WO1998044200A1

WO1998044200A1 - A coating apparatus for applying coating material

Info

Publication number: WO1998044200A1
Application number: PCT/US1998/004008
Authority: WO
Inventors: Robert Urscheler
Original assignee: Beloit Technologies, Inc.
Priority date: 1997-03-31
Filing date: 1998-02-27
Publication date: 1998-10-08
Also published as: CA2325698C; AU6444198A; CA2325698A1

Abstract

A coating apparatus is disclosed for applying coating material onto a moving surface. The apparatus includes a housing (16A) which defines a chamber (18A) for the reception therein of the coating material (12A). The housing (16A) also defines an exit slot (20A) for the passage therethrough of the coating material (12A) from the chamber (18A). A shear applying device (28 A-G) is disposed within the chamber for applying shear to the coating material prior to application of the coating material onto the surface (14A). The shear reduces the viscosity of the coating material and maintains a reduced viscosity of the coating material prior to application of the coating material onto the surface so that uniform flow of the coating through the exit slot taken in a cross-machine direction is facilitated.

Description

PATENT APPLICATION TITLE: A COATING APPARATUS FOR APPLYING COATING MATERIAL

Background of the Invention Field of the Invention

The present invention relates to a coating apparatus for applying coating material onto a moving web or surface.

More specifically, the present invention relates to a coating housing which precedes the application of the coating material to the web or surface.

Information Disclosure Statement

In a typical coater apparatus such as the BA 1 500 fountain type coater manufactured by Beloit Corporation, the housing defines a chamber for the reception therein of coating material.

The coating material under pressure flows from the chamber through a narrow slot which extends from the chamber to the vicinity of a web traveling around a smooth backing roll.

A thin ribbon of coating material is applied at the exit of the slot to the moving web and a metering blade or rod disposed immediately downstream relative to the slot meters and smoothes the coating material onto the moving web.

The metering or applicator blade is urged toward the coating material and web by means of at least one pneumatically inflatable tube or mechanical supports extending in a cross-machine direction. Additionally, a finishing blade is disposed downstream relative to the applicator blade such that the finishing blade is adjustably urged against the applied coating material for applying a finished coating contour to the coated web.

However, in recent years, there has been a tendency in the coating industry toward more specific or tailor-made coating compositions. Such specific coating compositions typically include an all synthetic composition as opposed to the more traditional types of coating material which include starch, or other materials as the binder, respectively, co-binder.

More specifically, in a typical coating composition utilizing starch as the binder, such compositions exhibit coating characteristics approaching that of a Newtonian liquid. More particularly, as in the case of water, such typical coating compositions display little change in viscosity when shear forces are applied thereto.

However, with the trend toward the use of the aforementioned synthetic coatings, there is a tendency for the viscosity of the coating material to decrease rapidly upon application of shear forces thereto.

Accordingly, in the prior art fountain coater when, for example, the coating material is supplied to the coating chamber from one side thereof, inherently, more shear is applied to the synthetic coating material at the inlet end of the chamber rather than at the opposite end of the coating chamber.

Consequently, the coating material flowing adjacent to the inlet end of the chamber acquires a lower viscosity leading towards splashing of the coating material adjacent to the inlet end. However, at the opposite end of the coating chamber, the coating material is subjected to lesser shear forces and the viscosity of such coating material will remain relatively high.

Although it is possible to supply the coating material from both ends of the chamber or indeed from multiple inlets along the cross-machine direction of the coating chamber, clearly such a supply arrangement becomes extremely complicated. Such is the case, particularly in view of the fact that the coater housing must be permitted to rotate for adjustment of the exit slot relative to the moving web or surface.

The present invention overcomes the aforementioned problem of variations in the viscosity in the cross machine direction by the application of uniform viscosity to the coating material at an exit slot of the coating chamber.

More specifically, in order to accommodate various coating formulations, the present invention provides a shear imparting means which can be rotatable or stationary and which can be conveniently mounted in the coating chamber. In the case of a rotatable shear imparting means, the arrangement is such that the rotational speed of the shear imparting means may be varied to optimize the degree of shear imparted to the coating composition in order to insure uniform viscosity in a cross-machine direction flowing through the exit slot and onto the moving web or surface.

Therefore, it is the primary feature of the present invention to provide a coating apparatus which overcomes the aforementioned inadequacies of the prior art arrangements and which makes a significant contribution to the art of coating a moving web or surface. Another feature of the present invention is the provision of a coating apparatus which imparts shear forces to the coating material so that the viscosity of the coating material in a cross-machine direction remains substantially uniform when such coating material is applied to a moving web or surface.

Another feature of the present invention is the provision of a rotatable shear imparting means which is driven at a speed commensurate with the type of coating formulation being used in order to optimize the cross-machine directional flow of such formulation onto the moving web.

Other features and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.

The present invention applies controllable or variable shear to the coating material thus decreasing its viscosity and as a result improving the flow of the coating material in the chamber.

Moreover, in a conventional coating applicator, such as a pre- metering chamber, as stated hereinbefore, the flow of coating material will be non-uniform along a cross-machine direction as there is a tendency for the coating material to Stagnate at the end of the coating chamber opposite to the chamber inlet.

By way of example, in Rotogravure Printing there is a trend toward the use of specific or tailor-made formulations which typically have very shear thinning flow characteristics. Such formulations exhibit large variations in coating material flow in the coating chamber from the inlet to the other side of the chamber. These variations result in uneven viscosities of the coating material across the width of the web or surface to be coated.

Applicant has discovered that the provision of perforate static elements within the coating chamber enhances the cross-machine directional uniformity of the applied coating.

Nevertheless, although the provision of a static triangular shaped perforate element together with a v-shaped static element between the triangular shaped element and the exit slot improved uniformity, it was also discovered that after cleaning the coating chamber with water, coating formulation was still found to be lodged within the static elements when the coating chamber was opened for inspection.

Accordingly, and as encompassed by the present invention, the provision of a rotatable shear imparting means includes a further advantage in that such rotary shear imparting means is self-cleaning without having to dismantle the coating apparatus when changing from one formulation to another.

Also, as stated hereinbefore, the provision of a rotary shear imparting means having a variable speed of rotation makes it possible for the speed of rotation and the applied shear to be adjusted to enhance the amount of shear applied to the formulation in order to optimize cross- machine directional uniformity.

Whereas, the inventive concept according to the present invention may be applied to a coating chamber of a typical BA 1 500 coater or any other chamber type coater, it has been further discovered that it is desirable to have the rotatable shear imparting means disposed as close as possible to the inlet end of the narrow exit slot, that is, as close as possible to the web or surface to be coated.

Therefore, although in the BA 1 500 coater, the coating chamber is typically of a pear-shaped or tear drop shaped configuration, a more ideal shape for the coating chamber would be cylindrical so that the rotary shear imparting means can be disposed concentrically within the coating chamber for rotation therein and so that the shear imparting element is disposed close to the exit slot. However, the ideal shape may not always be desirable taking into account the abrasion characteristics of highly pigment charged coating materials.

The present invention in its preferred form provides a coating apparatus having a driven shaft which is provided with readily replaceable shear imparting rotary elements.

Also, the apparatus according to the present invention permits the feeding of coating material from one side only into the coating chamber thereby avoiding the feeding of coating material from both ends of the coating chamber or at multiple points along the length thereof as in a so- called Christmas tree type configuration. The aforementioned one sided feed arrangement is clearly the type that is preferred by the coating industry.

The variable shear imparting mechanism according to the present invention also improves the distribution of the coating material in a cross- machine direction thereby providing more uniform flow characteristics and lower viscosity of the coating material. Additionally, as stated hereinbefore, the present invention provides a coating apparatus which avoids the problem of increased shear adjacent to the inlet end of the coating chamber. The increased shear results in improved viscosity which permits a lower operating pressure at the exit slot of the coater chamber thereby avoiding splashing at the inlet edge or inlet edges as in the case of a coating chamber fed from both sides thereof.

Moreover, coating formulations and particularly synthetic formulations unlike stock flowing through a papermachine headbox, exhibit shear thinning characteristics. Shear thinning material such as tomato ketchup and the like, tends to flow more readily when shear forces are imparted thereto. Thus, by rapidly shaking a bottle of ketchup, shear is imparted to the ketchup which enhances the uniform flow of the material through the neck of the ketchup bottle.

In an analogous manner, when shear is imparted to the coating formulation within the coating chamber as by the rotation therein of a perforate cylindrical wall disposed within the coating chamber, such shear has an affect on the shear thinning characteristics of the coating formulation thereby enhancing the uniform flow thereof through the exit slot.

More particularly, the imparting of shear forces to the coating material provides a more homogenous coating material having a uniform viscosity and flow behavior at the exit of the slot and at any point along the length of the slot in a cross-machine direction.

Additionally, with the rotary shear imparting means according to the present invention, it is possible to operate the coater with a lower pump pressure. Although the rotary shear imparting means rotates at a selectable rotational speed within the coating chamber, and a certain amount of clearance between the shear imparting means and the chamber is required for practical operation, it is envisaged that the aforementioned clearance may be as little as 2-3 millimeters.

The coating apparatus according to the present invention provides means for even and uniform application of coating material while providing rapid setting of the coating formulation upon application thereof to the web.

Summary of the Invention

The present invention relates to a coating apparatus and a method for applying coating material onto a moving web. The apparatus includes a housing which defines a chamber for the reception therein of the coating material. The housing also defines an exit slot for the passage therethrough of the coating material from the chamber.

Shear means are disposed within the chamber for applying shear to the coating material prior to application of the coating material onto the web or surface. The shear reduces the viscosity of the coating material and maintains a reduced viscosity of the coating material prior to application thereof onto the web or surface so that uniform flow of the coating material through the exit slot taken in a cross-machine direction is facilitated.

In a preferred embodiment of the present invention, the shear means includes a member of preferably cylindrical configuration. More specifically, the shear means includes a cylindrical member which has a peripheral perforate wall rotatably disposed within the chamber about a rotational axis disposed substantially parallel to the cross-machine direction of the moving web. The arrangement is such that during operation of the apparatus, the coating material flows into the member and through the perforate wall thereof toward the exit slot so that shear is applied to the coating material during passage through the perforate wall for facilitating the application of a uniform flow of coating material onto the moving web or surface.

More specifically, the shear means is rotatably disposed within the chamber. The coating apparatus also includes a variable speed drive means drivingly connected to the shear means for varying the rotational speed of the shear means within the chamber commensurate with the type of coating material being applied to the moving web in order to optimize the uniform flow of the coating material through the exit slot.

Many variations and modifications of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings. However, such modifications and variations fall within the spirit and scope of the present invention as defined by the appended claims.

Brief Description of the Drawings

Fig. 1 is a sectional view of a typical prior art fountain type coater.

Fig. 1 A is a side elevational view of another prior art coater.

Fig. 1 B is a side elevational view of yet another prior art coater.

Fig. 2 is a cross-sectional view of a coater apparatus according to one embodiment of the present invention.

Fig. 3 is a reduced bottom view partially in section of the apparatus shown in Fig. 2. Fig. 4 is a cross-sectional view of a coater apparatus according to another embodiment of the present invention.

Fig. 5 is an enlarged sectional view of a preferred embodiment of the coating apparatus according to the present invention.

Fig. 6 is a bottom view partially in section of the apparatus shown in Fig. 5.

Fig. 7 is a sectional view of yet another embodiment of the present invention.

Fig. 8 is a sectional view taken on the line of 8-8 of Fig. 7.

Fig. 9 is a sectional view taken on the line of 9-9 of Fig. 7.

Fig. 1 0 is a sectional view of yet a further embodiment of the present invention.

Fig. 1 1 is a sectional view of still another embodiment of the present invention; and

Fig. 1 2 is a sectional view of yet another embodiment of the present invention.

Similar reference characters refer to similar parts throughout the various embodiments of the present invention.

Detailed Description of the Drawings

Fig. 1 is a cross-sectional view of a typical fountain coater of the type known as the BA 1 500 coater manufactured by Beloit Corporation.

The coating apparatus generally designated 10 applies coating material 12 on to a moving web 14. The apparatus includes a housing 16 which defines a chamber 18 for the reception therein of the coating material 12. The housing 16 also defines an exit slot 20 for the passage therethrough of the coating material 12 from the chamber 18. The enlarged inset shown in Fig. 1 shows a metering or applicator blade 22 which is disposed immediately downstream relative to the exit slot 20 for metering or applying the coating 12 onto the moving web 14 supported by a rotatable backing roll 24.

A finishing blade 26 is disposed downstream relative to the applicator blade 22 for applying a finished configuration to the coating material 12.

Fig. 1 A is a side elevational view of a coater according to U.S. Patent No. 5, 104,697 assigned to Valmet.

Fig. 1 B is a side elevational view of a coater according to U.S. Patent No. 4,869,933 assigned to Voith.

The concept of the present invention may be applied as a retrofit to any of the coaters shown in Figs. 1 , 1 A or 1 B.

Fig. 2 is an enlarged cross-sectional view of a coating apparatus generally designated 10A according to one embodiment of the present invention. More specifically, Fig. 2 shows the concept of the present invention included as a retrofit to the BA 1 500 coater manufactured by Beloit Corporation. The coating apparatus 10A applies coating material 12A onto a moving web indicated by the dashed line 14A. The coating apparatus 10A includes a housing 16A defining a chamber 18A for the reception therein of the coating material 12A. The housing 16A also defines an exit slot 20A for the passage therethrough of the coating material 12A from the chamber 18A. Shear means generally designated 28A are disposed within the chamber 18A for applying shear to the coating material 12A prior to the application of the coating material 12A on the web 14A. The shear reduces the viscosity of the coating material 12A and maintains a reduced viscosity of the coating material 12A prior to the application of the coating material 12A onto the web 14A. The arrangement is such that a uniform flow as indicated by the arrow 15A of the coating material 12A through the exit slot 20A taken in a cross-machine direction is facilitated.

As shown in Fig. 2, the coating apparatus 10A also includes a frame 30A with the housing 16A being pivotally sectired to the frame 30A about a pivotal axis 32A which is disposed substantially parallel to the cross- machine direction of the moving web 14A. The arrangement is such that adjustment of the location of the exit slot 20A relative to the moving web 14A is permitted.

The BA 1 500 coater partially shown in Fig. 2 typically includes the chamber 18A which is of generally tear-drop shaped configuration when taken in a section perpendicular to the cross-machine direction of the moving web 14A.

More specifically, the tear-drop sectional configuration of the chamber 18A includes a first portion 38A having a partially cylindrical configuration and a second portion 40A which is disposed between the first portion 38A and the exit slot 20A. The second portion 40A is of triangular sectional configuration.

Fig. 3 is a reduced bottom plan view partially in section of the arrangement shown in Fig. 2 and shows the coating apparatus as including an inlet 42A which is disposed in fluid communication with the chamber 18A for permitting the flow as indicated by the arrow 44A of the coating material 12A through the inlet into the chamber 18A.

As shown in Fig. 3, the chamber 18A includes a first and a second end 46A and 48A, respectively, the inlet 42A being connected to the first end 46A of the chamber 18A.

The exit slot 20A also includes a first and a second extremity 50A and 52A, respectively with the first extremity 50A extending from the chamber 18A and the second extremity 52A being disposed adjacent to the moving web 14A during operation of the coating apparatus 10A.

As shown in Fig. 2, the exit slot 20A tapers from the first extremity 50A toward the second extremity 52A. The arrangement is such that the second extremity 52A of the exit slot 20A is more narrow than the first extremity 50A.

More specifically, the first extremity 50A has a width W within the range 2 to 4 millimeters and preferably 3 millimeters while the second extremity 52A has a width W within the range .6 to 1 .9 millimeters and preferable 1 .5 millimeters.

As shown in Figs. 2, the exit slot 20A further includes an expansion chamber 54A which is disposed between the first and the second extremity 50A and 52A, respectively. The expansion chamber 54A is of generally cylindrical sectional configuration having an axis of symmetry 56A disposed substantially parallel to the cross-machine direction of the moving web 14A. The expansion chamber 54A as shown in Fig. 2 also includes an upstream portion 58A which tapers outwardly in a direction from the first extremity 50A toward the second extremity 52A and a downstream portion 60A which tapers inwardly in a direction from the first extremity 50A toward the second extremity 52A.

Fig. 4 is a sectional view of a further embodiment of the subject invention in which the shear means 28B includes a perforated plate 62B which extends along substantially the entire width of the chamber 18B in a direction substantially parallel to the cross-machine direction of the moving web 14B. The arrangement is such that during operation of the apparatus 10B, when the coating material 12B flows through the perforated triangular shaped plate 62B toward the exit slot 20B, a shearing action is applied to the coating material 12B which reduces the viscosity of the coating material 12B so that such reduced viscosity is maintained during passage of coating material 12B through the exit slot 20B such that uniformity of flow of coating material 12B onto the moving web 14B in a cross-machine direction is enhanced.

Also, as shown in Fig. 4, coating material 12B is supplied from an inlet to the inside of the plate 62B. The coating material has shear applied thereto as the coating flows through the perforated plate 62B and a V- shaped perforated plate 63B disposed between the plate 62B and the exit slot 20B.

Fig. 5 is a sectional view of a preferred embodiment of the present invention, in which the chamber 180 is of cylindrical configuration. The chamber 180 has an axis of symmetry 360 which is disposed substantially parallel to the cross-machine direction of the moving web 140. In the preferred embodiment of the present invention as shown in Fig. 5, the shear means 280 includes a member 64C of substantially cylindrical configuration. The cylindrical member 640 has a peripheral perforate wall 660 which is rotatable disposed within the chamber 180 about rotational axis 36C disposed substantially parallel to the cross- machine direction of the moving web 140. The arrangement is such that during operation of the apparatus 100, the coating material 120 flows into a stationary perforated distribution tube 620 extending in a cross machine direction from the inlet. Thereafter, the coating 120 flows through the member 640 and through the perforate wall 660 thereof toward the exit slot 200 so that a shear force is applied to the coating material 120 during passage thereof through the wall 660 for facilitating the application of a uniform flow of coating material 120 onto the moving web 140.

In the preferred embodiment of the present invention, the shear means 280 is rotatably disposed within the chamber 180 as indicated by arrow 190.

Fig. 6 is a bottom view of the apparatus IOC shown in Fig. 5. As shown in Fig. 6, the coating apparatus 100 also includes a variable speed drive means 700 drivingly connected to the shear means 280 for varying the rotational speed of the shear means 280 within the chamber 180 commensurate with the type of coating material 120 being applied to the moving web 140 in order to optimize the uniform flow of the coating material through the exit slot 200 as shown in Fig. 5.

As shown in Figs. 2-6 coating apparatus 10A-10C applies a shear thinning coating material 12A-C onto a moving web 14A-C. The apparatus 10A-C includes a housing 16A-C defining a chamber 18A-C for the reception therein of the coating material 12A-C. The housing 16A-C also defines an exit slot 20A-C for the flow therethrough of the coating material 12A-C from the chamber 18A-C.

Shear means 28A-C are disposed within the flow for imparting shear to the coating material 12A-C prior to application of the coating material 12A-C on the web 14A-C. Such shear alters the shear thinning characteristics of the coating material 12A-C so that uniform flow of the coating material 12A-C through the exit slot 20A-C when taken in a cross- machine direction is maintained.

The present invention also encompasses a method of applying a coating 12A-C on a web 14A-C. The method comprises the steps of feeding the coating 12A-C into a chamber 18A-C defined by the coater housing 16A-C. The coater housing 16A-C also defines an outlet slot 20A- C which extends from the chamber 18A-C toward the web 14A-C.

The method includes the step of applying shear to the coating so that the viscosity of the coating flowing from the chamber 18A-C through the slot 20A-C is reduced such that taken in a cross-machine direction, a uniform flow rate of the coating is maintained as the coating flows through the slot 20A-C for application onto the web.

Fig. 7 is a sectional view of a further embodiment of the present invention. Fig. 7 shows a coating apparatus 10D having a shear means generally designated 28D. The shear means 28D includes a plurality of disks 72D, 73D and 74D of various diameters.

Fig. 8 is a sectional view taken on the line 8-8 of Fig. 7 and shows that each of the disks 72-74D and as shown in Fig. 8 the disk 74D as having a plurality of peripheral cutting edges 76D, 77D and 78D for imparting shear to the coating material 12D.

Fig. 9 is a sectional view taken on the line 9-9 of Fig. 7 and shows the plurality of disks of various diameters including disks 72D-74D. The drive means 70D drives the longitudinal shaft 71 D to which all of the disks 72-74D are rigidly secured.

Fig. 1 0 shows yet another embodiment of the present invention which is similar to the embodiment shown in Figs. 5 and 6. However, in the arrangement shown in Fig. 10, the apparatus 10E includes a cylindrical shear imparting means 28E in which the spacing of the shear imparting holes such as 80E and 81 E is greater at the inlet 42E than at the opposite end 48E of the chamber 18E. In the aforementioned manner, the amount of shear imparted to the coating can be varied from the first end 46E to the second end 48E of the chamber 18E.

Additionally, Fig. 1 1 is a diagrammatic representation of yet another embodiment of the present invention. Fig. 1 1 shows a coating apparatus 10F having a plurality of inlets 42F and a shear imparting means 28F which defines a plurality of holes 80F-81 F disposed between the first and second ends 46F and 48F of the chamber 18F.

Fig. 1 2 is a diagrammatic representation of another embodiment of the present invention. Fig. 1 2 shows a coating apparatus 10G in which the shear imparting means 28G includes a plurality of disks 72G, 73G and 74G disposed between the first and second ends 46G and 48G of the chamber 18G. The arrangement is such that a uniform flow and viscosity of the coating material is attained prior to the flow of the coating material through the exit slot for application on to the web. In both the arrangements shown in Figs. 1 1 and 1 2, the holes and disks, respectively, are dimensioned to accommodate the inlet points 100F and 100G respectively, where lower shear is needed.

As will be appreciated by those skilled in the art, there are many variations that fall within the spirit and scope of the inventive concept of the present invention. The configuration of the shear imparting means will in many respects depend on the type of coating material being used and the quality of the web that is to be coated.

The shear rate is influenced by the rotational speed of the motor and the number and diameter of the holes in the rotating cylinder.

In the case of the embodiment including rotating disks, the shear rate will be influenced by the diameter of the disks and the dimensions of the razor edges which may be of rectangular configuration.

Accordingly, the rate of shear will increase with the number of holes or slits provided in the rotating cylinder and will increase when the diameter of the holes or width of the slits is decreased.

Similarly, the shear rate will increase with the number and diameter of the disks and the size of the razor edges.

The shear rate can be optimized by varying the design of the rotor shear imparting means dependent on the number of inlets for the coating color. Additionally, the rate at which the shear imparting means is rotated may be adjusted relative to the coating color pump speed in order to optimize uniformity of flow.

In general, the shear generated by the shear imparting means should ideally be higher than the shear generated by the structure following the shear generator and prior to the metering or pre-metering elements such as a blade or rod.

The concept of the present invention also includes the application thereof in connection with a blade metering size press where the coating is applied to the surface of a roll for subsequent transfer to a web moving past such coated roll.

The present invention provides a unique coating apparatus which is eminently suitable for the application of highly synthetic coating compositions in which the application of shear to the coating material causes reduced viscosity and uniform flow of the coating material onto the web to be coated.

While the invention has been described in connection with certain shear producing elements which are currently considered to be the best practical way of imparting shear to the coating mixture, it will be understood by those skilled in the art that other shear inducing elements can be readily used. For example, a smooth non-perforate cylinder will impart a certain amount of shear and can be useful for certain coating formulations. Other shear inducing devices well known to those versed in the art of preparing coating mixture can be readily adapted to practice the principles of the present invention.

Claims

WHAT IS CLAIMED IS:

1 . A coating apparatus for applying coating material onto a moving surface, said apparatus comprising: a housing defining a chamber for the reception therein of the coating material, said housing also defining an exit slot for the passage therethrough of the coating material from said chamber; and shear means disposed within said chamber for applying shear to the coating material prior to application of the coating material onto the web, said shear reducing the viscosity of the coating material and maintaining a reduced viscosity of the coating material prior to application of the coating material onto the web so that uniform flow of the coating material through said exist slot taken in a cross-machine direction is facilitated.

2. A coating apparatus as set forth in claim 1 further including: a frame; said housing being pivotally secured to said frame about a pivotal axis which is disposed substantially parallel to said cross- machine direction of the moving web, the arrangement being such that adjustment of the location of said exit slot relative to the moving web is permitted.

3. A coating apparatus as set forth in claim 1 wherein said chamber is of cylindrical configuration, said chamber having an axis of symmetry disposed substantially parallel to said cross-machine direction of the moving web.

4. A coating apparatus as set forth in claim 1 wherein said chamber is of generally tear-drop shaped configuration when taken in a plane which extends along the direction of movement of the web and perpendicular to the web.

5. A coating apparatus as set forth in claim 4 wherein said chamber of tear drop sectional configuration includes: a first portion having a partially cylindrical configuration; a second portion disposed between said first portion and said exit slot, said second portion being of triangular sectional configuration.

6. A coating apparatus as set forth in claim 1 further including: an inlet disposed in fluid communication with said chamber for permitting the flow of the coating material through said inlet into said chamber.

7. A coating apparatus as set forth in claim 6 wherein said chamber includes a first and a second end, said inlet being disposed to said first end of said chamber.

8. A coating apparatus as set forth in claim 1 wherein said exit slot includes: a first and a second extremity, said first extremity extending from said chamber, said second extremity being disposed adjacent to the moving web during operation of said coating apparatus.

9. A coating apparatus as set forth in claim 8 wherein said exit slot tapers from said first extremity toward said second extremity, the arrangement being such that said second extremity of said exit slot is more narrow than said first extremity.

10. A coating apparatus as set forth in claim 9 wherein said first extremity has a width within the range 2 to 4 millimeters; said second extremity has a width within the range .6 to 1 .9 millimeters.

1 1 . A coating apparatus as set forth in claim 8 wherein said exit slot further includes: an expansion chamber disposed between said first and second extremity, said expansion chamber being of generally cylindrical sectional configuration having an axis of symmetry disposed substantially parallel to said cross-machine direction of the moving web.

1 2. A coating apparatus as set forth in claim 1 1 wherein said expansion chamber further includes: an upstream portion which tapers outwardly in a direction from said first extremity toward said second extremity; a downstream portion which tapers inwardly in a direction from said first extremity toward said second extremity.

1 3. A coating apparatus as set forth in claim 1 wherein said shear means includes: a perforated plate which extends along substantially the entire width of said chamber in a direction substantially parallel to the cross-machine direction of the moving web, the arrangement being such that during operation of the apparatus, when the coating material flows through said perforated plate toward said exit slot, a shearing action is applied to the coating material which reduces the viscosity of the coating material so that such reduced viscosity is maintained during passage of the coating material through said exit slot such that uniformity of flow of the coating material onto the moving web in a cross-machine direction is enhanced.

1 4. A coating apparatus as set forth in claim 1 wherein said shear means includes: a member of substantially cylindrical configuration, said cylindrical member having a peripheral perforate wall which is rotatably disposed within said chamber about a rotational axis disposed substantially parallel to said cross-machine direction of the moving web, the arrangement being such that during operation of the apparatus, the coating material flows into said member and through said perforate wall thereof toward said exit slot so that said shear is applied to the coating material for facilitating the application of a uniform flow of the coating material onto the moving web.

1 5. A coating apparatus as set forth in claim 1 wherein said shear means is rotatably disposed within said chamber; said coating apparatus further including: variable speed drive means drivingly connected to said shear means for varying a rotational speed of said shear means within said chamber commensurate with the type of coating material being applied to the moving web in order to optimize said uniform flow of the coating material through said exit slot.

1 6. A coating apparatus for applying a shear thinning coating material onto a moving web, said apparatus comprising: a housing defining a chamber for the reception therein of the coating material, said housing also defining an exit slot for the flow therethrough of the coating material from said chamber; and shear means disposed within said flow for applying shear to the coating material prior to application of the coating material onto the web, such shear altering the viscosity characteristics of the coating material so that uniform flow of the coating material through said exit slot when taken in a cross-machine direction is maintained.

1 7. A method of applying a coating on a surface, said method comprising the steps of: feeding the coating into a chamber defined by a coater housing, the coater housing also defining an outlet slot which extends from the chamber towards the surface; and applying shear to the coating so that the viscosity of the coating flowing from the chamber through the slot is reduced such that taken in a cross-machine direction, a uniform flow rate of the coating is maintained as the coating flows through the slot for application onto the web.

18. A coating apparatus for applying coating material onto a moving surface, said apparatus comprising: a housing defining a chamber for the reception therein of the coating material, said housing also defining an exit slot for the passage therethrough of the coating material from said chamber; and shear means disposed within said chamber for applying shear to the coating material prior to application of the coating material onto the surface, said shear reducing the viscosity of the coating material and maintaining a reduced viscosity of the coating material prior to applying of the coating material onto the surface so that uniform flow of the coating material through said exit slot taken in a cross-machine direction is facilitated, the arrangement being such that the shear generated by the shear means is higher than the shear generated subsequent to said shear means and prior to said application of the coating material onto the surface.