Catalyst for low-temperature curing flat powder coating and preparation method thereof

Abstract

A catalyst for low-temperature curing matte powder coatings is obtained by polymerization reaction of (3-bromopropyl)trimethylammonium bromide, 2-ethylimidazole, ethylene glycol monomethyl ether, octadecylamine polyoxyethylene ether, hydroxy acrylic resin, polyester resin, ultrafine active zinc oxide powder, etc. The catalyst can be used to prepare low-temperature curing 50 / 50 mixed powder coatings, which have good surface leveling and comprehensive performance. High-cost low-temperature curing polyester resins or matte polyester resins are not required, and only ordinary 50 / 50 mixed polyester resins need to be used. The curing temperature is reduced, and the coating film has a good matte effect. The catalyst is not only easy to use and has good stability, but also greatly reduces the cost of the powder coating, thereby having good economic value.

Description

Technical Field

[0001] The present invention relates to the field of powder coatings, in particular to a catalyst for low-temperature curing flat powder coatings and a preparation method thereof, and application of the catalyst in low-temperature curing low-gloss 50 / 50 mixed powder coatings. Background Art

[0002] Powder coatings are a new type of solvent-free, 100% solids coating. They offer advantages such as solvent-free operation, pollution-free operation, energy and resource conservation, reduced labor intensity, and high mechanical strength. They have seen rapid growth in recent years. Among mixed powder coatings for indoor use, 50 / 50 powder coatings are the most commonly used, offering excellent overall performance and wide applicability. With increasing energy conservation demands, downstream companies are generally demanding the use of powder coatings with low-temperature curing systems to achieve these benefits. To meet this demand, many polyester manufacturers have adjusted their formulations for low-temperature curing polyester resins, using specialized raw materials to lower the softening point and increase curing activity. This, however, results in the resins being prone to caking during storage, resulting in higher costs and inconvenience. Furthermore, demand for low-gloss powder coatings has also grown rapidly in recent years due to their decorative and aesthetic qualities. Currently, matting is often achieved using specialized low-gloss polyester resins with the addition of matting agents, which increases costs and makes them inconvenient to use. Currently, the most commonly used indoor mixed 50 / 50 powder coating has problems such as the high cost of low-temperature curing polyester resin and the need to use low-temperature curing polyester resin and matte polyester resin separately, which makes it inconvenient to use. These problems urgently need to be solved. Summary of the Invention

[0003] To address these issues, this proposal has developed a catalyst for low-temperature-curing, low-gloss 50 / 50 hybrid powder coatings. The catalyst is derived from the reaction of (3-bromopropyl)trimethylammonium bromide, 2-ethylimidazole, ethylene glycol monomethyl ether, octadecylamine polyoxyethylene ether, a hydroxylated acrylic resin, a specially selected polyester resin, and ultrafine activated zinc oxide. This catalyst can be used to prepare low-temperature-curing, 50 / 50 hybrid powder coatings, demonstrating excellent surface leveling and overall performance. It eliminates the need for expensive, specialized low-temperature-curing polyester resins, requiring only standard 50 / 50 hybrid polyester resins. This catalyst boasts excellent performance and low cost, allowing it to be directly added to general-purpose 50 / 50 hybrid powder coating systems, lowering the curing temperature while also providing matting performance. This product eliminates the need for specialized low-temperature-curing polyesters or matte-producing polyester resins and can be used directly with standard 50 / 50 general-purpose polyester resins. This makes it convenient to use and offers excellent stability, significantly reducing the cost of powder coatings and offering excellent economic value.

[0004] Specifically, the present invention relates to a catalyst for low-temperature curing matte powder coatings, which is obtained by polymerization reaction of raw materials including (3-bromopropyl)trimethylammonium bromide, 2-ethylimidazole, ethylene glycol monomethyl ether, octadecylamine polyoxyethylene ether, hydroxy acrylic resin, polyester resin, and ultrafine active zinc oxide powder. The raw materials are composed of the following components in parts by mass:

[0005]

[0006] For the above raw materials, preferably, the total amine value of octadecylamine polyoxyethylene ether is 18-22 mgKOH / g; the hydroxyl value of hydroxy acrylic resin is 98-104 mgKOH / g; the polyester resin used is a 60 / 40 polyester resin; the polyester resin is dispersed in the catalyst product by dry mixing; and the particle size of the ultrafine active zinc oxide powder is 50-100 nm.

[0007] The above raw materials can be selected from commercially available brands that meet the requirements. For example, the hydroxyl acrylic resin with a hydroxyl value of 98-104 mgKOH / g, model AC166B, is available from Shanghai Qizhan New Materials Technology Co., Ltd.; the polyester resin is a 60 / 40 polyester resin, model SJ6711, with an acid value of 48-52 mgKOH / g, purchased from Anhui Shenjian New Materials Co., Ltd.; and the ultrafine active zinc oxide powder with a particle size of 50-100 nm is available from Shanghai Yingfeng Ruihuang Metal Materials Co., Ltd.

[0008] The method for preparing a catalyst for low-temperature curing flat powder coatings as described above comprises the following steps:

[0009] A. Add the formulated amount of ethylene glycol monomethyl ether, (3-bromopropyl)trimethylammonium bromide and 2-ethylimidazole into a reaction kettle, start stirring and heat to 60-65°C for sufficient reaction;

[0010] B. Use gas chromatography to detect the content of 2-ethylimidazole. When the conversion rate of 2-ethylimidazole reaches 95% or more, stop the reaction. At this time, add octadecylamine polyoxyethylene ether and hydroxy acrylic resin, and heat to 90-100℃ to react.

[0011] C. After all the materials have reacted and become homogeneous, start the vacuum system and remove the solvent ethylene glycol monomethyl ether under reduced pressure;

[0012] D. When no obvious liquid is evaporated, turn off the vacuum system and put the material into a high-speed mixer. Add the formulated amount of ultrafine active zinc oxide into the mixer in advance, and then mix it at high speed to obtain the adsorbed and mixed material A;

[0013] E. Add the formulated amount of polyester resin into the grinder and grind it, then mix it with material A again at high speed, and after mixing evenly, discharge the material to obtain the product.

[0014] Furthermore, the heat preservation reaction in step A is carried out for more than 12 hours; most preferably, the heat preservation reaction is carried out for 12-24 hours;

[0015] Furthermore, in step C, the vacuum degree is controlled at -0.097 MPa to -0.099 MPa; in step D, the mixing speed is 2000-2500 rpm; in step E, the polyester resin is crushed to a particle size of 150-180 mesh; and the mixing speed is 2000-2500 rpm.

[0016] For example, the preparation method of the catalyst may include the following steps:

[0017] A. Add the formulated amount of ethylene glycol monomethyl ether, (3-bromopropyl)trimethylammonium bromide and 2-ethylimidazole into the reaction kettle, start stirring and heat to 60-65°C and keep warm for more than 12 hours;

[0018] B. Use gas chromatography to detect the content of 2-ethylimidazole. When the conversion rate of 2-ethylimidazole reaches above 95%, stop the reaction, indicating that most of the ionic liquid has been generated. At this time, add octadecylamine polyoxyethylene ether and hydroxy acrylic resin, and raise the temperature to 90-100℃ to react;

[0019] C. After all the materials have reacted and become homogeneous, start the vacuum system and remove the solvent ethylene glycol monomethyl ether under reduced pressure. The vacuum degree is controlled at -0.097 MPa to -0.099 MPa.

[0020] D. When no obvious liquid is evaporated (volatile matter is less than 1%), stop the vacuum system and put the material into a high-speed mixer. Add the formulated amount of ultrafine active zinc oxide into the mixer in advance, and then perform high-speed mixing at a speed of 2000-2500 rpm to obtain the adsorbed mixed material A;

[0021] E. Add the formulated amount of polyester resin into the grinder and grind it into a particle size of 150-180 mesh, then mix it with material A again at a high speed of 2000-2500 rpm. After mixing evenly, discharge the material to obtain the product.

[0022] The obtained product has the appearance of white powder and a softening point of 105-118°C.

[0023] The present invention also relates to a low-temperature curing low-gloss 50 / 50 mixed powder coating, which comprises the above-mentioned catalyst or the catalyst obtained by the preparation method.

[0024] For example, a powder coating formulation may include polyester resin, E-12 epoxy resin, the aforementioned catalyst, titanium dioxide, barium sulfate, a leveling agent, a brightener, benzoin, and the like. The coating may be prepared by uniformly mixing the materials according to the aforementioned powder coating formulation, extruding, tableting, and crushing the materials using a twin-screw extruder, and then crushing and sieving the tablets to produce the powder coating. The powder coating is then applied to a surface-treated tinplate substrate using an electrostatic spray gun and cured at 150°C for 20 minutes to produce the coating.

[0025] Beneficial effects of the present invention:

[0026] The invention first uses (3-bromopropyl)trimethylammonium bromide and 2-ethylimidazole to generate a special imidazole quaternary ammonium salt ionic liquid, and then adds octadecylamine polyoxyethylene ether with an amine value of 18-22 mgKOH / g to further enhance the compatibility and dispersibility of the imidazole quaternary ammonium salt ionic liquid with the powder coating resin system and the catalytic activity, thereby helping to eliminate coating defects. At the same time, by using the catalyst in a corresponding process with a hydroxy acrylic resin, a polyester resin, and ultrafine active zinc oxide, a catalyst is finally obtained that enables the corresponding powder coating to have low-temperature curing and extinction ability. The ultrafine active zinc oxide itself has excellent catalytic ability and serves as a carrier component for dispersing and adsorbing components such as the imidazole quaternary ammonium salt ionic liquid as a catalytic inorganic component, thereby helping the catalyst to improve the storage stability of the catalyst product. The hydroxyl group of the hydroxy acrylic resin and the carboxyl group of the polyester resin are significantly different from the carboxyl groups of the 50 / 50 polyester resin in the curing system, resulting in a significant extinction effect due to the difference in curing speed during the curing process. The selected polyester resin is dispersed in the catalyst product in a dry mixing manner. The catalyst is ultimately added directly to a general-purpose 50 / 50 mixed powder coating system, reducing its curing temperature from 185°C / 15 min to 150°C / 20 min, and achieving a gloss reduction of 20-35%. This product eliminates the need for special low-temperature curing polyesters or matte polyester resins and can be used directly with ordinary 50 / 50 general-purpose polyester resins. It is not only easy to use and has excellent stability, but also significantly reduces the cost of powder coatings, offering superior economic value. DETAILED DESCRIPTION

[0027] To facilitate understanding of the present invention, various exemplary embodiments of the present invention are now described in detail. This description should not be considered as a specific limitation of the present invention, but should be understood as a more detailed description of certain aspects, features and embodiments of the present invention.

[0028] The raw materials are all commercially available. Among them, the total amine value of octadecylamine polyoxyethylene ether is

[0029] 18-22 mgKOH / g, model AC-1860, purchased from Hai'an Petrochemical Plant, Jiangsu Province; hydroxyl acrylic resin hydroxyl value 98-104 mgKOH / g, model AC166B, Shanghai Qizhan New Materials Technology Co., Ltd.; polyester resin is 60 / 40 polyester resin, model SJ6711, acid value 48-52 mgKOH / g, purchased from Anhui Shenjian New Materials Co., Ltd.; ultrafine active zinc oxide powder with a particle size of 50-100 nm was purchased from Shanghai Yingfeng Ruihuang Metal Materials Co., Ltd.

[0030] Preparation Example 1

[0031] A catalyst for low-temperature curing matte powder coating, the raw materials comprising the following components by weight:

[0032]

[0033] The preparation method comprises the following steps:

[0034] A. Add the above-mentioned amount of ethylene glycol monomethyl ether, (3-bromopropyl)trimethylammonium bromide and 2-ethylimidazole into the reaction kettle, start stirring and heat to 65°C and keep warm for 12 hours;

[0035] B. Detect the content of 2-ethylimidazole by gas chromatography. When the conversion rate of 2-ethylimidazole reaches 95% or more, stop the reaction, indicating that most of the ionic liquid has been generated. At this time, add octadecylamine polyoxyethylene ether and hydroxy acrylic resin, and heat to 100° C. to react;

[0036] C. After all the materials have reacted and become homogeneous, start the vacuum system and remove the solvent ethylene glycol monomethyl ether under reduced pressure. The vacuum degree is controlled at -0.099MPa.

[0037] D. When no obvious liquid is evaporated (volatile matter is less than 1%), stop the vacuum system and put the material into a high-speed mixer. Add the formulated amount of ultrafine active zinc oxide into the mixer in advance, and then perform high-speed mixing at a speed of 2500 rpm to obtain the adsorbed and mixed material A;

[0038] E. Add the formulated amount of polyester resin into the grinder and grind it into a particle size of 150 mesh, then mix it again with material A at a high speed of 2500 rpm. After mixing evenly, discharge the material to obtain the product.

[0039] The obtained product has the appearance of white powder and the softening point is 106°C.

[0040] Preparation Example 2

[0041] A catalyst for low-temperature curing matte powder coating, the raw materials comprising the following components by weight:

[0042]

[0043] The preparation method is the same as that of Example 1.

[0044] The obtained product has the appearance of white powder and the softening point is 108°C.

[0045] Preparation Example 3

[0046] A catalyst for low-temperature curing matte powder coating, the raw materials comprising the following components by weight:

[0047]

[0048]

[0049] The preparation method is the same as that of Example 1.

[0050] The obtained product has the appearance of white powder and the softening point is 112°C.

[0051] Preparation Example 4

[0052] A catalyst for low-temperature curing matte powder coating, the raw materials comprising the following components by weight:

[0053]

[0054] The preparation method is the same as that of Example 1.

[0055] The obtained product has the appearance of white powder and the softening point is 115°C.

[0056] Examples 1-4 (corresponding to the powder coatings obtained using the catalysts in the above Preparation Examples 1-4):

[0057] Powder coating formula (parts by mass): 300 parts of polyester resin, 300 parts of E-12 epoxy resin, 20 parts of catalysts obtained in Preparation Examples 1-4 of the present invention, 200 parts of titanium dioxide, 200 parts of matting barium, 8 parts of leveling agent, 8 parts of brightener, and 3 parts of benzoin.

[0058] Coating Preparation: According to the powder coating formula, all materials were mixed thoroughly. Extruded, tableted, and crushed using a twin-screw extruder. The tablets were then crushed and sieved to produce the powder coating. The powder coating was then applied to the surface-treated tinplate substrate using an electrostatic spray gun and cured at 150°C for 20 minutes to obtain the coating.

[0059] Comparative Example 1:

[0060] Other aspects are the same as Examples 1-4, except that no catalyst is used and the curing conditions are still 150°C / 20min; Comparative Example 2:

[0061] Other aspects are the same as in Example 1-4, except that no catalyst is used and the curing conditions are increased to 185°C / 15min;

[0062] Performance Comparison

[0063] Coating index testing is based on GB / T 21776-2008 "Guide to the Testing Standards for Powder Coatings and Their Coatings"; adhesion grade is based on GB / T9286-1998 "Scratch Test for Paint and Varnish Films".

[0064] The polyester resins prepared in the above examples and comparative examples were used to prepare coatings according to the coating formulations provided by the present invention. The coating properties were tested and the results are shown in Table 1 below.

[0065] Table 1 Coating properties

[0066]

[0067]

[0068] As can be seen from Table 1, the 50 / 50 mixed powder coating of the present invention is fully cured at 150°C / 20 min after use. Without the need to use special low-temperature curing polyester resin and matte polyester resin, the coating film prepared using the universal 50 / 50 polyester resin has a smooth, flat, and fine surface, with a gloss basically between 20-35%, and passes both 50cm positive and negative impacts. The adhesion can reach level 0, and there is no obvious change after boiling in boiling water for 2 hours. The overall performance is excellent and the decorative effect is also good.

[0069] Comparative Example 1 is to use a general-purpose 50 / 50 polyester resin under low temperature curing conditions (150°C

[0070] / 20min) prepared by the powder coating film, due to incomplete curing, resulting in recoil cracking, adhesion and boiling water boiling also do not meet the requirements.

[0071] Comparative Example 2 is a powder coating film prepared using a general-purpose 50 / 50 polyester resin under normal high-temperature curing conditions (185°C / 15min). The coating film is completely cured and has excellent performance, but cannot achieve matte finish, has high gloss, and has average decorative properties.

[0072] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst for low-temperature curing flat powder coating, characterized in that: The raw materials are composed as follows by mass: The total amine value of octadecylamine polyoxyethylene ether is 18-22 mgKOH / g; the hydroxyl value of hydroxy acrylic resin is 98-104 mgKOH / g; the polyester resin used is 60 / 40 polyester resin; the particle size of ultrafine active zinc oxide powder is 50-100 nm; The preparation method comprises the following steps: A. Add the formulated amount of ethylene glycol monomethyl ether, (3-bromopropyl)trimethylammonium bromide and 2-ethylimidazole into a reaction kettle, start stirring and heat to 60-65°C for sufficient reaction; B. Detect the content of 2-ethylimidazole by gas chromatography. When the conversion rate of 2-ethylimidazole reaches 95% or more, stop the reaction; at this time, add octadecylamine polyoxyethylene ether and hydroxy acrylic resin, and heat to 90-100° C. to react; C. After all the materials have reacted and become homogeneous, start the vacuum system and remove the solvent ethylene glycol monomethyl ether under reduced pressure; D. When no obvious liquid is evaporated, turn off the vacuum system and put the material into a high-speed mixer. Add the formulated amount of ultrafine active zinc oxide powder into the mixer in advance, and then mix it at high speed to obtain the adsorbed and mixed material A; E. Add the formulated amount of polyester resin into the grinder and grind it, then mix it with material A again at high speed, and after mixing evenly, discharge the material to obtain the product.

2. The method for preparing a catalyst for low-temperature curing matte powder coating according to claim 1, further characterized in that the heat preservation reaction in step A is carried out for more than 12 hours.

3. The method for preparing a catalyst for a low-temperature curing matte powder coating according to claim 1, further characterized in that the vacuum degree in step C is controlled at -0.097 MPa to -0.099 MPa.

4. The method for preparing a catalyst for a low-temperature curing matte powder coating according to claim 1, further characterized in that the mixing speed in step D is 2000-2500 rpm; and the polyester resin is crushed to a particle size of 150-180 mesh in step E; and the mixing speed is 2000-2500 rpm.

5. A low-temperature curing low-gloss 50 / 50 hybrid powder coating comprising the catalyst obtained by the preparation method according to any one of claims 1 to 4.

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