Waterborne polyurethane emulsion synthesized from pure linear isocyanate and preparation method of waterborne polyurethane emulsion

Abstract

The invention provides a waterborne polyurethane emulsion synthesized from pure linear isocyanate and a preparation method of the waterborne polyurethane emulsion. The preparation method comprises the following steps: polymerizing polyol and isocyanate, and adding a chain terminator to obtain a prepolymer; adding a hydrophilic chain extender, a small molecule chain extender, a catalyst A and a solvent, and reacting to obtain a hydroxyl-terminated prepolymer; adding a solvent, an isocyanate group terminated compound and a catalyst B for reaction to obtain an isocyanate group terminated prepolymer; adding a solvent and a neutralizer for reaction; adding water, dispersing at a high speed, cooling, adding a post chain extender, and carrying out a chain extension reaction to obtain a waterborne polyurethane emulsion synthesized from pure linear isocyanate; the molar ratio of the isocyanate to the polyol is more than or equal to 3.5: 1, and the temperature of the added water is 20-60 DEG C. The waterborne polyurethane emulsion synthesized from pure linear isocyanate provided by the invention is excellent in performance, high in dispersity and good in storage stability.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane, and particularly relates to an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof. Background Art

[0002] With the development of society and environmental requirements, many application fields such as coatings and adhesives have gradually shifted from traditional solvent-based polyurethane resins to water-based polyurethanes with water as the medium.

[0003] But because the aqueous polyurethane contains a large amount of polar groups such as ester groups, carbamates, allophanates, etc., microphase separation is prone to occur, the intramolecular or intermolecular hydrogen bonding degree is high, the intermolecular action amount is large, and there is a strong physical property, but the phenomenon of hardening and stiffening very easily occurs at low temperatures, affecting its low temperature resistance and service life. There is no structure such as ring in the chain segment of pentamethylene diisocyanate and hexamethylene diisocyanate, and the molecular flexibility is good, which is particularly suitable for synthesizing polyurethane products with good flexibility. But the prior art cannot be fully synthesized by it for long-term stable aqueous polyurethane, the main reason is that the reactivity of their two functional groups is very high, causing the distribution of hydrophilic chain extension to be very uneven, which has a strong impact on its hydrophilicity. In addition, the molecular distribution is very wide in the prepolymerization process, and a large amount of free monomers will appear, and these free monomers will not only react and precipitate with small molecule alcohol in the subsequent chain extension process, but also cause the subsequent dispersion process in water to react with water to foam and gel. Because the molecule contains a large number of flexible methylene structures, the polymer segments are entangled together, making it difficult to evenly disperse them in water and unable to form a stable waterborne polyurethane emulsion. Currently, the industry mostly uses a large amount of isophorone diisocyanate or other isocyanates to synthesize relatively stable emulsions. Due to the introduction of a large number of rigid structures, the cohesive energy in the structure is increased, limiting its application in the soft and high-elastic fields.

[0004] CN117511487A mentions a method for synthesizing a pure PDI system waterborne polyurethane, which can only add a small amount of PDI as a hard segment, limiting the application field, and cannot solve the problem of free monomers and dispersion, and the storage stability of the emulsion is not high, making it difficult to achieve commercial production. CN111732708A synthesizes a soft and highly resilient waterborne polyurethane product, but introduces a large amount of isophorone diisocyanate to complete it, and cannot solve the problem of free monomers and dispersion, and the storage stability of the prepared emulsion is not high.

[0005] In the prior art, in the field of waterborne polyurethane synthesis, many problems arise during the prepolymerization, synthesis, emulsification and storage of pure linear diisocyanates, and there is currently no good solution.

[0006] Therefore, how to provide a method for preparing an aqueous polyurethane dispersion synthesized from pure linear isocyanate, which has the characteristics of regular molecules, narrow distribution, large molecular weight, high dispersion dispersibility, and good storage stability, has become a technical problem that needs to be solved urgently. Summary of the invention

[0007] In view of the shortcomings of the prior art, the object of the present invention is to provide a waterborne polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof. The present invention designs a preparation method for synthesizing a waterborne polyurethane emulsion from pure linear isocyanate, further designs the molar ratio of isocyanate to polyol in step (1) to be within a specific range, and simultaneously prepares a waterborne polyurethane with regular molecules, narrow distribution and large molecular weight by stepwise polymerization, and the waterborne polyurethane emulsion prepared thereby has high dispersibility and good storage stability.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing an aqueous polyurethane emulsion by synthesizing pure linear isocyanate, the preparation method comprising the following steps:

[0010] (1) After the polyol and isocyanate are polymerized, a chain terminator is added to remove the residual monomers to obtain an isocyanate-based prepolymer;

[0011] (2) adding a hydrophilic chain extender, a small molecule chain extender, a catalyst A and a solvent to the reaction system obtained in step (1), reacting to obtain a hydroxyl-terminated prepolymer;

[0012] (3) adding a solvent, an isocyanate-terminated compound and a catalyst B to the reaction system obtained in step (2) to react and obtain an isocyanate-terminated prepolymer;

[0013] (4) adding a solvent and a neutralizing agent to the reaction system obtained in step (3) to react;

[0014] (5) adding water to the reaction system obtained in step (4), dispersing at high speed, cooling, and then adding a post-chain extender thereto to carry out a chain extension reaction to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate;

[0015] The molar ratio of isocyanate to polyol in step (1) is ≥3.5:1;

[0016] The water temperature added in step (5) is 20-60°C.

[0017] Pentamethylene diisocyanate (HDI) and hexamethylene diisocyanate (PDI) have small molecular weights, and the reactivity of the -NCO groups in the two compounds is very high. Even after reacting with polyols, the terminal groups still have high reactivity, resulting in uneven molecular distribution and the presence of free HDI or PDI. In the synthesis of waterborne polyurethane, these short-chain or free isocyanate monomers not only lead to a wide molecular weight distribution of the prepolymer, but also react easily with water during the dispersion process, affecting the dispersibility and performance of the waterborne polyurethane. In addition, since the prepolymer segments synthesized from linear isocyanates are soft, the prepolymer molecular chains are entangled together, and it is difficult to uniformly disperse them in water by high-speed dispersion in conventional processes, which usually leads to a series of problems such as the inability of the emulsion to disperse and the paste-like state after chain extension, and it is impossible to obtain a waterborne polyurethane emulsion synthesized from pure HDI and / or pure PDI.

[0018] In this regard, the present invention designs a preparation method for synthesizing an aqueous polyurethane emulsion from pure linear isocyanate, further designs the molar ratio of isocyanate to polyol in step (1) to be within a specific range, and simultaneously prepares an aqueous polyurethane with regular molecules, narrow distribution and large molecular weight through a stepwise polymerization method, and the aqueous polyurethane emulsion prepared in this way has high dispersibility and good storage stability.

[0019] Furthermore, in the prepolymerization process of the present invention, an excess of linear isocyanate monomer is added to react with polyol, and then a chain terminator is added and the unreacted isocyanate monomer is removed by evaporation, and the residual amount of isocyanate monomer is controlled to be ≤1wt% to obtain a regular prepolymer structure, and then the hydrophilic group and the chain extender are uniformly introduced into the chain segment by step-by-step polymerization to synthesize a hydroxyl-terminated prepolymer, and finally an additional isocyanate-terminated compound is added and a solvent is added at a relatively low reaction temperature to form an isocyanate-terminated prepolymer, and then deionized water is added at a high speed to disperse and emulsify, and after complete dispersion, the emulsion is cooled to below 30°C by using ice water, and the chain is extended by dropwise addition, and distilled under reduced pressure to obtain an aqueous polyurethane dispersion synthesized from pure linear isocyanate.

[0020] The waterborne polyurethane resin synthesized by the preparation method provided by the present invention has regular molecules, narrow distribution and large molecular weight. The waterborne polyurethane emulsion synthesized from pure linear isocyanate prepared by the preparation method provided by the present invention has the characteristics of high permeability and good storage stability.

[0021] In the present invention, the molar ratio of isocyanate to polyol in step (1) is ≥3.5:1, for example, it can be 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1 or 12:1.

[0022] The present invention can obtain an aqueous polyurethane emulsion and an aqueous polyurethane resin with excellent performance by controlling the molar ratio of isocyanate to polyol in step (1) within a specific range. If the molar ratio of isocyanate to polyol is too small, the molecular distribution of the prepolymer obtained in step (1) becomes wider and the viscosity of the prepolymer becomes larger, making it more difficult to disperse the aqueous polyurethane emulsion and reducing the mechanical properties of the aqueous polyurethane.

[0023] In the present invention, the temperature of the water added in step (5) is controlled within a specific range, which can significantly shorten the phase transition time, making the aqueous polyurethane easier to disperse and the prepared aqueous polyurethane emulsion more stable.

[0024] It should be noted that the post-chain extender in step (5) of the present invention can be added to the reaction system in the form of a post-chain extender solution, and the solvent includes water. The present invention has no special restrictions on the mass percentage of the post-chain extender solution, and the mass percentage range commonly used in the field is applicable.

[0025] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0026] As a preferred technical solution of the present invention, the molar ratio of isocyanate to polyol in step (1) is (3.5-10):1, for example, it can be 3.5:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc., preferably (4-8):1.

[0027] In the present invention, the comprehensive performance of the aqueous polyurethane emulsion and aqueous polyurethane resin is further optimized and improved by further optimizing the molar ratio of isocyanate to polyol in a specific range. If the molar ratio of isocyanate to polyol is too small, even ≤3.5:1, the performance of the prepared aqueous polyurethane emulsion and aqueous polyurethane resin is poor; if the molar ratio of isocyanate to polyol is too large, it will lead to waste of isocyanate, and after adding the chain terminator in step (1), the time for evaporation and removal of excess isocyanate is too long, and the production efficiency is reduced.

[0028] Preferably, the molar ratio of the polyol to the chain terminator in step (1) is 1:(0.001-0.002), for example, it can be 1:0.001, 1:0.0011, 1:0.0012, 1:0.0013, 1:0.0014, 1:0.0015, 1:0.0016, 1:0.0017, 1:0.0018, 1:0.0019 or 1:0.002, etc.

[0029] Preferably, the molar ratio of the polyol in step (1) to the hydrophilic chain extender in step (2) is 1:(0.4-1.8), for example, it can be 1:0.4, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6 or 1:1.8, etc.

[0030] Preferably, the molar ratio of the polyol in step (1) to the small molecule chain extender in step (2) is 1:(0.3-1.7), for example, it can be 1:0.3, 1:0.5, 1:1, 1:1.05, 1:1.1, 1:1.15, 1:1.2, 1:1.25, 1:1.3, 1:1.35, 1:1.4, 1:1.45, 1:1.5 or 1:1.7, etc.

[0031] Preferably, the ratio between the mass of the prepolymer in step (1) and the mass of the solvent in step (2) is 100g:(5-40)g, for example, it can be 100g:5g, 100g:10g, 100g:15g, 100g:20g, 100g:25g, 100g:30g, 100g:35g or 100g:40g, etc.

[0032] Preferably, the molar ratio of the amount of the polyol in step (1) to the isocyanate-terminated compound in step (3) is 1:(1.2-4), for example, it can be 1:1.2, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc.

[0033] Preferably, the ratio between the mass of the hydroxyl-terminated prepolymer in step (2) and the mass of the solvent in step (3) is 100g:(5-40)g, for example, it can be 100g:5g, 100g:10g, 100g:15g, 100g:20g, 100g:25g, 100g:30g, 100g:35g or 100g:40g, etc.

[0034] As a preferred technical solution of the present invention, taking the mass content of the isocyanate-terminated prepolymer as 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 1-2% (for example, it can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%, etc.), and the mass percentage of the solvent added in step (4) is 150-300% (for example, it can be 150%, 160%, 180%, 200%, 220%, 240%, 260%, 280% or 300%, etc.).

[0035] Alternatively, based on the mass content of the isocyanate-terminated prepolymer as 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 2-3% (for example, it can be 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9% or 3%, etc.), and the mass percentage of the solvent added in step (4) is 100-200% (for example, it can be 100%, 110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190% or 200%, etc.).

[0036] Alternatively, based on the mass content of the isocyanate-terminated prepolymer as 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is greater than 3% (for example, it may be 3.1%, 3.2%, 3.4%, 3.6%, 3.8% or 4%, etc.), and the mass percentage of the solvent added in step (4) is 50-150% (for example, it may be 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140% or 150%, etc.).

[0037] The present invention controls the amount of solvent added in step (4) within a specific range, thereby providing more rotation space for the flexible chain segments of the linear isocyanate prepolymer in the subsequent dispersion process, improving the dispersion performance and the stability of chain extension in the later stage, and further preparing an aqueous polyurethane emulsion synthesized from pure linear isocyanate with good dispersibility and high stability. If the amount of solvent added is too small, the molecular chains of the linear isocyanate-based polyurethane prepolymer are seriously entangled, the amount of solvent used is small, and the molecular chains of the linear isocyanate-based polyurethane prepolymer cannot be completely opened during the water emulsification process, so that the aqueous polyurethane emulsion prepared thereby is difficult to stabilize; if the amount of solvent added is too large, water will be the continuous phase, the solvent will be the dispersed phase, the emulsion particle size will be large, and the stability of the aqueous polyurethane emulsion after desolventization will be poor.

[0038] Preferably, the molar ratio of the amount of the hydrophilic chain extender in step (2) to the neutralizer in step (4) is 1:(0.8-1.2), for example, it can be 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.05, 1:1.1, 1:1.15 or 1:1.2, etc.

[0039] Preferably, the ratio between the mass of the isocyanate-terminated prepolymer in step (4) and the mass of the water in step (5) is 100g:(66.7-400)g, for example, it can be 100g:66.7g, 100g:81.82g, 100g:100g, 100g:122.2g, 100g:150g, 100g:185.7g, 100g:233.33g, 100g:300g or 100g:400g, etc.

[0040] Preferably, the molar ratio of the amount of the polyol in step (1) to the post-chain extender in step (5) is 1:(0.2-0.6), for example, it can be 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.55 or 1:0.6, etc.

[0041] It should be noted that, in the present invention, the catalyst A used in step (2) and step (3) is applicable to the dosage range commonly used in the art.

[0042] As a preferred technical solution of the present invention, the polyol is selected from any one or a combination of at least two of polyoxypropylene polyol (PPG), polyoxyethylene polyol (PEG), polytetramethylene ether glycol (PTMEG), polytrimethylene ether glycol (PO3G), polycaprolactone diol (PCL), polycarbonate polyol (PCDL), polyoxypropylene ethylene oxide copolyether polyol (PO-EO copolyether), polytetramethylene oxide copolyether (PTMEG-EO copolyether), polyester polyol, silicone polyol, polyol containing hydrophobic side chains or polyol containing hydrophilic side chains, preferably polyoxypropylene polyol.

[0043] Preferably, the number average molecular weight of the polyol is 1000-4000, for example, 1000, 1200, 1500, 1800, 2000, 2300, 2500, 2700, 3000, 3300, 3600 or 4000, etc.

[0044] Preferably, the isocyanate is selected from hexamethylene diisocyanate (HDI) and / or pentamethylene diisocyanate (PDI).

[0045] Preferably, the chain terminator is selected from one or more of benzoyl chloride, dibutyl phosphate, p-toluenesulfonic acid, monochloroacetic acid, dodecylbenzenesulfonic acid, adipoyl chloride, o-methylbenzenesulfonyl, dimethyl sulfate, etc., preferably any one of benzoyl chloride, dibutyl phosphate or p-toluenesulfonic acid or a combination of at least two thereof.

[0046] Preferably, the hydrophilic chain extender is selected from any one of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid or N,N-dimethylolmaleamic acid or a combination of at least two thereof, and more preferably dimethylolpropionic acid.

[0047] Preferably, the small molecule chain extender is selected from any one or a combination of at least two of ethylene glycol, diethylene glycol, methyl propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol or neopentyl glycol, and is further preferably any one or a combination of at least two of 1,4-butanediol, trimethylolpropane, neopentyl glycol or methyl propylene glycol.

[0048] Preferably, the catalyst A and the catalyst B are each independently selected from any one or a combination of at least two of bismuth laurate, bismuth isooctanoate, bismuth carboxylate, bismuth neodecanoate, bismuth cyclohexaneate or bismuth nitrate.

[0049] As a preferred technical solution of the present invention, the isocyanate-terminated compound includes any one or a combination of at least two of hexamethylene diisocyanate (HDI), pentamethylene diisocyanate (PDI) or an isocyanate-terminated prepolymer obtained by reacting a polyol and an isocyanate;

[0050] In the isocyanate-terminated prepolymer obtained by reacting polyol and isocyanate, the isocyanate is selected from hexamethylene diisocyanate (HDI) and / or pentamethylene diisocyanate (PDI).

[0051] Preferably, the isocyanate-terminated compound comprises hexamethylene diisocyanate (HDI) and / or pentamethylene diisocyanate (PDI).

[0052] Preferably, the solvent in step (2), step (3) and step (4) independently comprises any one of acetone, butanone, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide or dimethylacetamide, or a combination of at least two thereof.

[0053] Preferably, the solvent in step (2), step (3) and step (4) is acetone;

[0054] Preferably, the neutralizing agent is selected from any one of triethylamine, ammonia water, sodium hydroxide or dimethylethanolamine, or a combination of at least two thereof.

[0055] Preferably, the post-chain extender is selected from any one or a combination of at least two of ethylenediamine, hydrazine hydrate, isophoronediamine, hydroxyethyldiethylamine, diethylenetriamine, triethylenetetramine, γ-aminopropyltriethoxysilane (KH550) or N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (KH602).

[0056] Preferably, the aqueous polyurethane emulsion synthesized from pure linear isocyanate further comprises an auxiliary agent, and the auxiliary agent comprises an antioxidant.

[0057] Preferably, the antioxidant includes antioxidant 1010.

[0058] In the present invention, the auxiliary agent can be added before the polymerization reaction of the polyol and the isocyanate in step (1), such as firstly mixing the polyol and the auxiliary agent, and then adding the isocyanate thereto. In the present invention, the polyol and the auxiliary agent can be mixed and then dehydrated, and then the isocyanate is added thereto for polymerization reaction.

[0059] As a preferred technical solution of the present invention, the temperature for adding the isocyanate in step (1) is 40-80°C, for example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C.

[0060] Preferably, the polymerization reaction temperature in step (1) is 60-100°C (for example, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, etc.), and the reaction time is 2-4h (for example, 2h, 2.5h, 3h, 3.5h or 4h, etc.).

[0061] Preferably, after adding the chain terminator in step (1), the reaction temperature is 110-140°C (for example, it can be 110°C, 113°C, 116°C, 118°C, 120°C, 122°C, 124°C, 127°C, 130°C, 133°C, 136°C or 140°C, etc.), and the reaction time is 2-8h (for example, it can be 2h, 3h, 4h, 5h, 6h, 7h or 8h, etc.).

[0062] Preferably, the reaction after adding the chain terminator in step (1) is simultaneously evaporated to remove excess isocyanate monomers, and the isocyanate monomers removed by evaporation can be reused.

[0063] Preferably, the evaporation method includes vacuum evaporation and thin film evaporation.

[0064] Preferably, after the evaporation, based on the mass percentage of the prepolymer obtained in step (1) as 100%, the residual amount of isocyanate in the prepolymer is ≤1wt%, for example, it can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt% or 1wt%, etc.

[0065] Preferably, the step (1) further comprises a pretreatment step before the polymerization reaction, and the pretreatment method comprises: dehydrating the polyol.

[0066] Preferably, the temperature of the water removal treatment is 100-120°C (for example, it can be 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C or 120°C, etc.), and the time is 1-3h (for example, it can be 1h, 1.5h, 2h, 2.5h or 3h, etc.).

[0067] Preferably, the water removal treatment is carried out under vacuum;

[0068] Preferably, the water content in the polyol after the water removal treatment is ≤500 ppm, for example, it may be 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm or 500 ppm.

[0069] As a preferred technical solution of the present invention, the reaction temperature in step (2) is 40-80°C (for example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc.), and the reaction time is 2-4h (for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, etc.).

[0070] As a preferred technical solution of the present invention, the reaction temperature in step (3) is 40-80°C (for example, it can be 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc.), and the reaction time is 2-4h (for example, it can be 2h, 2.5h, 3h, 3.5h or 4h, etc.).

[0071] As a preferred technical solution of the present invention, the reaction temperature in step (4) is 30-45°C (for example, it can be 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C or 45°C, etc.), and the reaction time is 10-20min (for example, it can be 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min or 20min, etc.).

[0072] As a preferred technical solution of the present invention, the cooling method in step (5) comprises: introducing chilled water into the outer jacket of the reaction system for cooling.

[0073] Preferably, the temperature after cooling in step (5) is ≤30°C, for example, it can be 8°C, 10°C, 12°C, 15°C, 18°C, 20°C, 23°C, 25°C, 27°C or 30°C.

[0074] Preferably, the rotation speed of the high-speed dispersion in step (5) is ≥1000 rpm, for example, it can be 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm or 2000 rpm, etc.

[0075] Preferably, the temperature of the chain extension reaction in step (5) is 25-35°C (for example, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C or 35°C, etc.), and the time is 25-35min (for example, it can be 25min, 26min, 27min, 28min, 29min, 30min, 31min, 32min, 33min, 34min or 35min, etc.).

[0076] Preferably, the chain extension reaction in step (5) further includes a post-treatment step, and the post-treatment method includes reduced pressure distillation.

[0077] As a preferred technical solution of the present invention, the preparation method specifically comprises the following steps:

[0078] (1) Mixing a polyol and an optional auxiliary agent, performing a water removal treatment at 100-120° C. for 1-3 hours in a vacuum state, cooling the reaction system to 40-80° C. when the water content is ≤500 ppm, adding isocyanate thereto, heating the reaction system to 80-100° C. for polymerization reaction for 2-4 hours, adding a chain terminator thereto, reacting at 110-140° C. for 2-8 hours, and evaporating the reaction system to remove excess isocyanate monomers to obtain a prepolymer;

[0079] Wherein, the molar ratio of isocyanate to polyol is (4-10):1, and the molar ratio of polyol to chain terminator is 1:(0.001-0.002);

[0080] Taking the mass percentage of the prepolymer obtained in step (1) as 100%, the residual amount of isocyanate in the prepolymer is ≤1wt%;

[0081] (2) adding a hydrophilic chain extender, a small molecule chain extender, a catalyst A and a solvent to the reaction system obtained in step (1), and reacting at 40-80° C. for 2-4 hours to obtain a hydroxyl-terminated prepolymer;

[0082] Wherein, the molar ratio of the polyol in step (1) to the hydrophilic chain extender in step (2) is 1:(0.4-1.8), and the molar ratio of the polyol in step (1) to the small molecule chain extender in step (2) is 1:(0.3-1.7); the ratio between the mass of the prepolymer in step (1) and the mass of the solvent in step (2) is 100g:(5-40)g;

[0083] (3) adding a solvent, an isocyanate-terminated compound and a catalyst B to the reaction system obtained in step (2) and reacting at 40-80° C. for 2-4 hours to obtain an isocyanate-terminated prepolymer;

[0084] The molar ratio of the amount of the polyol in step (1) to the isocyanate-terminated compound in step (3) is 1:(1.2-4), and the ratio of the mass of the hydroxyl-terminated prepolymer in step (2) to the mass of the solvent in step (3) is 100 g:(5-40) g.

[0085] (4) adding a solvent and a neutralizing agent to the reaction system obtained in step (3), and reacting at 30-45° C. for 10-20 min;

[0086] Wherein, the molar ratio of the amount of the hydrophilic chain extender substance in step (2) to the amount of the neutralizer in step (4) is 1:(0.8-1.2);

[0087] (5) adding water at a temperature of 20-60° C. to the reaction system obtained in step (4) at a rotation speed of ≥1000 rpm, dispersing at high speed, and introducing chilled water into the outer jacket of the reaction system to cool the temperature to ≤30° C., maintaining the rotation speed of ≥1000 rpm, continuing the high-speed dispersion for 10-15 min, and then adding a post-chain extender thereto, performing chain extension at 25-35° C. for 25-35 min, and then distilling under reduced pressure to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate;

[0088] The ratio of the mass of the isocyanate-terminated prepolymer in step (3) to the mass of the water in step (5) is 100 g:(66.7-400) g, and the molar ratio of the amount of the polyol in step (1) to the post-chain extender in step (5) is 1:(0.2-0.6).

[0089] In the prepolymerization process of the present invention, an excess of PDI or HDI monomer is added to react with a polyol, and then a chain terminator is added and the monomer (which can be recycled) is removed by thin film evaporation to obtain a regular prepolymer structure, and a hydrophilic group and a chain extender are uniformly introduced into the chain segment by stepwise polymerization to synthesize a hydroxyl-terminated prepolymer, and finally an additional isocyanate monomer or other isocyanate-based prepolymer after a monosaccharide removal treatment is added to react at a lower reaction temperature, preferably between 60 and 80° C., to form an NCO-terminated prepolymer. A solvent amount of not less than 50% of the prepolymer mass is added, and the prepolymer temperature is reduced to 40-50° C., and a neutralizer is added to neutralize the hydrophilic chain extender. Deionized water at 20-60° C. is added under high-speed conditions for dispersion and emulsification, and after complete dispersion, the emulsion is reduced to below 30° C. by using ice-cold water, and a chain extension solution is added dropwise, and finally the solvent is removed in vacuo to obtain an aqueous polyurethane dispersion synthesized from pure linear isocyanate.

[0090] The waterborne polyurethane resin synthesized by the preparation method provided by the invention has the characteristics of regular molecules, narrow distribution, large molecular weight, high emulsion dispersibility, good storage stability and the like.

[0091] In a second aspect, the present invention provides an aqueous polyurethane emulsion synthesized from pure linear isocyanate and prepared by the preparation method described in the first aspect.

[0092] Compared with the prior art, the present invention has the following beneficial effects:

[0093] (1) The present invention designs a preparation method for synthesizing an aqueous polyurethane emulsion from pure linear isocyanate, further designs the molar ratio of isocyanate to polyol in step (1) to be within a specific range, and simultaneously prepares an aqueous polyurethane with regular molecules, narrow distribution, and large molecular weight by a stepwise polymerization method. The aqueous polyurethane emulsion prepared in this way has high dispersibility and good storage stability.

[0094] (2) The present invention further optimizes and improves the comprehensive performance of the aqueous polyurethane emulsion and the aqueous polyurethane resin by controlling the molar ratio of isocyanate to polyol in step (1) within a specific range, and by gradually polymerizing the reaction mixture, controlling the amount of solvent added in step (4) within a specific range, and controlling the water temperature of water added in step (5) within a specific range. DETAILED DESCRIPTION

[0095] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0096] The sources of some components in the embodiments and comparative examples are shown in Table 1 below:

[0097] Table 1

[0098] Polyol Type illustrate Polyoxypropylene glycol N210 The number average molecular weight is 1000, purchased from Jurong Ningwu New Materials Co., Ltd. Polyoxypropylene glycol N220 The number average molecular weight is 2000, purchased from Jurong Ningwu New Materials Co., Ltd. Polyoxypropylene glycol N230 The number average molecular weight is 3000, purchased from Jurong Ningwu New Materials Co., Ltd. Polycarbonate diol UH100 The number average molecular weight is 1000, purchased from Ube Industries, Ltd. Polytrimethylene glycol H2000 The number average molecular weight is 2000, purchased from SK, South Korea Antioxidant 1010 Purchased from Double Bond Chemical Co., Ltd., Taiwan, China

[0099] It should be noted that, for the convenience of calculation, the masses of different types of prepolymers in steps (1) to (3) in the following embodiments are replaced by theoretical calculated values.

[0100] The mass of the prepolymer obtained in step (1) is m1=n 多元醇 ×M 多元醇 +2n 多元醇 ×M 异氰酸酯 +m 抗氧剂 ;

[0101] The mass of the hydroxyl-terminated prepolymer obtained in step (2) is m2=m1+n 亲水扩链剂 ×M 亲水扩链剂 +n 小分子扩链剂 ×M 小分扩链剂 ;

[0102] The mass of the isocyanate-terminated prepolymer obtained in step (3) is m3=m2+n 异氰酸酯封端化合物 ×M 异氰酸酯封端化合物 ;

[0103] The mass m′ of the isocyanate groups in the isocyanate-terminated prepolymer in step (3) is equal to (n 异氰酸酯基 -n 羟基 )×M 异氰酸酯基 .

[0104] Example 1

[0105] This embodiment provides an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof, the preparation method is as follows:

[0106] (1) polyoxypropylene diol N210 (0.1 mol) and antioxidant 1010 (0.3 g) were mixed, and dehydrated under vacuum at 110° C. to make the water content of the reaction system ≤500 ppm, and then the temperature was reduced to 60° C., pentamethylene diisocyanate (0.5 mol) was added thereto, and the temperature was increased to 90° C. to carry out polymerization reaction for 3 h, and then benzoyl chloride (0.00015 mol) was added thereto, and vacuum was opened at 130° C. for 6 hours to remove the remaining PDI monomer until the residual monomer content was <1 wt%, and the temperature was reduced to 50° C. to obtain a prepolymer;

[0107] (2) adding dimethylolpropionic acid (0.1 mol), 1,4-butanediol (0.11 mol), bismuth carboxylate (0.06 g) and acetone (20 g) to the reaction system obtained in step (1), and reacting at 60° C. for 3 h to obtain a hydroxyl-terminated prepolymer;

[0108] (3) adding acetone (26 g), pentamethylene diisocyanate (0.2 mol) and bismuth carboxylate (0.06 g) to the prepolymer obtained in step (2), and reacting at 65° C. for 3 h to obtain an isocyanate-terminated prepolymer, wherein the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 4.08%, based on the mass content of the isocyanate-terminated prepolymer being 100%);

[0109] (4) adding 180 g of acetone and triethylamine (0.1 mol) to the reaction system containing the isocyanate-terminated prepolymer obtained in step (3), and reacting at 40° C. for 15 min;

[0110] Wherein, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 4.08%, and the mass percentage of acetone added in step (4) is 97.2%;

[0111] (5) Under the condition of a rotation speed of 1200 rpm, deionized water (430 g) at a temperature of 50° C. was added to the reaction system obtained in step (4), and high-speed dispersion was performed. Chilled water was introduced into the outer jacket of the reaction system to cool the reaction system to 20° C., and the rotation speed was maintained at 1200 rpm. High-speed dispersion was continued for 15 min, and then ethylenediamine solution (0.04 mol of ethylenediamine and 24 g of water) was added thereto. After chain extension was carried out at 30° C. for 30 min, reduced pressure distillation was performed to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate with a solid content of 30%.

[0112] Example 2

[0113] This embodiment provides an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof, the preparation method is as follows:

[0114] (1) polyoxypropylene diol N220 (0.1 mol) and antioxidant 1010 (0.3 g) were mixed, and dewatered at 100° C. in a vacuum state to make the water content of the reaction system ≤500 ppm, and then the temperature was lowered to 40° C., pentamethylene diisocyanate (0.7 mol) was added thereto, and the temperature was raised to 80° C. for polymerization reaction for 4 h, and then dibutyl phosphate (0.00015 mol) was added thereto, and the reaction was carried out at 110° C. for 8 h, and the vacuum was opened at 130° C. for 6 hours to remove the remaining PDI monomer until the residual monomer content was <1wt%, and the temperature was lowered to 50° C. to obtain a prepolymer;

[0115] (2) adding dihydroxymethylbutyric acid (0.12 mol), 1,4-butanediol (0.13 mol), bismuth carboxylate (0.06 g) and acetone (23 g) to the reaction system obtained in step (1), and reacting at 40° C. for 4 h to obtain a hydroxyl-terminated prepolymer;

[0116] (3) adding acetone (28 g), pentamethylene diisocyanate (0.25 mol) and bismuth carboxylate (0.06 g) to the prepolymer obtained in step (2), and reacting the mixture at 40° C. for 4 h to obtain an isocyanate-terminated prepolymer, wherein the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 2.81%, based on the mass content of the isocyanate-terminated prepolymer being 100%);

[0117] (4) adding acetone (450 g) and triethylamine (0.08 mol) to the reaction system containing the isocyanate-terminated prepolymer obtained in step (3), and reacting at 30° C. for 20 min;

[0118] Wherein, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 2.81%, and the mass percentage of acetone added in step (4) is 150.5%;

[0119] (5) Under the condition of a rotation speed of 1200 rpm, deionized water (632 g) at a temperature of 40° C. was added to the reaction system obtained in step (4), and high-speed dispersion was performed. Chilled water was introduced into the outer jacket of the reaction system to cool the reaction system to 30° C., and the rotation speed was maintained at 1200 rpm. High-speed dispersion was continued for 10 min, and then ethylenediamine solution (0.02 mol of ethylenediamine and 72 g of water) was added thereto. After chain extension was carried out at 30° C. for 30 min, reduced pressure distillation was performed to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate with a solid content of 30%.

[0120] Example 3

[0121] This embodiment provides an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof, the preparation method is as follows:

[0122] (1) polyoxypropylene diol N230 (0.1 mol) and antioxidant 1010 (0.3 g) were mixed, and dehydrated under vacuum at 120° C. to make the water content of the reaction system ≤500 ppm, and then the temperature was reduced to 80° C., and hexamethylene diisocyanate (0.6 mol) was added thereto. The temperature was increased to 100° C. to carry out polymerization reaction for 2.5 h, and then benzoyl chloride (0.0001 mol) was added thereto. The vacuum was opened at 140° C. for 6 hours to remove the remaining HDI monomer until the residual monomer content was <1 wt %, and the temperature was reduced to 50° C. to obtain a prepolymer;

[0123] (2) adding dimethylolbutyric acid (0.18 mol), trimethylolpropane (0.08 mol), bismuth carboxylate (0.06 g) and acetone (33 g) to the reaction system obtained in step (1), and reacting at 80° C. for 3 h to obtain a hydroxyl-terminated prepolymer;

[0124] (3) adding acetone (35 g), hexamethylene diisocyanate (0.28 mol) and bismuth carboxylate (0.06 g) to the prepolymer obtained in step (2), and reacting at 80° C. for 2 h to obtain an isocyanate-terminated prepolymer, wherein the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 1.61%, based on the mass content of the isocyanate-terminated prepolymer being 100%);

[0125] (4) adding 800 g of acetone and triethylamine (0.18 mol) to the reaction system containing the isocyanate-terminated prepolymer obtained in step (3), and reacting at 45° C. for 10 min;

[0126] Wherein, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 1.61%, and the mass percentage of acetone added in step (4) is 191.3%;

[0127] (5) Under the condition of a rotation speed of 1200 rpm, water (960 g) at a temperature of 45° C. is added to the reaction system obtained in step (4), and high-speed dispersion is performed. Chilled water is introduced into the outer jacket of the reaction system to cool the reaction system to 20° C., and the rotation speed is maintained at 1200 rpm. High-speed dispersion is continued for 15 min, and then a hydrazine hydrate solution (0.03 mol of hydrazine hydrate, 20 g of water) is added thereto. After chain extension at 30° C. for 30 min, reduced pressure distillation is performed to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate with a solid content of 30%.

[0128] Example 4

[0129] This embodiment provides an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof, the preparation method is as follows:

[0130] (1) polycarbonate diol UH100 (0.1 mol) and antioxidant 1010 (0.3 g) were mixed, and dehydrated under vacuum at 120° C. to make the water content of the reaction system ≤500 ppm, and then the temperature was reduced to 70° C., pentamethylene diisocyanate (0.5 mol) was added thereto, and the temperature was increased to 90° C. to carry out polymerization reaction for 3 h, and then p-toluenesulfonic acid (0.0002 mol) was added thereto, and vacuum was opened at 120° C. for 7 hours to remove the remaining PDI monomer until the residual monomer content was <1 wt%, and the temperature was reduced to 50° C. to obtain a prepolymer;

[0131] (2) adding dimethylolpropionic acid (0.04 mol), methyl propanediol (0.17 mol), bismuth carboxylate (0.06 g) and acetone (40 g) to the reaction system obtained in step (1), and reacting at 60° C. for 3 h to obtain a hydroxyl-terminated prepolymer;

[0132] (3) adding acetone (30 g), pentamethylene diisocyanate (0.2 mol) and bismuth carboxylate (0.06 g) to the prepolymer obtained in step (2), and reacting at 60° C. for 3 h to obtain an isocyanate-terminated prepolymer, wherein the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 4.14%, based on the mass content of the isocyanate-terminated prepolymer being 100%);

[0133] (4) adding 162 g of acetone and triethylamine (0.04 mol) to the reaction system containing the isocyanate-terminated prepolymer obtained in step (3), and reacting at 35° C. for 15 min;

[0134] Wherein, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 4.14%, and the mass percentage of acetone added in step (4) is 88.7%;

[0135] (5) Under the condition of a rotation speed of 1200 rpm, deionized water (430 g) at a temperature of 30° C. is added to the reaction system obtained in step (4), and high-speed dispersion is performed. Chilled water is introduced into the outer jacket of the reaction system to cool the reaction system to 25° C., and the rotation speed is maintained at 1200 rpm. High-speed dispersion is continued for 10-15 min, and then ethylenediamine solution (0.02 mol of ethylenediamine and 20 g of water) is added thereto. After chain extension at 30° C. for 30 min, reduced pressure distillation is performed to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate with a solid content of 30%.

[0136] Example 5

[0137] This embodiment provides an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof, the preparation method is as follows:

[0138] (1) polytrimethylene glycol (0.1 mol) and antioxidant 1010 (0.3 g) were mixed, and dehydrated under vacuum at 120° C. to make the water content of the reaction system ≤500 ppm, and then the temperature was reduced to 60° C., hexamethylene diisocyanate (0.65 mol) was added thereto, and the temperature was increased to 90° C. to carry out polymerization reaction for 3 h, and then benzoyl chloride (0.00018 mol) was added thereto, and vacuum was opened at 130° C. for 6 hours to remove the remaining HDI monomer until the residual monomer content was <1 wt%, and the temperature was reduced to 50° C. to obtain a prepolymer;

[0139] (2) adding dimethylolpropionic acid (0.08 mol), 1,4-butanediol (0.15 mol), bismuth carboxylate (0.06 g) and acetone (35 g) to the reaction system obtained in step (1), and reacting at 60° C. for 3 h to obtain a hydroxyl-terminated prepolymer;

[0140] (3) adding acetone (28 g), hexamethylene diisocyanate (0.2 mol) and bismuth carboxylate (0.06 g) to the prepolymer obtained in step (2), and reacting the mixture at 60° C. for 3 h to obtain an isocyanate-terminated prepolymer, wherein the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 2.02%, based on the mass content of the isocyanate-terminated prepolymer being 100%);

[0141] (4) adding 580 acetone and triethylamine (0.08 mol) to the reaction system containing the isocyanate-terminated prepolymer obtained in step (3), and reacting at 40° C. for 20 min;

[0142] Wherein, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 2.02%, and the mass percentage of acetone added in step (4) is 198.8%;

[0143] (5) Under the condition of a rotation speed of 1200 rpm, deionized water (650 g) at a temperature of 35° C. was added to the reaction system obtained in step (4), and high-speed dispersion was performed. Chilled water was introduced into the outer jacket of the reaction system to cool the reaction system to 30° C., and the rotation speed was maintained at 1200 rpm. High-speed dispersion was continued for 15 min, and then hydrazine hydrate solution (0.06 mol of hydrazine hydrate, 40 g of water) was added thereto. After chain extension was carried out at 30° C. for 25 min, reduced pressure distillation was performed to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate with a solid content of 30%.

[0144] Example 6-Example 13, Comparative Example 1-Comparative Example 5

[0145] Example 6-Example 13 and Comparative Example 1-Comparative Example 5 respectively provide an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof, which differs from Example 1 only in that:

[0146] Example 6: The amount of pentamethylene diisocyanate used in step (1) is 0.35 mol;

[0147] Example 7: The amount of pentamethylene diisocyanate used in step (1) is 0.4 mol;

[0148] Example 8: The amount of pentamethylene diisocyanate used in step (1) is 0.8 mol;

[0149] Example 9: The amount of pentamethylene diisocyanate used in step (1) is 1 mol;

[0150] Example 10: The temperature of the deionized water added in step (5) is 20°C;

[0151] Example 11: The temperature of the deionized water added in step (5) is 60°C;

[0152] Embodiment 12: In step (4), the mass percentage of acetone added in step (4) is 50%, based on the mass content of the isocyanate-terminated prepolymer being 100%;

[0153] Embodiment 13: In step (4), the mass percentage of acetone added in step (4) is 150%, based on the mass content of the isocyanate-terminated prepolymer being 100%;

[0154] Comparative Example 1: The amount of pentamethylene diisocyanate used in step (1) is 0.3 mol;

[0155] Comparative Example 2: The temperature of the deionized water added in step (5) is 15°C;

[0156] Comparative Example 3: The temperature of the deionized water added in step (5) is 70° C.

[0157] Comparative Example 4: In step (4), the mass percentage of acetone added in step (4) is 30%, based on the mass content of the isocyanate-terminated prepolymer being 100%;

[0158] Comparative Example 5: In step (4), the mass content of the isocyanate-terminated prepolymer is 100%, and the mass percentage of acetone added in step (4) is 200%;

[0159] Other conditions are the same as in Example 1.

[0160] Comparative Example 6

[0161] This comparative example provides an aqueous polyurethane emulsion synthesized from pure linear isocyanate and a preparation method thereof, the preparation method is as follows:

[0162] (1) polyoxypropylene diol N210 (0.1 mol) and antioxidant 1010 (0.3 g) were mixed, and dewatered at 110° C. in a vacuum state to make the water content of the reaction system ≤500 ppm, and then the temperature was lowered to 60° C., dimethylol propionic acid (0.1 mol) and pentamethylene diisocyanate (0.4 mol) were added thereto, and the temperature was raised to 90° C. to carry out polymerization reaction for 3 h to obtain a prepolymer;

[0163] (2) adding 1,4-butanediol (0.12 mol), bismuth carboxylate (0.06 g) and acetone (40 g) to the reaction system obtained in step (1), and reacting at 60° C. for 3 h to obtain an isocyanate-terminated prepolymer, wherein the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 3.6%, based on the mass content of the isocyanate-terminated prepolymer being 100%);

[0164] (3) adding acetone (185.8 g) and triethylamine (0.1 mol) to the reaction system containing the isocyanate-terminated prepolymer obtained in step (2), and reacting at 40° C. for 15 min;

[0165] Wherein, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 3.6%, and the mass percentage of acetone added in step (3) is 100%;

[0166] (4) Under the condition of a rotation speed of 1200 rpm, deionized water (400 g) at a temperature of 50° C. was added to the reaction system obtained in step (3), and high-speed dispersion was performed. Chilled water was introduced into the outer jacket of the reaction system to cool the reaction system to 20° C., and the rotation speed was maintained at 1200 rpm. High-speed dispersion was continued for 15 min, and then an ethylenediamine aqueous solution (0.04 mol of ethylenediamine and 40 g of deionized water) was added thereto. After chain extension was carried out at 30° C. for 30 min, reduced pressure distillation was performed to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate with a solid content of 30%.

[0167] The properties of the aqueous polyurethane emulsion synthesized from pure linear isocyanate provided in the above examples and comparative examples were tested, and the specific testing method is as follows:

[0168] (1) Emulsion Appearance: Observe the appearance of the aqueous polyurethane emulsion synthesized from pure linear isocyanate provided in the above examples and comparative examples.

[0169] (2) Filtration performance (200 mesh): The aqueous polyurethane emulsion synthesized from pure linear isocyanate provided in the above examples and comparative examples was filtered using 200 mesh filter paper, and the filtration conditions were observed. The filtration rating was 1-5: 1 for being unable to filter, 2 for being difficult to filter, 3 for being able to filter but requiring repeated replacement of the filter screen, 4 for being easy to filter but with obvious particles after filtration, and 5 for being easy to filter but with no obvious particles.

[0170] (3) Stability: The aqueous polyurethane emulsions synthesized from pure linear isocyanate provided in the above examples and comparative examples with different storage times were placed in a centrifuge tube and centrifuged at 3000 rpm for 15 min to observe whether the aqueous polyurethane emulsion synthesized from pure linear isocyanate was separated. The storage time when separation occurred was recorded. If no separation occurred after centrifugation after 6 months of storage, it was recorded as "stable for 6 months".

[0171] The aqueous polyurethane emulsion synthesized from pure linear isocyanate provided in the above embodiment and comparative example is used to prepare a film. The preparation method of the film is as follows: the aqueous polyurethane emulsion synthesized from pure linear isocyanate provided in the above embodiment and comparative example is placed in a flat polytetrafluoroethylene mold respectively and weighed according to the solid content (dry film thickness is about 1 mm), and after natural drying to form a film, it is placed in an oven at 60° C. for aging for 6 hours, and then taken out for use; its mechanical properties are tested: the film is cut into a dumbbell shape of 30 mm×3 mm, and tested using a universal tensile testing machine, with a tensile speed of 100 mm / min, and the test standard refers to DIN 53504 (2017-03);

[0172] (4) 100% modulus: tested using a universal tensile testing machine at a tensile speed of 100 mm / min;

[0173] (5) Elongation at break: tested using a universal tensile testing machine at a tensile speed of 100 mm / min;

[0174] (6) Breaking strength: tested using a universal tensile testing machine at a tensile speed of 100 mm / min.

[0175] The above performance test results are shown in Table 2 below:

[0176] Table 2

[0177]

[0178]

[0179] As can be seen from the above content, the present invention designs a preparation method for synthesizing an aqueous polyurethane emulsion from pure linear isocyanate, further designs the molar ratio of isocyanate to polyol in step (1) to be within a specific range, and the water temperature of adding water in step (5) to be within a specific range, and simultaneously prepares an aqueous polyurethane with regular molecules, narrow distribution and large molecular weight by stepwise polymerization. The aqueous polyurethane emulsion prepared in this way has high dispersibility and good storage stability. The emulsion presents a blue light semi-transparent appearance, the filtration grade is level 4 or level 5, and no separation occurs after centrifugation after storage for 6 months. The 100% modulus is 0.35-1.4 MPa, the elongation at break is 720-1502%, and the breaking strength is 2.9-12.6 MPa.

[0180] It can be seen from Examples 1-13 and Comparative Examples 4-6 that the present invention further optimizes and improves the comprehensive performance of the aqueous polyurethane emulsion and the aqueous polyurethane resin by controlling the molar ratio of isocyanate to polyol in step (1) within a specific range, and by gradually polymerizing the step (4), controlling the amount of solvent added within a specific range, and the water temperature of water added in step (5) within a specific range.

[0181] In summary, the present invention designs a preparation method for synthesizing an aqueous polyurethane emulsion from pure linear isocyanate, further designs the molar ratio of isocyanate to polyol in step (1) to be within a specific range, and the water temperature of adding water in step (5) to be within a specific range, and simultaneously prepares an aqueous polyurethane with regular molecules, narrow distribution and large molecular weight by stepwise polymerization, and the aqueous polyurethane emulsion prepared thereby has high dispersibility and good storage stability.

[0182] The applicant declares that the present invention illustrates the detailed process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing an aqueous polyurethane emulsion by synthesizing pure linear isocyanate, characterized in that: The preparation method comprises the following steps: (1) after polymerizing polyol and isocyanate, adding a chain terminator and reacting to obtain a prepolymer; (2) adding a hydrophilic chain extender, a small molecule chain extender, a catalyst A and a solvent to the reaction system obtained in step (1), reacting to obtain a hydroxyl-terminated prepolymer; (3) adding a solvent, an isocyanate-terminated compound and a catalyst B to the reaction system obtained in step (2) to react and obtain an isocyanate-terminated prepolymer; (4) adding a solvent and a neutralizing agent to the reaction system obtained in step (3) to react; (5) adding water to the reaction system obtained in step (4), dispersing at high speed, cooling, and then adding a post-chain extender thereto to carry out a chain extension reaction to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate; The molar ratio of isocyanate to polyol in step (1) is ≥3.5:1; The water temperature added in step (5) is 20-60°C.

2. The preparation method according to claim 1, characterized in that: The molar ratio of isocyanate to polyol in step (1) is (3.5-10):1, preferably (4-8):1; Preferably, the molar ratio of the polyol to the chain terminator in step (1) is 1:(0.001-0.002); Preferably, the molar ratio of the polyol in step (1) to the hydrophilic chain extender in step (2) is 1:(0.4-1.8); Preferably, the molar ratio of the polyol in step (1) to the small molecule chain extender in step (2) is 1:(0.3-1.7); Preferably, the ratio between the mass of the prepolymer in step (1) and the mass of the solvent in step (2) is 100 g:(5-40) g; Preferably, the molar ratio of the amount of the polyol in step (1) to the isocyanate-terminated compound in step (3) is 1:(1.2-4); Preferably, the ratio between the mass of the hydroxyl-terminated prepolymer in step (2) and the mass of the solvent in step (3) is 100 g:(5-40) g.

3. The preparation method according to claim 1 or 2, characterized in that: Taking the mass content of the isocyanate-terminated prepolymer as 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 1-2%, and the mass percentage of the solvent added in step (4) is 150-300% of the mass of the isocyanate prepolymer; Alternatively, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is 2-3%, and the mass percentage of the solvent added in step (4) is 100-200% of the mass of the isocyanate prepolymer; Alternatively, based on the mass content of the isocyanate-terminated prepolymer being 100%, the mass percentage of isocyanate groups in the isocyanate-terminated prepolymer is greater than 3%, and the mass percentage of the solvent added in step (4) is 50-150% of the mass of the isocyanate prepolymer; Preferably, the molar ratio of the amount of the hydrophilic chain extender substance in step (2) to the amount of the neutralizer in step (4) is 1:(0.8-1.2); Preferably, the ratio between the mass of the isocyanate-terminated prepolymer in step (3) and the mass of the water in step (5) is 100 g: (66.7-400) g; Preferably, the molar ratio of the amount of the polyol in step (1) to the amount of the post-chain extender in step (5) is 1:(0.2-0.6).

4. The preparation method according to any one of claims 1 to 3, characterized in that The polyol is selected from any one or a combination of at least two of polyoxypropylene polyol, polyoxyethylene polyol, polytetramethylene ether glycol, polytrimethylene ether glycol, polycaprolactone diol, polycarbonate polyol, polyoxypropylene ethylene oxide copolyether polyol, polytetramethylene oxide copolymer, polyester polyol, silicone polyol, polyol containing hydrophobic side chains or polyol containing hydrophilic side chains, preferably polyoxypropylene polyol; Preferably, the number average molecular weight of the polyol is 1000-4000; Preferably, the isocyanate is selected from hexamethylene diisocyanate and / or pentamethylene diisocyanate; Preferably, the chain terminator is selected from one or more of benzoyl chloride, dibutyl phosphate, p-toluenesulfonic acid, monochloroacetic acid, dodecylbenzenesulfonic acid, adipoyl chloride, o-methylbenzenesulfonyl, dimethyl sulfate, etc., preferably any one of benzoyl chloride, dibutyl phosphate or p-toluenesulfonic acid or a combination of at least two thereof; Preferably, the hydrophilic chain extender is selected from any one or a combination of at least two of dimethylolpropionic acid, dimethylolbutyric acid, tartaric acid or N,N-dimethylolmaleamic acid, preferably dimethylolpropionic acid; Preferably, the small molecule chain extender is selected from any one or a combination of at least two of ethylene glycol, diethylene glycol, methyl propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol or neopentyl glycol, preferably any one or a combination of at least two of 1,4-butanediol, trimethylolpropane, neopentyl glycol or methyl propylene glycol; Preferably, the catalyst A and the catalyst B are each independently selected from any one or a combination of at least two of bismuth laurate, bismuth isooctanoate, bismuth carboxylate, bismuth neodecanoate, bismuth cyclohexaneate or bismuth nitrate.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The isocyanate-terminated compound includes any one or a combination of at least two of hexamethylene diisocyanate, pentamethylene diisocyanate, or an isocyanate-terminated prepolymer obtained by reacting a polyol with an isocyanate; The isocyanate in the isocyanate-terminated prepolymer obtained by the reaction of polyol and isocyanate is selected from hexamethylene diisocyanate and / or pentamethylene diisocyanate; Preferably, the isocyanate-terminated compound comprises hexamethylene diisocyanate and / or pentamethylene diisocyanate; Preferably, the solvent in step (2), step (3) and step (4) independently comprises any one of acetone, butanone, N-methylpyrrolidone, N-ethylpyrrolidone, dimethylformamide or dimethylacetamide, or a combination of at least two thereof; Preferably, the solvent in step (2), step (3) and step (4) is acetone; Preferably, the neutralizing agent is selected from any one or a combination of at least two of triethylamine, ammonia water, sodium hydroxide or dimethylethanolamine; Preferably, the post-chain extender is selected from any one or a combination of at least two of ethylenediamine, hydrazine hydrate, isophoronediamine, hydroxyethyldiethylamine, diethylenetriamine, triethylenetetramine, γ-aminopropyltriethoxysilane or N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The polymerization reaction temperature in step (1) is 60-100° C. and the reaction time is 2-4 hours; Preferably, after adding the chain terminator in step (1), the reaction temperature is 110-140° C. and the reaction time is 2-8 h; Preferably, the step (1) further includes a pretreatment step before the polymerization reaction, and the pretreatment method includes: removing water from the polyol; Preferably, the temperature of the water removal treatment is 100-120°C and the time is 1-3h; Preferably, the water removal treatment is carried out under vacuum; Preferably, the water content in the polyol after the water removal treatment is ≤500 ppm.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The reaction temperature in step (2) is 40-80°C and the reaction time is 2-4h; Preferably, the reaction temperature in step (3) is 40-80°C and the reaction time is 2-4h; Preferably, the reaction temperature in step (4) is 30-45°C and the reaction time is 10-20 min.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The cooling method in step (5) comprises: introducing chilled water into the outer jacket of the reaction system to cool it; Preferably, the temperature after cooling in step (5) is ≤30°C; Preferably, the speed of the high-speed dispersion in step (5) is ≥1000 rpm; Preferably, the temperature of the chain extension reaction in step (5) is 25-35°C and the time is 25-35min; Preferably, the chain extension reaction in step (5) further includes a post-treatment step, and the post-treatment method includes reduced pressure distillation.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The preparation method specifically comprises the following steps: (1) mixing a polyol and an optional auxiliary agent, performing a water removal treatment at 100-120° C. for 1-3 hours in a vacuum state, cooling the reaction system to 40-80° C. when the water content is ≤500 ppm, adding isocyanate thereto, heating the reaction system to 80-100° C. for polymerization reaction for 2-4 hours, adding a chain terminator thereto, and reacting at 110-140° C. for 2-8 hours to obtain a prepolymer; Wherein, the molar ratio of isocyanate to polyol is (4-10):1, and the molar ratio of polyol to chain terminator is 1:(0.001-0.002); (2) adding a hydrophilic chain extender, a small molecule chain extender, a catalyst A and a solvent to the reaction system obtained in step (1), and reacting at 40-80° C. for 2-4 hours to obtain a hydroxyl-terminated prepolymer; Wherein, the molar ratio of the polyol in step (1) to the hydrophilic chain extender in step (2) is 1:(0.4-1.8), the molar ratio of the polyol in step (1) to the small molecule chain extender in step (2) is 1:(0.3-1.7); the ratio between the mass of the prepolymer in step (1) and the mass of the solvent in step (2) is 100 g:(5-40) g; (3) adding a solvent, an isocyanate-terminated compound and a catalyst B to the reaction system obtained in step (2) and reacting the mixture at 40-80° C. for 2-4 hours to obtain an isocyanate-terminated prepolymer; The molar ratio of the amount of the polyol in step (1) to the isocyanate-terminated compound in step (3) is 1:(1.2-4), and the ratio of the mass of the hydroxyl-terminated prepolymer in step (2) to the mass of the solvent in step (2) is 100 g:(5-40) g. (4) adding a solvent and a neutralizing agent to the reaction system obtained in step (3), and reacting at 30-45° C. for 10-20 min; Wherein, the molar ratio of the amount of the hydrophilic chain extender substance in step (2) to the amount of the neutralizer in step (4) is 1:(0.8-1.2); (5) adding water at a temperature of 20-60° C. to the reaction system obtained in step (4) at a rotation speed of ≥1000 rpm, dispersing at high speed, and introducing chilled water into the outer jacket of the reaction system to cool the temperature to ≤30° C., maintaining the rotation speed of ≥1000 rpm, continuing the high-speed dispersion for 10-15 min, and then adding a post-chain extender thereto, performing chain extension at 25-35° C. for 25-35 min, and then distilling under reduced pressure to obtain an aqueous polyurethane emulsion synthesized from pure linear isocyanate; Among them, the ratio between the mass of the isocyanate-terminated prepolymer in step (3) and the mass of the water in step (5) is 100g:(66.7-400)g, and the molar ratio between the amount of the polyol in step (1) and the post-chain extender in step (5) is 1:(0.2-0.6).

10. An aqueous polyurethane emulsion synthesized from pure linear isocyanate prepared by the preparation method according to any one of claims 1 to 9.

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