Phenolic curing agent for epoxy powder coating and preparation method

Abstract

The invention relates to a phenolic curing agent for an epoxy powder coating. The phenolic curing agent is mainly obtained by reacting tartaric acid, isooctyl alcohol, epoxypropane, bisphenol F diglycidyl ether, ethylene glycol diglycidyl ether, bisphenol F and the like serving as raw materials. The phenolic curing agent product has the advantages of low softening point, high hydroxyl equivalent weight, soft main chain structure, excellent boiling resistance, excellent flexibility and high impact resistance, good curing activity of the bisphenol F terminated end group, and good curing effect. The phenolic curing agent product has the advantages of favorable water boiling resistance, favorable water boiling resistance, favorable impact resistance, favorable water boiling resistance, favorable water boiling resistance, favorable water boiling resistance, favorable water boiling resistance, favorable water boiling resistance, favorable water boiling resistance, favorable water boiling resistance, favorable water boiling resistance, favorable water boiling resistance and favorable water boiling resistance. And finally, after low-temperature curing with a powder coating prepared from E-12 epoxy resin, a coating film is good in leveling performance and high impact resistance, and excellent in bending resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coatings, and in particular relates to a phenolic curing agent and application thereof in an epoxy powder coating system. Background Art

[0002] Powder coating is a solid powdered synthetic resin coating composed of solid resin, pigment, filler and additives. Unlike ordinary solvent-based coatings and water-based coatings, its dispersion medium is not solvent and water, but air. It has the characteristics of no solvent pollution, 100% film formation and low energy consumption, and has become a widely used coating variety. In pure epoxy powder coating systems, phenolic curing agents are a very important type of curing agent. Ordinary phenolic curing agents are mostly prepared by chain extension reaction of linear liquid epoxy resin E-51 and bisphenol A. The chain segment lubricity of the product is insufficient, and the leveling grade of the coating after curing with E-12 epoxy resin can generally only reach level 5. In addition, the introduction of rigid bisphenol A structure blocks results in average leveling, flexibility and impact resistance of the cured coating, making it difficult to meet special high leveling and high impact resistance application requirements. ZL202011218167.7 uses the introduction of rigid phenolic structure for chain extension reaction. The product has high functionality and good high temperature resistance, but cannot meet the requirements of special fields such as coils, pipes, etc. with high leveling grade, high impact resistance and high flexibility.

[0003] In view of the existing problems and market demand of phenolic curing agents, the present invention mainly uses tartaric acid, isooctyl alcohol, propylene oxide, bisphenol F diglycidyl ether, ethylene glycol diglycidyl ether, bisphenol F and the like as raw materials for reaction. The obtained product has a low softening point, a high hydroxyl equivalent, a soft main chain structure and an ether bond composition with methyl side chains, not only excellent boiling resistance, but also excellent flexibility and impact resistance, good end group curing activity after bisphenol F end-capping, and finally the coating film after low-temperature curing with E-12 epoxy resin reaches a leveling grade of 7 or above, good impact resistance, and excellent bending resistance. Summary of the invention

[0004] The present invention relates to a phenolic curing agent for epoxy powder coating, which comprises raw materials composed of the following molar parts:

[0005]

[0006]

[0007] The raw materials also include catalyst 1 and catalyst 2.

[0008] Furthermore, the catalyst 1 is tetrabutyl titanate, and the amount used is 0.15-0.2% of the mass of tartaric acid.

[0009] Furthermore, the catalyst 2 is triphenylphosphine, and the amount used is 0.3-0.4% of the mass of tartaric acid.

[0010] The method for preparing a phenolic curing agent for epoxy powder coating as described above comprises the following steps:

[0011] A. Add the formula amount of isooctyl alcohol, tartaric acid and catalyst 1 into the reaction kettle, start stirring, and heat to 190-195° C. to perform reflux water separation esterification reaction;

[0012] B. Take samples to test the acid value of the reactants. When the acid value of the reactants reaches below 1 mgKOH / g, it indicates that the carboxyl group of tartaric acid has been completely esterified. At this time, start the vacuum system and continue to maintain the temperature at 190-195°C to perform reduced pressure distillation to remove excess unreacted isooctyl alcohol;

[0013] C. After no obvious material is evaporated, turn off the vacuum system, cool to 115-120°C, add catalyst 2 and seal the reactor, then drop the formulated amount of propylene oxide, and continue to keep warm after the addition is complete;

[0014] D. Take samples and detect them by gas chromatography. When the reaction conversion rate of propylene oxide reaches more than 98%, it means that the chain extension reaction of propylene oxide is basically completed. Then add the formula amount of bisphenol F diglycidyl ether and ethylene glycol diglycidyl ether to continue the chain extension polymerization reaction at 115-120°C;

[0015] E. Take samples and detect them by gas chromatography. When the reaction conversion rate of bisphenol F diglycidyl ether and ethylene glycol diglycidyl ether reaches more than 98%, add bisphenol F and perform end-capping reaction at 120-125° C.;

[0016] F. Take samples to detect the hydroxyl equivalent of the polymer. When the hydroxyl equivalent of the polymer reaches 620-675 g / mol, stop the reaction, discharge the material while hot, cool the resin, and then crush and granulate it to obtain a phenolic curing agent.

[0017] Furthermore, in step B, the vacuum system is started to maintain the vacuum degree at -0.095 MPa to -0.098 MPa.

[0018] Furthermore, in step C, the criterion for judging that no obvious material is evaporated is less than 1 drop within 30 seconds; and the dripping time of the formulated amount of propylene oxide is 1-1.5 hours.

[0019] Furthermore, in step F, the resin is cooled using a steel belt with condensed water.

[0020] The obtained product has the appearance of light yellow transparent particles, a hydroxyl equivalent of 620-675 g / mol, and a softening point of 77-83°C.

[0021] The present invention also relates to the use of the phenolic curing agent for epoxy powder coatings as described above or the phenolic curing agent for epoxy powder coatings prepared by the preparation method as described above in epoxy resin powder coating systems.

[0022] Preferably, in the epoxy resin powder coating system, the epoxy resin is E-12 epoxy resin.

[0023] Generally, the formula of the above-mentioned phenolic curing system powder coating contains E-12 epoxy resin, the above-mentioned phenolic curing agent, and may also contain barium sulfate, titanium dioxide, leveling agent, brightener, etc. The preparation method is: mix the materials according to the formula, extrude them at low temperature with a twin-screw extruder, and then press and crush the flakes to make powder coating. The powder coating is sprayed on the surface treated tinplate substrate with an electrostatic spray gun, and cured (for example, at 150°C / 15min) to obtain a coating.

[0024] Beneficial effects:

[0025] The present invention mainly uses tartaric acid, isooctyl alcohol, propylene oxide, bisphenol F diglycidyl ether, ethylene glycol diglycidyl ether, bisphenol F and the like as raw materials for reaction. The phenolic curing agent chain segment contains isooctyl tartaric acid structure with excellent lubricity, which is prepared into polyether with propylene oxide and then copolymerized with bisphenol F diglycidyl ether and ethylene glycol diglycidyl ether for chain extension, and finally end-capped with bisphenol F to obtain the obtained product, the obtained product has a low softening point, and the hydroxyl equivalent of the product is high, which is 620-675g / mol, the main chain structure is soft and is composed of ether bonds with methyl side chains, not only has excellent water boiling resistance, but also has excellent flexibility and impact resistance, the end group curing activity after bisphenol F end-capping is good, and the coating film leveling grade after finally curing with E-12 epoxy resin at low temperature (for example, 155°C / 15min) reaches above 7, and has good impact resistance, can pass both positive and negative 80cm impact, and the T bend value can also reach 0T, and has excellent bending resistance.

[0026] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0028] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0029] Preparation Example 1

[0030] A phenolic curing agent for epoxy powder coatings, comprising the following raw materials in molar proportions:

[0031] 10 parts of tartaric acid;

[0032]

[0033] Catalyst 1 is tetrabutyl titanate, and the amount used is 0.2% of the mass of tartaric acid;

[0034] Catalyst 2 is triphenylphosphine, and the amount used is 0.4% of the mass of tartaric acid.

[0035] The preparation method of the phenolic curing agent for epoxy powder coating comprises the following steps:

[0036] A. Add the formula amount of isooctyl alcohol, tartaric acid and catalyst 1 into the reaction kettle, start stirring, and heat to 190° C. to perform reflux water separation esterification reaction;

[0037] B. Take samples to test the acid value of the reactants. When the acid value of the reactants reaches below 1 mgKOH / g, it indicates that the carboxyl group of tartaric acid has been completely esterified. At this time, start the vacuum system, maintain the vacuum degree at -0.098 MPa, and continue to maintain the vacuum distillation at 190°C to remove excess unreacted isooctyl alcohol;

[0038] C. After no obvious material is evaporated (less than 1 drop within 30 seconds), turn off the vacuum system, cool to 115°C, add catalyst 2 and seal the reactor, then add the formula amount of propylene oxide dropwise for 1.5 hours. After the addition is complete, continue to keep warm for reaction;

[0039] D. Take samples and detect them by gas chromatography. When the reaction conversion rate of propylene oxide reaches more than 98%, it means that the chain extension reaction of propylene oxide is basically completed. Then add the formulated amount of bisphenol F diglycidyl ether and ethylene glycol diglycidyl ether to continue the chain extension polymerization reaction at 115°C.

[0040] E. Sampling was detected by gas chromatography. When the reaction conversion rates of bisphenol F diglycidyl ether and ethylene glycol diglycidyl ether reached 98% or more, bisphenol F was added and capping reaction was carried out at 120° C.;

[0041] F. Take samples to test the hydroxyl equivalent of the polymer. When the hydroxyl equivalent of the polymer reaches 620-675 g / mol, stop the reaction, discharge the material while hot, cool the resin with a steel belt with condensed water, and then crush and granulate to obtain a phenolic curing agent.

[0042] The obtained product has the appearance of light yellow transparent particles, a hydroxyl equivalent of 628 g / mol, and a softening point of 78°C.

[0043] Preparation Example 2

[0044] A phenolic curing agent for epoxy powder coatings, comprising the following raw materials in molar proportions:

[0045]

[0046]

[0047] Catalyst 1 is tetrabutyl titanate, and the amount used is 0.2% of the mass of tartaric acid;

[0048] Catalyst 2 is triphenylphosphine, and the amount used is 0.4% of the mass of tartaric acid.

[0049] The preparation method is the same as that of Preparation Example 1.

[0050] The obtained product has the appearance of light yellow transparent particles, a hydroxyl equivalent of 671 g / mol, and a softening point of 82°C.

[0051] Preparation Example 3

[0052] A phenolic curing agent for epoxy powder coatings, comprising the following raw materials in molar proportions:

[0053]

[0054] Catalyst 1 is tetrabutyl titanate, and the amount used is 0.2% of the mass of tartaric acid;

[0055] Catalyst 2 is triphenylphosphine, and the amount used is 0.4% of the mass of tartaric acid.

[0056] The preparation method is the same as that of Preparation Example 1.

[0057] The obtained product has the appearance of light yellow transparent particles, a hydroxyl equivalent of 637 g / mol, and a softening point of 79°C.

[0058] Preparation Example 4

[0059] A phenolic curing agent for epoxy powder coatings, comprising the following raw materials in molar proportions:

[0060]

[0061]

[0062] Catalyst 1 is tetrabutyl titanate, and the amount used is 0.18% of the mass of tartaric acid;

[0063] Catalyst 2 is triphenylphosphine, and the amount used is 0.4% of the mass of tartaric acid.

[0064] The preparation method is the same as that of Preparation Example 1.

[0065] The obtained product has the appearance of light yellow transparent particles, a hydroxyl equivalent of 652 g / mol, and a softening point of 81°C.

[0066] Comparative Preparation Example 1: The product of Example 1 in ZL201611039784.4 is used instead of the phenolic curing agent of the present invention as Comparative Example 1. The coating formula is shown in ZL201611039784.4, the curing conditions are: 200°C / 15min, and the coating thickness is 80-90μm.

[0067] Comparative Preparation Example 2: The product of Example 1 in ZL202011218167.7 is used instead of the phenolic curing agent product of the present invention as Comparative Example 2. The coating formula is shown in ZL202011218167.7, and the curing conditions are 160°C.

[0068] / 20min, coating thickness 80-90μm.

[0069] Examples 1-4 and Comparative Examples 1-2 (obtained using the phenolic curing agents described in Preparation Examples 1-4 and Comparative Preparation Examples 1 and 2, respectively)

[0070] The formula of the phenolic curing system powder coating of the present invention is as follows in parts by weight:

[0071]

[0072] The E-12 epoxy resin is a product of Anhui Hengtai New Materials Co., Ltd., model HT-243C; the curing accelerator is a curing accelerator product of Huangshan Xinjia Fine Materials Co., Ltd., model HB198.

[0073] Preparation method of powder coating: Mix all materials according to the formula of the above powder coating, extrude at low temperature with a twin-screw extruder (the screw temperature is controlled at 120-130°C), and then tablet and crush, and then crush and sieve the tablets to make powder coating (160-180 mesh). The powder coating is sprayed on the tinplate substrate after surface treatment with an electrostatic spray gun, and cured at 150°C / 15min to obtain a coating with a film thickness of 80-90μm.

[0074] Performance comparison

[0075] The coating index test is carried out according to GB / T 21776-2008 "Testing Standard Guide for Powder Coatings and Their Coatings"; the leveling grade is based on JB-T 3998-1999 "Paint Leveling Scrape Test Method"; the flexibility is mainly reflected in the T bend value of the bending test, the smaller the T bend value, the better the flexibility, and the T bend value test method is based on Part VII (Bending Test) of GB / T13448-2006 "Test Methods for Color Coated Steel Sheets and Strips". The coating performance results of the phenolic curing agent products prepared in the above examples and comparative examples according to the powder coating formula are shown in Table 1 below.

[0076] Table 1 Comparison of performance of powder coatings of embodiment and comparative example

[0077]

[0078]

[0079] From the performance comparison of Examples 1-4 and Comparative Examples 1-2 in Table 1, it can be seen that the products of the present invention adopt a specific raw material formula and process combination, and the obtained phenolic curing agent for epoxy resin curing system has excellent comprehensive properties such as leveling and impact resistance. The coating film after low-temperature curing at 150°C / 15min with E-12 epoxy resin has a smooth appearance and a gloss of more than 94%, especially excellent impact resistance. Whether it is a conventional 50cm impact or an 80cm high impact resistance, both positive and negative impacts pass without cracking. At the same time, the leveling grades are basically above level 7, the adhesion reaches level 0, and the T-bend value reaches 0T, showing excellent comprehensive properties such as high leveling and high impact resistance.

[0080] After high-temperature curing at 200°C / 15min, the gloss of the coating film of Comparative Example 1 is basically around 92%, the leveling grade is level 5, and it can pass the conventional 50cm impact test, but it has recoil cracking in the 80cm high impact resistance, and the T-bend value is lower than the product of the present invention, which is mainly caused by its excessive functionality and insufficient molecular lubrication ability. The phenolic curing agent of Comparative Example 2 has a strong rigid molecular structure, resulting in its 80cm high impact resistance, leveling grade and T-bend value being lower than the product of the present invention.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A phenolic curing agent for epoxy powder coatings, It is characterized in that The raw materials comprising the following molar compositions: The raw materials also include catalyst 1 and catalyst 2.

2. A phenolic curing agent for epoxy powder coatings as claimed in claim 1, further characterized in that the catalyst 1 is tetrabutyl titanate, and the amount used is 0.15-0.2% of the mass of tartaric acid.

3. A phenolic curing agent for epoxy powder coatings as claimed in claim 1, further characterized in that the catalyst 2 is triphenylphosphine, and the amount used is 0.3-0.4% of the mass of tartaric acid.

4. A method for preparing a phenolic curing agent for epoxy powder coatings as claimed in any one of claims 1 to 3, It is characterized in that The following steps are involved: A. Add the formula amount of isooctyl alcohol, tartaric acid and catalyst 1 into the reaction kettle, start stirring, and heat to 190-195° C. to perform reflux water separation esterification reaction; B. Take samples to test the acid value of the reactants. When the acid value of the reactants reaches below 1 mgKOH / g, start the vacuum system and continue to perform reduced pressure distillation at 190-195°C to remove excess unreacted isooctyl alcohol; C. After no obvious material is evaporated, turn off the vacuum system, cool to 115-120°C, add catalyst 2 and seal the reactor, then drop the formulated amount of propylene oxide, and continue to keep warm after the addition is complete; D. Take samples and detect them by gas chromatography. When the reaction conversion rate of propylene oxide reaches more than 98%, add the formulated amount of bisphenol F diglycidyl ether and ethylene glycol diglycidyl ether, and continue to carry out chain extension polymerization at 115-120° C.; E. Take samples and detect them by gas chromatography. When the reaction conversion rates of bisphenol F diglycidyl ether and ethylene glycol diglycidyl ether reach more than 98%, add bisphenol F and perform end-capping reaction at 120-125° C.; F. Take samples to detect the hydroxyl equivalent of the polymer. When the hydroxyl equivalent of the polymer reaches 620-675 g / mol, stop the reaction, discharge the material while hot, cool the resin, and then crush and granulate it to obtain a phenolic curing agent.

5. The method for preparing a phenolic curing agent for epoxy powder coatings as claimed in claim 4, further characterized in that, in step B, the vacuum system is started to maintain the vacuum degree at -0.095 MPa to -0.098 MPa.

6. The method for preparing a phenolic curing agent for epoxy powder coatings according to claim 4, further characterized in that, in step C, the dripping time of the formulated amount of propylene oxide is 1-1.5 hours.

7. The method for preparing a phenolic curing agent for epoxy powder coatings as claimed in claim 4, further characterized in that in step F, the resin is cooled by a steel belt with condensed water.

8. Use of the phenolic curing agent for epoxy powder coatings according to any one of claims 1 to 3 or the phenolic curing agent for epoxy powder coatings prepared by the preparation method according to any one of claims 4 to 7 in epoxy resin powder coating systems.

9. The use as claimed in claim 8, It is characterized in that In the epoxy resin powder coating system, the epoxy resin used is E-12 epoxy resin.

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