Die coaters

Feed liquid is spread across die coaters, slot and extrusion coaters, slide and many curtain coaters by chamber-and-slot distribution. The liquid is introduced into a chamber or manifold as long as the coating is to be wide, which delivers the liquid in turn to a narrow slot through which it flows to an exit aperture where it may be applied to a substrate, turn and run down an apron or slide, or fall free as a curtain. 

As a general rule of thumb, the doctor blade coater or knife coater and the "comma coater" or other round-bottomed coating tools are used for the manufacture of tape thicknesses from 50 to > 1000 pm (0.002 to > 0.040 in.). When thinner coatings are required, the industry has turned to lip coaters, microgravure coaters, and slot-die coaters. The lip coater is used to make multilayered ceramic capacitor tapes for thicknesses of 50 pm (0.002 in) or less. For tape thicknesses 25 pm (0.001 in.) and less, the microgravure and slot-die techniques have been used very effectively. 

A) Roll coater B) Slot die coater O Extrusion die coaler a) Chill roll b) Rotating rod... 

There are two types of coating dies In the slot die coaters the coating is pressed onto the substrate. The thickness of the layer is controlled by the gap between the die lips and the web, which is backed by a steel or hard rubber roller. At the forward lip there may be a rotating rod to reduce stripes caused by particles. The pressure improves the contact of the adhesive to the substrate. The thickness of the coating is influenced by the web thickness. Further details are given in [261]. 

In the extrusion die coater, the coating layer is formed and calibrated in the slot and laid down on the substrate. The thickness is independent of the web thickness and can be reduced by stretching. There is no penetration through open substrates like fribrics, and there is no influence of particles on the coating. Good contact to the substrates can be provided by an air knife or an electrostatic field. 

Application Equipment. Depending on melt viscosity and on the nature of the adhesive applications, various types of equipment are available. These include pressure nozzle, print wheel, doctor blade, calender, die-coater, fountain coater, and extrusion coater. Where high strength, high viscosity products are involved, equipment is now available with closed or pressurized melting zones plus screw feed to the point of application. Applicators using strands of adhesive fed to a melt zone just before application are also suitable. 

There are many excellent manufacturers of equipment for application of hot melt adhesives and coating systems by many different ways in different physical forms. These include high and low pressure applicators, extruders, slot die coaters, roll coaters, pattern coaters, nozzles, wheels, guns, spray applicators, and foam applicators. The following are some of the major manufacturers of these types of equipment. No intent is made to exclude any manufacturer. However, in the interest of space the following are offered for consideration ... 

Water based pessure sensitive adhesives can also be directly appHed on to the substrate web using a slot die coater (Fig. 8-12). Die coating is widespread in the USA (est. 60-70 % of total label production), but is only used occasionally in Europe. 

In most coatiag operatioas a single layer is coated. Whea more than one layer must be appHed one can make multiple passes, or use tandem coaters where the next layer is appHed at another coatiag statioa ioimediately foUowiag the dryer sectioa for the previous layer, or a multilayer coatiag statioa can be used. Slot, extmsion, sHde, and curtain coaters are used to apply multiple layers simultaneously. SHde and curtain coaters can apply an unlimited number of layers simultaneously, whereas slot and extmsion coaters are limited by the complexity of the die internals. 

The released intermediate is pumped from the stainless steel transfer vessels through a slot (extrusion) die situated within the coater/dryer/laminater (coater). The released intermediate, with active uniformly dispersed, is pumped through... 

EQUIPMENT IDENTIFICATION Mixer manufactured by (vendor), with an approximate volume of 20 Gallons Coater/Dryer/Laminator manufactured by (vendor), Slitter/Rewinder manufactured by (vendor) and, Pouching Machine (with Die Cutter) manufactured by (vendor). Equipment numbers are identified in the appropriate section of this document. 

Fig. 4.11 Production slot die tape caster, ceramic capacitor coater, Model OMD-S/3.5/D/8.5H, Photographs courtesy of Yasui Seiki Company, (USA), Bloomington, Indiana.

Sheet coaters are available to coat individual sheets. Many printing operations and all copying machines are sheet-fed. Sheet coaters are also used as laboratory coaters to develop new products where many different solutions need to be coated and only small volumes of sample are available. These methods use a variety of devices such as draw-down blades, dies, or wire-woimd rods to spread... 

These die or slot systems may be adapted on a roll coater. The opening of the slot may be adjusted very accurately as also the distance between the slot and the sheet and the angle. 

Figure 55 Cartridge style coater showing a slot die coating cartridge - mainly used for water based PSA adhesive (source FAUSTEL Inc. USA).

Roll coater Cl extrusion Cl slot die Cl stencil Cl valve (type) Cl other (spediy)... 

Standard equipment for solution based PSAs are knife over roll and reverse roll coaters (Fig. 15) [255, p. 13 ff]. For high-speed application, a closed reservoir or a slot die is preferred for better control of air bubbles [260]. Especially the knife over roll coater allows for an easy change of the coating material. 

For hot melts, roll coaters and die systems are used (Fig. 16). Typical coating temperatures are in the range of 120-160 °C. 

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