US3908590A

US3908590A - Opposed blade coater

Info

Publication number: US3908590A
Application number: US341928A
Authority: US
Inventors: Richard J Quint
Original assignee: Ethyl Corp
Current assignee: Ethyl Corp
Priority date: 1968-02-08
Filing date: 1973-03-16
Publication date: 1975-09-30
Anticipated expiration: 1992-09-30

Abstract

An opposed blade coating system for simultaneously coating the opposite sides of a paper web, the system including an applicator for applying coating material to the opposite sides of the web, 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 drying mechanism for thereafter drying the coated web.

Description

United States Patent Quint 1 1 Sept. 30, 1975 [541 OPPOSED BLADE COATER 3.001.219 9/1961 Miller 15/245 X '7 J 1 [75] Inventor: Richard J. Quint. Dixfield. Maine [73] Assignec: Ethyl Corporation. Richmond. Va. 3330938 M966 Smlmuke- 118/413 3.477.149 11/1969 Wagner 1. 15/245 X [22] Filed: Mar. 16, 1973 [21 1 Appl. No: 341,928 Primary Emminer-John P. McIntosh Related s. pp c o Data Attorney. Agnl, 0r Firm-Pennie & Edmonds [60] Continuation of Ser. No. 82.475. Oct. 20. 1970.

abandoned. which is a division of Ser. No. 703.924. [57] ABSTRACT Feb. 8. 1968. Pat. No. 3.575.134.

An opposed blade coatlng system for simultaneously 52 us. c1 118/122; 15/250.28 9 Opposite Sides of a the systeim [51] Int. Cl. B05C 11/04 mcludmg an app hcator for applymg 2 matenzll [58] Field of Search 118/121. 413, 122. 123. opposte sdes the flexblc blade 118/126 261; 15/245, 2565 25028 117 comprised of a pair of blades having flat bevelled 23 LR: 101/167 working surfaces engaging opposite s1des of the coated web in opposed relationship with each other for me- {561 References Cited tering the layer of coating on the opposite sides of the web. and drying mechanism for thereafter drying the UNITED STATES PATENTS C(mted web 2.603.808 7/1952 Slavin 15/245 X 2.699.565 1/1955 Brough 15/245 X 15 Claims, 6 Drawing Figures U.S. Patent Sept. 30,1975 Sheet 1 of 3 3,908,590

[KI HIT"??? M L l lllw l I Hull! INVENTOR.

Richard J. Quinr BY wM Mw m'fq 4M ATTORNEYS US. Patent Sept. 30,1975

Sheet 2 of 3 mun 11 iL 24 INVENTOR.

Richard J. Quint AT ORNEYS US. Patent Sept. 30,1975 Sheet3 01 3 3,908,590

FIG. 6

Increasing Pressure FIG. 5

Q WWI! r IIIII- III' Jlllllllll I8 INVENTOR.

Richard J. Quinr fias mym LAM TTORNEYS OPPOSED BLADE COATER This application is a continuation of application Ser. No. 82,475,filed Oct. 20, 1970, now abandoned, which is'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 a metering blade for a 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 often desirable. to apply a coating to the opposite sideszof 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 V 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 substantialamount 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 thepaper. 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 at which the web can be fed through the machinery is limited. In a con.

ventional 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 percent 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 is effected 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 operating 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 1000 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 certain coating materials in order to produce a quality coating. With the conventional blade coating apparatus using a steel trailing blade, speeds much lower than 1000 ft. per minute result in lower quality than that obtained at speeds over 1000 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 1400 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 conventionalcoating 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 applicants 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 bladcs 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 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 of the 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 that 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 of a pair of opposed doctor blades of the present invention showing their relationship 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. 1, the coating apparatus of the present invention generally includes a coating station 1 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 1 1, one of which is shown in FIG. 5, include opposed clamping members l4, 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 the clamping 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 15 at the outer extent of its wall surface 15 With this construction, the opposed blades will present 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 blades may 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 different construction for a particular coating operation. In addition, the cartridge is provided with a plurality of shims 18, 18' at the ends of the insert with the shims 18 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 blade. This is readily effected by removing one or more of the shims l8 and adding a corresponding number of shims 18' of the same thickness. Also, the inclusion of these

shims

18, 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 of the blade holders is controlled by a pair of 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 carriages 12 are moved horizontally along guide tracks 24 on which they are slidably mounted. Movement of the carriages is, in turn, controlled by the pneumatic piston-cylinder units 13 to which they are attached. Adjustable stop members 25 are provided so that once a particular angular setting for the blades has been determined, these steps 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 are constructed of flexible material. A material found admirably suited for this purpose is polyurethane such as that manufactured under the tradename ISOTI-IANE by The Carborundum Company. This material is of medium softness having a durometer hardness of 95 Shore A and a P & J (Pusey and Jones) plastometer value of 20. Other polyurethanes such as the harder polyurethane having a durometer hardness of 70 Shore D and a P & J plastometer value of 4 and the softer polyurethane having a durometer hardness of 90 Shore A and a P & .l 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 In addition to these polyurethane materials, such materials as Nylon, Teflon and polyethylene having operating characteristics equivalent to those of the polyurethane, as more fully 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 Vs 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 ofits 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 thisback sur face 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 FIGv 3, the angles of extension ranging from above 40 to about 60 have been found suitable. Preferably, the amount of extension of the blades is between inch and 1 /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 varyv 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 of 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 reaches, 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 affect of area of 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 ofincrease in area of contact with the web increases at a higher rate that 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 FG 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 AI-IJK.

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 be 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 particular 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 Shore A, H representing the hard polyurethane 7O Shore D, and PE representing polyethylene.

TABLE II Effect of Different Variables on Coat Weight With Two Polyurethane Blades Having Same Durometer Hardness (95 Shore A) Blade Blade Pressure (Air Solid Web Speed in Blade Angle of Cylinder Pressure) Coat Weight Variable (ontent Ft Pcr.M|n. Thickness Extension Extension in P.S.I.G. in lbs/ream Pressure 535 500 %g' /1" 55 8 14.3

53.5 500 /8" A" 55 15 11.9 53.5 500 A A 55 30 8.2

TABLE II Continued Effect of Different Variables on Coat Weight With Two Polyurethane Blades Having Same Durometcr Hardness (95 Shore A) Blade Pressure (Air 7: Solid Web Speed in Blade Blade Angle of Cylinder Pressure) Coat Weight Variable Content Ft.Per.Min. Thickness Extension Extension in P.S.l.G. in lbsjream Pressure 535 500 47 A 8 23.0 53.5 500 /1" 47/z 19.7 53.5 500 47V4 15.9 Angle of Extension 536 500 A" /1" 50 12 12.7 53.6 500 A" 52V! 12 8.3 53.6 500 A" "/1" 55 12 7.9 Angle of Extension 535 500 /a" 50 12 17.5 53.5 500 52V2 12 13.1 53.5 500 1$" 55 12 10.3 Blade Thickness 53.5 500 /5" 55 8 14.3 53.5 500 A" 55 8 8.2 Angle of Extension 535 500 55 8 14.3 53.5 500 A" 47/2 8 23.0 Angle of Extension 53.4 500 1" 55 8 10.5 53.4 500 16s" 1" 47% 8 2017 Web Speed 52.9 400 A" A" 47 13.4 52.9 600 Ma" 47 18.8 52.9 800 A" 47 23.4 Web Speed 50.1 400 A" 1" 48 11.8 50.1 600 A" 1" 48 14.0 50.1 800 V5" 1" 48 18.0

TABLE 111 Effect of Different Variables'on Coat Weight with Different Combinations of A" Blade Materials Blade Pressure (Air 7(S0lid Web Speed in Blade Blade Angle of Cylinder Pressure Coat Weight Variable Content Ft. Per Min. Material Extension Extension in P.S.I.G. in lbs/ream PE 1%" 44} 18.4 Angle of Extension 50.7 650 M 1%" 45 PE 1%" 54} 50.7 650 M 1%" 53 10.0 Length of Exten- 50.2 350 M 1%" 58} 65 sion and Angle of S 15/16" 54 Extension {M 46.4 350 S /z" 51 7.5 Length of Extension 53.5 350 {H 1%" and Angle of Exten- S 7 12.0 i {H 50} 53.5 350 S 53 9.4 Length of Extension 55.1 500 {PE 1%" 58 /2} Angle of Extension S W 579? 7 psig 16.4 and Pressure {PE 1%" 59 55.1 500 S A" 53% 30 psig 8.4 7zSolid Content 56.] 500 {S 5%" 56 and Web Speed s a" w 15 psig 7.5

S a" 55% 15 psig 10.1 Length of Extension 46.6 350 {H 1%" 58 Angle of Extension M 3'4" 54% 7 psig 6.7

M 1 /1" 52% 7 psig 8.3

As is seen from examination of the Tables lIand Ill, above, higher coat weights are obtained where a pair of 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 inch; the lower blade pressures and the smaller angles of extension.

As is seen from Table 111, other blade combinations mayralso 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 particulur 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 weight 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 lightweight 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 clue 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. An improved metering blade for use in a web coating apparatus, said improved blade being:

a. relatively thick and constructed of plastic material having a hardness value of between about 90 Shore A and 70 Shore D; and having b. a flat beveled rectangular working surface at a foreward portion of the blade for engagement against the coated web,

0. said blade having a uniform cross-sectional shape for a distance of at least V2 to 1% inches from said working surface;

(1. said blade being flexible and free from any reinforcement for at least V2 to 1 /2 inches from said working surface, which distance is greater than the thickness of the blade for permitting flexing thereof along an axis parallel to the plane of said working surface; and

e. means for clamping said blade at its rearward portion at least /2 to 1 /2 inches away from said working surface.

2. An improved metering blade as set forth in claim 1 wherein:

a. the angle of bevel of said working surface is between about 30 and 50.

3. An improved metering blade as set forth in claim 2 wherein:

a. the angle of bevel of said working surface is about 40; and

b. said blade is tapered back at the leading edge of said 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. I

4. An improved metering blade for use in a web coating apparatus, said blade being:

a. constructed of a flexible material; and having a front elongated edge and a rear edge;

a thickness between about A and V2 inch;

a flat beveled rectangular working surface extending along the front elongated edge on one side thereof for engagement against the coated web;

e. said blade having a uniform cross-sectional shape for a distance of at least /2 to 1% inches from said working surface;

f. said blade being flexible and free from any reinforcement for at least /2 to 1 /2 inches from said working surface; and

g. means for clamping said blade at its rearward portion at least V2 to 1 /2 inches away from said working surface.

5. An improved metering blade as set forth in claim 4 wherein:

a. the angle of bevel of said working surface is between about 30 and 50; and

b. said blade is tapered back at the leading edge of said 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.

6. An improved metering blade as set forth in claim 5 wherein:

a. said material is plastic having a P & J plastometer value of between about 4 and 27.

7. An improved metering blade as set forth in claim 6 wherein:

a. said material is polyurethane having a durometer hardness of about 95 Shore A.

8. An improved metering blade as set forth in claim 6 wherein:

a. said P & J plastometer value is about 20.

9. A blade assembly for use in a web coating apparatus, said assembly comprising:

a. a flexible metering blade having:

' l. a front elongated edge and a rear edge,

2. a thickness between about A and /2 inch,

3. a flat beveled rectangular working surface extending along the front elongated edge on one side thereof for engagement against the coated web,

4. said blade having a uniform cross-sectional shape for a distance of at least /2 to 1 /2 inches from said working surface, and

5. said blade being free from any reinforcement for at least /2 to 1% inches from said working surface; and

b. a cartridge resiliently clamping said blade at its rearward portion at least /2 to 1 /2 inches away from said working surface and along the major dimension of said blade.

10. A blade assembly as set forth in claim 9 wherein:

a. said cartridge is constructed of two halves removably connected together on each side of the blade.

11. A blade assembly as set forth in claim 9 further including:

a. a flat elongated flexible insert member extending along the major dimension of the blade at a location at least to 1% inches away from the working surface of the blade with one of its faces in contact with .the blade on the same side thereof as said working surface.

12. A blade assembly as set forth in claim 1 1 wherein:

a. said insert member is constructed of the same flexible material as used in the blade.

13. A blade assembly as set forth in claim 12 wherein:

a. said blade and said insert are both constructed of polyurethane having a hardness value of between about 90 Shore A and Shore D.

14. The blade assembly as set forth in claim 13 wherein said cartridge includes:

a. a first holding member engaging the side of the insert member facing away from the blade and having a portion in front of the edge of the insert member facing toward the one elongated edge of the blade;

b. a second holding member engaging the side of the blade opposite the insert member and having a portion behind the rear edge of the blade and insert member; and

said cartridge with the blade therein, said clamping members together defining a hollow interior for receiving said cartridge and having spaced walls defining an opening leading to the hollow interior through which said blade extends in spaced rela-

Claims

1. An improved metering blade for use in a web coating apparatus, said improved blade being: a. relatively thick and constructed of plastic material having a hardness value of between about 90 Shore A and 70 Shore D; and having b. a flat beveled rectangular working surface at a foreward portion of the blade for engagement against the coated web, c. said blade having a uniform cross-sectional shape for a distance of at least 1/2 to 1 1/2 inches from said working surface; d. said blade being flexible and free from aNy reinforcement for at least 1/2 to 1 1/2 inches from said working surface, which distance is greater than the thickness of the blade for permitting flexing thereof along an axis parallel to the plane of said working surface; and e. means for clamping said blade at its rearward portion at least 1/2 to 1 1/2 inches away from said working surface.

2. An improved metering blade as set forth in claim 1 wherein: a. the angle of bevel of said working surface is between about 30* and 50*.

2. a thickness between about 1/4 and 1/2 inch,

3. An improved metering blade as set forth in claim 2 wherein: a. the angle of bevel of said working surface is about 40*; and b. said blade is tapered back at the leading edge of said 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.

4. An improved metering blade for use in a web coating apparatus, said blade being: a. constructed of a flexible material; and having b. a front elongated edge and a rear edge; c. a thickness between about 1/4 and 1/2 inch; d. a flat beveled rectangular working surface extending along the front elongated edge on one side thereof for engagement against the coated web; e. said blade having a uniform cross-sectional shape for a distance of at least 1/2 to 1 1/2 inches from said working surface; f. said blade being flexible and free from any reinforcement for at least 1/2 to 1 1/2 inches from said working surface; and g. means for clamping said blade at its rearward portion at least 1/2 to 1 1/2 inches away from said working surface.

4. said blade having a uniform cross-sectional shape for a distance of at least 1/2 to 1 1/2 inches from said working surface, and

5. said blade being free from any reinforcement for at least 1/2 to 1 1/2 inches from said working surface; and b. a cartridge resiliently clamping said blade at its rearward portion at least 1/2 to 1 1/2 inches away from said working surface and along the major dimension of said blade.

5. An improved metering blade as set forth in claim 4 wherein: a. the angle of bevel of said working surface is between about 30* and 50*; and b. said blade is tapered back at the leading edge of said 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.

6. An improved metering blade as set forth in claim 5 wherein: a. said material is plastic having a P & J plastometer value of between about 4 and 27.

7. An improved metering blade as set forth in claim 6 wherein: a. said material is polyurethane having a durometer hardness of about 95 Shore A.

8. An improved metering blade as set forth in claim 6 wherein: a. said P & J plastometer value is about 20.

9. A blade assembly for use in a web coating apparatus, said assembly comprising: a. a flexible metering blade having:

10. A blade assembly as set forth in claim 9 wherein: a. said cartridge is constructed of two halves removably connected together on each side of the blade.

11. A blade assembly as set forth in claim 9 further including: a. a flat elongated flexible insert member extending along the major dimension of the blade at a location at least 1/2 to 1 1/2 inches away from the working surface of the blade with one of its faces in contact with the blade on the same side thereof as said working surface.

12. A blade assembly as set forth in claim 11 wherein: a. said insert member is constrUcted of the same flexible material as used in the blade.

13. A blade assembly as set forth in claim 12 wherein: a. said blade and said insert are both constructed of polyurethane having a hardness value of between about 90 Shore A and 70 Shore D.

14. The blade assembly as set forth in claim 13 wherein said cartridge includes: a. a first holding member engaging the side of the insert member facing away from the blade and having a portion in front of the edge of the insert member facing toward the one elongated edge of the blade; b. a second holding member engaging the side of the blade opposite the insert member and having a portion behind the rear edge of the blade and insert member; and c. a plurality of removable shims positioned between the front edge of the insert member and first holding member and between the rear edges of the blade and insert member and the second holding member.

15. A blade assembly as set forth in claim 14 further comprising: a. a pair of clamping members for removably holding said cartridge with the blade therein, said clamping members together defining a hollow interior for receiving said cartridge and having spaced walls defining an opening leading to the hollow interior through which said blade extends in spaced relation to said walls.