US 2320883 A
Description (OCR text may contain errors)
June 1,1943. L. PARKINSON I 2,320,883
PAPER-COATING APPARATUS Filed Nov. 16, 1959 2 Sheets-Sheet 1 Invfirgtnr L'FarKrnsun June 1, 1943. L. PARKINSON PAPER-COATING APPARATUS Filed Nov. 16, 1939 2 Sheets-Sheet 2 lnventui" LPaT'Ki-n EDT].
RQNH \\v Patented June 1, 1943 Leonard Parkinson, Park Falls, Wis. Application November 16, 1939, Serial No. 304,771
This invention pertains generally to the'manufacture of paper, and more particularly to apparatus for coating a wetweb of paper, by means of atomizing nozzles.
It is old in the art to spray paper for decorative and other purposes, such as altering the characteristics of the paper. However, methods heretofore practiced have presented serious objections, in that dripping of the spray mixture from the coating apparatus and other adjacent parts of the paper machine resulted in streak ng of the paper and an uneven homogenity in the coated surface. It was also found that dripping was accentuated by unabsorbed mist or vapor released into the surrounding atmosphere to accumulate upon adjacent parts of the paper machine. and
also contaminate the atmosphere in the room,
producing unfavorable working conditions.
The present invention has primarily for its object the provision of a comparatively simple and effective apparatus positioned above a wet web of paper as it travels through a paper ma-. chine in a continuous process of manufacture, for spraying a coating mixture upon the surface of the web, and designed to avoid all dripping of themixture upon the web, and remove free mist or vapor to prevent accumulation and condensation upon adjacent parts of the machine, as well as escape into surrounding atmosphere.
Incidental to the foregoing, a more specific object'of the invention resides in guidingthe wet web of paper as it leaves the press rolls in an upward and-lateral drection over a coating roll, against which the spray nozzles are directed in such manner that any dripping from the coating apparatus is prevented from coming in contact with the we x Another object of the invention resides in the provision of means for removing free and unabi0 sorbed mist or vapor from the atomizng nozzles and preventing its accumulation upon adjacent parts of the machine or escape to surrounding atmosphere, said means comprising a directional circulation of air across the webadjacent the coating apparatus. I
A still further object is to provide for the collection and return to the unabsorbed coating mixture that nfay accumulate and drip from parts of the apparatus.
With the above and other objects in view,-
which will appear as the description proceeds, the invention resides in the novel construction, combination, and arrangement of parts, substantially as hereinafter described, and more particularm In the drawings:
system of excessive 1y defined by the appended claims, it being understood that such changes in the precise em-- bodiment of the herein disclosed invention may be made as come within the scope of the claims.
5 In the accompanying drawings is illustrated one complete example of the physical embodiment of the present invention constructed according to the best mode so fardevised for the practical application of the principles thereof.
Figure l is a diagrammatic showing taken longitudnally through a portion of a paper making machine equipped with the present invention, the same being indicated on line 1l of Figure 2;
Figure 2 is a transverse section taken on the line 2-2 of Figure 1;
Figure 3 is a fragmentary, plan view illustrating the directed circulation of air across a web of paper adjacent the coating apparatus; 7
Figure 4 is an enlarged, detail, sectional view of the drip trough constituting part of thecoating apparatus.
Referring now more particularly to the accompanying drawings, the invention is illustrated as facture, and preferably the same is installed above the press rolls P interposed between the Fourdrinier screen F and the drier D.
In the drawings, dual press rolls are illustrated, but it is to be understod that the invention may press rolls, which receive the web W from the Fourdrinier screen F. From the hard roll 5 the web is trained upwardly over a guide roll 6, and from there laterally over a coating roll I to the rolls of-the drier D. J
The coating apparatus C. consists of a casing 8 for reception of'a transverse header 9, connected with a plurality of atomizing nozzleslll by tubes I I. The rear wall of the casing 8, through which the nozzles l0 project,constitutes a splash guard l2, the lower edge of which extends below the bottom of the casing 8 to'form a bathe in connection with the walls of a. drip trough-l3 positioned below the casing. v
Connected to the rear wall of the trough l3 by means of a shiftable hinge I4 is an inclined drip plate 15, which, inits normal position, terminates at its upper edge closely adjacent the coating roll I, but sufliciently spaced therefrom to avoid contact with the paper web W. A suit- 'able drain I6 is provided for the drip trough lit for return of collected slurry or coating mixture to a source of supply.
applied to a continuous process of paper manuapplied to any conventional arrangement of As shown in Figure 1, the atomized spray from the nozzles I is directed against the coating roll I, and, consequently, the force of the spray is opposed by the coating roll, thus preventing sagging or distortion of the wet web, to say nothing of mutilation or rupture of the same. Due to the fact that the paper web W travels at an angle from the guide roll 6 to the coating roll 1, as shown in Figure 1, it will be apparent that any unabsorbed coating mixture dripping from the upper edge of the plate l will fall upon the exposed face of the press roll 5, from which it is removed by a doctor blade 5'. To facilitate carrying the paper over the coating roll upon occurrence of a break in the web, the drip plate Hi can be shifted on its hinge connection and swung away from the coating roll, as indicated in Figure 4.
For the removal'of mist or fog released by the spray jets, a hot air flue i1 is positioned at the rear side of th machine, the flue being in communication with a suitable blower and heating apparatus (not shown) disposed below the base plate i8 of the paper machine. As best shown in'Figure 2, the flue ll extends across the paper machine and terminates in a laterally directed nozzle 19, which projects a blast of heated air across the paper web, after the same has left the coating roll I. Naturally, the heated air travelling across the webwill pick up loose vapor, and in order to collect the same, a hood 20 is positioned at the rear side of the machine, while a flue 2| connected to the hood serves to carry the collected vapors to outside atmosphere.
To further insure the collection and removal of mist or vapor, a curtain 22 is positioned rearwardly of the hood 20, the same being carried upon a reel 23, which permits the curtain to be wound up when the coating apparatus is not in operation. When in use, the curtain is drawn down over the smoothing press rolls 24, and anchored in any suitable manner, the lower edge of the curtain terminating closely adjacent the paper web W as it leaves the guide roll 25 to enter the drier D.
To further prevent escape of free suspended mist into the drier, the fluel'l is provided with a perforated duct 26, extending transversely across the web and applying heated air against the web in the direction of the spray apparatus C, thus serving to repel the mist and also partially dry and set the coating before the web engages the hot cylinder of the drier. After leaving the first drier cylinder, the coated surface of the web is further set and dried by an additional perforated hot air duct 21, also in communication with the From the foregoing explanation, considered in connection with the accompanying drawings, the structure and operation of the invention will be readily apparent. However, in order that a full appreciation of the resulting advantages may be had, various problems encountered and the action of the apparatus in overcoming the same will be discussed in detail.
Byactual tests and experiments it has beenestablished that the most satisfactory and economical method of applying certain coatings containing pigments which have a tendency to drop out of suspension, such as mica, titanium dioxide, metallic powders, etc., isby spraying the paper during a continuous process of manufacture, although, of course, the method established here will apply to the application of all forms of coat- Attempts have been made to spray the web while on the Fourdrinier screen, but these were found to be objectionable in that the pulp is highly saturated.and, therefore, easily affected by the force of the spray. Furthermore, a great part of the coating mixture is lost by drainage through the Fourdrinier wire with the white water, particularly in the zone of the suction boxes. In its saturated condition, the web is incapable of absorbing a sufficient amount of coating mixture.
Also, after the web leaves the Fourdrinier screen it must pass through press rolls, and fiaturally because of thesaturated condition of the paper, the coating mixture has no opportunity to set. Being of a tacky consistency, the same will adhere and accumulate on the press roll, interfering with feed of the web and causing uneven coating and homogenity in the surface of the paper.
To overcome the foregoing objections, the present invention provides for applying the coating to the web after it leaves the press rolls, and before entering the drier. The advantages of this are numerous, as will be pointed out. In the first place, the moisture content of th paper after leaving the press is such that it has sufficient tensile strength to permit the web to be trained over guide rolls in a direction most suitable to application of the coating spray; and due to its reduced moisture content at this point in the process, it is capable of absorbing exactly the desired amount of coating. By the foregoing arrangement, it is also possible to eliminate dripping from the spraying apparatus upon the face of the web, which causes streaking an un-- even homogenity irr'the same.
In'the actual spraying operation, it has been found necessary to use air pressure of approximately forty pounds, in order to effectively disperse the coating slurry so as to produce an ev n and continuous coverage of the paper. Consequently, the web must be supported adjacent the area of contact by thespray, to prevent rupture of the web. In that form of the invention disclosed, the foregoing is accomplished by a single roll against which the spray jets are directed, but it is to be understood that any form of support may be employed, such as a plurality of rolls closely adjacent the spray area.
Due to the amount of pressure required for the spray jets, it was found that considerable mist was normally released from the jets themselves, in
addition to that caused by rebound of the coating mixture from the web surface. Therefore, in a practical apparatus, it is absolutely emential that the mist or fog be controlled to prevent its entrance into the drier section, and its accumulation on the cylinders causing the web to stick and consequently break. As heretofore explained, mist suspended over that stretch of the web disposed between the spray apparatus Cand the drier D is prevented to a large extent from entering the drier by the curtain 22, augmented by the hot air duct 26; while the air circulated across the web from the'nozzle l9 toward the hood 20, removes the mist to outside atmosphere, thus preventing both accumulation of mist and convicinity of the jets proved to be impractical, due
.and collected in the drip trough.
to a tendency to build up back pressure under such conditions, which resulted in a distortion of the spray pattern. Forced draft could not be utilized for the same reason. Consequently, the problem presenting itself was to collect the unabsorbed solids in the spray mixture rebounding from the surface of the web, and at the same time release the air to avoid back pressure, or distortion of the spray.
The invention accomplishes the foregoing by the provision of the splash guard l2, so positioned with relation to the drip trough 13 as to provide a baffle for obstructing the rebound mist, causing liquids and solids to accumulate on the guard and drip into the drain trough, from which they are returned to the source of supply. During the foregoing action, the mist contacting the splash guard is directed downwardly, and passes in a circuitous path between the lower edge of the splash guard and the rear wall of the drip trough l3, as indicated by the arrows in Figure 1; during which travel practically all of the solids contained in themist are released from the same,
Having overcome the difliculty of controlling the mist or fog, the all important feature of eliminating dripping upon the surface of the web presented itself. To meet the situation, it is highly essential that the drip trough be positioned below that portion of the web contacted by the spray jets, and also the splash guard must be arranged at substantially a right angle to the axes of the spray jets, to obstruct rebounding mist and shed accumulated liquid into the,drip trough.
In actual practice, it was found that suflicient coating accumulated on the upper edge of the drip plate l5, adjacent the web, to cause dripping, and, therefore, to prevent the same from contacting the surface of the web with resultant streaking, the invention includes positioning of the drip trough above the press roll under which the paper travels, so that any dripping from the unit will fall upon the roll, from which it is removed by the doctor blade 5'. This arrangement necessitates training the web upwardly from the press roll so as to overhang the same, it being understood that the spraying operation takes place on the overhung portion of the web;
It will thusbe seen that an exceedingly simple and effective spraying apparatus has been de-' vised for coating a web or paper during a continuous process of manufacture, in which mist or fog and unabsorbed slurry is controlled and 001- I lected to prevent escape and accumulation on adjacent parts or the paper machine, and into the room. Also, possibility of dripping of the coating mixture upon the surface of the web is absolutely precluded.
1. An apparatus for coating a traveling web of paper comprising, a drip trough, means for guiding the web from immediately below said trough and in a path extending over one edge only, leaving the remainder of the trough exposed, and a spray unit including a splash guard extending transversely of the web and spaced therefrom, said guard being arranged to drain into said trough and allow free passage of air between the trough and guard, and spray nozzles extending through said guard for directing jets of coating material against the portion of web overhanging said trough. 2. An apparatus for coating a traveling web of paper comprising, a drip trough, means for guiding the web from immediately below said trough and in a path extending over one edge only, leaving the remainder of the trough exposed, a spray vunit including a splash guardkextending transversely of the web and spaced therefrom, said guard being arranged to drain into said trough andallow free upward passage of air between the trough and guard, and spray nozzles extending through said guard for directing jets of coating material at a downward angle against the surface of the web immediately above the drip plate, said guide means serving to support the web at the point of impact of said jets.
3. An apparatus for coating a traveling web of paper comprising, a drip trough, means for guiding the web from immediately above said trough and over one edge only, leaving the remainder of the trough exposed, said trough including a drip Plate extending to alpoint closely adjacent and below the overhung portion of the web, and a spray unit including a splash guard extending transversely of the web above said trough to drain into the ,same and allow free passage of air between the trough and guard, and spray nozzles fextendingthrough said guard for directing jets of coating material against the surface of the web immediately below the drip plate, said drip plate being movable toward and away from the web.