Polyester plastic bottle (PET) is currently one of the most important packaging containers. It is mainly used for the packaging of medicines, carbonated beverages, and can also be used for liquor, tea drinks, fruit juices, mineral water, edible oils, spices, cosmetics, pesticides. Packed with liquids such as detergents. As a pharmaceutical packaging container, polyester bottles have a variety of advantages. First of all, the polyester bottles are light in weight, easy to mold, and firm. The strength and elasticity are significantly higher than other plastic materials, can withstand considerable impact without damage, and are most suitable as thin-walled, light-weight, high-strength pharmaceutical bottles. After the introduction of PET bottle in China in the early 1980s, it quickly developed with an irresistible momentum. In just 20 years, it has become the world's leading liquid and solid packaging container. In the field of pharmaceutical packaging applications, the PET bottle weighs about 1/10th of that of a glass bottle when the volume of the drug is the same, and the diameter of a PET bottle is 1.5 times that of a glass bottle. Transparent or opaque brown bottles can be made from PET stock. Second, medicinal PET bottles have good gas barrier properties. Among commonly used plastic materials, PET bottles have the best performance in blocking water vapor and oxygen and can fully meet the special storage requirements of pharmaceutical packaging. PET has excellent chemical resistance properties and can be used to package all substances except alkali and some organic solvents. Thirdly, the PET resin has a higher recycling rate than other plastics. When it is burned as waste, it has a low calorific value and is flammable and does not produce harmful gases. Fourth, food packaging made of PET meets the requirements for food hygiene because PET resin is not only a harmless resin, but also a pure resin without any additives. It has passed strict standards including the US, Europe and Japan. The food hygiene inspection is considered to be a qualified and safe medicine and food packaging material. These advantages make polyester bottles a leader in plastics. At present, polyester production worldwide is increasing at a double-digit rate. The pharmaceutical plastic bottle made of polyester as the main raw material is one of the most ideal packaging products in terms of appearance, gloss, physical and chemical properties and quality assurance.
Medicinal Polyester Bottle Processing Technology
1, the characteristics of medicinal polyester raw materials
The polyester (PET) raw material used for bottle blow molding is saturated linear thermoplastic polyester. The main application performance index is: the intrinsic viscosity (IV) should be controlled at 70-85 ml/g, so that the blow-molded bottle has a high degree of mechanical Strength and transparency; For large volume (greater than 2 liters) of the bottle body, the intrinsic viscosity of polyester raw materials is selected to be 70-75ml/g. It is advisable to use injection-blow-moulded pharmaceutical small-volume bottles for the production of high-viscosity materials. Since the selection of raw material varieties is correct or not, it is related to the selection of molding process parameters in the production process and the quality of the bottle body. Therefore, in the production of pharmaceutical PET bottles, process data such as intrinsic viscosity, crystallization temperature, cooling rate, and orientation effects of the raw materials are particularly important. This is because the polyester material is a crystallizable polymer with a very low crystallization rate of only 6 μm/min (max). That is, by controlling the conditions of the crystallization temperature and the cooling rate through the process, the polyester bottle becomes non-crystalline or crystalline, and the crystal type and quantity can be changed. The crystallinity required for polyesters is generally around 30%. At a temperature just above the glass transition temperature or slightly below the melting point, the crystallization rate of the polyester is very small and the crystallization takes a long time. At temperatures around 175° C., the crystallization time is much shorter. In short, the polyester is crystallized only by heating, and its crystallization process is slower, and it is possible to form larger spherulites with crystal grains, which refract light, make the product white, and have high brittleness. In addition, the crystallization rate of polyester decreases as its IV increases. The orientation allows the polyester molecules to be arranged in an orderly manner and promotes crystallization. The crystals formed are called strain-inducing crystals. The crystallites are small and do not refract light, so the oriented polyester article is transparent. If the partially oriented polyester sample is heat set and crystallized further, the sample is still transparent. Therefore, crystallization and orientation are the key factors influencing the performance of the stretch blow molded polyester bottle during molding. If the bottle is hot-filled and disinfected with a bar-type disinfectant, it is also necessary to heat-set a part of the crystallized polyester to further crystallize to improve the heat resistance.
2. Dewetting and drying of polyester materials
Due to the processing of the polyester, the moisture contained therein is rapidly consumed by chemical reaction with the polyester melt during the hydrolysis process, that is, moisture generates bubbles in the product. Hydrolysis will reduce the intrinsic viscosity of the polyester melt, but also affect the mechanical strength and performance of the product, while the polyester raw material is a hygroscopic polymer, so it should be strictly dried before processing to make its residual moisture content less than 0.005%. Polyester raw materials are dried using a desiccant drying system. As the dry hot air provided by the drying device enters the raw material from the bottom of the hopper, it absorbs the moisture contained in the raw material and returns to the drying device. In order to prolong the life of the dehumidifying bed in the desiccant device and maintain its efficiency, the humid air from the hopper is passed through a post-cooling device (which can be cooled with circulating water) so that the air temperature is lower than 65°C. Constant temperature control of the post-cooling unit is required to prevent the over-temperature air from entering the dehumidifying bed. The cooled air passes through the filter to remove airborne particles. The air is dehumidified by the dehumidifying bed and finally heated by the heater and returned to the drying hopper again. Drying conditions of the raw materials in the drier: the drying temperature is 140° C. to 180° C., the air dew point is −40° C., and the air amount is 0.06 cubic meters/min (kg.h). Drying time is 4h. To master the above conditions, attention should be paid to: (1) When the air volume value is higher than 0.06 cubic meters/min (kg.h), the operation range can be widened, and the drying temperature can be lowered, and the energy consumption can be too high. (2) It is important to ensure that the dew point of drying is as low as possible, but there will be no problem when the dew point is as low as -10°C; however, the dew point of the air should be strictly monitored. If it is found to be too high, it should be promptly reduced. (3) The drying temperature is a key parameter, and the optimum drying temperature can be determined by drying and measuring the intrinsic viscosity of the parison at various temperatures, typically from 150°C to 163°C. When shutting down, the drying temperature should be reduced to about 120°C. (4) Longer drying time will reduce the intrinsic viscosity of polyester raw materials. A reasonable understanding of the drying temperature is a key parameter. A small increase in temperature will result in a significant decrease in the intrinsic viscosity of the polyester. Therefore, the drying time should be as short as possible. Broaden the operating range. In the drying process, due to the high drying temperature of the polyester, the hopper of the equipment should have good thermal insulation properties and be made of glass fiber as the heat insulation layer. The contact of the dry polyester raw material with the outside air should be avoided because the polyester raw material will Quickly absorb moisture from the air. For example, when the completely dried polyester raw material is contacted with air having a relative humidity of 35% to 40% for 12 minutes, the moisture content reaches 0.005%.
Medicinal polyester bottle forming method
Polyester bottle molding methods include extrusion blow molding and injection blow molding. Stretch blow molding is divided into one step and two steps. In one-step molding, parison molding, cooling, heating, stretching and blow molding, and removal of the bottle body are performed in one machine in turn. The two-step method uses extrusion or injection molding of the parison, and the parison is cooled to room temperature to become a semi-finished product. The parison is then reheated and made into a bottle in a stretch blow molding machine. That is, parison molding, stretching, and blow molding are performed on two machines, respectively. One-step injection of blow-molded PET bottles requires two molds in the injection-blowing equipment, namely the injection mould and the blow mould. The injection mould is mainly composed of the mould cavity and the mandrel. The correctness of the selection of the dimension parameters of each part is the key to whether the bottle can be formed or not. Therefore, it is necessary to reasonably select the mold parison size parameters in combination with the molding process. 1. The ratio of PET bottle height to neck thread diameter can determine the ratio of length to diameter (L/D) of parison and mandrel
The principle of length and diameter ratio of the mandrel is generally no more than 10:1. This is because the mandrel is a cantilever beam in the parison mold and is subjected to high injection pressure during mold filling. When the ratio of length to diameter is large, the mandrel has a large curvature, which may cause uneven distribution of the parison and wall thickness. However, by controlling the filling rate of the melt through a program or temporarily fixing the tip end of the mandrel with a sliding thimbler during filling, the mandrel bar is centered. At this time, the aspect ratio of the mandrel bar can take a large value. The height of the parison is obtained by referring to the bottle height multiplied by the height coefficient, which is generally 92% to 95% of the height of the bottle body. In order to ensure good transparency of the bottle body, after the melt is filled into the parison mold, the temperature should be reduced to 145° C. or less quickly, but higher than the glass transition temperature (82° C.) of the polyester material, and the closer to vitrification. The temperature, the higher the transparency of the blown bottle. The temperature of parison mold cooling water is as low as 10°C-35°C. In order to quickly cool the parisons, continuous cooling of the mandrels with liquid or gas is also required, in which the cool air makes the mandrels have a more uniform temperature distribution, and the air pressure is generally low. About 1MPa.
2. Melt temperature during parison injection Melt temperature is one of the important parameters that PET parison molding should pay attention to. From the equipment side, the screw design has a great influence on PET melting, mixing uniformity and melt temperature. PET injection uses a screw with low shear and low compression ratio (about 2/1). The feed section is longer and the transition section and metering section are shorter. The barrel temperature of the equipment has a great influence on the melt temperature. Increasing the barrel temperature will reduce the intrinsic viscosity of the PET melt. The barrel temperature has a significant effect on the transparency of the parison. Increasing the barrel temperature can improve the transparency of the parison. For example, when the barrel temperature is 280°C, the corresponding melt temperature is 290°C, which ensures that the parison has the best transparency. The further increase in barrel temperature does not improve transparency. When the barrel temperature is low, the screw speed is appropriately increased to increase the temperature of the gate to improve the transparency of the parison in a small amount. However, due to the shorter time for the melt to pass through the hot runner system, its temperature improves the degree of transparency of the parison. When the injection pressure is increased, ie, the injection rate, a higher shear heat is generated when the melt passes through the nozzle, the melt temperature is significantly increased, and the transparent parison can be formed when the barrel temperature is low. When the holding pressure is high, the crystallization rate during the cooling of the melt in the parison mold will be increased and the transparency of the parison will be reduced, especially when the barrel temperature is low. In the actual production process, for a given polyester resin and molding equipment, the appropriate melt temperature can be determined by gradually lowering the temperature to the beginning of the parison, and then raising the temperature to just reach the molding and transparent The temperature of the parison becomes the appropriate melt temperature.
Acetaldehyde is contained in the injection blow molded preform (ie, the polyester bottle resin), which tends to cause chemical reactions in the packaged medicine, especially liquid medicine. Therefore, the acetaldehyde content of the preform must be controlled, generally less than 10 ppm. Reducing the acetaldehyde content of preforms is an important issue in the production process of polyester bottles. The acetaldehyde content of the preform is related to the temperature and residence time of the melt. When the melt temperature is lower than 265°C, the acetaldehyde content has a linear relationship with time; when the melt temperature is higher than 265°C, the two have an exponential relationship. Since the acetaldehyde content in the parison increases linearly with the barrel temperature, the increase in branch pipe and gate temperature will also slightly increase the acetaldehyde content, but the increase in the acetaldehyde content at the increase in the flow channel temperature will be smaller, because the melt The passage of the body through the hot runner system takes less time than it does in the barrel. Increasing the screw speed of the equipment at a lower value has no effect on the acetaldehyde content in the parison, but when the speed is further increased, the shear heat generated will increase the melt temperature and increase the acetaldehyde content. Increasing the back pressure will increase the melt temperature, thereby increasing the acetaldehyde content. Therefore, under the premise of ensuring the uniform plasticization of the polyester raw material, the back pressure should be reduced as much as possible. The melt temperature is increased when the injection pressure increases, but the acetaldehyde content is only slightly increased due to the shorter time the melt passes through the nozzle, and the holding pressure and the mold temperature have no effect on the acetaldehyde content.
Medicinal Polyester Bottle Processing Technology
1, the characteristics of medicinal polyester raw materials
The polyester (PET) raw material used for bottle blow molding is saturated linear thermoplastic polyester. The main application performance index is: the intrinsic viscosity (IV) should be controlled at 70-85 ml/g, so that the blow-molded bottle has a high degree of mechanical Strength and transparency; For large volume (greater than 2 liters) of the bottle body, the intrinsic viscosity of polyester raw materials is selected to be 70-75ml/g. It is advisable to use injection-blow-moulded pharmaceutical small-volume bottles for the production of high-viscosity materials. Since the selection of raw material varieties is correct or not, it is related to the selection of molding process parameters in the production process and the quality of the bottle body. Therefore, in the production of pharmaceutical PET bottles, process data such as intrinsic viscosity, crystallization temperature, cooling rate, and orientation effects of the raw materials are particularly important. This is because the polyester material is a crystallizable polymer with a very low crystallization rate of only 6 μm/min (max). That is, by controlling the conditions of the crystallization temperature and the cooling rate through the process, the polyester bottle becomes non-crystalline or crystalline, and the crystal type and quantity can be changed. The crystallinity required for polyesters is generally around 30%. At a temperature just above the glass transition temperature or slightly below the melting point, the crystallization rate of the polyester is very small and the crystallization takes a long time. At temperatures around 175° C., the crystallization time is much shorter. In short, the polyester is crystallized only by heating, and its crystallization process is slower, and it is possible to form larger spherulites with crystal grains, which refract light, make the product white, and have high brittleness. In addition, the crystallization rate of polyester decreases as its IV increases. The orientation allows the polyester molecules to be arranged in an orderly manner and promotes crystallization. The crystals formed are called strain-inducing crystals. The crystallites are small and do not refract light, so the oriented polyester article is transparent. If the partially oriented polyester sample is heat set and crystallized further, the sample is still transparent. Therefore, crystallization and orientation are the key factors influencing the performance of the stretch blow molded polyester bottle during molding. If the bottle is hot-filled and disinfected with a bar-type disinfectant, it is also necessary to heat-set a part of the crystallized polyester to further crystallize to improve the heat resistance.
2. Dewetting and drying of polyester materials
Due to the processing of the polyester, the moisture contained therein is rapidly consumed by chemical reaction with the polyester melt during the hydrolysis process, that is, moisture generates bubbles in the product. Hydrolysis will reduce the intrinsic viscosity of the polyester melt, but also affect the mechanical strength and performance of the product, while the polyester raw material is a hygroscopic polymer, so it should be strictly dried before processing to make its residual moisture content less than 0.005%. Polyester raw materials are dried using a desiccant drying system. As the dry hot air provided by the drying device enters the raw material from the bottom of the hopper, it absorbs the moisture contained in the raw material and returns to the drying device. In order to prolong the life of the dehumidifying bed in the desiccant device and maintain its efficiency, the humid air from the hopper is passed through a post-cooling device (which can be cooled with circulating water) so that the air temperature is lower than 65°C. Constant temperature control of the post-cooling unit is required to prevent the over-temperature air from entering the dehumidifying bed. The cooled air passes through the filter to remove airborne particles. The air is dehumidified by the dehumidifying bed and finally heated by the heater and returned to the drying hopper again. Drying conditions of the raw materials in the drier: the drying temperature is 140° C. to 180° C., the air dew point is −40° C., and the air amount is 0.06 cubic meters/min (kg.h). Drying time is 4h. To master the above conditions, attention should be paid to: (1) When the air volume value is higher than 0.06 cubic meters/min (kg.h), the operation range can be widened, and the drying temperature can be lowered, and the energy consumption can be too high. (2) It is important to ensure that the dew point of drying is as low as possible, but there will be no problem when the dew point is as low as -10°C; however, the dew point of the air should be strictly monitored. If it is found to be too high, it should be promptly reduced. (3) The drying temperature is a key parameter, and the optimum drying temperature can be determined by drying and measuring the intrinsic viscosity of the parison at various temperatures, typically from 150°C to 163°C. When shutting down, the drying temperature should be reduced to about 120°C. (4) Longer drying time will reduce the intrinsic viscosity of polyester raw materials. A reasonable understanding of the drying temperature is a key parameter. A small increase in temperature will result in a significant decrease in the intrinsic viscosity of the polyester. Therefore, the drying time should be as short as possible. Broaden the operating range. In the drying process, due to the high drying temperature of the polyester, the hopper of the equipment should have good thermal insulation properties and be made of glass fiber as the heat insulation layer. The contact of the dry polyester raw material with the outside air should be avoided because the polyester raw material will Quickly absorb moisture from the air. For example, when the completely dried polyester raw material is contacted with air having a relative humidity of 35% to 40% for 12 minutes, the moisture content reaches 0.005%.
Medicinal polyester bottle forming method
Polyester bottle molding methods include extrusion blow molding and injection blow molding. Stretch blow molding is divided into one step and two steps. In one-step molding, parison molding, cooling, heating, stretching and blow molding, and removal of the bottle body are performed in one machine in turn. The two-step method uses extrusion or injection molding of the parison, and the parison is cooled to room temperature to become a semi-finished product. The parison is then reheated and made into a bottle in a stretch blow molding machine. That is, parison molding, stretching, and blow molding are performed on two machines, respectively. One-step injection of blow-molded PET bottles requires two molds in the injection-blowing equipment, namely the injection mould and the blow mould. The injection mould is mainly composed of the mould cavity and the mandrel. The correctness of the selection of the dimension parameters of each part is the key to whether the bottle can be formed or not. Therefore, it is necessary to reasonably select the mold parison size parameters in combination with the molding process. 1. The ratio of PET bottle height to neck thread diameter can determine the ratio of length to diameter (L/D) of parison and mandrel
The principle of length and diameter ratio of the mandrel is generally no more than 10:1. This is because the mandrel is a cantilever beam in the parison mold and is subjected to high injection pressure during mold filling. When the ratio of length to diameter is large, the mandrel has a large curvature, which may cause uneven distribution of the parison and wall thickness. However, by controlling the filling rate of the melt through a program or temporarily fixing the tip end of the mandrel with a sliding thimbler during filling, the mandrel bar is centered. At this time, the aspect ratio of the mandrel bar can take a large value. The height of the parison is obtained by referring to the bottle height multiplied by the height coefficient, which is generally 92% to 95% of the height of the bottle body. In order to ensure good transparency of the bottle body, after the melt is filled into the parison mold, the temperature should be reduced to 145° C. or less quickly, but higher than the glass transition temperature (82° C.) of the polyester material, and the closer to vitrification. The temperature, the higher the transparency of the blown bottle. The temperature of parison mold cooling water is as low as 10°C-35°C. In order to quickly cool the parisons, continuous cooling of the mandrels with liquid or gas is also required, in which the cool air makes the mandrels have a more uniform temperature distribution, and the air pressure is generally low. About 1MPa.
2. Melt temperature during parison injection Melt temperature is one of the important parameters that PET parison molding should pay attention to. From the equipment side, the screw design has a great influence on PET melting, mixing uniformity and melt temperature. PET injection uses a screw with low shear and low compression ratio (about 2/1). The feed section is longer and the transition section and metering section are shorter. The barrel temperature of the equipment has a great influence on the melt temperature. Increasing the barrel temperature will reduce the intrinsic viscosity of the PET melt. The barrel temperature has a significant effect on the transparency of the parison. Increasing the barrel temperature can improve the transparency of the parison. For example, when the barrel temperature is 280°C, the corresponding melt temperature is 290°C, which ensures that the parison has the best transparency. The further increase in barrel temperature does not improve transparency. When the barrel temperature is low, the screw speed is appropriately increased to increase the temperature of the gate to improve the transparency of the parison in a small amount. However, due to the shorter time for the melt to pass through the hot runner system, its temperature improves the degree of transparency of the parison. When the injection pressure is increased, ie, the injection rate, a higher shear heat is generated when the melt passes through the nozzle, the melt temperature is significantly increased, and the transparent parison can be formed when the barrel temperature is low. When the holding pressure is high, the crystallization rate during the cooling of the melt in the parison mold will be increased and the transparency of the parison will be reduced, especially when the barrel temperature is low. In the actual production process, for a given polyester resin and molding equipment, the appropriate melt temperature can be determined by gradually lowering the temperature to the beginning of the parison, and then raising the temperature to just reach the molding and transparent The temperature of the parison becomes the appropriate melt temperature.
Acetaldehyde is contained in the injection blow molded preform (ie, the polyester bottle resin), which tends to cause chemical reactions in the packaged medicine, especially liquid medicine. Therefore, the acetaldehyde content of the preform must be controlled, generally less than 10 ppm. Reducing the acetaldehyde content of preforms is an important issue in the production process of polyester bottles. The acetaldehyde content of the preform is related to the temperature and residence time of the melt. When the melt temperature is lower than 265°C, the acetaldehyde content has a linear relationship with time; when the melt temperature is higher than 265°C, the two have an exponential relationship. Since the acetaldehyde content in the parison increases linearly with the barrel temperature, the increase in branch pipe and gate temperature will also slightly increase the acetaldehyde content, but the increase in the acetaldehyde content at the increase in the flow channel temperature will be smaller, because the melt The passage of the body through the hot runner system takes less time than it does in the barrel. Increasing the screw speed of the equipment at a lower value has no effect on the acetaldehyde content in the parison, but when the speed is further increased, the shear heat generated will increase the melt temperature and increase the acetaldehyde content. Increasing the back pressure will increase the melt temperature, thereby increasing the acetaldehyde content. Therefore, under the premise of ensuring the uniform plasticization of the polyester raw material, the back pressure should be reduced as much as possible. The melt temperature is increased when the injection pressure increases, but the acetaldehyde content is only slightly increased due to the shorter time the melt passes through the nozzle, and the holding pressure and the mold temperature have no effect on the acetaldehyde content.
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