A self-reactive foaming polyurethane tile adhesive and its preparation method

Abstract

This invention relates to the field of adhesives and discloses a self-reactive foaming polyurethane tile adhesive, composed of component A and component B. The adhesive does not contain any added catalyst or foam stabilizer. Component A consists of polyether polyol and calcium carbonate, and component B consists of polymethylene polyphenyl isocyanate and calcium carbonate. The mixing weight ratio of component A to component B is 100:25-35, and at this mixing ratio, the NCO:OH molar ratio of the system is 1.05-1.2:1. This invention achieves rapid and controllable foaming by using a catalyst-free and foam stabilizer-free two-component adhesive composed of polyether polyol, PMDI, and calcium carbonate. The high viscosity of component A provides physical foam stabilization, while the high reactivity of PMDI provides chemical pore-locking. By setting a rigid microskeleton structure composed of high-functionality PMDI and 42%-45% highly filled calcium carbonate, and achieving a dry pull-out bond strength ≥2.1 MPa, this invention solves the engineering problem of hollowing and detachment caused by elastic adhesive creep in exterior wall tile bonding scenarios.

Description

Technical Field

[0001] This invention relates to the field of adhesives, specifically to a self-reactive foaming polyurethane tile adhesive and its preparation method. Background Technology

[0002] Traditionally, the adhesive used for bonding exterior wall tiles in residential buildings is a thermosetting adhesive, such as an epoxy resin system. This process requires a high-temperature oven at nearly 200°C to cure the adhesive, resulting in extremely high energy consumption and generating a large amount of fumes in the high-temperature environment, which seriously pollutes the environment and harms the health of operators.

[0003] To address the aforementioned issues, the industry has shifted towards room-temperature curing two-component polyurethane systems. Two-component polyurethanes utilize the addition reaction between isocyanate groups (-NCO) and hydroxyl groups (-OH) in polyols at room temperature to generate urethane bonds, thereby achieving room-temperature curing and solving the problems of high energy consumption and pollution associated with traditional thermosetting systems.

[0004] However, existing room-temperature curing two-component polyurethane adhesives still face the following technical challenges when dealing with the specific application scenario of connecting exterior wall tiles: 1. The contradiction between foam control and strength maintenance: To reduce material density and cost, and improve workability and insulation, it is often necessary to introduce foam structures. However, traditional polyurethane foam systems rely on external catalysts (such as tertiary amines and organotin compounds) and foam stabilizers (organosilicon surfactants) to regulate the foaming rate and cell structure. This not only increases the complexity and cost of the formulation, but catalyst residues may also have an adverse effect on the long-term weather resistance of the material. More importantly, conventional foaming processes are difficult to obtain a uniform and fine closed-cell structure under rapid construction site conditions, resulting in a significant decrease in the material's mechanical strength and adhesion.

[0005] 2. The contradiction between high filler content and high bond strength: In order to reduce raw material costs and improve material dimensional stability, inorganic fillers (such as calcium carbonate) are usually added to the formulation. However, the addition of conventional inorganic fillers will significantly reduce the continuity of the resin matrix, resulting in a sharp drop in the cohesive strength and bond strength of the adhesive. In particular, when the filler content exceeds 30%, the strength decay is particularly obvious, which seriously limits the economy and practicality of the formulation design.

[0006] 3. Mismatch between elasticity and rigidity: Traditional polyurethane elastic sealants pursue high elongation and flexibility to adapt to the displacement of building joints. However, in the case of bonding exterior wall tiles, excessive flexibility may become a defect. Under the continuous shear stress generated by the weight of the tile and thermal expansion, the adhesive layer may creep or slowly slip, eventually leading to hollowing or even detachment of the tile. The core requirement for the adhesive in this scenario is "rigid positioning and shear resistance", rather than "elasticity to follow displacement".

[0007] Therefore, how to achieve rapid and stable foaming with high inorganic filler content without relying on external catalysts and foam stabilizers, while simultaneously obtaining the high bonding strength and rigidity required for the connection of exterior wall tiles, is a problem that existing technologies have failed to solve. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a self-reactive foaming polyurethane tile adhesive, solving the problems mentioned in the background section. This invention utilizes a two-component adhesive composed of polyether polyol, PMDI, and calcium carbonate, without added catalysts or foam stabilizers. The high viscosity of component A provides physical foam stabilization, while PMDI's high reactivity provides chemical pore-locking, achieving rapid and controllable foaming. Furthermore, by establishing a rigid microskeleton structure composed of high-functionality PMDI and 42%-45% highly filled calcium carbonate, and achieving a dry pull-out bond strength ≥2.1 MPa, this invention solves the engineering problem of elastic adhesive creep leading to hollowing and detachment in exterior wall tile bonding scenarios.

[0009] A self-reactive foaming polyurethane tile adhesive comprises component A and component B, wherein the adhesive does not contain any added catalyst or foam stabilizer. Component A consists of polyether polyol and calcium carbonate, and component B consists of polymethylene polyphenyl polyisocyanate and calcium carbonate. When components A and B are mixed, the NCO:OH molar ratio of the system is 1.05-1.2:1. In this invention, the polyether polyol is the main reactant, and its terminal hydroxyl group -OH has high reactivity. The polymethylene polyphenyl polyisocyanate PMDI is a high-functionality curing agent, with each molecule containing an average of 2.6-2.9 -NCO groups. The calcium carbonate is an inert inorganic filler, which reduces costs and improves dimensional stability through physical filling. After mixing, -OH and -NCO undergo an addition polymerization reaction: R-NCO + HO-R' → R-NH-CO-O-R', generating urethane bonds and forming a highly cross-linked three-dimensional network structure. This invention eliminates the presence of any third component, such as catalysts, foam stabilizers, or chain extenders. Adding a catalyst would lead to an excessively rapid reaction, resulting in insufficient wetting and micro-defects at the interface. Adding a foam stabilizer would increase costs and leave residues that affect weather resistance. Adding a chain extender might disrupt the balance between high filler density and high crosslinking density. This invention achieves rapid and controllable foaming and curing solely through the reactivity of the two main materials, without any catalysts or foam stabilizers. The NCO:OH molar ratio is the NCO index. When the NCO index is controlled between 1.05 and 1.2, a suitable excess of NCO is formed, effectively avoiding self-polymerization side reactions at room temperature without a catalyst. Simultaneously, a suitable amount of CO2 is generated for foaming, and in the later stages of curing, it reacts with ambient moisture to form a dense polyurea layer, thereby achieving a wet bond strength retention rate of ≥90%.

[0010] The NCO:OH molar ratio is the NCO index, a core parameter in polyurethane design. An index of 1.0 represents a theoretically equivalent reaction, with the main reaction being: -NCO + -OH → -NH-COO-. When the mixing weight ratio of component A to component B is 100:25-35, the NCO index reaches 1.05-1.2. A small excess of these components will produce a side reaction: excess -NCO + H2O → -NH2+. CO2↑, thus providing the sole source of foaming gas by releasing an appropriate amount of CO2; if the NCO index <1.05, meaning component B is too little, there is not enough excess NCO to react with water to generate CO2, resulting in insufficient foaming or even no foaming; if the NCO index >1.2, meaning component B is too much, the excess NCO, under the condition of exothermic reaction accumulation leading to local high temperature, may undergo self-polymerization side reactions with the already formed urethane or urea bonds, generating urethane and biuret, causing uncontrolled crosslinking density, material elongation far below 10%, and tendency to crack; this invention precisely controls the NCO index within... 1.05-1.2, under normal temperature and catalyst-free conditions, the self-polymerization side reaction is effectively avoided, while an appropriate amount of NCO is retained for foaming and subsequent water resistance enhancement; under normal temperature and catalyst-free curing conditions, the self-polymerization side reaction hardly occurs due to the lack of sufficient activation energy, and the excess NCO is mainly used for: (1) reacting with trace amounts of water in the initial stage of mixing to generate CO2 foaming; (2) reacting with ambient moisture on the surface of the cell wall in the later stage of curing to generate a dense polyurea layer; after the formation of the polyurea layer, it effectively blocks moisture from penetrating into the adhesive layer, which is an important chemical mechanism for maintaining a wet bonding strength of up to 90%.

[0011] Preferably, the mixing weight ratio of component A to component B is 100:25-35; within this mixing ratio range; component A, by weight percentage, consists of the following raw materials: Polyether polyols: 55%-65%; Calcium carbonate: 35%-45%; Component B, by weight percentage, consists of the following raw materials: Polymethylene polyphenyl polyisocyanate: 50%-60%; Calcium carbonate: 40%-50%. In this invention, the mixing weight ratio of component A to component B is 100:25-35. Within this mixing ratio range, the NCO:OH molar ratio of the system falls exactly between 1.05 and 1.2:1. If the mixing weight ratio is lower than 100:25, i.e., component B is too little, the NCO index is <1.05, the excess NCO is insufficient, foaming is inadequate or even non-foaming, and the crosslinking density is low, resulting in insufficient strength. If the mixing weight ratio is higher than 100:35, i.e., component B is too much, the NCO index is >1.2, the excess NCO is prone to triggering self-polymerization side reactions under exothermic reaction conditions, generating urea-formate and biuret, leading to uncontrolled crosslinking density, material brittleness, i.e., elongation at break is far below 5%, and cost increases. This invention controls the mixing weight ratio at 100:25-35, achieving the optimal balance between foaming amount and crosslinking density. The polyether polyol is the main reactant providing -OH groups, and its total content determines the viscosity of component A and the amount of available -NCO reactants. The polymethylene polyphenyl polyisocyanate (PMDI) is the main reactant providing -NCO reactants, and its total content determines the crosslinking density and heat release. If the polyether polyol content is >65%, then calcium carbonate content is <35%, resulting in insufficient system viscosity and easy merging and escape of bubbles during foaming. If the polyether polyol content is <55%, then calcium carbonate content is >45%, resulting in excessively high viscosity, difficulty in stirring, and reduced reactivity of -NCO, leading to incomplete curing. If the polymethylene polyphenyl polyisocyanate content is >60%, then calcium carbonate content is <40%, resulting in excessively high heat release during curing, generating internal stress, and increasing costs. If the polymethylene polyphenyl polyisocyanate content (PMDI) content is <50%, then calcium carbonate content is >50%, resulting in excessively high viscosity of component B, uneven mixing, and insufficient local crosslinking.

[0012] Preferably, component A has a viscosity of 2500±700 mPa·s and a specific gravity of 1.60±0.03 at 23±2℃; component B has a viscosity of 200±50 mPa·s and a specific gravity of 1.22±0.03 at 23±2℃. In this invention, both components A and B are measured according to GB / T 2794-2013. The calcium carbonate particles form a physical filling network in the polyether polyol, which is the physical basis for "foam stabilization" and the main filler for the high viscosity of component A; the liquid properties of the polymethylene polyphenyl polyisocyanate (PMDI) in component B result in low viscosity, which facilitates rapid and uniform mixing with component A and promotes rapid construction. The viscosity of component A is controlled at 2500±700 mPa·s. If the viscosity of component A is <1800, the filler content is too low, and the system cannot effectively prevent bubble coalescence, resulting in large and uneven pores. If the viscosity is >3200, the filler content exceeds 45%, generating a large amount of frictional heat during stirring and mixing, accelerating the reaction and shortening the pot life. The viscosity of component B is >250, indicating that polymethylene polyphenyl polyisocyanate (PMDI) may have undergone partial self-polymerization, resulting in a decrease in NCO content and affecting reactivity. If the viscosity of component B is <150, the functionality of PMDI is too low, and crosslinking is insufficient.

[0013] Preferably, the polyether polyol is a propylene oxide-based polyether polyol with a number-average molecular weight (Mn) ranging from 3000 to 6000, a functionality ranging from 2.5 to 3.5, and a hydroxyl value ranging from 28 to 56 mg KOH / g. In this invention, Mn = 3000-6000 signifies a suitable molecular chain length. If Mn < 3000, the molecular chain is too short, resulting in a short network between crosslinking points after curing, leading to an overly brittle material and an elongation far below the target value. If Mn > 6000, the molecular chain is too long, the hydroxyl value is too low, the total amount of reactant -OH is insufficient, resulting in a high residual -NCO content after curing, a long post-curing time, and consequently, difficult construction and incomplete curing. A functionality between 2.5 and 3.5 means that each molecule has an average of about 3 -OH reaction sites, which is the basis for forming three-dimensional crosslinks. If the functionality is <2.5, mainly linear chains are formed, and sufficient crosslink density cannot be formed, resulting in a hardness that does not reach D48. If the functionality is >3.5, the crosslink density is too high, the elongation drops to near zero, and the adhesive layer may crack under thermal stress. In this invention, the polyether is selected to have a high content of primary hydroxyl groups, and the reaction rate with PMDI is sufficient to achieve rapid curing under catalyst-free conditions, thereby enabling a "self-reactive" chemical change.

[0014] Preferably, the NCO content of the polymethylene polyphenyl polyisocyanate is 30%-33%, the viscosity at room temperature is 100-250 mPa·s, and the average functionality is approximately 2.6-2.9. In this invention, the NCO content of the polymethylene polyphenyl polyisocyanate between 30%-33% is a standard indicator for polymerized MDI, which can effectively ensure the concentration of reactive groups; the functionality between 2.6-2.9 ensures that each PMDI molecule has an average of about 2.7 -NCO groups participating in crosslinking, thus effectively ensuring the source of high crosslinking density. If NCO < 30%, the PMDI has partially reacted with water and deteriorated, resulting in decreased activity; if NCO > 33%, the PMDI originates from a special process, which is costly and involves an excessively vigorous reaction. If the functionality < 2.6, the crosslinking density is insufficient, leading to decreased hardness and strength after curing; if the functionality > 2.9, the crosslinking density is too high, the elongation approaches zero, and the adhesive layer becomes brittle. The high functionality of the polymethylene polyphenyl polyisocyanate PMDI allows the CO2 generated during foaming to be rapidly trapped in a highly cross-linked network, forming uniform closed pores, thus achieving the effect of eliminating the need for a foam leveling agent.

[0015] Preferably, the average particle size of the calcium carbonate is 2-10 μm, and the water content is controlled below 0.3%; after mixing components A and B, calcium carbonate accounts for 42%-45% of the total weight of the adhesive. In this invention, the calcium carbonate (CaCO3) is an inert inorganic filler with stable chemical properties, wide availability, and low cost. The surface of the calcium carbonate (CaCO3) contains trace amounts of hydroxyl groups (-OH), which can form weak chemical adsorption with -NCO. If the average particle size of the calcium carbonate is <2 μm, the specific surface area is too large, the oil absorption value is too high, and the viscosity of component A will seriously exceed the standard, making construction impossible. If the average particle size of the calcium carbonate is >10 μm, the particles are too coarse, forming stress concentration points in the thin adhesive layer, increasing the risk of interface damage. If its water content is >0.3%, too much free water is introduced, the foaming reaction occurs earlier than the gelation reaction, a large amount of CO2 escapes, the pores are large, and the density fluctuates drastically. At the same time, excessive water consumes -NCO, causing a substantial decrease in the NCO index and incomplete curing. After the components A and B are mixed, although calcium carbonate accounts for as much as 42%-45% of the total weight of the adhesive, its dry pull-out bond strength is 2.1 MPa, which is higher than the 1.6 MPa of the low-filler comparison system. This is because the high-filler calcium carbonate and the high-functionality PMDI form a "micro-skeleton" stress dispersion structure, which makes the stress uniformly transmitted along the rigid filler network during pull-out, avoiding the problem of stress concentration at the resin and filler interface in the low-filler system.

[0016] Preferably, under conditions of 23±2℃ and 55±5% relative humidity, component A and component B are mixed at a weight ratio of 100:30. After stirring at 2500 rpm for 10 seconds, the foaming start time of the adhesive is 20±10 seconds, the foaming end time is 75±20 seconds, and the foam density is 0.66±0.07 g / cm³. In this invention, a foaming start time of 20±10 seconds means that there is approximately 10-30 seconds of open time after construction to complete the laying and pressing; a foaming end time of 75±20 seconds means that foaming is completed within approximately 1-2 minutes, entering the curing stage, which can effectively improve the operational efficiency at the construction site. A foam density of 0.66±0.07 g / cm³ means that compared to the density of non-foamed PU (approximately 1.2), the material of this invention has a weight reduction of approximately 50%. If the density is <0.59, the cells expand excessively, the cell walls are too thin, and the tensile strength and adhesive strength are below the acceptable level. If the density is >0.73, foaming is insufficient, the material is heavy, the cost increases, and the insulation performance decreases. This invention, without any catalyst or foam stabilizer, achieves stable foaming density and controllable foaming time by relying solely on the passive balance of raw material moisture content, ambient humidity, and exothermic reaction, realizing a "self-reactive foaming" effect. Furthermore, during the foaming process, the high viscosity of component A effectively inhibits excessive bubble growth and coalescence in the initial stage. Subsequently, the high reactivity of PMDI and polyether polyol precisely matches the gelation reaction rate with the foaming reaction rate, rapidly gelling and solidifying the bubbles after they reach the ideal size, thus "locking" the cell structure in a timely manner. This sequential synergistic mechanism of physical foam stabilization and chemical pore locking replaces the function of traditional foam stabilizers, achieving stable foaming without the need for external foam stabilizers.

[0017] Preferably, after the adhesive has cured, in the bonding test of glazed exterior wall tiles, the dry pull-out bond strength is ≥2.1 MPa, the wet-dry pull-out bond strength retention rate is ≥90%, and the failure mode is complete cohesive failure of the tile; the D-type hardness of the cured adhesive is 48±7, and the elongation at break is 5%-20%. In this invention, a pull-out strength of 2.1 MPa means that it can withstand approximately 525 kJ / m² on a 50 mm × 50 mm bonding surface. A tensile strength of kg; a wet retention rate ≥90% means that the adhesive strength hardly decreases after immersion in water; complete cohesive failure, i.e., 100% cohesive failure of the tile, means that the bonding force between the adhesive layer and the tile exceeds the strength of the tile itself; if the D-type hardness of the cured adhesive is <41, the material is too soft and creep will occur under the weight of the tile; if the D-type hardness of the cured adhesive is >55, the material is too hard and cannot buffer the stress generated by thermal expansion and contraction, and the tile may chip or the adhesive layer may crack; if the elongation at break is >20%, the material is too elastic, and the tile will slowly crack under continuous shear load. Slow slippage; if the elongation at break is <5%, the material is too brittle and hard, and the adhesive layer may crack internally under thermal stress; the high functionality of PMDI in this invention (2.6-2.9) brings high chemical crosslinking density, which works synergistically with the rigid particle network formed by inorganic calcium carbonate filler to form a "micro-skeleton" structure similar to microporous concrete. When subjected to tensile or shear stress, this structure can uniformly transfer stress along the rigid skeleton to the entire bonding surface, avoiding the local stress concentration common in low filler elastic systems, thereby changing the failure mode from interfacial failure to cohesive failure of the ceramic tile.

[0018] A method for preparing a self-reactive foaming polyurethane tile adhesive, used to prepare the self-reactive foaming polyurethane tile adhesive described in any one of the above claims, wherein the preparation process of component A is as follows: polyether polyol and calcium carbonate pretreated by drying at 110℃±5℃ are added into a mixing vessel in proportion, and stirred and dehydrated at 110-120℃ and vacuum degree ≤-0.095 MPa for 1.5-2 hours to reduce the water content of the mixture to below 0.08%. After dehydration, the mixture is cooled to below 40℃, discharged and sealed under nitrogen protection to obtain component A. The preparation process of component B is as follows: polymethylene polyphenyl polyisocyanate and dried calcium carbonate are added into a mixing vessel in proportion, stirred and mixed evenly at 40-50℃ under nitrogen protection, vacuum degassing, and sealed and packaged to obtain component B.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention relates to a self-reactive foaming polyurethane tile adhesive. Component A consists of polyether polyol and calcium carbonate, and component B consists of PMDI and calcium carbonate, neither of which contains any added catalysts or foam stabilizers. During foaming, component A, containing 35%-45% calcium carbonate, has a high viscosity of 2500±700 mPa·s, which initially inhibits excessive bubble growth and coalescence. Subsequently, the high functionality (2.6-2.9) of PMDI and the high reactivity of the primary hydroxyl groups in the polyether polyol cause rapid gelation, locking the cell structure in a timely manner. This invention eliminates the need for traditional foam stabilizers and catalysts, achieving a uniform closed-cell structure with a foam density of 0.66±0.07 g / cm³ without added additives. This overcomes the defects of traditional processes, such as complex formulations, high costs, and residues affecting weather resistance, which are caused by reliance on additives. 2. The self-reactive foaming polyurethane tile adhesive of this invention sets the mixing weight ratio of components A and B to 100:25-35, and the NCO index is precisely controlled at 1.05-1.2. Excess NCO first reacts with trace moisture in the raw materials to release CO2 as a foaming gas source. In the later stage of curing, a dense polyurea protective layer is generated on the surface of the cell wall by reacting with the ambient moisture. This makes the adhesive retain ≥90% of the wet-dry pull-out bond strength after 7 days of immersion in water, solving the problem of significant wet strength decay in conventional systems. 3. The self-reactive foaming polyurethane tile adhesive of this invention has a PMDI functionality of 2.6-2.9. Together with 42%-45% calcium carbonate filler, it forms a rigid micro-skeleton structure. When under stress, this structure uniformly transmits stress along the rigid network, avoiding localized stress concentration at the interface and changing the failure mode from interface failure to complete cohesive failure of the tile. In this invention, the high filler content of 42%-45% results in a dry pull-out bond strength of ≥2.1 MPa, which is higher than the 1.6 MPa of the low filler comparison system, breaking the conventional understanding that high filler content inevitably sacrifices bond strength. 4. The self-reactive foaming polyurethane tile adhesive of the present invention has a D-type hardness of 48±7 and a breaking elongation of 5%-20% after curing, forming a rigid adhesive layer. This rigidity ensures that the adhesive layer does not creep or slip under the continuous shear stress generated by the weight of the tile and thermal expansion and contraction, and reliably locks the tile to the wall. 5. The self-reactive foaming polyurethane tile adhesive of the present invention is composed of only four raw materials: polyether polyol, PMDI and calcium carbonate. It replaces the function of catalyst by the high reactivity of the raw materials themselves, replaces the function of foam stabilizer by the synergistic effect of high viscosity and rapid gelation, and replaces the function of chain extender by a rigid network with high functionality and high filling. 6. The preparation method of the self-reactive foaming polyurethane tile adhesive of the present invention only requires two steps: vacuum dehydration and mixing degassing. The types of raw materials are reduced from 7-10 in conventional formulas to 4, which greatly reduces the raw material cost, process complexity and batch quality control difficulty. Attached Figure Description

[0020] none. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0022] Example 1 This embodiment provides a self-reactive foaming polyurethane tile adhesive and its preparation method. The self-reactive foaming polyurethane tile adhesive includes component A and component B, wherein the weight parts of each raw material in component A are as follows: Polyether polyol: 57 parts; the polyether polyol is EP-330N produced by Shandong Lanxing Dongda Chemical Co., Ltd., which is propylene oxide based, with a number average molecular weight Mn≈5000, functionality≈3, and hydroxyl value≈33 mg KOH / g. Calcium carbonate: 43 parts; the calcium carbonate used is CC-1000 produced by Guangxi Huana New Material Technology Co., Ltd., with an average particle size of 5μm and a water content of <0.1%.

[0023] The weight parts of each raw material in component B are as follows: Polymethylene polyphenyl polyisocyanate PMDI: 57 parts; the polymethylene polyphenyl polyisocyanate PMDI is PM-200 produced by Wanhua Chemical Group Co., Ltd., with an NCO content of 31.2%, a viscosity of 180 mPa·s at room temperature, and an average functionality of about 2.7. Calcium carbonate: 43 parts; The calcium carbonate used in component B is the same as that used in component A, both of which are CC-1000 produced by Guangxi Huana New Material Technology Co., Ltd., with an average particle size of 5μm and a water content of <0.1%.

[0024] The mixing weight ratio of component A to component B is 100:30. Calculations show that the NCO:OH molar ratio of the system under this mixing ratio is 1.12:1. In this embodiment, no external catalyst or foam stabilizer is added.

[0025] Preparation method: Preparation of Component A: Polyether polyol and calcium carbonate were added to the reactor according to the formula ratio, stirring was started, the temperature was raised to 115℃, and the mixture was stirred and dehydrated for 1.8 hours under a vacuum of ≤-0.098MPa until the water content of the mixture dropped to below 0.08%; after dehydration was completed, the vacuum was turned off, nitrogen gas was introduced to purify the air, and the temperature was lowered to 38℃; the material was discharged under nitrogen protection, sealed and packaged to obtain Component A.

[0026] Preparation of Component B: PMDI and calcium carbonate pretreated at 110℃ were added to a mixing vessel according to the formula ratio; the mixture was stirred and mixed evenly at 45℃ under nitrogen protection, and then degassed under a vacuum of -0.09MPa for 15 minutes; finally, the mixture was discharged under nitrogen protection, sealed and packaged to obtain Component B.

[0027] According to the test results, the viscosity of component A obtained in this embodiment is 2480 mPa·s at 23°C and the specific gravity is 1.61; the viscosity of component B at 23°C is 195 mPa·s and the specific gravity is 1.22.

[0028] Example 2 This embodiment provides a self-reactive foaming polyurethane tile adhesive, comprising component A and component B, wherein the weight parts of each raw material in component A are as follows: Polyether polyol: 55 parts; the polyether polyol selected is Desmophen 4015T produced by Covestro Polymers (China) Co., Ltd., which is propylene oxide based, with a number average molecular weight Mn≈3000, functionality≈2.8, and hydroxyl value≈56 mg KOH / g. Calcium carbonate: 45 parts; the calcium carbonate used is GY-616 produced by Jiangxi Guangyuan Chemical Co., Ltd., with an average particle size of 8 μm and a moisture content of <0.2%; The weight parts of each raw material in component B are as follows: Polymethylene polyphenyl polyisocyanate PMDI: 60 parts; the polymethylene polyphenyl polyisocyanate PMDI is Lupranate M20S produced by BASF Polyurethane Specialty Products (China) Co., Ltd., with an NCO content of 31.5%, a viscosity of 210 mPa·s at room temperature, and an average functionality of approximately 2.8. Calcium carbonate: 40 parts, wherein the calcium carbonate in component B is the same as that used in component A.

[0029] The mixing weight ratio of component A to component B is 100:25. Calculations show that the NCO:OH molar ratio of the system under this mixing ratio is 1.08:1. In this embodiment, no external catalyst or foam stabilizer is added.

[0030] Preparation method: The preparation method is the same as in Example 1, except that the dehydration temperature of component A is 110°C and the time is 2.0 hours; and the mixing temperature of component B is 40°C.

[0031] According to the test results, the viscosity of component A obtained in this embodiment is 3250 mPa·s at 23°C and the specific gravity is 1.63; the viscosity of component B at 23°C is 230 mPa·s and the specific gravity is 1.19.

[0032] Example 3 This embodiment provides a self-reactive foaming polyurethane tile adhesive, comprising component A and component B, wherein the weight parts of each raw material in component A are as follows: Polyether polyol: 56 parts, wherein the polyether polyol is VORANOL™ 4703 provided by Dow Chemical Company, which is propylene oxide based, with a number average molecular weight Mn≈6000, functionality≈3.2, and hydroxyl value≈28 mg KOH / g; Calcium carbonate: 44 parts, wherein the calcium carbonate is Omyacarb2T produced by Omya (Shanghai) International Trading Co., Ltd., with an average particle size of 3μm and a moisture content of <0.05%; The weight parts of each raw material in component B are as follows: Polymethylene polyphenyl polyisocyanate PMDI: 56 parts; the polymethylene polyphenyl polyisocyanate PMDI is SUPRASEC 2185 produced by Huntsman Polyurethanes (China) Co., Ltd., with an NCO content of 30.8%, a viscosity of 150 mPa·s at room temperature, and an average functionality of about 2.6. Calcium carbonate: 44 parts; the calcium carbonate in component B is the same as that used in component A.

[0033] The mixing weight ratio of component A to component B is 100:35. Calculations show that the NCO:OH molar ratio of the system under this mixing ratio is 1.18:1. In this embodiment, no external catalyst or foam stabilizer is added.

[0034] Preparation method: The preparation method is the same as in Example 1, except that the dehydration temperature of component A is 120°C and the time is 1.5 hours; and the mixing temperature of component B is 50°C.

[0035] According to the test results, the viscosity of component A obtained in this embodiment is 1850 mPa·s at 23°C and the specific gravity is 1.58; the viscosity of component B at 23°C is 160 mPa·s and the specific gravity is 1.24.

[0036] Comparative Example 1 This comparative example provides a two-component polyurethane adhesive with low filler content, comprising component A and component B, wherein the weight parts of each raw material in component A are as follows: Polyether polyol: 85 parts, wherein the polyether polyol is EP-330N as in Example 1; Calcium carbonate: 15 parts, using CC-1000 as in Example 1.

[0037] The weight parts of each raw material in component B are as follows: PMDI: 85 portions; the PMDI used is PM-200, the same as in Example 1; Calcium carbonate: 15 parts; the calcium carbonate used is CC-1000, the same as in Example 1.

[0038] The mixing weight ratio of component A to component B is 100:20. Calculations show that the NCO:OH molar ratio of the system under this mixing ratio is 1.10:1, and the total weight percentage of calcium carbonate in the adhesive after mixing is 16.5%.

[0039] Preparation method: Refer to the preparation method in Example 1.

[0040] Comparative Example 2 This comparative example provides a two-component polyurethane adhesive with low filler content, comprising component A and component B, wherein the weight parts of each raw material in component A are as follows: Polyether polyol: 59.5 parts, wherein the polyether polyol is EP-330N as in Example 1; Calcium carbonate: 40 parts, using CC-1000 as in Example 1; Catalyst: 0.5 parts; the catalyst is dibutyltin dilaurate.

[0041] The weight parts of each raw material in component B are as follows: PMDI: 55 portions; the PMDI used is PM-200, the same as in Example 1; Calcium carbonate: 45 parts; the calcium carbonate used is CC-1000, the same as in Example 1.

[0042] The mixing weight ratio of component A to component B is 100:30. Calculations show that the NCO:OH molar ratio of the system under this mixing ratio is 1.12:1, and the total weight percentage of calcium carbonate in the adhesive after mixing is 42.8%.

[0043] Preparation method: In the preparation of component A, the catalyst is added and stirred evenly after dehydration and cooling and before discharge. The remaining steps are the same as in Example 1.

[0044] Performance Testing and Result Analysis The adhesives prepared in Examples 1-3 and Comparative Examples 1-2 were tested for performance according to the aforementioned standard test methods, and the results are summarized in Table 1.

[0045] Table 1. Performance Test Comparison Table of Examples and Comparative Examples

[0046] As shown in Table 1, the performance of Examples 1-3 all fall within the parameter range claimed in this invention: the foaming start time is 14-24 seconds, the foaming end time is 65-88 seconds, and the foaming density is 0.60-0.70 g / cm³, indicating that a controllable foaming process can be achieved under different formulation compositions; the dry pull-out bond strength is 2.05-2.25 MPa, all reaching the target value of ≥2.1 MPa; the wet-dry pull-out bond strength retention rate is 90.7%-93.8%, all reaching the target value of ≥90%; the D-type hardness is 43-52, and the elongation at break is 9%-12%, indicating that the cured adhesive has rigid characteristics, with a hardness higher than 40 and an elongation lower than 20%; the failure mode is 100% cohesive failure within the tile, indicating that the bond strength between the adhesive and the tile interface exceeds the strength of the tile itself. The above results show that Examples 1-3 of the present invention can achieve rapid and controllable foaming, high bonding strength, high wet strength retention rate and rigid mechanical characteristics without the addition of external catalysts and foam stabilizers.

[0047] The total filler content of Comparative Example 1 was 16.5%, significantly lower than the 42%-45% of Examples 1-3. As shown in Table 1, the dry pull-out bond strength of Comparative Example 1 was 1.58 MPa, lower than the 2.05-2.25 MPa of Examples 1-3. Comparative Example 1 exhibited a D-type hardness of 32 and an elongation at break of 28%, demonstrating elastomer characteristics, with a hardness below 40 and an elongation above 20%. The failure mode of Comparative Example 1 was interfacial failure. The above comparisons indicate that under low filler content conditions, the adhesive exhibits elastic characteristics and low bond strength. In contrast, the high filler content combined with high-functionality PMDI used in this invention can form a rigid microskeleton structure, achieving higher bond strength and rigid mechanical properties while increasing the filler content.

[0048] Comparative Example 2 added 0.5 parts of dibutyltin dilaurate as a catalyst. Its total filler content (42.8%) and NCO index (1.12) were basically the same as those of Example 1. As shown in Table 1, the foaming start time of Comparative Example 2 was 8 seconds, and the foaming end time was 38 seconds, significantly faster than the 18 seconds and 72 seconds of Example 1. The foaming density was 0.51 g / cm³, lower than the 0.64 g / cm³ of Example 1. The wet-dry pull-out bond strength retention rate of Comparative Example 2 was 81.5%, lower than the 90.7%-93.8% of Examples 1-3. The failure mode of Comparative Example 2 was mixed failure, that is, partial interfacial failure and partial cohesive failure, while Examples 1-3 were all 100% cohesive failure of the ceramic tile. The above comparison shows that the addition of catalyst accelerates the reaction process, resulting in a faster foaming process, lower cell density, and reduced wet bond strength retention rate. The catalyst-free solution of the present invention can achieve a more stable foaming process and better water resistance.

[0049] Based on Table 1 and the above analysis, Examples 1-3 of the present invention, without adding catalysts or foam stabilizers, achieve temporal synergy through the high viscosity physical foam stabilization of component A and the high reactivity chemical pore-locking of PMDI, resulting in a foaming start time of 14-24 seconds, a foaming end time of 65-88 seconds, and a foaming density of 0.60-0.70 g / cm³, thus achieving rapid and controllable foaming.

[0050] Examples 1-3 of the present invention use high-functionality PMDI with an average functionality of 2.6-2.9 and 42%-45% high-filled calcium carbonate, resulting in a dry pull-out bond strength ≥2.05 MPa, which is higher than the 1.58 MPa of the low-filler comparison system. Examples 1-3 of the present invention have a D-type hardness of 43-52, an elongation at break of 9%-12%, and a failure mode of 100% cohesive failure of the ceramic tile.

[0051] The NCO index of Examples 1-3 of the present invention is controlled at 1.05-1.2, so that the wet-dry pull-out bond strength retention rate is ≥90.7%, which is higher than 81.5% of the catalyst-containing comparative system.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Anyone skilled in the art can readily implement the present invention based on the above description. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention using the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still considered part of the technical solution of the present invention.

Claims

1. A self-reactive foaming polyurethane tile adhesive, characterized in that: The adhesive is composed of component A and component B, and does not contain any added catalyst or foam stabilizer. Component A is composed of polyether polyol and calcium carbonate, and component B is composed of polymethylene polyphenyl polyisocyanate and calcium carbonate. When component A and component B are mixed, the molar ratio of NCO:OH in the system is 1.05-1.2:

1.

2. The self-reactive foaming polyurethane tile adhesive according to claim 1, characterized in that: The mixing weight ratio of component A to component B is 100:25-35; Component A, by weight percentage, consists of the following raw materials: Polyether polyols: 55%-65%; Calcium carbonate: 35%-45%; Component B, by weight percentage, consists of the following raw materials: Polymethylene polyphenyl polyisocyanate: 50%-60%; Calcium carbonate: 40%-50%.

3. The self-reactive foaming polyurethane tile adhesive according to claim 2, characterized in that: The viscosity of component A at 23±2℃ is 2500±700 mPa·s, and the specific gravity is 1.60±0.03; the viscosity of component B at 23±2℃ is 200±50 mPa·s, and the specific gravity is 1.22±0.

03.

4. The self-reactive foaming polyurethane tile adhesive according to claim 2, characterized in that: The polyether polyol is a propylene oxide-based polyether polyol with a number-average molecular weight (Mn) ranging from 3000 to 6000, a functionality ranging from 2.5 to 3.5, and a hydroxyl value ranging from 28 to 56 mg KOH / g.

5. The self-reactive foaming polyurethane tile adhesive according to claim 2, characterized in that: The polymethylene polyphenyl polyisocyanate has an NCO content of 30%-33%, a viscosity range of 100-250 mPa·s at room temperature, and an average functionality of approximately 2.6-2.

9.

6. The self-reactive foaming polyurethane tile adhesive according to claim 2, characterized in that: The average particle size of the calcium carbonate is 2-10 μm, and the water content is controlled below 0.3%; after the A component and the B component are mixed, the calcium carbonate accounts for 42%-45% of the total weight of the binder.

7. The self-reactive foaming polyurethane tile adhesive according to any one of claims 1-6, characterized in that: Under conditions of 23±2℃ and 55±5% relative humidity, component A and component B are mixed at a weight ratio of 100:30 and stirred at 2500 rpm for 10 seconds. The foaming start time of the adhesive is 20±10 seconds, the foaming end time is 75±20 seconds, and the foaming density is 0.66±0.07 g / cm³.

8. The self-reactive foaming polyurethane tile adhesive according to claim 2, characterized in that: After the adhesive has cured, in the bonding test on glazed exterior wall tiles, the dry pull-out bond strength is ≥2.1 MPa, the wet-dry pull-out bond strength retention rate is ≥90%, and the failure mode is complete cohesive failure of the tile; the D-type hardness of the adhesive after curing is 48±7, and the elongation at break is 5%-20%.

9. A method for preparing a self-reactive foaming polyurethane tile adhesive, characterized in that: For preparing the self-reactive foaming polyurethane tile adhesive according to any one of claims 1-8, the preparation process of component A is as follows: polyether polyol and calcium carbonate pretreated by drying at 110℃±5℃ are added into a mixing vessel in proportion, and stirred and dehydrated for 1.5-2 hours at 110-120℃ and vacuum degree ≤-0.095 MPa to reduce the water content of the mixture to below 0.08%. After dehydration, the temperature is lowered to below 40℃, and the mixture is discharged and sealed under nitrogen protection to obtain component A.

10. The preparation process of component B is as follows: polymethylene polyphenyl polyisocyanate and dried calcium carbonate are added into a mixing vessel in proportion, stirred and mixed evenly at 40-50℃ under nitrogen protection, vacuum degassing, and sealed and packaged to obtain component B.

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