EP0299203B1 - Cleaning device for printing machines - Google Patents

Abstract

A process and device for cleaning the rubber blankets of web offset printing machine while the web is running, wherein the washing agent (detergent) used for loosening the ink and paper residues on the rubber blanket is partly absorbed by the print web and passes on to the drier. During cessation of printing, on which a rising and then a falling ink-residue curve and a corresponding washing agent loading curve are superimposed, an undesirably high level of volatilisation can take place. The quantity of vapour can, on the one hand, be controlled by the washing programme. On the other hand, the quantity of vapour can be regulated by intervention in the volatilisation process by means of a substance applied to the surface of the web. The application of the substance inhibits the volatilisation, modifies the ratio of components of the vapour and, in addition, the volatilising components can be sealed in. Water is of prime importance as the relevant substance. A spray device is arranged at the entrance of the drying unit, which device is charged quantitatively and time-wise with the objective of producing the lowest possible concentration of explosive or harmful vapours. <IMAGE>

Description

The invention relates to a printing machine cleaning device according to the preamble of claim 1.

A comparable device is known from DE 30 05 469 A1. It relates generally to the washing of blankets in rotary printing presses. The measure can be applied both to the blanket cylinder of a sheet-processing printing machine and to the blanket cylinder of a roll-processing printing machine.

From GB-A 660 001 a possibility is known of accelerating drying of a layer which only dries at elevated temperature and is applied to the carrier material. In order to achieve faster evaporation and a lower boiling temperature, for example of a printing ink which contains a first solvent, a second solvent is introduced into a drying chamber, which forms a solvent mixture with the first solvent, with which the desired acceleration occurs. However, the addition of additional solvent leads to an increased risk of explosion in printing machines.

The rubber blankets get dirty during the production process mainly due to the build-up of sticky paint residues and sticky paper dust. The point sharpness that is important in autotypical halftone printing is lost, some print lots no longer print out correctly.

In order to eliminate the fault from soiling the blanket, the pressure is interrupted and blanket washing is carried out by hand or by apparatus. According to DE 30 05 469 A1, a washing bar is attached for washing rubber blankets with apparatus to the rubber cylinder of the printing unit, which bears a pressure element which can be brought into and out of contact with the moving rubber blanket. The cleaning effect is due to the rubbing and dissolving of the soiled particles on the rubber blanket, the dirt being absorbed with the help of a washing cloth removed during the blanket washing.

A wash bar of a blanket washing system is usually arranged in the direction of rolling in front of the printing nip through which the printing material runs, that is to say in front of the inking. This area concerns the advance of the printing ink and the dampening solution in the shortest way and the shortest dwell time from the plate cylinder to Printing web. When detergent gets on the rubber cylinder, the path of the detergent to the printing path is the same as the path of the printing ink. Some of the detergent splits onto the printing web, some remains and drives back to the washing station.

On the other hand, for reasons of space and construction, the wash bar can also be located in the return area between the printing nip and the plate cylinder. The rubber blanket then gave off ink and dampening solution to the printing substrate during the splitting and picked up the youngest paper particles when it came into contact with the printing substrate, whereupon it was then rolled over again by the printing plate carrying the dampening solution and ink.

The inking unit and dampening unit are usually switched off during washing, i.e. in the lifted state, in order to avoid the splitting of dirt and washing solution, which otherwise occurs during the washing process, onto the inking and dampening rollers right down to the inking and dampening solution box.

However, switching off the inking unit and dampening unit during the washing process is not a one-sided condition. How to proceed depends on the type of press and is also based on experience. The risk of web breakage is greater, for example, when the dampening system is switched off during washing because the dampening solution is pushed when the dampening system is switched on again. From this point of view, it may be necessary to leave the dampening system on.

The appropriate control in the up and down position of the inking or dampening unit is decided based on the machine and production characteristics. In the case of a high non-printing portion and thus larger dampening solution transfer areas, conversely with a high proportion of ink, with coated and uncoated, with light and with heavy paper, a different driving style may be appropriate.

During the washing process itself, the printing unit cylinders are moved into the print-on position with the position rolling against one another under surface pressure, with the printing gap closed, through which the printing material is transported. It is also possible to carry out the washing process in the pressure-down position, in which the pressure gap is open. The cylinder circuit depends on the respective substrate, which is common in common four-cylinder systems due to the offset of the planes formed by the plate cylinder and blanket cylinder, which can be placed through the axes, so that in both positions the contact of the substrate with the blanket is guaranteed. By touching the substrate with the rubber blanket, dirt and detergent can be removed via the substrate.

In the case of satellite systems, the selection of the cylinder circuit depends on the printing unit assignment.

For washing, the pressure element goes from the rest position into the working position in frictional contact with the rubber blanket. The pressure element results in line or surface pressure between the washcloth and the rubber blanket, so that dirt and detergent can pass from one side to the other. The pressure element consists for example of a controllable membrane, it can also be designed as a rotating or non-rotating brush.

The detergent consists of aqueous phase components mainly for the paper dust and organic solvent components mainly for the softening or dissolving of the color residues. It can be a mixture. It is also common to feed individual components in a specific order.

The efficiency of the washing process depends largely on the respective washing program, after which the timing and quantity of the washing component supply is controlled. The advancement of the washcloth in the ratio of soiled, soaked parts to clean parts also plays an important role.

In the prior art according to DE 30 05 469 A1, the application of the liquid components in connection with the wash cloth advance is carried out via time-controlled valves switched into the supply lines and servo drives controlled together with them. The commands are issued by a control unit.

Washing is required when the print quality is no longer sufficient due to the soiling. Although modern alcohol film dampening systems can have a certain influence on the soiling of the blanket using various parameters such as zone-specific dampening solution guidance, ductor speed, alcohol percentage, etc., blanket washing is indispensable for longer printing periods, also for reasons of plate and blanket service life.

The washing process is put into the continuous printing phase with the machine running continuously, with the amount of waste being minimized with regard to the washing program, which can be designed specifically for the machine and the order. The washing process can also be controlled on occasions related to general set-up activities, e.g. on the occasion of a machine stop for the plate change, an intervention on the folder, etc. Shutting down from continuous printing to standstill and vice versa from standstill of the printing press to continuous printing operation offers itself, as it were, outside of the rubber blanket washing that is absolutely necessary.

Part of the soiling, including detergent, goes into the washcloth, and part is removed via the printing material web, which passes through the dryer and folder after the printing units. This inevitably creates the situation that the dryer, whose task it is in web offset printing to bring the heatset inks into a pasty state due to evaporation of the liquid components, is additionally burdened by detergent. Regarding the drying process in web offset, reference is made to the information in "Druckwelt" 13/1971, pages 590 to 592 and "Papier und Druck", 24, 1975, pages 74 ff.

During the washing period, the concentrations in the gas phase of the drying oven operated with a slight negative pressure therefore change. The shift in concentration that results between the steady state during continuous printing and the state during washing must be counteracted to the extent that possible disturbances both in the area of the dryer and in the area of the processes downstream of the drying process, e.g. afterburning are brought to the lowest possible level. This primarily includes the avoidance of impermissible concentrations which can lead to an explosion or which result in MAK values outside the legal requirements.

From the brochure on "Safety rules for explosion protection on continuous dryers of printing and paper processing machines", Carl Heymanns Verlag KG, Cologne, 1984, information about monitoring devices on the dryer is given. According to the regulation, the monitoring devices comprise a temperature indicator including a temperature controller, the mode of operation of which is designed to ensure that the limit temperature is not exceeded in the amount of 80% of the ignition temperature. According to the regulation, 5 measured values per minute and measuring point are recorded by means of a gas warning device. This state of the art with regard to dryer equipment is in contrast to practice, where hardly any sensing devices are used and the dryers are operated based on experience, without taking the washing process into account.

In view of the problem of the increased accumulation of steam during the washing process, individual dryer manufacturers recommend opening the exhaust air flap of the dryer fully to achieve better gas removal, but the burner of the dryer and the dryer recirculation fan continue to operate normally.

The operating instructions specified for the washing operation are rigid and purely precautionary, without any closer adaptation to the actual real process with the actual concentration values being shown.

It is known in the area of the post-combustion system that the increased proportion of combustible exhaust gases as a result of the washing process combined with the higher calorific value of the exhaust gases can lead to excess temperature in the combustion chamber.

Process control to reduce or eliminate malfunctions naturally depends on the various parameters of the printing process itself, the drying process and the input materials. The amounts evaporating in the dryer on the part of detergents can be influenced by the selection of the detergent composition with regard to the proportionate liquids. The printed image also plays a role in terms of the printing area, because in the maximum case there can be 400% coverage of the printed image when the colored inks are overlaid with black and a correspondingly high color vapor concentration. It is therefore advisable to take the printing area proportions into account as input parameters. If there is a high proportion of non-printed, i.e. paper-white, areas, the ink vapor content is lower and the dampening solution is more concentrated.

Furthermore, the knocking of the dampening solution parts into the printing material goes into the binding, the binding of the detergent parts compared to e.g. Natural paper and coated paper are also different.

It is therefore an object of the present invention to influence the course of the steam concentration in the dryer with simple means.

This object is solved by the features of claim 1.

The solution is essentially aimed at restricting the proportions that evaporate during the washing process by means of a material measure.

In contrast, according to CH 287 535, it is known to radiate steam onto the surface of the printing material web. With the superheated steam, to which additional heat can be added the moisture of the web can be evaporated. According to DE 27 59 666 B2, it is known to use superheated steam as a conditioning medium for the paper web, which is blown onto the printing web from a conditioning tunnel arranged in the initial region of the dryer.

Although the steam also interferes with the pressure in the drying oven, it is only used to condition the substrate in order to prevent it from over-drying.

According to the invention, the medium applied to the printing web before drying begins reacts physically or chemically on the web surface. From a physical point of view, its wetting hinders the evaporation of the gaseous products from the printing ink or from the detergent under the influence of heat. The medium itself absorbs heat, so that the heat transfer is changed. The detergent is heated later and with a different amount.

From a chemical point of view, a rapidly polymerizing substance can be applied that virtually forms a coating. In the case of inorganic agents, the precipitation of a coating from a previously aqueous solution can be achieved.
The coating seals the parts evaporating from the printing web.

Water as an applied substance is easy to handle and offers advantages with regard to the supply, non-aggressiveness and usability that exist with dangerous substances. The moistened web makes folding easier.

The quantities of the substance to be applied must be measured precisely. In the chronological sequence of the application, the temporal distribution of the color residues and detergents, as can be seen on the running printing web, is taken into account. When cleaning the rubber blankets one after the other, a different amount of detergent appears than when cleaning all dirty rubber blankets at the same time.

Zone-by-zone metering of the substance can compensate for zone-by-zone differences in the printed image that go into soiling and thus detergent use.

To keep the dryer entrance accessible, e.g. is necessary for the web feed, the applicator for the material, which is arranged in the area of the dryer entrance, is held displaceably in and against the web unwinding direction. When using a spraying device as an application unit, the nozzles arranged in a row transversely to the printing path can be individually adjusted and acted upon in order to take account of the possibility of zone-by-zone application in a specific profile.

Advantageous operability is achieved by equipping the applicator unit, which can be partially encapsulated in a box, with a rail guide and a servo drive for displacement.

The timely and qualitatively appropriate application of material to the ink residues and detergents appearing on the printing web is carried out with the aid of a control device that controls the various parameters that can be entered, such as area coverage in the print, web speed, times and transfer quantities of the detergent in the individual printing units and condition variables in the dryer. The latter includes the vapor concentration, supply and exhaust air that can be recorded by measuring sensors and, for example, gas flow. The corresponding actuating devices can be acted upon on the basis of the parameter values. Its scope relates to the wash cloth feed, detergent discharge, material application, dryer flaps and, if applicable, gas supply. In terms of control, the control device can be connected to the control center of the printing line.

Fig. 1:

Schematische Darstellung einer Rollenoffset-Druckmaschine.

Fig. 2:

Ansicht des Auftragswerks zwischen letztem Druckwerk und Trockner.

Fig. 3:

Schematischer Meß- und Stellaufbau bezüglich eines Druckwerks mit Gummituchwaschvorrichtung, Stoffauftragswerk und Trockner.

Fig. 4:

Dampfkonzentrationskurven über die Trocknerlänge.

The invention is explained in more detail below using an exemplary embodiment:

Fig. 1:

Schematic representation of a web offset printing press.

Fig. 2:

View of the application unit between the last printing unit and the dryer.

Fig. 3:

Schematic measurement and control setup with regard to a printing unit with blanket washing device, material application unit and dryer.

Fig. 4:

Steam concentration curves over the dryer length.

According to Figure 1, the printing web 1 runs from the roll into the printing units 2, in which the respective image colors are printed in register. When printing on the printing web 1, dampening solution originating from the dampening systems reaches the pressure-free areas of the plate and the ink and dampening solution mixture on the rubber blanket and consequently on the printing web 1. The moisture content of the printing web 1 increases. The inks of the heatset type are thickened in the dryer 3 to such an extent that after cooling while running over the cooling roller surfaces, they produce a surface which can be processed in the folder 4 and which no longer smears.
The dryer 3 has inlet connections and chimneys for the exhaust air.

From Fig. 2 is shown against the blanket cylinder 5 for fine and the blanket cylinder 5 for back pressure wash bar 6. Ink and dampening rollers transfer the printing inks and the dampening solution to the printing plate, which is clamped onto the plate cylinder.

The planes that can be laid by the axes of the cylinder pairs consisting of plate and rubber cylinders 5 are offset in the four-cylinder system shown, so that the printing web 1 the printing gap between the rubber cylinder 5 for straight printing and the rubber cylinder 5th S-shaped for counterpressure. The S-shaped course is also in the print-down position of the pressure cylinder. S-shaped course results in contact of printing web 1 and rubber cylinder 5 and thus transfer of detergent. In the latter of the several printing units 2, the inking is completed, so that the color coverage is at its highest. In the case of multicolor printing, the last printing unit 2 consequently rolls over the printing web 1 inked in the preceding printing units 2, as a result of which the foreign colors can mainly be split back onto the rubber blanket.

The web processing continues to the dryer 3 with its successive drying sections. In the first drying section from the dryer inlet, the temperature of the printing web 1 begins to rise sharply. The evaporation of the evaporable or evaporable parts from the printing ink and the detergent increases up to a maximum, with the vapor concentration increasing accordingly.

The dryer 3 has flaps 8 that can be opened for web intake and ventilation. An applicator unit 7 is arranged in front of the dryer entrance and consists of a spray device with nozzle bars 9. After leaving the printing units 2 before entering the dryer 3, a substance is applied to the surface of the printing web 1 with the application unit 7 (approximately during washing). In the case of perfecting and reverse printing, the stock feed refers to the top and bottom of the printing web 1 via a nozzle bar 9 which is arranged at a distance above and below the printing web 1 transversely to the web development.

The jet direction of the nozzles, which is indicated by the slashes, can be adjusted. The output can be regulated from zone to zone as required, the zones being comparable to the zones of decolorization in accordance with the ink slides of the ink fountain.

The application unit 7 is supplied via the nozzle 10. The applicator 7 can be moved by two rollers running on a rail 12, so that web feeding and work on the dryer 3 and applicator 7 are facilitated. The application unit 7 can be encapsulated by a wall 11. The servo drive 13 serves to shift the application unit 7.

Fig. 3 essentially shows the material flow and signal link that exists between cleaning device 6, i.e. Wash bar, applicator 7 and dryer 3 exists.

Since the ink coverage can also be decisive for the washing process, ink and fountain solution supply are also divided into zones. The mass flows include systematic: ink flow M1, dampening solution flow M2, detergent flow M3, material flow M4 of the application unit, gas supply M5, supply air M6, exhaust air M7. Signal lines lead to actuators, which are shown as valves V1 to V5 or as flaps V6, V7 see supply and exhaust air flow. Since valve V3 for the detergent flow M3 also symbolically stands for the wash cloth feed.

Sensors 14 for measuring the vapor concentration are arranged in the dryer 3 distributed over the drying section. Instead of the number of sensors 14 shown, a sensor can also be provided in the exhaust air chimney, wherein it should be borne in mind that its measuring signal, due to the distance to the printing web 1, with its decisive concentrations, is subject to dead time.

Sensors 14 that respond directly or indirectly to the vapor concentration can be used as sensors 14, e.g. FID, pressure, temperature sensor, hot wire probe. With the steam concentration measurement signal, the influencing variables pending at the dryer inlet are the amount of detergent M3 and time, amount of substance M4 and time.

Control is taken over by a control device 15, which can be switched to the control station of the web offset machine.

The advantage of controlling the mass flows M1 ... M7 in terms of time and quantity is convincingly evident from the fact that the steam concentration maxima appearing in time must be answered by the washing intervals with a corresponding time exposure to the application work.

4 shows the measurable advantage of the method according to the invention. The curve that extends higher shows the steam concentration curve without the flatter curve with fabric application.

Claims (5)

1. A cleaning machine for a printing machine, by which the cylinders of the printing units of a rotary printing machine are cleaned with the controlled supply of cleaning fluid and subsequently the printing stock web, which is moistened by the cleaning fluid and the printing ink, is thermally dried in a continuous-flow drier, whereby volatile constituents of the cleaning fluid and/or of the printing ink are evaporated,
   characterised in that in the region between the last printing unit (2) in the flow direction and the first drying section of the continuous-flow drier (3) is provided an applicator unit (7) for the metered application of a stock impeding the evaporation of the cleaning fluid and/or printing ink from the printing stock web,
   in that in the continuous-flow drier (3) is provided at least one sensor (14) to measure the steam concentration in the continuous-flow drier,
   and in that the sensor (14) is connected to a control device (15), which controls the quantitative and chronological application of the stock on to the printing stock web as a function of the steam concentration measured by the sensor (14).
2. A cleaning device according to Claim 1,
   characterised in that at least one sensor (14) records the concentration of explosive or pollutant-containing steam in the continuous-flow drier (3),
   and in that the control device (15) controls the application of the stock impeding evaporation as a function of the measurement values provided by the sensor (14) so that the concentration of explosive or pollutant-containing steam in the continuous-flow drier (3) is minimized.
3. A cleaning device according to Claim 1 or 2,
   characterised in that in addition to the steam concentration measured as a function of the sensor (14), the control device (15) controls the quantitative and chronological application of the stock preventing evaporation also as a function of the quantitative and chronological supply of cleaning fluid in the printing units.
4. A cleaning device according to one of Claims 1 to 3,
   characterised in that the control device (15) monitors various inputable parameters such as surface coverage in the print, web velocity, times and transported amounts of the cleaning fluid in the individual printing units and influencing variables in the continuous-flow drier (3), which include the steam concentration which can be detected by the sensors (14), incoming and outgoing air and, for example, the gas flow,, and corresponding regulating devices are operated on the basis of the parameter values with respect to the advance of the washing cloth in the printing units, ejection of the cleaning fluid, application of the stock on to the printing stock web, flap valves in the drier and optionally gas supply in the continuous-flow drier.
5. A cleaning device according to one of Claims 1 to 4,
   characterised in that the substance impeding evaporation is an inorganic substance, preferably water, which is distributed finely over the surface of the printing web.

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