Bidirectional easy-tear multilayer film of propylene-based polymers

Abstract

This disclosure relates to a multilayer film of a propylene-based polymer, a method for preparing the multilayer film of the propylene-based polymer, and articles comprising the multilayer film of the propylene-based polymer. The multilayer film of the propylene-based polymer of this disclosure is bidirectionally (longitudinal and transverse), particularly linearly tearable, and the multilayer film exhibits excellent stiffness, longitudinal and transverse tensile strength, and toughness. The method for preparing the multilayer film of this disclosure is simple, energy-efficient, and highly effective.

Description

Technical Field

[0001] This disclosure relates to a multilayer film of a propylene-based polymer, a method for preparing the multilayer film of the propylene-based polymer, and an article comprising the multilayer film of the propylene-based polymer. Background Technology

[0002] For ease of final use, the packaging film needs to be easily torn in a straight line in both directions. Existing methods are typically based on polyethylene (PE) and require the addition of polymer modifiers, such as cyclic olefin copolymers (COC). However, there are no reports on the preparation of biaxially tearable propylene-based polymer multilayer films using in-line longitudinal stretching (MDO).

[0003] Therefore, there is a need to provide a bidirectional tearable multilayer film of propylene-based polymer and a method for preparing the same. Summary of the Invention

[0004] In this disclosure, numerical ranges are used to indicate the range of the minimum and maximum values ​​recorded before and after the numerical values, respectively.

[0005] This article discloses specific values ​​of relevant features (including the endpoints of the range) that can be combined to form a new range.

[0006] In this document, several subheadings are provided for ease of reading; however, these subheadings do not imply that the content of these sections is isolated from each other, and those skilled in the art can combine them as needed without exceeding the scope of this disclosure. Similarly, those skilled in the art can combine the content of different embodiments as needed without exceeding the scope of this disclosure.

[0007] One aspect of this disclosure relates to a multilayer film made of a propylene-based polymer, wherein the multilayer film is prepared by co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner.

[0008] The longitudinal stretching has a stretching ratio of 1.8-5.5, and the longitudinal stretching is performed by roller stretching.

[0009] The multilayer film has at least three sublayers, and the thickness of the multilayer film is 15-50 micrometers; and

[0010] The propylene-based polymer contains at least 90% by weight of units derived from propylene, based on the total weight of the propylene-based polymer.

[0011] In one aspect, this disclosure relates to a method for preparing a multilayer film of a propylene-based polymer of the present disclosure, comprising co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner to obtain the multilayer film.

[0012] In one aspect, this disclosure relates to an article of manufacture comprising a multilayer film of a propylene-based polymer of this disclosure.

[0013] By combining a propylene-based polymer with a novel process, the propylene-based polymer multilayer film of this disclosure is bidirectionally (longitudinal and transverse) tearable, particularly linearly tearable, and the multilayer film exhibits excellent stiffness, longitudinal and transverse tensile strength, and toughness. The method for preparing the multilayer film of this disclosure is simple, energy-efficient, and highly effective. Attached Figure Description

[0014] Figure 1 A schematic diagram of the roller stretching unit is shown.

[0015] Figure 2 A schematic diagram of the samples used in longitudinal and transverse linear tear tests is shown.

[0016] Figure 3 Images of the samples after the longitudinal tearing experiment are shown, in which Figure 3 (a) is an image of the unstretched multilayer film sample of Comparative Example 1 after a longitudinal linear tearing experiment. Figure 3 (b) is a picture of the longitudinal linear tear test of the multilayer film sample of Example 1.

[0017] Figure 4 A schematic diagram of the sample from the trouser tear test is shown.

[0018] Figure 5 Images of samples from a transverse trouser tear test are shown, in which... Figure 5 (a) Image of the sample used in the trouser tear test. Figure 5 (b) is an image of the unstretched multilayer film sample of Comparative Example 1 after a transverse trouser-shaped tear test. Figure 5 (c) is a picture of the multilayer film sample of Example 1 after a transverse trouser tear test. Detailed Implementation

[0019] Multilayer films of propylene-based polymers

[0020] One aspect of this disclosure relates to a multilayer film made of a propylene-based polymer, wherein the multilayer film is prepared by co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner.

[0021] The longitudinal stretching has a stretching ratio of 1.8-5.5, and the longitudinal stretching is performed by roller stretching.

[0022] The multilayer film has at least three sublayers, and the thickness of the multilayer film is 15-50 micrometers; and

[0023] The propylene-based polymer contains at least 90% by weight of units derived from propylene, based on the total weight of the propylene-based polymer.

[0024] In one or more embodiments, the propylene-based polymer has an MFR of 5-15 g / 10 min, such as 6-10 g / 10 min, which is determined according to ASTM D1238 at a load of 2.16 kg and a temperature of 230 °C.

[0025] In one or more embodiments, the propylene-based polymer contains at least 90% by weight (e.g., 91% by weight, 92% by weight, 94% by weight, 95% by weight, 96% by weight, 97% by weight, 98% by weight, 98.5% by weight, 99% by weight, or 99.5% by weight), or at least 95% by weight, or 95-99.5% by weight, or 95-100% by weight, or 95-99% by weight, or 96-99% by weight, or 95-98.5% by weight, or 96-98.5% by weight, based on the total weight of the propylene-based polymer.

[0026] In one or more embodiments, the propylene-based polymer is selected from propylene homopolymers and propylene copolymers, particularly propylene random copolymers.

[0027] In one or more embodiments, the propylene copolymer (e.g., a propylene random copolymer) is derived from propylene and a comonomer, wherein the comonomer is a C2 olefin, i.e., ethylene. In the propylene copolymer (e.g., a propylene random copolymer), the amount of comonomer can be no more than 10 wt% (e.g., 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1.5 wt%, 1 wt%, 0.5 wt%), for example 0.5-10 wt%, 0.5-8 wt%, 1-5 wt%, 1-4 wt%, 1.5-5 wt%, or 1.5-4 wt%, based on the total weight of the propylene copolymer.

[0028] In one or more embodiments, the propylene-based polymer is a propylene-ethylene random copolymer, wherein the amount of units derived from propylene is as described above and / or the amount of units derived from ethylene is as described above for the comonomers.

[0029] In one or more embodiments, the multilayer film is made of a propylene-based polymer. In one or more embodiments, the multilayer film is made of a propylene homopolymer. In one or more embodiments, the multilayer film is made of a propylene random copolymer.

[0030] In this disclosure, an initial multilayer film is obtained by co-extruding a propylene-based polymer. In one or more embodiments, the co-extrusion is performed using an extruder. The number of extruders used is typically less than or equal to the number of sublayers in the multilayer film. When the number of extruders is less than the number of sublayers in the multilayer film, two or more sublayers can be separated from the die of the extruder. The operating temperature of the extruder can be 210-270°C (e.g., 220°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C, or 265°C), for example, 220-265°C or 230-250°C. The feed stream can be cooled by cooling rollers after leaving the die of the extruder to obtain the initial multilayer film.

[0031] The initial thickness of the multilayer film depends on the set thickness of the multilayer film and the stretch ratio. Usually, the initial film thickness is equal to the multilayer film thickness multiplied by the stretch ratio.

[0032] In this disclosure, the longitudinal stretching stretch ratio is 1.8-5.5, for example 1.9, 2, 2.1, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 4, 4.5, 5 or 5.2, for example 2-5, 2-4, 2-3.5 or 2.5-3.5.

[0033] In this disclosure, the longitudinal stretching is performed via online roller stretching. Roller stretching is performed by two stretching rollers with different speeds, such as a stretching roller comprising a slow stretching roller and a fast stretching roller. For example, the film is first passed through the slow stretching roller and then through the fast stretching roller, utilizing the speed difference for stretching. The speed ratio of the fast stretching roller to the slow stretching roller corresponds to the stretching ratio. In one or more embodiments, the roller stretching unit may include a preheating roller, a stretching roller, an annealing roller, and a cooling roller, wherein the stretching roller includes a slow stretching roller and a fast stretching roller. In one or more embodiments, the temperature of the preheating roller may be 95-105°C. In one or more embodiments, the temperature of the stretching roller may be 110-120°C. In one or more embodiments, the temperature of the annealing roller may be 2-8°C (e.g., 2-5°C lower) lower than that of the stretching roller, for example, 108-115°C. In one or more embodiments, the temperature of the cooling roller may be 70-90°C, for example, 75-85°C.

[0034] After the roll stretching, the resulting multilayer film can be wound up.

[0035] In this disclosure, the multilayer film has at least 3 sublayers (such as 4, 5, 6 or 7 sublayers), for example 3-7 sublayers, or 5-7 sublayers, or 7 sublayers.

[0036] In one or more embodiments, the thickness of each sublayer is 1-9 micrometers (e.g., 1.5, 2, 3, 3.5, 4, 5, 6, 7, 8 or 8.5 micrometers), for example 1.5-8 micrometers.

[0037] In one or more embodiments, the thickness of the outer sublayer exposed to air is 50-85% (e.g., 55%, 60%, 65%, 70%, 75%, or 80%) of the average thickness of all sublayers, for example, 60-75%. Those skilled in the art will understand that the multilayer film has two outer sublayers exposed to air. In one or more embodiments, the thickness of the outer sublayer is 1-4 micrometers (e.g., 1.5, 2, 2.5, 3, or 3.5 micrometers), for example, 1.5-3.5 micrometers.

[0038] In one or more embodiments, the multilayer film has at least five sublayers, wherein the thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer is 50-85% (e.g., 55%, 60%, 65%, 70%, 75%, or 80%), for example, 60-75%, of the average thickness of all sublayers. Those skilled in the art will understand that in the case where the multilayer film has at least five sublayers, the multilayer film has two outer sublayers exposed to air and two sublayers immediately adjacent to the outer sublayers. In one or more embodiments, the thickness of the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 1-4 micrometers (e.g., 1.5, 2, 2.5, 3, or 3.5 micrometers), for example, 1.5-3.5 micrometers.

[0039] In one or more embodiments, the thickness of the sublayers other than the outer sublayer and the sublayers immediately adjacent to the outer sublayer is 120-160% (e.g., 125%, 135%, 140%, 145%, 150%, or 155%) of the average thickness of all sublayers, for example, 130-150%. In one or more embodiments, the thickness of the sublayers other than the outer sublayer and the sublayers immediately adjacent to the outer sublayer can be 4-9 micrometers (e.g., 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, or 8.5 micrometers), for example, 4.5-8 micrometers or 4.5-7 micrometers.

[0040] In one or more embodiments, the multilayer film has seven sublayers, wherein the thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer is 50-85% (e.g., 55%, 60%, 65%, 70%, 75% or 80%) of the average thickness of all sublayers, for example 60-75%, and for example the thickness of the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 1-4 micrometers (e.g., 1.5, 2, 2.5, 3 or 3.5 micrometers), for example 1.5-3.5 micrometers.

[0041] In one or more embodiments, the multilayer film has seven sublayers, and the thickness of the sublayers other than the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 120-160% (e.g., 125%, 135%, 140%, 145%, 150% or 155%) of the average thickness of all sublayers, for example 130-150%. For example, the thickness of the sublayers other than the outer sublayer and the sublayer immediately adjacent to the outer sublayer can be 4-9 micrometers (e.g. 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 or 8.5 micrometers), for example 4.5-8 micrometers or 4.5-7 micrometers.

[0042] In this disclosure, the thickness of the multilayer film is 15-50 micrometers (e.g., 18, 20, 22, 25, 27, 28, 30, 32, 35, 38, 40, 42, 45 or 48 micrometers), for example 20-40 micrometers, or 20-35 micrometers, or 20-28 micrometers, or 22-28 micrometers.

[0043] In one or more embodiments, the propylene-based polymers of each sublayer may be the same or different, especially the same.

[0044] In this disclosure, the multilayer film is a bidirectional (longitudinal and transverse) straight easy-tear multilayer film.

[0045] In one or more embodiments, the multilayer film is prepared by co-extrusion to obtain an initial multilayer film, and then by online longitudinal stretching of the initial multilayer film;

[0046] The longitudinal stretching ratio is 2-3.5, and the longitudinal stretching is performed by roller stretching.

[0047] The multilayer film has at least 5 sublayers and the thickness of the multilayer film is 20-28 micrometers;

[0048] The content of propylene-derived units in the propylene-based polymer is 95-99% by weight, based on the total weight of the propylene-based polymer;

[0049] The thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer in the multilayer film is 60-75% of the average thickness of all sublayers, and the thickness of the other sublayers besides the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 130-150% of the average thickness of all sublayers; and

[0050] In the roller stretching process, the stretching unit includes a preheating roller, a stretching roller, an annealing roller, and a cooling roller. The temperature of the preheating roller is 95-105℃, the temperature of the stretching roller is 110-120℃, the temperature of the annealing roller is 2-8℃ lower than that of the stretching roller, and the temperature of the cooling roller is 70-90℃.

[0051] In one or more embodiments, the multilayer film is prepared by co-extrusion to obtain an initial multilayer film, and then by online longitudinal stretching of the initial multilayer film;

[0052] The longitudinal stretching ratio is 2.5-3.5, and the longitudinal stretching is performed by roller stretching.

[0053] The multilayer film has at least 5 sublayers and the thickness of the multilayer film is 20-28 micrometers;

[0054] The content of propylene-derived units in the propylene-based polymer is 95-98.5% by weight, based on the total weight of the propylene-based polymer;

[0055] The thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer in the multilayer film is 60-75% of the average thickness of all sublayers, and the thickness of the other sublayers besides the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 130-150% of the average thickness of all sublayers; and

[0056] In the roller stretching process, the stretching unit includes a preheating roller, a stretching roller, an annealing roller, and a cooling roller. The temperature of the preheating roller is 95-105℃, the temperature of the stretching roller is 110-120℃, the temperature of the annealing roller is 2-8℃ lower than that of the stretching roller, and the temperature of the cooling roller is 70-90℃.

[0057] In one or more embodiments, the multilayer film is prepared by co-extrusion to obtain an initial multilayer film, and then by online longitudinal stretching of the initial multilayer film;

[0058] The longitudinal stretching ratio is 2.5-3.5, and the longitudinal stretching is performed by roller stretching.

[0059] The multilayer film has 5-7 sublayers and the thickness of the multilayer film is 20-28 micrometers;

[0060] The propylene-based polymer contains 95-98.5% by weight of propylene-derived units based on the total weight of the propylene-based polymer, and the propylene-based polymer is a random copolymer of propylene and ethylene.

[0061] The thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer in the multilayer film is 60-75% of the average thickness of all sublayers, and the thickness of the other sublayers besides the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 130-150% of the average thickness of all sublayers; and

[0062] In the roller stretching process, the stretching unit includes a preheating roller, a stretching roller, an annealing roller, and a cooling roller. The temperature of the preheating roller is 95-105℃, the temperature of the stretching roller is 110-120℃, the temperature of the annealing roller is 2-8℃ lower than that of the stretching roller, and the temperature of the cooling roller is 70-90℃.

[0063] In one or more embodiments, the multilayer film is prepared by co-extrusion to obtain an initial multilayer film, and then by online longitudinal stretching of the initial multilayer film;

[0064] The longitudinal stretching ratio is 2.5-3.5, and the longitudinal stretching is performed by roller stretching.

[0065] The multilayer film has 7 sublayers and the thickness of the multilayer film is 20-28 micrometers;

[0066] The propylene-based polymer contains 95-98.5% by weight of propylene-derived units based on the total weight of the propylene-based polymer, and the propylene-based polymer is a random copolymer of propylene and ethylene.

[0067] The thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer in the multilayer film is 60-75% of the average thickness of all sublayers, and the thickness of the other sublayers besides the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 130-150% of the average thickness of all sublayers; and

[0068] In the roller stretching process, the stretching unit includes a preheating roller, a stretching roller, an annealing roller, and a cooling roller. The temperature of the preheating roller is 95-105℃, the temperature of the stretching roller is 110-120℃, the temperature of the annealing roller is 2-8℃ lower than that of the stretching roller, and the temperature of the cooling roller is 70-90℃.

[0069] The multilayer film disclosed herein may contain one or more additives, such as antiblocking agents, slip agents, antifogging agents, colorants, pigments, dyes, antioxidants, fillers, radiation stabilizers, and antistatic agents. The amount of additives is generally no more than 5% by weight, for example no more than 2% by weight, for example 0.5-5% by weight or 0.5-2% by weight, based on the total weight of the multilayer film.

[0070] In one or more embodiments, the propylene-based polymer content in the multilayer film of this disclosure is at least 95% by weight (e.g., 96% by weight, 97% by weight, 98% by weight, 99% by weight, 99.5% by weight, or 100% by weight), for example at least 98% by weight, for example 95-99.5% by weight or 98-99.5% by weight, based on the total weight of the multilayer film.

[0071] In one or more embodiments, the multilayer film of this disclosure is substantially free of other polymers besides the propylene-based polymer. In this disclosure, "substantially free" means that the content (e.g., the content of other polymers) is no more than 2% by weight, for example, no more than 1% by weight, or no more than 0.5% by weight or 0.1% by weight, based on the total weight of the multilayer film.

[0072] Methods for preparing multilayer films and articles containing multilayer films

[0073] One aspect of this disclosure relates to a method for preparing a multilayer film of a propylene-based polymer of this disclosure, comprising co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner to obtain the multilayer film.

[0074] In one or more embodiments, the operating temperature of the extruder can be 210-270°C (e.g., 220°C, 230°C, 235°C, 240°C, 245°C, 250°C, 255°C, 260°C or 265°C), for example 220-265°C or 230-250°C.

[0075] The specific details regarding extrusion and stretching are as described above.

[0076] One aspect of this disclosure relates to an article of manufacture comprising a multilayer film of a propylene-based polymer of this disclosure. In one embodiment, the article is a packaging article.

[0077] Those skilled in the art will be able to more readily understand the present invention based on the following embodiments:

[0078] 1. A multilayer film of a propylene-based polymer, wherein the multilayer film is prepared by co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner.

[0079] The longitudinal stretching has a stretching ratio of 1.8-5.5, and the longitudinal stretching is performed by roller stretching.

[0080] The multilayer film has at least three sublayers, and the thickness of the multilayer film is 15-50 micrometers; and

[0081] The propylene-based polymer contains at least 90% by weight of units derived from propylene, based on the total weight of the propylene-based polymer.

[0082] 2. A multilayer film of a propylene-based polymer according to embodiment 1, wherein the longitudinal stretching stretch ratio is 2-4 or 2-3.5.

[0083] 3. A multilayer film of a propylene-based polymer according to embodiment 1 or 2, wherein the multilayer film has 3-7 sublayers or 5-7 sublayers.

[0084] 4. A multilayer film of a propylene-based polymer according to any one of embodiments 1-3, wherein the thickness of each sublayer is 1-9 micrometers, for example 1.5-8 micrometers.

[0085] 5. A multilayer film of a propylene-based polymer according to any one of embodiments 1-4, wherein the thickness of the outer sublayer exposed to air is 50-85%, for example 60-75%, of the average thickness of all sublayers.

[0086] 6. A multilayer film of a propylene-based polymer according to any one of embodiments 1-5, wherein the multilayer film has at least 5 sublayers, wherein the thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer is 50-85%, for example 60-75%, of the average thickness of all sublayers.

[0087] 7. A multilayer film of a propylene-based polymer according to embodiment 6, wherein the thickness of the sublayers other than the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 120-160%, for example 130-150%, of the average thickness of all sublayers.

[0088] 8. A multilayer film of a propylene-based polymer according to any one of embodiments 1-7, wherein the thickness of the multilayer film is 20-40 micrometers, or 20-35 micrometers, or 20-28 micrometers.

[0089] 9. A multilayer film of a propylene-based polymer according to any one of embodiments 1-8, wherein the content of propylene-derived units in the propylene-based polymer is at least 92% by weight or at least 95% by weight, or 95-99% by weight or 95-98.5% by weight, based on the total weight of the propylene-based polymer.

[0090] 10. A multilayer film of a propylene-based polymer according to any one of embodiments 1-9, wherein the propylene-based polymer is selected from propylene homopolymers and propylene random copolymers.

[0091] 11. A multilayer film of a propylene-based polymer according to any one of embodiments 1-10, wherein the propylene random copolymer is derived from propylene and a comonomer, wherein the comonomer is a C2 olefin.

[0092] 12. A multilayer film of a propylene-based polymer according to any one of embodiments 1-11, wherein the propylene-based polymer has an MFR of 5-15 g / 10 min, such as 6-10 g / 10 min, said MFR being determined according to ASTM D1238 at a load of 2.16 kg and a temperature of 230 °C.

[0093] 13. A multilayer film of a propylene-based polymer according to any one of embodiments 1-12, wherein the multilayer film is a bidirectional linear tearable multilayer film.

[0094] 14. A multilayer film of a propylene-based polymer according to any one of embodiments 1-13, wherein the multilayer film is made of a propylene-based polymer.

[0095] 15. A multilayer film of a propylene-based polymer according to any one of embodiments 1-14, wherein the multilayer film is prepared by co-extrusion to obtain an initial multilayer film, and then by online longitudinal stretching of the initial multilayer film;

[0096] The longitudinal stretching ratio is 2.5-3.5, and the longitudinal stretching is performed by roller stretching.

[0097] The multilayer film has 5-7 sublayers and the thickness of the multilayer film is 20-28 micrometers;

[0098] The propylene-based polymer contains 95-98.5% by weight of propylene-derived units based on the total weight of the propylene-based polymer, and the propylene-based polymer is a random copolymer of propylene and ethylene.

[0099] The thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer in the multilayer film is 60-75% of the average thickness of all sublayers, and the thickness of the other sublayers besides the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 130-150% of the average thickness of all sublayers; and

[0100] In the roller stretching process, the stretching unit includes a preheating roller, a stretching roller, an annealing roller, and a cooling roller. The temperature of the preheating roller is 95-105℃, the temperature of the stretching roller is 110-120℃, the temperature of the annealing roller is 2-8℃ lower than that of the stretching roller, and the temperature of the cooling roller is 70-90℃.

[0101] 16. A method for preparing a multilayer film of a propylene-based polymer as defined in any one of embodiments 1-15, comprising co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner to obtain the multilayer film.

[0102] 17. The method according to embodiment 16, wherein the operating temperature of the extruder used in co-extrusion is 210-270°C, or 220-265°C, or 230-250°C.

[0103] 18. An article comprising a multilayer film of a propylene-based polymer as defined in any one of embodiments 1-15.

[0104] Example

[0105] The examples below are for illustrative purposes and not for limiting the invention. Unless otherwise stated, the amounts of each substance in the examples are based on weight.

[0106] raw material

[0107] RCP: PP9513 purchased from ExxonMobil, a random copolymer of propylene and ethylene, wherein the ethylene content is 2.8 wt%; MFR is 7.3 g / min, and the MFR is determined according to ASTM D1238 at a load of 2.16 kg and a temperature of 230 °C.

[0108] method

[0109] Tensile test: based on ASTM D882.

[0110] Needle puncture: according to CEN1447.

[0111] Longitudinal and transverse linear tear tests:

[0112] Take a rectangular sample with a length of 30cm and a width of 5cm. Make two 5cm long incisions at one end of the sample, 2cm apart, thus dividing this end into three parts. The two outer pieces are identical, with a length of 5cm and a width of 1.5cm, and the middle piece has a length of 5cm and a width of 2cm (see...). Figure 2 Using an electronic tensile testing machine, pull the ends of the two pieces on both sides and the middle piece of the specimen in reverse. Pull the two pieces on both sides to separate them from the middle piece. The pulling speed is set to 1000 mm / min. Measure the width of the strip between the middle piece and the starting tear 5 cm away. Use this width value as an indicator of linear tear resistance. The closer this width is to 2 cm, the better the linear tear resistance.

[0113] Pant tear test: based on ASTM D1938. A schematic diagram of the sample used in the pant tear test is shown below. Figure 4 As shown. The sample preparation for the trouser tear test is as follows. Figure 5 As shown in (a).

[0114] Example 1 - Preparation of multilayer film with a stretch ratio of 3

[0115] Copolymer polypropylene (PP9513) particles are fed into five single-screw extruders A, B, C, D, and E for heating, melting, and extrusion into straight dies. Extruders A, D, and E each produce one layer of material, while extruders B and C each produce two layers, resulting in a total of seven layers (corresponding to seven sub-layers). The extruded material is cooled and shaped on cooling rollers circulated with cooling water to form an initial multilayer film. The thickness ratio of each sublayer is 10:10:20:20:20:10:10. The initial multilayer film is then preheated using a preheating roller, followed by stretching using a speed difference between a slow stretching roller and a fast stretching roller. After stretching, it passes through annealing rollers and cooling rollers to obtain a multilayer film, which is then wound up. The thickness of this multilayer film is 25 micrometers. A schematic diagram of the roller stretching unit is shown below. Figure 1 As shown in Table 1, the main processing parameters are shown in Table 2, and the test results are shown in Table 3. Images of the multilayer film sample from Example 1 after the longitudinal linear tearing experiment are shown in Table 4. Figure 3 As shown in (b), it exhibits excellent straight-line tear performance. Images of the multilayer film sample from Example 1 after a transverse trouser-shaped tear test are shown below. Figure 5 As shown in (c), the crack is basically along the centerline, demonstrating excellent straight-line tear resistance.

[0116] Comparative Example 1 - Unstretched multilayer film

[0117] Copolymer polypropylene (PP9513) particles were fed into five single-screw extruders A, B, C, D, and E, heated and melted, and extruded into straight dies. Extruders A, D, and E produced one layer of material flow, while extruders B and C produced two layers, resulting in a total of seven layers (corresponding to seven sub-layers). The extruded material flow was cooled and shaped on cooling rollers circulated with cooling water to form an initial multilayer film. The thickness ratio of each sublayer was 10:10:20:20:20:10:10, and the thickness of this unstretched multilayer film was 25 micrometers. The main processing parameters are shown in Table 1, and the test results are shown in Table 2. Images of the unstretched multilayer film sample from Comparative Example 1 after a longitudinal linear tear test are shown below. Figure 3 As shown in (a), its linear tear performance is significantly worse than that of the sample in Example 1. The image of the unstretched multilayer film sample of Comparative Example 1 after the transverse trouser-shaped tear test is shown below. Figure 5 As shown in (b), the crack deviates from the centerline shortly after the pre-cut and breaks off obliquely at about halfway through the sample strip, which does not meet the requirements for a straight tear at all.

[0118] Table 1

[0119] Comparative Example 1 (Unstretched) Example 1 (stretch ratio of 3) Production (kg / h) 400 400 Extruder temperature (degrees Celsius) 240 240 Speed ​​of the stretching slow roller (m / min) - 70 Speed ​​of the stretching roller (m / min) - 210 stretch ratio - 3 Preheating roller temperature (degrees Celsius) - 100 Temperature of the stretching roller (degrees Celsius) - 116 Annealing roller temperature (degrees Celsius) - 113 Cooling roller temperature (degrees Celsius) - 80 Rewinding speed (m / min) 200 200

[0120] The main test results are as follows:

[0121] Table 2

[0122]

[0123]

[0124] Compared to the unstretched Comparative Example 1, the stiffness of the sample in Example 1, after being stretched three times, was significantly improved (1% secant modulus, 5% tensile strength), while the longitudinal tensile strength was significantly increased and the transverse tensile strength was also improved. The needle-punching strength was also significantly enhanced, indicating improved film toughness. Furthermore, the sample of Example 1 exhibited excellent straight-line tear resistance (the straight-line tear width was closer to the original 2cm un-tear width).

[0125] While the present invention has been disclosed above with reference to preferred embodiments, it is not limited thereto. Any variations and modifications made by those skilled in the art without departing from the spirit and scope of the invention should be included within the scope of protection of the invention. Therefore, the scope of protection of the invention should be determined by the scope defined in the claims.

Claims

1. A multilayer film of a propylene-based polymer, wherein the multilayer film is prepared by co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner. The longitudinal stretching ratio is 2.5-3.5, and the longitudinal stretching is performed by roller stretching. The multilayer film has 5-7 sublayers and the thickness of the multilayer film is 20-28 micrometers; The propylene-based polymer contains 95-98.5% by weight of propylene-derived units based on the total weight of the propylene-based polymer, and the propylene-based polymer is a random copolymer of propylene and ethylene. The thickness of the outer sublayer exposed to air and the sublayer immediately adjacent to the outer sublayer in the multilayer film is 60-75% of the average thickness of all sublayers, and the thickness of the other sublayers besides the outer sublayer and the sublayer immediately adjacent to the outer sublayer is 130-150% of the average thickness of all sublayers; and In the roller stretching process, the stretching unit includes a preheating roller, a stretching roller, an annealing roller, and a cooling roller. The temperature of the preheating roller is 95-105℃, the temperature of the stretching roller is 110-120℃, the temperature of the annealing roller is 2-8℃ lower than that of the stretching roller, and the temperature of the cooling roller is 70-90℃. The multilayer film mentioned above is a bidirectional linear easy-tear multilayer film.

2. The multilayer film of the propylene-based polymer according to claim 1, wherein the thickness of each sublayer is 1-9 micrometers.

3. The multilayer film of the propylene-based polymer according to claim 2, wherein the thickness of each sublayer is 1.5-8 micrometers.

4. A multilayer film of a propylene-based polymer according to any one of claims 1-3, wherein the propylene-based polymer has an MFR of 5-15 g / 10 min, said MFR being measured according to ASTM D1238 at a load of 2.16 kg and a temperature of 230 °C.

5. The multilayer film of the propylene-based polymer according to claim 4, wherein the propylene-based polymer has an MFR of 6-10 g / 10 min, said MFR being measured according to ASTM D1238 at a load of 2.16 kg and a temperature of 230 °C.

6. A multilayer film of a propylene-based polymer according to any one of claims 1-3, wherein the multilayer film is made of a propylene-based polymer.

7. The multilayer film of the propylene-based polymer according to claim 4, wherein the multilayer film is made of a propylene-based polymer.

8. The multilayer film of the propylene-based polymer according to claim 5, wherein the multilayer film is made of a propylene-based polymer.

9. A method for preparing a multilayer film of a propylene-based polymer as described in any one of claims 1-8, comprising co-extruding the propylene-based polymer to obtain an initial multilayer film, and then longitudinally stretching the initial multilayer film in an online manner to obtain the multilayer film.

10. An article comprising a multilayer film of a propylene-based polymer as described in any one of claims 1-8.

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