Blow molding processing technology for PET bottle without butt seam at bottom

Abstract

The invention relates to the technical field of plastic container forming, and discloses a blow molding processing technology for a PET bottle without a butt seam at the bottom, which comprises the following steps: step 1, preparation of a preform and material selection: using high-viscosity PET resin, adding 0.3-0.5% of nano silicon dioxide modifier, and improving the crystallization rate and thermal stability; a hot runner system is adopted, and an injection point is located at the position, 5-8 mm away from the bottom edge, of the side wall of the preformed blank; the process parameters are as follows: the injection pressure is 80-100MPa, the pressure holding time is 3-5s, the mold temperature is 40-60 DEG C, and the uniformity of the bottom wall thickness is ensured to be greater than or equal to 95%; and step 2, heating the preformed blank, and adopting an infrared heating system: adopting a subarea temperature control furnace, wherein the temperature of a bottom area is 5-8 DEG C lower than that of a main body. Through optimization design of injection points of the preform, the injection points are shifted to the side wall of the preform, the asymmetrical runner design is combined, fusion lines are prevented from being converged in the center of the bottle bottom, a hot runner system is adopted, it is ensured that materials in the injection point area are evenly filled, and the visibility of the fusion lines is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic container molding, and particularly relates to a processing method for realizing a seamless bottom of a PET bottle by improving the blow molding process, which is applicable to application scenarios with high requirements for container sealing performance, structural strength and appearance consistency in the packaging fields such as beverages, cosmetics, and pharmaceuticals. Background Art

[0002] A PET bottle is a plastic bottle made of polyethylene terephthalate (PET) as raw material, which has the characteristics of light weight, high transparency, strong impact resistance, etc., and is widely used in the fields of food and beverage, daily chemical packaging, etc. In the production of traditional two-step (injection - stretch blow molding) PET bottles, an injection point is usually set at the bottom of the preform. During blow molding, the molten PET material flows and fuses around the injection point, forming an obvious weld line. This structure has the following defects: Structural weakness: The material fusion strength at the weld line is lower than that of the main body, resulting in a decrease in the bottom pressure resistance performance, and it is easy to deform or leak during high-pressure filling or hot filling.

[0003] Appearance defect: The transparency of the weld line area decreases due to the difference in material orientation, showing visible flow marks or whitening phenomena, which affects the aesthetics of high-end packaging.

[0004] Material waste: To cover up the weld line defect, the traditional process needs to increase the bottom wall thickness, resulting in a reduction in material utilization rate; To solve the above problems, the industry has tried various technical solutions, but all have significant limitations: In-mold labeling (IML) technology for the bottom: By pre-setting labels in the mold to cover the weld line, but it increases the process complexity and cost, and cannot improve the structural strength.

[0005] Injection point offset technology: Moving the injection point to the side wall of the preform, but there is still a small weld line at the bottom, and the improvement of pressure resistance performance is limited.

[0006] 3D blow molding technology: Realizing non-symmetric bottom molding through a complex mold, but the equipment investment is high and the production efficiency is low, making it difficult to be applied on a large scale; Therefore, the present invention proposes a blow molding process for a PET bottle with a seamless bottom. By systematically optimizing the preform design, blow molding parameters and mold technology, it breaks through the limitations of the traditional process, provides an efficient and economical solution for the seamless bottom processing of PET bottles, and has significant technological innovation and market application value. Summary of the Invention

[0007] The purpose of the present invention is to provide a blow molding process for a PET bottle with a seamless bottom to solve the problems raised in the above background art.

[0008] To achieve the above object, the present invention provides the following technical solutions: A blow molding process for PET bottles without butt joints at the bottom, comprising the following steps: Step 1: Preparation of preforms Material selection: Use high-viscosity PET resin and add 0.3 - 0.5% nano-silica modifier to improve the crystallization rate and thermal stability; Mold design: Adopt a hot runner system, and the injection point is located 5 - 8 mm from the bottom edge on the side wall of the preform; Process parameters: Injection pressure 80 - 100 MPa, holding time 3 - 5 s, mold temperature 40 - 60 °C, ensuring that the bottom wall thickness uniformity ≥ 95%.

[0009] Step 2: Heating of preforms Infrared heating system: Adopt a zone temperature control furnace, and the temperature of the bottom area is 5 - 8 °C lower than that of the main body to prevent material degradation caused by overheating at the bottom; Axial temperature compensation: Through real-time feedback of a laser thermometer, perform dynamic compensation of 1 - 2 °C on the bottom edge to eliminate uneven heating; Step 3: Blow molding Stretch blow molding parameters: Stretching rod speed: Adopt three-stage control, namely initial rapid stretching, medium-speed transition, and low-speed holding pressure, and the stretching speed in the bottom area is reduced by 20%; Blow molding pressure: The pressure in the high-pressure stage is 12 - 15 MPa, and the holding time is 0.8 - 1.2 s to ensure that the bottom fully fits the mold; Temperature control: The temperature of the preform drops to 85 - 95 °C before blow molding to avoid bottom overheating and deformation; Key mold design: Bottom cavity: Set a demolding slope of 0.5 - 1°, and cooperate with surface chrome plating treatment (surface roughness Ra ≤ 0.1 μm); Exhaust system: Add a micro-exhaust groove (depth 0.02 - 0.05 mm) at the bottom edge to prevent wall thickness non-uniformity caused by gas retention; Step 4: Post-treatment Heat setting: Keep in a hot air circulation furnace at 80 - 90 °C for 10 - 15 s to eliminate internal stress at the bottom and improve the heat resistance performance to 85 °C (the traditional process is 75 °C); On-line inspection: Ultrasonic wall thickness inspection: The minimum wall thickness at the bottom ≥ 0.35 mm (tolerance ± 0.05 mm); Visual inspection system: Adopt an 8-million-pixel industrial camera to 100% detect butt joint traces at the bottom (detection accuracy 0.01 mm).

[0010] Preferably, the specific steps in Step 1 are as follows: S1.1. First, select a high-viscosity PET resin with an intrinsic viscosity IV = 0.80 - 0.85 dl / g. The molecular chain length of this resin can increase the material crystallization rate by more than 30%. At the same time, add 0.3 - 0.5% of fumed nano-silica (particle size 10 - 20 nm) through nano-modification technology to form a three-dimensional network structure in the resin matrix, raising the heat distortion temperature of the material to 135°C and shortening the injection molding cycle by 15%; S1.2. Use a dehumidifying dryer to pre-crystallize the PET raw material. The drying temperature is 165°C, the dew point ≤ -40°C, ensuring a moisture content ≤ 30 ppm to avoid silver streak defects during the blow molding process; S1.3. Adopt a valve-type hot runner system. The injection point is accurately positioned 5 - 8 mm from the bottom edge of the side wall of the preform. Balance the pressure difference between cavities ≤ 2 MPa through CAE runner simulation (Moldex3D) to ensure uniform melt filling; Plate the surface of the mold cavity with hard chromium (thickness 0.25 μm) and polish it to a mirror finish (Ra ≤ 0.05 μm) to reduce the melt flow resistance; S1.4. Injection stage: Adopt multi-stage injection (slow - fast - slow). The injection speed is stepped up from 50 mm / s to 200 mm / s, the injection pressure is 80 - 100 MPa, the holding pressure time is 3 - 5 s, and the holding pressure is designed to decrease (from 80 MPa to 60 MPa) to compensate for material shrinkage; Temperature control system: The temperature of the moving mold of the mold is 50°C, and the temperature of the stationary mold is 45°C. Real-time feedback is carried out through thermocouples, and the temperature fluctuation ≤ ±1°C; S1.6. Configure an infrared on-line thickness gauge (accuracy ±2 μm) to perform a 360° scan on the bottom of the preform. The wall thickness uniformity ≥ 95%, and the thickness tolerance of the key control point (KPC) is ±0.05 mm.

[0011] Preferably, the specific steps in Step 2 are as follows: S2.1. First, divide the furnace body into a bottle body area of 95 - 105°C, a transition area of 100 - 110°C, and a bottom area of 90 - 98°C. Use short-wave infrared heating tubes with a wavelength of 1.2 - 1.6 μm, and reduce the power density of the bottom area by 20% (from 120 W / cm² to 96 W / cm²); S2.2. Then configure a high-speed circulating fan with a wind speed of 8 m / s to strengthen the hot air convection and ensure the temperature field uniformity in the furnace ±2°C; S2.3. Real-time collect the temperature of the bottom edge through a laser temperature measurement array (8 points / bottle), and the PID control system dynamically adjusts the heating power with a compensation accuracy of ±1°C and a response time ≤ 0.2 s.

[0012] Preferably, the specific steps in Step 3 are as follows: S3.1. Three-stage stretching system driven by servo motor: Fast stretching section, 0 - 50 mm stroke: speed 800 mm / s to achieve pre-stretching; Medium-speed transition section, 50 - 100 mm stroke: speed reduced to 400 mm / s to avoid material rupture; Low-speed pressure-holding section, 100 - 150 mm stroke: speed 100 mm / s, pressure-holding time 0.8 - 1.2 s to ensure complete bottom mold sticking; the stretching speed in the bottom area is reduced by 20% compared with the traditional process to reduce excessive molecular chain orientation; S3.2. High-pressure blow molding pressure is 12 - 15 MPa, and pressure step loading is achieved through a proportional valve (linearly rising from 5 MPa to 15 MPa), and the pressure fluctuation in the pressure-holding stage ≤ ±0.5 MPa; S3.3. The bottom cavity is set with a demolding slope of 0.5 - 1°, and is combined with quenching treatment of P20 die steel (HRC52 - 55) to extend the die life to more than 1 million moldings.

[0013] S3.4. Surface chrome plating treatment (thickness 0.3 μm) and coated with PTFE coating (thickness 5 μm), the friction coefficient is reduced to 0.15; S3.5. 8 - 12 micro-exhaust grooves (depth 0.02 - 0.05 mm, width 0.5 mm) are evenly distributed at the bottom edge, and the layout is optimized through CFD simulation to avoid wall thickness deviation caused by gas retention.

[0014] Preferably, the specific steps in step four are as follows: S4.1. Specifically adopt two-stage heat treatment: Preheating stage: 80°C hot air circulation for 3 s to make the material enter the high elastic state; Sizing stage: Keep warm at 90°C for 10 - 15 s, precisely controlled by an infrared radiation heater (wavelength 2 - 3 μm) to eliminate the residual internal stress at the bottom and improve the heat resistance performance to 85°C (10°C higher than the traditional process); S4.2. For ultrasonic wall thickness detection, a 5 MHz focused probe is specifically used to perform spiral scanning (step 0.5 mm) on the bottom, and the minimum detected wall thickness ≥ 0.35 mm, and the CV value of the thickness distribution ≤ 3%; S4.3. The vision inspection system specifically uses an industrial camera with 8 million pixels to perform 100% full inspection under D65 light source, the inspection accuracy is 0.01 mm, and it can identify micro-defects with a width of 0.02 mm.

[0015] The present invention provides a blow molding process for PET bottles without butt joints at the bottom. It has the following beneficial effects: (1) Through the optimized design of the injection points of the preform, the injection points are offset to the side wall of the preform, and combined with the asymmetric runner design, to avoid the weld lines converging at the center of the bottle bottom. A hot runner system is adopted to ensure uniform filling of the material in the injection point area and reduce the visibility of the weld lines.

[0016] (2) Through the dynamic stretching control technology, a segmented stretching rod is developed. By controlling the velocity gradient, uniform stretching of the bottom material is achieved, avoiding the wall thickness deviation caused by uneven stretching in the traditional process. Combined with infrared heating and temperature gradient control, it ensures that the bottom material maintains the best ductility during the blow molding process.

[0017] (3) Through the compensation design of the mold cavity, the hydrodynamic simulation is used to optimize the bottom surface of the mold, offsetting the phenomenon of uneven thickness caused by the inertia of material flow, achieving a bottom wall thickness uniformity of ≥95%. Micro exhaust grooves are provided at the bottom of the mold to prevent uneven wall thickness caused by gas retention. Brief Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the process steps of the present invention; Figure 2 It is a view showing the comparison of key performance indicators of various test items in the blow molding process of the PET bottle of the present invention. Detailed Description of the Embodiment

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0020] Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation of the present invention. Embodiment 1

[0021] Taking the production of a 250 ml carbonated beverage bottle as an example A preferred embodiment of a blow molding process for a PET bottle without a butt joint at the bottom provided by the present invention is as Figure 1-2 shown: A blow molding process for a PET bottle without a butt joint at the bottom includes the following steps: Step 1. Preparation of the preform Raw material preparation: Select a high-viscosity PET resin with an intrinsic viscosity IV = 0.82 dl / g, add 0.4% of fumed nano-silica (particle size 15 nm), and after uniform dispersion by a high-speed mixer (rotation speed 1500 rpm), convey it to the dehumidifying and drying system. Drying process parameters: drying temperature 165 °C, dew point -45 °C, drying time 4 h, ensuring that the moisture content of the raw material ≤ 25 ppm.

[0022] Injection molding: Mold configuration: Adopt a valve-type hot runner system, and the injection point is accurately positioned 6 mm from the bottom edge on the side wall of the preform. The surface of the mold cavity is plated with hard chromium (thickness 0.25 μm) and polished to Ra ≤ 0.05 μm. The runner balance simulation (Moldex3D) shows that the pressure difference between cavities ≤ 1.5 MPa.

[0023] Process parameters: injection pressure 90 MPa, injection speed is controlled in three stages (initial 50 mm / s → middle section 150 mm / s → end 80 mm / s), holding pressure time 4 s, holding pressure decreases linearly from 80 MPa to 60 MPa. The moving mold temperature is 50 °C, and the fixed mold temperature is 45 °C. Through real-time feedback of thermocouples, the temperature fluctuation ≤ ±0.8 °C.

[0024] Quality inspection: An infrared on-line thickness gauge (accuracy ±1.5 μm) scans the bottom of the preform 360°. The results show that the wall thickness uniformity reaches 96.2%, and the thickness tolerance of the key control point (KPC) is ±0.04 mm.

[0025] Step two, preform heating Infrared heating system: The furnace body is divided into a bottle body area (100 °C), a transition area (105 °C), and a bottom area (95 °C). Short-wave infrared heating tubes (wavelength 1.4 μm) are used, and the power density of the bottom area is 96 W / cm². A high-speed circulating fan (wind speed 8 m / s) is configured, and the temperature field uniformity in the furnace is ±1.5 °C.

[0026] Dynamic compensation: A laser temperature measurement array (8 points / bottle) collects the temperature at the bottom edge in real time, and the PID control system dynamically adjusts the heating power. The compensation accuracy is ±0.8 °C, the response time is 0.15 s, and finally the temperature fluctuation at the bottom edge ≤ ±1.2 °C.

[0027] Step three, blow molding Stretch blow molding: Stretch rod control: Adopt a three-stage stretch system driven by a servo motor: Fast stretch section (0 - 50 mm stroke): speed 800 mm / s; Medium-speed transition section (50 - 100 mm stroke): speed drops to 400 mm / s; Low-speed pressure holding section (100 - 150 mm stroke): speed 100 mm / s, pressure holding time 1.0 s.

[0028] The stretching speed in the bottom area is reduced by 20% compared with the traditional process to avoid excessive molecular chain orientation.

[0029] Pressure control: The high-pressure blow molding pressure is 13 MPa, and the pressure step loading is achieved through a proportional valve (linearly rising from 5 MPa to 15 MPa), and the pressure fluctuation in the pressure holding stage is ≤ ±0.3 MPa.

[0030] Mold design: A demolding slope of 0.8° is set in the bottom cavity, combined with quenching treatment (HRC54) of P20 mold steel, surface chrome plating (thickness 0.3 μm) and PTFE coating (thickness 5 μm) are applied, and the friction coefficient is 0.15.

[0031] 10 micro exhaust grooves (depth 0.03 mm, width 0.5 mm) are evenly distributed at the bottom edge. After optimizing the layout by CFD simulation, the wall thickness deviation is reduced to ±0.03 mm.

[0032] Step Four, post-treatment Heat setting: Adopt a two-stage heat treatment process: Preheating stage: 80 °C hot air circulation for 3 s; Setting stage: Keep warm at 90 °C for 12 s, precisely controlled by an infrared radiation heater (wavelength 2.5 μm). After heat setting, the elimination rate of the residual internal stress at the bottom is ≥90%, and the heat resistance performance reaches 85 °C.

[0033] Online detection: Ultrasonic wall thickness detection: 5 MHz focused probe spiral scanning (step 0.5 mm), the minimum detectable wall thickness is 0.36 mm, and the CV value of the thickness distribution is 2.8%.

[0034] Vision detection system: A 8-million-pixel industrial camera conducts full inspection under D65 light source, successfully identifies micro defects with a width of 0.02 mm, and the qualified rate is 99.6%. Example Two

[0035] Taking the production of 500 ml hot-filled juice bottles as an example Please refer to Figures 1-2 ., and on the basis of Example One, further obtain: A blow molding process for PET bottles without butt joints at the bottom, and the key points of process adjustment are: Preform preparation: The addition amount of nano-silica is increased to 0.5% to improve the heat resistance of the material; the injection pressure is adjusted to 95 MPa, and the pressure holding time is extended to 5 s to compensate for the shrinkage of the hot-filled bottle.

[0036] Heating system: The temperature of the bottom area is raised to 98°C to enhance the material fluidity; the laser temperature measurement compensation accuracy is ±0.5°C to ensure heating uniformity.

[0037] Blow molding: The high-pressure blow molding pressure is increased to 14 MPa, and the holding time is extended to 1.2 s; the demolding taper of the bottom cavity is adjusted to 1°, and the depth of the exhaust groove is increased to 0.05 mm to meet the requirements of thicker wall thickness.

[0038] Heat setting: The temperature in the setting stage is raised to 92°C, and the heat preservation time is 15 s, so that the heat resistance performance reaches 88°C to meet the requirements of 95°C hot filling. Example 3

[0039] For the production of 100 ml cosmetic essence bottles Please refer to Figures 1-2 and on the basis of Example 1, further obtain: A blow molding process for PET bottles without butt joints at the bottom, and the key points of process adjustment are: Preform preparation: Use PET resin with IV = 0.80 dl / g, and the injection pressure is reduced to 80 MPa to avoid flashing of thin-walled parts; the accuracy of the infrared thickness gauge is improved to ±1 μm to ensure that the wall thickness uniformity is ≥97%.

[0040] Heating system: The temperature of the bottom area is reduced to 92°C to prevent overheating and deformation of thin-walled parts; the number of laser temperature measurement points is increased to 12 points / bottle, and the compensation accuracy is ±0.3°C.

[0041] Blow molding: The speed of the stretching rod is reduced by 10% overall, and the holding time is shortened to 0.8 s; the surface roughness of the mold is reduced to Ra ≤ 0.08 μm to improve the transparency of the bottle body.

[0042] Visual inspection: Use an industrial camera with 12 million pixels, and the detection accuracy is 0.005 mm to ensure that there are no visible defects at the bottom.

[0043] The products produced through the above examples, after testing: As Figure 2 shown in the comparison of key performance indicators: Bottom pressure resistance: Through dynamic stretching control and mold optimization, the pressure resistance of Examples 1-3 is increased by 37.5% - 62.5% compared with the traditional process, meeting the requirements of high-pressure carbonated beverages (≥1.2 MPa) and hot filling (≥0.9 MPa).

[0044] Straightness of the bottle body: Laser three-dimensional scanning shows that the straightness deviation of the process of the present invention is reduced by 60% - 73%, significantly improving the appearance consistency of the bottle body and reducing the subsequent labeling failure rate.

[0045] Material utilization rate: Through optimized preform design, the PET consumption per bottle is reduced by 3.5% - 4.1%. Calculated based on an annual production capacity of 100 million bottles, the annual cost savings are approximately 1.2 - 1.5 million yuan.

[0046] Bottom heat resistance: The heat resistance temperature is increased by 13.3% - 17.3% through nano - silica modification and heat - setting process. Example 2 meets the requirements of 95°C hot filling, while the traditional process can only withstand 75°C.

[0047] Detection accuracy: A 12 - megapixel industrial camera enables defect recognition with a precision of 0.005 mm, which is 10 times higher than that of the traditional 5 - megapixel system, ensuring no visible docking seam marks at the bottom.

[0048] In summary, through the dynamic stretching control technology (the stretching speed in the bottom area is reduced by 20%) and die - cavity optimization (0.5 - 1° draft angle + PTFE coating), the bottom pressure resistance of Examples 1, 2, and 3 is increased by 37.5% - 62.5% compared with the traditional process. Among them, the 250 - ml carbonated beverage bottle reaches 1.2 MPa, and the 500 - ml hot - filling bottle reaches 1.3 MPa, meeting the requirements of high - pressure containers (≥1.2 MPa) and 95°C hot filling, breaking through the pressure - resistance limit of the traditional process; The two - stage heat - setting process (pre - heating at 80°C + setting at 90 - 92°C) enables the elimination rate of residual internal stress at the bottom to be ≥90%, and the heat - resistance performance is increased by 13.3% - 17.3%. The heat - resistance temperature of the hot - filling bottle in Example 2 reaches 88°C, which is 13°C higher than that of the traditional process; The offset design of the preform injection point (5 - 8 mm on the side wall) combined with nano - silica modification (addition amount of 0.3 - 0.5%) reduces the PET consumption per bottle by 3.5% - 4.1%; The infrared heating system with zone - controlled temperature (the temperature of the bottom area is 5 - 8°C lower than that of the main body) and laser dynamic compensation (accuracy of ±0.3 - 0.8°C) reduces the heating energy consumption by 15% - 20% and increases the production efficiency by 8% - 10%; The surface of the die - cavity is chrome - plated + PTFE coating (Ra≤0.08μm) and the CFD - optimized exhaust groove (depth of 0.02 - 0.05 mm) increases the transparency of the bottle body by 60% - 73% (haze≤1.5%), meeting the requirement of light transmittance ≥90% for high - end cosmetic packaging; The upgrade of the visual inspection system (12 - megapixel industrial camera + 0.005 - mm detection accuracy) enables 100% detection of minute defects (≥0.02 mm) at the bottom, and the defect recognition ability is 10 times higher than that of the traditional process (5 - megapixel, 0.05 - mm accuracy), with a comprehensive qualification rate ≥99.5%.

[0049] It should be noted that in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0050] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A blow molding process for PET bottles without butt joints at the bottom, characterized in that: The following steps are involved: Step 1: Preform preparation Material selection: Use high-viscosity PET resin and add 0.3-0.5% nano-silica modifier to improve crystallization rate and thermal stability; Mold design: Using a hot runner system, the injection point is located 5-8mm from the bottom edge of the preform side wall; Process parameters: injection pressure 80-100MPa, holding time 3-5s, mold temperature 40-60℃, ensuring the bottom wall thickness uniformity ≥95%; Step 2: Preform heating Infrared heating system: Using a zoned temperature-controlled furnace, the bottom area temperature is 5-8°C lower than the main body to prevent overheating of the bottom and degradation of the material; Axial temperature compensation: Through real-time feedback from the laser thermometer, dynamic compensation of 1-2°C is performed on the bottom edge to eliminate uneven heating; Step 3: Blow molding Stretch blow molding parameters: Stretching rod speed: adopts three-stage control, namely initial rapid stretching, medium-speed transition, low-speed pressure holding, and the stretching speed in the bottom area is reduced by 20%; Blowing pressure: high pressure stage pressure 12-15MPa, holding time 0.8-1.2s, to ensure that the bottom is completely in contact with the mold; Temperature control: The preform temperature is reduced to 85-95°C before blow molding to avoid overheating and deformation of the bottom; Key mold design: Bottom cavity: set the demoulding angle to 0.5-1°, and match the surface with chrome plating (roughness Ra≤0.1μm); Exhaust system: Micro exhaust grooves (depth 0.02-0.05mm) are added to the bottom edge to prevent gas stagnation and uneven wall thickness; Step 4: Post-processing Heat setting: Keep in a hot air circulation oven at 80-90℃ for 10-15s to eliminate the internal stress at the bottom and improve the heat resistance to 85℃; Online detection: Ultrasonic wall thickness detection: minimum bottom wall thickness ≥0.35mm; Visual inspection system: uses an 8-megapixel industrial camera to 100% detect the bottom seam marks (detection accuracy 0.01mm).

2. The blow molding process of a PET bottle without a butt joint at the bottom according to claim 1, characterized in that: The specific steps in step one are as follows: S1.

1. First, a high-viscosity PET resin with an intrinsic viscosity (IV) of 0.80-0.85 dl / g is selected. Its molecular chain length can increase the material's crystallization rate by more than 30%. At the same time, 0.3-0.5% fumed nano-silica is added through nano-modification technology to form a three-dimensional network structure in the resin matrix, increasing the material's heat deformation temperature to 135°C and shortening the injection molding cycle by 15%. S1.

2. Use a dehumidifying dryer to pre-crystallize the PET raw material at a drying temperature of 165°C and a dew point ≤ -40°C, ensuring that the moisture content is ≤ 30ppm to avoid silver streaks during the blow molding process; S1.

3. A valve-type hot runner system is used, with the injection point precisely positioned 5-8 mm from the bottom edge of the preform sidewall. CAE runner simulation is used to balance the pressure difference between each cavity to ≤ 2 MPa, ensuring uniform melt filling. The mold cavity surface is hard chrome plated and polished to a mirror finish to reduce melt flow resistance. S1.4, Injection stage: Multi-stage injection is adopted, with the injection speed increasing step by step from 50mm / s to 200mm / s, injection pressure 80-100MPa, holding time 3-5s, and holding pressure decreasing design to compensate for material shrinkage; Temperature control system: The temperature of the moving die of the mold is 50°C, and the temperature of the fixed die is 45°C. Through real-time feedback of thermocouples, the temperature fluctuation is ≤±1°C; S1.

6. Configure an infrared on-line thickness gauge to perform a 360° scan on the bottom of the preform. The wall thickness uniformity is ≥95%, and the thickness tolerance at the key control points is ±0.05 mm.

3. A bottom-seamless PET bottle blow molding process according to claim 1, characterized in that: The specific steps in step two are as follows: S2.

1. First, divide the furnace body into a bottle body area of 95 - 105°C, a transition area of 100 - 110°C, and a bottom area of 90 - 98°C. Use short-wave infrared heating tubes with a wavelength of 1.2 - 1.6 μm, and the power density in the bottom area is reduced by 20%; S2.

2. Then configure a high-speed circulating fan with a wind speed of 8 m / s to strengthen the hot air convection and ensure the temperature field uniformity in the furnace is ±2°C; S2.

3. Real-time collect the bottom edge temperature through a laser temperature measurement array (8 points / bottle), and the PID control system dynamically adjusts the heating power with a compensation accuracy of ±1°C and a response time of ≤0.2 s.

4. A bottom-seamless PET bottle blow molding process according to claim 1, characterized in that: The specific steps in step three are as follows: S3.

1. Adopt a three-stage stretching system driven by a servo motor: Fast stretching section, 0 - 50 mm stroke: speed 800 mm / s to achieve pre-stretching; Medium-speed transition section, 50 - 100 mm stroke: speed reduced to 400 mm / s to avoid material rupture; Low-speed pressure-holding section, 100 - 150 mm stroke: speed 100 mm / s, pressure-holding time 0.8 - 1.2 s to ensure the bottom is fully in contact with the mold; The stretching speed in the bottom area is reduced by 20% compared with the traditional process to reduce the excessive orientation of molecular chains; S3.

2. The high-pressure blow molding pressure is 12 - 15 MPa, and the pressure step loading is achieved through a proportional valve (linearly rising from 5 MPa to 15 MPa). The pressure fluctuation in the pressure-holding stage is ≤±0.5 MPa; S3.

3. Set a demolding slope of 0.5 - 1° in the bottom cavity, and cooperate with the quenching treatment of P20 mold steel to extend the mold life to more than 1 million moldings; S3.

4. Perform surface chrome plating treatment and coat with a PTFE coating to reduce the friction coefficient to 0.15; S3.

5. Uniformly distribute 8 - 12 micro-exhaust grooves at the bottom edge, and optimize the layout through CFD simulation to avoid wall thickness deviation caused by gas retention.

5. A bottom-seamless PET bottle blow molding process according to claim 1, characterized in that: The specific steps in step four are as follows: S4.

1. Specifically adopt a two-stage heat treatment: Preheating stage: 80°C hot air circulation for 3 s to make the material enter the high elastic state; Settling stage: Keep warm at 90°C for 10 - 15 s, precisely controlled by an infrared radiation heater (wavelength 2 - 3 μm) to eliminate the residual internal stress at the bottom and improve the heat resistance performance to 85°C; S4.

2. For ultrasonic wall thickness detection, specifically use a 5 MHz focused probe to perform a spiral scan on the bottom. The minimum detected wall thickness is ≥0.35 mm, and the CV value of the thickness distribution is ≤3%; S4.

3. The vision detection system specifically uses an industrial camera with 8 million pixels to perform 100% full inspection under a D65 light source. The detection accuracy is 0.01 mm, and it can identify micro-defects with a width of 0.02 mm.

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