US3051125A - Coating of paper webs and the like - Google Patents

Description

Aug. 28, 1962 E. v. AHARA ETAL 3,051,125 COATING OF PAPER WEBS AND THE LIKE Filed Aug. 15, 1958 2 Sheets-Sheet l INVENTORS HOWARD S. DEGROOT RALPH A. JOHNSON,JR EDWARD V. AHARA CONSTANTINE .1 smLMuKs BYM ATTORNEY Aug. 28, 1962 E. v. AHARA El'AL COATING OF PAPER WEBS AND THE LIKE 2 Sheets-Sheet 2 Filed Aug. 13, 1958 INVENTORS HOWARD S. De GROOT RALPH A. JOHNSO N,JR. EDWARD v. AHARA CONSTANTINE ISTALMUKE BY rm, Kw 2... g4,

ATTORNEYS Patented Aug. 28, 1%62 3,951,125 COATING OF PAPER WEBS AND THE LIKE Edward V. Ahara, Ralph A. Johnson, Jr., Howard S. De

Great, and Constantine I. Stalmuke, Rumford, Maine,

assignors to Gxford Paper Company, New York, N.Y.,

a corporation of Maine Filed Aug. 13, 1958, Ser. No. 754,753 7 Claims. (Cl. 118-603) The present invention relates to the coating of webs f paper and like material, and more specifically to improved arrangements, including method and apparatus, for applying coatings to moving webs, whereby high quality coated surfaces of uniform smoothness may be obtained.

Coating of webs, particularly in the paper industry, has een carried out in a variety of ways, one of the oldest of which is known generally as knife coating. Typical arrangements for knife coating employ a suitable knife or blade, which is pressed against a Web, either unsupported or backed by a roll or belt, for the purpose of spreading a thin, relatively uniform layer of coating material on the web. The coating material is introduced onto the surface of the moving web, prior to the knife or blade, and, as the web moves past the blade, the coating material is metered onto the web surface.

A comparatively recent development in the art of knife coating is represented by the apparatus illustrated in United States Patent No. 2,368,176, to Arthur R. Trist. There, the web to be coated travels around or over a backing roll, provided with a resilient surface, and a knife or blade is pressed resiliently against the web supported by the roll. The blade is disposed at an angle of about 60 with respect to the web surface, with the working edge of the blade pointing in the direction of web movement, and coating material, applied to the web as it travels toward the blade edge, is metered onto the moving web surface by the blade. In some cases, the blade may form, in part, a reservoir for the coating material. A coating apparatus of the general type illustrated in the Trist patent is frequently referred to as a trailing blade apparatus, and the terms trailing blade, trailing blade coater, or the like, as used herein, refer to an apparatus of the general type shown in the patent, as distinguished from other types of blade or knife coaters.

Trailing blade coaters of known design are useful and generally satisfactory for the application to paper webs of coatings of light coat weight (i.e., in the order of 3-5 pounds per side per ream of 3300 square feet). However, notwithstanding a substantial commercial need or desire therefor, conventional trailing blade coaters have not been adaptable for successful utilization for the application of coatings of heavy coat weights (i.e., 7 or more pounds per side per ream of 3300 square feet). Thus, a conventional coater may be employed with relative satisfaction for applying a coating or film of light coat weight. But, if the coat weight exceeds, in any appreciable amount, about 7 pounds per side per 3300 square feet, coating defects, such as surface scratches, streaks, etc., become noticeable and the coated web is usually not commercially acceptable.

Our experimental work has indicated that trailing blade coaters of conventional design are inherently incapable of applying coatings of heavy coat weight in a manner such that the coated web is of a commercially acceptable quality. In this respect, the coating material always contains or acquires small foreign particles, such as grit, sand, fibers, quartz, etc., and such foreign particles are present even where substantial precautions are taken to filter or otherwise remove them, because foreign matter (e.g., fibers) is continually introduced by the moving web. These foreign particles tend to be trapped at or adjacent the working edge of the blade and, when this occurs, scratches or other coating defects will appear. In a coating of light coat weight, the problem of scratches and other defects is comparatively negligible. But such defects are readily noticeable in a coating of heavy coat weight and usually render the coated web commercially unacceptable.

In accordance with the present invention, novel arrangements are provided enabling trailing blade coaters to be utilized elfectively for applying coatings of heavy coat Weight and of a high quality, commercially acceptable nature while at the same time substantially improving the effectiveness of such coaters for the application of high quality coatings of light coat Weight. In this respect, it is recognized that, despite preliminary precautions, undesirable foreign particles will be introduced into the coating material, forming a potential source of coating defects, such as surface scratches, streaks, etc. Accordingly, the present invention deals with the handling of the coating material in such a manner that undesirable foreign particles are effectively minimized, by a continuous filtration of certain portions of the coating material during a coating operation. In addition, recognizing the fact that a period of delay will be incurred between the introduction of foreign particles into the coating material and the subsequent filtration of some or all of such particles, the invention includes novel arrangements for maintaining foreign particles in circulation in the coating material and thereby minimizing the likelihood that such particles will cause defects in the web coating.

In one of its more specific aspects, the present invention provides an improved trailing blade coater incorporating a coating material reservoir of novel design, Which permits a uniform, controlled flow of the coating material in the reservoir, Without eddies or undesirable velocity variations. With the improved reservoir, foreign particles in the coating material are kept in circulation to the greatest practicable extent until they are removed by filtration. Heretofore, forcing particles usually deposited in eddy current areas or precipitated toward the working edge of the blade as portions of the coating material, circulating toward the blade, were caused to undergo a substantial reduction in velocity.

Another specific feature of the invention resides in the provision, in a trailing blade coater having a reservior for holding a supply .of coating material, of improved and highly efiicient arrangements for recirculating portions of the coating material, during coating operations, whereby to maintain foreign particles in the coating material at a practical minimum level. To this end, the invention takes advantage of circulation phenomena occurring during coating operations, whereby the coating material withdrawn for filtration and recirculation is drawn from areas of high foreign particle concentration. In addition, the coating material withdrawn for filtration and recirculation is advantageously taken at a volume rate having a predetermined relation to the volume rate of application of coating material to the web, the relation being such as to assure highly effective filtration and removal of the foreign particles.

Advantageously, the present invention may be incorporated with the invention described and claimed in the co-pending application of Robert C. Brown et al., Ser. No. 754,752, filed August 13, 1958, for Coating of Webs and the Like, executed concurrently herewith and owned by the assignee of this application.

For a better understanding of the invention, reference should be made to the following detailed description, and to the accompanying drawing, in which:

FIG. 1 is an enlarged, fragmentary, cross-sectional enemas 3 view of a trailing blade coater incorporating features of the invention;

FIG. 2 is a simplified, schematic representation of the apparatus of FIG. 1, illustrating arrangements for circulating and filtering coating material; and

FIG. 3 is a fragmentary elevation view of a trailing blade coater incorporating the improved features of the invention.

Referring now to the drawing, the reference numeral designates generally a trailing blade coater apparatus, which may, except as hereinafter described, be of generally conventional construction. The coater includes a backing roll 11, which is mounted for rotation about an axis (not shown) and is arranged to be driven by suitable means (not shown). The backing roll 11 generally includes a cylindrical shell 12 having an outer cover 13 of rubber or other resilient material.

conventionally, the backing roll 11 has associated therewith suitable means (not shown) for delivering thereto a web 14 and removing the web therefrom. The web 14 travels around and with the roll, as the roll rotates, and, in the illustrated arrangement, the web and backing roll are adapted to move in a clockwise direction.

A supporting frame 50 of the illustrated apparatus includes spaced arms 51, on which are slidably supported blocks 52. The blocks 52 have suitable bearing means for rotatably supporting a shaft 15, the frame arms 51 being provided with elongated slots 53 to accommodate the shaft 15 in various positions. The shaft 15 has end portions 54 of non-circular cross-section, which are received in openings of corresponding shape in a reservoir frame 16, the arrangement being such that the reservoir frame 16 is effectively fixed to the shaft 15.

One end of the shaft 15 has keyed thereto an arm 55 adapted to be engaged on opposite sides by adjusting screws 56, 57 and, by appropriate manipulation of the screws, the shaft 15 and reservoir frame 16 may be held in various rotary positions with respect to the blocks 52. One end of the arm 55 may have a pointer 58 thereon cooperating with a suitable scale 58 to provide an indication of the adjusted position of the reservoir frame.

The blocks 52 are movable on the frame arms 51 by means of fluid actuators 59 mounted on the machine frame '50 and connected to the blocks by links 60 and pivoted levers 61, and inward movement of the blocks is limited by adjustable abutment means 62. The abutment means 62 may comprise micrometer-like devices having extendable plungers 63 adapted to engage arms 64 carried by the blocks 52. Operation in unison of actuators 59 on opposite sides of the machine causes the reservoir frame 16 to be moved in a generally radial direction, toward or away from the backing roll 12. And, to assure uniform movement of the opposite ends of the reservoir frame, an equalizer mechanism is provided, comprising links 65, arms 66, and a shaft 67 keyed to the arms 66.

wall 19 which connects the back and bottom walls.

Advantageously, the bottom wall 17 serves as part of a mounting means for holding a blade 20, the blade 20 being engaged at one end by an anchor block assembly 21 adapted for slidable movement in a recess 22 defined by the bottom wall 17 and by a supporting plate 23. The forward portion of the blade 20 passes between the forward edges 24, 25 of the bottom wall and supporting plate, respectively, and projects forwardly and downwardly therefrom a distance determined by the adjustable setting of the anchor block assembly 21. A suitable adjusting screw 26 is provided in the supporting plate 23 and engages the anchor block 21 to effect the desired adjustment of the latter. When the coating apparatus is in operation, the projecting portion of the blade 20 forms part of the bottom wall of the reservoir and the forward edge of the blade, constituting its working edge, is in pressure contact with the web 14.

Advantageously, the blade 20 is supported loosely between the wall 17 and plate 23 to provide for limited floating movement of the blade. By way of example, a clearance of between 0.004 and 0.012. inch may be provided. When the blade is deflected, as shown in FIG. 1, the blade is supported along the front edge of the plate 23 and presses upward against the wall 17 a short distance back from the front edge.

In accordance with usual practice, the reservoir includes end walls or dykes 27 of a suitable size and shape to be received closely between the walls 17-19 of the reservoir and the outer surface of the web passing over the backing roll. The dykes 27 are advantageously provided with means, such as peripheral felts 28, which may be adjustable to some degree, so that the dykes may be fitted in sealing engagement with the reservoir Walls 17-19 and with the web 14. And, in the event the range of adjustment of the dykes is insuflicient to accommodate the various rotary positions of the reservoir, several sets of dykes may be provided in appropriate sizes and shapes to fit properly throughout the desired range of reservoir adjustment.

Although the present invention is not necessarily limited by the characteristics and disposition of the blade 20, the blade is advantageously disposed at an angle of between 40 and 50 (measured from above the blade) to the web 14. The reasons for this are explained in detail in the beforementioned co-pending application, and it is to be observed that the present invention is employed to great advantage in combination with the apparatus of that application. However, it is contemplated that the instant invention may be utilized to advantage in other environments.

Advantageously, the bottom wall 17 of the reservoir has its upper surface 29 disposed at a small angle with respect to the blade 20, so that the cross section of the wall tapers toward its forward edge 24. Thus, in the illustrated arrangement, the bottom wall surface 29 is disposed at an angle of around 7 with respect to the sup ported portion of the blade 20, and the cross section of the wall tapers in a manner such that the forward edge of the bottom wall is of minimum thickness consistent with providing sufficient supporting strength.

As shown in FIG. 1, the back Wall 18 of the illustrated reservoir is disposed at a large angle with respect to the bottom wall 17. The appropriate angle between the walls will vary, depending upon the range of blade angle to be used and, in the illustrated apparatus, the angle is approximately 130. The arrangement is such that the back wall extends in a generally upward, though not necessarily vertical, direction.

In accordance with one of the important aspects of the invention, the spacing between the backing roll and the walls of the reservoir, at any level, is less than the spacing at any higher level. Accordingly, where the back wall 18 is formed of a substantially flat plate, as in the illustrated apparatus, the lower edge of the back wall lies at an angle A of not less than measured from inside the reservoir, to the radius line R extending from the rotational axis of the backing roll 11 to the lower edge of the back wall. At the same time, the angle A should not substantially exceed 90, for reasons which will become apparent. Accordingly, where the reservoir is capable of rotational adjustment through a range of operative positions, the back wall 18 should lie at an angle of not less than, but not substantially more than, 90 to the radius line R when the reesrvoir is adjusted in a counterclockwise direction to the limit of its operative range. When the reservoir is adjusted clockwise from the above described limit position, the angle will, of course, be increased somewhat, by an amount equal to the clockwise adjustment. The operative range of adjustment is usually such, however, that the angle A is not substantially greater than 90 at any time.

The back and bottom walls of the illustrated reservoir are advantageously connected by a transition wall 19, which is of arcuate shape, having a relatively large radius of curvature and arranged to merge with the back and bottom walls in substantially tangent relation, whereby to provide a smooth, unbroken transition between the angularly related surfaces of the back and bottom walls. Alternatively, the reservoir may be formed of a single, continuous, curving wall having, in effect, bottom and back portions and arranged to provide an unbroken surface for the smooth flow of coating material. In any case, the relationship of the rservoir wall to the backing roll should be such that, at any level, the spacing between the backing roll and the Wall is less than the spacing at any higher level. For the purposes of the present description, the term unbroken surface is used to distinguish from a configuration of angularly related surfaces meeting at a sharp corner.

Although it is not intended that the scope of the present invention be limited by the specific dimensions herein stated, in a coating apparatus having a backing roll of about 40 inches in diameter, the radius of curvature of the transition wall 19 may advantageously be in the order of 4 inches or more, while the back and bottom walls are around inches and 5 inches respectively.

The improved reservoir configuration described above has several important advantages. Thus, when the coating apparatus is in operation, the web 14 moves at high speed along one side of a body of coating material contained in the reservoir. The friction between the web and the coating material tends to cause layers of the material adjacent the web to move in a downward direction and thereby sets up a circulation of the coating material in the manner indicated generally by the arrows in FIG-'1. In prior apparatus the reservoir configuration did not provide for a cross section of the reservoir at any horizontal level to be less than the cross section at any higher level and for this reason eddy currents were set up in the circulating color at points of velocity variation. This reulted in precipitation or depositing of foreign particles present in the coating material, with the result-that a large proportion of the particles found their way tothe Working edge of the blade. The new reservoir configuration, on the other hand, substantially eliminates undesirable eddy currents and velocity variations, so that the foreign particles are kept in circulation to the greatest practicable extent. At the same time, the new configuration, in which the back wall 18 approximately follows the contours of the backing roll 11 'and is spaced therefrom a relatively short distance, provides fora relative volume of the coating material in the reservoir, so that foreign particles introduced into the reservoir may be disposed of with greater facility.

In accordance with another important aspect of the invention, improved arrangements are'provided for recirculating the coating material through appropriate filter means, during a coating operation, whereby to remove, to the greatest practicable extent, foreign particles introduced into the coating material during the operation. To this end, the invention takes advantage of circulation phenomena which we have observed, that foreign particles in the coating material tend to migrate in a spiral course, during operation of the coater, toward the ends of the reservoir and, in somecases, also toward other localized areas, depending uponthesize and shape of the reservoir and upon such factors as web speed, consistency of the coating material, etc. Thus, means are provided'adjacent the ends of the reservoir and at: other-areas of particle concentration for withdrawing portions of the circulating coating material and flowing the withdrawn coating material through appropriate filter means to remove foreign particles therefrom. The improved arrangement provides maximum efiiciency in'the removal of foreign particles, since the coating material withdrawn for filtration and recirculation to the reservoir is taken from areas of naturally high foreign particle concentration.

Referring specifically to FIG. 2 of the drawing, the reservoir of the illustrated apparatus is provided, adjacent each of the dykes '27, with outlet openings 30, which enter the back of the reservoir slightly above the level of the bottom wall 17. Appropriate tubes or conduits 3-1 communicate with the openings 30 and join with a conduit 32 leading to the intake of a pump 33. The pump 33 discharges through a conduit 34 into a suitable filter 35, and the filter 35 discharges into a return tube or conduit 36. In the'illustrated apparatus, the return tube 36 is connected to separate return tubes 37 leading to openings 38 in the back wall of the reservoir, whereby the recirculated, filtered coating material my be discharged into the reservoir.

In cases where the reservoir is of substantial width, it may be advantageous to provide one or more additional openings, such as the outlet opening 39, for withdrawing some of the color from areas spaced from the reservoir end walls. The optimum number and location of recirculation outlets may vary with reservoirs of different sizes and shapes, but may be determined readily by empirical methods. Thus, areas of particle concentration, in addition to the end areas of the reservoir, may be determined by introducing into a supply of coating material a quantity of foreign particles, such as sand, fibers, etc. Areas of concentration may be determined by observing the location, on the coated web, of surface defects. The foreign particles may also be distinctively colored, if desired, so that their presence in the supply of coating material or on the coated web is readily ascertainable. Generally, coating'apparatus is adaptable for the accommodation of webs of various widths, in which case the reservoir is advantageously provided with a plurality of outlet openings 39 (FIG. 2) which may he used or plugged on a selective basis, so that optimum operating conditions may be afforded under most circumstances.

In some instances, it may be desirable and advantageous to operate the coating apparatus with the end dykes 27 r,e moved from the reservoir, in which case the coating material is simply allowed to flow out of the ends of the reservoir, into suitable collector means (not shown), from which the material is drawn to the pump 33. When the end dykes are removed, the outflow of material at the ends of the reservoir is utilized to eflfect the eificient removal of foreign particles which would otherwise tend to concentrate =at.the ends, although additional withdrawal outlets may be utilized at other areas of concentration, if any, near the center of the reservoir.

The location of the inlet openings 38 is not deemed to be of particular importance. However, it is usually advantageous to locate the inlet openings near the center portions of the reservoir and adjacent the top level of the coating color. l

In order to achieve effective filtration of the foreign particles in the coating material, recirculation of the material through the filter 35 and back to the reservoir should take place at a rate appropriately related to the rate at which foreign particles are introduced into the reservoir. Accordingly, as one of the specific aspects of the invention, the recirculating system, including the pump,33, is of such capacity as to enable color to be withdrawn for recirculation at a rate not substantially less than, and advantageously several times as great as, the volume rate at which the coating material is applied to the moving web 14. v Withdrawal of coating material at this rate, from areas of high foreign particle concentration, provides for highly efiicient particle removal from the coating material supply.

As will be readily understood, as coating material is applied to the moving web, during operation of the coating apparatus, additional material must be supplied to J scopeof the invention,

' the reservoir tomaintain the desired head. of material therein. In, the illustrated system, the make-up material is provided from a supply source 40 arranged to discharge into the line 32 leading to the intake ,of the pump 33.

tageously, the ratezof introducing'make-up material is r 'so adjusted as tomaintain the coating material. in the reservoir at a minimum level consistent with providing adequate. contact between-the material and the moving web. The optimum level will vary with such factors as machine speed, viscosity, etc., and may be determinedi by visual, observations.

The new method and apparatus are highly advantageous, in. that the coating webs may be carried out in environment which is as free as practicable of foreign particles. Accordingly, extended coatingdefects here tofore caused by the lodgingrof foreign particles in and around 'theworking edge of theblade are substantially minimized, and 'coati'ngs of higher quality and greater coat weight may he applied' While it is contemplated that the method and apparatus of the present invention may be incorporated in" coating apparatus of various types, significant advantages are realized when the teachings of thepresent invention are applied in combination with the apparatus described and claimed :in' the beforementio ned' co-pending application: The combined inventions permit the successful application of highquality web coatings of heavy coat weights substantially free of scratches, streaks, etc., which have been unobtainable heretofore with trailing blade coating apparatus. For further discussionof the advantages ofthe combined inventions, reference should be made to the said co-pending application.

It shouldbe understood that the invention, as specifitherein without departing from the clear teachings of the disclosure. Accordingly, reference should be made, to the following appended claims in determining the full 7 What is; claimed is:

lQIn a trailing blade coater for app1ying-a-coating layer directly to a moving web and comprising a websupporting'backing'roll about which a web is passed,,a

reservoir placed against the backing roll for holding a i supply of coating materialpand a blade forming in part a wall .of said reservoir and engaging a web moving 7 around said. rolL; the; improvement characterized by said reservoir comprising abottom wall disposedat an angle to said backing roll, a back wall-L disposed at an obtuse angle to said bottom wall" andextending upward therefrom, and a transition wall joiningsaidback andibottom walls and merging. into substantially tangent relation H thereto, said" transition Well being of arcuate, form. and having a large radius of curvature, said botom, transition and back walls being so related and soariangedlw ithrer spectto said backing roll that the; spacing betweenlsa id backing roll and the wallsl of said" reservoir at any level is; less than the spacing at any higher level', andr'duct means 'ent'ering said reservoir at preselected points for r removal of coating. material"from areas surrounding said preselected'points. 1 V V a 1 2.1 1 aftrailing blade coater for applying a. coating layer directly to a moving web, and comprising a weba' wall of said reservoir and' engaging a web moving reservoir comprising means including saidblade forming a bottom wall, and a back wall extending downward toing material from areas surrounding said preselected points. V

3 Thecoater of claim 2, in'which said reservoir isadjustable about an axis parallel to the backing roll axis, for varying the angle, of said blade with respect to sa d web, an'd said reservoir has one operative limit of adjustment in- Which said back wall lies at an angle. of not less than 90 to said radius line and a second operative limit position in which said back wall lies at an angle of not substantially more than 90 to said radius line.

4. In a trailing blade coater for applying a coating layer directly to a moving web and comprising a web-supporting backing roll about which a web is passed, a reservoir placed against the backing roll for holding asupply of coating material, and a blade forming in part' a wall of 7 said, reservoir and engaging a Web moving around said ca-lly described herein, 'is intended to be'repre'sentativer i only, as certain changes and variations may be made roll, the improvement: characterized by said reservoir comprising meansformingt bottom and back walls extending outward and upward from said-blade,-said wall forming means forming a'substantially' unbroken surface along which circulating coating material may flow, and said wall forming means being so arranged and disposed with respect to said backing roll that the'spacin'g between said ,backing roll and the walls of, said reservoir at any level is less than the spacing at anylhigher level, and duct means entering said reservoir at preselected points for removal of coating material from areas surrounding said preselected points. 7 a a,

7 5. In a'trailing blade coater for applying acoating, layer directly to amoving web and comprising; a Web-support ing backing roll, about which, a webis passed, a. reservoir o placed againstjthe backing roll for holding a supply of a supporting backing, roll about which a web is passed, a r reservoir placed against the backingfroll for holding a supply of coating material, and a blade forming in part coating material, and, ablade formingjin part, a'wall of said-reservoir and; engaging a webhmoving around said roll,v the improvement characterized, by saidreservoir comprising means including; saidblade-forming a bottom wallqdisposed at an 'an'gl'e'to. saidibacking; roll, and means forming a, back wall extending upward from said. bottom wall forming; means, said back, wall following approximately the. contour of saidbacking, roll and being, spaced therefrom at any level a distance. no greater than the spacing; atany higher level, and duct meanssentering said reservoir; at, preselected pointsffor removal of coating material from areas surrounding: said preselected points. a

V 6. The improvement. of clainr 5., iniwhichsaid'bottom and back wall formi'ngmeans are relatively'iiatrwallpor tions disposed atan obtusefang'le, and altransition wall connects therespective wall'forming-mean's, said: transition wall -being of arcuate shape. and: having a large radius of curvature; r i i 7; The. improvementof claini5; which includes: filter meanslconnectedin said duct for removal" of foreign particlessfrom coating material flowing therethrough, and

means for circulating said coating material in said 'duct means. v p r V i References Cited inthe, fileof this patent V UNITED STATES PATENTS 1,993,055? Gerstenberg Mar.,5, 1935 $2,328,183 7 Barrett Ailg; 3-1, 1943 2,399,688" Metzfler et a1. May;7, 1946 [2,649,758? J COWgil1 ,Au'g. ,25', 1953

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