Treatment of a printing plate with a dampening liquid
United States Patent 11 1 [111 3,877,372  
 Leeds 1 1 Apr. 15, 1975 [54] TREATMENT OF A PRINTING PLATE 3,398,002 8/ 1968 Bondurant et al. 106/2 WITH A DAMPENING LIQUID 3,625,715 12/1971 Nasca l06/2 [76] Inventor: Kenneth W. Leeds, 2719 Elm Dr.,  
 N rth Bell r NY, 11710 Primary Examiner-Theodore Morris [22] Filed: Dec. 3, 1973 [21] Appl. No.: 421,442 [57] ABSTRACT A printing plate in lithographic offset or planographic [52] 101/ sgg f 9 0 printing is treated by application thereto of an aque- 511 Int. Cl. C09k 3/18; c091 3/00; B4lm 3/08 gf t&#39;r g &#39;gf 3 3 33333113,1 1 5113131 58 Field of Search 106/2 205 208- 101/451 y y e g y 101 ethylene glycol, 21 silicone-glycol copolymer and a defoamer. lsopropyl alcohol, which is contained in con- References Cited K212251181 dampening llqUldS, may be completely elimi- UNITED STATES PATENTS 3,354,824 1 l/l967 Griffith et al. 106/2 X 4 Claims, N0 Drawings TREATMENT OF A PRINTING PLATE WITH A DAMPENTNG LIQUID This invention relates to the application of dampening liquid to a printing plate in lithographic offset or planographic printing. More particularly, in the present invention a unique, advantageous dampening liquid is applied.  
  ln lithographic offset or planographic printing, the printing plate is chemically treated to provide a printing area and a nonprinting area, with the printing area, of course, being ink receptive and the nonprinting area being hydrophilic or water receptive. Pursuant to such treatment, a film of aqueous moistening or dampening liquid is applied to the surface of the plate, the liquid being retained by the hydrophilic area but repelled by the ink-receptive printing area, thus separating and isolating the nonprinting area from the ink which is applied to the printing area. As a result, only the image of the printing area is transferred to the blanket cylinder and onto the paper on which the image is printed.  
  To achieve successful printing by this method, it is necessary that the dampening liquid be applied to the surface of the printing plate in uniform and evenly distributed quantities and in regulated amounts to assure uniformly good quality reproduction of the printed image. To achieve such application of liquid, an arrangement of rollers is employed which transfers the dampening liquid onto the nonprinting areas of the cylinder.  
  For reasons which are well known in the lithographic art, the quantity of water which is applied is desirably kept at a minimum and only a sufficient amount is applied to form a minimum thickness of film on the nonprinting area to repel the ink and maintain that area ink free. Such regulation of the water or moistening liquid in correlation with the quantity of ink applied is commonly referred to as the ink-water balance, and proper control of this balance is essential to successful printing.  
  The reservoir of a dampening system, i.e., a mechanical system for the application of the dampening liquid or solution, is called a fountain. For that reason, the dampening solution is frequently called fountain solution&#34;. Fountain solutions usually contain in addition to water, a desensitizing gum such as gum arabic or Hydrogum (mesquite gum), an acid, usually phosphoric acid or an acid phosphate salt though sometimes gallic or tannic acid is used, ammonium bichromate and/or a nitrate salt such as ammonium nitrate, zinc nitrate or magnesium nitrate, and isopropyl alcohol. The constituents without the isopropyl alcohol may be referred to as fountain etch&#34; or gum and etch.&#34;  
  lsopropyl alcohol vapors are hazardous. Moreover, in times of petrochemical shortages, isopropyl alcohol may be in very short supply. In the present invention, isopropyl alcohol is eliminated as a necessary constituent of fountain or dampening solutions. While one may maintain isopropyl alcohol in the dampening solutions of the invention, no advantage is to be gained from so doing.  
  In the present invention, the isopropyl alcohol is replaced with a chemical system constituted of ethylene glycol monobutyl ether, at least one of hexylene glycol and ethylene glycol, a silicone-glycol copolymer and a defoamer. The silicone-glycol copolymer is preferably a polyglycolpolydimethylsiloxane copolymer, particularly 473 Fluid&#34; of the Chemical Products Division of Dow Corning Corporation, Midland, Mich., as described in its Bulletin 05-1853 of October, l967. The defoamer is preferably a silicone, particularly Antifoam l-l-lO Emulsion&#34; silicone emulsion defoamer of the Chemical Products Division of Dow Corning Corporation, as described in its Bulletin 04-071 of August, 1965.  
  Ethylene glycol monobutyl ether was selected for use because of its miscibility with water and because it is an effective coupler. Hexylene glycol was selected because of its coupling properties and because it causes the mixture to level well, producing a thin film of the material on the printing plate. Ethylene glycol can be used instead of hexylene glycol, for its humectant prop erties, i.e., keeping the plate damp. Dow Corning 473 Fluid was selected because of its solubility in water. The defoamer is utilized to break the foam which results from the blending operation and to prevent the formation of foam in the reservoir and the recirculating system of the dampening system. In the absence of defoamer, a foaming problem is particularly noticed in Dahlgren and Dahlgrentype dampening systems.  
  It is convenient to constitute the dampening solution additives of the invention as a two part system, with all the active constituents but the defoamer being contained in one of the formulations. For ease of identification, a dye may be incorporated in one of the formulations. For example, the two part system may be constituted as follows:  
  An exemplary fountain solution containing the additives of the invention is constituted of percent water, 2.5 percent fountain etch, 1.5 percent of formula A and &#39;1 percent of formula B, all by volume. A very typical conventional fountain etch contains 0.8 percent gum arabic, 0.1 percent phosphoric acid and 1.1 percent zinc nitrate. Two to four fluid ounces of formula A per gallon of fountain solution is typical.  
  While the defoamer prevents foam formation, the physicochemical action of the other active constituents of the fountain solution additive system of the invention, such as formula A, produce a thin, more uniform film of water across the dampening system and better wetting over the entire printing plate surface. Because of the thinner water film, pressmen can run with about 5 to 10 percent less water on the plate. By thus stabilizing ink-water balance, the additive system enables sharper printing, brighter colors and faster make-ready. The additive system also prevents stripping and the emulsification of ink. A few ounces of the additive system for each gallon of fountain&#39;solution is all that is necessary for optimum results. The additive system eliminates the need for isopropyl alcohol.  
  Throughout the history of offset printing, the function of the dampening system, the distribution of water to the printing plate, has been a troublesome variable requiring frequent adjustment. The total additive system of the invention enables uniform, minimum water flow to the plate and its use costs less than the typical automated dampening system. In fact, the additive system of the invention makes any conventional dampening system perform like a sophisticated automated system.  
  Additive adjustments will depend on the water hardness, pH, temperature and other press variables and can be made on the basis of routine trial and error.  
  A typical successful run involving the fountain solution additives of the invention is as follows:  
  In an uninterrupted production run of 92,000 sheets in two colors, front and back, on a 38 X 48 inches Harris lithographic offset press equipped with a Harris Microflow dampening system, the customary fountain solution used was 5 fluid ounces of the aforementioned fountain etch, 1.5 gallons of isopropyl alcohol and 3.5 gallons of water. (Fountain solutions are customarily prepared in approximately 5 gallon batches.) For comparison an identical run was carried out using a fountain solution containing the additives according to the invention constituted of 16 fluid ounces of the fountain etch, 9.6 fluid ounces of formula A, 6.4 fluid ounces of formula B and sufficient water to make 5 gallons. The additive system of the invention resulted in excellent print quality without any foam or other production problems and the use of considerably less, up to onethird less, ink, with the elimination of isopropyl alcohol.  
 . While the invention has been described by reference to specific embodiments thereof, it is to be understood that such description is intended to illustrate rather than limit the invention, the scope of which is to be determined by reference to the appended claims.  
 What is claimed is:  
  1. In the treatment of a printing plate in lithographic offset or planographic printing to maintain an ink receptive printing area and a hydrophilic nonprinting area on the plate in which treatment a film of an aqueous dampening liquid is applied to the surface of the plate, the liquid comprising a desensitizing gum, water and at least one member of the group consisting of phosphoric acid, acid phosphate salts, gallic acid and tannic acid and being retained by the hydrophilic nonprinting area but repelled by the ink receptive printing area, thus separating and isolating the non-printing area from the ink which is applied to the printing area, the improvement in which the dampening liquid contains an additive system comprising ethylene glycol monobutyl ether, at least one of hexylene glycol and ethylene glycol, a silicone-glycol copolymer and a silicone emulsion defoamer, the proportion of the additive system in the dampening liquid being sufficient to produce a thin, more uniform film of water and better wetting over the entire plate surface thereby permifting printing with less water on the plate and to prevent stripping and emulsification of ink and to effect sharper printing with brighter colors.  
  2. In the treatment of claim 1, in the improvement in which the silicone-glycol copolymer comprises a polyglycol-polydimethylsiloxane copolymer.  
  3. In the treatment of claim 1, in the improvement in which the dampening liquid is isopropyl alcohol-free.  
 4. In the treatment of claim 2, in the improvement in which the dampening liquid is isopropyl alcohol-free.