US 3628454 A
Description (OCR text may contain errors)
United States Patent Inventor David H. Eberly, Jr.
Fairfield, Conn. Appl. No. 842,252 Filed July 16, 1969 Patented Dec. 21, 1971 Assignee United States Banknote Corporation New York, N.Y.
OFFSET MISTER AIR DIE 16 Claims, 4 Drawing Figs.
US. Cl 101/147, 101/451 lnt.Cl B411 25/00 Field ofSearch l0l/l47, 148, 451
References Cited UNITED STATES PATENTS 1,065 10/1888 Osborne 101/147 7,578 11/1899 Hett 101/148 2,815 5/1935 Harrold 101/147X 3,995 6/1936 Goedike 101/148 X fi'flfaflflfl '7 fl Asp/Mme Primary Examiner-Clyde l. Coughenour AttorneyCushman, Darby & Cushman ABSTRACT: A method and apparatus for transferring moisture to a printing cylinder for use in lithographic and preferably offset lithographic printing. The difficulty of controlling the amount and distribution of water applied to the cylinder is substantially resolved as described below by first impinging on the rotating cylinder chilled, dry air to cool it. The chilled air is then removed and warm, substantially moisture-saturated air is directed to the just-cooled regions of the cylinder to cause water droplets to form and be deposited continuously on the cylinder. By establishing control of the conditions affecting droplet formation, such as the temperature of both the chilled and warm air, the quantities and velocity of both and the relative humidity of the warm air, the droplet size and density can be easily controlled to control the water-ink balance and hence the quality of printed matter produced from the cylinder.
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SHEET 2 OF 3 [NVENTOR azn Q mw ATToRNEYs PATENIEB 0E82l I971 SHEET 3 [IF 3 ATTORNEYS OFFSET MISTER AIR DIE BRIEF DESCRIPTION OF THE PRIOR ART AND SUMMARY OF THE INVENTION The invention relates to a method and apparatus for depositing droplets of water upon a plate cylinder for use in lithographic printing.
Lithography, which was invented, possibly by accident, only in 1798, roughly 350 years after Gutenberg, is based on the simple fact that grease and water do not mix. In the original process, the copy to be printed was transferred to or drawn on a slab of porous stone in greasy ink or with a greasy crayon. The surface of the stone was then sponged with a solution such as gum arabic which rendered the nonprinting portions receptive to water, but repellent to the greasy ink, and the printing portions receptive to grease but repellent to moisture. The stone surface was then dampened with water and then rolled with a greasy ink which adhered only to the printing image. Next, the stone was placed in contact with a sheet of paper and an image produced by pressure applied to the stone.
Although, this original technique still survives for a few minor applications, lithographic processes today are primarily carried out on offset presses rather than on a simple letter press. Such offset presses are usually comprised of a number of cylinders, frequently four and usually all of uniform diameter. One of these four cylinders, is usually termed the printing or plate cylinder because it carries a flexible, metal printing plate clamped tight around it. This plate actually bears the image which is to be printed, and is manufactured or treated so that the portions which are to print will retain greasy ink but not water and the nonprinting portions will retain water but not grease. Disposed about the printing cylinder are means for moistening the face of the plate with water and then for applying greasy ink to the plate, with the water adhering to the nonprinting parts of the plate and the greasy ink to the remaining printing parts.
Notwithstanding its name, the printing cylinder itself does not normally print the image on the paper. In fact, it normally does not even contact the paper, but instead prints the image onto the surface of a second or intermediate cylinder which is normally termed the rubber blanket cylinder because its surface is usually rubber or a rubberlike material. A third cylinder is usually mounted to one side of the rubber blanket cylinder and its purpose is to hold the paper against the rubber blanket cylinder as the cylinders revolve, and to move the paper along to cause the rubber blanket cylinder to print the image of the plate onto the paper. The fourth cylinder is usually below the third cylinder and revolves against it to cause delivery of the paper and to carry the printed sheet or web to the delivery end of the printing press.
The usual method of applying moisture to the printing or plate cylinder is by one or more rollers which rotate in contact with the plate cylinder as it rotates and carry moisture to the cylinder from a bath through which one or more of the rollers move. Similarly, the ink is transferred to the plate cylinder by other rollers which are also mounted in contact with the plate cylinder for rotation therewith.
One of the major difficulties with lithographic printing, however, is that it is very important that the correct amount of moisture in the correct distribution be deposited upon the plate cylinder to maintain closely the desired ink-water balance. Too much or too little water both result in poor printing quality and the pressman must normally compensate for vapor pressure and temperature changes within the press environment, which slightly alter the amount of water transferred to the plate cylinder, in order to produce a satisfactory final print. The original adjustment and this periodic compensation require a great deal of skill and experience and is wasteful of time and paper. Further, the additional expense of employing a highly skilled artisan to operate the printing press, in comparison with other printing techniques which a relatively unskilled person can manage, have unfortunately discouraged increases in the use of lithographic techniques which are otherwise superior for many applications.
The present invention relates to a method and apparatus for depositing moisture dropwise onto the plate cylinder rather than filmwise as with rollers. In the past, such dropwise deposition has been accomplished in a variety of manners, none of which has been wholly satisfactory in controlling the amount and distribution of the water deposited. For example, the patents to Goddard, U.S. Pat. No. 2,063,672 and Stevens et al., U.S. Pat. No. 2,063,636,'both describe devices for supplying moisture to a plate cylinder in an offset printing arrangement whereby the cylinders are cooled by refrigerant circulated within the plate cylinder and then moisture saturated air impinged upon the cold plate cylinder so that moisture droplets condense on the plate and provide the necessary water. The U.S. Fat. to Osborne No. 299,002 shows a similar arrangement in which warm and chilled air are combined adjacent the cylinder surface to produce droplets. The patent to Osborne, U.S. Pat. No. 391,065, shows a similar arrangement in which cool air is impinged upon a flat printing surface to cool it and then is permitted to escape into the atmosphere before moist air is impinged upon the cooled surface to cause moisture to condense onto that surface. The location at which the cool air impinges upon the printing surface is separated from the location at which the moist air impinges upon the printing surface by a shield or screen. In contrast, the arrangement described below cools the plate cylinder by dry, chilled air impinged directly upon the rotating plate cylinder from a die termed an air mister die and that chilled air is then swept up and removed through the die after moving a short distance with the rotating cylinder and cooling it. The chilled air thus swept up can be returned to the original source to be reused. Next, warm, moisture saturated air is then impinged from the die directly upon the cooled cylinder regions to cause droplets to form and be deposited on the cylinder. The droplet size and distribution can be easily controlled by adjusting the temperatures of the chilled and warm air, the velocity and quantity of the chilled and warm air and the relative humidity of the warm air.
The novel arrangement discussed in detail below is thus capable of controlling very accurately the amount and distribution of water deposited on the plate cylinder and thus the ink-water balance. This accurate control by simple adjustment of the various factors controlling droplet deposition enables adjustments for optimum printing quality to be made quickly and easily. Even further, it is expected that longer plate life and better printing consistency will result from this arrangement.
Many other objects and purposes of the invention will become clear from the following detailed description of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an air die of this invention mounted adjacent to a printing cylinder;
FIG. 2 shows a cutaway end view of the air die cylinder shown in FIG. 1;
FIG. 3 shows a side view of the air die cylinder of FIG. I; and
FIG. 4 shows one of the tubes for use in the air die on the FIGS. 1-3.
DETAILED DESCRIPTION OF THE DRAWINGS Reference is now made to FIGS. 1-3 which show a die 20 termed an air mister die which deposits moisture on a conventional rotating plate or printing cylinder 22 which will, of course, normally be associated with a blanket cylinder and the other cylinders conventionally used in lithographic printing.
As discussed briefly above, the novel arrangement shown in FIGS. 1-4 cools the rotating plate cylinder 22 by impinging relatively dry, chilled air on the cylinder 22 to cool it, sweeping up the chilled air after it has travelled with the rotating cylinder for a short distance, and then impinging warm, moist air at a controlled temperature and humidity upon the chilled cylinder surface so that dropwise deposition of dew takes lOlOlS 0l97 place forming a thin film of moisture on the plate cylinder with a droplet size and distribution satisfactory for the quality printing desired. As stated above, the accurate establishment of thermodynamic control of the air around the plate cylinder 22 permitted by the novel arrangement shown in FIGS. 1-4 enables accurate control of droplet size and distribution on cylinder 22.
In the embodiment of the invention shown in FIGS. 1-3, the chilled air is supplied to the plate cylinder 22 from a conventional chilled air source 24 which is shown in block representation in FIG. 1. Die is also depicted in outline form in FIG. 1. Source 24 also includes means to control the velocity and temperature of the chilled air. A line 26 which may be a plastic, rubber or other tube connects this source 24 to a metal tube 28 which is disposed in a hollow cavity in the air die 20 such as shown in FIGS. 2 and 3. As can be seen from FIG. 2, air die 20 is preferably made in at least three pieces which are then bolted or fastened together in any suitable fashion.
The tube 28, which is connected to the line 26, is preferably an aluminum tube which has a number of holes in it as shown in FIG. 4, and these holes connect tube 28 to the surface of the rotating plate cylinder 22, through matching holes in the air die 20 so that the chilled air from source 24 is continuously forced through line 26 into line 28 and then onto the plate cylinder 22 through the apertures 30. In a constructed model of the embodiment shown in FIGS. 1-4, the aluminum tube 28 was 26 /4 inches long and within that space 32, 0.19 inch diameter holes were disposed at uniform separations as illustrated. The aluminum tube used was 1.75 inches in diameter with a wall thickness of 0.062. Although the chilled source 24 is shown connected by line 26 to the line 28 only at one end, it is possible to connect both ends of the line 28 to the chilled air source 24, and this may be desirable to insure that all portions of the cylinder 22 are uniformly cooled.
The chilled air supplied to the rotating plate cylinder 22 via the apertures in tube 28 is then removed from cylinder 22 and transported via tube 34 and line 36 to the chilled air return 32. As can be best seen in FIG. 2, the cool air impinged on the cylinder 22 from the tube 28 is swept up after a short travel with cylinder 22 by the scuppers 38 of die 20 which are connected to the tube 36 by a number of holes 40. A vacuum pump or any other suitable device may be associated with the return 32 to draw the air from the vicinity of the cylinder 22 into the tube 34 and hence down line 36 to return 32. Preferably, the chilled air impinged upon cylinder 22 and subsequently removed is chilled and relatively dry air at a temperature of roughly 65-70 F. The temperature and velocity of the chilled air impinged upon cylinder 22 controls the temperature to which the cylinder 22 is cooled and this in turn affects the amount of moisture deposited by the saturated warm air onto the cylinder 22.
After the portion of the cylinder 22 upon which the chilled air is impinged has been adequately cooled and that air then removed through tube 34, relatively warm, moist air is impinged upon the cylinder 22 from the air source 48, which also includes means for controlling the temperature, relative humidity and velocity of the moist air, via line 42, tube 44, and apertures 46 in die 20. Tube 44 is preferably an aluminum tube such as illustrated in FIG. 4 with a similar pattern of holes therein to release the moist air adjacent the surface of cylinder 22. This warm air is preferably at a temperature of 95-l00 F. and at roughly 95 percent relative humidity. As this warm air leaves the tube 44 through the apertures therein, it is dispersed and spilled by the dynamics of the moving cylinder 22, and is quickly cooled by the cooled surface of plate cylinder 22 to pass through the dew point. A mist thus forms and the resulting droplets are deposited upon the surface of cylinder 22 to form a thin film. Chemicals such as gum arabic and other conventional substances which aid or cause maintenance of aquaphilic and aquaphobic areas may also be added to cylinder 22 with the warm air from aspirator 50. The variables of air velocity, temperature, relative humidity and the difference in temperature between the saturated air from the source 48 and the cooler cylinder 22 can all be easily regulated to achieve control of droplet size and distribution which is impossible with conventional film deposition with rollers. Of course, supersaturation should not occur prior to the impingement of the warm air onto plate cylinder 22, and a 100 percent humidity which would cause droplets of water to be blown from the die cast causing an unacceptable distribution, is likewise to be generally avoided.
The superior performance which results from this dropwise dampening of the plate cylinder 22 is believed attributable to the subtle migrator energy available at the plate surface. These small forces can better manipulate a dispersed vapor as compared to a continuous film fed from a roller. Even further, control of the amount of deposition by altering one of the several controllable variables associated with the thermodynamic condition of the air as described above permits swift and simple alteration of the amount and distribution of the droplets. Longer plate life and better consistency of printing products have been both shown to result from this type of water deposition onto the plate cylinder.
Many changes and modifications in the above-described embodiment can be accomplished without departing from the spirit of the invention, and the invention is intended to be limited only by the scope of the appended claims.
What is claimed is:
1. An apparatus for supplying water to a rotating cylinder on an offset lithographic printing press comprising:
means for supplying relatively dry air having a temperature less than the surface temperature of said cylinder to said surface so as to cool said surface including a dry air tube having a plurality of apertures for impinging said dry air onto said surface and a source of dry air connected to said dry air tube,
means for removing said dry air from said surface after said dry air has travelled a distance with said cylinder including a removal tube having a plurality of apertures therein for removing said dry air and means connected to said removal tube for drawing said dry air into said removal tube,
means for supplying relatively moist air having a temperature greater than the surface temperature of said cylinder after being cooled by said 'dry air to said surface so that droplets of water are deposited on said surface including a moisture tube having a plurality of apertures therein for impinging said moist air onto said surface and a source of moist air connected to said moist air tube, and
means for conducting said dry air from said supplying means to said removing means such that said dry air is confined closely adjacent to said cylinder surface.
2. An apparatus as in claim 1 including means to control the thermodynamic conditions adjacent said surface so as to control the deposition of said droplets.
3. An apparatus as in claim I wherein said dry air tube, said removal tube and said moist air tube are mounted substantially in parallel with each other and with said cylinder and including die means for holding said tubes in parallel and adjacent said cylinder.
4. Apparatus as in claim 3 wherein said dry air tube, said removal tube and said moist air tube are hollow, substantially inflexible tubes and including a first flexible tube connecting said dry air source to said dry air tube, second flexible tube connecting said drawing means to said removal tube, a third flexible tube connecting said moist air source to said moist air tube.
5. An apparatus as in claim 3 wherein said die means has scuppers for assisting the removal of said dry air.
6. An apparatus as in claim 1 wherein said dry air has a temperature between 65 and 70 F. and said moist air has a temperature between and F. and a relative humidity of approximately 95 percent.
7. An apparatus as in claim 1 including means for supplying chemicals to said cylinder.
8. Apparatus as in claim 7 wherein said chemicals are supplied to said cylinder with said moist air and including tube means connecting said means and said moist air source to said moist air tube.
9. An apparatus as in claim 1 including means to control the temperature of said dry air and the temperature of said moist air and means to control the relative humidity of said moist air.
10. An apparatus as in claim 1 including means to control the velocity of said dry air and the velocity of said moist air.
11. A method of depositing water on a rotating cylinder of an offset lithographic printing press comprising the steps of:
supplying relatively dry air having a temperature less than the surface temperature of said cylinder to said surface so as to cool said surface,
removing said dry air from said surface after said dry air has travelled a distance with said cylinder,
conducting the dry air from the location where it is supplied to the surface to the location where it is removed, confining the dry air closely adjacent the cylinder surface as it is conducted, and
supplying relatively moist air, having a temperature less than the surface temperature of said cylinder after being cooled by said dry air, to said surface so that droplets of water are deposited on said surface.
12. A method as in claim 11 including the step of controlling the thermodynamic conditions adjacent said surface so as to control the deposition of said droplets on said surface.
13. A method as in claim 12 wherein said step of thermodynamic controlling includes the steps of controlling the temperatures of said dry and moist air, controlling the relative humidity of said moist air and controlling the velocity of said moist and dry air supplied to said cylinder.
14. A method as in claim 11 including the step of supplying chemicals to said cylinder with said moist air.
15. A method as in claim 11 including the step of cooling said dry air after said dry air is removing and then resupplying the cooled dry air to said cylinder.
16. A method as in claim 11 including the step of rotating said cylinder.