A linear easily tearable and steam-resistant polyolefin film, its preparation method and application

Abstract

The present invention discloses a linear easy-to-tear and steam-resistant polyolefin film, which relates to the technical field of polyolefin materials. By controlling the ratio of homopolypropylene and high-impact polypropylene in the heat-sealing layer, the intermediate layer and the corona layer, the present invention realizes the improvement of the steam resistance performance of the polyolefin film, and at the same time prevents the polyolefin film from becoming brittle after high-temperature steaming; high-density polyethylene can promote the longitudinal arrangement of atoms during the film-forming process, and the inorganic powder can act as a stress concentration point during the tearing process. By controlling the dosages of high-density polyethylene and inorganic powder, the linear easy-to-tear performance of the polyolefin film can be improved. The polyolefin film of the present invention is particularly suitable for the field of packaging materials, has excellent linear easy-to-tear performance and steam resistance performance, the ratio of the transverse and longitudinal tear strengths is not less than 8, and it can withstand steaming at 121 °C.

Description

Technical Field

[0001] The present invention relates to the technical field of polyolefin materials, and more specifically, to a polyolefin film that is easily tearable in a straight line and resistant to cooking, and a preparation method and application thereof. Background Art

[0002] Currently, in the field of plastic packaging materials, more and more consumers pursue the functionality and convenience of packaging materials. For example, in some food packaging fields, the inclusions include both solids and liquids. If the straightness of the tear line is poor, the liquid in the inclusions may splash onto the hands, reducing the user experience. At present, the straight-line easy tearability of traditional straight-line easy tear films in the market is mostly provided by cyclic olefin copolymers or biaxially stretched nylon. These two materials have high costs, and the former has general straight-line easy tear performance, while the processing technology of the latter is relatively complex. In addition, poor resistance to cooking is also one of the problems existing in existing packaging films.

[0003] The prior art discloses a cast polyethylene film, its composite film and a preparation method of the composite film. The cast polyethylene film uses a polyethylene-based polymer resin as the material and is prepared by a three-layer co-extrusion casting process of a composite layer, a core layer, and a heat-sealing layer. It has good transverse easy tear effect, but low straight-line tear strength. However, the tear strengths in the transverse and longitudinal directions of this film are quite similar, and the straight-line easy tear performance still needs to be improved, and it cannot solve the problem that existing packaging films are not resistant to cooking at the same time. Summary of the Invention

[0004] In order to overcome the problem that existing straight-line easy tear films cannot improve the straight-line easy tear performance and the resistance to cooking at the same time, the present invention provides a polyolefin film that is easily tearable in a straight line and resistant to cooking. The resistance to cooking of the polyolefin film is achieved by controlling the ratio of homopolypropylene and high impact polypropylene in the heat-sealing layer, the intermediate layer, and the corona layer, and at the same time, the straight-line easy tear performance of the polyolefin film is achieved by controlling the content of high-density polyethylene and inorganic powder in each layer.

[0005] Another object of the present invention is to provide a preparation method of the above polyolefin film.

[0006] Another object of the present invention is to provide an application of the above polyolefin film in the field of packaging materials.

[0007] The above objects of the present invention are achieved by the following technical solutions:

[0008] A polyolefin film that is easily tearable in a straight line and resistant to cooking, the polyolefin film comprises the following components by mass percentage:

[0009] Heat-sealing layer: 50-70% of high impact polypropylene, 20-35% of homopolypropylene, 5-20% of high-density polyethylene, 0.1-2% of inorganic powder;

[0010] Intermediate layer: 20 - 50% high impact polypropylene, 30 - 60% homopolypropylene, 5 - 20% high density polyethylene, 1 - 5% inorganic powder;

[0011] Corona layer: 40 - 70% high impact polypropylene, 20 - 40% homopolypropylene, 5 - 20% high density polyethylene, 1 - 5% inorganic powder.

[0012] It should be noted that:

[0013] Linear easy tearability means that the force required to tear the film is small, and after tearing along the film notch, the deviation distance between the final crack and the notch is small. For non - biaxially stretched films, generally, the greater the ratio of transverse to longitudinal tear strength, the better the linear easy tearability.

[0014] Retort resistance means the degree of change in heat - seal strength, structure, appearance, etc. after the film undergoes high - temperature retorting. The lower the degree of change, the better the retort resistance.

[0015] The high - impact polypropylene in the polyolefin film of the present invention is polypropylene modified by ethylene - segment block copolymerization, that is, block copolymer polypropylene. Its heat - resistant temperature is relatively low, that is, the softening and melting temperatures are relatively low. When the content of high - impact polypropylene in the heat - seal layer is relatively high, it can better melt and adhere together during heating and pressurization, providing excellent heat - seal strength for the polyolefin film, avoiding the reduction of heat - seal strength after retorting of the film resulting in insecure heat - sealing, enhancing the retort resistance of the polyolefin film. Moreover, since the high - impact polypropylene is block copolymer polypropylene, it has strong flexibility and can reduce the embrittlement of the polyolefin film caused by the change of the film crystal structure after high - temperature retorting, which affects the mechanical properties of the polyolefin film.

[0016] When the content of high - impact polypropylene in each layer is too high, the heat - resistant performance of the polyolefin film decreases; when the content is too low, the toughness and heat - seal strength of the polyolefin film will be reduced, especially the heat - seal strength after retorting.

[0017] In the heat - seal layer, the mass percentage of homopolypropylene < the mass percentage of high - impact polypropylene. When the content of homopolypropylene in the heat - seal layer is higher than that of high - impact polypropylene, it will lead to an increase in the starting sealing temperature and a decrease in heat - seal firmness, that is, a decrease in heat - seal strength, which has an adverse effect on the retort resistance and increases the risk of bag breakage after retorting.

[0018] Homopolypropylene has good rigidity, high softening point and crystallinity. The content of homopolypropylene in the middle layer is relatively high, which can provide excellent heat resistance for polyolefin films, making the polyolefin films not easily soften or melt when heated. Since the heat-sealing layer needs to reduce the content of homopolypropylene to ensure the heat-sealing strength, in order to improve the overall heat resistance of the polyolefin film, the content of high-impact polypropylene in the middle layer is lower than that in the heat-sealing layer, while the content of homopolypropylene is relatively high. When the content of homopolypropylene in each layer is too high, the content of high-impact polypropylene relatively decreases, the toughness of the polyolefin film decreases, and the shrinkage rate of the homopolypropylene chain segments is relatively large when heated. When its content is too high, the film is prone to shrinkage deformation during cooking, and the retort resistance performance becomes poor; while when the content of homopolypropylene is too low, the heat resistance of the polyolefin film is poor, the degree of decrease in heat-sealing strength after cooking is large, and the film is prone to deformation, softening and adhesion, and the retort resistance performance is poor.

[0019] The chain structure of high-density polyethylene is regular, and due to its high density, its molecular weight and crystallinity are also high. During the film-forming process of polyolefin films, it is beneficial for the atoms in the crystal to be arranged along the longitudinal direction, making the polyolefin film have longitudinal linear tearability. When the content of high-density polyethylene is too low, it is not conducive to the longitudinal arrangement of atoms in the polyolefin film crystal, resulting in a decrease in the linear tearability of the polyolefin film. When the content is too high, the retort resistance performance of the polyolefin film decreases.

[0020] Inorganic powders can act as stress concentration points during the tearing process of polyolefin films, promote the growth of cracks, and improve the linear tearability of polyolefin films. When the content of inorganic powders is too low, it is not sufficient to act as a stress concentration point, and the linear tearability of the polyolefin film decreases. When the content is too high, the polyolefin film becomes brittle and the impact strength decreases. In order to prevent the polyolefin film from having poor heat-sealing (i.e., false sealing) due to excessive powders, resulting in insufficient heat-sealing strength after film bag-making, the proportion of inorganic powders in the heat-sealing layer is relatively small.

[0021] In addition, the high-density polyethylene in the corona layer of the present invention can extend the corona holding time of the polyolefin film, thereby improving the adhesion of the polyolefin film to adhesives and inks on the surface of packaging materials. The composition of the corona layer is similar to that of the heat-sealing layer, making the polyolefin film have better symmetry, avoiding the curling problem of the polyolefin film, and at the same time improving the linear tearability of the polyolefin film.

[0022] Specifically, the high-impact polypropylene also contains ethylene chain segments, which can improve the compatibility of high-impact polypropylene and high-density polyethylene, making the appearance of the polypropylene film product uniform and the performance stable.

[0023] Specifically, the impact strength of the high-impact polypropylene ≥ 9 kg-cm / cm; the density of the high-density polyethylene ≥ 0.946 g / cm 3 ; the flexural modulus of the homopolypropylene ≥ 1300 MPa.

[0024] Controlling the relevant properties of the above components can further improve the mechanical properties of the polypropylene film. In addition, defining the density of the high-density polyethylene is beneficial to further enhancing the linear easy-tearing performance.

[0025] Specifically, in the middle layer, the mass percentage of the homopolypropylene ≥ the mass percentage of the high-impact polypropylene.

[0026] When the content of the homopolypropylene in the middle layer is higher than that of the high-impact polypropylene, it is beneficial to further enhance the heat resistance of the polyolefin film, and then enhance the retort resistance performance.

[0027] Specifically, the inorganic powder is one or more of talc powder, calcium carbonate, mica, wollastonite, kaolin.

[0028] The present invention selects the flaky material as the inorganic powder, which is beneficial to further promote the formation of stress concentration points and promote crack growth.

[0029] Specifically, the particle size of the inorganic powder ≥ 2000 mesh.

[0030] Preferably, the polyolefin film comprises the following components by mass percentage:

[0031] Heat-sealing layer: 55-65% of high-impact polypropylene, 20-30% of homopolypropylene, 10-20% of high-density polyethylene, 0.5-1% of inorganic powder;

[0032] Middle layer: 25-35% of high-impact polypropylene, 45-55% of homopolypropylene, 10-20% of high-density polyethylene, 4-5% of inorganic powder;

[0033] Corona layer: 45-55% of high-impact polypropylene, 25-35% of homopolypropylene, 10-20% of high-density polyethylene, 4-5% of inorganic powder.

[0034] Specifically, the mass ratio of the heat-sealing layer, the middle layer and the corona layer is 1:(2-5):1, preferably 1:(2.5-4.5):1, more preferably 1:3:1.

[0035] The heat-sealing layer of the present invention mainly provides the heat-sealing strength. The size of the mass ratio of the heat-sealing layer during the extrusion process will affect the heat-sealing strength of the polyolefin film; the middle layer is the main structural layer of the polyolefin film, and its mass ratio will affect the mechanical properties and retort resistance performance of the polyolefin film; the mass ratio of the corona layer will affect the combination of the polyolefin film with other packaging materials. By controlling the mass ratio of the heat-sealing layer, the middle layer and the corona layer, each layer of the polyolefin film can play a better role, which is beneficial to further enhancing the linear easy-tearing performance and retort resistance performance of the polyolefin film.

[0036] Specifically, the homopolypropylene has a melt index of 0.1 to 5.0 g / 10 min at 230°C and 2.16 kg.

[0037] Specifically, the high-density polyethylene has a melt index of 0.1 to 5.0 g / 10 min at 190°C and 2.16 kg.

[0038] The homopolypropylene and high-density polyethylene have a relatively low melt index, a relatively high density, and a high crystallinity, which is beneficial to improving the linear easy-tearing performance and at the same time enhancing the mechanical properties of the polyolefin film. In addition, the melt index also affects the processing performance of the film, and controlling it is beneficial to the forming during the film production process.

[0039] Specifically, the thickness of the polyolefin film is 50 to 100 μm, preferably 50 to 80 μm, and more preferably 70 μm.

[0040] By controlling the thickness of the polyolefin film, the application requirements in the field of packaging materials can be further met.

[0041] Specifically, the thickness of the intermediate layer of the polypropylene film is 25 to 70 μm.

[0042] Preferably, the thickness of the intermediate layer of the polypropylene film is 30 to 50 μm, more preferably 40 to 50 μm, and still more preferably 42 μm.

[0043] Since the homopolypropylene can provide excellent mechanical strength and heat resistance for the polyolefin film, its dosage can improve the retort resistance performance of the polyolefin film within a certain range. And the content of homopolypropylene in the intermediate layer is relatively high. Therefore, controlling the thickness of the intermediate layer is beneficial to further enhancing the retort resistance performance of the polyolefin film. However, if the thickness of the intermediate layer is too thick, the polyolefin film will be too brittle after retorting and the impact strength will decrease.

[0044] The present invention specifically protects a method for preparing the above polyolefin film, which includes the following steps:

[0045] Take each component of the heat-sealing layer, intermediate layer, and corona layer according to the ratio, and mix them evenly respectively. Then add the mixtures of the heat-sealing layer, intermediate layer, and corona layer into different extruders. After mixing and co-extrusion, a three-layer structure film is obtained, and then through post-treatment, a linear easy-tearing and retort-resistant polyolefin film product is obtained.

[0046] The polyolefin film of the present invention is prepared by a three-layer co-extrusion process, and the preparation process is simple and the cost is low, which can realize large-scale industrial production.

[0047] Specifically, the process parameters of each section in the extruder are as follows: Zone 1: 100 to 150°C; Zone 2: 220°C; Zone 3: 230°C; Zones 4 to 8: 240°C; Die temperature: 220 to 260°C.

[0048] By controlling the temperatures of each section of the extruder, the layers of the polyolefin film are extruded uniformly and stably, which is beneficial to improving the appearance uniformity of the polyolefin film.

[0049] The present invention also protects the application of the above polyolefin film in the field of packaging materials.

[0050] The polyolefin film described in the present invention has both retort resistance and easy tearability in a straight line, and can be used for the innermost layer of packaging materials. Among them, the heat-sealing layer is on the inner surface of the polyolefin film with easy tearability in a straight line and retort resistance, and is in direct contact with the packaging contents. It has stable chemical properties, will not volatilize harmful substances, and can provide excellent heat-sealing strength and good easy tearability in a straight line; the intermediate layer is in the middle of the polyolefin film and is the main structural layer of the polyolefin film, which improves the mechanical strength, retort resistance and easy tearability in a straight line of the polyolefin film; the corona layer is the surface layer of the polyolefin film, which is in close contact with the surface of the product to be decorated during use and is usually in direct contact with glue, ink, etc. The corona layer of the polyolefin film of the present invention has a long corona retention time after corona treatment, can be directly printed or compounded with aluminum foil or PET to ensure the combination of the polyolefin film and the packaging material, and is used for preparing commercial packaging bags.

[0051] In addition, the polyolefin film has good toughness, which can avoid the problem of embrittlement of the packaging bag after high-temperature cooking.

[0052] The polyolefin film described in the present invention is particularly suitable for the field of food packaging materials. For foods with oil and water, such as pet foods, etc., when heating is required after packaging, if the retort resistance is poor, it is easy to cause damage to the packaging and contamination of the food, and if the easy tearability in a straight line is poor, the oil and water in the food will splash out when opening the packaging, making it inconvenient to use. The polyolefin film described in the present invention can well solve these problems.

[0053] Compared with the prior art, the present invention has at least the following beneficial effects:

[0054] The present invention provides a polyolefin film with easy tearability in a straight line and retort resistance. The polyolefin film includes a heat-sealing layer, an intermediate layer and a corona layer. By controlling the ratio of homopolypropylene and high-impact polypropylene in the heat-sealing layer, the intermediate layer and the corona layer, the retort resistance and the easy tearability in a straight line of the polyolefin film are improved, and at the same time, embrittlement of the polyolefin film after high-temperature cooking is prevented; high-density polyethylene can promote the longitudinal arrangement of atoms during the film-forming process, and the inorganic powder can act as a stress concentration point during the tearing process. By controlling the amounts of high-density polyethylene and inorganic powder, the easy tearability in a straight line of the polyolefin film can be further improved.

[0055] The polyolefin film of the present invention is applicable to the field of packaging materials, has excellent linear tearability and retort resistance, the ratio of transverse and longitudinal tear strengths is not less than 8, and it can withstand retorting at 121 °C. Detailed implementation mode

[0056] The present invention will be further described below in conjunction with the detailed implementation mode, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventionally purchased raw material reagents.

[0057] High impact polypropylene is purchased from SK Chemicals Co., Ltd. / J340F, with a melt index of 2.5 g / 10 min at 230 °C and 2.16 kg, and a density of 0.910 g / cm 3 , and the impact strength is 9 kg-cm / cm.

[0058] Homopolypropylene is purchased from Formosa Plastics Corporation, Taiwan, China / PT100, with a melt index of 1.6 g / 10 min at 230 °C and 2.16 kg, and a density of 0.901 g / cm 3 , and the flexural modulus is 1590 MPa.

[0059] High density polyethylene is purchased from Zhenhai Refining & Chemical Company / ZH6098; the melt index is 0.46 g / 10 min at 190 °C and 2.16 kg, and the density is 0.948 g / cm 3 .

[0060] The inorganic powder is purchased from Guiguang Talc Development Co., Ltd.: talc powder of 3000 mesh.

[0061] Example 1

[0062] A linear tearable and retort-resistant polyolefin film, comprising the following components by mass percentage:

[0063] Heat-sealing layer: high impact polypropylene: 60%, homopolypropylene: 24%, high density polyethylene: 15%, inorganic powder: 1%;

[0064] Intermediate layer: high impact polypropylene: 31%, homopolypropylene: 49%, high density polyethylene: 15%, inorganic powder: 5%;

[0065] Corona layer: high impact polypropylene: 51%, homopolypropylene: 29%, high density polyethylene: 15%, inorganic powder: 5%;

[0066] The inorganic powder is talc powder of 3000 mesh;

[0067] The mass ratio of the heat-sealing layer, the intermediate layer and the corona layer is 1:3:1;

[0068] The thickness of the intermediate layer is 42 μm;

[0069] The thickness of the polyolefin film is 70 μm.

[0070] Example 2

[0071] A linear easy-tear and steam-resistant polyolefin film, with the same structure and composition as in Example 1, the differences are as follows:

[0072] Heat-sealing layer: High-impact polypropylene: 50%, homopolypropylene: 30%, high-density polyethylene: 19.9%, inorganic powder: 0.1%;

[0073] Intermediate layer: High-impact polypropylene: 20%, homopolypropylene: 60%, high-density polyethylene: 19%, inorganic powder: 1%;

[0074] Corona layer: High-impact polypropylene: 40%, homopolypropylene: 40%, high-density polyethylene: 19%, inorganic powder: 1%.

[0075] The mass ratio of the heat-sealing layer, intermediate layer and corona layer is 1:2:1;

[0076] The thickness of the intermediate layer is 25 μm.

[0077] Example 3

[0078] A linear easy-tear and steam-resistant polyolefin film, with the same structure and composition as in Example 1, the differences are as follows:

[0079] Heat-sealing layer: High-impact polypropylene: 70%, homopolypropylene: 23%, high-density polyethylene: 5%, inorganic powder: 2%;

[0080] Intermediate layer: High-impact polypropylene: 50%, homopolypropylene: 30%, high-density polyethylene: 15%, inorganic powder: 5%;

[0081] Corona layer: High-impact polypropylene: 70%, homopolypropylene: 20%, high-density polyethylene: 5%, inorganic powder: 5%.

[0082] The mass ratio of the heat-sealing layer, intermediate layer and corona layer is 1:5:1;

[0083] The thickness of the intermediate layer is 70 μm.

[0084] Example 4

[0085] A linear easy-tear and steam-resistant polyolefin film, with the same structure and composition as in Example 1, the differences are as follows:

[0086] Heat-sealing layer: High-impact polypropylene: 55%, homopolypropylene: 30%, high-density polyethylene: 14.5%, inorganic powder: 0.5%;

[0087] Intermediate layer: High impact polypropylene: 25%, Homopolypropylene: 55%, High density polyethylene: 16%, Inorganic powder: 4%;

[0088] Corona layer: High impact polypropylene: 45%, Homopolypropylene: 35%, High density polyethylene: 16%, Inorganic powder: 4%.

[0089] Example 5

[0090] A linear easy-tear and retort-resistant polyolefin film, with the same structure and composition as in Example 1, the differences being:

[0091] Heat-sealing layer: High impact polypropylene: 65%, Homopolypropylene: 20%, High density polyethylene: 14%, Inorganic powder: 1%;

[0092] Intermediate layer: High impact polypropylene: 35%, Homopolypropylene: 45%, High density polyethylene: 15%, Inorganic powder: 5%;

[0093] Corona layer: High impact polypropylene: 55%, Homopolypropylene: 25%, High density polyethylene: 15%, Inorganic powder: 5%.

[0094] Example 6

[0095] A linear easy-tear and retort-resistant polyolefin film, with the same structure and composition as in Example 1, the differences being:

[0096] The mass ratio of the heat-sealing layer, intermediate layer and corona layer is 1:4:1;

[0097] The thickness of the intermediate layer is 50 μm.

[0098] Example 7

[0099] A preparation method of the linear easy-tear and retort-resistant polyolefin film of any one of Examples 1 to 6 above, comprising the following steps:

[0100] Take the components of the heat-sealing layer, intermediate layer and corona layer according to the ratio, and mix the components of each layer evenly in different mixers, remove dust, then add the mixed materials of the heat-sealing layer, intermediate layer and corona layer into different extruders respectively, and obtain a three-layer structure film after mixing and co-extrusion, and then obtain the finished product of the linear easy-tear and retort-resistant polyolefin film through corona treatment, traction and winding;

[0101] The process parameters of each section in the extruder are: Zone 1: 120 °C; Zone 2: 220 °C; Zone 3: 230 °C; Zones 4 - 8: 240 °C; Die temperature: 240 °C.

[0102] Comparative Example 1

[0103] A polyolefin film, with the same structure and composition as in Example 1, except that the high-impact polypropylene in the heat-sealing layer is 39% and the homopolypropylene is 45%.

[0104] Comparative Example 2

[0105] A polyolefin film, with the same structure and composition as in Example 1, except that the high-impact polypropylene in the middle layer is 57%, the homopolypropylene is 25%, the high-density polyethylene is 13%, and the inorganic powder is 5%.

[0106] Comparative Example 3

[0107] A polyolefin film, with the same structure and composition as in Example 1, except that the high-impact polypropylene in the middle layer is 20%, the homopolypropylene is 70%, the high-density polyethylene is 5%, and the inorganic powder is 5%.

[0108] Result Detection

[0109] (1) Tear strength test: According to GB / T 16578.1-2008, the test speed is 250 mm / min;

[0110] The larger the value of the transverse tear strength / longitudinal tear strength, the better the linear easy-tearing performance; where the longitudinal direction indicates the direction along which the film is produced.

[0111] (2) Retort resistance test: The sample film is heat-sealed into a three-side sealed rice bag, evacuated and then sealed: The sample bag filled with rice is placed in a retort sterilizer, and the lid is closed: Sterilize at 121 °C for 30 min, 35 min, and 40 min; After the test is completed and fully cooled, take out the test sample bag and observe the heat resistance. It is required that the film has no obvious deformation, no adhesion, and no burst bag, which means that the retort performance is good under the set conditions and passes the retort resistance test; where a burst bag means that the heat seal fails due to too low heat seal strength and the seal opens.

[0112] (3) Notch deviation degree: Tear the polyolefin films obtained in the above examples and comparative examples longitudinally by 80 mm, and measure the deviation range with the notch (the torn place) as the reference; A deviation degree within ±2 mm is considered to have good linear easy-tearing performance.

[0113] The results are shown in Table 1.

[0114] Table 1. Test results of the linear easy-tearing performance and retort resistance performance of polyolefin films

[0115]

[0116] As can be seen from Table 1, the polyolefin film obtained by the present invention takes into account both the straight-line easy-tearing performance and the retort resistance performance. Its longitudinal tear strength does not exceed 7 kN / m, and the ratio of the transverse and longitudinal tear strengths is not less than 9.8, having excellent straight-line easy-tearing performance. At the same time, after retorting at 121 °C for 30 min, there are no obvious problems such as deformation, bag bursting or adhesion, having good retort resistance performance. In Comparative Example 1, the content of homopolypropylene in the heat-sealing layer is too high, while the content of high-impact polypropylene is too low, resulting in a decrease in heat-sealing strength, and deformation and bag bursting occur during bag making after retorting. In Comparative Example 2, the content of high-impact polypropylene in the middle layer is relatively high, while the content of homopolypropylene is relatively low, resulting in poor overall heat resistance of the polyolefin film, and obvious deformation occurs after retorting. In Comparative Example 3, the content of homopolypropylene in the middle layer is too high, and both its straight-line easy-tearing performance and retort resistance performance decline.

[0117] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A linear easy-to-tear and steam-resistant polyolefin film, characterized in that, The polyolefin film comprises the following components by mass percentage: Heat-sealing layer: 50-70% of high-impact polypropylene, 20-35% of homopolypropylene, 5-20% of high-density polyethylene, 0.1-2% of inorganic powder; Intermediate layer: 20-50% of high-impact polypropylene, 30-60% of homopolypropylene, 5-20% of high-density polyethylene, 1-5% of inorganic powder; Corona layer: 40-70% of high-impact polypropylene, 20-40% of homopolypropylene, 5-20% of high-density polyethylene, 1-5% of inorganic powder.

2. The polyolefin film according to claim 1, wherein In the intermediate layer, the mass percentage of homopolypropylene ≥ the mass percentage of high-impact polypropylene.

3. The polyolefin film according to claim 1, wherein The polyolefin film comprises the following components by mass percentage: Heat-sealing layer: 55-65% of high-impact polypropylene, 20-30% of homopolypropylene, 10-20% of high-density polyethylene, 0.5-1% of inorganic powder; Intermediate layer: 25-35% of high-impact polypropylene, 45-55% of homopolypropylene, 10-20% of high-density polyethylene, 4-5% of inorganic powder; Corona layer: 45-55% of high-impact polypropylene, 25-35% of homopolypropylene, 10-20% of high-density polyethylene, 4-5% of inorganic powder.

4. The polyolefin film according to claim 1, characterized in that, The mass ratio of the heat-sealing layer, the intermediate layer and the corona layer is 1:(2-5):

1.

5. The polyolefin film according to claim 1, wherein The melt index of the homopolypropylene at 230 °C and 2.16 kg is 0.1-5.0 g / 10 min.

6. The polyolefin film according to claim 1, wherein The melt index of the high-density polyethylene at 190 °C and 2.16 kg is 0.1-5.0 g / 10 min.

7. The polyolefin film according to claim 1, wherein The thickness of the intermediate layer of the polyolefin film is 25-70 μm.

8. The polyolefin film according to claim 7, wherein, The thickness of the intermediate layer of the polyolefin film is 30-50 μm.

9. A method for preparing the polyolefin film according to any one of claims 1 to 8, characterized in that, Comprising the following steps: Take each component of the heat-sealing layer, the intermediate layer and the corona layer according to the ratio, and mix them evenly respectively. Then add the mixtures of the heat-sealing layer, the intermediate layer and the corona layer into different extruders, and obtain a three-layer structure film after mixing and co-extrusion, and then obtain the finished product of the linear easy-tear and retort-resistant polyolefin film after post-treatment.

10. Use of the polyolefin film according to any one of claims 1-8 in the field of packaging materials.

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