Polyester resin for salt-spray-resistant powder coating and preparation method of polyester resin

Abstract

The invention discloses polyester resin for a salt-spray-resistant powder coating and a preparation method of the polyester resin. The polyester resin comprises the following raw materials in percentage by mass: 25-45% of polyol; 40-65% of aromatic polybasic acid; 0.5 to 2.5 percent of a branching agent; 1.5 to 5% of polyamine; 5-15% of an acidolysis agent; 1.3-8% of a phosphorus-containing reagent; 0.1 to 1.4% of an esterification catalyst; 0.01-1% of a curing accelerator; and 0.1-2% of an antioxidant, wherein the sum of the mass percentages of the raw materials is 100%. The catalyst zinc and phosphate radical in the polyester resin form an insoluble complex precipitate with iron ions generated by electrochemical reaction of a substrate in an acid environment, so that the generation of the electrochemical reaction is remarkably inhibited, and the salt spray resistance of the powder coating is enhanced; an amido bond and a hydrogen-oxygen bond of a substrate form a strong hydrogen bond, and the amido bond and the hydrogen-oxygen bond synergistically improve the adhesive force of the coating and the substrate and are beneficial to further improvement of the salt spray resistance; the salt spray resistance of the powder coating is obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyester resins, and in particular relates to a polyester resin for salt spray resistant powder coating and a preparation method thereof. Background Art

[0002] The coating made of powder coating will be corroded by acid rain, salt, etc. during the application process and cause the coating to fail. Therefore, salt spray resistance is an important indicator parameter of powder coating, which is used to characterize the relative strength of the material's anti-corrosion (anti-corrosion) ability.

[0003] The principle of coating corrosion is that an electrochemical reaction occurs on the surface of a metal substrate such as iron. During the reaction, the metal loses electrons and is oxidized. The reaction process is called a negative electrode reaction process. The reaction products are metal ions entering the medium or metal oxides (or insoluble metal salts) covering the metal surface. Substances in the medium, such as oxygen, gain electrons from the metal surface and are reduced. The reaction process is called a positive electrode reaction process.

[0004] The prior art generally uses polyester resin, acrylic resin, epoxy resin and the like together with fillers to prepare anti-corrosion coatings to achieve the anti-corrosion performance of the coatings. However, although such coatings have certain anti-corrosion performance, the anti-corrosion effect is not ideal. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a polyester resin for salt spray resistant powder coating and a preparation method thereof. The catalyst zinc and phosphate in the polyester resin react with the iron ions generated by the electrochemical reaction of the substrate in an acidic environment to form an insoluble complex precipitate, which significantly inhibits the generation of the electrochemical reaction and enhances the salt spray resistance of the powder coating. The amide bond and the hydrogen-oxygen bond of the substrate form a strong hydrogen bond, which synergistically improves the adhesion between the coating and the substrate and is conducive to further improving the salt spray resistance. The polyester resin can significantly improve the salt spray resistance of the powder coating.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A polyester resin for salt spray resistant powder coating, comprising the following raw materials in mass percentage: 25-45% of polyol; 40-65% of aromatic polyacid; 0.5-2.5% of branching agent; 1.5-5% of polyamine; 5-15% of acidolysis agent; 1.3-8% of phosphorus-containing reagent; 0.1-1.4% of esterification catalyst; 0.01-1% of curing accelerator; 0.1-2% of antioxidant, the total mass percentage of the above raw materials is 100%;

[0008] The esterification catalyst is a mixture of component A and component B; the component A is a mixture of zinc acetate and lithium acetate; the component B is a titanate catalyst, such as tetraisopropyl titanate and n-butyl titanate.

[0009] The mass ratio of zinc acetate to lithium acetate is between 3:1 and 1:3.

[0010] The polyamine is any one or more of ethylenediamine, propylenediamine, hexamethylenediamine, butylenediamine, pentamethylenediamine, heptamethylenediamine, decanediamine, ethanolamine, propanolamine and butanolamine.

[0011] The phosphorus-containing reagent is any one or more of phosphoric acid, ester derivatives of phosphoric acid, phosphorous acid, and ester derivatives of phosphorous acid.

[0012] The ester derivative of phosphoric acid is at least one of primary phosphoric acid esters (monophosphate, alkyl phosphoric acid), secondary phosphoric acid esters (diester) and tertiary phosphoric acid esters (triester), such as monomethyl phosphate, dimethyl phosphate, trimethyl phosphate, monoethyl phosphate, diethyl phosphate and triethyl phosphate.

[0013] The ester derivative of the phosphorous acid is at least one of primary phosphites (monophosphites, hydrocarbon phosphorous acids), secondary phosphites (diesters of phosphoric acids) and tertiary phosphites (triesters of phosphorous acids), such as monomethyl phosphite, dimethyl phosphite, trimethyl phosphite, monoethyl phosphite, diethyl phosphite, triethyl phosphite, and phosphorous acid.

[0014] The esterification catalyst is a mixture of component A and component B; the component A is a mixture of zinc acetate and lithium acetate; the component B is a titanate catalyst.

[0015] The polyol is any one or more of neopentyl glycol, trimethylpentanediol, cyclohexanedimethanol, and ethylbutylpropylene glycol.

[0016] The aromatic polyacid is at least one of terephthalic acid and isophthalic acid.

[0017] The branching agent is any one or more of trimethylolpropane, trimethylolethane, or dimethylolpropionic acid.

[0018] The acidolysis agent is any one or more of isophthalic acid, adipic acid, 1,4-cyclohexanedicarboxylic acid, trimellitic anhydride, and fumaric acid.

[0019] The curing accelerator is one or more of tetraethylammonium bromide, tetramethylammonium bromide, benzyltriethylammonium chloride, triphenylethylphosphine bromide, and dibutyltin dilaurate.

[0020] The antioxidant is a compound of a phosphite antioxidant and a hindered phenol antioxidant in a mass ratio of 1:3 to 3:1; the phosphite antioxidant is selected from tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168) and bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite (antioxidant 626); the hindered phenol antioxidant is tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]pentaerythritol ester (antioxidant 1010) and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester (antioxidant 1076).

[0021] The present invention also provides a method for preparing the polyester resin for salt spray resistant powder coating, the method comprising the following steps:

[0022] 1) Put the formulated amount of polyol and branching agent into a reaction kettle and heat to 160-180°C to melt;

[0023] 2) Add the formulated amount of aromatic polyacid and esterification catalyst into a reaction kettle at the same time, and react at 235-255° C. in an inert atmosphere until the system becomes clear;

[0024] 3) Cooling to 200-210°C, adding the formulated amount of phosphorus-containing reagent, and stirring the reaction at 220-235°C in an inert atmosphere for 0.5-2h;

[0025] 4) Then the temperature is lowered to 210-220°C, and the acidolysis agent is added to the reaction kettle, and the temperature is raised to 235-250°C to react until the acid value of the system reaches 45-65 mgKOH / g, and acidolysis and end-capping are performed;

[0026] 5) Cooling to 230-240°C, polycondensing under vacuum, venting and cooling to 200-230°C after the acid value reaches 32-55 mgKOH / g;

[0027] 6) Add the formulated amount of polyamine and maintain for 1 to 2 hours, then cool to 180-200° C., add the formulated amount of antioxidant and curing accelerator, and maintain at -0.05 MPa to -0.07 MPa for 5 to 30 minutes.

[0028] The present invention also provides a salt spray resistant powder coating, which uses the polyester resin for salt spray resistant powder coating of the present invention as a raw material and can be directly sprayed on the surface of a pre-treated substrate to achieve better salt spray performance than conventional polyester resin on the pre-treated substrate.

[0029] The polyester resin for salt-fog resistant powder coating provided by the present invention uses zinc acetate, lithium acetate and titanate substances as catalysts in its synthetic raw materials, and simultaneously uses polyamines and phosphorus-containing reagents. During the construction of the powder coating prepared from such polyester resin, the catalyst zinc and phosphate in the polyester resin form insoluble complex precipitation with the iron ions generated by the electrochemical reaction of the substrate in an acidic environment, which can significantly inhibit the generation of the electrochemical reaction and further enhance the salt-fog resistance of the powder coating. Under the synergistic catalysis of phosphorus-containing reagents and curing accelerators, the polyamine can undergo amidation reaction with the terminal carboxyl group of the polyester resin to generate an amide bond, and the amide bond and the hydrogen-oxygen bond of the substrate form a strong hydrogen bond, which can significantly improve the adhesion between the coating and the substrate. The above synergistic effects improve the adhesion between the coating and the substrate and are conducive to the improvement of the salt-fog resistance of the coating.

[0030] The polyester resin for salt-fog resistant powder coating provided by the invention has an acid value of 25-55 mgKOH / g resin, a number average molecular weight of 2000-5000 g / mol, and a glass transition temperature (Tg) of ≥55°C.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] Compared with conventional powder coatings, the salt spray resistant powder coating provided by the present invention has a neutral salt spray test time of a coating obtained after baking and curing increased from 500 to 800 hours to more than 1500 hours, thereby significantly improving the salt spray resistance of the powder coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a sample photo of the coating formed by the powder coating in Example 1 after 1500h neutral salt spray test;

[0034] Figure 2 This is a sample photo of the coating formed by the powder coating in Example 2 after 1500h neutral salt spray test;

[0035] Figure 3 This is a sample photo of the coating formed by the powder coating in Example 3 after 1500h neutral salt spray test;

[0036] Figure 4 This is a sample photo of the coating formed by the powder coating in Example 4 after 1500h neutral salt spray test. DETAILED DESCRIPTION

[0037] The present invention is described in detail below with reference to the embodiments.

[0038] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0039] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0040] The preparation method of polyester resin B in the following examples is:

[0041] 1) Put the formulated amount of polyol and branching agent into a reaction kettle and heat to 165-170°C to melt;

[0042] 2) Add the formulated amount of aromatic polyacid and esterification catalyst into the reaction kettle at the same time, raise the temperature to 240-250°C at 1-2°C / min in a nitrogen atmosphere and maintain the temperature, and after the system is clarified, take a sample to detect the acid value (AV) reaching 7-10 mgKOH / g;

[0043] 3) Cooling to 200-210°C at a rate of 3-5°C / min, adding the formulated amount of phosphorus-containing reagent, and heating to 228-235°C at a rate of 1-2°C / min in a nitrogen atmosphere and maintaining for 1.5 hours;

[0044] 4) Then, the temperature is lowered to 210-220°C at a rate of 3-5°C / min, and an acidolysis agent is added to the reactor, and the temperature is raised to 240-250°C at a rate of 1-2°C / min and maintained for acidolysis and end-capping, until the acid value of the polyester reaches 45-65 mgKOH / g;

[0045] 5) Cooling to 230-245°C and polycondensing under -0.1MPa vacuum condition, venting and cooling to 200-230°C after the acid value reaches 33-55mgKOH / g;

[0046] 6) Add polyamine, maintain for 1-2 hours, then cool to 180-200°C, add the formulated amount of antioxidant and curing accelerator, and maintain under a small vacuum of -0.07MPa for 15-30 minutes before discharging.

[0047] Steps 1), 2), 3) and 5) require the use of industrial high-purity nitrogen with a purity greater than 99.99% for protection.

[0048] The preparation method of the polyester resin A1 used in the following comparative example is the same as the preparation method of the polyester resin in the example, except that a conventional organic tin catalyst (monobutyl tin oxide) is used as the esterification catalyst during the preparation process.

[0049] The preparation method of the polyester resin A2 used in the following comparative example is the same as the preparation method of the polyester resin in the example, except that no phosphorus-containing reagent is added during the preparation process.

[0050] The preparation method of the polyester resin A3 used in the following comparative example is the same as the preparation method of the polyester resin in the embodiment, except that no polyamine is added during the preparation process.

[0051] The raw materials and dosage of the polyester resin in each embodiment and comparative example, the control parameters in the production process and some properties are shown in Table 1.

[0052] Table 1

[0053]

[0054]

[0055] It can be seen from the above table that, under the same catalyst content and raw material formula, using only catalyst A or catalyst B to catalyze the synthesis of polyester resin for powder coating will cause the acid value of the polyester resin to be significantly higher, the viscosity and Tg to decrease, and the resin color to be very yellow, indicating that the catalytic activity of a single component is insufficient and cannot meet the requirements of polyester resin for powder coating. Its performance will no longer be shown in the subsequent powder coating preparation process.

[0056] The prepared polyester resins A1, A2, A3, polyester resins B1, B2 and B3, curing agents (triglycidyl cyanurate (TGIC), hydroxyalkylamide (HAA)), leveling agents, pigments, inorganic fillers and additives were used to prepare salt spray resistant powder coatings. The specific formula of the powder coating is shown in Table 2.

[0057] Table 2 Powder coating formulations of various embodiments and comparative examples

[0058]

[0059] The preparation method of the powder coatings of the above embodiments and comparative examples is: weigh different raw materials and fully premix them in a mixing tank according to the formula in Table 2 → extrude them together through an extruder → tablet press → crush → grind → sieve → package the finished product. Then, the powder coating is sprayed on the surface of the standard salt spray test phosphate plate produced by Biaogeda by electrostatic spraying, and the different properties of the coating are tested after baking at 200℃@10min. The results are shown in Table 3.

[0060] Table 3 Performance of powder coatings in various embodiments and comparative examples

[0061]

[0062] Remark:

[0063] *1: The PCI leveling grade from 1 to 10 represents the improvement of leveling performance, where PCI~10 represents the leveling performance is the same as a mirror. Currently, there are commercial standard plates for evaluating PCI grades;

[0064] *2: For salt spray corrosion, the maximum corrosion width is the average value of 6 different points.

[0065] It can be seen from Table 3 that the salt spray resistance of the polyester resin provided by the present invention is significantly better than that of the comparative example. The test time of the neutral salt spray test of the comparative example with a single-side corrosion width less than 2 mm increases from 500 to 1000 hours to more than 1500 hours for the polyester resin of the present invention.

[0066] The catalyst in the raw materials of the powder coating provided in Comparative Example 1 is a conventional organic tin catalyst, and the neutral salt spray test life is about 1000 hours; no phosphorus-containing reagent is added to the formula in Comparative Example 2, and no polyamine is added to the formula in Comparative Example 3, resulting in the salt spray resistance of the powder coating being significantly weaker than that of the embodiments.

[0067] The detailed description of a salt spray resistant powder coating and a preparation method thereof with reference to the above-mentioned embodiments is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A polyester resin for salt spray resistant powder coating, characterized in that: The raw materials include the following mass percentages: 25-45% polyol; 40-65% aromatic polyacid; 0.5-2.5% branching agent; 1.5-5% polyamine; 5-15% acidolysis agent; 1.3-8% phosphorus-containing reagent; 0.1-1.4% esterification catalyst; 0.01-1% curing accelerator; Antioxidant 0.1-2%, the sum of the mass percentages of the above raw materials is 100%; The esterification catalyst is a mixture of component A and component B; the component A is a mixture of zinc acetate and lithium acetate; the component B is a titanate catalyst.

2. The polyester resin for salt spray resistant powder coating according to claim 1, characterized in that: The polyamine is any one or more of ethylenediamine, propylenediamine, hexamethylenediamine, butylenediamine, pentamethylenediamine, heptamethylenediamine, decanediamine, ethanolamine, propanolamine and butanolamine.

3. The polyester resin for salt spray resistant powder coating according to claim 1, characterized in that: The phosphorus-containing reagent is any one or more of phosphoric acid, ester derivatives of phosphoric acid, phosphorous acid, and ester derivatives of phosphorous acid.

4. The polyester resin for salt spray resistant powder coating according to claim 1, characterized in that: The esterification catalyst is a mixture of component A and component B; the component A is a mixture of zinc acetate and lithium acetate; The component B is a titanate catalyst.

5. The polyester resin for salt spray resistant powder coating according to claim 1, characterized in that: The polyol is any one or more of neopentyl glycol, trimethylpentanediol, cyclohexanedimethanol, and ethylbutylpropylene glycol.

6. The polyester resin for salt spray resistant powder coating according to claim 1, characterized in that: The aromatic polyacid is at least one of terephthalic acid and isophthalic acid.

7. The polyester resin for salt spray resistant powder coating according to claim 1, characterized in that: The branching agent is any one or more of trimethylolpropane, trimethylolethane, or dimethylolpropionic acid.

8. The polyester resin for salt spray resistant powder coating according to claim 1, characterized in that: The acidolysis agent is any one or more of isophthalic acid, adipic acid, 1,4-cyclohexanedicarboxylic acid, trimellitic anhydride, and fumaric acid.

9. The method for preparing a polyester resin for salt spray resistant powder coating according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: 1) Put the formulated amount of polyol and branching agent into a reaction kettle and heat to 160-180°C to melt; 2) Add the formulated amount of aromatic polyacid and esterification catalyst into a reaction kettle at the same time, and react at 235-255° C. in an inert atmosphere until the system becomes clear; 3) Cooling to 200-210°C, adding the formulated amount of phosphorus-containing reagent, and stirring the reaction at 220-235°C in an inert atmosphere for 0.5-2h; 4) Then the temperature is lowered to 210-220°C, and the acidolysis agent is added to the reaction kettle, and the temperature is raised to 235-250°C to react until the acid value of the system reaches 45-65 mgKOH / g, and acidolysis and end-capping are performed; 5) Cooling to 230-240°C, polycondensing under vacuum, venting and cooling to 200-230°C after the acid value reaches 32-55 mgKOH / g; 6) Add the formulated amount of polyamine and maintain for 1 to 2 hours, then cool to 180-200° C., add the formulated amount of antioxidant and curing accelerator, and maintain at -0.05 MPa to -0.07 MPa for 5 to 30 minutes.

10. A salt spray resistant powder coating, characterized in that: The salt spray resistant powder coating uses the polyester resin for salt spray resistant powder coating according to any one of claims 1 to 8 as a raw material.

Images