Doctor Blade Assembly

Abstract

A doctor blade assembly for paper coaters and gravure rolls and other doctor blade applications includes a cantilever-support blade controlled by a tube-type actuator. The tube has a collapsible wall section adjacent the blade and a blade-engaging extension which bears against the blade between its supported and free end. In one embodiment, a transversely movable profile adjuster or series of profile adjusters are disclosed which selectively apply side forces to the wall section of the tube to permit corresponding selective pressure adjustments on the blade, for the purpose of reducing or eliminating localized coating non-uniformities. A novel blade retention assembly permits the clamping of blades of varying thicknesses and includes one or more transversely positioned magnets for temporarily retaining the blade on the support. An opposing clamp is formed with an elastomeric pad or expandable tube which engages the blade adjacent its inner edge and which forces or urges the blade downwardly against a machined seat to assure proper seating. In a further embodiment, a twin blade coater is disclosed in which the tips of the blades are independently rotatable about a common axis and which utilize a pair of the tube-type actuators connected to a common pressure source.

Description

BACKGROUND OF THE INVENTION

The present invention is directed to the positioning and control of doctor blades such as used with coaters, gravure rolls, or the like.

In coating apparatus, it is important that the doctor blade be precisely positioned and that the force applied to the blade be accurately controllable in order to regulate the amount of material which is doctored by the blade. Most commonly such blades are used to control the weight of coating material which is applied to a moving web of paper.

In the past, it has been found advantageous to support a doctor blade at one end and to apply a controlled force between its supported end and its free end by the direct application thereto of one wall of an elastic tube, to which a fluid pressure is applied. A successful embodiment is shown in the U.S. patent of Coghill U.S. Pat. No. 3,131,092 of 1964, assigned to the same assignee as this invention.

Among the references which were cited by the Examiner, during the prosecution of Coghill, the French Pat. No. 1,202,424 of 1959 (and its corresponding British Pat. No. 863,426 ) may be cited out as showing a typical example of apparatus for applying a blade-controlling force by means of the direct contact of one wall of a flexible elastomeric tube against the back side of the blade between its fixed support and its free end. Somewhat similar arrangements are shown in the U.S. patent of Faber, U.S. Pat. No. 3,026,824 and Krautzberger U.S. Pat. No. 3,722,465 of 1973. The latter additionally employs a thin leaf spring between the tube and the blade to compensate for a stated lack of uniformity of force by reason of irregularities or lack of uniformity in the wall thickness of the force-applying tube.

The above described arrangements, and other like them, in which a tube effectively rests against the back surface of a blade, while generally successful, suffer from the fact that the weight of coating which is applied is often a non-linear function of the air pressure within the tube. One reason for this is that the tube may be operated in an elastic mode rather than in a partially collapsed mode, and therefore the modules of the tube must be considered. Another factor is that inherently the contact region between the tube and the blade changes in location and in area during different operating conditions. For example, once the blade is in contact with the roller or the web, increasing the pressure will necessarily cause the adjacent wall of the tube to flatten, and at the same time, will cause the doctor blade to bend somewhat. Thus, even though the movement of the tube wall may be considered as being a function of air pressure (which it usually is not) the changes in relative contact area and position necessarily result in a non-linear relationship.

One of the Coghill references, namely the U.S. patent of Fuchs U.S. Pat. No. 2,920,557 of 1960, shows an arrangement for doctoring a gravure roller which is intended to provide a more linear relationship between air pressure and blade doctoring effort, and includes, in one embodiment, a tube acting upon a transverse series of individual plungers, the remote ends thereof making the contact with the blade. In another embodiment, the plungers themselves are operated from individual folding cylindrical diaphragms, and in either case the effort was to provide a uniform relation. While this arrangement is theoretically possible, it suffers adversely in the complexity of the parts, requiring the individual plungers. It also suffers from the fact of inherent non-uniformity in the transverse direction due again to the large number of individual plungers positioned in side-by-side relation, and which lack the continuous contact afforded by the direct contacting flexible tube.

Flexible tubes have also been used in blade clamps and have been used in pivot-supported blades as shown in the U.S. patents of Curtis U.S. Pat. No. 2,445,135 of 1948, Allison U.S. Pat. No. 3,085,275 of 1963 and Winterburn U.S. Pat. No. 3,748,686 of 1973.

SUMMARY OF THE INVENTION

In one aspect of this invention, many of the difficulties and deficiencies of the prior cantilever-supported and tube-actuated blades are overcome by the provision of an elongated flexible tube member which is formed with a flexible, collapsible wall section positioned adjacent the blade and which is integrally formed with a blade-engaging extension which engages the blade at a defined location or region. The flexible wall section acts similarly to a rolling diaphragm actuator except that it is transversely uniform throughout the length of the tube and thus presents, in the manner of a diaphragm actuator, a relatively constant area to the application of fluid pressure. Thus, the force exerted by the flexible wall section varies uniformly with air pressure applied to the tube. It is always operated in a partially collapsed state; that is it is never operated to the point where the tube itself becomes elastically expanded.

The integral extension which is formed on the flexible wall thus defines and predetermines the contact region on the blade. Since this remains constant, a fluid pressure operated doctor arrangement is provided in which the weight of coating or the amount of ink doctored on an etched roller, is a direct function of air pressure applied to the tube.

Accordingly this invention lends itself to automatic control, in effect, "closing the loop" of a control system, by applying pressure from a controllable regulated source of fluid pressure. In addition, a further advantage resides in the fact that an increased extent of overall blade movement is provided over that of the prior flexible tube arrangements.

One of the important advantages of the present invention is that the elastomeric linear actuator which is used provides for a relatively long stroke and accordingly provides for an increased wear compensation as compared to the coaters in which one wall of the tube itself is used for blade pressure control. Additionally, the arrangement provides improved sensitivity of blade control at lower air pressures.

A further feature of the invention includes an improved arrangement for making profile adjustments at transverse locations on the machine. A special profile adjuster is disclosed which applies localized side forces to one or both walls of the tube-type adjusters, to cause the material on the adjusters to bear with greater force against the blade, for the purpose of making localized adjustments in the weight of coating, such as for removing heavy streaks of coating.

The coater blades are mounted so that they may be adjusted in angle about an axis which passes substantially through the free end of the blade. This mounting arrangement may be the same as that which has been disclosed for rotating an air knife about the region of impingement in the U.S. patent of Phelps, U.S. Pat. No. 2,981,224 of 1969 assigned to the same assignee as this invention.

A further aspect of the invention provides a twinblade coater in which a pair of blades are positioned at opposite sides of a web with the tips thereof forming a common apex. The tube-type actuators are employed for each blade connected to a common source of air pressure. Additionally, mounting means are provided by which the blades are each adjustable through an axis in common with the apex.

In another aspect of the invention, an improved blade seating and holding arrangement is provided by means of which the doctor blade is temporarily supported in the holder and then is clamped into a predetermined seated relation on a machined surface. The temporary holding means comprises one or more transversely arranged magnets which clamp the metal blade and retain it in approximate position. When a relatively movable holding clamp comes in, a transverse elastomeric pad or tube engages the blade just above the machined ledge and when clamping pressure is applied, as by closing the clamp or inflating the tube a downward component of force is applied to assure that the blade fully seats against its mating surface.

It is accordingly an important object of this invention to provide an apparatus which uniformly controls the force of a doctor blade.

Another important object is the provision of a doctor blade actuator, as outlined above.

A still further object is the provision of a tubeactuator provided with a flexible wall and an extension so that the region of force application to a cantilever-supported blade does not change and so that the applied force is a substantially uniform function of applied fluid pressure.

Another object of the invention is the provision of an improved arrangement for retaining and holding a doctor blade, in which a blade seating force is applied to the blade by the blade clamp and in which blades of differing thicknesses may be accommodated.

A further object is the provision of a twin-blade coater in which each blade is acted upon by a tube-type actuator, as defined above. In addition, the blades are mounted for adjusting angular movement about an axis which includes the apex formed by the blades.

Another object of the invention is the provision of an improved profile adjuster which is movable transversely of the width of the machine and which provides for varying the force of the blade at localized regions by applying pressure to the flexible wall of the tube actuator.

These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end elevation, partially in section, of a blade coater constructed according to this invention;

FIG. 2 is a transverse fragmentary section of a portion of the coater of FIG. 1 showing the actuator in the fully retracted position;

FIG. 3 is an enlarged fragmentary cross section showing the actuator in engagement with the doctor blade in an intermediate position;

FIG. 4 is a view similar to FIG. 3 but showing the actuator in its fully extended position;

FIG. 5 is a fragmentary isometric view of the actuator showing the connection to the regulated air pressure;

FIG. 6 is an enlarged fragmentary section showing a modified blade clamping arrangement;

FIG. 7 is a broken away front elevation of a modification of the coater, providing for profile adjustments;

FIG. 8 is an enlarged side view of one of the profilers;

FIG. 9 is the diagram of the invention as applied to a twin blade coater; and

FIG. 10 is a fragmentary detail of the pivotal structure for supporting the blades of the embodiment of FIG. 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to FIG. 1, a blade type coater is shown in which a doctor blade 10 is cantilever-supported and is urged against the exposed surface of a moving web 12, supported on a backing roll 13. The arrangement shown in this embodiment is thus essentially the general type of coater as described in the Coghill patent above. The coating material may thus be supplied from any suitable downstream chamber or roll applicator. Also, a fountain applicator may be employed as described in the U.S. patents of Coghill, U.S. Pat. Nos. 3,418,970 and 3,521,602. Additionally, the blade 10 may be employed to doctor ink off of an etched gravure roller or may consist of a roll cleaning doctor.

Blade supporting means includes a relatively fixed transversely-elongated blade support member 15. A movable clamp member 16 is adjustable mounted on pivotally mounted arms 18. The arms 18 turn about pivots 20 as shown in FIG. 1. A fixed support 25 provides support for both the fixed blade support member 15 and the arms 18, and also supports a diaphragm type motor 26. The rod end 27 on the motor is connected to apply a closing force to the clamp member 16. It is understood that two or more fixed supports 25 and motors 26 are positioned transversely on the coater with associated arms 18 to provide opening and closing movements to the clamp member 16.

One of the aspects of the present invention relates to means by which the blade 10 is fixed in predetermined alignment. The clamp member 16 and the fixed blade support 15 together comprise one embodiment of an improved blade holder assembly for a flexible coater blade. The support member 15 is formed with a blade-receiving wall 30 for supporting one surface of the metallic blade 10. The wall 30 is terminated in a machined ledge 32, as shown in FIG. 2, for receiving the bottom edge of the blade 10.

Means for temporarily supporting the blade 10 against the wall 30 prior to the closing of the clamp includes a transverse series of individual magnets 35. The magents 35 may be ringshaped and received in recesses formed in the member 15 and retained by retainer screws 36.

In the embodiment of FIG. 2 the movable clamp member 16 is provided with a transversely extending elastomeric blade engaging pad 40. The pad 40 extends continuously the width of the member 16 and is positioned to engage the opposite surface of the blade 10 adjacent the ledge 32 upon closing movement of the clamp 16 as caused by the diaphragm motors 26. The pivot point 20 of the arms 18 is shown as being transversely offset with respect to the plane of the wall 30 so that when the pad 40 comes into engagement with the blade 10, the closing force is accompanied by a downward component of force which tends to urge the blade 10 firmly against the seat or ledge 32. In this manner, the blade 10 is held by compressive force on the pad 40 against the wall 30 and in engagement with the ledge 32. The compressive force is uniform through out the width of the coater and therefore any tendency for warpage of the blade 10 is eliminated.

It is understood that either member 15 or 16 may be the moving or clamping member. Also, the arrangement automatically accommodates blades of differing thicknesses, such as .010 , .020, or .030 inch thicknesses, for example.

In changing or inserting a blade, the member 16 is retracted on the arms 18 and the blade is inserted against the wall 30 and on the ledge 32. It is retained by the magnets 35. The clamp member 16 is then brought into the closed position shown in FIG. 2 and a clamping or closing force is applied by the motors 26. Since the pivot point 20 on the arms 18 is offset with respect to the plane of the wall 30, a downward component of force is applied to the blade 10 by the pad 40 causing the blade to be firmly set on the ledge 32 and thus precisely located.

In FIG. 6 there is illustrated a somewhat modified arrangement for clamping and supporting the blade 10. Instead of the pad 40, a modified tube support or clamp member 15' is provided with a semi-cylindrical recess to receive a conventional clamping tube 42. The tube 42 may be of the general type shown in the Coghill patent and identified therein by reference number 27. However, the tube support 15' is relieved as indicated at 43 adjacent the lower edge of the tube so that the force exerted by the tube is both outward and somewhat downward in relation to the plane of the blade 10, thus causing the blade to be firmly urged against the seat 32 as in the embodiment of FIGS. 1 and 2.

As previously mentioned, the clamping arrangement of this invention provides a cantilever-supported blade which, in the embodiment of FIG. 1, is urged against the web 12 to control the weight of the coating applied thereto. Thus, certain considerations become important. First, it is desirable that the blade 10 be controlled with precision and it is further desirable that the position of the blade be controlled to make up and compensate for blade wear. Since coatings are inherently abrasive, the blade 10 will wear and thus it is important that wear compensation be provided without substantially changing the characteristics of the coater. In this connection, it is preferred that the blade support assembly, including the parts 25, 15, and 16, be mounted on cross-machine supports which permit the blade 10 to be changed in angular relation to the web 12. The mounting preferred is that shown in the above-identified Phelps patent for an air doctor, which permits the blade to be pivoted about an axis coinciding with its free or web-engaging edge.

The doctor blade of this invention includes a transversely-elongated flexible tube-type actuator indicated generally at 50. The actuator is mounted on the clamp member 16 by a transverse support 52, the position of which is adjustable by a series of individual micrometer adjusters 55.

The support 52 is provided with a forwardly-opening, transversely-elongated support channel 58 which receives and supports at the actuator 50. It is understood that the actuator tube is hollow and is adapted to receive fluid pressure therein. It is formed with a relatively thick and semi-rigid back 60 which is received within the channel 58. The actuator 50 is further provided with a collapsible front wall section 62 which is positioned adjacent the front surface of the blade 10. The wall section 62 is movable between a retracted, partially-folded condition as shown in FIG. 2 in which it lies in close proximity to the back 60, to an extended and substantially rounded condition as shown in FIG. 4 when fluid pressure is applied thereto. The actuator 50, in effect, forms a transversely-elongated bellows type linear actuator, and it is operated with the wall section 62 always in a state of flexure, and not in a stretched state.

The wall section 62 is formed with a blade-engaging extension 65 formed integrally therewith and terminated in transverse serations 66. The extension 65 is formed substantially centrally on the wall section and is thus movable with the wall section 62. Only the extension 65 engages the blade 10, and as shown, it engages the blade between its supported and free ends to apply a doctoring force thereto. A suitable source for the actuator tube material consists of pressure seal PRS-581 of Presray Corporation, 159 Maple Blvd., Pawling, New York 12564.

Since the actuator 50 is always operated in a flexed condition, the effective area of the wall section 62 which is subject to pressure with the tube reamins substantially constant with the movement of the wall seciton. Additionally, the location of engagement of the extension 65 on the blade 10 remains substantially constant. In this manner, the doctoring effort of the blade 10 varies approximately as a direct function of fluid pressure, and the weight of coating varies approximately as an inverse function of pressure.

As shown in FIG. 5, the ends of the acuator 50 are closed and a regulated source of fluid pressure through a pressure regulator 70 is applied substantially at the center of the actuator through an inlet fitting 72. Preferably, air is used although other sources of fluid pressure, even a liquid with an accumulator, could be used.

The actuator arrangement of the present invention provides for precise control. For example, 2 P.S.I. of pressure may be used to bring the extension 65 into contact with the blade 10. Another 2 to 3 pounds of pressure may be employed to extend the actuator to its full stroke as shown in FIG. 4. The use of an actuator having a folded or folding wall permits up to a three-quarter inch stroke, which is substantially more than can be achieved by using the wall of a rounded tube as an actuator. In addition, the location of engagement of the actuator with respect to the blade remains constant for any engagement condition. Thus, the doctoring force may be increased or decreased without any change in contact position or area, providing for precise control. If desired, the regulator 70 may be automatically controlled by downstream sensors to regulate the weight of coating.

In some instances it may be desirable to apply a localized correcting pressure to the doctor blade 10 in order to eliminate a wet area or streaking or other cross-machine coating irregularities. For this purpose, there is shown in FIGS. 7 and 8 a profile arrangement by means of which localized pressure may be applied to the blade at selected transverse locations to cause the blade to engage the web with a force which somewhat exceeds that effected by the fluid pressure alone. For this purpose, a modified combined clamp and tube support 80 may be used which serves both as the blade clamping member 15 as identified above and as the support and backing member for the tube 50. The support 80 is shown as having a wall support section 82 which is in partial engagement with one of the side walls 62 of the tube 50 but which permits the walls to flex outwardly freely to bring the extension 65 into engagement with the blade.

A transversely movable profile assembly 85 is mounted on the member 80 and is adjustably supported thereon by a clamp portion 86 engaging an L-shaped support 87. The profile assembly 85 includes an adjustable pivotally mounted finger 90 which has an extended end 92 which engages the opposite flexible wall of the tube 50. The force by which the end 92 engages the tube may be regulated by a thumb screw 95. When it is desirable to apply a corrective or profile force, one or more of the assemblies 85 may be attached to the support 80 and the finger 90 brought into position. The force exerted by the finger 90 against the combined wall sections of the tube 50 causes the tube in the localized transverse region to be urged outwardly against the blade with a force which is greater than that which would be effected by the fluid pressure alone. The profile assembly 85 may have any convenient width, such as, for example, 4 inches, and several may be used at one time, if required.

The precise control which is afforded by the present invention particularly adapts the same to a twin blade coater, as diagrametically illustrated as FIGS. 9 and 10. A pair of identical, diagrametically-opposite flexible blades 100 and 102 are supported on identical holder assemblies 105, which may be as described above in connection with FIGS. 1 and 2 or FIGS. 7 and 8. Each of the blades 100 and 102 is operated by a separate pressure actuator 50 constructed as previously described. The actuators 50 are connected to a common source of fluid pressure as diagrametically illustrated by the lines 110. The blades 100 and 102 form a common apex and thus simultaneously engage the opposite surfaces of the moving web 115 which has been run through a coating bath 118. It is critically important that the position of the blades 100 and 102 be maintained so that the forces across the blades are balanced and so that the tips of the blades form a true apex with respect to the web 115. The employment of the sensitive actuator as described and the use of a common source of air pressure assures that each blade 100 and 102 will be acted upon with the same force.

It is also important that the blades 100 and 102 be mounted so that they can be pivoted about a common axis which includes the apex or tips of the blade, independently of each other, such as through a 15.degree. angle for example. One suitable arrangement for this is to provide blade support arms 120 and 121, at the extreme sides of the machine, with a common pivot 124. The pivot axis defined by the pivot 124 is substantially coincident with the apex 125 formed by the blades. In this manner, proper coincidence of the blades is assured throughout adjustments in angularity with respect to the web 115.

While the forms of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention.

Claims

What is claimed is:

1. In a blade type coater in which a cantilever-supported blade is urged against a moving web to control the weight of the coating applied thereto, the improvement comprising a transversely elongated flexible tube, means supporting said tube adjacent said blade between the supported end and the free end thereof, said tube being formed with a collapsible wall section adjacent said blade and a blade-engaging extension which is formed with an integral part of said wall section, said extension being movable by said wall section transversely of said tube upon the application of fluid pressure thereto and engageable with said blade at a relatively fixed location on said blade, the effective area of said wall section subject to pressure remaining substantially constant with movement of said wall section, and the location on said blade upon the application of force by said extension remaining substantially constant so that the weight of coating applied varies approximately as an inverse function of fluid pressure applied to said tube, and pressure regulating means for applying a regulated fluid pressure source to the interior of said tube.

2. The coater of claim 1 further comprising a second said cantilever-supported blade positioned to engage said web at the opposite surface thereof and at a diametrically opposed position relative to the first blade, and a second said flexible tube having its extension positioned to engage said second blade in the same manner as defined in claim 1, each of said tubes being connected to said pressure source so that each of said blades are thereby affected uniformly and urged with equal force against said web.

3. In a blade type coater, a transversely elongated cantilever-supported blade, a transversely elongated tube, means supporting said tube adjacent said blade between the supported end and the free end thereof, said tube having a flexible, collapsible wall section adjacent said blade, a transversely extending blade-engaging extension formed substantially centrally of said wall section and movable by said wall section upon the application of fluid pressure thereto and engageable with said blade at a relatively fixed location on said blade, the effective area of said wall section subject to pressure remaining substantially constant with movement of said wall section, and the position of said extension on said blade upon the application of pressure to said tube remaining substantially constant so that the weight of coating applied varies approximately as an inverse function of fluid pressure applied to said tube, and pressure regulating means for applying a regulated fluid pressure source to the interior of said tube.

4. In a blade doctor assembly, a blade, means supporting said blade at one end, a flexible tube, means supporting said tube extending adjacent said blade between the supported end and the free end thereof, said tube being formed with a collapsible wall section adjacent said blade and a blade-engaging extension which is formed as an integral part of said wall section, said extension being positioned centrally of said wall section and movable by said wall section upon the application of fluid pressure to said tube and engageable with said blade at a relatively fixed location on said blade, the effective area of said wall section subject to pressure remaining substantially constant with movement of said wall section, and the location on said blade upon the application of force by said extension remaining substantially constant so that the doctoring effort of said blade is a direct function of air pressure applied to said tube, and air pressure regulating means for applying a regulated air pressure source to the interior of said tube.

5. The assembly of claim 4 further including means for making profile corrections in blade doctoring forces, comprising at least one adjustable means engageable with said wall section at opposite sides of said extension for confining said wall section at a selectable transverse location to urge said extension against said blade with a force which exceeds that applied by the fluid pressure alone.

6. A blade type coater having improved sensitivity and blade wear compensation, comprising a doctor blade, means supporting said blade along one transverse edge thereof, said blade having a free doctoring edge, a transversely elongated tube-type fluid pressure actuator, said actuator having a relatively rigid back and having a front wall section which is movable from a retracted, partially-folded condition in which a portion thereof lies in close proximity to said back and an extended, substantially rounded condition with the application of fluid pressure thereto, a transversely elongated blade-engaging extension formed as an integral part of said wall section and movable therewith, means supporting said actuator with said extension in engagement with said blade between its supported edge and free edge to urge said blade with increasing doctoring effort with extending movement of said wall section, the region of engagement of said extension on said blade remaining relatively fixed with changes in fluid pressure in said actuator, and means for applying fluid under regulated pressure to said actuator to control the weight of coating and to compensate for wear of said blade.

7. The coater of claim 6 further comprising an adjuster for effecting profile corrections, means mounting said adjuster on said blade support means, said adjuster having a movable portion engageable with said actuator at said wall section to apply a force thereto at a localized region thereof in a direction normal to the transversely-elongated direction of said actuator, said adjuster being effective to cause said extension to be urged with somewhat increased force at said localized region against said blade.