Coatings continued applications

Mat and continuous glass fibre reinforcements theoretically all the thermoplastics are usable in these forms, but up to now developments have concentrated on polypropylenes (PP), polyamides (PA) and thermoplastic polyesters (PET) fibre-reinforced PEEK, polyetherimide (PEI) and polyphenylene sulfide (PPS) are used for high-performance applications. They are presented in a range of forms from stampable sheets to pellets, prepregs, ribbons, impregnated or coated continuous fibre rods. More rarely (as in the case of PA 12, for example), the thermoplastic is provided in liquid form. 

In the thermoplastics area, precipitated calcium carbonate is principally used in PVC applications, a market with which it has been associated since the early days of the polymer. Despite some erosion by coated natural products, the combination of small particle size and fatty acid coating continues to give a unique blend of properties in both unplasticised and plasticised PVC formulations. The advantages include easier processing, better surface finish, good low temperature properties and resistance to crease whitening and to scratching. 

Electrode. Preparation and Behaviour of Continuously Deposited Mercury Coatings and Applications to Stripping Analysis. Anal Chem. 33, 1201 (1961). 

The subcoat is an adhesive coat on which the smoothing coat can be built. A second purpose of the subcoat is to round off the sharp corners of the tablet to produce a smooth surface. The subcoat is a mixture of a sucrose solution and an adhesive gum, such as acacia or gelatin, which rapidly distributes over the tablet surface. A dusting follows each application of solution with a subcoat powder containing materials such as calcium carbonate, calcium sulphate, acacia, talc and kaolin that help to produce a hard coat. The application of the subcoat continues until the tablets have a rounded appearance and the edges are well covered. 

Emulsion polymerization is similar to suspension polymerization in the sense that the reaction also takes place in the presence of a water phase and the applied monomer forms a second liquid phase. However, in this case the added radical initiator is not soluble in the monomer droplets but in the water phase. To allow the monomer to come into contact with the initiator an emulsifier is added to the reaction mixture that creates micelles in the systems. By diffusion processes both monomer molecules and initiator molecules reach the micelle. Polymerization takes places and a polymer particle suspended in the water phase forms that is much smaller than the original monomer droplet (see Figure 5.3.12 for a graphical illustration of these steps). At the end of the overall emulsion polymerization process, all monomer droplets have been consumed by the polymerization reaction in the micelles. Typical emulsifiers for emulsion polymerization are natural or synthetic detergents, such as, for example, sodium palmitate or sodium alkyl sulfonates. Emulsion polymerization is very versatile and is applied for many polymers [e.g., PVC, styrene copolymers, poly(methacryl esters)] in batch, semi-continuous, and continuous processes. In some cases, the obtained polymer particles in water are directly applied as technical products for coatings, lacquer applications, or as adhesives. In other cases the formed product is further treated to obtain the dry polymer. Note that the aqueous phase in emulsion polymerization always contains some isolated emulsifier and also some monomer. Moreover, the formed polymer contains the emulsifier as impurity. 

TABLE 9.1 Properties and Applications of the Main Metallic Elements Used for Protective Coatings (Continued)... 

TABLE 9.6 Limits and Applicability of the Main Advanced Techniques for Producing Metallic Coatings Continued)... 

Table 7.1 Applications of Vacuum-Deposited Coatings (continued)...

The result showes that Tw/Td is independent of solvent s density. Snbstitnting polymer density pp and eoneentration c into Eq(4), we have Tw/Td for the speeifie polymer as a function of c. We can then calculate the wet thiekness of coatings needed to cast films with desired thickness. From simple calculation one knows, for example, 385 micron thick coating is needed to prodnce dry BPSH-35 films (with density of 1.34 g/cm ) with thickness of 50 micron if 20% (w/v) casting solution is used. It is assumed that the concentration of somewhere between 10% and 30% would be suitable for our continuous application. 

Emulsion polymerization also has the advantages of good heat transfer and low viscosity, which follow from the presence of the aqueous phase. The resulting aqueous dispersion of polymer is called a latex. The polymer can be subsequently separated from the aqueous portion of the latex or the latter can be used directly in eventual appUcations. For example, in coatings applications-such as paints, paper coatings, floor pohshes-soft polymer particles coalesce into a continuous film with the evaporation of water after the latex has been applied to the substrate. 

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