A kind of polyester resin composition for matting powder coating and its preparation method and application

Abstract

The application discloses a kind of extinction powder coating polyester resin compositions, including high acid value resin A and low acid value resin B;The acid value of the high acid value resin A is 55~65mgKOH / g, the hydroxyl value is less than 3mgKOH / g, the glass transition temperature is 65~75℃, and the 180℃ reactivity is 30~100s;The acid value of the low acid value polyester B is 13~19mgKOH / g, the hydroxyl value is less than 5mgKOH / g, the glass transition temperature is 59~69℃, and the 180℃ reactivity is 500~800s.The high acid value resin A of the application and low acid value resin B have suitable acid value, viscosity, glass transition temperature and other performance indicators and larger structural composition and reactivity difference, and the gloss of extinction powder coating coating prepared is 10~13% (60°), while coating film surface is delicate, has good leveling performance, and has excellent storage stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of powder coatings, and particularly relates to a polyester resin composition for matt powder coatings, and a preparation method and application thereof. BACKGROUND

[0002] With the diversified development of social aesthetic needs, the matt appearance surface giving people a soft and comfortable visual effect is more and more favored by consumers. In order to obtain a stable and consistent matt effect, various means need to be used to destroy the smoothness of the coating, increase the microscopic roughness, and reduce the light reflection ability to achieve matt, and the commonly used matt methods include physical method and chemical method. Physical matt is difficult to obtain a relatively rough surface, and the matt degree is limited. A general physical matt agent (such as matt wax) can only obtain about 50% of the matt effect. Chemical matt can obtain a rough surface of different degrees, and the lowest stable gloss can be obtained by using a chemical matt agent below 10%, but the cost is relatively high, and the matt agent has a great influence on the weather resistance of the coating, so the application range is limited. Dry mixing matt method is a commonly used chemical matt method in the field of powder coatings, which mainly uses different polyesters with different reaction activities to cause micro-unevenness on the surface of the coating during the curing process of the coating film to achieve the matt effect. Using this method, 25-35% of the gloss can be obtained without adding a matt aid, the comprehensive cost is relatively low, the coating surface has a unique dry mixing matt texture, and it is a relatively economical and affordable matt method.

[0003] The best effect of the conventional two-component dry mixing matt polyester on the market can only reach 20-30% of the gloss of the coating, and when a lower matt gloss is needed, the commonly used technical means is to match a certain amount of chemical matt agent to achieve this, which will increase the cost of the coating formula, reduce the weather resistance of the coating, and change the surface appearance effect. The existing technology has problems such as too low resin glass transition temperature, poor storage stability of the coating, high gloss of the dry mixing matt coating, and poor weather resistance and mechanical properties of the coating film. Therefore, it is urgent to develop a matt powder coating with suitable resin glass transition temperature, good storage stability of the coating, low gloss of the dry mixing matt coating, good weather resistance of the coating film, and good mechanical properties. SUMMARY

[0004] In order to overcome the problems of the prior art, one of the purposes of the present application is to provide a polyester resin composition for matt powder coatings. The second purpose of the present application is to provide a preparation method of the polyester resin composition for matt powder coatings. The third purpose of the present application is a matt powder coating.

[0005] In order to achieve the above purposes, the technical scheme adopted by the present application is:

[0006] The first aspect of the present application provides a polyester resin composition for matt powder coating, comprising a high acid value resin A and a low acid value resin B;

[0007] The high acid value resin A has an acid value of 55-65 mgKOH / g, a hydroxyl value of less than 3 mgKOH / g, a glass transition temperature of 65-75℃, a 200℃ melt viscosity of 3500-5500 mPa.s, and a 180℃ reactivity of 30-100 s;

[0008] The low acid value resin B has an acid value of 13-19 mgKOH / g, a hydroxyl value of less than 5 mgKOH / g, a glass transition temperature of 59-69℃, a 200℃ melt viscosity of 5000-7000 mPa.s, and a 180℃ reactivity of 500-800 s.

[0009] The mass ratio of the high acid value resin A to the low acid value resin B is 0.5:1-2:1.

[0010] Preferably, the high acid value resin A is prepared from raw materials comprising the following weight percentages: polyol: 35-42%, polybasic acid: 45-53%, acidolysis agent 1: 5-12%, acidolysis agent 2: 1-5%, esterification catalyst: 0.01-0.12%, auxiliary resin C: 0-5%, curing catalyst: 0.03-0.3%; the acidolysis agent 1 is a difunctional carboxylic acid; the acidolysis agent 2 is a polyfunctional carboxylic acid or acid;

[0011] The low acid value resin B is prepared from raw materials comprising the following weight percentages: polyol: 36-44%, polybasic acid: 52-60%, acidolysis agent 3: 1-5%, acidolysis agent 4: 1-5%, esterification catalyst: 0.01-0.12%; the acidolysis agent 3 is an aromatic polybasic acid; the acidolysis agent 4 is an aliphatic polybasic acid.

[0012] More preferably, the auxiliary resin C has an acid value of 100-300 mgKOH / g, a glass transition temperature of 65-105℃, a 200℃ melt viscosity of 5000-15000 mPa.s, and a 180℃ reactivity of 30-100 s;

[0013] More preferably, the auxiliary resin C is a solid acrylic resin.

[0014] More preferably, the acidolysis agent 1 is selected from one or a combination of isophthalic acid, 1,4-cyclohexane dicarboxylic acid.

[0015] More preferably, the acidolysis agent 2 is selected from one or more of trimesic acid, trimellitic anhydride, pyromellitic anhydride.

[0016] More preferably, the acid resolving agent 3 is selected from one or more of phthalic acid, isophthalic acid, trimellitic anhydride;

[0017] More preferably, the acid resolving agent 4 is selected from one or more of succinic acid, adipic acid, dodecanedioic acid.

[0018] More preferably, the solidification catalyst is a triphenylphosphine compound; further preferably, the solidification catalyst is selected from one or more of triphenylphosphine, triphenyl ethyl phosphonium bromide, benzyl triphenyl ethyl phosphonium bromide, triphenyl ethyl phosphonium chloride, tribenzyl ethyl phosphonium bromide, tribenzyl ethyl phosphonium chloride.

[0019] More preferably, in the raw material for preparing the high-acid-value resin A, the polyol is selected from at least one of neopentyl glycol, 2,2-dimethyl-3-hydroxypropionic acid neopentyl glycol ester, ethylene glycol, 2-methyl-1,3-propanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, trimethylolpropane, trihydroxyethylmethane, ditrimethylolpropane, and pentaerythritol.

[0020] More preferably, in the raw material for preparing the low-acid-value resin B, the polyol is selected from at least one of neopentyl glycol, 2,2-dimethyl-3-hydroxypropionic acid neopentyl glycol ester, ethylene glycol, 2-methyl-1,3-propanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, trimethylolpropane, trihydroxyethylmethane, ditrimethylolpropane, and pentaerythritol.

[0021] More preferably, in the raw material for preparing the high-acid-value resin A, the polybasic acid is selected from at least one of terephthalic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, hydrogenated bisphenol A, hexahydrophthalic anhydride, succinic acid, adipic acid.

[0022] More preferably, in the raw material for preparing the low-acid-value resin B, the polybasic acid is selected from at least one of terephthalic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, hydrogenated bisphenol A, hexahydrophthalic anhydride, succinic acid, adipic acid.

[0023] Preferably, the number of types of polyol and polybasic acid in the raw material for preparing the high-acid-value resin A is different from the number of types of polyol and polybasic acid in the low-acid-value resin B by ≥3. That is, the difference set 1 of the number of types of polyol and polybasic acid in the raw material for preparing the high-acid-value resin A from the low-acid-value resin B, the difference set 2 of the number of types of polyol and polybasic acid in the raw material for preparing the low-acid-value resin B from the high-acid-value resin A, and the sum of the difference set 1 and the difference set 2 is ≥3.

[0024] The large difference in the composition of the raw material monomers results in a large difference in the structure of the resin, which increases the difference in the reactivity of the high-acid-value resin and the low-acid-value resin, thereby reducing the gloss.

[0025] Preferably, the high-acid-value resin A and the low-acid-value resin B further comprise 0.1-1% of an antioxidant in the synthetic formula; more preferably, the antioxidant is at least one of tetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]pentaerythritol ester, tris(2,4-di-tert-butylphenyl) phosphite, β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid octadecyl ester, dioctadecyl thiodipropionate, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphite.

[0026] The second aspect of the present application provides a preparation method of the above-mentioned polyester resin composition for matt powder coating, comprising the following steps:

[0027] Preparation of the high-acid-value resin A:

[0028] A1) mixing the polyol, the polybasic acid and the esterification catalyst, and performing esterification reaction at elevated temperature to obtain esterification product 1;

[0029] A2) adding acidolysis agent 1 to the esterification product 1 to perform acidolysis reaction to obtain acidolysis product 1;

[0030] A3) adding acidolysis agent 2 to the acidolysis product 1 again to perform acidolysis reaction again to obtain acidolysis product 2;

[0031] A4) performing polycondensation reaction on the acidolysis product 2 until the acid value of the product 1 is 55-65 mgKOH / g, the hydroxyl value is less than 3 mgKOH / g, and the melt viscosity at 200°C is 3500-5500 mPa.s;

[0032] A5) adding auxiliary resin C and curing catalyst at reduced temperature, and stirring to disperse uniformly to obtain the high-acid-value resin A;

[0033] Preparation of the low-acid-value resin B:

[0034] B1) mixing the polyol, the polybasic acid and the esterification catalyst, and performing esterification reaction to obtain esterification product 2;

[0035] B2) adding acidolysis agent 3 to the esterification product to perform acidolysis reaction to obtain acidolysis product 3;

[0036] B3) adding acidolysis agent 4 to the acidolysis product 3 again to perform acidolysis reaction again to obtain acidolysis product 4;

[0037] B4) performing polycondensation reaction on the acidolysis product 4 until the acid value of the product 2 is 13-19 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200°C is 5000-7000 mPa.s to obtain the low-acid-value resin B.

[0038] Preferably, in the step A1) of preparing the high-acid-value resin A, the esterification reaction is carried out by adding the raw materials and catalyst in a reaction kettle in a proportioned amount, heating under an oxygen-free condition, raising the temperature to 180-190°C within 1 h, and then gradually raising the temperature to 240-250°C, and reacting for 5-10 h.

[0039] Preferably, in the step A1) of preparing the high-acid-value resin A, the esterification reaction is carried out by adding the raw materials and catalyst in a reaction kettle in a proportioned amount, heating under an oxygen-free condition, raising the temperature to 180-190°C within 1 h, and then gradually raising the temperature to 240-250°C, and reacting for 5-10 h.

[0040] Preferably, in the step A1) of preparing the high-acid-value resin A, the vacuum degree is -0.090 to -0.098 MPa.

[0041] Preferably, in the step A2) of preparing the high-acid-value resin A, the acidolysis reaction is carried out to an acid value of 40-55 mgKOH / g for the acidolysis product 1.

[0042] Preferably, in the step A2) of preparing the high-acid-value resin A, the acidolysis reaction is carried out at a temperature of 230-240°C for 1-3 h.

[0043] Preferably, in the step A3) of preparing the high-acid-value resin A, the acidolysis reaction is carried out to an acid value of 65-80 mgKOH / g for the acidolysis product 2.

[0044] Preferably, in the step A3) of preparing the high-acid-value resin A, the acidolysis reaction is carried out at a temperature of 220-230°C for 1-3 h.

[0045] Preferably, in the step A4) of preparing the high-acid-value resin A, the polycondensation reaction is a vacuum polycondensation; more preferably, the vacuum polycondensation is carried out at a vacuum degree of -0.090 to -0.098 MPa.

[0046] Preferably, in the step A4) of preparing the high-acid-value resin A, the polycondensation reaction is carried out for 1-3 h.

[0047] Preferably, in the step A5) of preparing the high-acid-value resin A, the temperature when the auxiliary resin C is added is 190-210°C, and the stirring and dispersing time is 0.5-1 h.

[0048] Preferably, in the step B1) of preparing the low-acid-value resin B, the esterification reaction is carried out to an acid value of 15-25 mgKOH / g for the esterification product 2.

[0049] Preferably, in the step B1) of preparing the low-acid-value resin B, the esterification reaction is carried out by adding the raw materials and catalysts in a proportioning ratio into a reaction kettle, heating under the condition of oxygen isolation, raising the temperature to 180-190℃ within 1 h, and then gradually raising the temperature to 240-250℃, and reacting for 5-10 h.

[0050] Preferably, in the step B1) of preparing the low-acid-value resin B, the vacuum degree is -0.090 to -0.098 MPa.

[0051] Preferably, in the step B2) of preparing the low-acid-value resin B, the acidolysis reaction is carried out to an acid value of 23-29 mgKOH / g of the acidolysis product 3.

[0052] Preferably, in the step B2) of preparing the low-acid-value resin B, the acidolysis reaction is carried out at a temperature of 230-240℃, and for 1-2 h.

[0053] Preferably, in the step B3) of preparing the low-acid-value resin B, the acidolysis reaction is carried out to an acid value of 28-34 mgKOH / g of the acidolysis product 4.

[0054] Preferably, in the step B3) of preparing the low-acid-value resin B, the acidolysis reaction is carried out at a temperature of 230-240℃, and for 1-2 h.

[0055] Preferably, in the step B4) of preparing the low-acid-value resin B, the polycondensation reaction is vacuum polycondensation, and more preferably, the vacuum polycondensation is carried out at a vacuum degree of -0.090 to -0.098 MPa.

[0056] Preferably, in the step B4) of preparing the low-acid-value resin B, the polycondensation reaction is carried out for 1-3 h.

[0057] The third aspect of the present application provides a matt powder coating, comprising the polyester resin composition for matt powder coating according to the first aspect.

[0058] Preferably, the matt powder coating comprises a component I and a component II, wherein the component I comprises the high-acid-value resin A, a curing agent and an auxiliary agent, and the component II comprises the low-acid-value resin B, a curing agent and an auxiliary agent.

[0059] More preferably, the mass ratio of the component I to the component II is 0.5-2:1.

[0060] More preferably, the curing agent comprises triglycidyl isocyanurate (TGIC), hydroxyalkylamide (HAA) or polybasic benzoic acid glycidyl ester; further preferably, the polybasic benzoic acid glycidyl ester is selected from the group consisting of terephthalic acid diglycidyl ester, trimellitic acid triglycidyl ester or trimesic acid triglycidyl ester and mixtures thereof.

[0061] More preferably, the auxiliary agent comprises a leveling agent, benzoin, ultraviolet light absorber and the like.

[0062] More preferably, the matt powder coating is prepared by a preparation method comprising the following steps: the matt powder coating is prepared by dry mixing of a component I and a component II.

[0063] The matt powder coating is used for coating on the surface of a workpiece to form a protective coating.

[0064] The present application has the following advantages:

[0065] The present application provides a polyester resin composition for matt powder coating, wherein the high-acid-value resin A and the low-acid-value resin B have suitable acid value, viscosity and other performance indicators, and large structural composition and reactivity difference, and the matt powder coating prepared therefrom has a glossiness of 10-13% (60°) and a fine surface with good leveling performance; in addition, the high-acid-value resin A and the low-acid-value resin B have a high glass transition temperature, and no powder agglomeration occurs during storage, and the matt powder coating prepared therefrom has excellent storage stability.

[0066] Specifically, the present application has the following advantages compared with the prior art:

[0067] 1. The high-acid-value resin A and the low-acid-value resin B of the present application have suitable acid value, viscosity and other performance indicators, and large structural composition and reactivity difference, and have a high glass transition temperature, and no powder agglomeration occurs during storage, and the matt powder coating prepared therefrom has excellent storage stability.

[0068] 2. The resin preparation method of the present application adopts two-step addition of acid solubilizer, which is beneficial to better control of the acid value and hydroxyl value of the resin, and the acid value and reactivity difference of the prepared resin is large.

[0069] 3. The matt powder coating prepared by the present application does not need to add a matt agent, and the coating formed after curing has low and stable gloss, good leveling, mechanical properties and weather resistance, the matt coating surface is fine, and is suitable for matt dry-mixed matt powder coating. DETAILED DESCRIPTION

[0070] The present application will be further described in detail by specific examples. The raw materials used in the following examples, unless otherwise specified, can be obtained from conventional commercial sources or prepared by simple synthesis and isolation; the processes used, unless otherwise specified, are conventional processes in the art.

[0071] 1. Preparation and performance test of the matt transparent polyester resin composition

[0072] The present application provides a matt transparent polyester resin composition, which contains high acid value resin A and low acid value resin B. As an example, the high acid value resin A can be synthesized by polycondensation of the raw materials shown in Table 1 as follows:

[0073] Table 1

[0074]

[0075] The preparation method of the high acid value resin A of Examples 1-5 includes the following steps:

[0076] 1) In a 5 L reaction kettle, the polyols listed in Table 1 in the proportions are added, heated to melt the material, the polybasic acid and esterification catalyst are added, and the esterification reaction is carried out under the condition of excluding oxygen, under the protection of nitrogen, the temperature is raised to 180 ℃ within 1 h, then the temperature is raised to 210 ℃ within 2 h, and the temperature is kept for 1.5 h, then the temperature is continuously raised to 220 ℃ within 1 h, and the temperature is raised to 248 ℃ within 2 h, and the temperature is kept for 3 h, the reaction is carried out until the acid value of the esterification product is 18-23 mgKOH / g, then vacuum is extracted to-0.098 MPa, until the acid value is 13-18 mgKOH / g, to obtain esterification product 1;

[0077] 2) Under the condition of excluding oxygen, acidolysis agent 1 is added to esterification product 1, and the acidolysis reaction is carried out, the temperature is about 235 ℃, the reaction is carried out for 1.5 h until the acid value is 40-55 mgKOH / g, to obtain acidolysis product 1;

[0078] 3) Under the condition of excluding oxygen, acidolysis agent 2 is added to acidolysis product 1, and the acidolysis reaction is carried out, the temperature is about 235 ℃, the reaction is carried out for 1.5 h until the acid value is 65-80 mgKOH / g, to obtain acidolysis product 2.

[0079] 4) Vacuum polycondensation reaction (vacuum degree-0.098 MPa) is carried out for 1 h, the reaction is carried out until the acid value is 55-65 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200 ℃ is 3500-5500 mPa.s.

[0080] 5) cooling to 190~210℃, adding auxiliary resin C (Examples 2~5), curing catalyst, stirring and dispersing for 0.5~1h to obtain high-acid-value resin A, denoted as A1-A5.

[0081] The preparation method of the polyester resin of Comparative Example 1 comprises the following steps:

[0082] 1) adding polyols in the proportions listed in Table 1, heating and warming the material to melting; then adding polybasic acid and esterification catalyst in sequence, continuing to warm the reaction under nitrogen, esterification water starts to generate and distill at about 180℃, then warming to 210℃ within 2h, keeping warm for 1.5h, then continuing to warm to 220℃ within 1h, warming to 240℃ within 2h, keeping warm for 3h, then 95% of the esterification water is discharged, the acid value reaches 6~20 mgKOH / g, and an esterification product is obtained.

[0083] 2) under the condition of oxygen isolation, adding acidolysis agent 1 to the esterification product to perform acidolysis reaction, reacting at about 235℃ for 1.5h to obtain acidolysis product 1 with an acid value of 50~65 mgKOH / g.

[0084] 3) under the condition of oxygen isolation, adding acidolysis agent 2 to the acidolysis product 1 to perform acidolysis reaction, reacting at about 235℃ for 1.5h to obtain acidolysis product 2 with an acid value of 65~75 mgKOH / g.

[0085] 4) vacuumizing (vacuum degree -0.098 MPa) for 1h, reacting to an acid value of 55~64 mgKOH / g, stopping the reaction after reaching the requirement, adding curing catalyst, stirring and dispersing for 0.5h to obtain polyester resin, denoted as A6.

[0086] The preparation method of the high-acid-value polyester resin of Comparative Example 2 comprises the following steps:

[0087] 1) adding polyols in the proportions listed in Table 1, heating and warming the material to melting; then adding polybasic acid and esterification catalyst in sequence, continuing to warm the reaction under nitrogen, esterification water starts to generate and distill at about 180℃, then warming to 210℃ within 2h, keeping warm for 1.5h, then continuing to warm to 220℃ within 1h, warming to 240℃ within 2h, keeping warm for 3h, then 95% of the esterification water is discharged, the acid value reaches 6~20 mgKOH / g, and an esterification product is obtained.

[0088] 2) under the condition of oxygen isolation, adding acidolysis agent 1 and acidolysis agent 2 to the esterification product at the same time to perform acidolysis reaction, reacting at about 235℃ for 3h to obtain acidolysis product with an acid value of 65~78 mgKOH / g.

[0089] 3) vacuum (-0.098 MPa) for 1.5 h, reaction until the acid value is 55-64 mgKOH / g, stop the reaction after reaching the requirement, add the curing catalyst, stir and disperse for 0.5 h to obtain the polyester resin, denoted as A7.

[0090] The properties of the high-acid-value resins A of Examples 1-5 and Comparative Examples 1-2 are shown in Table 2 below:

[0091] Table 2

[0092]

[0093] Note: The acid value, viscosity, glass transition temperature and reactivity are tested according to T / GDTL 004-2019; the hydroxyl value is tested according to GB / T 12008.3-2009; and the same applies below.

[0094] As can be seen from Table 2, the acid values of A1-A5 are higher than those of A6 and A7, and the hydroxyl values and 180℃ reactivity are lower than those of A6 and A7. It can be seen that using the auxiliary resin C as the raw material and the process of adding the acidolysis agent twice are helpful to prepare the resin with high acid value, low hydroxyl value and high reactivity.

[0095] The low-acid-value resin B can be synthesized by polycondensation of the raw materials shown in Table 3 below:

[0096] Table 3

[0097]

[0098] The preparation method of the low-acid-value resin B of Examples 6-10 includes the following steps:

[0099] 1) In a 5 L reaction kettle, add polyhydric alcohol, heat to melt the material, add polybasic acid and esterification catalyst, and perform esterification reaction under the condition of oxygen isolation. More specifically, after adding polybasic acid and esterification catalyst in the melted polyhydric alcohol, heat to 180℃ under nitrogen protection within 1 h, then heat to 210℃ within 2 h, keep for 1.5 h, then continue to heat to 220℃ within 1 h, heat to 248℃ within 2 h, keep for 3 h, and then vacuum to -0.098 MPa until the acid value is 15-19 mgKOH / g to obtain the esterification product.

[0100] 2) Under the condition of oxygen isolation, add acidolysis agent 3 to the esterification product to perform acidolysis reaction, and heat to 235℃ for 1.5 h until the acid value is 23-29 mgKOH / g to obtain the acidolysis product 1.

[0101] 3) Under the condition of isolating oxygen, acidolysis agent 4 is added into acidolysis product 1 to perform acidolysis reaction, and the reaction is performed at 235°C for 1.5h until the acid value is 28-34 mgKOH / g, to obtain acidolysis product 2.

[0102] 4) Vacuumizing (vacuum degree -0.098 MPa) for 2h, the reaction is performed until the acid value is 13-19 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200°C is 5000-7000 mPa.s, to obtain low-acid-value resin B, which is recorded as B1-B5.

[0103] The preparation method of the low-acid-value polyester resin of Comparative Example 3 comprises the following steps:

[0104] 1) The polyols in the proportions listed in Table 1 are added and heated to melt the materials; then the polybasic acid and esterification catalyst are sequentially added, and the reaction is continuously heated under nitrogen, and esterification water starts to generate and distill at about 180°C, and then the temperature is increased to 210°C within 2h, and the temperature is maintained at 210°C for 1.5h, and then the temperature is continuously increased to 220°C within 1h, and the temperature is increased to 240°C within 2h, and the temperature is maintained at 240°C for 3h until 95% of the esterification water is discharged, and then the acid value reaches 5-15 mgKOH / g, to obtain esterification product.

[0105] 2) Under the condition of isolating oxygen, acidolysis agent 3 is added into the esterification product to perform acidolysis reaction, and the reaction is performed at about 235°C for 1.5h until the acid value is 25-35 mgKOH / g, to obtain acidolysis product 1.

[0106] 3) Under the condition of isolating oxygen, acidolysis agent 4 is added into acidolysis product 1 to perform acidolysis reaction, and the reaction is performed at about 235°C for 1.5h until the acid value is 30-39 mgKOH / g, to obtain acidolysis product 2.

[0107] 4) Vacuumizing (vacuum degree -0.098 MPa) for 2h, the reaction is performed until the acid value is 17-25 mgKOH / g, and the reaction is stopped after the requirement is met, to obtain the product, which is recorded as B6.

[0108] The preparation method of the low-acid-value polyester resin of Comparative Example 4 comprises the following steps:

[0109] 1) The polyols in the proportions listed in Table 1 are added and heated to melt the materials; then the polybasic acid and esterification catalyst are sequentially added, and the reaction is continuously heated under nitrogen, and esterification water starts to generate and distill at about 180°C, and then the temperature is increased to 210°C within 2h, and the temperature is maintained at 210°C for 1.5h, and then the temperature is continuously increased to 220°C within 1h, and the temperature is increased to 240°C within 2h, and the temperature is maintained at 240°C for 3h until 95% of the esterification water is discharged, and then the acid value reaches 5-15 mgKOH / g, to obtain esterification product.

[0110] 2) Under the condition of isolating oxygen, acidolysis agents 3 and 4 are added into the esterification product at the same time to carry out acidolysis reaction, and the acid value is 30-39 mgKOH / g after reaction for 3h at about 235°C to obtain an acidolysis product.

[0111] 3) Vacuum (-0.098 MPa) for 2h, reaction to acid value of 17-25 mgKOH / g, and the reaction is stopped after reaching the requirement to obtain the product marked as B7.

[0112] The properties of the low-acid-value resins B of Examples 6-10 and Comparative Examples 3-4 are shown in Table 4 below:

[0113] Table 4

[0114]

[0115] As shown in Table 4, the acid values and hydroxyl values of B1-B5 are less than those of B6 and B7, and the reactivity at 180°C is higher than that of the resins B6 and B7.

[0116] 2. Preparation of powder coating and performance test

[0117] (1) The high-acid-value resin Al and the low-acid-value resin B are respectively mixed with the curing agent TGIC, titanium dioxide, 228 barium sulfate, the leveling agent GLP588 and benzoin according to the proportions shown in Table 5 below (Note: If not otherwise specified, the units of the components in Table 5 are g), and then the mixture is melt-extruded by a screw extruder, sheeted, broken, and then the sheet material is pulverized and sieved to obtain the first component and the second component of the powder coating. The first component and the second component of the powder coating are mixed according to the proportions shown in Table 6 to prepare the dry-mixed extinction powder coating of Examples 11-15 and Comparative Examples 5-6.

[0118] Table 5

[0119]

[0120] Table 6

[0121]

[0122] (2) The powder coating prepared in Examples 11-15 and Comparative Examples 5-6 is electrostatically sprayed on the surface-treated iron plate, and a powder coating layer with a thickness of about 60 μm is obtained after curing at 200°C for 10 min. Then, the following performance tests are carried out, and the test results are shown in Table 7.

[0123] Table 7

[0124]

[0125] Note: Coating appearance is observed by eyes; gloss, bending, impact, xenon lamp aging are tested according to T / GDTL 004-2019; hydroxyl value is tested according to GB / T 12008.3-2009.

[0126] As can be seen from Table 7, the powder coating prepared by using the polyester resin composition of the present application has lower gloss, 60° gloss is 10%-13%, and better coating film leveling performance, higher surface morphology (orange peel) grade, and good weather resistance compared with conventional matte polyester resin, and the matte coating surface is fine, which is more suitable for use in matte dry-mix matte powder coating. In combination with the data in Table 2 and Table 4, the excellent performance of the powder coating of the present application is due to the large difference in acid value and reactivity of the high-acid-value resin A1-A5 and the low-acid-value resin B1-B5, and the high glass transition temperature, and the prepared matte powder coating has excellent storage stability.

[0127] In summary, the two-step process of adding acid solubilizer in the present application is beneficial to better control the acid value and hydroxyl value of the resin, and the prepared resin has large difference in acid value and reactivity, and in the preparation of high-acid-value resin A, the auxiliary resin C is combined to further prepare high-acid-value resin A with low hydroxyl value and low reactivity. The high-acid-value resin A and the low-acid-value resin B prepared in the present application have suitable acid value, viscosity and other performance indicators, large structural composition and reactivity difference, and high glass transition temperature, and no powder agglomeration occurs during storage, and the prepared matte powder coating has excellent storage stability. The high-acid-value resin A1-A5 and the low-acid-value resin B1-B5 prepared in the present application have large difference in acid value and reactivity, and the prepared matte powder coating does not need to add matting agent, and the coating formed after curing has low and stable gloss, good leveling, mechanical properties and weather resistance, the matte coating surface is fine, and is suitable for use in matte dry-mix matte powder coating

[0128] The above embodiments are preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are all included in the protection scope of the present application.

Claims

1. A polyester resin composition for matte powder coatings, characterized in that, comprising a high acid value resin A and a low acid value resin B; the high acid value resin A has an acid value of 55-65 mgKOH / g, a hydroxyl value less than 3 mgKOH / g, a glass transition temperature of 65-75℃, a 200℃ melt viscosity of 3500-5500 mPa.s, and a 180℃ reactivity of 30-100 s; the low acid value resin B has an acid value of 13-19 mgKOH / g, a hydroxyl value less than 5 mgKOH / g, a glass transition temperature of 59-69℃, a 200℃ melt viscosity of 5000-7000 mPa.s, and a 180℃ reactivity of 500-800 s; the mass ratio of the high acid value resin A to the low acid value resin B is 0.5:1-2:1; the high acid value resin A is prepared from raw materials comprising the following weight percentages: polyol 35-42%, polybasic acid 45-53%, acidolysis agent 1 5-12%, acidolysis agent 2 1-5%, esterification catalyst 0.01-0.12%, auxiliary resin C 5%, and curing catalyst 0.03-0.3%; the low acid value resin B is prepared from raw materials comprising the following weight percentages: polyol 36-44%, polybasic acid 52-60%, acidolysis agent 3 1-5%, acidolysis agent 4 1-5%, and esterification catalyst 0.01-0.12%; the auxiliary resin C is a carboxyl-containing solid acrylic resin, the auxiliary resin C has an acid value of 100-300 mgKOH / g, a glass transition temperature of 65-105℃, a 200℃ melt viscosity of 5000-15000 mPa.s, and a 180℃ reactivity of 30-100 s; the acidolysis agent 1 is selected from one or a combination of isophthalic acid and 1,4-cyclohexane dicarboxylic acid; the acidolysis agent 2 is selected from one or more of trimesic acid, trimellitic anhydride, and pyromellitic anhydride; the acidolysis agent 3 is selected from one or more of phthalic acid, isophthalic acid, and trimellitic anhydride; the acidolysis agent 4 is selected from one or more of succinic acid, adipic acid, and dodecanedioic acid.

2. The matting powder coating polyester resin composition according to claim 1, characterized by, the curing catalyst is a triphenylphosphine compound.

3. The matting powder coating polyester resin composition according to claim 1, characterized in that, In the preparation of the high acid value resin A or the low acid value resin B, the polyol is independently selected from at least one of neopentyl glycol, 2,2-dimethyl-3-hydroxypropionic acid neopentyl glycol ester, ethylene glycol, 2-methyl-1,3-propanediol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexane dimethanol, trimethylolpropane, trimethylolethane, ditrimethylolpropane, and pentaerythritol, respectively.

4. The matting powder coating polyester resin composition according to claim 1, characterized by, In the preparation of the high acid value resin A or the low acid value resin B, the polybasic acid is independently selected from at least one of terephthalic acid, isophthalic acid, 1,4-cyclohexane dicarboxylic acid, hydrogenated bisphenol A, hexahydrophthalic anhydride, succinic acid, and adipic acid, respectively.

5. A method for preparing the matting powder coating polyester resin composition according to any one of claims 1 to 4, characterized in that: comprising the following steps: preparing a high acid value resin A: A1: mixing polyol, polybasic acid, and esterification catalyst, and performing esterification reaction at elevated temperature to obtain esterification product 1; A2: adding acidolysis agent 1 to the esterification product 1, and performing acidolysis reaction to obtain acidolysis product 1; A3: adding acidolysis agent 2 to acidolysis product 1 again, and performing acidolysis reaction again to obtain acidolysis product 2; A4: performing polycondensation reaction on acidolysis product 2 until the acid value is 55-65 mgKOH / g, the hydroxyl value is less than 3 mgKOH / g, and the 200°C melt viscosity is 3500-5500 mPa.s; A5: adding auxiliary resin C and curing catalyst after cooling, and stirring and dispersing uniformly to obtain high-acid-value resin A; Preparation of low-acid-value resin B: B1: mixing polyol, polyacid and esterification catalyst, and performing esterification reaction to obtain esterification product 2; B2: adding acidolysis agent 3 to the esterification product, and performing acidolysis reaction to obtain acidolysis product 3; B3: adding acidolysis agent 4 to acidolysis product 3 again, and performing acidolysis reaction again to obtain acidolysis product 4; B4: performing polycondensation reaction on acidolysis product 4 until the acid value is 13-19 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the 200°C melt viscosity is 5000-7000 mPa.s, to obtain low-acid-value resin B.

6. A matt powder coating, characterized in that: The matt powder coating polyester resin composition according to any one of claims 1-4.

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