EP1500499B1 - Method and means for measuring and controlling the concentration of chemical substances in process liquids for offset printing - Google Patents

Description

In offset printing presses, the respective printing plate is wetted by a so-called dampening unit with an aqueous liquid in order to achieve that in a subsequent process step, the image areas assume the color, while the non-image areas behave ink repellent. In addition to water, the aqueous liquid often consists of a mixture with alcohol, usually isopropanol, and a chemical mixture of up to about twenty substances, which is referred to below as an additive. The additive is used in concentrations of 1 to 8% vol., The alcohol of 0.5 to 20% vol. added. The concentration of water is therefore between 72% and 98.5% - Vol. Using optimized additives is the Part completely renounced the alcohol. In this case, the additive is also referred to as an alcohol substitute. The optimized additive then takes full or at least partially the function of isopropanol.

A major problem of offset printing is the insufficient availability of the process, which is typically around 80% and therefore characterized by high downtime of very investment intensive printing presses. For example, with a so-called 64-page offset rotary printing line, you would save around 35,000 EUR per year if the. pure production time per day could be extended on average by just two minutes. Recent, intensive practical investigations have clearly shown that the too low availability of offset printing presses is due in large part to an undefined, unknown and so far not measurable in the process and therefore in particular not controllable physical and chemical composition of the process liquid. In the context of these investigations, it was found, in particular and paradoxically, that even with exact realization of a given volumetric mixture of the components water and additive, eg by an exact control of two metering pumps, which eg the volumes 97% - Vol. Water and 3% - Vol. Inject additive into the process liquid, in the circulation of the process liquid a much lower value, eg. B. 0.8% - Vol. Of additive, is present. Even more surprising is the fact that analyzes have shown that the original percentage composition of the individual components of the additive in the fountain solution cycle does not match the composition originally intended and realized by the metering pumps by a feed control. Rather, what we call "cannibalistic effects" are processes that consist in the fact that in the printing process the constituents of the Additive more or less disappear, although in the intended concentration ratios is periodically added. The currently standard in offset printing technology, the additive concentrate as a single chemical formulation consisting of all the necessary chemical ingredients with defined concentrations specified and their composition of the print application, ie web offset, sheetfed offset or newsprint and machine type, paper type, color type, depends on feeding into the fountain solution circulation of a printing press, is an emergency solution that does not meet the modern requirements for high availability of the offset process. Although these disadvantages in printing with alcohol can be compensated to a certain extent by adding increased concentrations of isopropanol, which is currently the case in practice, this procedure should not be regarded as a future technical solution since isopropanol is a solvent and more volatile Offset printing is prohibited in many states in the USA, is subject to stringent emissions legislation in Europe, and is even punishable in Switzerland by a punitive tax, the so-called "steering levy", which is detrimental to the economic efficiency of the printing process. From an environmental point of view and especially to protect the health of the printer at the workplace, therefore, isopropanol or other solvents in the future massively reduced or ultimately disappear completely from the printing process. The concentrations of alcohol in the fountain solution are currently usually between 6% and 20% and facilitate in the case of roll and sheet offset the use of so-called film dampening. According to the prior art, the latter consist of several rollers coated with rubber mixtures and / or metals, which rotate with a certain pressure in contact with each other and the fountain solution in the form of a film adjustable Transport the layer thickness to the printing plate. This transport process is promoted by the addition of isopropanol due to the resulting reduction in the surface tension of the liquid film. In addition to state-of-the-art film dampening systems, it is also possible to use contactless systems, in particular jet-operated spray dampening units or dampening units, which have rolls with covers made of plush. Since in these cases the dampening solution is transported without a continuous liquid film, the use of alcohol can be omitted. Also in these embodiments according to the prior art, the new method according to the invention is of utmost importance, since it allows an optimal composition of the chemicals of the fountain solution.

In order to comply with the legal requirements regarding the avoidance of isopropanol, other solvents have been brought to market, especially in the USA. However, this approach was not followed in Europe, as it did not result in the elimination of solvents. Furthermore, the other solvents are partly considered to be carcinogenic or detrimental to health and therefore do not represent an alternative to alcohol.

A real alternative to alcohol are the so-called surfactants, which bring about comparable advantages with regard to the wetting properties of the dampening solution on the rollers of the dampening unit. In particular, it should be noted. surfactants are not VOCs. However, experience has shown that these positive properties of the surfactants can only be used if the required target concentrations can be exactly met. In the currently used alcohol-free processes according to the prior art, therefore, surfactants lead to undesirable foaming and to quality-reducing emulsification of paint and fountain solution, so that In many practical cases, the non-alcoholic printing fails and must be replaced again by printing with alcohol. In addition, the difficulty arises that surfactants are very often difficult to dissolve in a chemical multicomponent mixture, so that in addition substances must be introduced as solvent mediators in the additive concentrate to a separation, ie settling on the bottom of the additive - barrel of the supplier to prevent. This difficulty is also easily solved by the method according to the invention. It offers the possibility of using only those chemical components that are absolutely necessary for the printing process. Since the web speeds of modern printing presses are constantly being increased and the latter requires increasingly precise measurement and metering of the individual chemical components, the new process for printing without alcohol is indispensable. In addition, the composition of the individual components of the additive depends on the print job, ie on the currently used paper, on the special colors required by the specific customer, on the specially used blanket, roll coating, etc. must be changeable. The latter is possible only with the new method described here. This is especially proven by the fact that to date there is not a single additive in the world which allows printing without alcohol under all conditions encountered in a printing press. The latter explains why print shop managers always want to test other additive formulations to run their print jobs. Nevertheless, it has to be stated that every chemical formulation is a compromise and therefore only optimal for a limited range of print jobs. Overall, the current approach is inevitably associated with a high financial outlay, despite the above-mentioned legal requirements in Europe, which makes pressure without alcohol de facto impossible.

The aim of the present invention is therefore, by continuous measurement and control of the composition of the fountain solution, ie by continuous subsequent addition of the individual differently depleted chemical components or selected groups of components to readjust the respective setpoints to the availability of the offset printing process on values of competing Low pressure, ie to increase to about 90 to 95%. According to the prior art JP-A-4327940 is provided to carry out the control of the concentrations of individual components in the fountain solution of offset printing machines by measuring the pH, conductance, refractive index, specific gravity and gas concentration and make a re-dosing of the respective component via pumps over a specific period, if the concentration value is not within a range between an upper and lower limit. By way of example, the stated measuring principles are not selective or a significant number of substances are not sufficient. According to the invention, a method and a device are used for the first time in printing technology, which continuously measure the concentrations of the individual components of the additive on the basis of selective weakening of electromagnetic radiation and regulate them to predetermined optimal values. In this case, it is prevented that the process fluid suffers in particular a depletion but also an overdose of individual components of the additive, so that the printing process can be continued continuously with high stability and availability at the optimum operating point. Of utmost innovative importance is the fact that the method not only works in alcohol-free printing, ie substitutes, but that the selectivity of the measurement and control of the additive can be maintained even when printing with additional admixture of alcohol, ie the alcohol no falsification of the measurement of the concentrations of the individual components of the additive caused. According to the invention, the selective measurement of the concentrations of the individual components or of groups of different chemical compounds is coupled to a dosing system which removes the various components from different containers via a system consisting of cycled valves and pumps and feeds them to the dampening water. With this new procedure the offset printing with alcohol is decisively optimized. The pressure without alcohol is thereby placed for the first time on a basis, which allows a long-term process while fulfilling the boundary conditions of economy. The fact that the new method allows individual on-line adjustment of the dampening solution to the respective print job, ie paper type, color type, web speed, principle-related interaction between ink and dampening water as the main characteristic of the offset process, avoids the emergence of well-known problems such , B. unauthorized deposits on the blanket, unwanted ink residues in the dampening water, harmful chemical attacks of printing plates, etc. In particular, the too narrow window of the variations of the concentrations of the chemical components of ready-to-use additives supplied by the new method is arbitrarily extended, so that constant fountain solution , Especially by the already mentioned search for better fountain solution - additives in several hours of shutdowns of the printing process and corresponding negative consequences for the disposal of previously operated fountain solution and thus also for the efficiency of the printing process, omitted by the new process.

According to the current state of the art, dosing devices are used to volumetrically mix the two or three components under fixed conditions as part of a control and into the fluid circuit of the printing press according to the respective consumption, ie according to the removal of the liquid through the paper to be printed, feed. In addition to mixing stations that are operated by hand, systems with conventional metering pumps are currently being used in particular. A major disadvantage of these systems is that neither malfunctions of the mixing devices Changes in the physical and / or chemical composition, for example as a result of chemical reactions or of absorption or desorption processes by the printing ink, the paper, through the pipeline or the machine modules, can be detected. In particular, evaporation processes in these classic dosing methods lead to considerable concentration errors. The present as the only control instruments already in use sensors for detecting the electrical conductivity are not suitable because of the strong and fluctuating contamination of the process liquid for a quantitative measurement of the concentration of the respective additive or the substitute. Furthermore, the important chemical control components of the additives which make the printing process possible can not be detected by a conductivity measurement, since these substances are not dissociable in the water. The more or less introduced as standard in offset printing pH probe can be used as an indicator just before the collapse of the function of the printing process, since the required strong chemical buffering of the process fluid, eg by citric acid, a change in pH even at strong change in chemical composition, prevented.

The aim of the present invention is therefore a method and an apparatus for implementing the method, which comprises a quantitative, continuous measurement and control of the concentrations of the individual components of the respective additive or the substitute in a matrix of up to 20 chemical components without faulty influence by other substances , as in particular by alcohols, dirt, color and paper particles, gas bubbles, salts from the paper coating and other impurities typical for offset printing, allow. In addition, the This problem has not yet been solved in all practical cases. As our scientific studies have shown above all that the various chemical ingredients of a statically predetermined additive mixture are not consumed in proportion to the concentration Thus, the mixture changes in the course of the printing process, since both the colors, as well as the paper, as well as other effects cause a more or less selective depletion of the individual components. This particular situation in offset printing makes the present invention highly valuable in that Depletion effects are fully compensated, regardless of the customer's order in the printing press. The present invention solves the tasks set, inter alia, that the chemical components are continuously measured and the dampening solution controlled as pure raw materials and / or as partial mixtures of several components usually in mixtures with water, fed so that they are simply in the fountain solve and in particular do not form separate phases. In this way, in particular, chemical formulations can be realized which separate in a prefabricated additive concentrate and therefore would not lead to a homogeneous solution. For the determination of concentration, the weakening of electromagnetic radiation is used in the passage through the dampening water according to the invention.

Fig.1:

Das Gesamtsystem bestehend aus Meß- und Regelsystemen, Druckmaschine und Prozeßflüssigkeitskreislauf, wobei die Dosierung der verschiedenen chemischen Komponenten / Komponentengruppen direkt durch das Mess- und Regelgerät erfolgt.

Fig. 2:

Eine alternative Ausbildung der Erfindung, wobei die Dosierung über eine Venturi - Düse stattfindet.

Fig. 3:

Eine alternative Ausbildung der Erfindung, die dadurch gekennzeichnet ist, dass die chemischen Einzelkomponenten über einen statischen Mischer geführt werden.

Fig. 4:

Eine weitere Systemvariante, bei welcher eine Voranmischung in einem separaten Behälter stattfindet, welcher mit dem Gesamtsystem verbunden ist, wobei die Zusammensetzung dem optimalen Mischungsverhältnis entspricht.

Fig. 5:

System, bei welchem die optimale Zusammensetzung über kalibrierte Dosierpumpen erfolgt.

The invention will be described below in detail by means of figures. Show in detail:

Fig.1:

The complete system consisting of measuring and control systems, printing machine and process fluid circuit, wherein the dosage of the various chemical components / groups of components is carried out directly by the measuring and control device.

Fig. 2:

An alternative embodiment of the invention wherein the metering takes place via a Venturi nozzle.

3:

An alternative embodiment of the invention, which is characterized in that the individual chemical components are passed through a static mixer.

4:

Another system variant, in which a pre-mixing takes place in a separate container, which is connected to the entire system, wherein the composition corresponds to the optimum mixing ratio.

Fig. 5:

System in which the optimum composition is carried out via calibrated metering pumps.

The according to Fig. 1 in a tank (1) located process fluid (2) is circulated by circulation pumps (3) to the printing machine (4) and back to the tank (1) via pipes (5). The respective concentrations of the individual chemical components of the additive are continuously measured by a measuring system (6). The predetermined chemical components K1, K2, K3, .... to Kn are fed into the process liquid (2) via pumps (7) and via valves (8). The respective different desired concentrations of the chemical components K1 to Kn are required guaranteed by the fact that the measuring system (6) continuously measures the actual concentrations and, in the context of a regulation, replenishes so much of the respective component, that the actual value is equal to the predetermined target value. This ensures that the additive components constantly consumed by the printing process or removed from the walls of the printing line by chemical reactions or physical absorption processes are fed into the process liquid (2), so that the actual values of the concentration of the Additivs are equal to the default values specified by the printer. The loss of water in the process liquid (2) is compensated via a pipeline (9), wherein the filling level (10) via a level - measuring and control system (11) according to the ultrasonic echosounder principle or a method according to the prior Technology is kept constant. With a further measuring and control device (12), which may be integrated in another embodiment of the invention in the measuring system (6), the concentration of the alcohol is continuously measured, unless it is not alcohol-free, in the process liquid (2) and the Substantially alcohol lost by evaporation from a reservoir (13) via a unit consisting of valve and metering pump (14) fed so that even in the case of printing with alcohol target and actual value consistently match and ensures the availability and quality of the printing process are. To homogenize the process liquid, an agitator (15) is used.

Fig. 2 outlines the arrangement according to the invention consisting of printing press (16), fountain tank (17), fountain solution (18) with circulation (19) and the chemical components K1 to Kn (20), which via a venturi nozzle (21), and via a pump (22) is operated, the chemical components K1 to Kn via valves (23) sucks and fed into the dampening water (18), wherein the measurement of the concentrations of the chemical components via the measuring and control system (24). The make-up (25) of water with automatic level control and the agitator (26) correspond to the arrangements of Fig. 1 ,

In Fig. 3 is in the overall arrangement consisting of printing press (27), dampening water tank (28), fountain solution (29), measuring and control system (30), agitator (31), water feed (32) with Füllhöhenkontrolle (33) and dampening water circulation (34), as additional component realized a static mixer (35). The fountain solution (29) circulated via the pump (36) is mixed with the chemical components K1 to Kn (37), which are fed into the circuit (39) via the valves (38) in the static mixer (35) that both the measuring system (30) and the circuit (34) have homogeneous liquid mixtures with the aim that the overall system in Figure 3 works optimally.

Fig. 4 FIG. 12 illustrates a modified version of the invention compared to the preceding figures, characterized by a pre-mixing of the chemical components K1 to Kn (42) via pumps (50a) with a water supply (41) in a mixing vessel (40). By this arrangement it is achieved that the control process of the measuring system (43) for the respective achievement of the target concentrations of the chemical components K1 to Kn (42) is significantly shortened, so that the composition of the fountain solution (44) in the fountain solution tank (45) over shorter time intervals always has the specified setpoints. Further, a homogenizing device (39) is also used in the pre-mixing tank (40) analogously to the agitator (46) in the fountain solution tank. The latter can also according to Fig. 3 be a static mixer. In order to avoid possible fill level problems during the feed of the premixed liquid (47) into the fountain solution tank (45), the use of a sensor (48), preferably according to the ultrasonic sounder principle, is required. of great importance. The circulation (49) of the fountain solution (44) via the pump (49) to the printing press (50) takes place analogously to that in the FIGS. 1 to 3 ,

Fig. 5 shows the simplest variant according to the invention, in which the chemical components K1 to Kn (51) via the measuring system (52) controlled, calibrated metering pumps (53) according to the respective target value of the individual component via a valve (54) are metered. The level measurement (55) and the stirrer (56), in combination with the water supply (57), permit a homogeneous mixture of the moist water (58), which is circulated through the circulating pump (59) in the circuit (60) between the printing machine (61) and dampening water cooling unit (62) circulates.

Claims (16)

1. Method for direct, selective measurement and control of the concentrations of individual chemical components of chemical additives or of chemical alcohol substitutes in fountain solution for offset printing, characterised in that the concentrations of the individual chemical components or groups thereof are continuously determined by detecting the attenuation of electromagnetic radiation as it passes through the fountain solution and that the individual components or groups of individual components are topped up to their respective reference values.
2. Method in accordance with Claim 1, characterised in that the various chemical components are located in individual tanks and topping up is carried out by means of a measuring system that continuously measures the concentrations of the individual components or groups thereof and tops up the individual components via a control loop.
3. Method in accordance with Claims 1 and 2, characterised in that the individual chemical components/groups are topped up from the individual tanks via pumps that are each fitted with a valve and are connected in series.
4. Method in accordance with Claims 1 and 2, characterised in that the individual components/groups are drawn into the fountain solution circuit by a Bernoulli nozzle.
5. Method in accordance with Claims 1 to 4, characterised in that the mixing of fountain solution and individual components/groups is optimised by means of a static mixer.
6. Method in accordance with Claims 1 to 3, characterised in that the individual chemical components/groups are premixed with water in a premixing tank and that the liquid content of the premixing tanks is transferred to the fountain solution tank.
7. Method in accordance with Claims 1 and 2, characterised in that in each case the individual chemical components/groups are metered out of each tank via a separate pump for each tank, upstream of which a common valve is connected.
8. Apparatus for measuring and controlling the concentrations of individual chemical components or groups thereof in the fountain solution during offset printing, wherein the apparatus comprises both pumps and a measuring system for continuously monitoring the concentrations of the individual components in the fountain solution, characterised in that the apparatus is equipped with a measuring and control system (6, 24, 30, 43, 52) that measures the concentrations of the individual components based on selective attenuation of electromagnetic radiation through said fountain solution in the operating state and tops up the individual chemical components K1 to Kn via pumps (7, 21, 36, 50, 55) so as to ensure that the concentrations of the individual chemical components are identical to the reference concentrations at all times.
9. Apparatus in accordance with claim 8, characterised in that a Bernoulli nozzle (21) that is operated by a partial flow of the fountain solution (18) which is circulated by a pump (22) is used as the pump.
10. Apparatus in accordance with Claims 8 and 9, characterised in that the chemical components K1 to Kn are homogeneously mixed together with the fountain solution (29) by a static mixer (35) in a circuit (39) that is driven by a pump (38).
11. Apparatus in accordance with Claims 8 and 9, characterised in that the individual chemical components K1 to Kn are prepared in a premixing tank (40) with water from a water pipe (41) via pumps (50a) and the mixture (47) is subsequently routed to the main tank (44).
12. Apparatus in accordance with Claim 8, characterised in that the individual chemical components K1 to Kn are metered into the fountain solution (58) in each case via a pump (53), upstream of which a valve (54) is connected.
13. Apparatus in accordance with Claims 8 to 12, characterised in that a second measuring and control unit (12) is provided that continuously measures the concentration of alcohol in the fountain solution (2, 18, 29, 44, 58) and tops up the depleted alcohol from an alcohol reservoir (13) via a pump (14) with an upstream valve.
14. Apparatus in accordance with Claims 8 to 14, characterised in that the level (10, 27) is detected by a sensor (11, 28, 33, 48, 55) and that the fill level is kept constant by means of a control loop.
15. Apparatus in accordance with Claim 14, characterised in that an ultrasound unit that works according to the depth sounding principle is used as the level sensor (11, 28, 33, 48, 55).
16. Apparatus in accordance with Claims 8 to 15, characterised in that the fountain solution (2, 18, 29, 44, 58) is homogenised by means of stirrers (15, 26, 31, 39, 46, 58).

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