Polyester resin as well as preparation method and application thereof

Abstract

The invention discloses polyester resin as well as a preparation method and application thereof. The polyester resin is prepared from the following raw materials in parts by mass: 30 to 40 parts of polyhydric alcohol, 40 to 60 parts of polybasic acid, 3 to 20 parts of acidolysis agent, 0.1 to 2 parts of chain extender and 0.01 to 0.2 part of additive. The polyol comprises aliphatic polyol containing a side group; the polybasic acid comprises monocyclic aromatic polybasic acid and condensed ring aromatic polybasic acid; the chain extender is selected from a polymer containing an epoxy group. According to the invention, through combination of specific polybasic acid and polyhydric alcohol, the prepared polyester resin has appropriate acid value, melt viscosity, glass transition temperature and reaction activity; and the surface tension of the polyester resin is reduced by combining the use of the epoxy group-containing chain extender, so that the compatibility between macromolecular chain segments and between the resin and the filler in a coating film is enhanced in the film forming process, and the gas-liquid barrier property of the coating film is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymers, and in particular relates to a polyester resin and a preparation method and application thereof. Background Art

[0002] Powder coating is a solid coating that is completely solvent-free. It has the characteristics of no solvent emissions, no pollution, recyclability, environmental protection, high utilization rate, energy and resource saving, reduced labor intensity and excellent coating performance. It is currently recognized as the most environmentally friendly variety in the coating industry. Polyester powder coatings are often used in the protection of metal products in the fields of outdoor aluminum profiles, highway guardrails, railway infrastructure, etc. due to their excellent weather resistance, mechanical properties and other comprehensive properties. However, when polyester powder coatings are used for coating guardrails and building profiles near the coast, due to insufficient protection against seawater or salt spray, the coating is prone to bubbling, shedding, and large-scale corrosion of the substrate. Improving the corrosion resistance of polyester powder coatings, especially weather resistance, neutral salt spray resistance and mechanical properties, is of great significance to extending the service life of products, reducing maintenance costs and reducing losses caused by metal corrosion.

[0003] Among the existing solutions, a study has disclosed a polyester resin, powder coating and coating for powder coatings with corrosion resistance, weather resistance and high storage performance. The raw materials of the polyester resin include fluorine-containing dibasic acid and diol, and have excellent corrosion resistance and weather resistance; another study has disclosed a salt spray resistant powder coating and a preparation method thereof, and the salt spray resistant powder coating includes graphene and carbon nanotube modified polyester resin, and the layered fillers modified with graphene and polyaniline are used to improve the salt spray resistance of the coating; another study has disclosed a polyester resin for TGIC powder coating with excellent neutral salt spray resistance and a preparation method thereof, and the polyester resin enhances the hydrophobicity of the coating film and improves the neutral salt spray resistance by introducing hydrophobic fluorine and silicon raw materials.

[0004] Although the above-mentioned existing technologies utilize fluorinated monomers to synthesize polyesters and introduce graphene to improve the neutral salt spray resistance of the coating, they still have disadvantages such as high raw material costs, difficulty in coating color matching, and poor mechanical properties of the coating. Summary of the invention

[0005] In order to overcome at least one of the problems existing in the above-mentioned prior art, one of the objects of the present invention is to provide a polyester resin having good neutral salt spray resistance, corrosion resistance and weather resistance.

[0006] A second object of the present invention is to provide a method for preparing the above polyester resin.

[0007] A third object of the present invention is to provide a powder coating.

[0008] A fourth object of the present invention is to provide a workpiece.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] The first aspect of the present invention provides a polyester resin, comprising the following preparation raw materials: 30 to 40 parts of polyols, 40 to 60 parts of polyacids, 3 to 20 parts of acidolysis agents, 0.1 to 2 parts of chain extenders, and 0.01 to 0.2 parts of auxiliary agents; the polyols include aliphatic polyols containing side groups; the polyacids include monocyclic aromatic polyacids and condensed-ring aromatic polyacids; the chain extenders are selected from polymers containing epoxy groups.

[0011] The polyol of the present invention includes flexible side-group-containing monomers, and the polyacid includes rigid monocyclic monomers and condensed-ring monomers. The combination of these monomers is conducive to preparing a polyester resin with suitable acid value, melt viscosity, glass transition temperature and reaction activity; and the epoxy-containing polymer is combined as a chain extender. The epoxy group can react with the carboxyl group in the polyester, thereby reducing the surface tension of the polyester resin, and further in the film-forming process is conducive to enhancing the compatibility between the polymer segments in the coating film and between the resin and the filler, improving the gas-liquid barrier property of the coating film, and at the same time making the coating film have strong adhesion to substrates of different materials.

[0012] Preferably, the aliphatic polyol containing side groups is a C4-C20 aliphatic polyol containing side groups; further preferably, the aliphatic polyol containing side groups is a C5-C15 aliphatic polyol containing side groups; further preferably, the aliphatic polyol containing side groups is a C5-C10 aliphatic polyol containing side groups.

[0013] Preferably, the aliphatic polyol containing side groups includes at least one of aliphatic diol containing side groups, aliphatic triol containing side groups or aliphatic tetraol containing side groups; further preferably, the aliphatic polyol containing side groups includes aliphatic diol containing side groups, aliphatic triol containing side groups or a combination thereof.

[0014] Preferably, the side group-containing aliphatic polyol includes at least one of neopentyl glycol, isoprene glycol, 2-butyl-2-ethyl-1,3-propanediol, trimethylolethane or trimethylolpropane; further preferably, the side group-containing aliphatic polyol includes at least one of neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol or trimethylolpropane; further preferably, the side group-containing aliphatic polyol includes neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol and trimethylolpropane.

[0015] In the present invention, the specific selection of the side group-containing aliphatic polyol monomer needs to balance the side chain volume and the reactivity of the monomer functional group. 2-Butyl-2-ethyl-1,3-propanediol has a more suitable side chain volume and monomer functional group reactivity. It is combined with other polyols such as trimethylolpropane and neopentyl glycol, and reacts with polyacids to obtain a polyester resin with a more suitable acid value, melt viscosity, glass transition temperature and reactivity.

[0016] Preferably, the polyol includes at least one of neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol or trimethylolpropane; further preferably, the polyol includes neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol and trimethylolpropane.

[0017] Preferably, the polyol comprises the following components in mass fractions: 75-100 parts of neopentyl glycol, 0-15 parts of 2-butyl-2-ethyl-1,3-propanediol, and 0-5 parts of trimethylolpropane; further preferably, the polyol comprises the following components in mass fractions: 80-95 parts of neopentyl glycol, 0.1-12 parts of 2-butyl-2-ethyl-1,3-propanediol, and 0.1-4 parts of trimethylolpropane; further preferably, the polyol comprises the following components in mass fractions: 80-90 parts of neopentyl glycol, 1-10 parts of 2-butyl-2-ethyl-1,3-propanediol, and 1-3 parts of trimethylolpropane.

[0018] Preferably, the polyol further comprises a linear aliphatic polyol.

[0019] Preferably, the linear aliphatic polyol includes at least one of ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,5-pentanediol or 1,6-hexanediol; further preferably, the linear aliphatic polyol includes at least one of ethylene glycol, 1,2-propylene glycol or 1,4-butanediol; further preferably, the linear aliphatic polyol is selected from ethylene glycol.

[0020] Preferably, the polyol includes at least one of neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, trimethylolpropane or ethylene glycol; further preferably, the polyol includes neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, trimethylolpropane and ethylene glycol.

[0021] Preferably, the polyol comprises the following components in parts by mass: 75 to 100 parts of neopentyl glycol, 0 to 15 parts of 2-butyl-2-ethyl-1,3-propanediol, 0 to 5 parts of trimethylolpropane, and 0.1 to 5 parts of ethylene glycol; further preferably, the polyol comprises the following components in parts by mass: 80 to 95 parts of neopentyl glycol, 0.1 to 12 parts of 2-butyl-2-ethyl-1,3-propanediol, 0.1 to 4 parts of trimethylolpropane, and 0.5 to 12 parts of ethylene glycol; further preferably, the polyol comprises the following components in parts by mass: 80 to 90 parts of neopentyl glycol, 1 to 10 parts of 2-butyl-2-ethyl-1,3-propanediol, 1 to 3 parts of trimethylolpropane, and 1 to 10 parts of ethylene glycol.

[0022] Preferably, in the polyester resin, the condensed aromatic polyacid includes at least one of naphthyl polyacid, anthracene polyacid or phenanthryl polyacid; further preferably, the condensed aromatic polyacid includes at least one of 2,6-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 1,4-anthracene dicarboxylic acid, 9,10-anthracene dicarboxylic acid or 2,7-phenanthrene dicarboxylic acid; further preferably, the condensed aromatic polyacid includes at least one of 2,6-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid or 1,8-naphthalene dicarboxylic acid; more preferably, the condensed aromatic polyacid is selected from 2,6-naphthalene dicarboxylic acid.

[0023] Preferably, in the polyester resin, the monocyclic aromatic polyacid is selected from phenyl polyacid; further preferably, the monocyclic aromatic polyacid includes at least one of terephthalic acid, isophthalic acid or phthalic acid; further preferably, the monocyclic aromatic polyacid includes terephthalic acid and isophthalic acid.

[0024] Preferably, the polyacid comprises a group consisting of at least one of terephthalic acid and isophthalic acid, or a group consisting of 2,6-naphthalene dicarboxylic acid and at least one selected from terephthalic acid and isophthalic acid.

[0025] Preferably, the polyacid comprises the following components in mass fractions: 60-100 parts of terephthalic acid, 0-20 parts of isophthalic acid, and 0-20 parts of 2,6-naphthalene dicarboxylic acid; further preferably, the polyacid comprises the following components in mass fractions: 65-95 parts of terephthalic acid, 0-15 parts of isophthalic acid, and 1-18 parts of 2,6-naphthalene dicarboxylic acid; further preferably, the polyacid comprises the following components in mass fractions: 70-90 parts of terephthalic acid, 0-13 parts of isophthalic acid, and 4-16 parts of 2,6-naphthalene dicarboxylic acid.

[0026] Preferably, the polyacid further comprises an aliphatic polyacid.

[0027] Preferably, the aliphatic polyacid includes at least one of succinic acid, glutaric acid, adipic acid, pimelic acid or suberic acid; further preferably, the aliphatic polyacid includes at least one of glutaric acid, adipic acid or pimelic acid; further preferably, the aliphatic polyacid is adipic acid.

[0028] Preferably, the polyacid includes adipic acid and at least one selected from terephthalic acid and isophthalic acid, or adipic acid, 2,6-naphthalene dicarboxylic acid and at least one selected from terephthalic acid and isophthalic acid.

[0029] Preferably, the polyacid comprises the following components in mass fractions: 60-100 parts of terephthalic acid, 0-20 parts of isophthalic acid, 0-20 parts of 2,6-naphthalene dicarboxylic acid, and 1-20 parts of adipic acid; further preferably, the polyacid comprises the following components in mass fractions: 65-95 parts of terephthalic acid, 0-15 parts of isophthalic acid, 1-18 parts of 2,6-naphthalene dicarboxylic acid, and 1.5-15 parts of adipic acid; further preferably, the polyacid comprises the following components in mass fractions: 70-90 parts of terephthalic acid, 0-13 parts of isophthalic acid, 4-16 parts of 2,6-naphthalene dicarboxylic acid, and 2-13 parts of adipic acid.

[0030] Preferably, in the polyester resin, the acidolysis agent includes isophthalic acid, adipic acid or a combination thereof.

[0031] Preferably, at least one of the polyacids or acidolysis agents includes isophthalic acid, and the mass percentage of isophthalic acid in the raw material for preparing the polyester resin is 3-22%; more preferably 5-19%; and even more preferably 8-16%.

[0032] Since both the polyacid and the acidolysis agent of the polyester resin may be isophthalic acid, in order to make the polyester resin have more suitable properties such as acid value, melt viscosity, glass transition temperature and reaction activity, it is necessary to control the content of isophthalic acid in the raw material.

[0033] Preferably, in the polyester resin, the chain extender includes at least one of ethylene-methyl acrylate-glycidyl methacrylate, ethylene-ethyl acrylate-glycidyl methacrylate, ethylene-butyl acrylate-glycidyl methacrylate, ethylene-methyl methacrylate-glycidyl methacrylate, ethylene-ethyl methacrylate-glycidyl methacrylate or ethylene-butyl methacrylate-glycidyl methacrylate; further preferably, the chain extender includes ethylene-methyl acrylate-glycidyl methacrylate, ethylene-butyl acrylate-glycidyl methacrylate or a combination thereof.

[0034] In some specific embodiments of the present invention, the chain extender is selected from AX8900 (ethylene-methyl acrylate-glycidyl methacrylate) of SK Company, PTW (ethylene-butyl acrylate-glycidyl methacrylate copolymer) of DuPont Company, or a combination thereof.

[0035] The active ingredients of AX8900 and PTW are both ethylene terpolymers containing epoxy functional groups. They are highly active and can react with the carboxyl groups in polyester to increase toughness and reduce interfacial tension.

[0036] Preferably, in the polyester resin, the auxiliary agent includes an esterification catalyst, a curing catalyst and an antioxidant.

[0037] Preferably, the esterification catalyst includes at least one of a tin esterification catalyst, a germanium esterification catalyst or a titanium esterification catalyst; further preferably, the esterification catalyst includes at least one of monobutyl tin oxide, tin oxalate, monobutyl dihydroxytin chloride, germanium dioxide, activated titanium dioxide or an organic titanium-phosphorus complex; even more preferably, the esterification catalyst includes at least one of monobutyl tin oxide, germanium dioxide or activated titanium dioxide.

[0038] Preferably, the curing catalyst is selected from a phosphine curing catalyst; further preferably, the curing catalyst includes at least one of triphenylphosphine, butyltriphenylphosphine bromide, triphenylethylphosphine bromide, benzyltriphenylphosphine bromide, and triphenylethylphosphine chloride; further preferably, the curing catalyst includes butyltriphenylphosphine bromide, benzyltriphenylphosphine bromide, or a combination thereof.

[0039] Preferably, the antioxidant comprises a hindered phenol antioxidant, a phosphite antioxidant or a combination thereof; further preferably, the antioxidant comprises triphenyl phosphite, tris(2,4-di-tert-butylphenyl)phosphite (antioxidant 168), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1010), distearyl thiodipropionate or octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate. More preferably, the antioxidant comprises at least one of tris(2,4-di-tert-butylphenyl)phosphite (antioxidant 168), pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1010), distearyl thiodipropionate or β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076).

[0040] Preferably, the polyester resin comprises the following raw materials: 32 to 39 parts of polyol, 42 to 58 parts of polyacid, 4 to 18 parts of acidolysis agent, 0.3 to 1.8 parts of chain extender, and 0.03 to 0.18 parts of auxiliary agent; further preferably, the polyester resin comprises the following raw materials: 34 to 38 parts of polyol, 45 to 57 parts of polyacid, 5 to 16 parts of acidolysis agent, 0.5 to 1.5 parts of chain extender, and 0.05 to 0.15 parts of auxiliary agent.

[0041] Preferably, the acid value of the polyester resin is 40 to 60 mgKOH / g; more preferably, it is 45 to 55 mgKOH / g.

[0042] Preferably, the hydroxyl value of the polyester resin is ≤8 mgKOH / g; more preferably, it is 1 to 5 mgKOH / g.

[0043] Preferably, the glass transition temperature of the polyester resin is 60 to 75°C; more preferably 62 to 72°C.

[0044] Preferably, the polyester resin has a melt viscosity at 200° C. of 5000 to 10000 mPa.s; more preferably, 5500 to 9500 mPa.s.

[0045] Preferably, the reactivity of the polyester resin at 180° C. is 150 to 270 s; more preferably, it is 155 to 265 s.

[0046] The second aspect of the present invention provides a method for preparing the polyester resin according to the first aspect of the present invention, comprising the following steps:

[0047] 1) mixing polyol, polyacid and auxiliary agent, and carrying out esterification reaction to obtain esterification product;

[0048] 2) adding an acidolysis agent to the esterification product to carry out an acidolysis reaction to obtain an acidolysis product;

[0049] 3) subjecting the acid hydrolysis product to a vacuum polycondensation reaction to obtain a primary polyester resin product;

[0050] 4) Adding a chain extender to the polyester resin primary product to carry out a chain extension reaction to obtain a polyester resin.

[0051] Preferably, the specific process of step 1) is: mixing the polyol, the auxiliary agent and part of the polyacid to carry out a first esterification reaction; then adding the remaining polyacid to carry out a second esterification reaction to obtain an esterified product.

[0052] Through the step-by-step esterification of polyacids, the reaction process of monomers with larger steric hindrance can be promoted to proceed in the forward direction, and the positional distribution of different monomers in the molecule can be reasonably adjusted, so that the prepared polyester has better performance.

[0053] Preferably, the process of the first esterification reaction is: heating to 175-185°C within 0.5-1.5h, then heating to 205-215°C within 0.5-1.5h, then heating to 215-225°C within 0.5-1.5h, and finally heating to 240-250°C within 1-2h, and keeping warm for 1-2h; further preferably, the process of the first esterification reaction is: heating to 178-182°C within 1h, then heating to 208-212°C within 1h, then heating to 218-222°C within 1h, and finally heating to 240-250°C within 1.5h, and keeping warm for 1-2h.

[0054] Preferably, the temperature of the second esterification reaction is 230-260°C; more preferably 240-250°C.

[0055] Preferably, in step 2), the acidolysis reaction is carried out until the acid value of the acidolysis product is 40 to 60 mgKOH / g; more preferably 45 to 55 mgKOH / g.

[0056] Preferably, in step 2), the temperature of the acid hydrolysis reaction is 230-250°C; more preferably 235-245°C.

[0057] Preferably, in step 2), the acid hydrolysis reaction time is 1 to 5 hours; more preferably 2 to 4 hours.

[0058] Preferably, in step 3), the vacuum polycondensation reaction is carried out until the acid value of the polyester resin primary product is 30-50 mgKOH / g, the hydroxyl value is less than 8 mgKOH / g, and the melt viscosity at 200°C is 5000-10000 mPa.s; more preferably, it is 35-45 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200°C is 5500-9500 mPa.s.

[0059] Preferably, in step 3), the vacuum degree of the vacuum polycondensation reaction is -0.08 to -0.1 MPa; more preferably, it is -0.088 to -0.098 MPa.

[0060] Preferably, in step 3), the vacuum polycondensation reaction time is 0.5 to 4 hours; more preferably, it is 1 to 3 hours.

[0061] Preferably, the auxiliary agent added in step 1) is a partial auxiliary agent, and step 4) further comprises a step of cooling and adding the remaining auxiliary agent after the chain extension reaction is completed; further preferably, the auxiliary agent added in step 1) comprises an esterification catalyst, and the auxiliary agent added after the chain extension reaction in step 4) comprises a curing catalyst and an antioxidant.

[0062] Preferably, in step 4), the temperature of the step of cooling down and adding the remaining additives after the chain extension reaction is completed is 160-220°C; more preferably 170-210°C.

[0063] The third aspect of the present invention provides a powder coating, wherein the raw materials for preparing the powder coating include the polyester resin described in the first aspect of the present invention, or the polyester resin prepared by the preparation method described in the second aspect of the present invention.

[0064] Preferably, the mass percentage of the polyester resin in the raw material for preparing the powder coating is 40 to 70%; more preferably 45 to 65%; and even more preferably 50 to 60%.

[0065] Preferably, the raw materials for preparing the powder coating further include a curing agent, a filler and a functional additive.

[0066] Preferably, the curing agent is selected from isocyanate curing agents; further preferably, the curing agent is selected from triglycidyl isocyanurate (TGIC).

[0067] Preferably, the filler includes barium sulfate, titanium dioxide or a combination thereof; further preferably, the filler includes barium sulfate and titanium dioxide.

[0068] Preferably, the functional additive includes at least one of a leveling agent, a defoaming agent or a brightening agent; further preferably, the functional additive includes a leveling agent, a defoaming agent and a brightening agent.

[0069] In some specific embodiments of the present invention, the leveling agent is selected from silicone leveling agents, the defoaming agent is selected from benzoin, and the brightener is selected from acrylic copolymer brighteners.

[0070] A fourth aspect of the present invention provides a workpiece, comprising a substrate and a coating provided on the surface of the substrate; the coating is formed by the powder coating according to claim 9; and the thickness of the coating is 60 to 100 μm.

[0071] Preferably, the thickness of the coating is 65 to 95 μm; more preferably, 70 to 90 μm.

[0072] The beneficial effects of the present invention are as follows: the present invention combines specific polyacids and polyols to make the prepared polyester resin have suitable acid value, melt viscosity, glass transition temperature and reaction activity, which is beneficial to improve the weather resistance, leveling, mechanical properties and gas-liquid barrier properties of the powder coating; and combined with the use of epoxy-containing chain extenders, the surface tension of the polyester resin is reduced, which is beneficial to enhance the compatibility between polymer segments in the coating film and between the resin and the filler during the film forming process, further improve the gas-liquid barrier properties of the coating film, and at the same time make the coating film have strong adhesion to substrates of different materials, so as to have extremely strong corrosion resistance to neutral salt spray. In addition, the polyester resin preparation process of the present invention is simple, the synthetic raw materials are widely available, the cost is low, and it is conducive to large-scale industrial production. DETAILED DESCRIPTION

[0073] The content of the present invention is further described in detail below through specific examples. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles set forth in the present invention all belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific data exemplified below. The raw materials, reagents or devices used in the following examples and comparative examples, unless otherwise specified, can all be obtained from conventional commercial sources, or can be obtained by existing known methods.

[0074] Polyester resin example 1

[0075] A polyester resin, specific raw materials are shown in Table 1.

[0076] The preparation steps of polyester resin in this example are as follows:

[0077] 1) Add polyols in the reaction kettle according to the ratio in Table 1, heat until the material melts, then add polyacid I and esterification catalyst, and heat to 180°C within 1 hour under nitrogen protection, then heat to 210°C within 1 hour, heat to 220°C within 1 hour, and heat to 240-250°C within 1.5 hours, and keep warm for 1.5 hours. When the sampled material is clear or only a small amount of particles are present, add polyacid II and continue to keep warm until the sample reaches the clear point and the acid value reaches 6-9 mgKOH / g to obtain the esterification product;

[0078] 2) Under the protection of nitrogen, an acidolysis agent was added to the esterification product to carry out an acidolysis reaction at 240° C. for 2.5 hours to obtain an acidolysis product with an acid value of 46-49 mgKOH / g;

[0079] 3) subjecting the acidolysis product to a polycondensation reaction at a vacuum degree of -0.096 MPa for 1 hour, wherein the acid value reaches 38-40 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 6900-7800 mPa.s, thereby obtaining a polycondensation product;

[0080] 4) Cool down to 205°C, add chain extender, and stir for 20 minutes;

[0081] 5) Cooling to 180° C., then adding a curing catalyst and an antioxidant and stirring and dispersing them evenly to obtain a polyester resin.

[0082] Polyester resin example 2

[0083] A polyester resin, specific raw materials are shown in Table 1.

[0084] The preparation steps of polyester resin in this example are as follows:

[0085] 1) Add polyols in the reaction kettle according to the ratio in Table 1, heat until the material melts, then add polyacid I and esterification catalyst, and heat to 180°C within 1 hour under nitrogen protection, then heat to 210°C within 1 hour, heat to 220°C within 1 hour, and heat to 240-250°C within 1.5 hours, and keep warm for 1.5 hours. When the sampled material is clear or only a small amount of particles are present, add polyacid II and continue to keep warm until the sample reaches the clear point and the acid value reaches 4-7 mgKOH / g to obtain the esterification product;

[0086] 2) Under the protection of nitrogen, an acidolysis agent was added to the esterification product to carry out an acidolysis reaction at 240° C. for 2.5 hours to obtain an acidolysis product with an acid value of 44-46 mgKOH / g;

[0087] 3) subjecting the acidolysis product to a polycondensation reaction at a vacuum degree of -0.096 MPa for 1 hour, wherein the acid value reaches 35-37 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 5500-6800 mPa.s, thereby obtaining a polycondensation product;

[0088] 4) Cool down to 210°C, add chain extender, and stir for 20 minutes;

[0089] 5) Cooling to 200° C., then adding a curing catalyst and an antioxidant and stirring and dispersing them evenly to obtain a polyester resin.

[0090] Polyester resin example 3

[0091] A polyester resin, specific raw materials are shown in Table 1.

[0092] The preparation steps of polyester resin in this example are as follows:

[0093] 1) Add polyols in the reaction kettle according to the ratio in Table 1, heat until the material melts, then add polyacid I and esterification catalyst, and heat to 180°C within 1 hour under nitrogen protection, then heat to 210°C within 1 hour, heat to 220°C within 1 hour, and heat to 240°C within 1.5 hours, and keep warm for 1 hour. When the sampled material is clear or has only a small amount of particles, add polyacid II and continue to keep warm until the sample reaches the clear point and the acid value reaches 13-18 mgKOH / g to obtain the esterification product;

[0094] 2) Under the protection of nitrogen, an acidolysis agent is added to the esterification product to carry out an acidolysis reaction at 240° C. for 2.5 hours to obtain an acidolysis product with an acid value of 47-50 mgKOH / g;

[0095] 3) subjecting the acidolysis product to a polycondensation reaction at a vacuum degree of -0.096 MPa for 1 hour, wherein the acid value reaches 37-39 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 7100-8000 mPa.s, thereby obtaining a polycondensation product;

[0096] 4) Cool down to 205°C, add chain extender, and stir for 20 minutes;

[0097] 5) Cooling to 195° C., then adding a curing catalyst and an antioxidant and stirring and dispersing them evenly to obtain a polyester resin.

[0098] Polyester resin example 4

[0099] A polyester resin, specific raw materials are shown in Table 1.

[0100] The preparation steps of polyester resin in this example are as follows:

[0101] 1) Add polyols in the reaction kettle according to the ratio in Table 1, heat until the material melts, then add polyacid and esterification catalyst, and heat to 180°C within 1 hour under nitrogen protection, then heat to 210°C within 1 hour, heat to 220°C within 1 hour, and heat to 240°C within 1.5 hours, and keep warm for 1 hour. When the sampled material is clear or has only a small amount of particles, add polyacid II and continue to keep warm until the sample reaches the clear point and the acid value reaches 5-8 mgKOH / g to obtain the esterification product;

[0102] 2) Under the protection of nitrogen, an acidolysis agent was added to the esterification product to carry out an acidolysis reaction at 240° C. for 2.5 hours to obtain an acidolysis product with an acid value of 53-55 mgKOH / g;

[0103] 3) subjecting the acidolysis product to a polycondensation reaction at a vacuum degree of -0.096 MPa for 1 hour, wherein the acid value reaches 43-45 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 5600-6500 mPa.s, thereby obtaining a polycondensation product;

[0104] 4) Cool down to 200°C, add chain extender, and stir for 20 minutes;

[0105] 5) Cooling to 190° C., then adding a curing catalyst and an antioxidant and stirring and dispersing them evenly to obtain a polyester resin.

[0106] Polyester resin example 5

[0107] A polyester resin, specific raw materials are shown in Table 1.

[0108] The preparation steps of polyester resin in this example are as follows:

[0109] 1) Add polyols according to the proportion of Example 5 in Table 1 to a reaction kettle, heat until the material is melted, then add polyacids and esterification catalysts, and heat to 180° C. within 1 hour under nitrogen protection, then heat to 210° C. within 1 hour, heat to 220° C. within 1 hour, and heat to 240° C. within 1.5 hours, and keep warm for 1 hour. When the sampled material is clear or has only a small amount of particles, add polyacid II and continue to keep warm until the sample reaches a clear point and the acid value reaches 18-20 mgKOH / g, to obtain an esterification product;

[0110] 2) Under the protection of nitrogen, an acidolysis agent was added to the esterification product to carry out an acidolysis reaction at 240° C. for 2.5 hours to obtain an acidolysis product with an acid value of 47-49 mgKOH / g;

[0111] 3) subjecting the acidolysis product to a polycondensation reaction at a vacuum degree of -0.096 MPa for 1 hour, wherein the acid value reaches 35-37 mgKOH / g, the hydroxyl value is less than 5 mgKOH / g, and the melt viscosity at 200° C. is 6500-7300 mPa.s, thereby obtaining a polycondensation product;

[0112] 4) Cool down to 200°C, add chain extender, and stir for 20 minutes;

[0113] 5) Cooling to 190° C., then adding a curing catalyst and an antioxidant and stirring and dispersing them evenly to obtain a polyester resin.

[0114] Polyester resin comparative example 1

[0115] A polyester resin, specific raw materials are shown in Table 1.

[0116] The difference between the preparation steps of the polyester resin in this example and that in Example 1 is that step 4) is omitted in this example, and the other steps are the same as those in Example 1.

[0117] Polyester resin comparative example 2

[0118] A polyester resin, specific raw materials are shown in Table 1.

[0119] The difference between the preparation steps of the polyester resin in this example and that in Example 2 is that step 4) is omitted in this example, and the other steps are the same as those in Example 2.

[0120] Polyester resin comparative example 3

[0121] A polyester resin, specific raw materials are shown in Table 1.

[0122] The difference between the preparation steps of the polyester resin in this example and Example 1 is that in step 1) of this example, there is no step of adding polyacid II, that is, the polyacid is added at one time, and the other steps are the same as Example 1.

[0123] Polyester resin comparative example 4

[0124] A polyester resin, specific raw materials are shown in Table 1.

[0125] The difference between the preparation steps of the polyester resin in this example and that in Example 2 is that step 4) is omitted in this example, and the other steps are the same as those in Example 2.

[0126] Table 1 Raw materials and dosage of polyester resin examples 1 to 5 and polyester resin comparative examples 1 to 4 (unit: g)

[0127]

[0128]

[0129] Powder coating examples 1 to 5 and powder coating comparative examples 1 to 4

[0130] Powder coating examples 1 to 5 and powder coating comparative examples 1 to 4 each provide a powder coating, and the specific preparation process is as follows:

[0131] The polyester resins prepared from polyester resin examples 1 to 5 and polyester resin comparative examples 1 to 4 were weighed and mixed with curing agent TGIC, leveling agent GLP588, titanium dioxide, barium sulfate, benzoin and brightener 701 according to the proportions in Table 2 below, melt-extruded, tableted and crushed by a screw extruder, and then the tablets were crushed and sieved to obtain powder coatings.

[0132] Table 2 Raw materials and dosage of powder coating examples 1 to 5 and powder coating comparative examples 1 to 4 (unit: g)

[0133]

[0134]

[0135] Performance Testing

[0136] 1) For the polyester resins obtained in polyester resin examples 1 to 5 and polyester resin comparative examples 1 to 4: the acid value, viscosity, glass transition temperature and reactivity were tested according to T / GDTL004-2019; the hydroxyl value was tested according to GB / T12008.3-2009. The test results are shown in Table 3.

[0137] 2) The powder coatings prepared from the powder coating examples 1 to 5 and the powder coating comparative examples 1 to 4 were electrostatically sprayed on 0.5 mm degreased and derusted cold-rolled steel plates, and cured at 200° C. for 10 min to obtain a 70-90 μm powder coating, and the following performance tests were performed:

[0138] (1) PCI leveling grade is tested by visual comparison with the PCI standard.

[0139] (2) Gloss is tested according to GB / T 9754-2007;

[0140] (3) The bending test is carried out in accordance with GB / T 6742-2007;

[0141] (4) Impact test is carried out according to GB / T 1732-2020;

[0142] (5) Adhesion is tested according to GB / T 9286-2021;

[0143] (6) Neutral salt spray test is conducted according to ISO 7253:1996;

[0144] The test results are shown in Table 4.

[0145] Table 3 Test results of polyester resin examples 1 to 5 and polyester resin comparative examples 1 to 4

[0146]

[0147]

[0148] Table 4 Test results of powder coating examples 1 to 5 and powder coating comparative examples 1 to 4

[0149]

[0150] It can be seen from Tables 3 and 4 that the polyester resin provided in the embodiment of the present invention has a suitable acid value, melt viscosity, glass transition temperature and reaction activity, and the powder coating prepared therefrom has excellent leveling and mechanical properties, still has good adhesion after a 500h neutral salt spray test, and has good gas-liquid barrier properties, so that the sodium chloride solution in the test cannot penetrate into the coating and the substrate from the coating or the scratch damage to cause corrosion expansion, and the coating exhibits extremely strong corrosion resistance to neutral salt spray corrosion.

[0151] In the present invention, the specific selection of the side-group-containing aliphatic polyol monomer needs to balance the side chain volume and the reactivity of the monomer functional group. The 2-butyl-2-ethyl-1,3-propanediol used in the embodiment of the present invention has a more suitable side chain volume and monomer functional group reactivity. It is combined with other polyols such as trimethylolpropane and neopentyl glycol, and reacts with a specific polyacid to obtain a polyester resin with a more suitable acid value, melt viscosity, glass transition temperature and reactivity. Polyester resin comparative example 1 and polyester resin comparative example 2 do not add rigid condensed ring monomer 2,6-naphthalene dicarboxylic acid, nor do they add chain extenders, and the appearance performance, impact performance and salt spray resistance of the obtained powder coating are poor. The difference between polyester resin comparative example 4 and polyester resin comparative example 2 is that polyester resin comparative example 4 also adds rigid condensed ring monomer 2,6-naphthalene dicarboxylic acid, and in the obtained powder coating, powder coating comparative example 4 has better appearance performance, leveling performance and salt spray resistance than powder coating comparative example 2.

[0152] In addition, in the preparation method of the polyester resin of the present invention, the reaction process of the monomer with larger steric hindrance can be promoted to proceed in the forward direction by the step-by-step esterification of the polyacid, and the position distribution of different monomers in the molecule can be reasonably adjusted, so that the prepared polyester has better performance. The polyester resin comparative example 3 was not subjected to the step-by-step esterification of the polyacid, and the obtained powder coating had poor bending performance, impact performance, adhesion performance and salt spray resistance.

[0153] In summary, the present invention combines specific polyacids and polyols to make the prepared polyester resin have suitable acid value, melt viscosity, glass transition temperature and reaction activity, which is beneficial to improve the weather resistance, leveling, mechanical properties and gas-liquid barrier properties of the powder coating; and combined with the use of epoxy-containing chain extenders, the surface tension of the polyester resin is reduced, which is beneficial to enhance the compatibility between polymer segments in the coating and between the resin and the filler during the film forming process, further improve the gas-liquid barrier properties of the coating, and at the same time make the coating have strong adhesion to substrates of different materials, so as to have extremely strong corrosion resistance to neutral salt spray. In addition, the polyester resin preparation process of the present invention is simple, the synthetic raw materials are widely available, the cost is low, and it is conducive to large-scale industrial production.

Claims

1. A polyester resin, characterized in that The invention comprises the following raw materials in parts by weight: 30 to 40 parts of polyol, 40 to 60 parts of polyacid, 3 to 20 parts of acidolysis agent, 0.1 to 2 parts of chain extender and 0.01 to 0.2 parts of auxiliary agent; the polyol comprises aliphatic polyol containing side groups; the polyacid comprises monocyclic aromatic polyacid and condensed-ring aromatic polyacid; the chain extender is selected from polymers containing epoxy groups.

2. The polyester resin according to claim 1, characterized in that The side-group-containing aliphatic polyol is a C4-C20 side-group-containing aliphatic polyol; the side-group-containing aliphatic polyol includes at least one of a side-group-containing aliphatic diol, a side-group-containing aliphatic triol or a side-group-containing aliphatic tetraol; preferably, the side-group-containing aliphatic polyol includes at least one of neopentyl glycol, isoprene glycol, 2-butyl-2-ethyl-1,3-propanediol, trimethylolethane or trimethylolpropane; And / or, the condensed ring aromatic polyacid includes at least one of naphthyl polyacid, anthracene polyacid or phenanthrene polyacid; preferably, the condensed ring aromatic polyacid includes at least one of 2,6-naphthalene dicarboxylic acid, 2,3-naphthalene dicarboxylic acid, 1,8-naphthalene dicarboxylic acid, 1,4-anthracene dicarboxylic acid, 9,10-anthracene dicarboxylic acid or 2,7-phenanthrene dicarboxylic acid; And / or, the monocyclic aromatic polyacid is selected from phenyl polyacid; preferably, the monocyclic aromatic polyacid includes at least one of terephthalic acid, isophthalic acid or phthalic acid.

3. The polyester resin according to claim 1, characterized in that The polyol comprises the following components in parts by mass: 75 to 100 parts of neopentyl glycol, 0 to 15 parts of 2-butyl-2-ethyl-1,3-propanediol, and 0 to 5 parts of trimethylolpropane; And / or, the polyacid comprises the following components in parts by mass: 60 to 100 parts of terephthalic acid, 0 to 20 parts of isophthalic acid, and 0 to 20 parts of 2,6-naphthalene dicarboxylic acid.

4. The polyester resin according to claim 1, characterized in that The polyol further comprises a linear aliphatic polyol; preferably, the linear aliphatic polyol comprises at least one of ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, 1,5-pentanediol or 1,6-hexanediol; And / or, the polyacid further comprises an aliphatic polyacid; preferably, the aliphatic polyacid comprises at least one of succinic acid, glutaric acid, adipic acid, pimelic acid or suberic acid.

5. The polyester resin according to claim 1, characterized in that The acidolysis agent includes isophthalic acid, adipic acid or a combination thereof; preferably, at least one of the polyacids or acidolysis agents includes isophthalic acid, and the mass percentage of isophthalic acid in the raw material for preparing the polyester resin is 3 to 22%; and / or, the chain extender comprises at least one of ethylene-methyl acrylate-glycidyl methacrylate, ethylene-ethyl acrylate-glycidyl methacrylate, ethylene-butyl acrylate-glycidyl methacrylate, ethylene-methyl methacrylate-glycidyl methacrylate, ethylene-ethyl methacrylate-glycidyl methacrylate or ethylene-butyl methacrylate-glycidyl methacrylate; And / or, the auxiliary agent includes an esterification catalyst, a curing catalyst and an antioxidant.

6. A method for preparing a polyester resin according to any one of claims 1 to 5, characterized in that: The following steps are involved: 1) mixing polyol, polyacid and auxiliary agent, and carrying out esterification reaction to obtain esterification product; 2) adding an acidolysis agent to the esterification product to carry out an acidolysis reaction to obtain an acidolysis product; 3) subjecting the acid hydrolysis product to a vacuum polycondensation reaction to obtain a primary polyester resin product; 4) Adding a chain extender to the polyester resin primary product to carry out a chain extension reaction to obtain a polyester resin.

7. The preparation method according to claim 6, characterized in that: The specific process of step 1) is: mixing the polyol, the auxiliary agent and part of the polyacid to carry out a first esterification reaction; then adding the remaining polyacid to carry out a second esterification reaction to obtain an esterified product; Preferably, the process of the first esterification reaction is: heating to 175-185°C within 0.5-1.5h, then heating to 205-215°C within 0.5-1.5h, then heating to 215-225°C within 0.5-1.5h, and finally heating to 240-250°C within 1-2h, and keeping warm for 1-2h; and / or, the temperature of the second esterification reaction is 230-260°C.

8. The preparation method according to claim 6, characterized in that: In step 2), the acid hydrolysis reaction is carried out until the acid value of the acid hydrolysis product is 40 to 60 mgKOH / g; And / or, in step 2), the temperature of the acid hydrolysis reaction is 230-250°C; And / or, in step 2), the acid hydrolysis reaction time is 1 to 5 hours; And / or, in step 3), the vacuum polycondensation reaction is carried out until the acid value of the polyester resin primary product is 30-50 mgKOH / g, the hydroxyl value is less than 8 mgKOH / g, and the melt viscosity at 200° C. is 5000-10000 mPa.s; And / or, in step 3), the vacuum degree of the vacuum polycondensation reaction is -0.08 to -0.1 MPa; And / or, in step 3), the vacuum polycondensation reaction time is 0.5 to 4 hours.

9. A powder coating, characterized in that: The raw material for preparing the powder coating comprises the polyester resin described in any one of claims 1 to 5, or the polyester resin prepared by the preparation method described in any one of claims 6 to 8.

10. A workpiece, characterized in that: The workpiece comprises a substrate and a coating disposed on the surface of the substrate; the coating is formed by the powder coating according to claim 9; and the thickness of the coating is 60 to 100 μm.

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