A solder paste for soldering sterling silver jewelry, its preparation method and application

Abstract

The present invention relates to a solder paste for welding pure silver jewelry, a preparation method thereof, and an application thereof, and belongs to the technical field of silver jewelry welding materials. The solder paste for welding pure silver jewelry of the present invention is composed of metal solder powder, a soldering flux, and a carrier; the mass ratio of the metal solder powder to the soldering flux is (80-95):(5-20); the ratio of the sum of the mass of the metal solder powder and the soldering flux to the mass of the carrier is (70-85):(15-30). The carrier contains water-based polyurethane, cetostearyl alcohol, and polyethylene glycol octylphenyl ether, which can increase viscosity, thicken, and prevent sedimentation. The solder paste for welding pure silver jewelry of the present invention has a large initial viscosity, good film-forming ability, is not easy to dry, and is not easy to sediment. It can be positioned by dispensing glue using a dispensing machine. After dispensing, the silver jewelry to be welded can be welded in a tunnel furnace or a muffle furnace, thereby achieving constant temperature, constant quantity, and timed welding, thereby improving welding efficiency and welding quality.

Description

Technical Field

[0001] The invention relates to a solder paste for pure silver jewelry welding, a preparation method and application thereof, and belongs to the technical field of silver jewelry welding materials. Background Art

[0002] According to the national standard GB / T 11887-2012, "Regulations and Nomenclature for the Purity of Precious Metals in Jewelry," jewelry is considered pure silver if its purity reaches a minimum of 990 parts per thousand. Currently, the majority of handicrafts and jewelry in my country are made of pure silver. Pure silver products feature beautiful colors and a variety of shapes, often with irregular weld locations. Conventional production utilizes soldering lugs and wire. However, due to the irregular weld seams in jewelry, a wide variety of solder lug specifications are required, often requiring manual cutting by jewelry processing factories. However, the process of soldering wire, which fills the weld seam with molten droplets, is inefficient and requires high worker skill. Due to manual labor during the welding process, the quality of jewelry welds varies widely, impacting product quality. Pure silver jewelry is typically brazed using flame brazing, using borax or boric acid as flux. Due to incomplete combustion and high-temperature oxidation during the welding process, the surface of pure silver jewelry is prone to blackening and flux residue. Jewelry processing factories typically use alum boiling, grinding, and polishing to remove black stains and residual brazing flux from the surface. This process is cumbersome, time-consuming, and labor-intensive, especially for jewelry that needs to be mass-produced, resulting in a significant waste of materials and labor resources. Furthermore, flame brazing typically uses coal gas, kerosene, or white oil as igniters, and oxygen or air as combustion aids. The flame temperature can be controlled by adjusting the flow rates of the igniter and combustion aid. Pure silver jewelry is typically welded using a neutral flame and a reducing flame, both of which require a moderate increase in the igniter. This results in a high amount of residual carbon on the jewelry surface, forming black stains that require subsequent treatment. However, the surface of jewelry is often irregular, and especially for inlaid products, black stains can easily penetrate the bottom of the inlay, making them extremely difficult to treat and resulting in a significant waste of manpower and material resources.

[0003] With the advancement of welding technology, the form of welding materials has evolved from wire and sheet to composite, powder, and paste forms. Paste solder consists of metal brazing material powder, a flux, and a carrier. The metal brazing material powder in the paste is prepared from the brazing material to be welded. The flux acts as a flux, and the carrier serves to disperse, activate, and fix the metal brazing material powder and flux, helping to mix them into a uniform paste. During the brazing assembly process, the carrier's initial viscosity facilitates assembly of the components to be welded, even eliminating the need for spot welding of fine silver jewelry. During the brazing process, the carrier evaporates as the welding temperature rises, and the flux and brazing powder melt together to fill the weld. When brazing with paste solder, a dispensing machine can be used to dispense a fixed amount of solder, ensuring a consistent weight at each weld point. The components dispensed by the dispensing machine can then be welded in a tunnel furnace or muffle furnace, achieving constant temperature, fixed quantity, and timed welding, significantly improving welding efficiency and quality. However, there is currently no solder paste suitable for welding fine silver jewelry. Summary of the Invention

[0004] The present invention aims to provide a soldering paste that can be used for soldering pure silver jewelry.

[0005] A second object of the present invention is to provide a method for preparing solder paste for pure silver jewelry welding.

[0006] The third object of the present invention is to provide a solder paste for soldering pure silver jewelry and its application in soldering pure silver jewelry.

[0007] In order to achieve the above objectives, the technical solution adopted by the solder paste for pure silver jewelry welding of the present invention is:

[0008] A solder paste for pure silver jewelry welding, mainly composed of metal solder powder, a soldering flux and a carrier; the mass ratio of the metal solder powder to the soldering flux is (80-95):(5-20); the ratio of the sum of the mass of the metal solder powder and the soldering flux to the mass of the carrier is (70-85):(15-30); the metal solder powder mainly consists of Ag, Cu, Zn and Si elements, and the mass fraction of Ag in the metal solder powder is 53%-87%; the carrier mainly consists of an organic solvent and a thickener, and the thickener is selected from one or any combination of water-based polyurethane, cetostearyl alcohol and organic bentonite; the mass ratio of the organic solvent to the thickener is (45-100):(16-28).

[0009] The solder paste for pure silver jewelry welding of the present invention has a high initial viscosity, excellent film-forming ability, and is not prone to drying or settling. It can be positioned using a dispensing machine for dispensing. After dispensing, the silver jewelry to be welded can be welded in a tunnel furnace or muffle furnace, thereby achieving constant temperature, constant quantity, and constant time welding, thereby improving welding efficiency and quality. By adjusting the formula, the solder paste for pure silver jewelry welding of the present invention can be stored stably at room temperature for one month without delamination of the metal solder powder and the carrier, or precipitation of the flux and the carrier. The metal solder powder contains a high silver content of 53% to 87% by mass, making it suitable for welding various pure silver jewelry items. The main components have good wettability for pure silver and a moderate melting temperature. Si and Zn can increase the surface tension of the melt obtained by melting the metal solder powder, reduce the tendency of the solder to turbulent flow, and make the solder joint fuller and smoother. Si can reduce the volatilization of the Zn element and reduce porosity. The water-based polyurethane is soluble or dispersible in solvents and has a good initial viscosity. The addition of water-based polyurethane can improve the adhesion of the paste. Cetostearyl alcohol is a mixture of solid fatty alcohols, which is used as a thickener and lubricant in the present invention and can improve the initial viscosity of the solder paste. Organobentonite can be dispersed with solvent swelling to form a gel, which plays a thickening effect, increases the thixotropy, suspension stability, film-forming property, and stability of the paste, allowing the paste to be easier to dispense and stably store. In addition, the brazing agent plays a certain cleaning effect on the oil stain and impurities on the surface of pure silver, and also has a certain anti-settling effect. The ratio between the metal solder powder, the brazing agent and the carrier can affect the operation. The metal solder powder and the brazing agent are too much, which can cause the solder paste viscosity to be large, poor fluidity, and inconvenient operation. Adding too much carrier can cause the solder main component to be few, and the weld is not full.

[0010] Preferably, the mass fraction of the Ag element in the metal solder powder is 60% to 85.2%. Preferably, the mass ratio of the organic solvent to the thickener is (73 to 75):(22 to 25).

[0011] Preferably, the metal solder powder is mainly composed of the following elements in parts by weight: 60 to 85 parts of Ag, 9 to 35 parts of Cu, 4 to 15 parts of Zn, and 0.1 to 1.2 parts of Si.

[0012] Preferably, the metal brazing filler metal powder further includes corrosion-resistant elements, which are selected from one or any combination of Ti, Zr, Cr, V, Mo, Ni, Co, Pd, Pt, Ir, and Au. The corrosion-resistant active elements Ti, Zr, Cr, and V can improve the corrosion resistance of the alloy. In particular, after alloying, the active elements preferentially form stable metal oxides on the alloy surface, protecting the internal metal from oxidation and discoloration. Since Au, Pt, Pd, and Ir are precious metal elements with better chemical stability than Ag and Cu, they will increase the electrode potential of the alloy during the alloying process, thereby improving the corrosion resistance and anti-discoloration ability of the alloy. The corrosion-resistant elements Ni, Co, and Mo can refine the grain size and improve the corrosion resistance of the alloy.

[0013] Preferably, the mass ratio of the metal brazing filler metal powder to the brazing flux is (85-90):(10-15). Preferably, the mass ratio of the sum of the mass of the metal brazing filler metal powder and the brazing flux to the mass of the carrier is (80-85):(15-20).

[0014] Preferably, in the metal brazing filler metal powder, the weight portion of the Cu element is 9 to 30 parts. Preferably, in the metal brazing filler metal powder, the weight portion of the Zn element is 4 to 10 parts. Preferably, in the metal brazing filler metal powder, the weight portion of the Si element is 0.2 to 0.8 parts. Too high a total content of Zn and Cu elements will cause the brazing seam to turn yellow; too low a total content of Zn and Cu elements will cause the melting temperature of the brazing filler metal to be too high, affecting the welding effect. Experimental results show that too high a Cu element content will cause the brazing seam to turn yellow, while too low a Cu element content will cause the melting temperature of the brazing filler metal to be too high, affecting the welding effect; too low a Zn element content will cause the brazing seam to turn yellow; too high a Si element content will cause the brazing seam to be brittle and break easily, while too low a Si element content will lead to a decrease in corrosion resistance, an increase in brazing seam defects, and an easy discoloration of the weld.

[0015] Preferably, the weight percentage of the corrosion-resistant element in the metal brazing filler metal powder is no more than 2 parts. Preferably, the weight percentage of the corrosion-resistant element in the metal brazing filler metal powder is 0.1 to 2 parts. Preferably, the weight percentage of the corrosion-resistant element in the metal brazing filler metal powder is 0.4 to 1.4 parts. Excessive content of corrosion-resistant elements can easily lead to defects in the brazing seam.

[0016] Preferably, the metal brazing filler metal powder is composed of alloy powder and corrosion-resistant metal powder; the alloy powder is composed of Ag, Cu, Zn, and Si. Preferably, the metal brazing filler metal powder is composed of Ag-Cu-Zn-Si alloy powder and corrosion-resistant metal powder. Preferably, the Ag-Cu-Zn-Si alloy powder has a particle size of not less than 200 mesh. Preferably, the corrosion-resistant metal powder has a particle size of not less than 200 mesh. Preferably, the purity of the corrosion-resistant metal powder is greater than 99%. Preferably, the Ag-Cu-Zn-Si alloy powder is produced using an inert gas atomization method. Preferably, the inert gas is argon. Preferably, the method for producing the Ag-Cu-Zn-Si alloy powder further comprises the step of sieving the alloy powder produced by the atomization method to obtain a powder having a particle size of not less than 200 mesh, namely, the Ag-Cu-Zn-Si alloy powder. Preferably, the metal solder powder is a mixture of Ag-Cu-Zn-Si alloy powder and corrosion-resistant element metal powder. Preferably, the equipment used for the mixing is a three-dimensional mixer. Preferably, the mixing time is greater than 3 hours. Too high an oxygen content in the metal solder powder will result in low weld strength and decreased corrosion resistance. The use of an inert gas atomization method to prepare the metal solder powder can significantly reduce the oxygen content in the powder. At the same time, the aerosol method can ensure the sphericity of the prepared metal solder powder. A higher sphericity is beneficial to increasing the bulk density of the metal solder powder, increasing the proportion of metal solder powder in the paste, and making the weld fuller and smoother during the welding process.

[0017] It is understood that the corrosion-resistant element metal powder can be a single-powder of the corrosion-resistant element metal or a corrosion-resistant element metal alloy powder. For example, when the corrosion-resistant elements are Cr and Ir, the corrosion-resistant element metal powder can be composed of Cr powder and Ir powder, or can be a Cr-Ir alloy powder. Due to the low content of the corrosion-resistant element, in order to reduce costs, the corrosion-resistant element metal powder is preferably a single-powder of the corrosion-resistant element metal.

[0018] Preferably, the brazing flux is composed of the following components by weight: 5-30 parts potassium fluoroborate, 10-30 parts boron trioxide, 15-40 parts borax, and 20-40 parts alkaline chemical cleaner. Preferably, the brazing flux is composed of the following components by weight: 5-20 parts potassium fluoroborate, 10-20 parts boron trioxide, 30-35 parts borax, and 40 parts alkaline chemical cleaner. Preferably, the brazing flux has a particle size of no less than 120 mesh. Preferably, the purity of potassium fluoroborate, boron trioxide, borax, and alkaline chemical cleaner is greater than 98%. Potassium fluoroborate, boron trioxide, and borax are commonly used chemicals in silver brazing fillers. The addition of an alkaline chemical cleaner effectively removes oil stains and impurities from the surface of pure silver. Potassium fluoroborate has a melting point of 530°C and, at high temperatures, reacts with metal oxides on the surface of silver jewelry to form a low-melting-point substance that is expelled. Boron trioxide has a melting point of 450°C and can be mixed with various metal oxides to form glassy borates and metaborates. Borax, with a melting point of 741°C, dissolves a variety of metal oxides, effectively removing oxides from the surface of silver brazing filler metal powder and fine silver jewelry. Alkaline chemical cleaners are beneficial for removing impurities and oxide films from the surface of silver jewelry to be soldered. Potassium fluoroborate and boron trioxide are low-temperature brazing fluxes; excessive amounts can lead to failure at high temperatures. Borax is a high-temperature brazing flux, and excessive amounts can lead to failure at low temperatures. Alkaline chemical cleaners reduce brazing flux viscosity, facilitating oxide removal.

[0019] Borax may contain water of crystallization or may not contain water of crystallization, such as anhydrous borax (Na2B4O7), pentahydrate borax (Na2B4O7·5H2O), and decahydrate borax (Na2B4O7·10H2O). In order to increase the proportion of active ingredients and effectively remove metal oxides, the borax is preferably anhydrous borax.

[0020] Preferably, the alkaline chemical cleaning agent is selected from one or any combination of sodium hydroxide, sodium silicate, and sodium carbonate. Alkaline chemical cleaning agents such as sodium hydroxide, sodium silicate, and sodium carbonate are commonly used additives to metal cleaning agents, which are beneficial for removing impurities on the surface of silver jewelry to be soldered, and can also remove the oxide film on the surface of silver jewelry. The flux of the present invention leaves little residue during the soldering process, and only a small amount of glassy material is present at the weld. The glassy material is soluble in water and is easy to clean. The activation temperature range of the flux of the present invention is 600-900°C, which matches the temperature of the silver solder (i.e., the activation temperature of the flux is slightly lower than the melting temperature of the silver solder and can remain active during soldering).

[0021] Preferably, the flux is formed by mixing potassium fluoroborate, boron trioxide, borax, and an alkaline chemical detergent. Preferably, in the flux preparation method, the mixing is performed by ball milling. Preferably, the ball milling is performed using a ball mill. Preferably, the ball mill is a planetary ball mill. Preferably, the ball-to-material ratio during the ball milling is greater than 1:2. Preferably, the ball milling time is 5 hours. To screen out flux with a particle size of not less than 120 mesh, after the ball milling is completed, the ball-milled mixture is passed through a 120-mesh sieve.

[0022] Preferably, the viscosity of the carrier at 25° C. is 7800-8500 cp.

[0023] Preferably, the organic solvent is an alcohol and / or an ester. Preferably, the alcohol is glycerol and / or ethylene glycol. Preferably, the ester is ethyl acetate. Preferably, the carrier is composed of the following components in parts by weight: 5-30 parts glycerol, 20-35 parts ethylene glycol, 20-35 parts ethyl acetate, 10-15 parts water-based polyurethane, 5-10 parts cetostearyl alcohol, 2-5 parts polyethylene glycol octylphenyl ether, and 1-3 parts organic bentonite. Glycerol, also known as glycerin, is a solvent that is liquid at room temperature, has a high boiling point, and exhibits excellent moisturizing properties. Ethylene glycol, as a solvent, has a low molecular weight and decomposes without residue at high temperatures. Ethyl acetate, a common solvent, can dissolve a variety of ethers and esters. It has a low melting point, high volatility, and leaves no residue. Polyethylene glycol octylphenyl ether is a nonionic surfactant that can enhance the surface activity of the paste. The experimental results show that although excessive addition of water-based polyurethane, cetostearyl alcohol, and organic bentonite can help improve the stability of the solder paste, its usability is poor due to its excessive viscosity; too little addition will cause low carrier viscosity, resulting in poor anti-settling effect of the carrier and poor stability of the solder paste; polyethylene glycol octylphenyl ether is used to increase the activity and solubility of the solvent. Excessive addition will lead to too low carrier viscosity, which in turn leads to poor stability of the solder paste. Too little addition will reduce the solubility and cause the solder paste to easily delaminate.

[0024] In the present invention, the waterborne polyurethane is a polyurethane resin containing hydrophilic groups on its molecular chain. The waterborne polyurethane can be dispersed in water to form a waterborne polyurethane resin dispersion or emulsion, or dissolved in water to form a solution. To improve the stability of the carrier, the waterborne polyurethane is preferably soluble in the organic solvent in the carrier, that is, 10 to 15 parts by weight of the waterborne polyurethane can be dissolved in a mixed solvent consisting of 5 to 30 parts by weight of glycerol, 20 to 35 parts by weight of ethylene glycol, and 20 to 35 parts by weight of ethyl acetate.

[0025] Preferably, the carrier is composed of the following components by weight: 15-25 parts glycerol, 23-30 parts ethylene glycol, 25-30 parts ethyl acetate, 10-15 parts waterborne polyurethane, 5-10 parts cetostearyl alcohol, 2-5 parts polyethylene glycol octylphenyl ether, and 2-3 parts organic bentonite. The carrier in the present invention's pure silver jewelry soldering paste has a viscosity of 7800-8500 centipoise, which can withstand shear and provide a certain damping effect on the metal solder powder and flux, helping to prevent sedimentation.

[0026] Preferably, the molecular weight of the polyethylene glycol octylphenyl ether is 294.4.

[0027] Preferably, the carrier is a mixture of glycerol, ethylene glycol, ethyl acetate, aqueous polyurethane, cetostearyl alcohol, polyethylene glycol octylphenyl ether, and organobentonite. The glycerol, ethylene glycol, ethyl acetate, aqueous polyurethane, cetostearyl alcohol, polyethylene glycol octylphenyl ether, and organobentonite are uniformly mixed. Preferably, in the method for preparing the carrier, the mixing is performed by stirring. Preferably, the stirring speed is 800 to 1000 r / min. Preferably, the mixing time is 6 hours. Preferably, the mixing is performed by stirring. Preferably, the stirring speed is 800 to 1000 r / min. Preferably, the mixing is performed using a disperser.

[0028] The technical solution adopted in the method for preparing the solder paste for pure silver jewelry welding of the present invention is:

[0029] The preparation method of the solder paste for pure silver jewelry welding comprises the following steps: firstly, mixing the metal solder powder and the flux for the first time to obtain a mixture, and then mixing the mixture and the carrier for the second time to obtain the solder paste.

[0030] Preferably, the first mixing is performed using a three-dimensional mixer. Preferably, the first mixing time is 3 hours. Preferably, the second mixing is performed by stirring. Preferably, the stirring speed used in the second mixing is greater than 800 r / min. Preferably, the second mixing is performed using a disperser. Preferably, the method for the second mixing comprises the following steps: placing the carrier into a disperser, and then adding the mixture to the disperser in batches for mixing. Preferably, the mixture is added to the disperser in two batches for mixing.

[0031] The technical solution adopted by the application of the soldering paste for pure silver jewelry welding of the present invention in welding pure silver jewelry is as follows:

[0032] The application of the above-mentioned solder paste for welding pure silver jewelry in welding pure silver jewelry includes the following steps: applying the solder paste for welding pure silver jewelry to the part of the pure silver jewelry to be welded, and then heating the pure silver jewelry coated with the solder paste under an inert atmosphere and / or a reducing atmosphere until the solder paste melts to complete the welding.

[0033] Preferably, the coating is performed by drop coating. Preferably, the drop coating is performed by a dispensing machine. Preferably, the heating temperature is 800-850°C. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0035] The purity of potassium fluoroborate, boron trioxide, borax and alkaline chemical detergent used in Examples 1-12 and Comparative Examples 1-15 of the present invention is greater than 98%; the molecular weight of polyethylene glycol octylphenyl ether used is 294.4, and the water-based polyurethane used is a single-component water-based polyether polyurethane resin that can be dissolved in the organic solvent used in the corresponding carrier.

[0036] 1. The specific embodiment of the solder paste for pure silver jewelry welding of the present invention is as follows:

[0037] Example 1

[0038] The solder paste for pure silver jewelry soldering in this embodiment is composed of metal solder powder, soldering flux and carrier;

[0039] The mass ratio of the metal brazing filler metal powder to the brazing flux is 90:10, and the mass ratio of the sum of the mass of the metal brazing filler metal powder and the brazing flux to the mass of the carrier is 85:15;

[0040] The metal brazing filler metal powder is composed of Ag-Cu-Zn-Si alloy powder and corrosion-resistant metal powder. The Ag-Cu-Zn-Si alloy powder is obtained by smelting and melting Ag powder, Cu powder, Zn powder, and Si powder, then using an inert gas atomization method to form a powder, which is then passed through a 200-mesh sieve. The Ag-Cu-Zn-Si alloy powder has a particle size of 200 mesh. The corrosion-resistant metal powder is composed of Ti powder and Pt powder, both of which have a particle size of 200 mesh. The metal brazing filler metal powder is prepared by mixing the Ag-Cu-Zn-Si alloy powder and the corrosion-resistant metal powder in a three-dimensional mixer for 3 hours. In terms of component elements, the metal brazing filler metal powder of this embodiment is composed of the following elements in parts by weight: 60 parts Ag, 30 parts Cu, 8 parts Zn, 0.8 parts Si, and 1.2 parts corrosion-resistant element. The corrosion-resistant elements are Ti and Pt, and the mass ratio of Ti to Pt is 1:0.2.

[0041] The flux is composed of the following components by weight: 5 parts potassium fluoroborate, 20 parts boron trioxide, 35 parts borax, and 40 parts alkaline chemical cleaner, where the borax is anhydrous borax and the alkaline chemical cleaner is sodium carbonate. The flux has a particle size of 120 mesh. The flux is prepared by ball milling the above components in a planetary ball mill and then passing through a 120-mesh sieve. The ball-to-material ratio is 1:1, and the milling time is 5 hours.

[0042] The carrier is composed of the following components in parts by weight: 18 parts glycerol, 30 parts ethylene glycol, 25 parts ethyl acetate, 15 parts waterborne polyurethane, 8 parts cetostearyl alcohol, 2 parts polyethylene glycol octylphenyl ether, and 2 parts organobentonite. The carrier is prepared by uniformly stirring the above components in a high-speed disperser at a speed of 1000 r / min for 6 hours.

[0043] Example 2

[0044] The solder paste for pure silver jewelry soldering in this embodiment is composed of metal solder powder, soldering flux and carrier;

[0045] The mass ratio of the metal brazing filler metal powder to the brazing flux is 90:10, and the mass ratio of the sum of the mass of the metal brazing filler metal powder and the brazing flux to the mass of the carrier is 85:15;

[0046] The metal brazing filler metal powder is composed of Ag-Cu-Zn-Si alloy powder and corrosion-resistant metal powder. The Ag-Cu-Zn-Si alloy powder is obtained by smelting and melting Ag powder, Cu powder, Zn powder, and Si powder, then using an inert gas atomization method to form a powder, which is then passed through a 200-mesh sieve. The Ag-Cu-Zn-Si alloy powder has a particle size of 200 mesh. The corrosion-resistant metal powder is composed of Cr powder and Ir powder, both of which have a particle size of 200 mesh. The metal brazing filler metal powder is obtained by mixing the Ag-Cu-Zn-Si alloy powder and the corrosion-resistant metal powder in a three-dimensional mixer for 3 hours. In terms of component elements, the metal brazing filler metal powder of this embodiment is composed of the following elements in parts by weight: 65 parts Ag, 28 parts Cu, 5.7 parts Zn, 0.5 parts Si, and 0.8 parts corrosion-resistant element. The corrosion-resistant elements are Cr and Ir, and the mass ratio of Cr to Ir is 0.6:0.2.

[0047] The flux is composed of the following components by weight: 20 parts potassium fluoroborate, 10 parts boron trioxide, 30 parts borax, and 40 parts alkaline chemical cleaner, where the borax is anhydrous borax and the alkaline chemical cleaner is sodium silicate. The flux has a particle size of 120 mesh. The flux is prepared by ball milling the above components in a planetary ball mill, then passing through a 120-mesh sieve. The ball-to-material ratio is 1:1, and the milling time is 5 hours.

[0048] The carrier used in the solder paste for pure silver jewelry welding of this embodiment is the same as the carrier used in the solder paste for pure silver jewelry welding of Example 1.

[0049] Example 3

[0050] The solder paste for pure silver jewelry soldering in this embodiment is composed of metal solder powder, soldering flux and carrier;

[0051] The mass ratio of the metal brazing filler metal powder to the brazing flux is 90:10, and the mass ratio of the sum of the mass of the metal brazing filler metal powder and the brazing flux to the mass of the carrier is 85:15;

[0052] The brazing filler metal powder consists of Ag-Cu-Zn-Si alloy powder and corrosion-resistant metal powder. The Ag-Cu-Zn-Si alloy powder is obtained by smelting Ag powder, Cu powder, Zn powder, and Si powder, atomizing the powder using inert gas, and then passing it through a 200-mesh sieve. The particle size of the Ag-Cu-Zn-Si alloy powder is 200 mesh. The corrosion-resistant metal powder consists of Mo powder, Cr powder, and Ir powder. The particle size of each of the Mo powder, Cr powder, and Ir powder is 200 mesh. The brazing filler metal powder is obtained by mixing the Ag-Cu-Zn-Si alloy powder and the corrosion-resistant metal powder in a three-dimensional mixer for 3 hours. In terms of constituent elements, the metal solder powder of this embodiment is composed of the following elements in parts by weight: 70 parts of Ag, 22 parts of Cu, 6 parts of Zn, 0.6 parts of Si, and 1.4 parts of corrosion-resistant elements. The corrosion-resistant elements are Mo, Cr, and Ir, and the mass ratio of Mo, Cr, and Ir is 1:0.2:0.2.

[0053] The flux used in the solder paste for pure silver jewelry welding of this embodiment is the same as the flux used in the solder paste for pure silver jewelry welding of Example 2.

[0054] The carrier used in the solder paste for pure silver jewelry welding of this embodiment is the same as the carrier used in the solder paste for pure silver jewelry welding of Example 1.

[0055] Example 4

[0056] The solder paste for pure silver jewelry soldering in this embodiment is composed of metal solder powder, soldering flux and carrier;

[0057] The mass ratio of the metal brazing filler metal powder to the brazing flux is 85:15, and the mass ratio of the sum of the mass of the metal brazing filler metal powder and the brazing flux to the mass of the carrier is 80:20;

[0058] The metal brazing filler metal powder is composed of Ag-Cu-Zn-Si alloy powder and corrosion-resistant metal powder. The Ag-Cu-Zn-Si alloy powder is obtained by smelting and melting Ag powder, Cu powder, Zn powder, and Si powder, then using an inert gas atomization method to form a powder, which is then passed through a 200-mesh sieve. The Ag-Cu-Zn-Si alloy powder has a particle size of 200 mesh. The corrosion-resistant metal powder is composed of Pt powder and Ir powder, both of which have a particle size of 200 mesh. The metal brazing filler metal powder is obtained by mixing the Ag-Cu-Zn-Si alloy powder and the corrosion-resistant metal powder in a three-dimensional mixer for 3 hours. In terms of component elements, the metal brazing filler metal powder of this embodiment is composed of the following elements in parts by weight: 75 parts Ag, 20 parts Cu, 4 parts Zn, 0.6 parts Si, and 0.4 parts corrosion-resistant element. The corrosion-resistant elements are Pt and Ir, and the mass ratio of Pt to Ir is 0.2:0.2.

[0059] The flux is composed of the following components by weight: 15 parts potassium fluoroborate, 15 parts boron trioxide, 30 parts borax, and 40 parts alkaline chemical cleaner, where the borax is anhydrous borax and the alkaline chemical cleaner is sodium carbonate. The flux has a particle size of 120 mesh. The flux is prepared by ball milling the above components in a planetary ball mill, then passing through a 120-mesh sieve. The ball-to-material ratio is 2:1, and the milling time is 5 hours.

[0060] The carrier is composed of the following components in parts by weight: 25 parts glycerol, 23 parts ethylene glycol, 25 parts ethyl acetate, 10 parts waterborne polyurethane, 10 parts cetostearyl alcohol, 5 parts polyethylene glycol octylphenyl ether, and 2 parts organobentonite. The carrier is prepared by uniformly stirring the above components in a high-speed disperser at a speed of 1000 r / min for 6 hours.

[0061] Example 5

[0062] The solder paste for pure silver jewelry soldering in this embodiment is composed of metal solder powder, soldering flux and carrier;

[0063] The mass ratio of the metal brazing filler metal powder to the brazing flux is 85:15, and the mass ratio of the sum of the mass of the metal brazing filler metal powder and the brazing flux to the mass of the carrier is 80:20;

[0064] The metal brazing filler metal powder is composed of Ag-Cu-Zn-Si alloy powder and corrosion-resistant metal powder. The Ag-Cu-Zn-Si alloy powder is obtained by smelting and melting Ag powder, Cu powder, Zn powder, and Si powder, then using an inert gas atomization method to form a powder, which is then passed through a 200-mesh sieve. The Ag-Cu-Zn-Si alloy powder has a particle size of 200 mesh. The corrosion-resistant metal powder is Au powder, and the Au powder has a particle size of 200 mesh. The metal brazing filler metal powder is obtained by mixing the Ag-Cu-Zn-Si alloy powder and the corrosion-resistant metal powder in a three-dimensional mixer for 3 hours. In terms of component elements, the metal brazing filler metal powder of this embodiment is composed of the following elements in parts by weight: 80 parts Ag, 14 parts Cu, 5 parts Zn, 0.2 parts Si, and 0.8 parts corrosion-resistant element, with the corrosion-resistant element being Au.

[0065] The flux used in the solder paste for pure silver jewelry welding of this embodiment is the same as the flux used in the solder paste for pure silver jewelry welding of Example 4.

[0066] The carrier is composed of the following components in parts by weight: 15 parts glycerol, 30 parts ethylene glycol, 30 parts ethyl acetate, 15 parts waterborne polyurethane, 5 parts cetostearyl alcohol, 2 parts polyethylene glycol octylphenyl ether, and 3 parts organobentonite. The carrier is prepared by uniformly stirring the above components in a high-speed disperser at a speed of 1000 r / min for 6 hours.

[0067] Example 6

[0068] The solder paste for pure silver jewelry soldering in this embodiment is composed of metal solder powder, soldering flux and carrier;

[0069] The mass ratio of the metal brazing filler metal powder to the brazing flux is 85:15, and the mass ratio of the sum of the mass of the metal brazing filler metal powder and the brazing flux to the mass of the carrier is 80:20;

[0070] The metal brazing filler metal powder is composed of Ag-Cu-Zn-Si alloy powder and corrosion-resistant metal powder. The Ag-Cu-Zn-Si alloy powder is obtained by smelting Ag powder, Cu powder, Zn powder, and Si powder, then using an inert gas atomization method to form a powder, which is then passed through a 200-mesh sieve. The Ag-Cu-Zn-Si alloy powder has a particle size of 200 mesh. The corrosion-resistant metal powder is composed of V powder, Ni powder, and Co powder, each having a particle size of 200 mesh. The metal brazing filler metal powder is prepared by mixing the Ag-Cu-Zn-Si alloy powder and the corrosion-resistant metal powder in a three-dimensional mixer for 3 hours. The metal brazing filler metal powder of this embodiment is composed of the following elements in parts by weight: 85 parts Ag, 9 parts Cu, 5 parts Zn, 0.2 parts Si, and 0.6 parts corrosion-resistant element. The corrosion-resistant elements are V, Ni, and Co, with a mass ratio of V, Ni, and Co of 0.2:0.2:0.2.

[0071] The flux used in the solder paste for pure silver jewelry welding of this embodiment is the same as the flux used in the solder paste for pure silver jewelry welding of Example 4.

[0072] The carrier used in the solder paste for pure silver jewelry welding of this embodiment is the same as the carrier used in the solder paste for pure silver jewelry welding of Example 5.

[0073] Example 7

[0074] The only difference between the pure silver jewelry soldering paste of this embodiment and the pure silver jewelry soldering paste of Example 1 is that the weight proportion of the Cu element in the metal solder powder used in the pure silver jewelry soldering paste of this comparative example is 28 parts, and the weight proportion of the Zn element is 10 parts.

[0075] Comparative Example 1

[0076] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 1 only in that the carrier of the pure silver jewelry soldering paste of this comparative example contains 17 parts by weight of the aqueous polyurethane. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 7.

[0077] Comparative Example 2

[0078] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 4 only in that the carrier of the pure silver jewelry soldering paste of this comparative example contains 8 parts by weight of the water-based polyurethane. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 10.

[0079] Comparative Example 3

[0080] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 4 only in that the carrier used in this comparative example contains 12 parts by weight of cetostearyl alcohol. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 10.

[0081] Comparative Example 4

[0082] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 4 only in that the carrier used in this comparative example contains 6 parts by weight of polyethylene glycol octylphenyl ether. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 10.

[0083] Comparative Example 5

[0084] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 5 only in that the carrier used in this comparative example contains 4 parts by weight of cetostearyl alcohol. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 11.

[0085] Comparative Example 6

[0086] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 5 only in that the carrier used in this comparative example contains 1 part by weight of polyethylene glycol octylphenyl ether. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 11.

[0087] Comparative Example 7

[0088] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 5 only in that the organic bentonite in the carrier used in this comparative example contains 4 parts by weight. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 11.

[0089] Comparative Example 8

[0090] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 4 only in that the organic bentonite in the carrier used in this comparative example contains 0.5 parts by weight. The pure silver jewelry soldering paste of this comparative example was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 10.

[0091] Comparative Example 9

[0092] The pure silver jewelry solder paste of this comparative example differs from the pure silver jewelry solder paste of Example 1 only in that the metal brazing powder used in this comparative example contains 32 parts by weight of Cu and 6 parts by weight of Zn. The pure silver jewelry solder paste of this comparative example was prepared according to the preparation method of the pure silver jewelry solder paste of Example 7.

[0093] Comparative Example 10

[0094] The pure silver jewelry solder paste of this comparative example differs from the pure silver jewelry solder paste of Example 6 only in that the metal brazing powder used in this comparative example contains 8 parts by weight of Cu and 6 parts by weight of Zn. The pure silver jewelry solder paste of this comparative example was prepared according to the preparation method of the pure silver jewelry solder paste of Example 12.

[0095] Comparative Example 11

[0096] The pure silver jewelry solder paste of this comparative example differs from the pure silver jewelry solder paste of Example 1 only in that the metal brazing powder used in this comparative example contains 29.8 parts by weight of Cu and 1 part by weight of Si. The pure silver jewelry solder paste of this comparative example was prepared according to the preparation method of the pure silver jewelry solder paste of Example 7.

[0097] Comparative Example 12

[0098] The pure silver jewelry solder paste of this comparative example differs from the pure silver jewelry solder paste of Example 6 only in that the metal brazing powder used in this comparative example contains 9.1 parts by weight of Cu and 0.1 parts by weight of Si. The pure silver jewelry solder paste of this comparative example was prepared according to the preparation method of the pure silver jewelry solder paste of Example 12.

[0099] Comparative Example 13

[0100] The pure silver jewelry solder paste of this comparative example differs from the pure silver jewelry solder paste of Example 1 only in that the metal brazing powder used in this comparative example contains 22 parts by weight of Cu and 16 parts by weight of Zn. The pure silver jewelry solder paste of this comparative example was prepared according to the preparation method of the pure silver jewelry solder paste of Example 7.

[0101] Comparative Example 14

[0102] The pure silver jewelry solder paste of this comparative example differs from the pure silver jewelry solder paste of Example 4 only in that the metal brazing powder used in this comparative example contains 21 parts by weight of Cu and 3 parts by weight of Zn. The pure silver jewelry solder paste of this comparative example was prepared according to the preparation method of the pure silver jewelry solder paste of Example 10.

[0103] Comparative Example 15

[0104] The pure silver jewelry soldering paste of this comparative example differs from the pure silver jewelry soldering paste of Example 1 only in that the metal brazing powder used in this comparative example contains 2.2 parts by weight of the corrosion-resistant element. This comparative example's pure silver jewelry soldering paste was prepared according to the preparation method of the pure silver jewelry soldering paste of Example 7.

[0105] 2. The specific embodiment of the method for preparing the solder paste for pure silver jewelry welding of the present invention is as follows:

[0106] Example 8

[0107] The preparation method of the pure silver jewelry soldering paste of this embodiment is the same as the preparation method of the pure silver jewelry soldering paste of Example 1, and specifically comprises the following steps:

[0108] According to the formula in Example 1, metal solder powder, flux and carrier were measured, and then the metal solder powder and flux were mixed for the first time in a three-dimensional mixer. After mixing for 3 hours, a mixture was obtained. The carrier was placed in a disperser, and then the mixture was added to the disperser twice for a second mixing. During the second mixing process, the speed of the disperser was controlled to be greater than 800 r / min. After the mixture and the carrier were evenly mixed, a solder paste for pure silver jewelry welding was obtained.

[0109] Example 9

[0110] The preparation method of the solder paste for pure silver jewelry welding of this embodiment is the preparation method of the solder paste for pure silver jewelry welding of Example 2. The difference between the preparation method of the solder paste for pure silver jewelry welding of this embodiment and the preparation method of the solder paste for pure silver jewelry welding of Example 8 is that the metal solder powder, solder flux and carrier used in the preparation method of the solder paste for pure silver jewelry welding of this embodiment are the metal solder powder, solder flux and carrier in the solder paste for pure silver jewelry welding of Example 2.

[0111] Example 10

[0112] The preparation method of the solder paste for pure silver jewelry welding of this embodiment is the preparation method of the solder paste for pure silver jewelry welding of Example 3. The difference between the preparation method of the solder paste for pure silver jewelry welding of this embodiment and the preparation method of the solder paste for pure silver jewelry welding of Example 8 is that the metal solder powder, solder flux and carrier used in the preparation method of the solder paste for pure silver jewelry welding of this embodiment are the metal solder powder, solder flux and carrier in the solder paste for pure silver jewelry welding of Example 3.

[0113] Example 11

[0114] The preparation method of the solder paste for pure silver jewelry welding of this embodiment is the preparation method of the solder paste for pure silver jewelry welding of Example 4. The difference between the preparation method of the solder paste for pure silver jewelry welding of this embodiment and the preparation method of the solder paste for pure silver jewelry welding of Example 8 is that the metal solder powder, solder flux and carrier used in the preparation method of the solder paste for pure silver jewelry welding of this embodiment are the metal solder powder, solder flux and carrier in the solder paste for pure silver jewelry welding of Example 4.

[0115] Example 12

[0116] The preparation method of the solder paste for pure silver jewelry welding of this embodiment is the preparation method of the solder paste for pure silver jewelry welding of Example 5. The difference between the preparation method of the solder paste for pure silver jewelry welding of this embodiment and the preparation method of the solder paste for pure silver jewelry welding of Example 8 is that the metal solder powder, solder flux and carrier used in the preparation method of the solder paste for pure silver jewelry welding of this embodiment are the metal solder powder, solder flux and carrier in the solder paste for pure silver jewelry welding of Example 5.

[0117] Example 13

[0118] The preparation method of the solder paste for pure silver jewelry welding of this embodiment is the preparation method of the solder paste for pure silver jewelry welding of Example 6. The difference between the preparation method of the solder paste for pure silver jewelry welding of this embodiment and the preparation method of the solder paste for pure silver jewelry welding of Example 8 is that the metal solder powder, solder flux and carrier used in the preparation method of the solder paste for pure silver jewelry welding of this embodiment are the metal solder powder, solder flux and carrier in the solder paste for pure silver jewelry welding of Example 6.

[0119] Example 14

[0120] The preparation method of the solder paste for pure silver jewelry welding of this embodiment is the preparation method of the solder paste for pure silver jewelry welding of Example 7. The difference between the preparation method of the solder paste for pure silver jewelry welding of this embodiment and the preparation method of the solder paste for pure silver jewelry welding of Example 8 is that the metal solder powder, solder flux and carrier used in the preparation method of the solder paste for pure silver jewelry welding of this embodiment are the metal solder powder, solder flux and carrier in the solder paste for pure silver jewelry welding of Example 7.

[0121] 3. Specific examples of the application of the solder paste for pure silver jewelry welding of the present invention in welding pure silver jewelry are as follows:

[0122] Example 15

[0123] The application of the solder paste for welding pure silver jewelry of this embodiment in welding pure silver jewelry specifically includes the following steps: first, the solder paste for welding pure silver jewelry of Example 1 is placed in a dispensing syringe, and the solder paste is positioned and quantitatively dripped on the part of the pure silver jewelry to be welded using a dispensing machine. Then, the pure silver jewelry dripped with the solder paste is placed in an argon atmosphere tunnel furnace and hot-melt welded at 800°C.

[0124] Example 16

[0125] The application of the solder paste for welding pure silver jewelry of this embodiment in welding pure silver jewelry specifically includes the following steps: first, the solder paste for welding pure silver jewelry of Example 2 is placed in a dispensing syringe, and the solder paste is positioned and quantitatively dripped on the part of the pure silver jewelry to be welded using a dispensing machine. Then, the pure silver jewelry dripped with the solder paste is placed in a reducing atmosphere tunnel furnace and hot-melt welded at 820°C.

[0126] Example 17

[0127] The application of the solder paste for welding pure silver jewelry of this embodiment in welding pure silver jewelry specifically includes the following steps: first, the solder paste for welding pure silver jewelry of Example 3 is placed in a dispensing syringe, and the solder paste is positioned and quantitatively dripped on the part of the pure silver jewelry to be welded using a dispensing machine. Then, the pure silver jewelry dripped with the solder paste is placed in a reducing atmosphere tunnel furnace and hot-melt welded at 800°C.

[0128] Example 18

[0129] The application of the solder paste for welding pure silver jewelry of this embodiment in welding pure silver jewelry specifically includes the following steps: first, the solder paste for welding pure silver jewelry of Example 4 is placed in a dispensing syringe, and the solder paste is positioned and quantitatively dripped on the parts of the pure silver jewelry to be welded using a dispensing machine. Then, the pure silver jewelry dripped with the solder paste is placed in a reducing atmosphere tunnel furnace and hot-melt welded at 820°C.

[0130] Example 19

[0131] The application of the solder paste for welding pure silver jewelry in this embodiment in welding pure silver jewelry specifically includes the following steps: first, the solder paste for welding pure silver jewelry of Example 5 is placed in a dispensing syringe, and a dispensing machine is used to position and quantitatively drip the solder paste on the part of the pure silver jewelry to be welded. Then, the pure silver jewelry dripped with the solder paste is placed in a reducing atmosphere tunnel furnace and hot-melt welded at 850°C.

[0132] Example 20

[0133] The application of the solder paste for welding pure silver jewelry in this embodiment in welding pure silver jewelry specifically includes the following steps: first, the solder paste for welding pure silver jewelry of Example 6 is placed in a dispensing syringe, and a dispensing machine is used to position and quantitatively drip the solder paste on the part of the pure silver jewelry to be welded, and then the pure silver jewelry dripped with the solder paste is placed in a reducing atmosphere tunnel furnace and hot-melt welded at 850°C.

[0134] Example 21

[0135] The application of the solder paste for welding pure silver jewelry of this embodiment in welding pure silver jewelry specifically includes the following steps: first, the solder paste for welding pure silver jewelry of Example 7 is placed in a dispensing syringe, and the solder paste is positioned and quantitatively dripped on the part of the pure silver jewelry to be welded using a dispensing machine. Then, the pure silver jewelry dripped with the solder paste is placed in an argon atmosphere tunnel furnace and hot-melt welded at 800°C.

[0136] Experimental Example 1

[0137] The organic bentonite in the carrier used in the solder paste for pure silver jewelry welding of the embodiments of the present invention and the comparative examples can form a slag film with the flux during the welding process, which plays a role in isolating the air and protecting the brazing seam. At the same time, the organic bentonite has solid residues after burning. In order to evaluate the ash residue of the carrier used in the present invention after welding, and to eliminate the influence of the organic bentonite on the ash test results, the carriers (the remaining mixed components after removing the organic bentonite) in the solder paste for pure silver jewelry welding of Examples 1-6 and Comparative Examples 1-8 were respectively placed in a muffle furnace and calcined at 600°C for 10 minutes. The ratio of the mass of the calcined residue to the mass of the carrier before calcination was calculated, which is the ash content. The ash content test results of the carriers (the remaining mixed components after removing the organic bentonite) in the solder paste for pure silver jewelry welding of Examples 1-6 and Comparative Examples 1-5 after high-temperature calcination are shown in Table 1.

[0138] Table 1 Ash content of the carrier in the solder paste for pure silver jewelry welding of Examples 1-6 and Comparative Examples 1-5 after high temperature calcination

[0139] carrier Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 ash content ＜0.02％ ＜0.01％ ＜0.01％ ＜0.02％ ＜0.01％ ＜0.02％ carrier Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 - ash content ＜0.03％ ＜0.01％ ＜0.01％ ＜0.01％ ＜0.01％ -

[0140] The results show that the carriers in the solder paste for pure silver jewelry welding of Examples 1-6 have a residual carbon rate of less than 0.02% after high-temperature calcination at 500°C. This can avoid the formation of black stains on the surface of pure silver jewelry caused by excessive carbon residue during welding, thereby simplifying subsequent processing.

[0141] Experimental Example 2

[0142] During the use of solder paste, the carrier needs to withstand shear and provide a certain amount of damping to the metal and flux to prevent sedimentation. The viscosity is numerically equal to the shear stress of the fluid under a unit velocity gradient. According to the International System of Units, the unit of viscosity is Pa·s, also commonly used is poise or centipoise (1 poise = 10 -1 Pa·second, 1 centipoise = 10 -2 Pa·s). Generally, higher viscosity indicates greater material stability and less prone to sedimentation. To evaluate the stability of the pure silver jewelry solder pastes of Examples 1-6, the carriers in the pure silver jewelry solder pastes of Examples 1-6 and Comparative Examples 1-8 were tested for viscosity at 25°C using a dynamic viscosity tester. The dynamic viscosity values obtained are shown in Table 2.

[0143] Table 2 Dynamic viscosity of the carrier in the solder paste for pure silver jewelry welding of Examples 1-6 and Comparative Examples 1-8

[0144] carrier Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Viscosity (centipoise) 8000 7800 8200 8400 8500 8100 carrier Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Viscosity (centipoise) 9100 6600 9200 7900 6100 8500 carrier Comparative Example 7 Comparative Example 8 - - - - Viscosity (centipoise) 9300 7200 - - - -

[0145] The results show that the carriers in the pure silver jewelry solder pastes of Examples 1-6 are viscous, providing excellent load-bearing and damping properties for the powder material and flux. The viscosity test results of the carriers in the pure silver jewelry solder pastes of Comparative Examples 1-8 show that excessive additions of water-based polyurethane, cetostearyl alcohol, and organobentonite result in excessive carrier viscosity, hindering injection; while insufficient additions result in low carrier viscosity. Polyethylene glycol octylphenyl ether, used to increase solvent activity and compatibility, has little effect on carrier viscosity when added in insufficient amounts (Comparative Example 6), while excessive additions (Comparative Example 4) result in excessively low carrier viscosity.

[0146] To more intuitively evaluate the effect of the carrier composition ratio on the shelf stability and long-term usability of pure silver jewelry solder pastes, the pure silver jewelry solder pastes of Examples 1-6 and Comparative Examples 1-8 were placed in a sealed dispensing syringe and left at room temperature for one month before observation. The results showed that after one month, the pure silver jewelry solder pastes of Examples 1-6 showed no delamination of the metal brazing filler metal from the carrier, nor did the flux and carrier precipitate. This indicates that the pure silver jewelry solder pastes of Examples 1-6 have good stability and can be used stably and long-term. Furthermore, the pure silver jewelry solder pastes of Comparative Examples 1, 3, and 7 also showed no delamination or flux and carrier precipitation after one month, but their high viscosity made them difficult to inject and apply, making them unsuitable for use. However, the pure silver jewelry solder pastes of Comparative Examples 2, 4, 5, 6, and 8 showed delamination after one month.

[0147] Therefore, based on the viscosity test results and the stability test results, it can be seen that although excessive addition of water-based polyurethane, cetostearyl alcohol, and organic bentonite can help improve the stability of the solder paste, the usability is poor due to the excessive viscosity; too little addition will cause low carrier viscosity, resulting in poor solder paste stability; too much addition of polyethylene glycol octylphenyl ether will cause too low carrier viscosity, which in turn leads to poor solder paste stability, and too little addition will reduce the compatibility, causing the solder paste to easily delaminate.

[0148] Experimental Example 3

[0149] To evaluate the soldering performance of the present invention's solder paste for pure silver jewelry, the appearance of the welds of the pure silver jewelry pieces from Examples 15-21 after welding was observed, with the results shown in Table 3. To evaluate the corrosion resistance of the welds, the welded pure silver jewelry pieces from Examples 15-21 were placed in a 10% sodium sulfide solution, and the discoloration time of the welds was observed and recorded. The results are shown in Table 2. To evaluate the effect of the composition ratio of the metal brazing filler metal powder on welding performance, the solder pastes from Comparative Examples 9-15 were used to weld pure silver jewelry using the method of Example 15. The appearance of the welds after welding is shown in Table 4. The welded pure silver jewelry pieces were placed in a 10% sodium sulfide solution, and the discoloration time of the welds is shown in Table 4.

[0150] Table 3 Appearance of the weld seam and discoloration time of the weld seam of the pure silver jewelry after welding in Examples 15-21

[0151]

[0152]

[0153] Table 4 Welding effect of solder paste for pure silver jewelry welding of comparative examples 9-15

[0154]

[0155] The results show that when the total amount of metal brazing filler metal powder is fixed, a too high Cu content will cause the brazing seam to turn yellow, while a too low Cu content will cause the melting temperature of the brazing filler metal to be too high, affecting the welding effect; a too low Zn content will cause the brazing seam to turn yellow; a too high total content of Zn and Cu elements will cause the brazing seam to turn yellow; a too low total content of Zn and Cu elements will cause the melting temperature of the brazing filler metal to be too high, affecting the welding effect; a too high Si content will cause the brazing seam to be brittle, while a too low Si content will lead to a decrease in corrosion resistance, an increase in brazing seam defects, and easy discoloration of the weld; a too high content of corrosion-resistant elements will cause defects in the brazing seam to be easily generated.

Claims

1. A solder paste for pure silver jewelry welding, characterized in that: The invention mainly consists of metal solder powder, solder flux and carrier; the mass ratio of the metal solder powder to the solder flux is (80-95):(5-20); the mass ratio of the sum of the mass of the metal solder powder and the solder flux to the mass of the carrier is (70-85):(15-30); The metal solder powder is mainly composed of the following elements in parts by weight: 60 to 85 parts of Ag, 9 to 35 parts of Cu, 4 to 15 parts of Zn, and 0.2 to 0.8 parts of Si; The carrier is composed of the following components in parts by weight: 5-30 parts of glycerol, 20-35 parts of ethylene glycol, 20-35 parts of ethyl acetate, 10-15 parts of waterborne polyurethane, 5-10 parts of cetostearyl alcohol, 2-5 parts of polyethylene glycol octylphenyl ether, and 1-3 parts of organic bentonite.

2. The solder paste for pure silver jewelry welding according to claim 1, wherein: The metal brazing filler metal powder also includes corrosion-resistant elements, and the corrosion-resistant elements are selected from one or any combination of Ti, Zr, Cr, V, Mo, Ni, Co, Pd, Pt, Ir, and Au.

3. The solder paste for pure silver jewelry welding according to claim 2, wherein: In the metal brazing filler metal powder, the weight portion of the corrosion-resistant element is no more than 2 parts.

4. The solder paste for pure silver jewelry welding according to claim 1, wherein: The brazing flux is composed of the following components in parts by weight: 5 to 30 parts of potassium fluoroborate, 10 to 30 parts of boron trioxide, 15 to 40 parts of borax, and 20 to 40 parts of alkaline chemical cleaning agent.

5. The solder paste for pure silver jewelry welding according to claim 4, wherein: The alkaline chemical cleaning agent is selected from one or any combination of sodium hydroxide, sodium silicate and sodium carbonate.

6. The solder paste for pure silver jewelry welding according to claim 1, wherein: The viscosity of the carrier at 25° C. is 7800-8500 cp.

7. A method for preparing a solder paste for pure silver jewelry welding according to any one of claims 1 to 6, characterized in that: The following steps are involved: First, the metal solder powder and the brazing agent are mixed for the first time to obtain a mixture, and then the mixture and the carrier are mixed for the second time to obtain the product.

8. Application of the solder paste for pure silver jewelry welding according to any one of claims 1 to 6 in welding pure silver jewelry, characterized in that: The method comprises the following steps: applying the solder paste for welding pure silver jewelry to the part to be welded of the pure silver jewelry, and then heating the pure silver jewelry coated with the solder paste under an inert atmosphere and / or a reducing atmosphere until the solder paste melts, thereby completing welding.

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