Polyester resin composition for powder coating, matte powder coating and application of matte powder coating

Abstract

The invention discloses a polyester resin composition for a powder coating, a matte powder coating and application thereof, the polyester resin composition for the powder coating comprises a high-acid-value resin A and a low-acid-value resin B, and the low-acid-value resin B is prepared from the following raw materials: polyol, an organosilicon intermediate, polyacid, an acidolysis agent and a catalyst. The super-weather-resistant high-acid-value resin A and the super-weather-resistant low-acid-value resin B have appropriate difference in performance indexes such as acid value and viscosity, and meanwhile, an organic silicon intermediate is only introduced into the super-weather-resistant low-acid-value resin B, so that a relatively large structural composition and reaction activity difference is generated between the super-weather-resistant high-acid-value resin A and the super-weather-resistant low-acid-value resin B; the prepared super-weather-resistant matte powder coating is outstanding in matting performance, has relatively low matting gloss without adding a matting agent, and also has a comfortable and soft surface appearance.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coatings, and in particular relates to a polyester resin composition for powder coatings, matte powder coatings and applications thereof. Background Art

[0002] Powder coatings are increasingly used in the coatings industry due to their energy-saving and environmentally friendly advantages, and matte powder accounts for nearly half of the market share. With the increasing development of coating technology, the coatings industry has higher and higher requirements for the decorativeness, weather resistance, and water resistance of coatings, so the demand for super weather-resistant matte powder coatings is increasing day by day. Among them, polyester powder coatings are widely used in indoor and outdoor coating fields due to their excellent durability, decorativeness, and processability. The traditional method for preparing polyester matte powder coatings is mainly to first use silicone-modified polyester, fluorocarbon resin, and super weather-resistant polyester resin to prepare high-gloss powder coatings, and then add physical or chemical matting agents to obtain matte powder coatings. However, since the matting agent has a great influence on the weather resistance of the coating, it cannot meet the super weather resistance requirements of outdoor fields such as building materials.

[0003] At present, matte powder coatings are prepared by dry mixing, which is to mix two independent powder coatings, each of which uses different resins. The different resins cause different reactivity of the powder coatings, and produce a matte effect when cured. However, the matte powder coatings prepared by the prior art either cannot achieve a low matte gloss, or have poor water boiling resistance and insufficient weather resistance. Therefore, it is necessary to develop a new matte powder coating, which can form a coating with soft surface appearance, low matte gloss, good mechanical properties, high water boiling resistance and super weather resistance. Summary of the invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, one of the purposes of the present invention is to provide a polyester resin composition for powder coating. The second purpose of the present invention is to provide a matte powder coating. The third purpose of the present invention is to provide the application of the above-mentioned matte powder coating.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A first aspect of the present invention provides a polyester resin composition for powder coatings, 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 50-70 mgKOH / g, a hydroxyl value of less than 5 mgKOH / g, a melt viscosity of 7000-10000 mPa.s at 200° C., and a reactivity of 30-120 s at 180° C.; the high acid value resin A is prepared from the following raw materials: polyol, polyacid, catalyst, and curing accelerator;

[0008] The low acid value resin B has an acid value of 15-25 mgKOH / g, a hydroxyl value of less than 10 mgKOH / g, a glass transition temperature of 55-65° C., a melt viscosity of 200° C. of 2000-4000 mPa.s, and a reactivity of 450-1000 s at 180° C. The low acid value resin B is prepared from the following raw materials: polyol, organosilicon intermediate, polyacid, acidolysis agent, catalyst;

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

[0010] Preferably, the number average molecular weight of the high acid value resin A is 2500-4500.

[0011] Preferably, the number average molecular weight of the low acid value resin B is 3000-5000.

[0012] Preferably, the high acid value resin A is prepared from raw materials including the following weight percentages: 35-39% of polyol, 60-64% of polyacid, 0.04-0.15% of catalyst, 0.02-0.2% of curing accelerator, 0.1-1% of antioxidant, and 0.05-0.3% of 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine; the ratio of the amount of hydroxyl groups in the polyol to the amount of carboxyl groups in the polyacid is the alkyd-acid ratio, and the alkyd-acid ratio is (0.86-0.90):1.

[0013] Preferably, the low acid value resin B is prepared from raw materials including the following weight percentages: 30-37% of polyol, 8-30% of silicone intermediate, 30-48% of polyacid, 5-10% of acidolysis agent, 0.04-0.15% of catalyst, 0.1-2% of antioxidant; 0.05-0.3% of 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine; the alcohol-acid ratio is (1.04-1.14):1.

[0014] Preferably, the polyol is selected from at least one of neopentyl glycol, 2,2-dimethyl-3-hydroxypropionic acid neopentyl glycol ester, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, trimethylolpropane, trimethylolethane and pentaerythritol.

[0015] Preferably, the polyacid is selected from at least one of isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 1,2-cyclobutanedicarboxylic acid, phenylsuccinic anhydride, trimellitic anhydride and pyromellitic anhydride.

[0016] Preferably, the organosilicon intermediate is an organosilicon resin containing an alkoxy functional group, the volatile matter of the organosilicon intermediate is less than 5%, and the alkoxy content is 5%-20%.

[0017] More preferably, the organosilicon intermediate is selected from at least one of DOWSIL2080, Wuxi Xiyanuo MA-5231, and SILRESIC368.

[0018] Preferably, the acidolysis agent is selected from at least one of 1,6-hexanedicarboxylic acid, 1,2-cyclobutanedicarboxylic acid, isophthalic acid, and 1,4-cyclohexanedicarboxylic acid.

[0019] Preferably, the catalyst is selected from at least one of a tin catalyst, a germanium catalyst and a titanium catalyst.

[0020] More preferably, the acidolysis agent is selected from one of 1,6-hexanedicarboxylic acid, isophthalic acid, and 1,4-cyclohexanedicarboxylic acid, or a combination thereof.

[0021] Preferably, the curing accelerator is selected from at least one of triphenylphosphine, triphenylethylphosphine bromide, benzyltriphenylethylphosphine bromide, triphenylethylphosphine chloride, tribenzylethylphosphine bromide and tribenzylethylphosphine chloride.

[0022] More preferably, the pigment filler is selected from one or more of titanium dioxide, iron oxide, zinc oxide, metal hydroxide, metal powder, sulfide, sulfate, carbonate, silicate, carbon black, talc, china clay, barite, iron blue, lead blue, organic red and organic purple.

[0023] Preferably, the antioxidant is selected from 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol bis diphosphite, and distearyl thiodipropionate or a combination thereof.

[0024] Preferably, the high acid value resin A is prepared by a preparation method comprising the following steps:

[0025] A1) mixing a polyol, a polyacid and a portion of a catalyst, and performing an esterification reaction to obtain an esterification product;

[0026] A2) mixing and dispersing the esterification product with the remaining catalyst; then evacuating the esterification product to perform a vacuum polycondensation reaction until the acid value of the polycondensation product is 50-70 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 7000-10000 mPa.s;

[0027] A3) The polycondensation product is mixed and dispersed with a curing accelerator, an antioxidant, and 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine to obtain a high acid value resin A.

[0028] More preferably, in step A1, the temperature raising program of the esterification reaction is: the initial temperature is 15-30°C, the temperature is raised to 180-190°C at a rate of 3-4°C / min, and then the temperature is raised to 230-240°C at a rate of 0.1-0.8°C / min, and the temperature is kept for 1-5h.

[0029] More preferably, in step A1, the acid value of the esterification product is 65-80 mgKOH / g.

[0030] More preferably, in step A2, the esterification product and the remaining catalyst are mixed and dispersed at 200-210° C. for 0.1-0.5 h.

[0031] More preferably, in step A2, the temperature of the vacuum polycondensation reaction is 230-240° C., the reaction time is 1-5 h, and the vacuum degree is -0.090--0.010 MPa.

[0032] More preferably, in step A3, the polycondensation product is mixed and dispersed with a curing accelerator, an antioxidant, and 2,4-bis[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine at 190-210° C. for 0.5-1 h.

[0033] Preferably, the high acid value resin B is prepared by a preparation method comprising the following steps:

[0034] B1) mixing a polyol, an organosilicon intermediate and a portion of a catalyst, and performing a condensation dealcoholization reaction to obtain a condensation product;

[0035] B2) adding a polyacid and remaining catalyst to the condensation product to carry out an esterification reaction to obtain an esterified product;

[0036] B3) adding an acidolysis agent to the esterification product to perform an acidolysis reaction to obtain an acidolysis product;

[0037] B4) vacuumizing the acid hydrolysis product to carry out vacuum polycondensation reaction until the polycondensation product has an acid value of 15 to 25 mgKOH / g, a hydroxyl value of less than 10 mgKOH / g, and a melt viscosity of 200° C. of 2000 to 4000 mPa.s,

[0038] B5) cooling the mixture, adding a curing accelerator, an antioxidant, and 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine, stirring and dispersing the mixture evenly, and obtaining a low acid value resin B.

[0039] More preferably, in step B1, the temperature raising procedure of the condensation dealcoholation reaction is: the initial temperature is 15-30°C, the temperature is raised to 170-180°C at a rate of 3-4°C / min, and the temperature is kept for 1-5h.

[0040] More preferably, in step B1, the condensation product has a hydroxyl value of 500-700 mgKOH / g.

[0041] More preferably, in step B2, the temperature raising procedure of the esterification reaction is: the initial temperature is 15-30°C, the temperature is raised to 170-180°C at a rate of 3-4°C / min, and the temperature is kept for 1-5h.

[0042] More preferably, in step B2, the esterification reaction is carried out until the acid value of the esterification product is 10 to 20 mgKOH / g.

[0043] More preferably, in step B3, the temperature of the acid hydrolysis reaction is 230-240° C.; and the time of the acid hydrolysis reaction is 1-3 h.

[0044] More preferably, in step B3, the acid hydrolysis reaction is carried out until the acid value of the acid hydrolysis product is 30 to 36 mgKOH / g.

[0045] More preferably, in step B4, the vacuum degree of the vacuum polycondensation is -0.090 to -0.010 MPa.

[0046] More preferably, in step B4, the vacuum polycondensation reaction time is 1 to 5 hours.

[0047] More preferably, in step B4, the vacuum polycondensation reaction is carried out until the polycondensation product has an acid value of 15 to 25 mgKOH / g, a hydroxyl value of less than 10 mgKOH / g, and a melt viscosity of 200° C. of 2000 to 4000 mPa.s.

[0048] More preferably, in step B5, the temperature when adding the curing accelerator, antioxidant and 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine is 190-210° C., and the stirring and dispersing time is 0.5-1 h.

[0049] The second aspect of the present invention provides a matte powder coating, comprising the polyester resin composition for powder coating according to the first aspect.

[0050] Preferably, the matte powder coating comprises component I and component II; wherein component I comprises the high acid value resin A, a curing agent, pigments and fillers and additives, and component II comprises the low acid value resin B, a curing agent, pigments and fillers and additives.

[0051] More preferably, the mass ratio of component I to component II is (0.5-2):1.

[0052] More preferably, based on 100 parts, the component I is prepared from the following raw materials in parts by mass: 50-60 parts of high acid value resin A, 4-8 parts of curing agent, 35-45 parts of pigments and fillers, and 1-3 parts of auxiliary agents.

[0053] More preferably, based on 100 parts, the component II is prepared from the following raw materials by mass: 50-60 parts of low acid value resin B, 4-8 parts of curing agent, 35-45 parts of pigments and fillers, and 1-3 parts of additives.

[0054] More preferably, the curing agent is selected from at least one of triglycidyl isocyanurate (TGIC), hydroxyalkylamide (HAA), and polyglycidyl benzoate.

[0055] More preferably, the polybasic glycidyl benzoate is at least one selected from diglycidyl terephthalate, triglycidyl trimellitate, and triglycidyl trimellitate.

[0056] More preferably, the auxiliary agent includes a leveling agent, a degassing agent, and a charge regulator.

[0057] More preferably, the pigment filler is selected from at least one of titanium dioxide, iron oxide, zinc oxide, metal hydroxide, metal powder, sulfide, sulfate, carbonate, silicate, carbon black, talc, china clay, barite, iron blue, lead blue, organic red and organic purple.

[0058] More preferably, the matte powder coating is obtained by a preparation method comprising the following steps: respectively mixing high acid value resin A and low acid value resin B with a curing agent, a pigment filler, and an additive, and preparing a powder coating component I and a powder coating component II by melt extrusion, tableting, crushing, and sieving; and then mixing the powder coating component I and the powder coating component II to obtain a matte powder coating.

[0059] The third aspect of the present invention provides the use of the matte powder coating described in the second aspect in metal product coating, furniture coating or building material coating.

[0060] Preferably, the surface of the metal product coating, furniture coating or building material coating is coated with a coating formed by curing the matte powder coating described in the second aspect.

[0061] Preferably, the metal product coating, furniture coating or building material coating is prepared by the following steps: depositing matte powder coating on a substrate by using an electrostatic or friction-charged spray gun, or depositing matte powder coating on a substrate by using a fluidized bed technology, and then heating and curing to form a coating.

[0062] More preferably, the curing temperature is 180-220°C.

[0063] The beneficial effects of the present invention are:

[0064] 1. The super weather resistant high acid value resin A and the super weather resistant low acid value resin B of the present invention have appropriate differences in performance indicators such as acid value and viscosity. At the same time, the silicone intermediate is only introduced into the super weather resistant low acid value resin B, which creates a large difference in structural composition and reaction activity between the super weather resistant high acid value resin A and the super weather resistant low acid value resin B. The obtained super weather resistant matte powder coating has outstanding matting performance, has a low matting gloss (10%-25%) without adding a matting agent, and has a comfortable and soft surface appearance.

[0065] 2. The super weather-resistant matte polyester resin composition of the present invention adds an organosilicon intermediate, whose special bond energy of silicon-oxygen bond is 460 kJ / mol, which is much greater than 332 kJ / mol of carbon-carbon single bond, showing better heat resistance and weather resistance. At the same time, silicon atoms will be enriched on the coating surface in the form of rearrangement, which significantly reduces the surface energy of the coating, increases the static water contact angle, and makes the coating have excellent hydrophobicity. The super weather-resistant matte powder coating prepared in this way has excellent water boiling resistance.

[0066] 3. In the preparation method of the super weather-resistant low acid value resin B of the present invention, a special small molecule copolymerization synthesis process is adopted to introduce the organosilicon intermediate into the structure of the super weather-resistant low acid value resin B, thereby overcoming the problem of poor compatibility between traditional organosilicon resin and polyester resin. The obtained super weather-resistant matte powder coating has better compatibility, surface appearance and mechanical properties than the traditional polyester resin cold blending organosilicon resin method.

[0067] 4. The super weather-resistant matte polyester resin composition of the present invention and the curing agent, pigments, fillers, additives, etc. prepared to obtain the super weather-resistant matte powder coating has outstanding super weather-resistant performance. DETAILED DESCRIPTION

[0068] The present invention is further described in detail below through specific examples. The raw materials used in the following examples, unless otherwise specified, can be obtained from conventional commercial sources or prepared and separated by simple synthesis; the processes used, unless otherwise specified, are conventional processes in the art.

[0069] Examples 1-5

[0070] Examples 1-5 provide five kinds of high acid value resins A, which are synthesized by polycondensation of the raw materials shown in Table 1. The preparation method of the high acid value resin A is as follows:

[0071] 1) Add the polyols in the proportions listed in Table 1 to a 5L reactor, heat until the materials are melted, add the polyacid and half of the catalyst, and carry out esterification reaction under oxygen isolation conditions. Heat to 180°C within 1 hour under nitrogen protection, and then continue to heat to 248°C at a heating rate of 10°C / h, keep warm for 3 hours, and carry out esterification reaction until the acid value of the product is 65-80 mgKOH / g to obtain an esterified product;

[0072] 2) Under the condition of isolating oxygen, the esterification product is cooled to 210° C., the remaining catalyst is added, and the mixture is stirred and dispersed for 0.1 to 0.5 h, and then the temperature is rapidly raised to 230° C., and a vacuum polycondensation reaction (vacuum degree -0.098 MPa) is carried out for 1.5 h, until the acid value of the product is 50 to 70 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 7000 to 10000 mPa.s;

[0073] 3) Cool down to 200°C, add 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine, antioxidant, and curing accelerator, and stir and disperse for 0.5h to obtain a super weather-resistant high acid value resin, which is recorded as A1-A5.

[0074] Comparative Example 1

[0075] Comparative Example 1 provides a high acid value resin A, which is synthesized by polycondensation of the raw materials shown in Table 1, and the preparation method thereof is as follows:

[0076] 1) Add the polyol in the proportion listed in Table 1 and heat until the material melts; then add the polyacid and the catalyst in sequence, continue heating the reaction under nitrogen, esterification water begins to be generated and distilled at about 180°C, then continue to heat to 248°C at a heating rate of 10°C / h, keep warm for 3h, keep warm for 3h until 95% of the esterification water is discharged, the acid value reaches 6-20mgKOH / g, and the esterification product is obtained;

[0077] 2) under the condition of isolating oxygen, adding an acidolysis agent to the esterification product to carry out an acidolysis reaction, reacting at about 235° C. for 3 hours until the acid value reaches 65 to 75 mgKOH / g, thereby obtaining an acidolysis product;

[0078] 3) The acid hydrolysis product was evacuated (vacuum degree -0.098MPa) for 1h, and the reaction was continued until the acid value was 55-64mgKOH / g and the melt viscosity at 200℃ was 7000-10000mPa.s. When the requirements were met, the reaction was stopped, the temperature was lowered to 200℃, the additive was added, and the mixture was stirred and dispersed for 0.5h to obtain a high acid value resin, which was recorded as A6.

[0079] Comparative Example 2

[0080] Comparative Example 2 provides a high acid value resin A, which is synthesized by polycondensation of the raw materials shown in Table 1, and the preparation method thereof is as follows:

[0081] 1) Add the polyols in the proportions listed in Table 1 to a 5L reactor, heat until the materials are melted, add the polyacid and half of the catalyst, and carry out esterification reaction under oxygen isolation conditions. Heat to 180°C within 1 hour under nitrogen protection, and then continue to heat to 248°C at a heating rate of 10°C / h, keep warm for 3 hours, and carry out esterification reaction until the acid value of the product is 65-80 mgKOH / g to obtain an esterified product;

[0082] 2) Under the condition of isolating oxygen, the esterification product is cooled to 210° C., the remaining catalyst is added, and the mixture is stirred and dispersed for 0.1 to 0.5 h, and then the temperature is rapidly raised to 230° C., and a vacuum polycondensation reaction (vacuum degree -0.098 MPa) is carried out for 1.5 h, until the acid value of the product is 50 to 70 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 7000 to 10000 mPa.s;

[0083] 3) Cooling to 200°C, adding 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine, antioxidant and curing accelerator, stirring and dispersing for 0.5h to obtain a high acid value resin, which is recorded as A7.

[0084] Table 1

[0085]

[0086]

[0087] Embodiment 6-10

[0088] Examples 6-10 provide five kinds of low acid value resins B, which are synthesized by polycondensation of the raw materials shown in Table 2. The preparation method of low acid value resin B is as follows:

[0089] 1) Add the organosilicon intermediate and the polyol to a 5L reactor, heat until the materials are melted, add the catalyst 1, and perform a condensation dealcoholization reaction under the condition of isolating oxygen. More specifically, under the protection of nitrogen, the temperature is raised to 170°C within 1 hour, and then raised to 180°C within 2 hours, and kept warm for 3 hours, and the condensation dealcoholization reaction is performed until the hydroxyl value of the product is 500-700 mgKOH / g to obtain a condensation product;

[0090] 2) adding a polyacid and a catalyst 2 in a certain ratio to the condensation product under the condition of isolating oxygen, heating the mixture under the condition of isolating oxygen, raising the temperature to 200° C. within 2 hours, keeping the temperature for 1.5 hours, then continuing to raise the temperature to 220° C. within 1 hour, keeping the temperature for 1 hour, raising the temperature to 248° C. within 2 hours, keeping the temperature for 3 hours, and reacting until the acid value of the esterification product reaches 10 to 20 mgKOH / g, thereby obtaining an esterification product;

[0091] 3) adding an acidolysis agent to the esterification product under oxygen isolation conditions to carry out an acidolysis reaction at 235° C. for 3 h until the acid value reaches 30 to 36 mgKOH / g, thereby obtaining an acidolysis product;

[0092] 4) The acidolysis product is evacuated (vacuum degree -0.098MPa) for 2h, and reacted until the acid value is 15-25mgKOH / g, the hydroxyl value is less than 10mgKOH / g, and the melt viscosity at 200°C is 2000-4000mPa.s to obtain a polycondensation product;

[0093] 5) Cool down to 200°C, add 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine and antioxidant, stir and disperse for 0.5h to obtain super weather-resistant low acid value resin, recorded as B1-B5.

[0094] Comparative Example 3

[0095] Comparative Example 3 provides a low acid value resin B, which is synthesized by polycondensation of the raw materials shown in Table 1, and the preparation method thereof is as follows:

[0096] 1) Add the organosilicon intermediate and the polyol to a 5L reactor, heat until the materials are melted, add the catalyst 1, and perform a condensation dealcoholization reaction under the condition of isolating oxygen. More specifically, under the protection of nitrogen, the temperature is raised to 170°C within 1 hour, and then raised to 180°C within 2 hours, and kept warm for 3 hours, and the condensation dealcoholization reaction is performed until the hydroxyl value of the product is 500-700 mgKOH / g to obtain a condensation product;

[0097] 2) adding a polyacid and a catalyst 2 in a certain ratio to the condensation product under the condition of isolating oxygen, heating the mixture under the condition of isolating oxygen, raising the temperature to 200° C. within 2 hours, keeping the temperature for 1.5 hours, then continuing to raise the temperature to 220° C. within 1 hour, keeping the temperature for 1 hour, raising the temperature to 248° C. within 2 hours, keeping the temperature for 3 hours, and reacting until the acid value of the esterification product reaches 10 to 20 mgKOH / g, thereby obtaining an esterification product;

[0098] 3) adding an acidolysis agent to the esterification product under oxygen isolation conditions to carry out an acidolysis reaction at 235° C. for 3 h until the acid value reaches 30 to 36 mgKOH / g, thereby obtaining an acidolysis product;

[0099] 4) The acidolysis product was evacuated (vacuum degree -0.098MPa) for 2h, and reacted until the acid value was 15-25mgKOH / g, the hydroxyl value was less than 10mgKOH / g, and the melt viscosity at 200°C was 2000-4000mPa.s to obtain a condensation product, which was cooled to 200°C and an auxiliary agent was added. The mixture was stirred and dispersed for 0.5h to obtain a super weather-resistant low acid value resin, which was recorded as B6.

[0100] Comparative Example 4

[0101] Comparative Example 4 provides a low acid value resin B, which is synthesized by polycondensation of the raw materials shown in Table 2, and its preparation method is as follows:

[0102] 1) Add the polyol in the proportion listed in Table 2 and heat until the material melts; then add the polyacid and the catalyst in sequence, continue to heat the reaction under nitrogen, esterification water begins to be generated and distilled at about 180°C, then heat to 210°C within 2 hours, keep warm for 1.5 hours, then continue to heat to 220°C within 1 hour, heat to 240°C within 2 hours, keep warm for 3 hours until 95% of the esterification water is discharged, the acid value reaches 5-15 mgKOH / g, and the esterification product is obtained;

[0103] 2) under the condition of isolating oxygen, adding an acidolysis agent to the esterification product to carry out an acidolysis reaction, reacting at about 235° C. for 1.5 hours until the acid value reaches 30 to 39 mgKOH / g, thereby obtaining an acidolysis product;

[0104] 3) The acid hydrolysis product is evacuated (vacuum degree -0.098MPa) for 2h, and the reaction is carried out until the acid value reaches 17-25mgKOH / g and the melt viscosity at 200℃ reaches 2000-4000mPa. The reaction can be stopped when the requirements are met;

[0105] 4) Cool down to 200°C, add 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine and antioxidant, stir and disperse for 0.5h to obtain a super weather-resistant low acid value resin, recorded as B7.

[0106] Table 2

[0107]

[0108]

[0109] The properties of the super weather-resistant high acid value resin A of Examples 1-5 and Comparative Examples 1-2 are shown in Table 3 below:

[0110] Table 3

[0111]

[0112] Note: Acid value, viscosity, glass transition temperature and reactivity are tested according to T / GDTL004-2019; hydroxyl value is tested according to GB / T12008.3-2009; the same below.

[0113] It can be seen from Table 4 that the viscosity and glass transition temperature of Examples A1-A5 and Comparative Example A7 using the one-step feeding method are higher than those of the resin in Comparative Example A6, and the reactivity at 180° C. is shorter than that of the resin in Comparative Example A6.

[0114] The properties of the super weather-resistant low acid value resin B of Examples 6-10 and Comparative Examples 3-4 are shown in Table 4 below:

[0115] Table 4

[0116]

[0117]

[0118] As can be seen from Table 4, Comparative Example B7 does not use an organosilicon intermediate and has the shortest reactivity time at 180°C, while Comparative Example B6 uses the largest amount of organosilicon intermediate and has the longest reactivity at 180°C. However, as the amount of organosilicon intermediate increases, the viscosity of the resin decreases and the glass transition temperature also decreases accordingly.

[0119] Preparation and performance testing of powder coatings

[0120] (1) The high acid value resins A1-A7 and low acid value resins B1-B7 of the above-mentioned embodiments and comparative examples are weighed and mixed with the curing agent TGIC, titanium dioxide, 228 barium sulfate, leveling agent GLP588 and benzoin according to the a component and b component in Table 5 (Note: unless otherwise specified, the units of the components in Table 5 are all g), melt-extruded, tableted and crushed by a screw extruder, and then the tablets are crushed and sieved to obtain the a component and b component of the powder coating, which are recorded as A1a-A7a and B1b-B7b respectively. Then, the a component and the b component powder coating are mixed in a weight ratio of 1:1 according to Table 6 to prepare the matte powder coatings of embodiments 11-15 and comparative examples 5-6.

[0121] Table 5

[0122]

[0123] Table 6

[0124]

[0125]

[0126] (2) The powder coatings prepared in Examples 11-15 and Comparative Examples 5-6 were electrostatically sprayed onto the surface treated iron plate and cured at 200°C for 15 min to obtain a powder coating of about 70 μm in thickness. The commercially available silicone powder coating (Comparative Example 7) was electrostatically sprayed onto the preheated iron plate and cured at 220°C for 20 min to obtain a powder coating of 30 to 70 μm. The following performance tests were then performed. The test results are shown in Table 7:

[0127] Table 7

[0128]

[0129] Note: The appearance of the coating is visually inspected; gloss, bending, impact, boiling, heat resistance, and xenon lamp aging are tested according to T / GDTL004-2019; the hydroxyl value is tested according to GB / T12008.3-2009.

[0130] As shown in Table 7, the powder coating obtained by using the powder coating of Examples 11-15 has a lower gloss (60° gloss is 15%-20%), good coating leveling performance, and excellent water boiling resistance. The performance index difference between the high acid value resin A and the low acid value resin B in Comparative Example 5 is different from that of Examples 11-15, and the obtained powder coating has a worse matting performance than that of Examples 11-15. In addition, 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine is not added in Comparative Example 5, resulting in a low 1000h xenon lamp light retention rate and an antioxidant performance that is not as good as that of Examples 11-15. The polyester resin composition of Comparative Example 6 does not contain an organosilicon intermediate, and its matting performance, mechanical strength, water boiling resistance and aging resistance are not as good as those of Examples 11-15. Compared with conventional commercially available organosilicon powder coatings, the powder coatings obtained from the powder coatings of Examples 11-15 have better mechanical properties, the same super weather resistance, and the advantage of lower cost.

[0131] In summary, the super weather-resistant high acid resin A and the super weather-resistant low acid resin B of the present invention have suitable differences in performance indicators such as acid value and viscosity. At the same time, the organosilicon intermediate is only introduced into the super weather-resistant low acid resin B, so that a large difference in structure composition and reaction activity is generated between the super weather-resistant high acid resin A and the super weather-resistant low acid resin B. The obtained super weather-resistant matte powder coating has outstanding matting performance, has a low matting gloss (10%-25%) without adding a matting agent, and has a comfortable and soft surface appearance. The organosilicon intermediate is added to the super weather-resistant matte polyester resin composition of the present invention, and the bond energy of its special silicon oxygen bond is 460kJ / mol, which is much greater than 332kJ / mol of a carbon-carbon single bond, showing better heat resistance and weather resistance. At the same time, silicon atoms will be enriched on the surface of the coating in the form of rearrangement, so that the surface energy of the coating is significantly reduced, the static water contact angle is increased, and the coating has excellent hydrophobicity. The super weather-resistant matte powder coating thus obtained has excellent water boiling resistance. In the preparation method of the super weather-resistant low acid value resin B of the present invention, a special small molecule copolymerization synthesis process is adopted to introduce the organosilicon intermediate into the structure of the super weather-resistant low acid value resin B, thereby overcoming the problem of poor compatibility between traditional organosilicon resin and polyester resin. The obtained super weather-resistant matte powder coating has better compatibility, surface appearance and mechanical properties than the traditional polyester resin cold blending organosilicon resin method.

[0132] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A polyester resin composition for powder coating, characterized in that: It includes high acid value resin A and low acid value resin B; The high acid value resin A has an acid value of 50-70 mgKOH / g, a hydroxyl value of less than 5 mgKOH / g, a melt viscosity of 7000-10000 mPa.s at 200° C., and a reactivity of 30-120 s at 180° C.; the high acid value resin A is prepared from the following raw materials: polyol, polyacid, catalyst, and curing accelerator; The low acid value resin B has an acid value of 15-25 mgKOH / g, a hydroxyl value of less than 10 mgKOH / g, a glass transition temperature of 55-65° C., a melt viscosity of 200° C. of 2000-4000 mPa.s, and a reactivity of 450-1000 s at 180° C. The low acid value resin B is prepared from the following raw materials: polyol, organosilicon intermediate, polyacid, acidolysis agent, catalyst; The mass ratio of the high acid value resin A to the low acid value resin B is (0.5-2):

1.

2. The polyester resin composition for powder coating according to claim 1, characterized in that: The high acid value resin A is prepared by raw materials including the following weight percentages: 35-39% of polyol, 60-64% of polyacid, 0.04-0.15% of catalyst, 0.02-0.2% of curing accelerator, 0.1-1% of antioxidant, and 0.05-0.3% of 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine; the ratio of the amount of hydroxyl in the polyol to the amount of carboxyl in the polyacid is the alcohol-acid ratio, and the alcohol-acid ratio is (0.86-0.90):1; And / or, the low acid value resin B is prepared from the following raw materials in weight percentage: 30-37% of polyol, 8-30% of organosilicon intermediate, 30-48% of polyacid, 5-10% of acidolysis agent, 0.04-0.15% of catalyst, 0.1-2% of antioxidant; 0.05-0.3% of 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine; the alcohol-acid ratio is (1.04-1.14):

1.

3. The polyester resin composition for powder coating according to claim 2, characterized in that: The polyol is at least one selected from neopentyl glycol, 2,2-dimethyl-3-hydroxypropionic acid neopentyl glycol ester, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, trimethylolpropane, trimethylolethane, and pentaerythritol.

4. The polyester resin composition for powder coating according to claim 2, characterized in that: The polyacid is selected from at least one of isophthalic acid, 1,4-cyclohexanedicarboxylic acid, 1,2-cyclobutanedicarboxylic acid, phenylsuccinic anhydride, trimellitic anhydride, and pyromellitic anhydride.

5. The polyester resin composition for powder coating according to claim 2, characterized in that: The organosilicon intermediate is an organosilicon resin containing an alkoxy functional group, the volatile matter of the organosilicon intermediate is less than 5%, and the alkoxy content is 5%-20%.

6. The polyester resin composition for powder coating according to claim 2, characterized in that: The acidolysis agent is selected from at least one of 1,6-hexanedicarboxylic acid, 1,2-cyclobutanedicarboxylic acid, isophthalic acid, and 1,4-cyclohexanedicarboxylic acid.

7. The polyester resin composition for powder coating according to claim 2, characterized in that: The catalyst is selected from at least one of a tin catalyst, a germanium catalyst, and a titanium catalyst; And / or, the curing accelerator is at least one selected from triphenylphosphine, triphenylethylphosphine bromide, benzyltriphenylethylphosphine bromide, triphenylethylphosphine chloride, tribenzylethylphosphine bromide, tribenzylethylphosphine chloride.

8. The polyester resin composition for powder coating according to any one of claims 2 to 6, characterized in that: The high acid value resin A is prepared by a preparation method comprising the following steps: A1) mixing a polyol, a polyacid and a part of a catalyst, and performing an esterification reaction to obtain an esterification product; A2) mixing and dispersing the esterification product with the remaining catalyst; then evacuating the esterification product to perform a vacuum polycondensation reaction until the acid value of the polycondensation product is 50-70 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 7000-10000 mPa.s; A3) mixing and dispersing the polycondensation product with a curing accelerator, an antioxidant, and 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine to obtain a high acid value resin A; And / or, the high acid value resin B is prepared by a preparation method comprising the following steps: B1) mixing a polyol, an organosilicon intermediate and a portion of a catalyst, and performing a condensation dealcoholization reaction to obtain a condensation product; B2) mixing the condensation product with a polyacid and remaining catalyst to carry out an esterification reaction to obtain an esterified product; B3) adding an acidolysis agent to the esterification product to perform an acidolysis reaction to obtain an acidolysis product; B4) evacuating the acid hydrolysis product to perform vacuum polycondensation reaction until the polycondensation product has an acid value of 15 to 25 mgKOH / g, a hydroxyl value of less than 10 mgKOH / g, and a melt viscosity of 200° C. of 2000 to 4000 mPa.s, B5) The polycondensation product is mixed and dispersed with a curing accelerator, an antioxidant, and 2,4-di[2,2'-bis(5-butoxyphenol)]-6-(2,4-dibutoxybenzene)-1,3,5-triazine to obtain a super weather-resistant low acid value resin B.

9. A matte powder coating, characterized in that: The invention comprises the polyester resin composition for powder coating according to any one of claims 1 to 8.

10. Use of the matte powder coating according to claim 9 in coating of metal products, furniture or building materials.

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