hapter 4 Plastic Packaging Containers and Packaging Industry Essentials 169
DATE：2020/1/2 10:16:11 / READ： / SOURCE：This station
Chapter 4 Plastic Packaging Containers and Packaging Industry Essentials 169
Second, PET bottle molding process name meeting
The production process of biaxially stretched PET bottles is divided into two steps and one step. The two-step method is also called the cold parison method, and the one-step method is also called the hot parison method. No matter which process, the production process includes the three processes of raw material drying, parison production and parison stretch blow molding. (A) drying of raw materials
The water content in PET resin will be hydrolyzed during the PET melt molding process. As a result, the relative molecular mass of PET is reduced, the intrinsic viscosity of the PET raw resin is affected, the strength and other properties of PET bottles are reduced, and the
The alcohol leaves the terephthalic acid of the half ester and becomes acetaldehyde. For this reason, the water content in the raw PET resin should be below 50 mg / kg, preferably below 25 mg / kg. The most common drying method is the use of molecular sieve dehumidification. Several important aspects of molecular sieve dehumidification
The factors are: first, the average dew point of the gas operated by the molecular sieve dryer is lower than -40 ° C; second, the temperature of the dry hot air
Degree 170 ~ 180 ℃; third, the best hot air flow for drying 1kg injection molding PET pellets is 3.3m2 / h; fourth, the drying time is 4-7h
(Two) injection molding or extrusion
There are two types of PET bottle parison injection molding and strip cut molding, and most of them are produced by injection molding. In the selection of the injection molding process, the crystalline characteristics of the resin, the tendency to be easily whitened, and the possibility of acetaldehyde should be fully considered. The extrusion method first heats the extruded hollow pipe section, melts the bottom of the bottle, and finally forms a bottleneck. The injection method requires the melt to be fully plasticized, otherwise it will affect the transparency of the PET bottle. When the intrinsic viscosity is between 0.68 and 0.70, the barrel temperature is between 255280 ° C, 0.70 at about 255 ° C, and 0.68 at about 280 ° C in a linear relationship. To reduce the production of acetaldehyde,
Should limit the generation of shear heat; reduce back pressure (back pressure is less than 1.5 MPa); screw speed is 50 ～ 130r / min; injection speed is less than 280g / s; molding temperature should be as low as possible (but the material should be kept in the barrel (Internal energy can be fully plasticized); shorten the material
The residence time in the barrel requires a longer feed section, a shorter compression section for the homogenization section, and a compression ratio of 2. Generally, it is preferably between 251 and 270 ° C. As the gas above 21C of acetaldehyde has a strong taste, even a small amount will have a taste. Mold for parison, injection
Cooling conditions after injection affect transparency, stress, and dimensional accuracy. The parison injected into the cavity needs to be rapidly quenched below t
Temperature, otherwise it will be easy to shrink and affect the effect of biaxial stretching.
Reheating and stretch blow molding
In order to obtain a bottle with a uniform wall surface, if the parison needs to be reheated, the heating should be uniform. For crystalline forms such as PP and PET in the cold parison method and polymers, the suitable stretching temperature range is narrow and reheating is required. The temperature uniformity is particularly important, and for PVC and AN amorphous polymers, even if the temperature fluctuates during stretching, it has little effect. The comparison of the hot parison method and the stretch blow molding technology of different resins is shown in Table 4-3-4. The molding process of injection molding parison is shown in Figure 41. First
See Table 433 for the comparison of the forming methods.
Step, injection molding paper, molten magnetic resin is injected into the mold and quickly cooled to obtain transparent paper: in the second step, the injection molding paper is held by the lip mold at the thread part, and then sent to the heating station, and the inner and outer surfaces are heated; In three steps, the heated parison is sent to a stretch blow molding station for stretching and blow molding; in the fourth step, the stretch blow molded product is sent to a demolding station. PET bottle stretch ratio and performance comparison. See Table 4-3-5. It should be pointed out that PET stretch bottles, the bottle body is stretched more, so the wall thickness is thinner, and the bottle neck and the bottom of the bottle are stretched less, so it is thicker. In order to reduce the CO2 loss in carbonated beverage packaging, attention should be paid to : First, the surface area should be as small as possible, and a short and thick cylindrical shape should be designed. Second, the shoulder and bottom should be made of materials and designs that can increase the stretch rate as much as possible because stretching helps improve the gas barrier properties of PET. Third, as much as possible
Thin-walled
Second, PET bottle molding process name meeting
The production process of biaxially stretched PET bottles is divided into two steps and one step. The two-step method is also called the cold parison method, and the one-step method is also called the hot parison method. No matter which process, the production process includes the three processes of raw material drying, parison production and parison stretch blow molding. (A) drying of raw materials
The water content in PET resin will be hydrolyzed during the PET melt molding process. As a result, the relative molecular mass of PET is reduced, the intrinsic viscosity of the PET raw resin is affected, the strength and other properties of PET bottles are reduced, and the
The alcohol leaves the terephthalic acid of the half ester and becomes acetaldehyde. For this reason, the water content in the raw PET resin should be below 50 mg / kg, preferably below 25 mg / kg. The most common drying method is the use of molecular sieve dehumidification. Several important aspects of molecular sieve dehumidification
The factors are: first, the average dew point of the gas operated by the molecular sieve dryer is lower than -40 ° C; second, the temperature of the dry hot air
Degree 170 ~ 180 ℃; third, the best hot air flow for drying 1kg injection molding PET pellets is 3.3m2 / h; fourth, the drying time is 4-7h
(Two) injection molding or extrusion
There are two types of PET bottle parison injection molding and strip cut molding, and most of them are produced by injection molding. In the selection of the injection molding process, the crystalline characteristics of the resin, the tendency to be easily whitened, and the possibility of acetaldehyde should be fully considered. The extrusion method first heats the extruded hollow pipe section, melts the bottom of the bottle, and finally forms a bottleneck. The injection method requires the melt to be fully plasticized, otherwise it will affect the transparency of the PET bottle. When the intrinsic viscosity is between 0.68 and 0.70, the barrel temperature is between 255280 ° C, 0.70 at about 255 ° C, and 0.68 at about 280 ° C in a linear relationship. To reduce the production of acetaldehyde,
Should limit the generation of shear heat; reduce back pressure (back pressure is less than 1.5 MPa); screw speed is 50 ～ 130r / min; injection speed is less than 280g / s; molding temperature should be as low as possible (but the material should be kept in the barrel (Internal energy can be fully plasticized); shorten the material
The residence time in the barrel requires a longer feed section, a shorter compression section for the homogenization section, and a compression ratio of 2. Generally, it is preferably between 251 and 270 ° C. As the gas above 21C of acetaldehyde has a strong taste, even a small amount will have a taste. Mold for parison, injection
Cooling conditions after injection affect transparency, stress, and dimensional accuracy. The parison injected into the cavity needs to be rapidly quenched below t
Temperature, otherwise it will be easy to shrink and affect the effect of biaxial stretching.
Reheating and stretch blow molding
In order to obtain a bottle with a uniform wall surface, if the parison needs to be reheated, the heating should be uniform. For crystalline forms such as PP and PET in the cold parison method and polymers, the suitable stretching temperature range is narrow and reheating is required. The temperature uniformity is particularly important, and for PVC and AN amorphous polymers, even if the temperature fluctuates during stretching, it has little effect. The comparison of the hot parison method and the stretch blow molding technology of different resins is shown in Table 4-3-4. The molding process of injection molding parison is shown in Figure 41. First
See Table 433 for the comparison of the forming methods.
Step, injection molding paper, molten magnetic resin is injected into the mold and quickly cooled to obtain transparent paper: in the second step, the injection molding paper is held by the lip mold at the thread part, and then sent to the heating station, and the inner and outer surfaces are heated; In three steps, the heated parison is sent to a stretch blow molding station for stretching and blow molding; in the fourth step, the stretch blow molded product is sent to a demolding station. PET bottle stretch ratio and performance comparison. See Table 4-3-5. It should be pointed out that PET stretch bottles, the bottle body is stretched more, so the wall thickness is thinner, and the bottle neck and the bottom of the bottle are stretched less, so it is thicker. In order to reduce the CO2 loss in carbonated beverage packaging, attention should be paid to : First, the surface area should be as small as possible, and a short and thick cylindrical shape should be designed. Second, the shoulder and bottom should be made of materials and designs that can increase the stretch rate as much as possible because stretching helps improve the gas barrier properties of PET. Third, as much as possible
Thin-walled
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