A 45% OIT product looks like one product and is really three different things depending on the carrier behind it. The carrier decides which systems it can go into, how it must be added, what it contributes to VOC, and how it behaves after six months in a drum. This article is the practical companion to our OIT technical article: how to tell a solvent-borne grade from a water-based dispersion, how to add each one without shocking the binder, how to convert a target active level into grams of product, and how to diagnose the four failures that show up in the plant.
1. The one-line test: what the water content tells you
The specification line that separates the two product types is water. A solvent-borne 45% grade carries a limit of about 1.0% water and a density of 1.02 – 1.05 g/mL. A water-based dispersion cannot be 45% active and still be a clear liquid, because OIT is only sparingly soluble in water; dispersions are typically 20 – 30% active and opaque, and their water content is above 40%.
| Observation | Solvent-borne 45% | Water-based dispersion 20 – 30% |
|---|---|---|
| Appearance | clear, yellow, viscous | opaque, milky to off-white |
| Water in the product | ≤1.0% | 40 – 60% |
| Density | 1.02 – 1.05 g/mL | close to 1.0 g/mL |
| Active per kilogram | 0.45 kg | 0.20 – 0.30 kg |
| Freeze sensitivity | do not freeze, but no ice formation in the carrier | freezing can break the dispersion irreversibly |
| VOC contribution | yes, from the carrier | minimal |
| Goes naturally into | solvent-borne alkyd, epoxy, PU, high-solids, plastics, adhesives | water-borne acrylic, styrene-acrylic, vinyl |
If a supplier offers “45% OIT” with a water content above 5%, the product is either a dispersion mislabelled by active content, a solution in a water-miscible solvent that has picked up moisture, or a blend. Ask for the carrier identity and the water figure before quoting.
2. Adding a solvent-borne grade to a water-borne system
This is the operation that produces most complaints, and it fails for a physical reason rather than a chemical one. The solvent carrier is not miscible with the latex in the sense that matters: adding it neat to a polymer dispersion locally strips surfactant from the particle surface, which produces grit, a viscosity shift or a broken emulsion.
| Step | What to do | Why |
|---|---|---|
| 1. Pre-dilute | dilute the OIT-45 in a water-miscible solvent or in a portion of the paint’s own let-down solvent, with stirring | reduces the local solvent concentration at the point of contact with the latex |
| 2. Add slowly | add the pre-dilution under shear, below 40 °C, at the let-down stage | avoids local over-concentration and thermal stress |
| 3. Check stability | hold a sample for 24 h and for 2 weeks at 40 °C; check grit, viscosity, gloss and pH | latex shock may not appear immediately |
| 4. Confirm efficacy | run a film challenge test on the finished paint | the active must still be available at the surface |
For solvent-borne systems the operation is simpler: add at the let-down stage under low shear, after pigments and driers are dispersed, and never into a mill base at high temperature. Adding the active early in a bead mill exposes it to local heat and to freshly generated pigment surfaces, both of which reduce what survives into the film.
3. Compatibility matrix
| System | Solvent-borne 45% OIT | Water-based dispersion | Watch for |
|---|---|---|---|
| Solvent-borne alkyd | good, natural fit | usually unsuitable – brings water into a water-free system | driers, especially metal soaps, can interact with the active |
| Water-borne acrylic / styrene-acrylic | workable with pre-dilution and stability test | good, natural fit | latex shock, grit, gloss loss |
| Epoxy, two-pack | good in the resin side | not normally used | amine hardeners are nucleophiles and consume the active – add to the resin component, not the hardener |
| Polyurethane | good | limited | residual isocyanate and amine catalysts react with the active |
| High-solids and 100% solids | good, but viscosity rises | not suitable | dosage on a solvent-free basis changes the effective concentration |
| Silicate and high-pH binders | avoid – alkaline hydrolysis | avoid | ring opening at high pH; choose a different active family |
| Plastics and plastisols | good, direct addition to the plasticiser or polymer | not typical | process temperature and plasticiser compatibility |
The epoxy and polyurethane rows deserve emphasis. Amine hardeners and amine catalysts are exactly the nucleophiles that open the isothiazolinone ring, so adding a film fungicide to the hardener component guarantees a measurable loss before the coating has even cured. Add to the resin side, verify by assay if the batch is critical, and never assume that a visually acceptable film means the active survived.
4. Converting a target to grams: three worked calculations
Dosing is expressed on active ingredient. At 45% active, one gram of product delivers 0.45 g of OIT, so the conversion is the target mass divided by 0.45.
| Target | Active needed | OIT-45 needed | Check |
|---|---|---|---|
| 150 ppm active in 1,000 kg | 150 g | 150 / 0.45 = 333 g | 0.033% of batch weight |
| 200 ppm active in 1,000 kg | 200 g | 200 / 0.45 = 444 g | 0.044% of batch weight |
| 300 ppm active in 5,000 kg | 1,500 g | 1,500 / 0.45 = 3,333 g (3.33 kg) | 0.067% of batch weight |
Two handling cautions follow from the density. The product is around 1.03 g/mL, so one litre weighs about 1.03 kg and carries about 0.46 kg of active – if a plant doses volumetrically using the nominal density, a batch-to-batch density drift of 0.01 g/mL produces a 1% assay error, which is tolerable; measuring by eyeball in a jug is not, because the liquid is viscous and drains slowly. Weigh the product into a pre-diluted premix.
5. The four failures seen in the plant
| Symptom | Likely cause | Evidence | Fix |
|---|---|---|---|
| Haze or cloudiness in the concentrate | moisture pick-up above the 1.0% limit; incompatible carrier | water content of the drum contents vs the COA | keep containers closed, use within the campaign, reject drums with visible haze |
| Phase separation or sediment in the drum | carrier incompatibility, low-temperature exposure, or a dispersion rather than a solution | appearance at the top and bottom of the drum | homogenise and re-assay; if it recurs, change supplier or form |
| Grit or viscosity jump after addition to a latex | latex shock from neat solvent addition | compare with a pre-diluted addition trial | pre-dilute, add slowly under shear, below 40 °C |
| Mould on the film despite the correct dose | active consumed by amines or metal ions, or lost to leaching, or uneven distribution | film challenge test on the finished paint; assay of a solvent extract | change addition point, check the hardener and drier system, consider a partner active |
6. What the carrier means for VOC and labelling
The solvent carrier is part of the formulation’s volatile content and must be counted in the VOC calculation and in the label. At a typical dose of 0.04 – 0.05% product in the paint, the carrier contribution is small but not zero, and in low-VOC or ecolabel products even that small addition can push a formulation over a threshold. In those cases the water-based dispersion, despite carrying less active per kilogram, is the correct choice – not because it is more effective, but because the carrier is compatible with the label claim. This is a case where the technical optimum and the commercial optimum genuinely differ, and the label wins.
7. Storage and drum management
Store between 5 °C and 35 °C in the closed original container, out of sunlight, away from oxidisers, food and feed. Do not allow to freeze. Because the product is hygroscopic enough that repeated opening in a humid room can push water toward the limit, manage drums on a first-in-first-out basis and keep partial drums sealed with a tight bung rather than a cloth. A drum that has been open for a season should be re-assayed for water content before use in a critical batch. Consult the SDS for the flash point of the specific carrier before bulk storage, because flammability classification follows the carrier and not the active.
8. FAQ
Can I dilute OIT-45 with water before adding it?
No. The active is not water-soluble; adding water to the concentrate will produce a hazy or separated mixture rather than a usable dilution. Pre-dilute in a water-miscible solvent when the destination is a water-borne system.
Why is the product viscous?
Both the active and the carrier are high-viscosity materials at ambient temperature. It is normal and is the reason the product should be weighed or pumped with equipment sized for viscous liquids rather than metered like water.
Can I use the same grade in a solvent-borne and a water-borne paint?
Not without work. The solvent-borne 45% grade is the natural choice for solvent-borne systems; for water-borne paints a dispersion avoids the latex-shock risk and the VOC contribution.
How do I know whether the active survived my process?
Extract the active from the cured film or from the wet paint and assay it by HPLC, or run a film challenge test. A visually acceptable film tells you nothing about the active content.
Does the carrier affect the dry-film properties?
It can, through plasticisation and through compatibility with the binder. At typical doses the effect is small, but in high-solids and 100% solids systems it should be checked with hardness and blocking tests.
Conclusion
Carrier first, dose second, addition point third. A 45% solvent-borne OIT is the right product for solvent-borne systems, plastics and adhesives, and a workable one for water-borne paints only with a pre-dilution and a stability test. Determine the dose by film challenge test, convert it to grams by dividing by 0.45, weigh rather than measure, and add to the resin side of two-pack systems. For the chemistry and the family comparison see the OIT technical article, for active selection see dry-film preservative selection, and for the specification of our grade see the OIT-45 product page.