Polyurethane pressure-sensitive adhesive for protective film and preparation method thereof

Abstract

The invention discloses a polyurethane pressure-sensitive adhesive for a protective film and a preparation method of the polyurethane pressure-sensitive adhesive, and belongs to the technical field of pressure-sensitive adhesives. According to the invention, fluorinated acrylate is introduced into a polyol structure, so that not only is the viscosity of the polyurethane pressure-sensitive adhesive enhanced, but also excellent hydrophobicity and weather resistance are obtained. And the crosslinking density of the polyurethane pressure-sensitive adhesive is controlled through the combination and proportion of different crosslinking agents, so that the lasting viscosity of the pressure-sensitive adhesive is optimized.

Description

Technical Field

[0001] The invention belongs to the technical field of pressure-sensitive adhesives and relates to a polyurethane pressure-sensitive adhesive for a protective film and a preparation method thereof. Background Art

[0002] Pressure-sensitive adhesives are a type of special adhesive that can achieve adhesion under slight external pressure. They are widely used in labels, tapes, protective films, medical patches and other fields. The adhesive properties of pressure-sensitive adhesives enable them to be quickly pasted and peeled without the need for heating, solvents or other activation processes, making them extremely convenient in daily life and industrial applications. According to their chemical composition and properties, pressure-sensitive adhesives can be divided into several main types: rubber type, acrylate type, silicone type and polyurethane type. Rubber-type pressure-sensitive adhesives usually have good initial adhesion and peel strength, but poor weather resistance; acrylate-type pressure-sensitive adhesives are known for their excellent weather resistance and transparency, and are suitable for outdoor applications and electronic products. However, with the increasing requirements for the performance of pressure-sensitive adhesives, polyurethane pressure-sensitive adhesives have gradually attracted attention due to their unique performance advantages. Polyurethane pressure-sensitive adhesives combine the excellent properties of polyurethane materials, provide higher flexibility, wear resistance and chemical resistance, and have become an increasingly important member of the pressure-sensitive adhesive market.

[0003] Polyurethane pressure-sensitive adhesives are based on polyurethane polymers and have significant advantages due to the diversity and adjustability of their chemical structure. The urethane groups in the polyurethane molecular chain give the material excellent elasticity and flexibility, allowing polyurethane pressure-sensitive adhesives to maintain good adhesion properties at lower temperatures. In addition, the polar structure of polyurethane materials helps to improve the cohesive strength and adhesion of pressure-sensitive adhesives, making them suitable for use on various substrates. Polyurethane pressure-sensitive adhesives also excel in transparency, wear resistance, and chemical corrosion resistance, and can maintain stable performance under harsh environmental conditions. Due to these advantages, polyurethane pressure-sensitive adhesives are widely used in industries such as automobiles, electronics, construction, and medical, especially in applications that require high performance and high reliability.

[0004] Although polyurethane pressure-sensitive adhesives have many advantages, there are still some technical defects and challenges in their preparation process. First, the synthesis of polyurethane pressure-sensitive adhesives involves multiple chemical reactions and process steps, which may lead to a complex production process and high costs. Secondly, polyurethane materials are sensitive to moisture and temperature changes, which may affect their performance in practical applications, especially in high humidity or extreme temperature environments. In addition, the initial adhesion and peel strength of polyurethane pressure-sensitive adhesives need to be finely adjusted in the formula design to meet the needs of specific applications, which increases the difficulty of research and development and production. Summary of the invention

[0005] The invention provides a polyurethane pressure-sensitive adhesive for a protective film and a preparation method thereof, and belongs to the technical field of pressure-sensitive adhesives. The invention not only enhances the viscosity of the polyurethane pressure-sensitive adhesive by introducing fluorinated acrylate into a polyol structure, but also obtains excellent hydrophobic and weather-resistant properties. The cross-linking density of the polyurethane pressure-sensitive adhesive is controlled by combining and proportioning different cross-linking agents, thereby optimizing the long-lasting viscosity of the pressure-sensitive adhesive.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A polyurethane pressure-sensitive adhesive for a protective film comprises the following raw materials in parts by weight: 40-60 parts by weight of a modified polyol, 20-40 parts by weight of an isocyanate, 5-15 parts by weight of a chain extender, 0.1-1 parts by weight of a catalyst, and 1-5 parts by weight of a cross-linking agent.

[0008] As a preferred technical solution of the present invention, the modified polyol is a fluorinated acrylate modified polyol, and the preparation method is: dissolving the polyol in a solvent, then adding a fluorinated acrylate monomer and an initiator, stirring at 60-80°C for 4-8h, adding a terminator, and then preparing the modified polyol by precipitation washing.

[0009] As a preferred technical solution of the present invention, the fluorinated acrylate monomer is any one of perfluorooctyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, and (1,1,1,3,3,3-hexafluoro-2-phenylpropane-2-yl) methacrylate; the polyol is any one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran diol; the solvent is toluene or dichloromethane; the initiator is benzoyl peroxide or azobisisobutyronitrile; and the terminator is hydroquinone; the mass ratio of the fluorinated acrylate monomer, the polyol, the solvent, the initiator, and the terminator is 10-30:40-70:200-500:1-5:0.1-1.

[0010] As a preferred technical solution of the present invention, the isocyanate is any one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate.

[0011] As a preferred technical solution of the present invention, the chain extender is any one of 1,4-butanediol, ethylene glycol, diethanolamine, and dimethylglyoxime.

[0012] As a preferred technical solution of the present invention, the catalyst is dibutyltin dilaurate.

[0013] As a preferred technical solution of the present invention, the cross-linking agent is polycarbodiimide, triglycidyl isocyanurate and a silane coupling agent, and the mass ratio of the polycarbodiimide, triglycidyl isocyanurate and the silane coupling agent is 5-7:2-4:1-2.

[0014] Furthermore, the method for preparing the polyurethane pressure-sensitive adhesive for a protective film comprises the following steps:

[0015] (1) Dissolve the modified polyol in solvents of toluene and butanone and heat to 50-80°C;

[0016] (2) adding isocyanate and catalyst dropwise and stirring for 3-5 hours to obtain a prepolymer;

[0017] (3) Add the chain extender to the prepolymer and stir at 70-80°C for 4-6 hours;

[0018] (4) adding a crosslinking agent and stirring at 30-60° C. for 1-3 h;

[0019] (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

[0020] As a preferred technical solution of the present invention, the mass ratio of the modified polyol to the solvent is 1:5-10; the mass ratio of toluene to butanone is 1:1-2.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention combines the advantages of fluoride and acrylate by introducing fluorinated acrylate into polyol to prepare polyurethane pressure-sensitive adhesive, thereby significantly improving the performance of the material. The chemical inertness of the fluorine element enhances the chemical resistance and weather resistance of the material, resists ultraviolet and oxidative damage, and extends the service life. The acrylate part improves the viscosity of the material through its flexibility and polarity. Combined with these characteristics, the introduction of fluorinated acrylate not only improves the adhesion performance of the polyurethane pressure-sensitive adhesive, provides low surface energy, and makes the colloid have excellent hydrophobicity and oleophobicity, improves its stability and durability in various harsh environments, and can also maintain good adhesion in humid and oily environments.

[0023] (2) The present invention controls the crosslinking density of the polyurethane pressure-sensitive adhesive by combining polycarbodiimide, triglycidyl isocyanurate and silane coupling agent, thereby optimizing the long-lasting adhesiveness of the pressure-sensitive adhesive. Polycarbodiimide improves hydrolysis resistance and ensures that the colloid remains stable in a humid environment; triglycidyl isocyanurate enhances mechanical strength and chemical stability through high crosslinking density; and silane coupling agent improves adhesion between organic and inorganic substrates. This combination not only expands the application scope of the pressure-sensitive adhesive, but also improves its weather resistance and overall durability. DETAILED DESCRIPTION

[0024] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0025] In the following examples and comparative examples, the polyethylene glycol was purchased from Guangzhou Bolun Chemical Technology Co., Ltd. with the item number PEG600; the silane coupling agent was purchased from Kangjin Chemical Co., Ltd. with the model number KH-560; the polycarbodiimide was purchased from Deyu Co., Ltd. with the item number 0228-330; and the polypropylene glycol was purchased from Hai'an Petrochemical Plant in Jiangsu Province with the item number 00-2.

[0026] Example 1

[0027] A polyurethane pressure-sensitive adhesive for a protective film comprises the following raw materials in parts by weight: 60 parts by weight of a modified polyol, 30 parts by weight of an isocyanate, 10 parts by weight of a chain extender, 0.5 parts by weight of a catalyst, and 2 parts by weight of a cross-linking agent.

[0028] The modified polyol is a fluorinated acrylate modified polyol, and the preparation method is as follows: dissolving the polyol in a solvent, then dropping a fluorinated acrylate monomer and an initiator, stirring at 70° C. for 6 hours, adding a terminator, and then preparing the modified polyol by precipitation and washing.

[0029] The fluorinated acrylate monomer is perfluorooctyl acrylate, the polyol is polyethylene glycol, the solvent is toluene, the initiator is benzoyl peroxide, and the terminator is hydroquinone; the mass ratio of the fluorinated acrylate monomer, the polyol, the solvent, the initiator, and the terminator is 20:60:200:2:0.5.

[0030] The isocyanate is toluene diisocyanate.

[0031] The chain extender is 1,4-butanediol.

[0032] The catalyst is dibutyltin dilaurate.

[0033] The cross-linking agent is polycarbodiimide, triglycidyl isocyanurate and a silane coupling agent, and the mass ratio of the polycarbodiimide, triglycidyl isocyanurate and the silane coupling agent is 6:3:1.

[0034] The method for preparing a polyurethane pressure-sensitive adhesive for a protective film comprises the following steps:

[0035] (1) Dissolve the modified polyol in solvents of toluene and butanone and heat to 60°C;

[0036] (2) adding isocyanate and catalyst dropwise and stirring for 4 hours to obtain a prepolymer;

[0037] (3) Add the chain extender to the prepolymer and stir at 70°C for 5 hours;

[0038] (4) Add cross-linking agent and stir at 40°C for 2 h;

[0039] (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

[0040] As a preferred technical solution of the present invention, the mass ratio of the modified polyol to the solvent is 1:6; the mass ratio of toluene to butanone is 1:2.

[0041] Example 2

[0042] A polyurethane pressure-sensitive adhesive for a protective film comprises the following raw materials in parts by weight: 40 parts by weight of a modified polyol, 20 parts by weight of an isocyanate, 5 parts by weight of a chain extender, 0.2 parts by weight of a catalyst, and 1 part by weight of a cross-linking agent.

[0043] The modified polyol is a fluorinated acrylate modified polyol, and the preparation method is as follows: dissolving the polyol in a solvent, then dropping a fluorinated acrylate monomer and an initiator, stirring at 60° C. for 8 hours, adding a terminator, and then preparing the modified polyol by precipitation and washing.

[0044] The fluorinated acrylate monomer is trifluoroethyl methacrylate, the polyol is polypropylene glycol, the solvent is dichloromethane, the initiator is azobisisobutyronitrile, and the terminator is hydroquinone; the mass ratio of the fluorinated acrylate monomer, the polyol, the solvent, the initiator, and the terminator is 10:40:300:5:1.

[0045] The isocyanate is diphenylmethane diisocyanate.

[0046] The chain extender is ethylene glycol.

[0047] The catalyst is dibutyltin dilaurate.

[0048] The cross-linking agent is polycarbodiimide, triglycidyl isocyanurate and a silane coupling agent, and the mass ratio of the polycarbodiimide, triglycidyl isocyanurate and the silane coupling agent is 7:4:2.

[0049] The method for preparing a polyurethane pressure-sensitive adhesive for a protective film comprises the following steps:

[0050] (1) Dissolve the modified polyol in solvents of toluene and butanone and heat to 80°C;

[0051] (2) adding isocyanate and catalyst dropwise and stirring for 3 h to obtain a prepolymer;

[0052] (3) Add the chain extender to the prepolymer and stir at 80°C for 4 hours;

[0053] (4) Add cross-linking agent and stir at 30°C for 3 h;

[0054] (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

[0055] The mass ratio of the modified polyol to the solvent is 1:5; the mass ratio of toluene to butanone is 1:1.

[0056] Comparative Example 1

[0057] A polyurethane pressure-sensitive adhesive for a protective film comprises the following raw materials in parts by weight: 60 parts by weight of a polyol, 30 parts by weight of an isocyanate, 10 parts by weight of a chain extender, 0.5 parts by weight of a catalyst, and 2 parts by weight of a cross-linking agent.

[0058] The polyol is polyethylene glycol.

[0059] The isocyanate is toluene diisocyanate.

[0060] The chain extender is 1,4-butanediol.

[0061] The catalyst is dibutyltin dilaurate.

[0062] The cross-linking agent is polycarbodiimide, triglycidyl isocyanurate and a silane coupling agent, and the mass ratio of the polycarbodiimide, triglycidyl isocyanurate and the silane coupling agent is 6:3:1.

[0063] The method for preparing a polyurethane pressure-sensitive adhesive for a protective film comprises the following steps:

[0064] (1) Dissolve the polyol in solvents of toluene and butanone and heat to 60°C;

[0065] (2) adding isocyanate and catalyst dropwise and stirring for 4 hours to obtain a prepolymer;

[0066] (3) Add the chain extender to the prepolymer and stir at 70°C for 5 hours;

[0067] (4) Add cross-linking agent and stir at 40°C for 2 h;

[0068] (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

[0069] As a preferred technical solution of the present invention, the mass ratio of the modified polyol to the solvent is 1:6; the mass ratio of toluene to butanone is 1:2.

[0070] Comparative Example 2

[0071] A polyurethane pressure-sensitive adhesive for a protective film comprises the following raw materials in parts by weight: 60 parts by weight of a modified polyol, 30 parts by weight of an isocyanate, 10 parts by weight of a chain extender, 0.5 parts by weight of a catalyst, and 2 parts by weight of a cross-linking agent.

[0072] The modified polyol is a fluorinated acrylate modified polyol, and the preparation method is as follows: dissolving the polyol in a solvent, then dropping a fluorinated acrylate monomer and an initiator, stirring at 70° C. for 6 hours, adding a terminator, and then preparing the modified polyol by precipitation and washing.

[0073] The fluorinated acrylate monomer is perfluorooctyl acrylate, the polyol is polyethylene glycol, the solvent is toluene, the initiator is benzoyl peroxide, and the terminator is hydroquinone; the mass ratio of the fluorinated acrylate monomer, the polyol, the solvent, the initiator, and the terminator is 20:60:200:2:0.5.

[0074] The isocyanate is toluene diisocyanate.

[0075] The chain extender is 1,4-butanediol.

[0076] The catalyst is dibutyltin dilaurate.

[0077] The cross-linking agent is triglycidyl isocyanurate and a silane coupling agent, and the mass ratio of the triglycidyl isocyanurate to the silane coupling agent is 9:1.

[0078] The method for preparing a polyurethane pressure-sensitive adhesive for a protective film comprises the following steps:

[0079] (1) Dissolve the modified polyol in solvents of toluene and butanone and heat to 60°C;

[0080] (2) adding isocyanate and catalyst dropwise and stirring for 4 hours to obtain a prepolymer;

[0081] (3) Add the chain extender to the prepolymer and stir at 70°C for 5 hours;

[0082] (4) Add cross-linking agent and stir at 40°C for 2 h;

[0083] (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

[0084] As a preferred technical solution of the present invention, the mass ratio of the modified polyol to the solvent is 1:6; the mass ratio of toluene to butanone is 1:2.

[0085] Comparative Example 3

[0086] A polyurethane pressure-sensitive adhesive for a protective film comprises the following raw materials in parts by weight: 60 parts by weight of a modified polyol, 30 parts by weight of an isocyanate, 10 parts by weight of a chain extender, 0.5 parts by weight of a catalyst, and 2 parts by weight of a cross-linking agent.

[0087] The modified polyol is a fluorinated acrylate modified polyol, and the preparation method is as follows: dissolving the polyol in a solvent, then dropping a fluorinated acrylate monomer and an initiator, stirring at 70° C. for 6 hours, adding a terminator, and then preparing the modified polyol by precipitation and washing.

[0088] The fluorinated acrylate monomer is perfluorooctyl acrylate, the polyol is polyethylene glycol, the solvent is toluene, the initiator is benzoyl peroxide, and the terminator is hydroquinone; the mass ratio of the fluorinated acrylate monomer, the polyol, the solvent, the initiator, and the terminator is 20:60:200:2:0.5.

[0089] The isocyanate is toluene diisocyanate.

[0090] The chain extender is 1,4-butanediol.

[0091] The catalyst is dibutyltin dilaurate.

[0092] The cross-linking agent is polycarbodiimide and a silane coupling agent, and the mass ratio of the polycarbodiimide to the silane coupling agent is 6:4.

[0093] The method for preparing a polyurethane pressure-sensitive adhesive for a protective film comprises the following steps:

[0094] (1) Dissolve the modified polyol in solvents of toluene and butanone and heat to 60°C;

[0095] (2) adding isocyanate and catalyst dropwise and stirring for 4 hours to obtain a prepolymer;

[0096] (3) Add the chain extender to the prepolymer and stir at 70°C for 5 hours;

[0097] (4) Add cross-linking agent and stir at 40°C for 2 h;

[0098] (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

[0099] As a preferred technical solution of the present invention, the mass ratio of the modified polyol to the solvent is 1:6; the mass ratio of toluene to butanone is 1:2.

[0100] Comparative Example 4

[0101] A polyurethane pressure-sensitive adhesive for a protective film comprises the following raw materials in parts by weight: 60 parts by weight of a modified polyol, 30 parts by weight of an isocyanate, 10 parts by weight of a chain extender, 0.5 parts by weight of a catalyst, and 2 parts by weight of a cross-linking agent.

[0102] The modified polyol is a fluorinated acrylate modified polyol, and the preparation method is as follows: dissolving the polyol in a solvent, then dropping a fluorinated acrylate monomer and an initiator, stirring at 70° C. for 6 hours, adding a terminator, and then preparing the modified polyol by precipitation and washing.

[0103] The fluorinated acrylate monomer is perfluorooctyl acrylate, the polyol is polyethylene glycol, the solvent is toluene, the initiator is benzoyl peroxide, and the terminator is hydroquinone; the mass ratio of the fluorinated acrylate monomer, the polyol, the solvent, the initiator, and the terminator is 20:60:200:2:0.5.

[0104] The isocyanate is toluene diisocyanate.

[0105] The chain extender is 1,4-butanediol.

[0106] The catalyst is dibutyltin dilaurate.

[0107] The cross-linking agent is polycarbodiimide and triglycidyl isocyanurate, and the mass ratio of the polycarbodiimide to triglycidyl isocyanurate is 7:3.

[0108] The method for preparing a polyurethane pressure-sensitive adhesive for a protective film comprises the following steps:

[0109] (1) Dissolve the modified polyol in solvents of toluene and butanone and heat to 60°C;

[0110] (2) adding isocyanate and catalyst dropwise and stirring for 4 hours to obtain a prepolymer;

[0111] (3) Add the chain extender to the prepolymer and stir at 70°C for 5 hours;

[0112] (4) Add cross-linking agent and stir at 40°C for 2 h;

[0113] (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

[0114] As a preferred technical solution of the present invention, the mass ratio of the modified polyol to the solvent is 1:6; the mass ratio of toluene to butanone is 1:2.

[0115] Performance Test:

[0116] Adhesion test: Perform 180° peel strength test according to the method described in GB / T 2792-2014. The specific test method is as follows: evenly coat the polyurethane pressure-sensitive adhesive on the protective film, the dry adhesive thickness is 20μm, cut into 25mm×150mm wide samples, spread the sample on the glass, use a 2kg rubber roller to roll back and forth 3 times, let it stand at 23±2℃ for 20min, use a universal tensile testing machine, pull it apart at an angle of 180° and a speed of 300mm / min, and take the average value of the peel strength between 20 and 80mm displacement.

[0117] Persistent adhesiveness test: According to the peel strength test, the protective film rolled on the glass is placed at 85℃ 、 After 168 hours in an environment of 85% RH, the peeling force test was performed after the samples returned to room temperature.

[0118]

[0119] The test results show that introducing fluorinated acrylate into the polyol structure and combining polycarbodiimide, triglycidyl isocyanurate and silane coupling agent as a cross-linking agent not only enhances the viscosity of the pressure-sensitive adhesive, but also maintains good viscosity after high temperature and high humidity treatment.

[0120] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any indirect modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A polyurethane pressure-sensitive adhesive for a protective film, characterized in that: The invention comprises the following raw materials in parts by weight: 40-60 parts by weight of modified polyol, 20-40 parts by weight of isocyanate, 5-15 parts by weight of chain extender, 0.1-1 parts by weight of catalyst and 1-5 parts by weight of crosslinking agent.

2. The polyurethane pressure-sensitive adhesive for protective film according to claim 1, characterized in that: The modified polyol is a fluorinated acrylate modified polyol, and the preparation method is as follows: dissolving the polyol in a solvent, then dropping a fluorinated acrylate monomer and an initiator, stirring at 60-80° C. for 4-8 hours, adding a terminator, and then preparing the modified polyol by precipitation and washing.

3. The polyurethane pressure-sensitive adhesive for protective film according to claim 2, characterized in that: The fluorinated acrylate monomer is any one of perfluorooctyl acrylate, trifluoroethyl methacrylate, hexafluoroisopropyl methacrylate, and (1,1,1,3,3,3-hexafluoro-2-phenylpropane-2-yl) methacrylate; the polyol is any one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran diol; the solvent is toluene or dichloromethane; the initiator is benzoyl peroxide or azobisisobutyronitrile; and the terminator is hydroquinone; and the mass ratio of the fluorinated acrylate monomer, the polyol, the solvent, the initiator, and the terminator is 10-30:40-70:200-500:1-5:0.1-1.

4. The polyurethane pressure-sensitive adhesive for protective film according to claim 1, characterized in that: The isocyanate is any one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate.

5. The polyurethane pressure-sensitive adhesive for protective film according to claim 1, characterized in that: The chain extender is any one of 1,4-butanediol, ethylene glycol, diethanolamine and dimethylglyoxime.

6. The polyurethane pressure-sensitive adhesive for protective film according to claim 1, characterized in that: The catalyst is dibutyltin dilaurate.

7. The polyurethane pressure-sensitive adhesive for protective film according to claim 1, characterized in that: The cross-linking agent is polycarbodiimide, triglycidyl isocyanurate and a silane coupling agent, and the mass ratio of the polycarbodiimide, triglycidyl isocyanurate and the silane coupling agent is 5-7:2-4:1-2.

8. A method for preparing the polyurethane pressure-sensitive adhesive for protective film according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Dissolve the modified polyol in solvents of toluene and butanone and heat to 50-80°C; (2) adding isocyanate and catalyst dropwise and stirring for 3-5 hours to obtain a prepolymer; (3) Add the chain extender to the prepolymer and stir at 70-80°C for 4-6 hours; (4) adding a crosslinking agent and stirring at 30-60° C. for 1-3 h; (5) removing the solvent by distillation under reduced pressure to obtain a polyurethane pressure-sensitive adhesive.

9. The method for preparing a polyurethane pressure-sensitive adhesive for a protective film according to claim 8, characterized in that: The mass ratio of the modified polyol to the solvent is 1:5-10; the mass ratio of the toluene to butanone is 1:1-2.

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