Thermoplastic polyurethane and method for its preparation and use

Abstract

This invention discloses a thermoplastic polyurethane, its preparation method, and its applications, relating to the field of polyurethane materials technology. The thermoplastic polyurethane provided by this invention comprises polyisocyanate, polymeric polyol, and chain extender as raw materials, and contains no catalyst, thus avoiding the biotoxicity and hazards associated with the introduction of organometallic catalysts and other catalysts. The preparation method of the thermoplastic polyurethane provided by this invention utilizes a high-temperature activation-low-temperature polymerization reaction route, precisely controlling the temperature and temperature difference between the two stages. The resulting catalyst-free TPU exhibits better mechanical strength, lower viscosity decay than catalyst-containing TPU, and better thermal oxidation stability and processing stability.

Description

Technical Field

[0001] This invention relates to the field of polyurethane materials technology, and more specifically, to a thermoplastic polyurethane, its preparation method, and its application. Background Technology

[0002] Thermoplastic polyurethane (TPU) is an important type of engineering plastic produced through a stepwise addition polymerization reaction of polyisocyanates, polyols, and chain extenders. It combines the high elasticity of rubber with the easy processability of plastics. The TPU molecular chain consists of alternating hard segments (HS, composed of isocyanates and chain extenders) and soft segments (SS, composed of polyols). This unique microscopic phase separation structure endows TPU with excellent abrasion resistance, weather resistance, impact resistance, and biocompatibility, making it widely used in films, wires and cables, footwear materials, pipes, automotive parts, and other fields.

[0003] Traditional TPU synthesis processes mainly employ either a prepolymer method (two-step method) or a one-step method. During the reaction, a catalyst is typically added to accelerate the reaction between isocyanate and hydroxyl groups. Commonly used catalysts include tertiary amine catalysts and organometallic catalysts. Commonly used tertiary amine catalysts include triethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N'-dimethylpiperazine, 2-(dimethylamino-ethoxy)-ethanol, and diazabicyclo[2.2.2]octane. Commonly used organometallic catalysts include titanates, iron compounds, or tin compounds. Tin compounds mainly include tin diacetate, tin dioctanoate, tin dilaurate, or tin dialkyl salts of fatty carboxylic acids (such as dibutyltin diacetate or dibutyltin dilaurate).

[0004] However, these catalysts have the following problems: (1) Environmental and health risks: Some organometallic catalysts are biotoxic and pose potential hazards to aquatic organisms and the human endocrine system. The EU REACH regulation and RoHS directive impose strict restrictions on the use of organotin compounds. During the production process, catalyst residues may lead to toxicity and volatile organic compound (VOC) release problems in the product.

[0005] (2) Product performance limitations: The excessively fast catalytic reaction rate leads to low orderliness of the hard segments of the TPU molecular chain and imperfect microphase separation, affecting the material's mechanical strength, thermal stability, and aging resistance. Catalyst residues also accelerate the degradation of TPU during processing and use.

[0006] (3) Process complexity: The amount of catalyst added needs to be precisely controlled (usually 5-10 ppm). Excessive addition will lead to runaway reaction and reduced product performance. In addition, the catalyst is sensitive to moisture, and the moisture content of the raw materials needs to be strictly controlled, which increases the complexity of the production process.

[0007] In recent years, with increasingly stringent environmental regulations and the promotion of the "green chemistry" concept, the development of catalyst-free and solvent-free TPU synthesis technology has become an urgent need in the industry. Existing catalyst-free TPU synthesis methods mainly employ the prepolymer method, which involves first preparing isocyanate-terminated prepolymers and then reacting them with chain extenders. However, the prepolymer method suffers from problems such as long reaction cycles (typically requiring 6-12 hours), complex processes, and low production efficiency.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of this invention is to provide a thermoplastic polyurethane, its preparation method and application, aiming to provide a catalyst-free thermoplastic polyurethane with excellent comprehensive performance.

[0010] This invention is implemented as follows: In a first aspect, the present invention provides a thermoplastic polyurethane, which is obtained by reacting polyisocyanate, polymeric polyol and chain extender as raw materials, and the thermoplastic polyurethane does not contain a catalyst. The hardness of thermoplastic polyurethane is 70A-98A.

[0011] In an optional embodiment, the polyisocyanate is a diisocyanate; Preferably, the diisocyanate is selected from at least one of methane diphenyl diisocyanate, toluene diisocyanate, terephthalic diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate; Preferably, the mass percentage of isocyanate in the total amount of polyisocyanate, polymer polyol and chain extender is 25%-37%.

[0012] In an optional embodiment, the polymeric polyol is selected from at least one of polyester polyol, polyether polyol, polycaprolactone polyol, and polycarbonate polyol. Preferably, in the total amount of polyisocyanate, polymeric polyol and chain extender, the polymeric polyol accounts for 51%-66% by mass; Preferably, the number average molecular weight of the polymer polyol is 500 g / mol to 4000 g / mol.

[0013] In an optional embodiment, the chain extender comprises a small molecule diol with fewer than 12 C12 molecules; Preferably, the chain extender is selected from at least one of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptahydrol, neopentanediol, and cyclohexanediol; Preferably, the chain extender accounts for 5%-13% of the total amount of polyisocyanate, polymer polyol and chain extender; Preferably, the thermoplastic polyurethane has an R value of 0.9 to 1.2 and a hard segment content of 10 wt% to 60 wt%.

[0014] In a second aspect, the present invention provides a method for preparing any of the thermoplastic polyurethanes in the foregoing embodiments, comprising: mixing a polyisocyanate, a polymeric polyol and a chain extender without introducing a catalyst, first activating the mixture at a high temperature of 220°C-265°C to obtain an activated product, and then subjecting the activated product to a low-temperature polymerization reaction. The temperature difference between high-temperature activation and low-temperature polymerization is 50℃-90℃.

[0015] In an optional embodiment, the high-temperature activation temperature is 240℃-260℃; Preferably, the temperature for the low-temperature polymerization reaction is 160℃-200℃; Preferably, both the high-temperature activation and low-temperature polymerization reactions are carried out in a protective atmosphere, which is selected from at least one of nitrogen, carbon dioxide, and an inert gas.

[0016] In an optional embodiment, the reaction equipment for the high-temperature activation and low-temperature polymerization reactions is independently selected from a static mixer, a tubular reactor, a belt reactor, or a reactive extruder. Preferably, the reaction equipment for both the high-temperature activation and low-temperature polymerization reactions is a reaction extruder, more preferably a screw extruder, even more preferably a twin-screw extruder, and most preferably a co-rotating twin-screw extruder; Preferably, the high-temperature activation reaction time is 0.5 min to 5.0 min, more preferably 0.5 min to 2.0 min; Preferably, the reaction time of the low-temperature polymerization reaction is 0.5 min to 5.0 min, more preferably 1 min to 4 min.

[0017] In an optional embodiment, before high-temperature activation, the polyisocyanate, polymer polyol and chain extender are liquefied to heat the raw materials into a liquid state. Preferably, the liquefaction temperatures for the polyisocyanate, polymeric polyol, and chain extender are 40℃-70℃, 50℃-100℃, and 45℃-80℃, respectively. Preferably, before high-temperature activation, the water content of the polyisocyanate, polymer polyol, and chain extender is less than or equal to 200 ppm; Preferably, a functional additive is added to the reaction raw materials. The functional additive is selected from at least one of antioxidants, UV stabilizers, UV inhibitors, anti-yellowing agents, lubricants, and fillers.

[0018] In an optional embodiment, the method further includes: pelletizing or crushing the thermoplastic polyurethane obtained by low-temperature polymerization to obtain thermoplastic polyurethane particles; and aging the thermoplastic polyurethane particles. Preferably, the aging process is carried out at a temperature of 50℃-100℃ for 1h-30h.

[0019] Thirdly, the present invention provides the application of any thermoplastic polyurethane in the foregoing embodiments or the thermoplastic polyurethane prepared by any of the foregoing embodiments in the preparation of films, wires and cables, shoe materials, pipes or automotive parts.

[0020] The present invention has the following beneficial effects: The thermoplastic polyurethane provided by the present invention is obtained by reacting polyisocyanate, polymer polyol and chain extender as raw materials, and the thermoplastic polyurethane does not contain catalyst, thus avoiding the biotoxicity and hazards caused by the introduction of catalysts such as organometallic catalysts.

[0021] The method for preparing thermoplastic polyurethane provided by this invention uses a reaction route of high-temperature activation followed by low-temperature polymerization, and precisely controls the temperature and temperature difference between the two stages. The resulting catalyst-free TPU has better mechanical strength, lower viscosity decay than catalyst-containing TPU, and better thermal oxidation stability and processing stability. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The graph shows the rheological stability test results of the TPUs prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] This invention provides a thermoplastic polyurethane, which is obtained by reacting polyisocyanate, polymer polyol and chain extender as raw materials. The thermoplastic polyurethane does not contain a catalyst, thus avoiding the biotoxicity and hazards caused by the introduction of catalysts such as organometallic catalysts.

[0026] Specifically, the absence of catalysts in thermoplastic polyurethane means that no additional catalysts that can accelerate the polymerization reaction are added during the preparation of thermoplastic polyurethane. The hardness of thermoplastic polyurethane ranges from 70A to 98A, such as 70A, 75A, 80A, 85A, 90A, 95A, 98A, etc.

[0027] In some embodiments, the polyisocyanate may be a diisocyanate, but is not limited thereto. In a preferred embodiment, the diisocyanate is selected from at least one of methane diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), terephthalic diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI), and may be any one or more of the above. All of the above diisocyanates are suitable for the reaction route provided by this invention and can be used to prepare catalyst-free TPU, which exhibits good mechanical strength and low viscosity decay. In the total amount of polyisocyanate, polymer polyol, and chain extender, the mass percentage of isocyanate is 25%-37%, such as 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, etc.

[0028] In some embodiments, the polymeric polyol is selected from at least one of polyester polyols, polyether polyols, polycaprolactone polyols, and polycarbonate polyols, and the polymeric polyol can be any one or more of the above. Preferably, the number average molecular weight of the polymeric polyol is 500 g / mol to 4000 g / mol, such as 500 g / mol, 1000 g / mol, 1500 g / mol, 2000 g / mol, 2500 g / mol, 3000 g / mol, 3500 g / mol, 4000 g / mol, etc. In the total amount of polyisocyanate, polymeric polyol, and chain extender, the mass percentage of the polymeric polyol is 51% to 66%, such as 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, etc.

[0029] In some embodiments, the chain extender comprises a small-molecule diol with fewer than 12 carbon atoms, and the number of carbon atoms can be 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, etc. Preferably, the chain extender is selected from at least one of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptaethylene glycol, neopentanediol, and cyclohexanediol, and the chain extender can be any one or more of the above. The chain extender accounts for 5%-13% of the total amount of polyisocyanate, polymer polyol, and chain extender, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, etc.

[0030] Furthermore, the R-value of thermoplastic polyurethane (TPU) ranges from 0.9 to 1.2, and can be values ​​such as 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, and 1.20. Specifically, the R-value of TPU is equal to the ratio of the total number of moles of NCO functional groups in the system to the number of moles of NCO-reactive groups (mainly -OH). The hard segment content of TPU ranges from 10 wt% to 60 wt%, and can be values ​​such as 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, and 60 wt%. Specifically, TPU consists of hard segments composed of diisocyanate and small-molecule chain extenders, and soft segments composed of long-chain polyols. By controlling the R-value and hard segment content of TPU, it is beneficial to improve the overall properties of TPU, such as mechanical properties and thermal stability.

[0031] This invention also provides a method for preparing thermoplastic polyurethane. Without introducing a catalyst, polyisocyanate, polymeric polyol, and chain extender are mixed and sequentially subjected to high-temperature activation and low-temperature polymerization reactions. By using a high-temperature activation-low-temperature polymerization reaction route and precisely controlling the temperature and temperature difference between the two stages, the resulting catalyst-free TPU exhibits better mechanical strength, lower viscosity decay than catalyst-containing TPU, and better thermal oxidation stability and processing stability. The specific steps are as follows: S1, liquefaction treatment To improve the uniformity of the mixture, the polyisocyanate, polymer polyol, and chain extender are liquefied separately before high-temperature activation, causing the raw materials to be heated into a liquid state. In actual operation, the temperature is raised above their melting point. This treatment step allows the polyisocyanate, polymer polyol, and chain extender to be in a liquid state, enabling better mixing.

[0032] In other embodiments, liquefaction may be omitted, and other means may be used to mix the raw materials evenly.

[0033] The liquefaction temperature varies depending on the raw materials. For polyisocyanates, the liquefaction temperature is 40℃-70℃, such as 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, and 70℃. For polymer polyols, the liquefaction temperature is 50℃-100℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, and 100℃. For chain extenders, the liquefaction temperature is 45℃-80℃, such as 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, and 80℃. The liquefaction temperature can be set according to the melting temperature of the raw materials to liquefy them. Before high-temperature activation, the water content of the polyisocyanates, polymer polyols, and chain extenders should be less than or equal to 200 ppm to avoid the influence of water on the reaction.

[0034] In some embodiments, functional additives are added to the reaction raw materials. These functional additives are selected from at least one of antioxidants, UV stabilizers, anti-yellowing agents, lubricants, and fillers. The functional additives can be any one or more of these. Depending on the performance requirements of the desired product, the above functional additives are selected and added to prepare a TPU product with specific functions.

[0035] S2, High-temperature activation Without introducing a catalyst, polyisocyanate, polymeric polyol, and chain extender are mixed and first activated at a high temperature of 220℃-265℃ to obtain an activated product, preferably 240℃-260℃. By activating under specific temperature conditions, rapid reactions of the raw materials can be achieved without adding a catalyst. If the activation temperature is too high, degradation or decomposition of the raw materials will occur, preventing further polymerization of the activated product and resulting in poor physical properties and large viscosity variations in the prepared thermoplastic polyurethane. If the activation temperature is too low, the reactivity of the raw materials is poor, and without adding a catalyst, further polymerization and chain extension are impossible, also resulting in poor physical properties and large viscosity variations in the prepared thermoplastic polyurethane.

[0036] Specifically, the activation temperature can be 220℃, 223℃, 225℃, 228℃, 230℃, 233℃, 235℃, 238℃, 240℃, 243℃, 245℃, 248℃, 250℃, 253℃, 255℃, 258℃, 260℃, 263℃, 265℃, etc.

[0037] In some embodiments, high-temperature activation is carried out in a protective atmosphere to avoid the influence of gases such as oxygen. The type of protective gas is not limited and can be one or more of the following: gas that is not reactive with polyisocyanates, polymer polyols, and chain extenders, such as nitrogen, carbon dioxide, and inert gases.

[0038] Refer to the instructions in step S3 for the high-temperature activation time and equipment.

[0039] S3, Low-temperature polymerization reaction The activated material obtained in step S2 is subjected to a low-temperature polymerization reaction to obtain thermoplastic polyurethane. The temperature difference between the high-temperature activation and the low-temperature polymerization reaction is 50℃-90℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, etc. If the temperature difference is too large, the polymerization and chain propagation of the activated material will be significantly slowed down, resulting in poor physical properties and viscosity stability of the prepared thermoplastic polyurethane. If a screw extruder is used as the polymerization reaction equipment, it will also lead to increased screw shear force, which will further cause polymer molecular chain breakage. If the temperature difference is too small, the polymer degradation during the polymerization reaction will be obvious, resulting in poor physical properties and viscosity stability.

[0040] In some embodiments, the temperature of the low-temperature polymerization reaction is 160℃-200℃, such as 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, etc. The low-temperature polymerization reaction is carried out in a protective atmosphere to avoid the influence of gases such as oxygen. The type of protective gas is not limited and can be one or more gases that are not reactive with polyisocyanates, polymer polyols, and chain extenders, such as nitrogen, carbon dioxide, and inert gases.

[0041] In some embodiments, the reaction equipment for both the high-temperature activation and low-temperature polymerization reactions is independently selected from a static mixer, a tubular reactor, a belt reactor, or a reactive extruder. All of these types of equipment can be used as reaction equipment for either the high-temperature activation or low-temperature polymerization reactions. Preferably, the reaction equipment used is a reactive extruder, such as a screw extruder. Screw extruders include single-screw extruders and twin-screw extruders. Both single-screw and twin-screw extruders can be used for the reaction. Since the degree of mixing of the materials at the beginning of the reaction has a significant impact on the reaction result, and the extruder section mainly plays the role of mixing the materials to initiate the initial reaction, the optimal choice for the extruder section is a twin-screw extruder. The twin-screw extruder can be any one of co-rotating, counter-rotating, intermeshing, or non-intermeshing types; a co-rotating closely intermeshing twin-screw extruder is preferred.

[0042] When using a twin-screw extruder, the high-temperature activation reaction time is 0.5 min to 5.0 min, such as 0.5 min, 1.0 min, 1.5 min, 2.0 min, 2.5 min, 3.0 min, 3.5 min, 4.0 min, 4.5 min, 5.0 min, etc.; preferably 0.5 min to 2.0 min. The low-temperature polymerization reaction time is 0.5 min to 5.0 min, such as 0.5 min, 1.0 min, 1.5 min, 2.0 min, 2.5 min, 3.0 min, 3.5 min, 4.0 min, 4.5 min, 5.0 min, etc., preferably 1 min to 4 min. When using a screw extruder as the reaction equipment, the activation time refers to the residence time of the reactants in the screw extruder during the activation step; the polymerization reaction time refers to the residence time of the reactants in the screw extruder during the polymerization step.

[0043] In some embodiments of the present invention, the residence time of the raw material in the screw can be controlled by controlling the length-to-diameter ratio and screw speed of the screw extruder. For example, the length-to-diameter ratio of the screw extruder in the activation step is 6:1 to 15:1 (e.g., 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, etc.), and the screw speed is 300 rpm to 800 rpm (e.g., 300 rpm, 4...). The screw extruder in the polymerization step has a length-to-diameter ratio of 15:1 to 70:1 (e.g., 15:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, etc.) and a screw speed of 100 rpm to 400 rpm (e.g., 100 rpm, 200 rpm, 300 rpm, 400 rpm, etc.).

[0044] When using other equipment as the reaction equipment, the activation time and polymerization time can be adjusted according to requirements. The activation time should not be too long to avoid degradation of the activated material; the activation time should not exceed 5 minutes, preferably not exceeding 3 minutes. In some embodiments of this invention, when using a screw extruder as the activation equipment, the activation time does not exceed 2 minutes. The polymerization reaction time can be adjusted according to the degree of polymerization or the different reaction equipment; no special requirements are placed on the polymerization time. For example, when using a static mixer as the reaction equipment for the activation step, the mixing time of the raw materials in the mixer is 1-3 minutes. When the activated material is fed into the polymerization equipment, such as a belt reactor or a reactive extruder, the polymerization reaction continues to obtain thermoplastic polyurethane. The polymerization time in a belt reactor is 3 minutes to 2 hours, and the polymerization time in a reactive extruder is 0.5-5 minutes.

[0045] In other embodiments of the present invention, when a screw extruder or a belt reactor is used as the reaction equipment, the screw extruder or the belt reactor can be set to the same temperature or different temperature zones. For example, the temperature of the screw extruder or belt reactor in the activation step is set to the same temperature: 220-265℃, such as 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃, 265℃. The temperature of the screw extruder or belt reactor in the activation step is set to different temperature zones: the first temperature zone is set to 220-230℃, and the second temperature zone is set to 230-265℃. The temperature of the screw extruder or belt reactor in the polymerization step is set to the same temperature: 160-195℃, such as 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃. The temperature of the screw extruder or belt reactor in the polymerization step is set to different temperature zones: the first temperature zone is set to 160-170℃, the second temperature zone is set to 170-195℃, and the third temperature zone is set to 160-180℃.

[0046] S4, Post-processing Thermoplastic polyurethane obtained from low-temperature polymerization can be pelletized using an underwater pelletizer or pulverized using a pulverizer to obtain thermoplastic polyurethane granules; these granules are then subjected to a curing treatment. After twin-screw polymerization, pelletizing, or pulverizing, the melt is rapidly cooled, and neither the reaction nor phase separation has reached equilibrium. The curing treatment allows the chemical, molecular, and phase structures of the TPU particles to reach thermodynamic equilibrium, resulting in superior processing and performance.

[0047] In some embodiments, the curing temperature is 50℃-100℃, such as 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc.; the curing time is 1h-30h, such as 1h, 3h, 5h, 8h, 10h, 13h, 15h, 18h, 20h, 23h, 25h, 28h, 30h, etc.

[0048] The thermoplastic polyurethane provided in this invention can be further processed into films, wires and cables, shoe materials, pipes or automotive parts, etc. By improving the properties of thermoplastic polyurethane, the performance of the final product can be improved, such as mechanical strength and thermal oxidation stability.

[0049] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0050] The raw materials used in the following examples and comparative examples are shown in Table 1: Table 1 Raw materials used in the examples and comparative examples

[0051] In the examples and comparative examples, the water content of the polyisocyanate, polymer polyol and chain extender was controlled below 200 ppm before the activation step. The polyisocyanate is kept at a temperature of 40-70℃, the polymer polyol is kept at a temperature of 50-100℃, and the chain extender is kept at a temperature of 45-80℃ to ensure that the polyisocyanate, polymer polyol and chain extender remain in a liquid state.

[0052] Tensile strength and elongation at break tests: Thermoplastic polyurethane was made into a film with a thickness of (10±2) filaments. The film was cut into Die C type standard dumbbell specimens. The tensile speed was 500 mm / min. The tensile strength and elongation at break were tested according to ASTM D412.

[0053] Peel strength test: Cut two films that have been made into a roll and bonded together into a size of 1cm × 10cm. The thickness of a single film is controlled at (10±2) filaments. Tear the sample 1cm apart along the long axis of the sample. Hold the two ends of the tear apart on a tensile testing machine. Refer to ASTM D412 for the method of testing tensile strength. Record the maximum tensile strength after the film is torn apart, which is the peel strength. The greater the peel strength, the slower the thermoplastic polyurethane molding is, the more serious the adhesion between the films, and the more difficult the peeling is. Conversely, the faster the molding is, the less serious the adhesion between the films, and the easier the peeling is.

[0054] Example 1 This embodiment provides a method for preparing thermoplastic polyurethane, the steps of which are as follows: (1) High temperature activation step: Under nitrogen protection, MDI, PTMEG (Mn1000) and BDO are added to the first screw extruder through a mixing pump. The screw extruder temperature is 250℃, the screw length-to-diameter ratio is 10:1, and the screw speed is 500rpm, so that the material stays in the screw for about 1 minute to obtain the activated product. (2) Low-temperature polymerization reaction step: The activated material is transferred to the second screw extruder. The temperature of the screw extruder is 180℃, the length-to-diameter ratio of the screw is 60:1, and the screw speed is 150rpm, so that the material stays in the screw for about 2 minutes to obtain thermoplastic polyurethane.

[0055] (3) Post-treatment: The thermoplastic polyurethane obtained by low-temperature polymerization reaction is granulated to obtain thermoplastic polyurethane particles; the thermoplastic polyurethane particles are cured at a temperature of 80°C for 15 hours.

[0056] Example 2 The difference from Example 1 is that the mass ratios of MDI, PTMEG (Mn1000), PTMEG (Mn2000), and BDO are different, while the rest are the same.

[0057] Table 1. Mass ratios of Example 1 and Example 2

[0058] The performance of Examples 1 and 2 is shown in Table 2: Table 2 Performance test results of Example 1 and Example 2

[0059] The mass proportions of Examples 3-17 are shown in Table 3: Table 3 Mass ratios of Examples 3-17

[0060] Preparation methods of Examples 3-6: The difference from Example 1 is the activation temperature. Other preparation methods are the same as those of Example 1. Example 3 is 260℃, Example 4 is 250℃, Example 5 is 240℃, and Example 6 is 230℃.

[0061] Preparation methods for Examples 7-17: Same as those for Example 1.

[0062] The performance of Examples 3-6 is shown in Table 4: Table 4 Performance test results of Examples 3-6

[0063] As can be seen from Table 4, the tensile strength increases with increasing activation temperature.

[0064] The performance of Examples 7-14 is shown in Table 5: Table 5 Performance test results of Examples 7-14

[0065] As can be seen from Table 5, different formulation systems can all be produced using this process.

[0066] Example 15 The difference from Example 1 lies in the polymerization steps, as detailed below: Activation step: Under nitrogen protection, MDI, PTMEG (Mn1000) and BDO are added to the first screw extruder via a mixing pump according to the mass ratio in Table 1. The screw extruder temperature is 250℃, the screw length-to-diameter ratio is 10:1, and the screw speed is 500rpm, so that the material residence time in the screw is about 1 minute, and the activated product is obtained. Polymerization step: The activated material is transferred to the second screw extruder. The screw extruder has three temperature zones: the first temperature zone (sections 1-5) is set to 170°C, the second temperature zone (sections 5-10) is set to 180°C, and the third temperature zone (sections 11-14) is set to 165°C. The screw length-to-diameter ratio is 60:1, and the screw speed is 150 rpm, so that the material residence time in the screw is about 2 minutes, resulting in thermoplastic polyurethane.

[0067] The difference between Example 16 and Example 1 is that the screw temperature in the activation step was adjusted from 250°C to 220°C, and the screw temperature in the polymerization step was adjusted from 180°C to 170°C.

[0068] The difference between Example 17 and Example 1 is that the screw temperature in the activation step was adjusted from 250°C to 265°C, and the screw temperature in the polymerization step was adjusted from 180°C to 190°C.

[0069] The difference between Example 18 and Example 1 is that the screw temperature in the polymerization step is adjusted from 180°C to 160°C.

[0070] The difference between Example 19 and Example 1 is that the screw temperature in the polymerization step is adjusted from 180°C to 200°C.

[0071] The difference between Example 20 and Example 1 is that the screw speed in the activation step is 650 rpm, so that the material stays in the screw for about 0.5 minutes.

[0072] The difference between Example 21 and Example 1 is that the screw speed in the activation step is 270 rpm, so that the material stays in the screw for about 2 minutes.

[0073] The performance comparison between Example 1 and Examples 15-21 is shown in Table 6: Table 6 Performance test results of Examples 1 and 15-21

[0074] Comparative Example 1 The difference from Example 1 is that there is no activation step. MDI, PTMEG (Mn1000) and BDO are directly added to the screw extruder via a mixing pump, with the same mass ratio as in Example 1. Stannous octoate catalyst is added at a dosage of 10 ppm. Based on the mass of thermoplastic polyurethane, the screw extruder temperature is 180°C, the screw length-to-diameter ratio is 60:1, and the screw speed is 150 rpm, so that the material residence time in the screw is about 2 minutes, thus obtaining thermoplastic polyurethane.

[0075] Comparative Example 2 The difference from Example 2 is that there is no activation step. MDI, PTMEG (Mn1000) and BDO are directly added to the screw extruder via a mixing pump, with the same mass ratio as in Example 2. Stannous octoate catalyst is added at a dosage of 10 ppm. Based on the mass of thermoplastic polyurethane, the screw extruder temperature is 180°C, the screw length-to-diameter ratio is 60:1, and the screw speed is 150 rpm, so that the material residence time in the screw is about 2 minutes, resulting in thermoplastic polyurethane.

[0076] The performance comparison between Examples 1-2 and Comparative Examples 1-2 is shown in Table 7: Table 7 Performance test results of Examples 1-2 and Comparative Examples 1-2

[0077] The table above shows that the TPU prepared in Examples 1 and 2 of the present invention without the addition of a catalyst has higher mechanical strength and elongation at break, and the film peeling force is also significantly lower than that of Comparative Example 1 and Comparative Example 2, which can avoid the phenomenon of film adhesion during the processing of TPU films.

[0078] In addition, the TPUs of Example 1 and Comparative Example 1 were subjected to rheological stability tests (DMS, 200°C, 60 min), and their performance was compared. Figure 1 As shown. By Figure 1 It can be seen that the viscosity decay of Example 1 of the present invention is significantly lower than that of Comparative Example 1, indicating that Example 1 has a better effect in maintaining the integrity of the polymer structure and has better thermal oxidation stability and processing stability.

[0079] Comparative Example 3 The only difference from Example 1 is that the activation temperature is 210°C.

[0080] Comparative Example 4 The only difference from Example 1 is that the activation temperature is 280°C.

[0081] Comparative Example 5 The only difference from Example 1 is that the low-temperature polymerization temperature is 150°C.

[0082] Comparative Example 6 The only difference from Example 1 is that the low-temperature polymerization temperature is 210°C.

[0083] Comparative Example 7 The only difference from Example 1 is that the high-temperature activation step and the low-temperature polymerization step are swapped. The steps are as follows: (1) Low-temperature polymerization reaction step: Under nitrogen protection, MDI, PTMEG (Mn1000) and BDO are added to the first screw extruder through a mixing pump. The mass ratio is the same as in Example 1. The temperature of the screw extruder is 180°C, the screw length-to-diameter ratio is 60:1, and the screw speed is 150 rpm, so that the material stays in the screw for about 2 minutes to obtain the prepolymer. (2) High temperature activation step: The prepolymer is transferred to the second screw extruder. The temperature of the screw extruder is 250°C, the length-to-diameter ratio of the screw is 10:1, and the screw speed is 500 rpm, so that the material stays in the screw for about 1 minute to obtain thermoplastic polyurethane.

[0084] Comparative Example 8 The only difference from Example 1 is that the high-temperature activation step is omitted. The steps are as follows: Under nitrogen protection, MDI, PTMEG (Mn1000) and BDO were passed through a screw extruder in the same mass ratio as in Example 1. The screw extruder temperature was 180°C, the screw length-to-diameter ratio was 60:1, and the screw speed was 150 rpm, so that the material residence time in the screw was about 2 minutes, resulting in thermoplastic polyurethane.

[0085] Comparative Example 9 The only difference from Example 1 is that the low-temperature polymerization reaction step is omitted. The steps are as follows: Under nitrogen protection, MDI, PTMEG (Mn1000) and BDO were added to the screw extruder via a mixing pump, with the same mass ratio as in Example 1. The screw extruder temperature was 250°C, the screw length-to-diameter ratio was 10:1, and the screw speed was 500 rpm, so that the material residence time in the screw was about 1 minute, resulting in thermoplastic polyurethane.

[0086] The performance comparisons of Comparative Examples 3-9 are shown in Table 8: Table 8 Performance test results of Comparative Examples 3-9

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A thermoplastic polyurethane, characterized in that, The thermoplastic polyurethane is obtained by reacting polyisocyanates, polymeric polyols and chain extenders as raw materials, and does not contain a catalyst. The hardness of the thermoplastic polyurethane is 70A-98A.

2. The thermoplastic polyurethane according to claim 1, characterized in that, The polyisocyanate is a diisocyanate; Preferably, the diisocyanate is selected from at least one of methane diphenyl diisocyanate, toluene diisocyanate, terephthalic diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate; Preferably, the mass percentage of isocyanate in the total amount of polyisocyanate, polymer polyol and chain extender is 25%-37%.

3. The thermoplastic polyurethane according to claim 1, characterized in that, The polymer polyol is selected from at least one of polyester polyol, polyether polyol, polycaprolactone polyol, and polycarbonate polyol; Preferably, in the total amount of polyisocyanate, polymeric polyol and chain extender, the polymeric polyol accounts for 51%-66% by mass; Preferably, the number-average molecular weight of the polymeric polyol is 500 g / mol to 4000 g / mol.

4. The thermoplastic polyurethane according to claim 1, characterized in that, The chain extender includes a small molecule diol with fewer than 12 C12; Preferably, the chain extender is selected from at least one of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptahydrol, neopentanediol, and cyclohexanediol; Preferably, the chain extender accounts for 5%-13% of the total amount of polyisocyanate, polymer polyol and chain extender; Preferably, the thermoplastic polyurethane has an R value of 0.9 to 1.2 and a hard segment content of 10 wt% to 60 wt%.

5. A method for preparing thermoplastic polyurethane, characterized in that, include: Without introducing a catalyst, polyisocyanate, polymeric polyol and chain extender are mixed and first activated at high temperature at 220℃-265℃ to obtain an activated product, which is then subjected to a low-temperature polymerization reaction. The temperature difference between the high-temperature activation and the low-temperature polymerization reaction is 50℃-90℃.

6. The preparation method according to claim 5, characterized in that, The high-temperature activation temperature is 240℃-260℃; Preferably, the temperature of the low-temperature polymerization reaction is 160℃-200℃; Preferably, both the high-temperature activation and the low-temperature polymerization reaction are carried out in a protective atmosphere, which is selected from at least one of nitrogen, carbon dioxide and inert gas.

7. The preparation method according to claim 5, characterized in that, The reaction equipment for the high-temperature activation and the low-temperature polymerization reaction is independently selected from a static mixer, a tubular reactor, a belt reactor, or a reactive extruder; Preferably, the reaction equipment for the high-temperature activation and the low-temperature polymerization reaction is a reaction extruder, more preferably a screw extruder, even more preferably a twin-screw extruder, and most preferably a co-rotating twin-screw extruder; Preferably, the reaction time for high-temperature activation is 0.5 min to 5.0 min, more preferably 0.5 min to 2.0 min; Preferably, the reaction time of the low-temperature polymerization reaction is 0.5 min to 5.0 min, more preferably 1 min to 4 min.

8. The preparation method according to claim 5, characterized in that, Before the high-temperature activation, the polyisocyanate, the polymer polyol and the chain extender are respectively liquefied to heat the raw materials into a liquid state; Preferably, the temperatures for liquefying the polyisocyanate, the polymeric polyol, and the chain extender are 40°C-70°C, 50°C-100°C, and 45°C-80°C, respectively. Preferably, prior to the high-temperature activation, the water content of the polyisocyanate, the polymer polyol, and the chain extender is less than or equal to 200 ppm; Preferably, a functional additive is added to the reaction raw materials, wherein the functional additive is selected from at least one of antioxidants, UV stabilizers, UV inhibitors, anti-yellowing agents, lubricants, and fillers.

9. The preparation method according to claim 5, characterized in that, Also includes: The thermoplastic polyurethane obtained by the low-temperature polymerization reaction is pelletized or crushed to obtain thermoplastic polyurethane particles; the thermoplastic polyurethane particles are then subjected to a curing treatment. Preferably, the curing temperature is 50℃-100℃ and the curing time is 1h-30h.

10. The use of the thermoplastic polyurethane according to any one of claims 1-4 or the thermoplastic polyurethane prepared by the preparation method according to any one of claims 5-9 in the preparation of films, wires and cables, shoe materials, pipes or automotive parts.

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