Process for the production of a stretch-resistant polypropylene film

Abstract

The present application relates to the technical field of polypropylene film, in particular to a production method of anti-stretching polypropylene film, comprising: S1: raw material preparation, selecting polypropylene resin meeting specific melt index and isotacticity requirements as a basic raw material, the melt index of the polypropylene resin ranges from 0.5 to 3.5 g / 10 min, and the isotacticity ranges from 95% to 98%; the polypropylene film is heated to 260 DEG C as a whole by a PLC controller controlling a heating plate, to provide a suitable basic temperature environment for stretching, then a local heating assembly is used, the PLC controller detects light changes according to a light receiver, judges polypropylene film thickness changes, when detecting a thicker film position, controls the third motor, the fourth motor and the like to act, drives a heating sheet to further heat the thicker position, so that the molecular chain segment movement ability of the thicker position is enhanced, its viscosity and internal stress are reduced, the whole and local precise heating can be realized, and the problems of excessive softening or insufficient softening caused by uneven film thickness are avoided.

Description

Technical Field

[0001] This invention relates to the field of polypropylene film technology, and more specifically to a method for producing tensile polypropylene film. Background Technology

[0002] Polypropylene is a thermoplastic polymer with good tensile strength, toughness, and abrasion resistance. Due to the large number of methyl groups in its molecular structure, polypropylene has strong flexibility, which allows it to withstand large deformations during stretching without easily breaking. However, in order to improve the barrier properties, heat-sealing properties, and mechanical properties of polypropylene films, a co-extrusion process is used. This process involves melting different polypropylene raw materials separately in multiple extruders, then extruding them through an extrusion die, stretching them, and finally compositing them into a single film structure. This method can make the bonding between the layers tighter and the performance more stable. For example, a flexible multilayer co-extruded biaxially oriented label film disclosed in application number 202210377555.2 is a multilayer polypropylene film produced by a co-extrusion process.

[0003] To improve the tensile strength of polypropylene film, it is subjected to stretching treatment. Stretching changes the molecular chain orientation and crystallinity of the polypropylene film, which not only improves tensile strength but also tear strength and puncture resistance, making it more durable, able to withstand greater external forces and friction, and less prone to breakage.

[0004] Existing methods for improving the tensile strength of polypropylene films through stretching typically involve heating multilayer polypropylene films at a constant temperature and stretching them at a constant speed. However, the thickness of the polypropylene film can vary in different locations (this is because during co-extrusion production, the material from each layer enters the co-extrusion die from different extruders, resulting in uneven flow rates due to factors such as the shape and size of the flow channels and the material flow characteristics, leading to differences in film thickness at different locations). Therefore, for thinner areas of the film, the same temperature may result in excessively high temperatures, causing the material to soften excessively. During stretching, this can easily lead to localized overstretching, thinning, or even cracking. Conversely, for thicker areas of the film, the same temperature may result in excessively low temperatures, insufficient material softening, and difficulty in achieving the desired stretching effect, thus failing to effectively improve tensile strength.

[0005] Stretching at a high or low speed in the initial stage can lead to internal stress concentration because a high speed may cause the film molecular chains to not have enough time to align evenly. On the other hand, using a low speed may cause the movement of the film molecular chains to be too slow, and the molecular chains may not be able to reach the appropriate orientation and crystallization state in time during the stretching process. This results in uneven crystallinity or failure to reach the ideal crystallinity of the film, which in turn affects the mechanical properties of the film. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for producing tensile polypropylene film, which can effectively solve the problems that the prior art cannot adaptively adjust the heating temperature at different positions according to the actual thickness of the polypropylene film, and cannot adaptively adjust the stretching speed according to the actual stretching of the polypropylene film.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for producing tensile-strength polypropylene film, comprising:

[0009] S1: Raw material preparation: Select polypropylene resin that meets specific melt index and isotacticity requirements as the base raw material. The melt index of the polypropylene resin is in the range of 0.5 to 3.5 g / 10 min, and the isotacticity is in the range of 95% to 98%.

[0010] S2: Ingredient mixing: Polypropylene resins with different properties and additives are mixed in a certain proportion. The additives include, but are not limited to, antioxidants, slip agents, and opening agents. The amount of antioxidants added accounts for 0.05% to 1% of the total raw material mass.

[0011] S3: Melt extrusion. The mixed raw materials are fed into the extruder and melt extruded within the set temperature range. The molten polypropylene material is extruded through the extrusion die to form a film. The temperature of the extrusion die is controlled between 220°C and 260°C to ensure the stability and quality of the film forming.

[0012] S4: Cooling and shaping. The extruded melt is cooled and shaped by a quenching roller, with the temperature of the quenching roller controlled between 80°C and 95°C.

[0013] S5: Stretching process, stretching the film, stretching methods include synchronous stretching and asynchronous stretching. Asynchronous stretching first stretches longitudinally and then stretches transversely. Synchronous stretching stretches longitudinally and transversely at the same time. The longitudinal stretching ratio is 4.5 to 8 times and the transverse stretching ratio is 7.5 to 9 times.

[0014] S6: Rewinding and packaging. The stretched film is rewound, with the winding tension controlled between 30N and 50N. Then it is slit and packaged to complete the production of polypropylene film.

[0015] The stretching process in S5 includes stretching the film using a stretching device, which includes:

[0016] A stretching frame, wherein an observation window is provided on the outer wall of the stretching frame;

[0017] An adaptive heating mechanism is provided within a stretch frame. The adaptive heating mechanism includes a heating plate for overall heating and a local heating component for adaptive local heating.

[0018] An adaptive speed adjustment mechanism is provided inside the stretching frame, and is used to adaptively adjust the stretching speed according to the actual stretching situation.

[0019] Preferably, the adaptive heating mechanism further includes a movable through hole opened in the inner wall of the stretching frame, the inner wall of the movable through hole being slidably connected to the outer wall of the heating plate, the bottom end of the heating plate being provided with a toothed groove, a support plate being fixedly connected to the inner wall of the stretching frame on the side near the movable through hole, a first motor being fixedly connected to the outer wall of the support plate, the output end of the first motor being fixedly connected to a gear meshing with the toothed groove, and the heating plate and the first motor being electrically connected to a PLC controller to form a preliminary heating circuit.

[0020] Preferably, the local heating assembly further includes a connecting groove formed on the inner wall of the stretching frame away from the first motor, a second motor is fixedly connected to the side wall of the stretching frame, a first reciprocating screw is fixedly connected to the output end of the second motor, a first reciprocating block is sleeved on the outer wall of the first reciprocating screw and slidably connected to the connecting groove, a third motor is fixedly connected to the outer wall of the first reciprocating block, and a fixed shell is fixedly connected to the output end of the third motor.

[0021] Preferably, a heating strip and a light emitting plate are fixedly connected to the outer wall of the fixed shell, and a fourth motor is fixedly connected to the outer wall of the fixed shell on the side away from the third motor. A second reciprocating screw is fixedly connected to the output end of the fourth motor. A second reciprocating block is sleeved on the outer wall of the second reciprocating screw and slidably connected to the inner wall of the fixed shell. A heating element and a light emitter are fixedly connected to the two adjacent outer walls of the first reciprocating block, respectively. A light receiver for receiving light emitted by the light emitter and the light emitting plate is fixedly connected to the inner top wall of the tension frame. The heating element, the light emitter, the second motor, the third motor, the fourth motor, the light emitting plate, and the light receiver are electrically connected to the PLC controller to form a local heating circuit.

[0022] Preferably, the adaptive speed adjustment mechanism includes two symmetrical adjustment slots on the inner walls of opposite sides of the tension frame. The two adjustment slots on the same side are fixedly connected to the adjacent ends of the two adjustment slots. The extension ends of the multi-stage electromagnetic telescopic rods on the same longitudinal horizontal plane are fixedly connected to a connecting plate. The inner walls of the two adjustment slots on the same side are respectively provided with a primary adjustment component and a secondary adjustment component.

[0023] Preferably, the primary adjustment assembly includes a first electric telescopic rod fixedly connected to the inner wall of one of the adjustment slots. A first spring-shaped resistance wire is fixedly connected to the telescopic end of the first electric telescopic rod, and a first magnetic block is fixedly connected to the other end of the first spring-shaped resistance wire. The first magnetic block is magnetically attracted to the end of the connecting plate near the first spring-shaped resistance wire. A first electromagnetic plate for attracting the first magnetic block is embedded in the inner wall of the adjustment slot near the first magnetic block. A first conductive ring is fixedly connected to the outer wall of the connecting plate that is magnetically attracted to the first magnetic block, and the first conductive ring is slidably sleeved on the outer wall of the first spring-shaped resistance wire. The first conductive ring and the first spring-shaped resistance wire constitute a first sliding rheostat. The first electric telescopic rod, the first spring-shaped resistance wire, the first electromagnetic plate, the first conductive ring, the multi-stage electromagnetic telescopic rod, and the PLC controller electrical signal form a primary adjustment circuit. During the sliding of the first conductive ring on the first spring-shaped resistance wire toward the stretching direction, the resistance of the first sliding rheostat in the primary adjustment circuit gradually decreases.

[0024] Preferably, the secondary adjustment assembly includes a second electric telescopic rod fixedly connected to the inner wall of another adjustment slot. A second spring-shaped resistance wire is fixedly connected to the telescopic end of the second electric telescopic rod, and a second magnetic block is fixedly connected to the other end of the second spring-shaped resistance wire. The second magnetic block is magnetically attracted to the end of the connecting plate near the second spring-shaped resistance wire. A second electromagnetic plate for attracting the second magnetic block is embedded in the inner wall of the adjustment slot near the second magnetic block. A second conductive ring is fixedly connected to the outer wall of the connecting plate magnetically attracted to the second magnetic block, and the second conductive ring is slidably sleeved on the outer wall of the second spring-shaped resistance wire, away from one of the adjustment slots of the primary and secondary adjustment assemblies. An infrared emitter is fixedly connected to the inner wall, and an infrared receiver for receiving the emitted infrared rays from the infrared emitter is fixedly connected to the outer wall of the connecting plate. The second conductive ring and the second spring-shaped resistance wire constitute a second sliding rheostat. The second electric telescopic rod, the second spring-shaped resistance wire, the second electromagnetic plate, the second conductive ring, the multi-stage electromagnetic telescopic rod, and the PLC controller electrical signal form a two-stage adjustment circuit. During the sliding process of the second conductive ring on the second spring-shaped resistance wire towards the stretching direction, the resistance of the second sliding rheostat in the two-stage adjustment circuit gradually increases. The infrared receiver, the infrared emitter, and the PLC controller electrical signal are connected to form a detection circuit.

[0025] Preferably, it also includes a fixing mechanism, which includes two symmetrical clamping grooves opened on opposite sides of the two connecting plates. A drive motor is fixedly connected to the top of each of the two connecting plates. A bidirectional lead screw is fixedly connected to the output end of the drive motor. A threaded block is symmetrically threaded on the outer wall of the bidirectional lead screw, and the outer wall of the threaded block is slidably connected to the clamping groove. The two threaded blocks on the same connecting plate are jointly fixedly connected to the clamping plate.

[0026] The technical solution provided by this invention has the following advantages compared with the known prior art:

[0027] 1. The heating plate, controlled by a PLC controller, can heat the polypropylene film to 260℃, providing a suitable basic temperature environment for stretching. Then, using local heating components, the PLC controller judges the thickness change of the polypropylene film based on the light changes detected by the light receiver. When a thicker part of the film is detected, the third and fourth motors are controlled to drive the heating plate to further heat the thicker part, which enhances the mobility of molecular chain segments in the thicker part, reduces its viscosity and internal stress, and can achieve precise heating of the whole and local parts. This avoids the problem of over-softening or under-softening caused by uneven film thickness, ensuring the stretching effect and quality of the film.

[0028] 2. The stretching process is achieved through a combination of a primary and secondary adjustment assembly and a multi-stage electromagnetic telescopic rod. During the first half of the stretching process, the PLC controller controls the first electric telescopic rod to move one end of the first spring-shaped resistance wire to the position where the connecting plate is in the adjustment groove when the polypropylene film is half-stretched. The second electric telescopic rod then moves one end of the second spring-shaped resistance wire to the position where the connecting plate is in the adjustment groove when the polypropylene film is fully stretched. As the connecting plate moves, the first conductive ring slides on the first spring-shaped resistance wire, increasing the current flowing through the multi-stage electromagnetic telescopic rod, thus accelerating the telescopic rod's extension and retraction speed, and consequently, the film stretching speed. During the second half of the stretching process, the PLC controller controls the second electromagnetic plate to energize and fix the second magnetic block. The second conductive ring slides on the second spring-shaped resistance wire, decreasing the current flowing through the multi-stage electromagnetic telescopic rod, thus slowing down the telescopic rod's extension and retraction speed, and consequently, the film stretching speed. This achieves precise control over the degree of film stretching, ensuring the film achieves the ideal stretching effect and meeting the precision requirements of different products.

[0029] 3. The narrower or shorter the film, the shorter the moving distance and the faster the first and second conductive rings move on the first and second spring-shaped resistance wires, resulting in a faster change in the current flowing through the multi-stage electromagnetic telescopic rod and a faster change in the speed of the multi-stage electromagnetic telescopic rod, thus increasing the film stretching speed. Conversely, the longer or wider the film, the slower the stretching speed. In the production process, using a faster stretching speed for narrow or short films allows for the completion of more film stretching operations per unit time. For wide or long films, due to their large area and long and complex molecular chains, slowing down the stretching speed allows the molecular chains more time to adjust and align, avoiding problems such as stress concentration and uneven stretching. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0032] Figure 2 This is a schematic diagram of the internal three-dimensional structure of the stretch frame of the present invention;

[0033] Figure 3 This is a partial three-dimensional structural diagram of the present invention. Figure 1 ;

[0034] Figure 4 This is a three-dimensional cross-sectional view of the stretch frame structure of the present invention;

[0035] Figure 5 This is a partial three-dimensional structural diagram of the present invention. Figure 2 ;

[0036] Figure 6 This is a three-dimensional structural diagram of a partial local heating component of the present invention;

[0037] Figure 7 This is a three-dimensional structural diagram of part of the adaptive speed adjustment mechanism of the present invention;

[0038] Figure 8 This is a three-dimensional structural diagram of the fixing mechanism of the present invention.

[0039] Reference numerals: 1. Tension frame; 2. Observation window; 3. Adaptive heating mechanism; 31. Heating plate; 32. Local heating component; 321. Connecting groove; 322. Second motor; 323. First reciprocating screw; 324. First reciprocating block; 325. Third motor; 326. Fixed shell; 327. Heating strip; 328. Light emitting plate; 329. Fourth motor; 3210. Second reciprocating screw; 3211. Second reciprocating block; 3212. Heating element; 3213. Light emitter; 3214. Light receiver; 33. Moving through hole; 34. Gear; 35. Support plate; 36. First motor; 37. Gear 4. Wheel; 4. Adaptive speed adjustment mechanism; 41. Adjustment groove; 42. Multi-stage electromagnetic telescopic rod; 43. Connecting plate; 44. First-stage adjustment component; 441. First electric telescopic rod; 442. First spring-shaped resistance wire; 443. First magnetic block; 444. First conductive ring; 45. Second-stage adjustment component; 451. Second electric telescopic rod; 452. Second spring-shaped resistance wire; 453. Second magnetic block; 454. Second conductive ring; 455. Infrared transmitter; 456. Infrared receiver; 5. Fixing mechanism; 51. Clamping groove; 52. Drive motor; 53. Bidirectional lead screw; 54. Threaded block; 55. Clamping plate. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0041] The present invention will be further described below with reference to embodiments.

[0042] Example: Refer to Figures 1 to 8 A method for producing tensile-strength polypropylene film includes:

[0043] S1: Raw material preparation. Select polypropylene resin that meets specific melt index and isotacticity requirements as the base raw material. The melt index of the polypropylene resin is in the range of 0.5 to 3.5 g / 10 min, and the isotacticity is in the range of 95% to 98%.

[0044] S2: Ingredient mixing, mixing polypropylene resins with different properties and additives in a certain proportion, including but not limited to antioxidants, slip agents, opening agents, etc., wherein the amount of antioxidants added accounts for 0.05% to 1% of the total raw material mass;

[0045] S3: Melt extrusion. The mixed raw materials are fed into the extruder and melt extruded within the set temperature range. The molten polypropylene material is extruded through the extrusion die to form a film. The temperature of the extrusion die is controlled between 220°C and 260°C to ensure the stability and quality of the film forming.

[0046] S4: Cooling and shaping. The extruded melt is cooled and shaped by a quenching roller, with the temperature of the quenching roller controlled between 80°C and 95°C.

[0047] S5: Stretching process, stretching the film, stretching methods include synchronous stretching and asynchronous stretching. Asynchronous stretching first stretches longitudinally and then stretches transversely. Synchronous stretching stretches longitudinally and transversely at the same time. The longitudinal stretching ratio is 4.5 to 8 times and the transverse stretching ratio is 7.5 to 9 times.

[0048] S6: Rewinding and packaging. The stretched film is rewound, with the winding tension controlled between 30N and 50N. Then it is slit and packaged to complete the production of polypropylene film.

[0049] The stretching process in S5 includes stretching the film using a stretching device, which includes:

[0050] The stretching frame 1 has an observation window 2 on its outer wall.

[0051] An adaptive heating mechanism 3 is disposed within the stretch frame 1. The adaptive heating mechanism 3 includes a heating plate 31 for overall heating and a local heating component 32 for adaptive local heating.

[0052] The adaptive heating mechanism 3 also includes a movable through hole 33 opened in the inner wall of the tension frame 1. The inner wall of the movable through hole 33 is slidably connected to the outer wall of the heating plate 31. The bottom end of the heating plate 31 is provided with a toothed groove 34. A support plate 35 is fixedly connected to the inner wall of the tension frame 1 near the movable through hole 33. A first motor 36 is fixedly connected to the outer wall of the support plate 35. A gear 37 that meshes with the toothed groove 34 is fixedly connected to the output end of the first motor 36. The heating plate 31 and the first motor 36 are electrically connected to a PLC controller and form a preliminary heating circuit.

[0053] The local heating assembly 32 also includes a connecting groove 321 opened on the inner wall of the tension frame 1 away from the first motor 36. A second motor 322 is fixedly connected to the side wall of the tension frame 1. A first reciprocating screw 323 is fixedly connected to the output end of the second motor 322. A first reciprocating block 324 that is slidably connected to the connecting groove 321 is sleeved on the outer wall of the first reciprocating screw 323. A third motor 325 is fixedly connected to the outer wall of the first reciprocating block 324. A fixed shell 326 is fixedly connected to the output end of the third motor 325.

[0054] A heating strip 327 and a light emitting plate 328 are fixedly connected to the outer wall of the fixed housing 326. A fourth motor 329 is fixedly connected to the outer wall of the fixed housing 326 away from the third motor 325. A second reciprocating screw 3210 is fixedly connected to the output end of the fourth motor 329. A second reciprocating block 3211 is sleeved on the outer wall of the second reciprocating screw 3210 and slidably connected to the inner wall of the fixed housing 326. A heating element 3212 and a light emitting device 3213 are fixedly connected to the two adjacent outer walls of the first reciprocating block 324, respectively. A light receiver 3214 for receiving light emitted by the light emitting device 3213 and the light emitting plate 328 is fixedly connected to the inner top wall of the tension frame 1. The heating element 3212, the light emitting device 3213, the second motor 322, the third motor 325, the fourth motor 329, the light emitting plate 328, and the light receiver 3214 are electrically connected to the PLC controller to form a local heating circuit. The light receiver 3214 is composed of multiple photoresistors.

[0055] An adaptive speed adjustment mechanism 4 is installed inside the stretching frame 1. The adaptive speed adjustment mechanism 4 is used to adaptively adjust the stretching speed according to the actual stretching situation.

[0056] The adaptive speed adjustment mechanism 4 includes two symmetrical adjustment slots 41 on the inner walls of opposite sides of the tension frame 1. The two adjustment slots 41 on the same side are fixedly connected to the close ends of the two adjustment slots 41. The extension ends of the multi-stage electromagnetic telescopic rods 42 on the same longitudinal horizontal plane are fixedly connected to a connecting plate 43. The inner walls of the two adjustment slots 41 on the same side are respectively provided with a first-stage adjustment component 44 and a second-stage adjustment component 45.

[0057] The primary adjustment assembly 44 includes a first electric telescopic rod 441 fixedly connected to the inner wall of one of the adjustment slots 41. A first spring-shaped resistance wire 442 is fixedly connected to the telescopic end of the first electric telescopic rod 441, and a first magnetic block 443 is fixedly connected to the other end of the first spring-shaped resistance wire 442. The first magnetic block 443 is magnetically attracted to the end of the connecting plate 43 near the first spring-shaped resistance wire 442. A first electromagnetic plate for attracting the first magnetic block 443 is embedded in the inner wall of the adjustment slot 41 near the first magnetic block 443. A first conductive ring 444 is fixedly connected to the outer wall of the connecting plate 43 that is magnetically attracted to the first magnetic block 443, and the first conductive ring 444 is slidably sleeved on the outer wall of the first spring-shaped resistance wire 442. Ring 444 and the first spring-shaped resistance wire 442 constitute the first sliding rheostat. The first electric telescopic rod 441, the first spring-shaped resistance wire 442, the first electromagnetic plate, the first conductive ring 444, the multi-stage electromagnetic telescopic rod 42 and the PLC controller electrical signal form a first-stage adjustment circuit. During the sliding process of the first conductive ring 444 on the first spring-shaped resistance wire 442 toward the stretching direction, the resistance of the first sliding rheostat in the first-stage adjustment circuit gradually decreases. The attraction force of the first electromagnetic plate on the first magnetic block 443 is much greater than the attraction force of the connecting plate 43 on the first magnetic block 443. The attraction force of the second electromagnetic plate on the second magnetic block 453 is also much greater than the attraction force of the connecting plate 43 on the second magnetic block 453. The connecting plate 43 is ferromagnetic.

[0058] The secondary adjustment assembly 45 includes a second electric telescopic rod 451 fixedly connected to the inner wall of another adjustment slot 41. A second spring-shaped resistance wire 452 is fixedly connected to the telescopic end of the second electric telescopic rod 451, and a second magnetic block 453 is fixedly connected to the other end of the second spring-shaped resistance wire 452. The second magnetic block 453 is magnetically attracted to the end of the connecting plate 43 near the second spring-shaped resistance wire 452. A second electromagnetic plate for attracting the second magnetic block 453 is embedded in the inner wall of the adjustment slot 41 near the second magnetic block 453. A second conductive ring 454 is fixedly connected to the outer wall of the connecting plate 43, which is magnetically attracted to the second magnetic block 453, and the second conductive ring 454 is slidably sleeved on the outer wall of the second spring-shaped resistance wire 452. An infrared emitter 455 is fixedly connected to the inner wall of one of the adjustment slots 41 away from the primary adjustment assembly 44 and the secondary adjustment assembly 45. An infrared receiver for receiving infrared radiation emitted by the infrared emitter 455 is fixedly connected to the outer wall of the connecting plate 43. The infrared receiver 456, the second conductive ring 454, and the second spring-shaped resistance wire 452 constitute a second sliding rheostat. The second electric telescopic rod 451, the second spring-shaped resistance wire 452, the second electromagnetic plate, the second conductive ring 454, the multi-stage electromagnetic telescopic rod 42, and the PLC controller electrical signal form a two-stage adjustment circuit. During the sliding process of the second conductive ring 454 on the second spring-shaped resistance wire 452 towards the stretching direction, the resistance of the second sliding rheostat in the two-stage adjustment circuit gradually increases. The infrared receiver 456, the infrared transmitter 455, and the PLC controller electrical signal are connected to form a detection circuit. The first spring-shaped resistance wire 442 and the second spring-shaped resistance wire 452 can be compressed, and their overall resistance value remains unchanged. However, the moving distance of the first conductive ring 444 and the second conductive ring 454 on the first spring-shaped resistance wire 442 and the second spring-shaped resistance wire 452 is reduced, so the rate of current change increases.

[0059] An infrared rangefinder consists of a PLC controller, an infrared receiver 456, and an infrared transmitter 455. The rangefinder operates based on the principles of infrared propagation and reflection. The infrared transmitter 455 emits infrared signals towards the target object, which are then reflected back. The infrared receiver 456 receives the reflected infrared signals. The PLC controller controls the entire measurement process, such as controlling the time interval between signal transmissions from the infrared transmitter 455, receiving and processing signals from the infrared receiver 456, and calculating the distance based on the time difference between the transmitted and received signals.

[0060] It also includes a fixing mechanism 5, which includes two symmetrical clamping slots 51 opened on opposite sides of the two connecting plates 43. The top of each of the two connecting plates 43 is fixedly connected to a drive motor 52. The output end of the drive motor 52 is fixedly connected to a bidirectional lead screw 53. The outer wall of the bidirectional lead screw 53 is symmetrically threaded with threaded blocks 54, and the outer wall of the threaded blocks 54 is slidably connected to the clamping slots 51. The two threaded blocks 54 on the same connecting plate 43 are fixedly connected to a clamping plate 55. The clamping slots 51 are provided with a sealing door to block heat. The openings on both sides of the stretch frame 1 also have detachable baffles to ensure that the light detection is not affected.

[0061] The working principle of this invention is as follows:

[0062] First, place the unstretched film above the two clamping plates 55 at the bottom. Then, start the drive motor 52, which drives the bidirectional lead screw 53 to rotate. The screw block 54 is limited by the clamping groove 51, which in turn causes the screw block 54 to drive the clamping plates 55 on both sides to clamp the two sides of the polypropylene film. Then, perform lateral stretching.

[0063] Then, the PLC controller powers the multi-stage electromagnetic telescopic rod 42, which in turn pushes the two connecting plates 43 to move in opposite directions, thereby causing the clamping plate 55 to move synchronously, thus stretching the polypropylene film straight (after straightening, the operator can observe through the observation window 2). The PLC controller temporarily shuts off the power to the multi-stage electromagnetic telescopic rod 42, and then starts the heating plate 31 to heat the polypropylene film to 80-120℃ (detected by the operator using an air-cooled temperature detector). After heating is completed, the PLC controller controls the first motor 36 to start, which drives the gear 37 to rotate, thereby causing the gear 37 to move the heating plate 31 outward.

[0064] Subsequently, the position of the connecting plate 43 (the position of the connecting plate 43 when the polypropylene film is stretched) is detected using an infrared rangefinder. This position is used to determine the position between the two connecting plates 43 (i.e., the stretching length of the polypropylene film). Generally, the transverse stretching ratio of the polypropylene film is 8.21-8.44, and the longitudinal stretching ratio is 6-6.8 (taking the midpoint, then calculating the stretching length of the polypropylene film, calculating the position of the connecting plate 43 in the adjusting groove 41 when the polypropylene film is stretched halfway, designated as position x, and the position of the connecting plate 43 in the adjusting groove 41 when fully stretched, designated as position y). The PLC controller starts the first electric telescopic rod 441 and, according to the above calculation structure, controls the first electric telescopic rod 441 to push one end of the first spring-shaped resistance wire 442 to position x. Then, the PLC controller controls the second electric telescopic rod 451 to push one end of the second spring-shaped resistance wire 452 to position y. At the same time, the PLC controller controls the first electromagnetic plate to be energized, and then the first electromagnetic plate attracts the first magnetic block 443, fixing the first magnetic block 443 at that position. At this time, the distance between the first magnetic block 443 and the first electric telescopic rod 441 is half the length of the polypropylene film stretched.

[0065] Therefore, the PLC controller energizes the multi-stage electromagnetic telescopic rod 42, causing it to push the connecting plate 43, which in turn stretches the polypropylene film. As the connecting plate 43 moves, the first conductive ring 444 slides on the surface of the first spring-shaped resistance wire 442, thus changing the current flowing through the multi-stage electromagnetic telescopic rod 42. The longer the stretch, the greater the current flowing through the multi-stage electromagnetic telescopic rod 42, resulting in a faster telescopic speed. This is because, according to electromagnetic principles, an increased current generates a stronger magnetic field, which in turn exerts a stronger electromagnetic force on the magnetic material or current-carrying conductor in the electromagnetic telescopic rod. A larger current generates a stronger magnetic field, which in turn generates a weaker electromagnetic force, resulting in a smaller force that propels the telescopic rod and weakens its resistance. Consequently, the telescopic rod's extension and retraction speed may decrease, leading to a faster film stretching speed. This increases the stretching length in the same amount of time. In the initial stage of stretching, the polypropylene molecular chains are in a relatively disordered state. Increasing the stretching speed provides sufficient external force to enable the molecular chains to quickly overcome the internal intermolecular forces and rapidly align themselves along the stretching direction, laying the foundation for the formation of a good film structure and performance.

[0066] Until the first conductive ring 444 disengages from the first spring-shaped resistance wire 442, no current flows through the first sliding rheostat, so the PLC controller cannot detect the current passing through the first sliding rheostat. At this point, the polypropylene film is stretched into the second half of its stretch. The PLC controller then energizes the second electromagnetic plate, fixing the second magnetic block 453. The distance between the second magnetic block 453 and the second electric telescopic rod 451 is the stretching distance of the polypropylene film in the second half of its stretch. As the connecting plate 43 moves, the second conductive ring 454 slides on the surface of the second spring-shaped resistance wire 452, thereby changing the current flowing through it. The current flowing through the multi-stage electromagnetic telescopic rod 42 decreases as the stretching length increases, resulting in a slower telescopic speed. After the first half of the stretching process, the molecular chains have essentially completed their orientation. If the second half of the stretching process continues at a high speed, the molecular chains will be subjected to excessive tensile force, which can easily lead to stress concentration. When the stress exceeds the film's tolerance limit, defects such as cracking and tearing will occur, reducing product quality and yield. Reducing the stretching speed in the second half of the stretching process allows for more precise control of the film's stretching degree and final properties, enabling the film to achieve ideal thickness uniformity, mechanical properties, and optical properties.

[0067] Furthermore, during the aforementioned current change process, the shorter the length or width of the polypropylene film, the shorter the moving distance of the first conductive ring 444 and the second conductive ring 454 relative to the first spring-shaped resistance wire 442 and the second spring-shaped resistance wire 452, respectively. Consequently, the moving speed of the first conductive ring 444 and the second conductive ring 454 relative to the first spring-shaped resistance wire 442 and the second spring-shaped resistance wire 452, respectively, is also faster. According to the speed formula, when time is constant, the shorter the distance, the faster the speed. Therefore, the first conductive ring 444 and the second conductive ring 454, respectively, move along the first spring-shaped resistance wire 442 and the second spring-shaped resistance wire 452. The faster the spring-shaped resistance wire 452 moves, the faster the current changes through the multi-stage electromagnetic telescopic rod 42 (assuming it takes 10 minutes to stretch a 10cm long thin film to complete the movement of the spring-shaped resistance wire, but only 5 minutes to stretch a 5cm long thin film to complete the movement of the spring-shaped resistance wire; the movement process is faster, the current changes faster, and therefore the speed of change of the multi-stage electromagnetic telescopic rod 42 is faster). Therefore, the narrower or shorter the thin film, the faster its stretching speed; conversely, the longer or wider the thin film, the slower its stretching speed.

[0068] Due to its small size, it is subjected to external forces more evenly, with less noticeable edge effects and stress concentration, making it less prone to uneven local stress. It has efficient heat transfer and uniform heat distribution, which is conducive to the coordinated movement of molecular chain segments. With its small mass and inertia, it can respond quickly to tensile forces, and the internal stress generated inside is small, which will not hinder the stretching process, so it can be stretched more smoothly and quickly.

[0069] During the stretching process, the second motor 322 is started by the PLC control, which drives the first reciprocating screw 323 to rotate. The first reciprocating block 324 is limited by the connecting groove 321, causing the first reciprocating block 324 to move the fixed shell 326 back and forth. The moving shell drives the heating strip 327 and the light emitting plate 328 to move simultaneously. The heating strip 327 is used to maintain the temperature of the polypropylene film, while the light emitted by the light emitting plate 328 will pass through the polypropylene film and be received by the light receiver 3214. However, since the thickness of the polypropylene film may have errors, the light received by the light receiver 3214 will change. Therefore, the resistance of the photoresistor in the light receiver 3214 will change. The PLC controller will detect the change in the resistance of the photoresistor. When the resistance change is detected, it means that the thickness of the polypropylene film in this horizontal direction has changed (the thicker the polypropylene film, the more severe the light blocking, and therefore the lower the resistance). Therefore, the thicker part of the polypropylene film can be found by the change in resistance.

[0070] Therefore, the PLC controller starts the third motor 325 and the fourth motor 329. The third motor 325 drives the fixed shell 326 to rotate 90 degrees, and then the fourth motor 329 drives the second reciprocating screw 3210 to rotate. The fixed shell 326 limits the second reciprocating block 3211, causing the second reciprocating block 3211 to move back and forth. The movement of the second reciprocating block 3211 drives the light emitter 3213 to emit light. The movement of the light emitter 3213 can detect the specific location where the polypropylene film is thicker (the principle is the same as finding the approximate location as described above). After the specific location is detected, the PLC controller stops the fourth motor 329 and controls the third motor 325 to rotate 90 degrees again. Then, the heating plate 3212 further heats the thicker area (heating for 10 seconds). 10 seconds can ensure that the polypropylene film will not be damaged, but it can still be heated further. If the heating is not sufficient this time, it can be continued to heat in the next time. During the stretching process of the polypropylene film...

[0071] The reason for heating is as follows: the molecular chains in the thicker parts are densely packed, making them more difficult to stretch compared to the thinner parts. Continued heating can enhance the mobility of the molecular chain segments in the thicker parts, reduce their viscosity and internal stress, and allow the thicker and thinner parts to be stretched more evenly, ensuring the overall thickness uniformity and performance consistency of the film.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for producing tensile-strength polypropylene film, characterized in that, include: S1: Raw material preparation: Select polypropylene resin that meets specific melt index and isotacticity requirements as the base raw material. The melt index of the polypropylene resin is in the range of 0.5 to 3.5 g / 10 min, and the isotacticity is in the range of 95% to 98%. S2: Ingredient mixing, polypropylene resins with different properties and additives are mixed in a certain proportion, wherein the additives include antioxidants, slip agents and opening agents, wherein the amount of antioxidants added accounts for 0.05% to 1% of the total raw material mass; S3: Melt extrusion. The mixed raw materials are fed into the extruder and melt extruded within the set temperature range. The molten polypropylene material is extruded through the extrusion die to form a film. The temperature of the extrusion die is controlled between 220°C and 260°C to ensure the stability and quality of the film forming. S4: Cooling and shaping. The extruded melt is cooled and shaped by a quenching roller, with the temperature of the quenching roller controlled between 80°C and 95°C. S5: Stretching process, stretching the film, stretching methods include synchronous stretching and asynchronous stretching. Asynchronous stretching first stretches longitudinally and then stretches transversely. Synchronous stretching stretches longitudinally and transversely at the same time. The longitudinal stretching ratio is 4.5 to 8 times and the transverse stretching ratio is 7.5 to 9 times. S6: Rewinding and packaging. The stretched film is rewound, with the winding tension controlled between 30N and 50N. Then it is slit and packaged to complete the production of polypropylene film. The stretching process in S5 includes stretching the film using a stretching device, which includes: A stretching frame (1) has an observation window (2) on its outer wall. An adaptive heating mechanism (3) is provided inside the stretch frame (1). The adaptive heating mechanism (3) includes a heating plate (31) for overall heating and a local heating component (32) for adaptive local heating. An adaptive speed adjustment mechanism (4) is provided inside the stretching frame (1). The adaptive speed adjustment mechanism (4) is used to adaptively adjust the stretching speed according to the actual stretching situation. The adaptive speed adjustment mechanism (4) includes two symmetrical adjustment slots (41) on the inner wall of opposite sides of the tension frame (1). The two adjustment slots (41) on the same side are fixedly connected to the adjacent ends of the two adjustment slots (41). The extension ends of the multi-stage electromagnetic telescopic rods (42) on the same longitudinal horizontal plane are fixedly connected to a connecting plate (43). The inner walls of the two adjustment slots (41) on the same side are respectively provided with a first-stage adjustment component (44) and a second-stage adjustment component (45). The magnitude of the current flowing into the multi-stage electromagnetic telescopic rod (42) can be adjusted by the primary adjustment component (44) and the secondary adjustment component (45), thereby adjusting the extension and retraction speed of the multi-stage electromagnetic telescopic rod (42).

2. The method for producing tensile polypropylene film according to claim 1, characterized in that, The adaptive heating mechanism (3) further includes a movable through hole (33) opened in the inner wall of the tension frame (1). The inner wall of the movable through hole (33) is slidably connected to the outer wall of the heating plate (31). The bottom end of the heating plate (31) is provided with a toothed groove (34). A support plate (35) is fixedly connected to the inner wall of the tension frame (1) near the movable through hole (33). A first motor (36) is fixedly connected to the outer wall of the support plate (35). The output end of the first motor (36) is fixedly connected to a gear (37) that meshes with the toothed groove (34). The heating plate (31) and the first motor (36) are electrically connected to a PLC controller and form a preliminary heating circuit.

3. The method for producing tensile-strength polypropylene film according to claim 2, characterized in that, The local heating assembly (32) further includes a connecting groove (321) opened on the inner wall of the tension frame (1) away from the first motor (36). A second motor (322) is fixedly connected to the side wall of the tension frame (1). A first reciprocating screw (323) is fixedly connected to the output end of the second motor (322). A first reciprocating block (324) is sleeved on the outer wall of the first reciprocating screw (323) and slidably connected to the connecting groove (321). A third motor (325) is fixedly connected to the outer wall of the first reciprocating block (324). A fixed shell (326) is fixedly connected to the output end of the third motor (325).

4. The method for producing tensile polypropylene film according to claim 3, characterized in that, A heating strip (327) and a light emitting plate (328) are fixedly connected to the outer wall of the fixed shell (326). A fourth motor (329) is fixedly connected to the outer wall of the fixed shell (326) on the side away from the third motor (325). A second reciprocating screw (3210) is fixedly connected to the output end of the fourth motor (329). A second reciprocating block (3211) is sleeved on the outer wall of the second reciprocating screw (3210) and slidably connected to the inner wall of the fixed shell (326). The two adjacent outer walls of the first reciprocating block (324) are divided into A heating element (3212) and a light emitter (3213) are fixedly connected. A light receiver (3214) for receiving light emitted by the light emitter (3213) and the light emitting plate (328) is fixedly connected to the inner top wall of the stretch frame (1). The heating element (3212), the light emitter (3213), the second motor (322), the third motor (325), the fourth motor (329), the light emitting plate (328), and the light receiver (3214) are electrically connected to the PLC controller to form a local heating circuit.

5. The method for producing tensile polypropylene film according to claim 4, characterized in that, The primary adjustment assembly (44) includes a first electric telescopic rod (441) fixedly connected to the inner wall of one of the adjustment slots (41). A first spring-shaped resistance wire (442) is fixedly connected to the telescopic end of the first electric telescopic rod (441). A first magnetic block (443) is fixedly connected to the other end of the first spring-shaped resistance wire (442). The first magnetic block (443) is magnetically attracted to the end of the connecting plate (43) near the first spring-shaped resistance wire (442). A first electromagnetic plate for attracting the first magnetic block (443) is embedded in the inner wall of the adjustment slot (41) near the first magnetic block (443). The connecting plate (43) magnetically attracted to the first magnetic block (443) is... The outer wall of the first conductive ring (444) is fixedly connected to the first conductive ring (444), and the first conductive ring (444) is slidably sleeved on the outer wall of the first spring-shaped resistance wire (442). The first conductive ring (444) and the first spring-shaped resistance wire (442) constitute the first sliding rheostat. The first electric telescopic rod (441), the first spring-shaped resistance wire (442), the first electromagnetic plate, the first conductive ring (444), the multi-stage electromagnetic telescopic rod (42) and the PLC controller electrical signal form a first-stage adjustment circuit. During the sliding process of the first conductive ring (444) on the first spring-shaped resistance wire (442) towards the stretching direction, the resistance of the first sliding rheostat in the first-stage adjustment circuit gradually decreases.

6. The method for producing tensile-strength polypropylene film according to claim 5, characterized in that, The secondary adjustment component (45) includes a second electric telescopic rod (451) fixedly connected to the inner wall of another adjustment groove (41). A second spring-shaped resistance wire (452) is fixedly connected to the telescopic end of the second electric telescopic rod (451). A second magnetic block (453) is fixedly connected to the other end of the second spring-shaped resistance wire (452). The second magnetic block (453) is magnetically attracted to the end of the connecting plate (43) near the second spring-shaped resistance wire (452). A second electromagnetic plate for attracting the second magnetic block (453) is embedded in the inner wall of the adjustment groove (41) near the second magnetic block (453). A second conductive ring (454) is fixedly connected to the outer wall of the connecting plate (43) that is magnetically attracted to the second magnetic block (453). The second conductive ring (454) is slidably sleeved on the outer wall of the second spring-shaped resistance wire (452) and away from the primary adjustment component (44) and the secondary adjustment component (45). An infrared emitter (455) is fixedly connected to the inner wall of one of the adjustment slots (41). An infrared receiver (456) for receiving infrared rays emitted by the infrared emitter (455) is fixedly connected to the outer wall of the connecting plate (43). The second conductive ring (454) and the second spring-shaped resistance wire (452) constitute the second sliding rheostat. The second electric telescopic rod (451), the second spring-shaped resistance wire (452), the second electromagnetic plate, the second conductive ring (454), the multi-stage electromagnetic telescopic rod (42) and the PLC controller electrical signal form a secondary adjustment circuit. During the sliding process of the second conductive ring (454) on the second spring-shaped resistance wire (452) toward the stretching direction, the resistance of the second sliding rheostat in the secondary adjustment circuit gradually increases. The infrared receiver (456), the infrared emitter (455) and the PLC controller electrical signal are connected to form a detection circuit.

7. The method for producing tensile polypropylene film according to claim 1, characterized in that, It also includes a fixing mechanism (5), which includes two symmetrical clamping grooves (51) opened on opposite sides of two connecting plates (43). The top ends of the two connecting plates (43) are fixedly connected to a drive motor (52). The output end of the drive motor (52) is fixedly connected to a bidirectional lead screw (53). The outer wall of the bidirectional lead screw (53) is symmetrically threaded with threaded blocks (54), and the outer wall of the threaded blocks (54) is slidably connected to the clamping grooves (51). The two threaded blocks (54) on the same connecting plate (43) are fixedly connected to a clamping plate (55).

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