US3761305A

US3761305A - Squeegee shield

Info

Publication number: US3761305A
Application number: US00159747A
Authority: US
Inventors: H Franz
Original assignee: PPG Industries Inc
Current assignee: PPG Industries Inc
Priority date: 1971-07-06
Filing date: 1971-07-06
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25
Also published as: US3782328A

Abstract

A TRANSPARENT SUBSTRATE TO BE SPRAY COATED PASSES BENEATH A SQUEEGEE/SHIELD APPARATUS TO AVOID FORMATION OF FINGER-LIKE FRONTS OR PUDDLES IN THE SPRAY AREA AND TO PREVENT SPLASHING OF THE SPRAY MEDIUM ONTO THE SUBSTRATE SURFACE.

Description

H. FRANZ sQUEEGEE/SHIELD Sept. Z5, 1973 4v Sheets-Sheet l Filed July 6, 1971 INVENTOR www ATT RNEYS Non r X \r 4 k oww 0mm no# oom sepa. 25, 1913 H. FRANZ 3,761,305

SQUEEGEE/SHIELD Filed July 6, 1971 4 Sheets-Sheet 2 Ummm INVENTOR HELM uT FRANZ.

l FG 5 ATTORNEYS Sept. 25, 1973 H. FRANZ 3,761,305

SQUEEGEE/SHIELD Filed July 6, 1971 4 Sheets-Sheet :5

INVENTOR HZMW' FA/VZ,

@Im/1% www ATTORNEYS` Sept. 25, 1973 l H, FRANZ 3,76L305 Filed July 6, 1971 4 Sheets-Sheet 4 ff) N E i E Q .L INVENTOR NNN HELMUT FRA/vz ATTORNEYS` United States Patent O 3,761,305 SQUEEGEE/ SHIELD Helmut Franz, Pittsburgh, Pa., assigner to PPG Industries, Inc., Pittsburgh, Pa. Filed July 6, 1971, Ser. No. 159,747 Int. Cl. B44d 1 08 U.S. Cl. 117-105.3 6 Claims ABSTRACT OF THE DISCLOSURE A transparent substrate to be spray coated passes beneath a squeegee/shield apparatus to avoid formation of finger-like fronts or puddles in the spray area and to prevent splashing of the spray medium onto the substrate surface.

CROSS REFERENCES TO RELATED APPLICATIONS This application is related to U.S. patent application Ser. No. 829,705, filed in the names of Richard G. Miller et al. on June 2, 1969', and entitled Electroless Process for Forming Thin Metal Films, now U.S. Pat. No. 3,671,291. This application is also related to U.S. patent application Ser. No. 829,755, tiled on June 2, 1969, in the name of Richard G. Miller, and entitled Electroless Process for Forming Thin Metal Films, now U.S. Pat. No. 3,672,939. This application is also related to U.S. patent applications Ser. Nos. 57,451, 57,575, which is now abandoned, and 57,754, led on July 23, 1970, in the name of Richard G. Millen, and entitled Wet Chemical Method for Producing Transparent Metal Films, now U.S. Pat. No. 3,675,517, Transparent Metal- Boron Coated Glass Articles and Solution for Depositing Transparent Metal Films, respectively, and U.S. patent application Ser. No. 57,527 of Charles B. Greenberg et al., led on July 23, 1970, for Wet Chemical Method for Producing Transparent Metal Films. This application is also related to U.S. patent application Ser. No. 11,904, filed on Feb. 2, 1971, in the name of Helmut Franz et al. and entitled Chemical Filming Solution and Process for Plating Therewith. This application is also related to U.S. patent application Ser. No. 130,468, led on Apr. 1, 1971, in the name of Helmut Franz, and entitled Removal of Metal Containing Deposits from Non- Metallic Substrates.

BACKGROUND OF THE INVENTION (l) Field of the invention This invention relates to a method and an apparatus for providing non-conductive transparent substrates with transparent coatings having optical properties of good uniformity, and particularly relates to a squeegee/shield apparatus that avoids sources of non-uniformity of said optical properties.

(2) Description of the prior art In the past, transparent metal coated glass articles have been produced by various vapor deposition techniques which generally involve the deposition, from the vapor phase, of substantially pure metals, such as nickel or chromium on a prepared glass substrate. However, while such techniques are generally capable of providing metal lms of acceptably uniform thickness and specified visual transparency, commercial lilms of this type have been observed to possess an undesirably high number of visible pin-holes. Further, this process is expensive and complex. Metal coated metallic and non-metallic articles have been produced by various well-known electroless or chemical plating techniques. These techniques gen-V erally involve the immersion of a metallic article or a sensitized non-metallic article into a suitable electroless plating bath comprising an aqueous medium having dissolved therein a metal salt and an appropriate reducing agent, whereupon a metal film is deposited upon the immersed article by an autocatalytic mechanism.

The electroless process is an old and established one. For example, Brenner and Riddell disclosed in 1944 that an opaque coating of nickel could be autocatalytically deposited upon metallic substrates by immersing the substrate into a nickel salt solution containing sodium hypophosphite. U.S. Pat. Nos. 2,532,283 and 2,532,284 were issued to Brenner and Riddell upon their discoveries. The use of sodium hypophosphite as the reducing agent results in deposits which are not pure metal, but which contain about 2 to 10 percent elemental phosphorus by weight. In this connection, it is known that the presence of phosphorous in a deposited nickel lm affects certain of the film characteristics, including its dominant wave lengths, infrared absorption characteristics, excitation purity and electroconductivity. In addition, and for reasons not wholly understood, it has been found that the uniformity of deposited nickel-phosphorous lms generally decreases rapidly with increased thickness when the thickness of the coated glass substrates is greater than about 9&6 of an inch.

Other electroless immersion plating processes involve the use of boron-containing reducing agents which are effective at room temperature. U.S. Pat. Nos. 2,968,578, 3,140,188, 3,096,182 and 3,045,334 are representative of improved electroless plating processes of this type. U.S.

Pat. No. 2,956,600, issued to Carlson et al., describes a spraying process wherein two separate solutions are sprayed upon substrates to form nickel coatings. This process uses sodium hydrosulte and sodium hypophosphite as a reducing agent.

To a large extent the prior art has been concerned with production of opaque coatings by electroless coating, although it is understood that the assignee of U.S. Pat. No. 2,702,253 produces a glass plate having a transparent nickel coating possibly by the process therein disclosed. The problem of producing transparent glass or like articles is much more difficult because relatively minute variations in thickness are readily visible to the naked eye as unsightly defects. Other variations in such coatings can provide streaks with a glass region appearing almost opaque due to reflection of light in an otherwise transparent glass plate.

Many solutions suggested by the prior art develop a coating of gradually increasing thickness well beyond thicknesses which are opaque. The production of uniform transparent films with such solutions is especially difficult.

U.S. application Ser. No. 57,451, filed on July 23, 1970, in the name of Richard G. Miller, teaches a method whereby transparent substrates such as glass are provided with a uniform transparent coating by contacting the glass simultaneously with a mixture of a reducible metal salt in a solution and a reducing agent, which mixture becomes rapidly depleted of its lm forming capacity before the resulting coating becomes opaque. This produces a uniform coating at a rate which is relatively rapid and then relatively slower and which effectively ceases to produce coating while the coating remains transparent. According to said application, it has been found that by using such mixtures and discontinuing the contact therewith after the rate of deposition of coating has reached the slower rate, transparent films of improved uniformity with few pin-holes can be achieved. The application further states that coatings of the best uniformity may be obtained even with large plates having four or more square feet of surface when the coating is applied by separately spraying a solution of reducing agent and a solution of the reducible metal salt on the glass plate preferably while the major surfaces thereof are in a horizontal or substantially horizontal plane. The process has been found to be effective over a broad temperature range for coating any of the so-called catalytic metal substrates or non-catalytic substrates sensitized in a conventional manner to promote deposition of continuous, adherent transparent metal films. An advantage of the process is that it will deposit highly uniform transparent films when performed at about room temperature, i.e., from about 20 C. to about 30 C. The application further states that in order to insure that each of a plurality of substrates is provided with a coating that exhibits substantially the same physical and chemical characteristics, it is advantageous th'at the process temperature be held constant to within about '1 C., for example, over 100 substrates or over 1000 square feet of substrates, or the like. Best uniformity and appearance of transparent films is achieved when films are deposited to a thickness having a luminous transmission of about 35 to 40 percent or less, and when the films comprise nickel-boron, cobaltboron, iron-boron, and the like. Films comprising mixtures of boron and nickel, cobalt and/or iron may also be provided. In all such films, the boron is present in a minor amount (rarely exceeding about 15 percent by weight and normally between about 2 and 7 percent by weight) while the metal (nickel, cobalt and/or iron) is present in preponderant amounts (rarely less than 85 percent by weight and normally between about 93 and 98 percent by weight).

The transparent substrates obtained in accordance with the last-mentioned process may be employed, for example, as transparent windows or outside walls in a building such as a skyscraper or other multistory structure. These substrates may be especially advantageously employed as one of the plates which make up multiglazed units as described in the previously mentioned U.S. patent application Ser. No. 57,575, now abandoned. It will be understood that uniformity of coating in such uses is especially important because otherwise the reflected color of portions of the building differs sharply from that of other portions, thus distracting from its appearance.

To generalize, the prior art teaches a process whereby glass plates are conveyed along an article movement path through a sequence of rinse and spray stations. After a plate leaves a rinse station, it is normally covered with a layer of water. When the plate enters a spray station, this layer of water is normally pushed toward the trailing edge of the plate and tends to accumulate toward the trailing edge. As more Water accumulates at the trailing edge, the water tends to flow back into the spray zone. The problem is especially severe at the trailing edge where water is retained by the edge of the plate. After reaching equilibrium thickness at the trailing edge, some of the water flows back into the spraying zone so that the glass plate is sprayed while it is covered with a thin film of water of non-uniform thickness. As a result, there is an uneven dilution of the sprayed-on solutions in the sensitizing and coating stations, and this causes the coating on the plate to vary in thickness, in absorption and in reflectance. This is extremely pronounced adjacent to the trailing edge of the plate.

In addition, finger-like waves of sprayed-on solution form immediately downstream and immediately upstream of each spray station. The deposition of solution begins prematurely in those areas of the sensitized surface which are in contact with the rear wave, causing streaks in the final coating in the direction of travel of the plate. In addition, splashing of the spray medium onto the sensitized area causes streaks and mottle in the final coating. The prior art recognized the existence of the problem of non-uniformity of coating, but failed to recognize the cause and therefore the solution.

4 SUMMARY oF THE INVENTION It has now been discovered that the manner in which the solution contacts the sensitized glass surface is extremely critical, if a uniform coating is to be obtained. Optimum film quality is obtained when the first contact is made by fresh spray solution. The solution cannot be permitted to flow back onto the sensitized area or the glass surface will be covered non-uniformly by a mixture of fresh solution and spent solution, causing banding and streaking defects in the final coating. The solution cannot be permitted to accumulate at the trailing edge of the plate or defects will be most pronounced in this area. In addition, rinse water cannot be permitted to flow back into the spray zone in an uneven fashion or an uneven dilution of the solution (and therefore an uneven coating) will result.

According to the present invention, a squeegee/shield apparatus is installed immediately downstream of the first spray station. This apparatus prevents the formation of rear waves rearward of the apparatus and prohibits splashing of the solution onto the sensitized surface rearward of the apparatus, thereby eliminating any accumulation of solution at the trailing edge. In addition, it only permits a thin, uniform film of rinsing medium to pass beneath the spray station.

The location of the squeegee/shield apparatus relative to the surface to be coated and to the cone of dispensed rinsing medium is an important part of the present invention. The squeegee must touch the sensitized glass surface so that no dispensed solution passes rearward of the squeegee and only a thin, uniform layer of rinsing medium reaches the spray area. It must also cut off a portion of the spray fan to insure that initial contact with the glass surface is by fresh solution. Ideally, the squeegee should be placed so that it touches the tip of the spray fan, but since it is very impractical to maintain an exact relative positioning, the squeegee generally is positioned initially to overlap the spray fan by about 1A of an inch. If there is a gap between the spray fan and the squeegee, spent solution may contact the glass surface before fresh solution in random areas, causing coating defects. If the squeegee cuts olf, for example, about 2 inches of the spray fan, too much spray solution drips down onto the sensitized surface from the squeegee, instead of being sprayed onto the surface. The shield is above the squeegee to prevent splashing of the spray solution rearward onto the sensitized area before the sensitized surface reaches the dispensing station.

The squeegee may be made in the form of a lip seal of any soft, elastomeric material, such as natural rubber, neoprene, silicone rubber, and some plastic materials such as polyvinyl chloride. It is important to note that the material have a durometer of between about 50 and about 90, and preferably about 70. Certain plastics, such as polytetrauoroethylene, have been proven to be too hard, therefore damaging the surface.

In another embodiment of the present invention, the squeegee is made in the form of a roller rather than a lip seal as previously described. The roller can be, for example, 1-1/2 inches in diameter and driven by friction at the sensitized surface. As in the case of the lip seal, th'e roller can be made of any soft, elastomeric material, however, a closed cell foam rubber over a steel tube has proved very desirable.

Coated glass, made in accordance with the present invention, is capable of inhibiting transfer of radiant heat such as that from the suns rays by the light refiectance and absorption of the film and the fact that it permits transmittance of less than 35 to 40 percent of visible light from sunlight. Panels having light transmittance of 5 t0 25 percent are especially useful in warm to temperature climates such as the United States. In other climates such as Northern Europe, vpanels of greater transmittance are preferred.

The color of the panels is dependent upon the amount and composition of metal which is reduced. Especially attractive nickel-boron and like metal-boron coatings which have a neutral color reiiecting and passing essentially white light are provided according to this invention. Cobalt coatings are blue while iron coatings are brown. Other colors can be obtained by producing mixtures of these coatings.

The nickel-boron and metal-boron compounds herein contemplated are usually electroconductive. Thus, these films may be used as heating elements. For example, in a double-glazed window comprising two-spaced glass panels enclosed vby a glass, metal or organic sealing around the edge of the panel, one such panel may be coated on its interior side by the process of this invention. By applying an electromotive force across this coating, heat may be generated in the panel, thus minimizing or preventing substantial heat loss from the interior of the building in which such windows are mounted.

Coatings having one or more of the desirable properties set forth above are effectively produced according to this invention by spraying, as hereinafter disclosed in greater detail. Such a process is especially valuable in producing uniform coatings on large articles such as plates of glass or other substrates having one dimension in excess of 3 feet, with the other being in excess of 1.5 feet, for example, panels of 3 feet by 6 feet or larger.

Immersion processes have serious disadvantages. These disadvantages are especially acute where transparent coatings are desired since, for example, the composition of the plating bath changes during use, thereby requiring frequent chemical analysis and addition of materials to maintain a constant bath composition. If a constant bath composition is not maintained, the metal films formed thereon will not be uniform. In this latter connection, it should be appreciated that contamination of a bath composition, which may be caused, for example by an inadvertent admixture therewith of the solutions employed to activate the glass being coated, may necessitate a cornplete shut down of the process and a renewal of the bath. Furthermore, immersion processes are not especially adoptable to forming transparent films inasmuch as the rate of deposition is diiiicult to control. Thus, it is relatively common for a heavier coating to be deposited on that portion of the substrate which is first to enter and last to leave the plating bath.

Spraying a coating avoided the tapered coating thickness associated with dip coating in a plating bath. However, prior to the present invention, the non-uniformity of appearance of transparent coatings in some frequency made it necessary to improve the coating operation.

DESCRIPTION lOF THE DRAWINGS A complete understanding of the invention may be obtained from the foregoing recital of the prior art and following description of an illustrative embodiment of the present invention, taken together with the appended drawings, in which:

FIG. 1 is a diagrammatic top plan view, with portions removed for the sake of clarity, of an apparatus suitable for carrying out the process of the present invention on a continual basis;

FIG. 2 is a diagrammatic front elevation of the apparatus of FIG. 1;

FIG. 3 is a diagrammatic partial perspective view of a glass loading and cleaning section of the apparatus of FIG. l;

FIG. 4 is a diagrammatic partial perspective view of a sensitizing and activating section of the apparatus of FIG. 1;

FIG. 5 is a diagrammatic partial perspective view of a metal-boron deposition section of the apparatus of FIG. l;

FIG. 6 is a diagrammatic partial perspective view of a drying section in the apparatus of FIG. 1.;

FIG. 7 is a diagrammatic partial perspective view of 6 a film density measuring and unloading section included in the apparatus of FIG. 1;

FIG. 8 is a diagrammatic top plan view of a metal solution-reducing solution dispensing spray gun set of a metal-boron deposition coating of the apparatus of FIG. 1, illustrating the disposition of spray guns in said set relative to each other and to an advancing glass substrate, and illustrating a fan-shaped pattern assumed by the respective solutions beiny sprayed;

FIG. 9 is a diagrammatic side elevational view of the coating apparatus illustrated in FIG. 8;

FIG. 10 is a diagrammatic front elevational view of the apparatus illustrated in FIG. 8;

FIG. 1l is a diagrammatic perspective view of a metalboron spray gun set without a squeegee/ shield apparatus;

FIG. l2 is a diagrammatic side cross-sectional view showing the details of a squeegee/shield apparatus made in accordance with a first embodiment of the present invention together with a spray gun;

FIG. 13 is a diagrammatic side cross-sectional view showing the details of a squeegee/shield apparatus made in accordance with a second embodiment of the present invention together with a spray gun;

FIG. 14 is a diagrarnatic side cross-sectional View showing the details of a squeegee/shield apparatus made in accordance with a third embodiment of the present invention together with a spray gun; and

FIG. 15 is a diagrammatic side cross-sectional view showing the details of a squeegee/shield apparatus made in accordance with a fourth embodiment of the present invention together with a spray gun.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there are shown several embodiments of an apparatus suita'ble for coating a monolithic substrate, such as a glass plate, with a transparent metal and boron-containing film of superior uniformity of film appearance in accordance with the present invention. As shown, the apparatus comprises five basic units or sections, which are designated a glass loading and cleaning section (section a glass sensitizing and activating section (section 200), a metal-boron coating composition deposition section (section 300) a glass drying section (section 400) and a film density measuring and glass unloading section (section 500). The apparatus also comprises a conveyor means including a plurality of belts 1 in section 100 and rollers 2 in

sections

200, 300, 400 and 500 for carrying and advancing glass plates 3 (FIGS. 1 to 7) past the various sections 100 to S00 along an article movement path in the direction of the arrows Y. As explained below, the belts 1 and the rollers 2 are rotated by conventional means (not shown) so as to advance the plates 3 at a rate of from about 0.5 to

"about 7 feet per minute, and preferably from about 3 to about 6 feet per minute.

During continuous operation, a plurality of glass plates 3 are loaded onto the belts 1, so that the belts advance the plates into and through section 100 of the apparatus. Referring to FIGS. 1, 2 and 3, a plurality of rotating discs or blocks 101 gently abrade the uppermost surface of each plate, preferably with a mixture of cerium oxide or red rouge and water, to loosen and remove any dirt therefrom. I'his blocking operation is preferably carried out with cattle hair felt iblocks having a diameter of from about 4 to about 12 inches. Each of the blocks is mounted on a shaft 102 which is rotated by a suitable motor 103 and gear means (not shown) at a rate of from about 200 to about 600 revolutions per minute. In the preferred embodiment, the blocks are rotated at about 300 to about 500 revolutions per minute and are oscillated, for example, a distance of about 2 to 4 inches in a direction transverse to the direction Y of the advancing plate to insure that the entire uppermost surface of the plate is blocked.

While still in section 100, each plate advances beneath a plurality of rotary cup brushes 104 that wash the surface of the plate with tap water. The `brushes 104, which may have nylon bristles or the like, are generally rotated at the same rate as the blocks 101, and are preferably oscillated in the same manner as well. Each plate finally advances beneath a rotary cylinder brush 105 disposed across the advancing plate. The brush 105 may comprise nylon bristles or the like which contact the plate and complete the cleaning thereof. The brush is generally rotated at about 300 to about 400 revolutions per mlnute. Both the rotary cup brushes 104 and the rotary cylinder brush 105 may be driven by conventional means such as motors (not shown) that may be similar to motors 103.

Each plate 3 then enters into and passes through section 200 of the apparatus, wherein the surface thereof is sensitized and then activated (super-sensitized). As illustrated in FIGS. 1 and 2, and more particularly in FIG. 4, the plate is subjected to a first rinse, preferably with demineralized water, as it enters section 200 to remove any traces of cerium oxide, red rouge, tap water or any other undesirable matter carried over from section 100. The first rinse may be performed in any conventional manner. For example, the plate may Ibe rinsed by reciprocating a single water spray apparatus transversely of the advancing plate (i.e., in the direction of arrow X) while the plate advances in the direction indicated by arrow Y. However, the rinse is preferably performed by employing a cross-fire technique.

As illustrated in FIG. 4, when employing a cross-fire technique, a mutually opposed pair of

pipes

201 and 202 are supported from a carriage 203 that reciprocates along the X axis on a track 204 at a rate of between about 25 and about 70 single passes per minute, and preferably between about 45 and about 60 single passes per minute. The carriage 203 is driven by a chain or belt 205 that runs over a pair of pulleys 206 and 207 arranged at the opposite ends of the track 204. A motor 208 drives the chain 205 while a connection 205A between the chain and the carriage slides up and down in a vertical groove 205A between the chain and the carriage slides up and down in a vertical groove 205B in the carriage 203 as the connection moves around the pulleys. The drive construction is similar to that shown in Bramsen et al. U.S. Pat. No. 2,246,502.

During the reciprocating motion of the carriage 203, demineralized water is fed alternately to the

pipes

201 and 202 in such a program that water is sprayed only from nozzles 201A, 201B and 201C when the carriage is moving from left to right in FIG. 4, and only from nozzles 202A, 202B and 202C when the carriage is moving in the opposite direction. The

pipes

201 and 202 are supplied with water or other rinsing composition through

lines

209 and 210, respectively, by any suitable means. The pipes are advantageously operated at pressures between about 25 and about 80 pounds per square inch, preferably between about 25 and about 45 pounds per square inch, and at flow rates of about 500 to about 600 milliliters per minute per pipe.

There are many commercially available control means to alternate the fiow of rinsing medium between line 209 and line 210. Valves V1 and V2 are illustrated as an example of suitable control means, either automatic or manual, that become apparent to one skilled in the art.

After undergoing the first rinse with demineralized water, the plate advances beneath a reciprocating gun 211 which sprays a dilute solution of stannous chloride on the clean surface. The stannous chloride solution may comprise any of the formulations known in the art as being capable of sensitizing non-conductive substrates to metal deposition. However, a preferred formulation comprises from about 0.02 to about 1.0 gram of stannous chloride per liter of solution, together with a small amount of hydrochloric acid. Such a solution may be prepared, for example, by mixing about 20 grams of stannous ChlO- ride and 2 to 3 milliliters of concentrated hydrochloride acid (12 N) in enough demineralized water to form one gallon of stock concentrate, and then diluting each part of the concentrate with about 19 parts of demineralized water. In a preferred embodiment, about one part of the above-described concentrate is injected into a stream comprising about 19 parts of demineralized water, whereafter the combined stream is mixed with air at about 60 to about pounds per square inch, and sprayed through the gun 211 in a highly atomized state at a rate of about 500 to about 700 milliliters per minute.

As illustrated in FIG. 4, the stannous chloride composition dispensing spray gun 211 is supported from the same carriage 203 that supports the first rinse

pipes

201 and 202. In addition, a second set of rinse

pipes

212 and 213, a palladium chloride composition dispensing spray gun 214 and a third set of rinse

pipes

215 and 216 may also be supported from carriage 203.

As the plate 3 continues to advance along the article movement path Y, it passes beneath the second set of rinse

pipes

212 and 213. These pipes are operated in the same manner as

pipes

201 and 202.

The sheet 3 then passes under the gun 214 which sprays an atomized mixture of air and dilute palladium chloride on the now sensitized surface so as to activate (or supersensitize) the surface for the ensuing metal-boron deposition. As is the case with the stannous chloride solution, the palladium chloride may comprise any of the wellknown formulations that are suitable for activating a previously sensitized substrate. However, a formulation comprising from about 0.005 to about 1.0 gram of palladium chloride per liter of solution, together with a small amount of hydrochloric acid, is preferred. One such formulation may be prepared by mixing about 2 grams of palladium chloride and 2 to 3 milliliters of concentrated hydrochloric acid with a sufficient amount of demineralized water to form one gallon of concentrated stock solution, and then diluting each part of the stock solution with 19 parts of demineralized water. As is the case with the stannous chloride solution, the diluted palladium chloride is preferably mixed with air at a pressure of about 60 to about 80 pounds per square inch and sprayed onto the glass at a rate of about 500 to about 700 milliliters per minute.

After passing spray gun 214 and before leaving section 200 of the apparatus, the plate 3 undergoes a third demineralized water rinse. This rinse is carried out in the same manner as the first and second rinses, and is designed to remove any excess palladium chloride from the advancing plate before it reaches the metal-boron coating composition deposition section.

The spacing between the respective guns in section 200 of the apparatus may vary within wide limits depending, for example, upon the rate at which the plate 3 1s advancing, the dimensions of the fan-shaped spray pattern generated by each gun, the rate of traverse of each gun, and the like. However, it is preferred to arrange the various guns in section 200 such that the time required for the leading edge of the given plate 3 to ad- Vance from each gun or set of guns to the next successive gun or sets of guns is from about 10 to about 90 seconds.

As illustrated, the plate then passes from section 200 of the apparatus to section 300 thereof, wherein a metal and boron-containing coating, preferably nickel-boron, cobalt-boron, iron-boron or a mixture of at least two of said metal-boron coatings is deposited on the now activated surface thereof. The deposition is preferably accomplished by simultaneously spraying a metal-containing solution and a boron-containing reducing solution from separate spray nozzles and intermixing said solutions onto the activated surface such that the metal ions present in the contemplated metal solution become reduced to a transparent boron-containing metal film which tenaciously adheres to the activated surface,

It will be appreciated that the number, disposition, and the spacing of the guns which spray the metal solution and the boron-containing reducing solution, and the rate at which they are reciprocated, are determined generally by the rate at which the plate advances, the temperature, pH, and concentration of the intermixed lm forming composition and the like, and primarily by the time required for the lm forming composition to be substantially depleted in its film forming capacity, and the desired thickness and transparency of the deposited film. The importance of these latter two parameters will become more apparent in view of the illustrative example set forth below.

For the sake of illustration,section 300 is shown in FIGS. 1, 2 and 5 as having two reciprocating spray gun sets 302 and 303, each comprising a first nozzle for dispensing a metal-containing solution, 302A and 303A, respectively, and an opposed second nozzle, 302B and 303B, respectively, for dispensing a reducing solution. Section 300 also includes a mutually opposed pair of reciprocating

water pipes

304 and 305 arranged for cross-tire rinsing. As shown, spray gun sets 302. and 303 are supported for transverse reciprocating movement, for example, in the manner described for reciprocating spray guns 211 and 2114 in connection with FIG. 4. However, it should be noted that the gun set in section 300 must reciprocate much faster than those in section 200 or than those employed in conventional spray techniques for depositing silver, for example. In this connection, it has been found that uniformly and controllably transparent metal-boron coatings can best be made in ac cordance with the present invention only when the gun sets of section 300 are reciprocated at a rate of at least about 60 to about 65 single passes per minute, and preferably from about 72 to about 76 single passes per minute, when the plates being coated are about 4 feet wide and are advanced at a rate of from about 3 to about 6 feet per minute. Thus, for a 4-foot wide plate advancing at a rate of 31/2 feet per minute, i.e., 42 inches per minute, a spray gun set reciprocating at 74 single passes per minute will complete about 1.75 single passes over each inch segment of the advancing plate.

Accordingly, if the width of the applied spray in a direction of travel of the plate is from 10 to 12 inches, each inch segment of the plate will receive from about 17.5 to about 21.1 applications of solution per gun set. Of course, the required number of passes per minute will vary somewhat in accordance with changes in magnitude of the various parameters discussed herein. For example, the required number of passes would increase when the plate being coated or advanced more rapidly than approximately 3 to approximately -6 feet per minute.

Spray guns of each set 302 and 303 are connected through respective supply lines (not shown) to air under pressure at about 20 to about 60 pounds per square inch. In turn, the respective supply lines are in uid communication with prepared metal and reducing solutions stored in separate solution tanks or containers (not shown), preferably of such size to hold a reasonable supply of fluid, such that when the prepared solutions are injected into the supply lines by any conventional means (not shown), the solutions are fed through the lines and sprayed from the guns in a fanshaped pattern. It will be appreciated that the magnitude of air pressure required for a satisfactory spray varies considerably with the design ofjthe guns of the various parameters of the solutions employed. In this connection, satisfactory results have been obtained with pressures as low as about 2,0 pounds per square inch and as high as about 55 pounds per" square inch. Pressures in the range of about 25 to about 40 pounds per square inch are preferred. The rates at which the respective prepared solutions are sprayed from each gun may vary, but it is preferred that the rates of flow be maintained at about 300 to about 2000 Vrnillliters per minute per gun.

As illustrated in FIGS. 8, 9 and 10, each of the

nozzles

302A and 302B in the metal depositing spray gun set 302. is preferably designed to provide a substantially fanshaped stream which opens only a few degrees in the direction transverse to the advancing plate, and which opens in the direction of travel of the plate such that the stream contacts the advancing plae in an elliptical pattern having a major diameter of from about 8 inches to about 14 inches, and preferably from about 10 inches to about 12 inches in length (FIG. 8). Spray gun set 303 functions in the same manner.

The nozzles in each metal saltreducing solution set are arranged to have an included angle of from about to about 120 degrees between the streams of composition they dispense. To accomplish this end, each of the metal salt solution dispensing guns is inclined obliquely from the vertical about 40 to about 60 toward a mutually opposed reducing solution dispensing gun, and vice versa in a vertical plane common to the dispensing guns of the set (FIG. 10). This arrangement is desirable so that the metal and reducing solutions are effectively and thoroughly mixed as they approach and strike the surface of the activated glass plate.

Referring to FIG. 11, there is shown a schematic perspective view of an apparatus illustrating the state of the art prior to the present invention. FIG. 11 shows a metal-boron composition dispensing spray gun set 302 reciprocating along the X axis and applying solution to the transparent sheet 3 as said sheet travels along its article movement path Y. Note that set 302 produces a rear wave 306 and a front wave 307 on the surface of the glass sheet 3. The rear wave comprises a mixture of fresh solution and spent solution containing precipitated nickel, decomposed reactants, rinsing medium and gas bubbles. This mixture reaches and covers the sensitized surface of the glass sheet 3 before the sheet reaches a position where its upper surface is sprayed with fresh solution from gun set 302. As pointed out above, when the advancing glass sheet is contacted initially with spent solution, the resultant coating does not posess uniform optical properties. Further, note that the boundary 308 of rear wave 306 does not extend across the sheet in a straight line. Rather, it extends transversely of article movement path Y in a finger-like pattern, causing non-uniform surface coverage and, therefore, streaks in the final coating. In addition, the amount of old solution per unit area of glass sheet covered and the age of the old solution is not uniform for all portions of the rear wave 306. This non-uniformity of amount and age of coating manifests itself in inhomogeneities in the resulting film.

lFront wave 307 is principally composed of spent solution and rinsing medium. IIn the case of any front wave, spent solution is contacting the surface of a substrate after fresh solution has been applied. Since spent solution does not adhere as readily to a metal surface as it does to a glass surface, front wave 307 does not affect the uniformity of the iinished coating to the extent that rear wave 306 affects it.

The terms front and rear refer to the direction of movement of glass sheets along the article movement path as defined by the direction of arrow Y. iIn addition, the following description uses the terms upstream and downstream to define the direction of glass sheets along th'e article movement path. The sheets are presumed to travel in a downstream direction.

According to the present invention, rear wave 306 has been completely eliminated and front wave 307 has been reduced in size by the use of a stationary squeegee/ shield apparatus 301 immediately upstream of the lirst spray gun set 302, as shown in FIG. 5. The squeegee/ shield apparatus 301 extends in direction X that is transverse to the article movement path Y, and it functions to controlthe thickness of rinse water remaining on the surface of sheet 3 from rinse

pipes

215 and 216 to form a water lm of uniform thickness on the glass surface when said sheet 3 and said spray gun set 302 are in alignment, while avoiding the formation of finger-like waves of solution upstream of said spray gun set. Unlike spray gun sets 302 and 303, and rinse

pipes

304 and 305, the squeegee/shield apparatus is stationary and does not reciprocate along the X axis.

Referring to FIG. 12, there is shown the details of a first embodiment 301A of a squeegee/shield made in accordance with the present invention, together with spray gun set 302. squeegee/shield 301A includes a splash shield 310 and a squeegee 312 mounted beneath splash shield 310. Squeegee 312 comprises, for example, a loop made of soft rubber approximately 0.010 inch thick. The loop forms a lip portion 314 that engages the coated upper sensitized surface of each moving sheet of glass 3 that enters a spraying station. Squeegee 312 is held in place beneath shield 310 by any suitable means, such as, for example, an angular plate 316 which is bolted to a fiange 318. The squeegee is made of an elastomeric material having a durometer hardness of from about 50 to about 90, and preferably about 70. Examples of suitable materials are: natural rubber, neoprene, silicone rubber and plasticized polyvinyl chloride. Stiff plastics such as Teflon, Mylar, Lexan and many polycarbonates tend to scratch the sensitized surface.

Shield 310 and squeegee 312 prevent the spray-fan M from gun set 302 from splashing onto the glass surface and congregating in an upstream area 320 of set 302. Squeegee 312 prevents any of the spray M from flowing beneath shield 310 to upstream area 320. Together, the shield 310 and the squeegee 312 eliminate the rear wave and its associated problems.

Shield 310 may be constructed of any material that is capable of adding structural integrity to the apparatus 301 and is not attacked by the spray-fan M. Stainless steel is an example of a material suitable for use with a nickel-boron spray. Actually, the squeegee could be extended upward to replace the shield and perform its splash prevention function, as long as some measure is taken to add structural integrity to the apparatus. This could be done by, for example, reinforcing the upper portion of the squeegee or varying its thickness so that it is thicker, and therefore stronger, at its upper portion.

The squeegee 312 and particularly lip portion 314 performs two additional functions. Some of the rinse water from

pipes

215 and 216 remains on the glass sheet 3 in a random manner as it approaches gun set 302 along the article movement path Y. If this rinse water is allowed to sit on the glass surface beneath gun set 302, there will be a non-uniform dilution of the spray solution and a coating with inferior optical properties will result. Lip portion 314 acts as a wiper to insure that no puddles of rinse water pass beneath gun set 302. 'It allows only a thin uniform rinsing film of from about 0.03 inch to about 0.10 inch, and preferably about 0.05 inch, to sit on the glass beneath the coating station. In addition, lip 314 is positioned so that it slightly overlaps the side edge 309 of spray-fan M by about 1A; or about 1A of an inch at the upper glass surface to intercept a portion of spray M. Ideally, the tip of lip 314 should just touch the side edge of spray-fan M to insure that fresh spray solution contacts the glass surface first, but it is impractical to maintain this relationship with precision. If the squeegee is positioned so that lip 314 does not either touch the side edge or intercept a portion of spray-fan M, spent solution may contact the glass surface in random areas before fresh solution contacts the surface in those areas and a coating Referring to FIGS. 13, 14 and 15, alternate embodiments of the present invention are shown with similar numerals used to indicate similar parts. FIG. 13 shows a squeegee/ shield 301B including a squeegee 322 comprising a thin plastic reinforcement 324 enclosed Within a looped elastomeric covering 326. The covering 326 may be made, for example, of soft material, similar to the ones described in connection with squeegee 312. The reinforcement 324 can be made, for example, of polyvinyl butyral, approximately 0.030 inch thick.

Referring to FIG. 14, there is shown a third embodiment 301C of the squeegee/shield apparatus of the present invention. In this embodiment, the squeegee cornprises a curtain 332 approximately 3A of an inch to ll/z inches long and approximately 0.007 to approximately 0.040 inch thick, hanging freely from splash shield 310. The curtain 332 may be made of any of the suitable materials described above in connection with squeegee 312.

Referring to IFIG. 15, there is shown a fourth embodiment 301D of the squeegee/shield apparatus of the present invention. In this embodiment, the squeegee is in the form of a roller 340, driven by friction at the sensitized surface. It is possible to drive roller 340, but this is unnecessary and can lead to complications if roller 340 is not driven at the exact speed as the rollers 2 beneath the glass sheet 3. The roller may be made of any of the above-mentioned squeegee materials, but is preferably made of closed cell foam rubber. Enclosed within the foam rubber is a metallic tube 342. Shield 344 includes a sheet 346 and rods 348 with ribs 350 connecting the sheet to the rods. Axle 352 is rotatably connected to the base of rods 348 and roller 340 rotates about axle 352. In the embodiments illustrated in FIGS. 13-15, the squeegee operates to perform the functions described in connection with the embodiment of FIG. 12.

It is customary to use either two or three, or sometimes even four, spray gun sets. It might occur to one skilled in the art to use a squeegee/shield apparatus prior to each spray gun set. It has been discovered, however, that the installation of any squeegee/shield apparatus after the first spray gun set is detrimental in that it damages the freshly coated metal-boron surface. Further, a subsequent spray gun set appears to be able to sweep the spent solution from the surface of substrate 3 without damaging the prior coating. This can be explained by the fact that the spent solution does not adhere as readily to the fresh coating as it does to sensitized glass. Therefore, the use of squeegee/shield apparatus after the first spray gun set is unnecessary and even undesirable.

The

shields

310 and 344 have been illustrated as being oriented at an angle of about 30 with the vertical, but this angle is not critical. Actually, the shield may even lie within a vertically extending plane. By tilting the shield to an angle of from about 15 to about 50 with the vertical, the top portion of the shield is spaced from gun set 302 to make gun set 302 more accessible.

As the plate advances beyond each spray gun set 302 and 303, the intermixed film forming composition which is uniformly distributed on the surface of the plate is permitted to rest relatively quietly. This quiescent period or period of minimum turbulence is highly desirable since it enables the film forming composition to deposit a transparent coating which is substantially free from visual defects normally attributed to turbulence or agitation of the filming composition during deposition. In addition, it is during this quiescent period that the intermixed filming compositions contemplated herein undergo a change in their capacity for depositing a film such that the rate of film deposition, which is initially relatively rapid, decreases and then effectively completely ceases while the deposited film is still transparent. While the time required for this change in filming capacity to occur will vary considerably depending upon the chemistry of the actual filming composition employed, a filming composition comprising equal amounts of the nickel acetate solution and borohydride reducing solution, illustrated respectively in Tables I and II of U.S. patent application Ser. No. 57,451, will normally undergo a substantial decrease in its filming capacity within from about l seconds to a few minutes, e.g. minutes. In this regard, a glass plate that is coated with a metal and boron-containing film at room temperature by a single 15-second spray application of the above-illustrated intermixing filming composition will normally have a luminous transmission of from about 30 to about 40 percent when the filming capacity of the composition has depleted :and filming has effectively ceased.

Referringv once again to FIGS. 1 and 5, it will be appreciated that once the film forming composition has become dead, i.e., depleted of its filming capacity, it may be removed from the plate by any convenient means with out affecting the thick-ness, and thus the transparency of the film. It will also be appreciated that the lowest degree of transparency obtainable will depend primarily upon the amount of film that will deposit from a given film forming composition before it becomes dead, the number of gun sets in section 300, and the distance between each gu-n set. The effect of these variables on the thickness, uniformity and transparency of the metal-boron films formed in accordance with this invention will be more fully appreciated in light of the example recited hereinbelow.

After undergoing the quiescent period after its exposure to the mixed composition dispensed by spray gun set 303, the plate has a luminous transmittance of about 15 to 25 percent. If a third spray gun set is used (not illustrated), a luminous transmittance of as little as l0 percent may be obtained. Each additional gun provides a quiescent period designed to allow the partially formed metalborn film to increase in thickness uniformly in the substantial absence of adverse effects caused by turbulence. Even more important, however, this period is designed to allow suflicient time for the film forming composition on the surface of the plate to become substantially depleted of its film-forming capacity so that the rate of deposition of the metal-boron film will have materially slowed down, and preferably effectively ceased, before the plate is rinsed under

pipes

304 and 305. In this latter connection, it will be appreciated that the necessary distance between

pipes

304 and 305 and the last metal depositing gun set 303 is related to the rate at which the plate is advanced. Thus, while maintaining all of the various parameters within the bounds described herein, the distance between the final rinse

pipes

304 and 305 and the last spray gun set 303 should be at least about 30 inches, and preferably at least about 35 to 40 inches to provide a final film thickness corresponding to a luminous transmittance of about 20 percent.

After undergoing a final water rinse under rinse

pipes

304 and 305, the plate 3 advances into section 400 of the coating apparatus where it is dried by means of a suitable air knife 401 (FIG. `6). The air knife 401 may comprise any conventional blow-off device, but it is preferred to employ a high volume-low pressure knife to avoid disturbing the quality of the metal-boron film. For example, it is desirable to.l employ a knife that operates at a pressure of about 3 to 7 ounces per square inch', while forcing from about 3D0-to about 400 cubic feet of air .pery minute against the metal-boron coated glass plate.

After passing beneath the air knife, the completed metalfboron coated plate passes into section 500 where the thickness of the deposited film is measured by a conventional measuring device 501. Thereafter, the transparent glass plate is removed from the rollers z and is ready for use.

The present invention is Aapplicable in forming transparent metal-boron films on clear plastic (e.g. polymethy1 methacrylate) and glasses, especially soda-lime-silica glasses, 'but can be used to film awide variety of glass, ceramic, glass-ceramic, siliceous and'calcareous based compositions. For example, this invention can be used to provide metal-boron and particularly nickel-boron films on the following types of glasses: soda-lime-silica glasses; alkali-alumina-silica glasses, such as those containing lithia as a component alkali; alkali-zirconia-silica glasses; alkali-alumina-zirconia-silica glasses; borosilicate glasses, etc. Bearing this in mind, the present invention is described hereinbelow with specific reference to soda-limesilica glass.

The soda-lime-silica glass to be treated can be a clear glass or it can be a colored glass tinted by the introduction of various conventional materials into the glass forming batch. These latter glasses are often referred to as heat absorbing glasses especially when they contain iron oxide. Representative soda-lime-silica glass bases which can be treated in accordance with this invention usually contain 65 to 75 percent by weight Si02, 10 to 18 percent by weight Na20, 5 to l5 percent by weight CaO, 1 to 5 percent by weight MgO, 0 to 1.0 percent by weight Na2SO4, 0 to 5 percent by weight aluminum oxide (A1203), 0 to 8 percent by weight KZO, 0 to 8 percent by weight B203, 0 to l percent by weight iron oxide (Fe203), and 0 to 0.7 percent by weight of NaCl, S03, As205, BaO, NiO, C00 and Se and combinations thereof.

A representative range of composition for soda-limesilica glasses is listed as follows (wherein the given amounts of metals listed are determined as their oxides, except as otherwise noted):

The invention will be further understood from the specific example which follows. It should be noted, however, that the present invention is not necessarily limited to specific materials, temperatures, contact times, and pH values noted in the below example:

EXAMPLE A 40 inch x 70 inch x 1A: inch commercial soda-limesilica glass plate is coated with a nickel-boron film with the apparatus illustrated schematically in FIG. 1. Four blockers are used, each comprising a 3-inch thick cattle hair felt disc of S-inch diameter. The blockers are arranged at 12inch centers in the direction parallel to the rollers, hereafter referred to as the transverse direction, and are rotated at about 350 revolutions per minute. The blockers are oscillated about 4 inches in the transverse direction at a frequency of about 15 cycles per minute. Four 6-inch diameter rotary cup brushes are arranged at 12-inch centers in a transverse direction such that the longitudinal distance between the blockers and the rotary cup brushes is about 9 inches. The rotary cup brushesv are equipped with No. l2 nylon bristles and are rotated at about 350 revolutions per minute. The brushes are also oscillated about 4 inches in the transverse direction at a frequency of 15 cycles per minute. During operation, the blockers are supplied with a mixture of cerium oxides and 15 tap water, while a spray of tap water is apply beneath the rotary cup brushes. The rotary cylinder brush has a 6- inch diameter, comprising No. 13 nylon bristles, and has its axis disposed 8 inches from the rotary cup brushes. The first, second and third rinse sets, as well as the tin composition dispensing gun and the palladium composition dispensing gun, i.e., all of the rinse sets and the guns in section 200, are mounted from a single boom that reciprocates in a transverse direction at a rate of about 45 single passes per minute. Each of the rinse nozzles comprises a single Uni] et-T8002 spray nozzle (manufactured by Spraying Systems Company, Dellwood, Ill.) and is operated at a pressure of about 40 pounds per square inch, at an average flow rate of about 0.2 gallon of demineralized water per minute. Each of the tin and palladium composition dispensing guns comprises a single, type C, spray gun equipped with a Paasche U2, F2-8 nozzle, manufactured by Paasche Air Brush Company, Chicago, Ill., and operated at an air pressure of about 70 pounds per square inch and a ow rate of about 500 milliliters of the solution described below per minute. The distance between the rotary cylinder brush and the rst rinse

pipes

201 and 202 is about 30 feet, while the distance from each gun to the next respective gun is about 5 feet.

IThe gun sets in section 300 of the apparatus are spaced apart from those in section 200 such that the distance between rinse

pipes

215 and 216 and gun set 302 is about feet. In addition, gun set 302 is spaced about 3 feet from gun set 303. The distance between the tip of the gun dispensing nickel solution and the tip of the gun dispensing reducing solution in each respective set is about 10 inches. All of the guns in section 300 employ Paasche U2, F2-8 nozzles, which are arranged so that the tip of each nozzle is about 7 inches above the surface of the glass being coated, and so that each respective gun set generates a fan-shaped stream of intermixed film forming solution that contacts the glass surface in a generally elliptical pattern having a major diameter of about 11 inches extending in a longitudinal direction. All of the rinse sets and the spray guns in section 300 are mounted from a single boom that reciprocates in the transverse direction at a rate of about 72 passes per minute which is equal to 36 round trips per minute. During operation, each of the metal deposition gun sets in section 300 is maintained at a pressure of about 40 pounds per square inch and a flow rate of about 800 milliliters of solution per minute, while the final cross-fire rinse

pipes

304 and 305 are operated at a pressure of about 40 pounds per square inch at an average ow rate of about 0.2 gallon of demineralized water per minute per nozzle. The distance between rinse

pipes

304 and 305 and the last metal depositing gun set 303 is about 70 inches.

The air knife 401 comprises an elongated metal housing having a 0.002-inch Wide delivery slot extending along the length of its bottom wall. The knife 401 is disposed at a 45 angle relative to the advancing plate and had its centermost portion spaced about 8 feet from the final rinse

pipes

304 and 305. The air knife is operated at about 5 ounces per square inch and at a ilow rate of about 350 cubic feet per minute. The ambient air temperature is about 82 F., while the temperature of the demineralized and tap water used throughout this example is about 63 F. The glass plate is advanced at a rate of about 5 feet per minute, while the slot opening of the air knife is spaced about 1/2 inch from the plate. On the basis of a liter of solution, each of the prepared aqueous solutions employed has the following composition:

NICKEL SOLUTION Nickelous acetate 5.0 grams. Boric acid 2.5 grams. Sodium gluconate 9.0 grams. Hydrazine sulfate 0.5 gram. Water Added to 1 liter.

Ammonium hydroxide Added to pH 7.4. Ethomeen C-20 1 0.06 gram.

1Ethomeen C-20 (trademark of Armour and Company) is a cocoamine having an average molecular weight of 645 and the following generalized formula )CHICHzOMH R-N\ (CHgCHgO)yH wherein R ls derived from n cocoamine and w-l-y: VJ.

REDUCING SOLUTION The temperature of each of these solutions is about 70' F. The pH of the intermixed nickel and borohydride solutions is about 7.7. A nickel film is formed which contains about 5 to 10 percent by weight boron and the resulting coated plate has a luminous transmission of about 22 percent. The film is very adherent to the glass plate and is very uniform in appearance. It has an initial resistivity of 300 ohms per square.

Having now fully disclosed the invention, what I claim is as follows:

1. In a method of coating a surface of an article wherein the article is conveyed through a rinsing station to apply a rinsing medium to the surface and a coating station to apply a coating composition onto the rinsed surface, the improvement comprising:

removing a portion of the rinsing medium from the rinsed surface as the article is conveyed into the coating station to form a rinse medium film of uniform thickness on the surface of the article while avoiding the formation of a wave of the coating composition upstream of the coating station to provide a coating having uniform optical properties.

2. The method according to claim 1 wherein the coating composition is applied in a fan-shaped spray toward the surface of the article including the step of:

shielding succeeding portions of the surface conveyed into the coating station from a minor portion of the fan-shaped spray upstream of the coating station to eliminate linger-like flows of the coating composition upstream of the coating station wherein eliminatin of the finger-like ows prevents subsequent formation of streaks in the coating.

3. The method according to claim 2 wherein about 1A of an inch of the fan-shaped spray is shielded from the succeeding portions of the surface conveyed into the coating station.

4. In a method of coating a surface of an article wherein a sensitizing composition is applied to the surface, and thereafter the article having the sensitized surface is conveyed through a rinsing station to apply a rinsing medium to the sensitized surface and a coating station to apply a coating composition onto the rinsed, sensitized surface, the improvement comprising:

removing a portion of the rinsing medium from the rinsed, sensitized surface as the article is conveyed into the coating station to form a rinse medium film of uniform thickness on the surface of the article while avoiding the formation of a wave of the coat- 18 ing composition upstream of the coating station to ceeding portions of the surface conveyed into the coating provide a coating having uniform optical properties. station. 5. The method according to claim 4 wherein the coat- References Cited ing composition is applied in a fan-shaped spray toward UNITED STATES PATENTS the surface of the article and including the step of: 5

shielding succeeding portions of the surface conveyed 3,352,706 11/1967 Alkofef 117-64 R into the coating station from a minor portion of the 3,476,594 11/1969 Sodefbefg 117-54 fan-shaped spray upstream of the coating station to 3,507,682 4/1970 Flavm .et al- 117-64 R eliminate nger-like flows of the coating composition 3,669,770 6/1972 Feldsm 11,7130 E upstream of the coating station wherein elimination of the nger-like flows prevents subsequent forma- 10 EDWARD G' WHITBY Primary Exammer tion of streaks in the coating. U S C1 X R 6. The method according to claim 5 wherein about 1A of an inch of the fan-shaped spray is shielded from suc- 117-333, 64, 124 B, 130 E; 118-73 UNTTED STATES PATENT OTTTCT CETlFlCATE 0F CURECTON Patent No. 3,761,365 Dated September 25 1923 Inventods) Helmut Franz lt is certified that error appears in the above-identified patent and that said Letters Patent lare hereby corrected as shown below:

Column 16, line 52, in the third line of Claim 2, after the word "article" insert the word and.

sgnedfend `Seele@ this 25th dey ef Deeembelq 1973.

Attest: l l

EDWARDMTLETCTTEIRJR, RENE D. TEGTMETER Attesting Officer' Acting Commissioner of Patents uscoMM-Dc 603764269 U,S. GOVERNMENT PMNTING OFFICF |989 0-366-384,