FI118304B - Method and arrangement for controlling the amount of coating in the coating of a fiber web - Google Patents

Description

118304

The present invention relates to a method for controlling the amount of machine-facing coating in a double or double coating of a paper or board web according to the preamble of claim 1. The invention also relates to an arrangement for carrying out such a method.

10 For coating paper or board, either direct or indirect application can be used. In direct application, the coating material is applied to the web as it moves past the application area on the surface of the counter roll. In indirect application, the coating material is first applied to a film transfer roller or other transfer surface, from where it is transferred to the web in a coating nip. Often the coating agent is applied in excess and the amount of coating remaining on the moving substrate is adjusted, i.e. the coating is dispensed by means of a scraping element. The scraper element may be a scraper blade or a rotating scraper bar which is loaded against a moving base. The loading of the scraper element is achieved by the pressure medium ··. or by mechanical force to tear the scraper element. The loading of the scraper element • · · • · depends on how much coating material exits the application area with the moving substrate. Also known are non-contact coating methods, where no scraper element is required. In these methods everything is applied • · · ». . *. the coating material remains in the web, whereby the coating is dispensed by the applicator. * * ·. use a pump or valve to feed the coating.

··· 25:: *: The amount of coating, which refers to the dry weight of the coating mixture on paper ♦ ·· grams per square meter, is an important measure of the coating performance.

· * ·. Profile of the coating layer both in machine direction and in the transverse direction of the web • * • ·. ···. try to keep it as smooth as possible with feedback adjustments.

· «« *. 30 In the machine direction, the profile of the coating layer is most often adjusted by changing the load of the scraper • · · ”**. In the transverse direction of the web, the profile of the coating layer • · «• · 118304 2 is adjusted by locally changing the loading of the scraper element in areas where there is too much or too little coating. Both machine · and transverse profile adjustment require accurate coating quantity measurement. Usually, a gauge frame is used to measure the amount of overlay, with a tray with sensors moving across the entire width of the paper web.

In known methods, the machine direction profile of the coating amount is controlled by varying the pressure in the pressure medium hoses adapted to load the scraper element against the moving substrate. The useful pressure range of the hose pressure is quite narrow, typically 0.8 to 2.5 bar. Outside this range, the amount of overclocking currently cannot be controlled by automatic control. Too low a load pressure causes runnability problems and too high a pressure accelerates wear on the scraper element. The loading pressure of the scraper element also affects the response of the cross-profile adjustment of the coating amount. One major problem is that the pressure in the load hose very easily drifts out of the optimum operating range.

The coating amount measurement is based on the measurement of the dry weight of the web before the coating. after filling station and after coating station. In duplexing, * * · '..i 20 thus obtains the total amount of coating, but not the amount of coating applied across the web. There may also be situations in multilayer coating where • ·. · t. it is not possible to measure the amount of coating between two successive coatings.

In general, it is desired to apply different amounts of coating on different sides of the web. Kum-. Mankin side of the coating amounts must be measured separately by the direct coating · "" the number of measurement based on the coating material the various components of the measurement * »·: v. infra-red radiation. The measurement requires expensive infrared sensors, and the amount of overlay * obtained is strongly dependent on the paste recipe and the infrared radiation on the base paper. Compensation of the base paper fillers is abrasive- 118304 3 la. Typically, infrared measurement gives a good idea of the transverse profile of the amount of coating, but information about the level of coating remains inaccurate.

Control of one-sided amount of coating is also important on machines where there is no double-sided measurement of the amount of coating. The majority of such machines are such machines. At present, these cases have to be confined to controlling the total amount of coating. In this case, the coating amount is adjusted by varying the loading pressure of the two scraping elements by the same amount without knowing on which side of the coated web a deviation from the target coating value 10 occurs.

The object of the invention is to provide a method of adjustment which enables better control of the plurality of coatings.

To achieve this and the following objects, the method according to the invention is characterized in what is stated in the characterizing part of claim 1.

··. ·. Correspondingly, the arrangement according to the invention is characterized by what is precursor. ·: ·, As defined in the characterizing part of claim 9.

• · · *

Mt ··· «: The idea of the invention is that the total coating amount is still controlled by ··· i: by changing the loading pressure of both scraping elements, but at the same time by · · · 25 correcting the bias of the coating amounts by a separate regulator load pressure from one scraper element to another as required. The regulator calculates changes in the loading pressure of both scraping elements that are different in nature but equal in magnitude. Therefore, the coating ratio control does not affect the overall coating quantity, but only • ·. * * *. how the coating amount is distributed across the web or overlapping layers applied in multi-layer plating.

»·· * • · • · · · · · 118304 4

The consumption of the coating material for each appliance is measured by a measuring device in the machine cycle. On the basis of the mass or volume flow, the consumption of the coating agent can be calculated very accurately in the long term. The amount of coating can be calculated from the consumption of the coating material by the formula (1): 5 cw „= - ~ sc (1) dv where CWm is the calculated coating quantity, Q is the coating consumption, 10 d is the web width, v is the solids content of the coating .

Based on the coating material consumption and the total coating amount measured from the dough, the ratio of the coating amounts applied to the different webs is calculated. The amount of overcoat on the top and bottom of the web can be calculated using formulas (2) and (3):

CW

CWb = -zs * - CWM (2):. · CiF ^ + ar., ··· • Φ · m m φ m * «« ··· • ·

CW

20, CW = - ^ - CWM (3) '+ ^ CW, CW, "" 9 · «# · · · · · · · · • φ • CWmb wherein the underside of the web is calculated by the amount of coating. ·. CWmt the upper side of the web is calculated on the amount of coating, • * · M ·. · · ·, CWtot is the actual coating quantity measured from the web, • · * «· 25 CWB the web underside of the amount of coating relative to the total • · * •« '..I coating amount «· CWT the upper surface of the web the coating amount relative to the total • · · · ··! the coating amount.

· * · * • ·· • «j 118304

When the amount of coating on each side of the web is known, the load-modifying actions of the scraping elements can be conveniently applied to achieve and maintain the desired coating ratio. For each type of paper or board, guideline values are given for the coating amounts on different sides of the web.

S The Coating Rate Controller aims to maintain a predetermined coating ratio over the long term. The regulator has to be tuned slowly because the calculation of coating material consumption is not accurate in the very short term. The regulator must also be locked so that it does not turn on immediately after a production outage, as reliable measurement can only be obtained when the process is sufficiently stabilized.

The method according to the invention can also be applied in non-contact coating where no scraping elements are used. In this case, the actuator for dispensing the coating may be, for example, a pump or a valve through which the coating material is supplied to the applicator.

The new adjustment method allows for optimization and maximization of product quality (paper specifications) and better uniformity. The new control method ... .f also simplifies process control and reduces the risk of operator error • ·] ···, 20 times.

♦ ♦ · • ·:. ·. It is known that the consumption data of the coating material has not been previously utilized in the coating. , ·, In the feedback control, because the measurement is slow and the adjustment works. due to delay. In the invention, these problems are solved by combining the utilization data of the coating ··· 25 filler with the conventional coating quantity control: based on the measurement of the total coating quantity.

♦ ·· # ·· • · • t · ♦ ·

The invention will now be described with reference to the accompanying drawings, • · *. · · ·. however, the invention is not exclusively limited thereto.

30 ** ·· • · • · · I ·· • · 6 118304

Figure 1 shows a prior art waste system for controlling coating amount in double-sided film transfer coating.

Fig. 2 shows a waste system according to the invention in which, in addition to the total number of coatings 5, the ratio of the amount of coatings applied to different sides of the web is adjusted.

Fig. 1 schematically shows a coating station immersed in a film transfer technology equipped with a prior art coating amount management system. The coating station comprises two film transfer rolls 11, 12 which form a nip through which the web W to be coated is guided to pass. Ap-applicators 13, 14 and scraping elements 15, 16 are shown by way of reference only. The coating material is guided from the machine rotation 17, 18 through the feed connection 17 ', 18' to the applicator 13, 14, which spreads the coating material onto the surface of the film transfer roll 11, 12. The coating film is smoothed out and the excess scraped off by the scraping element 15 15, 16, which is loaded against the surface of the roll 11, 12. The amount of coating material leaving the application area with the roll surface is dependent on the loading of the scraper element 15.16, which is controlled by the actuator 25.26.

The dry basis weight of web W is measured before the coating station by the first measuring frame 19 and after the coating station by the second measuring frame 20. Dry * * * vanilla pulp signals G1 and G2 are applied to processor 21 which calculates; the amount of coating applied to the web at the coating station. The · C * output signal of the processor 21: C = total earth amount is compared to the C rate set value CWo supplied through the workstation 22. By comparison, the overflow volume regulator 23 provides actuators 25, 26 with a command signal Sj which determines: the pressure to be applied to the hoses loaded with the scraping elements 15, 16. The actuator • · · i, f t: 25.26 may be, for example, a pressure control valve.

• * «* · 1 • · • ·. ***. Measurement of the coating amount as shown gives information on the total coating quantity, but does not indicate how much coating has been applied to each of the web * ·! *; side. Often, different amounts of coating on the top and bottom of the web are desired. The coating agents applied to different sides of the strip may be different. The properties of the base paper, such as water absorption, are often different across the web. When it is not possible to separately measure the coating amounts, separate adjustment of the load on the scraper elements 15, 16 cannot be made. The coating rate regulator 5 23 controls the total coating quantity, whereby the load control actuator 25, 26 of each scraper element 15, 16 is provided with a similar control signal Si, regardless of which side any deviation from the coating rate setpoint occurs.

Figure 2 shows an improved system according to the invention comprising a coating ratio regulator 24 which monitors and adjusts the coating amounts applied to different sides of the web. The total coating amount is controlled in the same manner as in Figure 1. The processor 21 calculates the total coating amount CW from the dry weight W1, G2 measured from the web W, and compares it to the set value CWo of the coating quantity 15. By comparison, the coating amount regulator 23 produces a control signal Si to control the loading pressures of the scraping elements 15, 16. However, the change in the load pressure is not evenly distributed on each of the scraping elements 15, 16, but is distributed by the coating ratio control 24 as determined by: * · *:.

: T: 20 The coating ratio controller 24 receives information from processor 21 about the total coating quantity and the coating material consumption M 1, M 2 from the machine cycle 17, 18 of each applicator 13, 14. Based on these, the coating ratio regulator 24 lowers ap-25 on the lower and upper surface of the web with respect to the amount of coating applied. This ratio is compared to the setpoint RWo assigned to it through the workstation 22 • * · M. *. In the event of a deviation, the coating ratio regulator 24 provides the actuator 25, 26 with the same, but different, control signals +, S2 and -S2 for the load-controlling actuator elements 15, 16; .t ,: to correct the joint The end result is that the loading dimensions of the scrapers 15, 16 ··· 30 are changed in the same amount, but in different directions, so that the ratio of coating quantities: * ·. · As the tea changes, the total amount of coating remains constant.

• · 118304 δ

Many modifications of the invention are possible within the scope of the appended claims. The method can be applied not only in duplex but also in double coating, in which two coating layers are applied successively to the same side of the web without measuring the amount of coating in between. The application method may be direct or indirect. The actuator for dispensing the coating material may be a doctor blade or a rotating rod which is loaded against the transfer surface or web by means of compressed air hoses or other loading devices known per se. When applied to non-contact coating (spray coating, curtain coating, etc.), the actuator for dispensing the coating agent 10 may be, for example, a pump or a valve.

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Claims (11)

118304 A method for controlling the amount of coating in a double or double coating of a paper or board web, comprising: 5. applying a coating agent to a first movable substrate (11) by means of a first applicator (13), measuring the total coating amount of the coated web (W) and controlling therewith the actuators (15, 16) for dispensing the coating agent to the first and second movable substrates (11, 12), characterized in that: - measuring the first and second applicator (13, 14). and calculating the ratio of the coating amounts applied to the first and second mobile substrates (11, 12), and - controlling the coating agent dispensing actuators (15, 16) with respect to the coating quantities. • * · '· ll remain constant. 20 *: ··; A method according to claim 1, characterized in that it comprises the steps of: - generating a first command signal based on the total number of coatings ···: Mt! (Si) for controlling actuators (15, 16) for dispensing a coating agent to the first and second movable substrates (11, 25 12), and - when the ratio of the coating amounts differs from the target value, a second hand signal (S2) is generated; ) means: * · \ · the first command signal (Si) is generated so that two new command signals (S1 + S2, S1-S2) are generated whose total effect on the total plating-30 is equal to the effect of the first command signal (Si) ·· ··: would have been alone. • ·, 0 1 1 8304 Method according to claim 1 or 2, characterized in that said first and second movable substrates are first and second film transfer rolls (11, 12), from the surface of which the coating material is transferred to the web (W) in a nip formed by the rolls (11, 12). 5 A method according to claim 1 or 2, characterized in that the movable substrate is a web having a first coating layer applied to the first surface by a first applicator and a second coating layer applied to a second opposed surface by a second applicator. 10 Method according to Claim 1 or 2, characterized in that the movable substrate is a web, the first coating layer of which is applied by means of a first applicator and the second coating layer of which is applied to the same first surface by means of a second applicator. 15 A method according to any one of the preceding claims, characterized in that said actuators (15, 16) for dispensing the coating agent to the movable substrate (11,12) are scraping elements (15,16) which are loaded against the movable substrate (11, 12). after. '·. · 20 • · * • · · A method according to claim 6, characterized in that the scraping elements are scraper blades (15, 16) or rotating scraper bars, which are loaded by M »·. being pressed against a moving platform (11, 12) by means of a pressure medium operating on a pressure medium; ; or other loading devices known per se. ·· ♦ 25 A method according to any one of claims 1 to 5, characterized in that said actuators for dispensing the coating agent to the moving substrate are pumps or valves through which the coating agent is supplied by the applicator device ***. Ic. '·: 30 Ml ···· * · * 1 · • * * • · u 118304 An arrangement for controlling the amount of coating in a double or double coating of a paper or board web, comprising: - a first applicator (13) for applying a coating agent to a first movable base (11); a first applicator (13), - a second applicator (14) for applying a coating agent to the second movable substrate (12), a second actuator (16) for dispensing a coating agent, the actuator (16) cooperating with the second applicator (14), , 20, 21) for determining the total coating amount of the coated web (W), and - a first regulator (23) for controlling the coating material dispensing actuators 15 (15, 16) so as to maintain the total coating amount desired, it further comprises: - a processor (24) which receives (Mj, M2) information on the consumption of the coating material of each appli: · * · sizing device (13, 14) and calculates the first · ·: T: 20 on the second moving platform (11,12) with respect to the applied coatings *: ··: and • * 4: - a second regulator (24) which controls the actuators dispensing the coating agent (15, 16) so that the ratio of the coatings applied is maintained when the total amount of coating remains at the level specified by the first regulator (23). • * * • · · • I * »·· Arrangement according to Claim 9, characterized in that said actuating means for dispensing the coating material are scraping elements (15, 16) which are loaded against the moving substrate (11, 12) after application of the coating material. · * ·· * • · · * ·· * f 118304 12 11. An arrangement according to claim 9, characterized in that said actuators for dispensing the coating agent are pumps or valves which control the supply of the coating agent to the applicator. «· · * It •» • * • t * • * • • • «* • • • * * * ♦ • • • * * ♦ • • • * * ♦ • • • * · »• * · *» »•« «* * • * • * • * e« «« • tl • • • • • • • • • • • • • • •••••• ·· »· 118304 13