Plastic products are often made by a process known as plastic injection molding. Materials produced by plastic injection molding may be hard and solid, or soft and flexible. During the manufacturing process, an injector will squeeze molten resin into a metal die or cast. When the resin cools and sets, it is in the form of the die. A few problems can occur with plastic injection molding, whether due to human error or problems with machines and materials.
????? Blistering
Blistering of the plastic product made by the injection process is a common problem. Like blistering of the human skin, blistering in plastic products manifests as a raised area on the surface of the plastic. Usually, blistering is caused by a lack of cooling or venting during the manufacturing process. Excessive heat on the injection tool can also lead to the formation of blisters on the plastic.
????? Marks
Marks on the plastic surface can be caused by burning during the manufacturing process. These may appear as black scorch marks on the plastic material, and most usually are caused by a lack of ventilation for the molten resin that is injected into the die. It is important to keep the injection tool clean and running smoothly in order to avoid burn marks -- a clogged or dirty injection tool can cause resin to become trapped and overheated in the tool. This in turn can lead to burning or scorching of the plastic surface.
????? Pitting
Pitting, also known as sink marks, refers to the presence of small pucks or holes in the surface of the plastic. Allowing the material plenty of cooling time can reduce the appearance of sink marks in the final product. Sometimes pitting will occur when the material being used is not strong enough for the product being manufactured. Overly high temperatures in the resin material or the metal mold are also possible causes of sink marks in the plastic.

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