Anti-tack agents

The tendency of sheets of rubber to stick together, dusting and anti-tack agents are used to overcome this problem. 

Wet anti-tack agents can be soap or detergent solutions or suspensions of the dry agents in water. For example, dissolved polymers with non-ionic surface active agents which form a thin layer of polymer on unvulcanised rubber sheets magnesium stearate in water zinc stearate dispersion and aqueous dispersions of fatty acid salts. 

The uncured rubber, or stock, must fulfil several requirements to allow its successful presentation at the injection press. Most injection units are fed with strip rubber. The strip has to be of regular section and appropriate size. It should not be distorted or kinked and it should show little tendency to stick to itself. These are all features that are controlled by the choice of dump mill take-off machinery and selection of anti-tack agents. The latter should add sufficient coating to the surface of the rubber to leave the strip dry and dustless. Commercially available soap solutions have been found to be almost universally suitable for this purpose. 

Preparation of the compound for the moulding process, as for all injection processes, needs to be carefully controlled. The stock needs to be presented to the mould in a clean, fresh state. The strip must be free from excessive amounts of anti-tack agents and should be of a continuous and uniform section that will feed without hindrance into the injection moulding machine screw. If the compound is based on butadiene-acrylonitrile copolymer, or similar polar materials, then it is necessary to ensure that the anti-tack agent used is based on zinc stearate. 

The effect of mean particle size on the rate of dissolution is illustrated in Table 3 for fractions sieved from granulated SMR-5 bale rubber. Particles having a mean diameter of 1 mm are taken up by solvent 5-10 times faster than particles having a mean diameter of 7 mm. A rubber powder prepared from spray dried latex was marketed but proved difficult to produce. A small level of anti-tack agent such as calcium stearate is commonly used to minimize agglomeration during manufacture, and this can usually be ignored. 

Anti-Adhesive, Anti-Blocking, Anti-Tack Agent Foundry Shell Molding Resins Hot Melt Coatings... 

Lubricating and anti-tack solutions are water-based and include a wetting agent (soap or detergent) and a powder such as magnesium silicate, calcium carbonate, etc. 

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