A method of curing a powder coating composition and a coating thereof

Abstract

This invention discloses a method for curing a powder coating composition and the resulting coating. The powder coating composition includes at least a carboxyl polyester resin and an acrylic resin with epoxy groups. The acid value of the carboxyl polyester resin is not higher than 50 mg KOH / g, and the acrylic resin with epoxy groups serves as a curing agent for the carboxyl polyester resin. The powder coating composition is cured using infrared heating at a temperature not exceeding 140°C and for a duration not exceeding 5 minutes. This invention uses infrared heating to cure the powder coating composition at a temperature not exceeding 140°C and a heating time not exceeding 5 minutes, resulting in a coating with outstanding weather resistance.

Description

Technical Field

[0001] This invention belongs to the field of powder coatings, and specifically relates to a curing method for a powder coating composition. This invention also relates to a coating obtained by using the curing method of the powder coating composition. Background Technology

[0002] Thermosetting powder coatings are widely used to replace paints and water-based paints to achieve protective and decorative effects on products in various fields due to their advantages such as being green and environmentally friendly, having low energy consumption, being easy to apply, and having no (or at least very low) VOC emissions.

[0003] Furthermore, existing powder coating products typically lack both the excellent properties of low-temperature curing and weather resistance. In other words, existing low-temperature curing powder coating products generally struggle to achieve good weather resistance, while existing weather-resistant powder coating products are difficult to cure at low temperatures.

[0004] Therefore, the applicant hopes to conduct research and development to improve the aforementioned technical problems. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a curing method for a powder coating composition and a coating thereof, wherein the powder coating composition is cured by infrared heating at a heating temperature not exceeding 140°C and a heating time not exceeding 5 minutes, thereby obtaining a coating with outstanding weather resistance.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for curing a powder coating composition, wherein the powder coating composition comprises at least a carboxyl polyester resin and an acrylic resin with epoxy groups, wherein the acid value of the carboxyl polyester resin is not higher than 50 mg KOH / g, and the acrylic resin with epoxy groups is used as a curing agent for the carboxyl polyester resin; wherein the powder coating composition is cured by infrared heating, the heating temperature is not higher than 140°C and the heating time is not higher than 5 minutes.

[0008] Preferably, the weight ratio of the carboxylated polyester resin to the acrylic resin with epoxy groups is in the range of 6:1 to 2:1.

[0009] Preferably, the heating temperature range is 120-135℃, and / or the heating time range is 2-4 minutes.

[0010] Preferably, the acid value of the carboxylated polyester resin is in the range of 15-35 mg KOH / g.

[0011] Preferably, the softening point temperature of the carboxylated polyester resin is 105-115℃.

[0012] Preferably, the epoxy equivalent of the acrylic resin containing epoxy groups is in the range of 300-600 g / eq.

[0013] Preferably, the softening point temperature of the acrylic resin with epoxy groups is 90-100°C.

[0014] Preferably, the weight ratio of the carboxylated polyester resin to the acrylic resin with epoxy groups is in the range of 5:1 to 3:1.

[0015] Preferably, the sum of the weight parts of the carboxylated polyester resin and the acrylic resin with epoxy groups accounts for not less than 45 wt% of the weight parts of the weather-resistant low-temperature curing powder coating composition.

[0016] Preferably, a coating is formed by the curing method described above.

[0017] Preferably, the coating is tested for 1600 hours of UVA according to ASTM-G154-2016, and its gloss retention rate is not less than 85%.

[0018] It should be noted that the acid value testing standard involved in this application is based on ISO 3682-1998; the epoxy equivalent testing standard is based on GB / T 4612-2008; and the softening point temperature standard is based on ISO4625-1980.

[0019] The applicant has surprisingly discovered that in a specific powder coating composition resin curing system composed of a carboxyl polyester resin with an acid value not exceeding 50 mg KOH / g and an acrylic resin with epoxy groups, curing the powder coating composition by infrared heating at a heating temperature not exceeding 140°C and a heating time not exceeding 5 minutes can yield a coating with outstanding weather resistance. Detailed Implementation

[0020] This application provides a method for curing a powder coating composition. The powder coating composition includes at least a carboxyl polyester resin and an acrylic resin with epoxy groups. The acid value of the carboxyl polyester resin is not higher than 50 mg KOH / g, and the acrylic resin with epoxy groups is used as a curing agent for the carboxyl polyester resin. The powder coating composition is cured by infrared heating, with the heating temperature not higher than 140°C and the heating time not exceeding 5 minutes.

[0021] Preferably, in this embodiment, the weight ratio of carboxylated polyester resin to acrylic resin with epoxy groups is in the range of 6:1-2:1, more preferably 5:1-3:1, and even more preferably 5:1-4:1.

[0022] Preferably, in this embodiment, the acid value of the carboxylated polyester resin is in the range of 15-35 mgKOH / g; preferably, in this embodiment, the softening point temperature of the carboxylated polyester resin is 105-115℃.

[0023] Preferably, in this embodiment, the epoxy equivalent of the acrylic resin with epoxy groups is in the range of 300-600 g / eq; more preferably, it is 400-500 g / eq; preferably, in this embodiment, the softening point temperature of the acrylic resin with epoxy groups is 90-100°C.

[0024] Preferably, in this embodiment, the sum of the weight parts of carboxylated polyester resin and acrylic resin with epoxy groups accounts for not less than 45 wt% of the weight parts of the weather-resistant low-temperature curing powder coating composition, more preferably 50-90 wt%, and even more preferably 55-80 wt%.

[0025] Preferably, in this embodiment, the heating temperature range is 120-135°C, and / or the heating time range is 2-4 minutes.

[0026] Preferably, this embodiment also proposes a coating, which is formed by curing as described above; preferably, in this embodiment, the coating is tested for 1600 hours of UVA according to ASTM-G154-2016, and its gloss retention rate is not less than 85%.

[0027] All the raw materials involved in this application can be purchased directly on the market, and the source of raw materials is easy to obtain.

[0028] In specific implementations of this application, it is also possible to add known leveling agents, degassing agents, antioxidants, dispersants, fillers, pigments, stabilizers, curing accelerators, functional additives, or other additives to the powder coating composition. These are all conventional technical choices for those skilled in the art.

[0029] When preparing the powder coating composition of this application, any known preparation process can be used. Preferably, it is prepared by mixing the raw materials, melt extrusion and crushing, etc., according to known processes. Of course, other known preparation processes can also be used to obtain the powder coating composition of this embodiment. This application does not have any particular limitation on its preparation process.

[0030] To verify the technical effects of this application, the following sets of embodiments and comparative examples were specifically implemented, and the performance of each embodiment and comparative example was compared and tested:

[0031] Example 1: A powder coating composition, the raw material formulation of which is shown in Table 1 below:

[0032] Table 1 Formulation of the powder coating composition in Example 1

[0033]

[0034] The powder coating composition of Example 1 is obtained by weighing, premixing, melt extrusion, grinding, and cyclone separation according to the above raw material formula (a known process preparation technology).

[0035] An aluminum substrate was selected, and the powder coating composition provided in Example 1 was applied to the aluminum substrate by electrostatic spraying. The powder coating composition was then cured by infrared heating at a temperature of 130°C for 3 minutes to obtain the coating of Example 1.

[0036] Example 2: The remaining technical solutions of Example 2 are the same as those of Example 1, except that Example 2 provides a powder coating composition, the raw material formula of which is shown in Table 2 below:

[0037] Table 2 Formulation of the powder coating composition in Example 2

[0038]

[0039] Example 3: The remaining technical solutions of Example 3 are the same as those of Example 1, except that Example 3 provides a powder coating composition, the raw material formula of which is shown in Table 3 below:

[0040] Table 3 Formulation table of the powder coating composition in Example 3

[0041]

[0042] Example 4: The remaining technical solutions of Example 4 are the same as those of Example 1, except that Example 4 provides a powder coating composition, the raw material formula of which is shown in Table 4 below:

[0043] Table 4 Formulation of the powder coating composition in Example 4

[0044]

[0045]

[0046] Example 5: The remaining technical solutions of Example 5 are the same as those of Example 1, except that Example 5 provides a powder coating composition, the raw material formula of which is shown in Table 5 below:

[0047] Table 5. Formulation of the powder coating composition in Example 5.

[0048]

[0049] Example 6: The remaining technical solutions of Example 6 are the same as those of Example 1, except that Example 6 provides a powder coating composition, the raw material formula of which is shown in Table 6 below:

[0050] Table 6 Formulation of the powder coating composition in Example 6

[0051]

[0052]

[0053] Example 7: The remaining technical solutions of Example 7 are the same as those of Example 1, except that Example 7 provides a powder coating composition, the raw material formula of which is shown in Table 7 below:

[0054] Table 7 Formulation of the powder coating composition in Example 7

[0055]

[0056] Example 8: The remaining technical solutions of Example 8 are the same as those of Example 1, except that Example 8 provides a powder coating composition, the raw material formula of which is shown in Table 8 below:

[0057] Table 8 Formulation of the powder coating composition in Example 8

[0058]

[0059] Example 9: The remaining technical solutions of Example 9 are the same as those of Example 1, except that the powder coating composition is cured by infrared heating at a temperature of 135°C for 2 minutes to obtain the coating of Example 9.

[0060] Example 10: The remaining technical solutions of Example 10 are the same as those of Example 1, except that the powder coating composition is cured by infrared heating at a temperature of 125°C for 3 minutes to obtain the coating of Example 10.

[0061] Example 11: The remaining technical solutions of Example 11 are the same as those of Example 1, except that the powder coating composition is cured by infrared heating at a temperature of 120°C for 4 minutes to obtain the coating of Example 11.

[0062] Comparative Example 1: The remaining technical solutions of Comparative Example 1 are the same as those of Example 1, except that: Comparative Example 1 provides a powder coating composition, the raw material formulation of which is shown in Table 9 below:

[0063] Table 9 Formulation of the powder coating composition in Comparative Example 1

[0064]

[0065] Comparative Example 2: The remaining technical solutions of Comparative Example 2 are the same as those of Example 1, except that: Comparative Example 2 provides a powder coating composition, the raw material formulation of which is shown in Table 10 below:

[0066] Table 10 Formulation of the powder coating composition in Comparative Example 2

[0067]

[0068]

[0069] Comparative Example 3: The remaining technical solutions of Comparative Example 3 are the same as those of Example 1, except that: Comparative Example 3 provides a powder coating composition, the raw material formulation of which is shown in Table 11 below:

[0070] Table 11 Formulation of the powder coating composition in Comparative Example 3

[0071]

[0072] Comparative Example 4: The remaining technical solutions of Comparative Example 4 are the same as those of Example 1, except that: Comparative Example 4 provides a powder coating composition, the raw material formulation of which is shown in Table 12 below:

[0073] Table 12 Formulation table of powder coating compositions in Comparative Example 4

[0074]

[0075] Comparative Example 5: The rest of the technical solutions of Comparative Example 5 are the same as those of Example 1, except that the powder coating composition in Example 1 is cured by baking and heating, the heating temperature is 130°C and the heating time is 3 minutes (specifically, the time placed in the baking oven) to obtain the coating of Comparative Example 5.

[0076] Comparative Example 6: The rest of the technical solutions of Comparative Example 6 are the same as those of Example 1, except that the powder coating composition in Example 1 is cured by baking and heating at a temperature of 140°C for 10 minutes to obtain the coating of Comparative Example 6.

[0077] Comparative Example 7: The rest of the technical solutions of Comparative Example 7 are the same as those of Example 1, except that the powder coating composition in Example 1 is cured by baking and heating at a temperature of 150°C for 15 minutes to obtain the coating of Comparative Example 7.

[0078] Comparative Example 8: The rest of the technical solutions of Comparative Example 8 are the same as those of Example 1, except that the powder coating composition in Example 1 is cured by baking and heating at a temperature of 150°C for 25 minutes to obtain the coating of Comparative Example 8.

[0079] The performance of the cured coatings obtained in Examples 1-11 and Comparative Examples 1-8 was compared and tested as shown in Tables 13 and 14 below:

[0080] Table 13

[0081]

[0082]

[0083]

[0084] Table 14

[0085]

[0086]

[0087] It should be noted that the performance tests involved in this embodiment and the comparative example were conducted in accordance with the test standards or conditions described in Table 15 below.

[0088] Table 15 Test Items and Test Standards or Conditions

[0089] Test Project Perform test standards or test conditions Impact ISO 6272-1-2011 Cup protuberance ISO1520-2006 Grid ISO2409-2020 Withstands 50% alcohol concentration (24 hours) GB / T 4893.1-2021 Coffee tolerance test (24 hours) GB / T 4893.1-2021 Detergent resistant (24 hours) GB / T 4893.1-2021 Resistant to 10% acetic acid (24 hours) GB / T 4893.1-2021 Liquid wax resistant (31 hours) GB / T 4893.1-2021 Resistant to damp heat (1000 hours) GB / T1740-2007 Resistance to neutral salt spray (1000 hours) ISO9227-2022 UVA (1600 hours) ASTM-G154-2016

[0090] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0091] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for curing a powder coating composition, characterized in that, The powder coating composition comprises at least a carboxyl polyester resin and an acrylic resin with epoxy groups, wherein the acrylic resin with epoxy groups serves as a curing agent for the carboxyl polyester resin; wherein the powder coating composition is cured by infrared heating at a temperature of 120-140°C for a duration not exceeding 5 minutes; the acid value of the carboxyl polyester resin is in the range of 15-35 mgKOH / g; the softening point temperature of the carboxyl polyester resin is 105-115°C; the softening point temperature of the acrylic resin with epoxy groups is 90-100°C; and the epoxy equivalent of the acrylic resin with epoxy groups is in the range of 400-450 g / eq. The weight ratio of the carboxylated polyester resin to the acrylic resin with epoxy groups is in the range of 6:1 to 2:1; the sum of the weight parts of the carboxylated polyester resin and the acrylic resin with epoxy groups accounts for not less than 45 wt% of the weight parts of the weather-resistant low-temperature curing powder coating composition.

2. The curing method according to claim 1, characterized in that, The heating temperature range is 120-135℃, and / or the heating time range is 2-4 minutes.

3. The curing method according to claim 1, characterized in that, The weight ratio of the carboxylated polyester resin to the acrylic resin with epoxy groups ranges from 5:1 to 3:

1.

4. A coating, characterized in that, It is formed by the curing method described in any one of claims 1-3.

5. The coating according to claim 4, characterized in that, The coating was tested for 1600 hours of UVA according to ASTM-G154-2016, and its gloss retention rate was not less than 85%.

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