Q: Which impact modifier can be used in halogen‑free flame retardant PC systems without compromising the UL94 V‑0 rating?

A:When selecting an impact modifier for flame‑retardant PC, the key consideration is its interference with the flame‑retardant system. Conventional toughening agents – especially those containing a highly flammable rubber phase such as butadiene‑based MBS – tend to ignite easily and promote melt dripping, which significantly undermines flame‑retardant efficiency and can even cause loss of the V‑0 rating.

To ensure that the UL94 V‑0 performance is not compromised, the following two types of impact modification systems are recommended:

1. Silicone‑based impact modifiers (preferred choice)

Silicone toughening agents contain no flammable rubber components. They inherently exhibit excellent thermal stability and flame‑retardant synergism. During combustion, they promote the formation of a dense char layer on the material surface, which suppresses dripping and retards heat release. This results in minimal disruption to the V‑0 system, making them particularly suitable for PC modifications that demand a combination of flame retardancy, weatherability, and low‑temperature toughness.

2. Specially modified core‑shell acrylate impact modifiers

By controlling the addition level (typically 2%–4%) and using them in combination with an anti‑dripping agent (e.g., PTFE), these modifiers can effectively enhance impact strength while maintaining the V‑0 rating of halogen‑free flame‑retardant PC systems.

EVERSUN KINGFOX USI‑3305X is a representative silicone‑based impact modifier, particularly well‑suited for flame‑retardant PC housings and similar plastic parts. It delivers excellent low‑temperature impact resistance, humidity‑heat aging resistance, and high colorability, while having no significant negative effect on flame‑retardant efficiency. It stands as a preferred solution for applications requiring both flame retardancy and toughness.

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