Forming Film from Liquid Latex
Safety. Liquid latex concentrates carry ammonia odor, freeze risk, and metal-fitting hygiene. Coagulant dips use calcium salts as plant tools. Natural-rubber protein and accelerator chemistry can matter for skin contact; that is literacy, not a wear certificate. See Allergy and Skin Contact and Liquid ventilation and ammonia.
Executive summary
This pathway starts with liquid latex, an aqueous colloidal dispersion of polymer. You form a film by dipping, casting, or spreading, then you may join or finish that film.
A film from raw latex is not a saleable article until it is compounded. Elastomeric latex typically includes vulcanization. A vulcanized film is expected to stretch to at least twice its length and recover.
Use this when you are depositing latex from a bottle or tank onto a former, mould, or bed. For how to pick a forming method, see Former dip, mould cast, and flat spread. For bottle fields, see Decoding liquid latex bottle labels.
What is in the bottle
What is liquid latex?
In the handbook sense, latex is a colloidal dispersion of polymer in a mostly aqueous liquid. Rubber particles float in water with ammonia as the usual preservative. That is not the same thing as a solvent cement, and it is not automatically a finished film.
ISO 2004 specifies ammonia-preserved centrifuged or creamed natural-rubber concentrate (types include HA and LA; the 2024 edition also names MA). ASTM D1076 covers concentrated, ammonia-stabilized NR latex categories and does not apply to compounded concentrates.
A consumer bottle labeled “liquid latex” is not automatically D1076 concentrate. Read polymer family, solids, and whether the liquid is prevulcanized. See Decoding liquid latex bottle labels.
What is vulcanization?
Vulcanization crosslinks rubber so the film becomes elastic and durable. Uncured latex is weak and sticky. Vulcanized latex stretches and recovers. ISO 1382 language defines a state of the rubber, not a forming method.
How the film is formed
Film-making splits by where the deposit lives.
Dipping. Immerse a former (the shape you dip), withdraw a deposit, repeat for thickness, then leach, dry, and vulcanize as the process requires. Named types: straight (simple) dipping, coagulant dipping, heat-sensitized dipping, and electrodeposition.
A straight dip without coagulant usually leaves a very thin dry deposit per pass. Handbook data cluster around 0.01–0.05 mm for a single dip, so multi-dip builds thickness. Holes in one layer are unlikely to line up with holes in the next.
What is a coagulant?
A coagulant is a chemical, often a calcium salt (calcium nitrate or calcium chloride) or an acetic or formic acid, applied to the former so latex gels on contact. Most dipped articles with dry film thicker than 8 mils use coagulant because the film builds faster. Coagulant is a dip-line tool.
What is leach?
Leach is a warm-water wash that pulls soluble chemicals out of a wet dipped film. Industrial lines treat it as required for coagulant-dipped products.
Casting. Plaster moulds gel latex by water absorption plus calcium ions. Metal moulds need heat-sensitized latex. Slush (fill, gel, pour out) and rotational (meter and rotate) are separate subprocesses. See Heat-sensitized gelation.
Spreading. Lab work spreads compounded latex on glass with a wire-wound knife. Industrial patents describe spreading vulcanizable latex on a conveyor, coat after coat, with drying between. See Home-cast latex film.
A 1932 process map already listed spreading, dipping, electrodeposition, chemical deposition, and foam as distinct routes.
Plant discipline that travels
Equipment that touches latex must be free of copper, brass, or galvanized iron. Rotate formers 180–360° after a dip so the wet film does not run. Air in the compound makes pinholes; plants reject those. The handbook’s humidity window is about 20–26 °C and 45–50% RH.
Former glaze gives shiny dipped goods. Bisque or sandblast gives dull.
Exam-glove thickness often runs 0.10 mm at the cuff to 0.20 mm at the fingers. That is glove geometry.
Gloves are about half of natural-rubber latex consumption in the Practical Guide’s dipping chapter. That is industry mix, not a hobby business case.
Prevulcanized vs post-cure
Prevulcanized latex is vulcanized in the liquid without waiting for moisture loss. A proper prevulc can approach conventional post-dry properties. The handbook cites about 4,000–5,000 psi tensile when particles integrate on drying. Overcure makes a short, weak deposit.
Gloves from prevulcanized latex need only be warm-air dried. Historical wording: where vulcanized latex is used, deposit and dry; products from natural latex are ordinarily vulcanized after they are formed.
The optimum crosslink band for prevulcanized films differs from postvulcanized films. Tensile maxima sit at a lower relaxed modulus for prevulc deposits because high crosslink can interfere with particle integration on drying.
A film from raw latex still needs compounding. Post-form vulcanization of a dried compound is a separate branch (handbook example: air-dry, then circulating warm air at 93 °C).
In the Practical Guide’s casting section, strength is always low for film prepared from prevulcanized compound. That is the book’s casting-section context. It sits next to Vanderbilt’s “proper prevulc can approach conventional properties” for the prevulc definition chapter. Keep the two loci labeled.
Do not treat “I bought a bottle” as “this is prevulc, so drying finishes it.” See Prevulcanized consumer latex.
Polymer family mix-ups
Synthomer SyNovus-class TDS describes coagulant multi-dip nitrile latex. That is a parallel synthetic pathway. Hevea NR concentrate, prevulc NR, and nitrile dip compounds are different polymers. See Synthetic lattices.
REVACRYL-class styrene-acrylic dispersions are the wrong polymer family for prevulcanized NR. Theatrical or construction “liquid latex” that is acrylic is not NR feedstock. Read the polymer family on the TDS.
Historical dipping in cements from rubber and benzene or gasoline is a different process from latex dipping. Latex was described as less expedient because low viscosity needs many dips.
When this pathway fits
You want to form thickness, color, or shape from liquid. Industrial dipping is a plant with formers and named dip types, metal hygiene, leach, and a humidity window. Casting plaster versus metal is a different subprocess. Spreading is another.
Hobby dip and cast inherit metal hygiene (no copper, brass, or galvanized on latex equipment) and the idea of leach for coagulant work.
Once the film exists, joins are a later article: Liquid adhesives and seam integrity. Storage: Liquid aging, storage, and care. Defects: Liquid film defects.
Deep dives (optional)
Deep dive: Industrial dip / cast / spread tree
Thin-walled products are made by immersing a former in compounded latex and withdrawing a uniform deposit. Repeats build thickness. Types named: straight, coagulant, heat-sensitized, electrodeposition. Latex polymer need not be masticated, so it retains high molecular weight versus dry-rubber processing.
Single dips are very thin unless viscosity is high. Gorton data on three NR compounds: dry deposit about 0.01–0.05 mm per single dip. Thickness increases approximately linearly with log(viscosity) when solids and viscosity are co-varied by dilution. Condoms are a named multi–simple-dip product, commonly two dips.
Plant dipping: mechanical stability, predictable precure (handbook chloroform-number example 2–3), wet-gel strength, air-free compound. Dilute with deionized water. Wet-gauge levers: percent total solids, coagulant strength, dwell, viscosity, and withdrawal speed. Webbing leaves a weak spot when the web breaks.
Casting: plaster uses absorption plus calcium ions. Metal moulds need heat-sensitized latex. Prevulc is preferred for some solid articles (you can skip product vulcanization) but the casting section calls that film strength always low.
Lab spreading: Anode (coagulant then latex) versus Teague (latex first); leach 20–30 min at 40–50 °C. Historical industrial spreading on a conveyor, successive coats with drying between.
Deep dive: Prevulc tank and TDS films
Handbook prevulc example: about an hour at 79 °C under atmospheric pressure. Carried beyond a low combined-sulfur figure, the deposit is short and weak. Clarify (centrifuge) to remove excess sulfur and zinc oxide for storage.
Postvulcanized NR latex films: tensile maximum near relaxed modulus about 0.8 MPa. Prevulcanized NR latex films: maximum at about 0.4–0.5 MPa. High-crosslink drop in prevulcanizates is likely particle-integration failure on drying.
PVultex TDS: LA prevulcanized NR, dipping uses, TSC about 60%, frost-sensitive. A Revultex distributor TDS lists dipped articles and cold casting, with example ASTM D412 films at 0.12–0.15 mm. Those thicknesses are glove-class films.
US 3,755,232 (hydrogen peroxide / activator prevulc) lists adhesives, coatings, dips, threads, and foams. Sulfur, zinc oxide, and accelerators may still be added for additional film cure.