US3590733A

US3590733A - Device for applying wetting solution to a lithographic master sheet

Info

Publication number: US3590733A
Application number: US758921A
Authority: US
Inventors: Harry F Gammeter
Original assignee: Multigraphics Inc
Current assignee: AB Dick Co
Priority date: 1968-09-10
Filing date: 1968-09-10
Publication date: 1971-07-06
Anticipated expiration: 1988-07-06

Abstract

A rotating cylinder with a surface that clings tenaciously to wet duplicating masters. A supply of master wetting fluid is supplied to the cylinder surface. Rubber rollers in contact run at a greater speed to rub as the master is conveyed. A selfhoning stripper causes the wet master to separate from the cylinder.

Description

United States Patent [721 lnventor HarryF.Gammeter Cleveland Heights, Ohio [21] Appl. No 758,921 122] Filed Sept. 10, 1968 Division of Ser. No. 568.837. Feb. 29, 1966, Pat. No. 3,420,169. [45] Patented July 6, 1971 [731 Assignee Addressograph-Multigraph Corporation,

Cleveland, Ohio [54} DEVICE FOR APPLYING WETTING SOLUTION TO A LITHOGRAPHIC MASTER SHEET 2,008,374 7/1935 Von Hofe 118/245 2,044,472 6/1936 Ettl 118/245 2,142,318 1/1939 Langsner.... 118/249 2,252,204 8/1941 Reilly [18/258 X 2,352,658 7/1944 Richmond et a1. 117/111 F 2,369,378 2/1945 Thiele et a1. 118/227 2,559,908 7/1951 Warren 118/245 2,642,032 6/1953 Osgood 118/245 2,798,426 7/1957 .lanke et al.. 101/147 2,800,873 7/1957 .lalbert 118/245 X 3,306,255 2/1967 Kolibas 1 18/227 Primary Examiner-Robert E. Pulfrey Assistant Examiner-J. Reed Fisher Attorneys-Russell L. Root and Ray S. Pyle ABSTRACT: A rotating cylinder with a surface that clings tenaciously to wet duplicating masters. A supply of master wetting fluid is supplied to the cylinder surface. Rubber rollers in contact run at a greater speed to rub as the master is conveyed. A self-honing stripper causes the wet master to separate from the cylinder.

PATENTEU JUL 6 Ian CROSS REFERENCE This invention is a division of application Ser. No. 568,837 filed Feb. 29, I966, now U.S. Pat. No. 3,420,l69.

BACKGROUND OF THE INVENTION In the lithographic printing process, a master, whether it be on metal or paper, is treated in such manner that the imaged part of the surface becomes ink receptive and the background ink repelling. Thus, no raised configuration is needed to create an ink pattern and apply that pattern to a carrier paper.

In preparing lithographic masters, the historically accepted method has been to place the master on a bench and hand rub the surface with the wetting solution. With the advent of modern systems practices, the hand application has become too slow, and various efforts have been made to create fast processing.

Generally, this invention is directed to the procedure system wherein relatively short runs are made from one master, but many masters are required in a series. For example, prior to this invention, the production of 50 bulletins of 25 pages each would require considerable operator attention, even with the more modern fast-loading devices for masters.

The most practical prior systems have been to apply the master in a dry condition to the cylinder and rotate the master while pressing a mechanically held sponge to the master on the cylinder, which sponge is saturated with the wetting solution. Such operation is far more rapid than hand operation and is quite satisfactory for some purposes.

It is undesirable to have excess wetting solution on the cylinder because the inking system consists of a plurality of rollers, one operating against the other, which divide and distribute ink in order to eventually place the ink in an exceedingly thin, uniform layer on the form roll. However, such system is a two-way street, and moisture on the surface of the cylinder, especially if it is in excess supply, can find its way back along the form roller through the inking system and eventually produce enough moisture that the ink is emulsified and will fall from the inking system in chunks and otherwise become unsuitable. The ink-to-water ratio must be carefully balanced in the system to avoid such emulsification.

In prior practice excess moisture has not been too serious a problem because the rate of cycling of masters and the usual number of copies was balanced sufficiently to take away the excess moisture. Faster cycling and fewer copies, therefore, tend to pass more moisture into the inking system from the wetting of the masters than the printing operation takes away. This excess moisture will then find its way back through the ink system and actually collect in the ink fountain. Excessive moisture causes destructive emulsification.

This invention is directed to the improvement in fast operating printing systems using the basic lithographic type of equipment supplemented and improved for rapid replacement of masters and feeding of paper.

According to this invention, it is desired that the hand wetting of the master be circumvented, in order to speed the application of a series of masters, but go avoid excessive moisture conditions.

Therefore, it is an object of this invention to premoisten all masters before they are applied to the cylinder. Premoistening provides a side benefit in that paper masters function better if there is a few seconds dwell period for the moisture to react chemically with the master surface before ink is applied.

Machine wetting of masters is not necessarily an obvious procedure of dipping the master in a tank or rolling with a sponge. It is known that hand application on the bench produces a superior wetting effect that is not produced by merely applying moisture to the master surface. A rubbing effeet is obtained whenever a dry master is placed on the cylinder and a sponge held against the revolving master. This invention embraces the novel concepts 'of a means for scrubbing" the surface of a master to properly condition the master with moisture. There is no problem in differential speed rotation of a scrubbing roller with respect to a master whenever the master can be held against being dragged along by the scrubbing roller, but retaining the proper relative speed at the trailing end of a master as it passes through a scrub device has been found to present problems, which have been solved by using a roller having a type of surface to which a wet paper tends to adhere tenaciously.

DESCRIPTION OF DRAWINGS FIG. 1 is a perspective, substantially schematic and partially exploded illustration of a wetting structure for masters as employed in this invention.

FIG. 2 is a schematic longitudinal section view of the FIG. I device.

FIG. 3 is an enlarged perspective detail of a stripping guide shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Lithographic printing machines are well known in the art. It is known to install masters on the cylinder of such machines mechanically as well as manually. The related parent teaching explains mechanical handling of wet masters. This invention will provide prepared masters for either manual or machine installation.

Individual masters from a supply stack are picked up by means of any conventional feeding apparatus, such for example as the vacuum apparatus found on better quality highspeed lithographic machines. The individual master is thus lifted from the stack and placed into the bite of mated feed rollers 11 for transfer into a mechanical wetting device symbolized by the fountain roller 12 and the two scrub rollers 13 and 14.

Making of masters is an art of many ramifications. Many materials are available, and techniques for using those materials. The most commonly used material and process is a coating on a backing material which is receptive to the hydrophobic types of grease-ink-receptive materials but can then be chemically converted into water-receptive grease-ink-repelling characteristic. By this arrangement, the image can be applied, whereas it cannot be applied if the surface had been originally hydrophilie.

The materials which can thus be converted to a waterreceptive hydrophilic surface are normally of such nature that if the water solution used for such conversion is merely placed on the surface, it will stand away in droplets and fail to produce a uniform coating and hence fail to produce a uniform conversion. Thus, proper preparation of the surface requires a rubbing action to force the conversion material into intimate contact with each particle of the original coating.

In the past history of the lithographic process, such application of the conversion material was done by hand rubbing because there was no automatic equipment available. Hand application produces good conversion of the surface.

Later development for elimination of this hand task has provided for placing dry masters on the cylinder and pressing a sponge wetted with the solution against the surface of the master as it turns on the cylinder. This provides a rubbing application to cause the forcing of the solution into intimate contact with all of the surface material. The rubbing action is not of sufficient nature to disturb the image, and the surface under the image remains hydrophobic to hold the image. Thus, a master is created which has an ink-receptive image with the balance of the sheet being ink repelling.

In this invention, in order to produce the desired rubbing effect, it was contemplated that scrub rollers 13 and 14 could be operated at a differential speed with respect to the fountain roller 12, and no difficulty was seen to be expected so long as the master was held in the bite of the feed rollers II. By

running the scrub rollers 13 and 14 at a faster speed than the roller 12, in a direction tending to pull the master along the path, it was anticipated that once the master left the bite of the feed rollers, there would be no retarding force and, therefore, an acceleration of the master and lack of proper scrubbing at the end portion of the master. This invention embraces the discovery that the provision of fountain roller 12 in a material which tends to adhere to a wet surface of the master, will provide sufficient clinging power to prevent such loss of control, and the master can then be stripped from the face of the fountain roller by means of the stripping apparatus illustrated best in Figures 3 and 4.

Figure l, although'not in exact detail of structure, is an accurate schematic illustration of the apparatus to be found successful for the purpose of properly scrubbing the water-repellent solution onto the surface ofthe dry master.

A driving motor is employed to supply power to the entire machine, with various drive takeoff areas. This power source is not illustrated in the drawings, but a chain 24 is shown in FIG. 2 as the source of driving power to the wetting apparatus. A drive chain 25 interconnects the fountain roller 12 with the feed rollers 11 in order to coordinate their drive speed. Power is taken from the opposite end of the roller 12 in a system which includes a gear 27 driven by the roller 12 operating through two smaller gears 28 and 29. Gear 28 operates gear train 30 to drive the scrub roller [3, and gear 29 operates gear train 31 to drive the scrub roller 14. The size of the gear train and the driving apparatus for the gear train is such that the scrub rollers 13 and 14 operate in a direction and at a speed which causes the rollers 13 and 14 to overrun the fountain roller 12 and act to drive the master in its forward path.

In FIG. 2, the rollers 13 and M are indicated as being a resilient or rubber material mounted upon a more solid core. The surface material is of a sponge character in that it can carry and release moisture, and is relatively stiff to resist distortion and rapid deterioration, but not sufficiently stiff to tear and destroy a paper master. By rotating the rollers 13 and 14 at a peripheral speed greater than the peripheral speed of the roller 12, and in a direction to advance the master, the differential action will cause a rubbing and scrubbing action upon the master passing therethrough. There must be enough solution in the roller nips and/or cover material to wet the entire length of a l7-inch master. The master cuts off the supply as it enters the nip of the first applicator and fountain rollers.

This portion of the invention has been the discovery that a master can be gripped with sufficient holding force by selection of a material for the roller 12 of such nature that a wet paper master will cling to the surface of the roller 12 against the drive of the faster moving scrub-rollers. Thus, the difficulty of a rapid acceleration of the master after it is released from the bite of the feed rollers 11 is avoided. The surface of the fountain roller 12 is wetted by running in a bath 32 of solution and this solution is carried on the surface of the roller 12 to the sponge covers of the rollers 13 and 14 during the period when there is no master being prepared. Therefore, the rollers 13 and 14 are always properly supplied with moisture. As the master passes over roller 12, it is wetted on the back and is caused to cling to the surface of the roller and is held tight to the surface during the entire scrubbing operation. The preferred surface for roller 12 is polished hard chrome. This material will cling to wet paper with a high tenacity, and will resist wear of rubbing paper-separating devices.

In order to separate the master from the surface of the roller 12, to break the clinging action, a series of closely fitted stripper devices 35 has been devised. One of the strippers 35 is illustrated in FIG. 3 and 4, but the series of strippers is omitted in FIG. 2 to avoid confusion.

It has been found that unless the stripping device is properly formed, it will tend to collect the moisture and apply it in extra heavy strips along the area of the master which contacts the stripper. The illustrated stripping device 35 has been developed wherein a roof configuration top surface having two angular surface areas 36 extending laterally from a central ridge 37 causes a spreading and shedding of the moisture, and this spreading and shedding is further aided and emphasized by downwardly sloping forward flat areas 38. The face of the device 35 is formed to adhere closely to the shape of the fountain roller 12, and by making the body of the stripper device 35 of a material softer than the preferred hard chrome of the.

fountain roller 12, the edge of the flat area 38 is constantly honed to razor sharpness for faultless stripping of the wetted master from the fountain surface. Wet paper tends to become lodged in minute areas, and hence this constant honing is found to be a desirable adjunct to continuous maintenancefree and successful performance of this invention. The stripper device is held tight to the surface of the fountain roller 12 by means of a spring 40.

A conveyor system 42 is positioned to accept a master coming from the wetting device. The conveyor is composed of rollers 43 with interlaced elastic belts 44, and because the masters do not tend to cling to the surface of such elastic belts and convey properly, trucks 45 with rollers 46 thereon are positioned over the surface of the conveyor system and urge the wetted master against the elastic belts for conveyance.

INSTALLATION ON MASTER CYLINDER There are many devices for applying a master to a rotating cylinder, operating on various principles, and many of them which operate much in the manner of the feed rollers 11. However, such feed devices generally operate on dry masters which have an inherent stiffness enabling accuracy of projection, but even with dry, stiff masters, projection feeding results in some vagrancy. After some types of masters have passed through the wetting apparatus shown in FlG. 2, they no longer have the inherent stiffness of a dry sheet. Furthermore, it is desirable to wet the master for at least a brief period of a few seconds prior to its use in order that it may age and mature properly for better and clearer reproduction. However, such aging causes the masters, that tend to become limp, to become even more limp, and therefore a projection-type feed device becomes more unreliable.

Whereas the present invention has been shown and described herein in what is conceived to be the best mode contemplated, it is recognized that departures may be made therefrom within the scope of the invention which is, therefore, not to be limited to the details disclosed herein, but is to be afforded the full scope of the invention as hereinafter claimed.

lclaim:

1. In a lithographic master-sheet-processing apparatus, a mechanical device for applying wetting solution to a lith'ographic master sheet, comprising: a conveyor cylinder mounted for rotation in a first direction about its longitudinal axis, said conveyor cylinder having an exterior surface exhibiting a strong affinity for a wet paper master sheet;

at least one scrub cylinder having a longitudinal axis parallel to the axis of said conveyor cylinder and mounted for rotation in contact with said conveyor cylinder in a direction which will drive the master sheet therebetween, said scrub cylinder having a surface which exhibits substantially less affinity for a wet master sheet than said conveyor cylinder;

means for driving said conveyor cylinder at a first peripheral speed and said scrub cylinder at a second faster peripheral speed to overrun the conveyor cylinder and create a rubbing action between said cylinders;

means for delivering a lithographic master sheet to the nip of the conveyor and scrub cylinders;

means for mounting said conveyor cylinder and said scrub cylinder for rotation in the same peripheral direction at said nip;

means for presenting a continuous supply of wetting solution to said scrub cylinder and the surface of said conveyor cylinder; and

means for stripping said master sheet from said conveyor cylinder;

whereby scrubbing action occurs by the scrub cylinder with the conveyor cylinder firmly adhering to the master sheet.

2. A mechanical device for applying wetting solution as defined in claim 1, further charac terized in that:

Claims

1. In a lithographic master-sheet-processing apparatus, a mechanical device for applying wetting solution to a lithographic master sheet, comprising: a conveyor cylinder mounted for rotation in a first direction about its longitudinal axis, said conveyor cylinder having an exterior surface exhibiting a strong affinity for a wet paper master sheet; at least one scrub cylinder having a longitudinal axis parallel to the axis of said conveyor cylinder and mounted for rotation in contact with said conveyor cylinder in a direction which will drive the master sheet therebetween, said scrub cylinder having a surface which exhibits substantially less affinity for a wet master sheet than said conveyor cylinder; means for driving said conveyor cylinder at a first peripheral speed and said scrub cylinder at a second faster peripheral speed to overrun the conveyor cylinder and create a rubbing action between said cylinders; means for delivering a lithographic master sheet to the nip of the conveyor and scrub cylinders; means for mounting said conveyor cylinder and said scrub cylinder for rotation in the same peripheral direction at said nip; means for presenting a continuous supply of wetting solution to said scrub cylinder and the surface of said conveyor cylinder; and means for stripping said master sheet from said conveyor cylinder; whereby scrubbing action occurs by the scrub cylinder with the conveyor cylinder firmly adhering to the master sheet.

2. A mechanical device for applying wetting solution as defined in claim 1, further characterized in that: said scrub cylinder having a moisture reservoir surface capable of taking up moisture from said conveyor cylinder during idle running and applying the moisture to a master surface as a master is passing therethrough.