Roll Coaters

The selection of mix ingredients may depend heavily on the type of adhesive applieation equipment used. The main types of equipment for plywood and LVL are roll coaters, spray systems, eurtain coaters, and foam extruders. When foam extruders are used, animal blood and surfactants are usually added to the mill mix. For other application systems, resin producers typieally supply the non-filler additives as part of the resin eomposition. 

Forward approach, to qualitative reliability analysis, 26 984 Forward-roll coaters, 7 12-13 method summarized, 7 5t shear rates, 7 32t Fosamine-ammonium, 13 320 Fosfomycin, bacterial resistance mechanisms, 3 32t... 

Fig. 2. Vacuum processing chamber configuration (a) batch coater (b) load-lock coater (c) in-line coater (d) cluster tool (e) roll coater (batch) and (f) roll coater (air-to-air), [[ccsq]] represents the isolation valve with transfer tooling [[artl]], the motion of fixturing and [[art2]], the access door.

Lay-up proceeds by laying down the veneer which is to be the back surface of the panel. Then a sufficient number of pieces of core veneer are passed through the glue spreader to form the next layer of cross-oriented veneer. The glue spreader commonly used in hardwood plywood manufacture is a roll coater in which a pair of opposing mbber rolls are coated with a thin layer of adhesive. As the veneer is passed between the rolls, the adhesive is transferred to the surfaces of the veneer. Adhesive is applied only to the cross-plies and in sufficient quantity to provide a continuous layer on both opposing faces of veneer. Thus, in the case of a three-ply panel, only the core layer is spread with adhesive and in that of a five-ply panel, the second and fourth layers both of which are cross-plies, are spread with adhesive. Then the top surface veneer, which is normally the decorative surface, is placed on the assembly. 

In hardwood plywood, almost all applicators are roll coater types. In softwood plywood, the large production mills used roll coaters for 50 years or more, but are now moving more and more toward spray applicators and curtain coater applicators. In the southern section of our country where 57 softwood plywood mills are now located and have been built since 1963, approximately one-third of the mills use curtain coaters, one-third use spray applicators and the other third use roll coater applicators. 

Roll coaters can apply a coating simultaneously to both sides of the sheet, while blade coaters generally treat one side at a time and require intermediate drying. Roll and blade systems have been combined in the Billblade coater, which has found use in the production of carbonless copy papers and for paper precoating.224... 

Spraying, dipping, and mechanical-roll coaters are generally used on large production runs. Dipping is also used to cover large areas quickly. Areas that do not require adhesive can be masked off. Manual dipping is often effective and baskets, screens, and perforated drums are available to facilitate immersion of the part into the adhesive bath. 

Floor-mounted roll coaters are noted for their extreme efficiency with large webs and flat sheets. Their waste is also very low, less than 2 percent in some cases. Several types are available because no single model or type of roll coater is best for all the variables of the material surface, coating formulation, and end use. Table 17.2 summarizes the roll coaters that are commonly used, and these are illustrated in Fig. 17.8. 

Kiss No backup roll coater is in light contact with substrate contact is controlled by web tension. Best with adhesives having good flow characteristics and relatively slow drying rates... 

Recently, hot melt PSA systems have been introduced and radiation curable PSA systems are at the commercial development stage. High solids (50%-70% by wt.) nonaqueous dispersion acrylic PSA systems have also been reported(1). Unlike the hot melt and radiation cured systems which require new capital outlay in coating head and/or curing (drying) equipment, BFG has developed PSA systems, based on Hycar 2100R reactive acrylic liquid polymers and isocyanate terminated prepolymer, which can be processed at 80% solids (by wt.) with equipment presently used in the PSA industry, namely, the reverse roll and knife-over-roll coater. 

Figures VI and VII illustrate the initial viscosity of both the Hycar 2103 and Hycar 2106 systems as well as the viscosity increase with time due to the reactive nature of the 2-component system. These figures will help in determining the percent solids necessary for processing on a given piece of equipment depending upon its viscosity handling capability. Since the 100% solids PSA systems have high initial viscosities of over 100 Pa s (100,000 cps), the conventional knife-over-roll and reverse roll coaters can not process them.

Knife Over-Roll Coater Horizontal Pad Coating Floating Knife Coater Extrusion Coating... 

Two areas of major interest in 1955 were paper antiskid and investment castings. Wilson (19) used colloidal silica to increase the friction between paper surfaces. In this application (Figure 2), the silica sol is typically diluted to 1-7% as silica solids and then applied to multiwall bags, corrugated boxes, and linerboards. Various methods of applying the silica sol were used. Typical applicators were sprays, segmented applicator rollers, knife blades, full roll coaters, sponges, and brushes. 

Figure 1. Coil coating operation. Roll Coater, Inc., Kingsbury, Ind. 72 —in. Wean United coil coating line finish coater.

The use of the vinyl polymer in fluid form offers distinct advantages to the manufacturer of vinyl products. The most important obvious advantage is the relatively lower cost of liquid processing equipment and accessories as compared to those required for processing of solid or powder thermoplastics. For example, a spread coating line, for example, knife or roll coater, even with appropriate unwind and takeup accessories, is less expensive than a banbury-mixer-mill calender configuration. 

Taylor (1961) studied experimentally the bubble problem described while, at about the same time, Bretherton (1961) analyzed both theoretically and experimentally the slow motion in a capillary of a long bubble, where differently shaped interfaces at the front and rear menisci have to be considered. If, however, only the front meniscus and the film thickness to a point sufficiently far back of the front are examined, then the configuration is essentially the same as Taylor s. In the bubble problem the characteristic length scale is the tube radius a, and this length corresponds to the half-nip distance in the roll coater problem. Except for the appearance of a natural length scale, all of these problems may be recognized to have the same character as the Landau-Levich... 

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