Influencing factors and solutions of stress cracki

2022-08-22
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Influencing factors and solutions of stress cracking of carbonated beverage polyester bottles II

▲ 2. Adjustment of injection molding process

(1) screw temperature

adjust screw temperature according to melting point, DEG content and the amount of copolymer components added

(2) gram weight of bottle blank

by adjusting the injection molding process, the gram weight of bottle blank is controlled, there is no peeling phenomenon, the blank weight of 0.2g is reduced, and the corresponding stress is significantly improved. Adjust the temperature distribution of the preform according to the gram weight

(3) crystallinity of bottle blank

(a) crystallinity of bottle blank should be as low as possible

(b) if the crystallinity of the preform is high, the heating temperature of the preform should be increased correspondingly during bottle blowing

(c) ensure the correct cooling of bottle blank and the correct drying of raw materials

▲ 3. Blow molding process adjustment

(1) stretching speed

(a) select an appropriate stretching rate to ensure that the stretching end point is correct. If the injection point at the bottom of the bottle deviates from the center or the bottle body turns white, the stretching rate needs to be reset

(b) apply the stress-strain curve of polyester

will be more intense (2) tensile temperature

(a) the heating temperature of bottle blank is selected within 25 ~ 30 ℃ above the glass transition temperature (TG) of polyester, which varies according to viscosity, moisture, copolymer components and gram weight

(b) the higher the viscosity, the higher the tensile temperature

(c) the higher the moisture content, the lower the tensile temperature

(d) the higher the copolymer component, the lower the tensile temperature

(E) the temperature distribution of the preform changes with the gram weight

▲ 4. examples of optimization of process conditions to solve the problem of stress cracking

the following (table) is an example of our process optimization according to the above ideas on domestic machines (Zhende cj120 injection 2, tensile machine, severe oil leakage of oil pressure system, plastic machine, equipped with daylong cp22 bottle blowing machine), Several bottle types (including 500ml, 1.25l and 2L, only the first two are listed here) have passed the test (qscrt) (the qscrt time of the new bottle exceeds 1% accuracy, which is enough for more than 60min). Under the condition that the heating opening of the nozzle is 60%, the barrel temperatures of section 1, 2, 3 and 4 in the production process of 500ml and 1250ml carbonated beverage polyester packaging bottles are 2752800, 280275 ℃ respectively; The blowing temperature control parameters (voltage) of sections 6, 7, 8, 9 and 10 are all 0

the inherent characteristics of polyester are the basic factors that affect the stress cracking resistance of products, such as crystallinity, intrinsic viscosity and molecular weight distribution. The selection of appropriate injection and blow molding process conditions is very important to improve the stress cracking resistance of polyester bottles. The influencing factors and control methods of stress cracking resistance summarized in this paper have achieved satisfactory results in practice, and have practical application value and reference significance

(author/Zhuo junqian)

(Guangdong packaging, 2005, issue 1)

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