In EVA (Ethylene-Vinyl Acetate) Injection Process (IP) molding, the formation of bubbles can be attributed to several causes, along with their respective solutions:
Insufficient Material Drying
- Cause: Moisture trapped in the EVA material vaporizes during high-temperature melting and injection, creating bubbles.
- Solution: Ensure thorough pre-molding drying of the material according to the manufacturer's recommended conditions.
Improper Molding or Barrel Temperatures
- Cause: Excessive heat can degrade the material and generate gases, while low temperatures hinder material flow and gas escape.
- Solution: Adjust barrel and mold temperatures to optimal levels based on the specific material properties and product requirements.
Excessive Injection Speed
- Cause: Rapid injection does not allow gases to escape as the material rapidly fills the mold.
- Solution: Decrease injection speed to give gases more time to escape or employ a multi-stage injection profile with an initial slow phase.
Inadequate Venting
- Cause: Lack of efficient venting channels or holes traps gases within the mold.
- Solution: Modify mold designs to incorporate effective venting grooves or holes that facilitate gas release.
Issues with Color Masterbatch or Additives
- Cause: Incompatibility with EVA, poor pigment dispersion, or impurities in colorants can introduce bubbles.
- Solution: Switch to compatible color masterbatches, improve pigment wetting and dispersion, or purify raw materials.
Misuse of Crosslinking Agents
- Cause: Incorrect dosage of crosslinkers or gas generation from the crosslinking reaction not being adequately expelled.
- Adjustment: Adjust the crosslinker dosage according to recommendations and ensure effective gas removal from the crosslinking reaction.
Equipment Maintenance
- Cause: Malfunctioning vacuum systems in injection machines fail to extract gases from the mold effectively.
- Solution: Regularly inspect and maintain the vacuum system of the injection machine to guarantee its proper function.
Addressing bubble formation in EVA IP molding necessitates a holistic approach, encompassing material preparation, process parameter adjustments, mold optimization, and diligent equipment upkeep.
