US2970564A - Apparatus for coating paper - Google Patents

Description

Feb. 7, 1961 E. WARNER 2,970,564

APPARATUS FOR comm: PAPER Filed Dec. 23, 1955 2 A5? 5 26 23 25 Zmventor 20 a J EDGAR WARNER 21 T g- 5- 22 flaw-,4 M5

Ottomeg United States Paten o w .2,970,'564 APPARATUS FOR COATING PAPER Edgar Warner, Middletowm; Ohio, iassignor to The Champion Paper and Fibre Company, Hamilton, Ohio, :1 acorporation of Ohio Filed Dec. 23, 1955,'Ser. No. 554,970 2 Claims. (11. 118-249) on orolf of the paper making machine.

, According to one Well-known method of applying coatings of .the type composed of aqueous dispersions of adhesive and mineral pigment to moving paper we'bs, the

coating composition is worked between rotating and'usual- 1y oscillating rolls until it is finally tranferred as a thin substantially uniform film onto the surface of a rubber covered applicator roll from which it is transferred to the paper web as the web passes 'betweenthe applicator roll and a backing roll under a light to medium pressure.

"If it is desired to coat the paper on both sides, a film of coating is similarly spread on the backing roll and then the coating is transferred from the two rolls to both sides of the paper simultaneously. If coating is 'only desired on one side of the paper, no coating is applied to the backingroll and none is transferred to the back of the web.

The entire operation is similarto that of .printing a solid color with a conventional printing press, using a specially formulated aqueous coating composition in place of the usual ink.

I have now discovered that -I can eliminate the multiple distributing and smoothing rolls and greatly simplify the apparatus while securing onthe surface of the applicator roll "for transfer to the paper, a film of coating composition which is at least as smooth and uniform as that secured under the most favorable conditions by use of the more complex structures of the prior art. To accomplish this improvement, I find it desirable to apply the coating composition in excess directly to the surface of the applicator roll instead of applying it to the applicator as a ,pre-formed pre-worked and pre-smoothed :film of a thick- .ness which has already been limited to that desired on the applicator for transfer to the paper web. I then find that by taking advantage of the unique properties and operating characteristics of the spring-mounted, small-diameter, rotating doctor described and claimed in my copending application Serial No. 328,840, (now Patent No. 2,- 729,192) of which the present application is 'a continuation-in-part, I can remove the surplus coating composition from, and spread the remainder into a smooth substantially uniform layer of the desired thickness on, the smooth rubber surface of the applicator roll, from which surface it is .then transferred to the surfaceof the paper .in the usual manner.

Because the rubber surfaceof the applicator roll is sub- =stantiallyimpervious, there is no filter cake formation such was isutilizedin the process of the aforesaid application to control 'the thickness and uniformity of the layer of coating allowedto remain on thesurface of the :papervweb.

2,970,564 patented Feb. 7, 1961 The coating composition which must pass under the-doctor to 'form, on the surface of the applicator roll, the layer which is to be transferred from it to the paperweb,"is therefore as fiuid as that which mustbe wiped offbyt'he doctor, and'the'thickness of the layer passed is, therefore, controlled by a variety of factors, such as'the character and viscosity of the liquid, surface speed of the applicator roll, diameter, speed, and direction of rotation of the doctor rod, etc. -If a thicker film is desired for transfer to thepaper, it can be secured by-using a doctor rodwhich is wire wound or provided with fine, closelyspaced threadlike grooves in its surface, to provide a positive area through which liquid coating can pass. The larger the areas provided by these grooves, the more liquid coating can pass through on the surface of the roll and the thicker the'film 'of coating which will be transferredto the surface "of the paper. Obviously, one or both sides of the paper web can be coated in one operation, depending upon whether-or not coating applying devices and doctors are provided on one or both. of the rolls between which "the paper web passes.

The invention will be further described. with reference to the accompanying drawings, which illustrate suitable embodiments of the invention, and in which:

"Fig. 1 is 'a diagrammatic view-of"a device for applying coating to the upper side onlyofamoving paper web.

Fig. 2 is a similar diagrammatic -view of a device for applying coating to both surfacesof amoving paper web in one operation.

Fig. 3 is a similar diagrammatic view of a device 'for applying coating to bothsurfaces of a moving web in one operation, but embodying adilferent device for applying the excess of liquid coating composition to the surfaces of the applicator rolls.

Fig. 4 is a similar diagrammatic view of a similar device, showing a further modified method of applying an excess of coating composition to the applicator roll.

Figs. 5 and 6 are fragmentary detail views showing the V similar surface layer 15. For smoothing .a layer of coating material on the surface of the rubber covering -14'on -roll 12, a small diameter rotating doctorrod 20 is provided. This, as described in my aforesaid copending application, is held throughout its working length in a fiexible holder 22, 23 (-see also Figs. 5 and 6) which grasps rod 20 around more than half of its circumference, but leaves exposed a portion 25 of its surface which'serves as the working edge of the doctor. As shown in Fig. 5, this holder 22, 23 is in turn attached, throughout its length, by riveting, spot welding, or other suitable method, 'to one edge of sheet spring 24 which may be formed of a single sheet of spring metal or a plurality of wide or narrow strips closely spaced side by side along the workinglength of the doctor. The opposite edge of this plate-like spring mounting 24 is firmly mounted throughout its length on a rigid support 26 as, for'example, by a clamp strip 27. Screws 28 may also be provided on strip 27, if desired, at intervals along the length of the doctor to permit local adjustment of the pressure between doctor rod 20 and the rubber cover 14 on roll 12.

The positioning of the mounting parts 22, 23, 24, 26, and 27, which support the doctor rods, is such that contact of the doctor rod 20 with the surface of the roll 12, or 13 flexes the plate-like spring mount 24 to a degree substantially greater than any changes in flexure 'which 22, 23 is advantageously also made of rust proof metal,

desirably thin sheets of stainless steel. Because of the lack of resiliency of stainless steel, the spring mount 24 should normally be made of other material, preferably spring steel, to one edge of which the non-rusting holder 22, 23 is firmly attached by riveting, spot welding or other method, while the other edge is held firmly to .the support 26, as illustrated.

The excess of coating composition can be applied to the surface of the cover 14 on roll 12 by any suitable means such, for example, as a shower pipe 31 which desirably extends across at least the major portion of the working length of roll 12 and doctor rod 20. The coating material is, in this embodiment, so supplied as to form and maintain a pool 32 in the angle formed between the doctor blade and the surface of the roll, thus furnishing a reservoir from the bottom of which the film for transfer to the paper web is drawn under the doctor rod 20. This doctor rod is rotated at a low rate of speed, advantageously in a direction tending to wipe the film backward on the'surface of roll cover 14, by any convenient mechanism, not shown. If the doctor rod 20 is very long in proportion to its diameter, it may desirably be driven by simulaneous application of driving force to both ends, as set forth in my aforesaid copending application. i

As the roll 12 rotates, it carries with it some of the coating composition from pool 32, which, by virtue of the uniformly distributed pressure applied by spring mount 24, is reduced in amount and spread into a smooth thin,

uniform, film by the rotating doctor rod 20. This film V of coating composition is carried around with the roll until it 1s deposited on the paper web where the web passes between the rolls 12 and 13, thus producing a coated-one-side paper which is then dried, and finished,

as by calendering, in a usual manner.

If it is desired to coat both sides of the paper web at once in a single operation, the device may be arranged as illustrated .in Fig. 2. In this modification the roll 12, doctor rod 20, spring mount 24, support 26, 27, coating supply 31 and pool 32 are retained as described and as illustrated in Fig. 1.

The change consists in adding to the lower roll 13 with its rubber cover 15, a set of coating devices 20, 24, 26, 27, and 31, which are substantial duplicates of the correspondingparts associated with .roll 12 and operate in the same manner on the down- [applying the excess of coating composition to the surface of the applicator rolls. Instead of feeding the liquid coating composition directly into the angle between the doctor and the surface of the applicator roll, it is fed by distributing pipe 31 into a pool 34 maintained between the applicator roll'and an additional roll 35 adjustably ,located adjacent to and almost or quite touching the applicatorroll on its upwardly moving side. The reverse .movement of the roll 35v tends'to wipe the coating onto .-,.the cleansurface of the applicator roll which then, as

it rises out of pool 34, carries with it an excess of'coating composition up to' the doctor rod 20 which wipes off the surplus and leaves a substantially smooth, uniform film on the surface of the applicator for transfer to the 1 paper Web. 7

'Fig. 4 illustrates: use of a further modified means for .ofstainless steel or other rust resisting metal.

7 percent total solids.

applying an excess of coating composition to the surface of the applicator rolls 12, 13, which is found to be of advantage when using coating compositions which require a greater degree of working to suitably condition them for spreading into thin uniform films. Instead of the single rolls 35, illustrated in Fig. 3, two- roll fountains 37, 38 are provided. Coating composition is fed into the nip between the rolls 37 and 38 by the supply pipes 31, to form pools 39 from the bottom of which coating is carried by the rotation of the rolls, in an amount controlled by the spacing and speeds of the rolls. The coating composition withdrawn from the bottom of the nip on the surface of roll 37 is transferred to the surface of the applicator roll in the form of a film of a thickness depending on the spacing between the rolls, their relative speeds, etc. These films are then reduced in thickness and smoothed into uniformity by the spring mounted doctor rods 20, in the manner already described.

Although the devices illustrated in Figs.2, 3' and .4 are illustrated and described as applying coating to both sides of the paperweb in one operation, it willbe readily understood that the coating applying devices associated either with roll 12 or roll 13 can be omitted, orsimply not used in any given case, if it is desired to coat the .paper web on only its lower or its upper side.

In arrangements such as illustrated in Figs. 1 and in which a pool 32 of coating lies against the surface of the spring mount. 24, and particularly when aqueous coatings are used,;it is frequently found desirable to use the form of doctor mount illustrated in'Fig. 6 in which the holder 22 is formed on the edge of -a flat plate 21 Two advantages are secured thereby. It eliminates the necessity. of making a leak-proof joint where the holder 22, 23 is attached to spring mount 24, as shown in Fig. 5.

-It also protects the spring steel mount 24 from contact with-the aqueous coating which would result in rusting of spring 24 with the resulting damage to the spring 24 and possible staining of the coating. The spring 24 must still be provided, however, because of the lack of the necessary resiliency in the stainless steel 21.

The following example will illustrate the use of the present invention. In this case the device was arranged substantially as illustrated in Fig. 2. The rolls 12 and 13 were rubber covered rolls, each approximately 3.6 inches in diameter and approximately 134 inches long. The doctor rods 20 were each smooth surfaced and They were driven by independent motors at speeds of about 10revolutions per minute in .a direction reverse to the movement of the roll surface.

The rods were mounted as illustrated in Fig. 6 in holder 22, 23- formed of 0.025 inch thick stainless steel, the extending portion 21 of which covered the mount 24 which,

in this case, was made of 0.025 inch thick springsteel,

extending approximately 3 inches beyond the fixed holder 26. The coating used was a conventional aqueous clay-casein coating composition containing about 55 The device was located in the dryer section of a paper making machine and operated to apply 'thelast or surface coat weighing about 7 pounds per ream (500 sheets 25 x 38 inches) to each side of the paper web, each side of which already carried approxiearlier portion of the dryer section of, the same machine. The total weight of the finished coated paper was ap- "proximately pounds per ream.

I claim: I

J3. preformed film of coating composition comprising adhesive and mineral pigment in aqueous dispersion to at least one surface of a travelling web of paper: a pair of rolls with approximately true cylinderical resilient surweb of paper therebetween; means for applying an excess of fluid coating composition to an exposed portion of the cylindrical surface of at least one of said rolls; surplus removing means in contact with the cylindrical surfaces thereof for removing the surplus of the fluid coating composition from the surface of each roll to which an excess has been applied; said surplus-removing means comprising: a flexible small diameter doctor rod, 21 platelike spring steel support rigidly mounted along one of its edges, for pressing said doctor rod with substantially uniform yieldable pressure throughout its working length against the surface of the roll from which the surplus is to be doctored; a flexible holder continuous throughout the working length of said doctor rod, wherein said rod is rotatably mounted, which holder is formed of two arcuate portions of rust resisting thin sheet metal which together grasp said doctor rod around more than half of its circumference and holds it adjacent the other edge of said plate-like spring support; a flat sheet of said rust resisting sheet metal overlying and completely covering that surface of said plate-like spring steel support which lies towards the surplus coating composition which is being wiped off, said sheet being integral with that arcuate portion of said holder which lies on the side of the doctor rod away from the surplus coating composition which it is adapted to doctor from the roll surface.

2. In a device for spreading aqueous coating compositions into a substantially uniform smooth thin layer on a moving surface, a doctor structure comprising: a rotating small diameter rust-proofed doctor rod; 21 flexible holder comprising two unequal, but complementary parts of thin rust-resisting metal which together grasp said doctor rod around a major part of its circumference, but leave a substantial portion thereof exposed to serve as the .working edge of the doctor; a flat plate, of substantial width, of the same thin rust-resisting metal, one edge of which has been bent to shape to form the larger of said two complementary parts; a second and much narrower fiat plate of the same thin rust-resisting metal, one edge of which has been bent to shape to form the smaller of said two complementary parts, said second named flat plate being fixedly attached to the first-named plate so as to hold the formed edges of the two parts in position to grasp the doctor rod between them; a rigid support to which said first-named plate is clamped along its opposite edge; a flat plate-like spring element corresponding in width to the flat portion of said first-named plate, and being clamped together therewith to said rigid support and lying substantially in contact with the surface of said plate opposite to the surface to which said second-named plate is fixedly attached.

References Cited in the file of this patent UNITED STATES PATENTS 1,987,198 Lantz Ian. 8, 1935 2,117,032 Lodding May 10, 1938 2,213,117 Blackmore Aug. 27, 1940 2,229,621 Bradner Jan. 21, 1941 2,357,880 Dike et a1. Sept. 12, 1944 2,439,802 Francis Apr. 20, 1948 2,598,733 Warner June 3, 1952 2,605,684 Nagels et al. Aug. 5, 1952 2,676,563 Montgomery et a1 Apr. 27, 1954 2,729,192 Warner Jan. 3, 1956 FOREIGN PATENTS 1,094,628 France Dec. 8, 1954

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