Patent Publication Number: US-6214112-B1

Title: Device for direct or indirect single or double sided application of a liquid or viscous coating medium onto a moving surface

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for direct or indirect single or double sided application of a liquid or viscous coating medium onto a moving surface. 
     2. Description of the Related Art 
     An applicator unit of this type, referred to as a roll applicator, is known from German patent document no. 3,605,409. Such an applicator unit is typically categorized as a Long Dwell Time Applicator. 
     The scoop roll of an applicator unit typically applies a relatively large amount of coating medium to the moving surface, which is generally an applicator roll or a material web. The volume of coating medium applied onto the moving surface is proportional to the diameter and circumferential speed of the scoop roll. However, there are limits imposed due to splashing of the coating medium as the circumferential speed of the scoop roll increases. 
     If, due to space constraints or design considerations, a relatively small scoop roll is utilized, the scooping effect is often not sufficient to produce uniform coating on the material web. 
     Therefore, what is needed in the art is an apparatus which utilizes a relatively small scoop roll and yet produces a uniform coating on the moving surface, or material web. 
     SUMMARY OF THE INVENTION 
     The present invention spreads a coating medium evenly and uniformly across the machine width by use of a nozzle applicator device which is installed prior to the scoop roll of the applicator unit relative to the direction of travel of the material web or, equivalently, the rotational direction of the applicator roll. The scoop roll and the nozzle applicator device are assigned or positioned adjacent to the same applicator roll in the case of indirect application, or adjacent to the same backing roll in the case of direct application. In the case of direct application the backing roll is partially wrapped by the material web. This configuration results in a compact arrangement which requires little space. 
     The nozzle applicator device may be configured as an impulse coater which is equipped with a machine-wide metering nip, as described in WO 95/12031. The nozzle applicator device, however, may also be an applicator whereby the coating medium is directly applied onto the moving surface by individual nozzles which are arranged uniformly across the width of the machine. An individual nozzle applicator device of this type is described in the German patent application 197 22 159.9, which is assigned to the assignee of the present invention. In an applicator of the individual nozzle type, the nozzle arrangement is such that the jets of coating medium exiting from the nozzles overlap on the moving surface thereby ensuring complete coverage of the moving surface with the coating medium. 
     The present invention applies only a pre-coating to the moving surface with the nozzle applicator device. The main coating is accomplished by the scoop roll. Any excessively applied medium is subsequently removed with a doctoring device, thereby ensuring a uniform coating application both in the transverse and longitudinal direction of the material web relative to the direction of travel thereof. The uniform coating results from the thin layer of applied pre-coating and relatively low volume main coating application. The pre-coating compensates for, or supplements, the reduced scooping effect at relatively small, for example, 350 mm, scoop roll diameters. 
     This embodiment is particularly suitable for applications where there is already a roll applicator device of this type in the paper machine or the converting machine. In such an instance, the coating machine can easily be retrofitted with the nozzle applicator device, specifically the impulse coating device. In instances where application of coating medium by use of individual nozzles is preferred, the entire coating application is performed with this device. Sufficient coverage of the material web is accomplished by the overlapping areas of the individual nozzle jets. 
     Where there are already roll applicator units in the paper or converting machine, the scoop roll is not required to fulfill its actual purpose of scooping and applying the coating medium. In the embodiment having individual applicator nozzles, the scoop roll is utilized for leveling and/or averaging out of the applied coating medium, thereby providing an advantageous method of smoothing the overlapping end sections of the individual jets in the nip between the scoop roll and the moving surface by evenly distributing any applied excess of coating medium. 
     In the embodiment in which the scoop roll is utilized for scooping the main volume of the coating medium, the roll runs in the opposite direction of, and at a lower circumferential speed than, the moving surface or material web. 
     In the embodiment in which the scoop roll is used for spreading out or evenly distributing the layer of coating medium which was applied with the nozzle applicator device, rather than for scooping, then the scoop roll may run in the same direction as the moving surface or material web. When the scoop roll is used for spreading out or leveling the applied coating medium, it may or may not be driven. On new coating lines, a metering rod, particularly one having a large diameter and smooth surface, may be used for leveling the applied layer of coating medium rather than the scoop roll. 
    
    
     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 embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic side view of an applicator device for the direct application of a liquid or viscid coating medium onto a moving surface of the present invention; and 
     FIG. 2 is a schematic side view of a second, third, and fourth embodiment of an applicator of the present invention. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are 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, there is shown one embodiment of an applicator unit  20  of the present invention. 
     Applicator unit  20  includes scoop roll  1  rotating in a sump  2  of coating medium M. Sump  2  is in a trough (not shown) with a collecting pan  3 . Scoop roll  1 , as a moving surface, is assigned or positioned adjacent to backing roll  4 , which is wrapped by paper web B. Scoop roll  1  and backing roll  4  have opposite rotational directions relative to each other and form a nip N in which coating medium M is deposited directly onto paper web B. That is, scoop roll  1  is shown rotating in a counterclockwise direction, and backing roll  4  is shown rotating clockwise. Applicator device  6  is positioned adjacent to and a slight predetermined distance from backing roll  4 , prior to scoop roll  1  relative to the direction of travel W of material web B. Coating medium supply pipe  7  is equipped with a multitude of individual nozzles  8 , arranged along the length of coating medium supply pipe  7 . A pre-coating is applied to material web B with nozzles  8 . The main volume of the coating is then applied by scoop roll  1 . 
     Applicator device  6  can be configured to apply the entire volume of coating medium M. In this embodiment, no coating medium M is supplied to scoop roll  1 . Instead, scoop roll  1  functions to level the layer of coating medium M which was applied to material web B by applicator device  6 . In doing so, scoop roll  1  can be configured to rotate in the same direction as backing roll  4 , thereby achieving a better spreading effect (see broken line arrow indicating clockwise rotation of scoop roll  1  in FIG.  1 ). 
     Doctoring device  5  is positioned after scoop roll  1  relative to the direction of travel of material web B. Doctoring device  5  can be configured as a doctor blade, a metering rod or a stationary doctor bar. In the embodiment shown, doctoring device  5  is configured as a doctor blade which removes excess applied coating medium M from paper web B. The excess coating medium M is collected in a trough (not shown) and is recirculated to the coating process. 
     Referring now to FIG. 2, a second embodiment of an applicator unit  30  of the present invention for the application of a liquid or viscid coating medium onto a moving surface is presented. In this embodiment, coating medium M is indirectly applied to both sides  24  and  26  of material web B. Applicator rolls  10  and  10 ′ form nip N through which material web B travels. Coating medium M is transferred from applicator rolls  10  and  10 ′ to material web B in nip N. Scoop rolls  1  and  1 ′ with a corresponding one of collecting pans  3  and  3 ′ are respectively assigned or positioned adjacent to a respective one of applicator rolls  10  and  10 ′. Nozzle applicator devices  6  and  6 ′ are located prior to a respective one of scoop rolls  1  and  1 ′ relative to the rotational direction of their respective applicator rolls  10  and  10 ′, and at a small predetermined distance from their respective scoop rolls  1  and  1 ′. 
     In another embodiment, illustrated by showing nozzle applicator device  6  in broken lines on the lower-left side of FIG. 2 adjacent to scoop roll  1 , achieves single-sided application of a liquid or viscid coating medium onto moving material web B. In this embodiment, nozzle applicator device  6 , instead of being positioned adjacent to applicator roll  10 , is alternatively configured to be assigned or positioned adjacent to scoop roll  1 . In this position, nozzle applicator  6  pre-coats outer surface  14  of scoop roll  1 . Outer surface  14  of scoop roll  1  transfers coating medium M to outer surface  11  of applicator roll  10  which, in turn, transfers coating medium M onto moving material web B. This same structure described above when duplicated on the right side of applicator unit  30 , i.e. associated with each of scoop roll  1  and scoop roll  1 ′, achieves double-sided coating of material web B. 
     Yet another embodiment is illustrated on the right side of FIG. 2, in the area of scoop roll  1 ′, in broken lines. This embodiment achieves single-sided application of a liquid or viscid coating medium onto moving material web B. This embodiment includes continuous belt  12  traveling around scoop roll  1 ′ and around guide rolls  15 . In this configuration, scoop roll  1 ′ acts as a support roll, that is, it does not apply any coating medium M. Nozzle device  6 ″, of the same design as  6  or  6 ′, sprays or emits coating medium M, additionally or alone, onto continuous belt  12 . Continuous belt  12  transfers coating medium M onto applicator roll  10 ′ which, in turn, transfers coating medium M onto side  26  of material web B. If material web B is to be coated on both sides, the structure recited above is associated with each of scoop rolls  1  and  1 ′. If single sided coating is desired in a configuration in which the recited structure is associated with each of scoop roll  1  and scoop roll  1 ′, just one side of applicator unit  30  is selectively operated to place coating medium M onto continuous belt  12  or its counterpart associated with scoop roll  1 , i.e. on the left side of applicator unit  30 . 
     FIG. 2 illustrates a material web B moving upward away from applicator roll  10  and  10 ′ relative to scoop rolls  1  and  1 ′. It is to be understood that a different path for material web B may be selected with appropriately adjusted rotational direction for applicator rolls  10  and  10 ′ and scoop rolls  1  and  1 ′. This illustrated arrangement is only one example and is not intended to restrict the scope of protection of the present invention. 
     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.