US2534321A - Coating method and apparatus - Google Patents

Description

Dec. 19, 1950 w. P. TAYLOR 2,534,321

COATING METHOD AND APPARATUS Filed May 16, 1946 INVENTOR WJ /Imu PM 7 ATTORNEY Patented Dec. 19, 1950 [COATING METHOD 'AND APPARATUS Williamv Palmer Taylor, Hamilton, Ohio, assignor. to" The Champion Paper and Fibre Company, Hamilton, Ohio, a. corporation of Ohio Application May 16, 1946, Serial No. 670,276

This invention relates tov the application of coatings to paper webs and has particular reference to coating processes and apparatus wherein the web is carried on the moving surface of a belt or roller while the coating is spread uniformly thereover by means of a doctor bladev or the like.

In the past, coatings of various kinds have been applied tov paper and fabric Webs by the use of blade or knife spreading and smoothing devices.

In a large class of such coaters the: web has been supported on a moving carrier surface, sometimes in the form of a roller and at other times in the form of an endless belt. In most of these a defi ni-te clearance was provided between. the blade and the web carrier, though. in some cases pressure was exerted between the blade and the web.

Usually the surface of the web carrier was rigid but in some cases rubber, leather,.or similar material has been used for the web carriers. In many cases a mass or pool of thecoating material was maintained onthe web. in front of the blade.

With such prior art processes. and apparatus,

the application of the. coating is not always as perfect as desired in the production of high grade coated printing paper- Threadin of the paper between the blade and the carrier surface. frequently involves considerable dificulty and often necessitatesl'ifting the blade. from. the carrier surface to provide threading space. In those cases Where a pool. of coating material is, maintained against the blade, such, movement of the blade usually involves loss of .this coating material and: in general requireswashing up the blade and carrier surface. before re-threadihg. Further, difficulty is commonly experienced with wrinkling and tearing of the paper under the blade, due. frequently to. buckles or slack edges in the paper web. These. are portions less than the full width of the web, between. or at the edges of the web, whichare of: slightly greater length thanother portions of. the web. When. such a web is. carried on. av surface of. uniform. length across: its width,. and under a fixed doctor; blade, the. excess length in. the buckles and. slack edges tends to: accumulate in front: of: the blade until it is drawn through as. a wrinkle or fails. to'pull through. and starts. a tear. which. usually breaks down the. web: and. requires: washing up and rethreading the machine. The excess length in buckles. and slack edges may vary from. zero up occurrence ofi these defects is generally greater as their severity is less, but it has: been found, that solaims. (01. 117-111) 2 defects, of aseverity sufficient to cause trouble in coating operations of the type described, occur .with sufiicient frequency toconstitute a serious disadvantage in the use of such coating methods and apparatus.

The. primary objects .of the present invention are: to facilitate and improve the coating opera.- tion; to permit threading under doctor blades, even those in pressure contact with a yielding web-carrying surface, without lifting the. blade or wasting coating which may be held in, front of the blade; to carry through buckles and slack edges which may be presentv in the. paper; to. prevent wrinkling and tearing of the web under the blade in coating devices of the type described; and to provide apparatus for accomplishing these purposes. Other and more detailed objects and advantages of the inventionwill become. apparent from the following description.

I have now discovered that these objects can be accomplished if the carrier surface is made of rubber or similar yielding resilient material, the doctor blade is so held as to. indentthe. surface slightly as it. passes thereunder, and thepaper web is caused to adhere to said surface where. it is carried past the doctor blade. The degree of adhesion required. issuch that the paper will strongly resist any forces tending to cause it-to slide along the surface but. will readily part from the surface when pulled along a path which diversestherefrom.

Adhesion of this degree can, I find, be secured by dampening the. carrier surface prior to the contact of the paper therewith. The surface is advantageouslyfldampened with clear water, though the water may contain small. per ccntages of adhesive, usually the adhesive. used in the coating composition, since the surface is not ordinarily allowed to become dry duringthe time the device is in operation. The degree of dampness required can, I. find, be obtained. by thoroughly wetting the surface and squeezing. oil the excess by means of a roll pressed there against. The paper web is then laid smoothly on the. moist carrier surface either by tension or where the coated paper web is carried under the web which is under and immediately adjacent the blade at that instant, and is believed to equalize the length of that short section of the web, across its entire width, thus eliminating buckles and slack edges where theactual leveling of the coating is taking place. This increased tension in, and consequent stretching of, the paper at the blade is also believed to bring about the ob-' served equalization in the smoothing action of the blade on the coating.

The moisture applied to the carrier surface also acts as a lubricant between the blade and those parts of the surface not covered by the paper web so that they readily slide under the blade in spite of the pressure which may exist between the blade and the surface. I It also prevents any coating material which may spread over the carrier surface, where not covered by the web, from being carried under the blade and building up to form an objectionable deposit or causing other diiiiculties.

I. have also found that the adhesion which- I have provided between the paper and the carrier surface greatly facilitates threading, and makes it possible to thread a paper web through the device without lifting the blade from the carrier surface or releasing a pool of coating, if such is maintained on the surface in front of the blade. This is accomplished, as hereinafter more fully described, by threading a tail cover the carrier surface and then widening the tail to the full width of the web as is done in threading papermaking machines.

The invention will be further explained with reference to the accompanying drawing wherevin:

Fig. 1 is a diagrammatic illustration showing blade coater which uses aweb carrier in the form ,of an endless belt instead of in the form of a roll.

, Fig. 4 is a fragmentary view of one end of a web carrier roll anddoctor blade showing the ,method of threading paper under the blade.

Referring to Fig. l of the drawing, the covering H, of rubber or similar yielding resilient material, on the roll l2 which is mounted for rotation on journal bearings I3, carries the paper web I4, with the coating thereon, under the doctor blade I5 which smooths the coating in a manner which forms no part of the present invention and lwill not be further described. In order to cause the paper web to adhere to the surface of the rubber covering I! on roll [2, this surface 'is slightly moistened by contact with a roll 2! which dips into a pan 2| containing water which is carried up by the roll 20' and transferred to the rubber roll covering H. In order to regulate the degree of moistening of this surface, the mois- 'te ning roll 20 is held against the surface II with the desired degree of pressure which is adjusted by conventional means such as screws 22 acting on journal bearings 23.

In the modification illustrated in Fig. 2, the rubber covering ll, roll 12, journal bearings i3, paper web [4, and doctor blade 15 remain as described except for the direction of rotation of they roll and consequent direction of travel of the paper web. The degree of moistening is controlled as before by pressure of roll 2i! against the rubber covering H of roll 12. The application of water is made in this case by a shower 25 directed onto the surface I! as shown, onto roll 2U,'or into the nip between the two. The pan 2 6 is here provided merely for the purpose of catching any overflow or drip.

-Fig. 3 shows the application of the invention to a coater in which the web carrier is in the form of an endless belt 3| having a surface of the character described. This belt travels around pulleys 32 and 33 (and anadditional supporting roll 34 if desired), and carries the paper web .35

under the doctor blade 36 in a manner analogous to that described. The moistening of the surface of belt 3i is accomplished by roll 3'! which dips into water in pan 38 in the manner described in connection with Fig. 1. In this case, however, the paper web is contacted smoothly with the surface of belt Si by means of roll 43 instead of depending, as shown in Figs. 1 and 2, solely on the tension in the web to insure smooth contact.

Reference to Fig. 4 will make it clear how the paper may be threaded under the blade while it is in contact with and is continuously indenting the moving carrier surface Ii. The working edge of blade I5 is, for this purpose, rounded upward slightly at the end asshown at ti, leaving a tapered entry-way "52 between the blade and the carrier surface. With the carrier surface ii in motion, the moistening devices in operation, and the moist surfacesliding freely under, and being continuously indented by, the blade, as de' scribed, a narrow strip or tail of the paper to be threaded through the machine is passed around the protruding end of the carrier roll or belt H as indicated by the broken lines at 43. This tail travelling with the carrier surface H is then guided sideways under the end of the blade to the position illustrated at 44. The tail is then widened out in the manner familiar to papermakers until it becomes the full width of the web. I have found that, in spite of the continuous indentation of the carrier surface as it passes under the blade, this moistening of the surface makes it possible to thread the web under both the blade and a pool of coating material, if one is maintained on the carrier surface in front of the blade, without draining the coating material from the pool, lifting the blade, or even releasing the deforming pressure between the blade and the carrier surface.

In all of these and other embodiments of the present invention, the moistening of the carrier surface is so regulated that the surface of the roll is'damp but does not carry water to an extent that it will flow on the sunrface. Under these conditions the paper web adheres to the surface to a degree which strongly resists sliding along the surface but permits the sheetto part readily from the surface where its path diverges therefrom. Also, the carrier surface is so yielding and resilient and the machine is so adjusted that the carrier surface is indented and elongated slightly where it carries the paper web under the blade.

The term rubber as used herein is to be understood as referring to natural rubber or synthetic or other rubber-like compositions which are similarly yielding and resilient.

The term doctoring as used in the present specification and claims refers to a scraping or wiping action such as is accomplished by known types of doctor blades and is to be distinguished from the action of press rolls, squeeze rolls, and the like.

Alternatively it is possible, though in general less desirable, to secure the desired adhesion by wetting the surface of the paper web instead of the carrier surface before the paper is applied to the carrier surface. Also, methods other than water-wetting may be used for securing the required degree of adhesion in special cases Where circumstances render such methods desirable.

The described degree of adhesion to the carrier surface, combined with the indentation of the surface by the blade, I have found enables the device to successfully coat paper Webs having buckles, slack edges or the like, without the wrinkling and tearing formerly encountered in coating paper webs having such defects on coaters of the type described. It makes it possible, when desired, to thread the paper through the coater without releasing or lifting the blade or draining the pool of coating, when such is maintained in front of the blade. It has also been found to result in better and more uniform coating than is secured by the same device when the paper is not caused to adhere to the surface.

What is claimed is: 1

1. In a paper coating device wherein a paper web, at the location where freshly applied coating material is smoothed thereon by a doctor blade, is supported on the surface of a moving web-carrier at least the outer layer of which is formed of yielding resilient materials the combination with said web-carrier of means for continuously applying a thin film of water to the surface thereof prior to the application of the paper thereto; means for holding said doctor blade in a position to indent the surface of said web-carrier; and means for firmly supporting the yielding material of I said webcarrier against the pressure of .said doctor blade; whereby the surface of said web carrier is slightly elongated under and in the immediate vicinity of said doctor blade.

2. The device of claim 1 wherein means is provided for regulating the thicknessof the water film applied to the web-carrying surface.

3. The device of claim 1 wherein a roll with means for pressing it with adjustable pressure against the surface of said web-carrier, is provided for regulating the thickness ,of the water film applied to the resilient surface,-

4. In a paper coating device wherein the paper is carried on a moving surface at the location where freshly applied coating. material is smoothed thereon by a doctor blade: the combination of a yielding resilient surface layer on the web-carrier; means for causingthe web to adhere to the surface of said carrier at'said location; a lateral extension of theiWeb-carrier beyond one extremity of the web-contacting surface of the blade; and a tapering endfor said blade, overhanging said lateral extension of the webcarrier and gradually tapering to said web-contacting edge.

5. In a paper-coating device of the type wherein moist coating material on a moving paper web is smoothed by a doctor blade at a location where the web is carried on the correspondingly moving surface of a yielding resilient carrier: means for continuously pressing said doctor blade against the coated surface of the paper on said carrier; means for positively supporting said yielding carrier against bodily displacement by pressure exerted thereon by said doctor blade; and means for continuously moistening the surface of said carrier in advance of the application of the paper web thereto.

6. In a paper coating operation wherein a freshly coated paper web is carried on the surface of a moving, yielding, and resilient carrier of the nature of rubber, past a location where it is subjected to a doctoring operation in which pressure of a doctor member against the supported web deforms and locally elongates the supporting carrier surface to some degree, the method of preventing wrinkling and tearing of the paper at said location, which comprises moistening the moving surface of said carrier in advance of the position where the paper is carried thereon and thereby causing the paper to adhere to said surface where it is carried thereon.

7. In a paper coating process wherein a freshly coated paper web is carried on the surface of a moving, yielding, and resilient carrier of the nature of rubber, past a location where it is subjected to a doctoring operation in which pressure of a doctor member against the supported web deforms and locally elongates the supporting carrier surface to a slight degree, the method of preventing wrinkling and tearing of the paper at said location, which comprises moistening the moving surface of said carrier in advance of the position where the paper is carried thereon, and applying the paper smoothly to the moist surface, thereby causing the paper to adhere to said carrier surface and each portion of the length of ,the paper web successively to be slightly, locally, and temporarily elongated, by the said elongation of the part of the carrier surface to which it is adhering, as it passes the location of said doctoring operation.

8. In a paper coating device: a rubber-covered rotatable roll for carrying a freshly coated paper web, a doctor blade for smoothing freshly applied coating on the surface of a paper web carried on the surface of said roll; means for pressing said doctor blade against the coated surface of a paper web carried on the surface of said roll, whereby the surface of the rubber covering of said roll will be indented and slightly elongated in the immediate vicinity of said doctor blade; and means for continuously moistening the surface of said rubber covering in advance of the position where said roll is adapted to be contacted by the paper web.

WILLIAM PALMER TAYLOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,051,403 Boyer Aug. 18, 1936 2,094,348 Carlson Sept. 28, 1937 2,243,604 Parkinson May 27, 1941 2,271,458 Lionne Jan. 27, 1942 2,355,919 Lipsius Aug. 15, 1944

Claims (1)

1. 6. IN A PAPER COATING OPERATION WHEREIN A FRESHLY COATED PAPER WEB IS CARRIED ON THE SURFACE OF A MOVING, YIELDING, AND RESILIENT CARRIER OF THE NATURE OF RUBBER, PAST A LOCATION WHERE IT IS SUBJECTED TO A DOCTORING OPERATION IN WHICH PRESSURE OF A DOCTOR MEMBER AGAINST THE SUPPORTED WEB DEFORMS AND LOCALLY ELONGATES THE SUPPORTING CARRIER SURFACE TO SOME DEGREE, THE METHOD OF PREVENTING WRINKLING AND TEARING OF THE PAPER AT SAID LOCATION, WHICH COMPRISES MOISTENING THE MOVING SURFACE OF SAID CARRIER IN ADVANCE OF THE POSITION WHERE THE PAPER IS CARRIED THEREON AND THEREBY CAUSING THE PAPER TO ADHERE TO SAID SURFACE WHERE IT IS CARRIED THEREON.

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