Lubricating liquid for drawing superfine photovoltaic tungsten filament and preparation method of lubricating liquid

Abstract

The specific gravity of the lubricating liquid is 1.5-1.8, the pH value of the lubricating liquid is 9-11, the viscosity of the lubricating liquid is 150-250 cp, and the lubricating liquid is prepared from 1-5 wt% of boron nitride, 0.2-5 wt% of a wetting dispersant, 0.1-1 wt% of a thickening agent, 0.1-0.5 wt% of a suspending agent, 0.1-0.8 wt% of a film-forming agent, 1-3 wt% of a pH value regulator, 0.1-0.3 wt% of a defoaming agent and the balance of water. Nanoscale hexagonal boron nitride is obtained through ball milling of the sand mill and centrifugal separation of the separator, and when the superfine tungsten alloy wire is drawn, compared with micron-scale solid lubricating particles, the particles with the nanometer particle size can form a uniform coating on the surface of the wire. Meanwhile, nano hexagonal boron nitride is used as lubricating liquid, and compared with aquadag used in traditional drawing, the nano hexagonal boron nitride has more excellent high-temperature resistance, the completeness of a coating can be always kept in the drawing process, drawing grooves in the surface of the tungsten alloy wire are effectively reduced, and the drawing yield is increased.

Description

Technical Field

[0001] The invention belongs to the field of diamond wire saw manufacturing for photovoltaic processing, and specifically relates to a lubricating liquid for drawing ultra-fine photovoltaic tungsten wires and a preparation method thereof. Background Art

[0002] Diamond wire saw is a kind of wire saw that achieves the purpose of cutting by consolidating sharp diamond particles on the surface of metal wire by electroplating. It is usually used for cutting hard and brittle materials in industries such as semiconductors, photovoltaics, glass, and sapphire. Diamond wire saws generally use high-carbon steel or tungsten alloy wire as a carrier to consolidate diamond abrasives. As silicon wafers in the photovoltaic industry continue to thin, diamond wire saws urgently need to develop in the direction of thinning. The theoretical limit of the wire diameter of high-carbon steel wire is 30µm, and the industrial limit is about 35-36µm. Tungsten alloy wire has good physical and chemical properties such as high strength, corrosion resistance, flexibility, anti-sagging, and high temperature resistance. The industrial limit of the wire diameter of tungsten alloy wire is 24-25µm, which can make up for the shortcomings of high-carbon steel diamond wire in cutting the thickness of single-crystal silicon wafers.

[0003] Tungsten alloy wire is formed by powder metallurgy after high-purity tungsten powder is doped with rare earth elements, and then the wire is obtained through processes such as rotary forging, drawing, and electrolytic cleaning. The drawing of tungsten alloy wire is to coat the surface of the wire with graphite emulsion, and then form a layer of solid graphite lubrication layer after drying in an electric heating furnace. Then the wire passes through a diamond die hole with a gradually decreasing cross-section. Under high temperature and high pressure, a plastic deformation process occurs in which the cross-section becomes smaller and the wire length increases. As the diameter of the tungsten alloy wire decreases, the contact area between the tungsten alloy wire and the die hole increases under the same volume, and the deformation temperature of the tungsten alloy wire increases sharply. Therefore, the drawing of ultra-fine tungsten alloy wire requires a graphite emulsion lubricant to form a uniform, complete, strong adhesion and high temperature resistant solid lubrication layer. At present, the graphite emulsion for drawing ultrafine tungsten alloy wire mainly relies on imports from Japan. On the one hand, the graphite particle size in the domestic graphite emulsion is too large, and the thickness of the solid lubricating layer formed after drying may be uneven, which may easily lead to wire breakage and small ring diameter during the drawing process. On the other hand, when nano-level graphite powder is used, when the heating temperature reaches above 400°C, oxidation and combustion are likely to occur, resulting in incomplete graphite emulsion coating on the wire surface and unstable drawing process. Summary of the invention

[0004] The invention provides a lubricant replacing the graphite emulsion used in the prior art, namely a lubricating liquid suitable for drawing a tungsten alloy wire with a wire diameter of 26-33 μm under the condition of 300-800° C. and a preparation method thereof.

[0005] The first scheme provided by the present invention is: a lubricating liquid for drawing ultra-fine photovoltaic tungsten wires, wherein the lubricating liquid has a specific gravity of 1.5-1.8, a pH value of 9-11, a viscosity of 150-250cp, and is composed of 1-5wt% boron nitride, 0.2-5wt% wetting dispersant, 0.1-1wt% thickener, 0.1-0.5wt% suspending agent, 0.1-0.8wt% film former, 1-3wt% pH regulator, 0.1-0.3wt% defoamer and the remainder of water. The specific gravity of the lubricating liquid is the ratio of the density of the lubricating liquid (in a completely dense state) to the density of pure water.

[0006] Furthermore, the boron nitride is hexagonal boron nitride, which belongs to the hexagonal crystal system and has a layered structure similar to graphite. The layers are bonded by van der Waals forces, the structure is stable and easy to slide, and it has the advantages of high temperature resistance, oxidation resistance, low friction coefficient, good chemical stability, etc. It can be used as a solid lubricating particle in the lubricating fluid. The D50 particle size of the boron nitride is preferably 200-800nm.

[0007] The wetting and dispersing agent is one or more of sodium pyrophosphate, trisodium phosphate, sodium hexametaphosphate, sodium metasilicate, sodium disilicate, sodium polyacrylate, sodium polycarboxylate, polyethyleneimine, etc. One end of the active group of the wetting and dispersing agent is adsorbed on the hexagonal boron nitride, and the other end enters the aqueous solution to form an adsorption layer, thereby dispersing the hexagonal boron nitride particles through charge or steric hindrance effect.

[0008] The thickener is one or more organic substances such as sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl hydroxypropyl cellulose, polyvinyl alcohol, bis-triethanolamine diisopropyl titanate, polyacrylamide, etc.

[0009] The suspending agent is one or more of aluminum-based bentonite, hydrophilic silica, and attapulgite.

[0010] Preferably, the particle size of the suspending agent is 50-500 nm.

[0011] Thickeners and suspending agents can form thixotropic or three-dimensional network structures in aqueous solutions, which can effectively prevent hexagonal boron nitride from stratifying and settling in lubricating fluids.

[0012] The film-forming agent is one or more of diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, propylene glycol phenyl ether, and tripropylene glycol n-butyl ether. During the drying process of the lubricating fluid, the film-forming agent can dissolve and fuse the polymer droplets to form a continuous and uniform coating; the pH value adjusting agent is one or more of organic substances such as sodium hydroxide, ammonia water, and ethanolamine. The pH value adjusting agent can adjust the pH value of the lubricating fluid to alkaline, which can improve the storage stability and antimicrobial ability of the lubricating fluid, promote the dissolution of the thickener and the dispersion of boron nitride; the defoaming agent is a non-silicon defoaming agent, which can inhibit the bubbles generated by the lubricating fluid during high-speed shear stirring and use, thereby ensuring the integrity of the lubricating coating.

[0013] The second technical solution provided by the present invention is: a method for preparing the aforementioned lubricating liquid for ultra-fine photovoltaic tungsten wire drawing, comprising the following steps: Step 1: Put hexagonal boron nitride into a sand mill for ball milling, add a dispersant for dispersion during the ball milling process, and after the ball milling is completed, take out the ball-milled material and put it into a centrifugal separator to sort out hexagonal boron nitride with a D50 of 200-800nm; Step 2: Add deionized water to the material mixing barrel, turn on the high-speed shear emulsifier, adjust the pH of the aqueous solution to between 9 and 11 with a pH regulator, then add a wetting dispersant, and pour the sorted hexagonal boron nitride after it is completely dissolved. After the hexagonal boron nitride is evenly dispersed in the aqueous solution, add a thickener, a suspending agent, a film-forming agent and a defoaming agent in sequence, and finally fully emulsify and disperse to obtain a lubricating fluid.

[0014] The sand mill has a ball milling time of 10-20 hours, the grinding balls are made of zirconium oxide, the particle size is 1.5 mm, the grinding balls occupy 2 / 3 of the grinding chamber volume, and the sand mill has a rotation speed of 2000-3500 rpm / min.

[0015] The rotation speed of the high-speed shear emulsifier is 1000-3000 rpm / min.

[0016] The boron nitride is hexagonal boron nitride, which belongs to the hexagonal crystal system and has a layered structure similar to graphite. The layers are bonded by van der Waals forces, the structure is stable and easy to slide, and it has the advantages of high temperature resistance, oxidation resistance, low friction coefficient, good chemical stability, etc. It can be used as a solid lubricating particle in the lubricating fluid. The D50 particle size of the boron nitride is preferably 200-800nm.

[0017] The wetting and dispersing agent is one or more of sodium pyrophosphate, trisodium phosphate, sodium hexametaphosphate, sodium metasilicate, sodium disilicate, sodium polyacrylate, sodium polycarboxylate, polyethyleneimine, etc. One end of the active group of the wetting and dispersing agent is adsorbed on the hexagonal boron nitride, and the other end enters the aqueous solution to form an adsorption layer, thereby dispersing the hexagonal boron nitride particles through charge or steric hindrance effect.

[0018] The thickener is one or more organic substances such as sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl hydroxypropyl cellulose, polyvinyl alcohol, bis-triethanolamine diisopropyl titanate, polyacrylamide, etc.

[0019] The suspending agent is one or more of aluminum-based bentonite, hydrophilic silica, and attapulgite.

[0020] Preferably, the particle size of the suspending agent is 50-500 nm.

[0021] Thickeners and suspending agents can form thixotropic or three-dimensional network structures in aqueous solutions, which can effectively prevent hexagonal boron nitride from stratifying and settling in lubricating fluids.

[0022] The film-forming agent is one or more of diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, propylene glycol phenyl ether, and tripropylene glycol n-butyl ether. During the drying process of the lubricating fluid, the film-forming agent can dissolve and fuse the polymer droplets to form a continuous and uniform coating; the pH value adjusting agent is one or more of organic substances such as sodium hydroxide, ammonia water, and ethanolamine. The pH value adjusting agent can adjust the pH value of the lubricating fluid to alkaline, which can improve the storage stability and antimicrobial ability of the lubricating fluid, promote the dissolution of the thickener and the dispersion of boron nitride; the defoaming agent is a non-silicon defoaming agent, which can inhibit the bubbles generated by the lubricating fluid during high-speed shear stirring and use, thereby ensuring the integrity of the lubricating coating.

[0023] The aforementioned lubricating liquid for drawing ultrafine photovoltaic tungsten wires is used for drawing tungsten alloy wires with a wire diameter of 26-33 μm at 300-800°C.

[0024] Furthermore, the third technical solution provided by the present invention is an application method of the lubricating liquid for drawing ultra-fine photovoltaic tungsten wires, such as Figure 4 The figure shows a schematic diagram of a tungsten alloy wire drawing device. The application method specifically includes the following steps: Step 1: Use a fixture to fix the tungsten alloy wire from the pay-off end to the take-up end through the lubricating liquid tank, heating furnace and wire drawing die in sequence. The diameter of the tungsten alloy wire at the pay-off end is 50-80μm, and the diameter of the tungsten alloy wire at the take-up end is 26-33μm; Step 2: Turn on the circulation pump in the lubricating liquid tank, immerse the tungsten alloy wire in the lubricating liquid by overflow, then turn on the heating furnace and the take-up motor. Set the heating furnace temperature to 600-800℃ and the take-up motor speed to 140m / min.

[0025] The present invention obtains nano-scale hexagonal boron nitride by ball milling with a sand mill and centrifugal sorting with a sorter. When drawing ultra-fine tungsten alloy wires, nano-sized particles can form a uniform coating on the surface of the wire compared to micron-scale solid lubricating particles. At the same time, using nano hexagonal boron nitride as a lubricant has better high temperature resistance than the graphite emulsion used in traditional drawing, and can always maintain the integrity of the coating during the drawing process, effectively reducing the drawing grooves on the surface of the tungsten alloy wire and improving the drawing yield rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a scanning electron microscope image of nano hexagonal boron nitride; Figure 2 This is a scanning electron microscope image of the tungsten alloy wire after lubricating liquid drawing obtained in embodiment 1 of the present invention; Figure 3 This is a scanning electron microscope image of the tungsten alloy wire after graphite emulsion drawing obtained in Comparative Example 1; Figure 4 Schematic diagram of tungsten alloy wire drawing device. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to specific embodiments and comparative examples.

[0028] Example 1

[0029] A lubricating liquid for drawing ultrafine photovoltaic tungsten wires, wherein the mass percentages of the components are as follows: 5% boron nitride, 1.5% sodium lignin sulfonate, 0.8% sodium carboxymethyl cellulose, 0.3% hydrophilic fumed silica, 0.5% propylene glycol methyl ether, 2.5% ammonia water, 0.2% non-silicon defoaming agent and the balance water.

[0030] The preparation process is as follows: Hexagonal boron nitride with a particle size of 5µm, the SEM photo of which is shown in Figure 1 As shown, the material was put into a horizontal sand mill for ball milling for 10 hours, the speed of the sand mill was 3000 rpm / min, 0.2% sodium lignin sulfonate was added during the ball milling process for dispersion, and after the ball milling was completed, the ball-milled material was taken out and added into a centrifugal separator to separate the hexagonal boron nitride with a D50 of 800 nm.

[0031] Add deionized water to the material mixing barrel, turn on the high-speed shear emulsifier, adjust the speed to 2000rpm / min, use ammonia water to adjust the pH of the aqueous solution to 10, and then add sodium lignin sulfonate. After the dispersant is completely dissolved, pour the sorted hexagonal boron nitride. After the hexagonal boron nitride is evenly dispersed in the aqueous solution, add sodium carboxymethyl cellulose, hydrophilic fumed silica, propylene glycol methyl ether and non-silicon defoaming agent in sequence. Finally, set the shear speed to 2000rpm / min and stir for 20h to fully emulsify and disperse to obtain the wire drawing lubricant.

[0032] The application method of the lubricating liquid for drawing ultra-fine photovoltaic tungsten wires prepared in this embodiment is as follows: Figure 4 The figure shows a schematic diagram of a tungsten alloy wire drawing device, which includes a wire pay-off end, a lubricating liquid tank, a heating furnace, a wire drawing die and a wire take-up end in sequence. The application method specifically includes the following steps: Step 1: Use a fixture to fix the tungsten alloy wire from the pay-off end to the take-up end through the lubricating liquid tank, heating furnace and wire drawing die in sequence. The diameter of the tungsten alloy wire at the pay-off end is 50-80μm, and the diameter of the tungsten alloy wire at the take-up end is 26-33μm; Step 2: Turn on the circulation pump in the lubricating liquid tank, immerse the tungsten alloy wire in the lubricating liquid by overflow, then turn on the heating furnace and the take-up motor. Set the heating furnace temperature to 600-800℃ and the take-up motor speed to 140m / min.

[0033] Example 2

[0034] The mass percentages of the components in a lubricating liquid for drawing ultrafine photovoltaic tungsten wires are as follows: 3% boron nitride, 1% sodium metasilicate, 0.8% sodium carboxymethyl cellulose, 0.5% aluminum-based bentonite, 0.5% propylene glycol methyl ether, 3% ammonia water, 0.5% non-silicon defoaming agent and the balance water.

[0035] The hexagonal boron nitride with a particle size of 5µm was placed in a horizontal sand mill and ball-milled for 8 hours at a speed of 3000rpm / min. During the ball-milling process, 0.5% sodium metasilicate was added for dispersion. After the ball-milling was completed, the ball-milled material was taken out and added to a centrifugal separator to separate the hexagonal boron nitride with a D50 of 500nm.

[0036] Add deionized water to the material mixing barrel, turn on the high-speed shear emulsifier, adjust the speed to 2000rpm / min, use ammonia water to adjust the pH of the aqueous solution to 10, and then add sodium metasilicate. After the dispersant is completely dissolved, pour the sorted hexagonal boron nitride. After the hexagonal boron nitride is evenly dispersed in the aqueous solution, add sodium carboxymethyl cellulose, aluminum-based bentonite, propylene glycol methyl ether and non-silicon defoaming agent in sequence. Finally, set the shear speed to 2500rpm / min and stir for 15h to fully emulsify and disperse to obtain the wire drawing lubricant.

[0037] Comparative Example 1 The mass percentages of the components in a graphite emulsion for drawing ultrafine photovoltaic tungsten wires are as follows: 4.5% natural flake graphite, 0.5% sodium hexametaphosphate, 0.2% sodium carboxymethyl cellulose, 0.2% hydrophilic fumed silica, 2.5% ammonia water, and 0.5% non-silicon defoaming agent.

[0038] Natural flake graphite powder with a particle size of 3 μm was placed in a horizontal sand mill and ball-milled for 10 hours at a speed of 3000 rpm / min. 0.1% sodium hexametaphosphate was added during the ball milling process for dispersion. After the ball milling was completed, the ball-milled material was taken out and added to a centrifugal separator to separate the graphite powder with a D50 of 600 nm.

[0039] Add deionized water to the material mixing barrel, turn on the high-speed shear emulsifier, adjust the speed to 2500rpm / min, use ammonia water to adjust the pH of the aqueous solution to 10, and then add sodium metaphosphate. After the dispersant is completely dissolved, pour the sorted graphite powder. After the graphite powder is evenly dispersed in the aqueous solution, add sodium carboxymethyl cellulose, hydrophilic fumed silica and non-silicon defoaming agent in sequence. Finally, set the shear speed to 2500rpm / min and stir for 18h to fully emulsify and disperse to obtain drawing graphite emulsion.

[0040] The lubricating liquid in Example 1 and the lubricating liquid in Comparative Example 1 were used for drawing tungsten wires, and the results were as follows: Figure 2 and Figure 3 As shown, from Figure 2 and Figure 3 It can be seen that when using traditional graphite emulsion as a wire drawing lubricant, there are some drawing scratches on the surface of the tungsten alloy wire, while using the lubricating liquid of the present invention for drawing reduces the wire breakage rate during the tungsten alloy wire drawing process, and the surface of the tungsten alloy wire is flat and smooth. At the same time, the application conditions of the lubricating liquid of the present invention and the lubricating liquid in the comparative example were tested respectively, and the results are shown in Table 1: Table 1 Comparison of drawn tungsten alloy wires of Examples 1-2 and Comparative Example 1 sample Operating temperature Tungsten Alloy Wire Diameter Wire breakage rate Pulling effect Example 1 600-800℃ 26-33μm 1-5% Smooth surface Example 2 600-800℃ 26-33μm 7.8% Smooth surface Comparative Example 1 300-500℃ 26-33μm 23.5% Pulling groove It is not difficult to see from Table 1 that, compared with the existing graphite lubricant, the lubricant prepared by the present invention has a higher applicable temperature, a significantly lower wire breakage rate, and a better drawing effect.

[0041] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that those skilled in the art may make several modifications and improvements without departing from the principles of the present invention, and these modifications and improvements should also be considered as the protection scope of the present invention.

Claims

1. A lubricating liquid for drawing ultra-fine photovoltaic tungsten wires, characterized in that: The lubricating liquid has a specific gravity of 1.5-1.8, a pH value of 9-11, a viscosity of 150-250cp, and is composed of 1-5wt% boron nitride, 0.2-5wt% wetting and dispersing agent, 0.1-1wt% thickener, 0.1-0.5wt% suspending agent, 0.1-0.8wt% film-forming agent, 1-3wt% pH regulator, 0.1-0.3wt% defoaming agent and the balance of water.

2. The lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 1, characterized in that: The boron nitride is hexagonal boron nitride, and the D50 particle size of the boron nitride is 200-800nm.

3. The lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 1, characterized in that: The wetting and dispersing agent is one or more of sodium pyrophosphate, trisodium phosphate, sodium hexametaphosphate, sodium metasilicate, sodium disilicate, sodium polyacrylate, sodium polycarboxylate, and polyethyleneimine.

4. The lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 1, characterized in that: The thickener is one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl hydroxypropyl cellulose, polyvinyl alcohol, bis-triethanolamine diisopropyl titanate, and polyacrylamide.

5. The lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 1, characterized in that: The suspending agent is one or more of aluminum-based bentonite, hydrophilic silica, and attapulgite.

6. The lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 5, characterized in that: The particle size of the suspending agent is 50-500nm.

7. The lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 1, characterized in that: The film-forming agent is one or more of diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, propylene glycol phenyl ether, and tripropylene glycol n-butyl ether; the pH value adjuster is one or more of sodium hydroxide, ammonia water, or ethanolamine; and the defoaming agent is a non-silicon defoaming agent.

8. A method for preparing the lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 1, characterized in that: The following steps are involved: Step 1: Put hexagonal boron nitride into a sand mill for ball milling, add a dispersant for dispersion during the ball milling process, and after the ball milling is completed, take out the ball-milled material and put it into a centrifugal separator to sort out hexagonal boron nitride with a D50 of 200-800nm; Step 2: Add deionized water to the material mixing barrel, turn on the high-speed shear emulsifier, adjust the pH of the aqueous solution to between 9 and 11 with a pH regulator, then add a wetting and dispersing agent, and pour the sorted hexagonal boron nitride after it is completely dissolved. After the hexagonal boron nitride is evenly dispersed in the aqueous solution, add a thickener, a suspending agent, a film-forming agent and a defoaming agent in sequence, and finally fully emulsify and disperse to obtain a lubricating fluid. The composition of the lubricating fluid is 1-5wt% boron nitride, 0.2-5wt% wetting and dispersing agent, 0.1-1wt% thickener, 0.1-0.5wt% suspending agent, 0.1-0.8wt% film-forming agent, 1-3wt% pH regulator, 0.1-0.3wt% defoaming agent and the balance of water.

9. The method for preparing the lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 8, characterized in that: The sand mill has a ball milling time of 10-20 hours, the grinding balls are made of zirconium oxide, the particle size is 1.5 mm, the grinding balls occupy 2 / 3 of the grinding chamber volume, and the sand mill has a rotation speed of 2000-3500 rpm / min.

10. The method for preparing the lubricating liquid for drawing ultra-fine photovoltaic tungsten wires according to claim 8, characterized in that: The rotation speed of the high-speed shear emulsifier is 1000-3000 rpm / min.

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