What Are Phenolic And Urea Closures?

About the Resins

Phenolic and Urea are two types of thermosetting resins. The main characteristic of thermosets (literally setting under heat) is that they require curing, when they undergo a molecular cross-linking process which is irreversible and renders them infusible. They therefore offer high thermal stability, good rigidity and hardness, and resistance to creep. Unlike plastics that come in pellet form in their initial state, Phenolic and Urea’s comes in the form of a fine powder. The most noticeable characteristic of Phenolic and Urea resins are their colors. Phenolic comes in a polished black and Urea in a white finish. The resin’s colors are influenced by the color in their preliminary powder form. These two resins have a long history of being used to produce moulded goods including billiard balls, phone handsets, circuit boards, and closures.

Molding Process

Dissimilar to resins that undergo injection molding, Phenolic and Urea parts are manufactured through a process called compression molding.

The compression molding process is a completely closed system with no point of entry or gate for materials to flow through. The powder form resin is placed inside one-half of the cavity tool where the formation process will begin. The tool is moved upwards where it is met by a Force Plug to create a completely closed off mould cavity. A combination of increased pressure and heat is applied to the closed off mold to form the material into a solid component.

Advantages of Phenolic and Urea Closures

The compression moulding process of Phenolic and Urea resins ensures a clean, unmarked final product every time, unlike injection molding that can leave gate and sink marks on the finished part, compression molding avoids these distortions. While Phenolic will always produce black components, Urea can be mixed with a powder form colorant to produce colored components. Phenolic and Urea are 64% more dense than polypropylene which translates to an increased weight and heavier hand feel for a similar part. This increased rigidity offers a stronger, more heat tolerant component.

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