A high flow, storage-stable polyester resin, and methods of making and using the same

Abstract

The application belongs to the technical field of paint, and particularly relates to a high-flowing and storage-resistant polyester resin as well as a preparation method and application thereof. The preparation raw materials of the high-flowing and storage-resistant polyester resin include a first polyol, a second polyol, a monohydric alcohol, a polybasic acid, a monobasic acid and an acidolysis agent. Through the interaction of the components, especially the fact that the fluorene-containing polyol, the monohydric alcohol and the monobasic acid are all rigid high steric hindrance monomers, the positive correlation restriction between the glass transition temperature and the melt viscosity of the traditional amorphous polyester resin is well overcome to a certain extent, a good balance between the two is achieved, the polyester resin has a relatively high glass transition temperature and a relatively low melt viscosity, the prepared paint can simultaneously consider the storage stability and the flowability, and has good storage stability and flowability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coatings, and particularly relates to a polyester resin with high leveling and storage resistance, and a preparation method and application thereof. BACKGROUND

[0002] The TGIC type high leveling powder coating is a high-performance coating widely used on the surface of metal products. The excellent leveling performance of the TGIC type high leveling powder coating makes the coating surface smooth and flat, and can provide good decoration and protection, and is widely used in the fields of household appliances, automobile parts, building hardware, etc.

[0003] Balancing the leveling performance and the storage performance of the powder coating has always been a major challenge in the industry. The leveling performance is directly related to the smoothness, flatness and aesthetics of the coating surface, and is a key indicator for evaluating the decorative effect of the coating. The storage performance determines the stability of the powder coating during long-term storage, and is crucial for reducing production costs and improving production efficiency. However, these two performances often restrict each other, and it is difficult to achieve the optimal state at the same time. The main reason is the performance characteristics of the polyester resin, which is the core component of the powder coating. At present, the main raw material of the powder coating is amorphous polyester resin. This type of resin has an inherent characteristic that the glass transition temperature (Tg) is positively correlated with the melt viscosity. This means that in order to obtain a higher Tg to ensure the storage stability of the coating, a higher melt viscosity has to be accepted, which in turn sacrifices the leveling performance of the coating. Conversely, if low melt viscosity is pursued to optimize the leveling performance, the Tg will be reduced, which will affect the storage stability of the coating. Therefore, it is difficult to find an ideal balance between the two for the amorphous polyester resin.

[0004] Therefore, it is urgent to provide a polyester resin whose prepared coating can simultaneously consider the storage stability and the leveling performance, and has good storage stability and leveling performance. SUMMARY

[0005] The present application aims to solve one or more technical problems in the prior art, and at least provides a beneficial choice or creates conditions. Specifically, the present application provides a polyester resin whose prepared coating can simultaneously consider the storage stability and the leveling performance, and has good storage stability and leveling performance.

[0006] The raw materials for preparing the high-flowing and storage-resistant polyester resin of the present application include a first polyol, a second polyol, a monohydric alcohol, a polybasic acid, a monobasic acid, and an acid-decomposing agent, and the second polyol, the monohydric alcohol, and the monobasic acid are selected from specific types. The present application overcomes the positive correlation limitation between the glass transition temperature and the melt viscosity of the conventional amorphous polyester resin by selecting the second polyol, the monohydric alcohol, and the monobasic acid with specific types and high rigidity and high steric hindrance, and by the interaction of the components, realizes a good balance between the two, has a high glass transition temperature and a low melt viscosity, so that the prepared coating can simultaneously have storage stability and flowability, and has good storage stability and flowability.

[0007] Therefore, the first aspect of the present application provides a high-flowing and storage-resistant polyester resin.

[0008] Specifically, the raw materials for preparing the high-flowing and storage-resistant polyester resin include a first polyol, a second polyol, a monohydric alcohol, a polybasic acid, a monobasic acid, and an acid-decomposing agent.

[0009] The second polyol is a fluorene-containing polyol.

[0010] The monohydric alcohol is selected from at least one of 9-hydroxyfluorene, 2-benzyloxyethanol, cyclododecanol, 9-phenyl-9-fluorenol, 4-isopropylbenzyl alcohol, p-fluorobenzyl alcohol, and m-methoxybenzyl alcohol.

[0011] The monobasic acid is selected from at least one of 9-fluorene carboxylic acid, p-methylbenzoic acid, p-tert-butylbenzoic acid, 2,4-dimethylbenzoic acid, 3,4-dimethylbenzoic acid, 3-trifluoromethylbenzoic acid, 3-phenylpropionic acid, 4-phenylbutyric acid, 2,2-diphenylacetic acid, 4-phenylbenzoic acid, and cyclohexane carboxylic acid.

[0012] Preferably, the second polyol is selected from at least one of 9,9-fluorene dimethyl alcohol, 9,9-fluorene diethyl alcohol, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene.

[0013] Specifically, the second polyol is a fluorene-containing monomer, and the present application innovatively introduces a rigid and high-steric-hindrance fluorene-containing monomer as a key component. The fluorenyl group significantly enhances the rigidity of the polyester resin chain due to its unique conjugated benzene ring structure, effectively maintains the high glass transition temperature (Tg) of the polyester resin, and thus endows the powder coating with excellent storage stability. In addition, the non-coplanar structure of fluorene makes the side group of the suspended benzene ring perpendicular to the main chain, which not only increases the distance between the polyester molecular chains and reduces the mutual entanglement of the molecular chains, but also significantly reduces the viscosity of the polyester resin, so that the powder coating of the present application has good flowability while maintaining good storage stability.

[0014] Specifically, the application introduces monohydric alcohol and monobasic acid with rigidity and high steric hindrance characteristics, which can effectively reduce the viscosity of the resin and significantly enhance the leveling performance of the coating while ensuring the Tg of the polyester resin and the storage stability of the coating. By precisely controlling the monofunctional monomer, the molecular weight of the polyester resin is precisely controlled, further improving the processing performance of the coating. In addition, by using the competition and steric hindrance effect of monobasic acid and acidolysis agent, the activity of the end group of the polyester resin is reduced, the melt leveling time is prolonged, and a smooth, uniform and high performance coating surface can be formed after curing.

[0015] Preferably, the first polyol is at least one selected from ethylene glycol, propylene glycol, diethylene glycol, methyl propylene glycol, neopentyl glycol, butanediol, 1,2-propanediol, 1,4-cyclohexane dimethanol, isosorbide, 2-methyl-2,4-pentanediol, ethyl butyl propylene glycol, trimethylolpropane, and pentaerythritol.

[0016] Preferably, the polybasic acid is at least one selected from terephthalic acid, isophthalic acid, cyclohexane dicarboxylic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, phthalic anhydride, and trimellitic anhydride.

[0017] Preferably, the acidolysis agent is at least one selected from isophthalic acid, cyclohexane dicarboxylic acid, succinic acid, adipic acid, dodecanedioic acid, trimellitic anhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, pyromellitic dianhydride, and phenylmalonic acid.

[0018] Preferably, the preparation raw materials of the high-leveling and storage-resistant polyester resin include 15-40 parts by weight of the first polyol, 1-20 parts by weight of the second polyol, 0.5-5 parts by weight of the monohydric alcohol, 40-60 parts by weight of the polybasic acid, 0.5-5 parts by weight of the monobasic acid, and 5-15 parts by weight of the acidolysis agent.

[0019] Further preferably, the preparation raw materials of the high-leveling and storage-resistant polyester resin include 15-38 parts by weight of the first polyol, 1-18 parts by weight of the second polyol, 1-5 parts by weight of the monohydric alcohol, 40-58 parts by weight of the polybasic acid, 0.8-5 parts by weight of the monobasic acid, and 5-13 parts by weight of the acidolysis agent.

[0020] Preferably, the preparation raw materials of the high-leveling and storage-resistant polyester resin further include at least one of a catalyst and a curing accelerator.

[0021] Preferably, the raw materials for preparing the high-levelling and storage-resistant polyester resin further comprise an esterification catalyst and a curing accelerator, and the raw materials for preparing the high-levelling and storage-resistant polyester resin comprise 15-40 parts by weight of the first polyol, 1-20 parts by weight of the second polyol, 0.5-5 parts by weight of the monohydric alcohol, 40-60 parts by weight of the polybasic acid, 0.5-5 parts by weight of the monobasic acid, 5-15 parts by weight of the acid-lysis agent, 0.0001-0.002 parts by weight of the catalyst, and 0.00010-0.0015 parts by weight of the curing accelerator.

[0022] Further preferably, the raw materials for preparing the high-levelling and storage-resistant polyester resin further comprise an esterification catalyst and a curing accelerator, and the raw materials for preparing the high-levelling and storage-resistant polyester resin comprise 15-38 parts by weight of the first polyol, 1-18 parts by weight of the second polyol, 1-5 parts by weight of the monohydric alcohol, 40-58 parts by weight of the polybasic acid, 0.8-5 parts by weight of the monobasic acid, 5-13 parts by weight of the acid-lysis agent, 0.0001-0.0018 parts by weight of the catalyst, and 0.00010-0.0012 parts by weight of the curing accelerator.

[0023] Preferably, the catalyst comprises an esterification catalyst.

[0024] Preferably, the esterification catalyst comprises at least one of a tin catalyst, a zinc catalyst, a bismuth catalyst, a titanium catalyst.

[0025] Preferably, the tin catalyst comprises at least one of monobutyl tin oxide, monobutyl tin chloride, stannous oxalate, stannous octoate, stannous chloride, dibutyl tin dilaurate, stannous octoate, dibutyl tin dilauryl sulfide, dibutyl tin diacetate.

[0026] Preferably, the zinc catalyst comprises at least one of zinc iso-octoate, zinc oxalate.

[0027] Preferably, the bismuth catalyst comprises bismuth oxide.

[0028] Preferably, the titanium catalyst comprises n-butyl titanate.

[0029] Preferably, the curing accelerator comprises at least one of triphenyl ethyl phosphonium bromide, triphenyl phosphine.

[0030] Preferably, the polyester resin has an acid value of 24-40 mgKOH / g; further preferably, the polyester resin has an acid value of 26-40 mgKOH / g.

[0031] Preferably, the polyester resin has a melt viscosity of 1500-7000 mPa·s and a glass transition temperature of 58-80℃; further preferably, the polyester resin has a melt viscosity of 1800-6000 mPa·s and a glass transition temperature of 60-75℃.

[0032] Preferably, the number average molecular weight of the polyester resin is 1800-8000 g / mol; further preferably, the number average molecular weight of the polyester resin is 2000-7000 g / mol.

[0033] The second aspect of the present application provides a preparation method of the high-levelling, storage-resistant polyester resin according to the first aspect of the present application.

[0034] Specifically, the preparation method of the high-levelling, storage-resistant polyester resin comprises the following steps:

[0035] The raw material components are mixed and reacted to obtain the high-levelling, storage-resistant polyester resin.

[0036] Preferably, the preparation method of the high-levelling, storage-resistant polyester resin comprises the following steps:

[0037] (1) the first polyol, the second polyol, the monohydric alcohol and the polybasic acid are mixed and reacted to obtain a mixture 1;

[0038] (2) the mixture 1 obtained in step (1) is mixed with the acidolysis agent and the monobasic acid, and reacted to obtain a mixture 2;

[0039] (3) the mixture 2 obtained in step (2) is subjected to polycondensation to obtain the high-levelling, storage-resistant polyester resin.

[0040] Preferably, the reaction in step (1) is esterification polycondensation, and the esterification polycondensation is carried out in the presence of an esterification catalyst.

[0041] Preferably, in step (1), the temperature of the reaction is 60-280℃, and the time of the reaction is 6-24h; further preferably, the temperature of the reaction is 60-260℃, and the time of the reaction is 8-24h.

[0042] Preferably, in step (2), the temperature of the reaction is 150-260℃, and the time of the reaction is 0.5-10h; further preferably, the temperature of the reaction is 150-250℃, and the time of the reaction is 0.5-10h.

[0043] Preferably, in step (3), the polycondensation is vacuum polycondensation.

[0044] Preferably, in step (3), the temperature of the vacuum polycondensation is 180-270℃, the vacuum degree is -0.08 to -0.099 MPa, and the time of the vacuum polycondensation is 25-260 min; further preferably, the temperature of the vacuum polycondensation is 200-250℃, the vacuum degree is -0.09 to -0.099 MPa, and the time of the vacuum polycondensation is 30-240 min.

[0045] Preferably, in step (3), the acid value of the system after the vacuum polycondensation is 25-40 mgKOH / g; further preferably, the acid value of the system after the vacuum polycondensation is 26-40 mgKOH / g.

[0046] Preferably, in step (3), after the vacuum polycondensation, a curing accelerator is added to obtain the polyester resin.

[0047] The third aspect of the present application provides a coating.

[0048] Specifically, the coating comprises the high-levelling and storage-resistant polyester resin according to the first aspect of the present application.

[0049] Preferably, the coating is a powder coating.

[0050] Preferably, the coating further comprises a curing agent, a pigment and filler, and an auxiliary agent.

[0051] Preferably, the coating comprises the high-levelling and storage-resistant polyester resin 50-75 parts by weight, the curing agent 4.5-11 parts by weight, the pigment and filler 13-45 parts by weight, and the auxiliary agent 0.25-5.5 parts by weight.

[0052] Further preferably, the coating comprises the high-levelling and storage-resistant polyester resin 55-70 parts by weight, the curing agent 5-10 parts by weight, the pigment and filler 15-40 parts by weight, and the auxiliary agent 0.3-5 parts by weight.

[0053] Preferably, the curing agent is at least one selected from the group consisting of isocyanuric acid triglycidyl ester and hydroxyalkylamide.

[0054] Specifically, the types and amounts of the pigment and filler and the auxiliary agent can be determined according to actual needs in combination with common techniques in the art; the powder coating can also comprise gloss enhancer, pinhole eliminator or other auxiliary agents as needed, and the types and amounts of the gloss enhancer, the pinhole eliminator or other auxiliary agents can also be determined according to actual needs in combination with common techniques in the art, which are not specially limited.

[0055] Preferably, the pigment comprises at least one selected from the group consisting of titanium dioxide and barium sulfate.

[0056] Preferably, the auxiliary agent comprises at least one selected from the group consisting of levelling agent, gloss enhancer, and pinhole eliminator.

[0057] The leveling agent includes at least one of an acrylate leveling agent, a silicone leveling agent, and a fluorocarbon leveling agent; further preferably, the leveling agent includes an acrylate leveling agent, such as leveling agent GLP588.

[0058] Preferably, the gloss enhancer includes at least one of an acrylate gloss enhancer and a silicone gloss enhancer, further preferably, the gloss enhancer includes an acrylate gloss enhancer, such as gloss enhancer 701.

[0059] Preferably, the pinhole eliminating agent includes benzoin.

[0060] Compared with the prior art, the technical scheme provided by the present application has the following beneficial effects:

[0061] (1) The raw materials of the high-leveling and storage-resistant polyester resin prepared by the present application include a first polyol, a second polyol, a monohydric alcohol, a polybasic acid, a monobasic acid, and an acidolysis agent. The present application overcomes the positive correlation limitation between the glass transition temperature and the melt viscosity of the traditional amorphous polyester resin through the interaction of the components, realizes a good balance between the two, has a relatively high glass transition temperature and a relatively low melt viscosity, so that the prepared coating can simultaneously consider storage stability and leveling, and has good storage stability and leveling performance.

[0062] (2) The present application innovatively introduces a rigid high steric hindrance monomer containing fluorene, which can significantly reduce the viscosity of the polyester resin while imparting good storage stability to the powder coating, so that the powder coating can consider leveling performance and storage stability, and at the same time has good leveling performance and storage stability. In addition, the monohydric alcohol and the monobasic acid of the present application are also rigid high steric hindrance monomers, which can effectively reduce the viscosity of the resin without sacrificing the Tg of the polyester resin, improve the leveling performance of the coating, and at the same time, the monobasic acid can form competition with the acidolysis agent, reduce the end group activity of the polyester resin, reduce the reactivity of the polyester resin, prolong the melt leveling time, and make the coating obtain good leveling performance.

[0063] (3) The preparation process of the present application is simple and convenient for large-scale production and application. DETAILED DESCRIPTION

[0064] In order to make those skilled in the art more clearly understand the technical scheme of the present application, the following examples are given for illustration. It should be pointed out that the following examples do not constitute a limitation on the scope of protection required by the present application.

[0065] The raw materials, reagents or devices used in the following examples, if not specifically stated, can be obtained from conventional commercial channels or can be obtained by existing known methods.

[0066] The raw material components and amounts of the high leveling and storage resistant polyester resin of the present application are shown in Table 1.

[0067] Table 1: Raw material components and amounts (parts by weight) of the high leveling and storage resistant polyester resin of Examples 1-4

[0068]

[0069] "-" in Table 1 means not added.

[0070] Example 1

[0071] A high leveling and storage resistant polyester resin, the raw material components and amounts of which are shown in Table 1 by parts by weight.

[0072] A method for preparing a high leveling and storage resistant polyester resin, comprising the following steps:

[0073] (1) The first polyol, the second polyol, and the monohydric alcohol are added to a reaction kettle, and the kettle is stirred and melted at a temperature of 100°C. After the materials are completely melted, the polybasic acid and the esterification catalyst are added, and the temperature is gradually increased to 250°C and maintained for 2 hours until no obvious distillate is evaporated, to obtain a mixture 1;

[0074] (2) The acidolysis agent and the monobasic acid are sequentially added to the mixture obtained in step (1), and reacted at a temperature of 235°C for 2 hours until the acid value of the reactant reaches 46 mgKOH / g, to obtain a mixture 2;

[0075] (3) The mixture 2 obtained in step (2) is cooled to 230°C, and reacted at -0.098 MPa for 2 hours until the acid value of the reactant reaches 32.9 mgKOH / g. The solidification accelerator is added, and stirred for 30 minutes, and then discharged, to obtain the high leveling and storage resistant polyester resin.

[0076] Example 2

[0077] A high leveling and storage resistant polyester resin, the raw material components and amounts of which are shown in Table 1 by parts by weight.

[0078] In step (3) of the method for preparing the high leveling and storage resistant polyester resin of Example 2, the reaction is carried out at a temperature of 235°C for 2 hours (vacuum degree is -0.096 MPa), and the acid value is controlled at 33.8 mgKOH / g, and the others are the same as in Example 1.

[0079] Example 3

[0080] A high leveling and storage resistant polyester resin, the raw material components and amounts of which are shown in Table 1 by parts by weight.

[0081] In step (3) of the preparation method of the high leveling and storage stable polyester resin of Example 3, the reaction was carried out at a temperature of 228℃ for 3h (vacuum degree of-0.096MPa), and the acid value was controlled at 32.8mgKOH / g, and the others were the same as in Example 1.

[0082] Example 4

[0083] A high leveling and storage stable polyester resin, the raw material components and amounts thereof are shown in Table 1 by weight parts.

[0084] In step (3) of the preparation method of the high leveling and storage stable polyester resin of Example 4, the reaction was carried out at a temperature of 240℃ for 1h (vacuum degree of-0.096MPa), and the acid value was controlled at 33.4mgKOH / g, and the others were the same as in Example 1.

[0085] Comparative Example 1

[0086] Comparative Example 1 and Example 1 only differ in that Comparative Example 1 uses equimolar amount of neopentyl glycol to replace the second polyol 9.9-fluorene dimethanol, and the others are the same as in Example 1.

[0087] Comparative Example 2

[0088] Comparative Example 2 and Example 2 only differ in that Comparative Example 2 uses equimolar amount of neopentyl glycol to replace the monovalent alcohol 9-hydroxyfluorene, and the others are the same as in Example 2.

[0089] Comparative Example 3

[0090] Comparative Example 3 and Example 3 only differ in that Comparative Example 3 uses equimolar amount of isophthalic acid to replace the monovalent acid p-t-butylbenzoic acid, and the others are the same as in Example 3.

[0091] Comparative Example 4

[0092] Comparative Example 4 is a commercially available high leveling powder coating special polyester resin NH3309, purchased from Qitian Material Technology Co., Ltd., with an acid value of 33mgKOH / g and a viscosity of 3700mPa·s.

[0093] Performance Test

[0094] 1. Acid value, viscosity, glass transition temperature test of polyester resin

[0095] According to the T / GDTL 004-2019 standard, the acid value, viscosity, glass transition temperature of the polyester resin prepared in Examples 1-4 and Comparative Examples 1-4 were tested, and the results are shown in Table 2.

[0096] Table 2: Acid value, viscosity, glass transition temperature of polyester resin of Examples 1-4 and Comparative Examples 1-4

[0097]

[0098] As can be seen from Table 2, the glass transition temperatures of the polyester resins of the present application are all above 65℃, which ensures good storage stability of the powder coating, and the viscosities of the polyester resins are low, which to some extent overcomes the positive correlation contradiction between the glass transition temperature and the melt viscosity of the traditional amorphous polyester, and realizes a good balance between the two, which can make the coating have good storage stability and leveling performance at the same time.

[0099] The glass transition temperatures of Comparative Examples 2 and 3 are higher than that of Example 1, but the viscosities of Comparative Examples 2 and 3 at 200℃ are also significantly higher than that of Example 1, and Comparative Examples 2 and 3 cannot simultaneously consider storage stability and leveling performance.

[0100] The glass transition temperatures of Comparative Examples 1 and 4 are lower than that of Example 1, and the viscosities at 200℃ are also higher than that of Example 1, so Comparative Examples 2 and 3 also cannot simultaneously consider storage stability and leveling performance.

[0101] 2. Coating performance test

[0102] Take 279 parts of the polyester resins of Examples 1-4, Comparative Examples 1-3 and Comparative Example 4, and mix them uniformly with 21 parts of isocyanuric acid triglycidyl ester (TGIC), 100 parts of titanium white, 92 parts of barium sulfate, 2 parts of benzoin, 5 parts of Nanhai Chemical leveling agent GLP588 and 2 parts of Nanhai Chemical brightener 701, respectively, melt, extrude, press, break and crush the tablets to 200 mesh screen to prepare powder coatings. The process parameters of the screw extruder are controlled as follows: the temperature of Zone 1 is 100℃, the temperature of Zone 2 is 105℃, and the screw rotation speed is 40Hz.

[0103] The prepared powder coatings are sprayed on the surface of tinplate by using an electrostatic spray gun, and the spraying parameters are as follows: electrostatic voltage 70kV, powder feeding gas pressure 0.05MPa. After baking and curing at a temperature of 200℃ for 10min, a coating with a thickness of 75-80μm is obtained, and then performance test is carried out, and the test results are shown in Table 3.

[0104] Among them, the test items and test methods are as follows:

[0105] Surface appearance: visual inspection;

[0106] Storage stability: tested according to GB / T 21782.8-2008, the baking conditions of the powder coating are 40℃ / 7 days, and the storage stability of the powder coating is judged by the agglomeration level, and the larger the number from 0-3, the worse the storage stability;

[0107] Gloss (%) : tested according to GB / T 9754-2007 standard, 60° incident angle;

[0108] Impact performance (50cm) : tested according to T / GDTL004-2019 standard;

[0109] Horizontal flow (mm) : tested according to GB 6554-1986 standard;

[0110] Leveling property : tested according to PCI Leveling Scale standard board, the bigger the number, the better the leveling property.

[0111] In the above test items, the storage stability and horizontal flow are tested for the powder coating, and the other test items are tested for the coating.

[0112] Table 3: Test results of the powder coatings prepared from the polyester resins of Examples 1-4, Comparative Examples 1-3 and the commercial product of Comparative Example 4

[0113]

[0114] As can be seen from the test results in Table 3, the coating obtained from the polyester resin of the present application has good leveling property, surface appearance and mechanical property, high gloss, and the PCI leveling grade is above 7, the horizontal flow is above 30mm, and the powder coating does not form a lump after being baked at 40℃ for 7 days, and has good leveling property and storage stability.

[0115] Comparative Example 1 does not add the fluorene-containing polyol, so that the glass transition temperature of the polyester resin synthesized in Comparative Example 1 is obviously lower than that of Example 1, and the leveling property of the coating of Comparative Example 1 is poorer than that of Example 1. It is shown that the fluorene-containing compound has the effect of simultaneously improving the rigid chain structure of the polyester resin and reducing the viscosity of the polyester resin, and thus the coating has good leveling property and storage stability.

[0116] Comparative Example 2 uses an equal amount of neopentyl glycol to replace 9-hydroxyfluorene, although the polyester resin synthesized in Comparative Example 2 also has a high glass transition temperature and thus has good storage stability, but the appearance, gloss and leveling property of the coating of Comparative Example 2 are obviously poorer than those of Example 2, that is, Comparative Example 2 cannot simultaneously have good leveling property and storage stability. It is shown that the monohydric alcohol 9-hydroxyfluorene has a significant end-capping effect, can effectively control the functionality of the polyester resin, reduce the viscosity of the polyester resin, and ensure the storage stability of the coating while making the coating have excellent leveling property.

[0117] The p-hydroxybenzoic acid is replaced by an equal amount of isophthalic acid in Comparative Example 3, which makes the leveling property of Comparative Example 3 worse than that of Example 3. Because of the lack of p-hydroxybenzoic acid, the functionality of the polyester resin is higher, the melt viscosity is larger, the coating reaction speed is too fast, and the leveling property of the coating is greatly affected. However, the use of p-hydroxybenzoic acid, a high steric hindrance monobasic acid, can maintain a high viscosity of the polyester resin through the high steric hindrance effect, ensure the glass transition temperature, and form competition with the acidolysis agent to reduce the reactivity of the polyester resin, extend the melt leveling time, and make the coating obtain good leveling property.

[0118] Comparative Example 4 uses a conventional polyester resin on the market. Because it does not have a fluorenyl group and a capping structure, the leveling property, gloss, and storage stability of the coating obtained therefrom are significantly worse than those of the coating prepared from the polyester resin of the present application.

[0119] In summary, the fluorene-containing polyol, monobasic alcohol, and monobasic acid in the present application are all rigid high steric hindrance monomers. Their joint action successfully overcomes the positive correlation restriction between the glass transition temperature and the melt viscosity of the traditional amorphous polyester resin, realizes a good balance between the two, effectively reduces the resin viscosity without sacrificing the glass transition temperature of the polyester resin, improves the leveling property of the coating, and makes the coating have good storage stability and leveling property at the same time.

[0120] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A polyester resin, characterized in that, The raw materials for preparing the polyester resin, by weight, include 15-40 parts of a first polyol, 1-20 parts of a second polyol, 0.5-5 parts of a monohydric alcohol, 40-60 parts of a polybasic acid, 0.5-5 parts of a monobasic acid, and 5-15 parts of an acid hydrolysate. The first polyol is neopentyl glycol, butanediol, and trimethylolpropane; The second polyol is 9,9-fluorenediethanol; The monohydric alcohol is 9-hydroxyfluorene; The polybasic acid is selected from at least one of terephthalic acid and isophthalic acid; The monocarboxylic acid is p-tert-butylbenzoic acid; The acid hydrolysate is isophthalic acid and cyclohexanedicarboxylic acid.

2. The polyester resin according to claim 1, characterized in that, The raw materials for preparing the polyester resin also include at least one of a catalyst and a curing accelerator.

3. The polyester resin according to claim 2, characterized in that, The raw materials for preparing the polyester resin also include a catalyst and a curing accelerator, and by weight, the raw materials for preparing the polyester resin include 15-40 parts of a first polyol, 1-20 parts of a second polyol, 0.5-5 parts of a monohydric alcohol, 40-60 parts of a polybasic acid, 0.5-5 parts of a monobasic acid, 5-15 parts of an acid hydrolysate, 0.0001-0.002 parts of a catalyst, and 0.00010-0.0015 parts of a curing accelerator.

4. The polyester resin according to any one of claims 1-3, characterized in that, The polyester resin has an acid value of 24-40 mg KOH / g; and / or, the polyester resin has a melt viscosity of 1500-7000 mPa·s and a glass transition temperature of 58-80℃; and / or, the polyester resin has a number average molecular weight of 1800-8000 g / mol.

5. The method for preparing the polyester resin according to any one of claims 1-4, characterized in that, Includes the following steps: The raw material components are mixed and reacted to obtain the polyester resin.

6. The preparation method according to claim 5, characterized in that, Includes the following steps: (1) Mix the first polyol, the second polyol, the monohydric alcohol, and the polyacid, and react them to obtain mixture 1; (2) The mixture 1 obtained in step (1) is mixed with the acid hydrolysate and the monobasic acid, and reacted to obtain mixture 2; (3) The mixture 2 obtained in step (2) is polycondensed to obtain the polyester resin.

7. A coating, characterized in that, Includes the polyester resin according to any one of claims 1-4.

Images