US2199228A - Method of and apparatus for coating paper - Google Patents

Description

April 30, 1940. N. .OBENSHAIN ET AL METHOD OF AND APPARATUS FOR COATING PAPER Filed July 16, 1936 INVENTORS 0E5 NOEL IVE/EH7 ATTORNEY v I. Patented Apr. 30, 1940 UNITED STATES METHOD OF AND APPARATUS FOR COATING PAPER- Noel Obenshain and Wright M. Welton, Piedmont, W. Va., assignors to West Virginia Pulp and Paper Company, New York, N. Y., a corporation of Delaware Application July 16, 1936, Serial No. 90,832

6 Claims.

Our present invention relates to methods of and apparatus for coating paper,

The coating of paper with suspensions of mineral pigments, to which this application particularly applies, has presented serious problems for the reason that such suspensions commonly used in the paper art do not of themselves smooth out when applied with even slight irregularities. When the paper is coated by a direct application of the coating liquidthere are formed, un-' less special precautions are taken, ripples or irregularities of the coating material on the paper which, when dried, produce streaks. Therefore, in much of the prior art practice, provision is made for smoothing out the ripples or other irregularities formed upon application, either by the use of reciprocating brushes or of,smoothing or trowelling rolls. Such aids, however, have the drawbacks that they are cumbersome and are responsible for a comparatively low rate of output.

In view of these difficulties, proposals have been made to apply a measured amount of coating material upon the travelling sheet of paper to be coated, in such manner as to produce an even coating in the first instance and thus obviate the use of subsequent smoothing devices. It is to this latter class of coating methods and apparatus that our present invention is directed, and it is a principal object thereof to devise a, new method and apparatus which will produce a coating of the usual mineral or other pigments having in a high degree the qualities of smoothness and uniformity, and in addition having the advantages of high output and reliability of operation.

' In carrying out our invention we make use of coating rolls having cut or formed therein a multitude of liquid receiving indentations or groves, such rolls being preferably of metal and having the surface thereof formed either by mechanical cutting or by photo engraving or other processes known to that art.

Our invention will be best understood by reference to the following detailed description taken with the annexed drawing in which:

Fig. 1 shows diagrammatically an arrangement of coating rolls constituting a preferred embodiment of our invention.

Fig. 2 is a side view of same.

Fig. 3 is a view of a roll in which the grooves are of the screen type.

Fig. 4 is a view of a rollin which the grooves are of the inclined parallel type.

Fig. 5 shows an arrangement for coating both sides of the paper in one operation; and

Fig. 6 is a side view of same.

In Fig. 1 the coating material is sprayed through pipe 9 upon the coating roll l2 of the 5 type shown in Figs. 3 or 4 to be more fully de-' scribed hereinafter. The excess coating is caught in pan Ill and is pumped therefrom back to the spray pipe a by means not shown.' Roll I2 is driven from a source not shown and has in con- 10 tact therewith an offset or applicator roll M which may be driven simply by contact with roll I! or preferably is positively driven by means of gears l3 and Ba shown in Fig. 2 which operate to-drive said rolls at the same surface speed. The coating material fills to excess the multitude of pockets or grooves in the surface of the roll l2 and a portion of the liquid so picked up is transferred to the offset roll I4, which has a resilient surface as of rubber, the excess coating being squeezed out by-the contact or nip between rolls l2 and I4, so that roll l4 acquires a uniform amount of coating for each contact with the roll I! without the use of a doctor roll or blade. The

so-coated surface of the roll 14 then is brought v in contact with the paper web l6 which passes over the roll l4 and is held in proper juxtaposition with respect to roll l4 by means of the guide rolls I1, I 8 and I9. As revealed by Fig. 1, the transfer or offset roll l4 moves in a direction reverse to the travel of the web I6. I Various factors govern the uniformity of coating. imparted to the web l6.' One of these is the amount of slip between the web and the offset roll H. For convenience this slip may be reckoned as the algebraic difference between the speeds of the web and the roll l4 divided by the speed of the paper and multiplied by 100 to give a percentage ratio, a direction of rotation of the roll reverse to the web being considered 40 negative. Thus far we have found'that satisfactory results are had when the percent slip for the arrangement of Fig. 1 is between 200 and 450. These conditions, for example, will be fulfilled when the paper has a speed of 500 feet per minute and the roll a speed in reverse of the paper of 600 feet per minute, thereby giving a percent slip of 220. Another-factor is the nature and frequency of the markings on the roll I2. Good results have been obtained when a screen marking has been used of a frequency of- 25 to lines per inch, such a rollbeing shown in Fig. 3. The use of the parallel line marked roll of the type shown in Fig. 4 has given results as good as, if not better than, those obtained .with the .Jory choosing rollsfof the; axis of the cylinder. "-Thenumberof lines per inch may-vary from 25 =to' l50'more or less "with a groovetofwa'll thickness {ratiobf fmm3 to 1 to 4 to 1; it beingunderstood that the above i figures are given by way of example without limiting the invention to any exact size orarrangement of markings. The indented rolls may} desirably be made of copper or other non-corrod- 7 ing metal, and if deslredmay be cromium plated. Non-metallic indented rolls might also be em-v ployed. Such rolls in generalmay be made in a 'mannersimilan to the manufacture of the in .taglio cut rolls used in rotogravure printing, The

amount of coating applied may be. best regulated either by varyingthe consistency of the coating varying depth of cut-or by varying both these factors.

Thus .far when using the usual mineral pigments or fillers wehave obtained superior results by driving the offset roll in a direction reverse to the travel of the paper, in comparison with those especially when using coating compositions having greater coating or spreading power than those. 30

obtained by driving the offset roll in the same di- J rection as the paper. 7 However, in some instances satisfactory results may be had when driving the offset roll inthe same direction with the paper,

through a drying chamber, as is common'in the art.

In lieu of spraying the coating upon the indented roll, as by the spray pipe 9, the composition may be fed to the pan l and the latter around the applicator roll. variations in the degree of slip have very little raised so as partially to immerse the roll l2.

The improved method and apparatus described in'the foregoing is adapted to be used with a variety of paper coating compositions. Typical compositions containing in suspension the usual mineral fillers or pigments are as follows:

(1) Chalk 100 parts Casein 15 to 18 parts Water added to ve 35% solids The mixture is then ground through a 3 roll ink grinder, diluted to 25% solids and re-ground.

(2): Clay 500 parts Satin white 850 Chalk 150 Cas 215 Water added to give 20% solids and suitably ground. By varying the amountof solids in suspension and the depth of grooving on the indented rolls as aforesaid, coatings of the type of the above examples have been successfully applied ranging from .3 pound to 10 pounds per ream per' side.

This amount of coating seems not to vary appreciably with the degree of wrap of the paper Furthermore, slight effect on the amount of composition applied. The

'I Yscreen' markingQ-Y the the 25 have aj'pitch of approximately 30' degrees-to paper at a surface speed as low as100 to as high as 500ffeet per minute;

Our improved method and apparatus may be used to coat paper; previously formed and dried, 'or'it may be used to coat the paper while the latter is in the paper making machine and before the web hasvbeen fully dried. t ,In'the claims, by "paper is'meant to include cardboard or pasteboard or other paper products which it may be desired to coat.

. V arious changes from the detailed description and specific data above given will occur to those .skilled inthe art, without, however, departing from the'spirit of theinvention or the scope of the appended claims. Weclaim:

= 1. The method of coating a "web of paper or,

the like, whlchfcomprises applying a coating comv position comprising mineral pigments to a cylindrical surface having a multitude of liquid receiving indentations serving to hold a measured quantity of such composition, transferring a portion of said coating so appliedto a second surface having resilient properties by maintaining said surfaces in rolling contact whereby said resilient surface receives a uniform amount of coating composi- -,tion' whichis less than the amount initially present on said surface having indentations, then.

contacting said resilient surface with a web o paperor the like moving with respect to said resilient surface so as to occasion a substantial slip betweensaid vweb and said contacting surface, while maintaining said Web free to move slight amounts incident to variations in diameter and position of said resilient cylindrical surface. 2. The method according to claim 1 in which said slip varies from 200% to 500%. v 3. The method of coating a web of paper or the like, which comprises applying a coating compositioncomprising mineral pigments to a cylindrical surface having a multitude of liquid receiving indentations, transferring a portion of said coating so applied to a second surface having resilient properties by maintaining said surfaces in rolling contact whereby said resilient surface receives a uniform amount of coating composition which is less than the amount initially presvariations in diameter and position of said resilient cylindrical surface.

4. In a device adapted for coating paper with a liquid suspension of finely divided mineral pigments or fillers, a roll comprising a cylindrical surface having a multitude of liquid receiving indentations, means for supplying the coating composition to said roll, a resilient transfer roll receiving coating from said indented roll and applying same to a paper web, means for driving said transfer roll in reverse direction to thetravel of said web, guide rolls for passing the paper over said transfer roll, said guide rolls being disposed so as to permit the paper tomaintain contact with thetransfer roll regardless of minute variations in' the position of said.roll.

5. In a device adapted-for coating paper with a liquid suspension of finely divided mineral pigments or fillers, a roll comprising a-cylindrical surface of relatively hard material having liquid receiving indentations of a frequency from 25 to improved process has thus far'ienabledus to coat per inch, means for supplying the coating 5 rotating in contact with said indented roll and receiving coating from said indented roll and applying said coating to a paper web, and means for driving said transfer roll in reverse direction to the travel of said web. a

6. In a-device adapted for. coating paper with a liquid suspension of finely divided mineral pigcomposition to said roll, a resilient transfer roll w a a a, 2. 9 .92

composition to said roll, a resilient transfer roll receiving coating from said indented roll and applying same to a paper web, means for driving said transfer roll in reverse direction to the travel of said web, and means for driving said indented roll and said transfer roll at substantially the same surface speed, guide rolls for passing the paper over said transfer roll, said guide rolls be-

Images