How to choose the vulcanization system of silicone gel: platinum, peroxide, and condensation type

Why can some silicone be used in food and medical applications, while others can only be used as industrial components? The difference often lies not in the base rubber itself, but in the vulcanization system. The by-products, odor, transparency, and anti pollution ability of the three mainstream systems are completely different. If you choose the wrong one, all the process parameters will have to be overturned and restarted. This article explains how to distinguish and choose among the three.

Peroxide vulcanization: large quantity, cheap, but requires "post-treatment"

The most common organic peroxides are bis (2,4) (DCBP) and bis (2,5) (DBPMH). Heating decomposition generates free radicals, which crosslink the molecular chains of silicone rubber.

Advantages: The formula has a high tolerance. Not as sensitive to impurities in the substrate and environment as platinum, it is not easily "poisoned"; Low cost; The molding process is mature, and the vast majority of solid silicone parts follow this path.

Shortcoming: Decomposition produces by-products. Double 24 will produce chlorine containing decomposition products, and the byproduct of double 25 is acetophenone substances - this is the source of the odor in many ordinary silicone parts. So products vulcanized with peroxides usually require post vulcanization (usually 200 ℃ × 2-4 hours) to drive out volatile substances, and the transparency is not as good as that of platinum systems, making it impossible to make highly transparent parts.

Suitable for: industrial seals, buttons, shock absorbers, kitchenware (after completion, food contact testing is required), and all scenarios that do not require extreme transparency and low odor.

Platinum vulcanization: clean, transparent, and resistant to dirt

Addition reaction, platinum as catalyst, hydrogen containing silicone oil and vinyl silicone oil are added and crosslinked. In theory, there are no small molecule byproducts.

Advantages: low odor, high transparency, good physical properties; Fast vulcanization speed, suitable for injection molding (LSR); No need to sulfurize for a long time to remove odor. Platinum sulfide is also a common choice for medical implant grade and high-end food contact parts.

Fatal weakness: Catalysts are prone to "poisoning". Compounds containing nitrogen, sulfur, phosphorus, and tin (organotin) can inactivate platinum, resulting in non sulfurization of the rubber material or surface stickiness. Common sources of pollution include dust or contact with sulfur-containing rubber (natural rubber, nitrile), talcum powder on certain gloves, uncured epoxy or polyurethane, residual soldering flux, certain tapes and inks.

So the production line of platinum rubber material is usually physically separated from the sulfur-containing rubber production line, and the operation specifications, cleaning agents, gloves, and turnover boxes need to be managed separately. This hidden cost cannot be seen in the quotation.

Suitable for: medical parts, transparent parts, products with low odor requirements, liquid silicone injection products.

Condensation type RTV: room temperature curing, thickness with ceiling

Single component room temperature adhesive solidifies by absorbing moisture from the air and pushing from the surface inward. Common types include deacetylated type (with a sour taste, corrosive to metals and PC), dealcoholized type (neutral, mainstream for electronic sealing), and dehydroxime type (with a small odor but a risk of corrosion to copper).

Key limitation: curing depth. It is generally not recommended to use a single infusion of more than 6mm, as it is too thick and will not cure for a long time inside. Two component components can be deeply solidified, but they need to be mixed in proportion and have a time window for operation.

Suitable for "non mold forming" applications such as coating, potting, and adhesive sealing, without the use of compression molding and injection molding.

Four real questions to ask when choosing a model

One requirement is transparency - platinum is necessary for high transparency.

The second requirement is for odor and volatile compounds - platinum is more stable in medical, food, infant and child care, and automotive interiors.

The third is whether there is sulfur, nitrogen, and phosphorus pollution in the production environment - if sulfur-containing rubber is also produced in the workshop, the management cost of the platinum system will be very high, and once poisoned, it will be scrapped in bulk.

The fourth is cost - the unit price of peroxide rubber is indeed low, but if the energy consumption and working hours of post vulcanization are included, the gap will narrow.

The cost of changing the system

The adjustment of the vulcanization system will have a chain effect: vulcanization temperature, time, post vulcanization system, mold design (shrinkage rate may change), demolding performance, and even color stability. So after the adhesive material is set, don't move it easily. If you really want to change it, you have to go through the process of small-scale testing and verification again.

Industry Observation

In recent years, the proportion of platinum based materials has been increasing, not entirely due to industrial upgrading, but largely driven by acceptance standards for odors and volatile compounds - especially as car manufacturers and brands have increasingly specific requirements for odors in car interiors and product linings. But the platinum system has higher requirements for production management, and some factories have switched to expensive materials, resulting in a decrease in yield. The problem is mostly due to the failure to keep up with isolation and cleanliness standards, rather than the materials themselves.