A method of heat sealing and forming a multi-directional crack arrest heat shrink film

Abstract

The application provides a multi-directional crack-arrest heat-shrinkable film heat-seal forming method, comprising the following steps: step one, obtaining crack-arrest band boundary position coordinates; step two, controlling a heat-seal knife to drop a fusion line in a gap region between adjacent crack-arrest bands; step three, providing segmented heat energy distribution after the heat-seal knife contacts a film surface; step four, simultaneously with step three, applying different heat-seal pressures on the film surface by the heat-seal knife in a main fusion zone and a boundary transition zone; step five, after the heat-seal knife is lifted, sequentially passing a three-layer heat-shrinkable film structure just heat-sealed and formed through at least three cooling zones with decreasing temperatures; and step six, performing quality detection after cooling is completed. Through heat-seal knife control and segmented heating, the application improves the effective retention rate of the crack-arrest band, and through gradient cooling, reduces film surface wrinkling or crack-arrest band misplacement caused by different heat shrinkage rates of the three-layer material.

Description

Technical Field

[0001] This invention relates to the field of packaging consumables processing technology, and in particular to a heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film. Background Technology

[0002] Heat shrink film packaging excels in economy, operability, and high speed, and is widely used in the packaging industry. The general process of heat shrink film packaging is as follows: the packaged item is wrapped with heat shrink film, the joints are melted and sealed, and then the heat shrink film is heat-shrinked in a shrink oven or with hot air to complete the packaging.

[0003] Most products, such as mobile phones, cigarettes, and children's toys, have heat-shrink film on their outer packaging. However, sharp corners on the packaging or the product itself, or scratches, bumps, or drops after packaging, can easily cause the heat-shrink film to tear. While heat-shrink film itself has some tear resistance, this effect is only effective in areas with dispersed stress or large contact areas. When small scratches or cracks form sharp lacerations, its tear resistance drops significantly, making it highly susceptible to rapid tear propagation under stress or further scratches.

[0004] To address the aforementioned issues, the applicant previously proposed a multi-directional crack-resistant heat-shrinkable film, application number 202010443026.9, publication number CN111572998A. This patent achieves multi-directional protection against cracks by setting transverse and longitudinal films on the base film and heat-sealing the transverse and longitudinal crack-resistant bands of the two films in a cross shape.

[0005] However, this patent mainly discloses the product structure of the multi-directional crack-resistant heat shrink film, but does not involve the specific heat-sealing process for converting this structural design into mass production. During the subsequent trial production of this patented product, the applicant discovered the following proprietary technical challenges in the heat-sealing process of the aforementioned multi-layer composite heat shrink film with crack-resistant bands, challenges that are not present or not prominent in the heat-sealing process of conventional single-layer heat shrink films: Firstly, the crack-resistant band is easily damaged during the heat-sealing process. When the heat-sealing knife is pressed and fused, it may directly press against the edge of the crack-resistant band or cover the area of ​​the crack-resistant band, causing the edge of the crack-resistant band to overheat and melt or become brittle, partially losing its crack-resistant function. Excessively high heat-sealing temperatures can lead to overheating and carbonization of the film material, causing it to lose its original toughness. Once the edge of the crack-resistant band is damaged, it will affect the crack resistance of the entire cross-shaped crack-resistant network. Secondly, the difference in shrinkage between the layers in the multi-layer heat-shrinkable structure leads to molding defects. The multi-directional crack-resistant heat-shrinkable film is composed of three layers of heat-shrinkable film: a base film, a transverse film, and a longitudinal film. Due to differences in their processing history, actual thermal history experienced during the heat sealing process, and actual thickness, the three layers exhibit different shrinkage behaviors during the cooling stage. During the cooling and subsequent shrinkage process after heat sealing, inconsistent shrinkage between the layers can cause wrinkling of the film surface or misalignment of the crack-resistant bands, affecting the stress synergy effect of the crack-resistant network. Third, managing the heat-sealing temperature of the three-layer structure is difficult. The heat-sealing window and melting temperature of each heat-shrinkable film are not the same, and a single temperature setting is difficult to simultaneously ensure the welding quality of the three layers, which can easily lead to insufficient interlayer welding strength or local over-melting. Summary of the Invention

[0006] This invention addresses the aforementioned problems and aims to provide a heat-sealing method for multi-directional crack-resistant heat-shrinkable film. By implementing obstacle avoidance path planning in step two to maintain a safe distance between the heat-sealing blade and the crack-resistant band, and combining this with segmented heating in step three to reduce transient thermal shock, the effective retention rate of the crack-resistant band can be increased from approximately 85% in conventional heat-sealing processes to over 98%. This ensures that the crack-resistant band can fully perform its crack-resistant function in the finished heat-shrinkable film. Furthermore, the gradient cooling process in step five allows the three layers of heat-shrinkable film to gradually release internal stress at a controlled rate after heat sealing, reducing wrinkling or misalignment of the crack-resistant band caused by differences in heat shrinkage rates among the three layers. This ensures that the crack-resistant network maintains its correct cross-shaped relative position in subsequent heat-shrinking processes.

[0007] Specifically, the first aspect of the present invention provides a heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film, comprising: Step 1: Before the heat sealing station, perform real-time detection on the transverse and longitudinal crack-resistant zones of the multi-directional crack-resistant heat-shrinkable film during its movement to obtain the coordinates of the crack-resistant zone boundary positions. The multi-directional crack-resistant heat-shrinkable film is the same as the multi-directional crack-resistant heat-shrinkable film disclosed in the applicant's prior patent CN111572998A, which has a cross-shaped structure of crack-resistant bands composed of a base film and transverse and longitudinal films. In specific testing, the distinguishable characteristics of the crack-resistant bands and the base film in terms of optical and physical properties are utilized, including differences in thickness, transmittance, surface texture, and local thickness protrusions. Because the crack-resistant bands are additional composite films, they have minute protrusions or optical interfaces. A linear array camera or fiber optic sensor is used to scan the moving heat-shrinkable film in real time to determine the accurate boundary coordinates of each crack-resistant band. Step 2: Based on the coordinates of the crack-blocking zone, control the heat sealing knife to place the weld line in the gap area between adjacent crack-blocking zones, and the direction of the heat sealing knife is parallel to the length direction of the crack-blocking zone, with a safe distance between the edge of the heat sealing knife and the boundary of the crack-blocking zone. The function of controlling the heat sealing knife is to ensure that the heat sealing pressure and heat are applied only to the base membrane area between adjacent crack-resistant strips, and not directly pressed onto the crack-resistant strips, thereby avoiding heat-pressure damage to the edges of the crack-resistant strips; the direction of the heat sealing knife is parallel to the length direction of the crack-resistant strips, so that the weld line extends along the gap and ensures uniform weld strength; if the direction is perpendicular, it will cross the crack-resistant strips, causing structural damage; the safety distance further provides a buffer to prevent accidental pressing caused by positioning errors or membrane material vibration; Step 3: After the heat sealing knife contacts the film surface, it provides a segmented heat energy distribution by contacting at the first preheating temperature, applying pressure to weld at the second welding temperature, and then cooling down to remove the film. The first preheating stage involves slowly heating the three layers of heat-shrinkable film at a lower temperature to reduce transient thermal shock and prevent internal stress or microcracks from forming in the crack-resistant zone due to sudden temperature changes. At the same time, uniform preheating helps each layer of material reach a near-molten state simultaneously, creating conditions for subsequent welding. The second welding stage: reaching the true welding temperature, allowing the interlayer interface to fully melt and diffuse into each other, forming a strong weld. This stage requires sufficient temperature and duration, but at the same time, it is necessary to avoid excessive heat transfer to the crack-resistant zone. The third cooling stage: actively cool down to a non-stick temperature before the heat sealing knife is lifted to prevent the film surface from sticking to the heat sealing knife and avoid stretching of the crack-blocking strip or damage to the film surface. Step 4: Simultaneously with Step 3, apply different heat-sealing pressures to the film surface using the heat-sealing knife in the main welding area and the boundary transition area; The heat-sealing tool does not apply pressure uniformly to the bonding surface. Instead, the area corresponding to the gap in the fracture barrier is defined as the main welding zone, where higher pressure is applied to ensure a tight bond between layers. The area near the boundary of the fracture barrier is defined as the boundary transition zone, where lower and decreasing pressure is applied to prevent the high pressure from crushing the edge of the fracture barrier or squeezing out the molten material. This zoned design ensures both welding strength and protects the structural integrity of the fracture barrier. Step 5: After the heat sealing knife is lifted, the newly heat-sealed three-layer heat shrink film structure is passed through at least three cooling zones with decreasing temperatures. After heat sealing, the three layers of material remain at a high temperature, and the thermal shrinkage rate of each layer varies due to differences in thickness and orientation. If directly and rapidly cooled to room temperature, the interlayer stress will be released in an uncontrollable manner, leading to wrinkling of the film surface and displacement of the crack-resistant bands. This step uses gradient cooling, allowing each layer to gradually shrink within its respective thermal shrinkage temperature range, thus releasing stress evenly and ultimately maintaining the relative positional accuracy of the cross-shaped crack-resistant bands. Step 6: After cooling is complete, perform quality inspection and check the ratio of the width of the heat seal line to the width of the crack-resistant strip.

[0008] The width of the heat seal line directly reflects the effective area of ​​the weld. If the ratio is too large, that is, close to or equal to the width of the crack barrier, it means that the heat seal line may have pressed against the edge of the crack barrier. If it is too small, that is, much smaller than the width of the crack barrier, it indicates that the weld strength is insufficient and that the heat sealer may not be aligned with the center of the gap.

[0009] Furthermore, the safety distance mentioned in step two is 0.2mm-0.5mm.

[0010] Considering the accuracy of the detection system and the mechanical repeatability, a lower limit of 0.2mm can ensure that the crack-resistant zone will not be pressed even under the maximum deviation. An upper limit of 0.5mm is only a small part of the gap width and does not affect the effective width of the weld line. If the safety distance is too large, the weld line will be too narrow, resulting in insufficient weld strength.

[0011] Furthermore, in step three, the first preheating temperature is 100℃-120℃.

[0012] The glass transition temperature of commonly used heat shrink film materials is typically around 80℃-100℃, and the starting point of viscous flow temperature is approximately 110℃-130℃. Preheating to 100℃-120℃ softens the material without completely melting it, reducing the thermal shock required for subsequent heating and preventing deformation of the crack-resistant zone edges. Below 100℃, the effect is not significant, while above 120℃, the weak crack-resistant zone edges may begin to soften, losing their protective function.

[0013] Furthermore, in step three, the second welding temperature is 140℃-180℃.

[0014] This temperature range covers the optimal welding window for commonly used heat shrink films. PE is approximately 140℃-160℃, PVC approximately 150℃-170℃, and PET approximately 170℃-180℃; the specific temperature selection depends on the film formulation. Temperatures below 140℃ may result in insufficient weld strength; temperatures above 180℃ can easily cause carbonization or over-melting of the crack-resistant band edges, and the thinnest layer of the three materials may be burned through.

[0015] Furthermore, the heat sealing pressure of the main welding zone in step four is 0.3MPa-0.6MPa.

[0016] This pressure range is the commonly used pressure range for heat sealing of heat shrink film. 0.3MPa is sufficient to ensure that the layers of film in the softened state are in close contact and to expel interfacial air; 0.6MPa is the upper limit. Exceeding this limit may cause the melt to be excessively squeezed out, resulting in thinning of the weld line or deformation of the crack-resistant zone under pressure.

[0017] Furthermore, the heat sealing pressure of the boundary transition zone mentioned in step four is 0.1MPa-0.2MPa.

[0018] This pressure is only 1 / 3 to 1 / 2 of the normal pressure, its function being to gently adhere the membrane layers in the boundary area without forcibly pressing them together, thus avoiding stress concentration. 0.1 MPa is the minimum pressure to maintain contact; pressures above 0.2 MPa may cause visible indentations at the edges of the fracture-resistant zone. The width of the transition zone is typically set to 0.5 mm–1.0 mm, with the pressure decreasing linearly or in a stepped manner from the median value.

[0019] Furthermore, in step five, the temperature difference between adjacent cooling zones is 5℃-15℃.

[0020] If the temperature difference is too small, the cooling will be too gradual, increasing the production line length requirement and slowing down the stress release, thus affecting production efficiency. If the temperature difference is too large, the difference in instantaneous contraction between layers will exacerbate the internal stress and fail to achieve the effect of gradient release. Each cooling zone is achieved through air cooling or natural cooling, with a total cooling time of 2-5 seconds, matching the production line speed.

[0021] Furthermore, the ratio of the width of the heat-sealing line to the width of the crack-resistant strip in step six is ​​1:1 to 1:3.

[0022] Maximum ratio 1:1: The width of the heat seal line equals the width of the crack-resistant zone. At this ratio, the weld line almost fills the entire gap area, indicating that the heat sealer is positioned accurately and the pressure is sufficient. However, it is necessary to check whether the heat seal line is too wide and slightly touches the edge of the crack-resistant zone (this can be confirmed using a microscope). This maximum ratio is allowed to accommodate designs with narrower gaps (such as when the bandwidth is equal to the gap width).

[0023] The minimum ratio is 1:3: the width of the heat seal line is only 1 / 3 of the width of the crack barrier. For example, if the crack barrier width is 3mm, the heat seal line width should be 1mm. This is the minimum value to ensure sufficient peel strength. If it is less than 1 / 3, the weld area is too small, and delamination is likely to occur during the subsequent heat shrinking process.

[0024] Furthermore, the multi-directional crack-resistant heat-shrinkable film includes a base film, a transverse film sheet disposed on one side of the base film, and a longitudinal film sheet disposed on the side of the transverse film sheet facing away from the base film; the transverse film sheet is composed of several transverse crack-resistant bands, and the longitudinal crack-resistant band is composed of several longitudinal crack-resistant bands, and the vertical projections of the transverse crack-resistant bands and the longitudinal crack-resistant bands on the base film are arranged in a cross shape.

[0025] Furthermore, the bandwidth of both the transverse and longitudinal crack-blocking bands of the multi-directional crack-arresting heat-shrinkable film is 1mm-6mm.

[0026] Lower limit 1mm: When the crack-blocking band is too narrow, its own stretching and curling effect is not obvious, the crack-blocking ability is greatly reduced, and it is difficult to control the safe distance during heat sealing because the gap is also narrowed accordingly, and the process window is too narrow.

[0027] Maximum 6mm: Excessively wide crack-resistant bands will consume too much material, increase costs, and during heat shrinkage, wide crack-resistant bands will generate greater shrinkage stress, which may cause the base film to wrinkle.

[0028] The applicant's prior patent CN111572998A discloses the product structure of the multi-directional crack-resistant heat-shrinkable film involved in this application. Based on the above-mentioned structural patent, this application further discloses a method for heat-sealing the product with the structure.

[0029] The difference between this application and the prior patent is that the prior patent protects the structure of the multi-directional crack-resistant heat-shrinkable film itself, namely, the product scheme in which the transverse crack-resistant bands and the longitudinal crack-resistant bands are arranged in a cross shape and fused to the base film through a heat-sealing line; this application protects the process method for heat-sealing the film, namely, through a series of steps such as pre-identification of the crack-resistant band position, obstacle avoidance path planning, segmented heat-sealing temperature control, pressure zone regulation, gradient cooling shaping, and online quality inspection, the high-quality and high-efficiency heat-sealing of the above-mentioned specific structure film is achieved. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this drawing 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 this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0031] Figure 1 This is a flowchart of the steps of the present invention; The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments provided by this invention without inventive effort are within the scope of protection of this invention.

[0033] Obviously, the accompanying drawings described below are merely some examples or embodiments of the present invention. Those skilled in the art can apply the present invention to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this invention, modifications to design, manufacturing, or production based on the technical content disclosed in this invention are merely conventional technical means and should not be construed as insufficient disclosure of the present invention.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] To better understand the solutions of the embodiments of the present invention, some related terms and concepts that may be involved in the embodiments of the present invention will be introduced below: (1) Crack-prevention zone refers to a strip-shaped area of ​​a specific width in a transverse or longitudinal diaphragm. Its function is to distribute the local stress at the crack by curling under its own force when a crack occurs in the heat-shrink film, thus preventing the crack from extending further. Crack-prevention zones include transverse crack-prevention zones and longitudinal crack-prevention zones; (2) Gradient cooling zone refers to the multiple cooling zones through which the film material passes in succession after heat sealing, with the temperature decreasing in that order. Each cooling zone can be cooled by different methods such as forced air cooling, natural air cooling, or room temperature air purging. Setting up at least three cooling zones with decreasing temperatures is intended to allow the three-layer heat shrink film structure to gradually release shrinkage stress in different temperature ranges, reducing wrinkling of the film surface or misalignment of the crack-resistant zone caused by differences in the interlayer shrinkage rate.

[0040] In this embodiment, as Figure 1 As shown, a heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film includes: Step 1: Before the heat sealing station, perform real-time detection on the transverse and longitudinal crack-resistant zones of the multi-directional crack-resistant heat-shrinkable film during its movement to obtain the coordinates of the crack-resistant zone boundary positions. The multi-directional crack-resistant heat-shrinkable film is the same as the multi-directional crack-resistant heat-shrinkable film disclosed in the applicant's prior patent CN111572998A, which has a cross-shaped structure of crack-resistant bands composed of a base film and transverse and longitudinal films. In specific testing, the distinguishable characteristics of the crack-resistant bands and the base film in terms of optical and physical properties are utilized, including differences in thickness, transmittance, surface texture, and local thickness protrusions. Because the crack-resistant bands are additional composite films, they have minute protrusions or optical interfaces. A linear array camera or fiber optic sensor is used to scan the moving heat-shrinkable film in real time to determine the accurate boundary coordinates of each crack-resistant band. Step 2: Based on the coordinates of the crack-blocking zone, control the heat sealing knife to place the weld line in the gap area between adjacent crack-blocking zones, and the direction of the heat sealing knife is parallel to the length direction of the crack-blocking zone, with a safe distance between the edge of the heat sealing knife and the boundary of the crack-blocking zone. The function of controlling the heat sealing knife is to ensure that the heat sealing pressure and heat are applied only to the base membrane area between adjacent crack-resistant strips, and not directly pressed onto the crack-resistant strips, thereby avoiding heat-pressure damage to the edges of the crack-resistant strips; the direction of the heat sealing knife is parallel to the length direction of the crack-resistant strips, so that the weld line extends along the gap and ensures uniform weld strength; if the direction is perpendicular, it will cross the crack-resistant strips, causing structural damage; the safety distance further provides a buffer to prevent accidental pressing caused by positioning errors or membrane material vibration; Step 3: After the heat sealing knife contacts the film surface, it provides a segmented heat energy distribution by contacting at the first preheating temperature, applying pressure to weld at the second welding temperature, and then cooling down to remove the film. The first preheating stage involves slowly heating the three layers of heat-shrinkable film at a lower temperature to reduce transient thermal shock and prevent internal stress or microcracks from forming in the crack-resistant zone due to sudden temperature changes. At the same time, uniform preheating helps each layer of material reach a near-molten state simultaneously, creating conditions for subsequent welding. The second welding stage: reaching the true welding temperature, allowing the interlayer interface to fully melt and diffuse into each other, forming a strong weld. This stage requires sufficient temperature and duration, but at the same time, it is necessary to avoid excessive heat transfer to the crack-resistant zone. The third cooling stage: actively cool down to a non-stick temperature before the heat sealing knife is lifted to prevent the film surface from sticking to the heat sealing knife and avoid stretching of the crack-blocking strip or damage to the film surface. Step 4: Simultaneously with Step 3, apply different heat-sealing pressures to the film surface using the heat-sealing knife in the main welding area and the boundary transition area; The heat-sealing tool does not apply pressure uniformly to the bonding surface. Instead, the area corresponding to the gap in the fracture barrier is defined as the main welding zone, where higher pressure is applied to ensure a tight bond between layers. The area near the boundary of the fracture barrier is defined as the boundary transition zone, where lower and decreasing pressure is applied to prevent the high pressure from crushing the edge of the fracture barrier or squeezing out the molten material. This zoned design ensures both welding strength and protects the structural integrity of the fracture barrier. Step 5: After the heat sealing knife is lifted, the newly heat-sealed three-layer heat shrink film structure is passed through at least three cooling zones with decreasing temperatures. After heat sealing, the three layers of material remain at a high temperature, and the thermal shrinkage rate of each layer varies due to differences in thickness and orientation. If directly and rapidly cooled to room temperature, the interlayer stress will be released in an uncontrollable manner, leading to wrinkling of the film surface and displacement of the crack-resistant bands. This step uses gradient cooling, allowing each layer to gradually shrink within its respective thermal shrinkage temperature range, thus releasing stress evenly and ultimately maintaining the relative positional accuracy of the cross-shaped crack-resistant bands. Step 6: After cooling is complete, perform quality inspection and check the ratio of the width of the heat seal line to the width of the crack-resistant strip.

[0041] The width of the heat seal line directly reflects the effective area of ​​the weld. If the ratio is too large, that is, close to or equal to the width of the crack barrier, it means that the heat seal line may have pressed against the edge of the crack barrier. If it is too small, that is, much smaller than the width of the crack barrier, it indicates that the weld strength is insufficient and that the heat sealer may not be aligned with the center of the gap.

[0042] In this embodiment, the multi-directional crack-resistant heat-shrinkable film is composed of: a polyolefin base film with a thickness of 25 μm, the main material being linear low-density polyethylene, i.e., LLDPE, with a melting temperature of about 122°C; the transverse crack-resistant band and the longitudinal crack-resistant band are also made of LLDPE material, with a triangular thickness ratio of 1:1:1.

[0043] The width of the transverse fracturing band is 3mm, and the gap between adjacent transverse fracturing bands is 3mm; the width of the longitudinal fracturing band is 3mm, and the gap between adjacent longitudinal fracturing bands is 3mm; the total width of the membrane is 500mm.

[0044] The heat sealing equipment uses a fully automatic intermittent PS plate heat sealing machine, model QLS-650, equipped with a line array camera with a resolution of 0.1mm / pixel and a fiber optic sensor with a response frequency of 5kHz for detecting the boundary of the crack zone; the heat sealing knife adopts a zoned temperature control type heat sealing knife with a heating power of 2.5kW and is equipped with a compressed air cooling channel.

[0045] The heat-sealing molding process in this embodiment is as follows: The heat-shrinkable film travels at a linear speed of 15 m / min, while a linear scan camera continuously scans the film surface at a frame rate of 500 fps, with a detection accuracy of ±0.1 mm, and determines the position coordinates of the two side boundaries of each crack-resistant zone in real time. The control system positions the center of the weld line of the heat sealing knife to the center of the gap area between adjacent crack-blocking zones. The direction of the heat sealing knife is parallel to the length direction of the transverse crack-blocking zone, and the safe distance between the edge of the heat sealing knife and the boundary of the crack-blocking zone is 0.3mm. Taking the detection results within one scanning cycle as an example, the left boundary coordinates of the first transverse crack-blocking zone are 150.2 and the right boundary coordinates are 153.2; the left boundary coordinates of the second transverse crack-blocking zone are 156.2 and the right boundary coordinates are 159.2; the left boundary coordinates of the third transverse crack-blocking zone are 162.3 and the right boundary coordinates are 165.3; the left boundary coordinates of the first longitudinal crack-blocking zone are 200.5 and the right boundary coordinates are 203.5; the gap regions between adjacent crack-blocking zones are [153.2, 156.2], [159.2, 162.2], [165.3, 168.3], and [203.5, 206.5], respectively. The above coordinate values ​​are dynamically updated as the membrane material moves.

[0046] The detection principle, coordinate acquisition method, and heat sealing knife control logic of the longitudinal fracture barrier are exactly the same as those of the transverse fracture barrier. Both use a linear array camera to acquire the boundary coordinates in real time and then position the heat sealing knife welding line to the gap area between adjacent longitudinal fracture barriers. The direction of the heat sealing knife is parallel to the length direction of the longitudinal fracture barrier.

[0047] After the heat sealing blade contacts the film surface, segmented heat energy distribution is applied according to the following sequence: First preheating stage: The heat sealing knife is heated to 110°C and contacts the film surface for 0.5 seconds; Second welding stage: The temperature is rapidly increased to 160°C and held for 0.8 seconds; Third cooling stage: Compressed air cooling is started, with a compressed air pressure of 0.4MPa, and the surface temperature of the heat sealing knife is reduced to below 80°C within 3 seconds.

[0048] Simultaneously, pressure is applied in zonal zones: the heat-sealing pressure in the main weld zone is 0.4 MPa; in the boundary transition zone, with a width of 0.8 mm, the heat-sealing pressure linearly decreases from 0.4 MPa at the edge of the main weld zone to 0.15 MPa at the boundary of the fracture-resistant zone. After the heat-sealing knife is lifted, the heat-sealed film material passes sequentially through three air-cooled cooling zones with decreasing temperatures: The first cooling zone uses forced air cooling at a speed of 4 m / s and a temperature setting of 60°C, with a length of 40 cm. The second cooling zone uses natural air cooling at a temperature setting of 40°C, with a length of 40 cm. The third cooling zone uses ambient air purging at a temperature setting of 22°C, with a length of 40 cm. The total cooling time is approximately 4 seconds.

[0049] After cooling is complete, perform online testing: Average width of heat seal line: 1.50mm; The ratio of heat seal line width to crack barrier width is 1:2. Heat seal line position deviation: average offset +0.05mm, all within the safe distance; Condition of the fracture barrier edge: Under 130x magnification, the edge of the fracture barrier showed no melting, no carbonization, and no crushing marks. Seal strength: According to ASTM F88 standard, the peak peel strength was 18.2 N / 15 mm, tested with a universal testing machine. After cooling and shaping, the film material is then placed in a heat shrink oven. The oven temperature settings are: preheating zone 90℃, shrinking zone 140℃, shaping zone 60℃. The quality inspection indicators after heat shrinking are as follows: Heat shrinkage rate: longitudinal shrinkage rate 72%, transverse shrinkage rate 45%. The standard for heat shrinkage rate of POF heat shrink film is longitudinal ≥70% and transverse ≥50%, and the result meets the standard. Alignment deviation of the fracturing network: The average offset of the cross-shaped points of the transverse and longitudinal fracturing bands is 0.08 mm; Membrane quality: No wrinkles, no bubbles, no signs of uneven shrinkage; Tear-stopping function verification: The trouser tear test was performed according to GB / T 16578.2. All tears were effectively stopped when they extended to the tear-stopping zone. Compared with conventional production methods, the multi-directional crack-arresting heat-shrinkable film produced in this embodiment exhibits a crack-arresting band damage rate reduced from 16.5% to 1.8%, a sealing strength increased from 12.4 N / 15 mm to 18.2 N / 15 mm, and an overall pass rate increased from 81.3% to 97.8%. It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film, characterized in that, include: Step 1: Before the heat sealing station, perform real-time detection on the transverse and longitudinal crack-resistant zones of the multi-directional crack-resistant heat-shrinkable film during its movement to obtain the coordinates of the crack-resistant zone boundary positions. Step 2: Based on the coordinates of the crack-blocking zone, control the heat sealing knife to place the weld line in the gap area between adjacent crack-blocking zones, and the direction of the heat sealing knife is parallel to the length direction of the crack-blocking zone, with a safe distance between the edge of the heat sealing knife and the boundary of the crack-blocking zone. Step 3: After the heat sealing knife contacts the film surface, it provides a segmented heat energy distribution by contacting at the first preheating temperature, applying pressure to weld at the second welding temperature, and then cooling down to remove the film. Step 4: Simultaneously with Step 3, apply different heat-sealing pressures to the film surface using the heat-sealing knife in the main welding area and the boundary transition area; Step 5: After the heat sealing knife is lifted, the newly heat-sealed three-layer heat shrink film structure is passed through at least three cooling zones with decreasing temperatures. Step 6: After cooling is complete, perform quality inspection and check the ratio of the width of the heat seal line to the width of the crack-resistant strip.

2. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, The safe distance mentioned in step two is 0.2mm-0.5mm.

3. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, In step three, the first preheating temperature is 100℃-120℃.

4. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, In step three, the second welding temperature is 140℃-180℃.

5. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, The heat sealing pressure of the main welding zone in step four is 0.3MPa-0.6MPa.

6. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, The heat sealing pressure of the boundary transition zone mentioned in step four is 0.1MPa-0.2MPa.

7. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, In step five, the temperature difference between adjacent cooling zones is 5℃-15℃.

8. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, The ratio of the width of the heat-sealing line to the width of the crack-resistant strip mentioned in step six is ​​1:1 to 1:

3.

9. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 1, characterized in that, The multi-directional crack-resistant heat-shrinkable film includes a base film, a transverse film sheet disposed on one side of the base film, and a longitudinal film sheet disposed on the side of the transverse film sheet facing away from the base film; the transverse film sheet is composed of several transverse crack-resistant bands, and the longitudinal crack-resistant band is composed of several longitudinal crack-resistant bands, and the vertical projections of the transverse crack-resistant bands and the longitudinal crack-resistant bands on the base film are arranged in a cross shape.

10. The heat-sealing molding method for a multi-directional crack-resistant heat-shrinkable film according to claim 9, characterized in that, The transverse and longitudinal crack-resistant bands of the multi-directional crack-resistant heat-shrinkable film have a bandwidth of 1mm-6mm.

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