EP0732444B1 - Calander for treating a paper web and process for its use - Google Patents

Abstract

A paper processing calender, esp. for producing gravure-printable paper, has a stack of rolls which are loaded from one end. A working nip is formed between each adjacent hard and soft roll pair, and a change-over nip is formed between two adjacent soft rolls. The rolls are at least partly heated, and at least one of the end rolls can be controllably flexed. The number of rolls (2,9) in the stack is limited to not more than eight, and in order to increase the energy for deformation of the paper, the residence time in at least one nip is at least 0.1 ms. The heating arrangement for a heated roll (2,4,7,9) is such that a surface temp. of at least 100 degrees C is maintained, and the roll loading is such that the pressure in the working nip is at least 42 N/mm<2>. Also claimed is a process for operating a calender in which the average temp., pressure, and residence time in the nip are such that the following equation is satisfied: 1.378-0.00356 x T x (0.00825-5.12x10<-5>xT) x p - Ä0.039+(0.188-0.00112T) x p x e<-0.093>Ü x t x e<-0.412>t =0.8 to 0.9.

Description

The invention relates to a calender for the Treatment of a paper web, especially for production of gravure-proof paper, with one from the end resilient roll stack, between each one hard working gap formed by a soft roller and an alternating nip between two soft rollers has, with part of the rollers heated and at least an end roll is deflection controllable, and on a method of operating this calender.

Calenders of this type are widely known, for example from the brochure "The New Super Calender Concepts" from Sulzer Papertec from 1994 (code 05/94 d). They are used for the final treatment of a paper web so that it has a desired value for smoothness, gloss, thickness, bulk and the like. receives, and are set up separately from a paper machine. The "soft" or elastic rollers have a cover consisting mainly of fiber material. The heated rollers have a surface temperature limited to around 80 ° C. The average compressive stress in the nips is between 15 and 30 N / mm ² in normal operation, and values up to a maximum of about 40 N / mm ² have already been used in the lowest working gap. For papers that are easy to satin, such as writing paper, a stack of 9 or 10 rollers is sufficient. 12 to 16 rollers are required for higher quality papers, such as gravure papers, technical papers or compression papers. Such a large machine is expensive and takes up a lot of space.

So-called compact calenders are also known, where a heated roller with a deflection controllable soft roller forms a gap and for two-sided treatment of the paper web also two such calenders are connected in series can. However, this can only be easily satinized Papers, but not technical papers, e.g. Silicon base papers as well as papers for gravure printing, produce. In addition, a large part of the deformation energy be supplied as heat. The heatable Rollers therefore have a surface temperature of 160 to 200 ° C. A lot of heat energy is radiated, which must be removed by air conditioning. Because the roller diameter is larger due to the strength than with the supercalender, high line loads must be be applied to achieve a desired satin finish to generate the necessary compressive stresses. Of others are replacement rollers for the elastic rollers expensive because it is deflectable should be.

The invention has for its object a calender of the type described at the beginning, which also for the treatment of gravure and others suitable for high quality papers, but cheaper in Manufacture and operation.

This object is achieved according to the invention in that the stack has only eight rollers and, in order to increase the deformation energy to be supplied to the paper web, at least for one working gap, the condition is that the dwell time is at least 0.1 ms and that the heating of a heatable roller delimiting the working gap is designed for a surface temperature of at least 100 ° C and the load on the rollers for an average compressive stress in the working gap of at least 42 N / mm ² .

By reducing the stack height, the influence becomes of the roll weight reduced to the line load. Man can therefore load with the same distances in the lowest gap in the uppermost entrance gap with a higher line load than working with the well-known super calenders. Surprisingly, it is therefore sufficient to add the Increase deformation energy moderately to also high quality To be able to process papers satisfactorily. So the heat can be supplied at temperatures that are only slightly above the usual temperatures and therefore only slightly increase the heat radiation. Various heat transfer media are also available for this Disposal; there are no difficulties as with the high temperatures applied to a compact calender Need to become. A relatively small one is also sufficient Increase the compressive stress that mechanically without further notice can be endured and at most when choosing the The elastic roller must be taken into account. By taking both measures (increased heating and increased Load) at least in one working gap, preferably the lowest working gap, at the same time are used, can be extremely good Results even with a high-speed calender and with high quality paper. Because the roll stack has a lower height than known super calenders, you also need lower buildings, which is the set-up cost significantly lowers.

It is expedient to ensure that, at least for one working gap, the condition applies that the dwell time is at most 0.9 ms and that the heating to a surface temperature of at most 150 ° C. and the load to an average compressive stress of at most 60 N / mm ² is designed. In fact, only a moderate increase in surface temperature and compressive stress is required. In most cases, a surface temperature of less than 130 ° C and an average compressive stress of less than 50 N / mm ^{2 are} sufficient. The preferred dwell time is 0.2 to 0.5 ms.

It is particularly advantageous that the condition for the Majority or all of the six working columns apply. Because the increased values evenly across several working columns are distributed, very small increases are sufficient.

In this context it is recommended that top and Bottom roller are heated. About those hard rollers the heat energy can be supplied better than the adjacent soft roller. This also applies if the Deflection control of the upper and / or lower roll, because, for example, you have a heated hydraulic fluid can supply.

It is particularly favorable that the soft rollers have a plastic cover. Such plastic-related rollers are much better suited than rollers covered with fiber material for operation with increased medium compressive stress. They allow operation with a compressive stress of more than 42 N / mm ² . In particular, the reference should be designed for a compressive strength of up to about 60 N / mm ² .

This applies in particular if the plastic cover in the consists essentially of fiber-reinforced epoxy resin. Such a plastic cover has a service life of at least twelve weeks. An example of this is a Cover from "TopTec 4" from Scapa Kern, Wimpassing / Called Austria.

In a further embodiment of the invention is the stack arranged in-line of a paper machine or coating machine. The paper web therefore comes at an elevated temperature, for example at 60 ° C, at the inlet gap of the Calender and therefore only needs a small amount Heat input to a sufficient deformation energy to make available. With such an in-line operation are plastic covers that are for the sake of higher Compressive stress are desired, particularly suitable because - unlike paper covers - they are essential are less sensitive to markings and therefore rarely need to be removed and sanded.

Advantageously, all rollers have a drive. The paper web can therefore be drawn in with the calender running because all the reels are at the same speed can be brought before the column getting closed.

It is also recommended that the stack of one Protective cover is covered that the heat radiation reduced. Such a protective hood reduces the heat radiation, so the manufacturing hall isn't like that must be warmed up and excessively air-conditioned. Conversely, the temperature inside the hood increases kept at a higher value so that the heat supply can be kept low via the heating device.

A method for operating a previously described calender is characterized in particular in that the averaged numerical values of the surface temperature T [in ° C.], the mean compressive stress p [in N / mm ² ] and the dwell time t [in ms] of all working gaps are chosen in this way that the following relationship (I) applies to a target variable Zg: Zg = 1.378-0.00356 · T- (0.00825-5.12 · 10 -5 T) p- [0.039+ (0.188- 0.00112T) p · e -0.093p ] t · e -0.421t = 0.8 to 0.9.

Since the dwell time t for a given calender can vary only to a small extent, are to be fulfilled the above condition mainly the surface temperature T and the mean compressive stress p to disposal

Fig. 1

eine schematische Darstellung des erfindungsgemäßen Kalanders und

Fig. 2

in einem Diagramm die Abhängigkeit der Zielgröße Zg von Oberflächentemperatur T, Druckspannung p und Verweilzeit t.

The invention is explained below with reference to a preferred embodiment shown in the drawing. Show it:

Fig. 1

a schematic representation of the calender according to the invention and

Fig. 2

the dependence of the target variable Zg on the surface temperature T, compressive stress p and dwell time t in a diagram.

The illustrated calender 1 has a roll stack which consists of eight rollers, namely one heatable, deflection-controllable hard top roller 2, a soft roller 3, a heatable hard roller 4, a soft roller 5, a soft roller 6, a heatable hard roller 7, a soft roller 8 and a heatable, deflection-controllable hard Bottom roller 9. In this way there are six working gaps 10 to 15, each by a hard roller and a soft roller are limited, and a Alternating nip 16 formed by two soft rollers 5 and 6 is limited.

A paper web 17 is fed from a paper machine 18, passes under the guidance of idlers 19 the working column 10 to 12, the alternating gap 16 and the working column 13 to 15, whereupon it in a winding device 20 is wound up. In the top three Working columns 10 to 12 is the paper web with the one side, in the three lower working columns 13 to 15 with the other side on the hard rollers, see above that the desired surface structure on both sides, for example Gloss or smoothness is achieved.

Because of the direct connection of the calender 1 with the Paper machine 18 results in in-line operation. Out for this reason, each of the rollers 2 to 9 has its own Drive 21. This allows the Paper web 17 during operation. Each of the soft ones Rollers 3, 5, 6 and 8 have a cover 22 made of plastic, especially fiber-reinforced plastic. This Material is less sensitive to marking than paper, so that the longer ones essential for in-line operation Downtimes can be achieved. In addition, the cover with a higher compressive stress. He is also more resistant to higher temperatures than Paper.

a) Über eine Leitung 24 wird die Kraft P festgelegt, mit der die Oberwalze 2 nach unten gedrückt wird, wobei die Unterwalze 9 zweckmäßigerweise ortsfest gehalten ist. Die Belastung kann auch in umgekehrter Richtung erfolgen, wobei die Kraft P auf die Unterwalze 9 wirkt und die Oberwalze 2 ortsfest gelagert ist. Durch die Belastung ist auch die Druckspannung bestimmt, die in den einzelnen Arbeitsspalten 10 bis 15 herrscht. Diese Druckspannung nimmt von oben nach unten zu, weil sich zu der Belastungskraft P jeweils noch das Gewicht der einzelnen Walzen addiert. Allerdings ist der Kraftzuwachs geringer als bei bekannten Superkalandern mit 9 bis 16 Walzen.

b) Über die Leitungen 25 und 26 werden die Vorrichtungen 27 bzw. 28 zum Durchbiegungsausgleich der Oberwalze 2 und der Unterwalze 9 mit Druckmittel beaufschlagt. Diese Vorrichtungen sorgen dafür, daß über die Länge der Walzen eine gleichmäßige Druckspannung herrscht, wie dies an sich bekannt ist. Hierfür können alle üblichen Vorrichtungen verwendet werden, insbesondere solche, bei denen Stützelemente nebeneinander in einer Reihe angeordnet sind und einzeln oder zonenweise mit unterschiedlichem Druck beaufschlagt werden können.

c) Die Walzen 2, 4, 7 und 9 sind beheizbar, wie dies durch Pfeile H angedeutet ist. Die Heizenergie wird über strichpunktierte Pfade 27 bis 30 zugeführt. Dies kann durch elektrische Beheizung, durch Strahlungsheizung, mit Hilfe eines Wärmeträgers u.dgl. erfolgen. Eine Schutzhaube 31 dient der Wärmeisolation und sorgt dafür, daß die in Folge der Beheizung abgestrahlte Wärme nur in geringem Maß in die Umgebung abgeführt wird.

A control device 23 has several functions:

a) The force P with which the upper roller 2 is pressed down is determined via a line 24, the lower roller 9 advantageously being held stationary. The loading can also take place in the opposite direction, the force P acting on the lower roller 9 and the upper roller 2 being mounted in a stationary manner. The compressive stress that prevails in the individual working columns 10 to 15 is also determined by the load. This compressive stress increases from top to bottom because the weight of the individual rollers is added to the loading force P. However, the increase in force is less than in known supercalenders with 9 to 16 rolls.

b) Via lines 25 and 26, devices 27 and 28 for compensating for deflection of upper roller 2 and lower roller 9 are pressurized. These devices ensure that there is a uniform compressive stress over the length of the rollers, as is known per se. All conventional devices can be used for this, in particular those in which support elements are arranged next to one another in a row and can be subjected to different pressures individually or in zones.

c) The rollers 2, 4, 7 and 9 can be heated, as indicated by arrows H. The heating energy is supplied via dash-dotted paths 27 to 30. This can be done by electrical heating, by radiant heating, with the help of a heat transfer medium and the like. respectively. A protective hood 31 is used for thermal insulation and ensures that the heat radiated as a result of the heating is only dissipated to a small extent into the environment.

The force P ensures that the mean compressive stress p in the working gaps 10 to 12 and 13 to 15, in particular in the lowest gap, is between 42 and 60 N / mm ² , and preferably above 45 N / mm ² . With the help of the heater H it is ensured that the surface temperature of the heatable rollers 2, 4, 7 and 9 is between 100 and 150 ° C. The diameter of the rollers and the elasticity of the covering 22 are chosen so that there is a gap width of approximately 2 to 15 mm, preferably approximately 8 mm. Depending on the web speed, this leads to dwell times t in each working gap of 0.1 to 0.9 ms. It is preferred if the temperature T is only slightly above the lower limit, for example 110 ° C., and if the compressive stress is only slightly above the lower limit, for example 50 N / mm ² .

It was found that the printability of natural and light-coated papers is not necessarily related to the gloss or smoothness of the paper web, but rather to the compression or its reciprocal bulk (in cm ³ / g). The measure of the printability in the gravure printing process is determined by the number of "missing dots" (missing halftone dots in the quarter and halftone range). The best results in this regard can be obtained if all working columns ensure that the condition specified in the process claim is fulfilled.

In FIG. 2, the target quantity Zg, which corresponds to the above relationship (I), is plotted in a three-dimensional diagram in the ordinate, the compressive stress p in N / mm ² in one abscissa and the dwell time t in ms in the other abscissa. Three areas of constant temperature T are entered in ° C, of which the 100 ° C area with solid lines and points at the network crossings, the 125 ° C area with dash-dotted lines with circles at the network crossings and the 150 ° C area with dashed lines Crossing at the network crossings is shown. In order to arrive at the desired target values, the arithmetic mean of the dwell time t, the surface temperature T and the mean compressive stress p is first determined from all six working columns. If one goes into the diagram of FIG. 2 with these values, one can immediately determine whether the target variable Zg lies in the desired target range between 0.8 and 0.9. In many cases, the results of the paper treatment can be improved further by the fact that the rollers, in particular the center rollers, are mounted in levers in an unillustrated manner, the overhanging weights being advantageously compensated for by supporting devices, as is known from EP 0 285 942 B1.

Claims (11)

1. Calender for treatment of a paper web, in particular for producing paper capable of intaglio printing with a roll stack which can be loaded from the end and which comprises working gaps formed in each case between a hard roll and a soft roll and between two soft rolls a change-over gap, wherein some of the rolls can be heated and at least one end roll can be controlled for deflection, characterised in that the stack comprises only eight rolls (2 to 9), and to increase the energy of deformation to be supplied to the paper web (17) the condition that the dwell time is at least 0.1 ms and that the heating (H) of one heatable roll (2, 4, 7, 9) defining the working gap is designed for a surface temperature (T) of at least 100°C and the load (P) on the rolls is designed for a mean compressive stress in the working gap of at least 42 N/mm² applies to at least one working gap (15).
2. Calender according to claim 1, characterised in that the condition that the dwell time is at most 0.9 ms and that the heating (H) is designed for a surface temperature of at most 150°C and the load (P) is designed for a mean compressive stress of at most 60 N/mm² applies to at least one working gap (15).
3. Calender according to claim 1 or 2, characterised in that the condition applies to the majority or all of the six working gaps (10 to 15).
4. Calender according to claim 3, characterised in that the upper and/or lower rolls (2, 9) can be heated.
5. Calender according to any of claims 1 to 4, characterised in that the soft rolls (3, 5, 6, 8) carry a plastic covering (22).
6. Calender according to claim 5, characterised in that the plastic covering (22) is designed for a compressive stress bearing capacity of up to 60 N/mm².
7. Calender according to claim 5 or 6, characterised in that the plastic covering (22) essentially consists of fibre-reinforced epoxy resin.
8. Calender according to any of claims 1 to 7, characterised in that the stack is arranged in line with a paper-making machine (18) or spreading machine.
9. Calender according to any cf claims 1 to 8, characterised in that all the rolls (2 to 9) have a drive (21).
10. Calender according to any of claims 1 to 9, characterised in that the stack is covered by a protective hood (31) which reduces the heat radiation.
11. Method of operating a calender according to any of claims 1 to 10, characterised in that the averaged numerical values of surface temperature T [in °C], mean compressive stress p [in N/mm²] and dwell time t [in ms] of all the working gaps are selected so that the relationship below applies to a target quantity Zg: Zg = 1.378-0.00356·T-(0.00825-5.12·10-5T)p-[0.039+(0.188- 0.00112T)p·e-0.093p]t·e-0.421t = 0.8 to 0.9.

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