US3304910A

US3304910A - Doctor blade for coating apparatus

Info

Publication number: US3304910A
Application number: US259943A
Authority: US
Inventors: Warner Edgar
Original assignee: Champion Papers Inc
Current assignee: Champion Papers Inc
Priority date: 1963-02-20
Filing date: 1963-02-20
Publication date: 1967-02-21
Anticipated expiration: 1984-02-21
Also published as: BE642472A; GB1014948A

Description

Feb. 21, 1967 E. WARNER DOCTOR BLADE FOR COATING APPARATUS,

Filed Feb. 20, 1963 INVENTOR. EDGAR WARNER ATTORNEYS United States Patent Oflice 3,304,910 Patented Feb. 21, 1967 3,304,910 DOCTOR BLADE FOR COATING APPARATUS Edgar Warner, Middletown, Ohio, assignor to Champion Papers Inc., Hamilton, Ohio, a corporation of Ohio Filed Feb. 20, 1963, Ser. No. 259,943 6 Claims. (Cl. 118-104) The present application is a continuation-in-part of my co-pending application Serial No. 52,348 filed August 29, 1960, now United States Letters Patent No. 3,084,663 issued on April 9, 1963 for a Doctor Blade for Coating Apparatus.

The present invention relates to a method of and apparatus for the manufacture of a coated web and coated sheet material. One aspect of the invention resides in providing a method and apparatus for forming a coating on a moving web or sheet. Another aspect of this invention resides in a method and apparatus for forming a coating on a travelling web by means of a magnetically positioned coating means. While the invention has applicability to a wide variety of coating procedures and products and materials to be coated, it is particularly advantageous in applying a coating composition containing mineral pigment and adhesive to a travelling paper web and will be described in conjunction with the coating of such a Web by Way of illustration and not as a limitation.

The manufacture of coated paper by a doctoring process of the nature here involved is generally represented in United States Patents Nos. 2,598,733 and 2,729,192 both issued to Edgar Warner on June 3, 1952 and January 3, 1956, respectively. The coating procedure usually comprises the application of an excess of an aqueous dispersion of a mineral pigment and an adhesive to the surface of a moving web and subsequent removal of the surplus over and above the amount of coating composition required to form a coating of the desired dry Weight on (of coating) the surface of the web. In such a process the paper web absorbs aqueous vehicle from the portion of the applied coating layer in contact therewith to form a filter cake, which is firm enough to resist the wiping action of the doctor which then rides on the surface of the filter cake and wipes off the overlying fluid coating composition.

My co-pending application represents an improvement in doctor devices .in that it permits the application of greater coating weights per unit area by means of a moving doctor surface there illustrated as including a revolvable cylindrical rod having circumferential alternately arranged ribs and grooves. The rod is therein received in a partial socket extending along the rod and having spaced apart terminal edges whereby the rod is enabled to engage the workpiece, e.g. a travelling paper web having an excess of aqueous coating to be removed.

The present invention is an improvement on United States Patent No. 2,774,329 issued to Smith on December 18, 1956. The Smith patent is entirely incorporated herein by reference and teaches a doctoring device having a revolvable doctor rod of magnetic material magnetically held in position by magnetic or electromagnetic means (hereinafter collectively called magnetic means). The present invention includes a magnetic means to position a revolvable cylindrical rod having circumferential alternate ribs and grooves.

One object of the present invention is to provide a self-cleaning doctor rod and a method of coating paper employing the same.

One object of the present invention is to provide in a magnetic holder an improved doctor rod and a cleaning means therefor.

. in side elevation,

A specific object of the present invention resides in providing a method and apparatus for forming on a moving cellulosic web a coating with a magnetically positioned cylindrical moving doctor surface having alternately arranged peripheral ribs and grooves A further and broader object of the invention resides in providing a method and apparatus for forming coating with a magnetically positioned doctor rod Still another object resides in providing a method of and apparatus for the formation of a coating on paper, paperboard, and like surfaces with a magnetically positioned doctor rod.

The apparatus of the present invention may be described as constituting an improvement in the combination of a revolvable cylindrical doctor rod and a magnetic holder means for maintaining the rod in position during the forming of a coating on a web. One aspect of the improvement comprises a doctor surface on the doctor rod that is composed of a series of alternately arranged circumferential ribs and grooves. Another aspect of the improvement also includes a means for cleaning the doctor surface.

One embodiment of the aforesaid improvement includes a means for cleaning which is a member extending generally parallel to the doctor rod and which is complementarily shaped to engage the ribs and grooves of the doctor surface. I

Briefly, a method according to the invention is for forming a coating on a moving web with a magnetically moving doctor rod and includes the improvement of moving the web with an excess of coating thereon past a moving plurality of alternately arranged ribs and grooves which extends laterally of the web and cleaning the ribs and grooves with a complementarily shaped member. In the course of this method the step of moving causes removal of excess coating from the web.

One embodiment of the method includes cleaning the ribs and grooves from a position underneath the doctor rod. Another aspect of the method includes cleaning the ribs and grooves from one side of the doctor rod.

A further aspect of the invention resides in the manner in which the complementarily shaped cleaning member is formed. One aspect of this involves employing an elongated strip with a sharpened edge which is then held against the moving doctor rod and is thereby worn in to the proper conforming shape. This causes the shape of the strip or cleaning member to conform to the profile of the doctor rod.

One feature of the invention is an enhanced self-cleaning arrangement. A major feature of the invention is an improvement in the weight of coating which is applied in one pass through a coater mechanism. Still another major feature of the invention is the applicability of. a doctor rod with alternating circumferential ribs and grooves combined with a magnetic positioning means.

Other objects, advantages, and features will become apparent from the following more detailed description read in conjunction with the drawings wherein:

FIG. 1 is a view of a doctor blade, as viewed from above FIG. 2, with the web removed, according to the present invention, showing schematically the components presently involved.

FIG. 2 is a side view through section 22 of FIG. 1 showing one embodiment of the apparatus along the normally horizontal axis of the doctor rod according to the present invention.

FIG. 2A is a partly cutaway schematic elevation as seen from the left of the FIG. 2 embodiment, for example as applied to the system of FIG. 5.

FIG. 3 is another embodiment, shown schematically applicable to the systems of FIGS. 1

and wherein the doctor rod is cleaned from one side, and as viewed along 22 of FIG. 1.

FIG. 4 is an enlarged portion of FIG. 3 schematically representing one embodiment of a cleaning strip arrangement.

FIG. 5 is a diagram schematically illustrating the manner in which the invention may be incorporated into a coating procedure.

Where appropriate, the same reference numerals are employed throughout the specification. For the purpose of clarifying the fact that the present invention is applicable to a variety of coating systems, the disclosures of the aforesaid Warner patents and my copending application No. 52,438 are incorporated herein by reference.

Referring now in particular to FIGS. 1 and 2, it will be seen that the doctor blade comprises the doctor rod and a magnetic holder therefor. The doctor rod 10 is formed from a steel rod which has been machined, rolled or otherwise worked by one or the other of several methods to provide a doctor surface defined by a series of concentric alternately interdigitated circumferential ribs 2 and grooves 4 of ostensibly threadlike profile configuration. It is most significant to note that these ribs and grooves are defined as thread-like. They do not comprise a thread in that there is no spiral progression of the valley as is the case of a thread wherein the groove between adjacent ribs would be continuous throughout the length of the article provided with the thread from one end to the other. Rather in the present invention each groove between any two adjacent ribs is an annular recess extending around the circumference of the rod and singularly each circumferential groove is completely independent one from the other. As has been stated the profile configuration of the hills and

valleys

2 and 4 may be thread-like in profile appearance. A standard Whitworth profile is one embodiment. Of course the thread profile may assume a variety of configurations, for example, the Whitworth profile itself may be modified such that the tops of the ribs and the bottoms of the grooves may be slightly rounded rather than as angulated as shown in the drawing. Thus in general, it may be said that the thread-like profile, if Whitworth, of these alternating ribs and grooves should be such that the included angle between any two adjacent surfaces defining a valley should approximate 90.

The doctor rod is made from magnetic material such as a steel rod. The rod is chromium plated by any suitable process after the described profile has been imparted to its surface. The depth from top of the ribs 2 to the floor of the valleys 4 may be varied.

As the profile depth may be varied so also may the number of ribs per inch length of rod be varied. In my co-pending application, for example, the range of from 50 to 150 ribs or threads per inch along the entire length of the doctor rod 10 has been employed though this dimension may also vary.

Referring to FIGS. 2 and 2A, it is seen that the magnetic holder 20 may comprise a pair of

magnetic members

21, 22 extending vertically into contact with a horizontally arranged doctor rod 10. The doctor rod is supported in a seat 23 formed at the ends of the

members

21 and 22. The magnetic holder 20 may comprise either a permanent magnet or an electromagnet. The

members

21 and 22 are conveniently constructed as shown for the pole-pieces in the said Smith patent. The holder 20 may be mounted in the embodiments of FIGS. 1 and 5 hereof as shown in FIG. 4 of the said Smith patent.

An alternate arrangement is to provide

members

21 and 22 as magnets independent of each other with element 21 having its south pole adjacent the rod 10 and element 22 having its north pole adjacent to rod 10. The polarities may be reversed.

Referring again to FIG. 2 and FIG. 2A, the cleaning means 25 is shown as clamped at a position intermediate the two poles of the magnetic holder. The means 25 is of resilient nonmagnetic material, i.e. stainless steel and is provided for cleaning the doctor surface from underneath the rod and preferably comprises a member complementarily shaped to engage the ribs and grooves on the doctor surface. It is supported by a clamp comprising clamping bar 26 and a plurality of clamping bolts 27 threadedly engaged therewith. The bar 26 and bolts 27 are of nonmagnetic resilient nonabsorbent material. The complementarily shaped edge 28 of the strip 25 has ribs 28a and grooves 28b thereon which are interdigitated with the ribs and

grooves

2, 4 on the rod 10 so that the ribs on 28 extend into the grooves 4 on the rod 10 and the ribs 2 on the rod extend into the grooves on the strip 28.

It will be observed from the embodiment of FIGS. 2 and 2A that the cleaning means is supported at a position intermediate the poles of the magnets so as to clean the doctor rod from underneath. The groove 23 formed at the ends of the

magnetic support members

21, 22 is elongated and extends in parallelism with the axis of the doctor rod. Moreover a plurality of passages 29 are provided through at least one leg of the magnetic holder 20, illustrated as the leg 21. The upper end of the clamping bar 26 is cut off to be approximately even with the bottom of the hole 29, whereby a passage 30 is formed from underneath the rod down past the cleaning means 25 and out through the ports 29. This passage provides a drain for excess coating removed from a traveling web, and would be applicable for example in the embodiment of FIG. 5.

In FIGS. 3 and 4 there is illustrated an embodiment for cleaning the doctor rod 10 from one side of the magnet. In this embodiment a cleaning strip 40 is mounted by a clamping bar 41 and a plurality of clamping bolts 42 so that one edge thereof is engageable with the doctor rod 10. The member 40 is preferably of a soft but resilient material. It is advantageously formed by (FIG. 4) originally forming a sharp edge 44 on one end of the strip and rolling or otherwise bending such edge over so that it can be held against the revolving doctor. Initially the sharp edge rides on the crest of the ribs 2. After a period of running the rod with the sharp edge against it, the edge 44 wears so that the dotted line position of FIG. 4 is assumed wherein the ends of the rod extend down into the grooves and the ribs 2 of the rod ride in the worn portion. Returning to FIG. 3, the magnetic holder 20 is constructed in one of the fashions suitable for FIG. 1 and a nonmagnetic plug 45 is inserted between the two

legs

21, 22. The excess material therefore will be removed from the rod 10 and flow down over the cleaning strip 40 as well as the clamping mechanism 41, 42. The clamping mechanism and cleaning means (

elements

40, 41, 42) are of nonmagnetic material, e.g. stainless steel.

On occasion it may be desirable to offset the bias caused by the resilient action of cleaning strip 40 against the doctor 10. In such case an additional cleaning strip may be mounted opposite the member 40 to contact the opposite side of the doctor 10. An alternative embodiment is to put a soft magnetic facing 46 on the opposite face of the magnet (here shown as the upper end of leg 22) whereby the resiliency of member 40 will cause a wearing in of the member 46 against the rod. Cleaning strip 40 may be of stainless steel.

The circumferential grooves 4 operate as a series of metering devices arranged laterally of the web to permit coating to pass between the individual chambers formed by grooves 4 and the web as the latter contacts the tops of the ribs 2.

Referring to FIGS. 1, 2, 3 and 5, the rod 10 is driven or rotated, preferably counterclockwise (on occasion, clockwise) as shown, in holder 20 preferably at an extremely low rate of speed, on the order of from /3 feet per minute surface speed. This enhances the self-doctoring feature of the device on a continuous basis and additionally distributes wear evenly throughout the length of the rod 10. The driving mechanism may be conventional, such as an electric motor M coupled to the end of the rod through a speed reduction device. In FIG. 1 a drive mechanism is illustrated schematically as comprising a large sprocket 14 driven from small sprocket 8 via chain or belt 12; the large sprocket being mounted on the end of rod the smaller sprocket being carried on shaft 6 driven by a conventional motor M. A speed reducer, if needed, may be disposed between the motor and the sprocket 8. If desired the same shaft 6 could be connected to the opposite end of rod 10 such that the rod 10 is driven from both ends simultaneously. This arrangement is desirable to prevent torsional stresses from being developed in the rod 10 where the device is utilized in coating wide webs, such as in the paper making art.

FIG. 5 illustrates one of many ways of utilizing the invention. Exemplary other techniques for employing the invention are found in my copending application as well as the above said Warner patents. In FIG. 5, a tension blade coater is illustrated wherein the web W passes over a rotating applicator roll 50 which carries coating from the pan 51 onto the web, the coating being smoothed and metered to the correct weight as the web thereafter passes over rod 10. The tension on the web provides the requisite action to urge it against rod 10. The rod is constructed as described above. The method according to the invention will be seen to include the forming of a coating on a moving web using a magnetically positioned doctor rod 10. The steps of the method further include moving the web with an excess of coating thereon (e.g., as applied by the roll 50) through a sufficient distance to permit the forming of a filter cake prior to engaging the doctor rod 10. Then when the web engages the doctor rod, it will simultaneously engage a plurality of alternately arranged ribs and grooves advantageously extending laterally of the web and defining a metering doctor surface on the doctor rod. In this fashion the excess of coating is removed while at the same time permitting the application of a greater amount of coating and the formation of a heavier filter cake.

The doctor surface is, in both the method and the apparatus according to the invention, cleaned by engagement of the ribs and grooves thereof with a complementarily shaped member. In one embodiment, the cleaning is accomplished from a position intermediate the magnetic rod support members, from underneath the rod (for example see FIG. 2) and in another embodiment the cleaning is accomplished from at least one side (e.g., FIG. 3). The said members (25, 40) may be of a soft resilient nonmagnetic material selected from the class consisting of metals and resins, for example stainless steel and polytetrafluoroethylene, respectively, and should be nonabsorbent of the fluids and materials in the coating. Nonabsorbency avoids building up abrasive particles in the cleaning means 25, 40 thereby reducing wear on the rod 10.

The invention further includes forming the contour of the cleaning means by wearing the same against the doctor surface to the extent that the cleaning means is complementarily shaped to have a serrated edge such that the ribs 2 extend into the serrations on the cleaning means and the serrrations on the edge 28 also extend into the grooves 4 on the doctor rod.

While the invention has been described with respect to paper, and paper is referred to in some if not all of claims that follow below, it is to be understood that this term does not restrict itself to paper as often employed in the conventional sense. The term paper as employed here refers to webs or sheets formed of natural fiber, synthetic fiber, or a combination of the two whether they are bleached, dyed or the like. This term is used 6 in the application here to refer generically to paper, paperboard, cellulosic webs of all types formed of the materials indicated above in this paragraph. The single word is used as a matter of convenience and not of limitation.

Paper made in accordance with the present invention may therefore have a coating suitable for printing. As stated in my co-pending application, coating procedures of the general class here involved, and that includes the present invention, are useful in the production of coated paper and paperboard for printing purposes.

It will be appreciated that the various serrated cleaning means 25, 40 are at least coextensive with the working width of the rod 10, that is, the cleaning means is Wide enough to clean the length of the rod engaging the Web W' for removing excess coating. Also, the resilient action of the member 40 is preferably maintained by a slight outward spacing from the pole piece 21 and may have slots whereby it can be slipped into position over bolts 42 as during a replacement operation. The magnetic assembly 20 does not have to have means at its right and left hand ends (as viewed in FIG. 2A) to close off the passage 30 and may :be open to provide additional drainage ports in which case a conduit or catch basin ought to be provided to receive any end drainage.

It will be appreciated if the foregoing description and illustrated embodiments are for illustrative and representative purposes only and are not intended as limitations on the scope and spirit of the invention. The invention is intended to include all those modifications obvious to one skilled in the art, including the substitution of equivalents as fall both within the spirit, scope, or terms of the -fOllOWing claims.

I claim:

1. In the combination of a revolvable cylindrical doctor rod and a magnetic holder means having magnetic members for maintaining said rod in position during the forming of a coating on a web, the improvement comprising a doctor surface on said rod composed of a series of alternately arranged annular ribs and grooves;

said magnetic members having a seat in contact with said doctor surface and supporting said rod; and

a means for cleaning said doctor surface.

2. In combination of claim 1, a means for cleaning that comprises a member of resilient nonmagnetic material nonabsorbent of materials and fluids in the coating and complementarily shaped to engage said ribs and grooves supported in engagement with said ribs and grooves.

3. The combination of claim 1 wherein the seat of said magnetic holder means includes the poles of a magnet shaped to form an elongated groove in which said rod is seated, wherein said means for cleaning comprises a resilient nonmagnetic n'onabsorbent member complementarily shaped to engage said ribs and grooves; and further including means for supporting said means for cleaning on one side of both poles of such magnet.

4. The combination of claim 1 wherein said magnetic holder means includes the poles of a magnet shaped to form an elongated groove in which said rod is supported, wherein said means for cleaning comprises a member complementarily shaped to engage said ribs and grooves; and further including in the combination means for supporting said means for cleaning at a position intermediate the poles of such magnet, and conduit means for providing a passage through at least one pole of said magnet.

5. The combination of claim 1 where said means for cleaning comprises a strip supported parallel to the axis of said rod with one edge of such strip in engagement with and conforming to the profile of the periphery of said rod.

6. The combination of claim 1 wherein said means for cleaning comprises a strip supported parallel to the axis of said rod with one edge of such strip having a sharp edge in engagement with the periphery of said rod whereby contact with the doctor surface on said rod wears said edge to a serrated shape in conformance with the doctor surface profile.

References Cited by the Examiner UNITED STATES PATENTS 2,221,441 11/1940 Charters 118-118 8 Sherman et a1 118-118 Erther 118118 Smith 118-118 Uhleen 118102 X Warner 15256.52 X

RALPH S. KENDELL, Primary Examiner.

ALFRED L. LEAVITT, Examiner.

10 E. B. LIPSCOMB, Assistant Examiner.