High-weather-resistance polyester resin as well as preparation method and application thereof

Abstract

The invention discloses high-weather-resistance polyester resin as well as a preparation method and application thereof. The high-weather-resistance polyester resin is prepared from the following raw materials: polycarboxylic acid consisting of hexahydrophthalic anhydride and 1, 4-cyclohexanedicarboxylic acid; the polyhydric alcohol is prepared from neopentyl glycol, ethylene glycol, 2, 2-dimethyl-3-hydroxypropionic acid neopentyl glycol ester, 1, 6-hexanediol and trimethylolpropane. According to the technical scheme of the invention, the problem that the high-weather-resistance polyester finish paint is difficult to have good weather resistance, T-bend, constructability, appearance (high gloss retention rate and the like) at the same time when being used for pre-coating the metal coiled material is solved.

Description

Technical Field

[0001] The present invention relates to the field of weather-resistant coatings. More specifically, it relates to a highly weather-resistant polyester resin, its preparation method and applications. Background Art

[0002] Pre-coated metal coils are organic coating / metal composite materials formed by continuously and automatically coating a coating on a coiled metal sheet and curing the film by high-temperature baking. Since its main use is as a building material for the roofing and exterior walls of industrial plants, public facilities and residences, etc., it is required to have good outdoor weather resistance and service life.

[0003] The commonly used coating for pre-coated metal coils is mainly a coating with a polyester resin as the film-forming resin. However, the polyester resin is easily affected by harsh conditions such as ultraviolet rays, high temperature and moisture outdoors, and is prone to generate highly reactive free radicals and peroxides for degradation, greatly reducing its service life. Therefore, how to improve the weather resistance of pre-coated metal coils on the basis of ensuring their workability, appearance, etc. and extend the service life of buildings is a concern in the coil industry.

[0004] The commonly used method for evaluating the weather resistance of a coating film is QUV. QUV is an artificial accelerated aging test method that uses a fluorescent ultraviolet lamp to simulate sunlight. By artificially increasing environmental factors such as light intensity, temperature and humidity, the aging of the coating is accelerated, so as to obtain data information related to weather resistance faster. Usually, the coating is exposed to an artificially adjusted ultraviolet light and condensation environment, and after a specified test period, the aging phenomena such as loss of gloss, discoloration and chalking of the coating are evaluated. According to the different wavelength ranges covered, it can be divided into QUV A and QUV B. The wavelength range of UVA is 295 - 365 nm, and this band can most realistically simulate sunlight; the wavelength range of UVB is 280 - 315 nm. Because the wavelength is shorter and the energy is higher, the aging effect on the coating is also stronger. It is generally considered that QUV A has a better correlation with outdoor natural exposure, so the prior art usually pays more attention to QUV A and easily ignores QUV B. In fact, because QUV B can more quickly and economically predict the weather resistance of the coating film, it is receiving more and more attention in the industry. However, the currently available highly weather-resistant polyester topcoats usually cannot meet the performance indicators of QUV B. Some can meet the performance requirements of QUV B, but it is difficult to balance other comprehensive performances, such as poor pigment dispersion stability and workability, especially the T-bend performance (especially the performance of no cracks in the T-bend) is poor. Summary of the Invention

[0005] Based on the above problems, the object of the present invention is to provide a highly weather-resistant polyester resin, its preparation method and application, so as to at least solve the problems that it is difficult for highly weather-resistant polyester topcoats to simultaneously have good QUV (including QUVA and QUVB), T-bend (without cracks) performance (up to 5T), workability, appearance (high gloss retention rate, etc.). At the same time, the highly weather-resistant polyester topcoat prepared from the highly weather-resistant polyester resin in the present invention also has high weather resistance, good flexibility, good physical and mechanical properties, and water and chemical resistance.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] On the one hand, the present invention provides a highly weather-resistant polyester resin, and the raw materials for forming the highly weather-resistant polyester resin include:

[0008] Polycarboxylic acids, composed of hexahydrophthalic anhydride and 1,4-cyclohexanedicarboxylic acid;

[0009] Polyols, including neopentyl glycol, ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 1,6-hexanediol and trimethylolpropane.

[0010] Further, the number-average molecular weight of the highly weather-resistant polyester resin is 2500-4000, the acid value is not more than 5 mgKOH / g, and the hydroxyl value is 50-70 mgKOH / g.

[0011] Further, the glass transition temperature Tg of the highly weather-resistant polyester resin is 0-20 °C.

[0012] Further, the mass ratio of hexahydrophthalic anhydride to 1,4-cyclohexanedicarboxylic acid is (2-5):(1-7).

[0013] Further, the mass ratio of neopentyl glycol, ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 1,6-hexanediol and trimethylolpropane is 1:(0.1-2.5):(0.1-1.5):(0.1-2.5):(0.2-1.5).

[0014] Further, the ratio of the number of carboxyl groups derived from the polycarboxylic acids to the number of hydroxyl groups derived from the polyols is (80-90):100.

[0015] Further, in the raw materials, the mass percentage content of the polycarboxylic acids is 35-45%.

[0016] Further, in the raw materials, the mass percentage content of the polyols is 25-35%.

[0017] Further, in the raw materials, the mass percentage content of ethylene glycol is 4-10%.

[0018] On the other hand, the present invention provides a method for preparing the highly weather-resistant polyester resin as described above, the method comprising the following steps:

[0019] After mixing the polycarboxylic acid and polyol, a polycondensation reaction is carried out to obtain the highly weather-resistant polyester resin.

[0020] Further, the preparation method comprises the following steps:

[0021] The mixture of the polycarboxylic acid and polyol is heated to 150 - 160 °C under the protection of an inert gas. After the mixture is completely melted, stirring is carried out and heat preservation is carried out, and then the temperature is raised to 220 - 230 °C at a rate of 5 - 15 °C / h. The temperature of the distillate at the top of the condenser is controlled at 95 - 100 °C, and the reaction is carried out until the acid value is not more than 5 mgKOH / g; impurities are removed, the temperature is cooled to below 80 °C, and the highly weather-resistant polyester resin is obtained after dilution.

[0022] On the other hand, the present invention provides a topcoat, which is prepared from raw materials comprising the highly weather-resistant polyester resin, amino resin, pigment and topcoat solvent as described above.

[0023] On the other hand, the present invention provides the application of the highly weather-resistant polyester resin as described above or the topcoat as described above in the coating of pre-coated metal coils.

[0024] The beneficial effects of the present invention are as follows:

[0025] In the highly weather-resistant polyester resin provided by the present invention, through the combination of specific polycarboxylic acids, polyols, etc. in the raw materials, the topcoat prepared with the polyester resin as the film-forming resin has excellent comprehensive properties. This topcoat not only has both high weather resistance and excellent flexibility, but also has good physical and mechanical properties as well as water and chemical resistance. Detailed Embodiments

[0026] In order to more clearly illustrate the present invention, the present invention will be further described below in conjunction with preferred embodiments. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0027] According to a specific embodiment of the present invention, a highly weather-resistant polyester resin is provided, and the raw materials for forming the highly weather-resistant polyester resin include:

[0028] A polycarboxylic acid, composed of hexahydrophthalic anhydride and 1,4-cyclohexanedicarboxylic acid;

[0029] A polyol, including neopentyl glycol, ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 1,6-hexanediol and trimethylolpropane.

[0030] In this embodiment, by controlling the specific selection of polycarboxylic acid and polyol in the raw materials, the obtained highly weather-resistant polyester resin, after being used in polyester topcoats (especially as the topcoat for pre-coated metal coils), endows the resulting coating with excellent QUV (including QUVA and QUVB), T-bend (without cracks) performance (up to 5T), and cupping performance (able to pass the 8-mm cupping performance test), while also having good physical and mechanical properties, as well as water and chemical resistance. In addition, the highly weather-resistant polyester resin also has excellent pigment dispersion performance, and the coating formed by the polyester topcoat has a good appearance.

[0031] In some examples, the number-average molecular weight of the highly weather-resistant polyester resin is 2500 - 4000, the acid value is not more than 5 mgKOH / g, and the hydroxyl value is 50 - 70 mgKOH / g. If the hydroxyl value of the highly weather-resistant polyester resin is too high, the workability of the resulting coating is poor, and the T-bend effect is poor.

[0032] In some examples, the glass transition temperature Tg of the highly weather-resistant polyester resin is 0 - 20 °C

[0033] According to some preferred embodiments of the present embodiment, the mass ratio of hexahydrophthalic anhydride to 1,4-cyclohexanedicarboxylic acid is (2 - 5):(1 - 7). Selecting hexahydrophthalic anhydride and 1,4-cyclohexanedicarboxylic acid with this mass ratio as the polycarboxylic acid component helps to improve the T-bend (without cracks) performance and cupping performance of the coating in addition to obtaining good QUVA and QUVB. Exemplary mass ratios of hexahydrophthalic anhydride to 1,4-cyclohexanedicarboxylic acid include but are not limited to (0.3 - 3):1, (0.3 - 1):1, (1 - 3):1, 1:1, 0.3:1, 2.9:1, etc.

[0034] In this embodiment, in addition to neopentyl glycol and trimethylolpropane, the polyol component further contains ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, and 1,6-hexanediol. The addition of ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, and 1,6-hexanediol imparts certain polarity, mechanical strength, and pigment dispersion properties to the polyester resin, and can improve the flexibility and adhesion of the polyester resin, so that the finally obtained polyester resin has both high weather resistance, excellent flexibility, and appearance. Furthermore, it helps to improve the T-bend (without cracks) performance, cupping performance, and appearance (such as 60° gloss retention rate, etc.) of the coating. In some examples, the mass ratio of the neopentyl glycol, ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 1,6-hexanediol, and trimethylolpropane is 1:(0.1-2.5):(0.1-1.5):(0.1-2.5):(0.2-1.5). Preferred ratios include, but are not limited to, 1:(0.4-0.55):(0.1-0.5):(0.6-0.7):(0.3-0.45), 1:(0.47-0.52):(0.15-0.5):(0.6-0.7):(0.35-0.45), etc.

[0035] In some examples, the ratio of the number of carboxyl groups derived from the polycarboxylic acid to the number of hydroxyl groups derived from the polyol is (80-90):100. By controlling the content of the number of carboxyl groups and hydroxyl groups, the reaction during the preparation of the high weather resistance polyester resin is made more controllable.

[0036] In some instances, in the raw materials of the high weather resistance polyester resin, the mass ratio of the polycarboxylic acid to the polyol includes, but is not limited to, 1:(0.5-0.8), 1:(0.6-0.8), 1:(0.64-0.75), 1:0.64, 1:0.69, 1:0.7, etc. At this time, the T-bend (without cracks) performance, cupping performance, appearance, etc. of the obtained coating are better.

[0037] In some examples, the mass percentage content of the polycarboxylic acid in the raw materials is 35-45%. For example, the mass percentage content of the polycarboxylic acid in the raw materials includes, but is not limited to, 38-42%, 39-42%, etc.

[0038] In some examples, the mass percentage content of the polyol in the raw materials is 25-35%. For example, the mass percentage content of the polyol in the raw materials includes, but is not limited to, 25-30%, 26-28%, etc.

[0039] In some preferred examples, the mass percentage content of ethylene glycol in the raw materials is 4-10%. A suitable content of ethylene glycol in the raw materials helps to improve the dispersion of pigments in the topcoat, and thus improves the appearance of the topcoat. Exemplarily, the mass percentage content of ethylene glycol in the raw materials includes, but is not limited to, 4-8%, 4-6%, 4-5%, etc.

[0040] In this embodiment, according to actual needs, the raw materials preferably further contain one or more of an organometallic catalyst, a solvent, etc.

[0041] Exemplarily, the organometallic catalyst can be an organotin metal catalyst, an organotitanium metal catalyst, etc. Exemplary organotin metal catalysts include, but are not limited to, one or more combinations of monobutyltin triisooctoate, dibutyltin dilaurate, dibutyltin dioctoate, and dibutyltin diacetate. The organotitanium metal catalyst is one or more combinations of tetrabutyl titanate, tetraisopropyl titanate, and titanium acetylacetonate. The mass percentage content of the organometallic catalyst in the raw materials includes, but is not limited to, 0.01-0.1%, 0.03-0.08%, 0.03-0.07%, 0.035-0.07%, etc.

[0042] Exemplarily, the content of the solvent satisfies: making the mass solid content of the high weather-resistant polyester resin be 60-70%. For example, the solvent can be one or more combinations of solvent S-150, ethylene glycol monobutyl ether, xylene, and DBE. The solvent is preferably a high-boiling solvent. The high-boiling solvents include, but are not limited to, high-boiling solvents mainly composed of aromatic hydrocarbon solvent S-150 and aromatic hydrocarbon solvents.

[0043] Exemplarily, the solvent DBE is a commercially available environmentally friendly high-boiling solvent, which is a mixture of dibasic acid esters, and its main components are dimethyl succinate CH3OOC(CH2)2COOCH3, dimethyl glutarate CH3OOC(CH2)3COOCH3, and dimethyl adipate CH3OOC(CH2)4COOCH3.

[0044] Exemplarily, the aromatic hydrocarbon solvent S-150 is, for example, the commercially available ExxonMobil aromatic hydrocarbon solvent low-naphthalene S-150.

[0045] Exemplarily, the mass percentage content of the solvent in the raw materials includes, but is not limited to, 30-40%, 30-35%, 30-33%, etc.

[0046] In some specific examples, a high weather-resistant polyester resin is provided. Based on the mass percentage of the raw materials, the high weather-resistant polyester resin includes the following components:

[0047] Neopentyl glycol 5-15%;

[0048] Ethylene glycol 4-10%;

[0049] Neopentyl glycol 2,2-dimethyl-3-hydroxypropionate 1-6%;

[0050] 1,6-Hexanediol 5-10%;

[0051] Trimethylolpropane 3 - 6%;

[0052] Hexahydrophthalic anhydride 10 - 35%;

[0053] 1,4 - Cyclohexanedicarboxylic acid 10 - 35%;

[0054] Organometallic catalyst 0.01 - 0.1%;

[0055] Solvent 30 - 40%.

[0056] According to another specific embodiment of the present invention, there is provided a method for preparing the high weather - resistant polyester resin as described above, comprising the following steps:

[0057] Mix the polycarboxylic acid and polyol, and then carry out polycondensation reaction to obtain the high weather - resistant polyester resin.

[0058] In some examples, the preparation method comprises the following steps:

[0059] Heat the mixture of the polycarboxylic acid and polyol to 150 - 160°C under the protection of an inert gas. After the mixture is completely melted, stir and keep warm, then raise the temperature to 220 - 230°C at a rate of 5 - 15°C / h (preferably 10°C / h). Control the temperature of the distillate at the top of the condenser to be 95 - 100°C, and react until the acid value is not more than 5 mgKOH / g; remove impurities, cool down to below 80°C, and obtain the high weather - resistant polyester resin after dilution.

[0060] In some more specific examples, the preparation method comprises the following steps:

[0061] Slowly heat the mixture of neopentyl glycol, ethylene glycol, neopentyl glycol 2,2 - dimethyl - 3 - hydroxypropionate, 1,6 - hexanediol, trimethylolpropane, hexahydrophthalic anhydride, and 1,4 - cyclohexanedicarboxylic acid to 150 - 160°C under the protection of an inert gas. Start the condensation water circulation. After the mixture is completely melted, start stirring, add organotin catalyst, and keep warm at 150 - 160°C for 1 hour. Then raise the temperature to 220 - 230°C at a rate of 5 - 15°C / h (preferably 10°C / h), add an appropriate amount of reflux solvent xylene, control the temperature of the distillate at the top of the condenser to be 95 - 100°C, and react until the acid value is not more than 5 mgKOH / g; evacuate the xylene and small - molecule residues in the resin under vacuum, cool down to below 80°C, and add solvent for dilution to obtain the high weather - resistant polyester resin.

[0062] According to another specific embodiment of the present invention, there is provided a topcoat, which is prepared from raw materials comprising the high weather - resistant polyester resin, amino resin, pigment, and topcoat solvent as described above.

[0063] Among the raw materials of the topcoat, it is preferably to contain the high weather-resistant polyester resin with a mass percentage content of 40-60%. After using this high weather-resistant polyester resin in the preparation of the topcoat, it can endow the coating formed by the topcoat with excellent QUV (including QUVA and QUVB), T-bend (without cracks) performance (up to 5T), cupping performance (able to pass the 8mm cupping performance test) and appearance (high light retention rate), and at the same time have good physical and mechanical properties as well as water resistance, chemical resistance and other properties. In addition, this high weather-resistant polyester resin also has excellent pigment dispersion performance, and the coating formed by the polyester topcoat has good appearance.

[0064] Exemplarily, the amino resin is selected from one or a combination of more of methanol etherified melamine resin, butanol etherified melamine resin, methanol and butanol mixed etherified melamine resin, high imino methanol etherified melamine resin and polyhydroxy polymer modified methanol etherified melamine resin.

[0065] Exemplarily, the pigment is selected from one or a combination of more of weather-resistant inorganic / organic pigments such as titanium dioxide, iron chromium black, iron oxide red, chromium oxide green, cobalt titanium green, cobalt chromium green, titanium chromium yellow, nickel titanium yellow, cobalt aluminum blue and DPP red 254.

[0066] Exemplarily, the topcoat solvent is selected from one or a combination of more of aromatic solvents S-150 and S-100, solvent DBE, propylene glycol methyl ether acetate, ethylene glycol monobutyl ether and n-butanol.

[0067] Among the raw materials of the topcoat provided by this embodiment, additives such as hindered amine light stabilizers and acid catalysts can also be included.

[0068] Exemplarily, the hindered amine light stabilizer is preferably an alkyl or alkoxy substituted derivative of 2,2,6,6-tetramethylpiperidine suitable for an acid catalysis system, including but not limited to commercially available reagents 123, 292 and 765 in one or a combination of more.

[0069] Exemplarily, the acid catalyst includes but not limited to one or a combination of more selected from p-toluenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid and dodecylbenzenesulfonic acid and their blocked products.

[0070] The additives may also include one or a combination of more selected from wetting and dispersing agents, adhesion promoters, anti-settling agents, microcrystalline waxes, leveling agents, defoaming agents and matting agents. These additives can be defined as "optional other additives". The mass percentage content of these additives in the raw materials of the topcoat can be 0-10%, 0, 1-10% and so on.

[0071] In some specific embodiments, based on the mass percentage of raw materials, the raw materials for forming the topcoat include the following components:

[0072] High weather-resistant polyester resin 40 - 60%;

[0073] Amino resin 7 - 12%;

[0074] Pigment 8 - 28%;

[0075] Hindered amine light stabilizer 0.1 - 1%;

[0076] Acid catalyst 0.1 - 1.5%;

[0077] Optional other additives 0 - 10%;

[0078] Topcoat solvent 10 - 20%.

[0079] According to another specific embodiment of the present invention, there is provided the application of the high weather-resistant polyester resin or topcoat as described above in the coating of pre-coated metal coils.

[0080] Using the high weather-resistant polyester resin or topcoat for coating metal coils can well solve the problems that it is difficult for high weather-resistant polyester topcoats to simultaneously have good QUV (including QUVA and QUVB), T-bend (without cracks) performance (up to 5T) and cupping performance (able to pass the 8mm cupping performance test), and coating construction stability. At the same time, the obtained high weather-resistant polyester topcoat also has high weather resistance and good flexibility, and has good physical and mechanical properties as well as water and chemical resistance.

[0081] The high weather-resistant polyester resin is used in the topcoat, and the topcoat is preferably paired with the Nippon Enpuda series of primers, such as the exemplary primer NPEP 750, etc.

[0082] Hereinafter, the technical solutions of the present invention will be described in conjunction with some specific embodiments:

[0083] Polyester resin

[0084] Example 1. High weather-resistant polyester resin 1

[0085] A preparation method of a high weather-resistant polyester resin includes the following steps:

[0086] Into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a water separator, 98.38 g of neopentyl glycol, 47.67 g of ethylene glycol, 46.55 g of neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 63.89 g of 1,6-hexanediol, 38.54 g of trimethylolpropane, 308.32 g of hexahydrophthalic anhydride and 105.48 g of 1,4-cyclohexanedicarboxylic acid were added; the cooling water circulation was started, and it was slowly heated to 150-160 °C under nitrogen protection. After the reactants were melted, the stirring was started, and then 0.55 g of monobutyltin triisooctanoate was added. It was kept at 150-160 °C for 1 hour, then heated to 220-230 °C at a rate of 10 °C per hour, and then 20 g of the reflux solvent xylene was added. The reaction was continued to be kept at 220-230 °C. At this time, the reactants were clear and transparent. During the whole process, the temperature of the distillate at the top of the condenser was controlled at 95-100 °C;

[0087] The acid value was measured by sampling every 30 minutes until the reaction was completed when the acid value was not more than 3 mg KOH / g; after cooling to 150 °C, the xylene and small molecule residues in the resin were removed by vacuum; it was further cooled to 80 °C, and 247.00 g of aromatic solvent S-150 and 82 g of solvent ethylene glycol monobutyl ether were added for dilution; after cooling to room temperature, it was filtered and discharged to obtain high weather resistance polyester resin 1.

[0088] Example 2. High weather resistance polyester resin 2

[0089] A preparation method of a high weather resistance polyester resin, comprising the following steps:

[0090] Into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a water separator, 107.35 g of neopentyl glycol, 51.48 g of ethylene glycol, 19.17 g of neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 67.92 g of 1,6-hexanediol and 41.63 g of trimethylolpropane, 113.92 g of hexahydrophthalic anhydride and 333.00 g of 1,4-cyclohexanedicarboxylic acid were added; the cooling water circulation was started, and it was slowly heated to 150-160 °C under nitrogen protection. After the reactants were melted, the stirring was started, 0.4 g of tetrabutyl titanate was added, it was kept at 150-160 °C for 1 hour, then heated to 220-230 °C at a rate of 10 °C per hour, 20 g of the reflux solvent xylene was added, and the reaction was continued to be kept at 220-230 °C. At this time, the reactants were clear and transparent. During the whole process, the temperature of the distillate at the top of the condenser was controlled at 95-100 °C;

[0091] Sample and measure the acid value every 30 minutes until the reaction is completed when the acid value is no more than 3 mg KOH / g; cool down to 150 °C and then evacuate to remove xylene and small molecule residues in the resin; continue to cool down to 80 °C, add 245.00 g of aromatic solvent S-150 and 82 g of solvent ethylene glycol monobutyl ether for dilution; after cooling to room temperature, filter and discharge to obtain high weather resistance polyester resin 2.

[0092] Example 3. High weather resistance polyester resin 3

[0093] A preparation method of high weather resistance polyester resin, comprising the following steps:

[0094] Put 102.47 g of neopentyl glycol, 48.28 g of ethylene glycol, 35.67 g of neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 68.97 g of 1,6-hexanediol, 39.41 g of trimethylolpropane, 212.83 g of hexahydrophthalic anhydride and 212.83 g of 1,4-cyclohexanedicarboxylic acid into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a water separator; turn on the condensed water circulation, slowly heat to 150-160 °C under nitrogen protection, start stirring after the reactants are melted, add 0.73 g of dibutyltin dilaurate, keep the temperature at 150-160 °C for 1 hour, then raise the temperature to 220-230 °C at a rate of 10 °C per hour, add 20 g of reflux solvent xylene, continue to keep the temperature and react at 220-230 °C. At this time, the reactants are clear and transparent, and control the temperature of the distillate at the top of the condenser to be 95-100 °C throughout the process;

[0095] Sample and measure the acid value every 30 minutes until the reaction is completed when the acid value is no more than 3 mg KOH / g; cool down to 150 °C and then evacuate to remove xylene and small molecule residues in the resin; continue to cool down to 80 °C, add 245.00 g of aromatic solvent S-150 and 82 g of solvent ethylene glycol monobutyl ether for dilution; after cooling to room temperature, filter and discharge to obtain high weather resistance polyester resin 3.

[0096] Example 4. Polyester resin 4 (as a comparative example)

[0097] A preparation method of polyester resin, comprising the following steps:

[0098] Into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a water separator, 96.07 g of neopentyl glycol, 41.32 g of ethylene glycol, 47.42 g of neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 85.74 g of 1,6-hexanediol, 39.26 g of trimethylolpropane, 103.31 g of phthalic anhydride and 320.25 g of isophthalic acid were added. The condensation water circulation was started, and it was slowly heated to 150-160 °C under nitrogen protection. After the reactants melted, stirring was started, 0.55 g of monobutyltin triisooctoate was added, and it was kept at 150-160 °C for 1 hour, then it was heated to 220-230 °C at a rate of 10 °C per hour, 20 g of the reflux solvent xylene was added, and the reaction was continued to be kept at 220-230 °C. At this time, the reactants were clear and transparent, and the temperature of the distillate at the top of the condenser was controlled at 95-100 °C throughout the process;

[0099] Samples were taken every 30 minutes to measure the acid value until the reaction was completed when the acid value was not more than 5 mgKOH / g; After cooling down to 150 °C, xylene and small molecule residues in the resin were removed by vacuum; It was further cooled to 80 °C, and 246.00 g of aromatic solvent S-150 and 82 g of solvent ethylene glycol monobutyl ether were added for dilution; After cooling to room temperature, it was filtered and discharged to obtain polyester resin 4.

[0100] It should be noted that phthalic anhydride and isophthalic acid containing aromatic rings were used as the polycarboxylic acid components in the formulation of polyester resin 4.

[0101] Example 5. Polyester resin 5 (as a comparative example)

[0102] A preparation method of a polyester resin, comprising the following steps:

[0103] Into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a water separator, 86.68 g of 2-methyl-1,3-propanediol, 48.61 g of ethylene glycol, 47.48 g of neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 65.16 g of 1,6-hexanediol, 39.3 g of trimethylolpropane, 314.44 g of hexahydrophthalic anhydride and 107.57 g of 1,4-cyclohexanedicarboxylic acid were added. The condensation water circulation was started, and it was slowly heated to 150-160 °C under nitrogen protection. After the reactants melted, stirring was started, then 0.55 g of monobutyltin triisooctoate was added, and it was kept at 150-160 °C for 1 hour, then it was heated to 220-230 °C at a rate of 10 °C per hour, and then 20 g of the reflux solvent xylene was added, and the reaction was continued to be kept at 220-230 °C. At this time, the reactants were clear and transparent, and the temperature of the distillate at the top of the condenser was controlled at 95-100 °C throughout the process;

[0104] Samples were taken every 30 minutes to measure the acid value until the reaction was completed when the acid value was no more than 5 mg KOH / g; after cooling down to 150 °C, vacuum was applied to remove xylene and small molecule residues in the resin; the temperature was further lowered to 80 °C, and 247.00 g of aromatic solvent S-150 and 82 g of solvent ethylene glycol monobutyl ether were added for dilution; after cooling to room temperature, filtration was carried out to obtain polyester resin 5.

[0105] It should be noted that 2-methyl-1,3-propanediol was used as the polyol component in the formulation of polyester resin 5.

[0106] Example 6. Polyester resin 6 (as a comparative example)

[0107] A method for preparing a polyester resin, comprising the following steps:

[0108] 103.98 g of neopentyl glycol, 29.71 g of ethylene glycol, 45.45 g of neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 86.16 g of 1,6-hexanediol, 40.6 g of trimethylolpropane, 301.05 g of hexahydrophthalic anhydride and 102.99 g of 1,4-cyclohexanedicarboxylic acid were charged into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a water separator; the condensed water circulation was started, and it was slowly heated to 150 - 160 °C under nitrogen protection. After the reactants were melted, stirring was started, 0.55 g of monobutyltin triisooctoate was added, and it was kept at 150 - 160 °C for 1 hour, then it was heated to 220 - 230 °C at a rate of 10 °C per hour, 20 g of reflux solvent xylene was added, and the reaction was continued to be kept at 220 - 230 °C. At this time, the reactants were clear and transparent, and the temperature of the distillate at the top of the condenser was controlled at 95 - 100 °C throughout the process;

[0109] Samples were taken every 30 minutes to measure the acid value until the reaction was completed when the acid value was no more than 3 mg KOH / g; after cooling down to 150 °C, vacuum was applied to remove xylene and small molecule residues in the resin; the temperature was further lowered to 80 °C, and 248 g of aromatic solvent S-150 and 79 g of solvent ethylene glycol monobutyl ether were added for dilution; after cooling to room temperature, filtration was carried out to obtain polyester resin 6.

[0110] It should be noted that the content of ethylene glycol used in the formulation of polyester resin 6 was relatively low.

[0111] Example 7. Polyester resin 7 (as a comparative example)

[0112] A method for preparing a polyester resin, comprising the following steps:

[0113] Into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser and a water separator, 127.73 g of neopentyl glycol, 4.91 g of ethylene glycol, 45.1 g of neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 91.37 g of 1,6-hexanediol and 37.34 g of trimethylolpropane, 298.68 g of hexahydrophthalic anhydride and 102.18 g of 1,4-cyclohexanedicarboxylic acid were added; the condensed water circulation was started, and it was slowly heated to 150-160 °C under nitrogen protection. After the reactants were melted, stirring was started, and then 0.55 g of monobutyltin triisooctoate was added. It was kept at 150-160 °C for 1 hour, then heated to 220-230 °C at a rate of 10 °C per hour, and then 20 g of xylene as a reflux solvent was added. The reaction was continued to be kept at 220-230 °C. At this time, the reactants were clear and transparent. During the whole process, the temperature of the distillate at the top of the condenser was controlled at 95-100 °C;

[0114] The acid value was measured by sampling every 30 minutes until the reaction was completed when the acid value was not more than 5 mg KOH / g; after cooling to 150 °C, vacuum was applied to remove xylene and small molecule residues in the resin; the temperature was further lowered to 80 °C, and 247 g of aromatic solvent S-150 and 82 g of solvent ethylene glycol monobutyl ether were added for dilution; after cooling to room temperature, filtration was carried out to obtain polyester resin 7.

[0115] It should be noted that the ethylene glycol monomer affecting the molecular weight of polyester resin 7 in the formulation of polyester resin 7 is very low.

[0116] The conventional physical and chemical parameters of the above high weather-resistant polyester resins 1-3 and polyester resins 4-7 are shown in Table 1.

[0117] Table 1 Physical and chemical parameters of high weather-resistant polyester resins 1-3 and polyester resins 4-7

[0118]

[0119] As can be seen from Table 1, the mass solids of high weather-resistant polyester resins 1-3 and polyester resins 4-6 are 60-70%, the number average molecular weight is 2500-4000, the acid value is not more than 4 mg KOH / g, and the hydroxyl value is 50-70 mg KOH / g; the molecular weight of polyester resin 7 is relatively high and the hydroxyl value is relatively low.

[0120] Topcoat

[0121] Example 1. High weather-resistant white polyester topcoat 1

[0122] A preparation method of a high weather-resistant polyester resin topcoat comprises the following steps:

[0123] Take 220 g of high weather resistance polyester resin 1, 480 g of Ti-Pure R-960 titanium dioxide, 4 g of fumed silica, 8 g of BYK-110 dispersant, 56 g of propylene glycol methyl ether acetate, and 32 g of ethylene glycol monobutyl ether. After mixing evenly, grind to a fineness of less than 10 μm and filter to obtain a white paste;

[0124] Take 500 g of the above white paste, add 300 g of high weather resistance polyester resin 1, 51.3 g of YP5603 amino resin, 12 g of YP5627B amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 3 g of Versaflow Base leveling agent, 8 g of polyacrylate defoamer, 5 g of Tinuvin 292 hindered amine light stabilizer, 10 g of n-butanol, 30 g of aromatic solvent S-100, 20 g of DBE, and 18 g of propylene glycol methyl ether acetate, and stir evenly. Adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain high weather resistance white polyester topcoat 1.

[0125] Coating and panel making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, and bake it in an oven at 320°C for 24 s, with a metal peak temperature PMT of 232°C, to obtain a primer coating with a film thickness of 5 μm; take the high weather resistance white polyester topcoat of this example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, and bake it in an oven at 320°C for 26 s, with a metal peak temperature PMT of 241°C, to obtain a high weather resistance topcoat coating with a film thickness of 17 μm.

[0126] Example 2. High weather resistance white polyester topcoat 2

[0127] A preparation method of a high weather resistance polyester resin topcoat, comprising the following steps:

[0128] Take 220 g of high weather resistance polyester resin 2, 480 g of Ti-Pure R-960 titanium dioxide, 4 g of fumed silica, 8 g of BYK-110 dispersant, 56 g of propylene glycol methyl ether acetate, and 32 g of ethylene glycol monobutyl ether. After mixing evenly, grind to a fineness of less than 10 μm and filter to obtain a white paste;

[0129] Take 500 g of the above white paste, add 300 g of high weather resistance polyester resin 2, 51.3 g of YP5603 amino resin, 12 g of YP5627B amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 3 g of Versaflow Base leveling agent, 8 g of polyacrylate defoamer, 5 g of Tinuvin 292 hindered amine light stabilizer, 10 g of n-butanol, 30 g of aromatic solvent S-100, 20 g of DBE and 18 g of propylene glycol methyl ether acetate, and stir evenly; adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain high weather resistance white polyester topcoat 2.

[0130] Coating and panel preparation: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, bake it in an oven at 320°C for 24 s, with a metal peak temperature PMT of 232°C, to obtain a primer coating with a film thickness of 5 μm; take the high weather resistance white polyester topcoat of this example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, bake it in an oven at 320°C for 26 s, with a metal peak temperature PMT of 241°C, to obtain a high weather resistance topcoat coating with a film thickness of 17 μm.

[0131] Example 3. High weather resistance white polyester topcoat 3

[0132] A preparation method of a high weather resistance polyester resin topcoat, comprising the following steps:

[0133] Take 220 g of high weather resistance polyester resin 3, 480 g of Ti-Pure R-960 titanium dioxide, 4 g of fumed silica, 8 g of BYK-110 dispersant, 56 g of propylene glycol methyl ether acetate and 32 g of ethylene glycol monobutyl ether, mix evenly and grind to a fineness of less than 10 μm, and filter to obtain a white paste;

[0134] Take 500 g of the above white paste, add 300 g of high weather resistance polyester resin 3, 51.3 g of YP5603 amino resin, 12 g of YP5627B amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 3 g of Versaflow Base leveling agent, 8 g of polyacrylate defoamer, 5 g of Tinuvin 292 hindered amine light stabilizer, 10 g of n-butanol, 30 g of aromatic solvent S-100, 20 g of DBE and 18 g of propylene glycol methyl ether acetate, and stir evenly; adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain high weather resistance white polyester topcoat 3.

[0135] Coating and panel preparation: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, bake it in an oven at 320 °C for 24 s, with a metal peak temperature PMT of 232 °C, to obtain a primer coating with a film thickness of 5 μm; Take the high weather-resistant white polyester topcoat of this example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, bake it in an oven at 320 °C for 26 s, with a metal peak temperature PMT of 241 °C, to obtain a high weather-resistant topcoat coating with a film thickness of 17 μm.

[0136] Example 4. High weather-resistant red polyester topcoat 4

[0137] A preparation method of a high weather-resistant polyester resin topcoat, comprising the following steps:

[0138] Take 220 grams of high weather-resistant polyester resin 1, 44 grams of Ti-Pure R-960 titanium dioxide, 54.4 g of Bayferrox 120NM iron oxide red, 1.56 grams of fumed silica, 0.98 grams of BYK-110 dispersant, 56 grams of propylene glycol methyl ether acetate and 32 grams of ethylene glycol monobutyl ether, mix them evenly and grind to a fineness of less than 10 μm, and filter to obtain a mixed color paste; Take 220 grams of high weather-resistant polyester resin 1, 79.2 grams of SR1C DPP red 254, 8 grams of BYK-170 dispersant, 56 grams of propylene glycol methyl ether acetate and 32 grams of ethylene glycol monobutyl ether, mix them evenly and grind to a fineness of less than 10 μm, and filter to obtain a red paste.

[0139] Take 204.5 grams of the above-mentioned mixed color paste and 197.6 grams of the red paste, add 300 grams of high weather-resistant polyester resin 1, 51.3 grams of YP5603 amino resin, 12 grams of YP5627B amino resin, 1.7 grams of DNNSA acid catalyst, 2 grams of PTFE wax powder, 3 grams of Versaflow Base leveling agent, 8 grams of polyacrylate defoamer, 5 grams of Tinuvin 292 hindered amine light stabilizer, 10 grams of n-butanol, 30 grams of aromatic solvent S-100, 20 grams of DBE and 18 grams of propylene glycol methyl ether acetate, and stir evenly; Adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; Adjust the viscosity at 25 °C to 100 ± 10 seconds, measured with an F-4# cup; Filter and package to obtain high weather-resistant red polyester topcoat 4.

[0140] Coating and panel preparation: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, bake it in an oven at 320 °C for 24 s, with a metal peak temperature PMT of 232 °C, to obtain a primer coating with a film thickness of 5 μm; Take the high weather-resistant red polyester topcoat of this example, roll coat it on the NPEP 750 primer coating with an RDS28# wire bar, bake it in an oven at 320 °C for 26 s, with a metal peak temperature PMT of 241 °C, to obtain a high weather-resistant topcoat coating with a film thickness of 17 μm.

[0141] To verify the performance of the highly weather-resistant polyester resin and topcoat described in the present invention, the following Comparative Examples 1 to 7 are also provided:

[0142] Comparative Example 1. White Polyester Topcoat 1

[0143] A preparation method of a polyester resin topcoat includes the following steps:

[0144] Take 220 grams of highly weather-resistant polyester resin 1, 480 grams of Ti-Pure R-960 titanium dioxide, 4 grams of fumed silica, 8 grams of BYK-110 dispersant, 56 grams of propylene glycol methyl ether acetate, and 32 grams of ethylene glycol monobutyl ether. After mixing evenly, grind to a fineness of less than 10 μm, and filter to obtain a white paste;

[0145] Take 500 grams of the above white paste, add 300 grams of highly weather-resistant polyester resin 1, 51.3 grams of YP5603 amino resin, 12 grams of YP5627B amino resin, 1.7 grams of DNNSA acid catalyst, 2 grams of PTFE wax powder, 3 grams of Versaflow Base leveling agent, 8 grams of polyacrylate defoamer, 10 grams of n-butanol, 30 grams of aromatic solvent S-100, 20 grams of DBE, and 18 grams of propylene glycol methyl ether acetate, and stir evenly. Adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain white polyester topcoat 1;

[0146] It should be noted that this white polyester topcoat 1 does not contain a hindered amine light stabilizer.

[0147] Coating and panel making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, and bake it in an oven at 320°C for 24 s, with a metal peak temperature PMT of 232°C, to obtain a primer coating with a film thickness of 5 μm. Take the highly weather-resistant white polyester topcoat composition of this comparative example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, and bake it in an oven at 320°C for 26 s, with a metal peak temperature PMT of 241°C, to obtain a topcoat coating with a film thickness of 17 μm.

[0148] Comparative Example 2. White Polyester Topcoat 2

[0149] A preparation method of a polyester resin topcoat includes the following steps:

[0150] Take 220 grams of highly weather-resistant polyester resin 2, 480 grams of Ti-Pure R-960 titanium dioxide, 4 grams of fumed silica, 8 grams of BYK-110 dispersant, 56 grams of propylene glycol methyl ether acetate, and 32 grams of ethylene glycol monobutyl ether. After mixing evenly, grind to a fineness of less than 10 μm, and filter to obtain a white paste;

[0151] Take 500 g of the above-mentioned white paste, add 300 g of high weather resistance polyester resin 2, 51.3 g of YP5603 amino resin, 12 g of YP5627B amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 3 g of Versaflow Base leveling agent, 8 g of polyacrylate defoamer, 10 g of n-butanol, 30 g of aromatic solvent S-100, 20 g of DBE and 18 g of propylene glycol methyl ether acetate, and stir evenly; adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain white polyester topcoat 2;

[0152] It should be noted that the white polyester topcoat 2 does not contain hindered amine light stabilizers.

[0153] Coating and plate making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, bake it in an oven at 320°C for 24 s, and the metal peak temperature PMT is 232°C to obtain a primer coating with a film thickness of 5 μm. Take the white polyester topcoat of this comparative example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, bake it in an oven at 320°C for 26 s, and the metal peak temperature PMT is 241°C to obtain a topcoat coating with a film thickness of 17 μm.

[0154] Comparative Example 3. White polyester topcoat 3

[0155] A preparation method of a polyester resin topcoat, comprising the following steps:

[0156] Take 220 g of high weather resistance polyester resin 3, 480 g of Ti-Pure R-960 titanium dioxide, 4 g of fumed silica, 8 g of BYK-110 dispersant, 56 g of propylene glycol methyl ether acetate and 32 g of ethylene glycol monobutyl ether, mix evenly and grind to a fineness of less than 10 μm, and filter to obtain a white paste;

[0157] Take 500 g of the above-mentioned white paste, add 300 g of high weather resistance polyester resin 3, 51.3 g of YP5603 amino resin, 12 g of YP5627B amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 3 g of Versaflow Base leveling agent, 8 g of polyacrylate defoamer, 10 g of n-butanol, 30 g of aromatic solvent S-100, 20 g of DBE and 18 g of propylene glycol methyl ether acetate, and stir evenly. Adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain white polyester topcoat 3;

[0158] It should be noted that the white polyester topcoat 3 does not contain hindered amine light stabilizers.

[0159] Coating plate making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pretreated aluminized zinc substrate with an RDS10# wire bar, bake it in an oven at 320 °C for 24 s, with a metal peak temperature PMT of 232 °C, to obtain a primer coating with a film thickness of 5 μm. Take the white polyester topcoat of this comparative example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, bake it in an oven at 320 °C for 26 s, with a metal peak temperature PMT of 241 °C, to obtain a topcoat coating with a film thickness of 17 μm.

[0160] Comparative Example 4. White Polyester Topcoat 4

[0161] A preparation method of a polyester resin topcoat includes the following steps:

[0162] Take 220 grams of polyester resin 4, 480 grams of Ti-Pure R-960 titanium dioxide, 4 grams of fumed silica, 8 grams of BYK-110 dispersant, 56 grams of propylene glycol methyl ether acetate, and 32 grams of ethylene glycol monobutyl ether. After mixing evenly, grind it to a fineness of less than 10 μm, and filter to obtain a white paste;

[0163] Take 500 grams of the above white paste, add 300 grams of polyester resin 4, 51.3 grams of YP5603 amino resin, 12 grams of YP5627B amino resin, 1.7 grams of DNNSA acid catalyst, 2 grams of PTFE wax powder, 3 grams of Versaflow Base leveling agent, 8 grams of polyacrylate defoamer, 5 grams of Tinuvin 292 hindered amine light stabilizer, 10 grams of n-butanol, 30 grams of aromatic solvent S-100, 20 grams of DBE, and 18 grams of propylene glycol methyl ether acetate, and stir evenly; Adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; Adjust the viscosity at 25 °C to 100 ± 10 seconds, measured with an F-4# cup; Filter and package to obtain white polyester topcoat 4.

[0164] It should be noted that white polyester topcoat 4 uses the above-mentioned polyester resin 4 as a comparison.

[0165] Coating plate making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pretreated aluminized zinc substrate with an RDS10# wire bar, bake it in an oven at 320 °C for 24 s, with a metal peak temperature PMT of 232 °C, to obtain a primer coating with a film thickness of 5 μm. Take the white polyester topcoat of this comparative example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, bake it in an oven at 320 °C for 26 s, with a metal peak temperature PMT of 241 °C, to obtain a topcoat coating with a film thickness of 17 μm.

[0166] Comparative Example 5. White Polyester Topcoat 5

[0167] A preparation method of a polyester resin topcoat includes the following steps:

[0168] Take 220 g of polyester resin 5, 480 g of Ti-Pure R-960 titanium dioxide, 4 g of fumed silica, 8 g of BYK-110 dispersant, 56 g of propylene glycol methyl ether acetate, and 32 g of ethylene glycol monobutyl ether. After mixing evenly, grind to a fineness of less than 10 μm and filter to obtain a white paste.

[0169] Take 500 g of the above white paste, add 300 g of polyester resin 5, 51.3 g of YP5603 amino resin, 12 g of YP5627B amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 3 g of Versaflow Base leveling agent, 8 g of polyacrylate defoamer, 5 g of Tinuvin 292 hindered amine light stabilizer, 10 g of n-butanol, 30 g of aromatic solvent S-100, 20 g of DBE, and 18 g of propylene glycol methyl ether acetate, and stir evenly; adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain white polyester topcoat 5.

[0170] It should be noted that the white polyester topcoat 5 uses the above-mentioned polyester resin 5 as a comparison.

[0171] Coating and panel making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, and bake it in an oven at 320°C for 24 s, with a metal peak temperature PMT of 232°C, to obtain a primer coating with a film thickness of 5 μm. Take the white polyester topcoat of this comparative example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, and bake it in an oven at 320°C for 26 s, with a metal peak temperature PMT of 241°C, to obtain a topcoat coating with a film thickness of 17 μm.

[0172] Comparative Example 6 White Polyester Topcoat 6

[0173] A preparation method of a polyester resin topcoat, comprising the following steps:

[0174] Take 220 g of polyester resin 6, 480 g of Ti-Pure R-960 titanium dioxide, 4 g of fumed silica, 8 g of BYK-110 dispersant, 56 g of propylene glycol methyl ether acetate, and 32 g of ethylene glycol monobutyl ether. After mixing evenly, grind to a fineness of less than 10 μm and filter to obtain a white paste.

[0175] Take 500 g of the above-mentioned white paste, add 300 g of polyester resin 6, 51.3 g of YP5603 amino resin, 12 g of YP5627B amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 3 g of Versaflow Base leveling agent, 8 g of polyacrylate defoamer, 5 g of Tinuvin 292 hindered amine light stabilizer, 10 g of n-butanol, 30 g of aromatic solvent S-100, 20 g of DBE and 18 g of propylene glycol methyl ether acetate, and stir evenly; adjust the 60° gloss to 35 - 40, measured with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain white polyester topcoat 6.

[0176] It should be noted that the white polyester topcoat 6 uses the above-mentioned polyester resin 6 as a comparison.

[0177] Coating and plate making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, bake it in an oven at 320°C for 24 s, and the metal peak temperature PMT is 232°C to obtain a primer coating with a film thickness of 5 μm. Take the high weather-resistant white polyester topcoat of this example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, bake it in an oven at 320°C for 26 s, and the metal peak temperature PMT is 241°C to obtain a topcoat coating with a film thickness of 17 μm.

[0178] Comparative Example 7. Red polyester topcoat 4

[0179] A preparation method of a polyester resin topcoat, comprising the following steps:

[0180] Take 220 g of polyester resin 6, 44 g of Ti-Pure R-960 titanium dioxide, 54.4 g of Bayferrox 120NM iron oxide red, 1.56 g of fumed silica, 0.98 g of BYK-110 dispersant, 56 g of propylene glycol methyl ether acetate and 32 g of ethylene glycol monobutyl ether, mix evenly and grind to a fineness of less than 10 μm, and filter to obtain a mixed color paste; take 220 g of polyester resin 6, 79.2 g of SR1CDPP red 254, 8 g of BYK-170 dispersant, 56 g of propylene glycol methyl ether acetate and 32 g of ethylene glycol monobutyl ether, mix evenly and grind to a fineness of less than 10 μm, and filter to obtain a red paste;

[0181] Take 204.5 grams of the above-mentioned mixed color paste and 197.6 grams of red paste, and add 300 grams of polyester resin 6, 51.3 grams of YP5603 amino resin, 12 grams of YP5627B amino resin, 1.7 grams of DNNSA acid catalyst, 2 grams of PTFE wax powder, 3 grams of Versaflow Base leveling agent, 8 grams of polyacrylate defoamer, 5 grams of Tinuvin 292 hindered amine light stabilizer, 10 grams of n-butanol, 30 grams of aromatic solvent S-100, 20 grams of DBE, and 18 grams of propylene glycol methyl ether acetate, and stir evenly; adjust the 60° gloss to 35 - 40, and measure it with a BYK gloss meter; adjust the viscosity at 25°C to 100 ± 10 seconds, and measure it with an F-4# cup; filter and package to obtain red polyester topcoat 7.

[0182] Coating and plate making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, and bake it in an oven at 320°C for 24 s, with the metal peak temperature PMT of 232°C, to obtain a primer coating with a film thickness of 5 μm. Take the high weather-resistant red polyester topcoat of this comparative example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, and bake it in an oven at 320°C for 26 s, with the metal peak temperature PMT of 241°C, to obtain a high weather-resistant topcoat coating with a film thickness of 17 μm.

[0183] It should be noted that the red polyester topcoat 7 uses the above-mentioned polyester resin 6 as a comparison.

[0184] Another thing to note is that the above-mentioned polyester resin 7 used as a comparison was not tested for paint formulation because it has a relatively large molecular weight, a relatively high viscosity, and a hydroxyl value far lower than the target value.

[0185] Test the dry film conventional properties of the above-mentioned examples and comparative examples, and the results are shown in Table 2. Each property in Table 2 was detected in accordance with the national standard GB / T 13448-2019.

[0186] Table 2 Dry film conventional properties of each example and comparative example

[0187]

[0188]

[0189] Conduct QUVA and QUVB tests on the dry films of the above-mentioned examples and comparative examples, and the tests are carried out in accordance with the ASTM G154 standard.

[0190] The specific conditions of QUVA are: light source UVA-340, with a cycle period of 12 hours, 8 hours of ultraviolet light irradiation, light intensity 0.89W / m 2 , blackboard temperature 60 ± 3°C; 4 hours of condensation, blackboard temperature 50 ± 3°C.

[0191] The specific conditions for QUVB are as follows: light source UVB-313, with an 8-hour cycle period, 4 hours of ultraviolet light irradiation, and the light intensity is 0.71 W / m 2 , the blackboard temperature is 60 ± 3 °C; 4 hours of condensation, and the blackboard temperature is 50 ± 3 °C.

[0192] Gloss and color difference are detected in accordance with national standard GB / T 13448-2019; the chalking grade is evaluated in accordance with national standard GB / T 1766-2008.

[0193] The QUV A and QUVB test results of the above-mentioned examples and comparative examples are shown in Table 3 and Table 4 respectively.

[0194] Table 3 QUV A test results of each example and comparative example

[0195]

[0196] Table 4 QUVB test results of each example and comparative example

[0197]

[0198]

[0199] Comparative Example 8

[0200] Polyester resin 8:

[0201] A preparation method of a polyester resin, comprising the following steps:

[0202] Put 167.26 grams of neopentyl glycol, 40.27 grams of 2-ethyl-2-butyl-1,3-propanediol, 65.05 grams of trimethylolpropane, 216.82 grams of hexahydrophthalic anhydride, 61.95 grams of 1,4-cyclohexanedicarboxylic acid, 52.66 grams of adipic acid, and 15.49 grams of isononanoic acid into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a water separator. Start the condensation water circulation, slowly heat to 150-160 °C under nitrogen protection, start stirring after the reactants melt, then add 0.50 grams of monobutyltin triisooctoate, keep the temperature at 150-160 °C for 1 hour, then raise the temperature to 220-230 °C at a rate of 10 °C per hour, add 20 grams of reflux solvent xylene, and continue to keep the temperature for reaction at 220-230 °C. At this time, the reactants are clear and transparent, and the temperature of the distillate at the top of the condenser is controlled at 95-100 °C during the whole process;

[0203] Samples were taken every 30 minutes to measure the acid value until the reaction was completed when the acid value was no more than 5 mg KOH / g; after cooling down to 150 °C, vacuum was applied to remove xylene and small molecule residues in the resin. Then it was further cooled down to 80 °C, and 240.00 g of aromatic solvent S-100 and 120.00 g of solvent DBE were added for dilution; after cooling to room temperature, filtration was carried out to obtain the high weather-resistant polyester resin 8.

[0204] The mass solid content of the high weather-resistant polyester resin 8 was measured to be 60%, the molecular weight was 2100, the acid value was 5 mg KOH / g, and the hydroxyl value was 90 mg KOH / g.

[0205] Topcoat 8:

[0206] A preparation method of a polyester resin topcoat includes the following steps:

[0207] Take 240 g of high weather-resistant polyester resin 8, 480 g of Ti-Pure R-960 titanium dioxide, 4 g of fumed silica, 8 g of BYK-110 dispersant, 36 g of propylene glycol methyl ether acetate, and 32 g of ethylene glycol monobutyl ether, mix them evenly and grind to a fineness of less than 10 μm, and filter to obtain a white paste;

[0208] Take 500 g of the above white paste, add 325 g of high weather-resistant polyester resin 1, 51.3 g of YP5603 amino resin, 1.7 g of DNNSA acid catalyst, 2 g of PTFE wax powder, 5 g of Versaflow Base leveling agent, 5 g of polyacrylate defoamer, 5 g of Tinuvin 292 hindered amine light stabilizer, 10 g of n-butanol, 30 g of aromatic solvent S-150, 18 g of propylene glycol methyl ether acetate, and 12 g of ethylene glycol monobutyl ether, and stir evenly; adjust the 60° gloss of the topcoat composition to 30 - 35, measured with a BYK gloss meter; adjust the viscosity of the topcoat composition at 25 °C to 100 ± 10 seconds, measured with an F-4# cup; filter and package to obtain the high weather-resistant white polyester topcoat 8.

[0209] Coating and panel making: Take the commercially available Nippon NPEP 750 primer, roll coat it on the pre-treated aluminized zinc substrate with an RDS10# wire bar, and bake it in an oven at 320 °C for 24 s, with the metal peak temperature PMT of 232 °C, to obtain a primer coating with a film thickness of 5 μm. Take the white polyester topcoat 8 of this comparative example, roll coat it on the NPEP 750 primer coating with an RDS26# wire bar, and bake it in an oven at 320 °C for 26 s, with the metal peak temperature PMT of 241 °C, to obtain a high weather-resistant topcoat coating with a film thickness of 17 μm. Perform the performance tests on this topcoat coating as described in Table 2, and the result of the dry film T-bend (without cracks) of this coating was 7T.

[0210] The above test results show that:

[0211] The high weather-resistant polyester topcoat composition described in the present invention uses the high weather-resistant polyester resin provided by the present invention as the matrix resin, and at the same time adds a suitable hindered amine light stabilizer, which shows excellent performance in the QUV test, and at the same time meets the performance indicators of high light retention rate, small color difference, and chalking not greater than grade 1 at 1500 hours of QUVA and 800 hours of QUVB. Moreover, the obtained high weather-resistant polyester topcoat composition has excellent flexibility (the result of small T-bend without cracks), good physical and mechanical properties, and excellent water and chemical resistance.

[0212] In contrast, without using the high weather-resistant polyester resin of the present invention, for example, by changing the structure or content of specific components in the high weather-resistant polyester resin, or without adding a hindered amine light stabilizer, the topcoat composition cannot meet the QUV performance indicators. Usually, the light retention rate at 1500 hours of QUVA and / or 800 hours of QUVB is already lower than 75%, or even lower than 50%, or there is chalking to varying degrees, or the effect of T-bend without cracks is poor, or the finger rubbing color difference and heat storage color difference are too high.

[0213] Obviously, the above-mentioned embodiments of the present invention are only examples for clearly explaining the present invention, and are not intended to limit the implementation modes of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation modes here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A highly weather-resistant polyester resin, characterized in that, The raw materials for forming the highly weather-resistant polyester resin include: Polycarboxylic acids, composed of hexahydrophthalic anhydride and 1,4-cyclohexanedicarboxylic acid; Polyols, including neopentyl glycol, ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 1,6-hexanediol, and trimethylolpropane.

2. The high weather-resistant polyester resin according to claim 1, wherein The number-average molecular weight of the highly weather-resistant polyester resin is 2500 - 4000, the acid value is not more than 5 mgKOH / g, and the hydroxyl value is 50 - 70 mgKOH / g.

3. The high weather-resistant polyester resin according to claim 1, characterized in that, The mass ratio of the hexahydrophthalic anhydride to the 1,4-cyclohexanedicarboxylic acid is (2 - 5):(1 - 7).

4. The high weather-resistant polyester resin according to claim 1, wherein The mass ratio of the neopentyl glycol, ethylene glycol, neopentyl glycol 2,2-dimethyl-3-hydroxypropionate, 1,6-hexanediol, and trimethylolpropane is 1:(0.1 - 2.5):(0.1 - 1.5):(0.1 - 2.5):(0.2 - 1.5).

5. The high weather-resistant polyester resin according to claim 1, characterized in that, The ratio of the number of carboxyl groups derived from the polycarboxylic acids to the number of hydroxyl groups derived from the polyols is (80 - 90):

100.

6. The high weather-resistant polyester resin according to claim 1, wherein In the raw materials, the mass percentage content of the polycarboxylic acids is 35 - 45%; and / or In the raw materials, the mass percentage content of the polyols is 25 - 35%; Preferably, in the raw materials, the mass percentage content of the ethylene glycol is 4 - 10%.

7. The preparation method of the highly weather-resistant polyester resin according to any one of claims 1-6, characterized in that, It includes the following steps: After mixing the polycarboxylic acids and polyols, a polycondensation reaction is carried out to obtain the highly weather-resistant polyester resin.

8. The preparation method according to claim 7, wherein The preparation method includes the following steps: The mixture of the polycarboxylic acids and polyols is heated to 150 - 160 °C under the protection of an inert gas. After the mixture is completely melted, it is stirred and kept warm, and then heated to 220 - 230 °C at a rate of 5 - 15 °C / h. The temperature of the distillate at the top of the condenser is controlled at 95 - 100 °C, and the reaction is carried out until the acid value is not more than 5 mgKOH / g; impurities are removed, and the temperature is cooled to below 80 °C. After dilution, the highly weather-resistant polyester resin is obtained.

9. A topcoat, characterized in that, It is prepared from raw materials including the highly weather-resistant polyester resin according to any one of claims 1 - 6, an amino resin, a pigment, and a topcoat solvent.

10. Use of the highly weather-resistant polyester resin according to any one of claims 1 - 6 or the topcoat according to claim 9 in the coating of pre-coated metal coils.

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