GB1579587A

GB1579587A - Web coating apparatus

Info

Publication number: GB1579587A
Application number: GB1192477A
Authority: GB
Original assignee: Polychrome Corp
Current assignee: Polychrome Corp
Priority date: 1976-03-23
Filing date: 1977-03-22
Publication date: 1980-11-19
Also published as: FR2345223A1; FR2345223B1; AU497766B2; DE2711488A1; AU2336577A; CA1104812A; JPS52114634A; NL7703141A

Description

(54) WEB COATING APPARATUS (71) We, POLYCHROME CORPORA ILION, of 137 Alexander Sueet, Yonkers, ;State of New York 10702, United States of America, a corporation organised and existing under the laws of the State of New York, United States of America, (assignee of SIMON LONG CHU, RUBERT GUMBIN NER, AND WERNER ALBERT RODER), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to apparatus for liquid coating of a moving non-porous web and, more particularly, relates to apparatus of this type in which the coating roll surface and the web move in opposite directions.

Presensitized lithographic printing plates are usually manufactured by applying a controlled film of photographic liquid, such as a diazo resin, on a moving web or substrate of substantially non-porous material such as aluminum. Perhaps, the most simple coating apparatus utilize dip coating methods. In direct dip coating the portion of a web wound about a backing roller is guided for shallow dipping in a solution reservoir, and in indirect dip coating an applicator roll partially immersed in the solution reservoir transfers coating solution from the reservoir to the web.

Devices relying upon dip pickup of solution have great difficulty in maintaining uniform coating weight or thickness. Thus, mechanical '9Ost-metering" as by a doctor blade or squeeze roll is often utilized in an effort to control film thickness. However characteristics of the photographic liquid are such that it is difficult to prevent streaking when post metering is used and to control film thickness with variations in web speed or solution characteristics of viscosity, density and/or surface tension.

Devices for doctoring coating rolls have been found to be very sensitive to pressure, surface and solution characteristics, so that they are difficult to preset or to maintain at settings to obtain desired coating results. Thus, curtain and bar coater devices have been utilized to deposit a film of coating solution on a moving web. These latter devices require a high degree of operator attention and close maintenance for initial adjustment and adjustment as web speed changes. Here again physical properties of the photographic solution have presented difficulties especially in areas of smooth flow and leveling especially if thickness is to be controlled utilizing different solution mixes or over reasonable ranges of web speeds.

Other prior art coaters utilize gravure rolls.

While prior art gravure roll devices were satisfactory for coating porous webs, they were unsatisfactory for use with non-porous substrates since the cell pattern was often imparted to the surface coating and transfer of coating solution from the cells of the gravure roll to a non-porous surface is difficult to control.

Accordingly, a primary object of the invention is to provide novel apparatus for coating a web substrate of substantially non-porous material.

Another object is to provide apparatus of this type operating on a reverse offset gravure principle.

Still another object is to provide apparatus of this type that may be utilized for coating simultaneously both surfaces of a moving web.

A further object is to provide apparatus of this type that is easy to operate and maintain over a wide range of web speeds while utilizing coating solutions having varying characteristics.

A still further object is to provide apparatus of this type that does not require accurate control of web tension or accurate control of pressure settings between the coating roll and the web or the gravure roll.

According to the present invention apparatus is provided for applying a film of coating solution on to a web substrate of substantially non-porous material, said apparatus including a rotatable gravure roll, first means for sup plying the cells of said gravure roll with coating solution and for doctoring solution supplied to said cells a rotatable relatively smooth surfaced coating roll operatively positioned to receive solution from said cells, roll, and said coating roll having a central portion which is of greater diameter than adjoining end portions of said coating guide means for directing said web through a transfer region where said web receives said solution from said coating roll and for directing the movement of said web in said transfer region in a direction opposite to the direction of motion of the surface of said coating roll.

In the accompanying drawings, which are given by way of example: Figure 1 is a side elevation, in schematic form, of coating apparatus embodying the invention; Figure 2 is a plan view of the coating and gravure rolls looking in the direction of arrows 2, 2 in Figure 1; Figure 3 is an enlarged view looking into a cell of the gravure roll through the open end of the cells; and Figure 4 is a cross-section taken through the line 44 of Figure 3 looking in the direction of arrow 4, 4.

As shown in the drawings, a substrate, for example of aluminum, to receive coatings 11, 11 of photographically sensitive solution is constituted by a continuously moving web 10. The latter is guided by rolls 12, 13 so that in the region therebetween the web 10 moves vertically upward with respect to Figure 1.

At a transfer portion of this vertical region, the web 10 passes between a pair of relatively smooth surfaced rubber coated transfer or coating rolls 14, 15 which rotate on respective axes 16, 17. In this transfer region, the web 10 is planar being tangent to rolls 14, 15 rather than being partially wrapped therearound. A common plane containing the axes 16 and 17 is perpendicular to the web in this transfer region.

In addition to the foregoing, we have also found that it is possible to successfully practice the invention when the axes of the rolls are not contained in a common plane. We have found that it is possible to obtain satisfactory results when the axes of one set of rollers, i.e., 15 and 25 are in a plane which is offset, that is, higher or lower than the plane containing the axes of rollers 14 and 24. The amount of offset can be determined by the worker skilled in the art depending upon the coating results desired to be obtained. Likewise, when the rollers are in an offset position as aforesaid the distance between the sets of rollers can be altered in accordance with the results desired.

Disposed adjacent rolls 14, 15 are respective gravure rolls 24, 25 which are rotated on respective axes 26, 27. The latter are parallel to and laterally offset from axes 16, 17. Quadrangular cells 18 (Figure 3 and 4) are formed in the cylindrical surfaces of gravure rolls 24, 25. Disposed adjacent these cylindrical surfaces and extending parallel to axes 26, 27 are doctor blades 22, 23, respectively. Doctor blades 22, 23 cooperate with rolls 24, 25 to form open ended troughs wherein photosensitive coating solution delivered by respective distributor nozzle means 28, 29 is accumulated in shallow puddles 32, 33 adjacent the cellular surfaces of rolls 24, 25 res pectively. Disposed below the rolls 14, 24 is a pan 34 to catch drippings from these rolls and from the puddle 32. A similar pan 35 is disposed below rolls 15, 25 to catch drippings from these rolls and from the puddle 33.

In operation, coating solution supplied by nozzle means 28 overfills cells 18 of gravure roll 24. Doctor blade 22 levels the solution in the cells 18 of roll 24, after which the solution in these cells is picked up by coating roll 14 which transfers this solution to one surface of web 10. Roll 14 rotates clockwise so that the outer surface thereof moves opposite to the direction of movement of web 10. As seen in Figure 2, the end portions of roll 14 are undercut and the central portion between these undercuts is slightly narrower than web 10. Thus, coating solution is not placed across the entire width of web 10 so that solution applied by roll 14 will not migrate to the other surface of web 10. In a similar manner, this other surface is coated by solution delivered by nozzle means 29 to puddle 33.

Downstream of the transfer region between coating rollers 14, 15, and upstream of guide roll 13, the coated web 10 passes through a dryer or curing means which is illustrated as a single device 41 where photosensitive films 11, 11 are dried or cured.

In the event only one surface of the web, say the left vertical surface with respect to Figure 1, is to be coated, roll 15 operates as an idling backup roll and gravure roll 25 is moved out of operative engagement with roll 15.

It is noted that pneumatic devices not shown, are provided to adjust and maintain operating pressures between gravure rolls 24, 25 and coating rolls 14, 15 as well as pressure between the latter and web 10. The speeds of rolls 14, 15, 24, 25 are controlled and maintained individually. Either contact or meniscus transfer may be used for pickup of solution by web 10 and/or by coating rolls 14, 15. Nozzle means 28 and blade 22 may be connected to form a subassembly that is oscillated parallel to the longitudinal axis of blade 22. Similarly, another oscillating subassembly may be formed of nozzle means 29 and blade 23.

WHAT WE CLAIM IS:- 1. Apparatus for applying a film of coating solution on to a web substrate of substantially non-porous material, said apparatus including a rotatable gravure roll, first means for supplying the cells of said gravure roll with coating solution and for doctoring solution supplied to said cells, a rotatable relatively smooth-surfaced coating roll operatively positioned to receive solution from said cells, said coating roll having a central portion which is of greater diameter than adjoining end portions of said coating roll, and guide means for directing said web through a transfer region where said web receives said solution from said coating roll and for directing the movement of said web in said transfer region in a direction opposite to the direction of motion of the surface of said coating roll.

2. Apparatus as claimed in Claim 1 in which the web is substantially planer in the transfer region.

3. Apparatus as in Claim 1 or 2 in which the gravure and coating rolls are arranged for rotation in opposite directions.

4. Apparatus as in any of Claims 1 to 3 in which the first means includes a doctor blade operatively positioned adjacent the periphery of the gravure roll.

5. Apparatus as in Claim 4 in which the first means also includes delivery nozzle means distributed along the length of the gravure roll and operatively positioned to direct coating solution to a pool formed through co-operation between the doctor blade and the periphery of the gravure roll.

6. Apparatus as in any of Claims 1 to 5 also including a further rotatable gravure roll, second means for supplying the cells of said further gravure roll with coating solution and for doctoring solution supplied to cells of said further gravure roll, a further rotatable relatively smooth surfaced coating roll operatively positioned to receive solution from cells of said further gravure roll, at said transfer region said web being operatively positioned to receive coating solution from said further coating roll, said web moving in a direction opposite to the direction of motion of the surface of said further coating roll.

7. Apparatus as in Claim 6 in which the web passes between said coating roll and said further coating roll whereby coating solution is placed on both sidcs of said web.

8. Apparatus as in any of Claims 1 to 7 also including dryer means downstream of the transfer region and operatively positioned for said web to pass therethrough.

9. Apparatus as in Claim 7 in which the further gravure roll and the further coating roll are rotatable in opposite directions.

10. Apparatus as in any of Claims 6 to 9 in which the second means includes another doctor blade operatively positioned adjacent the periphery of the further gravure roll.

11. Apparatus as in Claim 10 in which said second means includes another delivery nozzle means distributed along the length of the further gravure roll and operatively positioned to direct coating solution to another pool formed through co-operation between the another doctor blade and the periphery of the further gravure roll.

12. Apparatus as set forth in Claim 6 in which at said transfer region the web is in a plane perpendicular to a plane passing between rotational axes of said coating roll and said further coating roll.

13. Apparatus as claimed in Claim 6 substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. may be connected to form a subassembly that is oscillated parallel to the longitudinal axis of blade 22. Similarly, another oscillating subassembly may be formed of nozzle means 29 and blade 23. WHAT WE CLAIM IS:-

1. Apparatus for applying a film of coating solution on to a web substrate of substantially non-porous material, said apparatus including a rotatable gravure roll, first means for supplying the cells of said gravure roll with coating solution and for doctoring solution supplied to said cells, a rotatable relatively smooth-surfaced coating roll operatively positioned to receive solution from said cells, said coating roll having a central portion which is of greater diameter than adjoining end portions of said coating roll, and guide means for directing said web through a transfer region where said web receives said solution from said coating roll and for directing the movement of said web in said transfer region in a direction opposite to the direction of motion of the surface of said coating roll.