US3889018A

US3889018A - Method of simultaneously coating the opposite sides of a paper web

Info

Publication number: US3889018A
Application number: US384689A
Authority: US
Inventors: Richard J Quint
Original assignee: Ethyl Corp
Current assignee: Ethyl Corp
Priority date: 1973-03-16
Filing date: 1973-08-01
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10

Abstract

A method for simultaneously coating the opposite sides of a paper web which involves employing an opposed blade coating system. Wet coating material is applied to the opposite sides of the web, the wet coated web is passed through the nip of a flexible blade unit comprised of a pair of blades having flat bevelled working surfaces engaging opposite sides of the coated web in opposed relationship with each other for metering the layer of coating on the opposite sides of the web, and thereafter the coated web is dried.

Description

0 United States Patent 11 1 1111 3,889,018 Quint 1 June 10, 1975 [54] METHOD OF SIMULTANEOUSLY 3,001,219 9/1961 Miller 15/245 COATING THE OPPOSITE SIDES OF A g a 1 1 1 rown eta. l3 PAPER WEB 3,078,825 2/1963 Munton et a1.. 118/413 [75] Inventor: Richard J. Quint, Dixfield, Maine 3,119,138 11/1964 Davis 15/245 3,187,718 6/1965 COghill..... 118/126 [73] Ass1gnee: Ethyl Corporation, R1chmond, \la. 3,190,263 6/1965 Bslak u [18/101 22 d: A 1, 3,230,928 Stalmuke 1 3,241,521 3/1966 Labombarde... 118 122 [21] Appl. No.: 384,689 3,251,339 5/1966 Whitfield 118/122 3,260,577 7/1966 Mayhew 29/1835 Related Appllcamn Data 3,477,149 11/1969 Wagner 15 245 [60] Division of Ser, No. 341,928, March 16, 1973, which 3,489,592 11/1970 wallsten 117/68 is a continuation of Ser. No. 82,475, Oct, 20, 1970, 3,575,134 4/1971 Quint 118/122 abandoned, which is a division of Ser. No. 703,924,

Feb. 8, 1968.

52 us. c1. 427/209; 118/122; 427/356 51 161.0. B056 11/02 [58] Field 61 Search..... 117/68, 68.5, 102 L, 111 R,

References Cited UNITED STATES PATENTS Jones 117/64 Seidell et a1. 118/122 Charch et a1. 118/65 Boyer et a1. 117/111 Forse 118/103 Nokes 118/121 Kierspe 118/122 Friedman 118/122 Knight ct a1. 118/68 Slavin 15/245 Brough 1 15/245 Faulkner.... 118/121 Paquette 118/405 Wolfe et al. 117/68 Oganowski 117/68 FOREIGN PATENTS OR APPLICATIONS 498,002 12/ 1938 United Kingdom 548,632 lO/l942 United Kingdom 741,371 11/1955 United Kingdom 7 639,538 12/1936 Germany 1,224,601 9/ 1 966 Germany Primary ExaminerMichacl Sofocleous Attorney, Agent, or Firm-Donald L. Johnson; John F. Sieberth [5 7] ABSTRACT A method for simultaneously coating the opposite sides of a paper web which involves employing an opposed blade coating system. Wet coating material is applied to the opposite sides of the web, the wet coated web is passed through the nip of a flexible blade unit comprised of a pair of blades having flat bevelled working surfaces engaging opposite sides of the coated web in opposed relationship with each other for metering the layer of coating on the opposite sides of the web, and thereafter the coated web is dried.

14 Claims, 6 Drawing Figures PATENTED JUH l 0 I975 SHEET I'll L IWU SHEET PATENTED JUN 10 I975 PATENTEDJUH I 0 I975 SHEET INCREASING PRESSURE METHOD OF SIMULTANEOUSLY COATING THE OPPOSITE SIDES OF A PAPER WEB REFERENCE TO RELATED APPLICATIONS This is a division of my prior copending application Ser. No. 341,928 filed Mar. 16, 1973, which is a continuation of application Ser. No. 82,475 filed Oct. 20, 1970 and now abandoned. which in turn is a division of application Ser. No. 703,924 filed Feb. 8, 1968. now US. Pat. No. 3,575,134.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to paper web coating systems and more particularly to a coating system for simultaneously coating the opposite sides of the paper web.

2. Description of the Prior Art In the production of paper, it is oftendesirable to apply a coating to the opposite sides of the paper when it is in web form and before cutting into sheets. Different types of coating apparatus are available for producing such coated web; however, presently available equipment is not altogether satisfactory as far as efficiency and versatility of the machinery and the quality of the coated paper is concerned. A primary source of difficulty in obtaining quality coated paper with presently available equipment resides in the mechanism used for doctoring the layer of coating as applied to the paper. Desirably, the coating on the final product should completely cover the paper fibers on both sides of the web and be uniform in thickness and coat weight throughout. Also, depending on the type of base sheet being run through the coating apparatus and the particular characteristics desired in the final product, different coating materials having varying properties will be required. With presently available coating apparatus, the conventionally constructed doctoring mechanisms impose various limitations on both the operating versatility and efficiency of the equipment and the products which it is capable of producing.

In the typical size press, for example, the thickness of the coating is controlled by passing the web between a pair of rotating doctor rolls. These rolls, which are relatively large in size so as to withstand the pressure created and to present an even nip for the incoming paper, create certain forces acting on the liquid coating material tending to disrupt the evenness of the final coating on the web. More particularly, the coating tends to neck down and stay with the rolls as the web exits therefrom to produce what is called a film split pattern. This action is more prevalent when higher coat weights are applied to the web; and in order to produce a quality coating of the web, the coat weight of the coating has to be kept relatively low. As a practical matter, these coat weights are not greater than 4 or 5 pounds per ream on each side of the paper; with attempts to attain higher coat weights resulting in unacceptable coatings having uneven thickness and surface patterns. Even with these coat weights of 4 to 5 pounds, some substantial amount of the coating material on the final product will be impregnated into the paper rather than adhered to its surfaces. This is due to the pressure created on the coated paper by the doctor rolls. Because of this, coated paper produced in a size press will not be of the same high quality as would be a coated'paper with the same coat weight but with the coating material substantially all adhered to the surfaces of the paper,

Also, because of the large size of the doctor rolls typically employed in a size press, the speed at which these rolls are driven and thus, the speed atwhich the web can be fed through the machinery is limited. In a conventional size press, the maximum acceptable speed of the web is about 1200 ft. per minute. Higher speeds of the web create problems in properly applying the coating to the web, with the doctor rolls tending to cause splattering of the coating material.

In addition to these limitations as to coat weight and web speed, size press units are usually best suited for coating paper webs with coating materials having no more than about 45% solids content. With higher solids content, more undesirable coating patterns are produced on the final product. The above-discussed operating characteristics of the conventional size press limit its versatility and thus the variety of coated paper products capable of being produced thereby.

In the conventional blade coating apparatus employing a steel doctor blade for scraping off excess coating, the coating of the opposite sides of the web iseffected in two successive single coating operations. This, in turn, requires that the web be dried after the first coating operation, before the web is coated on its other side, and then dried again after the second coating operation and before the web is further processed. This not only affects the ultimate cost of the finished product due to the very nature of the coating process; but also requires that considerable area be provided for installation of the necessary equipment. Also, the operating versatility of such'equipment is not completely satisfactory. For'example, such equipment is only suited for operating at web speeds above 600 to 800 ft. per minute and usually at speeds above 1,000 ft. per minute. In some coating applications, however, it is desirable to run the web through the coater at speeds below these values. These lower speeds may, for example, be found desirable with certaincoating materials in order to produce quality coating. With the conventional blade coating apparatus using a steel trailing blade, speeds'much lower than 1,000 ft. per minute result in lower quality than that obtained at speeds over 1,000 ft. per minute since at these lower speeds, the conventional blade coater cannot effectively control the coat weight of the coating.

SUMMARY OF THE INVENTION In accordance with the teachings of the present invention, there is provided a coating apparatus having a wider operating range than conventional devices. More particularly, with applicants coating system, web speeds in excess of 1,400 ft. per minute and web speeds below 600 ft. per minute may be used to thus permit the selection of a wider range of base sheets and coating materials. In addition, generally higher coat weights may be applied to opposite sides of the web than with conventional equipment, and coating materials having a wider range of solids content of pigment and adhesive may be used. For example, higher coat weights may be applied at lower solids content than is possible with conventional coating apparatus. By being able to use coating materials having varying characteristics and properties and by being able to selectively change the operating conditions of the coater, a wider range of high quality coated products can be produced.

Generally, the coating apparatus employed with applicant's coating system includes suitable means for applying a layer of coating to the opposite sides of the web, feeding means for feeding the coated web away from the coating station and through a metering station, and a drying station through which the web is then fed to dry the coating. In the metering station, there is provided a pair of metering blades engaging against the opposite sides of the coated web; and in accordance with the teachings of the present invention, these metering blades are constructed of flexible material and are each provided with a flat bevelled working surface for engagement with the coated web. The blades themselves extend freely from a support means on opposite sides of the web and at an acute angle relative to the movement ofthe web therebetween. This angle of extension or head angle of the blades and the angle of bevel of the individual blades is so chosen that positioning of the blades in opposed relationship with each other will cause their bevelled working surfaces to oppose each other and establish at least a partially flush engagement along their bevelled surfaces with the opposite sides of the coated web.

As compared to conventional coating apparatus where the doctoring mechanisms have a more or less line contact or at best a very limited area of contact with the coated web, the flat bevelled working surfaces of the opposed metering blades of the present invention engage against the opposite sides of the coated paper over a substantial area thus decreasing the pressure needed to effect a proper control of the coating application. Accordingly, the opposed blades of the present invention function to actually meter and smooth the layer of coating applied to the opposite sides of the paper rather than to merely remove excess coating with a scraping action. In addition, the construction and orientation of the opposed blades are such as to minimize wearing thereof and thereby increase their operating life to about four times that of the steel doctor blades used in conventional blade coating apparatus. Also, with the present invention, the coating is advantageously applied to the opposite surfaces of the paper without the undesirable impregnation of the coating material into the paper as occurs with conventional coating apparatus.

Generally, a higher quality coated paper can be produced with the coating system of the present invention; and by controlling such variables as the amount of extension and the angle of extension of the blades and by using blades having different flexing characteristics and bevelled working surfaces and by varying the pressure urging the blades against the opposite sides of the web, a wide variety of high quality coated paper may be produced under selected operating conditions of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of the improved coating system of the present invention;

FIG. 2 is an enlarged view of the opposed blade doctor mechanism shown in FIG. 1;

FIG. 3 is a cross-sectional view of one of the doctor blades shown in FIG. 2;

FIG. 4 is an enlarged view ofa pair of opposed doctor blades of the present invention showing their relative positioning with respect to the coated web;

FIG. 5 is a cross-sectional view of the blade holder shown in FIG. 2; and

FIG. 6 is a graph representing the affect of certain variables on the coat weight of the coated paper produced with the coating system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. I, the coating apparatus of the present invention generally includes a coating station I having a pair of applicator rolls 2 for applying coating material to opposite sides of the web being fed therebetween. The rolls 2 are rotatably mounted in associated troughs 3 in which the coating material to be applied to the web is contained. The web of paper to be coated, designated at 4, is supplied from a supply roll 5 rotatably mounted on suitable means, not shown. As the web is fed from the supply roll, it is initially directed around a guide roll 6 and fed in an upward, vertical direction through the coating station. A metering station 7 is disposed above the coating station 1; and above this, there is a drying station 8 having suitable drying devices such as infrared burner units 9 and steam can dryers, one of which is shown at 9'. For feeding the web through the coating apparatus, the steam can dryers are advantageously driven by a suitable motor, not shown.

In accordance with the teachings of the present invention, an improved metering mechanism is provided for metering the coating material applied to the web. As most clearly seen from FIG. 2, the improved metering mechanism of the present invention is constructed for operation under various positions of adjustment. More particularly, this mechanism includes a pair of opposed metering blades 10 for engaging against the opposite sides of the coated web, blade holders 11 for clamping the blades at a point rearwardly of their free working ends, slidable carriages 12 for mounting the blade holders in selected angular positions, and pneumatic piston-cylinder units 13 for urging the metering blades into selected opposed engagement with the coated web.

The presently preferred blade holders 11, one of which is shown in FIG. 5, include opposed clamping members 14, 15 extending the length of the blades across the web to be coated. The clamping members provide a hollow interior in which a blade cartridge 16 is removably disposed; and the cartridge itself is constructed of two halves removably connected together by suitable means (not shown) for holding the blade 10 therein. In order to assure an accurate, parallel alignment of the blades 10 with the coated web and to compensate for any irregularities in this alignment that may be caused due to theclamping members, the blades 10 are resiliently rather than rigidly mounted in their associated cartridges and in spaced relationship relative to the walls 14' and 15' of the clamping members 14 and 15. In the presently preferred construction, the resilient mounting of the blade within the clamping members and cartridge is accomplished by providing an insert 17 of the same flexible material as is used for the blade; this insert being positioned on the side of the blade facing the coated web to be metered. Therefore, upon engagement of the blade with the coated side of the web and flexing thereof as more fully described below, the rear end of the blade will tend to become bowed into the flexible insert and the surface of the blade facing away from the coated web will move into non-rigid engagement with the edge of the blade clamping member at the outer extent of its wall surface 15. With this construction, the opposed blades willpresent substantially parallel surfaces engaging opposite sides of the coated web and thereby produce an even metering and smoothing of the coating on the paper.

A further advantage of the blade holder as shown in FIG. 5 resides in the construction of the cartridge unit 16. As indicated above, the cartridge is'removably positioned in the hollow interior of the clamping members. Thus, the bladesmay be secured to the cartridge at a point remote from the coating apparatus and be ready for quick placement within the clamping members when it is desired to change blades because of wear or to substitute a'blade of differentconstruction for a particular coating operation. In addition, the cartridge-is provided with a plurality'ofshims 18, 18' at the ends of the insert with the shims l8 supporting'the rear end of the blade. With this construction, a blade having a worn working surface'may be reground and reinserted into the cartridge with the same length of extension from the blade clamping members as the length of extension of the original, new bladel This is readily efsetting for the blades has been determined, these stops may be positioned in the appropriate location along the tracks 24 to accurately align the blades relative to the path of movement of the web through the metering station.

In accordance with the teachings of the present invention, the metering blades 10 are constructed of flexible material. A material found admirably suited for this purpose is polyurethane such as that manufactured under the tradename ISOTHANE by The Carborundum Company. This material is of medium softness having a durometer hardness of 95 Shore A and a P and J (Pusey and Jones) plastometer value of 20. Other polyurethanes such as the harder polyurethane having a durometer hardness of 70 Shore Dand a P and J plastometer value of 4 and the softer polyurethane having a durometer hardness of 90 Shore A and a P and J plastometer value of 27 have also been found suitable especially where one of these blades is used in combination with a polyurethane blade of medium softness. Further properties of these polyurethanes are set out in Table I, below.

TABLE I Specifications of Polyurethane Material fected by removing one ormore of the shims 18 and adding a corresponding number of shims 18' of the same thickness. Also, the inclusion of these shins l8, 18 provides a convenient means by which the blade extension of any blade, new or reground, may be adjusted accurately within a limited range.

For permitting adjustment of the angle of extension or head angle of the opposed blades relative to the web passing through the metering station, the base of each blade holder 11 is rotatably secured to a support shaft 19 about which it may be rotated. The angular position ofthe blade holders is controlled by a pairof adjusting screws 20, each of which is pivoted to an upstanding support assembly 21 of one of the carriages l2 and threadedly received through an arm member 22 fixed to the base of the blade holder associated with the carriage. Accordingly, rotation of the screws will cause an angular adjustment of the blade holders; and for indicating the angle of extension at which the blades-are set, suitable scales 23 are provided.

For setting the metering blades in opposed engagement with the coated web, the cariiages '12 aremoved horizontally along g'uide tracks 24 'on which they are slidably mounted. Movement ofthe carriages is,'in turn, controlled by the pneumatic piston-cylinder units 13 to which they are attached. Adjustable stop members are provided so that once a particular angular In addition to these polyurethane materials, such materials as Nylon, Teflon and polyethylene having operating characteristics equivalent to those of the polyurethane, as morefully described below, are suitable for use as metering blades in the present invention. Also, certain rubber materials may be suitable although generally rubber would not have the same long wearing properties as polyurethane.

In constructing the metering blades for use in the coating system of the present invention, different angles of bevel ranging from 30 to 50 and different thicknesses ranging from A to /2 inch have been found suitable. In FIG. 3, the presently preferred construction of a polyurethane blade having a durometer hardness of 95 Shore A is shown. The thickness of the blade is inch and the angle of bevel of the working surface is 40. In addition, the blade is provided with a back surface 27 adjacent the leading edge of its working surface 26. This back surface has a total area which is a small fraction of the area of the working surface and is formed by tapering back the leading edge of the working surface at an angle of about or An alternative construction of the back surface of the blade is shown in dotted lines in FIG. 3. Here the back surface is divided into two segments 27' and 27". The particular construction chosen will depend mainly on the thickness of the blade. The creation of this back surface increases the thickness of the blade at the leading edge of the working surface. thus lessening imperfection due to wear along this edge and improving the coating characteristics of the web. A blade having a working surface with a thin feathered edge. as opposed to the blunt tip construction shown in FIG. 3, may tend to be too flexible and therefore non-responsive to pressure variations urging the blades against opposite sides of the web. Also, such thin edges on the working surfaces of the opposed blades tend to vibrate as the web is fed therebetween and wear rapidly to produce a ragged contour and-thus an irregular coating pattern.

In fixing the opposed blades in opposed working operation, the angle of extension of each blade, that is, the angle at which it extends from the blade holder as measured from the vertical path along which the web moves, is set at a value greater than the angle of bevel of its working surface so as to effect an initial toe-to-toe engagement of the blades with opposite sides of the coated web. With the blade construction of FIG. 3, the angles of extension ranging from about 40 to about 60 have been found suitable. Preferably, the amount of extension of the blades is between inch and l /2 inches.

As shown in FIG. 4, the blades are urged toward each other with a force sufficient to cause flexing thereof and to thus bring their working surfaces into at least a partially flush engagement with the opposite sides of the coated web. The amount of flexing is controlled by the setting of the stops and the setting of the pressure exerted by the two pneumatic piston-cylinder devices 13. Suitable pressure settings for producing the desired amount of flush contact of the blades with the coated web have been found to range from about 8 to psi gauge. The pressure exerted by the pneumatic piston-cylinder devices is in the horizontal direction. Due to the flexing of the blades, however, as they engage the opposite sides of the coated web, there is a component of force produced which is in a direction extending along the path of movement of the web; and therefore, the resultant force acting on either side of the coated web is in a direction extending at an acute angle to the path of movement of the web.

In setting the coating apparatus of the present invention for operation, there are two ultimate factors which can be varied by adjustment of the flexible opposed blade unit to vary the coat weight of the final product, these being the area of flush contact of the working surfaces of the blades with the opposite sides of the coated paper and the pressure per unit area exerted by these working surfaces against the opposite sides of the paper. These two ultimate factors are, in turn, dependent on certain secondary characteristics of the blade unit, namely the blade material, blade thickness, amount of blade extension, angle of blade extension and air cylinder pressure provided by the units 13.

Generally, an increase in air cylinder pressure causes the opposed blades to deflect. This deflection brings the blade bevels from toe-to-toe position towards flush position and thus increases the area of blade coming in contact with the web. The increase in air cylinder pressure tends to decrease the coat weight while the simultaneous increase in surface area of the blade contact with the web tends to increase coat weight. The actual coat weight obtained is the resultant of these two effects. When the flush position is reached, further increase in pressure decreases the area of contact because it moves from flush to a heel-to-heel contact and away from the toe. FIG. 6 shows the effect of area of contact and pressure on the final coat weight of the paper. The line ABC represents the drop in coat weight with increase in air cylinder pressure if the area of blade contact with the web would have remained constant. The graph AEFG shows the increase in coat weight due to increase in area of contact with the web if the air pressure would have remained constant. AHJK represents the resultant curve representing the resultant coat weight against air pressure.

When the bevels of the blades approach a full flush position, the rate of increase in area of contact with the web increases at a higher rate than a unit increase in air pressure and thus the curve AEFG is shallower first and it becomes increasingly steep. When the full flush position is reached, the further increase in air pressure causes the blades to ride on the heel only with subsequent reduction in contact area with the web and thus the graph PO is shown dropping back. The rate of decrease in coat weight due to increase in pressure remains constant while the rate of change in coat weight due to the change in contact area of bevels does not remain constant, and thus the resultant curve AHJ K.

Thick blades or lower blade extension or higher head angles (i.e., angle between the head and the vertical web) or combinations of all three gives lower blade flexibility and the shape of the curve AEFG will be replaced by curve ALMN, which is shallower for a wide range of air pressures and thus the new resultant coat weight decreases for a wider range of pressures. Thinner blades, higher extensions and lower head angles tend to give the curve APQR in place of curve AEFG. In this case, the area of contact with paper increases very rapidly and the heels are reached at lower air pressures. In a coating operation, the blades may be set anywhere between toe-to-toe and heel-to-heel relationship. Generally, with coating materials having higher solids content, less area of contact is required to produce a given coat weight. Here, the blades would near a toe-to-toe relationship. Conversely, with coatings having lower solids content, the opposed blades would be set nearer a full flush engagement with the opposite sides of the coated paper to produce a given coat weight.

By selecting blades having particularly physical characteristics and by selecting different operating conditions for the blade unit, a wide range of coated products having coat weight characteristics superior to the products of conventional coating apparatus can be produced. In addition, the coat weight of the final product can be varied by changing the solids content of the coating material and the speed at which the web is run through the opposed metering blades.

Representative results of tests run under various operating conditions of the coating apparatus of the present invention are set out in Table II and Table III below. The coat weights are a measurement of the coating on both sides of the paper and are given in pounds per book paper ream of 500 sheets of 25 inches X 38 inches. Also, the blade materials in Table III are designated by letters S, M, H and PE; with S representing the soft polyurethane 9O Shore A, M representing the medium soft polyurethane 95 Shore A, H representing the hard polyurethane Shore D, and PE representing polyethylene.

Effect of Different Variables on Coat Weight With Two Polyurethane Blades Having Same Durometer Hardness (95 Shore A) Blade Pressure (Air Cylin- 7! Solid Web Speed in Blade Blade Angle of der Pressure) Coat Weight Variable Content Ft.Per.Min. Thickness Extension Extension in P.S.l.G. in lbs/ream Pressure 53.5 500 /4" 55 8 14.3 53.5 500 "/1" 4" 55 11,9 53.5 500 4" 55 8,2 Pressure 53.5 500 At A" 47Vz 8 23.0 53.5 500 A1" A 47% 15 19,7 53.5 500 A" 47/ 30 15.9 Angle of Extension 53.6 500 A" 50 12 12,7 53.6 500 A" A" 52/ 12 8,3 53.6 500 A" 55 12 7.9 Angle of Extension 53.5 500 50 12 17,5 53,5 500 /s" A 52V2 12 13.1 53.5 500 4" 55 12 10,3 Blade Thickness 53.5 500 /1" 54" 55 8 14,3 53.5 500 W 55 8 8.2 Angle of Extension 53.5 500 /a" A" 55 8 14.3 53.5 500 A1" 47 /z 8 23.0 Angle of Extension 53.4 500 /8" 1 55 8 10.5 53.4 500 l' 47% 8 20.7 Web Speed 52.9 400 A" 47 13.4 52.9 600 A 47 18.8 52.9 800 A" 4" 47 23.4 Web Speed 50.1 400 A" 1" 48 11.8 50.1 600 A 1'' 48 14.0 50.1 800 A" 1'' 48 18.0

TABLE [II Effect of Different Variables on Coat Weight With Different Combinations of V4" Blade Materials Blade Pressure (Ai'r Cylin- %Solid Web Speed in Blade Blade Angle of der Pressure) Coat Weight Variable Content Ft. Per Min. Material Extension Extension in P.S.l.G. in lbs/ream Angle of Extension 50.7 650 PE 1%" 44 18.4

M 1%" 45 50.7 650 PE 1%" 54 10.0

M 1%" 53 Length of Exten- 50.2 350 M 1%" 58 6.5 sion and Angle of S 15/16" 54 Extension M 1%" 57 46.4 350 S 51 7.5 Length of Extension 535 350 H 1%" 12.0 and Angle of Exten- S 47% sion 53.5 350 H /4" 50 9.4

S 53 Length of Extension 55.1 500 {PE 1%" 589?} 7 psig 16.4 Angle of Extension S A" 57% and Pressure PE 1%" 59 30 psig 8.4

55.1 500 S 53 %Solid Content 56.1 500 S 56 15 psig 7.5 and Web Speed S b" 55% 56.1 750 S k" 56 15 psig 10.1

S k" 55% Length of Extension 46.6 350 {H 1%" 58 7 psig 6.7 Angle of Extension M 54% 46.6 350 H 1%" 525? 7 psig 8.3

As is seen from examination of the Tables 11 and 111, above, higher coat weights are obtained where a pair 0 polyurethane blades having a durometer hardness of 95 Shore A are used. Also, with such blades, the higher coat weights are obtained by using the thicker inch blades with a blade extension of 182 inch; the lower blade pressures and the smaller angles of extension.

As is seen from Table 111, other blade combinations may also be used although the coat weights of the final product are not as high. Generally, the control over the coat weight is affected by the flexibility of the blade unit. If the unit becomes too flexible, the pressure acting on opposite sides of the web cannot be properly regulated. If, on the other hand, the blade unit becomes too stiff, it will tend to produce an irregular coating because the loss of flexibility results in a loss in the metering and smoothing action of the blades on the coating. As indicated above, however, flexibility of any particular blade is dependent on the thickness of the blade, the amount of blade extension and the head angle of the blade. Accordingly, in choosing the particular materials for the blades, these factors are to be considered in setting the blade unit so as to provide the necessary flexibility for producing acceptable coated paper.

With the construction of the coating apparatus of the present invention, the quality of the coated paper for a given coat Wight and solids content is generally higher than that obtainable with presently available, conventional coating apparatus. The higher quality for a given coat weight as obtainable with the opposed blade construction of the present invention has special significance, for example, in high opacity light weight grades of paper where the highest ratio of base sheet weight to coating is desired so as to maintain the highest possible sheet strength and opacity.

With the flexible blade unit of the present invention, it is also possible to obtain higher and a greater range of coat weights for a coating material having a given solids content than with conventional coating methods. Not only may a wide variety of coating materials be satisfactorily used by the opposed blade construction of the present invention but also the flexible blade unit enables the apparatus to be run over a range of web speeds greater than is possible with conventional coaters while still maintaining a high quality coating. Also, the coating profile of the final product is enhanced due to the non-rigid mounting of the blades in the blade holders.

In addition to the versatility of the coating apparatus of the present invention and the variety of the quality coated products which it is capable of handling, the construction and physical properties of the opposed blades and the manner in which they are oriented relative to each other as a working flexible unit, contribute to increasing the life of the individual blades over that of steel blades used in conventional coating systems. Also, the overall construction of the system provides an apparatus which is compact in size and efficient in operation.

The above description of the present invention has been made with particular reference to the presently preferred embodiment; however, it is to be understood that various changes thereto may be made without departing from the scope of the invention as set forth in the following claims.

I claim:

1. The method of simultaneously coating the opposite sides of a paper web comprising the steps of:

a. applying a layer of coating material to the opposite sides of the web;

b. feeding said coated web along a predetermined path;

c. engaging said coated web, as it moves along said predetermined path, by a pair of flexible metering blades disposed and aligned on opposite sides of the web, each said blade extending freely at an acute angle relative to the plane of the coated web in the direction from which the coated web is approaching the blades, each said blade having a generally flat beveled working face where it engages the coated web; and

d. simultaneously applying equal and opposed pressure against aligned opposite sides of the coated web over an area defined by the width of the web and a distance along its length as it moves along said predetermined path by urging said blades toward each other with a force sufficient to establish and maintain at least a partially flush engagement of said working faces with the opposite sides of the coated web.

2. The method of coating a paper web as defined in claim 1 further characterized by applying said pressure against the aligned opposite sides of said coated web in a direction urging said web along its path of movement.

3. The method of coating a paper web as defined in claim 2 further characterized by feeding said web along a predetermined path extending in a vertically upward direction after said layer of coating is applied to the opposite sides thereof.

4. A process of coating a paper web wh ch Comprises moving a paper web with web coating on each face through a path that includes a straight portion, and at that straight portion passing said web between yieldable opposed blades, one blade engaging and extending across one of the coating-carrying surfaces, and the other blade engaging and extending across the other coating-carrying surface, each blade extending to a location spaced from the surface it engages, and being held at that location so that it is positioned for the web to approach it at an acute angle, each blade having a generally flat beveled working face where it engages the coating-carrying web; pressing said blades against each other on opposite sides of the coating-carrying web with a continuously applied equal and opposed force sufficient to maintain said blades in flexed position and to maintain at least a partially flush engagement of said working faces with the opposite sides of the coating-carrying web to meter and smooth the layer of coating carried by the opposite sides of the web; and drying the smoothed coatings on the web.

5. A process according to claim 4 further characterized by moving the web with wet coating material on each face in an upward, vertical direction through the straight portion of said path.

6. A process according to claim 4 further characterized by moving the web with wet coating material on each face at a speed in the range of from below 600 ft. per minute to above 1,400 ft. per minute.

7. A process according to claim 4 further characterized by moving the web with wet coating material on each face between flexible plastic blades each of which is of the order of about A to about /2 inch in thickness and is tapered back at the rearward edge of said working face at an angle to form a blunt tip.

8. A process according to claim 4 further characterized by moving the web with wet coating material on each face at a speed in excess of 1,400 ft. per minute.

9. A process according to claim 4 further characterized by moving the web with wet coating material on each face at a speed below 600 ft. per minute.

10. The method of simultaneously coating the opposite sides of a paper web comprising the steps of a. moving the web in a predetermined path that includes a vertical, straight portion in which the web moves in an upward direction;

b. in a lower region of said straight portion applying to and establishing on each of the opposite sides of the upwardly moving web a layer of wet coating material;

c. in a higher region of said straight portion simultaneously applying equal and opposed pressure against aligned opposite layercontaining sides of the upwardly moving coated web by passing the coated web between the rectangular nip of a pair of opposed downwardly extending flexed blades with beveled working surfaces pressed toward each other and extending across the width of the web;

and

d. in a still higher region of said straight portion drying the resulting smooth coatings on the web.

surface at an angle to form a back surface of an area equal to a small fraction of the area of said working surface.

14. The method of claim 10 wherein the blades are constructed of plastic material having a hardness value of between about 90 Shore A and Shore D.

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,889,018

DATED 1 June 10, 1975 INVENTOR(S): Lawrence H. Shepherd, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line +2, shins 18," should read shims l8, Column 9, line 59, "182 inch" should read 5/4 inch Column 10, line 67, "Wight" should read weight Column 12, line 7 (Claim t), "coating on" should read coating material on Signed and Scaled this tenth Day of February 1976 [SEAL] Arrest:

RUTH. C. MIAHSON C. MARSHALL DANN 011w" Commissioner uj'Parents and Trademarks PATENT NO.

DATED INVENTOR(S) 1 UNITED STATES PATENT OFFICE CE'HFICATE 0F CORRECTION June 10, 1975 Richard J. Quint It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line i2, shims l8,

3/4 inch weight read coat Column 9, line 59, Column 10, line 67,

"shins 18," should read "182 inch" should read "Wight" should read Column 12, line 7 Claim i) "coating on" should ing material on This certificate supersedes Certificate of Correction issued February 10, 1976.

[SEAL] A ttest:

RUTH C. MASON A nesting ()jficer Signed and Sealed this eighteenth Day of May 1976

Claims

1. The method of simultaneously coating the opposite sides of a paper web comprising the steps of: a. applying a layer of coating material to the opposite sides of the web; b. feeding said coated web along a predetermined path; c. engaging said coated web, as it moves along said predetermined path, by a pair of flexible metering blades disposed and aligned on opposite sides of the web, each said blade extending freely at an acute angle relative to the plane of the coated web in the direction from which the coated web is approaching the the blades, each said blade having a generally flat beveled working face where it engages the coated web; and d. simultaneously applying equal and opposed pressure against aligned opposite sides of the coated web over an area defined by the width of the web and a distance along its length as it moves along said predetermined path by urging said blades toward each other with a force sufficient to establish and maintain at least a partially flush engagement of said working faces with the opposite sides of the coated web.

4. A process of coating a paper web which comprises moving a paper web with web coating on each face through a path that includes a straight portion, and at that straight portion passing said web between yieldable opposed blades, one blade engaging and extending across one of the coating-carrying surfaces, and the other blade engaging and extending across the other coating-carrying surface, each blade extending to a location spaced from the surface it engages, and being held at that location so that it is positioned for the web to approach it at an acute angle, each blade having a generally flat beveled working face where it engages the coatingcarrying web; pressing said blades against each other on opposite sides of the coating-carrying web with a continuously applied equal and opposed force sufficient to maintain said blades in flexed position and to maintain at least a partially flush engagement of said working faces with the opposite sides of the coating-carrying web to meter and smooth the layer of coating carried by the opposite sides of the web; and drying the smoothed coatings on the web.

7. A process according to claim 4 further characterized by moving the web with wet coating material on each face between flexible plastic blades each of which is of the order of about 1/4 to about 1/2 inch in thickness and is tApered back at the rearward edge of said working face at an angle to form a blunt tip.

10. The method of simultaneously coating the opposite sides of a paper web comprising the steps of a. moving the web in a predetermined path that includes a vertical, straight portion in which the web moves in an upward direction; b. in a lower region of said straight portion applying to and establishing on each of the opposite sides of the upwardly moving web a layer of wet coating material; c. in a higher region of said straight portion simultaneously applying equal and opposed pressure against aligned opposite layercontaining sides of the upwardly moving coated web by passing the coated web between the rectangular nip of a pair of opposed downwardly extending flexed blades with beveled working surfaces pressed toward each other and extending across the width of the web; and d. in a still higher region of said straight portion drying the resulting smooth coatings on the web.

11. The method of claim 10 further characterized by moving the web at a speed in excess of 1,400 ft. per minute.

12. The method of claim 10 further characterized by moving the web at a speed below 600 ft. per minute.

13. The method of claim 10 wherein each blade is tapered back at the upper edge of said beveled working surface at an angle to form a back surface of an area equal to a small fraction of the area of said working surface.

14. The method of claim 10 wherein the blades are constructed of plastic material having a hardness value of between about 90 Shore A and 70 Shore D.