Preparation method of extremely cold-resistant thermo-oxidative aging-resistant waterborne polyurethane electrothermal film

Abstract

The invention discloses a preparation method of an extremely cold-resistant thermo-oxidative aging-resistant waterborne polyurethane electrothermal film, which can be used for heating an emergency camping tent in an extremely cold environment. Through molecular design and structural regulation, silicon-containing long-chain dihydric alcohol, DOPO flame-retardant dihydric alcohol and hindered phenol thermal oxidation resistant groups are introduced into a molecular chain of the waterborne polyurethane, so that the low temperature resistance, thermal oxidation aging resistance, bending resistance and flame retardance of the waterborne polyurethane are improved. The designed high and low temperature resistant waterborne polyurethane is taken as a base material, and is combined with conductive fillers such as carbon fibers, carbon nanotubes, graphene, conductive carbon black and the like to prepare the electrothermal film, and the designed electrothermal film can still keep the original electrothermal performance in extreme environments such as high and low temperatures, complex chemical environments (salt, alkali, acid and the like), long-time circulation and the like.

Description

Technical Field

[0001] The invention belongs to the field of polymer electric heating film materials, and in particular relates to a method for preparing an extreme cold-resistant and heat-oxidation-resistant waterborne polyurethane electric heating film. Background Art

[0002] The balance of human body temperature is the basic condition for ensuring normal human activities. Therefore, human thermal management in extremely cold environments (such as the Antarctic, the Arctic, and the high altitude areas of the Qinghai-Tibet Plateau) has received great attention since ancient times. At present, hair dryers and electric heaters are mainly used in emergency camping tents in extremely cold environments to achieve human thermal management. However, problems such as large mass, high noise, and inconvenience greatly limit their application in various complex outdoor extreme environments. Electric heating film is a kind of heating method that can perfectly solve the heating problem of emergency camping tents in extremely cold environments by converting electrical energy into thermal energy to obtain a suitable temperature. In addition, compared with the convection heating of hair dryers and electric heaters, electric heating films heat the tent in a more comfortable form of infrared radiation to achieve a suitable temperature. Restricted by the polymer matrix and preparation process of current electric heating film materials, commercial electric heating films currently have problems such as low electric heating radiation conversion efficiency, poor low temperature resistance, poor thermal oxygen aging resistance during long-term high temperature operation, and poor bending resistance. Long-term conversion between extremely cold storage environment and high temperature service leads to failure, resulting in a decrease in its service life, making it difficult to be used in extremely cold scenes. Therefore, the research on electric heating films that are both efficient and resistant to high and low temperatures has important practical significance, and can lay a solid foundation for the heating of emergency camping tents in extremely cold environments.

[0003] There are many kinds of polymer matrices used in electric heating film materials, such as aramid fiber, PBO fiber, polyurea, polyimide, etc. However, these polymer matrices have disadvantages such as high cost, difficulty in large-scale production, and complex preparation process. Among them, polyurethane is a multifunctional polymer material with excellent performance. It is called the "fifth plastic" and is widely used in elastomers, foams, coatings, adhesives, leather, inks and other industries. Waterborne polyurethane (WPU) is an important member of the polyurethane family and an emerging environmentally friendly coating. Different from traditional organic solvent-based polyurethane coatings, WPU uses water as a solvent and has a wider hardness range, wear resistance, high strength and high adhesion. At the same time, it has the advantages of low volatile organic compounds of water-based coatings. It has received extensive attention from the scientific research and industrial communities and has great application prospects and value.

[0004] However, when WPU is used at high temperatures for a long time, the unsaturated bonds (carbonyl, isocyanate, etc.) in the material will react with oxygen in the air, resulting in oxidative degradation and inactivation. Especially when the electric heating film is in long-term high-temperature service and in a humid environment, the molecular structure of WPU is more vulnerable to damage, thereby accelerating the thermal oxidative aging process. In addition, WPU will become brittle and crack in a long-term extremely cold storage environment. Therefore, how to coordinate and balance the high-temperature thermal oxidative aging resistance and low-temperature cracking of the electric heating film WPU matrix material is an urgent problem to be solved.

[0005] At present, the solution to the thermal oxidation problem of WPU is to add antioxidants to the WPU matrix, such as hindered phenol antioxidants (antioxidant 2,6-di-tert-butyl-4-methylphenol), peroxide decomposition antioxidants (such as zinc dialkyl dithiophosphate, etc.) and metal deactivated antioxidants. Antioxidants are eventually consumed during the use of the material, and the chemical loss caused by antioxidant activity or the physical loss of migration to the environment leads to the loss of polymer stability. In addition, such small molecule antioxidants are easy to precipitate and cause harm to the environment. Summary of the invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for preparing an extreme cold resistant and heat-oxidative aging resistant waterborne polyurethane electric heating film. The present invention introduces anti-aging groups into the WPU molecular chain through molecular design and structural regulation, which can creatively solve the problems of WPU heat-oxidative aging and precipitation of small molecule antioxidants at the same time. In addition, long-chain silanes are introduced into the molecular chain to regulate the glass transition temperature (Tg) of WPU, improve the low temperature resistance and bending resistance of WPU, so as to solve the problems of long-term high temperature service and low temperature cracking of waterborne polyurethane-based electric heating film materials in extremely cold environments.

[0007] The method for preparing the waterborne polyurethane electric heating film resistant to extreme cold and heat-oxidation aging of the present invention comprises the following steps: Step 1: Stir the silicon-containing long-chain diol, isophorone diisocyanate and N-methyldiethanolamine at 78°C in a nitrogen atmosphere for 10 min; then add a drop of catalyst dibutyltin dilaurate, and keep stirring until the prepolymer can hardly flow; then add 2-butanone to the system to dissolve the prepolymer, and add heat-resistant and oxidative aging diethanolamine monomer and DOPO flame-retardant diol, and react at 78°C in a nitrogen atmosphere for 2 hours; after the reaction is completed, cool to room temperature, use glacial acetic acid to adjust the pH of the system to 7, add deionized water to fully emulsify, and remove the solvent by rotary evaporation to obtain a cold-resistant and heat-resistant waterborne polyurethane emulsion.

[0008] Step 2: Slowly add the carbon fiber powder to the dispersant polyvinyl alcohol solution, and stir at a high speed of 1200 rpm in a high-speed mixer for 30 min; after uniform dispersion, add the conductive filler and the auxiliary conductive filler, and continue to stir at a high speed of 1200 rpm for 30 min; after the conductive filler is completely mixed, add the cold-resistant and heat-resistant oxygen aging waterborne polyurethane emulsion obtained in step 1, reduce the speed to 600 rpm and continue stirring for 1 h; pour the obtained conductive slurry on the high temperature resistant polyester film, and use a film scraping machine to prepare the cold-resistant and heat-resistant oxygen aging waterborne polyurethane electric heating film, and establish an excellent conductive network during the solvent volatilization process.

[0009] In step 1, the amount of each raw material added is: 0.4~0.8 mol of silicon-containing long-chain diol, 1.7 mol of isophorone diisocyanate, 0.69 mol of N-methyldiethanolamine, 0.2~0.3 mol of heat-resistant and oxidative aging diethanolamine monomer, and 0~0.3 mol of DOPO flame-retardant diol.

[0010] The silicon-containing long-chain diol is selected from one or more of poly(dimethylsiloxane) diol and 1,3-bis(4-hydroxybutyl)tetramethyldisiloxane. If there are multiple types, the mixing ratio is arbitrary.

[0011]

[0012] The heat-oxidative aging-resistant diethanolamine monomer is prepared by a method comprising the following steps: (1) The antioxidant 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid was added to chloroform solvent, and dithionyl chloride was added dropwise under nitrogen protection. The reaction was carried out at 50°C for 5 hours. After the reaction was completed, the solvent and unreacted dithionyl chloride were removed by vacuum distillation to obtain light yellow crystals (acyl chloride AO-Cl).

[0013] (2) Dissolve diethanolamine in dichloromethane, add triethylamine as an acid binding agent and stir for 10 min, then add a dichloromethane solution containing acyl chloride AO-Cl dropwise under nitrogen and react at 50 °C for 6 h. After the reaction, extract and remove impurities, and use rotary evaporation to remove the solvent to obtain a light yellow product, grafted antioxidant diethanolamine (AO-DA), which is used for the synthesis of cold-resistant and heat-resistant waterborne polyurethane.

[0014]

[0015] The DOPO flame retardant diol is selected from one or more of the DOPO derivatives DOPO-GY, DOPO-DH, and DOPO-GD. If there are multiple types, the mixing ratio is arbitrary. The corresponding structural formula is as follows:

[0016] In step 2, the raw materials are composed of 35-61 parts by mass of cold-resistant, heat-resistant and oxygen-resistant waterborne polyurethane emulsion, 4-5 parts by mass of polyvinyl alcohol solution, 35-50 parts by mass of conductive filler, and 0-10 parts by mass of auxiliary conductive filler.

[0017] The conductive filler is selected from carbon fiber powder (carbon crystal).

[0018] The auxiliary conductive filler is selected from one or more of graphene, carbon nanotubes, and carbon black. If there are multiple types, the mixing ratio is arbitrary.

[0019] The concentration of the polyvinyl alcohol solution is 8 wt %, and it is a polyvinyl alcohol aqueous solution.

[0020] In step 2, during the film scraping process, the scraper height is 200-1200 μm, the scraper speed is 5 cm / min, the scraper stroke is 350 mm, the drying temperature is 40°C, and the drying is 12 h.

[0021] The polyester film used in step 2 is a base film and a protective layer; the required parameters of the polyester film are resistance to a high temperature of 180°C; and resistance to a basic sinusoidal AC test voltage of 50 Hz and 3750V for 1 min without breakdown.

[0022] The synthetic route is shown below:

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention adopts molecular design and structural regulation, selects silicon-containing long-chain diols, antioxidant-grafted diethanolamine and DOPO flame-retardant diols as monomers for the synthesis of waterborne polyurethane, introduces different amounts of low-temperature resistant, thermal oxidation resistant and flame-retardant groups into the WPU molecular chain through appropriate reactions, and coordinates and balances the high-temperature thermal oxidation aging resistance, low-temperature cracking, flame retardancy and bending resistance of WPU. The selected silicon-containing long-chain diol can regulate the glass transition temperature (Tg) of WPU to give WPU low-temperature resistance and excellent bending resistance. The thermal oxidation aging resistant diethanolamine monomer selected in WPU is a hindered phenol antioxidant, which has migration resistance and durability, thereby achieving a long-term antioxidant effect. The selected DOPO derivative diol and silicon-containing diol realize intrinsic flame retardant WPU, and the hindered phenol or DOPO flame retardant diol can capture free radicals in the combustion stage to interrupt the combustion chain reaction. The present invention introduces low-temperature resistant, antioxidant and flame retardant groups into the WPU molecular chain through molecular design and structural regulation, and solves the problems of high-temperature thermal oxidation aging, low-temperature cracking, bending resistance and flame retardancy of traditional WPU electric heating film materials.

[0024] (2) The present invention uses anti-aging WPU as a matrix, carbon fiber powder as a main conductive filler, and graphene, carbon nanotubes and carbon black as auxiliary conductive fillers to prepare a WPU-based multifunctional electrothermal radiation heating material for extremely cold plateau areas. The electrothermal conversion efficiency of the WPU-based electrothermal radiation heating material is 96%, the electrothermal radiation conversion efficiency reaches 80%, and the normal infrared emissivity reaches 0.89. The electrothermal radiation conversion efficiency does not decrease significantly after 5000 bending, long-term high temperature (120 ℃*5000H) and low temperature (-50 ℃) treatment. Anti-aging WPU, as a binder between conductive materials, can establish a conductive network between the main conductive filler and the auxiliary conductive filler, thereby providing excellent electrothermal conversion performance; the selected conductive material has an extremely high emissivity, which can provide heat to the space in the form of infrared radiation. In addition, the prepared WPU matrix provides excellent flexibility, anti-aging performance and mechanical strength, and can cope with complex chemical environments (cold bending, cold folding, mechanical bending, acid, alkali, salt, high and low temperature).

[0025] In addition, the conductive network established gives the WPU-based multifunctional electric radiant heating material for extremely cold regions excellent electromagnetic shielding properties, which can resist electromagnetic interference from electronic equipment and protect human health. The intrinsically flame-retardant WPU synergistically combines with a high amount of added carbon materials to give the electric heating film excellent flame retardant properties, solving the fire hazard caused by the electric radiant film after overloading. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Corresponding to the hydrogen spectrum and infrared spectrum of AO-DA.

[0027] Figure 2 Corresponding hydrogen spectrum and infrared spectrum of DOPO-GY.

[0028] Figure 3 Corresponding hydrogen spectrum and infrared spectrum of DOPO-GH.

[0029] Figure 4 Corresponding hydrogen spectrum and infrared spectrum of DOPO-GD. DETAILED DESCRIPTION

[0030] In order to further illustrate the technical solution of the present invention, the preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention. Based on the examples in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. Embodiment 1:

[0031] 1. Preparation of AO-DA 5 g of antioxidant 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid was added to 50 mL of chloroform solvent, and reacted at 50 °C for 5 h under nitrogen protection in the presence of low-valent thionyl chloride. After the reaction, the solvent and unreacted thionyl chloride were removed by vacuum distillation to obtain light yellow crystals (acyl chloride AO-Cl).

[0032] Dissolve 5 g of diethanolamine in 50 mL of dichloromethane, add 5 g of triethylamine as an acid-binding agent and stir for 10 min, add 50 mL of dichloromethane solution containing the above reactants dropwise under nitrogen conditions, and react at 50 °C for 6 h; after the reaction, extract and remove impurities, and use rotary evaporation to remove the solvent to obtain a light yellow product AO-DA for the synthesis of anti-aging waterborne polyurethane.

[0033] 2. Preparation of DOPO-GY Take a 500ml three-necked flask and react with DOPO and glyoxal in a molar ratio of 1:0.5 as raw materials. First, dissolve 108.08g of DOPO in acetonitrile solution, then slowly add glyoxal solution, and apply a reflux condenser. Under mechanical stirring, react at 90°C for 6h. After the reaction is completed, filter, wash three times with acetonitrile, and dry the product at 55°C for 12h.

[0034] 3. Preparation of DOPO-DH Take a 500ml three-necked flask and dissolve 71.33g of DOPO in 300ml of chloroform solution. After DOPO is completely dissolved, add 29.73g of polyformaldehyde, and then slowly add 34.69g of diethanolamine solution, and apply a reflux condenser. Under mechanical stirring, react at 55°C for 12h. After the reaction is completed, cool the solution to room temperature, filter it, wash it with chloroform, and then dry it in a vacuum oven at 100°C for 12h.

[0035] 4. Synthesis of DOPO-GD Take a 500ml three-necked flask and dissolve 54g of DOPO in 150ml of toluene solution. After DOPO is completely dissolved, add 50g of glutaraldehyde aqueous solution dropwise within 20min using a dropping funnel, and apply a reflux condenser. Under mechanical stirring, react at 85°C for 5h. After the reaction is completed, cool the solution to room temperature, filter, wash with toluene, and then dry at 80°C for 12h. Embodiment 2:

[0036] 1. Preparation of WPU-AO anti-thermal and oxidative aging waterborne polyurethane emulsion 0.7 mol of poly(dimethylsiloxane) diol, 1.7 mol of isophorone diisocyanate and 0.69 mol of N-methyldiethanolamine were added to a 250 mL three-necked flask and stirred for 10 min in a nitrogen atmosphere at 78 °C. Then, a drop of catalyst dibutyltin dilaurate was added to the prepolymer and stirred until the prepolymer was white and almost unable to flow. 50 mL of 2-butanone was added to reduce the viscosity of the system. After the prepolymer was dissolved in 2-butanone, 0.3 mol of AO-DA was added in sequence and stirred for 2 h at 78 °C. When the reactants were cooled to room temperature, glacial acetic acid was added for neutralization for 30 minutes under stirring. Subsequently, 25 mL of deionized water was added for 2 h of emulsification and dispersion. Finally, 2-butanone was removed by rotary evaporation to obtain an anti-aging waterborne polyurethane dispersion a. The solid content of the anti-aging waterborne polyurethane dispersion was adjusted to 35%.

[0037] 2. Preparation of WPU-AO-GY thermal and oxygen aging resistant waterborne polyurethane emulsion 0.2 mol of poly(dimethylsiloxane) diol, 1.7 mol of isophorone diisocyanate and 0.69 mol of N-methyldiethanolamine were added to a 250 mL three-necked flask and stirred for 10 min in a nitrogen atmosphere at 78 °C. Then, a drop of catalyst dibutyltin dilaurate was added to the prepolymer and stirred until the prepolymer was white and almost unable to flow. 50 mL of 2-butanone was added to reduce the viscosity of the system. After the prepolymer was dissolved in 2-butanone, 0.5 mol of DOPO-GY and 0.3 mol of AO-DA were added in sequence and stirred for 2 h at 78 °C. When the reactants were cooled to room temperature, glacial acetic acid was added for neutralization for 30 min under stirring. Subsequently, 25 mL of deionized water was added for 2 h of emulsification and dispersion. Finally, 2-butanone was removed by rotary evaporation to obtain an anti-aging waterborne polyurethane dispersion b. The solid content of the anti-aging waterborne polyurethane dispersion was adjusted to 35%.

[0038] 3. Preparation of WPU-AO-DH thermal-oxidative-aging resistant waterborne polyurethane emulsion 0.5 mol of poly(dimethylsiloxane) diol, 1.7 mol of isophorone diisocyanate and 0.69 mol of N-methyldiethanolamine were added to a 250 mL three-necked flask and stirred for 10 min in a nitrogen atmosphere at 78 °C. Then, a drop of catalyst dibutyltin dilaurate was added to the prepolymer and stirred until the prepolymer was white and almost unable to flow. 50 mL of 2-butanone was added to reduce the viscosity of the system. After the prepolymer was dissolved in 2-butanone, 0.3 mol of DOPO-DH and 0.2 mol of AO-DA were added in sequence and stirred for 2 h at 78 °C. When the reactants were cooled to room temperature, glacial acetic acid was added for neutralization under stirring for 30 minutes. Subsequently, 25 mL of deionized water was added for 2 h of emulsification and dispersion. Finally, 2-butanone was removed by rotary evaporation to obtain an anti-aging waterborne polyurethane dispersion c. The solid content of the anti-aging waterborne polyurethane dispersion was adjusted to 35%.

[0039] 4. Preparation of WPU-AO-GD thermal and oxygen aging resistant waterborne polyurethane emulsion 0.4 mol of poly(dimethylsiloxane) diol, 1.7 mol of isophorone diisocyanate and 0.69 mol of N-methyldiethanolamine were added to a 250 mL three-necked flask and stirred for 10 min in a nitrogen atmosphere at 78 °C. Then, a drop of catalyst dibutyltin dilaurate was added to the prepolymer and stirred until the prepolymer was white and almost unable to flow. 50 mL of 2-butanone was added to reduce the viscosity of the system. After the prepolymer was dissolved in 2-butanone, 0.3 mol of DOPO-GD and 0.3 mol of AO-DA were added in sequence and stirred for 2 h at 78 °C. When the reactants were cooled to room temperature, glacial acetic acid was added for neutralization under stirring for 30 min. Subsequently, 25 mL of deionized water was added for emulsification and dispersion for 2 h. Finally, 2-butanone was removed by rotary evaporation to obtain an anti-aging waterborne polyurethane dispersion d. The solid content of the anti-aging waterborne polyurethane dispersion was adjusted to 35%. Comparative Example 2:

[0040] The preparation of the waterborne polyurethane in this comparative example is the same as that in Example 2, except that the poly(dimethylsiloxane) diol, DOPO diol and AO-DA in Example 2 are replaced with polycarbonate diol to synthesize pure waterborne polyurethane, and the other formula compositions are exactly the same as the preparation method.

[0041]

[0042] The results show that the four WPUs prepared in Example 2 have lower Tg, elongation at break retention rate and peak heat release rate (PHRR). Through molecular design and structural regulation, the thermal oxidation aging resistance, low temperature resistance and flame retardancy of WPU are improved. Embodiment 3:

[0043] In this embodiment, the anti-aging waterborne polyurethane-based electric heating radiation film for extreme cold environments includes the following components in parts by weight: 45 parts of WPU-AO anti-thermal and oxygen aging water-based polyurethane emulsion, Dispersant: 5 parts of 8 wt% PVA aqueous solution, Conductive filler: 50 parts of carbon fiber powder, The specific preparation method of the above-mentioned electrothermal radiation multifunctional anti-aging waterborne polyurethane film in extremely cold plateau regions is as follows: weigh WPU-AO-GY anti-thermal oxidation aging waterborne polyurethane emulsion, PVA dispersant, and carbon fiber powder according to the above formula. Slowly add the carbon fiber powder to 50 mL of the above-mentioned polyvinyl alcohol dispersant and stir at high speed for 30 minutes at 1200 rpm in a high-speed mixer; after uniform dispersion, add the anti-aging waterborne polyurethane emulsion, reduce the speed to 600 rpm and continue to stir at high speed for 1 hour. Pour the obtained conductive slurry on the high-temperature resistant polyester film, use a film scraping machine to prepare a multifunctional anti-aging waterborne polyurethane film, and establish an excellent conductive network during the solvent volatilization process. The scraper height is 200-1200 μm, the scraper speed is 5 cm / min, the scraper stroke is 350 mm, and the drying temperature is 40 ℃. Comparative Example 3:

[0044] The waterborne polyurethane film of this comparative example is the same as that of Example 3, except that 51 parts of the anti-aging waterborne polyurethane in Example 3 are replaced with pure waterborne polyurethane of Comparative Example 3, and the other formula compositions and preparation methods are exactly the same. Embodiment 4:

[0045] In this embodiment, the anti-aging waterborne polyurethane-based electric heating radiation film for extreme cold environments includes the following components in parts by weight: 55 parts of WPU-AO-GY anti-thermal oxygen aging water-based polyurethane emulsion, Dispersant: 5 parts of 8 wt% PVA aqueous solution, Conductive filler: 35 parts of carbon fiber powder, Auxiliary conductive filler: 5 parts of graphene.

[0046] The specific preparation method of the above-mentioned electrothermal radiation multifunctional anti-aging waterborne polyurethane film in extremely cold plateau regions is as follows: weigh WPU-AO-GY anti-thermal oxidation aging waterborne polyurethane emulsion, PVA dispersant, and carbon fiber powder according to the above formula. Slowly add the carbon fiber powder to 50 mL of the above-mentioned polyvinyl alcohol dispersant and stir at high speed for 30 minutes at 1200 rpm in a high-speed mixer; after uniform dispersion, add the anti-aging waterborne polyurethane emulsion, reduce the speed to 600 rpm and continue to stir at high speed for 1 hour. Pour the obtained conductive slurry on the high-temperature resistant polyester film, use a film scraping machine to prepare a multifunctional anti-aging waterborne polyurethane film, and establish an excellent conductive network during the solvent volatilization process. The scraper height is 200-1200 μm, the scraper speed is 5 cm / min, the scraper stroke is 350 mm, and the drying temperature is 40 ℃. Comparative Example 4:

[0047] The waterborne polyurethane film of this comparative example is the same as that of Example 3, except that 51 parts of the anti-aging waterborne polyurethane in Example 3 are replaced with pure waterborne polyurethane, and the other formula compositions and preparation methods are exactly the same. Embodiment 5:

[0048] In this embodiment, the anti-aging waterborne polyurethane-based electric heating radiation film for extreme cold environments includes the following components in parts by weight: 51 parts of WPU-AO-DH anti-thermal oxygen aging water-based polyurethane emulsion, Main dispersant: 4 parts of 8 wt% PVA aqueous solution, Main conductive filler: 35 parts of carbon fiber powder, Auxiliary conductive filler: 10 parts of multi-walled carbon nanotubes.

[0049] The specific preparation method of the above-mentioned electrothermal radiation multifunctional anti-aging waterborne polyurethane film in extremely cold plateau regions is as follows: weigh WPU-AO-GY anti-thermal and oxidative aging waterborne polyurethane emulsion, PVA dispersant, carbon fiber powder and carbon nanotubes according to the above formula. Slowly add the carbon fiber powder to 50 mL of the above-mentioned polyvinyl alcohol dispersant, and stir at high speed for 30 min at 1200 rpm in a high-speed mixer; after uniform dispersion, add carbon nanotubes and auxiliary conductive filler dispersant, and add an appropriate amount of deionized water to adjust the viscosity to a suitable range, and continue to stir at high speed for 30 min at 1200 rpm; after the conductive filler is completely mixed, add cold-resistant and anti-thermal and oxidative aging waterborne polyurethane emulsion, reduce the speed to 600 rpm and continue to stir at high speed for 1 h. Pour the obtained conductive slurry on the high temperature resistant polyester film, use a film scraper to prepare a multifunctional anti-aging waterborne polyurethane film, and establish an excellent conductive network during the solvent volatilization process. The scraper height is 200-1200 μm, the scraper speed is 5 cm / min, the scraper stroke is 350 mm, and the drying temperature is 40°C. Comparative Example 5:

[0050] The waterborne polyurethane film of this comparative example is the same as that of Example 5, except that 41 parts of the anti-aging waterborne polyurethane in Example 5 are replaced with pure waterborne polyurethane, and the other formula compositions and preparation methods are exactly the same. Embodiment 6:

[0051] In this embodiment, the anti-aging waterborne polyurethane-based electric heating radiation film for extreme cold environments includes the following components in parts by weight: 41 parts of WPU-AO-GD anti-thermal oxygen aging water-based polyurethane emulsion, Main dispersant: 4 parts of 8 wt% PVA aqueous solution, Main conductive filler: 45 parts of carbon fiber powder, Auxiliary conductive fillers include 5 parts of carbon nanotubes and 5 parts of graphene.

[0052] The specific preparation method of the above-mentioned electrothermal radiation multifunctional anti-aging waterborne polyurethane film in extremely cold plateau regions is as follows: WPU-AO-GH anti-thermal oxidation aging waterborne polyurethane emulsion, PVA dispersant, carbon fiber powder and graphene are weighed according to the above formula. Take the carbon fiber powder and slowly add it to 50 mL of the above-mentioned polyvinyl alcohol dispersant, and stir it at a high speed of 1200 rpm in a high-speed mixer for 30 min; after uniform dispersion, add graphene and auxiliary conductive filler dispersant, and add an appropriate amount of deionized water to adjust the viscosity to a suitable range, and continue to stir at a high speed of 1200 rpm for 30 min; after the conductive filler is completely mixed, add the anti-aging waterborne polyurethane emulsion, reduce the speed to 600 rpm and continue to stir at a high speed for 1 h. Pour the obtained conductive slurry on the high temperature resistant polyester film, use a scraping machine to prepare a multifunctional anti-aging waterborne polyurethane film, and establish an excellent conductive network during the solvent volatilization process. The scraper height is 200-1200 μm, the scraper speed is 5 cm / min, the scraper stroke is 350 mm, and the drying temperature is 40°C. Comparative Example 6:

[0053] The waterborne polyurethane film of this comparative example is the same as that of Example 6, except that 41 parts of the anti-aging waterborne polyurethane in Example 6 are replaced with pure waterborne polyurethane, and the other formula compositions and preparation methods are exactly the same.

[0054] The extreme cold resistant and heat oxidative aging resistant waterborne polyurethanes of Examples 3-6 and the pure waterborne polyurethanes of Comparative Examples 3-6 were made into electric heating films according to the methods in the corresponding embodiments. The electric heating films were tested for their electric thermal radiation conversion efficiency, electromagnetic shielding, and electric thermal radiation conversion efficiency after environmental treatment. The test results are shown in Table 2 below.

[0055]

[0056] The results show that Examples 3-6 using cold-resistant and heat-resistant waterborne polyurethane as the matrix have better flame retardant properties, electromagnetic shielding properties, electrothermal radiation conversion properties and resistance to extreme environments than pure WPU Comparative Examples 3-6.

Claims

1. A method for preparing an extreme cold resistant and heat resistant waterborne polyurethane electric heating film, characterized in that The steps include: Step 1: Stir and disperse the silicon-containing long-chain diol, isophorone diisocyanate and N-methyldiethanolamine at 78° C. in a nitrogen atmosphere; then drop the catalyst dibutyltin dilaurate and keep stirring until the prepolymer is almost unable to flow; then add 2-butanone to the system to dissolve the prepolymer, and add the heat-oxidation-resistant diethanolamine monomer and DOPO flame-retardant diol, and react at 78° C. in a nitrogen atmosphere for 2 hours; after the reaction is completed, cool to room temperature, use glacial acetic acid to adjust the system pH to 7, add deionized water to fully emulsify, and remove the solvent by rotary evaporation to obtain a cold-resistant and heat-oxidation-resistant waterborne polyurethane emulsion; Step 2: Slowly add the carbon fiber powder to the dispersant polyvinyl alcohol solution, stir and disperse evenly, then add the conductive filler and the auxiliary conductive filler, and continue stirring; after the conductive filler is completely mixed, add the cold-resistant and heat-resistant oxygen aging water-based polyurethane emulsion obtained in step 1, and stir and react for 1 hour; pour the obtained conductive slurry on the high temperature resistant polyester film, and use a film scraping machine to prepare the cold-resistant and heat-resistant oxygen aging water-based polyurethane electric heating film, and establish an excellent conductive network during the solvent volatilization process.

2. The preparation method according to claim 1, characterized in that: In step 1, the amount of each raw material added is: 0.4~0.8 mol of silicon-containing long-chain diol, 1.7 mol of isophorone diisocyanate, 0.69 mol of N-methyldiethanolamine, 0.2~0.3 mol of heat-resistant diethanolamine monomer, and 0~0.3 mol of DOPO flame-retardant diol.

3. The preparation method according to claim 1 or 2, characterized in that: The silicon-containing long-chain diol is selected from one or more of poly(dimethylsiloxane) diol and 1,3-bis(4-hydroxybutyl)tetramethyldisiloxane. If there are multiple types, the mixing ratio is arbitrary.

4. The preparation method according to claim 1 or 2, characterized in that: The heat-oxidative aging-resistant diethanolamine monomer is prepared by a method comprising the following steps: (1) Add the antioxidant 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionic acid to chloroform solvent, add dithionyl chloride dropwise under nitrogen protection, and react at 50°C for 5 hours; after the reaction, remove the solvent and unreacted dithionyl chloride by vacuum distillation to obtain acyl chloride AO-Cl; (2) Dissolve diethanolamine in dichloromethane, add triethylamine as an acid-binding agent and stir, add dichloromethane solution containing acyl chloride AO-Cl dropwise under nitrogen, and react at 50°C for 6 h; after the reaction, extract and remove impurities, and use rotary evaporation to remove the solvent to obtain a light yellow product, grafted antioxidant diethanolamine AO-DA; The synthetic route is as follows: 。 5. The preparation method according to claim 1 or 2, characterized in that: The DOPO flame retardant diol is selected from one or more of the DOPO derivatives DOPO-GY, DOPO-DH, and DOPO-GD. If there are multiple types, the mixing ratio is arbitrary; the corresponding structural formula is as follows: 。 6. The preparation method according to claim 1, characterized in that: In step 2, the raw materials are composed of 35-61 parts by mass of cold-resistant, heat-resistant and oxygen-resistant waterborne polyurethane emulsion, 4-5 parts of polyvinyl alcohol solution, 35-50 parts of conductive filler, and 0-10 parts of auxiliary conductive filler.

7. The preparation method according to claim 1 or 6, characterized in that: The conductive filler is selected from carbon fiber powder.

8. The preparation method according to claim 1 or 6, characterized in that: The auxiliary conductive filler is selected from one or more of graphene, carbon nanotubes, and carbon black. If there are multiple types, the mixing ratio is arbitrary.

9. The preparation method according to claim 1 or 6, characterized in that: The concentration of the polyvinyl alcohol solution is 8 wt %, and it is a polyvinyl alcohol aqueous solution.

10. The preparation method according to claim 1, characterized in that: In step 2, during the film scraping process, the scraper height is 200-1200 μm, the scraper speed is 5 cm / min, the scraper stroke is 350 mm, the drying temperature is 40°C, and the drying is 12 h.

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