Bubbles (or voids) are a phenomenon in which air bubbles are left inside the molded product. In the case of transparent molded products such as lenses or prisms, bubbles become external appearance defects or defects in the optical characteristics. In mechanical parts, these lead to a reduction in strength or ultimately breakage.

The causes for the generation of bubbles can be broadly classified into two types.

One type is the bubbles that are caused by bubbles that got mixed with the molten plastic. These are called bubbles.

The other type is a vacuum void generated when the molded product shrinks. When sufficient dwell pressure did not act on the parts where the wall thickness of the molded product is thick, this phenomenon occurs simultaneously with the generation of sink marks due to abnormal shrinkage.

The following countermeasures can be taken for these types of defects.

Countermeasures for Bubbles:

(1) Countermeasures related to molds

	1.	There are no air vents, or they are insufficient.
	2.	There is no cold slag well, or it is too small.

(2) Countermeasures related to the injection molding conditions

	1.	The screw rotation speed is too high.
	2.	The cylinder temperature is too high.
	3.	The injection speed is too high.

(3) Countermeasures related to the design of the molded product

1.

Insufficient preliminary drying of the molded material.

Countermeasures for Voids:

(1) Countermeasures related to molds

	1.	There are no air vents, or they are insufficient.
	2.	There is no cold slag well, or it is too small.
	3.	The sprue and the runners are too thin.
	4.	The gate is too small.

(2) Countermeasures related to the injection molding conditions

	1.	The cavity surface temperature is too high.
	2.	The dwell pressure is too low.
	3.	The dwell time is insufficient.

(3) Countermeasures related to the design of the molded product

	1.	Insufficient preliminary drying of the molded material.
	2.	The wall thickness of the molded product is too high.