Water-soluble polyester resin and preparation method thereof

Abstract

The invention relates to the technical field of polyester processes, in particular to water-soluble polyester resin and a preparation method thereof. The invention relates to a water-soluble polyester resin, which is prepared from dibasic acid, aliphatic dihydric alcohol, alicyclic dihydric alcohol, dimethylolpropionic acid, bis (2-hydroxyethyl) isophthalate-5-sodium sulfonate, single-ended dihydroxy polydimethylsiloxane and the like, and the alicyclic dihydric alcohol comprises 1, 4-cyclohexanedimethanol and cyclohexanediol. Single-ended dihydroxy polydimethylsiloxane and trimellitic anhydride react to prepare a siloxane modified segment, distribution of an organosilicon chain segment on a polyester main chain can be controlled, dense side chain modified waterborne polyester is formed, then the dense side chain modified waterborne polyester is introduced into a polyester reaction system, and the high-temperature-resistant waterborne polyester is obtained. The organic silicon side chains of the modified waterborne polyester resin are densely concentrated in some areas in a polyester chain segment, so that the organic silicon enrichment degree on the surface of an adhesive film is far higher than that of the corresponding random side chain modified waterborne polyester, a continuous hydrophobic layer is formed, and the surface hydrophobicity of the prepared coating is improved.

Description

Technical Field

[0001] The invention relates to the technical field of polyester technology, and in particular to a water-soluble polyester resin and a preparation method thereof. Background Art

[0002] Waterborne polyester resin is an environmentally friendly resin, commonly used in waterborne coatings, adhesives and other fields. Compared with traditional solvent-based resins, waterborne polyester resins have lower VOC emissions, better safety and environmental friendliness. When used to prepare waterborne coatings, waterborne polyester resins are usually formulated with amino resin curing agents, titanium dioxide, additives and other raw materials to form coatings, such as waterborne polyester coil coatings. At the same time, the formed coating film has the advantages of solvent-based high gloss, high adhesion, high hardness and good weather resistance. However, there are easily hydrolyzed ester bonds in the water-based polyester molecular chain and poor storage stability, resulting in poor hydrophobicity on the coating surface. Therefore, silicone is usually used to graft and modify the water-soluble polyester resin to improve its water resistance. Silicone is rich in Si-O bonds and has low surface energy. It can be enriched on the film surface during film formation to form a stable protective layer rich in Si-O-Si chains, thereby improving the water resistance of the modified polymer coating. However, there is a problem of poor compatibility when grafting silicone into the water-based polyester molecular chain. Therefore, silane coupling agent surface treatment is usually used to increase the compatibility between polyester and silicone.

[0003] Patent CN106220838B discloses a hydrophobic and heat-resistant silicone-modified polyester resin and a preparation method thereof. In its background technology, it is mentioned that a silane coupling agent is generally used to increase the compatibility of silicone and polyester and improve the stability of the blending system; it is also mentioned that the chemical modification method of silicone-modified polyester is to connect the polyester resin to the end or side chain of the polyorganosiloxane main chain through a condensation reaction to form a block, graft or interpenetrating network copolymer, and the two polymers with large polarity differences are combined together by chemical bonds.

[0004] However, in the organosilicon-modified water-soluble polyester resin of patent CN106220838B, an organosilicon monomer containing a hydrolyzable alkoxy group is used. Due to the randomness of the hydrolysis reaction of the alkoxy group, a random side chain-modified water-based polyester is formed, and the organosilicon segments are unevenly distributed on the polyester main chain. Some organosilicon segments may be trapped inside the coating and cannot effectively migrate to the surface, resulting in a low degree of organosilicon enrichment on the film surface, resulting in insufficient hydrophobicity on the coating surface. In addition, patent CN108623797B discloses a water-soluble organosilicon-modified polyester resin and a water-soluble coating. In its background technology, it is mentioned that the water-soluble organosilicon-modified polyester resin in the prior art has a low transparency and is generally in a relatively turbid state, or can only meet one performance index requirement, and cannot simultaneously meet the requirements of heat resistance, good transparency, and good water solubility. Therefore, a water-soluble polyester resin and a preparation method thereof are needed to solve the above problems. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a water-soluble polyester resin and a preparation method thereof.

[0006] A water-soluble polyester resin is composed of the following raw materials in parts by weight: 40-70 parts of dibasic acid, 20-40 parts of aliphatic diol, 5-20 parts of alicyclic diol, 5-10 parts of dihydroxymethylpropionic acid, 1-3 parts of sodium bis(hydroxyethyl)-5-sulfonate isophthalate (SIPE), 5-10 parts of single-ended bis(hydroxy)polydimethylsiloxane (α, α-PDMS), 0.1-0.5 parts of dibutyltin dilaurate and 0.2-0.5 parts of antioxidant.

[0007] Furthermore, the dibasic acid includes one or more of terephthalic acid, isophthalic acid, maleic acid, dodecane dibasic acid (DCA) and phthalic acid (PA); the aliphatic diol includes one or more of 1,3-propylene glycol, 1,5-pentanediol, 1,6-hexanediol and ethylene glycol, and the alicyclic diol is 1,4-cyclohexanedimethanol or cyclohexanediol.

[0008] More specifically, the dibasic acid comprises 20-30 parts of terephthalic acid, 10-20 parts of isophthalic acid and 0-20 parts of maleic acid, by weight.

[0009] Specifically, based on weight, the aliphatic diol includes 15-25 parts of 1,3-propylene glycol and 5-10 parts of 1,6-hexanediol, and the alicyclic diol includes 10-15 parts of 1,4-cyclohexanedimethanol.

[0010] Furthermore, the average molecular weight of the single-ended dihydroxy polydimethylsiloxane is 3200 Da.

[0011] Specifically, the single-terminated bis-hydroxy polydimethylsiloxane is first reacted with trimellitic anhydride to synthesize a siloxane-modified segment, and then introduced into the polyester reaction system according to the weight proportion of the single-terminated bis-hydroxy polydimethylsiloxane.

[0012] Furthermore, the antioxidant is triphenyl phosphate.

[0013] A method for preparing a water-soluble polyester resin comprises the following steps: S1. Alkyd polycondensation reaction: add dibasic acid, aliphatic diol and dibutyltin dilaurate into a reaction kettle in proportion, raise the temperature to 200-220°C, and maintain the polycondensation reaction for 3-5 hours under nitrogen protection until the acid value drops below 30 mg KOH / g to obtain polyester polyol; S2, introducing aqueous monomers: adding dimethylol propionic acid and sodium bis(hydroxyethyl)-5-sulfonate isophthalate to the polyester polyol in proportion at 150-160° C., and continuing the reaction for 1-2 hours until the monomers are completely dissolved to form a polyester reaction system; S3, polysiloxane modification: add single-end dihydroxy polydimethylsiloxane to the reactor, add organic bismuth catalyst, stir and heat to 100°C, slowly add trimellitic anhydride, keep warm and react for 3 hours after the addition, to prepare siloxane modified fragments; slowly add the siloxane modified fragments to the polyester reaction system and evenly disperse them, and continue to react at 150°C for 3-5 hours; S4, alicyclic diol integration: continue to add alicyclic diol into the reaction system, react until it is completely dissolved to form a uniform polymer; S5. Neutralization and water solubility adjustment: cool the reaction product to 60-80°C, use a neutralizer to neutralize the reaction system, adjust the pH value to 7.0-8.0, add an antioxidant, dilute with deionized water as needed, adjust the viscosity, cool the reaction product to room temperature, filter to remove impurities, and obtain a water-soluble polyester resin.

[0014] Furthermore, the neutralizing agent is dimethylethanolamine or triethylamine.

[0015] Furthermore, in the process of preparing the siloxane modified fragment, acetone is added to reduce viscosity as needed during the reaction process, wherein the molar ratio of the single-ended bishydroxy polydimethylsiloxane to trimellitic anhydride is 1:1, and the amount of the organic bismuth catalyst is 0.01% of the total weight of the single-ended bishydroxy polydimethylsiloxane and trimellitic anhydride.

[0016] The beneficial effects achieved by the present invention are as follows: 1. The present invention uses a single-terminal bis-hydroxy polydimethylsiloxane to react with trimellitic anhydride to obtain a siloxane-modified segment, which can control the distribution of the organic silicon segment on the polyester main chain to form a dense side chain modified waterborne polyester, which is then introduced into the polyester reaction system to form a modified waterborne polyester resin in which the organic silicon side chains are densely concentrated in certain areas of the polyester segment, so that the organic silicon enrichment degree on the film surface is much higher than that of the corresponding random side chain modified waterborne polyester; the single-terminal bis-hydroxy polydimethylsiloxane is a linear polysiloxane, and the hydroxyl groups at both ends of the single-terminal bis-hydroxy polydimethylsiloxane react with trimellitic anhydride to form an ester bond, which is easy to combine with other polymer segments, so that the distribution of the organic silicon segment on the polyester main chain is more uniform, and it is easier to migrate to the surface of the prepared coating to form a continuous hydrophobic layer, thereby improving the hydrophobicity of the coating surface; At the same time, the excellent heat resistance and chemical stability of the siloxane chain segment are utilized to improve the heat resistance of the resin. The uniform dispersion and enrichment effect of the silicone chain segment can reduce phase separation and improve the transparency of the film. A variety of hydrophilic monomers are used to improve the water solubility and dispersibility of the resin. The rigid structure of the alicyclic diol is utilized to reduce the disordered arrangement of the molecular chains to improve the transparency and heat resistance of the resin, thereby achieving a good balance between transparency, heat resistance and water solubility of the water-soluble polyester resin.

[0017] 2. The present invention forms ester bonds and retains hydroxyl groups by reacting dimethylol propionic acid with polyacids and polyols, and introduces sulfonic acid groups using sodium bis(hydroxyethyl)-5-sulfonate isophthalate, which can form ionic bonds in water, thereby increasing the hydrophilicity and water solubility of the resin.

[0018] 3. The present invention utilizes the lower surface energy and higher migration ability of the organosilicon chain segments, which will preferentially migrate to the surface of the film during the film-forming process. The organosilicon layer formed on the surface of the film can improve the surface properties of the film and enhance the hydrophobicity, weather resistance and wear resistance of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic flow chart of the preparation method of the water-soluble polyester resin. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0021] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0023] In the following examples, the preparation method of the siloxane-modified fragment is as follows: adding single-ended bishydroxy polydimethylsiloxane (α, α-PDMS, Mn=3200) into a reactor, adding an organic bismuth catalyst (bismuth octanoate), stirring and heating to 100°C, slowly dripping trimellitic anhydride, and keeping the temperature for 3 hours after the dripping is completed to prepare the siloxane-modified fragment, wherein the molar ratio of single-ended bishydroxy polydimethylsiloxane to trimellitic anhydride is 1:1, and the amount of the organic bismuth catalyst is 0.01% of the total weight of the single-ended bishydroxy polydimethylsiloxane and trimellitic anhydride.

[0024] Embodiment 1: A water-soluble polyester resin is composed of the following raw materials in parts by weight: 25 parts of terephthalic acid, 15 parts of isophthalic acid, 15 parts of maleic acid, 20 parts of 1,3-propylene glycol, 12 parts of 1,4-cyclohexanedimethanol, 7 parts of 1,6-hexanediol, 7 parts of dimethylolpropionic acid, 2 parts of sodium bis(hydroxyethyl)isophthalate-5-sulfonate, 8 parts of single-end bis(hydroxy)polydimethylsiloxane, 0.3 parts of dibutyltin dilaurate and 0.3 parts of triphenyl phosphate.

[0025] A method for preparing a water-soluble polyester resin, such as Figure 1 As shown, the following steps are included: S1. Alkyd polycondensation reaction: According to the raw material formula, terephthalic acid, isophthalic acid, maleic acid, 1,3-propylene glycol, 1,6-hexanediol and dibutyltin dilaurate were added into a reaction kettle, the temperature was raised to 210°C, and the polycondensation reaction was maintained for 4 hours under nitrogen protection until the acid value dropped below 30 mg KOH / g to obtain polyester polyol; S2, introducing aqueous monomers: at 155° C., adding dimethylolpropionic acid and sodium bis(hydroxyethyl)-5-sulfonate isophthalate to the polyester polyol in proportion, and continuing the reaction for 1.5 hours until the monomers are completely dissolved, thereby forming a polyester reaction system; S3, polysiloxane modification: slowly add the siloxane modified fragment into the polyester reaction system and evenly disperse it, and continue to react at 150°C for 4 hours; S4, alicyclic diol integration: continue to add 1,4-cyclohexanedimethanol into the reaction system, react until it is completely dissolved to form a uniform polymer; S5. Neutralization and water solubility adjustment: cool the reaction product to 70° C., use dimethylethanolamine to neutralize the reaction system, adjust the pH value to 7.5, add triphenyl phosphate, dilute with deionized water, adjust the viscosity, cool the reaction product to room temperature, filter to remove impurities, and obtain a water-soluble polyester resin.

[0026] Embodiment 2: A water-soluble polyester resin is composed of the following raw materials in parts by weight: 28 parts of terephthalic acid, 18 parts of isophthalic acid, 12 parts of maleic acid, 5 parts of dodecanedioic acid, 22 parts of 1,3-propylene glycol, 13 parts of 1,2-cyclohexanediol, 6 parts of 1,6-hexanediol, 3 parts of ethylene glycol, 8 parts of dihydroxymethylpropionic acid, 2.5 parts of sodium bis(hydroxyethyl)isophthalate-5-sulfonate, 9 parts of single-end bis(hydroxy)polydimethylsiloxane, 0.4 parts of dibutyltin dilaurate and 0.4 parts of triphenyl phosphate.

[0027] A method for preparing a water-soluble polyester resin, such as Figure 1 As shown, the following steps are included: S1. Alkyd polycondensation reaction: According to the raw material formula, terephthalic acid, isophthalic acid, maleic acid, dodecane dicarboxylic acid, 1,3-propylene glycol, 1,6-hexanediol, ethylene glycol and dibutyltin dilaurate were added into a reaction kettle, the temperature was raised to 215° C., and the polycondensation reaction was maintained for 4.5 hours under nitrogen protection until the acid value dropped below 30 mg KOH / g to obtain polyester polyol; S2, introducing aqueous monomers: at 155° C., adding dimethylolpropionic acid and sodium bis(hydroxyethyl)-5-sulfonate isophthalate to the polyester polyol in proportion, and continuing the reaction for 1.5 hours until the monomers are completely dissolved, thereby forming a polyester reaction system; S3, polysiloxane modification: slowly add the siloxane modified fragment into the polyester reaction system and evenly disperse it, and continue to react at 150°C for 4 hours; S4, alicyclic diol integration: continue to add 1,4-cyclohexanedimethanol into the reaction system, react until it is completely dissolved to form a uniform polymer; S5. Neutralization and water solubility adjustment: cool the reaction product to 70° C., use ethylenediamine to neutralize the reaction system, adjust the pH value to 7.5, add triphenyl phosphate, dilute with deionized water, adjust the viscosity, cool the reaction product to room temperature, filter to remove impurities, and obtain a water-soluble polyester resin.

[0028] Embodiment 3: A water-soluble polyester resin is composed of the following raw materials in parts by weight: 22 parts of terephthalic acid, 16 parts of isophthalic acid, 18 parts of maleic acid, 5 parts of phthalic acid, 23 parts of 1,3-propylene glycol, 14 parts of 1,4-cyclohexanedimethanol, 8 parts of 1,6-hexanediol, 4 parts of ethylene glycol, 9 parts of dihydroxymethylpropionic acid, 2.5 parts of sodium bis(hydroxyethyl)isophthalate-5-sulfonate, 10 parts of single-end bis(hydroxy)polydimethylsiloxane, 0.5 parts of dibutyltin dilaurate and 0.5 parts of triphenyl phosphate.

[0029] A method for preparing a water-soluble polyester resin, such as Figure 1 As shown, the following steps are included: S1. Alkyd polycondensation reaction: According to the raw material formula, terephthalic acid, isophthalic acid, maleic acid, phthalic acid, 1,3-propylene glycol, 1,6-hexanediol, ethylene glycol and dibutyltin dilaurate are added into a reaction kettle, the temperature is raised to 220° C., and the polycondensation reaction is maintained for 5 hours under nitrogen protection until the acid value drops below 30 mg KOH / g to obtain polyester polyol; S2, introducing aqueous monomers: at 160° C., adding dimethylol propionic acid and sodium bis(hydroxyethyl)-5-sulfonate isophthalate to the polyester polyol in proportion, and continuing the reaction for 2 hours until the monomers are completely dissolved to form a polyester reaction system; S3, polysiloxane modification: slowly add the siloxane modified fragment into the polyester reaction system and evenly disperse it, and continue to react at 150°C for 5 hours; S4, alicyclic diol integration: continue to add 1,4-cyclohexanedimethanol into the reaction system, react until it is completely dissolved to form a uniform polymer; S5. Neutralization and water solubility adjustment: cool the reaction product to 70° C., use dimethylethanolamine to neutralize the reaction system, adjust the pH value to 7.5, add triphenyl phosphate, dilute with deionized water, adjust the viscosity, cool the reaction product to room temperature, filter to remove impurities, and obtain a water-soluble polyester resin.

[0030] Comparative Example 1: 1,4-cyclohexanedimethanol was removed and the amount of polyol was increased.

[0031] A water-soluble polyester resin is composed of the following raw materials in parts by weight: 25 parts of terephthalic acid, 15 parts of isophthalic acid, 15 parts of maleic acid, 26 parts of 1,3-propylene glycol, 13 parts of 1,6-hexanediol, 7 parts of dihydroxymethylpropionic acid, 2 parts of sodium bis(hydroxyethyl)isophthalate-5-sulfonate, 8 parts of single-end bis(hydroxy)polydimethylsiloxane, 0.3 parts of dibutyltin dilaurate and 0.3 parts of triphenyl phosphate.

[0032] A method for preparing a water-soluble polyester resin comprises the following steps: S1. Alkyd polycondensation reaction: According to the raw material formula, terephthalic acid, isophthalic acid, maleic acid, 1,3-propylene glycol, 1,6-hexanediol and dibutyltin dilaurate were added into a reaction kettle, the temperature was raised to 210°C, and the polycondensation reaction was maintained for 4 hours under nitrogen protection until the acid value dropped below 30 mg KOH / g to obtain polyester polyol; S2, introducing aqueous monomers: at 155° C., adding dimethylolpropionic acid and sodium bis(hydroxyethyl)-5-sulfonate isophthalate to the polyester polyol in proportion, and continuing the reaction for 1.5 hours until the monomers are completely dissolved, thereby forming a polyester reaction system; S3, polysiloxane modification: slowly add the siloxane modified fragment into the polyester reaction system and evenly disperse it, and continue to react at 150°C for 4 hours; S4, neutralization and water solubility adjustment: cool the reaction product to 70°C, use dimethylethanolamine to neutralize the reaction system, adjust the pH value to 7.5, add triphenyl phosphate, dilute with deionized water, adjust the viscosity, cool the reaction product to room temperature, filter to remove impurities, and obtain a water-soluble polyester resin.

[0033] Comparative Example 2: The single-terminal dihydroxy polydimethylsiloxane was removed, that is, the siloxane-modified segment was not used, and the amount of polyol was increased.

[0034] A water-soluble polyester resin is composed of the following raw materials in parts by weight: 25 parts of terephthalic acid, 15 parts of isophthalic acid, 15 parts of maleic acid, 26 parts of 1,3-propylene glycol, 14 parts of 1,4-cyclohexanedimethanol, 13 parts of 1,6-hexanediol, 7 parts of dimethylolpropionic acid, 2 parts of sodium bis(hydroxyethyl)isophthalate-5-sulfonate, 0.3 parts of dibutyl dilauric acid and 0.3 parts of triphenyl phosphate.

[0035] A method for preparing a water-soluble polyester resin, such as Figure 1 As shown, the following steps are included: S1. Alkyd polycondensation reaction: According to the raw material formula, terephthalic acid, isophthalic acid, maleic acid, 1,3-propylene glycol, 1,6-hexanediol and dibutyl dilauric acid were added into a reaction kettle, the temperature was raised to 210°C, and the polycondensation reaction was maintained for 4 hours under nitrogen protection until the acid value dropped below 30 mg KOH / g to obtain polyester polyol; S2, introducing aqueous monomers: at 155° C., adding dimethylolpropionic acid and sodium bis(hydroxyethyl)-5-sulfonate isophthalate in proportion to the polyester polyol obtained by polycondensation, continuing the reaction for 1.5 hours until the mixture is completely dissolved to form a polyester reaction system, and continuing the reaction at 150° C. for 4 hours; S3, alicyclic diol integration: continue to add 1,4-cyclohexanedimethanol into the reaction system, react until it is completely dissolved to form a uniform polymer; S4, neutralization and water solubility adjustment: cool the reaction product to 70°C, use dimethylethanolamine to neutralize the reaction system, adjust the pH value to 7.5, add triphenyl phosphate, dilute with deionized water, adjust the viscosity, cool the reaction product to room temperature, filter to remove impurities, and obtain a water-soluble polyester resin.

[0036] The water-soluble polyester resins obtained in Examples 1-3 and Comparative Examples 1 and 2 were used to prepare water-based coatings, and relevant performance tests were performed; Preparation of water-based coatings using water-soluble polyester resins and curing methods: (1) Preparation: Add half of the water-soluble polyester resin into a high-speed disperser, add titanium dioxide, additives, and deionized water, fully wet and disperse evenly, transfer to a grinding tank and grind to a fineness of ≤15μm, transfer back to a mixing barrel, add the remaining water-soluble polyester resin and amino resin curing agent, add a leveling agent and stir for 30 minutes, add deionized water and a thickener to adjust the viscosity of the system, and prepare a water-based coating; (2) Curing: Use tinplate as the substrate, use a spray gun, brush or roller for coating, with a thickness of 30-50μm, and bake in an oven at 140℃ for 30min to form a cured coating.

[0037] 1. Transparency test: According to GB / T 2680-1994 "Determination of visible light transmittance, direct solar transmittance, total solar transmittance, ultraviolet transmittance and related window glass parameters of architectural glass", dilute the water-based paint to a certain concentration, pour it into a standard cuvette, use a UV-visible spectrometer, set the wavelength to 550 nm, put the cuvette into the spectrometer, and record the transmittance.

[0038] 2. Heat resistance test: According to GB / T 19466.5-2004 "Plastics Differential Scanning Calorimetry (DSC) Part 5: Determination of Oxidation Induction Time (Isothermal OIT) and Oxidation Induction Temperature (Dynamic OIT)", the cured coating was ground into fine powder, 10 mg was weighed and put into a TGA sample crucible, and a thermogravimetric analyzer was used with a nitrogen atmosphere and a heating rate of 10°C / min from room temperature to 600°C to evaluate the thermal stability.

[0039] 3. Water solubility test: According to GB / T 1725-2007 "Determination of non-volatile matter content of paints, varnishes and plastics", dilute the water-based paint to a certain concentration, pour it into a beaker, and let it stand at room temperature for 24 hours. Observe the dispersion of the resin in water and record the solubility and stability.

[0040] 4. Mechanical properties test: According to GB / T 1040.1-2006 "Determination of tensile properties of plastics Part 1: General", the cured coating is made into a standard specimen (such as ISO 527-1 dumbbell specimen, using a universal material testing machine, set the tensile speed to 50 mm / min, and measure the tensile strength and elongation at break.

[0041] Hardness test: Use a Shore hardness tester to press the hardness tester head vertically on the surface of the cured coating and record the hardness value.

[0042] 5. Adhesion test: According to GB / T 9286-1998 "Cross-cut test for paint and varnish films", apply water-based paint on the substrate and form a standard coating after curing. Use a cross-cutting tool to scratch 100 small grids of 1 mm × 1 mm on the coating. Use tape to stick on the cross-cut area and quickly tear off the tape. Observe and record the shedding of the coating and rate it according to the standard of GB / T9286-1998.

[0043] 6. Gloss test: According to GB / T 9754-2007 "Paints and varnishes - Determination of specular gloss at 20°, 60° and 85° of paint films without metallic pigments", apply the water-based paint on the substrate and form a standard coating after curing. Use a gloss meter with a measurement angle of 60°, place the gloss meter on the coating surface and record the gloss value.

[0044] 7. Chemical resistance test: According to GB / T 1763-1979 "Determination of chemical resistance of paint film", apply water-based paint on the substrate, form a standard coating after curing, immerse the coating in chemicals (acid, alkali, solvent) for 24 hours, record the changes of the coating in the chemicals, and rate it according to the standard of GB / T 1763-1979.

[0045] 8. Weathering test: According to GB / T 1865-2009 "Artificial weathering and artificial radiation exposure of paint and varnish coatings to filtered xenon arc radiation", apply the water-based paint on the substrate and form a standard coating after curing. Use a QUV aging box, set the light cycle to 8 hours light + 4 hours dark, and the light intensity is 0.35 W / m². Expose in the aging box for 1000 hours, observe and record the discoloration, blistering, and shedding of the coating, and rate it according to the standard of GB / T 1865-2009.

[0046] 9. Yellowing resistance test: According to GB / T 11942-1989 "Artificial Climate Accelerated Color Aging Test Method for Colored Building Materials", apply water-based paint on the substrate and form a standard coating after curing. Use a QUV aging box, set the light cycle to 8 hours of light + 4 hours of darkness, and the light intensity is 0.35 W / m². Expose in the aging box for 500 hours, observe and record the color changes of the coating, use a colorimeter to measure the color difference value, and rate according to the standard of GB / T 11942-1989.

[0047] The above performance test results are shown in Table 1, Table 2 and Table 3.

[0048] Table 1 Test results of transparency, heat resistance and water solubility of water-based coatings

[0049] Table 2 Mechanical properties and adhesion test results of water-based coatings

[0050] Table 3 Gloss, chemical resistance, weather resistance and yellowing resistance test results of water-based coatings

[0051] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A water-soluble polyester resin, characterized in that It is composed of the following raw materials in parts by weight: 40-70 parts of dibasic acid, 20-40 parts of aliphatic diol, 5-20 parts of alicyclic diol, 5-10 parts of dihydroxymethylpropionic acid, 1-3 parts of sodium bis(hydroxyethyl)isophthalate-5-sulfonate, 5-10 parts of single-end bis(hydroxy)polydimethylsiloxane, 0.1-0.5 parts of dibutyltin dilaurate and 0.2-0.5 parts of antioxidant.

2. A water-soluble polyester resin according to claim 1, characterized in that: The dibasic acid includes one or more of terephthalic acid, isophthalic acid, maleic acid, dodecane dibasic acid and phthalic acid; the aliphatic diol includes one or more of 1,3-propylene glycol, 1,5-pentanediol, 1,6-hexanediol and ethylene glycol; the alicyclic diol is 1,4-cyclohexanedimethanol or cyclohexanediol.

3. A water-soluble polyester resin according to claim 1, characterized in that: In parts by weight, the dibasic acid comprises 20-30 parts of terephthalic acid, 10-20 parts of isophthalic acid and 10-20 parts of maleic acid.

4. The method for preparing a water-soluble polyester resin according to claim 1, characterized in that: In parts by weight, the aliphatic diol includes 15-25 parts of 1,3-propylene glycol and 5-10 parts of 1,6-hexanediol, and the alicyclic diol includes 10-15 parts of 1,4-cyclohexanedimethanol.

5. A water-soluble polyester resin according to claim 1, characterized in that: The average molecular weight of the single-ended dihydroxy polydimethylsiloxane is 3200 Da.

6. A water-soluble polyester resin according to claim 1, characterized in that: The single-terminal bis-hydroxy polydimethylsiloxane is first reacted with trimellitic anhydride to synthesize a siloxane-modified segment, and then introduced into a polyester reaction system according to the weight proportion of the single-terminal bis-hydroxy polydimethylsiloxane.

7. A water-soluble polyester resin according to claim 1, characterized in that: The antioxidant is triphenyl phosphate.

8. The method for preparing a water-soluble polyester resin according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Alkyd polycondensation reaction: add dibasic acid, aliphatic diol and dibutyltin dilaurate into a reaction kettle in proportion, raise the temperature to 200-220°C, and maintain the polycondensation reaction for 3-5 hours under nitrogen protection until the acid value drops below 30 mg KOH / g to obtain polyester polyol; S2, introducing aqueous monomers: adding dimethylol propionic acid and sodium bis(hydroxyethyl)-5-sulfonate isophthalate to the polyester polyol in proportion at 150-160° C., and continuing the reaction for 1-2 hours until the monomers are completely dissolved to form a polyester reaction system; S3, polysiloxane modification: add single-end dihydroxy polydimethylsiloxane to the reactor, add organic bismuth catalyst, stir and heat to 100°C, slowly add trimellitic anhydride, keep warm and react for 3 hours after the addition, to prepare siloxane modified fragments; slowly add the siloxane modified fragments to the polyester reaction system and evenly disperse them, and continue to react at 150°C for 3-5 hours; S4, alicyclic diol integration: continue to add alicyclic diol into the reaction system, react until it is completely dissolved to form a uniform polymer; S5. Neutralization and water solubility adjustment: cool the reaction product to 60-80°C, use a neutralizer to neutralize the reaction system, adjust the pH value to 7.0-8.0, add an antioxidant, dilute with deionized water as needed, adjust the viscosity, cool the reaction product to room temperature, filter to remove impurities, and obtain a water-soluble polyester resin.

9. The method for preparing a water-soluble polyester resin according to claim 8, characterized in that: The neutralizing agent is dimethylethanolamine or triethylamine.

10. The method for preparing a water-soluble polyester resin according to claim 8, characterized in that: In the process of preparing the siloxane modified fragment, acetone is added to reduce viscosity as needed during the reaction process, wherein the molar ratio of the single-ended bishydroxy polydimethylsiloxane to trimellitic anhydride is 1:1, and the amount of the organic bismuth catalyst is 0.01% of the total weight of the single-ended bishydroxy polydimethylsiloxane and trimellitic anhydride.

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