Defect Analysis of PET Bottles-Surface Whitening

Custom Plastic Bottle Manufacturers , Bottle surface whitening phenomenon

PET bottles through the General Assembly cause partial crystallization bleaching. This phenomenon has three stages, namely, when the preform injection whitening, crystal surface when reheating preforms whitening, whitening oriented crystallization stretching blow. (1) The entire surface of the preform molding whitening and reheating the entire surface of the crystal whitening basic reason as stated in 3.1.1, the degree of crystallinity is higher than the crystallinity of whitened hair dark. But for local preform surface crystallization process genesis block is not the same. When the cooling effect of the mold is very good, regular or irregular crystal parabolic fog may form. This is mainly because each cavity injection speed, pressure, temperature coordination inconsistent results. High-speed, high-pressure injection, and the melt shear gate, generates heat, melt flow is good, the cavity is filled quickly, and rapidly cooled. If because of the injection pressure, low injection speed, primary injection failed to fill the cavity, then the level of the injection stream forward because leaving a bad contact with the mold wall temperature drop is less than the glass transition temperature or less to form a large number of nuclei; when injected with the secondary stream meet, will absorb heat and secondary injection stream atomization crystal shape is regular or irregular parabolic and parabolic thickness of some small, due to the molding temperature The formation of such a parabolic shape low fogging, an appropriate increase in temperature can be eliminated, but repeated experiments show that this argument is wrong. If the primary injection stroke is small to a critical value, raising the temperature until the material decomposition can not eliminate this frosting parabolic shape.

(2) If no whitening in the above case, the reheating phase PET preforms easy to generate the corresponding parts of bulk crystals. Also due to the preform reheat temperature is not the same inside and outside, outside the high in the low, easy to make the surface temperature is too high and crystallize into a mist whitened.

(3) In the stretch blowing stage, due to the fast stretching or cold drawing, to form a whitened stretched crystallized (with information that such a fog as "pearlescent"). Actual production, preform injection molding stage, regulate a secondary injection velocity, an appropriate increase in the melt temperature, can eliminate parabolic (or plane) shapes albino. Reheating stage, using less to make internal and external temperature heating method, such as the use of good quality far infrared heating tube, quartz tube, radio frequency heating is available, if necessary, and as far as possible to shorten the heating time, can reduce the crystallinity bleaching possibility. Caused by the stretching of the crystal can be appropriately reduced speed to avoid stretching.

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