Flame-retardant crosslinked polypropylene film and protective housing comprising the same

Abstract

The present application discloses a flame-retardant crosslinked polypropylene film and a protective housing comprising the same. The crosslinked PP film has a crosslinking degree of not less than 36%. The flame-retardant crosslinked PP film retains the mechanical and insulating properties of the PP resin, enabling its use as a protective housing for electrical devices. In addition, the flame-retardant crosslinked PP film exhibits excellent heat resistance, with an increased melting temperature, so that it is less prone to deformation under heat, thereby enhancing the reliability and broadening the application scope of the flame-retardant crosslinked PP film. Moreover, the flame-retardant crosslinked PP film of the present application is prepared using irradiation crosslinking, which simplifies the crosslinking process and facilitates easier processing and forming of the film.

Description

Attorney Docket No. 69482WO01 (71453-WO)FLAME-RETARDANT CROSSLINKED POLYPROPYLENE FILM AND PROTECTIVE HOUSING COMPRISING THE SAMERELATED APPLICATIONS

[0001] The present application claims the benefit of Chinese Patent Application No. 202411380113.9, filed September 29, 2024. The entirety of Chinese Patent Application No. 202411380113.9 is expressly incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] The present application relates to the field of films, and in particular, to a flameretardant crosslinked polypropylene film and a protective housing comprising the same.BACKGROUND

[0003] Polypropylene (PP) possesses excellent insulating properties and mechanical performance; however, it has a low melting temperature, and conventional polypropylene is flammable, which limits the application of polypropylene plastics in electronic devices.SUMMARY

[0004] The present application provides a flame-retardant cross-linked polypropylene film. The flame-retardant crosslinked polypropylene film also exhibits good flame-retardant properties and high melting temperatures on the basis of maintaining the insulation and mechanical properties of the polypropylene material.

[0005] The present application provides, in a first aspect, a flame-retardant crosslinked polypropylene film, wherein the degree of crosslinking of the flame-retardant crosslinked polypropylene film is not less than 36%.

[0006] According to the first aspect, the flame-retardant crosslinked polypropylene film comprises polypropylene (PP) resin, flame retardants, and cross-linking agents. The flame retardant is selected from at least two of ammonium polyphosphate (APP), or a derivative thereof, melamine polyphosphate (MPP), or a derivative thereof, and piperazine pyrophosphate (PAPP), or a derivative thereof.Attomey Docket No. 69482WO01 (71453-WO)

[0007] According to the first aspect described above, the weight percentage of the polypropylene resin is: 36-76%. The weight percentage ofthe flame retardant is: 15-40%. and the weight percentage of the cross-linking agent is: 3-8%.

[0008] According to the first aspect described above, the flame-retardant crosslinked polypropylene film further comprises: polyethylene (PE) resin.

[0009] According to the first aspect described above, the weight percentage of the polyethylene resin does not exceed 0-15%.

[0010] According to the first aspect described above, the cross-linking agent is selected from at least one of the following: amide-based cross-linking agents, acrylate-based cross-linking agents, alkyne-based cross-linking agents, and polyolefin-based cross-linking agents.

[0011] According to the first aspect described above, the cross-linking agent is selected from one or more of the following: diallyl adipate, diallyl sebacate, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, methyltriallyl isocyanurate (TMAIC), trimethylolpropane trimethacrylate (TMPTMA), pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate (TMPTA), allyl methacrylate, N,N'-m-phenylenedimaleimide, N,N-dimethylacrylamide, 2,4-hexadiyne-l,6- di(butyl carbamate), and 1,2-polybutadiene oligomers.

[0012] According to the first aspect described above, the cross-linking agent is an acrylate- based cross-linking agent.

[0013] According to the first aspect described above, the cross-linking agent is selected from one or more of the following: triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), methyl triallyl isocyanurate (TMAIC), trimethylolpropane trimethacrylate (TMPTMA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and propyl methacrylate.

[0014] According to the first aspect described above, the flame-retardant crosslinked polypropylene film is obtained by extrusion molding followed by irradiation crosslinking.

[0015] According to the first aspect described above, the irradiation crosslinking is carried out at an irradiation dose of 60KGy~120KGy.

[0016] According to the first aspect described above, the flame-retardant crosslinked polypropylene film comprises an upper layer, a middle layer, and a lower layer, wherein the upper layer, middle layer, and lower layer are first bonded together through a co-extrusion process, anAttomey Docket No. 69482WO01 (71453-WO) adhesive lamination process, or a hot-press lamination process, and then subjected to irradiation crosslinking to form the flame-retardant crosslinked polypropylene fdm.

[0017] According to the first aspect described above, the upper film layer and the lower film layer are identical in composition.

[0018] According to the first aspect described above, the upper layer and the lower layer of the film comprise polypropylene resin, flame retardants, and cross-linking agents; the middle layer of the film comprises polypropylene resin. Wherein the combined thickness of the upper and lower layers accounts for 50-95% of the total thickness of the flame-retardant crosslinked polypropylene film, while the thickness of the middle layer accounts for 5-50% of the total thickness.

[0019] According to the first aspect described above, the upper layer and the lower layer of the film comprise polypropylene resin, while the middle layer of the film comprises polypropylene resin, flame retardants, and cross-linking agents. Wherein the combined thickness of the upper and lower layers accounts for 5-50% of the total thickness of the flame-retardant crosslinked polypropylene film, and the thickness of the middle layer accounts for 50-95% of the total thickness.

[0020] According to the above first aspect, the upper layer, middle layer, and lower layer of the film collectively comprise polypropylene resin in a total amount of 36-76% by weight, a flame retardant in a total amount of 15-40% by weight, and a cross-linking agent in a total amount of 3-8% by weight.

[0021] According to the first aspect described above, the heat-melting temperature of the flame-retardant crosslinked polypropylene film is not less than 350 °C.

[0022] According to the first aspect described above, the flame-retardant crosslinked polypropylene film has a thickness of 0.08~3mm.

[0023] According to the first aspect described above, the flame-retardant crosslinked polypropylene film exhibits a flame-retardant rating of at least VTM-0 at 0.2 mm thickness.

[0024] In a second aspect, the present application provides a protective housing for protecting electronic devices, wherein the protective housing is made of the flame-retardant crosslinked polypropylene film according to any one of the embodiments of the first aspect.

[0025] Other features, advantages, and embodiments of the present application may be set forth or become apparent from consideration of the following detailed description of embodiments, drawings, and claims. Furthermore, it should be understood that the above summary of theAttomey Docket No. 69482WO01 (71453-WO) invention and the following detailed description of embodiments are exemplary and are intended to provide further explanation without limiting the scope of the claimed application. It should also be understood that, although specific component arrangements are disclosed and illustrated in these exemplary embodiments, other arrangements are also within the scope of the present application. However, the detailed description of embodiments and specific examples only indicate preferred embodiments of the present application. Various variations and modifications within the spirit and scope of the present application will become apparent to those skilled in the art from the detailed description of embodiments.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1A is a structural schematic diagram of a flame-retardant crosslinked PP film according to one embodiment of the present application;

[0027] FIG. IB is a structural schematic diagram of a flame-retardant crosslinked PP film according to another embodiment of the present application;

[0028] FIG. 2 is a structural schematic diagram of an electrical device comprising the flameretardant crosslinked PP film according to one embodiment of the present application.DETAILED DESCRIPTION

[0029] Various specific embodiments of the present application will be described below with reference to the accompanying drawings that form a part of the present specification. It should be understood that while terms denoting orientation, such as “front,” “rear,” “upper,” “lower,” “left,” “right,” “top,” “bottom,” “inside,” “outside,” etc., are used in the present application to describe various exemplary structural parts and elements of the present application, these terms are used herein for convenience of illustration only and are determined based on the exemplary orientations shown in the accompanying drawings. Since the examples disclosed in the present application may be disposed in different orientations, these terms denoting orientation are for illustrative purposes only and should not be considered as limiting.

[0030] In the present application, unless otherwise specified, all equipment and materials may be purchased from the market or are commonly used in the industry. The methods in the following examples, unless specifically stated, are conventional methods in this field.Attomey Docket No. 69482WO01 (71453-WO)

[0031] Polypropylene (PP) film materials are a commonly used plastic material with excellent mechanical performance, processing and molding performance, and relatively low cost. They are widely used, for example, in the electrical field as insulating films. When polypropylene film material is used in electrical applications, it needs to be modified for flame retardancy to meet the flame-retardant requirements of electrical devices. Furthermore, in applications with higher performance requirements, the polypropylene film material also needs to be crosslinked, so that it exhibits improved mechanical properties and a higher melting temperature. This prevents the polypropylene film material from undergoing local melting when exposed to heat, even if it does not catch fire, which could otherwise lead to local thinning or deformation of the film.

[0032] The inventors of the present application have found that the flame-retardant performance of polypropylene film material is related to both the thickness of the polypropylene film and the amount of flame retardant added. In general, the greater the thickness of the polypropylene film, the better the flame-retardant effect. However, thick polypropylene films are unable to meet the lightweight and miniaturization development requirements of electrical parts, such as power adapters or batteries. To meet the lightweight and miniaturization development requirements of electrical parts, such as power adapters or batteries, it is desirable to manufacture thinner polypropylene film materials with good flame-retardant performance.

[0033] The inventors of the present application have further found that, in general, increasing the degree of crosslinking of PP film material can significantly raise its melting temperature. However, the addition of conventional flame retardants to the PP film can affect the improvement of the crosslinking degree, causing the PP resin to tend to degrade rather than crosslink, and may even prevent the PP film from undergoing crosslinking.

[0034] The present application provides a flame-retardant crosslinked polypropylene (PP) film having a degree of crosslinking of not less than 36%. In some embodiments, the flame-retardant crosslinked PP film has a thickness of 0.08~3mm. By incorporating appropriate types of flame retardants into the PP resin and selecting suitable formulation ratios and crosslinking methods, a flame-retardant crosslinked polypropylene film can be obtained that has a heat-melting temperature of not less than 350 °C and exhibits a flame-retardant rating of at least VTM-0 at 0.2 mm thickness.

[0035] The flame-retardant crosslinked PP film of the present application comprises PP resin, a flame retardant, and a cross-linking agent. In this embodiment, the flame retardant is selectedAttomey Docket No. 69482WO01 (71453-WO) from at least two of ammonium polyphosphate (APP), or a derivative thereof, melamine polyphosphate (MPP), or a derivative thereof, and piperazine pyrophosphate (PAPP), or a derivative thereof. The weight percentage of the PP resin is 36-76%, the weight percentage of the flame-retardant agent is 15-40%, and the weight percentage of the cross-linking agent is 3-8%. By incorporating the above two or three different types of halogen-free flame retardants, the flameretardant effect can be enhanced while reducing the total amount of flame retardant added, and the adverse effect of the flame retardant on the crosslinking of PP resin can be reduced.

[0036] In some embodiments, the flame-retardant cross-linking PP film further comprises a polyethylene (PE) resin with a weight percentage no greater than 0-15%. The addition of PE resins at a certain range of contents in the PP resin does not significantly affect the inherent properties of the PP resin, but can have a positive effect on increasing the degree of crosslinking of the PP resin.

[0037] In some embodiments, the cross-linking agent is selected from at least one of amide- based cross-linking agents, acrylate-based cross-linking agents, alkyne-based cross-linking agents, and polyolefin-based cross-linking agents. In certain specific embodiments, the cross-linking agent is selected from one or more of the following: diallyl adipate, diallyl sebacate, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, methyl-triallyl isocyanurate (TMAIC), trimethylolpropane trimethacrylate (TMPTMA), pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate (TMPTA), allyl methacrylate, N,N'-m-phenylenedimaleimide, N,N- dimethylacrylamide, 2,4-hexadiyne-l,6-di(butyl carbamate), and 1,2-polybutadiene oligomers. In more specific embodiments, the cross-linking agent is an acrylate-based cross-linking agent, for example, selected from one or more of the following: triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), methyl triallyl isocyanurate (TMAIC), trimethylolpropane trimethacrylate (TMPTMA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and propyl methacrylate.

[0038] In some embodiments, the flame-retardant crosslinked PP film further comprises 0.3-1 parts by weight of an antioxidant. The antioxidants may include conventional antioxidants. In some embodiments, the antioxidant comprises at least one of the following: 2,6-di-tert-butyl-4- methylphenol, octadecyl P-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, dilauryl thiodipropionate, distearyl thiodipropionate, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-Attomey Docket No. 69482WO01 (71453-WO) tert-butylphenyl) pentaerythritol diphosphite, pentaerythritol bis(stearyl alcohol) diphosphite, and benzofuranone.

[0039] FIGS. 1A and IB illustrate structural schematic diagrams of two embodiments of a flame-retardant crosslinked PP film, according to the present application. As shown in FIG. 1A, the flame-retardant crosslinked PP film 110 comprises a single film layer 111, wherein the single film layer 111 collectively comprises 36-76% by weight of PP resin, 15-40% by weight of a flame retardant, and 3-8% by weight of a cross-linking agent.

[0040] The flame-retardant crosslinked PP film 110 shown in FIG. 1 A is obtained by extrusion molding the PP resin, flame retardant, and cross-linking agent, followed by irradiation crosslinking. In some embodiments, the irradiation crosslinking is performed at the irradiated dose of 60KGy~120KGy. In some specific embodiments, the method of preparing the flame-retardant crosslinked PP film 110 comprises the steps of:

[0041] a. Weighing each raw material according to its weight percentage and adding them into a mixing device for blending;

[0042] b. Extruding the mixture obtained in Step a into a film shape;

[0043] c. Subjecting the film obtained in Step b to irradiation crosslinking to obtain the flameretardant crosslinked PP film.

[0044] The flame-retardant crosslinked PP film of the present application uses PP resin as a base material, retaining the fundamental properties of the PP resin, such as mechanical properties and insulation performance, enabling its use in electrical devices. Moreover, by modifying the film with halogen-free flame retardants, the flame-retardant crosslinked PP film achieves enhanced flame-retardant performance while remaining environmentally friendly.

[0045] The high-crosslinking flame-retardant crosslinked PP film of the present application, while ensuring the flame-retardant performance and mechanical properties of the PP film, also exhibits an increased melting temperature. This makes the film less prone to deformation when exposed to heat, thereby providing the flame-retardant crosslinked PP film with improved reliability and broader applicability.

[0046] The flame-retardant crosslinked PP film of the present application employs a combination of two or more flame retardants to reduce the adverse effects of the flame retardants on the crosslinking of the PP resin, thereby enabling the flame-retardant crosslinked PP film to achieve a degree of crosslinking of 36% or higher. In some embodiments, the degree ofAttomey Docket No. 69482WO01 (71453-WO) crosslinking of the flame-retardant crosslinked PP film can be further increased by incorporating a small amount of PE resin into the raw materials.

[0047] Furthermore, the present application further avoids the adverse effects of the flame retardant on the crosslinking of PP resin by selecting appropriate types and contents of PP resin, flame retardant, and cross-linking agent. By employing irradiation crosslinking, the crosslinking process is simplified, making the flame-retardant crosslinked PP film easier to process and mold.

[0048] The effects of the flame-retardant crosslinked PP film 110 of the present application are illustrated through flame-retardant crosslinked PP film samples of Examples 1-6 and Comparative Examples 1-3. Table 1 shows the contents of each component in the flame-retardant crosslinked PP film samples of Examples 1-6 and Comparative Examples 1-3, and Table 2 shows the performance data of the flame-retardant crosslinked PP film samples of Examples 1-6 and Comparative Examples 1-3.

[0049] The flame-retardant crosslinked PP film samples of Examples 1-6 and Comparative Examples 1-3 were prepared by the following method:

[0050] a. Weigh the raw materials according to the components and weight percentages shown in Table 1, and add all the raw materials into a mixing device for blending;

[0051] b. Extrude the mixture obtained in Step a into a film at a temperature of 200-230°C;

[0052] c. Subject the film obtained in Step b to irradiation crosslinking to obtain the flameretardant crosslinked PP film, and then cut the film into standard test specimens of uniform thickness, for example, 0.4 mm or 0.2 mm, for performance testing.

[0053] The PP resin and PE resin used in Examples 1-6 and Comparative Examples 1-3 are commercially available conventional resins. The cross-linking agent used in each Example and Comparative Example is the triallyl isocyanurate (TAIC).

[0054] The flame-retardant performance was tested based on UL-94 test standards. The tensile strength was tested based on the ASTM standard. The dart drop impact weight test was conducted according to the ISO 7765 method. Except for flame-retardant testing, all other tests were performed on 0.4 mm thick flame-retardant crosslinked PP films.Attorney Docket No. 69482WO01 (71453-WO)Table 1 Components and Their Weight Percentages in Examples 1-6 and Comparative Examples 1-3Table 2 Performance of the Flame -Retardant Crosslinked PP Film Samples in Examples 1-6 andComparative Examples 1-3Attorney Docket No. 69482WO01 (71453-WO)

[0055] As can be seen from Tables 1 and 2, the flame-retardant crosslinked PP film samples of Examples 1-6 exhibit a degree of crosslinking of 36% or higher, which is significantly higher than that of Comparative Examples 1-3. Due to the higher degree of crosslinking, the heat resistance and elongation at break of the flame-retardant crosslinked PP film samples in Examples 1-6 are superior to those of Comparative Examples 1-3. Moreover, the flame-retardant crosslinked PP film samples of Examples 1-6 can all meet the V-0 flame-retardant requirement at a thickness of 0.4 mm, and can even meet the VTM-0 flame-retardant requirement at 0.2 mm thickness. In contrast, Comparative Examples 1-3 fail to meet the flame-retardant requirements.

[0056] Specifically, compared with Comparative Examples 1-3, Examples 1-6 use roughly the same cross-linking agent and crosslinking process, but at least two flame retardants are combined in Examples 1-6, resulting in a significantly higher degree of crosslinking than inAttomey Docket No. 69482WO01 (71453-WO)Comparative Examples 1-3. This demonstrates that by selecting a combination of more than two flame retardants, the adverse effects of the flame retardants on the crosslinking of PP resin can be reduced, allowing the flame-retardant crosslinked PP film to achieve a higher degree of crosslinking. In contrast, using any single flame retardant alone not only hinders the crosslinking reaction but also compromises the flame-retardant performance of the flame retardant. Furthermore, the comparison between Examples 1-6 and Comparative Examples 1-3 shows that the higher degree of crosslinking in Examples 1-6 also improves the mechanical properties of the flame-retardant crosslinked PP resin. This indicates that an increase in crosslinking degree can enhance mechanical properties such as tensile strength and elongation at break of the film.

[0057] In Examples 1-6, Examples 3-6 include a small amount of PE resin in addition to PP resin. The resulting flame-retardant crosslinked PP films exhibit a higher degree of crosslinking than those in Examples 1 and 2, indicating that the addition of a small amount of PE resin is beneficial for the crosslinking reaction of PP resin. Moreover, compared with Examples 1-2, the flame-retardant crosslinked PP films of Examples 3-6 not only show a higher degree of crosslinking but also exhibit better heat resistance. The films can withstand 5 minutes at 350 °C without any molten softening, demonstrating that an increased degree of crosslinking enhances the heat resistance of the film.

[0058] In addition, insulation tests were conducted on the films of Examples 1-6 and Comparative Examples 1-3, and the insulation performance was generally comparable. The surface resistivity of all films reached 1015 Q or higher, meeting the insulation requirements for use in the electronics and electrical industry.

[0059] In some embodiments, the flame-retardant crosslinked PP film comprises an upper layer, a middle layer, and a lower layer. Each film layer includes polypropylene resin, and the composition of each film layer may be the same or different. However, the total composition of the three film layers includes PP resin with a weight percentage of 36-76%, a flame retardant with a weight percentage of 15-40%, and a crosslinking agent with a weight percentage of 3-8%.

[0060] As shown in FIG. IB, the flame-retardant crosslinked PP film adopts a three-layer structure, comprising an upper film layer 121, a middle film layer 122, and a lower film layer 123. The upper film layer 121 , middle film layer 122, and lower film layer 123 are combined by coextrusion, adhesive lamination, or hot-press lamination, followed by radiation crosslinking to form the flame-retardant crosslinked PP film 120. The overall degree of crosslinking of the upper filmAttomey Docket No. 69482WO01 (71453-WO) layer 121, middle film layer 122, and lower film layer 123 is not less than 36%. As one example, the upper film layer 121, middle film layer 122, and lower film layer 123 in total include PP resin with a weight percentage of 36-76%, a flame retardant with a weight percentage of 15-40%, and a cross-linking agent with a weight percentage of 3-8%. Wherein the flame retardant is selected from at least two of APP or derivatives thereof, MPP or derivatives thereof, and PAPP or derivatives thereof.

[0061] In some embodiments, the upper layer 121 and the lower layer 123 of the film comprise PP resin, flame retardant, and cross-linking agent. The middle film layer 122 comprises PP resin but excludes flame retardant and cross-linking agent. The combined thickness of the upper film layer 121 and the lower film layer 123 accounts for 50-95% of the total thickness of the flameretardant PP film, while the thickness of the middle layer 122 accounts for 5-50% of the total thickness of the flame-retardant PP film. In some embodiments, the upper film layer and the lower film layer have the same composition.

[0062] In some embodiments, the upper film layer 121 and the lower film layer 123 comprise PP resin but exclude flame retardant and cross-linking agent. The middle film layer 122 comprises PP resin, flame retardant, and crosslinking agent. The combined thickness of the upper film layer 121 and the lower film layer 123 accounts for 5-50% of the total thickness of the flame-retardant PP film, while the thickness of the middle film layer 122 accounts for 50-95% of the total thickness of the flame-retardant PP film. In some embodiments, the upper film layer and the lower film layer have the same composition.

[0063] It should be noted that the formulations of the upper film layer 121 and the lower film layer 123 may be identical or different, provided that the overall composition of the upper film layer 121, the middle film layer 122, and the lower film layer 123 meets the requirements described above.

[0064] As shown in FIG. IB, the method for preparing the flame-retardant cross-linked PP film 120 comprises the following steps:

[0065] a. Weigh the raw materials for the upper film layer, the middle film layer, and the lower film layer according to their weight percentages, and separately add them into a mixing blender for mixing;

[0066] b. Extrude each mixture obtained in Step a into a film to form three layers;Attorney Docket No. 69482WO01 (71453-WO)

[0067] c. Combine the three film layers obtained in Step b by a co-extrusion process, an adhesive lamination process, or a hot-press lamination process;

[0068] d. Subject the combined three-layer film obtained in Step c to radiation crosslinking to obtain the flame-retardant cross-linked PP film.

[0069] The applicant has found that, because at least one layer in the three-layer structure of the flame-retardant cross-linked PP film 120 is made of PP resin without a flame retardant, when the contents of PP resin and flame retardant are fixed, the flame retardant tends to be more concentrated in the one or two layers containing the flame retardant. As a result, the flameretardant cross-linked PP film 120 can achieve better flame-retardant efficiency or require a smaller amount of flame retardant. Furthermore, compared with the flame-retardant cross-linked PP film 110, the flame-retardant cross-linked PP film 120 retains more of the inherent properties of PP resin, thereby providing improved puncture resistance.

[0070] The effects of the flame-retardant crosslinked PP film 120 of the present application are illustrated below through specific samples of Examples 7-12. Table 3 presents the thickness of each layer in the samples of the flame-retardant crosslinked PP film 120 from Examples 7—12, as well as the corresponding performance data of the samples.

[0071] In Examples 7-12, the total composition of each layer of the flame-retardant crosslinked PP film 120 is the same as the composition of the flame-retardant crosslinked PP film 110 in Examples 1-6. Moreover, in Examples 7-9, the upper film layer 121 and the lower film layer 123 have the same composition, including PP resin, flame retardant, and cross-linking agent, while the middle film layer 122 includes only PP resin. In Examples 10-12, the upper film layer 121 and the lower film layer 123 have the same composition, including only PP resin, while the middle film layer 122 includes PP resin, flame retardant, and cross-linking agent.Table 3 Thicknesses of Layers and Performance Data of Flame -Retardant Crosslinked PP Film Samples inExamples 7-12Attorney Docket No. 69482WO01 (71453-WO)

[0072] As can be seen from Tables 2 and 3, the crosslinking degree, mechanical properties, and flame retardancy of the three-layer flame-retardant crosslinked PP films 120 in Examples 7- 12 are roughly equivalent to those of Examples 1-6. This indicates that forming a three-layer structured flame-retardant crosslinked PP film 120 does not adversely affect the crosslinking reaction, mechanical properties, or flame-retardant performance of the PP resin. Furthermore, compared with the single-layer flame-retardant crosslinked PP films 110 of Examples 1-6, the three-layer flame-retardant crosslinked PP films 120 exhibit superior puncture resistance.

[0073] FIG. 2 is a structural schematic diagram of an electrical device comprising the flameretardant crosslinked PP film according to one embodiment of the present application. As shown in FIG. 2, the electrical device 200 includes a protective housing 201 and an electronic component 202 disposed within the protective housing 201. The electronic device 202 is indicated by theAttomey Docket No. 69482WO01 (71453-WO) dashed box. The protective housing 201 is made from any one of the flame-retardant crosslinked PP film samples of Examples 1-2. The protective housing 201 surrounds the exterior of the electronic component 202, thereby enabling the protective housing 201 to protect the electronic component 202.

[0074] By using the flame-retardant crosslinked PP film of the present application as the protective housing 201 for the electronic component 202, the protective housing 201 is prevented from softening or deforming even when the electronic component 202 generates localized heat, thereby improving the reliability of the protective housing 201 in electrically insulating and protecting the electronic component 202. The electronic component 202 of the present application may be a high-heat-generating part, such as a battery.

[0075] The flame-retardant crosslinked PP film of the present application has multiple beneficial technical effects. At least some of these technical effects are listed as follows:

[0076] 1. It retains the mechanical properties and insulating performance of the PP resin, enabling the flame-retardant crosslinked PP film to be used as a protective housing for electrical devices.

[0077] 2. Halogen-free flame retardants are used, making the flame-retardant crosslinked PP film environmentally friendly.

[0078] 3. Even at very small thicknesses, the flame-retardant crosslinked PP film exhibits excellent flame-retardant performance, meeting the requirements for miniaturization and lightweight design of electrical components, and allowing broader application in electronic devices.

[0079] 4. Excellent heat resistance increases the melting temperature of the flame-retardant crosslinked PP film, making it less prone to deformation under heat, thereby improving reliability and expanding its range of applications.

[0080] 5. The use of irradiation crosslinking simplifies the crosslinking process, making the flame-retardant crosslinked PP film easier to process and form.

[0081] Although the present disclosure has been described in connection with the exemplary examples outlined above, various alternatives, modifications, variations, improvements, and / or substantial equivalents, whether known or foreseeable now or in the near future, may be apparent to those having at least ordinary skill in the art. Therefore, the exemplary examples of the present disclosure set forth above are intended to be illustrative and not limiting. Various changes may beAttomey Docket No. 69482WO01 (71453-WO) made without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is intended to include all known or earlier developed alternatives, modifications, variations, improvements and / or substantial equivalents. The technical effects and technical problems in this specification are exemplary and not limiting. It should be noted that the examples described in this specification may have other technical effects and may solve other technical problems.

Claims

Attorney Docket No. 69482WO01 (71453-WO)CLAIMSWhat is claimed is:

1. A flame-retardant crosslinked polypropylene film, wherein the crosslinked PP film has a crosslinking degree of not less than 36%.

2. The flame-retardant crosslinked polypropylene film according to claim 1, comprising: polypropylene (PP) resin; a flame retardant, wherein the flame retardant is selected from at least two of ammonium polyphosphate (APP), or a derivative thereof, melamine polyphosphate (MPP), or a derivative thereof, and piperazine pyrophosphate (PAPP), or a derivative thereof; and a cross-linking agent.

3. The flame-retardant crosslinked polypropylene film according to claim 2, wherein: the weight percentage of the polypropylene resin is 36-76%; the weight percentage of the flame retardant is 15-40%; and the weight percentage of the cross-linking agent is 3-8%.

4. The flame-retardant crosslinked polypropylene film according to claim 2, further comprising polyethylene (PE) resin.

5. The flame-retardant crosslinked polypropylene film according to claim 4, wherein the weight percentage of the polyethylene resin does not exceed 0-15%.

6. The flame-retardant crosslinked polypropylene film according to claim 2, wherein the cross-linking agent is selected from at least one of amide-based cross-linking agents, acrylate- based cross-linking agents, alkyne-based cross-linking agents, and polyolefin-based cross-linking agents.

7. The flame-retardant crosslinked polypropylene film according to claim 6, wherein the cross-linking agent is selected from any one or more of the following: diallyl adipate, diallylAttomey Docket No. 69482WO01 (71453-WO) sebacate, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), 1,6-hexanediol dimethacrylate, polyethylene glycol dimethacrylate, methyl-triallyl isocyanurate (TMAIC), trimethylolpropane trimethacrylate (TMPTMA), pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, trimethylolpropane triacrylate (TMPTA), allyl methacrylate, N,N'-m-phenylenedimaleimide, N,N-dimethylacrylamide, 2,4-hexadiyne-l,6-di(butyl carbamate), and 1,2-polybutadiene oligomers.

8. The flame-retardant crosslinked polypropylene film according to claim 7, wherein the cross-linking agent is an acrylate-based cross-linking agent.

9. The flame-retardant crosslinked polypropylene film according to claim 8, wherein the cross-linking agent is selected from any one or more of the following: triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), methyl triallyl isocyanurate (TMAIC), trimethylolpropane trimethacrylate (TMPTMA), trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, and propyl methacrylate.

10. The flame-retardant crosslinked polypropylene film according to claim 2, wherein the flame-retardant crosslinked polypropylene film is obtained by extrusion molding followed by irradiation crosslinking.

11. The flame-retardant crosslinked polypropylene film according to claim 10, wherein: the irradiation crosslinking is carried out with an irradiation dose of 60KGy~120KGy.

12. The flame-retardant crosslinked polypropylene film according to claim 1, wherein the flame-retardant crosslinked polypropylene film comprises an upper film layer, a middle film layer, and a lower film layer, wherein the upper, middle, and lower film layers are first combined by co-extrusion, adhesive lamination, or hot-press lamination, and then subjected to irradiation crosslinking to form the flame-retardant crosslinked polypropylene film.

13. The flame-retardant crosslinked polypropylene film according to claim 12, wherein the upper film layer and the lower film layer are identical in composition.Attomey Docket No. 69482WO01 (71453-WO)14. The flame-retardant crosslinked polypropylene film according to claim 13, wherein: the upper film layer and the lower film layer comprise polypropylene resin, flame retardant, and cross-linking agent; and the middle film layer comprises polypropylene resin; wherein the combined thickness of the upper and lower layers accounts for 50-95% of the total thickness of the flame-retardant crosslinked polypropylene film, while the thickness of the middle layer accounts for 5-50% of the total thickness.

15. The flame-retardant crosslinked polypropylene film according to claim 13, wherein: the upper film layer and the lower film layer comprise polypropylene resin; and the middle film layer comprises polypropylene resin, flame retardant, and cross-linking agent; wherein the combined thickness of the upper and lower layers accounts for 5-50% of the total thickness of the flame-retardant crosslinked polypropylene film, and the thickness of the middle layer accounts for 50-95% of the total thickness.

16. The flame-retardant crosslinked polypropylene film according to claim 13, wherein in the upper film layer, the middle film layer, and the lower film layer, the total content comprises a weight percentage of 36-76% of polypropylene resin, a weight percentage of 15-40% of flame retardant, and a weight percentage of 3-8% of cross-linking agent.

17. The flame-retardant crosslinked polypropylene film according to Claim 1, wherein the heat-resistant melting temperature of the flame-retardant crosslinked polypropylene film is not less than 350 °C.

18. The flame-retardant crosslinked polypropylene film according to claim 1, wherein the flame-retardant crosslinked polypropylene film has a thickness of 0.08~3mm.

19. The flame-retardant crosslinked polypropylene film according to claim 1, whereinAttomey Docket No. 69482WO01 (71453-WO) the flame-retardant rating of the flame-retardant crosslinked polypropylene film at a thickness of 0.2 mm is not lower than VTM-0.

20. A protective housing for an electronic device, wherein the protective housing is made from the flame-retardant crosslinked polypropylene film according to any one of Claims 1- 19.

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