US2220278A - Damping mechanism for lithographic presses - Google Patents

Description

,Nov. 5, 1940.

Dv M. RAPPORT DAMPING MECHANISM FOR LITHOGRAPHIC PRESSES .Filed Jan. 24, 1938 Patented Nov. 5, 1940 UNITED STATES PATENT OFFICE David M. Rapport, Chicago, 111., assignor to Rapid Roller 00., Chicago, 111., a corporation of Illinois Application January 24, 1938, Serial No, 186,517

17 Claims.

The present invention relates in general to lithographic presses utilizing planographic plates of any kind including deep-etch plates, and is in particular concerned with novel means for preventing undesirable changes in the pH value of the damping solution in the damping attachment or mechanism of the press.

Heretofore, it has been the general practice to utilize in the damping mechanism for the plates 10 of lithographic presses fountain and distributor rollers which were constructed of metals such as brass, copper, bronze and the like. These metal rollers were cooperatively associated with damping and ductor rollers covered with molleton,

flannel, moleskin, or other suitable fabric material having absorptive properties to form 'a train of rollers for conducting damping solution from a metallic container or fountain to the printing plates.

Objections to the foregoing arrangement arise from the electrolytic action which takes place in the damping fountain, and from galvanic action due to the formation of electric couples between the rollers and the printing plates, and between the rollers and the damping fountain.

As a result of these actions, the stability of the damping solution is materially disturbed. For example, the acid condition of the damping solution is changed, that is, its pH value does not remain constant. The tendency is for the damping solution to become less and less acid, and as a result its pH value is increased. This change in acidity of the damping solution has to be counteracted by the addition of more and more acid in order that its effectiveness on the printing plate may be maintained.

This continued addition of acid to the damping solution is detrimental in that the life of the printing plates is shortened; the surfaces of the 4 metal rollers are attacked, making frequent'polishing of these surfaces necessary; and the fabric coverings of the other associated rollers are caused to collapse after slight usage, whereupon they lose their ability to efliciently carry the damping solution.

Moreover, the metallic rollers have another serious defect. The damping rollers, which pick up some ink during peripheral contact with the printing plates, have a tendency to reconvey this ink to the metal rollers, and eventually all the rollers of the damping mechanism may acquire an accumulation of ink thereon. This accumula* tion is accentuated by the galvanic and electrolytic actions heretofore described. As a result, the 5 damping solution is not fed in a smooth film;

and, with continued operation, this lack of feeding a continuous, smooth film to the printing plates leaves non-printing surfaces of the plates unprotected. Ink will then be deposited on these surfaces, and scumming takes place. Under 5 such conditions, the ink is improperly distributed, and the quality of the printing will be unsatisfactory.

The quality of the printing further suffers as a result of the hastening of the emulsification of 10 the ink with the damping solution, due to a decrease in its acidity. Emulsification of the ink seriously decreases its brilliancy and its aflinity for the printing surfaces. At the same time the non-printing surfaces become less repellant to the 15 ink. As a consequence, the printing becomes blurred and indistinct. 1

Various arrangements have been suggested in an attempt to overcome the foregoing difliculties. One such arrangement proposes to prevent 20 the formation of electric couples and resulting galvanic action by making the distributing rollers, the fountain, and the printing plates of corresponding metal. For example, a zinc distributing roller would be-used with a zinc plate, an 25 aluminum roller with an aluminum plate, etc.

While such'use of corresponding metals should theoretically overcome the disadvantages heretofore experienced, such an arrangement has not proved commercially practical. distributing roller, although presumably made of the same metal, would actually have different metallic constituencies, unless they were made from the same melt, However, this would be extremely diflicult, if not impossible, not only because they are supplied from different sources, but for the reason that they are alloyed differently for the different purposes they are required to serve. But, even if they could be made of metal from the same melt, the metal would, as commercially produced, contain impurities which would be acted upon by the acid of the damping solution, and the same difficulties as previously encountered would result from the change in the pH value of the damping solution. Having in mind the foregoing objections and difliculties experienced with presently known damping mechanisms, it is a primary object of the present invention to provide in a damping mechanism, rollers constructed of a non-metallic material which is not only a non-conductor of electricity but has a relatively high dielectric constant, whereby the formation of an electric couplefthe depositing of foreign matter on the roller, oxidization of roller surfaces, electrolytic The plate and action, etc., will be eliminated, and the pH value of the damping solution maintained constant during long periods of use. A further object of the invention is to provide an improved fountain construction in the damping mechanism.

Other objects and features of the invention will more fully appear from the following detailed description taken in connection with the accompanying drawing which, illustrates a single embodiment thereof, and in which:

Figure l is a diagrammatic view illustrating a damping mechanism embodying the features of my invention applied to a lithographic press;

Figure 2 is an enlarged broken away plan view of a roller such as I prefer to use for the damping and ductor rollers of my invention; and

Figure 3 is a similar view of a roller such as used'for the distributing roller and fountain roller of my invention.

As shown on the drawing:

For purposes of illustrating my invention, there is shown in Figure 1 a printing cylinder l0 such as used in lithographic presses, this cylinder being adapted to have a printing plate II secured to its surface for rotation therewith.

Asthe cylinder is rotated, the plate is moved into contact with form rollers l2 on the inking attachment, from which the ink is picked up by the plate. The form rollers are supplied with ink from a series of intermediate rollers 13 which engage dist ibuting riders M on which ink films are deposited by peripheral contact with a distributing drum shown at I 5. Ink is carried from an ink reservoir 6 by means of a carrier roller H from which it is alternately transferred to the distributing drum by means of a pivotally mounted roller It in the usual manner.

According to the principles involved in lithographic printing, itis necessary that the printing plates be subjected to or dampened with an appropriate damping solution, in order to render non-printing portions of the plate repellant to the ink and prevent them from picking up ink from the form rollers. This damping is accomplished by means of a damping attachment or mechanism. It is with this part of the lithographic press that my present invention is particularly concerned.

Damping rollers l9 are arranged to engage the plate before the ink is applied thereon, these rollers being adapted to peripherally distribute a suitable damping solution to the plate. The dan ping rollers are peripherally engaged with a distributing roller as indicated at 20. Damping solution is transferred from a fountain roll 2| rotatably supported in a reservoir 22 containing the damping solution, by means of a ductor roller 23 which is pivotally mounted for swinging movement back and forth into alternate peripheral engagement with the carrying roll and distributor roller.

Heretofore, it has been the usual practice to construct the distributor roller 20 andthe'carrying roll it of brass, although other metals have been used. The other rollers, namely, the damping rollers l9 and the ductor roller 23, have been provided with a covering of molleton, flannel, moleskin, or other suitable absorptive material.

In such an arrangement, it has been found that electric couples are formed between the printing plate and the metal rollers and between the fountain and the metal rollers, and that due to these couples, undesirable galvanic and electrolytic actions take place in the damping mechanism. As a. result, the stability of the damping solution is materially disturbed and the pH value of the solution is changed. Usually, the acidity of the solution is decreased and its pH value increased, thus necessitating the addition of more and more acid in order to maintain its effectiveness. However, this maintained acidity causes deterioration of the fabric on the damping and ductor rollers, shortens the life of the printing plates, and attacks themetal rollers, making it necessary to polish these rollers at frequent intervals. Moreover, under these conditions foreign materials are deposited on the surface of the rollers and the proper distribution of damping fluid to the printing plates is prevented due to ink accumulations on the rollers. In order to overcome these disadvantages, it is proposed in the present invention to utilize a non-metallic material for the fountain and distributing rollers, which is not only non-conductive but also has a high dielectric constant. By the use of such material, the possibility of setting up an electric couple is eliminated, .the surfaces of the rollers will not become oxidized, and the pH value of the damping solution will ,be maintained constant, since there will be no electrolytic action in the damping fountain or galvanic action between the rollers and the printing plates or between the rolls and the fountain.

In practice it has been found that the life of the printing plates, when using my novel combination of rollers, will be approximately 50% longer than heretofore, and the plates will be kept cleaner and produce a more perfect print. The life of the damping rollers wil be more than doubled.

Any suitable non-metallic material which is a non-conductor of electricity and has a high dielectric constant may be utilized according .to my invention, and for this purpose I have found that excellent results are obtained by using a hard rubber material, such as ebonite, which possesses suflicient porosity for carrying the required amount of damping solution to the ductor roller and distributing it to the damping rollers uniformly. Such a roller is disclosed in Figure 3.

While satisfactory operation of the dampening mechanism is obtained by vusing non-metallic carrying and distributing rollers with fabric covered rollers as previously explained, I prefer to use in my novel arrangement damping and ductor rollers of the type shown in Figure 2, and as fully described in my United States Patent No. 2,119,491.

This roller, in general, comprises a metal shaft 24 to which there may be directly secured, as by 'vulcanizing, a surfacing layer of a rubber composition comprising a binder of rubber, either natural or synthetic, or a rubber-like substance, and a filler of absorbent material, such as absorptive cotton, unsized paper pulp, leather powder, cork powder, wool-flock, powdered natural sponge, wood flour, and the like. Such a roller surface is both resilient and water absorptive,

while at the same time it is relatively resistant to deterioration under the action of air, light,

and oil. By using a roller of this type in the improved combination of my invention, the life of the printing plates is materially prolonged.

As an additional feature of the invention, instead of utilizing a reservoir for the damping solution, in which the solution is in contact with a metallic surface, I employ a container having an inner surface which is inert to the acid of the damping solution. For such purpose, I have found that a material such as bakelite" is admirably suited for the purpose. However, if desired, the container may be constructed of any suitable metal and provided with an inner lining 2B of suitable inert material, such as hard rubber, which may be a coating or a separate removable container. By constructing the reservoir in this manner, the damping solution may beleftin the reservoir and not used for long period s-of time, and its pH value will remain constant.

It is, of course, to be understood that although I have described in detail the preferred embodiment of my invention, the invention is not to be thus limited, but only insofar as defined by the scope and spirit of the appended claims.

I claim as my invention:

1. In a printing press adapted to use a pianographic plate of any kind for direct or offset printing and including deep-etch plates, a damping mechanism for said plate, and at least one member for distributing damping solution for said plate, said member being composed of a non-metallic absorptive material inhibitive to the galvanic action of an electric couple between said member and said plate.

2. In a lithographic press adapted to use a metallic printingplate, a roller for conducting a damping solution during its movement from a reservoir to the printing plate, said roller being made of a non-metallic, non-conductive absorptive material having a high dielectric constant.

3. In a lithographic press having a metallic printing plate, a distributing roller for peripherally distributing a damping solution on damping rollers, said roller being made of a different material than said plate and inhibitive to galvanic action of an electric couple between said roller and said plate.

4. In a printing press adapted to use printing plates. a 'damping mechanism for said plates comprising a roller for transferring damping solution to said plates, said roller made of an absorptive material inactive to vary the pH value of the damping solution.

5. In a printing press adapted to use pianographic plates, a damping mechanism for said plat-es comprising a fountain for damping solution, and a roller in the solution in said fountain, said roller made of a porous material inhibitive to electrolytic action in said solution.

5. In a printing press adapted to use planographic plates, a damping mechanism for said plates comprising a fountain for damping solution, and a non-metallic roller in the solution in said fountain, said roller being porous and in-' being made of non-metallic porous material inhibitive to electrolytic action in the presence of said solution.

8. In a printing press adapted to use printing plates, a fountain adapted to contain a solution for damping said plates, and a series of rollers for transferring damping solution from said fountain and applying it to said plates, all of said.

rollers having non-metallic surfaces.

9. A damping mechanism for the plates of a lithographic press comprising a fountain for a damping solution, and a plurality of rollers for .carrying the damping solution from the fountain damping solution, and means for transferring the solution from saidcontainer to said plates, said container having a solution contacting surface of a material inert to the solution.

11. In a damping mechanism for presses, a reservoir for a damping solution, said reservoir being made of "bakelite".

12. In a damping mechanism for presses, a metallic reservoir for a damping solution, said reservoir having an inner lining of a material inert to the solution.

13. In a damping mechanism for presses,.a metallic reservoir for a damping solution, and a non-metallic lining on the inside of the reservoir, said lining being inactive to the solution.

14. In a damping mechanism for presses, a reservoir for a dampingsolution having an acid characteristic, said reservoir having an inner surface of a material inert to said solution, whereby the pH value of the solution therein will resolution from said fountain to the press plates,

said rollers and said fountain having solution contacting surfaces inactive to the solution.

17. A damping mechanism for applying a damping solution having electrolytic characteristics to the printing plates in a printing press and preventing the setting of electric couples which would result in galvanic action, said mechanism comprising a fountain for, the damping solution having solution contacting surfaces inactive to the solution, a plurality of rollers for conducting the damping solution from the fountain to the press plates, said rollers having surfaces of non-metallic porous material inhibitive to electrolytic action in the presence of said solution.

DAVID M. RAPPORT.

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