Dry-process preparation of waterproofing agent for porcelain insulators before glazing, preparation method and application thereof

Abstract

The present invention belongs to the technical field of ceramic waterproofing agents, specifically relating to a dry-process waterproofing agent for use before glazing porcelain insulators, its preparation method, and its application. The dry-process waterproofing agent for use before glazing porcelain insulators comprises the following raw materials by weight: 1-3% silicon micropowder, 0.2-0.7% polyvinyl alcohol solution, 5.3-9.8% methyltriethoxysilane, 4.7-7.2% n-butyl acetate, and 81-87% anhydrous ethanol. The waterproofing agent exhibits excellent water resistance and bonding properties, resulting in a glaze blank free of moisture-induced cracking, such as umbrella-base cracking or umbrella-tip cracking.

Description

Technical Field

[0001] The invention belongs to the technical field of ceramic waterproofing agents, and particularly relates to a waterproofing agent used for preparing porcelain insulators before glazing by a dry process, and a preparation method and application thereof. Background Art

[0002] Ceramic insulators generally require glazing to enhance their chemical stability, strength, thermal stability, and anti-fouling properties, while also improving their surface gloss and brightness. Glaze is a continuous, uniform, and smooth glassy substance that covers the surface of ceramic products. The thickness of the glaze layer on dry-process ceramic insulators before sintering is generally about 0.5 to 0.8 mm.

[0003] When preparing ceramic insulators using the dry method, the granulated and aged powder (with a moisture content of 0.7-1.5%) is pressed into shape using a cold isostatic press. It is then trimmed and shaped according to the design drawings on a CNC blank trimming machine. After the blank is cleaned with compressed air, the surface is transferred to a drying room for preheating, typically at a temperature of around 35-65°C. After preheating, the blank can be glazed. Unlike wet glazing, the dry method typically involves spraying glaze, which involves spraying the glaze slurry into small, mist-like particles that adhere to the surface of the blank to form a glaze blank, which is then fired in a kiln. However, during the glazing process, the fluidity of the glaze slurry is directly related to its moisture content. High moisture content results in good fluidity, while low moisture content leads to poor fluidity. Therefore, to prevent defects such as excessive glaze thickness and glaze heaping, the amount of moisture in the glaze slurry is strictly controlled during preparation. Currently, the moisture content is normally controlled within the range of 31-35%. Due to the moisture content of the glaze slurry, the blanks prepared by the dry method are extremely easy to absorb moisture, especially in the humid summer or cold winter seasons. After spraying the glaze, the glaze blanks often have moisture absorption cracks such as umbrella tip cracks, umbrella base cracks or umbrella falling, which affects the quality stability of the product and the pass rate of the entire process. Summary of the Invention

[0004] The purpose of the present invention is to provide a waterproofing agent for preparing porcelain insulators before glazing by a dry process, which has excellent waterproofness and bonding properties, and the prepared glaze blank has no moisture absorption cracks such as umbrella root cracks and umbrella tip cracks; the present invention also provides a simple and easy preparation method and application thereof.

[0005] The dry method for preparing a waterproofing agent for porcelain insulators before glazing comprises the following raw materials in percentage by mass: 1-3% silicon micropowder, 0.2-0.7% polyvinyl alcohol solution, 5.3-9.8% methyltriethoxysilane, 4.7-7.2% n-butyl acetate, and 81-87% anhydrous ethanol.

[0006] In the present invention, the silica micropowder is of the H series, with a median particle size of less than 0.3 μm and a content of particles less than 1 μm exceeding 90 wt%. The silica micropowder is the sole inorganic ingredient in the formulation. Its inclusion serves the following purposes: firstly, to enhance the dispersing and suspending properties of the water repellent; secondly, to enhance cross-linking between the water repellent and the particles of the base and glaze layer, improving the bonding strength of the glaze base and the fired product. If the silica micropowder particle size is too large, it will struggle to disperse and suspend, reducing the water repellent's performance. If the particle size is too small, production costs will be significantly increased and water repellency will be reduced.

[0007] In the present invention, the preparation method of the polyvinyl alcohol (PVA) solution is as follows:

[0008] With a polyvinyl alcohol mass concentration of 19-26%, add polyvinyl alcohol into cold water at 18-22°C, swell for 150-300 minutes, heat to 70-80°C under stirring, keep warm for 100-180 minutes, and cool to obtain a polyvinyl alcohol solution.

[0009] Polyvinyl alcohol (PVA) comes in granular, powdered, or flocculent forms. Dissolution times and temperatures vary slightly due to differences in its degree of polymerization and alcoholysis. Swelling the PVA in cold water at a relatively low temperature allows water molecules to slowly penetrate and evenly distribute within the PVA molecular structure. Then, heating the PVA while stirring to raise the dissolution temperature, the molecular chain activity within the PVA gradually intensifies, widening the molecular gaps and making it easier for water molecules to penetrate, causing swelling and disintegration. This process then mixes with water, forming a colloidal liquid. If the PVA is heated directly without pre-swelling it in cold water, the water and clumps may struggle to completely merge, or undissolved solids may be dispersed within the clumps, affecting normal use.

[0010] The present invention adopts polyvinyl alcohol solution to improve the suspension property of solid medium in the solution and improve the adhesion of the coating.

[0011] In the present invention, methyltriethoxysilane is a Class I silane. As a silicon source, due to its low degree of cross-linking, the islands or chains formed are well dispersed in the solution and will not over-polymerize into gel or precipitation. When forming a coating, it can produce a network-like coating on other components in the solution, providing good waterproof performance.

[0012] In the present invention, n-butyl acetate is an excellent organic solvent that can promote the hydrolysis and condensation of silanes, and the methyl group in its molecular formula has hydrophobic properties.

[0013] In the present invention, anhydrous ethanol is used as a solvent, mainly for preparing a transparent solution and a coating.

[0014] The dry method for preparing a waterproofing agent for use before glazing porcelain insulators according to the present invention comprises the following steps:

[0015] (1) dry-mixing silicon micropowder and polyvinyl alcohol solution to obtain a dry mix;

[0016] (2) mixing methyltriethoxysilane and n-butyl acetate, and then adding anhydrous ethanol and continuing to mix and stir to obtain a mixed solution;

[0017] (3) adding the dry mixture of step (1) to the mixed solution of step (2), mixing, stirring, and aging to obtain a waterproofing agent for porcelain insulators before glazing prepared by a dry process.

[0018] In step (1), the dry mixing time is 15 to 25 hours. The polyvinyl alcohol solution is a colloidal substance and is added in a small amount. The dry mixing adopts a grinding method to break the agglomeration of the macromolecular chains of the polyvinyl alcohol solution and make it adhere to the surface of the silicon powder in the form of tiny particles.

[0019] In step (2), when methyltriethoxysilane and n-butyl acetate are mixed, the stirring speed is 800-1000 r / min and the stirring time is 2-3 h; when anhydrous ethanol is added and mixed, the stirring speed is 600-800 r / min and the stirring time is 12-18 h.

[0020] In step (3), the mixing and stirring time is 5 to 7 hours, and the aging time is not less than 24 hours.

[0021] During the entire preparation process and storage of the finished waterproofing agent, the temperature should not exceed 35°C to prevent the waterproofing agent from polymerizing faster at high temperature and forming a colloid, increasing viscosity or losing its flow effect.

[0022] The polyvinyl alcohol solution prepared in the present invention is almost insoluble in organic solvents, but is an indispensable raw material for improving the adhesion of the coating to the green body and the glaze layer. Therefore, a staged mixing and stirring method is adopted. First, the silicon micropowder is dry-mixed with the homemade polyvinyl alcohol solution for a long time to break the agglomeration of the macromolecular chains of the polyvinyl alcohol solution, so that the polyvinyl alcohol adheres to the surface of the silicon micropowder in the form of tiny particles. In addition, the polyvinyl alcohol has a high degree of polymerization and can form a certain cohesive and encapsulating effect on the silicon micropowder, thereby reducing the water absorption capacity of the green body surface.

[0023] Methyltriethoxysilane and n-butyl acetate have good compatibility. At the same time, n-butyl acetate can promote the hydrolysis and condensation of methyltriethoxysilane and make full use of the hydrophobic methyl group in the molecular formula of both. When forming a gel, it is spread on the surface of the white blank in a network structure, thereby changing the hydrophilicity of the white blank surface to hydrophobicity, thereby achieving modification of the ceramic surface.

[0024] During the preparation process, the order of adding raw materials or the process operation process changes, and the phenomena produced during the solution preparation process and the final effect are different. Only by following the above steps can a waterproofing agent that meets the requirements be obtained.

[0025] The application of the dry method for preparing a waterproofing agent for use before glazing porcelain insulators according to the present invention comprises the following steps:

[0026] Stir the waterproofing agent in advance for 30 to 50 minutes, spray it onto the surface of the porcelain insulator blank, bake it at 45-55℃ for 3 to 5 hours, and then glaze it.

[0027] Specifically, the dry method for preparing a waterproofing agent for use before glazing porcelain insulators comprises the following steps:

[0028] (1) Stir the waterproofing agent for 30 to 50 minutes, then pour it into a pressure spray bottle;

[0029] (2) Place the porcelain insulator blank on the glazing rotating rack, keep the porcelain insulator blank in a rotating state, and use compressed air to blow away the dust on the surface of the porcelain insulator blank;

[0030] (3) The porcelain insulator blank continues to rotate, and the surface of the porcelain insulator blank is sprayed from top to bottom using a pressure spray pot, wherein the spraying pressure is set to 0.3-0.5 MPa;

[0031] (4) The sprayed porcelain insulator blank is transported to the drying room and baked for 3 to 5 hours at a temperature of 45-55°C.

[0032] (5) The baked porcelain insulator blank with waterproofing agent is placed back on the glazing rotating rack to start the glazing operation. The glazed blank is transported back to the drying room for firing.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The waterproofing agent of the present invention uses silicon micropowder, PVA, and silane as main raw materials. Except for silicon micropowder, the rest are organic components. Most of them will volatilize during the baking process. The remaining part will be decomposed and eliminated in the range of 300-400°C during the product firing process after exerting its hydrophobic properties. There is no residue and no additional energy consumption, which is energy-saving and environmentally friendly.

[0035] (2) Among the raw materials for the waterproofing agent of the present invention, silicon micropowder is the only inorganic raw material, and its main chemical component is silicon dioxide. Its particle size and material properties determine that its high-temperature viscosity is low at high temperatures, which can achieve interface fluxing, facilitate the removal of gas in the blank, and fill the pores at the interface, thereby improving the density and bonding strength of the interface;

[0036] (3) The waterproofing agent of the present invention is sprayed on the surface of the product body, which can modify the body and convert the surface of the body from hydrophilic to hydrophobic, thereby reducing the body's adsorption of glaze slurry water, eliminating the moisture absorption cracking phenomenon such as umbrella tip cracking, umbrella base cracking or umbrella falling that may occur during the glazing process, and greatly improving the process qualification rate;

[0037] (4) The preparation method of the present invention is scientific and reasonable, simple to operate, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a diagram showing the effect of water dripping on the surface of a porcelain insulator blank after spraying a waterproofing agent on the surface of the porcelain insulator blank according to Example 1 of the present invention;

[0039] Figure 2 This is a diagram showing the effect of water dripping on the surface of a porcelain insulator blank without spraying a waterproofing agent in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further illustrated below with reference to the following examples. The raw materials used in the examples, unless otherwise specified, are all commercially available raw materials; the processing methods used in the examples, unless otherwise specified, are all conventional methods in the art; and to facilitate comparison of the effects of the waterproofing agents, the glazing and firing procedures described in each example and comparative example are the same.

[0041] Example 1

[0042] A dry-process preparation method for a waterproofing agent used before glazing porcelain insulators comprises the following raw materials in percentage by weight: 2.5% silicon micropowder (with a median particle size of less than 0.3 μm and a content of particles less than 1 μm greater than 90 wt.%), 0.3% polyvinyl alcohol solution, 6.7% methyltriethoxysilane, 5% n-butyl acetate, and 85.5% anhydrous ethanol;

[0043] The preparation method of the polyvinyl alcohol solution is as follows: adding polyvinyl alcohol to cold water at 20°C with a polyvinyl alcohol mass concentration of 23%, swelling for 240 minutes, heating to 80°C with stirring, keeping warm for 120 minutes, and cooling to obtain the polyvinyl alcohol solution.

[0044] The preparation method of waterproofing agent is as follows:

[0045] (1) The silicon micropowder and polyvinyl alcohol solution in the above raw material ratio were placed in an agate ball mill and dry-mixed for 20 hours to obtain a dry mix;

[0046] (2) placing methyltriethoxysilane and n-butyl acetate in the above raw material ratio in a frosted glass bottle, stirring at 800 r / min for 2 h, then adding anhydrous ethanol in the above raw material ratio, and continuing to stir at 600 r / min for 15 h to obtain a mixed solution;

[0047] (3) Add the dry mixture of step (1) to the mixed solution of step (2), mix and stir for 6 hours, and age for 24 hours to obtain a waterproofing agent for porcelain insulators prepared by a dry method before glazing, and let it stand for use.

[0048] The application method of waterproofing agent is as follows:

[0049] (1) Stir the waterproofing agent for 35 minutes, then pour it into a pressure spray bottle;

[0050] (2) Place the porcelain insulator blank on the glazing rotating rack, keep the porcelain insulator blank in a rotating state, and use compressed air to blow away the dust on the surface of the porcelain insulator blank;

[0051] (3) The porcelain insulator blank continues to rotate, and the surface of the porcelain insulator blank is sprayed from top to bottom using a pressure spray pot, wherein the spraying pressure is set to 0.3 MPa;

[0052] (4) The sprayed porcelain insulator blank is transported to the drying room and baked for 4 hours at a temperature of 50°C.

[0053] (5) The baked porcelain insulator blank with waterproofing agent is placed back on the glazing rotating rack to start the glazing operation. The glazed blank is transported back to the drying room for firing.

[0054] Example 2

[0055] A waterproofing agent for preparing porcelain insulators before glazing by a dry process comprises the following raw materials in percentage by mass: 1% silicon micropowder (with a median particle size of less than 0.3 μm and a content of particles less than 1 μm greater than 90 wt.%), 0.2% polyvinyl alcohol solution, 9.8% methyltriethoxysilane, 7.2% n-butyl acetate, and 81.8% anhydrous ethanol.

[0056] The preparation method of the polyvinyl alcohol solution is as follows: adding polyvinyl alcohol to cold water at 18°C ​​with a polyvinyl alcohol mass concentration of 19%, swelling for 150 minutes, heating to 70°C under stirring, keeping warm for 100 minutes, and cooling to obtain the polyvinyl alcohol solution.

[0057] The preparation method of waterproofing agent is as follows:

[0058] (1) The silicon micropowder and polyvinyl alcohol solution in the above raw material ratio were placed in an agate ball mill and dry-mixed for 25 hours to obtain a dry mix;

[0059] (2) placing methyltriethoxysilane and n-butyl acetate in the above raw material ratio in a frosted glass bottle, stirring at 800 r / min for 3 h, then adding anhydrous ethanol in the above raw material ratio, and continuing to stir at 600 r / min for 18 h to obtain a mixed solution;

[0060] (3) Add the dry mixture of step (1) to the mixed solution of step (2), mix and stir for 7 hours, and age for 24 hours to obtain a waterproofing agent for porcelain insulators prepared by a dry method before glazing, and let it stand for use.

[0061] The application method of waterproofing agent is as follows:

[0062] (1) Stir the waterproofing agent for 50 minutes, then pour it into a pressure spray bottle;

[0063] (2) Place the porcelain insulator blank on the glazing rotating rack, keep the porcelain insulator blank in a rotating state, and use compressed air to blow away the dust on the surface of the porcelain insulator blank;

[0064] (3) The porcelain insulator blank continues to rotate, and the surface of the porcelain insulator blank is sprayed from top to bottom using a pressure spray pot, wherein the spraying pressure is set to 0.5 MPa;

[0065] (4) The sprayed porcelain insulator blank is transported to the drying room and baked for 5 hours at a temperature of 45°C.

[0066] (5) The baked porcelain insulator blank with waterproofing agent is placed back on the glazing rotating rack to start the glazing operation. The glazed blank is transported back to the drying room for firing.

[0067] Example 3

[0068] A dry-process preparation of a waterproofing agent for use before glazing porcelain insulators, comprising the following raw materials in percentage by mass: 3% silicon micropowder (median particle size less than 0.3 μm, content of particles less than 1 μm greater than 90 wt.%), 0.7% polyvinyl alcohol solution, 5.3% methyltriethoxysilane, 4.7% n-butyl acetate, and 86.3% anhydrous ethanol;

[0069] The preparation method of the polyvinyl alcohol solution is as follows: adding polyvinyl alcohol to cold water at 22°C with a polyvinyl alcohol mass concentration of 26%, swelling for 300 minutes, heating to 75°C under stirring, keeping warm for 180 minutes, and cooling to obtain the polyvinyl alcohol solution.

[0070] The preparation method of waterproofing agent is as follows:

[0071] (1) The silicon micropowder and polyvinyl alcohol solution in the above raw material ratio were placed in an agate ball mill and dry-mixed for 15 hours to obtain a dry mix;

[0072] (2) placing methyltriethoxysilane and n-butyl acetate in the above raw material ratio in a frosted glass bottle, stirring at 1000 r / min for 2.5 h, then adding anhydrous ethanol in the above raw material ratio, and continuing to stir at 800 r / min for 12 h to obtain a mixed solution;

[0073] (3) Add the dry mixture of step (1) to the mixed solution of step (2), mix and stir for 5 hours, and age for 48 hours to obtain a waterproofing agent for porcelain insulators prepared by a dry method before glazing, and let it stand for use.

[0074] The application method of waterproofing agent is as follows:

[0075] (1) Stir the waterproofing agent for 30 minutes, then pour it into a pressure spray bottle;

[0076] (2) Place the porcelain insulator blank on the glazing rotating rack, keep the porcelain insulator blank in a rotating state, and use compressed air to blow away the dust on the surface of the porcelain insulator blank;

[0077] (3) The porcelain insulator blank continues to rotate, and the surface of the porcelain insulator blank is sprayed from top to bottom using a pressure spray pot, wherein the spraying pressure is set to 0.4 MPa;

[0078] (4) The sprayed porcelain insulator blank is transported to the drying room and baked for 3 hours at a temperature of 55°C.

[0079] (5) The baked porcelain insulator blank with waterproofing agent is placed back on the glazing rotating rack to start the glazing operation. The glazed blank is transported back to the drying room for firing.

[0080] Comparative Example 1

[0081] In order to investigate the application effect of the waterproofing agent, this comparative example did not spray the waterproofing agent, but directly glazed and fired the surface of the porcelain insulator blank.

[0082] Comparative Example 2

[0083] In order to investigate the effect of the mixing order of the raw materials of the waterproofing agent on its effect, the difference between this comparative example and Example 1 is only that the silicon micropowder, polyvinyl alcohol solution, methyltriethoxysilane, n-butyl acetate, and anhydrous ethanol that meet the raw material ratio are directly mixed, stirred for 6 hours, and aged for 24 hours to obtain a waterproofing agent.

[0084] During application, it was found that the waterproofing agent prepared by this method contained a colloid that was insoluble in anhydrous ethanol (research showed it to be polyvinyl alcohol gel). The colloid easily clogged the spray gun when spraying the waterproofing agent, and the waterproofing agent system was not homogeneous, which would cause uneven bonding between the body and the glaze. Therefore, the experiment was abandoned.

[0085] Comparative Example 3

[0086] In order to investigate the effect of silica micropowder particle size on the effect of waterproofing agent, the difference between this comparative example and Example 1 is only that the median particle size of silica micropowder is between 0.9 and 1.2 μm, and the content of particles with a size less than 1 μm is about 20 wt.%. The other formulas and processes are exactly the same as those in Example 1.

[0087] The application effects of the embodiments and comparative examples were compared. Before glazing, the water repellency of the porcelain insulator blanks sprayed with a waterproofing agent and baked and the porcelain insulator blanks not sprayed with a waterproofing agent were tested. The results are shown in Table 1.

[0088] Table 1

[0089] project Static water contact angle (°) hydrophobicity Example 1 97 good Example 2 101 good Example 3 93 good Comparative Example 1 0 No hydrophobicity Comparative Example 3 91 good

[0090] As can be seen from Table 1, compared with the comparative example 1 without spraying the waterproofing agent, the porcelain insulator blank surfaces of Examples 1-3 have better hydrophobicity after spraying the waterproofing agent, while the comparative example 1 has no hydrophobicity at all; Figure 1-2 A comparison clearly shows that the water droplets in Example 1 formed balls, while the water droplets in Comparative Example 1 were instantly absorbed upon contact with the blank, penetrating into the body. While the surface of the porcelain insulator blank in Comparative Example 3 exhibited excellent hydrophobicity, the larger particle size of the silica powder resulted in poorer dispersion and suspension properties. The time difference during spraying may have resulted in differences in the solid phases of the sprayed materials, leading to more defects.

[0091] Furthermore, during the product development process, machine testing was conducted on each of the examples and comparative examples. These tests were conducted in July, in an ambient humidity range of 45-55%. Comparative testing was conducted directly on 30 products of the same model. No moisture-absorbing cracking was observed in the glaze blanks of Examples 1-3 with a water-repellent agent. However, one pinhole defect was observed in the glaze blank of Comparative Example 1 without a water-repellent agent. Comparative Example 2 was abandoned for testing. Comparative Example 3 exhibited one glaze shrinkage and two pinholes.

Claims

1. A waterproofing agent for use before glazing porcelain insulators prepared by a dry process, characterized in that: The method comprises the following raw materials in percentage by mass: 1-3% silicon micropowder, 0.2-0.7% polyvinyl alcohol solution, 5.3-9.8% methyltriethoxysilane, 4.7-7.2% n-butyl acetate, and 81-87% anhydrous ethanol; Among them, the median particle size of silicon micropowder is less than 0.3μm, and the content of particles less than 1μm is greater than 90wt.%; The dry method for preparing a waterproofing agent for porcelain insulators before glazing is prepared by the following steps: (1) Dry-mixing silicon micropowder and polyvinyl alcohol solution to obtain a dry mix; (2) Mixing methyltriethoxysilane and n-butyl acetate, and then adding anhydrous ethanol and continuing to mix and stir to obtain a mixed solution; (3) Adding the dry mixture of step (1) to the mixed solution of step (2), mixing and stirring, and aging, thereby obtaining a waterproofing agent for porcelain insulators before glazing prepared by a dry method.

2. The waterproofing agent for dry-process porcelain insulators before glazing according to claim 1, characterized in that: The preparation method of the polyvinyl alcohol solution is as follows: Based on a polyvinyl alcohol mass concentration of 19-26%, add polyvinyl alcohol into cold water at 18-22°C, swell for 150-300 minutes, heat to 70-80°C with stirring, keep warm for 100-180 minutes, and cool to obtain a polyvinyl alcohol solution.

3. The waterproofing agent for dry-process porcelain insulators before glazing according to claim 1, characterized in that: In step (1), the dry mixing time is 15 to 25 hours.

4. The waterproofing agent for dry-process porcelain insulators before glazing according to claim 1, characterized in that: In step (2), when methyltriethoxysilane and n-butyl acetate are mixed, the stirring speed is 800-1000 r / min and the stirring time is 2-3 h.

5. The waterproofing agent for dry-process porcelain insulators before glazing according to claim 1, characterized in that: In step (2), when adding anhydrous ethanol and mixing, the stirring speed is 600-800 r / min and the stirring time is 12-18 h.

6. The waterproofing agent for dry-process porcelain insulators before glazing according to claim 1, characterized in that: In step (3), the mixing and stirring time is 5 to 7 hours, and the aging time is not less than 24 hours.

7. Use of the waterproofing agent for dry-process porcelain insulators before glazing according to claim 1 or 2, characterized in that: The following steps are involved: Stir the waterproofing agent in advance for 30 to 50 minutes, spray it onto the surface of the porcelain insulator blank, bake it at 45 to 55°C for 3 to 5 hours, and then glaze it.

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