Zero voc waterborne polyester resin and method of making same

Abstract

The application provides a zero-VOC water-based polyester resin and a preparation method thereof, and belongs to the technical field of paints.The application comprises the following raw material components: neopentyl glycol, adipic acid, phthalic anhydride, isophthalic anhydride, trimellitic anhydride, a catalyst, an antioxidant, a neutralizing agent and deionized water; the application only uses water as a dispersion dilution solvent throughout the whole process, completely replaces benzene, ketone, ester, alcohol ether organic solvents used in traditional processes, completely eliminates VOC generation sources from molecular design and formula system, and realizes zero-VOC emission of resin finished products, which is green, environmentally-friendly and non-polluted.Because flammable and explosive organic solvents are not used, the flash point of the system is significantly improved, there is no flammable and explosive risk in production and construction, and the operation safety is greatly improved; meanwhile, the high-priced organic solvents, waste gas treatment and solvent recovery costs are saved, the production raw material and operation comprehensive cost are significantly reduced under the premise of realizing environmental protection up to the standard, and the environmental protection, safety and economy are considered.

Description

Technical Field

[0001] This invention relates to the field of coating manufacturing technology, specifically to a zero-VOC waterborne polyester resin and its preparation method. Background Technology

[0002] Polyester resin is a core film-forming matrix material in the coatings and baking paint industry. Currently, the mainstream products on the market are mainly divided into three categories: oil-based polyester resin, alcohol ether-based water-based polyester resin, and emulsion-type polyester resin. However, all of them have insurmountable technical defects. 1. Traditional oil-based polyester resins must be diluted and dissolved with benzene, ketone, and ester organic solvents during production and construction, resulting in extremely high VOC emissions. This not only seriously pollutes the ecological environment but also endangers the health of operators. In addition, the materials are flammable and explosive, posing high safety risks during production and construction, and do not meet current environmental protection requirements. 2. Conventional alcohol ether-based waterborne polyester resins require a high acid value during synthesis. After neutralization with an alkaline neutralizer, they are dispersed and diluted with water using an alcohol ether cosolvent. The system still has a relatively high VOC content, and the resin molecular chains are very prone to hydrolysis and chain breakage in acidic or alkaline water environments. The storage period is short and the performance of the paint film deteriorates severely in the later stages. 3. Emulsion-type polyester resins rely on emulsifiers to achieve water dispersion, resulting in poor system storage stability and easy delamination and emulsion breakage during long-term storage. At the same time, the resin itself has poor wetting and dispersion properties for pigments and color powders, which can easily lead to floating color and mottling after coating. Furthermore, after curing into a film, its water resistance and chemical corrosion resistance are poor, which cannot meet the requirements of high-end baking paint applications.

[0003] Therefore, developing a waterborne polyester resin with zero VOC emissions, stable water solubility, large molecular weight, excellent chemical resistance, and strong pigment wetting and dispersion capabilities is a pressing technical challenge that the industry needs to address. Summary of the Invention

[0004] To address the numerous shortcomings of the existing three types of polyester resins, this invention provides a zero-VOC waterborne polyester resin and its preparation method. The method employs a two-step controllable polymerization process, completely replacing organic solvents with pure water to synthesize a zero-VOC environmentally friendly waterborne polyester resin, while also taking into account the excellent film performance, stable water solubility, and super pigment dispersion ability brought about by high molecular weight.

[0005] This invention provides the following technical solution: A zero-VOC waterborne polyester resin comprises, by mass fraction, the following raw material components: 15-25 parts neopentyl glycol, 3-8 parts adipic acid, 6-12 parts phthalic anhydride, 3-8 parts isophthalic anhydride, 3-8 parts trimellitic anhydride, 0.1-0.3 parts catalyst, 0.1-0.5 parts antioxidant, 4-6 parts neutralizer, and 45-60 parts deionized water.

[0006] As a further technical solution, the catalyst is monobutyltin trichloride.

[0007] As a further technical solution, the antioxidant is either a phosphite or hypophosphite.

[0008] As a further technical solution, the neutralizing agent is dimethylethanolamine.

[0009] A method for preparing a zero-VOC waterborne polyester resin includes the following steps: Step a: Weigh each component according to its respective weight, and heat neopentyl glycol to 120°C until it is completely melted; Step b: Add adipic acid, phthalic anhydride, isophthalic anhydride, catalyst, and antioxidant into the reactor and gradually increase the temperature; Step c: Gradually increase the temperature to 230℃ and keep the column temperature below 105℃; Step d: Stop the reaction once the acid value is below 8, and cool to 160℃; Step e: Add trimellitic anhydride and reheat to 180℃. Stop the reaction when the acid value reaches 40-50. Step f: Cool to 95°C and add neutralizing agent; Step g: Add deionized water to adjust the viscosity and solid content to obtain the finished resin.

[0010] As a further technical solution: in step g, the solid content of the finished resin product is 42-46 wt%.

[0011] An application of a zero-VOC waterborne polyester resin in waterborne baking paint coatings. The resin uses pure water as the sole dispersion medium, has zero VOC emissions, and exhibits excellent wetting and dispersing ability for color powders. It can be used with little or no dispersant.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This invention uses only water as the dispersion and dilution solvent throughout the entire process, completely replacing the benzene, ketone, ester, and alcohol ether organic solvents used in traditional processes. It eliminates the source of VOC generation from the molecular design and formulation system, resulting in truly zero VOC emissions in the finished resin product, making it green, environmentally friendly, and pollution-free. Because no flammable or explosive organic solvents are used, the system's flash point is significantly increased, eliminating the risk of flammability and explosion during production and construction, and greatly improving operational safety. Simultaneously, it eliminates the costs of expensive organic solvents, waste gas treatment, and solvent recovery, significantly reducing the overall cost of raw materials and operation and maintenance while achieving environmental compliance, thus balancing environmental friendliness, safety, and economy.

[0013] This invention employs a two-step controlled polymerization process for synthesis. The two reactions have clearly defined roles and form a synergistic mechanism at the molecular structure level: In the first step, neopentyl glycol, adipic acid, phthalic anhydride, and isophthalic anhydride undergo high-temperature polycondensation under the action of a catalyst, gradually dehydrating to form a long-chain, highly regular, and high-molecular-weight polyester backbone. The strong cohesive force of the molecular chain and moderate chain segment mobility fundamentally improve the flexibility, adhesion, and chemical corrosion resistance of the resin film after formation. In the second step, trimellitic anhydride is precisely added after the backbone is formed for secondary esterification. Utilizing its trifunctional structure, a quantitative amount of carboxyl hydrophilic groups are introduced at the ends / side chains of the polyester molecular chain, controlling the acid value to 40–50 mg KOH / g. While retaining the excellent mechanical and chemical resistance properties brought by the high molecular weight backbone, the resin can be stably dispersed in pure water after neutralization.

[0014] The resin of this invention, synthesized via a two-step method, possesses a stable and controllable high acid value. Its molecular chain contains high-density, highly active carboxyl hydrophilic groups, enabling it to form hydrogen bonds, van der Waals forces, and electrostatic adsorption with the surface of inorganic / organic pigments. This results in strong wetting, encapsulation, and dispersion capabilities for the pigments. During coating formulation, minimal or no dispersant is required to achieve uniform dispersion, avoiding the problem of reduced water and salt spray resistance due to dispersant residue. Furthermore, the resin is an emulsifier-free self-dispersing system, relying on its own carboxyl groups for aqueous phase dispersion. There is no migration or precipitation of small-molecule emulsifiers. Its dense molecular chain structure and strong hydrolytic stability ensure that it does not separate, hydrolyze, or break down during long-term storage. This completely solves the defects of emulsion-type polyester resins being prone to demulsification during storage and alcohol ether resins being prone to hydrolysis. Overall, its performance is stable and reliable, making it highly suitable for industrial-scale production and long-term storage of water-based baking paints. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] This invention provides a zero-VOC waterborne polyester resin, comprising the following raw material components by mass fraction: 15-25 parts neopentyl glycol, 3-8 parts adipic acid, 6-12 parts phthalic anhydride, 3-8 parts isophthalic anhydride, 3-8 parts trimellitic anhydride, 0.1-0.3 parts catalyst, 0.1-0.5 parts antioxidant, 4-6 parts neutralizer, and 45-60 parts deionized water.

[0017] In this invention, the catalyst is preferably monobutyltin trichloride, the antioxidant is preferably one of phosphite or hypophosphite, and the neutralizing agent is preferably dimethylethanolamine.

[0018] This invention also provides a method for preparing a zero-VOC waterborne polyester resin, comprising the following steps: Step a: Weigh each component according to its respective weight, and heat neopentyl glycol to 120°C until it is completely melted; Step b: Add adipic acid, phthalic anhydride, isophthalic anhydride, catalyst, and antioxidant into the reactor and gradually increase the temperature; Step c: Gradually increase the temperature to 230℃ and keep the column temperature below 105℃; Step d: Stop the reaction once the acid value is below 8, and cool to 160℃; Step e: Add trimellitic anhydride and reheat to 180℃. Stop the reaction when the acid value reaches 40-50. Step f: Cool to 95°C and add neutralizing agent; Step g: Add deionized water to adjust the viscosity and solid content to obtain the finished resin. The preferred solid content of the finished resin is 42-46 wt%.

[0019] The zero-VOC waterborne polyester resin provided by this invention uses pure water as the sole dispersion solvent throughout the entire process, without the addition of any organic solvents, thus achieving zero VOC emissions. It adopts a two-step controllable polycondensation process, resulting in stable water solubility of the resin, no stratification or hydrolysis during storage, excellent pigment wetting and dispersion properties, and outstanding flexibility, acid and alkali resistance, and solvent resistance after film formation. It can be applied to waterborne baking paint coatings, solving the technical defects of traditional waterborne polyester resins such as high VOC content, easy hydrolysis, poor storage stability, and weak pigment dispersion, making it suitable for industrial production.

[0020] To further illustrate the present invention, the following embodiments and comparative examples are provided in detail.

[0021] Example 1: Step 1: Weigh the raw materials according to the following mass fractions: 15 parts neopentyl glycol, 3 parts adipic acid, 6 parts phthalic anhydride, 3 parts isophthalic anhydride, 3 parts trimellitic anhydride, 0.1 parts monobutyltin trichloride, 0.1 parts hypophosphite, 4 parts dimethylethanolamine, and 45 parts deionized water.

[0022] Step 2: Add the weighed neopentyl glycol to the reaction vessel, heat to 120°C, and keep warm until the neopentyl glycol is completely melted and liquefied.

[0023] Step 3: Add adipic acid, phthalic anhydride, isophthalic anhydride, monobutyltin trichloride, and hypophosphoric acid into the reactor, stir and mix evenly, and then gradually increase the temperature.

[0024] Step 4: Continue to gradually increase the temperature to 230℃ to carry out the polycondensation reaction, and control the column temperature of the distillation column below 105℃ during the reaction.

[0025] Step 5: Continue the reaction at the specified temperature, monitoring the acid value of the system in real time. When the acid value drops below 8, stop the reaction and cool the system to 160℃. Step 6: Add trimellitic anhydride to the reactor, stir and mix thoroughly, then reheat to 180℃ to continue the esterification reaction. Stop the reaction when the acid value reaches 40.

[0026] Step 7: Cool the system to 95°C, add dimethylethanolamine and stir thoroughly to carry out the neutralization reaction.

[0027] Step 8: Add deionized water while stirring, adjust the viscosity and solid content of the system, control the solid content of the finished product to 42wt%, stir evenly, filter and discharge to obtain zero VOC waterborne polyester resin.

[0028] Example 2: Step 1: Weigh the raw materials according to the following mass fractions: 20 parts neopentyl glycol, 5 parts adipic acid, 9 parts phthalic anhydride, 5 parts isophthalic anhydride, 5 parts trimellitic anhydride, 0.2 parts monobutyltin trichloride, 0.3 parts phosphite, 5 parts dimethylethanolamine, and 52 parts deionized water.

[0029] Step 2: Add the weighed neopentyl glycol to the reaction vessel, heat to 120°C, and keep warm until the neopentyl glycol is completely melted and liquefied.

[0030] Step 3: Add adipic acid, phthalic anhydride, isophthalic anhydride, monobutyltin trichloride, and phosphite into the reactor, stir and mix evenly, and then gradually increase the temperature.

[0031] Step 4: Continue to gradually increase the temperature to 230℃ to carry out the polycondensation reaction, and control the column temperature of the distillation column below 105℃ during the reaction.

[0032] Step 5: Continue the reaction at a constant temperature, monitor the acid value of the system in real time, and stop the reaction when the acid value is below 8. Then cool the system to 160℃.

[0033] Step 6: Add trimellitic anhydride to the reactor, stir and mix evenly, then reheat to 180°C and continue the esterification reaction. Stop the reaction when the acid value of the system reaches 45.

[0034] Step 7: Cool the system to 95°C, add dimethylethanolamine and stir thoroughly to carry out the neutralization reaction.

[0035] Step 8: Add deionized water while stirring, adjust the viscosity and solid content of the system, control the solid content of the finished product to 44wt%, stir evenly, filter and discharge to obtain zero VOC waterborne polyester resin.

[0036] Example 3: Step 1: Weigh the raw materials according to the following mass fractions: 25 parts neopentyl glycol, 8 parts adipic acid, 12 parts phthalic anhydride, 8 parts isophthalic anhydride, 8 parts trimellitic anhydride, 0.3 parts monobutyltin trichloride, 0.5 parts phosphite, 6 parts dimethylethanolamine, and 60 parts deionized water.

[0037] Step 2: Add the weighed neopentyl glycol to the reaction vessel, heat to 120°C, and keep warm until the neopentyl glycol is completely melted and liquefied.

[0038] Step 3: Add adipic acid, phthalic anhydride, isophthalic anhydride, monobutyltin trichloride, and phosphite into the reactor, stir and mix evenly, and then gradually increase the temperature.

[0039] Step 4: Continue to gradually increase the temperature to 230℃ to carry out the polycondensation reaction, and control the column temperature of the distillation column below 105℃ during the reaction.

[0040] Step 5: Continue the reaction at a constant temperature, monitor the acid value of the system in real time, and stop the reaction when the acid value is below 8. Then cool the system to 160℃.

[0041] Step 6: Add trimellitic anhydride to the reactor, stir and mix evenly, then reheat to 180°C and continue the esterification reaction. Stop the reaction when the acid value of the system reaches 50.

[0042] Step 7: Cool the system to 95°C, add dimethylethanolamine and stir thoroughly to carry out the neutralization reaction.

[0043] Step 8: Add deionized water while stirring, adjust the viscosity and solid content of the system, control the solid content of the finished product to 46wt%, stir evenly, filter and discharge to obtain zero VOC waterborne polyester resin.

[0044] Comparative Example 1: The difference from Example 2 is that trimellitic anhydride was not added, but the other raw materials and preparation steps are exactly the same.

[0045] Step 1: Weigh the raw materials according to the following mass fractions: 20 parts neopentyl glycol, 5 parts adipic acid, 9 parts phthalic anhydride, 5 parts isophthalic anhydride, 0.2 parts monobutyltin trichloride, 0.3 parts phosphite, 5 parts dimethylethanolamine, and 52 parts deionized water.

[0046] Step 2: Add the weighed neopentyl glycol to the reaction vessel, heat to 120°C, and keep warm until the neopentyl glycol is completely melted and liquefied.

[0047] Step 3: Add adipic acid, phthalic anhydride, isophthalic anhydride, monobutyltin trichloride, and phosphite into the reactor, stir and mix evenly, and then gradually increase the temperature.

[0048] Step 4: Continue to gradually increase the temperature to 230℃ to carry out the polycondensation reaction, and control the column temperature of the distillation column below 105℃ during the reaction.

[0049] Step 5: Continue the reaction at a constant temperature, monitor the acid value of the system in real time, and stop the reaction when the acid value is below 8. Then cool the system to 95°C.

[0050] Step 6: Add dimethylethanolamine and stir thoroughly to carry out the neutralization reaction.

[0051] Step 7: Add deionized water while stirring, adjust the viscosity and solid content of the system, control the solid content of the finished product to 44wt%, stir evenly, filter and discharge to obtain the comparison resin.

[0052] Comparative Example 2: The difference from Example 2 is that an alcohol ether solvent was used to replace part of the deionized water, no antioxidant was added, and the other raw materials and preparation steps were exactly the same.

[0053] Step 1: Weigh the raw materials according to the following mass fractions: 20 parts neopentyl glycol, 5 parts adipic acid, 9 parts phthalic anhydride, 5 parts isophthalic anhydride, 5 parts trimellitic anhydride, 0.2 parts monobutyltin trichloride, 5 parts dimethyl ethanolamine, 10 parts propylene glycol methyl ether, and 42 parts deionized water.

[0054] Step 2: Add the weighed neopentyl glycol to the reaction vessel, heat to 120°C, and keep warm until the neopentyl glycol is completely melted and liquefied.

[0055] Step 3: Add adipic acid, phthalic anhydride, isophthalic anhydride, and monobutyltin trichloride into the reactor, stir and mix evenly, and then gradually increase the temperature.

[0056] Step 4: Continue to gradually increase the temperature to 230℃ to carry out the polycondensation reaction, and control the column temperature of the distillation column below 105℃ during the reaction.

[0057] Step 5: Continue the reaction at a constant temperature, monitor the acid value of the system in real time, and stop the reaction when the acid value is below 8. Then cool the system to 160℃.

[0058] Step 6: Add trimellitic anhydride to the reactor, stir and mix evenly, then reheat to 180°C and continue the esterification reaction. Stop the reaction when the acid value of the system reaches 45.

[0059] Step 7: Cool the system to 95°C, add dimethylethanolamine and stir thoroughly to carry out the neutralization reaction.

[0060] Step 8: Add propylene glycol methyl ether and deionized water while stirring to adjust the viscosity and solid content of the system. Control the solid content of the finished product to 44 wt%. After stirring evenly, filter the material to obtain the comparison resin.

[0061] Performance testing: Experiment 1: VOC content and storage stability test: Experimental methods: VOC content test: The content of volatile organic compounds in the resin sample was detected by gas chromatography, and the test results were recorded.

[0062] Storage stability test: The resin sample was stored in a 50℃ constant temperature chamber for 60 days. The results were recorded as no abnormality, slight stratification, severe stratification, demulsification and hydrolysis.

[0063] Experimental data: Table 1 Examples 1-3 all had a VOC content of 0, meeting the zero-VOC requirement. They showed no stratification, hydrolysis, or demulsification after 60 days of storage, demonstrating excellent stability. Comparative Example 1, lacking trimellitic anhydride, had insufficient hydrophilic groups in the resin, resulting in poor water solubility and slight stratification during long-term storage. Comparative Example 2, with the addition of alcohol ether solvents, had excessive VOC content. Lacking antioxidants, the resin molecular chains were easily degraded, leading to severe stratification and hydrolysis, and poor storage stability.

[0064] Experiment 2: Pigment wetting and dispersibility test: Experimental methods: Titanium dioxide was selected as the pigment and mixed at a mass ratio of resin to pigment of 7:3. The mixture was stirred at high speed for 30 minutes. The dispersion state of the pigment was observed, and the presence of floating color, blooming, or particles was detected by scraper method. The pigment was rated as excellent, good, or poor.

[0065] Experimental data: Table 2 The resins in Examples 1-3 contain abundant hydrophilic groups, exhibiting strong wetting and encapsulation capabilities for titanium dioxide, resulting in uniform pigment dispersion without floating color, blooming, or particles. Comparative Example 1, lacking trimellitic anhydride regulation, suffers from insufficient acid value and hydrophilic groups, leading to uneven pigment dispersion and the appearance of floating color and particles. Comparative Example 2 contains alcohol-ether solvents, resulting in poor system compatibility. The absence of antioxidants further degrades resin performance, causing poor pigment dispersion and noticeable blooming.

[0066] Experiment 3: Film-forming flexibility and chemical resistance test: Experimental methods: Flexibility test: The resin is made into a paint film, and the flexibility of the paint film is tested using the shaft bar method. The minimum shaft bar diameter is recorded. The smaller the diameter, the better the flexibility.

[0067] Acid and alkali resistance test: Immerse the paint film in 5% sulfuric acid solution and 5% sodium hydroxide solution for 24 hours respectively, and observe whether the paint film blisters, peels off, or changes color.

[0068] Solvent resistance test: Wipe the paint film with anhydrous ethanol 100 times and observe whether the paint film loses its gloss or is damaged.

[0069] Experimental data: Table 3 Examples 1-3 employed a two-step method to synthesize a high molecular weight backbone, resulting in film with excellent flexibility and outstanding resistance to acids, alkalis, and ethanol wiping. Comparative Example 1, lacking trimellitic anhydride, exhibited an incomplete molecular chain structure, decreased flexibility, and poorer chemical resistance. Comparative Example 2 used an alcohol ether solvent, resulting in low film density; the absence of antioxidants led to easy molecular chain damage, poor flexibility, and severely deteriorated acid, alkali, and solvent resistance.

[0070] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not describe all details exhaustively, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification.

Claims

1. A zero-VOC waterborne polyester resin, characterized in that, By mass fraction, it includes the following raw material components: 15-25 parts neopentyl glycol, 3-8 parts adipic acid, 6-12 parts phthalic anhydride, 3-8 parts isophthalic anhydride, 3-8 parts trimellitic anhydride, 0.1-0.3 parts catalyst, 0.1-0.5 parts antioxidant, 4-6 parts neutralizer, and 45-60 parts deionized water.

2. The zero-VOC waterborne polyester resin according to claim 1, characterized in that, The catalyst is monobutyltin trichloride.

3. The zero-VOC waterborne polyester resin according to claim 1, characterized in that, The antioxidant is either phosphite or hypophosphite.

4. The zero-VOC waterborne polyester resin according to claim 1, characterized in that, The neutralizing agent is dimethylethanolamine.

5. A method for preparing a zero-VOC waterborne polyester resin according to any one of claims 1-4, characterized in that, Includes the following steps: Step a: Weigh each component according to its respective weight, and heat neopentyl glycol to 120°C until it is completely melted; Step b: Add adipic acid, phthalic anhydride, isophthalic anhydride, catalyst, and antioxidant into the reactor and gradually increase the temperature; Step c: Gradually increase the temperature to 230℃ and keep the column temperature below 105℃; Step d: Stop the reaction once the acid value is below 8, and cool to 160℃; Step e: Add trimellitic anhydride and reheat to 180℃. Stop the reaction when the acid value reaches 40-50. Step f: Cool to 95°C and add neutralizing agent; Step g: Add deionized water to adjust the viscosity and solid content to obtain the finished resin.

6. The method for preparing a zero-VOC waterborne polyester resin according to claim 5, characterized in that: In step g, the solid content of the resin product is 42-46 wt%.

7. The application of the zero-VOC waterborne polyester resin according to claim 1, characterized in that, It is used in water-based baking paint coatings.

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