Composites World / NetComposites

Connecting you to the composites industry


NetComposites Ltd has transferred the rights and ownership of this website to Gardner Business Media Inc.

On 1st January 2020, NetComposites' media assets including, newsletters and conferences were transferred to Composites World (Gardner Business Media).

This site is no longer being updated. Please direct all enquiries to

For further details see our joint press release.

Release Agents

  • Thursday, 24th January 2019
  • Reading time: about 3 minutes

Whether release agents are incorporated into the resin matrix or applied externally to the mould surface, correct selection can optimise not only cycle time, but also consistency of surface finish maintaining detail, minimising post mould operation prior to painting or bonding, even helping with fibre wet out.

To work well a release agent must fit within the scope of the overall process and be cost effective. Application must be simple with clearly defined steps, drying times should be short and cure time if any must not delay the process. The product must not contain any ingredients which will affect the final product properties or post mould treatments. Finally release must be smooth and clean with no pre-release prior to cure.

Qualification costs are high and suppliers should ensure their products and chemical pre-cursors are available long term, anticipating changes in legislation and using safe ingredients whenever possible.

Internal Mould Release Agent (IMR)

A product dissolved in the resin mix, which is highly soluble in the carrier solvent i.e. styrene. During cure the product drops out of solution and migrates to the surface due to volumetric shrinkage, pressure and temperature.

The following criteria are desirable:

  • Total solubility in the system 
  • Minimal effect on cure 
  • Minimal effect on colour 
  • No negative and preferably positive influence on physical properties 
  • No silicone, non-stearate and no natural waxes which would adversely affect painting or bonding adhesives 
  • A consistent clean release with no build-up or mould fouling caused by deposits 
  • Measurable reduction in cycle time

Using an internal requires careful introduction. Each release agent application is not an individual event, it is part of a long running sequence. Each moulding relies as much on previous moulding as it does on the IMR it deposits during its own cycle. (This is a continuous process in pultrusion).

IMR’s are more commonly associated with mechanised processes, but can assist in difficult highly detailed hand lay-up mouldings.

One major advantage is consistency and in high volume production, externally applied release systems rely solely on operator skill, not always meeting the requirements of the designer or formulating chemist.

External Mould Release Agent

Externals are applied to the mould surface and as such rely on care and attention during application to ensure successful release.

The following criteria are desirable:

  • Easy application with no complex instructions 
  • No harmful solvents 
  • Good wetting of all surfaces i.e. should not shrink back when applied 
  • Surface tension should be correct for gel coat application 
  • Quick drying 
  • Easy to polish 
  • Transfer to moulding should be easily removed, (preferably with water) 
  • Predictable multiple release

Wax release agents are used typically in low volume manufacturing where products are individual and cycle times are not critical, semi-permanents are used in high volume applications.

The semi-permanent system is ideal for all contact mouldings, large or small, giving exceptional surface finish with low maintenance, but without critical application procedures. In high production processes such as RTM, the use of semi-permanent systems maximises cycle times because of their consistent release properties.

Published courtesy of Keith Godber, Chemical Release Company

Share this article

Back to Other Resins

Comments (0)

Leave your comment