Abstract:
A doctor apparatus is disclosed and includes a doctor roll ( 12 ) supported in a coater ( 1 ) suitable for applying coating to a paper web surface or a roll surface ( 4 ) for subsequent transfer to the paper web. The doctor includes a doctor roll ( 12 ), a support ( 11 ) for the doctor roll ( 12 ), a front support ( 3 ) for holding the roll support ( 11 ) and a rear support or retainer ( 18 ) cooperates with and helps stabilize the support ( 11 ) and doctor roll ( 12 ). The present invention minimizes the variation moving of the doctor roll ( 12 ) has on the coating on the moving surface ( 4 ), be it web or roll, and thus can improve coating quality.

Description:
[0001]    This application is a divisional application of U.S. application Ser. No. 10/537,241, filed Nov. 22, 2006 which was the National Stage application of No. PCT/US03/038695, filed on Dec. 5, 2003 which in turn was a continuation-in-part of U.S. Provisional Patent Application Ser. No. 60/431,270, filed Dec. 6, 2002, of the same title and by the same inventor on which a claim of priority and benefit of filing date is made. This invention relates to a type of doctor for a coating apparatus for coating a traveling web material, such as paper, or for coating the surface of a roll and then transferring said coating to a traveling web in a pressure nip form by another roll, blade or other pressure applying device. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    It is known to use a doctor roll in a coater such as a short dwell time applicator (“SDTA”) or a film coater as shown in U.S. Pat. Nos. 4,250,211 and 5,749,972, these patents being incorporated herein by reference, in conjunction with a backing roll to meter coating applied to a moving paper web or first to a roll surface and then onto a moving web of paper. These doctor rolls are difficult to locate or hold in a coater as space is restricted. Heretofore, when the doctor roll was loaded into the web or roll surface being coated, the doctor roll was moved toward or away from the web or roll surface to increase or decrease the loading, respectively. Generally, the doctor roll also tended to move downstream in the direction of the web or roll surface travel. This latter movement was somewhat inconsistent, and consequently variation and/or inconsistency in the coating lay and metering by the doctor roll could occur. 
       SUMMARY OF THE INVENTION 
       [0003]    The disadvantages of the prior art are overcome by the apparatus of the present invention which provides a method and means for supporting the doctor roll to minimize any movement or travel of the doctor roll in a direction of that of the moving surface of the web or roll and minimizes the inconsistency of coating applied to the surface of the web or roll. To accomplish this, the roll is supported in a roll carrier or support which is permitted to move or generally pivot on a support rod, generally being used as the motion may be somewhat greater than a true pivot connection. The support rod itself may form and close off part of the coater application chamber. To support the doctor roll, a rear or downstream (relative to the direction of web or roll surface movement or travel) support for the doctor roll is provided. To accommodate movement of the roll due to loading by a conventional means (such as a load tube), relative contact surfaces between the roll carrier and roll rear support may be curved or radiused to permit the roll carrier or support and roll therein to move, slide or pivot more freely. Preferably, the rear roll support can be in the form of a releasable element or blade, while the curved or radiused surface may be formed on the rear of the roll carrier or support. Thus, the pivoting of the roll support and moving along the radius provides a more consistent environment for the doctor roll, and therefore lay of coating and/or doctoring of coating on the moving web or roll surface, and consequently more consistently coated paper web. 
     
    
     
       DESCRIPTION OF THE DRAWING 
         [0004]      FIG. 1  is a schematic, full scale as filed, cross sectional elevational view of a doctor assembly of the present invention. 
           [0005]      FIG. 2  is a full scale as filed, view similar to  FIG. 1  but of a second embodiment. 
           [0006]      FIG. 3  is a partial view similar to  FIGS. 1 and 2 , but showing a roll carrier or support for a solid doctor roll. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0007]    Referring to  FIG. 1 , the coater device is given reference numeral  1 . Also part of the coater is body  2  which forms part of the coating chamber  3  and also forms one wall of the coating inlet  3 A. The movable wall of the coating chamber as well as the outer wall of the coating chamber is formed by members  4  and  5 . Member  5  can be designed to include a clamp tube (not shown but similar to  14  described below) to secure the orifice plate member  6 . 
         [0008]    An internal coating inlet seal  7  seals the ends of the coating inlet outside of the web run and under the edge dams  8  and  9 . There is a metal support for the felt edge dam  9 . This assembly seals the ends of the applicator between the orifice plate  7 , roll  10  and doctor assembly  11 . The edge dam assembly can be adjusted laterally on the dovetail or groove  7 A on seal  7 . 
         [0009]    The doctor assembly  11 A comprises the carrier, bed or support  11  for the doctor roll or bar  12 . The bed or carrier  11  is made of UHMW polyethylene or similar material. 
         [0010]    The doctor roll or device  12  can be a solid bar ( FIG. 3 ) or a hollow tube ( FIG. 1  or  2 ), with or without grooves on its outer surface. If solid, the doctor device is consequently generally of a smaller diameter than a hollow rod type doctor roll. Either type of doctor roll may be driven to rotate in a direction, usually, opposite the direction of the moving surface travel, be it a web or roll surface. The doctor&#39;s diameter can range from ⅜″ to 1½″. If a hollow tube is used for the doctor device  12 , it can be of sweated construction with cold water flowing through its center. A curved bar  13  supports the front of the support  11 . The curved bar  13  is clamped to the main coater by an air pressurized clamp tube  14 . The upper surface of the curved bar  13 , as shown in  FIG. 1 , forms a side of the application zone and seals against the edge dam assembly. Reliefs or cutouts  15  are provided in the support  11  for the doctor bar  12 . These reliefs allow the bar  12  to rotate more easily. Lateral grooves  16  with the pipe taps or other type connections are provided in either end of the support bed  11 . Water is provided to these connections and circulated through these grooves or channels  16  to clean and lubricate the doctor bar or roll  12 . A convex radius  17  is provided on the support or bed  11  swung from a pivot point (pivot axis)  17 A on its wall. A support plate  18  supports the rear of the support bed  11  of the doctor assembly so that it is contained and not allowed to be moved by the friction against the travel of the web or surface being doctored. Alternatively, the support plate could be provided with a concave contact surface of the support. 
         [0011]    When the doctor roll is driven (as indicated by the small arrow  18 A) in a direction opposite backing roll rotation (as indicated by the large arrow  18 B), it has a tendency to lift the roll up at the rear when not in contact with the backing roll. In order to counteract this tendency, associated means both on the doctor roll support  11  and the rear support plate  18  can be provided. For example, the rear support plate or retainer  18  may have an upper hooked end  118  which engages in a retaining groove  118 B in the doctor support  11  (see  FIGS. 2 and 3 ). This arrangement acts as a baffle to prevent coating from egressing towards the loading tube  119 . A doctor load tube  19  (somewhat similar to tube  14  in construction) is provided. It is pressurized with air or other fluid to increase the force of the doctor device against the traveling surface or web being doctored. A flexible profile bar  20  supports the load tube  19 . This bar can be profiled (adjusted in its cross machine direction) to give the desired doctor force by adjusting the differential screws thread profile screws  21 . There is a plurality of the screws  21  spaced 3 to 4 inches apart laterally across the coater assembly. The doctor support  11 , on the enlarged shaped  13 A end of the curved bar  13 , allows the doctor assembly to pivot on the extended tip of the curved bar  13  when the loading by the load tube  19  is changed. The pivot point  17 A shown at dovetail groove  23  retains the support  11  to the complementary shaped end or tip  13 A of the curved bar  13 . This connection allows movement and also seals the pivot. It should be understood there are other generally pivot type connection options, such as a rod and socket assembly, or other means that could be used. 
         [0012]      FIG. 2  is similar to  FIG. 1 , except it shows the hooked plate or retainer  118  which can engage with the groove  118 B on the support  11  to limit lift of the doctor. As the coaters shown in  FIGS. 1 and 2  are generally similar except for this difference, similar reference numerals are used in  FIG. 2 , except the number is 100 higher. For example,  4  of  FIG. 1  is shown as  104  in  FIG. 2 . 
         [0013]      FIG. 3  is similar to  FIGS. 1 and 2 , but only shows the solid doctor rod  212  and its support  211 . Note that the doctor rod  212  and its complementary groove receiving the rod are smaller in diameter than for a hollow doctor roll. Again, except for these differences, the rod and support of  FIG. 3  is similar to those of  FIGS. 1 and 2 , and reference numerals are also similar, except given numbers 200 higher, that is,  23  in  FIG. 1  or  123  in  FIG. 2 , becomes  223  in  FIG. 3 . 
         [0014]    It should be understood that the doctor support of the present invention that can be used with any doctor be it generally integral in a coater, such as a short dwell time applicator type, or in a stand alone doctor roll, such as in a dip roll, separate doctor. It should also be understood that the doctor roll could have a plain smooth surface roll or a grooved roll. It should be further understood that the invention could be used when coating a paper or board web either directly or indirectly via a transfer roll. While specific elements and steps have been described, it should be understood that equivalent elements and steps will fall within the scope of the following claims.