A phosphate-modified polyester resin, a preparation method and application thereof, and a coating

Abstract

The application provides a phosphate-modified polyester resin and a preparation method and application thereof, and a coating, and belongs to the technical field of industrial coatings.The phosphate-modified polyester resin has a main chain and a side chain containing phosphate groups.The P atom of the phosphate group has a large electronegativity, so that the phosphate-modified polyester resin has a large polarity and the phosphate group contains a hydrocarbon group, which makes the phosphate-modified polyester resin have good wettability;the phosphate group has strong acidity, can be chemically bonded with metal ions on the surface of a coated substrate, generates an organic metal phosphate, and forms an organic metal phosphate film, so as to form a "chemical bridge" between the surface of the substrate and the coating, which greatly improves the adhesion between the coated substrate and the coating, so that the surface of the coated substrate can be directly coated without chemical pretreatment when the powder coating is sprayed, thereby improving the spraying efficiency, saving the cost, and reducing the environmental pollution.

Description

A phosphate-modified polyester resin, its preparation method and application, and coatings. Technical Field

[0001] This invention relates to the field of industrial coatings technology, and in particular to a phosphate-modified polyester resin, its preparation method and application, and coatings. Background Technology

[0002] Powder coatings are a type of 100% solid synthetic resin coating that exists in a fine powder state and contains no solvents. The main film-forming substance is polyester resin. It is characterized by being harmless, efficient, economical, and environmentally friendly, and is internationally known as "4E" coating. It is one of the most ideal alternatives to solvent-based coatings. However, before applying powder coatings to an object, surface treatment (also called pretreatment) is necessary to ensure the quality and effect of the coating.

[0003] Chemical treatment in the surface preparation of coated objects typically involves physical degreasing and rust removal followed by chemical treatment with phosphating solution. However, chemical treatment not only reduces efficiency but also generates large amounts of waste liquid and residue, causing serious environmental pollution. With the increasing national emphasis on energy conservation and environmental protection, there is an urgent need for a powder coating that does not require chemical treatment, thereby meeting environmental requirements and improving spraying efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a phosphate-modified polyester resin, its preparation method and application, and a coating. The powder coating prepared by the phosphate-modified polyester resin of this invention can be directly sprayed without chemical treatment of the substrate, which improves the spraying efficiency and saves costs.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] The present invention provides a phosphate ester modified polyester resin, wherein the main chain and side chains of the phosphate ester modified polyester resin contain phosphate ester groups.

[0007] Preferably, the glass transition temperature of the phosphate-modified polyester resin is 55°C.

[0008] The present invention also provides a method for preparing the phosphate-modified polyester resin described above, characterized by comprising the following steps:

[0009] A first esterification reaction is carried out by mixing polyol, primary polyacid, antioxidant and esterification catalyst to obtain polyester prepolymer;

[0010] The polyester prepolymer is subjected to a second esterification reaction with phosphate ester to obtain phosphate ester modified polyester resin prepolymer.

[0011] The phosphate-modified polyester resin prepolymer was subjected to a polycondensation reaction to obtain a phosphate-modified polyester resin precursor.

[0012] The phosphate-modified polyester resin precursor is mixed with a second polybasic acid and then acidified and capped to obtain the phosphate-modified polyester resin.

[0013] Preferably, the molar ratio of the phosphate ester to the polyol is 0.06 to 0.3:1;

[0014] The molar ratio of hydroxyl groups to carboxyl groups of the first polyacid in the polyol is 1.05 to 1.1:1.

[0015] Preferably, by mass fraction, the first polyacid comprises 40-100% terephthalic acid; 0-30% isophthalic acid; 0-20% trimellitic anhydride; 0-20% pyromellitic anhydride; 0-6% 1,6-adipic acid; and 0-5% hexahydrophthalic anhydride.

[0016] By mass fraction, the second polyacid comprises trimellitic anhydride 0–100%, pyromellitic anhydride 0–20%, 1,6-adipic acid 0–100%, and hexahydrophthalic anhydride 0–10%.

[0017] Preferably, the temperature of the first esterification reaction is 180–250°C; the acid value of the polyester prepolymer is 15–25 mg KOH / g, and the viscosity is 1.2–1.6 Pa·s / 175°C.

[0018] Preferably, the temperature of the second esterification reaction is 250℃~260℃, the acid value of the phosphate ester modified polyester resin prepolymer is 20~35mgKOH / g, and the viscosity is 1.38~1.8Pa.s / 175℃.

[0019] Preferably, the polycondensation reaction is carried out at a temperature of 250℃ to 260℃ and a vacuum degree of -0.09MPa to -0.1MPa; the phosphate ester modified polyester resin precursor has an acid value of 10 to 25 mgKOH / g and a viscosity of 4.9 to 6.5 Pa·s / 175℃.

[0020] The present invention also provides the application of the phosphate-modified polyester resin described in the above-described scheme or the phosphate-modified polyester resin prepared by the preparation method described in the above-described scheme in coatings.

[0021] The present invention also provides a coating comprising the following components: phosphate-modified polyester resin, epoxy resin, curing accelerator, leveling agent, brightener, benzoin, precipitated barium sulfate, and titanium dioxide;

[0022] The phosphate-modified polyester resin is the phosphate-modified polyester resin described in the above scheme or the phosphate-modified polyester resin prepared by the preparation method described in the above scheme.

[0023] This invention provides a phosphate-modified polyester resin, wherein the main chain and side chains of the phosphate-modified polyester resin contain phosphate groups. The phosphate groups have high electronegativity (P atoms), giving the phosphate-modified polyester resin high polarity, and the presence of hydrocarbon groups in the phosphate groups provides excellent wettability. Simultaneously, because the phosphate groups have strong acidity, they can chemically bond with metal ions on the surface of the substrate, generating organometallic phosphates and forming an organometallic phosphate film. This creates a "chemical bridge" between the substrate surface and the coating, significantly improving the adhesion between the substrate and the coating. This allows for direct coating without chemical pretreatment of the substrate surface during powder coating, thereby improving coating efficiency, saving costs, and reducing environmental pollution.

[0024] The preparation method of the phosphate ester modified polyester resin of the present invention is simple and easy to control, and is basically consistent with the existing polyester resin synthesis process. It does not require additional investment in new equipment and can easily achieve industrial mass production. Detailed Implementation

[0025] The present invention provides a phosphate ester modified polyester resin, wherein the main chain and side chains of the phosphate ester modified polyester resin contain phosphate ester groups.

[0026] In this invention, the molecular weight of the phosphate-modified polyester resin is preferably 3500-5000, more preferably 4000-4500.

[0027] In this invention, the glass transition temperature of the phosphate-modified polyester resin is 55°C. The phosphate-modified polyester resin has good processability, and the powder coating made from it is not easily melted due to its high glass transition temperature, thus exhibiting excellent anti-caking properties.

[0028] The present invention also provides a method for preparing the phosphate-modified polyester resin described above, comprising the following steps:

[0029] A first esterification reaction is carried out by mixing polyol, primary polyacid, esterification catalyst and antioxidant to obtain polyester prepolymer;

[0030] The polyester prepolymer and phosphate ester are simultaneously subjected to a second esterification reaction to obtain a phosphate ester modified polyester resin prepolymer.

[0031] The phosphate-modified polyester resin prepolymer was subjected to a polycondensation reaction to obtain a phosphate-modified polyester resin precursor.

[0032] The phosphate-modified polyester resin precursor is mixed with a second polybasic acid and then acidified and capped to obtain the phosphate-modified polyester resin.

[0033] This invention involves mixing a polyol, a first polyacid, an esterification catalyst, and an antioxidant to carry out a first esterification reaction, thereby obtaining a polyester prepolymer.

[0034] In this invention, the molar ratio of the hydroxyl group to the carboxyl group of the first polyacid in the polyol is preferably 1.05 to 1.1:1, more preferably 1.06 to 1.08:1.

[0035] In this invention, the polyol preferably comprises 50-100% neopentyl glycol by mass fraction, more preferably 60-90%, and even more preferably 70-80%.

[0036] The polyol preferably comprises 0-25% 1,4-cyclohexanediethanol by mass fraction, more preferably 5-20%, and even more preferably 10-15%.

[0037] The polyol preferably comprises 0-25% 1,2-propanediol by mass fraction, more preferably 5-20%, and even more preferably 10-15%.

[0038] The polyol preferably comprises 0-20% 2-methyl-1,3-propanediol by mass fraction, more preferably 2-8%, and even more preferably 4-6%.

[0039] The polyol preferably comprises 0-10% 1,4-butanediol by mass fraction, more preferably 2-8%, and even more preferably 4-6%.

[0040] The polyol preferably comprises 0-40% hexanediol by mass fraction, more preferably 10-30%, and even more preferably 15-20%.

[0041] The polyol preferably comprises 0-20% 2-ethyl-2-n-butyl-1,3-propanediol by mass fraction, more preferably 5-15%, and even more preferably 8-12%.

[0042] The polyol preferably comprises 0-25% diethylene glycol by mass fraction, more preferably 5-15%, and even more preferably 8-12%.

[0043] The polyol preferably comprises 0-5% trimethylolethane by mass fraction, more preferably 1-4%, and even more preferably 2-3%.

[0044] The polyol preferably comprises 0-5% trimethylolpropane by mass fraction, more preferably 1-4%, and even more preferably 2-3%.

[0045] In this invention, the polyol is more preferably neopentyl glycol 78.2%, 1,4-cyclohexanediol 18.5% and trimethylolpropane 3.3% by mass fraction;

[0046] The polyol is preferably 65.4% by mass fraction, 20.2% by mass fraction, 12% by mass fraction, 2-methyl-1,3-propanediol, and 2.4% by mass fraction.

[0047] More preferably, by mass fraction, the polyol is 76.5% neopentyl glycol, 17.1% 2-methyl-1,3-propanediol, and 6.4% 1,4-butanediol.

[0048] By mass fraction, the polyol is more preferably neopentyl glycol 60.5%, 1,6-hexanediol 37.6%, and trimethylolpropane 1.9%.

[0049] By mass fraction, the polyol is more preferably neopentyl glycol 69.7%, diethylene glycol 21.4%, 2-ethyl-2-n-butyl-1,3-propanediol 6.4%, and trimethylolethane 2.5%.

[0050] The polyol, by mass fraction, is more preferably neopentyl glycol 93.8% and trimethylolpropane 6.2%.

[0051] In this invention, the first polybasic acid preferably comprises 40-100% terephthalic acid by mass fraction, more preferably 45-65%, and even more preferably 50-55%.

[0052] The first polybasic acid preferably comprises 0-30% isophthalic acid, more preferably 10-25%, and even more preferably 15-20% by mass fraction;

[0053] The first polyacid preferably comprises trimellitic anhydride at a mass fraction of 0-20%, more preferably 5-15%, and even more preferably 8-12%.

[0054] The first polyacid preferably comprises 0-20% pyromellitic anhydride by mass fraction, more preferably 5-15%, and even more preferably 8-12%.

[0055] The first polyacid preferably comprises 0-6% 1,6-adipic acid, more preferably 1-4%, and even more preferably 2-3% by mass fraction;

[0056] The first polybasic acid preferably comprises 0-5% hexahydrophthalic anhydride by mass fraction, more preferably 1-4%, and even more preferably 2-3%.

[0057] In this invention, the first polybasic acid is more preferably 82.7% terephthalic acid and 17.3% isophthalic acid by mass fraction;

[0058] The first polybasic acid is more preferably 93.7% terephthalic acid, 1.4% adipic acid, and 4.9% isophthalic acid by mass fraction.

[0059] The first polybasic acid is more preferably 94.3% terephthalic acid and 5.7% adipic acid, by mass fraction;

[0060] The first polybasic acid is more preferably 91.6% terephthalic acid and 8.4% isophthalic acid by mass fraction;

[0061] The first polybasic acid is more preferably 86.3% terephthalic acid and 13.7% isophthalic acid by mass fraction.

[0062] Terephthalic acid and isophthalic acid have suitable reaction rates. Adding terephthalic acid and isophthalic acid can ensure that they undergo a relatively gentle esterification reaction with polyols, reduce the occurrence of side reactions, and thus ensure that the molecular weight distribution of the modified polyester resin is narrow, giving it good physical and mechanical properties.

[0063] In this invention, the antioxidant is preferably 0.06-3% of the total mass of the first polyacid, polyol, and phosphate ester, more preferably 1-2%. In this invention, the antioxidant preferably includes one or more of the following: triphenyl phosphite, N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite, and calcium bis(3,5-di-tert-butyl-4-hydroxybenzylphosphonate). The antioxidant selected in this invention has good compatibility with polyester resin and is dispersed in phosphate-modified polyester resin. Adding the antioxidant protects the polyester resin from oxidation and yellowing.

[0064] In this invention, the mass of the esterification catalyst is preferably 0.07-0.23% of the total mass of the first polyacid, polyol, and phosphate ester, more preferably 0.08-0.1%. The esterification catalyst preferably includes an organotin catalyst; the tin catalyst preferably includes one or more of monobutyltin oxide, monobutyl dihydroxytin chloride, tri-(2-ethylhexanoic acid) monobutyltin, and stannous oxalate.

[0065] In this invention, the mixing preferably includes heating and melting the polyol, then introducing nitrogen gas and mixing it with the first polyacid, antioxidant, and esterification catalyst.

[0066] When the polyol includes a solid polyol, the present invention preferably involves adding water to the polyol for a first mixing, followed by heating and melting, and then introducing nitrogen gas for a second mixing with a first polyacid, an antioxidant, and an esterification catalyst. In this invention, the mass of the water is preferably 5% of the mass of the solid polyol. Water can accelerate the liquefaction rate of the solid polyol. The purpose of introducing nitrogen gas is to displace the air in the reaction vessel and prevent the polyester resin from being oxidized and turning yellow.

[0067] In this invention, the preferred temperature for heating and melting is 60–130°C.

[0068] In this invention, the temperature of the first esterification reaction is preferably 180–255°C. In this invention, the first esterification reaction is preferably a first ' esterification reaction and a second ' esterification reaction. In this invention, the temperature of the first ' esterification reaction is preferably 180–200°C, and the holding time is 0 min; the temperature of the second ' esterification reaction is preferably 245–255°C.

[0069] In this invention, it is preferable to raise the temperature to the second esterification reaction temperature at a distillation temperature not exceeding 101°C. Dividing the first esterification reaction into a first 'esterification reaction and a second 'esterification reaction' allows the esterification reaction to proceed gently, preventing the water generated during the esterification reaction from carrying away the raw materials during evaporation and causing waste.

[0070] In this invention, the acid value of the polyester prepolymer is preferably 15-25 mg KOH / g, more preferably 18-20 mg KOH / g; the viscosity is preferably 1.2-1.6 Pa·s / 175℃, more preferably 1.3-1.5 Pa·s / 175℃. This invention does not specifically limit the time of the second esterification reaction; the reaction can proceed until the polyester prepolymer is clear and reaches the target acid value.

[0071] After obtaining the polyester prepolymer, the present invention simultaneously carries out a second esterification reaction with the polyester prepolymer and phosphate ester to obtain phosphate ester modified polyester resin prepolymer.

[0072] In this invention, the molar ratio of the phosphate ester to the polyol is preferably 0.06 to 0.3:1, more preferably 0.1 to 0.2:1, and the acid value of the phosphate ester is preferably 75 to 90 mg KOH / g, more preferably 80 to 85 mg KOH / g.

[0073] In this invention, the phosphate ester comprises, by mass fraction, 0-100% dodecyl phosphate, preferably 50-80%, more preferably 60-70%;

[0074] The phosphate ester preferably comprises 0-80% isotretinoin phosphate, more preferably 20-60%, and even more preferably 30-40% by mass fraction;

[0075] The phosphate ester preferably comprises 0-100% 2-hydroxyethyl methacrylate phosphate, more preferably 20-80%, and even more preferably 40-60% by mass fraction;

[0076] The phosphate ester preferably comprises 0-100% ethylene glycol methacrylate phosphate, more preferably 50-80%, and even more preferably 60-70% by mass fraction.

[0077] The phosphate ester preferably comprises 0-30% bis[2-(methacryloyloxy)ethyl] phosphate by mass fraction, more preferably 5-25%, and even more preferably 10-20%.

[0078] In this invention, the phosphate ester is more preferably 85.4% dodecyl phosphate and 14.6% 2-hydroxyethyl methacrylate phosphate by mass fraction.

[0079] In this invention, the temperature of the second esterification reaction is preferably 250–260°C, more preferably 255–258°C. In this invention, the acid value of the phosphate-modified polyester resin prepolymer is 20–35 mg KOH / g; the viscosity is preferably 1.38–1.8 Pa·s / 175°C, more preferably 1.4–1.6 Pa·s / 175°C. The heating rate to the second esterification reaction temperature is preferably 4–10°C / min. This invention does not have a specific limitation on the time of the second esterification reaction; the reaction can proceed until the target acid value is reached. The phosphate ester contains both phosphate ester groups and phosphate groups, which can undergo esterification with the alcohol hydroxyl groups in the prepolymer, thereby introducing phosphate ester groups into the molecular chain of the polyester resin.

[0080] This invention prepares a phosphate-modified polyester resin with a glass transition temperature of 55°C by controlling the timing and amount of phosphate ester addition and the process.

[0081] After obtaining the phosphate-modified polyester resin prepolymer, the present invention subjects the phosphate-modified polyester resin prepolymer to a polycondensation reaction to obtain the phosphate-modified polyester resin phosphate. In this invention, the preferred temperature for the polycondensation reaction is 250–260°C; the preferred vacuum level is -0.09 MPa to -0.1 MPa; achieving the desired vacuum level preferably involves holding at a vacuum level of -0.02 MPa for 5 minutes, at -0.04 MPa for 5 minutes, at -0.06 MPa for 5 minutes, at -0.08 MPa for 5 minutes, and then evacuating to -0.09 MPa to -0.1 MPa. This stepped vacuum evacuation method allows for precise control of the molecular weight distribution of the modified polyester resin.

[0082] In this invention, the acid value of the phosphate-modified polyester resin is preferably 10–25 mg KOH / g, more preferably 15–20 mg KOH / g; the viscosity is preferably 4.9–6.5 Pa·s / 175°C, more preferably 5.5–6 Pa·s / 175°C. Unreacted carboxyl and hydroxyl groups in the polycondensation reaction further undergo esterification, and transesterification also occurs. This invention does not have specific requirements regarding the duration of the polycondensation reaction; the reaction can proceed to the acid value within the above-mentioned range. During the polycondensation reaction, the carboxyl and hydroxyl groups further undergo esterification reactions between hydroxyl and carboxyl groups and between phosphate and hydroxyl groups, and transesterification reactions also occur between ester bonds and hydroxyl groups.

[0083] After obtaining the phosphate-modified polyester resin precursor, the present invention mixes the phosphate-modified polyester resin precursor with a second polyacid for acidification and end-capping to obtain the phosphate-modified polyester resin.

[0084] In this invention, the molar ratio of the first polyacid to the second polyacid is preferably 4:1.

[0085] In this invention, the second polyacid preferably comprises, by mass fraction, 0-100% trimellitic anhydride, more preferably 20-90%, and even more preferably 40-60%.

[0086] The second polyacid preferably comprises 0-100% pyromellitic anhydride by mass fraction, more preferably 20-80%, and even more preferably 40-60%.

[0087] The second polyacid preferably comprises 0-10% 1,6-adipic acid, more preferably 2-8%, and even more preferably 4-6% by mass fraction;

[0088] The second polyacid preferably comprises 0-10% hexahydrophthalic anhydride by mass fraction, more preferably 2-8%, and even more preferably 4-6%.

[0089] In this invention, the second polybasic acid is more preferably trimellitic anhydride 74.1% and pyromellitic tetracarboxylic anhydride 25.9% by mass fraction;

[0090] The second polyacid is more preferably trimellitic anhydride 84.7% and adipic acid 15.3% by mass fraction;

[0091] The second polyacid is more preferably 90.2% pyromellitic anhydride and 9.8% hexahydrophthalic anhydride by mass fraction;

[0092] The second polyacid is more preferably trimellitic anhydride 94.9% and hexahydrophthalic anhydride 5.1% by mass fraction.

[0093] Trimeric trioxide, pyromellitic anhydride, 1,6-adipic acid, and hexahydrophthalic anhydride exhibit strong reactivity, particularly trimellitic anhydride and pyromellitic anhydride. These reactivity levels can acidify the ends of phosphate-modified polyester resin prepolymer chains, thereby attaching highly reactive carboxyl groups to the ends of the modified polyester resin chains. Simultaneously, they can increase the branching degree of the modified polyester resin chain ends by 2–3 times. This ensures complete curing of the coating film and a high crosslinking density during crosslinking and curing reactions with curing accelerators (e.g., one or more of hexadecylamine, octadecylamine, triphenylphosphine, ethyltriphenylphosphine bromide, tetraethylammonium bromide, tetrabutylammonium bromide, and benzyltriethylammonium chloride), guaranteeing good adhesion of the coating film.

[0094] In this invention, the acidification and sealing temperature is preferably 180-220°C, more preferably 200-210°C; the time is preferably 0.5-1h, more preferably 0.6-0.8h.

[0095] The present invention also provides the application of the phosphate-modified polyester resin described in the above-described scheme or the phosphate-modified polyester resin prepared by the preparation method described in the above-described scheme in coatings.

[0096] The present invention provides a coating comprising the following components: phosphate-modified polyester resin, epoxy resin, curing accelerator, leveling agent, gloss agent, benzoin, precipitated barium sulfate, and titanium dioxide.

[0097] In this invention, the curing accelerator is preferably 0-0.8% of the total mass of the first polyacid, polyol, and phosphate ester; the curing accelerator preferably includes one or more of a mixture of hexadecylamine and octadecylamine, triphenylphosphine, ethyltriphenylphosphine bromide, tetraethylammonium bromide, tetrabutylammonium bromide, and benzyltriethylammonium chloride. In this invention, the mass ratio of hexadecylamine to octadecylamine in the mixture of hexadecylamine and octadecylamine is preferably 1-1.5:1. The addition of the curing accelerator can reduce the activation energy of the chemical crosslinking reaction between the phosphate ester modified polyester resin and the epoxy resin, accelerate the curing reaction, and thus ensure complete curing of the coating film during the crosslinking and curing reaction between the phosphate ester modified polyester resin and the epoxy resin, resulting in a coating film with good adhesion.

[0098] The preferred mass ratio of the phosphate-modified polyester resin to the epoxy resin is 9:11; the epoxy resin preferably includes E12 epoxy resin.

[0099] The preferred mass ratio of the phosphate-modified polyester resin to the leveling agent is 27:10; the leveling agent preferably includes polybutyl acrylate.

[0100] The mass ratio of the leveling agent to the brightener is preferably 1:1; the brightener preferably includes polymethyl methacrylate-butyl acrylate copolymer.

[0101] The preferred mass ratio of the phosphate-modified polyester resin to benzoin is 27:4;

[0102] The preferred mass ratio of the phosphate-modified polyester resin to the precipitated barium sulfate is 27:17.

[0103] The preferred mass ratio of the phosphate-modified polyester resin to titanium dioxide is 27:20.

[0104] In this invention, the method for preparing the coating preferably includes the following steps:

[0105] The phosphate-modified polyester resin is first mixed with a curing accelerator, and then secondly mixed with epoxy resin, curing accelerator, leveling agent, gloss agent, benzoin, precipitated barium sulfate and titanium dioxide. The resulting mixture is then extruded, pressed into sheets, crushed and sieved in sequence to obtain the coating.

[0106] In this invention, the temperature of the first mixing is preferably 180–220°C, more preferably 200–210°C; the time is preferably 0.5–1.5 h, more preferably 0.8–1 h. In this invention, the first mixing is preferably carried out under stirring conditions. To save energy, the first mixing is preferably added after the polycondensation reaction is completed, utilizing the residual heat after the polycondensation reaction for the first mixing.

[0107] In this invention, the particle size of the coating is preferably 30-40 μm.

[0108] The coating is preferably applied by electrostatic spraying; the electrostatic spraying voltage is preferably 60-90KV, more preferably 70-80KV; the current is preferably 10-20uA, more preferably 15-18uA; the flow rate pressure is preferably 0.3-0.55MPa, more preferably 0.4-0.5MPa; and the atomization pressure is preferably 0.3-0.45MPa, more preferably 0.35-0.4MPa.

[0109] The substrate preferably includes one of iron, aluminum and magnesium, and the physical treatment preferably includes high-temperature heating and mechanical grinding to remove rust.

[0110] The powder coating is fully cured at 200°C, and the coating film has good adhesion and mechanical properties, with an adhesion level greater than 0.

[0111] The following detailed description, in conjunction with embodiments, illustrates the phosphate-modified polyester resin, its preparation method, applications, and coatings provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0112] Example 1

[0113] 605g of neopentyl glycol, 142.8g of 1,4-cyclohexanediol, and 25.6g of trimethylolpropane were added to a reaction vessel, along with 32g of water. The mixture was heated to 120°C. After the diols were completely melted, nitrogen gas was introduced, and stirring was started. 1099.5g of terephthalic acid, 1.8g of triphenyl phosphite, and 1.7g of monobutyltin oxide were then added. The mixture was heated to 190°C to begin generating esterified water. The distillation temperature was controlled at 100°C, and the temperature was gradually increased to 250°C. The mixture was kept at this temperature until the reaction solution became clear. A sample was taken and the acid value was measured to be 18.5mgKOH / g, and the viscosity was 1.2Pa·s / 175°C.

[0114] 111.5g of dodecyl phosphate was added, and the temperature was gradually increased to 255℃ at a rate of 4℃ / min for esterification reaction. The temperature was maintained for 2h until the reaction solution was clear. The acid value was measured to be 25.1mgKOH / g and the viscosity was 1.6Pa.s / 175℃.

[0115] The mixture was held under a vacuum of -0.02 MPa for 5 min, -0.04 MPa for 5 min, -0.06 MPa for 5 min, and -0.08 MPa for 5 min. Then, it was maintained at a vacuum of -0.095 MPa and 255 °C for 2.5 h. Samples were taken and the acid value was measured to be 13.5 mg KOH / g, and the viscosity was 5.5 Pa·s / 175 °C. The mixture was then cooled to 210 °C, and 255 g of trimellitic anhydride was added. The mixture was stirred for 1 h, and then 7.9 g of a mixture of hexadecylamine and octadecylamine (mass ratio of hexadecylamine to octadecylamine was 2:3) was added. The mixture was stirred for 1 h and then discharged.

[0116] Example 2

[0117] 520.5g neopentyl glycol, 160.8g 1,2-propanediol, 95.4g 2-methyl-1,3-propanediol, and 19.6g trimethylolethane were added to a reaction vessel along with 25g water. The mixture was heated to 80°C. After the polyols were completely melted, nitrogen gas was introduced, and stirring was started. Then, 1076.2g terephthalic acid, 225.8g isophthalic acid, 1.4g N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine, and 1.8g monobutyl dihydroxytin chloride were added. The mixture was heated to 200°C to begin generating esterified water. The distillation temperature was controlled at 100°C, and the temperature was gradually increased to 255°C. The mixture was kept at this temperature until the reaction solution was clear. A sample was taken and the acid value was measured to be 21.5mgKOH / g, and the viscosity was 1.4Pa·s / 175°C.

[0118] 112.1g of isotretinoin phosphate and 32.6g of bis[2-(methacryloyloxy)ethyl] phosphate were added, and the temperature was gradually increased to 260℃ at a rate of 10℃ / min for esterification reaction. The temperature was maintained for 3h until the reaction solution was clear. The acid value was measured to be 28.1mgKOH / g and the viscosity was 1.672Pa.s / 175℃.

[0119] The mixture was held under a vacuum of -0.02 MPa for 5 minutes, then at -0.04 MPa for 5 minutes, then at -0.06 MPa for 5 minutes, then at -0.08 MPa for 5 minutes, and finally at -0.09 MPa and 260°C for 4 hours. Samples were taken and the acid value was measured to be 17.5 mg KOH / g, and the viscosity was 6.2 Pa·s / 175°C. The mixture was then cooled to 215°C, and 195.6 g of trimellitic anhydride and 68.5 g of pyromellitic tetracarboxylic anhydride were added. The mixture was stirred for 1 hour, and then 4.5 g of triphenylphosphine was added and stirred for another hour before being discharged.

[0120] Example 3

[0121] 416.2g of neopentyl glycol, 92.8g of 2-methyl-1,3-propanediol, and 34.8g of 1,4-butanediol were added to a reaction vessel and heated to 105℃. After the alcohols were completely melted, nitrogen gas was introduced, and stirring was started. 785.9g of terephthalic acid, 11.8g of adipic acid, 40.7g of isophthalic acid, 1.3g of diethyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, and 1.5g of tris-(2-ethylhexanoic acid) monobutyltin were added. The temperature was raised to 200℃ to start the formation of esterified water. The distillation temperature was controlled at 100℃, and the temperature was gradually raised to 248℃. The temperature was maintained until the reaction solution was clear. The acid value was measured to be 19.5mgKOH / g, and the viscosity was 1.35Pa·s / 175℃.

[0122] 102.5g of dodecyl phosphate and 56.4g of ethylene glycol methacrylate phosphate were added, and the temperature was gradually increased to 258℃ at a rate of 5℃ / min for esterification reaction. The temperature was maintained for 2.5h until the reaction solution was clear. The acid value was measured to be 31.2mgKOH / g and the viscosity was 1.772Pa.s / 175℃.

[0123] The mixture was held under a vacuum of -0.02 MPa for 5 minutes, then at -0.04 MPa for 5 minutes, then at -0.06 MPa for 5 minutes, then at -0.08 MPa for 5 minutes, and finally at -0.097 MPa and 258°C for 3 hours. Samples were taken and the acid value was measured to be 16.5 mg KOH / g, and the viscosity was 6.5 Pa·s / 175°C. The mixture was then cooled to 220°C, and 168.5 g of trimellitic anhydride and 30.5 g of adipic acid were added. The mixture was stirred for 1 hour, and then 8.2 g of beryllium triethylammonium chloride was added and stirred for 1 hour before being discharged.

[0124] Example 4

[0125] 360.8g of neopentyl glycol, 224.5g of 1,6-hexanediol, and 11.5g of trimethylolpropane were added to a reaction vessel, along with 45g of water. The mixture was heated to 95°C. After the alcohols were completely melted, nitrogen gas was introduced, and stirring was started. Then, 797.2g of terephthalic acid, 48.5g of 1,6-adipic acid, 1.4g of tris(2,4-di-tert-butylphenyl) phosphite, and 1.6g of stannous oxalate were added. The mixture was heated to 192°C to begin generating esterified water. The distillation temperature was controlled at 100°C, and the temperature was gradually increased to 254°C. The mixture was kept at this temperature until the reaction solution was clear. A sample was taken and the acid value was measured to be 17.2mgKOH / g, and the viscosity was 1.55Pa·s / 175°C.

[0126] 114.5g of ethylene glycol methacrylate phosphate was added, and the temperature was gradually increased to 260℃ at a rate of 4℃ / min for esterification reaction. The temperature was maintained for 1.5h until the reaction solution was clear. The acid value was measured to be 24.1mgKOH / g and the viscosity was 1.782Pa.s / 175℃.

[0127] The mixture was kept under a vacuum of -0.02 MPa for 5 min, under a vacuum of -0.04 MPa for 5 min, under a vacuum of -0.06 MPa for 5 min, under a vacuum of -0.08 MPa for 5 min, and then kept under a vacuum of -0.1 MPa at (260) °C for 2 h. The acid value was measured to be 13.5 mg KOH / g and the viscosity was 5.87 Pa·s / 175 °C. The temperature was lowered to 180 °C, 148.5 g of pyromellitic anhydride was added, and the mixture was stirred for 1 h. Then 5.5 g of tetrabutylammonium bromide was added, and the mixture was stirred for 1 h before being discharged.

[0128] Example 5

[0129] 497.3g of neopentyl glycol, 152.8g of diethylene glycol, 45.8g of 2-ethyl-2-n-butyl-1,3-propanediol, and 17.5g of trimethylolethane were added to a reaction vessel and heated to 115°C. After the alcohols were completely melted, nitrogen gas was introduced, and stirring was started. 955.2g of terephthalic acid, 87.5g of isophthalic acid, 1.8g of bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, and 1.85g of monobutyltin oxide were added. The temperature was raised to 180°C to begin generating esterified water. The distillation temperature was controlled at 100°C, and the temperature was gradually raised to 245°C. The temperature was maintained until the reaction solution was clear. A sample was taken and the acid value was measured to be 23.6mgKOH / g, and the viscosity was 1.22Pa·s / 175°C.

[0130] 91g of 2-hydroxyethyl methacrylate phosphate was added, and the temperature was gradually increased to 256℃ at a rate of 5℃ / min for esterification reaction. The temperature was maintained for 1h until the reaction solution was clear. The acid value was measured to be 31.5mgKOH / g and the viscosity was 1.385Pa.s / 175℃.

[0131] The mixture was held under a vacuum of -0.02 MPa for 5 min, then at -0.04 MPa for 5 min, then at -0.06 MPa for 5 min, then at -0.08 MPa for 5 min, and finally at -0.1 MPa and 256 °C for 2.5 h. Samples were taken and the acid value was measured to be 19.5 mg KOH / g, and the viscosity was 4.95 Pa·s / 175 °C. The mixture was then cooled to 205 °C, and 172.5 g of pyromellitic anhydride and 18.8 g of hexahydrophthalic anhydride were added. The mixture was stirred for 1 h, and then 6.8 g of ethyltriphenylphosphine bromide was added and stirred for 1 h before being discharged.

[0132] Example 6

[0133] 598.4g of neopentyl glycol and 39.5g of trimethylolpropane were added to a reaction vessel, along with 38g of water. The mixture was heated to 125°C. After the alcohol was completely melted, nitrogen gas was introduced, and stirring was started. 828.2g of terephthalic acid, 131.8g of isophthalic acid, 1.5g of calcium bis(3,5-di-tert-butyl-4-hydroxybenzylphosphonate monoethyl ester) and 2.0g of stannous oxalate were added. The mixture was heated to 200°C to begin generating esterified water. The distillation temperature was controlled at 100°C, and the temperature was gradually increased to 250°C. The temperature was maintained until the reaction solution was clear. A sample was taken and the acid value was measured to be 20.2mgKOH / g, and the viscosity was 1.512Pa.s / 175°C.

[0134] 159.8g of dodecyl phosphate and 27.4g of 2-hydroxyethyl methacrylate phosphate were added, and the temperature was gradually increased to 258℃ at a rate of 10℃ / min for esterification reaction. The temperature was maintained for 2h until the reaction solution was clear. The acid value was measured to be 28.5mgKOH / g and the viscosity was 1.665Pa.s / 175℃.

[0135] The mixture was kept under a vacuum of -0.02 MPa for 5 min, under a vacuum of -0.04 MPa for 5 min, under a vacuum of -0.06 MPa for 5 min, under a vacuum of -0.08 MPa for 5 min, and then kept under a vacuum of -0.95 MPa at (258) °C for 2.5 h. The acid value was measured to be 16.8 mg KOH / g and the viscosity was 5.95 Pa·s / 175 °C. The temperature was lowered to 195 °C, and 198.8 g trimellitic anhydride and 10.7 g hexahydrophthalic anhydride were added. The mixture was stirred and reacted for 1 h. Then 9.25 g tetraethylammonium bromide was added and stirred for 1 h before discharging.

[0136] Application Examples 1-6

[0137] The mixtures obtained in Examples 1-6 were respectively mixed with epoxy resin E-12, barium sulfate, benzoin, pigment, polybutyl acrylate, and polymethyl methacrylate-butyl acrylate copolymer according to the proportions in Table 1. The mixtures were then melt-extruded, tableted, crushed, and sieved using a twin-screw extruder to obtain powder coatings with a particle size of 30-40 μm. These powder coatings were then electrostatically sprayed (voltage 80 KV, current 15 μA, flow rate pressure 0.4 MPa, atomization pressure 0.4 MPa) onto cold-rolled steel sheets that had undergone high-temperature degreasing and rust removal without chemical pretreatment. The sheets were cured at 200°C for 10 min. Various performance tests were then conducted on the prepared samples, and the test results are shown in Table 1.

[0138] Table 1 Composition and coating performance of powder coatings

[0139]

[0140]

[0141] As shown in Table 1, the powder coating made from the phosphate-modified polyester resin prepared by the method of the present invention has the characteristics of high gloss, good mechanical properties and excellent adhesion. It can be sprayed without chemical pretreatment of the surface of the object to be coated, and the coating film has very good adhesion, which can meet the coating and protection requirements of the surface of the object.

[0142] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A coating, characterized in that, The components include: phosphate-modified polyester resin, epoxy resin, leveling agent, brightener, benzoin, precipitated barium sulfate, and titanium dioxide; the epoxy resin is E-12; the main chain and side chains of the phosphate-modified polyester resin contain phosphate groups, and the preparation method includes the following steps: mixing a polyol, a primary polyacid, an antioxidant, and an esterification catalyst to carry out a first esterification reaction to obtain a polyester prepolymer; by mass fraction, the polyol is neopentyl glycol 78.2%, 1,4-cyclohexanediol 18.5%, and trimethylolpropane 3.3%, or the polyol is neopentyl glycol 65.4%. The polyol is composed of 1,2-propanediol 20.2%, 2-methyl-1,3-propanediol 12%, and trimethylolpropane 2.4%, or neopentyl glycol 93.8% and trimethylolpropane 6.2%; the primary polyacid is terephthalic acid 82.7% and isophthalic acid 17.3%, or the primary polyacid is terephthalic acid 93.7%, adipic acid 1.4%, and isophthalic acid 4.9%, or the primary polyacid is terephthalic acid 94.3% and adipic acid 5.7%; the secondary polyacid is pyromellitic anhydride 100%, or the secondary polyacid is trimellitic acid. The prepolymer is composed of 94.9% trimellitic anhydride and 5.1% hexahydrophthalic anhydride, or the second polyacid is composed of 94.9% trimellitic anhydride and 5.1% hexahydrophthalic anhydride; the polyester prepolymer is subjected to a second esterification reaction with a phosphate ester to obtain a phosphate ester modified polyester resin prepolymer; by mass fraction, the phosphate ester is 100% dodecyl phosphate, or the phosphate ester is 85.4% dodecyl phosphate and 14.6% 2-hydroxyethyl methacrylate phosphate; the phosphate ester modified polyester resin prepolymer is subjected to a polycondensation reaction to obtain a phosphate ester modified polyester resin precursor; the phosphate ester modified polyester resin precursor is subjected to a polycondensation reaction to obtain a phosphate ester modified polyester resin precursor. The body is mixed with a second polyacid and acidified to obtain a phosphate-modified polyester resin; the molar ratio of phosphate ester to polyol is 0.06~0.3:1; the molar ratio of hydroxyl groups in the polyol to carboxyl groups in the first polyacid is 1.05~1.1:1; the preparation method of the coating includes the following steps: the phosphate-modified polyester resin is first mixed with a curing accelerator, and then mixed with epoxy resin, curing accelerator, leveling agent, brightener, benzoin, precipitated barium sulfate and titanium dioxide in a second mixing process; the resulting mixture is then extruded, pressed into sheets, crushed and sieved in sequence to obtain the coating.

2. The coating according to claim 1, characterized in that, The glass transition temperature of the phosphate-modified polyester resin is 55°C.

3. The coating according to claim 1, characterized in that, The temperature of the first esterification reaction is 180~250℃; the acid value of the polyester prepolymer is 15~25mgKOH / g, and the viscosity is 1.2~1.6Pa.s / 175℃.

4. The coating according to claim 1, characterized in that, The temperature of the second esterification reaction is 250℃~260℃, the acid value of the phosphate ester modified polyester resin prepolymer is 20~35mgKOH / g, and the viscosity is 1.38~1.8Pa.s / 175℃.

5. The coating according to claim 1, characterized in that, The polycondensation reaction is carried out at a temperature of 250℃~260℃ and a vacuum degree of -0.09MPa~-0.1MPa; the phosphate ester modified polyester resin precursor has an acid value of 10~25mgKOH / g and a viscosity of 4.9~6.5Pa.s / 175℃.

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