WO1997029911A1

WO1997029911A1 - A method and device for controlling the temperature of an image cylinder in a printing-press

Info

Publication number: WO1997029911A1
Application number: PCT/AU1996/000084
Authority: WO
Inventors: Martin David Allum
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-08-18
Filing date: 1996-02-16
Publication date: 1997-08-21
Anticipated expiration: 1998-08-16
Also published as: AU3013695A

Abstract

The present invention discloses a method and device for controlling the temperature of a plate cylinder in an offset printing-press. In one embodiment a first heat transfer element (26) constructed of a copper tube is retrofitted to a known offset printing-press (10). The copper tube is configured to sit in the base of a water bath (20). Iced water is pumped through the copper tube which thus controls the temperature of fountain water (22) in the water bath (20). In a preferred example, the temperataure of the water (22) is controlled within a temperature range of approximately 1 °C to 8 °C. It is apparent from comparative trials that temperature control of a plate cylinder in accordance with the present invention consistently produces a sharp image. Furthermore, the risk of emulsification is reduced.

Description

A METHOD AND DEVICE FOR CONTROLLING THE TEMPERATURE OF AN IMAGE CYLINDER IN A PRINTING-PRESS

FIELD OF THE INVENTION

The present invention relates generally to a method and device for controlling the temperature of an image cylinder in a printing-press and relates particularly, though not exclusively, to controlling the temperature of a plate cylinder in an offset printing-press.

BACKGROUND TO THE INVENTION In a typical offset printing-press there is provided a bank of ink rollers, a bank of water rollers, a plate cylinder, a blanket cylinder, and a bottom cylinder. The plate cylinder has a paper or metal plate, which carries an image to be printed, secured to its circumferential surface. The paper or metal plate has the image burnt into its surface, the image consisting of silver or aluminium. The bank of ink rollers transfer ink from an ink tray to the plate cylinder. The bank of water rollers transfer water from a water bath to the plate cylinder. The water roller in contact with the plate cylinder is referred to as a molloton. The molloton has a sleeve fitted around its circumferential surface. The sleeve is constructed of a cylindrical mesh with a wool fibre woven therein. The molloton together with the water keeps the non-image regions of the plate clean to prevent excessive ink build¬ up thereon.

The plate cylinder contacts the blanket cylinder and transfers the image from the blanket cylinder onto paper or other print media. Typically paper in the form of a sheet or a continuous roll is fed between the blanket cylinder and the bottom cylinder. Adjacent rollers contact each other, except for an ink or a water duetor roller whic radially oscillates or swings within the bank of ink or water rollers, respectively. The rotational speed of the ink and water rollers can be varied by an operator. The frequency of oscillation of the ink or water ductor rollers can also be adjusted to control the transfer of ink or water, respectively, to the plate cylinder. The amount and rate of ink or water transferred to the plate cylinder can thus be controlled by a combination of the rotational speed of the ink or water rollers and the frequency of oscillation of the ink or water ductor rollers.

For quality offset printing it is important that the water solution be controlled at an optimum pH level and hardness/softness level. This is presently achieved by, for example, the addition of a fountain concentrate which maintains the pH level between 4.8 to 5.2 and the hardness level between 8° dH to 14° dH. This, however, will depend largely on the pH and hardness levels of the water to be treated. The water solution when treated with the fountain concentrate is referred to as fountain water.

A common problem experienced in particular with offset printing is in relation to emulsification. Emulsification is where fine droplets of water become dispersed in the ink resulting in a dull or unacceptable image. This is particularly common in regions where there is high relative humidity, as for example in Sydney, Australia. Moisture from the humid atmosphere is then dispersed in the ink possibly resulting in emulsification.

Another problem experienced with offset printing is in connection with bleed-off. Bleed-off is where ink builc.s up either on the plate cylinder around the periphery of the plate or on a leading edge of the plate, where it is connected to the plate cylinder, and is then transferred to the blanket cylinder and the paper printed. This can occur where, for example, the viscosity of the ink is gradually reduced during operation of the press and consequently ink builds up in these areas.

When the above mentioned problems occur it is usually necessary to shut down the printing-press and clean the rollers, cylinders, and ollotons. The mollotons are removed and cleaned with a solvent or safety wash using a brush and subsequently scraped with a blade. The mollotons are then dried using, for example, a sheet of newspaper. The other rollers can either be cleaned in-situ or removed and cleaned using a cloth and, for example, methylated spirits. Alternatively the ink rollers can be cleaned in- situ using a wash-up tray. The printing-press is then reinked, milled-up and printing recommenced. The cleaning and reinking alone may take up to fifty (50) minutes depending on the ink used. The lower viscosity inks, such as gold ink, are likely to consume more time than the higher viscosity inks, such as black ink.

In some offset printing-presses a mixture of alcohol and water may be used as an alternative cleaning fluid to solely fountain water as hereinbefore described. Similar problems with emulsification and bleed-off are also experienced with alcohol and water mixtures.

Down-time associated with problems such as emulsification and bleed-off can consume a large percentage of the total print time. Consequently the total cost of a print run to the printer and, therefore, his client is increased.

SUMMARY OF THE INVENTION

An intention of the present invention is to provide a method and device for controlling the temperature of an image cylinder in a printing-press to substantially inhibit problems, such as emulsification or bleed-off, associated with the quality of the image resulting therefrom. According to a first aspect of the present invention there is provided a method for controlling the temperature of an image cylinder in a printing-press, wherein the image cylinder is used for transferring ink to a print medium, said method comprising the step of: maintaining the temperature of the image cylinder within a first effective temperature range whereby, in use, the printing-press can more consistently produce a sharp image on the print medium.

Typically, the image cylinder is in fluid communication with a cleaning fluid and said method further comprises the step of controlling the temperature of the cleaning fluid within a second effective temperature range so that the temperature of the image cylinder is maintained within the first effective temperature range by heat transfer between the image cylinder and the cleaning fluid.

According to a second aspect of the present invention there is provided a device for controlling the temperature of an image cylinder in a printing-press, wherein the image cylinder is used for transferring ink to a print medium, said device comprising: temperature control means for maintaining the image cylinder within a first effective temperature range whereby, in use, the printing-press can more consistently produce a sharp image on the print medium.

Typically, the image cylinder is in fluid communication with a cleaning fluid wherein the temperature control means comprises : a heat exchange device in heat conductive communication with the cleaning fluid so that the cleaning fluid is maintained within a second effective temperature range, and the temperature of the image cylinder is maintained within the first effective temperature range by heat transfer between the image cylinder and the cleaning fluid.

Typically, the first effective temperature range is 0°C to 10°C. More typically the first effective temperature range is 2°C to 5°C.

Preferably, the second effective temperature range is 0°C to 20°C.

More preferably, the second effective temperature range is 1°C to 8°C.

Preferably, the heat exchange device comprises a first heat transfer element in contact with the cleaning fluid.

Typically, the first heat transfer element contains a heat exchange fluid at a controlled temperature whereby, in use, the cleaning fluid transfers heat to the heat exchange fluid via the first element.

In one example, the controlled temperature is between 0°C to 5°C.

Typically, the cleaning fluid is at least partly contained in a cleaning fluid bath which is in fluid communication with the image cylinder.

Alternatively, the heat exchange device comprises means for recirculating the cleaning fluid through the cleaning fluid bath whereby, in use, the cleaning fluid is returned to said bath at a temperature within the second effective temperature range.

In yet another embodiment, the heat exchange device comprises a second heat transfer element in heat conductive communication with the cleaning fluid bath so that, in use, heat from the cleaning fluid is transferred to the second heat transfer element via a wall of said bath.

Typically, the second heat transfer element is part of a solid state device.

Typically, the cleaning fluid comprises a water based solution. Alternatively, the cleaning fluid comprises a mixture of water and alcohol.

It has been discovered that by maintaining the temperature of the image cylinder within the first effective temperature range results in emulsification being substantially inhibited.

Advantageously, maintaining the temperature of the image cylinder within the first effective temperature range also appears to substantially inhibit bleed-off.

BRIEF DESCRIPTION OF THE DRAWING

In order to achieve a better understanding of the nature of the present invention preferred embodiments of the method and device for controlling the temperature of an image cylinder in a printing-press will now be described, by way of example only, with reference to the accompanying drawing in which:

Figure 1 is a schematic diagram of a known offset printing-press showing the configuration and disposition of rollers (excluding a blanket and a bottom cylinder) together with a preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As shown in Figure 1, a typical printing-press, in this example a known offset printing-press 10, comprises a bank of ink rollers 12, a bank of water rollers 14, and a plate cylinder 16. The known offset printing-press 10 further comprises a header-reservoir 18 plumbed to a water bath 20. The header-reservoir 18 provides cleaning fluid, in this example, water 22, to the water bath 20. The reservoir 18 includes a seal plug (not shown) releasably located in its base. The plug is opened when an actuating rod (not shown) coupled thereto is forced against the base of the water bath 20. A tube 24 surrounding the plug and connected to the base of the reservoir 18 is set at a predetermined height relative to the water bath 20. The reservoir 18 then fills the water bath 20 to this predetermined height and thus maintains a constant level of water 22 in the water bath 20.

A preferred example of a device according to the present invention retrofitted to the known offset printing-press 10 will now be described. The device comprises temperature control means, in this example a first heat transfer element 26 constructed of a copper tube formed in a continuous loop arrangement. The copper tube is configured to sit in the base of the water bath 20. The copper tube has an inlet and an outlet each coupled to an upstream and a downstream tube, respectively. A heat exchange fluid, in this embodiment iced water or a refrigerant, can be recirculated through the first element 26 using a pump (not shown) . The pump is activated by a temperature controller having a temperature probe submerged in the water 22 in the water bath 20. In this example, the temperature of the water 22 is controlled within a temperature range of approximately 1°C to 8°C. When the temperature of the water 22 rises above a first set point, for example 8°C, the pump is activated and the iced water or refrigerant recirculates through the first element 26. The water 22 in the water bath 20 is thus cooled and the pump deactivated once the temperature of the water 22 falls below a second set point, for example 1°C. In this embodiment the second effective temperature range is thus 1°C to 8°C. In another possible embodiment, the water 22 can be recirculated through the water bath 20, being cooled to the required temperature outside of the bath 20 and returned to the bath 20 thereafter.

Alternatively the bath 20 can be cooled using a second heat transfer element of a solid state device which is in heat conductive communication therewith. Semiconductor thermoelectric devices working on the Peltier effect are an example of the second heat transfer element suitable for this purpose.

In a further embodiment the second heat transfer element may be similar to the firεt heat transfer element 26 described above but located below the base of the water bath 20 and clad with a suitable insulation material.

In the above embodiments of the present invention the device for controlling the temperature of the offset printing-press 10 uses a first or second heat transfer element in contact or heat conductive communication with the cleaning fluid or water bath 20, respectively. The temperature of the plate cylinder 16 may in fact be controlled by removing heat directly from its circumferential surface using, for example, a solid state cooling device located within the roller. One of the bank of water rollers 14 may be cooled in a similar manner, to facilitate heat transfer to it from the plate cylinder 16 via the cleaning fluid and/or intermediate rollers. A further alternative is to isolate a section of the offset printing-press 10 within a housing and control the temperature of the atmosphere contained therein, so as to control the temperature of the plate cylinder 16.

An example of the method for controlling the temperature of an image cylinder in a printing-press will now be described with reference to the device fitted to an offset printing- press 10 as described above.

The offset printing-press 10 was firstly set up so that the appropriate amount and rate of both ink and water were fed to the plate to produce a sharp image. The temperature of the water 22 in the water bath 20, and the rotational speed setting of the bank of ink rollers 12 and bank of water rollers 14 was then recorded (see Table 1) .

The press 10 was then operated without controlling the temperature of the water 22. During a print run of 1250 copies the following observations were made. After 400 copies excessive water had built up in the mollotons and they were showing ink tracking around their circumferential surface. After 600 copies the blanket cylinder was showing signs of picking or dust build up. At the completion of the run the paper plate was deteriorating and both the plate cylinder 16 and the blanket cylinder had excessive ink built up on each of their circumferential surfaces. The mollotons needed to be removed and cleaned with a solvent, and the plate cylinder 16, the blanket cylinder, and the bottom cylinder each cleaned with a solvent. Furthermore, the stack of copies had to be unloaded every 400 copies to reduce set-off on the reverse side thereof as a consequence of insufficient drying time. The ink coverage, ink usage, water usage, plate condition, blanket cylinder condition, molloton condition, and time elapsed for the image to dry on a copy are recorded in Table 1.

The offset printing-press 10 was then operated while controlling the temperature of the water 22 by the periodic addition of ice to the water bath 20. Similar data to that described above was then recorded before and after another print run of 1250 copies (see Table 1) . Each run was printed at the same paper feed speed. The only interruption during this print run, was for approximately 20 seconds, due to a paper misfeed. TABLE 1

Without With Temperature Temperature Control of Control of the Water the Water

Water Temperature 22°C 5°C

Water Setting No. 3 No. 1

Water Usage 240 ml 1 ml

Ink Setting No. 2 No. 1

Ink Coverage Light Light

Ink Usage 5 grams 4 grams

Duration of Print 20 minutes 14 minutes Run

Plate Condition Average Excellent

Blanket Condition Average Excellent

Molloton Poor Excellent Condition

Drying Time 26 minutes 21 minutes

Table 2 below shows the results of another comparative trial where the water bath 20 was periodically filled with ice. Results are shown both without and with the addition of ice to the water bath 20. The print runs in each instance were for a total of 10,000 copies at the same paper feed speed. After approximately 7700 copies ice was no longer added to the bath and the water 22 temperature progressively rose. As the temperature rose there was a deterioration in the sharpness of the image and the transfer of water 22 to the plate cylinder 16 was subsequently increased so as to improve the sharpness of the image. TABLE 2

Without With Temperature

Temperature Control of

Control of the Water the Water

Water Temperature 21°C 5°C

Water Setting 2 0

Ink Setting 5 2

Ink Coverage Medium Medium

Ink Usage 134 g 100 g

Plate Condition Poor Excellent

Blanket Condition Poor Good

Molloton Poor Excellent Condition

Table 3 below shows the results of another comparative trial where iced water was recirculated through the copper tube 26 of the first heat transfer element of the possible embodiment described above. During a print run of 10,000 copies without temperature control the following observations were made. After 5100 copies the blanket and plate cylinders required cleaning taking approximately 3.5 minutes and resulting in the loss of approximately 100 sheets. After 8000 copies the plate was showing signs of deterioration. After 8900 copies the blanket and plate cylinders again required cleaning taking approximately 2.5 minutes. After 9100 copies a new plate was required due to deterioration of the old plate, and this resulted in approximately five (5) minutes of down-time. The offset printing-press 10 required a complete clean after this print run, taking approximately 20 minutes.

During a print run of 10,000 copies with temperature control of the water, the printing-press 10 ran continuously without any loss of production time associated with cleaning or any other problems. Furthermore, the plate did not require replacement during the temperature controlled print run. The copies printed were substantially flat showing no signs of possible paper curl. Both comparative trials were run at the same paper feed speed.

TABLE 3

Without With Temperature

Temperature Control of

Control of the Water the Water

Water Temperature 17°C to 20.5°C 3.3°C to 5.0°C

Water Setting No. 3 No. 1

Ink Setting No. 4 to No. 5 No. 3

Ink Coverage Medium Medium

Ink Usage 129 Grams 109 Grams

Duration of 1 hour 52 minutes 1 hour 36 minutes Print Run

Water Usage 500 ml 250 ml

Plate Condition Poor Excellent

Blanket Condition Poor Excellent

Molloton Poor Excellent Condition

Bottom Cylinder Poor Excellent Condition

A comparison of the results in Tables 1, 2, and 3 indicate that when the temperature of the plate cylinder 16 of the printing-press 10 is controlled in accordance with the present invention, at least the following advantages may be observed:

1. the sharpness of the image is consistently improved;

2. there is a reduced risk of emulsification; 3. bleed-off is substantially inhibited;

4. the amount of ink used for the same number of copies is reduced; 5. the time taken for the ink to dry on the copies is reduced;

6. down-time associated with cleaning plates, rollers, cylinders or mollotons is reduced thereby increasing productivity;

7. the amount of cleaning fluid, (in the embodiment described, water) , used for a given number of copies is reduced;

8. the likelihood of set-off is reduced because of a reduction in drying time;

9. tracking is reduced where ink can be transferred from feed rollers to the edges and/or the surface of the paper; and,

10. paper curl is reduced so that the paper does not need to be flattened prior to printing on an opposite face thereof.

It will be apparent to persons skilled in the relevant arts that numerous variations and modifications can be made to the described method and device, in addition to those already mentioned above, without departing from the basic inventive concepts. For example, the device described herein could alternatively be fitted to an integrated type printing-press rather than the molloton type printing-press disclosed herein. Furthermore the temperature control device need not be retrofitted to an existing printing- press but may be manufactured as an integral component thereof. The temperature of the image cylinder may be controlled within a first effective temperature range by a variety of means only some of which have been described above as possible embodiments of the present invention. All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS;

1. A method for controlling the temperature of an image cylinder in a printing-press, wherein the image cylinder is used for transferring ink to a print medium, said method comprising the step of: maintaining the temperature of the image cylinder within a first effective temperature range whereby, in use, the printing-press can more consistently produce a sharp image on the print medium.

2. A method for controlling the temperature of an image cylinder in a printing-press as defined in claim 1 wherein the first effective temperature range is 0°C to 10°C.

3. A method for controlling the temperature of an image cylinder in a printing-press as defined in claim 1 wherein the first effective temperature range is 2°C to 5°C.

4. A method for controlling the temperature of an image cylinder in a printing-press as defined in any one of the preceding claims wherein the image cylinder is in fluid communication with a cleaning fluid, and said method further comprises the step of controlling the temperature of the cleaning fluid within a second effective temperature range so that the temperature of the image cylinder is maintained within the first effective temperature range by heat transfer between the image cylinder and the cleaning fluid.

5. A method for controlling the temperature of an image cylinder in a printing-press as defined in claim 4 wherein the second effective temperature range is 0°C to 20°C.

6. A method for controlling the temperature of an image cylinder in a printing-press as defined in claim 4 wherein the second effective temperature range is 1°C to 8°C.

7. A device for controlling the temperature of an image cylinder in a printing-press, wherein the image cylinder is used for transferring ink to a print medium, said device comprising: temperature control means for maintaining the image cylinder within a first effective temperature range whereby, in use, the printing-press can more consistently produce a sharp image on the print medium.

8. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 7 wherein the first effective temperature range is 0°C to 10°C.

9. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 7 wherein the first effective temperature range is 2°C to 5°C.

10. A device for controlling the temperature of an image cylinder in a printing-press as defined in any one of claims 7 to 9 wherein the image cylinder is in fluid communication with a cleaning fluid and the temperature control means comprises: a heat exchange device in heat conductive communication with the cleaning fluid so that the cleaning fluid is maintained within a second effective temperature range, and the temperature of the image cylinder is maintained within the first effective temperature range by heat transfer between the image cylinder and the cleaning fluid.

11. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 10 wherein the second effective temperature range is 0°C to 20°C.

12. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 10 wherein the second effective temperature range is 1°C to 8°C.

13. A device for controlling the temperature of an image cylinder in a printing-press as defined in any one of claims 10 to 12 wherein the cleaning fluid is at least partly contained in a cleaning fluid bath which is in fluid communication with the image cylinder.

14. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 13 wherein the heat exchange device comprises means for recirculating the cleaning fluid in the cleaning fluid bath whereby, in use, the cleaning fluid is returned to said bath at a temperature within the second effective temperature range.

15. A device for controlling the temperature of an image cylinder in a printing-press as defined in any one of claims 10 to 14 wherein the heat exchange device comprises a first heat transfer element in contact with the cleaning fluid.

16. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 15 wherein the first heat transfer element contains a heat exchange fluid at a controlled temperature whereby, in use, the cleaning fluid transfers heat to the heat exchange fluid via the first element. AMENDED CLAIMS

[received by the International Bureau on 16 July 1996 (16.07.96); new claims 17-19 added; remaining claims unchanged (1 page)]

17. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 16 wherein the controlled temperature is between 0°C to 5°C.

18. A device for controlling the temperature of an image cylinder in a printing-press as defined in claim 13 wherein the heat exchange device comprises a second heat transfer element in heat conductive communication with the cleaning fluid bath so that, in use, heat from the cleaning fluid iε transferred to the second heat transfer element via a wall of said bath.

19. A device for controlling the temperature of an image cylinder in a printing-press aε defined in claim 18 wherein the second heat transfer element iε part of a εolid state device.