Thermal shrinkage film for protection and preparation method thereof

Abstract

The invention belongs to the technical field of packaging film material preparation, and particularly relates to a heat shrink film for protection and a preparation method thereof, the shrink film comprises 100 parts of polyolefin, 25-40 parts of SEBS, 0.5-1 part of an antioxidant, 0.5-1.5 parts of a lubricant, 0.5-1 part of an anti-ultraviolet agent, 0.5-1.5 parts of a nucleating transparent agent and 1-3 parts of a processing aid, and the polyolefin is a combination of polypropylene and linear low density polyethylene according to a mass ratio of 30-40: 60-70. The preparation method comprises the following steps: mixing and granulating the components, extruding by using a single-layer film blowing machine, blowing for the first time, cooling and shaping to obtain a film pipe, preheating the film pipe, carrying out secondary blowing under traction driving, carrying out air ring cooling treatment on the film pipe, and annealing and cooling the film pipe after the transverse blowing stretching multiple is 4-6 times and the longitudinal traction stretching multiple is 5-7 times.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of packaging film material preparation, and particularly relates to a protective heat-shrinkable film and a preparation method thereof. BACKGROUND

[0002] The heat-shrinkable film is mainly designed based on the stretching orientation principle of macromolecular chains. When the plastic extruded embryo film is forced to stretch in the longitudinal and transverse directions between the glass transition temperature and the viscous flow temperature, the polymer macromolecular chains of the embryo film are oriented along the stretching direction. After the orientation reaches a certain degree, the oriented macromolecular chains are frozen by rapid cooling. Thereafter, when the temperature is raised to the "thawing" temperature again, the molecular chains are restored to the original unoriented state by relying on their own recovery. This process causes the size of the film to be shortened on the macroscopic scale.

[0003] As a film material that can greatly shrink under heat, the heat-shrinkable film can achieve conformal packaging of products of different shapes when the heat-shrinkable film is tightened. For example, after a plurality of beverage bottles are orderly placed together, the bottles are packaged as a whole by the heat-shrinkable film. The heat-shrinkable film can tightly package the bottles, avoid mutual sliding and collision between the bottles, and facilitate transportation and storage. Compared with traditional packaging cartons, the heat-shrinkable film has better mechanical properties and moisture resistance, and is transparent, so that the goods inside the package can be directly identified without opening the package. It can be seen that the heat-shrinkable film is an ideal protective packaging film material.

[0004] The conformality and tightness of the heat-shrinkable film when packaging goods are closely related to the heat-shrinking performance of the packaging film itself. When the heat-shrinking degree of the packaging film is insufficient, the goods wrapped inside cannot be effectively tightened, which increases the risk of collision and damage between the goods during transportation and transfer. The composition of the heat-shrinkable film has a great influence on the shrinkage rate. SUMMARY

[0005] To solve the above technical problems and increase the shrinkage degree of the heat-shrinkable film during use, thereby forming more stable protective packaging for goods, the present application provides a protective heat-shrinkable film. The heat-shrinkable film comprises, by weight fraction, polyolefin 100 parts, SEBS 25-40 parts, antioxidant 0.5-1 part, lubricant 0.5-1.5 parts, ultraviolet resistance agent 0.5-1 part, nucleating transparent agent 0.5-1.5 parts, and processing aid 1-3 parts. The polyolefin is a combination of polypropylene and linear low-density polyethylene in a mass ratio of 30-40:60-70.

[0006] As a preferred embodiment, the mass ratio of the polypropylene and the linear low-density polyethylene is 30:70.

[0007] Preferably, the lubricant includes one or a combination of barium stearate, calcium stearate, magnesium stearate, and silicone masterbatch.

[0008] Preferably, the nucleating transparent agent is a sorbitol transparent agent, such as dibenzylidene sorbitol, di-p-chlorobenzylidene sorbitol, di(p-methylbenzylidene) sorbitol, and the like.

[0009] The present invention also provides a method for preparing the above-mentioned protective heat shrink film: the components are fully mixed and then extruded into granules through a screw extruder, the obtained granules are extruded and blown once through a single-layer film blowing machine, and then cooled and shaped as a film tube, after which the film tube is dried, preheated to 90°C to 120°C and blown a second time under traction drive, so that the transverse blowing stretching ratio of the film tube reaches 4 to 6 times, and the longitudinal traction stretching ratio reaches 5 to 7 times, and then the film tube obtained by the secondary blowing is subjected to air ring cooling treatment, annealing treatment at 65°C to 80°C, and then cooled at 15°C to 25°C.

[0010] Preferably, the components are mixed thoroughly and then extruded into granules through a twin-screw extruder, wherein the temperatures of the various zones of the twin-screw extruder are 130°C to 145°C, 150°C to 165°C, 170°C to 180°C, 180°C to 195°C, 195°C to 205°C, 205°C to 215°C, and 210°C to 225°C, and the die temperature is 210°C to 225°C.

[0011] Preferably, the temperature of the melting section of the single-layer film blowing machine is 200°C to 230°C.

[0012] Preferably, the pellets are blown up once and then passed through a cooling water ring to achieve cooling and shaping. The cooling water ring can perform circumferential cooling on the blown film tube, which is conducive to uniform cooling and ensures the stability of the film tube during the cooling process. The cooling water temperature in the cooling water ring is 10°C to 15°C to achieve rapid cooling of the film tube. The diameter of the film tube obtained after cooling and shaping is 200mm to 500mm.

[0013] After the film tube is cooled by the water ring, if the moisture adhering to the surface of the film tube is not removed, irregular patterns will appear on the surface of the shrink film product, affecting the appearance and quality of the product. Therefore, the film tube will pass through the herringbone plate on the film blowing machine under traction drive to remove water.

[0014] As a preference: the air ring cooling adopts the upward blowing method, specifically adopting a five-level air ring, the distance between each air ring is 5-10mm, the angle between the air outlet of each air ring and the membrane tube is 10°-20°, among which, from the first to the fifth level air ring, the air volume is 1500-2500m 3 / h, 1500~2000m 3 / h, 1000~2000m 3 / h, 500~1000m3 / h, 500~800m 3 / h; the air temperatures from the first to the fifth air rings are 15°C to 25°C, 10°C to 20°C, 10°C to 15°C, 10°C to 15°C, and 10°C to 15°C, respectively, to achieve rapid cooling of the film tube. Under the action of the air rings, the film tube is cooled by circumferential air blowing, which is more conducive to maintaining uniform thickness, shrinkage rate, and other indicators of the film tube and the subsequent heat shrink film.

[0015] Preferably, the method for preparing the protective heat shrink film further includes annealing and cooling, then splitting the film tube in half and flattening it, followed by trimming and winding. The annealing treatment helps reduce stress within the heat shrink film, preventing the film from shrinking naturally when not heated.

[0016] Preferably, the protective heat shrinkable film obtained after flattening has a thickness of 10 μm to 20 μm.

[0017] The present invention achieves the beneficial effect of adding SEBS to polypropylene or polyethylene as the base resin for heat-shrinkable films. SEBS is a styrene / ethylene / butadiene / styrene block copolymer, a hydrogenated product of SBS (styrene / butadiene / styrene block copolymer). Its molecular configuration is an ABA triblock, where A represents the hard segment PS and B represents the elastic soft segment EB. SEBS has traditionally been frequently added to blended resins as a compatibilizer. This is because the EB segments in SEBS are structurally similar to those in PE, resulting in good compatibility. Furthermore, the PS segments in SEBS are structurally similar to methylbenzene rings and methylcycloalkanes, resulting in good compatibility. Therefore, SEBS is often used to improve the compatibility between linear polyolefins and macromolecular resins with cyclic structures.

[0018] However, the matrix resin (polypropylene, polyethylene, the same below) of this scheme does not have a ring structure in its molecular structure, and the compatibility between linear low-density polyethylene and polypropylene is also ideal. The purpose of introducing SEBS in this scheme is: on the one hand, through the compatibility between the EB chain segment on SEBS and the matrix resin chain structure, the SEBS macromolecule can maintain a certain dispersion in the matrix resin mixture of polypropylene and polyethylene. From the perspective of molecular chain distribution, it can be understood that the SEBS macromolecular chain can be dispersed and doped to a certain extent between different macromolecular chains of the matrix resin to form a certain barrier, thereby first reducing the mutual interaction between the molecular chains of the matrix resin itself (such as entanglement, etc.); and on this basis, since the PS chain segment on SEBS is incompatible with the molecular chain structure of polypropylene and polyethylene, this also greatly reduces the interaction and entanglement between SEBS and the matrix resin molecular chain. In summary, this solution is equivalent to utilizing the intervention of SEBS to reduce the degree of interaction between the molecular chains of the matrix resin itself, and SEBS itself has less entanglement with these molecular chains of the matrix resin. The applicant believes that: after the overall degree of interaction between the molecular chains in the heat shrinkable film is weakened, the orientation degree of the molecular chains when being stretched will be higher, and the molecular chains will be less affected and restrained when shrinking when exposed to heat again. Therefore, under the same conditions, it can shrink more fully, which is manifested macroscopically as an increase in the thermal shrinkage rate of the film. DETAILED DESCRIPTION

[0019] Example 1

[0020] According to the weight parts, 30 parts of polypropylene (5020, the same below), 70 parts of linear low-density polyethylene (7042, the same below), 30 parts of SEBS (6150, the same below), 0.8 parts of antioxidant 1010, 1 part of lubricant magnesium stearate, 0.5 parts of anti-ultraviolet agent UV-531, 1 part of nucleating transparent agent dibenzylidene sorbitol, 1.5 parts of processing aid PPA (FX-5924), and 1.2 parts of anti-blocking agent talc were added to a high-speed mixer, mixed and stirred at 300 rpm for 10 minutes, then mixed and stirred at 900 rpm for 3 minutes, and then transferred to a twin-screw extruder for extrusion granulation. The temperatures of the twin-screw extruder zones were 140°C, 155°C, 175°C, 195°C, 205°C, 215°C, and 220°C, and the head temperature was 220°C. The obtained pellets are extruded and blown once by a single-layer film blowing machine at a melting section temperature of 215℃~225℃, and then cooled and shaped by a cooling water ring. The cooling water temperature in the cooling water ring is 12℃. The diameter of the film tube obtained after cooling and shaping is 350mm. The film tube is dehydrated and dried by the herringbone plate on the film blowing machine under traction drive. The film tube is preheated to 95℃ and then blown twice under traction drive, so that the transverse blowing stretching ratio of the hot film tube reaches 4.8 times, and the longitudinal traction stretching ratio reaches 5.2 times. The film tube obtained by the secondary blowing is then cooled by an air ring. The air ring cooling adopts the upward blowing method, specifically using a five-level air ring. The distance between each level of air ring is 6mm, and the angle between the air outlet of each air ring and the film tube is 15°. Among them, the air outlet from the first level to the fifth level is 2000m 3 / h、1800m 3 / h、1500m 3 / h、1000m 3 / h、600m 3 / h; the wind temperatures from the first to the fifth air ring are 25℃, 20℃, 12℃, 12℃, and 12℃ respectively; the film tube after air ring cooling is annealed at 70℃, then cooled at 15℃, the film tube is split open and flattened, and then trimmed and rolled to obtain a protective heat shrink film with a thickness of about 13μm.

[0021] Example 2

[0022] According to the weight parts, 35 parts of polypropylene, 65 parts of linear low-density polyethylene, 25 parts of SEBS, 0.5 parts of antioxidant 168, 1.5 parts of lubricant calcium stearate, 0.5 parts of anti-ultraviolet agent UV-531, 0.5 parts of nucleating transparent agent dibenzylidene sorbitol, 2 parts of processing aid PPA, and 1.5 parts of anti-blocking agent talc were added to a high-speed mixer, mixed and stirred at 300 rpm for 5 minutes, and then mixed and stirred at 1200 rpm for 1 minute, and then transferred to a twin-screw extruder for extrusion granulation. The temperatures of the twin-screw extruder zones were 145°C, 165°C, 180°C, 195°C, 200°C, 210°C, and 220°C, respectively, and the head temperature was 220°C. The obtained pellets were passed through a single-layer film blowing machine at a melting section temperature of 145°C. After extrusion and primary inflation at 220℃~230℃, the film is cooled and shaped by a cooling water ring. The cooling water temperature in the cooling water ring is 10℃. The diameter of the film tube obtained after cooling and shaping is 350mm. The film tube is driven by traction and then passes through the herringbone plate on the film blowing machine to achieve dehydration and drying. After that, the film tube is preheated to 90℃ and then continues to be inflated for the second time under traction drive, so that the transverse inflation stretching ratio of the hot film tube reaches 4.5 times, and the longitudinal traction stretching ratio reaches 5 times. Then, the film tube obtained by the secondary inflation is cooled by an air ring. The air ring cooling adopts the upward blowing method, specifically using a five-level air ring. The distance between each level of air ring is 6mm, and the angle between the air outlet of each air ring and the film tube is 15°. Among them, the air outlet from the first level to the fifth level is 2200m 3 / h、1700m 3 / h、1400m 3 / h、1000m 3 / h、700m 3 / h; the wind temperatures from the first to the fifth air rings are 20°C, 20°C, 15°C, 15°C, and 10°C respectively; the film tube after air ring cooling is annealed at 75°C, then cooled at 15°C, the film tube is split open and flattened, and then trimmed and rolled to obtain a protective heat shrink film with a thickness of about 14.5μm.

[0023] Comparative Example 1

[0024] No SEBS resin was added, and the missing SEBS resin was replaced by polypropylene and linear low-density polyethylene in the same proportion as in the raw material components. The remaining components and preparation process were the same as in Example 1:

[0025] According to the weight parts, 39 parts of polypropylene, 91 parts of linear low-density polyethylene, 0.8 parts of antioxidant 1010, 1 part of lubricant magnesium stearate, 0.5 parts of anti-ultraviolet agent UV-531, 1 part of nucleating transparent agent dibenzylidene sorbitol, 1.5 parts of processing aid PPA, and 1.2 parts of anti-blocking agent talc were added to a high-speed mixer, mixed and stirred at 300 rpm for 10 minutes, and then mixed and stirred at 900 rpm for 3 minutes, and then transferred to a twin-screw extruder for extrusion granulation. The temperatures of the twin-screw extruder zones were 140°C, 155°C, 175°C, 195°C, 205°C, 215°C, and 220°C, respectively, and the head temperature was 220°C. The obtained pellets were passed through a single-layer film blowing machine at a melting section temperature of 215°C to 2 After extrusion and one-time inflation at 25°C, the film is cooled and shaped through a cooling water ring. The cooling water temperature in the cooling water ring is 12°C. The diameter of the film tube obtained after cooling and shaping is 350mm. The film tube is driven by traction and then passes through the herringbone plate on the film blowing machine to achieve dehydration and drying. After that, the film tube is preheated to 95°C and then continues to be inflated for the second time under traction drive, so that the transverse inflation stretching ratio of the hot film tube reaches 4.8 times, and the longitudinal traction stretching ratio reaches 5.2 times. The film tube obtained by the secondary inflation is then cooled by an air ring. The air ring cooling adopts the upward blowing method, specifically using a five-level air ring. The distance between each level of air ring is 6mm, and the angle between the air outlet of each air ring and the film tube is 15°. Among them, the air outlet from the first level to the fifth level is 2000m 3 / h、1800m 3 / h、1500m 3 / h、1000m 3 / h、600m 3 / h; the wind temperatures from the first to the fifth air rings are 25°C, 20°C, 12°C, 12°C, and 12°C respectively; the film tube after air ring cooling is annealed at 70°C, then cooled at 15°C, the film tube is split open and flattened, and then trimmed and rolled to obtain a protective heat shrink film.

[0026] Comparative Example 2

[0027] "SEBS" was replaced with an equal amount of "polystyrene", and the remaining components and preparation process were the same as in Example 1:

[0028] According to the weight parts, 30 parts of polypropylene, 70 parts of linear low-density polyethylene, 30 parts of polystyrene (GON535 blown film grade), 0.8 parts of antioxidant 1010, 1 part of lubricant magnesium stearate, 0.5 parts of anti-ultraviolet agent UV-531, 1 part of nucleating transparent agent dibenzylidene sorbitol, 1.5 parts of processing aid PPA, and 1.2 parts of anti-blocking agent talc were added to a high-speed mixer, mixed and stirred at 300 rpm for 10 minutes, and then mixed and stirred at 900 rpm for 3 minutes, and then transferred to a twin-screw extruder for extrusion granulation. The temperatures of the twin-screw extruder zones were 140°C, 155°C, 175°C, 195°C, 205°C, 215°C, and 220°C, respectively, and the head temperature was 220°C. The obtained pellets were passed through a single-layer blown film machine at a melt After being extruded and blown once at a melting temperature of 215℃~225℃, the film is cooled and shaped by a cooling water ring. The cooling water temperature in the cooling water ring is 12℃. The diameter of the film tube obtained after cooling and shaping is 350mm. The film tube is driven by traction and then passes through the herringbone plate on the film blowing machine to achieve dehydration and drying. After that, the film tube is preheated to 95℃ and then blown twice under traction drive, so that the transverse blowing stretching ratio of the hot film tube reaches 4.8 times, and the longitudinal traction stretching ratio reaches 5.2 times. The film tube obtained by the secondary blowing is then cooled by an air ring. The air ring cooling adopts the upward blowing method, specifically using a five-level air ring. The distance between the air rings at each level is 6mm, and the angle between the air outlet of each air ring and the film tube is 15°. Among them, the air outlet from the first level to the fifth level is 2000m 3 / h、1800m 3 / h、1500m 3 / h、1000m 3 / h、600m 3 / h; the wind temperatures from the first to the fifth air rings are 25°C, 20°C, 12°C, 12°C, and 12°C respectively; the film tube after air ring cooling is annealed at 70°C, then cooled at 15°C, the film tube is split open and flattened, and then trimmed and rolled to obtain a protective heat shrink film.

[0029] control group

[0030] Comparative Example 1

[0031] Replace "polypropylene" with "polystyrene":

[0032] According to the weight parts, 20 parts of polystyrene (GON535 blown film grade, the same below), 80 parts of linear low-density polyethylene, 15 parts of SEBS, 1 part of antioxidant 1010, 1.8 parts of lubricant magnesium stearate, 0.5 parts of anti-ultraviolet agent UV-531, 0.5 parts of nucleating transparent agent dibenzylidene sorbitol, 2 parts of processing aid PPA, and 1.2 parts of anti-blocking agent talc were added to a high-speed mixer, mixed and stirred at 300 rpm for 10 minutes, and then mixed and stirred at 900 rpm for 3 minutes, and then transferred to a twin-screw extruder for extrusion granulation. The temperatures of the twin-screw extruder zones were 155°C, 170°C, 185°C, 200°C, 210°C, 215°C, and 220°C, respectively, and the head temperature was 220°C. The obtained pellets were subjected to single-layer blown film After the film is extruded and inflated once at a melting section temperature of 220℃~230℃, it is cooled and shaped through a cooling water ring. The cooling water temperature in the cooling water ring is 15℃. The diameter of the film tube obtained after cooling and shaping is 350mm. The film tube is driven by traction and then passes through the herringbone plate on the film blowing machine to achieve dehydration and drying. After that, the film tube is preheated to 105℃ and then continues to be inflated for the second time under traction drive, so that the transverse expansion and stretching ratio of the hot film tube reaches 4 times, and the longitudinal traction and stretching ratio reaches 6 times. Then, the film tube obtained by the secondary blowing is cooled by an air ring. The air ring cooling adopts the upward blowing method, specifically using a five-level air ring. The distance between each level of air ring is 5mm, and the angle between the air outlet of each air ring and the film tube is 15°. Among them, the air outlet from the first level to the fifth level is 2300m 3 / h、2000m 3 / h、1600m 3 / h、1200m 3 / h、800m 3 / h; the wind temperatures from the first to the fifth air rings are 25°C, 20°C, 18°C, 12°C, and 10°C respectively; the film tube after air ring cooling is annealed at 70°C, then cooled at 15°C, the film tube is split open and flattened, and then trimmed and rolled to obtain a protective heat shrink film.

[0033] Comparative Example 2

[0034] No SEBS resin was added, and polystyrene and linear low-density polyethylene in the same proportion as in the raw material components were used to replace the missing SEBS resin. The remaining components and preparation process were the same as those in Control Example 1:

[0035] According to the weight parts, 23 parts of polystyrene, 92 parts of linear low-density polyethylene, 1 part of antioxidant 1010, 1.8 parts of lubricant magnesium stearate, 0.5 parts of anti-ultraviolet agent UV-531, 0.5 parts of nucleating transparent agent dibenzylidene sorbitol, 2 parts of processing aid PPA, and 1.2 parts of anti-blocking agent talc were added to a high-speed mixer, mixed and stirred at 300 rpm for 10 minutes, and then mixed and stirred at 900 rpm for 3 minutes, and then transferred to a twin-screw extruder for extrusion granulation. The temperatures of the twin-screw extruder zones were 155°C, 170°C, 185°C, 200°C, 210°C, 215°C, and 220°C, respectively, and the head temperature was 220°C. The obtained pellets were passed through a single-layer film blowing machine at a melting section temperature of 220°C. After extrusion at 230℃ and one-time inflating, the film is cooled and shaped by a cooling water ring. The temperature of the cooling water in the cooling water ring is 15℃. The diameter of the film tube obtained after cooling and shaping is 350mm. The film tube is driven by traction and then passes through the herringbone plate on the film blowing machine to achieve dehydration and drying. After that, the film tube is preheated to 105℃ and then continues to be inflated for the second time under traction drive, so that the transverse inflating and stretching ratio of the hot film tube reaches 4 times, and the longitudinal traction and stretching ratio reaches 6 times. The film tube obtained by the secondary inflating is then cooled by an air ring. The air ring cooling adopts the upward blowing method, specifically using a five-level air ring. The distance between each level of air ring is 5mm, and the angle between the air outlet of each air ring and the film tube is 15°. Among them, the air outlet from the first level to the fifth level is 2300m 3 / h、2000m 3 / h、1600m 3 / h、1200m 3 / h、800m 3 / h; the wind temperatures from the first to the fifth air rings are 25°C, 20°C, 18°C, 12°C, and 10°C respectively; the film tube after air ring cooling is annealed at 70°C, then cooled at 15°C, the film tube is split open and flattened, and then trimmed and rolled to obtain a protective heat shrink film.

[0036] The heat shrinkable films prepared in the above embodiments, comparative embodiments, and control examples were tested for shrinkage in accordance with GB / T 13519-2016 (immersed in 140±2°C heat transfer oil for 20 seconds, removed, immediately placed in a room temperature cooling medium for 5 seconds, removed, and then left horizontally for 10 minutes before measurement. Three samples were tested and the average was calculated.) and tensile strength was tested in accordance with GB / T 1040.3-2006 (using type 2 specimens with a width of 15 mm, an initial distance between clamps of 100 mm, a test rate of 500±50 mm / min, and three samples were tested and the average was calculated. The specific results are shown in Table 1.

[0037] Table 1

[0038]

[0039] As shown in Table 1, while the heat-shrinkable film prepared in Comparative Example 1 already exhibited a considerable heat shrinkage rate, Example 1, representative of the present solution, further improved its heat shrinkage rate (by 24%) by introducing SEBS as an intervening agent. This is because the dispersed presence of SEBS in the shrinkable film in Example 1 reduced the interactions between the molecular chains of the matrix resins, linear low-density polyethylene and polypropylene, resulting in a higher degree of orientation of these chains during stretching and smoother orientation-induced shrinkage upon heating. While the mechanical strength of Example 1 was lower than that of Comparative Example 1 (the decrease was only approximately 15%), it still met the requirements for use. This confirms the analysis that "the heat-shrinkable film prepared in Example 1, representative of the present solution, exhibits reduced entanglement between molecular chains" and demonstrates the advantage that "while the interactions between molecular chains have a negative impact on the mechanical properties of the film after formation, their positive impact on heat shrinkage is significantly greater."

[0040] However, after intervention with pure polystyrene in Comparative Example 2, the shrinkage effect achieved by Example 1 was not achieved. This is because the polystyrene molecular chain does not contain a soft segment similar to EB (ethylene / butadiene) that is well compatible with the matrix resins polypropylene and linear low-density polyethylene. Therefore, the polystyrene segments cannot be effectively dispersed between the matrix resin molecular chains, resulting in the mutual entanglement between the matrix resin molecular chains not being effectively improved, and the added polystyrene is also significantly aggregated in the matrix resin. The mechanical properties of Comparative Example 2 are not only significantly lower than those of Comparative Example 1, but also significantly lower than those of Example 1, which represents this solution. This also indicates that the polystyrene added to Comparative Example 2 is not effectively dispersed in the matrix resin, but tends to aggregate, causing phase separation in the film-forming resin, which greatly affects the mechanical properties.

[0041] Furthermore, looking at the control groups, Control Example 2 is equivalent to a blank control, while Control Example 1 is equivalent to introducing SEBS for intervention on the basis of the blank control. However, the matrix resin that SEBS intervenes in in the control group is a mixture of polystyrene and linear low-density polyethylene. Originally, the compatibility between polystyrene and linear low-density polyethylene was not very ideal. There were interactions between the molecular chains of polystyrene itself and between the molecular chains of polyethylene itself, but the interactions between the polystyrene segments and the polyethylene segments were relatively weak. However, after the introduction of SEBS, the hard segments PS on SEBS were better compatible with and interacted with the polystyrene segments. At the same time, the elastic soft segments EB on SEBS were better compatible with and interacted with the linear low-density polyethylene segments. SEBS was now equivalent to a traditional compatibilizer that linked the polystyrene segments and the polyethylene segments. Ultimately, the overall interaction and entanglement between the molecular chains in the entire resin mixture increased, resulting in a decrease in shrinkage rather than an increase. This also shows from another aspect that SEBS is far from being a compatibilizer in this scheme. At the same time, when this scheme intervenes in the thermal shrinkage rate through SEBS, it also has stricter selection of the matrix resin composition.

Claims

1. A protective heat shrink film, characterized in that: The shrink film comprises, by weight, 100 parts of polyolefin, 25-40 parts of SEBS, 0.5-1 part of antioxidant, 0.5-1.5 parts of lubricant, 0.5-1 part of anti-ultraviolet agent, 0.5-1 part of nucleating transparent agent, and 1-3 parts of processing aid, wherein the polyolefin is a combination of polypropylene and linear low-density polyethylene in a mass ratio of 30-40:60-70.

2. The protective heat shrink film according to claim 1, wherein: The mass ratio of the polypropylene to the linear low-density polyethylene is 30:

70.

3. The protective heat shrink film according to claim 1, wherein: The lubricant includes one or a combination of barium stearate, calcium stearate, magnesium stearate, and silicone masterbatch.

4. A method for preparing a protective heat shrinkable film according to any one of claims 1 to 3, characterized in that: After the components are fully mixed, they are extruded into granules through a screw extruder. The obtained granules are extruded and blown once through a single-layer film blowing machine and then cooled and shaped to form a film tube. After the film tube is dried, it is preheated to 90°C to 120°C and then blown a second time under traction drive, so that the transverse blowing stretching ratio of the film tube reaches 4 to 6 times, and the longitudinal traction stretching ratio reaches 5 to 7 times. The film tube obtained by the second blowing is then subjected to air ring cooling treatment, annealing treatment, and then cooling.

5. The method for preparing a protective heat shrinkable film according to claim 4, wherein: After fully mixing the components, they are extruded into granules through a twin-screw extruder. The temperatures of the zones of the twin-screw extruder are 130°C to 145°C, 150°C to 165°C, 170°C to 180°C, 180°C to 195°C, 195°C to 205°C, 205°C to 215°C, and 210°C to 225°C, and the die temperature is 210°C to 225°C.

6. The method for preparing a protective heat shrinkable film according to claim 4, wherein: After the primary inflation, the pellets are passed through a cooling water ring to achieve cooling and shaping. The temperature of the cooling water in the cooling water ring is 10° C. to 15° C. The diameter of the membrane tube obtained after cooling and shaping is 200 mm to 500 mm.

7. The method for preparing a protective heat shrinkable film according to claim 4, wherein: The air ring cooling adopts the upward blowing method, specifically adopting a five-level air ring, the distance between the air rings at each level is 5-10mm, the angle between the air outlet of each air ring and the membrane tube is 10°-20°, wherein, from the first level air ring to the fifth level air ring, the air volume is 1500-2500m 3 / h, 1500~2000m 3 / h, 1000~2000m 3 / h, 500~1000m 3 / h, 500~800m 3 / h; from the first-level air ring to the fifth-level air ring, the air temperature is 15℃~25℃, 10℃~20℃, 10℃~15℃, 10℃~15℃, and 10℃~15℃ respectively.

8. The method for preparing a protective heat shrinkable film according to claim 4, wherein: The temperature of the annealing treatment is 65° C. to 80° C., and the temperature of the cooling performed after the annealing treatment is 15° C. to 25° C.

9. The method for preparing a protective heat shrinkable film according to claim 4, wherein: After the annealing treatment and the cooling treatment, the film tube is split open and flattened, and then trimmed and rolled up. The thickness of the protective heat shrinkable film obtained after flattening is 10 μm to 20 μm.

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