The Dipping Process

Dipping solution Carefully mix equal volumes of solutions I and II immediately before the dipping process. 

Note The full fluorescence intensity usually only develops about 30 min after the dipping process it then remains stable for several days if the chromatograms are stored in the dark (1, 5]. Fluorescein sodium can be employed in the reagent in place of 2, 7 -dichlorofluorescein [5]. The detection limits lie in the lower nanogram to picogram range [1, 5]. 

The dipping processes are of three basic types (1) continuous lengths of strip, wire or tube pass through the molten coating metal (2) semimanufactured products such as cut tube lengths or sheets are dipped into the molten metal in batches in specially designed and automatically operated plants and (3) fabricated products are dipped into the molten metal. 

In situ quantitation The photometric measurement in reflectance was carried out at X = 525 nm (Fig. IB). In order to ensure that the zone coloration had stabilized, scanning was not commenced iintil ca. 30 min after the dipping process. The detection limit for sugars was of the order of 25 ng substance per chromatogram zone. 

The Colton machine illustrated in Fig. 1 is a fully automatic implementation of the dipping process. The steps are as follows ... 

A true solution consists of molecules or ions of a solid substance uniformly distributed throughout a liquid. A rubber solution is colloidal, i.e., intermediate between a true solution and a coarse suspension. Rubber solutions are used as adhesives and in the manufacture of rubber products by the dipping process. 

The dipping process, as the name implies, involves the immersion of a former into either a latex, or a rubber solution, and then its slow withdrawal to leave a uniform deposit on the former. Subsequent processes involve, amongst others, drying the deposit, and curing it, if this is required. 

The use of porous formers in the dipping process, or porous molds prepared from plaster of Paris or unglazed porcelain with a surface pore size smaller than the majority of mbber particles, has been widely adopted in the latex industry. With the porous porcelain formers, the mbber particles are filtered on the surface of the formers. The mbber latex coagulates because of its high concentration to form a film of increasing thickness as more water is absorbed into the ceramic. Its rate of increase diminishes sharply beyond an optimum period of time, however, depending on the various characteristics of the ceramic. 

If the molecules stand on edge and are oriented by the dipping process, there will exist an optical anisotropy which will manifest itself in dichroism or, if the material is thick enough, in birefringence. On the other hand, if the molecules lie flat, no optical anisotropy will be shown when the material is examined by transmitted light. Thus polarising... 

Fundamentals of the various methods of plastisol technology have been considered in a number of papers, nevertheless the theoretical analysis and the construction of mathematical models have not yet been completed so far. The dipping process has been studied in more detail cf.2 6 10). 

The approach to the quantitative analysis and mathematical modelling of the dipping process is based on the solution of the well-known problem of physicochemical hydrodynamics of the thickness of liquid layers retained on the surface of a body removed from the liquid (see, e.g., u,12>). Upon the assumption that the body (support, prototype, mould) is taken out of the plastisol liquid vertically, the general relationships may be written in the following form 2> 7 11"14> ... 

The dipping process is also used for coating metal objects with vinyl plastic. For example, wire dish drainers, coat hangers, and other industrial and household metal items can be coated with a thick layer of flexible vinyl plastic by simply dipping in plastisol and applying fusion. 

The high-tech version of the dipping process used to glaze pottery. 

Adhesion promoters added to the mixture (so-called direct bonding systems such as resorcin-formaldehyde-silica), are advantageous because the dipping process is unnecessary. Disadvantages include the high resin consumption level and the potential elastomer property changes similar to the effects of mold release agents in the mixture [32]. 

Our group initially reported that the average deposition ratio of 7(A) (down stroke) was about 0.5 to 0.7, and the average transfer ratio of 8(B) (up stroke) was about 0.9 to 1.5 (70). Recently, it was found that if the Langmuir films are replaced after only about 50% is consumed in the dipping process (compared to about 90% in the first case), transfer ratios were always between 0.95 and 1.0. Work is presently underway to characterize the optical properties of new bilayer films prepared with transfer ratios close to unity. 

The dipping process is capable of speeding up the coating of relatively large surfaces. Automatic units are the most satisfactory, but hand dipping can also be used to speed up the application of adhesives. The devices used... 

Z-type deposition) [238], In the case of certain substituted monomeric phthalo-cyanines a Z-type deposition is reported [189b, 224,228] while polymeric liquid crystalline polysiloxanes are transferred both on the down- and up-stroke (Y-type deposition) [239], For the dipping process the pH of the subphase and the surface pressure at which the dipping occurs are important variables which must be optimized in order to achieve high quality films. 

The DIP process control was accomplished with a Distributed Control Stystem (DCS) system equipped with an APC algorithm. The controller was set to target 10% nCs in the overhead and 10% /C5 in the product, and would increase reboiler steam and reflux rate until reaching the maximum limits for these flows. The tower pressure was also controlled within a specified range by the APC, and this could indirectly limit the reboiler duty as well, if the tower pressure increased beyond its maximum limit. Inferential estimates for product tCs and Cs qualities were calculated based on tower temperatures and pressures, and a bias for these values was continually updated based on daily laboratory (lab) data. 

Note 2. The Landau-Levich law applies only to conditions where viscosity dominates over inertial terms. This is appropriate for the coating techniques used in the manufacture of spectacles, where the lenses are emersed from a liquid bath at speeds less than 1 cm/s (the dip process). However, for the coating of fibres (fibre finishing), where films may be deposited at speeds of up to 100 m/s, inertial effects come into play as soon as Pi = /2 becomes... 

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