Coating processes – Falling curtain of coating material utilized
Reexamination Certificate
1997-05-06
2001-05-08
Bareford, Katherine A. (Department: 1762)
Coating processes
Falling curtain of coating material utilized
C118SDIG004
Reexamination Certificate
active
06228431
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a gravure coating feed apparatus and method. More particularly, the invention concerns a gravure coating feed apparatus and method which deposits a uniform curtain-like layer of coating composition to a gravure print surface without producing associated coating effects, such as flow lines and flow patterns.
BACKGROUND OF THE INVENTION
Gravure print surfaces, for instance gravure cylinders, are a common means of supplying liquid compositions to webs. U.S. Pat. No. 4,373,443 describes the use of a gravure cylinder to provide ink in newspaper presses. Engraved upon the surface of the gravure cylinder are cells, which retain the liquid composition after being immersed in the reservoir. A doctor blade scrapes excess liquid composition from the surface of the gravure cylinder, such that the cylinder delivers a precise amount of liquid to a second surface upon contact. A number of distinct feed apparatus types which produce a variety of coating flow patterns are used to coat a gravure cylinder.
One common means of coating a gravure cylinder is a feed pan, similar to U.S. Pat. No. 3,936,549. The pan is constructed to hold a supply of the liquid composition with a means to maintain the liquid level. The gravure cylinder, while partially immersed in the reservoir, rotates to fill the cells and transfer the composition to a web. Drawbacks of the feed pan design include liquid waste due to large holdup volumes and the creation of “flow lines” in the coating. “Flow lines” occur when the gravure cylinder surface initially dips into the liquid composition and contacts a region with impurities. The impurities include air bubbles, globules of concentrated dye and binder, and pieces of partially dried foam. The feed pan design is conducive for the formation of stagnation regions where impurities may form and collect. Experiments with alternative pan designs were unsuccessful in eliminating “flow lines,” particularly at high coating speeds.
An additional common means to coat the gravure cylinder is a reverse doctor-pond feed, as seen in U.S. Pat. No. 4,158,333. The pond feed, which may be open or enclosed, is centered at the nine o'clock position with a reverse angled doctor blade at the seven o'clock position. The reverse doctor blade scrapes the surface of the gravure cylinder as the surface exits the reservoir and the doctored cells pass through three quarters of a rotation before reaching the impression nip. The volatile solvents in the liquid composition remaining in the cells evaporate or “dry in” and create a leading edge pattern on the second cylinder or web. Additionally, foam generation on the pond surface may lead to “flow line” problems as with the feed pan method.
Another alternative apparatus to coat the gravure cylinder is an X-hopper coater, which is an extrusion device. A high degree of accuracy and precision are required to position the device relative to the gravure cylinder. The feed applies a thick (2-5 mils) coating to the cylinder at the three o'clock position. The surface remains wetted until reaching the doctor blade at the standard 10 o'clock position. The disadvantage of the design is primarily the cost associated with constructing a precise metering slot and a high pressure metering pump. The design is also inadequate for startup procedures, where the feeder coats the cylinder while the doctor blade and impression nip are disengaged. Under those conditions the excess coating solution would pool and splash at the hopper's lip.
More recent methods developed to coat the gravure cylinder for thermal donor media melts is the feedbar pond, the patent application for which is pending. It combines a knife coater with a puddle or pond feed with a continuous solution delivery means, an overflow and recycle. The knife or feedbar spacing provides a means for metering the coating of solution on the gravure cylinder, as it exits the bottom of the pond, at an three o'clock position, prior to being doctored off at the 10 o'clock position. The main disadvantages of this device is that at high speeds, the pond becomes turbulent and wavy, forming standing oscillating waves and eddies, which can cause ‘flowline’ defects. It also fails to uniformly wet the gravure cylinder at high speeds and viscosity's due to air entrainment at the air-cylinder-solution interface, causing ‘flowpattern’ defects.
The problems identified and solved by the present invention include an apparatus which supplies a uniform curtain-like layer of coating to a gravure cylinder at high coating speeds. More specifically, the apparatus of the invention supplies a coating solution to the gravure cylinder without coating defects associated with high coating speeds such as ‘flowlines’ and ‘flowpatterns’, and at the same time increases the onset speed of wetting failure due to air entrainment at the cylinder-liquid-air interface. Moreover, the apparatus of the invention reduces waste and costs associated with the gravure coating process.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide a coating feed apparatus that deposits coating composition onto a gravure surface without coating effects such as flowlines and flowpatterns.
Another object of the invention is to provide a coating feed apparatus that delivers coating composition in a curtain-like overflow layer to a gravure surface.
It is a feature of the apparatus of the invention that a reservoir for containing the coating composition includes an upwardly sloped base terminating in an outlet end configured to produce a curtain-like overflow coating layer for deposition onto the gravure surface.
It is an advantageous effect of the invention that when the coating composition is delivered from the reservoir and then deposited onto the gravure surface, coating effects, such as flowlines and flow patterns are eliminated.
Accordingly, for accomplishing these and other objects, features and advantages of the invention, there is provided, in one aspect of the invention, an apparatus for depositing a coating composition onto a gravure surface. A reservoir containing the coating composition includes opposing sidewalls, a rear wall, a base having lateral edges connecting the sidewalls and a first end portion connecting the back wall with the sidewalls. The base slopes upwardly from the rear wall to form an outlet end or weir at a second end portion opposite the first end portion. Further, the outlet end is configured to deliver a uniform overflow curtain-like layer of coating composition from the outlet end or weir onto the gravure surface. In this embodiment, moreover, means is provided for delivering the coating composition in the reservoir through the outlet end. Finally, at least one baffle is disposed in the reservoir downstream of the outlet end. According to the embodiment of the invention, the baffle includes a first portion attached to the base and a second portion directed substantially toward the rear wall of the reservoir.
In another aspect of the invention, a method is provided for depositing a coating composition onto a gravure surface which includes the steps of providing a coating composition, such as coating compositions described in U.S. Pat. Nos. 4,695,287; 4,700,207; and 4,698,651; hereby incorporated herein by reference, and a reservoir having a base sloped upwardly towards the outlet end, the outlet end being configured to form an uniform overflow curtain-like layer of coating composition. Also important to this embodiment is the step of providing means for delivering the coating composition from the reservoir to the gravure surface. Within this step, the coating composition in an uniform overflow curtain-like layer exits the outlet end of the reservoir, across the widthwise lip and finally deposits onto the gravure surface.
REFERENCES:
patent: 1921953 (1933-08-01), Stephens
patent: 2641220 (1953-06-01), Weber et al.
patent: 3339485 (1967-09-01), Rytterholm
patent: 3936549 (1976-02-01), Kohler et al.
patent: 4158333 (1979-06-01), Navi
pate
Fitzgerald Barry Anthony
Lobo Rukmini Bezbaruah
Ruschak Kenneth John
Bailey, Sr. Clyde E.
Bareford Katherine A.
Eastman Kodak Company
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