GB2139561A

GB2139561A - Dampening system

Info

Publication number: GB2139561A
Application number: GB08412109A
Authority: GB
Inventors: John Macphee
Original assignee: Baldwin Technology Corp
Current assignee: Baldwin Technology Corp
Priority date: 1983-05-11
Filing date: 1984-05-11
Publication date: 1984-11-14
Also published as: DE8413874U1; FR2550994A1; DE3416845A1; JPS59212268A; IT8467472A0; IT1218869B; GB2139561B; FR2550994B1; GB8412109D0

Abstract

A system for applying dampening fluid to the plate cylinder (36) of printing presses is particularly adapted to contacting continuous dampening systems. The dampening fluid applying roller (38) is in contact with the rotating plate cylinder (36) and there is a wiping action between the dampening fluid applying roller and the plate cylinder which loosens foreign particles from the plate cylinder so they can be removed. The dampening fluid applying roller rotates at a different speed from that of the plate cylinder to cause the wiping action. Preferably, the dampening fluid applying roller rotates at a slower speed than the plate cylinder. <IMAGE>

Description

SPECIFICATION Dampening system This invention relates to a new and improved dampening system for use in connection with lithographic printing presses. Generally speaking, the invention relates to a new and improved dampening system of the continuous contacting type (but is not necessarily limited thereto) which is particularly useful in connection with lithographic printing presses. More particularly, the invention relates to a new and improved dampening system for applying fountain or dampening solution in lithographic presses, wherein a differential surface speed is provided between a dampening roller and a plate cylinder which results in the achievement of improved performance in the areas of reducing ghosting, hickey removal, reducing ink feedback into the dampening solution and improved printing.

It is well known that a lithographic offset printing plate is treated chemically so that the printing area is receptive to ink, to produce printing and non-printing areas. The non-printing area on the other hand, is hydrophilic and accepts moistening fluid. In order to achieve the desired printing,a film of moistening fluid is applied to the surface of the plate. This is retained by the hydrophilic area but is repelled by the printing area so that the printing area is capable of receiving the printing ink.

The non-printing area, on the other hand, is separated and isolated from the printing ink by the film of moistening fluid formed. In this manner only the image of the printing area is transferred to the blanket cylinder and on to the paper on which the image is printed.

Generally speaking, there are two classifications of dampening systems: contacting and non-contacting. The non-contacting type consists of a brush and spray type system in which there is a physical gap in the path the dampening fluid takes to the plate. In such systems there is no ink feedback into the dampening system fluid.

The contact category of dampening system has two broad sub-categories; namely, continuous systems, and conventional,or ductor type systems which utilize fabric covered or bareback form rollers. It is generally accepted that continuous dampening systems are preferred because they produce high quality printing and are relatively maintenance free because cloth or paper covered rollers are not required.

On the other hand, a disadvantage of continuous systems is the problem of ghosting on the printed material.

The continuous type dampening systems may be classified into three groups, i.e. plate feed systems, ink feed systems,and combination type systems.

In the plate feed type system dampening solution is applied directly to the plate by a series of rollers which are independent from the inking system. In such a system a roller is in contact with a supply of dampening fluid which is transferred to a dampening form roller via an intermediate roller. The dampening form roller is in rotating contact with the plate cylinder thereby to transfer the dampening fluid. Another series of rollers including an ink form roller and a vribrating roller,tranfers ink to the plate cylinder.

The inker feed-type system functions so that the dampening solution is fed to one of the ink system rollers rather than to the plate.

Generally, the dampening fluid is directed to the first ink form roller.

In the combination type system a separate dampening form roller is provided which applies dampening fluid to the plate. In the combination type the dampening roller is connected to the inking system by a vibrating bridge roller. A typical example of the combination system is illustrated in United States Patent No. 4,290,360.

The inker feed continuous-type dampening system is widely used in the printing industry even though there are areas where improvement would be desirable. One problem with the inker feed continuous type dampening system is that the stripe setting of the vibrator roller to the first ink form roller and the first ink form roller to the plate cylinder is very critical. This setting is critical because the first ink form roller runs at essentially the same speed as the plate cylinder and is friction driven by the vibrator roller and the plate cylinder. In certain instances, e.g. sheet-fed presses, there is a large gap in the plate cylinder so that there are substantial periods during the plate cylinder revolution in which the only drive for the first form roller is through frictional contact with the vibrator roller.This can be troublesome because the dampening fluid on the surface of the roller is slippery, making driving contact difficult. In addition, the slip nip between the rollers is an additional load which tends to slow down the roller. In order to insure that the form roller runs at the same speed as the vibrator roller, it is generally considered necessary to maintain a relatively large stripe between the vibrator roller and the first ink form roller. If this stripe is not heavy enough or if the plate cylinder stripe is too heavy, there will be speed variations resulting in poor printing.

But, on the other hand, where a heavy stripe is required to the vibrator roller, good ink transfer is interefered with which contributes to the problem of mechanical ghosting. As used herein, mechanical ghosting refers to the appearance of an unwanted phantom image in a printed area. Ghosting is a faint image of a repeat of some other printed area or a repeat of one of the regions of the same printed area.

The cause is the same in both types of mechanical ghosting, and is related to the principle which governs ink transfer from an inking roller to the plate in the press. That is, when an ink roller transfers ink to the printing plate, a mirror image of the printed area is formed on the ink roller. The boundary of this mirror image represents the dividing line between (i) those areas of the roller which contacted and transferred ink to the ink receptive image area of the plate and (ii) those areas of the inked roller which transferred no ink but received a charge of dampening fluid as a result of contacting the dampened non-image areas of the plate.

Thus, the ink form rollers (i.e. those in contact with the plate cylinder) contain areas of thinner ink films and little dampening fluid and areas of thicker ink films having much emulsified water, which produce undesired phantom images on the printed form.

Inker feed dampening systems have been in wide-spread use in the industry for about ten years. A typical inker feed dampening system is described and shown in United States Patent No. 3,168,037.

There are certain advantages to these systems such as less maintenance in that cloth or paper coverings for rollers are not required.

There is a very fast response time at the beginning of a run so that very few sheets are lost due to waste and there are less demands on the operator.

In a typical inker feed dampening system the dampening solution is metered into a relatively thin film by the metering nip formed between the chrome transfer roller and the resilient metering roller. Typically, these rollers are geared together and driven at the same surface speed by a separate variable speed motor. Due to the fact that the rollers are run at the same surface speed, the thickness of the dampening fluid film at the exit of the nip is determined by the speed of the rollers, the hardness of the resilient roller, the pressure between the rollers and the viscosity of the dampening fluid.

Generally speaking, all of these factors tend to remain constant except for the speed of the rollers so that the thickness of the dampening fluid at the exit of the metering nip and the feed rate of the dampening solution is varied by using the variable speed controller to vary the speed of the transfer roller and the resilient metering roller. The metered film of dampening solution goes to the nip between the first ink form roller and the transfer roller and some dampening solution is transferred from the first form roller to the plate cylinder. The transfer roller and the metering roller run at a slower speed and a "slip nip" is formed at the juncture of the transfer roller and the first form roller.

With the above described arrangement it is generally found necessary, except on very small presses, for the metering roller to be skewed so as to provide a greater dampening fluid feed rate at the ends than at the middle of the rollers. In addition, it has been found that isopropyl alcohol must be added to the fountain solution so that it remains in a thin film rather than agglomerating into small water droplets. Another problem with the aforesaid arrangement is that when the presses are run at high speeds the slip nip can cause emulsification of the fountain solution and ink resulting in small particles of ink being fed back and disbursed in the fountain solution which causes an effect known as tinting, which means that non-image areas on the printed sheet appear to be tinted. One solution to the problem is offered by U.S. Patent No. 3,937,141.The solution offered by the aforesaid patent is to rearrange the rollers so that the slip nip is moved to a point where there is no ink. The chrome transfer roller is run at the same speed as the ink form roller and the resilient metering roller also functions as the fountain pan roller. In this modiffication, the fountain pan roller is driven by a variable speed motor which controls the fountain solution feed rate. A slip nip is, therefore, formed only where there is fountain solution present. This arrangement provides a partial solution to the emulsiffication or ink feedback problem but requires that the first ink form roller and the transfer roller be friction driven plus placing a greater demand on the vibrating roller. Additional maintenance problems are presented where the resilient roller is used as the fountain pan roller.

A problem with continuous systems has been ghosting. There have been several efforts to solve the ghosting problem arising in plate feed type systems.

One proposal to solve the ghosting problem is to use a separate dampening form roller but in this proposal a vibrating bridge roller is used to connect the dampening form roller to the first ink form roller.

The foregoing system has been modified in several ways. One modification was to provide a mechanism to move the vibrating bridge roller whereby the dampening system can be disconnected from the ink system during certain phases of the printing operation. Thus, the vibrating bridge roller can be moved out of engagement with the dampening form roller so as to reduce the problem of ghosting.

in summary, the prior art can be generally characterized as having the following characteristics: 1. The form roller which supplies dampening fluid to the plate is run at essentially the same surface speed as the plate cylinder.

2. The water feed rate is controlled by a separate motor drive which drives at least one of the dampening system rollers at a slower speed than the plate cylinder.

3. The initial metering of the dampening fluid into a thin metered film is caused by forming a metering nip between two rollers.

Where the press is wide the rollers must be skewed so that there is a higher rate of feed at the ends of the roller.

While these prior art systems have found industry acceptance due to their fast response time, reduction waste and less need for skilled operators, several areas remain for improvement.

One problem area involves the tendency for ghosting to occur despite prior efforts to prevent it from occurring. In addition, the prior art systems tend to have an initial high cost, and the slip nips cause emulsification which can result in ink feedback into the fountain solution which can cause tinting. Also, some prior art systems require the additon of alcohol to the fountain solution.

There is also known in the prior art an inking system (sometimes referred to as the "Delta System") which is used to reduce the accumulation of foreign particles (referred to as "hickeys" on lithographic printing plates during printing. This system is illustrated in United States Patent No. 3,467,008 issued to Domotor. The Domotor patent is directed to a conventional system having one set of rollers for applying ink and another set of rollers for applying dampening solution. The dampening system in Domotor is not a continuous system and employs the conventional ductor roller.

In the system described in the Domotor patent, a gear drive is added to the first ink form roller so that it is driven at a lower surface speed relative to the speed of the plate cylinder and the vibrator roller. This causes two slip nips to form, one at the nip between the first ink form roller and the plate cylinder, and the second at the nip between the first ink form roller and vibrator roller. A scrubbing action occurs at the slip nip adjacent the plate cylinder which causes hickeys to be removed from the plate cylinder. The hickeys are transported along the ink train and are collected on a rider roller or in the ink fountain. This system, it has been found, substantially increases production and results in improved inking particularly in solid areas.

The Domotor system does have certain limitations. One is that the initial cost is high caused in part by designing a gear drive for the ink form roller. Another, limitation is the relatively high power requirement of the drive for the ink rollers and the need for helical drive gears to eliminate gear streaks.

In addition, the system described in the Domotor patent has, heretofore, been used only with conventional ink and dampening systems. This has occurred because it was thought necessary to run the dampening form roller at the same speed as the plate cylinder.

If this was not done it was feared that slurring of half-tones and slurring of the trailing edges ofsolids would result.

In view of the foregoing, the following are objects of embodiments of this invention.

a) To provide a new and improved dampening system.

b) To provide a new and improved dampening system having improved performance achievements.

c) To provide a new and improved dampening system which is inexpensive to manufacture.

d) To provide a new and improved dampening system which eliminates the need for variable speed drive motors for the transfer roller and the metering. rollers.

e) To provide a new and improved dampening system which substantially eliminates ghosting in continuous type lithographic printing presses.

f ) To provide a new and improved dampening system having a less expensive drive mechanism.

g) To provide a new and improved dampening system which substantially eliminates foreign particles and/or hickeys in a simple expeditious manner.

h) To provide a new and improved dampening system wherein there is a differential surface speed between the dampening roller and the plate cylinder so that foreign matter and/or hickeys are removed and ghosting is substantially reduced.

i) To provide a new and improved dampening system for lithographic presses wherein the dampening roller and the plate cylinder rotate and at different surface speeds to remove foreign particles and/or hickeys.

j) To provide a new and improved dampening system which prevents ink feedback into the dampening solution.

k) To provide a new and improved dampening system having a dampening roller having a different surface speed than the plate cylinder so that there is a wiping action which removes foreign particles.

1) To provide a new and improved process for use in connection with lithographic printing presses 'for improving printing quality by reducing ghosting.

m) To provide a new and improved process for use in lithographic printing presses of the contacting continuous type wherein the dampening fluid is applied so as to loosen foreign particles ànd substantially reduce ghosting.

n) To provide a new and improved process for use in connection with lithographic printing presses of the contacting continuous type having a plate cylinder and a dampening roller wherein the plate cylinder and dampening roller rotate at different surface speeds so as to cause a wiping action which loosens foreign particles from the plate cylinder.

According to one aspect of the present invention there is provided a device for dampening a rotatable plate cylinder of a lithographic press, comprising a pan for a supply of dampening fluid; pan roller means for rotation in said supply of dampening fluid; metering means which cooperate with said pan roller to meter the thickness of dampening fluid thereon; a rotatable roller which during operation is in contact with said plate cylinder and adapted to receive on its surface metered dampening fluid which fluid is transferred from the dampening fluid supply via said rotatable roller to said plate cylinder, and drive means adapted to rotate said rotatable roller so that said rotatable roller and said plate cylinder rotate at different surface speeds to provide a wiping action between said plate cylinder and said rotatable roller in order to remove foreign particles and reduce ghosting.

According to another aspect of the present invention there is provided a lithographic press of the type having drive means for rotating a plate cylinder and for rotating other rollers in the lithographic press system, wherein there is provided a pan for a supply of dampening fluid; pan roller means for rotation in said supply of dampening fluid, metering means which cooperate with said pan roller to meter the thickness of dampening fluid thereon, and a rotatable roller in contact with said plate cylinder and adapted to receive on its surface metered dampening fluid which fluid is transferred from the dampening fluid supply via said rotating roller to said plate cylinder, and wherein said drive means are adapted to provide relative rotation between said plate cylinder and said rotating roller such that the difference between the surface speeds of said rotating roller and said plate cylinder provides a wiping action between said plate cylinder and said rotatable roller so as to remove foreign particles and reduce ghosting.

According to a further aspect of the present.

invention, there is provided a process for removing hickeys and preventing ghosting in a printing process employing a rotating plate cylinder which comprises applying, by means of a roller, a metered amount of dampening fluid to the rotating plate cylinder such that a wiping action is produced between said roller and said cylinder.

According to a still further aspect of the present invention there is provided a process for dampening the rotatable plate cylinder of a lithographic press of the type having drive means for rotating said plate cylinder and for rotating other rollers in the lithographic press system, which system comprises: a pan supply of dampening fluid; pan roller means arranged for rotation in said supply of dampening fluid; metering means which are in cooperative relationship with said pan roller and are adapted to meter the thickness of dampening fluid thereon; a rotatable roller in contact with said rotating plate cylinder adapted to receive on its surface metered dampening fluid and transfer this fluid from said dampening fluid supply to said plate cylinder and wherein said drive means rotate said rotatable roller and said rotatable roller and said plate cylinder rotate at different surface speeds such that a wiping action is provided between said plate cylinder and said rotating roller so as to remove foreign particles and reduce ghosting.

Briefly described, the present invention relates to a new and improved dampening system. More particularly, in a preferred embodiment, there is provided an improvement for a dampening system of the continuous type wherein the speed of the roller carrying the dampening fluid is different relative to the plate cylinder speed. In a preferred embodiment the speed af the dampening roller is less than the speed of the plate cylinder.

Broadly speaking, an embodiment of the invention includes an ink form roller, a dampening fluid transfer roller, and a conventional metering mechanism for metering the dampening fluid. The dampening form roller can be conveniently interconnected to the drive mechanism for the lithographic press so that the dampening form roller runs at a constant speed which is less than the plate cylinder speed so that there is a wiping action between the form roller and the plate cylinder which loosens foreign matter and/or hickeys so that they can be subsequently removed.

An unexpected benefit of the invention is that ghosting is substantially eliminated which is normally a problem with continuous systems.

The first dampening form roller may be gear driven through gear interconnection with a chrome transfer roller at a speed which is intermediate the transfer roller and the plate cylinder.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1(a), (b) and (c) are schematic drawings illustrating certain of the prior art devices and practices.

Figure 2 is a schematic view of one embodiment of the invention.

Figure 3 is a schematic view of another embodiment of the invention.

Figure 4 is a schematic view of a further embodiment of the invention.

Figure 1 (a) shows in schematic form, a means and method for removing foreign particles from lithographic presses as shown in more detail in United States Patent No.

3,467,008 issued to Domotor. Such a system has been referred to herein as the "Delta" system.

As shown therein a rotatable lithographic plate cylinder 2 is provided which rotates in a counter-clockwis'e direction by conventional means not shown.

The inking system shown in Figure 1 (a) comprises an ink form roller 4, a dampening form roller 6, a vibrating roller 7 and a pan roller 8 rotating in a pan supply 10 containing fountain solution. The ductor roller 1 2 moves from an engagement position with the pan roller 8 to the dotted position where the dampening form roller 6 can transfer dampening fluid to the rotating cylinder 2 received from the vibrating roller 7. The ink form roller 4 moves in the same direction as the plate cylinder at their point of contact but at a slower surface speed. Skip nips are at the points labelled "S". It has been found that this arrangement substantially eliminates foreign particles known as hickeys so as to improve what is referred to in the trade as ink laydown.

In the system the roller 4 is part of the inking system which cooperates to remove the hickeys.

Figure 1(b) is a schematic showing of a prior art dampening system taught by various U. S. Patents such as 3,168,037; 3,259,062; 3,343,484: and 3,937,141. In such dampening systems a plate cylinder 14 engages a first ink form roller 1 6 which in turn engages a chrome pan roller 1 8 which rotates within a fountain solution pan 1 7. A metering roller 20 is provided which meters the fountain solution. The metering roller 20 is driven by a separate drive motor and controller 1 9 while the pan roller 18 is in geared relationship with the metering roller 20 so as to rotate the pan roller 1 8. In this system foreign particles (hickeys) can cause printing problems.

In Figure 1 (c) another prior art dampening form of mechanism is illustrated in schematic form.

This device comprises a rotating plate cylinder 22, a first ink form roller 24, and a dampening form roller 26. Optionally, there may be a bridge roller 32 between and in engagement with the first ink form roller 24 and the dampening roller 26. The pan roller 28 rotates in the fountain solution pan 29 and is in engagement with the dampening form roller 26 and the metering roller 30. The metering roller is driven by a separate drive motor and controller (not shown).

Referring to Figure 2, a first embodiment of the invention is shown in schematic form wherein a continuous inker feed type dampening system is provided.

In this embodiment, dampening means are provided whereby ghosting is substantially eliminated and hickeys and other foreign matter are removed.

As embodied, these dampening means include a rotatable plate cylinder 36 which rotate in a counter-clockwise direction. The rotating plate cylinder 36 engages a first ink form roller 38 which is rotated in the opposite direction to that of the plate cylinder, namely, in a clockwise direction. In this way, the surfaces of these rollers at their point of contact, move in the same direction. The dampening system includes a dampening fluid pan 40 within which extends a chrome pan roller 42. The chrome pan roller 42 is in rotating engagement with a resilientmetering roller 44 which meters the film of dampening fluid. Preferably, this resilient metering roller 44 is rubber covered. There is a separate drive motor and controller for the metering roller.

The metering roller 44 is geared to the chrome pan roller 42 which in turn contacts the first ink form roller 38. The ink form roller 38 moves in the opposite direction at the point of contact and at a surface speed slower than that of the plate cylinder. The difference in speed causes a wiping action between the plate cylinder 36 and the first ink form roller 38 thereby to loosen and remove foreign debris (sometimes referred to as hickeys) which accumulate in the ink regions of the plate cylinder.

Figure 3 illustrates another embodiment of this invention known as a continuous plate feed type dampening system.

This system has separate ink and dampening systems. As illustrated, there is a plate cylinder 46 and ink form rollers 48 in rolling contact with a vibrating roller 51. A dampening fluid applying roller 50 is in contact with the dampening roller 52 which in turn is in contact with a metering roller 54.

In this embodiment, the dampening fluid applying roller 50 is driven at a slower surface speed than that portion of the plate cylinder 46 which it contacts, so as to cause a wiping action which loosens foreign particles and permits their removal.

This system has the advantage that hickeys are removed. In addition, considerably less power is required for driving the dampening fluid applying roller 50 because one of the rollers it contacts is covered only with dampening fluid. Further, with this embodiment ghosting is substantially lessened.

Figure 4 illustrates, in schematic form, another embodiment of the invention. This embodiment relates to a combination version of the present invention. In this embodiment there is a plate cylinder 64, a dampening form roller 66 and a pan roller 68 rotating in the dampening fluid or fountain pan 70.

There is also a first ink form roller 72 and a bridge roller 74 between the first ink form roller and the dampening form roller. A conventional metering roller 76 may also be used to meter the dampening fluid.

The common denominator for all the embodiments of this invention is that the dampening fluid applying roller applies dampening fluid solution to the plate cylinder while moving at a different surface speed (preferably slower) from that of the plate cylinder. With such an arrangement foreign particles are loosened and ultimately removed, ghosting is substantially reduced, power consumption is reduced, and ink feedback to the dampening fluid is lessened.

Claims

1. A device for dampening a rotatable plate cylinder of a lithographic press, comprising a pan for a supply of dampening fluid; pan roller means for rotation in said supply of dampening fluid; metering means which cooperate with said pan roller to meter the thickness of dampening fluid thereon; a rotatable roller which during operation is in contact with said plate cylinder and adapted to receive on its surface metered dampening fluid which fluid is transferred from the dampening fluid supply via said rotatable roller to said plate cylinder, and drive means adapted to rotate said rotatable roller so that said rotatable roller and said plate cylinder rotate at different surface speeds to provide a wiping action between said plate cylinder and said rotatable roller in order to remove foreign particles and reduce ghosting.

2. A device as defined in claim 1 wherein said drive means are adapted to rotate said rotatable roller at a surface speed slower than that of said plate cylinder.

3. A device as defined in claim 1 or 2 which constitutes an inker feed type dampening system.

4. A device as defined in claim 1 or 2 which constitutes a plate feed type damping system.

5. A device as defined in claim 1 or 2 which constitutes a combination type damping system.

6. A device for dampening a rotatable plate cylinder of a lithographic press substantially as herein described with reference to any of Figures 2 to 4 of the accompanying drawings.

7. A lithographic press of the type having drive means for rotating a plate cylinder and for rotating other rollers in the lithographic press system, wherein there is provided a pan for a supply of dampening fluid; pan roller means for rotation in said supply of dampening fluid, metering means which cooperate with said pan roller to meter the thickness of dampening fluid thereon, and a rotatable roller in contact with said plate cylinder and adapted to receive on its surface metered dampening fluid which fluid is transferred from the dampening fluid supply via said rotating roller to said plate cylinder, and wherein said drive means are adapted to provide relative rotation between said plate cylinder and said rotating roller such that the difference between the surface speeds of said rotating roller and said plate cylinder provides a wiping action between said plate cylinder and said rotatable roller so as to remove foreign particles and reduce ghosting.

8. A process for removing hickeys and preventing ghosting in a printing process employing a rotating plate cylinder which comprises applying, by means of a roller, a metered amount of dampening fluid to the rotating plate cylinder such that a wiping action is produced between said roller and said cylinder.

9. A process for dampening the rotatable plate cylinder of a lithographic press of the type having drive means for rotating said plate cylinder and for rotating other rollers in the lithographic press system, which system comprises: a pan supply of dampening fluid; pan roller means arranged for rotation in said supply of dampening fluid; metering means which are in cooperative relationship with said pan roller and are adapted to meter the thickness of dampening fluid thereon; a rotatable roller in contact with said rotating plate cylinder adapted to receive on its surface metered dampening fluid and transfer this fluid from said dampening fluid supply to said plate cylinder and wherein said drive means rotate said rotatable roller and said rotatable roller and said plate cylinder rotate at different surface speeds such that a wiping action is provided between said plate cylinder and said rotating roller so as to remove foreign particles and reduce ghosting.

18. A process as defined in claim 9 wherein said rotatable roller is rotated at a surface speed slower than that of said plate cylinder.

11. A process for dampening the rotatable plate cylinder of a lithographic press substantially as herein described with reference to any of Figures 2 to 4 of the accompanying drawings.