US3877418A

US3877418A - Apparatus and method for coating metallic strips

Info

Publication number: US3877418A
Application number: US499520A
Authority: US
Inventors: Kenneth H Shaner
Original assignee: GTE Sylvania Inc
Current assignee: GTE Sylvania Inc
Priority date: 1974-08-22
Filing date: 1974-08-22
Publication date: 1975-04-15
Anticipated expiration: 1992-04-15

Abstract

There is disclosed an apparatus and method for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip and for substantially drying said photosensitive material thereon as said metallic strip moves in a substantially horizontal direction along a predetermined path. Drying of the photosensitive coating in order to achieve uniformity is accomplished in a substantially progressive manner whereby the upper portion of the strip is substantially dried before the lower portion.

Description

United States Patent 91 Shaner APPARATUS AND METHOD FOR COATING METALLIC STRIPS [75] Inventor: Kenneth H. Shatter, Towanda, Pa.

[73] Assignee: GTE Sylvania Incorporated,

Stamford, Conn.

22 Filed: Aug. 22, 1974 21 Appl. No.: 499,520

[52] US. Cl. 118/642; 118/326; 118/68; l17/93.3; 34/4; 34/41; 34/152 [51] Int. Cl. B05c 5/02 [58] Field of Search 118/49.5, 68, 642; 117/933; 34/4, 41, 152

[56] References Cited UNITED STATES PATENTS 2,235,978 3/1941 Braucher 118/68 2,786,443 3/1957 Mears 118/326 3,385,745 5/1968 Mears 118/325 [4 1 Apr. 15, 1975 3,808,702 5/1974 Laessig 34/229 Primary Examiner-Mervin Stein Assistant ExaminerStev'en'A. Hawkins Attorney, Agent, or FirmNorman J. OMalley; Lawrence R. Fraley; Donald R, Castle [57] ABSTRACT There is disclosed an apparatus and method for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip and for substantially drying said photosensitive material thereon as said metallic strip moves in a substantially horizontal direction along a predetermined path. Drying of the photosensitive coating in order to achieve uniformity is accomplished in a substantially progressive manner whereby the upper portion of the strip is substantially dried before the lower portion.

15 Claims, 6 Drawing Figures PATENTEDAPRISIQYS 877', 41 8 3x15511052 PRIOR ART PATENTEDAPRISIQYS 77, 41 SHEET 2 OF 2 PRIOR ART APPARATUS AND METHOD FOR COATING METALLIC STRIPS BACKGROUND OF INVENTION This invention relates to coating'apparatus and methods and particularly to coating vertically aligned metallic strips as said strips move in substantially horizontal direction.

More specifically, this invention relates to the application of a relatively thin coating to at leastone side of a moving metallic strip and to the drying of the coating thereon.

Even more specifically. this invention relates to the application and drying of relatively thin coatings of photosensitive material on moving metallic strips to eventually be utilized in the production of aperture masks for color television cathode ray tubes.

As is known in the art, most color television cathode ray tubes employ an apertured metallic mask positioned within the tube to aid in directing the electron beams emitted from the tubes electron guns in striking the tubes screen. These beams excite in a preestablished manner the pattern of cathodoluminescent materials positioned on the screen to produce a desired color. A typical aperture mask contains hundreds of thousands of openings therein for this purpose and, as can be appreciated, producing masks of this variety is a highly complicated and precision demanding process.

Previous methods for manufacturing apertured masks for color television tubes have substantially included coating a thin metallic strip with a photosensitive material. drying the material thereon, photoprinting a desired pattern on the strip, removing selective portions of the coating from the strip, and thereafter subjecting the strip to an etching process whereby the unprotected metal surfaces are etched through.

A typical example of an apparatus and method for producing light sensitive coatings on metal sheets is illustrated in US. Pat. No. 2,786,443. The coating material is applied via utilization of a nozzle member to deposit the coating material along the upper surface of the upright sheet. As' explained in US. Pat. No. 2,786,443, excessive coating along the lower edge of the sheet is removed by hand, using a squeegee or sponge.

While this and similar methods have resulted in a coating being applied to a metallic strip, on most occasions the coating thicknesses at the bottom of the strip have proven greater than at the top. This in turn has usually been the result of thicker concentrations of coating material accumulating at the bottom and not being able to dryat a sufficient rate with those concentrations along the upper surfaces. As can be appreciated, in precisely defined articles such as aperture masks, this difference in thicknesses can result in misalignment of the photoprinters during the subsequent photoprinting process. This in turn results in the production of uneven patterns of exposed or unexposed areas. Additionally. nonuniform thicknesses of the coatings can result in unequal rates of etching of the 'metal. thereby resulting in some openings being larger or smaller than desired. I

Still another prior art method involves the dipping of individual metallic plates into photosensitive solutions and thereafter withdrawing the plates and permitting them to dry. However, it has been found that this process also yields the coating wedge" described above wherein the coatings at the bottom are thicker than those along the upper areas of the panel. Still another prior art method incorporates a press apparatus which presses a dried photosensitive material having a polymeric backing onto the metallic strip. While this process eliminates the coatin wed e, it does not rove satisfactory in obtaining relatively thin coatings on the strip and is therefore excessively time consuming and expensive. I

It is believed therefore that an apparatus and method for applying a relatively thin and substantially uniform coating to at least one sidof a substantially vertically oriented metallic strip moving in a substantially horizontal direction which would overcome the above cited disadvantages of prior artmethods would constitute an advancement in the art.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore a primary object of this invention to provide an apparatus and method for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a moving metallic strip.

lt is a further object of this invention to provide an apparatus and method for applying said coating which obviates the above cited disadvantages of prior art methods.

It is a still further object of this invention to provide an apparatus and method for coating moving vertically oriented metallic strips as said strips move in a substantially horizontal direction.

An even further object of thisinvention is to provide an apparatus and method forapplying a relatively thin and substantially uniform coating of photosensitive material to a moving metallic strip to be utilized in the production of apparatus masks for color television cathode ray tubes.

In accordance with one aspect of this invention there is provided an apparatus for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip and for substantially drying said photosensitive material thereon as said metallic strip moves in a substantially horizontal direction. The apparatus comprises a means for supplying the strip to the apparatus along a predetermined path, said strip having at least one side having an upper and lower portion. The apparatus further comprises a coating means for applying a relatively thin coating of photosensitive material to said side in a manner whereby the coating will flow substantially downward and cover both upper and lower portions. The apparatus even further comprises a drying means for drying the coating on said side of the strip in a substantially progressive manner whereby the coating on the upper portion of the side will be substantially dried before the coating on the lower portion.

In accordance with another aspect of the invention, a method is provided for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip and for drying the material thereon as the strip moves in a substantially horizontal direction. The method comprises the steps of continuously supplying the moving vertically oriented strip having at least one side having an upper and lower portion in a substantially horizontal direction along a predetermined path, applying a relatively thin coating of the photosensitive material to the side of the strip in a man ner whereby the coating will flow substantially downward along the side and cover both upper and lower portions, and thereafter drying the coating in a substantially progressive manner whereby the coating on the upper portion of the side will be substantially dried before the coating on the lower portion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a known prior art coating apparatus for coating metallic strips;

FIG. '2 is a section view as taken along the line 22 in FIG. 1;

FIG. 3 is a side elevational view of the coating apparatus in accordance with a preferred embodiment of the present invention;

FIG. 4 is a section view as taken along the line 4--4 in FIG 3;

FIG. 5 is a side elevational view of an alternate embodiment of the present invention; and

FIG. 6 is an end elevational view of still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages. and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above described drawings of the invention.

With particular reference to FIG. I, there is illustrated an example of a known apparatus for applying light sensitive coatings to substantially vertically oriented moving metallic strips and for thereafter drying said coatings. A prior art apparatus substantially similar to that illustrated in FIG. 1 is described in US. Pat. No. 3,385,745 and comprises a supply reel 10, a cleaning and coating means 13, and a drying oven 14. Drying oven 14 usually consists of a closed container having either a series of vertically positioned heaters or a means whereby hot air or a similar media is forced therein to dry the coating. As illustrated and described in the aforementioned patent, the strip with the dried coating thereon is further subjected to subsequent processes including photoprinting, etching, scrubbing, etc. Such processes are well known in the production of metallic apertured masks for utilization in color television cathode ray tubes and further description of these processes is not believed necessary. In FIG. 1, as well as in the apparatus referred to, the metallic strip receives a coating on both sides at the described coating station 13. This coating is applied via a piping or similar nozzle member'15 and is allowed to flow in a substantially downward manner across both sides of the vertically oriented strip.

FIG. 2, taken along the line 22 in FIG. 1, illustrates in cross-section the described coating as applied. As evidenced in FIG. 2, the downward flowing coating produces a wedge" or similar configuration on each side of the metallic strip when coated and dried in the methods known in the prior art. That is, the resulting thicknesses at the lower portion 17 of the strip (dimension [1) tend to be substantially greater than those at the upper portion 19 (dimension :1). As described previously in the application, this resulting differences in thicknesses as typically found in the prior art results in a deleterious effect with particular regard to the described subsequent photoprinting and etching pro-.

cesses. More specifically, the greater thickness at the bottom results in misalignment of the photoprinters during the photoprinting step, resulting in theproduction of uneven patterns of exposed and unexposed areas. The described differences in thicknesses additionally results in the unequal etching of the metal, in turn producing openings either larger or smaller than desired. As has been stated, the described results are highly disadvantageous to the production of precision metallic articles such as aperture masks and lead frames for integrated circuitry.

With particular reference to FIG. 3, there is illustrated a coating and drying apparatus in accordance with a preferred embodiment of the present invention. Apparatus 20 is adapted for applying a relatively thin and substantially uniform coating of photosensitive ma terial 21 to at least one side of a substantially vertically oriented metallic strip 23 and for substantially drying material 21 thereon as strip 23 moves in a substantially horizontal direction. In FIG. 3, apparatus 20 is illustrated as coating and drying photosensitive material on both sides of strip 23. It is to be understood, however, that apparatus 20, in the broader concepts of the present invention, can be adapted for coating and drying only a single side of a vertically oriented metal strip.

Apparatus 20 is illustrated as comprising a supply means 25 (illustrated as supply reel 27) for supplying the substantially vertically oriented metallic strip 23 to apparatus 20 in a substantially horizontal direction along a predetermined path, indicated by arrow 29. Strip 23 includes at least one side having an upper portion 31 and a lower portion 33. As in understood, strip 23 also has an opposing side (not shown) also having an upper portion and lower portion similar to those described.

Apparatus 20 further comprises a coating means 35 for applying a relatively thin coating of photosensitive material 21 to the strip 23 in a manner whereby the coating will flow substantially downward and cover upper and lower portions 3land 33 respectively. As illustrated, coating means 35 comprises at least one nozzle member 37 for providing a continuous flow of the photosensitive material to the uppermost portion of upper portion 31. A substantially similar nozzle member also provides the coating in the manner described to the other side of strip 23.

The coating material preferably utilized in the present invention is one well known in the art of manufacturing color television aperture masks, that being dichromated glue, often referred in the industry as fish glue." This photosensitive material is preferred to have a specific gravity of between 1.025 and 1.060. When using the photosensitive material as defined, it is preferred to move the metallic strip 23 through apparatus 20 at a speed of from about 30 to about 200 inches per minute. The described speeds through apparatus 20 are more than suitable for production and thus constitute a particular advantage of the present invention.

Prior to the described application of the coating material on strip 23, the strip is subjected to a cleaning or similar process to remove residue or other contaminates which may have accumulated on the strip during manufacture or packaging. Such a cleaning process is well known in the art and further description is not believed necessary at this time. Should apparatus 20 be employed in the manufacture of aperture masks for color television cathode ray tubes or similar relatively thin and fragile articles. it is often desirable to protect the wound metallic strip with backing paper or similar material. This paper is interwound onto spool 27 bev tween each layer of strip 23 by the manufacturer of the unfinished strip. It is necessary therefore to provide a means for unwinding this paper concurrently with the unwinding of the strip. To do so a winder (not shown) may be relatively positioned near supply means 25 to provide this function.

Apparatus 20, as illustrated in FIG. 3, further comprises a drying means 39 for drying the coating on strip 23 in a substantially progressive manner whereby upper portion 3lwill be substantially dried before lower portion 33. With particular regard to coating of photosensitive materials. substantially dried is meant to define a condition whereby the applied material is sufficiently dried to prohibit further downward draining of the material. More specifically, sufficiently dried in this particular regard is meant to define the condition whereby the coated solution has reached a set condition. Drying means 39 is illustrated in FIG. 3 as comprising a angularly positioned heater means 41 positioned substantially adjacent strip 23 and adapted for having the strip pass thereby. Heater means 41, preferably a low temperature infrared heater having an output of approximately 750 watts per square foot, is shown as comprising first and second opposing ends 43 and 45, with first end 43 positioned relative to upper portion 31 of strip 23 and second end 45 positioned relative to lower portion 33. As illustrated, angularly positioned heater means 41 is positioned preferably at an angle within the range of from about 2 to about 20 degrees to the horizontal direction of travel indicated by arrow 29. This angle, illustrated by the designate c, is preferred when utilizing the formulations described and the speeds mentioned for strip 23 through apparatus 20. Furthermore, when using the infrared heater as described, in addition to the solutions and strip speeds mentioned, it is preferred to position heater means 41 at a distance of from about 3 to about 9 inches from the side of strip 23 being coated.

As further illustrated in FlG. 3, it is preferred to position heater means 41 within a housing 47 or similar containing article. Housing 47 substantially eliminates the possibility of air currents or similar undesirable motion between heater means 41 and strip 23 during the coating and drying process. As can be appreciated, such motion could result in the deposition of undesirable contaminates to the freshly coated surface in addition to upsetting the drying rate of the coating. When using the described ranges for the above mentioned variables, housing 47 is preferably from about to about 45 feet in length.

FIG. 4, taken along the line 44 in FIG. 3, illustrates the resulting cross-sectional configuration for the coatings as applied by apparatus 20. As can be seen, the previously disadvantageous coating wedge" has been eliminated with the thickness of the coating along the upper portion 31 being substantially identical to that along lower portion 33. As has been described, this uniform thickness for the substantially dried coating has been achieved as the result of the initial heating of upper portion 31 prior toheating of lower portion 33. With particular regard to the production of precision metallic articles. the described advantage of a uniform coating on strip 23 results in a more precise "drawing up. of the photoprinters in the subsequent photoprinting process. In addition, this even coating along the entirety of strip 23 assures a more precise etching of the strip when the established portions of the exposed or unexposed coating are removed. 7

Referring back to FIG. 3, it is preferred to position nozzle 37 of coating means 35 substantially adjacent first end 43 of heater means 41. In this manner, the uppermost coated areas of upper portion 31 are thus almost immediately subjected to heater 41. This in turn substantially eliminates any excessive downward flow or draining of the photosensitive material prior to its sufficient drying.

In FIG. 5 there is illustrated an alternate embodiment of the invention, apparatus 20. Similar to apparatus 20 in FIG. 3, apparatus 20' comprises a coating means 35 having at least one nozzle 37 for providing a substantially continuous flow of photosensitive material 21' to strip 23. Apparatus 20' is further illustrated as comprising a drying means 39 which in turn comprises a pair of spacedly positioned heater means 41 and 41 Similar to heater means 41 in apparatus 20, heater means 41' and 41" are preferably low temperature infrared heater assemblies having an output of approximately 750 watts per square foot. Additionally similar to apparatus 20, heater means 41' and 41 are preferably positioned within a housing or similar member 47' (illustrated in phantom). Each of the spacedly positioned heater means are respectively angularly positioned (designates d and e) to the substantially horizontal direction of travel of strip 23, illustrated as arrow 29'. Angle d is preferably within the range of from about 2 to about 5. Angle e is preferably from about 2 to about 15. The described angle ranges-for heaters 41' and 41" are particularly adaptable to housings of substantial length, e.g. approximately 45 feet. As can be seen, first heater means 41' is positioned relative to upper portion 31' of strip 23 while the second heater means 41" is preferably positioned relative to lower portion 33'. As can be appreciated, the embodiment in FIG. 5 provides greater drainage periods for the lower portion of the metallic strip.

As also illustrated in FIG. 5, it is preferred that oone of the opposing ends of first means 41 be positioned substantially adjacent nozzle 37' of coating means 35. The resulting coating as achieved by apparatus 20 is substantially identical to that achieved in FIG. 4 by apparatus 20.

With particular regard to FIG. 6, there is illustrated an end elevational view, partly in section, of still another embodiment of .the present invention. In this view, heater means 42 is illustrated as being angularly positioned (designate g) with regard to the substantially vertically oriented metallic strip 23. Angle g is preferably within the range of from about 5 to about 15. ln FlG. 6, strip 23 is illustrated as moving either directly toward or away from the viewer. Thus heater means 42 is also angularly positioned with regard to the substantially horizontal direction of travel for strip 23. Coating means 35", substantially similar to coating means 35 in apparatus 20, is also illustrated as comprising a singular nozzle member 37" for providing a continuous flow of photosensitive material 21" to at least one side of the strip. vAs further illustrated in HO. 6, it is preferred to substantially encase heater means 42 within a housing or similar member 47" in much the same manner as previously described for apparatus 20 and It is to be further understood that the apparatus as illustrated in FIG. 6 could be utilized in a manner to provide a coating to both sides of strip 23 with the mere addition of a second coater and heater means on the opposing side of strip 23 from that as illustrated. The embodiment as described in FIG. 6 thus permits a means whereby the upper portion 31" of strip 23 having the coating thereon is subjected to a drying means of substantially greater intensity than that of lower portion 33". With the formulation and strip speeds as described, it is preferred to position the upper end 43 at approximately 2 inches from the uppermost portion of upper portion 31". Accordingly, it is preferred to position the lower opposing end 45' of heater means 42 at approximately 9 inches from the lowermost portion of lower portion 33". The end result as illustrated is a substantially uniform coating along the entire side of strip 23 from the described uppermost to the described lowermost portion of the strip as coated.

Thus there has been shown and described an apparatus and a method for applying and drying a relatively thin and substantially uniform coating to at least one side of a substantially vertically aligned moving metallic strip as the strip moves in a substantially horizontal direction along a predetermined path. The resulting uniform coatings produced by the described apparatus and method are achieved through the progressive drying of the coating in a manner whereby the upper portion of the coating on the strip are substantially dried before the lower portion.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. An apparatus for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip and for substantially drying said photosensitive material thereon as said metallic strip moves in a substantially horizontal direction along a predetermined path, said apparatus comprising:

means for supplying a substantially vertically oriented metallic strip to said apparatus in a substantially horizontal direction along a predetermined path, said strip having at least one side having an upper and a lower portion;

coating means for applying a relatively thin coating of photosensitive material to said side of said metallic strip in a manner whereby said coating will flow substantially downward and cover said upper and lower portions; and

drying means angularly positioned with regard to said horizontal direction of travel of said metallic strip for drying said coating in a substantially progressive manner whereby said coating on said upper portion of said side will be substantially dried before said coating on said lower portion.

2. The apparatus according to claim 1 wherein said coating means comprises at least one nozzle member adapted for providing a continuous flow of said photosensitive material to the uppermost portion of said upper portion of said side.

3. The apparatus according to claim 1 whereinsaid angularly positioned drying means comprises at least one heater means positioned substantially adjacent said side of said metallic strip.

4. The apparatus according to claim 3 wherein said heater means includes first and second opposing ends, said first end positioned relative to said upper portion of said side of said metallic strip, said second end positioned relative to said lower portion of said side of said metallic strip.

5. The apparatus according to claim 4 wherein said coating means comprises at least one nozzle member adapted for providing a continuous flow of said photosensitive material to the uppermost portion of said upper portion of said side, said nozzle member positioned immediately adjacent said first end of said heater means.

6. The apparatus according to claim 3 wherein said heater means is a low temperature infrared heater member.

7. The apparatus according to claim 3 wherein said angularly positioned heater means is positioned at an angle within the range of from about 2 to about 20 to said substantially horizontal direction of travel of said metallic strip.

8. The apparatus according to claim 3 wherein said angularly positioned drying means comprises first and second heater means positioned substantially adjacent said side of said strip, said first heater means positioned relative to said upper portion of said side of said metallic strip, said second heater means positioned relative to said lower portion of said side of said metallic strip. 9. The apparatus according to claim 8 wherein said first heater means is positioned at an angle within the range of from about 2 to about 5 to said substantially horizontal direction of travel of said metallic strip.

10. The apparatus according to claim 9 wherein said second heater means in positioned at an angle within the range of from about 2 to about l5 to said substantially horizontal direction of travel of said strip.

11. The apparatus according to claim 8 wherein said first and second heater means are low temperatureinfrared heater members.

12. A method for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip having an upper and a lower portion and for substantially drying said photosensitive material thereon as said metallic strip moves in substantially horizontal direction, said method comprising:

continuously supplying a moving substantially vertically oriented metallic strip having at least one side having an upper and lower portion in a substantially horizontal direction along a predetermined path; applying a relatively thin coating of photosensitive material to said side of said metallic strip in a manner whereby said coating will flow substantially downward along said side of said metallic strip and cover said upper and lower portions and thereafter substantially drying said coating on said side of said strip in a substantially progressive manner whereby said coating on said upper portion of said side will be substantially-dried before said coating on said lower portion.

13. The method according to claim 12 wherein said photosensitive material is dichromated glue.

14. The method according to claim 13 wherein said metallic strip continuously moves along said predetermined path at a rate of from about 30 inches per minute to about 200 inches per minute.

15. The method according to claim 14 wherein said dichromated glue has a specific gravity within the range of from about 1.025 to about 1.060.

Claims

1. An apparatus for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip and for substantially drying said photosensitive material thereon as said metallic strip moves in a substantially horizontal direction along a predetermined path, said apparatus comprising: means for supplying a substantially vertically oriented metallic strip to said apparatus in a substantially horizontal direction along a predetermined path, said strip having at least one side having an upper and a lower portion; coating means for applying a relatively thin coating of photosensitive material to said side of said metallic strip in a manner whereby said coating will flow substantially downward and cover said upper and lower portions; and drying means angularly positioned with regard to said horizontal direction of travel of said metallic strip for drying said coating in a substantially progressive manner whereby said coating on said upper portion of said side will be substantially dried before said coating on said lower portion.

3. The apparatus according to claim 1 wherein said angularly positioned drying means comprises at least one heater means positioned substantially adjacent said side of said metallic strip.

7. The apparatus according to claim 3 wherein said angularly positioned heater means is positioned at an angle within the range of from about 2* to about 20* to said substantially horizontal direction of travel of said metallic strip.

8. The apparatus according to claim 3 wherein said angularly positioned drying means comprises first and second heater means positioned substantially adjacent said side of said strip, said first heater means positioned relative to said upper portion of said side of said metallic strip, said second heater means positioned relative to said lower portion of said side of said metallic strip.

9. The apparatus according to claim 8 wherein said first heater means is positioned at an angle within the range of from about 2* to about 5* to said substantially horizontal direction of travel of said metallic strip.

10. The apparatus according to claim 9 wherein said second heater means in positioned at an angle within the range of from about 2* to about 15* to said substantially horizontal direction of travel of said strip.

11. The apparatus according to claim 8 wherein said first and second heater means are low temperature infrared heater members.

12. A method for applying a relatively thin and substantially uniform coating of photosensitive material to at least one side of a substantially vertically oriented metallic strip having an upper and a lower portion and for substantially drying said photosensitiVe material thereon as said metallic strip moves in substantially horizontal direction, said method comprising: continuously supplying a moving substantially vertically oriented metallic strip having at least one side having an upper and lower portion in a substantially horizontal direction along a predetermined path; applying a relatively thin coating of photosensitive material to said side of said metallic strip in a manner whereby said coating will flow substantially downward along said side of said metallic strip and cover said upper and lower portions and thereafter substantially drying said coating on said side of said strip in a substantially progressive manner whereby said coating on said upper portion of said side will be substantially dried before said coating on said lower portion.