Low-temperature-resistant high-performance epoxy modified polyester back paint based on hyperbranched epoxy resin and preparation method of low-temperature-resistant high-performance epoxy modified polyester back paint

Abstract

The invention discloses low-temperature-resistant high-performance epoxy modified polyester back paint based on hyperbranched epoxy resin and a preparation method of the low-temperature-resistant high-performance epoxy modified polyester back paint. The epoxy modified polyester back paint comprises the following components: polyester polyurethane resin, hyperbranched epoxy resin, an amino resin curing agent, a pigment filler, wax powder, an auxiliary agent and a mixed solvent, the polyester polyurethane resin is prepared by an addition polymerization reaction of polyester polyol resin and a diisocyanate compound; the hyperbranched epoxy resin is prepared through a two-stage step-by-step proton transfer reaction of a polyol compound and an epoxy compound, and the molecular weight distribution index is 1.5-2.5. The back paint provided by the invention has excellent low temperature resistance, and is especially suitable for application of coiled material coatings in the field of building materials. Compared with the prior art, the back paint provided by the invention can significantly improve the punch forming processing performance of the pre-coated color steel plate in a low-temperature environment, and solves the problems of insufficient flexibility and reduced adhesive force of the existing color steel plate coating under a low-temperature condition.

Description

Technical Field

[0001] This invention relates to the field of coil coatings, and in particular to a low-temperature resistant, high-performance epoxy-modified polyester backing paint based on hyperbranched epoxy resin and its preparation method. Background Technology

[0002] In recent years, large domestic steel companies have been exporting pre-coated color steel coils to overseas markets, where they are processed into various metal cladding systems for public buildings, including walls, roofs, and internal structures. It is worth noting that these pre-coated color steel sheets are mainly used in high-latitude regions, primarily to provide insulation, decoration, and protection for buildings.

[0003] High-latitude regions generally have cold climates with long, harsh winters and short summers, and low average annual temperatures, typically below 10°C. Therefore, it is urgent to develop corresponding standards for color-coated steel sheet coatings to address the unique climatic conditions of these regions, with particular attention to the coating's low-temperature resistance, especially its post-processing performance, namely its flexibility and adhesion to the substrate under low-temperature conditions.

[0004] To ensure that pre-coated color steel sheets meet the stamping process requirements of various processing molds under harsh low-temperature environments—that is, to ensure the coating can be used for a long time after stamping without cracking or peeling—it is necessary to improve the flexibility and adhesion of the coating in low-temperature environments. Therefore, relevant performance tests need to be conducted under low-temperature conditions. Specifically, the samples are placed in an environment of -18℃ (referring to the annual average temperature of high-latitude regions) for 1 hour, and then tested. The standards are: back paint T-bend (-18℃ / 1h, no peeling) ≤ 4T, reverse impact (-18℃ / 1h) ≥ 9J.

[0005] However, currently, the commonly used coil back coatings in the domestic color-coated steel sheet industry, such as epoxy resin, polyester resin, and epoxy-polyester blend systems, lack mature low-temperature resistant products that can fully meet the performance requirements of applications in harsh low-temperature environments. Therefore, there is an urgent need to develop a high-coating-rate coil back coating that is adaptable to different types of metal substrates, possesses excellent mechanical properties and adhesion, solves the challenge of achieving high flexibility in the processing of pre-coated color-coated steel sheets under harsh low-temperature environments, and meets the special needs of building materials in high-latitude regions. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a low-temperature resistant, high-performance epoxy-modified polyester backing paint based on hyperbranched epoxy resin and its preparation method.

[0007] In a first aspect, the present invention provides a low-temperature resistant, high-performance epoxy-modified polyester back coating based on hyperbranched epoxy resin, which is achieved by the following technical solution.

[0008] A low-temperature resistant, high-performance epoxy-modified polyester backing paint based on hyperbranched epoxy resin comprises the following components in parts by weight:

[0009]

[0010] The polyester polyurethane resin is prepared by addition polymerization of polyester polyol resin and diisocyanate compound, and is used to improve the flexibility and low-temperature resistance of the coating. The hyperbranched epoxy resin is prepared by two-stage stepwise proton transfer reaction of polyol compound and epoxy compound to form a hyperbranched structure with terminal active epoxy groups and a molecular weight distribution index (PDI) of 1.5-2.5, which is used to enhance the crosslinking density and low-temperature adhesion of the coating.

[0011] Furthermore, the preparation method of the polyester polyurethane resin includes the following steps:

[0012] a. In the presence of a catalyst, diols and diacids are subjected to esterification at 180-230℃ to generate linear hydroxyl-terminated polyester resin prepolymers (acid value ≤5mgKOH / g); wherein the ratio of the number of moles of hydroxyl groups in the diol to the number of moles of carboxyl groups in the diacid is 1.3-1.6:1, that is, the excess of alcohol is 30%-60%;

[0013] b. Under the action of a catalyst, the polyester resin prepolymer obtained in step a is subjected to an addition polymerization reaction with a diisocyanate compound at 50-80°C to generate a hydroxyl-terminated polyester polyurethane resin; wherein the molar ratio of isocyanate groups (-NCO) to hydroxyl groups (-OH) in the polyester resin prepolymer is 0.1-0.3:1, so as to balance the molecular weight and crosslinking density and improve the flexibility under low temperature conditions.

[0014] Furthermore, in step a, the diacid is selected from one or more mixtures of adipic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, and 1,2-cyclohexanedicarboxylic acid; the diol is selected from one or more mixtures of neopentyl glycol, methylpropanediol, 1,4-cyclohexanediethanol, 1,2-cyclohexanediethanol, 3-methyl-1,5-pentanediol, and 1,6-hexanediol. Preferably, the diol is selected from at least one of 1,4-cyclohexanediethanol and 1,2-cyclohexanediethanol; the diacid is selected from at least one of 1,4-cyclohexanedicarboxylic acid and 1,2-cyclohexanedicarboxylic acid. In this application, the amounts of the diol and diacid must satisfy at least one non-zero condition to ensure the esterification reaction proceeds and improve low-temperature resistance.

[0015] Furthermore, in step a, the esterification reaction conditions are as follows: slowly increase the temperature at a rate of 10-15℃ / h, reflux the reaction at 140-145℃, hold at 200-205℃ for 1-2 hours, and then slowly increase the temperature to 230℃ and hold the reaction until the measured acid value remains stable.

[0016] Furthermore, in step a, the esterification reaction catalyst is monobutyltin oxide, and the amount of the catalyst added is 0.03 to 0.3% of the total mass of the reactants in step a.

[0017] Furthermore, in step b, the diisocyanate compound is an aromatic diisocyanate with a benzene ring structure, and at least one of 2,4-toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI) is selected to improve the heat resistance and mechanical strength of the coating through its rigid structure.

[0018] Furthermore, in step b, the conditions for the addition polymerization reaction are: slowly heating to 50-60℃ for 1 hour, then heating to below 70℃ for 1 hour, and continuing to heat to 70-80℃ and holding the temperature until the measured NCO ≤ 5 mg NCO / g of the system.

[0019] Furthermore, in step b, the catalyst for the addition polymerization reaction is dibutyltin dilaurate, and the amount of the catalyst added is 0.1 to 0.2% of the total mass of the reactants in step b.

[0020] Furthermore, the preparation method of the hyperbranched epoxy resin includes the following steps:

[0021] I. In the presence of the catalyst tetrabutylammonium chloride, a two-stage stepwise proton transfer reaction is carried out with a polyol compound as the core and an epoxy compound (branched monomer), followed by heating and cooling. The polyol compound is trihydroxymethylethane, and the epoxy compound is trimethylolpropane triglycidyl ether, with a molar ratio of 1:1 to 3. The reaction temperature is controlled in two stages: prepolymerization stage: reacting at 45-55℃ for 2-4 hours to form a partially cross-linked structure; post-cross-linking stage: heating to 90-100℃ for 16-20 hours to generate a hyperbranched structure.

[0022] II. The product obtained in step I is separated by supercritical CO2 extraction, dried, filtered, and purified by vacuum distillation to obtain an aliphatic hyperbranched epoxy resin with terminal active epoxy groups.

[0023] Furthermore, in step I, the amount of the catalyst tetrabutylammonium chloride is 4 to 6% of the amount of the epoxide compound.

[0024] Furthermore, in step II, the solution is separated by supercritical CO2 extraction, then anhydrous sodium sulfate is added, dried for 12-15 hours, filtered, and then subjected to vacuum distillation. Specifically, the extraction temperature of supercritical CO2 extraction is controlled at 40-60℃, and the critical pressure of CO2 is 10-20 MPa.

[0025] Furthermore, the amino resin curing agent is a mixture of methyl etherified high-imino melamine resin and n-butyl etherified urea-formaldehyde resin, with the mass ratio of n-butyl etherified urea-formaldehyde resin to the total curing agent being 0.1–0.3:1, to enhance curing efficiency and crosslinking density. Specifically, the methyl etherified high-imino melamine resin is selected from Cytec's CYMEL325 or a commercially available similar high-imino amino resin. The n-butyl etherified urea-formaldehyde resin is selected from Cytec's ETERMINO 9115-60-2 or a commercially available similar urea-formaldehyde resin.

[0026] Furthermore, the pigments and fillers are selected from at least one of titanium dioxide, carbon black, iron oxide red, iron oxide yellow, precipitated barium sulfate, talc, and organobentonite.

[0027] Furthermore, the wax powder is a fluorinated wax powder, and the fluorinated wax powder is selected from at least one of fluorinated polyethylene wax and fluorinated synthetic wax.

[0028] Furthermore, the fluorinated modified wax powder has a particle size of 5-10 μm and its surface is treated with a silane coupling agent to enhance its compatibility with the resin, and is selected from at least one of MP-28XF, Polyfluo150, Polyfluo523XF, and Synfluo180XF from Micron Technology, Inc.

[0029] Furthermore, the additives include polyurethane dispersants, non-silicone defoamers, non-silicone leveling agents, and curing catalysts. These additives are used to improve the leveling properties, defoaming properties, and curing efficiency of the coating.

[0030] Furthermore, the dispersant is selected from at least one of AFCONA-4010, AFCONA-4017, AFCONA-4060, AFCONA-4080, AFCONA-4072, and AFCONA-4565.

[0031] Furthermore, the defoamer is selected from at least one of BYK-054, BYK352, and BYK-057.

[0032] Furthermore, the leveling agent is selected from at least one of AFCONA-3700, AFCONA-3750, AFCONA-3775, AFCONA-3777, and AFCONA-3779.

[0033] Furthermore, the curing catalyst includes an acid catalyst selected from at least one of the following: NACURE 1051, NACURE 2500, and NACURE 5225 from King's Labs.

[0034] Furthermore, the mixed solvent is selected from at least one of butanol, propylene glycol methyl ether acetate, cyclohexanone, xylene, S-100# aromatic solvent, S-150# aromatic solvent, and divalent ester DBE.

[0035] Secondly, the present invention provides a method for preparing a low-temperature resistant, high-performance epoxy-modified polyester backing paint based on hyperbranched epoxy resin, which is achieved by the following technical solution.

[0036] A method for preparing the above-mentioned low-temperature resistant, high-performance epoxy-modified polyester backing paint based on hyperbranched epoxy resin includes the following steps:

[0037] S1. At room temperature, mix 50%-70% of the total amount of polyester polyurethane resin, dispersant, pigments, fillers, and wax powder, then add 30%-50% of the total amount of mixed solvent, stir at 300-500 rpm and grind until the particle size is below 10 μm to obtain a slurry.

[0038] S2. Add the remaining polyester polyurethane resin, hyperbranched epoxy resin, and remaining additives to the slurry obtained in step S1 and mix; then add the amino resin curing agent and the remaining mixed solvent, mix evenly, and filter to obtain epoxy modified polyester back coating.

[0039] Furthermore, in step S2, a high-speed disperser is used to stir the mixture at 800-1000 rpm during the mixing process.

[0040] This application has the following beneficial effects.

[0041] 1. This invention innovatively introduces urethane bonds and rigid benzene rings into the polyester polymer chain through structural modification of polyester resin, thereby synthesizing a novel polyester polyurethane resin. Compared with traditional backing coatings, this resin coating significantly improves chemical resistance while maintaining excellent flexibility and adhesion. This is attributed to the flexibility provided by the urethane bonds and the rigidity provided by the benzene ring structure, which together optimize the overall performance of the coating.

[0042] 2. This invention prepares polyester polyurethane resin through the addition polymerization reaction of hydroxyl-terminated polyester resin prepolymer and aromatic diisocyanate. By optimizing the combination of diol, diacid, and diisocyanate, a high degree of tunability in molecular structure is achieved, thereby obtaining back coatings with different properties.

[0043] 3. In traditional methods, to impart flexibility to polyester resins, long-chain aliphatic diacids (such as adipic acid and sebacic acid) or diols (such as methyl propylene glycol) are often introduced to lower the glass transition temperature (Tg) of the polyester resin. However, the resulting coatings often exhibit poor long-term flexibility, possibly due to the tendency of long-chain aliphatic segments to become excessively entangled. To address this problem, this invention proposes an improved strategy: introducing cyclic diol or diacid monomers. This method can form a structure with alternating cyclic groups and aliphatic segments, effectively shortening the length of continuous aliphatic chains, thereby inhibiting chain segment entanglement and significantly improving the long-term flexibility of the coating. Simultaneously, the introduction of the cyclic structure also helps to balance the flexibility and rigidity of the resin.

[0044] 4. This invention uses polyols and epoxy compounds as monomers to synthesize an aliphatic hyperbranched epoxy resin through a two-stage stepwise proton transfer reaction. This resin possesses a highly branched structure; compared to traditional linear polymers, its molecular chains are less prone to entanglement, resulting in lower melt viscosity and a significantly increased surface functional group density. Its core is rich in regularly distributed secondary hydroxyl groups, while the outer layer consists of epoxy functional groups. This core-shell structure facilitates the formation of an effective interfacial crosslinking network with various resin matrices, particularly improving incompatibility with polyesters. When applied to polyester backing coatings, it significantly improves coating adhesion, crosslinking density, hardness, and flexibility while ensuring good compatibility.

[0045] 5. In the synthesis process of aliphatic hyperbranched epoxy resin, the present invention uses supercritical CO2 extraction and separation to replace the organic solvent extraction in the prior art, thereby improving environmental protection and product purity.

[0046] 6. The low-temperature resistant, high-performance epoxy-modified polyester backing paint based on hyperbranched epoxy resin provided by this invention has a solid content of over 65% (high solid content) and a coating thickness of up to 380m³. 2 With a coating coverage of over / kg·μ (high coating rate), the coating exhibits superior flexibility and adhesion to the substrate under harsh low-temperature conditions. Furthermore, the polyurethane foam adhesive has excellent and stable performance and a wide range of applications.

[0047] 7. The back coating preparation method of this invention is simple, meets the requirements of green and environmentally friendly production, and is easy to mass-produce. Detailed Implementation

[0048] The present patent application will be further described below with reference to the embodiments. Unless otherwise stated, the raw materials used in the embodiments and comparative examples are all commercially available industrial products that can be purchased through commercial channels.

[0049] The preparation of polyester polyurethane resins A to M in Table 1 is as follows (polyester polyurethane resins K, L, and M are all adjustments based on polyester polyurethane resin I):

[0050] (1) Add diol (I in Table 1), diacid (II in Table 1), 0.25g monobutyltin oxide and 80g xylene to a clean reaction flask equipped with a stirrer, thermometer, water separator, condenser and inert gas inlet. Under continuous stirring and inert atmosphere protection, after the components are fully mixed, heat the material to 140°C at a rate of 10°C / h and reflux for 1 hour. Then heat to 200°C and keep for 2 hours. Then heat to 230°C and keep for 2 hours until the acid value of the reaction system is stable. Cool down to obtain linear polyester resin with terminal hydroxyl groups.

[0051] (2) Add diisocyanate compound (see Table 1, section III) and 0.5 g of dibutyltin dilaurate, then slowly heat to 60°C and react for 1 h, then heat to below 70°C and react for 1 h, then continue heating to 80°C and maintain the temperature until the NCO content of the system is ≤ 5 mg NCO / g (the reaction endpoint is determined by hexachloropyridine-chlorobenzene titration using bromocresol green as an indicator). Cool down while stirring thoroughly, filter, and the resulting filtrate is the modified polyester resin.

[0052] The specific selection of each reactant is shown in Table 1:

[0053] Table 1

[0054]

[0055]

[0056]

[0057] The preparation of hyperbranched epoxy resins N to P in Table 2 is as follows:

[0058] (1) Add trihydroxymethyl ethane (I in Table 2), trihydroxymethyl propane triglycidyl ether (II in Table 2), and tetrabutylammonium chloride (III in Table 2) to a clean reaction flask equipped with a stirrer, thermometer, condenser, and inert gas (nitrogen) inlet. Under continuous stirring and inert atmosphere (nitrogen) protection, after the components are fully mixed, heat the material to 50°C at a rate of 10°C / h. After reacting for 4 hours, continue to heat to 95°C. After reacting for 20 hours, cool down.

[0059] (2) The aliphatic hyperbranched epoxy resin was obtained by supercritical CO2 extraction (extraction temperature controlled at 50℃, critical pressure of CO2 was 15MPa), 200g of anhydrous sodium sulfate was added, dried for 12 hours, filtered, and the solution was distilled under reduced pressure.

[0060] The specific selection of each reactant is shown in Table 2:

[0061] Table 2

[0062]

[0063] Based on the polyester polyurethane resins in Table 1 and the hyperbranched epoxy resins in Table 2, low-temperature resistant high-performance epoxy-modified polyester back coatings based on hyperbranched epoxy resins were prepared respectively. (Comparative Examples 1, 2, and 3 were based on Example 5 with adjustments to the polyester polyurethane resin, while the other components remained unchanged; Comparative Examples 4 and 5 were based on Example 7 with adjustments to the amino resin curing agent, while the other components remained unchanged; Comparative Examples 6 and 7 were based on Example 5 with adjustments to the hyperbranched epoxy resin, and were all non-hyperbranched epoxy resins. The E-44 and 601 epoxy resins used were commercially available, and the other components remained unchanged. The preparation process is as follows:)

[0064] Step (1): At room temperature, mix 50% polyester polyurethane resin, dispersant, pigments and fillers, wax powder, and then add 50% mixed solvent. Stir at 500 rpm and grind until the particle size is below 10 μm to obtain slurry.

[0065] Step (2): Add the remaining polyester polyurethane resin, hyperbranched epoxy resin, and remaining additives to the slurry and mix; then add the amino resin curing agent and the remaining mixed solvent, mix evenly, and use a high-speed disperser to stir at 1000 rpm during the mixing process, and filter to obtain the epoxy modified polyester back coating.

[0066] The specific selection and weight of each component are shown in Table 3:

[0067] Table 3

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076] It should be noted that: Comparative Example 1, based on Example 5, does not contain 1,4-cyclohexanediethanol or 1,2-cyclohexanedicarboxylic acid in the synthesis of the polyester polyurethane resin, and therefore is not within the scope of this invention; Comparative Example 2, based on Example 5, does not contain diisocyanate compounds in the synthesis of the polyester polyurethane resin, and therefore is not within the scope of this invention; Comparative Example 3, based on Example 5, does not contain aromatic diisocyanates in the synthesis of the polyester polyurethane resin, but uses aliphatic isocyanates, and therefore is not within the scope of this invention; Comparative Example 4, based on Example 7, adjusts the curing agent while keeping the other components unchanged. Specifically, the curing agent... The first example uses only a high-imino-amino resin, therefore it is not within the scope of this invention; Comparative Example 5 is based on Example 7, but the curing agent is adjusted, while the other components remain unchanged. Specifically, the curing agent is only urea-formaldehyde resin, therefore it is not within the scope of this invention; Comparative Example 6 is based on Example 5, but the hyperbranched epoxy resin is adjusted to a non-hyperbranched epoxy resin, while the other components remain unchanged. Specifically, E-44 epoxy resin is used, therefore it is not within the scope of this invention; Comparative Example 7 is based on Example 5, but the hyperbranched epoxy resin is adjusted to a non-hyperbranched epoxy resin, while the other components remain unchanged. Specifically, 601 epoxy resin is used, therefore it is not within the scope of this invention.

[0077] Performance testing

[0078] Coating process for panel fabrication:

[0079] Coating and panel preparation: The obtained epoxy-modified polyester back paint is coated onto a 12cm×15cm×0.5mm pretreated galvanized steel plate using a wire rod roller, and baked in a 300℃ oven for 40s. The metal plate temperature PMT is 224℃, resulting in a back paint coating with a film thickness of 5-7μm.

[0080] Testing showed that the low-temperature resistant high-performance epoxy-modified polyester back coatings of Examples 1-20, after the above operations, all met the various quality standards, as shown in Table 4.

[0081] Table 4

[0082]

[0083] Note: "-18℃ / 1h" in the table means that the sample was placed at -18℃ (referencing the annual average temperature in high-latitude regions) for 1 hour before relevant performance tests were performed.

[0084] Other performance characteristics not listed in this application form, but known to those skilled in the art, can meet the performance requirements.

[0085] The performance test results of the back coatings formed by the above operations for the epoxy-modified polyester back coatings of Comparative Examples 1-7 are shown in Table 5 below:

[0086] Table 5

[0087]

[0088]

[0089]

[0090] The experimental results in Tables 4 and 5 show that:

[0091] (1) The low-temperature resistant high-performance epoxy modified polyester backing paint prepared by the present invention is suitable for the surface of substrates such as hot-dip galvanized steel plate, electro-galvanized steel plate, cold-rolled steel plate, zinc-aluminum-magnesium steel plate, and aluminized zinc steel plate. The paint film has excellent mechanical properties and adhesion, which solves the problem of high flexibility in the processing of pre-coated color steel plate in harsh low-temperature environment, thereby meeting the application requirements of the product in harsh low-temperature environment and meeting the special requirements of high-latitude regions for building materials.

[0092] (2) The polyester polyurethane resin in Comparative Example 1 does not contain cyclic diol or diacid monomers, so the long-chain aliphatic segments are prone to excessive winding, and the resulting coating often has poor long-term flexibility.

[0093] (3) The polyester polyurethane resin in Comparative Example 2 does not contain diisocyanate compounds. Therefore, the final synthesized polyester polyurethane resin has a smaller molecular weight, a larger hydroxyl value, and does not contain urethane bonds. The coating has poor resistance, and its flexibility and adhesion are weakened.

[0094] (4) The polyester polyurethane resin in Comparative Example 3 does not contain aromatic diisocyanate, but aliphatic isocyanate. It does not contain rigid aromatic (benzene ring) structures, and its adhesion to metal substrates is insufficient.

[0095] (5) The curing agent in Comparative Example 4 contains only high imino amino resin, resulting in a hard coating with poor flexibility and weak adhesion.

[0096] (6) The curing agent in Comparative Example 5 contains only urea-formaldehyde resin, the paint film is too soft, the degree of cross-linking is insufficient, and the hardness is insufficient.

[0097] (7) Comparative Example 6 used E-44 epoxy resin; Comparative Example 7 used 601 epoxy resin. Neither Comparative Example 6 nor Comparative Example 7 contained non-hyperbranched epoxy resin. Hyperbranched epoxy resin has a highly branched structure. Compared with traditional linear epoxy polymers, its molecular chains are less prone to entanglement, its melt viscosity is low, and its surface functional group density is significantly increased, which can significantly improve the coating adhesion, crosslinking density, hardness, and flexibility.

[0098] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin, characterized in that, The components include the following weight parts: The polyester polyurethane resin is prepared by addition polymerization reaction of polyester polyol resin and diisocyanate compound; the hyperbranched epoxy resin is prepared by two-stage stepwise proton transfer reaction of polyol compound and epoxy compound, and the molecular weight distribution index is 1.5-2.

5.

2. The low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to claim 1, characterized in that, The preparation method of the polyester polyurethane resin comprises the following steps: a. esterification reaction of dihydric alcohol and diacid at 180-230 DEG C in the presence of catalyst to generate linear hydroxyl-terminated polyester resin prepolymer; wherein the ratio of the number of moles of hydroxyl contained in dihydric alcohol to the number of moles of carboxyl contained in diacid is 1.3-1.6:1; b. addition polymerization reaction of the polyester resin prepolymer obtained in step a and diisocyanate compound at 50-80 DEG C under the action of catalyst to generate hydroxyl-terminated polyester polyurethane resin; wherein the molar ratio of isocyanate group to hydroxyl in polyester resin prepolymer is 0.1-0.3:

1.

3. The low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to claim 2, characterized in that, In step a, the diacid is selected from one or more mixtures of adipic acid, isophthalic acid, 1,4-cyclohexane dicarboxylic acid and 1,2-cyclohexane dicarboxylic acid; the dihydric alcohol is one or more mixtures of neopentyl glycol, methyl propylene glycol, 1,4-cyclohexane dimethanol, 1,2-cyclohexane dimethanol, 3-methyl-1,5-pentanediol and 1,6-hexanediol.

4. The low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to claim 2, characterized in that, In step b, the diisocyanate compound is aromatic diisocyanate with benzene ring structure, and at least one of 2,4-toluene diisocyanate and 4,4'-diphenyl methane diisocyanate is selected.

5. The low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to claim 1, characterized in that, The preparation method of the hyperbranched epoxy resin comprises the following steps: Ⅰ. in the presence of catalyst tetrabutylammonium chloride, two-stage stepwise proton transfer reaction of polyol compound as core and epoxy compound, after warming reaction, cooling; wherein the polyol compound is selected from trihydroxymethyl ethane, the epoxy compound is selected from trimethylolpropane triglycidyl ether, the molar ratio of polyol compound and epoxy compound is 1:1-3; the reaction temperature is controlled in two stages, pre-polymerization stage: reaction at 45-55 DEG C for 2-4 hours to form partial crosslinking structure; post-crosslinking stage: warming to 90-100 DEG C for 16-20 hours to generate hyperbranched structure; Ⅱ. the product obtained in step I is separated by supercritical CO2 extraction, dried, filtered and then distilled under reduced pressure to purify the product, thereby obtaining aliphatic hyperbranched epoxy resin with terminal active epoxy groups.

6. The low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to claim 1, characterized in that, The amino resin curing agent is a mixture of methyl etherified high imino melamine resin and n-butyl etherified urea resin, and the mass ratio of n-butyl etherified urea resin to total curing agent is 0.1-0.3:

1.

7. The low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to claim 1, characterized in that, The wax powder is fluorine-modified wax powder, and at least one of fluorine-modified polyethylene wax and fluorine-modified synthetic wax is selected.

8. The low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to claim 1, characterized in that, The auxiliary agent includes polyurethane dispersant, non-silicon defoaming agent, non-silicon leveling agent and curing catalyst.

9. A process for the preparation of a low temperature resistant high performance epoxy modified polyester backsize based on hyperbranched epoxy resin according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: S1. At room temperature, mix polyester polyurethane resin, dispersant, pigment and filler, and wax powder, which are 50%-70% of the total amount of polyester polyurethane resin, then add mixed solvent which is 30-50% of the total amount of mixed solvent, stir at 300-500 rpm and sand mill to a particle size of less than 10 μm to obtain a slurry; S2. Mix the remaining polyester polyurethane resin, hyperbranched epoxy resin, and remaining additives into the slurry obtained in step S1, then add amino resin curing agent and the remaining mixed solvent, mix uniformly, and filter to obtain an epoxy modified polyester primer.

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