Medical PET bottle processing and molding (2)

(4) injection molding parison mouth and neck size

The parison mouth diameter and thread size should be consistent with the bottle mouth thread size and match the cap thread size. 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 should also be considered. The inflation pressure of the PET bottle in the parison is l.2 MPa, and the water temperature is used to cool the cooling water at 5-10°C. The mold is blown so that the parison can be rapidly cooled after being blown.

(5) The function and effect of the injection blow molding mandrel

The role and function of the mandrel used for injection blow molding are mainly five aspects: a. Determine the shape of the formed parison and the inner diameter of the bottle neck, b. Take the parison or bottle body during the mechanical indexing process c. Mandrels are provided with air passages and air inlets and outlets for conveying compressed air to inflate parisons; d. The interiors of the mandrels can be circulated with liquid or air to adjust the parison temperature; e. The tails of the mandrels are close to the mating face. A 0.10 mm deep groove is provided to wedge the end of the parison into the groove to avoid misalignment of the neck thread caused by the elastic contraction of the parison during the transfer from the parison forming station to the blow molding station. Sealing function reduces the leakage of compressed air during inflation.

(6) Selection of mandrel length and diameter

The length and diameter of the mandrel are mainly determined by the parison, and the diameter of the mandrel body is smaller than the inner diameter of the neck of the bottle body, so that the bottle body can be demoulded, but the mandrel diameter should be as large as possible within the inner diameter of the bottleneck. To avoid causing too much blow ratio. The mandrel coaxiality shall be within 0.05-0.08 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 mandrel diameter equal to the outer diameter of the bottle mouth minus two Times of bottle wall thickness.

(7) Determination of the distance between the bottom of the mandrel and the bottom of the parison

This distance dimension 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 commonly used 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 HRC52-54. Harder than 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 to ensure a more consistent temperature distribution of the mandrel. The temperature of each section of the mandrel is: the head (corresponding to the neck of the parison) takes 45°C-55°C,

The middle (corresponding blank body) takes the tail of 40°C-50°C

Take 23°C-35°C. In the parison injection station, because the melt temperature is high and the mandrel temperature is at the upper limit of the above range, the temperature at which the mandrel is transferred 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 blow molding process parameters

The PET bottle is controlled at a melt temperature during injection blow molding to a temperature in the range of 275°C to 285°C, which is about 50°C higher than that of most injection blown grade polymers. 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-35°C to quickly cool the parison. The internal cooling of the mandrel also takes place using liquids or gases. The air cooling allows a more uniform temperature distribution in the axial direction of the mandrel and does not cause leakage problems such as liquid cooling. The pressure inside the mandrel is generally 1 MPa. It is best to use a liquid/gas combination cooling method. The PET parison inflation pressure is about 1.2 MPa. The temperature of the chilled water is 5° C.-10° C. in order to cool the blow mold, and also the parison is rapidly cooled after being blown.