Epoxy modified polyester coating for steel coil and preparation method thereof

Abstract

The present application relates to the technical field of steel coil coatings, and more specifically, to an epoxy-modified polyester coating applied to steel coils and a preparation method thereof. By mass, the raw materials include: 30-60 parts of epoxy-modified polyester resin, 10-25 parts of curing agent, 5-20 parts of pigment filler, 2-5 parts of cellulose nano whiskers, 1-5 parts of anti-settling agent, 0.2-2 parts of wetting dispersant, 0.2-1 parts of leveling agent, 0.1-1 parts of acid catalyst, 0.1-0.5 parts of pH regulator, and 20-40 parts of deionized water. The present application solves the technical problems that solvent-based steel coil coatings are not environmentally friendly and cannot balance environmental protection with flexibility, water resistance, salt spray resistance, moisture and heat resistance, and acid and alkali resistance. The obtained coating can be used for bottom and surface integration, and the coating film has excellent flexibility, water resistance, salt spray resistance, moisture and heat resistance, and acid and alkali resistance.

Description

Technical Field

[0001] The present application relates to the technical field of steel coil coatings, and more specifically, to an epoxy-modified polyester coating applied to steel coils and a preparation method thereof. Background Art

[0002] Coil coating refers to a coating used in the pre-coating process of coiled steel. It is increasingly used in the fields of construction, home appliances, automobiles, decoration, etc. In order to ensure that the coil coating does not crack and wear during the coil processing and forming process, it is necessary for the coil coating to have better flexibility and friction resistance than ordinary metal coatings.

[0003] At present, coil coatings are usually solvent-based coatings. Water-based coil coatings are limited due to poor water resistance and flexibility, and the coating is prone to cracking and damage during the coil processing and forming process.

[0004] In addition, coil coatings used in home appliances have higher quality requirements than coil coatings used in buildings. The coatings need to be resistant to pollution, corrosion, and detergents, etc. Moreover, due to the wide variety of home appliances, different uses and usage environments, higher requirements are placed on coil coatings. For example, coil coatings used in washing machines need to have better salt spray resistance, moisture and heat resistance, and acid and alkali resistance, etc., because washing machines are generally placed in bathrooms.

[0005] The Chinese patent with publication number CN110845710A discloses an epoxy-modified polyester resin and its preparation method and application. The raw materials thereof include the following components by weight percentage: neopentyl glycol 20-40%; 2-methyl-1,3-propanediol 2-10%; trimethylolpropane 0-5%; terephthalic acid 5-25%; isophthalic acid 5-25%; sebacic acid 5-15%; epoxy resin 2-8%; organic tin catalyst 0.1-0.5%; solvent 35-45%. The resin is suitable for steel coil home appliance primer, especially steel coil home appliance primer that can match high-smooth surface galvanized sheet, and the primer obtained has excellent adhesion to the high-smooth surface galvanized sheet, and has good physical and mechanical properties as well as water resistance and chemical resistance. However, the technical solution is a solvent-based coating, which is inconsistent with the trend of green and environmentally friendly coil coatings.

[0006] The Chinese patent with publication number CN114836111A discloses a fluorine-modified polyester system water-based coil coating and its preparation method, which is composed of water-based fluorine-modified polyester resin, amino resin, pigment filler, catalyst, leveling agent, adhesion promoter, deionized water, dispersant, film-forming aid, defoamer, wetting agent, pH adjuster, etc. Among them, the fluorine-modified polyester resin is prepared by reacting hexafluoroalkylene oxide, methanol, diethylene glycol, trimethylolpropane, tert-butyl glycidyl carbonate, 1,4-cyclohexanedicarboxylic acid, phthalic anhydride, isophthalic acid, neutralizer, deionized water and other raw materials; this technical solution has both the ultra-long weather resistance of fluorine-containing polyester coatings and the salt spray resistance, corrosion resistance, powdering resistance, folding resistance and other properties of fluorine-containing polyester coatings, and has very good environmental protection. It is a water-based protective coating that is very suitable for metal coils. However, the flexibility, acid and alkali resistance of this technical solution can be further improved, and the moisture and heat resistance performance is not disclosed. It may be subject to certain restrictions when used in washing machines. In addition, the coil coatings in the prior art are mostly used for the base layer and the surface layer respectively, and the coatings that combine the base and the surface are rarely used. Summary of the invention

[0007] The purpose of the present application is to provide an epoxy-modified polyester coating for steel coils and a preparation method thereof, so as to solve the technical problems in the prior art that solvent-based steel coil coatings are not environmentally friendly and water-based coatings are not flexible and water-resistant. The prior art steel coil coatings are mostly used for the base layer and the surface layer separately, and the base-surface integrated coatings are rarely used. When used for household appliances, especially for washing machines, they cannot achieve a balance between environmental protection and flexibility, water resistance, salt spray resistance, moisture and heat resistance, and acid and alkali resistance.

[0008] The first aspect of the present application provides an epoxy-modified polyester coating for coil steel, wherein the raw materials include, by weight: 30-60 parts of epoxy-modified polyester resin, 10-25 parts of curing agent, 5-20 parts of pigment filler, 2-5 parts of cellulose nano whiskers, 1-5 parts of anti-settling agent, 0.2-2 parts of wetting and dispersing agent, 0.2-1 parts of leveling agent, 0.1-1 parts of acid catalyst, 0.1-0.5 parts of pH regulator, and 20-40 parts of deionized water;

[0009] The pigments and fillers are titanium dioxide and talcum powder; the titanium dioxide is modified titanium dioxide;

[0010] The preparation method of the modified titanium dioxide is as follows: adding anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water to titanium dioxide, reacting for 30-60 minutes at a temperature of 40-50° C. and a stirring speed of 4000-6000 r / min, and cooling to 25° C. to obtain the modified titanium dioxide;

[0011] The mass ratio of titanium dioxide, anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water is 1: (15-20): (0.1-0.5): (0.01-0.05);

[0012] The mass ratio of the modified titanium dioxide, talc powder and cellulose nano whiskers is (5-10): (2-5): (2-3).

[0013] Preferably, the preparation method of the epoxy-modified polyester resin comprises the following steps:

[0014] S1. Under the protection of inert gas, polyol and polyacid react at 180-200°C for 3-4h to obtain polyester resin;

[0015] S2, cooling to 60-80°C, adding epoxy resin to polyester resin to react to obtain epoxy-modified polyester resin;

[0016] S3, cooling to 30-50°C, adding triethanolamine to adjust the pH to 7;

[0017] S4, adding a co-solvent and diluting to 60-70wt% solid content;

[0018] S5. Add water and dilute to 45-50wt% solid content.

[0019] Preferably, the molar ratio of the polyol to the polyacid is (1.1-1.5):1.

[0020] Preferably, the molar ratio of the polyol to the polyacid is (1.1-1.3):1, preferably 1.1:1.

[0021] Preferably, the polyol is selected from at least one of 1,4-butanediol, ethylene glycol, propylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, trimethylolpropane and trimethylolethane, preferably a combination of 1,4-butanediol and ethylene glycol.

[0022] Preferably, the mass ratio of 1,4-butanediol to ethylene glycol is (2-5):(1-3), preferably 4:2.

[0023] Preferably, the polyacid is selected from at least one of isophthalic acid, adipic acid, 1,4-succinic acid and phthalic anhydride, preferably a combination of isophthalic acid and adipic acid.

[0024] Preferably, the mass ratio of isophthalic acid to adipic acid is (1-3):(2-3), preferably 2:3.

[0025] Preferably, the mass ratio of the epoxy resin to the polyester resin is (5-20):100.

[0026] Preferably, the mass ratio of the epoxy resin to the polyester resin is (5-15):100, preferably 10:100.

[0027] Preferably, the epoxy resin is a hydrogenated epoxy resin.

[0028] Preferably, the epoxide equivalent of the hydrogenated epoxy resin is 400-700 g / mol, preferably 550-650 g / mol.

[0029] The applicant found in the experiment that when the specific polyol, polyacid, epoxy resin, specific polyol, polyacid molar ratio and specific epoxy resin, polyester resin mass ratio of the present application are selected, the coating prepared by the epoxy-modified polyester resin is used for steel coils as a bottom-to-surface coating. The cured coating film is smooth and flat, has good adhesion, and unexpectedly found that the hardness of the coating film can reach 3H while the T-bend achieves 0T. The applicant speculates that this is because the epoxy-modified polyester resin obtained in the present application has a suitable molecular weight, active group and polar group, on the one hand, it can avoid the coating viscosity from being too large to affect the coating performance, and at the same time, the active groups distributed on the molecular chain of the epoxy-modified polyester resin can more evenly undergo cross-linking reaction, so that the curing cross-linking is more sufficient, forming a more uniform and dense network structure, on the other hand, the appropriate amount of polar groups in the epoxy-modified polyester resin can interact with the polar groups on the surface of the steel coil, so the coating film has good adhesion; in addition, the expansion effect of the epoxy resin embedded in the molecular chain of the epoxy-modified polyester resin during the curing process offsets the volume shrinkage of the polyester during the curing process, so that the coating film has high hardness and high flexibility.

[0030] Preferably, the co-solvent is selected from at least one of n-butanol, isopropanol, ethylene glycol monobutyl ether and propylene glycol methyl ether, preferably a combination of n-butanol and ethylene glycol monobutyl ether.

[0031] Preferably, the mass ratio of n-butanol to ethylene glycol monobutyl ether is (1.5-2):1, preferably 1.8:1.

[0032] The applicant discovered during the experiment that the coating film prepared by epoxy-modified polyester resin has good adhesion and flexibility, but because it is a water-based coating, its water resistance, especially water boiling resistance, is poor. To solve the above problems, the applicant discovered that when the pigment filler is titanium dioxide modified with a specific particle size and talcum powder with a specific particle size, the obtained coating film has excellent water boiling resistance and does not break after being boiled in boiling water for 2 hours. At the same time, the applicant unexpectedly discovered that when the mass ratio of modified titanium dioxide, talcum powder and cellulose nano whiskers is controlled to be (5-10): (2-5): (2-3), the moisture and heat resistance of the bottom and top integrated coating film is significantly improved. The applicant speculates that this is because the modified titanium dioxide is dispersed in the coating and gradually migrates to the outer surface of the coating, making it difficult for water molecules to contact the hydrophilic groups. At the same time, the flaky talcum powder and needle-shaped cellulose nanowhiskers can cooperate with the migrated titanium dioxide to form a more dense and dense protective layer on the surface of the coating, avoiding the existence of tiny gaps in the coating, so that the coating has excellent resistance to boiling water and moisture and heat.

[0033] Preferably, the curing agent comprises an amino resin and an isocyanate, and the mass ratio of the epoxy-modified polyester resin, the amino resin and the isocyanate is (35-55):(5-15):(2-8), preferably (35-45):(8-12):(4-6), and further preferably 40:10:5.

[0034] Preferably, the amino resin is selected from at least one of methyl etherified melamine resin, butyl etherified melamine resin and benzoguanamine formaldehyde resin.

[0035] Preferably, the amino resin is methyl etherified melamine resin.

[0036] Preferably, the methyl etherified melamine resin is a high-imino methyl etherified melamine resin.

[0037] Preferably, the high-iminomethyletherified melamine resin has a low-volatile component content (45°C / 45′) of 76-87%, preferably 76-81%.

[0038] Preferably, the isocyanate is selected from at least one of aliphatic isocyanate and aromatic isocyanate.

[0039] Preferably, the isocyanate is an aliphatic isocyanate.

[0040] Preferably, the aliphatic isocyanate is a blocked aliphatic polyisocyanate.

[0041] Preferably, the NCO content (based on solid content) of the blocked aliphatic polyisocyanate is 8-20%, preferably 10-15%, and more preferably 11.5±0.5%.

[0042] The applicant discovered during the experiment that when amino resin is used as a curing agent, bubbles are likely to appear during the curing process when the obtained coating is used as a bottom surface. However, when amino resin and isocyanate are used as curing agents, the blocked aliphatic polyisocyanate and high iminomethyl etherified melamine resin are cross-linked with the epoxy-modified polyester resin in stages during the curing process, which effectively adjusts the chemical reaction rate and cross-linking density of the coating and avoids bubbles during the curing process. At the same time, the applicant discovered that controlling the mass ratio of epoxy-modified polyester resin, amino resin and isocyanate to (35-55): (5-15): (2-8), especially when (35-45): (8-12): (4-6), avoids the problem of increased internal stress and reduced flexibility due to excessive curing speed, and avoids the self-polymerization of isocyanate that affects the water resistance of the coating.

[0043] Preferably, the diameter of the cellulose nanowhiskers is 4-20 nm, preferably 4-10 nm.

[0044] Preferably, the anti-settling agent is selected from at least one of organic bentonite, fumed silica, and polyolefin wax, preferably fumed silica.

[0045] Preferably, the wetting and dispersing agent is selected from at least one of polycarboxylic acid amine salt and polycarboxylic acid sodium salt.

[0046] Preferably, the wetting and dispersing agent is a polycarboxylic acid amine salt.

[0047] Preferably, the leveling agent is selected from at least one of an acrylic leveling agent, a silicone leveling agent, and a fluorocarbon leveling agent.

[0048] Preferably, the leveling agent is an acrylate leveling agent.

[0049] Preferably, the acid catalyst is selected from at least one of dodecylbenzenesulfonic acid, isooctanoic acid and p-toluenesulfonic acid.

[0050] Preferably, the pH regulator is selected from at least one of dimethylethanolamine and ammonia water.

[0051] The second aspect of the present application provides a method for preparing an epoxy-modified polyester coating for coiled steel, comprising the following steps: adding deionized water, a dispersing wetting agent, an epoxy-modified polyester resin, a curing agent, an acid catalyst, a pigment filler, a cellulose nanowhisker, an anti-settling agent, a leveling agent, and a pH adjuster in sequence according to parts by mass and mixing them evenly.

[0052] Beneficial effects:

[0053] 1. When the specific polyol, polyacid, epoxy resin, specific molar ratio of polyol and polyacid and specific mass ratio of epoxy resin and polyester resin are used in the present application, the coating prepared by epoxy-modified polyester resin is used for coiled steel as a bottom-to-top coating. The cured coating film is smooth and flat, has good adhesion, and the hardness of the coating film can reach 3H while the T-bend achieves 0T.

[0054] 2. When the pigments and fillers of the present application are titanium dioxide modified with a specific particle size and talc powder with a specific particle size, the obtained coating film has excellent water boiling resistance and does not break after being boiled in boiling water for 2 hours.

[0055] 3. When the mass ratio of modified titanium dioxide, talc and cellulose nano whiskers is controlled to (5-10): (2-5): (2-3) in this application, the moisture and heat resistance of the bottom and top integrated coating is significantly improved.

[0056] 4. When the present application adopts amino resin and isocyanate as curing agents, the blocked isocyanate and amino resin are cross-linked with the epoxy-modified polyester resin in stages during the curing process, which effectively adjusts the chemical reaction rate and cross-linking density of the coating and avoids bubbles during the curing process.

[0057] 5. The present application controls the mass ratio of epoxy modified polyester resin, amino resin and isocyanate to (35-55): (5-15): (2-8), thereby avoiding the problem of increased internal stress and reduced flexibility due to too fast curing speed, and avoiding the self-polymerization of isocyanate that affects the water resistance of the coating. DETAILED DESCRIPTION

[0058] In order to better explain the present application, the following will combine the examples in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. The embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other implementation methods obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0059] Example 1

[0060] Example 1 provides an epoxy-modified polyester coating for coil steel, wherein the raw materials include, by mass: 40 parts of epoxy-modified polyester resin, 10 parts of high-imino methyl etherified melamine resin, 5 parts of blocked aliphatic polyisocyanate, 8 parts of modified titanium dioxide, 3 parts of talc, 3 parts of cellulose nano whiskers, 3 parts of fumed silica, 1 part of polycarboxylic acid amine salt, 0.5 parts of acrylate leveling agent, 0.5 parts of dodecylbenzene sulfonic acid, 0.3 parts of ammonia water, and 30 parts of deionized water;

[0061] The preparation method of the modified titanium dioxide is as follows: adding anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water to titanium dioxide, reacting for 45 minutes at a temperature of 45° C. and a stirring speed of 5000 r / min, and cooling to 25° C. to obtain the modified titanium dioxide;

[0062] The mass ratio of the titanium dioxide, anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water is 1:18:0.3:0.02; the titanium dioxide is rutile titanium dioxide with a particle size of 20 nm, purchased from Beijing Zhongke Keyou Technology Co., Ltd., model: ZKKY-T220.

[0063] The talcum powder has a D50 of 2.7±0.2 µm and is purchased from Hetai Powder, model: TP-999A.

[0064] The preparation method of the epoxy-modified polyester resin comprises the following steps:

[0065] S1. Under the protection of inert gas, polyol and polyacid react at 190°C for 3h to obtain polyester resin;

[0066] S2, cooling to 65°C, adding epoxy resin to polyester resin to obtain epoxy-modified polyester resin;

[0067] S3, cooling to 45°C, adding triethanolamine to adjust the pH to 7;

[0068] S4, adding a co-solvent and diluting to 65wt% solid content;

[0069] S5. Add water and dilute to 50 wt% solid content.

[0070] The molar ratio of the polyol to the polyacid is 1.1:1.

[0071] The polyol is a combination of 1,4-butanediol and ethylene glycol.

[0072] The mass ratio of 1,4-butanediol to ethylene glycol is 4:2.

[0073] The polyacid is a combination of isophthalic acid and adipic acid.

[0074] The mass ratio of isophthalic acid to adipic acid is 2:3.

[0075] The mass ratio of the epoxy resin to the polyester resin is 10:100.

[0076] The epoxy resin is a hydrogenated epoxy resin.

[0077] The hydrogenated epoxy resin has an epoxy equivalent of 550-650 g / mol and is purchased from Shanghai Li Luo Industrial Co., Ltd., model: XY-5080.

[0078] The co-solvent is a combination of n-butanol and ethylene glycol monobutyl ether.

[0079] The mass ratio of n-butanol to ethylene glycol monobutyl ether is 1.8:1.

[0080] The high-iminomethyl etherified melamine resin has a low-volatile content (45°C / 45′) of 76-81% and is purchased from Changxin Resin (Guangdong) Co., Ltd. Model: CYMEL-385.

[0081] The NCO content (based on solid content) of the blocked aliphatic polyisocyanate is 11.5±0.5%, and the model is Imprafix® 2794 from Covestro.

[0082] The cellulose nano whiskers have a diameter of 4-10 nm and are purchased from Guilin Qihongke Co., Ltd.

[0083] The fumed silica, model: Degussa AEROSIL R202.

[0084] The polycarboxylate amine salt, model: TRITON@ CF-10 from Dow Chemical.

[0085] The acrylic leveling agent, model: BYK-381.

[0086] A preparation method of an epoxy-modified polyester coating for coiled steel comprises the following steps: adding deionized water, polycarboxylic acid amine salt, epoxy-modified polyester resin, high-imino methyl etherified melamine resin, blocked aliphatic polyisocyanate, dodecylbenzene sulfonic acid, modified titanium dioxide, talcum powder, cellulose nano whiskers, fumed silica, acrylate leveling agent and ammonia water in order by mass and mixing them evenly to obtain the coating.

[0087] Example 2

[0088] Example 2 provides an epoxy-modified polyester coating for coil steel, wherein the raw materials include, by mass: 35 parts of epoxy-modified polyester resin, 8 parts of high-imino methyl etherified melamine resin, 4 parts of blocked aliphatic polyisocyanate, 5 parts of modified titanium dioxide, 2 parts of talc, 2 parts of cellulose nano whiskers, 2 parts of fumed silica, 0.5 parts of polycarboxylic acid amine salt, 0.3 parts of acrylate leveling agent, 0.3 parts of dodecylbenzene sulfonic acid, 0.2 parts of ammonia water, and 25 parts of deionized water;

[0089] The preparation method of the modified titanium dioxide is as follows: adding anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water to titanium dioxide, reacting for 45 minutes at a temperature of 45° C. and a stirring speed of 5000 r / min, and cooling to 25° C. to obtain the modified titanium dioxide;

[0090] The mass ratio of the titanium dioxide, anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water is 1:18:0.3:0.02; the titanium dioxide is rutile titanium dioxide with a particle size of 20 nm, purchased from Beijing Zhongke Keyou Technology Co., Ltd., model: ZKKY-T220.

[0091] The talcum powder has a D50 of 2.7±0.2 µm and is purchased from Hetai Powder, model: TP-999A.

[0092] The preparation method of the epoxy-modified polyester resin comprises the following steps:

[0093] S1. Under the protection of inert gas, polyol and polyacid react at 190°C for 3h to obtain polyester resin;

[0094] S2, cooling to 65°C, adding epoxy resin to polyester resin to obtain epoxy-modified polyester resin;

[0095] S3, cooling to 45°C, adding triethanolamine to adjust the pH to 7;

[0096] S4, adding a co-solvent and diluting to 65wt% solid content;

[0097] S5. Add water and dilute to 50 wt% solid content.

[0098] The molar ratio of the polyol to the polyacid is 1.1:1.

[0099] The polyol is a combination of 1,4-butanediol and ethylene glycol.

[0100] The mass ratio of 1,4-butanediol to ethylene glycol is 4:2.

[0101] The polyacid is a combination of isophthalic acid and adipic acid.

[0102] The mass ratio of isophthalic acid to adipic acid is 2:3.

[0103] The mass ratio of the epoxy resin to the polyester resin is 10:100.

[0104] The epoxy resin is a hydrogenated epoxy resin.

[0105] The hydrogenated epoxy resin has an epoxy equivalent of 550-650 g / mol and is purchased from Shanghai Li Luo Industrial Co., Ltd., model: XY-5080.

[0106] The co-solvent is a combination of n-butanol and ethylene glycol monobutyl ether.

[0107] The mass ratio of n-butanol to ethylene glycol monobutyl ether is 1.8:1.

[0108] The high-iminomethyl etherified melamine resin has a low-volatile content (45°C / 45′) of 76-81% and is purchased from Changxin Resin (Guangdong) Co., Ltd. Model: CYMEL-385.

[0109] The NCO content (based on solid content) of the blocked aliphatic polyisocyanate is 11.5±0.5%, and the model is Imprafix® 2794 from Covestro.

[0110] The cellulose nano whiskers have a diameter of 4-10 nm and are purchased from Guilin Qihongke Co., Ltd.

[0111] The fumed silica, model: Degussa AEROSIL R202.

[0112] The polycarboxylate amine salt, model: TRITON@ CF-10 from Dow Chemical.

[0113] The acrylic leveling agent, model: BYK-381.

[0114] A preparation method of an epoxy-modified polyester coating for coiled steel comprises the following steps: adding deionized water, polycarboxylic acid amine salt, epoxy-modified polyester resin, high-imino methyl etherified melamine resin, blocked aliphatic polyisocyanate, dodecylbenzene sulfonic acid, modified titanium dioxide, talcum powder, cellulose nano whiskers, fumed silica, acrylate leveling agent and ammonia water in order by mass and mixing them evenly to obtain the coating.

[0115] Example 3

[0116] Example 3 provides an epoxy-modified polyester coating for coil steel, wherein the raw materials include, by mass: 50 parts of epoxy-modified polyester resin, 15 parts of high-imino methyl etherified melamine resin, 8 parts of blocked aliphatic polyisocyanate, 10 parts of modified titanium dioxide, 5 parts of talc, 3 parts of cellulose nano whiskers, 5 parts of fumed silica, 1.5 parts of polycarboxylic acid amine salt, 1 part of acrylate leveling agent, 1 part of dodecylbenzene sulfonic acid, 0.5 parts of ammonia water, and 40 parts of deionized water;

[0117] The preparation method of the modified titanium dioxide is as follows: adding anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water to titanium dioxide, reacting for 45 minutes at a temperature of 45° C. and a stirring speed of 5000 r / min, and cooling to 25° C. to obtain the modified titanium dioxide;

[0118] The mass ratio of the titanium dioxide, anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water is 1:18:0.3:0.02; the titanium dioxide is rutile titanium dioxide with a particle size of 20 nm, purchased from Beijing Zhongke Keyou Technology Co., Ltd., model: ZKKY-T220.

[0119] The talcum powder has a D50 of 2.7±0.2 µm and is purchased from Hetai Powder, model: TP-999A.

[0120] The preparation method of the epoxy-modified polyester resin comprises the following steps:

[0121] S1. Under the protection of inert gas, polyol and polyacid react at 190°C for 3h to obtain polyester resin;

[0122] S2, cooling to 65°C, adding epoxy resin to polyester resin to obtain epoxy-modified polyester resin;

[0123] S3, cooling to 45°C, adding triethanolamine to adjust the pH to 7;

[0124] S4, adding a co-solvent and diluting to 65wt% solid content;

[0125] S5. Add water and dilute to 50 wt% solid content.

[0126] The molar ratio of the polyol to the polyacid is 1.1:1.

[0127] The polyol is a combination of 1,4-butanediol and ethylene glycol.

[0128] The mass ratio of 1,4-butanediol to ethylene glycol is 4:2.

[0129] The polyacid is a combination of isophthalic acid and adipic acid.

[0130] The mass ratio of isophthalic acid to adipic acid is 2:3.

[0131] The mass ratio of the epoxy resin to the polyester resin is 10:100.

[0132] The epoxy resin is a hydrogenated epoxy resin.

[0133] The hydrogenated epoxy resin has an epoxy equivalent of 550-650 g / mol and is purchased from Shanghai Li Luo Industrial Co., Ltd., model: XY-5080.

[0134] The co-solvent is a combination of n-butanol and ethylene glycol monobutyl ether.

[0135] The mass ratio of n-butanol to ethylene glycol monobutyl ether is 1.8:1.

[0136] The high-iminomethyl etherified melamine resin has a low-volatile content (45°C / 45′) of 76-81% and is purchased from Changxin Resin (Guangdong) Co., Ltd. Model: CYMEL-385.

[0137] The NCO content (based on solid content) of the blocked aliphatic polyisocyanate is 11.5±0.5%, and the model is Imprafix® 2794 from Covestro.

[0138] The cellulose nano whiskers have a diameter of 4-10 nm and are purchased from Guilin Qihongke Co., Ltd.

[0139] The fumed silica, model: Degussa AEROSIL R202.

[0140] The polycarboxylate amine salt, model: TRITON@ CF-10 from Dow Chemical.

[0141] The acrylic leveling agent, model: BYK-381.

[0142] A preparation method of an epoxy-modified polyester coating for coiled steel comprises the following steps: adding deionized water, polycarboxylic acid amine salt, epoxy-modified polyester resin, high-imino methyl etherified melamine resin, blocked aliphatic polyisocyanate, dodecylbenzene sulfonic acid, modified titanium dioxide, talcum powder, cellulose nano whiskers, fumed silica, acrylate leveling agent and ammonia water in order by mass and mixing them evenly to obtain the coating.

[0143] Comparative Example 1

[0144] Comparative Example 1 provides an epoxy-modified polyester coating for coil steel, and its specific implementation method is the same as that of Example 1, except that, by weight, the raw materials include: 40 parts of epoxy-modified polyester resin, 15 parts of high-imino methyl ether melamine resin, 8 parts of modified titanium dioxide, 3 parts of talc, 3 parts of cellulose nanowhiskers, 3 parts of fumed silica, 1 part of polycarboxylic acid amine salt, 0.5 parts of acrylate leveling agent, 0.5 parts of dodecylbenzene sulfonic acid, 0.3 parts of ammonia water, and 30 parts of deionized water.

[0145] A method for preparing an epoxy-modified polyester coating for use in coiled steel, the specific implementation method of which is the same as that of Example 1.

[0146] Comparative Example 2

[0147] Comparative Example 2 provides an epoxy-modified polyester coating for use in coiled steel. Its specific implementation method is the same as that of Example 1, except that, measured in parts by mass, the raw materials include: 40 parts of epoxy-modified polyester resin, 6 parts of high-imino methyl etherified melamine resin, 9 parts of blocked aliphatic polyisocyanate, 8 parts of modified titanium dioxide, 3 parts of talc, 3 parts of cellulose nanowhiskers, 3 parts of fumed silica, 1 part of polycarboxylic acid amine salt, 0.5 parts of acrylate leveling agent, 0.5 parts of dodecylbenzene sulfonic acid, 0.3 parts of ammonia water, and 30 parts of deionized water.

[0148] A method for preparing an epoxy-modified polyester coating for use on coiled steel, the specific implementation method of which is the same as that of Example 1.

[0149] Comparative Example 3

[0150] Comparative Example 3 provides an epoxy-modified polyester coating for use in steel coils, and its specific implementation is the same as that of Example 1, except that the titanium dioxide is not modified.

[0151] A method for preparing an epoxy-modified polyester coating for use on coiled steel, the specific implementation method of which is the same as that of Example 1.

[0152] Comparative Example 4

[0153] Comparative Example 4 provides an epoxy-modified polyester coating for use in coiled steel, and its specific implementation method is the same as that of Example 1, except that the mass ratio of titanium dioxide, anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water is 1:25:0.6:0.05.

[0154] A method for preparing an epoxy-modified polyester coating for use on coiled steel, the specific implementation method of which is the same as that of Example 1.

[0155] Comparative Example 5

[0156] Comparative Example 5 provides an epoxy-modified polyester coating for use in steel coils, and its specific implementation is the same as that of Example 1, except that the cellulose nano whiskers are replaced with talcum powder.

[0157] A method for preparing an epoxy-modified polyester coating for use on coiled steel, the specific implementation method of which is the same as that of Example 1.

[0158] Comparative Example 6

[0159] Comparative Example 6 provides an epoxy-modified polyester coating for use in coiled steel. Its specific implementation method is the same as that of Example 1, except that, in parts by mass, the raw materials include: 40 parts of epoxy-modified polyester resin, 10 parts of high-imino methyl etherified melamine resin, 5 parts of blocked aliphatic polyisocyanate, 4 parts of modified titanium dioxide, 5 parts of talc, 5 parts of cellulose nanowhiskers, 3 parts of fumed silica, 1 part of polycarboxylic acid amine salt, 0.5 parts of acrylate leveling agent, 0.5 parts of dodecylbenzene sulfonic acid, 0.3 parts of ammonia water, and 30 parts of deionized water.

[0160] A method for preparing an epoxy-modified polyester coating for use on coiled steel, the specific implementation method of which is the same as that of Example 1.

[0161] Comparative Example 7

[0162] Comparative Example 7 provides an epoxy-modified polyester coating for use in steel coils, and its specific implementation is the same as that of Example 1, except that the hydrogenated epoxy resin is replaced by epoxy resin E44.

[0163] A method for preparing an epoxy-modified polyester coating for use on coiled steel, the specific implementation method of which is the same as that of Example 1.

[0164] Performance test: The coating prepared in Examples 1-3 and Comparative Examples 1-7 was roller-coated on the coiled steel and cured at 230°C for 60s. The coating thickness was 15µm. Referring to the test method of GB / T 13448-2019, the coating was tested for the items shown in Table 1.

[0165] Table 1 Performance test results of coatings prepared in Examples 1-3 and Comparative Examples 1-7

[0166]

[0167] It can be seen from Table 1 that in Comparative Example 1, when the curing agent contains only high-imino methyl etherified melamine resin and does not contain blocked aliphatic polyisocyanate, bubbles appear in the coating film. Compared with Example 1, the coating film appearance, hardness, T-bend, boiling water resistance, acid resistance, alkali resistance, solvent resistance, neutral salt spray resistance and moisture and heat resistance are significantly reduced, and the adhesion is slightly reduced.

[0168] In Comparative Example 2, when the mass ratio of epoxy-modified polyester resin, high-iminomethyl etherified melamine resin, and blocked aliphatic polyisocyanate is not in the range of (35-55): (5-15): (2-8), compared with Example 1, the hardness, T-bend, and adhesion of the coating film are slightly reduced, and the boiling water resistance, neutral salt spray resistance, and moisture and heat resistance are significantly reduced.

[0169] In Comparative Example 3, when titanium dioxide is not modified, the adhesion of the coating is slightly reduced compared with Example 1, and the boiling water resistance, acid resistance, alkali resistance, neutral salt spray resistance and moisture and heat resistance are significantly reduced.

[0170] Comparative Example 4 When the mass ratio of titanium dioxide, anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water during the titanium dioxide modification process is not in the range of 1: (15-20): (0.1-0.5): (0.01-0.05), compared with Example 1, the adhesion, boiling water resistance, acid resistance, alkali resistance, solvent resistance, neutral salt spray resistance and moisture and heat resistance of the coating film are significantly reduced.

[0171] Comparative Example 5 When cellulose nano whiskers do not exist in the system, compared with Example 1, the hardness, T-bend and adhesion of the coating are slightly reduced, and the boiling water resistance, acid resistance, alkali resistance, neutral salt spray resistance and moisture and heat resistance are significantly reduced.

[0172] In Comparative Example 6, when the mass ratio of modified titanium dioxide, talc and cellulose nanowhiskers is not in the range of (5-10): (2-5): (2-3), compared with Example 1, the hardness and adhesion of the coating film are slightly reduced, and the T-bend, boiling water resistance, acid resistance, alkali resistance, solvent resistance, neutral salt spray resistance and moisture and heat resistance properties are significantly reduced.

[0173] In Comparative Example 7, when the hydrogenated epoxy resin in the preparation process of the epoxy-modified polyester resin is replaced by epoxy resin E44, compared with Example 1, the hardness, T-bend and adhesion of the coating film are slightly reduced, and the moisture and heat resistance is significantly reduced.

[0174] The above description is only a specific embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent transformation made using the present application, or directly or indirectly applied in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. An epoxy-modified polyester coating for steel coils, characterized in that: The raw materials include, by weight: 30-60 parts of epoxy modified polyester resin, 10-25 parts of curing agent, 5-20 parts of pigment and filler, 2-5 parts of cellulose nano whiskers, 1-5 parts of anti-settling agent, 0.2-2 parts of wetting and dispersing agent, 0.2-1 parts of leveling agent, 0.1-1 parts of acid catalyst, 0.1-0.5 parts of pH regulator, and 20-40 parts of deionized water; The preparation method of the epoxy-modified polyester resin comprises the following steps: S1. Under the protection of inert gas, polyol and polyacid react at 180-200°C for 3-4h to obtain polyester resin; S2, cooling to 60-80°C, adding epoxy resin to polyester resin to react to obtain epoxy-modified polyester resin; S3, cooling to 30-50°C, adding triethanolamine to adjust the pH to 7; S4, adding a co-solvent and diluting to 60-70wt% solid content; S5, add water and dilute to 45-50wt% solid content; The epoxy resin is a hydrogenated epoxy resin; the epoxy equivalent of the hydrogenated epoxy resin is 400-700 g / mol; The pigments and fillers are modified titanium dioxide and talcum powder; The preparation method of the modified titanium dioxide is as follows: adding anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water to titanium dioxide, reacting for 30-60 minutes at a temperature of 40-50° C. and a stirring speed of 4000-6000 r / min, and cooling to 25° C. to obtain the modified titanium dioxide; The mass ratio of titanium dioxide, anhydrous ethanol, 3,3,3-trifluoropropylmethyldimethoxysilane and ammonia water is 1: (15-20): (0.1-0.5): (0.01-0.05); The mass ratio of the modified titanium dioxide, talc and cellulose nano whiskers is (5-10): (2-5): (2-3); The curing agent comprises amino resin and isocyanate, and the mass ratio of the epoxy-modified polyester resin, amino resin and isocyanate is (35-55): (5-15): (2-8).

2. The epoxy-modified polyester coating for steel coil according to claim 1, characterized in that: The molar ratio of the polyol to the polyacid is (1.1-1.5):

1.

3. The epoxy-modified polyester coating for steel coil according to claim 1 or 2, characterized in that: The mass ratio of the epoxy resin to the polyester resin is (5-20):

100.

4. The epoxy-modified polyester coating for steel coil according to claim 3, characterized in that: The amino resin is selected from at least one of methyl etherified melamine resin, butyl etherified melamine resin and benzoguanamine formaldehyde resin.

5. The epoxy-modified polyester coating for steel coil according to claim 4, characterized in that: The isocyanate is selected from at least one of aliphatic isocyanate and aromatic isocyanate.

6. A method for preparing the epoxy-modified polyester coating for coiled steel according to claim 1, characterized in that: The method comprises the following steps: adding deionized water, a dispersing wetting agent, an epoxy modified polyester resin, a curing agent, an acid catalyst, a pigment filler, a cellulose nano whisker, an anti-settling agent, a leveling agent and a pH regulator in order by weight and mixing them evenly to obtain the product.

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