US2313497A - Method of coating paper - Google Patents

Description

March 9, 1943. H. J. ADRIAN METHOD OF COATING PAPER Filed Jan. 12, 1940 machine.

Patented Mar. 9, 1943 METHOD OF COATING PAPER Harry J. Adrian, Stevens Point, Wis., assignor to Consolidated Water Power and Paper Company, Wisconsin Rapids, Wis, a corporation of Wisconsin Application January 12, 1940, Serial No. 313,476

2 Claims.

This invention relates to improvements in a process and apparatus for coating paper, par

ticularly relatively lightweight paper on a Yankee" type paper machine, the process and apparatus being characterized in that the resulting coated paper is uniformly and smoothly coated and the paper is rendered substantially opaque with a weight or quantity of coating material heretofore deemed insuiiicient for that purpose.

In the manufacture of relatively light weight papers upon a Yankee machine, the paper after formation is subjected to mechanical pressure and then passed to the single drier drum of the The fact that the paper is of light weight permits drying on one drum, the drum, however, being of relatively large diameter. One characteristic of paper so made is that, that surface of the paper web which contacts the drum surface is glazed by such contact and the paper is accordingly known to the art as a machine glazed paper. To obtain a uniformly glazed sheet the drum surface must be perfectly smooth and this surface isvery jealously guarded by the paper maker to make sure that the drum surface is maintained in this condition.

The paper being very thin and very smooth on the glazed side is normally quite translucent which is objectionable for many uses. Consequently, it is frequently desirable to opacify the paper, which has been accomplished by loading the paper with mineral matter usually in the form of a filler or as a surface coating. It has frequently been the practice to apply the mineral matter in the beater or on the forming wire. However, either operation involved many difllculties including waste of mineral matter and loading of the blankets which carry the paper to the drier, which latter necessitates frequent cleaning of the blankets and, hence, frequent shut-downs.

To obviate the diificulties hereinbefore set forth, it has been proposed to apply the mineral matter as a coating to the web while the same is on the drier drum. My invention constitutes an improvement-on this latter type of operation.

Briefly described,.my invention comprises passing a newly formed web forwardly after it has had a portion of its water removed mechanically, applying the web to the surface of the drying drum and substantially immediately thereafter subjecting the web on the drum to rolling pressure, and subsequently coating the web while the same is firmly adhered to the drum.

The novel step in my process comprises essentially the step of smoothing and pressing the substantially wet web into intimate contact with the highly finished drum surface. Many advantages flow from the use of this step in my process which are set forth as follows: The web, being relatively damp is firmly and uniformly pressed into contact with the hot surface and, in effect, is stuck onto said surface; the outer surface of the web is smoothed to a proper degree of uniformity to serve as an ideal foundation for the film of coating material subsequently applied thereto; the caliper of the finished paper is controlled at a point when the paper is in the best condition to have such control exercised without the production of glazed spots or crushing, as may be the case where the caliper is controlled by an after-calendering operation; my process results in better bonding of the coating film to the web as a result of providing-a smoother foundation for the coating, and to secure a predetermined degree of opacity a lesser amount of coating material is necessary than has hereto fore been the case.

Other objects and advantages of my invention will be apparent from the accompanying drawing 'is diagrammatically shown for carrying out my invention.

In the drawing, I indicates an upper endlessly traveling blanket trained around guide rolls 2, and 3 indicates 'a lower endlessly traveling blanket trained around guide rolls 4. Blankets I and 3 are conventional expedients employed in the usual Yankee paper machine and are adapted to support or embrace a web 5 in its passage from the forming wire (not shown) of a conventional paper machine.

The web 5, confined between blankets I and 3, is passed between the press rolls 6 and 1 whereby a portion of the moisture is mechanically expelled from the web and absorbed by the blankets. After passing between the rolls 6 and I the lower blanket 3.leaves the web and returns to the wet end of the machine over guide rolls 4.

The web accompanied by the upper blanket I passes undercouch roll 8 and around guide roll 2'; which is disposed adjacent the periphery of drier drum 9; thence between the surface of said drier drum and roll 8. At this point in the travel of the web it is stripped from the blanket I and adheres more or less imperfectly to the surface of the drum. The blanket then continues its travel over guide rolls 2 to the wet end of the which is journalled upon each side of the drum in bearings ll, only one of which is shown. The bearings H, in turn, are carried by beams l2 supported by standards I3 which constitute a portion of the frame of the machine.

Roll 8 is mounted upon shaft l4 which is journalled in opposite bearings l5 which are supported by link [6 pivotally mounted at its end, as at 11, to a portion 18 of the frame of the machine. A link is is: also connected to bearing l5 on each side of the machine and each link is pivotally joined to a rod 20.

A standard 2| is mounted upon beam [2 on each side of the machine and pivotally supports a lever 22, as at 23. The lever 22 is pivoted adjacent one end thereof, so as to secure a high mechanical advantage, the short arm of the lever being connected to rod 24. The ends of rods and 24 are connected by means of a tumbuckle 25 whereby the effective length of the connection between lever 22 and arm l9 may be changed by proper manipulation of the turnbuckles.

The opposite or long arm of lever 22 is con-- nected to rod 26 which carries at its opposite enda piston 21. Piston 21 is adapted to operate in cylinder 28, the lower endof which pivotally connects with rod 29. A hand wheel is threadedly mounted adjacent the endof rod 29 and a coil spring 3 I, embracing said'rod, is confined between handwheel 38 and the lower surface of beam i2. Of course, it is to be understood that a similar mechanism is provided upon the opposite side of the machine.

It can readily be seen that by the provision of turnbuckle 25 and handwheel 30 the effective length of the connecting rods at each end of the lever 22 may be regulated, and by the provision of spring 3| and cylinder 28, which latter is adapted to contain a compressible fluid, the roll 8 may be brought to bear upon the drum 8, confining the web 5 and blanket I therebetween, with resilient pressure.

A roll 32, mountedupon shaft 33, is carried by bearings 34 on each side of the machine. A link 35 connects said bearing to a lug 36 suspended from beam I2, the end of link 35 being pivoted to said lug, as at 31. An arm 38 is also connected to bearing 34 and is pivotally attached to rod 39.

A lever. 40 is pivotally mounted upon standard 2|, as at 4|, said lever being fulcrumed adjacent one end whereby a high mechanical advantage may be obtained. The short arm of the lever 40 is connected to rod 42, the end of which is, in turn, connected by means of turnbuckle 43 to rod 39 whereby the effective length of the connection between lever 48 and arm 38 may be conveniently changed.

The opposite or long arm of lever connects with rod 44 which in turn carries a piston (not shown) which operates in cylinder 45, which latter is similar in construction and operation to cylinder 28. The lower end of cylinder 45 is pivotally connected to rod 46 which is threadedly associated adjacent its opposite endwith a handwheel 41. A coil spring 48 embraces rod 46 and is confined between handwheel 41 and beam 12.

The arrangement is such that by the proper manipulation of handwheel 41, roll 32 can be brought to bear upon web 5 carried on the surface of drum 9 with a desired degree of pressure. Also, by the provision of the pneumatic cylinder 45 and the spring 48 the roll 32 is urged under resilient pressure.

It has been found that when the drum 9 of a Yankee machine is heated to different temperatures or when the steam pressure therein varies, the shape of the drier surface changes. Accordingly, in order that roll 32 shall be capable of firmly smoothing and uniformly sticking the web to the drum surface, its surface is preferably such that it will conform to the variations in shape of the drum surface. The roll 32, therefore, may be provided with a resilient surface, such as a medium hard rubber or may be constructed with coaxial layers of hard rubber, soft rubber and an outer surface of relatively hard rubber, somewhat similar to the roll described in Wightman, Patent No. 2,031,872.

of course,-I do not wish to be limited to the specific structure of roll 32 since a smooth surfaced roll of substantially any suitable material can be employed to secure an improved resultant coated sheet.

In the conventional method of making paper the prime control of the bulk (caliper) and finish of the paper resides in a calender stack positioned after the Yankee drier 9, However, by the proper manipulation of roll 32 by means of handwheel 41, less and sometimes no machine calendering is necessary. On some grades of paper where high caliper is desired the after-calendering operation can be dispensed with entirely. In other instances the number of nips through which the paper i passed and the pressure used in the nips may be reduced. This is an important advantage since excessive calendering results in a product having spots which are excessively glazed or crushed. Further, by the use of the roll 32 a higher caliper for a predetermined fin- -ish can be obtained since less calendering is necessary. .Thus, the double control of caliper and finish can be exercised to give lower or higher bulk and lower or higher finishfdepending on the grade of paper desired) than could possibly be accomplished by the calender.

The web 5 when contacted by the roll 32 has a relatively high moisture content ranging in the neighborhood of 50 percent, Normally when a web passes through the conventional machine calender it has a relatively low moisture content It isclear, there in the neighborhood of 6%. fore, that greater smoothing and compacting can be accomplished-by roll 32 than could possibly be obtained by the use of a machine calender without damaging the web. Excessive calendering frequently injures the machine glaze finish; reduces the tear properties of the web, and results in excessively glazed and crushed spots on the coated surface of the web.

After the web 5 has been smoothed, reduced in caliper and firmly and uniformly stuck upon the drum surface, said web is carried into operative contact with a coating roll 45 whereby coating material having a relatively high solids content is applied as a finished film upon the smooth surface of the web 5.

The condition of the surface of the paper web is of vital importance, particularly in roll coating operations, and greatly influences the finished coated sheet, In addition, it has been found that different type papers taken directly from the paper making machine and passed through the coating device will have resulting finishes which are different even though the coating operation in each case is the same. However, in passing the web through the step which characterizes my invention, that is, by firmly sticking the web to the drum surface and smoothing and compacting the web previous to the coating operation, a responsive control is obtained over the characteristics of the finished surface regardless of the base paper stock.

In previously smoothing the web surface by means of the roll 32 while the web is carried on the hot surface of the drum, an action resembling an ironing action takes place, probably due to the combination of the simultaneous application of pressure and heat upon the wet web. A very smooth and compact surface results and inasmuch as the film of coating material applied by the roll 49 tend to conform with the surface of the web, .a smooth coated surface results.

The coating roll 45 is in osculating relationship with a distributing roll 50 which in turn contacts a gate roll or metering roll 5|. Another gate roll 52 is disposed in osculatory relationship with gate roll 50 and rolls 5| and 52 are adapted to carry in their nip, a coating suspension of mineral material, the suspension being of relatively high solids content. A dam 53 is disposed between rolls 5| and 52 adjacent each end thereof and is adapted to confine the mobile coating material in the nip.

In the manufacture of paper, particularly relatively light weight paper, pin-holes inherently exist in the paper. If extreme care is not taken in coating the paper upon the drum, the coating material may seep through said pin-holes and reach the drum surface. In this event the drum surface, which is very jealously guarded by the paper maker, may be injured and may involve the expensive and time-consuming task of cleaning or resurfacing the drum.

By applying pressure to the web 5 while it is still in a pliable condition, that is, while it is still relatively wet, most of the pin holes can be permanently ironed closed and, hence, the subsequent coating operation can be carried out in complete safety insofar as the drum surface is concerned.

By the provision of the gate rolls 5| and 52, a predetermined quantity of coating material may be fed forwardly per unit of time.- By passing the coating material over the surfaces of a plurality of rolls, the coating material is transformed into a smooth film of uniform thickness. This film is applied to the web substantially bodily and is dried upon the web during the remainder of the travel of the web over the drum surface without further treatment or smoothing. The coated web may then be stripped from the drum surface and passed around guide roller 54 to be rolled, out into sheets or otherwise operate upon.

It can readily be seen that herein is described a process which possesses at least four important attributes. One, the-wet web is stuck to the drier drum which is of great importance in the subsequent coating step, and this sticking of the web cannot be effectively accomplished by the couch roll; two, the surface of the web is smoothed and compacted to provide an ideal support for the coating film; three, the compacting action closes substantially all pin holes which preserve the life of the drum surface, and, four, the desired caliper and finish of the web is secured by the ironing action when the web is in the best condition to have such action performed mineral coating suspension while the web ad heres to said rotating surface, drying said web and coating thereon while the web is carried by said rotating surface, maintaining the coated surface intact while the web is carried by said surface, stripping said dry coated web from said rotating surface, and maintaining said web in substantially smooth condition while stripping the same from said surface.

2. A method of coating paper of the type made on a Yankee paper machine to form a surface thereon which is uniformly smooth and suitable for the reception of printing which comprises, passing a newly formed wet web forwardly, mechanically removing a portion of the moisture therefrom, thereafter carrying one surface of the partially wet web into contact with a heated, imperforate, rotating surface, thereafter sticking said web upon said rotating surface and simultaneously smoothing the other surface of said web by resilient rollingpressure, coating said other surface with a mineral coating suspension while the web adheres to said rotating surface, drying said web and coating thereon while the web is carried by said rotating surface, maintaining the coated surface intact while the web is carried by said surface, stripping said dry

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