CN113501934B - Epoxy resin for self-leveling low-temperature curing powder coating and preparation method thereof - Google Patents

Abstract

A self-leveling epoxy resin for low-temperature curing powder coatings and a preparation method thereof, mainly using tartaric acid, methacrylic acid, oleic acid, bisphenol A, E-51 liquid epoxy resin, hydrogen peroxide, xylene, etc. as raw materials To carry out the reaction to obtain an epoxy resin with an epoxy equivalent of 660-710g/mol. The chain segment of the epoxy resin has a special esterification group, which has the function of quickly promoting the leveling of the coating film, and the esterification group is It still has an epoxy group and has high curing activity. It can cure the powder coating containing 50:50 polyester resin at low temperature without adding additional leveling agent, and the surface leveling level and gloss of the cured coating film are high. .

Description

Epoxy resin for self-leveling low-temperature curing powder coating and preparation method thereof

technical field

The invention belongs to the field of powder coatings, in particular to an epoxy resin for self-leveling low-temperature curing powder coatings and a preparation method thereof.

Background technique

Powder coating is a solid powder synthetic resin coating composed of solid resin and pigments, fillers and additives. Unlike ordinary solvent-based paints and water-based paints, its dispersion medium is not solvent and water, but air. It has the characteristics of no solvent pollution, 100% film formation and low energy consumption.

Ordinary E-12 epoxy resin matched with 50:50 polyester resin is obtained by direct reaction of bisphenol A and epichlorohydrin under the action of a strong base. The product has a low degree of molecular branching and a high epoxy equivalent , generally at 800-900g/mol, the curing activity is low, it is difficult to cure at low temperature, generally it needs to be cured at a temperature above 180°C, and the energy consumption is high.

In addition, it is necessary to add a leveling agent in the powder coating formula. Because the leveling agent is used in a small amount, generally about 1% in the powder coating formula, it is difficult to fully mix it in the powder coating, resulting in poor leveling, especially In the low-temperature curing system, the lack of leveling is more obvious, and it is difficult to prepare a high-level coating film.

In industry, in order to fully mix the 1% leveling agent with the resin material, it needs to stay in the mixer and mill for a long time, which brings high energy consumption.

Therefore, need badly a kind of epoxy resin for new self-leveling type low-temperature curing powder coating and preparation method thereof to solve the above-mentioned technical problems.

Contents of the invention

The invention provides a self-leveling epoxy resin for low-temperature curing powder coating, which comprises the following raw materials in molar fractions:

Wherein, the first catalyst is phosphotungstic acid or phosphomolybdic acid, and the second catalyst is triphenylphosphine.

The first catalyst acts as a catalyst for esterification and epoxidation at the same time.

Wherein, the hydrogen peroxide is added in the form of a 30 wt % aqueous hydrogen peroxide solution, that is, a total of 7-12 mole parts of hydrogen peroxide is added in the form of an aqueous hydrogen peroxide solution.

Wherein, the appearance of the epoxy resin is colorless transparent particles, its epoxy equivalent is 660-710g/mol, its softening point is 78-84°C, and its iodine value is less than 1g/100g.

The present invention also provides a preparation method of the epoxy resin for the self-leveling low-temperature curing type powder coating, comprising:

(1) Add tartaric acid, methacrylic acid, oleic acid, and xylene in the recipe amount into the reaction kettle, start stirring, and after mixing evenly, add the first catalyst in the recipe amount, then heat up to the boiling point of xylene, and carry out the esterification with water Chemical reaction;

(2) Take a sample to detect the hydroxyl value of the reactant in the system. When the hydroxyl value is less than 5mgKOH/g, cool down to 100-105°C, and then add bisphenol A, E-51 liquid epoxy resin, and the second catalyst in the formulated amount. Insulation for chain extension reaction;

(3) Sampling and detecting the epoxy equivalent of the polymer in the system, when the epoxy equivalent reaches 500-550g/mol, heat up to 125-130°C, and continue to keep warm for polymerization chain extension reaction;

(4) Take a sample to detect the epoxy equivalent of the polymer in the system. When the epoxy equivalent reaches 700-750g/mol, stop the reaction, lower the temperature to 50-55°C, add the formula amount of aqueous hydrogen peroxide solution, and heat it at 50-55°C Carry out the epoxidation reaction under insulation at a certain temperature;

(5) Sampling detection system polymer iodine value, when iodine value＜1 and epoxy equivalent when 660-710g/mol, stop reaction, stand layering, after removing the aqueous phase of hydrogen peroxide, wash again, then Stand still, remove water layer, thereby remove catalyst and impurity (as residual hydrogen peroxide etc.), obtain organic phase solution;

(6) Start the vacuum system and heat up to 115-120°C under reduced pressure to remove xylene and water from the organic phase solution under reduced pressure;

(7) After no obvious distillate is distilled out (i.e. when the mass fraction of volatile matter in the sampling test is less than 1%), the vacuum is released, and then the material is discharged, cooled, crushed and granulated to obtain the epoxy resin.

Wherein, in the steps (2), (3), (4), and (5), the sampling detection is carried out after removing the xylene solvent in a vacuum oven.

Wherein, in the step (5), the washing is 1-2 times of washing with tap water whose mass is 1-1.5 times the mass of xylene.

Wherein, in the step (6), the degree of vacuum is controlled at -0.097 to -0.099Mpa.

Wherein, in the step (7), the discharging is discharging at a high temperature while it is hot, and the cooling is cooling with a steel belt with condensed water.

The present invention also provides a self-leveling low-temperature curing powder coating, which contains the above-mentioned epoxy resin.

Wherein, the powder coating is a 50:50 mixed powder coating

The present invention has the following beneficial technical effects:

The present invention mainly uses tartaric acid, methacrylic acid, oleic acid, bisphenol A, E-51, hydrogen peroxide, xylene, phosphotungstic acid, etc. <1g/100g of epoxy resin.

The chain segment of the epoxy resin has a special esterification group, which has the function of quickly promoting the leveling of the coating film, and the esterification group still has an epoxy group, which has high curing activity and can finally make a 50:50 mixture Type powder coating can be fully cured at low temperature (140°C/20min) without additional leveling agent, and the surface leveling level and gloss of the cured coating film are very high, and the leveling level can reach above 7. The gloss is more than 94.3%, and there is no need for long-time grinding, which saves energy and has very important application value.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

If no specific experimental steps or conditions are indicated in the examples, it can be carried out according to the operation or conditions of the conventional experimental steps described in the literature in this field. The reagents or instruments used, whose manufacturers are not indicated, are all commercially available conventional reagent products.

Example 1

This embodiment provides a method for preparing an epoxy resin for self-leveling low-temperature curing powder coatings, including:

(1) Add 4.3 molar parts of tartaric acid, 8 molar parts of methacrylic acid, 2.5 molar parts of oleic acid, and 26 molar parts of xylene into the reactor, start stirring, and after mixing evenly, add 0.035 molar parts of phosphotungsten acid, then warming up to the boiling point of xylene to carry out esterification with water;

(2) Sampling, after removing the xylene solvent in a vacuum oven, detect the hydroxyl value of the system reactant, and when the hydroxyl value is less than 5mgKOH/g, cool down to 101°C, then add 12 molar parts of bisphenol A, 19 Mole parts of E-51 liquid epoxy resin, 0.0025 mole parts of triphenylphosphine, heat preservation for chain extension reaction;

(3) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the polymer in the system, and when the epoxy equivalent reaches 520g/mol, heat up to 129°C, and continue to keep warm for polymerization chain extension reaction;

(4) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the polymer in the system, and when the epoxy equivalent reaches 745g/mol, stop the reaction, cool to 50°C, and use 30% hydrogen peroxide 8 molar parts of hydrogen peroxide are added in the form of an aqueous solution, and the epoxidation reaction is carried out at a temperature of 50° C.;

(5) Sampling, after removing the xylene solvent in a vacuum oven, detect the iodine value of the polymer in the system, when the iodine value<1 and the epoxy equivalent is at 690g/mol, stop the reaction, leave the layer to stand, and remove the peroxide After the aqueous phase of hydrogen, add the tap water that quality is 1.4 times of xylene quality again and wash 2 times, then leave standstill, remove water layer, thereby remove impurity such as catalyst and residual hydrogen peroxide, obtain organic phase solution;

(6) Start the vacuum system and heat up to 119°C under reduced pressure to remove xylene and water from the organic phase solution under reduced pressure, wherein the vacuum degree is controlled at -0.099Mpa;

(7) After no obvious distillate is distilled out (that is, when the mass fraction of volatile matter in the sampling test is less than 1%), the vacuum is released, and then the material is discharged at a high temperature while it is hot, cooled with a steel belt with condensed water, crushed and granulated , to obtain the epoxy resin.

The appearance of the epoxy resin is colorless transparent particles, the epoxy equivalent is 690g/mol, the softening point is 79°C, and the iodine value is 0.8g/100g.

Example 2

This embodiment provides a method for preparing an epoxy resin for self-leveling low-temperature curing powder coatings, including:

(1) Add 5.5 molar parts of tartaric acid, 7 molar parts of methacrylic acid, 4 molar parts of oleic acid, and 21 molar parts of xylene into the reactor, start stirring, and after mixing evenly, add 0.05 molar parts of molybdenum phosphorus acid, then warming up to the boiling point of xylene to carry out esterification with water;

(2) Sampling, after removing the xylene solvent in a vacuum oven, detect the hydroxyl value of the system reactant, and when the hydroxyl value is less than 5mgKOH/g, cool down to 102°C, then add 11 molar parts of bisphenol A, 19 Mole parts of E-51 liquid epoxy resin, 0.003 mole parts of triphenylphosphine, heat preservation for chain extension reaction;

(3) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the polymer in the system, and when the epoxy equivalent reaches 537g/mol, heat up to 125°C, and continue to keep warm for polymerization chain extension reaction;

(4) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the system polymer, and when the epoxy equivalent reaches 721g/mol, stop the reaction, cool down to 53°C, and use 30% hydrogen peroxide 12 molar parts of hydrogen peroxide are added in the form of an aqueous solution, and the epoxidation reaction is carried out at a temperature of 53° C.;

(5) Sampling, after removing the xylene solvent in a vacuum oven, detect the iodine value of the polymer in the system, when the iodine value<1 and the epoxy equivalent is 665g/mol, stop the reaction, leave the layer to stand, and remove the peroxide After the aqueous phase of hydrogen, add tap water whose mass is 1 times of the mass of xylene to wash once, then let it stand and remove the water layer, thereby removing impurities such as catalyst and residual hydrogen peroxide to obtain an organic phase solution;

(6) Start the vacuum system and heat up to 117°C under reduced pressure to remove solvents such as xylene and water from the organic phase solution under reduced pressure, wherein the vacuum degree is controlled at -0.098Mpa;

(7) After no obvious distillate is distilled out (that is, when the mass fraction of volatile matter in the sampling test is less than 1%), the vacuum is released, and then the material is discharged at a high temperature while it is hot, cooled with a steel belt with condensed water, crushed and granulated , to obtain the epoxy resin.

The appearance of the epoxy resin is colorless transparent particles, the epoxy equivalent is 665g/mol, the softening point is 83°C, and the iodine value is 0.9g/100g.

Example 3

This embodiment provides a method for preparing an epoxy resin for self-leveling low-temperature curing powder coatings, including:

(1) Add 6 molar parts of tartaric acid, 8.5 molar parts of methacrylic acid, 3.8 molar parts of oleic acid, and 24 molar parts of xylene into the reaction kettle, start stirring, and after mixing evenly, add 0.04 molar parts of phosphotungsten acid, then warming up to the boiling point of xylene to carry out esterification with water;

(2) Sampling, after removing the xylene solvent in a vacuum oven, detect the hydroxyl value of the system reactant, when the hydroxyl value is less than 5mgKOH/g, cool down to 102°C, then add 14 molar parts of bisphenol A, 21 Mole parts of E-51 liquid epoxy resin, 0.0035 mole parts of triphenylphosphine, heat preservation for chain extension reaction;

(3) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the polymer in the system, and when the epoxy equivalent reaches 518g/mol, heat up to 127°C, and continue to keep warm to carry out the polymerization chain extension reaction;

(4) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the polymer in the system, and when the epoxy equivalent reaches 732g/mol, stop the reaction, cool to 55°C, and use 30% hydrogen peroxide 11 molar parts of hydrogen peroxide were added in the form of an aqueous solution, and the epoxidation reaction was carried out at a temperature of 55° C.;

(5) Sampling, after removing the xylene solvent in a vacuum oven, detect the iodine value of the polymer in the system, when the iodine value<1 and the epoxy equivalent is at 700g/mol, stop the reaction, leave to stand for stratification, and remove the peroxide After the aqueous phase of hydrogen, add the tap water that quality is 1.5 times of xylene quality again and wash 2 times, then leave standstill, remove water layer, thereby remove impurity such as catalyst and residual hydrogen peroxide, obtain organic phase solution;

(6) Start the vacuum system and heat up to 116°C under reduced pressure to remove solvents such as xylene and water from the organic phase solution under reduced pressure, wherein the vacuum degree is controlled at -0.098Mpa;

(7) After no obvious distillate is distilled out (that is, when the mass fraction of volatile matter in the sampling test is less than 1%), the vacuum is released, and then the material is discharged at a high temperature while it is hot, cooled with a steel belt with condensed water, crushed and granulated , to obtain the epoxy resin.

The appearance of the epoxy resin is colorless transparent particles, the epoxy equivalent is 700g/mol, the softening point is 83°C, and the iodine value is 0.8g/100g.

Example 4

This embodiment provides a method for preparing an epoxy resin for self-leveling low-temperature curing powder coatings, including:

(1) Add 5.5 molar parts of tartaric acid, 7 molar parts of methacrylic acid, 4 molar parts of oleic acid, and 29 molar parts of xylene into the reactor, start stirring, and after mixing evenly, add 0.055 molar parts of molybdenum phosphorus acid, then warming up to the boiling point of xylene to carry out esterification with water;

(2) Sampling, after removing the xylene solvent in a vacuum oven, detect the hydroxyl value of the system reactant, and when the hydroxyl value is less than 5mgKOH/g, cool down to 102°C, then add 13 molar parts of bisphenol A, 21 Mole parts of E-51 liquid epoxy resin, 0.002 mole parts of triphenylphosphine, heat preservation for chain extension reaction;

(3) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the polymer in the system, and when the epoxy equivalent reaches 525g/mol, heat up to 130°C, and continue to keep warm for polymerization chain extension reaction;

(4) Sampling, after removing the xylene solvent in a vacuum oven, detect the epoxy equivalent of the polymer in the system, and when the epoxy equivalent reaches 745g/mol, stop the reaction, cool to 52°C, and use 30% hydrogen peroxide 10 molar parts of hydrogen peroxide are added in the form of an aqueous solution, and the epoxidation reaction is carried out at a temperature of 52° C.;

(5) Sampling, after removing the xylene solvent in a vacuum oven, detect the iodine value of the polymer in the system, when the iodine value<1 and the epoxy equivalent is at 708g/mol, stop the reaction, leave it to stand for layering, and remove the peroxide After the aqueous phase of hydrogen, add the tap water whose mass is 1 times of the xylene mass to wash twice, then let stand, remove the water layer, thereby remove impurities such as catalyst and residual hydrogen peroxide, and obtain the organic phase solution;

(6) Start the vacuum system and heat up to 120°C under reduced pressure to remove solvents such as xylene and water from the organic phase solution under reduced pressure, wherein the vacuum degree is controlled at -0.099Mpa;

(7) After no obvious distillate is distilled out (that is, when the mass fraction of volatile matter in the sampling test is less than 1%), the vacuum is released, and then the material is discharged at a high temperature while it is hot, cooled with a steel belt with condensed water, crushed and granulated , to obtain the epoxy resin.

The appearance of the epoxy resin is colorless transparent particles, the epoxy equivalent is 660-708g/mol, the softening point is 81°C, and the iodine value is 0.7g/100g.

Comparative example 1

A commercially available common E-12 epoxy resin was used instead of the epoxy resin of the present invention as Comparative Example 1, with an epoxy equivalent of 798g/mol and a softening point of 92°C, purchased from Huangshan Jinfeng Industrial Co., Ltd.

The epoxy resins of Examples 1-4 and Comparative Example 1 were used to prepare powder coatings and coatings respectively, and performance tests were performed.

Preparation of powder coating: Mix the materials according to the powder coating formula shown in Table 1 below, extrude with a twin-screw extruder at low temperature (screw temperature is controlled at 95-100 ° C), and then go through tableting, crushing, and then The flakes were pulverized and sieved to make a powder coating (160-180 mesh), which was used to prepare the coatings of Examples A1-A4 and Comparative Examples B1-B3.

Wherein, when preparing the powder coating used in the coating of Comparative Example B3, the mixing time and milling time of each material were increased by 30 minutes compared with each of Examples 1-4.

Among them, the model of 50:50 polyester resin is SJ3702, which was purchased from Anhui Shenjian New Material Co., Ltd.; the model of brightening agent GLP588 was purchased from Ningbo Nanhai Chemical Co., Ltd.

Coating preparation: Spray the powder coating on the surface-treated tinplate substrate with an electrostatic spray gun. The film thickness is 80-90 μm. Coatings of ratios B1-B3.

The preparation parameter of the coating of table 1 embodiment A1-A4 and comparative example B1-B3

*: When preparing the powder coating used in the coating of Comparative Example B3, the mixing time and milling time of each material were increased by 30 minutes compared with each embodiment 1-4

Performance Testing:

Coating index testing: according to GB/T 21776-2008 "Guidelines for Testing Standards of Powder Coatings and Coatings";

Leveling grade: according to JB-T 3998-1999 "Measurement method of paint leveling and scratching", the higher the leveling grade, the better the leveling of the coating surface;

Adhesion test: According to GB/T9286-1998 "Cross-cut test of paint and varnish film", the smaller the number, the better the adhesion.

Table 2 shows the performance test results of the coatings of the above-mentioned Examples A1-A4 and Comparative Examples B1-B3.

The performance test result of the coating of table 2 embodiment A1-A4 and comparative example B1-B4

As can be seen from the comparison of Examples 1-4 and Comparative Examples 1-3 in Table 1, the present invention cooperates and synergizes between each component, and the epoxy resin obtained and the 50:50 polyester resin form a powder coating system, without additional mixing and milling time, the prepared powder coatings after 140℃/20min low-temperature curing have high gloss, high self-leveling grade, excellent impact resistance, excellent adhesion and boiling performance.

In Comparative Example 1, ordinary E-12 epoxy resin was used instead of the epoxy resin of the present invention, and no additional leveling agent was added. Due to the low epoxy activity at the end of E-12 epoxy resin, it could not be used at 140°C/20min. The curing and leveling process is successfully completed, resulting in rough coating film and poor mechanical properties.

In Comparative Example 2, the curing conditions in Comparative Example 1 were adjusted from 140°C/20min for low-temperature curing to 180°C/20min for high-temperature curing, so that the coating film could be fully cured, but since no additional leveling agent was added, the final coating The level of film leveling is poor, the surface gloss is low, and the adhesion and boiling resistance are also relatively poor.

In Comparative Example 3, an additional leveling agent was used on the basis of Comparative Example 2, and the material mixing time and milling time were increased by 30 minutes compared with Examples 1-4, which can achieve full curing of the coating film, and the final coating film leveling is relatively Better (but still weaker than Examples 1-4), the surface gloss is moderate, and the adhesion and boiling resistance also basically meet the requirements, but the energy consumption for preparing the powder coating and the energy consumption for coating film curing are obviously higher than those of the product of the present invention .

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (9)

1. The preparation method of the epoxy resin for the self-leveling low-temperature cured powder coating comprises the following steps of:

wherein the first catalyst is phosphotungstic acid or phosphomolybdic acid, and the second catalyst is triphenylphosphine;

the preparation method of the epoxy resin for the powder coating comprises the following steps:

(1) Adding the tartaric acid, the methacrylic acid, the oleic acid and the dimethylbenzene in the formula amount into a reaction kettle, starting stirring, adding the first catalyst in the formula amount after uniformly mixing, and heating to the boiling point of the dimethylbenzene to carry out esterification reaction with water;

(2) Sampling and detecting the hydroxyl value of a system reactant, cooling to 100-105 ℃ when the hydroxyl value is less than 5mgKOH/g, adding a formula amount of bisphenol A, E-51 liquid epoxy resin and a second catalyst, and carrying out chain extension reaction by heat preservation;

(3) Sampling and detecting the epoxy equivalent of the system polymer, and heating to 125-130 ℃ when the epoxy equivalent reaches 500-550g/mol, and continuing to perform polymerization chain extension reaction by heat preservation;

(4) Sampling and detecting the epoxy equivalent of the system polymer, stopping the reaction when the epoxy equivalent reaches 700-750g/mol, cooling to 50-55 ℃, adding the formula amount of hydrogen peroxide aqueous solution, and carrying out epoxidation reaction at the temperature of 50-55 ℃ by heat preservation;

(5) Sampling and detecting the iodine value of the system polymer, stopping the reaction when the iodine value is less than 1 and the epoxy equivalent is 660-710g/mol, standing and layering, removing the aqueous phase of hydrogen peroxide, washing, and then standing and removing the aqueous layer to remove the catalyst and residual impurities, thereby obtaining an organic phase solution;

(6) Starting a vacuum system, heating to 115-120 ℃ under the condition of reduced pressure, and decompressing and removing dimethylbenzene and water from the organic phase solution;

(7) And after no obvious distillate is distilled out, releasing vacuum, discharging, cooling, crushing and granulating to obtain the epoxy resin.

2. The method for producing an epoxy resin for powder coating according to claim 1, wherein the hydrogen peroxide is added in the form of a 30wt% aqueous hydrogen peroxide solution.

3. The process for producing an epoxy resin for powder coating according to claim 1 or 2, wherein the epoxy equivalent of the resulting epoxy resin for powder coating is 660-710g/mol, the softening point is 78-84 ℃ and the iodine value is < 1g/100g.

4. The method for producing an epoxy resin for powder coating according to claim 1 or 2, wherein in the steps (2), (3), (4) and (5), the sampling test is performed after removing the xylene solvent in a vacuum oven.

5. The method for producing an epoxy resin for powder coating according to claim 1 or 2, wherein in the step (5), the washing is performed 1 to 2 times by adding tap water having a mass 1 to 1.5 times the mass of xylene.

6. The method for producing an epoxy resin for powder coating according to claim 1 or 2, wherein in the step (6), the vacuum degree is controlled to-0.097 to-0.099 Mpa.

7. An epoxy resin for self-leveling low-temperature cured powder coating, which is prepared by the preparation method of the epoxy resin for self-leveling low-temperature cured powder coating according to any one of claims 1 to 6.

8. A self-leveling low-temperature-curable powder coating material comprising the epoxy resin according to claim 7.

9. The powder coating of claim 8, wherein the powder coating is a 50:50 hybrid powder coating.