US 3844994 A
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United States Patent 3,844,994 LITHOGRAPHIC INK COMPRISING POLYSTYRENE SULFONATE Bheema R. Vijayentlran, Bridgeport, Conn., assignor to Pitney-Bowes, Inc., Stamford, Conn. No Drawing. Filed Mar. 12, 1973, Ser. No. 340,329 Int. Cl. C09d 11/02, 11/10 U.S. Cl. 260-22 R 9 Claims ABSTRACT OF THE DISCLOSURE A novel ink formulation useful in lithographic printing processes which eliminates the necessity to dampen the lithographic master between printing cycles is disclosed. The novel ink formulation of this invention is a stable emulsion comprising an oleophilic phase and a hydrophilic phase, comprising one or more polyhydric alcohols, a surfactant and polystyrene sulfonate. The specific polymeric surfactants are: polyoxyethylene alcohols, polyoxyethylene esters, polymeric condensation products of ethylene oxide-propylene oxide, the reaction product of ethylene oxide and propylene oxide with ethylene diamine, and polyvinyl pyrrolidone.
BACKGROUND OF THE INVENTION This invention relates to a novel ink formulation useful in planographic and lithographic printing processes. More particularly, this invention relates to a novel ink formulation useful in connection with lithographic printing processes, whereby the use thereof eliminates the need for separate and repeated dampening of the lithographic master plate between printing of copies.
Basically, a lithographic master plate is prepared by producing on the surface thereof ink receptive and water receptive areas, the latter being ink repellent areas. When the plate is contacted with an aqueous liquid, the aqueous liquid is attracted to the water receptive areas and then when the ink is applied the ink is selectively attracted by the ink receptive surface of the plate and rejected by the ink repellent areas. In the case of indirect or offset lithography, the plate bearing the ink in only those selective areas, is contacted with a printing blanket. The inked image is transferred to the blanket which in turn transfers the image to the sheet of paper or surface upon which the image is desired. However, in case of direct lithography, the ink bearing plate is contacted directly with the sheet of paper or other printing surface.
The various processes presently in use for preparing printing plates range from lithographic processes, where a design is made on the surface of the material with a water-repellent, ink receptive material such as crayon or lithographic chalk. Photographic processes may also be used wherein light sensitive bi-chrornated gums or light sensitive diazo materials are exposed to an image pattern and the exposed materials are then treated to obtain ink receptive areas. Lithography plates may also be prepared by electrostatic copying methods. Any of these plates may be used with the printing ink of this invention.
In situations where many copies are to be made from the original lithographic plate, flexible plates are wrapped around cylinders and an aqueous solution and ink from separate fountains are supplied by rollers. In a typical printing operation, the cylinder bearing the lithographic plate is first contacted with a roller wetted by a water or other suitable aqueous solution. The aqueous solution is absorbed by the hydrophilic surfaces but repelled by ink receptive or oleophilic surfaces. The plate is then contacted with a roller wetted with an oil base ink and the ink is adsorbed by the ink receptive surfaces and rejected by the ink repellent surfaces which have been rendered Patented Oct. 29, 1974 oil repellent by the initial treatment with the aqueous solution. The plate is then contacted with the printing blanket to which the ink is transferred, and the blanket in turn contacts the sheet of paper upon which the design is to be printed. The ink is transferred from the blanket to the sheet and the entire process is repeated to obtain the individual sheets bearing the design. This process requires the sequential application of Water and ink each time a print is made, and this repeated operation decreases the useful life of the plate. Troubles are also encountered through partial comingling or emulsification of the oil and water on the plate.
In addition to the foregoing, another problem is faced in the case where the lithographic printing process is conducted automatically in the absence of human supervision. It is very difficult to control the water supply which is applied to the rollers to prevent print offset. Without uniform water application there occurs background print offset in the case of insufficient water application, or weak print quality in the case of a surplus of water application.
One of the proposed methods for overcoming some of the defects of the described process has been the use of water-in-oil emulsion inks. However, the emulsion inks heretofore suggested for use possessed drawbacks which have not made their use completely acceptable. Some of the inks previously proposed did not have the capacity to remain in an emulsive state, that is, these inks have a tendency to demulsify or break in the ink fountain or during storage. Others may not provide satisfactory prints, particularly where a great number of copies are to be produced. In order to be effective for lithographic printing the aqueous phase dispersed in the oily printing ink must not significantly change those characteristics of the ink which are requisite to satisfactory printing. When an ink emulsion demulsifies in the ink fountain or does not properly separate or break upon application to the printing surface, the printed image is dull, less intense, and spotted or stippled. The non-image area is sometimes toned or discolored.
Among the methods and/or formulations heretofore suggested for use in overcoming the problems associated with the water-in-oil emulsion inks are those disclosed in U.S. Pat. 3,615,750 which discloses a relatively anhydrous polyhydric alcohol-in-oil emulsion ink which can be employed in lithographic printing processes without repeated applications of water to the lithographic master plate before each printing. However, the ink formulations disclosed in U.S. Pat. 3,615,750 have been found to be relatively unstable and very sensitive to heat. As a result, these prior art ink formulations required curing or aging for from about seven to thirty days to obtain equilibration before they could be successfully employed. In addition, these prior art formulations have been found to suffer from a further disadvantage. It often occurs that after repeated use of a single lithographic master plate with the prior art ink formulations, it may be necessary for one reason or another to stop the printing process for an extended period of time, for example, for an hour or more for repairs or for some other reason. Upon restarting the printing process after this prolonged stand down time, it has been found that the master plate and/ or the internal phase of the ink formulation on the rollers has dried out and that the prior art ink formulations cause ink offset to occur, i.e., ink is picked up by the previously ink repellent areas of the master plate and is transferred to the paper on which the image is to be printed. This offset continues until the master plate is redampened and results in poor quality reproductions which must be discarded. Accordingly, it is an object of the invention to provide lithographic ink formulations which are stable over a substantial period of time.
It is a further object of the invention to provide lithographic ink formulations of the above character which require less curing or aging time than do prior art formulations.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
SUMMARY OF THE INVENTION I have now discovered a new and novel ink formulation suitable for use in lithographic printing processes which obviates the disadvantages experienced with the prior art formulations. I have found new ink formulations which eliminate the necessity for separate and repeated dampening of the lithographic master plate between copies. In addition, the ink formulations of this invention are extremely stable and may be employed after be ing aged or cured for as little as four hours. Furthermore, even after stand down times in excess of six hours, it has been found that the ink formulations of this invention may be employed without the necessity of redampening the lithographic master plate and has greatly reduced ink ofiset problems.
The novel ink formulations of this invention comprise a stable and persistent emulsion of two dissimilar phases; i.e., an oleophilic phase and a hydrophilic phase. These two dissimilar phases are held in a stable emulsion form by the employment of a polymeric surfactant and a small but effective amount of polystyrene sulfonate. The stability of the resultant emulsions of the instant invention is such that the emulsion is storably stable even over extended periods of time while at the same time is capable of being broken by the operation of the press rollers by which they are applied to the master plate during the lithographic printing process.
The oleophilic phase of the ink formulations of this invention may be comprised of various materials which are commonly employed in inks useful in lithographic printing processes, and includes such material as pigments, resins, oils, varnishes, gels, waxes, drying agents such as metal soaps, anti-oxidants, and other like materials as are well known to the skilled worker to be useful for such purposes.
The hydrophilic phase of the ink formulations of this invention are preferably comprised of such hydrophilic substances as one or more polyhydric alcohols in combination with a polymeric surfactants and polystyrene sulfonate to impart stable characteristics to the ink formulations. The polyhydric alcohols which may be satisfactorily employed either singly or in combination, include glycerine, ethylene glycol, glycerol, propylene glycol, sorbitol, mannitol and the like. In addition, in the practice of this invention, there may be added to the polyhydric alcohol many other hydrophilic additives such as an alkanol, for example methanol or ethanol, and/or water. Although the formulations of this invention may be anhydrous,it has been found that satisfactory results are obtained even when about up to 20% by weight of water or up to by weight of an alkanol is incorporated in the polyhydric alcohol fraction.
The classes of surfactants are Polyoxyethylene esters of fatty acids; Polyoxyethylene alcohols, polymeric Poly- 01s and Polyvinyl Pyrrolidone, each having specific characteristics as more fully set forth below.
The preferred range for the surfactants is from about 1 to 10 percent of the hydrophilic phase of the ink formulation and preferably from about 2 to about 7.5 percent by weight. A polystyrene sulfonate is employed in a small but effective amount as a stabilizer. For those formulations set forth in Examples I and II below it has been found that from about .05 to about 1 percent by weight of the hydrophilic phase of the ink formulation, and preferably from about .1 to about .5 percent by weight of the hydrophilic phase may be used.
4 DETAILED DESCRIPTION OF THE INVENTION The lithographic ink of the invention is made by emulsification of the hydrophilic and oleophilic phases by any known manner of creating emulsions. The hydrophilic phase of the ink should comprise from about 15 to about 60 parts with the oleophilic phase comprising from about 85 to about 40 parts of the ink formulation.
The polymeric surfactants which are preferred are as follows:
(1) Polyoxyethylene alcohols of the formula wherein n is preferably 2.
An example of such a surfactant is BRII 92 which is commercially available from Atlas Chemical Co. a division of ICI America, Inc.
(2) Polyoxyethylene esters of saturated fatty acid of the formula R-COO(CH CH O),,CH OH wherein n is greater than 50.
An example of such a surfactant which is commercially available is MYRJ 59 from Atlas Chemical Co.
(3) Polymeric condensation products of Ethylene Oxide-Propylene Oxide having a molecular weight of from 1,000 to 5,000 and preferaby less than 2,000 with the Hydrophilic Ethylene Oxide units comprising less than 50 percent of the polymer.
Examples of commercially available polymeric surfactants are Pluronic L-35, Pluronic 10-R5 and Pluronic P- from BASF Wyandotte Corp.
(4) Reaction product of Ethylene Oxide and Propylene Oxide with Ethylene Diamine and having a molecular weight of around 4,000 with the hydrophilic polyoxyethylene unit making up about 10 percent of the polymer.
Examples of such commercially available surfactants are Tetronic 701 and Tetronic 901 from BASF Wyandotte Corp.
(5) Polyvinyl Pyrrolidone having a molecular weight of less than 200,000. Examples of commercially available polyvinyl Pyrrolidone are made by GAF Corporation under the designation PVP-K-60 and PVP-K-30. Other sources for the above surfactants may also be used within the scope of the invention.
Examples of commercially available polystyrene sulfonate made by National Starch and Chemical Corp. and sold under the trademark Versa-TL, as shown in the following examples, Versa-TL 700, Versa-TL 500 and Versa-TL 70 may be used. These polystyrene sulfonates have a molecular weight of 6 to 8 million, 800,000 and 80,000 respectively.
The invention may be further illustrated by the following examples:
EXAMPLE I A. The oleophilic phase of the ink formulation of the instant invention may be prepared as follows:
The following materials in the requisite amounts are All of the above materials except for the carbon black pigment are charged into a change can mixer, and are mixed until uniform consistency is obtained. The carbon black is then added slowly with constant stirring. The resultant mixture is then dispersed in a 3 roll mill until the particle size thereof is reduced to less than microns as determined by a Hegmans gauge. The resultant mixture is then employed as the oleophilic phase in thepreparation of the various ink formulations of the instant invention.
B. The hydrophilic phase 'of the ink formulation of the instant invention may be prepared as follows:
The following materials in the requisite amounts are employed:
Formulation number Amount gram Material Ethylene glycol MYRJ 59 (Atlas Chemical Co.)
BEN 92 (Atlas Chemical Co.)
Verse-TL 500 (National Starch and Chemical 00.).
Total mixture is then cooled and tested as a lithographic ink' after two hours.
EXAMPLE II The procedure set forth in Example I is followed except that the following hydrophilic compositions are substituted for the hydrophilic composition set forth in Example I, Part B.
Formulation number Material Ethylene glycol.
Ethylene glycol Pluronic L- (BASF Wyandotte Corp.). Tetronic 701 (BASF Wyandotte Corp.) Versa-TL 70 Ethylene glycol PVP K-30 (GAF Corp.) Tetronic 701 Versa TL 70 r e em Pa s r. 010. 0 :00 O
Verse-TL 700 Glyoeri n A P Verse-TL 700 The ink formulations prepared in accordance with the procedure set forth in Examples I and II above, were tested and evaluated. The testing was done on a lithographic press employing Zinc Oxide coated paper to make lithographic master plates by means of an electrostatic copying process. The lithographic master plate is etched and placed on the master cylinder of the press and prints were made employing the various ink formulations without any water unit in the press to dampen the master plate between printings. The print quality, clean background in the non-imaged areas and ease of ink control in a long run are some of the factors considered in evaluating the ink formulations. The results obtained are tabulated in Table I below: i
TAB LE I No. of acceptable copies Aging period (hours) Formulation number teammates-1o Formulation No. 2 did not contain polystyrene sulfonate and dried on the press in 3-4 hours. All of the other formulations containing polystyrene sulfonate were usable for more than 6 hours.
EXAMPLE III The same procedure as set forth in Example 1 was followed except that a hydrophilic composition according to the prior art was used instead of the composition of Example I, part B as follows:
Grams Ethylene Glycol 20.0 Glycerine 15.0 Atlas G-1300 (Atlas Chemical Co.) 1.8 Arlacel 186-A (Atlas Chemical Co.) 0.2
TABLE II Aging Period (Hours): No. of Acceptable Copies 17 65 41 .As will be noted, less than acceptable copies could be made and even with extended aging of these prior art ink formulations there was no substantial increase in the number of acceptable copies produced. Thus the ink formulations of the invention provide a substantial number of lithographic copies with less aging and more ink stability.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above compositions and formulations without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.
What is claimed is:
1. A lithographic ink formulation comprising an oleophilic and a hydrophilic phase and further comprising A. a small but effective amount of at least one polymeric surfactant taken from the group consisting of (1) Polyoxyethylene alcohols of the formula R--CO(CH CH O),,-H wherein n is 2; (2) Polyoxyethylene esters of saturated fatty acids of the formula R-COO (CH CH O),,CH OH; (3) Polymeric polyol condensation products of Ethylene Oxide-Propylene Oxide having a molecular weight of from 1,000 to 5,000 and preferably less than 2,000 with the hydrophilic Eth- .ylene Oxide units comprising less than 50, per-. cent of the polymer; V 1 v (4)'.The polymeric polyol reaction .product of Ethylene Oxide and Propylene Oxide with Ethylene Diamine and having a molecular weight of about 4,000, with the hydrophilic polyoxyethylene unit making up about percent of the polymer; and
(5) Polyvinyl Pyrrolidone having a molecular Weight of less than 200,000; and
B. a small but effective amount of a polystyrene sulfonate.
2. The ink formulation claimed in claim 1 wherein said oleophilic phase comprises from about 40 to about 85 parts by weight of the ink and said hydrophilic pha'se comprises from about to about 60 parts by weight of the ink and said surfactant comprises from about 1 to 10 percent of the hydrophilic phase by weight.
3. The ink formulation claimed in claim 2 wherein said surfactant comprises from about 2 to about 7.5 percent by weight of said hydrophilic phase.
4. The ink formulation claimed in claim 1 wherein said polystyrene sulfonate comprises from about .05 to 1.0 percent by Weight of said hydrophilic phase.
5. The ink formulation claimed in claim 1 wherein said polystyrene sulfonate comprises from about .1 to about .5 percent by weight of said hydrophilic phase.
6. A lithographic ink formulation comprising an oleophilic phase, a hydrophilic phase, and a polymeric surfactant taken from the group consisting of at least one of A. polyoxyethylene esters of fatty acids;
B. polyoxyethylene alcohols;
C. polymeric polyol condensation products of ethylene oxide-propylene oxide;
D. a polymeric polyol reaction product of ethylene oxide and propylene oxide with ethylene diamine;
E. polyvinyl pyrrolidone; and a small but effective amount of polystyrene sulfonate.
7. The ink formulation claimed in claim 6 wherein said polystyrene sulfonate comprises from about .05 to 1.0 percent by weight of said hydrophilic phase.
V The,,ink .-for.mulationclaimed in claim 6 wherein said polystyren sulfonate' comprises from about. .1 to. about -5 p s a- -yw i sht ff Said. ro l phase ,9. Theink formulationclaimed in claim 6 wherein said polymeric surfactant is taken from the group consisting of, g
A. Polyoxyethylene alcohols of the formula R'CO(CH 'CH O') -'H wherein n is 2;
B. Polyoxyethylene esters of saturated fatty acids of the formula R- COO(CH CH O),,CH 0H wherein n is greater than C. Polymeric polyol condensation products of Ethylene -Oxide-Propoylene Oxide having a molecular Weight of from 1,000 to 5,000 and preferably less than 2,000 with the hydrophilic Ethylene Oxide units comprising less than 50 perecnt of the polymer;
D. the polymeric polyol reaction product of Ethylene Oxide and Propylene Oxide with Ethylene Diamine and having a molecular weight of about 4,000, with the hydrophilic polyoxyethylene unit making up about 10 percent of the polymer; and
-E. Polyvinyl Pyrrolidone having a molecular weight of less than 200,000;
and comprises from about 1 percent to about 10 percent of said hydrophilic phase.
References Cited UNITED STATES PATENTS 2,640,782 6/1953 Bloch et al. 106-28 2,794,747 6/1957 Bloch 106-28 3,615,750 10/1971- Blair 106-27 3,615,791 10/1971 Thomas et al. 106170 3,685,446 8/1972 Walles et al. 101-453 RONALD W. GRIFFIN, Primary Examiner US. Cl. X.R.
10l--451, 455, 465, 466; 106-40, 27, 28; 260-29.2 R, 29.6 R, 32.2, Dig. 38
- UNITED STATES PATENT OFFI( :E CERTIFICATE OF CORRECTION Patent No. q gL Lqqu Dated October 29, 197 1 lnv n fl Bheema R. Vijayendran It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:
Column 5, line ll, under the column heading "Formulation number" insert --2-.
Claim 1, column 6, line 69, change"R-CO(CH CH O) -H" to RCO(CH CH O) -H;
a line 71, after R COO(CH CH2O)nCH2OH insert --wherein n is greater than 50--;
Signed and sealed this 4th day of March 1975.
- C. MARSHALL DANN RUTH C. ASON Commissioner: of Patents Arresting Officer and Trademarks FORM po'mso (10569) USCOMM-DC 60376-P69 a ".5. GOVERNMENT PRINTING OFFICE 1 I!" 0-36-334.