US2214772A - Process and apparatus for coating paper - Google Patents

Description

Sept, 17, 1940.

G. D. MUGGLETON PROCESS AND APPARATUS FOR COATING PAPERl Filed Nov. 1s, 195'? Patented Sept. 17, 1940 PATENT OFFICE d y 2,214,772 rnocpss AND APPARATUS Fon coA'rrNG f PAPER Gerald D. Muggleton, WisconsinRapidav Wis., as-

' signor to Consolidated-Water Power & Paper Company, Wisconsin v tion of Wisconsin Rapids, Wis., a corpora- 4 Application November 18, 1937, Serial No. 175,182

8 Claims.

This `invention relates to improvements in a method and means for coating, paper, and refers specically to a continuous method of applying l a controllable -amount of coating material to 'op- 5 posite surfaces of a newly formed web of paper. while the same is on the paper forming Wire, and means for carrying out said method.

In making paper upon the conventional Fourdrinier machine, difficulty is encountered in that 1 opposite sides of the paper are not alike in appearance, or in structure, that is, the paper is two sided. This diculty is more or less inherent in the paper making operation and is caused in part by the fact that one side of the paper is in contact with the Wire during its formation and, consequently, almost invariably has a wire mark. In addition, the paper making operation is in the nature of a ltering action wherein the aqueous carrier of the pulp 4is filtered through 80 rst the'wire and then the wire and the fibrous layer upon the wire. As a consequence those fibres having one 'set of characteristics will settle or be deposited first and will form the lower faceor wire side of the`web, whereas those which form s the upper facemay have slightly diierent characteristics. For instance, the top surface of the web will contain more fine bres and more filler, -where filler is used, than the wire side and will normally be brighter and smoother than the wire side.

Broadly, my method and apparatus is adapted i to overcome thistwosidedness of the paper by applying a coating material to both faces of the web while it is on the paper forming wire. Speu 'ci'flically, my invention provides a method for closely controlling the continuous application of coating material to Lboth faces of the web whereby, after the'desiredquality and quantity of coating applied to each face is initially determined, the 40 entire web may be coated with a desired weight and quality on each face without necessitatin further anchustments.

As another feature of my invention, a web may be coated continuously as hereinbefore described with the loss of a minimum amount of coating material, since, the coating material which would normally be discarded during the coating of one face of the web, is used as the major bulk of the n' coating material -used upon the opposite face of the web.

Other objects and advantages of my invention will be apparent from the accompanying draw-- :lng and following detailed description.v The single drawing is a diagrammatic side sec- .machine in conjunction with/which apparatus for carrying out my invention may be employed. The machinel comprises the usual head box 2 in which a quantity of pulp 3 is stored and from which said pulp is continuously fed tothe upper pass of an endlessly moving paper forming wire 10 4. The wire 4 travels in endless fashion around breast roll 5, adjacent the head box 2 and at the opposite end of itstravel said wire passes around a suction couch roll 6. The wire 4 on its upper pass travels substantially horizontally from the r'oll 5 to the couch roll 6 and is supported for a predetermined distance from the breast roll 5 by means of table orrtube rolls 1. Between the last tube roll I and the couch roll 6, the wire passes over a plurality of suction boxes 8. The wire during itsl lower or rearward pass travels into contact with a wire tightening roll 9 andk carrier rolls I0.

The pulp 3 comprises a dilute suspension of fibres in an aqueous carrier and when said pulp is flowed on to the paper forming wire 4, the aqueous carrier together with a portion of the suspendedrflbres pass through the wire. 'Ihe paper forming action is in the nature of a ltering operation, the wire tending to retain a quan-f tity of the fibres upon its upper surface until a fibrous mat or web II is formedupon said sur' face. 'I'he tube or table rolls I contact the lower surface of the wire and tend to assist in the removal of the aqueous carrier. 'When the wire 35 carrying the web I I passes over the suction boxes 8, a lfurther quantity of the carrier is removed.

At thecouch roll Iithe web II has been sufil-i ciently dehydrated to form a coherent mat which may be stripped from the couch roll. This mat 40 or web is then carried forwardly through suitable press rolls (not shown) and is eventually dried by passing the same over a plurality of heated drying drums (not shown). ,l

yIn the forming of the web II upon this type of paper machine, difficulty has heretofore been encountered in obtaining opposite surfaces of uniform appearance. As has been hereinbefore described, tlgiis diiculty is inherent in `the paper making operation and is cured by my invention.

A chamber I2 is positioned adjacent and preferably beneath the couch roll end of the paper machine and is adapted to carry a quantity of coating material I 3 which may be introduced into said chamber through pipe I4 controlled by valve 55 I5, the opposite end of saidfpipe being connected to 'a suitable source of supply. 'I'he coating material I3 may comprise any of the conventional coating suspensions or solutions which have heretofore been used in the coating of paper for printing or opacating purposes.

A pump I6 is connected by means of pipe I1 to a lower portion of the container I2, the pipe I1 comprising the intake of the pump I6. The pump I6 may -be driven by any conventional means (not shown). Coating material I3 drawn by the pump I6 is forced upwardly through pipe I8 which is controlled by valve I9, said pipe discharging into fountain positioned immediately beneath the upper pass of the wire 4 between the last suction box 8 and the couch roll 6. A roll 2| is disposed with its surface in contact with the lower surface of the paper forming wire 4, the surface of said roll being adapted to dip in the coating material I3 carried in the fountain 28. By means of this arrangement coating material I3 is carried upon the surface of roll 2| and is applied to the lower surface of the wire 4. A portion of the coating material I2 passes through the interstices of the wire 4 and forms a film or layer of 'coating material upon the lower surface of the web II. This coating operation per se has heretofore been employed and comprises no part of my invention except in the combination to be hereinafter more fully described.

As has been hereinbefore described, roll 6 is of the suction couch type, the condition of vacuum Within the rollbeing established by means of a suitable suction pump not shown, connected to the end of pipe 22 which, in turn, connects into the interior of the roll 6. It can readily be seen that a portion of the coating material which is not applied to the lower surface of the web II, will be drawn into the interior of the suction couch roll 6 and will be removed therefrom through the pipe 22. A pipe 23 connects into pipe 22 and discharges into the storage container I2. A suitable trap (not shown) of conventional construction, may be provided in the pipe 22 and the pipe 23 may connect with said trap whereby the coating material retrieved through pipe 22 is returned to the storage container I2.

In view of the fact that the coating material I3 is in a relatively dense state when applied t0 the lower surface of the wire 4, the major por -tion of said coating material which is not applied to the lower surface of the web II, remains on the wire and is not drawn through the suction couch. However, there will bel a portion of said material drawn through the couch roll 6 and returned through the pipe 23 to the storage container I2.

A vat or pan 24 is positioned beneath the lower pass of Wire 4 between the wire tightening roll 9 and the couch roll'6. Immediately above vat 24, one or more rolls 25 may be positioned, wire 4 upon leaving couch roll 6 being adapted to pass over said rolls. A pipe 26 controlled by valve 21 carries a shower head 26 at its end, said pipe being connected to a suitable source of water (not shown). The shower head 28 is positioned above wire 4 and slightly in advance of roll 25 and is adapted to direct a spray 23 of water upon the wire 4. Av pipe 30 controlled'by valve 3I is connected at its end to a suitable source of water and carries at its opposite end a shower'head 32 which is positioned above wire 4 and slightly in advance of the second roll 25. In like manner a pipe 33 is connected to a suitable source of water under pressure and is controlled by valve 34, the opposite end vof said pipe carrying a shower head 35 which is positioned above wire 4 and slightly in advance of the third roll 25. Both shower heads 32 and 35 are adapted to direct a spray of water 36 and 31 upon wire 4 as shown in the drawing.

By this arrangement all of the coating material I3'which remains upon the wire 4 after the lsame leaves the couch roll, will'be driven from the wireby the sprays 29, 36 and 31. In addition, each roll 25 will assist in the removal of the coating material and a scraper or doctor blade 38 is\positioned in contact with the surface of each of th rolls 25 to remove coating material which may be carried upon the surface of the rolls 25.-

It can readily be se'en that the coatingmaterial thus removed from the wire 4 is retrieved in the vat or pan 24. A pipe 39 connects into the bottom of vat 24 and discharges into a storage container 48 at its opposite end whereby the coating material 4I retrieved is passed to the.

storage container 48.

A pump 42, driven by any suitable means (not shown), is connected to a lower portion of the storage container 48 by means of pipe 43 which constitutes the intake of the pump 42. The discharge of the pump 42 is connected to pipe 44 controlled by -valve 45. -The upper end of said pipe connects into the bottom of the fountain 46 which is positioned above the upper pass of wire 4. A roll 41 is disposed in the fountain 46 in such a manner as to have its surface dip into the coating material 4I maintained in the fountain. A member 48 is disposed in contact with the upper portion of roll 41 and forms an inclined surface which leads to the upper surface of web II upon wire 4. The member 48 is adapted to remove coating material from the surface of roll 41 and said coating material travels downwardly along the inclined face of the member 48 and is deposited web II.

It can readily be seen that by the arrangement hereinbefore described both surfaces of the web I I may be coated before the web leaves the paperforming wire. However, in view of the fact that the opposite faces of the web are initially different in character, the coating material applied to the respective faces must be closely controlled as to amount and consistency or density so that inthe final web both faces are alike. In addition, since the coating material charged to the'` system comes from the same source, namely, the storage container I2, the system must be susceptible to upon the upper surface of the constant, continuous operation after once ad- Justed.

For example, to obtain a predetermined finish on each surface of the web, a coating material of a predetermined density or consistency must be initially delivered to the surface of roll'2 I Of the total coating material delivered to the under side of wire 4, a percentage, depending on the density or consistency of the coating material, the mesh of the wire, the wire speed, and to a degree the character of the web, will be delivered to the lower surface of the web. Theremaining coating material delivered to the wire obviously remains upon-the Wire. A relatively small percentage of this remainder is drawn through the couch roll and is returned to the storage chamber I2. The major portion of the coating mawhich constitutes th'e charging stock for the coating of the upper face of the web, and inasmuch as this material plus the water from the pipes 26, and 33 is passed directly to the storage chamber from whence it is delivered to the upper surface of the web, the control of the density or con. sistency of the material 4I is controllable by the proper setting of the valves 21, 3| and 34. Hence, for a predetermined wire speed and a material I3 of predetermined density or consistency, Aa continuous supply of material 4I of predetermined, constant .density or consistency may be` obtained.

It can readily be seen that substantiallyone hundred percent of the coating material charged to the system is eventually carried 'away on the web, making my .process both efficient and economical. As has been hereinbefore mentioned, the broad idea of applying a coating material to the wire s ide of a web by means of a roll similar to roll 2I, is in itself not my invention. However, to merely carry outA this. operation is a wasteful and uneconomical process since it would be commercially impracticable to retrieve the material carried by the wire, after the wire has left the couch roll, and recycle this materiaL'be- 'cause to remove the material fromthe wire', it must be diluted to such an extent that without a subsequent concentration operation it would not be usable, that is, it could not be charged back to the` storage container I2. 'Ihis expensive -handling of the unused material, therefore,

.makes the recovery thereof an uneconomical basis of charging stock of the second operation,

' unlocked for economies are obtained.' In addition, the function of the controlled sprays 29, 36

vand 31 is unique since they not only serve to clean the wire and assist in the recovery of the coating material from the under coating operation, but serve to proportion and control in a continuous manner the density or consistency of the material charged to the upper surface of the web.

As an example of my process, a paper web is formed having a weight of pounds, on a wire of 80 mesh; th'e wire traveling at a speed of approximately 600 feet per minute. 'I'he coating material I3 has a density or consistency of about 'I1/2 per cent solids. About'40 percent of the material I3 applied to the wire 4 byA roll 2l is taken by the lower surface of the web, and neglecting the small amount of coating 4material retrieved by the suction couch roll (which operated at about 15 inches of water) about 60 percent of the .I coating material is carried by the wire past the.

ycouch roll. 'I'he valves 21, 3| and- 34 are set to remove all of the coating material from the wire .and the resulting material 4I has a consistency of about 2 percent solids. This material is in toto deposited upon the upper surface of the web. It has been found that a' web so formed has sides of equal brightness and smoothness.

Of course, the above example is given merely forpurposes of illustration and I do not wish to M belimited to the specific conditions stated.

It will be noted that lin the example stated, 40 percent of the material is applied to one sideof the web, whereas 60 percent is applied to -the other and yet both sides are of substantially equal brightness. 'I'his seemingly lunlikely condition is the result of the different initial characters of the upper and lower surfaces and the manner in which the coating material is applied'. In the case of the lower surface, the coating material is applied in a more dense state to a surface which.

is more or less dense. Hence, more of the solids tend to remain onthe surface. In the case of the upper surface, the coating material ,is less dense and is applied to a surface which is more porous and hence a proportion of the solids stray into the body of the web. In effect, however, the process can be controlled so as to balance these factors and obtain opposite surfaces of uniform brightness.

If desired, the manipulation of valves 21, 3| and 34 as a control, can be supplemented by moving the point of application of the coating material tothe upper surface. For instance, the member 48 and fountain 46 may be moved closer to, or further away from, head box 2. It can readily be seen that by so moving this coating applicator, the coating material ,may be depositedupon the web while the upper surface thereof is more or less receptive to lthe coating and, hence, there will be more or less straying of the solids into the body of the web.

If desired, theI characteristics of the coating material 4I inthe storage chamber 40 may be a1- tered by introducing more liquid carrier through the pipe 49 controlled by valve 50, or by introducing more solid material through pipe 5I, controlled byvalve 52. However, these controls are extraneous of my broad process and are adapted to be used only as occasion may demand.

One of the important advantages which accrue from the use of my process is as follows: The proportion of the material applied by the roll 2I to the wire 4 and not taken up by the web Il, increases as the density or solids content of the material increases.' 'I'he weight of coating applied to the web is dependent upon the density or Asolids content of the coating material. Hence,

unless all thoughts of economy arebanished, an economic limit is soon reached as to the weight of coating which may be applied by the under.

wire svstem operating alone. However, by re covering and using the otherwise wasted coating material as part of a continuous process of coat-v ing both sides of the web, an increase in density, even with a.decrease in the proportion taken up by the underside of the web merely ,results in in-` creasing the density of the charging stock applied to the upper side of the web. Hence, it can be seen that these factors are compensating in my process and the upper limits of coating weight which can be obtained are dependent onlywupon the wire mesh and the character of the web'.

I claim as my invention:

1. A process of coating a newly formed web as the same i's carried forwardly on an edlessly moving paper forming wire which comprises, depositing coating material upon the upper surface of said web, then carrying said web forwardly and applying a coatingmaterial to the lower surface of the wire upon which the web-is carried whereby a portion of said coating material is deposited upon the lower surface of the web, washing said 2. A process of coating a newly formed web as the same is carried forwardly on an endlessly moving paper forming wire which comprises, de-

positing a relatively dilute coating material upon the upper surface ofsaid web, carrying said web forwardly and applying a relatively concentrated coating material' to the lower surface of the wire upon which the web is carried whereby a portion of said coating material is deposited upon the lower surface of the web, washing said wire to remove the remaining portion of the coatingmaterial and dilute the same, retrieving said washing liquid and coating material, and using the same as 'the charging stock for said first mentioneglcoating operation.

' 3. -A lprocess of coating a newly formed web as the same is carried forwardly on an endlessly moving paper forming wire which comprises, depositing afrelatively dilute coating material upon the upper surface of said web, carrying said web forwardly and applying a relatively concentrated coating material to the lower surface of the wire upon which the web is carried whereby a portion of said coating material is deposited .upon the lower surface of the web, washing said wire with a controlled quantity of liquid to remove the remaining portion of the coating material and dilute the same, retrieving said Washing liquid and coating material, and using the same as the charging stock for said rst mentioned coating operation.

4. A process of coating a newly formed web as the lsame is carried forwardly on an endlessly moving paper forming wire which comprises, depositing coating material upon the upper surface of said web, applying a coating material to the lower surface of the wire upon which the web is carried whereby a portion-of said coating material is deposited upon the lower surface of the web, Washing said wire to remove the remaining portion of the coating material, retrieving said Awashing liquid and coating material, and using the same as the charging stock for said first mentioned coating operation.

5. A process'of coating a newly formed Web as the same is carried forwardly on an endlessly moving paper forming wire which comprises the following successive steps, depositing a coating material having a relatively high proportion of solids `to the lower surface of said paper forming Wire whereby a portion thereof passes through the mesh of said wire and is deposited upon the lower face of the web, washing said wire to re- Y upper surface of the web at a predetermined distance from the point of application of the coating material to the lower surface of the web.

6. In combination with a paper machine ofthe type wherein a web of paper is continuously.

formed on an endlessly moving paper-forming wire, a'coating roll disposed in rolling contact with the lower face of the paper-forming wire during its upper passmeans for applying coatingl material to the roll surface which in turn is transferred to said wire and the lower face of the web carried thereon, liquid spraymeans for removing residual coating material from said wire during its lower pass, means for collecting said sprayed liquid and coating material, means for passing said mixture of liquid and coating material above said web upon said paper-forming wire, and means for depositing said materials upon the upper surface of the web to coat said surface.

7. In combination with a paper machine of the type .wherein a web of paper is continuously formed on an endlessly moving paper-forming wire, a coating roll disposed in rolling contact with the lower face of the paper-forming wire during its upper pass, means for applying coating material to the vroll surface-which in turn is transferred to said wire and the lower facefof the web carried thereon, liquid spray means for removing residual coating material from said wire during its lower pass, means for controlling said liquid spray, means for collecting said sprayed liquid and coating material, means for passing said mixture of liquid and coating' material above said web upon said paper-forming wire, and means for depositing said materials upon the upper surface of the web to coat said surface..

8. In combination with a paper machine of the type wherein a web of paper is continuously' formed on an endlessly moving paper-forming wire, a coating roll disposed in rolling contact with the lower face of the paper-forming wire during its upper pass, means for applying coating material to the roll surface .which in turn is .transferred to said wire and the lower face of the web carried thereon, means for removing the residual coating material .from saidwire and di-f luting the same during the lower pass ofv said wire,`means for passing said diluted coating malterial above said web upon saidpaper-forming wire, and means for depositing said diluted coating material upon the web to coat said surface.

GERALD D. MUGGLETON.

upper surface of the

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