A method of reducing the freeze point of a bio-based polyamide

Abstract

The application belongs to the technical field of polyamide preparation, and particularly relates to a preparation method for reducing the freezing point of bio-based polyamide. Bio-based polyamide prepolymer is prepared from raw materials of dimer acid, isomerized stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkyl amine monomer, antioxidant dispersant and high-temperature stabilizer, and then is mixed with alcohol-soluble polyester and a compatilizer to obtain bio-based polyamide, which has a low freezing point, good gel resistance and environmental friendliness, and can significantly improve the printing quality in a low-temperature environment.

Description

Technical Field

[0001] This invention belongs to the field of polyamide preparation technology, specifically relating to a method for preparing bio-based polyamides that lowers the freezing point. Background Technology

[0002] With the development of printing, plastic packaging, and decorative culture, high-end specialized color plastic printing inks have experienced rapid growth. Polyamide resin is used as a binder for these inks. Polyamide resins for inks are typically prepared by the condensation of dimer fatty acids and diamines, primarily used in letterpress printing inks, and are also indispensable binders for printing on packaging materials such as cellophane, polyethylene, and polypropylene films. Freezing point is an important indicator for bio-based polyamides in ink applications. Low-freezing-point bio-based polyamide resin inks can meet diverse printing needs due to their superior performance. In cold regions or under low-temperature production, storage, and usage conditions, low-freezing-point bio-based polyamide resins ensure that the ink does not experience problems such as decreased fluidity or clumping due to excessively low temperatures, guaranteeing normal printing performance. For example, in winter outdoor advertising printing, inks using low-freezing-point polyamide resins can be smoothly printed at low temperatures without clogging the printhead or causing uneven printing.

[0003] Chinese Patent CN120059174A discloses an alcohol-soluble polyamide resin for printing inks, its preparation method, and its application. It is prepared using carboxylic acid compounds, polyamine compounds, polyether diamine, silane monomers, and fluorinated monomers as main raw materials. By embedding flexible polyether segments into the resin molecular chain, its solubility in alcohol solvents is improved, ensuring the uniformity and stability of the printing ink. The introduction of fluorinated monomers effectively lowers the resin's freezing point, allowing it to maintain good fluidity even at low temperatures and preventing gelation from affecting printing quality. Chinese Patent CN120192522A discloses an alcohol-soluble polyamide resin for inks, its preparation method, applications, and an alcohol-soluble gravure printing ink. The resin is prepared primarily from vegetable oil dimer acid, ethylenediamine, hexamethylenediamine, methylpentanediamine, propionic acid, and acrylic acid. The resulting polyamide resin has a low freezing point and maintains good fluidity and performance even at low temperatures. When used as a binder in inks, it significantly improves the adhesion of the ink to plastic films, ensures the durability of printed materials, and enhances overall printing quality and aesthetics. However, it still suffers from insufficient performance synergy optimization and limited adaptability to extreme low temperatures.

[0004] Therefore, it is of great significance to develop a low-freezing-point bio-based polyamide to achieve a precise balance of freezing point, solubility, and adhesion, so as to better meet the high-end and environmentally friendly application needs of high-grade plastic printing inks. Summary of the Invention

[0005] To address at least one of the above problems, the present invention provides a method for preparing bio-based polyamides with reduced freezing points, comprising the following steps: S100. Dimer acid, isomeric stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkylamine monomer, antioxidant dispersant, and high-temperature stabilizer are placed in a reaction vessel in proportion to synthesize a bio-based polyamide prepolymer. S200. Polyamide prepolymer, alcohol-soluble polyester, and compatibilizer are placed in a reaction vessel in proportion and blended to obtain the bio-based polyamide.

[0006] Furthermore, the isomeric stearic acid is a mixture of branched methyl stearic acids without double bonds, wherein the methyl group can be located in different positions, and its structural formula is: Where m+n=14.

[0007] Furthermore, step S100 specifically includes: S110. Place dimer acid, isomeric stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkylamine monomer, antioxidant dispersant, and high-temperature stabilizer in a reactor according to the specified proportions. Inert gas is introduced, stirring is started, and the temperature is raised to 135-150℃. The temperature is maintained for 2.5-3.5 hours. Before the temperature reaches 130℃, the total reflux condenser is turned on, and the amine-water mixture is refluxed. After reaching 130℃, the temperature at the top of the column is controlled to be ≤98℃. The amine and water are separated, the amine is refluxed, and the water is discharged. S120, continue heating to 210-220℃, hold for 2.5-3.5h, turn off nitrogen, turn on vacuum pump, reduce pressure and evacuate, control vacuum degree to 4000-6000Pa, hold for 40-60min, the reaction ends, cool down to 140-150℃, hold for later use, to obtain bio-based polyamide prepolymer.

[0008] Furthermore, the branched alkyl monomer is obtained by mixing hydroxypropylhexylamine and 2-ethylhexylamine in a mass ratio of 2-6:1-4.

[0009] Further, the polyether crosslinking monomer is one or more of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, and glyceryl diglycidyl ether; the antioxidant dispersant is one or more of triethyl citrate, tri-n-butyl citrate, tripropyl citrate, and pentaerythritol stearate; and the high-temperature stabilizer is one or more of zinc lactate, calcium lactate, zinc stearate, and hydroxyapatite.

[0010] Further, step S200 specifically involves: placing the bio-based polyamide prepolymer, alcohol-soluble polyester, and compatibilizer in a reaction vessel in a certain proportion, maintaining the temperature at 140-150°C for 1-1.5 hours, continuing to stir and cooling to 70-80°C, and discharging the material under nitrogen to break the vacuum, thereby obtaining the bio-based polyamide.

[0011] Further, the compatibilizer preparation process is as follows: polyethylene glycol monomethyl ether is added to a reactor, the temperature is raised to 100-110℃, vacuum is applied under reduced pressure, dehydration is carried out for 2-3 hours, the temperature is lowered to 55-65℃, toluene diisocyanate is added under inert gas protection, after the addition is complete, the temperature is raised to 75-85℃, kept at that temperature for 3-4 hours, the temperature is lowered to below 40℃, and nitrogen is used to break the vacuum to obtain toluene diisocyanate modified polyether, which is the compatibilizer.

[0012] Furthermore, the alcohol-soluble polyester is one or more of poly(1,4-butanediol adipate), poly(ethylene adipate), and poly(1,4-butanediol adipate).

[0013] The present invention has the following beneficial effects: This invention introduces isomeric stearic acid into the preparation process. It is iodine-free and possesses excellent antioxidant properties, improving the oxidative stability of bio-based polyamides. Simultaneously, it exhibits good stability, enhancing the thermal stability of the bio-based polyamide resin. The introduction of polyether crosslinking monomers introduces flexible polyether segments into the bio-based polyamide prepolymer molecular chain, further weakening intermolecular forces and helping to lower the freezing point. The addition of antioxidant dispersants effectively inhibits the oxidative degradation of raw materials and products during high-temperature polymerization, while promoting uniform dispersion of each component. The addition of high-temperature stabilizers forms coordination with the prepolymer molecular chain during the high-temperature polymerization stage, inhibiting thermal degradation and excessive crosslinking of the molecular chain. The polyether segments contained in the compatibilizer enhance compatibility with alcohol-soluble polyesters and polyether crosslinking monomers, and the isocyanate-modified groups react with the active groups on the polyamide prepolymer molecular chain to form chemical bonds, thereby significantly improving the compatibility of the polyamide prepolymer, preventing separation, and ensuring a low freezing point for the prepared product. Detailed Implementation

[0014] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0015] Bio-based polyamide is a core raw material in the field of ink printing. Its freezing point directly affects the performance of ink in low-temperature environments. In existing technologies, monomeric acids such as glacial acetic acid, propionic acid, and stearic acid are usually added to adjust the viscosity of bio-based polyamide. However, these monomeric acids cannot lower the freezing point and may even raise it above 0°C, leading to problems such as poor ink flow, clumping, nozzle clogging, and uneven printing at low temperatures. This severely restricts the application of bio-based polyamide in low-temperature environments. Therefore, this invention provides a method for preparing bio-based polyamide to lower its freezing point, comprising the following steps: S100. Dimer acid, isomeric stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkylamine monomer, antioxidant dispersant, and high-temperature stabilizer are placed in a reaction vessel in proportion to synthesize a bio-based polyamide prepolymer. S200. Polyamide prepolymer, alcohol-soluble polyester, and compatibilizer are placed in a reaction vessel in proportion and blended to obtain the bio-based polyamide.

[0016] In step S100, the isomeric stearic acid is a mixture of branched methyl stearic acids without double bonds, wherein the methyl group can be located in different positions, and its structural formula is: Where m+n=14.

[0017] The relevant physical properties of isomeric stearic acid are as follows: In this step, isostearic acid is an isomer of stearic acid with an extremely low freezing point, typically around -10°C. Adding isostearic acid to the formulation can adjust viscosity and lower the freezing point of the resin. As a special fatty acid, isostearic acid exhibits good low-temperature fluidity, thermal stability, and antioxidant properties. Due to the absence of double bonds in its structure, it possesses excellent stability. Adding it to the formulation in a certain proportion lowers the freezing point of bio-based polyamides while also improving their high-temperature stability and oxidative stability.

[0018] Specifically, step S100 is as follows: S110. Place dimer acid, isomeric stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkylamine monomer, antioxidant dispersant, and high-temperature stabilizer in a reactor according to the specified proportions. Purge with nitrogen, start stirring and heat to 135-150℃, and maintain the temperature for 2.5-3.5 hours. Before the temperature reaches 130℃, turn on the total reflux condenser to reflux the amine-water mixture. After reaching 130℃, control the top temperature of the tower to ≤98℃, separate the amine and water, reflux the amine and discharge the water. S120, continue heating to 210-220℃, hold for 2.5-3.5h, turn off nitrogen, turn on vacuum pump, reduce pressure and evacuate, control vacuum degree to 4000-6000Pa, hold for 40-60min, the reaction ends, cool down to 140-150℃, hold for later use, to obtain bio-based polyamide prepolymer.

[0019] In step S110, the mass ratio of dimer acid (high-purity dimer acid BIODA-95, Wilmar Oils & Fats Technology Co., Ltd.), isomeric stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkylamine monomer, antioxidant dispersant, and high-temperature stabilizer is 35-50:12-20:8-15:6-10:3-5:5-8:0.8-1.5:0.5-1.1.

[0020] The branched alkyl monomer is obtained by mixing hydroxypropylhexylamine and 2-ethylhexylamine in a mass ratio of 2-6:1-4, preferably in a mass ratio of 3:2. The addition of hydroxypropylhexylamine introduces hydroxyl groups, which improves the alcohol solubility of the prepared product and helps lower the freezing point. The introduction of the long branched structure of 2-ethylhexylamine further enhances the steric hindrance effect of the molecular chain, disrupts the regularity of the molecular chain, and synergistically lowers the freezing point.

[0021] The polyether crosslinking monomer is one or more of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, and glycerol diglycidyl ether, preferably polyethylene glycol diglycidyl ether; the epoxy groups in its molecular structure can undergo ring-opening reactions with the active groups on the prepolymer molecular chain to form a crosslinked structure, and its flexible polyether segments can further weaken the intermolecular forces and help lower the freezing point.

[0022] The antioxidant dispersant is one or more of triethyl citrate, tri-n-butyl citrate, tripropyl citrate, and pentaerythritol stearate, preferably triethyl citrate. It has antioxidant properties and a certain degree of dispersibility. During high-temperature polymerization, it can inhibit the oxidative degradation of raw materials and products, while promoting the uniform dispersion of each component and avoiding uneven crystallization due to excessively high local component concentrations.

[0023] The high-temperature stabilizer is one or more of zinc lactate, calcium lactate, zinc stearate, and hydroxyapatite, preferably zinc lactate; it can form coordination with the prepolymer molecular chain during the high-temperature polymerization stage, inhibiting the thermal degradation and excessive cross-linking of the molecular chain, and ensuring the stability of the subsequent blending reaction.

[0024] Specifically, step S200 involves placing the bio-based polyamide prepolymer, alcohol-soluble polyester, and compatibilizer in a reactor in a specific ratio, maintaining the temperature at 140-150°C for 1-1.5 hours, continuing to stir and cooling to 70-80°C, and discharging the material under nitrogen to break the vacuum, thereby obtaining the bio-based polyamide.

[0025] In this step, the mass ratio of bio-based polyamide prepolymer, alcohol-soluble polyester, and compatibilizer is 65-80:15-25:4-8. The alcohol-soluble polyester is one or more of poly(1,4-butanediol adipate), poly(ethylene adipate), and poly(1,4-butylene adipate), preferably poly(1,4-butanediol adipate). It possesses good alcohol solubility and flexible segments, allowing it to form a partially compatible system with the polyamide prepolymer. The flexible segments can insert into the polyamide molecular chains, further weakening intermolecular forces and lowering the freezing point. Simultaneously, the ester groups on it can form hydrogen bonds with the polyamide prepolymer molecular chains, improving component compatibility and preventing phase separation.

[0026] The compatibilizer preparation process is as follows: polyethylene glycol monomethyl ether is added to a reactor, the temperature is raised to 100-110℃, vacuum is applied under reduced pressure, dehydration is carried out for 2-3 hours, the temperature is lowered to 55-65℃, toluene diisocyanate is added under nitrogen protection, after the addition is complete, the temperature is raised to 75-85℃, kept at that temperature for 3-4 hours, the temperature is lowered to below 40℃, and the vacuum is broken with nitrogen to obtain toluene diisocyanate modified polyether, which is the compatibilizer.

[0027] In this step, the mass ratio of polyethylene glycol monomethyl ether (average molecular weight 1000) to toluene diisocyanate ((2,4-approx. 80%, 2,6-approx. 20%)) is 10:2-3. The compatibilizer molecule contains both polyether segments and isocyanate-modifying groups. The polyether segments are compatible with alcohol-soluble polyesters and polyether crosslinking monomers, while the isocyanate-modifying groups react with the active groups of the polyamide prepolymer to form chemical bonds, thereby significantly improving the compatibility between the polyamide prepolymer and the alcohol-soluble polyester, preventing separation, and ensuring the prepared product has a low freezing point.

[0028] Preparation Example 1 The compatibilizer preparation process is as follows: 10 parts by weight of polyethylene glycol monomethyl ether are added to a reactor, the temperature is raised to 100°C, the pressure is reduced and a vacuum is drawn (≤1000Pa), the water is dehydrated for 2 hours, the temperature is lowered to 55°C, and 2 parts by weight of toluene diisocyanate are added dropwise under nitrogen protection. After the addition is complete, the temperature is raised to 75°C and kept at that temperature for 3 hours. Then the temperature is lowered to below 40°C, and the vacuum is broken with nitrogen to obtain toluene diisocyanate modified polyether, which is the compatibilizer.

[0029] Preparation Example 2 This preparation example differs from Preparation Example 1 in the following ways: In the preparation of the compatibilizer, 10 parts by weight of polyethylene glycol monomethyl ether were added to the reactor, the temperature was raised to 105°C, vacuum was applied under reduced pressure, and the mixture was dehydrated for 3 hours. The temperature was then lowered to 60°C, and 2.5 parts by weight of toluene diisocyanate were added dropwise under nitrogen protection. After the addition was completed, the temperature was raised to 80°C and maintained for 4 hours.

[0030] Preparation Example 2 Compared with Preparation Example 1, this preparation example has the following disadvantages: In the preparation of the compatibilizer, 10 parts by weight of polyethylene glycol monomethyl ether were added to the reactor, the temperature was raised to 110°C, vacuum was applied under reduced pressure, and the mixture was dehydrated for 3 hours. The temperature was then lowered to 65°C, and under nitrogen protection, 3 parts by weight of toluene diisocyanate were added dropwise. After the addition was completed, the temperature was raised to 85°C and maintained for 4 hours.

[0031] Example 1 A method for preparing bio-based polyamide with a lower freezing point includes the following steps: S1. Place 45 parts by weight of dimer acid, 18 parts by weight of isomeric stearic acid, 12 parts by weight of ethylenediamine, 8 parts by weight of hexamethylenediamine, 4 parts by weight of polyethylene glycol diglycidyl ether, 6 parts by weight of branched alkylamine monomer (hydroxypropylhexylamine and 2-ethylhexylamine mixed in a mass ratio of 3:2), 1.2 parts by weight of triethyl citrate, and 0.9 parts by weight of zinc lactate into a reactor. Introduce nitrogen gas to purge the air from the reactor. Stir at 200 r / min and heat to 140°C. Hold at this temperature for 3 hours. Before the temperature reaches 130°C, turn on the total reflux condenser to reflux the amine-water mixture. After reaching 130°C, control the top temperature of the column to ≤98°C, separate the amine and water, reflux the amine, and discharge the water. S2. Continue heating to 215℃, hold for 3 hours, turn off nitrogen, turn on vacuum pump, reduce pressure and evacuate, control vacuum degree to 5000Pa, maintain for 45 minutes, the reaction ends, cool down to 140℃, hold for later use, and obtain bio-based polyamide prepolymer. S3. Place 75 parts by weight of bio-based polyamide prepolymer, 22 parts by weight of poly(1,4-butanediol adipate), and 6 parts by weight of the compatibilizer prepared in Preparation Example 2 into a reactor, maintain the temperature at 145°C for 1.5 hours, continue stirring and cool down to 75°C, and discharge the material under nitrogen to break the vacuum, thus obtaining bio-based polyamide.

[0032] Example 2 This embodiment differs from Embodiment 1 in the following ways: In step S1, 40 parts by weight of dimer acid, 16 parts by weight of isomeric stearic acid, 10 parts by weight of ethylenediamine, 6.5 parts by weight of hexamethylenediamine, 3.5 parts by weight of polyethylene glycol diglycidyl ether, 5.5 parts by weight of branched alkylamine monomer (hydroxypropylhexylamine and 2-ethylhexylamine mixed at a mass ratio of 3:2), 1 part by weight of triethyl citrate, and 0.65 parts by weight of zinc lactate are placed in a reaction vessel, nitrogen gas is introduced, the mixture is stirred at a speed of 200 r / min and heated to 140°C, and kept at that temperature for 3 h.

[0033] Step S2 is the same as step S2 in Example 1.

[0034] In step S3, 70 parts by weight of bio-based polyamide prepolymer, 18 parts by weight of poly(1,4-butanediol adipate), and 5 parts by weight of the compatibilizer prepared in Preparation Example 2 are placed in a reactor, kept at 145°C for 1.5 hours, stirred continuously, and cooled to 75°C. The mixture is then discharged under nitrogen to break the vacuum, yielding bio-based polyamide.

[0035] Example 3 This embodiment differs from Embodiment 1 in the following ways: In step S1, 35 parts by weight of dimer acid, 12 parts by weight of isomeric stearic acid, 8 parts by weight of ethylenediamine, 6 parts by weight of hexamethylenediamine, 3 parts by weight of polyethylene glycol diglycidyl ether, 5 parts by weight of branched alkylamine monomer (hydroxypropylhexylamine and 2-ethylhexylamine mixed in a mass ratio of 3:2), 0.8 parts by weight of triethyl citrate, and 0.5 parts by weight of zinc lactate are placed in a reaction vessel, nitrogen gas is introduced, the mixture is stirred and heated to 130°C, and the temperature is maintained for 2.5 hours.

[0036] In step S2, the temperature is further increased to 210℃ and held for 2.5h. Nitrogen gas is turned off, vacuum pump is turned on, vacuum is reduced and evacuated, and the vacuum degree is controlled at 4000Pa for 40min. The reaction ends, the temperature is lowered to 140℃ and held for later use to obtain bio-based polyamide prepolymer. In step S3, 65 parts by weight of bio-based polyamide prepolymer, 15 parts by weight of poly(1,4-butanediol adipate), and 4 parts by weight of the compatibilizer prepared in Preparation Example 2 are placed in a reactor, kept at 140°C for 1 hour, stirred continuously, and cooled to 70°C. The mixture is then discharged under nitrogen to break the vacuum, yielding bio-based polyamide.

[0037] Example 4 This embodiment differs from Embodiment 1 in the following ways: In step S1, 50 parts by weight of dimer acid, 20 parts by weight of isomeric stearic acid, 15 parts by weight of ethylenediamine, 10 parts by weight of hexamethylenediamine, 5 parts by weight of polyethylene glycol diglycidyl ether, 8 parts by weight of branched alkylamine monomer (hydroxypropylhexylamine and 2-ethylhexylamine mixed in a mass ratio of 3:2), 1.5 parts by weight of triethyl citrate, and 1.1 parts by weight of zinc lactate are placed in a reaction vessel, nitrogen gas is introduced, the mixture is stirred and heated to 150°C, and the temperature is maintained for 3.5 hours.

[0038] In step S2, the temperature is further increased to 220℃ and held for 3.5h. Nitrogen gas is turned off, the vacuum pump is turned on, the vacuum is reduced and evacuated, and the vacuum degree is controlled at 6000Pa for 60min. The reaction ends, the temperature is lowered to 150℃ and held for later use to obtain the bio-based polyamide prepolymer. In step S3, 80 parts by weight of bio-based polyamide prepolymer, 25 parts by weight of poly(1,4-butanediol adipate), and 8 parts by weight of the compatibilizer prepared in Preparation Example 2 are placed in a reactor, kept at 150°C for 1.5 hours, stirred continuously, and cooled to 80°C. The mixture is then discharged under nitrogen to break the vacuum, yielding bio-based polyamide.

[0039] Comparative Example 1 Compared with Example 1, this comparative example does not include isomeric stearic acid in step S1, while all other steps are the same as in Example 1. Specifically: Step S1 is as follows: 45 parts by weight of dimer acid, 12 parts by weight of ethylenediamine, 8 parts by weight of hexamethylenediamine, 4 parts by weight of polyethylene glycol diglycidyl ether, 6 parts by weight of branched alkylamine monomer (hydroxypropylhexylamine and 2-ethylhexylamine are mixed at a mass ratio of 3:2), 1.2 parts by weight of triethyl citrate, and 0.9 parts by weight of zinc lactate are placed in a reaction vessel. Nitrogen gas is introduced to purge the air from the reaction vessel. The mixture is stirred at 200 r / min and heated to 140°C. The temperature is maintained for 3 hours. Before the temperature reaches 130°C, the total reflux condenser is turned on, and the amine-water mixture is refluxed. After reaching 130°C, the temperature at the top of the column is controlled to be ≤98°C. The amine and water are separated, the amine is refluxed, and the water is discharged. Steps S2 and S3 are the same as in Example 1.

[0040] Comparative Example 2 Compared with Example 1, this comparative example does not add branched alkyl monomers in the preparation process of step S1, while all other steps are the same as in Example 1. Specifically: Step S1 is as follows: 45 parts by weight of dimer acid, 18 parts by weight of isomeric stearic acid, 12 parts by weight of ethylenediamine, 8 parts by weight of hexamethylenediamine, 4 parts by weight of polyethylene glycol diglycidyl ether, 1.2 parts by weight of triethyl citrate, and 0.9 parts by weight of zinc lactate are placed in a reaction vessel. Nitrogen gas is introduced to purge the air from the reaction vessel. The mixture is stirred at 200 r / min and heated to 140°C. The temperature is maintained for 3 hours. Before the temperature reaches 130°C, the total reflux condenser is turned on, and the amine-water mixture is refluxed. After reaching 130°C, the temperature at the top of the column is controlled to be ≤98°C. The amine and water are separated, the amine is refluxed, and the water is discharged. Steps S2 and S3 are the same as in Example 1.

[0041] Comparative Example 3 Compared with Example 1, this comparative example does not add polyether crosslinking monomers in the preparation process of step S1, while all other steps are the same as in Example 1. Specifically: Step S1 is as follows: 45 parts by weight of dimer acid, 18 parts by weight of isomeric stearic acid, 12 parts by weight of ethylenediamine, 8 parts by weight of hexamethylenediamine, 6 parts by weight of branched alkylamine monomer (hydroxypropylhexylamine and 2-ethylhexylamine are mixed at a mass ratio of 3:2), 1.2 parts by weight of triethyl citrate, and 0.9 parts by weight of zinc lactate are placed in a reaction vessel. Nitrogen gas is introduced to purge the air from the reaction vessel. The mixture is stirred at 200 r / min and heated to 140°C. The temperature is maintained for 3 hours. Before the temperature reaches 130°C, the total reflux condenser is turned on, and the amine-water mixture is refluxed. After reaching 130°C, the temperature at the top of the column is controlled to be ≤98°C. The amine and water are separated, the amine is refluxed, and the water is discharged. Steps S2 and S3 are the same as in Example 1.

[0042] Comparative Example 4 Compared with Example 1, this comparative example does not add a compatibilizer in step S3, while all other steps are the same as in Example 1. Specifically: Steps S1 and S2 are the same as in Example 1; Step S3 is as follows: 75 parts by weight of bio-based polyamide prepolymer and 22 parts by weight of poly(1,4-butanediol adipate) are placed in a reactor, kept at 145°C for 1.5 hours, stirred continuously and cooled to 75°C, and discharged under nitrogen to obtain bio-based polyamide.

[0043] Comparative Example 5 The preparation process for this comparative example is as follows: A method for preparing bio-polyamide with a lower freezing point is as follows: 45 parts by weight of dimer acid, 18 parts by weight of isomeric stearic acid, 12 parts by weight of ethylenediamine, and 8 parts by weight of hexamethylenediamine are placed in a reactor. Nitrogen gas is introduced to purge the air from the reactor. The mixture is stirred at 200 r / min and heated to 130°C. Before the temperature reaches 130°C, a total reflux condenser is turned on, and the amine-water mixture is refluxed. After reaching 130°C, the temperature at the top of the distillation packed column is controlled below 100°C to allow the amine and water to separate. The amine condensate continues to reflux, and the water vapor is discharged from the system after condensation. The reaction is continued at 130–150°C for about 2 hours to separate the water. Then, the temperature is further increased, and when it reaches 210–220°C, the reaction is maintained for 2 hours. The nitrogen gas is then turned off, and a vacuum pump is turned on to reduce the pressure and create a vacuum of about 5000 Pa. This vacuum is maintained for 40 minutes to complete the reaction. The temperature is then lowered to 180°C, and the nitrogen gas is released to break the vacuum and discharge the product.

[0044] Related tests: 1. Alcohol solubility test: Anhydrous ethanol was used as the solvent. The prepared bio-based polyamide and anhydrous ethanol were mixed at a mass ratio of 2:3. The stability and homogeneity of the solution were observed at 25°C. If the solution could be formed, it was considered qualified; otherwise, it was unqualified. The test results are shown in Table 1.

[0045] 2. The acid value, amine value, softening point, viscosity and freezing point were tested according to the test methods in QB / T 4752-2014 "Alcohol-soluble polyamide resins for inks". The test results are shown in Table 1.

[0046] Table 1 Gel recovery time: The prepared bio-based polyamide resin was formulated into a 40% bio-based polyamide resin solution and placed in an environment of -10℃ for 6 hours to obtain a gel. The gel was then placed in an environment of 25℃ and timing was started until the gel resumed flow. The recorded time was the gel recovery time. The test results are shown in Table 2.

[0047] Product storage stability test: The stability test (softening point detection) of the product was carried out according to the test method in QB / T 4752-2014 "Alcohol-soluble polyamide resin for ink" after a certain period of time. The test results are shown in Table 2.

[0048] Table 2 The test results above show that the bio-based polyamide resin prepared by this invention has a low freezing point, good anti-gel properties and good alcohol solubility, which can meet the application requirements of ink in low-temperature environments.

[0049] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0050] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing bio-based polyamides with a lower freezing point, characterized in that, Includes the following steps: S100. Dimer acid, isomeric stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkylamine monomer, antioxidant dispersant, and high-temperature stabilizer are placed in a reaction vessel in proportion to synthesize a bio-based polyamide prepolymer. S200. Polyamide prepolymer, alcohol-soluble polyester, and compatibilizer are placed in a reaction vessel in proportion and blended to obtain the bio-based polyamide. The branched alkyl monomer is obtained by mixing hydroxypropylhexylamine and 2-ethylhexylamine in a mass ratio of 2-6:1-4; the polyether crosslinking monomer is one or a mixture of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, and glyceryl diglycidyl ether; the antioxidant dispersant is one or a mixture of triethyl citrate, tri-n-butyl citrate, tripropyl citrate, and pentaerythritol stearate; the high-temperature stabilizer is one or a mixture of zinc lactate, calcium lactate, zinc stearate, and hydroxyapatite. The compatibilizer preparation process is as follows: polyethylene glycol monomethyl ether is added to a reactor, the temperature is raised to 100-110℃, vacuum is applied under reduced pressure, dehydration is carried out for 2-3 hours, and the temperature is lowered to 55-65℃. Under inert gas protection, toluene diisocyanate is added. After the addition is complete, the temperature is raised to 75-85℃ and kept at that temperature for 3-4 hours. The temperature is then lowered to below 40℃, and nitrogen is used to break the vacuum to obtain toluene diisocyanate modified polyether, which is the compatibilizer.

2. The preparation method for reducing the freezing point of bio-based polyamide according to claim 1, characterized in that, In step S100, the isomeric stearic acid is a mixture of branched methyl stearic acids without double bonds, wherein the methyl group can be located in different positions, and its structural formula is: Where m+n=14.

3. The preparation method for reducing the freezing point of bio-based polyamide according to claim 1, characterized in that, Step S100 is as follows: S110. Place dimer acid, isomeric stearic acid, ethylenediamine, hexamethylenediamine, polyether crosslinking monomer, branched alkylamine monomer, antioxidant dispersant, and high-temperature stabilizer in a reactor according to the specified proportions. Inert gas is introduced, stirring is started, and the temperature is raised to 135-150℃. The temperature is maintained for 2.5-3.5 hours. Before the temperature reaches 130℃, the total reflux condenser is turned on, and the amine-water mixture is refluxed. After reaching 130℃, the temperature at the top of the column is controlled to be ≤98℃. The amine and water are separated, the amine is refluxed, and the water is discharged. S120, continue heating to 210-220℃, hold for 2.5-3.5h, turn off nitrogen, turn on vacuum pump, reduce pressure and evacuate, control vacuum degree to 4000-6000Pa, hold for 40-60min, the reaction ends, cool down to 140-150℃, hold for later use, to obtain bio-based polyamide prepolymer.

4. The preparation method for reducing the freezing point of bio-based polyamide according to claim 1, characterized in that, Step S200 specifically involves placing the bio-based polyamide prepolymer, alcohol-soluble polyester, and compatibilizer in a reactor in a specific ratio, maintaining the temperature at 140-150°C for 1-1.5 hours, continuing to stir and cooling to 70-80°C, and discharging the material under nitrogen to break the vacuum, thereby obtaining the bio-based polyamide.

5. The preparation method for reducing the freezing point of bio-based polyamide according to claim 1, characterized in that, The alcohol-soluble polyester is one or a mixture of poly(1,4-butanediol adipate), poly(ethylene adipate), and poly(1,4-butanediol adipate).

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