Coating operations sheet

Laminates. Laminate manufacture involves the impregnation of a web with a Hquid phenoHc resin in a dip-coating operation. Solvent type, resin concentration, and viscosity determine the degree of fiber penetration. The treated web is dried in an oven and the resin cures, sometimes to the B-stage (semicured). Final resin content is between 30 and 70%. The dry sheet is cut and stacked, ready for lamination. In the curing step, multilayers of laminate are stacked or laid up in a press and cured at 150—175°C for several hours. The resins are generally low molecular weight resoles, which have been neutralized with the salt removed. Common carrier solvents for the varnish include acetone, alcohol, and toluene. Alkylated phenols such as cresols improve flexibiUty and moisture resistance in the fused products. 

In general, polycarbonate resins have fair chemical resistance to aqueous solutions of acids or bases, as well as to fats and oils. Chemical attack by amines or ammonium hydroxide occurs, however, and aUphatic and aromatic hydrocarbons promote crazing of stressed molded samples. Eor these reasons, care must be exercised in the choice of solvents for painting and coating operations. Eor sheet appHcations, polycarbonate is commonly coated with a sihcone—sihcate hardcoat which provides abrasion resistance as well as increased solvent resistance. Coated films are also available. 

Heating of the surfaces before densification pressures are reached and mass transfers to the core cause the density distribution through the sheet shown in Figure 7. Mass transfer to the core not only adds mass to the core but transfers heat and acts as sorbed material to plasticize core fibers effecting greater density there. Soft surfaces are detrimental to machining and coating operations. 

The main disadvantage is the capital cost of the additional coating operation. Also, the whole sheet must be coated (not a disadvantage in some applications), and tiie complete drying of the ink film under the protective coating requires a long time. 

The immiscibility between both polymers is an important drawback that obliges us to look for a well-balanced set of properties, namely, mechanical, vapor, and gas permeability for barrier applications. Most applications are as multilayer, or sandwich sheet stmctures (polymer A/adhesive layer/polymer B), obtained by coextrusion, lamination or coating operations. The high operation costs associated with these processing techniques and the inability to obtain complex shapes that can expand... 

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... 

In the process of roll coating, a sheet is produced much as in calendering but usually for polymeric solutions. In such flows, surface tension becomes important. Both forward and reverse roll-coating operations are used in practice. The important work by Coyle et al. [84—86] has done much to increase our understanding of the fluid dynamics in both forward and reverse roll coating. The reverse process is schemat-... 

To an experienced operator trained in the handling of industrial chemicals, the dimers present Httle cause for concern in handling or storage. The finished polymer coating presents even less of a health problem contact with the reactive monomer is unlikely. In the ancillary operations, such as cleaning or adhesion promotion, the operator must observe suitable precautions. Before using the process chemicals, operators must read and understand the current Material Safety Data Sheets, which are available from the manufacturers. 

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