Large-capacity carrier-removing filtering basket

Abstract

The invention discloses a large-capacity carrier-free filtering basket, and particularly relates to the technical field of forensic science DNA extraction and detection.The large-capacity carrier-free filtering basket comprises an outer pipe, an inner pipe is arranged in the outer pipe, a filtering membrane is arranged at the bottom of the inner pipe, a pressing ring is arranged above the filtering membrane, a cover body is arranged on one side of the outer pipe, and a rubber connecting rib is arranged between the outer pipe and the cover body; the cover body is connected with the outer pipe through a rubber connecting rib, and the filtering membrane comprises a supporting layer and a PTFE (Polytetrafluoroethylene) coating. According to the invention, a filter membrane technology is utilized to effectively remove a sample and impurities attached to the sample, so that the obtained DNA solution is purer, adverse effects of impurities such as fine particles on subsequent DNA detection are avoided, DNA liquid can be enriched to the maximum extent, the detection success rate of trace sample DNA is remarkably improved, no liquid leakage phenomenon exists in the heating and cracking process, and the detection efficiency is improved. And the filtering membrane has good chemical stability and thermal stability, and has no adsorption effect on DNA (Deoxyribose Nucleic Acid).

Description

Technical Field

[0001] The present invention relates to the technical field of forensic science DNA extraction and detection, and more particularly to a large-capacity carrier removal filter basket. Background Art

[0002] At present, the collection and analysis of biological samples plays a vital role in the investigation of criminal cases. These samples come in various forms, among which wipes of various sizes are one of the most common types. They may contain key DNA evidence and have a decisive impact on the detection of the case. However, how to extract DNA from these samples efficiently and accurately has always been an important topic in the field of forensic medicine and criminal technology.

[0003] Although traditional DNA extraction methods can meet the processing needs of general samples to a certain extent, their processing capabilities and effects are often limited when faced with special samples (such as bones, large items, large system difficult samples, etc.). These special samples have low DNA content, large sample size, and complex composition, making it difficult for traditional extraction methods to achieve ideal extraction efficiency and recovery rate.

[0004] As an advanced DNA extraction technology, the basket method has been widely used in the field of DNA extraction due to its advantages such as high efficiency, high recovery rate and low pollution. The basket method can effectively separate the DNA from impurities in the sample through specific centrifugation and filtration devices to obtain pure DNA samples. However, the basket products currently available on the market are limited by their processing volume and are often unable to meet the processing needs of large-scale difficult samples.

[0005] In view of this, the present invention provides a large-capacity carrier removal filter basket. Summary of the invention

[0006] In order to overcome the above defects of the prior art, the present invention provides a large-capacity carrier removal filter basket to solve the problems raised in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solution: a large-capacity carrier removal filter basket, comprising an outer tube, an inner tube is arranged inside the outer tube, a filter membrane is arranged at the bottom of the inner tube, a pressure ring is arranged above the filter membrane, a cover body is arranged on one side of the outer tube, and a rubber connecting rib is arranged between the outer tube and the cover body, and the cover body is connected to the outer tube through the rubber connecting rib; The filter membrane includes a support layer and a PTFE coating, wherein the support layer is installed at the bottom of the inner tube by laser welding, and the PTFE coating is coated on the upper surface of the support layer. Preferably, the bottom of the outer tube is in an inverted cone shape, and the top and bottom ends of the inner tube are connected to each other.

[0008] Preferably, a plurality of protrusions for tightly pressing the filter membrane against the bottom of the inner tube are provided on the inner side wall of the retaining ring, and the retaining ring is integrally divided into a "pin" shape by the protrusions.

[0009] Preferably, the PTFE coating is a film with a microporous structure, and the number of micropores is 1400000000 / cm 2 , the porosity > 85%, and the pore diameter is 0.02 μm - 15 μm.

[0010] Preferably, the PTFE coating specifically comprises the following components: 65 - 75 parts of PTFE resin, 5 - 10 parts of nano - scale inorganic filler, 12 - 18 parts of additive aids, and 3 - 5 parts of other aids, where; The nano - scale inorganic filler is specifically silica and alumina; The additive aids include a dispersant, a surfactant, a cross - linker, a curing agent, and an anti - ultraviolet aid; The other aids are specifically a lubricant and an antistatic agent.

[0011] Preferably, the dispersant includes an inorganic dispersant and an organic dispersant. The inorganic dispersant specifically includes sodium silicate, sodium tripolyphosphate, sodium hexametaphosphate, and sodium pyrophosphate. The organic dispersant specifically includes triethylhexyl phosphate, sodium dodecyl sulfate, methyl pentanol, cellulose derivatives, and polyacrylamide; The surfactant includes any one of an anionic surfactant, a cationic surfactant, an amphoteric ionic surfactant, and a non - ionic surfactant; The cross - linker specifically includes polyamide, polyether, and polyurethane; The curing agent specifically includes aliphatic amines, aromatic amines, and acid anhydrides; The anti - ultraviolet aid specifically includes UV absorbers, HALS, and light stabilizers.

[0012] Preferably, the lubricant specifically includes silicone oil, fatty acid amide, oleic acid, polyester, synthetic ester, and carboxylic acid. The antistatic agent is any one of a cationic antistatic agent, anionic antistatic agent, and non - ionic antistatic agent.

[0013] Preferably, the preparation of the PTFE coating specifically comprises the following steps: S1. Mixing: Place the PTFE resin and the nano - scale inorganic filler in a mixer and stir at a speed of 2000 - 3000 r / min for 30 - 60 min. During this period, continuously add the additive aids to fully mix and disperse the PTFE resin and the nano - scale inorganic filler, and the temperature is 15 - 18 °C; S2, calendering, calendering the mixed coating in S1 through a calender to form a 0.12-2 mm thick film, the calender temperature is 60-80°C, the pressure is 10-25 MPa, and the speed is 0.1-1 m / min; S3, biaxial stretching, biaxially stretching the film calendered in S2, with the stretching temperature being 40-327°C; S4, winding up, winding up the stretched film to form a PTFE coating.

[0014] Technical effects and advantages of the present invention: 1. The present invention can enrich DNA to the maximum extent, and utilizes advanced filtration membrane technology to effectively remove samples and impurities attached to them, such as fine particles, proteins, and other cell components. This not only significantly improves the recovery rate of trace sample DNA, but also ensures that the extracted DNA is purer, thereby avoiding the adverse effects of impurities on subsequent DNA testing, and provides a solid foundation for high-quality DNA detection, analysis, and research; 2. The present invention adopts a unique membrane welding technology to ensure that there is no liquid leakage during the heating and lysis process, ensuring the full lysis of cells and the effective release of DNA. In addition, the specially designed filter membrane has no stringent requirements on the centrifuge and can be competent for centrifugal operation at any angle without centrifugal blind spots, achieving a full and thorough centrifugation process, which not only improves the flexibility and convenience of the experiment, but also ensures the efficiency and effect of DNA extraction; 3. The filter membrane of the present invention is made of inert materials, has good chemical stability and thermal stability, can maintain its performance and integrity under various experimental conditions, has no adsorption effect on DNA, avoids DNA loss and contamination, and at the same time, ensures that there is no risk of exogenous DNA contamination, thereby ensuring the accuracy and reliability of the experimental results.

[0015] In summary, the present invention has the beneficial effects of efficient enrichment and pure DNA extraction, heating lysis without liquid leakage and centrifugal flexibility, good chemical thermal stability and no exogenous DNA contamination, etc., providing a more efficient, accurate and reliable technical means for DNA extraction and analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0017] Figure 2 It is a schematic diagram of the structure of the filter membrane of the present invention.

[0018] Figure 3 The following is a flow chart of the preparation of the PTFE coating of the present invention.

[0019] The figures are marked as follows: 1. outer tube; 2. inner tube; 3. filter membrane; 4. pressure ring; 5. cover body; 6. rubber connecting rib; 30. support layer; 31. PTFE coating; 7. protrusion. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Embodiment 1, The embodiment of the present invention provides a large-capacity carrier removal filter basket, combined with the attached Figure 1-2 As shown, it specifically includes an outer tube 1, an inner tube 2 is arranged inside the outer tube 1, a filter membrane 3 is arranged at the bottom of the inner tube 2, a pressure ring 4 is arranged above the filter membrane 3, a cover body 5 is arranged on one side of the outer tube 1, and a rubber connecting rib 6 is arranged between the outer tube 1 and the cover body 5, the cover body 5 is connected to the outer tube 1 through the rubber connecting rib 6, the filter membrane 3 includes a support layer 30 and a PTFE coating 31, wherein the support layer 30 is installed on the bottom of the inner tube 2 by laser welding, and the PTFE coating 31 is coated on the upper surface of the support layer 30.

[0022] Specifically, in this structure, the filter membrane 3 is divided into a support layer 30 and a PTFE coating 31. The support layer 30 is fixed to the bottom of the inner tube 2 by laser welding. The specific thickness of the support layer 30 only needs to ensure that the thickness can be laser welded. The PTFE coating 31 is coated on the support layer 30, and the filter membrane 3 is fixed by the pressing ring 4 to prevent the filter membrane 3 from falling off, so that the filter membrane 3 is connected to the inner tube 2. The inner tube 2 is installed inside the outer tube 1. The carrier in the inner tube 2 is centrifugally filtered through the filter membrane 3, so that the DNA-rich liquid enters the outer tube 1 for storage. The cover body 5 is connected to the outer tube 1 by a rubber connecting rib 6, which is convenient for opening and closing the cover body 5.

[0023] In this embodiment, as shown in the attached Figure 1 As shown, the bottom of the outer tube 1 is in an inverted cone shape, and the top and bottom ends of the inner tube 2 are connected to each other.

[0024] Specifically, in this structure, the bottom of the outer tube 1 is in an inverted cone shape, which can make the size of the outer tube 1 meet international standards and match the groove for installing the outer tube 1 on most metal bath heating modules on the market. The inner tube 2 is configured to be connected up and down, which can ensure that after the carrier enters the inner tube 2, it can be centrifugally filtered through the filter membrane 3 to allow the DNA-rich liquid to enter the inner part of the outer tube 1 for storage.

[0025] In this embodiment, as shown in the appendix Figure 1 As shown, several protrusions 7 are provided on the inner side wall of the pressure ring 4 for tightly pressing the filter membrane 3 against the bottom of the inner tube 2, and the protrusions 7 divide the entire pressure ring 4 into a "pin" shape.

[0026] Specifically, in this structure, the protrusions 7 on the inner wall of the pressure ring 4 are used to prevent the filter membrane 3 from falling off, thereby avoiding liquid leakage during the heating process. The number of protrusions 7 depends on the situation, and only needs to ensure that the filter membrane 3 is tightly pressed.

[0027] The specific principle of Embodiment 1 is as follows: First, the support layer 30 in the filter membrane 3 is fixed to the bottom of the inner tube 2 by laser welding, and a pressure ring 4 is installed to tightly press the filter membrane 3, completing the installation of the filter membrane 3 and the inner tube 2. The inner tube 2 with the installed filter membrane 3 and pressure ring 4 is placed entirely inside the outer tube 1. The carrier attached with DNA is placed in the inner tube 2, lysate is added, and then the inner tube 2 and the whole are placed in the slot of the metal bath heating module for heating to fully lyse the cells and release DNA; Then, it is taken out as a whole and centrifuged in a centrifuge, so that the liquid rich in DNA flows through the filter membrane 3 and into the bottom of the outer tube 1 after filtration. At the same time, the useless carriers and impurities will be intercepted inside the inner tube 2 and above the filter membrane 3. Finally, the cover 5 on the outer tube 1 is opened, the inner tube 2 is taken out, and the DNA-rich liquid in the outer tube 1 is taken out for subsequent detection. This device can store 50 ml of DNA liquid.

[0028] Embodiment 2, Based on Embodiment 1, the PTFE coating in the filter membrane is described. Specifically, as shown in the appendix Figure 3 As shown, the PTFE coating is a thin film with a microporous structure. The number of micropores is 1400000000 / cm 2 , the porosity > 85%, and the pore diameter is 0.02 μm - 15 μm.

[0029] The PTFE coating mainly contains 80 parts of PTFE resin, 5 parts of nanoscale silica, 3 parts of dispersant (sodium silicate), 2 parts of surfactant (anionic type), 4 parts of crosslinking agent (polyamide), and 3 parts of curing agent (aliphatic amine type). The specific preparation steps are as follows: S1. Place the PTFE resin and nanoscale silica in a mixer and stir at a speed of 2200 r / min for 40 min. During this period, gradually add the dispersant and surfactant, and keep the mixing temperature at 16 °C until the PTFE resin and nanoscale inorganic fillers are fully mixed and dispersed; S2, the mixed coating is rolled through a calender to form a 0.5 mm thick film, the temperature of the calender is set to 65°C, the pressure is 15 MPa, and the speed is 0.3 m / min; S3, biaxially stretching the calendered film at a stretching temperature of 175° C. to form a PTFE coating with a microporous structure; S4, rolling up the stretched film to form a PTFE coated coil for subsequent cutting and installation.

[0030] Embodiment 3, The PTFE coating of this embodiment mainly comprises 75 parts of PTFE resin, 10 parts of nano-alumina, 4 parts of dispersant (sodium tripolyphosphate), 3 parts of surfactant (non-ionic), 5 parts of cross-linking agent (epoxy resin), and 4 parts of curing agent (phenolic resin), and specifically comprises the following preparation steps: S1. Place PTFE resin and nano-alumina in a mixer and stir at a speed of 2500 r / min for 50 min. During this period, gradually add dispersant and surfactant, and keep the mixing temperature at 17° C. until the PTFE resin and nano-inorganic filler are fully mixed and dispersed. S2, using a scraper to apply the coating of S1 on the support layer in Example 1 to form a coating with a thickness of 0.1 mm; S3, heat-treating the coating at 55° C. to form a PTFE coating with a microporous structure, and finally cutting and installing the PTFE coating and the support layer to form a filter membrane.

[0031] Embodiment 4, The PTFE coating of this embodiment mainly comprises 70 parts of PTFE resin, 15 parts of a mixture of nano-scale silicon dioxide and aluminum oxide (ratio of 1:1), 5 parts of a dispersant (a mixture of sodium silicate and sodium tripolyphosphate), 3 parts of a surfactant (anionic and non-ionic mixture), 6 parts of a cross-linking agent (a mixture of polyamide and epoxy resin), and 4 parts of a curing agent (a mixture of aliphatic amines and phenolic resin), and specifically comprises the following preparation steps: S1. Place the PTFE resin and the mixture of nano-scale silica and alumina in a mixer and stir at a speed of 2600 r / min for 45 min, during which time gradually add a dispersant and a surfactant, and keep the mixing temperature at 17° C. until the PTFE resin and the nano-scale inorganic filler are fully mixed and dispersed; S2, using a scraper to apply the coating of S1 on the support layer in Example 1 to form a coating with a thickness of 0.8 mm; S3. The coating is biaxially stretched and heat treated to form a PTFE coating with a microporous structure. The stretching temperature is 224° C. and the heat treatment temperature is 45° C. Finally, the PTFE coating and the support layer are cut and installed to form a filter membrane.

[0032] The following is a performance test of the PTFE coatings prepared in Examples 2-4; 1. Chemical resistance test: The samples prepared in Examples 2-4 were immersed in 10% hydrochloric acid, sodium hydroxide solution and common organic solvents (such as ethanol and acetone) respectively. Each solution was immersed for 24 hours. The morphological changes, weight loss and whether the film was dissolved, expanded or cracked before and after immersion were observed and recorded. 2. High temperature resistance test: place the PTFE film sample in a high temperature oven, gradually raise the temperature to 260°C, and keep it for 2 hours to observe and record the morphological changes, color changes, and whether decomposition, melting, etc. of the film at high temperature; 3. Low friction coefficient test: Use a friction coefficient tester to perform friction test on the PTFE film sample and a standard friction material (such as a stainless steel plate), record the friction coefficient value, and compare the friction coefficient differences of the films prepared in different embodiments; 4. Hydrophobicity test: place a water drop on the surface of the PTFE film, observe the contact angle and diffusion of the water drop, and use a contact angle meter to measure the contact angle of the water drop on the film surface; 5. Micropore structure test: use scanning electron microscope (SEM) to observe the micropore structure of PTFE film, measure and record the diameter, distribution and porosity of micropores; 6. Biocompatibility test: PTFE film samples are cultured in contact with biological tissues (such as skin cells, blood, etc.), and cell growth, inflammatory response, and toxicity are observed and recorded. If necessary, animal experiments are conducted to further verify biocompatibility. 7. High strength test: use a universal material testing machine to test the tensile strength of the PTFE film, record the breaking strength and elongation at break, and compare the tensile strength differences of the films prepared in different embodiments; 8. Anti-aging test: Place the PTFE film sample in a UV aging box to simulate long-term exposure to the natural environment. Take out the sample at regular intervals (such as 24 hours, 48 ​​hours, 72 hours, etc.) to observe and record its morphological changes, color changes, and whether cracks, embrittlement, etc. occur.

[0033] The final test results are shown in the following table: Chemical resistance High temperature resistance Low coefficient of friction Hydrophobicity Microporous structure Biocompatibility High strength Anti-aging Example 2 No significant changes, weight loss <0.5%, no dissolution, expansion or cracking Stable shape, no color change, no decomposition, shrinkage rate <2% Friction coefficient = 0.08 Contact angle = 110° Micropore diameter 0.2-0.5μm, evenly distributed, porosity = 85% Good cell growth and no inflammatory response Breaking strength = 50MPa, breaking elongation = 200% The morphology is stable after aging, with no obvious changes Example 3 No significant changes, weight loss <0.4%, no dissolution, expansion or cracking Stable shape, no color change, no decomposition, shrinkage rate <1.5% Friction coefficient = 0.075 Contact angle = 115° Micropore diameter 0.1-0.4μm, more evenly distributed, porosity = 88% Cells grow well, there is no inflammatory response, and cells proliferate faster Breaking strength = 55MPa, breaking elongation = 220% After aging, the shape is stable and the color becomes slightly lighter Example 4 No significant changes, weight loss <0.3%, no dissolution, expansion or cracking Stable shape, no color change, no decomposition, shrinkage <1% Friction coefficient = 0.07 Contact angle = 120° Micropore diameter 0.1-0.3μm, highly uniform, porosity = 90% Good cell growth, no inflammatory response, better cell morphology Breaking strength = 60MPa, breaking elongation = 250% The morphology is stable after aging, the color changes are smaller and more stable According to the above table data, the PTFE coatings prepared in Examples 2-4 of the present invention have good chemical resistance, high temperature resistance, extremely low friction coefficient, excellent hydrophobicity, optimized microporous structure, good biocompatibility, high strength and excellent anti-aging performance, which are specifically manifested as follows: Chemical resistance: After being immersed in 10% hydrochloric acid, sodium hydroxide solution and organic solvent for 24 hours, the films of all examples showed no significant morphological changes and extremely low weight loss (less than 0.5%). This indicates that the films have excellent chemical stability and can maintain their structure and performance in harsh chemical environments; High temperature resistance: after baking at 260°C for 2 hours, the film has a stable morphology, no color change or decomposition, and a low shrinkage rate (the shrinkage rate of Example 3 is the lowest, only 1%), which shows the stability and dimensional retention ability of the film under high temperature conditions; Very low friction coefficient. The films of all embodiments showed very low friction coefficient (less than 0.08), which means that the films have excellent lubrication properties, can reduce friction and wear, and are suitable for applications requiring low friction surfaces; Excellent hydrophobicity, the water drop contact angle on the film surface is large (the contact angle of Example 3 is the highest, 120°), indicating that the film has excellent hydrophobic properties, can resist the penetration and adsorption of water molecules, and is suitable for waterproof and moisture-proof applications; The optimized microporous structure has small and evenly distributed micropores and a high porosity (the porosity of Example 3 is as high as 90%). This microporous structure helps to improve the air permeability and filtration efficiency of the film while maintaining its structural strength and stability. Good biocompatibility. After the film comes into contact with biological tissue, cells grow well and there is no inflammatory reaction, which indicates that the film has potential biomedical value and can be used in fields such as medical implants and biosensors. High strength and excellent anti-aging performance, the film has high breaking strength and large breaking elongation (Example 3 has the highest breaking strength of 60MPa and breaking elongation of 250%), indicating that the film has excellent mechanical properties and toughness. At the same time, the film is stable in shape after simulating long-term exposure in a UV aging box, with no obvious changes, showing good anti-aging performance.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A large-capacity carrier removal filter basket, comprising an outer tube (1), characterized in that: An inner tube (2) is arranged inside the outer tube (1). A filter membrane (3) is arranged at the bottom of the inner tube (2). A retaining ring (4) is arranged above the filter membrane (3). A cover body (5) is arranged on one side of the outer tube (1), and a rubber connecting rib (6) is arranged between the outer tube (1) and the cover body (5). The cover body (5) is connected to the outer tube (1) through the rubber connecting rib (6). The filter membrane (3) includes a support layer (30) and a PTFE coating (31). Among them, the support layer (30) is installed at the bottom of the inner tube (2) by laser welding, and the PTFE coating (31) is coated on the upper surface of the support layer (30).

2. The large-capacity carrier removal filter basket according to claim 1 is characterized in that: The bottom of the outer tube (1) is in an inverted cone shape, and the top and bottom of the inner tube (2) are interconnected.

3. The large-capacity carrier removal filter basket according to claim 1 is characterized in that: Several protrusions (7) for tightly pressing the filter membrane (3) against the bottom of the inner tube (2) are arranged on the inner side wall of the retaining ring (4). The protrusions (7) divide the retaining ring (4) as a whole into a shape like the Chinese character "pin".

4. The large-capacity carrier removal filter basket according to claim 1 is characterized in that: The PTFE coating (31) is a thin film with a microporous structure, and the number of micropores is 1400000000 / cm 2 , porosity>85%, pore size 0.02μm-15μm.

5. The large-capacity carrier removal filter basket according to claim 1 is characterized in that: The PTFE coating (31) specifically includes the following components: 65-75 parts of PTFE resin, 5-10 parts of nano-scale inorganic filler, 12-18 parts of additive and 3-5 parts of other additives. Among them; The nano-scale inorganic filler is specifically silica and alumina; The additive includes dispersant, surfactant, crosslinking agent, curing agent and anti-ultraviolet additive; The other additives are specifically lubricant and antistatic agent.

6. The large-capacity carrier removal filter basket according to claim 5, characterized in that: The dispersant includes inorganic dispersant and organic dispersant. The inorganic dispersant specifically includes sodium silicate, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate. The organic dispersant specifically includes triethylhexyl phosphate, sodium dodecyl sulfate, methyl amyl alcohol, cellulose derivative and polyacrylamide; The surfactant includes any one of anionic surfactant, cationic surfactant, zwitterionic surfactant and non-ionic surfactant; The crosslinking agent specifically includes polyamide, polyether and polyurethane; The curing agent specifically includes aliphatic amines, aromatic amines and acid anhydrides; The anti-ultraviolet additive specifically includes UV absorber, HALS and light stabilizer; 7. The large-capacity carrier removal filter basket according to claim 5, characterized in that: The lubricant specifically includes silicone oil, fatty acid amide, oleic acid, polyester, synthetic ester and carboxylic acid. The antistatic agent adopts any one of cationic antistatic agent, anion antistatic agent and non-ionic antistatic agent.

8. The large-capacity carrier removal filter basket according to claim 1, characterized in that: The PTFE coating (31) specifically includes the following preparation steps: S1. Mixing: Place the PTFE resin and nano-scale inorganic filler in a mixer and stir at a speed of 2000-3000 r / min for 30-60 min. During this period, continuously add the additive to fully mix and disperse the PTFE resin and nano-scale inorganic filler. The temperature is 15-18 °C; S2. Calendering: Calender the mixed coating in S1 through a calender to form a film with a thickness of 0.12-2 mm. The temperature of the calender is 60-80 °C, the pressure is 10-25 mpa, and the speed is 0.1-1 m / min; S3, biaxial stretching, biaxially stretching the film calendered in S2, with the stretching temperature being 40-327°C; S4, winding up, winding up the stretched film to form a PTFE coating (31).

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