At the Jec 2012 Momentive Specialty Chemicals were still talking about a ‘less than five minutes cycle’ for composite parts. Now, a year later, it has proved possible to present a two-minute time barrier. In addition, the company has introduced a range of composite products for automotive Class A production as well as a binder system for automotive composites in hot-melt preforming processes. Plastics spoke to Dr Francis Defoor, Global Market Leader Transportation, Momentive Specialty Chemicals, about the exhibits.
Momentive Specialty Chemicals claims to have broken the 2min barrier for mass production of composite parts. A new fast-cure epoxy system has been developed for resin transfer moulding (RTM) and liquid compression moulding (LCM) processes for automotive composite parts. “The technology we are presenting here at Jec is an advancement of the technology shown here in 2012,” explains Dr Defoor. “The question always is if the technologies are fast enough to enter mass production. With our two-minutes system around 50 to 100,000 parts/year can be manufactured on a mass-production basis.”
The system’s properties in terms of thermolatency and low viscosity are said to ensure good fibre wetting and cavity filling, leading to good handling and processing properties. In addition the new cure process is further accelerated without an extensive exothermic reaction. The high pressure RTM process is preferred for the processing of more complex part geometries, whereas it is possible to produce flat panels in less than 2min using the LCM process. In this process the liquid resin is applied onto the reinforcement preform before it is pressed in the closed mould. High injection pressures are not necessary here.
The system has been introduced under the name of Epikote 05475resin / Epikure 05500 curing agent and has already gone through the qualification procedures at the premises of some of the OEMs.
Class A parts
The products on display for the automotive Class A production of composite parts include the Epikote Resin 04695-1 and the Epikure 05490A curing agent. “For these products our chemists reduced the amount of shrinkage during curing,” explains Dr Defoor. “Together with a higher glass transition temperature, this results in a good surface quality.” The high glass transition temperature is intended to prevent damage during the de-moulding step. Furthermore the amount of finishing work is reduced. According to the company, the system cures in less than 15min at 90°C with gap RTM and can be used with standard RTM processes as well.
Composite preforms in hot-melt processes
For the automotive composite preform production in hot-melt processes, Momentive Specialty Chemicals introduced the Epikote System 620 binder. It is a one-component, cross-linkable powder binder that can be applied to carbon or glass fibres and fabrics as a powder using a hot-melt coating process line. In the softening temperature range of 80-90°C, the binder is said to provide the fabric with good workability and drapeability. Once the desired shape of preform is achieved, a short cure above 100°C will initiate internal crosslinking of the binder. The higher-temperature fixation gives the preform its stiffness and ensures the dimensional stability also under high-pressure RTM production.
The system is currently in qualification mode.