Waterproof putty powder and preparation method thereof

Abstract

The present application relates to the field of coating technology, in particular to a waterproof putty powder and a preparation method thereof. The waterproof putty powder comprises heavy calcium carbonate, quartz powder, Portland cement, calcium hydroxide, hydroxyethyl cellulose ether, hydrophilic fumed silica, hydrophobic fumed silica and a specific redispersible polymer powder. The polymer powder is prepared by spray drying of ethylene-vinyl acetate copolymer dispersion, polyvinyl alcohol, silane coupling agent, triethylamine and colloidal silica. The preparation method of the present application comprises first preparing the modified polymer powder, and then mixing it with the remaining dry powder components in steps. The construction method involves mixing with acidic water, standing for curing, and then scraping in two batches. Through the design of the core-shell structure of the polymer powder and the sequential addition of functional components, the waterproofness, workability, flexibility and bonding strength after immersion of the putty layer are synergistically improved.

Description

Technical Field

[0001] This invention relates to the field of coating technology, and in particular to a waterproof putty powder and its preparation method. Background Technology

[0002] Currently, building exterior walls and damp environments such as kitchens and bathrooms require higher water resistance. Traditional interior wall putty typically uses heavy calcium carbonate as the main filler, supplemented with organic binders such as starch glue and carboxymethyl cellulose. Its water resistance is poor, and it is prone to softening, bubbling, and even peeling when exposed to water, making it unsuitable for use in high-humidity or intermittently immersed environments.

[0003] To improve the waterproof performance of putty layers, the industry generally adopts a "direct dry-mixing" technique. A common practice is to directly incorporate redispersible polymer latex powder into the putty powder formulation, utilizing its ability to redisperse and form a film after mixing with water to improve the flexibility and adhesion of the putty layer. However, the polymer film of such ordinary latex powders is still hydrophilic and has limited ability to block liquid water. In long-term high-humidity environments, moisture can still penetrate and lead to a significant decrease in bond strength.

[0004] To further enhance hydrophobicity, existing technologies typically involve directly adding hydrophobic agents such as silane powder during the dry-mixing stage. While this method can reduce the water absorption rate of the putty layer to some extent, it also introduces new problems: First, the uniform dispersion of the silane component in the powder is difficult to guarantee, which can easily lead to excessive hydrophobicity in certain areas, causing roughness and curling during application, or insufficient hydrophobicity in certain areas, affecting the overall waterproofing effect. Second, free silane may undergo uneven hydrolysis and self-condensation during the construction mixing stage, which not only reduces its effective bonding efficiency with the inorganic substrate but may also interfere with the continuous film formation of the polymer film, negatively impacting the flexibility and initial drying crack resistance of the putty layer.

[0005] In addition, some technologies attempt to modify the polymer emulsion stage with silanes, followed by spray drying to obtain hydrophobic redispersible polymer powders. However, such methods often focus on the hydrophobicity of the powder itself, without fully considering its synergistic effect in the final putty system. Simple overall modification may lead to poor redispersibility of the powder in the putty slurry, or poor compatibility between the hydrophobic surface and the hydrophilic inorganic filler or cement hydration products, which may damage the overall bonding strength of the putty layer. Especially after immersion in water, the interface is prone to become a weak point, resulting in softening and powdering.

[0006] In summary, existing technologies cannot simultaneously achieve low water absorption, high retention rate of post-water resistant bond strength, and excellent resistance to interfacial softening while ensuring excellent workability, smoothness of application, and initial drying stability of the putty. This is the core technical bottleneck that urgently needs to be solved in the development of high-performance waterproof putty. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a waterproof putty powder and its preparation method to solve the problems of uneven dispersion of hydrophobic components, uncontrollable reaction sites, reduced workability, significant attenuation of bonding strength after immersion in water, and easy softening of the interface in existing direct dry-mix waterproof putty.

[0008] To achieve the above objectives, the present invention provides a waterproof putty powder, comprising the following components by weight: 537-575 parts of heavy calcium carbonate; 100-130 parts quartz powder; 150-170 parts silicate cement; 55-60 parts calcium hydroxide; 3-5 parts hydroxyethyl cellulose ether; 3-5 parts hydrophilic fumed silica; 1-3 parts hydrophobic fumed silica; and 80-125 parts of redispersible polymer powder; The redispersible polymer powder is a redispersible polymer powder modified with silane and colloidal silica, which is prepared by spray drying of ethylene-vinyl acetate copolymer dispersion, polyvinyl alcohol, 3-glycidoxypropyltrimethoxysilane, triethylamine and colloidal silica dispersion.

[0009] Preferably, the redispersible polymer powder is prepared by the following method: first, polyvinyl alcohol is dissolved in water and then mixed with ethylene-vinyl acetate copolymer dispersion to obtain an outer premix; 3-glycidyl etheroxypropyltrimethoxysilane is premixed with anhydrous ethanol and then added dropwise to the outer premix, and reacted in the presence of triethylamine to obtain an outer silanization reaction solution; then, the outer silanization reaction solution is mixed with colloidal silica dispersion and spray-dried to obtain the redispersible polymer powder.

[0010] Preferably, the amounts of water, polyvinyl alcohol, ethylene-vinyl acetate copolymer dispersion, anhydrous ethanol, 3-glycidyl etheroxypropyltrimethoxysilane, triethylamine, and colloidal silica dispersion, by weight, are 68-76 parts, 6-10 parts, 320-340 parts, 15-21 parts, 4.5-8 parts, 0.3-0.8 parts, and 24-40 parts, respectively.

[0011] Preferably, the 3-glycidoxypropyltrimethoxysilane is premixed with anhydrous ethanol for 4-6 min, and then added dropwise to the outer premixed solution within 8-12 min. The mixture is then reacted for 50-80 min at 48-55°C, a stirring speed of 320-380 rpm, and a pH of 5.9-6.6. The resulting outer silanized reaction solution is added to the colloidal silica dispersion within 4-6 min while stirring at 280-320 rpm. After stirring for 15-25 min at 38-42°C, the mixture is spray-dried. The inlet air temperature of the spray dryer is 145-160°C, and the outlet air temperature is 60-70°C.

[0012] Preferably, the waterproof putty powder is prepared by the following method: first, dry-mixing heavy calcium carbonate, quartz powder, silicate cement, calcium hydroxide, hydroxyethyl cellulose ether and hydrophilic fumed silica for 4-6 minutes, then adding the redispersible polymer powder and continuing to dry-mix for 3-4 minutes, and finally adding hydrophobic fumed silica and dry-mixing for 2 minutes.

[0013] Preferably, the number average molecular weight of the ethylene-vinyl acetate copolymer dispersion is 40,000-50,000.

[0014] Preferably, the solid content of the colloidal silica dispersion is 30 wt%.

[0015] Preferably, the hydrophilic fumed silica is of type HDK N20.

[0016] Preferably, the hydrophobic fumed silica is of type HDK H18.

[0017] This invention also provides a method for preparing waterproof putty powder, comprising the following steps: (1) Mix water, polyvinyl alcohol and ethylene-vinyl acetate copolymer dispersion to obtain outer premix liquid; (2) 3-glycidyl etheroxypropyltrimethoxysilane was premixed with anhydrous ethanol and added to the outer premixed solution, and reacted in the presence of triethylamine to obtain the outer silanization reaction solution. (3) The outer silanization reaction solution is mixed with the colloidal silica dispersion and then spray-dried to obtain redispersible polymer powder; (4) Dry mix heavy calcium carbonate, quartz powder, silicate cement, calcium hydroxide, hydroxyethyl cellulose ether, hydrophilic fumed silica and the redispersible polymer powder, and then add hydrophobic fumed silica and dry mix again to obtain waterproof putty powder.

[0018] This invention also provides a method for applying waterproof putty powder, comprising the following steps: (1) Mix 278-281 parts by weight of deionized water with 0.8-1.2 parts by weight of glacial acetic acid to obtain mixing water for construction; (2) Add 1000 parts by weight of the waterproof putty powder to the mixing water for construction in three parts, stir at 480-520 rpm for 3 minutes, let stand and mature for 5-6 minutes, and then stir again at 480-520 rpm for 2 minutes to obtain the construction slurry. (3) Apply the construction slurry to the cement mortar base layer that has been cleaned of floating dust and moistened to the surface dry state. The thickness of the first layer is controlled to be 0.7-1.1 mm. After an interval of 3.5-4.5 h, apply the second layer with a thickness of 0.7-1.1 mm. The total thickness is controlled to be 1.4-2.2 mm. After molding, cure for 7 days at 23-27℃ and 65%-75% relative humidity.

[0019] The beneficial effects of this invention are: (1) This invention prepares a redispersible polymer powder with a core-shell structure by first constructing an ethylene-vinyl acetate / polyvinyl alcohol composite outer layer, then introducing a silane coupling agent pre-dissolved in ethanol and carrying out a site-directed reaction under triethylamine catalysis, and finally spray-drying it with colloidal silica. This design allows the hydrophobic reaction sites and nano-silica anchors to be preferentially located on the outer layer of the polymer particles, which can quickly construct a dense hydrophobic-reinforcing network after rehydration during construction, significantly reducing the water absorption of the putty layer (as low as 0.63 g / 10 min), and greatly alleviating the surface powdering and interface softening phenomena after immersion in water.

[0020] (2) This invention employs a stepwise addition strategy of hydrophilic and hydrophobic fumed silica, combined with the timing control of silane hydrolysis initiated by acidic mixing water and condensation completed in an alkaline environment, thereby optimizing the spatial and reaction sequence of functional components. This synergistic effect ensures good workability and dispersibility of the slurry while promoting the uniform distribution and effective curing of hydrophobic components in the putty layer. This results in the putty film achieving excellent flexibility (minimum diameter of the shaft rod can reach 50 mm) while significantly improving the retention rate of bonding strength after immersion in water and after freeze-thaw cycles (the bonding strength after immersion can reach up to 0.97 MPa), thus resolving the contradiction between hydrophobicity and bonding performance in traditional methods. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0022] The raw materials used are as follows: The ethylene-vinyl acetate copolymer dispersion was obtained using WACKER's VINNAPAS EP 8010, with a number average molecular weight of 43,000.

[0023] Polyvinyl alcohol, using KURARAY POVAL 22-88 S2 from KURARAY.

[0024] The colloidal silica dispersion used was SNOWTEX-30 from Nissan Chemical Industries, with a solid content of 30 wt%.

[0025] Hydroxyethyl cellulose ether, using DOW's WALOCEL MKX 60000 PF01.

[0026] Hydrophilic fumed silica, using HDK N20 from WACKER.

[0027] Hydrophobic fumed silica, using HDK H18 from WACKER.

[0028] Silicate cement, using Aalborg White PW52.5.

[0029] Heavy calcium carbonate is a 1250-mesh building-grade product, quartz powder is a 600-mesh building-grade product, and calcium hydroxide is a building-grade product. Example 1

[0030] Step 1: Add 72g of deionized water to a container equipped with a stirrer, heat to 90℃, add 8g of polyvinyl alcohol, stir at 500rpm for 40min until a homogeneous and transparent solution is formed, and then cool to 40℃; filter 330g of ethylene-vinyl acetate copolymer dispersion through a 100-mesh filter and add it to the above solution, stir at 300rpm for 20min to obtain the outer premixed solution; Step 2: Mix 18g of anhydrous ethanol with 6g of 3-glycidyl etheroxypropyltrimethoxysilane for 5 min, then add the mixture dropwise to the outer premixed solution obtained in Step 1 within 10 min. Add 0.5g of triethylamine, control the system temperature at 50℃ and the stirring speed at 350 rpm, keep the reaction at this temperature for 60 min, and control the pH of the system at 6.2 to obtain the outer silanization reaction solution. Step 3: Add 30g of colloidal silica dispersion to another container. While stirring at 300rpm, transfer the outer silanization reaction solution obtained in Step 2 into the colloidal silica dispersion within 5 minutes. Then continue stirring at 40℃ for 20 minutes to obtain the spray drying precursor liquid. Then dry it using the spray drying method, controlling the inlet air temperature at 150℃ and the outlet air temperature at 65℃. Collect the powder to obtain the redispersible polymer powder. Step 4: Add 550g of heavy calcium carbonate, 120g of quartz powder, 160g of silicate cement, 60g of calcium hydroxide, 4g of hydroxyethyl cellulose ether, and 4g of hydrophilic fumed silica to a mixer and dry mix for 5 minutes; then add 100g of the redispersible polymer powder obtained in Step 3 and continue to dry mix for 3 minutes; finally, add 2g of hydrophobic fumed silica and dry mix for another 2 minutes to obtain 1000g of waterproof putty powder. Step 5: Mix 279g of deionized water with 1g of glacial acetic acid evenly to obtain the mixing water for construction; add 1000g of waterproof putty powder obtained in step 4 to the mixing water in three batches, stir at 500rpm for 3 minutes, let stand and mature for 5 minutes, and then stir again at 500rpm for 2 minutes to obtain the construction slurry. Step Six: Apply the construction slurry obtained in Step Five to the cement mortar base layer that has been cleaned of loose dust and moistened to a surface dry state. The thickness of the first coat should be controlled at 0.8-1.0 mm. After an interval of 4 hours, apply the second coat, with a thickness of 0.8-1.0 mm. The total thickness should be controlled at 1.6-2.0 mm. After curing, maintain the slurry at 25℃ and 70% relative humidity for 7 days. Example 2

[0031] Step 1: Add 68g of deionized water to a container equipped with a stirrer, heat to 88℃, add 6g of polyvinyl alcohol, stir at 450rpm for 35min until a homogeneous and transparent solution is formed, and then cool to 38℃; filter 320g of ethylene-vinyl acetate copolymer dispersion through a 100-mesh filter and add it to the above solution, stir at 280rpm for 18min to obtain the outer premixed liquid; Step 2: Mix 15g of anhydrous ethanol with 4.5g of 3-glycidyl etheroxypropyltrimethoxysilane for 4 min, then add the mixture dropwise to the outer premixed solution obtained in Step 1 within 12 min. Add 0.3g of triethylamine, control the system temperature at 48℃ and the stirring speed at 320 rpm, keep the reaction at this temperature for 50 min, and control the pH of the system at 5.9 to obtain the outer silanization reaction solution. Step 3: Add 24g of colloidal silica dispersion to another container. While stirring at 280rpm, transfer the outer silanization reaction solution obtained in Step 2 into the colloidal silica dispersion within 6 minutes. Then continue stirring at 38℃ for 15 minutes to obtain the spray drying precursor liquid. Then dry it using the spray drying method, controlling the inlet air temperature at 145℃ and the outlet air temperature at 60℃. Collect the powder to obtain the redispersible polymer powder. Step 4: Add 575g of heavy calcium carbonate, 130g of quartz powder, 150g of silicate cement, 58g of calcium hydroxide, 3g of hydroxyethyl cellulose ether, and 3g of hydrophilic fumed silica to a mixer and dry mix for 4 minutes; then add 80g of the redispersible polymer powder obtained in Step 3 and continue to dry mix for 3 minutes; finally, add 1g of hydrophobic fumed silica and dry mix for 2 minutes to obtain 1000g of waterproof putty powder. Step 5: Mix 281g of deionized water with 0.8g of glacial acetic acid evenly to obtain the mixing water for construction; add 1000g of waterproof putty powder obtained in step 4 to the mixing water for construction in three parts, stir at 480rpm for 3min, let stand and mature for 5min, and then stir again at 480rpm for 2min to obtain the construction slurry. Step Six: Apply the construction slurry obtained in Step Five to the cement mortar base layer that has been cleaned of loose dust and moistened to a surface dry state. The thickness of the first coat should be controlled at 0.7-0.9 mm. After an interval of 3.5 hours, apply the second coat, with a thickness of 0.7-0.9 mm. The total thickness should be controlled at 1.4-1.8 mm. After curing, maintain the slurry at 23℃ and 65% relative humidity for 7 days. Example 3

[0032] Step 1: Add 76g of deionized water to a container equipped with a stirrer, heat to 92℃, add 10g of polyvinyl alcohol, stir at 550rpm for 45min until a homogeneous and transparent solution is formed, and then cool to 42℃; filter 340g of ethylene-vinyl acetate copolymer dispersion through a 100-mesh filter and add it to the above solution, stir at 320rpm for 22min to obtain the outer premixed liquid; Step 2: Mix 21g of anhydrous ethanol with 8g of 3-glycidyl etheroxypropyltrimethoxysilane for 6 min, then add the mixture dropwise to the outer premixed solution obtained in Step 1 within 8 min. Add 0.8g of triethylamine, control the system temperature at 55℃ and the stirring speed at 380 rpm, keep the reaction at this temperature for 80 min, and control the pH of the system at 6.6 to obtain the outer silanization reaction solution. Step 3: Add 40g of colloidal silica dispersion to another container. While stirring at 320rpm, transfer the outer silanization reaction solution obtained in Step 2 into the colloidal silica dispersion within 4 minutes. Then continue stirring at 42℃ for 25 minutes to obtain the spray drying precursor liquid. Then dry it using the spray drying method, controlling the inlet air temperature at 160℃ and the outlet air temperature at 70℃. Collect the powder to obtain the redispersible polymer powder. Step 4: Add 537g of heavy calcium carbonate, 100g of quartz powder, 170g of silicate cement, 55g of calcium hydroxide, 5g of hydroxyethyl cellulose ether, and 5g of hydrophilic fumed silica to a mixer and dry mix for 6 minutes; then add 125g of the redispersible polymer powder obtained in Step 3 and continue to dry mix for 4 minutes; finally, add 3g of hydrophobic fumed silica and dry mix for 2 minutes to obtain 1000g of waterproof putty powder. Step 5: Mix 278g of deionized water with 1.2g of glacial acetic acid evenly to obtain the mixing water for construction; add 1000g of waterproof putty powder obtained in step 4 to the mixing water for construction in three parts, stir at 520rpm for 3min, let stand and mature for 6min, and then stir again at 520rpm for 2min to obtain the construction slurry. Step Six: Apply the construction slurry obtained in Step Five to the cement mortar base layer that has been cleaned of loose dust and moistened to a surface dry state. The thickness of the first coat should be controlled at 0.9-1.1 mm. After an interval of 4.5 hours, apply the second coat with a thickness of 0.9-1.1 mm. The total thickness should be controlled at 1.8-2.2 mm. After curing, maintain the slurry at 27℃ and 75% relative humidity for 7 days. Example 4

[0033] Step 1: Add 74g of deionized water to a container equipped with a stirrer, heat to 91℃, add 9g of polyvinyl alcohol, stir at 520rpm for 42min until a homogeneous and transparent solution is formed, and then cool to 41℃; filter 335g of ethylene-vinyl acetate copolymer dispersion through a 100-mesh filter and add it to the above solution, stir at 310rpm for 21min to obtain the outer premixed liquid; Step 2: Mix 19g of anhydrous ethanol with 7g of 3-glycidoxypropyltrimethoxysilane for 5 min, then add the mixture dropwise to the outer premixed solution obtained in Step 1 within 9 min. Add 0.6g of triethylamine, control the system temperature at 52℃ and the stirring speed at 360 rpm, keep the reaction at this temperature for 70 min, and control the pH of the system at 6.4 to obtain the outer silanization reaction solution. Step 3: Add 34g of colloidal silica dispersion to another container. While stirring at 300rpm, transfer the outer silanization reaction solution obtained in Step 2 into the colloidal silica dispersion within 5 minutes. Then continue stirring at 41℃ for 22 minutes to obtain the spray drying precursor liquid. Then dry it using the spray drying method, controlling the inlet air temperature at 155℃ and the outlet air temperature at 67℃. Collect the powder to obtain the redispersible polymer powder. Step 4: Add 543g of heavy calcium carbonate, 110g of quartz powder, 162g of silicate cement, 60g of calcium hydroxide, 4g of hydroxyethyl cellulose ether, and 5g of hydrophilic fumed silica to a mixer and dry mix for 5 minutes; then add 113g of the redispersible polymer powder obtained in Step 3 and continue to dry mix for 3 minutes; finally, add 3g of hydrophobic fumed silica and dry mix for 2 minutes to obtain 1000g of waterproof putty powder. Step 5: Mix 279g of deionized water with 1.1g of glacial acetic acid evenly to obtain the mixing water for construction; add 1000g of waterproof putty powder obtained in step 4 to the mixing water for construction in three parts, stir at 500rpm for 3min, let stand and mature for 5min, and then stir again at 500rpm for 2min to obtain the construction slurry. Step Six: Apply the construction slurry obtained in Step Five to the cement mortar base layer that has been cleaned of loose dust and moistened to a surface dry state. The thickness of the first coat should be controlled at 0.8-1.0 mm. After an interval of 4 hours, apply the second coat, with a thickness of 0.8-1.0 mm. The total thickness should be controlled at 1.6-2.0 mm. After curing, maintain the slurry at 26℃ and 72% relative humidity for 7 days. Example 5

[0034] Step 1: Add 69g of deionized water to a container equipped with a stirrer, heat to 89°C, add 7g of polyvinyl alcohol, stir at 470rpm for 38min until a homogeneous and transparent solution is formed, and then cool to 39°C; filter 325g of ethylene-vinyl acetate copolymer dispersion through a 100-mesh filter and add it to the above solution, stir at 290rpm for 19min to obtain the outer premixed liquid; Step 2: Mix 17g of anhydrous ethanol with 5g of 3-glycidyl etheroxypropyltrimethoxysilane for 4 min, then add the mixture dropwise to the outer premixed solution obtained in Step 1 within 11 min. Add 0.4g of triethylamine, control the system temperature at 49℃ and the stirring speed at 330 rpm, keep the reaction at this temperature for 55 min, and control the pH of the system at 6.0 to obtain the outer silanization reaction solution. Step 3: Add 26g of colloidal silica dispersion to another container. While stirring at 290rpm, transfer the outer silanization reaction solution obtained in Step 2 into the colloidal silica dispersion within 6 minutes. Then continue stirring at 39℃ for 18 minutes to obtain the spray drying precursor liquid. Then dry it using the spray drying method, controlling the inlet air temperature at 148℃ and the outlet air temperature at 62℃. Collect the powder to obtain the redispersible polymer powder. Step 4: Add 560g of heavy calcium carbonate, 125g of quartz powder, 152g of silicate cement, 60g of calcium hydroxide, 3g of hydroxyethyl cellulose ether, and 3g of hydrophilic fumed silica to a mixer and dry mix for 4 minutes; then add 95g of the redispersible polymer powder obtained in Step 3 and continue to dry mix for 3 minutes; finally, add 2g of hydrophobic fumed silica and dry mix for another 2 minutes to obtain 1000g of waterproof putty powder. Step 5: Mix 281g of deionized water and 0.9g of glacial acetic acid evenly to obtain the mixing water for construction; add 1000g of waterproof putty powder obtained in step 4 to the mixing water for construction in three parts, stir at 490rpm for 3min, let stand and mature for 5min, and then stir again at 490rpm for 2min to obtain the construction slurry. Step Six: Apply the construction slurry obtained in Step Five to the cement mortar base layer that has been cleaned of loose dust and moistened to a surface dry state. The thickness of the first coat should be controlled at 0.8-1.0 mm. After an interval of 4 hours, apply the second coat with a thickness of 0.8-1.0 mm. The total thickness should be controlled at 1.6-2.0 mm. After curing, maintain the slurry at 24℃ and 68% relative humidity for 7 days.

[0035] Comparative Example 1: The difference from Example 1 is that 0.5g of triethylamine is not added in step two, while the other conditions are the same as in Example 1.

[0036] Comparative Example 2: The difference from Example 1 is that 6g of 3-glycidoxypropyltrimethoxysilane is not added in step two, while the other conditions are the same as in Example 1.

[0037] Comparative Example 3: The difference from Example 1 is that: in step two, 6g of 3-glycidyl etheroxypropyltrimethoxysilane is not added to the outer premixed liquid obtained in step one; in step five, 279g of deionized water is adjusted to 273g, and 6g of 3-glycidyl etheroxypropyltrimethoxysilane is mixed evenly with 273g of deionized water and 1g of glacial acetic acid and used as mixing water for construction. The other conditions are the same as in Example 1.

[0038] Comparative Example 4: The difference from Example 1 is that 30g of colloidal silica dispersion is not added in step three, and the outer silanization reaction solution obtained in step two is directly spray-dried. The other conditions are the same as in Example 1.

[0039] Comparative Example 5: The difference from Example 1 is that in step four, 4g of hydrophilic fumed silica and 2g of hydrophobic fumed silica are added to the mixer at the same time and dry-mixed with other raw materials. Instead of adding 2g of hydrophobic fumed silica separately at the end, the other conditions are the same as in Example 1.

[0040] Comparative Example 6: The difference from Example 1 is that 2g of hydrophobic fumed silica is not added in step four, and the 550g of heavy calcium carbonate is adjusted to 552g. The other conditions are the same as in Example 1.

[0041] Comparative Example 7: The difference from Example 1 is that 4g of hydrophilic fumed silica is not added in step four, and the 550g of heavy calcium carbonate is adjusted to 554g. The other conditions are the same as in Example 1.

[0042] Comparative Example 8: The difference from Example 1 is that 1g of glacial acetic acid is not added in step five, and the mixing water used for construction is replaced with 280g of deionized water. The other conditions are the same as in Example 1.

[0043] Performance testing: Sample preparation was as follows: The waterproof putty powders of Examples 1-5 and Comparative Examples 1-8 were prepared according to steps one to four of their respective examples or comparative examples; the samples used for application performance testing were prepared from their respective waterproof putty powders into construction slurry according to step five, and molded on the substrate according to the corresponding method in step six. The substrate used for workability, surface drying time, initial drying crack resistance and water resistance tests was an asbestos-free fiber cement board; the substrate used for water absorption, standard state bond strength, bond strength after immersion in water and bond strength after freeze-thaw cycles tests was a 70mm×70mm×20mm cement mortar block, which was prepared by using general silicate cement, medium sand and water in a mass ratio of 1:2:0.40, and cured under standard conditions for 14 days after molding, and then placed under laboratory conditions for 7 days for later use; the substrate used for putty film flexibility testing was a 155mm×85mm×0.25mm tinplate. Unless otherwise specified, all samples were conditioned for 48 hours at 23±2℃ and 50±5% relative humidity before testing.

[0044] Workability, surface drying time, and initial drying crack resistance: Workability, surface drying time, and initial drying crack resistance were evaluated using the slurry obtained in step five. The sample was evenly applied to a 200mm × 150mm × 5mm asbestos-free fiber cement slab using a stainless steel trowel. The thickness of a single wet film was controlled at 1.0mm. Observation was conducted for any significant difficulty in trowel application, edge curling, powdering, localized accumulation, or uneven application. The smoothness of film formation was recorded. Surface drying time was determined according to GB / T [standard / requirement]. Method B (1728-2020) was used. A 2.0 mm wet film was prepared on a 150 mm × 70 mm × 5 mm asbestos-free fiber cement plate and placed at 23 ± 2 °C and 50 ± 5% relative humidity. The surface drying endpoint was defined as the surface not being sticky to the touch and not showing significant damage. The time was recorded. For initial drying crack resistance, a putty layer with a total wet film thickness of 2.0 mm was prepared on a 200 mm × 150 mm × 5 mm asbestos-free fiber cement plate and placed under standard conditions for 6 hours. Cracks were observed under a 4x magnifying glass, and the maximum crack width was recorded. No visible cracks were recorded as 0 mm.

[0045] Water absorption: Apply the construction slurry obtained in step five to the surface of a 70mm×70mm×20mm cement mortar block, controlling the wet film thickness to 2.0mm. Cure for 7 days at 23±2℃ and 50±5% relative humidity, then let it sit for 1 day before use. Before testing, remove surface dust and weigh the sample (m1). Place the sample with the putty side down in a water container, supporting it with two glass triangular blocks, ensuring the water level is 15mm from the bottom of the mortar block. Immerse for 10 minutes, then remove within 10 seconds. Gently absorb the free water from the sides and bottom with filter paper, and weigh again (m2). Calculate the water absorption as m2-m1, in g / 10min. Test 5 parallel samples for each sample and take the average value.

[0046] Water resistance: Water resistance was tested according to the relevant methods of GB / T 1733-1993. The construction slurry obtained in step five was applied to a 150mm×70mm×5mm asbestos-free fiber cement slab, with the wet film thickness controlled at 2.0mm. The slurry was cured for 7 days at 23±2℃ and 50±5% relative humidity. Subsequently, the sample was vertically immersed in deionized water at 23±2℃ for 96 hours. After removal, it was placed under standard conditions for 24 hours, and the surface was observed for blistering, cracking, significant softening, peeling, and significant powdering. Three test panels were used for each sample. A test was considered complete after 96 hours if at least two test panels showed no blistering, cracking, or peeling, and no significant powdering was observed after five rubs with a finger.

[0047] Standard state bond strength, post-immersion bond strength, and post-freeze-thaw cycle bond strength: The construction slurry obtained in step five was applied to the surface of a 70mm×70mm×20mm cement mortar block, with the wet film thickness controlled at 2.0mm; the standard state bond strength specimen was cured at 23±2℃ and 50±5% relative humidity for 14 days, and then a 40mm×40mm pull-out block was bonded to the putty surface. After the adhesive cured for 24 hours, a vertical tensile test was performed using an electronic tensile testing machine at a speed of 5mm / min, and the failure load was recorded and converted into bond strength; the post-immersion bond strength specimen was cured under standard conditions for 7 days and then immersed in 23±2℃ water. The samples were immersed in deionized water at ℃ for 48 hours, then dried at 50±3℃ for 24 hours, and then placed at 23±2℃ and 50±5% relative humidity for 24 hours. The tensile strength test was then performed in the same manner. After freeze-thaw cycles, the bond strength samples were cured under standard conditions for 14 days and then subjected to 5 freeze-thaw cycles. Each cycle was performed under the following conditions: immersion in water at 23±2℃ for 18 hours, freezing at -20±2℃ for 3 hours, and drying at 50±2℃ for 3 hours. After completing 5 cycles, the samples were dried at 50±2℃ for 24 hours and then placed at 23±2℃ and 50±5% relative humidity for 24 hours. Finally, the tensile test was performed in the same manner. Six parallel samples were tested for each sample under each condition. The maximum and minimum values ​​were removed, and the average of the remaining four values ​​was taken.

[0048] Putty film flexibility: The putty film flexibility was tested according to GB / T 1731-2020. The construction slurry obtained in step five was applied to the surface of a 155mm×85mm×0.25mm tinplate, with the wet film thickness controlled at 1.0mm. It was cured for 7 days at 23±2℃ and 50±5% relative humidity. Subsequently, the film surface was lightly sanded with fine sandpaper to control the dry film thickness at 0.80-1.00mm. During the test, the test plate was bent 180° around a cylindrical shaft with a diameter of 100mm, and the bending time was controlled within 2-3 seconds. The film layer was observed for cracks, peeling, or obvious breakage. If no cracks were visible to the naked eye, it was recorded as passing. If cracks appeared, the minimum diameter of the passing shaft was recorded, in mm.

[0049] The test results are shown in Table 1.

[0050] Table 1 Performance Test Results

[0051] As can be seen from Table 1, no visible cracks were observed in Examples 1-5 under 2.0mm wet film conditions for 6 hours, and no abnormalities were observed in water resistance for 96 hours. This indicates that the waterproof putty system constructed in this application can achieve good water resistance while ensuring workability and initial film formation stability. In Examples 2-5, as the amounts of 3-glycidyl etheroxypropyltrimethoxysilane and triethylamine in step two, colloidal silica in step three, and redispersible polymer powder and biphasic silica in step four increased from low to high and then moderately decreased, the water absorption, bonding strength after immersion in water, and bonding strength after freeze-thaw cycles generally showed a trend of first improving and then slightly decreasing. Among them, Example 3 had the best overall performance, with water absorption reduced to 0.63 g / 10 min, and bonding strength under standard conditions, bonding strength after immersion in water, and bonding strength after freeze-thaw cycles reaching 1.31 MPa, 0.97 MPa, and 0.95 MPa, respectively. The putty film flexibility reached 50 mm. Although the surface drying time was extended to 4.6 h, it still met the requirements for putty for building exterior walls.

[0052] Combining Example 1 and Comparative Example 2, it can be seen that, under basically the same other conditions, after introducing 3-glycidyl etheroxypropyltrimethoxysilane and forming outer silanized-nano silica composite particles through steps two and three, the water absorption decreased from 1.24 g / 10 min to 0.77 g / 10 min, and the bonding strength after immersion in water increased from 0.55 MPa to 0.85 MPa. This indicates that the pre-positioning of reaction sites significantly improved the water resistance and wet interface bonding stability of the putty layer. Comparative Example 1 shows that the lack of triethylamine reduces the silane fixation efficiency, resulting in a significant decrease in bond strength after immersion in water and after freeze-thaw cycles. Comparative Example 3 further illustrates that although adding 3-glycidoxypropyltrimethoxysilane directly to the mixing water for construction can provide a certain surface hydrophobic effect and slightly reduce the water absorption compared to Comparative Example 2, since it is not pre-fixed to the outer layer of the redispersible polymer powder, it is more prone to local self-condensation and phase separation during construction. This results in a rougher construction, poorer initial drying crack resistance, decreased flexibility, and a further reduction in bond strength to 0.44 MPa after immersion in water.

[0053] Combined with Comparative Examples 4-8, it can also be seen that the pre-placement of colloidal silica, the sequential arrangement of adding hydrophilic fumed silica first and hydrophobic fumed silica later, and the use of acidic mixing water to promote the hydrolysis of trimethoxysilane functional groups during the construction stage, followed by the use of the alkaline environment provided by silicate cement and calcium hydroxide to complete the subsequent polycondensation, all contribute synergistically to reducing water absorption, mitigating interface softening after immersion in water, and improving the retention rate of bond strength after water resistance.

[0054] In summary, this application is not a simple superposition of a single hydrophobic component, a single nanofiller, or a single redispersible polymer powder. Instead, it achieves the technical effects of reduced water absorption, improved water resistance, and more stable interfacial bonding after freeze-thaw cycles without sacrificing workability and trowelability through a combination design of outer silanized redispersible polymer powder + colloidal silica nano-anchors + sequential control of two-phase silica + hydrolysis followed by polycondensation.

[0055] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A waterproof putty powder, characterized in that, By mass parts, it includes the following components: 537-575 parts of heavy calcium carbonate; 100-130 parts quartz powder; 150-170 parts silicate cement; 55-60 parts calcium hydroxide; 3-5 parts hydroxyethyl cellulose ether; 3-5 parts hydrophilic fumed silica; 1-3 parts hydrophobic fumed silica; as well as 80-125 parts of redispersible polymer powder; The redispersible polymer powder is a redispersible polymer powder modified with silane and colloidal silica, which is prepared by spray drying of ethylene-vinyl acetate copolymer dispersion, polyvinyl alcohol, 3-glycidoxypropyltrimethoxysilane, triethylamine and colloidal silica dispersion.

2. The waterproof putty powder according to claim 1, characterized in that, The redispersible polymer powder is prepared by the following method: first, polyvinyl alcohol is dissolved in water and then mixed with ethylene-vinyl acetate copolymer dispersion to obtain an outer premix; 3-glycidyl etheroxypropyltrimethoxysilane is premixed with anhydrous ethanol and then added dropwise to the outer premix, and reacted in the presence of triethylamine to obtain an outer silanization reaction solution; then, the outer silanization reaction solution is mixed with colloidal silica dispersion and spray-dried to obtain the redispersible polymer powder.

3. The waterproof putty powder according to claim 1, characterized in that, When preparing the redispersible polymer powder, the amounts of water, polyvinyl alcohol, ethylene-vinyl acetate copolymer dispersion, anhydrous ethanol, 3-glycidyl etheroxypropyltrimethoxysilane, triethylamine, and colloidal silica dispersion, by weight, are 68-76 parts, 6-10 parts, 320-340 parts, 15-21 parts, 4.5-8 parts, 0.3-0.8 parts, and 24-40 parts, respectively.

4. The waterproof putty powder according to claim 1, characterized in that, In preparing the redispersible polymer powder, the 3-glycidyl etheroxypropyltrimethoxysilane is premixed with anhydrous ethanol for 4-6 min, and then added dropwise to the outer premixed solution within 8-12 min. The mixture is then reacted for 50-80 min at 48-55°C, a stirring speed of 320-380 rpm, and a pH of 5.9-6.

6. The resulting outer silanized reaction solution is added to the colloidal silica dispersion within 4-6 min while stirring at 280-320 rpm. After stirring for 15-25 min at 38-42°C, the mixture is spray-dried. The inlet air temperature of the spray dryer is 145-160°C, and the outlet air temperature is 60-70°C.

5. The waterproof putty powder according to claim 1, characterized in that, The waterproof putty powder is prepared by the following method: first, dry-mixing heavy calcium carbonate, quartz powder, silicate cement, calcium hydroxide, hydroxyethyl cellulose ether and hydrophilic fumed silica for 4-6 minutes, then adding the redispersible polymer powder and continuing to dry-mix for 3-4 minutes, and finally adding hydrophobic fumed silica and dry-mixing for 2 minutes.

6. The waterproof putty powder according to claim 1, characterized in that, The number average molecular weight of the ethylene-vinyl acetate copolymer dispersion is 40,000-50,000.

7. The waterproof putty powder according to claim 1, characterized in that, The solid content of the colloidal silica dispersion is 30 wt%.

8. The waterproof putty powder according to claim 1, characterized in that, The hydrophilic fumed silica is of type HDK N20.

9. The waterproof putty powder according to claim 1, characterized in that, The hydrophobic fumed silica is of type HDK H18.

10. A method for preparing waterproof putty powder according to any one of claims 1-9, characterized in that, Includes the following steps: (1) Mix water, polyvinyl alcohol and ethylene-vinyl acetate copolymer dispersion to obtain outer premix liquid; (2) 3-glycidyl etheroxypropyltrimethoxysilane was premixed with anhydrous ethanol and added to the outer premixed solution, and reacted in the presence of triethylamine to obtain the outer silanization reaction solution. (3) The outer silanization reaction solution is mixed with the colloidal silica dispersion and then spray-dried to obtain redispersible polymer powder; (4) Dry mix heavy calcium carbonate, quartz powder, silicate cement, calcium hydroxide, hydroxyethyl cellulose ether, hydrophilic fumed silica and the redispersible polymer powder, and then add hydrophobic fumed silica and dry mix again to obtain waterproof putty powder.

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