Yellowing-resistant modified polyvinylidene fluoride material, heat shrinkable tube and preparation method

Abstract

The present invention provides a yellowing-resistant modified polyvinylidene fluoride material, including the following components by mass: 100 parts of polyvinylidene fluoride, 1 5 parts of alkaline macromolecules, 1 10 parts of silicon-containing substances, and 0.05 2 parts of sensitizers. The modified polyvinylidene fluoride material does not yellow during heat treatment and ionizing radiation modification, and can reach the cross-linking degree required for the heat shrink tube production process under low-dose ionizing radiation. Based on the above formula, the present invention also provides a heat shrink tube made of the modified polyvinylidene fluoride material. The heat shrink tube finished product is pure transparent, without yellowing and embrittlement defects, and the preparation process is simple and reasonable, the finished product is of high quality, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The patent of this invention relates to the technical field of radiation modification processing of fluoroplastics, and further relates to a yellowing-resistant modified polyvinylidene fluoride material, a heat shrinkable tube and a preparation method. Background Art

[0002] Polyvinylidene fluoride (PVDF, also known as PVF2) is a linear, semicrystalline polymer whose polymer chain structure primarily consists of repeating monomer units—[CH2CF2]—linked head-to-tail. Among commercial fluoroplastics, it is second only to the king of plastics, polytetrafluoroethylene (PTFE). However, PTFE cannot be melt-extruded and undergoes chain scission reactions upon exposure to ionizing radiation without special treatment. Therefore, PVDF, which can be melt-extruded and radiation-crosslinked, has become the preferred fluoromaterial for heat-shrink tubing.

[0003] However, when processing PVDF resin into heat-shrink tubing, it undergoes high-temperature (200-300°C) extrusion molding and high-dose (15-25MRad) ionizing radiation cross-linking modification. When unmodified PVDF resin is subjected to high-temperature or high-dose ionizing radiation processing, its color changes from its natural color (transparent) to yellow, and its transparency decreases. This phenomenon, commonly known as "yellowing," is very common in the PVDF resin manufacturing process. This yellowing phenomenon affects the product appearance and limits the application range of PVDF resin. Summary of the Invention

[0004] In response to the problem in the prior art that yellowing occurs during the processing and manufacturing of polyvinylidene fluoride, resulting in poor overall application effect, the present invention provides a yellowing-resistant modified polyvinylidene fluoride material. The modified polyvinylidene fluoride material does not yellow during heat treatment and ionizing radiation modification, and can also achieve the cross-linking degree required for the heat shrink tube production process under low-dose ionizing radiation. The modified polyvinylidene fluoride heat shrink tube finished product produced based on the formula of the modified polyvinylidene fluoride material and the corresponding preparation process is pure and transparent, without yellowing and brittle defects.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] A yellowing-resistant modified polyvinylidene fluoride material comprises the following components in parts by mass: 100 parts of polyvinylidene fluoride, 1-5 parts of alkaline macromolecules, 1-10 parts of silicon-containing substances, and 0.05-2 parts of a sensitizer.

[0007] In some technical solutions, the alkaline macromolecule is any one or more of cationic polyacrylamide and its derivatives, polyquaternary ammonium salts and its derivatives, guar gum and its derivatives, and xanthan gum and its derivatives.

[0008] In some technical solutions, the silicon-containing substance is any one or more of silicon dioxide and its derivatives, silicon-based organic polymers and their derivatives, and silane and its derivatives.

[0009] In some technical solutions, the sensitizer is any one or more of trimethylallyl isocyanate and its derivatives, triallyl cyanurate and its derivatives, tripropargyl cyanurate and its derivatives, trimethylolpropane trimethacrylate and its derivatives, trimethylolpropane triacrylate and its derivatives.

[0010] The present invention also provides a method for preparing a yellowing-resistant modified polyvinylidene fluoride heat shrinkable tube, which is characterized by comprising the following steps:

[0011] S1. Weighing the components according to the above-mentioned modified polyvinylidene fluoride material formula, uniformly mixing polyvinylidene fluoride, the dried alkaline macromolecule, the silicon-containing substance, and the sensitizer to obtain a polymer block, crushing the polymer block, extruding and pelletizing to obtain modified polyvinylidene fluoride resin particles;

[0012] S2. Extruding the modified polyvinylidene fluoride resin particles at a preset extrusion temperature to obtain a modified polyvinylidene fluoride pipe, and controlling the residence time of the modified polyvinylidene fluoride resin particles in the extruder to be no more than 5 minutes;

[0013] S3. The modified polyvinylidene fluoride tube is subjected to irradiation cross-linking and then subjected to a heating and inflation expansion process to obtain a finished product of a modified polyvinylidene fluoride heat shrinkable tube that is resistant to yellowing.

[0014] In some technical solutions, the preset extrusion temperature in step S2 is 200-250° C., and / or the electron beam energy of the radiation cross-linking in step S3 is 2-5 MRad.

[0015] In some technical solutions, the drying temperature in step S1 is 70° C. and the drying time is 5 hours.

[0016] The present invention also provides a yellowing-resistant modified polyvinylidene fluoride heat shrinkable tube. The modified polyvinylidene fluoride heat shrinkable tube is made of the above-mentioned yellowing-resistant modified polyvinylidene fluoride material, or is prepared by the above-mentioned preparation method of the yellowing-resistant modified polyvinylidene fluoride heat shrinkable tube.

[0017] Compared with the prior art, the present invention can bring the following beneficial effects:

[0018] 1. Based on the mechanism of yellowing during PVDF processing, the present invention uses alkaline macromolecules and silicon-containing substances as effective HF consumption agents. The above two materials are blended with polyvinylidene fluoride to obtain a modified polyvinylidene fluoride material that is resistant to yellowing during heat treatment and radiation processing. The alkaline macromolecules and silicon-containing substances can effectively reduce the yellowing phenomenon of PVDF during processing, reduce the formation of conjugated double bond structures in the PVDF resin structure, and ensure the appearance color, transparency and toughness of the final product;

[0019] 2. The modified polyvinylidene fluoride heat shrink tubing prepared using the modified polyvinylidene fluoride material provided by the present invention greatly reduces the electron beam energy required in the irradiation processing of conventional PVDF heat shrink tubing, thereby saving energy costs, fundamentally reducing the occurrence of dehalogenation reactions, and further reducing yellowing caused by high irradiation doses;

[0020] 3. The additive components used in the present invention are all industrially mature chemical substances, and do not require special blending processes, blending equipment, etc. The preparation method is simple and does not increase the production process, which is conducive to large-scale mass production and promotion;

[0021] 4. The yellowing-resistant modified polyvinylidene fluoride material provided by the present invention has excellent yellowing resistance and does not require high-dose ionizing radiation processing. It can be used in situations where yellowing may occur during other PVDF processing processes, such as the production and processing of PVDF membranes, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Figure 1 This is a microscopic mechanism diagram of the yellowing phenomenon of PVDF. DETAILED DESCRIPTION

[0024] The present invention will be further described below with reference to specific embodiments. However, these embodiments are merely exemplary and do not limit the scope of the present invention. It should be understood by those skilled in the art that various improvements and modifications may be made without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

[0025] An academic paper from Japan's Kureha Chemical Company summarized the research on the yellowing phenomenon of PVDF, pointing out that the yellowing of PVDF resin and its degree are affected by temperature, namely heat treatment and electron beam irradiation.

[0026] 1. Effect of heat treatment on yellowing of PVDF resin:

[0027] PVDF resin turns slightly yellow after heat treatment at 250°C for 5 minutes; turns yellowish-brown after heat treatment at 250°C for 10 minutes; and turns brown after heat treatment at 200°C with stirring for 30 minutes. Based on these results, we can conclude that at high temperatures, the yellowing of PVDF increases with heat treatment time.

[0028] 2. The effect of electron beam irradiation on the yellowing of PVDF resin:

[0029] Under electron beam irradiation of 0 and 2.7 MRad, the color of PVDF resin did not change; when the electron beam energy was increased to 5.9 MRad, the PVDF resin was slightly yellow; when it was increased to 12 MRad, the PVDF resin was yellow; when it was increased to 24 MRad, the PVDF resin was yellow-brown; when it was increased to 40 MRad, the PVDF resin was light brown; when it was increased to 80 MRad, the PVDF resin was brown.

[0030] From the above experimental results, it can be concluded that the yellowing of PVDF has the following characteristics:

[0031] 1. Under certain high temperature, the degree of yellowing will increase with the heat treatment time.

[0032] 2. There is a threshold for the yellowing phenomenon caused by electron beam irradiation. Below the threshold, there is no yellowing phenomenon. Above the threshold, the degree of yellowing deepens with the increase of electron beam energy, from light yellow to yellow and then to brown.

[0033] These two features are basically consistent with the inventor's findings and experience in actual production practice, as shown in Table 1 below, where the yellowing index YI value is measured by a colorimeter (NR110 Guangdong 3nh Group).

[0034] Table 1 Yellowing parameter values of unmodified PVDF after irradiation

[0035] Electron beam energy color Yellowing index YI Elongation at break 0 Transparent and colorless 1.2 460％ 2MRad Transparent and colorless 1.4 450％ 6MRad Slightly yellow and transparent 3.4 320％ 12MRad Yellow transparent 5.8 260％

[0036] Yellowing changes the appearance and color of PVDF products, reducing their transparency and failing to meet the demands of customers with stringent appearance requirements. Furthermore, yellowing is accompanied by a decrease in material toughness, with the deeper the yellowing, the more brittle the PVDF pipe becomes. This embrittlement directly impacts product performance and lifespan, creating disadvantages and instability for downstream customers. Therefore, developing a formula and supporting processing technology that effectively mitigates PVDF yellowing has significant production benefits. These can fundamentally improve product appearance, ensure product consistency, reduce rejection rates, extend product lifespan, and ultimately gain customer recognition, among other benefits.

[0037] To prevent yellowing, from a macroscopic perspective, it's necessary to avoid high-temperature heat treatments exceeding 5 minutes and to reduce the electron beam irradiation dose to below 5 MRad. The former can be achieved by increasing the extrusion speed to shorten the time the PVDF resin remains in the extruder, thereby preventing prolonged heat yellowing. However, reducing the electron beam irradiation dose cannot be achieved through process conditions alone. This is because the low-energy electron beam is unable to break the covalent bonds in the PVDF molecules to form free radicals for the crosslinking reaction. The expansion of heat shrink tubing, in turn, relies on the molecular chain memory effect and crosslinking network strength brought about by the crosslinking structure.

[0038] Figure 1 This is a microscopic diagram of the mechanism of PVDF yellowing. When the PVDF molecular chain receives energy (thermal energy or high-speed electron beam), it is prone to dehalogenation, generating hydrogen fluoride (HF) and accompanying C=C double bonds. At the same time, due to the steric effect, the dehalogenation reaction is often completed one molecule at a time. In other words, each carbon atom in each repeating unit can only undergo one molecule of HF to dissociate, thus forming a conjugated double bond structure. The large number of conjugated double bonds is the main reason for light absorption color change and macroscopic embrittlement.

[0039] With the core mechanism of the yellowing phenomenon clearly understood, it's easy to analyze why the degree of yellowing is positively correlated with temperature, heating time, and irradiation dose. The HF removal reaction of PVDF is endothermic, and as enthalpy decreases and entropy increases, the reaction continues in a positive direction. Furthermore, similar to the classic HCl removal reaction mechanism of polyvinyl chloride (PVC), the release of the acidic gas hydrogen fluoride (HF) in the acidic environment promotes dehalogenation, further exacerbating the yellowing and embrittlement.

[0040] At the same time, the dehalogenation reaction dissipates the electron beam energy originally used to open covalent bonds and initiate crosslinking. The resulting conjugated double bonds, due to the formation of conjugated orbitals, are significantly more susceptible to the electron beam, making crosslinking more difficult. These mechanisms ultimately require an ultra-high-energy electron beam to induce PVDF to generate free radicals and form crosslinks. In short, the HF removal reaction is an unfavorable competing reaction for PVDF radiation crosslinking and is the primary cause of macroscopic yellowing and embrittlement.

[0041] Based on the in-depth understanding of the above mechanism, the inventors found two ways to solve the yellowing problem:

[0042] 1. Adjust the chain structure. By selecting initiators and chain transfer agents, polymerization can produce PVDF containing more head-to-head and tail-to-tail structural units. Only head-to-tail structures will spontaneously form conjugated double bonds. Removal of HF from head-to-head and tail-to-tail structures also generates relatively independent double or triple bonds. Isolated double bonds are more easily broken open to generate free radicals, which then trigger crosslinking reactions. Furthermore, isolated double and triple bonds do not produce noticeable light absorption or color development.

[0043] 2. Adding a component that absorbs HF gas to the PVDF resin prevents HF-induced dehydrogenation reactions that produce conjugated bonds, thereby suppressing the exacerbation of the yellowing reaction. Simultaneously, an initiator is added to promote the opening of double bonds to form free radicals, completing the crosslinking reaction. This allows low-energy electron beam irradiation to achieve a certain degree of crosslinking between PVDF molecules. This reduces the radiation dose and, in turn, the probability of dehalogenation reactions at the source.

[0044] However, the first approach requires a high degree of control over the polymerization stage. In reality, head-to-tail structures rarely form during polymerization because they minimize steric hindrance and allow molecules to spontaneously arrange themselves in this manner. Forcing a fully head-to-head or tail-to-tail molecular chain structure would inevitably sacrifice molecular weight growth, thereby reducing product performance. Until new polymerization methods or processes emerge, this approach will undoubtedly be unworkable.

[0045] Therefore, a feasible solution lies in the second approach. This involves using suitable alkaline substances or substances that react with HF as additives to consume the HF generated by the dehalogenation reaction, thereby suppressing the acidic environment's inductive effect on the dehalogenation reaction. Simultaneously, the introduction of suitable free radical initiators can open the generated double bonds and promote the unbundling of the main chain molecules. Both promote the formation of crosslinked structures, thereby reducing the required irradiation dose.

[0046] Finally, the inventors provided a modified formula of yellowing-resistant polyvinylidene fluoride and a preparation method of yellowing-resistant modified polyvinylidene fluoride heat shrink tubing based on the formula to overcome the problem of yellowing and brittleness in the existing PVDF processing process, and thus solve the defects of existing polyvinylidene fluoride heat shrink tubing such as difficulty in color uniformity, easy yellowing and brittle cracking, and short product life.

[0047] The yellowing-resistant modified polyvinylidene fluoride material provided by the present invention comprises the following components in parts by weight:

[0048] 100 parts of polyvinylidene fluoride, 1-5 parts of alkaline macromolecule, 1-10 parts of silicon-containing substance, and 0.05-2 parts of sensitizer.

[0049] In some embodiments, the alkaline macromolecule is any one or more of cationic polyacrylamide and its derivatives, polyquaternium salt and its derivatives, guar gum and its derivatives, and xanthan gum and its derivatives.

[0050] The silicon-containing substances mentioned above as HF consuming agents specifically include any one or more of silicon dioxide and its derivatives, silicon-based organic polymers and their derivatives, and silane and its derivatives.

[0051] Due to the strong interaction between hydrogen and fluorine atoms, HF is acidic and can react with most alkaline substances. However, experiments have shown that strong bases such as potassium hydroxide and potassium bicarbonate, when mixed with PVDF, will greatly promote the dehalogenation reaction, producing brown-black polyfluoroacetylene. This goes against the original intention of suppressing PVDF discoloration during processing.

[0052] However, weakly alkaline small molecules mostly degrade during high-temperature blending, failing to effectively inhibit dehalogenation reactions and HF spillage. This is best demonstrated by the fact that high irradiation doses are still required to achieve a high degree of crosslinking. Therefore, the inventors selected alkaline macromolecules as HF depleting agents, using cationic polyacrylamide as an example. The quaternary ammonium ions on its side groups are alkaline and react with HF. As macromolecules, strong intermolecular interactions make them difficult to decompose during high-temperature blending, allowing them to be preserved until HF is generated and reacted with it.

[0053] However, since cationic polyacrylamide is highly soluble in water, meaning it readily absorbs water, adding a large amount will inevitably increase the hygroscopicity of the original resin, significantly hindering processing. Insufficient amounts of polyacrylamide are also insufficient to fully consume the HF generated by dehalogenation. Therefore, the present invention introduces a second HF depleting agent—a silicon-containing substance.

[0054] Taking nano-silica as an example, although silica is a weakly acidic substance, the higher electronegativity of fluorine atoms compared to oxygen atoms makes the resulting silicon fluoride a covalent compound with greater stability than silicon oxide. Therefore, silica can be used as an HF depleting agent. Furthermore, silica has excellent heat resistance and is not easily decomposed during the blending and granulation process. Nano-sized silica is also more conducive to more uniform dispersion in PVDF resin.

[0055] In some embodiments, the sensitizer is any one or more of trimethylallyl isocyanate and its derivatives, triallyl cyanurate and its derivatives, tripropargyl cyanurate and its derivatives, trimethylolpropane trimethacrylate and its derivatives, and trimethylolpropane triacrylate and its derivatives. The addition of the sensitizer increases the number of active free radicals in the system, thereby reducing the energy of the electron beam originally required and further reducing the occurrence of dehalogenation reactions. In addition, even if some dehalogenation reactions inevitably occur, sufficient active free radicals can reopen the C=C double bonds generated by the dehalogenation reaction, consuming the conjugated double bonds while promoting the desired cross-linking reaction. The two HF consuming agents further ensure that the PVDF resin will not yellow during processing, and the product can maintain its original transparent color and transparency.

[0056] More preferably, considering the temperature resistance required for the modified polyvinylidene fluoride material in subsequent processing, the sensitizer is selected from high-temperature resistant trimethylallyl isocyanate and its derivatives.

[0057] Based on the formula of the modified polyvinylidene fluoride material, the present invention also provides a yellowing-resistant modified polyvinylidene fluoride heat shrinkable tube and a preparation method thereof. The preparation steps of the heat shrinkable tube are as follows:

[0058] S1. Weighing the components according to the above-mentioned modified polyvinylidene fluoride material formula, uniformly mixing the polyvinylidene fluoride, the dried alkaline macromolecule, the silicon-containing substance and the sensitizer to obtain a polymer block, crushing the polymer block, extruding and pelletizing to obtain modified polyvinylidene fluoride resin particles;

[0059] S2. Extruding the modified polyvinylidene fluoride resin particles at a preset extrusion temperature to obtain a modified polyvinylidene fluoride pipe, and controlling the residence time of the modified polyvinylidene fluoride resin particles in the extruder to be no more than 5 minutes;

[0060] S3. The modified polyvinylidene fluoride tube is subjected to irradiation cross-linking and then subjected to a heating and blowing expansion process to obtain a finished product of a modified polyvinylidene fluoride heat shrink tube that is resistant to yellowing.

[0061] In some embodiments, the preset extrusion temperature in step S2 is 200-250° C., and the electron beam energy for radiation cross-linking in step S3 is 2-5 MRad.

[0062] In some embodiments, the temperature for drying the basic macromolecules in step S1 is 70° C. for 5 hours. Since most basic macromolecules are prone to water absorption, drying is performed before mixing with other components to improve the quality of the subsequent finished product.

[0063] In order to better understand and apply the above solutions and effectively demonstrate the corresponding benefits, this application also provides the following multiple embodiments:

[0064] Example 1:

[0065] 100 parts by mass of polyvinylidene fluoride, 5 parts of dried cationic polyacrylamide, 5 parts of nano-silica, and 1 part of trimethylallyl isocyanate were put into an internal mixer and mixed uniformly at 200°C to obtain a modified polyvinylidene fluoride polymer block, which was then crushed and extruded into granules using a twin-screw extruder to obtain modified polyvinylidene fluoride resin particles;

[0066] Modified PVDF pellets are extruded through an extruder at a temperature of 180-230°C and a speed of 25 RPM to produce modified PVDF tubing. The extruded PVDF tubing is then cross-linked by electron irradiation at 5 MRad energy. Finally, a heat expansion step produces transparent, yellowing-resistant PVDF heat-shrink tubing.

[0067] Example 2:

[0068] 100 parts by mass of polyvinylidene fluoride, 5 parts of dried cationic polyacrylamide, 10 parts of nano-silica, and 1 part of trimethylallyl isocyanate were put into an internal mixer and mixed uniformly at 200°C to obtain a modified polyvinylidene fluoride polymer block, which was then crushed and extruded into granules using a twin-screw extruder to obtain modified polyvinylidene fluoride resin particles;

[0069] Modified PVDF pellets are extruded through an extruder at a temperature of 180-230°C and a speed of 25 RPM to produce modified PVDF tubing. The pellets are kept in the extruder for no more than 5 minutes. The extruded PVDF tubing is then cross-linked by electron irradiation at 3 MRad energy. Finally, a heat expansion step produces transparent, yellowing-resistant PVDF heat-shrink tubing. The final product, as measured by a colorimeter, has a yellowing index of 1.2.

[0070] Example 3:

[0071] 100 parts by mass of polyvinylidene fluoride, 1 part of dried cationic polyacrylamide, 10 parts of nano-silica, and 1 part of trimethylallyl isocyanate were put into an internal mixer and mixed uniformly at 200°C to obtain a modified polyvinylidene fluoride polymer block, which was then crushed and extruded into granules using a twin-screw extruder to obtain modified polyvinylidene fluoride resin particles;

[0072] Modified PVDF pellets are extruded through an extruder at a temperature of 180-230°C. The extrusion speed is set at 25 RPM, ensuring that the resin pellets remain in the extruder for no more than 5 minutes. The extruded PVDF tubing is then cross-linked by electron irradiation at 5 MRad energy. Finally, a heat expansion step produces a transparent, yellowing-resistant PVDF heat-shrink tubing. The final product, measured by a colorimeter, has a yellowing index of 1.4.

[0073] Comparative Example 1:

[0074] The difference from Example 1 is that in Comparative Example 1, unmodified PVDF was directly extruded at a temperature of 180-230°C to produce a semi-finished tubing, with the same extrusion speed as in Example 1. The extruded PVDF tubing required electron irradiation at 12 MRad energy to complete crosslinking. Finally, a heat-expansion expansion step was performed to produce a yellow, transparent PVDF heat-shrink tubing. The yellowing index (YI) measured by a colorimeter was 5.4.

[0075] Comparative Example 2:

[0076] In Comparative Example 2, 100 parts of unmodified polyvinylidene fluoride (PVDF) were mixed with only 1 part of a sensitizer (trimethylallyl isocyanate) and granulated. The mixture was then extruded at the same speed as in Example 1. The PVDF tubing, with only the sensitizer added, was cross-linked by electron irradiation at 6 MRad energy. Finally, a slightly yellowish, transparent PVDF heat-shrink tubing was obtained by thermal expansion. The yellowing index (YI) measured by a colorimeter was 4.4.

[0077] The above examples 1-3 are compared with comparative examples 1-2, as shown in Table 2.

[0078] Table 2 Performance comparison of polyvinylidene fluoride heat shrink tubing produced by different formulas

[0079] sample Radiation dose (MRad) Finished product appearance Yellowing index YI Elongation at break Example 1 5 Colorless and transparent 1.5 420％ Example 2 3 Colorless and transparent 1.2 460％ Example 3 5 Colorless and transparent 1.4 435％ Comparative Example 1 12 Yellow transparent 5.4 245％ Comparative Example 2 6 Slightly yellow and transparent 4.4 310％

[0080] As can be seen from Table 2:

[0081] 1. The modified polyvinylidene fluoride with the addition of sensitizer ingredients can significantly reduce the dose required for electron irradiation. At a lower dose, the cross-linking degree that meets the production requirements of heat shrink tubing can be achieved, and at the same time, the yellowing effect can be improved to a certain extent.

[0082] 2. The polyvinylidene fluoride modified by alkaline macromolecules, nano-silica, and sensitizer (Examples 1, 2, and 3) requires significantly reduced irradiation doses, and the final product is colorless and transparent without yellowing, showing excellent yellowing resistance.

[0083] 3. Similarly, by comparing Examples 1, 2, and 3, it can be found that the higher the total addition ratio of alkaline macromolecules and nano-silica, the less the required dosage, the lower the yellowing index, and the better the yellowing resistance and radiation dose reduction effects.

[0084] 4. The present invention's modified formula for yellowing resistance and radiation dose reduction also significantly enhances the toughness of PVDF. Unmodified PVDF maintains an elongation at break of only around 240% after electron radiation and heat treatment. However, the yellowing-resistant modified PVDF heat shrink tubing provided by the present invention maintains an elongation at break of over 400% even after electron radiation and heat treatment, with minimal change in toughness.

[0085] The above are only preferred embodiments of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A yellowing-resistant modified polyvinylidene fluoride material, characterized in that: It includes the following components in parts by mass: 100 parts of polyvinylidene fluoride, 1-5 parts of alkaline macromolecule, 1-10 parts of silicon-containing substance, 0.05-2 parts of sensitizer; The alkaline macromolecule is any one or more of cationic polyacrylamide and its derivatives; The silicon-containing material is any one or more of silicon dioxide and its derivatives.

2. The modified polyvinylidene fluoride material according to claim 1, characterized in that The sensitizer is any one or more of trimethylallyl isocyanate and its derivatives, triallyl cyanurate and its derivatives, tripropargyl cyanurate and its derivatives, trimethylolpropane trimethacrylate and its derivatives, and trimethylolpropane triacrylate and its derivatives.

3. A method for preparing a yellowing-resistant modified polyvinylidene fluoride heat shrinkable tube, characterized in that: The following steps are involved: S1. Weighing the components according to the formula of the modified polyvinylidene fluoride material according to claim 1 or 2, uniformly mixing the polyvinylidene fluoride, the dried alkaline macromolecule, the silicon-containing substance, and the sensitizer to obtain a polymer block, crushing the polymer block, extruding and pelletizing to obtain modified polyvinylidene fluoride resin particles; S2. Extruding the modified polyvinylidene fluoride resin particles at a preset extrusion temperature to obtain a modified polyvinylidene fluoride pipe, and controlling the residence time of the modified polyvinylidene fluoride resin particles in the extruder to be no more than 5 minutes; S3. The modified polyvinylidene fluoride tube is subjected to irradiation cross-linking and then subjected to a heating and inflation expansion process to obtain a finished product of a modified polyvinylidene fluoride heat shrinkable tube that is resistant to yellowing.

4. The preparation method according to claim 3, characterized in that The preset extrusion temperature in step S2 is 200-250° C., and / or; The electron beam energy for the irradiation cross-linking in step S3 is 2-5 MRad.

5. The preparation method according to claim 3, characterized in that The drying process in step S1 is performed at a temperature of 70° C. and for 5 hours.

6. A yellowing-resistant modified polyvinylidene fluoride heat shrink tubing, characterized in that: The heat shrinkable tube is prepared by the method for preparing the yellowing-resistant modified polyvinylidene fluoride heat shrinkable tube according to any one of claims 3 to 5.

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