Abstract:
An apparatus for one of direct and indirect application of a coating medium onto a traveling fiber material web includes at least one doctor element for application and/or metering of the coating medium. At least one doctor element is formed of a carbon fiber material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention. 
     The present invention relates to doctor blades, and, more particularly, to a doctor blade for leveling and/or metering a layer of liquid or viscous coating medium. 
     2. Description of the Related Art. 
     A doctor blade is used to level and/or meter coating medium onto a moving background. With direct application of the coating medium, a moving background is a material web, such as a paper or cardboard web. With indirect application, a moving background is the surface of a transfer element which transfers the coating medium onto the material web. 
     It is known for a doctor blade to be formed of materials such as high carbon spring steel, beryllium copper, stainless steel or fiberglass. A problem is that these materials have generally poor wear characteristics. 
     What is needed in the art is a doctor blade that has higher strength and better wear characteristics. 
     SUMMARY OF THE INVENTION 
     The present invention provides a doctor blade formed of a high strength composite material, such as carbon fiber. Also provided are various arrangements for positioning such a doctor blade relative to the moving background. 
     The invention comprises, in one form thereof, an apparatus for one of direct and indirect application of a coating medium onto a traveling fiber material web. At least one doctor element applies and/or meters the coating medium, and is formed of a carbon fiber material. 
     An advantage of the present invention is that, because of the higher strength and wear characteristics of the carbon fiber material, the doctor blade has a longer useful life. 
     Another advantage is that the doctor blade has better lubricity because of the carbon material. 
     Yet another advantage is that the position of the doctor blade relative to the moving background can be closely controlled. 
    
    
     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 fragmentary, side view of one embodiment of the apparatus of the present invention; 
     FIG. 2 is a fragmentary, side view of another embodiment of the apparatus of the present invention; 
     FIG. 3 is a fragmentary, side view of yet another embodiment of the apparatus of the present invention; and 
     FIG. 4 is a fragmentary, side view of a further embodiment of the apparatus 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 more particularly to FIG. 1, there is shown one embodiment of a doctor blade apparatus  10  of the present invention, which generally includes a doctor blade  12 , a doctor holder  14 , a first air hose  16  and a second air hose  18 . Doctor blade apparatus  10  operates to level and/or meter coating medium on a surface  20  of roll  22 . 
     Doctor blade  12  is formed of a carbon fiber material, providing doctor blade  12  with high levels of strength and durability. Doctor blade  12  includes a body portion  24  and a T-shaped projection  26  extending therefrom. Body portion  24  includes a chamfered first end  28  for engaging the coating medium on surface  20 . An opposite end  30  of body portion  24  is clamped in a fixed position in doctor holder  14 . Projection  26  includes a base  32  and head portion  34  oriented perpendicular to base  32 . 
     Doctor holder  14  includes a base  36  and an extending arm  38  having respective clamping devices  40  and  42  for securely holding end  30  of doctor blade  12 . Base  36  includes a cavity  44  having a through slot  46  opening into a wider chamber  48 . Chamber  48  retains each of air hoses  16 ,  18  and head  34  of projection  26  therein. 
     During operation, end  28  of doctor blade  12  can be moved away from or toward surface  20  by adjusting the relative air pressures in hoses  16  and  18 . For example, if the pressure within hose  16  is increased relative to the air pressure in hose  18 , hose  16  exerts a force on head  34 , thereby moving projection  26  away from wall  50  of chamber  48 . Movement of projection  26  away from wall  50  tends to cause a rotation of doctor blade  12  about its end  30 , clockwise in FIG. 1, such that end  28  is moved toward surface  20  of roll  22 . A gap  52  is shown between end  28  and surface  20 . Increasing the air pressure in air hose  16  reduces gap  52  and may cause end  28  to come into contact with surface  20  and/or the coating medium that is carried in direction  54  on surface  20 . 
     Conversely, increasing the air pressure in hose  18  relative to the air pressure in hose  16  exerts a force on projection  26  that moves projection  26  away from wall  56  of chamber  48 . Such movement of projection  26  causes end  28  to move away from surface  20  to thereby increase or create gap  52 . Thus, by adjusting the air pressure in hoses  16  and  18 , the size of gap  52 , or the force exerted by end  28  on surface  20 , can be tightly controlled. 
     In an alternative embodiment (not shown), air hose  16  or air hose  18  is replaced by a spring, such as a coil spring. Thus, the spring and the air hose exert opposite forces on projection  26  to establish an equilibrium position of end  28 . By adjusting the air pressure within the air hose, the position of end  28  can be closely controlled. 
     In another embodiment (FIG.  2 ), a doctor holder  58  includes a slot  60  for retaining an air hose  62  which actuates an end  64  of carbon fiber doctor blade  66 . Doctor blade  66  includes a pivot point in the form of a recess  68  for receiving a projection  70  of doctor holder  58 . Projection  70  extends parallel to doctor blade  66  and includes, at its distal end, a ball  72  with a circular cross section. Ball  72  and recess  68  form a ball-and-socket type of joint which allows doctor blade  66  to rotate in the plane of the page, as indicated by double arrow  74 . 
     In operation, increasing the air pressure within air hose  62  causes hose  62  to inflate and thereby push end  64  away from doctor holder  58 . As doctor blade  66  rotates about recess  68 , end  76  of doctor blade  66  is moved toward surface  20  of roll  22 , as described above with respect to FIG.  1 . Conversely, deflation of air hose  62  allows end  76  to move further away from surface  20 . 
     In a third embodiment (FIG.  3 ), a carbon fiber doctor blade  78  includes a projection  80  having a ball  82  at the distal end thereof. Doctor holder  84  includes a recess  86  for receiving ball  82 . Together, ball  82  and recess  86  form a ball-and-socket type joint for allowing pivoting of doctor blade  78  in the directions indicated by double arrow  88 . 
     Doctor blade  78  is symmetrical about a imaginary line  90  that bisects doctor blade  78  through projection  80 . End  92  of doctor blade  78  is also chamfered and is identical to end  94 . Thus, once end  94  has become worn down from use to the point where it no longer operates effectively, doctor blade  78  can be reversed such that the unworn end  92  is repositioned adjacent to surface  20 , and the worn end  94  is repositioned such that it can be actuated by hose  62 . More particularly, ball  82  can be removed from recess  86  such that doctor blade  78  is disengaged from doctor holder  84 . Doctor blade  78  can then be turned 180 degrees and reattached to doctor holder  84  by inserting projection  80  into recess  86 . 
     In use, similarly to the embodiment of FIG. 2, inflation of air hose  62  results in end  94  being moved toward or biased against surface  20  of roll  22 . Conversely, deflation of hose  62  results in a decrease in pressure on end  92 , thereby allowing end  94  to rotate away from surface  20 . 
     In a fourth embodiment (FIG.  4 ), doctor holder  96  includes a projection in the form of a T-shaped post  98  with a base  100  and a dovetailed head  102 . Carbon fiber doctor blade  104  includes a pivot point in the form of a recess  106  having a throughslot  108  leading into a relatively wider chamber  110 . 
     In operation, the dovetailed configuration of head  102  allows doctor blade  104  to pivot about post  98  as air hose  62  actuates end  112  of doctor blade  104 . Similarly to the embodiments of FIGS. 2 and 3, inflation of air hose  62  results in end  114  of doctor blade  104  being moved toward or being biased against surface  20  of roll  22 . Deflation of air hose  62  allows end  114  to rotate away from surface  20  in the direction of arrow  116 . 
     In the embodiments shown herein, the doctor blades include a projection or a recess on the same side of the doctor blade that is actuated by an air hose. However, it is to be understood that the doctor blade can also have a projection or a recess on a side of the doctor blade that is opposite from the side of the doctor blade that is actuated by an air hose. 
     It is also possible for the doctor blades of FIGS. 1 and 4 to have identically chamfered opposite ends that allow the doctor blade to be reversed, similarly to the doctor blade of FIG.  3 . 
     The actuators may be in a form other than an air hose. For example, the actuators may be in the form of an electromagnetically actuated ram. 
     Backing roll  22  has been shown as rotating clockwise in FIGS. 1-4. However, it is also possible for roll  22  to rotate counterclockwise in each of the embodiments. In this case, the doctor blade would function to clean roll  22  or to remove a sheet from surface  20  of roll  22 . 
     The doctor blade has been shown in FIGS. 1-4 as being in a linear, unloaded state. However, it is to be understood that the doctor blade can be deflected if the doctor blade is loaded against roll  22 , for instance. 
     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.