Low-temperature-shrinkage gasoline-resistant thermal shrinkage material as well as preparation method and application thereof

Abstract

The invention discloses a low-temperature-shrinkage gasoline-resistant thermal shrinkage material as well as a preparation method and application thereof, and belongs to the technical field of high polymer materials. The technical problems to be solved are high shrinkage temperature and poor gasoline resistance of the thermal shrinkage material. The heat-shrinkable material comprises the following components: base material resin, a halogen-free environment-friendly flame retardant, a processing aid, an antioxidant and color master batch, the base material resin is formed by mixing ultra-low density polyethylene and an ethylene-vinyl acetate copolymer with low VA content; the halogen-free environment-friendly flame retardant is formed by mixing at least one of zinc diethyl hypophosphite and aluminum diethyl hypophosphite with aluminum hydroxide. The prepared heat-shrinkable material has low-temperature shrinkage, excellent gasoline resistance and flame retardance, and on the basis, the prepared heat-shrinkable material further has the advantages of being environmentally friendly and safe.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically, it relates to a low-temperature shrinkage gasoline-resistant heat-shrinkable material, its preparation method and application. Background Technology

[0002] Heat-shrinkable materials, also known as thermotropic shape memory polymers, belong to the category of shape memory materials within smart materials. As the name suggests, these are materials that can change their shape under heating conditions.

[0003] Shape memory polymers, after being processed into their original shape, can temporarily change their shape to a second shape and maintain it under certain conditions. When this shape memory polymer, still in its second shape, is exposed to appropriate stimuli, it will quickly revert to its original shape – this is the "memory effect" of shape memory polymers. Based on the different conditions that stimulate the shape change, shape memory polymers can be classified into five main categories: thermotropic, phototropic, electrotropic, magnetotropic, and chemitropic. Currently, thermotropic shape memory polymers are the most researched and widely used. In practical applications, these polymers are mainly heated to induce shrinkage and deformation; therefore, they are generally called heat-shrinkable materials.

[0004] Due to the inherent flammability of polymer materials, many countries and regions have imposed increasingly stringent requirements on their flame-retardant properties. In the past, bromine- and chlorine-containing flame retardants were commonly used in the production of polymer materials to achieve this effect. These halogenated flame retardants, due to their low dosage and strong flame-retardant effect, were once widely used in various polymer materials, including heat-shrinkable materials. However, halogenated flame retardants produce toxic and harmful gases during combustion, posing a significant threat to the environment and human health. Today, with increasing emphasis on environmental protection, there are growing calls to abolish the use of halogenated flame retardants. Therefore, the market demand for the preparation of novel halogen-free flame-retardant heat-shrinkable materials has emerged.

[0005] Currently, in the automotive, aerospace, and electronics industries, there are frequent situations where heat-shrinkable materials need to be used in confined spaces or on temperature-sensitive components. This necessitates that the heat-shrinkable materials have a low initial shrinkage temperature. Furthermore, in environments such as automotive fuel lines, heat-shrinkable materials need to be in prolonged contact with organic solvents such as gasoline, therefore they must possess excellent gasoline resistance to prevent swelling, deformation, or performance degradation. Simultaneously, for safety reasons, heat-shrinkable materials used in such environments also need to have good flame-retardant properties. Some existing heat-shrinkable materials often struggle to simultaneously achieve low-temperature shrinkage, solvent resistance (such as gasoline), and environmentally friendly flame retardancy. For example, heat-shrink tubing with added polyethylene has a high shrinkage temperature, which may damage heat-sensitive components; while some modified materials may have insufficient gasoline resistance or flame retardancy.

[0006] Currently, heat-shrinkable materials commonly use ethylene-vinyl acetate copolymer (EVA) as the base material, achieving flame retardancy by adding antimony trioxide and decabromodiphenyl ethane. However, since November 2025, the REACH regulation has explicitly restricted the use of decabromodiphenyl ethane. Using halogen-free flame retardants simply by adding metal hydroxides requires significantly increasing their proportion, leading to a decrease in tensile strength, elongation at break, and other properties of the material. In known technologies, appropriately selecting EVA with high VA content and surface-treating the metal hydroxides can relatively improve the mechanical properties of the material. However, high-VA-content EVA materials will show a significant decrease in gasoline resistance, and may even completely fail to meet gasoline resistance requirements. Other studies have used materials such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE) as the base material for heat-shrinkable materials. Although these materials are resistant to gasoline in the short term, long-term contact with gasoline leads to swelling and significant performance degradation. Furthermore, their high shrinkage temperature makes them unsuitable for applications requiring low-temperature shrinkage. Heat-shrinkable materials involving oil resistance often use relatively low-cost base material components such as ethylene-propylene-diene monomer (EPDM), polypropylene (PP), silicone rubber, ethylene-ethyl acrylate copolymer (EEA), and polyolefin ester copolymer (POE). However, the processing technology is complex, especially for POE, which exhibits significant degradation and reduction in mechanical properties after exposure to gasoline, making it unsuitable for long-term gasoline contact. Adding oil-resistant rubbers such as acrylate rubber (ACM), hydrogenated nitrile butadiene rubber (HNBR), and phenyl silicone rubber will significantly increase the cost, thus limiting the application of such materials.

[0007] Relevant patent documents retrieved: This document, published in China (CN106589569A) on April 26, 2017, discloses a halogen-free flame-retardant and anti-adhesive heat shrink tubing and its preparation method. The document specifies its components as follows: 100 parts vinyl polymer, 20-40 parts red phosphorus, 50-80 parts flame retardant, 0.5-3 parts antioxidant, 0.5-3 parts lubricant, and 5-8 parts color masterbatch. The vinyl polymer is identified as low-density polyethylene, medium-density polyethylene, or ethylene glycol. The blend of two or more of the following: ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, ethylene-octene copolymer; ethylene acrylate maleic anhydride copolymer, methyl vinyl silicone rubber and ethylene propylene rubber; wherein the antioxidant is a compound of pentaerythritol tetrakis[methyl-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (1010) and tris(2,4-di-tert-butyl)phosphite (168) in a ratio of 3:1.

[0008] This document, published in China (CN103172926A) on June 26, 2013, discloses a low-temperature shrinkable halogen-free flame-retardant heat-shrink tubing and its processing technology. The document specifies its components as: ethylene-vinyl acetate copolymer, low-density polyethylene, ultrafine magnesium hydroxide, ultrafine aluminum hydroxide, maleic anhydride graft polymer, composite antioxidant, zinc stearate, and color masterbatch. The composite antioxidant is a mixture of a hindered phenolic primary antioxidant and a phosphite auxiliary antioxidant. In ratio 1: (1-3), the hindered phenolic antioxidant is disclosed as pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or octadecyl tetrakis[4-hydroxy-3,5-di-tert-butylphenyl)propionate] and the phosphite-based auxiliary antioxidant is tris[2,4-di-tert-butylphenyl] phosphite or bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite. This low-temperature shrinkable halogen-free flame-retardant heat-shrink tubing is suitable for harsh environments such as low temperatures, while protecting the internal cable from damage by high temperatures.

[0009] The prior art represented by the aforementioned documents has at least the following unresolved technical problems or defects: 1. Although the stability of heat-shrinkable materials containing red phosphorus is improved by microencapsulation, red phosphorus itself may still decompose under high temperature and humid conditions, releasing toxic gases (such as phosphine). Furthermore, if the microcapsule coating is damaged during processing or long-term use, it will lead to the exposure of red phosphorus and cause safety risks.

[0010] 2. Ultrafine magnesium hydroxide and ultrafine aluminum hydroxide are used as halogen-free flame retardants, with the total addition of these two types of inorganic flame retardants accounting for an extremely high percentage. While the high filling amount of inorganic flame retardants can improve the flame retardant effect, it may lead to a decrease in the material's flexibility, tensile strength, and other mechanical properties. This fails to solve the balance problem between "high flame retardancy" and "excellent mechanical properties," posing a potential risk of easy cracking and poor bending resistance in practical applications.

[0011] In solving the above problems or overcoming the above defects, the present invention encountered the following difficulties and obstacles: There is very little research on the effects of irradiation dose on the expansion processing and gasoline resistance of heat shrink tubing materials. Theoretically, the higher the irradiation dose, the greater the degree of crosslinking of the heat shrink tubing. After exceeding a certain critical value, irradiation crosslinking and decrosslinking reactions may occur. Low irradiation dose results in low crosslinking degree, while high irradiation dose results in high crosslinking degree. When it exceeds a certain value, decrosslinking will cause the material molecular chains to break, leading to a decrease in performance. Through extensive research, it has been found that when the irradiation dose of the heat shrink material of this invention is in the range of 140-180 kGY, the degree of crosslinking of the material can reach 90%-95%. Below 140 kGY, the degree of crosslinking is below 90%, and the tensile strength of the heat shrink material after gasoline resistance is less than 10 MPa. Above 180 kGY, the degree of crosslinking is above 95%. Excessive crosslinking prevents the material from expanding smoothly.

[0012] Performance studies on gasoline resistance: The technology of using ethylene-vinyl acetate copolymer (EVA) as the base material for heat-shrinkable materials is widely known, achieving flame retardancy by adding antimony trioxide and decabromodiphenyl ethane. However, since November 2025, the REACH regulation has explicitly restricted the use of decabromodiphenyl ethane. Using halogen-free flame retardants solely by adding metal hydroxides requires significantly increasing their proportion, leading to a decrease in tensile strength, elongation at break, and other properties of the material. In known technologies, appropriately selecting EVA with high VA content and surface-treating the metal hydroxides can relatively improve the mechanical properties of the material. However, high VA content EVA materials show a significant decrease in gasoline resistance, even failing to meet gasoline resistance requirements entirely. The technology of using LDPE, LLDPE, MDPE, and HDPE as the base material for heat-shrinkable materials is also commonly known. Although these materials exhibit short-term gasoline resistance, long-term gasoline contact leads to swelling and significant performance degradation, and their high shrinkage temperature makes them unsuitable for applications requiring low-temperature shrinkage.

[0013] Therefore, there is an urgent need for a heat-shrinkable material that is highly flame-retardant, has good gasoline resistance, high mechanical properties, high thermal shrinkage properties, and is environmentally friendly and safe. Summary of the Invention

[0014] The purpose of this invention is to provide: A low-temperature shrinkable gasoline-resistant heat-shrinkable material, its preparation method and application, and related technologies are disclosed to solve technical problems such as high shrinkage temperature, gasoline resistance, flame retardancy, poor mechanical properties, and environmental safety of heat-shrinkable materials, or combinations thereof.

[0015] Terminology Explanation: Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0016] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0017] Technical terminology reference book: *Handbook of Chinese Insulation Materials Products and Applications*, published by China Quality Standards Publishing & Media Co., Ltd., China Standards Press. Chief Editor: Zhu Wanhua, First Edition: April 2023. Reference standards include UL224, UL 94, etc.

[0018] Unless specifically defined herein, the use of all commercially available products herein employs standard techniques. For example, it may be carried out using the manufacturer's instructions for use with the kit, or in accordance with methods known in the art or the description of this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0019] The terms “optional / arbitrary” or “optionally / arbitrarily” mean that the event or situation described below may or may not occur, including both the occurrence and non-occurrence of the event or situation.

[0020] The term "high flame retardancy" as used in this article refers to the following: Under specified test conditions, the material has a strong ability to prevent or delay combustion, is not easily ignited by an open flame, has a slow flame spread rate, and can quickly self-extinguish after the ignition source is removed, while meeting the flame retardant performance indicators specified in this invention (such as oxygen index ≥32% and vertical burning rating reaching V-0).

[0021] The term "tensile strength" used in this article refers to the maximum tensile stress that a standard specimen can withstand before fracture when subjected to a tensile test at room temperature and a specified tensile rate. Its value is equal to the ratio of the maximum tensile load to the original cross-sectional area of ​​the specimen, and the unit is usually MPa. It is a core mechanical performance indicator that characterizes the ability of a material to resist tensile failure.

[0022] The term "elongation at break" used in this article refers to the percentage of elongation at break relative to the original gauge length when a standard specimen is subjected to a tensile test at room temperature and a specified tensile rate. It is a key indicator for measuring the plastic deformation capacity of a material; a higher value indicates stronger flexibility and resistance to fracture deformation.

[0023] The term "melting" as used in this article refers to the physical process in which the forces between molecular chains of a solid polymer material are broken under heat or external force, and the material gradually transforms from a crystalline or glassy state into a fluid viscous flow state. During this process, the material only undergoes a phase change and does not produce new chemical substances.

[0024] The term "Ethanox" as used in this article refers to an ethoxy antioxidant, which is a hindered phenolic primary antioxidant that inhibits the oxidative degradation of polymers / oils by capturing free radicals. In this article, it refers to pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

[0025] The term "BHT" as used in this article refers to: Butylated Hydroxytoluene, an ethoxy antioxidant with a typical hindered phenolic structure, high oil solubility, low cost, good compatibility, and heat resistance. In this article, it refers to 2,6-di-tert-butyl-p-cresol.

[0026] The term "DNP" used in this article refers to an antioxidant, N,N-Di-2-naphthyl-p-phenylenediamine, which has both free radical chain termination and metal ion complexation capabilities, and provides excellent protection against thermo-oxidative aging, climate aging, and harmful metal catalytic oxidation such as copper / manganese. In this article, it refers to N,N'-di(β-naphthyl)-p-phenylenediamine.

[0027] In a first aspect, the present invention provides: a low-temperature shrinkage gasoline-resistant heat-shrinkable material, comprising, by weight, the following components: 50-100 parts of a base resin, 50-100 parts of a halogen-free environmentally friendly flame retardant, 1-5 parts of a processing aid, 1.5-2.5 parts of an antioxidant, and 0-5 parts of a color masterbatch; wherein the base resin is a mixture of ultra-low density polyethylene and ethylene-vinyl acetate copolymer in a weight ratio of 1-3:14-18; and the halogen-free environmentally friendly flame retardant is composed of at least one of zinc diethylphosphite and aluminum diethylphosphite mixed with aluminum hydroxide.

[0028] Preferably, the density of the ultra-low density polyethylene is 0.880-0.910 g / cm³.

[0029] As a preferred embodiment, the base resin is selected from any value or range between 50 and 100 parts by weight.

[0030] Preferably, the base resin, by weight, is selected from any value or range between 50 and 100 parts, specifically from: 51 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts, 100 parts, or a range between the two.

[0031] More preferably, the base resin, by weight, is selected from any value or range between 50 and 100 parts, specifically from: 51 parts, 60 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts, 100 parts, or a range between the two.

[0032] More preferably, the base resin, by weight, is selected from any value or range between 50 and 100 parts, specifically from 51 parts, 80 parts, 95 parts, or a range between the two.

[0033] More preferably, the base resin comprises 95 parts by weight.

[0034] As a preferred embodiment, the halogen-free environmentally friendly flame retardant is selected from any value or range between 50 and 100 parts by weight.

[0035] Preferably, the halogen-free environmentally friendly flame retardant is selected from any value or range between 50 and 100 parts by weight, specifically from: 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, 85 parts, 90 parts, 95 parts, 100 parts or a range between the two.

[0036] More preferably, the halogen-free environmentally friendly flame retardant is selected from any value or range between 50 and 100 parts by weight, specifically from: 50 parts, 65 parts, 70 parts, 80 parts, 85 parts, 90 parts, 95 parts, 100 parts or a range between the two.

[0037] More preferably, the halogen-free environmentally friendly flame retardant is selected from any value or range between 50 and 100 parts by weight, specifically from 50 parts, 70 parts, 100 parts or a range between the two.

[0038] More preferably, the halogen-free environmentally friendly flame retardant comprises 70 parts by weight.

[0039] As a preferred embodiment, the processing aid, by weight, is selected from any value or range between 1 and 5 parts.

[0040] Preferably, the processing aid, by weight, is selected from any value or range between 1 and 5 parts, specifically from: 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, and 5 parts, or any value between the two.

[0041] More preferably, the processing aid, by weight, is selected from any value or range between 1 and 5 parts, specifically from: 1.5 parts, 2 parts, 2.5 parts, 4.5 parts, 5 parts, or a range between the two.

[0042] More preferably, the processing aid, by weight, is selected from any value or range between 1 and 5 parts, specifically from: 1.5 parts, 2 parts, 5 parts, or a range between the two.

[0043] More preferably, the processing aid is 1.5 parts by weight.

[0044] As a preferred embodiment, the antioxidant, by weight, is selected from any value or range between 1.5 and 2.5 parts.

[0045] Preferably, the antioxidant, by weight, is selected from any value or range between 1.5 and 2.5 parts, specifically from the range of 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, 2 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, and 2.5 parts.

[0046] More preferably, the antioxidant, by weight, is selected from any value or range between 1.5 and 2.5 parts, specifically from: 1.5 parts, 1.6 parts, 1.9 parts, 2 parts, 2.1 parts, 2.4 parts, 2.5 parts, or a range between the two.

[0047] More preferably, the antioxidant, by weight, is selected from any value or range between 1.5 and 2.5 parts, specifically from 1.5 parts, 2 parts, 2.5 parts, or a range between the two.

[0048] More preferably, the antioxidant is 1.5 parts by weight.

[0049] As a preferred embodiment, the color masterbatch, by weight, is selected from any value or range between 0 and 5 parts.

[0050] Preferably, the color masterbatch, by weight, is selected from any value or range between 0 and 5 parts, specifically from: 0 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts or a range between the two.

[0051] More preferably, the color masterbatch, by weight, is selected from any value or range between 0 and 5 parts, specifically from: 0 parts, 2.5 parts, 3 parts, 3.5 parts, 4.5 parts, 5 parts, or a range between the two.

[0052] More preferably, the color masterbatch, by weight, is selected from any value or range between 0 and 5 parts, specifically from: 0 parts, 3 parts, 5 parts or a range between the two.

[0053] In a further preferred embodiment, the color masterbatch is 0 parts by weight.

[0054] Preferably, the color masterbatch is a black masterbatch.

[0055] In a preferred embodiment, the base resin is a mixture of ultra-low density polyethylene and ethylene-vinyl acetate copolymer in a weight ratio selected from any value or range between 1-3:14-18.

[0056] Preferably, the base resin is a mixture of ultra-low density polyethylene and ethylene-vinyl acetate copolymer in a weight ratio selected from any value or range between 1-3:14-18, specifically selected from: 1:14, 1:16, 1:18, 2:14, 2:16, 2:18, 3:16, 3:18 or a range between the two.

[0057] More preferably, the base resin is a mixture of ultra-low density polyethylene and ethylene-vinyl acetate copolymer in a weight ratio selected from any value or range between 1-3:14-18, specifically selected from: 1:18, 2:14, 2:16, 3:16, 3:18 or a range between the two.

[0058] More preferably, the base resin is a mixture of ultra-low density polyethylene and ethylene-vinyl acetate copolymer in a weight ratio selected from any value or range between 1-3:14-18, specifically selected from: 1:18, 2:14, 3:16 or a range between the two.

[0059] More preferably, the base resin is a mixture of ultra-low density polyethylene and ethylene-vinyl acetate copolymer in a weight ratio of 1:18.

[0060] Preferably, the VA content of the ethylene-vinyl acetate copolymer is selected from 8-14 wt%.

[0061] More preferably, the VA content of the ethylene-vinyl acetate copolymer is selected from 8-14 wt%, specifically from: 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or a range between the two.

[0062] More preferably, the VA content of the ethylene-vinyl acetate copolymer is selected from 8-14 wt%, specifically from 8 wt%, 11 wt%, 14 wt%, or a range between the two.

[0063] More preferably, the VA content of the ethylene-vinyl acetate copolymer is 14wt%.

[0064] Preferably, the melt index of the ethylene-vinyl acetate copolymer is selected from 1.0-5.0 g / 10 min.

[0065] More preferably, the melt index of the ethylene-vinyl acetate copolymer is selected from 1.0-5.0 g / 10 min, specifically from: 1.0 g / 10 min, 2.0 g / 10 min, 3.0 g / 10 min, 4.0 g / 10 min, 5.0 g / 10 min or a range between the two.

[0066] More preferably, the melt index of the ethylene-vinyl acetate copolymer is selected from 1.0-5.0 g / 10 min, specifically from 1.0 g / 10 min, 3.0 g / 10 min, 5.0 g / 10 min or a range between the two.

[0067] More preferably, the melt index of the ethylene-vinyl acetate copolymer is 1.0 g / 10 min.

[0068] Preferably, the halogen-free environmentally friendly flame retardant is composed of at least one of zinc diethylphosphite and aluminum diethylphosphite, mixed with aluminum hydroxide.

[0069] Preferably, the halogen-free environmentally friendly flame retardant is a mixture of zinc diethylphosphite and aluminum hydroxide in a weight ratio selected from any value or range between 25-40:30-45.

[0070] More preferably, the halogen-free environmentally friendly flame retardant is a mixture of zinc diethylphosphite and aluminum hydroxide in a weight ratio selected from any value or range between 25-40:30-45, specifically selected from: 25:30, 25:45, 30:30, 30:35, 30:40, 35:30, 35:35, 35:40, 40:30, 40:35, 40:40, 40:45 or a range between the two.

[0071] More preferably, the halogen-free environmentally friendly flame retardant is a mixture of zinc diethylphosphite and aluminum hydroxide in a weight ratio selected from any value or range between 25-40:30-45, specifically selected from: 25:30, 35:35, 40:45 or a range between the two.

[0072] More preferably, the halogen-free environmentally friendly flame retardant is a mixture of zinc diethylphosphite and aluminum hydroxide in a weight ratio of 35:35.

[0073] Preferably, the halogen-free environmentally friendly flame retardant is a mixture of aluminum diethylphosphite and aluminum hydroxide in a weight ratio selected from any value or range between 25-40:30-45.

[0074] More preferably, the halogen-free environmentally friendly flame retardant is a mixture of aluminum diethylphosphite and aluminum hydroxide in a weight ratio selected from any value or range between 25-40:30-45, specifically selected from: 25:30, 25:45, 30:30, 30:35, 30:40, 35:30, 35:35, 35:40, 40:30, 40:35, 40:40, 40:45 or a range between the two.

[0075] More preferably, the halogen-free environmentally friendly flame retardant is a mixture of aluminum diethylphosphite and aluminum hydroxide in a weight ratio selected from any value or range between 25-40:30-45, specifically selected from: 25:30, 30:40, 40:45 or a range between the two.

[0076] More preferably, the halogen-free environmentally friendly flame retardant is a mixture of aluminum diethylphosphite and aluminum hydroxide in a weight ratio of 30:40.

[0077] Preferably, the antioxidant is a mixture of Ethanox, BHT and DNP in a weight ratio selected from any value or range between 0.8-1:0.7-0.8:0.5-0.7.

[0078] More preferably, the antioxidant is a mixture of Ethanox, BHT and DNP in a weight ratio selected from any value or range between 0.8-1:0.7-0.8:0.5-0.7, specifically selected from: 0.8:0.7:0.5, 0.8:0.8:0.5, 0.8:0.7:0.6, 0.8:0.7:0.7, 0.8:0.8:0.6, 0.8:0.8:0.7, 0.9:0.8:0.5, 0.9:0.8:0.6, 0.9:0.7:0.6, 0.9:0.7:0.7, 0.9:0.8:0.6, 0.9:0.8:0.7, 1:0.7:0.7, 1:0.8:0.7 or a range between two of these.

[0079] More preferably, the antioxidant is a mixture of Ethanox, BHT and DNP in a weight ratio selected from any value or range between 0.8-1:0.7-0.8:0.5-0.7, specifically selected from: 0.8:0.7:0.5, 0.8:0.8:0.5, 0.8:0.7:0.6, 0.9:0.8:0.5, 0.9:0.8:0.6, 0.9:0.7:0.6, 0.9:0.7:0.7, 1:0.7:0.7, 1:0.8:0.7 or a range between two of them.

[0080] More preferably, the antioxidant is a mixture of Ethanox, BHT and DNP in a weight ratio selected from any value or range between 0.8-1:0.7-0.8:0.5-0.7, specifically selected from: 0.8:0.7:0.5, 0.9:0.8:0.6, 1:0.8:0.7 or a range between the two.

[0081] More preferably, the antioxidant has a weight ratio of 1:0.8:0.7.

[0082] Preferably, the processing aid is polyethylene wax.

[0083] Based on further solutions to the technical problems of the present invention, or simultaneous solutions to multiple technical problems, the preferred solution in the technical solution provided in the first aspect of the present invention includes: The first preferred solution is a low-temperature shrinking, gasoline-resistant heat-shrinkable material. This solution addresses the technical problems of "high shrinkage temperature and poor flame retardant effect" and further solves the technical problem of "poor mechanical properties".

[0084] The second preferred solution is a low-temperature shrinking, gasoline-resistant heat-shrinkable material. This solution addresses the technical problems of "high shrinkage temperature, poor flame retardant effect, and poor mechanical properties" and further solves the technical problem of "poor heat aging resistance".

[0085] The third preferred solution is a low-temperature shrinkable gasoline-resistant heat-shrinkable material. This solution, in addition to addressing the technical problems of "high shrinkage temperature, poor flame retardant effect, poor mechanical properties, and poor heat aging resistance," further solves the technical problems of "high pollution and safety issues."

[0086] Secondly, the present invention provides the application of the above-mentioned heat-shrinkable material in the insulation protection, sealing, corrosion prevention, or wrapping and fixing of components at wire and cable connections.

[0087] Preferably, the above-mentioned heat-shrinkable material is used in the insulation protection, sealing, corrosion protection, or wrapping and fixing of components at wire and cable joints.

[0088] Thirdly, the present invention provides: a low-temperature shrinkable gasoline-resistant heat shrink tubing, made from the aforementioned heat shrinkable material.

[0089] Fourthly, the present invention provides a method for preparing the above-mentioned heat shrink tubing, comprising the following steps: (1) The base resin, halogen-free environmentally friendly flame retardant, processing aid, antioxidant and color masterbatch are put into a mixer, heated and mixed evenly to obtain material 1; (2) The material 1 obtained in step (1) is pre-granulated to obtain masterbatch granules; (3) The masterbatch particles obtained in step (2) are homogenized, then heated, melted, mixed and granulated to obtain heat shrinkable masterbatch; (4) The heat shrink masterbatch obtained in step (3) is extruded into a blank tube, and then subjected to irradiation crosslinking, heating expansion and cooling shaping in sequence to obtain the final product.

[0090] Preferably, the heating temperature in step (1) is selected from any value or range between 140-180°C.

[0091] More preferably, the heating temperature in step (1) is selected from any value or range between 140-180℃, specifically from: 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃ or a range between the two.

[0092] More preferably, the heating temperature in step (1) is selected from any value or range between 140-180℃, specifically from: 140℃, 160℃, 180℃ or a range between the two.

[0093] More preferably, the heating temperature in step (1) is 160°C.

[0094] Preferably, the specific operation of step (2) is as follows: the material 1 obtained in step (1) is fed into a single screw granulator through a double cone feeder for preliminary granulation to obtain masterbatch granules.

[0095] Preferably, the specific operation of the homogenization process in step (3) is as follows: the masterbatch particles obtained in step (2) are placed in the homogenization chamber for homogenization for 10 minutes.

[0096] Preferably, the heating and melting temperature in step (3) is selected from any value or range between 110-180°C.

[0097] More preferably, the heating and melting temperature in step (3) is selected from any value or range between 110-180℃, specifically from: 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃ or a range between the two.

[0098] More preferably, the heating and melting temperature in step (3) is selected from any value or range between 110-180℃, specifically from: 110℃, 140℃, 145℃, 150℃, 155℃, 175℃, 180℃ or a range between the two.

[0099] More preferably, the heating and melting temperature in step (3) is selected from any value or range between 110-180℃, specifically from: 110℃, 150℃, 180℃ or a range between the two.

[0100] More preferably, the heating and melting temperature in step (3) is 150°C.

[0101] Preferably, the extrusion temperature in step (4) is selected from any value or range between 100-130°C.

[0102] More preferably, the extrusion temperature in step (4) is selected from any value or range between 100-130℃, specifically from: 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃ or a range between the two.

[0103] More preferably, the extrusion temperature in step (4) is selected from any value or range between 100-130°C, specifically from 100°C, 120°C, 130°C or a range between the two.

[0104] More preferably, the extrusion temperature in step (4) is 120°C.

[0105] Preferably, the irradiation dose in step (4) is selected from any value or range between 140kGY and 180kGY.

[0106] More preferably, the irradiation dose in step (4) is selected from any value or range between 140kGY and 180kGY, specifically from: 140kGY, 145kGY, 150kGY, 155kGY, 160kGY, 165kGY, 170kGY, 175kGY, 180kGY or a range between the two.

[0107] More preferably, the irradiation dose in step (4) is selected from any value or range between 140kGY and 180kGY, specifically from: 140kGY, 145kGY, 150kGY, 155kGY, 175kGY, 180kGY or a range between the two.

[0108] More preferably, the irradiation dose in step (4) is selected from any value or range between 140kGY and 180kGY, specifically from: 140kGY, 150kGY, 180kGY or a range between the two.

[0109] More preferably, the irradiation dose in step (4) is 150 kGy.

[0110] Preferably, the temperature for heating expansion in step (4) is selected from any value or range between 140-150°C.

[0111] More preferably, the heating expansion temperature in step (4) is selected from any value or range between 140-150℃, specifically from: 140℃, 141℃, 142℃, 143℃, 144℃, 145℃, 146℃, 147℃, 148℃, 149℃, 150℃ or a range between the two.

[0112] More preferably, the heating expansion temperature in step (4) is selected from any value or range between 140-150℃, specifically from: 140℃, 141℃, 144℃, 145℃, 146℃, 149℃, 150℃ or a range between the two.

[0113] More preferably, the heating expansion temperature in step (4) is selected from any value or range between 140-150°C, specifically from: 140°C, 145°C, 150°C or a range between the two.

[0114] More preferably, the heating expansion temperature in step (4) is 140°C.

[0115] Preferably, the heating expansion ratio in step (4) is selected from 1.5 to 2.5 times.

[0116] More preferably, the heating expansion ratio in step (4) is selected from 1.5-2.5 times, specifically from: 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2.0 times, 2.1 times, 2.2 times, 2.3 times, 2.4 times, 2.5 times or a range between the two.

[0117] More preferably, the heating expansion ratio in step (4) is selected from 1.5-2.5 times, specifically from: 1.5 times, 2.0 times, 2.5 times or a range between the two.

[0118] More preferably, the heating expansion ratio in step (4) is 2.0 times.

[0119] Preferably, the specific operation of cooling and shaping in step (4) is: cooling and shaping with cooling water.

[0120] As the most preferred embodiment, the method for preparing the heat shrink tubing includes the following steps: (1) The base resin, halogen-free environmentally friendly flame retardant, processing aid, antioxidant and color masterbatch are put into a mixer and mixed at 160°C until uniform to obtain material 1; (2) The material 1 obtained in step (1) is fed into a single screw granulator via a double cone feeder for preliminary granulation to obtain masterbatch granules; (3) The masterbatch particles obtained in step (2) are homogenized in a homogenization chamber for 10 minutes. After the homogenization, they are mixed and granulated at 150°C by a twin-screw extruder to obtain heat shrinkable masterbatch. (4) The heat shrinkable masterbatch obtained in step (3) is extruded into a blank tube at 120°C using a single screw extruder. The tube is then irradiated and crosslinked with an electron accelerator at a dose of 150 kGY. The tube is then expanded 2.0 times in an expander at 140°C and cooled and shaped by water to obtain the final product.

[0121] The first preferred solution is a method for preparing a low-temperature shrinking, gasoline-resistant heat-shrinkable material. This solution, based on solving the technical problems of "high shrinkage temperature, poor flame retardant effect, poor mechanical properties and gasoline resistance, high pollution and safety issues", further solves the technical problem of "poor gasoline resistance and mechanical strength".

[0122] The second preferred solution is a method for preparing a low-temperature shrinking, gasoline-resistant heat-shrinkable material. This solution, in addition to addressing the technical problems of "high shrinkage temperature, poor flame retardant effect, mechanical properties, gasoline resistance, poor gasoline resistance and mechanical strength, high pollution and safety issues," further solves the technical problem of "inaccurate performance."

[0123] Examples 1-8 of this invention at least support the protection scope of the components of the heat-shrinkable material.

[0124] Regarding the components involved in claim 1: 50-100 parts of base resin, 50-100 parts of halogen-free environmentally friendly flame retardant, 1-5 parts of processing aid, 1.5-2.5 parts of antioxidant, and 0-5 parts of color masterbatch. The technical feature "the base resin is 50-100 parts by weight" is derived from the common feature "parts by weight of the base resin," which is summarized by the corresponding technical features of 51 parts, 80 parts, and 95 parts by weight in the foregoing explanation and / or Examples 1-8. Therefore, those skilled in the art can reasonably infer that the technical feature "the base resin is 50-100 parts by weight," its subordinate concepts, and its basically equivalent technical means, as well as technical means that can replace "the base resin is 50-100 parts by weight" based on existing technology and conventional technical means and common knowledge, should all fall within the protection scope of the components of the heat-shrinkable material claimed in the claims. For example, replacing "the base resin is 50-100 parts by weight" with 100 parts by weight while keeping other technical features unchanged still falls within the protection scope of the components of the heat-shrinkable material involved in claim 1 of this invention.

[0125] The technical feature “halogen-free environmentally friendly flame retardant in 50-100 parts by weight” is derived from the common feature “parts by weight of halogen-free environmentally friendly flame retardant”, which is summarized from the corresponding technical feature “halogen-free environmentally friendly flame retardant in 55, 65, 70, 85 parts by weight” in the foregoing explanation and / or Examples 1-8. Therefore, those skilled in the art can reasonably presume that the technical feature "halogen-free environmentally friendly flame retardant in 50-100 parts by weight", its subordinate concepts and their basically equivalent technical means, and the technical means that can replace "halogen-free environmentally friendly flame retardant in 50-100 parts by weight" based on existing technical levels and conventional technical means and common knowledge, should all fall within the protection scope of the components of the heat-shrinkable material claimed in the claims. For example, if other technical features remain unchanged, replacing "halogen-free environmentally friendly flame retardant in 50-100 parts by weight" with "halogen-free environmentally friendly flame retardant in 50-100 parts by weight" or 100 parts by weight, etc., still falls within the protection scope of the components of the heat-shrinkable material involved in claim 1 of this invention.

[0126] The technical feature "processing aids in parts by weight" is derived from the aforementioned explanation and / or the corresponding technical features in Examples 1-8, such as 1.5 parts, 2 parts, and 5 parts by weight of processing aids, summarized by the common feature "parts by weight of processing aids". Therefore, those skilled in the art can reasonably infer that the technical feature "processing aids in parts by weight", its subordinate concepts and their basically equivalent technical means, and technical means that can replace "processing aids in parts by weight" based on existing technology and conventional technical means and common knowledge, should all fall within the protection scope of the components of the heat-shrinkable material claimed in the claims. For example, replacing "processing aids in parts by weight" with 3 parts by weight while keeping other technical features unchanged still falls within the protection scope of the components of the heat-shrinkable material involved in claim 1 of this invention.

[0127] The technical feature "1.5-2.5 parts by weight of antioxidant" is derived from the common feature "parts by weight of antioxidant," which is summarized from the aforementioned explanation and / or the corresponding technical features of 1.5, 2, and 2.5 parts by weight of antioxidant in Examples 1-8. Therefore, those skilled in the art can reasonably infer that the technical feature "1.5-2.5 parts by weight of antioxidant," its subordinate concepts, and its basically equivalent technical means, as well as technical means that can replace "1.5-2.5 parts by weight of antioxidant" based on existing technology and conventional technical means and common knowledge, should all fall within the protection scope of the components of the heat-shrinkable material claimed in the claims. For example, replacing "1.5-2.5 parts by weight of antioxidant" with 2.3 parts by weight of antioxidant while keeping other technical features unchanged still falls within the protection scope of the components of the heat-shrinkable material involved in claim 1 of this invention.

[0128] The technical feature "0-5 parts by weight of color masterbatch" is derived from the common feature "parts by weight of color masterbatch" by summarizing the corresponding technical features of 0, 3, and 5 parts by weight of color masterbatch in the foregoing explanation and / or Examples 1-8. Therefore, those skilled in the art can reasonably infer that the technical feature "0-5 parts by weight of color masterbatch", its subordinate concepts and their basically equivalent technical means, and technical means that can replace "0-5 parts by weight of color masterbatch" based on the existing level of technology and conventional technical means and common knowledge, should all fall within the protection scope of the components of the heat-shrinkable material claimed in the claims. For example, replacing "0-5 parts by weight of color masterbatch" with 2.3 parts by weight of color masterbatch while keeping other technical features unchanged still falls within the protection scope of the components of the heat-shrinkable material involved in claim 1 of this invention.

[0129] Examples 1-8 of this invention at least support the protection range of VA content and melt index of ethylene-vinyl acetate copolymer.

[0130] Regarding the VA content and melt index of the ethylene-vinyl acetate copolymer involved in claim 2. The technical feature "the VA content of the ethylene-vinyl acetate copolymer is 8-14 wt%" is derived from the VA content of the ethylene-vinyl acetate copolymer (8 wt%, 11 wt%, 14 wt%) in the foregoing explanation and / or Examples 1-8, summarized by the common feature "VA content of the ethylene-vinyl acetate copolymer". Therefore, those skilled in the art can reasonably infer that the technical feature "the VA content of the ethylene-vinyl acetate copolymer is 8-14 wt%", its subordinate concepts and their basically equivalent technical means, and technical means that can replace "the VA content of the ethylene-vinyl acetate copolymer is 8-14 wt%" based on existing technology and conventional technical means and common knowledge, should all fall within the protection scope of the VA content of the ethylene-vinyl acetate copolymer claimed in the claim. For example, replacing "the VA content of the ethylene-vinyl acetate copolymer is 8-14 wt%" with 10 wt% of the ethylene-vinyl acetate copolymer while keeping other technical features unchanged still falls within the protection scope of the VA content of the ethylene-vinyl acetate copolymer involved in claim 2 of this invention.

[0131] The technical feature “the melt index of the ethylene-vinyl acetate copolymer is 1.0-5.0 g / 10 min” is summarized from the common feature “melt index of the ethylene-vinyl acetate copolymer” by the corresponding technical features of ethylene-vinyl acetate copolymer being 1.0 g / 10 min, 3 g / 10 min, 5.0 g / 10 min, etc. in the foregoing explanation and / or Examples 1-8. Therefore, those skilled in the art can reasonably presume that the technical feature "the melt index of the ethylene-vinyl acetate copolymer is 1.0-5.0 g / 10 min", its subordinate concepts and their basically equivalent technical means, and technical means that can replace "the melt index of the ethylene-vinyl acetate copolymer is 1.0-5.0 g / 10 min" based on existing technology and conventional technical means and common knowledge, should all fall within the protection scope of the melt index of the ethylene-vinyl acetate copolymer in claim 2. For example, if other technical features remain unchanged, replacing "the melt index of the ethylene-vinyl acetate copolymer is 1.0-5.0 g / 10 min" with the melt index of the ethylene-vinyl acetate copolymer is 2 g / 10 min, it still falls within the protection scope of the melt index of the ethylene-vinyl acetate copolymer involved in claim 2 of this invention.

[0132] Examples 1-8 of this invention at least support the protection of the composition and proportion of halogen-free environmentally friendly flame retardants.

[0133] Regarding the composition and proportion of the halogen-free environmentally friendly flame retardant involved in claim 3. The technical feature “halogen-free environmentally friendly flame retardant is a mixture of zinc diethyl phosphite and aluminum hydroxide in a weight ratio of 25-40:30-45” is summarized from the common feature “composition and proportion of halogen-free environmentally friendly flame retardant” in the foregoing explanation and / or the corresponding technical features in Examples 2-3 and Examples 5-6, such as the halogen-free environmentally friendly flame retardant being a mixture of zinc diethyl phosphite and aluminum hydroxide in a weight ratio of 35:35, 25:30, and 40:45. Therefore, those skilled in the art can reasonably presume that the technical feature "halogen-free environmentally friendly flame retardant is a mixture of zinc diethyl phosphite and aluminum hydroxide in a weight ratio of 25-40:30-45", its subordinate concepts and their basically equivalent technical means, and technical means that can replace "halogen-free environmentally friendly flame retardant is a mixture of zinc diethyl phosphite and aluminum hydroxide in a weight ratio of 25-40:30-45" within the scope of conventional technical means and common knowledge based on the existing technical level, should all fall within the protection scope of the composition and proportion of the halogen-free environmentally friendly flame retardant claimed in the claim. For example, if other technical features remain unchanged, replacing "halogen-free environmentally friendly flame retardant is a mixture of zinc diethyl phosphite and aluminum hydroxide in a weight ratio of 25-40:30-45" with a mixture of zinc diethyl phosphite and aluminum hydroxide in a weight ratio of 26:36, etc., still falls within the protection scope of the composition and proportion of the halogen-free environmentally friendly flame retardant of claim 3 of this invention.

[0134] The technical feature “halogen-free environmentally friendly flame retardant is a mixture of diethyl aluminum hypophosphite and aluminum hydroxide in a weight ratio of 25-40:30-45” is summarized from the common feature “composition and proportion of halogen-free environmentally friendly flame retardant” in the foregoing explanation and / or the corresponding technical features in Examples 1, 4 and 7-8, such as the mixture of diethyl aluminum hypophosphite and aluminum hydroxide in a weight ratio of 25:40, 35:35, 25:30, and 40:45. Therefore, those skilled in the art can reasonably presume that the technical feature "halogen-free environmentally friendly flame retardant is a mixture of diethyl aluminum hypophosphite and aluminum hydroxide in a weight ratio of 25-40:30-45", its subordinate concepts and their basically equivalent technical means, and technical means that can replace "halogen-free environmentally friendly flame retardant is a mixture of diethyl aluminum hypophosphite and aluminum hydroxide in a weight ratio of 25-40:30-45" based on existing technical levels and conventional technical means and common knowledge, should all fall within the protection scope of the composition and proportion of the halogen-free environmentally friendly flame retardant claimed in the claim. For example, if other technical features remain unchanged, replacing "halogen-free environmentally friendly flame retardant is a mixture of diethyl aluminum hypophosphite and aluminum hydroxide in a weight ratio of 25-40:30-45" with a mixture of diethyl aluminum hypophosphite and aluminum hydroxide in a weight ratio of 26:36, etc., still falls within the protection scope of the composition and proportion of the halogen-free environmentally friendly flame retardant of claim 3 of this invention.

[0135] The beneficial effects of this invention are as follows: The present invention has at least the following beneficial effects: 1. Low-temperature shrinkage: By using a composite base material system of ULDPE and ethylene-vinyl acetate with low VA content, the crystallinity and melting point of the material are significantly reduced, allowing the heat shrink tubing to begin shrinking at lower temperatures, making it suitable for protecting heat-sensitive components.

[0136] 2. Excellent gasoline resistance: The three-dimensional network structure formed after irradiation cross-linking effectively resists the penetration and swelling of solvents such as gasoline, maintaining the structural integrity and performance stability of the tube in harsh environments.

[0137] 3. Environmentally friendly and highly efficient flame retardant: It adopts a halogen-free composite flame retardant system with good synergistic effect and high flame retardant efficiency, meeting the requirements of environmental protection and high flame retardant level (such as UL94 V-0).

[0138] 4. Outstanding heat aging resistance: A blend of three flame retardants is used. Antioxidant 1010 serves as the primary antioxidant, providing long-term thermal stability to the material. BHT antioxidant ensures processing stability, while DNP is a key substance for enhancing resistance to gasoline extraction and metal embrittlement. This composite antioxidant system, compared to traditional or single antioxidants, provides excellent protection against the swelling and extraction of EVA and ULDPE in gasoline environments. 5. Reasonable process and controllable performance: The process of mixing, homogenization and twin-screw granulation ensures the full dispersion and compatibility of each component; by controlling the irradiation dose and expansion process parameters, the degree of crosslinking, shrinkage rate and final size of the product are precisely controlled. Detailed Implementation

[0139] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0140] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0141] Table 1

[0142] Examples 1-4: Preparation of a Low-Temperature Shrinkable Gasoline-Resistant Heat Shrink Tube The prescriptions are shown in Table 2. Table 2 Raw materials for heat shrink tubing preparation

[0143] Preparation methods of Examples 1-2: (1) The base resin, halogen-free environmentally friendly flame retardant, processing aid, antioxidant and color masterbatch are put into a mixer and mixed at 140°C until uniform to obtain material 1; (2) The material 1 obtained in step (1) is fed into a single screw granulator via a double cone feeder for preliminary granulation to obtain masterbatch granules; (3) The masterbatch particles obtained in step (2) are homogenized in a homogenization chamber for 10 minutes. After the homogenization, they are mixed and granulated at 180°C by a twin-screw extruder to obtain heat shrinkable masterbatch. (4) The heat shrinkable masterbatch obtained in step (3) is extruded into a blank tube at 110°C using a single screw extruder. The tube is then irradiated and crosslinked with an electron accelerator at a dose of 140 kGY. The tube is then expanded 2.5 times in an expander at 145°C and cooled and shaped by water to obtain the final product.

[0144] Preparation methods of Examples 3-4: (1) The base resin, halogen-free environmentally friendly flame retardant, processing aid, antioxidant and color masterbatch are put into a mixer and mixed at 160°C until uniform to obtain material 1; (2) The material 1 obtained in step (1) is fed into a single screw granulator via a double cone feeder for preliminary granulation to obtain masterbatch granules; (3) The masterbatch particles obtained in step (2) are homogenized in a homogenization chamber for 10 minutes. After the homogenization, they are mixed and granulated at 150°C by a twin-screw extruder to obtain heat shrinkable masterbatch. (4) The heat shrinkable masterbatch obtained in step (3) is extruded into a blank tube at 120°C using a single screw extruder. The tube is then irradiated and crosslinked with an electron accelerator at a dose of 150 kGY. The tube is then expanded 1.5 times in an expander at 140°C and cooled and shaped by water to obtain the final product.

[0145] Examples 5-8: Preparation of a Low-Temperature Shrinkable Gasoline-Resistant Heat Shrink Tube The prescriptions are shown in Table 3. Table 3 Raw materials for heat shrink tubing preparation

[0146] Preparation methods of Examples 5-8: (1) The base resin, halogen-free environmentally friendly flame retardant, processing aid, antioxidant and color masterbatch are put into a mixer and mixed at 180°C until uniform to obtain material 1; (2) The material 1 obtained in step (1) is fed into a single screw granulator via a double cone feeder for preliminary granulation to obtain masterbatch granules; (3) The masterbatch particles obtained in step (2) are homogenized in a homogenization chamber for 10 minutes. After the homogenization, they are mixed and granulated at 110°C by a twin-screw extruder to obtain heat shrinkable masterbatch. (4) The heat shrinkable masterbatch obtained in step (3) is extruded into a blank tube at 110°C using a single screw extruder. The tube is then irradiated and crosslinked with an electron accelerator at a dose of 180 kGY. The tube is then expanded 2.5 times in an expander at 150°C and cooled and shaped by water to obtain the final product.

[0147] Comparative Example 1 The difference from Example 3 is that the base resin material is changed, and ultra-low density polyethylene is replaced with low density polyethylene. The remaining amounts and steps are the same as in Example 3.

[0148] Comparative Example 2 The difference from Example 3 is that the base resin material is changed, and the ethylene-vinyl acetate copolymer is replaced with ethylene vinyl acetate. The remaining amounts and steps are the same as in Example 3.

[0149] Comparative Example 3 The difference from Example 3 is that the base resin material is changed, and the ethylene-vinyl acetate copolymer is replaced with ethylene octyl copolymer. The remaining amounts and steps are the same as in Example 3.

[0150] Comparative Example 4 The difference from Example 3 is that the base resin material and the content of halogen-free environmentally friendly flame retardant are changed. Ultra-low density polyethylene is replaced with low density polyethylene, and the content of halogen-free environmentally friendly flame retardant is changed to 20 parts of zinc diethylphosphite and 50 parts of aluminum hydroxide. The remaining dosages and steps are the same as in Example 3.

[0151] Comparative Example 5 The difference from Example 5 is that the content of the base resin material and the halogen-free environmentally friendly flame retardant are changed. Ultra-low density polyethylene is replaced with low density polyethylene, and the content of the halogen-free environmentally friendly flame retardant is changed to 20 parts of diethyl aluminum hypophosphite and 50 parts of aluminum hydroxide. The remaining dosages and steps are the same as in Example 5.

[0152] Comparative Example 6 The difference from Example 3 is that the base resin material and the irradiation dose are changed. Ultra-low density polyethylene is replaced with low density polyethylene, and the irradiation dose is changed to 130 kGY. The remaining dosages and steps are the same as in Example 3.

[0153] Comparative Example 7 The difference from Example 3 is that the base resin material and the irradiation dose are changed. Ultra-low density polyethylene is replaced with low density polyethylene, and the irradiation dose is changed to 190 kGY. The remaining dosages and steps are the same as in Example 3.

[0154] Comparative Examples 8-10 The difference from Example 3 is that the content of each component in the heat shrink tubing is changed, as shown in Table 4: Table 4 Raw materials for heat shrink tubing preparation

[0155] The remaining steps are the same as in Example 3.

[0156] Detection Example 1 1. Experimental Methods: In this embodiment, the corresponding shrinkage temperature refers to the lowest fully shrinkage temperature of the heat shrink tubing. The detection method is as follows: place the expanded heat shrink tubing in an oven. When the oven temperature is at a certain value, the inner diameter changes to the required range within 30 minutes. For example, for Φ15 / 10 (1.5 times expansion), the shrinkage inner diameter is required to be ≤10mm. The shrinkage temperature corresponding to the shrinkage inner diameter reaching ≤10mm is as follows; or for Φ25 / 10 (2.5 times expansion), the shrinkage inner diameter is required to be ≤10mm. The shrinkage temperature corresponding to the shrinkage inner diameter reaching ≤10mm is as follows.

[0157] For testing methods of tensile strength and elongation at break, refer to UL 224; for testing methods of tensile strength after heat aging, refer to UL 224.

[0158] Low temperature resistance test method: After shrinking, the test sample is placed in a -55℃ low temperature test chamber for 4 hours, and then wound around a Φ7.9 mandrel at 360°. If it does not break brittle and has no cracks, it is considered qualified.

[0159] Flame retardancy testing method: Refer to UL 94 vertical burning test method, and the test sample is uniformly 3.0mm.

[0160] Gasoline resistance test method: Immerse the sample completely in gasoline at 24°C for 72 hours, then remove and dry it before testing the tensile strength of the sample according to UL224.

[0161] 2. Experimental Results Compared to the shrinkage temperature of the heat shrink tubing prepared in Comparative Examples 1 and 10, the shrinkage temperature of the heat shrink tubing prepared in Examples 1-8 was controlled between 95-98℃, which fully meets the low-temperature shrinkage requirement of ≤100℃. This is due to the use of a composite substrate system of ultra-low density polyethylene and ethylene-vinyl acetate copolymer with low VA content and its specific ratio.

[0162] Compared with the performance test results of heat shrink tubing prepared by Comparative Examples 1-10, it can be seen that the gasoline resistance of the heat shrink tubing prepared by using EVA with high VA content or replacing it with POE is significantly reduced. It was also found that the irradiation dose has a significant impact on the gasoline resistance of the heat shrink tubing. This may be because: (1) the EVA substrate with low VA content has good gasoline resistance, avoiding the swelling problem of high VA content materials; (2) the specific irradiation dose makes the material form a stable three-dimensional network structure, effectively blocking the penetration of solvents such as gasoline.

[0163] Moreover, it was unexpectedly discovered that flame retardant systems using specific components and their proportions have high flame retardant efficiency, achieving high flame retardancy without the need for large amounts of additives while meeting environmental protection requirements.

[0164] By optimizing the ratio of ULDPE to EVA with low VA content and adjusting the substrate system, and by using a flame retardant system with specific composition and ratio, an antioxidant system with specific composition and ratio (a compound of three components), and process control of irradiation dose and temperature at each stage, the problem of difficulty in simultaneously achieving low-temperature shrinkage, gasoline resistance, flame retardancy, mechanical properties and environmental protection in existing heat-shrinkable materials has been successfully solved.

[0165] Table 5 Performance Test Results

[0166] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A low-temperature shrinkage, gasoline-resistant heat-shrinkable material, characterized in that, The product comprises, by weight, the following components: 50-100 parts of base resin, 50-100 parts of halogen-free environmentally friendly flame retardant, 1-5 parts of processing aid, 1.5-2.5 parts of antioxidant, and 0-5 parts of color masterbatch; the base resin is a mixture of ultra-low density polyethylene and ethylene-vinyl acetate copolymer in a weight ratio of 1-3:14-18; the halogen-free environmentally friendly flame retardant is composed of at least one of zinc diethylphosphite and aluminum diethylphosphite mixed with aluminum hydroxide.

2. The heat-shrinkable material according to claim 1, characterized in that, The VA content of the ethylene-vinyl acetate copolymer ranges from 8 to 14 wt%, and the melt index is 1.0 to 5.0 g / 10 min.

3. The heat-shrinkable material according to claim 1, characterized in that, The halogen-free environmentally friendly flame retardant is a mixture of zinc diethylphosphite and aluminum hydroxide in a weight ratio of 25-40:30-45; Alternatively, the halogen-free environmentally friendly flame retardant may be a mixture of aluminum diethylphosphite and aluminum hydroxide in a weight ratio of 25-40:30-45.

4. The heat-shrinkable material according to claim 3, characterized in that, The halogen-free environmentally friendly flame retardant is a mixture of zinc diethylphosphite and aluminum hydroxide in a weight ratio of 35:

35.

5. The heat-shrinkable material according to claim 1, characterized in that, The antioxidant is a mixture of Ethanox, BHT and DNP in a weight ratio of 0.8-1:0.7-0.8:0.5-0.

7.

6. The use of the heat-shrinkable material according to any one of claims 1-5 in the insulation protection, sealing, corrosion protection or covering and fixing material of wire and cable joints.

7. A low-temperature shrinkable gasoline-resistant heat shrink tubing, characterized in that, Includes the heat-shrinkable material as described in any one of claims 1-5.

8. The method for preparing the heat shrink tubing according to claim 7, characterized in that, Includes the following steps: (1) The base resin, halogen-free environmentally friendly flame retardant, processing aid, antioxidant and color masterbatch are put into a mixer, heated and mixed evenly to obtain material 1; (2) The material 1 obtained in step (1) is pre-granulated to obtain masterbatch granules; (3) The masterbatch particles obtained in step (2) are homogenized, then heated, melted, mixed and granulated to obtain heat shrinkable masterbatch; (4) The heat shrink masterbatch obtained in step (3) is extruded into a blank tube, and then subjected to irradiation crosslinking, heating expansion and cooling shaping in sequence to obtain the final product.

9. The preparation method according to claim 8, characterized in that, The heating temperature in step (1) is 140-180℃; The heating and melting temperature in step (3) is 110-180℃.

10. The preparation method according to claim 8, characterized in that, The irradiation dose in step (4) is 140-180 kGY, and the heating expansion temperature is 140-150℃.

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