Preparation Method of Solvent-Free Aqueous Ink Binder Polyurethane

Abstract

The present invention discloses a method for preparing a solvent-free water-based ink binder polyurethane, belonging to the technical field of water-based ink materials. In response to the problems of low solid content, poor stability, and poor adhesion in existing polyurethane emulsions, the present invention provides a method for preparing a solvent-free water-based ink binder polyurethane, comprising: preparing prepolymers of different particle sizes at a rotation speed of 1500 to 2000 rpm and direct addition of water, and at a rotation speed of 300 to 500 rpm and dropwise addition of water; then mixing the two prepolymers, methyl methacrylate, and an initiator, and subjecting the mixture to a free radical polymerization reaction to obtain the polyurethane emulsion. By controlling the rotation speed during the shearing process and the method of adding water, and then controlling the mixing ratio of prepolymers of different particle sizes, and adding a non-solvent-type diluent and introducing a HEA terminal crosslinking agent, the present invention obtains a polyurethane emulsion with a high solid content and a multivariate particle size distribution, significantly improving the performance of the polyurethane.

Description

Technical Field

[0001] The invention belongs to the technical field of water-based ink materials, and particularly relates to a solvent-free water-based ink binder polyurethane, a preparation method and an application thereof. Background Art

[0002] Water-based inks are increasingly used in the printing industry due to their safety, environmental friendliness, non-toxicity, non-flammability, non-explosion, and near-zero volatile organic compounds (VOCs). However, current water-based gravure inks still suffer from drawbacks such as complex preparation, high costs, limited applications, and poor water resistance, adhesion, abrasion resistance, and drying properties.

[0003] Water-based inks are composed of binders, pigments, and additives. The water-based resin binder, as the "heart" of the ink, plays a crucial role, its properties determining the performance of the water-based ink. Currently, the most commonly used water-based resin binders are water-based acrylic resins and water-based polyurethane resins. Water-based polyurethane, with its excellent wear resistance, scratch resistance, solvent resistance, low-temperature performance, and high gloss, has been widely used in printing inks for a wide range of food packaging.

[0004] Among the existing waterborne polyurethane synthesis methods, the prepolymer method and the acetone method are generally used. The viscosity of the polyurethane prepolymer before emulsification in the prepolymer method is usually large, which easily causes dispersion difficulties and even emulsification failure. In addition, the high-viscosity prepolymer will also adhere to the equipment, resulting in low yield and difficult equipment cleaning. The acetone method is intended to solve the solubility problem of some raw materials in the synthesis stage on the one hand, and to adjust the viscosity of the prepolymer dispersion stage on the other hand. The solvent in the system cannot be completely removed by distillation, and the presence of organic solvents increases costs and causes environmental pollution. These are all not conducive to the promotion and application of waterborne polyurethane. In addition, polyurethane emulsions still have problems such as low solid content, poor stability, and poor adhesion. Summary of the Invention

[0005] In response to the problems of the prior art, the present invention starts with the synthesis of polyurethane, a water-based ink binder, and introduces an acrylic copolymer through molecular structure design, hoping that the hybrid aqueous dispersion can complement each other's advantages. The high tensile strength and impact strength of polyurethane are organically combined with the good adhesion, weather resistance, and acid and alkali resistance of acrylic ester at a low cost to synthesize a solvent-free polyurethane emulsion. At the same time, through step-by-step synthesis, small-sized polyurethane prepolymers are added to increase the solid content of the polyurethane emulsion.

[0006] The present invention first provides a method for preparing a solvent-free water-based ink binder polyurethane, which comprises the following steps:

[0007] A. Synthesis of polyurethane prepolymers WPU-P and WPU-L:

[0008] Synthesis of WPU-P:

[0009] a1. After the diol and isocyanate are uniformly mixed, a first chain extension reaction is carried out. After the reaction is completed, 2,2-dimethylol propionic acid and a catalyst are added to carry out a second chain extension reaction. After the reaction is completed, hydroxyethyl acrylate and a diluent are added to carry out an end-capping reaction. After the reaction is completed, the system is cooled to room temperature (25-35°C) and triethylamine is added to neutralize the system to a pH of 7-8 (after adding triethylamine, the reaction can be allowed to react for 10-20 minutes to ensure sufficient neutralization);

[0010] b1. Add water to the system neutralized in step a1 (directly add all the water to the system by pouring, etc.) while stirring at 1500-2000 rpm. The amount of water is controlled to keep the solid content of the system at 30-60%, and shear the mixture to obtain a polyurethane prepolymer WPU-P.

[0011] Synthesis of WPU-L:

[0012] a2. After the diol and isocyanate are uniformly mixed, a first chain extension reaction is carried out. After the reaction is completed, 2,2-dimethylol propionic acid and a catalyst are added to carry out a second chain extension reaction. After the reaction is completed, hydroxyethyl acrylate and a diluent are added to carry out an end-capping reaction. After the reaction is completed, the system is cooled to room temperature (25-35° C.) and triethylamine is added to neutralize the system to a pH of 7-8 (after adding triethylamine, the reaction can be allowed to react for 10-20 minutes to ensure sufficient neutralization);

[0013] b2. Add water dropwise to the system neutralized in step a2 under stirring at 300-500 rpm, controlling the solid content of the system to 30-60%, and complete the addition within 10 min. Shear the mixture to obtain a polyurethane prepolymer WPU-L.

[0014] B. Synthesis of polyurethane as solvent-free water-based ink binder:

[0015] The WPU-P obtained in step b1, the WPU-L obtained in step b2, methyl methacrylate and an initiator are mixed to carry out a free radical polymerization reaction. After the reaction is completed, the temperature is lowered and the material is discharged to obtain a solvent-free water-based ink binder polyurethane;

[0016] In step a1, the molar ratio of the diol, isocyanate, 2,2-dimethylolpropionic acid (DMPA) and hydroxyethyl acrylate (HEA) is 4-6:2:1-3:0.5-1.5;

[0017] In step a1, the catalyst is dibutyltin dilaurate (DBTDL) or organic bismuth; in step a1, the amount of the catalyst is 0.1 to 2% of the molar amount of the isocyanate;

[0018] In step a1, the diluent is an acrylic ester diluent; in step a1, the amount of the diluent is 1 to 3% of the isocyanate mole;

[0019] In step a2, the molar ratio of the diol, isocyanate, 2,2-dimethylolpropionic acid (DMPA) and hydroxyethyl acrylate (HEA) is 4-6:2:1-3:0.5-1.5;

[0020] In step a2, the catalyst is dibutyltin dilaurate (DBTDL) or organic bismuth; in step a2, the amount of the catalyst is 0.1 to 2% of the mole of isocyanate;

[0021] In step a2, the diluent is an acrylic ester diluent; in step a2, the amount of the diluent is 1 to 3% of the isocyanate mole;

[0022] In step B, the mass ratio of WPU-P to WPU-L is 1 to 3:6.

[0023] Among them, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a1, the diol is at least one of polyether diol (PD), polybutylene adipate (BPBA), and polycaprolactone diol (PCL), and its number average molecular weight is 500 to 2000, and the moisture content is not higher than 0.05% (it can be dried in a vacuum drying oven at a temperature of 100°C for 3 to 5 hours before use).

[0024] Among them, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a1, the isocyanate is at least one of isophorone diisocyanate (IPDI) or toluene diisocyanate (TDI).

[0025] Preferably, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a1, the acrylate diluent is at least one of trimethylolpropane trimethacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, 4-hydroxybutyl acrylate, 1,4-butanediol diacrylate, octyl acrylate, tetradecyl acrylate, lauryl methacrylate, and lauryl acrylate.

[0026] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a1, the temperature of the first chain extension reaction is 50-100°C.

[0027] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a1, the time of the first chain extension reaction is 1 to 2 hours.

[0028] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a1, the temperature of the second chain extension reaction is 50-100°C.

[0029] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a1, the time of the second chain extension reaction is 0.5 to 2 hours.

[0030] Wherein, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a1, the temperature of the end-capping reaction is 50-100°C.

[0031] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a1, the time of the end-capping reaction is 1 to 2 hours.

[0032] Among them, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a2, the diol is at least one of polyether diol (PD), polybutylene adipate (BPBA), and polycaprolactone diol (PCL), and its number average molecular weight is 500 to 2000, and the moisture content is not higher than 0.05% (dried in a vacuum drying oven at a temperature of 100°C for 3 to 5 hours before use).

[0033] Among them, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a2, the isocyanate is at least one of isophorone diisocyanate (IPDI) or toluene diisocyanate (TDI).

[0034] Preferably, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a2, the acrylate diluent is at least one of trimethylolpropane trimethacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, 4-hydroxybutyl acrylate, 1,4-butanediol diacrylate, octyl acrylate, tetradecyl acrylate, lauryl methacrylate, and lauryl acrylate.

[0035] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a2, the temperature of the first chain extension reaction is 50-100°C.

[0036] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a2, the time of the first chain extension reaction is 1 to 2 hours.

[0037] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a2, the temperature of the second chain extension reaction is 50-100°C.

[0038] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a2, the time of the second chain extension reaction is 0.5 to 2 hours.

[0039] Wherein, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step a2, the temperature of the end-capping reaction is 50-100°C.

[0040] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step a2, the time of the end-capping reaction is 1 to 2 hours.

[0041] Preferably, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step b1, the rotation speed is controlled to be 1500 rpm.

[0042] Wherein, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step b1, the shearing time is 45 minutes to 1 hour.

[0043] Preferably, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step b2, the rotation speed is controlled to be 300 rpm.

[0044] Wherein, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step b2, the shearing time is 45 minutes to 1 hour.

[0045] Wherein, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step B, the amount of methyl methacrylate used is 2 to 5 times the molar amount of hydroxyethyl acrylate used to prepare WPU-L.

[0046] Wherein, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step B, the amount of the initiator used is 0.5-2% by mole of methyl methacrylate.

[0047] Among them, in the preparation method of the above-mentioned solvent-free water-based ink binder polyurethane, in step B, the initiator is a free radical initiator potassium persulfate.

[0048] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step B, the temperature of the free radical polymerization reaction is 70-90°C.

[0049] Wherein, in the above-mentioned method for preparing the solvent-free water-based ink binder polyurethane, in step B, the time of the free radical polymerization reaction is 1 to 2 hours.

[0050] The solvent-free water-based ink binder polyurethane prepared by the invention has the advantages of high solid content, storage stability, high adhesion, high hardness, low water absorption rate and the like, and its solid content can reach 50-60%.

[0051] Based on the excellent performance of the above-mentioned solvent-free water-based ink binder polyurethane, the present invention also provides its application in water-based gravure printing ink.

[0052] In the present invention, the water used can be deionized water, distilled water, ultrapure water, etc.

[0053] Beneficial effects of the present invention:

[0054] The present invention adjusts the viscosity of the system by adding a non-solvent diluent and controlling the amount of the added diluent, and the residual diluent can be used as a crosslinking agent. By introducing a HEA terminal crosslinking agent and crosslinking with MMA, the adhesion of the water-based polyurethane is effectively improved, the water absorption rate is reduced, and the excellent performance of acrylate is integrated. At the same time, the rotation speed during the shearing process and the water addition method are used to control the particle size of the polyurethane emulsion, and then the mixing ratio of prepolymers with different particle sizes is controlled to increase the packing density of the latex particles and reduce the hydration layer. That is, by controlling the size and volume, a polyurethane emulsion with a multivariate particle size distribution and a high solid content is obtained, thereby improving the performance of the emulsion.

[0055] The present invention obtains a high-solid-content water-based polyurethane emulsion through a green, environmentally friendly, solvent-free method. The emulsion has a stability of more than 3 months. The obtained high-solid-content water-based polyurethane can improve the space utilization rate of equipment in the preparation process, reduce the energy consumption and cost of unit mass product, give full play to its inherent characteristics, and enable it to be used in water-based gravure printing ink. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The synthetic route of the solvent-free water-based ink binder polyurethane of the present invention is shown in FIG. DETAILED DESCRIPTION

[0057] Specifically, a method for preparing a solvent-free water-based ink binder polyurethane comprises the following steps:

[0058] A. Synthesis of polyurethane prepolymers WPU-P and WPU-L:

[0059] Synthesis of WPU-P:

[0060] a1. After the diol and isocyanate are uniformly mixed, a first chain extension reaction is carried out. After the reaction is completed, 2,2-dimethylol propionic acid and a catalyst are added to carry out a second chain extension reaction. After the reaction is completed, hydroxyethyl acrylate and a diluent are added to carry out an end-capping reaction. After the reaction is completed, the system is cooled to room temperature (25-35°C) and triethylamine is added to neutralize the system to a pH of 7-8 (after adding triethylamine, the reaction can be allowed to react for 10-20 minutes to ensure sufficient neutralization);

[0061] b1. Add water to the system neutralized in step a1 while stirring at 1500-2000 rpm, controlling the solid content of the system to 30-60%, and shear to obtain a polyurethane prepolymer WPU-P;

[0062] Synthesis of WPU-L:

[0063] a2. After the diol and isocyanate are uniformly mixed, a first chain extension reaction is carried out. After the reaction is completed, 2,2-dimethylol propionic acid and a catalyst are added to carry out a second chain extension reaction. After the reaction is completed, hydroxyethyl acrylate and a diluent are added to carry out an end-capping reaction. After the reaction is completed, the system is cooled to room temperature (25-35° C.) and triethylamine is added to neutralize the system to a pH of 7-8 (after adding triethylamine, the reaction can be allowed to react for 10-20 minutes to ensure sufficient neutralization);

[0064] b2. Add water dropwise to the system neutralized in step a2 under stirring at 300-500 rpm, controlling the solid content of the system to 30-60%, and complete the addition within 10 min. Shear the mixture to obtain a polyurethane prepolymer WPU-L.

[0065] B. Synthesis of polyurethane as solvent-free water-based ink binder:

[0066] The WPU-P obtained in step b1, the WPU-L obtained in step b2, methyl methacrylate and an initiator are mixed to carry out a free radical polymerization reaction. After the reaction is completed, the temperature is lowered and the material is discharged to obtain a solvent-free water-based ink binder polyurethane;

[0067] In step a1, the molar ratio of the diol, isocyanate, 2,2-dimethylolpropionic acid (DMPA) and hydroxyethyl acrylate (HEA) is 4-6:2:1-3:0.5-1.5;

[0068] In step a1, the catalyst is dibutyltin dilaurate (DBTDL) or organic bismuth; in step a1, the amount of the catalyst is 0.1 to 2% of the molar amount of the isocyanate;

[0069] In step a1, the diluent is an acrylic ester diluent; in step a1, the amount of the diluent is 1 to 3% of the isocyanate mole;

[0070] In step a2, the molar ratio of the diol, isocyanate, 2,2-dimethylolpropionic acid (DMPA) and hydroxyethyl acrylate (HEA) is 4-6:2:1-3:0.5-1.5;

[0071] In step a2, the catalyst is dibutyltin dilaurate (DBTDL) or organic bismuth; in step a2, the amount of the catalyst is 0.1 to 2% of the mole of isocyanate;

[0072] In step a2, the diluent is an acrylic ester diluent; in step a2, the amount of the diluent is 1 to 3% of the isocyanate mole;

[0073] In step B, the mass ratio of WPU-P to WPU-L is 1 to 3:6.

[0074] When preparing WPU-P and WPU-L using the method of the present invention, the relevant operations and parameters of step a1 and step a2 may be the same or different. In actual production, to save steps, step a1 and step a2 can generally be combined, and WPU-P and WPU-L can be synthesized separately.

[0075] In steps a1 and a2 of the present invention, the viscosity of the system can be adjusted by adding a non-solvent diluent and accurately controlling its amount. The residual diluent can also serve as a crosslinking agent. Experiments have shown that the amount of diluent used in steps a1 and a2 of the present invention is controlled to be 1 to 3% by mole of the isocyanate.

[0076] In steps a1 and a2 of the method of the present invention, the diol is at least one of polyether diol (PD), polybutylene adipate (BPBA), and polycaprolactone diol (PCL), and has a number average molecular weight of 500 to 2000 and a moisture content of not higher than 0.05% (it can be dried in a vacuum drying oven at a temperature of 100°C for 3 to 5 hours before use); the isocyanate is at least one of isophorone diisocyanate (IPDI) or toluene diisocyanate (TDI); and the acrylate diluent is at least one of trimethylolpropane trimethacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, 4-hydroxybutyl acrylate, 1,4-butanediol diacrylate, octyl acrylate, tetradecyl acrylate, lauryl methacrylate, and lauryl acrylate.

[0077] In steps a1 and a2 of the present invention, the temperature of the first chain extension reaction is 50-100° C. and the time is 1-2 hours; the temperature of the second chain extension reaction is 50-100° C. and the time is 0.5-2 hours; and the temperature of the end-capping reaction is 50-100° C. and the time is 1-2 hours.

[0078] In the present method, the rotational speed during the shearing process and the method of adding deionized water are crucial. These factors control the particle size and solids content of the polyurethane emulsion, thereby increasing the bulk density of the latex particles and reducing the hydration layer by using two different prepolymers. This allows for the production of a polyurethane emulsion with a multivariate particle size distribution and a high solids content by controlling size and volume, thereby improving the emulsion's performance. Therefore, in steps b1 and b2 of the present invention, the rotational speed and the method and amount of water added must be strictly controlled.

[0079] Experiments have shown that for prepolymer WPU-P, as the rotational speed increases, the particle size first decreases and then increases. A rotational speed of 1500 rpm can produce a prepolymer resin with a small particle size and a high solid content. For prepolymer WPU-L, as the rotational speed increases, the particle size first increases and then decreases. A rotational speed of 300 rpm can produce a prepolymer resin with a large particle size and a high solid content. Therefore, in step b1 of the method of the present invention, the rotational speed is controlled to 1500-2000 rpm, preferably 1500 rpm; in step b2, the rotational speed is controlled to 300-500 rpm, preferably 300 rpm.

[0080] In steps b1 and b2 of the method of the present invention, the shearing time is controlled to be 45 minutes to 1 hour.

[0081] The present method also effectively improves the adhesion of the waterborne polyurethane by introducing a terminal crosslinker called HEA and crosslinking it with MMA, reducing water absorption and integrating the excellent properties of acrylates. Therefore, in step B, the amount of methyl methacrylate is controlled to be 2 to 5 times the molar amount of hydroxyethyl acrylate used to prepare WPU-L (the amount of WPU-L is determined based on the formulation in step B).

[0082] In step B of the method of the present invention, the amount of the initiator is controlled to be 0.5-2% of the mole of methyl methacrylate; the initiator is a free radical initiator potassium persulfate.

[0083] In step B of the method of the present invention, the temperature of the free radical polymerization reaction is controlled to be 70-90° C. and the time is 1-2 hours.

[0084] The solvent-free water-based ink binder polyurethane prepared by the invention has the advantages of high solid content, storage stability, high adhesion, high hardness, low water absorption rate and the like, and its solid content can reach 50-60%.

[0085] Based on the excellent performance of the above-mentioned solvent-free water-based ink binder polyurethane, the present invention also provides its application in water-based gravure printing ink.

[0086] The present invention is further described in detail below through examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0087] Test Example 1

[0088] Synthesis of polyurethane prepolymer WPU-P:

[0089] (1) According to the WPU-P1 raw material ratio in Table 2, IPDI and diol (PCL or BPBA, molecular weight of 1000) were added to the reaction bottle, mixed evenly and reacted at 80°C for 2 hours, then DMPA and DBTDL were added, and the chain extension reaction was continued at this temperature for 1 hour, and then HEA and diluent lauryl acrylate were added, and the temperature was maintained and the reaction was continued for 1 hour;

[0090] (2) The system was cooled to 30°C, triethylamine was added for neutralization until the pH was neutral, and the reaction was carried out for 10 minutes. Subsequently, 68 g of deionized water was directly added under high-speed stirring at 500 rpm to 2000 rpm (the solid content of the system was controlled to be 30-60% during the emulsification process), and shearing was carried out for 45 minutes to obtain a polyurethane prepolymer WPU-P.

[0091] Synthesis of polyurethane prepolymer WPU-L:

[0092] (1) According to WPU-L1 in Table 3, IPDI and diol (PCL or BPBA, molecular weight of 1000) were added to the reaction bottle, mixed evenly and reacted at 80°C for 2 h. DMPA and DBTDL were then added and the chain extension reaction was continued at this temperature for 1 h. HEA and diluent were then added and the reaction was continued at this temperature for 1 h.

[0093] (2) The system was cooled to 30°C, and triethylamine was added for neutralization until the pH was neutral. The reaction was carried out for 10 minutes. Subsequently, 48.5 g of deionized water was added dropwise under low-speed stirring at 100 rpm to 1000 rpm (the solid content of the system was controlled to be 30-60% during the emulsification process). The addition was completed within 10 minutes, and the mixture was sheared for 45 minutes to obtain a polyurethane prepolymer WPU-L.

[0094] Table 1 Analysis of prepolymer particle size and solid content

[0095] sample Speed (rpm) Average particle size (nm) Solid content (%) WPU-P1-1 500 128 32.36％ WPU-P1-2 1000 60 36.87％ WPU-P1-3 1500 40 39.48％ WPU-P1-4 2000 45 37.65％ WPU-L1-1 100 145 39.97％ WPU-L1-2 300 203 48.45％ WPU-L1-3 500 192 46.37％ WPU-L1-4 1000 165 44.84％

[0096] Table 1 shows that the average particle size and solids content of the prepolymers are significantly affected by the stirring speed and water addition method, whether dropwise or directly adding water. Dropwise addition is more likely to produce larger particles and a relatively higher solids content. For prepolymer WPU-P1, as the speed increases, the particle size first decreases and then increases, and a speed of 1500 rpm produces a prepolymer resin with a small particle size and a high solids content. For prepolymer WPU-L1, the particle size first increases and then decreases as the speed increases, and a speed of 300 rpm produces a prepolymer resin with a large particle size and a high solids content.

[0097] The greater the difference in particle size between the two prepolymers, the wider the emulsion particle size distribution, which is conducive to the coexistence of large and small emulsion particles, and can effectively improve space utilization and emulsion solid content. Therefore, the present invention controls the speed of preparing polyurethane prepolymer WPU-P to 1500-2000 rpm and the speed of preparing polyurethane prepolymer WPU-P to 300-500 rpm.

[0098] Example 1

[0099] Synthesis of polyurethane prepolymer WPU-P:

[0100] (1) According to Table 2, IPDI and diol (PCL or BPBA, molecular weight 1000) were added to a reaction flask, mixed well, and reacted at 80°C for 2 h. DMPA and DBTDL were then added, and the chain extension reaction continued at this temperature for 1 h. HEA and diluent were then added, and the reaction continued at this temperature for 1 h.

[0101] (2) The system was cooled to 30°C, triethylamine was added for neutralization until the pH was neutral, and the reaction was carried out for 10 minutes. Subsequently, 68 g of deionized water was directly added under stirring at 1500 rpm (the solid content of the system was controlled to be 30% to 60% during the emulsification process), and shearing was carried out for 45 minutes to obtain a polyurethane prepolymer WPU-P.

[0102] Synthesis of polyurethane prepolymer WPU-L:

[0103] (1) According to Table 3, IPDI and diol (PCL or BPBA, molecular weight of 1000) were added to a reaction flask, mixed well, and reacted at 80°C for 2 h. DMPA and DBTDL were then added, and the chain extension reaction continued at this temperature for 1 h. HEA and diluent were then added, and the reaction continued at this temperature for 1 h.

[0104] (2) The system was cooled to 30°C, and triethylamine was added for neutralization until the pH was neutral. The reaction was carried out for 10 minutes. Subsequently, 48.5 g of deionized water was added dropwise under stirring at 300 rpm (the solid content of the system was controlled to be 30-60% during the emulsification process). The addition was completed within 10 minutes, and the mixture was sheared for 45 minutes to obtain a polyurethane prepolymer WPU-L.

[0105] Synthesis of solvent-free polyurethane emulsion WPU:

[0106] (1) According to Table 4, part of the WPU-P prepared above, all of the WPU-L prepared above, MMA and KPS were added, the emulsion was heated to 80°C, free radical polymerization was carried out, and the reaction was continued for 2 hours, and the temperature was lowered and the material was discharged to prepare solvent-free polyurethane emulsion WPU; the performance test results of the obtained WPU1 to 7 are shown in Table 5.

[0107] Table 2 WPU-P raw material ratio

[0108]

[0109] Table 3 WPU-L raw material ratio

[0110]

[0111] Table 4 WPU raw material ratio

[0112]

[0113]

[0114] Table 5 WPU performance test

[0115]

[0116] It can be seen that the polyurethane emulsion obtained in the present invention has high solid content, high storage stability, high adhesion, high hardness and low water absorption, among which WPU-5 has the best comprehensive performance.

Claims

1. A method for preparing a solvent-free water-based ink binder polyurethane, characterized in that: The following steps are involved: A. Synthesis of polyurethane prepolymers WPU-P and WPU-L: Synthesis of WPU-P: a1. After the diol and isocyanate are uniformly mixed, a first chain extension reaction is carried out. After the reaction is completed, 2,2-dimethylol propionic acid and a catalyst are added to carry out a second chain extension reaction. After the reaction is completed, hydroxyethyl acrylate and a diluent are added to carry out an end-capping reaction. After the reaction is completed, the system is cooled to room temperature and triethylamine is added to neutralize the system to a pH of 7 to 8; b1. Add water to the system neutralized in step a1 while stirring at 1500-2000 rpm, controlling the solid content of the system to 30-60%, and shear to obtain a polyurethane prepolymer WPU-P; Synthesis of WPU-L: a2. After the diol and isocyanate are uniformly mixed, a first chain extension reaction is carried out. After the reaction is completed, 2,2-dimethylol propionic acid and a catalyst are added to carry out a second chain extension reaction. After the reaction is completed, hydroxyethyl acrylate and a diluent are added to carry out an end-capping reaction. After the reaction is completed, the system is cooled to room temperature and triethylamine is added to neutralize the system to a pH of 7 to 8; b2. Add water dropwise to the system neutralized in step a2 under stirring at 300-500 rpm, controlling the solid content of the system to 30-60%, and complete the addition within 10 min. Shear the mixture to obtain a polyurethane prepolymer WPU-L. B. Synthesis of polyurethane as solvent-free water-based ink binder: The WPU-P obtained in step b1, the WPU-L obtained in step b2, methyl methacrylate and an initiator are mixed to carry out a free radical polymerization reaction. After the reaction is completed, the temperature is lowered and the material is discharged to obtain a solvent-free water-based ink binder polyurethane; In step a1, the diol is at least one of polyether diol, polybutylene adipate, and polycaprolactone diol, and has a number average molecular weight of 500 to 2000 and a water content of no more than 0.05%; In step a1, the molar ratio of the diol, isocyanate, 2,2-dimethylolpropionic acid and hydroxyethyl acrylate is 4-6:2:1-3:0.5-1.5; In step a1, the catalyst is dibutyltin dilaurate or organic bismuth; in step a1, the amount of the catalyst is 0.1 to 2% of the molar amount of the isocyanate; In step a1, the diluent is an acrylic ester diluent; in step a1, the amount of the diluent is 1 to 3% of the isocyanate mole; In step a1, the acrylate diluent is at least one of trimethylolpropane trimethacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, 4-hydroxybutyl acrylate, 1,4-butanediol diacrylate, octyl acrylate, tetradecyl acrylate, lauryl methacrylate, and lauryl acrylate; In step a1, the temperature of the first chain extension reaction is 50-100° C.; in step a1, the temperature of the second chain extension reaction is 50-100° C.; in step a1, the temperature of the end-capping reaction is 50-100° C.; In step a2, the diol is at least one of polyether diol, polybutylene adipate, and polycaprolactone diol, and has a number average molecular weight of 500 to 2000 and a water content of no more than 0.05%; In step a2, the molar ratio of the diol, isocyanate, 2,2-dimethylolpropionic acid and hydroxyethyl acrylate is 4-6:2:1-3:0.5-1.5; In step a2, the catalyst is dibutyltin dilaurate or organic bismuth; in step a2, the amount of the catalyst is 0.1 to 2% of the molar amount of the isocyanate; In step a2, the diluent is an acrylic ester diluent; in step a2, the amount of the diluent is 1 to 3% of the isocyanate mole; In step a2, the acrylate diluent is at least one of trimethylolpropane trimethacrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, 4-hydroxybutyl acrylate, 1,4-butanediol diacrylate, octyl acrylate, tetradecyl acrylate, lauryl methacrylate, and lauryl acrylate; In step a2, the temperature of the first chain extension reaction is 50-100° C.; in step a2, the temperature of the second chain extension reaction is 50-100° C.; in step a2, the temperature of the end-capping reaction is 50-100° C.; In step B, the mass ratio of WPU-P to WPU-L is 1 to 3:

6.

2. The method for preparing the solvent-free water-based ink binder polyurethane according to claim 1, characterized in that: At least one of the following must be met: In step a1, the isocyanate is at least one of isophorone diisocyanate or toluene diisocyanate; In step a1, the time of the first chain extension reaction is 1 to 2 hours; In step a1, the second chain extension reaction time is 0.5 to 2 hours; In step a1, the end-capping reaction time is 1 to 2 hours.

3. The method for preparing the solvent-free water-based ink binder polyurethane according to claim 1, wherein: At least one of the following must be met: In step a2, the isocyanate is at least one of isophorone diisocyanate or toluene diisocyanate; In step a2, the time of the first chain extension reaction is 1 to 2 hours; In step a2, the second chain extension reaction time is 0.5 to 2 hours; In step a2, the end-capping reaction time is 1 to 2 hours.

4. The method for preparing the solvent-free water-based ink binder polyurethane according to claim 1, wherein: In step b1, the rotation speed is controlled to be 1500 rpm.

5. The method for preparing the solvent-free water-based ink binder polyurethane according to claim 1, characterized in that: In step b1, the shearing time is 45 minutes to 1 hour.

6. The method for preparing the solvent-free water-based ink binder polyurethane according to claim 1, characterized in that: In step b2, the rotation speed is controlled to 300 rpm.

7. The method for preparing the solvent-free water-based ink binder polyurethane according to claim 1, characterized in that: In step b2, the shearing time is 45 minutes to 1 hour.

8. The method for preparing the solvent-free water-based ink binder polyurethane according to claim 1, characterized in that: At least one of the following must be met: In step B, the amount of methyl methacrylate used is 2 to 5 times the molar amount of hydroxyethyl acrylate used to prepare WPU-L; In step B, the amount of the initiator is 0.5 to 2% by mole of methyl methacrylate; In step B, the initiator is a free radical initiator potassium persulfate; In step B, the temperature of the free radical polymerization reaction is 70-90°C; In step B, the free radical polymerization reaction time is 1 to 2 hours.

9. The solvent-free water-based ink binder polyurethane prepared by the method according to any one of claims 1 to 8, characterized in that: Its solid content is 50-60%.

10. Use of the solvent-free water-based ink binder polyurethane prepared by the method of any one of claims 1 to 8 or the solvent-free water-based ink binder polyurethane according to claim 9 in water-based gravure printing ink.

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