Inner release agent for polyurethane shoe soles and its preparation method

Abstract

This invention relates to the field of mold release agent technology, and more particularly to an internal mold release agent for polyurethane shoe soles and its preparation method. The internal mold release agent prepared by rationally compounding hydrophobic silica with high-density polyethylene wax (HDPE wax), low-density polyethylene wax (LDPE wax), long-chain lauric polysiloxane, reactive hydroxyl-terminated silicone oil, and low-molecular-weight polyamide not only exhibits excellent compatibility with polyurethane raw materials and leaves minimal residue after demolding, but also breaks the technical bias in the field that polyethylene wax is only used for lubrication and silica is only used for reinforcement. It avoids the technical prejudice of compounding these two in mold release agents, achieving both lubrication and reinforcement.

Description

Technical Field

[0001] This invention relates to the field of mold release agent technology, and more particularly to an inner mold release agent for polyurethane shoe soles and its preparation method. Background Technology

[0002] Polyurethane soles are widely used in the production of various footwear types, including casual shoes, athletic shoes, and work shoes, due to their lightweight, wear-resistant, and excellent toughness. Internal mold release agents, as key additives in the polyurethane sole molding process, directly affect demolding efficiency, sole surface quality, and mechanical properties.

[0003] Currently, the application of existing polyurethane shoe sole release agents and related mature products mainly suffers from the following technical defects: Poor compatibility: Traditional internal release agents often use non-reactive silicone oils (such as dimethyl silicone oil DC-2000) or low molecular weight waxes or single silicone oils, which are prone to delamination and have poor compatibility with polyurethane (polyether polyol, isocyanate) systems. During processing, the release agent is prone to migrate and precipitate from the matrix, resulting in a decrease in interfacial bonding force. This not only weakens the release effect but also easily forms micro-defects inside the sole, leading to deterioration of mechanical properties.

[0004] The dual function of release and reinforcement is incompatible: Existing internal release agents focus on reducing the interface to facilitate release, lacking a multi-functional synergistic design. Particularly in the field of polyurethane processing aids, mature reinforcing agents (such as fumed silica) and mature release base materials (such as conventional silicone oils) face severe agglomeration and phase separation problems when directly blended due to their significant polarity differences. Therefore, those skilled in the art generally tend to avoid directly blending the two, believing it will disrupt the homogeneity of the system, leading to processing difficulties and deterioration of product performance, thus forming a certain technical bias.

[0005] The problem of residue is prominent: after demolding, polyurethane workpieces are prone to release of mold release agent, which not only increases the cleaning process and production costs, but also affects the adhesion of subsequent processes such as spraying and labeling, causing the coating or shoe label to fall off easily.

[0006] Therefore, in view of the shortcomings of the existing technology, it is necessary to develop a release agent with better compatibility, high demolding efficiency, and the ability to improve the mechanical properties of polyurethane shoe soles. Summary of the Invention

[0007] Based on the above background, the present invention provides an inner release agent for polyurethane shoe soles and its preparation method. The inner release agent prepared by rationally compounding hydrophobic silica with high-density polyethylene wax (HDPE wax), low-density polyethylene wax (LDPE wax), long-chain lauryl polydimethylsiloxane, reactive hydroxyl-terminated silicone oil and its low molecular weight polyamide not only has excellent compatibility with polyurethane raw materials and leaves little residue after demolding, but also breaks the technical prejudice of using polyethylene wax only for lubrication and silica only for reinforcement in the field. It tends to avoid compounding the two in the release agent, and can achieve both lubrication and reinforcement.

[0008] The technical solution of the present invention: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent, by weight, is as follows: The formula consists of 65-70% lauryl polydimethylsiloxane, 15-20% hydroxyl-terminated dimethyl silicone oil, 5-8% high-density polyethylene wax, 3-5% low-density polyethylene wax, 2-5% hydrophobically modified silica, 1-3% polyamide, and 0.2-0.5% antioxidant.

[0009] Furthermore, the composition of its raw materials is as follows: The composition includes 63.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 5% hydrophobically modified silica, 3% polyamide, and 0.5% antioxidant.

[0010] Furthermore, the number-average molecular weight of the polyamide is 1000-2000 g / mol.

[0011] Furthermore, the hydrophobically modified silica is obtained by using fumed silica as raw material and hydrophobically modifying it with a silane coupling agent.

[0012] Furthermore, the silane coupling agent is selected from at least one of hexamethyldisilazane, dimethyldichlorosilane, methyltrimethoxysilane, and methyltriethoxysilane.

[0013] Furthermore, the content (by mass) of terminal hydroxyl groups in the terminal hydroxyl dimethyl silicone oil is 0.1%~0.3%, and its number average molecular weight is 2000~5000 g / mol.

[0014] Furthermore, the number-average molecular weight of the lauryl polydimethylsiloxane is 3000–5000 g / mol.

[0015] Furthermore, the antioxidant is selected from antioxidant 1010.

[0016] Based on the same inventive concept, the present invention also provides a method for preparing the aforementioned polyurethane shoe sole inner release agent, comprising the following steps: ① Raw material pretreatment High-density polyethylene wax and low-density polyethylene wax are respectively pulverized to a particle size ≤5mm; The hydrophobically modified silica was dried at a temperature of 100-110℃. ② After mixing lauryl polydimethylsiloxane and hydroxyl-terminated dimethyl silicone oil evenly, heat the mixture to 120-135℃, then slowly add high-density polyethylene wax and low-density polyethylene wax, and stir until dissolved to obtain the first mixture. ③ Maintain the temperature of the first mixture at 120-130℃, slowly add the hydrophobic silica into it, and stir until the hydrophobic silica is evenly dispersed to obtain the second mixture. ④ Maintain the temperature of the second mixture at 120-130℃, add polyamide and antioxidant to the second mixture in sequence, stir evenly, and then cool.

[0017] Based on the same inventive concept, the present invention also provides a method for preparing a polyurethane shoe sole, wherein 1-1.5 wt% of the aforementioned polyurethane shoe sole inner release agent, or the inner release agent prepared by the aforementioned method for preparing the polyurethane shoe sole inner release agent, is added to the polyurethane shoe sole preparation raw materials.

[0018] The beneficial effects achieved by this invention are as follows: This invention relates to an internal release agent prepared by rationally compounding hydrophobic silica with high-density polyethylene wax, low-density polyethylene wax, long-chain lauryl polydimethylsiloxane, reactive hydroxyl-terminated silicone oil and its low molecular weight polyamide. The components work synergistically with each other, exhibiting excellent compatibility. Not only is it not prone to delamination, but the release agent also does not easily migrate and precipitate from the matrix, leaving little residue after demolding. Furthermore, it has both lubricating and reinforcing functions.

[0019] The synergistic combination of lauryl polydimethylsiloxane, hydroxyl-terminated dimethyl silicone oil, and low-molecular-weight polyamide in this invention imparts excellent compatibility to the mold release agent system. The lauryl polydimethylsiloxane's lauric acid groups (long-chain alkyl groups) can form hydrophobic associations and van der Waals forces with the soft segments of the polyurethane molecular chain, achieving hydrophobic compatibility. Simultaneously, its polysiloxane backbone possesses excellent lubricity, thus providing the basis for the mold release agent's lubrication and compatibility with polyurethane. Furthermore, the hydroxyl-terminated dimethyl silicone oil forms a synergistic compound with lauryl polydimethylsiloxane; their molecular chain structures are complementary, and the polysiloxane backbones intertwine, reducing system viscosity and improving lubrication. The uniformity of the film; the terminal hydroxyl groups of dimethyl silicone oil form weak intermolecular hydrogen bonds with polyurethane segments, achieving stable bonding with the matrix; on the other hand, they form weak interactions with the silicon-oxygen backbone of lauryl polydimethylsiloxane, improving the compatibility and uniformity of the system, thereby inhibiting component migration and reducing surface precipitation; the amino and carboxyl groups contained in low molecular weight polyamide can simultaneously form weak interactions with polyurethane molecular chains, the silanol groups on the surface of silica, and the silicone oil system, further significantly improving the compatibility of the entire release agent system with polyurethane, and inhibiting the layering and aggregation of each component, ensuring that the release agent is uniformly dispersed in the polyurethane system, leaving no residue after demolding.

[0020] This invention achieves both mold release lubrication and reinforcement of polyurethane workpieces by synergistically combining HDPE wax / LDPE wax with hydrophobically modified silica. HDPE wax and LDPE wax complement each other in melting point and structure: HDPE wax has high crystallinity and hardness, which can form a dense solid lubricating layer at the interface between the mold and the polyurethane material, enhancing anti-adhesion and improving demolding smoothness; LDPE wax has many branches and good flexibility, which can adjust the flexibility of the lubricating film, avoid cracks during demolding, and improve the dispersibility of HDPE wax, preventing wax agglomeration. The hydrophobic modification groups (such as methyl groups) of hydrophobically modified silica can synergistically interact with the hydrophobic groups of silicone oil and waxes, preventing silica agglomeration, achieving uniform dispersion, and improving the dispersion stability of silica. Silica can also enhance the hardness and wear resistance of wax lubricating films, preventing damage to the lubricating film during demolding and improving the demolding ability of the release agent. At the same time, the high specific surface area of ​​silica can adsorb silicone oil and wax components, preventing system stratification and physically adsorbing and reinforcing polyurethane molecular chains, thus playing a reinforcing role and improving the tensile strength, wear resistance, and hardness of shoe soles. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the experiments used in the following embodiments... Unless otherwise specified, all materials were purchased from commercial channels.

[0023] The raw materials used in the following examples are listed below: The lauryl polydimethylsiloxane (Lauryl polydimethylsiloxane) had an average number-average molecular weight of 4500 g / mol and a PDI of 1.0–1.2. It was purchased from Hubei Langbowan Biopharmaceutical Co., Ltd. The lauryl polydimethylsiloxane used in the following examples did not contain PEG.

[0024] The content (by mass) of terminal hydroxyl groups in the hydroxyl-terminated dimethyl silicone oil is 0.2%, and its average number-average molecular weight is 4200 g / mol.

[0025] The hydrophobically modified silica is prepared by chemical modification with dimethyldichlorosilane and is selected from Evonik's R972 hydrophobic fumed silica.

[0026] The high-density polyethylene wax was purchased from Nanjing Baiju Technology Co., Ltd., model number MD2300.

[0027] The low-density polyethylene wax, CAS number 9002-88-4, was purchased from Qingdao Haihao Chemical Co., Ltd., and its model number is H1080.

[0028] The polyamide has an average number-average molecular weight of 1300 g / mol, a PDI of 1.1–1.5, an amine value of 67 mg KOH / g, an acid value of 3–6 mg KOH / g, and a melting point of 95–105 °C.

[0029] The average number-average molecular weights of the above raw materials were obtained by GPC gel permeation chromatography.

[0030] Example 1: The composition of the raw materials for preparing a polyurethane shoe sole inner release agent by weight is as follows: The composition includes 63.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 5% hydrophobic modified silica, 3% polyamide, and 0.5% antioxidant 1010.

[0031] Its preparation includes the following steps: S1. Mix pure lauryl polydimethylsiloxane and hydroxyl-terminated dimethyl silicone oil evenly and pour into a dry high-speed disperser container; crush HDPE wax and LDPE wax to a particle size ≤5mm for easy dissolution; The hydrophobically modified silica was dried in an oven at 105℃ for 2 hours to remove the surface adsorbed moisture, and then cooled to room temperature for later use. S2: Turn on the heating jacket of the high-speed disperser and stir continuously. When the system temperature rises to 120℃, slowly add the crushed HDPE wax and LDPE wax and stir continuously for 30-40 minutes until the waxes are completely dissolved and the system is a uniform, transparent, viscous liquid.

[0032] S3. Keep the system temperature at 130±2℃, slowly add the dried hydrophobic modified silica into the reactor, and continue to disperse for 35±2 minutes. During this period, stop the machine every 10 minutes to observe the dispersion effect, ensuring that the silica does not agglomerate and the system is a uniform milky white viscous liquid.

[0033] Under the stirring condition of S4, polyamide and antioxidant 1010 are added sequentially and stirred continuously for 10 minutes to ensure that the low molecular weight polyamide and antioxidant are evenly dispersed in the system. The low molecular weight polyamide can further improve the compatibility of each component.

[0034] S5. Close the heating jacket, transfer the vessel to the cooling tank, keep stirring, and allow it to cool naturally to room temperature (25±2℃).

[0035] Example 2: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 67.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 1% hydrophobically modified silica, 3% polyamide, and 0.5% antioxidant 1010.

[0036] Other matters not covered herein are the same as in Example 1.

[0037] Example 3: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 65.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 3% hydrophobically modified silica, 3% polyamide, and 0.5% antioxidant 1010.

[0038] Other matters not covered herein are the same as in Example 1.

[0039] Example 4: The composition of the raw materials for preparing a polyurethane shoe sole inner release agent by weight is as follows: The composition includes 61.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 7% hydrophobic modified silica, 3% polyamide, and 0.5% antioxidant 1010.

[0040] Other matters not covered herein are the same as in Example 1.

[0041] Comparative Example 1: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 68.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 3% polyamide, and 0.5% antioxidant 1010.

[0042] Compared to Example 1, the hydrophobic modified silica in this comparative example is replaced with the same amount of lauryl polydimethylsiloxane.

[0043] Other matters not covered herein are the same as in Example 1.

[0044] Comparative Example 2: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 66.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 5% hydrophobic modified silica, and 0.5% antioxidant 1010.

[0045] Compared to Example 1, this comparative example replaces the polyamide with the same amount of lauryl polydimethylsiloxane.

[0046] Other matters not covered herein are the same as in Example 1.

[0047] Comparative Example 3: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 61.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 5% hydrophobic modified silica, 5% polyamide, and 0.5% antioxidant 1010.

[0048] Other matters not covered herein are the same as in Example 1.

[0049] Comparative Example 4: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 63.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 5% hydrophobically modified silica, 3% polyamide, and 0.5% antioxidant BHT.

[0050] Compared to Example 1, this comparative example uses the same amount of antioxidant BHT to replace antioxidant 1010.

[0051] Other matters not covered herein are the same as in Example 1.

[0052] Comparative Example 5: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 63.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 4% high-density polyethylene wax, 6% low-density polyethylene wax, 5% hydrophobic modified silica, 3% polyamide, and 0.5% antioxidant 1010.

[0053] Other matters not covered herein are the same as in Example 1.

[0054] Comparative Example 6: The composition of the raw materials for preparing the polyurethane shoe sole inner release agent by weight is as follows: The composition includes 58.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 9% high-density polyethylene wax, 6% low-density polyethylene wax, 5% hydrophobically modified silica, 3% polyamide, and 0.5% antioxidant 1010.

[0055] Other matters not covered herein are the same as in Example 1.

[0056] Related performance experiments and testing (1) Compatibility ① The release agents prepared in the above examples and their comparative examples were sealed and placed at room temperature for 6 months. The appearance was observed at the initial (0 months), 1st, 3rd and 6th months. The presence of layering, precipitation, sedimentation, discoloration and clumping was observed. The viscosity (25℃) at the initial (0 months), 1st, 3rd and 6th months was measured using a rotational viscometer.

[0057] ② The release agent prepared in the above examples and comparative examples is mixed with polyether polyol at an amount of 1.5wt%, and left to stand at room temperature for 24 hours. Observe whether there is layering, oil floating, or precipitation.

[0058] The results are shown in Table 1.

[0059] Table 1: Compatibility Test of Release Agents Table 1 shows that Example 1 exhibits the best demolding stability. Within 6 months of sealed storage at room temperature, it remains uniformly milky white, without stratification, precipitation, or sedimentation. While the viscosity decreases slightly with prolonged storage, the overall fluctuation is minimal. It does not stratify or exhibit oil shedding after mixing with polyether polyol, demonstrating the best compatibility and storage stability. In Example 2, the hydrophobic modified silica content is lower than in Example 1, with a significantly lower viscosity. Slight stratification to obvious stratification occurs with prolonged storage, and the viscosity continues to decrease. Slight stratification with polyether polyol is observed. Analysis suggests that insufficient silica addition prevents effective adsorption, and the silica's silanol and silicone oil system do not interact sufficiently, resulting in insufficient system stability. This leads to phase separation between the silicone oil and waxes due to density differences, causing decreased storage stability and a continuous decrease in viscosity as components migrate. Example 3 exhibits a uniform appearance, minimal viscosity change, and excellent compatibility. Compared to Example 2, the increased silica content enhances the system's stability, maintaining good overall uniformity, but the stabilizing effect is slightly inferior to Example 1. In Example 4, the amount of hydrophobically modified silica was higher than in Example 1, resulting in a higher initial viscosity. After 3 months of storage, the system exhibited a slightly viscous state, and after 6 months, slight agglomeration occurred, with a slight decrease in viscosity. Analysis suggests that the excessive silica content led to overly strong hydrophobic interactions between particles, making them prone to self-agglomeration, resulting in increased viscosity, decreased dispersion uniformity, and reduced stability. In Comparative Example 1, without added hydrophobically modified silica, significant stratification occurred after 3 months of storage, and the stratification worsened after 6 months. When mixed with polyether polyol, oil floated. Analysis suggests this may be due to the lack of silica adsorption, thickening, and interaction with other components. Furthermore, the significant difference in polarity and density between silicone oil and polyethylene wax led to phase separation and poor stability after prolonged standing. In Comparative Example 2, without added polyamide, slight stratification occurred after 1 month of storage, significant stratification after 3 months, and severe stratification after 6 months, with a decrease in viscosity. When mixed with polyether polyol, stratification and precipitation occurred. Analysis suggests that the absence of low-molecular-weight polyamide may have prevented the formation of stable bonds between silicone oil, waxes, and silica, leading to a sharp decrease in component compatibility and rapid phase separation. In Comparative Example 3, the amount of low-molecular-weight polyamide was too high, resulting in a higher initial viscosity. Agglomeration and hard agglomeration occurred during later storage, and micro-precipitation occurred when mixed with polyether polyol. Analysis suggests that excessive polyamide may have led to excessively high polarity and strong intermolecular interactions, resulting in excessively high overall viscosity, difficulty in dispersion, and easy formation of localized agglomeration, thus disrupting the system's homogeneity and flowability. In Comparative Example 4, BHT was used instead of antioxidant 1010. During storage, the system gradually yellowed, and the viscosity continued to decrease, but no obvious stratification occurred. Analysis suggests that BHT's heat and oxygen aging resistance is far lower than that of 1010, and it cannot effectively inhibit the oxidative degradation of silicone oil and waxes during high-temperature preparation and long-term storage, leading to discoloration and viscosity decrease, but without significant impact on the compatibility between components. In Comparative Example 5, the amount of HDPE wax was too low, and the amount of LDPE wax was too high. Slight stratification occurred during later storage, and the stability was weaker than in Example 1.Analysis showed that an excessively high proportion of LDPE wax made the lubricating components too soft, altered their polarity and compatibility, decreased the system's structural stability, and caused slight phase separation after long-term standing. Comparative Example 6 had a higher total amount of HDPE and LDPE wax compared to the examples, resulting in a higher initial viscosity. During storage, it exhibited agglomeration and hard precipitation, and when mixed with polyether polyols, micro-precipitates appeared. Analysis indicated that an excessively high total amount of wax made it difficult to disperse the wax uniformly, leading to crystallization, agglomeration, and sedimentation, thus compromising the system's homogeneity.

[0060] (2) Demolding ability Test the demolding ability of the polyurethane formulation.

[0061] Component A: 100 parts of polyether polyol (highly active polyether 330N (molecular weight 4800-5000)); 10 parts of 1,4-butanediol; Two parts of trimethylolpropane; 0.4 parts of organobismuth (BiCAT 8108); 0.5 parts deionized water; 1.5 parts of polyether-modified silicone oil; Component B: 48 parts of isocyanate.

[0062] The release agent was added to the polyether polyol at 1.5 wt% of the weight of the polyurethane raw materials and stirred until uniform. After adding other raw materials, the mixture was poured into an aluminum alloy mold and heated at 85°C for 6 minutes. After naturally cooling to the mold temperature of 60°C, the maximum demolding force (N) was measured by a 90° peel test using an electronic tensile tester at a peel speed of 100 mm / min. Five parallel samples were tested in each group, and the average value was taken.

[0063] ① Surface Residue Detection After demolding, visually inspect the mold cavity and the surface of the polyurethane workpiece. Gently wipe the surface of the polyurethane workpiece with a dust-free white paper and observe whether there are oil stains on the paper. Classification: Grade 1: No sticking to the mold, no oil stains, and leaves no trace after wiping; Grade 2: Slight adsorption, no residual oil spots; Level 3: Localized sticking to the mold, with obvious oil stains; Level 4: Large areas of sticking to the mold or breakage.

[0064] The results are shown in Table 2.

[0065] Table 2: Demolding performance test As can be seen from Table 2, Example 1 has the best demolding performance, the smallest maximum demolding force, and no sticking or oil stains.

[0066] Example 2: Compared to Example 1, the demolding force increased, and the residue level was 2. Analysis showed that the amount of silica added was insufficient, resulting in a weak lubricating film, decreased film integrity and wear resistance, and easy occurrence of minor damage in some areas. This led to a slight increase in demolding resistance and a slight decrease in the residue level. Example 3: Compared to Example 1, the amount of silica added was increased, but the demolding force decreased, with a residue level of 1, indicating excellent demolding performance. Example 4: Excess silica increased the demolding force, with a residue level of 2. Analysis showed that slight agglomeration of silica slightly reduced the uniformity of the lubricating film, leading to a slight increase in demolding resistance. Comparative Example 1: Without the addition of hydrophobic modified silica, the demolding force increased significantly, with a residue level of 3. The lubricating film strength was insufficient, easily migrated and damaged, and could not form effective interface isolation, resulting in significant interface adhesion, a substantial increase in demolding resistance, and obvious oil stains. Comparative Example 2: No polyamide added. Demolding force increased, residue level 3. Due to the lack of polyamide, system compatibility decreased, components were unevenly dispersed, the lubricating film was discontinuous and locally missing, demolding stability deteriorated, and surface residue was significant. Comparative Example 3: Excess polyamide. Demolding force was 23 N, residue level 2. The system polarity was high, lubricating film spreadability and fluidity decreased, and demolding resistance increased slightly. Comparative Example 4: BHT was used to replace antioxidant 1010. Demolding force was similar to Example 1, residue level 1. Demolding performance was good, indicating that the type of antioxidant has little impact on demolding effect. Comparative Example 5: High HPDE wax ratio. Demolding force increased, residue level 2. Analysis shows that a high HPDE ratio causes the lubricating film to be softer, with insufficient strength, decreased interfacial anti-adhesion ability, and increased demolding resistance. Comparative Example 6: High total wax content. Demolding force increased, residue level 2. Analysis shows that excessive wax easily precipitates locally, resulting in poor lubricating film uniformity.

[0067] ② Test the hardness of the polyurethane workpiece For polyurethane workpieces, cut out a flat, bubble-free area with a thickness ≥6mm; When the Shore A hardness tester is pressed vertically, the pointer stabilizes for 1 second before taking the reading. Five points were measured for each sample, and the maximum and minimum values ​​were removed and the average was taken.

[0068] ③ GB / T 528-2009 Standard for testing the tensile strength and elongation at break of polyurethane workpieces Standard dumbbell-shaped specimens were punched using a punching machine; The gauge length of the tensile testing machine is set to 40mm, and the tensile speed is 500mm / min. Record the maximum tensile force at fracture and the elongation at fracture. Calculate tensile strength and elongation at break, and take the average of 5 values ​​for each group.

[0069] ④ Abrasion resistance test Cut a circular sample and weigh it, recording the initial mass m1. Martindale testing machine, load 12 kPa, friction speed 5000 rpm; After testing, clean the surface dust and weigh it (m2). The wear amount Δm = m1−m2 is calculated, and the smaller the value, the more wear-resistant the wear.

[0070] ⑤ Aging ability test The polyurethane workpiece was kept at a constant temperature of 85℃ for 1000 hours. The hardness, tensile strength, and elongation at break were tested before and after aging. The retention rate of mechanical properties was calculated, and it was observed whether the workpiece became brittle, cracked, or yellowed. The results are shown in Table 4.

[0071] Mechanical property retention rate = performance value after aging treatment × 100% / initial untreated performance value.

[0072] The results are shown in Table 3.

[0073] Table 3: Mechanical Properties Testing of Polyurethane As shown in Table 3, the hardness, tensile strength, elongation at break, and wear resistance of Examples 1-4 are significantly better than those of the comparative examples, with Example 1 exhibiting the best overall mechanical properties. Compared to Example 1, Example 2 has a lower amount of hydrophobically modified silica, resulting in slightly lower hardness, tensile strength, and elongation at break, increased wear, and decreased mechanical properties. This is attributed to insufficient silica content, which fails to form an effective reinforcing network, resulting in weak physical support. Furthermore, the system's stability is lower, making it prone to minor interfacial defects, leading to reduced strength and wear resistance, and a slight decrease in toughness. In Example 3, the increased amount of hydrophobically modified silica improves mechanical properties. In Example 4, the higher amount of hydrophobically modified silica increases hardness and tensile strength, reduces wear, but slightly decreases elongation at break. This is because excessive silica can cause slight self-agglomeration, forming localized micro-stress concentration points. While improving strength and wear resistance, this slightly reduces the material's toughness, while maintaining excellent overall mechanical properties. Comparative Example 1, without the addition of hydrophobically modified silica, exhibited high wear and the worst mechanical properties. Analysis revealed that the lack of silica as a reinforcing phase resulted in a lack of physical support and cross-linking reinforcement in the polyurethane matrix. Simultaneously, the lubricating components easily migrated, forming weak interfaces, leading to low strength, poor toughness, and significantly deteriorated wear resistance. Comparative Example 2, without the addition of low-molecular-weight polyamide, showed significantly lower mechanical properties. Analysis indicated that the absence of polyamide reduced system compatibility, causing uneven dispersion of the release agent components and the formation of interface defects within the polyurethane, creating weak points and reducing overall performance. Comparative Example 3, with excessive polyamide addition, showed higher hardness and tensile strength, but a significantly decreased elongation at break and lower wear. Analysis revealed that excessive polyamide resulted in excessively high system polarity, leading to excessive interaction with the polyurethane, increasing material rigidity and significantly decreasing toughness, exhibiting a hard and brittle characteristic. Comparative Example 4, using BHT instead of antioxidant 1010, showed slightly lower mechanical properties than Example 1, indicating that the type of antioxidant has a relatively small impact on static mechanical properties. However, differences in heat and oxygen stability slightly affected system homogeneity, causing a slight decrease in performance. Comparative Example 5 had a high proportion of HDPE wax and a low proportion of LDPE wax, resulting in moderate mechanical properties. This was attributed to the high proportion of LDPE wax, which resulted in a softer lubricating phase that easily formed minute interfacial slippage, leading to a decrease in strength and wear resistance. Comparative Example 6 had a high total wax content and weak mechanical properties. This was attributed to the high-melting-point HDPE wax's tendency to crystallize and precipitate, causing uneven dispersion and disrupting the continuity of the polyurethane matrix, thus reducing mechanical properties.

[0074] Table 4: Aging Performance Testing of Polyurethane Workpieces As shown in Table 4, Example 1 exhibited the smallest decrease in mechanical properties after 85℃ and 1000h of thermo-oxidative aging, with no yellowing or cracking, demonstrating the best aging resistance. Example 2 showed a significantly increased decrease in mechanical properties and a slight yellowing. This was due to insufficient silica content, which weakened the physical shielding effect, reduced the barrier against heat and oxygen, and made the system more susceptible to oxidative degradation, leading to accelerated mechanical property decay. Example 3 showed aging resistance close to that of Example 1. Example 4 showed a slightly lower retention rate of mechanical properties than Example 1, with a slightly harder appearance and slight yellowing. Analysis suggests that excessive silica caused slight self-agglomeration, forming localized micro-stress concentration points, resulting in a slight loss of toughness after aging, but overall maintaining excellent aging resistance. Comparative Example 1 showed a significantly reduced retention rate of mechanical properties, with noticeable yellowing and slight cracking. Analysis indicates the lack of silica's physical shielding effect allowed heat and oxygen to rapidly penetrate the material, accelerating oxidation of the polyurethane and release agent components, leading to a sharp decline in mechanical properties. Comparative Example 2 showed the lowest retention rates of mechanical properties among all groups, exhibiting significant yellowing and embrittlement. Analysis revealed that the lack of polyamide led to poor system compatibility, numerous internal defects, and the formation of many aging channels, exacerbating thermo-oxidative corrosion and resulting in the most severe aging. Comparative Example 3, with excessive polyamide addition, showed a decrease in mechanical property retention, a slightly yellowed appearance, and increased hardness. Analysis indicated that excessive polyamide resulted in excessively high system polarity and material rigidity, making it more prone to hardening and embrittlement after aging, with a significant loss of toughness. Comparative Example 4, using BHT to replace antioxidant 1010, showed a significantly reduced retention rate, severe yellowing, and obvious embrittlement. BHT's thermo-oxidative aging resistance is far lower than that of 1010, rapidly failing at 85℃ and unable to inhibit free radical chain reactions, leading to severe oxidation, degradation, yellowing, and embrittlement of the system. Comparative Example 5 showed a decrease in mechanical property retention and a slightly yellowed appearance. Comparative Example 6 had an excessively high total wax content and a high HDPE ratio, which further reduced the retention rate of mechanical properties and caused yellowing and slight brittleness. Analysis showed that high-melting-point waxes were prone to crystallization and precipitation, forming weak interfacial areas and accelerating thermo-oxidative aging.

[0075] ⑤ According to the national standard GB / T9286-2021 "Cross-cut test for paint and varnish films", the polyurethane workpieces prepared in the above groups were sprayed with commercially available standard two-component polyurethane plastic paint without any alcohol wiping or surface degreasing treatment. After baking and curing at 80℃, 100 grids of 1mm×1mm were cut on the paint film surface using a special cross-cut knife. 3M-600 standard test tape was then applied tightly and torn off at a 60-degree angle. The paint film peeling was observed and the adhesion level was evaluated. Level 0 was the best, with completely smooth edges and no peeling; Level 5 was the worst, with a peeling area greater than 65%. The results are shown in Table 5. Table 5: Test data on adhesion of polyurethane coatings on workpieces As shown in Table 5, the coating adhesion of Examples 1, 3, and 4 all reached level 0, with no peeling of the paint film and the best bonding strength. Example 2 was level 1, with only a very small amount of edge peeling, but overall it still maintained excellent adhesion. Among them, Example 1 performed the best. The amount of silica added in Example 2 was relatively low. Analysis shows that due to the slightly lower stability of the system, there was a tendency for trace components to migrate, which slightly reduced the surface energy of the polyurethane workpiece, resulting in a very small amount of edge peeling of the paint film, but the overall impact was small. Comparative Example 1 had an adhesion level of 4, with large-area paint film peeling. Analysis shows that due to the lack of adsorption and fixation effect of silica, silicone oil and wax components easily migrated and precipitated to the surface, forming a low surface energy weak interface layer on the surface of the polyurethane workpiece. The paint film could not adhere effectively, and severe peeling occurred after demolding without cleaning. Comparative Example 2 showed an adhesion level of 4, with large-area peeling. Analysis indicated that the lack of polyamide led to poor system compatibility and severe phase separation, resulting in a large accumulation of silicone oil and wax on the surface, forming a continuous weak interfacial layer, and the paint film completely lost its bonding ability. Comparative Example 3 showed an adhesion level of 1, with only minor edge peeling. Analysis indicated that excessive polyamide made the system more polar, exhibiting a slight migration trend, which had a slight impact on local paint film bonding. Comparative Example 4 used BHT to replace antioxidant 1010, maintaining an adhesion level of 0. The type of antioxidant does not affect component migration and surface condition, therefore it has no significant adverse effect on coating adhesion. Comparative Example 5 showed an adhesion level of 2, with local peeling, decreased lubricant film stability, a slight oily feel on the polyurethane workpiece surface, and reduced paint layer adhesion. Comparative Example 6 showed an adhesion level of 2, with significant local peeling. Analysis indicated that excessive wax easily caused local wax precipitation, increased surface oiliness, and further reduced paint film adhesion.

[0076] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. An inner release agent for polyurethane shoe soles, characterized in that, The composition of its raw materials by weight is as follows: The formula consists of 65-70% lauryl polydimethylsiloxane, 15-20% hydroxyl-terminated dimethyl silicone oil, 5-8% high-density polyethylene wax, 3-5% low-density polyethylene wax, 2-5% hydrophobically modified silica, 1-3% polyamide, and 0.2-0.5% antioxidant.

2. The polyurethane shoe sole inner release agent according to claim 1, characterized in that, The composition of its raw materials by weight is as follows: The composition includes 63.5% lauryl polydimethylsiloxane, 18% hydroxyl-terminated dimethyl silicone oil, 6% high-density polyethylene wax, 4% low-density polyethylene wax, 5% hydrophobically modified silica, 3% polyamide, and 0.5% antioxidant.

3. The polyurethane shoe sole inner release agent according to claim 1 or 2, characterized in that, The polyamide has a number-average molecular weight of 1000-2000 g / mol.

4. The inner release agent for polyurethane shoe soles according to claim 1 or 2, characterized in that, The hydrophobically modified silica is obtained by using fumed silica as raw material and hydrophobically modifying it with a silane coupling agent.

5. The polyurethane shoe sole inner release agent according to claim 4, characterized in that, The silane coupling agent is selected from at least one of hexamethyldisilazane, dimethyldichlorosilane, methyltrimethoxysilane, and methyltriethoxysilane.

6. The inner release agent for polyurethane shoe soles according to claim 1 or 2, characterized in that, The terminal hydroxyl content (by mass) of the terminal hydroxyl dimethyl silicone oil is 0.1%~0.3%, and its number average molecular weight is 2000~5000 g / mol.

7. The inner release agent for polyurethane shoe soles according to claim 1 or 2, characterized in that, The number-average molecular weight of the lauryl polydimethylsiloxane is 3000–5000 g / mol.

8. The inner release agent for polyurethane shoe soles according to claim 1 or 2, characterized in that, The antioxidant used is antioxidant 1010.

9. A method for preparing the polyurethane shoe sole inner release agent according to any one of claims 1 to 8, characterized in that, Includes the following steps: ① Raw material pretreatment High-density polyethylene wax and low-density polyethylene wax are respectively crushed to a particle size ≤5mm; The hydrophobically modified silica was dried at a temperature of 100-110℃. ② After mixing lauryl polydimethylsiloxane and hydroxyl-terminated dimethyl silicone oil evenly, heat the mixture to 120-135℃, then slowly add high-density polyethylene wax and low-density polyethylene wax, and stir until dissolved to obtain the first mixture. ③ Maintain the temperature of the first mixture at 120-130℃, slowly add the hydrophobic silica into it, and stir until the hydrophobic silica is evenly dispersed to obtain the second mixture. ④ Maintain the temperature of the second mixture at 120-130℃, add polyamide and antioxidant to the second mixture in sequence, stir evenly, and then cool.

10. A method for preparing a polyurethane shoe sole, characterized in that, An inner mold release agent prepared by adding 1 to 1.5 wt% of the inner mold release agent for polyurethane shoe soles as described in any one of claims 1 to 8, or the inner mold release agent for polyurethane shoe soles prepared by the method described in claim 9, to the raw materials for preparing polyurethane shoe soles.

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