Browse Prior Art Database

Control of Coating Thickness

IP.com Disclosure Number: IPCOM000047318D
Original Publication Date: 1983-Nov-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 78K

Publishing Venue

IBM

Related People

Schneider, CR: AUTHOR [+2]

Abstract

The thickness (or gloss) of the layer of magnetic recording ink, which is placed on a flexible substrate by the use of the coating head (for example, the one disclosed in U. S. Patent 4,345,543), is closed-loop-controlled by the use of sample-and-hold techniques which are related to the time period which expires between the step of coating the ink and the later step of measuring its thickness (or the step of calendaring the dry coating and the later step of measuring its gloss). The desired characteristic (thickness or gloss) is represented by a DC voltage. A servo system 18 utilizes feedback of a control voltage 24 which is summed with a deviation voltage 17.

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Control of Coating Thickness

The thickness (or gloss) of the layer of magnetic recording ink, which is placed on a flexible substrate by the use of the coating head (for example, the one disclosed in U. S. Patent 4,345,543), is closed-loop-controlled by the use of sample-and-hold techniques which are related to the time period which expires between the step of coating the ink and the later step of measuring its thickness (or the step of calendaring the dry coating and the later step of measuring its gloss). The desired characteristic (thickness or gloss) is represented by a DC voltage. A servo system 18 utilizes feedback of a control voltage 24 which is summed with a deviation voltage 17. When gloss-control is implemented, the coating's gloss is measured, after calendaring, and the servo system's output is used to control calendar pressure, thus providing automatic gloss control (see 116-119, Fig. 1). Fig. 1 is an exemplary coating line having a coating head 10 for placing a liquid coating ink on the top surface of web 12. A reel 11 of polyethylene terephthalate supplies a continuous run of web 12 which extends to take-up reel 15. Coating ink is applied to the web at coating head 10. Thereafter, the ink is dried as web 12 passes through oven 13. The dry ink is then calendared, at 14. Lastly, the web is wound onto take-up reel 15. A thickness gage 16 is located any place in the line after coating head 10, for example, after oven 13. An electrical signal 17 representing the difference or deviation between the actual coating thickness and the target thickness is supplied as an input to controller 18 (see Fig. 3). The output signal 19 derived from controller 18 is applied to control coating station 10 (via a voltage-to-air-pressure transducer when the coating head of U.S. Patent 4,345,543 is used). When signal 17 indicates that the coating thickness is not correct, signal 19 changes in the proper direction to thereby change the coating head's membrane pressure, as described in U.S. Patent 4,345,543. For example, if the layer of dry ink is too thick, the membrane pressure is increased, and the liquid layer placed onto the top of web 12 is accordingly reduced in thickness. Fig. 2 shows controller 18 in block diagram form, whereas Fig. 3 shows the detail thereof. The polarity of signal 17 indicates the direction of deviation from the desired thickness (or gloss) --- for example, signal 17 is of a positive polarity when the coating is too thick, and is negative when the coating is too thin. Signal 17 is applied as one input to summing amplifier 23. The second amplifier input 24 is derived from the second sample-and-hold circuit 25. Signal 19 (which is signal 24 attenuated) controls the coating thickness placed onto web 12 by coating head 10 (by controlling the air-pressure-magnitude applied to the coating head's membrane). At any given time, signal 24 represents the control of coating head 10 which is necessary to achieve the desired coat...