A heat-triggered aqueous carbodiimide crosslinker composition and use thereof

Abstract

The application discloses a heat-triggered water-based carbodiimide crosslinking agent composition and application thereof. By introducing a latent acid and setting an alkaline environment during storage, the hydrolysis of carbodiimide and the pre-reaction of carbodiimide and carboxyl are simultaneously inhibited from the kinetic aspect, and the system is 'frozen' in a stable state. When used, the latent acid is triggered to decompose by heating, and the system pH is suddenly reduced to acidity by instantaneous release of protons, which not only quickly protonates and activates the carbodiimide, but also creates an optimal kinetic window in which the reaction rate of carbodiimide and carboxyl is much faster than the hydrolysis reaction, thereby accurately, synchronously and efficiently guiding the reaction path to the target crosslinking direction, and realizing the unification of'stable storage' and 'on-demand efficient reaction' in a single component.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a thermally triggered aqueous carbodiimide crosslinking agent composition and its application. Background Technology

[0002] Water-soluble carbodiimides are a class of highly efficient crosslinking agents, widely used in bioconjugations, waterborne coatings, and adhesives for condensation crosslinking reactions between carboxyl and amino groups. However, a significant contradiction exists in their practical applications: to achieve sufficient storage stability, carbodiimide crosslinking agents need to be stored in alkaline or at least neutral aqueous solutions to inhibit rapid hydrolysis; while for the highest crosslinking efficiency, the optimal pH environment of the reaction system is acidic.

[0003] In existing technologies, the use of carbodiimide crosslinking agents (especially water-soluble EDC, etc.) has long been limited by a core contradiction: to maintain storage stability, carbodiimide and acidic catalysts (or carboxyl-containing resins) must be packaged separately. On-site mixing is required during use, which not only results in a short operating window but also leads to uneven crosslinking due to uneven mixing.

[0004] If a single-component formulation is to be forcibly produced, the industrial practice typically involves chemically modifying the carbodiimide molecule itself. However, such methods involve complex synthetic routes, high costs, and a single modified product is usually only effective for a specific resin system, limiting its versatility. Summary of the Invention

[0005] To address the challenge of balancing high reactivity and long lifespan in existing technologies for carbodiimides, this invention proposes a thermally triggered aqueous carbodiimide crosslinking agent composition and its application. The environmental pH value is utilized as the triggering mechanism for the crosslinking reaction. By introducing a latent acid, a flexible transformation of reactivity is successfully achieved: maintaining an alkaline environment during storage to ensure the system's chemical inertness; and releasing protons to create an acidic environment during application, instantly activating high reactivity and thus completing efficient crosslinking.

[0006] One technical solution of the present invention is to provide a thermally triggered aqueous carbodiimide crosslinking agent composition, comprising: carbodiimide, a latent acid, and a pH stabilizer; the pH value of the aqueous carbodiimide crosslinking agent composition is 7.5-11.0; the mass ratio of the carbodiimide crosslinking agent to the latent acid in the aqueous carbodiimide crosslinking agent composition is (35-45):(0.1-5); the composition also includes deionized water with a conductivity not higher than 10 μS / cm; the latent acid is one or more of the following: dimethylamine salt of dodecylbenzenesulfonic acid, isopropylamine salt of dodecylbenzenesulfonic acid, blocked dodecylbenzenesulfonic acid, blocked dinonylnaphthalene disulfonic acid, and pyridine salt of p-toluenesulfonic acid. The latent acid catalyst decomposes and releases proton acid, causing the pH value of the system to drop to 4.5-6.5, thereby activating the crosslinking activity of the carbodiimide crosslinking agent.

[0007] Preferably, the latent acid is one or more of the dimethylamine salt of dodecylbenzenesulfonic acid and the isopropylamine salt of dodecylbenzenesulfonic acid.

[0008] Furthermore, the pH stabilizer is one or more of sodium hydroxide, potassium hydroxide, ammonia, triethylamine, triethanolamine, N,N-dimethylethanolamine, aminomethylpropanol, bicarbonate, and borate.

[0009] The second technical solution of the present invention is to provide a method for preparing the above-mentioned aqueous carbodiimide crosslinking agent composition, comprising the following steps: (1) Mix diisocyanate with catalyst and stir under nitrogen atmosphere to carry out decarbonylation polycondensation reaction until the degree of polymerization is 2-6.

[0010] (2) Lower the temperature to 70~90℃ and add a hydrophilic end-capping agent to react with the remaining isocyanate groups; the number of moles of the hydrophilic end-capping agent added is 1~1.1 times the number of moles of the remaining isocyanate group; the reaction endpoint is when the measured NCO% is 0.

[0011] (3) Lower the temperature to 30~40℃, add deionized water containing pH stabilizer under stirring at 500~800r / min for dispersion, and add latent acid after dispersion for 15~50min to obtain carbodiimide crosslinking agent aqueous dispersion.

[0012] Furthermore, the catalyst is one or more of 3-methyl-1-phenylphosphine heterocyclopentene-1-oxide and triphenyl phosphate.

[0013] Furthermore, the reaction temperature in step (1) is 130~180℃ and the stirring speed is 150~300r / min.

[0014] Further, the hydrophilic end-capping agent is N,N-dimethylethanolamine (DMEA), sodium hydroxyethyl sulfonate (SHES), or methoxy polyethylene glycol (MPEG, 300~1000 Da). Preferably, the hydrophilic end-capping agent is methoxy polyethylene glycol (MPEG, 500 Da), methoxy polyethylene glycol (MPEG, 600 Da), or N,N-dimethylethanolamine (DMEA).

[0015] Furthermore, the mass ratio of diisocyanate to catalyst is 100:(0.35~0.7).

[0016] The diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 1,12-dodecane diisocyanate, and tetramethylphenyldimethyl diisocyanate.

[0017] Preferably, the diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate, and toluene diisocyanate.

[0018] The third technical solution of the present invention is to provide the application of the above-mentioned thermally triggered aqueous carbodiimide crosslinking agent composition.

[0019] The specific method is as follows: The aqueous carbodiimide crosslinking agent composition according to claim 1 is added to a carboxyl-containing resin and cured at 80-180°C for 0.5-2 hours; the mass ratio of the carboxyl-containing resin to the aqueous carbodiimide crosslinking agent composition is 100:(1-3). At this temperature, the aqueous carbodiimide crosslinking agent composition undergoes thermal triggering, causing the latent acid to decompose and instantaneously release protons, resulting in a rapid drop in the pH of the system to acidity. This not only rapidly protonates and activates the carbodiimide but also creates an optimal kinetic window where its reaction rate with the carboxyl group is much faster than that of the hydrolysis reaction, thereby precisely, synchronously, and efficiently guiding the reaction pathway towards the target crosslinking direction.

[0020] Preferably, the curing temperature is 80~120℃.

[0021] The carboxyl-containing resin is one or more of the following: waterborne acrylic resin, waterborne polyurethane resin, waterborne epoxy resin, and waterborne alkyd resin.

[0022] The advantages of this invention lie in its innovative construction of a "thermally triggered pH switching" mechanism by introducing a latent acid into an alkaline aqueous solution of carbodiimide. This design perfectly solves the fundamental contradiction that the storage of carbodiimide crosslinking agents requires alkalinity while the reaction requires acidity, thus achieving for the first time both excellent long-term storage stability and convenient on-demand thermal activation capability in a single aqueous component. During use, heating rapidly decomposes the latent acid, instantly switching the system pH from alkaline to the optimal acidic reaction window, thereby simultaneously, efficiently, and globally activating the crosslinking activity of carbodiimide. This not only simplifies the process and avoids the tediousness and unevenness of two-component mixing, but also ensures the reaction proceeds under optimal conditions, significantly improving crosslinking efficiency and the performance reliability of the final product. Furthermore, compared to complex molecular modification routes, it offers significant versatility and cost advantages. Detailed Implementation

[0023] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0024] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0025] The carbodiimide described in this invention is a polycarbodiimide with a degree of polymerization of 2-6.

[0026] The degree of polymerization described in this invention is obtained by measuring the NCO% value.

[0027] The NCO% test method is as follows: Weigh 1 gram of sample into a 250 mL stoppered conical flask and add 20 mL of anhydrous toluene to dissolve the sample. Add excess di-n-butylamine-toluene solution (concentration 0.1 mol / L) and let it stand at room temperature for 15 minutes. After the reaction is complete, add 4 mL of isopropanol or ethanol to dilute the system and add 2 drops of bromocresol green indicator. At this point, the solution turns blue. Finally, titrate with standard hydrochloric acid solution (concentration usually 0.1 mol / L) until the solution changes from blue to yellow and remains stable as the endpoint. A blank test is performed simultaneously. The NCO% calculation formula is: NCO% = [(V0 - V1) × C × 4.2] / m, where V0 and V1 are the volumes of hydrochloric acid consumed (mL) for the blank and sample, respectively, C is the hydrochloric acid concentration (mol / L), and m is the sample mass (g).

[0028] The embodiments of the present invention will be further described below with reference to several examples.

[0029] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0030] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0031] Example 1 a) Add 100 parts by mass of isophorone diisocyanate (IPDI) and 0.35 parts by mass of catalyst 3-methyl-1-phenylphosphine heterocyclopentene-1-oxide (MPPO) to a dry reactor. Under nitrogen protection, stir at 150 r / min and heat to 130 °C. Monitor the reaction by NCO% test, and stop the reaction when the degree of polymerization reaches approximately 2.

[0032] b) Cool the reaction system to 70°C and add methoxy polyethylene glycol (MPEG-500, 500 Da) in a molar ratio equal to 1.0 times the remaining NCO groups as a hydrophilic end-capping agent. Continue the reaction until the NCO% is titrated to be 0.

[0033] c) Cool the system to 30°C, and slowly add 150 parts by weight of deionized water containing the pH stabilizer triethylamine (TEA) while stirring at a high speed of 500 r / min. Adjust the pH of the system to 10.5 and disperse for 15 minutes to form a stable dispersion (solid content approximately 38%). Finally, add 2.0 parts by weight of the latent acid dimethyl dodecylbenzenesulfonate salt and continue stirring for 5 minutes to obtain a one-component aqueous carbodiimide crosslinking agent composition.

[0034] Take 100 parts of water-based acrylic resin, add 2 parts by weight of the above crosslinking agent composition, and stir evenly to obtain a one-component coating. Apply the coating to the substrate and cure it in an oven at 80°C for 3 hours.

[0035] Example 2 a) Add 100 parts by mass of hexamethylene diisocyanate (HDI) and 0.5 parts by mass of triphenyl phosphate catalyst to the reactor. Under nitrogen protection, stir at 220 r / min and heat to 155℃ (midpoint). Monitor the reaction until the degree of polymerization reaches approximately 4 (midpoint, corresponding to a theoretical NCO% of approximately 19.5%), then stop the reaction.

[0036] b) Cool to 80°C and add N,N-dimethylethanolamine (DMEA) in a molar ratio of 1.05 times the remaining NCO groups for end-capping. React until NCO% reaches 0%.

[0037] c) Cool to 35°C, add 150 parts by weight of deionized water containing the pH stabilizer potassium hydroxide (KOH) at 650 r / min to adjust the pH of the system to 12.4, and disperse for 30 minutes to form a stable dispersion (solid content of about 40%). Finally, add 3.0 parts by weight of the latent acid isopropylamine dodecylbenzenesulfonate, stir evenly, and obtain a one-component aqueous carbodiimide crosslinking agent composition.

[0038] Take 100 parts by weight of waterborne polyurethane resin, add 3 parts by weight of the above crosslinking agent composition, and stir until homogeneous. After applying the coating, place it in an oven at 100°C for curing for 2 hours.

[0039] Example 3 a) Add 100 parts by mass of toluene diisocyanate (TDI) and 0.7 parts by mass of catalyst MPPO to the reactor. Under nitrogen protection, stir at 300 r / min and heat to 180 °C. Monitor the reaction until the degree of polymerization reaches approximately 6 and then stop.

[0040] b) Cool to 90°C and add sodium hydroxyethyl sulfonate (SHES) in a molar ratio of 1.1 times the remaining NCO groups for end-capping. React until NCO% reaches 0%.

[0041] c) Cool to 40°C, add 150 parts by weight of deionized water containing the pH stabilizer borax at 800 r / min to adjust the pH of the system to 9.6, and disperse for 50 minutes to form a stable dispersion (solid content approximately 42%). Finally, add 5.0 parts by weight of latent acid p-toluenesulfonic acid pyridine salt, stir evenly, and obtain a one-component aqueous carbodiimide crosslinking agent composition.

[0042] Take 100 parts by weight of waterborne alkyd resin, add 1 part by weight of the above crosslinking agent composition, and stir until homogeneous. After applying the coating, place it in an oven at 120°C for 1 hour to cure.

[0043] Example 4 a) Add 70 parts by mass of IPDI and 30 parts by mass of TDI, along with 0.4 parts by mass of catalyst 3-methyl-1-phenylphosphine heterocyclopentene-1-oxide, to the reactor. Under nitrogen protection, stir at 200 r / min and heat to 140 °C. Monitor the reaction until the degree of polymerization reaches approximately 4, then stop.

[0044] b) Cool to 75°C and add methoxy polyethylene glycol (MPEG-600, 600 Da) in a molar ratio of 1.02 times the remaining NCO groups for end-capping. React until the NCO% reaches 0.

[0045] c) Cool to 32°C, and at 600 r / min, add 150 parts by weight of deionized water containing a composite pH stabilizer of triethanolamine and sodium bicarbonate to adjust the pH of the system to 9.7. Disperse for 25 minutes to form a stable dispersion (solid content approximately 39%). Finally, add 2.5 parts by weight of a mixed latent acid consisting of equal mass ratios of blocked dodecylbenzenesulfonic acid and isopropylamine dodecylbenzenesulfonic acid, and stir until homogeneous to obtain a single-component aqueous carbodiimide crosslinking agent composition.

[0046] Take 100 parts by weight of waterborne epoxy resin, add 2.5 parts by weight of the above crosslinking agent composition, and stir until homogeneous. After applying the coating, place it in a 90°C oven to cure for 2.5 hours.

[0047] Example 5 a) Add 100 parts by mass of HDI and 0.35 parts by mass of MPPO catalyst to the reactor. Under nitrogen protection, stir at 180 r / min and heat to 135℃. Monitor the reaction until the degree of polymerization reaches approximately 4, then stop.

[0048] b) Cool to 85°C and add DMEA in a molar ratio of 1.08 times the remaining NCO groups for end-capping. React until NCO% reaches 0%.

[0049] c) Cool to 38°C, add 150 parts by weight of deionized water containing the pH stabilizer aminomethylpropanol at 700 r / min to adjust the pH of the system to 11.0, and disperse for 40 minutes to form a stable dispersion (solid content of about 41%). Finally, add 4.0 parts by weight of isopropylamine dodecylbenzenesulfonate and stir evenly to obtain a one-component aqueous carbodiimide crosslinking agent composition.

[0050] Take 100 parts by weight of water-based acrylic resin, add 1.5 parts by weight of the above crosslinking agent composition, and stir until homogeneous. After applying the coating, place it in an oven at 110°C for curing for 1.5 hours.

[0051] Example 6 a) Add 80 parts by mass of hexamethylene diisocyanate (HDI) and 20 parts by mass of tetramethylphenyl dimethyl diisocyanate (TMXDI) to a dry reactor, along with 0.45 parts by mass of triphenyl phosphate catalyst. Under nitrogen protection, stir at 200 rpm and heat to 150 °C. Monitor the reaction by NCO%, stopping when the degree of polymerization reaches approximately 4.

[0052] b) Cool the system to 75°C and add N,N-dimethylethanolamine (DMEA) in a molar ratio of 1.05 times the remaining NCO groups for end-capping. React until the NCO% reaches 0%.

[0053] c) Cool to 35°C, and while stirring at 600 r / min, slowly add 120 parts by weight of deionized water containing the pH stabilizer aminomethylpropanol to adjust the pH of the system to 10.8. Disperse for 25 minutes to form a stable dispersion (solid content approximately 42%). Finally, add 3.5 parts by weight of the latent acid dimethylamine dodecylbenzenesulfonate and stir until homogeneous to obtain a one-component aqueous carbodiimide crosslinking agent composition.

[0054] Take 100 parts by weight of water-based acrylic resin, add 1.5 parts by weight of the above crosslinking agent composition, and stir until homogeneous. After applying the coating, place it in an oven at 85°C for curing for 1.5 hours.

[0055] Comparative Example 1 a) Add 100 parts by mass of isophorone diisocyanate (IPDI) and 0.35 parts by mass of catalyst 3-methyl-1-phenylphosphine heterocyclopentene-1-oxide (MPPO) to a dry reactor. Under nitrogen protection, stir at 150 r / min and heat to 130 °C. Monitor the reaction by NCO% test, and stop the reaction when the degree of polymerization reaches approximately 2.

[0056] b) Cool the reaction system to 70°C and add methoxy polyethylene glycol (MPEG-500, 500 Da) in a molar ratio equal to 1.0 times the remaining NCO groups as a hydrophilic end-capping agent. Continue the reaction until the NCO% is titrated to be 0.

[0057] c) Cool the system to 30°C, and slowly add 150 parts by mass of deionized water containing the pH stabilizer triethylamine (TEA) under high-speed stirring at 500 r / min. Adjust the pH of the system to 10.5, disperse for 15 minutes to form a stable dispersion (solid content of about 38%), and obtain a single-component aqueous carbodiimide crosslinking agent composition.

[0058] Take 100 parts of water-based acrylic resin, add 2 parts by weight of the above crosslinking agent composition, and stir evenly to obtain a one-component coating. Apply the coating to the substrate and cure it in an oven at 80°C for 3 hours.

[0059] Comparative Example 2 a) Add 100 parts by mass of hexamethylene diisocyanate (HDI) and 0.5 parts by mass of triphenyl phosphate catalyst to the reactor. Under nitrogen protection, stir at 220 r / min and heat to 155℃ (midpoint). Monitor the reaction until the degree of polymerization reaches approximately 4 and then stop.

[0060] b) Cool to 80°C and add N,N-dimethylethanolamine (DMEA) in a molar ratio of 1.05 times the remaining NCO groups for end-capping. React until NCO% reaches 0%.

[0061] c) Cool to 35°C, add 150 parts by mass of deionized water containing the pH stabilizer potassium hydroxide (KOH) at 650 r / min to adjust the pH of the system to 12.4, and disperse for 30 minutes to form a stable dispersion (solid content of about 40%). A single-component aqueous carbodiimide crosslinking agent composition is obtained.

[0062] Take 100 parts by weight of waterborne polyurethane resin, add 3 parts by weight of the above crosslinking agent composition, and stir until homogeneous. After applying the coating, place it in an oven at 100°C for curing for 2 hours.

[0063] Storage stability test The prepared one-component crosslinking agent composition and its mixture with a carboxyl-containing resin were sealed and placed in a constant temperature oven at 35°C. Samples were taken periodically (e.g., on days 1, 7, 14, 28, and 60), and the pH value was measured using a precision pH meter.

[0064] Table 1. Storage stability (pH value) test results of Examples 1-7 and Comparative Examples 1-2 Crosslinking speed test The prepared single-component crosslinking agent composition and its single-component coating mixed with carboxyl-containing resin were placed in a tetrafluoroethylene mold and placed in a 95°C oven to obtain samples after heating for different times (1h, 2h, 3h, 4h). The samples were then immersed in acetone to observe the swelling or dissolution.

[0065] Table 2. Crosslinking rate test results of Examples 1-6 and Comparative Examples 1-2 From the above description, it can be seen that the present invention achieves the following effects: After 3 hours of heating treatment, the resin material in the examples showed a significant improvement in stability, while the comparative material remained dissolved in acetone, indicating that the comparative material had not yet undergone a crosslinking reaction at that time point. When the heating time was extended to 5 hours, the resin material in the examples maintained its morphological stability and did not show obvious swelling, confirming that under these conditions, carbodiimide, as a crosslinking agent, fully exerted its crosslinking efficiency.

[0066] The present invention achieves the following effects: This application prepares a single-component aqueous carbodiimide crosslinking agent composition by introducing a heat-generating acidifier, which has the characteristics of strong storage stability and fast reaction speed; tests on Examples 1-6 and Comparative Examples 1-2 prove that the introduction of the heat-generating acidifier does not affect its storage performance at room temperature, and at the same time can promote the rapid action of the crosslinking agent when used under hot conditions.

[0067] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A thermally triggered aqueous carbodiimide crosslinking agent composition, characterized in that, include: The composition comprises carbodiimide, a latent acid, and a pH stabilizer; the pH value of the aqueous carbodiimide crosslinking agent composition is 7.5-11.0; the latent acid is one or more of the following: dimethylamine salt of dodecylbenzenesulfonic acid, isopropylamine salt of dodecylbenzenesulfonic acid, blocked dodecylbenzenesulfonic acid, blocked dinonylnaphthalene disulfonic acid, and pyridine salt of p-toluenesulfonic acid.

2. The aqueous carbodiimide crosslinking agent composition according to claim 1, characterized in that, The pH stabilizer is one or more of the following: sodium hydroxide, potassium hydroxide, ammonia, triethylamine, triethanolamine, N,N-dimethylethanolamine, aminomethylpropanol, bicarbonate, and borate.

3. A method for preparing the aqueous carbodiimide crosslinking agent composition as described in claim 1, characterized in that, It includes the following steps: (1) Mix diisocyanate with catalyst and stir under nitrogen atmosphere to carry out polymerization reaction until the degree of polymerization is 2-6; (2) Lower the temperature to 70~90℃ and add a hydrophilic end-capping agent to react the remaining isocyanate groups; (3) Lower the temperature to 30~40℃, add deionized water containing pH stabilizer under stirring at 500~800r / min for dispersion, and add latent acid to obtain carbodiimide crosslinking agent aqueous dispersion.

4. The method according to claim 3, characterized in that, The catalyst is one or more of 3-methyl-1-phenylphosphine heterocyclopentene-1-oxide and triphenyl phosphate.

5. The method according to claim 3, characterized in that, The reaction temperature in step (1) is 130~180℃ and the stirring speed is 150~300r / min.

6. The method according to claim 3, characterized in that, The hydrophilic end-capping agent is N,N-dimethylethanolamine, sodium hydroxyethyl sulfonate, or methoxy polyethylene glycol.

7. The method according to claim 3, characterized in that, The mass ratio of diisocyanate to catalyst is 100:(0.35~0.7).

8. The use of a thermally triggered aqueous carbodiimide crosslinking agent composition as described in claim 1.

9. The application according to claim 8, characterized in that, The aqueous carbodiimide crosslinking agent composition of claim 1 is added to a carboxyl-containing resin and cured at 80-120°C for 0.5-2 hours; the mass ratio of the carboxyl-containing resin to the aqueous carbodiimide crosslinking agent composition is 100:(1-3).

10. The application according to claim 9, characterized in that, The carboxyl-containing resin is one or more of the following: waterborne acrylic resin, waterborne polyurethane resin, waterborne epoxy resin, and waterborne alkyd resin.

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