A method for preparing epoxy resin-based powder coating with texture effect

Abstract

The invention discloses a preparation method of epoxy resin-based powder coating with texture effect, belonging to the technical field of powder coating. Melamine and p-hydroxybenzaldehyde are reacted to obtain an intermediate, and the intermediate and epichlorohydrin are reacted to obtain a modified epoxy resin; bisphenol A epoxy resin and the modified epoxy resin are ball-milled and mixed, and then melt-extruded by a twin-screw, tableted, crushed, and sieved to obtain a composite epoxy resin; the composite epoxy resin, modified nano silicon dioxide, modified pigment, leveling agent, curing agent, sand grain agent and benzoin are added into a ball mill and ball-milled, and sieved to obtain an epoxy resin-based powder coating with texture effect; after the modified epoxy resin and the bisphenol A epoxy resin are compounded, the adhesion of the material is improved; the carbon-nitrogen double bond in the modified epoxy resin is a Schiff base type, and the paint film after the powder coating is cured is treated with an acid-containing paint stripper, so that the paint stripping time is significantly shortened, which is conducive to improving the paint stripping efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coatings, and in particular relates to a method for preparing an epoxy resin-based powder coating with texture effect. Background Art

[0002] Powder coatings are solid powder coatings made of solid resins, fillers and pigments. They are different from solvent-based coatings and water-based coatings. The dispersion medium of powder coatings is not liquid, but air, so they are more environmentally friendly than solvent-based coatings. They do not require primer during construction, and a thicker paint film can be obtained after one construction, which is safe and economical. Powder coatings include thermoplastic powder coatings and thermosetting powder coatings. The film appearance of thermoplastic powder coatings is poor, and the adhesion between them and metal substrates is also poor, so they are not widely used. Thermosetting powder coatings are more widely used, and the most commonly used thermosetting powder coatings are epoxy powder coatings, that is, epoxy resin-based powder coatings.

[0003] Epoxy resin-based powder coatings have excellent metal adhesion, corrosion resistance, hardness, flexibility and impact strength. They are mainly composed of epoxy resin, curing agent, pigment, filler and other additives. Like most powder coatings, epoxy resin-based powder coatings are generally brighter and have a single color after baking. If the surface of the substrate using powder coatings is not flat enough, defects such as dents will appear to a certain extent after baking. In order to improve the decorativeness of powder coatings, powder coatings with texture effects have emerged.

[0004] Powder coatings with texture effects will have regular bumps or patterns on the surface of the paint film after baking. If the paint film is damaged, simply filling the damaged area cannot achieve the original decorative effect, so it is necessary to strip the paint and then re-spray the powder coating. If the area to be stripped is large, a longer stripping time is required. In order to improve the stripping efficiency, an epoxy resin-based powder coating with texture effects that meets the use requirements and utilizes stripping treatment is proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing an epoxy resin-based powder coating with texture effect, so as to solve the problems in the background technology.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing an epoxy resin-based powder coating with a texture effect comprises the following steps:

[0008] Step 1: Add N,N-dimethylformamide and melamine to a flask, stir and mix for 10-15 minutes, then add p-hydroxybenzaldehyde, reflux for 60-70 hours under nitrogen protection and magnetic stirring. After the reaction, wash the product with anhydrous ethanol for 3-5 times, and then vacuum dry at 80°C for 24 hours to obtain an intermediate. The reaction process is as follows:

[0009]

[0010] Step 2: Add the intermediate, epichlorohydrin and tetrabutylammonium bromide into a flask, reflux for 8-9 hours under nitrogen protection and magnetic stirring, then adjust the temperature of the reaction system to 60°C, add a 25% sodium hydroxide solution to the reaction system, continue stirring for 6-8 hours and then cool down, wash the product with deionized water 2-3 times, remove unreacted raw materials by rotary evaporation, and dry; obtain a modified epoxy resin; the reaction process is as follows:

[0011]

[0012] Step 3: ball-milling and mixing bisphenol A epoxy resin with an epoxy equivalent of 600-650 and modified epoxy resin in a mass ratio of 1-1.5:1, and then melt-extruding with a twin-screw at a speed of 100-110 r / min, a temperature of 95° C. in the first zone, and a temperature of 105° C. in the second zone; tableting, crushing, and passing through a 200-mesh sieve to obtain a composite epoxy resin;

[0013] Step 4: Add 10% ammonia water into the flask, then slowly add butyl orthosilicate and hexadecyltrimethylammonium bromide into the flask under magnetic stirring, and continue stirring for 30-40 minutes to obtain a milky suspension; add the milky suspension into a reactor for hydrothermal reaction for 8-10 hours, cool it and centrifuge to obtain a precipitate, wash the precipitate with deionized water until the last washing liquid is neutral, and obtain amphiphilic nano-silica;

[0014] Step 5: placing the amphiphilic nano-silica and the pigment in an oven at 120° C. for 12 hours, respectively, adding the dried amphiphilic nano-silica and the pigment together with 10 times the mass of anhydrous ethanol into a flask for ultrasonic dispersion for 15-20 minutes, then adding 0.1wt% of anhydrous ethanol to a silane coupling agent and magnetically stirring at 75-85° C. for 24 hours, cooling, centrifuging, washing the precipitate with deionized water for 3-5 times, and drying to obtain modified nano-silica and modified pigment respectively;

[0015] Step 6: Add the composite epoxy resin, modified nano-silica, modified pigment, leveling agent, curing agent, sand grain agent and benzoin into a ball mill, ball mill for 3 hours at 500 r / min, and pass through a 200-mesh sieve to obtain an epoxy resin-based powder coating with a texture effect.

[0016] Furthermore, in step 1, the usage ratio of N,N-dimethylformamide, melamine and p-hydroxybenzaldehyde is 500mL:12g:48g.

[0017] Furthermore, in step 2, the usage ratio of the intermediate, epichlorohydrin, tetrabutylammonium bromide and sodium hydroxide solution is 50g:300mL:3g:150mL.

[0018] Furthermore, in step 4, the usage ratio of ammonia water, butyl orthosilicate and hexadecyltrimethylammonium bromide is 70mL:8g:4.2-4.5mg.

[0019] Furthermore, in step five, the silane coupling agent is any one of 3-aminopropyltriethoxysilane and tetraethyl orthosilicate.

[0020] Furthermore, in step six, the usage ratio of the composite epoxy resin, modified nano-silica, modified pigment, leveling agent, curing agent, sand grain agent and benzoin is 130-150g: 7-9g: 15-20g: 0.2-1g: 8-10g: 0.5-1.5g: 0.5-1g.

[0021] Furthermore, in step six, the curing agent is any one of 2-phenylimidazole and 2-phenylimidazoline.

[0022] Beneficial effects of the present invention:

[0023] The epoxy resin-based powder coating with texture effect of the present invention has strong adhesion to the metal substrate after thermal curing, and has good mechanical properties and salt spray resistance. After the modified epoxy resin and bisphenol A epoxy resin are compounded, it is beneficial to improve the adhesion of the material; the carbon-nitrogen double bond in the modified epoxy resin as a covalent bond is beneficial to promote the occurrence of the curing reaction and is conducive to the thermal curing treatment. The carbon-nitrogen double bond is a Schiff base type and can be decomposed into a carbonyl group and an amino group under acidic conditions. The paint film after the powder coating is cured is treated with an acid-containing paint stripper, and the paint stripping time is significantly shortened, which is beneficial to improving the paint stripping efficiency.

[0024] There are differences in surface tension and compatibility between the sand grain agent and the molten composite epoxy resin, which achieves the effects of sanding, increasing hardness and increasing texture; benzoin helps to eliminate bubbles entrained in the powder coating after melting, thereby eliminating pinhole defects in the coating film; modified nano-silica is hydrothermally synthesized by butyl orthosilicate, and the surface of the silica nanoparticles contains more hydroxyl groups, which can provide more active sites for subsequent silane coupling agent treatment, helping to improve its dispersion performance; the compatibility of the pigment with the composite epoxy resin is also improved after being treated with the silane coupling agent; hexadecyltrimethylammonium bromide is used as a surfactant to further modify the generated silica nanoparticles, making the silica nanoparticles lipophilic. The modified silica nanoparticles as amphiphilic particles have better compatibility with the composite epoxy resin, and are beneficial to improving the hydrophobicity of the powder coating, and have a certain improvement in the pollution resistance of the paint film, preventing the paint film from being easily corroded. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] The preparation of composite epoxy resin comprises the following steps:

[0028] Step 1: Add 5L N,N-dimethylformamide and 120g melamine into a flask, stir and mix for 10min, then add 480g p-hydroxybenzaldehyde, reflux for 60h under nitrogen protection and magnetic stirring, wash with anhydrous ethanol 3 times after the reaction, and then vacuum dry at 80°C for 24h to obtain an intermediate;

[0029] Step 2: 500 g of the intermediate, 3 L of epichlorohydrin and 30 g of tetrabutylammonium bromide were added to a flask, and refluxed for 8 h under nitrogen protection and magnetic stirring, and then the temperature of the reaction system was adjusted to 60 ° C, 1.5 L of a 25% sodium hydroxide solution was added to the reaction system, and the stirring was continued for 6 h and then cooled, and the product was washed twice with deionized water, and the unreacted raw materials were removed by rotary evaporation, and dried to obtain a modified epoxy resin;

[0030] Step 3: 500g of bisphenol A epoxy resin with an epoxy equivalent of 600-650 and 500g of modified epoxy resin are ball-milled and mixed, and then melt-extruded using a twin-screw at a speed of 100r / min, a temperature of 95°C in zone 1, and a temperature of 105°C in zone 2; tabletted, crushed, and sieved through a 200-mesh sieve to obtain a composite epoxy resin.

[0031] Example 2

[0032] The preparation of composite epoxy resin comprises the following steps:

[0033] Step 1: Add 5L N,N-dimethylformamide and 120g melamine into a flask, stir and mix for 12 minutes, then add 480g p-hydroxybenzaldehyde, reflux for 65h under nitrogen protection and magnetic stirring, wash with anhydrous ethanol 4 times after the reaction, and then vacuum dry at 80°C for 24h to obtain an intermediate;

[0034] Step 2: 500 g of the intermediate, 3 L of epichlorohydrin and 30 g of tetrabutylammonium bromide were added to a flask, and refluxed for 8.5 h under nitrogen protection and magnetic stirring, and then the temperature of the reaction system was adjusted to 60 ° C, 1.5 L of a 25% sodium hydroxide solution was added to the reaction system, and the stirring was continued for 7 h and then cooled, and the product was washed twice with deionized water, and the unreacted raw materials were removed by rotary evaporation, and dried to obtain a modified epoxy resin;

[0035] Step 3: 600g of bisphenol A epoxy resin with an epoxy equivalent of 600-650 and 500g of modified epoxy resin are ball-milled and mixed, and then melt-extruded using a twin-screw at a speed of 105r / min, a temperature of 95°C in zone 1, and a temperature of 105°C in zone 2; tabletted, crushed, and sieved through a 200-mesh sieve to obtain a composite epoxy resin.

[0036] Example 3

[0037] The preparation of composite epoxy resin comprises the following steps:

[0038] Step 1: Add 5L N,N-dimethylformamide and 120g melamine into a flask, stir and mix for 15 minutes, then add 480g p-hydroxybenzaldehyde, reflux for 70h under nitrogen protection and magnetic stirring, wash with anhydrous ethanol 5 times after the reaction, and then vacuum dry at 80°C for 24h to obtain an intermediate;

[0039] Step 2: 500 g of the intermediate, 3 L of epichlorohydrin and 30 g of tetrabutylammonium bromide were added to a flask, and refluxed for 9 h under nitrogen protection and magnetic stirring, and then the temperature of the reaction system was adjusted to 60 ° C, 1.5 L of a 25% sodium hydroxide solution was added to the reaction system, and the stirring was continued for 8 h and then cooled, and the product was washed with deionized water for 3 times, and the unreacted raw materials were removed by rotary evaporation, and dried to obtain a modified epoxy resin;

[0040] Step 3: 750 g of bisphenol A epoxy resin with an epoxy equivalent of 600-650 and 500 g of modified epoxy resin are ball-milled and mixed, and then melt-extruded using a twin-screw at a speed of 110 r / min, a temperature of 95°C in zone 1, and a temperature of 105°C in zone 2; tabletted, crushed, and sieved through a 200-mesh sieve to obtain a composite epoxy resin.

[0041] Example 4

[0042] Preparation of epoxy resin-based powder coating with texture effect, comprising the following steps:

[0043] Step 1: add 7L of 10% ammonia water into a flask, then slowly add 800g of butyl orthosilicate and 420mg of hexadecyltrimethylammonium bromide into the flask under magnetic stirring, and continue stirring for 30min to obtain a milky suspension; add the milky suspension into a reactor for hydrothermal reaction for 8h, cool it and centrifuge to obtain a precipitate, wash the precipitate with deionized water until the last washing liquid is neutral, and obtain amphiphilic nano-silica;

[0044] Step 2: placing the amphiphilic nano-silica and the pigment in an oven at 120° C. for 12 h, respectively, adding the dried amphiphilic nano-silica and the pigment together with 10 times the mass of anhydrous ethanol into a flask for ultrasonic dispersion for 15 min, then adding 0.1wt% of 3-aminopropyltriethoxysilane and tetraethyl orthosilicate in anhydrous ethanol and magnetically stirring at 75° C. for 24 h, cooling, centrifuging, washing the precipitate with deionized water for 3 times, and drying to obtain modified nano-silica and modified pigment respectively;

[0045] Step 3: Add 130g of the composite epoxy resin prepared in Example 1, 15g of modified nano-silica, 7g of modified pigment, 0.2g of leveling agent, 8g of 2-phenylimidazole, 0.5g of sand grain agent and 0.5g of benzoin into a ball mill, ball mill for 3h at 500r / min, and pass through a 200-mesh sieve to obtain an epoxy resin-based powder coating with a texture effect.

[0046] Example 5

[0047] Preparation of epoxy resin-based powder coating with texture effect, comprising the following steps:

[0048] Step 1: add 7L of 10% ammonia water into a flask, then slowly add 800g of butyl orthosilicate and 430mg of hexadecyltrimethylammonium bromide into the flask under magnetic stirring, and continue stirring for 35min to obtain a milky suspension; add the milky suspension into a reactor for hydrothermal reaction for 9h, cool and centrifuge to obtain a precipitate, wash the precipitate with deionized water until the last washing liquid is neutral, and obtain amphiphilic nano-silica;

[0049] Step 2: placing the amphiphilic nano-silica and the pigment in an oven at 120° C. for drying for 12 h, respectively, adding the dried amphiphilic nano-silica and the pigment together with 10 times the mass of anhydrous ethanol into a flask for ultrasonic dispersion for 18 min, then adding 0.1wt% of 3-aminopropyltriethoxysilane and tetraethyl orthosilicate in anhydrous ethanol and magnetically stirring at 80° C. for 24 h, cooling, centrifuging, washing the precipitate with deionized water for 4 times, and drying to obtain modified nano-silica and modified pigment respectively;

[0050] Step 3: Add 140g of the composite epoxy resin prepared in Example 2, 18g of modified nano-silica, 8g of modified pigment, 0.6g of leveling agent, 9g of 2-phenylimidazole, 0.9g of sand grain agent and 0.7g of benzoin into a ball mill, ball mill for 3h at 500r / min, and pass through a 200-mesh sieve to obtain an epoxy resin-based powder coating with a texture effect.

[0051] Example 6

[0052] Preparation of epoxy resin-based powder coating with texture effect, comprising the following steps:

[0053] Step 1: add 7L of 10% ammonia water into a flask, then slowly add 800g of butyl orthosilicate and 450mg of hexadecyltrimethylammonium bromide into the flask under magnetic stirring, and continue stirring for 40min to obtain a milky suspension; add the milky suspension into a reactor for hydrothermal reaction for 10h, cool it and centrifuge to obtain a precipitate, wash the precipitate with deionized water until the last washing liquid is neutral, and obtain amphiphilic nano-silica;

[0054] Step 2: placing the amphiphilic nano-silica and the pigment in an oven at 120° C. for drying for 12 h, respectively, adding the dried amphiphilic nano-silica and the pigment together with 10 times the mass of anhydrous ethanol into a flask for ultrasonic dispersion for 20 min, then adding 0.1wt% of 3-aminopropyltriethoxysilane and tetraethyl orthosilicate in anhydrous ethanol and magnetically stirring at 85° C. for 24 h, cooling, centrifuging, washing the precipitate with deionized water for 5 times, and drying to obtain modified nano-silica and modified pigment respectively;

[0055] Step 3: Add 150g of the composite epoxy resin prepared in Example 3, 20g of modified nano-silica, 9g of modified pigment, 1g of leveling agent, 10g of 2-phenylimidazoline, 1.5g of sand grain agent and 1g of benzoin into a ball mill, ball mill for 3h at 500r / min, and pass through a 200-mesh sieve to obtain an epoxy resin-based powder coating with a texture effect.

[0056] In Examples 4 to 6, the sand grain agent and leveling agent were purchased from Hangzhou Zhongshun Chemical Industry and Trade Co., Ltd.; the pigments were purchased from Shandong Anquan Chemical Technology Co., Ltd.

[0057] Comparative Example 1: Based on Example 6, the composite epoxy resin was directly replaced with a bisphenol A epoxy resin with an epoxy equivalent of 600-650 of the same mass, and the other steps remained unchanged to prepare an epoxy resin-based powder coating with a texture effect.

[0058] Comparative Example 2: On the basis of Example 6, the modified epoxy resin in Example 3 of the same mass was directly used to replace the composite epoxy resin, and the other steps remained unchanged to prepare an epoxy resin-based powder coating with a texture effect.

[0059] Comparative Example 3: Based on Example 6, commercially available nano-silicon dioxide was directly used and then treated with the same silane coupling agent to prepare an epoxy resin-based powder coating with a texture effect.

[0060] Performance tests were conducted on Examples 4 to 6 and Comparative Examples 1 to 3. The epoxy resin-based powder coatings with texture effects were sprayed on aluminum alloy plates with a side length of 2 cm by electrostatic spraying, and then heated and cured at 180°C to form paint films. The impact strength of the paint films was tested according to GB / T 1732-2020, and the positive and negative impacts were ≥50 kg / cm, which was considered to be passed. The pencil hardness of the paint films was tested according to GB / T 6739-2006, and the adhesion of the paint films was tested according to GB / T 9286-2021, with a total of 6 levels, with 0 being the best and 5 being the worst. The salt spray resistance of the paint films was tested according to GB / T 1771-2007, and the paint films were considered to be passed if they were not affected for more than 500 hours. The water contact angle of the coating before and after the aging test was measured using a contact angle meter for different paint films (the volume of the water droplet was 2 μL). The paint stripping test was conducted using an alkyd paint stripper, and the time required for complete paint stripping was recorded. The results are shown in Table 1:

[0061] Table 1

[0062] project Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Impact strength test pass pass pass pass pass pass Pencil hardness 2H 2H 2H 2H 3H 2H Adhesion Level 0 Level 0 Level 0 Level 0 Level 1 Level 0 Salt spray resistance test pass pass pass pass pass pass Water contact angle 118° 119° 119° 117° 119° 89° Paint stripping time 86s 84s 84s 108s 66s 79s

[0063] It can be seen from Table 1 that the epoxy resin-based powder coatings with texture effect in Examples 4 to 6 have better adhesion after being thermally cured into paint films, and have a larger water contact angle, better hydrophobic effect, and a shorter paint stripping time.

[0064] It should be noted that, in this article, terms such as "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0065] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an epoxy resin-based powder coating with a texture effect, characterized in that: The steps include: Step 1: Add N,N-dimethylformamide and melamine to a flask, stir and mix, then add p-hydroxybenzaldehyde, reflux for 60-70 hours under nitrogen protection and magnetic stirring, wash and dry the product to obtain an intermediate; add the intermediate, epichlorohydrin and tetrabutylammonium bromide to a flask, reflux for 8-9 hours under nitrogen protection and magnetic stirring, then adjust the temperature of the reaction system to 60°C, add sodium hydroxide solution to the reaction system, continue stirring for 6-8 hours, then cool and cool, wash, rotary evaporate and dry the product to obtain a modified epoxy resin; Step 2: Mix the bisphenol A epoxy resin and the modified epoxy resin by ball milling in a mass ratio of 1-1.5:1, and then melt extrude with a twin-screw, press into sheets, crush, and pass through a 200-mesh sieve to obtain a composite epoxy resin; Step 3: Add the composite epoxy resin, modified nano-silica, modified pigment, leveling agent, curing agent, sand grain agent and benzoin into a ball mill, ball mill for 3 hours at 500 r / min, and pass through a 200-mesh sieve to obtain an epoxy resin-based powder coating with a texture effect; The modified nano-silicon dioxide and modified pigment are prepared by the following steps: After drying, the amphiphilic nano-silica and the pigment are added to a flask with 10 times the mass of anhydrous ethanol and ultrasonically dispersed for 15-20 minutes, and then 0.1wt% of a silane coupling agent in anhydrous ethanol is added and magnetically stirred at 75-85°C for 24 hours, cooled, centrifuged, and the precipitate is washed and dried to obtain modified nano-silica and modified pigment, respectively.

2. The method for preparing a textured epoxy resin-based powder coating according to claim 1, characterized in that: The amphiphilic nano-silica is prepared by the following steps: Ammonia water is added to the flask, and then butyl orthosilicate and hexadecyltrimethylammonium bromide are added to the flask under magnetic stirring, and stirred for 30-40 minutes to obtain a milky white suspension; the milky white suspension is hydrothermally reacted for 8-10 hours, cooled, centrifuged to obtain a precipitate, and washed to obtain amphiphilic nano-silica.

3. The method for preparing a textured epoxy resin-based powder coating according to claim 2, characterized in that: The usage ratio of the ammonia water, butyl orthosilicate and hexadecyltrimethylammonium bromide is 70 mL: 8 g: 4.2-4.5 mg.

4. The method for preparing a textured epoxy resin-based powder coating according to claim 1, characterized in that: The silane coupling agent is any one of 3-aminopropyltriethoxysilane and tetraethyl orthosilicate.

5. The method for preparing an epoxy resin-based powder coating with texture effect according to claim 1, characterized in that: The usage ratio of N,N-dimethylformamide, melamine and p-hydroxybenzaldehyde in step 1 is 500mL:12g:48g.

6. The method for preparing a textured epoxy resin-based powder coating according to claim 1, characterized in that: The usage ratio of the intermediate, epichlorohydrin, tetrabutylammonium bromide and sodium hydroxide solution in step 1 is 50g:300mL:3g:150mL.

7. The method for preparing a textured epoxy resin-based powder coating according to claim 1, characterized in that: The curing agent in step 3 is any one of 2-phenylimidazole and 2-phenylimidazoline.

8. The method for preparing a textured epoxy resin-based powder coating according to claim 1, characterized in that: The usage ratio of the composite epoxy resin, modified nano-silica, modified pigment, leveling agent, curing agent, sand grain agent and benzoin in step three is 130-150g: 7-9g: 15-20g: 0.2-1g: 8-10g: 0.5-1.5g: 0.5-1g.

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