Rubber Mold Release

A release agent (also called a mold release agent, release coating, or mold release coating) is a chemical coating used to prevent  materials from adhering / sticking to other surfaces, typically the inside of molds or other manufacturing equipment and tools. Release agents aid in processes involving mold of parts, die-casting, tire manufacturing, and hose manufacturing, to name just a few. 

Release agents are a little-know, often overlooked, process aid which make many of the things we use day to day possible to manufacture. 

Release agents are typically liquid coatings but can also come in the form of pastes or powders. Most release agents are either water-based or solvent-based coatings and may be semi-permanent or sacrificial. 

Click here to learn more about release agents and what type of release agent may be right for your manufacturing process. 

Internal release agents are either liquid or solid/powder additives mixed with the molded material in very small quantities to aid in release of the part. Internal mold release agents are common in rubber, polyurethane, and composites industries. Internal release additives consist of chemistry which "blooms" to the surface of the molded material during curing to impart some release characteristics and reduce tackiness. 

When internal release additives cannot be used or provide inadequate release characteristics, molders use external release coatings which are coatings applied to the mold or tool where sticking occurs.

McLube offers a wide range of external mold release agents for molding of elastomers, thermoplastics, polyurethane, and a variety of composite materials. 

Solvent-based 

PROS

• Fast-drying, even in ambient temperature applications
• Longer shelf-life

CONS

• Many solvents are flammable and require special handling and safety procedures. 
• Generally not environmentally friendly due to the VOCs. 
• Higher shipping costs and special storage considerations.  
• Dilution is possible but a hazardous process requiring additional solvent diluents to be handles and stored. 

Water-based 

PROS 

• Generally safer to handle
• More environmentally friendly
• No HAZMAT shipping costs
• Some coatings are easily diluted inhouse

CONS 

• Wetting can be more difficult at ambient temperatures 
• Biological growth and reduced shelf-life compared to many solvent-based products. 
• Slow drying times and water incompatibility with materials such as isocyanates/ polyurethanes. 

Hybrid Coatings
Hybrid coatings contain a mixture of water and solvent diluents. They are often a middle ground between the benefits of solvent and water-based release coatings. 

Carrier-free, 100% Active Ingredient Formulations

PROS

• Eliminate many of the drawbacks of solvent-based and water-based options 
• Some options can be diluted extensively for additional cost/ shipping savings

CONS

• Can require specialized equipment to apply
• Easy to overapply

Semi-permanent release coatings offer significantly more releases per application than sacrificial mold releases. Semi-permanents also offer little or no transfer to the molded part due to their ability to bond with the surface of the mold. The downside is these coatings require more careful application that can take time. 

McLube offers a number of semi-permanent release agents that cure instantly, offering the benefits of semi-permanence without the drawbacks of lengthy cure cycles and extensive operator training. 

Sacrificial coatings are easier and typically faster to apply. Sacrificial coatings may be more appropriate for operations that do not have time or temperature to cure a semi-permanent coating. These conventional release coatings may also be more appropriate for molds with intricate details or extremely tenacious materials. 

Used Together

Some processes can benefit from the use of both semi-permanent release and sacrificial mold release. Sacrificials may be applied over a semi-permanent coating as a touch-up coating in difficult areas to provide additional slip. 

Sacrificial mold release agents are generally non-functional, non-reactive coatings that create a physical barrier between the mold and material that is transferred to and removed with the molded part. Sacrificial release agents are designed for frequent application and generally offer limited releases per application. Since the advent of semi-permanent coatings, sacrificial release agents have also been referred to as “conventional” coatings. Semi-permanent release coatings have largely replaced conventional, sacrificial mold release because they offer multiple releases per application with little transfer to the molded part. While based on antiquated technology, sacrificial mold release agents are still the best choice for some molding applications.

Molders may opt for a sacrificial mold release agent when their material is simply too tacky to release without a more robust physical barrier between the substrate and material. Sacrificial coatings can also be used for touchup in difficult areas of a complex mold. Some molders may want a shinier surface finish created when sacrificial coatings transfer to the molded part. Transfer of high-slip sacrificial coatings will also pass on a certain degree of slip to the surface of the part which can aid assembly/insertion by end users in the automotive and aerospace industries. Some processes may also require a sacrificial release coating when sufficient time and effort cannot be allocated to cure a semi-permanent.

Contact McLube® and an experienced technical representative will help you select the ideal mold release agent for your operation.

This issue can be caused by inadequate cure of the semi-permanent coating, buildup on the mold surface, or the mold geometry.

Steps you can take: 

1. Contact us for technical assistance and application help
2. Consider using a touchup coating - read more below: 

Semi-permanent release technology was developed with functional, crosslinking additives to increase the durability of the release coating and allow for more releases per application. Unfortunately, semi-permanent release agents often do not possess the flow characteristics to reach deep drawls, cavities, threads, small sprue openings, and other difficult-to-release areas of complex substrates. This shortcoming is especially evident in semi-permanent wax coatings used in the polyurethane industry.

Sacrificial release coatings, while based on older release technology, by their nature possess excellent flow characteristics and are the ideal choice for touchup in difficult areas. McLube’s line of sacrificial release coatings may be wiped or sprayed directly over a semi-permanent coating before each cycle for easy touchup.

Follow all safety precautions when cleaning a mold and ensure proper personal protective (PPE) equipment is worn at all times.  

Start by removing any buildup on the mold surface. Use the least abrasive methods possible to avoid damaging the mold surface. Selecting the right cleaning agent or solvent can reduce the amount of physical abrasion (and effort) required to clean your mold. Click here to learn more about our mold cleaners and industrial cleaners. If available, use compressed air to remove residues loosened by the cleaner or left over from mechanical scrubbing. Some molders may find it necessary to bead blast molds to remove tenacious residues.

Wipe the mold clean with a lint-free towel after all residues have been removed. It may be beneficial to rinse molds with clean water/ or a mold solvent to ensure all debris is removed. Ensure the mold is dry before application of release agent. If your mold will not be used or stored after cleaning, it is often beneficial to apply your release agent to the mold to protect it during downtime. Consult the release agent TDS or contact McLube® for more information about mold protective coatings.  

Other Tips:

• Conduct a tape test to determine if the mold is properly prepared and ready for release agent application. Learn about conducting a tape test. 
• After applying a mold cleaner or suitable cleaning solvent, it is often beneficial to let the cleaning agent sit on the mold surface for a period of time to break down residues before scrubbing.
• Mold cleaning can be a time consuming and expensive process. If your molding line experiences excessive downtime for cleaning, it may be beneficial to consider a different release agent or application method. Overapplication or improper cure of semi-permanent release coatings are common issues which leads to extra downtime for cleaning. In many cases, molders using sacrificial release agents can cut down on downtime due to cleaning by switching to a semi-permanent mold release agent.
• During mold cleaning downtime, also clean dilution equipment (if applicable) as well as your application equipment.  

The most common confounding factors in a release agent trial are: 

1. Prior coatings on the mold surface/ test surface is not cleaned before trial
2. Release agent was not properly mixed before use (if applicable)
3. Improper application method
4. Dilution ratio is too high/ low

READ AND UNDERSTAND the safety data sheet for a new chemical material before use, handling, or other disposition. 

Ask your McLube product specialist for help selecting the appropriate release agent for your application. Share as much information as possible to guide product selection.

When preparing to evaluate a new release agent, we recommend thoroughly cleaning the mold surface before running the trial. Use a suitable cleaning solvent or mold cleaner to ensure the surface is properly prepared. Prior coatings, resin buildup, debris, etc. can affect the performance of the new release agent. Conduct a tape test on all areas of the mold to ensure it is clean; the tape should adhere. A tape test should be used to verify the surface is properly prepared. Learn how to perform a tape test here. 

Ensure the equipment used to conduct the test is also clean, free of any other coatings or contaminants. 

If the release agent must be mixed before use, ensure all solid, active ingredients are redispersed from the bottom of the container before running trials. 

Consult the release agent's TDS and your McLube Technical Sales specialist for tailored application instructions for your process. Carefully follow application instructions for the new release agent, especially if you trialing a semi-permanent release coating for the first time that requires specific curing conditions. For semi-permanent coatings, conduct a tape test to ensure the release agent is properly applied and cured; the tape should not adhere, or not adhere as well as it did on the clean mold surface.

NOTE: Many molders experience poor results with a new release agent because they do not properly apply the release agent, or use an application method recommended for a different coating. Different mold release agents may require different application methods to achieve the desired results. 

Test the release agent in a lab setting first, if possible. Following success, select a test mold or tool that best reflects your actual process conditions. Document the trial to be sure results can be repeated. Consider having the trials conducted by the actual mold operator. 

If your material, process, application method, or dilution ratio (if applicable) changes, retest the release agent to ensure the changes will not affect release performance and lead to molding issues on the line. 

When a release agent is suitable for dilution before use, consult the product TDS and your McLube product specialist for recommended starting dilution ratios for your process. Begin trials at the starting dilution ratio and achieve success before attempting further dilution. Ensure dilution equipment is clean and free of contaminants or other coatings.  

McLube product specialists are available to conduct testing with you at your facility. Molders may also send a sample of their materials to McLube for initial tests before sampling.

How the release coating is applied directly impacts the performance characteristics of the coating. Molders must pay careful attention to application methods and ensure consistency day-to-day, shift-to-shift. 

Improper application can cause reduced productivity, higher scrap rates, or even failure of the part to release from the mold. 

Overapplication is the most common operator error. For semi-permanent release coatings, not allowing the coating to cure, if applicable, is also a common issue which leads many molders to assume the coating does not work for their material or application. 

Release agents can be applied by many methods which are often process- or user-specific. Generally, release agents may be wiped, sprayed, brushed, or flow coated onto molds and tooling. Semi-permanent coatings may require time to cure on the surface before molding can begin. Sacrificial release coatings generally allow molders to begin molding parts as soon as the coating has been applied to the mold.

Heat often plays a factor in application methods (and the choice of release agent). For processes that involve heat or heated molds, such as rubber molding, manufacturers have many options. For some processes, manufacturers must wait for water-based release agents to dry before molding their first part. This can slow productivity in processes with little or no heat and sometimes a fast-drying, solvent-based release coating is better suited. 

Spray application is generally preferred with fine atomizing spray guns or systems. Spray application aids in even uniform coverage of areas where materials stick to tooling. Spray application can be either air-assisted  (forced air atomizes the liquid into fine droplets) or airless. 

Mold release aerosols are also common in the industry, providing convenient, portable spray capability, although aerosol release agents may be impractical for some applications. 

McLube product specialists not only help with product selection but also help customers optimize their application method. Contact us for application instructions tailored to your process. 

Silicone-based mold release agents are ubiquitous in the industry. Many coatings contain one or more types of silicones. 

Some molders wish to avoid silicone-based release agents due to silicone migration around manufacturing facilities or material incompatibility.

Silicone migration is a particular concern in facilities where painting or gluing occurs because migrating silicones can interfere with proper adhesion. 

While the basic silicone oils found in most over-the-counter silicone release sprays are prone to migration, more advanced silicone-containing release agents typically contain nonmigrating resins that bond to the mold surface and will not migrate or transfer when applied correctly. 

All silicone-containing release agents are not created equal in terms of performance and migration risk. Except in circumstances where post-molding steps will be affected or there is a material incompatibility, molders should not discount the performance of silicone-containing release options. 

McLube product specialists can help you navigate product selection and testing to determine the ideal coating for your needs. 

Diluting concentrated release agents offers molders more control over their process, reduces shipping costs, and can also allow molders to tailor coatings to different processes within their facility. In every case, consistency is crucial. 

McLube recommends: 

• Placing one team, shift, or supervisor in charge of all dilution to ensure consistency. 
• Keep lids closed when not in use to prevent evaporation and contamination.
• If the product requires agitation before use, mix periodically before AND during dilution. 
• Adding water to product, not product to water. 
• Regularly cleaning dilution equipment. 
• Testing dilutions in a lab setting before moving to the production floor.
• Always consult your McLube product specialist before attempting dilution or if your molded material composition changes. 

Follow this link to read more about dilution or contact us for assistance.