Highly flexible powder coatings and their preparation methods

Abstract

This invention belongs to the field of powder coating technology, specifically relating to a high-flexibility powder coating and its preparation method, comprising the following steps: Step S1, surface treatment of pigments and fillers using a silane coupling agent and a plasticizer; Step S2, surface coating of the surface-treated pigments and fillers using a thermoplastic polyester resin; Step S3, mixing and stirring the surface-coated pigments and fillers with the main resin and additives, extruding, crushing and sieving to obtain a high-flexibility powder coating. The high-flexibility powder coating and its preparation method of this invention, by using a surface-active treatment agent to modify the pigments and fillers to improve the adhesion between the resin and the pigments and fillers, creatively introduces a plasticizer into the system and further sets up a secondary coating with thermoplastic polyester resin, significantly improving the flexibility of the coating and broadening the application of powder coatings in fields such as powder-coated steel sheets.

Description

Technical Field

[0001] This invention belongs to the field of powder coating technology, specifically relating to a high-flexibility powder coating and its preparation method. Background Technology

[0002] Powder coating is characterized by its environmental friendliness, energy efficiency, high efficiency, and high quality, and has always been a coating method actively promoted in various coating fields. The invention and development of powder coating is actually the process of replacing liquid coatings with powder coatings, commonly known as the "paint-to-powder" conversion.

[0003] In recent decades, powder coatings have developed rapidly and have replaced liquid coatings in many fields, such as furniture, home appliances, building materials, and tools, making powder coating a common coating method. However, liquid coatings are still used in many fields due to a series of technical limitations faced by powder coatings. For example, in the coating of color steel sheets, my country currently coats 27 million tons of color steel sheets annually using liquid coatings.

[0004] To achieve the shift from paint to powder coating in the coating of color-coated steel sheets, both domestic and international researchers have conducted years of technical research to overcome related challenges, gradually resolving issues related to coating technology and coating equipment. For example, after coating, color-coated steel sheets require molding, demanding that the coating possess excellent flexibility; otherwise, cracking will affect the coating's corrosion resistance. This places high flexibility requirements on the color-coated steel sheet coating. The common practice is to synthesize a flexible resin using monomers with high flexibility to increase the coating's flexibility.

[0005] In fact, the research and development of related resin formulations has yielded good results, basically meeting the performance requirements of conventional color steel sheet coatings. However, current resin technology still has limitations: firstly, the cost is too high, and secondly, the flexibility cannot yet meet higher performance requirements. As is well known, color steel sheet coating is a huge industry with extremely high demands on cost and efficiency; any technological achievement in reducing costs will bring significant economic benefits. Therefore, how to further improve the flexibility of powder coatings without increasing costs has become a hot research topic in the industry. In fact, if powder-coated color steel sheets can completely replace liquid-coated color steel sheets, it will represent a huge market, and any cost reduction will bring enormous economic benefits.

[0006] Therefore, there is an urgent need for a method to improve the flexibility of powder coatings, in addition to resin modification. Summary of the Invention

[0007] This invention provides a highly flexible powder coating and its preparation method to solve the problem of insufficient flexibility of existing monomer synthetic resins.

[0008] To solve the above-mentioned technical problems, the present invention provides a method for preparing a high-flexibility powder coating, comprising the following steps: Step S1, surface treatment of pigments and fillers using silane coupling agent and plasticizer; Step S2, surface coating of the surface-treated pigments and fillers using thermoplastic polyester resin; Step S3, mixing and stirring the surface-coated pigments and fillers with the main resin and additives, extruding, crushing and sieving to obtain a high-flexibility powder coating.

[0009] In another aspect, the present invention also provides a highly flexible powder coating obtained by the preparation method described above.

[0010] The beneficial effects of this invention are that the high-flexibility powder coating and its preparation method of this invention, by using a surface-active treatment agent to modify pigments and fillers to improve the adhesion between the resin and pigments and fillers, creatively introduces a plasticizer into the system and further uses thermoplastic polyester resin for secondary coating, which greatly improves the flexibility of the coating and broadens the application of powder coatings in fields such as powder-coated steel sheets.

[0011] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention.

[0012] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] This invention provides a method for preparing a high-flexibility powder coating, comprising the following steps: Step S1, surface treatment of pigments and fillers using a silane coupling agent and a plasticizer; Step S2, surface coating of the surface-treated pigments and fillers using a thermoplastic polyester resin; Step S3, mixing and stirring the surface-coated pigments and fillers with the main resin and additives, extruding, crushing and sieving to obtain a high-flexibility powder coating.

[0015] In this embodiment, the silane coupling agent is preferably γ-glycidoxypropyltrimethoxysilane, which has an epoxy active group in its molecule and has a good cross-linking adsorption effect on inorganic substances; its mass ratio is 0.3-2.5% of the total pigment and filler components.

[0016] In this embodiment, the plasticizer is preferably a phthalate plasticizer, and its mass percentage is 0.3% to 2.5% of the total pigment and filler components.

[0017] In this embodiment, specifically, the phthalate plasticizer includes any one or a combination of dimethyl phthalate, dibutyl phthalate, and dioctyl phthalate.

[0018] In this embodiment, specifically, the pigments and fillers include inorganic pigments and fillers; wherein the inorganic pigments include titanium dioxide, iron oxide red, iron oxide yellow, ultramarine, phthalocyanine blue, and phthalocyanine green; the fillers include barium sulfate, silica fume, mica powder, and glass powder; their function is to fill and enhance properties such as hardness while reducing costs. Because most conventional pigments and fillers are inorganic compounds, they do not readily fuse with resin; insufficient pigments and fillers result in poor hiding power, while excessive addition affects the density and flexibility of the coating. To increase the flexibility of the coating, the first thought is to prepare resins with better flexibility, but this significantly increases costs and has limited effectiveness. This embodiment uses a siloxane coupling agent to treat various pigments and fillers, and adds a plasticizer to improve their compatibility with the resin, thereby improving the flexibility of the coating.

[0019] In this embodiment, specifically and further, it was found that adding a certain amount of thermoplastic polyester resin also significantly increases the flexibility of the powder coating. Improving the flexibility of powder coatings by adding flexible resins or additives to the powder coating formulation is a very common method. The corresponding problem is that too little addition will not have a sufficient effect, while too much addition will affect the powder coating's pulverization efficiency. Through the embodiment, it was found that adding thermoplastic polyester resin during pigment and filler processing better utilizes the toughening effect of the thermoplastic resin. That is, adding the same amount of thermoplastic resin during pigment and filler processing has a better toughening effect than conventionally adding it during powder coating extrusion.

[0020] In this embodiment, the thermoplastic polyester resin is preferably a carboxyl-terminated polyester resin with a molecular weight of 20,000 and a melting temperature of 120°C, provided by Changzhou Bekale Resin Co., Ltd., and its mass percentage is 1-20% of the total pigment and filler components.

[0021] In this embodiment, specifically, the mass ratio of the thermoplastic polyester resin to the pigments and fillers is 5-15:100.

[0022] In this embodiment, specifically, the main resin is a polyester resin cured with triglycidyl isocyanurate; the mass ratio of triglycidyl isocyanurate to polyester resin is 7.5:92.5, and the mass ratio of their total content is 50-90% of the total components; the high-flexibility polyester resin used in this embodiment, a carboxyl-terminated polyester thermosetting resin, is provided by Shanghai Xitai Company, code 0624D.

[0023] In this embodiment, specifically, the additives include a breathable agent and a leveling agent; the breathable agent is preferably benzoin to expel gas and avoid pores; the leveling agent is preferably an acrylic leveling agent.

[0024] Example 1: Example of an untreated titanium dioxide formulation

[0025] 569g of polyester resin (Xitai 0624D), 46g of TGIC, 370g of untreated titanium dioxide (DuPont 902), 10g of acrylic leveling agent, and 5g of benzoin were mixed and extruded. The resulting sheet was ground using a laboratory mill and passed through a 200-mesh sieve. The powder was then sprayed onto a 0.6mm thick steel plate using an electrostatic spray gun and baked in an oven at 280℃ for 80 seconds. The coating properties were tested, and the resulting coating was smooth and even with a gloss level of 52℃ and a T-bending performance of 2T. Cracks were observed under a 10x magnifying glass.

[0026] Example 2: Conventionally processed titanium dioxide formulation example

[0027] Add 20 g of γ-glycidoxypropyltrimethoxysilane to 200 ml of ethanol, then pour the mixture into a mixing jar containing 1000 g of titanium dioxide (DuPont 702). Stir at high speed for 5 minutes, then heat and continue stirring until the temperature reaches approximately 60°C. Remove from heat and dry until the moisture content is less than 0.5%. Set aside for later use.

[0028] Take 569g of polyester resin (Xitai 0624D), 46g of TGIC, 370g of titanium dioxide treated by the above method, 10g of acrylic leveling agent, and 5g of benzoin. Mix them and extrude them into an extruder. The extruded sheet is then ground using a laboratory grinder and passed through a 200-mesh sieve. The resulting powder is sprayed onto a 0.6mm thick steel plate using an electrostatic spray gun and baked in an oven at 280℃ for 80 seconds. The coating performance is then tested. The resulting coating is smooth and even, with a gloss level of 62℃ and a T-bending performance of 1T. Numerous cracks are observed under a 10x magnifying glass.

[0029] Example 3: Titanium dioxide formulation with added plasticizer

[0030] Add 20 g of γ-glycidyl etheroxypropyltrimethoxysilane and 40 g of dioctyl phthalate to 200 ml of ethanol. Mix well and pour into a mixing jar containing 1000 g of titanium dioxide (DuPont 702). Stir at high speed for 5 minutes, then heat and continue stirring until the temperature reaches about 60°C. Remove and dry until the moisture content is less than 0.5%. Set aside for later use.

[0031] Take 569g of polyester resin (Xitai 0624D), 46g of TGIC, 370g of the above-treated titanium dioxide, 10g of acrylic leveling agent, and 5g of benzoin. Mix them and extrude them using an extruder. The extruded sheets are then ground using a laboratory grinder and passed through a 200-mesh sieve. The resulting powder is sprayed onto a 0.6mm thick steel plate using an electrostatic spray gun and baked in an oven at 280℃ for 80 seconds. The coating properties are then tested. The resulting coating is smooth and even, with a gloss level of 69℃, a T-bending performance of 0T, and very little cracking observed under a 10x magnifying glass.

[0032] Example 4: Titanium dioxide formulation co-treated with plasticizer and thermoplastic resin

[0033] Add 20 g of γ-glycidyl etheroxypropyltrimethoxysilane and 40 g of dioctyl phthalate to 200 ml of ethanol. Mix well and pour into a mixing jar containing 1000 g of titanium dioxide (DuPont 702). Stir at high speed for 5 minutes, then heat and continue stirring until the temperature reaches about 60°C. Add 100 g of powdered thermoplastic polyester resin and continue stirring until the temperature in the jar reaches 130°C. Maintain this temperature for 5 minutes, then release and cool. Set aside for later use.

[0034] Take 569g of polyester resin (Xitai 0624D), 46g of TGIC, 370g of the above-treated titanium dioxide, 10g of acrylic leveling agent, and 5g of benzoin. Mix them and extrude them using an extruder. The extruded sheets are then ground using a laboratory grinder and passed through a 200-mesh sieve. The resulting powder is sprayed onto a 0.6mm thick steel plate using an electrostatic spray gun and baked in an oven at 280℃ for 80 seconds. The coating properties are then tested. The resulting coating is smooth and even, with a gloss level of 66℃, a T-bending performance of 0T, and no cracks observed under a 10x magnifying glass.

[0035] Examples 5-7: Examples of thermoplastic resins with different proportions

[0036] Similar to Example 4, the difference was that the proportions of thermoplastic polyester resin and titanium dioxide added were 1%, 5%, and 20%, respectively. The flexibility tests of the resulting powder-coated samples were 1T (significant cracking), 0T (cracking present), and 0T (no cracking). However, at a 20% addition, the powder coating became very difficult to crush.

[0037] As can be seen from the above seven examples, with the same powder formulation, the coating flexibility of the treated titanium dioxide is significantly improved. Adding dioctyl phthalate to the treatment agent further enhances the flexibility, and the coating treated with 10% thermoplastic resin exhibits the best flexibility.

[0038] Examples 8-10: Treatment of Barium Sulfate

[0039] Barium sulfate was treated using the same method as described in Example 4 for treating titanium dioxide. The amounts of thermoplastic polyester added to the formulation were 5%, 10%, and 15%, respectively. Powders were prepared from 185 grams of barium sulfate treated at the three different ratios and 185 grams of titanium dioxide treated in Example 4. The coating samples of the three powders were tested, and the flexibility was 0T (significant cracking); 0T (no cracking); and 0T (no cracking). The powder with 15% thermoplastic polyester resin showed increased grinding difficulty.

[0040] Example 11: Formulation example of treated iron oxide red.

[0041] Add 35 g of γ-glycidyl etheroxypropyltrimethoxysilane and 40 g of dioctyl phthalate plasticizer to 300 ml of ethanol. Pour this mixture into a mixing jar containing 1000 g of iron oxide red and stir at high speed for 5 minutes. Then heat and continue stirring until the temperature reaches approximately 60°C. Add 100 g of powdered thermoplastic polyester resin and continue stirring until the temperature inside the jar reaches 130°C. Maintain this temperature for 5 minutes, then release and cool. Set aside for later use.

[0042] Take 569g of polyester resin (Xitai 0624D), 46g of TGIC, 100g of titanium dioxide treated in Example 4, 150g of barium sulfate treated in Example 9, 100g of iron oxide red treated above, 10g of acrylic leveling agent, and 5g of benzoin. Mix them and extrude them using an extruder. The extruded sheets are then ground using a laboratory grinder and passed through a 200-mesh sieve. The resulting powder is sprayed onto a 0.6mm thick steel plate using an electrostatic spray gun and baked in an oven at 280°C for 80 seconds. The coating flexibility is tested; the T-bend is 0T with no cracking.

[0043] Example 12: Formulation Example of Phthalocyanine Blue Treatment

[0044] Add 35 g of γ-glycidyl etheroxypropyltrimethoxysilane and 40 g of dioctyl phthalate plasticizer to 300 ml of ethanol. Pour this mixture into a mixing jar containing 1000 g of phthalocyanine blue and stir at high speed for 5 minutes. Then heat and continue stirring until the temperature reaches approximately 60°C. Add 100 g of powdered thermoplastic polyester resin and continue stirring until the temperature inside the jar reaches 130°C. Maintain this temperature for 5 minutes, then release and cool. Set aside for later use.

[0045] Take 569g of polyester resin (Xitai 0624D), 46g of TGIC, 100g of titanium dioxide treated in Example 4, 150g of barium sulfate treated in Example 9, 100g of iron oxide red treated above, 10g of acrylic leveling agent, and 5g of benzoin. Mix them and extrude them using an extruder. The extruded sheets are then ground using a laboratory grinder and passed through a 200-mesh sieve. The resulting powder is sprayed onto a 0.6mm thick steel plate using an electrostatic spray gun and baked in an oven at 280°C for 80 seconds. The coating flexibility is then tested; the T-bend is 0T, and there is no cracking.

[0046] In this embodiment, specifically, as can be seen from all the above embodiments, inorganic pigments and fillers treated with plasticizers and thermoplastic polyester resins, when used in powder coatings, can maximize the flexibility of the coating.

[0047] In another aspect, the present invention also provides a highly flexible powder coating obtained by the preparation method described above.

[0048] In summary, the high-flexibility powder coating and its preparation method of the present invention, by modifying pigments and fillers with a surface-active treatment agent to improve the adhesion between the resin and pigments and fillers, creatively introduces a plasticizer into the system and further uses thermoplastic polyester resin for secondary coating, which greatly improves the flexibility of the coating and broadens the application of powder coatings in fields such as powder-coated steel sheets.

[0049] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a highly flexible powder coating, characterized in that, Includes the following steps: Step S1: Surface-treat the pigments and fillers using a silane coupling agent and a plasticizer, and then surface-coat the surface-treated pigments and fillers using a thermoplastic polyester resin. Add 20 g of γ-glycidyl etheroxypropyltrimethoxysilane and 40 g of dioctyl phthalate plasticizer to 200 ml of ethanol. Mix well and pour into a mixing jar containing 1000 g of titanium dioxide. Stir at high speed for 5 minutes, then heat and continue stirring until the temperature reaches about 60°C. Add 100 g of powdered thermoplastic polyester resin and continue stirring until the temperature in the jar reaches 130°C. Maintain this temperature for 5 minutes, then remove and cool for later use. Add 20 g of γ-glycidyl etheroxypropyltrimethoxysilane and 40 g of dioctyl phthalate plasticizer to 200 ml of ethanol. Mix well and pour into a mixing jar containing 1000 g of barium sulfate. Stir at high speed for 5 minutes, then heat and continue stirring until the temperature reaches about 60°C. Add 100 g of powdered thermoplastic polyester resin and continue stirring until the temperature in the jar reaches 130°C. Maintain this temperature for 5 minutes, then remove and cool for later use; or Add 35 g of γ-glycidyl etheroxypropyltrimethoxysilane and 40 g of dioctyl phthalate plasticizer to 300 ml of ethanol. Pour this mixture into a mixing jar containing 1000 g of iron oxide red and stir at high speed for 5 minutes. Then heat and continue stirring until the temperature reaches approximately 60°C. Add 100 g of powdered thermoplastic polyester resin and continue stirring until the temperature inside the jar reaches 130°C. Maintain this temperature for 5 minutes, then remove and cool for later use. Add 35 g of γ-glycidyl oxypropyltrimethoxysilane and 40 g of dioctyl phthalate plasticizer to 300 ml of ethanol, pour into a mixing jar containing 1000 g of phthalocyanine blue, stir at high speed for 5 minutes, then heat and continue stirring until the temperature reaches about 60°C, add 100 g of powdered thermoplastic polyester resin, continue stirring until the temperature inside the jar reaches 130°C, maintain for 5 minutes, release and cool, and set aside for use. Step S2: The surface-coated pigments and fillers are mixed with the main resin and additives, stirred, extruded, crushed and sieved to obtain a high-flexibility powder coating. The thermoplastic polyester resin is a carboxyl-terminated polyester resin with a molecular weight of 20,000 and a melting temperature of 120°C. The main resin is a polyester resin cured with triglycidyl isocyanurate.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the triglycidyl isocyanurate to the polyester resin is 7.5:92.

5.

3. The preparation method according to claim 1, characterized in that, The additives include breathable agents and leveling agents.

4. A highly flexible powder coating obtained by the preparation method according to any one of claims 1-3.