Mold Release Agents

In general, post mold treatment of surfaces can be adversely affected by the residual presence of release agents if the release agent is not compatible with such treatment or if it is present in excess on the released part surface. The choice of release agent chemistries compatible with post release operations, the adjustment of the application level onto the mold and the choice for low transferring release agents (like semi-permanent ones) can lead to successful post molding operations and minimize any part contamination issues.

In general, the release agent should not be chemically compatible with the material being molded: offering a good chemical and physical barrier preventing the molded compound from chemically interacting with the mold (substrate). It is the old adage “like dissolves like”, so if the release agent and material are too compatible, the material can penetrate the release agent film and adhere to the mold surface. The composition of the material being molded, as well physical characteristics like hardness and abrasion (often influenced by fillers and reinforcing agents), influence the choice of release agent. Different metal alloys, thermosets, thermoplastics and elastomeric materials have different molding processes and conditions which demand different requirements from the release agent, affecting mold release selection.

The shift greatly depends on the industry and process requirements. Several industries no longer tolerate solvent-based products due to health, safety and environment concerns or other regulatory issues. Industries such as die casting, tire manufacturing, and general rubber molding use predominantly water based release agents. The polyurethane industry uses both water based and solvent based mold release agents, the composites and thermoplastics industries use mostly solvent based release agents at this time.

Water-based products are more sensitive to application (offering more challenges to film formation) and have slower evaporation rates (which can be influenced by the application method, process conditions and environment humidity levels) than solvent based products. Water-based products are more prone to cause chemical interaction of residual water remaining on the mold surface with the material being molded during the molding process (e.g. generation of urea byproducts in polyurethane molding). This category of release agents also requires more technology to ensure emulsion stability and bio-activity resistance. These challenges have to be addresses to expand the use of water based release agents across a wider range of industries.

Non-aerosol products are best applied in thermoplastic processing using a high quality spray gun or with clock-controlled spraying equipment.

Application methodology depends on the carrier of choice as well as on the nature of the release agent and the process and process environment. Application is a key aspect to be observed and may significantly influence the performance of the release agent. In most cases, release agents are applied using a spray gun (manual or robot application). In some applications programmable spray systems with multiple spray nozzles allowing for the application of one or more release agents are used. The nozzle size is regulated to ensure proper atomization (influenced by the expected throughput and release agent viscosity) and good film formation. Spray application can be air assisted (where air is used to further shear and atomize droplets) or airless (where the nozzle operating at high pressure shears the release agent stream to obtain the necessary atomization). Electrostatic spray guns can also be used to apply solid and liquid release agents. In some applications, release agents can also be applied by aerosols or even through manual or automated wiping.

Each type of agent has its own particular strengths (S) and limitations (L). Here is a brief overview by type of release agent:

• Solvent-based release agents:
  • S: Easier to apply. The solvent carrier also helps with the film formation. The evaporation rate can be adjusted based on the solvent blend. The choice of solvent may ease the dissolution / dispersion of the release agent active ingredients.
  • L: Not highly environmentally friendly. Offer higher health (VOC’s) and safety concerns (fire hazards) than non-solvent based products.
• Water-based release agents:
  • S: Environmentally friendly and presents no fire hazards. May sometimes be dilutable (can be shipped as concentrates). They can be used to cool the die if necessary. May be developed with a level of technology that ensures mold release agent performance equivalent with solvent based release agents.
  • L: Require more complex technology to manufacture. Proper film formation can be more challenging. This category of release agents may be more prone to stability issues and biological attack. Water-based release agents have slower evaporation rates than their solvent based counterparts and may not be appropriate for some room temperature molding operations or operations with short cycle times. Residual water onto the mold may affect molding performance (entrapped steam) or even chemically react with the material being molded. The latter is particularly an issue when molding polyurethane parts.
• Carrier-free Release Agents:
  • S: Can be applied “as is” due to the absence of carrier. No vapors emission. Less noisy application is observed. Do not require dilution or tank storage. No waste stream.
  • L: Can create a dust hazard if not applied properly. Require special application equipment (often being electrostatic spray guns), which may require expensive investment. The use of carrier-free release agents may also require additional modifications to the molding equipment to ensure thermal balancing of the mold. These factors often limit the application of this category of release agents.
• Sacrificial Release Agents:
  • S: Easy to apply. Require less application technique and offer more tolerance of work (less dependent on trained operators).
  • L: Tend to build up on the mold if over applied. In general, the release coating is partly transferred to the molded part, which may cause negative side effects on post molding operations (painting, adhesion, etc.) if applied in excess or if the release agent chemistry is not compatible with the post molding operation. If water-based, tend to cool the mold, removing heat & energy from the system (this may represent a disadvantage if the process is not designed for that).
• Semi-Permanent Release Agents:
  • S: Require significantly lower application frequency than sacrificial release agents because the release agent film lasts for multiple molding cycles (frequency depends on the process conditions). Allow for a more steady and continued production without interruption for release agent application. There is very little transfer to the molded part, which allows for better post molding operations (coating, adhesion). The release agent can be reapplied regularly on the coated mold refreshing the release agent film. This category of release agents provides an excellent combination of chemical and physical barriers, preventing build up and providing the desired release performance.
  • L: Requires more training of operators to ensure the right touch up frequency is observed. Molds need to be clean to allow for good interaction between the release agent and the mold surface during the initial application of the release agent.
• Internal Mold Release Agents:
  • S: Reduce the need for external mold release agents.
  • L: May continue to exude to the surface over time compromising post molding operations (coating and adhesion) or the surface cosmetics of the part. Often do not eliminate the need for external releasants as the internal mold release agents do not always migrate to the mold interface or may not ensure 100% release efficiency. Limited in their capability of performing high performance release agent functions such as affecting part surface characteristics.

The advantage of silicone-containing release agents is that they offer a very good release effect. The disadvantage of silicone-containing release agents is that the subsequent treatment of the released parts, such as gluing or painting, may be difficult or even impossible. Additional post molding part processing will be required.

Mold release agents provide not only a physical and/or chemical barrier as the means of separation between the material being molded and the mold surface, but also impact process characteristics like the flow rate of the material being molded within the mold cavity, molding cycle time and, of course, release ease. The choice of mold release agents also affects finish characteristics of the released part like gloss level, accurate texture reproduction, post molding operations (e.g. adhesion or coating of the molded part) in addition to influencing the mold service life in between maintenance cycles, and overall productivity.

Factors to be considered for selecting the proper release agent include:

• Mold material / substrate
• Material being molded
• Process conditions:
  • Temperature
  • Line speed / cycle time
  • Pressure
  • Specific molding process such as injection molding, high pressure, gravity fill, compression, etc.
  • Process variable fluctuations
• Geometry of the mold
• Post molding operations (adhesion, coating)
• Expected performance level and productivity (number of good releases or good parts demolded per time period)
• Existing process issues (cavity filling challenges, soldering, release-related scrap rates, process condition fluctuations etc.)
• Mold maintenance expectations (mold cleaning frequency)
• Part finish requirements (gloss, marring, etc.)
• Application methodology
• Health Safety and Environmental (HSE) requirements

Applying too much release agent can make subsequent process treatment of the parts more difficult by creating an oily or slick surface on the molded part.

The advantage of aerosol cans for thermoplastic processing is that the spray valve system allows the product to be applied very thin, consistently and with a predictable spray pattern. This allows material to be saved and prevents over application. Spray cans also offer easy handling and flexibility.

Buildup of release agents, the material being molded, or byproducts and residues generated by chemical reactions that take place within the mold cavity (in situations where the compound is chemically being changed along the molding process) negatively affect molding performance in terms of heat transfer, part dimensional properties, cosmetic appearance and process efficiency. Mold cavity fouling needs to be regularly removed mechanically or chemically to ensure part quality. Every time the mold needs to be cleaned on-site or otherwise maintained, productivity is lost.

Build up issues can be created by two primary sources:

• Excess of release agent present on the mold. This may be the result of a poor choice of release agent for the specific application (e.g. not compatible with the process temperature) or over application of the release agent onto the mold.
• Lack of release barrier causing build-up of the material being molded or byproducts and residues generated during the molding process. In this case, the choice of release agent may not be adequate for the process conditions (not suitable for the process temperature, poor film formation, etc.). This may also be caused by application deficiencies (not enough release agent film present on the mold) or lack of physical and/ or chemical resistance of the release agent to the material which then penetrates the release agent film and physically or chemically adheres to the mold.

Industries are molding more exotic materials to produce parts with better performance under increasingly demanding conditions in which the finished products operate. These exotic materials are not always easy to mold. One good example comes from the automotive sector, where engine components (molded parts) are subject to chemical and physical challenges to withstand more aggressive operating conditions. As a result, newly developed, tougher materials (like fluoro-polymer based compounds), are required to be molded at high production rates with minimal scrap levels (given their higher unit formulation cost). This poses a challenge to the release agent industry, due to their chemical and physical properties which make them difficult to mold and release.

Part appearance has also become more demanding, and in many cases the parts are being used as molded with very minimal subsequent finishing done to the parts. The automotive industry requires that highly visible components like steering wheels or dashboards have exacting cosmetic properties (e.g. texture, gloss and marring resistance) directly following release.

In recent years high-pressure aluminum die casting has seen an increase in the complexity of the molds, with an increase in high integrity (semi-solid and squeeze) casting, as well as a reduction in cycle times and further increasing die temperatures. These factors require the release agent to provide improved anti-solder properties as well as better release and lubrication properties to produce quality parts under the more difficult casting conditions. This has to be achieved without compromising on other performance attributes of the release agent.

More complex and sophisticated mold designs are created for other industries as well, such as the low profile tires made by tire manufacturers. These mold designs place higher performance demands on the release agents with regard to release ease and rubber flow. The post molding appearance of tires is also critically important as well, resulting in significant challenges to easily release these types of tires while also achieving high appearance standards.

The use of lower VOC (volatile organic compound) products continues to be enforced by manufacturing facilities as a result of HSE regulations, being particularly important in processes that require higher direct involvement of operators, like in the composite segment. There will continue to be increased focus on developing products that are more environmental friendly and safer to use. This will stimulate new release agent develop to meet these needs while still providing the same, or greater, level of performance of the products currently in use.