Polyester resin powder coating and preparation method thereof

Abstract

The invention belongs to the technical field of powder coatings, and discloses a polyester resin powder coating and a preparation method thereof.The powder coating takes amorphous polyester resin as a main component, and a small amount of crystalline polyester resin is added to serve as a curing accelerator carrier; the crystal polyester resin is gradually melted at the curing temperature of about 200 DEG C and the curing accelerator is delayed to release, so that the time sequence control of the curing process is realized, that is, leveling is performed firstly and then rapid curing is performed, and the powder coating has excellent surface leveling property and balanced mechanical property and has important application value and industrial production value.

Description

Technical Field

[0001] This invention belongs to the field of polyester resin powder coating technology, specifically relating to a polyester resin powder coating and its preparation method. Background Technology

[0002] Powder coatings are solid powdered resin coatings composed of solid resins, pigments, fillers, and additives. They are characterized by solvent-free production, 100% film formation, and low energy consumption, and have therefore become a substitute for paints in many fields such as building materials, construction machinery, and furniture and home appliances.

[0003] However, because powder coatings require a high-temperature melt cross-linking and curing process, their leveling properties are lower than those of paints, making them difficult to replace in some fields where leveling is crucial. Therefore, the development and preparation of mirror-finish powder coatings and their polyester resins is one of the key areas the industry needs to focus on. Currently, many people in the industry are working on related areas, such as reducing viscosity and Tg, and reducing reactivity. However, the decrease in viscosity and Tg affects the storage stability of polyester resins and powder coatings, and the decrease in reactivity leads to a decline in mechanical properties.

[0004] In summary, developing a powder coating that meets both high leveling requirements and good mechanical properties has become a pressing technical challenge for the industry. Summary of the Invention

[0005] The purpose of this invention is to provide a polyester resin powder coating. By introducing a crystalline polyester resin containing a curing accelerator into the powder coating system, the temperature-triggered delayed release of the accelerator during the curing process is achieved, thereby significantly improving the mechanical properties of the coating while ensuring excellent leveling performance, and solving the contradiction between high leveling and high mechanical properties in the prior art.

[0006] Another objective of this invention is to provide a method for preparing the polyester resin powder coating.

[0007] This invention provides a polyester resin powder coating, which is prepared from the following raw materials in the indicated mass percentages:

[0008] Amorphous polyester resin 48-65%;

[0009] 3-5% crystalline polyester resin;

[0010] Hardener 3-6%;

[0011] Leveling agent 0.8-1.2%;

[0012] Inorganic pigments: 0.7-30%;

[0013] Filler content 3-15%;

[0014] Additives 0-2%.

[0015] In the above-mentioned polyester resin powder coating, the filler is one or more of nano-silica, barium sulfate, calcium carbonate or talc.

[0016] In the above-mentioned polyester resin powder coating, the additive is a mixture of benzoin and 701B wetting accelerator, wherein the mass ratio of benzoin to 701B wetting accelerator is 1:2-2:1.

[0017] In the above-mentioned polyester resin powder coating, the inorganic pigment is one or more of iron oxide yellow, carbon black or titanium dioxide.

[0018] In the above-mentioned polyester resin powder coating, the amorphous polyester resin is prepared from the following raw materials in the indicated mass percentages:

[0019] Polyol a: 32-42%;

[0020] Aromatic polyacids: 47-57%;

[0021] Acid hydrolysate: 5-15%;

[0022] Esterification catalyst: 0.03-0.15%;

[0023] Antioxidant: 0.2-0.8%;

[0024] The polyol a is a mixture of neopentyl glycol (NPG) and non-neopentyl glycol diol a, wherein the mass percentage of NPG in the polyol a is ≥80%, and the non-neopentyl glycol diol a is one or more of ethylene glycol (EG), methyl propylene glycol (MPO), or ethyl butyl propylene glycol (BEPD). By increasing the neopentyl glycol content, the rigid structure of neopentyl glycol will disrupt the regularity of the molecular chain, significantly reducing the crystallization tendency of the polyester, thereby making the resin exhibit an amorphous state, showing an amorphous amorphous structure.

[0025] In the above-mentioned polyester resin powder coating, the amorphous polyester resin has an acid value of 28-45 mgKOH / g, a hydroxyl value of 0-8 mgKOH / g, a glass transition temperature (Tg) ≥60℃, and a viscosity of 1800-4000 mPa.s. / 200℃.

[0026] In the above-mentioned polyester resin powder coating, the crystalline polyester resin is prepared from the following raw materials in the indicated mass percentages:

[0027] Polyol b: 31-45%;

[0028] Aromatic polyacids: 46-58%;

[0029] Acid hydrolysate: 4-10%;

[0030] Esterification catalyst: 0.03-0.15%;

[0031] Curing accelerator: 3-8%;

[0032] The polyol b is a mixture of neopentyl glycol (NPG) and non-neopentyl glycol diol b, wherein the mass percentage of NPG in the polyol b is ≤20%, and the non-neopentyl glycol diol b is one or more of 1,2-ethylene glycol, 1,4-butanediol, 1,6-hexanediol, and cyclohexanediol (CHDM). By reducing the neopentyl glycol content, the monomers of the symmetrical flexible structure are significantly increased, thereby improving the crystallinity of the system. By increasing the content of alicyclic polyols, the melting temperature is controlled to be close to the baking and curing temperature of the powder coating, which promotes the slow release of the curing accelerator at this temperature and improves the mechanical properties.

[0033] The crystalline polyester resin has an acid value of 28-45 mgKOH / g, a hydroxyl value of 0-8 mgKOH / g, and a crystal melting initiation temperature T. onset The peak melting temperature of the crystal is 197-205℃. peak The temperature is 205-210℃.

[0034] The aromatic polyacid is one or more of terephthalic acid (PTA) or isophthalic acid (IPA).

[0035] The acid hydrolysate is one or more of isophthalic acid (IPA), adipic acid (ADA), or 1,4-cyclohexanedicarboxylic acid (CHDA).

[0036] The esterification catalyst is one or more of dibutyltin oxide, tributyltin oxide, dihydroxybutyltin chloride, stannous oxalate, or monobutyltin oxide.

[0037] The curing accelerator is one or more of tetraethylammonium bromide, tetramethylammonium bromide, benzyltriethylammonium chloride, triphenylethylphosphine bromide, or dibutyltin dilaurate. Preferably, the curing accelerator is one or more of triphenylethylphosphine bromide or benzyltriethylammonium chloride.

[0038] In the above-mentioned polyester resin powder coating, the leveling agent is GLP588 leveling agent.

[0039] In the above-mentioned polyester resin powder coating, the curing agent is triglycidyl isocyanurate.

[0040] The present invention also provides a method for preparing the polyester resin powder coating, the method comprising the following steps:

[0041] The polyester resin powder coating is obtained by mixing, extruding, pressing, pulverizing and sieving the raw materials of each component according to the stated mass percentage.

[0042] Compared with the prior art, the present invention has the following advantages:

[0043] Because amorphous polyester resin has low viscosity and does not contain curing accelerators, the polyester resin powder coating of this invention first flows and forms a highly leveled surface during the baking and curing process at 200°C for 10 minutes, achieving a PCI of 8-9. At this time, the crystalline polyester resin, due to its crystal melting temperature being near the baking temperature, gradually melts and releases curing accelerators, significantly accelerating the reaction between the amorphous polyester resin and the curing agent TGIC, resulting in high crosslinking density and high mechanical properties, with impact strength reaching 50 / 50 kg·cm or 120 / 120 inch pound, thus achieving high leveling and high mechanical properties. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0046] The amorphous polyester resins A1-A3 used in the following embodiments and comparative examples were prepared from the raw materials shown in Table 1 below, and the preparation method included the following steps:

[0047] 1) Add polyol a, aromatic polyacid and esterification catalyst into the reactor, raise the temperature to 243℃ and maintain it;

[0048] 2) After the system has clarified, take a sample to test the acid value (AV). When the AV reaches 5-20 mg KOH / g, add the acid hydrolysate and maintain the temperature at 240℃ to perform acid hydrolysis and end sealing.

[0049] 3) When the secondary acid value reaches 40-50 mg KOH / g, start cooling down. After cooling down to 235℃, perform polycondensation under vacuum of -0.1 MPa to achieve an acid value of 28-36 mg KOH / g after vacuum.

[0050] 4) Then cool down to 215℃, add antioxidants and maintain for 30 minutes before discharging.

[0051] Steps 1), 2), and 4) require protection using industrial-grade high-purity nitrogen with a purity greater than 99.99%.

[0052] Table 1 Raw material list for amorphous polyester resins A1-A3

[0053]

[0054] The crystalline polyester resins B1-B2 used in the following embodiments and comparative examples were prepared from the raw materials shown in Table 2 below, and the preparation method included the following steps:

[0055] 1) Add polyol b, aromatic polyacid and esterification catalyst to the reactor simultaneously, raise the temperature to 243℃ and maintain it;

[0056] 2) After the system has clarified, take a sample to test the acid value. When the acid value reaches 5-20 mg KOH / g, add the acid hydrolysis agent and maintain the temperature at 240℃ to perform acid hydrolysis and end sealing.

[0057] 3) When the secondary acid value of the system reaches 40-48 mgKOH / g, start cooling down. After cooling down to 235℃, perform polycondensation under vacuum of -0.1 MPa to make the acid value of the polyester reach 28-34 mgKOH / g after vacuum.

[0058] 4) Then cool down to 215℃, add curing accelerator and maintain for 30 minutes before discharging.

[0059] Table 2 Raw material list for crystalline polyester resins B1-B2

[0060]

[0061] The polyester resins C1-C2 used in the following comparative examples were prepared from the raw materials shown in Table 3 below, and the preparation methods included the following steps:

[0062] 1) Add polyol, aromatic polyacid and esterification catalyst to the reactor at the same time, raise the temperature to 243°C and maintain it;

[0063] 2) After the system has clarified, take a sample to test the acid value. When the acid value reaches 5-20 mg KOH / g, add the acid hydrolysate and maintain the temperature at 235℃ to perform acid hydrolysis and end sealing.

[0064] 3) When the secondary acid value of the system reaches 40-48 gKOH / g, start cooling down. After cooling down to 235℃ and polycondensing under vacuum of -0.1MPa, the acid value of the polyester after vacuum reaches 28-34 mgKOH / g.

[0065] 4) Then, cool down to 210-220℃, add curing accelerator, maintain for 30 minutes, and then discharge the material.

[0066] Table 3 Raw material list for polyester resins C1-C2

[0067]

[0068] The polyester resin C1 was not mixed with a curing accelerator, and the crystal melting temperature of the polyester resin C2 was not within the crystal melting temperature range of crystalline polyester resins.

[0069] Example 1

[0070] A polyester resin powder coating, said powder coating being prepared from the following raw materials in parts by weight:

[0071] 530 parts of amorphous polyester resin A1;

[0072] 34 parts of crystalline polyester resin B1;

[0073] TGIC 36 copies;

[0074] 10 copies of GLP588;

[0075] 3 portions of benzoin;

[0076] 701B (3 copies);

[0077] 250 parts of titanium dioxide;

[0078] 134 portions of barium sulfate.

[0079] The preparation method of the above-mentioned polyester resin powder coating includes the following steps:

[0080] The polyester resin powder coating raw material described in this embodiment is premixed, co-extruded through an extruder, pressed into sheets, crushed, and sieved to obtain the polyester resin powder coating.

[0081] Example 2

[0082] A polyester resin powder coating, said powder coating being prepared from the following raw materials in parts by weight:

[0083] 524 parts of amorphous polyester resin A2;

[0084] 34 parts of crystalline polyester resin B1;

[0085] TGIC 42 copies;

[0086] 10 copies of GLP588;

[0087] 3 portions of benzoin;

[0088] 701B (3 copies);

[0089] 250 parts of titanium dioxide;

[0090] 134 portions of barium sulfate.

[0091] The preparation method of the above-mentioned polyester resin powder coating is the same as that in Example 1.

[0092] Example 3

[0093] A polyester resin powder coating, said powder coating being prepared from the following raw materials in parts by weight:

[0094] 524 parts of amorphous polyester resin A3;

[0095] 34 parts of crystalline polyester resin B2;

[0096] TGIC 42 copies;

[0097] 10 copies of GLP588;

[0098] 3 portions of benzoin;

[0099] 701B (3 copies);

[0100] 250 parts of titanium dioxide;

[0101] 134 portions of barium sulfate.

[0102] The preparation method of the above-mentioned polyester resin powder coating is the same as that in Example 1.

[0103] Comparative Example 1

[0104] A polyester resin powder coating, said powder coating being prepared from the following raw materials in parts by weight:

[0105] 524 parts of amorphous polyester resin A2;

[0106] 34 parts of polyester resin C1;

[0107] TGIC 42 copies;

[0108] 10 copies of GLP588;

[0109] 3 portions of benzoin;

[0110] 701B (3 copies);

[0111] 250 parts of titanium dioxide;

[0112] 134 portions of barium sulfate.

[0113] The preparation method of the above-mentioned polyester resin powder coating is the same as that of Example 1.

[0114] Comparative Example 2

[0115] A polyester resin powder coating, said powder coating being prepared from the following raw materials in parts by weight:

[0116] 524 parts of amorphous polyester resin A2;

[0117] 34 parts of polyester resin C2;

[0118] TGIC 42 copies;

[0119] 10 copies of GLP588;

[0120] 3 portions of benzoin;

[0121] 701B (3 copies);

[0122] 250 parts of titanium dioxide;

[0123] 134 portions of barium sulfate.

[0124] The preparation method of the above-mentioned polyester resin powder coating is the same as that of Example 1.

[0125] Comparative Example 3

[0126] A polyester resin powder coating, said powder coating being prepared from the following raw materials in parts by weight:

[0127] 564 parts of amorphous polyester resin A2;

[0128] TGIC 36 copies;

[0129] 10 copies of GLP588;

[0130] 3 portions of benzoin;

[0131] 701B (3 copies);

[0132] 250 parts of titanium dioxide;

[0133] 134 portions of barium sulfate.

[0134] Test Example 1

[0135] The powder coatings described in the above embodiments and comparative examples were sprayed onto the surface of an iron plate using electrostatic spraying. After baking at 200°C for 15 minutes, the different properties of the coatings were tested. The film thickness test method followed GB / T 13452.2-2008, the gelation time test method followed GB / T 16995-1997, and the gloss (60°) test method followed GB / T 9754-2007. Impact strength was divided into frontal impact strength and reverse impact strength, abbreviated as forward impact and reverse impact, and the test methods followed GB / T 1732-2020 and ASTM D5420, respectively. GB / T 1732-2020 uses kg·cm, and ASTM D5420 uses inch-pound. The adhesion test method followed GB / T... 9286-2021, the leveling rating of PCI was tested using a standard PCI board. Ratings from 1 to 10 represent improvements in leveling performance, with rating 1 indicating severe orange peel (extremely poor leveling) and rating 10 indicating no orange peel and a smooth surface. Test results are shown in Table 4.

[0136] Table 4 Performance of Powder Coatings in Each Example and Comparative Example Formulation

[0137]

[0138] As can be seen from Table 4, Examples 1-3 of the present invention have excellent mechanical properties while exhibiting high leveling properties. Comparative Example 1 shows that the crystallizing resin without curing accelerator has good leveling properties but poor mechanical properties, and the test results according to GB / T 1732-2020 standard do not exceed the detection limit. Comparative Example 2 shows that the mechanical properties of polyester resin C2 are excellent but the leveling properties are poor when the crystal melting temperature is not within the specified range. Comparative Example 3 shows that the leveling properties are excellent but the mechanical properties are poor when only polyester resin A is added, and the test results according to GB / T 1732-2020 standard do not exceed the detection limit.

[0139] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0140] The above description of the embodiments is intended to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A polyester resin powder coating, characterized in that, The powder coating is prepared from the following raw materials in the indicated mass percentages: Amorphous polyester resin: 48-65%; Crystalline polyester resin: 3-5%; Hardener: 3-6%; Leveling agent: 0.8-1.2%; Inorganic pigments: 0.7-30%; Filler: 3-15%; Additives: 0-2%.

2. The polyester resin powder coating according to claim 1, characterized in that, The filler is one or more of nano-silica, barium sulfate, calcium carbonate, or talc; the leveling agent is GLP588 leveling agent; and the curing agent is triglycidyl isocyanurate.

3. The polyester resin powder coating according to claim 1, characterized in that, The adjuvant is a mixture of benzoin and 701B wetting accelerator, wherein the mass ratio of benzoin to 701B wetting accelerator is 1:2-2:

1.

4. The polyester resin powder coating according to claim 1, characterized in that, The amorphous polyester resin is prepared from the following raw materials in the indicated mass percentages: Polyol a: 32-42%; Aromatic polyacids: 47-57%; Acid hydrolysis agent: 5-15%; Esterification catalyst: 0.03-0.15%; Antioxidant: 0.2-0.8%; The polyol a is a mixture of neopentyl glycol and non-neopentyl glycol diol a, wherein the mass percentage of NPG in the polyol a is ≥80%, and the non-neopentyl glycol diol a is one or more of ethylene glycol, methyl propylene glycol or ethyl butyl propylene glycol.

5. The polyester resin powder coating according to claim 1 or 4, characterized in that, The amorphous polyester resin has an acid value of 28-45 mgKOH / g, a hydroxyl value of 0-8 mgKOH / g, a glass transition temperature ≥60℃, and a viscosity of 1800-4000 mPa.s. / 200℃.

6. The polyester resin powder coating according to claim 1, characterized in that, The crystalline polyester resin is prepared from the following raw materials in the indicated mass percentages: Polyol b: 31-45%; Aromatic polyacids: 46-58%; Acid hydrolysis agent: 4-10%; Esterification catalyst: 0.03-0.15%; Curing accelerator: 3-8%; The polyol b is a mixture of neopentyl glycol and non-neopentyl glycol type diol b, wherein the mass percentage of neopentyl glycol in the polyol b is ≤20%, and the non-neopentyl glycol type diol b is one or more of 1,2-ethylene glycol, 1,4-butanediol, 1,6-hexanediol and cyclohexanediethanol.

7. The polyester resin powder coating according to claim 1 or 6, characterized in that, The crystalline polyester resin has an acid value of 28-45 mgKOH / g, a hydroxyl value of 0-8 mgKOH / g, and a crystal melting initiation temperature T. onset The peak melting temperature of the crystal is 197-205℃. peak The temperature is 205-210℃.

8. The polyester resin powder coating according to claim 4, characterized in that, The aromatic polyacid is one or more of terephthalic acid or isophthalic acid; the acid hydrolysate is one or more of isophthalic acid, adipic acid or 1,4-cyclohexanedicarboxylic acid; and the esterification catalyst is one or more of dibutyltin oxide, tributyltin oxide, dihydroxybutyltin chloride, stannous oxalate or monobutyltin oxide.

9. The polyester resin powder coating according to claim 4 or 6, characterized in that, The curing accelerator is one or more of tetraethylammonium bromide, tetramethylammonium bromide, benzyltriethylammonium chloride, triphenylethylphosphine bromide, or dibutyltin dilaurate.

10. A method for preparing a polyester resin powder coating as described in claim 1, characterized in that, The preparation method includes the following steps: The polyester resin powder coating is obtained by mixing, extruding, pressing, pulverizing and sieving the raw materials of each component according to the stated mass percentage.

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