processes for effecting the printing steps. The which the terms are introduced. description will then discuss typical variations to con 25 Lithographic reproduction of original line art or con ventional offset printing, including the use of random tinuous tone art involves a smooth, flat printing plate. pattern screens to replace one or more of the conven The printing plate containing the image of the original tional halftone grid screens in forming the printing copy to be reproduced is fixed to a cylinder. When the plates, and including the use of waterless press pro cylinder runs in a typical ink and water emulsion print cesses to replace the water and ink emulsions of conven 30 ing press, the rotating plate is wetted so that water tional printing presses in effecting the printing steps. adheres to the plate in the non-imaged areas, and then Conventional printing of original copy involves the inked with an oil-based ink so that the ink adheres to the use of a printing plate which contains an image of the plate only in the imaged areas. Because oil and water do original copy to be reproduced. The original copy may not mix, this differentiates the imaged areas from the be line art or continuous tone art, and may, in either 35 non-imaged areas. In letterpress and other direct print case, be single colored (monochrome) or multi-colored. ing processes, the printing plate works directly on a Monochrome line art, which includes most typogra substrate which passes beneath the plate. In offset and phy, is original copy having only a base color of con other indirect printing processes, the printing plate does stant tone value applied over a substrate. The substrate not contact the substrate directly, but rather works may be paper, but can also include any suitable surface through a blanket. The blanket is a mat of suitable mate of natural or synthetic material, such as metal, fabric, rial, rubber for example, fixed to a cylinder which picks wood or plastics, including polystyrene, polyester, up the inked image from the printing plate and which, in polypropylene and sheet vinyl. The base color of con turn, transfer the inked image to the substrate. stant tone value is referred to as a monotone. Because of In photolithographic printing, the image of the origi the characteristic monotone which appears over the 45 nal copy is transferred to the printing plate by photo substrate, line art itself may be referred to generally as graphic processes. Typical steps include forming a pho monotone. tographic transparency of the original copy, exposing a Monochrome continuous tone art, which includes photosensitive plate to the photographic transparency, single-color photographs, is original copy having a and then developing the photosensitive plate. The pho single base color and also having gradations of tone 50 tosensitive plate, when developed, is used as the print value in that base color applied over a substrate. The ing plate. By well known techniques and combinations gradations of tone value may be referred to as shades of process camera work and contact exposures, it is occupying a scale of more or less continuous tones from possible to create photographic positive or negative, light to dark in the range between clear, or no color right-reading or wrong-reading copy (wrong-reading value, and full, or complete color value. Any individual 55 copy is related to right-reading copy as a mirror image shade is referred to as a halftone of the color involved, is to an original image) in order to form appropriately and the color itself is also sometimes loosely referred to oriented printing plates. as a halftone. Where the color involved is black, its By way of example, and to illustrate one method of gradations are shades of gray, the shades of gray are forming and using a "negative working' offset printing halftones between white (clear) and black (full), and the plate: (i) a photographic negative right-reading trans scale of tone values comprising all of the halftones may parency of the original image, when exposed to a photo be encompassed on a Grey Scale in common use. By sensitive plate, transfers its opposite, (ii) a photographic common usage, halftones of colors other than black are positive right-reading image of the original copy, to the still referred to as "gray' tones of the non-black color. printing plate, which in turn transfers, (iii) a positive Because of the characteristic halftone or halftone range 65 wrong-reading image to the blanket, which reproduces in the base color which appears over the substrate, the desired result, (iv) a positive right-reading image, on continuous tone art itself may be referred to generally as the substrate. While it is common in offset printing to halftone. use negative working plates, so called because they are 5,283,154 3 4 formed from photographic negatives, it is also possible, ing each overprint to be a separate step, basic multi-col using well known methods, to use positive working ored printing can be considered to be multi-step print plates formed from photographic positive transparen ing, involving three or four steps depending on whether CCS. three of four halftone plates are used. Where the original copy is monotone, there is no 5 The halftone plates used for color work are formed need for generating a scaled range of intermediate tone by the use of color filters to create color photographic values on the printing plate to achieve adequate repro separations of the original, or are generated on a scan ductions of the original. But where the original copy is ner which produces the same effect electronically as continuous tone, a means has been devised, using half can be produced by the photomechanical process. From tone screens, to generate halftones on the printing O the original copy, which might be a multicolored pho plates. Halftone printing plates are typically produced tograph or a painting, a separate continuous tone color by exposing a previously screened transparency of the separation is made for each of the colors cyan, magenta, original copy to the plate. The conventional halftone yellow and black. A continuous tone color separation is screen has a regular grid pattern defined by intersecting made by exposing the original copy to a photographic lines.