US3309438A

US3309438A - Method and means for controlling the consistency of casting compositions during casting

Info

Publication number: US3309438A
Application number: US526993A
Authority: US
Inventors: Frank D Bergstein; Jr Alfred B Kleingers; Back Leonard
Original assignee: Bergstein Packaging Trust
Current assignee: Bergstein Packaging Trust
Priority date: 1966-02-14
Filing date: 1966-02-14
Publication date: 1967-03-14
Anticipated expiration: 1984-03-14

Description

arch 1967 .D.BERGSTE|N ETAL 3,309,438

CONTROLLING THE CONSISTENCY OF C COMPOSITIONS DURING CASTING Filed Feb. 14, 1966 2 Sheets-Sheet 1 METHOD AND MEANS ASTING INVENTORS FRANK D. BERGSTEIN,

- ALFRED B KLEINGERS JQAND LEONARD BAcK,

ATTORNEYS arch 14. 19 7 F. D. BERGSTEIN ETAL 3,309,438

METHOD AND MEANS FOR CONTROLLING THE CONSISTENCY OF CASTING COMPOSITIONS DURING CASTING Filed Feb. 14, 1966 2 Sheets-Sheet 2 INVENTORS FRANK D. Bsszcsrsm, ALFRED B. KLEINGERS J12.,AND

LEONARD BACK,

BY 7% W495;

ATTORNEYS which may be on the order of one mil.

United States Patent 3,309,438 METHOD AND MEANS FOR CONTROLLING THE CONSISTENCY OF CASTING COMPOSITIONS DURING CASTING Frank D. Bergstein, Wyoming, and Alfred B. Kleingers, Jr., and Leonard Back, Middletown, Ohio, assignors to Bergstein Packaging Trust, Middletown, Ohio, a corporation of Ohio Filed Feb. 14, 1966, Ser. No. 526,993

8 Claims. (Cl. 26437)' conjunction with the type of cast coating operation taught in Bergstein Patent 2,934,467 issued Apr. 26, 1960, and entitled, Dry Gloss Pro-cast Clay Laminated Paper and Method of Making It. In accordance with the teachings of this patent, a thin layer or film of mineral coating composition is applied by an applicator roll to a casting surface, such as a polished metal drum or endless belt, and dried in contact therewith, whereupon the adhesively coated surface of a web of paper or board is adhered to the exposed surface of the dry coating and the Web utilized to strip the dried mineral layer from the casting surface. The resultant product is characterized by an essentially clay surface having a cast finish corresponding to the finish of the casting surface. For the most part,

.such technique is utilized in the production of cast coatings characterized by an extremely high gloss.

The presence of entrained air bubbles or foam in the aforementioned mineral coating composition at the time it is applied to the casting surface and dried thereagainst has a deleterious effect on the coating in that it cuts down the gloss and adversely affects the printability of the 'coated web. When viewed through a magnifying glass,

the foam spots in the cast coating are seen to be in the fnature of cavities or depressions.

The principal cause of foam and air entrainment lies in the practical necessity of recirculating and reusing excess coating composition doctored from the casting surface as an incident of the casting operation. The applicator roll initially applies the coating composition to the casting drum in an excessive amount, whereupon a doctoring means, such as the air knife means taught in Bergstein et al. US. Patent 3,054,716, acts to smooth and even the applied coating to the desired uniform thickness, Consequently, a substantial quantity of the initially applied coating composition is removed, and the still highly fluid material from the blow-off pan and hence recirculated to the applicator roll. Even the initial admixing of the coating compositionwhich comprises a slurry composed of major proportion of mineral pigment, such as clay, titanium dioxide, calcium carbonate, or mixture thereof, and a minor proportion of a natural or synthetic binder, such as casein or a synthetic resinproduce some degree of air entrainment and foam, and while a fresh batch of coating com- 3,309,438 Patented Mar. 14, 1967 ICC position is not nearly as heavily contaminated as recirculated material, it nonetheless may contain sufficient foam bubbles to noticeably affect the cast coating.

Accordingly, a principal object of the instant invention is the provision of apparatus and techniques for use in conjunction with a casting device to effectively eliminate foam and entrained air from the casting composition during its application, recovery and recirculation. A further object of the instant invention is the provision of a vibratory blow-off pan positioned to receive fluid casting composition doctored from the casting surface to which it was initially applied, such vibratory blowoff pan acting to rapidly dissipate foam and air bubbles in the recovered composition.

Still a further object of the instant invention is the provision of a recirculating system for the recovered composition which system incorporates means for automatically controlling both the viscosity and the temperature of the composition, it having been found that both the temperature and the viscosity of the composition are major factors in the elimination of foam and entrained air.

Still a further object of the instant invention is the provision of procedures by means of which the viscosity of a mineral coating composition can be carefully controlled, thereby providing the heaviest possible coating up to but just short of the point at which foam would be generated, such heavy coating being highly advantageous in that it provides for maximum opacity and gloss in the coating layer cast against the casting surface.

The foregoing, together with other objects of the instant invention which will appear hereinafter of which will be apparent to the skilled worker in the art upon reading this specification, are accomplished by that construction and arangement of parts and by those procedures of which an exemplary embodiment shall now be described.

Reference is now made to the accompanying drawings wherein:

FIGURE 1 is a fragmentary side elevational view of a casting unit incorporating a vibratory blow-off pan in accordance with the instant invention.

FIGURE 2 is a schematic diagram illustrating the circulating system for the casting unit, which system incorporates both the vibratory blow-off pan and means for automatically controlling both the viscosity and temperature of the composition being cast.

FIGURE 3 is a diagrammatic perspective view illustrating a blow-off pan incorporating a set of cooling coils.

Referring first to FIGURE 1 of the drawings which illustrates an exemplary casting unit of the type to which the instant invention is particularly applicable, a revolving casting drum 1 is supported by a suitable machine frame 2 and, 'as the drum is rotated in the direction of the arrow A, a layer or film of casting composition is applied to the surface of the drum by means of an applicator 3, which may conveniently comprise a coating roller 4 rotating in reverse direction to the drum 1 and dipping into a pan 5 containing the composition to be applied to the drum. Immediately following the application of a layer of the composition to the casting drum, excess material is doctored from the casting surface by means of an air knife 6 and the material so removed collected in the blow-off pan 7 which has a conduit 8 for returning the collected material for reuse. The smooth and uniform layer of composition remaining on the casting surface is then dried as the casting drum rotates beneath the dryer 9 through which currents of heated air are circulated to effect thorough and rapid drying of the cast layer.

If the cast layer is to be laminated to a supporting web, a web of backing material 10, which usually comprises a continuous strip of paper or boxboard, is lead into contact with the dried layer, as by passage around the roller 11, and hence juxtaposed to the outer or exposed surface of the cast layer. It will be understood that the backing material will have been previously coated with a thin layer of adhesive which is tempered to a consistency such that, upon juxtaposition of the adhesive coated web to the layer on the drum, the layer will be intimately bonded to the web and yet the adhesive will not strike through the layer to wet or otherwise disrupt the surface thereof in contact with the casting drum. The backing material is then utilized to strip the layer from the drum, the backing material passing around the roller 12 for this purpose,

whereupon the coated web will be conveyed from the coater, as by means of guide roller 13, the coated web being delivered to a roll winding stand or to a sheeter and stacker, not shown. If the cast layer is in the form of a non-fibrous film which is to be removed as such from the casting surface, it too may be stripped from the drum by passage around the roller 12.

In the operation of the device just described, a considerable quantity of casting composition is removed by the air knife and this material cascades into the blowotf pan in a continuous stream, thereby generating a considerable quantity of foam. Such foam is generated not only by the cascading casting composition but also by the action of the air knife which, while of relatively low velocity, nonetheless acts to entrain air in the casting composition. Consequently, a considerable head of foam is built up in the blow-off pan which, unless rapidly dissipated, is carried through the conduit 8 and ultimately recirculated to the coating applicator 3.

In accordance with the instant invention, it has been found that. the foam in the blow-off pan can be rapidly dissipated by means of a vibrator 14 secured to the blowoff pan and operative to vibrate at high speed. For this purpose, it has been found that an air actuated vibrator capable of operating at from 2000-5000 vibrations per minute is highly effective. In order to permit free vibration of the blow-off pan, it is preferred to spring mount the pan, as by means of springs 15. Alternatively, the spring mounting may comprise strips of spring metal suspending the blow-off pan from the machine frame.

It is also preferred to construct the blow-off pan so that it is relatively deep. Normally, a recovery pan of this character would be relatively shallow and provided with a large drain opening so that no appreciable quantity of material is retained in the pan. However, by making the pan narrow and deep, the foam-laden casting composition is held for a longer period of time and the foam is allowed to rise to the top of the pan. With the return conduit at the bottom of the pan, the casting composition is drained from the pan at the point furthest removed from the area of greatest foaming, which is at the surface of the composition in the pan. Preferably, a valve 16 will be interposed in the return conduit 8 so that the rate of flow from the pan may be adjusted to maintain the desired deep pool of material in the pan. Alternatively, return flow may be controlled by an elbow or loop in the return conduit 8. It also has been found helpful to provide a bafile 7a extending upwardly from the blow-off pan 7 to a point immediately beneath the air knife 6. As the casting material is removed from the drum it will flow down the baffle in a thin flowing sheet; and since the bafile vibrates with the blow-off pan, the baffle acts to rapidly dissipate foam and air bubbles from the composition flowing thereover.

Referring now to FIGURE 2 of the drawings which schematically illustrates the circulating system for the casting composition, it will be seen that the return conduit 8 acts to return the composition from blow-01f pan 7 to the storage tank 17. If necessary a pump 18 may be interposed in the return conduit. The casting composition is delivered from the storage tank 17 to the applicator 3 by means of conduit 19 and pump 20; and as an incident of such delivery, the composition is first passed through a heat exchanger 21 and a filter 22. The purpose of the heat exchanger is to control the temperature of the com position which, while initially cool, nonetheless becomes heated during its recirculation. That is, when the composition is applied to the casting drum it becomes heated due to the fact that the drum itself is either heated internally or has absorbed considerable heat by reason of its passage beneath the drier 9. In either event, the temperature of the composition in the circulating system will rapidly rise. Since it has been found that the quality of the cast layer and its freedom from foam and entrained air will vary depending upon its viscosity, which in turn is directly affected by the temperature of the composition, it becomes necessary to control both viscosity and temperature.

In accordance with the instant invention, the casting composition is fed through a small enclosed tank 23 containing a viscosity probe 24, which may comprise a unit of the type wherein the probe acts as a transducer, the probe shearing the liquid being measured and measuring the damping effect or viscous drag of the liquid. A controller, which forms a part of the unit, translates the damping action of the liquid on the probe into useful meter readings and will act, as through a circuit 25, to energize solenoid controlled metering valve 26 which serves to add water or solvent in controlled amounts to the blow-off pan 7 through conduit 27. It has been found that more effective admixing of the added water or solvent is obtained by introducing it into the blow-off pan rather than into the storage tank. When introduced in the blow-off pan, the water or solvent materially aids defoaming by lowering the viscosity locally in the area where the foaming is the greatest. Alternatively, for some types of casting compositions, such as those which incorporate casein or protein binder, it is preferred to employ the type of viscosity measuring unit wherein density is determined by weighing a measured quantity of the composition.

The temperature of the casting composition is controlled by means of an automatic temperature controller 28 which acts through the circuit 29 and solenoid actuated valve 30 to control the flow of cooling water through heat exchanger 21. Thus, the temperature of the composition is so controlled that it will be essentially uniform at the time the viscosity of the composition is measured. The viscosity probe 24 and temperature controller 28 thus coact to automatically control the consistency of the composition and will be calibrated accordingly. The setting of the controls will be determined in large measure by the nature of the casting composition and the properties desired in the layer being cast.

For example, where a mineral coating composition composed essentially of pigment and binder is being cast, it has been found that the more viscous the composition the better the gloss and opacity of the cast layer. However, as the viscosity of the composition is increased, its tendency to form and retain foam is also increased. Consequently, it becomes necessary to strike a balance by operating the system at a point just short of foaming. It has also been found that as the solids content of a given composition is increased, the amount of aqueous fluid in the layer being cast decreases, which, in turn, means less drying of the cast layer and less total excess composition which must be doctored from the casing surface. It will be understood, of course, that neither the viscosity nor the solids content of the casting composition can be increased to a point where the free flow of the composition through the system is impaired, or to a point where the composition becomes difiicult to apply to the casting surface and doctored into a smooth and even layer or film. In essence, however, by utilizing the controls of the instant invention, the quality of the casting composition may be materially enhanced by utilizing composition having higher solids content than were heretofore practical and yet the undesirable side effects of higher solids con-- tent, particularly foaming and air entrainment, are effectively eliminated.

It also may be pointed out that the application of a casting composition to a metallic casting surface does not permit the extensive use of chemical defoamers. A metallic casting surface does not wet well, the applied coating tending to draw up into beads if the surface tension of the composition is improper. Chemical defoamers have an adverse effect on the composition, acting to form imperfections which are known in the art as fish eyes or orange-pealings in the cast layer. Consequently, chemical defoamers cannot be tolerated in quantities sufficient to overcome foam; and the controls of the instant invention must be relied upon to control foaming,

Generally speaking, it has been found that for best results the viscosity of the casting composition should be held between 100 and 300 cps. (centipoise seconds), the viscosities being determined on a Brookfield rpm. viscosimeter using a 2M spindle. In maintaining the viscositi es within the desired range, it is preferred to hold the temperature of the coating composition in the range of 70 to 100 F., with atemperature on the order of 90 F. particularly suited where emulsion binders, such as acrylic polymer resin emulsions or vinyl acetate emulsions, are employed. It has been found that higher temperatures tend to adversely affect the emulsions and hence are to be avoided.

Where the casting composition comprises a mineral coating composition composed of 70-90 parts of clay, calcium carbonate, titanium dioxide or mixtures thereof and the binder comprises 30-10 parts fine particle size vinyl acetate emulsion or an acrylic emulsion, with the pigment and binder dispersed in water to form a slurry containing about 50-65 percent solids, excellent results are achieved by maintaining the composition delivered to the coating unit at a temperature of about 90 F. and at a viscosity of about 104 cps.

Similar considerations apply where the casting composition comprises a film forming emulsion, such as a polyethylene emulsion, vinylidene chloride copolymer latex, and film forming styrene copolymer latex. All of these emulsions are highly foamable and require careful control during their application to a casting surface.

Typical casting compositions areas follows:

COATING MIXTURES OF PIGMENT AND BINDER a sonic defoamer, or a device of the type wherein the casting composition is placed in a centrifuge which carries the non-foam laden composition to the outside of the device where it is removed, with the foam gathering in the center where it is subjected to the action of one or more sonic devices which effectively break up the foam. Such foam breaking devices may be used in conjunction with the vibrating blow-off pan disclosed herein or in replacement there-of. Of course, some form of a blow-off pan will be required to collect the casting composition removed from the drum; and while such pan may not itself be of the vibrating type, it will nonetheless serve to collect the composition and deliver it to the foam dissipating means.

As seen in FIGURE 3 of the drawings, it is also within the spirit of the invention to provide a set of cooling coils 31 within the blow-off pan 7irrespective of whether or not it is adapted to vibrate-to assist in cooling the recirculating casting composition which, as previously indicated, israpidly heated upon contact with the heated casting surface. In the illustrated embodiment, the coil system comprises a pair of

manifolds

32 and 33 interconnected by pairs of

conduits

34, 35 through which water or other coolant fluid will be circulated, as indicated by the arrows B. Such preliminary cooling of the casting composition will effectively reduce its temperature by as much as 2030 so that the collected composition will be returned to the storage tank 17 in a partially cooled condition. This is advantageous in that it minimizes possible breakdown or degrading of the casting composition, particularly its binder constituents, by reason of the composition being held at an elevated temperature in the storage tank. In addition, the preliminary cooling reduces the extent of cooling required during passage of the recirculating composition through heat exchanger 21 and hence tends to stabilize the temperature within a narrower and more readily controllable range.

Having thus described the invention in certain exemplary embodiments and with the understanding that additional modification may be made therein without departing from its spirit and purpose, what is desired to be secured and protected by letters Patent is set forth in the claims which follow.

The embodiments of the invention in which an exclu- As should now be evident the recirculating system of the instant invention provides for an essentially automatic casting operation and at the same time permits the use of casting compositions having higher solids content in the absence of undesirable foaming and air entrainment which would adversely affect the quality of the layer or film being cast.

Modifications may be made in the invention without departing from its spirit and purpose. For example, while in the foregoing exemplary embodiment the blowoff pan has been provided with a vibrating means to dissipate foam and entrained air from the recovered casting composition, it is within the ambit of the invention to employ other forms of foam dissipating means such, for example, as a high vacuum type de-aerator or defoamer,

sive property or privilege is claimed are defined as follows:

1. A method for controlling the consistency of a mineral coating composition during a casting operation wherein the mineral coating composition is applied to a heated casting surface and the applied coating doctored to a predetermined thickness, and wherein the mineral coating composition comprises an aqueous slurry containing from 70-90 parts mineral pigment and from 30-10 parts adhesive binder and has a solids content of from 50-65 percent, which method comprises collecting the excess mineral coating composition doctored from the casting surface, recirculating the said collected coating composition and, as an incident of such recirculation, removing foam and entrained air bubbles therefrom, cooling the coating composition as it is being recirculated to maintain its temperature between about 70* to 100 F., and selectively adding sufficient liquid thereto as required to maintain the viscosity of the coating composition from between 100 and 300 centipoise seconds.

2. The method claimed in claim 1 wherein foam and entrained air bubbles are removed by subjecting the collected coating composition to high frequency vibration on the order of from 2000-5000 vibrations per minute.

3. The method claimed in claim 1 including the step of effecting a preliminary cooling of the casting composition as it is collected from the casting surface for recirculation.

4. In a system for circulating an aqueous casting composition used in conjunction with a casting operation wherein the aqueous casting composition is applied to a heated casting surface by means of an applicator and wherein an air knife is employed to doctor excess coating 7 composition from the casting surface, a supply tank for the casting composition, collection means positioned to collect excess coating composition doctored from said casting surface and deliver the same to said supply tank, said collection means including a blow-01f pan and means operative to dissipate foam and entrained air bubbles in the collected casting composition, a heat exchanger, a first conduit connecting the inlet side of said heat exchanger to said supply tank, a second conduit connecting the outlet side of said heat exchanger to said applicator, a temperature controller in said second conduit, a control valve for introducing a fluid coolant into said heat exchanger, said control valve being operatively connected to said temperature controller so as to regulate the flow of coolant through said heat exchanger in accordance with the temperature of the coating composition as it is delivered to said applicator, a viscosity probe interposed in said second conduit, valve means for introducing a liquid into said blow-01f pan for delivery to said supply tank along with the casting composition doctored from said casting surface, and means operatively connecting said viscosity probe to said last named valve means, whereby the addition of liquid into the system is controlled in accordance with the viscosity of the coating composition being delivered to said applicator.

5. The system claimed in claim 4 wherein said collecting means includes means for partially cooling the casting composition between the time of its collection and its introduction into said supply tank.

6. The system claimed in claim 5 wherein said cooling means comprises a coil structure mounted in said blow-off pan for contact with casting composition collected therein.

7. In -a system for circulating an aqueous casting composition used in conjunction with a casting operation wherein the aqueous composition is applied to a casting surface by means of an applicator and wherein an air knife is employed to doctor excess coating composition from the casting surface, a blow-off pan positioned to collect such excess coating composition, a vibrator connected to said blow-off pan to effect rapid vibration thereof, a supply tank for the casting composition, a conduit connecting said blow-01f pan to said supply tank, a heat exchanger, a supply line connecting the inlet side of said heat exchanger to said supply tank, a second conduit connecting the outlet side of said heat exchanger to the said applicator, an adjustable temperature controller in said second conduit, a control valve for introducing a fluid coolant into said heat exchanger, said control valve being operatively connected to said temperature controller so as to regulate the flow of coolant through said heat exchanger in accordance with the temperature of the coating composition as it is delivered to the said applicator, a viscosity probe interposed in said second conduit, valve means for introducing a liquid into said blow-01f pan for delivery to said supply tank along with the coating composition doctored from said casting surface, and means operatively connecting said viscosity probe to said last named valve means, whereby to control the addition of liquid into the system in accordance with the viscosity of the coating composition being delivered to the said applicator.

8. The system claimed in claim 7 including cooling means mounted in said blow-off pan for preliminary cooling of coating composition collected in said blow-off pan.

References Cited by the Examiner UNITED STATES PATENTS 1,418,273 6/1922 Benjamine 118 429 2,168,972 8/1939 Carver 264 349 X 2,485,857 10/1949 Bower 264102 X 2,556,954 6/1951 Zeigler et al 264l44 X 2,739,567 3/1956 Jones et a1. 118-429 References Cited by the Applicant UNITED STATES PATENTS 2,996,038 8/1961 Hunicke.

ALEXANDER H. BRODMERKEL, Primary Examiner.

ROBERT F. WHITE, Examiner.

B. SNYDER, Assistant Examiner.

Claims

1. A METHOD FOR CONTROLLING THE CONSISTENCY OF A MINERAL COATING COMPOSITION DURING A CASTING OPERATION WHEREIN THE MINERAL COATING COMPOSITION IS APPLIED TO A HEATED CASTING SURFACE AND THE APPLIED COATING DOCTORED TO A PREDETERMINED THICKNESS, AND WHEREIN THE MINERAL COATING COMPOSITION COMPRISES AN AQUEOUS SLURRY CONTAINING FROM 70-90 PARTS MINERAL PIGMENT AND FROM 30-10 PARTS ADHESIVE BINDER AND HAS A SOLIDS CONTENT OF FROM 50-65 PERCENT, WHICH METHOD COMPRISES COLLECTING THE EXCESS MINERAL COATING COMPOSITION DOCTORED FROM THE CASTING SURFACE, RECIRCULATING THE SAID COLLECTED COATING COMPOSITION AND, AS AN INCIDENT OF SUCH RECIRCULATION, REMOVING FOAM AND ENTRAINED AIR BUBBLES THEREFROM, COOLING THE COATING COMPOSITION AS IT IS BEING RECIRCULATED TO MAINTAIN ITS TEMPERATURE BETWEEN ABOUT 70 TO 100*F., AND SELECTIVELY ADDING SUFFICIENT LIQUID THERETO AS REQUIRED TO MAINTAIN THE VISCOSITY OF THE COATING COMPOSITION FROM BETWEEN 100 AND 300 CENTIPOISE SECONDS.

4. IN A SYSTEM FOR CIRCULATING AN AQUEOUS CASTING COMPOSITION USED IN CONJUNCTION WITH A CASTING OPERATION WHEREIN THE AQUEOUS CASTING COMPOSITION IS APPLIED TO A HEATED CASTING SURFACE BY MEANS OF AN APPLICATOR AND WHEREIN AN AIR KNIFE IS EMPLOYED TO DOCTOR EXCESS COATING COMPOSITION, FROM THE CASTING SURFACE, A SUPPLY TANK FOR THE CASTING COMPOSITION, COLLECTION MEANS POSITIONED TO COLLECT EXCESS COATING COMPOSITION DOCTORED FROM SAID CASTING SURFACE AND DELIVER THE SAME TO SAID SUPPLY TANK, SAID COLLECTION MEANS INCLUDING A BLOW-OFF PAN AND MEANS OPERATIVE TO DISSIPATE FOAM AND ENTRAINED AIR BUBBLES IN THE COLLECTED CASTING COMPOSITION, A HEAT EXCHANGER, A FIRST CONDUIT CONNECTING THE INLET SIDE OF SAID HEAT EXCHANGER TO SAID SUPPLY TANK, A SECOND CONDUIT CONNECTING THE OUTLET SIDE OF SAID HEAT EXCHANGER TO SAID APPLICATOR, A TEMPERATURE CONTROLLER IN SAID SECOND CONDUIT, A CONTROL VALVE FOR INTRODUCING A FLUID COOLANT INTO SAID HEAT EXCHANGER, SAID CONTROL VALVE BEING OPERATIVELY CONNECTED TO SAID TEMPERATURE CONTROLLER SO AS TO REGULATE THE FLOW OF COOLANT THROUGH SAID HEAT EXCHANGER IN ACCORDANCE WITH THE TEMPERATURE OF THE COATING COMPOSITION AS IT IS DELIVERED TO SAID APPLICATOR, A VISCOSITY PROBE INTERPOSED IN SAID SECOND CONDUIT, VALVE MEANS FOR INTRODUCING A LIQUID INTO SAID BLOW-OFF PAN FOR DELIVERY TO SAID SUPPLY TANK ALONG WITH THE CASTING COMPOSITION DOCTORED FROM SAID CASTING SURFACE, AND MEANS OPERATIVELY CONNECTING SAID VISCOSITY PROBE TO SAID LAST NAMED VALVE MEANS, WHEREBY THE ADDITION OF LIQUID INTO THE SYSTEM IS CONTROLLED IN ACCORDANCE WITH THE VISCOSITY OF THE COATING COMPOSITION BEING DELIVERED TO SAID APPLICATOR.