Calcium nitrate as a latex coagulant: how it is used in glove and dipped-rubber manufacturing
Calcium nitrate is the most commonly used coagulant in dipped latex products such as examination gloves. A hand-shaped former is dipped into an aqueous calcium nitrate solution and dried; when it is then dipped into liquid latex, the calcium ions destabilise the latex particles next to the former so they aggregate into a soft “wet gel” film that is later dried and cured into the glove.[1][2][7] Published patent examples use roughly 250–300 g/L calcium nitrate in a first coagulant dip and 300–400 g/L in a second, both at 60–75 °C.[8] Gloves are the best-documented use, but the same coagulant-dip principle applies to other dipped latex goods.[18]
Key facts at a glance
| Item | Value / answer |
|---|---|
| Role in the process | Coagulant (electrolyte) that makes latex particles aggregate on the former surface[2][7] |
| Form used | Aqueous solution of calcium nitrate, applied to the former and dried before the latex dip[7][8][9] |
| Example concentration, 1st coagulant dip | 250–300 g/L calcium nitrate (patent example)[8] |
| Example concentration, 2nd (stronger) dip | 300–400 g/L calcium nitrate (patent example)[8] |
| Example dip temperature | 60–75 °C for both coagulant dips (patent example)[8] |
| Latex solids in the dip tank | About 10% solids, per Cambridge glove-dipping research[7] |
| Film stage formed on the former | “Wet gel” — weak, water-containing film, later consolidated and dried[2][3][4] |
| Common latex types | Natural rubber latex and synthetic nitrile (acrylonitrile-butadiene) latex[2][19][20] |
| Alternative calcium salt | Calcium chloride, also studied for glove latex[5] |
| Compound identity | Ca(NO3)2; Wikipedia lists latex coagulation among its industrial uses[1][17] |
What a latex coagulant does
Liquid latex is a stable colloid: tiny rubber particles are kept apart by surface charge and surfactant. To build a thin solid film on a mould, that stability has to be broken exactly where you want rubber to deposit. A coagulant is an electrolyte that does this. Calcium nitrate supplies divalent calcium ions (Ca2+) that diffuse out of the dried coating on the former into the latex, and where their concentration is high enough the particles flocculate and stick to the former.[2][4] The nitrate ion is the soluble, non-chloride counter-ion that carries the calcium.[1]
The coagulant-dipping process, step by step
The sequence below is the published, generic coagulant dipping route used for thin examination gloves.[7][8]
- Clean the former. Ceramic hand-shaped formers are washed and conditioned.[8]
- Coagulant dip. The former is dipped in an aqueous solution containing calcium nitrate (commonly with a wetting agent and an anti-tack/release agent).[7][8][13]
- Dry. The coagulant layer is dried onto the former so a defined amount of salt sits on the surface.[7]
- Latex dip. The former is dipped into a dilute latex compound (about 10% solids). The coagulant diffuses into the latex and a wet-gel layer builds up; thickness grows with dwell time.[2][4][7]
- Optional second coagulant dip and second latex dip for layered or thicker products; the second coagulant is typically more concentrated to speed gelation and bond the layers.[8]
- Leach, dry and cure. The film is leached to remove residual salts, dried and cured, then stripped from the former.[7][13]
Typical concentrations and temperatures
| Parameter | Published example | Source |
|---|---|---|
| Calcium nitrate, first coagulant dip | 250–300 g/L | Ansell patent US8192834[8] |
| Calcium nitrate, second coagulant dip | 300–400 g/L | Ansell patent US8192834[8] |
| Coagulant dip temperature | 60–75 °C | Ansell patent US8192834[8] |
| Older example: concentrated vs dilute coagulant | 43% calcium nitrate solution on the cuff, 8.6% on the hand portion | US3859410 (1975)[16] |
| Latex solids content | ~10% | Cambridge IEEF[7] |
These are examples from patent literature, not a recipe. Real lines tune concentration, temperature and dwell for the latex grade, glove thickness and former speed, and often use calcium carbonate or stearate as a former-release agent alongside the coagulant.[10][13] Always develop your own set-points on your own line.
Why calcium nitrate rather than another salt
- Very high water solubility — roughly 1,200 g/L at 20 °C for the anhydrous salt — so strong coagulant baths can be made up without precipitation.[1][17]
- No chloride. Calcium chloride is also studied for glove latex,[5] but a chloride-free coagulant avoids chloride carry-over into the product and equipment corrosion in the dip line.
- Divalent cation. Divalent ions such as Ca2+ are far more effective at destabilising latex than monovalent ions at the same molar concentration (the Schulze–Hardy rule of colloid chemistry).
Quality issues linked to the coagulant stage
- Residual calcium nitrate on the glove. Leaching must remove it; a 2020 Moratuwa study links residual calcium nitrate/calcium ions and release agent to a “wet look” defect in thick nitrile gloves.[13]
- Uneven coagulant film. Non-uniform coagulant deposition gives thickness variation and pinholes; pinhole testing is a core acceptance test for examination gloves.[6][15]
- Insoluble particles in the coagulant tank deposit on formers and become defects — the practical reason a fully soluble salt matters.
- Dipping-tank coagulum. Coagulated latex in the dip tanks is scheduled waste in Malaysia and must be disposed of or recycled under regulation.[11]
Regulation and standards context
In the United States, patient examination gloves are regulated medical devices under 21 CFR 880.6250,[12] and nitrile examination gloves are commonly tested to ASTM D6319 for dimensions, physical properties and freedom from holes.[15] Natural rubber latex gloves carry a protein-allergy risk that NIOSH has documented, which is one reason synthetic nitrile latex is widely used.[14] The coagulant is a process aid; its residue is controlled through leaching and final-product testing.
What to ask a calcium nitrate supplier for latex dipping
- Calcium (Ca) and nitrogen content, and the hydrate/moisture form, so you can dose accurately by calcium.
- Insoluble residue (should be zero or near zero) — request a Certificate of Analysis per batch.
- Chloride, sulphate and heavy-metal limits that match your product specification.
- Whether a pH-adjusted or additive-ready blend is needed, since coagulant baths may be pH-adjusted.
- A sample for a small-scale dip trial before committing a line.
When calcium nitrate is NOT the right choice
- As a drop-in without a trial. Coagulant concentration, additives and leach conditions are line-specific; run a pilot first.[8][13]
- Foam, cast-film or non-dipped latex processes that coagulate by heat or acid rather than ionic dipping are different routes.
- If your specification demands low-chloride, trace-metal-controlled or pharma-grade salt you must confirm the exact limits in writing before ordering any grade.
What HRSU supplies — and what it does not
HRSU Indore supplies fertilizer-grade calcium nitrate powder: 18.5–19% calcium, 15.5% minimum nitrogen, 100% water-soluble with 0% insoluble residue, with a Certificate of Analysis for every batch. That solubility profile is what a coagulant make-up tank needs. HRSU does not claim this grade is certified for any glove or medical-device specification — share your coagulant bath specification (limits for chloride, heavy metals, insolubles) and request the TDS and a sample so you can validate it on your own line.
Sample calcium nitrate for your coagulant bath
100% water-soluble · 0% insoluble residue · 25 kg & 50 kg bags · bulk/export available.
Buy online WhatsApp usFrequently asked questions
What does calcium nitrate do in latex gloves?
How much calcium nitrate is used in a coagulant dip?
Patent examples cite roughly 250–300 g/L for a first coagulant dip and 300–400 g/L for a second, at 60–75 °C. Actual values are tuned per line, so treat these as published examples, not a specification.[8]
Is calcium nitrate used for nitrile and natural rubber latex?
Why not use calcium chloride instead?
What defects can the coagulant cause?
Can HRSU calcium nitrate be used as a glove coagulant?
HRSU supplies a 100% water-soluble, 0%-insoluble-residue calcium nitrate powder with batch COAs. It is sold as fertilizer grade, so confirm your specification limits and run a trial before production use.
Related guides
- Uses of calcium nitrate: the complete guide
- Calcium nitrate vs calcium chloride
- Calcium nitrate as a concrete accelerator
- Buying bulk calcium nitrate from India
References
- Calcium nitrate (PubChem compound summary) — U.S. National Library of Medicine / NCBI. Government database
- The coagulant dipping process of nitrile latex: investigations of former motion effects and coagulant loss into the dipping compound (Groves et al.) — Soft Matter, Royal Society of Chemistry, 2023. Peer-reviewed
- Mechanisms of electrolyte (coagulant) dipping for thin nitrile gloves — PubMed, U.S. National Library of Medicine. Peer-reviewed (PubMed record)
- Film deposition and consolidation during thin glove coagulant dipping (Groves et al.) — Journal of Polymer Science Part B: Polymer Physics, Wiley, 2017. Peer-reviewed
- Multifunctional role of calcium chloride in improving the chemical, mechanical, and physical properties of natural and synthetic rubber latex for gloves and transdermal patch films — Elsevier / ScienceDirect. Peer-reviewed
- Comparison of test methods for pinhole and non-uniform defects in nitrile examination gloves — Polymer Testing, Elsevier. Peer-reviewed
- Rubber gloves: the dipping process — Innovation and Enterprise Research Group (IEEF), University of Cambridge. University research
- US 8,192,834 B2 — Production of gloves and other articles of flexible polymer material (Ansell Healthcare Products) — U.S. Patent and Trademark Office, via Google Patents. Patent
- US 7,048,884 — Production of gloves and other articles of flexible polymer material — U.S. Patent and Trademark Office. Patent
- CA 2128670 — Canadian patent summary (glove manufacture) — Canadian Intellectual Property Office, Government of Canada. Patent
- Utilization of waste from natural rubber glove manufacturing line (Devaraj et al.) — ASEAN Journal on Science and Technology for Development, 2017. Peer-reviewed
- 21 CFR 880.6250 — Non-powdered patient examination glove — U.S. Electronic Code of Federal Regulations. Government regulation
- Investigation of the effect of mold releasing agent and residual calcium nitrate/calcium ion of nitrile higher mil gloves to wet look defect (Weerakon, 2020) — University of Moratuwa, Sri Lanka. University thesis
- NIOSH Alert: Preventing allergic reactions to natural rubber latex in the workplace (DHHS/NIOSH 97-135) — U.S. Centers for Disease Control and Prevention / NIOSH. Government
- ASTM D6319-19 — Standard specification for nitrile examination gloves for medical application — ASTM International. Standard
- US 3,859,410 A — Manufacture of gloves, such as surgical gloves, from latex — Google Patents. Patent
- Calcium nitrate — Wikipedia. Encyclopedia
- Dip moulding — Wikipedia. Encyclopedia
- Nitrile rubber — Wikipedia. Encyclopedia
- Latex — Wikipedia. Encyclopedia