An environmentally friendly matting agent for powder coatings and its preparation method

Abstract

This invention relates to the field of powder coating technology and discloses an environmentally friendly matting agent for powder coatings and its preparation method. The matting agent is made from high-acid-value carboxylic acid resin, pyromellitic acid, 2-phenylimidazolium, N,N'-ethylene bis-stearamide, and epoxidized soybean oil. During melt mixing, pyromellitic acid and 2-phenylimidazolium generate a closed-type catalyst salt precursor in situ, which is used to regulate the coating curing rate and improve gloss uniformity. The preparation method of the matting agent employs a multi-stage extrusion process, with vacuum devolatilization at the end of the extrusion stage. This promotes a ring-opening addition reaction between the epoxidized soybean oil and the free carboxyl groups in the system, covalently anchoring the aliphatic long-chain structure of the epoxidized soybean oil into the resin network. This invention utilizes the catalyst salt precursor to regulate the curing rate and anchors the aliphatic long-chain structure of the epoxidized soybean oil through ring-opening addition, reducing the migration and precipitation of low-molecular-weight components and improving the coating gloss uniformity and pinhole defects.

Description

Technical Field

[0001] This invention relates to the field of powder coating technology, specifically to an environmentally friendly matting agent for powder coatings and its preparation method. Background Technology

[0002] Powder coatings are widely used because they do not contain volatile organic solvents. In practical applications, in order to meet specific decorative appearance requirements or alleviate light pollution, matting agents are usually added to the coating formulation to reduce the surface gloss of the coating film. Conventional matting agents mostly use acrylic resins with active groups such as carboxyl groups and corresponding catalysts. By utilizing the difference in crosslinking rates of different components during the baking and curing process, a micro-rough structure is generated on the surface of the coating film, thereby achieving matting.

[0003] However, existing matting agents have some drawbacks in industrial applications. In traditional matting agent systems, the catalyst components mostly exist in a free physical mixture state. When the powder coating enters the high-temperature baking stage, the reactivity of these free catalysts is often high and difficult to control in stages, which will cause localized excessively fast or uneven cross-linking reactions within the system. This uncontrolled curing rate will eventually lead to uneven gloss distribution on the coating surface.

[0004] On the other hand, in order to reduce the melt viscosity of the system and help disperse the components of each phase, existing matte formulations usually add small molecule waxes or greases as lubricants. Since these small molecule additives are only bonded to the resin matrix by physical van der Waals forces and lack stable chemical bond anchoring, they are likely to migrate and precipitate to the coating surface under the drive of thermal motion during the heat-forming process of powder coating, or even volatilize when heated. This freeing and release of low molecular weight substances often forms tiny pinhole defects on the coating surface, and at the same time, it will destroy the compactness of the internal network structure of the coating, resulting in a decrease in the adhesion, impact resistance and other physical and mechanical properties of the cured coating. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an environmentally friendly matting agent for powder coatings and its preparation method, which solves the problems of uneven gloss caused by the difficulty in controlling the catalytic activity of existing matting agents during baking, and the pinholes in the coating film caused by the easy volatilization and precipitation of small molecule additives.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides an environmentally friendly matting agent for powder coatings, said matting agent being made from the following raw materials in parts by weight:

[0008] High-acid-value carboxylated acrylic resin: 60.0–70.0 parts; pyromellitic acid: 8.0–12.0 parts; 2-phenylimidazolium: 1.5–2.5 parts; N,N'-ethylene bis-stearamide: 15.0–25.0 parts; epoxidized soybean oil: 2.0–5.0 parts; wherein, the pyromellitic acid and 2-phenylimidazolium are melt-mixed to form a closed-type catalyst salt precursor; at least some of the epoxy groups in the epoxidized soybean oil undergo ring-opening addition with the free carboxyl groups in the system, thereby anchoring the aliphatic long-chain structure of the epoxidized soybean oil in the resin network.

[0009] In this invention, the term "high-acid-value carboxylated acrylic resin" refers to a carboxylated acrylic resin whose molecular chain contains a large number of carboxyl reaction sites and can participate in subsequent salt formation and ring-opening addition reactions; the term "free carboxyl groups in the system" includes free carboxyl groups in the high-acid-value carboxylated acrylic resin and residual carboxyl groups in pyromellitic acid that have not fully participated in the salt formation reaction; the term "resin network" refers to a solid resin carrier structure or resin phase structure formed mainly by the high-acid-value carboxylated acrylic resin, and is not limited to the cross-linked network after the coating film is fully cured.

[0010] By adopting the above technical solution, the free carboxyl group in the molecular structure of pyromellitic acid can undergo an in-situ salt formation reaction with 2-phenylimidazolium in an acid-base neutralization manner under the heated melting environment provided by the extruder. After pyromellitic acid donates a proton, 2-phenylimidazolium combines with a proton and is converted into an imidazolium cation, thereby forming a closed catalyst salt precursor, 2-phenylimidazolium-pyromellitic acid salt, in situ. This closed catalyst salt precursor exists in the matting agent as a curing rate regulating component. Due to the formation of a salt structure, this substance has low activity at room temperature or during the normal storage of powder coatings, which can reduce the risk of premature curing of the catalyst.

[0011] When the coating enters the high-temperature baking stage, the salt dissociates upon heating and releases catalytically active 2-phenylimidazole. The free 2-phenylimidazole catalyzes the cross-linking reaction between the carboxyl groups in the additive and the epoxy groups in the coating base, thereby adjusting the curing speed of the system to produce the surface roughness required for matte finish.

[0012] Meanwhile, under the heat and shearing action in the extruder, the epoxy groups in epoxidized soybean oil can undergo ring-opening addition with the free carboxyl groups on the high-acid-value carboxylic acid resin or the residual carboxyl groups of incompletely neutralized pyromellitic acid, forming a hydroxyl-containing ester bond structure. This covalent bonding method anchors the aliphatic long-chain structure of epoxidized soybean oil in the resin network, which can reduce the free volatilization or outward precipitation of low molecular weight substances during the baking process to a certain extent, thereby improving the defects of pinholes on the coating surface.

[0013] In addition, the added N,N'-ethylene bis-stearamide can act as a lubricant in the melt. It is distributed around the resin and catalyst salt, reducing the overall melt viscosity of the system and making the components of each phase more uniformly dispersed. This is beneficial to maintaining the stability of the final coating matte effect.

[0014] Preferably, the high-acid-value carboxylated acrylic resin is made from the following polymeric monomers and initiators in parts by weight: styrene: 32.0-37.0 parts; methyl methacrylate: 35.0 parts; butyl acrylate: 14.5-15.5 parts; methacrylic acid: 12.5-18.5 parts; benzoyl peroxide: 2.0 parts, wherein the high-acid-value carboxylated acrylic resin has an acid value of 81.4-119.8 mgKOH / g and a glass transition temperature of 63.2-73.6℃.

[0015] By adopting the above technical solution, the introduction of methacrylic acid is mainly to provide the necessary free carboxyl groups as reaction sites for subsequent binding with components such as epoxidized soybean oil, and to maintain the crosslinking density required for coating application. Styrene and methyl methacrylate constitute the main skeleton structure, and butyl acrylate is used to adjust the flexibility of the molecular chain. Under this specific ratio, the glass transition temperature of the synthetic resin is controlled between 63.2 and 73.6°C, which can usually reduce the probability of matting additives becoming sticky or clumping when heated during storage.

[0016] Preferably, the N,N'-ethylene bis-stearamide is a micro powder that can pass through a 150-250 mesh sieve and has a melting point of 140-145℃; the epoxidized soybean oil has an epoxy value ≥6.0% and an iodine value ≤3.0gI2 / 100g.

[0017] By adopting the above technical solution, when the particle size of N,N'-ethylene bis-stearamide is in the range of 150 to 250 mesh, it will enter the voids of resin particles during mixing, which can reduce material agglomeration. Setting the epoxy value of epoxidized soybean oil to not less than 6.0% is to retain more active groups to support the ring-opening addition reaction. Controlling its iodine value to not more than 3.0 gI2 / 100g can limit the residual amount of unsaturated double bonds to a certain extent, which is beneficial to improving the antioxidant performance of the system under high temperature conditions and reducing the yellowing phenomenon of coatings.

[0018] A second aspect of the present invention provides a method for preparing a matting agent, used to prepare the matting agent described in any of the technical solutions of the first aspect, comprising the following steps:

[0019] The high acid value carboxylated acrylic resin, pyromellitic acid and 2-phenylimidazolium were mixed to prepare a solid premix.

[0020] The solid premix is ​​fed into an extruder for preliminary melt extrusion, so that pyromellitic acid and 2-phenylimidazole undergo an in-situ salt formation reaction in the molten state to generate a closed catalyst salt precursor.

[0021] In the middle section of the extruder, the N,N'-ethylene bis-stearamide and the epoxidized soybean oil are added and dispersed in the melt;

[0022] Vacuum devolatilization is performed at the end of the extruder to induce an in-situ ring-opening addition reaction in the material.

[0023] The extruded molten material is cooled, crushed, and sieved to obtain the environmentally friendly matting agent for powder coatings.

[0024] By adopting the above technical solution, the material processing combines solid-phase premixing and multi-stage feeding extrusion process. Since pyromellitic acid and 2-phenylimidazole have already melted with the resin in the front stage, the acid-base neutralization reaction can occur first and generate salt precursors. At the same time, N,N'-ethylene bis-stearamide and epoxidized soybean oil are added separately in the middle stage. At this time, the resin melt generated in the front stage just serves as their mixing carrier.

[0025] When the material is being transported to the end, residual small molecule volatiles are removed by vacuuming. The negative pressure environment also promotes the addition reaction inside the system towards the product to a certain extent, thereby promoting at least some of the epoxy groups in the epoxidized soybean oil to undergo in-situ ring-opening addition with the free carboxyl groups, so that the aliphatic long-chain structure of the epoxidized soybean oil is fixed in the resin phase. Thus, the closed catalyst salt precursor formed in the first stage and the aliphatic long-chain anchoring structure formed in the last stage are both retained in the final powder additive.

[0026] Preferably, the step of mixing the high-acid-value carboxylated acrylic resin, pyromellitic acid and 2-phenylimidazolium to obtain a solid premix includes: taking the high-acid-value carboxylated acrylic resin, pyromellitic acid and 2-phenylimidazolium into a high-speed mixer, and dry mixing at room temperature for 10 to 15 minutes at a speed of 350 to 450 rpm to obtain a solid premix.

[0027] By adopting the above technical solution and setting the mixing speed to 350 to 450 rpm, suitable mechanical force can be provided at room temperature to disperse the raw material powder, so that the acidic and alkaline components can be relatively uniformly dispersed on the solid phase layer. This is beneficial for them to contact and undergo neutralization reaction more quickly after entering the extruder and being heated.

[0028] Preferably, the step of feeding the solid premix into an extruder for preliminary melt extrusion, so that pyromellitic acid and 2-phenylimidazole undergo an in-situ salt formation reaction in the molten state to generate a closed catalyst salt precursor includes: continuously feeding the solid premix into the main feed port of a co-rotating parallel twin-screw extruder, setting the barrel temperature of the first to third zones of the extruder to 130-140°C, and maintaining the screw speed at 250-300 rpm, so as to promote the in-situ salt formation reaction between pyromellitic acid and 2-phenylimidazole.

[0029] By adopting the above technical solution, the temperature of the first to third zones of the extruder is maintained at 130 to 140°C. The main purpose is to provide the heat required for the aforementioned salt formation reaction. Under this temperature condition, combined with the corresponding screw speed, the resin system can quickly establish a melt state without causing excessive heating of subsequent materials.

[0030] Preferably, the step of adding the N,N'-ethylene bis-stearamide and the epoxidized soybean oil in the middle section of the extruder and dispersing them in the melt includes: setting the barrel temperature of the fourth to sixth zones of the extruder to 95-105°C, continuously and uniformly adding the N,N'-ethylene bis-stearamide through the side feeder in the fourth zone, wherein the N,N'-ethylene bis-stearamide enters the melt in a micro-powder state that can pass through a 150-250 mesh sieve and is dispersed in the system under the shearing action of the screw, while simultaneously continuously injecting the epoxidized soybean oil in the fifth zone through a metering pump.

[0031] By adopting the above technical solution, the temperature of the barrel in the middle section is reduced to 95 to 105°C, which can reduce the probability of unintended thermal degradation of epoxidized soybean oil at high temperature. With the help of side feeding and metering pump injection, liquid soybean oil and powdered amide substances are directly mixed into the interior of the resin melt that has been formed in the early stage under the continuous shearing of the screw.

[0032] Preferably, the step of performing vacuum devolatilization at the end of the extruder to induce in-situ ring-opening addition reaction of the material includes: turning on the water ring vacuum pump in the penultimate zone of the extruder, maintaining the barrel temperature at 95-105°C, controlling the internal vacuum gauge pressure at -0.095MPa to -0.085MPa, and controlling the residence time of the material in this vacuum zone at 15-25s.

[0033] By adopting the above technical solution, maintaining a residence time of 15 to 25 seconds under the set negative pressure and temperature, the vacuum operation can remove some of the volatile byproducts generated inside the system. According to the principle of reaction equilibrium, the removal of small molecules can usually promote the further reaction of free groups, thereby increasing the amount of chemical bonding between them.

[0034] Preferably, the step of cooling, crushing and sieving the extruded molten material to obtain the environmentally friendly matting agent for powder coatings includes: guiding the molten material extruded from the extruder head to a conveyor belt cooling tablet press to roll it into a sheet with a thickness of 1.0 to 2.0 mm, cooling it to room temperature, crushing it with a pulverizer and passing it through a 180 to 220 mesh vibrating screen to obtain the environmentally friendly matting agent for powder coatings.

[0035] By adopting the above technical solution, after the extruded molten product is tableted and cooled to room temperature, the movement of macromolecular chain segments inside the system basically stops, and the microstructure of the material gradually becomes fixed. By limiting the tablet thickness to 1.0 to 2.0 mm and cooperating with 180 to 220 mesh sieving, a final additive product with relatively uniform particle size can be obtained, which makes it have good dispersion compatibility when used in combination with coating base materials.

[0036] This invention provides an environmentally friendly matting agent for powder coatings and its preparation method. It has the following beneficial effects:

[0037] 1. This invention generates a closed catalyst salt precursor in situ during the melting process of pyromellitic acid and 2-phenylimidazole, which makes the system relatively chemically inert when stored at room temperature. During the high-temperature baking stage of the coating, the system is heated and dissociates to release catalytically active substances, thereby regulating the cross-linking and curing rate of the resin system and improving the problem of uneven coating gloss caused by uncontrollable catalytic activity.

[0038] 2. This invention, by combining a vacuum devolatilization process at the end of the extrusion stage, promotes the ring-opening addition reaction between the epoxy groups in epoxidized soybean oil and the free carboxyl groups in the system. This anchors the aliphatic long-chain structure of epoxidized soybean oil in a covalently bonded manner within a resin network or resin phase structure mainly composed of high-acid-value carboxylic acid resin. This reduces the free volatilization or outward precipitation of low molecular weight substances under high-temperature conditions, lowers the probability of pinhole defects on the coating surface, and maintains the physical and mechanical properties.

[0039] 3. This invention employs a multi-stage extrusion feeding process and independently adds N,N'-ethylene bis-stearamide with a specific particle size range in the middle stage. By utilizing the characteristic of this component to reduce the local melt viscosity after heating, the micro-dispersion state between the catalytic component and the resin matrix in the system is improved. At the same time, it avoids the slippage phenomenon caused by low-melting-point lipids at the main feed port, maintaining the continuity of the extrusion process. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the local infrared spectral transmittance curves of Embodiment 1 and Comparative Example 5 of the present invention;

[0041] Figure 2 This is a schematic diagram of the differential scanning calorimetry test curves of Embodiment 1 and Comparative Example 2 of the present invention;

[0042] Figure 3 This is a schematic diagram of the zinc emission spectrum test curves of Example 1 and Comparative Example 1 of the present invention;

[0043] Figure 4 This is a schematic diagram of the interlayer peeling force and displacement curves of Embodiment 1, Comparative Example 1, and Comparative Example 3 of the present invention;

[0044] Figure 5 This is a schematic diagram of the 60° gloss scanning curves of the coating surface of Embodiment 1 and Comparative Example 4 of the present invention;

[0045] Figure 6 This is a schematic diagram of the long-wave and short-wave undulation value scanning curves of the coating surface in Embodiment 1, Comparative Example 1, and Comparative Example 4 of the present invention. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0047] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0048] Styrene, CAS number 100-42-5, purity ≥99.5%.

[0049] Methyl methacrylate, CAS number 80-62-6, purity ≥99.5%.

[0050] Butyl acrylate, CAS number 141-32-2, purity ≥99.5%.

[0051] Methacrylic acid, CAS number 79-41-4, purity ≥99.5%.

[0052] Benzoyl peroxide, CAS number 94-36-0, purity ≥99.0%.

[0053] Xylene, CAS number 1330-20-7.

[0054] Pyromellitic acid, CAS number 89-05-4, purity ≥99.0%, melting point 281℃ to 284℃, contains four free carboxyl groups in its molecular structure.

[0055] 2-Phenylidene, CAS No. 670-96-2, purity ≥98.0%, melting point 142℃ to 148℃.

[0056] N,N'-Ethylene bis-stearamide, CAS No. 110-30-5, purity ≥98.0%, can pass through a 200-mesh sieve, melting point 140℃ to 145℃.

[0057] Epoxidized soybean oil, CAS number 8013-07-8, epoxy value ≥6.0%, iodine value ≤3.0gI2 / 100g.

[0058] 2-Mercaptobenzothiazole zinc salt, CAS No. 155-04-4, purity ≥98.0%.

[0059] Polyethylene wax, CAS number 9002-88-4, has a softening point of 100℃ to 110℃ and can pass through a 150-250 mesh sieve.

[0060] Preparation Example 1:

[0061] This preparation example provides a method for preparing a high-acid-value carboxylated acrylic resin, including the following steps:

[0062] 35.0 parts by weight of styrene, 35.0 parts by weight of methyl methacrylate, 14.5 parts by weight of butyl acrylate and 15.5 parts by weight of methacrylic acid were mixed evenly, and 2.0 parts by weight of benzoyl peroxide were added and stirred to dissolve, thus obtaining a monomer mixture.

[0063] Add 45.0 parts by weight of xylene to the reactor, purge with nitrogen for protection, start stirring and heat to 120°C.

[0064] The monomer mixture obtained in the first step was added dropwise to the reaction vessel at a uniform rate over 3 hours. After the addition was completed, the reaction was continued at 120°C for 2 hours.

[0065] The reactor was heated to 190℃, and the vacuum system was turned on to draw the vacuum gauge pressure to -0.09MPa. This was maintained for 1.5 hours to remove xylene and unreacted small molecule monomers. The material was discharged while hot, cooled, and pulverized to obtain high acid value carboxylated acrylic resin A1. The acid value of the resin was 101.2mgKOH / g, and the glass transition temperature was 68.5℃.

[0066] Preparation Example 2:

[0067] This preparation example provides a method for preparing a high-acid-value carboxylated acrylic resin, including the following steps:

[0068] 37.0 parts by weight of styrene, 35.0 parts by weight of methyl methacrylate, 15.5 parts by weight of butyl acrylate and 12.5 parts by weight of methacrylic acid were mixed evenly, and 2.0 parts by weight of benzoyl peroxide were added and stirred to dissolve, thus obtaining a monomer mixture.

[0069] Add 45.0 parts by weight of xylene to the reactor, purge with nitrogen for protection, start stirring and heat to 120°C.

[0070] The monomer mixture obtained in the first step was added dropwise to the reaction vessel at a uniform rate over 3 hours. After the addition was completed, the reaction was continued at 120°C for 2 hours.

[0071] The reactor was heated to 190℃, and the vacuum system was turned on to draw the vacuum gauge pressure to -0.09MPa. This was maintained for 1.5 hours to remove xylene and unreacted small molecule monomers. The material was discharged while hot, cooled, and pulverized to obtain high acid value carboxylated acrylic resin A2. The resin was tested and found to have an acid value of 81.4 mgKOH / g and a glass transition temperature of 63.2℃.

[0072] Preparation Example 3:

[0073] This preparation example provides a method for preparing a high-acid-value carboxylated acrylic resin, including the following steps:

[0074] 32.0 parts by weight of styrene, 35.0 parts by weight of methyl methacrylate, 14.5 parts by weight of butyl acrylate and 18.5 parts by weight of methacrylic acid were mixed evenly, and 2.0 parts by weight of benzoyl peroxide were added and stirred to dissolve, thus obtaining a monomer mixture.

[0075] Add 45.0 parts by weight of xylene to the reactor, purge with nitrogen for protection, start stirring and heat to 120°C.

[0076] The monomer mixture obtained in the first step was added dropwise to the reaction vessel at a uniform rate over 3 hours. After the addition was completed, the reaction was continued at 120°C for 2 hours.

[0077] The reactor was heated to 190°C, and the vacuum system was turned on to draw the vacuum gauge pressure to -0.09 MPa. This was maintained for 1.5 hours to remove xylene and unreacted small molecule monomers. The material was discharged while hot, cooled, and pulverized to obtain high acid value carboxylated acrylic resin A3. The resin was tested and found to have an acid value of 119.8 mg KOH / g and a glass transition temperature of 73.6°C.

[0078] Example 1:

[0079] This embodiment provides a method for preparing an environmentally friendly matting agent for powder coatings, comprising the following steps:

[0080] Take 65.0 parts by weight of high acid value carboxylated acrylic resin A1, 10.09 parts by weight of pyromellitic acid and 1.91 parts by weight of 2-phenylimidazolium, put the above materials into a high-speed mixer, and dry mix at room temperature for 12 minutes at 400 rpm to obtain a solid premix.

[0081] The solid premixed material is continuously fed into the main feed port of the co-rotating parallel twin-screw extruder. The barrel temperature of the first to third zones of the extruder is set at 135°C, and the screw speed is maintained at 280 rpm.

[0082] The barrel temperature of the extruder from the fourth to the sixth zone is set to 100℃. 20.0 parts by weight of N,N'-ethylene bis-stearamide are continuously and uniformly added through the side feeder in the fourth zone. N,N'-ethylene bis-stearamide enters the melt in a micro powder state that can pass through a 200-mesh sieve and is dispersed in the system under the shearing action of the screw. At the same time, 3.0 parts by weight of epoxidized soybean oil are continuously injected into the fifth zone through a metering pump.

[0083] Turn on the water ring vacuum pump in the second-to-last zone of the extruder, maintain the barrel temperature at 100℃, control the internal vacuum gauge pressure at -0.09MPa, and control the material residence time in this vacuum zone to 20s.

[0084] The molten material extruded from the extruder head is guided to a track-cooled tablet press and rolled into 1.5mm thick sheets. After cooling to room temperature, the sheets are crushed by a pulverizer and passed through a 200-mesh vibrating sieve to obtain an environmentally friendly matting agent for powder coatings.

[0085] Example 2:

[0086] This embodiment provides a method for preparing an environmentally friendly matting agent for powder coatings, comprising the following steps:

[0087] Take 70.0 parts by weight of high acid value carboxylated acrylic resin A2, 8.18 parts by weight of pyromellitic acid and 2.32 parts by weight of 2-phenylimidazolium, put the above materials into a high-speed mixer, and dry mix at room temperature for 13 minutes at 420 rpm to obtain a solid premix.

[0088] The solid premixed material is continuously fed into the main feed port of the co-rotating parallel twin-screw extruder. The barrel temperature of the first to third zones of the extruder is set at 135°C, and the screw speed is maintained at 280 rpm.

[0089] The barrel temperature of the extruder from the fourth to the sixth zone is set to 100℃. 15.0 parts by weight of N,N'-ethylene bis-stearamide are continuously and uniformly added through the side feeder in the fourth zone. N,N'-ethylene bis-stearamide enters the melt in a micro powder state that can pass through a 220-mesh sieve and is dispersed in the system under the shearing action of the screw. At the same time, 4.5 parts by weight of epoxidized soybean oil are continuously injected into the fifth zone through a metering pump.

[0090] Turn on the water ring vacuum pump in the second-to-last zone of the extruder, maintain the barrel temperature at 100℃, control the internal vacuum gauge pressure at -0.09MPa, and control the material residence time in this vacuum zone to 20s.

[0091] The molten material extruded from the extruder head is guided to a track-cooled tablet press and rolled into 1.8mm thick sheets. After cooling to room temperature, the sheets are crushed by a pulverizer and passed through a 200-mesh vibrating sieve to obtain an environmentally friendly matting agent for powder coatings.

[0092] Example 3:

[0093] This embodiment provides a method for preparing an environmentally friendly matting agent for powder coatings, comprising the following steps:

[0094] Take 60.0 parts by weight of high acid value carboxylated acrylic resin A3, 11.39 parts by weight of pyromellitic acid and 1.61 parts by weight of 2-phenylimidazolium, put the above materials into a high-speed mixer, and dry mix at room temperature for 11 minutes at 380 rpm to obtain a solid premix.

[0095] The solid premixed material is continuously fed into the main feed port of the co-rotating parallel twin-screw extruder. The barrel temperature of the first to third zones of the extruder is set at 135°C, and the screw speed is maintained at 280 rpm.

[0096] The barrel temperature of the extruder from the fourth to the sixth zone is set to 100℃. 25.0 parts by weight of N,N'-ethylene bis-stearamide are continuously and uniformly added through the side feeder in the fourth zone. N,N'-ethylene bis-stearamide enters the melt in a micro powder state that can pass through a 180-mesh sieve and is dispersed in the system under the shearing action of the screw. At the same time, 2.0 parts by weight of epoxidized soybean oil are continuously injected into the fifth zone through a metering pump.

[0097] Turn on the water ring vacuum pump in the second-to-last zone of the extruder, maintain the barrel temperature at 100℃, control the internal vacuum gauge pressure at -0.09MPa, and control the material residence time in this vacuum zone to 20s.

[0098] The molten material extruded from the extruder head is guided to a track-cooled tablet press and rolled into 1.2mm thick sheets. After cooling to room temperature, the sheets are crushed by a pulverizer and passed through a 200-mesh vibrating sieve to obtain an environmentally friendly matting agent for powder coatings.

[0099] Example 4:

[0100] This embodiment provides a method for preparing an environmentally friendly matting agent for powder coatings, comprising the following steps:

[0101] Take 65.0 parts by weight of high acid value carboxylated acrylic resin A1, 10.09 parts by weight of pyromellitic acid and 1.91 parts by weight of 2-phenylimidazolium, put the above materials into a high-speed mixer, and dry mix at room temperature for 10 minutes at 350 rpm to obtain a solid premix.

[0102] The solid premixed material is continuously fed into the main feed port of the co-rotating parallel twin-screw extruder. The barrel temperature of the first to third zones of the extruder is set at 130°C, and the screw speed is maintained at 250 rpm.

[0103] The barrel temperature of the extruder from the fourth to the sixth zone is set to 95℃. 20.0 parts by weight of N,N'-ethylene bis-stearamide are continuously and uniformly added through the side feeder in the fourth zone. N,N'-ethylene bis-stearamide enters the melt in a micro powder state that can pass through a 150-mesh sieve and is dispersed in the system under the shearing action of the screw. At the same time, 3.0 parts by weight of epoxidized soybean oil are continuously injected into the fifth zone through a metering pump.

[0104] Turn on the water ring vacuum pump in the second-to-last zone of the extruder, maintain the barrel temperature at 95℃, control the internal vacuum gauge pressure at -0.085MPa, and control the material residence time in this vacuum zone to 15s.

[0105] The molten material extruded from the extruder head is guided to a track-cooled tablet press and rolled into 1.0 mm thick sheets. After cooling to room temperature, the sheets are crushed by a pulverizer and passed through a 180-mesh vibrating sieve to obtain an environmentally friendly matting agent for powder coatings.

[0106] Example 5:

[0107] This embodiment provides a method for preparing an environmentally friendly matting agent for powder coatings, comprising the following steps:

[0108] Take 65.0 parts by weight of high acid value carboxylated acrylic resin A1, 10.09 parts by weight of pyromellitic acid and 1.91 parts by weight of 2-phenylimidazolium, put the above materials into a high-speed mixer, and dry mix at room temperature for 15 minutes at 450 rpm to obtain a solid premix.

[0109] The solid premixed material is continuously fed into the main feed port of the co-rotating parallel twin-screw extruder. The barrel temperature of the first to third zones of the extruder is set at 140°C, and the screw speed is maintained at 300 rpm.

[0110] The barrel temperature of the extruder from the fourth to the sixth zone is set at 105℃. 20.0 parts by weight of N,N'-ethylene bis-stearamide are continuously and uniformly added through the side feeder in the fourth zone. N,N'-ethylene bis-stearamide enters the melt in a micro powder state that can pass through a 250-mesh sieve and is dispersed in the system under the shearing action of the screw. At the same time, 3.0 parts by weight of epoxidized soybean oil are continuously injected into the fifth zone through a metering pump.

[0111] Turn on the water ring vacuum pump in the penultimate zone of the extruder, maintain the barrel temperature at 105℃, control the internal vacuum gauge pressure at -0.095MPa, and control the material residence time in this vacuum zone at 25s.

[0112] The molten material extruded from the extruder head is guided to a track-cooled tablet press and rolled into 2.0mm thick sheets. After cooling to room temperature, the sheets are crushed by a pulverizer and passed through a 220-mesh vibrating sieve to obtain an environmentally friendly matting agent for powder coatings.

[0113] Comparative Example 1:

[0114] Compared with Example 1, the differences are as follows: 10.09 parts by weight of pyromellitic acid and 1.91 parts by weight of 2-phenylimidazolium were replaced with 12.00 parts by weight of 2-mercaptobenzothiazole zinc salt; 20.0 parts by weight of N,N'-ethylene bis-stearamide were replaced with 20.0 parts by weight of polyethylene wax, and 3.0 parts by weight of epoxidized soybean oil were not added, resulting in a total of 97.0 parts by weight of the comparative additive formulation; the water ring vacuum pump was not turned on to maintain atmospheric pressure exhaust, and all other aspects were the same.

[0115] Comparative Example 2:

[0116] Compared with Example 1, the difference is that 10.09 parts by weight of pyromellitic acid is not added, and the 10.09 parts by weight of pyromellitic acid is replaced with an equal weight of 2-phenylimidazole, that is, the total amount of 2-phenylimidazole added is 12.00 parts by weight, and the rest are the same.

[0117] Comparative Example 3:

[0118] The difference from Example 1 is that N,N'-ethylene bis-stearamide was replaced with an equal weight of polyethylene wax, otherwise the same.

[0119] Comparative Example 4:

[0120] Compared with Example 1, the difference is that 3.0 parts by weight of epoxidized soybean oil is not added in the third step, and the total amount of the comparative auxiliary agent formula is 97.0 parts by weight, while the rest are the same.

[0121] Comparative Example 5:

[0122] Compared with Example 1, the difference is that the water ring vacuum pump is not turned on in the fourth step, and atmospheric pressure is maintained for exhaust; the rest are the same.

[0123] Test Example 1:

[0124] This test example is used to test the intrinsic molecular structure characteristics, thermal properties, and curing latency of the additive. The specific steps are as follows:

[0125] Powder samples prepared in Examples 1, 2, and 3, as well as Comparative Examples 2 and 5, were selected as test objects.

[0126] Molecular structural characteristics were determined using Fourier transform infrared spectroscopy. Approximately 1.5 mg of each of the above samples was mixed and ground with 200 mg of dry potassium bromide powder, and the samples were prepared using the pellet method. The testing was conducted at room temperature, with the scanning range set to 4000 cm⁻¹. -1 Up to 400cm -1 The resolution is 4cm. -1 The scan was performed 32 times. After baseline correction of the obtained spectra, the main data was recorded at 825 cm⁻¹. -1 The transmittance of the characteristic peaks of nearby epoxy groups, and 3300 cm⁻¹ -1 The peak position of the stretching vibration peak of the amide NH in the vicinity.

[0127] The thermal properties and curing latency of the samples were tested using a differential scanning calorimeter. 5.2 mg to 6.5 mg of the above samples were placed in a standard aluminum crucible and capped. An empty crucible was used as a reference. High-purity nitrogen was introduced into the test environment at a flow rate of 50 mL / min. The initial temperature was set to 20 °C and the temperature was linearly increased to 250 °C at a heating rate of 10 °C / min. The glass transition temperature and the onset temperature of curing exotherm were recorded and extracted for each sample.

[0128] The test results are shown in Table 1.

[0129] Table 1. Infrared spectral data, thermal properties, and curing latency test data for each embodiment and comparative example:

[0130] From Table 1 and Appendix Figure 1 and attached Figure 2 The data obtained are:

[0131] Examples 1 to 3 were performed at 825cm. -1 The transmittance at this point is above 95%, and no obvious characteristic absorption peaks were observed. The transmittance at this point in Comparative Example 5 is 72.4%, and the characteristic peaks of epoxy groups are retained. This indicates that in the preparation process of the examples, the epoxy groups in the epoxidized soybean oil are relatively fully consumed. The vacuum treatment at the end of the extrusion process is beneficial for removing volatiles and gases, increasing the probability of interfacial contact between materials, and promoting the ring-opening addition reaction between carboxyl groups and epoxy groups in the system.

[0132] The glass transition temperature of Comparative Example 5 was 52.3°C, which was lower than that of Example 1 (65.4°C). This is related to the presence of some unreacted free epoxidized soybean oil in Comparative Example 5, which played a plasticizing role in the matrix and increased the degree of freedom of chain segment movement. The curing exothermic onset temperature of Comparative Example 2 was 112.5°C, which was lower than that of Example 1 (158.2°C). This was because pyromellitic acid was absent from in-situ salt formation, and the catalytic groups in the system initiated the cross-linking reaction at a lower temperature.

[0133] Example sample at 3279cm -1 Up to 3284cm -1 The change in the peak position of the amide NH stretching vibration in the range reflects the formation of the hydrogen bond network inside the system. At the same time, it can keep the organic salt in a closed state at a lower temperature, while it dissociates and exerts a catalytic effect above the set curing temperature.

[0134] Test Example 2:

[0135] This test case is used to test the safety and stability of the additive processing and the anti-caking storage performance of the finished product. The specific steps are as follows:

[0136] Powder samples prepared in Examples 1, 2, and 3, as well as Comparative Examples 2 and 5, were selected as experimental test objects.

[0137] The melt flow characteristics of the samples were determined using a melt flow rate meter. The test temperature of the barrel was set to 135℃, the constant temperature standing time was 5 minutes, a standard loading weight of 2.16 kg was used, the automatic cutting device was turned on, the time interval was set to 30 seconds, and the melt sample flowing out within 10 minutes was collected. After cooling, the sample was weighed using an analytical balance, and the melt flow rate data of each sample were calculated and recorded.

[0138] To conduct an accelerated anti-caking storage experiment for powder, 50.0g of powder was taken from each sample and placed into a cylindrical glass graduated cylinder with an inner diameter of 50mm. A layer of polytetrafluoroethylene gasket was laid on the powder surface, and a 1.0kg counterweight was placed on top of the gasket to simulate the stacking and siloing state.

[0139] The graduated cylinder containing the sample was moved into a constant temperature and humidity test chamber. The temperature was set at 40℃ and the relative humidity at 75%. The chamber was left for 30 consecutive days. After the set time was reached, the sample was removed, the weights and pads were removed, and the block sample was naturally poured into a 30-mesh standard test sieve with a collection tray.

[0140] Place the test sieve on a standard vibrating sieve, set the amplitude to 1.5 mm, vibrate continuously for 5 minutes, collect and weigh the mass of powder that passes through the 30-mesh sieve, calculate its percentage of the total mass of the initial sample, and record it as the sieve penetration rate.

[0141] The test results are shown in Table 2.

[0142] Table 2. Test data on melt flow rate and sieve penetration rate for each embodiment and comparative example:

[0143] From the data in Table 2, we can obtain:

[0144] The melt flow rate of Comparative Example 2 was only 1.4, and its fluidity was relatively low. This is consistent with the aforementioned mechanism, indicating that Comparative Example 2 underwent a premature cross-linking reaction under the test condition of 135℃, which led to an increase in viscosity.

[0145] The melt flow rate of the sample in the example was between 22.3 and 27.6, indicating that its precursor structure has good stability at the processing temperature, which is beneficial to ensuring the continuity of the processing technology.

[0146] The melt flow rate of Comparative Example 5 was 34.2, and its sieve clearance rate after 30 days of storage was 11.7%, indicating that the free oily components increased the short-term fluidity of the system, but under pressure, they aggravated the interfacial adhesion between powder particles, causing agglomeration.

[0147] The sieve penetration rate of the sample in the examples remained above 96.0%, indicating that anchoring liquid components through chemical fixation can reduce the powder compaction effect caused by free oil and maintain the long-term physical stability of the material.

[0148] Test Example 3:

[0149] This test example is used to test the residual heavy metals in powder coatings containing different additives and the interfacial mechanical properties under multilayer coating conditions. The specific steps are as follows:

[0150] The powder additives prepared in Examples 1, 2, and 3, as well as Comparative Examples 1 and 3, were selected as experimental comparison objects.

[0151] Premixing is carried out according to a fixed base powder formula. The base powder formula includes 93% curable carboxylated polyester powder base material, 5% of the above-mentioned auxiliary materials and 2% conventional leveling and benzoin components by mass fraction. The curable carboxylated polyester powder base material is prepared by premixing carboxylated polyester resin and its matching curing agent according to the equivalent ratio recommended by the supplier. It is then melt-extruded at 100°C using a twin-screw extruder, cooled and pressed into sheets, and pulverized to an average particle size of about 40μm to obtain the finished powder coating.

[0152] The prepared powder coating was evenly sprayed onto the surface of a standard cold-rolled steel plate using an electrostatic spray gun, and then cured in an oven at 200°C for 15 minutes to obtain a single-layer cured sample. About 0.2g of the cured coating sample was scraped off with a knife and placed in a microwave digester with nitric acid for thorough acid digestion.

[0153] After the digestion solution was brought to a final volume, zinc was quantitatively detected using inductively coupled plasma atomic emission spectrometry (ICP-AES). The intensity of the characteristic emission lines of zinc was monitored. The method detection limit for zinc was 5.0 mg / kg. Results below this detection limit were recorded as not detected.

[0154] A new double-layer recoated sample was prepared for interlayer peel force testing. The same powder coating was directly electrostatically sprayed onto the surface of the cured sample without any mechanical polishing. A polyimide film was inserted at one end as an isolation strip to reserve the peeling end, and then it was placed at 200°C for another 15 minutes for curing.

[0155] The double-layer recoated sample was fixed on the universal testing machine. The pre-reserved peeling end of the upper layer was clamped in the moving fixture. The tensile speed was set to 50 mm / min, and a 180° peel test was performed. The data of peel force change with displacement fed back by the testing machine sensor were recorded to form the interlayer peel force and displacement curve. The force value of the effective peeling range was extracted, and the average 180° interlayer peel strength was calculated per unit width.

[0156] The test results are shown in Table 3.

[0157] Table 3. Heavy metal detection levels and interlaminar mechanical test data for each embodiment and comparative example:

[0158] From Table 3 and Appendix Figure 3 and attached Figure 4 The data obtained are:

[0159] The sample of Comparative Example 1 showed a zinc residue of 1856.4 mg / kg; while the zinc content in the test system of the present invention, including the examples, was below the detection limit. This indicates that the technical solution of using specific acid-base organic compounds to form salt precursors reduces the probability of introducing heavy metal elements from traditional catalysts, provided that it has the corresponding catalytic activity.

[0160] The average 180° interlayer peel strength of the system in the examples ranged from 7.95 N / mm to 8.42 N / mm, while the peel strength of Comparative Example 1 and Comparative Example 3 was relatively low, at 1.13 N / mm and 1.45 N / mm, respectively. The polyethylene wax molecules used in Comparative Example 1 and Comparative Example 3 lacked polar groups, and were prone to migrate to the coating surface during the high-temperature curing stage, thereby forming a low surface energy layer on the surface, which hindered interlayer adhesion during the recoating process.

[0161] The system in the example uses a component containing amide bonds. The hydrogen bonding between the amide bond and the free carboxyl group limits the excessive diffusion and precipitation of the chain segments to the outermost surface. This allows the underlying coating to retain appropriate surface polarity, which is beneficial for the secondary spray coating to form interfacial wetting and adhesion with it, thereby reducing the risk of peeling between recoating layers.

[0162] Test Example 4:

[0163] This test example is used to test the optical matting properties and macroscopic leveling of powder coatings containing different additives. The specific steps are as follows:

[0164] The powder additives prepared in Examples 1, 2, and 3, as well as Comparative Examples 1 and 4, were selected as experimental subjects. The powder coating products were prepared according to the bottom powder formulation and melt extrusion process described in Test Example 3. The powder coatings were electrostatically sprayed onto standard cold-rolled steel plates and cured in an oven at 200°C for 15 minutes. The cured test samples were then cooled to obtain the cured test samples.

[0165] The gloss of the sample was measured using a miniature multi-angle gloss meter. After calibrating the instrument, five test areas were randomly selected on the sample surface. The incident geometric angle was set to 60°, and the gloss values ​​were read. The five sets of data were recorded and their arithmetic mean was calculated as the 60° gloss of the sample. Three samples were prepared and tested in parallel for each group of samples. The final result was the average of the test results of the three samples.

[0166] The leveling of the sample surface was evaluated using a miniature corrugated scanner, also known as an orange peel analyzer. The instrument was attached to the sample surface and slid along the longitudinal direction at a constant speed for 10 cm. The instrument recorded the surface contour data through the principle of laser optical reflection and extracted and calculated the surface long-wave undulation value, which corresponds to a wavelength range of 1.2 mm to 12 mm, and the surface short-wave undulation value, which corresponds to a wavelength range of 0.3 mm to 1.2 mm. The relevant data were recorded. The higher the values ​​of the surface long-wave undulation value and the surface short-wave undulation value, the more obvious the surface undulation and the worse the leveling of the corresponding wavelength band. Each group of samples was tested in parallel for 3 times, and the final result was the average value.

[0167] The test results are shown in Table 4.

[0168] Table 4. Test data on coating gloss and surface roughness for each embodiment and comparative example:

[0169] From Table 4 and Appendix Figure 5 and attached Figure 6 The data obtained are:

[0170] The surface long-wave undulation values ​​of Comparative Example 1 and Comparative Example 4 reached 68.7 and 88.5 respectively, and their surface macroscopic undulations were relatively obvious. The zinc-containing metal salt used in Comparative Example 1 had high reactivity in the early stage of baking, which caused the powder melt to gel in advance. The system of Comparative Example 4 lacked grafted long-chain oily components and lacked corresponding viscosity reduction and lubrication rheological effects. These factors caused the coating to solidify before it was fully leveled, resulting in a rough surface structure.

[0171] The surface long-wave undulation values ​​of Examples 1 to 3 are all below 20, and the surface undulations are relatively gentle. At the same time, their 60° gloss is maintained in the range of 2.1% to 3.4%. The epoxidized soybean oil aliphatic long-chain structure grafted in the extrusion stage of the examples can improve the degree of freedom of movement of local chain segments and reduce melt viscosity in the early stage of heating during the final coating, thus providing a leveling window for the coating film before curing.

[0172] As the temperature rises and the time increases, the organic salts dissociate and release active catalytic groups, which creates a difference in crosslinking rate and microscopic volume shrinkage inside and outside the system. This helps to improve the matting effect of the coating while maintaining the smoothness of the overall appearance.

[0173] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An environmentally friendly matting agent for powder coatings, characterized in that, The matting agent is made from the following raw materials in parts by weight: High acid value carboxylated acrylic resin: 60.0–70.0 parts; Pyromellitic acid: 8.0–12.0 parts; 2-Phenylidene imidazole: 1.5–2.5 parts; N,N'-Ethylene bis-stearamide: 15.0–25.0 parts; Epoxidized soybean oil: 2.0–5.0 parts; In this process, pyromellitic acid and 2-phenylimidazolium are melt-mixed to form a closed catalyst salt precursor; at least some of the epoxy groups in the epoxidized soybean oil undergo ring-opening addition with the free carboxyl groups in the system, thereby anchoring the aliphatic long-chain structure of the epoxidized soybean oil in the resin network.

2. The environmentally friendly matting agent for powder coatings according to claim 1, characterized in that, The high acid value carboxylated acrylic resin is made from the following parts by weight of polymeric monomers and initiators: Styrene: 32.0–37.0 parts; Methyl methacrylate: 35.0 parts; Butyl acrylate: 14.5–15.5 parts; Methacrylic acid: 12.5–18.5 parts; Benzoyl peroxide: 2.0 parts.

3. The environmentally friendly matting agent for powder coatings according to claim 1, characterized in that, The high-acid-value carboxylated acrylic resin has an acid value of 81.4–119.8 mgKOH / g and a glass transition temperature of 63.2–73.6 °C.

4. The environmentally friendly matting agent for powder coatings according to claim 1, characterized in that, The N,N'-ethylene bis-stearamide is a micro powder that can pass through a 150-250 mesh sieve and has a melting point of 140-145℃; the epoxidized soybean oil has an epoxy value ≥6.0% and an iodine value ≤3.0gI2 / 100g.

5. A method for preparing an environmentally friendly matting agent for powder coatings, characterized in that, The preparation of the matting agent according to any one of claims 1-4 includes the following steps: The high acid value carboxylated acrylic resin, pyromellitic acid and 2-phenylimidazolium were mixed to prepare a solid premix. The solid premix is ​​fed into an extruder for preliminary melt extrusion, so that pyromellitic acid and 2-phenylimidazole undergo an in-situ salt formation reaction in the molten state to generate a closed catalyst salt precursor. In the middle section of the extruder, the N,N'-ethylene bis-stearamide and the epoxidized soybean oil are added and dispersed in the melt; Vacuum devolatilization is performed at the end of the extruder to induce an in-situ ring-opening addition reaction in the material. The extruded molten material is cooled, crushed, and sieved to obtain the environmentally friendly matting agent for powder coatings.

6. The preparation method of the environmentally friendly matting agent for powder coatings according to claim 5, characterized in that, The step of preparing a solid premix by mixing the high-acid-value carboxylated acrylic resin, pyromellitic acid, and 2-phenylimidazole includes: The high-acid-value carboxylated acrylic resin, pyromellitic acid, and 2-phenylimidazolium are added to a high-speed mixer and dry-mixed at room temperature for 10-15 minutes at a speed of 350-450 rpm to obtain a solid premix.

7. The preparation method of the environmentally friendly powder coating matting agent according to claim 5, characterized in that, The step of feeding the solid premix into an extruder for preliminary melt extrusion, allowing pyromellitic acid and 2-phenylimidazole to undergo an in-situ salt formation reaction in the molten state to generate a closed catalyst salt precursor includes: The solid premix is ​​continuously fed into the main feed port of a co-rotating parallel twin-screw extruder. The barrel temperature of the first to third zones of the extruder is set at 130-140°C, and the screw speed is maintained at 250-300 rpm to promote the in-situ salt formation reaction between pyromellitic acid and 2-phenylimidazolium.

8. The method for preparing the environmentally friendly matting agent for powder coatings according to claim 5, characterized in that, The step of adding the N,N'-ethylene bis-stearamide and the epoxidized soybean oil and dispersing them in the melt in the middle section of the extruder includes: The barrel temperature of the extruder in zones four to six is ​​set to 95–105°C. N,N'-ethylene bis-stearamide is continuously and uniformly added through the side feeder in zone four. The N,N'-ethylene bis-stearamide enters the melt in a micro-powder state that can pass through a 150–250 mesh sieve and is dispersed in the system under the shearing action of the screw. At the same time, epoxidized soybean oil is continuously injected in zone five through a metering pump.

9. The preparation method of the environmentally friendly matting agent for powder coatings according to claim 5, characterized in that, The step of performing vacuum devolatilization at the end of the extruder to induce an in-situ ring-opening addition reaction in the material includes: In the penultimate zone of the extruder, the water ring vacuum pump is turned on, the barrel temperature is maintained at 95-105℃, the internal vacuum gauge pressure is controlled at -0.095MPa to -0.085MPa, and the residence time of the material in this vacuum zone is controlled at 15-25s.

10. The method for preparing the environmentally friendly matting agent for powder coatings according to claim 5, characterized in that, The step of cooling, pulverizing, and sieving the extruded molten material to obtain the environmentally friendly matting agent for powder coatings includes: The molten material extruded from the extruder head is guided to a track-type cooling tablet press and rolled into a sheet with a thickness of 1.0 to 2.0 mm. After cooling to room temperature, it is crushed by a pulverizer and passed through a 180 to 220 mesh vibrating sieve to obtain the environmentally friendly matting agent for powder coatings.

Images