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Thermal Isolation in Die Coating

IP.com Disclosure Number: IPCOM000189209D
Publication Date: 2009-Oct-30
Document File: 3 page(s) / 32K

Publishing Venue

The IP.com Prior Art Database

Abstract

This article discloses mechanical expedients for thermally isolating actuators used to manipulate, e.g. choker bars in the performing of die coating.

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Thermal Isolation in Die Coating

One of the fundamental problems associated with slot-type coaters and extruders, (for, e.g. die coating, hot melt die coating, and film extruding) is that of achieving a uniform flow per unit width across the entire width of the die. All slot-type coaters and extruders have at least one slot, and the narrowest dimension between the two parallel surfaces defining the slot is commonly called the slot height. A fundamental issue in attaining the uniformity of the flow in the cross-web direction, and thus the critical uniformity of the coated product, is the ability to construct a die with the best possible uniformity of the die slot height. It is understood by the art that this sensitivity is greater than linear.

It has long been know to provide die coaters with a slot with a height that is adjustable via a choker bar manipulated by devices that can apply force at multiple points along the die's lateral dimension. One of the earliest embodiments of this concept used a plurality of differential bolts to apply these forces. More specifically, it is known to use bolts with two threaded sections of different pitch to provide both coarse and fine adjustment of the force applied by the bolt to the choker bar. Differential bolts are still the most prevalent means of adjusting a die slot, but they do have limitations, especially when extreme uniformity is required. For example, only one bolt can be adjusted at a time, and can be moved in only limited amount relative to its adjacent neighbor bolts without binding, or even worse damaging the die itself. This is especially inconvenient when, for example, there is a bit of particulate trapped in the slot, causing streaks in the coating.

More recently, other expedients have been developed providing better and more convenient control over slot height. For example, it is known to provide die slots having bolts which use thermal expansion controlled by heaters to provide the adjustment. Another alternative is actuators having piezo stacks that can be manipulated by an applied voltage. More recently, it has been taught that motor control can be applied. For example, see US patent 5,770,129, "Apparatus and method for controlling mass flow in an extrusion die," which discloses control schemes for choker bar and die slot actuation in integration with measurement of the extrudate uniformity. Also see United States Patent 6,106,671, "Intelligent gap control for improved paper machine profile control."

In die coating, the choker bar may be at a high and variable temperature from being adjacent to the material being dispensed from the die. When motorized control of the choke...