Rubber composition for rubber sheath and preparation method thereof
By grafting a long-chain alkyl polymer layer onto the surface of aluminum hydroxide powder, the problem of plasticizer migration in rubber sheaths at high temperatures was solved, achieving a balance between the material's flexibility and flame retardancy, and improving the durability and user experience of the rubber sheaths.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- TAIZHOU MINDRAY RUBBER & PLASTIC PRODUCTS CO LTD
- Filing Date
- 2025-12-26
- Publication Date
- 2026-04-21
AI Technical Summary
Existing rubber sheaths are prone to plasticizer migration at high temperatures, leading to surface hardening and embrittlement, which affects flexibility and appearance. Moreover, existing methods are difficult to effectively suppress this problem without compromising processability and flame retardancy.
A modified flame retardant was used to fix the plasticizer by in-situ grafting a long-chain alkyl polymer layer onto the surface of aluminum hydroxide powder and anchoring it within the flame retardant network using the similar structure to the plasticizer. A rubber composition was prepared by combining this with a specific process to fix the plasticizer.
It effectively inhibits the migration of plasticizers at high temperatures, maintains the flexibility and flame retardancy of materials, extends service life, avoids surface precipitation and adhesion problems, and improves durability and user experience.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of rubber materials technology, specifically relating to a rubber composition for rubber sheaths and its preparation method. Background Technology
[0002] Rubber sheaths are widely used in new energy vehicle charging pile cables and high-end home appliance cables, and their base material is often made of chlorinated polyethylene or EPDM rubber. To meet stringent halogen-free and environmentally friendly flame-retardant standards, such as achieving UL94V-0 rating, a large amount of inorganic flame retardants, such as aluminum hydroxide or magnesium hydroxide, needs to be added to the rubber system. The high filling amount of solid fillers occupies the free volume of the rubber molecular chains, resulting in insufficient space for the system to accommodate liquid plasticizers.
[0003] To maintain the processability of the rubber compound and the flexibility of the final product, plasticizers, such as aromatic oils or ester compounds, must be added. During long-term high-temperature use or thermal aging, these small plasticizer molecules gradually migrate from the interior of the rubber matrix to the surface due to increased thermal motion. The plasticizer accumulates on the surface, forming an oil film, which increases the hardness and embrittlement of the sheath, while also making the surface sticky. The sticky surface easily attracts dust, causing adhesion during cable winding or stacking, affecting the product's appearance, feel, and service life.
[0004] Existing technologies attempt to suppress migration by reducing the amount of plasticizer, but this leads to excessively high hardness in the rubber compound, resulting in a loss of the required flexibility. Other approaches use plasticizers with higher molecular weights, which, while migrating more slowly, have lower plasticizing efficiency and often impair the low-temperature performance of the compound. Furthermore, adding fillers with oil-absorbing properties, while temporarily binding some plasticizers, further increases the system viscosity, making processing more difficult. Therefore, in highly filled halogen-free flame-retardant sheaths based on chlorinated polyethylene or EPDM rubber, effectively suppressing plasticizer migration and surface exudation after thermal aging without compromising processability, flexibility, and flame retardancy has become a problem that needs to be solved. Summary of the Invention
[0005] The purpose of this invention is to provide a rubber composition for rubber sheaths and a method for preparing the same, in order to solve the problems mentioned in the background art.
[0006] To achieve the above objectives, according to one aspect of the present invention, a rubber composition for rubber sheaths is provided, comprising, by weight, the following components: 100 parts of chlorinated polyethylene rubber, 100-140 parts of modified flame retardant, 30-50 parts of plasticizer, 3-8 parts of metal oxide activator, 1.5-3.5 parts of peroxide crosslinking agent, 1-3 parts of co-crosslinking agent, 0.5-2 parts of antioxidant, and 0.5-2 parts of processing aid.
[0007] Preferably, the modified flame retardant is prepared from the following raw materials in parts by weight: 100 parts aluminum hydroxide powder, 1.0-2.0 parts silane coupling agent containing double bonds, 2.0-4.0 parts long-chain alkyl methacrylate monomer, and 0.02-0.1 parts free radical initiator.
[0008] Preferably, the preparation of the modified flame retardant includes the following steps: first, heating aluminum hydroxide powder to 100-110℃ for drying; then, adding a silane coupling agent containing double bonds at a stirring speed of 1500-2000 rpm, and reacting at 110℃ for 10-15 minutes; finally, adding premixed long-chain alkyl methacrylate monomers and free radical initiators, increasing the stirring speed to 2200-2800 rpm, using shear heat to control the material temperature at 135-145℃, reacting for 20-25 minutes, and obtaining the product after cooling.
[0009] Preferably, the silane coupling agent containing double bonds is γ-methacryloyloxypropyltrimethoxysilane; the long-chain alkyl methacrylate monomer is dodecyl methacrylate; and the free radical initiator is dicumyl peroxide.
[0010] Preferably, the chlorinated polyethylene rubber has a chlorine content of 30%-40%; the plasticizer is selected from one or more of trioctyl trimellitate, dioctyl phthalate, or dioctyl adipate.
[0011] Preferably, the peroxide crosslinking agent is dicumyl peroxide or 1,1-di(tert-butylperoxide)-3,3,5-trimethylcyclohexane; the co-crosslinking agent is triallyl isocyanurate; and the metal oxide activator is magnesium oxide.
[0012] According to another aspect of the present invention, a method for preparing a rubber composition for rubber sheaths is provided, comprising the following steps: First, chlorinated polyethylene rubber, modified flame retardant, metal oxide activator, processing aid and antioxidant are added to a mixing mill and mixed, followed by the addition of a plasticizer and mixing until the rubber is discharged; then, the obtained rubber compound is passed through a roller mill on an open mill, a peroxide crosslinking agent and a co-crosslinking agent are added, and after being mixed evenly in a thin pass, it is sheeted out; finally, the rubber sheet is vulcanized by pressing and heating in a mold.
[0013] Preferably, in the internal mixing step, the initial temperature of the internal mixer is controlled at 80-95℃, the discharge temperature is controlled at 125-135℃, and the mixing time is 6-10 minutes.
[0014] Preferably, in the vulcanization molding step, the vulcanization temperature is 165-175℃, the vulcanization pressure is 10-20MPa, and the vulcanization time is T90+1 to T90+3 minutes.
[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) By reacting aluminum hydroxide powder with a silane coupling agent containing double bonds and a long-chain alkyl methacrylate monomer under specific temperature and high shear conditions, the long-chain alkyl polymer is grafted in situ onto the surface of aluminum hydroxide particles through chemical bonds. This process forms a novel modified flame retardant with a long-chain alkyl polymer layer on the surface with a high grafting density. When this modified flame retardant is added to a rubber matrix together with a plasticizer, the polymer layer on its surface can effectively adsorb and anchor the plasticizer molecules around it due to the similar molecular structure. This fixes the originally easily free plasticizer inside the highly filled flame retardant network, thereby reducing its migration tendency at high temperatures from the source.
[0016] (2) The rubber sheath material prepared by the modified flame retardant, after being in a high temperature environment for a long time or after experiencing thermal aging, has stable anchoring of the plasticizer inside, making it difficult to seep to the surface. Finally, the cable sheath or hose product made from this material can keep the surface dry for a long time, avoiding the stickiness and dust problems caused by plasticizer precipitation. Moreover, since the plasticizer is well retained inside the material, the flexibility of the product decreases more slowly during its service life and will not harden and become brittle too early, thereby improving the durability and user experience of the rubber sheath. Detailed Implementation
[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0018] This invention provides a rubber composition for rubber sheaths. The composition uses chlorinated polyethylene rubber as a matrix and improves performance in high-filler systems by introducing a specific modified flame retardant as a key component.
[0019] In the composition, chlorinated polyethylene rubber serves as the matrix material, providing basic mechanical properties and weather resistance. It is used in an amount of 100 parts by weight, serving as a basis for calculating the amounts of other components.
[0020] The modified flame retardant is the core of the composition of this invention, and its dosage is 100 to 140 parts by weight. It not only provides the necessary flame retardant function, but more importantly, its unique surface structure acts as an anchoring plasticizer. This modified flame retardant is prepared by surface chemical modification of aluminum hydroxide powder. The specific modification process is as follows: First, the aluminum hydroxide powder is heated and dried to remove surface moisture and expose active hydroxyl groups. Then, a silane coupling agent containing double bonds is added, causing the siloxane groups to undergo a condensation reaction with the hydroxyl groups on the aluminum hydroxide surface, thereby firmly anchoring the unsaturated double bonds to the powder surface via chemical bonds. Next, under solvent-free and high-speed shear conditions, long-chain alkyl methacrylate monomers and a free radical initiator are added. The free radicals generated by the thermal decomposition of the initiator initiate the polymerization reaction of the monomer at the double bond sites already anchored to the powder surface, causing long-chain polymer chains to "grow" from the powder surface, forming a dense, oleophilic polymer brush layer. This polymer brush, due to its long-chain alkyl structure being highly similar and compatible with plasticizer molecules, can effectively adsorb and bind plasticizer molecules in its surrounding network through physical entanglement and dissolution.
[0021] In a preferred embodiment, the silane coupling agent containing double bonds may be γ-methacryloyloxypropyltrimethoxysilane, which simultaneously provides a methoxy group that reacts with inorganic surfaces and a methacryloxy group that can be used for polymerization. The long-chain alkyl methacrylate monomer is preferably dodecyl methacrylate, whose C12 long chain provides excellent lipophilicity. The free radical initiator is preferably dicumyl peroxide, whose decomposition temperature matches the process temperature of the in-situ polymerization.
[0022] In a preferred embodiment, the chlorinated polyethylene rubber contains 30% to 40% chlorine, a range that balances the material's flame retardancy, flexibility, and processability. The plasticizer may be selected from one or more of trioctyl trimellitate, dioctyl phthalate, or dioctyl adipate. Trioctyl trimellitate is particularly favored due to its excellent heat resistance, which helps to further improve the stability of the final product at high temperatures.
[0023] The composition also contains 30 to 50 parts by weight of the plasticizer, the main function of which is to soften the rubber matrix, imparting the necessary processing fluidity and flexibility to the final product. Due to the presence of the modified flame retardant, this portion of the plasticizer is more effectively fixed within the system.
[0024] Other components in the composition include 3 to 8 parts by weight of a metal oxide activator, such as magnesium oxide, which absorbs acidic substances that may be generated during processing or aging, stabilizing the rubber compound; 1.5 to 3.5 parts by weight of a peroxide crosslinking agent, such as dicumyl peroxide, which decomposes upon heating to generate free radicals, initiating crosslinking between rubber molecular chains to form a three-dimensional network structure; 1 to 3 parts by weight of a co-crosslinking agent, such as triallyl isocyanurate, which improves crosslinking efficiency and the structure of crosslinking bonds, thereby enhancing the material's heat resistance and mechanical strength; 0.5 to 2 parts by weight of an antioxidant to delay the material's thermo-oxidative aging; and 0.5 to 2 parts by weight of a processing aid, such as stearic acid, which acts as a lubricant and promotes mold release.
[0025] The present invention also provides a method for preparing the above-mentioned rubber composition, which includes three main stages: mixing, vulcanization and curing.
[0026] The first step is mixing: chlorinated polyethylene rubber, the modified flame retardant, metal oxide activator, processing aids, and antioxidants are added together to a Banbury mixer. At this stage, the initial temperature of the Banbury mixer should be controlled between 80 and 95°C; excessively high initial temperatures may cause premature plasticization of the rubber matrix or decomposition of the additives. After the basic components are initially mixed, the plasticizer is added for further mixing. The entire mixing process continues until the rubber compound temperature reaches 125 to 135°C, at which point the compound is discharged. The purpose of this step is to ensure that all solid fillers and additives are uniformly dispersed and impregnated in the rubber matrix, especially allowing the plasticizer to fully penetrate the surface polymer brush layer of the modified flame retardant, while avoiding premature decomposition of the crosslinking agent.
[0027] As a preferred embodiment, the entire mixing time is controlled within 6 to 10 minutes to ensure uniform dispersion and avoid excessive shearing and heat generation.
[0028] The second step is vulcanization: the compound obtained in the first step is transferred to a two-roll mill and cooled by rolling through relatively low-temperature rollers (usually below 60°C). Then, peroxide crosslinking agents and co-crosslinking agents are added, and the vulcanization system is evenly dispersed in the rubber compound by repeatedly passing the compound through thin streams. This stage must be completed quickly at a low temperature to prevent the crosslinking agents from reacting prematurely under uncontrolled conditions, which could lead to scorching of the rubber compound.
[0029] The third step is vulcanization molding: the rubber sheet obtained in the second step, which now uniformly contains the vulcanization system, is placed into a preheated mold and vulcanized under specific pressure and temperature. The vulcanization temperature is preferably between 165 and 175°C, and the pressure between 10 and 20 MPa. The vulcanization time is usually determined based on the optimal vulcanization time of the rubber compound, for example, by increasing the optimal vulcanization time T90 in the measured standard vulcanization curve by 1 to 3 minutes to ensure sufficient cross-linking both inside and outside the product, resulting in optimal physical and mechanical properties.
[0030] Through the above component design and preparation method, the resulting rubber composition is particularly suitable for extrusion or compression molding into products such as cable sheaths for new energy vehicle charging piles and cable sheaths for high-end home appliances.
[0031] Example 1 (1) Pretreatment: Preparation of modified flame retardant The modified flame retardant was prepared by weight as follows: 100 parts of micron-sized aluminum hydroxide powder, 1.5 parts of γ-methacryloyloxypropyltrimethoxysilane (KH-570), 3.0 parts of dodecyl methacrylate (LMA), and 0.05 parts of dicumyl peroxide (DCP).
[0032] Preparation steps: Aluminum hydroxide powder was added to a high-speed mixer and stirred at 2000 rpm. The mixture was heated to 105°C by friction and maintained for 5 minutes. KH-570 was mixed with 0.5 parts of ethanol and sprayed into the mixer. The mixture was reacted at 105°C and 1500 rpm for 12 minutes. LMA and DCP were premixed and added dropwise to the mixer. The mixing speed was increased to 2500 rpm, and the material temperature was controlled at 140±2°C. The mixture was reacted for 22 minutes. After the reaction, the mixture was cooled to below 60°C and discharged to obtain modified aluminum hydroxide (hereinafter referred to as modified ATH) with poly(dodecyl methacrylate) polymer brushes grafted onto its surface.
[0033] (2) Prepare the raw materials according to the following parts by weight: 100 parts of chlorinated polyethylene rubber (chlorine content 35%), 120 parts of the above-mentioned self-made modified ATH, 40 parts of trioctyl trimellitate, 5 parts of high-activity magnesium oxide, 1 part of stearic acid, 1 part of antioxidant 1010, 2.5 parts of dicumyl peroxide, and 2 parts of triallyl isocyanurate.
[0034] (3) Internal mixing: Set the initial temperature of the internal mixer to 90°C, add CPE rubber and plasticize for 1 minute. Add modified ATH, magnesium oxide, stearic acid, antioxidant 1010 and plasticizer in sequence, mix for 7 minutes until the material temperature reaches 130°C and then discharge the rubber.
[0035] (4) Vulcanization: Transfer the masterbatch to a two-roll mill with a roller temperature of 55°C, add DCP and TAIC, and pass through the mill 6 times to disperse evenly, then sheet it.
[0036] (5) Vulcanization: The rubber compound is molded and vulcanized at 170°C and 15MPa pressure for 12 minutes to obtain a standard test sample.
[0037] Example 2 (1) Pretreatment: Preparation of modified flame retardant The raw materials for preparing the modified flame retardant, by weight, are: 100 parts of micron-sized aluminum hydroxide powder, 1.5 parts of γ-methacryloyloxypropyltrimethoxysilane (KH-570), 2.5 parts of dodecyl methacrylate (LMA), and 0.05 parts of dicumyl peroxide (DCP).
[0038] Preparation steps: Aluminum hydroxide powder was added to a high-speed mixer and stirred at 2000 rpm. The mixture was heated to 105°C by friction and maintained for 5 minutes. KH-570 was mixed with 0.5 parts of ethanol and sprayed into the mixer. The mixture was reacted at 105°C and 1500 rpm for 12 minutes. LMA and DCP were premixed and added dropwise to the mixer. The mixing speed was increased to 2500 rpm, and the material temperature was controlled at 138±2°C. The mixture was reacted for 20 minutes. After the reaction, the mixture was cooled to below 60°C and discharged to obtain modified aluminum hydroxide (hereinafter referred to as modified ATH) with poly(dodecyl methacrylate) polymer brushes grafted onto its surface.
[0039] (2) Prepare the raw materials according to the following weight parts: This step is exactly the same as in Example 1.
[0040] (3) Refining: This step is exactly the same as in Example 1.
[0041] (4) Sulfurization: This step is exactly the same as in Example 1.
[0042] (5) Vulcanization: This step is exactly the same as in Example 1.
[0043] Example 3 (1) Pretreatment: Preparation of modified flame retardant The raw materials for preparing the modified flame retardant, by weight, are: 100 parts of micron-sized aluminum hydroxide powder, 2.0 parts of γ-methacryloyloxypropyltrimethoxysilane (KH-570), 4.0 parts of dodecyl methacrylate (LMA), and 0.08 parts of dicumyl peroxide (DCP).
[0044] Preparation steps: Aluminum hydroxide powder was added to a high-speed mixer and stirred at 2000 rpm. The mixture was heated to 110°C by friction and maintained for 5 minutes. KH-570 was mixed with 0.5 parts of ethanol and sprayed into the mixer. The mixture was reacted at 110°C and 1500 rpm for 15 minutes. LMA and DCP were premixed and added dropwise to the mixer. The mixing speed was increased to 2500 rpm, and the material temperature was controlled at 145±2°C. The mixture was reacted for 25 minutes. After the reaction, the temperature was lowered to below 60°C before discharge, yielding modified aluminum hydroxide (hereinafter referred to as modified ATH) with a surface grafted with poly(dodecyl methacrylate) polymer brushes.
[0045] (2) Prepare the raw materials according to the following weight parts: 100 parts of chlorinated polyethylene rubber (chlorine content 35%), 140 parts of the above-mentioned self-made modified ATH, 30 parts of trioctyl trimellitate, 5 parts of high-activity magnesium oxide, 1 part of stearic acid, 1 part of antioxidant 1010, 2.5 parts of dicumyl peroxide, and 2 parts of triallyl isocyanurate.
[0046] (3) Refining: This step is exactly the same as in Example 1.
[0047] (4) Sulfurization: This step is exactly the same as in Example 1.
[0048] (5) Vulcanization: This step is exactly the same as in Example 1.
[0049] Comparative Example 1 (1) Pretreatment: Preparation of silanized flame retardant The raw materials prepared by weight are: 100 parts of micron-sized aluminum hydroxide powder, 1.5 parts of γ-methacryloyloxypropyltrimethoxysilane (KH-570), without the addition of dodecyl methacrylate (LMA) and dicumyl peroxide (DCP).
[0050] Preparation steps: Aluminum hydroxide powder is added to a high-speed mixer and stirred at 2000 rpm. The mixture is heated to 105°C by friction and held for 5 minutes. KH-570 is mixed with 0.5 parts of ethanol and sprayed in. The mixture is reacted at 105°C and 1500 rpm for 12 minutes. After the reaction is completed, the mixture is directly cooled to below 60°C and discharged to obtain aluminum hydroxide that has only undergone silane surface treatment and has not been grafted with polymer brushes (hereinafter referred to as silanized ATH).
[0051] (2) Prepare the raw materials according to the following parts by weight: 100 parts of chlorinated polyethylene rubber (chlorine content 35%), 120 parts of the above-mentioned silanized ATH (substitute modified ATH), 40 parts of trioctyl trimellitate, 5 parts of highly active magnesium oxide, 1 part of stearic acid, 1 part of antioxidant 1010, 2.5 parts of dicumyl peroxide, and 2 parts of triallyl isocyanurate.
[0052] (3) Refining: This step is exactly the same as in Example 1.
[0053] (4) Sulfurization: This step is exactly the same as in Example 1.
[0054] (5) Vulcanization: This step is exactly the same as in Example 1.
[0055] Comparative Example 2 (1) Use untreated micron-sized aluminum hydroxide powder.
[0056] (2) Prepare the raw materials according to the following weight parts: 100 parts of chlorinated polyethylene rubber (chlorine content 35%), 120 parts of untreated aluminum hydroxide powder, 40 parts of trioctyl trimellitate, 5 parts of highly active magnesium oxide, 1 part of stearic acid, 1 part of antioxidant 1010, 2.5 parts of dicumyl peroxide, and 2 parts of triallyl isocyanurate.
[0057] (3) Refining: This step is exactly the same as in Example 1.
[0058] (4) Sulfurization: This step is exactly the same as in Example 1.
[0059] (5) Vulcanization: This step is exactly the same as in Example 1.
[0060] Comparative Example 3 (1) Pretreatment: Preparation of physical blend components a. Preparation of free polymer: Weigh 3.0 parts of dodecyl methacrylate (LMA) and 0.05 parts of dicumyl peroxide (DCP), and react them in a container at 140°C for 22 minutes in the absence of aluminum hydroxide to synthesize poly(dodecyl methacrylate) (PLMA) homopolymer.
[0061] b. Physical mixing: 100 parts of untreated micron-sized aluminum hydroxide powder and 3.0 parts of the above-synthesized PLMA polymer were mixed in a high-speed mixer at 60°C for 10 minutes to obtain a physical blend.
[0062] (2) Prepare the raw materials according to the following parts by weight: 100 parts of chlorinated polyethylene rubber (chlorine content 35%), 123 parts of the above aluminum hydroxide / PLMA physical blend, 40 parts of trioctyl trimellitate, 5 parts of highly active magnesium oxide, 1 part of stearic acid, 1 part of antioxidant 1010, 2.5 parts of dicumyl peroxide, and 2 parts of triallyl isocyanurate.
[0063] (3) Refining: This step is exactly the same as in Example 1.
[0064] (4) Sulfurization: This step is exactly the same as in Example 1.
[0065] (5) Vulcanization: This step is exactly the same as in Example 1.
[0066] According to the formulations and processes of the examples and comparative examples, the corresponding rubber compounds were prepared, and then each rubber compound was vulcanized and molded under standard vulcanization conditions. The resulting standard test strips were then cut to obtain the test strips for performance testing. The following performance tests were then performed on the samples.
[0067] Mass loss after thermal aging: The test was conducted according to the Chinese national standard GB / T3512 "Accelerated Aging and Heat Resistance Test of Vulcanized Rubber or Thermoplastic Rubber in Hot Air". During the test, the vulcanized standard sample was placed in a hot air aging chamber at 135℃±2℃ for 168 hours. After removal, it was cooled to room temperature in a desiccator, and its mass before and after aging was accurately measured. The mass loss rate (expressed as a percentage) is mainly caused by the volatilization and migration of low molecular weight substances (especially plasticizers) in the sample. A lower loss rate indicates a stronger ability of the rubber composition to lock in plasticizers and better internal compatibility. For the final product, lower mass loss means that after long-term high-temperature use, the surface of the cable or hose sheath is less prone to stickiness and dust accumulation caused by plasticizer precipitation. Simultaneously, the flexible components within the material are retained, effectively maintaining the product's soft feel and mechanical properties, and extending its service life.
[0068] Elongation at break: Tested according to Chinese National Standard GB / T528 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber". During testing, a dumbbell-shaped standard specimen is stretched at a constant speed on a tensile testing machine until it breaks. The elongation at break is calculated by measuring the ratio of the elongation at break to the original gauge length, expressed as a percentage (%). This indicator directly reflects the maximum plastic deformation capacity that the material can withstand before fracture; a higher value indicates better flexibility and ductility. For the final product, a higher initial elongation at break means that the cable sheath can withstand greater bending and tensile deformation during actual installation and use without easily breaking. More importantly, after heat aging tests, a high retention rate of elongation at break (aged value / original value) demonstrates that the material has minimal loss of internal plasticizers and a stable network structure under long-term heat exposure, enabling it to maintain the required flexibility and resistance to damage for a long time. This is crucial for ensuring the reliability of products such as charging pile cables during long-term use.
[0069] Elongation retention rate after aging: This indicator is calculated based on the elongation at break measured before and after the thermal aging test. First, the samples are subjected to standard thermal aging according to GB / T3512 (e.g., 135℃ × 168h), and then the elongation at break of the samples before and after aging is tested according to GB / T528. The elongation retention rate after aging is obtained by the formula (elongation at break after aging ÷ original elongation at break × 100%), expressed as a percentage. This indicator is a key comprehensive indicator for evaluating the heat aging resistance and plasticizer retention ability of materials. The higher the retention rate, the stronger the material's ability to maintain flexibility under long-term thermal action, the less internal plasticizer migration loss, and the lower the degree of thermal damage to the cross-linked network. For the final product, a high retention rate directly means that the cable sheath's resistance to bending and deformation decays more slowly throughout its entire service life, and can meet the mechanical reliability requirements of dynamic laying or flexible use for a long time.
[0070] Flame retardancy performance: Evaluation is based on Underwriters Laboratories' UL94 standard, "Tests on the flammability of plastic materials for use in equipment and appliance components," a widely recognized and authoritative method for determining flame retardancy ratings. During testing, a strip specimen of specified dimensions is vertically ignited. The flame retardancy rating is determined by measuring key parameters such as the time for flaming and extinguished combustion, whether it ignites absorbent cotton, and the length of combustion, with the highest rating being V-0. This test directly simulates the material's resistance to combustion when in contact with an open flame. A V-0 rating indicates that the specimen self-extinguishes within a very short time after being removed from the flame source and does not ignite materials below. For the final product, achieving a UL94 V-0 rating means that the cable sheath has extremely high fire safety, effectively preventing the spread of flames in the event of an accidental ignition source such as a short circuit or overload. This is an indispensable core guarantee for applications with stringent safety requirements, such as new energy vehicle charging stations and high-end home appliances. The performance of the test samples obtained from the above embodiments and comparative examples was tested, and the results are summarized in the table below: The flame retardant performance test results showed that all samples prepared according to the examples and comparative examples passed the UL94V-0 level test. This means that whether it is the example using the modified filler of this invention or the control sample using the conventional filler, its flame retardant safety meets the highest requirements of the standard. This indicates that the modification process of grafting polymer brushes onto the surface of aluminum hydroxide does not destroy its core function as a flame retardant, and the material's self-extinguishing ability under flame is fully preserved.
[0071] Based on the test results of mass loss after thermal aging, the data shows that the mass loss rates of Examples 1 to 3 using the modified flame retardant of this invention after thermal aging were 0.7%, 0.9%, and 1.2%, respectively. Compared with Comparative Example 1, which used ordinary silane to treat the flame retardant, its mass loss reached 2.8%, while Comparative Example 2, which used completely unmodified ATH, had a mass loss as high as 3.5%. These differences directly indicate that this invention, by constructing a high-graft-density long-chain alkyl polymer layer on the filler surface in situ, can effectively anchor the plasticizer within the system, thereby significantly inhibiting plasticizer migration under high-temperature aging conditions. The reduction in mass loss rate is due to the strong affinity and entanglement between the polymer layer on the surface of the modified flame retardant and the plasticizer molecules. This effect makes it difficult for the plasticizer molecules to detach, thus the internal composition of the example samples remains stable after long-term thermal aging.
[0072] Further analysis showed that although Comparative Example 3 incorporated polymers through physical blending, its mass loss was 2.0%, lower than Comparative Examples 1 and 2, but still significantly higher than all other examples. This indicates that simply mixing the polymer into the system is not as effective as chemically grafting it onto the filler surface in stabilizing the plasticizer. Therefore, this test demonstrates that the modified flame retardant of this invention is the core component for solving the plasticizer migration problem in highly filled rubber systems.
[0073] The test results of elongation at break showed that the original elongation at break of Examples 1 to 3 reached 245%, 238% and 220% respectively, which were all higher than those of Comparative Example 1 (185%) and Comparative Example 2 (170%), which represent the prior art. This indicates that the surface-grafted modified ATH filler can form a better interfacial bond with the rubber matrix, thereby giving the vulcanizate higher initial ductility and flexibility, so that the material can withstand greater deformation in the early stages of processing and use.
[0074] Furthermore, after thermal aging, Example 1 exhibited an elongation retention rate as high as 88%, while Examples 2 and 3 reached 85% and 80%, respectively. This contrasts sharply with Comparative Example 1 (52%) and Comparative Example 2 (45%). A sharp decrease in elongation after aging typically indicates a significant loss of plasticizer within the material, leading to hardening and brittleness of the rubber network. Therefore, the embodiments of this invention maintain a high retention rate, demonstrating that the surface polymer successfully locks the plasticizer within the system, effectively delaying the decline in flexibility of the material under long-term thermal action. This is crucial for ensuring the long-term durability of products such as cable sheaths. The descriptions of the above specifications and embodiments are used to explain the scope of protection of this invention, but do not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the teachings of this invention or the above embodiments, combined with common knowledge, general technical knowledge in the art, and / or existing technology, should all be included within the scope of protection of this invention.
Claims
1. A rubber composition for rubber sheaths, characterized in that, The rubber composition comprises, by weight, the following components: 100 parts of chlorinated polyethylene rubber, 100-140 parts of modified flame retardant, 30-50 parts of plasticizer, 3-8 parts of metal oxide activator, 1.5-3.5 parts of peroxide crosslinking agent, 1-3 parts of co-crosslinking agent, 0.5-2 parts of antioxidant, and 0.5-2 parts of processing aid.
2. The rubber composition for rubber sheaths according to claim 1, characterized in that, The modified flame retardant is prepared from the following raw materials in parts by weight: 100 parts aluminum hydroxide powder, 1.0-2.0 parts silane coupling agent containing double bonds, 2.0-4.0 parts long-chain alkyl methacrylate monomer, and 0.02-0.1 parts free radical initiator.
3. The rubber composition for rubber sheaths according to claim 2, characterized in that, The modified flame retardant is prepared through the following steps: P1. Dry the aluminum hydroxide powder by heating it to 100-110℃; P2. Add a silane coupling agent containing double bonds at a stirring speed of 1500-2000 rpm and react at 110℃ for 10-15 minutes; P3. Add premixed long-chain alkyl methacrylate monomers and free radical initiators, increase the stirring speed to 2200-2800 rpm, use shear heat to control the material temperature at 135-145℃, react for 20-25 minutes, and obtain the modified flame retardant after cooling.
4. The rubber composition for rubber sheaths according to claim 2, characterized in that, The silane coupling agent containing double bonds is γ-methacryloyloxypropyltrimethoxysilane; the long-chain alkyl methacrylate monomer is dodecyl methacrylate; and the free radical initiator is dicumyl peroxide.
5. The rubber composition for rubber sheaths according to claim 1, characterized in that, The chlorinated polyethylene rubber has a chlorine content of 30%-40%; the plasticizer is selected from one or more of trioctyl trimellitate, dioctyl phthalate, or dioctyl adipate.
6. The rubber composition for rubber sheaths according to claim 1, characterized in that, The peroxide crosslinking agent is dicumyl peroxide or 1,1-di(tert-butylperoxide)-3,3,5-trimethylcyclohexane; the co-crosslinking agent is triallyl isocyanurate; and the metal oxide activator is magnesium oxide.
7. A method for preparing a rubber composition for a rubber sheath as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Add chlorinated polyethylene rubber, modified flame retardant, metal oxide activator, processing aid and antioxidant into a mixer and mix, then add plasticizer and mix until the rubber is discharged; S2. The rubber compound obtained in step S1 is passed through rollers on a two-roll mill, and peroxide crosslinking agent and co-crosslinking agent are added. After being mixed evenly in a thin pass, it is sheeted out. S3. The film obtained in step S2 is subjected to pressure and heating in a mold for vulcanization molding.
8. The preparation method according to claim 7, characterized in that, In step S1, the initial temperature of the internal mixer is 80-95℃, the discharge temperature is controlled at 125-135℃, and the mixing time is 6-10 minutes.
9. The preparation method according to claim 7, characterized in that, In step S3, the vulcanization temperature is 165-175℃, the vulcanization pressure is 10-20MPa, and the vulcanization time is T90+1 to T90+3 minutes.