Preparation method of TMA-free polyester resin as well as product and application of TMA-free polyester resin

Abstract

The invention belongs to the technical field of powder coatings, and particularly relates to a preparation method of TMA-free polyester resin, a product and application of the TMA-free polyester resin. Polyhydric alcohol serves as an initial raw material, is melted and then is subjected to esterification reaction with polybasic acid and an acidification end-capping reagent which are added in batches in the presence of an organic tin catalyst and an antioxidant; and carrying out vacuum polycondensation, curing, discharging, cooling, crushing and packaging to obtain the TMA-free polyester resin with excellent performance. The coating is not only suitable for indoor coatings, but also more suitable for outdoor occasions with high durability and high decoration requirements, such as automobile coating, building exterior walls and outdoor furniture, and can also be used for manufacturing base materials for molding after coating, such as traveling cases and tempered doors, so that the construction difficulty of molding before coating is effectively reduced, and the application range is greatly widened.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coatings, and in particular relates to a preparation method, a product and an application of a TMA-free polyester resin. Background Art

[0002] As an important type of polymer material, resin has a wide range of applications in the fields of coatings, adhesives, composite materials, etc. Among them, powder resin has gradually become the preferred material for industrial coatings due to its unique solvent-free volatilization characteristics and environmental advantages. Powder resin not only has excellent mechanical properties and chemical stability, but also can achieve a variety of functions and effects by adjusting the formula to meet different application requirements. In the traditional powder resin formula, epoxy resin and polyester resin are its two main components. Epoxy resin is known for its superior adhesion, mechanical strength and chemical resistance, and is widely used in applications that require high strength and high corrosion resistance. However, epoxy resin has poor weather resistance and is easily degraded and discolored under ultraviolet radiation, which limits its service life and aesthetics in outdoor applications. In contrast, polyester resin has excellent weather resistance and decorative properties, and is particularly suitable for outdoor coatings and applications that require high durability. However, polyester resin has relatively low mechanical strength and adhesion, and performs poorly in applications that require greater mechanical stress.

[0003] In order to overcome the limitations of a single resin, attempts were made to mix epoxy resin and polyester resin in a certain ratio (50:50 or 60:40 or 70:30) to obtain a hybrid powder resin with both excellent mechanical properties and good weather resistance. However, in the current hybrid powder resin formula, in order to increase the reactivity of the resin, TMA (trimellitic anhydride) is usually used as a carboxyl end-capping agent. Although TMA can significantly increase the reaction rate of the resin, it is toxic and long-term exposure may have adverse effects on the environment and human health. With increasingly stringent environmental regulations, it is critical to reduce or eliminate the use of TMA in powder resins.

[0004] There are studies on TMA-free powder resins in the prior art, such as patent application CN112063276A - polyester resin for indoor TMA-free matte powder coatings, which solves the problem of current powder resins causing harm when using toxic TMA by adjusting the proportion of each component in the formula and introducing acrylic resin. However, the existing TMA-free polyester resins focus more on the application of matte powder coatings, which greatly limits the application scope of TMA-free polyester resins. Therefore, a new technical solution is needed to solve the above problems. Summary of the invention

[0005] The object of the present invention is to provide a preparation method, product and application of a TMA-free polyester resin, so as to solve the problems mentioned in the above background technology that the current TMA-free polyester resin focuses more on the application of matte powder coatings, which greatly limits the application scope of the TMA-free polyester resin.

[0006] To achieve the above object, the present invention provides the following technical scheme: a method for preparing a polyester resin without TMA, comprising the following specific steps: first, using a polyol selected from one or a mixture of neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane and castor oil as a starting material, and melting the polyol under nitrogen; second, starting an esterification reaction with a part of the polyacid and a part of the acidified end-capping agent and the melted polyol under an organic tin catalyst, and when the acid value reaches 30 to 40 mgKOH / g, adding an antioxidant to the remaining polyacid and the remaining acidified end-capping agent under nitrogen protection, and continuing the esterification reaction. Esterification reaction is carried out; when the acid value reaches 79-83 mgKOH / g, vacuum polycondensation is carried out for 2-4 hours at a vacuum degree of -0.095-0.1 MPa; when the acid value reaches 65-75 mgKOH / g and the viscosity reaches 3000-4000 mPas@200°C, the vacuum polycondensation is stopped and a curing accelerator is added for curing; finally, after discharging, cooling, crushing and packaging, a polyester resin without TMA having an acid value of 45-75 mgKOH / g, a viscosity of 2000-4000 mPas@200°C and a glass transition temperature of 55-63°C is obtained; The raw material components of the polyester resin include, by mass, 20 to 55 parts of polyol, 45 to 70 parts of polyacid, 5 to 10 parts of acidification end-capping agent, 0.01 to 0.12 parts of organic tin catalyst, 0.01 to 0.15 parts of antioxidant, and 0.5 to 1.5 parts of curing accelerator. The polyacid is one or a mixture of terephthalic acid, isophthalic acid, pyromellitic anhydride, phthalic anhydride, maleic anhydride, and nitrilotriacetic acid. The terminal agent is one or a mixture of pyromellitic anhydride, adipic acid, maleic anhydride, and isophthalic acid; the organic tin catalyst is one or a mixture of two of monobutyltin oxide, stannous oxalate, and stannous octoate; the antioxidant is one or a mixture of two of phosphorous acid and N-phenyl-2-naphthylamine; and the curing accelerator is one or a mixture of two of triphenylethylphosphonium bromide, butyltriphenylphosphonium chloride, benzyltriethylammonium chloride, and octadecadecyldimethyl tertiary amine.

[0007] The TMA-free polyester resin is obtained by adopting the above-mentioned preparation method, and then the obtained TMA-free polyester resin is applied to the preparation of powder coating.

[0008] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention adopts a specific raw material combination and reaction conditions, including the selection of polyols, the step-by-step addition of polyacids and acidified end-capping agents, the use of organic tin catalysts and antioxidants, and the precise control of vacuum polycondensation and curing, to successfully prepare a TMA-free polyester resin with excellent performance, which is not only suitable for indoor coatings, but also more suitable for outdoor occasions with high durability and high decorative requirements, such as automobile painting, building exterior walls, outdoor furniture, etc. It can also be used to make base materials such as suitcases and tempered doors that are shaped after painting, effectively reducing the construction difficulty of first shaping and then painting, and greatly broadening the scope of application; 2. The present invention achieves an ideal range of key performance indicators such as acid value, viscosity, and glass transition temperature of the prepared polyester resin by precisely controlling the raw material ratio, reaction conditions, and subsequent processing steps, which not only ensures the processing performance of the resin, but also ensures the comprehensive performance of the final coating such as hardness, toughness, and weather resistance, meeting the diverse needs in different application scenarios; 3. The present invention carefully selects polyols such as neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane, castor oil, etc. as starting materials. The combination of these raw materials not only provides rich functional groups, but also optimizes the molecular structure of the polyester resin, and improves its reactivity and mechanical properties. Through the combination of polyacids such as terephthalic acid, isophthalic acid, pyromellitic anhydride, etc. and acidifying end-capping agents such as pyromellitic anhydride and adipic acid, the performance of the polyester resin is precisely controlled, and the environmental and health problems caused by the use of toxic TMA as a carboxyl end-capping agent are completely avoided, which meets the current development trend of green environmental protection and regulatory requirements; 4. The preparation method of the present invention is simple, efficient, and easy to implement industrially. By adjusting the types and proportions of raw materials, the performance of the polyester resin can be flexibly adjusted to meet the customized needs of different customers, so that the application of TMA-free polyester resin in the field of powder coatings not only improves the environmental protection and durability of coating products, but also provides technical support and demonstration effect for the transformation and upgrading of the industry; 5. The TMA-free polyester resin prepared by the present invention also has good mechanical properties, chemical stability and weather resistance, further improving the service life and aesthetics of the powder coating, achieving the optimization of product performance and the expansion of application fields, and has high practical value and market prospects. DETAILED DESCRIPTION

[0009] The following examples are used to further illustrate the content of the present invention, but do not limit the application of the present invention. Embodiment 1:

[0010] This embodiment provides a method for preparing a polyester resin without TMA, and the preparation method comprises the following steps: First, the raw materials are taken according to the following mass parts: neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane, castor oil, terephthalic acid, isophthalic acid, adipic acid, monobutyltin oxide, N-phenyl-2-naphthylamine, and triphenylethylphosphonium bromide, the mass parts of which are 10:13:5:2:61.5:1.5:3:0.1:0.05:0.5 respectively; Then, neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane and castor oil were added to the reactor as polyols, heated to 100°C to melt them, and nitrogen was introduced for protection; 61.5 parts of terephthalic acid, 0.9 parts of isophthalic acid in 1.5 parts, 2 parts of adipic acid in 3 parts and monobutyltin oxide were added, and under nitrogen protection, the temperature was raised to 180°C to start esterification and water was discharged, and the cooling water of the distillation column was opened to control the column top temperature not to exceed 102°C, and the temperature was continued to be raised to 245°C for further esterification reaction. After 12 hours of reaction, the acid value was measured by sampling. When the acid value reached 36 mgKOH / g, the first step of esterification reaction was completed; the temperature was lowered to 220°C, Under nitrogen protection, 5 parts of 0.6 parts of isophthalic acid out of 1.5 parts, 1 part of adipic acid out of 3 parts and N-phenyl-2-naphthylamine are added, the temperature is raised to 230-250° C., and the esterification reaction is continued for 2-4 hours. When the acid value reaches 83 mgKOH / g, vacuum polycondensation is carried out at a vacuum degree of -0.098 MPa. After polycondensation for 3 hours, samples are taken to measure the acid value. When the acid value reaches 72 mgKOH / g and the viscosity is 4000 mPas@200° C., the vacuum polycondensation is completed. Nitrogen is introduced to break the vacuum, triphenylethylphosphonium bromide is added, and the material is discharged after stirring for 0.5 hours, cooled, crushed and packaged to obtain a polyester resin without TMA having a glass transition temperature of 56.5° C. Embodiment 2:

[0011] This embodiment provides a method for preparing a polyester resin without TMA, and the preparation method comprises the following steps: First, the raw materials are taken according to the following mass parts: neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane, castor oil, terephthalic acid, isophthalic acid, maleic anhydride, maleic anhydride, stannous oxalate, phosphorous acid, and octadecadecyl dimethyl tertiary amine, the mass parts of which are 10:13:5:2:61.5:1.5:1:2:0.1:0.05:0.5 respectively; Then, neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane and castor oil were added to the reactor as polyols, heated to 100°C to melt them, and nitrogen was introduced for protection; then 61.5 parts of terephthalic acid, 1.2 parts of isophthalic acid in 1.5 parts, 0.6 parts of maleic anhydride in 1 part, 1.4 parts of maleic anhydride in 2 parts and stannous oxalate were added, and under nitrogen protection, the temperature was raised to 180°C to start esterification and water was discharged, and the cooling water of the distillation column was opened to control the column top temperature not to exceed 102°C, and the temperature was continued to be raised to 245°C for further esterification reaction. After 12 hours of reaction, the acid value was measured by sampling, and when the acid value reached 37 mgKOH / g, the first step of esterification reaction was completed; the temperature was lowered to 220°C, Under nitrogen protection, 5 parts of 0.3 parts of isophthalic acid in 1.5 parts, 0.4 parts of maleic anhydride in 1 part, 0.6 parts of maleic anhydride in 2 parts and phosphorous acid are added, the temperature is raised to 230-250°C, and the esterification reaction is continued for 2-4 hours. When the acid value reaches 82 mgKOH / g, vacuum polycondensation is carried out at a vacuum degree of -0.098 MPa. After 3 hours of polycondensation, samples are taken to measure the acid value. When the acid value reaches 71 mgKOH / g and the viscosity is 3500 mPas@200°C, the vacuum polycondensation is completed; nitrogen is introduced to break the vacuum, octadecyl dimethyl tertiary amine is added, and the material is discharged, cooled, crushed and packaged after stirring for 0.5 hours to obtain a polyester resin without TMA having a glass transition temperature of 55.4°C. Embodiment 3:

[0012] This embodiment provides a method for preparing a polyester resin without TMA, and the preparation method comprises the following steps: First, the raw materials are taken according to the following mass parts: neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane, castor oil, terephthalic acid, isophthalic acid, pyromellitic anhydride, adipic acid, stannous octoate, phosphorous acid, and triphenylethylphosphonium bromide, the mass parts of which are 10:13:5:2:61.5:1.5:0.5:2.5:0.1:0.05:0.5 respectively; Then, neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane and castor oil were added to the reactor as polyols, heated to 100°C to melt them, and nitrogen was introduced for protection; 61.5 parts of terephthalic acid, 0.6 parts of isophthalic acid in 1.5 parts, 0.26 parts of pyromellitic anhydride in 0.5 parts, 1.8 parts of adipic acid in 2.5 parts and stannous octoate were added, and under nitrogen protection, the temperature was raised to 180°C to start esterification and water was discharged, the cooling water of the distillation column was opened, and the temperature at the top of the column was controlled not to exceed 102°C, and the temperature was continued to be raised to 245°C for further esterification reaction. After 12 hours of reaction, the acid value was measured by sampling. When the acid value reached 34 mgKOH / g, the first step of esterification reaction was completed; the temperature was lowered to 22 0℃, under nitrogen protection, continue to add 0.9 parts of isophthalic acid in 1.5 parts, 0.24 parts of pyromellitic anhydride in 0.5 parts, 0.7 parts of adipic acid in 2.5 parts and phosphorous acid, raise the temperature to 230-250℃ and continue esterification reaction for 2-4 hours, when the acid value reaches 80mgKOH / g, carry out vacuum polycondensation at a vacuum degree of -0.098MPa, after polycondensation for 3 hours, take samples to measure the acid value, when the acid value reaches 68mgKOH / g and the viscosity is 3800mPas@200℃, the vacuum polycondensation is completed; nitrogen is introduced to break the vacuum and triphenylethylphosphonium bromide is added, stirring for 0.5 hours, then discharging, cooling, crushing and packaging to obtain a polyester resin without TMA having a glass transition temperature of 57.2℃. Embodiment 4:

[0013] This embodiment provides a method for preparing a polyester resin without TMA, and the preparation method comprises the following steps: First, the raw materials are taken according to the following mass parts: neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane, castor oil, terephthalic acid, isophthalic acid, phthalic anhydride, pyromellitic anhydride, monobutyltin oxide, N-phenyl-2-naphthylamine, and triphenylethylphosphonium bromide, the mass parts of which are 10:13:5:2:61.5:1.5:1.5:1.5:0.1:0.05:0.5 respectively; Then, neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane and castor oil were added to the reactor as polyols, heated to 100°C to melt them, and nitrogen was introduced for protection; 61.5 parts of terephthalic acid, 0.4 parts of isophthalic acid in 1.5 parts, 0.8 parts of phthalic anhydride in 1.5 parts, 1.1 parts of pyromellitic anhydride in 1.5 parts and monobutyl tin oxide were added, and under nitrogen protection, the temperature was raised to 180°C, and water was esterified, and the cooling water of the distillation column was opened to control the column top temperature not to exceed 102°C, and the temperature was continued to be raised to 245°C for further esterification reaction. After 12 hours of reaction, samples were taken to measure the acid value. When the acid value reached 38 mgKOH / g, the first step of esterification reaction was completed; the temperature was lowered to 220°C , under nitrogen protection, continue to add 1.1 parts of isophthalic acid in 1.5 parts, 0.7 parts of phthalic anhydride in 1.5 parts, 0.4 parts of pyromellitic anhydride in 1.5 parts and N-phenyl-2-naphthylamine, raise the temperature to 230-250°C and continue the esterification reaction for 2-4 hours. When the acid value reaches 81 mgKOH / g, vacuum polycondensation is carried out at a vacuum degree of -0.098 MPa. After polycondensation for 3 hours, take a sample to measure the acid value. When the acid value reaches 74 mgKOH / g and the viscosity is 4000 mPas@200°C, the vacuum polycondensation is completed; nitrogen is introduced to break the vacuum and triphenylethylphosphonium bromide is added. After stirring for 0.5 hours, the material is discharged, cooled, crushed and packaged to obtain a polyester resin without TMA having a glass transition temperature of 59.6°C.

[0014] A TMA-free polyester resin prepared in Example 1-4 was used to prepare a powder coating, which was powder sprayed and cured and tested for application performance. The test results were compared with the application performance of a powder coating prepared by an existing TMA acid-terminated polyester resin as a comparative example. The results are as follows: ; Remarks The test methods for the above test items are as follows: Adhesion performance test method: According to the national standard GB / T 9286, powder coating resin is used to make powder coating, which is sprayed on a 1mm thick steel plate by electrostatic spraying. After curing, the adhesion performance is tested by the 100-grid method; Flexibility test method: According to the national standard GB / T 6742, powder coating resin is used to make powder coating, which is sprayed on a 1mm thick steel plate by electrostatic spraying. After curing, the flexibility is tested by cylindrical bending method; Impact performance test method: According to the national standard GB / T 1732, powder coating resin is used to make powder coating, which is sprayed on a 1mm thick steel plate by electrostatic spraying. After curing, the impact resistance of the paint film is tested by a gravity impact instrument; Weather resistance was measured in a UVA test box according to GB / T 23987-2009, with a light intensity of 0.52W / m2, irradiation for 8h, blackboard temperature of (60±3)℃, condensation for 4h, (50±3)℃; Leveling performance rating is based on the leveling effect rating standard of the US PCI, and horizontal fluidity is measured in accordance with GB / T21782; It can be seen from the above table that the powder coatings prepared using the TMA-free polyester resin prepared in Examples 1-4 have good impact resistance and flexibility, while also improving the environmental protection and durability of the powder coatings, thereby further improving the service life and aesthetics of the powder coatings, achieving optimization of product performance and expansion of application areas, and having high practical value and market prospects.

Claims

1. A method for preparing a TMA-free polyester resin, characterized in that: The specific steps are as follows: first, using one or more mixtures of polyols selected from neopentyl glycol, dipropylene glycol, 4,4-dihydroxydiphenylmethane and castor oil as starting materials, and melting them under nitrogen; second, adding polyacids selected from one or more mixtures of terephthalic acid, isophthalic acid, pyromellitic anhydride, phthalic anhydride, maleic anhydride and nitrilotriacetic acid and acidifying end-capping agents selected from one or more mixtures of pyromellitic anhydride, adipic acid, maleic anhydride and isophthalic acid in batches to the melted polyols, and performing esterification reaction in the presence of an organic tin catalyst and an antioxidant; and performing vacuum polycondensation when the acid value reaches 79-83 mgKOH / g; When the acid value reaches 65-75 mgKOH / g and the viscosity reaches 3000-4000 mPas@200°C, the vacuum polycondensation is stopped and a curing accelerator is added for curing; finally, the polyester resin free of TMA is obtained through discharging, cooling, crushing and packaging.

2. The method for preparing a TMA-free polyester resin according to claim 1, characterized in that: The raw material components of the TMA-free polyester resin include, by mass, 20 to 55 parts of polyol, 45 to 70 parts of polyacid, 5 to 10 parts of acidification end-capping agent, 0.01 to 0.12 parts of organic tin catalyst, 0.01 to 0.15 parts of antioxidant, and 0.5 to 1.5 parts of curing accelerator.

3. The method for preparing a TMA-free polyester resin according to claim 2, characterized in that: The organic tin catalyst is one or a mixture of two of monobutyltin oxide, stannous oxalate and stannous octoate.

4. The method for preparing a TMA-free polyester resin according to claim 2, wherein: The antioxidant is phosphorous acid, N-phenyl-2-naphthylamine or a mixture of the two.

5. The method for preparing a TMA-free polyester resin according to claim 2, characterized in that: The curing accelerator is one of triphenylethylphosphonium bromide, butyltriphenylphosphonium chloride, benzyltriethylammonium chloride, and octadecadecyldimethyl tertiary amine, or a mixture of two of them.

6. The method for preparing a TMA-free polyester resin according to claim 1, characterized in that: During the esterification reaction, part of the polyacid and part of the acidifying end-capping agent are firstly reacted with the molten polyol in the presence of an organic tin catalyst to start the esterification reaction. When the acid value reaches 30-40 mgKOH / g, the remaining polyacid and the remaining acidifying end-capping agent are added with an antioxidant under nitrogen protection to continue the esterification reaction.

7. The method for preparing a TMA-free polyester resin according to claim 1, characterized in that: The vacuum degree of the vacuum polycondensation is -0.095 to -0.1 MPa, and the time of the vacuum polycondensation is 2 to 4 hours.

8. The method for preparing a TMA-free polyester resin according to claim 1, characterized in that: The TMA-free mixed polyester resin has an acid value of 45-75 mgKOH / g, a viscosity of 2000-4000 mPas@200°C, and a glass transition temperature of 55-63°C.

9. A TMA-free polyester resin obtained by the method for preparing a TMA-free polyester resin according to any one of claims 1 to 8.

10. Use of the TMA-free polyester resin obtained by the method for preparing the TMA-free polyester resin according to any one of claims 1 to 8 in powder coatings.