EP0277879B1 - Method of measuring the thickness of a dampening-solution film on a printing plate of a rotary offset machine, and system for carrying out the method - Google Patents

Description

The present invention relates to a method for measuring the thickness of a film of a wetting solution deposited on a printing plate of an offset press and to a system for implementing this method.

It is known that the offset printing process provides for the use of a printing plate, or offset plate, carrying the image to be printed, the inking being transferred from the plate to the paper to be printed by means of a blanket cylinder rotating between a cylinder carrying the printing plate and the paper to be printed and transferring the ink received from the plate onto the paper.

The separation between the printing areas and the non-printing areas of the offset plate is maintained by the presence of a thin film of an aqueous solution called "wetting solution" on the plate.

This solution is generally applied to the plate by one or more rollers, called "wetters", usually filled with elastomer, whose axes of rotation are parallel to that of the plate cylinder, which these rollers contact by a common generator.

The ink, generally of the fatty ink type, is deposited on the plate by another series of rollers, called "ink touchers", of the same kind as the wet rollers, these rollers contacting the plate installed around the plate cylinder. after it has been wetted by the wetting rollers, these being upstream of the ink-touching rollers relative to the direction of rotation.

If the film of solution deposited on the plate by the wetting rollers is suitable in thickness, temperature, pH, alcoholic degree, etc., the ink will take on the plate only on certain areas treated on the surface to receive the ink.

If the wetting solution film is not thick enough, the ink will take up on the whole surface of the plate while if the film is too thick the ink will not take anywhere.

It is therefore necessary to maintain a suitable balance between the thicknesses of the solution film first deposited on the plate and the thickness of the ink film subsequently deposited.

In addition to maintaining this balance, it is also necessary to adjust the optical density of the print (on the printed sheet), this density depending in particular on the nature of the paper, that of the plate and the ink, the chemical qualities. fountain solution, printing conditions such as the speed of the press, etc.

The parameters on which we can act to adjust this density are the thickness of the ink film and the thickness of the fountain solution film.

Means for adjusting these thicknesses are therefore provided on offset machines, both for adjusting the necessary balance between these thicknesses and for adjusting the optical density obtained on the printed paper.

To adjust the thickness of the wetting film, we generally act on an adjustment point provided in the wetting device of the plate integrating the wetting rollers, but this adjustment is extremely difficult to achieve because we do not know the thickness actually deposited. on plate. It is therefore desirable to have a measuring system indicating this thickness.

This measurement system would, in fact, for given operating conditions (nature of paper, ink, temperature, etc.), when an ideal setting is obtained by trial and error, know exactly what thickness of solution it corresponds to .

It will thus be possible not only to maintain this setting for the printing in progress, but also to adjust very quickly the press in the case where the printing to be carried out must be done under operating conditions encountered previously.

Methods for measuring the thickness of the film of wetting solution deposited on the plate and systems implementing these methods are already known, based on various physical principles.

There is in particular a method in which the reflection of a visible light beam on the wet surface of the plate is measured. This, in the non-printing areas, has a relatively rough surface, this roughness coming from porosities which are filled with the wetting solution which is deposited on the plate. The greater the thickness of the liquid, the more the porosities are filled.

The surface of the solution being smoother than the rough surface of the plate, it reflects light better, and consequently the thicker the film of solution deposited compared to the roughness of the plate, the better the reflection. The illumination and the reading of the reflected beam are done under grazing incidence, and the thickness of the deposited film is deduced from the intensity of the reflected beam.

Another method is also known in which the absorption of two infrared light beams of different wavelengths sent onto the plate is compared, one of which is much more absorbed by the wetting solution than the other. The incident beams are of identical intensities, which makes it possible to deduce the thickness of the film from the ratio of the intensities of the two reflected beams.

Yet another method is known from DE-A-3,414,573, where the thickness measurement is also carried out with optical means.

The processes mentioned and the systems implementing them give precise values but they present the disadvantage of being poorly suited to industrial requirements. Said systems are in particular expensive, bulky, delicate and sensitive to projections of wetting solution and ink on the optics.

The present invention seeks to overcome these drawbacks and proposes a method for this purpose which is characterized in that a volume consumed of fountain solution is measured, the surface of the printing plate having been treated is measured by consuming said volume , and the thickness of the film deposited is deduced from these measurements, this being equal to said volume divided by said surface.

There is thus a process perfectly suited to an industrial environment, since it suffices to carry out measurements of consumption in volume and of treated surface, which are themselves adapted to such an environment.

This method also offers the advantage of eliminating the need to make thickness measurements on the plate itself, these measurements being difficult and delicate, in particular due to the thinness of the solution (its order of magnitude is micrometer), the rotational movement which animates the plate, as well as the risks of ink projection or solution previously mentioned.

In addition, with this method, an average value much more significant is determined than point values capable of varying randomly around this average value.

According to a characteristic of the process which is the subject of the invention, said treated surface of the printing plate is measured by counting the number of revolutions carried out, while said volume of wetting solution is consumed, by a blanket cylinder reporting an image received from the printing plate on a paper to be printed, said surface being equal to the width of the plate multiplied by the circumference of the blanket cylinder and by the number of turns measured. The blanket cylinder has a circumference equal to the length of the treated plate.

The operation of measuring the treated surface is thus carried out very easily since it is sufficient to count a number of turns carried out by a cylinder.

This measurement is all the more advantageous since in most offset presses this counting is already carried out which corresponds to the number of paper copies printed.

One turn (or length) of plate corresponds to one turn of the blanket cylinder and one printed copy while the width (or width) of the plate is equal to that of the paper to be printed. The surface of the treated plate is equal to the surface of paper that it has allowed to print.

According to another characteristic of the process which is the subject of the invention, said volume consumed of wetting solution is measured in a supply basin of a device for wetting the plate, previously filled with solution, by measuring a high level there while said measurement of the treated plate surface is started, then a low level while said surface measurement is stopped, the difference between said levels corresponding to the consumption of said wetting device for treating said surface.

The volume measurement is thus carried out by simple level measurements which can be easily carried out.

According to an advantageous characteristic of the method according to the invention, said level measurements are made in the basin by detecting a predefined high level and a low level corresponding to a known volume of wetting solution, and the measurement of the surface of the treated plate is started. when we have detected this high level while we stop it when we have detected this low level.

This fixes a predefined volume of solution while measuring the area treated with this volume.

This has the advantage of making it possible to carry out only the only measurement of the surface, and to make only one simple level detection in the basin easier than a variable level measurement.

The invention also relates to a system implementing the method described above. This system is characterized in that it comprises a device for measuring a consumed volume of wetting solution and a device for measuring the surface of the printing plate having been treated by consuming said volume of wetting solution.

It suffices to use the data from this device to determine the thickness of the film, manually or more advantageously using a device specially designed for this purpose.

According to a characteristic of the system which is the subject of the invention, said device for measuring a surface of the printing plate comprises a device for counting a number of revolutions made, while said volume of wetting solution is consumed, by a blanket cylinder transferring an image received from the printing plate onto a printing paper.

These characteristics offer the advantage of being extremely simple to implement, since such a counting device generally exists on offset presses (see above). It is sufficient to take the information only when the volume consumed of fountain solution is measured. This measurement device is preferably completed by means of display of the width of the printing plate and by means of calculation of the surface corresponding to this width and to the number of turns measured, the circumference of the blanket cylinder being a known constant.

According to another characteristic of the system according to the invention, implemented in an offset press comprising a solution supply basin of a device for wetting the plate, said device for measuring a volume of solution consumed comprises means rapid filling of the basin and means for measuring the level of solution in this basin. Preferably, said means for measuring the level of solution in the basin comprise means for detecting a predefined high level and low level corresponding to a known volume of wetting solution.

This provides an easy-to-make device for implementing the volume measurement operation.

• ― la figure 1 est une représentation schématique simplifiée en élévation latérale d'une rotative offset;
• ― la figure 2 est une représentation schématique en élévation transversale de la rotative montrée sur la figure 1, munie d'un système conforme à l'invention;
• ― la figure 3 est une vue en perspective avec arrachement partiel du dispositif détecteur de niveau à réducteur de vagues représenté sur la figure 2.

Other characteristics, features and advantages of the invention will emerge, with those and those previously exposed, from the description of a particular embodiment given below solely by way of example, without limitation, with reference to the accompanying drawings. . On these:

• - Figure 1 is a simplified schematic representation in side elevation of an offset press;
• - Figure 2 is a schematic representation in transverse elevation of the press shown in Figure 1, provided with a system according to the invention;
• FIG. 3 is a perspective view with partial cutaway of the level detector device with wave reducer shown in FIG. 2.

In the offset press shown in FIG. 1, the paper 1 is printed on both sides simultaneously by pressure between two blanket cylinders 2 which themselves receive the ink and the wetting solution deposited by cylinders 3 carrying offset plates.

The press shown comprises a wetting device 4, comprising a roller 5 applying a wetting solution to the plate, called "wetting", lined with rubber, with a chrome roller 6 called "transfer", with a rubberized roller 7 says "sliding roller" and a chrome roller 8 says "bowl roller".

In this embodiment of a wetting device, given as an indication, the rollers 8 and 7, and 7 and 6 have different peripheral speeds. More precisely, the roller 6 has a peripheral speed substantially equal to the speed of movement of the paper 1, the roller 7 has a speed lower than that of the roller 6 and the roller 8 has an even lower speed.

For adjusting the solution film, the rollers 7 and 8 can be clamped more or less against each other, thus varying the solution film which can pass between these two rollers, these being driven by an independent motor. at variable speed.

The roller 8 soaks in a container 9 called "basin" in which, in known offset presses, a substantially constant level is maintained using a weir 10. The basin 9 is supplied with wetting solution by an electric pump 11 which flows through a pipe 12 into the tank 9.

The pump is immersed in a solution tank 13 inside which the solution is prepared and refrigerated to remain in optimum conditions of pH, temperature and concentration of various additives such as acid, alcohol, etc ...

An adjustment valve 14 makes it possible, in offset presses of known type, to limit the flow in circulation in order to avoid an overflow of the basin 9. An overflow pipe 15 returns to the tank 13 the overflow of the basin 9 passed above the weir 10.

The purpose of this wetting device is to deposit on the plate wound around the plate cylinder 3, a film of wetting solution as uniform as possible, suitably dosed and of a thickness generally less than 1 micrometer.

The rollers 16, called "touch rollers" deposit on the plate a fatty ink which they receive from the roller 17.

Of course the upper plate cylinder 3 cooperates with similar wetting and inking devices (not shown).

According to the process which is the subject of the invention, a volume consumed of wetting solution is measured as well as the surface of the printing plate having been treated by consuming this volume, to deduce the thickness of the film deposited.

According to a characteristic of this method, said treated surface of the printing plate is measured by counting the number of revolutions carried out, while said volume of wetting solution is consumed, by the blanket cylinder 2 reporting an image received from the plate printing on the paper to be printed 1, said surface being equal to the width of the plate multiplied by the circumference of the blanket cylinder and by the number of turns measured.

In accordance with another characteristic of the process which is the subject of the invention, said volume consumed of wetting solution is measured in the supply basin 9, which is first filled with solution, and in which a high level is measured while begins said measurement of the surface of the treated plate, then a low level while said surface measurement is stopped, the difference between said levels corresponding to the consumption of said wetting device for treating said surface. For this, care is taken to avoid any solution arriving in the basin while making the volume measurement, as well as measuring levels for which there is no risk of loss of liquid by the device. 10 overflow spill.

In accordance with a preferred characteristic of the invention, said level measurements are made in the basin by detecting a predefined high level and low level corresponding to a known volume of fountain solution, and the surface measurement of the treated plate is started when we detected this high level while we stopped it when we detected this low level.

A volume of wetting solution is thus predetermined, which means that the only variable to be measured is the surface treated and more precisely here the number of revolutions made by the blanket cylinder.

It is understood that methods in which a predetermined number of revolutions would be fixed and the volume consumed would be measured, for example in the basin; or in which one would simultaneously measure, between a starting top and an end top, the surface treated and the volume consumed, would be variants in accordance with the method according to the invention.

We will now describe in support of FIGS. 2 and 3 a measurement system implementing the method described above.

This system comprises a device for measuring a consumed volume of wetting solution and a device for measuring the surface of the printing plate having been treated by consuming the volume of wetting solution.

In accordance with the invention, the device for measuring the treated surface of the plate comprises a device for counting the number of revolutions carried out, while said volume of wetting solution is consumed, by a blanket cylinder 2 carrying an image received from the printing plate on the paper to be printed 1.

Here this counting device comprises a fixed proximity sensor 26 and a pallet 27 linked to the blanket cylinder, said sensor 26 detecting, once per revolution, the passage of the pallet 27. The sensor 26 is connected to an electrical box 25 to which it delivers one pulse per revolution of cylinder printing 2, pulses which are counted by appropriate means well known to the skilled person in the box 25.

The device for measuring the treated surface further comprises means for displaying the width of the printing plate, here a display button driving the cursor 29 of a potentiometer 30, and means for calculation of the surface corresponding to this width and to the number of measured turns, which are sufficient data since the circumference of the printing cylinder or blanket 2 is a constant. These calculation means are integrated in the electrical box 25 and are made with means well known to those skilled in the art such as digital calculation elements (microprocessor, etc.) or analog calculation elements.

According to another characteristic of the invention, the device for measuring a volume of wetting solution consumed comprises means for rapidly filling the basin 9 and means for measuring the level of solution in this basin.

These rapid supply means are here a pump 11, drawing from a tank of wetting solution 13 and leading this solution into the basin 9, via a pipe 12. On the pipe 12, a solenoid valve 18 allows '' authorize or interrupt the supply of solution to the basin.

Here, it is a timer 31 integrated in the box 25 which controls the closing of the solenoid valve 18 after a predetermined time after a filling has been ordered.

According to a preferred characteristic of the invention, the means for measuring the level of solution in the basin comprise means for detecting a predefined high level 23 and a low level 24 corresponding to a known volume of wetting solution.

The means for detecting a high level and a low level comprise, for each of these levels, a measuring electrode, respectively 21 and 22, at least partially immersed in the solution for a level higher than the level to be detected while 'below it it no longer dips.

The detection means also include means, integrated in the box 25, for applying a potential difference between each of these electrodes and a ground, here a wall 19 of a device described later, in permanent contact with the solution, the electrodes 21, 22 and the ground being connected by electrical conductors to the box 25 which also includes means for detecting an electric current between the ground and each of the electrodes 21 and 22, this current being established for each electrode when it is brought into contact with the solution because the latter is conductive. Of course the current is interrupted when an electrode is no longer in contact with the solution.

The means for applying a potential difference and the current detection means are produced in a well-known manner and therefore do not need to be described here.

The measurement system according to the invention further comprises a control unit for the device for measuring the treated surface of the plate, which is sensitive to the detection means of levels 23 and 24, and which controls the starting of the device for measuring surface when the high level is detected and which interrupts it when the low level is detected.

It is thus sure to measure the number of turns corresponding only to the consumption of the volume of solution between the high 23 and low 24 levels.

The unit which controls the surface measurement device also controls the means for rapidly filling the basin 9, their actuation being effected when the low level 24 is detected.

This control unit is integrated into the box 25 to which the solenoid valve 18 is also connected.

The operation of the system, governed by the control unit, is as follows: the solenoid valve 18 is open, the solution coming from the tank 13 is discharged by the pump 11 into the basin 9, the excess returning to the tank 13 by the overflow pipe 15 until the solenoid valve 18 is closed by the time delay 31 provided for this purpose.

The arrival of solution to the basin 9 being interrupted while the solution is consumed by the wetting device comprising the roller 8, the level in the basin 9 will gradually drop, the weir will stop being submerged, then the high level 23 will be reached, the tip of the electrode 21 comes out of the liquid, the counting means of the box 25 are put into action to count one pulse per revolution of cylinder 2, coming from the sensor 26 excited by the pallet 27.

When the level of the solution in the basin 9 reaches the low level 24, the tip of the electrode 22 comes out of the liquid, which causes the counting of the tops from the sensor 26 to stop, the number N being memorized of laps completed, the opening of the solenoid valve 18 and the start of the time delay 31 delaying the command to close it.

The solenoid valve 18 being open and delivering more than the roller 8 consumes, the bowl 9 fills then overflows towards the tank 13 through the pipe 15.

When the time provided in timer 31 has elapsed, the cycle begins again: closing of the solenoid valve 18, descent of the solution level in the basin 9, start of counting of the cylinder revolutions at the high level, stop of this counting at the low level and opening of the solenoid valve.

The tips of the electrodes 21 and 22 having been adjusted beforehand so that the slice of liquid located between the levels 23 and 24 corresponds to a known volume V, the width L having been displayed on the button 29, the development or circumference C of the As the plate cylinder is known, the thickness E of the liquid film distributed by the wetting device is:
$$\text{E = V / LCN}$$

The box 25 also includes means for calculating and displaying the thickness of the film, connected to the surface and level measurement devices of which it uses the data.

Thus, at each filling and consumption cycle, the system will calculate and display on a reading screen 28 a new thickness of film of wetting solution. The reading screen and the width display button are preferably integrated into the press control panel.

The box 25 includes an electromagnetic logic unit based on relays for the management of the commands of the devices to which it is connected and that of the information it receives, as well as analog elements for the calculation, display and input of data such as the width (potentiometer 30).

In another embodiment, the box 25 is a programmed digital calculator (a computer) managing the measurements of all the anchorages of the press, which are 8 in number for a four-color press printing on both sides of paper.

To make it possible to perform level measurements which are not disturbed by the waves likely to occur in the basin, the device for measuring a volume of solution comprises, placed in the basin 9, a wave reduction device illustrated on FIG. 3. This device comprises a wall 19, preferably sealed, delimiting an enclosure in which the measurement is carried out, a communication orifice 20 of small dimensions being formed in the lower part of the wall 19 so that the level of solution in the enclosure corresponds to the average level in the basin.

In the embodiment shown in Figure 3, the wall 19 is cylindrical and is capped at its top by a cover 40 carrying the electrodes 21 and 22, which are mounted there on mounting devices 41 and 42 making it possible to isolate the electrodes from the electrical ground constituted by the wall 19. It will be noted that these electrodes have a thread cooperating with a corresponding threaded bore in the mounting devices 41 and 42, this thread making it possible to adjust the height of the tips of the electrodes .

It is understood that the above description has been given by way of non-limiting indication, the person skilled in the art being capable of making numerous variants to it.

The device for level measurement by variation of the resistivity could in particular be replaced by any other known device (float, bubbling, ultrasound, capacitive), possibly in the feed tank of a wetting device of a type different from that described, such as so-called "conventional, grab", "brush" or "impeller" moorings.

Claims (15)

1. Process for measuring the thickness of a film of a wetting solution deposited on a printing plate of a rotary offset printer, characterized in that a consumed volume of wetting solution is measured, the surface of the said printing plate which has been treated whilst consuming the said volume is measured, and the thickness of the deposited film is calculated from these measurements, it being equal to the said volume divided by the said surface.

2. Process according to Claim 1, characterized in that the said treated surface of the printing plate is measured by counting the number of revolutions performed, when the said volume of wetting solution is consumed, by a blanket cylinder (2) transferring an image received from the printing plate on to a paper to be printed (1), the said surface being equal to the width of the plate multiplied by the circumference of the blanket cylinder (2) and by the number of revolutions measured.

3. Process according to any one of Claims 1 or 2, characterized in that the said volume of wetting solution consumed is measured in a pan (9), previously filled with solution, supplying a device for wetting (4) the plate, by measuring a high level (23) in it when the said measurement of plate surface treated is begun, then a low level (24) when the said measurement of surface is stopped, the difference between the said levels corresponding to the amount consumed by the said wetting device to treat the said surface.

4. Process according to Claim 3, characterized in that the said measurements of levels in the pan (9) are made by detecting a preset high level (23) and a preset low level (24) corresponding to a known volume of wetting solution, and in that measurement of the plate surface treated is started when the high level has been detected whereas it is stopped when the low level has been detected.

5. System for measuring the thickness of a film of a wetting solution deposited on a printing plate of a rotary offset printer, characterized in that it comprises a device (18, 19, 21, 22, 25) for measuring a volume of wetting solution consumed and a device (25, 26, 27) for measuring the surface of the said printing plate which has been treated whilst consuming the said volume of wetting solution.

6. System according to Claim 5, characterized in that it also comprises a device for calculating and displaying (25) the thickness of the deposited film, connected to the said measuring devices the results of which it uses.

7. System according to any one of Claims 5 or 6, characterized in that the said device for measuring a treated surface of the said printing plate comprises a device for counting a number of revolutions performed, when the said volume of wetting solution is consumed, by a blanket cylinder (2) transferring an image received from the printing plate on to a paper to be printed (1).

8. System according to Claim 7, characterized in that the said device for measuring a treated surface also comprises means for displaying (29, 30) the width of the printing plate and means for calculating the surface corresponding to this width and to the number of revolutions measured, the circumference of the blanket cylinder (2) being a constant.

9. System according to any one of Claims 7 or 8, characterized in that the said counting device comprises a fixed proximity sensor (26) and a blade (27) connected to the blanket cylinder, the said sensor (26) detecting the passing of the said blade (27) once per revolution.

10. System according to any one of Claims 5 to 9, characterized in that, the said rotary offset printer comprises a pan (9) supplying a solution to a device for wetting a plate, the said device for measuring a volume of solution consumed comprises means (18, 25, 31) for rapidly refilling the pan (9) and means (19, 21, 22, 25) for measuring the level of solution in this pan.

11. System according to Claim 10, characterized in that the said means for measuring the level of solution in the pan comprise means of detecting a preset high level (23) and a preset low level (24) corresponding to a known volume of wetting solution.

12. A system according to Claim 11, characterized in that it also comprises a control unit for the said device for measuring a treated surface of the printing plate, responding to the said means for measuring levels, controlling the starting of the device for measuring the surface when the high level is detected and for stopping it when the low level is detected.

13. System according to Claim 12, characterized in that the said control unit also controls the said means for rapidly refilling the pan (9), their operation being started when the said low level is detected.

14. System according to any one of Claims 11 to 13, characterized in that the said means for detecting a high level and a low level comprise, for each of these levels, a measuring electrode immersed at least partially in the solution for a level higher than the level to be detected whilst below this it is no longer wetted, means for applying a potential difference between each of the electrodes and a mass (19) in permanent contact with the solution, and means for detecting an electric current between the mass (19) and each of the electrodes (21, 22), this current being established with each electrode when it is put in contact with the solution, the said current being interrupted when the contact is broken.

15. System according to any one of Claims 10 to 14, characterized in that the said means for measuring a volume of solution consumed comprise, disposed in the said pan (9), a device for reducing waves comprising a wall (19) delimiting an enclosure within which the measurement is made, a small sized communicating orifice (20) being made in the bottom part of the said wall (19) so that the level of solution in the enclosure corresponds to the mean level in the pan.

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