Apparatus for meniscus coating of a moving web

A moving essentially non-porous web is positioned above and in close proximity to the upper surface of a narrow, very shallow pool of coating solution. A coating meniscus extends directly from the upper surface to the web to transfer coating solution from the pool to the web. Stagnation of solution in the pool is eliminated by feeding solution to the pool at the center and bottom thereof, and removing excess solution through ports at the top surface of the pool at each end thereof.

This invention relates to apparatus for meniscus coating of a moving web. 
For the most part, coating processes for applying a thin film or coating to 
a continuously moving web of metal, or other essentially non-porous 
materials, are of the metered or non-metered types. These processes are 
often used in the manufacture of pre-sensitized lithographic printing 
plates by applying a coating of photographic liquid, such as diazo resin, 
on a thin substrate of aluminum or other suitable metal. 
A metered type process is utilized where accurate control of coating 
thickness is essential so that apparatus for the metered type usually 
includes a special coating head that typically comprises a number of 
critically dimensioned elements to form a closely controlled gap or slot. 
Clearance between the coating head and web is very small and is critical. 
Thus, a metered type process requires relatively sophisticated equipment 
and experienced operating personnel. This equipment is expensive and is 
easily damaged during frequent disassembly for cleaning and other 
maintenance. Overall, a metered-type coating process is costly. 
Non-metered coating processes, such as the dip-pan process, are limited not 
only by properties of the coating solution and by coating speed, but also 
by distribution of coating solution to the coating pan. That is, the 
solution stagnates at certain regions of pan and interferes with the 
application of a continuously uniform, streak-free coating on the moving 
web. 
In accordance with the instant invention, meniscus coating of a moving web 
is achieved by utilizing a very shallow pool of coating solution confined 
in a pan that is constructed to prevent stagnation of the coating solution 
thereby improving coating quality. 
Accordingly, a primary object of this invention is to provide novel 
apparatus for applying a coating solution to a continuously moving web of 
relatively non-porous material. 
Another object is to provide apparatus of this type that is economical and 
which will applly a uniform streak-free coating. 
Still another object is to provide apparatus of this type that operates on 
a principal which includes a meniscus formed directly between a pool of 
the coating solution and a web moving above the upper surface of the pool. 
A further object is to provide apparatus of this type in which the coating 
solution is fed to the moving web from a very shallow pool confined in a 
pan that is constructed to prevent stagnation. 
A still further object is to provide apparatus of this type in which the 
pool is very narrow as compared with the diameter of a roller supporting 
the moving web in the meniscus region.

Now referring to the figures. Continuously moving metal web 10 is partially 
wrapped around elongated support roller 11 mounted for rotation about its 
longitudinal axis 12 which is positioned horizontally. Roller 11 is 
positioned above pan 14 wherein narrow, shallow pool 15 of a coating 
solution is confined. Coating solution is fed to pool 15 through inlet 
tube 16 at enlarged port 17 provided to reduce turbulance. Port 17 is 
located at the bottom of pool 15 midway between the ends thereof. Some of 
the fluid entering pool 15 at port 17 exits through two enlarged ports 19 
connected to a return reservoir (not shown) by tubes 18 located at 
opposite ends of pool 15. Ports 19 extend to the upper surface 21 of pool 
15. The inlet and outlet ports, as observed in FIGS. 2 and 3, are 
positioned in a plane containing a longitudinally extending groove within 
the pan and the longitudinal axis of said pan. 
Roller 11 positions web 10 so that it passes above upper surface 21 in 
close proximity thereto. A bridge or meniscus 25 of coating solution is 
formed directly between upper pool surface 21 to web 10. Meniscus 25 is 
maintained as web 10 moves by solution entering pool 15 through inlet 16. 
At start-up, meniscus 25 is formed by utilizing a plastic strip (not 
shown). 
Generally, the diameter of roller 11 should be at least four times the 
width of pool 15 at its upper surface 21 and preferably roller diameter 
should be between five and six times pool width at its upper surface. 
In a practical example, web 10 is 60 inches wide and support roller 11 is 
14 inches in diameter. Contact between coating meniscus 25 and web 10 is 
limited to an angle 27 (FIG. 3) of no more than 20.degree. and spacing 
between web 10 and upper pool surface 21 is in the range of 15 to 35 mils. 
The latter is adjustable by raising and lowering horizontal table 28 which 
supports pan 14. 
Pan 14 may be milled from an aluminum block 63 inches long by 5 inches wide 
by 1/2 inches high. Pool 15 is 61 inches long by 3 inches wide, at upper 
surface 21, by slightly less than one-quarter inch high. This height may 
be reduced to one-eighth inch. While pool 15 is illustrated as being 
generally of uniform width, this width may be narrower at the ends than at 
the center. Further, the bottom of pool 15 may be rounded. 
Tubes 16 and 18 are one-quarter inch in diameter and ports 17 and 19 are 
one-half inch. Overflow at ports 19 is 5% of solution infeed at port 17. 
Although in the foregoing, a preferred embodiment has been discussed, many 
variations and modifications will now become apparent to those skilled in 
the art and it is therefore understood that this invention is not limited 
by the disclosure but only by the appending claim.