Preparation method of uniaxially stretched polypropylene film with high transverse tearing strength

Abstract

The invention provides a preparation method of a uniaxially stretched polypropylene film with high transverse tearing strength, and belongs to the technical field of high polymer material processing. The uniaxial stretching polypropylene film has a three-layer structure, and an upper surface layer and a lower surface layer are formed by mixing homo-polypropylene, anti-blocking master batch and smooth master batch; the middle layer is prepared from homo-polypropylene, block co-polypropylene, an olefin elastomer, linear low-density polyethylene, a thermoplastic elastomer, dynamic vulcanized rubber, a polylactic acid graft polymer, a polyethylene glycol graft polymer and modified silicon dioxide nanosheets. Compared with the existing production technology, the method has the advantages that the tear resistance of the film is improved by introducing the elastomer and compatibilizer components into the middle layer, and the transverse orientation degree of a polymer molecular chain is enhanced through secondary calendering and post-treatment of a shaping process, so that the tear strength of the film in the transverse direction is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material processing, and in particular relates to a method for preparing a uniaxially stretched polypropylene film with high transverse tearing strength. Background Art

[0002] With the increasing awareness of global environmental protection, the replacement of packaging materials has gradually become an industry consensus, among which single materials have become the dominant direction of the packaging industry. Due to its excellent longitudinal tensile strength and stiffness, uniaxially oriented polypropylene film is widely used in packaging, electronic appliances, agriculture, architectural decoration and daily necessities. Its high transparency and excellent optical properties give it significant advantages in food packaging, labeling and printing. In addition, the good chemical resistance and moisture resistance of uniaxially oriented polypropylene film enable it to maintain stable performance in various environments.

[0003] Although uniaxially oriented polypropylene film exhibits extremely high tensile strength in the longitudinal direction, which gives it significant advantages in applications such as handle straps, 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 transverse external forces. This performance defect not only directly affects the service life and reliability of uniaxially oriented films, but also shows obvious lack of toughness when used in combination with biaxially oriented films or cast films, resulting in the products being prone to tearing in practical applications. Specifically, this performance deficiency is mainly due to the combined influence of multiple factors such as raw material selection, formula design and preparation process. The combined effect of these factors limits the widespread application of uniaxially oriented polypropylene films in certain packaging fields. In order to overcome these limitations, future research needs to conduct systematic exploration in material selection, formula optimization and process improvement to improve the transverse tear strength and overall performance of uniaxially oriented films, thereby expanding their scope of application.

[0004] The present invention aims to solve the above-mentioned shortcomings of the existing uniaxially oriented polypropylene film by selecting a polypropylene raw material with a special structure and adding a rubber elastomer, a polyolefin elastomer and a solubilizer to the formula to improve the transverse tear strength of the film. Under the premise of not reducing the longitudinal tensile strength of the product, by adjusting the proportion of the elastomer material and regulating the distribution of the material microstructure, the tear resistance of the film in the transverse direction is significantly improved. Summary of the invention

[0005] The present invention provides a method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, and belongs to the technical field of polymer material processing. The uniaxially stretched polypropylene film has a three-layer structure, wherein the upper surface layer and the lower surface layer are mixed with homopolymer polypropylene, anti-adhesion masterbatch and smooth masterbatch, and the middle layer is composed of homopolymer polypropylene, block copolymer polypropylene, olefin elastomer, linear low-density polyethylene, thermoplastic elastomer, dynamic vulcanized rubber, polylactic acid grafted polymer, polyethylene glycol grafted polymer and modified silica nanosheets; and then the film is formed by calendering and shaping through a special shaping machine. Compared with the existing production technology, this method improves the tear resistance of the film by introducing elastomer and compatibilizer components into the middle layer, and then enhances the orientation degree of the polymer molecular chain in the transverse direction through secondary calendering and shaping process post-treatment, thereby significantly improving the tear strength of the film in the transverse direction.

[0006] The purpose of the present 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 preparation method comprising the following steps:

[0008] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain a polymer melt of the upper surface layer, a polymer melt of the middle layer, and a polymer melt of the lower surface layer;

[0009] (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 through the die head to a quenching roller, and forming a film after cooling;

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

[0011] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0012] (5) The uniaxially oriented polypropylene film is processed by a calendering device and rolled up after cooling to obtain a uniaxially oriented polypropylene film with high transverse tear strength.

[0013] Furthermore, the uniaxially stretched polypropylene film has a three-layer structure, which is an upper surface layer, a middle layer and a lower surface layer in sequence, and the upper surface layer raw material and the lower surface layer raw material both include the following components in parts by weight:

[0014] Homopolymer polypropylene 88-97 parts

[0015] Anti-adhesion masterbatch 3-10 parts

[0016] 1-2 portions of lubricating masterbatch.

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

[0018]

[0019] Furthermore, the homopolymer polypropylene has an isotacticity greater than 97.

[0020] As a preferred technical solution of the present invention, the preparation method of the polylactic acid graft polymer is:

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

[0022] As a preferred technical solution of the present invention, the preparation method of the polyethylene glycol grafted polymer is:

[0023] The polyethylene glycol and the initiator are dissolved in toluene, homopolymerized polypropylene is added and mixed evenly, and after stirring at 70-100° C. for 1-4 hours, the polyethylene glycol grafted polymer is obtained through cooling, washing, filtering and drying.

[0024] As a preferred technical solution of the present invention, the method for preparing the modified silicon dioxide nanosheets is:

[0025] The silica nanosheets are dispersed in ethanol or deionized water and ultrasonicated for 30 minutes, a surface modifier 3-aminopropyltriethoxysilane is added, the mixture is heated to 60-100° C. and stirred for 1-4 hours, and the modified silica nanosheets are obtained by filtering, washing and drying.

[0026] Furthermore, the temperature of the mixed high-temperature melt in step (1) is 240-260°C, the temperature of the co-extrusion die in step (2) is 220-240°C, and the temperature of the chill roll is 25-55°C; the temperature of the stretching in step (3) is 80-110°C; the voltage of the corona treatment unit in step (4) is 10-20kV, the frequency is 20-30kHz, and the pulling speed is 50-200m / min; the temperature of the calendering equipment in step (5) is 100-150°C, and the calendering pressure is 10-50MPa.

[0027] Furthermore, the calendering equipment in step (5) has two calendering rollers with independently controlled temperatures, and the calendering equipment is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to 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°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 130-150°C.

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

[0029] Furthermore, the anti-adhesion masterbatch is at least one of silicon dioxide, talc, stearic acid amide and polypropylene wax.

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

[0031] Beneficial effects of the present invention:

[0032] (1) The present invention utilizes bio-based material polylactic acid combined with polypropylene to form a polylactic acid grafted polymer as a compatibilizer. The polar groups of polylactic acid can form a strong interface interaction with other polar polymers or elastomers, thereby improving compatibility and having good biocompatibility and biodegradability.

[0033] (2) The present invention utilizes polyethylene glycol combined with polypropylene to form a polylactic acid graft polymer as a compatibilizer. Polyethylene glycol has a flexible chain segment and can provide better flexibility and compatibility in the polymer matrix. The ether radical 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 an extremely high specific surface area, which enables them to form a large amount of interfacial contact with the polymer matrix and the elastomer, thereby improving compatibility. After the silica nanosheets are chemically modified with 3-aminopropyltriethoxysilane to obtain amino groups, they can form stronger interfacial interactions with the polymer matrix and the elastomer. The silica nanosheets themselves have a good reinforcement effect and can effectively improve the tear strength of the polypropylene film.

[0035] (4) The present invention uses a post-calendering treatment process to orient the polymer molecular chains in the film at a small ratio in the transverse direction, thereby significantly improving the transverse tear strength, making it more suitable as a packaging material. DETAILED DESCRIPTION

[0036] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0037] In the following embodiments and comparative examples, the homopolymer polypropylene has an isotacticity of 98; the lubricating masterbatch is a composite lubricating masterbatch purchased from Hangzhou Kaijie Plastic Co., Ltd., model KJ-Z01; the block copolymer polypropylene is purchased from Daqing Refining and Chemical, 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., brand 3206; the dynamic vulcanized rubber is purchased from Haozheng New Materials Technology (Dongguan) Co., Ltd., brand VU424-80A.

[0038] Example 1

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

[0040] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain an upper surface layer polymer melt, an middle layer polymer melt, and a lower surface layer polymer melt;

[0041] (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 through the die head to a quenching roller, and forming a film with a thickness of 200 μm after cooling;

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

[0043] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0044] (5) The uniaxially stretched film is processed by calendering equipment, and then rolled up after cooling to obtain a uniaxially stretched polypropylene film with high transverse tear strength.

[0045] The uniaxially stretched polypropylene film has a three-layer structure, which includes an upper surface layer, a middle layer and a lower surface layer in sequence. The thickness ratio of the upper surface layer, the middle layer and the lower surface layer is 1:1:1. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight:

[0046] Homopolymer polypropylene 90 parts

[0047] 8 parts of silicon dioxide

[0048] 2 parts of lubricating masterbatch.

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

[0050]

[0051]

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

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0054] The preparation method of the polyethylene glycol grafted polymer is:

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polyethylene glycol grafted polymer was obtained after cooling, washing, filtering and drying.

[0056] The modified silicon dioxide nanosheet preparation method is:

[0057] 1 part by weight of silica nanosheets (purchased from Shanghai Huijing Sub-Nano New Materials Co., Ltd., model 10nm-15nm) were dispersed in 79 parts by weight of ethanol and ultrasonicated for 30 minutes, 1 part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours, and modified silica nanosheets were obtained by filtering, washing and drying.

[0058] The temperature of the mixed high-temperature melt in step (1) is 250°C, the temperature of the co-extrusion die in step (2) is 230°C, and the temperature of the chill roll 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 pulling 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 independently controlled temperatures, and is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to the release surface of the high-temperature resistant PET release film; the temperature of the heating roller contacted by the polypropylene film is 120°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 140°C.

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

[0061] Example 2

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

[0063] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain an upper surface layer polymer melt, an middle layer polymer melt, and a lower surface layer polymer melt;

[0064] (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 through the die head to a quenching roller, and forming a film with a thickness of 200 μm after cooling;

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

[0066] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0067] (5) The uniaxially stretched film is processed by calendering equipment, and then rolled up after cooling to obtain a uniaxially stretched polypropylene film with high transverse tear strength.

[0068] The uniaxially stretched polypropylene film has a three-layer structure, which includes an upper surface layer, a middle layer and a lower surface layer in sequence. The thickness ratio of the upper surface layer, the middle layer and the lower surface layer is 1:1:1. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight:

[0069] Homopolymer polypropylene 95 parts

[0070] 3 parts of silicon dioxide

[0071] 2 parts of lubricating masterbatch.

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

[0073]

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

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0076] The preparation method of the polyethylene glycol grafted polymer is:

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polyethylene glycol grafted polymer was obtained after cooling, washing, filtering and drying.

[0078] The modified silicon dioxide nanosheet preparation method is:

[0079] 1 part by weight of silica nanosheets (purchased from Shanghai Huijing Sub-Nano New Materials Co., Ltd., model 10nm-15nm) were dispersed in 79 parts by weight of ethanol and ultrasonicated for 30 minutes, 1 part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours, and modified silica nanosheets were obtained by filtering, washing and drying.

[0080] The temperature of the mixed high-temperature melt in step (1) is 250°C, the temperature of the co-extrusion die in step (2) is 230°C, and the temperature of the chill roll 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 pulling 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 independently controlled temperatures, and is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to the release surface of the high-temperature resistant PET release film; the temperature of the heating roller contacted by the polypropylene film is 120°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 140°C.

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

[0083] Example 3

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

[0085] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain a polymer melt of the upper surface layer, a polymer melt of the middle layer, and a polymer melt of the lower surface layer;

[0086] (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 through the die head to a quenching roller, and forming a film with a thickness of 200 μm after cooling;

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

[0088] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0089] (5) The uniaxially stretched film is processed by calendering equipment, and then rolled up after cooling to obtain a uniaxially stretched polypropylene film with high transverse tear strength.

[0090] The uniaxially stretched polypropylene film has a three-layer structure, which includes an upper surface layer, a middle layer and a lower surface layer in sequence. The thickness ratio of the upper surface layer, the middle layer and the lower surface layer is 1:1:1. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight:

[0091] Homopolymer polypropylene 90 parts

[0092] 8 parts of silicon dioxide

[0093] 2 parts of lubricating masterbatch.

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

[0095]

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

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0098] The preparation method of the polyethylene glycol grafted polymer is:

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polyethylene glycol grafted polymer was obtained after cooling, washing, filtering and drying.

[0100] The modified silicon dioxide nanosheet preparation method is:

[0101] 1 part by weight of silica nanosheets (purchased from Shanghai Huijing Sub-Nano New Materials Co., Ltd., model 10nm-15nm) were dispersed in 79 parts by weight of ethanol and ultrasonicated for 30 minutes, 1 part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours, and modified silica nanosheets were obtained by filtering, washing and drying.

[0102] The temperature of the mixed high-temperature melt in step (1) is 250°C, the temperature of the co-extrusion die in step (2) is 230°C, and the temperature of the chill roll 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 pulling 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 independently controlled temperatures, and is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to the release surface of the high-temperature resistant PET release film; the temperature of the heating roller contacted by the polypropylene film is 120°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 140°C.

[0104] The thickness of the uniaxially stretched polypropylene film with high transverse tear strength after being processed by the calendering equipment in step (5) is 90% of the thickness of the 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 preparation method comprising the following steps:

[0107] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain an upper surface layer polymer melt, an middle layer polymer melt, and a lower surface layer polymer melt;

[0108] (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 through the die head to a quenching roller, and forming a film with a thickness of 200 μm after cooling;

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

[0110] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0111] (5) The uniaxially stretched film is processed by calendering equipment, and then rolled up after cooling to obtain a uniaxially stretched polypropylene film with high transverse tear strength.

[0112] The uniaxially stretched polypropylene film has a three-layer structure, which includes an upper surface layer, a middle layer and a lower surface layer in sequence. The thickness ratio of the upper surface layer, the middle layer and the lower surface layer is 1:1:1. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight:

[0113] Homopolymer polypropylene 90 parts

[0114] 8 parts of silicon dioxide

[0115] 2 parts of lubricating masterbatch.

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

[0117]

[0118]

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

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0121] The preparation method of the polyethylene glycol grafted polymer is:

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polyethylene glycol grafted polymer was obtained after cooling, washing, filtering and drying.

[0123] The modified silicon dioxide nanosheet preparation method is:

[0124] 1 part by weight of silica nanosheets (purchased from Shanghai Huijing Sub-Nano New Materials Co., Ltd., model 10nm-15nm) were dispersed in 79 parts by weight of ethanol and ultrasonicated for 30 minutes, 1 part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours, and modified silica nanosheets were obtained by filtering, washing and drying.

[0125] The temperature of the mixed high-temperature melt in step (1) is 250°C, the temperature of the co-extrusion die in step (2) is 230°C, and the temperature of the chill roll 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 pulling 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 independently controlled temperatures, and is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to the release surface of the high-temperature resistant PET release film; the temperature of the heating roller contacted by the polypropylene film is 120°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 140°C.

[0127] The thickness of the uniaxially stretched polypropylene film with high transverse tear strength after being processed by the calendering equipment in step (5) is 90% of the thickness of the 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 preparation method comprising the following steps:

[0130] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain an upper surface layer polymer melt, an middle layer polymer melt, and a lower surface layer polymer melt;

[0131] (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 through the die head to a quenching roller, and forming a film with a thickness of 200 μm after cooling;

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

[0133] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0134] (5) The uniaxially stretched film is processed by calendering equipment, and then rolled up after cooling to obtain a uniaxially stretched polypropylene film with high transverse tear strength.

[0135] The uniaxially stretched polypropylene film has a three-layer structure, which includes an upper surface layer, a middle layer and a lower surface layer in sequence. The thickness ratio of the upper surface layer, the middle layer and the lower surface layer is 1:1:1. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight:

[0136] Homopolymer polypropylene 90 parts

[0137] 8 parts of silicon dioxide

[0138] 2 parts of lubricating masterbatch.

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

[0140]

[0141]

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

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0144] The preparation method of the polyethylene glycol grafted polymer is:

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polyethylene glycol grafted polymer was obtained after cooling, washing, filtering and drying.

[0146] The modified silicon dioxide nanosheet preparation method is:

[0147] 1 part by weight of silica nanosheets (purchased from Shanghai Huijing Sub-Nano New Materials Co., Ltd., model 10nm-15nm) were dispersed in 79 parts by weight of ethanol and ultrasonicated for 30 minutes, 1 part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours, and modified silica nanosheets were obtained by filtering, washing and drying.

[0148] The temperature of the mixed high-temperature melt in step (1) is 250°C, the temperature of the co-extrusion die in step (2) is 230°C, and the temperature of the chill roll 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 pulling 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 independently controlled temperatures, and is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to the release surface of the high-temperature resistant PET release film; the temperature of the heating roller contacted by the polypropylene film is 120°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 140°C.

[0150] The thickness of the uniaxially stretched polypropylene film with high transverse tear strength after being processed by the calendering equipment in step (5) is 90% of the thickness of the 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 preparation method comprising the following steps:

[0153] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain a polymer melt of the upper surface layer, a polymer melt of the middle layer, and a polymer melt of the lower surface layer;

[0154] (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 through the die head to a quenching roller, and forming a film with a thickness of 200 μm after cooling;

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

[0156] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0157] (5) The uniaxially stretched film is processed by calendering equipment, and then rolled up after cooling to obtain a uniaxially stretched polypropylene film with high transverse tear strength.

[0158] The uniaxially stretched polypropylene film has a three-layer structure, which includes an upper surface layer, a middle layer and a lower surface layer in sequence. The thickness ratio of the upper surface layer, the middle layer and the lower surface layer is 1:1:1. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight:

[0159] Homopolymer polypropylene 90 parts

[0160] 8 parts of silicon dioxide

[0161] 2 parts of lubricating masterbatch.

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

[0163]

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

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0166] The preparation method of the polyethylene glycol grafted polymer is:

[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 homopolypropylene were added and mixed evenly, and after stirring at 80°C for 2 hours, a polyethylene glycol grafted polymer was obtained after cooling, washing, filtering and drying.

[0168] The modified silicon dioxide nanosheet preparation method is:

[0169] 1 part by weight of silica nanosheets (purchased from Shanghai Huijing Sub-Nano New Materials Co., Ltd., model 10nm-15nm) were dispersed in 79 parts by weight of ethanol and ultrasonicated for 30 minutes, 1 part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours, and modified silica nanosheets were obtained by filtering, washing and drying.

[0170] The temperature of the mixed high-temperature melt in step (1) is 250°C, the temperature of the co-extrusion die in step (2) is 230°C, and the temperature of the chill roll 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 pulling 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 independently controlled temperatures, and is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to the release surface of the high-temperature resistant PET release film; the temperature of the heating roller contacted by the polypropylene film is 120°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 140°C.

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

[0173] Comparative Example 4

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

[0175] (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain an upper surface layer polymer melt, an middle layer polymer melt, and a lower surface layer polymer melt;

[0176] (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 through the die head to a quenching roller, and forming a film with a thickness of 200 μm after cooling;

[0177] (3) the film sheet enters a uniaxial stretching unit and is stretched 5 times in the longitudinal direction to obtain a first film;

[0178] (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film;

[0179] The uniaxially oriented polypropylene film has a three-layer structure, which includes an upper surface layer, a middle layer and a lower surface layer in sequence. The thickness ratio of the upper surface layer, the middle layer and the lower surface layer is 1:1:1. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight:

[0180] Homopolymer polypropylene 90 parts

[0181] 8 parts of silicon dioxide

[0182] 2 parts of lubricating masterbatch.

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

[0184]

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

[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, and after stirring at 80°C for 2 hours, a polylactic acid grafted polymer was obtained by cooling, washing, filtering and drying.

[0187] As a preferred technical solution of the present invention, the preparation method of the polyethylene glycol grafted polymer is:

[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, and 10 parts by weight of homopolypropylene were added and mixed evenly. After stirring at 80°C for 2 hours, a polyethylene glycol grafted polymer was obtained by cooling, washing, filtering and drying.

[0189] As a preferred technical solution of the present invention, the method for preparing the modified silicon dioxide nanosheets is:

[0190] 1 part by weight of silica nanosheets (purchased from Shanghai Huijing Sub-Nano New Materials Co., Ltd., model 10nm-15nm) were dispersed in 79 parts by weight of ethanol and ultrasonicated for 30 minutes, 1 part by weight of surface modifier 3-aminopropyltriethoxysilane was added, heated to 80°C and stirred for 2 hours, and modified silica nanosheets were obtained by filtering, washing and drying.

[0191] The temperature of the mixed high-temperature melt in step (1) is 250°C, the temperature of the co-extrusion die in step (2) is 230°C, and the temperature of the chill roll 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 pulling 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 strength tests respectively;

[0194] The longitudinal tensile strength of the polypropylene film was tested according to GB / T3830-2008, and the transverse tear strength of the polypropylene film was tested according to the right-angle tear test of GB / T3830-2008. 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] From the test results in Table 1, it can be seen that compared with Comparative Examples 1-4, the uniaxially stretched polypropylene film with high transverse tear strength prepared in Examples 1-3 of the present invention has significantly better tensile strength and tear resistance than Comparative Examples 1-4.

[0197] By comparing Examples 1-3 with Comparative Example 1, combined with the analysis in Table 1, it can be seen that the lack of introduction of polylactic acid grafted polymer, that is, the lack of polar group carboxyl, weakens the strong interface interaction between the polar group and the elastomer, reduces the compatibility of the components, and leads to a decrease in the transverse tear strength.

[0198] By comparing Examples 1-3 with Comparative Example 2, combined with the analysis in Table 1, it can be seen that the absence of polyethylene glycol causes the polymer matrix to lose important flexible segments, resulting in decreased 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 lack of polyethylene glycol grafted polymers leads to a decrease in transverse tear strength.

[0199] Compared with Comparative Example 3, examples 1-3 can be analyzed in combination with Table 1. The silica nanosheets have an extremely high specific surface area and can form a large amount of interfacial contact with the polymer matrix and the elastomer, thereby significantly improving the compatibility. The silica nanosheets chemically modified with 3-aminopropyltriethoxysilane can form a stronger interfacial interaction with the polymer matrix and the elastomer; and the silica nanosheets themselves have a good reinforcement effect, which can effectively improve the tear strength of the polypropylene film. Therefore, the lack of 3-aminopropyltriethoxysilane-modified silica nanosheets leads to a decrease in interfacial interaction, thereby reducing the transverse tear strength of the film.

[0200] By comparing Example 1 with Comparative Example 4, combined with the analysis in Table 1, it can be seen that without secondary calendering, the orientation degree of the polymer molecular chains in the transverse direction is insufficient, resulting in a significant decrease in the tear strength of the film in the transverse direction.

[0201] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a uniaxially stretched polypropylene film with high transverse tear strength, characterized in that: The preparation method comprises the following steps: (1) mixing and melting the raw materials of the upper surface layer, the middle layer, and the lower surface layer at high temperature to obtain an upper surface layer polymer melt, an middle layer polymer melt, and a 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 through the die head to a quenching roller, and forming a film after cooling; (3) the film enters a uniaxial stretching unit and is stretched 4-6 times in the longitudinal direction to obtain a first film; (4) After cooling, the first film is sequentially passed through a corona treatment unit, a traction unit, and a winding unit to form a uniaxially stretched polypropylene film; (5) The uniaxially oriented polypropylene film is processed by a calendering device and rolled up after cooling to obtain a uniaxially oriented polypropylene film with high transverse tear strength.

2. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 1, characterized in that: The uniaxially stretched polypropylene film has a three-layer structure, which is an upper surface layer, a middle layer and a lower surface layer in sequence. The raw materials of the upper surface layer and the lower surface layer both include the following components in parts by weight: Homopolymer polypropylene 88-97 parts Anti-adhesion masterbatch 3-10 parts 1-2 portions of lubricating masterbatch.

3. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 1, characterized in that: The intermediate layer raw material includes the following components in parts by weight:

4. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 2 or 3, characterized in that: The homopolymer polypropylene has an isotacticity greater than 97.

5. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 3, characterized in that: The preparation method of the polylactic acid grafted polymer is: The polylactic acid and the initiator azobisisobutyronitrile are dissolved in dichloromethane, homopolymerized polypropylene is added and mixed evenly, and after stirring at 70-100° C. for 1-4 hours, the polylactic acid grafted polymer is obtained by cooling, washing, filtering and drying.

6. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 3, characterized in that: The preparation method of the polyethylene glycol grafted polymer is: The polyethylene glycol and the initiator are dissolved in toluene, homopolymerized polypropylene is added and mixed evenly, and after stirring at 70-100° C. for 1-4 hours, the polyethylene glycol grafted polymer is obtained through cooling, washing, filtering and drying.

7. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 3, characterized in that: The modified silicon dioxide nanosheet preparation method is: The silica nanosheets are dispersed in ethanol or deionized water and ultrasonicated for 30 minutes, a surface modifier 3-aminopropyltriethoxysilane is added, the mixture is heated to 60-100° C. and stirred for 1-4 hours, and the modified silica nanosheets are obtained by filtering, washing and drying.

8. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 1, characterized in that: The temperature of the mixed high-temperature melt in step (1) is 240-260°C, the temperature of the co-extrusion die in step (2) is 220-240°C, and the temperature of the chill roll is 25-55°C; the temperature of the stretching in step (3) is 80-110°C; the voltage of the corona treatment unit in step (4) is 10-20kV, the frequency is 20-30kHz, and the pulling speed is 50-200m / min; the temperature of the calendering equipment in step (5) is 100-150°C, and the calendering pressure is 10-50MPa.

9. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 1, characterized in that: The calendering equipment in step (5) has two calendering rollers with independently controlled temperatures, and is equipped with two unwinding racks and two winding racks, which are respectively an unwinding rack for high-temperature resistant PET release film and an unwinding rack and a winding rack for uniaxially stretched polypropylene film; the two different films are unwound by the unwinding racks, and are laminated up and down, and pass through the calendering equipment at the same time, with one side of the uniaxially stretched polypropylene film laminating to the heating roller and the other side laminating to 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°C, and the temperature of the heating roller contacted by the PET surface of the high-temperature resistant PET release film is 130-150°C.

10. The method for preparing a uniaxially oriented polypropylene film with high transverse tear strength according to claim 1, characterized in that: The thickness of the uniaxially oriented polypropylene film with high transverse tear strength after being processed by the calendering equipment in step (5) is 85-95% of the thickness of the original uniaxially oriented polypropylene film.

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