FR2610399A1 - METHOD FOR MEASURING THE THICKNESS OF A FILM OF ANY WET SOLUTION REMOVED FROM A PRINTING PLATE OF A ROTARY OFFSET AND A SYSTEM FOR IMPLEMENTING SAID METHOD - Google Patents

Abstract

A METHOD FOR MEASURING THE THICKNESS OF A FILM OF A WETTING SOLUTION DEPOSITED ON A PRINTING PLATE OF A ROTARY OFFSET IN WHICH A CONSUMED VOLUME OF WETTING SOLUTION IS MEASURED, THE SURFACE AREA OF THE SAID PLATE D IS MEASURED THE PRINTING HAS BEEN PROCESSED BY CONSUMING THIS VOLUME AND THE THICKNESS OF THE FILM DEPOSITED, THE THICKNESS OF THE FILM DEPOSITED, IT IS EQUAL AUDIT VOLUME DIVIDED BY THE SAID SURFACE. A SYSTEM FOR IMPLEMENTING THIS PROCESS WHICH INCLUDES A DEVICE 18, 19, 21, 22, 25 FOR MEASURING A CONSUMED VOLUME OF WETTING SOLUTION AND A DEVICE 25, 26, 27 FOR MEASURING THE SURFACE OF THE SAID PLATE OF PRINT HAS BEEN PROCESSED CONSUMING SUCH VOLUME OF ANCHORING SOLUTION.

Description

26 0399

  The present invention relates to a method for measuring the thickness of a film of a fountain solution deposited on a printing plate of an offset press and to a system for carrying out this method. It is known that the offset printing method 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 via a blank cylinder rotating between a cylinder carrying the printing plate and the paper to be printed and transferring the ink received from the plate to 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 a so-called aqueous solution

  "wetting solution" on the plate.

  This solution is generally applied to the plate by one or more rollers, called "moisteners", usually filled with elastomer, whose axes of rotation are parallel to that of the platen cylinder,

  that these rollers contact by a common generator.

  The ink, generally of the oily ink type, is deposited on the plate by another series of rollers, called "ink-touchers", of the same kind as the moistening rollers, these rollers contacting the plate installed around the plate-cylinder after that it has been wetted by the wet rollers, the latter being upstream of the ink-pressing rollers with respect to the direction of

rotation.

  If the solution film deposited on the plate by the wet rollers is suitable in thickness, temperature, pH, alcoholic degree, etc ..., the ink will take on the plate only on certain areas treated with

surface to receive the ink.

  If the foor solution film is not

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  quite thick, the ink will take over the entire surface of the plate while if the film is too thick the ink does not

will not take anywhere.

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

ink deposited thereafter.

  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. chemical qualities of the fountain solution, printing conditions such as the speed of the

rotary, etc ...

  The parameters that can be used 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 the offset machines, both for adjusting the necessary balance between these thicknesses. for that of

  the optical density obtained on the printed paper.

  To adjust the thickness of the wetting film, it acts generally on a set point provided in the wetting device of the plate incorporating the wet rollers, but this setting is extremely difficult to achieve because we do not know the thickness actually deposited on plate. It is therefore desirable to have a measurement system indicating this thickness. This measurement system would, indeed, for given operating conditions (nature of paper, ink, temperature ...), when an ideal setting is obtained by trial and error, to know exactly how

  solution thickness it corresponds.

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

previously encountered.

  Methods for measuring the thickness of the fountain solution film deposited on the surface are already known.

  plate and systems implementing these methods.

  based on various physical principles.

  In particular, there is a method where the reflection of a beam of visible light on the wet surface of the plate is measured. This, in non-printing areas, has a relatively rough surface, this roughness from porosities that are filled by the fountain solution that is deposited on the plate. The greater the thickness of the liquid, the greater the porosity

are met.

  The surface of the solution being smoother than the rough surface of the plate, it reflects the light better, and therefore the more the deposited solution film is thick compared to the roughness of the plate, the better the reflection. The illumination and reading of the reflected beam are at 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 beams of infrared light 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.

  The processes mentioned and the systems implementing them give precise values but they have the disadvantage of being poorly adapted to industrial requirements. Said systems are particularly expensive, cumbersome, delicate and sensitive to projections of

  wetting solution and ink on the optics.

  The present invention aims to obviate these drawbacks and proposes for this purpose a method which is characterized in that a consumed volume of fountain solution is measured, the surface of the printing plate having been treated by consuming said volume is measured. and the thickness of the deposited film is deduced from these measurements, the latter being equal to said volume divided by said surface. This provides a method perfectly suited to an industrial environment, since it is sufficient to make consumption measurements in volume and treated surface, which are themselves adapted to such an environment. This method also has the advantage of making it possible to no longer have to make measurements of thickness on the plate itself, these measurements being difficult and delicate, in particular because of the small thickness of the solution (its order of magnitude is the micrometer), the rotational movement of which the plate is animated, as well as the risks of projection of ink or solution

previously mentioned.

  In addition, with this method, a mean value that is much more significant than point values that can vary randomly is determined.

around this average value.

  According to a feature of the method which is the subject of the invention, said treated surface of the printing plate is measured by counting the number of revolutions effected, whereas said volume of fountain solution is consumed by a blanket cylinder carrying an image received from the printing plate on a printing paper, said surface being equal to the width of the plate multiplied by the circumference of the blanket cylinder and the number of revolutions measured. The blanket cylinder has indeed

  a circumference equal to the length of the treated plate.

  The measurement operation of the treated surface is thus very easily carried out since one is satisfied with

  count a number of turns made by a cylinder.

  This way of doing the measurement is all the more advantageous as in most offset presses this count is already carried out which corresponds to the number

printed paper copies.

  One round (or length) of plate corresponds to a blanket cylinder tower and a printed copy while the width (or width) of the plate is equal to that of the paper to be printed. The treated plate surface is equal to the paper surface it was able to print. According to another characteristic of the process which is the subject of the invention, said consumed volume of fountain solution is measured in a feed basin of a wetting device of the plate, previously filled with solution, by measuring a high level thereon. begins said surface plate measurement treated, then a low level while stopping said surface measurement, the difference between said levels corresponding to the consumption of said wetting device to treat

said surface.

  The volume measurement is thus carried out by

  simple level measurements easily achievable.

  According to an advantageous characteristic of the process 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 fountain solution, and the measurement of the surface of the treated plate is started. when we detected this high level while we

  stop it when this low level is detected.

  This fixes a predefined volume of solution

  while the area treated with this volume is measured.

  This offers the advantage of allowing only the measurement of the surface to be made, and to simply detect levels in the easier basin.

as a measure of varying level.

  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 fountain solution and a device for measuring the surface of the printing plate that has been processed while consuming said volume.

fountain solution.

  It suffices to use the data of this device to determine the thickness of the film, manually or more advantageously through a device

specially provided 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 turns effected, whereas said volume of fountain solution is consumed by a blanket cylinder carrying an image received from the printing plate on a

paper to print.

  These characteristics offer the advantage of being extremely simple to implement, because such a counting device is generally available on offset presses (see above). It is sufficient to collect the information only when measuring the volume of fountain solution consumed. This measurement device is preferably completed by means for displaying the width of the printing plate and by means for calculating the area corresponding to this width and to the number of revolutions 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 feed basin in solution of a device for wetting the plate, said device for measuring a volume of consumed solution comprises means

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  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 high level and a predefined low level corresponding to a volume

known fountain solution.

  There is thus an easy to implement device for implementing the volume measurement operation. Other characteristics, peculiarities and advantages of the invention will emerge with those

  previously exposed, description of a mode

  particular embodiment given hereinafter only by way of example, not limiting, with reference to the accompanying drawings. On these: - Figure 1 is a simplified schematic representation in side elevation of an offset press; FIG. 2 is a diagrammatic representation in transverse elevation of the press mounted in FIG. 1, provided with a system according to the invention; FIG. 3 is a partially cutaway perspective view of the level detector device at

  wave reducer shown in Figure 2.

  In the offset press shown in FIG. 1, the paper 1 is printed on its two faces simultaneously by pressure between two blanket cylinders 2 which themselves receive the ink and the fountain solution deposited by

  cylinders 3 carrying offset plates.

  The press shown comprises a wetting device 4, comprising a wetting solution applicator roller on the plate, called "moistener", lined with rubber, a chrome-plated roll 6 called "transfer", a rubberized roll 7 said 'slider roll' and a

  roll 8 chromed said 'basin roll'.

  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 roll 6 has a peripheral speed substantially equal to the speed of travel of the paper 1, the roll 7 has a lower speed than the roll 6 and the roll 8 has an even lower speed. For the adjustment of the solution film, the rollers 7 and 8 can be tightened more or less against each other, thus varying the solution film which can pass between these two rollers, these being driven by motor.

independent variable speed.

  The roll 8 quenched in a container 9 called "basin" in which, in the known offset presses, a substantially constant level is maintained by means of a weir 10. The basin 9 is supplied with fount solution by an electropump 11 which debits by a

piping 12 in the basin 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 rate in circulation to prevent an overflow of the basin 9. An overflow pipe 15 returns to the tank 13 the overflow of the basin 9,

passed over the spillway 10.

  This wetting device is intended to deposit on the plate wound around the plate cylinder 3, a wetting solution film as uniform as possible, suitably dosed and of a thickness in general.

less than 1 micrometer.

  The rollers 16, so-called "touch rollers" deposit on the plate a greasy ink that they receive from the

roll 17.

  Of course, the upper plate cylinder 3 cooperates with damping and inking devices

similar (not shown).

  According to the method which is the subject of the invention, a consumed volume of fountain solution and the surface of the printing plate which has been processed while consuming this volume are measured in order to deduce the thickness of the deposited film. According to a characteristic of this method, said treated surface of the printing plate is measured by counting the number of revolutions made, while said volume of fountain solution is consumed by the blanket cylinder 2 carrying an image received from the plate of printing on the printing paper 1, said surface being equal to the width of the plate multiplied by the circumference of the blanket cylinder and by the number of

measured towers.

  According to another characteristic of the method which is the subject of the invention, said consumed volume of fountain solution is measured in the feed basin 9, which is filled beforehand with solution, and in which a high level is measured while begins said surface plate measurement treated, then a low level while stopping said surface measurement, the difference between said levels corresponding to the consumption of said wetting device to treat said surface. For this purpose, care is taken to avoid any arrival of solution in the basin while the volume measurement is being made, just as levels are measured for which there is no risk of loss of liquid by the

  device 10 for discharging the overflow.

  According to a preferred feature of the invention, said level measurements are made in the basin by detecting a predefined high and low level corresponding to a known volume of fountain solution, and the surface measurement of the treated plate is started. this high level has been detected while

  stop it when this low level is detected.

  This predetermines a volume of fountain solution, so that the only variable to be measured is the treated surface and more precisely here the number of

  laps made by the blanket cylinder.

  It is understood that processes in which one would set a predetermined number of turns and one would measure, for example in the basin, the volume

  consumed; or in which one would measure simultaneously.

  between a starting and ending top, the treated surface and the volume consumed, would be variants in accordance with

process according to the invention.

  We will now describe in support of Figures 2 and 3 a measuring system implementing the method

previously described.

  This system comprises a device for measuring a consumed volume of fountain solution and a device for measuring the surface of the printing plate having been

  treated by consuming the volume of fountain solution.

  According to the invention, the device for measuring the treated surface of the plate comprises a device for counting the number of revolutions effected, while the said volume of fountain 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 connected to the blanket cylinder, said sensor 26 detecting, once per turn, the passage of the pallet 27. The sensor 26 is connected to an electrical box 25 to which it provides a pulse per cylinder revolution printing 2 pulses which are counted by appropriate means well known to those skilled in the art

that includes 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 a slider 29 of a potentiometer 30, and means for calculating the area corresponding to this width and the number of revolutions measured, 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 numerical calculation elements (microprocessor, ...) or

analog computing elements.

  According to another characteristic of the invention, the device for measuring a consumed volume of fountain solution 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 fountain solution tank 13 and leading this solution into the basin 9, via a pipe 12. On the pipe 12, a solenoid valve 18 allows 'allow or interrupt

  solution feeding of the basin.

  Here, it is a delay 31 integrated in the box 25 which controls the closing of the solenoid valve 18 after a predetermined time after being commanded

a filling.

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

  corresponding to a known volume of fountain solution.

  The means for detecting a high level and a low level comprise, for each of these levels, a measurement electrode, respectively 21 and 22, at least partially bathed in the solution for a level higher than the level to be detected whereas 'under

this one, it does not soak anymore.

  The detection means also comprise means, integrated in the box 25, for applying a potential difference between each of these electrodes and a mass, here a wall 19 of a device described later, in permanent contact with the solution, the electrodes 21. 22 and the mass being connected by electrical conductors to the box 25 which also comprises means for detecting an electric current between the mass 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 it 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 made in a well-known manner and therefore do not have

need to be described here.

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

detected the low level.

  We are thus sure to measure the number of turns corresponding only to the consumption of the volume of

  solution between high 23 and low 24.

  The unit which controls the surface measuring device also controls the rapid filling means of the basin 9, their actuation being carried out

  when the low level is detected 24.

  This control unit is integrated in the box

  which is also connected the solenoid valve 18.

  The operation of the system, governed by the control unit, is as follows: the solenoid valve 18 is open, the solution 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 delay 31 provided for in FIG.

this effect.

  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 activated to count a pulse per turn of cylinder 2, from

  of 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 coming from the sensor 26 to stop, the storage of the number N of turns made, the opening of the solenoid valve 18 and the start of the delay 31 delaying the

control of its closure.

  The solenoid valve 18 being open and debiting more than the roll 8 consumes, the basin 9 fills and then

  overflow to the tank 13 by the pipe 15.

  When the time provided in the delay 31 has elapsed, the cycle starts again: closing of the solenoid valve 18, lowering of the solution level in the basin 9, beginning of counting of the high cylinder revolutions, stopping of this count at the low level and

opening of the solenoid valve.

  The tips of the electrodes 21 and 22 having been previously adjusted so that the slice of liquid 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 plate cylinder being known, the thickness E of the liquid film distributed by the wetting device is:

E = V / LCN

  The box 25 also comprises means for calculating and displaying the thickness of the film, connected to the surface and level measuring devices of which it

exploits the data.

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

control console of the press.

  The box 25 comprises a relay-based electromagnetic logic unit for managing the commands of the devices to which it is connected and that of the information it receives from it, as well as analog elements for the calculation, display and input of

  data such as the width (potentiometer 30).

  In another embodiment, the cabinet 25 is a programmed digital computer (a computer) managing the measurements of all the moorings of the press, which are 8 in number for a four-color press printing on both sides of paper, In order to make it possible to take measurements of levels which are not disturbed by the waves that may occur in the basin, the device for measuring a volume of solution comprises, arranged in the basin 9, a wave-reducing device illustrated on FIG. 3. This device comprises a wall 19, preferably sealed, delimiting an enclosure in which the measurement takes place, a small communication orifice 20 being provided in the lower part of the wall 19 so that the level of solution in the speaker 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 on mounting devices 41 and 42 to isolate the electrodes of the electric mass constituted by the wall 19. Note that these electrodes have a thread cooperating with a corresponding threaded bore in the mounting devices 41 and 42. This thread for adjusting the height of the tips of the electrodes.

  It is understood that the description which

  precedes has been made as a non-limitative indication, the person skilled in the art being able to bring

many variants.

  The device for level measurement by varying the resistivity could in particular be replaced by any other known device (float, bubbling, ultrasonic, capacitive), possibly in the feed basin of a different type of wetting device described, such as the so-called "classic, at taker" moorings,

"brushes" or "impeller".

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Claims (15)

  1. A method for measuring the thickness of a film of a fountain solution deposited on a printing plate of an offset press, characterized in that a consumed volume of fountain solution is measured, the surface area of the filler solution is measured. said printing plate having been treated while consuming said volume and deduced from these measurements the thickness of the deposited film, the latter being equal   said volume divided by said surface.   2. Method according to claim 1, characterized in that said treated surface of the printing plate is measured by counting the number of turns made, while said volume of fountain solution is consumed by a blanket cylinder (2). transferring an image received from the printing plate to a printing paper (1), said area being equal to the width of the plate multiplied by the circumference of the blanket cylinder (2) and by the number of turns measured.   3. Process according to any one of the claims   1 or 2, characterized in that said consumed volume of fountain solution is measured in a basin (9) for feeding a device (4) for wetting the plate, previously filled with solution, by measuring a high level (23) while one begins said measurement of treated plate surface, then a low level (24) while one stops said measurement of surface, the difference between said levels corresponding to the consumption of said   wetting device for treating said surface.   4. Method according to claim 3, characterized in that said measurements of levels in the basin (9) by detecting a high level (23) and a low level (24) predefined corresponding to a known volume of fountain solution and in that the measurement of the treated plate surface is started when this high level has been detected while it is stopped when this low level has been detected. 2610 3 9 9   5. System for measuring the thickness of a film of a fountain solution deposited on a printing plate of an offset press, characterized in that it comprises a device (18, 19, 21, 22, 25 ) measuring a consumed volume of fountain solution and a device (25,26,27) for measuring the surface of said printing plate having been processed while consuming said volume fountain solution.   6. System according to claim 5, characterized in that it further comprises a device for calculating and displaying (25) the thickness of the deposited film, connected   said measuring devices from which he exploits the data.   7. System according to any one of the claims   5 or 6, characterized in that said device for measuring a treated surface of the printing plate comprises a device for counting a number of revolutions made, while said volume of fountain solution is consumed by a blanket cylinder. (2) reporting an image received from the printing plate on a paper to print (1).   8. System according to claim 7, characterized in that said device for measuring a treated surface further comprises means (29, 30) for displaying the width of the printing plate and means for calculating the surface corresponding to this width and the number of revolutions measured, the circumference of the blanket cylinder (2) being a constant.   9. System according to any one of the claims   7 or 8, characterized in that said counting device comprises a fixed proximity sensor (26) and a pallet (27) connected to the blanket cylinder, said sensor (26) detecting, once per turn, the passage of said pallet (27).   10. System according to any one of the claims   5 to 9, characterized, said offset press comprising a basin (9) for supplying a solution of 2610 3 9 9   wetting device for the plate, in that said device for measuring a volume of consumed solution comprises means (18,25,31) for rapidly filling the basin (9) and means (19,21,22, 25) to measure the level of solution in this basin. 11. System according to claim 10, characterized in that said means for measuring the level of solution in the basin comprises means for detecting a high level (23) and a low level (24) predefined   0corresponding to a known volume of fountain solution.   12. System according to claim 11, characterized in that it further comprises a control unit of said device for measuring a treated surface of the printing plate, sensitive to said level detection means, controlling the start of this surface measuring device when the   high level and stop when the low level is detected.   13. System according to claim 12, characterized in that said control unit also controls said rapid filling means of the basin (9). their putting into action being carried out when detected said low level.   14. System according to any one of the claims   11 to 13, characterized in that said means for detecting a high level and a low level comprise, for each of these levels, a measurement electrode at least partially bathed in the solution for a level greater than the level at detecting while below it it does not quench, means for applying a potential difference between each of these electrodes and a mass (19) in permanent contact with the solution, and means for detecting a current between the mass (19) and each of the electrodes (21.22). this current establishing for each electrode when it is brought into contact with the solution, said current being interrupted when this contact is broken.   15. System according to any one of the claims   10 to 14, characterized in that said device for measuring a volume of consumed solution comprises, disposed in said basin (9), a wave reducing device having a wall (19) defining an enclosure in which is carried out the measuring, a small communication orifice (20) being provided in the lower part of said wall (19) so that the level of solution in the chamber corresponds to the average level in the basin.