US3424126A - Air-knife coater - Google Patents

Description

Jan. 28, 1969 R. MAHONEY 3,

AIR-KNIFE COATER Filed Jan- 25, 1963 Sheet of 2 ZIZ v INVENTOR. Rala/z/pMa/wfley A TT )RNEYS Jan. 28, 1.969 v MAHONEY 3,424,126

AIR-KNIFE COATER Filed Jan. 25, 1963 I Sheet g of 2 INVENTOR. RalafiP/Mafioney BY I W w AORNEYS United States Patent 9 Claims ABSTRACT OF THE DISCLOSURE A coating apparatus or coater wherein a traveling paper web has an excess of coating applied initially thereto by a coating applicator (preferably at a submerged coating nip); then the coater moves the web with the excess coating thereon to a type of metering device (preferably a dam or doctor blade) which presents a notched surface to the coating on the web to remove the excess and leave retained coating in the form of alternating ridges and valleys; and finally such retained coating is next subjected to a transverse gas jet (or air-knife) which essentially smooths the coating down on the web.

This invention relates to improvements in coating porous webs such as webs of paper and the like, and more particularly, to an apparatus for the application of smooth coating layers in relatively high weights.

In the paper coating arts, the amount of coating applied to a paper web is generally referred to as the coating weight, and the coating weight is expressed in terms of pounds per unit of web area. The coating weight may thus be expressed in terms of so many pounds per 1000 square feet or so many pounds per ream (which is slightly over 3000 square feet). Also, the liquid coating composition itself is generally described in the art solely on the basis of the percent solids therein, which is of course indicative of viscosity and other characteristics of the coating composition. Coating of paper webs may be carried out in a so-called on-machine coater which operates at the speed of the paper making machine, or coating may be carried out on the so-called off-machine coater which is operated independently. Coating production is generally expressed in terms of the machine speed in feet per minute and may thus range from a practical minimum machine speed of about 300 to 500 feet per minute to a practical maximum coating machine speed of approximately 2500 feet per minute.

The instant invention provides an improved apparatus for applying relatively high coating weights to paper webs at high production rates.

One method of applying high coating weights at high coating speeds involves the use of coating compositions having relatively high solids, e.g., 60% solids and coating compositions of such high solids content have relatively high viscosities and must ordinarily be smoothed with a trailing blade which has certain limitations of application pressure, smoothing effect and quantities of coating handled by the blade, particularly with respect to excess coating that may have to be removed by the blade.

The so-called air-brush or air-knife method of coating is disclosed, for example, in United States Patent No. 1,980,925 to Lebel and in Patent No. 2,139,628 to Terry. It is known that such air-knife coating apparatus which normally comprises means such as a roller or backup roll for supporting one side of the web and means to apply a substantially non-divergent jet of air emitted through a straight slit orifice of a nozzle to the coating on the web tends to leave a uniformly thick layer of coating on the web under certain operating conditions. In practice, the jet of air issues from the nozzle with substantially uniform velocity throughout its entire extent and impinges Patented Jan. 28, 1969 upon the wet coating at an angle and in a direction opposite to the generally longitudinal direction of web travel, thereby cutting excess coating and leaving the desired quantity of coating on the web in a layer of uniform thickness. It is known that the air-knife is less effective with comparatively high solids coatings and the air-knife has been found to leave something to be desired in operations involving the removal of a substantial excess of coating. In removing excess coating, the air-knife effects what is known as a coating split whereby excess coating is effectively split off the coating layer on the web and at certain coating weights and consistencies the splitting effect of the air-knife leaves something to be desired in the resulting uniformity of the layer as well as in atomizing of the coating composition split off.

The instant invention affords an improved apparatus for applying high coating weights to a web to obtain a uniform, smooth coating layer of extremely desirable properties.

The instant invention also provides an improved apparatus applying coating uniformly to a paper web, and effecting metering and smoothing of the coating layer in a superior manner.

Other and further objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed disclosure thereof and the drawings attached hereto and made a part hereof.

On the drawings:

FIGURE 1 is an essentially diagrammatic elevational view showing one embodiment of the instant invention;

FIGURE 2 is a fragmentary detail elevational view of a trailing blade edge employed in the practice of the instant invention;

FIGURE 3 is a fragmentary sectional view of the surface portion of a metering roll which may be employed in the practice of the instant invention; and

FIGURES 4, 5 and 6 are essentially diagrammatic elevational views showing different embodiments of the instant invention.

As shown on the drawings:

In FIGURE 1, it will be seen that a coating device indicated generally by the reference numeral 10 is shown for coating a paper web W that is traveling or continuously advancing in the direction indicated generally by the arrows in FIGURE 1, which direction will be referred to hereinafter as the longitudinal direction of travel of the web and will be contrasted to the transverse or cross-machine direction generally perpendicular to the longitudinal direction extending in the general direction of the width of the traveling web W.

The coating device 10 of FIGURE 1 comprises transverse support means which are substantially transversely co-extensive with the web W traveling thereover and firmly supported thereby, in the form of a conventional coating backup roll 11, which is preferably mounted for rotation as here shown in the direction indicated by the arrow 11a so that its peripheral surface is that of the speed of the traveling web W.

Means are provided for applying a layer of liquid coating to the traveling web W on the side opposite that supported by the backup roll 11, and such means are preferably in the form of an applicator roll indicated at 12 submerged or partially submerged in a coating bath 13 in a coating pan 14. The applicator roll 12 is also mounted for rotation in the direction indicated by the arrow and it extends transversely so as to define a transverse coating nip N-l with the backup roll 11. The coating nip N-l has an oncoming side (in the direction of web travel) at which coating is applied to the web W1 entering the nip and an off-running side from which the coated web W-2 departs.

Preferably, in thepractice of the instant invention, a

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coating bath level Ll is maintained at the oncoming side of the nip N1 sufficient to submerge the oncoming side of the nip. The coating bath may, of course, be maintained at a level so that both the oncoming and off-running sides of the nip N1 are submerged, but it is particularly important to have the level Ll at least at the oncoming side of the nip N1 sufficiently high to submerge the same, and the level at the off-running side LZ in FIGURE 1 may be lower. The differences in level are possible because a substantial amount of coating is taken from the bath and applied to the Web W at the nip N1. The higher coating level Ll may be maintained at the oncoming side of the nip N-1 by a number of means which include the speed of rotation of the roll (driven by a motor indicated diagrammatically at M), draw-off of the coating bath for example at a line into a reservoir R back through a pump P and into the coating pan through a line 16 (all of which are indicated diagrammatically in FIGURE 1), or merely feeding of the coating into the pan 14 via the inlet line 16 at a predetermined rate so the speed at which coating is removed from the bath 13 on the web W will effectively maintain a slight difference between the levels L1 and L2.

A particular advantage of the device 10 is that a substantial excess of coating is applied at the nip N-l by virtue of a hydraulic effect that is generated at the submerged oncoming side of the nip N1, so that the coating is applied to the web with sufficient force to penetrate at least the surface portion thereof in a substantially uniform manner. As shown in FIGURE 1, this is preferably done by positioning the applicator roll 12 so as to define the applicator nip N-l with the underside of the backup roll 11. At the off-running side of the nip N1 the web W-2 travels toward a trailing blade 17 which functions as a dam to remove excess coating applied to the web. The amount of excess coating applied to the web at the nip N1 may range from a minimum practical excess of about of the ultimately desired coating weight to a practical maximum of as much as ten times the ultimately desired coating weight. The use of excess coating is advantageous in that a more complete, uniform and effective application and penetration of coating is obtained by the use of such excesses and such excesses do not interfere with subsequent operation of the device by virtue of the fact that the excess is readily removed by the trailing blade 17 and, in the embodiment of FIGURE 1, readily returned to the coating bath 13.

The trailing blade 17 is mounted in conventional manner for trailing blades which have been used in the art for some time. The instant trailing blade 17, however, is different in structure in that it has what may be referred to as a nip-defining surface portion which is indicated generally at 17a in FIGURE 2. This transversely aligned surface portion or blade edge 17a operates at close running relation with the backup roll in the usual manner for trailing blade devices, but the edge or surface portion 17a is provided with a multiplicity of transversely, closely spaced generally longitudinally aligned notches or narrow grooves indicated in FIGURE 2 at 18a. Transversely spaced between the notches or grooves 18a are bills or ridges indicated by the reference numeral 181) which present generally fiat top surfaces aligned approximately with the operating line of a conventional trailing blade presenting a continuous operating line along the edge thereof. As indicated fragmentarily in FIGURE 2, the coated web W-2 passes through the so-called blade nip N-Z (or transverse slot between blade 17 and the supporting roll 11 receiving the coated web) with the paper sheet S firmly supported by the backup roll 11 and carrying on its surface the coating layer L. The coating layer L which actually passes through this transverse slot N-2 is preferably continuous across the entire Width of the paper sheet S and, in fact, the coating being applied in substantial excess and under hydraulic pressure at the applicator nip N-l results in not only the application of a continuous coating layer L across the sheet S but penetration thereof at least along the interface indicated at F in FIGURE 2.

The notched or grooved blade 17 functions to remove the excess coating over and beyond the predetermined coating weight that is ultimately desired and this coating weight is retained on the paper sheet S in the form of the layer indicated at L in FIGURE 2 with corresponding longitudinally extending hills L and valleys L It will be appreciated that there are a number of advantages in the use of the grooved blade 17 for metering off excess coating in this fashion. The blade 17 operates relatively closely to the paper sheet S only to a limited extent along the upper surfaces 1812, while still removing the total amount of excess desired. Blade removal of coating causes a splitting effect on the coating layer, but this splitting effect is less drastic in the immediate vicinity of the sheet S because it is applied along only localized areas (18a) rather than being permitted to generate a substantially uniform force continuously across the transverse line of the slot N2. The excess coating is thus easily wiped away by the notched blade 17 so as to leave the previously determined coating weight on the Web W3 at the off-running side of the notched trailing blade 17.

The layer of coating L at the off-running side of the notched trailing blade 17, of course, is contoured with the hills and valleys hereinbefore described and the notched blade 17 has effected a splitting of the coating along the exposed surfaces of such hills and valleys L and L but this surface contour is completely smoothed by the airknife or air jet 18. As previously indicated, the air-knife 18 applies a transverse jet of gas against the contoured coating layer L on the web W3 to conform the coating layer to a substantially uniform transverse profile on the web. It will be appreciated that in the practice of the instant invention one of the particular advantages is that the air-knife at 18 does not have to split off excess coating. Instead, it is applied at relatively low air pressures in a manner sufficient to move the longitudinally extending coating layer hills L so that they will fill in the valleys L on the coating layer. This moving of the coating by the air-knife 18 tends to smooth the coating surface, not only avoiding a splitting effect on the coating that might be characteristic of some air-knife operations when an excess is removed, but also effectively smoothing out the coating so as to eliminate any so-called splitting surface effects resulting from the trailing blade 17. The trailing blade 17 thus carries out essentially all of the metering function required in the instant coating operation whereas the airknife 18 carries out the greater part of the smoothing function required in the operation of the instant coating device 10.

A spe-cific example of a coating composition used in the practice of the instant invention has the following formulation:

Parts Clay Titanium dioxide 10 Casein ...l 4 Latex adhesive (Dow Latex 512L-solid spaces) 12 20% ammonium hydroxide 0.6 Ammonium stearate 2 Water 156 The above coating formulation has a solids content of about 43% and a viscosity of approximately 550 centipoises. The viscosity preferably used with the air-knife is not necessarily limited to the lower viscosities of coatings which are employed when the air-knife involves a splitting action (such viscosities Ibeing within the range of about to 1500 centipoises measured with a Brookfield viscometer at a rotational speed of 6 rpm, which coating compositions are generally 30% to 45% solids), but the instant invention permits the use of coating compositions having greater solids contents (e.g. up to 50 or 60%) and higher viscosities (e.g. up to 30,000 centipoises), since the air-knife is required only to smooth and move slightly the various ridges or hills of coating L in the layer L.

Operating at a coating speed of 500 feet per minute, and using the coating formulation specifically described hereinbefore, it is found that a particularly satisfactory coating may be applied in final coating weights of 5, 6, 7 and 10 pounds per 1000 square feet. And operating at 1200 feet per minute satisfactory final coating weights of 3% pounds per 1000 square feet may be obtained. In such procedure excesses of coating of approximately 50% of the desired coating weight are applied at the applicator nip N-l, and the air-knife 18 is operated at approximately 3 pounds per square inch gauge air pressure so as to obtain the preferred smoothing effect without disrupting the coating.

The instant method may be employed with coating formulations ranging from 30% to 60% solids, for the application of coatings at weights ranging from 0.5 to at least 10 pounds per 1000 square feet, and at coater speeds ranging from the practical minimum of about 300 feet per minute to a practical maximum of about 2000 to 2500 feet per minute. At higher speeds, lower weights and lower solids contents are used. It will also be appreciated that application of the coating initially under the hydraulic pressure (i.e. superatmospheric pressure as contrasted to the use of mere atmospheric pressure) affords a number of advantages in penetration of the coating into the web surface.

Referring now to FIGURE 4, it will be seen that the embodiment of the invention shown therein indicated generally by the reference numeral 100 comprises a rotary backup roll 111, defining a coating nip N-10 with the underside of the backup roll 111, and a coating pan 114 maintaining a coating level L-10 submerging the oncoming side of the coating nip N-10 for applying excess coating to the web W-10 at the nip N-10. A trailing blade 117 is also provided having substantially the same structure as that described in connection with the blade 17 of FIGURE 1 and carrying out substantially the same function, except that the trailing blade 117 is not mounted for close running relation with the backup roll 111. The trailing blade 117 may operate against the reach of coated web W-11 extending from the backup roll 111 to a second back roll 130 (if a low viscosity, low solids coating formulation is used) or the trailing blade 117 may cooperate with still another backup roll 131 (indicated in phantom lines at 131). In any event, the trail ing blade 117 is preferably mounted in conjunction with a wall 1170 for returning the excess coating back to the coating bath 113 in the pan 114. The air-knife 118 in the embodiment 100 of Figure 4 also operates with a separate backup roll 130, but its function is substantially the same as the function of the air-knife 18 hereinbefore described in connection with FIGURE 1.

Referring to FIGURES 5 and 6, it will also be noted that air-knives with backup rolls are indicated by the same reference numerals in the 200 and '300 series and have the same function as that already described in connection with the air-knife 118 and backup roll 130.

In FIGURE 5, there is shown a coating backup roll 211 defining with an applicator roll 212a in a pan 214 a coating nip N12 that is submerged at its oncoming side by the level L-12 of a coating lbath 213 in a coating pan 214. The web W20 passes through the nip N-12 to receive coating and the. coated web at the off-running side of the nip N-12 (designated W-21) then passes on to the air-knife 218 as indicated. In the device 200 of FIG- URE 5, however, the applicator roll 212a does not have the conventional plain applicator roll surface. It is rotated preferably at a comparatively lesser speed than the web W-20 is traveling and a substantial excess of coating is forced against and exposed to the web W-20, but the applicator roll 212a in the embodiment 200 carries out the additional function of metering the coating. For this purpose the applicator roll 2120: has a surface portion (indicated at 240 in FIGURE 3) presenting to the coating nip N-12 a multiplicity of transversely spaced generally longitudinally aligned (i.e. circumferential) grooves 240a for defining a corresponding transverse contour of hills and valleys in the coating layer applied to the off-running web W-21. As indicated in FIGURE 3, the applicator roll 212a comprises a steel shell 21% with a rubber coating 2120 (or a coating of solid natural or synthetic elastomer). The grooves 240a are shown as generally rectangular in cross section as compared to the V-shaped notches 18a shown in FIGURE 2. It will be appreciated that the grooves used in the practice of the instant invention may have various configurations.

In the embodiment of FIGURE 5, the applicator roll 212 carries out the dual function of exposing the web W-22 a substantial excess of coating and metering the coating actually applied to the web so as to obtain substantially the predetermined desired weight on the web W-21 at the off-running side of the nip N-12. In general, it has been found that substantially better control of the overall coating operation is obtained, however, if the application of coating in excess and the metering to remove the excess coating are carried out at separate stations as indicated in previously discussed FIGURES 1 and 4 and in FIGURE 6. In the embodiment 300 of FIGURE 6, it will be seen that a backup roll 311 cooperates with an applicator roll 312 to define the coating nip N-31 submerged by the coating bath 313 in the pan 314, in substantially the manner hereinbefore described in connection with the corresponding elements shown in FIGURES 1 and 4. The web W-30 is thus coated with an excess of coating and departs from the nip N-31 as the web W-31 with such excess of coating thereon.

The web W-31 then passes through a nip N-32 defined by a pair of rollers 350 and 351. The roller 351 is exposed to the coated side of the web W-31 and this roller is provided with a substantial multiplicity of transversely spaced generally longitudinally aligned grooves of the general structure hereinbefore described in connection with the roll 212a in FIGURE 5. The roller 351 may be rotated in either direction for purposes of carrying out its metering function most advantageously. For example, if substantial excesses of coating are applied to the web W-31, it might be advantageous to rotate the metering roll 351 in a generally clockwise direction. In other situations, it might be advantageous to rotate the roller 351 in a counterclockwise direction. The arrows in FIGURES 4, 5 and 6, otherwise, indicate preferred directions for rotating the roll. The excess .coating removed by the roller 351 is collected in a bath 313a and preferably returned via a line 3131: to the main bath 313 in the pan 314. The resulting web W-31 with a layer of coating thereon having the hills and valleys hereinbefore described passes on around the backup roll 330 and the coating layer is smoothed by the air-knife 318 in the manner herernbefore described.

In the embodiment 300 of FIGURE 6 the rolls are preferably all rubber covered. In fact, a particularly satlsfactory operation is obtained using rubber covers on the rolls 311 and 350 having a P and J hardness of approxlmately and using substantially softer rubber covers on the rolls 312 and 351 (having a P and J hardness of about The P and J hardness is expressed numerically on the basis of a conventional known Pusey and Jones scale.

In the practice of the invention, it is found that the best results are obtained using air-knife pressures of approximately 3 to 4 pounds per square inch gauge to accomplish the desired smoothing and blending of the ridges. It will thus .be seen that processwise the instant invention involves a method of applying coating of 30% to 60% solids on a web at a predetermined weight of 0.5 to 10 pounds per 1000 square feet, which comprises continuously advancing a paper web in a generally longitudinal direction, applying a layer of said coating thereto in excess of said predetermined Weight and under superatmospheric pressure to effect penetration of the web surface with coating, continuously removing closely spaced portions of the coating layer equal in total volume to the excess coating applied, thereby leaving the predetermined amount of coating in an uneven contour on the web, and then continuously applying a high speed gas jet transversely and generally opposed to the longitudinal movement of the advancing web against the contoured coating layer on the web to Smooth the same into a substantially uniform transverse coating profile. In addition, it will be appreciated that the notches in the elements 17 or 212a (and, therefore, the resulting hills L have transverse dimensions of substantially 0.4 to 0.5 inch. The depths of these notches (and therefore the height of the hills L are preferably within the range of substantially 0.1 to 0.5 inch; and the overall configuration in cross section of the hills L may be triangular as indicated in FIGURE 2 or the resulting hills may be generally rectangular as would result from the use of the roll 212a of FIGURE 3. The transverse spacing from centerto-center between adjacent grooves or notches (18a or 240a) is preferably substantially 1.5 to 5 times the aforesaid transverse dimension thereof.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

I claim as my invention:

1. In a coating device, in combination, rotary backup means substantially transversely coextensive with a Web traveling longitudinally thereover and firmly supported thereby, transverse applicator means defining with said backup means a transverse nip receiving the web and having an oncoming side at which coating is applied to the web entering the nip and an off-running side from which the coated web departs with an excess of coating thereon, means defining a dam at the off-running side of the nip presenting a surface portion in close-running relation to said backup means and having a multiplicity of closely spaced generally longitudinally aligned notches for removing excess coating from the web and retaining on the Web a contoured coating layer having corresponding longitudinally aligned hills and valleys, and means at the off-running side of said dam for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web.

2. In a coating device, in combination, rotary backup means substantially transversely coextensive with a web traveling longitiudinally thereover and firmly supported thereby, transverse applicator means defining with said backup means a transverse nip receiving the web and having an oncoming side at which coating is applied to the web entering the nip and an off-running side from which the coated web departs with an excess of coating thereon, a pair of rollers having surface portions defining contoured structure at the nip having a multiplicity of closely spaced generally longitudinally aligned grooves and adapted for removing excess coating from the Web and retaining on the web a contoured coating layer having corresponding longitudinally aligned hills and valleys, and means at the off-running side of said contoured nip [for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web.

3. A coating device comprising a rotary backup roll, an applicator roll defining a coating nip with the underside of said backup roll, a coating pan maintaining a coating level submerging the on-coming side of the coating nip for applying excess coating to the web at such coating nip, a trailing blade at the off-running side of the coating nip presenting a surface portion in close-running relation to said backup roll and having a multiplicity of closely spaced generally longitudinally aligned notches for removing excess coating from the web and retaining on the web a contoured coating layer having corresponding longitudinally aligned hills and valleys, means for returning such excess coating to the pan, and means at the offrunning side of the trailing blade for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web.

4. A coating device comprising a rotary backup roll, an applicator roll defining a coating nip with the underside of said backup roll, a coating pan maintaining a coating level submerging the oncoming side of the coating nip forapplying excess coating to the web at such coating nip, a trailing blade at the off-running side of the coating nip and posiitoned in the coating pan presenting a surface portion in close-running relation to said backup roll and having a multiplicity of closely spaced generally longitudinally aligned notches for removing excess coating from the web and retaining on the web a contoured coating layer having corresponding longitudinally aligned hills and valleys, and means at the off-running side of the trailing blade for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web.

5. A coating device comprising a rotary backup roll, an applicator roll defining a coating nip with the underside of said backup roll, a coating pan maintaining a coating level submerging the oncoming side of the coating nip for applying excess coating to the web at such coating nip, a pair of rollers defining a metering nip receiving the coated web at the off-running side of the coating nip, one of said rollers having a sunface portion presenting to the metering nip a multiplicity of closely spaced generally longitudinally aligned notches for removing excess coating from the web and retaining on the web a contoured coating layer having corresponding longitudinally aligned hills and valleys, and means at the off-running side of said metering nip for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web.

6. A coating device comprising a rotary backup roll, an applicator roll defining a coating nip with the underside of said backup roll, a coating pan maintaining a coating level submerging the oncoming side of the coating nip for applying excess coating to the web at such coating nip, a pair of rollers defining a metering nip receiving the coated web at the off-running side of the coatin nip, one of said rollers having a surface portion presenting to the metering nip a multiplicity of closely spacedgenerally longitudinally aligned notches for removing excess coating from the web and retaining on the web a contoured coating layer having corresponding longitudinally aligned hills and valleys, and means at the offrunning side of said metering nip for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web, said backup and applicator rolls being covered with a solid elastomer.

7. A coating device comprising a rotary backup roll, an applicator roll defining a coating nip with the underside of said backup roll, a coating pan maintaining a coating level submerging the oncoming side of the coating nip for applying excess coating to the Web at such coating nip, a pair of rollers defining a metering nip receiving the coated web at the off-running side of the coating nip, one of said rollers having a surface portion presenting to the metering nip a multiplicity of closely spaced generally longitudinally aligned notches for removing excess coating from the web and retaining on the web a contoured coating layer having corresponding longitudinally aligned hills and valleys, and means at the off-running side of said metering nip for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web, said backup and applicator rolls being covered with a solid elastomer and said metering rollers also being covered with a solid elastomer, the rubber covers on the rolls exposed to the coating being softer.

8. A coating device comprising a rotary back-up roll, an applicator roll defining a coating nip with the underside of said backup roll, a coating pan maintaining a coating level submerging the oncoming side of the coating nip for applying excess coating to the web at such coating nip, a trailing blade at the off-running side of the coating nip presenting a surface portion to the coated side of the web and having a multiplicity of closely spaced generally longitudinally aligned notches for removing excess coating from the web and retaining on the web a contoured coating layer having corresponding longitudinally aligned hills and valleys, and means at the oil-running side of the trailing blade for applying a transverse jet of gas to such contoured coating layer to conform the coating layer to a substantially uniform transverse profile on the web.

9. A device for applying coatings of 30% to 60% solids on a web at a predetermined weight of 0.5 to pounds per 1000 square feet, which comprises means continuously advancing a paper web in a generally longitudinal direction, means applying a layer of said coating thereto in excess of said predetermined weight and under superatmospheric pressure to eifect penetration of the web surface with coating, means continuously removing closely spaced portions of the coating layer equal in total volume to the excess coating applied, thereby leaving the predetermined amount of coating in an uneven contour on the web, and subsequent means continuously 10 applying a high speed gas jet transversely and generally opposed to the longitudinal movement of the advancing web against the contoured coating layer on the web to smooth the same into a substantially uniform transverse coating profile.

References Cited UNITED STATES PATENTS 2,066,780 1/1937 Holt 118119 X 2,257,373 9/1941 Fanselow 117 2,038,607 4/ 1939 Sauer.

2,312,927 3/1943 Murray 118126 3,029,780 4/1962 Justus et a1 118-126 3,080,847 3/1963 Justus 118-126 X 3,088,842 5/1963 Kuhnel 117--102 3,158,498 11/1964 Carpenter 11764 3,186,861 6/1965 Smith et al 11863 3,187,716 6/1965 Peterson et al. 11863 X 3,202,536 8/ 1965 Brezinski 118-126 2,257,113 9/1941 George 11863 3,03 8,441 6/1962 Wamsley 11863 2,536,186 1/1951 Keller 117-64 2,583,220 1/ 1952 Lanigan 117-6 FOREIGN PATENTS 4,590 1907 Great Britain.

DANIEL BLUM, Primary Examiner.

U.S. Cl. X.R. 118429

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