When designing extruded Pet Preform, if the material is high-density polyethylene or polypropylene, the PET preforms should have a rectangular or elliptical cross section. For low-density polyethylene or other flexible PET preforms, Its cross section is preferably a circle. This facilitates the extrusion of the contents from the PET preform. The PET parts used in conjunction with the PET preform blank are mainly caps and seals. The design of the PET preform blank should focus on how the PET preform can be better fitted to the lid and sealer. The bottom of the PET preform is the weak part of the mechanical properties of the PET preform. Therefore, the bottom of the PET preform is generally designed to be concave; the corners of the PET preform and the concave portion are excessively curved. In order to facilitate the stacking of PET preforms and increase the stacking stability of PET preforms, the bottom of the PET preforms should be designed with internal grooves.
When the surface of the PET preform is marked, the surface of the label should be flat. A “sash” can be designed on the surface of the PET preform to make the label accurately positioned without moving. At the time of blow molding, the portion where the parison inflates first contacts always tends to be hardened first. Therefore, the wall thickness of this part is also larger. The edge and the corner portion are the portions where the parison inflates the last contact, and the wall thickness of the portion is small. Therefore, the edges and horns of the PET preform should be designed to be rounded. Changing the surface shape of the PET preform, such as the relatively thin middle portion of the PET preform, increases the circumferential grooves or ribs on the surface of the PET preform to improve the rigidity and bending resistance of the PET preform. Longitudinal grooves or ribs eliminate the offset, sagging or deformation of PET preforms under long-term load.
The printed surface of PET preforms is the most concentrated part of consumers’ attention. The printing surface should be flat and continuous; if the PET preform contains handles, grooves, ribs, etc., care should be taken not to inconvenience the printing operation. Elliptical PET preforms have higher stiffness, but the molds are more expensive to manufacture. Therefore, in order to ensure the rigidity of the PET preform, in addition to selecting the material with high rigidity, the shape and design of the PET preform are also used to enhance the rigidity and load resistance of the PET preform.
Since most PETs have notch sensitivity, PET preforms are prone to cracks and cracks at sharp corners, roots of the mouth threads, necks, etc., so these parts should be designed to be rounded. For the transfer of rectangular PET preforms, it is necessary to support most of the load of the PET preform, so locally increasing the wall thickness at this location is also beneficial to improve the rigidity and load strength of the PET preform.
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