Due to the safety and economy of PET bottles, they are widely used in juice drinks and tea drinks when they become mainstream products.

1、 Special quality requirements of hot filling process for PET bottles

   

     The bottle has good heat resistance. It is necessary to overcome the influence of hot liquid (high temperature) on the shape of the bottle: high temperature makes the bottle soft, and high temperature and hot liquid cause high pressure in the bottle. At high temperature (85 ℃～ 90 ℃), it is better to control the volume shrinkage between 1% ～ 1.5%.

    

     Bottles shall be able to withstand negative pressure. To overcome the negative pressure in the bottle after liquid cooling; The bottle wall shrinks inwards (flattening, and the side wall of the bottle is deformed and elliptical during negative pressure contraction).

2、 Blowing method of hot filled PET bottle

     

     One step method: the produced preform is crystallized at the bottle mouth in the crystallization furnace, and then directly formed by blowing the bottle with a high-temperature mold. Advantages: high output, convenient for mass production. Disadvantages: the high temperature resistance is poor, and the high temperature resistance decreases significantly with time. The storage time cannot be too long.

     Two step method: the produced preform is crystallized at the bottle mouth in the crystallization furnace, and then the hot filling bottle blowing forming is completed with two sets of molds. First, use the first set of mold with large volume (low temperature mold) to stretch and blow the preform into a super large volume bottle; Then the bottle is sent to the heating furnace for heat treatment (to eliminate the internal stress caused by stretching); After heat treatment, the bottle is sent to the hot mold (the mold with the final required volume) for further heat treatment (improving the crystallinity of the bottle body) and shaping, and finally blown into the bottle with the required shape and size. Advantages: The bottle has good high temperature resistance and long storage time. Disadvantages: low output is not suitable for large-scale production.

◆ Steps of bottle blowing process:

(1) The preform is sorted by the preform supply system and then transported to the preform heating furnace.

(2) The bottle preform heating furnace heats the bottle preform, cools the bottle mouth while the bottle preform rotates to make it uniformly heated, and then the furnace fan blows the bottle preform to make the inner and outer walls of the bottle preform evenly heated.

(3) The heated preform is input into the bottle blowing station by the preform conveying manipulator.

(4) After the preform enters the bottle blowing mold, the pre blowing enters the preform for circumferential stretching; When the stretching rod reaches the bottom of the mold (position 10), high-pressure air enters the mold cavity to further stretch the preform, making the bottle wall close to the mold wall.

(5) The high-pressure gas is kept in the mold for a certain time, which can eliminate the internal stress caused by the stretching of the preform on the one hand. On the other hand, the bottle wall is closely attached to the mold wall to improve the crystallinity of the bottle plastic.

(6) After the high-pressure blowing, start to exhaust, and blow high-pressure cooling gas from the hollow stretching rod to cool and shape the cylinder wall. When demoulding, blow out the low pressure air from the bottom mold to facilitate demoulding. If there is no air blowing out from the bottom mold, the bottle bottom will protrude and the bottle will not be taken out.

(7) At the end of the whole bottle blowing process, the bottle conveying manipulator takes the bottle out of the mold and sends it to the bottle conveying air conveying assembly line.

3、 Several main factors affecting the quality of heat-resistant PET bottles in the production process

    Bottle preform: intrinsic viscosity ≥ 0.81cm3/g, viscosity drop ≤ 4%, storage time shall not exceed 3 months. The color is pure, transparent, free of impurities and foreign colors, and the length of the injection point and the surrounding halo spots are appropriate. 2. Heating: In the oven, the far-infrared lamp emits far-infrared radiation to heat the preform, and the fan at the bottom of the oven circulates heat to make the temperature in the oven uniform. The preform rotates while moving forward in the oven, so that the preform wall is heated evenly. The heat of the oven is set by the number of lamp tubes opened and the overall temperature. The power of the oven and the heating ratio of each section are jointly controlled.

     Pre blowing: start pre blowing when the stretching rod descends to make the preform take shape. Pre blowing position, pre blowing pressure and blowing flow are three important process factors.

     Mold temperature: the mold temperature is controlled at 120 ℃~145 ℃, which is used to eliminate the internal stress caused by the bottle embryo stretching, improve the crystallinity of the bottle body plastic to withstand the high temperature hot liquid, so that the bottle does not deform. 5. Environment: room temperature and low temperature (air conditioning) are preferred.