High weatherable polyester aqueous dispersion for use in a web and its preparation and use

Abstract

The application belongs to the technical field of polyester aqueous dispersion preparation, and particularly relates to a high-weatherability polyester aqueous dispersion suitable for a coiled material and preparation and application thereof. The application comprises the following steps: prepolymer synthesis; gradient end-capping and chain extension of the prepolymer; and nanosizing and dispersing of the end-capped polyester. The application controls temperature and polycondensates 1,1-cyclobutyl dicarboxylic acid, adipic acid, 1,4-cyclohexane dimethanol and 2-butyl-2-ethyl-1,3-propanediol in stages under nitrogen protection. The structure of 1,1-cyclobutyl dicarboxylic acid is stably embedded in the main chain to form a polymer network capable of absorbing and converting ultraviolet light. The butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol cooperates with the flexible segment of adipic acid to make the polymer network maintain the ultraviolet-resistant weather-resistant rigidity of the alicyclic structure, and ensure that the butyl-ethyl branch is uniformly distributed on the side of the molecular chain while the alicyclic structure of 1,1-cyclobutyl dicarboxylic acid is completely reserved, thereby constructing active sites for subsequent end-capping reaction.

Description

Technical Field

[0001] This invention belongs to the field of polyester aqueous dispersion preparation technology, and particularly relates to a high weather-resistant polyester aqueous dispersion suitable for roll materials, its preparation and application. Background Technology

[0002] Waterborne polyester dispersions, as environmentally friendly polymer systems, form colloidal particles by stably dispersing polyester resin in an aqueous phase. They have been applied in fields such as metal coils, automotive primers, and industrial corrosion protection. Especially in the coating of color steel coils for construction, their low VOC characteristics meet stringent environmental regulations, while the designable molecular chains allow the coating to possess both decorative and protective properties.

[0003] Traditional waterborne polyester dispersions have long faced the inherent challenge of balancing weather resistance and flexibility in outdoor roll coating applications. On one hand, conventional technologies rely on aromatic dicarboxylic acids to construct a rigid framework to improve UV aging resistance. However, the benzene ring structure exhibits strong electronic transitions in the UV band, leading to irreversible yellowing and molecular chain breakage after sun exposure. On the other hand, improving low-temperature flexibility requires the introduction of long-chain aliphatic monomers, but excessive use weakens coating hardness and exacerbates the risk of thermo-oxidative aging. Existing technologies attempt to compensate by compounding UV absorbers or nanoparticles, but these additives are prone to migration and precipitation, not only causing a decline in protective efficacy over time but also disrupting the continuity of the polymer's bulk structure, leading to stress cracking under extreme conditions. Summary of the Invention

[0004] To address the aforementioned technical deficiencies, this invention presents a highly weather-resistant polyester aqueous dispersion suitable for roll materials and its preparation method. The resulting polyester aqueous dispersion exhibits high weather resistance and mechanical properties.

[0005] A method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials includes the following steps: S1: Prepolymer Synthesis 1,1-Cyclobutyldicarboxylic acid, adipic acid, 1,4-cyclohexanediethanol and 2-butyl-2-ethyl-1,3-propanediol were prepolymerized at 170-175°C under a nitrogen atmosphere, and then prepolymerized at 195-200°C to obtain a prepolymer. S2: Gradient end-capping and chain extension of the prepolymer After cooling the prepolymer to 140-150℃, tetrahydrophthalic anhydride is added, and the mixture is stirred and reacted under a nitrogen atmosphere to obtain the first end-capped prepolymer. The first end-capped prepolymer is heated to 180-185℃, trimellitic anhydride is added, and the mixture is stirred and reacted under a vacuum of 0.07-0.08MPa to obtain the second end-capped prepolymer. Then, a chain extender is added, and the mixture is stirred and reacted again at 160-165℃ to obtain the end-capped polyester. S3: Nanoscale dispersion of capped polyester The capped polyester was cooled to 80-85℃, N,N-dimethylcyclohexylamine was added and mixed evenly, and then emulsified in a high-speed dispersion dish to obtain an emulsion. Hot water and an aqueous solution containing nano-cerium dioxide were added to the emulsion in sequence for dispersion to obtain an aqueous dispersion. After filtration, a weather-resistant polyester aqueous dispersion was obtained.

[0006] Further, step S1, the synthesis of the prepolymer, specifically includes the following steps: S1.1: Add 30-35 parts by weight of 1,1-cyclobutyldicarboxylic acid, 18-22 parts by weight of adipic acid, 28-32 parts by weight of 1,4-cyclohexanediethanol and 8-10 parts by weight of 2-butyl-2-ethyl-1,3-propanediol to a high-pressure reactor, and purge with nitrogen to completely replace the air in the reactor. S1.2: Start the heating device and raise the temperature in the high-pressure reactor to 170-175℃ at a heating rate of 10-15℃ / min. Hold the temperature for 1-1.5h, then raise the temperature to 195-200℃ at a heating rate of 5-6℃ / min. Hold the temperature and then stir continuously at a speed of 200-250r / min for 3.5-4h to obtain the prepolymer.

[0007] Furthermore, the gradient end-capping and chain extension of the prepolymer in step S2 specifically includes the following steps: S2.1: After the prepolymer obtained in step S1.2 is naturally cooled to 140-150℃, tetrahydrophthalic anhydride is added, and the mixture is stirred at a stirring speed of 120-150r / min for 40-45min under nitrogen protection to obtain the first end-capped prepolymer. S2.2: Heat the first end-capped prepolymer to 180-185℃, add trimellitic anhydride, evacuate to 0.07-0.08MPa and stir for 80-100min, control the final acid value of the reaction system to 52-55mgKOH / g, and obtain the second end-capped prepolymer; S2.3: Add 0.8-1 parts by weight of chain extender to the second end-capped prepolymer, and continue to react at 160-165℃ and 150-165r / min for 50-60min to obtain end-capped polyester.

[0008] Furthermore, the nano-dispersion of the end-capped polyester in step S3 S3.1: Cool the end-capped polyester obtained in step S2.3 to 80-85℃, add 1.2-1.5wt% of N,N-dimethylcyclohexylamine to the end-capped polyester and mix evenly. Then emulsify with a high-speed dispersion disc with a linear speed of 20-25m / s for 10-15min to obtain an emulsion. S3.2: Add hot water at 80-85℃ to the emulsion, control the dropping rate at 0.8-1L / min, disperse for 12-15min after dropping, then add an aqueous solution containing 0.3-0.5% nano-cerium dioxide, control the dropping rate at 2-3L / min, and then perform ultrasonic dispersion treatment at a frequency of 25-30kHz for 30-35min to obtain an aqueous dispersion; S3.3: The aqueous dispersion is filtered through a ceramic membrane with a pore size of 0.1 μm to remove residual monomers and obtain a highly weather-resistant polyester aqueous dispersion.

[0009] Furthermore, in step S2.1, the amount of tetrahydrophthalic anhydride added is 6-8% of the total mass of the prepolymer.

[0010] Furthermore, in step S2.2, the amount of trimellitic anhydride added is 10-12% of the total mass of the first end-capped prepolymer.

[0011] Furthermore, the chain extender in step S2.3 is ADR-4468 chain extender.

[0012] Furthermore, in step S3.2, hot water accounts for 40-45% of the emulsion mass, and the aqueous solution containing nano-cerium dioxide accounts for 55-60% of the emulsion mass.

[0013] A highly weather-resistant polyester aqueous dispersion suitable for roll materials is prepared by the above-mentioned method for preparing a highly weather-resistant polyester aqueous dispersion suitable for roll materials.

[0014] Another aspect of this application provides a method for applying a highly weather-resistant polyester aqueous dispersion suitable for roll materials, for coating and protecting metal roll materials.

[0015] The beneficial effects are as follows: 1. This invention involves the staged temperature-controlled polycondensation of 1,1-cyclobutyldicarboxylic acid, adipic acid, 1,4-cyclohexanediethanol, and 2-butyl-2-ethyl-1,3-propanediol under nitrogen protection. The structure of 1,1-cyclobutyldicarboxylic acid is stably embedded in the main chain during the low-temperature initiation stage at 170-175℃. In the subsequent polycondensation at 195-200℃, it forms a structure capable of absorbing and converting ultraviolet light. The butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol works synergistically with the flexible segments of adipic acid to plasticize and form molecular-level buffer cavities between the rigid framework composed of cyclohexanediethanol. This allows the polymer network to maintain the UV resistance and weather resistance rigidity of the alicyclic structure, while ensuring the complete preservation of the alicyclic structure of 1,1-cyclobutyldicarboxylic acid. At the same time, it forces the butyl-ethyl branch to be evenly distributed on the side positions of the molecular chain, thus constructing active sites for the subsequent end-capping reaction.

[0016] 2. This invention utilizes a gradient end-capping operation with precise control of temperature and reaction sequence. First, the cyclic anhydride of tetrahydrophthalic anhydride is selectively grafted onto the terminal hydroxyl groups of the prepolymer at a mild temperature of 140-150℃ to form rigid end groups. This structure acts as a "molecular anchor" to suppress the tendency of chain segment crystallization and avoid ring-opening side reactions at high temperatures. Then, under negative pressure, the three anhydride groups of trimellitic anhydride are directionally grafted onto the prepolymer. The free carboxyl groups at the ends form discrete high-density ion clusters under vacuum dehydration, which not only endows the final acid value of 52-55 mgKOH / g with precise hydrophilicity but also prevents the molecular chains from stacking tightly through steric hindrance. Finally, a trace amount of chain extender is introduced to obtain a rigid-flexible structure with hydrolytic stability, which significantly improves the adhesion. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the preparation method of a high weather-resistant polyester aqueous dispersion suitable for roll materials, as used in embodiments of the present invention.

[0018] Figure 2 The particle size and sedimentation of the high weather-resistant polyester aqueous dispersions prepared in Examples 1-4 of this invention were analyzed.

[0019] Figure 3 The tensile shear strength of the high weather-resistant polyester aqueous dispersions obtained in Examples 1-4 of this invention.

[0020] Figure 4 The weather resistance of the high weather-resistant polyester aqueous dispersions prepared in Examples 1-4 of this invention is shown. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0022] A method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials, such as Figure 1 As shown, the specific steps include: S1: Prepolymer Synthesis S1.1: Add 30 parts by weight of 1,1-cyclobutyldicarboxylic acid, 18 parts by weight of adipic acid, 28 parts by weight of 1,4-cyclohexanediethanol and 8 parts by weight of 2-butyl-2-ethyl-1,3-propanediol to a high-pressure reactor, and purge with nitrogen to completely replace the air in the reactor. S1.2: Start the heating device and raise the temperature in the high-pressure reactor to 170°C at a heating rate of 10°C / min. Hold the temperature for 1 hour, then raise the temperature to 195°C at a heating rate of 5°C / min. Maintain the temperature and then stir continuously at 200 r / min for 3.5 hours to obtain the prepolymer. By performing staged temperature-controlled polycondensation of 1,1-cyclobutyldicarboxylic acid, adipic acid, 1,4-cyclohexanediethanol, and 2-butyl-2-ethyl-1,3-propanediol under nitrogen protection, the structure of 1,1-cyclobutyldicarboxylic acid is obtained at low temperature. During the active phase, the butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol is stably embedded in the main chain. During polycondensation, it forms a structure capable of absorbing and converting ultraviolet light. The butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol works synergistically with the flexible segments of adipic acid to plasticize and form molecular-level buffer cavities between the rigid framework composed of cyclohexanediethanol. This allows the polymer network to maintain the UV resistance and weather resistance rigidity of the alicyclic structure and ensure the complete preservation of the 1,1-cyclobutyldicarboxylic acid alicyclic structure. At the same time, it forces the butyl-ethyl branch to be evenly distributed on the side positions of the molecular chain, thus constructing active sites for subsequent end-capping reactions.

[0023] S2: Gradient end-capping and chain extension of the prepolymer S2.1: After the prepolymer obtained in step S1.2 is naturally cooled to 140℃, 6% of the total mass of the prepolymer is added to tetrahydrophthalic anhydride. The mixture is stirred at a stirring speed of 120r / min for 40min under nitrogen protection to obtain the first end-capped prepolymer. S2.2: Heat the first end-capped prepolymer to 180℃, add trimellitic anhydride at 10% of the total mass of the first end-capped prepolymer, evacuate to 0.07MPa and stir for 80min, control the final acid value of the reaction system to 52mgKOH / g, and obtain the second end-capped prepolymer; S2.3: Add 0.8 parts by weight of ADR-4468 chain extender to the second end-capped prepolymer and continue the reaction at 160℃ and 150r / min for 50min to obtain end-capped polyester. Through gradient end-capping operation and precise control of temperature and reaction sequence, firstly, the cyclic anhydride of tetrahydrophthalic anhydride is selectively grafted onto the terminal hydroxyl groups of the prepolymer at a mild temperature to form rigid end groups. This structure acts as a "molecular anchor" to suppress the tendency of chain segment crystallization and avoid ring-opening side reactions at high temperatures. Then, under negative pressure, the three anhydride groups of trimellitic anhydride are directionally grafted, and the free carboxyl groups at the ends form discrete high-density ion clusters under vacuum dehydration. This not only gives the final acid value of 52-55mgKOH / g precise hydrophilicity, but also prevents the molecular chains from being tightly stacked through steric hindrance. Then, a trace amount of chain extender is introduced to finally obtain a rigid-flexible structure with hydrolytic stability, which greatly improves the adhesion.

[0024] S3: Nanoscale dispersion of capped polyester S3.1: Cool the end-capped polyester obtained in step S2.3 to 80°C, add 1.2 wt% N,N-dimethylcyclohexylamine to the end-capped polyester and mix evenly. Then emulsify with a high-speed dispersion disc with a linear velocity of 20 m / s for 10 min to obtain an emulsion. S3.2: Add 80℃ hot water to the emulsion, with the hot water accounting for 40% of the emulsion mass. Control the dropping rate at 0.8L / min. After dropping, disperse for 12min. Then add an aqueous solution containing 0.3% nano-cerium dioxide, with the aqueous solution containing nano-cerium dioxide accounting for 55% of the emulsion mass. Control the dropping rate at 2L / min. After dropping, perform ultrasonic dispersion treatment at a frequency of 25kHz for 30min to obtain an aqueous dispersion. S3.3: The aqueous dispersion is filtered through a ceramic membrane with a pore size of 0.1 μm to remove residual monomers and obtain a highly weather-resistant polyester aqueous dispersion. Example 2

[0025] A method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials, such as Figure 1 As shown, the specific steps include: S1: Prepolymer Synthesis S1.1: Add 35 parts by weight of 1,1-cyclobutyldicarboxylic acid, 22 parts by weight of adipic acid, 32 parts by weight of 1,4-cyclohexanediethanol and 10 parts by weight of 2-butyl-2-ethyl-1,3-propanediol to a high-pressure reactor, and purge with nitrogen to completely replace the air in the reactor. S1.2: Start the heating device and raise the temperature in the high-pressure reactor to 170°C at a heating rate of 10°C / min. Hold the temperature for 1 hour, then raise the temperature to 195°C at a heating rate of 5°C / min. Maintain the temperature and then stir continuously at 200 r / min for 3.5 hours to obtain the prepolymer. By performing staged temperature-controlled polycondensation of 1,1-cyclobutyldicarboxylic acid, adipic acid, 1,4-cyclohexanediethanol, and 2-butyl-2-ethyl-1,3-propanediol under nitrogen protection, the structure of 1,1-cyclobutyldicarboxylic acid is obtained at low temperature. During the active phase, the butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol is stably embedded in the main chain. During polycondensation, it forms a structure capable of absorbing and converting ultraviolet light. The butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol works synergistically with the flexible segments of adipic acid to plasticize and form molecular-level buffer cavities between the rigid framework composed of cyclohexanediethanol. This allows the polymer network to maintain the UV resistance and weather resistance rigidity of the alicyclic structure and ensure the complete preservation of the 1,1-cyclobutyldicarboxylic acid alicyclic structure. At the same time, it forces the butyl-ethyl branch to be evenly distributed on the side positions of the molecular chain, thus constructing active sites for subsequent end-capping reactions.

[0026] S2: Gradient end-capping and chain extension of the prepolymer S2.1: After the prepolymer obtained in step S1.2 is naturally cooled to 140℃, tetrahydrophthalic anhydride of 8% of the total mass of the prepolymer is added, and the mixture is stirred at a stirring speed of 120r / min for 40min under nitrogen protection to obtain the first end-capped prepolymer. S2.2: Heat the first end-capped prepolymer to 180℃, add trimellitic anhydride at 12% of the total mass of the first end-capped prepolymer, evacuate to 0.07MPa and stir for 80min, control the final acid value of the reaction system to 52mgKOH / g, and obtain the second end-capped prepolymer; S2.3: Add 1 part by weight of ADR-4468 chain extender to the second end-capped prepolymer and continue the reaction at 160℃ and 150r / min for 50min to obtain end-capped polyester. Through gradient end-capping operation and precise control of temperature and reaction sequence, firstly, the cyclic anhydride of tetrahydrophthalic anhydride is selectively grafted onto the terminal hydroxyl groups of the prepolymer at a mild temperature to form rigid end groups. This structure acts as a "molecular anchor" to suppress the tendency of chain segment crystallization and avoid ring-opening side reactions at high temperatures. Then, under negative pressure, the three anhydride groups of trimellitic anhydride are directionally grafted, and the free carboxyl groups at the ends form discrete high-density ion clusters under vacuum dehydration. This not only gives the final acid value of 52-55mgKOH / g precise hydrophilicity, but also prevents the molecular chains from being tightly stacked through steric hindrance. Then, a trace amount of chain extender is introduced to finally obtain a rigid-flexible structure with hydrolytic stability, which greatly improves the adhesion.

[0027] S3: Nanoscale dispersion of capped polyester S3.1: Cool the end-capped polyester obtained in step S2.3 to 80°C, add 1.5 wt% N,N-dimethylcyclohexylamine to the end-capped polyester and mix evenly. Then emulsify with a high-speed dispersion disc with a linear velocity of 20 m / s for 10 min to obtain an emulsion. S3.2: Add 80℃ hot water to the emulsion, with the hot water accounting for 45% of the emulsion mass. Control the dropping rate at 0.8L / min. After dropping, disperse for 12min. Then add an aqueous solution containing 0.3% nano-cerium dioxide, with the aqueous solution containing nano-cerium dioxide accounting for 60% of the emulsion mass. Control the dropping rate at 2L / min. After dropping, perform ultrasonic dispersion treatment at a frequency of 25kHz for 30min to obtain an aqueous dispersion. S3.3: The aqueous dispersion is filtered through a ceramic membrane with a pore size of 0.1 μm to remove residual monomers and obtain a highly weather-resistant polyester aqueous dispersion. Example 3

[0028] A method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials, such as Figure 1 As shown, the specific steps include: S1: Prepolymer Synthesis S1.1: Add 30 parts by weight of 1,1-cyclobutyldicarboxylic acid, 18 parts by weight of adipic acid, 28 parts by weight of 1,4-cyclohexanediethanol and 8 parts by weight of 2-butyl-2-ethyl-1,3-propanediol to a high-pressure reactor, and purge with nitrogen to completely replace the air in the reactor. S1.2: Start the heating device and raise the temperature in the high-pressure reactor to 175°C at a heating rate of 15°C / min. Hold the temperature for 1.5 hours, then raise the temperature to 200°C at a heating rate of 6°C / min. Maintain the temperature and then stir continuously at 250 r / min for 4 hours to obtain the prepolymer. By performing staged temperature-controlled polycondensation of 1,1-cyclobutyldicarboxylic acid, adipic acid, 1,4-cyclohexanediethanol, and 2-butyl-2-ethyl-1,3-propanediol under nitrogen protection, the structure of 1,1-cyclobutyldicarboxylic acid is obtained at low temperature. The butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol is stably embedded in the main chain, forming a molecular-level buffer cavity in the subsequent polycondensation process. This allows the polymer network to maintain the UV resistance and weather resistance of the alicyclic structure, while ensuring the complete preservation of the 1,1-cyclobutyldicarboxylic acid alicyclic structure. At the same time, it forces the butyl-ethyl branch to be evenly distributed on the side of the molecular chain, thus constructing active sites for the subsequent end-capping reaction.

[0029] S2: Gradient end-capping and chain extension of the prepolymer S2.1: After the prepolymer obtained in step S1.2 is naturally cooled to 150℃, 6% of the total mass of the prepolymer is added to tetrahydrophthalic anhydride. The mixture is stirred at a stirring speed of 150r / min for 45min under nitrogen protection to obtain the first end-capped prepolymer. S2.2: Heat the first end-capped prepolymer to 185℃, add trimellitic anhydride at 10% of the total mass of the first end-capped prepolymer, evacuate to 0.08MPa and stir for 100min, control the final acid value of the reaction system to 55mgKOH / g, and obtain the second end-capped prepolymer; S2.3: Add 0.8 parts by weight of ADR-4468 chain extender to the second end-capped prepolymer and continue the reaction at 165℃ and 165r / min for 60min to obtain end-capped polyester. Through gradient end-capping operation and precise control of temperature and reaction sequence, firstly, the cyclic anhydride of tetrahydrophthalic anhydride is selectively grafted onto the terminal hydroxyl groups of the prepolymer at a mild temperature to form rigid end groups. This structure acts as a "molecular anchor" to suppress the tendency of chain segment crystallization and avoid ring-opening side reactions at high temperatures. Then, under negative pressure, the three anhydride groups of trimellitic anhydride are directionally grafted, and the free carboxyl groups at the ends form discrete high-density ion clusters under vacuum dehydration. This not only gives the final acid value of 52-55mgKOH / g precise hydrophilicity, but also prevents the molecular chains from being tightly stacked through steric hindrance. Then, a trace amount of chain extender is introduced to finally obtain a rigid-flexible structure with hydrolytic stability, which greatly improves the adhesion.

[0030] S3: Nanoscale dispersion of capped polyester S3.1: Cool the end-capped polyester obtained in step S2.3 to 85°C, add 1.2 wt% N,N-dimethylcyclohexylamine to the end-capped polyester and mix evenly. Then emulsify with a high-speed dispersion disc with a linear velocity of 25 m / s for 15 min to obtain an emulsion. S3.2: Add 85℃ hot water to the emulsion, with the hot water accounting for 40% of the emulsion mass. Control the dropping rate at 1L / min. After dropping, disperse for 15min. Then add an aqueous solution containing 0.3% nano-cerium dioxide, with the aqueous solution containing nano-cerium dioxide accounting for 55% of the emulsion mass. Control the dropping rate at 3L / min. After dropping, perform ultrasonic dispersion treatment at a frequency of 30kHz for 35min to obtain an aqueous dispersion. S3.3: The aqueous dispersion is filtered through a ceramic membrane with a pore size of 0.1 μm to remove residual monomers and obtain a highly weather-resistant polyester aqueous dispersion. Example 4

[0031] A method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials, such as Figure 1 As shown, the specific steps include: S1: Prepolymer Synthesis S1.1: Add 32 parts by weight of 1,1-cyclobutyldicarboxylic acid, 20 parts by weight of adipic acid, 30 parts by weight of 1,4-cyclohexanediethanol and 9 parts by weight of 2-butyl-2-ethyl-1,3-propanediol to a high-pressure reactor, and purge with nitrogen to completely replace the air in the reactor. S1.2: Start the heating device and raise the temperature in the high-pressure reactor to 172°C at a heating rate of 12°C / min. Hold the temperature for 1.2 hours, then raise the temperature to 197°C at a heating rate of 5.5°C / min. Maintain the temperature and then stir continuously at 225 r / min for 3.8 hours to obtain the prepolymer. By performing staged temperature-controlled polycondensation of 1,1-cyclobutyldicarboxylic acid, adipic acid, 1,4-cyclohexanediethanol, and 2-butyl-2-ethyl-1,3-propanediol under nitrogen protection, the structure of 1,1-cyclobutyldicarboxylic acid is obtained at low temperature. During the initial stage, the butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol is stably embedded in the main chain. In the subsequent polycondensation, it forms a structure capable of absorbing and converting ultraviolet light. The butyl-ethyl branch of 2-butyl-2-ethyl-1,3-propanediol works synergistically with the flexible segments of adipic acid to plasticize and form molecular-level buffer cavities between the rigid framework composed of cyclohexanediethanol. This allows the polymer network to maintain the UV resistance and weather resistance rigidity of the alicyclic structure and ensure the complete preservation of the 1,1-cyclobutyldicarboxylic acid alicyclic structure. At the same time, it forces the butyl-ethyl branch to be evenly distributed on the side positions of the molecular chain, thus constructing active sites for the subsequent end-capping reaction.

[0032] S2: Gradient end-capping and chain extension of the prepolymer S2.1: After the prepolymer obtained in step S1.2 is naturally cooled to 145℃, tetrahydrophthalic anhydride of 7% of the total mass of the prepolymer is added, and the mixture is stirred at a stirring speed of 135r / min for 42min under nitrogen protection to obtain the first end-capped prepolymer. S2.2: Heat the first end-capped prepolymer to 183℃, add trimellitic anhydride at 11% of the total mass of the first end-capped prepolymer, evacuate to 0.075MPa and stir for 90min, control the final acid value of the reaction system to 54mgKOH / g, and obtain the second end-capped prepolymer; S2.3: Add 0.9 parts by weight of ADR-4468 chain extender to the second end-capped prepolymer and continue the reaction at 163℃ and 155r / min for 55min to obtain end-capped polyester. Through gradient end-capping operation and precise control of temperature and reaction sequence, firstly, the cyclic anhydride of tetrahydrophthalic anhydride is selectively grafted onto the terminal hydroxyl groups of the prepolymer at a mild temperature to form rigid end groups. This structure acts as a "molecular anchor" to suppress the tendency of chain segment crystallization and avoid ring-opening side reactions at high temperatures. Then, under negative pressure, the three anhydride groups of trimellitic anhydride are directionally grafted, and the free carboxyl groups at the ends form discrete high-density ion clusters under vacuum dehydration. This not only gives the final acid value precise hydrophilicity, but also prevents the molecular chains from being tightly stacked through steric hindrance. Then, a trace amount of chain extender is introduced to finally obtain a rigid-flexible structure with hydrolytic stability, which greatly improves the adhesion.

[0033] S3: Nanoscale dispersion of capped polyester S3.1: Cool the end-capped polyester obtained in step S2.3 to 82°C, add 1.4 wt% N,N-dimethylcyclohexylamine to the end-capped polyester and mix evenly. Then emulsify with a high-speed dispersion disc with a linear velocity of 23 m / s for 12 min to obtain an emulsion. S3.2: Add 83℃ hot water to the emulsion, with the hot water accounting for 43% of the emulsion mass. Control the dropping rate at 0.9L / min. After dropping, disperse for 13min. Then add an aqueous solution containing 0.4% nano-cerium dioxide, with the aqueous solution containing nano-cerium dioxide accounting for 58% of the emulsion mass. Control the dropping rate at 2.5L / min. After dropping, perform ultrasonic dispersion treatment at a frequency of 28kHz for 33min to obtain an aqueous dispersion. S3.3: The aqueous dispersion is filtered through a ceramic membrane with a pore size of 0.1 μm to remove residual monomers and obtain a highly weather-resistant polyester aqueous dispersion.

[0034] Comparative Example 1 The difference from Example 1 is that 1,1-cyclobutyldicarboxylic acid in step S1.1 is replaced with an equal mass of cyclohexanedicarboxylic acid, while the remaining steps are the same as in Example 1, to obtain a polyester aqueous dispersion.

[0035] The high weather-resistant polyester aqueous dispersions prepared in Examples 1-4 were subjected to particle size testing, and were placed at 25°C for three months to check for precipitation. The test results are as follows: Figure 2 As shown.

[0036] It can be seen that the average particle size of the high weather-resistant polyester aqueous dispersion is small, and no precipitation occurred after being placed at 25℃ for three months, indicating good storage stability.

[0037] The high weather-resistant polyester aqueous dispersions prepared in Examples 1-4 and the polyester aqueous dispersion prepared in Comparative Example 1 were coated onto the surface of an aluminum plate with an emulsion thickness of 0.3 mm. The emulsions were dried at 100°C for 1 hour. Then, another aluminum plate was laminated onto the surface of the aluminum plate coated with the high weather-resistant polyester aqueous dispersion. A hot press was used to hot press the plates at 200°C and 3 MPa for 20 seconds. After cooling, the tensile shear strength was tested using a universal testing machine, with three tests performed. The test results are as follows: Figure 3 As shown.

[0038] It can be seen that the high weather-resistant polyester aqueous dispersion prepared by using 1,1-cyclobutyldicarboxylic acid and the phased temperature-controlled polycondensation of this application has excellent adhesive properties.

[0039] The high weather-resistant polyester aqueous dispersions prepared in Examples 1-4 and the polyester aqueous dispersion prepared in Comparative Example 1 were coated on the surface of an aluminum plate with an emulsion thickness of 0.3 mm. The emulsions were dried at 100°C for 1 hour, serving as the test group. The weather-promoting properties were then evaluated using a xenon lamp weathering tester. After 2000 hours, the gloss of the coatings in the test group was compared with the gloss of the coatings that had not undergone the weather-promoting test. The comparison results are as follows: Figure 4 As shown.

[0040] It can be seen that the gloss of the coating film in the experimental group hardly decreased, while the gloss of the comparative example 1 decreased significantly, indicating that the polyester aqueous dispersion prepared by 1,1-cyclobutyldicarboxylic acid and the staged temperature-controlled polycondensation of this application has excellent weather resistance.

[0041] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can 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 those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials, characterized in that, Includes the following steps: S1: Prepolymer Synthesis 30-35 parts by weight of 1,1-cyclobutyldicarboxylic acid, 18-22 parts by weight of adipic acid, 28-32 parts by weight of 1,4-cyclohexanediethanol and 8-10 parts by weight of 2-butyl-2-ethyl-1,3-propanediol were prepolymerized at 170-175°C under a nitrogen atmosphere, and then prepolymerized at 195-200°C to obtain a prepolymer. S2: Gradient end-capping and chain extension of the prepolymer After cooling the prepolymer to 140-150℃, add 6-8% of tetrahydrophthalic anhydride by weight of the prepolymer and stir under a nitrogen atmosphere to obtain the first end-capped prepolymer. Then, heat the first end-capped prepolymer to 180-185℃ and add 10-12% of trimellitic anhydride by weight of the first end-capped prepolymer. Stir under a vacuum of 0.07-0.08 MPa to obtain the second end-capped prepolymer. Finally, add 0.8-1 parts by weight of chain extender and continue stirring at 160-165℃ to obtain the end-capped polyester. S3: Nanoscale dispersion of capped polyester The capped polyester is cooled to 80-85℃, and N,N-dimethylcyclohexylamine, accounting for 1.2-1.5 wt% of the capped polyester, is added and mixed evenly. Then, it is added to a high-speed dispersion tray for emulsification to obtain an emulsion. Hot water and an aqueous solution containing 0.3-0.5% nano-cerium dioxide are added to the emulsion for dispersion. The aqueous solution containing nano-cerium dioxide accounts for 55-60% of the emulsion mass to obtain an aqueous dispersion. After filtration, a weather-resistant polyester aqueous dispersion is obtained.

2. The method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials according to claim 1, characterized in that, Step S1, prepolymer synthesis, specifically includes the following steps: S1.1: Add 30-35 parts by weight of 1,1-cyclobutyldicarboxylic acid, 18-22 parts by weight of adipic acid, 28-32 parts by weight of 1,4-cyclohexanediethanol and 8-10 parts by weight of 2-butyl-2-ethyl-1,3-propanediol to a high-pressure reactor, and purge with nitrogen to completely replace the air in the reactor. S1.2: Start the heating device and raise the temperature in the high-pressure reactor to 170-175℃ at a heating rate of 10-15℃ / min. Hold the temperature for 1-1.5h, then raise the temperature to 195-200℃ at a heating rate of 5-6℃ / min. Hold the temperature and then stir continuously at a speed of 200-250r / min for 3.5-4h to obtain the prepolymer.

3. The method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials according to claim 2, characterized in that, Step S2, gradient end-capping and chain extension of the prepolymer, specifically includes the following steps: S2.1: After the prepolymer obtained in step S1.2 is naturally cooled to 140-150℃, tetrahydrophthalic anhydride is added, and the mixture is stirred at a stirring speed of 120-150r / min for 40-45min under nitrogen protection to obtain the first end-capped prepolymer. S2.2: Heat the first end-capped prepolymer to 180-185℃, add trimellitic anhydride, evacuate to 0.07-0.08MPa and stir for 80-100min, control the final acid value of the reaction system to 52-55mgKOH / g, and obtain the second end-capped prepolymer; S2.3: Add 0.8-1 parts by weight of chain extender to the second end-capped prepolymer, and continue to react at 160-165℃ and 150-165r / min for 50-60min to obtain end-capped polyester.

4. The method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials according to claim 3, characterized in that, Step S3, the nano-dispersion of the end-capped polyester, specifically includes the following steps: S3.1: Cool the end-capped polyester obtained in step S2.3 to 80-85℃, add 1.2-1.5wt% of N,N-dimethylcyclohexylamine to the end-capped polyester and mix evenly. Then emulsify with a high-speed dispersion disc with a linear speed of 20-25m / s for 10-15min to obtain an emulsion. S3.2: Add hot water at 80-85℃ to the emulsion, control the dropping rate at 0.8-1L / min, disperse for 12-15min after dropping, then add an aqueous solution containing 0.3-0.5% nano-cerium dioxide, control the dropping rate at 2-3L / min, and then perform ultrasonic dispersion treatment at a frequency of 25-30kHz for 30-35min to obtain an aqueous dispersion; S3.3: The aqueous dispersion is filtered through a ceramic membrane with a pore size of 0.1 μm to remove residual monomers and obtain a highly weather-resistant polyester aqueous dispersion.

5. The method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials according to claim 3, characterized in that, The chain extender in step S2.3 is ADR-4468 chain extender.

6. The method for preparing a high weather-resistant polyester aqueous dispersion suitable for roll materials according to claim 4, characterized in that, In step S3.2, hot water accounts for 40-45% of the emulsion's mass.

7. A highly weather-resistant polyester aqueous dispersion suitable for roll materials, characterized in that, It is prepared by the preparation method of a high weather-resistant polyester aqueous dispersion suitable for roll materials as described in any one of claims 1-6.

8. The high weather-resistant polyester aqueous dispersion suitable for roll materials according to claim 7, characterized in that, Used for coating and protecting metal coils.

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