Polyester resin for indoor powder coating as well as preparation and application of polyester resin

Abstract

The invention discloses polyester resin for indoor powder coating as well as preparation and application thereof, and belongs to the technical field of polyester resin. The polyester resin comprises the following raw material components in percentage by mass: 32.0-45.0% of linear aliphatic dihydric alcohol with a side group; 1.0 to 2.5 percent of a branching agent; 0 to 1.5 percent of aliphatic cyclic dihydric alcohol; 45 to 58 percent of aromatic polybasic acid; 0 to 1.5 percent of alicyclic polybasic acid; 1.0-6.0% of an end-capping reagent A saturated long straight chain single fatty acid; 4.0 to 8.0 percent of end-capping reagent B isophthalic acid; 1.0-3.0% of an auxiliary agent A hydroxyl acrylic resin; 0.03 to 0.5 percent of an auxiliary agent B; and 0.05 to 0.15% of an esterification catalyst. According to the polyester resin for the indoor powder coating, a main chain structure, a branched structure and an end-capping structure of the polyester resin are improved, and the hydroxyl acrylic resin is added, so that the polyester resin can be cured with a TGIC (or HAA) curing agent, a cured coating film has the advantages of excellent leveling property, excellent boiling resistance, fine surface and the like, and can replace a polyester / epoxy powder coating system; therefore, the residues of bisphenol A and trimellitic anhydride in the powder coating are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of polyester resins, in particular to a polyester resin for indoor powder coatings and its preparation and application. Background Art

[0002] As an environmentally friendly coating, powder coating has penetrated into many fields of the coating industry. Unlike traditional solvent-based coatings and water-based coatings, it exists in a micron-sized powder state and is dispersed in the air medium. It does not require the use of solvents or water for dispersion. After high-temperature melting, the resin cross-links and solidifies into a smooth coating film. Currently, the most widely used is the carboxyl-terminated polyester resin powder coating, which has good mechanical properties and easy control of the reaction process. It is becoming more and more the mainstream direction of polyester powder coatings. Carboxyl-terminated polyester resin can be cured with epoxy resin (mainly E-12), TGIC (triglycidyl isocyanurate), and HAA (β-hydroxyalkylamide) to form a film, which can be used in different occasions.

[0003] The carboxyl-terminated polyester resin and E-12 curing system are mainly used to prepare indoor powder coatings. There are many types of matching polyester resins and the technology is mature. Because E-12 has the characteristic of low melt viscosity at the curing temperature of powder coatings, the coating prepared by it has outstanding leveling performance; at the same time, E-12 has good dispersibility for pigments and fillers, and the surface of the prepared coating is fine. Conventional polyester / TGIC and polyester / HAA systems are difficult to prepare the excellent leveling performance and surface fineness shown by the polyester / epoxy system (E-12). At the same time, the unique bisphenol A structure of E-12 makes the coating prepared by it have excellent water boiling resistance, which is significantly better than the conventional polyester / TGIC and polyester / HAA systems.

[0004] In recent years, the requirements for environmental protection of coatings have become increasingly higher. Among them, the Food Contact Plastics Regulation (EU) 10 / 2011 has been revised several times since its release, and the application of BPA (bisphenol A) in food contact materials and products has been revised several times. As the starting raw material for the synthesis of bisphenol A epoxy resin, BPA will inevitably remain in the epoxy resin.

[0005] In the carboxyl-terminated polyester resin and epoxy resin curing system, since epoxy resin (E-12) is a linear polymer structure with epoxy groups at both ends, the polyester resin in the epoxy resin curing system needs a higher functional group to meet the density of the coating film. The industry mainly uses trimellitic anhydride (TMA) as a capping agent for polyester resins. Some foreign regions, such as the European Union, have issued Resolution (EU) 2018 / 594 to restrict the export of products containing trimellitic anhydride. In addition, the price of trimellitic anhydride (TMA) fluctuates greatly, so non-TMA polyester products have become the research and development direction of polyesters. However, the current research on non-TMA polyesters is mainly focused on the curing system with epoxy.

[0006] Therefore, with the widespread application of powder coatings in indoor applications, it is urgent to develop an indoor powder coating that can avoid the residual BPA in epoxy resin E-12 and the residual trimellitic anhydride in polyester resin. Summary of the invention

[0007] The object of the present invention is to provide a carboxyl polyester resin which does not use trimellitic anhydride as a capping agent and can be cured with a curing agent TGIC (triglycidyl isocyanurate) or HAA (β-hydroxyalkylamide) to avoid residual bisphenol A; another object of the present invention is to provide a method for preparing a carboxyl polyester resin which does not use trimellitic anhydride as a capping agent and can be cured with a curing agent TGIC or HAA; another object of the present invention is to provide a powder coating which has a high leveling grade, a plump surface and is resistant to boiling water after being cured with a curing agent TGIC or HAA.

[0008] The present invention discloses a polyester resin for indoor powder coatings. The raw material components include, by mass percentage:

[0009] Straight-chain fatty diols with side groups: 32.0-45.0%;

[0010] Branching agent: 1.0-2.5%;

[0011] Aliphatic cyclic diols: 0-1.5%;

[0012] Aromatic polybasic acid: 45-58%;

[0013] Alicyclic polyacid: 0-1.5%;

[0014] Capping agent A saturated long straight chain mono fatty acid: 1.0-6.0%;

[0015] Capping agent B isophthalic acid: 4.0-8.0%;

[0016] Auxiliary agent A hydroxy acrylic resin: 1.0-3.0%;

[0017] Additive B: 0.03-0.5%;

[0018] Esterification catalyst 0.05~0.15%.

[0019] The straight-chain fatty diol with side groups is selected from one or a combination of neopentyl glycol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 1,3-butanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,4-diethyl-1,5-pentanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, 2-methyl-1,8-octanediol, and hydroxy neopentyl alcohol hydroxypivalate.

[0020] The use of straight-chain fatty diols with side groups as raw materials, which account for a large mass ratio in the raw material components, will give the polyester resin after polymerization the properties of low surface tension and low viscosity. Low surface tension will be conducive to the wetting and dispersion of pigments and fillers by the polyester resin as the main film-forming substance, which helps to obtain a coating surface with high surface decorative properties. Low viscosity is conducive to the strong mobility of the polyester resin at the curing temperature, and a high-leveling coating is obtained after leveling. At the same time, the presence of side groups plays a certain protective role on the ester bond during the boiling process of the coating.

[0021] Furthermore, the straight-chain fatty diol with side groups includes neopentyl glycol, and the mass percentage of the neopentyl glycol in the straight-chain fatty diol component with side groups is 40.0-75.0%.

[0022] Furthermore, the capping agent A is a saturated long straight-chain monofatty acid selected from one or a combination of caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid.

[0023] Furthermore, the auxiliary agent B includes a curing accelerator and an antioxidant, wherein the mass percentage of the curing accelerator in the raw material components is 0.03-0.2%; the mass percentage of the antioxidant in the raw material components is 0.2-0.5%.

[0024] Furthermore, the branching agent includes tris(2-hydroxyethyl)isocyanurate.

[0025] The branching agent is a combination of tris(2-hydroxyethyl)isocyanurate and trimethylolpropane, or a combination of tris(2-hydroxyethyl)isocyanurate and triethylolpropane, or a combination of tris(2-hydroxyethyl)isocyanurate, trimethylolpropane and triethylolpropane.

[0026] Tris(2-hydroxyethyl)isocyanurate with a triazine ring structure is introduced into the branching agent component. Compared with the single use of trimethylolpropane and triethylolpropane, the branching agent gives the polyester resin a certain spatial structure, which is beneficial to the molecular movement after the introduction of saturated long straight-chain monofatty acids. The triazine ring structure gives the coating film excellent chemical resistance and plays a stabilizing role in the water boiling resistance of the coating film.

[0027] The aliphatic cyclic diol is selected from 1,4-cyclohexanedimethanol and hydrogenated bisphenol A, or a combination of the two.

[0028] The addition of aliphatic cyclic diols can be used to adjust the glass transition temperature of the polyester resin after polymerization.

[0029] Furthermore, the alicyclic polyacid is selected from one or a combination of 1,4-cyclohexanedicarboxylic acid, hexahydrophthalic anhydride, 1,2-cyclobutanedicarboxylic acid, and furan dicarboxylic acid.

[0030] The aromatic polyacids are terephthalic acid and isophthalic acid.

[0031] The esterification catalyst is selected from one or a combination of stannous oxalate, n-butyl titanate, and tetraisopropyl titanate.

[0032] Addition of additive A hydroxy acrylic resin, part of the hydroxy acrylic resin participates in the reaction and is grafted onto the polyester resin. During the film-forming process of the powder coating, the acrylic hydrophobic groups that are incompatible with the polyester face outward, protecting the ester bonds of the polyester resin. The other part of the hydroxy acrylic resin molecules are evenly dispersed in the polyester resin system through physical mixing, reducing the surface tension of the overall powder coating system and ensuring that the powder coating film is better spread on the surface of the substrate.

[0033] The present invention ingeniously utilizes the acrylic hydrophobic groups of the auxiliary agent A hydroxy acrylic resin and the polyester-incompatible part. The hydrophobic groups have good compatibility with the matting agent (mainly composed of acrylic resin) in the low-gloss system, which is more conducive to the dispersion of the matting agent in the powder coating system, and a uniform low-gloss coating film is prepared, and the obtained coating film has higher fineness.

[0034] Furthermore, in the auxiliary agent A hydroxyl acrylic resin, the content of hydroxyl groups is 60 to 120 mgKOH / g.

[0035] Furthermore, the preparation method of the auxiliary agent A hydroxy acrylic resin comprises the following steps:

[0036] (1) Mixing the monomer and the initiator uniformly to form a mixed solution;

[0037] (2) adding an organic solvent to a reaction vessel, gradually raising the temperature to 130-140° C. under the protection of a protective gas, and dropping the mixed solution. After the dropwise addition is complete, 1 wt % of an initiator is added to the reaction vessel, and the reaction is continued for 0.8-1.5 hours, and then the heating is stopped;

[0038] (3) removing the organic solvent to obtain the auxiliary agent A hydroxy acrylic resin.

[0039] Furthermore, the organic solvent is xylene.

[0040] Furthermore, the monomers include acrylate monomers and hydroxyacrylate monomers, the acrylate monomers are selected from one or a combination of at least two of methyl methacrylate, butyl acrylate, isooctyl methacrylate, and lauryl acrylate; the hydroxyacrylate monomers are selected from one or a combination of at least two of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0041] Furthermore, the initiator is azobisisobutylcyanide.

[0042] Furthermore, the raw materials for synthesizing the auxiliary agent A hydroxy acrylic resin include isooctyl methacrylate and / or lauryl acrylate; the content of isooctyl methacrylate and / or lauryl acrylate accounts for 15-25wt% of the total monomer feed amount.

[0043] The curing accelerator is selected from one of triphenylethyl phosphonium bromide, triphenylbutyl phosphonium bromide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetraethylammonium chloride, tetrapropylammonium bromide, methyltriethylammonium chloride, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, or a combination of several thereof.

[0044] The antioxidant is a combination of a hindered phenol antioxidant and a phosphite antioxidant.

[0045] The hindered phenol antioxidant is selected from one or a combination of tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate] pentaerythritol ester, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-(3,5-di-tert-butyl-4-hydroxyphenyl)-s-triazine-2,4,6(1H,3H,5H)trione or N,N'-bis-[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionyl] hexanediamine.

[0046] The phosphite antioxidant is selected from one or a combination of tris(2,4-di-tert-butylphenyl)phosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite or bis(2,6-di-tert-butyl-4-tolyl)pentaerythritol diphosphite.

[0047] The technical solution disclosed in the present invention does not add unbranched straight-chain fatty diols and straight-chain fatty dibasic acids to the raw material components of the polyester resin, which can better balance the viscosity and glass transition temperature of the polyester resin, that is, the balance between the fluidity and storage stability of the powder coating. At the same time, it avoids that the coating film of the processed powder coating has more ester bonds that are not protected by the hydrophobic group during the water boiling process.

[0048] The present invention also discloses a method for preparing a polyester resin for indoor powder coating, comprising the following steps:

[0049] S1: Add a straight-chain fatty diol with a side group, an aliphatic cyclic diol, a branching agent and an esterification catalyst into a reaction vessel, heat it to 110-130° C. at normal pressure, then add an aromatic polyacid and an alicyclic polyacid, stir under the protection of a protective gas, heat it to 170-240° C., and keep the temperature to react until the esterification reaction is completed;

[0050] S2: Cool down, add end-capping agent A saturated long straight chain mono fatty acid, raise the temperature to 230-240°C, and react for 30-40 minutes;

[0051] S3: Cooling down, adding end-capping agent B isophthalic acid, controlling the temperature at 230-250°C, and reacting for 60-80 minutes;

[0052] S4: At a temperature of 235 to 238° C., evacuate to -0.098 to -0.095 MPa, and continue the reaction for 60 to 150 minutes;

[0053] S5: Cooling the reactant material, adding auxiliary agent A hydroxy acrylic resin, controlling the temperature at 225-230° C., and reacting for 30-40 minutes.

[0054] S6: Keeping the temperature of the reaction material at 210-215° C., adding the auxiliary agent B, and reacting for 35-45 minutes to obtain the polyester resin for indoor powder coating as described above.

[0055] The preparation method disclosed in the present invention ingeniously adds a branching agent with a relatively high mass ratio in the polyester esterification stage, and at the same time uses a saturated long straight-chain mono fatty acid as the end-capping agent A to first cap the end in the end-capping stage. The branching agent with a relatively high mass ratio ensures that a single polyester molecule has multiple hydroxyl functional groups in the esterification stage, and cooperates well with the saturated long straight-chain mono fatty acid as the end-capping agent A added in the end-capping stage, and the mono fatty acid first caps part of the hydroxyl functional groups. The combination of the two successfully introduces a long-chain saturated fatty acid into the polyester molecular structure, while ensuring that there are enough functional groups for re-crosslinking reaction to ensure the crosslinking density of the coating. The introduction of the saturated long straight-chain mono fatty acid as the end-capping agent A further reduces the viscosity of the reaction system and the reaction speed, while the long chain improves the wetting and dispersibility of the pigment and filler and improves the fullness of the coating; the long chain structure as a hydrophobic group can well protect the ester bond of the polyester resin from hydrolysis during the boiling process.

[0056] The invention also discloses an indoor powder coating, comprising the polyester resin obtained by the preparation method described above, a curing agent and a leveling agent.

[0057] The powder coating prepared from the polyester resin disclosed in the present invention and a curing agent, a pigment, an auxiliary agent, etc. is cured under the condition of 180°C / 15min, and the obtained high-gloss coating and low-gloss coating have excellent leveling performance, a fine surface, and good decorative properties; the high-gloss coating after TGIC curing has excellent water boiling resistance, and the HAA-cured high-gloss coating and the TGIC / HAA-cured low-gloss coating both have good water boiling resistance.

[0058] The polyester resin for indoor powder coating provided by the present invention has the advantages of low viscosity, low surface tension, high glass transition temperature, storage stability, etc. by improving the main chain structure, branching structure and end-capping structure of the polyester resin and adding hydroxyl acrylic resin; and can be cured with TGIC (or HAA) curing agent, and the cured coating film has the advantages of excellent leveling, excellent water boiling resistance, fine surface, etc., and can replace the polyester / epoxy powder coating system, thereby avoiding the residue of bisphenol A and trimellitic anhydride in the powder coating. DETAILED DESCRIPTION

[0059] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments.

[0060] The acid value of polyester resin is tested according to GB / T 6743-2008; the viscosity is tested according to GB / T 9751.1-2008; the glass transition temperature (T g ) Test according to GB / T 19466.2-2004, heating rate 10℃ / min.

[0061] Table 1 Polyester resin raw material formula list and synthetic polyester performance indicators of the embodiment and comparative example

[0062]

[0063]

[0064] Example 1

[0065] Synthesis of additive A hydroxy acrylic resin:

[0066] (1) The required amount of monomers is weighed according to the following mass: 106.6 g of methyl methacrylate, 29.4 g of butyl acrylate, 37.0 g of hydroxyethyl acrylate, 16.2 g of isooctyl methacrylate, 20.5 g of lauryl acrylate and 4.0 g of initiator azobisisobutylcyanide. The weighed materials are mixed evenly by magnetic stirring and added to a constant pressure dropping funnel for later use.

[0067] (2) Add 130 ml of xylene to a four-necked flask with a spare heating jacket and a stirrer, gradually raise the temperature to 130-140°C under nitrogen protection, and add the reactants to the flask by continuous dropwise addition through a constant pressure dropping funnel. The entire dropwise addition time is controlled within 4-5 hours. After the dropwise addition is completed, add 2 g of initiator azobisisobutyl cyanide to the reaction flask, continue the reaction for 1 hour, and then stop heating.

[0068] (3) Most of the xylene solvent was removed by atmospheric distillation at 140° C., and then the temperature was slowly raised to 200° C. and the pressure was evacuated to -0.093 MPa to remove the solvent and residual monomers in the system to obtain a hydroxyl acrylic resin with a hydroxyl value of 110 mgKOH / g, which was used as auxiliary agent A for standby use.

[0069] Synthesis of polyester resin for indoor powder coatings:

[0070] S1: In a reaction kettle equipped with a heating device, a stirrer and a distillation column, add the formula amount of straight-chain fatty diol with side groups, aliphatic cyclic diol, branching agent and esterification catalyst shown in Table 1, heat to 110-130°C at normal pressure, then add the formula amount of aromatic polyacid and aliphatic polyacid, and heat at a rate of 2-3°C per minute while stirring under nitrogen protection; the material temperature rises to 170-180°C, esterification water begins to be generated and evaporated through the distillation column; at this time, the heating rate is controlled at 2-3°C per 30 minutes; when the material temperature rises to 195±2°C, the heating rate is controlled at 4-6°C per 30 minutes, and when the material temperature rises to 240±2°C, the heat preservation reaction is carried out for 1-1.5 hours; when the air temperature at the top of the distillation column drops to less than 70°C, and the esterification water output reaches 95% or more of the theoretical output, the heat preservation ends.

[0071] S2: The material temperature is lowered to 220-225°C, and a formula amount of end-capping agent A saturated long straight-chain monofatty acid is added. The temperature is controlled at 235±2°C and the reaction is carried out for 30-40 minutes.

[0072] S3: The material temperature is reduced to 220-225°C, and the formula amount of end-capping agent B isophthalic acid is added, the temperature is controlled at 240±2°C, and the reaction is carried out for 60-80 minutes.

[0073] S4: At a temperature of 235 to 238° C., gradually evacuate to -0.098 to -0.095 MPa, and continue the reaction for 60 to 150 minutes.

[0074] S5: the material temperature is reduced to 225-230°C, and the formulated amount of auxiliary agent A hydroxy acrylic resin is added, the temperature is controlled at 225-230°C, and the reaction is carried out for 30-40 minutes.

[0075] S6: Finally, the material temperature is maintained at 210-215° C., a curing accelerator and an antioxidant are added, and the mixture is stirred for reaction for 40 minutes to obtain a polyester resin.

[0076] Embodiment 2-5

[0077] Examples 2-5 use the same synthesis process as Example 1, with only the ratio of the raw material components being different. The specific formula is shown in Table 1.

[0078] Comparative Example 1 and Comparative Examples 4-6

[0079] Comparative Example 1 and Comparative Examples 4-6 adopt the same synthesis process as Example 1, only the ratio of the raw material components is different. The specific formula is shown in Table 1.

[0080] Comparative Example 2

[0081] Comparative Example 2 does not contain the end-capping agent A saturated long straight-chain monofatty acid, and Step S2 in the synthesis of the polyester resin is omitted. The rest is the same as Example 1.

[0082] Comparative Example 3

[0083] Comparative Example 3: No auxiliary agent A hydroxy acrylic resin, step S5 in the synthesis of polyester resin is omitted, and the rest is the same as Example 1.

[0084] Preparation of powder coating and performance testing

[0085] The five polyester resins synthesized in Examples 1-5 and the six polyester resins synthesized in Comparative Examples 1-6 were mixed evenly with curing agent TGIC (or HAA), barium sulfate, carbon black, leveling agent, brightener, etc. according to the ratios recorded in Tables 2 and 3, and dispersed, ground and sieved by an extruder; then electrostatically sprayed on a surface treated (phosphating) metal plate, cured to form a film under the curing conditions of 180°C / 15min, and the coating performance was tested. Table 2 is the component ratio of the high gloss powder coating, and Table 3 is the component ratio of the low gloss powder coating. Since the performance of the flat powder coating is close to that of the high gloss powder coating, this embodiment is not studied here.

[0086] Table 2 High gloss powder coating component ratio (unit: g)

[0087] name Polyester resin Curing agent Precipitated Barium Carbon Black Leveling agent Brightener Benzoin TGIC Highlight 279 21 185.5 2.5 5 5 2 HAA Highlight 285 15 185.5 2.5 5 5 2

[0088] Curing agent: TGIC (triglycidyl isocyanurate) high gloss, PT810 is used in this embodiment; Curing agent: HAA (β-hydroxyalkylamide) high gloss, QM1260 is used in this embodiment. Leveling agent: GLP588 from Ningbo Nanhai Chemical Company; Brightener: 701B from Ningbo Nanhai Chemical Company.

[0089] Table 3 Low gloss powder coating component ratio (unit: g)

[0090] name Polyester resin Curing agent Barium sulfate Carbon Black Leveling agent Brightener Benzoin Matting agent TGIC extinction 279 21 165.5 2.5 5 5 2 20 HAA matting 270 10 175.5 2.5 5 0 2 35

[0091] Curing agent: TGIC matting In this embodiment, Ningbo Nanhai Chemical XG60 is used, and Guangzhou Zehe A9, Wuhan Yincai 2018, etc. can also be used. Curing agent HAA matting In this embodiment, Wuhan Yincai L2019 is used, and Guangzhou Zehe A5, etc. can also be used.

[0092] Performance test methods for powder coatings:

[0093] The coating appearance, gloss, leveling grade, impact resistance, water resistance, solvent resistance, neutral salt spray resistance and other properties are tested by spraying onto ordinary steel plates.

[0094] The leveling grade of the coating film adopts the PCI grade, which specifically refers to visually comparing the coating film to be tested with the PCI leveling grade control plate (0-10 grades) to determine the corresponding leveling grade of the coating film to be tested. This is a common leveling grade determination method in the industry.

[0095] Fineness of the coating: Observed with the naked eye, the fineness of the coating refers to the fineness of the surface texture of the coating after baking. The denser the texture and the more uniform the size, the better the fineness.

[0096] The gloss (60°C) test of the coating film is carried out in accordance with GB / T 9754-2007.

[0097] The impact performance test of the coating is carried out in accordance with the standard of GB / T1732-2020.

[0098] The water resistance of the coating was tested according to the standard method B of GB / T 1733-1993. The surface changes of the coating at different boiling times were observed, and the gloss change of the coating surface was tested by TGIC curing high gloss and the gloss retention rate was calculated.

[0099] The neutral salt spray resistance of the coating is tested in accordance with the standard GB / T 10125-2021.

[0100] The adhesion test of the coating film is carried out in accordance with the standard of GB / T 9286-2021.

[0101] The performance test results of the high gloss powder coating cured by TGIC are shown in Table 4, and the performance test results of the high gloss powder coating cured by HAA are shown in Table 5.

[0102] The performance test results of the low-gloss powder coating cured by TGIC are shown in Table 6, and the performance test results of the low-gloss powder coating cured by HAA are shown in Table 7.

[0103] "Example 1-TGIC high"-"Comparative Example 6-TGIC high" represent TGIC-cured high-gloss powder coatings prepared by using the polyester resins prepared in Examples 1-5 and Comparative Examples 1-6 according to the formula of the high-gloss powder coating in Table 2.

[0104] "Example 1-HAA High"-"Comparative Example 6-HAA High" represent HAA-cured high-gloss powder coatings prepared using the polyester resins obtained in Examples 1-5 and Comparative Examples 1-6 according to the formula of the high-gloss powder coating in Table 2.

[0105] "Example 1-TGIC low"-"Comparative Example 6-TGIC low" represent TGIC-cured low-gloss powder coatings prepared using the polyester resins obtained in Examples 1-5 and Comparative Examples 1-6 according to the formula of the low-gloss powder coating in Table 3.

[0106] "Example 1-HAA low"-"Comparative Example 6-HAA low" represent HAA-cured low-gloss powder coatings prepared using the polyester resins obtained in Examples 1-5 and Comparative Examples 1-6 according to the formula of the low-gloss powder coating in Table 3.

[0107] Table 4 Test results of coating properties of TGIC-cured high-gloss powder coatings Table 5 Test results of film properties of HAA-cured high-gloss powder coatings Table 6 Test results of coating properties of TGIC-cured low-gloss powder coatings Table 7 Test results of coating properties of HAA-cured low-gloss powder coatings

[0108]

[0109] It can be seen from Tables 4 to 7 that the high-gloss and low-gloss powder coatings made from the polyester resins prepared in Examples 1 to 5 have smooth, full and delicate coating surfaces after curing; and have excellent mechanical properties, decorative properties, water boiling resistance and neutral salt spray resistance.

[0110] As shown in Tables 4-5, the high-gloss coatings prepared by the polyester resins in Examples 1-5 after being cured by curing agents TGIC and HAA have high clarity, a leveling grade of 7-8, a gloss of more than 97%, and excellent decorative properties. The high-gloss coatings are resistant to boiling for 2 hours, and there is no peeling, wrinkling, or bubbles on the surface. The adhesion can reach level 0, and the TGIC-cured high-gloss coatings have a gloss retention rate of 93.0-94.5% after boiling for 2 hours. The high-gloss coatings can pass 50kg.cm in both forward and reverse flushing, are resistant to solvent wiping (25 times back and forth), and are resistant to neutral salt spray for 500 hours.

[0111] As shown in Table 6-7, the low-gloss coating prepared by the polyester resin in Example 1-5 after curing with curing agent TGIC and HAA has low gloss and stability, and the leveling can reach 6-7 levels. The gloss of the coating with TGIC and matting agent is 6.8-8.2%, and the gloss of the coating with HAA and matting agent is 14.5-16.0%, which has excellent decorative properties; the coating can withstand boiling for 2 hours, and there is no shedding, wrinkling, bubbles, etc. on the surface, and the adhesion can reach 0 level. The low-gloss coating can pass 50kg.cm in the forward impact, resist solvent wiping (25 times back and forth), and resist neutral salt spray for 500 hours.

[0112] Compared with the high-gloss and low-gloss powder coatings prepared in Example 1, the high-gloss coating has higher gloss, while the low-gloss has lower gloss, a higher leveling grade, a finer surface, and slightly better water boiling resistance. This indicates that in addition to neopentyl glycol, the regularity of the polyester prepared by using a linear diol with a side group in combination with neopentyl glycol is reduced. It is speculated that the presence of irregularities and long side chains gives the polyester a lower surface tension, that is, the linear diol with a side group is more conducive to the wetting and dispersion of pigments, fillers, and matting agents, resulting in a coating with high surface decorative properties; the polyester has better wetting and wrapping of pigments and fillers, which also helps to improve the water resistance of the coating.

[0113] Compared with the high-gloss and low-gloss powder coatings prepared in Example 1 and the high-gloss and low-gloss powder coatings prepared in Comparative Example 2, the high-gloss coating has higher gloss, while the low-gloss has lower gloss; the leveling is better; and the surface is smoother. This shows that the long straight-chain saturated fatty acid in the end-capping agent A can effectively reduce the viscosity of the system and control the reaction rate in the presence of a high content of branching agent. At the same time, the long straight-chain saturated fatty acid also has better wetting and dispersibility for pigments, fillers, and matting agents.

[0114] Compared with the high-gloss and low-gloss powder coatings prepared in Example 2 and the high-gloss and low-gloss powder coatings prepared in Comparative Example 3, the leveling performance is better and the water boiling performance is also more excellent. It shows that the auxiliary agent A hydroxy acrylic resin designed and synthesized by the present invention plays a role in protecting the polyester ester bond, making the water boiling performance more excellent. At the same time, it plays a role in reducing the surface tension of the overall system, which is conducive to better spreading of the coating film on the surface of the substrate, and the high-gloss shows better leveling. The hydroxy acrylic resin has good compatibility with the matting agent, so that the matting agent is more evenly dispersed in the system and plays a better role, so the low-gloss gloss prepared is lower and the surface is more delicate.

[0115] The high-gloss and low-gloss powder coatings prepared in Example 2 are compared with the high-gloss and low-gloss powder coatings prepared in Comparative Example 4, mainly showing better water resistance, better chemical resistance and better neutral salt spray resistance of the coating film. This shows that when trihydroxypropane, trihydroxyethane and tris(2-hydroxyethyl)isocyanurate with a triazine ring structure are simultaneously present as branching agents, a certain triazine ring structure gives the coating film excellent chemical resistance, which plays a positive role in the water boiling resistance and neutral salt spray resistance of the coating film.

[0116] The high-gloss and low-gloss powders prepared in Example 3 are compared with the high-gloss and low-gloss powder coatings prepared in Comparative Examples 5 and 6, and the water boiling performance is better. This shows that the absence of unbranched straight-chain fatty diols and straight-chain fatty dibasic acids in the polyester component can prevent more ester bonds in the coating film from being unprotected by the hydrophobic groups during the water boiling process.

[0117] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A polyester resin for indoor powder coating, characterized in that: In terms of mass percentage, the raw material components include: Straight-chain fatty diols with side groups: 32.0-45.0%; Branching agent: 1.0-2.5%; Aliphatic cyclic diols: 0-1.5%; Aromatic polybasic acid: 45-58%; Alicyclic polyacid: 0-1.5%; Capping agent A saturated long straight chain mono fatty acid: 1.0-6.0%; Capping agent B isophthalic acid: 4.0-8.0%; Auxiliary agent A hydroxy acrylic resin: 1.0-3.0%; Additive B: 0.03-0.5%; Esterification catalyst 0.05~0.15%.

2. The polyester resin for indoor powder coating according to claim 1, characterized in that: The linear fatty diol with side groups includes neopentyl glycol, and the mass percentage of the neopentyl glycol in the linear fatty diol component with side groups is 40.0-75.0%.

3. The polyester resin for indoor powder coating according to claim 1, characterized in that: The end-capping agent A is a saturated long straight-chain mono-fatty acid selected from one or a combination of caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and arachidic acid.

4. The polyester resin for indoor powder coating according to claim 1, characterized in that: The auxiliary agent B comprises a curing accelerator and an antioxidant. The mass percentage of the curing accelerator in the raw material components is 0.03-0.2%; the mass percentage of the antioxidant in the raw material components is 0.2-0.5%.

5. The polyester resin for indoor powder coating according to claim 1, characterized in that: The branching agent includes tris(2-hydroxyethyl)isocyanurate.

6. The polyester resin for indoor powder coating according to claim 1, characterized in that: The alicyclic polyacid is selected from one or a combination of 1,4-cyclohexanedicarboxylic acid, hexahydrophthalic anhydride, 1,2-cyclobutanedicarboxylic acid, and furan dicarboxylic acid.

7. The polyester resin for indoor powder coating according to claim 1, characterized in that: The auxiliary agent A, the hydroxyl acrylic resin, has a hydroxyl content of 60 to 120 mgKOH / g.

8. The polyester resin for indoor powder coating according to claim 7, characterized in that: The raw materials for synthesizing the auxiliary agent A hydroxy acrylic resin include isooctyl methacrylate and / or lauryl acrylate; the content of isooctyl methacrylate and / or lauryl acrylate accounts for 15-25wt% of the total monomer feed amount.

9. A method for preparing a polyester resin for indoor powder coatings, characterized in that: The following steps are involved: S1: Add a straight-chain fatty diol with a side group, an aliphatic cyclic diol, a branching agent and an esterification catalyst into a reaction vessel, heat it to 110-130° C. at normal pressure, then add an aromatic polyacid and an alicyclic polyacid, stir under the protection of a protective gas, heat it to 170-240° C., and keep the temperature to react until the esterification reaction is completed; S2: Cool down, add end-capping agent A saturated long straight chain mono fatty acid, raise the temperature to 230-240°C, and react for 30-40 minutes; S3: Cooling down, adding end-capping agent B isophthalic acid, controlling the temperature at 230-250°C, and reacting for 60-80 minutes; S4: At a temperature of 235 to 238° C., evacuate to -0.098 to -0.095 MPa, and continue the reaction for 60 to 150 minutes; S5: Cooling the reaction materials, adding auxiliary agent A hydroxy acrylic resin, controlling the temperature at 225-230° C., and reacting for 30-40 minutes. S6: Keep the temperature of the reaction material at 210-215° C., add the auxiliary agent B, and react for 35-45 minutes to obtain the polyester resin for indoor powder coatings as described in any one of claims 1 to 8.

10. An indoor powder coating, characterized in that: The method comprises a polyester resin obtained by the preparation method according to claim 9, a curing agent and a leveling agent.

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