A plastic bottle blow molding processing system and a molding processing method

Abstract

This invention discloses a plastic bottle blow molding system and method, relating to the field of plastic packaging molding technology. The system includes a zoned precision preheating mechanism, a multi-stage air-blowing stretch blow molding mechanism, an internal and external composite cooling mechanism, and a PLC control mechanism, arranged sequentially along the preform processing direction. The method includes preform conveying, zoned precision preheating, multi-stage air-blowing stretch blow molding, internal and external composite cooling, and demolding. This invention improves the preform temperature control accuracy to within ±1℃ and reduces wall thickness deviation to within ±0.05mm through independent cooling at the bottle mouth, 5-segment axial zone heating, and PID closed-loop temperature control. The precise synchronous coordination of three independent air paths with the stretch rod movement solves molding defects such as wrinkles and pitting. Synchronous cooling through a double-spiral reverse cooling channel outside the mold and a through-type cooling channel inside the stretch rod shortens the molding cycle from 3-4 seconds to 2-2.5 seconds.

Description

Technical Field

[0001] This invention relates to the field of plastic packaging molding technology, and in particular to a plastic bottle blow molding system and molding method. Background Technology

[0002] Plastic bottles are widely used in the packaging of beverages, food, pharmaceuticals, cosmetics, and other industries due to their advantages such as light weight, transparency, high strength, and corrosion resistance. Currently, plastic bottles are mainly produced using injection stretch blow molding. This process first prepares a preform with a threaded neck using an injection molding machine, and then heats and softens the preform before stretch blow molding it into shape.

[0003] Patent document CN106273360A published by the State Intellectual Property Office discloses a method and equipment for blow molding of plastic bottles. It mainly includes a preform conveying device, a heating device, a blow molding die, and an air blowing mechanism. The preform is heated and then fed into the die, where compressed air is introduced to inflate it into shape. After cooling, the bottle is demolded to obtain a plastic bottle. However, this existing technology still has significant shortcomings: the preform is heated as a single unit, making it impossible to control the temperature of different parts of the preform in sections. This easily leads to uneven heating of the bottle body, local overheating, or underheating, directly resulting in uneven wall thickness distribution of the molded plastic bottle, easily causing local thinning and cracking or local excessive thickness and wasting material; the air blowing process uses a single pressure for one-time blow molding, resulting in poor synchronization between preform stretching and inflation, poor molding effect for irregularly shaped or large-diameter bottles, and defects such as wrinkles and pitting on the bottle appearance; the die only has external cooling channels, resulting in low cooling efficiency and long cooling time. This not only prolongs the molding cycle but also easily causes bottle shrinkage and deformation due to asynchronous internal and external cooling, affecting the dimensional accuracy and pass rate of the finished product.

[0004] Patent document CN107856289B discloses a plastic bottle blow molding machine with zoned heating, which divides the heating device into 3 independent temperature control sections, but does not have an independent bottle mouth cooling protection structure, making the bottle mouth susceptible to heat deformation and resulting in insufficient thread precision; Patent document CN109263123A discloses a two-stage blow molding device, which adopts a two-stage structure of pre-blowing + main blowing, but does not have an independent pressure holding unit, and the pressure holding pressure naturally decreases with the main blowing pressure, resulting in insufficient internal pressure when the bottle body cools and shrinks, and poor dimensional stability.

[0005] Furthermore, existing technologies generally suffer from the following drawbacks: the infrared heating module uses open-loop control, resulting in low temperature control accuracy with errors exceeding ±5℃, further exacerbating uneven wall thickness; the internal cooling channels of the stretching rod are mostly blind-hole structures, leading to low heat exchange efficiency and asynchronous cooling between the inside and outside of the bottle, resulting in high shrinkage deformation rates; single-pressure blow molding is prone to over- or under-stretching, causing bottle bottom cracks and bottle body wrinkles; and the production process lacks data recording and traceability, making it difficult to pinpoint quality problems. None of the aforementioned existing technologies simultaneously solve the three major technical problems of "regional precise preheating + multi-stage synchronous blowing + independent internal and external flow cooling," making it impossible to simultaneously achieve high wall thickness accuracy, high yield, and short molding cycle. The wall thickness deviation of plastic bottles produced by existing technologies is generally above ±0.15mm, the finished product yield is below 95%, the molding cycle is as long as 3-4 seconds, production efficiency is low, and energy consumption is high, failing to meet the demands of high-speed, high-quality industrial production. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems in the prior art and provide a plastic bottle blow molding processing system and molding method. This invention can achieve precise preheating of bottle preforms in different zones, optimize the synchronization of preform stretching and blowing, greatly improve cooling efficiency, effectively improve the qualification rate and production efficiency of finished plastic bottles, and reduce energy consumption.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A plastic bottle blow molding processing system includes a zoned precision preheating mechanism, a multi-stage blowing and stretching blow molding mechanism, an internal and external composite cooling mechanism, and a PLC control mechanism electrically connected to each of the above mechanisms, arranged sequentially along the preform processing direction.

[0009] The zoned precision preheating mechanism includes a heating furnace body, a bottle neck cooling protection cover located at the furnace inlet, multiple independently temperature-controlled infrared heating modules arranged sequentially along the preform conveying direction, and infrared temperature sensors located at corresponding positions in each infrared heating module to detect the surface temperature of the preform within its heating area. The bottle neck cooling protection cover is an annular water-cooled structure with annular cooling channels surrounding the bottle neck, providing continuous cooling protection during preheating to prevent heat deformation and reduced thread precision. The multiple independently temperature-controlled infrared heating modules are arranged sequentially from top to bottom along the preform axis, corresponding to the area below the bottle neck, upper part of the bottle body, middle part of the bottle body, lower part of the bottle body, and bottom of the bottle body, enabling precise temperature control according to the molding requirements of different parts. The infrared heating modules use carbon fiber infrared heating tubes with a heating wavelength of 2–15 μm, matching the infrared absorption wavelength of PET material, resulting in higher heating efficiency and lower energy consumption.

[0010] The multi-stage blowing and stretching blow molding mechanism includes a blow molding die, a stretching rod that can move up and down along the preform axis, and a pre-blowing unit, a main blowing unit, and a pressure-holding blowing unit, each connected to the central air passage inside the stretching rod and independently controlled for on / off and pressure. Each of the pre-blowing unit, main blowing unit, and pressure-holding blowing unit includes an independent air tank, a high-speed solenoid valve, and a precision pressure regulating valve, capable of providing stable blowing pressures within different ranges. The blow molding die cavity wall has multiple vent holes with diameters of 0.1–0.3 mm evenly distributed. These vent holes are connected to a vacuum pumping device via an air collection pipe. The start and stop of the vacuum pumping device are controlled synchronously with the mold closing action by a PLC control mechanism, enabling rapid removal of residual air from the mold cavity after mold closing, avoiding air bubbles and pitting defects.

[0011] The internal and external composite cooling mechanism includes a spiral cooling water channel installed inside the blow mold cavity wall, a central cooling channel installed inside the stretching rod, and a closed-loop chiller unit with two independent water outlet branches, each independently controlling the cooling water flow of the spiral cooling water channel and the central cooling channel. The spiral cooling water channel adopts a double-spiral counter-flow channel structure, with the water flow directions of the two spiral channels being opposite and both flowing from the bottom of the bottle to the mouth, which improves heat exchange efficiency and makes the mold temperature distribution more uniform. The central cooling channel of the stretching rod is a through-channel, with the outlet located at the center of the bottom end of the stretching rod. After flowing through the central cooling channel, the cooling water is directly sprayed into the bottle body, achieving rapid forced cooling of the bottle body.

[0012] The PLC control mechanism is electrically connected to the infrared temperature sensor, each section of the infrared heating module, the pre-blowing unit, the main blowing unit, the pressure-holding blowing unit, the closed-loop chiller, and the vacuum pumping device. The PLC control mechanism also includes a human-machine interface, a data storage module, and an alarm module, used to set process parameters, display the operating status in real time, store production data, and issue audible and visual alarms when parameters are abnormal.

[0013] A method for blow molding plastic bottles includes the following steps:

[0014] Step 1: The injection-molded PET preforms are continuously fed into the zoned precision preheating mechanism at a set speed through the preform conveying mechanism;

[0015] Step 2: The bottle mouth cooling protection cover continuously cools and protects the bottle mouth. Multiple infrared heating modules independently heat the corresponding parts of the preform. Infrared temperature sensors detect the temperature of each part in real time and feed it back to the PLC control mechanism. The PLC uses a PID algorithm to automatically adjust the power of each heating module so that each part of the preform reaches the preset temperature.

[0016] Step 3: The preheated preform is conveyed into the blow molding mold. After the mold is closed, the vacuum pump is immediately activated to remove residual air from the mold cavity. At the same time, the stretching rod moves downward at a set speed to stretch the preform longitudinally. As the stretching rod is activated, the pre-blowing unit introduces low-pressure air to initially expand the preform. When the stretching rod reaches the preset bottom position, the main blowing unit is immediately activated to introduce high-pressure air to fully inflate the preform and make it tightly fit the inner wall of the mold cavity. Then, the system switches to the pressure-holding blowing unit to introduce medium-pressure air for pressure holding and shaping.

[0017] Step 4: At the same time as the pressure holding and shaping begins, the closed-loop chiller unit introduces cooling water at the set temperature into the spiral cooling water channel and the central cooling channel to simultaneously and forcibly cool the outside and inside of the bottle.

[0018] Step 5: After the pressure holding and cooling are completed simultaneously, the closed-loop chiller unit stops supplying water, opens the mold, and ejects the finished plastic bottle through the ejection mechanism, which is then transported to the next process.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. Precise preheating in zones significantly improves wall thickness uniformity: Through independent cooling at the bottle mouth, 5-segment axial zone heating, and PID closed-loop temperature control, the temperature control accuracy of each part of the preform is improved to within ±1℃, avoiding the problems of heat deformation at the bottle mouth and uneven heating of the bottle body. This reduces the wall thickness deviation of plastic bottles from more than ±0.15mm in the existing technology to within ±0.05mm, and increases the finished product qualification rate from below 95% to above 99%.

[0021] 2. Multi-stage synchronous blowing completely solves molding defects: Through the precise synchronous coordination of three independent air paths—pre-blowing, main blowing, and pressure-holding blowing—with the movement of the stretching rod, the matching between preform stretching and inflation is optimized, enabling the preform to expand uniformly and completely solving appearance defects such as wrinkles, pitting, and bottle bottom cracks. It is especially suitable for molding irregularly shaped bottles and large-diameter bottles.

[0022] 3. Internal and external composite cooling significantly shortens the molding cycle: Through the synchronous cooling of the external double spiral reverse cooling water channel of the mold and the internal through-type cooling channel of the tension rod, and the independent control of the flow rate of the two cooling water channels, the heat exchange efficiency is improved by more than 50%, the molding cycle is shortened from 3-4s to 2-2.5s, the production efficiency is increased by more than 40%, and the shrinkage deformation rate of the bottle body is reduced from more than 3% in the existing technology to less than 0.5%, and the dimensional accuracy is significantly improved.

[0023] 4. Closed-loop control throughout the entire process reduces energy consumption and labor costs: The PLC monitors and adjusts all process parameters in real time, significantly improving production stability and reducing energy consumption by more than 25%. At the same time, it enables full traceability of production data, facilitating the location of quality problems and process optimization. Attached Figure Description

[0024] Figure 1 This is a flowchart of a plastic bottle blow molding process according to the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that the technical means not described in detail in the following embodiments are all conventional means in the field, are not the key points of the invention, and will not be elaborated upon.

[0027] Example 1

[0028] This embodiment discloses a plastic bottle blow molding system and molding method for producing 500ml PET beverage bottles. The processing method of this embodiment is as follows: Figure 1 As shown.

[0029] The plastic bottle blow molding processing system includes a preform conveying mechanism, a zoned precision preheating mechanism, a multi-stage blowing and stretching blow molding mechanism, an internal and external composite cooling mechanism, and a PLC control mechanism connected in sequence.

[0030] The preform conveying mechanism adopts a chain conveyor, and the conveying speed is synchronized with the cycle of the preheating mechanism and the blow molding mechanism, which can smoothly and accurately convey the preform to each station.

[0031] The zoned precision preheating mechanism includes a heating furnace body, a bottle neck cooling protection cover located at the furnace inlet, five independently temperature-controlled infrared heating modules arranged sequentially along the preform conveying direction, and infrared temperature sensors corresponding to each heating module. The bottle neck cooling protection cover is a ring-shaped water-cooled structure with an internal ring-shaped cooling water channel surrounding the bottle neck, connected to a closed-loop chiller unit. The five independently temperature-controlled infrared heating modules correspond to the lower part of the bottle neck, the upper part of the bottle body, the middle part of the bottle body, the lower part of the bottle body, and the bottom of the bottle preform, respectively. The distance between adjacent heating modules is 5cm, and each heating module is 8cm long, matching the length of the corresponding part of the PET preform. The infrared heating modules use carbon fiber infrared heating tubes with a heating wavelength of 8μm. The infrared temperature sensors are installed directly above the corresponding heating module, with a detection distance of 15cm, covering the entire heating area of ​​the corresponding module.

[0032] The multi-stage blow molding mechanism includes a blow mold, a stretching rod that can move up and down along the preform axis, and a pre-blowing unit, a main blowing unit, and a pressure-holding blowing unit connected to the central air passage inside the stretching rod. The blow mold cavity wall has evenly distributed vent holes with a diameter of 0.2 mm and a spacing of 1.5 cm. These vent holes are connected to a vacuum pump via a 10 mm diameter gas collecting pipe at a 30° angle to the mold cavity wall. The outlets of the pre-blowing unit, main blowing unit, and pressure-holding blowing unit are all connected to the central air passage inside the stretching rod via one-way valves. The on / off state and pressure of the three units are independently controlled by a PLC control mechanism.

[0033] The internal and external combined cooling system includes a spiral cooling water channel installed inside the blow mold cavity wall, a central cooling channel installed inside the stretching rod, and a closed-loop chiller unit connected to the spiral cooling water channel and the central cooling channel. The spiral cooling water channel adopts a double-spiral counter-flow channel structure, with both spiral channels having a pitch of 2cm and a diameter of 6mm. The water flow directions in the two channels are opposite, both flowing from the bottom of the bottle to the mouth. The central cooling channel of the stretching rod is a through-channel with a diameter of 4mm, and its outlet is located at the center of the bottom end of the stretching rod. The closed-loop chiller unit has two independent water outlet branches, supplying water to the spiral cooling water channel and the central cooling channel respectively. The water flow rate of each branch is controlled by an independent electric regulating valve.

[0034] The PLC control mechanism is electrically connected to each of the above components and also includes a human-machine interface, a data storage module, and an alarm module.

[0035] The plastic bottle blow molding process using the above system includes the following steps:

[0036] Step 1: The injection-molded 500ml PET beverage bottle preform is continuously fed into the zoned precision preheating mechanism through the preform conveying mechanism;

[0037] Step Two: The bottle mouth cooling protection cover continuously cools and protects the bottle mouth. Five infrared heating modules independently heat different parts of the preform. Infrared temperature sensors detect the temperature of each part in real time and feed it back to the PLC control mechanism. The PLC uses a PID algorithm to automatically adjust the power of each heating module. Specifically, the cooling water temperature of the bottle mouth cooling protection cover is controlled at 18℃, keeping the bottle mouth temperature of the preform at 45℃; the temperature of the upper part of the bottle body is controlled at 92℃, the temperature of the middle part of the bottle body is controlled at 98℃, the temperature of the lower part of the bottle body is controlled at 102℃, and the temperature of the bottom of the bottle body is controlled at 108℃.

[0038] Step 3: The preheated preform is conveyed into the blow molding mold. After the mold closes, the vacuum pump is immediately activated to remove residual air from the mold cavity. At the same time, the stretching rod moves downward at a speed of 2.0 m / s to stretch the preform longitudinally, with a stretching ratio of 3:1. Simultaneously, the pre-blowing unit introduces low-pressure air at 0.3 MPa to initially expand the preform, with a pre-blowing time of 0.15 s. When the stretching rod reaches the preset bottom position, the main blowing unit immediately activates to introduce high-pressure air at 3.0 MPa to fully inflate the preform and tightly adhere it to the inner wall of the mold cavity, with a main blowing time of 0.25 s. Subsequently, the system switches to the pressure-holding blowing unit to introduce medium-pressure air at 1.2 MPa for pressure holding and shaping, with a pressure holding time of 0.4 s.

[0039] Step 4: At the same time as the pressure holding and shaping begins, the closed-loop chiller unit introduces 18°C ​​cooling water into the spiral cooling channel and the central cooling channel to simultaneously and forcibly cool the exterior and interior of the bottle. The cooling time is the same as the pressure holding time, which is 0.4 seconds.

[0040] Step 5: After the pressure holding and cooling are completed simultaneously, the closed-loop chiller unit stops supplying water, opens the mold, and ejects the finished plastic bottle through the ejection mechanism, which is then transported to the inspection and packaging process.

[0041] Example 2

[0042] This embodiment is basically the same as Embodiment 1, except that:

[0043] This example is used to produce 300ml PET mineral water bottles.

[0044] In step two, the cooling water temperature of the bottle mouth cooling protection cover is controlled at 15℃, so that the bottle mouth temperature of the preform is maintained at 40℃; the upper part of the bottle body temperature is controlled at 90℃, the middle part of the bottle body temperature is controlled at 95℃, the lower part of the bottle body temperature is controlled at 100℃, and the bottom of the bottle body temperature is controlled at 105℃.

[0045] In step three, the pre-blowing pressure is 0.2 MPa and the pre-blowing time is 0.1 s; the main blowing pressure is 2.0 MPa and the main blowing time is 0.2 s; the pressure holding blowing pressure is 1.0 MPa and the pressure holding time is 0.3 s; the stretching speed of the stretching rod is 1.5 m / s and the stretching ratio is 2.5:1.

[0046] In step four, the cooling water temperature is controlled at 15℃ and the cooling time is 0.3s.

[0047] Comparative Example 1

[0048] This comparative example uses the plastic bottle blow molding equipment and method disclosed in CN106273360A to produce 500ml PET beverage bottles. The specific parameters are as follows:

[0049] The system features integrated heating at 100℃, single-pressure blow molding with a blow pressure of 3.0MPa and a blow time of 0.6s, external mold cooling with a cooling time of 0.8s, and a molding cycle of 3.5s.

[0050] Performance test results

[0051]

[0052] As shown in the table above, compared with the prior art, the present invention can significantly improve the uniformity of wall thickness and the yield of finished products of plastic bottles, greatly shorten the molding cycle, improve production efficiency and reduce energy consumption.

[0053] This invention is not only applicable to blow molding of PET plastic bottles, but also to the production of other thermoplastic plastic bottles such as PP, PE, PC, and PETG. The system can adopt single-station, double-station, multi-station, or rotary structures to meet the needs of different production scales.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A plastic bottle blow molding processing system, characterized in that, It includes a zoned precision preheating mechanism, a multi-stage blowing and stretching blow molding mechanism, an internal and external composite cooling mechanism, and a PLC control mechanism that are electrically connected to each of the above mechanisms, arranged sequentially along the preform processing direction. The partitioned precision preheating mechanism includes a heating furnace body, a bottle mouth cooling protection cover set at the inlet of the heating furnace body, multiple independently temperature-controlled infrared heating modules arranged sequentially along the bottle preform conveying direction, and infrared temperature sensors set at corresponding positions of each infrared heating module to detect the surface temperature of the bottle preform within the heating area of ​​the module. The multi-stage blowing and stretching blow molding mechanism includes a blow molding die, a stretching rod that can move up and down along the preform axis, and a pre-blowing unit, a main blowing unit, and a pressure-holding blowing unit, all of which are connected to the central air passage inside the stretching rod and are independently controlled for on / off and pressure. The internal and external composite cooling mechanism includes a spiral cooling water channel installed in the mold cavity wall of the blow molding die, a central cooling channel installed inside the tension rod, and a closed-loop chiller unit with two independent water outlet branches that independently control the cooling water flow of the spiral cooling water channel and the central cooling channel. The PLC control mechanism is electrically connected to the infrared temperature sensor, each section of the infrared heating module, the pre-blowing unit, the main blowing unit, the pressure-holding blowing unit, and the closed-loop chiller unit.

2. The plastic bottle blow molding processing system according to claim 1, characterized in that, The bottle mouth cooling protection cover is an annular water-cooled structure with an annular cooling water channel surrounding the outer circumference of the bottle mouth inside. The annular cooling water channel is connected to a closed-loop chiller unit.

3. The plastic bottle blow molding processing system according to claim 1, characterized in that, The multi-segment independently temperature-controlled infrared heating module is arranged from top to bottom along the bottle preform axis, corresponding to the positions below the bottle mouth, the upper part of the bottle body, the middle part of the bottle body, the lower part of the bottle body, and the bottom of the bottle body. The infrared heating module adopts a carbon fiber infrared heating tube with a heating wavelength of 2-15μm, which matches the infrared absorption wavelength of PET material.

4. The plastic bottle blow molding processing system according to claim 1, characterized in that, The spiral cooling water channel adopts a double spiral reverse flow channel structure, with the water flow directions of the two spiral channels being opposite and both flowing from the bottom of the bottle to the mouth of the bottle; the central cooling channel of the tension rod is a through channel, with the outlet located at the center of the bottom end of the tension rod.

5. The plastic bottle blow molding processing system according to claim 1, characterized in that, The blow molding mold has multiple vent holes with a diameter of 0.1 to 0.3 mm evenly distributed on the cavity wall. The vent holes are connected to a vacuum pumping device through an air collection pipe. The start and stop of the vacuum pumping device are controlled synchronously by a PLC control mechanism and the mold closing action.

6. The plastic bottle blow molding processing system according to claim 1, characterized in that, The PLC control mechanism also includes a human-machine interface, a data storage module, and an alarm module, which are used to set process parameters, display the operating status in real time, store production data, and issue audible and visual alarms when parameters are abnormal.

7. A method for blow molding plastic bottles using the system described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: The injection-molded PET preforms are continuously fed into the zoned precision preheating mechanism at a set speed through the preform conveying mechanism; Step 2: The bottle mouth cooling protection cover continuously cools and protects the bottle mouth. Multiple infrared heating modules independently heat the corresponding parts of the preform. Infrared temperature sensors detect the temperature of each part in real time and feed it back to the PLC control mechanism. The PLC uses a PID algorithm to automatically adjust the power of each heating module so that each part of the preform reaches the preset temperature. Step 3: The preheated preform is conveyed into the blow molding mold. After the mold is closed, the vacuum pump is immediately activated to remove residual air from the mold cavity. At the same time, the stretching rod moves downward at a set speed to stretch the preform longitudinally. As the stretching rod is activated, the pre-blowing unit introduces low-pressure air to initially expand the preform. When the stretching rod reaches the preset bottom position, the main blowing unit is immediately activated to introduce high-pressure air to fully inflate the preform and make it tightly fit the inner wall of the mold cavity. Then, the system switches to the pressure-holding blowing unit to introduce medium-pressure air for pressure holding and shaping. Step 4: At the same time as the pressure holding and shaping begins, the closed-loop chiller unit introduces cooling water at the set temperature into the spiral cooling water channel and the central cooling channel to simultaneously and forcibly cool the outside and inside of the bottle. Step 5: After the pressure holding and cooling are completed simultaneously, the closed-loop chiller unit stops supplying water, opens the mold, and ejects the finished plastic bottle through the ejection mechanism, which is then transported to the next process.

8. The plastic bottle blow molding process according to claim 7, characterized in that, In step two, the cooling water temperature of the bottle mouth cooling protective cover is controlled at 15-20℃, so that the bottle mouth temperature of the preform is maintained at 40-50℃; the temperature of the upper part of the bottle body is controlled at 90-95℃, the temperature of the middle part of the bottle body is controlled at 95-100℃, the temperature of the lower part of the bottle body is controlled at 100-105℃, and the temperature of the bottom of the bottle is controlled at 105-110℃.

9. The plastic bottle blow molding process according to claim 7, characterized in that, In step three, the pre-blowing pressure is 0.2–0.5 MPa, and the pre-blowing time is 0.1–0.2 s; the main blowing pressure is 2.0–4.0 MPa, and the main blowing time is 0.2–0.3 s; the pressure holding blowing pressure is 1.0–1.5 MPa, and the pressure holding time is 0.3–0.5 s; the stretching speed of the stretching rod is 1.5–2.5 m / s, and the stretching ratio is 2.5:1–3.5:

1.

10. The plastic bottle blow molding process according to claim 7, characterized in that, In step four, the cooling water temperature is controlled at 15-20°C, and the cooling time is the same as the pressure holding time, which is 0.3-0.5 seconds.

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