Rolling coating systems

E-beam roll coating system LEYBOLD TOP BEAM for the production of transparent barrier coatings on plastic foils for food packaging. 

Figure 6. Reserve roll coating system (System Pagendarm) a) Adhesive...

Roll and coil coating systems utilize liquid coating materials with organic solvents, which must be stored, manifested, and disposed of according to 40 CFR Part 262 if classified as hazardous waste under 40 CFR Part 261. 

The use of roll and coil coating systems leads to pollution prevention over traditional spray application systems due to their higher transfer efficiency (>95%) and lower volatilization of organic solvents. 

Another specialty area is coil coating, which involves coating metal coils by continuous operation. Modern roller systems afford speeds of up to 200 m/min. Most coils are made of cold-rolled and surface treated steel, aluminum, or alloys of the latter with manganese or magnesium. Coating systems are based on alkyd or acrylic resins, oil-free polyester, silicone-modified polyester or acrylic resin, poly(vinylidene fluoride), or poly(vinyl fluoride). Water-reducible systems, mainly based on acrylic resins, have been developed for aluminum as well as for steel coils [21-24], Drying is carried out by continuous operation in gas- or oil-heated multichamber ovens. 

The coat weights are critical for fhe release properties of the liner. They are typically in the 0.7 to 1.0 g/m range and are applied most frequently by multiroll reverse coating systems or by offset gravure rolls. 

Typical of the temporary or manufacturing aid coating systems is the RISTON dry film photoresist for printed circuit (PC) board fabrication. This was the first of these systems developed. The RISTON product structure and the basic steps in its use are shown in Figure 2. It consists of a photopolymer sheet laminated between a Mylar cover sheet and a polyolefin separation sheet. It is manufactured as a continuous web (see Coating processes, survey), and is supplied in rolls of varying width and photopolymer composition. 

Figure 56 Methods of metering (a) Percentage roller metering (b) Coating system with metering roll (c) Dipping and scraping...

Screen coating is described later in this chapter. The system used most widely is reverse-roll coating, which is capable of applying uniform coating of weights ranging from 80 to several hundred g m-2, within limits better than 5% and at speeds up to 150 m min-1. The usual form of the equipment is three-rolls, nip-fed, as illustrated in Figure 108. 

Proper solvent selection ensures that the vinyl-based polymers can be applied via conventional fluid techniques of spread and roll coating, dipping, spraying, brushing, etc. When used alone they behave as conventional lacquers. When used in conjunction with other polymer systems the reactive vinyl polymers permit crosslinking. 

Schematic representaton of die roll-to-roll coating aparatus detail and vacuum system showing the magnetron source in position. 1 = motor, 2 = main drum, 3 = wind-on roll, 4 = wind-off roll,...

Navarrete R.C. 1991. Rheology and Structure of Hocculated Suspensions. [CWM, LES] Chen K.S.A. 1992. Studies of Multilayer Slide Coating and Related Processes. [LES] Cai J.J. 1993. Coating Rheology Measurements, Modeling and Applications. [CWM, LES] Benjamin D.F. 1994. Roll Coating Flows and Multiple Roll Systems. [LES]... 

Fig. 37 Schematic cross section of typical paint systems for steel and galvanized steel (a) automotive coating system including an ED-paint and (b) a coil-coating system for the building industry including a roll-coated paint as corrosion-resistant primer.

The roll mill system consists of a pair of heatable counter-rotating metal cylinders arranged parallel to one other with an adjustable gap, or nip, between them. A pre-mixed feedstock is dropped on these rolls and is drawn into the gap between the two rolls where high-shear mixing occurs. One roll normally turns faster than the other, and because of this speed difference (friction ratio) the shear force is amplified. The feedstock usually forms a coating around the slower roll. 

Multilayer co-extrusion is another technique used in the preparation of starch/ synthetic sheets or films [164, 263-266], in which TPS is laminated with appropriate biodegradable polymers to improve the mechanical, water-resistance and gas-barrier properties of final products. These products have shown potential for applications such as food packaging and disposable product manufacture. Three-layer co-extrusion is most often practiced, in which a co-extrusion line consists of two single-screw extruders (one for the inner starch layer and the other for the outer polymer layers) a feedblock a coat-hanger-type sheet die and a three-roll calendering system [164]. Biodegradable polyesters such as PCL [164, 264], PLA [164, 263], and polyesteramide, PBSA and poly(hydroxybutyrate-co-valerate) [164] are often used for the outer layers. These new blends and composites are extending the utilization of starch-based materials into new value-added products. 

Uses Corrosion inhibitor for oil-, solv.-, or water-based coating systems provides corrosion protection for galvanized metal, phosphated steel, cold rolled steel... 

When large flat surfaces and webs of materials are to be coated, mechanical-roller methods are commonly used to apply a uniform layer of adhesive via a continuous roll. Such systems are used with adhesives that have a long working life and low viscosity. 

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