Two-coat one-bake powder coating for construction machinery and preparation method and application thereof

Abstract

The application discloses an engineering machine two-coat-one-bake powder coating and a preparation method and application thereof, and comprises a bottom layer powder coating and a surface layer powder coating, and the mass ratio of the bottom layer powder coating and the surface layer powder coating is 40-60:20-40; polyurethane resin and polypropylene resin are used as the binder of the surface layer powder coating, the polarity and hydrophilicity of the polypropylene resin are increased through multivalent hydroxy acid, the combination effect is improved, compared with the traditional polyester resin used as the binder of the surface layer powder coating, the molecular weight distribution of the polyester resin is wider, thereby affecting the fluidity, the molecular chain structure of the polypropylene resin is simple, the molecular weight distribution is narrower, and the fluidity is better, after being combined with the polyurethane resin, the melting point and the viscosity of the polyurethane resin can be reduced, the surface layer powder coating and the bottom layer powder coating can uniformly flow and cover the bottom layer powder coating after being combined and coated, and the stability and wear resistance of the coating are enhanced, and the impact resistance and corrosion resistance of the coating are improved.

Description

Technical Field

[0001] This invention relates to the field of coating compositions, and more particularly to the field of anti-corrosion coating technology, specifically to a two-coat, one-bake powder coating for engineering machinery, its preparation method, and its application. Background Technology

[0002] Construction machinery is an important component of the equipment manufacturing industry. It plays an irreplaceable role in major sectors concerning national welfare, such as national defense, transportation, industrial construction and production, mining, water conservancy, building construction, urban construction, and environmental protection.

[0003] Powder coating is a green coating that does not produce volatile organic solvents. It has a completely different form from ordinary coatings, existing in the state of fine powder. It has the characteristics of saving resources, being solvent-free, low-pollution, high-efficiency, and forming in one coating, and has a wide range of applications.

[0004] Construction machinery, as equipment used in field construction operations, operates in harsh environments for extended periods. Its high operational intensity and resistance to extreme conditions necessitate extremely high corrosion resistance and aesthetic appeal. This places very high demands on the coatings used. Traditional solvent-based coatings, such as paints, have a mature two-coat, one-bake process. However, paints are flammable and explosive, and solvent evaporation during use pollutes the environment and harms the health of construction workers. Therefore, construction machinery has gradually abandoned traditional solvent-based coatings in favor of powder coatings, which offer superior coating effects, fewer defects, less pollution, lower toxicity, and better performance. Ordinary single-coat powder coatings struggle to simultaneously meet weather resistance and corrosion resistance requirements; therefore, construction machinery powder coatings typically employ a two-coat solution.

[0005] Traditional coating processes involve two coats and two bakes, with common combinations including: zinc-rich primer powder coating + polyester topcoat powder coating; and epoxy primer powder coating + polyester topcoat powder coating. This process effectively covers the sharp edges and corners of the workpiece, improving edge and corner coverage and thus enhancing corrosion resistance and weather resistance. However, this traditional coating process is complex, energy-intensive, and has low production efficiency.

[0006] Therefore, it is necessary to improve existing powder coatings to solve the above problems. Summary of the Invention

[0007] This invention overcomes the shortcomings of the prior art and provides a two-coat, one-bake powder coating for engineering machinery, its preparation method, and its application.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a two-coat, one-bake powder coating for engineering machinery, comprising: a base powder coating and a top powder coating, wherein the mass ratio of the base powder coating to the top powder coating is 40-60:20-40;

[0009] The underlying powder coating comprises the following raw materials in parts by weight: 30-40 parts epoxy resin, 30-40 parts polyester resin, 4-6 parts curing agent, 1-5 parts leveling agent, 15-25 parts filler, and 10-20 parts pigment.

[0010] The surface powder coating comprises the following raw materials in parts by weight: 40-50 parts polyurethane resin, 20-30 parts modified polypropylene resin, 4-6 parts curing agent, 1-5 parts crosslinking agent, 15-25 parts filler, and 10-20 parts pigment.

[0011] The preparation method of the modified polypropylene resin includes the following steps:

[0012] S1. Prepare polypropylene resin and polyhydroxy acid in a mass ratio of 1:0.05-0.2. Add the polypropylene resin to the reaction vessel and dissolve it in the solvent.

[0013] S2. Add the polyhydroxy acid to the dissolved polypropylene resin, stir until homogeneous, complete the heating reaction, wash with water and dry to obtain the modified polypropylene resin.

[0014] In a preferred embodiment of the present invention, the polyurethane resin has an average molecular weight of 4,000-5,000, and the modified polypropylene resin has an average molecular weight of 300,000-450,000.

[0015] In a preferred embodiment of the present invention, the curing agent is one of triglycidyl isocyanurate or β-hydroxyalkylamide; the leveling agent is PV88 leveling agent; the crosslinking agent is tetramethoxymethyl glycourea; the filler is one of calcium carbonate, barium sulfate or glass microspheres; and the pigment is one of ultramarine or iron oxide.

[0016] In a preferred embodiment of the present invention, in step S1, the solvent is one of acetone, methanol or ethanol.

[0017] In a preferred embodiment of the present invention, in step S2, the heating reaction is carried out at a temperature of 80-100°C for 1-3 hours; the drying temperature is 50-70°C for 1-2 hours.

[0018] This invention provides a method for preparing a two-coat, one-bake powder coating for engineering machinery, comprising the following steps:

[0019] S1. Add epoxy resin and curing agent to the mixer Misacla cylinder and mix to obtain mixture A. Add mixture A, polyester resin, leveling agent, filler and pigment to the mixer Misacla cylinder and mix to obtain mixture B.

[0020] S2. The mixture B is sequentially subjected to melt extrusion, tableting, crushing, pulverizing, and sieving to obtain the base powder coating.

[0021] S3. Add polyurethane resin, modified polypropylene resin, curing agent, crosslinking agent, filler and pigment to the mixer Misacla cylinder and mix to obtain mixture C;

[0022] S4. The mixture C is sequentially subjected to melt extrusion, tableting, crushing, pulverizing, and sieving to obtain the surface powder coating.

[0023] In a preferred embodiment of the present invention, in S1 and S3, the mixing time is: 2-4 min for low-speed mixing and 5-8 min for high-speed mixing; the rotation speed of the low-speed mixing is 110 r / min and the rotation speed of the high-speed mixing is 320 r / min.

[0024] In a preferred embodiment of the present invention, in S2 and S4, the melt extrusion method is as follows: extrusion is performed using a twin-screw extruder, wherein the feeding section temperature is 80-85℃, the extruder head temperature is 95-100℃, and the residence time of mixture B is 45-60s; the tableting process refers to: tableting the melt-extruded product using a tablet press; the pulverization process is performed by classifying and pulverizing using an airflow vortex pulverizer, wherein the main mill frequency is 35-45Hz and the auxiliary mill frequency is 30-35Hz.

[0025] In a preferred embodiment of the present invention, in step S2, the sieving and grading process involves passing the material through a 180-200 mesh sieve. In step S4, the sieving and grading process involves passing the material through a 230-250 mesh sieve.

[0026] This invention provides a method for applying a two-coat, one-bake powder coating to engineering machinery, comprising substrate pretreatment, electrostatic spraying of the base layer powder coating, electrostatic spraying of the top layer powder coating, and curing treatment;

[0027] The method for pretreatment of the substrate is either a chemical treatment method or a physical treatment method;

[0028] The chemical treatment method is one or more of phosphating or silane treatment;

[0029] The physical treatment method is one or more of sandblasting, shot blasting, or grinding.

[0030] The curing conditions are: curing temperature 180-220℃, processing time 15-30min.

[0031] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0032] This invention provides a two-coat, one-baked powder coating for engineering machinery, its preparation method, and its application. Polyurethane resin and polypropylene resin are used as the base materials for the topcoat powder coating. A free radical reaction occurs between poly(hydroxy acids) and polypropylene resin under heating conditions, increasing the polarity and hydrophilicity of the polypropylene resin. This improves the compatibility between the polypropylene and polyurethane resins and enhances the bonding effect. Compared to traditional polyester resin as the base material for the topcoat powder coating, polyester resin has a wider molecular weight distribution, higher melting point, and higher crystallinity, which affects its flowability. Polypropylene resin has a simpler molecular chain structure, a narrower molecular weight distribution, and weaker intermolecular forces, resulting in better flowability. When combined with polyurethane resin, it lowers the melting point and viscosity of the polyurethane resin, allowing the topcoat powder coating to flow evenly and cover the bottom powder coating after bonding. This avoids problems such as uneven coating or sagging, resulting in good coating adhesion, enhanced coating stability and wear resistance, and improved coating protection for the substrate, impact resistance, and corrosion resistance.

[0033] This invention employs a two-coat, one-bake coating process, utilizing a special charging method to overcome Faraday electrostatic shielding, preventing the bottom powder coating from floating. The top powder coating completely covers the bottom powder coating, resulting in excellent surface appearance, superior edge coverage, and corrosion resistance. The top powder coating can be applied directly after the bottom powder coating, eliminating the need for a drying process between the two coatings. This improves production efficiency, reduces energy consumption and costs, and ensures the quality and performance of the coating.

[0034] In this invention, by controlling the molecular weight of polyurethane resin and polypropylene resin, as well as the particle size of the topcoat powder coating, the surface area is relatively increased, and the contact area with the bottom powder coating is also relatively increased. This allows for better coverage of the bottom powder coating and provides a better hiding effect. By controlling the molecular weight of polyurethane resin and polypropylene resin, as well as the particle size of the topcoat powder coating, within a suitable range, the surface area is kept from becoming too large, which would increase the viscosity of the coating and affect its flowability and coating effect. Furthermore, this invention prevents uneven spraying from causing a decrease in the hiding power, weather resistance, and other properties of the coating.

[0035] In this invention, epoxy resin and polyester resin are used as the base materials for the bottom powder coating. Since epoxy resin is polar and polyester resin is non-polar, there is a certain degree of mutual repulsion when they are directly compatible. By first cross-linking the epoxy resin and the curing agent to form a three-dimensional network structure, and then adding the polyester resin, the interaction force between molecules can be improved, giving it good compatibility. This can enhance the adhesion and wear resistance of the coating, improve its durability and protective effect, and the polar groups contained in its molecular structure can react with acid and alkali substances to form stable chemical bonds, thereby improving the corrosion resistance of the coating. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a flowchart of a preferred embodiment of the present invention for preparing a two-coat, one-bake powder coating for engineering machinery; Detailed Implementation

[0038] The technical solutions of 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.

[0039] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0040] It should be noted that the raw materials, equipment and reagents used in this invention can all be purchased from the market or obtained through existing preparation methods.

[0041] A two-coat, one-bake powder coating for engineering machinery includes: a base powder coating and a top powder coating, wherein the mass ratio of the base powder coating to the top powder coating is 40-60:20-40.

[0042] The base powder coating comprises the following raw materials in parts by weight: 30-40 parts epoxy resin, 30-40 parts polyester resin, 4-6 parts curing agent, 1-5 parts leveling agent, 15-25 parts filler, and 10-20 parts pigment.

[0043] The topcoat powder coating comprises the following raw materials in parts by weight: 40-50 parts polyurethane resin, 20-30 parts modified polypropylene resin, 4-6 parts curing agent, 1-5 parts crosslinking agent, 15-25 parts filler, and 10-20 parts pigment.

[0044] The average molecular weight of polyurethane resin is 4,000-5,000, and the average molecular weight of modified polypropylene resin is 300,000-450,000.

[0045] The curing agent is either triglycidyl isocyanurate or β-hydroxyalkylamide; the leveling agent is PV88 leveling agent; the crosslinking agent is tetramethoxymethylglycosanol; the filler is either calcium carbonate, barium sulfate or glass microspheres; and the pigment is either ultramarine or iron oxide.

[0046] The preparation method of modified polypropylene resin includes the following steps:

[0047] S1. Prepare polypropylene resin and polyhydroxy acid in a mass ratio of 1:0.05-0.2. Add the polypropylene resin to the reaction vessel and dissolve it in the solvent.

[0048] S2. Add the polyhydroxy acid to the dissolved polypropylene resin, stir until homogeneous, complete the heating reaction, wash with water and dry to obtain the modified polypropylene resin.

[0049] In S1 of this invention, the solvent is one of acetone, methanol or ethanol.

[0050] In S2 of this invention, the heating reaction is carried out at a temperature of 80-100°C for 1-3 hours; the drying temperature is 50-70°C for 1-2 hours.

[0051] like Figure 1 As shown, a two-coat, one-bake powder coating for engineering machinery, its preparation method, and its application include the following steps:

[0052] S1. Add epoxy resin and curing agent to the mixer Misacla cylinder and mix to obtain mixture A. Add mixture A, polyester resin, leveling agent, filler and pigment to the mixer Misacla cylinder and mix to obtain mixture B.

[0053] S2. The mixture B is sequentially subjected to melt extrusion, tableting, crushing, pulverizing, and sieving to obtain the base powder coating.

[0054] S3. Add polyurethane resin, modified polypropylene resin, curing agent, crosslinking agent, filler and pigment to the mixer Misacla cylinder and mix to obtain mixture C;

[0055] S4. The mixture C is sequentially subjected to melt extrusion, tableting, crushing, pulverizing, and sieving to obtain the surface powder coating.

[0056] In S1 and S3 of this invention, the mixing time is: 2-4 min for low-speed mixing and 5-8 min for high-speed mixing; the rotation speed for low-speed mixing is 110 r / min and the rotation speed for high-speed mixing is 320 r / min.

[0057] In S2 and S4 of this invention, the melt extrusion method is as follows: extrusion is performed using a twin-screw extruder, wherein the temperature of the feeding section is 80-85℃, the temperature of the extruder head is 95-100℃, and the residence time of mixture B is 45-60s; the tableting process refers to: tableting the melt-extruded product using a tablet press; the pulverization process is performed by classifying and pulverizing using an airflow vortex pulverizer, wherein the main mill frequency is 35-45Hz and the auxiliary mill frequency is 30-35Hz.

[0058] In S2 of this invention, the sieving and grading process involves passing the material through a 180-200 mesh sieve. In S4, the sieving and grading process involves passing the material through a 230-250 mesh sieve.

[0059] The following is a detailed description of the overall implementation scheme of the present invention in conjunction with specific embodiments.

[0060] The raw materials for the bottom layer powder coating and the top layer powder coating in Examples 1-6 are different, as are the specific proportions shown in Tables 1 and 2, with the raw materials used measured in parts by mass.

[0061] Table 1: Preparation of Base Powder Coating Raw Materials and Proportions

[0062]

[0063] Table 2: Preparation of Raw Materials and Proportions for Topcoat Powder Coatings

[0064]

[0065] The modified polypropylene resin used in Examples 1 and 3 was prepared by the following method:

[0066] S1. Prepare polypropylene resin and polyhydroxy acid in a mass ratio of 1:0.15. Add the polypropylene resin to the reaction vessel and dissolve it in acetone.

[0067] S2. Add the polyhydroxy acid to the dissolved polypropylene resin, stir evenly, and treat at 95°C for 1.5 hours to complete the heating reaction. After washing with water, dry at 50°C for 2 hours to obtain the modified polypropylene resin.

[0068] The modified polypropylene resin preparation methods used in Examples 2, 4 and 5 are basically the same as those used in Examples 1 and 3, except that: the mass ratio of polypropylene resin to polyhydroxy acid is 1:0.2; the solvent is ethanol; the heating temperature is 80°C; and the treatment time is 3 hours.

[0069] The modified polypropylene resin preparation method used in Example 6 is basically the same as that in Examples 1 and 3, except that the mass ratio of polypropylene resin to polyhydroxy acid is 1:0.05; the heating reaction temperature is 100°C; and the treatment time is 1 hour.

[0070] Example 1

[0071] A method for preparing a two-coat, one-bake powder coating for engineering machinery includes the following steps:

[0072] S1. Add epoxy resin and triglycidyl isocyanate to the Misacral mixer tank and mix at a low speed of 110 r / min for 3 min, and then mix at a high speed of 320 r / min for 7 min to obtain mixture A. Add mixture A, polyester resin, PV88 leveling agent, calcium carbonate and iron oxide to the Misacral mixer tank and mix at a low speed of 110 r / min for 4 min, and then mix at a high speed of 320 r / min for 8 min to obtain mixture B.

[0073] S2. Add mixture B to a twin-screw extruder for extrusion. The feeding section temperature is 80℃, the extruder head temperature is 100℃, and the residence time of mixture B is 60s. After melt extrusion, the mixture is tableted by a tablet press, cooled, and then crushed by a crusher. After crushing, it is graded and pulverized by an airflow vortex pulverizer. The main mill frequency is 40Hz, and the auxiliary mill frequency is 30Hz. After pulverization, the mixture is sieved through a 200-mesh sieve in a screening machine to obtain the bottom powder coating.

[0074] S3. Add polyurethane resin, modified polypropylene resin, triglycidyl isocyanate, tetramethoxymethyl urea, calcium carbonate and iron oxide into the mixer Misacla cylinder, mix at a low speed of 110 r / min for 4 min, and mix at a high speed of 320 r / min for 8 min to obtain mixture C.

[0075] S4. Add mixture C to a twin-screw extruder for extrusion. The feeding section temperature is 85℃, the extruder head temperature is 95℃, and the residence time of mixture B is 60s. After melt extrusion, the mixture is tableted by a tablet press, cooled, and then crushed by a crusher. After crushing, it is graded and pulverized by an airflow vortex pulverizer. The main mill frequency is 45Hz, and the auxiliary mill frequency is 35Hz. After pulverization, the mixture is sieved through a 250-mesh sieve to obtain the surface powder coating.

[0076] The average molecular weight of the polyurethane resin is 4,500, and the average molecular weight of the modified polypropylene resin is 400,000.

[0077] Example 2

[0078] This embodiment is basically the same as Embodiment 1, except that the raw materials and proportions are different, as shown in Tables 1 and 2; in step S2, the material is sieved through a 190-mesh sieve; in step S4, the material is sieved through a 240-mesh sieve; wherein, the average molecular weight of the polyurethane resin is 4000, and the average molecular weight of the modified polypropylene resin is 350000.

[0079] Example 3

[0080] This embodiment is basically the same as embodiment 1, except that the raw materials and proportions are different, as shown in Table 1 and Table 2.

[0081] Example 4

[0082] This embodiment is basically the same as Embodiment 1, except that the raw materials and proportions are different, as shown in Tables 1 and 2; in step S2, the material is sieved through a 180-mesh sieve; in step S4, the material is sieved through a 240-mesh sieve; wherein, the average molecular weight of the polyurethane resin is 5000 and the average molecular weight of the modified polypropylene resin is 300000.

[0083] Example 5

[0084] This embodiment is basically the same as embodiment 1, except that the raw materials and proportions are different, as shown in Table 1 and Table 2; in step S2, the material is sieved through a 190-mesh sieve; in step S4, the material is sieved through a 230-mesh sieve.

[0085] Example 6

[0086] This embodiment is basically the same as Embodiment 1, except that the raw materials and proportions are different, as shown in Tables 1 and 2; wherein, the average molecular weight of the polyurethane resin is 5000 and the average molecular weight of the modified polypropylene resin is 350000.

[0087] Comparative Example 1: It is basically the same as the two-coat, one-bake powder coating for engineering machinery in Example 1, except that in step S3, 45 parts by weight of polyurethane resin and 30 parts by weight of modified polypropylene resin are replaced with 60 parts by weight of polyester resin.

[0088] Comparative Example 2: It is basically the same as the two-coat, one-bake powder coating for engineering machinery in Example 1, except that in step S3, the modified polypropylene resin is replaced with polypropylene resin.

[0089] Comparative Example 3: It is basically the same as the two-coat, one-bake powder coating for engineering machinery in Example 1, except that: Step S1 is as follows: epoxy resin, triglycidyl isocyanate, polyester resin, PV88 leveling agent, calcium carbonate and iron oxide are added to the mixer Misacla cylinder, and mixed at a low speed of 110 r / min for 4 min, and at a high speed of 320 r / min for 8 min to obtain mixture B.

[0090] Comparative Example 4: It is basically the same as the two-coat, one-bake powder coating for engineering machinery in Example 1, except that in step S4, the coating is sieved through a 300-mesh sieve; wherein the average molecular weight of the polyurethane resin is 8000 and the average molecular weight of the modified polypropylene resin is 500000.

[0091] Examples 1-6 and Comparative Examples 1-4, their application methods include the following steps:

[0092] After grinding and phosphating, the hardware parts are electrostatically sprayed with a base coat of powder coating, followed by a top coat of powder coating. The mass ratio of the base coat to the top coat is 50:30. The coated hardware parts are then placed in an oven and cured at 200°C for 20 minutes. After curing, the coating thickness on the hardware parts is 200μm. The powder coating is applied using a JF500 electrostatic powder coating machine and an HGP series integrated powder recovery and supply spraying chamber.

[0093] It should be noted that by adopting a two-coat, one-bake coating process and using a special charging method to solve the Faraday electrostatic shielding problem, the base powder coating does not float to the surface, and the top powder coating completely covers the base powder coating. This results in excellent surface appearance as well as superior edge coverage and corrosion resistance. The top powder coating can be applied directly after the base powder coating is sprayed, eliminating the drying process between the base and top powder coatings, improving production efficiency, reducing energy consumption and costs, and ensuring the quality and performance of the coating.

[0094] Performance testing: The coatings obtained in Examples 1-6 and Comparative Examples 1-4 were named Samples 1-10 in sequence. Then, Samples 1-10 were subjected to performance tests in sequence for impact resistance, abrasion resistance, leveling, adhesion, gloss, salt spray resistance, acid resistance, alkali resistance and edge coverage.

[0095] Impact resistance test: Refer to GB / T 1732-1993 "Determination of impact resistance of paint film", and test the impact resistance at different conditions at room temperature and low temperature. The average value is taken for three parallel tests.

[0096] Abrasion resistance test: The test was conducted according to GB / T 23988-2009 "Determination of Abrasion Resistance of Coatings - Falling Sand Method". Three parallel tests were performed, and the average value was taken. The higher the test value, the more sand is required to remove a unit of coating wear, indicating better abrasion resistance of the coating.

[0097] Leveling test: The test shall be conducted in accordance with GB / T 1750-1979 "Leveling of Coatings".

[0098] Adhesion test: The test shall be conducted in accordance with GB / T 9286-2021 "Cross-cut test for paints and varnishes".

[0099] Gloss test: The 60 gloss level was tested in accordance with GB / T 9754-2007 "Determination of 20°, 60° and 85° specular gloss of paint films without metallic pigments".

[0100] Salt spray resistance test: The test was conducted in accordance with GB / T 1771-2007 "Paints and Varnishes - Determination of resistance to neutral salt spray".

[0101] Acid resistance test: The sample was immersed in 15wt% hydrogen chloride for 24 hours to test the acid resistance change of the coating on the surface.

[0102] Alkali resistance test: The sample was immersed in 15wt% sodium hydroxide for 24 hours, and the alkali resistance of the coating on the surface was tested.

[0103] Corner coverage test: The test shall be conducted in accordance with GB / T 6554.

[0104] The test results of impact resistance, abrasion resistance, leveling, adhesion, gloss, salt spray resistance, acid resistance, alkali resistance and edge coverage of samples 1-10 are shown in Table 3.

[0105] Table 3:

[0106]

[0107] As can be seen from Tables 2 and 3:

[0108] A comparison of Sample 1 and Sample 7 reveals that using polyurethane resin and polypropylene resin as the base material for the topcoat powder coating, and modifying the polypropylene resin with polyhydroxy acids, results in a more uniform flow and coverage of the topcoat powder coating after bonding with the base powder coating, compared to traditional polyester resin. This avoids problems such as uneven coating or sagging, thus forming good coating adhesion, enhancing the stability and wear resistance of the coating, and increasing the coating's ability to protect the substrate, improving the coating's impact resistance and corrosion resistance.

[0109] A comparison of Sample 1 and Sample 8 shows that the free radical reaction between polypropylene resin and polypropylene resin under heating conditions increases the polarity and hydrophilicity of polypropylene resin, resulting in better compatibility between polypropylene resin and polyurethane resin and improved bonding effect. After bonding with polyurethane resin, the melting point and viscosity of polyurethane resin can be reduced, leading to a more significant increase in coating effect.

[0110] A comparison of Sample 1 and Sample 9 reveals that by first cross-linking epoxy resin and curing agent to form a three-dimensional network structure, and then adding polyester resin, the intermolecular interaction forces can be improved, giving it good compatibility. This enhances the coating's adhesion, abrasion resistance, durability, and protective effect. Furthermore, its molecular structure contains polar groups, which can react with acidic and alkaline substances to form stable chemical bonds, thereby improving the coating's corrosion resistance.

[0111] A comparison of Sample 1 and Sample 10 shows that by controlling the molecular weight of polyurethane resin and polypropylene resin, as well as the particle size of the topcoat powder coating, the surface area is relatively increased, and the contact area with the bottom powder coating is also relatively increased. This allows for better coverage of the bottom powder coating and provides a better hiding effect. However, excessively small molecular weight and particle size will increase the viscosity of the coating, affecting its flowability and coating effect, and causing uneven spraying, which leads to a decrease in the hiding power, weather resistance, and other properties of the coating.

[0112] In summary, the two-coat, one-bake powder coating for engineering machinery prepared by this invention has an impact resistance of 69.8 kg / cm at room temperature and 67.5 kg / cm at -20℃, and an abrasion resistance of 3.62. It also has excellent leveling properties, adhesion, gloss, and edge coverage, while possessing good corrosion resistance and acid and alkali resistance.

[0113] Based on the preferred embodiments of the present invention described above, 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. An engineered machinery two-coat-one-bake powder coating, characterized in that, Comprise: The mass ratio of the base layer powder coating and the surface layer powder coating is 40-60:20-40; The base layer powder coating comprises the following mass parts of raw materials for preparation: epoxy resin 30-40 parts, polyester resin 30-40 parts, curing agent 4-6 parts, leveling agent 1-5 parts, filler 15-25 parts, pigment 10-20 parts; The surface layer powder coating comprises the following mass parts of raw materials for preparation: polyurethane resin 40-50 parts, modified polypropylene resin 20-30 parts, curing agent 4-6 parts, crosslinking agent 1-5 parts, filler 15-25 parts, pigment 10-20 parts; The modified polypropylene resin is modified by using polybasic acid; in the preparation method of the base layer powder coating, the epoxy resin and the curing agent are crosslinked and combined to form a three-dimensional network structure, and then the polyester resin is added; The average molecular weight of the polyurethane resin is 4000-5000, and the average molecular weight of the modified polypropylene resin is 300000-450000.

2. A two-coat-one-bake powder coating for construction machines according to claim 1, characterized in that: The curing agent is one of isocyanuric acid triglycidyl ester or beta-hydroxy alkyl amide; the filler is one of calcium carbonate, barium sulfate or glass beads; and the pigment is one of ultramarine or iron oxide.

3. A two-coat-one-bake powder coating for construction machines according to claim 1, characterized in that: The leveling agent is PV88 leveling agent.

4. A two-coat-one-bake powder coating for construction machines according to claim 1, characterized in that: The crosslinking agent is tetramethoxymethyl glycoluril.

5. A method of producing a two-coat-one-bake powder coating for construction machines according to any one of claims 1 to 4, characterized in that, Comprise the following steps: S1, the epoxy resin and the curing agent are added into a mixer mica tank for mixing to obtain a mixture A, and the mixture A, polyester resin, leveling agent, filler and pigment are added into the mixer mica tank for mixing to obtain a mixture B; S2, the mixture B is sequentially subjected to melt extrusion, tabletting treatment, crushing treatment, pulverization treatment and sieving classification treatment to obtain a base layer powder coating; S3, the polyurethane resin, modified polypropylene resin, curing agent, crosslinking agent, filler and pigment are added into a mixer mica tank for mixing to obtain a mixture C; S4, the mixture C is sequentially subjected to melt extrusion, tabletting treatment, crushing treatment, pulverization treatment and sieving classification treatment to obtain a surface layer powder coating.

6. A method of preparing a two-coat-one-bake powder coating for construction machines according to claim 5, characterized in that: In the S1 and the S3, the mixing time is: low-speed mixing for 2-4 min and high-speed mixing for 5-8 min; the low-speed mixing speed is 110 r / min, and the high-speed mixing speed is 320 r / min.

7. A method of preparing a two-coat-one-bake powder coating for construction machines according to claim 5, characterized in that: In the S2 and the S4, the melt extrusion method is: extrusion in a double-screw extruder, wherein the feeding section temperature is 80-85℃, the extrusion head temperature is 95-100℃, and the mixture B residence time is 45-60 s; the tabletting treatment refers to tabletting the product after melt extrusion by using a tabletting machine; and the pulverization treatment refers to classified pulverization by using an airflow vortex type pulverizer, wherein the main mill frequency is 35-45 Hz, and the auxiliary mill frequency is 30-35 Hz.

8. A method of preparing a two-coat-one-bake powder coating for construction machines according to claim 5, characterized in that: In the S2, the sieving classification treatment is passing through a 180-200 mesh sieve; and in the S4, the sieving classification treatment is passing through a 230-250 mesh sieve.

9. A method of applying a two-coat-one-bake powder coating to a construction machine according to any one of claims 1 to 4, characterized in that: Substrate pretreatment, electrostatic spraying of the base layer powder coating, electrostatic spraying of the surface layer powder coating, curing treatment; The method of the substrate pretreatment is a chemical treatment method or a physical treatment method; The method of the chemical treatment is one or more of phosphating treatment or silane treatment; The method of the physical treatment is one or more of sand blasting, shot blasting or polishing; The condition of the solidification treatment is a solidification temperature of 180-220℃ and a treatment time of 15-30min.

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