Low-temperature curing twice-coating twice-baking powder coating

Abstract

The invention relates to the technical field of powder coatings, in particular to a low-temperature curing twice-coating twice-baking powder coating which is prepared from the following components: modified epoxy resin, a polyamide curing agent, polyester resin, composite filler, a flatting agent, an accelerant and a brightener. The low-temperature curing twice-coating twice-baking powder coating provided by the invention has an obvious improvement effect in the aspects of adhesive force, wear resistance and the like, a silane functional group in gamma-glycidyl ether oxypropyl trimethoxy silane in the modified epoxy resin is hydrolyzed to generate a silanol group, and the silanol group can be subjected to a condensation reaction with a hydroxyl group on the surface of a base material to form a covalent bond; and the adhesive force between the coating and the base material is enhanced. And meanwhile, the modified epoxy resin forms a more compact three-dimensional network structure when the coating is cured, so that the hardness and strength of the coating are improved, and the wear resistance is improved.

Description

Technical Field

[0001] The invention relates to the technical field of powder coatings, in particular to a low-temperature curing two-coating and two-baking powder coating. Background Art

[0002] As a new type of environmentally friendly coating, powder coating has been widely used in the field of modern industrial coating. Compared with traditional solvent-based coatings, powder coating does not contain organic solvents, reduces the emission of volatile organic compounds (VOCs), is environmentally friendly, and also avoids the fire hazard caused by solvent volatilization. In addition, powder coating has a high coating efficiency and can be applied by a variety of construction methods such as electrostatic spraying and fluidized bed dipping, which can realize automated production and reduce labor costs.

[0003] However, there are still some problems in the actual application of powder coatings on the market, among which low adhesion is a more prominent disadvantage. In many application scenarios, such as metal furniture surface coating, building decoration material surface protection, etc., the adhesion between the coating and the substrate directly affects the service life and protective effect of the coating. When the adhesion is insufficient, the coating is prone to shedding and peeling, which not only affects the appearance, but also makes the coated object lose protection, reducing its performance and service life.

[0004] Therefore, it is of great practical significance to develop a low-temperature curing two-coat and two-bake powder coating. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a low-temperature curing two-coat and two-bake powder coating.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A low-temperature curing two-coat and two-bake powder coating: composed of the following components in parts by weight: 52-56 parts of modified epoxy resin, 22-24 parts of polyamide curing agent, 26-30 parts of polyester resin, 25-28 parts of composite filler, 1-3 parts of leveling agent, 2-3 parts of accelerator, and 0.5-0.8 parts of brightener.

[0008] As a further technical solution, the modified epoxy resin preparation method is:

[0009] γ-glycidyloxypropyltrimethoxysilane and bisphenol A epoxy resin were mixed in a mass ratio of 1-2:12, stirred at 120° C. for 2 hours, and cooled to room temperature to obtain a modified epoxy resin;

[0010] The epoxy value of the bisphenol A epoxy resin is 0.45-0.55 eq / 100 g; the stirring speed during stirring is 200-300 r / min.

[0011] As a further technical solution, the composite filler preparation method is:

[0012] Calcium carbonate, talcum powder and bentonite are mixed in a mass ratio of 40%, 30% and 30%, and then stirred with a silane coupling agent in a mass ratio of 100:3 in a high-speed stirrer at a speed of 1800r / min for 30 minutes, and then 2% of the total mass of stearic acid is added and stirred for 40 minutes to obtain.

[0013] As a further technical solution, the leveling agent is an acrylic leveling agent with a number average molecular weight of 13500, a glass transition temperature of -22°C, and a surface tension of 25.5 mN / m.

[0014] As a further technical solution, the accelerator is a mixture of a silane coupling agent and a titanate coupling agent, and the mass ratio of the two is 1:1.

[0015] As a further technical solution, the brightener is nano mica powder.

[0016] As a further technical solution, the method for using the powder coating comprises the following steps: (1) preparing primer powder, (2) preparing topcoat powder, and (3) a two-coating and two-baking process.

[0017] As a further technical solution, the primer powder is prepared as follows:

[0018] The modified epoxy resin, polyamide curing agent, accelerator and 60% by weight of composite filler are mixed in proportion, melt-extruded through a twin-screw extruder at 85-100° C. and a screw speed of 30 r / min, and crushed and sieved to obtain a primer powder.

[0019] As a further technical solution, the topcoat powder is prepared as follows:

[0020] The polyester resin, the remaining 40% of the composite filler, the leveling agent and the brightener are mixed, and then melt-extruded through a twin-screw extruder at 102-105° C. and a screw speed of 45 r / min to obtain a top coating powder.

[0021] As a further technical solution, the two-coating and two-baking process is:

[0022] After spraying the primer, cure at 100°C for 10 minutes;

[0023] After topcoat spraying, cure at 115°C for 5 minutes;

[0024] The electrostatic spraying process is adopted, the spray gun voltage is 60-80kV, and the spraying distance is 15-20cm.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The low-temperature curing two-coat two-bake powder coating provided by the present invention has a significant improvement effect in terms of adhesion, wear resistance and other properties. The silane functional group in the γ-glycidyloxypropyltrimethoxysilane in the modified epoxy resin is hydrolyzed to form a silanol group, which can undergo a condensation reaction with the hydroxyl group on the surface of the substrate to form a covalent bond, thereby enhancing the adhesion between the coating and the substrate. At the same time, the modified epoxy resin forms a denser three-dimensional network structure when the coating is cured, thereby improving the hardness and strength of the coating and improving the wear resistance.

[0027] One end of the silane coupling agent in the composite filler reacts with the hydroxyl group on the filler surface, and the other end interacts with the resin matrix to establish a connection between the filler and the resin, enhance the interfacial bonding force, make the filler better dispersed in the resin, improve the uniformity and stability of the coating, and thus enhance the adhesion. Calcium carbonate, talcum powder and bentonite have a certain hardness and wear resistance. After treatment, they can more effectively exert their physical properties, fill the microstructure of the coating, and increase the wear resistance. Stearic acid reduces filler agglomeration and makes the filler distribution more uniform, which helps to improve the overall performance of the coating.

[0028] The two-coat and two-bake process includes the preparation of primer powder, the preparation of topcoat powder and the specific two-coat and two-bake operation. The primer powder contains modified epoxy resin, polyamide curing agent, etc., which is tightly bonded to the substrate after spraying and curing, providing a basis for the topcoat. The primer curing process allows the coating and substrate molecules to diffuse and penetrate each other, enhancing adhesion. The topcoat powder contains polyester resin, leveling agent and brightener, etc., which is sprayed and cured on the basis of the primer to form a smooth, flat surface with a certain hardness. The topcoat curing improves the coating structure and makes it more dense and uniform. The two-coat and two-bake process allows the coating to form a multi-layered structure with each layer tightly bonded, improving the overall adhesion of the coating and its ability to resist external friction and wear, and significantly improving wear resistance.

[0029] In summary, the present invention effectively improves the adhesion and wear resistance of the low-temperature curing two-coat and two-bake powder coating through the synergistic effect of modified epoxy resin, composite filler treatment and two-coat and two-bake process. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a histogram of wear of each group in the test of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present application provides a low-temperature curing two-coat two-bake powder coating and a preparation and use method thereof.

[0033] Among them, the low-temperature curing two-coat and two-bake powder coating of the present application is composed of 52-56 parts of modified epoxy resin, 22-24 parts of polyamide curing agent, 26-30 parts of polyester resin, 25-28 parts of composite filler, 1-3 parts of leveling agent, 2-3 parts of accelerator, and 0.5-0.8 parts of brightener.

[0034] The modified epoxy resin is prepared by mixing γ-glycidyloxypropyltrimethoxysilane and bisphenol A epoxy resin in a mass ratio of 1-2:12, stirring the mixture at 120° C. at a stirring speed of 200-300 r / min for 2 hours, and cooling the mixture to room temperature. The epoxy value of the bisphenol A epoxy resin is 0.45-0.55 eq / 100 g.

[0035] The composite filler is prepared by mixing calcium carbonate, talcum powder and bentonite in a mass ratio of 40%, 30% and 30%, stirring with a silane coupling agent in a mass ratio of 100:3 in a high-speed mixer at a speed of 1800r / min for 30 minutes, and then adding stearic acid accounting for 2% of the total mass of the filler and continuing to stir for 40 minutes.

[0036] The leveling agent is an acrylic leveling agent with a number average molecular weight of 13500, a glass transition temperature of -22°C, and a surface tension of 25.5 mN / m; the accelerator is a mixture of a silane coupling agent and a titanate coupling agent in a mass ratio of 1:1; and the brightener is nano mica powder.

[0037] In the following examples, the polyester resin used is Yantai Fenglin FL-2007; the glass transition temperature is 60°C, and the acid value is 32-38 mgKOH / g;

[0038] The preferred silane coupling agent is KH-550;

[0039] The titanate coupling agent is TMC-311W;

[0040] The acrylic leveling agent is ZY-1853.

[0041] The use of powder coatings includes primer powder preparation, topcoat powder preparation and two-coat and two-bake process:

[0042] Preparation of primer powder: Modified epoxy resin, polyamide curing agent, accelerator and 60% by weight of composite filler are mixed in proportion, melt-extruded through a twin-screw extruder at 85-100°C and a screw speed of 30r / min, and crushed and sieved to obtain primer powder.

[0043] Preparation of topcoat powder: After mixing the polyester resin, the remaining 40% of the composite filler, the leveling agent and the brightener, the topcoat powder is melt-extruded through a twin-screw extruder at 102-105°C and a screw speed of 45r / min to obtain the topcoat powder.

[0044] Two-coat and two-bake process: after spraying the primer, cure at 100℃ for 10 minutes; after spraying the topcoat, cure at 115℃ for 5 minutes; use electrostatic spraying process, the spray gun voltage is 60-80kV, and the spraying distance is 15-20cm.

[0045] The raw materials and reagents used in the following examples are all commercially available or homemade.

[0046] Example 1

[0047] Preparation of modified epoxy resin: Mix 1 part of γ-glycidyloxypropyltrimethoxysilane with 12 parts of bisphenol A epoxy resin, the epoxy value of bisphenol A epoxy resin is 0.45eq / 100g, react at 120°C and stirring speed of 200r / min for 2 hours, cool to room temperature, and obtain modified epoxy resin.

[0048] Preparation of composite filler: Calcium carbonate, talc and bentonite are weighed and mixed in a mass ratio of 40%, 30% and 30%, and then 100 parts of the mixture and 3 parts of silane coupling agent are stirred in a high-speed stirrer at a speed of 1800 r / min for 30 minutes, and then 2% of stearic acid accounting for the total mass of the filler is added and stirring is continued for 40 minutes to obtain a composite filler.

[0049] Preparation of primer powder: Weigh 52 parts of the modified epoxy resin prepared above, 22 parts of polyamide curing agent, 2 parts of accelerator, and 60% by weight of composite filler, mix them, melt-extrude them through a twin-screw extruder at 85°C and a screw speed of 30 r / min, and crush and sieve to obtain primer powder.

[0050] Preparation of topcoat powder: weigh 26 parts of polyester resin, the remaining 40% by mass of composite filler, 1 part of acrylic leveling agent with a number average molecular weight of 13500, a glass transition temperature of -22°C, a surface tension of 25.5 mN / m, and 0.5 parts of nano-mica powder, mix and melt-extrude through a twin-screw extruder at 102°C and a screw speed of 45 r / min to obtain the topcoat powder.

[0051] Two-coat and two-bake process: Use the electrostatic spraying process to spray the primer powder on the substrate, set the spray gun voltage to 60kV, the spray distance to 15cm, and then cure at 100℃ for 10 minutes; then spray the topcoat powder on the primer coating, keep the spray gun voltage and spray distance unchanged, and cure at 115℃ for 5 minutes.

[0052] Example 2

[0053] Preparation of modified epoxy resin: 1.5 parts of γ-glycidyloxypropyltrimethoxysilane were mixed with 12 parts of bisphenol A epoxy resin, the epoxy value of bisphenol A epoxy resin was 0.5eq / 100g, reacted at 120°C and stirring speed of 250r / min for 2 hours, cooled to room temperature, and obtained modified epoxy resin.

[0054] Preparation of composite filler: the same as the preparation method of composite filler in Example 1.

[0055] Preparation of primer powder: Weigh 54 parts of modified epoxy resin, 23 parts of polyamide curing agent, 2.5 parts of accelerator, and 60% by weight of composite filler, mix them, melt-extrude them through a twin-screw extruder at 90°C and a screw speed of 30 r / min, and crush and sieve to obtain primer powder.

[0056] Preparation of topcoat powder: weigh 28 parts of polyester resin, the remaining 40% by mass of composite filler, 2 parts of acrylic leveling agent with a number average molecular weight of 13500, a glass transition temperature of -22°C, a surface tension of 25.5 mN / m, and 0.6 parts of nano-mica powder, mix and melt-extrude through a twin-screw extruder at 103°C and a screw speed of 45 r / min to obtain the topcoat powder.

[0057] Two-coat and two-bake process: During electrostatic spraying, the spray gun voltage is 70kV and the spraying distance is 18cm. After the primer is sprayed, it is cured at 100℃ for 10 minutes, and after the topcoat is sprayed, it is cured at 115℃ for 5 minutes.

[0058] Example 3

[0059] Preparation of modified epoxy resin: Mix 2 parts of γ-glycidyloxypropyltrimethoxysilane with 12 parts of bisphenol A epoxy resin, the epoxy value of bisphenol A epoxy resin is 0.55eq / 100g, react at 120°C and stirring speed of 300r / min for 2 hours, cool to room temperature, and obtain modified epoxy resin.

[0060] Preparation of composite filler: The operation steps are consistent with those in Example 1.

[0061] Preparation of primer powder: Weigh 56 parts of modified epoxy resin, 24 parts of polyamide curing agent, 3 parts of accelerator, and 60% by weight of composite filler, mix them, melt-extrude them through a twin-screw extruder at 100°C and a screw speed of 30r / min, and crush and sieve to obtain primer powder.

[0062] Preparation of topcoat powder: weigh 30 parts of polyester resin, the remaining 40% by weight of composite filler, 3 parts of acrylic leveling agent with a number average molecular weight of 13500, a glass transition temperature of -22°C, a surface tension of 25.5 mN / m, and 0.8 parts of nano-mica powder, mix and melt-extrude through a twin-screw extruder at 105°C at a screw speed of 45 r / min to obtain the topcoat powder.

[0063] Two-coat and two-bake process: During electrostatic spraying, the spray gun voltage is 80kV and the spraying distance is 20cm. The primer is cured at 100℃ for 10 minutes and the topcoat is cured at 115℃ for 5 minutes.

[0064] Example 4

[0065] Preparation of modified epoxy resin: 1.2 parts of γ-glycidyloxypropyltrimethoxysilane were mixed with 12 parts of bisphenol A epoxy resin, the epoxy value of bisphenol A epoxy resin was 0.48eq / 100g, reacted at 120°C and stirring speed of 220r / min for 2 hours, cooled to room temperature, and obtained modified epoxy resin.

[0066] Preparation of composite filler: The preparation method is the same as that of Example 1.

[0067] Preparation of primer powder: Weigh 53 parts of modified epoxy resin, 22.5 parts of polyamide curing agent, 2.2 parts of accelerator, and 60% by weight of composite filler, mix them, melt-extrude them through a twin-screw extruder at 95°C at a screw speed of 30 r / min, and crush and sieve to obtain primer powder.

[0068] Preparation of topcoat powder: weigh 27 parts of polyester resin, the remaining 40% by mass of composite filler, 1.5 parts of acrylic leveling agent with a number average molecular weight of 13500, a glass transition temperature of -22°C, a surface tension of 25.5 mN / m, and 0.7 parts of nano-mica powder, mix and melt-extrude through a twin-screw extruder at 104°C at a screw speed of 45 r / min to obtain the topcoat powder.

[0069] Two-coat and two-bake process: During electrostatic spraying, the spray gun voltage is 65kV and the spraying distance is 16cm. The primer is cured at 100℃ for 10 minutes and the topcoat is cured at 115℃ for 5 minutes.

[0070] Comparative Example 1

[0071] Based on Example 1, the difference from Example 1 is that the epoxy resin is not modified.

[0072] Comparative Example 2

[0073] Based on Example 1, the difference from Example 1 is that the composite filler is replaced by an equal amount of calcium carbonate.

[0074] test:

[0075] Adhesion test: refer to GB / T 9286-1998 "Scratch test for paint and varnish film" to test and compare the coatings of the embodiment and the comparative example;

[0076] Table 1

[0077] Adhesion / Grade Example 1 0 Example 2 0 Example 3 0 Example 4 0 Comparative Example 1 2 Comparative Example 2 1

[0078] It can be seen from Table 1 that the powder coating prepared in the present invention has excellent adhesion.

[0079] Wear resistance test

[0080] The powder coatings of the embodiments and comparative examples were tested with reference to GB / T 1768-2006 "Determination of abrasion resistance of paints and varnishes - Rotating rubber grinding wheel method", and the abrasion revolution number was set to 1000 revolutions;

[0081] Table 2

[0082] Wear amount g Example 1 0.026 Example 2 0.029 Example 3 0.031 Example 4 0.027 Comparative Example 1 0.026 Comparative Example 2 0.058

[0083] It can be seen from Table 2 that the powder coating prepared by the present invention has excellent wear resistance.

[0084] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all details in detail, nor do they limit the invention to only the specific embodiments described. Obviously, many modifications and changes can be made according to the content of this specification.

Claims

1. A low temperature curing two-coat two-bake powder coating: characterized in that: The following components are included in parts by weight composition: 52-56 parts of modified epoxy resin; 22-24 parts of polyamide curing agent; 26-30 parts of polyester resin; 25-28 parts of composite filler; 1-3 parts of leveling agent; 2-3 parts of accelerator; 0.5-0.8 parts of brightener.

2. A low temperature curing two-coat two-bake powder coating according to claim 1, characterized in that: The modified epoxy resin preparation method is: γ-glycidyloxypropyltrimethoxysilane and bisphenol A epoxy resin were mixed in a mass ratio of 1-2:12, stirred at 120° C. for 2 hours, and cooled to room temperature to obtain a modified epoxy resin; The epoxy value of the bisphenol A epoxy resin is 0.45-0.55 eq / 100 g; the stirring speed during stirring is 200-300 r / min.

3. A low temperature curing two-coat two-bake powder coating according to claim 1, characterized in that: The composite filler preparation method is as follows: Calcium carbonate, talcum powder and bentonite are mixed in a mass ratio of 40%, 30% and 30%, and then stirred with a silane coupling agent in a mass ratio of 100:3 in a high-speed stirrer at a speed of 1800r / min for 30 minutes, and then 2% of the total mass of stearic acid is added and stirred for 40 minutes to obtain.

4. A low temperature curing two-coat two-bake powder coating according to claim 1, characterized in that: The leveling agent is an acrylic leveling agent with a number average molecular weight of 13500, a glass transition temperature of -22°C, and a surface tension of 25.5 mN / m.

5. A low temperature curing two-coat two-bake powder coating according to claim 1, characterized in that: The promoter is a mixture of a silane coupling agent and a titanate coupling agent, and the mass ratio of the two is 1:

1.

6. A low temperature curing two-coat two-bake powder coating according to claim 1, characterized in that: The brightener is nano mica powder.

7. A low temperature curing two-coat two-bake powder coating according to claim 1, characterized in that: The method for using the powder coating comprises the following steps: (1) preparing a primer powder, (2) preparing a topcoat powder, and (3) a two-coating and two-baking process.

8. A low temperature curing two-coat two-bake powder coating according to claim 7, characterized in that: The primer powder is prepared as follows: The modified epoxy resin, polyamide curing agent, accelerator and 60% by weight of composite filler are mixed in proportion, melt-extruded through a twin-screw extruder at 85-100° C. and a screw speed of 30 r / min, and crushed and sieved to obtain a primer powder.

9. A low temperature curing two-coat two-bake powder coating according to claim 7, characterized in that: The topcoat powder is prepared as follows: The polyester resin, the remaining 40% of the composite filler, the leveling agent and the brightener are mixed, and then melt-extruded through a twin-screw extruder at 102-105° C. and a screw speed of 45 r / min to obtain a top coating powder.

10. A low temperature curing two-coat two-bake powder coating according to claim 7, characterized in that: The two-coating and two-baking process is: After spraying the primer, cure at 100°C for 10 minutes; After topcoat spraying, cure at 115°C for 5 minutes; The electrostatic spraying process is adopted, the spray gun voltage is 60-80kV, and the spraying distance is 15-20cm.

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