阅读说明：本技术 高光泽自身固化型粉末涂料用环氧树脂及双釜制备方法 (Epoxy resin for high-gloss self-curing powder coating and double-kettle preparation method ) 是由 王永垒 李海云 江蓉 魏文静 孙继影 孙巧巧 王景 于 2019-11-18 设计创作，主要内容包括：本发明属于涂料原料技术领域,具体涉及一种高光泽自身固化型粉末涂料用环氧树脂及其双釜联用方法。本发明所提供的高光泽自身固化型粉末涂料用环氧树脂,主要原料是双酚A、1,10-癸二酸、环氧氯丙烷、氢氧化钠、偏苯三甲酸、正丁醇、己二酸、对苯二甲酸、二甘醇、一异硬脂酸甘油酯、异氰尿酸三缩水甘油酯；该环氧树脂是由以上主要原料通过聚合反应制得的。本发明借助双釜联用工艺制备出同时具有羧基封端及环氧基封端的环氧树脂,在熔融状态下进行充分混合可以保证最终参与固化的环氧树脂产品处于均匀分散状态,实现了同一批次粉末涂料有较好的稳定性,克服了由于活性不同导致的固化不均一的问题,涂膜性能完全达到粉末涂料的常规要求。(The invention belongs to the technical field of coating raw materials, and particularly relates to an epoxy resin for a high-gloss self-curing powder coating and a double-kettle combined method thereof. The high-gloss self-curing epoxy resin for the powder coating provided by the invention mainly comprises bisphenol A, 1, 10-sebacic acid, epichlorohydrin, sodium hydroxide, trimellitic acid, n-butyl alcohol, adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and triglycidyl isocyanurate; the epoxy resin is prepared by the polymerization reaction of the main raw materials. According to the invention, the epoxy resin with both carboxyl end capping and epoxy end capping is prepared by means of a double-kettle coupling process, and the epoxy resin product finally participating in curing can be ensured to be in a uniform dispersion state by fully mixing in a molten state, so that the same batch of powder coating has better stability, the problem of nonuniform curing caused by different activities is solved, and the performance of the coating film completely meets the conventional requirements of the powder coating.)

1. The epoxy resin for the high-gloss self-curing powder coating is characterized in that the main raw materials of the epoxy resin are bisphenol A, 1, 10-sebacic acid, epichlorohydrin, sodium hydroxide, trimellitic acid, n-butyl alcohol, adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and triglycidyl isocyanurate; the epoxy resin is prepared by polymerization reaction of the main raw materials.

2. The epoxy resin for high gloss self-curable powder coating according to claim 1, wherein a first catalyst and a second catalyst are further used in the preparation of the epoxy resin;

the first catalyst is triphenyl phosphine ethyl bromide; the second catalyst is tetrabutyl titanate.

3. The epoxy resin for high gloss self-curable powder coating according to claim 2, wherein the amount of the first catalyst is 0.05 to 0.1% of the total molar amount of the main raw materials;

the dosage of the second catalyst is 0.05-0.1% of the total molar amount of the main raw materials.

4. The epoxy resin for high gloss self-curable powder coating according to claim 1, wherein the molar parts ratio of the raw materials is:

3-8 parts of bisphenol A, 4-10 parts of 1, 10-sebacic acid, 8-18 parts of epoxy chloropropane, 10-20 parts of sodium hydroxide, 4-12 parts of monobutyl trimellitate, 5-15 parts of adipic acid, 6-18 parts of terephthalic acid, 8-17 parts of diethylene glycol, 4-11 parts of glyceryl monoisostearate and 4-9 parts of triglycidyl isocyanurate.

5. The epoxy resin for high gloss self-curable powder coating according to claim 1, wherein the molar parts ratio of the raw materials is:

the preparation method of the monobutyl trimellitate comprises the following steps:

taking trimellitic acid and n-butyl alcohol, adding p-toluenesulfonic acid as a catalyst in a toluene solvent, taking toluene as a water-carrying agent to carry out water-carrying esterification reaction, stopping the reaction when no obvious free n-butyl alcohol is detected, and removing the toluene solvent and part of unreacted raw materials under reduced pressure to obtain a trimellitic acid monobutyl ester product;

preferably, the preparation method of the monobutyl trimellitate comprises the following steps:

taking a mixture with a molar ratio of 0.8-1.2: adding trimellitic acid and n-butyl alcohol of 1 into a toluene solvent, adding p-toluenesulfonic acid as a catalyst, carrying out esterification reaction with water at 105-110 ℃ for 3-6 h, stopping the reaction when no obvious free n-butyl alcohol is detected, and removing the toluene solvent and part of unreacted raw materials under reduced pressure to obtain a trimellitic acid monobutyl ester product;

wherein the molar ratio of the toluene solvent to the trimellitic acid is 2-4: 1; the molar ratio of the dosage of the catalyst to the trimellitic acid is 0.02-0.08: 1.

6. the epoxy resin for high-gloss self-curable powder coating according to claim 1, wherein the monobutyl trimellitate has an acid value of 415 to 430 mgKOH/g.

7. The two-pot process for preparing an epoxy resin for a high gloss self-curable powder coating according to claim 1, comprising the steps of:

(1) preparing a sodium hydroxide solution, adding the sodium hydroxide solution into a first reaction kettle, heating, adding bisphenol A, 1, 10-sebacic acid and a first catalyst, heating, carrying out heat preservation reaction, adding epoxy chloropropane, reacting, stopping the reaction, carrying out heat preservation and static layering, separating out a water phase, and washing with boiling water to obtain epoxy group-terminated epoxy resin;

(2) adding monobutyl trimellitate into the epoxy-terminated epoxy resin obtained in the step (1), reacting to obtain a first carboxyl-terminated epoxy resin, and preserving heat for later use;

(3) adding adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and a second catalyst into a second reaction kettle, heating for esterification reaction, carrying out vacuum reaction, cooling, adding triglycidyl isocyanurate, and carrying out heat preservation reaction to obtain second epoxy resin for later use;

(4) and adding the first epoxy resin in the first reaction kettle into the second reaction kettle to be mixed and reacted with the second epoxy resin, discharging at high temperature when the reaction is stopped, cooling, crushing and granulating to obtain the high-gloss self-curing epoxy resin for the powder coating.

8. The two-pot process for preparing an epoxy resin for a high gloss self-curable powder coating according to claim 4, comprising the steps of:

(1) dissolving sodium hydroxide in water to prepare a sodium hydroxide solution with the mass concentration of 38-42%, adding the sodium hydroxide solution into a first reaction kettle, heating to 45-55 ℃, adding bisphenol A, 1, 10-sebacic acid and a first catalyst, heating to 55-65 ℃, carrying out heat preservation reaction for 1-3 h, starting to dropwise add epoxy chloropropane when the pH reaches 9-10, keeping the reaction at 90-100 ℃ for 3-6 h after dropwise addition is completed within 1-3 h, stopping the reaction when the epoxy equivalent of a test system is 1000-1200 g/mol, carrying out heat preservation at 95-105 ℃, carrying out static layering for 0.3-0.8 h, separating out a water phase, and washing for 2-4 times by using boiling water to obtain epoxy group-terminated epoxy resin;

(2) adding monobutyl trimellitate into the epoxy-terminated epoxy resin obtained in the step (1), reacting for 0.5-2 h at 105-115 ℃, stopping the reaction when the epoxy equivalent of the resin is more than 2500g/mol and the acid value is 60-90 mgKOH/g to obtain a carboxyl-terminated first epoxy resin, and preserving heat at 105-115 ℃ for later use;

(3) adding adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and a second catalyst into a second reaction kettle, heating to 200-220 ℃, carrying out esterification reaction for 8-12 h, starting a vacuum system when the acid value of the system reaches 20-35 mgKOH/g, keeping the vacuum below-0.092 Mpa, carrying out vacuum reaction for 1-3 h, cooling to 105-115 ℃ when the acid value of a reactant reaches 10-18 mgKOH/g, slowly adding triglycidyl isocyanurate, carrying out heat preservation reaction for 0.5-2 h at 105-115 ℃, stopping the reaction when the acid value is less than 3mgKOH/g and the epoxy equivalent reaches 500-600 g/mol, and obtaining a second epoxy resin for later use;

(4) adding the first epoxy resin in the first reaction kettle into the second reaction kettle, mixing and reacting with the second epoxy resin at 105-115 ℃ for 0.5-1 h, stopping reaction when the acid value of the mixture is 25-45 mgKOH/g and the epoxy equivalent is 1200-1400 g/mol, discharging at high temperature while the mixture is hot, cooling the epoxy resin by using a steel belt with condensed water, and then crushing and granulating to obtain the high-gloss self-curing epoxy resin for the powder coating.

9. The two-pot process for preparing an epoxy resin for a high gloss self-curable powder coating according to claim 4, comprising the steps of:

(1) dissolving sodium hydroxide in water to prepare a sodium hydroxide solution with the mass concentration of 40%, adding the sodium hydroxide solution into a first reaction kettle, heating to 50 ℃, adding bisphenol A, 1, 10-sebacic acid and a first catalyst, heating to 60 ℃, preserving heat and reacting for 2 hours, starting to dropwise add epoxy chloropropane when the pH reaches 9-10, keeping at 95 ℃ for reacting for 4 hours after dropwise adding is completed within 2 hours, stopping reaction when the epoxy equivalent of a test system is 1100g/mol, preserving heat at 100 ℃, standing and layering for 0.5 hour, separating out a water phase, and washing for 3 times by using boiling water to obtain epoxy group-terminated epoxy resin;

(2) adding monobutyl trimellitate into the epoxy-terminated epoxy resin obtained in the step (1), reacting for 1h at 110 ℃, stopping the reaction when the epoxy equivalent of the resin is more than 2500g/mol and the acid value is 60-90 mgKOH/g to obtain a carboxyl-terminated first epoxy resin, and preserving heat at 110 ℃ for later use;

(3) adding adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and a second catalyst into a second reaction kettle, heating to 210 ℃, carrying out esterification reaction for 10 hours, starting a vacuum system when the acid value of the system reaches 30mgKOH/g, keeping the vacuum below-0.092 Mpa, carrying out vacuum reaction for 2 hours, cooling to 110 ℃ when the acid value of a reactant reaches 15mgKOH/g, slowly adding triglycidyl isocyanurate, carrying out heat preservation reaction for 1 hour at 110 ℃, stopping the reaction when the acid value is less than 3mgKOH/g and the epoxy equivalent reaches 550g/mol, and obtaining a second epoxy resin for later use;

(4) adding the first epoxy resin in the first reaction kettle into the second reaction kettle, mixing and reacting with the second epoxy resin at 110 ℃ for 0.8h, stopping the reaction when the acid value of the mixture is 35mgKOH/g and the epoxy equivalent is 1300g/mol, discharging at high temperature while the mixture is hot, cooling the epoxy resin by using a steel belt with condensed water, and then crushing and granulating to obtain the high-gloss self-curing epoxy resin for the powder coating.

10. The epoxy resin for high-gloss self-curable powder coating prepared by the method according to any one of claims 7 to 9, wherein the epoxy resin has an acid value of 25 to 45mgKOH/g and a softening point of 80 to 90 ℃ when the epoxy equivalent is 1200 to 1400 g/mol.

Technical Field

The invention belongs to the technical field of coating raw materials, and particularly relates to an epoxy resin for a high-gloss self-curing powder coating; also relates to a double-kettle combination method of the epoxy resin.

Background

At present, if the epoxy resin type powder coating is to realize film formation, the curing is generally carried out by polyester resin or curing agent such as 2-phenylimidazole, dicyandiamide and the like, and the following defects still exist:

(1) the polyester resin or the curing agent and the granular epoxy resin are difficult to be fully and uniformly mixed in a physical mixing way, and the subsequent extrusion and mixing by a double-screw extruder are easy to cause uneven dispersion, so that the epoxy resin and the curing agent or the polyester resin in the final powder coating are unevenly distributed, and the problem of larger curing effect difference of the powder coating in the same batch is often caused;

(2) because the curing agents such as 2-phenylimidazole, dicyandiamide, etc. have high activity, and the compatibility of epoxy resin and polyester resin is poor, the curing speed is not uniform at high temperature, so that the requirement of high gloss is difficult to realize by the conventional powder coating formula.

Regarding the epoxy resin for high gloss powder coating, the following patent documents are disclosed:

CN110028880A discloses a TGIC cured polyester resin for high gloss powder coatings and a method for preparing the same, in which a TGIC cured polyester resin for high gloss powder coatings is characterized in that the formulation comprises, in mass percent: 25-33% of neopentyl glycol, 0.5-1.5% of hydroxypivalic acid hydroxypivalyl hydroxypivalate, 3-7% of ethylene glycol, 1-3% of 2-butyl-2-ethyl-1, 3-propanediol, 48-61% of terephthalic acid and 4.1-11.4% of a blocking agent.

CN109207030A discloses polyester resin for high-gloss powder coating and a preparation method and application thereof, which comprises the following steps:

(1) mixing selected amounts of the neopentyl glycol, the glyceryl isostearate, the 2-hydroxy-5-methyl m-xylene glycol and the 1, 6-hexanediol dimethacrylate, and heating and melting at a temperature of below 125 ℃;

(2) adding a selected amount of octadecanedioic acid, isophthalic acid and 4-trifluoromethyl salicylic acid into the mixed material, adding a selected amount of catalyst, gradually heating under the protection of nitrogen to react until no obvious distillate is evaporated, controlling the acid value of reactants to be less than 30mgKOH/g, and controlling the reaction temperature to be not more than 245 ℃;

(3) adding a selected amount of the antioxidant, maintaining the vacuum degree of 40-60mmHg for 2-7h, promoting the formation of polyester resin, and stopping vacuum pulling when the acid value is reduced to below 14 mgKOH/g;

(4) cooling the materials to 210-220 ℃, adding a selected amount of 2, 3-quinolinedicarboxylic acid, slowly heating to 240 ℃ to react for 2-8h, stopping the reaction when the acid value of the reactant is 68-74mgKOH/g, discharging at high temperature when the reactant is hot, cooling, crushing and granulating to obtain the polyester resin.

CN109180925A provides a polyester resin for high-gloss powder coating, which is characterized by comprising the following raw material components in percentage by mole based on the total amount of raw materials for preparing the polyester resin:

8-25 mol% of terephthalic acid; 5-15 mol% of 6-aminocaproic acid; 5-12 mol% of domoic acid; 8-20 mol% of 3, 6-dithia-1, 8-octanediol; 6-12 mol% of 2, 18-dihydroxy-4, 7,10,13, 16-pentaoxanonadecane-1, 19-diyl 2-acrylate; 7-15 mol% of neopentyl glycol; 3-8 mol% of 3- (2, 3-epoxypropoxy) propyl trimethoxy silane; 5-15 mol% of 3, 5-di-tert-butyl-4-hydroxybenzyl alcohol.

The polyester resins provided in the above patent documents require the addition of a curing agent or epoxy resin particles in the preparation of a powder coating. The method has the following obvious characteristics: firstly, the premixing time is long, the physical mixing needs to be fully and uniformly ensured, and the physical mixing needs to be carried out for more than 30min at high speed in a high-speed mixer generally; in addition, in the melt extrusion link, twin-screw extrusion is required to be used, the extrusion time is long (the screw length is long) so as to ensure good miscibility, the general twin-screw extrusion link needs more than 30min, batch curing difference is easy to occur in production due to the miscibility problem, powder coating with poor curability can be obtained only by extruding again through twin-screw extrusion, the production efficiency is low, the requirements of the products on extrusion equipment are high, and the qualified products are difficult to prepare by single-screw extruders of some customers.

Therefore, there is a need to improve the disadvantages of the above patents by inventing an epoxy resin which has good self-compatibility, self-curing at high temperature and uniform curing speed after being applied to a coating, and can be easily and rapidly extruded to obtain a uniformly dispersed powder coating by only a single screw extruder.

Disclosure of Invention

In order to solve the technical problems, the invention provides a high-gloss self-curing epoxy resin for a powder coating, which has good self-compatibility, can be cured at high temperature and has uniform curing speed after being applied to the coating, and can be extruded easily and rapidly by only a single-screw extruder to obtain a uniformly dispersed powder coating.

The main raw materials of the epoxy resin are bisphenol A, 1, 10-sebacic acid, epichlorohydrin, sodium hydroxide, trimellitic acid, n-butyl alcohol, adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and triglycidyl isocyanurate; the epoxy resin is prepared by polymerization reaction of the main raw materials.

The preparation process of the epoxy resin also adopts a first catalyst and a second catalyst;

the first catalyst is triphenyl phosphine ethyl bromide; the second catalyst is tetrabutyl titanate.

The dosage of the first catalyst is 0.05-0.1% of the total molar amount of the main raw materials;

the dosage of the second catalyst is 0.05-0.1% of the total molar amount of the main raw materials.

The molar ratio of each raw material is as follows:

the molar ratio of each raw material is as follows:

3-8 parts of bisphenol A, 4-10 parts of 1, 10-sebacic acid, 8-18 parts of epoxy chloropropane, 10-20 parts of sodium hydroxide, 4-12 parts of monobutyl trimellitate, 5-15 parts of adipic acid, 6-18 parts of terephthalic acid, 8-17 parts of diethylene glycol, 4-11 parts of glyceryl monoisostearate and 4-9 parts of triglycidyl isocyanurate.

The molar ratio of each raw material is as follows:

the preparation method of the monobutyl trimellitate comprises the following steps:

taking trimellitic acid and n-butyl alcohol, adding p-toluenesulfonic acid as a catalyst in a toluene solvent, taking toluene as a water-carrying agent to carry out water-carrying esterification reaction, stopping the reaction when no obvious free n-butyl alcohol is detected, and removing the toluene solvent and a small amount of unreacted raw materials under reduced pressure to obtain a trimellitic acid monobutyl ester product;

preferably, the preparation method of the monobutyl trimellitate comprises the following steps:

taking a mixture with a molar ratio of 0.8-1.2: adding trimellitic acid and n-butyl alcohol of 1 into a toluene solvent, adding p-toluenesulfonic acid as a catalyst, carrying out esterification reaction with water at 105-110 ℃ for 3-6 h, stopping the reaction when no obvious free n-butyl alcohol is detected, and removing the toluene solvent and a small amount of unreacted raw materials under reduced pressure to obtain a trimellitic acid monobutyl ester product; wherein the molar ratio of the toluene solvent to the trimellitic acid is 2-4: 1; the molar ratio of the dosage of the catalyst to the trimellitic acid is 0.02-0.08: 1; .

The acid value of the monobutyl trimellitate is 415-430 mgKOH/g.

The double-kettle preparation method of the epoxy resin for the high-gloss self-curing powder coating comprises the following steps:

(1) preparing a sodium hydroxide solution, adding the sodium hydroxide solution into a first reaction kettle, heating, adding bisphenol A, 1, 10-sebacic acid and a first catalyst, heating, carrying out heat preservation reaction, adding epoxy chloropropane, reacting, stopping the reaction, carrying out heat preservation and standing for layering, separating out a water phase, and washing with boiling water to obtain epoxy group-terminated epoxy resin;

(2) adding monobutyl trimellitate into the epoxy-terminated epoxy resin obtained in the step (1), reacting to obtain a first carboxyl-terminated epoxy resin, and preserving heat for later use;

(3) adding adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and a second catalyst into a second reaction kettle, heating for esterification reaction, carrying out vacuum reaction, cooling, adding triglycidyl isocyanurate, and carrying out heat preservation reaction to obtain second epoxy resin for later use;

(4) and adding the first epoxy resin in the first reaction kettle into the second reaction kettle to be mixed and reacted with the second epoxy resin, discharging at high temperature when the reaction is stopped, cooling, crushing and granulating to obtain the high-gloss self-curing epoxy resin for the powder coating.

The double-kettle preparation method of the epoxy resin for the high-gloss self-curing powder coating comprises the following steps:

(1) dissolving sodium hydroxide in water to prepare a sodium hydroxide solution with the mass concentration of 38-42%, adding the sodium hydroxide solution into a first reaction kettle, heating to 45-55 ℃, adding bisphenol A, 1, 10-sebacic acid and a first catalyst, heating to 55-65 ℃, carrying out heat preservation reaction for 1-3 h, starting to dropwise add epoxy chloropropane when the pH reaches 9-10, keeping the reaction at 90-100 ℃ for 3-6 h after dropwise addition is completed within 1-3 h, stopping the reaction when the epoxy equivalent of a test system is 1000-1200 g/mol, carrying out heat preservation at 95-105 ℃, carrying out static layering for 0.3-0.8 h, separating out a water phase, and washing for 2-4 times by using boiling water to obtain epoxy group-terminated epoxy resin;

(2) adding monobutyl trimellitate into the epoxy-terminated epoxy resin obtained in the step (1), reacting for 0.5-2 h at 105-115 ℃, stopping the reaction when the epoxy equivalent of the resin is more than 2500g/mol and the acid value is 60-90 mgKOH/g to obtain a carboxyl-terminated first epoxy resin, and preserving heat at 105-115 ℃ for later use;

(3) adding adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and a second catalyst into a second reaction kettle, heating to 200-220 ℃, carrying out esterification reaction for 8-12 h, starting a vacuum system when the acid value of the system reaches 20-35 mgKOH/g, keeping the vacuum below-0.092 Mpa, carrying out vacuum reaction for 1-3 h, cooling to 105-115 ℃ when the acid value of a reactant reaches 10-18 mgKOH/g, slowly adding triglycidyl isocyanurate, carrying out heat preservation reaction for 0.5-2 h at 105-115 ℃, stopping the reaction when the acid value is less than 3mgKOH/g and the epoxy equivalent reaches 500-600 g/mol, and obtaining a second epoxy resin for later use;

(4) adding the first epoxy resin in the first reaction kettle into the second reaction kettle, mixing and reacting with the second epoxy resin at 105-115 ℃ for 0.5-1 h, stopping reaction when the acid value of the mixture is 25-45 mgKOH/g and the epoxy equivalent is 1200-1400 g/mol, discharging at high temperature while the mixture is hot, cooling the epoxy resin by using a steel belt with condensed water, and then crushing and granulating to obtain the high-gloss self-curing epoxy resin for the powder coating.

Preferably, the above two-pot preparation method of the epoxy resin for the high-gloss self-curing powder coating comprises the following steps:

(1) dissolving sodium hydroxide in water to prepare a sodium hydroxide solution with the mass concentration of 40%, adding the sodium hydroxide solution into a first reaction kettle, heating to 50 ℃, adding bisphenol A, 1, 10-sebacic acid and a first catalyst, heating to 60 ℃, preserving heat and reacting for 2 hours, starting to dropwise add epoxy chloropropane when the pH reaches 9-10, keeping at 95 ℃ for reacting for 4 hours after dropwise adding is completed within 2 hours, stopping reaction when the epoxy equivalent of a test system is 1100g/mol, preserving heat at 100 ℃, standing and layering for 0.5 hour, separating out a water phase, and washing for 3 times by using boiling water to obtain epoxy group-terminated epoxy resin;

(2) adding monobutyl trimellitate into the epoxy-terminated epoxy resin obtained in the step (1), reacting for 1h at 110 ℃, stopping the reaction when the epoxy equivalent of the resin is more than 2500g/mol and the acid value is 60-90 mgKOH/g to obtain a carboxyl-terminated first epoxy resin, and preserving heat at 110 ℃ for later use;

(3) adding adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate and a second catalyst into a second reaction kettle, heating to 210 ℃, carrying out esterification reaction for 10 hours, starting a vacuum system when the acid value of the system reaches 30mgKOH/g, keeping the vacuum below-0.092 Mpa, carrying out vacuum reaction for 2 hours, cooling to 110 ℃ when the acid value of a reactant reaches 15mgKOH/g, slowly adding triglycidyl isocyanurate, carrying out heat preservation reaction for 1 hour at 110 ℃, stopping the reaction when the acid value is less than 3mgKOH/g and the epoxy equivalent reaches 550g/mol, and obtaining a second epoxy resin for later use;

(4) adding the first epoxy resin in the first reaction kettle into the second reaction kettle, mixing and reacting with the second epoxy resin at 110 ℃ for 0.8h, stopping the reaction when the acid value of the mixture is 35mgKOH/g and the epoxy equivalent is 1300g/mol, discharging at high temperature while the mixture is hot, cooling the epoxy resin by using a steel belt with condensed water, and then crushing and granulating to obtain the high-gloss self-curing epoxy resin for the powder coating.

The epoxy resin prepared by the method is colorless and transparent granular in appearance, and has a softening point of 80-90 ℃ when the acid value is 25-45 mgKOH/g and the epoxy equivalent is 1200-1400 g/mol.

In order to meet the requirement of high gloss, the flexible dibasic acid 1, 10-sebacic acid is specially used in the first epoxy resin to adjust the flexibility and the flowability of molecules, and the monobutyl trimellitate contains a butyl ester group which is helpful for brightening, so that the compatibility and the lubricity can be promoted, the high-temperature leveling and brightening capability can be improved, and meanwhile, the monobutyl trimellitate is used as a carboxyl end-capping agent with large steric hindrance, so that the curing reaction speed with an epoxy group in the second epoxy resin can be reduced due to the steric hindrance, and the leveling time can be prolonged; besides introducing flexible dibasic acid adipic acid to adjust molecular flexibility and reduce softening point, the second epoxy resin also introduces a reaction type monomer glyceryl monoisostearate with lubricating and light-enhancing functions to participate in reaction, so that the melt viscosity is reduced, the compatibility and the high-temperature fluidity are increased, and the functions of high gloss and self-curing are finally realized.

The epoxy resin provided by the invention has self-curing performance, can realize high-temperature curing without additionally adding a curing agent or a mixed polyester resin, and has moderate activity, so that the epoxy resin contains groups for increasing compatibility and lubricity, and the final coating film has high glossiness and good leveling property; bisphenol A, 1, 10-sebacic acid, epichlorohydrin, sodium hydroxide, trimellitic acid, n-butyl alcohol, triglycidyl isocyanurate, adipic acid, terephthalic acid, diethylene glycol, glyceryl monoisostearate, triphenyl ethyl phosphine bromide and the like are mainly used as raw materials for polymerization, the obtained epoxy resin product contains active carboxyl and epoxy groups at the same time, after the epoxy resin product is prepared into a powder coating, the carboxyl in a first epoxy resin material and the epoxy group in a second epoxy resin material are subjected to crosslinking curing at a high temperature (180 ℃/15min), no additional curing agent or polyester resin is needed, a self-cured coating film can be obtained, and the performance of the coating film can completely meet the application requirements of the conventional powder coating. And because the molecule contains a side chain ester group for smoothing and brightening, the coating film with the gloss of more than 95 percent is favorably obtained.

The epoxy resin with both carboxyl-terminated end and epoxy-terminated end is prepared by means of a double-kettle combined process, the epoxy resin is fully mixed in a molten state, so that the epoxy resin product finally participating in curing is in a uniformly dispersed state, the powder coating of the same batch has better stability, the powder coating is a uniformly mixed epoxy resin product after being molten and mixed in a kettle, the compatibility requirement is lower when the powder coating is prepared, and the powder coating can be quickly extruded by adopting a single-screw extruder. The problem of nonuniform curing of the traditional powder coating resin caused by the difference of miscibility is solved, and the performance of the coating film completely meets the conventional requirements of the powder coating.

Detailed Description

In order that those skilled in the art will better understand the present invention, the inventors will further describe the present invention by the following examples and comparative examples.