Medicinal PET Plastic Bottle Mold Processing Technology (2)

It can be seen that the barrel temperature has a significant effect on the acetaldehyde content of the polyester preform, and the screw speed, injection rate, back pressure and hot runner temperature have little effect on the acetaldehyde content. Therefore, by increasing the injection rate and lowering the barrel temperature, parisons with high transparency and low acetaldehyde content can be formed. The use of high injection pressure during the initial filling of the mold to stabilize the filling process and then injection at low pressure can achieve better results. Therefore, when forming a polyester parison, the choice of melt temperature should be appropriate to ensure the transparency of the parison, and at the same time it can control the generation of acetaldehyde. The melt temperature is generally about 280°C.

3. Injection blow-molding ratio of bottle and bottle body When injecting and blowing small-volume polyester bottles, the parison mainly undergoes axial stretching during the process of molding. The smaller the axial stretch, the greater the blow-up ratio (the ratio of the bottle diameter to the parison diameter) and the greater the possibility of uneven bottle wall thickness distribution, which can easily cause bottle shoulders and bottle bodies or bottles and bottles. The thickness of the curve at the bottom transition region is not uniform. Blowing ratio of small-capacity bottles is generally between 1.5 and 1.8. For a bottle with an oval cross-section, if the ratio of the ellipse to the length of the major and minor axes of the ellipse is less than 1.5:1, a parison having a circular cross-section may be used for molding. When the ellipse ratio is not more than 2:1, a mandrel having a circular cross-section and an elliptical parison can be molded. When the elliptic ratio is greater than 2:1, it is generally required that the mandrel and the parison mold cavity be designed to be elliptical. With the increase of the elliptic ratio, the design difficulty and manufacturing cost of the parison mold increase, and generally it should not exceed 3:1.

4, injection molding parison mouth and neck size parison mouth diameter and thread size should be consistent with the bottle size thread, and can match the thread size of the cap. Because there is no unified national standard for this, the size of the bottle mouth is determined based on the contents of the bottle body. When determining the neck size of the parison and the size of the blow mold cavity, the shrinkage of the bottle body after molding should also be taken into account. The inflation pressure of the PET bottle in the parison is 1.2 MPa, and the cooling water is blown at 5 to 10°C. The mold allows the parison to cool quickly after being blown.

5, the function of the body injection blow molding core rod injection blow molding used in the function of the mandrel are mainly five aspects: (1) determine the shape of the molded parison and the inner diameter of the bottle neck (2) in the mechanical transposition In the process, the parison or bottle body is taken away; (3) The air passage and the air inlet and outlet are provided in the mandrel, and the compressed air is fed to blow the parison; (4) The liquid or air can be circulated inside the mandrel to adjust the parison. Temperature; (5) A 0.10mm deep groove is formed near the mating surface at the tail end of the mandrel so that the end of the parison is wedged in the groove to prevent the parison from being transferred from the parison forming station to the blowing station. Its elastic contraction leads to misalignment of the neck thread. The groove acts as a seal, reducing the leakage of compressed air during inflation.

6. Mandrel length and diameter selection The length and diameter of the mandrel are mainly determined by the parison. The diameter of the mandrel is smaller than the inner diameter of the neck of the bottle body to facilitate the demoulding of the bottle body. However, the diameter of the mandrel should be as large as possible within the inner diameter of the bottleneck in order to avoid excessive blow-up ratios. The mandrel coaxiality should be within 0.05 to 0.08 mm in diameter. The diameter of the mandrel at the mouth is determined by the outer diameter of the bottle mouth and the thickness of the bottle mouth. The value range is generally the bottle mouth diameter equal to the outer diameter of the bottle mouth minus twice the wall thickness of the bottle mouth.
7. Determination of the distance between the bottom of the mandrel and the bottom of the parison The distance is the thickness of the bottom of the parison. Whether it is reasonable or not depends on whether the thickness of the bottom of the bottle meets the requirements. The general calculation method is: the thickness of the bottom of the parison (B) is equal to the minimum thickness (T) of the bottom of the bottle plus 0.1 times the weight of the bottle. The material of the core rod body is an alloy tool steel with a hardness of HRC 52-54, which is slightly lower than the hardness of the mold collar. The surface of the mandrel in contact with the melt is polished along the flow direction of the melt and plated with hard chrome to facilitate melt filling and mold release. In the blowing and demoulding station of the PET bottle, the gas continues to circulate in the mandrel, ensuring that the mandrel has a relatively uniform temperature distribution. The temperature of each section of the mandrel is taken as follows: the head (corresponding to the neck of the parison) is taken from 45°C to 55°C, the middle (corresponding parison body) is taken from 40°C to 50°C, and the tail is taken from 23°C to 35°C. In the parison injection station, the temperature of the mandrel is at the upper limit of the above range due to the high melt temperature, and the temperature at the mandrel transfer to the demolding station is reduced to the lower limit due to internal cooling. After the bottle body is ejected at the demolding station, the head of the mandrel rod is air-cooled from outside to lower the temperature of the mandrel.

8,PET bottle injection molding process parameters value PET bottle in the injection blow molding to control the melt temperature, it is in the range of 275 °C ~ 285 °C, higher than the temperature of most injection blow molding grade polymer about 50 °C . The hot runner system should adopt a streamlined and symmetrical design to avoid dead ends. The nozzle is a lockable structure and the outer surface is heated. In order to ensure high transparency of the parison, after the melt is filled into the parison mold, it must be quickly cooled to below 145°C, but higher than its glass transition temperature (82°C), and the closer to the glass transition temperature, the blowing bottle The higher the transparency, the wider the processing range. The parison mold cooling water temperature is as low as 10°C to 35°C to rapidly cool the parison. The internal cooling of the mandrel also takes place using liquids or gases. Air-cooling allows a more consistent temperature distribution in the mandrel axial direction without leakage. The pressure inside the mandrel is generally 1 MPa. It is best to use liquid and gas combined cooling methods. The PET parison inflation pressure is about 1.2MPa. The cooling water temperature used is 5°C to 10°C. In order to cool the blow mould, the parison is also blown and rapidly cooled.

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