Highly light shielding petg shrink film and preparation system thereof

Abstract

The application discloses a high-shading PETG shrink film and a preparation system thereof, and relates to the technical field of plastic film production. The preparation system comprises a feeding cylinder, a first conveying screw rod rotatably installed in the feeding cylinder, a driving element connected with the first conveying screw rod and installed at one end of the feeding cylinder, an extrusion die head installed at the other end of the feeding cylinder, a second conveying screw rod installed in the feeding cylinder, a supporting and mixing mechanism installed between the first conveying screw rod and the second conveying screw rod, and a reciprocating filtering assembly movably installed between the supporting and mixing mechanism and the second conveying screw rod. The application limits the shading agent to be rutile titanium dioxide with a specific particle size range and the adding proportion, so that the shrinkage performance of the film is considered while the high-shading property is ensured. The supporting and mixing mechanism driven by the first conveying screw rod is arranged in the preparation system, so that the forced mixing and stirring of the material are realized in the conveying process.

Description

A high-light-shielding PETG shrink film and its preparation system Technical Field

[0001] This invention relates to the field of plastic film production technology, specifically to a high-light-shielding PETG shrink film and its preparation system. Background Technology

[0002] PETG heat shrink film is a new type of heat shrink packaging material. Due to its easy recyclability, non-toxicity, and odorless properties, it particularly meets environmental protection requirements. As a heat shrink film for labels, it needs to possess excellent shrinkage performance, abrasion resistance, weather resistance, and printability. Compared with other materials, PETG heat shrink film has characteristics such as high ultimate shrinkage rate, low natural shrinkage rate, smooth shrinkage curve, high transparency and gloss, and excellent printability. Furthermore, PETG, like the plastic bottle body, belongs to the polyester family, giving it a unique advantage in recycling. It is an internationally recognized environmentally friendly heat shrink packaging material.

[0003] The existing patent application, with publication number CN222022049U and publication date November 19, 2024, is titled "A Plastic Film Extruder Structure." This patent includes a work frame and a barrel fixedly connected to the top surface of the work frame. A film discharge assembly is fixedly connected to the outlet end of the barrel, and a forming frame is fixedly connected to the side of the work frame. A casting film-forming mechanism is installed on the forming frame. The film discharge assembly includes a filter connection box, a filter frame, a filter screen, a T-die, and a nozzle. This plastic film extruder structure filters the molten film-forming material through the film discharge assembly, preventing impurities from affecting film manufacturing. Simultaneously, the T-die and nozzle assist in film production. The film discharge assembly primarily filters the molten material through the filter screen in the filter frame. The T-discharge port and nozzle shape the film, and the casting film-forming mechanism further ensures film quality. The stretching component in the casting film-forming mechanism allows the film to be adjusted according to requirements during the casting stage.

[0004] The aforementioned application has shortcomings. With increasingly diversified market demands, ordinary PETG shrink film is no longer sufficient to meet the light-shielding protection requirements of some high-value products that need to be stored away from light. Furthermore, the uniform dispersion of the light-shielding agent in the PETG matrix is ​​a key challenge. Uneven dispersion can easily lead to appearance defects such as crystal points, white spots, or uneven light-shielding, severely affecting the packaging's aesthetics and light-shielding stability. Traditional screw extruders lack sufficient dispersion and mixing capabilities, easily leading to filler agglomeration and uneven distribution, affecting film performance and appearance. Plasticizing and mixing mainly relies on the shearing of the screw, which has limited ability to disperse additives such as fillers and color masterbatches. A single long screw rotates at high speed in the feed barrel and can only be supported by the bearings at both ends and the limited gap between the barrel walls. When conveying high-viscosity melts, the middle of the screw is subjected to huge radial pressure, which makes it very easy to bend, deflect, or even scrape against the barrel wall. In addition, if the insufficiently dispersed opacifier agglomerates or gel particles in the melt cannot be effectively filtered out during the melt blending process, they will enter the extrusion die with the melt, eventually causing film breakage or obvious defects in the film-forming stage. Summary of the Invention

[0005] The purpose of this invention is to provide a high-light-shielding PETG shrink film and its preparation system to overcome the shortcomings of the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A system for preparing a high-light-shielding PETG shrink film includes a feeding cylinder, a first feeding screw rotatably mounted inside the feeding cylinder, a drive unit connected to the first feeding screw mounted at one end of the feeding cylinder, an extrusion die mounted at the other end of the feeding cylinder, a second feeding screw mounted inside the feeding cylinder, and a support mixing mechanism installed between the first and second feeding screws. The support mixing mechanism is drivenly connected to the inner wall of the feeding cylinder. A reciprocating filter assembly is movably mounted between the support mixing mechanism and the second feeding screw. When the first feeding screw rotates and conveys material, it drives the support mixing mechanism to mix and stir the material between the first and second feeding screws, and the reciprocating filter assembly filters the mixed material.

[0008] Preferably, a feed hopper is installed on one side of the top of the feed cylinder, and an anti-clogging screen frame is installed inside the feed hopper. A sealing ring is installed on the first conveying screw, and a plurality of annularly distributed abutment blocks are fixedly connected to one side of the sealing ring. The abutment blocks abut against the bottom of the anti-clogging screen frame.

[0009] Preferably, the support mixing mechanism includes a connecting main shaft, with end caps connected to the first conveying screw and the second conveying screw respectively installed at both ends of the connecting main shaft, and multiple stirring shafts installed on the connecting main shaft, and multiple sets of material feeding rods distributed in a ring around the outer side of the connecting main shaft.

[0010] Preferably, a transmission gear ring is fixedly sleeved on the end cap, a support gear ring corresponding to the transmission gear ring is installed on the inner wall of the conveying cylinder, and gears are fixedly connected to both ends of the stirring shaft. The gears are located between the transmission gear ring and the support gear ring and mesh with both of them respectively.

[0011] Preferably, the end cap connected to the first conveying screw has annularly distributed guide grooves, which are offset from the tooth grooves of the transmission gear ring.

[0012] Preferably, the end cap connected to the second conveying screw has a ring-shaped discharge hole that extends through it, and the discharge end of the discharge hole is inclined outward along the axial direction.

[0013] Preferably, the reciprocating filter assembly includes a filter screen slidably sleeved on one end of the second conveying screw, an elastic abutment ring fixedly connected to one side of the end cap, one side of the filter screen in contact with the elastic abutment ring, and an abutment block fixedly connected to the other side, and a pair of stops that abut against the abutment blocks are fixedly connected to the inner wall of the conveying cylinder.

[0014] Preferably, a shearing and homogenizing head is installed at one end of the second conveying screw near the extrusion die. Several elliptical baffles are sequentially fitted onto the shearing and homogenizing head along the discharge direction, and the installation angle of each elliptical baffle is different.

[0015] Preferably, micro-motion hydraulic push rods are installed on both the upper and lower surfaces of the extrusion die, and the ends of the micro-motion hydraulic push rods abut against the material outlet of the extrusion die.

[0016] A high-opacity PETG shrink film prepared by the above-described preparation system includes a base layer, wherein, by weight, the raw materials of the base layer include...

[0017] PETG copolyester: 70-95 parts;

[0018] Sunscreen: 5-30 parts;

[0019] Additives: 0.5-5 parts;

[0020] The light-blocking agent is rutile titanium dioxide with a particle size of 0.1-0.5 μm. The visible light transmittance of the substrate is not higher than 5%, and the heat shrinkage rate is 40% to 80%. The heat shrinkage rate is the transverse heat shrinkage rate and / or longitudinal heat shrinkage rate of the film after being treated in glycerol at 90±2℃ for 10 seconds.

[0021] Preferably, the overall thickness of the base layer is 30μm to 100μm, and a functional coating is further provided on the outer surface of the base layer. The functional coating is at least one of an antistatic coating, an anti-fog coating, or a slip coating.

[0022] In the above technical solution, by limiting the opacifier to rutile titanium dioxide with a specific particle size range and its addition ratio, high opacity is ensured while also taking into account the shrinkage performance of the film. The preparation system is equipped with a support mixing mechanism driven by the first conveying screw, which achieves forced mixing and stirring of materials during the conveying process, ensuring the high dispersion and uniformity of the opacifier in the PETG matrix. The support mixing mechanism is not only responsible for stirring the mixture, but also plays a supporting role in the middle of the two conveying screws, turning the originally easily bent long screw into two shorter and effectively supported stable structures, which greatly enhances the rigidity of the entire system and fundamentally eliminates the problems of screw deflection and vibration, laying the foundation for the stable extrusion of high-quality films. The twin-screw combination design allows the system to be disassembled and maintained in sections. At the same time, the reciprocating filter component can dynamically filter the mixed melt, effectively filtering out impurities and undispersed agglomerates, and preventing the filter channel from clogging, ensuring the continuity of production.

[0023] It should be understood that the foregoing general description and the following detailed description are exemplary and illustrative only, and are not intended to limit this disclosure.

[0024] This application provides an overview of various implementations or examples of the technology described in this disclosure, and is not a full disclosure of the entire scope or all features of the disclosed technology. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0026] Figure 1 is a schematic diagram of the overall structure of a high-light-shielding PETG shrink film preparation system according to the present invention;

[0027] Figure 2 is an overall cross-sectional view of a high-light-shielding PETG shrink film preparation system of the present invention;

[0028] Figure 3 is a partial cross-sectional view of the feed cylinder in a high-light-shielding PETG shrink film preparation system of the present invention;

[0029] Figure 4 is a schematic diagram showing the connection between the first conveying screw and the second conveying screw in a high-light-shielding PETG shrink film preparation system of the present invention.

[0030] Figure 5 is a schematic diagram of the installation of the reciprocating filter assembly in a high-light-shielding PETG shrink film preparation system of the present invention;

[0031] Figure 6 is a schematic diagram of the support mixing mechanism in a high-light-shielding PETG shrink film preparation system of the present invention.

[0032] Figure 7 is a schematic diagram of the reciprocating filter component in a high-shielding PETG shrink film preparation system of the present invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Feeding cylinder; 101. Feed hopper; 102. Anti-clogging screen frame; 103. Support gear ring; 104. Stop block; 2. First conveying screw; 201. Sealing ring; 202. Abutment block; 3. Driving component; 4. Extrusion die head; 401. Micro-motion hydraulic push rod; 5. Second conveying screw; 6. Support mixing mechanism; 601. Connecting main shaft; 602. End cover; 603. Stirring shaft; 604. Feeding rod; 605. Transmission gear ring; 606. Gear; 607. Guide chute; 608. Discharge hole; 609. Connecting frame; 7. Reciprocating filter assembly; 701. Filter screen; 702. Elastic abutment ring; 703. Abutment block; 9. Shearing homogenizing head; 901. Elliptical baffle. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure 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 this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0036] Please refer to Figures 1-7. This embodiment of the invention provides a preparation system for a high-light-shielding PETG shrink film, including a feeding cylinder 1 and a first feeding screw 2, which is rotatably installed inside the feeding cylinder 1. A drive component 3 connected to the first feeding screw 2 is installed at one end of the feeding cylinder 1, and an extrusion die 4 is installed at the other end of the feeding cylinder 1. A second feeding screw 5 is installed inside the feeding cylinder 1, and a support mixing mechanism 6 is installed between the first feeding screw 2 and the second feeding screw 5. The support mixing mechanism 6 is drivenly connected to the inner wall of the feeding cylinder 1. A reciprocating filter assembly 7 is movably installed between the support mixing mechanism 6 and the second feeding screw 5. When the first feeding screw 2 rotates to convey material, it drives the support mixing mechanism 6 to mix and stir the material between the first feeding screw 2 and the second feeding screw 5, and the reciprocating filter assembly 7 filters the mixed material.

[0037] A high-opacity PETG shrink film prepared by the above-described preparation system includes a base layer. By weight, the base layer comprises: 70-95 parts of PETG copolyester; 5-30 parts of an opacifier; and 0.5-5 parts of an additive. The opacifier is rutile titanium dioxide with a particle size of 0.1-0.5 μm. The visible light transmittance of the shrink film is not higher than 5%, and the heat shrinkage rate is 40%-80%. The heat shrinkage rate is the transverse heat shrinkage rate and / or longitudinal heat shrinkage rate of the film after being treated in glycerin at 90±2℃ for 10 seconds. The overall thickness of the base layer is 30 μm to 100 μm. A functional coating is also provided on the outer surface of the base layer. The functional coating is at least one of an antistatic coating, an anti-fog coating, or a slip coating.

[0038] Specifically, 85 parts of PETG copolyester resin, 14 parts of rutile titanium dioxide with a specific particle size, and 1 part of additives are thoroughly mixed in a high-speed mixer. The mixed material is then fed into a drying system and dried at 120-140℃ for 4-6 hours to reduce its moisture content to below 50 ppm to prevent hydrolytic degradation during subsequent melt extrusion. The dried mixture is then fed into the inlet of the feed cylinder 1 of the preparation system. The drive unit 3 is activated, driving the first conveying screw 2 to rotate. Under the conveying and shearing action of the first conveying screw 2, the material begins to plasticize and melt. The molten material is conveyed to the middle region of the feed cylinder 1, where a support mixing mechanism 6 driven by the first conveying screw 2 is installed. This mechanism rotates with the screw... During this process, the material itself generates strong shearing and agitation, forcing the PETG melt to undergo secondary, high-intensity mixing with the rutile titanium dioxide particles. This process effectively breaks up titanium dioxide agglomerates, ensuring that they are uniformly dispersed in the PETG matrix at their original particle size, thereby achieving efficient light-blocking. The fully mixed melt continues to pass through the reciprocating filter assembly 7, which reciprocates under the rotation of the second screw, filtering out any possible gels, carbonized particles, or large agglomerates of undispersed light-blocking agents. The reciprocating motion design effectively prevents the filter from being quickly clogged by impurities, ensuring continuous and stable production. The pure, uniform melt after filtration is received by the second conveying screw 5 and further homogenized and stabilized. The film is conveyed and finally extruded through a specially designed extrusion die 4. The extruded preform is immediately cooled by cooling rollers to form an amorphous sheet. The sheet is then reheated to a high-elasticity state above the glass transition temperature and subjected to simultaneous or stepwise bidirectional stretching in both longitudinal and transverse directions. By controlling a specific stretching ratio and temperature, the film molecular chains are oriented to obtain a shrink film with a heat shrinkage rate between 40% and 80%. Finally, after cooling, edge trimming, and winding, the final high-light-shielding PETG shrink film is obtained. When the length-to-diameter ratio of a traditional single screw is too large, the screw is prone to bending and vibration due to its own weight and material pressure. This is addressed by dividing the screw into a first conveying screw 2 and a second conveying screw 5, with a supporting mixing mechanism 6 installed in the middle. Structure 6 not only plays a mixing role, but its key function lies in its transmission connection with the inner wall of the conveying cylinder 1. This is equivalent to adding a reliable intermediate bearing seat in the middle of the two screws, which greatly enhances the rigidity of the entire extrusion system and fundamentally suppresses screw deflection and vibration. This lays the mechanical foundation for stable and uniform film extrusion. Before entering the second conveying screw 5, the uniformly mixed melt must pass through the reciprocating filter assembly 7. The reciprocating motion of this assembly causes the filter area to change dynamically. Even if impurities temporarily block part of the filter holes, the reciprocating motion can use the melt pressure to flush them out, allowing the unblocked areas to continue working. This effectively avoids the problem of easy clogging of the fixed filter screen in the conveying cylinder and the need for frequent shutdowns for replacement, ensuring the efficiency of continuous production.

[0039] Compared with existing technologies, the embodiments of the present invention limit the opacifier to rutile titanium dioxide with a specific particle size range and its addition ratio, ensuring high opacity while also taking into account the shrinkage performance of the film. The preparation system is equipped with a support mixing mechanism 6 driven by the first conveying screw 2, which achieves forced mixing and stirring of materials during the conveying process, ensuring the high dispersion and uniformity of the opacifier in the PETG matrix. The support mixing mechanism 6 is not only responsible for stirring the mixture, but also plays a supporting role in the middle of the two conveying screws, turning the originally easily bent long screw into two shorter and effectively supported stable structures, which greatly enhances the rigidity of the entire system and fundamentally eliminates the problems of screw deflection and vibration, laying the foundation for stable extrusion of high-quality films. The twin-screw combination design allows the system to be disassembled and maintained in sections. At the same time, the reciprocating filter assembly 7 can dynamically filter the mixed melt, effectively filtering out impurities and undispersed agglomerates, and preventing the filter channel from clogging, ensuring the continuity of production.

[0040] In a further embodiment of the present invention, a feed hopper 101 is installed on one side of the top of the feed cylinder 1, and an anti-clogging screen frame 102 is installed inside the feed hopper 101. One side of the anti-clogging screen frame 102 is slidably connected to the inner wall of the feed hopper 101. A sealing ring 201 is installed on the first conveying screw 2, and a plurality of annularly distributed abutment blocks 202 are fixedly connected to one side of the sealing ring 201. The abutment blocks 202 abut against the bottom of the anti-clogging screen frame 102. Specifically, when the anti-clogging screen frame 102 is not lifted, it rests inside the feed hopper 101. When the first conveying screw 2 rotates under the drive of the drive member 3, the sealing ring 201 and the abutment blocks 202 on it rotate synchronously. These rotating abutment blocks 202 will periodically impact and scrape the bottom of the anti-clogging screen frame 102. This continuous, low-intensity impact and scraping action... The high-frequency micro-vibration of the screen frame causes the material particles stuck in the feed hopper 101 to be shaken off, effectively breaking the material accumulation and bridging in the feed hopper 101. The sealing ring 201 can also play a sealing role to prevent material powder from leaking back from the root of the screw, thus combining the two functions of sealing and anti-clogging.

[0041] In a further embodiment of the present invention, the support mixing mechanism 6 includes a connecting main shaft 601. End caps 602, connected to the first conveying screw 2 and the second conveying screw 5 respectively, are installed at both ends of the connecting main shaft 601. The end caps 602 are frustoconical, with the smaller diameter side used for docking with the screws. Multiple stirring shafts 603 are installed on the connecting main shaft 601. Multiple sets of material-pulling rods 604 are distributed in a ring around the outer side of the connecting main shaft 601. A connecting frame 609 is rotatably sleeved on the connecting main shaft 601. A bracket 610 for the material-pulling rods 604 to pass through is installed on the connecting frame 609. Specifically, when the driving component 3 drives the first conveying screw 2 to rotate, the power is transmitted to the connecting main shaft 601 through the end caps 602, causing the entire support mixing mechanism 6 to rotate synchronously. During rotation, the stirring shafts 603 act as the main mixing elements, strongly shearing, cutting, and diverting the flowing PETG melt and opacifier mixture. The multiple stirring shafts 603 directly break the laminar flow state of the material, forcing the material to generate... The eddy currents and exchange greatly promote the uniform dispersion of rutile titanium dioxide in the PETG matrix. The feed rods mainly serve to propel and assist in mixing. They rotate close to the inner wall of the feed cylinder 1, scraping off any material that may adhere to the cylinder wall to prevent carbonization. On the other hand, they generate a forward pushing force on the material, ensuring that the material passes smoothly through the mixing area and moves towards the second conveying screw 5, avoiding material accumulation. The combination of central radial stirring and peripheral circumferential scraping achieves comprehensive and high-intensity chaotic mixing of the material, ensuring the uniform distribution of opacifier particles from macroscopic to microscopic scales. The entire support mixing mechanism 6, through its end caps 602 at both ends, cooperates with the support structure inside the feed cylinder to form a solid intermediate support, transforming the original slender screw into the first conveying screw 2 and the second conveying screw 5, fundamentally solving the problem of long screws being prone to bending and vibration, and ensuring the stability of the extrusion process.

[0042] In a further embodiment of the present invention, a transmission gear ring 605 is fixedly sleeved on the end cap 602, and a support gear ring 103 corresponding to the transmission gear ring 605 is installed on the inner wall of the conveying cylinder 1. Gears 606 are fixedly connected to both ends of the stirring shaft 603. The gears 606 are located in the annular space between the transmission gear ring 605 and the support gear ring 103 and mesh with both respectively. Specifically, when the driving member 3 drives the first conveying screw 2 to rotate, the power is transmitted to the transmission gear ring 605 through the end cap 602, so that the entire support mixing mechanism 6 revolves around the axis of the connecting main shaft 601 as a whole. At this time, since the gears 606 at both ends of the stirring shaft 603 not only mesh with the rotating transmission gear ring 605, but also mesh with the fixed support gear ring 103, this meshing relationship forces the gears 606 to rotate themselves. The rotation of the gears 606 drives the stirring shaft 603 to rotate around its own axis. Therefore, each stirring shaft 603 performs two motions simultaneously during operation. It rotates planetarily around the central axis of the system with the connecting main shaft 601, scraping and pushing the material over a wide area. It also rotates at high speed around its own axis, generating strong local shearing, grinding, and stirring effects on the surrounding material. This combined revolution and rotation motion can form an extremely complex and efficient flow field within the conveying cylinder 1, dispersing and mixing the PETG melt and opacifier far beyond that of ordinary stirring mechanisms. At the same time, multiple gears 606 mesh with two gear rings simultaneously, which is equivalent to setting multiple evenly distributed and continuous radial support points at both ends of the supporting mixing mechanism 6. These meshing points greatly enhance the bending and vibration resistance of the connecting main shaft 601, making the intermediate support more stable and reliable, and providing radial and full-circumferential support for the entire supporting mixing mechanism 6, further enhancing its rigidity and stability during operation.

[0043] In a further embodiment of the present invention, annularly distributed guide grooves 607 are provided on the end cap 602 connected to the first conveying screw 2. The guide grooves 607 are offset from the tooth grooves of the transmission gear ring 605. Specifically, when the material is pushed into the support mixing mechanism 6 area by the first conveying screw 2, it will first impact the end face of the end cap 602. Without a guide structure, the material is prone to forming a relatively stagnant area here. In this design, the guide grooves 607 on the rotating end cap 602 will generate a guiding force on the material impacting it, smoothly pumping the material from the central area of ​​the end cap 602 and guiding it to the periphery, so that it can quickly enter the main mixing area created by the stirring shaft 603 and the feeding rod 604. These grooves provide a flow channel for the material, significantly reducing the shear resistance between the material and the end face of the end cap 602, thereby reducing the load on the drive motor and the local shear heat generation of the material. By forcibly guiding the material to the periphery, it effectively prevents the material from stagnating in the central area of ​​the end cap 602, especially... The material is stored within the complex tooth structure of the transmission gear ring 605, preventing material degradation or carbonization caused by prolonged heating and ensuring product purity. The flow guide groove 607 is offset from the tooth groove of the transmission gear ring 605, ensuring the structural strength of the end cover 602. If the flow guide groove were located in stress concentration areas such as the tooth root, it would severely weaken the tooth root strength of the gear 606, affecting the reliability of power transmission and the stability of the support. The offset design makes the load-bearing structure and flow guide functional area of ​​the end cover 602 independent and do not interfere with each other, thus optimizing the flow field while ensuring the robustness and durability of the mechanical structure.

[0044] In a further embodiment of the present invention, annularly distributed discharge holes 608 are provided through the end cap 602 connected to the second conveying screw 5. The discharge end of the discharge holes 608 is inclined outward along the axial direction. Specifically, after the material undergoes planetary high-intensity shearing and mixing in the support mixing mechanism 6, a portion of the material flows to the periphery under the thrust of subsequent materials and the material-pushing action of the mixing mechanism. At this time, the discharge holes 608 on the end cap 602 provide the core outflow path. Under pressure, the material is guided directly and through a short path to the receiving area of ​​the second conveying screw 5 through these discharge holes 608. This avoids the material needing to go around the entire outer edge of the end cap 602 to enter the next stage, significantly reducing flow resistance. The axially outward inclined design of the discharge end of the discharge holes 608 provides a guiding effect for the outflowing material. This design allows for better matching of the flow direction with the thread direction and conveying direction of the second conveying screw 5, achieving a smooth transition from the mixing zone to the conveying zone, reducing flow energy loss and pulsation. The inclined discharge port forms a smooth, guiding nozzle effect, making the material flow more smoothly and completely eliminating any dead zones that may exist at the outlet corner of the end cap 602. This ensures that all materials can be discharged in a timely manner, minimizing the residence time of materials in this high-temperature and high-pressure area, effectively preventing degradation and carbonization caused by local overheating, and ensuring the purity and quality of the final product. This discharge hole 608 and the guide chute 607 at the end of the mixing mechanism form a functional echo, one responsible for efficiently introducing materials into the center of the mixing zone, and the other responsible for thoroughly guiding the mixed materials out and smoothly conveying them to the next stage.

[0045] In a further embodiment of the present invention, the reciprocating filter assembly 7 includes a filter screen 701 slidably sleeved on one end of the second conveying screw 5. An elastic abutment ring 702 is fixedly connected to one side of the end cap 602. One side of the filter screen 701 contacts the elastic abutment ring 702, and a stop block 703 is fixedly connected to the other side. A pair of stops 104 that abut against the stop blocks 703 are fixedly connected to the inner wall of the feed cylinder 1. Specifically, when the second conveying screw 5 rotates, it rotates along with the filter screen 701. When the filter screen 701... When the abutment 703 and the stop block 104 inside the feed cylinder 1 come together, the filter screen 701 moves toward the end cover 602. There is an annular gap between the filter screen 701 and the feed cylinder 1. When the abutment 703 and the stop block 104 are misaligned, they move back to their original position under the pressure of the material and the elastic abutment ring 702. The reciprocating motion of the filter screen 701 can both push the blocked material back and prevent the material from accumulating and clogging at the filter screen 701, thus ensuring the mixing effect of the material and the efficiency of film production.

[0046] In a further embodiment of the present invention, a shearing and homogenizing head 9 is installed at one end of the second conveying screw 5 near the extrusion die head 4. Several elliptical baffles 901 are sequentially fitted onto the shearing and homogenizing head 9 along the discharge direction, and the installation angles of each elliptical baffle 901 are different. Specifically, the major axis directions of adjacent elliptical baffles 901 are different, forming a baffle sequence with irregular or regularly changing installation angles. The melt homogenized and conveyed by the second conveying screw 5 must continuously pass through this series of elliptical baffles 901 at different angles under pressure. Because the baffles are elliptical, the gap between them and the inner wall of the conveying cylinder 1 changes periodically. When the melt flows through each baffle, it will reach the point where the gap is at its widest. The melt is subjected to strong shearing at small points and relaxes at the largest gaps. When the melt flows through an elliptical baffle 901 at a certain angle, the stream is split. When it continues to flow to a baffle at a different angle, the previously split stream is split again and recombined in a new way. Multiple baffles at different angles are connected in series, so that the shear-relaxation-splitting-recombining process is repeated many times, which can produce extremely strong stretching and shearing mixing effects on the melt. This can completely break down any smaller uniformity problems that may remain in the melt, ensuring that the material entering the extrusion die 4 is highly uniform. This is crucial for producing PETG shrink films with extremely high optical performance requirements, high light blocking, and uniform surface.

[0047] In a further embodiment of the present invention, micro-motion hydraulic push rods 401 are installed on both the upper and lower surfaces of the extrusion die 4. The ends of the micro-motion hydraulic push rods 401 abut against the material outlet of the extrusion die 4. Specifically, multiple micro-motion hydraulic push rods 401 are evenly distributed along the width direction of the die lip. The tails of these push rods are fixed to the base of the extrusion die 4, while their precision-machined ends abut against the back of the material outlet of the extrusion die 4. Each micro-motion hydraulic push rod 401 can be independently controlled by a high-precision hydraulic servo system. If the control system detects that the thickness of a certain point of the film exceeds the set tolerance range, The micro-hydraulic push rod 401 located directly above the point will then be instructed to perform a slight extension and retraction. When a very slight thrust is applied to the end of the push rod, the die lip at the corresponding position will undergo micron-level elastic bending deformation, thereby locally and precisely changing the die lip gap at that point. The slight change in the die lip gap will directly adjust the melt flow rate and pressure at that point, thereby adjusting the thicker preform area to the target thickness. Through this closed-loop feedback control, the uneven film thickness caused by uneven material flow, temperature fluctuations, or die head deformation can be compensated in real time and dynamically.

[0048] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A system for preparing a high-light-shielding PETG shrink film, comprising a feed cylinder (1), characterized in that, Also includes: A first conveying screw (2) is rotatably mounted inside a conveying cylinder (1). A drive unit (3) connected to the first conveying screw (2) is mounted at one end of the conveying cylinder (1), and an extrusion die (4) is mounted at the other end of the conveying cylinder (1). A second conveying screw (5) is mounted inside the conveying cylinder (1), and a support mixing mechanism (6) is installed between the first conveying screw (2) and the second conveying screw (5). The support mixing mechanism (6) is connected to the inner wall of the conveying cylinder (1) via a transmission connection. The system includes a connecting spindle (601), with end caps (602) at both ends connected to the first conveying screw (2) and the second conveying screw (5), and multiple stirring shafts (603) mounted on the connecting spindle (601). Multiple sets of material feeding rods (604) are distributed in a ring around the outer side of the connecting spindle (601). A transmission gear ring (605) is fixedly fitted onto the end caps (602), and the inner wall of the conveying cylinder (1) is fitted with a material corresponding to the transmission gear ring (605). The support gear ring (103) has gears (606) fixedly connected to both ends of the stirring shaft (603). The gears (606) are located between the transmission gear ring (605) and the support gear ring (103) and mesh with both of them respectively. The end cover (602) connected to the first conveying screw (2) has annularly distributed guide grooves (607), which are offset from the tooth grooves of the transmission gear ring (605). The end cover (602) connected to the second conveying screw (5) has a ring-shaped distribution of guide grooves (607). 2) A circularly distributed discharge hole (608) is provided through the upper part, and the discharge end of the discharge hole (608) is inclined outward along the axial direction; the reciprocating filter assembly (7) is movably installed between the support mixing mechanism (6) and the second conveying screw (5); when the first conveying screw (2) rotates to convey materials, it drives the support mixing mechanism (6) to mix and stir the materials between the first conveying screw (2) and the second conveying screw (5), and filters the mixed materials through the reciprocating filter assembly (7).

2. The preparation system for a high-light-shielding PETG shrink film according to claim 1, characterized in that, A feed hopper (101) is installed on one side of the top of the feed cylinder (1). An anti-clogging screen frame (102) is installed inside the feed hopper (101). A sealing ring (201) is installed on the first conveying screw (2). Several ring-shaped abutment blocks (202) are fixedly connected to one side of the sealing ring (201). The abutment blocks (202) abut against the bottom of the anti-clogging screen frame (102).

3. The preparation system for a high-opacity PETG shrink film according to claim 1, characterized in that, The reciprocating filter assembly (7) includes a filter screen (701) slidably sleeved on one end of the second conveying screw (5). An elastic abutment ring (702) is fixedly connected to one side of the end cap (602). One side of the filter screen (701) is in contact with the elastic abutment ring (702), and an abutment block (703) is fixedly connected to the other side. A pair of stops (104) that abut against the abutment block (703) are fixedly connected to the inner wall of the conveying cylinder (1).

4. The preparation system for a high-light-shielding PETG shrink film according to claim 1, characterized in that, The second conveying screw (5) is equipped with a shearing and homogenizing head (9) at one end near the extrusion die (4). Several elliptical baffles (901) are sequentially sleeved on the shearing and homogenizing head (9) along the discharge direction, and the installation angles of each elliptical baffle (901) are different.

5. A high-opacity PETG shrink film prepared by the preparation system according to any one of claims 1-4, comprising a base layer, characterized in that, By weight, the raw material of the base layer includes 70-95 parts of PETG copolyester; Sunscreen: 5-30 parts; Additives: 0.5-5 parts; the opacifier is rutile titanium dioxide with a particle size of 0.1-0.5 μm; the visible light transmittance of the substrate is not higher than 5%; the heat shrinkage rate is 40%-80%; the heat shrinkage rate is the transverse heat shrinkage rate and / or longitudinal heat shrinkage rate of the film after being treated in glycerol at 90±2℃ for 10 seconds.

6. The high-light-shielding PETG shrink film according to claim 5, characterized in that, The overall thickness of the base layer is 30μm to 100μm, and a functional coating is provided on the outer surface of the base layer. The functional coating is at least one of an antistatic coating, an anti-fog coating, or a slip coating.

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