US3496012A - Coating apparatus and method - Google Patents

Description

Feb. 17, 1970 E. BIORSETH 3,496,012

COATING APPARATUS AND METHOD Filed Feb. 13, 19s? 3 Sheets-Sheet 1 FIG. I.

INVENTOR ELWIN J. BIORSETH Feb. 17, 1970 BDRSETH 3,496,012

COATING APPARATUS AND METHOD Filed Feb. 13, 1967 3 Sheets-Sheet 2 QINVVENTOR ELWIN .1. BIIORSETH AGENT W E J. BIORSETH Feb. 17, 1970 COATING APPARATUS AND METHOD 3 Sheets-Sheet 5 Filed Feb. 13, 1967 FIG. 5.

INVENTOR ELWIN J. BIORSETH AGENT United States Patent US. Cl. 117111 Claims ABSTRACT OF THE DISCLOSURE An apparatus and method for coating moving webs consisting of a stationary tubular member and a longitudinal fluid-metering means positioned adjacent thereto is disclosed. The tubular member is provided with apertures for the admission and discharge of coating fluid into a cavity formed by the tubular member and the metering device. In use a moving web is drawn over the tubular member so as to completely enclose the cavity. Coating fluid is fed through the admission apertures and completely fills the cavity, thus preventing exposure of the coating fluid to the atmosphere. Return of excess coating may be controlled by adjusting the angle by which the advancing web wraps the tubular member.

FIELD OF THE INVENTION This invention relates to apparatus and method for coating moving webs wherein fluid coating material is applied in excess; the excess material being distributed across the web and then removed from the coated surface. It relates further to coating apparatus wherein the coating material is maintained in an enclosed environment during the coating process.

PRIOR ART Any coating apparatus must perform the functions of application, distribution, and metering. Each of these functions presents special problems. Inventors in this field have generally devoted their attention toward the individual solution of those problems. As a result the present art includes numerous knives, airknives, blades, aprons, and bars for accurately metering the surface flow of a coating fluid which has previously been applied and distributed. Application devices include pans, rolls, sprayers, and extruders. Distribution is performed in many Ways, often in combination with the application or meterings steps. In general, machines which perform all three functions well are large, complex, and expensive combinations of well known components. In the usual case these machines are limited, in practical application, to a narrow class of coating materials.

In addition to the above limitations, existing apparatus are generally unsatisfactory for handling hot melts or other fast setting coatings. This is caused either by early exposure to the air, or by inadequate means to remove excess coating material from the application and metering area. Evaporation, coagulation, and build-up are typical results. Also it is not uncommon for excessive aeration to lead to frothing of aqueous type coatings. When hot melts are handled it is usually necessary to apply heat to numerous parts of the coating apparatus as well as to the coating fluid itself.

SUMMARY OF THE INVENTION My invention is a coating method and a compact, mechanically simple, and inexpensive coating apparatus adapted to apply, distribute, and meter coating fluid in a single combined operation without exposure to the air and with provision for removal of excess coating material from the coating area. The apparatus has as its main structure a large tubular member over which is drawn the uncoated web. This tubular member remains stationary dullng the coating operation. My apparatus includes also a longitudinal fluid-metering means positioned adjacent and parallel to the main tubular member; the intersection of the parallel members forming a longitudinal fluid holdmg cavity. The main tubular member is provided with one or more fluid admission apertures and one or more fluid discharge apertures. The admission apertures are so located as to provide a continuous supply of coating to the fluid holding cavity. The discharge apertures are so located as to be enclosed by the web in its approach to the fluid holding cavity. When the web is drawn over the tubular member it completely encloses a supply of coating fluid which has been forced through the admission apertures and into the fluid-holding cavity. Hydrostatic pressure forces excess coating fluid out through the discharge apertures. This arrangement of web and coating structure serves to isolate the coating fluid from the atmosphere. Furthermore, when the web is rapidly drawn across the relatively small coating region, the duration of the actual coating operation, or coating dwell time, is much reduced over conventional coating methods.

It is readily apparent to one skilled in the art that my invention may be used with a large variety of webs and coatings without the disadvantages which have been pointed out for prior apparatus. In particular coagulation, drying out, loss of solvent, build up of excess coating material, frothing, and contamination from air borne dirt are substantially entirely eliminated. Metering can be accurately controlled with a minimum of surface tension ridges in the completed coating. No local heating is required for application of hot melts. Furthermore, when hot melts are applied the reduced coating dwell time facilitates application at temperatures near the fluid congealing point, thus improving coating holdout. When water base coatings are applied, the reduced dwell time decreases soak-up of water into the web, thus eliminating the local viscosity increase which commonly causes defects such as film split marks in coatings applied at higher solids content. For application of solvent base coatings, such as overprints for printed webs, the shortened coating dwell time makes it possible to apply overprints that would normally dissolve the inks. Also, isolating the solvent base coating from the air reduces fire hazards.

Further advantages of the apparatus are simplicity and low cost of construction. Except for the metering means which, in the preferred embodiment, is a rotating wire wound rod, no moving parts are used. The main structure may be fabricated from pipe and flat metal plates.

Accordingly it is a principal object of my invention to provide a simple, compact coating apparatus for use with a wide variety of coatings, particularly those which are fast setting in nature.

Another object of my invention is to provide a method of coating a moving web wherein the coating dwell time is very short in duration and wherein the coating material is isolated from the atmosphere before and during the coating operation.

Another object of my invention is to provide a stationary coating apparatus capable of applying an excess of coating fluid to a moving web and removing the excess through surface apertures.

Another object of my invention is to provide a coating apparatus adapted to apply, distribute, and meter coating fluid to a moving web with no exposure of the coating material to the atmosphere until after completion of the metreing.

Other and further objects will be apparent from the description which follows.

3 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic drawing of a typical machine embodying my invention. For simplicity of illustration, the end plates which support the metering bar and prevent fluid seepage about the web edges have been omitted.

FIG. 2 is an enlarged sectional elevation drawing of the coating area for a machine using my invention in the form shown in FIG. 1.

FIG. 3 is an enlarged sectional elevation drawing of the coating area for a machine using my invention in a different form.

FIG. 4 is a sectional drawing of my coating apparatus in the preferred embodiment.

FIG. 5 is a sectional drawing of an alternate configuration of my coating apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a web of material is being pulled across a tubular member 11 which is supported by stand 18. The tubular member 11 may have any desired cross section, but, for manufacturing reasons, a circular cross-section is most desirable. Stand 18 rigidly supports member 11 so as to prevent any tendency to rotate with the moving web. A metering means, in this case a wire wound rotating bar 12, is placed in a small groove which has been milled into member 11. The crest of bar 12 rises above the surface of member 11 so that when web 10 is wrapped around the combined structure there is formed an enclosed pocket 15 which is best illustrated in FIGURE 2. Referring still to FIG- URE 1, the numeral 13 represents any of a series of small apertures which have been drilled into the surface of member 11. Apertures 13 provide a passageway for coating fluid which is most desirably pumped into line 16 filling a supply cavity within member 11 and thence out through apertures 13 into the pocket 15. A series of discharge apertures 14 provide passages through which excess coating fluid flows into the interior of member 11 and thence out through line 19 to a recirculation system which is not illustrated. A motor 17 rotates bar 12 in a direction either following or opposing the movement of web 10. The machine shown in FIG. 1 would ordinarily be provided with end plates to reduce seepage of coating fluid around the edges of the web, but for purposes of clarity they are omitted from the illustration.

FIGURE 2 illustrates in better detail the coating function itself. The rotating wire wound bar is completely wetted by coating fluid, but its rotation prevents the coating from running down the back side of member 11. I have found that the metering function is best performed when the wire wound bar is rotated at speeds between 20 and 40 r.p.m. A particularly novel feature of this :onfiguration is the location of the discharge apertures under the web in its approach path to the pocket 15. The web controls the return of excess fluid by restricting flow to the discharge apertures. Coating fluid should be supplied to the admission apertures at a pressure great enough to maintain a full coating pocket as well as a steady excess flow. However, this pressure must not be so great as to cause seepage of fluid around the edges of the web. Pressure relief may be achieved by throttling the supply, opening drain 27, or in many other obvious ways. Adjustments in internal fluid pressure may also be accomplished by altering the angle by which the web wraps member 11; particularly the wrap forward of discharge apertures 14 as designated in FIG. 2 by the angle on. I have found that a magnitude of about 60 degrees is most ideal for 0:. This wrap assures good contact, aids in preventing the formation of wrinkles, and seals the pocket [5. I have used this arrangement quite successfully in the :oating of hot melts.

FIGURE 3 illustrates the coating function for an alternate configuration. The various elements are numbered to correspond with similar elements in FIG. 2. The illustrated apparatus differs from that of FIGURE 2 in that the arrangement of the surface apertures has been changed and the rotating metering bar has been replaced by a knife. However the basic principle of the invention is present in both configurations. It will be apparent to one skilled in the art that many other variations may be employed. I do not intend to limit the scope of my invention by illustrating only 2 of the many possible configurations of the numbered elements. Furthermore, the use of the top of member 11 rather than the bottom or a side is not significant. My invention may be practiced in any desired vertical orientation.

The preferred structural arrangement is shown in detail in FIG. 4. Tubular member 11 has been cut away in sectioning fashion to expose a supply cavity 20 which has been formed by fastening plate 22 into member 11 with bolts 25. Coating fluid is forced into cavity 20- through an end plate aperture which is not illustrated but which is represented generally by 23. The coating fluid is forced through aperture 13 into pocket 15 where it is distributed and metered as previously described. The excess coating is forced down aperture 14 into discharge cavity 21 which is also formed in member 11 by plate 22. The excess coating continues out of cavity 21 through aperture 24 and thence into the recirculation system. For coating fluids which may be adversely affected by the drop through cavity 21, it might be desirable to install baflles or to maintain cavity 21 in a completely filled condition. A drain plug 27 is provided at the bottom of supply cavity 20. A guide roll 29 is mounted on an adjustable arm 34 to alter the wrap angle as above stated. Additional features which are illustrated in FIGURE 4 are a far end plate (near plate cut away) and a blade 26 for holding the web down in firm contact with the coating apparatus. Blade 26 is required in only a relatively few types of coating operations but it is shown for completeness of illustration. The tubular member 11 with its internal cavities and supply lines along with apertures 13 and 14 and the metering means 12 hereafter will be referred to as the coating head.

An alternate internal structure is illustrated in FIG. 5. Here the admission apertures 13 are replaced by a longitudinal slot (also denoted by 13 because of identity of function) which extends the entire length of member 11. A longitudinal weakening groove 32 also extends the entire length of member 11. A set of bolts 30' are fitted through openings in the wall of member 11 and threaded into plate 22. Washers 33 provide working surfaces between the wall of member 11 and the heads of bolts 30'. When bolts 30 are tightened down, the wall of member 11 is deflected longitudinally about the weakening groove 32 thus closing slot 13. In this manner the flow of coating fluid into pocket 15 may be accurately adjusted. Springs 31 may be provided if necessary for the reverse operation.

The process which is inherent in the invention is not specifically illustrated in any single figure but is generally shown in all figures. It consists of wrapping a web over a tubular structure adapted to form an enclosed cavity between the web and the said tubular structure. Coating fluid is continually forced into the said cavity and metered by drawing or pulling the web across a metering device forming part of the back wall of the cavity. Excess coating is continually removed from the cavity; the entire operation being carried out in such a manner as to prevent exposure of the coating fluid to the atmosphere.

I have successfully carried out the above process using apparatus as suggested by FIG. 1. Rolls of 33#/M.s.f. corrugating medium were coated at coat weights of approximately 10# /M.s.f. uniformly across the entire width of a 73% inch web at speeds up to 200 ft. per min. I used a commercial wax having a congealing temperature near F. and applied it at temperatures of to F. A 4 inch diameter rod wound with 0.024

inch diameter wire was used for metering and was rotated at 35 rpm. in the direction of web travel. The melted wax was pumped in through V inch diameter holes and removed through slots A inch wide. Wax flow to the coating head was controlled by throttling the supply valve. All excess molten wax supplied to the coating head readily flowed into the return slots and was carried back into the supply tank by means of a trough located under the entire length of the coating head. I found that it was necessary to continually circulate the hot wax through the coating head, when the unit was not being used, to prevent the wax from freezing in the lines and coating head.

What I claim as my invention is:

1. An apparatus for coating an unstable fluid upon a continuously moving web comprising a stationary, tubular, web-supporting member provided at its surface with at least one fluid admission aperture and at least one fluid discharge aperture, and a fluid metering means oriented with its axis parallel to the axis of said web-supporting member; said web-supporting member and said fluid metering means by the juncture of their surfaces defining a longitudinal fluid-holding cavity, and said apertures for fluid admission and fluid discharge each providing non exposed passage between the longitudinal fluid holding cavity and the interior of the web-supporting member.

2. A coating apparatus according to claim 1, said discharge apertures being arranged substantially along a first longitudinal line and said admission apertures being arranged substantially along a second longitudinal line, said second longitudinal line being located on the surface of said web-supporting member between said first longitudinal line and said metering means.

3. A coating apparatus according to claim 2, the surface of said tubular member being shaped in the form of a continuously curved arch in the area between said longitudinal lines, and the placement of said first longitudinal line being sufficiently remote from said metering means that a plane extending between said first longitudinal line and the crest of the metering means will intersect the surface of said tubular member; the line of intersection being situated between the metering means and said first longitudinal line.

4. A coating apparatus according to claim 3, said metering means comprising a rotatable bar.

5. A coating apparatus according to claim 4 and further comprising a backing means for holding said web firmly against said rotatable bar.

6. A coating apparatus according to claim 4 and further comprising a guide roll for adjusting the wrap angle of said web.

7. A coating apparatus according to claim 1 said at least one fluid admission aperture being a longitudinal slot running the full length of said tubular member and said coating apparatus further comprising means for defleeting the wall of said tubular member thereby to alter the width of said slot and adjust the rate of coating fluid movement therethrough.

8. A method of coating an unstable fluid upon a moving web comprising the steps of:

creating an enclosed pocket by wrapping said web around a stationary tubular member having a longitudinal surface cavity and discharge means communicating with said cavity, introducing coating fluid into said pocket under pressure and at a rate in excess of that required for application to the web, whereby said pocket is maintained completely full at all times with said excess being continually expelled via said discharge means, and

pulling said web across said longitudinal surface cavity and against the rear wall thereof, thereby metering and distributing non-expelled coating material onto the surface of said Web.

9. A coating method according to claim 8 and further comprising the steps of continually recirculating said coating fluid from said discharge means to said surface cavity.

10. A coating method according to claim 9, said coating fluid being thermally unstable and said method further comprising the step of preheating the coating fluid to a temperature near but above the fluid congealing point thereby promoting rapid post-application congealing for improvement of coating holdout.

' References Cited UNITED STATES PATENTS 1,983,982 12/1934 Knallenberg 118414 X 2,464,771 3/1949 Van Guelpen 118413 X 2,765,769 10/1956 Schroeder 118411 3,413,143 11/1968 Cameron et al 117--120 ALFRED L. LEAVITT, Primary Examiner C. R. WILSON, Assistant Examiner U.S. Cl. X.R.

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