Flexible PP particles for cold laminating film and preparation method of flexible PP particles

Abstract

The invention discloses flexible PP particles for a cold laminating film and a preparation method of the flexible PP particles, and relates to the technical field of cold laminating films.The flexible PP particles for the cold laminating film comprise, by weight, 80-85 parts of film-grade homo-polypropylene; 5 to 8 parts of an ethylene-propylene block copolymer; 3 to 5 parts of a hydrogenated styrene-isoprene-styrene block copolymer; 2 to 4 parts of ethylene-vinyl acetate copolymer; 0.5 to 1.0 part of polyether modified siloxane; 0.2 to 0.4 part of a sorbitol transparent nucleating agent; 0.3 to 0.6 part of a composite antioxidant; 0.4 to 0.7 part of a composite light stabilizer; and 2-4 parts of an alkyl-terminated hyperbranched poly-alpha-olefin flexible modifier, wherein the composite antioxidant comprises a main antioxidant and an auxiliary antioxidant. According to the invention, the problems of edge warping, blistering, poor mounting compliance, insufficient flexibility and poor crimpness during cold mounting of the traditional cold mounting film base material are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cold laminating film, in particular to a flexible PP particle for cold laminating film and a preparation method thereof. BACKGROUND

[0002] The cold laminating film is a kind of film material for image protection and surface decoration, which is usually composed of a transparent substrate layer and a self-adhesive layer, and is attached to the surface of an object by applying pressure without heating. The cold laminating film is widely used for the protection and decoration of printed products, advertising materials and posters, etc. The existing cold laminating film substrate still has some shortcomings.

[0003] The patent for invention with publication number CN108178885B discloses a raw material composition and a cold laminating film. The raw material composition includes 100 parts of PVC and 20-38 parts of plasticizer. The polymerization degree of PVC is 700-950. Since the raw material composition includes 100 parts of PVC and 20-38 parts of plasticizer by weight, and the polymerization degree of PVC is 700-950, the plasticizing effect of the cold laminating film is improved by using the PVC with the above polymerization degree, the phenomenon of uneven surface of the cold laminating film is reduced, and thus the prepared cold laminating film can have excellent surface spraying effect.

[0004] Although the above-mentioned raw material of the cold laminating film can improve the spraying effect, the existing cold laminating film substrate is mainly PVC film, ordinary BOPP or modified material added with POE, EVA and plasticizer. However, such substrate still has some defects. The ordinary PP or BOPP film has high crystallinity and strong rigidity, but is prone to edge lifting and bubbling during cold laminating, and has poor laminating compliance and flexibility. It is easy to be brittle and yellow in outdoor sunlight, hot and humid and oxidizing environment, resulting in discoloration of the advertising picture, and insufficient weather resistance and ultraviolet resistance. In addition, the surface lubricity and light transmittance of the existing substrate are not good. After adding plasticizer or non-compatible copolymer, it is easy to separate or produce haze, which affects the picture clarity. The traditional cold laminating film still relies on PVC and o-phenyl plasticizer, which releases harmful gases after burning or aging, and has poor environmental performance. SUMMARY

[0005] The present application aims to solve the problems of the traditional cold laminating film substrate, such as edge lifting and bubbling during cold laminating, poor laminating compliance, insufficient flexibility and poor curling, and provides a flexible PP particle for cold laminating film and a preparation method thereof.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a flexible PP particle for cold laminating film, which comprises the following components by weight fraction: 80-85 parts of film grade homopolymer polypropylene; 5-8 parts of ethylene-propylene block copolymer; Hydrogenated styrene-isoprene-styrene block copolymer 3-5 parts; Ethylene-vinyl acetate copolymer 2-4 parts; Polyether modified siloxane 0.5-1.0 parts; Sorbitol transparent nucleating agent 0.2-0.4 parts; Composite antioxidant 0.3-0.6 parts; Composite light stabilizer 0.4-0.7 parts; End alkyl terminated hyperbranched poly-alpha-olefin flexible modifier 2-4 parts.

[0007] As a further scheme of the present application: the composite antioxidant comprises a primary antioxidant and a secondary antioxidant.

[0008] As a further scheme of the present application: the primary antioxidant comprises n-octadecyl beta-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and the secondary antioxidant comprises tris(2,4-di-tert-butylphenyl) phosphite, and the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1-1:2.

[0009] As a further scheme of the present application: the composite light stabilizer comprises an ultraviolet absorber and a hindered amine light stabilizer.

[0010] As a further scheme of the present application: the ultraviolet absorber is 2-(2'-hydroxy-3',5'-di-tert-amylphenyl) benzotriazole, and the hindered amine light stabilizer is bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and the mass ratio of the ultraviolet absorber to the hindered amine light stabilizer is 1:1-1:1.5.

[0011] As a further scheme of the present application: the melt flow rate (230℃, 2.16kg) of the film grade homopolymer polypropylene is 2.0-3.5 g / 10min, the mass content of ethylene units in the ethylene-propylene block copolymer is 5%-8%, and the styrene content of the hydrogenated styrene-isoprene-styrene block copolymer is 15%-25%.

[0012] As a further scheme of the present application: the mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 18%-28%, and the kinematic viscosity of the polyether modified siloxane at 25℃ is 500-1500 cSt.

[0013] As a further scheme of the present application: the main chain and the branch chain of the end alkyl terminated hyperbranched poly-alpha-olefin flexible modifier are composed of C8-C12 alpha-olefin units, the terminal end capping group is C14-C20 linear alkyl, the number average molecular weight is 1000-5000 g / mol, and the flexible modifier forms a uniformly dispersed flexible nanospheric phase structure in the polypropylene matrix.

[0014] The application discloses a preparation method of flexible PP particles for cold laminating film. S1: premixing, taking film-grade homopolypropylene, ethylene-propylene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, sorbitol transparent nucleating agent, composite antioxidant, composite light stabilizer and end alkyl-terminated hyperbranched poly-alpha-olefin flexible modifier according to the weight fractions, and feeding into a mixing device to mix for 5-10 min to obtain a mixed material A; S2: side injection and extrusion granulation, feeding the mixed material A into a double-screw extruder through a main feeding port; meanwhile, feeding the polyether-modified siloxane with the weight fraction into the double-screw extruder through a side liquid injection pump at a melting section; after melting blending, extrusion, drawing, cooling and granulation, a primary particle is obtained; S3: drying and packaging, drying the primary particle, vacuum packaging after drying treatment, and obtaining a finished product of the flexible PP particle for cold laminating film.

[0015] As a further scheme of the application, the processing temperature of the double-screw extruder is set as follows: the temperature of a first zone is 150-160 DEG C, the temperature of a second zone is 170-180 DEG C, the temperature of a third zone is 180-190 DEG C, the temperature of a fourth zone is 190-200 DEG C, the temperature of a fifth zone is 195-205 DEG C, and the temperature of a die head is 190-195 DEG C; the screw rotation speed is 250-350 rpm; the cooling mode in S2 is water tank cooling; and the primary particle is blow-dried at 80-90 DEG C for 2-4 h.

[0016] Compared with the prior art, the application has the following beneficial effects: 1. The hydrogenated styrene-isoprene-styrene block copolymer and the ethylene-vinyl acetate copolymer are used to form a composite flexible system, which cooperates with the polypropylene matrix, effectively reduces the material rigidity and crystallinity, significantly improves the flexibility, curling compliance and laminating performance of the film, and solves the edge warping and blistering problems of the traditional BOPP film caused by excessive rigidity; the composite stabilizing system composed of specific primary and secondary antioxidants and ultraviolet absorber-hindered amine light stabilizer realizes efficient synergistic thermal-oxidative aging and light aging effects, improves the long-term weather resistance of the material under outdoor humid heat, oxidation and ultraviolet radiation, and effectively inhibits the embrittlement, yellowing and picture fading phenomena; 2、By introducing polyether modified siloxane and using side injection process, it ensures the formation of a persistent lubricating layer on the surface of the film, greatly improves the surface smoothness, and ensures the smooth processing of cold laminating; by selecting sorbitol transparent nucleating agent and cooperating with excellent compatibility elastomer, it realizes toughening while significantly reducing haze, ensuring high light transmittance and clearness of the film, the present application does not use PVC and o-benzene plasticizer, all components are environmentally friendly polyolefin materials and non-toxic additives, solving the problem of harmful gas release during burning or aging of traditional materials, having excellent environmental performance.

[0017] 3、The introduced end alkyl terminated hyperbranched polyalphaolefin (HB-PAO) can be compatible with the polypropylene molecular chain, reduce the crystallinity, improve the melt flowability and flexibility, make the cold laminating film have higher light transmittance and anti-brittle cracking performance, further enhance the anti-aging ability of the material, and at the same time, do not contain halogen and plasticizer, improve the comprehensive performance and environmental protection of the material. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0019] Embodiment 1: A flexible PP particle for cold laminating film, comprising the following components in parts by weight: Film grade homopolymer polypropylene 82 parts; Ethylene-propylene block copolymer 6.8 parts; Hydrogenated styrene-isoprene-styrene block copolymer 3 parts; Ethylene-vinyl acetate copolymer 2 parts; Polyether modified siloxane 1 part; Sorbitol transparent nucleating agent 0.2 parts; Composite antioxidant 0.3 parts; Composite light stabilizer 0.7 parts; End alkyl terminated hyperbranched polyalphaolefin flexible modifier 4 parts.

[0020] The composite antioxidant comprises a primary antioxidant and a secondary antioxidant.

[0021] The primary antioxidant comprises beta-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate, and the secondary antioxidant comprises tris(2,4-di-tert-butylphenyl) phosphite, and the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1.

[0022] The composite light stabilizer comprises an ultraviolet absorber and a hindered amine light stabilizer.

[0023] The ultraviolet absorber is 2-(2'-hydroxy-3',5'-di-tert-amylphenyl)benzotriazole, the hindered amine light stabilizer is bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and the mass ratio of the ultraviolet absorber to the hindered amine light stabilizer is 1:1.

[0024] The melt flow rate (230℃, 2.16kg) of the film grade homopolymer polypropylene is 2.0-3.5g / 10min, the mass content of ethylene units in the ethylene-propylene block copolymer is 5%, and the styrene content of the hydrogenated styrene-isoprene-styrene block copolymer is 15%.

[0025] The mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 18%, and the kinematic viscosity of the polyether-modified siloxane at 25℃ is 500cSt.

[0026] The main chain and the branch chain of the end alkyl-terminated hyperbranched polyalpha-olefin flexible modifier are composed of C8-C12 alpha-olefin units, the terminal end capping group is a C14-C20 linear alkyl group, the number average molecular weight is 1000g / mol, and the flexible modifier forms a uniformly dispersed flexible nanospherical phase structure in the polypropylene matrix.

[0027] The preparation method of the flexible PP granules for cold laminating film in the embodiment comprises the following steps: S1: premixing, taking the film grade homopolymer polypropylene, the ethylene-propylene block copolymer, the hydrogenated styrene-isoprene-styrene block copolymer, the ethylene-vinyl acetate copolymer, the sorbitol transparent nucleating agent, the composite antioxidant, the composite light stabilizer and the end alkyl-terminated hyperbranched polyalpha-olefin flexible modifier by weight parts, and feeding them into a mixing device for mixing for 5min to obtain a mixed material A; S2: side injection and extrusion granulation, feeding the mixed material A into a twin-screw extruder through a main feeding port; at the same time, feeding the polyether-modified siloxane by weight parts into the twin-screw extruder through a side liquid injection pump at a melting section; and after melting blending, extrusion, drawing, cooling and granulation, obtaining primary granules; S3: drying and packaging, drying the primary granules, vacuum packaging after drying treatment, and obtaining the finished product of the flexible PP granules for cold laminating film.

[0028] The processing temperature of the twin-screw extruder is set as follows: the temperature of zone 1 is 150℃, the temperature of zone 2 is 170℃, the temperature of zone 3 is 180℃, the temperature of zone 4 is 190℃, the temperature of zone 5 is 195℃, and the temperature of the die head is 190℃; the screw rotation speed is 250rpm, the cooling mode in S2 is water tank cooling, and the primary granules are air-dried at 80℃ for 2h.

[0029] The flexible PP particles for cold lamination film prepared in Example 1 were used to prepare a 25 μm thick film by a cast molding process, and the performance test results are shown in the following table: Comparative Example 1 A PP particle for cold lamination film, which has the same components as Example 1 but does not add the end alkyl-terminated hyperbranched polyalpha-olefin flexible modifier, and the other conditions are the same as Example 1. The preparation method is the same as Example 1. The PP particles for cold lamination film prepared in Comparative Example 1 were used to prepare a 25 μm thick film by a cast molding process, and the performance test results are shown in the following table: Comparative Example 1 does not add the end alkyl-terminated hyperbranched polyalpha-olefin flexible modifier, which leads to a decrease in film elongation at break, a decrease in impact resistance, a slight decrease in light transmittance, an increase in haze, an increase in yellowing index, a decrease in strength retention rate, and a deterioration in low-temperature bending performance, proving that the end alkyl-terminated hyperbranched polyalpha-olefin flexible modifier plays a key role in improving the comprehensive performance of the film.

[0030] Example 2 A flexible PP particle for cold lamination film, which includes the following components in parts by weight: 80 parts of film-grade homopolymer polypropylene; 7 parts of ethylene-propylene block copolymer; 4 parts of hydrogenated styrene-isoprene-styrene block copolymer; 3 parts of ethylene-vinyl acetate copolymer; 0.8 parts of polyether-modified siloxane; 0.3 parts of sorbitol-based transparent nucleating agent; 0.5 parts of composite antioxidant; 0.4 parts of composite light stabilizer; 4 parts of end alkyl-terminated hyperbranched polyalpha-olefin flexible modifier.

[0031] The composite antioxidant includes a primary antioxidant and a secondary antioxidant.

[0032] The primary antioxidant includes n-octadecanol β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and the secondary antioxidant includes tris(2,4-di-tert-butylphenyl) phosphite. The mass ratio of the primary antioxidant to the secondary antioxidant is 1:2.

[0033] The composite light stabilizer includes an ultraviolet absorber and a hindered amine light stabilizer.

[0034] The ultraviolet absorber is 2-(2'-hydroxy-3',5'-di-tert-amylphenyl) benzotriazole, the hindered amine light stabilizer is bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and the mass ratio of the ultraviolet absorber to the hindered amine light stabilizer is 1:1.5.

[0035] The melt flow rate (230℃, 2.16kg) of the film grade homopolymer polypropylene is 3.5g / 10min, the mass content of ethylene units in the ethylene-propylene block copolymer is 8%, and the styrene content of the hydrogenated styrene-isoprene-styrene block copolymer is 25%.

[0036] The mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 28%, and the kinematic viscosity of the polyether-modified siloxane at 25℃ is 1500cSt.

[0037] The main chain and the branch chain of the end alkyl-terminated hyperbranched poly-α-olefin flexible modifier are composed of C8-C12 α-olefin units, the terminal end capping group is a C14-C20 linear alkyl group, the number average molecular weight is 5000g / mol, and the flexible modifier forms a uniformly dispersed flexible nanospherical phase structure in the polypropylene matrix.

[0038] The preparation method of the flexible PP granules for cold laminating film in the embodiment includes the following steps: S1: premixing, taking the film grade homopolymer polypropylene, the ethylene-propylene block copolymer, the hydrogenated styrene-isoprene-styrene block copolymer, the ethylene-vinyl acetate copolymer, the sorbitol transparent nucleating agent, the composite antioxidant, the composite light stabilizer, and the end alkyl-terminated hyperbranched poly-α-olefin flexible modifier by weight parts, and feeding them into a mixing device to mix for 10min to obtain a mixed material A; S2: side injection and extrusion granulation, feeding the mixed material A into a twin-screw extruder through a main feeding port; at the same time, feeding the polyether-modified siloxane by weight parts into the twin-screw extruder through a side liquid injection pump at a melting section; and after melting blending, extrusion, drawing, cooling, and granulation, obtaining primary granules; S3: drying and packaging, drying the primary granules, vacuum packaging after drying treatment, and obtaining the finished product of the flexible PP granules for cold laminating film.

[0039] The processing temperature of the twin-screw extruder is set as follows: the temperature of zone 1 is 160℃, the temperature of zone 2 is 180℃, the temperature of zone 3 is 190℃, the temperature of zone 4 is 200℃, the temperature of zone 5 is 205℃, and the temperature of the die head is 195℃; the screw rotation speed is 350rpm, the cooling mode in S2 is water tank cooling, and the primary granules are air-dried at 90℃ for 4h.

[0040] The flexible PP granules for cold laminating film prepared in Example 2 are used to prepare a 25μm thick film through a flow casting process, and the performance test results are shown in the following table: Comparative Example 2: A kind of PP granules for cold lamination film, its components are the same as example 2, but no end alkyl capped hyperbranched poly-alpha-olefin flexible modifier is added, and the rest conditions are the same as example 2.The preparation method is the same as example 2.The PP granules for cold lamination film prepared by comparative example 2, a 25 μm thick film is prepared by a flow forming process, and the performance test results are shown in the following table: Comparative example 2 compared with example 2, no end alkyl capped hyperbranched poly-alpha-olefin flexible modifier is added, which leads to the decrease of film elongation at break, impact resistance, the slight decrease of light transmittance, the increase of haze, the increase of yellow index, the decrease of strength retention rate, and the deterioration of low temperature bending performance, which proves that the end alkyl capped hyperbranched poly-alpha-olefin flexible modifier plays a key role in improving the comprehensive performance of the film.

[0041] Example 3: A kind of flexible PP granules for cold lamination film, which comprises the following components in weight fraction: Film grade homopolymer polypropylene 82.7 parts; Ethylene-propylene block copolymer 6.5 parts; Hydrogenated styrene-isoprene-styrene block copolymer 4 parts; Ethylene-vinyl acetate copolymer 3 parts; Polyether modified siloxane 0.6 parts; Transparent nucleating agent of sorbitol 0.3 parts; Composite antioxidant 0.4 parts; Composite light stabilizer 0.5 parts; End alkyl capped hyperbranched poly-alpha-olefin flexible modifier 2 parts.

[0042] The composite antioxidant includes a primary antioxidant and a secondary antioxidant.

[0043] The primary antioxidant includes n-octadecanol β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, and the secondary antioxidant includes tris(2,4-di-tert-butylphenyl) phosphite, and the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1.

[0044] The composite light stabilizer includes an ultraviolet absorber and a hindered amine light stabilizer.

[0045] The ultraviolet absorber is 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl) benzotriazole, and the hindered amine light stabilizer is bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and the mass ratio of the ultraviolet absorber to the hindered amine light stabilizer is 1:1.3.

[0046] The melt flow rate (230℃, 2.16kg) of the film grade homopolymer polypropylene is 3g / 10min, the mass content of ethylene units in the ethylene-propylene block copolymer is 7%, and the styrene content of the hydrogenated styrene-isoprene-styrene block copolymer is 20%.

[0047] The mass content of vinyl acetate in the ethylene-vinyl acetate copolymer is 23%, and the kinematic viscosity of the polyether-modified siloxane at 25℃ is 1000cSt.

[0048] The main chain and branch chain of the end alkyl-terminated hyperbranched poly-α-olefin flexible modifier are composed of C8-C12 α-olefin units, the terminal end capping group is C14-C20 linear alkyl, the number average molecular weight is 3500g / mol, and the flexible modifier forms a uniformly dispersed flexible nanospherical phase structure in the polypropylene matrix.

[0049] The preparation method of the flexible PP granules for cold laminating film in the embodiment comprises the following steps: S1: premixing, taking the film grade homopolymer polypropylene, ethylene-propylene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, sorbitol transparent nucleating agent, composite antioxidant, composite light stabilizer and end alkyl-terminated hyperbranched poly-α-olefin flexible modifier by weight fraction, feeding into the mixing equipment for mixing for 7min to obtain the mixed material A; S2: side injection and extrusion granulation, feeding the mixed material A into the twin-screw extruder through the main feeding port; at the same time, feeding the polyether-modified siloxane by weight fraction into the melt section of the twin-screw extruder through the side liquid injection pump; after melt blending, extrusion, drawing, cooling and granulation, the primary granules are obtained; S3: drying and packaging, drying the primary granules, vacuum packaging after drying treatment, and obtaining the finished product of the flexible PP granules for cold laminating film.

[0050] The processing temperature of the twin-screw extruder is set as follows: the temperature of zone 1 is 155℃, the temperature of zone 2 is 175℃, the temperature of zone 3 is 185℃, the temperature of zone 4 is 195℃, the temperature of zone 5 is 200℃, and the temperature of the die head is 193℃; the screw rotation speed is 300rpm, the cooling method in S2 is water tank cooling, and the primary granules are air-dried at 85℃ for 3h.

[0051] The flexible PP granules for cold laminating film prepared in Example 3 are used to prepare a 25μm thick film by a flow casting process, and the performance test results are shown in the following table: Comparative Example 3: A kind of PP granules for cold laminating film, its components are the same as example 3, but no end alkyl capped hyperbranched poly-alpha-olefin flexible modifier is added, and the rest conditions are the same as example 3.The preparation method is the same as example 3.The PP granules for cold laminating film prepared by comparative example 3 are made into 25 μm thick film by a flow forming process, and the performance test results are shown in the following table: Comparative example 3 compared with example 3, no end alkyl capped hyperbranched poly-alpha-olefin flexible modifier is added, the elongation at break of the film decreases, the impact resistance decreases, the light transmittance decreases slightly, the haze increases, the yellow index increases, the strength retention rate decreases, and the low temperature bending performance deteriorates, which proves that the end alkyl capped hyperbranched poly-alpha-olefin flexible modifier plays a key role in improving the comprehensive performance of the film.

[0052] It should be noted that the flexible modifier forms a uniformly dispersed flexible nanosphere phase structure in the polypropylene matrix, which is used to reduce the crystallinity of polypropylene and increase the elongation at break and light transmittance of the film; the twin-screw extruder is set from near the feed port to near the machine head discharge port in the direction of material advancement as follows: Zone 1 temperature: 150-160℃, this zone is a solid conveying zone, low temperature prevents material from prematurely melting and clogging the feed; Zone 2 temperature: 170-180℃, this zone is a compression section, the temperature is raised, and the material begins to melt; Zone 3 temperature: 180-190℃, this zone is a melting section, the material is completely plasticized, and it is a key area for side injection and mixing; Zone 4 temperature: 190-200℃, this zone is a homogenization and metering section, to ensure further homogenization of the melt and establish pressure; Zone 5 temperature: 195-205℃, this zone is a high temperature purification section, to ensure the flowability of the melt and prevent the accumulation of deteriorated materials; Die temperature: 190-195℃, this zone connects the mold, the temperature is slightly reduced, which is beneficial to the setting of the extruded strip.

[0053] The above is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can make equivalent substitutions or changes within the technical scope disclosed by the present application according to the technical solution and inventive concept of the present application, which should be covered within the protection scope of the present application.

Claims

1. A type of flexible PP granules for cold lamination film, characterized in that, It comprises the following components in parts by weight: 80-85 parts of membrane-grade homopolymer polypropylene; 5-8 parts of ethylene-propylene block copolymer; 3-5 parts of hydrogenated styrene-isoprene-styrene block copolymer; 2-4 parts of ethylene-vinyl acetate copolymer; 0.5-1.0 parts of polyether-modified siloxane; Sorbitol-based transparent nucleating agent, 0.2-0.4 parts; 0.3-0.6 parts of compound antioxidant; 0.4-0.7 parts of composite light stabilizer; 2-4 parts of alkyl-terminated hyperbranched polyα-olefin flexible modifier.

2. The flexible PP granules for cold lamination film according to claim 1, characterized in that, The composite antioxidant includes a primary antioxidant and a secondary antioxidant.

3. The flexible PP granules for cold lamination film according to claim 2, characterized in that, The primary antioxidant includes β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester, and the secondary antioxidant includes tris(2,4-di-tert-butylphenyl) phosphite, wherein the mass ratio of the primary antioxidant to the secondary antioxidant is 1:1 to 1:

2.

4. The flexible PP granules for cold lamination film according to claim 1, characterized in that, The composite light stabilizer includes an ultraviolet absorber and a hindered amine light stabilizer.

5. The flexible PP granules for cold lamination film according to claim 4, characterized in that, The ultraviolet absorber is 2-(2'-hydroxy-3',5'-di-tert-pentylphenyl)benzotriazole, the hindered amine light stabilizer is bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, and the mass ratio of the ultraviolet absorber to the hindered amine light stabilizer is 1:1 to 1:1.

5.

6. The flexible PP granules for cold lamination film according to claim 1, characterized in that, The melt flow rate (230℃, 2.16kg) of the film-grade homopolymer polypropylene is 2.0-3.5g / 10min, the mass content of ethylene units in the ethylene-propylene block copolymer is 5%-8%, and the styrene content of the hydrogenated styrene-isoprene-styrene block copolymer is 15%-25%.

7. The flexible PP granules for cold lamination film according to claim 1, characterized in that, The vinyl acetate content in the ethylene-vinyl acetate copolymer is 18%-28% by mass, and the kinematic viscosity of the polyether-modified siloxane at 25°C is 500-1500 cSt.

8. The flexible PP granules for cold lamination film according to claim 1, characterized in that, The main chain and branches of the alkyl-terminated hyperbranched polyα-olefin flexible modifier are composed of C8-C12 α-olefin units, and the end-capping group is a C14–C20 straight-chain alkyl group with a number average molecular weight of 1000-5000 g / mol. The flexible modifier forms a uniformly dispersed flexible nanosphere phase structure in the polypropylene matrix.

9. A method for preparing flexible PP particles for cold lamination film as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1: Premixing: Take the following components by weight: film-grade homopolymer polypropylene, ethylene-propylene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, sorbitol-based transparent nucleating agent, composite antioxidant, composite light stabilizer, and alkyl-terminated hyperbranched polyα-olefin flexible modifier, and mix them in a mixing device for 5-10 minutes to obtain mixture A; S2: Side-line injection and extrusion granulation: The mixture A is fed into the twin-screw extruder through the main feed port; simultaneously, the weight proportion of polyether-modified siloxane is injected into the melting section of the twin-screw extruder through a side-line liquid injection pump; after melt blending, extrusion, stranding, cooling and pelletizing, primary granules are obtained; S3: Drying and packaging: The primary particles are dried and then vacuum-sealed to obtain the finished flexible PP particles for cold lamination film.

10. The method for preparing flexible PP particles for cold lamination film according to claim 9, characterized in that, The processing temperature settings of the twin-screw extruder are as follows: Zone 1 temperature 150-160℃, Zone 2 temperature 170-180℃, Zone 3 temperature 180-190℃, Zone 4 temperature 190-200℃, Zone 5 temperature 195-205℃, and die head temperature 190-195℃; the screw speed is 250-350 rpm; the cooling method in S2 is water tank cooling; and the primary particles are dried by forced air at 80-90℃ for 2-4 hours.

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