IBC barrel blow molding to produce various materials forming post-processing methods

Generally, plastic parts should be processed after molding according to their subsequent processes and requirements, so that the subsequent process can be carried out smoothly.

The post-sequence process generally refers to a surface modification process such as spraying and electroplating of plastic products, bonding printing, and the like. Regardless of which type of modification is performed, the surface of the part is required to be smooth, free of oil (mainly a release agent), and the internal stress of the part should be eliminated.

1. Removal of oil on the surface of the part

If the plastic parts are required to be electroplated, sprayed, etc., use as little or no release agent as possible in the production, and keep the parts clean to reduce the difficulty of the subsequent cleaning process. If the plastic part must be used as a release agent, it can be washed with 1% white cat detergent aqueous solution and then rinsed with plenty of water. If special treatment is required, special treatment of the surface, such as ultrasonic cleaning and surface roughening, can be performed.

2. Generation of residual stress and elimination of residual stress

(1) Stress cracking

If the stress generated inside the molded article during molding or during cooling is sealed inside the molded article as it is, a so-called residual stress (internal stress) is formed. When the molded product suddenly encounters an external force or contacts with a drug substance, cracks sometimes occur on the surface or inside of the molded article. Such a phenomenon is generally called stress cracking, and is particularly likely to be a problem in secondary processing or long-term use of a molded article. Since stress cracking is mostly promoted by the surrounding conditions of contact with plastic materials, it is also called environmental stress cracking.

(2) The main reason for the formation of residual stress

1 is formed by excessive molding pressure applied to certain portions of the molded article. For example, a molded product of a direct gate, a radial crack generated around a gate, or the like.

2 If the wall thickness of each part of the molded product is different, or the cooling grooves (holes) of the mold are not arranged properly, the cooling rate of each part is not uniform, and the post-cooled part is pulled to the first cooling part, thereby forming internal stress residual. Come down.

3 If a metal insert is embedded, an object having a significantly different thermal expansion coefficient from that of the plastic material is inserted into the molded product, and unevenness in the cooling state is also caused, which causes cracking.

4 is formed by orientation (molecular orientation) when the molten resin flows in the mold. Due to the orientation when the molten resin flows, the stress generated by the elongation of the molecular chain of the resin becomes a residual stress as the material is cooled.

In addition, in the case of a thermosetting resin molded article, the degree of solidification of each portion is uneven due to the difference in wall thickness of the molded article or uneven heating during molding, and is also a factor that causes residual stress.

(3) Stress cracking and forming conditions

In order to easily check the residual stress, it is often judged by immersing the molded article in a chemical solution such as a solvent or a surfactant, and then determining the size of the crack and the time required for the crack to occur. .

In general, the higher the mold temperature or the lower the injection pressure, the smaller the residual stress and the less stress cracking, which is understood from the above-mentioned causes of cracking.

(4) Method of eliminating internal stress

1 annealing treatment

Annealing is to remove the residual stress of the plastic resin molded article, and heat treatment after molding, which can obtain the effects of: improving dimensional stability of the molded article; improving thermal deformation temperature and mechanical properties; eliminating stress cracking or reducing occurrence thereof Degree.

Because of its advantages, in the precision molded articles of polycarbonate, especially in order to obtain dimensional stability, annealing treatment is often performed.

However, while the quality of the annealing is utilized, the size of the molded article changes due to the secondary shrinkage (heat shrinkage) due to heating, and it is necessary to fully consider the point before performing the heat treatment. Further, since such secondary shrinkage is performed based on the resin flow orientation, it is also possible to estimate the degree of orientation by measuring the amount of shrinkage.

The method of annealing varies depending on the type of resin. In general, it is preferable to anneal the amorphous resin at a temperature lower than the heat distortion temperature by about 10 ° C, but the annealing conditions of the crystalline resin vary depending on the type of the resin, and Table 10.4 lists several plastics. Standard heat treatment conditions.