FAQs

Zinc stearate based antitacks have been in use in the dry rubber industry for over a century, and is preferred due to its easy availability in the market, competitive pricing and easily available; besides it has the advantage of a lower melting point of 115-116 deg C. This lower melting point allows the zinc stearate to completely melt into the rubber/polymer and leaves very little or no trace of powder marks; if the dosage is correctly applied. Too much will render the polymer with some degree of dust or migration to surface as a waxy substance/layer.

It is most likely due to other Suppliers not having this knowledge about zinc stearate being a better antitack as explained in Q1 above.Or it could be that most glove manufacturers are not being fed the right information, thinking that Zinc is a heavy metal, and poses environmental hazards.

This may not necessarily be true. The amount of antitack used in the coagulant is only 1.5-2% (for zinc stearate based antitack), and bulk of the powder is absorbed into the polymer(rubber), and the discharge/effluent is very low, compared to the amount of zinc based accelerators used in the latex compounding process. Using zinc stearate based antitack will give a”real” powder free feeling in NR gloves, and its lower melting point at 115 deg C is an advantage as glove curing temperature is 150 – 160 deg C.

Contrary, calcium stearate melting point is around 165 deg C, and is higher than the temperature of curing of the latex glove. This may cause more powder to be retained on both formers and glove surface. Most glove producers using calcium stearate based antitack faces a serious former fouling problem, foemrs gets very dirty and brownish very fast, and poses a difficult task of cleaning of the formers, not to mention high cost of cleaning chemicals used.

There are a few options available; magnesium, potassium and aluminium or ammonium stearate based antitacks.

Choice depends on price, availability and ease of supply in Asia. Magnesium Stearate based antitacks are slightly more expensive, due to less supply and availability. Main advantage is it is USP grade and locally available if there is substantial interest.

Stearate scan be made from 2 main processes: dry fusion method and direct precipitation method; and also the stearic acid used can be made from palm/vegetable based stearic acid or animal/tallow based. Each grade will have its different properties, and also prices.

Dry fusion powder processed antitacks have a bigger particle size ranging from 30-45 microns, while direct precipitation grades are much finer and have a narrower distribution base, normally 1-5 microns.

Potassium Stearate is soap, and have surfactant properties, and it is partially soluble in hot water. This is an advantage when former cleaning is concerned. The dosage used in a potassium stearate based powder free coagulant ranges form 1.2 – 1.5% (as compared to 2.2 -3.0% for a calcium stearate based antitack). Less dosage means also less powder is deposited onto the formers, and being partially soluble in hot water, the formers are basically also self cleansing in the hot water, with a bit of surfactant added inside wash tanks.

In the long run, glove manufacturers save a lot on paying for expensive former cleaners as well as prolonging the life span of the formers, and cost savings on downtime when performing frequent “off-line former cleaning”

The only shortfall of using a potassium stearate antitack is pH sensitive and extra care have to be taken to ensure during addition of acidic Calcium Nitrate, pH of coagulant should stay above 8.