Platinum catalysts are highly effective but also sensitive. Their high activity is an advantage; their sensitivity to the environment is a weakness. In practice, many production failures are not caused by defective catalysts, but by handling errors.

This article compiles the most practical operating tips and common troubleshooting experiences from frontline production to help avoid common pitfalls.

1. Storage: Three Do’s and Three Don’ts

Three Do’s

1. Keep sealed. Platinum catalysts must be stored in sealed containers to avoid air exposure. Moisture and oxygen in the air can gradually reduce catalyst activity and shorten shelf life.
2. Protect from light. UV light can decompose platinum complexes. Store in opaque containers, or wrap transparent containers in aluminum foil.
3. Store at low temperature. The recommended storage temperature is 10–20°C, sealed and protected from light. Some high-concentration products are better stored at 4°C. Under proper storage conditions, shelf life can reach 6–12 months.

Three Don’ts

1. Do not contact strong oxidizers. Platinum in these catalysts is in the zero-valent state and can be oxidized and deactivated by strong oxidizing agents.
2. Do not contact sulfur-, nitrogen-, or phosphorus-containing materials. Keep storage areas away from rubber products (containing sulfur vulcanizing agents), amine chemicals, phosphorus flame retardants, and similar substances.
3. Do not use beyond shelf life without verification. After expiration, catalytic activity may drop significantly. If use is necessary, perform a small-scale activity test first: run a cure test with a standard formula, and continue use only if the curing time at 120°C increases by no more than 15%.

2. Mixing: Temperature Is Critical

The most important principle for platinum-cured systems is temperature control.

Key mixing practices

1. Mixing temperature must not exceed 40°C. This is a strict rule. Above 40°C, the inhibitor begins to lose effectiveness, platinum catalyst activity is released, and the compound may start to cure locally during mixing—commonly called “scorch” or “dead rubber”—resulting in scrap. During hot seasons, open mills must have cooling water fully engaged.
2. Follow the correct mixing sequence. First, soften the base compound (roll gap 4–6 mm). After cooling below 40°C, add the platinum catalyst and crosslinker. Finally, add inhibitors, color paste, and other functional additives, then pass through the mill 2–3 times before sheeting off.
3. Use separate tools for Component A and Component B. Tools used for Component A and Component B must be strictly separated, or thoroughly cleaned before switching. Cross-contamination causes local gelation and affects normal use.
4. Use mixed material promptly. Two-component platinum-cured compounds should be used within 48 hours at room temperature; otherwise, room-temperature crosslinking will harden and ruin the material. One-component delayed-action catalyst systems have longer pot life (3–6 months); refer to the product datasheet.

3. Molding: Five Key Parameters

1. Compression molding

• Mold temperature: 120–180°C, adjusted according to part thickness and hardness.
• Cure time: thin-wall parts (<2 mm) about 2–3 minutes; thick-wall parts (>5 mm) about 5–10 minutes.
• Typical platinum catalyst dosage reference: about 0.6% for 30° Shore A, 0.8% for 50° Shore A, 1.0% for 70° Shore A, and 1.5% or above for 80° Shore A and higher. Fine-tune according to the actual formula.

2. Extrusion

• Extruder temperature zones: feed section 30–40°C (to prevent scorch), plasticizing section 40–50°C, die head 50–60°C.
• Oven/curing tunnel temperature: front section 120–140°C (low-temperature setting), middle section 160–200°C (main cure), rear section 120–150°C (stabilization).
• Line speed: thin-wall small tubing (1–2 mm) can reach 10–20 m/min; thicker products require lower speeds.

3. Injection molding (LSR)

• Components A and B are mixed at a 1:1 ratio through a static mixer.
• Mold temperature: 150–200°C.
• Cure time: typically 10 seconds to several minutes, depending on part size.
• Safe pot life after mixing: about 7 days at 23°C.

4. Inhibitors: The “Brake System” for Platinum Catalysts

Inhibitors are essential auxiliaries in platinum-cure systems. Their main function is to temporarily “block” platinum catalytic activity at room temperature, extending working time. When heated to the curing temperature, the inhibitor volatilizes or dissociates, allowing platinum to regain activity and complete cure rapidly.

Common inhibitor types

• Ethynylcyclohexanol (ECH): The most widely used inhibitor. Thermal release temperature is 80–110°C. It leaves no residue and does not yellow, making it the preferred choice for medical and electronic silicones. Typical dosage is 0.1–0.8% of total system mass.
• 3-Methyl-1-butyn-3-ol (MBI): Release temperature is 70–90°C. Lower cost; suitable for general industrial silicones.
• Maleate esters: Provide very long inhibition periods, suitable for long-storage two-component AB systems. May cause slight yellowing at high temperatures; not suitable for optical applications.

Inhibitor dosage adjustment principles

• Need longer working time → increase inhibitor dosage slightly (by 0.1–0.3% each time).
• Cure speed too slow → reduce inhibitor dosage.
• High ambient temperature → increase inhibitor slightly (heat accelerates reaction).
• Low ambient temperature → may reduce slightly.

5. Six Common Faults and Troubleshooting

Fault 1: No cure or incomplete cure

Possible causes:

• Inaccurate A/B ratio.
• Platinum catalyst deactivation (expired or improperly stored).
• Excessive inhibitor.
• Poisoning (sulfur-, nitrogen-, or phosphorus-containing substances in the environment).
• Insufficient cure temperature.

Troubleshooting: First run an independent control cure test to rule out ratio and catalyst issues. Then check the environment and raw materials for poisoning sources.

Fault 2: Rapid gelation at room temperature (dead rubber)

Possible causes:

• Mixing temperature exceeded 40°C.
• Insufficient inhibitor.
• Excessive platinum catalyst.
• Cross-contamination between Component A and Component B.

Solutions: Increase ECH dosage by 0.1–0.3 percentage points; confirm mixing temperature; check whether tools were mixed.

Fault 3: Tacky product surface

Possible causes:

• Insufficient cure temperature or time.
• Surface contact with sulfur- or nitrogen-containing substances (e.g., rubber gloves, epoxy work surfaces).
• Insufficient Component A (platinum catalyst).

Solutions: Increase cure temperature or extend time; check work surfaces and glove materials; confirm catalyst dosage.

Fault 4: Yellowing

Possible causes:

• Use of Speier-type catalyst (chlorine-containing, prone to yellowing).
• Overcure due to excessive temperature.
• Impurities in the catalyst (e.g., iron ions).

Solutions: Switch to Karstedt- or Ashby-type catalyst; reduce cure temperature; select higher-purity catalyst.

Fault 5: Black platinum black precipitation during reaction

Possible causes:

• Excessive temperature (above 200°C).
• Oxygen ingress.
• Low pH or residual chloride ions.

Solutions: Reduce temperature immediately; exclude air (nitrogen purge); add a small amount of divinyltetramethyldisiloxane or similar ligand to complex free platinum.

Fault 6: Platinum catalyst solution becomes cloudy and loses activity quickly

Possible causes:

• Moisture in solvent.
• Air exposure.
• Excessive storage temperature.

Solutions: Use molecular sieves to dry solvent; store at 4°C in the dark; seal and store under nitrogen.

6. Safety Notes

Although platinum catalysts generally have very low toxicity, basic safety precautions are still required:

• Avoid skin and eye contact. Wear nitrile gloves during handling; do not use sulfur-containing rubber gloves, as they can poison the catalyst.
• Maintain good ventilation in the operating area.
• Platinum catalysts are combustible liquids (flash point >60°C); keep away from open flames.
• In case of eye contact, rinse immediately with plenty of water and seek medical attention.

7. Quick Reference Table

Summary

The key to using platinum catalysts can be summarized in four principles: control temperature and prevent poisoning. Keep mixing temperature below 40°C, avoid contact with sulfur-, nitrogen-, or phosphorus-containing substances, store sealed and protected from light at low temperature, and use mixed material promptly. Mastering these basics prevents most production issues. When problems occur, troubleshoot systematically—check process conditions first, then poisoning sources—rather than blindly increasing catalyst dosage. This approach helps identify the root cause and resolve the issue efficiently.


Diethylenetetramethyldisiloxane platinum complex (platinum catalyst) MY 8113-Mingyi Silicone