Coagulant dipping

Neoprenes. Of the synthetic latices, a type that can be processed similarly to natural mbber latex and is adaptable to dipped product manufacture, is neoprene (polychloroprene). Neoprene latices exhibit poor initial wet gel strength, particularly in coagulant dipped work, but the end products can be made with high gum tensile strength, oil and aUphatic solvent resistance, good aging properties, and flame resistance. There are several types of neoprene latex, available at moderately high (ca 50 wt %) and medium soHds content. Differences in composition between the types include the polymer s microstmcture, eg, gel or sol, the type of stablizer, and the total soHds content (Table 22). 

Ca(N03)2, used in an alcoholic solution in coagulant dipping for the manufacture of latex dipped goods. 

The glove may be built up from multiple dips into various substances. For example, the formers may be initially dipped into a composition of a powder free release agent and a coagulant. Release agent and coagulant dip supply a release material for the subsequent removal of the finished glove from the formers. In addition, the coagulant material will destabilize subsequent liquid resin materials, such as elastomers. ... 

After the release agent/coagulant dip is applied, Ae formers are preferably conveyed to the next station in the production line where the laminate layer is applied to the formers. The laminate layer may be comprised of an elastomeric or liquid resin dip, such as natural rubber latex. Alternatively, the laminate layer may be a natural or synthetic rubber, such as S5mthetic latex, polyiuethane, nitrile or polychloroprene. By varying the content of the latex material, the laminate layer may be varied to provide different degrees of strength, comfort, and flexibility. In any event, the content of the latex applied to the former will preferably be adjusted to provide the desired gripability, protection from cuts and abrasions, and liquid repellency. ... 

The zinc oxide also reduces the colloidal stabihty of the mix and so influences the amount deposited on the former during coagulant dipping. 

The possibility of achieving complete autohesion between two layers of latex films, obtained by means of coagulant dipping method. Is demonstrated. 

Dispersion Resins. Polytetrafluoroethylene dispersions in aqueous medium contain 30—60 wt % polymer particles and some surfactant. The type of surfactant and the particle characteristics depend on the appHcation. These dispersions are appHed to various substrates by spraying, flow coating, dipping, coagulating, or electro depositing. 

The Uniroyal process differs from that of American anode, principally in that the first dip is in the latex compound rather than in the coagulant. The resulting thin mbber film acts as a carrier for a coagulant subsequently absorbed by it. Volatile acids, eg, formic, acetic, or lactic acid, or cyclohexylamine dissolved in alcohol or acetone or both, have generally been used in this process, but in the 1990s water is more commonly used than ethanol. 

For natural or neoprene latex dipping, suitable coagulants are as foUow ... 

In dipping generally, but particularly with the anode process, it is desirable to use tanks that circulate the coagulant and latex compound, particularly the latter. Use of circulation keeps the Hquid surface clean and free from lumps, scum, or bubbles. Mechanical circulation can cause mbber particle instabihty, however, and eventually coagulate the compound. Therefore, tanks should be designed to minimize friction or shear action, and the compound stabilized to maintain mechanical stabiUty. 

Dipped goods are manufactured by dipping a coagulant coated form into a latex compound. The object is then washed, dried, and cured on the form. If a cloth support is used, the coUoidal properties of the compound must be such that mbber wiU adhere to the lining but not penetrate it (166). 

Any substance which will bring about coagulation. In the preparation of natural rubber the usual coagulants are acetic or formic acids. In the manufacture of dipped goods from latex, the coagulant used depends on the method of dipping employed. 

Latex used in the manufacture of dipped goods using a heated former. The latex is heat-sensitised by addition of polyvinylmethyl ether (PVME) or certain polyglycols and the action of the hot former causes a layer of coagulated mbber to be deposited. 

Before World War II, hevea rubber accounted for over 99% of all elastomers used, but synthetic elastomers account for more than 70% of all rubber used today. NR and many synthetic elastomers are available in latex form. The latex may be used, as such, for adhering carpet fibers or for dipped articles, such as gloves, but most of the latex is coagulated and the dried coagulant used for the production of tires and mechanical goods. 

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. 

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