US3526535A - Method for producing surface coatings - Google Patents

Description

Sept. 1, 1970 E, PLUM 3,526,535

METHOD FOR PRODUCING SURFACE COATINGS Filed July 25,. 1967 4 Sheets-Sheet 1 PRIOR ART 5/ PRIOR ART V//\////// X A INVENTOR Emile Plumut Sept. 1, 1970 PLUMAT v 3,526,535

METHOD FOR PRODUCING SURFACE COATINGS Filed July 25. 1 67 4 Sheets-Sheet 2 ATTORNEYS Sept 1,1976 v E. PLUMAT 3,526,535

METHOD FOR PRODUCING SURFACE COATINGS Filed July 25. 41967 4 Sheets-Sheet 3 I mvsmon Emile Plume? ATTORNEYS Sept 1, 1970 PLUMAT 3,526,535

METHOD FOR PRODUCING SURFACE COATINGS Filed July-25. ,196'? 4 Sheets-Sheet 4.

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- INVENIOR Emile Piumoi ATTORNEYS United States Patent 3,526,535 METHOD FOR PRODUCING SURFACE COATINGS Emile Plumat, Gilly, Belgium, assignor to Glaverbel S.A., Watermael-Boitsfort, Belgium Filed July 25, 1967, Ser. No. 655,785 Claims priority, application Luxembourg, Aug. 1, 1966,

Int. Cl. l305c 5/02 US. Cl. 117120 21 Claims ABSTRACT OF THE DISCLOSURE A method for producing surface coatings by applying a liquid film from a dispenser orifice to the surface being coated while producing a relative movement between the surface and the dispenser orifice and creating a relationship between the volume flow rate of liquid from the orifice and the rate of relative movement between the surface and the orifice so as to maintain, at the point where the liquid descending from the orifice contacts the work surface, a swelling of the liquid in the direction of movement of the orifice relative to the work surface, and while maintaining a spacing between the orifice and the work surface which is large enough to prevent the liquid from forming a bead which could be maintained by surface tension.

BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for applying liquids to surfaces, and particularly for applying liquid in the form of a film.

There are various well known methods of machine coating surfaces. These include spray coating, coating by transfer of the liquid directly to the surface to be coated by means of an applicator such as a brush or a roller, dip coating, and methods wherein the surface is displaced past a slot-like orifice through which the liquid is dispensed in the form of a continuous stream, or flow.

The present invention relates to such continuous flow coating. The known coating methods in this field include bead-coating and extrusion coating. In bead-coating, a bead of the coating composition is produced, or struck, between the dispenser orifice and the surface to be coated and is maintained by surface tesion. Liquid is continuously withdrawn from the bead by the travelling surface and the bead is continuously replenished from the dispenser.

The head coating principle is illustrated in FIGS. 1 and 1a of the accompanying drawings. FIG. 1 shows the situation after a bead B of the liquid has been permitted to form between a sheet S to be coated and the mouth M of the dispenser. FIG. 1a shows the situation created after the sheet S has commenced to move in the direction of the arrow so that a coating, or film, C of the liquid has commenced to form on the sheet.

The bead-coating technique involves, as a necessary condition, an appropriate relationship between, on the one hand, the interfacial tension between the surface to be coated and the liquid, and, on the other hand, the surface tension of the liquid and can not be used for applying liquids to surfaces which will not be wetted by the liquids. Another important point in bead-coating is the fact that the accuracy and finish of the surfaces defining the dispenser mouth M are critical for the quality of the coating. If there are imperfections in the dispenser month, they are likely to make it impossible to form a truly uniform coating free of defects.

Another continuous flow coating method is the extrusion, or casing, method wherein the liquid composition 3,526,535 Patented Sept. 1, 1970 ice discharge as a free-flowing film onto the surface as this surface and the extrusion, or casting head, are being relatively displaced. The term extrusion is normally used in relation to the application of plastics or other easily solidifiable compositions. For the purposes of the present invention, the nature of the liquid is not of primary importance and the word casting is used generically to denote the dispensing of liquid as a free-flowing film, regardless of the nature of the liquid.

The casting method is diagrammatically represented in FIG. 2 of the accompanying drawings. The liquid leaves the slot of the dispenser mouth M as a film, or ribbon, F and becomes deposited as such on the surface of the sheet S to be coated as the latter moves past the dispenser in the direction of the arrow.

Assuming a certain minimum viscosity for the coating liquid, the thickness of the coating C formed on the sheet depends on the width of the discharge slot. It is rather difficult, when applying the casting technique in the known way, to form very thin coatings of uniform quality over large surfaces as, for example, is necessary in the mass production of coated glass wherein the thickness of the coatings is critical for achieving predetermined optical effects.

SUMMARY OF THE INVENTION It is a primary object of the present invention to over come these drawbacks and difficulties inherent in the prior art techniques.

Another object is to improve the coating of article surfaces with thin films.

A further object of the present invention is to provide an improved casting technique for producing thin films of uniform quality.

These and other objects according to the present invention are achieved by a novel method for applying a liquid coating to a work surface by causing liquid to flow as a film downwardly from a dispenser orifice in a splashand turbulence-free manner. The method according to the invention is carried out while maintaining a spacing between the orifice and the work surface which is large enough to prevent the liquid from forming a head which could be maintained by rusface tension. The method is carried out by producing a relative movement between the work surface and the orifice in a direction normal to the spacing therebetween for coating the surface with a layer of the liquid, and by giving the liquid flowing from the orifice a volume flow rate which is so related to the rate of relative movement between the work surface and the orifice that, at the point where the liquid descending from the orifice contacts the work surface, the liquid swells out in the direction of movement of the orifice relative to the work surface.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic, cross-sectional, elevational view illustrating the starting conditions for one coating process according to the prior art.

FIG. 1a is a view similar to that of FIG. 1 illustrating the carrying out of such a prior art process.

FIG. 2 is a view similar to that of FIG. 1a for another prior art coating process.

FIG. 3 is a view similar to that of FIG. 1a for the process according to the present invention.

FIG. 4 is a view similar to that of FIG. 1a for another form of the process according to the present invention.

FIG. 5 is an elevational, cross-sectional view, taken along the line 55 of FIG. 6, of one type of apparatus for carrying out the present invention.

FIG. 6 is a cross-sectional view taken along the line 66 Of FIG. 5.

FIG. 7 is an elevational, cross-sectional view, taken along the line 7-7 of FIG. 8, of another embodiment of apparatus for carrying out the present invention.

FIG. 8 is a cross-sectional view taken along the line 88 of FIG. 7.

FIG. 9 is an elevational, cross-sectional view of a further embodiment of such apparatus.

FIG. 10 is a view similar to that of FIG. 9 of yet another embodiment of such apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1, la and 2 relate to prior art processes and have been described in detail above.

Referring now to the present invention, it has been found that the principle of applying liquid by casting can be successfully utilized for forming thin coatings having the desirable characteristics previously referred to for a given liquid, if certain conditions are observed for the relationship between the rate of displacement of the surface to be coated relative to the dispenser and the volume rate of flow of the liquid from the dispenser. This relationship should be such that a kind of liquid bead incorporating a constant excess quantity of coating liquid is maintained on the surface at the foot, or base, of the descent path of the liquid, as is diagrammatically illustrated in FIGS. 3 and 4. In these figures, reference letters already used in preceding figures have the same meaning as before.

In FIG. 3 there is shown a liquid flow configuration producing a wedge W of liquid which contains liquid in excess of that required for coating that part of the surface which, at the instant considered, is immediately below the orifice in dispenser mouth M. The liquid head should have this shape when the surface to be coated is of a type which will be wetted by the liquid.

On the other hand, the corresponding head should take the form shown in FIG. 4 if the surface is not wetted by the liquid. However, even in this case there is a slight excess of liquid since the descending film F of liquid, at the bottom of its descending path, swells under the lefthand lip of the discharge orifice.

The term bead is not used, in connection with the present invention, in the same sense as in the bead-coating method hereinbefore referred to since in the method according to the invention the liquid bridge between the surface to be coated and the discharge orifice is not inherently maintained due to surface tension. On the contrary, if, in the practice of the present invention, the downward movement of liquid through the discharge slot were interrupted then the liquid bridge would instantly collapse.

The descent of the liquid from the discharge orifice is preferably a free descent wholly or partly under the influence of gravity. It is preferred that the liquid be allowed to descend freely under the influence of gravity from a reservoir in which the liquid level is maintained constant. Depending on the width of the discharge slot and the surface tension of the liquid, it may be necessary that the pressure above the liquid level be above atmospheric pressure in order to sustain the discharge of liquid.

If the liquid falls freely from the dispenser, the free fall height must be limited so that a steady state, or socalled dynamic equilibrium, is maintained. This will help to assure that there will be no splash or turbulence.

As an alternative to the free fall of liquid, the liquid descent may be controlled by one or more guide elements extending downwardly from the dispenser, e.g., a piece of fabric.

The present invention, broadly defined, accordingly involves a method of applying liquid onto a surface wherein the liquid is caused to flow from a dispenser steadily downwardly as a film, without splash or turbulence, onto the surface to be coated, while this surface and the dispenser are displaced relative to one another so that the surface becomes progressively coated with a layer of the liquid, the volume rate of descent of the liquid in relation to the rate of the relative displacement being such that at the bottom of the descent path of the flow the liquid swells out over the surface to be coated to form a bead 'which extends in the direction in which the coating progresses, i.e., in the direction of the relative movement of the dispenser with respect to the surface.

It will be understood that, while the viscosity and density of the liquid are factors which must be taken into account in any given case, the volume rate of descent of the liquid and the rate of relative displacement of the surface to be coated and the dispenser can be set for any given liquid so as to achieve the desired result.

The method can be employed for coating a surface with a liquid which does not wet the surface, as was described above with reference to FIG. 4. Any kind of liquid dispensing means may be used. If a dispenser with a solt-like discharge opening is used, the physical condition of the surfaces forming the orifice of the dispenser is not nearly as critical as in a classic bead-coater.

In order to commence the coating of a surface according to the invention by means of a dispenser With a sl0tlike orifice, the dispenser can be initially placed sufliciently close to the work surface for a stable meniscus or head to be struck between the orifice and the surface and then, after striking such head, the spacing between the orifice and surface can be increased to a point just beyond that at which the bead is self-maintaining under the influence of surface tension eflects. Instead of striking the bead on the work surface to be coated, it may be struck on an auxiliary surface which is both flush and contiguous with the work surface, and coating can then commence as if the auxiliary surface were part of the work surface. In this way, any imperfections in the coating at the starting zone will not spoil the work and a high quality coating can be formed along the whole length of the work.

The invention is primarily intended for forming coatings of uniform thickness, but a coating which varies in thickness in some predetermined manner can be formed by varying one of the factors which influences the coating thickness, e.g., the volume rate of descent of the liquid, provided the relationship between the volume rate of descent of the liquid and the speed of relative. displacement between the surface to be coated and the dispenser is still such that an excess of liquid is maintained at the point of application of the liquid to the surface.

The method can be utilized for applying any liquid substance, e.g., an enamel or a solution of a hydrolyzable metallic salt. If desired the liquid can contain dispersed solid particles or it may be a mixture of immiscible liquids, e.g., an emulsion. The method has been developed primarily for coating glass but it can also be used for coating other materials, e.g., metal, plastics or ceramics.

Liquid may be applied according to the invention to form each of two or more successive layers on a surface. A second or subsequent layer can be applied onto a preceding layer before this has dried and the successively applied quantities of liquid can contain ingredients which react to form a compound which it is required to deposit on the surface.

Reference will now be made to FIGS. 5 to 10 of the accompanying drawings illustrating various forms of apparatus for carrying out the invention.

The apparatus shown in FIGS. 5 and 6 includes a stationary, curved support 1 for supporting a similarly curved sheet S of glass or other material having a work surface to be coated. A fixed end strip 2 presenting an auxiliary surface is provided on the support 1 so that when the sheet S to be coated is in position its upper, work surface is flush and contiguous with the upper, auxiliary surface of the strip 2.

At a small distance above the support 1, there is provided a pair of curved guide rails 3 and 3a which support a dispenser 4 in the form of a trough on which end rollers 5 and 5a are rotatably mounted so as to run on the rails 3 and 3a, respectively. Liquid is supplied to the trough from a reservoir 6 via a down pipe 7 and a discharge pipe 8 extending longitudinally of the trough and provided with a series of liquid discharge orifices. The trough and the reservoir, with its liquid delivery pipes, are connected together by means (not shown) and are displaceable as a unit along the rails 3 and 3a by a suitable drive mechanism (not shown). The reservoir has a gas inlet opening 6a which, in use, communicates with the atmosphere or with a source of gas under a suitable pressure. A control valve 9 in the down pipe 7 controls the flow of liquid to the dispenser trough to maintain the level of liquid therein constant during coating of the sheet S.

Prior to the commencement of the coating operation the dispenser is located at the left-hand end of the rails 3 and 3a, with regard to the view of FIG. 5. At this point the rails 3 and 3a are angled downwardly so that the distance between them and the strip 3 is such that the discharge slot 10 at the bottom of the trough 4 touches the strip. Then, the trough is driven in the direction of arrow A. As the dispenser leaves its starting point it rises slightly due to the upward sloping of the rails 3 and 3a so that liquid begins to flow from the orifice 10 onto the surface beneath.

By the time the orifice is above the sheet S contiguous with the strip 3 the discharge slot 10 is at the correct height for coating and this height is maintained over the whole of the subsequent travel path of the dispenser above the sheet S. Over this part of the dispenser travel path its velocity is maintained constant. FIG. shows the dispenser about half way along this path. At each instant there is an excess quantum of coating liquid at the point of application to the work surface so that the liquid at the bottom of the descent path from the discharge slot swells out over the work surface in the direction in which the coating is progressing, as was shown in FIG. 3. A liquid coating C of uniform thickness is thereby formed on the sheet S.

The apparatus shown in FIGS. 7 and 8 is designed for coating sheets S while they are moved relative to the coating apparatus. To this end, there is a sheet conveyor composed of fixed side supports 11 between which a series of conveying rollers 12 are mounted. The dispenser for the coating liquid includes a trough 13 having a slot-like bottom discharge orifice and mounted in a conditioning chamber 14 having pipes 15 and 15a for the admission of a suitable gas. Liquid is fed to the trough from a reservoir 16 via a down pipe 17 fitted with a control valve 18.

As appears from FIG. 8, the trough is supported within the conditioning chamber 14 by rods 19 and 1911 which extend outwardly through slots 20 and 20a, respectively, in the end walls of the chamber and upwardly through the top wall of the chamber. The upper free end portions of the rods are screw threaded and carry nuts 21 and 21a, respectively, by adjustment of which the height of the dispenser trough can be accurately preset.

Downstream of the conditioning chamber 14 is a drying chamber 22 having pipes 23 and 23a for the admission of a suitable gas for drying the liquid coating which forms on the sheet as the latter is conveyed beneath the dispenser 13 in the direction of arrow A.

During the coating operation the chamber 14 can be maintained filled with an inert gas. This is an important step when, for example, the liquid being applied is a solution of a hydrolyzable salt of a metal which is to be caused to deposit from the liquid layer onto the surface of sheet S by some subsequent treatment.

The apparatus shown in FIG. 9 includes a dispenser trough 24 to which liquid is supplied from a reservoir 25 via a down pipe 26 fitted with a valve 27. This reservoir is fitted with horizontal blades 28 and 28a which define the slot-like discharge orifice through which the liquid flows onto the sheet S to be coated. Screw threaded pins 29 extend from the blades to the outside 6 of the trough and are fitted with nuts 30 by which the spacing of the blades can be adjusted.

During coating, the sheet S is conveyed beneath the dispenser in the direction of arrow A by a roller conveyor 31. Assuming that a liquid composition is to be appl ed which can form a static bead, or meniscus, between the sheet and the discharge mouth of the dispenser when the latter is sufficiently close to the surface of the sheet, it is advantageous to form such a meniscus just prior to commencement of the coating operation and to then raise the dispenser trough so that the distance between the work surface of sheet S and the dispenser mount becomes just too large to be bridged by a head which can be maintained by surface tension effects.

To permit this procedure to be followed, the dispenser trough 24 is provided at each end with a cam 32 rotatably mounted on a stud fixed to the corresponding end of the trough. The cams 32 at the opposite ends of the trough rest on horizontal tracks 33 fixed to the frame of the conveyor 31. Just preparatory to the coating operation, the dispenser trough occupies a position on the tracks 33 just a little to the right of the position which it occupies in FIG. 9. In other words, the small radius parts of the cams 32 are in contact with the tracks 33 and the mouth of the dispenser trough is nearer to the surface of the sheet S to be coated.

Liquid is supplied to the trough and a meniscus is struck between the dispenser mouth and the sheet. Then the dispenser trough is moved, either manually, or mechanically, along the tracks 33 to the left, with respect to the plane of FIG. 9, so that the larger radius parts of the cams 32 roll against the tracks 33 and lift the trough to the required higher level in order that coating can proceed by the method according to the invention. As the trough reaches its correct level for this coating operation the cams 32 come to abut against stops 34 fixed to the tracks 33 and the trough is thereby stably supported in its raised position.

It will be understood that instead of forming the initial bead or meniscus against the actual sheet to be coated it can be formed against a leader sheet or strip contiguous with the leading edge of the sheet to be coated so that the correct coating flow according to the invention commences before the leading edge of the sheet to be coated moves below the discharge orifice of the dispenser.

The apparatus shown in FIG. 10 is useful for applying different liquid compositions as superimposed layers on a sheet S during its conveyance in the direction of arrow A by a conveyor composed of a series of driven rollers 35. Liquid for forming the first, or bottom, layer is applied from a dispenser 36 to which the liquid is fed from a reservoir 37 via a down pipe 38 fitted with a valve 39. At the top of the dispenser 36 there is a gas inlet pipe 40 fitted with a valve 41. Prior to the commencement of the coating operation, gas can be admitted to the dispenser via this pipe to establish the requisite pressure therein for maintaining the rate of flow of liquid from the dispenser required for ensuring that the coating operation will proceed according to the invention. During the coating operation, the rate of flow of liquid into the dispenser is controlled so that the liquid level in the dispenser remains constant.

The sheet S provided with such a liquid coating C then passes beneath a conditioning chamber 42 having ports 43 for the passage of gas. By maintaining the chamber filled with an appropriate gas, or gases, various physical and/or chemical treatments of the coating C can be performed, e.g., drying or oxidation.

Immediately after each portion of the sheet S carrying the coating C leaves the conditioning chamber 42, a second liquid layer C is applied from a second dispenser 44'. This dispenser is similar to dispenser 36 and is likewise fed from a reservoir via a down pipe fitted with a control valve.

The liquid flow from dispenser 44 occurs via two slots defined between the lower edges of the side walls of the dispenser and an intermediate bar 45 of triangular cross section. This bar is supported by screw threaded rods 46 extending through the top of the dispenser and held by nuts 47 by means of which the height of the bar 45, and thus the width of the discharge slots, can be adjusted. The fiow from the dispenser is regulated so that the liquid is applied by the method according to the invention to form the second coating C.

The coating operation according to the present invention can be further illustrated by the following specific examples of the dimensions employed for applying selected compositions to produce coatings of selected thicknesses.

Titanium Organic paint butylate (15 (mixture of Regardless of whether the relationship between the material of the surface to be coated and the composition of the coating liquid is such that the liquid wets the surface, thus creating the condition illustrated in FIG. 3, or does not wet the surface, as illustrated in FIG. 4, it is only necessary, in order to achieve the novel results of the present invention, that the relation between the volume flow rate of liquid and that rate of displacement of the surface be such that, once the bead has been established, sufficient liquid is supplied to produce the desired coating thickness.

The bead according to the present invention helps to improve the quality' of the resulting coating and to facilitate control of the coating thickness. In effect, this bead serves as a bridge between the coating being formed and the liquid leaving the dispenser orifice and thus assures a uniform flow of coating liquid and an absence of splash and turbulence. The bead also acts, in a certain sense, as an intermediate liquid supply which receives liquid from the dispenser and delivers it to the work surface. Because the bead tends to maintain its shape, the amount of liquid which it delivers will be equal to the amount which it receives. As a result, for a given rate of displacement of the work surface relative to the dispenser, the thickness of the resulting coating can be varied over a substantial range by simply varying the volume flow rate of liquid from the dispenser, the presence of the bead assuring that such variation will not produce any turbulence. The liquid flow rate can be varied by acting on the pressure above the liquid in the dispenser or in the reservoir, or by varying the width of the dispenser orifice.

The thickness of the resulting coating could also be altered by modifying the relative displacement speed between the work surface and the dispenser while maintaining the liquid flow rate constant.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. A method of applying a liquid coating to a work surface by causing liquid to flow as a film downwardly from a dispenser orifice onto such surface in a splashand turbulence-free manner, said method comprising the steps of: establishing, at the surface, a head of the coating liquid which swells out in a direction parallel to the surface; maintaining a spacing between the orifice and the work surface which is large enough to enable such bead to be maintained only as long as liquid flows from such dispenser; producing a relative movement between the work surface and the orifice in a direction normal to the spacing therebetween for coating the surface with a layer of the liquid; and dispensing the liquid from the orifice at a volume flow rate which is so related to the rate of relative movement between the work surface and the orifice that, at the point where the liquid descending from the orifice contacts the work surface, the liquid continues to swell out in the direction of movement of the orifice relative to the work surface.

2. A method as defined in claim 1 wherein said step of establishing is carried out prior to the commencement of liquid fiow from the dispenser by: striking a liquid bead between the dispenser and the surface to be coated while the spacing between the orifice dispenser and the work surface is sufficiently small for this bead to be maintained by surface tension effects; and then increasing this spacing just until it becomes too large to be bridged by a bead maintained by solely surface tension effects.

3. A method as defined in claim 1 comprising the preliminary steps of: providing, as part of the work surface, an auxiliary surface flush with, and contiguous with, a main surface to be coated; commencing the flow of liquid from the orifice onto the auxiliary surface; and producing a relative movement of the auxiliary surface and the main surface as a unit with respect to the orifice in a direction which causes the main surface to be coated as if it were a continuation of the auxiliary surface.

4. A method as defined in claim 1 wherein the dispenser is in the form of a container with at least one slotlike bottom discharge opening and wherein, during the coating operation the container is maintained filled with the liquid coating composition up to a constant level.

5. A method as defined in claim 4 comprising the further step of at least initially assisting the flow of liquid from the container by the admission of gas under pressure into the container above the liquid therein.

6. A method as defined in claim 1 wherein said step of producing a relative movement is carried out by displacing the dispenser while maintaining the surface to be coated stationary.

7. A method as defined in claim 1 wherein the surface to be coated is the surface of a flat object and said step of producing a relative movement is carried out by continuously moving the flat object while maintaining the dispenser stationary.

8. A method as defined in claim 1 wherein the liquid is of the type which wets the surface onto which it is applied.

9. A method as defined in claim 1 wherein the surface onto which the liquid is applied is a glass surface.

10. A method as defined in claim 1 wherein the surface onto which the liquid is applied is of a metal, plastic, or ceramic material.

11. A method as defined in claim 1 wherein the surface onto which the liquid is applied is constituted by the surface of a sheet.

12. A method as defined in claim 1 comprising the further steps of applying a subsequent coating by delivering a second liquid onto the first-mentioned coating by carrying out the steps defined in claim 1.

13. A method as defined in claim 12 wherein the second liquid contains at least one constituent which reacts with at least one constituent of the first-mentioned coating to form a precipitate which deposits on the work surface.

14. A method as defined in claim 1 further comprising the step of delivering coating liquid from a liquid reservoir to the dispenser in the form of a plurality of sprays.

15. A method as defined in claim 14 further comprising the step of maintaining the liquid in the reservoir under pressure.

16. A method as defined in claim 14 further comprising the step of maintaining the liquid in the dispenser under pressure.

17. A method as defined in claim 14 further comprising the step of drying the coating after it has been applied.

18. A method as defined in claim 14 further comprising the step of varying the width of the dispenser orifice.

19. A method as defined in claim 14 wherein the work surface is arcuate and said step of producing a relative movement is carried out by maintaining the work surface stationary and moving the dispenser along tracks tangent to the work surface.

20. A method as defined in claim 19 further comprising the steps of: providing, as part of the work surface, an auxiliary surface flush with, and contiguous with, a main surface to be coated; initially placing the dispenser adjacent the auxiliary surface and in contact therewith; and gradually moving the dispenser along the auxiliary surface toward the main surface and progressively in- UNITED STATES PATENTS 2,970,5 64 2/ 1961 Warner 1l8259 X 3,303,816 2/1967 Lauring. 3,341,354 9/1967 Woods et a1.

FOREIGN PATENTS 722,5 82 11/1965 Canada.

RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R.

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