Pigment and Filler Compounding for Liquid Latex
Safety. Pigments and fillers change what can extract at the skin and how the film ages. A food-contact colorant list is not a wear certificate. Copper and manganese consume antioxidant. This page is compounding literacy, not a home recipe card.
Executive summary
Color and opacity in a film you cast or dip start in the compound, before the film forms. Dyes and pigments sit with sulfur, zinc oxide, accelerators, clays, and antidegradants as optional elastomer-phase modifiers. Insoluble powders and oils have to be dispersed or emulsified first or they shock the latex. Fillers raise modulus and can cut stretch; some polymeric fillers raise tear and set. Metal in a pigment speeds aging.
Use this when you are tinting a batch, chasing opacity, or someone proposes dumping dry craft pigment into the bottle. Brush-on color is a different class: see Painting vs Compounding Pigment. Stiffness as a fit lever sits in Gauge, Modulus, and Reduction.
Compound before the film forms
A film from raw latex is not a finished article until it is compounded. Color is part of that package, not a coat you add after cure.
What is compounding?
Compounding is mixing latex with curatives, fillers, pigments, and protective chemicals while it is still liquid. You tint the batch, then cast or dip. The pigment particles sit inside the rubber network as it forms.
Industrial aqueous pigment dispersions marketed for rubber latex (vendor TDS will say so) are the documented tint path. Dry powder, oil colorants, and mineral fillers each have a prep rule. See the buckets.
Pigment and filler buckets
Think in prep form, not brand names.
| Bucket | What it is | Prep before the latex | What goes wrong |
|---|---|---|---|
| Aqueous pigment dispersion | Pre-ground pigment in water with dispersants | Add when the compound is already stable | Vendor TDS may list rubber latex |
| Dry pigment powder | Water-insoluble powder | Grind to a dispersion under 5 µm | Undispersed powder shocks the colloid and leaves weak spots |
| Oil-phase colorant | Immiscible liquid or low-melt solid | Make an oil-in-water emulsion first | Poor emulsion leaves oil spots on the film |
| Mineral filler (clay, whiting, talc) | Cost, opacity, stiffness | Slurry in water plus dispersant | Modulus goes up; keep load low for a soft film |
| Polymeric filler (high-styrene SBR latex) | Separate emulsion-polymer particles | Add as a latex | Tear often rises; so do modulus and set |
Insoluble solids and immiscible liquids must be dispersed or emulsified before they meet the latex, or colloidal stability is upset.
What is a dispersion?
A dispersion is solid particles ground into water with a wetting aid so they stay apart. The handbook target is under 5 µm (many industrial dispersions have 90% at or under 2 µm). Check with a Hegman grind gauge. Remix before every weigh-up; settled pigment is not the same batch.
What is an oil-in-water emulsion?
An oil-in-water (o/w) emulsion is oil broken into tiny droplets in water with soap or a dedicated emulsifier, so the oil can enter the latex without floating out. A drop of good emulsion disappears in a beaker of water. A bad one leaves an oil slick. Homogenize at or below 38°C. Casein-thickened mixes have a swell window around 54–71°C; miss it and the emulsion fails.
What does phr mean?
phr means parts per hundred rubber: 5 phr zinc oxide is 5 parts ZnO per 100 parts dry rubber. Tables sometimes write pphr. Adhesive tables may use pphp (parts per hundred polymer). Same idea, different denominator.
Concrete prep. Aqueous dispersion: shake the vendor jug, weigh, add to a stable compound. Dry iron-oxide powder: mill it in water with a dispersant until it passes a Hegman check; do not stir handfuls into ammonia-smelling latex. A liquid dye dissolved in oil: emulsify the oil first, drop-test it, then add. Kaolin or whiting: slurry in water plus dispersant, then add. High-styrene SBR: add as a latex, not as dry crumbs.
Loading you will feel in wear
Fillers trade stretch for stiffness, opacity, or tear.
Mineral clay. A handbook clay series (DIXIE clay, 0 → 50 phr in a CR compound) dropped tensile from 3100 → 1500 psi while stress at 500% stretch rose 500 → 1100 psi. Substantial clay in a soft garment film buys opacity at the expense of hand.
High-styrene SBR filler. At 20 phr in an NR film series, crescent tear rose to 1769 N/cm, 300% modulus to 2.76 MPa, and permanent set to 30%. The handbook flags that modulus rise as a disadvantage for some uses. Tear-first zones might tolerate it; a body-hug panel that must snap back should not treat 20 phr as a default.
What do modulus and permanent set mean?
Modulus is how much force the film takes to stretch a given amount. Higher modulus means a boardier film at the same thickness. Permanent set is leftover stretch after you let go. High set looks baggy after wear.
Adhesive-filler band (same stiffness tension). Mineral fillers in latex adhesives typically sit at 0–30 pphp. Higher load cuts tack and raises stiffness. That is an adhesive table, not a garment recipe, but the stiffness-versus-extensibility tension is the same.
Metal impurities and aging
When copper protection is needed, use 2 phr total antioxidant: conceptually one part against ordinary oxidation and one against the metal. Coarse or settled dispersions leave unprotected patches. Spec-grade NR concentrate limits copper and manganese at 8 mg/kg solids (ISO 2004). Pigments, dyes, and fillers can put those metals back in.
A “cheap pigment” is an identity-bucket risk. Raising antioxidant without changing the dirty pigment is only partial cover. Pair this with Antidegradants in DIY Compounds and Aging, Storage, and Care.
Decision cues
Tint in the compound when you need batch color match, opacity, or a tear tweak from a polymeric filler, and you can run dispersion or emulsion prep.
Use an aqueous dispersion made for rubber latex when a vendor TDS lists that use. Add it after the cure package is stable.
Stop and remake the prep if you see oil spots, grit, or a suddenly thick, shocked compound. Those are colloid failures, not “stir harder.”
Deep dives (optional)
Deep dive: High-styrene SBR polymeric filler
NR latex base (100 dry), KOH 0.5, sulfur 1, activated dithiocarbamate 3, ZnO 5, octylated diphenylamines 1; high-styrene SBR copolymer latex at 0 / 10 / 15 / 20 phr; vulcanize 15 min at 93°C. Plant example, not a home mixing card.
| phr filler | Modulus 300% (MPa) | Tensile (MPa) | Eb (%) | Tear (N/cm) | Set (%) |
|---|---|---|---|---|---|
| 0 | 0.90 | 28.6 | 880 | 1156 | 6 |
| 10 | 2.07 | 30.0 | 800 | 1489 | 20 |
| 15 | 2.41 | 30.7 | 760 | 1664 | 22 |
| 20 | 2.76 | 26.9 | 730 | 1769 | 30 |
Deep dive: Dispersion and emulsion prep
Dispersions. Anionic or nonionic wetting aids (DARVAN-class in the handbook). Pebble mill at about 50% media charge. Target under 5 µm. Hegman draw-down around 30% total solids. Remix before every weigh-up. Overgrinding can agglomerate particles again.
Emulsions. In-situ soaps or DARVAN ME / WAQ. 2–10% extra oil in the oil phase often helps stability. A 65% antioxidant emulsion example uses phase inversion, then homogenize at or below 38°C. Drop-test on water.
Deep dive: Mineral clay direction
CR 750 compound with DIXIE clay at 0 / 25 / 50 phr (cure 60 min at 127°C): tensile 3100 / 1800 / 1500 psi; stress at 500% 500 / 600 / 1100 psi. Direction (modulus up, tensile down) is the teaching point. Absolute psi will not match a hobby cure.