Food Contact Declarations for Custom Molded Plastic Components
Food contact declarations for custom molded plastics require finished part migration testing to cover processing degradation and additive changes beyond raw resin certificates.
Mold Release Agent Contamination
Meaning
Unintentional transfer of silicones or oils from the tool surface to the plastic part creates barrier layers that prevent the adhesion of paints or labels in later steps. Mold release agent contamination is a common issue in the injection molding process that can lead to significant quality problems. These agents are applied to the mold to help the part eject more easily, but if too much is used or if the wrong type is chosen, they can migrate to the surface of the part.
Once on the surface, they act as a non-stick coating that is very difficult to remove. This contamination can cause paint to peel, labels to fall off or adhesives to fail. Identifying and preventing this issue is essential for parts that require secondary finishing operations.
Surface Tension
Lowering the energy of the plastic surface is the mechanism by which these agents cause adhesion failure. In mold release agent contamination, the presence of silicone or other low surface energy molecules prevents the paint or adhesive from wetting the surface. Instead of spreading out and forming a strong bond, the liquid beads up and sits on top of the contamination layer.
This lack of wetting is a clear indicator that the surface has been contaminated. Measuring the surface energy using dyne pens or contact angle measurements can help to quantify the level of contamination. A low surface energy reading usually means that the part will need to be cleaned before it can be finished.
Secondary Operation
Performing further steps on a part, such as printing, gluing or plating, requires a clean and reactive surface. Mold release agent contamination can make these operations impossible or very unreliable. If a part with contamination is painted, the paint may look good at first but will soon start to flake or bubble.
In the assembly of multi part products, the failure of an adhesive bond can lead to the total failure of the device. Manufacturers must be aware of the potential for contamination and must choose their mold release agents carefully. If secondary operations are required, it is often better to use a paintable grade of release agent or to design the mold to eject without any lubricant.
Root Cause
Identifying the source of the contamination is the first step in resolving the problem. Mold release agent contamination can be caused by the over application of spray on lubricants by the operator or by the use of internal release agents in the resin itself. It can also occur if the mold has leaks in its hydraulic system that allow oil to enter the cavity.
In some cases, the contamination can be carried over from a previous job if the mold was not properly cleaned. A thorough investigation of the molding process and the materials used is necessary to find the cause. Regular cleaning of the tool and strict control over the use of release agents can help to prevent the problem from occurring in the first place.
This proactive approach saves time and money by reducing the amount of scrap and rework.