High-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly belongs to a high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition as well as a preparation method and application of the high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition. A reactive phosphorus-nitrogen flame retardant; expanded graphite; a nano reinforcing agent; and an auxiliary agent. The reactive P / N flame retardant is covalently bonded to a TPU main chain, so that the problems of migration and precipitation of the flame retardant are solved, and the flame-retardant efficiency and durability are improved; by adopting the synergistic effect of the expanded graphite and the nano reinforcing agent, the carbon layer structure is enhanced, and the flame retardant property and the mechanical strength are improved; through a micro-layer co-extrusion technology, local enrichment of the flame-retardant filler is realized, and the flame retardance and the mechanical property are both considered; the composition can still reach the UL94 V0 level under the thickness of 0.7 mm, the tensile strength is larger than or equal to 20 MPa, the aging resistance is excellent, the appearance is smooth and free of defects, and the composition is suitable for high-end application such as electric vehicle charging cables.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and specifically belongs to a high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition, a preparation method thereof and an application thereof. BACKGROUND

[0002] Thermoplastic polyurethane elastomer (TPU) is widely used in the fields of wire and cable, automobile parts, electronic equipment, etc. due to its excellent mechanical properties, wear resistance, oil resistance and processing performance. However, TPU itself is flammable and needs to be flame-retardant modified to meet safety standards.

[0003] At present, the industry mainly adopts a double-screw extruder melt blending method to modify TPU, that is, by melt blending TPU base material with a certain weight percentage of additive flame retardant in a double-screw extruder, extruding, granulating and drying to obtain a modified product. This method has the following problems: most additive flame retardants do not match the polarity and chemical structure of the TPU matrix, resulting in poor compatibility between the two, and the flame-retardant components are difficult to disperse uniformly between the TPU molecular chains, and are prone to phase separation and flame-retardant agglomeration; in order to achieve high flame-retardant grade, especially the UL94 V0 requirement for thin-walled products (such as 0.7mm), a large amount of flame retardant (usually more than 25 wt%) is often needed. High filling amount will seriously damage the molecular chain continuity and crystallinity of TPU, resulting in significant decrease in key mechanical properties such as tensile strength and elongation at break; in the extrusion process, excessive addition of flame retardants with poor compatibility is easy to seep from the matrix and accumulate at the die, forming accumulated materials. These accumulated materials will periodically fall off and adhere to the surface of the cable, resulting in rough and nodular product appearance, seriously affecting product quality; physical blending makes the flame retardant and the polymer lack strong binding force, and is prone to migration and precipitation during long-term use or heat aging, not only causing the flame-retardant efficiency to decay over time, but also possibly affecting the electrical performance and long-term service life of the product.

[0004] Especially in demanding applications such as electric vehicle charging cables, the flame-retardant TPU material needs to meet UL94 V0 flame-retardant grade, tensile strength ≥ 20 MPa, and good heat aging resistance and hydrolysis resistance according to the standard GB / T33594-2017 "Cables for electric vehicle charging". The thickness specifications of the test pieces for UL94 flame-retardant test are generally 0.70 mm, 1.5 mm, 3.0 mm, 6.0 mm, 8.0 mm, etc. The thinner the thickness, the easier it is to burn, so more flame retardants need to be added. However, if the proportion of the flame retardant is high, such as more than 25%, the flame retardant can achieve 0.7 mm or 1.5 mm V0 effect, but it will cause the tensile strength of the product to decrease, which is lower than the 20 MPa required by GB / T33594-2017, such as between 15-20 MPa. The increase of the proportion of the flame retardant makes it difficult to be compatible with the TPU, and the material accumulation at the die of the extruder increases during the extrusion of the cable, which seriously affects the appearance of the cable. In order to achieve V0 level flame retardation of thin-walled parts, high-dose flame retardant must be added; and high addition of flame retardant will directly cause the tensile strength of the material to be lower than the standard requirement of 20 MPa, and cause serious processing and appearance problems. SUMMARY

[0005] The purpose of the present application is to solve the technical problem of achieving extremely high flame retardance of thin-walled products of TPU materials without being able to ensure the mechanical and processing properties of TPU materials in the prior art.

[0006] In order to achieve the above-mentioned purpose, the present application provides a high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition, comprising the following components by weight percentage: Thermoplastic polyurethane base: 69 wt% - 80 wt%; Reaction-type phosphorus-nitrogen flame retardant: 3 wt% - 8 wt%, which is covalently bonded to the TPU molecular backbone; Expanded graphite: 5 wt% - 15 wt%; Nano-enhancing agent: 0.5 wt% - 5 wt%; Auxiliary agent: 0 - 3 wt%.

[0007] Preferably, the reaction-type phosphorus-nitrogen flame retardant is at least one of DOPO or its derivative functionalized diol, phosphoramide type small molecule, or polyphosphate diol.

[0008] Preferably, the nano-enhancing agent is at least one of surface functionalized nano-clay, graphene oxide, and functionalized carbon nanotube.

[0009] Preferably, the expanded graphite or nano-enhancing agent is surface treated, and the surface treatment agent is a silane coupling agent.

[0010] The application also provides a method for manufacturing high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition, comprising the following steps: Prepolymerizing the polyol with diisocyanate to generate an NCO group terminated prepolymer; Adding a reactive phosphorus-nitrogen flame retardant to the prepolymer for chain extension reaction, so that the phosphorus-nitrogen flame retardant component is covalently bonded to the TPU molecular chain to obtain a flame-retardant modified TPU base material; After surface treatment of the expanded graphite and nano-enhancing agent, mixing with part of the flame-retardant modified TPU base material to prepare a high-concentration master batch; Melt blending and granulating the flame-retardant modified TPU base material with the high-concentration master batch to obtain the composition.

[0011] The application also provides a flame-retardant TPU cable, the sheath layer or the insulation layer of which is made of the high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition.

[0012] The application also provides a microlayer co-extrusion method for manufacturing the flame-retardant TPU cable, comprising the following steps: Providing phase A and phase B, wherein phase A is a flame-retardant filler-rich phase containing the composition of any one of claims 1-5, and phase B is a low-filler or filler-free TPU phase; Melt conveying phase A and phase B to a layer multiplier, respectively; Alternately laminating phase A and phase B in the layer multiplier, and forming a co-extruded body with tens to thousands of microlayer structures through multiple division and recombination; Coating the co-extruded body outside the conductor to form a cable sheath layer or an insulation layer.

[0013] Compared with the prior art, the application has the following advantages: The application covalently bonds the reactive P / N flame retardant to the TPU main chain, solves the migration and precipitation of the flame retardant, improves the flame retardant efficiency and durability, synergistically enhances the carbon layer structure by using expanded graphite and nano-enhancing agent, enhances the flame retardant performance and mechanical strength, realizes local enrichment of the flame-retardant filler through microlayer co-extrusion, and balances the flame retardancy and mechanical properties; the composition can still reach UL94 V0 level at a thickness of 0.7 mm, the tensile strength is ≥20 MPa, the aging resistance is excellent, the appearance is smooth and defect-free, and is suitable for high-end applications such as electric vehicle charging cables. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 , and a TPU flame-retardant modification process flowchart in the prior art. DETAILED DESCRIPTION

[0015] The terms used in the present application have meanings generally understood by those of ordinary skill in the art, unless otherwise defined.

[0016] In the following examples, various processes and methods which are not described in detail are conventional methods well known in the art.

[0017] The reagents used in the following examples are commercially available and the experimental procedures and experimental conditions not mentioned are conventional procedures and conditions in the art.

[0018] The specific embodiments of the present application are described below with reference to the following examples.

[0019] Based on the detailed technical content you provided, the following are the examples in the "Specific Embodiment" section of the patent specification you wrote. These examples aim to fully disclose the specific implementation schemes, process parameters, and excellent effects achieved, providing solid implementation support for the patent.

[0020] Example 1 (Preparation of high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition) 1. Raw materials and proportions Table 1

[0021] 2. Preparation process (1) Surface treatment of fillers Expandable graphite (EG) and aminated graphene oxide were vacuum dried at 80°C for 4 hours. Then, they were dispersed in a mixed solvent of isopropanol and water (volume ratio 9:1), and silane coupling agent KH-550 was slowly added under mechanical stirring (amount of 1.5% of the total mass of EG and graphene oxide). After reacting at 65°C for 2 hours, filtration and vacuum drying at 90°C to constant weight were performed to obtain surface-functionalized composite fillers.

[0022] (2) Synthesis of reactive P / N flame-retardant TPU base material (prepolymerization-chain extension method) Prepolymerization: Dry polytetrahydrofuran ether glycol (PTMEG, Mn=1000) was added to the reaction kettle under nitrogen protection and heated to 80°C. 4,4'-diphenylmethane diisocyanate (MDI) was slowly added at a molar ratio of NCO:OH of 2.05:1, and the temperature was maintained at 80-85°C for 90 minutes to obtain a terminal NCO group prepolymer.

[0023] Chain extension: The temperature of the system was lowered to 75°C, a mixture of DOPO based diol and 1,4-butanediol (BDO) as chain extender (wherein the DOPO based diol provides 30% of the molar equivalent of the total chain extender) was added to the prepolymer in portions, and 0.02 wt% of the catalyst dibutyltin dilaurate (DBTDL) was added. The reaction was allowed to proceed for 60 minutes until the NCO content was below 0.2%. Finally, the mixture was degassed under a vacuum of <10 mbar for 20 minutes, extruded and pelletized to obtain the flame-retardant modified TPU base particles.

[0024] (3) Preparation of high concentration masterbatch The surface functionalized composite filler obtained in step (1) and part of the TPU base particles obtained in step (2) (in a mass ratio of 35:65) were melt blended in a twin-screw extruder to prepare a high concentration masterbatch with a filler content of 35 wt%. The extrusion temperature was set to 170-195°C, and the screw rotation speed was 250 rpm, and vacuum degassing was performed.

[0025] (4) Blending and pelletizing of the final composition The remaining flame-retardant modified TPU base particles and the above high concentration masterbatch were melt blended and pelletized in a main twin-screw extruder according to the final formulation ratio (i.e. the masterbatch addition amount needs to make EG and graphene oxide reach 15 wt% and 2 wt% in the total composition, respectively). The extrusion temperature was set to 175-205°C, and the screw rotation speed was 300 rpm.

[0026] Example 2 (Preparation of flame-retardant TPU cable) The composition particles prepared in Example 1 were used to manufacture a cable sheath through a micro-layer co-extrusion device.

[0027] A phase (flame-retardant filler-rich phase): the composition particles prepared in Example 1 were used.

[0028] B phase (mechanical reinforcement phase): pure polyester TPU base (brand: 1185A) was used.

[0029] Equipment: two single-screw extruders were used to transport A phase and B phase respectively, and an 8-stage layer multiplier was connected.

[0030] Process parameters: the extrusion temperature was 185-210°C; the volume feeding ratio of A phase to B phase was 15:85; and the screw rotation speed was 80 rpm.

[0031] Molding process: the A phase and B phase melts were subjected to a repeated process of division, superposition, and re-division in the layer multiplier, and finally formed a co-extrusion body with a 256-layer (2 8 ) micro-layer structure. The co-extrusion body was directly wrapped around the conductor to form a cable sheath layer.

[0032] The flame-retardant TPU was prepared by traditional physical blending method. The same model of TPU base material as in Example 1 was used, 25 wt% of additive phosphorus flame retardant (melamine polyphosphate) and 5 wt% of untreated expanded graphite were added, and the mixture was blended and granulated by a twin-screw extruder once. The extrusion process parameters were similar to those of Example 1 (4).

[0033] The micro-layer co-extrusion sheath samples of Example 1, Example 2 and the sample of Comparative Example 1 were respectively injection molded or pressed into standard test bars for performance testing, and the results are shown in Table 2 below: Table 2

[0034] From the test results, it can be seen that the flame-retardant TPU composition and cable product prepared by Example 1 and Example 2 of the present application have more excellent comprehensive performance under the condition that the total amount of flame retardant added (about 22.5 wt%) is lower than that of Comparative Example 1 (about 30 wt%): the flame retardancy still reaches UL94 V-0 level under the harsh condition of 0.7 mm thin wall, while Comparative Example 1 can only reach V-1; the tensile strength is significantly higher than that of Comparative Example 1, and meets the standard requirement of ≥20 MPa, while maintaining high elongation at break; the heat aging and hydrolysis aging resistance performance is excellent, and the retention rate is more than 70%, which is much better than that of Comparative Example 1; there is little material accumulation in the die during the processing, and the final product has smooth appearance without defects, completely solving the problem of rough surface caused by traditional blending method.

[0035] Example 2 further optimizes the spatial distribution of flame-retardant fillers by micro-layer co-extrusion technology, while maintaining the same flame-retardant level, the mechanical properties and aging performance are improved.

[0036] The above is a detailed description of the examples, which facilitates the correct understanding and use of the present application by those skilled in the art. Any improvement or modification of technical solutions obtained by those skilled in the art on the basis of the present application without innovative labor, only through analysis, analogy or limited enumeration, etc. should be within the protection scope determined by the claims.

Claims

1. A high performance halogen-free flame retardant thermoplastic polyurethane elastomer composition characterized in that, By weight percentage, comprising the following components: Thermoplastic polyurethane base material: 69 wt% - 80 wt%; Reactive phosphorus-nitrogen flame retardant: 3 wt% - 8 wt%, which is covalently bonded to the TPU molecular backbone; Expanded graphite: 5 wt% - 15 wt%; Nano-reinforcing agent: 0.5 wt% - 5 wt%; Auxiliary agent: 0 - 3 wt%.

2. The high performance halogen-free flame retardant thermoplastic polyurethane elastomer composition according to Claim 1, characterized in that, The reactive phosphorus-nitrogen flame retardant is at least one of DOPO or its derivative functionalized diol, phosphoramide type small molecule, or polyphosphate diol.

3. The high performance halogen-free flame retardant thermoplastic polyurethane elastomer composition of claim 1, wherein, The nano-reinforcing agent is at least one of surface functionalized nano-clay, graphene oxide, and functionalized carbon nanotube.

4. The high performance halogen-free flame retardant thermoplastic polyurethane elastomer composition of claim 1, wherein, The expanded graphite or nano-reinforcing agent is surface treated, and the surface treatment agent is a silane coupling agent.

5. A process for the manufacture of the high performance halogen-free flame retardant thermoplastic polyurethane elastomer composition as claimed in any one of claims 1 to 4, characterized by, Comprising the following steps: Prepolymerization of polyol with diisocyanate to form NCO group terminated prepolymer; Chain extension reaction of reactive phosphorus-nitrogen flame retardant added to the prepolymer to covalently incorporate the phosphorus-nitrogen flame retardant component into the TPU molecular chain to obtain flame-retardant modified TPU base material; Surface treatment of the expanded graphite and nano-reinforcing agent, and mixing with part of the flame-retardant modified TPU base material to prepare high-concentration masterbatch; Melt blending and granulation of the flame-retardant modified TPU base material and the high-concentration masterbatch to obtain the composition.

6. A flame-retardant TPU cable, the sheath layer or insulation layer of which is made of the high-performance halogen-free flame-retardant thermoplastic polyurethane elastomer composition according to any one of claims 1-4.

7. A microlayer co-extrusion process for making the flame retardant TPU cable of claim 6, characterized by, Comprising the steps of: Providing phase A and phase B, wherein phase A is a flame-retardant filler-rich phase containing the composition according to any one of claims 1-5, and phase B is a low filler or filler-free TPU phase; Melt conveying phase A and phase B to a layer multiplier respectively; Alternating stacking phase A and phase B in the layer multiplier, and forming a co-extrusion body with tens to thousands of layer microstructures through multiple division and recombination; Coating the co-extrusion body outside the conductor to form a cable sheath layer or insulation layer.

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