Preparation method of anti-light-transmission PET bottle based on two-way stretching process

Abstract

The invention relates to the technical field of PET (polyethylene terephthalate) bottle preparation, and discloses an anti-light-transmission PET bottle preparation method based on a two-way stretching process, raw material pretreatment: compounding a food-grade PETG (polyethylene terephthalate glycol) resin base material, a titanium dioxide or carbon black opacifying agent and auxiliaries containing a dispersing agent and the like, premixing for 5-10 minutes in a high-speed mixer at the speed of 800-1200 rpm, and carrying out vacuum drying for 4 hours at the temperature of 120 DEG C to obtain a premix with the water content of less than or equal to 30 ppm; melting and injection molding: plasticizing the premix through a twin-screw extruder, and carrying out injection molding to obtain a tubular preform with the wall thickness of 2-3mm; and cooling and heating: cooling the preformed blank in a water bath at 25 DEG C, and heating the surface layer to 90-00 DEG C and the core to 60-70 DEG C by using an infrared heating furnace. Stretching and blow molding are conducted, axial stretching is conducted at 50-80 mm / s, radial high-pressure air blow molding is conducted at 2.5-3.5 MPa, the temperature of a mold is 80-100 DEG C, and pressure maintaining is conducted for 5-8 seconds. And post-treatment: cooling in three sections, cutting off excess materials, and carrying out UV treatment to improve weather resistance. By optimizing dispersion of the opacifying agent and selecting a proper opacifying agent, light is effectively blocked, and the light transmittance is controlled at an extremely low level.

Description

Technical Field

[0001] The present invention belongs to the technical field of PET bottle preparation, and particularly relates to a method for preparing an anti-light-transmitting PET bottle based on a biaxial stretching process. Background Art

[0002] In the field of food packaging, PET (polyethylene terephthalate) bottles have become one of the most widely used packaging containers due to their many advantages such as light weight, transparency, high strength, and good chemical stability. The transparent PET bottle body can intuitively display the food contents, allowing consumers to clearly see the product state, so it has long been the mainstream choice in the market. However, not all foods are suitable for storage in a light environment. Some foods, such as dairy products, fruit juices, and seasonings, contain light-sensitive components such as vitamins, pigments, and oils. Light will accelerate the oxidation and decomposition reactions of these components, resulting in changes in the color, flavor, and nutritional components of the food, thereby affecting the quality and shelf life of the food. To meet the demand for light-proof storage of such foods, adding solid color masterbatches during the production of PET bottles has become a common solution.

[0003] Currently, ordinary color masterbatches on the market can meet the needs of most colors and can achieve a certain degree of light-shielding effect for PET bottles. Their preparation process usually involves simply mixing pigments or dyes with carrier resins and granulating them through equipment such as twin-screw extruders. During the molding process of PET bottles, ordinary color masterbatches are mixed with PET raw materials in a certain proportion, and then PET bottles are made through processes such as injection molding and blow molding.

[0004] For some special colors, such as apricot, during the mixing and processing of ordinary color masterbatches with PET substrates, bottle wall delamination is likely to occur. This is because the compatibility between the color masterbatch and the PET substrate is poor, and the bonding force between the two is weak. During the molding processes such as injection molding and blow molding, affected by factors such as temperature and pressure, the color masterbatch and the PET substrate cannot be evenly fused, resulting in delamination. Delamination not only affects the appearance quality of the bottle body but also causes light transmission problems, making it impossible for food to be effectively protected from light, not meeting the relevant regulatory requirements for food packaging, and seriously affecting the fresh-keeping effect of food. The existing ordinary color masterbatches have limited light-shielding performance and are difficult to effectively block the irradiation of ultraviolet and visible light on food. On the one hand, the dispersibility of the light-shielding agent used in the color masterbatch is poor and cannot be evenly distributed in the PET substrate, resulting in inconsistent light-shielding effects in different parts of the bottle body; on the other hand, the type and addition amount of the light-shielding agent are not selected accurately enough to meet the requirements of some food packaging with extremely high light-shielding requirements. Due to the existence of the delamination problem, the mechanical strength of the bottle body is affected. The structure of the delaminated part is relatively weak, and during transportation, storage, and use, problems such as cracking and deformation are likely to occur, reducing the reliability and practicality of the bottle body. At the same time, delamination will also cause defects in the appearance of the bottle body, affecting the overall image and market competitiveness of the product. To achieve a certain light-shielding and color effect, the existing technology may need to use color masterbatch materials with higher prices or increase the addition amount of the color masterbatch, which undoubtedly increases the production cost. Moreover, due to the high scrap rate caused by problems such as delamination, the production cost is further increased, reducing the economic benefits of the enterprise.

[0005] In view of this, a method for preparing an anti-light-transmitting PET bottle based on a biaxial stretching process is proposed to solve the above problems. Summary of the Invention

[0006] The present invention aims to solve the technical problems in the above-mentioned prior art that during the mixing and processing of ordinary color masterbatches with PET substrates, specific colors are prone to cause delamination, insufficient light-shielding performance, unstable bottle body quality, and relatively high costs.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing an anti-light-transmitting PET bottle based on a biaxial stretching process, specifically including the following steps:

[0009] S1. Pretreatment of raw materials

[0010] A composite system composed of a light-shielding agent, a carrier resin, and additives is used as a masterbatch. The carrier resin uses a food-grade PETG resin substrate, the light-shielding agent uses titanium dioxide or carbon black, and the PETG resin substrate and the light-shielding agent together constitute the core components of the masterbatch. The additives include a dispersant, a compatibilizer, and a viscosity enhancer. The PETG resin substrate, the light-shielding agent, and the additives are premixed in a high-speed mixer at a rotation speed of 800 - 1200 rpm for 5 - 10 minutes, and then vacuum dried at 120 °C for 4 hours to obtain a premixed material with a moisture content of ≤ 30 ppm.

[0011] Among them, the dispersant selects a composite system of polyethylene glycol and maleic anhydride grafted PET, the compatibilizer selects the addition of an ethylene - acrylate - maleic anhydride terpolymer, and the viscosity enhancer selects an epoxy chain extender.

[0012] S2. Melting and plasticizing and injection molding

[0013] Add the premixed material to a twin-screw extruder, melt and plasticize it, and then form it into a tubular preform with a wall thickness of 2 - 3 mm through an injection molding machine.

[0014] S3. Cooling and reheating of the preform

[0015] The injection-molded preform is quickly cooled below the glass transition temperature in a 25 °C water bath, and after shaping, it is transferred to an infrared heating furnace for reheating; the surface temperature of the preform reaches 90 - 100 °C, and the core temperature remains at 60 - 70 °C.

[0016] S4. Biaxial stretching and blow molding

[0017] Longitudinal stretching: The preform is axially stretched by a mechanical stretching rod at a speed of 50 - 80 mm / s, and the stretching ratio L / L 0 = 2.5 - 3.0, inducing the molecular chains to orient along the axial direction;

[0018] Transverse stretching: High-pressure air with a pressure of 2.5 - 3.5 MPa is introduced for radial blow molding, causing the preform to radially expand to the designed size, and the radial stretching ratio L / L 0 = 3.0 - 3.5, forming a biaxial network molecular chain structure;

[0019] Synchronous shaping: During the stretching process, the mold temperature is controlled at 80 - 100 °C, and after blow molding, it is pressure-held for 5 - 8 seconds, so that the light-shielding agent and the PETG substrate are uniformly distributed through molecular chain orientation locking.

[0020] S5. Gradient cooling and post-treatment

[0021] After blow molding, it is cooled in three stages:

[0022] The first stage: Spray cold water at 10 °C for 5 seconds, and the surface layer is quickly solidified and shaped;

[0023] Second stage: Air cooling at 30°C for 10 seconds to release internal stress;

[0024] Third stage: Water mist cooling to room temperature at 15°C;

[0025] Remove the remaining material at the bottle mouth, perform UV surface treatment to improve the weather resistance of the bottle body.

[0026] Preferably, cyclohexanedimethanol monomer which can improve the flexibility of the material and the compatibility with color masterbatch is introduced into the molecular chain of PETG resin, and the moisture content of the PETG resin substrate is controlled at ≤50 ppm to avoid hydrolysis degradation during the processing.

[0027] Preferably, the addition amount of the light-shielding agent is 3-5% of the mass of the PETG resin substrate, rutile-type titanium dioxide with a particle size of 0.2-0.5 μm is selected, and food-grade carbon black with a particle size of 50-100 nm is used for the carbon black.

[0028] Preferably, the addition amount of the dispersant is 2-3% of the total mass of the color masterbatch to ensure uniform dispersion of the color masterbatch particles;

[0029] The addition amount of the compatibilizer is 1.5-2% of the total mass of the color masterbatch to improve the interfacial bonding force between the color masterbatch and PETG;

[0030] The addition amount of the viscosity enhancer is 0.5-1% of the total mass of the color masterbatch to improve the melt strength of PET through end-group reaction.

[0031] Preferably, the dispersant is compounded by polyethylene glycol with a molecular weight of 4000-6000 and maleic anhydride grafted PET in a mass ratio of 1:1.

[0032] Preferably, in step S2, the premix is added to the twin-screw extruder and melted and plasticized according to the following temperature zones: feeding section 240°C, compression section 260°C, homogenization section 270°C, die head 275°C; the screw speed of the twin-screw extruder is 60-80 rpm, the injection back pressure of the injection molding machine is 8-12 MPa, the injection pressure is 80-100 MPa, and the mold temperature is 10-15°C.

[0033] Preferably, the infrared heating furnace reheats in a way of segmented temperature rise. First, the temperature is raised to 80°C, then to 100°C, and finally to 120°C. The total time of segmented temperature rise is 30-40 seconds.

[0034] Preferably, the process of infrared heating furnace segmented reheating is as follows:

[0035] First stage: Raise the temperature to 80°C and keep it warm for 10 seconds;

[0036] Second stage: Raise the temperature to 100°C and keep it warm for 15 seconds;

[0037] The third stage: Heat up to 120°C and keep warm for 5 seconds;

[0038] Preferably, during the injection molding process, the surface of the mold cavity is treated by plasma with a power of 200 W and a time of 5 minutes, and the surface roughness Ra ≤ 0.1 μm to enhance the melt flow uniformity.

[0039] Preferably, the UV surface treatment uses a dual-band light source of 254 nm + 365 nm, and the total energy density is 80 - 100 mJ / cm 2 .

[0040] Compared with the prior art, the technical effects and advantages of the present invention are:

[0041] In the raw material pretreatment stage of the preparation method of the light-blocking PET bottle based on the biaxial stretching process, a composite system composed of a light-blocking agent, a food-grade PETG resin substrate, a dispersant, a compatibilizer, and an adhesion enhancer and other additives is fully premixed in a high-speed mixer and vacuum dried to make each component evenly distributed and reduce the moisture content. Subsequently, the premixed material is melted and plasticized by a twin-screw extruder and formed into a tubular preform by an injection molding machine. Then, the preform is cooled and reheated to reach a suitable temperature state. In the biaxial stretching and blow molding stage, first, axial stretching is performed by a mechanical stretching rod to induce the molecular chains to orient along the axial direction, and then high-pressure air is introduced for radial blow molding to make the preform expand radially, forming a biaxial network molecular chain structure. At the same time, the mold temperature is controlled and pressure is maintained during the stretching process to lock the light-blocking agent and the PETG substrate evenly distributed through molecular chain orientation. Finally, gradient cooling and post-treatment are carried out, the internal stress is released by staged cooling, the excess material at the bottle mouth is cut off, and UV surface treatment is performed.

[0042] In terms of light-blocking performance, by optimizing the dispersibility of the light-blocking agent and selecting a suitable light-blocking agent (such as titanium dioxide or carbon black), it can effectively block ultraviolet rays and visible light, control the light transmittance at an extremely low level, have a good ultraviolet barrier rate, provide good light-shielding protection for food, prevent food from deteriorating due to light, and extend the shelf life of food. In terms of anti-delamination performance, by improving the compatibility between the color masterbatch and the PET substrate, adding a dispersant, and optimizing the plastic blowing process, the delamination problem is completely solved, the bottle wall structure is uniform, the light-transmitting problem caused by delamination is avoided, the light-blocking performance of the bottle body is ensured to be consistent, and at the same time, the mechanical strength of the bottle body is improved.

[0043] In terms of cost, by optimizing the formula, selecting cost-effective raw materials, and carrying out large-scale production, the cost of the masterbatch can be controlled within a reasonable range. Moreover, the scrap rate during the production process is reduced, the production cost is lowered, and the economic benefits of the enterprise are improved. In terms of industry development, this method provides the feasibility for the large-scale production of special-color PET bottles, meets the customers' demands for diverse colors, promotes the innovation and development of the food packaging industry, makes special-color PET bottles more competitive in the market, and is suitable for food packaging in different scenarios. Description of the Drawings

[0044] Figure 1 It is the process flow chart of the present invention. Detailed Embodiments

[0045] 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0046] Embodiment 1: High-blocking-apricot-color PET bottle (titanium dioxide system)

[0047] Raw Materials and Process Parameters

[0048] Masterbatch Formula

[0049] Food-grade PETG resin substrate (CHDM content 35%, moisture content ≤ 30 ppm): 94.5 kg;

[0050] Light-blocking agent: rutile titanium dioxide (particle size 0.3 μm, addition amount 5%) → 4.5 kg;

[0051] Dispersant: polyethylene glycol (molecular weight 5000) and maleic anhydride-grafted PET (mass ratio 1:1) → total addition amount 2% → 2.0 kg;

[0052] Compatibilizer: ethylene-acrylate-maleic anhydride terpolymer → addition amount 1.5% → 1.5 kg;

[0053] Viscosity enhancer: epoxy chain extender (model ADR-4468) → addition amount 0.5% → 0.5 kg;

[0054] Pretreatment and Injection Molding

[0055] High-speed mixing: premix at 1000 rpm for 8 minutes, vacuum dry at 120 °C for 4 hours, moisture content ≤ 25 ppm;

[0056] Twin-screw extrusion temperature: feeding section 240°C / compression section 260°C / homogenization section 270°C / die head 275°C;

[0057] Injection molding parameters: back pressure 10 MPa, injection pressure 90 MPa, mold temperature 12°C (the cavity is treated with 200 W plasma for 5 minutes, Ra = 0.08 μm);

[0058] Preform dimensions: wall thickness 2.5 mm, diameter 40 mm, height 120 mm;

[0059] Biaxial stretching and blow molding

[0060] Infrared reheating: 80°C (10 s) → 100°C (15 s) → 120°C (5 s), surface temperature 95°C, core temperature 65°C;

[0061] Longitudinal stretching: speed 65 mm / s, stretching ratio 3.0 (the preform is stretched to 360 mm);

[0062] Transverse blow molding: pressure 3.0 MPa, radial stretching ratio 3.2 (the diameter expands to 128 mm);

[0063] Simultaneous shaping: mold temperature 90°C, pressure holding for 7 s;

[0064] Gradient cooling and post-treatment

[0065] Spraying with 10°C cold water for 5 s → air cooling at 30°C for 10 s → water mist cooling to 25°C at 15°C;

[0066] UV treatment: dual wavelength of 254 nm + 365 nm, total energy density 90 mJ / cm 2 ;

[0067] Effect verification of the prepared PET bottles, including verification of light-shielding performance, anti-delamination performance, and mechanical strength verification;

[0068] 1. Verification of light-shielding performance

[0069] Testing method

[0070] Visible Light Transmittance (VLT):

[0071] Equipment: UV-visible spectrophotometer (such as PerkinElmer Lambda 950), integrating sphere accessory.

[0072] Standard: ASTM D1003 (Testing of Haze and Light Transmittance of Transparent Materials).

[0073] Steps:

[0074] Cut the PET bottle wall into 10×10 mm2 Specimen, with the same thickness as the bottle body (2 - 3 mm);

[0075] Scan the transmission spectrum within the wavelength range of 400 - 700 nm, and calculate the average transmittance of the entire wavelength band by integration.

[0076] Formula: (Unit: %);

[0077] where T(λ) is the transmittance at wavelength λ, and N is the number of sampling points.

[0078] UV Blocking Rate:

[0079] Equipment: UV - Visible Spectrophotometer (wavelength range 200 - 400 nm).

[0080] Steps:

[0081] Measure the transmittance of the specimen in the UV - A (315 - 400 nm) and UV - B (280 - 315 nm) bands;

[0082] Calculate the average transmittance of the UV band and convert it to the blocking rate.

[0083] Formula:

[0084] 2. Verification of anti - delamination

[0085] Test method

[0086] Thermal cycle test:

[0087] Standard: ASTM D4332 (Environmental Stress Cracking Test for Packaging Materials).

[0088] Steps:

[0089] Place the PET bottle in a low - temperature chamber at - 20 °C for 2 hours;

[0090] Transfer it to a high - temperature chamber at 60 °C for 2 hours to complete 1 cycle;

[0091] After repeating 10 cycles, observe whether there is delamination, light - transmitting points or cracks on the bottle body.

[0092] Judgment criteria:

[0093] No delamination: There is no interface peeling in the cross - section of the bottle wall under an optical microscope (100 times magnification);

[0094] No light - transmitting points: The fluctuation of the light transmittance test result is ≤ ±0.1%.

[0095] 3. Verification of mechanical strength

[0096] Test method

[0097] Axial tensile strength:

[0098] Equipment: Universal material testing machine (such as Instron5967), fixture speed 5mm / min. Standard: ASTM D638 (Plastic tensile properties testing).

[0099] Steps:

[0100] Cut the bottle body into dumbbell-shaped specimens (gage length 50mm, width 10mm);

[0101] Stretch until fracture, record the maximum load Fmax;

[0102] Formula: (Unit: MPa);

[0103] Wherein, A is the cross-sectional area of the specimen (thickness × width).

[0104] Bursting pressure:

[0105] Equipment: Air tightness tester (such as Labthink MFY-01), pressurization rate 0.1MPa / s. Standard: ASTM D3078 (Internal pressure bursting test of packaging containers).

[0106] Steps:

[0107] Fill the bottle with water and seal it, gradually pressurize until the bottle body bursts;

[0108] Record the pressure value P at the moment of rupture burst。

[0109] Formula: (Simplified formula of thin-walled cylinder theory);

[0110] Wherein, σhoop is the circumferential stress, t is the wall thickness of the bottle, and D is the diameter of the bottle body.

[0111] Supplementary instructions:

[0112] For the light-shielding performance test, it is necessary to ensure that the surface of the specimen is clean and free of scratches to avoid interference from stray light;

[0113] For the anti-layering property test, the cross-sectional microstructure can be observed by combining with a scanning electron microscope (SEM);

[0114] The bursting pressure formula is an engineering simplified model, and the actual test shall be based on the direct reading of the instrument.

[0115] Through the above standardized test methods and formulas, the light-shielding property, anti-layering property and mechanical strength of the present invention can be quantitatively verified whether they meet the design requirements.

[0116] Light-shielding performance: Transmittance ≤ 0.3% (in the wavelength range of 400 - 700 nm), ultraviolet blocking rate ≥ 99%;

[0117] Anti-delamination property: After 10 cycles of -20°C - 60°C testing, there is no delamination or light-transmitting point on the bottle body;

[0118] Mechanical strength: Axial tensile strength 88 MPa, burst pressure 3.2 MPa;

[0119] Example 2: Low-cost carbon black light-shielding PET bottle (carbon black system)

[0120] Raw materials and process parameters

[0121] Masterbatch formula

[0122] Food-grade PETG resin substrate (CHDM content 30%, moisture content ≤ 40 ppm): 95.2 kg;

[0123] Light-shielding agent: Food-grade carbon black (particle size 80 nm, addition amount 3%) → 3.0 kg;

[0124] Dispersant: Polyethylene glycol (molecular weight 4000) and maleic anhydride grafted PET (mass ratio 1:1) → total addition amount 3% → 3.0 kg;

[0125] Compatibilizer: Ethylene-acrylate-maleic anhydride terpolymer → addition amount 2% → 2.0 kg;

[0126] Viscosity enhancer: Epoxy chain extender (model Joncryl ADR-4300) → addition amount 1% → 1.0 kg; Pretreatment and injection molding

[0127] High-speed mixing: Premix at 800 rpm for 10 minutes, vacuum dry at 120°C for 4 hours, moisture content ≤ 28 ppm;

[0128] Twin-screw extrusion temperature: Feeding section 240°C / Compression section 260°C / Homogenization section 270°C / Die head 275°C;

[0129] Injection molding parameters: Back pressure 8 MPa, injection pressure 80 MPa, mold temperature 15°C (without plasma treatment);

[0130] Formed blank size: Wall thickness 3.0 mm, diameter 50 mm, height 150 mm;

[0131] Biaxial stretching and blow molding

[0132] Infrared reheating: 80°C (10 s) → 100°C (15 s) → 120°C (5 s), surface temperature 98°C, core temperature 68°C;

[0133] Longitudinal stretching: speed 50 mm / s, stretching ratio 2.5 (the blank extends to 375 mm);

[0134] Transverse blowing: pressure 2.5 MPa, radial stretching ratio 3.0 (the diameter expands to 150 mm);

[0135] Synchronous shaping: mold temperature 80 °C, pressure holding for 5 seconds;

[0136] Gradient cooling and post-treatment

[0137] Spraying with 10 °C cold water for 5 seconds → air cooling at 30 °C for 10 seconds → water mist cooling to 25 °C at 15 °C;

[0138] UV treatment: single wavelength 254 nm, intensity 50 mJ / cm 2 ;

[0139] Effect verification

[0140] Light shielding performance: light transmittance ≤ 0.1% (full wavelength band), visible light completely blocked;

[0141] Economy: the cost of color masterbatch is reduced by 18% compared with Example 1, and the scrap rate ≤ 4%;

[0142] Weather resistance: the surface scratch resistance is improved by 30% after UV treatment (pencil hardness ≥ 2H);

[0143] Example 3: High mechanical property light-blocking PET bottle (optimized stretching ratio)

[0144] Raw materials and process parameters

[0145] Color masterbatch formula

[0146] Food-grade PETG resin substrate (CHDM content 40%, moisture content ≤ 20 ppm): 93.8 kg;

[0147] Light shielding agent: rutile titanium dioxide (particle size 0.5 μm, addition amount 4%) → 4.0 kg;

[0148] Dispersant: polyethylene glycol (molecular weight 6000) and maleic anhydride grafted PET (mass ratio 1:1) → total addition amount 2.5% → 2.5 kg;

[0149] Compatibilizer: ethylene-acrylate-maleic anhydride terpolymer → addition amount 1.8% → 1.8 kg;

[0150] Viscosity enhancer: epoxy chain extender (model BASFHPN-20L) → addition amount 0.8% → 0.8 kg;

[0151] Pretreatment and injection molding

[0152] High-speed mixing: Premix at 1200 rpm for 6 minutes, vacuum dry at 120 °C for 4 hours, water content ≤ 22 ppm;

[0153] Twin-screw extrusion temperature: Feeding section 240 °C / Compression section 260 °C / Homogenization section 270 °C / Die head 275 °C;

[0154] Injection molding parameters: Back pressure 12 MPa, injection pressure 100 MPa, mold temperature 10 °C (the cavity is treated with 200 W plasma for 5 minutes, Ra = 0.05 μm);

[0155] Formed blank size: Wall thickness 2.0 mm, diameter 35 mm, height 100 mm;

[0156] Biaxial stretching and blow molding

[0157] Infrared reheating: 80 °C (10 s) → 100 °C (15 s) → 120 °C (5 s), surface temperature 100 °C, core temperature 70 °C;

[0158] Longitudinal stretching: Speed 80 mm / s, stretching ratio 3.0 (the blank is stretched to 300 mm);

[0159] Transverse blow-up: Pressure 3.5 MPa, radial stretching ratio 3.5 (the diameter expands to 122.5 mm);

[0160] Synchronous setting: Mold temperature 100 °C, pressure holding for 8 s;

[0161] Gradient cooling and post-treatment

[0162] Spray with 10 °C cold water for 5 s → Air-cool at 30 °C for 10 s → Water mist cool to 25 °C at 15 °C;

[0163] UV treatment: Dual wavelength 254 nm + 365 nm, total energy density 100 mJ / cm 2 ;

[0164] Effect verification

[0165] Mechanical properties: Axial tensile strength 95 MPa, burst pressure 3.8 MPa (10% higher than that in Example 1);

[0166] Degree of molecular orientation: The crystallinity reaches 18% after biaxial stretching (DSC test), and the CV value of the uniformity of the light-shielding agent distribution ≤ 2%;

[0167] Production efficiency: The blow molding cycle is shortened to 25 s / piece, suitable for high-speed production lines;

[0168] The above examples verified the applicability of the present invention in different scenarios by adjusting key parameters such as the masterbatch formula (type and addition amount of light-shielding agent), stretching ratio, and cooling process:

[0169] Example 1 is applicable to food packaging with high requirements for light shielding and appearance (such as dairy products);

[0170] Example 2 meets the demand for bulk commodities through a low-cost carbon black solution;

[0171] Example 3 achieves a high-strength bottle body by optimizing the draw ratio and molecular orientation, and is applicable to high-pressure scenarios such as carbonated beverages.

[0172] All examples solve the core problem of delamination and light transmission of traditional PET bottles through a light shielding agent dispersion locking mechanism (biaxial stretching + gradient cooling) and an interface enhancement technology (plasma treatment + compatibilizer).

[0173] Finally, it should be noted that the above are only the 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 principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an anti-light transmission PET bottle based on a biaxial stretching process, characterized in that: The specific steps include: S1. Raw material pretreatment A composite system consisting of a sunscreen agent, a carrier resin and an auxiliary agent is used as a masterbatch, the carrier resin adopts a food-grade PETG resin base material, the sunscreen agent adopts titanium dioxide or carbon black, the PETG resin base material and the sunscreen agent together constitute the core component of the masterbatch, and the auxiliary agents include a dispersant, a compatibilizer and a viscosity enhancer. The PETG resin base material, the sunscreen agent and the auxiliary agent are premixed in a high-speed mixer with a rotation speed of 800-1200rpm for 5-10 minutes, and then vacuum dried at 120°C for 4 hours to obtain a premix with a moisture content of ≤30ppm; Among them, the dispersant is a composite system of polyethylene glycol and maleic anhydride grafted PET, the compatibilizer is a terpolymer of ethylene-acrylate-maleic anhydride, and the viscosity enhancer is an epoxy chain extender; S2, melt plasticization and injection molding The premix is ​​added into a twin-screw extruder, and after being melted and plasticized, it is formed into a tubular preform with a wall thickness of 2-3 mm by an injection molding machine; S3, preform cooling and reheating The preform after injection molding is quickly cooled to below the glass transition temperature in a 25°C water bath, and after being shaped, it is transferred to an infrared heating furnace for reheating; the surface temperature of the preform reaches 90-100°C, and the core temperature is maintained at 60-70°C; S4, biaxial stretching and blow molding Longitudinal stretching: The preform is stretched axially by a mechanical stretching rod at a speed of 50-80 mm / s, with a stretching ratio of L / L0 = 2.5-3.0, inducing the molecular chain to be oriented in the axial direction; Transverse stretching: high-pressure air with a pressure of 2.5-3.5MPa is introduced for radial blowing to expand the preform radially to the designed size, with a radial stretching ratio of L / L0=3.0-3.5 to form a bidirectional network molecular chain structure; Synchronous shaping: During the stretching process, the mold temperature is controlled at 80-100℃, and the pressure is maintained for 5-8 seconds after blow molding, so that the sunscreen agent and the PETG substrate are evenly distributed through molecular chain orientation locking; S5, gradient cooling and post-processing After blow molding, cooling is divided into three stages: The first stage: spray with 10℃ cold water for 5 seconds, the surface will quickly solidify and set; The second stage: 30℃ air cooling for 10 seconds to release internal stress; The third stage: 15℃ water mist cooling to room temperature; Cut off the excess material at the bottle mouth and perform UV surface treatment to improve the weather resistance of the bottle.

2. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 1, characterized in that: Cyclohexanedimethanol monomer is introduced into the molecular chain of PETG resin to improve the flexibility of the material and the compatibility with the masterbatch. The moisture content of the PETG resin substrate is controlled at ≤50ppm.

3. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 1, characterized in that: The amount of the sunscreen added is 3-5% of the mass of the PETG resin substrate, the titanium dioxide is rutile and has a particle size of 0.2-0.5 μm, and the carbon black is food-grade carbon black with a particle size of 50-100 nm.

4. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 1, characterized in that: The amount of dispersant added is 2-3% of the total mass of the masterbatch; The amount of compatibilizer added is 1.5-2% of the total mass of the masterbatch; The amount of viscosity enhancer added is 0.5-1% of the total mass of the masterbatch.

5. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 4, characterized in that: The dispersant is compounded by polyethylene glycol with a molecular weight of 4000-6000 and maleic anhydride grafted PET in a mass ratio of 1:

1.

6. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 1, characterized in that: In step S2, the premix is ​​added to a twin-screw extruder and melt-plasticized according to the following temperature zones: 240°C for the feeding section, 260°C for the compression section, 270°C for the homogenization section, and 275°C for the die head; the screw speed of the twin-screw extruder is 60-80rpm, the injection molding back pressure of the injection molding machine is 8-12MPa, the injection pressure is 80-100MPa, and the mold temperature is 10-15°C.

7. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 1, characterized in that: The infrared heating furnace adopts a staged heating method for reheating, first raising the temperature to 80°C, then raising the temperature to 100°C, and finally raising the temperature to 120°C. The total time for staged heating is 30-40 seconds.

8. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 7, characterized in that: The infrared heating furnace segmented reheating process is as follows: Stage 1: Heat to 80°C and keep warm for 10 seconds; The second stage: heating to 100°C and keeping warm for 15 seconds; The third stage: heat to 120℃ and keep warm for 5 seconds.

9. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 1, characterized in that: During the injection molding process, the mold cavity surface was treated with plasma at a power of 200 W for 5 minutes, with a roughness Ra ≤ 0.1 μm.

10. The method for preparing an anti-light transmission PET bottle based on a biaxial stretching process according to claim 1, characterized in that: UV surface treatment uses a dual-band light source of 254nm+365nm, with a total energy density of 80-100mJ / cm 2 .

Images