To dip-mould thin rubber items such as gloves, balloons and membranes, stabilise liquid latex with ammonia at about 0.6% by volume, add vulcanising agents to make pre-vulcanised latex, dip a clean ceramic, glass or metal form, withdraw it slowly and let it drip and dry. Each dip adds roughly 0.1-0.2 mm, so repeat the dip for a thicker wall, then cure at 100 °C for 30 minutes or sun-cure for 24 hours and peel the film off the form.
Part of Rubber Processing
Building thin seamless rubber items by dipping a form into liquid latex.
A Form Dipped In Latex Makes A Seamless Film
Latex dries into a continuous rubber film on whatever it wets, so a form in the shape of a hand, a balloon or a tube gives a seamless item. The carrier gives the method; Latex Collection and Preservation explains how to keep the latex liquid to start with.
What You Need
- Stabilised liquid latex. The carrier gives ammonia at 0.6% by volume; the strength of the ammonia solution is not given.
- Vulcanising agents, stirred into the latex for pre-vulcanised latex. The carrier does not specify which agents or amounts; see Compounding Recipe for the sulfur, zinc and accelerator system used elsewhere, which may need adapting for latex.
- A clean form of ceramic, glass or metal, shaped like the product.
- A dipping vessel deeper than the form, and a rack to hold it while it dries.
- A curing place: an oven or bath at 100 °C, or a sunny, dry spot.
Method: A Thin Item
Step 1: Prepare the latex with the vulcanising agents.
Step 2: Clean the form and, optionally, powder it so the film peels off later.
Step 3: Dip and withdraw slowly. A slow withdrawal gives an even film.
Step 4: Let it drip and dry on the rack.
Step 5: Dip again for a thicker item. The carrier says each dip adds about 0.1-0.2 mm.
Step 6: Cure. Either heat to 100 °C for 30 minutes, or sun-cure for 24 hours.
Step 7: Peel off the form.
Worked Example
Dips for a target wall. A glove wall of 0.4 mm (illustrative) needs 0.4 ÷ 0.2 = 2 dips at the thick end and 0.4 ÷ 0.1 = 4 dips at the thin end. A balloon of 0.2 mm needs 1-2. A 2 mm inner-tube wall needs 2 ÷ 0.2 = 10 to 2 ÷ 0.1 = 20 dips, which is the number of coats the carrier’s dip-moulded inner tube implies, with a drying interval between dips. The number is a count, not a thickness guarantee; measure a sample wall with a micrometer or calipers.
Common Mistakes
- A dirty form. The film pinholes.
- Withdrawing quickly, which leaves runs and thin spots.
- Dipping before the last coat has set, which lifts it off.
- Skipping the cure, which leaves a weak, tacky film.
Safety
Ammonia vapour and latex allergy
Stabilised latex gives off ammonia, which burns the eyes and lungs in a closed room (recalled general fact, not from the corpus); dip outdoors or in moving air with eye protection, and keep the face away from the vessel. Wearers of dipped gloves and workers dipping them can develop allergic reactions to latex proteins; anyone who develops a rash or wheeze should stop. Curing at 100 °C is a hot-water or oven burn hazard: use tongs.
What’s Next
- Learn next: Tire Basics — inner tubes by dipping
- Combine with: Essential Rubber Products — gloves and medical items