US3340090A

US3340090A - Method and apparatus to grind a coating while applying a coating to a web

Info

Publication number: US3340090A
Application number: US320036A
Authority: US
Inventors: Jr Hoyt Nordeman
Original assignee: Champion Papers Inc
Current assignee: Champion Papers Inc
Priority date: 1963-10-30
Filing date: 1963-10-30
Publication date: 1967-09-05
Anticipated expiration: 1984-09-05
Also published as: BE649773A; NL6408646A; CH429425A; GB1021310A

Description

p 1967 H. NORDEMAN, JR 3,340,090

METHOD AND APPARATUS TO GRIND A COATING WHILE APPLYING A COATING TO A WEB Filed Oct. 30, 1963 3 Sheets-Sheet l Eda/2 6722/ I NVENTOR flay? flrdamn, J1",

WWMORNEYE 5, 1967 H. NORDEMAN, JR 90 METHOD AND APPARATUS TO GRIND A COATING WHILE APPLYING A COATING TO A WEB Filed Oct. 30, 1963 '3 Sheets-Sheet 2 Q I INVENTOR N .G H y% A Zrdem; 1.77

BY M W ATTORNEY5 Sept. 5, 1967 NORDEMAN, JR 3,340,090

METHOD AND APPARATUS TO GRIND A COATING WHILE APPLYING A COATING TO A WEB Filed Oct. 30, 1965 5 Sheets-Sheet 3 N N N N F a W O) N L x v q Q. T

Q n L. Q

Q INVENTOR flkyiv' A brdemn, J7;

ATTORNEYS United States Patent C 3,340,090 METHOD AND APPARATUS T GRIND A COAT- ING WHILE APPLYING A COATING TO A WEB Hoyt Nordeman, Jr., Oxford, Ohio, assignor to Champion Papers Inc., a corporation of Ohio Filed Oct. 30, 1963, Ser. No. 320,036 20 Claims. (Cl. 117-102) This invention relates to coating apparatus and methods. More particularly, the invention is directed to such apparatus and methods as may find use in the coating of a moving web, for example manufacture of coated paper, though it is not necessarily so limited nor is the invention to be construed as limited to any particular coating system or compositions, that is whether or not the coating is a solvent or aqueous system.

In the art of coating paper, a moving web, usually continuous, is coated by the application thereto of a coating, for example, an aqueous base-mineral pigment coating. The coating operation may be carried out either on machine, i.e., the coating is applied at various stages in the paper machine or off machine, i.e., the coating operation is a separate and distinct operation. The present invention is directed to either type of operation and to the application of any and all of the usual coating compositions to the web. By usual coating compositions is meant any fluid base pigmented coating such as an aqueous base-mineral pigment, adhesive coating; for example, a clay, casein coating to which various other compatible ingredients may be added; for example, defoaming agents, wetting agents, setting agents, solvents, dyestuffs and the like. Other examples of coatings as applied to paper will be found in vol. 3, Manufacture and Testing of Paper and Board, First Edition, 1953, by McGraw-Hill Book Company, hereinafter referred to as Manufacture.

Such coatings, as have been referred to, whether applied oif or on machine may be applied to the web by providing a color roll in contact with the web; the color roll rotating in a coating pan to which the coating is furnished by one or more various means. This type of coating operation is exemplified in US. Patents 2,598,- 733; 2,729,192 as applied via blade coating and by U. S. Patent 2,316,202, among others, as applied in a cast coating operation where the coating and web are adhered to a polished casting surface and dried to reproduce a coated surface which is a mirror-image of the casting surface. Obviously, as the color roll rotates, coating from the pool formed in the pan is carried up to the moving web.

Another application of the present invention is found in the so-called roll coating process which may be on or off machine and in which the color roll applies the coating to a transfer roll rather than directly to the web and wherein the transfer roll, in turn, contacts the web to print the coating on the web surface. Such a process is exemplified in US. Patent 2,676,563.

In addition, the invention may be applied to the socalled air knife process wherein an air knife acts as the doctor means as distinguished from a blade in contact with the web, and in some cases the system may also be used with a spray coating system wherein the application of the coating is via a spray device substituted for an applicator roll.

In each instance of use mentioned, serious problems are encountered in assuring that the coating carried to the Web is free of contamination, dirt, grit, stray fibers, lumps and the like, all of which result in imperfect application of the coating to the web.

Obviously, if the coating is not applied with reasonable perfection, the paper or other product produced is 35403 090 Patented Sept. 5, 1967 ice imperfect; its surface being marred by streaks, hard spots, dirt specks, holes, etc., all of which reduce the quality and salability of the finished product.

There are various causes for coating contamination. For example, the adhesive in the case of paper coating tends to set despite agitation of the coating in the pan. This results in an accumulation of dry or lumpy coating at the pan edges on the roller shafts, etc., with the result that portions of the dried coating often are carried into the pan. Also, because the surface of the coating in the pan is exposed, dirt and dust can be entrapped in the coating. In addition, the coating or applicator roll often picks up fibers from the web carrying these fibers into the coating itself.

Another phenomenon encountered particularly in the coating of paper is adhesive depletion. It is known that on any coating operation wherein the coating is applied by a nip arrangement, i.e., as between a cast coating drum and the press roll or between a doctor blade and a back-up roll, the coating carried into the nip is several times greater than can be adhered to the web and pass through the nip. The excess coating is rejected back to the coating pan or system. There is a definite selection of fine particle size and rejection of coarse particles at the nip, the coarse material being rejected while the fines pass through the nip. Since greater amounts of adhesive are passed through with the fines it is found that adhesive consumption is higher than should be necessary so that ultimately the adhesive is depleted and of course the coarse particles tend to agglomerate as they are recirculated ultimately requiring shutdown and washup of the coating operation.

Various remedies have been proposed and used to remedy the situations mentioned. Circulating systems have been proposed to keep the pan suplied with re circulated coating. Screens have been included in such recirculation systems and other various arrangements have been proposed, with the general result being that circulation systems operate at extremely high volumes requiring a massive screening area and that foaming due to high volume circulation has become an almost inescapable fact of life. In the final analysis, however, it has been found that the only sure cure to the problem is a complete shutdown of the coating operation for a complete washup of the applicator roll, pan and the remainder of the equipment at the point where uniform coating application is a practical impossibiliy due to contamination of the coating or the inability of the circulation system to clean out contaminates.

It is obvious that cleanups and the resulting loss of production time reduce the efiiciency of any coating operation. Too, coating is thrown away during any cleanup, adding to the overhead costs that are charged to the coating operation. In addition, production losses have grown more and more significant as the speeds of paper machines and coaters have increased over the years. With many such operations approaching speeds of two thousand feet per minute or more, any downtime represents a significant loss of production with loss of revenue.

This invention, then, is concerned with a coating system and method wherein downtime for coating cleanup is reduced to an absolute minimum and wherein coating losses are reduced to bare necessity. Conversely, it is an object of the invention to extend the production periods of coaters of the pan-roll type.

Another object of the invention is to enable use of a maximum amount of the adhesive content of a coating, thus reducing further coating losses occasioned by the excessive use of adhesive.

A further object of the invention is to provide a coating system and method which results in an improved coated product.

An additional object of the invention is to produce a coating system wherein circulation of high volumes of coating is avoided hence foaming is reduced and the usual massive screening areas may be dispensed with for all practical purposes.

Still another object of the invention is to produce a coating apparatus which continually'recirculates coating in the pan at a relatively low volume and treats at least a portion of the recirculated coating to remove or reduce contamination thereof.

An additional object of the inventionis to produce a coating system and method characterized by highly efficient operation.

Still another object of the invention is to produce a coating apparatus and method characterized in that downtime is reduced to a minimum for cleanup purposes.

A further object of the invention is to produce a coating apparatus and method particularly adaptable to use in high speed papermaking or coating operations.

These and other objects of the invention, not specifically referred to but nonetheless inherent therein and apparent to those skilled in the art, are accomplished by a method of coating including the steps of maintaining a pool of liquid coating adjacent a web to be coated; withdrawing from said pool a first portion of coating and applying ame to the web; simultaneously and concurrently therewith removing a further portion of said pool; grinding said further portion of said coating and thereafter returning said further portion of said coating uniformly to said coating pool. Advantageously, the coating may be preground before introducing same in said pool and, further,

the pool may be continuously replenished, as coating is 7 applied to the web, from a suitable supply source.

Apparatus for practicing the invention comprises a means for applying a liquid coating to a moving Web, means for supplying coating to said applying means and means associated with said supply means for continuously and concurrently treating said coating to render the coating liquid free of solid material at said applying means.

The advantages and mode of carrying out the present invention will be more readily understood from the detailed description which follows, reference being made therein to the drawings appended to and forming a part thereof, and wherein:

FIG. 1 is a schematic illustration of one form of the invention, particularly as applied to a cast coating operation.

'FIG. 2 is a schematic illustration of the invention as applied to a blade coating operation whether on or off machine.

FIG. 3 is an illustration in some detail of a preferred form of treating means for the coating.

FIG. 4 is a view partly in cross section showing details of a modification of the invention shown in FIGS. 1-3.

FIG. -5 'isa cross-sectional view of the modification illustrated in FIG. 4 and taken along the line 55 of that figure.

Turning, now, to FIG. 1, it may be seen thatthe invention is applied to a cast coating operation. In this instance, the web W is continuously fed from a source of supply (not shown), passes in contact with an applicator roll 1, thence is'directed by a guide roll 3 upwardly to a nip formed between a press roll-5 and a large casting drum 7. The drum 7 is heated and the coating is dried while in contact therewith to produce a high gloss paper of outstanding quality.

As also shown, applicator roll 1 has its lower surface area immersed in a pool of coating C maintained in coating pan 9. As the applicator rollis caused'to rotate by a suitable drive means (not shown), the peripheral surface of roll 1 will carry coating from the pool C upwardly to the web W. Since the cast coating operation per se forms no part of the invention, the process need not be described in great detail, except to state that coating carried up into the nip between drum 7 and press roll 5 and in excess of that which is adhered to web W, returns to the coating pool C via a suitable bafile arrangement 11.

In ordinary operations, the coating pool C is maintained by supp-lying coating to the pan 9 from a coating preparation system wherein the coating ingredients are formulated and blended and, thence, are pumped or flow to the pan under a regulatory control which maintains the pool C at an adequate level. In the present arrangement, however, coating from the preparation system S, of conventional design, is pumped or flows into va suitably arranged supply line 13, which in this case discharges into a closed loop system designated generally as 10 and which will be described in detail subsequently.

Disposed in supply line 13 is a regulatory valve means 15, of any suitable-type, which valve is adjustedto maintain the supply of fresh coating from system S suflicient to replenish the pool C as coating is carried therefrom to the web W by applicator roll 1.

Also in communication with supply line 13 immediately upstream of its juncture with closed loop 10, is a dilutent supply line 17 also provided with a regulatory valve19. Dilutent, in this case water, from a suitable source is added to the fresh coating to assure proper consistency thereof as it is introducedinto the closed loop system.

It is believed quite obvious that valves 15 and 19 may be simply manually controlled. However, in more sophisticated installations these valves will be monitored automatically via automatic control 20. One form of automatic control 20 is comprised of a strain gauge type which measures by weight the amount of coating in pan 9 and regulates both coating and dilutent supply to the system in response to the weight so measured. Such controllers are conventional and, per se, form no part of the present invention.

The coating, of proper consistency, flows from line 13 to line 21, which along with pump 23, line 25, grinding means 30, line 29, distribution trough 31, coating pan 9 and line 33 forms a closed loop system, as will now be described.

Pump 23 is a variable speed pump and receives at its inlet side both fresh coating from line 13 and coating from pan 9, the latter through line 33, via line 21. The discharge side of the pump is directly connected to grinding means 30. The latter means, which will be described hereinafter, discharges ground coating into trough supply line 29 which, in turn, supplies coating to the distribution trough 31. Coating supplied to trough 31 flows over a Weir 32 into coating pan 9 and forms in said pan the coating pool C in which applicator roll 1 is immersed as previously described. Thus the coating pool C is continuously supplied with fresh coating and also is supplied with a considerable volume of recirculated coating which has passed through the closed loop 10 and has been treated in grinding means 30.

Referring, now, to FIG. 3, the grinding means which, per se, forms no part of the invention but which is essential thereto, is shown in some detail. Essentially, the grinding means is an attrition mill in the sense that the grinding is carried out by rubbing contact of certain grinding media with material. which flows therethrough. As seen in FIG. 3, mill 30 comprises a grinding tank 47 of generally frusto-con ical form having a closed bottom 41 and provided with a side inlet 49. The tank 47 is surrounded by a jacket 50 into which a suitable fluid cooling medium may be circulated via inlet 51 and outlet 53 to control the temperature of the tank and its contents.

The upper end of the grinding tank is open and capped by collection manifold 55. Disposed between the tank 47 and manifold 55 is a suitable screen 59' through which the contents of the grinding jacket must pass to enter manifold 55 and thence pass outwardly therefrom through discharge outlet 61. e

The interior of the jacket 47 defines a grinding chamber and is at least partially filled with spherical grinding elements 63 formed of a suit-able ceramic, steel or other hard material. Also disposed within the interior of jacket 47 is an agitating means, in this case comprised of a vertical shaft 65 provided with a series of horizontally extending agitator fingers or vanes 67 throughout the shaft length within the jacket interior. Preferably the fingers 67 vary in length from top to bottom of the shaft so that their terminal ends are uniformly spaced from the jacket 47 throughout its interior. The top of shaft 65 extends upwardly through the collection manifold 55 and is journaled and sealed therein by conventional bearing and seal means, so as to be rotatably suspended within the interior of jacket 47. Any suitable source of power, in this case an electric motor B, may be used to drive the shaft 65.

By way of example and not limitation, one form of attrition mill quite similar to the described mill and acceptable for use in the invention described herein is illustrated in US. Patent 2,764,359 to Andrew Szegv-ari. In general, the material used for, and the size of, the grinding spheres are described in detail in said patent and the data therein set forth holds valid for the present use of the mill herein described. In any event, it will be seen that coating introduced into jacket 47 via inlet 49 will be intermingled with and crushed and pulverized by the spheres 63 which rub against each other and the jacket 47 as the fingers 67 and shaft 65 are rotated by motor E. The rubbing action and frictional contact between the spherical elements and the material introduced into jacket 47, in this case coating, produces an extremely beneficial grinding of the coating, keeping same fluent and, in addition, having in mind that the coating itself contains abrasive materialsclay-calcium carbonate-it will be seen that any foreign substance, i.e., dried coating, fibers, dirt, etc., will be completely disintegrated and ground into such a fine state as to be, in effect, homogenized into the coating so as to no longer represent a problem when the material is processed back to the coating pan 9.

As has been shown, the coating is discharged at the top of the attrition mill, passing through suitable screening means 59 into collection manifold 55 and thence through outlet 61. The treated material then enters line 29 and is carried thereby to distribution trough 31. Trough 31 is formed, in this case, as an integral part of pan 9 by bending the edge of the pan into a U-shaped channel concurrently forming a weir 32 between the main body of the pan and trough 31. Thus as the coating is discharged into the trough 31, it is caused to flow therealong until the depth thereof exceeds the height of Weir 32 at which time coating flows over the weir into pool C. The purpose of this arrangement is twofold. First, the flow of coating into trough 31 rather than directly into pan 9 prevents undue agitation of the coating in pan 9 as might be the case where the pump pressure was acting to discharge directly therein; there-fore, foaming in pool C is avoided. Secondly, the discharge of the recirculated coating over weir 32 is uniform from end to end of pan 9 thus assuring that there is no localization of the recirculated or fresh coating in pan 9; therefore, the coating carried by applicator roll 1 to web W is a uniform mixture of fresh and recirculated coating.

It is now believed obvious that the system disclosed in association with the cast coating operation of FIG. 1 is also applicable without substantial modification to the blade coating operation illustrated schematic-ally in FIG. 2. Also, as will be apparent, while FIG. 2 illustrates a modification of the system as associated with a blade coating operation, it will be apparent to those skilled in the art that this modified system can readily be applied to the cast coating operation of FIG. 1.

Turning, now, to FIG. 2, it will be seen that like elements of this system have been given like, but primed, reference numerals to those equivalent parts of the system shown in FIG. 1 and, thus, need not be described in repetitious detail. Thus, it Willi be seen that coating from pan 9 is circulated by pump 23" through the loop comprising line 25, attrition mill 30', line 29', distribution trough 31', pan 9 and line 33 back to the pump, as was the case in FIG. 1. However, instead of a casting roll or drum, the pan 9 is extended to support at its trailing edge a blade B forming a nip with backup roll R. Thus, the blade B doctors the excess effluent coating from web W after it has been in contact with the applicator roll 1, as explained fully in aforesaid patent.

In addition to the aforesaid arrangement of the coating apparatus, per se, FIG. 2 differs from FIG. 1 in that fresh or makeup coating is not fed directly into loop 10, but rather it is fed via line 71 and pump 73 directly to trough 31'. In addition, the fresh coating is passed through attrition mill 4i prior to reaching weir 31'. Thus, not only are contaminates in the pool C reduced to an ineffective condition by attrition mill 30, but also the fresh coating is treated by mill 40 before it enters the coating system. This arrangement may be particularly advantageous where the coating preparation system S has been shown to be conducive to the production of contaminated coating or where it is known that one or more of the ingredients of the coating is not of the consistent good quality as may be desirable. Again dilutent and fresh coating may be controlled by valves 15 and 19'. With respect to mill 40, to all practical purposes, it is identical with mill 30, though the size and composition of the grinding spheres 63 may be varied according to the treatment desirable for fresh coating.

Thus it may be seen that the system of the invention may be readily adaptable to any one of a variety of coating operations, cast coating, blade coating, air knife coating, etc., and, further, that modifications in the method are entirely feasible to adapt the invention to varying conditions of application.

As described to this point, both with respect to FIGS. 1 and 2, the method is carried out by a system in which the various components may be located adjacent but not necessarily as a part of the coating apparatus. In FIGS. 4 and 5, however, an apparatus of extremely compact and convenient form is illustrated, which apparatus will now be described in detail.

Referring, now, to FIG. 4, there is shown a modified coating pan 75 having closed

sides

77, 77 within which is disposed a conventional rotating applicator roll 79. The roll 79 is mounted in suitable bearing on seal assemblies 81, 81' and is driven by electric motor 83 or other means as may be desired. The far edge of the pan (as viewed in FIG. 4) terminates in a vertical weir 85 which is disposed between

sides

77, 77 and divides pan 75 from distribution trough 87 having a lateral width coextensive with that ofpan 75. The trailing edge of the trough 87 is extended upwardly at 89 and has fixed thereto a combination baflle and blade support 91.

Suitably mounted on the baffle 91 is a doctor blade which may be of any form, rotating blade, trailing blade, bull-nose blade, etc., but which is illustrated as a rotating doctor blade of the type shown in aforesaid Warner Patis shown in simple form though it will be appreciated is shown in simple form through it will be appreciated that the blade may be mounted in a variety of ways. Too, a backup roll (not shown) may contact the web A to form, with the blade v100, a nip through which the web W passes, which arrangement is also illustrated in said patents and also exemplified in the article, The Chamflex Coater, by C. G. Whelpton, April 10, 1961, Southern Pulp and Paper Manufacturer.

The bottom of the pan 75 slopes from one end wall 77 toward the other end wall 77 and is provided adjacent the latter member with a drain opening 93 which may be provided with a suitable perforated cover 95. The drain 93 has its lower end in communication with a generally cylindrical housing 97 which, as will be described, forms the grinding jacket of an attrition mill 110.

Disposed within the housing 97 is a horizontal shaft 101 generally paralleling the shaft of applicator roll 79, which shaft is suitably journaled at 103, 103- in bearing and seal members carried by

end plates

105, 105" which with jacket 97 form a closed chamber. At least one end of shaft 101 is driven by a suitable motor or equivalent power source 107 so as to rotate at a relatively constant speed which is much slower than the speed of applicator roll 79. The shaft 101 carries a plurality of radially extending agitation bars or vanes 109 spaced along its length. Obviously, as shaft 101 rotates, the vanes 109 will sweep' rotatably through the closed chamber.

The chamber defined by the housing 99 and the end plates 105, 105' is filled with a suitable quantity of spherical ginding elements 111 so that as the shaft 101 and agitation bars 109 rotate, these spherical elements will be agitated or moved relative to one another to produce the type of grinding and smearing action between their surfaces characteristic of an attrition mill. Thus mill 110 serves the same operative function as mills 30 and 30', FIGS. 1 and 2, though in this case mill 110 is incorporated directly into the coating head, so-called, and the coating from pan 75 flows horizontally along the length of the mill 110 instead of vertically therethrough as in the case of mill 30'.

A suitable outlet 113 is provided through the jacket 99 closely adjacent the end wall 105. This outlet'113 is in communication with the inlet side of pump 115. Pump 115 is driven by a suitable-source of power, for example, motor 117, and has its outlet in communication with a suitable conduit 119 which, in turn, communicates via opening 121 with the interior of distribution trough.

Thus coating which is introduced into the coating apparatus will flow over weir 85 uniformly into the pan 75, a portion thereof will be picked up by applicator roll 79 and carried to web W. Meanwhile the remaining portion of coating will flowin the pan 75 toward drain 93 through which it flows into mill 120, is treated, flows out through outlet '113 to pump 115, thence through line 119 to distribution trough 87 from which it passes over weir 85 again to .pan 75.

.For the purpose of adding makeup coating of fresh constituents into the system, the jacket 97 of mill 120 is provided with inlet opening 123 (see FIG. which also is disposed closer to end plate 105' than end plate 105 so that the makeup coating along with recirculated coating is also treated in mill llllbefore it enters pan 75.

As in the case of FIG.' 1, makeup coating is passed by pump through control valve 130. Valve 130 is controlled automatically to supply the demand for makeup coating in response to signals generated by sensing means 113, in this case a level sensing float disposed in pan 75. Valve 133 may also be controlled via sensory means 131 to add a suitable dilutent as the coating is added to the system. The ratio of dilutent to coating added may be preselectedin accordance with experience and prevailing practice.

Also provided for the purpose of controlling temperature of the mill 1'10 and pan 75, and, of course, their respective contents, is a chamber 137 surrounding the bottom of pan 75 and at least a major part of jacket 97. This temperature control chamber is formed by plate members 139, 139' (see FIG. 5) having their upper marginal edges joined with pan 75 as by welding or the like and their respective lower edges similarly joined to jacket 97. The two lateral ends of plates 139, 139' are joined to side plates 141, 141 (see FIG. 4) so that they, with plates 139, 139' and the bottom of pan 75 and the top and sides of jacket 97, form a closed temperature control chamber through which a suitable coolant or heating fluid may be circulated via inlet 143 and outlet 145.

Having described the invention in detail, it will be ap-.

parent that various changes and modifications may oc-"- cur to those skilled in the art. Such changes and modifications are considered within the spirit and scope of the invention which is limited to the extent defined in the following claims. Y

What is claimed is:

1. A method of coating a moving web of material With fluid coatings comprising the steps of supplying coating material to a point adjacent the web, applying a portion of said coating directly to the web, removing from said point a further portion of said supplied coating, said further portion containing agglomerates, subjecting said removed coating to a frictional grinding to reduce agglomerates and contaminating constituents therein, and after said frictional grinding returning said further portion of said coating in a uniformly distributed pattern to the point of application adjacent said web.

2. The method of coating a moving web of material as defined in claim 1, including the further step of supplying fresh coating to the further portion of coating prior to the step of uniformly distributing said further portion of coating to the point of application adjacent the web.

3. The method of coating a moving web as defined in claim 2, wherein said fresh coating is supplied to said further portion of coating prior to the step of frictionally grinding said further coating.

4. The method of coating a moving web as defined in claim 2, including the step of adding a dilutent to said further portion of coating.

5. The method of coating a moving web as defined in claim 4, wherein the steps of adding fresh coating and dilutent are automatically controlled in response to demand conditions of the coating adjacent the Web.

6. A method of coating a moving web with a fluid coating comprising the steps of forming a pool of coating adjacent the web, transferring a portion of the coating in said pool directly to said web, continuously withdrawing at least a portion of said coating from said pool, said last-mentioned portion containing agglomerates, subjecting said last-mentioned portion of the coating to a grinding action to form a ground portion and thereafter returning said ground portion of said coating to a point adjacent said pool and thereafter uniformly adding the ground portion of coating uniformly to the coating confined within said pool.

7. A coating method as defined in claim 6, wherein said grinding step is carried out by subjecting the withdrawn portion of said coating to frictional wiping in contact with moving spherical members of a harder material than the coating constituents.

8. The method of coating as defined in claim 6, wherein additional coating is added to the withdrawn coating responsive to the demand for additional coating existing in said pool due to direct application of a portion of said coating to the web.

9. A combination for coating a :web with a fluid coating comprising a coating means for applying coating to such web and a means for grinding at least a portion of the coating applied to the web and means for circulating coating from said coating means to said grinding means and then back to said coating means after grinding.

10. A combination according to claim 9, wherein said coating system includes pan means and means disposed in said pan means for withdrawing a portion of coating from said pan means and applying said portion to said web.

11. A combination according to claim 10, further comprising means for controllably admitting fresh coating into said means for grinding, and control means responsive to the quantity in said pan means acting on said admitting means,

12. A combination according to claimrll, further comprising means for controllably admitting a coating dilutent ia q sai mean for g inding- 13. An apparatus for coating a moving web comprising a pan, an applicator roll disposed in said pan and in contact with said Web, a distribution trough associated with said pan, weir means disposed between said pan and said trough, outlet means in said pan and inlet means in said trough, means in communication with said outlet means and said inlet means for removing coating from said pan and delivering same to said trough, said means including a grinding means acting on said coating during its passage from said pan to said trough.

14. An apparatus as defined in claim 13, wherein said grinding means comprises a closed chamber, rotatable means in said chamber and a plurality of spherical means at least partially filling said chamber and agitated by said rotating means.

15. An apparatus as defined in claim 13, including inlet means for admitting fresh coating to said grinding means.

16. An apparatus as defined in claim 14, wherein said grinding means is disposed with the rotatable means in a vertical plane.

17. An apparatus as defined in claim 14, wherein said grinding means is disposed with the rotatable means on a horizontal plane.

18. An apparatus for coating paper comprising a coating pan and a distribution trough lying parallel to said pan, weir means interposed between said trough and said pan, an applicator roll disposed in said pan and at least partly immersed in coating supplied to said pan, said pan having a drain outlet provided in the bottom thereof, conduit means in communication with said outlet at one end and having its other end in communication with the interior of an attrition mill, said jacket including a discharge outlet at one end opposite to the end into which said conduit means extends; pump means in communication with said outlet in said jacket and discharging into said distribution trough whereby coating in said pan is circulated under pressure through said mill and discharged after grinding into said trough.

19. A coating apparatus as defined in claim 18, wherein said mill is positioned directly beneath said pan and at least a portion of said jacket of said mill, and a portion of the bottom of said pan are surrounded by a further jacket means defining therewith a temperature control chamber.

20. A coating apparatus as defined in claim 18, wherein said distribution trough is parallel to and coextensive with the width of said coating pan.

References Cited UNITED STATES PATENTS 4/1961 Umbricht 11861O 9/1966 Harada et al 264-37 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,340,090 September 5, 1967 Hoyt Nordeman, Jr.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 34, for "suplied" read supplied column 3, line 38, for "supply" read supplying column 5, line 75, for "willi" read will column 6, line 13, for "line 71 and pump 73" read line 73 and pump at S prime line 58, after "Pat-" insert ent 2,598,733. For simplicity's sake the blade mounting line 60, strike out "is shown in simple form through it will be appreciated"; column 7, line l6,l 1)r "ginding" read grinding line 54, for "113" read Signed and sealed this 3rd day of December 1968.

(SEAL) Attest:

Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. A METHOD OF COATING A MOVING WEB OF MATEIAL WITH FLUID COATINGS COMPRISING THE STEPS OF SUPPLYING COATING MATERIAL TO A POINT ADJACENT THE WEB, APPLYING A PORTION OF SAID COATING DIRECTLY TO THE WEB, REMOVING FROM SAID POINT A FURTHER PORTION OF SAID SUPPLIED COATING, SAID FURTHER PORTION CONTAINING AGGLOMERATES, SUBJECTING SAID REMOVED COATING TO A FRICTIONAL GRINDING TO REDUCE AGGLOMERATES AND CONTAMINATING CONSTITUENTS THEREIN, AND AFTER SAID FRICTIONAL GRINDING RETURNING SAID FURTHER PORTION OF SAID COATING IN A UNIFORMLY DISTRIBUTED PATTERN TO THE POINT OF APPLICATION ADJACENT SAID WEB.