Process for manufacturing film by recycling and calendering polytetrafluoroethylene material

Abstract

The invention discloses a technology for manufacturing a thin film by recycling and calendering a polytetrafluoroethylene material, and belongs to the technical field of high polymer material recycling and processing, the technology for manufacturing the thin film by recycling and calendering the polytetrafluoroethylene material comprises the following steps: crushing waste products, and carrying out three-stage screening impurity removal and melt index detection; after being cleaned by supercritical carbon dioxide, the qualified material is mixed with industrial by-product filler, waste tire rubber powder and the like, low-temperature mixing is conducted through a double-screw extruder, and mixing parameters are automatically regulated and controlled through a tension sensor; performing calendaring forming by a five-roller calendaring unit, preheating the first two rollers, performing differential stretching by the middle three rollers, engraving a micro groove by the third roller, and controlling the thickness precision to be + / -3% by an online thickness gauge; the film is slit after being compounded according to requirements, and scrap edges are crushed and recycled. The method realizes efficient recovery of waste polytetrafluoroethylene, and has the advantages of thorough impurity removal, stable performance, environmental protection and energy saving.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material recycling and processing, and in particular relates to a process for recycling polytetrafluoroethylene materials and making films by calendering. Background Art

[0002] As the "king of plastics", polytetrafluoroethylene (PTFE) has excellent corrosion resistance, high temperature resistance and chemical stability, and is widely used in chemical, construction, electronics and other fields. However, with the extensive use of PTFE products, the recycling of waste PTFE has become an urgent problem to be solved. The current existing technology has the following shortcomings: the impurity removal process is not thorough, and conventional screening only relies on a single magnetic separation or screening, and it is impossible to simultaneously remove impurities such as non-ferromagnetic metals and organic matter. Residual impurities are prone to cause defects such as pores and fractures in the film; the modification treatment is inefficient, the microporous structure of polytetrafluoroethylene is not effectively opened, the adsorption rate of the modifier is low, and it is difficult to improve the weather resistance, compatibility and mechanical properties of the recycled material through fillers and additives; the quality control is extensive, and key parameters such as tension changes and film thickness during mixing lack real-time monitoring and automatic adjustment, and the product quality consistency is poor, which makes it difficult to meet the high standards of waterproof membranes, moisture-proof layers and other scenes; environmental protection measures are missing, waste edge materials have not been recycled in a closed loop, and the use of organic solvents in the cleaning process may cause secondary pollution, which does not conform to the concept of green manufacturing.

[0003] Therefore, it is urgent to develop an efficient and environmentally friendly waste PTFE recycling process to improve resource recycling. Summary of the invention

[0004] In response to the above pain points, the present invention provides a process for recycling polytetrafluoroethylene materials and making thin films by calendering. Through three-stage screening and impurity removal, supercritical cleaning, intelligent mixing and five-roller differential calendering, high-purity and high-precision films are prepared to achieve efficient resource utilization of waste PTFE.

[0005] The scheme of the present invention is as follows:

[0006] A process for recycling polytetrafluoroethylene materials and making films by calendering, characterized in that it comprises the following steps:

[0007] S1. The collected waste polytetrafluoroethylene products are crushed and then transported to the three-stage screening and impurity removal line. First, the metal impurities are removed by magnetic separation and eddy current separation, and then the large-size hard particles are removed by vibration screening. After the initial impurity removal, the material enters the flotation classification stage, and the density difference between polytetrafluoroethylene and impurities in the aqueous solution is used to separate organic and inorganic impurities, so that the residual impurities are ≤0.3%; then the CF bond characteristic peak area of ​​the recycled material is detected online by a near-infrared spectrometer, and the melt index is calculated according to the polytetrafluoroethylene molecular weight-spectrum calibration method in the ISO20558 standard. Unqualified recycled materials with estimated values ​​<0.5g / 10min and >3g / 10min are eliminated, and qualified recycled materials enter the next step;

[0008] S2. Send the qualified recycled materials into the supercritical cleaning equipment for cleaning under specific pressure and temperature conditions, using its expansion effect to open the microporous structure of polytetrafluoroethylene and improve the adsorption efficiency of subsequent modifiers;

[0009] S3, adding the qualified recycled materials after degreasing, industrial by-product fillers, waste tire rubber powder, weathering modifier and interfacial compatibilizer into a mixer in proportion to form a mixture;

[0010] S4, the mixed material is subjected to low temperature mixing at a temperature of 300-340°C through a twin-screw extruder, and a tension sensor is used to monitor the change of tension during the mixing process in real time, and the screw speed and mixing time are automatically adjusted;

[0011] S5. Calendering is performed using a five-roll calendering unit with an integrated online thickness gauge. The first two rollers are preheated and softened, the middle three rollers are stretched at differential speeds, and micro grooves are engraved on the surface of the third roller to form a rough texture. The online thickness gauge monitors the film thickness in real time and automatically adjusts the roller spacing to control the film thickness accuracy.

[0012] S6, cutting the film, directly crushing the waste edge material and returning it to step S1 for reproduction.

[0013] Preferably, the magnetic separation process of the three-stage screening and impurity removal line adopts a permanent magnetic drum magnetic separator with a magnetic field strength of 1000-3000 Gauss, which is used to adsorb ferromagnetic metal impurities in waste polytetrafluoroethylene products; the eddy current separation adopts an eddy current separation device with a frequency of 50-100Hz, which is used to separate non-ferromagnetic metal impurities; the vibration screening adopts a linear vibration screen with a vibration frequency of 15-30Hz and an amplitude of 2-5mm, which is used to remove hard particles with a particle size of >2mm; in the flotation classification link, the aqueous solution is distilled water, and a surfactant with a mass fraction of 0.1%-0.5% is added to enhance the separation effect of polytetrafluoroethylene and impurities.

[0014] Preferably, the supercritical cleaning equipment is a supercritical carbon dioxide cleaning equipment, which is used to remove oil stains on the surface of the recycled material at a pressure of 20 MPa and a temperature of 50° C. for 30-60 minutes.

[0015] Preferably, when the industrial by-product filler is silica fume, the specific surface area of ​​the silica fume is 15000-20000m 2 / kg, silicon dioxide content ≥90%; when graphite tailings are selected, the carbon content in the graphite tailings is 10%-20%, and the particle size is 200-300 mesh; the particle size of the waste tire rubber powder is 60-80 mesh, and the rubber content is ≥70%.

[0016] Preferably, the screw length-to-diameter ratio of the twin-screw extruder is 30-40:1, and the initial screw speed is set to 100-150 r / min.

[0017] Preferably, the tension sensor is used to monitor the tension change in the mixing process in real time and automatically adjust the screw speed and mixing time. The specific process is as follows:

[0018] 6-1. Before mixing begins, the operator sets the upper limit value F of the tension in the control system. max , lower limit F min , initial screw speed n 0 and initial mixing time t 0 ;

[0019] 6-2. Real-time monitoring: During the mixing process, the tension sensor measures the tension F of the material on the screw in real time. real ;

[0020] 6-3. Data analysis and judgment: judge according to the following rules:

[0021] If F real >F max , indicating that the material is highly viscous and the mixing difficulty increases;

[0022] If F real <F min , indicating that the material has low viscosity and the mixing degree may not be enough;

[0023] If F min ≤F real ≤F max , the mixing is normal;

[0024] 6-4. Automatic adjustment:

[0025] 6-4-1. Screw speed adjustment:

[0026] When F real >F max When the screw speed is adjusted

[0027] n 1 =k 1 ×n 0 ,in

[0028] α is the empirical coefficient;

[0029] When F real <F min When the screw speed is adjusted

[0030] n 2 =k 2 ×n 0 ,in

[0031] β is the empirical coefficient;

[0032] 6-4-2. Adjustment of mixing time:

[0033] If the tension value deviates from the preset range, the accumulated time t deviation , adjusted mixing time

[0034] t 1 =t 0 +k 3 ×t deviation

[0035] k 3 is a coefficient determined experimentally.

[0036] Preferably, the preheating temperature of the first two rollers of the five-roll calendering unit is 100-120°C, and the speed differential ratio of the middle three rollers is 1:1.2:1.5; the depth of the micro-grooves on the surface of the third roller is 0.05-0.1mm, the width is 0.1-0.2mm, and they are distributed in a diamond grid, which is used to increase the surface roughness of the film to enhance friction.

[0037] Preferably, the online thickness gauge monitors the film thickness in real time and automatically adjusts the roller spacing to control the thickness accuracy to ±3%. The specific process is as follows:

[0038] 8-1. Initialization setting: Before the calendering process begins, the operator sets the target film thickness d according to the process requirements. 0 , and the upper limit of thickness d max =1.03d 0 and the lower limit d min =0.97d 0 ;

[0039] 8-2. Real-time monitoring: During the calendering process, the online thickness gauge measures the film thickness in real time. real ;

[0040] 8-3. Data analysis and judgment: Calculate thickness deviation Δd = d real -d 0 ; and judge according to the following rules:

[0041] If d real >d max , indicating that the film thickness exceeds the upper limit;

[0042] If d real <d min , indicating that the film thickness is below the lower limit;

[0043] If d min ≤d real ≤d max , then the film thickness meets the requirements;

[0044] 8-4. Automatic adjustment: The roller spacing adjustment device is controlled according to the thickness deviation Δd:

[0045] When real >d max When , the roller spacing adjustment amount Δs = -k × Δd;

[0046] When real <d min When , the roller spacing adjustment amount Δs=k×|Δd|;

[0047] Where k is the adjustment coefficient determined by experiment;

[0048] Adjusted roller spacing: s 1 =s 0 +Δs, where s 0 The online thickness gauge continuously monitors the film thickness until it is within the preset accuracy range.

[0049] Compared with the prior art, the advantages of the present invention are:

[0050] (1) Thorough impurity removal: Magnetic separation is used to remove ferromagnetic metals, eddy current separation is used to separate non-ferromagnetic metals, vibration screening is used to remove hard particles > 2 mm, flotation separation is used to grade organic and inorganic matter, and near-infrared spectroscopy is used to detect the melt index to ensure high purity of the recycled material and avoid impurities causing film defects;

[0051] (2) Improved cleaning and modification efficiency: Supercritical carbon dioxide cleaning opens the microporous structure, which improves the adsorption efficiency of the modifier. Combined with specific fillers and waste tire rubber powder, the compatibility and mechanical properties of the recycled materials are improved;

[0052] (3) Precise control of process parameters: The tension sensor monitors the mixing tension in real time and automatically adjusts the screw speed and mixing time to ensure uniform mixing of the materials. The online thickness gauge dynamically adjusts the roller spacing to control the film thickness accuracy of ±3%. The micro grooves on the third roller enhance the surface friction to meet the strict requirements of film thickness and surface properties in waterproof and moisture-proof scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The figure is a schematic diagram of the process flow of a polytetrafluoroethylene material recycling and calendering process for making a film. DETAILED DESCRIPTION

[0054] 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.

[0055] Example 1

[0056] S1. Raw material processing.

[0057] Crushing and three-stage screening and impurity removal: 100kg of waste polytetrafluoroethylene products, including metal inserts, sand and gravel impurities and organic binder residues, are crushed to a particle size of ≤5mm by a jaw crusher and transported to the three-stage screening and impurity removal line;

[0058] Magnetic separation: A permanent magnetic drum magnetic separator with a magnetic field strength of 2000 Gauss is used to adsorb and remove ferromagnetic metal impurities, including iron nails and iron wires, with a metal removal rate of ≥99%;

[0059] Eddy current separation: Use 80Hz eddy current separation equipment to separate non-ferromagnetic metals, and the residual non-metallic impurities are ≤0.1%;

[0060] Vibration screening: Use a linear vibrating screen with a vibration frequency of 20Hz and an amplitude of 3mm to remove hard particles with a particle size >2mm, and a screening efficiency of ≥95%;

[0061] Flotation classification: put the material into a distilled water solution containing 0.3% by mass of sodium dodecyl sulfate, stir for 5 minutes and then let it stand for stratification to separate the floating organic matter, including the binder fragments and the sinking inorganic sediment. The residual impurity detection value is 0.25%;

[0062] Spectral detection: The characteristic peak area of ​​the CF bond of the recycled material was detected by a near-infrared spectrometer, and the melt index was calculated according to the ISO20558 standard. Materials with a melt index of <0.5g / 10min and >3g / 10min were eliminated, and finally 85kg of qualified recycled material with a melt index of 1.8g / 10min was obtained.

[0063] S2. Supercritical cleaning.

[0064] The qualified recycled materials were put into supercritical carbon dioxide cleaning equipment and cleaned for 45 minutes at a pressure of 20MPa and a temperature of 50°C to remove surface oil and small molecular pollutants. After cleaning, the surface contact angle of the recycled materials dropped from 85° to 60°, the pore size of the microporous structure increased to 5-10μm, and the adsorption efficiency of the modifier increased by 40%.

[0065] S3. Mix the ingredients.

[0066] Weigh qualified recycled materials according to the mass ratio of 70:20:5:3:2; the specific surface area of ​​silica ash is 18000m 2 / kg, SiO2 content 92%; waste tire rubber powder, particle size 70 mesh, rubber content 75%; ultraviolet absorber; maleic anhydride grafted polyethylene, add into high-speed mixer, mix at 150r / min speed for 10min, to form a uniform mixture.

[0067] S4, low temperature mixing.

[0068] The mixed material is fed into a twin-screw extruder with a screw length-to-diameter ratio of 35:1 and an initial speed of n 0 =120r / min, initial mixing time t 0 = 30min, mixing at 320°C;

[0069] Tension sensor control: set the tension upper limit F max =50N, lower limit F min =30N; the actual tensile force F at the initial stage of mixing real =55N, exceeding F max , and record the cumulative time t of the tension exceeding the limit deviation =10min, the speed adjustment coefficient is automatically calculated according to the formula:

[0070] Substitute the data into Adjusted screw speed n 1 =k 1 ×n 0 =0.95×120=114r / min; when the tension is stable at 35N, at F min ~F max When the interval is reached, the current parameters are maintained.

[0071] The total mixing time calculation formula is:

[0072] t 1 =t 0 +k 3 ×t deviation (k 3 =0.1) into

[0073] t 1 =30min+1×10min=40min

[0074] The final total mixing time was 40 min.

[0075] S5, calendering.

[0076] Five-roll calender unit: the first two rollers are preheated to 110°C to soften the material; the speed differential ratio of the middle three rollers is 1:1.2:1.5, the first roller is 50r / min, the second roller is 60r / min, and the third roller is 75r / min. The surface of the third roller is engraved with micro grooves with a depth of 0.08mm and a width of 0.15mm, and a diamond grid distribution;

[0077] Online thickness control: set target thickness d 0 =0.4mm, upper limit of thickness d max =1.03d 0 =0.412mm, lower limit d min =0.97d 0 =0.388mm; d measured during calendering real =0.42mm exceeds d max , calculate the thickness deviation Δd = d real -d 0 = +0.02mm, the roller spacing adjustment amount is according to the formula: Δs = -k × Δd (k = 0.8) to get Δs = -0.016mm, the roller spacing after adjustment is s 1 =s 0 +Δs, until the thickness stabilizes within the range of 0.4±0.012mm with an accuracy of ±3%.

[0078] S6. Slitting and recycling of waste materials.

[0079] Slitting and waste material treatment: The composite film is slit into 1m wide rolls, and the waste materials generated, about 5kg, are crushed and reused in step S1.

[0080] Example 2

[0081] S1. Raw material processing.

[0082] Crushing and three-stage screening and impurity removal: 100kg of waste polytetrafluoroethylene building formwork, including concrete debris, metal screws and organic release agent residues, is selected and crushed to a particle size of ≤4mm by a cone crusher and transported to the three-stage screening and impurity removal line;

[0083] Magnetic separation: A permanent magnetic drum magnetic separator with a magnetic field strength of 1800 Gauss is used to adsorb and remove ferromagnetic metals such as iron nails and iron sheets, with a metal removal rate of ≥99.2%;

[0084] Eddy current separation: Use 70Hz eddy current separation equipment to separate non-ferromagnetic metals such as aluminum screws, and the residual non-metallic impurities are ≤0.15%;

[0085] Vibration screening: Use a linear vibrating screen with a vibration frequency of 22Hz and an amplitude of 4mm to remove concrete fragments with a particle size > 2mm, and a screening efficiency of ≥ 96%;

[0086] Flotation classification: put the material into a distilled water solution containing 0.25% by mass of sodium dodecylbenzene sulfonate, stir for 6 minutes and then let it stand for stratification to separate the floating release agent fragments and the sinking sediment. The residual impurity detection value is 0.28%, which meets the requirement of ≤0.3%;

[0087] Spectral detection: The characteristic peak area of ​​the CF bond of the recycled material was detected by a near-infrared spectrometer, and the melt index was calculated according to the ISO20558 standard. Materials with a melt index of <0.5g / 10min and >3g / 10min were eliminated, and 80kg of qualified recycled materials with a melt index of 2.0g / 10min were obtained.

[0088] S2. Supercritical cleaning.

[0089] The qualified recycled materials were put into supercritical carbon dioxide cleaning equipment and cleaned for 50 minutes at a pressure of 20MPa and a temperature of 50°C to remove surface oil and release agent residues; after cleaning, the surface contact angle of the recycled materials dropped from 82° to 58°, the pore size of the microporous structure increased to 4-10μm, and the adsorption efficiency of the modifier increased by 35%.

[0090] S3. Mix the ingredients.

[0091] Weigh qualified recycled materials according to the mass ratio of 65:25:5:2:3; graphite tailings with a carbon content of 18% and a particle size of 200 mesh; waste tire rubber powder with a particle size of 80 mesh and a rubber content of 72%; benzotriazole ultraviolet absorbers; and silane coupling agents, add them into a high-speed mixer, mix at a speed of 160r / min for 12 minutes, and form a uniform mixture.

[0092] S4, low temperature mixing.

[0093] The mixed material is fed into a twin-screw extruder with a screw length-to-diameter ratio of 32:1 and an initial speed of n 0=110r / min, initial mixing time t 0 = 30min, mixing at 310°C;

[0094] Tension sensor control: set the tension upper limit F max =45N, lower limit F min =25N. The actual tensile force F at the initial stage of mixing real =22N, lower than F min , the cumulative time of insufficient pulling force t deviation =5min, the speed adjustment coefficient is automatically calculated according to the formula:

[0095] Substitute the data into Adjusted screw speed n 2 =k 2 ×n 0 =1.072×110=117.9r / min; when the tension is stable at 30N, at F min ~F max When the interval is reached, the current parameters are maintained.

[0096] The total mixing time calculation formula is:

[0097] t 1 =t 0 +k 3 ×t deviation (k 3 =0.1) into

[0098] t 1 =30min+1×5min=35min

[0099] The final total mixing time was 35 min.

[0100] S5, calendering.

[0101] Five-roll calender unit: the first two rollers are preheated to 105℃ to soften the material; the speed differential ratio of the middle three rollers is 1:1.2:1.5, the first roller is 40r / min, the second roller is 48r / min, and the third roller is 60r / min. The surface of the third roller is engraved with micro grooves with a depth of 0.05mm and a width of 0.1mm, and a diamond grid distribution to enhance the bonding force with concrete;

[0102] Online thickness control: set target thickness d 0 =0.3mm, upper limit of thickness d max =1.03d 0 =0.309mm, lower limit d min =0.97d 0 =0.291mm; d measured during calendering real=0.285mm, lower than d min , calculate the thickness deviation Δd = d real -d 0 =-0.015mm, the roller spacing adjustment amount is according to the formula: Δs = k × |Δd| (k = 0.7) to get Δs = 0.0105mm, the roller spacing after adjustment is s 1 =s 0 +Δs, until the thickness stabilizes within the range of 0.3±0.009mm with an accuracy of ±3%.

[0103] S6. Slitting and recycling of waste materials.

[0104] The calendered film is cut into 1.2m wide coils, and about 4kg of scrap material is generated, which is crushed and reused in step S1.

[0105] Example 3

[0106] S1. Raw material processing.

[0107] Crushing and three-stage screening and impurity removal: 120kg of waste polytetrafluoroethylene electronic equipment parts, containing a small amount of metal pins, plastic fragments and dust impurities, were selected and crushed with a hammer crusher to a particle size of ≤3mm;

[0108] Magnetic separation: A 1500 gauss permanent magnetic drum magnetic separator is used to remove ferromagnetic metals, with a metal removal rate of 99.5%;

[0109] Eddy current separation: Use 60Hz eddy current separation equipment to separate non-ferromagnetic metals, and the residual non-metallic impurities are 0.08%;

[0110] Vibration screening: The vibrating screen with a vibration frequency of 25Hz and an amplitude of 4mm can remove particles with a size > 2mm, and the screening efficiency is 96%;

[0111] Flotation classification: Place the material in a distilled water solution containing 0.2% by mass fraction of Tween-80, stir for 8 minutes and then let it stand to separate the organic and inorganic substances. The residual impurity detection value is 0.15%;

[0112] Spectral detection: using near infrared spectrometer to detect, the materials with melt index <0.6g / 10min and >2.8g / 10min were eliminated, and 90kg of qualified recycled materials with a melt index of 2.2g / 10min were obtained.

[0113] S2. Supercritical cleaning.

[0114] The qualified recycled materials were placed in a supercritical carbon dioxide cleaning equipment and cleaned for 50 minutes at a pressure of 22MPa and a temperature of 55°C to remove surface oil and tiny pollutants. After cleaning, the surface contact angle of the recycled materials dropped from 88° to 62°, the pore size of the microporous structure increased to 6-12μm, and the adsorption efficiency of the modifier increased by 42%.

[0115] S3. Mix the ingredients.

[0116] Weigh qualified recycled materials according to the mass ratio of 75:15:5:3:2; silica ash, specific surface area 16000m 2 / kg,SiO 2 Content 90%; waste tire rubber powder; hindered amine light stabilizer; ethylene-vinyl acetate copolymer, add into high speed mixer, mix at 180r / min speed for 12min, to form a uniform mixture.

[0117] S4, low temperature mixing.

[0118] The mixed material is fed into a twin-screw extruder with a screw length-to-diameter ratio of 38:1 and an initial speed of n 0 =130r / min, initial mixing time t 0 = 35min, mixing at 330°C;

[0119] Tension sensor control: set the tension upper limit F max =55N, lower limit F min =35N; actual tensile force F during mixing real =58N, exceeding F max , the cumulative time of tension exceeding the limit t deviation =10min, calculated according to the formula: Get k 1 =0.97, screw speed after adjustment n 1 =126.1r / min; when the tension stabilizes at 40N, maintain the current parameters.

[0120] The total mixing time calculation formula is:

[0121] t 1 =t 0 +k 3 ×t deviation (k 3 =0.1) into

[0122] t 1 =30min+1×15min=45min

[0123] The final total mixing time was 45 min.

[0124] S5, calendering.

[0125] Five-roll calender unit: the first two rollers are preheated to 115°C to soften the material; the speed differential ratio of the middle three rollers is 1:1.1:1.4, the first roller is 45r / min, the second roller is 49.5r / min, and the third roller is 63r / min. The surface of the third roller is engraved with micro grooves with a depth of 0.06mm and a width of 0.12mm, and a diamond grid distribution;

[0126] Online thickness control: set target thickness d 0 =0.2mm, upper limit of thickness d max =0.206mm, lower limit d min =0.194mm; d measured during calendering real =0.21mm, calculate Δd=+0.01mm, roller spacing adjustment: Δs=-k×Δd(k=0.8) to get Δs=-0.008mm, after adjustment, the thickness is stable within the range of 0.2±0.006mm, with an accuracy of ±3%.

[0127] S6. Slitting and recycling of waste materials.

[0128] The calendered film is cut into 0.5m wide coils, and about 6kg of scrap material is generated, which is crushed and reused in step S1.

[0129] Comparative Example 1

[0130] S1. Raw material processing.

[0131] After 100 kg of waste polytetrafluoroethylene products were simply crushed, only part of the ferromagnetic metal was removed by magnetic separation, and no eddy current separation, vibration screening and flotation classification were performed.

[0132] S2. Cleaning and modification.

[0133] Use organic solvent acetone to clean the recycled material and remove surface oil stains;

[0134] Add regular calcium carbonate filler and a small amount of plasticizer and simply stir to mix.

[0135] S3, mixing and calendering.

[0136] Mixing is carried out at a high temperature of 380°C without tension sensor control;

[0137] A three-roll calender is used, without online thickness control, and the roller spacing is manually adjusted.

[0138] Performance Testing

[0139] Performance test data recording

[0140]

[0141] Summary of individual test data.

[0142] 1. Residual impurities: Examples 1-3 were subjected to multi-stage screening to remove impurities, and the residual impurities were all ≤0.3%, which was significantly lower than 2% of the comparative example, proving that the impurity removal process was highly efficient.

[0143] 2. Film thickness: The thickness accuracy of the examples is ±3%, and the standard deviation is ≤0.011mm. The comparison examples lack online thickness control, so the accuracy does not meet the standard and the deviation is large.

[0144] 3. Surface friction coefficient: In the embodiment, the friction coefficient is increased to 0.25-0.32 by the micro-groove design of the third roller, while in the comparative example, it is only 0.10, and the surface performance is insufficient.

[0145] 4. Tensile strength and weather resistance: The tensile strength of the example is 18-22MPa, and the retention rate is ≥85% after UV aging for 500h; the strength of the comparative example is low, only 10MPa, and the weather resistance is poor, reflecting the advantages of intelligent mixing and supercritical cleaning.

[0146] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A process for recycling polytetrafluoroethylene materials and making films by calendering, characterized in that: The following steps are involved: S1. The collected waste polytetrafluoroethylene products are crushed and then transported to the three-stage screening and impurity removal line. First, the metal impurities are removed by magnetic separation and eddy current separation, and then the large-size hard particles are removed by vibration screening. After the initial impurity removal, the material enters the flotation classification stage, and the density difference between polytetrafluoroethylene and impurities in the aqueous solution is used to separate organic and inorganic impurities, so that the residual impurities are ≤0.3%; then the CF bond characteristic peak area of ​​the recycled material is detected online by a near-infrared spectrometer, and the melt index is calculated according to the polytetrafluoroethylene molecular weight-spectrum calibration method in the ISO20558 standard. Unqualified recycled materials with estimated values ​​<0.5g / 10min and >3g / 10min are eliminated, and qualified recycled materials enter the next step; S2. Send the qualified recycled materials into the supercritical cleaning equipment for cleaning under specific pressure and temperature conditions, using its expansion effect to open the microporous structure of polytetrafluoroethylene and improve the adsorption efficiency of subsequent modifiers; S3, adding the qualified recycled materials after degreasing, industrial by-product fillers, waste tire rubber powder, weathering modifier and interfacial compatibilizer into a mixer in proportion to form a mixture; S4, the mixed material is subjected to low temperature mixing at a temperature of 300-340°C through a twin-screw extruder, and a tension sensor is used to monitor the change of tension during the mixing process in real time, and the screw speed and mixing time are automatically adjusted; S5. Calendering is performed using a five-roll calendering unit with an integrated online thickness gauge. The first two rollers are preheated and softened, the middle three rollers are stretched at differential speeds, and micro grooves are engraved on the surface of the third roller to form a rough texture. The online thickness gauge monitors the film thickness in real time and automatically adjusts the roller spacing to control the film thickness accuracy. S6, cutting the film, directly crushing the waste edge material and returning it to step S1 for reproduction.

2. A process for making thin films by calendering of recycled polytetrafluoroethylene materials according to claim 1, characterized in that: The magnetic separation process of the three-stage screening and impurity removal line adopts a permanent magnetic drum magnetic separator with a magnetic field strength of 1000-3000 Gauss, which is used to adsorb ferromagnetic metal impurities in waste polytetrafluoroethylene products; the eddy current separation adopts an eddy current separation device with a frequency of 50-100Hz, which is used to separate non-ferromagnetic metal impurities; the vibration screening adopts a linear vibration screen with a vibration frequency of 15-30Hz and an amplitude of 2-5mm, which is used to remove hard particles with a particle size of more than 2mm; in the flotation classification link, the aqueous solution is distilled water, and a surfactant with a mass fraction of 0.1%-0.5% is added to enhance the separation effect of polytetrafluoroethylene and impurities.

3. According to claim 1, a process for making thin films by calendering of recycled polytetrafluoroethylene materials, characterized in that: The supercritical cleaning equipment is a supercritical carbon dioxide cleaning equipment, which cleans for 30-60 minutes at a pressure of 20 MPa and a temperature of 50° C. to remove oil stains on the surface of the recycled material.

4. According to claim 1, a process for making thin films by recycling polytetrafluoroethylene materials by calendering, characterized in that: When the industrial by-product filler is silica fume, the specific surface area of ​​the silica fume is 15000-20000m 2 / kg, silicon dioxide content ≥90%; when graphite tailings are selected, the carbon content in the graphite tailings is 10%-20%, and the particle size is 200-300 mesh; the particle size of the waste tire rubber powder is 60-80 mesh, and the rubber content is ≥70%.

5. According to claim 1, a process for making thin films by recycling polytetrafluoroethylene materials by calendering, characterized in that: The screw length-to-diameter ratio of the twin-screw extruder is 30-40:1, and the initial screw speed is set at 100-150 r / min.

6. According to claim 1, a process for making thin films by recycling polytetrafluoroethylene materials by calendering, characterized in that: The tension sensor is used to monitor the tension change in the mixing process in real time and automatically adjust the screw speed and mixing time. The specific process is as follows: 6-1. Before mixing begins, the operator sets the upper limit value F of the tension in the control system. max , lower limit F min , initial screw speed n0 and initial mixing time t0; 6-2. Real-time monitoring: During the mixing process, the tension sensor measures the tension F of the material on the screw in real time. real ; 6-3. Data analysis and judgment: judge according to the following rules: If F real >F max , indicating that the material is highly viscous and the mixing difficulty increases; If F real <F min , indicating that the material has low viscosity and the mixing degree may not be enough; If F min ≤F real ≤F max , then the mixing is normal; 6-4. Automatic adjustment: 6-4-1. Screw speed adjustment: When F real >F max When the screw speed is adjusted n1=k1×n0,where α is the empirical coefficient; When F real <F min When the screw speed is adjusted n2=k2×n0,where β is the empirical coefficient; 6-4-2. Adjustment of mixing time: If the tension value deviates from the preset range, the accumulated time t deviation , adjusted mixing time t1=t0+k3×t deviation k3 is a coefficient determined by experiments.

7. According to claim 1, a process for making thin films by recycling polytetrafluoroethylene materials by calendering, characterized in that: The preheating temperature of the first two rollers of the five-roll calender unit is 100-120°C, and the speed differential ratio of the middle three rollers is 1:1.2:1.5; the depth of the micro-grooves on the surface of the third roller is 0.05-0.1mm, the width is 0.1-0.2mm, and they are distributed in a diamond grid, which is used to increase the surface roughness of the film to enhance the friction.

8. According to claim 1, a process for making thin films by recycling polytetrafluoroethylene materials by calendering, characterized in that: The online thickness gauge monitors the film thickness in real time and automatically adjusts the roller spacing to control the thickness accuracy to ±3%. The specific process is as follows: 8-1. Initialization setting: Before the calendering process begins, the operator sets the target film thickness d0 and the upper thickness limit d according to the process requirements. max =1.03d0 and lower limit d min =0.97d0; 8-2. Real-time monitoring: During the calendering process, the online thickness gauge measures the film thickness in real time. real ; 8-3. Data analysis and judgment: Calculate thickness deviation Δd = d real -d0; and judge according to the following rules: If d real >d max , indicating that the film thickness exceeds the upper limit; If d real <d min , indicating that the film thickness is below the lower limit; If d min ≤d real ≤d max , then the film thickness meets the requirements; 8-4. Automatic adjustment: The roller spacing adjustment device is controlled according to the thickness deviation Δd: When real >d max When , the roller spacing adjustment amount Δs = -k × Δd; When real <d min When , the roller spacing adjustment amount Δs=k×|Δd|; Where k is the adjustment coefficient determined by experiment; The adjusted roller spacing is: s1=s0+Δs, where s0 is the current roller spacing. The online thickness gauge continuously monitors until the film thickness is within the preset accuracy range.

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