Matting curing agent for powder coating and preparation method thereof

Abstract

The present application relates to a kind of powder coating hydroxyalkylamide matting curing agent and its preparation method, the matting curing agent using including citric acid, 2-methyl-1,3-propanediol, dimethylbenzene, anhydrous methanol, N-methyl monoethanolamine, catalyst, nanometer titanium dioxide is reacted to obtain raw materials.In first, citric acid and 2-methyl-1,3-propanediol are grafted to carry out reaction, then the remaining four carboxyl groups of grafting are methyl esterification reaction, obtain methyl esterification product, then with N-methyl monoethanolamine acylation reaction obtains hydroxyalkylamide curing agent;Add nanometer titanium dioxide, fully mix and process to obtain the matting curing agent.The curing agent product functionality is higher, the hardness of coating film after curing is higher, and the boiling water resistance is excellent;And the coating film after curing has obvious matting effect, coating film gloss is basically reached 50-70%, and the decorative property is excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of powder coating, in particular to a matt curing agent for powder coating, a preparation method thereof and application in polyester resin. BACKGROUND

[0002] Powder coating has the characteristics of no solvent pollution, 100% film forming and low energy consumption, and has been widely used in various metal coating fields in recent years. Among them, the thermosetting powder coating is a solid powder synthetic resin coating composed of solid resin and pigment, filler, curing agent and additive. At present, the curing agent for outdoor powder coating mainly includes two systems, epoxy-based curing agent and hydroxyalkyl amide-based curing agent. The epoxy-based curing agent is represented by TGIC, which uses epoxy group to participate in the curing reaction of polyester resin. The hydroxyalkyl amide-based curing agent is mainly composed of amide polyhydroxy products, and the typical product is represented by N,N,N',N'-tetra(2-hydroxyethyl)adipamide (HAA for short). Compared with the epoxy-based curing agent, the HAA curing agent has the advantages of no irritation, environmental protection, non-toxicity and high cost performance, and is widely used at home and abroad. With the expansion of the application range of hydroxyalkyl amide curing agent, some fields with high decorative requirements require the cured product to achieve certain matt effect to realize decoration, and it is also expected to obtain a curing agent product with higher functionality to achieve impact resistance and improve the hardness of the coating film. SUMMARY

[0003] In view of the above problems, the present application develops a hydroxyalkyl amide matt curing agent for powder coating. The matt curing agent is prepared by using raw materials including citric acid, 2-methyl-1,3-propanediol, dimethylbenzene, anhydrous methanol, N-methyl monoethanolamine, a catalyst and nano titanium dioxide. First, the grafting reaction of citric acid and 2-methyl-1,3-propanediol is carried out, then the remaining four carboxyl groups of the grafting product are subjected to methyl esterification reaction to obtain a methyl esterification product, and then the amide reaction of the methyl esterification product and N-methyl monoethanolamine is carried out to obtain a hydroxyalkyl amide curing agent. The nano titanium dioxide is added, mixed and treated to obtain the matt curing agent. The curing agent product has six active hydroxyl groups, high functionality, high hardness of the coating film after curing and excellent water boiling resistance. Moreover, due to the different active hydroxyl groups, the curing agent has obvious activity difference when it is cured with carboxyl polyester resin, and the coating film after curing has obvious matt effect, the gloss of the coating film is basically 50-70%, and the decoration is excellent.

[0004] A matt curing agent for powder coating, the matt curing agent is a hydroxyalkyl amide matt curing agent, which comprises the following raw materials in mole parts:

[0005]

[0006] The raw materials also include an appropriate amount of nano-titanium dioxide, catalyst 1, and catalyst 2.

[0007] The matt curing agent for powder coating is as described above, preferably, the catalyst 1 is tetrabutyl titanate, and the amount is 0.4-0.6% of the mass of the citric acid; the catalyst 2 is sodium hydroxide, and the amount is 1-1.5% of the mass of the N-methyl monoethanolamine; the molar ratio of 2-methyl-1,3-propanediol to citric acid is controlled to be between 1:2-2.1.

[0008] The nano-titanium dioxide is used as a forming and anti-caking aid, and has a significant difference from the filler particle size of the powder formula, has a certain matt effect, the particle size is 40-50 nm, and the amount is 5-20% of the total mass of the raw materials (more preferably 10 wt%), which can be purchased from Shanghai Liangjiang Titanium Dioxide Chemical Products Co., Ltd.

[0009] The matt curing agent for powder coating has the following molecular structure:

[0010]

[0011] The preparation method of the matt curing agent for powder coating comprises the following steps:

[0012] The preparation method of the matt curing agent for powder coating comprises the following steps:

[0013] A. The formula amount of xylene, citric acid, 2-methyl-1,3-propanediol, and catalyst 1 are added to a reaction kettle, stirring is started, and the temperature is raised to the boiling point of xylene for water-carrying esterification reaction;

[0014] B. The content of 2-methyl-1,3-propanediol in the system is detected by gas chromatography, and when the conversion rate of 2-methyl-1,3-propanediol reaches more than 98%, the reaction is stopped, and a vacuum system is started to remove xylene solvent in the system under reduced pressure;

[0015] C. When the content of xylene is less than 1%, the vacuum is released, the temperature is lowered to 55-60°C, and anhydrous methanol is added to the reaction product for methyl esterification reaction of the remaining carboxyl groups;

[0016] D. The acid value of the reaction product is detected, and when the acid value of the reaction product is less than 3 mgKOH / g, the temperature is gradually raised to 105-110°C, and the methanol and water in the system are removed during the temperature rising process;

[0017] E, sample detection, when the methanol content in the reactant is less than 2%, add the formula amount of catalyst 2, stir uniformly, then add the formula amount of N-methyl monoethanolamine dropwise for amidation reaction; after dropping, continue to heat at 105-110℃ for amidation reaction;

[0018] F, sample detection, when the conversion rate of N-methyl monoethanolamine reaches more than 95%, at this time, start the vacuum system, remove the excess unreacted N-methyl monoethanolamine and a small amount of by-product methanol in the system under reduced pressure;

[0019] G, when the volatile content is less than 1%, remove the vacuum, add nano titanium dioxide and mix thoroughly, then discharge at high temperature, and then obtain the matt curing agent through rapid cooling molding and crushing.

[0020] The preparation method of the matt curing agent for powder coating as described above, preferably, in step B, the vacuum degree is controlled at-0.095Mpa to-0.097Mpa, and the distillation temperature is 130-135℃; in step F, the vacuum degree is controlled at-0.098Mpa to-0.099Mpa; in step E, the dropwise adding time is controlled at 1-1.5h; in step G, the steel belt rapid cooling molding is used.

[0021] For example, the preparation method of the matt curing agent for powder coating comprises the following steps:

[0022] A, add the formula amount of xylene, citric acid, 2-methyl-1,3-propanediol and catalyst 1 into the reaction kettle, start stirring, and heat to the boiling point of xylene for water-carrying esterification reaction;

[0023] B, sample the content of 2-methyl-1,3-propanediol in the system by gas chromatography, when the conversion rate of 2-methyl-1,3-propanediol reaches more than 98%, stop the reaction, start the vacuum system to remove the xylene solvent in the system under reduced pressure, and the vacuum degree is controlled at-0.095Mpa to-0.097Mpa, and the distillation temperature is 130-135℃;

[0024] C, when the content of xylene is less than 1%, remove the vacuum, and cool to 55-60℃, then add anhydrous methanol to perform methyl esterification reaction on the residual carboxyl group of the reactant;

[0025] D, sample the acid value of the reactant, when the acid value of the reactant is less than 3mgKOH / g, it indicates that the methyl esterification reaction is basically completed, at this time, gradually heat to 105-110℃, and remove the methanol and water in the system during the heating process;

[0026] E, sample detection, when the methanol content in the reactant is less than 2%, add the amount of catalyst 2, stir evenly, then add the amount of N-methyl monoethanolamine for amidation reaction, control the drop time for 1-1.5h; after the drop is completed, continue to heat at 105-110℃ for amidation reaction;

[0027] F, sample detection, when the conversion rate of N-methyl monoethanolamine reaches more than 95%, it means that the amidation reaction is basically completed, at this time, start the vacuum system, remove the excess unreacted N-methyl monoethanolamine and a small amount of by-product methanol in the system under reduced pressure, the vacuum degree is controlled at-0.098Mpa to-0.099Mpa;

[0028] G, when the volatile matter is less than 1%, release the vacuum, add 10% of the reactor reactant mass of nano titanium dioxide for sufficient stirring and mixing as a molding and anti-caking aid, after mixing evenly, high temperature discharge, then speed cooling molding through steel belt, and crushing to obtain the matting curing agent.

[0029] The appearance of the obtained product is white powder, and the hydroxyl equivalent weight is 97-106g / mol.

[0030] The application of the matting curing agent for powder coating or the matting curing agent prepared by the preparation method in a polyester resin powder coating system.

[0031] The hydroxyalkylamide curing type powder coating formula can include polyester resin, the above prepared matting curing agent, titanium dioxide, barium sulfate, leveling agent, benzoin, etc.; the preparation method is: mix the materials according to the above powder coating formula, extrude, press, and crush with a double screw extruder, then crush the sheet material to make a powder coating; the powder coating is sprayed on the surface treated tinplate substrate by electrostatic spray gun, and after curing, the powder coating layer is obtained.

[0032] Beneficial effects:

[0033] The present application relates to a kind of powder coating hydroxyalkylamide matting curing agent and its preparation method, which is prepared using raw materials including citric acid, 2-methyl-1,3-propanediol, dimethylbenzene, anhydrous methanol, N-methyl monoethanolamine, catalyst, nano titanium dioxide.The grafting reaction of citric acid and 2-methyl-1,3-propanediol is first carried out, then the remaining four carboxyl groups of the grafting product are subjected to methyl esterification reaction to obtain the methyl esterification product, and then subjected to amidation reaction with N-methyl monoethanolamine to obtain the hydroxyalkylamide curing agent;Nano titanium dioxide is added, fully mixed and treated to obtain the matting curing agent.The curing agent product has 6 active hydroxyl groups, higher functionality, higher hardness of the coating film after curing, and excellent water boiling resistance.Furthermore, due to the different active hydroxyl groups, the curing activity difference is obvious when it is cured with carboxyl polyester resin, and the coating film after curing has obvious matting effect, and the coating film gloss basically reaches 50-70%, with excellent decoration. DETAILED DESCRIPTION

[0034] The present application will be further described below in conjunction with examples.It should be noted that the examples and technical features in the examples in the present application can be combined with each other without conflict.The present application uses all technical and scientific terms with the same meaning as generally understood by ordinary skilled in the art to which the present application belongs unless otherwise specified.The present application discloses that "including" or "containing" and similar words mean that the elements or objects before the words cover the elements or objects listed after the words and their equivalents, without excluding other elements or objects.

[0035] The raw materials described in the present application are commercially available.

[0036] Preparation Example 1

[0037] A powder coating matting curing agent, the matting curing agent is a hydroxyalkylamide matting curing agent, which comprises the following raw materials in mole parts:

[0038]

[0039] Catalyst 1 is tetrabutyl titanate, and the amount is 0.6% of the mass of citric acid;Catalyst 2 is sodium hydroxide, and the amount is 1.5% of the mass of N-methyl monoethanolamine;The particle size of nano titanium dioxide is 40-50 nm, and the amount is 10 wt% of the total mass of raw materials, which is purchased from Shanghai Liangjiang Titanium Dioxide Chemical Products Co., Ltd.

[0040] The preparation method of the powder coating matting curing agent comprises the following steps:

[0041] A, add the formula amount of xylene, citric acid, 2-methyl-1, 3-propanediol and catalyst 1 into the reaction kettle, start stirring, and heat to the boiling point of xylene to carry out water-removing esterification;

[0042] B, sample and detect the content of 2-methyl-1, 3-propanediol in the system by gas chromatography, when the conversion rate of 2-methyl-1, 3-propanediol reaches more than 98%, stop the reaction, start the vacuum system to remove xylene solvent in the system under reduced pressure, and the vacuum degree is controlled at-0.097 Mpa and the distillation temperature is 130℃;

[0043] C, when the content of xylene is less than 1%, release the vacuum, and heat to 55℃, and add anhydrous methanol to carry out methyl esterification reaction on the residual carboxyl group of the reactant;

[0044] D, sample and detect the acid value of the reactant, when the acid value of the reactant is less than 3 mgKOH / g, it indicates that the methyl esterification reaction is basically completed, at this time, gradually heat to 105℃, and remove methanol and water in the system during the heating process;

[0045] E, sample and detect, when the content of methanol in the reactant is less than 2%, add the formula amount of catalyst 2, stir uniformly, and then drop the formula amount of N-methyl monoethanolamine to carry out amidation reaction, and the drop time is controlled at 1.5 h; after the dropping is completed, continue to heat at 105℃ to carry out amidation reaction;

[0046] F, sample and detect, when the conversion rate of N-methyl monoethanolamine reaches more than 95%, it indicates that the amidation reaction is basically completed, at this time, start the vacuum system to remove excess unreacted N-methyl monoethanolamine and a small amount of byproduct methanol in the system under reduced pressure, and the vacuum degree is controlled at-0.098 Mpa;

[0047] G, when the volatile matter is less than 1%, release the vacuum, add 10% of the nano titanium dioxide of the mass of the reactant in the kettle to fully stir and mix, after fully mixing, discharge at high temperature, and then form by steel belt speed cooling, and crush to obtain the matting curing agent.

[0048] The obtained product has white powder appearance, and the hydroxyl equivalent weight is 101 g / mol.

[0049] Preparation Example 2

[0050] A matting curing agent for powder coating, which is a hydroxyalkyl amide matting curing agent, comprises the following raw materials in mole parts:

[0051]

[0052] Catalyst 1 is tetrabutyl titanate, the amount of which is 0.5% of the mass of citric acid; catalyst 2 is sodium hydroxide, the amount of which is 1.5% of the mass of N-methyl monoethanolamine; the nano-titanium dioxide has a particle size of 40-50 nm, and the amount of which is 10% of the total mass of raw materials, and is purchased from Shanghai Liangjiang Titanium Dioxide Chemical Products Co., Ltd.

[0053] The preparation method is the same as that of Example 1.

[0054] The appearance of the obtained product is white powder, and the hydroxyl equivalent weight is 104 g / mol.

[0055] Preparation Example 3

[0056] An extinction curing agent for powder coatings, the extinction curing agent being a hydroxyalkyl amide extinction curing agent, comprising the following raw materials in mole parts:

[0057]

[0058] Catalyst 1 is tetrabutyl titanate, the amount of which is 0.6% of the mass of citric acid; catalyst 2 is sodium hydroxide, the amount of which is 1% of the mass of N-methyl monoethanolamine; the nano-titanium dioxide has a particle size of 40-50 nm, and the amount of which is 10% of the total mass of raw materials, and is purchased from Shanghai Liangjiang Titanium Dioxide Chemical Products Co., Ltd.

[0059] The preparation method is the same as that of Example 1.

[0060] The appearance of the obtained product is white powder, and the hydroxyl equivalent weight is 98 g / mol.

[0061] Preparation Example 4

[0062] An extinction curing agent for powder coatings, the extinction curing agent being a hydroxyalkyl amide extinction curing agent, comprising the following raw materials in mole parts:

[0063]

[0064] Catalyst 1 is tetrabutyl titanate, the amount of which is 0.6% of the mass of citric acid; catalyst 2 is sodium hydroxide, the amount of which is 1.5% of the mass of N-methyl monoethanolamine; the nano-titanium dioxide has a particle size of 40-50 nm, and the amount of which is 10% of the total mass of raw materials, and is purchased from Shanghai Liangjiang Titanium Dioxide Chemical Products Co., Ltd.

[0065] The preparation method is the same as that of Example 1.

[0066] The appearance of the obtained product is white powder, and the hydroxyl equivalent weight is 102 g / mol.

[0067] Examples 1-4 (extinction curing agents obtained using Preparation Examples 1-4 described above)

[0068] A hydroxyalkylamide curing type powder coating formulation, the formulation is as follows in parts by weight:

[0069]

[0070] The polyester resin is ZJ9505 type polyester resin from Huangshan Zhengjie New Material Co., Ltd. The other raw materials are all common commercially available products.

[0071] Comparative Example 1: A common hydroxyalkylamide curing agent HAA product commercially available, ZJ552 type from Anhui Huizhou Zhengjie New Material Co., Ltd. Product index: appearance: white powder, hydroxyl equivalent weight: 83 g / mol. In the powder coating formulation, the polyester resin is adjusted to 570 parts by mass, and the HAA curing agent is adjusted to 30 parts by mass, and the other components are the same as in Example 1.

[0072] Coating layer preparation: according to the above powder coating formulation, the materials are mixed, extruded by a twin-screw extruder, tabletted, broken, and then the tablet is crushed and sieved (160-180 mesh) to make a powder coating. The powder coating is sprayed on the surface treated tinplate substrate using an electrostatic spray gun, the spraying thickness is 80 μm, and the powder coating layer is obtained by curing at 180℃ for 15 min.

[0073] The coating index detection is according to GB / T 21776-2008 "Guidelines for the Test Standards of Powder Coatings and Their Coatings", and the film hardness test is according to GB / T 6379-2006 "Pencil Method for the Determination of Film Hardness of Paints and Varnishes".

[0074] Table 1 Powder coating application performance test results

[0075]

[0076] As can be seen from Table 1, the hydroxyalkylamide matting curing agent product prepared by the specific formulation and process of the present application has different active hydroxyl functional groups and high hydroxyl functionality. The final product is used in powder coatings, which has matting effect while curing. The final coating film is smooth and flat in appearance, has excellent impact resistance, and the gloss of the cured coating film is basically 50-70%, the matting effect is obvious, the decorative property is good, and the hardness of the coating film is higher than that of the coating film cured by the common hydroxyalkylamide curing agent HAA, which is basically 2H or more. The hardness and matting effect are better than those of the commercially available product, so it is suitable for use in fields with high requirements for decorative property and coating film hardness, and has good economic application value.

[0077] The foregoing merely illustrates some exemplary embodiments of the application, and it will be appreciated that those skilled in the art will be able to devise various modifications without departing from the spirit and scope of the application. The described embodiments are to be considered in all respects as illustrative only and not restrictive in character, and the scope of the application is indicated not by the foregoing description but by the claims that follow.

Claims

1. A matting curing agent for powder coatings, characterized in that, The matting curing agent is a hydroxyalkylamide matting curing agent, and its molecular structure is as follows: It includes the following raw materials in molar amounts: The raw materials also include nano-titanium dioxide, catalyst 1, and catalyst 2; catalyst 1 is tetrabutyl titanate, and its dosage is 0.4-0.6% of the mass of citric acid; catalyst 2 is sodium hydroxide, and its dosage is 1-1.5% of the mass of N-methylmonoethanolamine. The preparation method of the matting curing agent for powder coatings includes the following steps: A. Add the prescribed amounts of xylene, citric acid, 2-methyl-1,3-propanediol and catalyst 1 to the reaction vessel, start stirring, and heat to the boiling point of xylene to carry out the aqueous esterification reaction. B. The content of 2-methyl-1,3-propanediol in the system was detected by gas chromatography. When the conversion rate of 2-methyl-1,3-propanediol reached more than 98%, the reaction was stopped and the vacuum system was started to remove xylene solvent from the system under reduced pressure. C. When the xylene content is less than 1%, release the vacuum, cool to 55-60℃, and add anhydrous methanol to carry out the methyl esterification reaction of the remaining carboxyl groups of the reactants. D. Take samples to test the acid value of the reactants. When the acid value of the reactants is lower than 3 mg KOH / g, gradually raise the temperature to 105-110℃. During the heating process, remove methanol and water from the system. E. Sampling and testing: When the methanol content in the reactants is less than 2%, add the prescribed amount of catalyst 2, stir evenly, and then add the prescribed amount of N-methylmonoethanolamine dropwise to carry out the amidation reaction; after the addition is complete, continue to keep warm at 105-110℃ to carry out the amidation reaction. F. Sampling and testing: When the conversion rate of N-methylmonoethanolamine reaches 95% or more, start the vacuum system to remove excess unreacted N-methylmonoethanolamine and a small amount of byproducts from the system under reduced pressure. G. When the volatile content is less than 1%, release the vacuum, add nano titanium dioxide and stir thoroughly. After thorough mixing, discharge at high temperature, and then rapidly cool and mold and crush to obtain the matte curing agent.

2. The matting curing agent for powder coatings as described in claim 1, characterized in that, The molar ratio of 2-methyl-1,3-propanediol to citric acid is controlled between 1:2 and 2.

1.

3. The matting curing agent for powder coatings as described in claim 1, characterized in that, The particle size of nano titanium dioxide is 40-50 nm, and the amount used is 5-20% of the total mass of the raw materials.

4. A method for preparing a matting curing agent for powder coatings according to any one of claims 1-3, characterized in that, Includes the following steps: A. Add the prescribed amounts of xylene, citric acid, 2-methyl-1,3-propanediol and catalyst 1 to the reaction vessel, start stirring, and heat to the boiling point of xylene to carry out the aqueous esterification reaction. B. The content of 2-methyl-1,3-propanediol in the system was detected by gas chromatography. When the conversion rate of 2-methyl-1,3-propanediol reached more than 98%, the reaction was stopped and the vacuum system was started to remove xylene solvent from the system under reduced pressure. C. When the xylene content is less than 1%, release the vacuum, cool to 55-60℃, and add anhydrous methanol to carry out the methyl esterification reaction of the remaining carboxyl groups of the reactants. D. Take samples to test the acid value of the reactants. When the acid value of the reactants is lower than 3 mg KOH / g, gradually raise the temperature to 105-110℃. During the heating process, remove methanol and water from the system. E. Sampling and testing: When the methanol content in the reactants is less than 2%, add the prescribed amount of catalyst 2, stir evenly, and then add the prescribed amount of N-methylmonoethanolamine dropwise to carry out the amidation reaction; after the addition is complete, continue to keep warm at 105-110℃ to carry out the amidation reaction. F. Sampling and testing: When the conversion rate of N-methylmonoethanolamine reaches 95% or more, start the vacuum system to remove excess unreacted N-methylmonoethanolamine and a small amount of byproducts from the system under reduced pressure. G. When the volatile content is less than 1%, release the vacuum, add nano titanium dioxide and stir thoroughly. After thorough mixing, discharge at high temperature, and then rapidly cool and mold and crush to obtain the matte curing agent.

5. The preparation method of the matting curing agent for powder coatings as described in claim 4, characterized in that, In step B, the vacuum degree is controlled between -0.095 MPa and -0.097 MPa, and the distillation temperature is 130-135℃; in step F, the vacuum degree is controlled between -0.098 MPa and -0.099 MPa.

6. The method for preparing the matting curing agent for powder coatings as described in claim 4, characterized in that, In step E, the dripping time is controlled to be 1-1.5h; in step G, the steel strip is rapidly cooled and formed.

7. The application of the matting curing agent for powder coatings as described in any one of claims 1-3 or the matting curing agent for powder coatings prepared by the method described in any one of claims 4-6 in polyester resin powder coating systems.

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