Processing technology of polyester plastic bottle

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Processing technology of medical polyester plastic bottles

polyester plastic bottles are one of the most important plastic packaging materials at present. They are mainly used for drugs, carbonated beverages, and can also be used for the packaging of alcoholic beverages, tea beverages, fruit juices, mineral water, edible oil, condiments, cosmetics, pesticides, detergents and other liquids. As a drug packaging container. Pet has many advantages. First, PET bottles are light and firm, and their strength and elasticity are significantly higher than those made of other plastic materials. They can withstand considerable impact without damage. It is most suitable for making drug packaging bottles with thin walls, light weight and high strength. With the same volume of medicine, the weight of PET bottle is only 1/10 of that of glass bottle; For packaging bottles with the same outer diameter, PET bottles are 1.5 times easier than glass bottles. Transparent or opaque brown bottle bodies can be made from PET raw materials. Medical PET bottles have good gas barrier property. Among the commonly used plastics, PET bottles have the best performance of blocking water vapor and oxygen, which can fully meet the special storage requirements of drug packaging. PET bottles have excellent chemical resistance and can be used for the packaging of all items except strong alkali and some organic solvents. The recycling rate of PET resin is higher than that of other plastics. When it is burned as waste, it is flammable due to its low combustion heat card value and does not produce harmful gases. The food packaging made of pet meets the requirements of food hygiene, because PET resin is not only a harmless resin, but also a pure resin without any additives. It has passed the inspection of quite strict food hygiene regulations including the United States, Europe and Japan, and is considered to be a qualified and safe packaging material for drugs and food.

script> I. main processing technology of pharmaceutical polyester bottles

1. The PET raw material used for bottle blow molding is saturated linear thermoplastic polyester, and the main application performance indicators are: the intrinsic viscosity (IV) should be controlled at 70 ~ 85ml/g, so that the blow molding bottle has high mechanical properties and transparency. It is used to stretch blow molded bottles with large volume (more than 2L). The intrinsic viscosity of polyester raw material is 70 ~ 75ml/g. Injection blow molding pharmaceutical small volumetric flasks should preferably be produced with higher intrinsic viscosity index. Because the correct selection of raw material varieties is related to the selection of molding process parameters in the production process and the quality of the bottle after molding, the process data such as the intrinsic viscosity, crystallization temperature, cooling rate and orientation effect of raw materials are particularly important in the production of pharmaceutical PET bottles. This is because polyester material is a crystallizable polymer with a crystallization rate of 6 μ m/min(max)。 That is, by controlling the crystallization temperature and cooling rate, the polyester bottle can become amorphous or crystalline, and the type and quantity of crystals can be changed. The crystallinity of polyester is generally about 30%. The orientation effect of polyester raw materials can make polyester molecules orderly arrange and promote crystallization. The formed crystals are called strain induced crystals. Their grains are very small and will not refract light. Therefore, the orientation produced by polyester bottles makes the bottle transparent. If you want to produce the bottle into hot filling and can be used for bar disinfection treatment, you also need to heat set the oriented and partially crystallized polyester to further crystallize it to improve heat resistance. Therefore, in the process characteristics of polyester raw materials, molecular crystallization and orientation are the key factors affecting the quality and performance of stretch blow molding polyester bottle.

2. Dehumidification and drying of polyester materials

as polyester materials are hygroscopic polymers, they should be strictly dried before processing and molding to make their residual moisture content less than 0 005%。 Polyester raw materials should be dried by dehumidification drying system. Drying conditions: drying temperature 140 ~ 180 ℃, air dew point 40 ℃, air volume 0 06 cmm/kgh。 The drying time is 4H. Attention should be paid to mastering these conditions: ① when the value of air volume is higher than 0 At 06cmm/kg · h, the operation range can be widened, the drying temperature can be reduced, and the energy consumption will be too high; ② It is very important to ensure that the dry dew point is as low as possible, but there will be no problem if the dew point is as high as 10 ℃, but it should also be strictly monitored until the reduced aperture is focused on the same plane as the slide to measure the air dew point. If it is found to be too high, it should be reduced in time. ③ The drying temperature is a key parameter. The best drying temperature can be determined by drying at various

temperatures and measuring the intrinsic viscosity of the parison, generally 150 ~ 163 ℃. The drying temperature should be reduced to about 120 ℃ during shutdown; ④ Lengthening the drying time will reduce the intrinsic viscosity of polyester raw materials. A reasonable grasp of the drying temperature has become a key parameter. A small increase in temperature will lead to a large reduction in the intrinsic viscosity of polyester. Therefore, the drying time should be as short as possible to broaden the operation range. In the drying process, due to the high drying temperature of polyester, the hopper of the equipment should have good heat insulation performance and use glass fiber as the heat insulation layer. It should avoid the contact between the dried polyester raw material and the outside air, because the polyester raw material will quickly absorb the moisture in the air. For example, the moisture content of completely dried polyester raw materials will reach 0.5% after contacting with air with a relative humidity of 35% - 40% for 12 minutes 005%。

II. Molding methods of pharmaceutical PET bottles

the molding methods of PET bottles include extrusion stretch blow molding and injection blow molding. Stretch blow molding can be divided into one-step and two-step methods. In one-step molding, the molding, cooling, heating, stretching and blow molding of the parison and the taking out of the bottle body are all completed on one machine in turn. The two-step method adopts extrusion or injection molding of the parison, and the parison is cooled to room temperature to become a semi-finished product, and then the parison is sent to the reheating stretch blow molding machine to become a bottle body. That is, the forming, stretching and blow molding of the parison are completed on two machines respectively. For one-step injection blow molding of PET bottles, two sets of molds are required in the injection and blow molding equipment, namely, injection mold and blow molding mold. The injection mold is mainly composed of mold cavity and mandrel. Whether the size parameters of each part are selected correctly is the key to whether the bottle body can be formed. Therefore, it is necessary to reasonably select the size parameters of the mold blank in combination with the molding process

1 ﹐ injection mold blank height and diameter parameters ﹐ the ratio of PET bottle height to neck thread diameter can determine the length diameter ratio (l/d) of parison and mandrel. Generally, the length diameter ratio of the mandrel should not exceed 10:1, because the mandrel in the parison mold is a cantilever beam and is subject to high injection pressure during mold filling. When the length diameter ratio is large, the bending is large, which is easy to cause uneven distribution of parison wall thickness. However, the filling speed of the melt can be controlled by program or the head end of the mandrel can be temporarily fixed with a sliding top gauge during the filling process to align the mandrel. At this time, the length diameter ratio of the mandrel can be taken as a larger value. The parison height is obtained by multiplying the height of the reference bottle body by the height coefficient, which is generally 92% - 95% of the bottle body height. In order to ensure the high transparency of the parison, after the melt is filled into the parison mold, the temperature should be quickly reduced to below 145 ℃. However, the glass transition temperature of the melt is higher than that of the polyester material (82 ℃), and the closer it is to the glass transition temperature, the higher the transparency of the blow molding bottle. The cooling water temperature of the parison mold is as low as 10 ~ 35 ℃. In order to quickly cool the parison, liquid or gas should be used to continuously internally cool the mandrel. The air cooling, Secretary General Cai Hengzhi of the injection molding special committee of Guangdong Plastic Association, can make the mandrel have a more consistent temperature distribution, and its cold air pressure is generally about 1MPa.

2. The value of the expansion ratio of the injection molding blank

injection blow molding of PET bottles with small volume mainly occurs in the circumferential tension during injection and blowing. The smaller the axial tension is, the greater the expansion ratio (refers to the ratio of the diameter of the bottle body to the diameter of the molding blank) is, the greater the possibility of uneven distribution of the bottle wall thickness is, and it is easy to cause uneven wall thickness at the curve between the bottle shoulder and the bottle body or between the bottle body and the filter area at the bottom of the bottle. The expansion ratio of small volume bottle is generally 1 5~1. 8. For the bottle body with elliptical cross-section, if its elliptical ratio, that is, the ratio of the length of the long and short axes of the ellipse, is less than 1.5 ∶ 1, the preform with circular cross-section can be formed. When the ellipse ratio does not exceed 2:1, the mandrel with circular cross-section and the oval blank cavity can be used to form the blank. When the ellipse ratio is greater than 2:1, it is generally required that both the mandrel and the blank die cavity be designed as ellipses. With the increase of ellipse ratio, the design difficulty and manufacturing cost of parison mold are increased, generally not more than 3:1.

3. The size of the mouth and neck of the injection molding blank

the diameter and thread size of the mouth of the molding blank should be consistent with the thread size of the bottle mouth, and can match the thread size of the bottle cap. Since there is no unified national standard for this at present, the size of the bottle mouth is determined according to the contents of the bottle body. When determining the neck size of the parison and the cavity size of the blow mold, the shrinkage of the bottle body after molding should also be considered. The inflation pressure of PET bottle in the parison is 1 2MPa, using cooling water with a water temperature of 5 ~ 10 ℃, how do you judge whether there is a problem with these equipment? This is very simple to mold, so that the mold can be cooled quickly after blowing.

4. The function and function of pet injection blow molding mandrel

the function and function of the mandrel used in injection blow molding mainly include five aspects: ① determine the shape of the molding blank and the inner diameter of the bottle neck; ② Take away the parison or bottle body in the process of mechanical transposition; ③ An air passage and an air inlet and outlet are arranged in the mandrel to convey compressed air to blow up the parison; ④ Liquid or air can be circulated inside the mandrel to adjust the parison temperature; ⑤ The depth at the end of the mandrel close to the mating surface is 0 10mm groove makes the end of the parison wedge into the groove to avoid the dislocation of neck threads caused by the elastic shrinkage of the parison during the process of transferring from the parison forming station to the blow molding station. The groove plays a sealing role and reduces the leakage of compressed air during the blow molding process.

5. Selection value of mandrel length and diameter

mandrel length and diameter are mainly determined by the parison, and the diameter of mandrel body is smaller than the inner diameter of bottle neck, so as to facilitate the demoulding of bottle body. However, the diameter of the mandrel should be within the inner diameter of the bottleneck, and the first tempering temperature should be taken as high as 585 ℃ as possible to avoid excessive expansion ratio. The coaxiality of mandrel should be within 0 05~0. Within 08mm, the diameter of the mandrel at the bottle mouth is determined by the outer diameter of the bottle mouth and the thickness of the bottle mouth. The value range is generally that the diameter of the mandrel at the bottle mouth is equal to the outer diameter of the bottle mouth minus twice the wall thickness of the bottle mouth.

6. Determination of the distance size between the bottom of the mandrel and the bottom of the parison

this distance size is the thickness of the bottom of the parison. Whether its size is reasonable or not directly affects whether the thickness of the bottom of the bottle meets the requirements. The commonly used calculation method is: the thickness (b) of the bottom of the parison is equal to the minimum thickness (T) of the bottle bottom plus 0 Twice the weight of the bottle (W)/g. The material selected for the mandrel body is alloy tool steel, and the hardness is hrc52-54. The hardness is slightly lower than that of the mold collar. The surface of the mandrel in contact with the melt should be polished along the melt flow direction and plated with hard chromium, so as to facilitate the melt filling and parison demoulding. In the blow molding and film removal station of PET bottle, the gas continues to circulate in the mandrel to ensure that the mandrel has a relatively consistent temperature distribution

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