Why Is It Important to Remove Coagulant from Rubber Film by Leaching ?

Manufacturer: We are manufacturing toy balloons but without leaching. Why is it important to remove the coagulant from the rubber film by leaching ?

John Woon (Senior Latex Consultant): Leaching is important not only for the removal of coagulant salt such as calcium nitrate but also all other hydrophilic chemicals such as naturally present proteins, soaps, KOH, etc. If there is no leaching or the leaching process is not effective, the rubber film would tend to discolour when exposed to warm air, gas fumes and UV light. The physical properties would also be negatively affected due to poor particle-to-particle integration during drying.There is also a tendency for mold and fungus growth and bad odour.

I strongly advise you to install a leaching process in your Production as this would also improve the brilliance of the colour and gloss of your inflated balloons.

Factors Affecting Thickness of Latex Dipped Products

Manufacturer:  I am wondering if you can explain the factors that affect thickness and surface finish of dipped latex articles such as gloves. How can thickness be predicted from material properties?

I imagine factors might include:

- Temperature of latex solution

- Temperature of former

- Airflow for drying

- Concentration of water in latex solution

- Type/concentration of of thickening agent

- Type/use of coagulating agent on former

What affects the outside surface finish, to make it really mirror-smooth or relatively rough?

John Woon (Senior Latex Consultant):  Thickness of latex dipped products depends generally on the following factors:

1) Latex stability against cationic chemicals such as calcium nitrate. The higher the stability, the thinner is the latex gel picked up. The reverse is true. Types of surfactants used is important. Nonionic surfactants as opposed to anionic surfactants would tend to increase the latex stability against calcium nitrate.

2) The age of latex. I'm referring to natural rubber latex. The older the latex the thicker would be the latex dipped product.

3) The higher the former temperature, the thicker would be the product especially when the latex compound is sensitive to heat.

(Latex compounds are normally more heat sensitive when the ZnO and ammonia level are high)

4) The higher the latex solid content (i.e. TSC) the higher would be thickness.

5) The higher the concentration of the coagulant (e.g. calcium nitrate), the higher would be the thickness.

6) If the viscosity of the latex compound is increased by adding a thickener, the product would be thicker.

7) The longer the latex dwell time i.e. the time the former with a coating of coagulant remains immersed in the latex, the thicker would be the product.

To make the surface smooth and shiny, include an extra final dip into a much more diluted latex compound.

To make the surface matt i.e. no more shine and gloss, soak the product in chlorine solution (with about 800 to 1000 ppm of chlorine). The surface after this treatment would appear rough under microscope but not the naked eyes.