High-temperature-resistant polyester dispersion adhesive and preparation method thereof

Abstract

The invention discloses a high-temperature-resistant polyester dispersion adhesive and a preparation method thereof, and relates to the field of adhesives, the preparation method comprises the following steps: preparing a prepolymer a with Tg greater than 60 DEG C, introducing ammonium carboxylate on the prepolymer a to obtain a prepolymer b, then adding a dispersion medium into the prepolymer b to obtain a rigid emulsion containing rigid latex particles; wherein the particle size of the rigid latex particles is 80-120nm, and the rigid latex particles contain carboxyl; diluting the rigid emulsion to obtain a diluent, and dropwise adding a flexible monomer mixture into the diluent to obtain a dispersion comprising composite latex particles; wherein the composite latex particles are of an asymmetric structure with a rigid surface and a flexible surface; and carrying out selective surface modification on the rigid surface of the composite latex particles by using PDMS, and carrying out pH regulation and filtration to obtain the high-temperature-resistant polyester dispersion adhesive. The adhesive can effectively prevent the plasticizer from migrating from the PVC base material to the adhesive layer, and ensures that the adhesive layer has good flexibility and initial adhesion.

Description

Technical Field

[0001] This invention relates to the field of adhesive preparation, and more particularly to a high-temperature resistant polyester dispersion adhesive and its preparation method. Background Technology

[0002] In the bonding applications of flexible polyvinyl chloride (PVC) materials, plasticizer migration has always been a technical problem that has plagued the industry. Because this material contains a large amount of plasticizer, when it is combined with high-temperature resistant polyester dispersion adhesives, the plasticizer will migrate into the adhesive layer and plasticize the polyester molecular chains, resulting in a decrease in the glass transition temperature of the adhesive and a deterioration in the bonding performance. This migration and plasticization process constitutes the core contradiction between the two materials and has become a key technical bottleneck restricting its reliable application.

[0003] While traditional high-temperature resistant polyester dispersion adhesives offer environmental advantages, small-molecule plasticizers can leach from the substrate and migrate into the adhesive layer during prolonged contact with PVC materials containing plasticizers. Existing technologies typically address this issue by adding external crosslinking agents or physically blending nanomaterials. However, these methods have significant limitations. For instance, while adding small-molecule crosslinking agents can construct a three-dimensional network, it often leads to decreased adhesive storage stability, and its anti-migration performance depends entirely on the completion of the later curing reaction, which is uncertain. Furthermore, some highly efficient crosslinking agents pose toxicity and environmental risks. On the other hand, physically blending nanomaterials faces challenges such as filler agglomeration, difficulty in ensuring dispersion uniformity, and often sacrifices the flexibility and transparency of the adhesive layer while improving anti-migration properties.

[0004] Therefore, a high-temperature resistant polyester dispersion adhesive and its preparation method are proposed to solve the problems of unstable anti-migration properties and the sacrifice of other properties. Summary of the Invention

[0005] The purpose of this invention is to provide a high-temperature resistant polyester dispersion adhesive and its preparation method, which solves the problems of unstable anti-migration performance and sacrifice of other properties.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for preparing a high-temperature resistant polyester dispersion adhesive, the method comprising the following steps: Step S1: Prepare prepolymer a with Tg > 60℃, and introduce ammonium carboxylate salt onto prepolymer a to obtain prepolymer b. Then add dispersion medium to prepolymer b to obtain rigid emulsion containing rigid latex particles; wherein the rigid latex particles have a particle size of 80-120nm and contain carboxyl groups. Step S2: Dilute the rigid emulsion to obtain a diluted solution, and add a mixture of flexible monomers dropwise to the diluted solution to obtain a dispersion containing composite latex particles; wherein the composite latex particles have an asymmetric structure with rigid and flexible surfaces; Step S3: Selectively modify the rigid surface of the composite latex particles using PDMS, and after pH adjustment and filtration, obtain a high-temperature resistant polyester dispersion adhesive.

[0007] The prepolymer a is obtained according to the following steps: PTA, NDA, NPG and monobutyltin oxide were placed in a reactor under nitrogen atmosphere and heated to obtain a melt. Then, the reactor was evacuated and the melt was heated to a first temperature to carry out a polycondensation reaction to obtain prepolymer a. The weight ratio of PTA, NDA, NPG to monobutyltin oxide is (40-50):(5-10):(30-40):(0.04-0.06), the heating temperature is 180-220℃, the first temperature is 240-250℃, and the intrinsic viscosity of prepolymer a is 0.50-0.55 dL / g. -1 .

[0008] The prepolymer b is obtained according to the following steps: Prepolymer a was kept at the second temperature and TMA was added to maintain the reaction. After the reaction was completed, the temperature was lowered and then DMEA was added to neutralize the pH to 7.5-8.0 to obtain prepolymer b.

[0009] The second temperature is 170-180℃, the heat preservation reaction time is 30-50 min, the cooling temperature is 80-90℃, and the weight ratio of prepolymer a to TMA is 100:(1.5-2.5).

[0010] The rigid emulsion is obtained according to the following steps: The prepolymer b is stirred and a dispersion medium is added to the prepolymer b to form a mixture. The continuous phase of the mixture changes from an oil phase to an aqueous phase, resulting in a rigid emulsion. The stirring speed is 8000-10000 rpm, the dispersion medium is hot water with a temperature of 65-70℃, and the solid content of the rigid emulsion is 28-32%.

[0011] Step S2 specifically includes the following steps: Step S21: Mix the rigid emulsion with deionized water to obtain mixture a, and then add SDBS to mixture a to obtain a diluted solution; Step S22: Mix and emulsify AA, BDO, isooctyl mercaptoacetate, alkylphenol polyoxyethylene ether and water to obtain a flexible monomer mixture; Step S23: Heat the diluted solution to the third temperature and stir it, while simultaneously adding the flexible monomer mixture dropwise to obtain the dispersion.

[0012] In step S21, the solid content of the diluent is 10-14%, and the amount of SDBS added is 0.05-0.2% of the mass of mixture a; in step S22, the weight ratio of AA, BDO, isooctyl mercaptoacetate, alkylphenol polyoxyethylene ether and water is (25-35):(20-30):(0.2-0.5):(0.5-1.0):(40-60), and the mixing and emulsification temperature is 55-65℃; in step S23, the third temperature is 70-80℃, the stirring speed is 200-300 rpm, the dripping time of the flexible monomer mixture is 4-6 h, and the weight ratio of the diluent to the flexible monomer mixture is 1:(0.5-1.5).

[0013] Step S3 specifically includes the following steps: Step S31: Maintain the dispersion at the fourth temperature and add PDMS for heat preservation and stirring to obtain the gel solution; Step S32: Add ammonia to the adhesive solution to adjust the pH of the adhesive solution to 8.0-8.5, and then remove the gel from the adhesive solution with a sieve to obtain a high-temperature resistant polyester dispersion adhesive.

[0014] In step S31, the fourth temperature is 45-55℃, the heat preservation and stirring time is 1-1.5h, and the weight ratio of the dispersion to PDMS is 100:(0.5-2.0); in step S32, the sieve is 200-300 mesh, and the solid content of the adhesive is 21-27%.

[0015] A high-temperature resistant polyester dispersion adhesive, wherein the high-temperature resistant polyester dispersion adhesive is prepared by the preparation method of the high-temperature resistant polyester dispersion adhesive as described above.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a high-temperature resistant polyester dispersion adhesive and its preparation method. The method involves sequentially constructing a rigid emulsion with a high glass transition temperature, performing asymmetric grafting on the surface of rigid latex particles to form composite latex particles with both rigid and flexible surfaces, and selectively modifying the rigid surfaces of the composite latex particles using PDMS. This results in the final adhesive having inherent, self-assembly-driven forces in the composite latex particles within the dispersion, independent of subsequent crosslinking reactions. These forces originate from the surface energy differences generated by the asymmetric structure of the particles and the further increased surface energy difference between the rigid and flexible surfaces after PDMS modification. During the drying process after coating onto a PVC substrate, the composite… Latex particles can spontaneously orient their low-surface-energy rigid surfaces and tightly pack them at the interface between the adhesive layer and PVC, forming a dense physical barrier. This effectively blocks the migration of plasticizers from the PVC substrate to the adhesive layer without the need for small-molecule crosslinking agents, thus improving the adhesive's anti-migration and temperature resistance properties. At the same time, this method avoids the use of small-molecule crosslinking agents, eliminating the storage stability problems and toxicity risks caused by them. Furthermore, the flexibility contributed by the flexible surfaces of the particles themselves ensures that the adhesive layer has good flexibility and initial tack, solving the problem of decreased flexibility that may occur when physically blending nanomaterials. This achieves a balance of high anti-migration properties, excellent storage stability, good flexibility, and environmental friendliness. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0019] Figure 1 This is a flowchart of the preparation method in this invention. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0022] Example 1: Please see Figure 1 This embodiment describes a method for preparing a high-temperature resistant polyester dispersion adhesive, which includes the following steps: Step S1: Prepare prepolymer a with Tg > 60℃, and introduce ammonium carboxylate salt onto prepolymer a to obtain prepolymer b. Then add dispersion medium to prepolymer b to obtain rigid emulsion containing rigid latex particles; wherein the rigid latex particles have a particle size of 80-120nm and contain carboxyl groups. Step S2: Dilute the rigid emulsion to obtain a diluted solution, and add a mixture of flexible monomers dropwise to the diluted solution to obtain a dispersion containing composite latex particles; wherein the composite latex particles have an asymmetric structure with rigid and flexible surfaces; Step S3: Selectively modify the rigid surface of the composite latex particles using PDMS, and after pH adjustment and filtration, obtain a high-temperature resistant polyester dispersion adhesive.

[0023] Specifically, in step S1, a prepolymer a with a Tg > 60℃ is prepared, and an ammonium carboxylate salt is introduced onto the prepolymer a to obtain prepolymer b. Then, a dispersion medium is added to the prepolymer b to obtain a rigid emulsion containing rigid latex particles. The rigid latex particles have a particle size of 80-120 nm and contain carboxyl groups. Prepolymer a is obtained according to the following steps: PTA (terephthalic acid), NDA (2,6-naphthalenedicarboxylic acid), NPG (neopentyl glycol) and monobutyltin oxide were placed in a reactor under nitrogen atmosphere and heated to obtain a melt. Then, the reactor was evacuated and the melt was heated to a first temperature to carry out a polycondensation reaction to obtain prepolymer a. The weight ratio of PTA, NDA, NPG to monobutyltin oxide is (40-50):(5-10):(30-40):(0.04-0.06), the heating temperature is 180-220℃, the initial temperature is 240-250℃, and the intrinsic viscosity of prepolymer a is 0.50-0.55 dL / g. -1 Preferably, the weight ratio of PTA, NDA, NPG to monobutyltin oxide is 45:8:35:0.05, the heating temperature is 200°C, and the first temperature is 245°C.

[0024] It should be noted that, using PTA and NDA as rigid acid components and NPG as a rigid alcohol component, under nitrogen protection and monobutyltin oxide catalysis, an esterification reaction first occurs at 180-220℃ to generate oligomers. Subsequently, a polycondensation reaction is carried out at a first temperature of 240-250℃ under vacuum conditions, causing the molecular chains to further grow. The material, initially a mixture of solid powder and crystalline particles, is melted upon heating into a homogeneous and transparent liquid, ultimately transforming into a high-viscosity polyester melt with an intrinsic viscosity of 0.50-0.55 dL / g. -1 .

[0025] It is known that a rigid polyester skeleton with a Tg > 60℃ was constructed according to the above steps. The naphthalene ring structure of NDA provides a huge steric hindrance, which restricts the mobility of molecular chain segments and provides the cohesive energy basis for the entire adhesive system to resist heat deformation and plasticizer penetration. In addition, the rigid polyester skeleton also lays the foundation for the subsequent construction of the rigid surface of composite latex particles. Its inherent high Tg (glass transition temperature) and dense structure can effectively resist plasticizer plasticization. The dense structure is composed of rigid chain segments packed tightly together, with strong intermolecular forces, which constitutes an initial physical barrier to the diffusion of small molecule plasticizers.

[0026] Prepolymer b is obtained according to the following steps: Prepolymer a was kept at the second temperature and TMA (trimeric triphenyl benzoic anhydride) was added to maintain the reaction. After the reaction was completed, the temperature was lowered and then DMEA (dimethylethanolamine) was added to neutralize the pH to 7.5-8.0 to obtain prepolymer b.

[0027] The second temperature is 170-180℃, the holding time is 40 min, the cooling temperature is 80-90℃, and the weight ratio of prepolymer a to TMA is 100:(1.5-2.5); preferably, the second temperature is 175℃, the holding time is 40 min, the cooling temperature is 85℃, and the weight ratio of prepolymer a to TMA is 100:2.

[0028] It should be noted that the anhydride group of TMA undergoes a ring-opening reaction with the hydroxyl groups at the end of the prepolymer α molecular chain at a second temperature of 170-180℃, thereby introducing carboxyl groups into the polyester chain end. Subsequently, the temperature is lowered to 80-90℃, and DMEA is added for neutralization, converting the carboxyl groups into hydrophilic groups of ammonium carboxylate salt. During this process, the material remains in a molten state macroscopically, but its chemical structure changes from a hydrophobic linear polyester to a polymer with hydrophilic ionic groups at the end. In addition, in the above reaction, cooling can prevent further esterification reactions between residual carboxyl groups and hydroxyl groups, which would reduce the number of introduced carboxyl groups and thus affect the subsequent water-based efficiency and the reactivity of the particle surface. Furthermore, neutralization at a temperature of 80-90℃ ensures that the amine molecules in DMEA have sufficient kinetic energy to fully react with the carboxyl groups, while avoiding the loss of a large amount of DMEA due to excessively high temperatures, which would affect the neutralization efficiency and cause safety hazards.

[0029] It is known that by covalently introducing ammonium carboxylate salts as strongly hydrophilic groups at the polyester chain ends, prepolymer b is transformed from a hydrophobic material into a water-dispersible polymer. This allows for the subsequent preparation of rigid emulsions using an environmentally friendly phase inversion method with water as the medium, completely avoiding the use of organic solvents and conforming to environmental protection trends. At the same time, the aqueous system is easier to coat and clean, and reduces safety risks during production and application. In addition, the carboxyl groups introduced in prepolymer b, after phase inversion to form a rigid emulsion, will be oriented on the surface of rigid latex particles due to their amphiphilicity. These surface carboxyl groups become the preset chemical anchoring points for asymmetric grafting in subsequent steps. They ensure that the polycondensation reaction of the flexible monomer mixture can be precisely guided and confined to the surface of the rigid latex particles, rather than homopolymerizing in the bulk phase. This is the basis for the subsequent formation of asymmetric composite latex particles.

[0030] Rigid emulsions are obtained according to the following steps: The prepolymer b is stirred and a dispersion medium is added to the prepolymer b to form a mixture. The continuous phase of the mixture changes from an oil phase to an aqueous phase, resulting in a rigid emulsion. The stirring speed is 8000-10000 rpm, the dispersion medium is hot water with a temperature of 65-70℃, and the solid content of the rigid emulsion is 28-32%; preferably, the stirring speed is 9000 rpm, the hot water temperature is 65℃, and the solid content of the rigid emulsion is 30%.

[0031] It should be noted that when hot water at 65-70℃ is added to prepolymer b under high-speed shearing at 8000-10000 rpm, an oil-in-water (W / O) emulsion is initially formed. As the amount of water continues to increase, the system undergoes a phase transformation, and the continuous phase changes from an oil phase to an aqueous phase (O / W type). The material changes from a high-viscosity paste to a milky white liquid with good flowability. Prepolymer b is divided and stabilized into spherical latex particles with a particle size of 80-120 nm. The hydrophilic groups of the ammonium carboxylate salt on its surface are oriented at the oil-water interface, giving the particles electrostatic stability.

[0032] It is known that this step yields a rigid emulsion with uniform particle size and containing carboxyl groups through phase inversion. The particle size of 80-120 nm in the rigid emulsion provides a suitable specific surface area and steric hindrance for subsequent asymmetric grafting, while the solid content of 28-32% is the balance point to ensure that the emulsion has good stability and fluidity. This rigid emulsion is not only the base for subsequent reactions, but the carboxyl groups on its surface are also the chemical basis for realizing asymmetric grafting and final self-assembly.

[0033] It is worth noting that by controlling the stirring speed, the temperature of the dispersion medium, and the amount added, the particle size and stability of the particles in the rigid emulsion can be precisely controlled, ensuring the progress of subsequent steps; the hot water temperature maintains the fluidity of prepolymer b and promotes the smooth progress of the phase transformation process, while the stirring speed ensures the formation of stable nanoscale particles.

[0034] It is important to emphasize that step S1 pre-positions and confines the rigidity and high cohesive energy properties required for the anti-migration function within nanoscale latex particles, rather than distributing them uniformly throughout the entire adhesive layer. Specifically, the rigid polyester skeleton composed of PTA and NDA provides the high glass transition temperature and dense microstructure necessary to resist plasticizer plasticization. Because the rigidity is encapsulated within particles of 80-120 nm, the resulting adhesive layer is not a monolithic, rigid material. Simultaneously, by introducing TMA and DMEA to create a hydrophilic layer of ammonium carboxylate on the surface of the rigid emulsion particles, the particles are endowed with water-based properties while also having clearly defined surface chemical reaction sites. This ensures that the rigidity property exists as a function, preparing for the subsequent construction of asymmetric structures without causing abnormally high viscosity or storage instability in the product adhesive. This avoids sacrificing processability and stability in pursuit of temperature resistance.

[0035] Specifically, in step S2, the concentration of the rigid emulsion is diluted to obtain a diluted solution, and a mixture of flexible monomers is added dropwise to the diluted solution to obtain a dispersion containing composite latex particles; wherein, the composite latex particles have an asymmetric structure with rigid and flexible surfaces; Step S2 specifically includes the following steps: Step S21: Mix the rigid emulsion with deionized water to obtain mixture a, and then add SDBS (sodium dodecylbenzene sulfonate) to mixture a to obtain a diluted solution; In step S21, the solid content of the diluent is 10-14%, and the amount of SDBS added is 0.05-0.2% of the mass of mixture a. Alternatively, the solid content of the diluent is 12%, and the amount of SDBS added is 0.08% of the mass of mixture a. It should be noted that diluting the rigid emulsion creates a low-solids environment, providing ample space for the free movement of latex particles and preventing the grafting reaction from being uniformly covered due to the particles being too close together. The amount of SDBS added is slightly higher than its critical micelle concentration to ensure sufficient coverage and stability of the rigid latex particle surface, while ensuring that there are no large amounts of free micelles in the system.

[0036] It is known that step S21 transforms the material from a high-concentration rigid emulsion into a diluted and stable dispersion, creating a controlled reaction environment and laying the necessary physicochemical foundation for subsequent asymmetric grafting.

[0037] Step S22: Mix and emulsify AA (adipic acid), BDO (1,4-butanediol), isooctyl mercaptoacetate, alkylphenol polyoxyethylene ether and water to obtain a flexible monomer mixture; In step S22, the weight ratio of AA, BDO, isooctyl mercaptoacetate, alkylphenol polyoxyethylene ether, and water is (25-35):(20-30):(0.2-0.5):(0.5-1.0):(40-60), and the mixing and emulsification temperature is 60°C; preferably, the weight ratio of AA, BDO, isooctyl mercaptoacetate, alkylphenol polyoxyethylene ether, and water is 30:25:0.3:0.8:50, and the mixing and emulsification temperature is 60°C. It should be noted that alkylphenol polyoxyethylene ether, as an emulsifier, has lipophilic groups in its molecules that interact with the oily monomer mixture (formed by emulsification of AA and BDO) and isooctyl mercaptoacetate, while hydrophilic groups extend into the aqueous phase. Under the shear force provided by mechanical stirring, the oily monomer mixture is dispersed into micron-sized droplets, forming a stable oil-in-water emulsion. Furthermore, isooctyl mercaptoacetate, as a chain transfer agent, is uniformly dispersed in these droplets.

[0038] It is known that the mixed emulsification forms a uniform dispersion system between the originally incompatible oily monomers and water, preventing phase separation and floating of the oily monomers and ensuring that they can participate in the reaction with a constant composition during subsequent droplet addition. Meanwhile, isooctyl mercaptoacetate is pre-dispersed uniformly in the oily monomer droplets, which can effectively control the molecular weight growth of the flexible polyester chain in the subsequent polycondensation reaction, preventing the formation of gel due to excessively high molecular weight or excessive cross-linking, and ensuring the controllability of the molecular structure of the final product.

[0039] It is important to emphasize that step S22, by providing a well-structured and controllably reactive mixture of flexible monomers, ensures that the flexible monomers can diffuse to specific active sites on the surface of rigid latex particles at a controllable rate. This enables the selective and directional growth of flexible chains on one side of the particle, constructing a composite latex particle with an asymmetric structure. This well-structured asymmetric structure provides the self-assembly driving force for adhesive particles and is the basis for the spontaneous formation of a dense anti-migration barrier at the PVC substrate interface, giving the product adhesive stable and reliable anti-migration properties.

[0040] Step S23: Heat the diluted solution to the third temperature and stir it, while simultaneously adding the flexible monomer mixture dropwise to obtain the dispersion.

[0041] In step S23, the third temperature is 70-80℃, the stirring speed is 200-300rpm, the dropping time of the flexible monomer mixture is 4-6h, and the weight ratio of the diluent to the flexible monomer mixture is 1:(0.5-1.5); preferably, the third temperature is 75℃, the stirring speed is 250rpm, the dropping time of the flexible monomer mixture is 5h, and the weight ratio of the diluent to the flexible monomer mixture is 1:1.2.

[0042] It should be noted that maintaining a reaction temperature of 70-80℃ aims to provide sufficient activation energy for the subsequent polycondensation reaction, while avoiding instability caused by excessively high temperatures. A stirring speed of 200-300 rpm ensures the mass and heat transfer efficiency of the system and avoids damage to the particle structure caused by excessive shear force. In addition, the continuous dropping time of 5 hours is to maintain a low instantaneous monomer concentration in the system. Under this environment, the newly added flexible monomer cannot form new micelles, so the flexible monomer preferentially diffuses to the active sites with higher surface energy of the rigid latex particles and undergoes a polycondensation reaction. Due to the asymmetry of the reaction sites and the steric hindrance effect, the flexible segments can selectively grow on one side of the rigid latex particles, ultimately forming a composite latex particle with an asymmetric structure of clearly defined rigid and flexible surfaces.

[0043] It is known that step S23 transforms the diluent into a dispersion containing asymmetric composite latex particles, thereby realizing the asymmetric structure construction of the composite latex particles. The duality of the asymmetric structure of the composite latex particles is the original driving force for their self-assembly at the PVC interface, enabling the adhesive to spontaneously form a dense, rigid surface barrier at the PVC interface during film formation. This lays the foundation for solving the plasticizer migration problem, allowing the adhesive to have anti-migration capabilities upon completion of preparation, no longer relying on subsequent curing, and avoiding uncertainties.

[0044] Understandably, under the action of steps S1 and S2, self-assembling composite latex particles are formed in the dispersion, and the anti-plasticizer migration ability of these particles allows the adhesive to no longer rely on the later cross-linking reaction, thus solving the problem of unstable anti-migration performance. It should be emphasized that the water contact angle of the rigid surface of the composite latex particles in the dispersion is 85-95°, and the water contact angle of the flexible surface is 60-75°.

[0045] It is important to emphasize that step S2, through controlled low solids content and dripping time, allows flexible segments (provided by AA and BDO) to selectively grow on one side of the rigid emulsion particles, forming an asymmetric composite latex particle structure with both rigid and flexible surfaces. This structure allows the composite latex particle to simultaneously possess two functions: its rigid surface provides the material basis for the subsequent formation of an anti-migration barrier, while its flexible surface contributes to the flexibility, initial tack, and adaptability to the substrate of the adhesive layer. The flexibility of the adhesive layer obtained by curing the adhesive is not achieved by adding plasticizers, but is provided by the inherent polymer segments of the flexible surface of the composite latex particle itself, ensuring flexibility. Therefore, this method abandons the method of adjusting flexibility by physically blending flexible resins or plasticizers, thereby avoiding performance degradation caused by the migration, volatilization, or compatibility issues of these additives, and ensuring the coexistence of high anti-migration properties and excellent flexibility.

[0046] Specifically, in step S3, the rigid surface of the composite latex particles is selectively modified using PDMS, and after pH adjustment and filtration, a high-temperature resistant polyester dispersion adhesive is obtained.

[0047] Step S3 specifically includes the following steps: Step S31: Maintain the dispersion at the fourth temperature and add PDMS (amino-terminated polydimethylsiloxane) for heat preservation and stirring to obtain a gel solution; In step S31, the fourth temperature is 45-55℃, the holding and stirring time is 1-1.5h, and the weight ratio of dispersion to PDMS is 100:(0.5-2.0); preferably, the fourth temperature is 50℃, the holding and stirring time is 1h, and the weight ratio of dispersion to PDMS is 100:1.5. It should be noted that the amidation reaction between the primary amino groups in the PDMS molecule and the residual carboxyl groups on the rigid surface of the composite latex particles achieves selective covalent modification of the rigid surface. Specifically, when the dispersion is maintained at the fourth temperature, the mobility of the PDMS molecules is enhanced, and the terminal amino functional groups are more likely to undergo directional reactions with the carboxyl groups on the rigid surface. Due to its inherent hydrophobicity and low surface energy, the rigid surface of the composite latex particles exhibits a stronger affinity for PDMS, while the flexible surface hardly participates in the reaction due to its hydrophilicity and steric hindrance. In this process, PDMS is permanently anchored to the rigid surface of the composite latex particles through covalent bonding, forming a low surface energy modification layer, while the macroscopic physical state of the flexible surface and the entire dispersion system remains unchanged.

[0048] It is known that after step S31, the surface energy difference between the rigid and flexible surfaces of the composite latex particles is increased. The water contact angle of the rigid surface increases from 85-95° before modification to 105-115°, while the water contact angle of the flexible surface remains at 60-75°. The amplified surface energy difference, as a driving force, can more effectively promote the composite latex particles to orient their low surface energy rigid surfaces and pack them tightly onto the high surface energy PVC substrate interface during the subsequent coating and drying process.

[0049] Understandably, under the action of step S31, the directionality and orderliness of the self-assembly of composite latex particles are improved, thereby ensuring that a denser and more complete physical barrier can be formed at the interface between the adhesive layer (formed after the product adhesive is cured) and the PVC substrate, so as to improve the anti-migration ability of the adhesive. In addition, the optimization of the above method makes up for the deficiency that the self-assembly driving force of composite latex particles is insufficient to achieve a single-layer arrangement at the interface in all cases. By selectively modifying the rigid surface with PDMS, the reliability and consistency of the anti-migration function are ensured.

[0050] Step S32: Add ammonia to the adhesive solution to adjust the pH of the adhesive solution to 8.0-8.5, and then remove the gel from the adhesive solution with a sieve to obtain a high-temperature resistant polyester dispersion adhesive.

[0051] In step S32, the sieve is 200-300 mesh and the solid content of the adhesive is 21-27%; preferably, the sieve is 200 mesh and the solid content of the adhesive is 25%.

[0052] It should be noted that by adding ammonia to adjust the pH of the adhesive solution to a weakly alkaline range of 8.0-8.5, the acid-base neutralization reaction is used to fully ionize the residual carboxyl groups on the surface of the composite latex particles into carboxylate anions. This ensures the long-term kinetic stability of the dispersion system through enhanced electrostatic repulsion of the double electric layer between particles. Subsequently, the adhesive solution is filtered through a 200-mesh sieve to remove a small amount of larger gel particles or mechanical impurities generated in the early preparation process. This avoids coating defects or stress concentration in the subsequent coating process of the product adhesive. In addition, the pH change of the adhesive solution during this process increases the absolute value of the Zeta potential on the surface of the composite latex particles, enhancing the repulsive force between particles.

[0053] It is important to emphasize that modifying the rigid surface of the composite latex particles with amino-terminated polydimethylsiloxane (PDMS) enhances the directionality and efficiency of the self-assembly of the composite latex particles without altering the overall chemical composition of the adhesive or introducing small molecules that would impair performance. PDMS is permanently anchored to the rigid surface via covalent bonds, reducing its surface energy and allowing the composite latex particles to align more precisely at the PVC substrate interface during film formation, creating a denser barrier. This process does not involve the flexible surface of the particles, thus preserving the inherent flexibility and adhesion of the adhesive layer. Furthermore, adjusting the pH to 8.0-8.5 enhances the repulsive force of the electric double layer, ensuring the storage stability of the product adhesive and preventing performance loss due to flocculation and precipitation. Screen filtration removes potential gels, ensuring a smooth and intact adhesive layer and avoiding mechanical weakness caused by macroscopic defects. This, in turn, ensures the excellent performance of the adhesive layer formed by steps S1 and S2.

[0054] It is worth noting that the asymmetric structure of the rigid and flexible surfaces of the composite latex particles can be observed by cryo-transmission electron microscopy; the water contact angle between the rigid and flexible surfaces of the composite latex particles is obtained by measuring the static water contact angle of the adhesive or dispersion film using a contact angle measuring instrument.

[0055] In summary, the preparation method of this embodiment constructs asymmetric composite latex particles and enhances their self-assembly ability, enabling the adhesive to possess inherent and stable anti-migration properties while maintaining flexibility and other properties, effectively solving the problem of unstable anti-migration properties and sacrifice of other properties in the prior art.

[0056] Data for adhesive A obtained according to Example 1, adhesive B (traditional external crosslinking type), and adhesive C (traditional physical blend nanotype) obtained by conventional methods are shown in Tables 1, 2, and 3: Table 1 Table 1 shows the tests for the migration resistance and heat resistance of each adhesive. Adhesive A, due to the formation of a dense and sufficient barrier that hinders plasticizer penetration, exhibits the least increase in mass and the highest Tg retention rate. It retains most of its bond strength at high temperatures, demonstrating excellent durability. Adhesives B and C, however, show performance degradation due to insufficient migration resistance. It is understandable that the plasticizer migration resistance was tested using ASTM D1239 as the standard, and specific data were obtained using equipment such as an oven and analytical balance. The glass transition temperature (Tg) retention rate was tested using ISO 6721-1 as the standard, and specific data were obtained using equipment such as a dynamic thermomechanical analyzer. The high-temperature bond strength retention rate was tested using ASTM D3330 as the standard, and specific data were obtained using equipment such as a universal tensile testing machine and a temperature control chamber.

[0057] Table 2 Table 2 shows the mechanical and adhesive properties of each adhesive. Adhesive A not only has high adhesive strength, but also the highest strength retention rate after aging (95%), and its flexibility is better than that of adhesives B and C, proving that it has both flexibility and rigidity. It is understandable that the peel strength at 180°C at room temperature is tested according to GB / T 2792, and specific data are obtained using equipment such as a universal testing machine; the peel strength retention rate after aging is tested according to GB / T 2792, and specific data are obtained using equipment such as a universal testing machine and an oven; the T-bending flexibility is tested according to ASTM D4145, and specific data are obtained using equipment such as a bending tester.

[0058] Table 3 Table 3 shows the testing of the processing and physical properties of each adhesive. Adhesive A exhibits good storage stability and low VOC characteristics while maintaining good transparency, making it the most versatile. Adhesive B, on the other hand, suffers from inherent defects such as poor storage stability and high VOC. Adhesive C, due to nanoparticle aggregation and light scattering, suffers from severely degraded transparency, affecting the product's appearance. It is understood that storage stability was tested according to ISO 3219, with specific data obtained using equipment such as a rotational viscometer; VOC content was tested according to GB / T 23986, with specific data obtained using equipment such as gas chromatography-mass spectrometry; and adhesive layer transparency was tested according to ASTM D1003, with specific data obtained using equipment such as a haze meter.

[0059] Example 2: This embodiment provides a high-temperature resistant polyester dispersion adhesive, which is prepared using the preparation method for high-temperature resistant polyester dispersion adhesive as described in Example 1.

[0060] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high temperature resistant polyester dispersion adhesive, characterized in that, The preparation method comprises the following steps: Step S1, preparing a prepolymer a with Tg>60℃, and introducing an ammonium carboxylate salt on the prepolymer a to obtain a prepolymer b, and then adding a dispersion medium to the prepolymer b to obtain a rigid emulsion containing rigid latex particles; wherein the particle size of the rigid latex particles is 80-120 nm, and the rigid latex particles contain carboxyl groups; Step S2, diluting the concentration of the rigid emulsion to obtain a dilution liquid, and adding a flexible monomer mixture to the dilution liquid to obtain a dispersion containing composite latex particles; wherein the composite latex particles are non-symmetrical structures of rigid surfaces and flexible surfaces; Step S3, using PDMS to selectively modify the rigid surface of the composite latex particles, and after pH adjustment and filtration, a high-temperature-resistant polyester dispersion adhesive is obtained.

2. The method for preparing the high-temperature resistant polyester dispersion adhesive according to claim 1, characterized in that, The prepolymer a is obtained according to the following steps: PTA, NDA, NPG and monobutyl tin oxide are placed in a reaction kettle in a nitrogen environment and heated to obtain a melt, then the reaction kettle is vacuumized, the melt is heated to a first temperature for polycondensation reaction to obtain the prepolymer a; The weight ratio of the PTA, NDA, NPG and monobutyl tin oxide is (40-50):(5-10):(30-40):(0.04-0.06), the heating temperature is 180-220℃, the first temperature is 240-250℃, and the intrinsic viscosity of the prepolymer a is 0.50-0.55dL / g -1 .

3. The method for preparing the high-temperature resistant polyester dispersion adhesive according to claim 2, characterized in that, The prepolymer b is obtained according to the following steps: The prepolymer a is maintained at a second temperature, and TMA is added for heat preservation reaction, and then cooled after the heat preservation reaction is completed, and then DMEA is added for neutralization to a pH value of 7.5-8.0 to obtain the prepolymer b. The second temperature is 170-180℃, the heat preservation reaction time is 30-50min, the cooling temperature is 80-90℃, and the weight ratio of the prepolymer a to TMA is 100: (1.5-2.5).

4. The method for preparing the high-temperature resistant polyester dispersion adhesive according to claim 3, characterized in that, The rigid emulsion is obtained according to the following steps: The prepolymer b is stirred, and a dispersion medium is added to the prepolymer b to form a mixture, the continuous phase of the mixture changes from an oil phase to a water phase, and the rigid emulsion is obtained; The stirring speed is 8000-10000 rpm, the dispersion medium is hot water, and the temperature of the hot water is 65-70℃, and the solid content of the rigid emulsion is 28-32%.

5. The method for preparing the high-temperature resistant polyester dispersion adhesive according to claim 1, characterized in that, The step S2 specifically comprises the following steps: Step S21, mixing the rigid emulsion with deionized water to obtain a mixed liquid a, and then adding SDBS to the mixed liquid a to obtain a dilution liquid; Step S22, mixing and emulsifying AA, BDO, mercaptoacetic acid isooctyl ester, and alkylphenol polyoxyethylene ether with water to obtain a flexible monomer mixture; Step S23, heating the dilution liquid to a third temperature and stirring, and synchronously adding the flexible monomer mixture to obtain the dispersion.

6. The method for preparing the high-temperature resistant polyester dispersion adhesive according to claim 5, characterized in that, The solid content of the diluent is 10-14% in the step S21, and the adding amount of the SDBS is 0.05-0.2% of the mass of the mixed solution a; the weight ratio of the AA, BDO, mercaptoacetic acid isooctyl ester, alkylphenol polyoxyethylene ether and water is (25-35):(20-30):(0.2-0.5):(0.5-1.0):(40-60) in the step S22, and the temperature of the mixed emulsion is 55-65℃; the third temperature is 70-80℃ in the step S23, the stirring speed is 200-300rpm, the dropping time of the flexible monomer mixture is 4-6h, and the weight ratio of the diluent and the flexible monomer mixture is 1:(0.5-1.5).

7. The method for preparing the high-temperature resistant polyester dispersion adhesive according to claim 1, characterized in that, The step S3 specifically comprises the following steps: In the step S31, the dispersion is maintained at a fourth temperature, and PDMS is added for heat preservation stirring to obtain a glue solution; in the step S32, ammonia is added to the glue solution, the pH of the glue solution is adjusted to 8.0-8.5, and then a screen is used to remove the gel in the glue solution to obtain the high-temperature-resistant polyester dispersion adhesive. In the step S31, the fourth temperature is 45-55℃, the heat preservation stirring time is 1-1.5h, and the weight ratio of the dispersion and the PDMS is 100:(0.5-2.0); in the step S32, the screen is 200-300 meshes, and the solid content of the adhesive is 21-27%.

8. The method for preparing the high-temperature resistant polyester dispersion adhesive according to claim 7, characterized in that, The high-temperature-resistant polyester dispersion adhesive is prepared by the preparation method of the high-temperature-resistant polyester dispersion adhesive according to any one of claims 1-8.

9. A high temperature resistant polyester dispersion adhesive, characterized in that, ​

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