Abstract:
An apparatus for direct or indirect application of liquid or pasty coating medium onto a traveling material web, notably of paper or cardboard, includes a paint curtain applicator mechanism and at least one sensor unit to register the flow quantity of the coating medium layer applied onto the material web and to provide a corresponding flow quantity signal. At least one regulation device regulates at least one manipulated variable of the paint curtain applicator mechanism upon which the flow quantity of the coating medium layer applied onto the material web depends. A control unit, which receives the flow quantity signal provided by the at least one sensor device, determines at least one face value for the at least one manipulated variable and controls the at least one regulation device on the basis of the at least one manipulated variable-face value.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an apparatus in which liquid or pasty coating medium is applied directly or indirectly onto a traveling material web, especially of paper or cardboard. 
     2. Description of the Related Art 
     The application of liquid or pasty coating medium by use of a paint curtain or paint veil, the so-called “curtain coating” itself, is already known. U.S. Pat. No. 5,624,715, for example, shows a paint curtain applicator mechanism for the direct coating of a material web. To put it more precisely, U.S. Pat. No. 5,624,715 deals with the impairment/disturbance problem of the coating medium-veil&#39;s even distribution onto the material web caused by the carried-on air of the traveling material web. Furthermore, from the German patent document no. EP 0 517 223 B1, an apparatus is known with the help of which air bubbles are to be removed from the coating medium in the run-up of the application process so that the bubbles cannot influence the regularity/evenness of the application. 
     A further problem, which arises during “curtain coating,” and with which the above mentioned printing does not deal, is the dosage of the coating medium. Usually, the coating medium applied by use of curtain coating is not metered out by a subsequent doctor device, so high demands are made on the measured emission/discharge of the coating medium from the paint curtain applicator mechanism. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for direct or indirect application of liquid or pasty coating medium onto a traveling material web, especially of paper or cardboard. Besides a paint curtain applicator mechanism, this apparatus includes at least one sensor equipment to register the flow quantity of the applied coating medium layer and to prepare a corresponding flow-quantity signal. Additionally, it includes at least one regulator device to change at least one manipulated variable of the paint curtain applicator mechanism, of which the flow quantity of the applied coating-medium-layer onto the material web depends. Finally, it includes a regulation unit which receives the prepared flow-quantity signal from at least one sensor device, which, dependent on this flow quantity signal, determines at least one face value for the at least one manipulated variable. The sensor transmits the at least one manipulated variable-face value to the at least one regulator device. 
     Through the inventional planned flow quantity regulation, the coating medium can be emitted well-dispensed from the paint curtain applicator mechanism so that the desired even layer application onto the material web results. Furthermore, inventional planned flow quantity regulation is constructed in a simple way, because it does not monitor each of the application result influencing parameters separately, nor does it maintain them at a preset face values. Rather, dependent on the registration of the flow quantity, it regulates the per unit time dispensed quantity of the coating medium. The paint curtain applicator mechanism can, for example, include a distribution arrangement which evenly distributes the coating medium in cross direction of the material web. The distribution arrangement, for this purpose, includes a distribution channel, a supply opening/feed opening for introducing the coating medium into the distribution channel, at least one outflow/exit slot for evenly depositing the coating medium in the form of a coating-medium-curtain or veil, as well as, if desired, a depositing opening to divert superfluous coating medium which has been introduced into the distribution channel. 
     In order to be able to ensure the application&#39;s evenness not only in lengthwise direction of the material web, but also in its cross direction, it is suggested to influence the coating medium quantity, which is emitted per unit time from the paint curtain applicator mechanism by several successive application sections installed in cross direction of the material web and which are independent from each other. This can, for example, be carried out by ensuring that the regulator device includes some regulator units which are arranged in cross direction of the material web in order to adjust, section by section, the width of the least one outflow exit slot of the paint curtain applicator mechanism. 
     In a majority of cases, however, it will suffice to adjust the overall coating medium quantity which has been emitted from the paint curtain applicator apparatus per unit time to a desired value. For this purpose, the regulator device can include, for example, a device to adjust the output conveying capacity of the coating-medium-pump, which has been assigned to the paint curtain applicator apparatus. Additionally or alternatively, the regulator device can include a valve arrangement to influence the quantity of the coating medium which is introduced per unit time through the supply opening feed opening into the distribution channel. Again, additionally or alternatively, the regulator device can include a regulator unit to adjust the width of the at least one exit slot of the paint curtain applicator apparatus. Furthermore, it is possible for the regulator device to include a valve arrangement to influence the exit opening redischarged fraction of the coating medium which is introduced into the distribution channel via the feed supply opening. 
     The flow-quantity-sensor-equipment can be developed for the direct or indirect registration of the flow quantity of the coating medium layer applied onto the material web. 
     For a direct registration, the flow quantity sensor equipment can display a first sensor unit which is arranged in running course direction of the material web in front of the paint curtain applicator apparatus, and it can provide a first sensor signal. Furthermore, it can display a second sensor unit, which is arranged in running direction of the material web behind the paint curtain applicator apparatus and provides a second sensor signal. Finally, it can display a difference formation unit which deducts the first sensor signal from the second one and provides the difference signal as the flow quantity signal. 
     Through this process, the first sensor unit measures the characteristics properties of the material web in its rough state natural condition, i.e., before the herein discussed coating process, which, however, does not exclude that the material web has been coated already once or several times. The second sensor unit measures the achieved final condition so that the coating is reflected as such in the difference of the two measured signals. The running time of the material web between the first sensor unit and the second sensor unit can be taken into consideration through the formation of the difference signal. In principle, however, it is also possible to assume that the signals produced by the two sensor units are quasi stationary signals which change only slowly, so that the running time does not have to be considered. 
     The flow quantity can be determined, for example by an optical measuring procedure, during which the luminous reflectance or the coefficient of transmission of the material web can be measured. But there are also known radioactive measuring procedures, during which the radiation extinction of a radioactive source, usually a radiation source, of known intensity is determined through the material web. The latter measuring method can be calibrated from time to time by putting the radiation source next to the material web or by determining the intensity of the not evaporated radioactive sources. All the above mentioned measuring procedures are suitable for determining the flow quantity, independent from its locale in cross direction of the material web. For this purpose, for example, a measuring head along a guide running in cross direction of the material web can be moved back and forth. 
     An indirect flow quantity registration can be effected, for example, by use of a flow quantity sensor device, which includes a first sensor unit assigned to the feed opening of the distribution device (i.e., a sensor unit which, if desired, is arranged to be located possibly a larger distance away from the distribution device but stands in sensor connection with the distribution device). A second sensor unit is assigned to the exit opening of the distribution device and a difference formation unit deducts the sensor signals provided by the sensor unit from each other and provides the difference signal as the flow quantity signal. The first sensor unit and the second sensor unit can also be arranged in pipes, cables or carriers which lead at the feed or exit opening into the distribution channel. However, they can also be furnished directly at the feed or exit opening. 
     At the above discussed indirect flow quantity measurements, the first and second sensor units can each include a volume flow meter device. But it is also possible for the first and second sensor units to each include a mass flow meter device. For further improvement of the flow quantity registrations precision, it is suggested that the inventional applicator apparatus include a sensor device to register the operation speed of the material web or a sensor device to register the solid substance content of the coating medium, that is to say, of the coated material web width. In addition to this, a drying device can be provided in running direction of the material web after the paint curtain applicator apparatus for direct flow quantity registration. This drying device is preferably arranged in front of the second sensor unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a rough, schematic view of the inventional paint curtain applicator apparatus; and 
     FIG. 2 is a sectional view along the line II—II of the color-curtain-applicator apparatus according to FIG.  1 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and particularly to FIG. 1, an inventional applicator apparatus is generally labeled with  10 . It includes an applicator mechanism  12 , which applies liquid or pasty coating medium  14  in the form of a paint-curtain or paint-veil  16  onto a material web  18 , which is running in direction of the arrow L. In this description demonstration, the material web  18  is, within the area of the applicator mechanism  12 , guided around a supporting roll  20  rotating in direction of arrow P. However, there are also other suitable guideways possible. 
     As demonstrated in FIG. 2, the applicator mechanism  12  includes a distribution arrangement  22  with a distribution channel  24 , which is supplied with the coating medium  14  from the coating medium supply  30  via a feed supply opening  26  and a feed pump  28 . The majority of the coating medium, which is introduced into the distribution channel  24  via the feed opening  26 , is emitted from this distribution channel  24  again via an exit discharge opening  32 . Only a small proportion of coating medium  14  is supplied to an exit gap  36  via an exit channel  34 , and there it is delivered in the form of a paint veil  16 . In this way, it is insured that the application/coating medium is moving in the distribution channel  24  with such a high flow velocity that a depositing of the solid substances contained in the coating medium  14  is reliably avoided. 
     In order to define the width of the exit gap  36 , several arranged sliding elements  38  are designated, which are distributed in cross direction Q of the material web  18 , and they can be adjusted by actuators  40  (in the direction of double arrow A in FIG.  1 ). The sliding elements  38  make possible a section-wise adjustment of the width of the exit gap  36  and, consequently, facilitate profiling the line  14   a , which is applied onto the material web  18  in cross direction Q of the material web  18 . 
     The actuators  40  are approached by a control unit  42 , which determines the set rated values for the actuators  40  on basis of various sensor signals, which are chosen in such a way that they give information about the flow quantity of the layer applied onto the material web  18 . Thus, according to FIG. 1, a first measuring frame  44  can be arranged in running direction L of the material web  18  in front of the application apparatus  12  to measure the properties/characteristics of the uncoated material web  18 . A second measuring frame  46 , identical with the first measuring frame  44  in set-up and function, can be designated after applicator mechanism  12  in running direction L. Each of the measuring frames  44  and  46  includes a measuring head (not shown), which can be moved back and forth alongside a guide (not shown) in cross direction Q of the material web  18 . The way of measurement of the measuring heads measuring frames  44 ,  46  can be based upon, for example, an optical measurement of the coefficient of absorption or the coefficient of transmission of the material web  18 . It is also possible, however, to determine the extinction capability of the material web  18  for radioactive energy, preferably beta radiation. 
     The first and second measuring frames  44  and  46  prepare flow quantity signals G 1  and G 2 , which are supplied to a differential formation link or comparator  48  via signal carriers  44   a  and  46   a . The differential formation link  48  deducts the flow quantity signal G 1  of the first measuring frame  44  from the flow quantity signal G 2  of the second measuring frame  42  in order to provide a differential signal Δ G , which indicates the flow quantity properties of the applied coating layer  14   a  onto the material web  18 . The above-mentioned differential signal Δ G  is supplied to the control unit  42  via a signal carrier  48   a . The control unit  42  determines from this differential signal Δ G  and, if desired, on the basis of registration signals of more sensors, adjustment signals S 1  which are transmitted to actuators  40  via signal carriers  42   a.    
     There is no limit to the number of further sensor signals which can be utilized in addition to the flow quantity signals G 1  and G 2  of the two measuring frames  44  and  46  or Δ G  the differential link  48  by the control unit  42  to determine the adjustment signals S 1  for the actuators  40 . As examples, only two of such sensor signals are listed: namely first, the speed signal V of a velocity sensor  50 , which, for example, derives the traveling running speed of the material web  18  from the number of revolutions of the paper cylinder  20 , and, secondly, the signal F of a coating medium sensor  52 , which gives information about the composition and especially the solid substance coating medium  14  in the coating medium supply  30 . These two registration signals V and F are supplied to the control unit  42  via signal carriers  50   a  or  52   a.    
     The regulation device built by the sliding elements  38  and the affiliated actuators  40  can principally handle by itself the dosage of the discharged coating medium  14  disposed onto the material web  18 . Additionally or alternatively, however, the coating medium can also be dispensed via further regulation devices. For example, the conveying capacity output of the delivery pump  28  can be varied in that the control unit  42  issues via signal carrier  42   b  a corresponding relevant regulation signal S 2  to a drive unit  54  of the pump  28 . An additional or alternative method of exerting influence is to transmit regulation signal S 3  to regulation unit  56  of a valve device  58  via a signal carrier  42   c . In the performance examples according to FIG. 2, the valve device  58  is developed as sliding valve and is arranged to an eduction/deposit pipe, which follows the eduction deposit opening  32  of the distribution channel  24 . By use of the sliding valve  58 , the fraction of the coating medium  14  that is emitted through the outlet gap  36  in the form of the paint curtain  16  to the material web  18 , and that is introduced into the distribution channel  24  via the supply opening  26 , can be varied. 
     Besides the above described, direct flow quantity measurement by use of the measuring frames  44  and  46 , the flow quantity of the applied layer  14   a  onto the material web  18  can also be determined indirectly, for example by use of two current meters  62  and  64 . One current meter  62  is connected to a supply pipe  66  which leads to a supply opening. The other current meter  64 , is attached to the eduction pipe  60 . The current meters can be, for example, volume flow metering measuring devices  62  and  64 . But it is also possible for them to be mass current or mass flow metering devices  62  and  64 . The registration signals G 1 ′ and G 2 ′ of the current meter  62  and  64  or  62 ′ and  64 ′ are forwarded via signal carriers  62   a  and  64   a  to a differential formation link or comparator  68 , which deducts the signal G 2 ′ of the depositing discharging flow meter  64  from the registration signal G 1 ′ of the supplying flow meter  62 . Comparator  68  supplies a differential signal Δ G ′, which provides information about the coating medium emitted through the outlet gap  36  onto the material web  18 . This differential signal Δ G ′ is transmitted via a signal carrier  68   a  to the control unit  42 . Control unit  42  may determine from this the flow quantity of the coating layer  14   a  by consulting further sensor signals, for example via the running traveling speed of the material web  18  or the solid substance content of the coating medium. 
     It is certainly possible to provide in just one paint curtain coating apparatus  10  both the measuring frames  44  and  46  and the volume current or mass flow meters  62  and  64  in any combination to increase the accuracy of the flow quantity registration by comparing the various flow quantity signals. Furthermore, it is possible to carry out a predosage of the quantity of the coating medium  14 , which is emitted onto the material web  18 , and to carefully control the amount of this coating medium by use of the sliding devices  38  and the actuators  40 . This pre-dosaging can be accomplished by varying the output capacity of the supply pump  28  or the emission deposit cross section profile by influencing the valve device  58 . 
     Between the coating mechanism  12  and the second measuring frame  46 , a drying device  70  of known construction can be designated. With the help of this drying device  70 , measuring errors, which could be caused, for example, by a still existing humidity in the coating layer, can be decreased or preferably totally avoided. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.