A paint plant, a paper machine, a sawmill line and a machining centre all write the same word on the order form: preservative. They are buying four different things. Under the EU Biocidal Products Regulation (EU) No 528/2012 the same molecule sits in a different product type in each of those plants, is judged against a different dossier, and reaches the market under a different restriction. Dosing by habit, or by price per kilogram, is how a tank of emulsion turns in week three and nobody can explain why.
The four systems we supply for are different enough to need one guide, as long as the questions stay the same: what actually fails, what the matrix does to the active, and what the register allows.
One word, eight product types
Annex V of the BPR splits preservatives by what is protected, not by chemistry. Our range lands in eight of those boxes:
| Product type | What it protects | Where it shows up |
|---|---|---|
| PT6 — Preservatives for products during storage | The wet product, in the container | Water-based paints, adhesives, putty pastes |
| PT7 — Film preservatives | The cured film or coating | Exterior facade paints, roof and render coatings |
| PT8 — Wood preservatives | Wood, from the sawmill stage on | Logs, boards, furniture |
| PT9 — Fibre, leather, rubber and polymerised materials preservatives | Plastics and polymerised materials | Thermoplastics, engineering plastics |
| PT10 — Construction material preservatives | Masonry and composite building materials | Render, texture systems, sealants |
| PT11 — Preservatives for liquid-cooling and processing systems | The water or fluid in the loop | Circulating cooling water, process water |
| PT12 — Slimicides | Slime films on equipment and structures | Paper machine white water, pulp |
| PT13 — Working or cutting fluid preservatives | Metalworking fluid in the sump | Soluble oils, semi-synthetic and synthetic fluids |
The practical consequence is blunt. A supplier who quotes one dose for "our preservative" for both a wall paint and a paper machine has not decided which product type they are selling. The number that matters is not the price per kilogram. It is the grams of active per tonne of product needed for that specific failure mode, and whether that active is permitted there at all.
1. In-can preservation: the wet state is the vulnerable state (PT6)
Water-based acrylic and polyurethane coatings, wood coatings, alkyd emulsions, white latex adhesives and putty pastes are all nutrient broths before they dry. The cellulose thickeners, the protective colloids and the raw water itself carry the inoculum. What fails first is usually viscosity: a spoiled emulsion loses its rheology, then its odour, then its adhesion.
The dose ladder in our coating and building-material range follows the level of protection, not the size of the drum:
| Product | Function edge | Typical dose | pH window | Max dosing temperature |
|---|---|---|---|---|
| YS-704 | Salt-free, headspace protection | 0.05–0.1% | 4–9 | below 40 °C |
| YS-701 | Formaldehyde-free, general in-can | 0.1–0.2% | 4–9 | below 50 °C |
| YS-702 | Formaldehyde-free, copper salt protector | 0.1–0.2% | 4–9 | below 50 °C |
| YS-703 | Headspace protection, cost-optimised | 0.1–0.2% | 4–9 | below 50 °C |
| YS-EPW | In-can plus dry-film fungicidal protection | 0.5–1.5% | 6–10 | below 80 °C |
Three columns cause most of the failures:
- Temperature ceiling. Isothiazolinone actives are thiol-reactive electrophiles; hot, reactive media consume them. Dosing at 60 °C into a batch specified for below 50 °C burns active you have already paid for and leaves a partly protected product. Add the preservative in the let-down stage, after the batch has cooled, under agitation.
- Antagonism. Organic amines, mercaptans, sulfites and other strong reducing agents neutralise the active, which is why every card in this family carries the same warning. It also means the preservative should not go in through the same addition port as an amine neutraliser or a redox-polymerisation reducing agent.
- Salt-free versus standard. "Salt-free" means the blend carries no inorganic salts of the kind some liquid grades use as stabilisers. In an emulsion with a narrow stability window, or where zinc or calcium ions would crosslink the binder, the salt-free grade removes a variable you cannot see in the wet paint but can see in a failed film.
YS-702 deserves its own line: the copper salt protector function exists for formulations that contain copper-bearing components or contact copper. Copper ions catalyse oxidative degradation of the binder and can deactivate some actives, so a blend that tolerates or sequesters them keeps the paint stable and the biocide available.
The reference active behind most in-can blends is 1,2-benzisothiazolin-3-one, BIT, CAS 2634-33-5, C7H5NOS, molecular weight 151.19. Its minimum inhibitory concentrations tell you what it is good at: roughly 25–100 ppm against bacteria, 50–200 ppm against yeasts and 100–400 ppm against moulds. It is stable from pH 2 to 12 and tolerates brief excursions around 150 °C, which is why one active fits both alkaline latex paints and acidic systems. In the EU it is an approved active substance for PT6, PT12 and PT13.
The regulatory cliff worth planning around now is 2-methylisothiazol-3-one, MIT, CAS 2682-20-4. Its approval as an active substance for PT6 takes effect on 1 February 2027. Under CLP it has specific concentration limits: at 0.00015% (1.5 ppm) it triggers the supplementary statement EUH208, and at 0.0015% (15 ppm) it triggers H317, the skin sensitisation hazard statement. Because the BPR bars products carrying H317 from sale to the general public and to non-professionals, a retail DIY paint and an industrial coating have effectively different formulation space at the same active level. If your paint is sold through retail, the MIT content of the blend is a channel decision as much as a formulation decision.
2. The film keeps working after the tin is empty (PT7, PT10)
An in-can preservative is finished the day the paint dries. Mould and algae on a facade are a different problem: they feed on dirt, on leached plasticiser and on the cellulose and starch residues that migrate to the film surface, and the water they need arrives as condensation and rain. The active has to sit in the film, survive UV and rain for years, and resist leaching in the first season.
That pushes the selection towards actives with low water solubility and high photostability. 2-Octyl-4-isothiazolin-3-one, OIT, CAS 26530-20-1, is the standard exterior workhorse: practically insoluble in water, thermally stable, and effective at 0.1–0.3% of formulation. Its antibacterial activity alone is only moderate, around 100 µg/mL MIC against Pseudomonas aeruginosa, but its strength is antifungal and anti-algal, which is exactly the balance a facade needs. Dry-film loads typically run 0.2–1.0% for interior and 0.3–1.5% for exterior and render systems, which is the range YS-EPW occupies at 0.5–1.5%.
Note the pH difference between the two jobs. YS-EPW is specified from pH 6 to 10, while the in-can-only grades cover pH 4 to 9. Alkaline systems are normal for silicate and cementitious building materials, and a blend that also protects the dry film has to stay usable there.
3. Paper and water: you are killing slime, not spoiling a product (PT12, PT11)
On a paper machine the target is not a product in a container. It is a biofilm on the wire, the headbox, the white water tank and the pipe walls — a mixed community of bacteria and moulds held together by extracellular polymer. Slime breaks loose and becomes a hole in the sheet, and it shelters bacteria from whatever you dose next. Water treatment and cooling loops show the same physics at a different scale.
Two consequences shape dosing. The treated volume is enormous, so the numbers are in ppm rather than percent; and dosing is continuous or by slug, not once per batch.
| Product | Position | Typical dose | pH window |
|---|---|---|---|
| YS-601 | Formaldehyde-free pulp preservation | 0.05–0.2% | 2–9 |
| YS-602 | Broad spectrum, closes the Pseudomonas and mould gap of Kathon-type products | 0.05–0.2% | 2–9 |
| YS-DB | Fast-acting biocide for pulp and water systems, slime and spoilage control | 0.05–0.2% | 4–9 |
The Kathon line in the YS-602 description is the most useful buying signal in this family. CMIT/MIT blends are cheap, fast and broadly effective against bacteria, but they have recognised weak spots, notably against some Pseudomonas species and against moulds, and a paper system is exactly where those organisms dominate. A second active with a different mechanism closes the gap. The same logic explains why a mill that switches to a cheaper single-active product starts seeing slime on a monthly cycle instead of a quarterly one.
For bench-marking a programme, the two workhorse actives in this segment behave like this. DBNPA, 2,2-dibromo-3-nitrilopropionamide, CAS 10222-01-2, runs 10–20 mg/L as a shock dose in circulating cooling water, 30–40 mg/L as a slime stripper and 1–4 mg/L in paper fresh water over a three-hour treatment. THPS, tetrakis(hydroxymethyl)phosphonium sulfate, CAS 55566-30-8, runs 200–400 ppm at the wet end of a paper machine and 50–150 ppm in cooling towers, is stable from pH 2 to 10, and degrades to THPO rather than persisting. Notice that pH matters more than the headline dose: DBNPA performs poorly in alkaline water, and paper systems drift alkaline.
4. Wood and plastics: pH 12, 150 °C and a cationic active (PT8, PT9)
Wood and plastic protection is an in-service problem. The treatment has to survive weathering and wet-dry cycling and, for plastics, the compounding and moulding step itself. That produces two very different specifications inside one family.
YS-MKT is the high-stress grade: salt-free, stable from pH 3 to 12, thermally stable to 150 °C with the recommendation to add below 120 °C. That headroom is what allows in-process protection during wood-plastic composite manufacture and use in thermoplastics and engineering plastics, where the biocide is added before or during extrusion. Typical dose is 0.1–0.2%.
YS-ACQ is the treatment-bath grade for logs, boards and furniture, applied by spraying or soaking at a 0.5–1.5% dilution. Its active is didecyldimethylammonium chloride, DDAC, CAS 7173-51-5, C22H48ClN, molecular weight 362.08 — a C10 dialkyl quaternary ammonium compound with markedly higher biocidal efficacy than the mixed C12–C18 benzyl quaternaries used in general disinfection. DDAC has been an approved active substance for PT8, wood preservatives, in the EU since 1 February 2015; its approvals for PT6, PT10, PT11 and PT12 were still under evaluation, so confirm the specific product type before writing one into a specification.
The instruction to dilute freshly and keep the working solution sealed for short periods only is not a storage detail — it is the chemistry of a cation. DDAC is a cationic surfactant. Nearly every other component of a treatment bath, including anionic wetting agents, soaps, lignosulfonate carriers and anionic dispersants, will complex with it and precipitate, taking both the biocide and the wetting performance out of the bath. Mix in the wrong order, or leave a diluted bath standing where it can pick up anionic contamination, and you get a cloudy bath and a poorly protected board.
5. Metalworking fluids: the sump is a bioreactor (PT13)
A water-miscible cutting fluid at a 20:1 dilution is warm, aerated, carries tramp oil as a carbon source and is topped up with fresh water daily. It is close to an ideal growth medium, and the consequences are specific: bacteria produce the rotten-egg odour and split the emulsion, moulds form slime that blinds filters and blocks lines, and both cause operator dermatitis. Sump life is the economic measure of a preservative programme, because cleaning, disposal and refill cost far more than the biocide.
| Product | Active on the card | Strength | Typical dose | pH window |
|---|---|---|---|---|
| YS-MK | 1,2-Benzisothiazolin-3-one, CAS 2634-33-5 | Heat-resistant, salt-free, cost-efficient bacterial control | 0.1–0.2% | add below 80 °C |
| YS-HEY | Sodium pyrithione, CAS 3811-73-2 | Fungal control, closes the Kathon gap against Pseudomonas and mould | 0.1–0.3% | 2–11 |
Two addition rules follow from the chemistry rather than from the label.
BIT is the efficient bacterial answer. It is formaldehyde-free, works from pH 2 to 12, and in metalworking fluids is used at 0.05–0.2%, which lines up with the 0.1–0.2% on the YS-MK card. The temperature instruction is the one to enforce: dosing into a cooled sump keeps the active in the fluid instead of reacting it away.
Sodium pyrithione is the fungal answer. Its activity profile is genuinely complementary — MIC around 256 ppm against Pseudomonas aeruginosa, 128 ppm against Aspergillus niger, 256 ppm against Fusarium species and 64 ppm against Cephalosporium — which is why a Kathon-type programme that looks adequate on plate counts still grows mould. The published EPA directions for sodium pyrithione in metalworking fluids give an initial dose equivalent to 50 ppm of the powder followed by 25 ppm maintenance every 7 to 10 days, or, on newer labels, up to 1250 ppm in the diluted fluid with typical levels of 200–500 ppm. Three handling facts come with it: it photodegrades, so it belongs in opaque packaging; below pH 4.5 the sodium salt is in equilibrium with free pyrithione, which is still active but very unstable in light and air; and oxidising agents convert it first to dipyrithione, which remains microbiologically active, and then to pyrithione sulfinic and sulfonic acids, which are not. Do not pair it with peroxide or hypochlorite boosters, and do not expect it to hold in a loosely covered sump in daylight.
Monitoring is part of the programme, not an audit of it. Weekly dip-slide counts with corrective action at 105 bacteria/mL and 102 fungi/mL, a daily refractometer check for evaporation losses, and a weekly look at tramp oil, pH and odour will tell you which of the two actives you are short of long before the sump smells.
What to put on the purchase order
Every failure described above is preventable at the ordering stage. Seven lines are enough:
- Application and product type. Name the system and the BPR product type. "Preservative" is not a specification; PT6 and PT13 are.
- Measured pH window of the matrix. Not the pH of the preservative, and not the pH of the water. A grade specified from pH 4 will not protect a system that drifts to 10.
- Maximum process temperature at the point of addition. Then confirm that the addition point really is downstream of it.
- Target dose and the active content behind it. A 0.2% dose of a 20% active blend is 400 ppm of active. Ask for the active content and dose on active, not on product.
- The antagonism list for your own formula. Check every amine, sulfite, mercaptan and reducing agent in the recipe against the preservative before you scale up.
- Salt-free and formaldehyde-free requirements. These are not marketing. Salt-free matters for emulsion stability; formaldehyde-free matters for indoor air and eco-label schemes.
- Active substance CAS numbers, not "Mixture". Where our card lists a single active — DDAC 7173-51-5, BIT 2634-33-5, sodium pyrithione 3811-73-2 — the register check is straightforward. For the blend products the card correctly shows "Mixture"; the individual actives and their concentrations still exist and you need them from the COA and the SDS, because the CLP classification, the H317 question and the product type approval all hang on the individual actives, not on the blend.
For the consumer-facing side of the same question — pH, compatibility and the challenge test in a personal-care or household formula — see our earlier guide to preservative systems for home care and personal care. That article works through PT6 for cosmetic-adjacent products; this one covers the industrial product types, and the two sets of actives only partly overlap.
Supply
All twelve products are in stock and shipped worldwide from our Shanghai facility:
- Coating and building material: YS-701, YS-702, YS-703, YS-704, YS-EPW
- Papermaking and water treatment: YS-601, YS-602, YS-DB
- Wood and plastic: YS-MKT, YS-ACQ (didecyldimethylammonium chloride, CAS 7173-51-5)
- Metalworking fluids: YS-MK (1,2-benzisothiazolin-3-one, CAS 2634-33-5), YS-HEY (sodium pyrithione, CAS 3811-73-2)
Send us the matrix, the pH and the process temperature and we will confirm the grade and the dose before you place the order.