GB2147527A - Curtain coater - Google Patents

Abstract

Curtain coater for coating a travelling web includes a lip 54 which cooperates with an air pressure chamber 42 so as to control discharge of coating composition onto slide surface 56. The lip 54 is adjusted uniformly across the machine width by motors 68 and it is also variably adjusted laterally of the machine width by means of spaced microjacks 80 so as to permit the discharge of variable amounts of the coating composition across the machine in accordance with the lip opening set by the respective microjacks. <IMAGE>

Description

SPECIFICATION Method of and apparatus for applying a liquid coating to a travelling web This invention concerns the application of a liquid coating to a travelling web and to apparatus, e.g. in the form of a web saturator or coater which accepts a web moving therepast and saturates or coats same before its passage onto another work operation such as a drying procedure.

More particularly, the invention relates to a method and apparatus for saturating or coating a travelling web of material by means of a controlled curtain of the saturant or coating in which the travelling web is treated e.g. by the controlled cascading of the saturant over an inclined slideway and applying same in the form of a free-falling vertical curtain of the saturant which impinges onto the travelling web so as to form a layer thereupon and/or to saturate therethrough, according to the particular characteristics of the saturant and/or of the web, and/or the exploitation of various suction devices according to the desired characteristics of the end product.

The apparatus may be used singly to allow a single layer of the coating, such as a binder, to be added to the travelling web, or a plurality thereof may be used in tandem to allow a plurality of seriatim layers of coating to be added thereto. If desired, the apparatus may be used cooperantly with a series of suction or vacuum devices for purposes of more precisely conditioning the web by a progressive series of operations applying varying degrees of negative pressure.

A primary object of the invention is to provide a method of saturating or coating a travelling web with a layer or layers of an appropriate liquid composition such as a binder by the steps of moving the web along a path through a work zone and forming at the work zone a free-falling vertical curtain of the saturant or coating extending transversely of the web path and impinging same on the travelling web.

In the preferred embodiment, the apparatus comprises means for forming a free-falling vertical curtain inclusive of a well or reservoir or cavity for containing the saturating or coating composition and flowing same outwardly therefrom through a pressurized headbox, over a dam on the downstream side of the well and along an inclined slide through a variable slice disposed adjacent the slide, with the slide terminating in a lip along its lowermost edge from whence the liquid falls by gravity as a vertically disposed curtain onto the travelling web therebelow.

An air pressure chamber may be provided to permit the discharge of a controlled increased amount of binder to the web.

Additionally, the apparatus is conveniently provided with a lip which can be adjusted uniformly across the machine width and relative to the inclined side and with a mechanical jack arrangement located on top of the air cap for controlling the size of the defined slice between lip and slide.

It may also be adjusted by means of a plurality of microjacks positioned at intervals across the machine width so as to allow the discharge of a variable amount of binder in accordance with the set lip opening at the different intervals along the machine width, wherefor a relatively heavy or light discharge of the binder can be made centrally of the web and/or at one side of the median line thereof and/or at a side edge of the web, all as may be desired.

Advantageously, means may be provided for varying the vertical spacing between the terminus of the slide lip and web moving along the path, thereby regulating the curtain height, the distance over which free fall occurs depending on the nature of the specific application involved and the characteristics of the particular liquid composition employed. In selecting any optimum height for any particular application, a chief criterion is to make the height as small as practical while yet affording a desired result. The greater the curtain height, the more susceptible it is to being affected by influences such as ambient air currents which may create curtain fluctuations with unwanted attendant variations in the deposited layer on the web.

A vertical height has to be selected which will satisfy the dictate that the free-falling curtain will have such momentum upon impingement that it will penetrate any existing air barrier or at least will displace it so as to permit the desideratum of adhering to the web or penetrating therethrough. Any air barrier so encountered may be found to vary with such different factors as the surface character of the work being treated, and the velocity of the work as it is advanced relative to the apparatus.

The law of momentum, as the product of velocity and mass, teaches that, if the rate of liquid flow is reduced, while the web velocity of the web remains constant, the height of free-fall must, normally, be increased in order to increase the impingement velocity and to give the freefalling curtain such adequacy of momentum as to penetrate the air barrier without disruption.

The accompanying drawings serve to illustrate the method and apparatus of the present invention by way of example. In these drawings: Figure 1 is a diagrammatic sectional elevational view of a preferred embodiment of the apparatus of the invention; and Figure 2 is a transverse sectional view through a typical treated web showing the effect of varying the amount of deposition of binder thereon.

The illustrated preferred embodiment of the apparatus of the invention comprises a pair of spaced vertically-extending stands 10, each being footed on a mill flooring F on opposite sides of a travelling wire or belt B upon which a web or work W is moved past and below the to-be-described operating mechanism of the apparatus.

A clevis 14 extends upwardly from each stand and through each of which a pin 1 6 extends for pivotally supporting a foot 1 8 at both the tending and drive sides of the machine.

Also supported upwardly vertically above a respective stand 10 on each side of the apparatus is an air-ride 20 connected by means (not shown) to a valved air source (not shown) wherewith pressurized air may be charged to or released from the air-rides for purposes later to be referred to.

An adjustable jacking mechanism 21 may be provided on each stand for purposes of elevating the applicator box about to be described.

Spaced upwardly from stands 10 and from the belt B and the web W is a horizontallyextending header 22 which extends centrally through an applicator box defined by a horizontally-extending bottom wall 24 supported by a lower frame 26, a transverse verticallyextending rear wall 28, an inclined front wall or slide 30, and inwardly converging front and rear top walls 32 and 34 respectively, which front and rear top walls are connected at their lower extremities astride opposite sides of a slot 36 extending through the topmost portion of the header 22. Opposite side walls 38 at opposite sides of the applicator box complete the enclosure, all of the walls being interjoined in conventional manner to define a unitary construction.

If desired, slot 36 through the top side of the header 22 may be substituted for a plurality of spaced apertures.

The header 22 extends outboard of the enclosure through one of the side walls and will be fed from an outside source of material (not shown) in a conventional so-called "side inlet" manner.

By the means thus far described, the enclosure may be raised or lowered upon the pins 1 6 by pressurizing or releasing the air-rides 20 so as to allow ready access to the transporting or travelling wire B for threading or other purposes as well as to allow varying of the vertical distance between the edge of the lip at the lower terminus of the slide 30 and the travelling wire B.

Upwardly of the applicator box, a sealed pressure chamber is defined by opposite side walls 42 extending upwardly from and connecting with respective side walls 38, a cover 44 extending transversely of the apparatus and having a forward portion 46 terminating at a pivot point 48 and a rearward portion 50 connecting with rear top wall 34, and a lower wall 52 extending transversely of the apparatus and extending between the pivot point 48 and a downwardly facing lip 54.

The inside wall of the lip 54 has a transversely-extending sealing tip 56 so as effectively to seal off the pressure chamber.

The pivot 48 mounts a pivot pin 58 by means of which the lower wall 52 may be pivotally moved so that the lip 54 is moved toward or away from the outer surface of the inclined front wall 30 defining a slide 56.

The pivot 48 is supported by a pair of vertically depending beams 60 extending downwardly from and pivoted at 62 from the respective one of a pair of horizontally extending posts 64 which project outwardly from and are moved in fore and aft directions, as indicated by arrows a, by respective motors 68 mounted on the cover 44.

Selective operation of motors 68 drives the posts 64 forwardly or rearwardly and controls the movement of the lip 54 toward and away from the slide 56 and hence controls the general dimension of the slice therebetween for the obvious control of the flow of material passing therethrough.

Pressurized air is introduced to the gas pressure chamber through a manhole 70 and a level control blowhole 72 allows maintenance of a stock level L in the housing under the pressure as applied by compressed air through the manhole 70. The level L is maintained so as just to submerge dam or weir 74 defined by the apex of the front wall 30 and the front top wall 32 over which liquid flows upwardly from the header 22 through the slot 36 (or apertures) into and out of the well thereabove and thence over the dam 74 and downwardly along the slide 30/56.

The usual tending side and distant side deckles (not shown) are disposed on each side of the front wall 36, which deckles may be adjusted in inboard and outboard directions for the known function of varying the work area width.

The height of the free-falling curtain, that is, the vertical distance from lip to web over which free fall occurs can be varied to accommodate to the nature of a specific application and the particular characteristics of the liquid composition therein employed, but preferentially, the height will be as small as is practical.

The higher the curtain, the greater the opportunity for ambient air currents to take their toll in curtain fluctuations and resultant variations in the manner in which the liquid contacts the web.

Under typical operating conditions, the height of the free-falling curtain will be in the range of i" to i" but operations at smaller or greater heights are within the scope hereof.

The coating or saturant is continuously fed as a curtain at a rate at least as great as it is removed by the moving web, and in order to maintain this the lip of the slide 56 is positioned in close proximity to the surface of the moving web.

The layer can be oriented in any desired manner with wide variation permissible with respect to thickness and/or viscosity of the particular liquid coating composition.

The space between lip and slide is such that the stock receiving chamber is closed so that air pressure may be built up therein by the air inlet.

It is to be appreciated that stock in this chamber may be maintained under pressure merely by a suitable stock flow pump and without the use of air under pressure as shown.

In either case the sealing means is effective to maintain such pressure.

The sealing means will comprise a rubber sealing strip.

To increase the mass, certain interior space 100 within the enclosure may be filled with concrete.

As shown schematically, the applicator can be used in combination with a series of three suction or vacuum boxes 90, 93 and 94, wherein suction box 90 is disposed in advance of the applicator operating area for use in conditioning the web to attain an optimum or minimum water content before the initiation of the saturation step, wherein suction box 92 is disposed in the applicator operating area for use in applying a low degree of vacuum so as to draw the saturant through the web and removing any excess thereof, and wherein suction box 94 is disposed outboard of the applicator operating area for use in fine-tuning with minute or discrete vacuum control so as to allow retention of the precise desired amount of saturant on the web or sheet.

The invention is specifically illustrated with no reference to any other particular type of application, although it is to be understood that it offers opportunity for wide application, with utilization to advantage in numerous fields, wherein it is desired to effect application of a superposed layer of liquid coating composition or of a liquid saturant.

It will be appreciated that the invention is not limited to the particular construction of the exemplary embodiment illustrated but includes variants and equivalents within the scope of the invention as defined by the

Claims (4)

claims. CLAIMS

1. A method of applying a layer of a saturating substance to a travelling web comprising the steps of a. transporting the web along a horizontal path below a hopper b. feeding a charge of the saturating substance in the hopper upwardly over a hopper dam and onto a downwardly inclined slide where adjacent edge means defines a seal producing a pressurized chamber containing the charge of saturating substance which overflows the dam opening, and c. adjusting the edge means with respect to the slide for closing off the pressure chamber for the buildup of pressure therewithin and for controlling the amount of saturating substance allowed to escape from the pressurized chamber and thereby controlling the amount of saturating substance allowed to proceed further down the slide where at the termination of the slide the saturating substance freefalls onto the travelling web therebelow.

2. Apparatus for applying a liquid coating to a travelling web comprising means for transporting the web to be coated along a predetermined horizontal path relative to and below the machine, coating liquid means extending transversely across the path in spaced overlying relation thereto and including:: an enclosed hopper, a hopper dam upwardly of the hopper and within the enclosure, means for forcing the coating liquid outwardly of the hopper and over the dam, a downwardly inclined slide disposed adjacent to the dam for accommodating the coating liquid forced over the dam, edge means defining a seal to produce jointly with the enclosure a pressurized chamber and being adjustable with respect to the slide for closing off the pressure chamber for air pressure buildup therewithin and for controlling the amount of coating material allowed to escape from the chamber and to proceed down the slide where at its termination the coating material freefalls onto the web passing beneath the coating liquid means.

3. A method of applying a layer of saturating substance to a travelling web substantially as hereinbefore described with reference to the accompanying drawings.

4. Apparatus for applying a liquid coating to a travelling web substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.