US1901080A - Wiper mechanism for coating machines and process - Google Patents

Description

March 14, 1933. p. B, BRADNER 1,901,

WIPE-R MECHANISM FOR COATING MACHINES AND PROCESS Filed Feb. 1932 gwomto;

- at removing the excess Patented Mar. '14, 33 c UNITED srAras PATIENT oi-r ce nommn 3.3mm, or oxroan, 0310, rissm'non. 'ro THE cnmrrorr coa'rnn rum 7 comm, or mun-r011, 01110, a coarona'rrorr or one WEB MECHANISM. FOR GCTATING AND PROCESS Application filed February a, 1932. Serial no. 591,207..

r This invention relates to an improvement in coating machines adapted for use 111 ap- Y plying to a moving surface a coating or layer position is applied to a web of paper and all except the desired quantity is removed from the aper by means of a doctor member whose sur ace moves in the op osite direction to the go paper. Instead of app ying the coating di-* rectly tothe paper, the desired film of coat- 1 ing may be formed on an applicator member by applying an excess of the aqueous coating composition to said applicator member and y means of a doctor member moving in the opposite direction to the applicator member, and thereafter transferring the film of coating from the applicator member to a web of paper moving in 80 the opposite direction thereto. The latter process is disclosed in my copending application, No. 581,955, filed December 18, 1931.

I11 either case, forthe proper functioning of the doctor member, it is essential that 5 there be provided means associated therewith for wiping or cleaning the surface of the same whereby the doctormember may continuously present a relatively clean surface to the coating composition on which it acts. There 4 has been provided for this purpose a wiper blade maintained in contactwith the useful surface of the doctor member.

The heretofore suggested wiping or cleaning means has not proven to be whollysatisfactory in commercial operation: it (the aforesaid single wiper blade; is dificult to control, requires careful a justment, and must be replaced rather frequently; Whenever the wiper blade fails toremove all of the coating adhering to the doctor member surface, the amounts not removed form streaks or spots in the resulting coating: such a result in the case of a fine coating operation requlring a high quality product makes necessary the rejection of relatively large amounts of the coated. product.- This is especially true in the production of high quality coated papers where any minute irregu larity in the coating makes the product un salable.

I I have found that the above and other disadvantages resulting from an attempt to cleanthe doctor member surface by, means of'only a single wiper blade may be very largely overcome and that improved coated paper may be produced by providing the doctor member with a second wiper mechanism in series with the first and by treating, or at least thoroughly wetting, the doctor surface w th a washing liquid between the two wipers. The said washing liquid ma be water or some aqueous solution. I ave found that adoctor member .wetted with liquid is much more easily cleaned than is one covered with a film of coating.

. 7 Furthermore, I have discovered that the second wiping in most instances need not re- 1 move the last traces of the washing liquid,

but rather that the coatings may be improved in smoothness or flatness of lay by leaving over the whole surface of the doctor member.

a film. of the washing liquid. It may be ob-i served, in this connection,that if the doctor 'member surface carries a film of liquid in some portions but is wholly dry in other portions there usually results a corresponding unevenness of smoothing of the coating with the consequent production of a s otted, streaked, orotherwise blemished coate product. Accordingly, rather than to attempt to 9 layer: one portion or area of the doctor mem ber surface may carry a somewhat greater quantity of the wetting liquid than another without detriment to the smoothness ofthe coating (provided, of course, that no rela-' tively great quantity of the wetting liquid be carried past the second wiping means). This is especially advantageous, because it is a very difficult task continuously to wipe the doctor member surface wholly dry at all points thereon. Therefore, I prefer to take advantage of the phenomenon above noted by simply at adjusting the second wiping means .50 t

a thin film of the washing liquid passes the same at all times.

An embodiment of the invention is illustrated in the accompanying drawing, in which:

The figure is a diagrammatic representation of an apparatus for carrying out the process.

In the drawing 1 is a web of paper which passes around an applicator roll 2 in the direction of the arrow. 3 is a substantially rigidly surfaced doctor roll which'is adjacent to roll 2 and is revolvable in the same angular direction as the applicator roll 2; that is to say, the surfaces of the two rolls are traveling in opposite directions at their points of closest approach, i. e., the nip. Between rolls 2 and 3 is a pool of aqueous mineral coating composition 4 which is supplied by a delivery pipe 5.

6 and 7 are wiper blades, which may be of rubber or have a rubber edge. These wiper blades 6 and 7 are spaced apart fromeach' other and are adjustably held in association with doctor roll-3 by any suitable means such as the adjustable supports 6a and 7 (1, respectively. At any suitable point between blades 6 and 7 is a pipe 8 connected to a source of water under pressure and having perforations through that portion of its wall which is adjacent roll 3. The pipe 8 is substantially parallel with the axis of roll 3.

In operation, the web of paper 1 to be coated is passed around roll 2 and through the nip between rolls 2 and 3, said rolls 2 and 3 being revolved in the same angular direc-' tion and at any desired speeds. A pool of a ueous mineral coating composition 4 is est'a lished between rolls 2 and 3, and maintained by delivery theretoof amounts of the composition from a source thereof by delivery vpipe 5: the web of paper 1 thus passing through said pool. Coating composition which may be carried out of said pool by roll 3 is wi ed off of said roll by wiper blade 6- sprayed thereon from pipe 8, and any solids and excess of liquid thereon are removed by.

the second wiper blade 7, whichis so adjustable as to pass only a very thin film of water, thus presenting a coating-free but waterfilmed surface for smoothing the layer of coating carried into the nip between rolls 2 and 3 by the web 1. So long as the surface of doctor roll 3 is not dry in some areas and wetted in others, the resultin coating is not streaked or spotted. It is, 0 course, within the scope of the invention to so adjust the second wiper that there will be no film of water on the doctor surface after passing the second wiper, but this is not as convenient a method of operation. 7

Instead of passing the paper through the nip of the rolls 2 and 3, the desired film of coating may be formed directly on the applicator roll 2 and thereafter transferred to the paper by a wiping action. Also either the applicator member or the doctor member may be in the form of a belt. In any of these modifications of method and apparatus, the doc tor member is given a double wiping treatment with a washing operation inter osed between the wipers. Also in place 0 a wiper blade other wiping means may be employed, such as for example, a resilient surfaced roll, and the washing liquid may be delivered to and distributed on the surface of the doctor member by other means than the perforated pipe shown. I

In this connection, I have observed that a somewhat higher doctor surface speed is required to avoid ridges in the coated pa er when the doctor roll surface carries a m of water than when it is dry. On the other hand, if the doctor roll surface is wetted with a film of liquid having a lower surface tension than that of the aqueous mineral coating composition employed, a lower doctor roll speed is required to avoid rippled coatings.

'I claim:

1. In a process of coating involving the operations of applying .an excess of coating composition to a moving surface, removing all except the desired weight of coating therefrom by means of a doctor member moving in the opposite direction to said moving surface at the point of closest approach thereto, the method of cleaning the doctor member surface and preparing it for reuse, which consists essentially. in wiping it, then thor oughly wetting it'with a washing liquid and again wiping it.

2. In a process of'coating involving the operations of applying-anexcess of coating composition to a moving surface, removing all except the desired weight ofcoating therefrom by means of a doctor member moving in the opposite direction to said movingsurface at the point of closest approach thereto, the method of cleaning the doctor member surface and preparing it for reuse, which consists essentially in wiping it, then thoroughly wetting it with a washing liquid, and finally wiping any solids and excess of washing liquid from it whereby to present for reuse a surface free of solids and carrying there- 7 on a film of the washing liquid.

3. In a process of coating involving the operations of applying anexcess of coating composition to a moving surface, removing all except'the desired weight of coating therefrom by means of a doctor member movingin the opposite direction to said move ng surface at the point of closest approach 4 thereto, the method of cleaning the doctor member surface and preparing it for reuse, which consists essentially in wiping it, then thoroughly wetting it with water, and finally wiping any solids and excess of water from it whereby to present for reuse a surface free of solids and carrying thereon a film of water.

4. In a process of coating involving the operations of applying an excess of coating composition to a moving surface, removing all except the desired weight of coating therefrom by means of a doctor member moving in the opposite direction to said moving surfaceat the point of closest approach thereto, the method of cleaning the doctor member surface and preparing it for reuse, which consists essentially in wiping it, then-wash ing it with a stream of water, and finally wiping any solids and excess of water from it wherebyto present for reuse a surface free of solids and carrying thereon a film of water.

5. In an apparatus for formingonamoving v surface an even layer of coating composition said doctor roll of plural means for cleanwith the surface of containing a liquid vehicle, including a movable doctor member, the association with said doctor member of plural means for cleaning the surface of the latter and preparing it for reuse which in the order of their occurrence are a wiping means, a means for delivering a stream of washing liquid, and a'second wipmg means. a

6. In an apparatus for forming on a moving surface an even layer of coating composi tion containing a liquid vehicle, including a rotatable doctor roll, the association with a said doctor roll of plural means for cleaning the surface of the latter and preparing it for reuse which in the order of their occurrence are a wiping means, a means for delivering a stream of washing liquid, anda second wiping means.

7 In an apparatus for forming on a moving surface an even layer of coating composition containing a liquid vehicle, including, a rotatable, doctor roll, the association with

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