An aqueous protective baking paint for hardware parts and its preparation method

Abstract

The present invention belongs to the technical field of amino baking varnishes, and particularly relates to a waterborne protective baking varnish for hardware parts and a preparation method thereof. As the film-forming substance of the waterborne protective baking varnish, the obtained waterborne hydroxyl acrylic resin has poor adhesion on the surface of the metal substrate and poor salt spray resistance. In view of the above problems, the present invention provides a waterborne protective baking varnish for hardware parts, and the obtained epoxy-modified polyurethane dispersion retains rich epoxy polar groups in the main resin structure, significantly improving the adhesion and salt spray resistance of the amino baking varnish.

Description

Technical Field

[0001] The present invention belongs to the technical field of amino baking varnishes, and particularly relates to an aqueous protective baking varnish for hardware parts and a preparation method thereof. Background Art

[0002] At present, the main disadvantages of the aqueous protective baking varnishes for hardware parts in the domestic and foreign markets are as follows: As the film-forming substance of the aqueous protective baking varnish, the obtained film of the aqueous hydroxyl acrylic resin has poor adhesion on the surface of the metal substrate and poor salt spray resistance. In addition, the baking temperature of the aqueous amino baking varnish reaches 120 - 140 °C, and the acrylic resin is prone to yellowing at high temperatures. Therefore, it is necessary to develop an aqueous protective amino baking varnish for hardware parts with good adhesion, excellent salt spray resistance, and not easily discolored during high-temperature baking to meet the market demand. Summary of the Invention

[0003] The problems existing in the prior art are: As the film-forming substance of the aqueous protective baking varnish, the obtained film of the aqueous hydroxyl acrylic resin has poor adhesion on the surface of the metal substrate and poor salt spray resistance. To solve the above problems, the present invention provides an aqueous protective baking varnish for hardware parts, which comprises the following components in parts by weight:

[0004]

[0005] Specifically, the preparation method of the epoxy-modified polyurethane dispersion comprises the following steps:

[0006] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane are added to the reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system rises to 100 °C, a catalyst is added, and while stirring, the temperature of the reaction system is raised to 130 - 180 °C. After constant-temperature stirring reaction until 0.9 mol of epoxy groups in the reaction system are reduced, 15 g of a yellowing-resistant oligomer is added. The progress of the reaction is monitored by FTIR. After constant-temperature stirring reaction until the POO - absorption peak in the reaction system disappears in the infrared spectrum, the temperature of the reaction system is then lowered to 100 - 120 °C, and then a diluent and 0.7 mol of dimethylolpropionic acid are added. After that, the temperature is lowered to 80 °C while stirring, and then 0.4 mol of diisocyanate is added. The progress of the reaction is monitored by FTIR. After stirring reaction until the absorption peak of NCO - in the reaction system disappears in the infrared spectrum, the temperature of the reaction system is then lowered to 60 °C, a neutralizing agent and deionized water are added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of (40 ± 2)%.

[0007] The addition amount of the catalyst is 0.05% of the mass of the phenolic epoxy resin added.

[0008] The addition amount of the diluent is 25% of the added mass of the phenolic epoxy resin;

[0009] The addition amount of the neutralizer is 2% of the added mass of the phenolic epoxy resin.

[0010] Specifically, the catalyst includes at least one of dibutyltin dilaurate, monobutyltin oxide, dioctyltin dilaurate, concentrated phosphoric acid, and concentrated sulfuric acid.

[0011] Specifically, the diluent includes at least one of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and dipropylene glycol monobutyl ether.

[0012] Specifically, the neutralizer includes at least one of ammonia water, N,N-dimethylethanolamine, and triethylamine.

[0013] Specifically, the diisocyanate includes at least one of toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), trimethylhexane diisocyanate (TMDI), and hexamethylene diisocyanate (HDI).

[0014] Specifically, the preparation method of the yellowing-resistant oligomer includes the following steps:

[0015] Mix 35 g of γ-methacryloxypropyltrimethoxysilane, 50 g of acrylic end-capped polyphosphate (PAM100 from Solvay Co., Ltd.), 0.4 g of azobisisobutyronitrile, and 85 g of diluent evenly by stirring, then raise the temperature of the reaction system to 75 °C, stir and react at a constant temperature for 3 - 5 h, take out the product, and remove the solvent by rotary evaporation to obtain the yellowing-resistant oligomer.

[0016] Specifically, the diluent includes at least one of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and dipropylene glycol monobutyl ether.

[0017] Specifically, the amino resin includes at least one of Cymel 325 from Allnex and MR 625 from Changchun.

[0018] Specifically, the wetting and dispersing agent includes at least one of DIS-188A, BYK-190, BYK-191, EFKA-4550, EFKA-4560, Tego Dispers 760W, and W-518.

[0019] Specifically, the film-forming aid includes at least one of dipropylene glycol methyl ether, dipropylene glycol monobutyl ether, ethylene glycol monobutyl ether, tripropylene glycol monobutyl ether, diethylene glycol monobutyl ether, and ethylene glycol hexyl ether.

[0020] Specifically, the wetting agent includes at least one of Tego Wet 270, TEGO Twin 4100, Defom W-77, and Levaslip-455.

[0021] Specifically, the leveling agent includes at least one of BYK-306, BYK-307, BYK-333, BYK-346, BYK-348, and BYK-349.

[0022] The present invention has the following beneficial effects:

[0023] (1) The epoxy-modified polyurethane dispersion obtained in the present invention retains abundant epoxy polar groups in the main resin structure, which is very beneficial for improving the adhesion and salt spray resistance of amino baking varnish;

[0024] (2) The epoxy-modified polyurethane dispersion obtained in the present invention contains a large number of urethane groups in the main resin structure, which is very beneficial for improving the gloss of amino baking varnish;

[0025] (3) In the main resin structure of the epoxy-modified polyurethane dispersion obtained in the present invention, siloxane groups and phosphate groups are simultaneously introduced. The phosphate groups are similar to the phosphate fragments in the structure of phosphite antioxidants and have good high-temperature antioxidant properties. Therefore, the introduction of phosphate groups endows the obtained amino baking varnish with good high-temperature yellowing resistance, and the introduction of siloxane groups with high-temperature oxidation resistance further increases the yellowing resistance of the polymer;

[0026] (4) By using the free radical polymerization method, γ-methacryloxypropyltrimethoxysilane and acrylic acid-terminated polyphosphate are formed into oligomers. The obtained oligomers have a much higher molecular weight than the two reactants. The internal rotation of the silicon-containing oligomers is relatively large, and the entire oligomer chain segment is more likely to exist in a coiled form in the solvent water. This also makes the siloxane groups tend to be wrapped by the main resin of the dispersion, reducing the probability of contact between the siloxane groups and water, and then reducing the hydrolysis tendency of the siloxane groups, so that the obtained epoxy-modified polyurethane aqueous dispersion has better stability. Detailed Embodiments

[0027] The present invention will be described in detail below with reference to the embodiments. It should be understood that the following embodiments are only illustrative examples of the implementation modes of the present invention, rather than limiting the scope of the present invention.

[0028] The phenolic epoxy resin used in the following embodiments of the present invention is the South Asia phenolic epoxy resin NPPN-638S.

[0029] The titanium dioxide used in the following embodiments of the present invention is R706 produced by DuPont.

[0030] The preparation method of the yellowing-resistant oligomer used in the following embodiments of the present invention is as follows:

[0031] 35 g of γ-methacryloxypropyltrimethoxysilane, 50 g of acrylic acid-terminated polyphosphate (PAM100 from Solvay Limited), 0.4 g of azobisisobutyronitrile, and 85 g of ethylene glycol monobutyl ether were stirred and mixed evenly. Then, the temperature of the reaction system was raised to 75 °C, and the mixture was stirred and reacted at a constant temperature for 3 h. The product was taken out, and the solvent was removed by rotary evaporation to obtain a yellowing-resistant oligomer.

[0032] Example 1

[0033] An aqueous protective baking paint for hardware parts, by weight, has the following components:

[0034]

[0035] The amino resin is Cymel 325 from Allnex.

[0036] The preparation method of the epoxy-modified polyurethane dispersion is as follows:

[0037] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane were added to a reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system reached 100 °C, a catalyst was added. While stirring, the temperature of the reaction system was raised to 130 °C, and the reaction was stirred at a constant temperature until 0.9 mol of epoxy groups in the reaction system decreased. Then, 15 g of the yellowing-resistant oligomer was added. The progress of the reaction was monitored by FTIR. The reaction was stirred at a constant temperature until the absorption peak of POO- in the reaction system disappeared in the infrared spectrum. Then, the temperature of the reaction system was lowered to 100 °C, and a diluent and 0.7 mol of dimethylolpropionic acid were added. Then, while stirring, the temperature was lowered to 80 °C, and 0.4 mol of diisocyanate was added. The progress of the reaction was monitored by FTIR. The reaction was stirred until the absorption peak of NCO- in the reaction system disappeared in the infrared spectrum. Then, the temperature of the reaction system was lowered to 60 °C, a neutralizer and deionized water were added, and the mixture was stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 39%;

[0038] The addition amount of the catalyst is 0.05% of the mass of the phenolic epoxy resin added;

[0039] The addition amount of the diluent is 25% of the mass of the phenolic epoxy resin added;

[0040] The addition amount of the neutralizer is 2% of the mass of the phenolic epoxy resin added.

[0041] The catalyst is dibutyltin dilaurate.

[0042] The diluent is ethylene glycol monobutyl ether.

[0043] The neutralizer is ammonia water with a mass concentration of 25%.

[0044] The diisocyanate is TDI.

[0045] Example 2

[0046] An aqueous protective baking paint for hardware parts, by weight, the components are as follows:

[0047]

[0048] The amino resin is Cymel 325 from Allnex.

[0049] The preparation method of the epoxy-modified polyurethane dispersion is as follows:

[0050] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane are added to the reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system rises to 100 °C, a catalyst is added, and while stirring, the temperature of the reaction system is raised to 150 °C. After stirring and reacting at a constant temperature until 0.9 mol of epoxy groups in the reaction system are reduced, 15 g of yellowing-resistant oligomer is added. The progress of the reaction is monitored by FTIR. After stirring and reacting at a constant temperature until the absorption peak of POO- in the reaction system disappears in the infrared spectrum, the temperature of the reaction system is then lowered to 110 °C, then a diluent and 0.7 mol of dimethylolpropionic acid are added. After that, the temperature is lowered to 80 °C while stirring, then 0.4 mol of diisocyanate is added. The progress of the reaction is monitored by FTIR. After stirring and reacting until the absorption peak of NCO- in the reaction system disappears in the infrared spectrum, the temperature of the reaction system is then lowered to 60 °C, a neutralizer and deionized water are added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 41%;

[0051] The addition amount of the catalyst is 0.05% of the mass of the phenolic epoxy resin added.

[0052] The addition amount of the diluent is 25% of the mass of the phenolic epoxy resin added.

[0053] The addition amount of the neutralizer is 2% of the mass of the phenolic epoxy resin added.

[0054] The catalyst is monobutyltin oxide.

[0055] The diluent is diethylene glycol butyl ether.

[0056] The neutralizer is N,N-dimethylethanolamine.

[0057] The diisocyanate is IPDI.

[0058] Example 3

[0059] An aqueous protective baking paint for hardware parts, by weight, the components are as follows:

[0060]

[0061] The amino resin is Changchun MR 625.

[0062] The preparation method of the epoxy-modified polyurethane dispersion is as follows:

[0063] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane are added to the reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system rises to 100 °C, a catalyst is added, and while stirring, the temperature of the reaction system is raised to 160 °C. After stirring and reacting at a constant temperature until 0.9 mol of epoxy groups in the reaction system are reduced, 15 g of yellowing-resistant oligomer is added. The progress of the reaction is monitored by FTIR. After stirring and reacting at a constant temperature until the POO- absorption peak in the reaction system disappears in the infrared spectrum, the temperature of the reaction system is then lowered to 120 °C, then a diluent and 0.7 mol of dimethylolpropionic acid are added, and then the temperature is lowered to 80 °C while stirring. Then 0.4 mol of diisocyanate is added. The progress of the reaction is monitored by FTIR. After stirring and reacting until the absorption peak of NCO- in the reaction system disappears in the infrared spectrum, the temperature of the reaction system is then lowered to 60 °C, a neutralizer and deionized water are added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 38.5%;

[0064] The addition amount of the catalyst is 0.05% of the mass of the phenolic epoxy resin added.

[0065] The addition amount of the diluent is 25% of the mass of the phenolic epoxy resin added.

[0066] The addition amount of the neutralizer is 2% of the mass of the phenolic epoxy resin added.

[0067] The catalyst is dioctyltin dilaurate.

[0068] The diluent is dipropylene glycol butyl ether.

[0069] The neutralizer is triethylamine.

[0070] The diisocyanate is TMDI.

[0071] Example 4

[0072] An aqueous protective baking paint for hardware parts, in parts by weight, the components are as follows:

[0073]

[0074] The amino resin is Changchun MR 625.

[0075] The preparation method of the epoxy-modified polyurethane dispersion is as follows:

[0076] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane were added to a reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system reached 100 °C, a catalyst was added, and while stirring, the temperature of the reaction system was raised to 170 °C. After stirring and reacting at a constant temperature until 0.9 mol of epoxy groups in the reaction system decreased, 15 g of a yellowing-resistant oligomer was added. The progress of the reaction was monitored by FTIR. After stirring and reacting at a constant temperature until the POO- absorption peak in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was then lowered to 120 °C, then a diluent and 0.7 mol of dimethylolpropionic acid were added. After that, while stirring, the temperature was lowered to 80 °C, then 0.4 mol of diisocyanate was added. The progress of the reaction was monitored by FTIR. After stirring and reacting until the absorption peak of NCO- in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was then lowered to 60 °C, a neutralizer and deionized water were added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 42%;

[0077] The addition amount of the catalyst is 0.05% of the mass of the added phenolic epoxy resin;

[0078] The addition amount of the diluent is 25% of the mass of the added phenolic epoxy resin;

[0079] The addition amount of the neutralizer is 2% of the mass of the added phenolic epoxy resin.

[0080] The catalyst is concentrated phosphoric acid with a mass concentration of 85%.

[0081] The diluent is ethylene glycol monobutyl ether.

[0082] The neutralizer is triethylamine.

[0083] The diisocyanate is HDI.

[0084] Example 5

[0085] An aqueous protective baking paint for hardware parts, in parts by weight, the components are as follows:

[0086]

[0087] The amino resin is Changchun MR 625.

[0088] The preparation method of the epoxy-modified polyurethane dispersion is as follows:

[0089] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane were added to a reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system reached 100 °C, a catalyst was added, and while stirring, the temperature of the reaction system was raised to 180 °C. After constant-temperature stirring reaction until 0.9 mol of epoxy groups in the reaction system decreased, 15 g of yellowing-resistant oligomer was added. The progress of the reaction was monitored by FTIR. After constant-temperature stirring reaction until the POO- absorption peak in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was then lowered to 110 °C, then a diluent and 0.7 mol of dimethylolpropionic acid were added. After that, while stirring, the temperature was lowered to 80 °C, then 0.4 mol of diisocyanate was added. The progress of the reaction was monitored by FTIR. After stirring reaction until the absorption peak of NCO- in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was then lowered to 60 °C, a neutralizer and deionized water were added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 40%;

[0090] The addition amount of the catalyst is 0.05% of the added mass of the phenolic epoxy resin;

[0091] The addition amount of the diluent is 25% of the added mass of the phenolic epoxy resin;

[0092] The addition amount of the neutralizer is 2% of the added mass of the phenolic epoxy resin.

[0093] The catalyst is concentrated sulfuric acid with a mass concentration of 98%.

[0094] The diluent is ethylene glycol monobutyl ether.

[0095] The neutralizer is triethylamine.

[0096] The diisocyanate is TDI.

[0097] Comparative Example 1 was the same as Example 1, except that in Comparative Example 1, only a phosphate ester structure was introduced into the main resin structure of the epoxy-modified polyurethane dispersion, and no siloxane structure was introduced. The specific preparation method was as follows:

[0098] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane were added to a reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system reached 100 °C, a catalyst was added, and while stirring, the temperature of the reaction system was raised to 170 °C. After stirring and reacting at a constant temperature until 0.9 mol of epoxy groups in the reaction system decreased, 15 g of acrylic end-group polyphosphate (PAM100 from Solvay Co., Ltd.) was added. The progress of the reaction was monitored by FTIR. After stirring and reacting at a constant temperature until the absorption peak of POO- in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was lowered to 120 °C, then a diluent and 0.7 mol of dimethylolpropionic acid were added. After that, while stirring, the temperature was lowered to 80 °C, and then 0.4 mol of diisocyanate was added. The progress of the reaction was monitored by FTIR. After stirring and reacting until the absorption peak of NCO- in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was lowered to 60 °C, a neutralizing agent and deionized water were added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 39%;

[0099] The addition amount of the catalyst is 0.05% of the mass of the phenolic epoxy resin added;

[0100] The addition amount of the diluent is 25% of the mass of the phenolic epoxy resin added;

[0101] The addition amount of the neutralizing agent is 2% of the mass of the phenolic epoxy resin added.

[0102] The catalyst is dibutyltin dilaurate.

[0103] The diluent is ethylene glycol monobutyl ether.

[0104] The neutralizing agent is ammonia water with a mass concentration of 25%.

[0105] The diisocyanate is TDI.

[0106] Comparative Example 2 was the same as Example 1, except that in Comparative Example 2, only a siloxane structure was introduced into the main resin structure of the epoxy-modified polyurethane dispersion, and no phosphate structure was introduced. The specific preparation method was as follows:

[0107] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane were added to a reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system reached 100 °C, a catalyst was added, and while stirring, the temperature of the reaction system was raised to 170 °C. After stirring and reacting at a constant temperature until 0.9 mol of epoxy groups in the reaction system decreased, 15 g of γ-methacryloxypropyltrimethoxysilane was added. Then the temperature of the reaction system was lowered to 120 °C, and then a diluent and 0.7 mol of dimethylolpropionic acid were added. After that, the temperature was lowered to 80 °C while stirring, and then 0.4 mol of diisocyanate was added. The progress of the reaction was monitored by FTIR. After stirring and reacting until the absorption peak of NCO- in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was lowered to 60 °C, a neutralizer and deionized water were added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 39%;

[0108] The addition amount of the catalyst is 0.05% of the added mass of the phenolic epoxy resin;

[0109] The addition amount of the diluent is 25% of the added mass of the phenolic epoxy resin;

[0110] The addition amount of the neutralizer is 2% of the added mass of the phenolic epoxy resin.

[0111] The catalyst is dibutyltin dilaurate.

[0112] The diluent is ethylene glycol monobutyl ether.

[0113] The neutralizer is ammonia water with a mass concentration of 25%.

[0114] The diisocyanate is TDI.

[0115] Comparative Example 3 is the same as Example 1, except that in Comparative Example 3, the aqueous polyurethane dispersion Juneng Chemical PUD-643 was used to replace the epoxy-modified polyurethane dispersion in Example 1.

[0116] Comparative Example 4 is the same as Example 1, except that in Comparative Example 4, the aqueous hydroxyl acrylic resin dispersion Wuxi Honghui Acust1121 was used to replace the epoxy-modified polyurethane dispersion in Example 1.

[0117] Comparative Example 5 is the same as Example 1, except that in Comparative Example 5, both a phosphate ester structure and a siloxane structure were introduced into the main resin structure of the epoxy-modified polyurethane dispersion. The specific preparation method is as follows:

[0118] Under nitrogen protection, 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane were added to a reaction kettle, stirred and heated to dissolve. When the temperature of the reaction system reached 100 °C, a catalyst was added, and while stirring, the temperature of the reaction system was raised to 170 °C. After stirring and reacting at a constant temperature until 0.9 mol of epoxy groups in the reaction system decreased, 8.82 g of acrylic-terminated polyphosphate (PAM100 from Solvay Co., Ltd.) was added. The progress of the reaction was monitored by FTIR. After stirring and reacting at a constant temperature until the absorption peak of POO- in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was then lowered to 120 °C, and 6.18 g of γ-methacryloxypropyltrimethoxysilane was added. Then the temperature of the reaction system was lowered to 120 °C, and then a diluent and 0.7 mol of dimethylolpropionic acid were added. After that, the temperature was lowered to 80 °C while stirring, and then 0.4 mol of diisocyanate was added. The progress of the reaction was monitored by FTIR. After stirring and reacting until the absorption peak of NCO- in the reaction system disappeared in the infrared spectrum, the temperature of the reaction system was then lowered to 60 °C, a neutralizer and deionized water were added, and stirred and dispersed for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of 39%;

[0119] The addition amount of the catalyst is 0.05% of the mass of the added phenolic epoxy resin;

[0120] The addition amount of the diluent is 25% of the mass of the added phenolic epoxy resin;

[0121] The addition amount of the neutralizer is 2% of the mass of the added phenolic epoxy resin.

[0122] The catalyst is dibutyltin dilaurate.

[0123] The diluent is ethylene glycol monobutyl ether.

[0124] The neutralizer is ammonia water with a mass concentration of 25%.

[0125] The diisocyanate is TDI.

[0126] Comparative Example 6

[0127] An aqueous protective baking paint for hardware parts, in parts by weight, the components are as follows:

[0128]

[0129] The amino resin is Cymel 325 from Allnex.

[0130] Performance test

[0131] The water-based protective baking paints for the hardware parts obtained in Examples 1-5 of the present invention and the comparative examples were respectively subjected to relevant performance tests. Among them, the baking paints obtained in the examples and comparative examples of the present invention were respectively coated on the surface of a flat, clean metal substrate in the same manner, and the baking paints were baked and cured at 140 °C to obtain 11 kinds of paint films with the same thickness (25 μm). The specific test results are shown in Table 1.

[0132] The salt spray performance was tested according to the neutral salt spray method;

[0133] Glossiness: It was tested using a BGD 513 / 1 - basic gloss meter (graduation value 0.1 GU) from Biogenda;

[0134] High-temperature yellowing resistance performance: After the paint film was baked at high temperature, its color was tested using a BGD 555 precision computer color difference meter from Biogenda, and the color difference from the white paint with the same titanium dioxide addition amount was compared to calculate ΔE. When ΔE > 2, the yellowing was relatively serious.

[0135] Ductility: It was tested according to the "Method for Determining Impact Resistance of Paint Films" in GB1732-79.

[0136] Flexibility: It was tested according to GB / T1731-1993.

[0137] Hardness: Pencil hardness test was carried out according to GB / T 6739-1996.

[0138] Adhesion: It was tested according to the "Method for Determining Adhesion of Paint Films" in GB / T 1720-1979(1989).

[0139] Storage stability: The colored paint was placed in an oven at 50 °C for 30 days, and then taken out to observe whether its state was the same as before being put in.

[0140] Table 1

[0141]

[0142] Inspired by the ideal embodiments of the present invention as described above, through the above description, relevant staff can completely make various changes and modifications without departing from the technical idea of this invention. The technical scope of this invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. An aqueous protective baking paint for hardware parts, characterized in that, Comprising the following components by parts by weight: Epoxy-modified polyurethane dispersion: 65 - 75 parts Amino resin: 6.5 - 7.5 parts Wetting and dispersing agent: 0.8 - 1.2 parts Film-forming auxiliary agent: 4.5 - 5.5 parts Titanium dioxide: 20 - 22 parts Wetting agent: 0.2 - 0.5 parts Leveling agent: 0.2 - 0.5 parts; The preparation method of the epoxy-modified polyurethane dispersion comprises the following steps: Under nitrogen protection, add 1 mol of phenolic epoxy resin and 0.3 mol of trimethylolpropane into a reaction kettle, stir and heat to dissolve. When the temperature of the reaction system rises to 100 °C, add a catalyst, and while stirring, raise the temperature of the reaction system to 130 - 180 °C. Keep stirring at a constant temperature until 0.9 mol of epoxy groups in the reaction system decrease. Then add 15 g of yellowing-resistant oligomer, and monitor the progress of the reaction by FTIR. Keep stirring at a constant temperature until the POO- absorption peak in the reaction system disappears in the infrared spectrum. Then lower the temperature of the reaction system to 100 - 120 °C, then add a diluent and 0.7 mol of dimethylolpropionic acid. After that, while stirring, cool down to 80 °C, then add 0.4 mol of diisocyanate, and monitor the progress of the reaction by FTIR. Stir and react until the absorption peak of NCO- in the reaction system disappears in the infrared spectrum. Then lower the temperature of the reaction system to 60 °C, add a neutralizing agent and deionized water, and stir and disperse for 30 min to obtain an epoxy-modified polyurethane dispersion with a solid content of (40 ± 2)%; The addition amount of the catalyst is 0.05% of the mass of the phenolic epoxy resin added; The addition amount of the diluent is 25% of the mass of the phenolic epoxy resin added; The addition amount of the neutralizing agent is 2% of the mass of the phenolic epoxy resin added; The preparation method of the yellowing-resistant oligomer comprises the following steps: Stir and mix 35 g of γ-methacryloxypropyltrimethoxysilane, 50 g of PAM100 acrylic end-capped polyphosphate from Solvay Co., Ltd., 0.4 g of azobisisobutyronitrile, and 85 g of diluent evenly. Then raise the temperature of the reaction system to 75 °C, and keep stirring at a constant temperature for 3 - 5 h. Take out the product and remove the solvent by rotary evaporation to obtain the yellowing-resistant oligomer.

2. The water-based protective baking paint for hardware parts according to claim 1, wherein, The neutralizing agent includes at least one of ammonia water, N,N-dimethylethanolamine, and triethylamine.

3. An aqueous protective baking paint for hardware parts according to claim 1, characterized in that, The diisocyanate includes at least one of TDI, IPDI, TMDI, and HDI.

4. The water-based protective baking paint for hardware parts according to claim 1, characterized in that, The diluent includes at least one of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and dipropylene glycol monobutyl ether.

5. The water-based protective baking paint for hardware parts according to claim 1, wherein The wetting and dispersing agent includes at least one of DIS-188A, BYK-190, BYK-191, EFKA-4550, EFKA-4560, TegoDispers760W, and W-518.

6. The water-based protective baking paint for hardware parts according to claim 1, characterized in that, The film-forming auxiliary agent includes at least one of dipropylene glycol methyl ether, dipropylene glycol butyl ether, ethylene glycol butyl ether, tripropylene glycol butyl ether, diethylene glycol butyl ether, and ethylene glycol hexyl ether.

7. An aqueous protective baking paint for hardware parts according to claim 1, characterized in that, The wetting agent includes at least one of TegoWet270, TEGOTwin4100, DefomW-77, and Levaslip-455.

8. The water-based protective baking paint for hardware parts according to claim 1, wherein, The leveling agent includes at least one of BYK-306, BYK-307, BYK-333, BYK-346, BYK-348, and BYK-349.

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