A method for preparing powder coating for coiled steel

Abstract

This invention discloses a method for preparing powder coatings for coiled steel, comprising the following steps: S1, weighing the following raw materials by mass percentage: linear polyester; epoxy resin; curing agent; diamond coating wax powder; leveling agent; benzoin; pigment; filler; by modifying the epoxy resin with polycarboxylic acid and further modifying it with sulfonyl chloride, the polarity of the coating can be increased due to the high reactivity and polarity of the sulfonyl group. When the sulfonyl group reacts with the benzene ring in the linear polyester, it leads to the destruction of structures such as conjugated double bonds or triple bonds, thereby increasing the polarity and chemical stability of the coating. The increase in polarity can change the intermolecular interaction forces, increase the regularity and order of the molecules, and the increase in chemical stability can inhibit the occurrence of chemical reactions, thereby reducing the reaction of electron transitions on π→π orbitals, avoiding the problems of yellowing and degradation caused by transition reactions under ultraviolet radiation, and improving the anti-aging effect of the coating.

Description

Technical Field

[0001] This invention relates to the field of powder coatings, and more particularly to a method for preparing powder coatings for coiled steel. Background Technology

[0002] Powder coating is a new type of solvent-free, easy-to-use, and non-volatile solid coating that can form a protective, decorative, and special functional coating when sprayed onto a metal surface.

[0003] Currently, most coil coatings use paint as the coating material. Paint spraying is easy to operate and produces a thin coating. However, in practical applications, paint produces a large amount of harmful substances such as formaldehyde, which can have a certain impact on the physical and mental health of workers and the environment. Therefore, reducing VOC emissions from the industrial coating industry has become a top priority in the work of controlling air pollution. Powder coatings have the advantages of being harmless and environmentally friendly, highly efficient and inexpensive. Compared with paint, they save energy, have a simple process, and have better weather resistance and corrosion resistance.

[0004] In the prior art, linear polyester is often used as the base material in powder coatings applied to coil steel. However, when this type of powder coating is actually applied to coil steel, linear polyester is quite sensitive to ultraviolet radiation. Due to the presence of benzene rings in its chemical structure (including benzene rings introduced by aromatic diacids / anhydrides and styrene), electrons in the π→π orbitals of the benzene rings are prone to transition when exposed to ultraviolet radiation for a long time. This transition makes the polymer chain unstable, thus making it prone to yellowing and degradation.

[0005] Therefore, it is necessary to improve existing powder coatings to solve the above problems. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides a method for preparing powder coatings for coiled steel.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for preparing powder coating for coiled steel, comprising the following steps:

[0008] S1. Weigh the following raw materials by mass percentage:

[0009]

[0010]

[0011] S2. Add the epoxy resin and polyhydroxy acid from S1 into the reaction vessel, mix them in the solvent, and heat the mixture to obtain mixture A.

[0012] S3. The sulfonyl chloride and mixture A are reacted in a reactor to complete the sulfonylation reaction. The pH is adjusted to 5-7 by alkaline solution. After washing with water and drying, the modified epoxy resin is obtained.

[0013] S4. Modified epoxy resin, linear polyester, curing agent, diamond coating wax powder, leveling agent, benzoin, pigment and filler are added to the mixer Misacla cylinder and mixed. Then, the mixture is sequentially processed through melt extrusion, tableting, crushing and pulverizing.

[0014] S5. The product from S4 is sieved and graded in a screening machine to obtain powder coating for coiled steel.

[0015] In a preferred embodiment of the present invention, in step S1, the curing agent is one of triglycidyl isocyanurate, m-phenylenediamine, or diaminodiphenylmethane; the leveling agent is PV88 leveling agent; the pigment is one of ultramarine, ultramarine violet, or iron oxide; and the filler is one of calcium carbonate, barium sulfate, mica powder, or glass microspheres.

[0016] In a preferred embodiment of the present invention, in step S2, the solvent is one of acetone, methanol or ethanol; the processing temperature is 60-100℃ and the processing time is 1-3h.

[0017] In a preferred embodiment of the present invention, in step S3, the treatment temperature of the oxyacetylation reaction is 80-150°C, and the treatment time is 2-4 hours; the alkaline solution is potassium hydroxide with a concentration of 5-10 wt%; and the drying temperature is 50-70°C, and the drying time is 1-2 hours.

[0018] In a preferred embodiment of the present invention, in S2 and S3, the mass ratio of epoxy resin, polyhydroxy acid and sulfonyl chloride is 1:0.05-0.2:0.03-0.1.

[0019] In a preferred embodiment of the present invention, in step S4, the mixing time is: 2-4 minutes for low-speed mixing and 5-8 minutes 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.

[0020] In a preferred embodiment of the present invention, in step S4, the melt extrusion refers to adding the mixed product to a twin-screw extruder for extrusion, wherein the temperature of the feeding section is 80-85°C, the temperature of the extruder head is 95-100°C, and the residence time is 45-60s.

[0021] In a preferred embodiment of the present invention, in step S4, the tableting process refers to: pressing the melt-extruded product into tablets using a tableting machine.

[0022] In a preferred embodiment of the present invention, in step S4, the pulverization process is performed by using an airflow vortex pulverizer for graded pulverization, wherein the main mill frequency is 35-45Hz and the auxiliary mill frequency is 30-35Hz.

[0023] In a preferred embodiment of the present invention, in step S5, the sieving and grading process is to pass through a 180-200 mesh sieve.

[0024] In a preferred embodiment of the present invention,

[0025] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0026] (1) This invention provides a method for preparing a powder coating for coiled steel. The method uses linear polyester and epoxy resin as base materials. The epoxy resin is modified by using polycarboxylic acids and then modified again by sulfonyl chloride to introduce sulfonyl groups. Since sulfonyl groups have high reactivity and polarity, the introduction of sulfonyl groups can increase the polarity of the coating. The increased polarity can suppress the generation of internal stress in the coating and further enhance the bending performance of the coating. When the sulfonyl groups react with the benzene ring in the linear polyester, the conjugation effect on the benzene ring will be destroyed, leading to the destruction of structures such as conjugated double bonds or triple bonds, increasing the polarity and chemical stability of the coating. The increase in polarity can change the intermolecular interaction force, increase the regularity and order of the molecules, and the increase in chemical stability can inhibit the occurrence of chemical reactions, thereby reducing the reaction of electron transitions on π→π orbitals, avoiding the problems of yellowing and degradation caused by transition reactions when exposed to ultraviolet radiation, and improving the anti-aging effect of the coating.

[0027] (2) In this invention, the modified epoxy resin can react with linear polyester and curing agent to form a three-dimensional network cross-linked structure. The modified epoxy resin contains epoxy groups, which can undergo ring-opening reaction or esterification reaction with active groups such as carboxyl or hydroxyl groups in linear polyester, thereby forming chemical bonds to enhance the bonding force between them. This results in a coating with higher cross-linking density and crystallinity, improving the durability and chemical stability of the coating.

[0028] (3) In this invention, the mixing of diamond-coated wax powder makes the coating surface smooth and improves the scratch resistance. The mixing of brightening agent can improve the wettability of pigments and fillers in the film-forming material. At the same time, the surface tension is reduced during the melting process, so that the surface tension is evenly distributed and the coating is free from defects such as pinholes and shrinkage cavities. Meanwhile, the mixing of leveling agent can reduce the surface tension of the coating and make the coating evenly level. Attached Figure Description

[0029] 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.

[0030] Figure 1 This is a flowchart of a preferred embodiment of the present invention for preparing a powder coating for coiled steel; Detailed Implementation

[0031] 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.

[0032] 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.

[0033] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0034] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0035] 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.

[0036] like Figure 1 As shown, a method for preparing a powder coating for coiled steel includes the following steps:

[0037] S1. Weigh the following raw materials by mass percentage:

[0038]

[0039] S2. Add the epoxy resin and polyhydroxy acid from S1 into the reaction vessel, mix them in the solvent, and heat the mixture to obtain mixture A.

[0040] S3. The sulfonyl chloride and mixture A are reacted in a reactor to complete the sulfonylation reaction. The pH is adjusted to 5-7 by alkaline solution. After washing with water and drying, the modified epoxy resin is obtained.

[0041] S4. Modified epoxy resin, linear polyester, curing agent, diamond coating wax powder, leveling agent, benzoin, pigment and filler are added to the mixer Misacla cylinder and mixed. Then, the mixture is sequentially processed through melt extrusion, tableting, crushing and pulverizing.

[0042] S5. The product from S4 is sieved and graded in a screening machine to obtain powder coating for coiled steel.

[0043] In S1 of this invention, the curing agent is one of triglycidyl isocyanurate, m-phenylenediamine, or diaminodiphenylmethane; the leveling agent is PV88 leveling agent; the pigment is one of ultramarine, ultramarine violet, or iron oxide; and the filler is one of calcium carbonate, barium sulfate, mica powder, or glass microspheres.

[0044] In S2 of this invention, the solvent is one of acetone, methanol or ethanol; the treatment temperature is 60-100℃ and the treatment time is 1-3h.

[0045] In S3 of this invention, the treatment temperature of the acylation reaction is 80-150℃, and the treatment time is 2-4h; the alkaline solution is potassium hydroxide with a concentration of 5-10wt%; the drying temperature is 50-70℃, and the drying time is 1-2h.

[0046] In S2 and S3 of this invention, the mass ratio of epoxy resin, polyhydroxy acid, and sulfonyl chloride is:

[0047] 1:0.05-0.2:0.03-0.1.

[0048] In S4 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.

[0049] In S4 of this invention, melt extrusion refers to adding the mixed product to a twin-screw extruder for extrusion, wherein the temperature of the feeding section is 80-85℃, the temperature of the extruder head is 95-100℃, and the residence time is 45-60s; tableting refers to tableting the melt-extruded product using a tablet press; and pulverization is performed by using an airflow vortex pulverizer for graded pulverization, wherein the main mill frequency is 35-45Hz and the auxiliary mill frequency is 30-35Hz.

[0050] In S5 of this invention, the sieving and grading process involves passing the material through a 180-200 mesh sieve.

[0051] It should be noted that by using linear polyester and epoxy resin as base materials, modifying the epoxy resin with polycarboxylic acids, and further modifying it with sulfonyl chloride to introduce sulfonyl groups, the high reactivity and polarity of sulfonyl groups can increase the polarity of the coating. This increased polarity can suppress the generation of internal stress in the coating, further enhancing its bending performance. When the sulfonyl groups react with the benzene ring in the linear polyester, they disrupt the conjugation effect on the benzene ring, leading to the destruction of conjugated double or triple bonds, thus increasing the polarity and chemical stability of the coating. Increased polarity can alter intermolecular forces, increasing molecular regularity and order. Increased chemical stability can inhibit chemical reactions, thereby reducing the π→π orbital electron transition reactions and preventing yellowing and degradation caused by ultraviolet radiation, thus improving the coating's anti-aging effect.

[0052] The following is a detailed description of the overall implementation scheme of the present invention in conjunction with specific embodiments.

[0053] The raw material ratios for the preparation of Examples 1-6 are different, as shown in Table 1, with the raw materials measured as a percentage by mass.

[0054] Table 1:

[0055]

[0056] Example 1

[0057] A method for preparing a powder coating for coiled steel includes the following steps:

[0058] S1. Prepare epoxy resin, polyhydroxy acid and sulfonyl chloride in a mass ratio of 1:0.1:0.06. Add epoxy resin and polyhydroxy acid to the reaction vessel, mix in acetone, and treat at 80°C for 2 hours to complete the heating reaction and obtain mixture A.

[0059] S2. Add sulfonyl chloride and mixture A into the reactor and treat at 130°C for 3 hours to complete the sulfonylation reaction. Add 8 wt% potassium hydroxide to adjust the pH to 6, wash the unreacted residue with water, and dry at 60°C for 1.5 hours to obtain the modified epoxy resin.

[0060] S3. Modified epoxy resin, linear polyester, triglycidyl isocyanurate, diamond coating wax powder, PV88 leveling agent, benzoin, iron oxide, and barium sulfate are added to the Misacral tank of a mixer. The mixture is low-speed mixed at 110 rpm for 4 minutes, and then high-speed mixed at 320 rpm for 8 minutes. The resulting mixture is then fed into a twin-screw extruder for extrusion. The feeding section temperature is 80℃, the extruder head temperature is 95℃, and the material residence time is 60 seconds. After melt extrusion, the mixture is tableted using a tablet press, cooled, and then crushed. The crushed material is then graded and pulverized using an airflow vortex mill, with the main mill frequency at 40 Hz and the auxiliary mill frequency at 30 Hz.

[0061] S4. The product from S3 is sieved through a 200-mesh sieve in a screening machine to obtain powder coating for coiled steel.

[0062] Example 2

[0063] This embodiment is basically the same as Embodiment 1, except that: in step S1, epoxy resin, polyhydroxy acid and sulfonyl chloride are prepared in a mass ratio of 1:0.15:0.1; the heating reaction is completed at 100°C for 1 hour; in step S2, the xanylation reaction is completed at 150°C for 2 hours.

[0064] Example 3

[0065] This embodiment is basically the same as Embodiment 1, except that: in step S1, the heating reaction is completed at 60°C for 3 hours; in step S2, the cytosylation reaction is completed at 80°C for 4 hours; and in step S3, the mixture is mixed at low speed for 2 minutes and then at high speed for 7 minutes.

[0066] Example 4

[0067] This embodiment is basically the same as embodiment 1, except that: in step S3, low-speed mixing is performed for 3 minutes and high-speed mixing for 6 minutes; the temperature of the feeding section is 85°C, the temperature of the extruder head is 95°C, and the material residence time is 45 seconds; in step S4, the material is sieved and graded through a 190-mesh sieve.

[0068] Example 5

[0069] This embodiment is basically the same as Embodiment 1, except that: in step S1, epoxy resin, polyhydroxy acid and sulfonyl chloride are prepared in a mass ratio of 1:0.05:0.1; the heating reaction is completed at 100°C for 3 hours; in step S2, the xanylation reaction is completed at 150°C for 3 hours; in step S3, low-speed mixing is performed for 3 minutes and high-speed mixing for 6 minutes; the feeding section temperature is 85°C and the material residence time is 50 seconds; in step S4, the material is sieved and graded through an 180-mesh sieve.

[0070] Example 6

[0071] This embodiment is basically the same as Embodiment 1, except that: in step S1, epoxy resin, polyhydroxy acid and sulfonyl chloride are prepared in a mass ratio of 1:0.2:0.03; in step S3, they are mixed at low speed for 4 minutes and at high speed for 5 minutes.

[0072] Comparative Example 1: It is basically the same as the new energy strong acid and strong alkali resistant powder coating in Example 1, except that: step S1 is omitted, and step S2 is as follows: prepare epoxy resin and sulfonyl chloride with a mass ratio of 1:0.06, add sulfonyl chloride and epoxy resin to the reaction vessel, and treat at 130°C for 3 hours to complete the sulfonylation reaction. Add potassium hydroxide with a concentration of 8wt% to adjust the pH to 6, and wash the unreacted residue with water. Dry at 60°C for 1.5 hours to obtain modified epoxy resin.

[0073] Comparative Example 2: It is basically the same as the new energy strong acid and strong alkali resistant powder coating in Example 1, except that: there is no S2 step, and the S1 step is: prepare epoxy resin and polyhydroxy acid with a mass ratio of 1:0.1, add epoxy resin and polyhydroxy acid to the reaction vessel, mix in acetone, and treat at 80°C for 2 hours to complete the heating reaction and obtain modified epoxy resin.

[0074] Comparative Example 3: This is essentially the same as the new energy acid and alkali resistant powder coating in Example 1, except that steps S1 and S2 are omitted. Step S3 is as follows: epoxy resin, linear polyester, triglycidyl isocyanurate, diamond coating wax powder, PV88 leveling agent, benzoin, iron oxide, and barium sulfate are added to the Misacral cylinder of a mixer and mixed at a low speed of 110 r / min for 4 min, followed by a high speed of 320 r / min for 8 min. The mixed product is then added to a twin-screw extruder for extrusion, with the feeding section temperature at 80°C, the extruder head temperature at 95°C, and the material residence time at 60 s. After melt extrusion, the material is tableted by a tablet press, cooled, and then crushed. After crushing, the material is graded and pulverized using an airflow vortex pulverizer, with the main mill frequency at 40 Hz and the auxiliary mill frequency at 30 Hz.

[0075] Comparative Example 4: It is basically the same as the new energy strong acid and strong alkali resistant powder coating in Example 1, except that: in step S1, the solvent is methanol; in step S2, potassium hydroxide with a concentration of 10wt% is added to adjust the pH to 5; in step S3, the curing agent is m-phenylenediamine and the filler is glass microspheres.

[0076] Comparative Example 5: It is basically the same as the new energy strong acid and strong alkali resistant powder coating in Example 1, except that: in step S1, the solvent is ethanol; in step S2, potassium hydroxide with a concentration of 5wt% is added to adjust the pH to 7; in step S3, the curing agent is m-diaminodiphenylmethane and the filler is mica powder.

[0077] Comparative Example 6: It is basically the same as the new energy-resistant powder coating for strong acids and alkalis in Example 1, except that: in step S1, the solvent is methanol; in step S3, the curing agent is m-phenylenediamine, the pigment is ultramarine, and the filler is calcium carbonate.

[0078] Performance testing: The powder coatings prepared in Examples 1-6 and Comparative Examples 1-6 were applied to 100mm×100mm aluminum sheets by spraying. They were then cured in an oven at 200℃ for 1.5h. After curing, the thickness of the coating on the aluminum sheet was 100μm. The coatings obtained in Examples 1-6 and Comparative Examples 1-6 were named Samples 1-12. Then, Samples 1-12 were subjected to performance tests of impact resistance, abrasion resistance, bending resistance, cupping test, and pencil hardness.

[0079] 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.

[0080] 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.

[0081] Bending resistance: Tested in accordance with GB / T 6742-1986 "Bending test of paint film (cylindrical shaft)".

[0082] Cupping test: The test shall be conducted in accordance with GB / T 9753-2007 "Cupping test for paints and varnishes".

[0083] Pencil hardness: Tested according to GB / T 6739-2006 "Determination of Hardness of Paints and Varnishes by Pencil Method". Pencil lead hardness is divided into 13 grades. The hardness decreases progressively from 6H, 5H, 4H, 3H, 2H, H, HB, B, 2B, and 6B. Here, H represents hardness, and B represents blackness.

[0084] The results of the impact resistance, abrasion resistance, flexural strength, cupping test, and pencil hardness tests of samples 1-12 are shown in Table 2.

[0085] Table 2:

[0086]

[0087]

[0088] Samples 1-12 were tested for gloss retention and resistance to yellowing.

[0089] Light retention: Parts of samples 1-12 were covered and irradiated with a xenon lamp for 2000 hours. The light retention rate of the irradiated parts was compared with that of the unirradiated parts.

[0090] Yellowing resistance: The powder coatings prepared in Examples 1-6 and Comparative Examples 1-6 were applied to frosted glass by spraying and cured in an oven at 180°C for 1 hour. After curing, the samples obtained in Examples 1-6 and Comparative Examples 1-6 were named Samples 1-12 and placed in a desiccator containing saturated potassium sulfate solution. After 24 hours, the X, Y, and Z values ​​of the color were measured, and the yellowing degree value D was calculated. Calculation formula: D = 1.28X - 1.06Z / Y, where X, Y, and Z are three parameters in the C, I, E coordinate system published by the International Commission on Illumination, i.e., the reflectance measured with a red filter is the X value under a fixed light source; the Y value is measured with a green filter; and the Z value is measured with a blue filter.

[0091] The test results of gloss retention and yellowing resistance of samples 1-12 are shown in Table 3.

[0092] Table 3:

[0093]

[0094]

[0095] As can be seen from Tables 2 and 3:

[0096] A comparison of Sample 1 and Sample 7 reveals that by first modifying the epoxy resin with polycarboxylic acids to ensure that the modified epoxy resin does not contain benzene rings, the performance impact caused by the increase of benzene rings is avoided when combining it with linear polyester. The introduction of sulfonyl groups can improve the polarity and chemical stability of the coating, thereby reducing the reaction of electronic transitions on the π→π orbitals and avoiding yellowing and degradation caused by transition reactions under ultraviolet radiation, thus improving the anti-aging effect of the coating.

[0097] A comparison of Sample 1 and Sample 8 reveals that modifying epoxy resin with polycarboxylic acids and then further modifying it with sulfonyl chloride introduces sulfonyl groups. Due to the high reactivity and polarity of sulfonyl groups, their introduction increases the polarity of the coating. This increased polarity can suppress the generation of internal stress in the coating and further enhance its bending performance. When sulfonyl groups react with the benzene ring in the linear polyester, they disrupt the conjugation effect on the benzene ring, leading to the destruction of structures such as conjugated double or triple bonds. The increase in polarity can alter the intermolecular interaction forces, increase the regularity and order of molecules, and enhance the overall performance of the coating.

[0098] A comparison of Sample 1 and Sample 8 shows that the modified epoxy resin can react with linear polyester and curing agent to form a three-dimensional network cross-linked structure. The modified epoxy resin contains epoxy groups, which can undergo ring-opening or esterification reactions with active groups such as carboxyl or hydroxyl groups in the linear polyester, thereby forming chemical bonds that enhance the bonding force between them. This results in a coating with higher cross-linking density and crystallinity, improving the durability and chemical stability of the coating.

[0099] In summary, this invention first modifies epoxy resin with polycarboxylic acids to eliminate benzene rings, and then further modifies it with sulfonyl chloride to introduce sulfonyl groups. When combined with linear polyesters, curing agents, and other raw materials, the introduced sulfonyl groups, through their reaction with the benzene rings in the linear polyester, disrupt the conjugation effect on the benzene rings, leading to the destruction of conjugated double or triple bonds, increasing the polarity and chemical stability of the coating, and forming a three-dimensional cross-linked network structure. Furthermore, ring-opening or esterification reactions with active groups such as carboxyl or hydroxyl groups in the linear polyester enable the formation of chemical bonds, strengthening the bonding force and resulting in higher cross-linking density and crystallinity. The coating is effective and, when exposed to ultraviolet light, can inhibit chemical reactions, thereby reducing the electron transition reaction on the π→π orbital and improving the anti-aging effect of the coating. The powder coating for coiled steel prepared by this invention has an impact resistance of 69.3 kg / cm at room temperature and 67.4 kg / cm at -20℃, and an abrasion resistance of 3.56. It also has a bending resistance of ≤1 mm for cylindrical shafts and a cupping value of 9 mm, exhibiting excellent mechanical properties. The pencil hardness also meets national standards. In the application of coiled steel coating, it can provide excellent gloss retention (weather resistance) and yellowing resistance (anti-aging), and can be widely used in coiled steel coating.

[0100] 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. A method for preparing a powder coating for coiled steel, characterized in that, Includes the following steps: S1. Weigh the following raw materials by mass percentage: S2. Add the epoxy resin and polyhydroxy acid from S1 into the reaction vessel, mix them in the solvent, and heat the mixture to obtain mixture A. S3. The sulfonyl chloride and mixture A are placed in a reaction vessel to complete the sulfonation reaction. The pH is adjusted to 5-7 by alkaline solution. After washing with water and drying, the modified epoxy resin is obtained. S4. Modified epoxy resin, linear polyester, curing agent, diamond coating wax powder, leveling agent, benzoin, pigment and filler are added to the mixer Misacla cylinder and mixed. Then, the mixture is sequentially processed through melt extrusion, tableting, crushing and pulverizing. S5. The product from S4 is sieved and graded in a screening machine to obtain powder coating for coiled steel.

2. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In S1, the curing agent is one of triglycidyl isocyanurate, m-phenylenediamine, or diaminodiphenylmethane; the leveling agent is PV88 leveling agent; the pigment is one of ultramarine, ultramarine violet, or iron oxide; and the filler is one of calcium carbonate, barium sulfate, mica powder, or glass microspheres.

3. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In step S2, the solvent is one of acetone, methanol, or ethanol; the processing temperature is 60-100℃, and the processing time is 1-3h.

4. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In step S3, the sulfonation reaction is carried out at a temperature of 80-150°C for 2-4 hours; the alkaline solution is potassium hydroxide with a concentration of 5-10 wt%; and the drying temperature is 50-70°C for 1-2 hours.

5. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In S2 and S3, the mass ratio of epoxy resin, polyhydroxy acid and sulfonyl chloride is 1:0.05-0.2:0.03-0.

1.

6. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In step S4, the mixing time is: 2-4 minutes for low-speed mixing and 5-8 minutes 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.

7. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In S4, melt extrusion refers to adding the mixed product to a twin-screw extruder for extrusion, wherein the temperature of the feeding section is 80-85℃, the temperature of the extruder head is 95-100℃, and the residence time is 45-60s.

8. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In S4, the tableting process refers to: compressing the melt-extruded product into tablets using a tableting machine.

9. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In step S4, the pulverization process is performed by using an airflow vortex pulverizer for graded pulverization, wherein the main mill frequency is 35-45Hz and the auxiliary mill frequency is 30-35Hz.

10. The method for preparing a powder coating for coiled steel according to claim 1, characterized in that: In S5, the sieving and grading process involves passing the material through a 180-200 mesh sieve.

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