CN115991023A

CN115991023A - Flame-retardant polypropylene composite film and preparation method and application thereof

Info

Publication number: CN115991023A
Application number: CN202111221972.XA
Authority: CN
Inventors: 白弈青; 徐萌; 高达利; 吕芸; 侴白舸; 权慧; 初立秋; 解娜; 张冯倩
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Priority date: 2021-10-20
Filing date: 2021-10-20
Publication date: 2023-04-21

Abstract

The invention belongs to the field of films, and relates to a flame-retardant polypropylene composite film, and a preparation method and application thereof. The polypropylene composite film comprises at least one film layer A formed by a polypropylene composition A, at least one film layer B formed by a polypropylene composition B and at least one film layer C formed by a polypropylene composition C; wherein the polypropylene composition A comprises a homo-polypropylene a, a propylene impact copolymer B and a polyolefin elastomer C, the polypropylene composition B comprises a random polypropylene x and optionally a polyolefin elastomer y, and the polypropylene composition C comprises a polypropylene m and a flame retardant n. The composite film has good impact resistance, tensile property and flame retardant property, and has good heat sealing strength at a lower heat sealing temperature.

Description

Flame-retardant polypropylene composite film and preparation method and application thereof

Technical Field

The invention belongs to the field of films, and particularly relates to a flame-retardant polypropylene composite film, and a preparation method and application thereof.

Background

Polypropylene films are typically produced by casting, biaxially oriented drawing, and the like, but polypropylene films produced from homopolymerized polypropylene materials typically have lower impact strength. Polypropylene films are commonly used in packaging applications and require higher impact properties for the films, methods for improving the impact properties of polypropylene films, block impact polypropylene can be used to make the films, or polyolefin elastomers can be added to the polypropylene, but films made by the above methods generally have higher haze. It is also possible to add a nucleating agent to the film at the same time to reduce the haze of the film by thinning the crystals in the film, but this method results in a decrease in impact properties.

In order to improve the impact resistance and toughness of the film, the film can be prepared by a multilayer coextrusion method, for example, CN101913279A adopts a three-layer coextrusion method to prepare a composite film, the middle layer of the film is elastomer and PP which are blended according to the proportion of 1:10-1:3, and the elastomer provides better impact resistance, but the method has the problem that the elastomer is difficult to disperse uniformly under the condition of higher content, and the addition amount of the elastomer has a certain limit, because the problem of phase separation occurs when the addition amount is up to a certain level, the further improvement of the impact resistance is limited. Moreover, when the film is used for packaging purposes, it is generally desirable to have better heat seal properties at lower heat seal temperatures.

The polypropylene has poor flame resistance and low oxygen index of only 17.0-17.5%, belongs to inflammable materials, has high heat release rate and high heat value during combustion, is extremely easy to spread flame and cause fire, and greatly limits the use of polypropylene film products in industries such as electric appliances, chemical industry, machinery, military products and the like. Therefore, how to improve the flame retardant properties of polymers has also received much attention.

Disclosure of Invention

The invention aims to solve the problem that the existing polypropylene film is difficult to have good impact resistance and flame retardance at the same time, and provides a flame-retardant polypropylene composite film and a preparation method thereof. The polypropylene film has good impact resistance, tensile property and flame retardant property, and has good heat sealing strength at a lower heat sealing temperature.

The first aspect of the present invention provides a flame retardant polypropylene composite film comprising at least one film layer a formed from a polypropylene composition a, at least one film layer B formed from a polypropylene composition B, and at least one film layer C formed from a polypropylene composition C; wherein the polypropylene composition A comprises a homo-polypropylene a, a propylene impact copolymer B and a polyolefin elastomer C, the polypropylene composition B comprises a random polypropylene x and optionally a polyolefin elastomer y, and the polypropylene composition C comprises a polypropylene m and a flame retardant n.

The second aspect of the present invention provides a method for preparing the above flame retardant polypropylene composite film, comprising: the raw material composition for forming each layer is extrusion-cast after an optional granulating process to form the composite film.

A third aspect of the present invention provides the use of the flame retardant polypropylene composite film described above in the field of packaging materials.

The composite film has good impact resistance, tensile property and flame retardant property, and has good heat sealing strength at a lower heat sealing temperature. The film has a Machine Direction (MD) tensile strength of 38MPa or more, preferably 45MPa or more. The pendulum impact strength is more than or equal to 0.4J, preferably more than or equal to 0.9J. And the heat seal strength at 150 ℃ is not less than 15N/15mm, preferably not less than 18N/15mm. The oxygen index of the film is more than or equal to 22%, preferably more than or equal to 23%.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Detailed Description

The following describes specific embodiments of the present invention in detail. It should be understood that the detailed description and specific examples, while indicating and illustrating the invention, are not intended to limit the invention.

The invention provides a flame-retardant polypropylene composite film, which comprises at least one film layer A formed by a polypropylene composition A, at least one film layer B formed by a polypropylene composition B and at least one film layer C formed by a polypropylene composition C; wherein the polypropylene composition A comprises a homo-polypropylene a, a propylene impact copolymer B and a polyolefin elastomer C, the polypropylene composition B comprises a random polypropylene x and optionally a polyolefin elastomer y, and the polypropylene composition C comprises a polypropylene m and a flame retardant n.

According to some embodiments of the invention, a rubber phase is present in the composite film, the rubber phase having an average width of 20 to 200nm and an average aspect ratio of 5 to 20. The rubber phase was observed by atomic force microscopy and was in the form of a bar. The meaning of aspect ratio is well known to those skilled in the art, and for the bar particle test, the aspect ratio is the same concept as aspect ratio, namely: the ratio of the longest diameter passing through the interior of the particle to the longest diameter perpendicular thereto corresponds to the length of the particle, and the width of the particle.

According to some embodiments of the invention, the polypropylene composite film has at least one of the following features: the tensile strength in the Machine Direction (MD) is more than or equal to 38MPa, and the tensile strength in the Machine Direction (MD) is more than or equal to 45MPa; the oxygen index is more than or equal to 22%, preferably more than or equal to 23%; the impact strength of the pendulum bob is more than or equal to 0.4J, and the impact strength of the pendulum bob is more than or equal to 0.9J; the heat sealing strength at 150 ℃ is more than or equal to 15N/15mm; preferably, the heat seal strength at 150 ℃ is more than or equal to 18N/15mm.

According to some embodiments of the invention, the melt mass flow rate of the homo-polypropylene a at 230℃under a load of 2.16kg is from 2 to 15g/10min, the isotacticity is greater than 97% and the molecular weight distribution Mw/Mn is from 4.5 to 7.0. Homo-polypropylene meeting the above characteristics is commercially available. Such as the homopolypropylene with the PPH-FA03 of Qingdao brand, the homopolypropylene with the PPH-FA03 of China petrochemical brand and the homopolypropylene with the FC801 of Shanghai petrochemical brand. Or may be prepared by methods conventional in the art.

According to the present invention, the propylene impact copolymer is preferably a propylene impact copolymer containing ethylene units, the propylene impact copolymer comprising an elastic portion which is a copolymerized portion containing ethylene units, preferably selected from the group consisting of an ethylene-propylene copolymerized portion and an ethylene-butene copolymerized portion.

Preferably, the propylene impact copolymer comprises a propylene homo-polymer portion and the ethylene unit containing co-polymer portion. The propylene homo-portion may comprise an isotactic polymeric structure.

The content of the copolymerized portion containing ethylene units in the propylene impact copolymer b is preferably 3 to 15% by weight based on the total weight of the propylene impact copolymer b by ¹³ C NMR measurement.

The ethylene content of the propylene impact copolymer b is preferably from 1 to 12wt%, based on the total weight of the propylene impact copolymer b.

The melt mass flow rate of the propylene impact copolymer b at 230℃under a load of 2.16kg is preferably from 1 to 10g/10min.

The propylene impact copolymer may have a block structure or comprise a propylene block copolymer.

Propylene impact copolymers meeting the above characteristics are commercially available. Such as propylene impact copolymer with the trade name EP200K, propylene impact copolymer with the trade name M180R, and propylene impact copolymer with the trade name PPB-M02D. Or may be prepared by methods conventional in the art.

According to some embodiments of the invention, the polyolefin elastomer C is an elastomeric copolymer of ethylene and an alpha olefin, wherein the alpha olefin is preferably C ₃ -C ₁₂ More preferably at least one selected from the group consisting of propylene, 1-butene, 1-hexene and 1-octene.

According to some embodiments of the invention, the polyolefin elastomer y is an elastomeric copolymer of ethylene and an alpha olefin, wherein the alpha olefin is preferably C ₃ -C ₁₂ More preferably at least one selected from the group consisting of propylene, 1-butene, 1-hexene and 1-octene.

Polyolefin elastomers meeting the above characteristics are commercially available. For example, the polyolefin elastomer of Exxon brand 6102, the polyolefin elastomer of Santa Clay brand DF640, and the polyolefin elastomer of ExACT 3139. Or may be prepared by methods conventional in the art.

According to some embodiments of the present invention, the random polypropylene x is a copolymer of propylene and ethylene and/or butene, that is, at least one of a copolymer of propylene and ethylene, a copolymer of propylene and butene, and a copolymer of propylene and ethylene and butene, preferably at least one selected from an ethylene-propylene-butene ternary random copolymer, a propylene-ethylene binary random copolymer, and a propylene-butene binary random copolymer.

The melt mass flow rate of the atactic polypropylene x at 230℃under a load of 2.16kg is preferably 2-10g/10min.

Random polypropylene meeting the above characteristics is commercially available. Such as atactic polypropylene with the brand of F5006, atactic polypropylene with the brand of F500EPS, and atactic polypropylene with the brand of F800 EPS. Or may be prepared by methods conventional in the art.

The film layer C of the present invention exists mainly as a flame retardant functional layer, and therefore, the polypropylene m in the polypropylene composition C may be various types of polypropylene, preferably, the composition thereof is the same as the composition of the following components, compositions or mixtures thereof: the composition of the homo-polypropylene a, the random polypropylene x, the polypropylene composition A and the polypropylene composition B is, for example, the same as the composition of the mixture of the polypropylene composition A and the polypropylene composition B.

The kind of the flame retardant is not particularly limited, and the flame retardant is preferably at least one selected from the group consisting of a hydrate of a metal or nonmetal hydroxide and/or oxide, a phosphorus flame retardant, a boron flame retardant, an antimony flame retardant, and an intumescent flame retardant. The hydrate of the metal or nonmetal hydroxide and/or oxide may be at least one of hydroxides of aluminum, magnesium, boron, zinc, and layered double hydroxides; the phosphorus flame retardant can be at least one of red phosphorus, phosphate, polyphosphate and phosphate; the boron-based flame retardant can be boric acid and/or a borate, and the borate is preferably ammonium borate and/or zinc borate; the antimony-based flame retardant may be at least one of antimony trioxide, antimony pentoxide and sodium antimonate; the intumescent flame retardant may be at least two of sulfuric acid, pentaerythritol or a dimer or trimer thereof, tetrol, inositol, sorbitol, glucose, maltose, starch, resorcinol, ammonium polyphosphate, dicyandiamide, melamine, urea, melamine, glycine, expandable graphite, and carbon nanotubes. According to one embodiment of the invention, the flame retardant is an intumescent flame retardant, preferably ammonium polyphosphate and pentaerythritol, in particular the weight ratio of ammonium polyphosphate to pentaerythritol is 0.5-5:1. According to another embodiment of the invention, the flame retardant is a mixture of magnesium hydroxide and aluminum hydroxide, in particular, the weight ratio of magnesium hydroxide to aluminum hydroxide is 0.5-2:1. The flame-retardant polypropylene film prepared by adding the flame retardant has the advantages of easy processing, good performance and the like.

According to some embodiments of the present invention, the polypropylene composition a comprises from 40 to 90wt% of the homo-polypropylene a, from 5 to 45wt% of the propylene impact copolymer b and from 2 to 40wt% of the polyolefin elastomer c, based on the total weight of the polypropylene composition a.

According to a preferred embodiment of the present invention, the polypropylene composition A comprises 55 to 75wt% of the homo-polypropylene a, 10 to 30wt% of the propylene impact copolymer b and 5 to 20wt% of the polyolefin elastomer c, based on the total weight of the polypropylene composition A.

Because the homo-polypropylene contains larger spherulites, the propylene impact copolymer and the polyolefin elastomer contain rubber phases with different sizes, and the components can be influenced together. According to the composition provided by the invention, the rubber phase in the composition can absorb impact energy well, so that the requirement of impact performance is met, and the film has good impact performance. Meanwhile, as the macromolecular chain segments of the homo-polymer phase are more regular, crystallization occurs in the film preparation process, so that the film also has better tensile property.

According to some embodiments of the invention, the polypropylene composition B comprises from 40 to 100wt% of the random polypropylene x and from 0 to 60wt% of the polyolefin elastomer y, based on the total weight of the polypropylene composition B.

According to a preferred embodiment of the present invention, the polypropylene composition B comprises from 75 to 90wt% of atactic polypropylene x and from 10 to 25wt% of polyolefin elastomer y, based on the total weight of the polypropylene composition B.

The polyolefin elastomer can play a role in improving the impact property of the film, but can be separated from the matrix under the condition of larger addition amount, so that the mechanical property is reduced. According to the composition of the composition B provided by the invention, the heat sealing strength of the film can be improved.

According to some embodiments of the invention, the polypropylene composition C comprises 30-80wt% of polypropylene m and 20-70wt% of flame retardant n, based on the total weight of the polypropylene composition C.

According to a preferred embodiment of the present invention, the polypropylene composition C comprises 40-70wt% of polypropylene m and 30-60wt% of flame retardant n, based on the total weight of the polypropylene composition C.

According to some embodiments of the invention, the polyolefin elastomer c is present in parts by weight Wc based on 100 parts by weight of the total weight of the polypropylene composition a, based on 100 parts by weight of the total weight of the polypropylene composition B, the weight fraction of the polyolefin elastomer y is Wy, and the ratio of Wc to Wy is 6:1-1:4, and may be, for example, 5.5:1, 5:1, 4.5:1, 4:1, 3.5:1, 3:1, 2.5:1, 2:1, 1.5:1, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, and any value therebetween.

According to a preferred embodiment of the invention, the ratio of Wc to Wy is 1:1-1:2.

As a result of the study of the present inventors, when the ratio of Wc to Wy is in the range of the present invention, the impact properties of the film can be further improved and at the same time the extrusion process can be more stable.

According to some embodiments of the invention, the melt mass flow rate of the polypropylene composition A is in the range of 2-10g/10min, preferably 2-7g/10min, at 230℃under a load of 2.16 kg.

According to some embodiments of the invention, the melt mass flow rate of the polypropylene composition B is 2-10g/10min, preferably 3-8g/10min, at 230℃under a load of 2.16 kg.

According to some embodiments of the invention, the melt mass flow rate of the polypropylene composition C is in the range of 2-10g/10min, preferably 2-7g/10min, at 230℃under a load of 2.16 kg.

When the melt mass flow rates of the polypropylene composition A, the polypropylene composition B and the polypropylene composition C are in the above ranges, the film preparation process can be more stable, so that the film is ensured to have better uniformity and mechanical properties.

The composite film can be of a three-layer or more than three-layer film structure, other layers can be the same as the film layer A, the film layer B or the film layer C in composition, can be different from the film layer A, the film layer B or the film layer C in composition, and can be formed by mixing a polypropylene composition A, a polypropylene composition B and a polypropylene composition C. The film layer C as the flame-retardant functional layer is preferably arranged between the film layer B and the film layer A, when the polypropylene composite film has a three-layer structure, the B layer and the A layer can be respectively positioned at two sides of the C layer, and when the number of layers of the polypropylene composite film exceeds three, such as five layers, the two B layers are respectively used as an upper surface layer and a lower surface layer, the two C layers are used as an intermediate layer, and the one A layer is used as a core layer.

According to some embodiments of the invention, the ratio of the sum of the thicknesses of the film layer B, the film layer C and the film layer A is 0.1-3:0.1-1:1, preferably 0.5-2:0.2-0.6:1. At this ratio, the composite film has good mechanical properties.

In the present invention, in order to improve the performance of the composite film during processing, it is preferable that the composite film further contains an antioxidant and/or a lubricant, and may be contained in the polypropylene composition a and/or the polypropylene composition B and/or the polypropylene composition C.

In the present invention, the antioxidant may be various antioxidants commonly used in the art, and is not particularly limited. For example, antioxidant 1076, antioxidant 1010, antioxidant 168, and thioester antioxidants (such as DLTP and DSTP) can be used. The antioxidant may be contained in an amount of 0.1 to 0.8 parts by weight, preferably 0.2 to 0.4 parts by weight, based on 100 parts by weight of the total amount of the polypropylene composition a, the polypropylene composition B or the polypropylene composition C.

In the present invention, the lubricant is preferably a PEG-based lubricant and/or a mono Gan Zhilei lubricant. The lubricant is contained in an amount of 0.01 to 0.5 parts by weight, preferably 0.05 to 0.2 parts by weight, based on 100 parts by weight of the total amount of the polypropylene composition A, the polypropylene composition B or the polypropylene composition C.

In order to enhance other properties (e.g., stability, etc.) of the composite film according to the present invention, the composite film preferably further comprises a film forming aid. The film forming aid may be at least one selected from the group consisting of an anti-halogen agent, a light stabilizer, a heat stabilizer, a colorant, a filler, a slip agent, and an anti-blocking agent (anti-blocking agent). The specific type of the film forming aid may be selected as is conventional in the art and will not be described in detail herein.

In the present invention, the content of the film forming aid may be 0.01 to 0.5 parts by weight, preferably 0.05 to 0.3 parts by weight, based on 100 parts by weight of the total amount of the polypropylene composition a, the polypropylene composition B or the polypropylene composition C.

The invention also provides a preparation method of the polypropylene composite film, which comprises the following steps: the raw material composition for forming each layer is extrusion-cast after an optional granulating process to form the composite film.

In the preparation method of the present invention, the process of granulating the pellets may generally include: and uniformly mixing the components of the polypropylene composition, an optional antioxidant, a lubricant and a film forming auxiliary agent in a high-speed stirrer, adding the uniformly mixed materials into a double-screw extruder, performing melt mixing, uniformly extruding, granulating and drying to obtain granules. Wherein, the processing temperature of the double-screw extruder can be controlled to be 170-230 ℃.

According to some embodiments of the invention, the pellets may be processed using extrusion casting. The process of the extrusion casting method can comprise the steps of respectively conveying the granules of different compositions into a plurality of extruders, enabling the granules to flow out through coextrusion compounding of die openings of the extruders, sequentially passing through a casting roller, a traction roller, cutting edges and rolling, and thus obtaining the composite film. Wherein the temperature of the extrusion casting may be controlled to 170-230 ℃ and the temperature of the casting roll may be 10-50 ℃. The specific process of preparing the film by the extrusion casting method is a common choice in the field, and will not be described herein.

The resulting composite film may be stretched in a subsequent process, such as biaxially stretching, to advantageously further improve the mechanical properties of the composite film.

According to one embodiment of the present invention, the polypropylene composition a, the polypropylene composition B and the polypropylene composition C are pelletized, extrusion cast and optionally stretched to produce the polypropylene composite film.

The polypropylene composite film can be used in the field of packaging materials, such as high-end packaging fields with high requirements on film impact resistance, including but not limited to battery packaging and electronic product packaging.

Specific embodiments of the present invention will be described in detail below by way of examples. It should be understood that the examples described below are illustrative and explanatory only and are not restrictive of the invention.

In the following examples and comparative examples:

the film casting apparatus was purchased from Labtech, sweden under the model LCR400.

The polypropylene composition and film properties were tested according to the following methods, the film test results are shown in table 1:

(1) Melt Mass Flow Rate (MFR): the measurement was carried out according to the method specified in GB/T3682-2000, wherein the test temperature was 230℃and the load was 2.16kg.

(2) Film tensile strength: the measurement was carried out according to the method specified in GB/T1040.3-2006.

(3) Film pendulum impact strength: the measurement was performed according to the method specified in GB/T8809-2015.

(4) Oxygen index: measured according to the method specified in GB/T2406-2008.

(5) Film heat seal strength: the measurement was performed according to the method specified in QB/T2358. When the sample is prepared, the heat sealing temperature is 150 ℃, the heat sealing pressure is 0.2MPa, and the heat sealing time is 3s.

(6) Method for measuring average width and average length-diameter ratio of film rubber phase: the cross section of the film sample was scanned and observed using a model Dimension FastScan Icon atomic force microscope from Bruker, usa, using a quantitative nanomechanical scanning mode, and the width of the rubber phase was measured and counted to obtain an average width (based on 200 sample points). The aspect ratio of the rubber phase is the ratio of the dimension in the length direction to the dimension in the width direction, and the average aspect ratio (based on 200 sample points) is obtained through measurement, calculation and statistics.

(7) Degree of isotacticity: by passing through ¹³ C NMR measurement, nuclear magnetic carbon Spectrometry of propylene Polymer at 400MHz was measured by Nuclear magnetic resonance spectrometer (NMR) of model AVANCE III of Bruker, switzerland ¹³ C-NMR), wherein the solvent was deuterated o-dichlorobenzene and the sample concentration was 250mg sample/2.5 mL solvent. To prevent oxidative degradation of the sample during dissolution and data collection, 2mg of 2, 6-di-tert-butyl-4-methylphenol antioxidant (BHT for short) was added to the sample. Dissolving the sample at 140 ℃ and collecting ¹³ C-NMR, test temperature 125 ℃, probe gauge 10 mm, 90 pulse, sampling time AQ 5 seconds, delay time D1 seconds, number of scans 6000. Isotatic with two sets of units [ mm]The content of (2) is taken as isotacticity.

(8) Molecular weight distribution (Mw/Mn): the gel permeation chromatograph was used in combination with an IR5 type infrared detector, and the gel permeation chromatograph was used as a model PL-GPC 220 by UK Polymer Laboratories, wherein the gel permeation chromatograph comprises 3 columns of Plgel 10 μm MIXED-B connected in series, the solvent and mobile phase were 1,2, 4-trichlorobenzene (containing 0.3g/1000mL of antioxidant 2, 6-di-tert-butyl-p-cresol), the column temperature was 150℃and the flow rate was 1.0mL/min, and the well-suited calibration was performed using EasiCal PS-1 narrow distribution polystyrene standard produced by PL.

Example 1

This example is used to illustrate the preparation of the polypropylene composite film provided by the present invention.

(1) Preparation of polypropylene composition A:

the component a is homopolymerized polypropylene with the brand name of PPH-FA03, and is purchased from Qingdao refining, the mass flow rate of a melt is 3.1g/10min, the isotacticity is 98%, and the molecular weight distribution Mw/Mn is 4.7; component b is a propylene impact copolymer with the brand EP200K, purchased from Zhongsha petrochemical industry, ethylene content of 8wt%, ethylene-propylene copolymerThe content of the poly part is 13 weight percent, and the mass flow rate of the melt is 3.2g/10min; component c was a polyolefin elastomer having a trade designation 6102, available from Exxon, and was an ethylene-propylene copolymer having an ethylene structural unit content of 16% by weight. The components prepared above are weighed and mixed according to the proportion, wherein the weight part Wa of the component a is 75 weight parts, the weight part Wb of the component b is 10 weight parts, and the weight part Wc of the component c is 15 weight parts. Adding lubricant (PEG lubricant manufactured by Swiss Corp., molecular weight 10000, and the total amount of the above component a, component b and component c is 100 weight parts, and the amount of the lubricant is 0.1 weight part), adding the mixture into a high-speed stirrer, mixing, and adding the mixed material into W &In a feeder of a double-screw extruder manufactured by P company, materials enter a double screw through the feeder, the temperature of the screw is kept between 160 ℃ and 230 ℃ in the processing process, and the materials are evenly mixed by melting the screw, extruded, granulated and dried to obtain polypropylene composition granules, and the melt mass flow rate MFR of the polypropylene composition granules is detected _A ＝3.6g/10min。

(2) Preparation of polypropylene composition B:

the component x is random polypropylene with the brand number of F5006, is purchased from the petrifaction of Yanshan and is an ethylene-propylene-butene terpolymer, and the melt mass flow rate is 5.2g/10min; component y was a polyolefin elastomer having a trade designation 6102, available from Exxon and was an ethylene-propylene copolymer having an ethylene structural unit content of 16% by weight. The components prepared above are weighed and mixed according to the proportion, wherein the weight part Wx of the component x is 75 weight parts, and the weight part Wy of the component y is 25 weight parts. Wc: wy is 3:5. Other steps are the same as in step (1), and pellets of the polypropylene composition B are finally obtained, which are examined for melt mass flow rate MFR _B ＝3.2g/10min。

(3) Preparation of polypropylene composition C:

the polypropylene component m is random polypropylene with the brand number of F5006, is purchased from the petrifaction of Yanshan and is an ethylene-propylene-butene terpolymer, and the melt mass flow rate is 5.2g/10min; the flame retardant n is a composition of ammonium polyphosphate and pentaerythritol, and is purchased from Jinan Taixing Fine chemical Co. The components prepared by the method are weighed and mixed according to the proportion, wherein the weight part Wm of the component m is 50 weight parts, the weight part Wn of the component n is 50 weight parts, and the weight ratio of the ammonium polyphosphate to the pentaerythritol in the component n is 2:1. The other steps are the same as the step (1), and finally the polypropylene composition C pellets are obtained.

(4) Preparation of a composite film:

drying the polypropylene composition A, the polypropylene composition B and the polypropylene composition C granules prepared in the step (1), the step (2) and the step (3), adding the polypropylene composition A into a core layer extruder of a multilayer extrusion casting machine, adding the polypropylene composition B into an upper surface layer extruder of the multilayer extrusion casting machine, and adding the polypropylene composition C into an intermediate layer extruder of the multilayer extrusion casting machine, wherein an inorganic anti-sticking agent (silicon dioxide, the same applies below) is added into the upper surface layer extruder, and the weight ratio of the anti-sticking agent to the polypropylene composition granules is 0.2:100. In the casting process, the casting quenching roller temperature is set to 30 ℃, and the casting quenching roller is rolled to prepare a composite film which is three layers and sequentially comprises an upper surface layer (film layer B), a middle layer (film layer C) and a core layer (film layer A). The film thickness was 60 μm, with the thickness ratio of film layer B, film layer C and film layer A being 1:1:2.

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 81nm and an average aspect ratio of 10.3.

Example 2

(1) Preparation of polypropylene composition A:

the component a is homopolymerized polypropylene with the brand name of PPH-FA03, and is purchased from original petrochemical industry, the mass flow rate of a melt is 3.0g/10min, the isotacticity is 98%, and the molecular weight distribution Mw/Mn is 4.6; the component b is propylene impact copolymer with the mark of M180R, which is purchased from Shanghai petrochemical industry, the ethylene content is 11wt%, the ethylene-propylene copolymerization part content is 15wt%, and the melt mass flow rate is 2.0g/10min; component c is a polyolefin elastomer sold under the trademark DF640, available from Sanjing Inc., ethylene-1-butene copolymer, butylThe content of olefin structural unit was 32% by weight. The components prepared above are weighed and mixed according to the proportion, wherein the weight part Wa of the component a is 65 weight parts, the weight part Wb of the component b is 30 weight parts, and the weight part Wc of the component c is 5 weight parts. Adding lubricant (PEG lubricant manufactured by Swiss Corp., molecular weight 10000, and the total amount of the above component a, component b and component c is 100 weight parts, and the amount of the lubricant is 0.1 weight part), adding the mixture into a high-speed stirrer, mixing, and adding the mixed material into W&In a feeder of a double-screw extruder manufactured by P company, materials enter a double screw through the feeder, the temperature of the screw is kept between 160 ℃ and 230 ℃ in the processing process, and the materials are evenly mixed by melting the screw, extruded, granulated and dried to obtain polypropylene composition A granules, and the melt mass flow rate MFR of the polypropylene composition A granules is detected _A ＝3.2g/10min。

(2) Preparation of polypropylene composition B:

the component x is random polypropylene with the brand of F500EPS, is purchased from Shanghai petrochemical industry, is an ethylene-propylene-butene terpolymer, and has a melt mass flow rate of 5.3g/10min; the component y is a polyolefin elastomer with the brand DF640, which is purchased from Sanjing corporation and is an ethylene-1-butene copolymer, and the butene structural unit content is 32 weight percent. The components prepared above are weighed and mixed according to the proportion, wherein the weight part Wx of the component x is 90 weight parts, and the weight part Wy of the component y is 10 weight parts. Wc: wy is 1:2. Other steps are the same as in step (1), and pellets of the polypropylene composition B are finally obtained, which are examined for melt mass flow rate MFR _B ＝5.2g/10min。

(3) Preparation of polypropylene composition C:

the polypropylene component m is the polypropylene composition B prepared in the step (2); the flame retardant n is a composition of ammonium polyphosphate and pentaerythritol, and is purchased from Jinan Taixing Fine chemical Co. The components prepared by the method are weighed and mixed according to the proportion, wherein the weight part Wm of the component m is 50 weight parts, the weight part Wn of the component n is 50 weight parts, and the weight ratio of the ammonium polyphosphate to the pentaerythritol in the component n is 2:1. The other steps are the same as the step (1), and finally the polypropylene composition C pellets are obtained.

(4) Preparation of a composite film:

drying the polypropylene composition A, the polypropylene composition B and the polypropylene composition C granules prepared in the step (1), the step (2) and the step (3), adding the polypropylene composition A into a core layer extruder of a multilayer extrusion casting machine, adding the polypropylene composition B into an upper surface layer extruder of the multilayer extrusion casting machine, and adding the polypropylene composition C into an intermediate layer extruder of the multilayer extrusion casting machine, wherein an inorganic anti-sticking agent (silicon dioxide, the same applies below) is added into the upper surface layer extruder, and the weight ratio of the anti-sticking agent to the polypropylene composition granules is 0.2:100. In the casting process, the casting chill roll temperature was set to 30 ℃, and wound up to produce a composite film consisting of upper and lower skin layers (film layer B), two intermediate layers (film layer C) on both sides of the core layer, and a core layer (film layer a). The film thickness was 50 μm, wherein the ratio of the sum of the upper and lower skin thicknesses, the sum of the intermediate layer thicknesses on both sides of the core layer to the thickness of the core layer was 2:1:2.

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 69nm and an average aspect ratio of 13.2.

Example 3

(1) Preparation of polypropylene composition A:

component a is homo-polypropylene with the brand of FC801, which is purchased from Shanghai petrochemical industry, the melt mass flow rate is 7.8g/10min, the isotacticity is 98%, and the molecular weight distribution Mw/Mn is 4.8; the component b is propylene impact copolymer with the brand name of PPB-M02D, which is purchased from the luxuriant petrochemical industry, has the ethylene content of 8wt%, the ethylene-propylene copolymer part content of 10wt% and the melt mass flow rate of 1.5g/10min; component c was a polyolefin elastomer having the trade designation EXACT3139, available from Exxon and was an ethylene-1-octene copolymer having an octene structural unit content of 14wt%. Weighing and mixing the above prepared components according to a proportion, wherein the weight part Wa of the component a is 55 weight parts, the weight part Wb of the component b is 25 weight parts, and the weight part of the component c is 55 weight partsThe weight portion Wc is 20 weight portions. Adding lubricant (PEG lubricant manufactured by Swiss Corp., molecular weight 10000, and the total amount of the above component a, component b and component c is 100 weight parts, and the amount of the lubricant is 0.1 weight part), adding the mixture into a high-speed stirrer, mixing, and adding the mixed material into W&In a feeder of a double-screw extruder manufactured by P company, materials enter a double screw through the feeder, the temperature of the screw is kept between 160 ℃ and 230 ℃ in the processing process, and the materials are evenly mixed by melting the screw, extruded, granulated and dried to obtain polypropylene composition A granules, and the melt mass flow rate MFR of the polypropylene composition A granules is detected _A ＝6.6g/10min。

(2) Preparation of polypropylene composition B:

the component x is random polypropylene with the brand of F800EPS, is purchased from Shanghai petrochemical industry, is an ethylene-propylene-butene terpolymer, and has a melt mass flow rate of 8.2g/10min; component y was a polyolefin elastomer having the trade designation EXACT3139, available from Exxon and was an ethylene-1-octene copolymer having an octene structural unit content of 14wt%. The components prepared above are weighed and mixed according to the proportion, wherein the weight part Wx of the component x is 80 weight parts, and the weight part Wy of the component y is 20 weight parts. Wc: wy is 1:1. Other steps are the same as in step (1), and pellets of the polypropylene composition B are finally obtained, which are examined for melt mass flow rate MFR _B ＝7.9g/10min。

(3) Preparation of polypropylene composition C:

the polypropylene composition C pellets were obtained as in example 2 except that the polypropylene component m was the polypropylene composition B obtained in the above step (2).

(4) Preparation of a composite film:

the preparation procedure is the same as in step (4) of example 1.

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 95nm and an average aspect ratio of 9.6.

Example 4

(1) Preparation of polypropylene composition A:

the procedure is as in example 1. The difference is that the part by weight Wa of the component a is 80 parts by weight, the part by weight Wb of the component b is 18 parts by weight, and the part by weight Wc of the component c is 2 parts by weight. To obtain pellets of the polypropylene composition A, the melt mass flow rate MFR of which was measured _A ＝2.8g/10min。

(2) Preparation of polypropylene composition B:

the procedure is as in example 1. The difference is that the weight part Wx of the component x is 92 weight parts, and the weight part Wy of the component y is 8 weight parts. Wc: wy is 1:4. Other steps are the same as in step (1), and pellets of the polypropylene composition B are finally obtained, which are examined for melt mass flow rate MFR _B ＝7.7g/10min。

(3) Preparation of polypropylene composition C:

the procedure was as in example 2, except that the polypropylene component m was the polypropylene composition B obtained in the above-mentioned step (2), and pellets of the polypropylene composition C were finally obtained.

(4) Preparation of a composite film:

the procedure is as in example 1. The film thickness was 60 μm, with the thickness ratio of film layer B, film layer C and film layer A being 1:1:3.

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 105nm and an average aspect ratio of 8.7.

Example 5

(1) Preparation of polypropylene composition A:

the procedure was as in example 3, except that the part by weight Wa of component a was 90 parts by weight, the part by weight Wb of component b was 5 parts by weight, and the part by weight Wc of component c was 5 parts by weight. To obtain pellets of the polypropylene composition A, the melt mass flow rate MFR of which was measured _A ＝9.6g/10min。

(2) Preparation of polypropylene composition B:

the procedure is as in example 3.

(3) Preparation of polypropylene composition C:

the procedure was as in example 2, wherein the polypropylene component m was the polypropylene composition B obtained in the above step (1), the mass fraction Wm of the component m was 65 parts by weight, the mass fraction Wn of the component n was 35 parts by weight, and finally pellets of the polypropylene composition C were obtained.

(4) Preparation of a composite film:

the procedure is as in example 2. The film thickness was 60 μm, wherein the ratio of the sum of the thicknesses of the upper and lower surface layers, the sum of the thicknesses of the intermediate layers on both sides of the core layer to the thickness of the core layer was 2:1:1.

Example 6

(1) Preparation of polypropylene composition A:

the procedure was as in example 3, except that Wa, wb, and Wc were 50 parts by weight, 40 parts by weight, and 10 parts by weight, respectively. To obtain pellets of the polypropylene composition A, the melt mass flow rate MFR of which was measured _A ＝4.6g/10min。

(2) Preparation of polypropylene composition B:

the procedure is as in example 3, except that the mass fraction Wx of component x is 60 parts by weight and the mass fraction Wy of component y is 40 parts by weight. Wc: wy is 1:4. Finally, pellets of the polypropylene composition B were obtained, the melt mass flow rate MFR of which was examined _B ＝9.8g/10min。

(3) Preparation of polypropylene composition C:

the procedure was as in example 3, except that the polypropylene component m was the polypropylene composition B obtained in the above-mentioned step (2), and pellets of the polypropylene composition C were finally obtained.

(4) Preparation of a composite film:

the procedure is as in example 3. The film thickness was 60 μm, wherein the ratio of the sum of the thicknesses of the upper and lower surface layers, the sum of the thicknesses of the intermediate layers on both sides of the core layer to the thickness of the core layer was 1:1:4.

Example 7

A polypropylene composite film was prepared as in example 1. In the preparation of polypropylene composition C, the flame retardants ammonium polyphosphate and pentaerythritol used were replaced by magnesium hydroxide and aluminium hydroxide, with the difference. The weight part Wm of the component m is 50 parts by weight, the weight part Wn of the component n is 50 parts by weight, and the weight ratio of the magnesium hydroxide to the aluminum hydroxide in the component n is 1:1.

Example 8

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition A, the component a was 40 parts by weight of Wa, the component b was 40 parts by weight of Wb, and the component c was 20 parts by weight of Wc. Wc: wy is 4:5. To obtain pellets of the polypropylene composition A, the melt mass flow rate MFR of which was measured _A ＝2.8g/10min。

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 140nm and an average aspect ratio of 7.1.

Example 9

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition A, the component a was 50 parts by weight of Wa, the component b was 45 parts by weight of Wb, and the component c was 5 parts by weight of Wc. Wc: wy is 1:5. To obtain pellets of the polypropylene composition A, the melt mass flow rate MFR of which was measured _A ＝3.1g/10min。

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 176nm and an average aspect ratio of 6.4.

Example 10

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition A, the component a was 50 parts by weight of Wa, the component b was 10 parts by weight of Wb, and the component c was 40 parts by weight of Wc. Wc: wy is 8:5. To obtain pellets of the polypropylene composition A, the melt mass flow rate MFR of which was measured _A ＝2.7g/10min。

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 150nm and an average aspect ratio of 6.8.

Example 11

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition B, the component x was 50 parts by weight of Wx and the component y was 50 parts by weight of Wy. Wc: wy is 3:10. To obtain pellets of the polypropylene composition B, the melt mass flow rate MFR of which was measured _B ＝4.7g/10min。

The composite film was observed under an atomic force microscope to see a rubber phase having an average width of 98nm and an average aspect ratio of 15.1.

Example 12

A polypropylene composite film was prepared as in example 1. The polypropylene composition B, however, only contains component x.

Example 13

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition B, the component x was 92.5 parts by weight of Wx and the component y was 7.5 parts by weight of Wy. Wc: wy is 2:1. Finally, pellets of the polypropylene composition B were obtained, the melt mass flow rate MFR of which was examined _B ＝5.5g/10min。

Example 14

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition B, the component x was 85 parts by weight of Wx and the component y was 15 parts by weight of Wy. Wc: wy is 1:1. Finally, pellets of the polypropylene composition B were obtained, the melt mass flow rate MFR of which was examined _B ＝5.1g/10min。

Example 15

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition B, the component x was 70 parts by weight of Wx and the component y was 30 parts by weight of Wy. Wc: wy is 1:2. Finally, pellets of the polypropylene composition B were obtained, the melt mass flow rate MFR of which was examined _B ＝4.4g/10min。

Example 16

According to realityThe polypropylene composite film was prepared by the method of example 1. In the preparation of the polypropylene composition B, the component x was 40 parts by weight of Wx and the component y was 60 parts by weight of Wy. Wc: wy is 1:4. Finally, pellets of the polypropylene composition B were obtained, the melt mass flow rate MFR of which was examined _B ＝2.9g/10min。

Example 17

A polypropylene composite film was prepared as in example 1. In the preparation of the polypropylene composition B, the mass fraction Wx of the component x was 97 parts by weight and the mass fraction Wy of the component y was 3 parts by weight. Wc: wy is 5:1. Finally, pellets of the polypropylene composition B were obtained, the melt mass flow rate MFR of which was examined _B ＝6.0g/10min。

Comparative example 1

A polypropylene composite film was prepared as in example 1. In contrast, a composite film was produced using the polypropylene composition A and the polypropylene composition C, and the composite film was composed of an upper surface layer (film layer C) and a core layer (film layer A). The film thickness was 60 μm, with a thickness ratio of film layer C to film layer A of 1:2.

Comparative example 2

A polypropylene composite film was prepared as in example 2. In contrast, a composite film was produced using the polypropylene composition B and the polypropylene composition C, and the composite film was composed of an upper surface layer (film layer B) and a core layer (film layer C). The film thickness was 60 μm, with a thickness ratio of film layer B to film layer C of 2:1.

Comparative example 3

A polypropylene composite film was prepared as in example 1. In contrast, a composite film was produced using the polypropylene composition A and the polypropylene composition B, and the composite film was composed of an upper surface layer (film layer B) and a core layer (film layer A). The film thickness was 60 μm, with a thickness ratio of film layer B to film layer A of 1:2.

Comparative example 4

A polypropylene composite film was prepared as in example 1. Except that the polypropylene composition a contains only component b.

Comparative example 5

A polypropylene composite film was prepared as in example 1. The polypropylene composition A, however, contained only the component a and the component b, wherein the component a was 75 parts by weight of Wa and the component b was 25 parts by weight of Wb.

TABLE 1

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As can be seen from the results of the examples in Table 1, the polypropylene composite film provided by the invention has both good impact resistance and tensile properties, and also has good heat seal strength and flame retardant properties. The film of the invention has a Machine Direction (MD) tensile strength of not less than 38MPa, an oxygen index of not less than 22%, a pendulum impact strength of not less than 0.4J, and a heat seal strength at 150 ℃ of not less than 15N/15mm. As can be seen from the preferred examples, the films of the present invention have a Machine Direction (MD) tensile strength of 45MPa or more, an oxygen index of 23% or more, a pendulum impact strength of 0.9J or more, and a heat seal strength of 18N/15mm or more at 150 ℃. As can be seen from the comparative examples, it is difficult to achieve a balance of various properties by changing the composition ratio of the film layer, and it is difficult to obtain a film having a uniform thickness because the film surface is unstable during extrusion casting.

The foregoing description of embodiments of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described.

The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

Claims

1. A flame retardant polypropylene composite film, characterized in that the polypropylene composite film comprises at least one film layer A formed by a polypropylene composition A, at least one film layer B formed by a polypropylene composition B and at least one film layer C formed by a polypropylene composition C; wherein the polypropylene composition A comprises a homo-polypropylene a, a propylene impact copolymer B and a polyolefin elastomer C, the polypropylene composition B comprises a random polypropylene x and optionally a polyolefin elastomer y, and the polypropylene composition C comprises a polypropylene m and a flame retardant n.

2. The flame retardant polypropylene composite film according to claim 1, wherein a rubber phase is present in the polypropylene composite film, the average width of the rubber phase being 20 to 200nm and the average aspect ratio being 5 to 20.

3. The flame retardant polypropylene composite film according to claim 1 or 2, wherein the polypropylene composite film has at least one of the following characteristics: the longitudinal tensile strength is more than or equal to 38MPa, preferably more than or equal to 45MPa; the oxygen index is more than or equal to 22%, preferably more than or equal to 23%; the impact strength of the pendulum bob is more than or equal to 0.4J, and the impact strength of the pendulum bob is more than or equal to 0.9J; the heat sealing strength at 150 ℃ is more than or equal to 15N/15mm; preferably, the heat seal strength at 150 ℃ is more than or equal to 18N/15mm.

4. A flame retardant polypropylene composite film according to any one of claims 1 to 3, wherein the melt mass flow rate of the polypropylene composition a is 2-10g/10min, preferably 2-7g/10min, at 230 ℃ under a load of 2.16 kg; and/or

The melt mass flow rate of the polypropylene composition B is 2-10g/10min, preferably 3-8g/10min, under the action of a load of 2.16kg at 230 ℃; and/or

The melt mass flow rate of the polypropylene composition C is 2-10g/10min, preferably 2-7g/10min, at 230℃under a load of 2.16 kg.

5. The flame retardant polypropylene composite film according to any one of claims 1 to 4, wherein the melt mass flow rate of the homo-polypropylene a at 230 ℃ under a load of 2.16kg is 2 to 15g/10min, the isotacticity is more than 97%, and the molecular weight distribution Mw/Mn is 4.5 to 7.0.

6. The flame retardant polypropylene composite film according to any one of claims 1 to 5, wherein the propylene impact copolymer b is a propylene impact copolymer containing ethylene units; the ethylene content of the propylene impact copolymer b is 1-12wt% based on the total weight of the propylene impact copolymer b; and/or the number of the groups of groups,

the content of the copolymerization part containing ethylene units in the propylene impact copolymer b is 3-15wt%; and/or the number of the groups of groups,

the melt mass flow rate of the propylene impact copolymer b at 230 ℃ and under a load of 2.16kg is 1-10g/10min.

7. The flame retardant polypropylene composite film according to any one of claims 1 to 6, wherein the polyolefin elastomer C and the polyolefin elastomer y are each independently an elastomeric copolymer of ethylene and an alpha olefin, wherein the alpha olefin is preferably C ₃ -C ₁₂ More preferably at least one selected from the group consisting of propylene, 1-butene, 1-hexene and 1-octene.

8. The flame retardant polypropylene composite film according to any one of claims 1 to 7, wherein the random polypropylene x is a copolymer of propylene with ethylene and/or butene, preferably at least one selected from the group consisting of ethylene-propylene-butene ternary random copolymer, propylene-ethylene binary random copolymer, propylene-butene binary random copolymer; and/or the melt mass flow rate of the atactic polypropylene x at 230 ℃ under a load of 2.16kg is 2-10g/10min.

9. The flame retardant polypropylene composite film according to any one of claims 1 to 8, wherein the composition of polypropylene m is the same as the composition of the following components, compositions or mixtures thereof: homo polypropylene a, random polypropylene x, polypropylene composition a, polypropylene composition B.

10. The flame retardant polypropylene composite film according to any one of claims 1 to 9, wherein the flame retardant is at least one selected from the group consisting of metal or nonmetal hydroxides and/or oxide hydrates, phosphorus-based flame retardants, boron-based flame retardants, antimony-based flame retardants and intumescent flame retardants;

preferably, the hydrate of the metal or nonmetal hydroxide and/or oxide is at least one of aluminum, magnesium, boron, zinc hydroxide and layered double hydroxide; the phosphorus flame retardant is at least one of red phosphorus, phosphate, polyphosphate and phosphate; the boron-based flame retardant is boric acid and/or borate, and the borate is preferably ammonium borate and/or zinc borate; the antimony flame retardant is at least one of antimony trioxide, antimony pentoxide and sodium antimonate; the intumescent flame retardant is at least two of sulfuric acid, pentaerythritol or dimers or trimers thereof, butyl tetrol, cyclohexane hexaol, sorbitol, glucose, maltose, starch, resorcinol, ammonium polyphosphate, dicyandiamide, melamine, urea, melamine, glycine, expandable graphite and carbon nanotubes.

11. The flame retardant polypropylene composite film according to any one of claims 1 to 10, wherein the polypropylene composition a comprises 40 to 90wt% of the homo-polypropylene a, 5 to 45wt% of the propylene impact copolymer b and 2 to 40wt% of the polyolefin elastomer c, based on the total weight of the polypropylene composition a; preferably, the polypropylene composition A comprises 55 to 75wt% of the homo-polypropylene a, 10 to 30wt% of the propylene impact copolymer b and 5 to 20wt% of the polyolefin elastomer c.

12. The flame retardant polypropylene composite film according to any one of claims 1 to 11, wherein the polypropylene composition B comprises from 40 to 100wt% of the random polypropylene x and from 0 to 60wt% of the polyolefin elastomer y, based on the total weight of the polypropylene composition B; preferably, the polypropylene composition B comprises 75 to 90wt% of a random polypropylene x and 10 to 25wt% of a polyolefin elastomer y.

13. The flame retardant polypropylene composite film according to any one of claims 1 to 12, wherein the polypropylene composition C comprises 30 to 80wt% of polypropylene m and 20 to 70wt% of flame retardant n based on the total weight of the polypropylene composition C; preferably, the polypropylene composition C comprises 40-70wt% of polypropylene m and 30-60wt% of flame retardant n.

14. Flame retardant polypropylene composite film according to any one of claims 1 to 13 wherein the parts by weight of the polyolefin elastomer c are Wc based on 100 parts by weight of the total weight of the polypropylene composition a and the parts by weight of the polyolefin elastomer y are Wy based on 100 parts by weight of the total weight of the polypropylene composition B, the ratio of Wc to Wy being from 6:1 to 1:4, preferably from 1:1 to 1:2.

15. Flame retardant polypropylene composite film according to any one of claims 1 to 14, wherein the ratio of the sum of the film layer B thickness, the sum of the film layer C thickness and the sum of the film layer a thickness in the polypropylene composite film is 0.1 to 3:0.1 to 1:1, preferably 0.5 to 2:0.2 to 0.6:1.

16. The flame retardant polypropylene composite film according to any one of claims 1 to 15, wherein film layer C is disposed between film layer B and film layer a.

17. The flame retardant polypropylene composite film according to any one of claims 1 to 16, wherein the polypropylene composition a and/or the polypropylene composition B and/or the polypropylene composition C further comprises an antioxidant and/or a lubricant;

preferably, the antioxidant is selected from at least one of antioxidant 1076, antioxidant 1010, antioxidant 168 and a thioester antioxidant;

Preferably, the antioxidant is contained in an amount of 0.1 to 0.8 parts by weight, preferably 0.2 to 0.4 parts by weight, based on 100 parts by weight of the total amount of the polypropylene composition a, the polypropylene composition B or the polypropylene composition C;

preferably, the lubricant is a PEG-based lubricant and/or a mono Gan Zhilei lubricant;

preferably, the lubricant is contained in an amount of 0.01 to 0.5 parts by weight, preferably 0.05 to 0.2 parts by weight, based on 100 parts by weight of the total amount of the polypropylene composition a, the polypropylene composition B or the polypropylene composition C.

18. The flame retardant polypropylene composite film according to any one of claims 1 to 17, wherein the polypropylene composition a and/or polypropylene composition B and/or polypropylene composition C further comprises a film forming aid, preferably at least one selected from the group consisting of halogen-resistant agents, light stabilizers, heat stabilizers, colorants, fillers, slip agents and anti-tackifiers; more preferably, the content of the film forming aid is 0.01 to 0.5 parts by weight, preferably 0.05 to 0.3 parts by weight, based on 100 parts by weight of the total amount of the polypropylene composition a, the polypropylene composition B or the polypropylene composition C.

19. A method of preparing the flame retardant polypropylene composite film of any one of claims 1 to 18, comprising: extruding and casting the raw material composition for forming each layer after an optional granulating process to form the composite film; optionally, the method further comprises stretching, preferably biaxially stretching, the resulting composite film.

20. Use of the flame retardant polypropylene composite film according to any one of claims 1 to 18 in the field of packaging materials; the package is preferably a battery package or an electronic product package.