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Surface Treatment 18 MoldMaking Technology —— APRIL 2017 By Brent Barbee and Dave Duff Figures courtesy of United Protective Technologies (UPT). This illustration shows the contact angle of a water droplet on a surface. The greater the angle between the droplet of water and a surface, the lower the surface energy of that surface. A contact angle greater than 90 degrees signifies that a surface is hydrophobic, while an angle equal to or less than 90 degrees is considered hydrophilic. A tensiometer is used to analyze this property. M old wear and part sticking can be a constant battle and potential profit-killer when it comes to aggres- sive polymer molding materials. In many cases, mas- ter batches (a concentrated mixture of additives) formulated for release can be blended into certain resins to ease part release, but with glass-filled materials wear is still a major issue. Also, molds and cores can be hardened to a level that minimizes wear, but the elevated temperatures cause extreme brittleness. A more viable option is to use a coating to protect the mold and its components while eliminating the part- sticking challenge. Finding the right coating and then the ideal balance of coat- ing surface energy, hardness, toughness and corrosion resis- tance that is required for the molding of sticky and/or highly abrasive molding materials is a challenge. Many articles review coatings that appear to meet the required criteria but rarely meet production expectations. Coatings do not come with a "one size fits most" tag attached, but require a cooperative effort between coat- ing providers and customers to determine the best fit for each application. For example, a company that produces swimming pool accessories was injec- tion-molding polyvinyl chloride (PVC) components and experiencing problems with parts sticking in the mold. The operator had to apply mold release every two shots, which had a major impact on achieving the required cycle times. By applying a nanocomposite diamond-like carbon (DLC) coating, the company was able to reduce the need for mold release to once every 7,000 shots. And the likeli- hood of mold damage due to digs and scratches from tools used in part removal was eliminated. Solving the Part- Sticking Challenge Low-surface-energy mold coatings can eliminate part sticking, reduce cycle time and increase mold life. The ABCs of DLC Nanocomposite DLC coatings are basically diamond-like car- bon that has been improved through the addition of molecular additives to reduce internal film stress and modify surface properties. These coatings can be applied to cavities, cores and ejector pins made from most alloys used in plastic molding and can increase mold life, eliminate part sticking and reduce cycle times. This is due to a balanced combination of surface energy, hardness, toughness, corrosion resistance, thermal properties, thickness and temperature to ensure maximum performance and durability. Surface energy. Water contact angle is a common mea- surement used to determine the surface energy of a mate- rial. The surface energy is the energy excess relative to the bulk necessary to form a surface in a crystal. Generally, if the water contact angle is less than 90 degrees, the surface is considered hydrophilic, the tendency for the water to wet or