Film stretching control system and film preparation method

Abstract

The present invention relates to the technical field of film production equipment, and its purpose is to provide a film stretching control system and a film preparation method. Among them, the film stretching control system includes a traction mechanism and a heating cylinder, a temperature sensor is arranged in the heating cylinder, the traction mechanism includes a traction roller, a rotary drive device, a coupling, a controller and an operation panel; the two ends of the coupling are respectively connected to the output shaft of the rotary drive device and the shaft end of the traction roller; the traction mechanism is provided with two groups, and the two groups of traction mechanisms are divided into an upper traction mechanism arranged at the top of the heating cylinder and a lower traction mechanism arranged at the bottom of the heating cylinder; the operation panel, the rotary drive device in the upper traction mechanism, the rotary drive device in the lower traction mechanism and the temperature sensor are all electrically connected to the controller. The present invention can display the force value of the stretching force in real time, which is convenient for users to adjust the speed difference of the upper and lower traction rollers or the temperature of the auxiliary heating cylinder.

Description

Technical Field

[0001] The invention relates to the technical field of film production equipment, and in particular to a film stretching control system and a film preparation method. Background Art

[0002] The strong cross film uses two layers of high-strength PE film compounded along a 45-degree oblique cross, which can ensure the transverse and longitudinal tensile strength and has high strength puncture resistance. In addition, in addition to the characteristics of ordinary plastic films, the strong cross film also has the characteristics of light resistance, moisture resistance, corrosion resistance, insect resistance, and folding resistance. Therefore, it has a wider range of uses than ordinary plastic films.

[0003] When producing strong cross films, the stretching process of HDPE (High Density Polyethylene) original film is a very important link. In this process, the blown pipe is oriented and stretched through a film stretching control system. The stretching force and heating temperature of the HDPE original film in the film stretching control system have a direct impact on the mechanical properties of the strong cross film, such as thermal stability. If the film stretching control system stretches the HDPE too much, it will cause excessive stress in the film, resulting in shrinkage, curling and other problems in the oriented film. The film stretching control system in the prior art cannot control the traction tension of the HDPE original film, and it is difficult to confirm whether the film is stretched with an appropriate stretching force, which affects the quality of the film. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a film stretching control system and a film preparation method.

[0005] The technical solution adopted by the present invention is:

[0006] A film stretching control system comprises a traction mechanism and a heating cylinder, wherein a temperature sensor is arranged in the heating cylinder, and the traction mechanism comprises a traction roller, a rotation drive device, a coupling, a controller and an operation panel; the two ends of the coupling are respectively connected to the output shaft of the rotation drive device and the shaft end of the traction roller; the traction mechanism is provided with two groups, and the two groups of traction mechanisms are divided into an upper traction mechanism arranged at the top of the heating cylinder and a lower traction mechanism arranged at the bottom of the heating cylinder; the operation panel, the rotation drive device in the upper traction mechanism, the rotation drive device in the lower traction mechanism and the temperature sensor are all electrically connected to the controller.

[0007] Preferably, the film stretching control system also includes a laminating machine, which includes a telescopic drive device and a laminating roller, the side wall of the laminating roller is fixedly connected to the output shaft of the telescopic drive device, the central axis of the laminating roller is parallel to the central axis of the traction roller, and the central axis of the output shaft of the telescopic drive device is perpendicular to the central axis of the traction roller.

[0008] Preferably, the traction mechanism further includes a reducer, and one end of the coupling is connected to the output shaft of the rotary drive device via the reducer.

[0009] Preferably, the film stretching control system also includes an unwinding machine and a guide roller group, the guide roller group includes a first guide roller, a second guide roller and a third guide roller, the central axes of the first guide roller, the second guide roller and the third guide roller are all parallel to the central axis of the traction roller, the top surface of the first guide roller and the bottom surface of the second guide roller are located on the same plane, the third guide roller is located on the upper side of the first guide roller and the second guide roller, and the top surface of the third guide roller is located on the same plane as the top surface of the traction roller.

[0010] Preferably, the heating cylinder comprises a preheating cylinder, a stretching cylinder and a shaping cylinder which are arranged in sequence from top to bottom.

[0011] A method for preparing a thin film comprises the following steps:

[0012] Film blowing process: high-density polyethylene is extruded and formed into a tube;

[0013] Stretching process: after the pipe is cooled and formed, it is stretched by the film stretching control system to form an HDPE original film, and then the HDPE original film is flattened and rolled up;

[0014] Peeling process: unfold, rotate and re-inflate the original HDPE film, then cut the original HDPE film in a spiral at 45° along the processing direction and roll it up;

[0015] Cross-composite process: The two layers of spirally cut HDPE original films are cross-compositely laminated together to form a film.

[0016] Further preferably, in the stretching process, the real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are both 7.5-8.5N; wherein the calculation formula of the real-time tension F1 of the traction roller in the upper traction mechanism is:

[0017] F1=T1 / R1, T1=U1*I1*M1;

[0018] Wherein, T1 is the torque of the rotary drive device in the upper traction mechanism, R1 is the radius of the traction roller in the upper traction mechanism, U1 is the real-time torque percentage of the frequency converter in the rotary drive device in the upper traction mechanism, I1 is the speed ratio of the reducer in the upper traction mechanism, and M1 is the rated torque of the rotary drive device in the upper traction mechanism;

[0019] The calculation formula of the real-time pulling force F2 of the traction roller in the lower traction mechanism is:

[0020] F2=T2 / R2, T2=U2*I2*M2;

[0021] Wherein, T2 is the torque of the rotary drive device in the lower traction mechanism, R2 is the radius of the traction roller in the lower traction mechanism, U2 is the real-time torque percentage of the inverter in the rotary drive device in the lower traction mechanism, I2 is the speed ratio of the reducer in the lower traction mechanism, and M2 is the rated torque of the rotary drive device in the lower traction mechanism.

[0022] Further preferably, the stretching process further includes the following steps:

[0023] The real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are obtained and processed in real time. When the real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are greater than 8.5N, the temperature of the heating tube is increased by 5°C for every 0.5N that the real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are greater than 8.5N. After each adjustment, wait for 30 seconds until the real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are stabilized within 7.5-8.5N; when the real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are less than 7.5 N, the temperature of the heating tube will be lowered by 5°C for every 0.5N that the real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are less than 7.5N. Wait for one minute after each adjustment until the real-time tension F1 of the traction roller in the upper traction mechanism and the real-time tension F2 of the traction roller in the lower traction mechanism are stabilized within 7.5-8.5N.

[0024] Preferably, the two layers of spirally cut HDPE original films are cross-laminated and laminated into one, and the cross-laminated layers are oriented at 90°.

[0025] Preferably, the two layers of spirally cut HDPE original film are compounded using glue or polyethylene.

[0026] The beneficial effects of the present invention are mainly reflected in that the force value of the tensile force can be displayed in real time, which is convenient for users to adjust the speed difference of the upper and lower traction rollers or the temperature of the auxiliary heating cylinder. Specifically, during use, the present invention first extrudes high-density polyethylene through a film blowing process to form a pipe, and after the pipe is cooled, the cooled pipe is pulled into the heating cylinder by an upper traction mechanism, and then guided out by a lower traction mechanism. In this process, the cooled pipe is heated by the heating cylinder, and the upper traction mechanism and the lower traction mechanism continue to stretch the pipe in the process of pulling the pipe; at the same time, the controller collects and processes the operating data of the rotary drive device in the upper traction mechanism, the rotary drive device in the lower traction mechanism, and the temperature sensor in real time, obtains the real-time torque percentage of the frequency converter in the rotary drive device and the temperature of the heating cylinder, and displays it through the operation panel, so that the user can grasp the tensile force of the upper traction mechanism and the lower traction mechanism on the pipe, the temperature of the heating cylinder, etc. in real time, and then perform corresponding control to avoid the problem of excessive film forming stress, thereby greatly improving the tensile performance of the original film stretching and stabilizing the product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 is a schematic structural diagram of Example 1;

[0029] Figure 2 yes Figure 1 Force analysis diagram of the film in the structure shown;

[0030] Figure 3 is a schematic structural diagram of Example 2;

[0031] Figure 4 It is an enlarged schematic diagram of the traction mechanism, heating cylinder and guide roller group in Example 2. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be noted that although the description of these embodiments is used to help understand the present invention, it does not constitute a limitation of the present invention. The specific structures and functional details disclosed herein are only used to describe the exemplary embodiments of the present invention. However, the present invention can be embodied in many alternative forms, and it should not be understood that the present invention is limited to the embodiments set forth herein.

[0033] It should be understood that although the terms first, second, etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are only used to distinguish one unit from another unit. For example, a first unit can be referred to as a second unit, and similarly, a second unit can be referred to as a first unit without departing from the scope of the exemplary embodiments of the present invention.

[0034] It should be understood that the terms used herein are only used to describe specific embodiments and are not intended to limit the exemplary embodiments of the present invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates the opposite meaning. It should also be understood that when the terms "include", "comprising", "including", and / or "comprising" are used herein, the existence of the features, integers, steps, operations, units, and / or components stated are specified, and the existence or increase of one or more other features, quantities, steps, operations, units, components, and / or their combinations is not excluded.

[0035] It should be understood that it should also be noted that in some alternative embodiments, the functions / actions that appear may be different from the order in which the drawings appear. For example, depending on the functions / actions involved, two figures shown in succession may actually be performed substantially concurrently, or may sometimes be performed in reverse order.

[0036] It should be understood that certain details are provided in the following description to facilitate a complete understanding of the example embodiments. However, it should be understood by those of ordinary skill in the art that the example embodiments may be implemented without these certain details. For example, the system may be shown in a block diagram to avoid obscuring the example with unnecessary details. In other instances, well-known processes, structures, and techniques may not be shown in unnecessary detail to avoid obscuring the example embodiments.

[0037] Embodiment 1:

[0038] This embodiment provides a film stretching control system, such as Figure 1 and 2As shown, it includes a traction mechanism 1 and a heating cylinder 2, wherein a temperature sensor is arranged in the heating cylinder 2, and the traction mechanism 1 includes a traction roller 11, a rotation drive device 12, a coupling 13, a controller and an operation panel; the two ends of the coupling 13 are respectively connected to the output shaft of the rotation drive device 12 and the shaft end of the traction roller 11; the traction mechanism 1 is provided with two groups, and the two groups of traction mechanisms 1 are divided into an upper traction mechanism 1a arranged on the top of the heating cylinder 2 and a lower traction mechanism 1b arranged at the bottom of the heating cylinder 2, and the rotation speed of the rotation drive device 12 in the lower traction mechanism 1b is greater than the rotation speed of the rotation drive device 12 in the upper traction mechanism 1a, specifically, the rotation speed of the rotation drive device 12 in the lower traction mechanism 1b is 2.5 times the rotation speed of the rotation drive device 12 in the upper traction mechanism 1a; in this embodiment, the traction mechanism 1 also includes a reducer 14, and one end of the coupling 13 is connected to the output shaft of the rotation drive device 12 through the reducer 14, and the arrangement of the reducer 14 can improve the stability of the traction mechanism 1.

[0039] The operation panel, the rotary drive device 12 in the upper traction mechanism 1a, the reducer 14 in the upper traction mechanism 1a, the rotary drive device 12 in the lower traction mechanism 1b, the reducer 14 in the lower traction mechanism 1b and the temperature sensor are all electrically connected to the controller.

[0040] In the implementation process of this embodiment, high-density polyethylene is first extruded and formed into a pipe through a film blowing process. After the pipe is cooled, the cooled pipe is pulled by the upper traction mechanism 1a and enters the heating cylinder 2, and then guided out through the lower traction mechanism 1b. In this process, the cooled pipe is heated by the heating cylinder 2, and the upper traction mechanism 1a and the lower traction mechanism 1b continue to stretch the pipe in the process of pulling the pipe; at the same time, the controller collects and processes the operation data of the rotary drive device 12 in the upper traction mechanism 1a, the reducer 14 in the upper traction mechanism 1a, the rotary drive device 12 in the lower traction mechanism 1b, the reducer 14 in the lower traction mechanism 1b and the temperature sensor in real time, obtains the real-time torque percentage of the frequency converter in the rotary drive device 12, the speed ratio of the reducer 14 and the temperature of the heating cylinder 2, and displays them through the operation panel, so that the user can grasp the tensile force of the upper traction mechanism and the lower traction mechanism on the pipe, the temperature of the heating cylinder 2, etc. in real time, and then perform corresponding control to avoid the problem of excessive film stress.

[0041] In order to achieve comprehensive stretching of the HDPE original film and avoid the problem of curling of the HDPE original film when it enters from the upper traction mechanism 1a or is output from the lower traction mechanism 1b, in this embodiment, the film stretching control system also includes a laminating machine 3, and the laminating machine 3 includes a telescopic drive device 31 and a laminating roller 32. The side wall of the laminating roller 32 is fixedly connected to the output shaft of the telescopic drive device 31, and the central axis of the laminating roller 32 is parallel to the central axis of the traction roller 11, and the central axis of the output shaft of the telescopic drive device 31 is perpendicular to the central axis of the traction roller 11.

[0042] Embodiment 2:

[0043] like Figure 3 and 4 As shown, on the basis of Example 1, in this embodiment, the film stretching control system also includes a unwinder 4 and a guide roller group 5, the guide roller group 5 includes a first guide roller 51, a second guide roller 52 and a third guide roller 53, the central axes of the first guide roller 51, the second guide roller 52 and the third guide roller 53 are all parallel to the central axis of the traction roller 11, the top surface of the first guide roller 51 and the bottom surface of the second guide roller 52 are located on the same plane, the third guide roller 53 is located on the upper side of the first guide roller 51 and the second guide roller 52, and the top surface of the third guide roller 53 is located on the same plane as the top surface of the traction roller 11.

[0044] Furthermore, the heating cylinder 2 includes a preheating cylinder 21, a stretching cylinder 22 and a shaping cylinder 23 which are arranged in sequence from top to bottom. The HDPE original film can be dried and preheated by the preheating cylinder 21, heated to the orientation temperature by the stretching cylinder 22, shaped at high temperature by the shaping cylinder 23, and then flattened and rolled up by the lower traction mechanism 1b.

[0045] Embodiment 3:

[0046] This embodiment provides a thin film preparation method, which is based on Embodiment 2 or 3 and includes the following steps:

[0047] Film blowing process: high-density polyethylene is extruded and formed into a tube;

[0048] Stretching process: After the pipe is cooled and formed, it is stretched by the film stretching control system in Example 1 or 2 to form an HDPE original film, thereby aligning the polyethylene molecules in a directional manner, thereby increasing the strength of the film in the machine direction (MD), and then the HDPE original film (i.e., the oriented pipe film) is flattened and rolled up;

[0049] Peeling process: unfold, rotate and re-inflate the original HDPE film, then cut the original HDPE film in a spiral at 45° along the processing direction and roll it up;

[0050] Cross-composite process: The two layers of spiral cut HDPE original film are cross-composite and laminated into one to form a film. The two layers of spiral cut HDPE original film are cross-laminated at a certain angle and then hot-pressed or glued.

[0051] In this embodiment, the two layers of spirally cut HDPE original films are cross-laminated and laminated into one, and the cross-laminated layers are oriented at 90 degrees.

[0052] In this embodiment, the two layers of spirally cut HDPE original films are compounded using glue or polyethylene.

[0053] Specifically, in the stretching process, the controller collects and processes the operating data of the rotary drive device 12 in the upper traction mechanism 1a, the reducer 14 in the upper traction mechanism 1a, the rotary drive device 12 in the lower traction mechanism 1b, the reducer 14 in the lower traction mechanism 1b and the temperature sensor in real time, and obtains the real-time torque percentage of the inverter in the rotary drive device 12, the speed ratio of the reducer 14 and the temperature of the heating cylinder 2. The real-time tension F1 of the traction roller 11 in the upper traction mechanism 1a and the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b are both 7.5-8.5N; wherein, the calculation formula of the real-time tension F1 of the traction roller 11 in the upper traction mechanism 1a is:

[0054] F1=T1 / R1, T1=U1*I1*M1;

[0055] Wherein, T1 is the torque of the rotary drive device 12 in the upper traction mechanism 1a, R1 is the radius of the traction roller 11 in the upper traction mechanism 1a, U1 is the real-time torque percentage of the frequency converter in the rotary drive device 12 in the upper traction mechanism 1a, I1 is the speed ratio of the reducer 14 in the upper traction mechanism 1a, and M1 is the rated torque of the rotary drive device 12 in the upper traction mechanism 1a;

[0056] The calculation formula of the real-time pulling force F2 of the traction roller 11 in the lower traction mechanism 1b is:

[0057] F2=T2 / R2, T2=U2*I2*M2;

[0058] In the formula, T2 is the torque of the rotary drive device 12 in the lower traction mechanism 1b, R2 is the radius of the traction roller 11 in the lower traction mechanism 1b, U2 is the real-time torque percentage of the inverter in the rotary drive device 12 in the lower traction mechanism 1b, I2 is the speed ratio of the reducer 14 in the lower traction mechanism 1b, and M2 is the rated torque of the rotary drive device 12 in the lower traction mechanism 1b.

[0059] Specifically, the higher the temperature set for the heating cylinder 2, the smaller the real-time tension F1 of the traction roller 11 in the upper traction mechanism 1a and the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b. When the tensions F1 and F2 are in the range of 7.5-8.5N, it can be ensured that the film produces minimum stress during stretching; if the tensions F1 and F2 are too large, the stretched film will experience problems such as shrinkage and curling; if the tensions F1 and F2 are too small, the film will wrinkle and the bubble shape will be unstable.

[0060] In order to achieve precise adjustment of the tensions F1 and F2, the stretching process also includes the following steps:

[0061] The real-time tension F1 of the traction roller 11 in the upper traction mechanism 1a and the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b are obtained and processed in real time. When the real-time tension F1 of the traction roller 11 in the upper traction mechanism 1a and the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b are greater than 8.5N, the temperature of the heating tube 2 is increased by 5°C for every 0.5N that the real-time tension F1 of the traction roller 11 in the upper traction mechanism 1a and the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b are greater than 8.5N. After each adjustment, wait for 30 seconds until the real-time tension F1 of the traction roller 11 in the upper traction mechanism 1a and the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b are greater than 8.5N. The real-time tension F2 of roller 11 is stabilized within 7.5-8.5N; when the real-time tension F1 of traction roller 11 in upper traction mechanism 1a and the real-time tension F2 of traction roller 11 in lower traction mechanism 1b are less than 7.5N, the temperature of heating tube 2 is reduced by 5°C for every 0.5N that the real-time tension F1 of traction roller 11 in upper traction mechanism 1a and the real-time tension F2 of traction roller 11 in lower traction mechanism 1b are less than 7.5N, and wait for one minute after each adjustment until the real-time tension F1 of traction roller 11 in upper traction mechanism 1a and the real-time tension F2 of traction roller 11 in lower traction mechanism 1b are stabilized within 7.5-8.5N.

[0062] For example, the standard value of tension is set to 8.5N, that is, the standard value of the tension of the traction roller 11 in the upper traction mechanism 1a and the standard value of the tension of the traction roller 11 in the lower traction mechanism 1b is 8.5N. When the width of the film to be stretched is 750 mm, the color is black, and the temperature of the heating cylinder 2 is set to 250°C, if the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b is 7.5N, which is 1N lower than the standard value (8.5N), then the temperature of the heating cylinder 2 needs to be reduced by 10°C. At this time, the temperature in the heating cylinder 2 is adjusted by reducing the temperature in the heating cylinder 2 by 5°C each time and waiting for 30 seconds after each adjustment until the real-time tension F2 of the traction roller 11 in the lower traction mechanism 1b stabilizes to the standard value of 8.5N.

[0063] The multiple embodiments described above are merely illustrative. If a unit described as a separate component is involved, it may or may not be physically separated; if a component displayed as a unit is involved, it may or may not be a physical unit, that is, it may be located in one place, or it may be distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention is described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

[0065] Finally, it should be noted that the present invention is not limited to the above optional implementations, and anyone can derive other various forms of products under the enlightenment of the present invention. The above specific implementations should not be understood as limiting the scope of protection of the present invention. The scope of protection of the present invention should be based on the definition in the claims, and the description can be used to interpret the claims.

Claims

1. A film preparation method based on a film stretching control system, characterized in that: The film stretching control system comprises a traction mechanism (1) and a heating cylinder (2), wherein a temperature sensor is arranged in the heating cylinder (2), and the traction mechanism (1) comprises a traction roller (11), a rotary drive device (12), a coupling (13), a controller and an operation panel; the two ends of the coupling (13) are respectively connected to the output shaft of the rotary drive device (12) and the shaft end of the traction roller (11); the traction mechanism (1) is provided with two groups, and the two groups of traction mechanisms (1) are divided into an upper traction mechanism (1a) arranged at the top of the heating cylinder (2) and a lower traction mechanism (1b) arranged at the bottom of the heating cylinder (2); the operation panel, the rotary drive device (12) in the upper traction mechanism (1a), the rotary drive device (12) in the lower traction mechanism (1b) and the temperature sensor are all electrically connected to the controller; the film preparation method comprises the following steps: Film blowing process: high-density polyethylene is extruded and formed into a tube; Stretching process: after the pipe is cooled and formed, it is stretched by the film stretching control system to form an HDPE original film, and then the HDPE original film is flattened and rolled up; Peeling process: unfold, rotate and re-inflate the original HDPE film, then cut the original HDPE film in a spiral at 45° along the processing direction and roll it up; Cross-composite process: cross-composite and laminate two layers of spirally cut HDPE original films to form a film; In the stretching process, the real-time tension F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time tension F2 of the traction roller (11) in the lower traction mechanism (1b) are both 7.5-8.5N; wherein the calculation formula of the real-time tension F1 of the traction roller (11) in the upper traction mechanism (1a) is: F1=T1 / R1, T1=U1*I1*M1; In the formula, T1 is the torque of the rotary drive device (12) in the upper traction mechanism (1a), R1 is the radius of the traction roller (11) in the upper traction mechanism (1a), U1 is the real-time torque percentage of the frequency converter in the rotary drive device (12) in the upper traction mechanism (1a), I1 is the speed ratio of the reducer (14) in the upper traction mechanism (1a), and M1 is the rated torque of the rotary drive device (12) in the upper traction mechanism (1a); The calculation formula of the real-time pulling force F2 of the traction roller (11) in the lower traction mechanism (1b) is: F2=T2 / R2, T2=U2*I2*M2; In the formula, T2 is the torque of the rotary drive device (12) in the lower traction mechanism (1b), R2 is the radius of the traction roller (11) in the lower traction mechanism (1b), U2 is the real-time torque percentage of the frequency converter in the rotary drive device (12) in the lower traction mechanism (1b), I2 is the speed ratio of the reducer (14) in the lower traction mechanism (1b), and M2 is the rated torque of the rotary drive device (12) in the lower traction mechanism (1b); The stretching process also includes the following steps: The real-time pulling force F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time pulling force F2 of the traction roller (11) in the lower traction mechanism (1b) are obtained and processed in real time. When the real-time pulling force F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time pulling force F2 of the traction roller (11) in the lower traction mechanism (1b) are greater than 8.5N, the real-time pulling force F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time pulling force F2 of the traction roller (11) in the lower traction mechanism (1b) are For every 0.5N that the tension F2 is greater than 8.5N, the temperature of the heating cylinder (2) is raised by 5°C. After each adjustment, the heating cylinder (2) is kept at a temperature of 30 seconds, until the real-time tension F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time tension F2 of the traction roller (11) in the lower traction mechanism (1b) are stabilized within a range of 7.5-8.5N. When the real-time tension F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time tension F2 of the traction roller (11) in the lower traction mechanism (1b) are less than 7.5 N, the temperature of the heating tube (2) is lowered by 5°C for every 0.5N of the real-time tension F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time tension F2 of the traction roller (11) in the lower traction mechanism (1b) being less than 7.5N, and one minute is waited after each adjustment until the real-time tension F1 of the traction roller (11) in the upper traction mechanism (1a) and the real-time tension F2 of the traction roller (11) in the lower traction mechanism (1b) are stabilized within a range of 7.5-8.5N.

2. A method for preparing a thin film according to claim 1, characterized in that: When the two layers of spirally cut HDPE original films are cross-laminated and laminated into one, they are cross-oriented at 90 degrees.

3. A method for preparing a thin film according to claim 1, characterized in that: The two layers of spirally cut HDPE original film are compounded with glue or polyethylene.

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