WO2009101255A1

WO2009101255A1 - Method for adjusting the printing process

Info

Publication number: WO2009101255A1
Application number: PCT/FI2009/050107
Authority: WO
Inventors: Tatu PITKÄNEN; Petteri Lannes; Mika Sundquist; Teuvo LEPPÄNEN; Raimo Rajala; Matti Innala; Teemu KÄLKÄJÄ; Klaus JERNSTRÖM; Mika J. Kosonen; Petri V. Hirvonen; Erik Ohls; Juha Vattulainen
Original assignee: Upm-Kymmene Oyj; Metso Paper, Inc.
Priority date: 2008-02-12
Filing date: 2009-02-11
Publication date: 2009-08-20
Also published as: EP2250112A1; JP2011514869A; FI20080103A0; CN101952188B; CN101952188A

Abstract

The invention relates to a method for adjusting the printing process in which, at some process site of the printing press, the cross-directional profile of tension of the paper web in the machine direction is measured from at least one roller. The tension profile obtained as a measurement result is compared to an earlier basic tension profile after which the deviation and/or profile difference between the basic tension profile and the measured tension profile is analysed. The printing process is adjusted on the basis of the deviation and/or profile difference. The invention also relates to a computer program into which is fed the information obtained from the method according to the invention and which guides the automatic adjustment of the printing process, and the printing press guidance model which is obtained by using the information obtained from the method according to the invention.

Description

Method for adjusting the printing process

Background of the invention

The invention relates to a method for adjusting the printing process in which, at some process site of the printing press, the cross-directional profile of tension in the machine direction is measured from at least one roller, the obtained tension profile is compared to an earlier basic tension profile, the deviation and/or profile difference between the basic tension profile and the measured tension profile is analysed, and the printing process is adjusted on the basis of the deviation and/or profile difference.

The invention also relates to a computer program into which is fed the information obtained from the method according to the invention and which guides the automatic adjustment of the printing process, and the printing press guidance model which is obtained by using the information obtained from the method according to the invention.

The paper produced by a paper machine, i.e. the mill roll, is made to have as uniform quality as possible both lengthwise and crosswise of the press. In practise, however, in particular printing rolls made from the edge areas of the mill roll have cross-directional variations such that a compromise must be made on the desired uniform quality, for example, in tension, moisture or thickness profiles.

In a printing press, a slanted tension profile has previously been found visually and slanted profiles are typically fixed as maintenance operations in the printing process. Traditionally, this has almost always required stopping the press, i.e. an interruption of production. Because the operator circles the printing press and observes the behaviour of the web, then a problem in one step of the process has, additionally, caused the other parts of the printing press to be left alone, monitored only by automation and, in these parts, new problems could have arisen which the operator will not have time to discover.

Offset printing technique is currently the most commonly used printing method, hi offset printing technique, the printing and non-printing surfaces are on the same level, wherein it can also be referred to as a planographic printing method. The printing element (printing plate) is a level surface on which can be discerned neither clearly raised areas (letterpress printing method) nor recesses (gravure printing method). The planographic printing method is based on the mutual relationship between oil and water, i.e. on that they repel one another.

The offset printing method is based on the fact that oil (ink) and water repel one another. The surface of the printing plate is exposed in a plate printer such that the areas to be printed become areas that attract oily printing ink but repel water. The non-printing areas, on the other hand, attract water but repel the oily ink. Because the printing ink is oily, it attaches only to areas accepting ink.

In the offset printing method, the image to be printed is not transferred directly from the printing plate to the paper rather first as a reversed image to the surface of the rubber cylinder, then from there the right way up to the paper. This has also given rise to the term "offset" because, in this printing technique, the blank to be printed (the printing plate) is never in direct contact with the printing substrate (the paper) rather the blank is transferred from the printing plate to the rubber blanket of the printing unit and then from there to the paper. The material of the paper is too hard and it would quickly wear down and damage the surface of the printing plate.

When printing occurs in the offset printing method, the dampening rollers dampen the surface of the printing plate and, at the same time, the inking rollers spread ink on the printing plate, wherein the dampening water attaches to the non-printing areas and the printing ink attaches to the printing areas. After this, the printing ink transfers from the printing plate to the rubber cylinder and the paper travels between the rubber cylinder and the counter cylinder, wherein the ink transfers to the printing paper.

Offset printing can be done in rotary printing or in sheet-fed printing. In rotary printing presses, an unbroken paper web travelling from a paper roll between the printing rollers is used as the printing paper, which paper web is cut into page sheets only at the end of the presswork. Rotary printing is a faster printing method than sheet-fed printing and, for this reason, it is used when the amounts to be printed are relatively large. Gravure printing is a typographical printing method in which gravure printing presses are used. In the gravure printing method, the printing portion of the printing surface is lower than the non-printing surface. The printing ink transfers to the material to be printed from the recesses in the printing surface from which the method got its name. Gravure printing does not use as a printing surface printing plates secured around a cylinder, as in the offset printing, rather, on each printing occasion, the content to be printed is engraved into the copper surfaces of cylinders with an engraving diamond. In addition to a high printing speed and sharp printing quality, the advantage of gravure printing is that relatively cheap mechanical supercalenderized paper can be used.

Gravure printing presses are also generally web printing presses (i.e. rotary printing presses), i.e. presses whose printing material comes from a roll. In the printing process, the gravure printing cylinder is first inked with a liquid printing ink, wherein the recessed cells on the surface of the cylinder are filled. Immediately after inking, a thin steel scraper, i.e. the doctor blade, removes the excess ink from the neck areas between the recessed cells. The material to be printed travels between the impression cylinder and the gravure cylinder, wherein the printing ink is transferred from the recessed cells to the material to be printed with a great compression force. After printing, the printing material travels through a drying device which evaporates the solvent of the printing ink and dries the printing ink.

The runnability in different parts of the printing process of the paper web travelling through the printing press is generally controlled by changing the web strain in the direction of travel. Traditionally, the effects of the cross-directional profile variation of the paper web have also been fixed by increasing the web strain, i.e. by tightening the web, which has caused an increased breakage risk, for example, in connection with changing rolls and, for given grades of paper, led to alignment problems caused by the stretching of the web.

Additionally, the development of web printing, i.e. the growth of production speeds and of the width of the web to be printed, has made the control of runnability, i.e. the adjustment of the printing process, more critical than ever. Brief description of the invention

The object of the invention is to solve the above mentioned problems. The object of the invention is achieved by a method according to independent claim 1 and by using a computer program according to independent claim 11 and/or a printing press guidance model according to independent claim 12. The preferred embodiments of the invention are presented in the dependent claims.

The invention applies to the runnability behaviour of paper in a web printing process, hi the invention, the tension profile and tension profile differences of a paper web are measured and by analysing these measurements, a printing press or paper web can be adjusted for optimal runnability.

The present invention is directed to the optimal and efficient control of runnability in a web printing press for papers having different profiles and profile behaviours. By using the method according to the invention in web printing processes, it is possible to control a printing roll or paper web whose tension profile is, for one reason or another, bad and causes problems.

In the invention, there are preferably, but not necessarily, used measurement methods of the types in publications WO 2006/075055 and WO 2006/075056 (METSO PAPER, INC.).

The tension profile and profile differences of the paper web between given process steps can be measured with iRoll technology or other corresponding technology. In the invention, there is preferably, but not necessarily, used a piezo film. An EMFi film sensor, which is a permanently electrically charged cell plastic film which functions in the same manner as a piezoelectric sensor, can also be used. The voltage signal produced by an EMFi film depends on the sum pressure change exerted on the element such that, when a pressure change occurs, each portion of the element produces an equally large change in the initial voltage. Consequently, the short-term voltage measured with a large-impedance amplifier is the integral of the sum pressure of the sensor. The sensor functions as a dynamic sensor, it does not give a steady result for a sustained applied pressure rather the direct- current voltage component influencing across the sensor changes as a result of leakage currents. Because of this, the sensor functions only when it experiences changes in pressure. A solution according to the invention can also be implemented by means of another sensor, for example, by means of a resistive pressure sensitive film, a piezoelectric PVDF film (polyvinylidene fluoride film) or a PLL film (piezo- pyroluminescent film).

Preferably, the pressure sensor used in the method according to the invention, by means of which the tension profile can be measured, is either a movable film-like pressure sensor that can be installed on the surface of a roller or a fixed roller which contains a film-like pressure sensor and can be installed at some site in the printing process.

Instead of having measurement films installed on the roller at standard angles, the film- like sensors installed on the roller can be installed on the roller at different angles, wherein the roller can be used in positions having different overlap angles. This kind of movability of the roller makes it possible to use just one roller as the diagnostic tool in the printing press. This way, problems relating to the travel of the web in the printing press can be solved with flexibility.

Web tension is measured in an iRoll measurement in the machine direction, i.e. lengthwise in relation to the web. If the measuring sensor is installed cross-directionally, then a measurement result is obtained for the entire length of the web. In that case, a cross-directional profile is obtained for the lengthwise tension of the web. In practise, the tension of the web is never entirely even throughout the entire length of the web.

This tension profile measured at some site in the printing process is compared to a basic tension profile which can be a tension profile obtained from the paper factory for a given printing roll, a tension profile obtained earlier from the same roller, so-called long-term data or a tension profile obtained from another process site in the printing process, such as a tension profile obtained from a measurement after the unwinder. These profile differences are calculated by means of two or more measurements. On the basis of the measurement information and utilizing the exchange of information between the measurements of the printing process and the paper process, web tension can be controlled in the printing press by either instructing the operator or by using adjustment solutions based on the technologies described below manually or by means of an automation system.

Preferably, the invention can be applied to such web printing processes in which the width of the web and the speed of printing are great and in which are typically used grades of paper whose profile behaviour is critical, such as thin, non-coated papers.

Additionally, the invention is particularly well applicable in web printing processes in which a wide web is cut into strips, i.e. sub-webs, which are gathered as folded and cut printing sheets in the folder units of the printing press.

The tension profile and profile differences can be measured and, on the basis of these, the printing process can be adjusted either manually or through an automation system.

In one embodiment of the method according to the invention, the tension profiles of the customer (printing) rolls are measured at the paper factory after which the mill roll information is aligned and the printing order of the customer (printing) rolls is selected on the basis of the profile measurement information.

The method, to which the invention relates, can also be implemented by measuring the tension profile of the unwinder, i.e. of the unwinding paper web, during unwinding before the web is fed into the printing units and by adjusting the web regionally or according to each location by drying or dampening the web, for example, according to the method described in the WO2006/075055 (METSO PAPER, INC.). For example, dampening can be done by adding dampening water at a given site on the paper web, wherein the tension of the web decreases locally at this site because the addition of moisture decreases the web tension.

Preferably, after the above mentioned adjustment, the tension profile of the unwinding paper web can be measured before the infeed unit or before the web guidance of 1. printing unit and, at this step of the printing process, the adjustment according to the invention is done, preferably, by adjusting the guide rollers, roller nip and/or dancing rollers. By using the method according to the invention, the tension profile and tension profile difference of the printed web in comparison to the unwinding web can also be measured, and the profiling adjustment can be done by adjusting the profilable leading rollers and/or roller structures.

The profiling adjustment of the printed web can also be done between the printing units.

Preferably, the tension profile of the printed web can be measured before splitting and folding, wherein the adjustment is done, preferably, by adjusting the turnable, movable or profilable leading rollers and/or drawing rollers.

One embodiment according to the invention covers the measurement of the tension profile of printed sub-webs split into strips. Preferably, these are adjusted according to each sub- web using the drawing difference of the drawing rollers before turning, collection, folding and cutting of the webs.

By using the method according to the invention, on the basis of collected material regarding different grades of paper and profiles and difference profiles, it is possible, preferably, to make ready-made guidance models for the printing press.

The profile information obtained from web printing processes can also be utilized in the paper production, i.e. on the basis of the information, the paper production process can be developed, which can also influence production process costs downward or the process towards efficiency.

The invention improves the efficiency of the web printing process, mainly in terms of runnability but also in terms of print quality. The alignment of partial colouring, folding and cutting can also be guided on the basis of the tension information.

In web printing presses, the cross-directional profile variation of the paper web is neither measured nor adjusted. The traditional means has been to adjust the sum web strain in the printing press - and even that only in the direction of travel. The advantage of the invention is the possibility of optimising the web strain used in printing, which decreases breakage risk and is advantageous for energy use. Preferably, the method, to which the invention described above relates, can be used as a problem-solving service, especially by using a mobile measuring apparatus.

The method according to the invention can also be used in a printing press to indicate a changing tension profile, wherein it can be indicated that the bad or problematic tension profile of a customer roll at a given site in the printing process did not oπginate from the paper factory.

The information of the method, to which the invention relates, can be used as a tool for guidance and intensification of keeping in operation and maintenance. Users or manual adjusters of the printing process can create adjustment solutions on the basis of the profile measurement information. Another way is to attach to the printing press adjustment systems relating to the control of web tension to utilize the tension measurement information "on-line".

One embodiment of the method according to the invention is attaching to the printing press an automation system that reacts to an extreme profile peak or other corresponding deviant form in the cross-directional tension profile measured from some roller.

Preferably, the automation system drives the speed of the printing press to a lower level when the system registers a deviation of above mentioned type. At the same time, the system warns the operator. Thus, the operator can come and check whether the problem is real and then react to the situation in an appropriate manner.

Such a profile peak can, for example, result from an edge rip or pleating of the web. If the operator does not have time to notice a developing pleat or other deviant web behaviour, these will cause runnability and quality problems in the form of lost production or faulty products.

When studying power trends in the machine direction, extreme peaks / changes are noticed particularly in connection with changing rolls. Before the printing unit, the tension level observed remains relatively well constant due to the tension adjustment used before the printing units. Instead, the tension level after the printing units clearly changes when a customer roll is unwinded and, in connection with changing a roll, there occurs an extreme change in the level. This can cause the breakage risk to increase. By using the tension adjustment after the printing units, the profile peaks and changes caused by this can be removed and/or controlled.

Such an automation system can be integrated into the automation of the printing press and delivered to the printer as a part of the printing press or automation system.

Detailed description of the invention

The invention relates to a method for adjusting the printing process in which, at some process site of the printing press, the cross-directional profile of tension in the machine direction is measured from at least one roller, the obtained tension profile is compared to an earlier basic tension profile, the deviation and/or profile difference between the basic tension profile and the measured tension profile is analysed and the printing process is adjusted on the basis of the deviation and/or profile difference. The basic tension profile of the method according to the invention is a tension profile obtained from the paper factory for the paper roll, the basic tension profile is based on data collected earlier from the same roller, or the basic tension profile is a tension profile obtained from another process site in the printing process, such as a tension profile obtained from a measurement after the unwinder. The tension profile can be measured with a movable film-like pressure sensor installed detachably on the surface of the roller or with a roller containing a fixedly and/or permanently installed film-like pressure sensor. The roller itself can also be fixedly installed or movable.

In one embodiment, the method according to the invention comprises the adjustment of the printing process by adjusting a roller of the printing press. The roller to be adjusted can be a guide roller, roller nip, dancing roller, leading roller or drawing roller. In the second embodiment, the printing process is adjusted by drying and/or dampening the web or, alternatively, by changing the web strain or the speed of the press.

The step of the method can comprise guiding the alignment of partial colouring, folding and cutting on the basis of the tension information. In one advantageous embodiment, the deviation of the tension profile is a profile peak on the basis of which the automation system drives the speed of the printing press to a lower level. Preferably, the automation system guides the increasing and decreasing of web strain.

The adjustment of the printing process and/or printing apparatus can be done manually but the method also enables the use of an automation system. The invention also relates to a computer program into which is fed the information obtained from the method according to the invention and which guides the above described type of automatic adjustment of the claim.

The invention also relates to a computer program into which is fed the information obtained from tension profile measurements and deviations and/or profile differences, wherein the program guides the adjustments made to the printing process.

Additionally, the invention relates to a printing press guidance model, which guidance model is obtained by using the information obtained from tension profile measurements and profile differences and modelling this, for example, as guidance models suitable for different grades of paper. By means of the model, the information measured from the printing press can be used for running the same kinds of printing rolls.

It is obvious to a person skilled in the art that, as technology develops, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are not then limited only to the examples presented in the above rather many variations are possible within the scope of the claims.

Claims

1. A method for adjusting the printing process, characterized in that the method contains the following steps

a. measuring, at some process site of the printing press, the cross-directional profile of tension of the paper web in the machine direction from least one roller,

b. comparing the obtained tension profile to an earlier basic tension profile,

c. analysing the deviation or profile difference between the basic tension profile and the measured tension profile, and

d. adjusting the printing process on the basis of the deviation and/or profile difference,

and that the basic tension profile is a tension profile obtained from the paper factory for the paper roll, the basic tension profile is based on data collected earlier from the same roller, or the basic tension profile is a tension profile obtained from another process site in the printing process, such as a tension profile obtained from a measurement after the unwinder,

and that said tension profile is measured with a movable film-like pressure sensor installed detachably on the surface of the roller or with a roller containing a fixedly and/or permanently installed film-like pressure sensor.

2. A method according to claim 1 , characterized in that the speed of the press and/or web strain is adjusted.

3. A method according to any one of the preceding claims, characterized in that a roller of the printing press is adjusted.

4. A method according to claim 3, characterized in that a guide roller, roller nip, dancing roller, leading roller or drawing roller is adjusted.

5. A method according to any one of the preceding claims, characterized in that the dryness and/or dampness of the web is adjusted.

6. A method according to any one of the preceding claims, characterized in that the guidance of the alignment of partial colouring, folding and cutting is adjusted.

7. A method according to any one of the preceding claims, characterized in that the adjustment of the printing process and/or printing apparatus is done manually or by means of an automation system.

8. A method according to claim 1, characterized in that said deviation is a profile peak.

9. A method according to claim 8, characterized in that, on the basis of said profile peak, the automation system drives the speed of the printing press to a lower level.

10. A method according to claim 9, characterized in that, on the basis of said profile peak, the automation system increases or decreases the web strain.

11. A computer program, characterized in that the information obtained from the method according to claim 1 is fed into the program and the program guides the adjustment according to claims 2-6.

12. A printing press guidance model, characterized in that the guidance model is created by using the information obtained from the method according to claim 1.

13. A guidance model according to claim 12, characterized in that different guidance models are used for different grades of paper.