Gypsum-based ceramic tile adhesive with high bonding strength and preparation method thereof

Abstract

The invention relates to the technical field of inorganic adhesives, and particularly discloses a high-bonding-strength gypsum-based ceramic tile adhesive and a preparation method thereof.The high-bonding-strength gypsum-based ceramic tile adhesive comprises building gypsum powder, desulfurized gypsum, modified coarse sand, modified fine sand, redispersible latex powder, cellulose, a polycarboxylate superplasticizer, a retarder and a thixotropic lubricant; wherein the modified coarse sand takes coarse river sand as a base material, superfine glass fiber powder is loaded through chemical bonding, the modified fine sand takes fine river sand as a base material, a calcium carbonate curing layer is arranged on the surface, and secondary modification is carried out through an alum solution; the preparation method comprises the following steps: S1, mixing main powder with modified sand to obtain premixed dry powder; s2, adding other auxiliary materials, and continuously performing dry mixing to obtain finished product dry powder; s3, adding water into the finished product dry powder, and stirring at different rotating speeds to obtain tile glue; through cooperation of the modified coarse sand and the modified fine sand, crystal morphology is regulated and controlled, micro gaps are filled, the bonding performance of tile glue and an interface is improved, and the bonding strength and the bonding firmness of a tile and a base layer are improved.

Description

Technical Field

[0001] This invention relates to the field of inorganic adhesive technology, specifically to a gypsum-based tile adhesive with high bonding strength and its preparation method. Background Technology

[0002] Gypsum-based tile adhesive is mainly composed of building gypsum, aggregates, and various functional additives. Its core bonding material, gypsum, forms a network structure of interwoven calcium sulfate dihydrate crystals after hydration and hardening. The density of this structure is one of the key factors determining the final bonding strength of the tile adhesive. Higher density of the cured body and fewer internal pores not only provide a more uniform stress distribution but also enhance the mechanical interlocking and physical adsorption with the back of the tile and the surface of the substrate, thus achieving higher bonding strength. Therefore, optimizing the raw material ratio and introducing special modifying components to improve the paste structure and promote the formation of a denser cured network are important technical approaches to improving the bonding performance of gypsum-based tile adhesive.

[0003] Various tile adhesive formulations designed to optimize performance have been proposed in the prior art. For example, patent CN202411735428.0 discloses a tile adhesive, its preparation method, and its application. This tile adhesive, by weight, comprises 20-40 parts cement, 30-50 parts anhydrous gypsum, 20-25 parts β-gypsum, 4-6 parts an activator composed of calcium oxide and alum in a weight ratio of (1-5):(1-5), as well as retarder, water-retaining agent, and crosslinking agent. This technical solution, by combining cement with various gypsums and using a specific activator, aims to regulate the setting time and meet certain bond strength requirements.

[0004] However, the existing technical solutions mainly focus on the compounding and activation of the cementitious material system, but the microstructure after curing is not dense enough. This may result in the presence of voids in the microstructure of the hardened body and insufficient density of the internal crystal interwoven network, making it difficult to further improve the final bonding strength performance when facing higher requirements. Summary of the Invention

[0005] To address the technical deficiencies in the prior art, this invention proposes a gypsum-based tile adhesive with high bonding strength and its preparation method, solving the aforementioned technical problems and meeting practical needs. The specific technical solution is as follows: A high-bonding-strength gypsum-based tile adhesive, comprising, by weight, the following components: 330-370 parts of building gypsum powder, 130-170 parts of desulfurized gypsum, 190-210 parts of modified coarse sand, 190-210 parts of modified fine sand, 4.5-5.5 parts of redispersible latex powder, 3.0-4.0 parts of cellulose, 0.4-0.6 parts of polycarboxylate-based high-efficiency water-reducing agent, 1.2-1.8 parts of retarder, and 0.8-1.2 parts of thixotropic lubricant; The modified coarse sand is a modified sand particle with ultrafine glass fiber powder loaded by chemical bonding, based on coarse river sand; the modified fine sand is a modified sand particle with fine river sand as the base material, having a calcium carbonate curing layer on the surface and being modified twice by alum solution.

[0006] As a further technical solution of the present invention, the building gypsum powder is β-type building gypsum powder with a fineness of 90-100 mesh, and the desulfurized gypsum contains ≥90% calcium sulfate dihydrate with a fineness of 200-250 mesh.

[0007] As a further technical solution of the present invention, the retarder is a DS-type citric acid retarder, and the cellulose is hydroxypropyl methylcellulose.

[0008] A method for preparing a gypsum-based tile adhesive with high bonding strength includes the following steps: S1. Add building gypsum powder, desulfurized gypsum, modified coarse sand, and modified fine sand to a mixer and mix at a speed of 200 r / min for 10 min to obtain a uniform premixed dry powder. S2. Add redispersible latex powder, cellulose, polycarboxylate-based high-efficiency water-reducing agent, retarder and thixotropic lubricant to the premixed dry powder obtained in step S1, and continue to dry mix at a speed of 200 r / min for 5 min to obtain a uniform finished dry powder. S3. Add water to the finished dry powder obtained in step S2. The mass ratio of water to finished dry powder is (2-5):10. Stir at 300r / min for 2 minutes, then stir at 500r / min for 3 minutes to obtain the gypsum-based tile adhesive.

[0009] As a further technical solution of the present invention, the method for preparing the modified coarse sand includes the following steps: A1. Add aminosilane coupling agent HK550 to a 95% ethanol solution with a pH of 4-5 and stir until homogeneous to obtain a modified solution; the concentration of aminosilane coupling agent HK550 in the modified solution is 3-5%; A2. Mix 50-70 mesh coarse river sand base material and 1000-1200 mesh ultrafine glass fiber powder with the modified liquid obtained in step A1, and carry out the amination reaction by stirring at 50-55℃ and 300 r / min for 2.5 hours. After the reaction is completed, filter, wash and dry respectively to obtain amino-modified coarse sand and amino-modified glass fiber powder. The liquid-to-mass ratio (mL:g) of the coarse river sand base material to the modifying liquid is (3-5):1, and the liquid-to-mass ratio (mL:g) of the ultrafine glass fiber powder to the modifying liquid is (4-6):1. A3. Mix amino-modified coarse sand and amino-modified glass fiber powder in a mass ratio of 95:5. Add anhydrous DMF equal to 1.5 times the total volume of amino-modified coarse sand and amino-modified glass fiber powder. Heat to 55-65℃ and stir at 250 r / min. Under nitrogen protection, slowly add an activation reaction solution containing organic acid. After the addition is complete, keep the reaction at a constant temperature for 60 min. After the reaction solution is cooled, filter it. Wash the solid thoroughly with DMF, ethanol, and deionized water in sequence. Finally, dry it at 50-60℃ and sieve it to obtain the modified coarse sand with a mesh size of 30-60.

[0010] As a further technical solution of the present invention, in step A3, the preparation method of the activation reaction solution is as follows: in a dry container, organic acid and equimolar amounts of EDC and NHS are dissolved in an appropriate amount of anhydrous DMF, and the mixture is stirred and activated at room temperature for 15 minutes. The amount of organic acid added is 1-5% of the mass of amino-modified coarse sand, and the organic acid is selected from any one of citric acid, triglyceride, malic acid, and adipic acid.

[0011] As a further technical solution of the present invention, the method for preparing the modified fine sand includes the following steps: B1. Mix 80-100 mesh fine river sand base material, calcium sulfate and auxiliary materials in a mass ratio of 80:10:10, and then ball mill to obtain a 200-250 mesh mixed powder; the auxiliary materials are composed of kaolin, fly ash and slag powder in a mass ratio of 5:1:1. B2. The mixed powder obtained in step B1 is fed into a round pot granulator for granulation. The speed of the pot is adjusted to 60 r / min. Deionized water mist is sprayed evenly. The amount of water added is controlled to be 10-20% of the total mass of the mixture. After granulation, the intermediate particles of 60-100 mesh are obtained by sieving. B3. Spray a 7% sodium carbonate aqueous solution onto the surface of intermediate particle one obtained in step B2. Spray 10% of the mass of intermediate particle one evenly onto the particle surface, let it stand for 30-60 minutes, and then dry it in an oven at 45-55℃ for 1 hour to obtain intermediate particle two with a calcium carbonate solidified layer on the surface. B4. The intermediate particles obtained in step B3 are soaked in an alum solution with a mass concentration of 2.5% at a liquid-to-material ratio of 3:1 (mL:g) at room temperature for 30 minutes. After soaking, they are placed in an oven at 30-35℃ and dried to constant weight to obtain the modified fine sand.

[0012] The beneficial effects of this invention are as follows: Through the combined action of modified coarse sand, modified fine sand, and other components, the microstructure density of the cured gypsum-based tile adhesive is effectively improved, thereby enhancing its final bonding strength. The modified coarse sand, through chemical bonding and loading of ultrafine glass fiber powder and the introduction of polycarboxylic acid, allows its surface carboxyl groups to selectively adsorb onto specific growth surfaces of calcium sulfate dihydrate crystals during gypsum hydration, effectively controlling crystal morphology and promoting its transformation from slender needle-like structures to short, thick columnar structures. This results in a more uniform and dense crystal network, significantly reducing internal porosity. The modified fine sand, through surface construction... The calcium carbonate curing layer and alum secondary modification, the kaolin layered structure in its components can provide space for the interpenetration and bonding of calcium sulfate dihydrate crystals. At the same time, the active components and alum in the auxiliary materials can generate gel substances, further filling the microscopic gaps between crystals. The modified coarse sand and modified fine sand work together in the tile adhesive, and with the optimized ratio of redispersible latex powder, cellulose and other auxiliary materials, the slurry structure and interface bonding performance are effectively improved, the mechanical interlocking and physical adsorption with the tile and substrate are enhanced, the bonding performance is improved, and the bonding strength between the tile and the substrate is effectively increased. Detailed Implementation

[0013] The embodiments of the present invention will be described below with reference to relevant examples. The embodiments of the present invention are not limited to those described below, and the present invention relates to necessary knowledge in this technical field. It should be considered as well-known technology in this technical field, and is known and mastered by those skilled in the art. Experimental methods in the following examples that do not specify specific conditions are generally performed under conventional conditions in the art or according to the manufacturer's recommendations. Unless otherwise specified, the raw materials and reagents used are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0014] A high-bonding-strength gypsum-based tile adhesive, comprising, by weight, the following components: 330-370 parts of building gypsum powder, 130-170 parts of desulfurized gypsum, 190-210 parts of modified coarse sand, 190-210 parts of modified fine sand, 4.5-5.5 parts of redispersible latex powder, 3.0-4.0 parts of cellulose, 0.4-0.6 parts of polycarboxylate-based high-efficiency water-reducing agent, 1.2-1.8 parts of retarder, and 0.8-1.2 parts of thixotropic lubricant; The modified coarse sand is a modified sand particle with ultrafine glass fiber powder loaded by chemical bonding, based on coarse river sand; the modified fine sand is a modified sand particle with fine river sand as the base material, having a calcium carbonate curing layer on the surface and being modified twice by alum solution.

[0015] This invention effectively improves the bonding strength of gypsum-based tile adhesive through the combination of its components, while optimizing the slurry properties and post-curing structural stability. Building gypsum powder and desulfurized gypsum are used as base materials, and particle size distribution reduces internal porosity. Modified coarse sand is chemically bonded to ultrafine glass fiber powder, and the carboxyl groups on the surface of the modified coarse sand interact with the calcium sulfate dihydrate crystals. 2+ The modified sand combines and regulates the transformation of crystal morphology towards short and thick columnar shapes, forming a dense crystal network. The calcium carbonate solidification layer on the surface of the modified fine sand enhances its stability. The fly ash, slag powder, and surface alum inside the modified fine sand can generate gel substances to fill the gaps between crystals. The layered structure of kaolin provides space for the interpenetration and bonding of calcium sulfate dihydrate crystals, improving the bonding ability between the modified fine sand and the tile adhesive matrix. The synergistic effect of the two modified sands reduces the porosity inside the solidified body, increases the overall density, and enhances the mechanical bonding ability with tiles and substrates.

[0016] The redispersible latex powder, cellulose, and other additives work well with building gypsum powder, desulfurized gypsum, and modified sand. The redispersible latex powder enhances the physical adsorption of the tile adhesive on the bonding surface, while cellulose regulates the consistency and water retention of the slurry, preventing structural defects caused by excessive water loss during hydration. The polycarboxylate superplasticizer optimizes the slurry's fluidity, the retarder ensures sufficient construction time, and the thixotropic lubricant improves workability. The synergistic effect of these components comprehensively improves bonding strength and structural stability, allowing the tile adhesive to firmly bond tiles to the substrate and meet practical application requirements.

[0017] As a further technical solution of the present invention, the building gypsum powder is β-type building gypsum powder with a fineness of 90-100 mesh, and the desulfurized gypsum contains ≥90% calcium sulfate dihydrate with a fineness of 200-250 mesh.

[0018] 90-100 mesh β-type building gypsum powder is selected, which reacts with water to form calcium sulfate dihydrate crystals, forming the basic bonding carrier. Appropriate particle size is used to create a gradation with modified coarse and fine sand, filling the gaps between sand particles and reducing internal porosity in the cured body. Desulfurized gypsum with a calcium sulfate dihydrate content controlled at ≥90% ensures sufficient effective hydration components and avoids excessive impurities affecting overall performance. Its 200-250 mesh fineness is finer than building gypsum powder, further filling the tiny gaps between the base material and sand particles, improving the system's density. The combination of these two gypsum types enhances the cured strength of the tile adhesive and is better compatible with modified sand, redispersible latex powder, and other components, ensuring sufficient hydration reaction, reducing structural defects, and improving overall bonding performance.

[0019] As a further technical solution of the present invention, the retarder is a DS-type citric acid retarder, and the cellulose is hydroxypropyl methylcellulose.

[0020] Citric acid-based retarder is selected to regulate the hydration rate of gypsum and prevent the system from setting too quickly, which would affect the construction operation. Hydroxypropyl methylcellulose with a viscosity of 200,000 is selected to effectively improve the water retention of the slurry, prevent water from evaporating too quickly or being absorbed by the substrate, which would lead to insufficient hydration and structural pores. At the same time, the consistency of the slurry is adjusted to enhance the workability of the construction.

[0021] In addition, the thixotropic lubricant selected is model FB-1, which has good compatibility with the above components, redispersible latex powder, and water-reducing agent. It can give the slurry excellent thixotropic properties, making it less prone to flowing when standing and easy to restore fluidity after stirring, which is convenient for application and construction. It can also optimize the interfacial performance of the slurry and help improve the bonding effect with tiles and substrates.

[0022] A method for preparing a gypsum-based tile adhesive with high bonding strength includes the following steps: S1. Add building gypsum powder, desulfurized gypsum, modified coarse sand, and modified fine sand to a mixer and mix at a speed of 200 r / min for 10 min to obtain a uniform premixed dry powder. S2. Add redispersible latex powder, cellulose, polycarboxylate-based high-efficiency water-reducing agent, retarder and thixotropic lubricant to the premixed dry powder obtained in step S1, and continue to dry mix at a speed of 200 r / min for 5 min to obtain a uniform finished dry powder. S3. Add water to the finished dry powder obtained in step S2. The mass ratio of water to finished dry powder is (2-5):10. Stir at 300r / min for 2 minutes, then stir at 500r / min for 3 minutes to obtain the gypsum-based tile adhesive.

[0023] In the above preparation steps, the base material and modified sand are first dry-mixed to allow building gypsum powder of different particle sizes, desulfurized gypsum and modified coarse sand and fine sand to be fully and evenly mixed to form a stable premixed system. Then, the auxiliary materials are dry-mixed. Maintaining the same speed can prevent the additives from agglomerating and ensure that redispersible latex powder, cellulose and other materials can be evenly distributed in the premixed dry powder to ensure that the synergistic effect of each component is exerted. Finally, water is added in proportion and a two-step stirring process is adopted. First, the water is fully penetrated into the dry powder at a low speed, and then the potential agglomerates are dispersed at a high speed to make the slurry more uniformly mixed.

[0024] As one of the preferred embodiments of the present invention, the method for preparing the modified coarse sand includes the following steps: A1. Add aminosilane coupling agent HK550 to a 95% ethanol solution with a pH of 4-5 and stir until homogeneous to obtain a modified solution; the concentration of aminosilane coupling agent HK550 in the modified solution is 3-5%; A2. Mix 50-70 mesh coarse river sand base material and 1000-1200 mesh ultrafine glass fiber powder with the modified liquid obtained in step A1, and carry out the amination reaction by stirring at 50-55℃ and 300 r / min for 2.5 hours. After the reaction is completed, filter, wash and dry respectively to obtain amino-modified coarse sand and amino-modified glass fiber powder. The liquid-to-mass ratio (mL:g) of the coarse river sand base material to the modifying liquid is (3-5):1, and the liquid-to-mass ratio (mL:g) of the ultrafine glass fiber powder to the modifying liquid is (4-6):1. A3. Mix amino-modified coarse sand and amino-modified glass fiber powder in a mass ratio of 95:5. Add anhydrous DMF equal to 1.5 times the total volume of amino-modified coarse sand and amino-modified glass fiber powder. Heat to 55-65℃ and stir at 250 r / min. Under nitrogen protection, slowly add an activation reaction solution containing organic acid. After the addition is complete, keep the reaction at a constant temperature for 60 min. After the reaction solution is cooled, filter it. Wash the solid thoroughly with DMF, ethanol, and deionized water in sequence. Finally, dry it at 50-60℃ and sieve it to obtain the modified coarse sand with a mesh size of 30-60.

[0025] Further, in step A3 above, the method for preparing the activation reaction solution is as follows: in a dry container, an organic acid and an equimolar amount of EDC and NHS are dissolved in an appropriate amount of anhydrous DMF, and the mixture is stirred and activated at room temperature for 15 min. The amount of organic acid added is 1-5% of the mass of the amino-modified coarse sand, and the organic acid is selected from any one of citric acid, triglyceride, malic acid, and adipic acid.

[0026] Steps A1-A2 achieve substrate amination using the aminosilane coupling agent HK550. An acidic ethanol-water solution promotes the hydrolysis of the coupling agent to generate active groups. A 3-5% concentration of HK550 ensures uniform grafting of amino groups onto the surfaces of both the coarse sand and ultrafine glass fiber powder. Different liquid-to-mass ratios are used to accommodate the differences in specific surface areas, preventing insufficient modification of the glass fiber powder due to its large specific surface area. A reaction at 50-55℃ and 300 rpm for 2.5 hours ensures the amino grafting rate. Filtration, washing, and drying remove unreacted coupling agent, preventing impurities from affecting subsequent bonding. In step A3, the activated reaction solution is activated with EDC and NHS to activate the carboxyl groups of the organic acid. Under nitrogen protection, an amidation reaction chemically bonds the amino-modified glass fiber powder to the surface of the amino-modified coarse sand. Multiple washing steps remove residual additives, and drying and sieving control the particle size to 30-60 mesh, adapting to the overall component gradation of the tile adhesive.

[0027] In the above reaction, chemical bonding ensures a strong bond between the glass fiber powder and the coarse sand, preventing it from detaching during the preparation and use of tile adhesive. The glass fiber powder enhances the structural strength of the coarse sand and introduces unreacted carboxyl groups onto the surface of the modified coarse sand, which can react with the Ca produced during gypsum hydration.2+ Its function is to regulate the transformation of calcium sulfate dihydrate crystals into short, thick columnar shapes, reducing the internal porosity of the cured body. Simultaneously, the 30-60 mesh modified coarse sand, along with other base materials and modified fine sand, forms a reasonable particle size distribution, further filling the system's voids and improving the density of the cured tile adhesive. When combined with other components, it enhances the mechanical bonding ability between the tile adhesive and the tile / substrate, directly improving the overall bonding strength and preventing debonding problems during long-term use.

[0028] As one of the preferred embodiments of the present invention, the method for preparing the modified fine sand includes the following steps: B1. Mix 80-100 mesh fine river sand base material, calcium sulfate and auxiliary materials in a mass ratio of 80:10:10, and then ball mill to obtain a 200-250 mesh mixed powder; the auxiliary materials are composed of kaolin, fly ash and slag powder in a mass ratio of 5:1:1. B2. The mixed powder obtained in step B1 is fed into a round pot granulator for granulation. The speed of the pot is adjusted to 60 r / min. Deionized water mist is sprayed evenly. The amount of water added is controlled to be 10-20% of the total mass of the mixture. After granulation, the intermediate particles of 60-100 mesh are obtained by sieving. B3. Spray a 7% sodium carbonate aqueous solution onto the surface of intermediate particle one obtained in step B2. Spray 10% of the mass of intermediate particle one evenly onto the particle surface, let it stand for 30-60 minutes, and then dry it in an oven at 45-55℃ for 1 hour to obtain intermediate particle two with a calcium carbonate solidified layer on the surface. B4. The intermediate particles obtained in step B3 are soaked in an alum solution with a mass concentration of 2.5% at a liquid-to-material ratio of 3:1 (mL:g) at room temperature for 30 minutes. After soaking, they are placed in an oven at 30-35℃ and dried to constant weight to obtain the modified fine sand.

[0029] In the above modification reaction, step B1 first mixes 80-100 mesh fine river sand, calcium sulfate, kaolin, fly ash, and slag powder according to the specified ratio, and then ball mills them to 200-250 mesh to fully disperse the components and form a uniformly sized mixed powder. Step B2 uses a round pot granulator to granulate at 60 r / min speed and 10-20% water addition, and then sieves to obtain 60-100 mesh intermediate particles, agglomerating the ultrafine mixed powder into regular particles. Step B3 sprays a 7% sodium carbonate aqueous solution onto the intermediate particles in the form of water mist. The sodium carbonate reacts with the calcium sulfate in the particles to generate calcium carbonate on the particle surface and form a solidified layer. After standing for 30-60 minutes to ensure complete reaction, the particles are dried at 45-55℃ to remove free moisture, so that the calcium carbonate layer is firmly attached to the particle surface and the structural stability of the particles is improved. Step B4 involves immersing intermediate particles with a calcium carbonate curing layer in a 2.5% alum solution at a liquid-to-material ratio of 3:1 for 30 minutes at room temperature, allowing the alum to be loaded onto the surface of intermediate particles. After drying at 30-35°C to constant weight, modified fine sand is obtained.

[0030] In the prepared modified fine sand, the layered structure of kaolin allows the calcium sulfate dihydrate crystals generated by gypsum hydration to interpenetrate and grow, increasing the bonding ability between the fine sand and the tile adhesive matrix. During the tile adhesive hydration process, aluminum ions generated by alum hydrolysis hydrate to form aluminum hydroxide colloid. Alumina from fly ash and active calcium oxide and alumina from slag powder can participate in the tile adhesive hydration process, generating hydration gels. These various gels are synergistically generated and interpenetrate each other, filling the spaces between calcium sulfate dihydrate crystals and between sand particles and the matrix, effectively reducing the porosity of the tile adhesive matrix and improving the overall density. At the same time, the particle size of the modified fine sand complements that of the modified coarse sand, optimizing the bulk density of the entire system, strengthening the mechanical interlocking between the tile adhesive and the tile / substrate, and further enhancing the overall bonding strength of the tile adhesive by combining with the crystal regulation effect of the modified coarse sand, ensuring the stability of the structure after curing.

[0031] The present invention will be further described below through examples and comparative examples. Example 1 Preparation of modified coarse sand A1. Add aminosilane coupling agent HK550 to a 95% ethanol solution with a pH of 4-5 and stir until homogeneous to obtain a modified solution; the concentration of aminosilane coupling agent HK550 in the modified solution is 4%.

[0032] A2. Mix 50-70 mesh coarse river sand base material and 1000-1200 mesh ultrafine glass fiber powder with the modification liquid prepared in step A1, and carry out the amination reaction by stirring at 52℃ and 300 r / min for 2.5 hours. The liquid-to-mass ratio (mL:g) of the coarse river sand base material to the modification liquid is 4:1, and the liquid-to-mass ratio (mL:g) of the ultrafine glass fiber powder to the modification liquid is 5:1. After the reaction is completed, filter, wash and dry them respectively to obtain amino-modified coarse sand and amino-modified glass fiber powder.

[0033] A3. Mix amino-modified coarse sand and amino-modified glass fiber powder at a mass ratio of 95:5, add anhydrous DMF equal to 1.5 times the total volume of the two, heat to 60℃, stir at 250 r / min, and slowly add an activation reaction solution containing organic acid under nitrogen protection. The activation reaction solution is prepared as follows: in a dry container, dissolve citric acid and equimolar amounts of EDC and NHS in an appropriate amount of anhydrous DMF, stir and activate at room temperature for 15 min, and add organic acid at 3% of the mass of amino-modified coarse sand (take the intermediate value of 1-5%). After the addition is complete, react at a constant temperature for 60 min, cool the reaction solution and filter it, wash the solid thoroughly with DMF, ethanol and deionized water in sequence, and finally dry at 55℃ and sieve to obtain 30-60 mesh modified coarse sand.

[0034] Preparation of modified fine sand B1. Mix 80-100 mesh fine river sand base material, calcium sulfate and auxiliary materials in a mass ratio of 80:10:10, and then ball mill to obtain a 200-250 mesh mixed powder; the auxiliary materials are composed of kaolin, fly ash and slag powder in a mass ratio of 5:1:1.

[0035] B2. The mixed powder obtained in step B1 is fed into a round pot granulator for granulation. The speed of the pot is adjusted to 60 r / min. Deionized water mist is sprayed evenly. The amount of water added is controlled to be 15% of the total mass of the mixture. After granulation, the intermediate particles of 60-100 mesh are obtained by sieving.

[0036] B3. Spray a 7% sodium carbonate aqueous solution evenly onto the surface of intermediate particle one at 10% of its mass, let it stand for 45 minutes to react, and then dry it in an oven at 50°C for 1 hour to obtain intermediate particle two with a calcium carbonate solidified layer on its surface.

[0037] B4. Soak the intermediate particles obtained in step B3 in a 2.5% alum solution at a liquid-to-solid ratio of 3:1 (mL:g) at room temperature for 30 minutes. After soaking, remove the particles and dry them in a 32°C oven until constant weight to obtain modified fine sand.

[0038] Preparation of tile adhesive S1. Add 350 parts of building gypsum powder (90-100 mesh β type), 150 parts of desulfurized gypsum (calcium sulfate dihydrate content ≥90%, 200-250 mesh), 200 parts of the modified coarse sand prepared above, and 200 parts of the modified fine sand prepared above to a mixer and mix at a speed of 200 r / min for 10 min to obtain a uniform premixed dry powder.

[0039] S2. Add 5.0 parts of redispersible latex powder, 3.5 parts of hydroxypropyl methylcellulose (200,000 viscosity), 0.5 parts of polycarboxylate superplasticizer, 1.5 parts of DS type citric acid retarder and 1.0 part of FB-1 type thixotropic lubricant to the premixed dry powder obtained in step S1, and continue to dry mix at a speed of 200 r / min for 5 min to obtain a uniform finished dry powder.

[0040] S3. Add water to the finished dry powder obtained in step S2. The mass ratio of water to finished dry powder is 0.22:1. Stir at 300 r / min for 2 min and then at 500 r / min for 3 min to obtain the gypsum-based tile adhesive.

[0041] Example 2 The difference between Example 2 and Example 1 is that the dosage of each component is adjusted. Specifically, the dosage is adjusted as follows: 330 parts of building gypsum powder, 170 parts of desulfurized gypsum, 190 parts of modified coarse sand, 210 parts of modified fine sand, 4.5 parts of redispersible latex powder, 3.0 parts of hydroxypropyl methylcellulose, 0.4 parts of polycarboxylate-based high-efficiency water-reducing agent, 1.2 parts of DS-type citric acid-based retarder, 0.8 parts of FB-1 type thixotropic lubricant, and the mass ratio of deionized water to finished dry powder is 0.20:1. The remaining preparation processes (preparation steps and parameters of modified coarse sand, modified fine sand, and tile adhesive) are the same as in Example 1.

[0042] Example 3 The difference between Example 3 and Example 1 is that the dosage of each component was adjusted. Specifically, the dosages were: 370 parts of building gypsum powder, 130 parts of desulfurized gypsum, 210 parts of modified coarse sand, 190 parts of modified fine sand, 5.5 parts of redispersible latex powder, 4.0 parts of hydroxypropyl methylcellulose, 0.6 parts of polycarboxylate-based high-efficiency water-reducing agent, 1.8 parts of DS-type citric acid-based retarder, and 1.2 parts of FB-1 type thixotropic lubricant. The mass ratio of deionized water to the finished dry powder was 0.25:1. The remaining preparation processes (preparation steps and parameters for modified coarse sand, modified fine sand, and tile adhesive) were the same as in Example 1.

[0043] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the modified coarse sand in Example 1 was replaced with ordinary dry river sand of equal weight and same particle size (30-60 mesh). The dosage of other components, the preparation process of modified fine sand and the preparation process of tile adhesive are the same as in Example 1.

[0044] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the modified fine sand in Example 1 was replaced with ordinary dry river sand of equal weight and same particle size (60-100 mesh). The dosage of other components, the preparation process of modified coarse sand and the preparation process of tile adhesive are the same as in Example 1.

[0045] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the modified coarse sand in Example 1 was replaced with an equal weight of ordinary dry river sand with the same particle size (30-60 mesh), and the modified fine sand was replaced with an equal weight of ordinary dry river sand with the same particle size (60-100 mesh). The dosage of other components and the tile adhesive preparation process were the same as in Example 1.

[0046] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that step B4 (soaking in alum solution) is omitted when preparing modified fine sand. Only intermediate particles with a calcium carbonate solidified layer on the surface are prepared through steps B1-B3, and are directly used as "alum-free modified fine sand" for tile adhesive preparation. The dosage of other components, the preparation process of modified coarse sand and the preparation process of tile adhesive are the same as those in Example 1.

[0047] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is as follows: In step B1 of preparing modified fine sand, fly ash in the auxiliary materials is removed, and its mass is made up by equal amounts of kaolin and slag powder in the original ratio (5:1) (i.e., the auxiliary materials are adjusted to 5.83 parts of kaolin, 0 parts of fly ash, and 1.17 parts of slag powder, with the total mass remaining unchanged); the dosage of other components, the preparation process of modified coarse sand, other steps of modified fine sand, and the preparation process of tile adhesive are all the same as in Example 1.

[0048] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is as follows: In step B1 of preparing modified fine sand, the slag powder in the auxiliary materials is removed, and its mass is made up by equal amounts of kaolin and fly ash in the original ratio (5:1) (i.e., the auxiliary materials are adjusted to 5.83 parts of kaolin, 1.17 parts of fly ash, and 0 parts of slag powder, with the total mass remaining unchanged); the dosage of other components, the preparation process of modified coarse sand, other steps of modified fine sand, and the preparation process of tile adhesive are all the same as in Example 1.

[0049] The tile adhesives prepared in Examples 1-3 and Comparative Examples 1-6 were subjected to relevant performance tests according to GB / T 41059-2021 "Technical Requirements for Ceramic Tile Adhesives". The test results are shown in the table below.

[0050] The test data from the examples and comparative examples show that the gypsum-based tile adhesive prepared by the present invention exhibits good bonding strength and durability. The tensile bond strength of Examples 1-3 all exceed 1.28 MPa, the slip is controlled below 0.20 mm, and the strength retention rate is high after immersion in water, heat aging, and freeze-thaw cycles, indicating that the formula can achieve stable performance within a given range.

[0051] The test data from Comparative Examples 1-3 show that when ordinary river sand is used to replace modified coarse sand or modified fine sand, the performance indicators decrease significantly. In Comparative Example 3, where both modified coarse sand and modified fine sand are used, the tensile bond strength decreases to 0.70 MPa and the slip increases to 0.45 mm. This indicates that the modified coarse sand can effectively reduce porosity and increase density by regulating the morphology of calcium sulfate dihydrate crystals through surface carboxyl groups to form a dense network, and the modified fine sand and internal additives can form a gel to fill the gaps.

[0052] Further analysis of Comparative Examples 4-6 revealed that the performance of Comparative Example 4, which omitted alum modification, was reduced, indicating that the colloid generated by alum hydrolysis helps fill the intercrystalline gaps. Comparative Examples 5 and 6, which removed fly ash or slag powder, also showed a decrease in strength, indicating that the alumina in fly ash and the active ingredients in slag powder participate in the hydration reaction, generating additional gel substances and further optimizing the internal structure.

[0053] In summary, the high bonding strength of the gypsum-based tile adhesive is achieved through the particle size distribution of building gypsum and desulfurized gypsum, the complementary design of modified coarse sand and fine sand, and the reasonable combination of various functional additives. The modified coarse sand focuses on crystal morphology control and mechanical reinforcement, while the modified fine sand focuses on gel formation and gap filling. The combination of the two effectively improves the integrity and durability of the tile adhesive after curing.

[0054] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A gypsum-based tile adhesive with high bonding strength, characterized in that, By weight, it comprises the following components: 330-370 parts of building gypsum powder, 130-170 parts of desulfurized gypsum, 190-210 parts of modified coarse sand, 190-210 parts of modified fine sand, 4.5-5.5 parts of redispersible latex powder, 3.0-4.0 parts of cellulose, 0.4-0.6 parts of polycarboxylate-based high-efficiency water-reducing agent, 1.2-1.8 parts of retarder, and 0.8-1.2 parts of thixotropic lubricant; The modified coarse sand is a modified sand particle with ultrafine glass fiber powder loaded by chemical bonding, based on coarse river sand; the modified fine sand is a modified sand particle with fine river sand as the base material, having a calcium carbonate curing layer on the surface and being modified twice by alum solution.

2. The gypsum-based tile adhesive according to claim 1, characterized in that, The building gypsum powder is β-type building gypsum powder with a fineness of 90-100 mesh, and the desulfurized gypsum contains ≥90% calcium sulfate dihydrate with a fineness of 200-250 mesh.

3. The gypsum-based tile adhesive according to claim 1, characterized in that, The retarder is a DS-type citric acid retarder, and the cellulose is hydroxypropyl methylcellulose.

4. The method for preparing the high-bonding-strength gypsum-based tile adhesive according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Add building gypsum powder, desulfurized gypsum, modified coarse sand, and modified fine sand to a mixer and mix at a speed of 200 r / min for 10 min to obtain a uniform premixed dry powder. S2. Add redispersible latex powder, cellulose, polycarboxylate-based high-efficiency water-reducing agent, retarder and thixotropic lubricant to the premixed dry powder obtained in step S1, and continue to dry mix at a speed of 200 r / min for 5 min to obtain a uniform finished dry powder. S3. Add water to the finished dry powder obtained in step S2. The mass ratio of water to finished dry powder is (2-5):

10. Stir at 300r / min for 2 minutes, then stir at 500r / min for 3 minutes to obtain the gypsum-based tile adhesive.

5. The method for preparing gypsum-based tile adhesive according to claim 4, characterized in that, The method for preparing the modified coarse sand includes the following steps: A1. Add aminosilane coupling agent HK550 to a 95% ethanol solution with a pH of 4-5 and stir until homogeneous to obtain a modified solution; the concentration of aminosilane coupling agent HK550 in the modified solution is 3-5%; A2. Mix 50-70 mesh coarse river sand base material and 1000-1200 mesh ultrafine glass fiber powder with the modified liquid obtained in step A1, and carry out the amination reaction by stirring at 50-55℃ and 300 r / min for 2.5 hours. After the reaction is completed, filter, wash and dry respectively to obtain amino-modified coarse sand and amino-modified glass fiber powder. The liquid-to-mass ratio (mL:g) of the coarse river sand base material to the modifying liquid is (3-5):1, and the liquid-to-mass ratio (mL:g) of the ultrafine glass fiber powder to the modifying liquid is (4-6):

1. A3. Mix amino-modified coarse sand and amino-modified glass fiber powder in a mass ratio of 95:

5. Add anhydrous DMF equal to 1.5 times the total volume of amino-modified coarse sand and amino-modified glass fiber powder. Heat to 55-65℃ and stir at 250 r / min. Under nitrogen protection, slowly add an activation reaction solution containing organic acid. After the addition is complete, keep the reaction at a constant temperature for 60 min. After the reaction solution is cooled, filter it. Wash the solid thoroughly with DMF, ethanol, and deionized water in sequence. Finally, dry it at 50-60℃ and sieve it to obtain the modified coarse sand with a mesh size of 30-60.

6. The method for preparing gypsum-based tile adhesive according to claim 5, characterized in that, In step A3, the method for preparing the activation reaction solution is as follows: in a dry container, organic acid and equimolar amounts of EDC and NHS are dissolved in an appropriate amount of anhydrous DMF, and the mixture is stirred and activated at room temperature for 15 minutes. The amount of organic acid added is 1-5% of the mass of amino-modified coarse sand, and the organic acid is selected from any one of citric acid, triglyceride, malic acid, and adipic acid.

7. The method for preparing gypsum-based tile adhesive according to claim 4, characterized in that, The method for preparing the modified fine sand includes the following steps: B1. Mix 80-100 mesh fine river sand base material, calcium sulfate and auxiliary materials in a mass ratio of 80:10:10, and then ball mill to obtain a 200-250 mesh mixed powder; the auxiliary materials are composed of kaolin, fly ash and slag powder in a mass ratio of 5:1:

1. B2. The mixed powder obtained in step B1 is fed into a round pot granulator for granulation. The speed of the pot is adjusted to 60 r / min. Deionized water mist is sprayed evenly. The amount of water added is controlled to be 10-20% of the total mass of the mixture. After granulation, the intermediate particles of 60-100 mesh are obtained by sieving. B3. Spray a 7% sodium carbonate aqueous solution onto the surface of intermediate particle one obtained in step B2. Spray 10% of the mass of intermediate particle one evenly onto the particle surface, let it stand for 30-60 minutes, and then dry it in an oven at 45-55℃ for 1 hour to obtain intermediate particle two with a calcium carbonate solidified layer on the surface. B4. The intermediate particles obtained in step B3 are soaked in an alum solution with a mass concentration of 2.5% at a liquid-to-material ratio of 3:1 (mL:g) at room temperature for 30 minutes. After soaking, they are placed in an oven at 30-35℃ and dried to constant weight to obtain the modified fine sand.

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