Modified new material-based anti-ultraviolet plastic woven bag and forming process thereof

Abstract

The invention provides a modified new material-based anti-ultraviolet plastic woven bag and a forming process thereof, and relates to the technical field of plastic woven bag processing. The modified new material-based anti-ultraviolet plastic woven bag specifically comprises the following specific components: polylactic acid, poly (butylene terephthalate)-adipate, flaky nano titanium dioxide, nano cerium oxide, an absorption enhancer, an interlayer compatilizer and a degradation regulator. By adopting bio-based materials such as polylactic acid and a degradation regulator, the plastic woven bag has controllable degradability, white pollution can be reduced, flaky nano titanium dioxide and nano cerium oxide are compounded, and ultraviolet shielding and reflection are improved; the absorption efficiency and the weather resistance of the material are improved by combining the cellulose nanocrystals grafted with the ultraviolet absorption monomer, the interface combination is improved through the interlayer compatilizer, and the flat filament structure is optimized by adopting a two-step stretching process, so that the plastic woven bag is high in strength and firm in structure.

Description

Technical Field

[0001] This invention relates to the field of plastic woven bag processing technology, specifically to a modified new material-based UV-resistant plastic woven bag and its molding process. Background Technology

[0002] Woven plastic bags, also known as plastic woven bags, are widely used in agriculture, industry, and daily life for packaging and transportation due to their advantages such as light weight, good mechanical strength, good chemical properties, and low cost. The raw materials for woven plastic bags are mainly chemical plastics such as polyethylene and polypropylene. Based on the raw materials, they can be divided into two main categories: polypropylene woven plastic bags and polyethylene woven plastic bags.

[0003] Currently, the main production process for woven plastic bags involves extruding plastic raw materials into film, cutting, and unidirectionally stretching them into flat filaments, which are then woven together to create the final product. However, existing woven plastic bags are prone to aging, have a short lifespan, poor UV resistance, and low tensile strength, making the goods they contain highly susceptible to spoilage. Furthermore, during transport, tears or damage to the woven bags can cause goods to scatter and become difficult to organize. Therefore, there is an urgent need to improve the performance of woven plastic bag materials, refine the weaving technology, enhance sun protection, extend lifespan, and improve tensile strength. Summary of the Invention

[0004] To achieve the above objectives, the present invention is implemented through the following technical solution: a modified new material-based UV-resistant woven plastic bag, specifically comprising the following components: polylactic acid, polybutylene terephthalate-adipate, sheet-like nano titanium dioxide, nano cerium oxide, absorption enhancer, interlayer compatibilizer, and degradation regulator; The specific mass fractions of the above ingredients are as follows: 40-60 parts of polylactic acid, 20-30 parts of polybutylene terephthalate-adipate, 5-7 parts of sheet-like nano titanium dioxide, 3-5 parts of nano cerium oxide, 4-6 parts of absorption enhancer, 3-5 parts of interlayer compatibilizer, and 1-3 parts of degradation regulator.

[0005] Preferably, the sheet-like nano-titanium dioxide has a diameter of 10-50 nm and a thickness of 1-5 nm, and is surface-treated with a silane coupling agent. The mass ratio of the sheet-like nano-titanium dioxide to the nano-cerium oxide is 10:1.

[0006] Preferably, the absorption enhancer comprises cellulose nanocrystals and a UV-absorbing functional group monomer, wherein the UV-absorbing functional group monomer is grafted onto the surface of the cellulose nanocrystals through an esterification reaction to form a composite enhanced UV absorber; wherein the UV-absorbing functional group monomer is one of 2,4-dihydroxybenzophenone and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine.

[0007] Preferably, the interlayer compatibilizer is an oxazoline compatibilizer, and the degradation regulator is polycaprolactone micro powder.

[0008] Preferably, a molding process for a modified new material-based UV-resistant woven plastic bag is characterized by specifically including the following steps: Step 1: Raw material pretreatment and drying: Polylactic acid and polybutylene terephthalate were vacuum dried at 80°C for 6-8 hours to reduce the moisture content to ≤0.05%. Flake-shaped nano-titanium dioxide and nano-cerium oxide were surface modified with a silane coupling agent and dried at 60°C for later use. Cellulose nanocrystals in the absorption enhancer were grafted with UV-absorbing functional group monomers in advance through esterification reaction to prepare a composite enhanced UV absorber. Step 2: High-speed blending and pre-dispersion: Weigh out 40-60 parts of dried polylactic acid and 20-30 parts of polybutylene terephthalate (PET) according to the mass ratio, and add them to a high-speed mixer; then add 5-7 parts of flake nano titanium dioxide, 3-5 parts of nano cerium oxide, 4-6 parts of absorption enhancer, 3-5 parts of interlayer compatibilizer, and 1-3 parts of degradation regulator in sequence. Control the rotation speed to 300-500 r / min and mix for 10-15 minutes to ensure uniform dispersion of all components; Step 3: Melt extrusion and granulation: The blended material is fed into a twin-screw extruder. The extruder temperature is set as follows: Zone 1 150-160℃, Zone 2 160-170℃, Zone 3 170-180℃, and Zone 4 180-190℃. The screw speed is 200-300 r / min. The melt is extruded, water-cooled, and pelletized to obtain modified UV-resistant masterbatch. Step 4: Wire drawing and stretching for shaping: The modified masterbatch is fed into a wire drawing machine, and the extrusion temperature is controlled at 170-185℃. It is then extruded into a film through a die. After the film is cooled by the cooling roller, it is cut into narrow strips, and then subjected to hot stretching and heat setting treatment. The stretching ratio is 1:4-1:6 and the setting temperature is 110-130℃ to obtain high-strength UV-resistant braided yarn. Step 5: Weaving and Shaping The woven yarns are woven into tubular or sheet-shaped woven fabrics on a circular or flat loom; then, according to the bag shape requirements, they are cut, printed, sewn, or heat-sealed to produce finished woven plastic bags. Step Six: Performance Testing and Packaging The finished woven plastic bags are tested for UV transmittance, tensile strength, and degradation performance. After passing the tests, they are packaged and put into storage.

[0009] Preferably, the stretching and shaping in step four adopts a two-step stretching process: the first step is longitudinal stretching at a temperature of 100-120℃, the second step is transverse stretching at a temperature of 110-130℃, and the total stretching time is controlled at 8-12 seconds.

[0010] Beneficial effects This invention provides a modified novel material-based UV-resistant woven plastic bag and its molding process. It has the following beneficial effects: This invention provides a modified novel material-based UV-resistant woven plastic bag and its molding process. It uses bio-based or biodegradable materials such as polylactic acid and polybutylene terephthalate (PET) as the main raw materials, combined with degradation regulators, to give the woven plastic bag controllable degradation properties, which helps reduce white pollution. The addition of flake-shaped nano-titanium dioxide and nano-cerium oxide, used in combination, provides excellent UV shielding and reflection. The absorption enhancer uses cellulose nanocrystals grafted with UV-absorbing functional group monomers to improve UV absorption efficiency and enhance the material's weather resistance and service life. By using interlayer compatibilizers to enhance the interfacial compatibility of each component, the overall strength and toughness of the material are improved. A two-step stretching process is employed, controlling the stretching temperature and time to ensure a uniform flat yarn structure, high strength, and a robust bag body after weaving. Detailed Implementation

[0011] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0012] Example 1: This invention provides a modified new material-based UV-resistant woven plastic bag, specifically comprising the following components: polylactic acid, polybutylene terephthalate-adipate, sheet-like nano-titanium dioxide, nano-cerium oxide, absorption enhancer, interlayer compatibilizer, and degradation regulator; The specific mass fractions of the above ingredients are as follows: 50 parts polylactic acid, 20 parts polybutylene terephthalate-adipate, 5 parts sheet-like nano titanium dioxide, 3 parts nano cerium oxide, 4 parts absorption enhancer, 3 parts interlayer compatibilizer and 1 part degradation regulator.

[0013] A molding process for a modified new material-based UV-resistant woven plastic bag specifically includes the following steps: Step 1: Raw material pretreatment and drying: Polylactic acid and polybutylene terephthalate (PET) were vacuum dried at 80°C for 6 hours to reduce the moisture content to ≤0.05%. The sheet-like nano-titanium dioxide was 30 nm in diameter and 3 nm thick, and was surface-treated with a silane coupling agent. The mass ratio of the sheet-like nano-titanium dioxide to nano-cerium oxide was 10:1, and the nano-titanium dioxide was dried at 60°C for later use. The absorption enhancer consisted of cellulose nanocrystals and a UV-absorbing functional group monomer. The UV-absorbing functional group monomer was grafted onto the surface of the cellulose nanocrystals through an esterification reaction to form a composite enhanced UV absorber. The UV-absorbing functional group monomer was 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine. Step 2: High-speed blending and pre-dispersion: Weigh each component according to the mass fractions, and put the dried polylactic acid, polybutylene terephthalate-adipate, flake nano titanium dioxide, nano cerium oxide, absorption enhancer, oxazoline compatibilizer and polycaprolactone micro powder degradation regulator into a high-speed mixer and mix for 15 minutes at room temperature to obtain the mixture. Step 3: Melt extrusion and granulation: The mixture is added to a twin-screw extruder for melt blending and extrusion granulation. The temperatures of each section of the extruder are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 170℃, Zone 4 175℃, and Die Head 180℃; the screw speed is 200 r / min; after extrusion, the material is cooled by water and pelletized to obtain modified composite material particles. Step 4: Wire drawing and stretching for shaping: Modified composite material particles are added to a single-screw extruder, and after melt extrusion, cooling, filament separation, stretching, and shaping, flat filaments are obtained. The extrusion temperature is 165℃, the cooling water temperature is 30℃, the stretching temperature is 100℃, the stretching ratio is 4.5 times, and the stretching and shaping adopts a two-step stretching process. The first step is longitudinal stretching at 100℃, and the second step is transverse stretching at 110℃. The total stretching time is controlled at 8 seconds, the shaping temperature is 100℃, the flat filament width is 1.5mm, and the thickness is 0.06mm. Step 5: Weaving and Shaping Flat yarns are woven on a circular loom at a speed of 300 rpm and a weaving density of 60 yarns / 10cm to form a tubular fabric. The tubular fabric is then cut to a set length and sealed at the bottom and edges using ultrasonic or heat sealing methods to produce woven plastic bags. Subsequently, surface curing treatment is performed in a UV curing chamber to a curing strength of 200 mJ / cm². 2 The curing time is 20 seconds, resulting in the modified new material-based UV-resistant woven plastic bag; Step Six: Performance Testing and Packaging The finished woven plastic bags are tested for UV transmittance, tensile strength, and degradation performance. After passing the tests, they are packaged and put into storage.

[0014] Example 2: A modified new material-based UV-resistant woven plastic bag specifically comprises the following components: 60 parts polylactic acid, 30 parts polybutylene terephthalate-adipate, 7 parts sheet-like nano titanium dioxide, 5 parts nano cerium oxide, 6 parts absorption enhancer, 5 parts interlayer compatibilizer, and 3 parts degradation regulator.

[0015] A molding process for a modified new material-based UV-resistant woven plastic bag specifically includes the following steps: Step 1: Raw material pretreatment and drying: Polylactic acid and polybutylene terephthalate (PET) were vacuum dried at 80°C for 6 hours to reduce the moisture content to ≤0.05%. The sheet-like nano-titanium dioxide was 30 nm in diameter and 3 nm thick, and was surface-treated with a silane coupling agent. The mass ratio of the sheet-like nano-titanium dioxide to nano-cerium oxide was 10:1, and the nano-titanium dioxide was dried at 60°C for later use. The absorption enhancer consisted of cellulose nanocrystals and a UV-absorbing functional group monomer. The UV-absorbing functional group monomer was grafted onto the surface of the cellulose nanocrystals through an esterification reaction to form a composite enhanced UV absorber. The UV-absorbing functional group monomer was 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine. Step 2: High-speed blending and pre-dispersion: Weigh each component according to the mass fractions, and put the dried polylactic acid, polybutylene terephthalate-adipate, flake nano titanium dioxide, nano cerium oxide, absorption enhancer, oxazoline compatibilizer and polycaprolactone micro powder degradation regulator into a high-speed mixer and mix for 15 minutes at room temperature to obtain the mixture. Step 3: Melt extrusion and granulation: The mixture is added to a twin-screw extruder for melt blending and extrusion granulation. The temperatures of each section of the extruder are set as follows: Zone 1 150℃, Zone 2 160℃, Zone 3 170℃, Zone 4 175℃, and Die Head 180℃; the screw speed is 200 r / min; after extrusion, the material is cooled by water and pelletized to obtain modified composite material particles. Step 4: Wire drawing and stretching for shaping: Modified composite material particles are added to a single-screw extruder, and after melt extrusion, cooling, filament separation, stretching, and shaping, flat filaments are obtained. The extrusion temperature is 165℃, the cooling water temperature is 30℃, the stretching temperature is 100℃, the stretching ratio is 4.5 times, and the stretching and shaping adopts a two-step stretching process. The first step is longitudinal stretching at 100℃, and the second step is transverse stretching at 110℃. The total stretching time is controlled at 8 seconds, the shaping temperature is 100℃, the flat filament width is 1.5mm, and the thickness is 0.06mm. Step 5: Weaving and Shaping Flat yarns are woven on a circular loom at a speed of 300 rpm and a weaving density of 60 yarns / 10cm to form a tubular fabric. The tubular fabric is then cut to a set length and sealed at the bottom and edges using ultrasonic or heat sealing methods to produce woven plastic bags. Subsequently, surface curing treatment is performed in a UV curing chamber to a curing strength of 200 mJ / cm². 2 The curing time is 20 seconds, resulting in the modified new material-based UV-resistant woven plastic bag; Step Six: Performance Testing and Packaging The finished woven plastic bags are tested for UV transmittance, tensile strength, and degradation performance. After passing the tests, they are packaged and put into storage.

[0016] Example 3: A modified new material-based UV-resistant woven plastic bag specifically comprises the following components: 60 parts polylactic acid, 30 parts polybutylene terephthalate-adipate, 7 parts sheet-like nano titanium dioxide, 5 parts nano cerium oxide, 6 parts absorption enhancer, 5 parts interlayer compatibilizer, and 3 parts degradation regulator.

[0017] A molding process for a modified new material-based UV-resistant woven plastic bag specifically includes the following steps: Step 1: Raw material pretreatment and drying: Polylactic acid and polybutylene terephthalate (PET) were vacuum dried at 80°C for 8 hours to reduce the moisture content to ≤0.05%. The sheet-like nano-titanium dioxide was 50 nm in diameter and 5 nm thick, and was surface-treated with a silane coupling agent. The mass ratio of sheet-like nano-titanium dioxide to nano-cerium oxide was 10:1, and the nano-titanium dioxide was dried at 60°C for later use. The absorption enhancer consisted of cellulose nanocrystals and a UV-absorbing functional group monomer. The UV-absorbing functional group monomer was grafted onto the surface of the cellulose nanocrystals through an esterification reaction to form a composite enhanced UV absorber. The UV-absorbing functional group monomer was 2,4-dihydroxybenzophenone. Step 2: High-speed blending and pre-dispersion: Weigh each component according to the mass fractions, and put the dried polylactic acid, polybutylene terephthalate-adipate, flake nano titanium dioxide, nano cerium oxide, absorption enhancer, oxazoline compatibilizer and polycaprolactone micro powder degradation regulator into a high-speed mixer and mix for 15 minutes at room temperature to obtain the mixture. Step 3: Melt extrusion and granulation: The mixture is added to a twin-screw extruder for melt blending and extrusion granulation. The temperatures of each section of the extruder are set as follows: Zone 1 160℃, Zone 2 170℃, Zone 3 175℃, Zone 4 180℃, and Die Head 180℃; the screw speed is 300 r / min; after extrusion, the mixture is cooled by water and pelletized to obtain modified composite material particles. Step 4: Wire drawing and stretching for shaping: Modified composite material particles are added to a single-screw extruder, and after melt extrusion, cooling, filament separation, stretching, and shaping, flat filaments are obtained. The extrusion temperature is 165℃, the cooling water temperature is 30℃, the stretching temperature is 100℃, the stretching ratio is 5 times, and the stretching and shaping adopts a two-step stretching process. The first step is longitudinal stretching at 100℃, and the second step is transverse stretching at 110℃. The total stretching time is controlled at 12 seconds, the shaping temperature is 100℃, the flat filament width is 2mm, and the thickness is 0.07mm. Step 5: Weaving and Shaping Flat yarns are woven on a circular loom at a speed of 400 rpm and a density of 80 threads / 10cm to form tubular fabric. The tubular fabric is then cut to a set length and sealed at the bottom and edges using ultrasonic or heat sealing methods to produce woven plastic bags. Subsequently, surface curing treatment is performed in a UV curing chamber to a curing strength of 300 mJ / cm². 2 The curing time is 20 seconds, resulting in the modified new material-based UV-resistant woven plastic bag; Step Six: Performance Testing and Packaging The finished woven plastic bags are tested for UV transmittance, tensile strength, and degradation performance. After passing the tests, they are packaged and put into storage.

[0018] Comparative Example 1: Without adding an absorption enhancer, the other parameters are the same as in Example 1; A molding process for a modified new material-based UV-resistant woven plastic bag specifically includes the following steps: Step 1: Raw material pretreatment and drying: Polylactic acid and polybutylene terephthalate were vacuum dried at 80°C for 6 hours to reduce the moisture content to ≤0.05%. The sheet-like nano-titanium dioxide had the same specifications and surface treatment as in Example 1, and was compounded with nano-cerium oxide at a ratio of 10:1 and dried at 60°C for later use.

[0019] Steps two through six: Except for the absence of an absorption enhancer in the mixture, all other process parameters, equipment, and operating procedures are exactly the same as in Example 1.

[0020] Comparative Example 2: A molding process for a modified new material-based UV-resistant woven plastic bag specifically includes the following steps: Step 1: Raw material pretreatment and drying: The polylactic acid and polybutylene terephthalate (PET) were dried in the same manner as in Example 1. The sheet-like nano-titanium dioxide had the same specifications as in Example 1, but without any silane coupling agent surface treatment, it was directly compounded with nano-cerium oxide at a ratio of 10:1 and dried at 60°C for later use. The absorption enhancer treatment was the same as in Example 1.

[0021] Steps two through six: Except for the use of untreated sheet-like nano-titanium dioxide, all other process parameters, equipment and operating procedures are exactly the same as in Example 1.

[0022] Table 1 is a comparison table of key information between the examples and comparative examples. ; Table 1 According to Table 1, compared to Comparative Examples 1 and 2, the addition of an absorption enhancer in this embodiment achieves a dual synergistic mechanism of "physical shielding" and "chemical absorption." The expected UV blocking rate of this embodiment is significantly higher than that of Comparative Example 1. Comparative Example 1 relies solely on nanoparticles, which may result in UV shielding blind spots at low addition levels, and the nanoparticles themselves may exhibit photocatalytic activity under strong UV light, affecting the matrix. Furthermore, in this embodiment, the sheet-like nano-titanium dioxide underwent surface treatment with a silane coupling agent. Uniformly dispersed sheet-like nanoparticles can reflect / scatter UV light layer by layer within the material like "miniature mirrors," resulting in a longer light path and higher shielding efficiency. In contrast, the untreated nanoparticles in Comparative Example 2 are prone to agglomeration, forming macroscopic defects that not only reduce the effective shielding area but may also become stress concentration points. Furthermore, agglomerates may cause localized UV penetration. Surface treatment of the nanoparticles is crucial to ensuring their uniform dispersion during melt blending and extrusion processing. In this embodiment, the treated nanoparticles can mix more smoothly with the polymer melt, avoiding blockage in the screw or die, ensuring production continuity and stability.

[0023] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A modified new material-based UV-resistant woven plastic bag, characterized in that, Specifically, it includes the following components: polylactic acid, polybutylene terephthalate, sheet-like nano titanium dioxide, nano cerium oxide, absorption enhancer, interlayer compatibilizer, and degradation regulator; The specific mass fractions of the above ingredients are as follows: 40-60 parts of polylactic acid, 20-30 parts of polybutylene terephthalate-adipate, 5-7 parts of sheet-like nano titanium dioxide, 3-5 parts of nano cerium oxide, 4-6 parts of absorption enhancer, 3-5 parts of interlayer compatibilizer, and 1-3 parts of degradation regulator.

2. The modified new material-based UV-resistant woven plastic bag and its molding process according to claim 1, characterized in that: The sheet-like nano-titanium dioxide has a diameter of 10-50 nm and a thickness of 1-5 nm, and is surface-treated with a silane coupling agent. The mass ratio of the sheet-like nano-titanium dioxide to nano-cerium oxide is 10:

1.

3. The modified new material-based UV-resistant woven plastic bag and its molding process according to claim 1, characterized in that: The absorption enhancer comprises cellulose nanocrystals and a monomer with ultraviolet absorbing functional group. The monomer with ultraviolet absorbing functional group is grafted onto the surface of the cellulose nanocrystals through an esterification reaction to form a composite enhanced ultraviolet absorber. The monomer with ultraviolet absorbing functional group is one of 2,4-dihydroxybenzophenone and 2,4,6-tris(4-aldehydephenyl)-1,3,5-triazine.

4. The modified new material-based UV-resistant woven plastic bag and its molding process according to claim 1, characterized in that: The interlayer compatibilizer is an oxazoline-based compatibilizer, and the degradation regulator is polycaprolactone micro powder.

5. A molding process for a modified new material-based UV-resistant woven plastic bag, characterized in that, Specifically, the following steps are included: Step 1: Raw material pretreatment and drying: Polylactic acid and polybutylene terephthalate were vacuum dried at 80°C for 6-8 hours to reduce the moisture content to ≤0.05%. Flake-shaped nano-titanium dioxide and nano-cerium oxide were surface modified with a silane coupling agent and dried at 60°C for later use. Cellulose nanocrystals in the absorption enhancer were grafted with UV-absorbing functional group monomers in advance through esterification reaction to prepare a composite enhanced UV absorber. Step 2: High-speed blending and pre-dispersion: Weigh each component according to the mass fractions, and put the dried polylactic acid, polybutylene terephthalate-adipate, flake nano titanium dioxide, nano cerium oxide, absorption enhancer, interlayer compatibilizer and degradation regulator into a high-speed mixer and mix at room temperature for 10-15 minutes to obtain the mixture. Step 3: Melt extrusion and granulation: The mixture is added to a twin-screw extruder for melt blending and extrusion granulation. The temperatures of each section of the extruder are set as follows: Zone 1 150-160℃, Zone 2 160-170℃, Zone 3 170-180℃, Zone 4 175-185℃, and Die Head 180-190℃; the screw speed is 200-300 r / min; after extrusion, the material is water-cooled and pelletized to obtain modified composite material particles. Step 4: Wire drawing and stretching for shaping: Modified composite material particles are added to a single screw extruder, and flat filaments are obtained through melt extrusion, cooling, filament splitting, stretching, and shaping. The extrusion temperature is 165-185℃, the cooling water temperature is 25-35℃, the stretching temperature is 100-130℃, the stretching ratio is 4.5-5.5 times, the setting temperature is 100-120℃, the flat yarn width is 1.5-2.5mm, and the thickness is 0.04-0.08mm. Step 5: Weaving and Shaping Flat yarns are woven on a circular loom at a speed of 300-400 rpm and a density of 60-80 yarns / 10cm to form a tubular fabric. The tubular fabric is then cut to a set length and sealed at the bottom and edges using ultrasonic or heat sealing methods to produce woven plastic bags. Subsequently, surface curing treatment was carried out in a UV curing chamber, with a curing strength of 200-400 mJ / cm². 2 The curing time is 10-30 seconds to obtain the modified new material-based UV-resistant woven plastic bag; Step Six: Performance Testing and Packaging The finished woven plastic bags are tested for UV transmittance, tensile strength, and degradation performance. After passing the tests, they are packaged and put into storage.

6. The molding process for a modified new material-based UV-resistant woven plastic bag according to claim 5, characterized in that: The stretching and shaping process described in step four adopts a two-step stretching process. The first step involves longitudinal stretching at a temperature of 100-120℃, and the second step involves transverse stretching at a temperature of 110-130℃. The total stretching time is controlled within 8-12 seconds.