Solvent-free polyurethane composition, solvent-free polyurethane protective film and preparation method of solvent-free polyurethane protective film

Abstract

The invention provides a solvent-free polyurethane composition, a solvent-free polyurethane protective film and a preparation method of the solvent-free polyurethane composition and the solvent-free polyurethane protective film, and relates to the field of high polymer materials. The solvent-free polyurethane composition is prepared from the following raw materials in parts by mass: 50 to 70 parts of polyether polyol, 10 to 20 parts of hydroxyl-terminated polybutadiene, 0.5 to 1 part of an antioxidant, 13 to 17 parts of isocyanate, 0.1 to 0.5 part of a catalyst, 0.5 to 1 part of a coupling agent, 3 to 8 parts of hydroxyethyl acrylate and 3 to 6 parts of an initiator, the number-average molecular weight of the initiator is 3500 to 5500. The composition is solvent-free and zero in VOC (volatile organic compound) emission, and meets the requirements of green and environment-friendly production; the odor is low, and small molecule residues are low; uV fast curing can be realized, and the production efficiency is high; the crosslinking density is high, and high and low temperature resistance and weather resistance are excellent; the coating property is excellent, slit coating can be used, and the coating thickness error is small; and the produced PU protective film finished product is easy to peel off a pasted object and has no adhesive residue.

Description

Technical Field

[0001] This application relates to the field of polymer materials, and more particularly to a solvent-free polyurethane composition and a solvent-free polyurethane protective film and a method for preparing the same. Background Technology

[0002] Traditional solvent-based PU protective films have problems such as volatile organic compound (VOC) residue, strong odor after curing, small molecule migration, high curing energy consumption, and solvent residue. Especially in the vehicle environment, the volatile small molecules released under high temperature conditions not only affect the driving experience, but may also have a negative impact on the air quality inside the vehicle.

[0003] Existing UV-curable protective films generally have the following problems: (1) The use of a solvent system presents a VOC emission problem; (2) The small molecule monomers remaining in the photoinitiator and prepolymer can easily lead to problems such as strong odor, yellowing and poor weather resistance in the finished product; (3) Insufficient crosslinking density leads to poor resistance to high temperature, damp heat and ultraviolet radiation, and is prone to residual glue or degumming. (4) Directly mixing monomers with photoinitiators can easily lead to uneven curing and excessive monomer residue.

[0004] Therefore, there is an urgent need to provide a PU protective film to solve the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a solvent-free polyurethane composition and a solvent-free polyurethane protective film, and a method for preparing the same, in order to solve the above-mentioned problems.

[0006] To achieve the above objectives, the first aspect of this application provides a solvent-free polyurethane composition, wherein the raw materials, by weight, comprise: 50-70 parts of polyether polyol, 10-20 parts of hydroxyl-terminated polybutadiene, 0.5-1 part of antioxidant, 13-17 parts of isocyanate, 0.1-0.5 parts of catalyst, 0.5-1 part of coupling agent, 3-8 parts of hydroxyethyl acrylate, and 3-6 parts of initiator; The number-average molecular weight of the initiator is 3500-5500.

[0007] Optionally, the polyether polyol includes one or more of polytetrahydrofuran diol, polypropylene glycol, and polyethylene glycol; And / or, the number average molecular weight of the polyether polyol is 2000-6000; And / or, the hydroxyl-terminated polybutadiene contains 75%-80% by mass of the 1,4-structure and 20%-25% by mass of the 1,2-structure.

[0008] Optionally, the antioxidant includes one or more of 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 2,6-di-tert-butyl-p-cresol. And / or, the catalyst comprises one or more of bismorpholino diethyl ether, dibutyltin dilaurate, and organobismuth catalysts; And / or, the coupling agent comprises one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, mercaptopropyltrimethoxysilane, 3-isocyanate-propyltrimethoxysilane, and γ-aminopropyltriethoxysilane. And / or, the raw materials for the initiator include isocyanate and 4-hydroxybenzophenone.

[0009] Optionally, the solvent-free polyurethane protective film has a VOC content of less than 50 ppm.

[0010] A second aspect of this application provides a method for preparing a solvent-free polyurethane composition, comprising: A first mixture is prepared by mixing polyether polyol, hydroxyl-terminated polybutadiene and antioxidant to obtain a first mixture. The first mixture is then vacuum dried to obtain a dried first mixture. Under a nitrogen atmosphere, the dried first mixture and isocyanate are subjected to a second mixing and a first negative pressure reaction to obtain a first reactant; the first reactant and catalyst are subjected to a third mixing and a second negative pressure reaction to obtain a second reactant; the second reactant and hydroxyethyl acrylate are subjected to a fourth mixing and a positive pressure reaction to obtain a third reactant; the third reactant and initiator are subjected to a fifth mixing and a third negative pressure reaction to obtain a solvent-free polyurethane composition.

[0011] Optionally, the vacuum drying temperature is 120-130℃, and the vacuum degree is ≤-0.1MPa; And / or, the moisture content of the first mixture after drying is <400 ppm; And / or, the temperature of the first negative pressure reaction, the second negative pressure reaction and the third negative pressure reaction are each independently 80-85°C, and the time is each independently 50-70 min; And / or, the positive pressure reaction is carried out at a temperature of 80-85°C for a time of 20-40 min.

[0012] Optionally, the method for preparing the hydroxyl-terminated polybutadiene includes: mixing ethanol, butadiene monomer, hydrogen peroxide, and n-thiol in a sixth mixing and a first reaction, and adding hydroquinone at the endpoint of the first reaction; And / or, the preparation method of the initiator includes: mixing a portion of toluene and 4-hydroxybenzophenone in a seventh process to obtain a diluted solution; mixing another portion of toluene and isocyanate in an eighth process under a nitrogen atmosphere; and sequentially adding the diluted solution, dibutyltin laurate, and toluene to carry out a second reaction to obtain the initiator.

[0013] Optionally, the mass ratio of ethanol, butadiene monomer, hydrogen peroxide, n-thiol and hydroquinone is 30-45:35-50:10-25:0.5-1:0.1-0.5; And / or, the temperature of the first reaction is 128-135℃, and the time is 3.5-4.5h; And / or, the mass ratio of the isocyanate, the 4-hydroxybenzophenone, the dibutyltin laurylate, and toluene is 6-10:40-50:0.1-0.5:40-50; And / or, the temperature of the second reaction is 62-68°C, and the time is 3.5-4.5h.

[0014] A third aspect of this application provides a solvent-free polyurethane protective film, comprising an adhesive layer and a PET substrate; The adhesive layer comprises the solvent-free polyurethane composition described above; The thickness of the adhesive layer is 10-50 μm.

[0015] A fourth aspect of this application provides a solvent-free polyurethane protective film, comprising: A solvent-free polyurethane composition is coated onto the surface of a PET substrate and cured and aged under a nitrogen atmosphere to obtain a solvent-free polyurethane protective film. The UV energy for curing is 400-1200 mJ / cm. 2 The linear velocity is 10-60 m / min, and the wavelength range of the UV light source is 250-400 nm; The ripening temperature is 50-60℃, and the time is 24-48h.

[0016] Compared with the prior art, the beneficial effects of this application include: The solvent-free polyurethane composition provided in this application is solvent-free, has zero VOC emissions, and meets the requirements of green and environmentally friendly production; it has low odor and low small molecule residue; it can be UV-cured quickly, resulting in high production efficiency; it has high crosslinking density, excellent resistance to high and low temperatures and weather resistance; it has excellent coatability, can be applied by slot coating, and has small coating thickness error; the produced PU protective film is easy to peel off from the substrate, leaving no adhesive residue.

[0017] The method for preparing the solvent-free polyurethane composition provided in this application uses readily available raw materials.

[0018] The solvent-free polyurethane protective film provided in this application is suitable for applications requiring low odor, high weather resistance, and high temperature resistance, such as surface protection for automotive electronic equipment, automotive interiors, and high-end display devices.

[0019] The method for preparing the solvent-free polyurethane protective film provided in this application is simple to operate. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0021] Figure 1 This is a physical image of the solvent-free polyurethane protective film provided in Example 1. Detailed Implementation

[0022] First, the solution provided in this application will be explained in more detail as follows: The first aspect of this application provides a solvent-free polyurethane composition, wherein the raw materials, by weight, comprise: 50-70 parts of polyether polyol, 10-20 parts of hydroxyl-terminated polybutadiene, 0.5-1 part of antioxidant, 13-17 parts of isocyanate, 0.1-0.5 parts of catalyst, 0.5-1 part of coupling agent, 3-8 parts of hydroxyethyl acrylate, and 3-6 parts of initiator; Optionally, the raw materials of the solvent-free polyurethane composition, by weight, may be: polyether polyol, any value between 50, 60, 70, or 50-70 parts; hydroxyl-terminated polybutadiene, any value between 10, 15, 20, or 10-20 parts; antioxidant, any value between 0.5, 0.6, 0.7, 0.8, 0.9, 1 part, or 0.5-1 part; and isocyanate, any value between 13, 15, 17 parts, or 13-17 parts. The catalyst can be any value between 0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, or 0.1-0.5 parts; the coupling agent can be any value between 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, or 0.5-1 parts; the hydroxyethyl acrylate can be any value between 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, or 3-8 parts; and the initiator can be any value between 3 parts, 4 parts, 5 parts, 6 parts, or 3-6 parts. The number-average molecular weight of the initiator is 3500-5500.

[0023] Optionally, the number average molecular weight of the initiator can be 3500, 4000, 4500, 5000, 5500 or any value between 3500 and 5500.

[0024] The molecular weight of the initiator is in the range of 3500-5500. When it is less than 3500, some small molecules will migrate. When it is greater than 5500, the curing degree is not sufficient and there are not enough groups to react with the double bonds.

[0025] It is important to note that through systematic molecular design, a composite structure of "thermal-photochemical dual crosslinking + highly hydrophobic soft segments + macromolecular initiation system" is constructed to achieve comprehensive performance characteristics of low VOC, low odor, high weather resistance, and no residue. The functions of each component are as follows: Polyether polyols, as the soft segments of the PU backbone, provide flexibility and film-forming properties. Preferred polytetrahydrofuran glycol (PTMG), propylene oxide glycol, or ethylene oxide glycol have a number-average molecular weight of 2000–6000, which ensures chain mobility while avoiding excessive small molecule migration due to excessively low molecular weight. The main chain of hydroxyl-terminated polybutadiene has a hydrocarbon structure, exhibiting low polarity and strong hydrophobicity, significantly inhibiting water penetration and small molecule volatilization; simultaneously, the 75-80% 1,4-structure composition imparts excellent resistance to heat and oxygen aging. This invention strictly controls its microstructure and purity to ensure stable participation in reactions in solvent-free systems without introducing impurities or odor sources. Isocyanates, as hard segment building units, react with polyols, HEA, etc. to form urethane bonds, thereby regulating the crosslinking density; MDI, TDI or HDI trimers are preferred to balance reactivity and the final film's resistance to yellowing. Hydroxyethyl acrylate is a bifunctional monomer. Its hydroxyl groups participate in the prepolymerization of PU, and its acryloyl groups are used for subsequent UV curing, realizing the "prepolymerization-coating-instant photocrosslinking" process, which greatly improves production efficiency. The initiator is prepared by polycondensation and chain extension of isocyanate and 4-hydroxybenzophenone. It has both photoinitiating ability (benzophenone structure absorbs 250-400 nm UV light to generate active free radicals) and a high molecular skeleton (Mn≈3500-5500). Because it cannot migrate or volatilize, it fundamentally avoids the problems of odor, yellowing and residue caused by traditional small molecule photoinitiators. Antioxidants, catalysts, and coupling agents are used to inhibit thermo-oxidative degradation, accelerate the NCO-OH reaction, and enhance the interfacial adhesion between the membrane and the substrate, respectively, to synergistically ensure process stability and end-product performance.

[0026] Key synergistic effects: HTPB and polyether polyols work synergistically to form "low polarity-high flexibility" composite soft segments, reducing free volume and inhibiting small molecule diffusion pathways, resulting in VOC < 50 ppm; HEA and macromolecular initiators work synergistically to achieve uniform and deep UV crosslinking, increasing crosslinking density (>90%), ensuring no glue flow and no residue at 125℃ / 168h; a triple guarantee of solvent-free system + macromolecular initiator + vacuum dehydration process: eliminating solvent residue at the source, preventing initiator migration from the structure, and controlling moisture in the process, together achieving an odor level ≤ 2; It should also be noted that although hydroxyl-terminated polybutadiene (HTPB) is a commercially available product, this invention makes clear limitations on its microstructure ratio (1,4- vs 1,2-butadiene) and purification process (polymerization → centrifugation → water washing → deep dehydration and small molecule removal) to make it suitable for solvent-free and low-odor applications, which is different from conventional elastomer applications. The initiator is prepared by covalently bonding the photosensitive group (4-hydroxybenzophenone) to the main chain of PU prepolymer to form a non-migrating polymer photoinitiation system, which solves the long-standing problem in the industry of "yellowing and odor caused by migration of small molecule initiators".

[0027] The formulation in this application is not a simple additive combination of components, but rather based on a three-in-one design concept of "low migration, high cross-linking, and strong weather resistance." The introduction of hydroxyl-terminated polybutadiene not only improves temperature resistance but also blocks the escape of small molecules through its non-polar long chains; the high molecular weight initiator "locks" the photoinitiation function within the network, achieving green, efficient, and stable UV curing. The synergistic effect between these two components and other elements such as polyether polyol and HEA at multiple scales is key to the high performance achieved in this invention.

[0028] In some embodiments, the polyether polyol includes one or more of polytetrahydrofuran diol, polypropylene glycol, and polyethylene glycol; Preferably, the polyether polyol includes polytetrahydrofuran diol; And / or, the number average molecular weight of the polyether polyol is 2000-6000; Optionally, the number average molecular weight of the polyether polyol can be 2000, 3000, 4000, 5000, 6000 or any value between 2000 and 6000; Preferably, the number average molecular weight of the polyether polyol is 4000; And / or, the hydroxyl-terminated polybutadiene contains 75%-80% by mass of the 1,4-structure and 20%-25% by mass of the 1,2-structure.

[0029] Optionally, the mass content of the 1,4-structure in the hydroxyl-terminated polybutadiene can be any value between 75%, 80%, 85% or 75-85%, and the mass content of the 1,2-structure can be any value between 20%, 21%, 22%, 23%, 24%, 25% or 20-25%.

[0030] It is important to note that the introduction of hydroxyl-terminated polybutadiene is to improve cohesion, weather resistance, and flexibility. 1,2-Butadiene has numerous vinyl side groups on its main chain, resulting in poor molecular chain regularity and flexibility. It typically exhibits high hardness, a high glass transition temperature, weak elasticity, and good aging resistance. 1,4-Butadiene, on the other hand, has substituents on both sides of the double bond distributed on the same side, resulting in a loosely packed molecular chain, excellent elasticity, good low-temperature performance, and wear resistance. The optimal ratio of 1,2-butadiene to 1,4-butadiene, based on a balance of hardness and flexibility, is beneficial for improving cohesion, temperature resistance, and flexibility.

[0031] In some embodiments, the antioxidant includes one or more of 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 2,6-di-tert-butyl-p-cresol. And / or, the catalyst comprises one or more of bismorpholino diethyl ether, dibutyltin dilaurate, and organobismuth catalysts; Preferably, the catalyst comprises dibutyltin dilaurate; And / or, the coupling agent comprises one or more of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-(methacryloyloxy)propyltrimethoxysilane, mercaptopropyltrimethoxysilane, 3-isocyanate-propyltrimethoxysilane, and γ-aminopropyltriethoxysilane. And / or, the raw materials for the initiator include isocyanate and 4-hydroxybenzophenone.

[0032] It should be noted that the initiator mainly involves the chain extension reaction between hydroxyl groups and NCO, which increases the molecular weight, improves ghosting precipitation and small molecule residue, and reduces odor.

[0033] In some embodiments, the solvent-free polyurethane protective film has a VOC content of less than 50 ppm.

[0034] Optionally, the VOC content of the solvent-free polyurethane protective film can be any value of 10ppm, 20ppm, 30ppm, 40ppm or less than 50ppm.

[0035] It should be noted that the performance comparison between traditional PU protective films and the solvent-free polyurethane composition provided in this application is shown in Table 1.

[0036] Table 1 Performance Comparison

[0037] A second aspect of this application provides a method for preparing a solvent-free polyurethane composition, comprising: A first mixture is prepared by mixing polyether polyol, hydroxyl-terminated polybutadiene and antioxidant to obtain a first mixture. The first mixture is then vacuum dried to obtain a dried first mixture. Under a nitrogen atmosphere, the dried first mixture and isocyanate are subjected to a second mixing and a first negative pressure reaction to obtain a first reactant; the first reactant and catalyst are subjected to a third mixing and a second negative pressure reaction to obtain a second reactant; the second reactant and hydroxyethyl acrylate are subjected to a fourth mixing and a positive pressure reaction to obtain a third reactant; the third reactant and initiator are subjected to a fifth mixing and a third negative pressure reaction to obtain a solvent-free polyurethane composition.

[0038] It should be noted that the preparation principle of solvent-free polyurethane compositions is as follows: hydroxyl groups react with NCO to obtain NCO-terminated polyurethane prepolymers, then acrylic monomers are added to obtain polyurethane acrylates containing double bonds, and the above steps are followed sequentially to prepare the product.

[0039] The first, second, and third negative pressure reactions begin with negative pressure to remove small molecules under vacuum. The positive pressure reaction begins with positive pressure because the addition of hydroxyethyl acrylate is volatile at high temperatures, which affects stability. Therefore, a high-temperature polymerization reaction under positive pressure is performed first, and only after completion is the negative pressure removed to eliminate small molecules. In some embodiments, the preparation process includes sampling to test the NCO content; the positive pressure is switched to negative pressure only when the NCO content is zero.

[0040] In some embodiments, the vacuum drying temperature is 120-130℃, and the vacuum degree is ≤-0.1MPa; Optionally, the vacuum drying temperature can be any value between 120℃, 125℃, 130℃ or 120-130℃, and the vacuum degree can be any value between -0.1MPa, -0.2MPa, -0.3MPa or less than or equal to -0.1MPa; And / or, the moisture content of the first mixture after drying is <400 ppm; Optionally, the moisture content of the first mixture after drying can be any value of 100ppm, 200ppm, 300ppm, 390ppm or <400ppm; And / or, the temperature of the first negative pressure reaction, the second negative pressure reaction and the third negative pressure reaction are each independently 80-85°C, and the time is each independently 50-70 min; Optionally, the temperatures of the first negative pressure reaction, the second negative pressure reaction, and the third negative pressure reaction can each be independently any value between 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, or 80-85℃, and the times can each be independently any value between 50min, 60min, 70min, or 50-70min. And / or, the positive pressure reaction is carried out at a temperature of 80-85°C for a time of 20-40 min.

[0041] Optionally, the temperature of the positive pressure reaction can be any value between 80℃, 81℃, 82℃, 83℃, 84℃, 85℃ or 80-85℃, and the time can be any value between 20min, 30min, 40min or 20-40min.

[0042] In some embodiments, the method for preparing the hydroxyl-terminated polybutadiene includes: mixing ethanol, butadiene monomer, hydrogen peroxide, and n-thiol in a sixth mixture and a first reaction, and adding hydroquinone at the endpoint of the first reaction; And / or, the preparation method of the initiator includes: mixing a portion of toluene and 4-hydroxybenzophenone in a seventh process to obtain a diluted solution; mixing another portion of toluene and isocyanate in an eighth process under a nitrogen atmosphere; and sequentially adding the diluted solution, dibutyltin laurate, and toluene to carry out a second reaction to obtain the initiator.

[0043] In some embodiments, the mass ratio of ethanol, butadiene monomer, hydrogen peroxide, n-thiol, and hydroquinone is 30-45:35-50:10-25:0.5-1:0.1-0.5; Optionally, the mass ratio of ethanol, butadiene monomer, hydrogen peroxide, n-thiol, and hydroquinone can be (30:35:10:0.5:0.1), (35:35:10:0.5:0.1), (40:35:10:0.5:0.1), (45:35:10:0.5:0.1), (35:40:10:0.5:0.1), (35:45:10:0.5:0.1), (35:50:10:0.5:0.1), (35:35:15: The ratios are 0.5:0.1, (35:35:20:0.5:0.1), (35:35:25:0.5:0.1), (35:35:25:0.75:0.1), (35:35:25:1:0.1), (35:35:25:0.5:0.5) or any value between 30-45:35-50:10-25:0.5-1:0.1-0.5; and / or, the temperature of the first reaction is 128-135℃ and the time is 3.5-4.5h; Optionally, the temperature of the first reaction can be any value between 128℃, 130℃, 132℃, 135℃ or 128-135℃, and the time can be any value between 3.5h, 4h, 4.5h or 3.5-4.5h. And / or, the mass ratio of the isocyanate, the 4-hydroxybenzophenone, the dibutyltin laurylate, and the toluene is 6-10:40-50:0.1-0.5:40-50; Optionally, the mass ratio of isocyanate, 4-hydroxybenzophenone, dibutyltin laurylate, and toluene can be (6:40:0.1:40), (8:40:0.1:40), (10:40:0.1:40), (8:45:0.1:40), (8:50:0.1:40), (8:45:0.25:40), (8:45:0.5:40), (8:45:0.25:45), (8:45:0.25:50) or any value between 6-10:40-50:0.1-0.5:40-50; And / or, the temperature of the second reaction is 62-68°C, and the time is 3.5-4.5h.

[0044] Optionally, the temperature of the second reaction can be any value between 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃ or 62-68℃, and the time can be any value between 3.5h, 4h, 4.5h or 3.5-4.5h.

[0045] A third aspect of this application provides a solvent-free polyurethane protective film, comprising an adhesive layer and a PET substrate; The adhesive layer comprises the solvent-free polyurethane composition described above; The thickness of the adhesive layer is 10-50 μm.

[0046] Optionally, the thickness of the adhesive layer can be any value between 10μm, 20μm, 30μm, 40μm, 50μm or 10-30μm.

[0047] Preferably, the thickness of the adhesive layer is 10 μm.

[0048] A fourth aspect of this application provides a solvent-free polyurethane protective film, comprising: A solvent-free polyurethane composition is coated onto the surface of a PET substrate and cured and aged under a nitrogen atmosphere to obtain a solvent-free polyurethane protective film. The UV energy for curing is 400-1200 mJ / cm. 2 The linear velocity is 10-60 m / min, and the wavelength range of the UV light source is 250-400 nm; Optionally, the curing UV energy can be 400 mJ / cm. 2 500 mJ / cm 2 600 mJ / cm 2 700 mJ / cm 2 800 mJ / cm 2 900 mJ / cm 2 1000 mJ / cm 2 1100 mJ / cm 2 1200 mJ / cm 2 Or 400-1200 mJ / cm 2 The linear velocity can be any value between 10 m / min, 20 m / min, 30 m / min, 40 m / min, 50 m / min, 60 m / min or any value between 10-60 m / min, and the wavelength range of the UV light source can be any value between 250nm, 300nm, 350nm, 400nm or 250-400nm. The ripening temperature is 50-60℃, and the time is 24-48h.

[0049] Optionally, the curing temperature can be any value between 50℃, 55℃, 60℃ or 50-60℃, and the time can be any value between 24h, 30h, 36h, 42h, 48h or 24-48h.

[0050] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0051] Example 1 This first aspect of Example 1 provides a solvent-free polyurethane composition, the raw materials of which, by mass parts, include: 60 parts polyether polyol, 15 parts hydroxyl-terminated polybutadiene, 0.8 parts antioxidant, 15 parts isocyanate, 0.3 parts catalyst, 0.8 parts coupling agent, 5 parts hydroxyethyl acrylate, and 4 parts initiator; The number-average molecular weight of the initiator is 4500; Polyether polyols include polytetrahydrofuran diol, Mn=4000; The hydroxyl-terminated polybutadiene contains 75% by mass of the 1,4-structure and 25% by mass of the 1,2-structure. The antioxidant is 3,5-di-tert-butyl-4-hydroxyhydrocinnamate; The isocyanate is diphenylmethane diisocyanate; The catalyst is dibutyltin dilaurate; The coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0052] The second aspect of this embodiment provides a method for preparing a solvent-free polyurethane composition, the specific preparation method including: S1: Preparation of hydroxyl-terminated polybutadiene: Industrial ethanol was added to a high-pressure reactor and the temperature was slowly raised to 90°C. Butadiene monomer, hydrogen peroxide initiator and n-thiol chain transfer agent were added. Stirring was started and the temperature was raised to 130°C for 4 hours. Hydroquinone was added to terminate the reaction and crude hydroxyl-terminated polybutadiene was obtained. After centrifugation, water washing and deep dehydration and small molecule removal, high-purity hydroxyl-terminated polybutadiene was obtained for later use. S2: Preparation of initiator: Prepare a diluted solution of toluene and 4-hydroxybenzophenone at a 1:1 ratio. Add toluene and isocyanate to a high-pressure reactor, purge with nitrogen three times, heat to 65°C, and add the diluted 4-hydroxybenzophenone solution dropwise over 10 minutes, stirring for 15 minutes. Then add a dibutyltin laurate toluene solution dropwise over 5 minutes, and react for 4 hours. Subsequently, add a diethylamine toluene solution and continue the reaction for 4 hours. Cool down, discharge the material, remove the solvent, and dry. S3: Add polyether polyol, hydroxyl-terminated polybutadiene, and antioxidant to the reactor, stir and heat to 125°C, dehydrate to <400 ppm under ≤-0.1 MPa vacuum, and cool to 80°C; S4: Under nitrogen protection, add isocyanate and react under vacuum at ≤-0.1MPa for 1 hour; then under nitrogen protection, add catalyst and react under vacuum at ≤-0.1MPa for 1 hour; under nitrogen protection, add hydroxyethyl acrylate and react under positive pressure for 0.5 hours; under nitrogen protection, add initiator and react under vacuum at ≤-0.1MPa for 1 hour, and discharge into a sealed container for storage away from light.

[0053] The third aspect of this embodiment provides a solvent-free polyurethane protective film and its preparation method, the specific steps of which are as follows: A solvent-free polyurethane composition was coated onto the antistatic surface of a 50 μm antistatic PET substrate using a slot coater, with an adhesive layer thickness of 10 μm. After laminating with a transparent release film, the coating was applied under nitrogen protection at 800 mJ / cm². 2 The UV energy was used for curing at a linear velocity of 30 m / min, with a mercury lamp as the UV light source and a wavelength range of 250-400 nm. The cured roll was then placed in an environment of 55°C for 48 hours to obtain a solvent-free polyurethane protective film.

[0054] The actual product of this solvent-free polyurethane protective film is shown below. Figure 1 As shown.

[0055] Example 2 The difference from Example 1 is that the types and amounts of raw materials are different, specifically: 55 parts polyether polyol, 18 parts hydroxyl-terminated polybutadiene, 1 part antioxidant, 16 parts isocyanate, 0.2 parts catalyst, 0.6 parts coupling agent, 7 parts hydroxyethyl acrylate, and 5 parts initiator; Polyether polyols include propylene oxide glycol, Mn=4000; The hydroxyl-terminated polybutadiene contains 78% by mass of the 1,4-structure and 25% by mass of the 1,2-structure. The antioxidant is β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate octadecyl alcohol ester; The catalyst is bismorpholino diethyl ether; The isocyanate is toluene diisocyanate; The coupling agent is γ-aminopropyltriethoxysilane.

[0056] Example 3 The difference from Example 1 is that the types and amounts of raw materials are different, specifically: 65 parts polyether polyol, 12 parts hydroxyl-terminated polybutadiene, 0.9 parts antioxidant, 14 parts isocyanate, 0.25 parts catalyst, 0.9 parts coupling agent, 7 parts hydroxyethyl acrylate, and 5 parts initiator (Mn=5500). The polyether polyol is polytetrahydrofuran diol, Mn=4000; The hydroxyl-terminated polybutadiene contains 78% by mass of the 1,4-structure and 25% by mass of the 1,2-structure. The antioxidant is 3,5-di-tert-butyl-4-hydroxyhydrocinnamate; The catalyst is dibutyltin dilaurate; The coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane; The isocyanate is diphenylmethane diisocyanate.

[0057] Example 4 The difference from Example 1 is that the types and amounts of raw materials are different, specifically: Propylene oxide diol (Mn=2000) 50 parts; Hydroxyl-terminated polybutadiene (76% 1,4-structure) 20 parts; Antioxidant (2,6-di-tert-butyl-p-cresol) 0.6 parts; 16 parts of isophorone diisocyanate; 0.4 parts of organic bismuth catalyst (BiCAT 8108); 0.7 parts of γ-aminopropyltriethoxysilane; 8 parts of hydroxyethyl acrylate; Initiator (Mn≈4800) 6 parts.

[0058] Example 5 The difference from Example 1 is that the types and amounts of raw materials are different, specifically: Polytetrahydrofuran diol (Mn=6000) 70 parts; Hydroxyl-terminated polybutadiene (80% 1,4-structure) 10 parts; Antioxidant (β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate octadecyl alcohol ester) 0.5 parts; 13 parts of hexamethylene diisocyanate trimer; 0.1 parts of bismorpholino diethyl ether; 0.5 parts of mercaptopropyltrimethoxysilane; 3 parts hydroxyethyl acrylate; Initiator (Mn≈3500) 3 parts.

[0059] Comparative Example 1 The difference from Example 1 is that a high molecular weight initiator is not added, but an equal amount of polyether polyol is used instead.

[0060] Comparative Example 2 The difference from Example 1 is that the raw material composition is the same as in Example 1, but 20 parts of ethyl acetate are added as solvent in S1, and the solvent is removed by drying at 60°C after coating.

[0061] Comparative Example 3 The difference from Example 1 is that the raw material composition is the same as in Example 1, but the high molecular weight initiator is replaced with an equal amount of 2-hydroxy-2-methyl-1-phenyl-1-propanone (a common photoinitiator).

[0062] Comparative Example 4 The difference from Example 1 is that the amount of raw materials used is different, as detailed below: 40 parts polyether polyol, 30 parts hydroxyl-terminated polybutadiene, 0.4 parts antioxidant, 10 parts isocyanate, 1.2 parts catalyst, 0.4 parts coupling agent, 10 parts hydroxyethyl acrylate, and 8 parts initiator.

[0063] Comparative Example 5 The difference from Example 1 is that isocyanate and hydroxyethyl acrylate are not added.

[0064] To demonstrate that the PU protective film prepared in this application has the effects of low odor, good weather resistance, good temperature resistance, and no residue, the PU protective films prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to performance testing. The specific test results are shown in Table 2.

[0065] The testing standards are as follows: Odor Assessment: The cured protective film sample was placed in a 1L sealed glass jar and placed in an 85℃ oven for 2 hours. Then, 5 professional odor assessors opened the jar and smelled it, scoring it on a scale of 1-5 (1: odorless; 2: slight odor; 3: noticeable but acceptable odor; 4: strong odor; 5: irritating odor). Small molecule residues (VOCs): headspace gas chromatography-mass spectrometry, refer to GB / T 39107-2020; Yellowing resistance test: A UV aging test chamber was used, according to standard GB / T 14522, under the following conditions: 60℃, UVB-313 lamp, and irradiance of 0.76W / m². 2 The sample was continuously irradiated for 168 hours. The change in b-value (yellowness index) before and after irradiation (Δb) was measured using a colorimeter. The smaller the Δb*, the better the anti-yellowing performance. High temperature resistance: Apply the protective film to a stainless steel plate and place it in a 125℃ oven for 168 hours. Observe whether the surface becomes sticky, drips glue, or the peeling force changes significantly. Residual adhesive test: The protective film was applied to steel plate and CG plate respectively at (23±2)℃ and 50%RH. It was subjected to a 2kg roller for 3 back and forth cycles. After 72 hours at 85℃ / 85%RH, it was peeled off at 180° and 300mm / min. The surface of the film was then observed to see if there was any residual adhesive. Peel force: The peel force at 180° (g / inch) was measured in accordance with GB / T 2792 standard.

[0066] Table 2 Performance Tests

[0067] analyze: Examples 1-5 all achieved the technical effects described in this application: small molecule residue (VOC) ≤50 ppm, odor level ≤2, no change in heat resistance at 125℃ / 168h, yellowing index Δb<1.0, and no residue, verifying the universality and reliability of the formulation system of this invention.

[0068] Comparison of Example 1 and Comparative Example 1: Comparative Example 1 did not use a high molecular weight initiator, resulting in greater small molecule residue and odor, and decreased heat resistance and temperature resistance. This indicates that a high molecular weight initiator is crucial for improving crosslinking density and weather resistance.

[0069] Comparison of Example 1 and Comparative Example 2: Comparative Example 2 uses a solvent system, which results in serious small molecule residue, obvious odor, severe yellowing, and high risk of residual adhesive, proving that the solvent-free system has advantages in terms of environmental protection and temperature resistance.

[0070] Comparison of Example 1 and Comparative Example 3: Comparative Example 3 used a common small molecule photoinitiator, illustrating the key role of macromolecular initiators in reducing migration and improving resistance to yellowing.

[0071] In summary, this application has successfully prepared a low-odor, highly transparent, high-temperature and humid heat resistant, and residue-free PU protective film by using solvent-free formulation design and high molecular weight initiators to improve weather resistance and reduce small molecule residues. It is particularly suitable for high-end fields such as automotive and optical displays.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0073] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A solvent-free polyurethane composition, characterized by, The raw materials thereof include, by mass fraction: polyether polyol 50-70 parts, hydroxyl-terminated polybutadiene 10-20 parts, antioxidant 0.5-1 part, isocyanate 13-17 parts, catalyst 0.1-0.5 part, coupling agent 0.5-1 part, hydroxyethyl acrylate 3-8 parts, initiator 3-6 parts; the number average molecular weight of the initiator is 3500-5500.

2. The solvent-free polyurethane composition according to claim 1, characterized in that, the polyether polyol includes one or more of polytetrahydrofuran diol, polypropylene oxide diol and polyethylene oxide diol; and / or, the number average molecular weight of the polyether polyol is 2000-6000; and / or, the mass content of 1,4-structure in the hydroxyl-terminated polybutadiene is 75%-80%, and the mass content of 1,2-structure is 20%-25%.

3. The solvent-free polyurethane composition according to claim 1, characterized in that, the antioxidant includes one or more of 3,5-di-tert-butyl-4-hydroxyhydrocinnamate, β-(3,5-di-tert-butyl-4-hydroxyphenyl) octadecyl propionate and 2,6-di-tert-butyl-p-cresol; and / or, the catalyst includes one or more of dimorpholinyl diethyl ether, dibutyl tin dilaurate and organic bismuth catalyst; and / or, the coupling agent includes one or more of γ-(2,3-epoxypropoxy) propyl trimethoxysilane, γ-(methacryloyloxy) propyl trimethoxysilane, mercapto propyl trimethoxysilane, 3-isocyanate propyl trimethoxysilane and γ-aminopropyl triethoxysilane; and / or, the raw materials of the initiator include isocyanate and 4-hydroxybenzophenone.

4. The solvent-free polyurethane composition according to any one of claims 1 to 3, characterized in that, the VOC content of the solvent-free polyurethane protective film is less than 50 ppm.

5. A process for preparing the solvent-free polyurethane composition according to any one of claims 1 to 4, characterized in that, including: polyether polyol, hydroxyl-terminated polybutadiene and antioxidant are first mixed to obtain a first mixture, and the first mixture is vacuum dried to obtain a dried first mixture; the dried first mixture and isocyanate are second mixed and first subjected to negative pressure reaction to obtain a first reactant; the first reactant and catalyst are third mixed and second subjected to negative pressure reaction to obtain a second reactant; the second reactant and hydroxyethyl acrylate are fourth mixed and subjected to positive pressure reaction to obtain a third reactant; the third reactant and initiator are fifth mixed and third subjected to negative pressure reaction to obtain a solvent-free polyurethane composition.

6. The method for preparing a solvent-free polyurethane composition according to claim 5, characterized by, the temperature of the vacuum drying is 120-130℃, and the vacuum degree is ≤-0.1MPa; and / or, the moisture content of the dried first mixture is <400 ppm; and / or, the temperature of each of the first negative pressure reaction, the second negative pressure reaction and the third negative pressure reaction is independently 80-85℃, and the time of each of the first negative pressure reaction, the second negative pressure reaction and the third negative pressure reaction is independently 50-70min; and / or, the temperature of the positive pressure reaction is 80-85℃, and the time is 20-40min.

7. The method of claim 5, wherein the solvent-free polyurethane composition is prepared by mixing the polyol, the polyisocyanate, and the chain extender in the presence of the catalyst. the preparation method of the hydroxyl-terminated polybutadiene includes: sixth mixing of ethanol, butadiene monomer, hydrogen peroxide and n-mercaptan and first reaction, and adding hydroquinone at the end of the first reaction. And / or, the preparation method of the initiator comprises: mixing part of toluene and 4-hydroxybenzophenone to obtain a diluent; mixing another part of toluene and isocyanate under nitrogen atmosphere, and sequentially adding the diluent, dibutyltin laurate and toluene dropwise to carry out a second reaction to obtain an initiator.

8. The method for preparing a solvent-free polyurethane composition according to claim 7, characterized by, The mass ratio of the ethanol, butadiene monomer, hydrogen peroxide, n-thiol and hydroquinone is 30-45:35-50:10-25:0.5-1:0.1-0.5; And / or, the temperature of the first reaction is 128-135℃, and the time is 3.5-5h; And / or, the mass ratio of the isocyanate, the 4-hydroxybenzophenone, the dibutyltin laurate and toluene is 6-10:40-50:0.1-0.5:40-50; And / or, the temperature of the second reaction is 62-68℃, and the time is 3.5-4.5h.

9. A solvent-free polyurethane protective film, characterized by, It comprises a glue layer and a PET substrate; The glue layer comprises the solvent-free polyurethane composition according to any one of claims 1-4; The thickness of the glue layer is 10-50 μm.

10. The solvent-free polyurethane protective film according to claim 9, characterized in that, It comprises: The solvent-free polyurethane protective film is obtained by coating the solvent-free polyurethane composition to the surface of the PET substrate, and curing and aging under nitrogen atmosphere; The curing UV energy is 400-1200 mJ / cm 2 , linear speed is 10-60 m / min, and the wavelength range of the UV light source is 250-400 nm; The temperature of the aging is 50-60℃, and the time is 24-48h.

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