A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength

Abstract

This invention provides a method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, belonging to the field of polymer material processing technology. The uniaxially stretched polypropylene film has a three-layer structure. The upper and lower layers are composed of a mixture of homopolymer polypropylene, anti-blocking masterbatch, and slip masterbatch. The middle layer is composed of homopolymer polypropylene, block copolymer polypropylene, olefin elastomer, linear low-density polyethylene, thermoplastic elastomer, dynamically vulcanized rubber, polylactic acid graft polymer, polyethylene glycol graft polymer, and modified silica nanosheets. Compared to existing production technologies, this method improves the tear resistance of the film by introducing elastomer and compatibilizer components into the middle layer. Furthermore, post-treatment through secondary calendering and shaping processes enhances the transverse orientation of the polymer molecular chains, thereby significantly improving the tear strength of the film in the transverse direction.

Description

Technical Field

[0001] This invention belongs to the field of polymer material processing technology, specifically relating to a method for preparing a uniaxially stretched polypropylene film with high transverse tear strength. Background Technology

[0002] With increasing global awareness of environmental protection, the upgrading of packaging materials has gradually become an industry consensus, with single-material packaging becoming the dominant trend. Uniaxially oriented polypropylene (OOP) film, due to its excellent longitudinal tensile strength and stiffness, is widely used in packaging, electronics, agriculture, building decoration, and daily necessities. Its high transparency and excellent optical properties give it significant advantages in food packaging, labeling, and printing. Furthermore, the good chemical resistance and moisture resistance of OOP film ensure stable performance in various environments.

[0003] While uniaxially oriented polypropylene (OOP) film exhibits extremely high tensile strength in the longitudinal direction, giving it a significant advantage in applications such as handles, its tear strength in the transverse direction is relatively low. This low tear strength makes the film prone to splitting in the transverse direction when subjected to lateral external forces. This performance defect not only directly affects the service life and reliability of OOP film, but also shows significant insufficient toughness when used in combination with biaxially oriented films or cast films, leading to easy tearing in practical applications. Specifically, this performance deficiency mainly stems from the combined effects of multiple factors, including raw material selection, formulation design, and manufacturing processes. The combined effect of these factors limits the widespread application of OOP film in certain packaging fields. To overcome these limitations, future research needs to systematically explore material selection, formulation optimization, and process improvement to enhance the transverse tear strength and overall performance of OOP film, thereby expanding its application range.

[0004] This invention aims to address the aforementioned shortcomings of existing uniaxially stretched polypropylene films. By selecting polypropylene raw materials with special structures and adding rubber elastomers, polyolefin elastomers, and solubilizers to the formulation, the transverse tear strength of the film is improved. Without reducing the longitudinal tensile strength of the product, the tear resistance of the film in the transverse direction is significantly enhanced by adjusting the proportion of elastomer materials and controlling the distribution of the material's microstructure. Summary of the Invention

[0005] This invention provides a method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, belonging to the field of polymer material processing technology. The uniaxially stretched polypropylene film has a three-layer structure. The upper and lower layers are composed of a mixture of homopolymer polypropylene, anti-blocking masterbatch, and slip masterbatch. The middle layer is composed of homopolymer polypropylene, block copolymer polypropylene, olefin elastomer, linear low-density polyethylene, thermoplastic elastomer, dynamically vulcanized rubber, polylactic acid graft polymer, polyethylene glycol graft polymer, and modified silica nanosheets. The film is then calendered and shaped using a dedicated calendering machine. Compared to existing production technologies, this method improves the tear resistance of the film by introducing elastomer and compatibilizer components into the middle layer. Furthermore, the secondary calendering and shaping post-treatment enhances the transverse orientation of the polymer molecular chains, thereby significantly improving the tear strength of the film in the transverse direction.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, the method comprising the following steps:

[0008] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0009] (2) The upper surface polymer melt, the middle layer polymer melt, and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller, and form a film after cooling.

[0010] (3) The diaphragm enters the uniaxial stretching unit and is stretched 4-6 times in the longitudinal direction to obtain the first film;

[0011] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0012] (5) The uniaxially stretched polypropylene film is processed by calendering equipment, cooled and then wound up to obtain a uniaxially stretched polypropylene film with high transverse tear strength.

[0013] Furthermore, the uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, wherein the raw materials for the upper surface layer and the lower surface layer each comprise the following components in parts by weight:

[0014] 88-97 parts of homopolymer polypropylene

[0015] 3-10 parts of anti-blocking masterbatch

[0016] 1-2 parts of smooth masterbatch.

[0017] Furthermore, the intermediate layer raw material comprises the following components in parts by weight:

[0018]

[0019] Furthermore, the isotacticity of the homopolymer polypropylene is greater than 97.

[0020] As a preferred embodiment of the present invention, the method for preparing the polylactic acid grafted polymer is as follows:

[0021] Polylactic acid and initiator azobisisobutyronitrile are dissolved in dichloromethane, and homopolymer polypropylene is added and mixed evenly. After stirring at 70-100℃ for 1-4 hours, the polylactic acid grafted polymer is obtained by cooling, washing, filtering and drying.

[0022] As a preferred embodiment of the present invention, the method for preparing the polyethylene glycol graft polymer is as follows:

[0023] Polyethylene glycol and an initiator are dissolved in toluene, and homopolymer polypropylene is added and mixed evenly. After stirring at 70-100℃ for 1-4 hours, the polyethylene glycol grafted polymer is obtained by cooling, washing, filtering and drying.

[0024] As a preferred embodiment of the present invention, the method for preparing the modified silica nanosheets is as follows:

[0025] Silica nanosheets were dispersed in ethanol or deionized water and sonicated for 30 minutes. Surface modifier 3-aminopropyltriethoxysilane was added, and the mixture was heated to 60-100℃ and stirred for 1-4 hours. Modified silica nanosheets were obtained by filtration, washing, and drying.

[0026] Further, in step (1), the temperature of the high-temperature melting of the mixture is 240-260℃; in step (2), the temperature of the co-extrusion die is 220-240℃; and the temperature of the quenching roller is 25-55℃. In step (3), the temperature of the stretching is 80-110℃. In step (4), the voltage of the corona treatment unit is 10-20kV, the frequency is 20-30kHz, and the traction speed is 50-200m / min. In step (5), the temperature of the calendering equipment is 100-150℃, and the calendering pressure is 10-50MPa.

[0027] Further, the calendering equipment in step (5) has two calendering rollers with independent temperature control. The calendering equipment is equipped with two unwinding frames and two winding frames, which are the high-temperature resistant PET release film unwinding frame and the uniaxial stretch polypropylene film unwinding frame and winding frame, respectively. By unwinding through the unwinding frame, the two different films are bonded together and pass through the calendering equipment at the same time. One side of the uniaxial stretch polypropylene film is bonded to the heating roller, and the other side is bonded to the release surface of the high-temperature resistant PET release film. The temperature of the heating roller in contact with the polypropylene film is 110-130℃, and the temperature of the heating roller in contact with the PET surface of the high-temperature resistant PET release film is 130-150℃.

[0028] Furthermore, the thickness of the high transverse tear strength uniaxially stretched polypropylene film after processing by the calendering equipment in step (5) is 85-95% of the thickness of its original uniaxially stretched polypropylene film.

[0029] Furthermore, the anti-blocking masterbatch is at least one of silica, talc, stearamide, and polypropylene wax.

[0030] Furthermore, the initiator used in the preparation process of the polyethylene glycol graft polymer is benzoyl peroxide or azobisisobutyronitrile.

[0031] The beneficial effects of this invention are:

[0032] (1) This invention utilizes polylactic acid grafted polymer formed by combining bio-based material polylactic acid with polypropylene as a compatibilizer. The polar groups of polylactic acid can form strong interfacial interactions with other polar polymers or elastomers, improving compatibility, and have good biocompatibility and biodegradability.

[0033] (2) In this invention, polyethylene glycol is combined with polypropylene to form polylactic acid graft polymer as a compatibilizer. Polyethylene glycol has flexible segments, which can provide better flexibility and compatibility in the polymer matrix. The ether oxygen group of polyethylene glycol can form hydrogen bonds with hydrogen bond donors in other polymers to enhance compatibility.

[0034] (3) The silica nanosheets of the present invention have extremely high specific surface area, which enables them to form a large number of interfacial contacts with the polymer matrix and elastomer, thereby improving compatibility. After obtaining amino groups by chemically modifying silica nanosheets with 3-aminopropyltriethoxysilane, they can form stronger interfacial interactions with the polymer matrix and elastomer. Silica nanosheets themselves have a good reinforcing effect and can effectively improve the tear resistance of polypropylene films.

[0035] (4) The present invention uses a calendering post-processing process to make the polymer molecular chains in the film undergo small-scale orientation in the transverse direction, which significantly improves the tear strength in the transverse direction, making it more suitable as a packaging material. Detailed Implementation

[0036] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0037] In the following examples and comparative examples, the isotacticity of the homopolymer polypropylene is 98; the slip masterbatch is a composite slip masterbatch, purchased from Hangzhou Kaijie Plastics Co., Ltd., model KJ-Z01; the block copolymer polypropylene is purchased from Daqing Petrochemical, model EPS30R; the olefin elastomer is ethylene-vinyl acetate copolymer, purchased from Merck Life Sciences Co., Ltd., model 437247; the linear low-density polyethylene is purchased from Merck Sigma-Aldrich, model 429015; the thermoplastic elastomer is styrene-butadiene-styrene copolymer, purchased from Dongguan Yingxiang Plastic Raw Materials Co., Ltd., grade 3206; and the dynamic vulcanized rubber is purchased from Haozheng New Material Technology (Dongguan) Co., Ltd., grade VU424-80A.

[0038] Example 1

[0039] A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, the method comprising the following steps:

[0040] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0041] (2) The upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller. After cooling, a film with a thickness of 200μm is formed.

[0042] (3) The diaphragm enters the uniaxial stretching unit and is stretched 4 times in the longitudinal direction to obtain the first film;

[0043] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0044] (5) Use calendering equipment to process uniaxial stretching, and after cooling, roll it up to obtain a uniaxial stretching polypropylene film with high transverse tear strength.

[0045] The uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, with a thickness ratio of 1:1:1. The raw materials for both the upper and lower surface layers comprise the following components by weight:

[0046] 90 parts of homopolymer polypropylene

[0047] 8 parts of silica

[0048] Two parts of smooth masterbatch.

[0049] The intermediate layer raw material comprises the following components in parts by weight:

[0050]

[0051]

[0052] The preparation method of the polylactic acid grafted polymer is as follows:

[0053] 10 parts by weight of polylactic acid (purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., model number 31852-84-3) and 0.1 parts by weight of initiator azobisisobutyronitrile were dissolved in 133 parts by weight of dichloromethane. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0054] The preparation method of the polyethylene glycol graft polymer is as follows:

[0055] 10 parts by weight of polyethylene glycol-1000 and 0.1 parts by weight of benzoyl peroxide were dissolved in 87 parts by weight of toluene. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polyethylene glycol graft polymer was obtained by cooling, washing, filtering and drying.

[0056] The method for preparing the modified silica nanosheets is as follows:

[0057] One part by weight of silica nanosheets (purchased from Shanghai Huijingya Nanomaterials Co., Ltd., model 10nm-15nm) was dispersed in 79 parts by weight of ethanol and sonicated for 30 minutes. One part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours. Modified silica nanosheets were obtained by filtration, washing and drying.

[0058] The temperature of the high-temperature melting in step (1) is 250°C; the temperature of the co-extrusion die in step (2) is 230°C; the temperature of the quenching roller is 40°C; the temperature of the stretching in step (3) is 95°C; the voltage of the corona treatment unit in step (4) is 15kV, the frequency is 25kHz, and the traction speed is 100m / min; the temperature of the calendering equipment in step (5) is 125°C, and the calendering pressure is 30MPa.

[0059] The calendering equipment in step (5) has two calendering rollers with independent temperature control. The calendering equipment is equipped with two unwinding frames and two winding frames, which are the high-temperature resistant PET release film unwinding frame and the uniaxial stretch polypropylene film unwinding frame and winding frame, respectively. The two different films are bonded together by unwinding through the unwinding frame and pass through the calendering equipment at the same time. One side of the uniaxial stretch polypropylene film is bonded to the heating roller, and the other side is bonded to the release surface of the high-temperature resistant PET release film. The temperature of the heating roller in contact with the polypropylene film is 120°C, and the temperature of the heating roller in contact with the PET surface of the high-temperature resistant PET release film is 140°C.

[0060] The thickness of the high transverse tear strength uniaxially stretched polypropylene film after processing by the calendering equipment in step (5) is 90% of the thickness of its original uniaxially stretched polypropylene film.

[0061] Example 2

[0062] A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, the method comprising the following steps:

[0063] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0064] (2) The upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller. After cooling, a film with a thickness of 200μm is formed.

[0065] (3) The diaphragm enters the uniaxial stretching unit and is stretched 4 times in the longitudinal direction to obtain the first film;

[0066] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0067] (5) Use calendering equipment to process uniaxial stretching, and after cooling, roll it up to obtain a uniaxial stretching polypropylene film with high transverse tear strength.

[0068] The uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, with a thickness ratio of 1:1:1. The raw materials for both the upper and lower surface layers comprise the following components by weight:

[0069] 95 parts of homopolymer polypropylene

[0070] 3 parts silicon dioxide

[0071] Two parts of smooth masterbatch.

[0072] The intermediate layer raw material comprises the following components in parts by weight:

[0073]

[0074] The preparation method of the polylactic acid grafted polymer is as follows:

[0075] 10 parts by weight of polylactic acid (purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., model number 31852-84-3) and 0.1 parts by weight of initiator azobisisobutyronitrile were dissolved in 133 parts by weight of dichloromethane. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0076] The preparation method of the polyethylene glycol graft polymer is as follows:

[0077] 10 parts by weight of polyethylene glycol-1000 and 0.1 parts by weight of benzoyl peroxide were dissolved in 87 parts by weight of toluene. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polyethylene glycol graft polymer was obtained by cooling, washing, filtering and drying.

[0078] The method for preparing the modified silica nanosheets is as follows:

[0079] One part by weight of silica nanosheets (purchased from Shanghai Huijingya Nanomaterials Co., Ltd., model 10nm-15nm) was dispersed in 79 parts by weight of ethanol and sonicated for 30 minutes. One part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours. Modified silica nanosheets were obtained by filtration, washing and drying.

[0080] The temperature of the high-temperature melting in step (1) is 250°C; the temperature of the co-extrusion die in step (2) is 230°C; the temperature of the quenching roller is 40°C; the temperature of the stretching in step (3) is 95°C; the voltage of the corona treatment unit in step (4) is 15kV, the frequency is 25kHz, and the traction speed is 100m / min; the temperature of the calendering equipment in step (5) is 125°C, and the calendering pressure is 30MPa.

[0081] The calendering equipment in step (5) has two calendering rollers with independent temperature control. The calendering equipment is equipped with two unwinding frames and two winding frames, which are the high-temperature resistant PET release film unwinding frame and the uniaxial stretch polypropylene film unwinding frame and winding frame, respectively. The two different films are bonded together by unwinding through the unwinding frame and pass through the calendering equipment at the same time. One side of the uniaxial stretch polypropylene film is bonded to the heating roller, and the other side is bonded to the release surface of the high-temperature resistant PET release film. The temperature of the heating roller in contact with the polypropylene film is 120°C, and the temperature of the heating roller in contact with the PET surface of the high-temperature resistant PET release film is 140°C.

[0082] The thickness of the high transverse tear strength uniaxially stretched polypropylene film after processing by the calendering equipment in step (5) is 90% of the thickness of its original uniaxially stretched polypropylene film.

[0083] Example 3

[0084] A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, the method comprising the following steps:

[0085] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0086] (2) The upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller. After cooling, a film with a thickness of 200μm is formed.

[0087] (3) The diaphragm enters the uniaxial stretching unit and is stretched 4 times in the longitudinal direction to obtain the first film;

[0088] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0089] (5) Use calendering equipment to process uniaxial stretching, and after cooling, roll it up to obtain a uniaxial stretching polypropylene film with high transverse tear strength.

[0090] The uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, with a thickness ratio of 1:1:1. The raw materials for both the upper and lower surface layers comprise the following components by weight:

[0091] 90 parts of homopolymer polypropylene

[0092] 8 parts of silica

[0093] Two parts of smooth masterbatch.

[0094] The intermediate layer raw material comprises the following components in parts by weight:

[0095]

[0096] The preparation method of the polylactic acid grafted polymer is as follows:

[0097] 10 parts by weight of polylactic acid (purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., model number 31852-84-3) and 0.1 parts by weight of initiator azobisisobutyronitrile were dissolved in 133 parts by weight of dichloromethane. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0098] The preparation method of the polyethylene glycol graft polymer is as follows:

[0099] 10 parts by weight of polyethylene glycol-1000 and 0.1 parts by weight of benzoyl peroxide were dissolved in 87 parts by weight of toluene. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polyethylene glycol graft polymer was obtained by cooling, washing, filtering and drying.

[0100] The method for preparing the modified silica nanosheets is as follows:

[0101] One part by weight of silica nanosheets (purchased from Shanghai Huijingya Nanomaterials Co., Ltd., model 10nm-15nm) was dispersed in 79 parts by weight of ethanol and sonicated for 30 minutes. One part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours. Modified silica nanosheets were obtained by filtration, washing and drying.

[0102] The temperature of the high-temperature melting in step (1) is 250°C; the temperature of the co-extrusion die in step (2) is 230°C; the temperature of the quenching roller is 40°C; the temperature of the stretching in step (3) is 95°C; the voltage of the corona treatment unit in step (4) is 15kV, the frequency is 25kHz, and the traction speed is 100m / min; the temperature of the calendering equipment in step (5) is 125°C, and the calendering pressure is 30MPa.

[0103] The calendering equipment in step (5) has two calendering rollers with independent temperature control. The calendering equipment is equipped with two unwinding frames and two winding frames, which are the high-temperature resistant PET release film unwinding frame and the uniaxial stretch polypropylene film unwinding frame and winding frame, respectively. The two different films are bonded together by unwinding through the unwinding frame and pass through the calendering equipment at the same time. One side of the uniaxial stretch polypropylene film is bonded to the heating roller, and the other side is bonded to the release surface of the high-temperature resistant PET release film. The temperature of the heating roller in contact with the polypropylene film is 120°C, and the temperature of the heating roller in contact with the PET surface of the high-temperature resistant PET release film is 140°C.

[0104] The thickness of the high transverse tear strength uniaxially stretched polypropylene film after processing by the calendering equipment in step (5) is 90% of the thickness of its original uniaxially stretched polypropylene film.

[0105] Comparative Example 1

[0106] A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, the method comprising the following steps:

[0107] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0108] (2) The upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller. After cooling, a film with a thickness of 200μm is formed.

[0109] (3) The diaphragm enters the uniaxial stretching unit and is stretched 4 times in the longitudinal direction to obtain the first film;

[0110] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0111] (5) Use calendering equipment to process uniaxial stretching, and after cooling, roll it up to obtain a uniaxial stretching polypropylene film with high transverse tear strength.

[0112] The uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, with a thickness ratio of 1:1:1. The raw materials for both the upper and lower surface layers comprise the following components by weight:

[0113] 90 parts of homopolymer polypropylene

[0114] 8 parts of silica

[0115] Two parts of smooth masterbatch.

[0116] The intermediate layer raw material comprises the following components in parts by weight:

[0117]

[0118]

[0119] The preparation method of the polylactic acid grafted polymer is as follows:

[0120] 10 parts by weight of polylactic acid (purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., model number 31852-84-3) and 0.1 parts by weight of initiator azobisisobutyronitrile were dissolved in 133 parts by weight of dichloromethane. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0121] The preparation method of the polyethylene glycol graft polymer is as follows:

[0122] 10 parts by weight of polyethylene glycol-1000 and 0.1 parts by weight of benzoyl peroxide were dissolved in 87 parts by weight of toluene. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polyethylene glycol graft polymer was obtained by cooling, washing, filtering and drying.

[0123] The method for preparing the modified silica nanosheets is as follows:

[0124] One part by weight of silica nanosheets (purchased from Shanghai Huijingya Nanomaterials Co., Ltd., model 10nm-15nm) was dispersed in 79 parts by weight of ethanol and sonicated for 30 minutes. One part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours. Modified silica nanosheets were obtained by filtration, washing and drying.

[0125] The temperature of the high-temperature melting in step (1) is 250°C; the temperature of the co-extrusion die in step (2) is 230°C; the temperature of the quenching roller is 40°C; the temperature of the stretching in step (3) is 95°C; the voltage of the corona treatment unit in step (4) is 15kV, the frequency is 25kHz, and the traction speed is 100m / min; the temperature of the calendering equipment in step (5) is 125°C, and the calendering pressure is 30MPa.

[0126] The calendering equipment in step (5) has two calendering rollers with independent temperature control. The calendering equipment is equipped with two unwinding frames and two winding frames, which are the high-temperature resistant PET release film unwinding frame and the uniaxial stretch polypropylene film unwinding frame and winding frame, respectively. The two different films are bonded together by unwinding through the unwinding frame and pass through the calendering equipment at the same time. One side of the uniaxial stretch polypropylene film is bonded to the heating roller, and the other side is bonded to the release surface of the high-temperature resistant PET release film. The temperature of the heating roller in contact with the polypropylene film is 120°C, and the temperature of the heating roller in contact with the PET surface of the high-temperature resistant PET release film is 140°C.

[0127] The thickness of the high transverse tear strength uniaxially stretched polypropylene film after processing by the calendering equipment in step (5) is 90% of the thickness of its original uniaxially stretched polypropylene film.

[0128] Comparative Example 2

[0129] A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, the method comprising the following steps:

[0130] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0131] (2) The upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller. After cooling, a film with a thickness of 200μm is formed.

[0132] (3) The diaphragm enters the uniaxial stretching unit and is stretched 4 times in the longitudinal direction to obtain the first film;

[0133] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0134] (5) Use calendering equipment to process uniaxial stretching, and after cooling, roll it up to obtain a uniaxial stretching polypropylene film with high transverse tear strength.

[0135] The uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, with a thickness ratio of 1:1:1. The raw materials for both the upper and lower surface layers comprise the following components by weight:

[0136] 90 parts of homopolymer polypropylene

[0137] 8 parts of silica

[0138] Two parts of smooth masterbatch.

[0139] The intermediate layer raw material comprises the following components in parts by weight:

[0140]

[0141]

[0142] The preparation method of the polylactic acid grafted polymer is as follows:

[0143] 10 parts by weight of polylactic acid (purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., model number 31852-84-3) and 0.1 parts by weight of initiator azobisisobutyronitrile were dissolved in 133 parts by weight of dichloromethane. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0144] The preparation method of the polyethylene glycol graft polymer is as follows:

[0145] 10 parts by weight of polyethylene glycol-1000 and 0.1 parts by weight of benzoyl peroxide were dissolved in 87 parts by weight of toluene. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polyethylene glycol graft polymer was obtained by cooling, washing, filtering and drying.

[0146] The method for preparing the modified silica nanosheets is as follows:

[0147] One part by weight of silica nanosheets (purchased from Shanghai Huijingya Nanomaterials Co., Ltd., model 10nm-15nm) was dispersed in 79 parts by weight of ethanol and sonicated for 30 minutes. One part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours. Modified silica nanosheets were obtained by filtration, washing and drying.

[0148] The temperature of the high-temperature melting in step (1) is 250°C; the temperature of the co-extrusion die in step (2) is 230°C; the temperature of the quenching roller is 40°C; the temperature of the stretching in step (3) is 95°C; the voltage of the corona treatment unit in step (4) is 15kV, the frequency is 25kHz, and the traction speed is 100m / min; the temperature of the calendering equipment in step (5) is 125°C, and the calendering pressure is 30MPa.

[0149] The calendering equipment in step (5) has two calendering rollers with independent temperature control. The calendering equipment is equipped with two unwinding frames and two winding frames, which are the high-temperature resistant PET release film unwinding frame and the uniaxial stretch polypropylene film unwinding frame and winding frame, respectively. The two different films are bonded together by unwinding through the unwinding frame and pass through the calendering equipment at the same time. One side of the uniaxial stretch polypropylene film is bonded to the heating roller, and the other side is bonded to the release surface of the high-temperature resistant PET release film. The temperature of the heating roller in contact with the polypropylene film is 120°C, and the temperature of the heating roller in contact with the PET surface of the high-temperature resistant PET release film is 140°C.

[0150] The thickness of the high transverse tear strength uniaxially stretched polypropylene film after processing by the calendering equipment in step (5) is 90% of the thickness of its original uniaxially stretched polypropylene film.

[0151] Comparative Example 3

[0152] A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, the method comprising the following steps:

[0153] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0154] (2) The upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller. After cooling, a film with a thickness of 200μm is formed.

[0155] (3) The diaphragm enters the uniaxial stretching unit and is stretched 4 times in the longitudinal direction to obtain the first film;

[0156] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0157] (5) Use calendering equipment to process uniaxial stretching, and after cooling, roll it up to obtain a uniaxial stretching polypropylene film with high transverse tear strength.

[0158] The uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, with a thickness ratio of 1:1:1. The raw materials for both the upper and lower surface layers comprise the following components by weight:

[0159] 90 parts of homopolymer polypropylene

[0160] 8 parts of silica

[0161] Two parts of smooth masterbatch.

[0162] The intermediate layer raw material comprises the following components in parts by weight:

[0163]

[0164] The preparation method of the polylactic acid grafted polymer is as follows:

[0165] 10 parts by weight of polylactic acid (purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., model number 31852-84-3) and 0.1 parts by weight of initiator azobisisobutyronitrile were dissolved in 133 parts by weight of dichloromethane. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0166] The preparation method of the polyethylene glycol graft polymer is as follows:

[0167] 10 parts by weight of polyethylene glycol-1000 and 0.1 parts by weight of benzoyl peroxide were dissolved in 87 parts by weight of toluene. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polyethylene glycol graft polymer was obtained by cooling, washing, filtering and drying.

[0168] The method for preparing the modified silica nanosheets is as follows:

[0169] One part by weight of silica nanosheets (purchased from Shanghai Huijingya Nanomaterials Co., Ltd., model 10nm-15nm) was dispersed in 79 parts by weight of ethanol and sonicated for 30 minutes. One part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours. Modified silica nanosheets were obtained by filtration, washing and drying.

[0170] The temperature of the high-temperature melting in step (1) is 250°C; the temperature of the co-extrusion die in step (2) is 230°C; the temperature of the quenching roller is 40°C; the temperature of the stretching in step (3) is 95°C; the voltage of the corona treatment unit in step (4) is 15kV, the frequency is 25kHz, and the traction speed is 100m / min; the temperature of the calendering equipment in step (5) is 125°C, and the calendering pressure is 30MPa.

[0171] The calendering equipment in step (5) has two calendering rollers with independent temperature control. The calendering equipment is equipped with two unwinding frames and two winding frames, which are the high-temperature resistant PET release film unwinding frame and the uniaxial stretch polypropylene film unwinding frame and winding frame, respectively. The two different films are bonded together by unwinding through the unwinding frame and pass through the calendering equipment at the same time. One side of the uniaxial stretch polypropylene film is bonded to the heating roller, and the other side is bonded to the release surface of the high-temperature resistant PET release film. The temperature of the heating roller in contact with the polypropylene film is 120°C, and the temperature of the heating roller in contact with the PET surface of the high-temperature resistant PET release film is 140°C.

[0172] The thickness of the high transverse tear strength uniaxially stretched polypropylene film after processing by the calendering equipment in step (5) is 90% of the thickness of its original uniaxially stretched polypropylene film.

[0173] Comparative Example 4

[0174] A method for preparing a uniaxially oriented polypropylene film, the method comprising the following steps:

[0175] (1) Mix the upper surface material, the middle layer material and the lower surface material separately and melt them at high temperature to obtain the upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt;

[0176] (2) The upper surface polymer melt, the middle layer polymer melt and the lower surface polymer melt are respectively conveyed to the three-layer co-extrusion die, and flow out through the die to the quenching roller. After cooling, a film with a thickness of 200μm is formed.

[0177] (3) The diaphragm enters the unidirectional stretching unit and is stretched 5 times in the longitudinal direction to obtain the first film;

[0178] (4) After cooling, the first film passes through the corona treatment unit, the traction unit and the winding unit in sequence to form a uniaxial stretched polypropylene film.

[0179] The uniaxially oriented polypropylene film has a three-layer structure, consisting of an upper surface layer, a middle layer, and a lower surface layer, with a thickness ratio of 1:1:1. The raw materials for both the upper and lower surface layers comprise the following components by weight:

[0180] 90 parts of homopolymer polypropylene

[0181] 8 parts of silica

[0182] Two parts of smooth masterbatch.

[0183] The intermediate layer raw material comprises the following components in parts by weight:

[0184]

[0185] The preparation method of the polylactic acid grafted polymer is as follows:

[0186] 10 parts by weight of polylactic acid (purchased from Hubei Biaoyue Biotechnology Development Co., Ltd., model number 31852-84-3) and 0.1 parts by weight of initiator azobisisobutyronitrile were dissolved in 133 parts by weight of dichloromethane. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0187] As a preferred embodiment of the present invention, the method for preparing the polyethylene glycol graft polymer is as follows:

[0188] 10 parts by weight of polyethylene glycol-1000 and 0.1 parts by weight of benzoyl peroxide were dissolved in 87 parts by weight of toluene. 10 parts by weight of homopolymer polypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, the polyethylene glycol graft polymer was obtained by cooling, washing, filtering and drying.

[0189] As a preferred embodiment of the present invention, the method for preparing the modified silica nanosheets is as follows:

[0190] One part by weight of silica nanosheets (purchased from Shanghai Huijingya Nanomaterials Co., Ltd., model 10nm-15nm) was dispersed in 79 parts by weight of ethanol and sonicated for 30 minutes. One part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours. Modified silica nanosheets were obtained by filtration, washing and drying.

[0191] The temperature of the high-temperature melting in step (1) is 250°C; the temperature of the co-extrusion die in step (2) is 230°C; the temperature of the quenching roller is 40°C; the temperature of the stretching in step (3) is 95°C; and the voltage of the corona treatment unit in step (4) is 15kV, the frequency is 25kHz, and the traction speed is 100m / min.

[0192] Performance testing

[0193] The polypropylene films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to longitudinal tensile strength tests and transverse tear resistance tests, respectively.

[0194] The longitudinal tensile strength of polypropylene film was tested according to GB / T3830-2008, and the transverse tear strength of polypropylene film was tested according to GB / T3830-2008 right-angle tear test. The test results are shown in Table 1 below:

[0195] Group Tensile strength (MPa) Right-angle tear strength kN / m Example 1 23.3 231 Example 2 22.8 232 Example 3 22.5 221 Comparative Example 1 22.3 203 Comparative Example 2 21.8 197 Comparative Example 3 22.3 189 Comparative Example 4 19.8 165

[0196] As can be seen from the test results in Table 1, compared with Comparative Examples 1-4, the uniaxially stretched polypropylene film with high transverse tear strength prepared by the present invention has significantly better tensile strength and tear resistance than Comparative Examples 1-4.

[0197] Compared with Comparative Example 1, Examples 1-3 and Table 1 show that the lack of polylactic acid grafted polymer, i.e. the lack of polar carboxyl groups, weakens the strong interfacial interaction between polar groups and elastomers, reduces the compatibility of components, and leads to a decrease in transverse tear strength.

[0198] Compared with Comparative Example 2, the analysis in Table 1 shows that the absence of polyethylene glycol causes the polymer matrix to lose important flexible segments, resulting in a decrease in the flexibility and compatibility of the material. In addition, the ether oxygen groups of polyethylene glycol cannot form hydrogen bonds with hydrogen bond donors in other polymers, further weakening the compatibility of the material. Therefore, the polymer lacking polyethylene glycol grafting results in a decrease in transverse tear strength.

[0199] Compared with Comparative Example 3, Examples 1-3 and Table 1 show that silica nanosheets have extremely high specific surface area, enabling them to form numerous interfacial contacts with the polymer matrix and elastomer, thereby significantly improving compatibility. Silica nanosheets chemically modified with 3-aminopropyltriethoxysilane can form stronger interfacial interactions with the polymer matrix and elastomer. Furthermore, silica nanosheets themselves have a good reinforcing effect, effectively improving the tear resistance of the polypropylene film. Therefore, the lack of 3-aminopropyltriethoxysilane-modified silica nanosheets leads to reduced interfacial interactions, thereby reducing the transverse tear resistance of the film.

[0200] As can be seen from the analysis of Table 1, when comparing Example 1 with Comparative Example 4, the polymer molecular chains without secondary calendering are not sufficiently oriented in the transverse direction, resulting in a significant reduction in the tear strength of the film in the transverse direction.

[0201] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A process for the production of a uniaxially stretched polypropylene film having a high transverse tear strength, characterized in that, The preparation method comprises the following steps: (1) mixing and high-temperature melting the upper surface layer raw material, the middle layer raw material and the lower surface layer raw material respectively to obtain upper surface layer polymer melt, middle layer polymer melt and lower surface layer polymer melt; (2) conveying the upper surface layer polymer melt, the middle layer polymer melt and the lower surface layer polymer melt to a three-layer co-extrusion die head respectively, flowing out to a quenching roller through the die head, and forming a film after cooling; (3) the film enters a unidirectional stretching unit, is stretched by 4-6 times along the longitudinal direction to obtain a first film; (4) after cooling, the first film sequentially passes through a corona treatment unit, a traction unit and a winding unit to form a unidirectional stretched polypropylene film; (5) the unidirectional stretched polypropylene film is treated by a calendering equipment with a temperature of 100-150 ℃ and a calendering pressure of 10-50 MPa, and is wound after cooling to obtain a unidirectional stretched polypropylene film with high transverse tear strength; The middle layer raw material comprises the following components by weight: homopolymer polypropylene 70-100 parts block copolymer polypropylene 1-25 parts olefin-based elastomer 1-25 parts linear low-density polyethylene 1-25 parts thermoplastic elastomer 1-25 parts dynamic vulcanized rubber 1-25 parts poly lactic acid grafted polymer 1-5 parts polyethylene glycol grafted polymer 1-5 parts modified silicon dioxide nanosheet 1-5 parts.

2. The process for producing a uniaxially stretched polypropylene film having high transverse tear strength according to claim 1, characterized by, The unidirectional stretched polypropylene film has a three-layer structure, sequentially comprising an upper surface layer, a middle layer and a lower surface layer, and the upper surface layer raw material and the lower surface layer raw material each comprise the following components by weight: homopolymer polypropylene 88-97 parts anti-blocking masterbatch 3-10 parts slip masterbatch 1-2 parts.

3. The process for producing a uniaxially stretched polypropylene film having high transverse tear strength according to claim 1 or 2, characterized in that, The homopolymer polypropylene has a degree of isotacticity greater than 97.

4. The process for producing a uniaxially stretched polypropylene film having high transverse tear strength according to claim 1, characterized in that, The preparation method of the poly lactic acid grafted polymer is as follows: poly lactic acid and initiator azobisisobutyronitrile are dissolved in dichloromethane, homopolymer polypropylene is added and uniformly mixed, stirring is carried out at a temperature of 70-100 ℃ for 1-4 hours, and then poly lactic acid grafted polymer is obtained through cooling, washing, filtering and drying.

5. The process for producing a uniaxially stretched polypropylene film having high transverse tear strength according to claim 1, characterized in that, The preparation method of the polyethylene glycol grafted polymer is as follows: polyethylene glycol and initiator are dissolved in toluene, homopolymer polypropylene is added and uniformly mixed, stirring is carried out at a temperature of 70-100 ℃ for 1-4 hours, and then polyethylene glycol grafted polymer is obtained through cooling, washing, filtering and drying.

6. The process for producing a uniaxially stretched polypropylene film having high transverse tear strength according to claim 1, characterized by, The preparation method of the modified silicon dioxide nanosheet is as follows: silicon dioxide nanosheet is dispersed in ethanol or deionized water and ultrasonically treated for 30 minutes, surface modifier 3-aminopropyl triethoxysilane is added, heating is carried out to 60-100 ℃ and stirring is carried out for 1-4 hours, and then the modified silicon dioxide nanosheet is obtained through filtering, washing and drying.

7. The process for producing a uniaxially stretched polypropylene film having high transverse tear strength according to claim 1, characterized in that, In step (1), the temperature of the mixing and high-temperature melting is 240-260 ℃, in step (2), the temperature of the co-extrusion die head is 220-240 ℃ and the temperature of the quenching roller is 25-55 ℃; in step (3), the temperature of the stretching is 80-110 ℃; in step (4), the voltage of the corona treatment unit is 10-20 kV, the frequency is 20-30 kHz, and the traction speed is 50-200 m / min.

8. The process for producing a uniaxially stretched polypropylene film having high transverse tear strength according to claim 1, characterized by, The calendering equipment in step (5) has two calendering rollers with independent temperature control, and two unwinding frames and two winding frames are arranged on the calendering equipment, which are high-temperature-resistant PET release film unwinding frame and uniaxially stretched polypropylene film unwinding frame and winding frame; the two different films are pasted together through the unwinding frames and pass through the calendering equipment, one side of the uniaxially stretched polypropylene film is pasted with a heating roller, and the other side is pasted with the release surface of the high-temperature-resistant PET release film; the temperature of the heating roller contacted by the polypropylene film is 110-130 DEG C, and the temperature of the heating roller contacted by the PET surface of the high-temperature-resistant PET release film is 130-150 DEG C.

9. The process for producing a uniaxially-stretched polypropylene film having high transverse tear strength according to claim 1, characterized by, The thickness of the uniaxially stretched polypropylene film with high transverse tear strength after the treatment of the calendering equipment in step (5) is 85-95% of the thickness of the original uniaxially stretched polypropylene film.

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