Low-temperature extinction transparent polyester resin composition as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of coatings, and particularly relates to a low-temperature extinction transparent polyester resin composition as well as a preparation method and application thereof. The polyester resin composition comprises carboxyl-terminated polyester resin with a high acid value and carboxyl-terminated polyester resin with a low acid value, the high-acid-value carboxyl-terminated polyester resin is prepared from the following raw material components: dihydric alcohol A, polyhydric alcohol, nitrogen-containing dihydric alcohol, polyatomic acid A, an acidolysis agent A and an esterification catalyst, the low-acid-value carboxyl-terminated polyester resin is prepared from the following raw material components: dihydric alcohol B, nitrogen-containing dihydric alcohol, polyacid B, an acidolysis agent B and an esterification catalyst, the polyol does not include a diol. After the carboxyl-terminated polyester resin with the high acid value and the low acid value is applied to a powder coating, the powder coating can have extinction and low-temperature curing (140-160 DEG C curing) performance at the same time and has good spraying powdering rate, and an obtained coating is low in gloss (lower than 40 GU), high in transparency and excellent in impact resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of polyester resins, and particularly relates to a low-temperature matt transparent polyester resin composition and a preparation method and application thereof. Background Art

[0002] Powder coatings have the advantages of simple preparation, efficient spraying, economic and environmental protection, and superior performance. They are widely used in the fields of automobiles, building materials, home decoration, etc. In order to protect the coating surface and achieve higher decorativeness, transparent powder coatings are used for surface finishing when painting furniture, car wheels, bathroom accessories, etc. The traditional finishing process is mainly high gloss, but with the expansion of application scenarios and the diversification of social aesthetic needs, matte surface appearance that gives people a soft and comfortable visual effect is increasingly favored by consumers.

[0003] Matte transparent powder coatings are usually of the following types: polyurethane matte powder coatings, which are prepared with high-hydroxy polyester and low-hydroxy polyester in combination with polyurethane curing agent. The preparation process is simple, but the curing agent used is relatively expensive, and it is difficult to achieve low-temperature curing, and the curing temperature is generally above 180°C; pure polyester matte powder coatings, which use matting agents for matting, but the addition of matting agents often affects the transparency of the coating, and it is also difficult to achieve matting at low temperatures; dry-mixed matte powder coatings, which are prepared from high-acid polyester and low-acid polyester powders into powder coatings, which are then physically mixed to achieve co-blending matting using the difference in activity of the two components. The preparation process is relatively complex, and the gloss of the transparent powder coatings prepared using this method is generally above 40GU, ​​and it is difficult to prepare low-gloss coatings. In addition, the curing temperature of the powder coatings prepared by this method is generally above 180°C, which is not suitable for use in low-temperature curing fields.

[0004] A study disclosed a skin-like matte transparent powder coating with a matte gloss of 21-38GU, which is suitable for aluminum hub cover polishing, but the curing temperature is above 180°C, which is not suitable for low-temperature curing fields; a study disclosed a polyester resin for high-leveling transparent powder coating. The prepared polyester can effectively improve the transparency and leveling properties of the transparent powder coating after being applied to TGIC-cured polyester transparent powder. The polyester is suitable for preparing high-gloss transparent powder coatings, but the curing temperature is 200°C, which makes it difficult to achieve low-temperature curing. A study disclosed a polyester resin for transparent powder coatings with low curing temperature and high leveling properties, whose curing temperature can be as low as 150°C. The polyester is suitable for preparing high-gloss transparent powder coatings, and the gloss of the prepared coating is greater than 100GU, which makes it difficult to achieve a matte effect. A study disclosed a matte transparent powder coating for automotive aluminum hub cover polishing, which is prepared by dry mixing matte method, and the gloss can be less than 70GU, and has high leveling properties and high transparency, but the curing temperature is 180°C, which is high. Therefore, the current polyester resin is usually only suitable for preparing high-gloss transparent powder coatings, or the prepared matte powder coatings cannot achieve low-temperature matting performance, and it is difficult to simultaneously take into account the matting and low-temperature curing performance of transparent powder coatings.

[0005] Therefore, it is of great significance to provide a polyester resin composition that can simultaneously take into account the matte and low-temperature curing properties of a transparent powder coating. Summary of the invention

[0006] The present invention aims to solve one or more technical problems existing in the above-mentioned prior art and at least provide a beneficial choice. Specifically, the present invention provides a polyester resin composition, the powder coating prepared by the polyester resin composition can have both matte and low-temperature curing properties, and has a good spraying powdering rate, and the obtained coating has low gloss, high transparency, and excellent impact resistance.

[0007] The inventive concept of the present invention is as follows: the present invention introduces nitrogen-containing diols into the polyester structure, and the nitrogen-containing diol structure with large side groups can effectively inhibit polyester crystallization, so that the coating has higher transparency and lower matte gloss, and effectively improves the powder coating rate of the powder coating; high- and low-acid value terminal carboxyl polyesters use different acidolysis agents to achieve different ways of controlling the activity of the terminal carboxyl groups, thereby achieving different acidolysis processes, and combining with other components to obtain high- and low-acid value terminal carboxyl polyester resins. After applying the high- and low-acid value terminal carboxyl polyester resins to the powder coating, the powder coating can have both matte and low-temperature curing (140-160°C curing) properties, and has a good spray powder coating rate, and the obtained coating has low gloss (gloss less than 40GU), high transparency, and excellent impact resistance.

[0008] Therefore, the first aspect of the present invention provides a low-temperature matt transparent polyester resin composition.

[0009] Specifically, the low-temperature matt transparent polyester resin composition comprises a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin;

[0010] The raw material components of the high acid value carboxyl-terminated polyester resin include diol A, polyol, nitrogen-containing diol, polyacid A, acidolysis agent A, and esterification catalyst;

[0011] The raw material components of the low acid value carboxyl-terminated polyester resin include diol B, nitrogen-containing diol, polyacid B, acidolysis agent B, and esterification catalyst;

[0012] The polyols do not include diols.

[0013] Preferably, the diol A includes at least one of neopentyl glycol, 1,4-cyclohexanedimethanol and hydrogenated bisphenol A.

[0014] Preferably, the diol B includes at least one of neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol and diethylene glycol.

[0015] Preferably, when the diol B includes the 2-methyl-1,3-propanediol and at least one of the neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol and diethylene glycol, the molar content of the 2-methyl-1,3-propanediol is not less than 35 mol% of the diol B; further preferably, the molar content of the 2-methyl-1,3-propanediol is not less than 38 mol% of the diol B.

[0016] Preferably, the polyacid A includes at least one of terephthalic acid, isophthalic acid, furandicarboxylic acid, trimellitic anhydride and pyromellitic dianhydride.

[0017] Preferably, when the polyacid A includes isophthalic acid and at least one of terephthalic acid, furandicarboxylic acid, trimellitic anhydride and pyromellitic dianhydride, the molar content of isophthalic acid is not less than 43 mol% of the polyacid A; further preferably, the molar content of isophthalic acid is not less than 46 mol% of the polyacid A.

[0018] Preferably, the polyacid B includes at least one of terephthalic acid and 1,4-cyclohexanedicarboxylic acid.

[0019] Preferably, when the polyacid B comprises 1.4-cyclohexanedicarboxylic acid and terephthalic acid, the molar content of the 1.4-cyclohexanedicarboxylic acid is not less than 52 mol % of the polyacid B; further preferably, the molar content of the 1.4-cyclohexanedicarboxylic acid is not less than 55 mol % of the polyacid B.

[0020] Preferably, the acidolysis agent A comprises at least one of isophthalic acid and pyromellitic dianhydride.

[0021] Preferably, when the acidolysis agent A comprises isophthalic acid and pyromellitic dianhydride, the molar content of the pyromellitic dianhydride is not less than 5 mol% of the acidolysis agent A; further preferably, the molar content of the pyromellitic dianhydride is not less than 6.5 mol% of the acidolysis agent A.

[0022] Preferably, the acidolysis agent B comprises trimesic acid.

[0023] Preferably, the polyol is selected from at least one of trimethylolpropane, trimethylolethane, pentaerythritol and glycerol.

[0024] Preferably, the esterification catalyst comprises an organotin catalyst; further preferably, the organotin catalyst comprises dimethyl tin oxide.

[0025] Preferably, the structural formula of the nitrogen-containing diol is:

[0026]

[0027] R1 is a benzene ring or a saturated aliphatic ring having 2 to 10 carbon atoms;

[0028] The R2 and R3 are saturated fatty chains with 2 to 5 carbon atoms.

[0029] Preferably, the raw material components of the high acid value carboxyl-terminated polyester resin further include at least one of sodium distyryl biphenyl disulfonate and an antioxidant.

[0030] Preferably, the raw material components of the low acid value carboxyl-terminated polyester resin further include an antioxidant.

[0031] Preferably, the antioxidants in the high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin both include at least one of poly(dipropylene glycol)-based phosphite and diisooctylphenyl phosphite.

[0032] Preferably, the raw material components of the high acid value carboxyl-terminated polyester resin further include sodium distyryl biphenyl disulfonate and an antioxidant, and the raw material components of the low acid value carboxyl-terminated polyester resin further include an antioxidant; and in terms of mass percentage, the raw material components of the high acid value carboxyl-terminated polyester resin include 18-45% of diol A, 0.1-5.5% of polyol, 4.5-28% of nitrogen-containing diol, 32-65% of polyacid A, 5.5-26% of acidolysis agent A, 0 .005-0.02% of esterification catalyst, 0.001-0.01% of distyryl biphenyl disulfonate sodium, and 0.1-0.8% of antioxidant; the raw material components of the low acid value terminal carboxyl polyester resin include 27-54% of diol B, 4.5-22% of nitrogen-containing diol, 32-64.7% of polyacid B, 3.5-11% of acidolysis agent B, 0.001-0.02% of esterification catalyst, and 0.2-1.1% of antioxidant.

[0033] Further preferably, the raw material components of the high acid value carboxyl-terminated polyester resin further include sodium distyryl biphenyl disulfonate and an antioxidant, and the raw material components of the low acid value carboxyl-terminated polyester resin further include an antioxidant; and in terms of mass percentage, the raw material components of the high acid value carboxyl-terminated polyester resin include 20-43% of diol A, 0.1-5% of polyol, 5-25% of nitrogen-containing diol, 35-60% of polyacid A, 6-24% of acidolysis agent A, 0.005-0.02% of esterification catalyst, 0.001-0.01% of distyryl biphenyl disulfonate sodium, and 0.1-0.8% of antioxidant; the raw material components of the low acid value carboxyl-terminated polyester resin include 30-49% of diol B, 5-20% of nitrogen-containing diol, 35-60.7% of polyacid B, 4-10% of acidolysis agent B, 0.001-0.02% of esterification catalyst, and 0.2-1.0% of antioxidant.

[0034] Preferably, the high acid value carboxyl-terminated polyester resin has an acid value of 65-80 mgKOH / g, a glass transition temperature of 56-65° C., and a melt viscosity of 2300-4000 mPa·s at 200° C.

[0035] Preferably, the low acid value carboxyl-terminated polyester resin has an acid value of 23-28 mgKOH / g, a glass transition temperature of 52-58° C., and a melt viscosity of 4500-6000 mPa·s at 200° C.

[0036] The second aspect of the present invention provides a method for preparing the low-temperature matt transparent polyester resin composition according to the first aspect of the present invention.

[0037] Specifically, the method for preparing the low-temperature extinction transparent polyester resin composition comprises the following steps:

[0038] The diol A, polyol, nitrogen-containing diol, polyacid A and esterification catalyst are mixed, heated, and subjected to a first reaction, then cooled, and the acidolysis agent A is added to conduct a second reaction, and then vacuum polycondensed to obtain the high acid value carboxyl-terminated polyester resin;

[0039] The diol B, nitrogen-containing diol, polyacid B and esterification catalyst are mixed, heated, and reacted for the first time, then cooled, vacuumed and polycondensed, and then the acidolysis agent B is added and kept warm to obtain the low acid value carboxyl-terminated polyester resin;

[0040] The high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are mixed to obtain the polyester resin composition.

[0041] Preferably, during the preparation of the high acid value carboxyl-terminated polyester resin, the heating temperature is 225-245°C, and more preferably, the heating temperature is 230-240°C.

[0042] Preferably, in the preparation process of the high acid value carboxyl-terminated polyester resin, the first reaction time is 2.5-6.5 hours; more preferably, the first reaction time is 3-6 hours.

[0043] Preferably, after the first reaction is completed until the material is clarified, a sample is taken to test the acid value, and the acid value is 10-25 mgKOH / g.

[0044] Preferably, during the preparation of the high acid value carboxyl-terminated polyester resin, the temperature of the cooling is 203-220°C; further preferably, the temperature of the cooling and heating is 208-216°C.

[0045] Preferably, during the preparation of the high acid value carboxyl-terminated polyester resin, the second reaction time is 0.5-3.5 h; more preferably, the second reaction time is 1-3 h.

[0046] Preferably, after the second reaction, a sample is taken to test the acid value, and the acid value is 90-95 mgKOH / g.

[0047] Preferably, during the preparation of the high acid value terminal carboxyl polyester resin, the time of the vacuum polycondensation is 0.5-3.5 h, and the vacuum degree of the vacuum polycondensation is -0.099 to -0.085 MPa; further preferably, the time of the vacuum polycondensation is 1-3 h, and the vacuum degree of the vacuum polycondensation is -0.099 to -0.090 MPa.

[0048] Preferably, in the preparation process of the high acid value carboxyl-terminated polyester resin, the vacuum polycondensation further includes cooling the temperature, and then adding sodium distyrene biphenyl disulfonate and an antioxidant.

[0049] Preferably, after the acid value of the high acid value carboxyl-terminated polyester resin reaches 65-80 mgKOH / g and the melt viscosity at 200° C. reaches 2300-4000 mPa·s, the vacuuming is stopped, the temperature is lowered, and sodium distyrene biphenyl disulfonate and an antioxidant are added.

[0050] Preferably, the cooling temperature is 170-190°C; further preferably, the cooling temperature is 175-185°C; further preferably, the cooling temperature is 180°C.

[0051] Preferably, during the preparation of the low acid value carboxyl-terminated polyester resin, the heating temperature is 225-245°C, and more preferably, the heating temperature is 230-240°C.

[0052] Preferably, in the preparation process of the low acid value carboxyl-terminated polyester resin, the first reaction time is 2.5-6.5 hours; more preferably, the first reaction time is 3-6 hours.

[0053] Preferably, after the first reaction is completed until the material is clarified, a sample is taken to test the acid value, and the acid value is 10-25 mgKOH / g.

[0054] Preferably, during the preparation of the low acid value carboxyl-terminated polyester resin, the temperature of the cooling is 220-240°C; further preferably, the temperature of the cooling and heating is 225-235°C.

[0055] Preferably, in the preparation process of the low-acid value terminal carboxyl polyester resin, the time of the vacuum polycondensation is 0.5-3.5 hours, and the vacuum degree of the vacuum polycondensation is -0.099 to -0.085 MPa; further preferably, the time of the vacuum polycondensation is 1-3 hours, and the vacuum degree of the vacuum polycondensation is -0.099 to -0.090 MPa.

[0056] Preferably, during the vacuum polycondensation process, samples are taken to test the acid value. When the acid value is 3-7 mgKOH / g, the vacuuming is stopped, the acidolysis agent B is added, and the temperature is kept constant.

[0057] Preferably, in the preparation process of the low acid value carboxyl-terminated polyester resin, the heat preservation further includes cooling the temperature and then adding an antioxidant.

[0058] Preferably, the insulation time is 1.5-4.5 hours; further preferably, the insulation time is 2-4 hours.

[0059] Preferably, after the heat preservation, a sample is taken to test the acid value, and after the acid value reaches 23-28 mgKOH / g, the temperature is lowered, and then an antioxidant is added.

[0060] Preferably, the cooling temperature is 170-190°C; further preferably, the cooling temperature is 175-185°C; further preferably, the cooling temperature is 180°C.

[0061] A third aspect of the present invention provides a powder coating.

[0062] Specifically, the powder coating comprises the polyester resin composition described in the first aspect of the present invention and a curing agent.

[0063] Preferably, the curing agent comprises a hydroxyalkylamide curing agent.

[0064] Preferably, the powder coating further comprises an additive.

[0065] Preferably, the curing temperature of the powder coating is 130-160° C., and the curing time of the powder coating is 9-33 min; further preferably, the curing temperature of the powder coating is 140-160° C., and the curing time of the powder coating is 10-30 min.

[0066] Preferably, the method for preparing the powder coating comprises the following steps:

[0067] The raw material components are mixed, melt-extruded, cooled and crushed to obtain the powder coating.

[0068] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0069] (1) The present invention introduces nitrogen-containing diols into the polyester structure. The nitrogen-containing diol structure with large side groups can effectively inhibit the crystallization of polyester, achieve higher transparency and lower matte gloss of the coating, and effectively improve the powder coating rate; high and low acid value terminal carboxyl polyesters use different acidolysis agents to achieve different ways of controlling the activity of the terminal carboxyl groups, thereby achieving different acidolysis processes, and combining with other components to obtain high and low acid value terminal carboxyl polyester resins. After applying them to powder coatings, the powder coatings can have both matte and low temperature curing (140-160°C curing) properties, and have a good spray coating rate. The obtained coating has low gloss (gloss less than 40GU), high transparency, and excellent impact resistance.

[0070] (2) The present invention adopts different acidolysis processes when preparing high- and low-acid value terminal carboxyl polyester resins, and the high- and low-acid value terminal carboxyl polyesters are co-extruded to obtain powder coatings, which simplifies the powder coating preparation process and achieves the performance of matting and low-temperature curing below 160°C. DETAILED DESCRIPTION

[0071] In order to make the technical scheme of the present invention more clearly understood by those skilled in the art, the following embodiments are listed for illustration. It should be pointed out that the following embodiments do not limit the protection scope of the present invention.

[0072] Unless otherwise specified, the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources or by existing known methods.

[0073] The raw material components and amounts of the polyester resin compositions of Examples 1-4 and Comparative Examples 1-2 of the present invention are shown in Table 1.

[0074] Table 1: Raw material components and dosages (g) of polyester resin compositions of Examples 1-4 and Comparative Examples 1-2

[0075]

[0076]

[0077] In Table 1, “-” means no addition.

[0078] Example 1

[0079] A polyester resin composition comprises a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin; the raw material components and amounts of the high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are shown in Table 1.

[0080] The preparation method of high acid value carboxyl-terminated polyester resin comprises the following steps:

[0081] Add diol, polyol, nitrogen-containing diol, polyacid and esterification catalyst into a reaction vessel, gradually heat up to 233° C. under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value, and the acid value is 17 mgKOH / g; cool down to 215° C., add an acidolysis agent into the reactor and continue to react for 2 hours, take a sample to test the acid value, and the acid value reaches 92 mgKOH / g; vacuum polycondensation for 2.5 hours, the vacuum degree is -0.099 MPa, the acid value reaches 75 mgKOH / g, and the melt viscosity at 200° C. reaches 3100 mPa·s, stop vacuuming, cool down to 180° C., add sodium distyrene biphenyl disulfonate and an antioxidant, stir and disperse evenly, and then discharge the material to obtain a high acid value carboxyl-terminated polyester resin;

[0082] The preparation method of low acid value carboxyl-terminated polyester resin comprises the following steps:

[0083] Add diol, nitrogen-containing diol, polyacid and esterification catalyst into the reaction container, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 18mgKOH / g; cool down to 230°C, vacuum polycondense for 2 hours, vacuum degree -0.099MPa, stop vacuuming when the acid value reaches 5mgKOH / g; add acidolysis agent, keep warm for 3 hours, when the acid value reaches 26mgKOH / g, cool down to 180°C, add antioxidant, stir and disperse evenly, then discharge to obtain low acid value carboxyl-terminated polyester resin;

[0084] A polyester resin composition is obtained by mixing a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin.

[0085] Example 2

[0086] A polyester resin composition comprises a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin; the raw material components and amounts of the high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are shown in Table 1.

[0087] The preparation method of high acid value carboxyl-terminated polyester resin comprises the following steps:

[0088] Add diol, polyol, nitrogen-containing diol, polyacid and esterification catalyst into a reaction vessel, gradually heat up to 233° C. under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 17 mgKOH / g; cool down to 215° C., add an acidolysis agent into the reactor and continue to react for 2 hours, take a sample to test the acid value, and the acid value reaches 93 mgKOH / g; vacuum polycondensation for 2.5 hours, vacuum degree -0.099 MPa, acid value reaches 76 mgKOH / g, melt viscosity at 200° C. reaches 3600 mPa·s, stop vacuuming, cool down to 180° C., add sodium distyrene biphenyl disulfonate and an antioxidant, stir and disperse evenly, and then discharge to obtain a high acid value carboxyl-terminated polyester resin;

[0089] The preparation method of low acid value carboxyl-terminated polyester resin comprises the following steps:

[0090] Add diol, nitrogen-containing diol, polyacid and esterification catalyst into the reaction container, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 18mgKOH / g; cool down to 230°C, vacuum polycondense for 2 hours, vacuum degree -0.099MPa, stop vacuuming when the acid value reaches 5mgKOH / g; add acidolysis agent, keep warm for 3 hours, when the acid value reaches 25mgKOH / g, cool down to 180°C, add antioxidant, stir and disperse evenly, then discharge to obtain low acid value carboxyl-terminated polyester resin;

[0091] A polyester resin composition is obtained by mixing a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin.

[0092] Example 3

[0093] A polyester resin composition comprises a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin; the raw material components and amounts of the high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are shown in Table 1.

[0094] The preparation method of high acid value carboxyl-terminated polyester resin comprises the following steps:

[0095] Add diol, polyol, nitrogen-containing diol, polyacid and esterification catalyst into a reaction vessel, gradually heat up to 233° C. under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 17 mgKOH / g; cool down to 215° C., add an acidolysis agent to the reactor and continue to react for 2 hours, take a sample to test the acid value, and the acid value reaches 93 mgKOH / g; vacuum polycondensation for 2.5 hours, vacuum degree -0.099 MPa, acid value reaches 75 mgKOH / g, melt viscosity at 200° C. reaches 3850 mPa·s, stop vacuuming, cool down to 180° C., add sodium distyrene biphenyl disulfonate and an antioxidant, stir and disperse evenly, and then discharge to obtain a high acid value carboxyl-terminated polyester resin;

[0096] The preparation method of low acid value carboxyl-terminated polyester resin comprises the following steps:

[0097] Add diol, nitrogen-containing diol, polyacid and esterification catalyst into the reaction container, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 18mgKOH / g; cool down to 230°C, vacuum polycondense for 2 hours, vacuum degree -0.099MPa, stop vacuuming when the acid value reaches 5mgKOH / g; add acidolysis agent, keep warm for 3 hours, when the acid value reaches 26mgKOH / g, cool down to 180°C, add antioxidant, stir and disperse evenly, then discharge to obtain low acid value carboxyl-terminated polyester resin;

[0098] A polyester resin composition is obtained by mixing a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin.

[0099] Example 4

[0100] A polyester resin composition comprises a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin; the raw material components and amounts of the high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are shown in Table 1.

[0101] The preparation method of high acid value carboxyl-terminated polyester resin comprises the following steps:

[0102] Add diol, polyol, nitrogen-containing diol, polyacid and esterification catalyst into a reaction vessel, gradually heat up to 233° C. under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 17 mgKOH / g; cool down to 215° C., add an acidolysis agent into the reactor and continue to react for 2 hours, take a sample to test the acid value, and the acid value reaches 93 mgKOH / g; vacuum polycondensation for 2.5 hours, vacuum degree -0.099 MPa, acid value reaches 73 mgKOH / g, melt viscosity at 200° C. reaches 3050 mPa·s, stop vacuuming, cool down to 180° C., add sodium distyrene biphenyl disulfonate and an antioxidant, stir and disperse evenly, and then discharge to obtain a high acid value carboxyl-terminated polyester resin;

[0103] The preparation method of low acid value carboxyl-terminated polyester resin comprises the following steps:

[0104] Add diol, nitrogen-containing diol, polyacid and esterification catalyst into the reaction container, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 18mgKOH / g; cool down to 230°C, vacuum polycondense for 2 hours, vacuum degree -0.099MPa, stop vacuuming when the acid value reaches 5mgKOH / g; add acidolysis agent, keep warm for 3 hours, when the acid value reaches 25mgKOH / g, cool down to 180°C, add antioxidant, stir and disperse evenly, then discharge to obtain low acid value carboxyl-terminated polyester resin;

[0105] A polyester resin composition is obtained by mixing a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin.

[0106] Comparative Example 1

[0107] A polyester resin composition comprises a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin; and the raw materials and component amounts of the high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are shown in Table 1.

[0108] The preparation process of the high acid value carboxyl-terminated polyester resin in Comparative Example 1 is as follows:

[0109] Add diol, polyol, polyacid and esterification catalyst into the reaction vessel, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 18 mgKOH / g; cool down to 215°C, add an acidolysis agent into the reactor and continue to react for 2 hours, take a sample to test the acid value, and the acid value reaches 92 mgKOH / g; vacuum polycondensation for 2.5 hours, vacuum degree -0.099MPa, acid value reaches 75mgKOH / g, melt viscosity at 200°C reaches 5600mPa·s, stop vacuuming, cool down to 180°C, add an antioxidant, stir and disperse evenly, and then discharge to obtain a high acid value carboxyl-terminated polyester resin;

[0110] The preparation process of the low acid value carboxyl-terminated polyester resin in Comparative Example 1 is as follows:

[0111] Add diol, polyacid and esterification catalyst into the reaction container, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 14mgKOH / g; cool down to 230°C, vacuum polycondense for 2 hours, vacuum degree -0.099MPa, stop vacuuming when the acid value reaches 6mgKOH / g; add acidolysis agent, keep warm for 3 hours, when the acid value reaches 25mgKOH / g, cool down to 180°C, add antioxidant, stir and disperse evenly, then discharge to obtain low acid value carboxyl-terminated polyester resin;

[0112] A polyester resin composition is obtained by mixing a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin.

[0113] Comparative Example 2

[0114] A polyester resin composition comprises a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin; the raw material components and amounts of the high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are shown in Table 1.

[0115] The preparation process of the high acid value carboxyl-terminated polyester resin in Comparative Example 2 is as follows:

[0116] Add diol, polyol, polyacid and esterification catalyst into the reaction vessel, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 12 mgKOH / g; cool down to 215°C, add an acidolysis agent into the reactor and continue to react for 2 hours, take a sample to test the acid value, and the acid value reaches 91 mgKOH / g; vacuum polycondensation for 2.5 hours, vacuum degree -0.099MPa, acid value reaches 73mgKOH / g, melt viscosity at 200°C reaches 4200mPa·s, stop vacuuming, cool down to 180°C, add an antioxidant, stir and disperse evenly, and then discharge to obtain a high acid value carboxyl-terminated polyester resin;

[0117] The preparation process of the low acid value carboxyl-terminated polyester resin in Comparative Example 2 is as follows:

[0118] Add diol, polyacid and esterification catalyst into the reaction container, gradually heat up to 233°C under nitrogen protection, react for 4 hours until the material is clarified, take a sample to test the acid value of 13 mgKOH / g; cool down to 230°C, add acidolysis agent, continue to keep warm for 3 hours, after the acid value reaches 42 mgKOH / g, vacuum polycondensate for 2 hours, vacuum degree -0.099MPa, acid value reaches 26mgKOH / g, melt viscosity at 200°C reaches 5300mPa·s, stop vacuuming, cool down to 180°C, add antioxidant, stir and disperse evenly, then discharge to obtain low acid value carboxyl-terminated polyester resin;

[0119] A polyester resin composition is obtained by mixing a high acid value carboxyl-terminated polyester resin and a low acid value carboxyl-terminated polyester resin.

[0120] Performance Testing

[0121] The acid value, viscosity and glass transition temperature of the high and low acid value carboxyl-terminated polyester resins prepared in Examples 1-4 and Comparative Examples 1-2 were measured. The test results are shown in Table 2.

[0122] Among them, the acid value is tested according to GB / T 6743-2008; the viscosity is tested according to GB / T9751.1-2008; and the glass transition temperature is tested according to GB / T 19466.2-2004.

[0123] Table 2: Acid value, viscosity and glass transition temperature of high and low acid value carboxyl-terminated polyester resins prepared in Examples 1-4 and Comparative Examples 1-2

[0124]

[0125] The polyester resin compositions prepared in Examples 1-4 and Comparative Examples 1-2 (453 g of high acid value terminal carboxyl polyester resin and 453 g of low acid value terminal carboxyl polyester resin) were mixed with 74 g of curing agent Primid@XL552 (purchased from Degussa), 13 g of leveling agent PLP-100 (purchased from KS Chemical Co., Ltd), and 7 g of benzoin, respectively, melt-extruded, cooled, crushed, pulverized and sieved to obtain powder coatings, and then each group of powder coatings was sprayed on an iron plate and cured at 145°C for 20 minutes to obtain a matte transparent coating.

[0126] The obtained coating was subjected to performance tests, and the test items and test methods are as follows:

[0127] Board appearance and transparency: visual inspection;

[0128] Powder coating rate assessment method: on cold-rolled steel plates, electrostatically spray at 50kV, spray the spray gun up and down for 3 times, and test the coating thickness. If the coating thickness is less than 60 microns, the powder coating rate is low; if the coating thickness is between 60-90 microns, the powder coating rate is good; if the coating thickness is greater than 90 microns, the powder coating rate is excellent.

[0129] Light transmittance: Tested in accordance with GB / T 2410-2008;

[0130] Gloss test: Test according to GB / T 9754-2007;

[0131] Impact resistance test: Tested in accordance with T / GDTL 004-2019.

[0132] The performance test results of the coatings obtained after the polyester resin compositions of Examples 1-4 and Comparative Examples 1-2 were applied to powder coatings are shown in Table 3.

[0133] Table 3: Properties of coatings obtained after the polyester resin compositions of Examples 1-4 and Comparative Examples 1-2 were applied to powder coatings

[0134] Test items Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Powder coating rate excellent excellent excellent excellent good good Board appearance Delicate and smooth Delicate and smooth Delicate and smooth Delicate and smooth Rough orange peel Rough orange peel transparency High transparency High transparency High transparency High transparency Slightly whitish Slightly whitish Light transmittance / % 87 86 86 87 68 69 Gloss / GU(60°) 25 27 30 26 55 63 Impact resistance / cm 50 50 50 50 30 40

[0135] It can be seen from Table 3 that the powder coating prepared from the polyester resin composition of the present invention has a good spraying powdering rate, and the coating obtained by curing the powder coating at a temperature of 145° C. has lower matte gloss and higher transparency, and also has excellent impact resistance.

[0136] The gloss of the coatings in Comparative Examples 1 and 2 is higher than that in the embodiment of the present invention, indicating that their matting performance is poor, and the transparency, light transmittance, impact resistance, powder coating rate and appearance are all worse than those in the present invention, indicating that Comparative Examples 1-2 cannot achieve lower matting gloss and higher transparency after low-temperature curing.

[0137] In summary, the present invention introduces nitrogen-containing diols into the polyester structure, and the nitrogen-containing diol structure with large side groups can effectively inhibit the crystallization of polyester, achieve higher transparency and lower matte gloss of the coating, and effectively improve the powder coating rate; high and low acid value terminal carboxyl polyesters use different acidolysis agents to achieve different ways of controlling the activity of the terminal carboxyl groups, and then achieve different acidolysis processes, and combine with other components to obtain high and low acid value terminal carboxyl polyester resins. After applying them to powder coatings, the powder coatings can have both matte and low-temperature curing (140-160°C curing) properties, and have a good spray coating rate. The obtained coating has low gloss (gloss less than 40GU), high transparency, and excellent impact resistance.

[0138] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A polyester resin composition, characterized in that Including high acid value carboxyl-terminated polyester resin and low acid value carboxyl-terminated polyester resin; The raw material components of the high acid value carboxyl-terminated polyester resin include diol A, polyol, nitrogen-containing diol, polyacid A, acidolysis agent A, and esterification catalyst; The raw material components of the low acid value carboxyl-terminated polyester resin include diol B, nitrogen-containing diol, polyacid B, acidolysis agent B, and esterification catalyst; The polyols do not include diols.

2. The polyester resin composition according to claim 1, characterized in that The diol A includes at least one of neopentyl glycol, 1,4-cyclohexanedimethanol, and hydrogenated bisphenol A; And / or, the diol B includes at least one of neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, and diethylene glycol; And / or, the polyacid A comprises at least one of terephthalic acid, isophthalic acid, furandicarboxylic acid, trimellitic anhydride and pyromellitic dianhydride; And / or, the polyacid B includes at least one of terephthalic acid and 1,4-cyclohexanedicarboxylic acid; And / or, the acidolysis agent A comprises at least one of isophthalic acid and pyromellitic dianhydride; And / or, the acidolysis agent B includes trimesic acid.

3. The polyester resin composition according to claim 1, characterized in that The polyol includes at least one of trimethylolpropane, trimethylolethane, pentaerythritol and glycerol; and / or the esterification catalyst includes an organic tin catalyst.

4. The polyester resin composition according to claim 1, characterized in that The structural formula of the nitrogen-containing diol is: R1 is a benzene ring or a saturated aliphatic ring having 2 to 10 carbon atoms; The R2 and R3 are saturated fatty chains with 2 to 5 carbon atoms.

5. The polyester resin composition according to claim 1, characterized in that The raw material components of the high acid value carboxyl-terminated polyester resin further include at least one of sodium distyryl biphenyl disulfonate and an antioxidant; and / or the raw material components of the low acid value carboxyl-terminated polyester resin further include an antioxidant.

6. The polyester resin composition according to claim 5, characterized in that The raw material components of the high acid value carboxyl-terminated polyester resin further include sodium distyryl biphenyl disulfonate and an antioxidant, and the raw material components of the low acid value carboxyl-terminated polyester resin further include an antioxidant; and in terms of mass percentage, the raw material components of the high acid value carboxyl-terminated polyester resin include 18-45% of diol A, 0.1-5.5% of polyol, 4.5-28% of nitrogen-containing diol, 32-65% of polyacid A, 5.5-26% of acidolysis agent A, 0.0 05-0.02% of esterification catalyst, 0.001-0.01% of distyryl biphenyl disulfonate sodium, and 0.1-0.8% of antioxidant; the raw material components of the low acid value terminal carboxyl polyester resin include 27-54% of diol B, 4.5-22% of nitrogen-containing diol, 32-64.7% of polyacid B, 3.5-11% of acidolysis agent B, 0.001-0.02% of esterification catalyst, and 0.2-1.1% of antioxidant.

7. The polyester resin composition according to any one of claims 1 to 5, characterized in that: The high acid value carboxyl-terminated polyester resin has an acid value of 65-80 mgKOH / g, a glass transition temperature of 56-65°C, and a melt viscosity at 200°C of 2300-4000 mPa·s; and / or the low acid value carboxyl-terminated polyester resin has an acid value of 23-28 mgKOH / g, a glass transition temperature of 52-58°C, and a melt viscosity at 200°C of 4500-6000 mPa·s.

8. The method for preparing the polyester resin composition according to any one of claims 1 to 7, characterized in that: The following steps are involved: The diol A, polyol, nitrogen-containing diol, polyacid A and esterification catalyst are mixed, heated, and subjected to a first reaction, then cooled, and the acidolysis agent A is added to conduct a second reaction, and then vacuum polycondensed to obtain the high acid value carboxyl-terminated polyester resin; The diol B, nitrogen-containing diol, polyacid B and esterification catalyst are mixed, heated, and reacted for the first time, then cooled, vacuumed and polycondensed, and then the acidolysis agent B is added and kept warm to obtain the low acid value carboxyl-terminated polyester resin; The high acid value carboxyl-terminated polyester resin and the low acid value carboxyl-terminated polyester resin are mixed to obtain the polyester resin composition.

9. The preparation method according to claim 8, characterized in that: In the preparation process of the high acid value carboxyl-terminated polyester resin, the vacuum polycondensation further includes cooling the temperature and then adding sodium distyrene biphenyl disulfonate and an antioxidant; And / or, in the preparation process of the low acid value carboxyl-terminated polyester resin, the heat preservation further includes cooling the temperature and then adding an antioxidant.

10. A powder coating, characterized in that: The invention comprises the polyester resin composition according to any one of claims 1 to 7 and a curing agent.

Images