A clean bio-based strippable waterborne polyurethane coating and its preparation method and application

Abstract

The invention provides a clean bio-based strippable waterborne polyurethane coating and a preparation method and application thereof, belonging to the technical field of polymer material preparation; the invention introduces renewable polyol sorbitan monooleate, epoxy soybean oil and fluoroalkyl chain extender into a waterborne polyurethane skeleton, thereby preparing a clean bio-based strippable waterborne polyurethane coating; the clean bio-based strippable waterborne polyurethane coating has a solid content of 30% and a storage stability of more than 6 months; the clean bio-based strippable waterborne polyurethane coating film has a tensile strength of 28.3-37.8MPa and an elongation at break of 432.8-597.3%; the preparation method of the bio-based strippable waterborne polyurethane coating is simple, a transfer film can be prepared by a casting or coating process, and then can be used to prepare a printed sensor, a transparent electrode, a packaging material, an anti-counterfeiting material or a protective material, and has good practicality.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation, and specifically relates to a clean bio-based strippable waterborne polyurethane coating and a preparation method and application thereof. Background Art

[0002] During the preparation and construction of solvent-based transfer coatings (films), the emission of volatile organic compounds (VOCs) can cause haze and photochemical smog in addition to the toxicity of VOCs themselves. In addition, the polymer substrates used as transfer films mainly include biaxially oriented films such as polyethylene terephthalate (PET), polypropylene and polyamide. Usually, there is a strong adhesion between the biaxially oriented polymer film substrate and the traditional polymer coating cast on the film substrate. Therefore, if rapid online stripping is achieved, a release agent is required between the coating and the substrate. The introduction of a release agent will inevitably lead to difficulties in downstream processing, as well as the additional procedures and costs required to introduce a release agent.

[0003] Waterborne polyurethane (WPU) can be used to make transfer coatings (films) with excellent performance. Transfer coatings (films) can be quickly peeled off from some low surface energy substrates such as PET and polypropylene, and actual online peeling can be achieved. They can be used to prepare printed sensors, transparent electrodes, high-end packaging materials, anti-counterfeiting materials and protective materials. However, polymer substrates cannot be self-peeled due to their electrostatic adsorption and interaction with the materials directly coated or cast on them. Therefore, it is usually necessary to use some low surface energy release agents between the substrate and the WPU film, such as silicone release agents, fluorine release agents and paraffin wax, to achieve online rapid peeling. Although these low surface energy compounds do show excellent peeling performance, there is residual release agent on the surface of the WPU after demolding, which can hardly be further processed in subsequent processes such as metallization, printing, printing, etching, etc. In addition, although some release agents have good peeling effects, they have certain toxicity, which limits the application field of WPU products and is harmful to the environment and human health.

[0004] Therefore, it is necessary to provide a clean bio-based strippable waterborne polyurethane coating so that the prepared WPU coating has good strippability on low surface energy substrates such as PET while avoiding the use of harmful release agents. Summary of the invention

[0005] In view of some deficiencies in the prior art, the present invention provides a clean bio-based strippable waterborne polyurethane coating and a preparation method and application thereof; the present invention introduces renewable polyol sorbitan monooleate, epoxy soybean oil and fluoroalkyl chain extender into a waterborne polyurethane skeleton, thereby preparing a clean bio-based strippable waterborne polyurethane coating; the clean bio-based strippable waterborne polyurethane coating has a solid content of 30% and a storage stability of more than 6 months; the clean bio-based strippable waterborne polyurethane coating film has a tensile strength of 28.3-37.8MPa and an elongation at break of 432.8-597.3%; the preparation method of the bio-based strippable waterborne polyurethane coating is simple, and a transfer film can be made by a casting or coating process, and then can be used to prepare printed sensors, transparent electrodes, packaging materials, anti-counterfeiting materials or protective materials, and has good practicality.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical means:

[0007] The present invention first provides a clean bio-based strippable waterborne polyurethane coating, wherein the solid content of the clean bio-based strippable waterborne polyurethane coating reaches 30%, the viscosity is 56.2-70.7 mPa.s, and the average particle size ranges from 220-400 nm; the clean bio-based strippable waterborne polyurethane coating is an aqueous polyurethane system with polytetramethylene glycol (PTMG) and sorbitan monooleate (SP) as soft segments, and a fluoroalkyl chain extender and epoxidized soybean oil are introduced into the polyurethane skeleton, so that the prepared bio-based strippable waterborne polyurethane coating has excellent self-stripping performance on low surface energy substrates such as PET.

[0008] The present invention also provides a method for preparing the above-mentioned clean bio-based strippable waterborne polyurethane coating, the preparation method comprising:

[0009] (1) Preparation of clean bio-based strippable waterborne polyurethane (WPU) prepolymer:

[0010] Isophorone diisocyanate (IPDI), PTMG and SP are stirred and mixed uniformly, and then the temperature is raised for heat preservation reaction 1, dimethylolbutyric acid (DMBA) is added and heat preservation reaction 2 is carried out after the reaction is completed, and then the temperature is lowered, and then an organic bismuth catalyst, 1,4-butanediol (BDO) and hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol (HF) are added to carry out heat preservation reaction 3, acetone is added to adjust the viscosity after the reaction is completed, and epoxy soybean oil is added thereto and heat preservation reaction 4 is carried out, and after the reaction is completed, the temperature is lowered and triethylamine (TEA) is added to carry out heat preservation reaction 5, and after the reaction is completed, a clean bio-based strippable waterborne polyurethane (WPU) prepolymer is obtained;

[0011] (2) Preparation of clean bio-based strippable waterborne polyurethane (WPU) coatings:

[0012] Acetone is added to a clean bio-based strippable waterborne polyurethane (WPU) prepolymer to adjust the viscosity, and then deionized water is added and stirred to obtain a clean bio-based strippable waterborne polyurethane (WPU) dispersion;

[0013] The acetone in the clean bio-based strippable waterborne polyurethane (WPU) dispersion is removed to obtain the clean bio-based strippable waterborne polyurethane (WPU) coating.

[0014] Preferably, the mass percentages of raw materials for preparing the clean bio-based strippable water-based polyurethane coating are: 42.32-48.44% of isophorone diisocyanate, 24.22-25.86% of polytetramethylene glycol, 4.84-7.05% of dehydrated sorbitan monooleate, 3.53-3.63% of dihydroxymethylbutyric acid, 0.02-0.03% of organic bismuth catalyst, 3.53-6.66% of 1,4-butanediol, 6.05-9.40% of hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol, 3.63-5.88% of epoxidized soybean oil, and 2.41-2.48% of triethylamine.

[0015] Preferably, the molecular weight of the polytetrahydrofuran diol is 1000 g / mol.

[0016] Preferably, in step (1),

[0017] The conditions of the heat preservation reaction 1 are: reacting at 85-90° C. for 1-2 hours;

[0018] The conditions of the heat preservation reaction 2 are: reacting at 85-90° C. for 1.5-2 hours;

[0019] The conditions of the heat preservation reaction 3 are: reacting at 60-65° C. for 2-3 hours;

[0020] The conditions of the heat preservation reaction 4 are: reacting at 60-65° C. for 1-1.5 hours;

[0021] The conditions of the heat preservation reaction 5 are: reacting at 50° C. for 25 to 40 minutes.

[0022] Preferably, in step (1), the amount of acetone added is 5 to 10 wt % of the clean bio-based strippable waterborne polyurethane (WPU) prepolymer.

[0023] Preferably, in step (1), when the amount of NCO substance in the system reaches 25.72-27.71% (based on the amount of total NCO substance), epoxidized soybean oil is added.

[0024] Preferably, in step (2), the amount of acetone added is 5wt% of the clean bio-based strippable waterborne polyurethane (WPU) prepolymer;

[0025] The temperature of the deionized water is 25-30°C.

[0026] Preferably, in step (2), the stirring treatment is performed at 1000 rpm for 30 min.

[0027] Preferably, in step (2), acetone is removed at a temperature of 35 to 40° C. and a vacuum degree of -0.06 to -0.08 MPa.

[0028] The present invention also provides the use of the clean bio-based strippable waterborne polyurethane coating in the preparation of printed sensors or transparent electrodes.

[0029] The present invention also provides the use of the clean bio-based strippable waterborne polyurethane coating in the preparation of packaging materials, anti-counterfeiting materials or protective materials.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The clean bio-based strippable waterborne polyurethane coating of the present invention will hardly emit VOC into the environment, whether it is WPU dispersion or film, and realizes the clean production of WPU dispersion and film. In addition, the present invention regulates the content of hard segment and soft segment of WPU through unique molecular structure design, and introduces bio-derived polyol SP into the WPU molecular chain. SP has high thermal stability, toughness and hydrolysis stability. The WPU film introduced with SP has good hydrophobicity, resulting in a decrease in the surface energy of the film, which promotes the WPU film to be more easily stripped from low surface energy substrates such as PET.

[0032] During the preparation process of the clean bio-based strippable waterborne polyurethane coating of the present invention, a fluoroalkyl chain extender HF is introduced into the WPU molecular chain, which can enhance the hydrogen bonding effect within the WPU molecule. At the same time, the higher hard segment content of WPU causes more hydrogen bonds to accumulate in the WPU structure. These structural domains are like physical cross-linking points in an amorphous matrix, spontaneously forming network cross-linking, greatly improving the rigidity of the entire WPU chain, and causing the entire macromolecular chain to generate sufficiently high cohesive energy, thereby reducing or eliminating the adhesion of the WPU molecular chain to substrates such as PET.

[0033] During the preparation process of the clean bio-based strippable waterborne polyurethane coating of the present invention, an appropriate amount of renewable epoxy soybean oil is introduced into WPU. Epoxidized soybean oil is introduced into WPU as a plasticizer, which can not only increase the intermolecular distance and free volume of WPU macromolecules, but also promote the separation of WPU film from PET substrate. Therefore, the clean bio-based strippable waterborne polyurethane coating of the present invention can be quickly stripped from low surface energy substrates such as PET without a release agent, and can be used for the production of printed sensors, transparent electrodes, high-end packaging materials, anti-counterfeiting materials, and protective materials.

[0034] The clean bio-based strippable waterborne polyurethane coating prepared by the method of the present invention has a solid content of 30wt%, a viscosity of 56.2-70.7mPa.s, an average particle size range of 220-400nm, a storage stability of more than 6 months, and a surface wetting tension of 35-37mN.m -1 , T-peel strength on PET substrate 0.8~1.1Nm -1 , the tensile strength reaches 28.3-37.8MPa, and the elongation at break reaches 432.8-597.3%. The preparation method of the bio-based strippable waterborne polyurethane coating is simple, and a transfer film can be prepared by a casting or coating process, which has high practicality. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0036] Embodiment 1:

[0037] The amounts of raw materials used in preparing the clean bio-based strippable waterborne polyurethane coating described in this embodiment are as follows:

[0038] Isophorone diisocyanate (IPDI): 36 g;

[0039] 1,4-Butanediol (BDO): 3g;

[0040] Polytetrahydrofuran diol (PTMG): molecular weight 1000 g / mol, mass 22 g;

[0041] Dihydroxymethylbutyric acid (DMBA): 3g;

[0042] Sorbitan monooleate (SP): 6 g;

[0043] Hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol (HF): 8 g;

[0044] Epoxidized soybean oil: 5g;

[0045] Triethylamine (TEA): 2.05 g;

[0046] Organic bismuth catalyst: 0.017 g.

[0047] The specific preparation method is as follows:

[0048] (1) Preparation of clean bio-based strippable waterborne polyurethane (WPU) prepolymer:

[0049] After adding IPDI, PTMG and SP to an oil bath reactor with stirring, nitrogen and condensation and stirring evenly, the reactor temperature was raised to 85°C and kept warm for 2 hours, and then DMBA was added to it in three equal amounts, with an interval of 5 minutes between each addition of DMBA, and the reaction was continued for 1.5 hours after all were added. After the reaction was completed, the reactor temperature was lowered to 60°C, and the organic bismuth catalyst, BDO and HF were added to the reactor, and the reaction was continued for 2 hours. During this process, 5wt% (accounting for the total mass of the prepolymer) of acetone was added to adjust the viscosity of the system. When the amount of NCO substance in the system reached 25.72% (accounting for the amount of total NCO substance), epoxy soybean oil was added to the reactor and the reaction was continued for 1 hour. After the reaction was completed, the reactor temperature was lowered to 50°C and TEA was added to the reaction system for 30 minutes of warm reaction, and then the reaction was stopped to obtain WPU prepolymer.

[0050] (2) Preparation of clean bio-based strippable waterborne polyurethane (WPU) coatings:

[0051] 5 wt% (based on the total mass of the prepolymer) of acetone was added to the clean bio-based strippable waterborne polyurethane (WPU) prepolymer to adjust the viscosity of the system. Deionized water at 25°C was then slowly added to the reactor. The mechanical stirring speed was gradually increased to 1000 rpm. After stirring for 30 minutes, stirring was stopped to obtain a WPU dispersion.

[0052] Then, the acetone in the WPU dispersion was removed under the conditions of a temperature of 35° C. and a vacuum degree of −0.06 MPa, thereby finally obtaining the clean bio-based strippable waterborne polyurethane (WPU) coating.

[0053] Embodiment 2:

[0054] The amounts of raw materials used in preparing the clean bio-based strippable waterborne polyurethane coating described in this embodiment are as follows:

[0055] Isophorone diisocyanate (IPDI): 40 g;

[0056] 1,4-Butanediol (BDO): 5.5 g;

[0057] Polytetrahydrofuran diol (PTMG): molecular weight 1000 g / mol, mass 20 g;

[0058] Dihydroxymethylbutyric acid (DMBA): 3g;

[0059] Sorbitan monooleate (SP): 4g;

[0060] Hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol (HF): 5 g;

[0061] Epoxidized soybean oil: 3g;

[0062] Triethylamine (TEA): 2.05 g;

[0063] Organic bismuth catalyst: 0.024 g.

[0064] The specific preparation method is as follows:

[0065] (1) Preparation of clean bio-based strippable waterborne polyurethane (WPU) prepolymer:

[0066] After adding IPDI, PTMG and SP to an oil bath reactor with stirring, nitrogen and condensation and stirring evenly, the reactor temperature was raised to 90°C for 2h of heat preservation, and then DMBA was added to it in three equal amounts, with an interval of 3 minutes between each addition of DMBA. After all were added, the heat preservation reaction was continued for 1.5h. After the reaction was completed, the reactor temperature was lowered to 60°C, and the organic bismuth catalyst, BDO and HF were added to the reactor, and the reaction was continued for 2h. During this process, 10wt% (accounting for the total mass of the prepolymer) of acetone was added to adjust the viscosity of the system. When the amount of NCO substance in the system reached 27.71% (accounting for the amount of total NCO substance), epoxy soybean oil was added to the reactor, and the heat preservation reaction was continued for 1h. After the reaction was completed, the reactor temperature was lowered to 50°C and TEA was added to the reaction system for 30 minutes of heat preservation reaction, and then the reaction was stopped to obtain WPU prepolymer.

[0067] (2) Preparation of clean bio-based strippable waterborne polyurethane (WPU) coatings:

[0068] 5 wt% (based on the total mass of the prepolymer) of acetone was added to the clean bio-based strippable waterborne polyurethane (WPU) prepolymer to adjust the viscosity of the system. Deionized water at a temperature of 30°C was then slowly added to the reactor. At the same time, the mechanical stirring speed was gradually increased to 1000 rpm. After stirring for 30 minutes, the stirring was stopped to obtain a WPU dispersion.

[0069] Then, the acetone in the WPU dispersion is removed under the conditions of a temperature of 40° C. and a vacuum degree of −0.08 MPa, thereby finally obtaining the clean bio-based strippable waterborne polyurethane (WPU) coating.

[0070] Embodiment 3:

[0071] The amounts of raw materials used in preparing the clean bio-based strippable waterborne polyurethane coating described in this embodiment are as follows:

[0072] Isophorone diisocyanate (IPDI): 37 g;

[0073] 1,4-Butanediol (BDO): 4g;

[0074] Polytetrahydrofuran diol (PTMG): molecular weight 1000 g / mol, mass 21 g;

[0075] Dihydroxymethylbutyric acid (DMBA): 3g;

[0076] Sorbitan monooleate (SP): 5g;

[0077] Hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol (HF): 7 g;

[0078] Epoxidized soybean oil: 4g;

[0079] Triethylamine (TEA): 2.05 g;

[0080] Organic bismuth catalyst: 0.016 g.

[0081] The specific preparation method is as follows:

[0082] (1) Preparation of clean bio-based strippable waterborne polyurethane (WPU) prepolymer:

[0083] After adding IPDI, PTMG and SP to an oil bath reactor with stirring, nitrogen and condensation and stirring evenly, the reactor temperature was raised to 87°C and kept warm for 2 hours, and then DMBA was added three times in equal amounts, with an interval of 4 minutes between each addition of DMBA, and the reaction was continued for 1.5 hours after all were added. After the reaction was completed, the reactor temperature was lowered to 63°C, and the organic bismuth catalyst, BDO and HF were added to the reactor, and the reaction was continued for 2 hours. During this process, 8wt% (accounting for the total mass of the prepolymer) of acetone was added to adjust the viscosity of the system. When the amount of NCO substance in the system reached 25.83% (accounting for the amount of total NCO substance), epoxy soybean oil was added to the reactor and the reaction was continued for 1 hour. After the reaction was completed, the reactor temperature was lowered to 50°C and TEA was added to the reaction system for 30 minutes of warm reaction, and then the reaction was stopped to obtain WPU prepolymer.

[0084] (2) Preparation of clean bio-based strippable waterborne polyurethane (WPU) coatings:

[0085] 5 wt% (based on the total mass of the prepolymer) of acetone was added to the clean bio-based strippable waterborne polyurethane (WPU) prepolymer to adjust the viscosity of the system. Deionized water at 27°C was then slowly added to the reactor. The mechanical stirring speed was gradually increased to 1000 rpm. After stirring for 30 minutes, stirring was stopped to obtain a WPU dispersion.

[0086] Then, the acetone in the WPU dispersion was removed under the conditions of a temperature of 36° C. and a vacuum degree of −0.07 MPa, thereby finally obtaining the clean bio-based strippable waterborne polyurethane (WPU) coating.

[0087] Embodiment 4:

[0088] This example tests the solid content, average particle size, viscosity and storage stability of the clean bio-based exfoliative waterborne polyurethane dispersions prepared in Examples 1 to 3. The specific inspection method is as follows:

[0089] Solid content determination: weigh a certain amount of waterborne polyurethane dispersion (M 1 ) in a 40 mm diameter watch glass, and put it in a 110 ° C oven to dry until the weight is constant. The mass of the remaining solids in the watch glass (M 2 ). Calculate the solid content according to the following formula:

[0090] C(%)=M 2 / M 1 ×100%

[0091] Wherein: C—solid content of waterborne polyurethane resin dispersion (%).

[0092] Average particle size determination: The particle size was tested by dynamic light scattering method. The average particle size of the aqueous polyurethane dispersion was measured by a particle size analyzer at 25° C. Before the test, the polyurethane dispersion was first diluted with distilled water to a concentration of 0.5%.

[0093] Storage stability determination: Place a certain amount of polyurethane dispersion in a centrifuge tube, put it into a centrifuge, and centrifuge it for 15 minutes at a temperature of 25°C and a rotation speed of 3000r / min. Observe the state of the dispersion and evaluate its stability. If there is no stratification or precipitation, it can be considered stable at room temperature for 6 months.

[0094] Viscosity measurement: The viscosity of the waterborne polyurethane dispersion was measured using a digital viscometer. The test was conducted at 25°C and a rotor speed of 100 rpm.

[0095] The results of the investigation are shown in Table 1:

[0096] Table 1. Properties of clean bio-based strippable waterborne polyurethane dispersions

[0097] sample Average particle size (nm) Solid content (%) Viscosity(mPa.s) Storage stability Example 1 360.7±5 30.3±0.4 58.3±0.1 >6 months Example 2 319.2±4 30.1±0.2 63.4±0.1 >6 months Example 3 301.5±4 30.4±0.4 66.7±0.1 >6 months

[0098] As can be seen from Table 1, the average particle size of the clean bio-based strippable waterborne polyurethane dispersion in the example is 301.5-360.7nm, the solid content is 30.1-30.4%, the viscosity is 58.3-66.7mPa.s, and the storage stability is greater than 6 months. Compared with similar products, the average particle size of the WPU dispersion in the present invention is larger, which can prevent the WPU particles from penetrating into the natural pores on the surface of the substrate, thereby avoiding the formation of strong bonding points. Secondly, the dispersion viscosity is low, which is conducive to the construction of subsequent casting and coating processes.

[0099] In this example, a clean bio-based peelable waterborne polyurethane film was prepared, and the surface wetting tension, tensile strength, elongation at break and T-peel strength of the clean bio-based peelable waterborne polyurethane film were investigated. The specific investigation method is as follows:

[0100] T-peel strength measurement: The T-peel strength of the waterborne polyurethane film on the PET substrate was measured using a peel tester. The test temperature was 23±2°C and the relative humidity was 50±5%. The instrument was set at a peel speed of 300mm / min and a peel angle of 180°.

[0101] Surface wetting tension measurement: The surface wetting tension of waterborne polyurethane film was measured according to the national standard GB 14216-2008-T.

[0102] Tensile property determination: The tensile property of the waterborne polyurethane film was determined using an electronic universal testing machine at room temperature. The film sample was cut into three identical specimens (10 mm × 30 mm × 0.02 mm) and tested at a tensile speed of 50 mm / min to obtain tensile property data.

[0103] The results of the investigation are shown in Table 2:

[0104] Table 2. Properties of clean bio-based peelable waterborne polyurethane films

[0105] sample <![CDATA[Surface wetting tension (mN.m -1 )]]> Tensile strength(MPa) <![CDATA[T - Peel Strength (N.m -1 )]]> Elongation at break (%) Example 1 35.7±1 37.2±1 0.8±0.1 547.3±10 Example 2 36.3±1 34.6±1 1.1±0.2 445.1±10 Example 3 36.8±1 36.1±1 1.0±0.1 478.9±10

[0106] It can be seen from Table 2 that the surface wetting tension of the clean bio-based peelable waterborne polyurethane film in the example is 35.7-36.8 mN.m -1 , tensile strength 36.1~37.2MPa, elongation at break 478.9~547.3%, T-peel strength 0.8~1.1Nm -1 However, in the prior art, the T-peel strength does not reach 0.8-1.1 Nm without a release agent. -1 In comparison, the clean bio-based peelable waterborne polyurethane described in the present invention has a lower peel strength, and the tensile properties of the film are also better than similar products.

[0107] In summary, the clean bio-based strippable waterborne polyurethane coating prepared in the present invention has a solid content of 30wt%, a viscosity of 56.2-70.7mPa.s, an average particle size range of 220-400nm, a storage stability of >6 months, and a surface wetting tension of 35-37mN.m -1 , the T-peel strength on the PET substrate is 0.8-1.1Nm-1, the tensile strength reaches 28.3-37.8MPa, and the elongation at break reaches 432.8-597.3%; the preparation method of the bio-based peelable waterborne polyurethane coating is simple, and a transfer film can be made by a casting or coating process, and then can be used to prepare printed sensors, transparent electrodes, packaging materials, anti-counterfeiting materials or protective materials, and has good practicality.

[0108] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A method for preparing a clean bio-based strippable waterborne polyurethane coating, characterized in that: The preparation method comprises: (1) Preparation of clean bio-based strippable waterborne polyurethane prepolymer: Isophorone diisocyanate, polytetrahydrofuran diol and dehydrated sorbitan monooleate are stirred and mixed uniformly, and then the temperature is raised for heat preservation reaction 1, after the reaction is completed, dimethylolbutyric acid is added and heat preservation reaction 2 is carried out, after the reaction is completed, the temperature is lowered, and then an organic bismuth catalyst, 1,4-butanediol and hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol are added for heat preservation reaction 3, after the reaction is completed, acetone is added to adjust the viscosity, and epoxy soybean oil is added thereto and heat preservation reaction 4 is carried out, after the reaction is completed, the temperature is lowered and triethylamine is added for heat preservation reaction 5, after the reaction is completed, a clean bio-based strippable waterborne polyurethane prepolymer is obtained; (2) Preparation of clean bio-based strippable waterborne polyurethane coatings: Acetone is added to the clean bio-based strippable waterborne polyurethane prepolymer to adjust the viscosity, and then deionized water is added for stirring to obtain a clean bio-based strippable waterborne polyurethane dispersion; The acetone in the clean bio-based strippable waterborne polyurethane dispersion is removed to obtain the clean bio-based strippable waterborne polyurethane coating.

2. The method for preparing a clean bio-based strippable waterborne polyurethane coating according to claim 1, characterized in that: The mass percentages of raw materials for preparing the clean bio-based strippable waterborne polyurethane coating are as follows: 42.32-48.44% of isophorone diisocyanate, 24.22-25.86% of polytetramethylene glycol, 4.84-7.05% of dehydrated sorbitan monooleate, 3.53-3.63% of dihydroxymethylbutyric acid, 0.02-0.03% of organic bismuth catalyst, 3.53-6.66% of 1,4-butanediol, 6.05-9.40% of hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol, 3.63-5.88% of epoxidized soybean oil, and 2.41-2.48% of triethylamine.

3. The method for preparing a clean bio-based strippable waterborne polyurethane coating according to claim 2, characterized in that: The molecular weight of the polytetramethylene ether glycol is 1000 g / mol.

4. The method for preparing a clean bio-based strippable waterborne polyurethane coating according to claim 1, characterized in that: In step (1), The conditions of the heat preservation reaction 1 are: reacting at 85-90° C. for 1-2 hours; The conditions of the heat preservation reaction 2 are: reacting at 85-90° C. for 1.5-2 hours; The conditions of the heat preservation reaction 3 are: reacting at 60-65° C. for 2-3 hours; The conditions of the heat preservation reaction 4 are: reacting at 60-65° C. for 1-1.5 hours; The conditions of the heat preservation reaction 5 are: reacting at 50° C. for 25 to 40 minutes.

5. The method for preparing a clean bio-based strippable waterborne polyurethane coating according to claim 1, characterized in that: In step (1), the amount of acetone added is 5-10wt% of the clean bio-based strippable waterborne polyurethane prepolymer; When the amount of NCO substance in the system reaches 25.72~27.71% of the total NCO substance, epoxidized soybean oil is added.

6. The method for preparing a clean bio-based strippable waterborne polyurethane coating according to claim 1, characterized in that: In step (2), the amount of acetone added is 5wt% of the clean bio-based strippable waterborne polyurethane prepolymer; The temperature of the deionized water is 25-30°C.

7. The method for preparing a clean bio-based strippable waterborne polyurethane coating according to claim 1, characterized in that: In step (2), the stirring treatment condition is stirring at 1000 rpm for 30 minutes.

8. The clean bio-based strippable waterborne polyurethane coating prepared by the method according to any one of claims 1 to 7, characterized in that: The clean bio-based strippable waterborne polyurethane coating has a solid content of 30%, a viscosity of 56.2-70.7 mPa.s, and an average particle size range of 220-400 nm; The clean bio-based strippable waterborne polyurethane coating is a waterborne polyurethane system with polytetramethylene ether glycol and sorbitan monooleate as soft segments, and epoxy soybean oil is introduced into the polyurethane skeleton.

9. Use of the clean bio-based strippable waterborne polyurethane coating according to claim 8 in the preparation of printed sensors or transparent electrodes.

10. Use of the clean bio-based strippable waterborne polyurethane coating according to claim 8 in the preparation of packaging materials, anti-counterfeiting materials or protective materials.