US3502768A - Method of making a dampening roller - Google Patents

Description

' March 24, 1970 E. D. ILL 3,502,768

METHOD OF MAKING A'DAMPENING ROLLER Filed Nov. 25, 1966 mvmon 50/144 Q0 Q ///ZL a%,m 00mm,

ATTORNEYS United States Patent 3,502,768 METHOD OF MAKING A DAMPENING ROLLER Edward D. Hill, 11212 Edgewater Drive, Cleveland, Ohio 44102 Filed Nov. 25, 1966, Ser. No. 596,959 Int. Cl. B29c 1/04; B29h 9/10 U.S. Cl. 264-331 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally as indicated to a dampening roller for use in lithographic processes and to a method of making the same, and more particularly to such a roller having improved ability to effectively and efficiently transfer dampening fluid.

In lithographic offset or planographic printing, a printing plate is chemically treated to provide printing and non-printing areas, with the printing area, of course, being ink receptive and the non-printing area being water receptive. Pursuant to such treatment, a film of dampening fluid is applied to the surface of the plate which is retained by the hydrophilic area but repelled by the ink receptive printing area, thereby separating and isolating the nonprinting area from the ink which is applied to the printing areas. 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 fluid 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. In the application of such fluid, an arrangement of rollers is employed to transfer the dampening fluid onto the nonprinting areas of the plate.

Such arrangement of rollers commonly includes rollers known as dampening rollers which are in contact with the printing cylinder and the plate carried thereon to apply and peripherally distribute a suitable dampening solution to the plate. Since dampening solutions are generally water based solutions, the prior practice has been to use dampening rollers which have a water absorptive surface such as a covering of cotton, molleton, mole skin, etc. Due to the nature of such material, however, they tend to pick up and absorb particles of ink from the plate with which the dampening rollers are in contact and also to carry the ink back into the dampening solution, thus dirtying the rollers and preventing a clean layer of solution from being deposited on the plate. When this occurs, the. rollers must be cleaned and/ or replaced.

Various substitutes have been tried for the cotton or molleton rollers as for example a surface comprising a fabric of glass fibers coated with tetrafluoroethylene. It has been found, however, that with sustained use, the glass fibers are not satisfactorily maintained on the surface of the roller. Coverings of wool have also been tried, as well as roller surfaces of glue-glycerin, but these also tend to pick up particles of ink and thus become inked up and dirty within relatively short periods of time.

It is accordingly a principal object of the present invention to provide a method of making such roller which is free from the above-mentioned disadvantages of prior rollers.

3,502,768 Patented Mar. 24, 1970 Another object of this invention is to provide a method of producing a dampening roller which has less tendency to pick up ink than previously-known rollers and which will eifectively and efficiently transfer a film of dampening fluid.

Yet another object of this invention is the provision of a method of producing a dampening roller having a surface of a highly durable material which is capable of being readily cleaned by the use of low grade distillates or a solution of lye without having its surface adversely affected.

These and other objects are achieved by means of this invention in which a dampening roller is provided having a water transfer surface of a smooth, substantially porefree normally ink-attractive plastic, such as polyurethane or polyvinyl chloride. Such roller is produced by the process of this invention in which the interior of a roller mold is uniformly coated with a parting solution prior to molding of the roller.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawings:

FIG. 1 is a perspective view of the dampening roller of this invention; and

FIG. 2 is a cross-sectional view of such roller taken on the line 2-2 of FIG. 1.

Referring now more particularly to the drawings, the dampening roller of this invention is designated generally by the numeral 1 and is seen as comprising a central metal shaft 2 having a surrounding surface of a smooth, substantially pore-free plastic material 3. Contrary to the dampening rollers previously known, such plastic material is a normally ink-attractive material, such as polyurethane or polyvinyl chloride.

To produce the dampening roller of this invention, a roller mold is coated with a substantially uniform coating of a parting agent. The parting agent is not applied to the mold with a swab as in the usual prior procedure, however, as it has been found that it is not possible to obtain a uniform coating from such method of application. Rather, the parting agent is applied to the interior of the mold in the form of a solution or suspension of the agent in a solvent.

Preferably, the roller mold is polished to a high degree prior to coating with the parting agent, and is thereafter preferably preheated to a temperature on the order of approximately -200 F. and filled with a solution of a parting agent, such as a wax, which has been dissolved in a suitable solvent such as, for example, trichloroethylene. The parting agent solution is generally heated to a temperature sufliciently high to dissolve the agent, as for example approximately 180 F. in the case of wax and trichloroethylene. A small opening is provided in the bottom of the mold, which permits the wax solution to be removed therefrom slowly and evenly thereby applying a uniform coating to the interior of the mold. The mold is thereafter charged with the desired plastic, and the roller is molded in the usual manner.

There are several parting agents which are suitable for use in the present invention, including various wax sub stances, such as Carnauba wax, spermacetti wax, Chinese wax or beeswax. Similarly, suitable parting agents include silicone based substances such as silicone greases.

The parting agent is dissolved in a suitable solvent, which may be any solvent capable of dissolving the particular agent in question. Preferably, the solvent will be highly volatile, low boiling solvent, such as the various halogenated hydrocarbons, including chlorinated hydrocarbons such as trichloroethylene, tetrachloroethylene, chloroprene, chlorobenzene, etc. and aromatic hydrocarbons such as benzene, toluene, xylene and naptha. As mentioned, the solvent is preferably highly volatile, as this will facilitate drying and hence the application of a uniform coating to the interior of the mold.

The amount of parting agent in the solution may be varied, but is normally Within the range of approximately 1 to about 10 weight percent, and preferably within the the range of about 2 to about by weight. It has been found that better results are produced if the quantity of parting agent is kept Within the specified general limits, as the use of too much of such agent produces a coating which is of such thickness that it Will not readily dry on the surface of the mold.

As mentioned previously, the plastic material comprising the surface of the dampening roller is an ink-attractive material rather than the hydrophilic or water absorptive materials previously used. An example of such material is polyurethane, particularly polyester-based polyurethanes, as for example, those produced by reacting a branched adipate polyester with a diisocyanate.

A particularly suitable polyurethane is that disclosed in my co-pending application Ser. No. 483,263 filed Aug. 27, 1965 and entitled Roller for Applying Paint, Ink and the Like. In general, such polyurethane is formed by reacting a polyethylene glycol, a polyol and an isocyanate.

Materials other than polyurethanes may also be used for the surface of the dampening roller, as for example polyvinyl chlorides. An example of a suitable such polyvinyl chloride is that disclosed in US. Patent 2,631,358. which may be formed by reacting a polyvinyl chloride resin with a high boiling plasticizer such as dioctyl phthalate. A suitable polyvinyl chloride composition comprising approximately 4 parts of plasticizing agent to one part of pvc resin and including the usual inhibitors such as tribasic lead sulfate, ricinoleate of tin, etc. Will produce a satisfactory roller surface.

The dampening rollers of this invention have been found to perform quite satisfactorily in the transfer of dampening fluids in offset printing operations. The plastic surface of such rollers has a highly polished or glassy appearance and is exceptionally smooth and pore-free. As a result of this, the roller is able to provide an actual sheet or film of dampening fluid which is very effective in separating the ink-attractive roller surface from the ink contained on the printing plate. This ability to transfer a sheet or film of fluid is in contrast to previously known dampening rollers which have tended to produce a pattern of dots of fluid due to the hydrophilic or water absorptive nature of the surface. As can be readily appreciated, such surfaces are less capable of preventing contact with the ink on the printing plate than the roller of the present invention which transfers an actual film of fluid.

This invention will be better understood by reference to the following specific but non-limiting example.

Example Approximately 5% of Carnauba Wax was dissolved in trichloroethylene by heating to approximately 180 F. Such solution was thereafter poured into a highly polished roller mold, which was preheated to approximately 180-200" F., until such mold was completely filled. Thereafter, the wax solution was permitted to slowly and evenly run out from the bottom of the mold, and thus an even and uniform coating was applied to the interior of the mold.

A metal roller shaft was thereafter centered within the mold and the mold was charged with the following polyurethane composition: approximately parts by weight of polyethylene glycol having a hydroxyl number of 55 (heated to approximately F. to place it in liquid form), 7.5 parts by weight of trimethylolpropane and 12.7 parts of Mondur I'D-80 toluene diisocyanate. The mold was thereafter heated to approximately 250 F. and permitted to remain there for approximately 2 hours to cure.

Such roller was subsequently used in a lithographic offset printing press and was found to perform quite satisfactorily in the transfer of dampening fluid to the printing plate without being adversely affected by the ink present on the printing plate.

It will thus be appreciated that the dampening rollers of this invention having a smooth, pore-free or glassy surface of an ink attractive plastic have distinct advantages over the cotton or molleton covered rollers previously known. Additionally, such rollers have been found to remain substantially free of ink deposits for extended periods of time during operation on a press. Similarly, because of the durable nature of the surface of such rollers, they may very readily be cleaned if any ink is picked up, simply by cleaning with a low grade distillate or a solution of lye and water.

I therefore particularly point out and distinctly claim as my invention:

1. A process of making a dampening roller comprising substantially completely filling the interior of a roller mold with a solution of a parting agent in a suitable solvent comprising approximately 1 to about 10 Weight percent of such parting agent, slowly and evenly removing such solution from such mold thereby applying a substantially uniform coating to the interior surface thereof, charging such coated mold with a normally ink attractive plastic composition, and applying sufiicient heat to such mold and composition to form a dampening roller having a smooth, substantially pore-free surface effective to transfer a film of dampening fluid.

2. The process of claim 1 in which such parting agent is a wax.

3. The process of claim 2 in which such solution comprises approximately 2 to about 5 weight percent of such wax.

4. The process of claim 3 in which the solvent for such solution is trichloroethylene.

5. The process of claim 1 in which such mold is heated prior to filling with such solution.

6. The process of claim 1 in which such plastic is a polyurethane.

7. The process of claim 1 in which such plastic is polyvinyl chloride.

References Cited UNITED STATES PATENTS 2,491,097 12/1949 Feagin l855.1 3,101,244 8/1963 Hood 264-338 2,908,040 10/ 1959 Schneider 1l7-94 2,045,913 6/1936 Hoy 106-3825 3,002,866 10/1961 Gartrell 264338 2,536,323 1/1951 Spencer 1l794 ROBERT F. WHITE, Primary Examiner R. SHEAR, Assistant Examiner U..S. Cl. X.R. 264338

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