A kind of synthesis method of ammonium iminodisulfonate and its application in cyanide-free silver plating

Abstract

The present invention relates to a synthesis method of ammonium iminodisulfonate and its application in cyanide-free silver plating, belonging to the technical field of compound preparation, and solves the problems of low safety, poor quality and consistency of the obtained product and low yield of the existing melting preparation method of ammonium iminodisulfonate. The method for synthesizing ammonium iminodisulfonate comprises: adding ammonium sulfamic acid and aminosulfonic acid to a reaction solvent, heating, and reacting. The reaction solvent not only promotes the uniformity of material mixing and improves reaction efficiency, but also disperses part of the reaction heat into the solvent through heat conduction, and dissipates it through heat exchange, greatly alleviating the intensity of reaction heat release, improving reaction safety, reducing side reactions, improving product yield and quality, and enabling large-scale production. The ammonium iminodisulfonate prepared by the present invention is applied to cyanide-free silver plating, which is beneficial to improving the stability of the plating solution and the appearance, glossiness, corrosion resistance and other properties of the coating.

Description

Technical Field

[0001] The invention relates to the technical field of compound preparation, in particular to a synthesis method of ammonium iminodisulfonate and application of the same in cyanide-free silver plating. Background Art

[0002] Silver plating is an important metal surface treatment technology and is widely used in various fields. Among them, the cyanide-free silver plating process can avoid the use of highly toxic cyanide in cyanide silver plating. The electroplating waste liquid is easy to treat and has broad market prospects and huge application value.

[0003] The key to cyanide-free silver plating is to select a complexing agent. + Complexation can improve the deposition quality of Ag on the coating. Electroplating with double complexing agents is a new trend in electroplating research at home and abroad. In the double complexing agent system, due to the generation of composite complex ions, the cathode polarization is increased, thus obtaining a better coating. When ammonium iminodisulfonate (NS) is used as a double complexing agent in an alkaline cyanide-free silver plating solution, it can react with silver to generate Ag(NS). 1-2 Complex ion, has good complexing ability to silver.

[0004] At present, the product yield of NS prepared by ammonolysis, hydrolysis and deamination is low. Therefore, it has been proposed that equivalent amounts of ammonium aminosulfonate and aminosulfonic acid can be melt-reacted to directly obtain ammonium iminodisulfonate. This melting method has good atom economy.

[0005] However, the following problems exist in the synthesis process of the melting method: uneven mixing between materials, serious exothermic reaction, strong reaction, concentrated exothermic reaction and dangerous situation of large amount of gas release, high production safety requirements, and no large-scale production has been seen so far; the product obtained by the melting method is a hard, agglomerated solid that needs to be crushed before use, but it is difficult to crush, the particle size distribution range is wide, and the product consistency is poor; at the same time, because the product contains impurities such as S, it cannot be used directly in the electroplating solution, and needs to be processed with cumbersome procedures such as activated carbon, thus limiting the application of NS in the electroplating solution.

[0006] Therefore, in the face of the fact that cyanide-free silver plating technology is increasingly valued in the fields of electronic electroplating, material modification, etc. due to its environmental protection and safety, as well as its good performance and potential shown in practical applications, there is an urgent need for a safe and efficient preparation method that can improve the quality of NS, so as to improve the stability and electroplating effect of the cyanide-free silver plating system containing NS, which is conducive to promoting the application of cyanide-free silver plating process in actual production. Summary of the invention

[0007] In view of the above analysis, the embodiments of the present invention aim to provide a method for synthesizing ammonium iminodisulfonate and its application in cyanide-free silver plating, so as to solve at least one of the problems that the existing method for preparing ammonium iminodisulfonate by melting has concentrated reaction exothermicity, low production safety, no large-scale production, and the obtained product is a hard and hard block that needs to be crushed before use, resulting in poor product quality and consistency.

[0008] In a first aspect, an embodiment of the present invention provides a method for preparing ammonium iminodisulfonate, the method comprising: (1) adding ammonium sulfamate and aminosulfonic acid to a reaction solvent A, heating, reacting, cooling, filtering, and obtaining a crude ammonium iminodisulfonate product and a filtrate.

[0009] Further, the reaction solvent A is at least one of pyridine, xylene, diethylene glycol dimethyl ether, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and anisole, preferably at least one of xylene, diethylene glycol dimethyl ether, N,N-dimethylformamide, pyridine, dimethyl sulfoxide, ethyl acetate, ethanol, and anisole.

[0010] Furthermore, the molar ratio of the ammonium sulfamate to the sulfamic acid is 1:1, and the amount of the reaction solvent is 100-1000 mL / 1 mol of ammonium sulfamate, preferably 400-1000 mL / 1 mol of ammonium sulfamate.

[0011] Furthermore, the heating time is 0-1h, preferably 0.2-0.8h; the temperature reached by the heating is 60-200°C, preferably 60-160°C.

[0012] Furthermore, the reaction time is 1-3 h, preferably 1-2 h.

[0013] Furthermore, the method further comprises: (2) using the filtrate obtained in step (1) as a reaction solvent and returning it to step (1) for recycling.

[0014] Furthermore, the number of times the reaction solvent is recycled is 2-5.

[0015] Furthermore, the method further comprises: (3) washing the crude product obtained by filtering in step (2) with solvent B, and vacuum drying.

[0016] Furthermore, the solvent B is one or two of chloroform, methanol, ethanol, acetone, isopropanol, acetonitrile, triethylamine, toluene, ethyl acetate, cyclohexane, and n-hexane; preferably one or two of acetone, ethyl acetate, methanol, propanol, ethanol, isopropanol, acetonitrile, triethylamine, toluene, and cyclohexane.

[0017] Furthermore, the amount of the solvent B is 25-100 mL / 100 g of ammonium iminodisulfonate, preferably 40-60 mL / 100 g of ammonium iminodisulfonate.

[0018] In a second aspect, an embodiment of the present invention provides ammonium iminodisulfonate prepared by the above method, wherein the ammonium iminodisulfonate is a white powder.

[0019] In a third aspect, an embodiment of the present invention provides a use of ammonium iminodisulfonate prepared by the above method in cyanide-free silver plating, wherein the ammonium iminodisulfonate is used as a main ligand in cyanide-free silver plating.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1. The present invention allows the raw materials of ammonium sulfamate and sulfamic acid for preparing ammonium iminodisulfonate to react in a solvent, thereby promoting the uniformity of material mixing, improving raw material utilization, reaction safety and product consistency; compared with the existing system of preparing ammonium iminodisulfonate from ammonium sulfamate and sulfamic acid by melting method, the synthesis method of the present invention puts the raw materials into a solvent, which not only promotes the uniformity of raw material mixing, but also has good thermal conductivity of the solvent, can disperse the reaction exotherm into the solvent, alleviate the phenomenon of local excessive temperature caused by concentrated reaction exotherm, significantly alleviate the intensity of the exothermic phenomenon in the reaction process, generate little or no foam, and rarely overflow ammonia, avoiding the material rushing phenomenon in kilogram-level reactions, ensuring production safety, solving the potential safety hazard problem caused by gas release, and realizing large-scale production; and the product has good color, uniform particle size and texture, is loose, has no agglomeration phenomenon, and is in a uniform powder state, such as Figure 1 shown.

[0022] 2. The reaction solvent used in the preparation method of the present invention is an organic solvent, which can promote the uniformity of material mixing under stirring conditions and improve the reaction efficiency; the boiling point of the reaction solvent is higher than the temperature at which the reaction system reaches the reaction activation energy, ensuring that the raw material reaction can be carried out in the solvent, and the phenomenon of local excessive temperature caused by concentrated reaction heat is alleviated through solvent heat conduction, so as to take away part of the heat in the reaction system, alleviate the side reaction of generating ammonia caused by the violent reaction and concentrated reaction caused by the self-exothermic reaction, overcome the potential safety hazard caused by gas release, and improve the yield and quality of the product.

[0023] In addition, since there are dissolved residues in the product in the reaction solvent, the amount of the reaction solvent used will affect the yield of the final product. Therefore, the present invention not only limits the amount of the reaction solvent used, but also recycles it to improve the product yield.

[0024] 3. The reaction of the raw materials in the solvent of the present invention is an exothermic reaction, so after the reaction system is heated to the temperature at which the raw materials start to react by using an external heat source, an intermittent heating method can be used to maintain the required temperature of the reaction together with the heat release of the reaction, 60-200°C;

[0025] Compared with the current melting method (160°C) for preparing ammonium iminodisulfonate from ammonium sulfamate and sulfamic acid, the present invention can control the heating mode and / or speed of the external heat source to regulate the heating rate and the temperature reached during the reaction process, control the reaction of the raw materials to be completed within a certain time, allow the reaction solvent to have time and opportunity to take away part of the reaction heat, ensure that the reaction exotherm becomes moderate, and after a certain period of time, 20 minutes to 1 hour, ensure the safety of the preparation process; it can be seen from some specific embodiments of the present invention that no side reaction of raw material decomposition and generation of ammonia occurs during the reaction process, only a small amount of foam is generated or even no foam is generated, the risk of material impact can be avoided, the product yield and quality are improved, the yield is as high as 97%, the product purity is greater than 99%, the gloss is good, the product is loose and free of agglomerates, the particle size is fine and the product is in powder form, and the texture is uniform.

[0026] 4. In order to remove the residual reaction solvent in the product after the reaction, the present invention uses a suitable solvent B to wash and dry the product to obtain a high-purity product; using the synthesis method of the present invention, the subsequent purification method of the product is simple, and the obtained product has high purity. It is applied to the cyanide-free silver plating process to obtain a coating with good appearance, gloss and corrosion resistance, as shown in Table 1.

[0027] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components;

[0029] Figure 1 This is a morphology picture of the white ammonium iminodisulfonate powder prepared in Example 12. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0031] Silver has become one of the most widely used precious metals due to its excellent performance and relatively low cost. Silver plating is an important metal surface treatment technology, widely used in various fields, among which cyanide-free silver plating process has broad market prospects and huge application value.

[0032] The key to solving the problem of cyanide-free silver plating is to select a complexing agent. + Complexation can improve the deposition quality of Ag on the coating. Electroplating with double complexing agents is a new trend in electroplating research at home and abroad. In the double complexing agent system, composite complex ions are generated, which increases the cathode polarization and thus obtains a better coating.

[0033] Ammonium iminodisulfonate (NS) is a good double complexing agent for silver plating. In alkaline solution, NS has a good complexing ability with silver and can generate Ag(NS) with silver. 1-2 Complex ion, wherein the molecular structure of ammonium iminodisulfonate is In the ammonium iminodisulfonate silver plating system, silver nitrate is the main salt, ammonium iminodisulfonate is the main ligand, and ammonium sulfate, ammonium citrate and citric acid are added. The plating solution has simple composition and is easy to configure. The coating is clean and delicate, with good dispersion and covering ability. At the same time, the electroplating waste liquid is easy to treat.

[0034] In the study of cyanide-free silver plating using NS, it was found that the product yield of NS prepared by ammonolysis, hydrolysis, and deamination was low. Therefore, it was proposed that ammonium iminodisulfonate can be directly obtained by melting equivalent amounts of ammonium sulfamate and aminosulfonic acid. This synthesis method has good atom economy:

[0035] .

[0036] However, the inventors of the present application have found in their research that in the process of silver-plating materials using the ammonium iminodisulfonic acid silver-plating system, the following problems are prone to occur when synthesizing by the melting method: uneven mixing between materials, serious exothermic reaction, strong reaction, concentrated exothermic reaction and dangerous gas release, production safety cannot be guaranteed, and it is difficult to carry out large-scale production; at the same time, the product obtained by the melting method is relatively hard and difficult to crush, has a wide range of particle size distribution, poor product consistency, and low yield and purity, which affects the stability of the cyanide-free silver-plating system containing NS, the appearance and performance of the coating, and limits the application of NS in cyanide-free silver-plating.

[0037] In addition, the inventors also found that there are no commercialized ammonium iminodisulfonic acid products on the market, and each application unit prepares it by itself when needed, which has become an important factor restricting the application of NS.

[0038] Therefore, the present invention provides a method for synthesizing atom-economic ammonium iminodisulfonate with high production safety and good product performance, comprising the following steps: adding a special organic solvent A to solid raw materials of ammonium sulfamate and aminosulfonic acid, reacting at a temperature of 60-200° C. for a reaction time of 1-3 hours, and obtaining high-quality ammonium iminodisulfonate powder with uniform particle size in high yield and high purity.

[0039] Specifically, when the organic solvent A is a non-polar solvent, although it has a dispersing effect on the reaction raw materials and improves the uniformity of the raw material mixing to a certain extent, after heating for a certain period of time, the reaction mixture can also reach the reaction activation energy. However, since the reactant is an inorganic salt, if the solubility in the solvent is not enough, the two cannot be mixed to achieve a homogeneous phase, and the reaction is bound to be non-uniform, the reaction is concentrated, the reaction is fast, the heat is not dissipated in time, the material is easily washed out, and the product forms a hard lump, which is difficult to post-process.

[0040] Specifically, the organic solvent A should make the reaction raw materials disperse more evenly, contact more fully, and be conducive to reaction, which requires that the solvent preferably has certain solubility for the two raw materials. Because the reaction raw materials are inorganic substances, they have poor compatibility with organic solvents. From the reaction effect, the solvent dielectric constant is lower than 10 toluene, dimethylbenzene, ethyl acetate and other effects are poor, and the reaction effects of some solvents such as pyridine, isopropanol and the like between dielectric constants of 10 to 20 are improved, and the dielectric constant is greater than 20 DMF, dimethyl sulfoxide and other solvents. The reaction is significantly improved. On the other hand, the boiling point of the reaction solvent cannot be too low, otherwise the temperature of the reaction in the solvent cannot achieve the activation energy required for the reaction, and the reaction cannot proceed normally, so the solvent is required to have a suitable boiling point, and the activation energy of the reaction can be reached before the solvent is evaporated during the reaction temperature rise, so that the reaction proceeds normally; At the same time, the reaction solvent enables the final product to solidify in a dispersed state in the reaction system, avoids the product from forming a hard lump, improves product quality, and is convenient for subsequent drying and packaging, which is also related to the polarity of the solvent. Compared with the solvent-free melting reaction, the reaction using organic solvent as the medium avoids the concentrated heat release of the reaction. The solvent acts as a heat transfer medium and dissipates the heat through the heat exchanger, which can solve the problems of concentrated heat release and difficult product post-processing in the melting method. Organic solvent A makes the raw materials mixed evenly, improves the reaction efficiency, and the raw materials are heated evenly; it also alleviates the violent reaction caused by the self-heat release of the reaction, avoids the side reaction of producing ammonia caused by local heat release, and solves the safety hazard caused by the release of a large amount of gas.

[0041] Furthermore, the synthesis method of the present invention uses a polar protic solvent with better effect than a non-polar solvent, and a dipolar solvent has a better effect; the reaction in the dipolar solvent can be carried out more steadily at a certain temperature, avoiding concentrated reaction heat release. In addition, the product precipitates while reacting, the product is loose and does not agglomerate, and impurities tend to remain in the solution, so the product purity is better.

[0042] In summary, the use of the solvent A changes the dangerous situation of uneven material mixing, violent reaction, concentrated heat release and gas release in the melting reaction of ammonium sulfamate and sulfamic acid, and the production safety is guaranteed. The synthesis method of the present invention can obtain a kilogram-level powder product with good color and uniform texture. Figure 1 The obtained ammonium iminodisulfonate was used in the cyanide-free silver plating system. Compared with the ammonium iminodisulfonate product synthesized by the melting method, the plating solution was stable, the coating had a smooth and delicate appearance, uniform brightness, fine grains, and strong anti-discoloration ability, as shown in Table 1.

[0043] The product obtained by the synthesis method of the present invention is loose and powdery, and the subsequent purification method of the obtained product is simple. According to some preferred embodiments of the present invention, since there is a certain amount of reaction solvent remaining in the product, the purification effect can be achieved by selecting a suitable solvent B for washing.

[0044] Specifically, the solvent B is miscible with the reaction solvent A, can wash away the reaction solvent remaining on the surface of the product, and has a low solubility in the prepared product and is almost insoluble.

[0045] The synthesis method of the present invention specifically comprises the following steps:

[0046] (1) Ammonium sulfamate and sulfamic acid are mixed uniformly in a molar ratio of 1:1 and placed in a three-necked flask reaction vessel equipped with an electric stirrer, a thermometer and a reflux condenser;

[0047] (2) When the amount of ammonium sulfamate and sulfamic acid is 1 mol, 100-1000 ml of organic solvent A is added to the reaction vessel. When the amount of ammonium sulfamate and sulfamic acid is 2 mol, the amount of A added is 200-2000 ml. When the number of moles continues to increase, the amount of solvent is also increased in the same proportion, and stirring is started;

[0048] (3) Gradually raise the temperature to 60-200°C within 0-1h, maintain this temperature, react for 1-2h, and then cool naturally under stirring;

[0049] (4) filtering under reduced pressure to obtain a crude product and a filtrate of organic solvent A;

[0050] (5) washing the product with 50-200 ml of organic solvent B, filtering under reduced pressure to obtain a washing solution of organic solvent B, and drying in vacuo at 60° C. to obtain the product;

[0051] (6) recycling the organic solvent A filtrate obtained in (4) and putting it into the reaction vessel of the next batch, continuing to use it as the reaction solvent for 2 to 5 times to participate in the reaction of synthesizing the ammonium iminodisulfonic acid product;

[0052] (7) Recover the organic solvents A and B in the filtrate by distillation.

[0053] Specifically, since the reaction of ammonium sulfamate and aminosulfonic acid in the reaction solvent is an irreversible reaction, the molar ratio of ammonium sulfamate and aminosulfonic acid in step (1) is 1:1, and an equivalent raw material ratio is selected to avoid excess raw materials affecting product quality, improve raw material conversion rate and product quality, and simplify subsequent processing.

[0054] According to some preferred embodiments of the present invention, the organic solvent A is at least one of pyridine, xylene, diethylene glycol dimethyl ether, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and anisole;

[0055] Preferably, it is at least one of xylene, diethylene glycol dimethyl ether, pyridine, N,N-dimethylformamide, dimethyl sulfoxide, ethanol and anisole.

[0056] Specifically, in order to reduce the dissolution residue of the product in the reaction solvent and improve the yield of the final product while ensuring the uniformity of the mixing of the reaction materials and alleviating the intense heat release during the reaction, the present invention needs to limit the amount of the reaction solvent. In step (2), the amount of the reaction solvent is 100-1000 mL / 1 mol of ammonium sulfamate, preferably 400-1000 mL / 1 mol of ammonium sulfamate.

[0057] Specifically, since the NS product obtained by the reaction has a certain solubility in the reaction solvent, in order to improve the yield of the ammonium iminodisulfonic acid product, the present invention recycles the filtrate containing the reaction solvent obtained after filtering in step (4), and the number of times of recycling is 2-5.

[0058] Even if the materials in the existing melting method are ground, the uniformity of mixing is far less than that of mixing in a solvent. During the heating process of the melting method, the materials at the bottom or other parts of the container that are in contact with the heat source are prone to overheating, but the materials in other parts of the container that are not in contact with the heat source are far from reaching the activation energy; the material that reaches the reaction temperature first by heating starts to react, and the self-heat after the reaction and the external heat source trigger the reaction of other materials. At this time, the material that reacts first is prone to overheating, resulting in side reactions such as decomposition; after the reaction of the material that reacts later, the self-heating phenomenon is serious, the reaction is strong, the heat is concentrated, and it is easy to overheat, which also leads to side reactions such as decomposition, and the obtained product is agglomerated, the particle size distribution range is wide, the hardness is large, it is difficult to crush, and the subsequent treatment is difficult; it seriously affects the stability of the NS-containing cyanide-free silver plating solution and the appearance and performance of the coating.

[0059] The inventors of the present invention have found through many experiments that the temperature required for the raw materials for preparing NS to react in the solvent is lowered. When the reaction solvents are pyridine, dimethyl sulfoxide and N,N-dimethylformamide (DMF), the temperatures at which ammonium sulfamate and sulfamate start to react are 65°C, 75°C and 75°C, respectively, which are much lower than 120°C at which the materials start to react in the melting method. Since the reaction of the raw materials in the solvent is an exothermic reaction, after the reaction system is heated to the temperature at which the raw materials start to react using an external heat source, intermittent heating can be used together with the reaction exotherm to maintain the required temperature for the reaction, which is 60-200°C.

[0060] In the reaction process of the present invention, the reaction solvent A is used as a medium for reaction, and the solvent is used as a heat transfer medium to dissipate heat through a heat exchanger. Compared with the solvent-free melting reaction, the concentrated heat release of the reaction is avoided, and the problems of concentrated and intense heat release of the reaction and difficult handling of product solidification can be solved. The organic solvent A makes the raw materials mixed evenly, improves the reaction efficiency, and the reaction raw materials are heated evenly, and has good thermal conductivity, disperses part of the reaction heat, avoids local overheating generated by the reaction, alleviates the violent reaction caused by the self-exothermic reaction, and avoids the side reaction of generating ammonia caused by local heat release in the melting method, and solves the safety hazard problem caused by gas release.

[0061] In addition, during the reaction process of the present invention, the heating method and / or speed of the external heat source can be controlled to regulate the heating rate and the temperature reached during the reaction process, so as to control the reaction of the raw materials to be completed within a certain time, so that the reaction solvent has time and opportunity to take away part of the reaction heat, and ensure that the reaction exotherm becomes moderate, and after a certain period of time, 1-2h, the safety of the preparation process is ensured; it can be seen from some specific embodiments of the present invention that side reactions are reduced during the reaction process, only a small amount of foam is generated or even no foam is generated, the risk of material impact can be avoided, and the product yield and quality are improved, with a yield of up to 98%, a purity greater than 99%, good gloss, looseness without agglomeration, uniform particle size and texture, and the product is in a uniform powder state.

[0062] According to some preferred embodiments of the present invention, the solvent B is one or two of chloroform, methanol, ethanol, acetone, isopropanol, acetonitrile, triethylamine, toluene, ethyl acetate, cyclohexane, and n-hexane; preferably one or two of acetone, ethyl acetate, methanol, propanol, ethanol, isopropanol, acetonitrile, triethylamine, toluene, and cyclohexane.

[0063] Specifically, in order to ensure that the residual reaction solvent in the product after the reaction is removed, the amount of solvent B should be limited to avoid using excessive solvent B to cause waste and product loss. In step (5), the amount of solvent B is 25-100 mL / 100 g of ammonium iminodisulfonate, preferably 40-60 mL / 100 g of ammonium iminodisulfonate.

[0064] Specifically, in order to remove the solvent remaining on the product after purification, the present invention further performs vacuum drying on the product.

[0065] Specifically, in order to avoid environmental pollution and save costs, the present invention distills the filtrate obtained by filtration in step (4) and step (5) to recover the organic solvents A and B.

[0066] The present invention provides ammonium iminodisulfonate, which is prepared by the above method. The yield of the product prepared by the method of the present invention is high, which is more than 97%, and the product has good color, uniform particle size and texture, is in the form of white powder, is loose, and has no agglomeration phenomenon. Figure 1 shown.

[0067] The present invention also provides an application of the ammonium iminodisulfonate prepared by the above method in cyanide-free silver plating, wherein the ammonium iminodisulfonate is used as a main ligand in the cyanide-free silver plating system. Because the ammonium iminodisulfonate product prepared by the method of the present invention has a relatively high quality, when it is applied to the cyanide-free silver plating process, the cyanide-free silver plating solution containing NS has a relatively good stability, and a coating with a relatively good appearance, gloss, and corrosion resistance can be obtained, as shown in Table 1.

[0068] The glossiness of silver plating is an important indicator to measure its decorative appearance and reflective properties; the glossiness of silver plating not only affects the appearance, but may also affect its corrosion resistance and welding performance, thereby affecting the service life of the silver plating.

[0069] Methods for measuring the glossiness of silver coatings generally include visual inspection, sample comparison and instrument measurement. Visual inspection relies on the experience of the inspector, while sample comparison uses a reference sample with a certain glossiness for comparison; the present invention adopts an instrumental measurement method using a gloss meter for precise measurement, which can provide a more objective and accurate glossiness value.

[0070] Unless otherwise stated, the raw materials and reagents described in the examples are commercially available products.

[0071] Comparative Example 1

[0072] The synthesis of ammonium iminodisulfonate (NS) by the melt method includes the following steps:

[0073] 97.1 g of aminosulfonic acid (1 mole) and 114.1 g of ammonium aminosulfonate (1 mole) were ground and mixed, and then heated in a dry pot electric furnace. The temperature was slowly raised to about 120°C. The edge of the mixture began to partially melt, and the system had a self-exothermic temperature rise phenomenon and local melting. When the temperature was raised to about 140°C, the system began to release heat and a large number of bubbles were generated. At this time, heating was stopped, and the temperature of the reaction system quickly rose to about 180°C and then stopped, and a large amount of foam continued to be generated. After that, as the temperature dropped, the product gradually solidified and slowly solidified into a hard large block of solid. The product was transferred out of the dry pot and crushed for later use.

[0074] From the synthesis process of NS in Comparative Example 1, it can be seen that due to severe self-exotherm, the raw materials decompose and produce a large amount of foam, which will cause material impaction. The reaction self-exotherm is severe and there is a danger when the reaction is scaled up. The product is hard and difficult to remove from the reactor and crush, making post-processing difficult. The particle size of the product after crushing is uneven.

[0075] Example 1

[0076] (1) In a 5-liter three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a thermometer, add 97.1 g of aminosulfonic acid (1 mol), 114.1 g of ammonium aminosulfonate (1 mol), and 1000 ml of xylene, and mix well;

[0077] (2) using an electric heating pack to heat the mixed solution obtained in step (1), raising the temperature to 120°C after 40 minutes to react, and self-exothermic temperature rise occurs. After 10 minutes, the temperature is raised to 135°C and reflux occurs, generating a large number of bubbles. The temperature is maintained at 135°C for 50 minutes, and the heating is stopped.

[0078] (3) The reaction system was cooled, solidified, and filtered to obtain a crystalline solid block 1 of crude ammonium iminodisulfonic acid. The product yield was 72% and the purity was 80% by weighing and calculation.

[0079] The product obtained in Example 1 still has a certain hardness. Although the hardness is significantly lower than that of the comparative example, it is still difficult to transfer the product out of the reaction bottle in post-processing. However, it can be transferred out of the reaction bottle after crushing, and the uniformity of the product texture is increased. However, the reaction exotherm is still relatively intense and concentrated, and the exotherm time is short, which poses a safety risk. A large amount of foam is generated during the reaction, there are many side reactions, and the product yield and purity are low. In addition, the residual xylene in the product still remains after filtration, resulting in a greasy product, and the solvent is difficult to volatilize due to its high boiling point, has a strong smell, and is somewhat toxic.

[0080] Example 2

[0081] (1) In a 5-liter three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a thermometer, add 97.1 g of aminosulfonic acid (1 mol), 114.1 g of ammonium aminosulfonate (1 mol), and 1000 ml of diethylene glycol dimethyl ether, and mix well;

[0082] (2) using an electric heating pack to heat the mixed solution obtained in step (1), raising the temperature to 115°C after 30 minutes, reacting, and self-exothermic temperature rise phenomenon occurs, and raising the temperature to 140°C after 15 minutes and refluxing, maintaining the temperature at 140°C for 1 hour, and then stopping heating;

[0083] (3) The reaction system was cooled, solidified, cooled, and filtered to obtain a crude product of 2-iminodisulfonic acid ammonium in the form of a yellowish-white loose solid having a crystalline form; by weighing and calculation, the product yield was 78% and the purity was 82%.

[0084] The product obtained in Example 2 is loose, easy to transfer, and has a uniform texture, indicating that the reaction heat can be taken away by using diethylene glycol dimethyl ether as a solvent, but the reaction heat is still very concentrated, and there is still a safety risk after a short heat release period; a large amount of foam is generated during the reaction, there are many side reactions, and the product yield and purity are low.

[0085] Example 3

[0086] (1) In a 5-liter three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a thermometer, add 97.1 g of aminosulfonic acid (1 mol), 114.1 g of ammonium aminosulfonate (1 mol), and 1000 ml of pyridine, and mix well;

[0087] (2) using an electric heating pack to heat the mixed solution obtained in step (1) to 65°C for 20 minutes, reacting and causing self-heating. The heating rate can be controlled to raise the temperature to 110°C for another 40 minutes and reflux. The temperature is maintained at 110°C for 1 hour, and the heating is stopped.

[0088] (3) The reaction system was cooled, solidified, cooled, and filtered to obtain a crude product of 3-iminodisulfonic acid ammonium in the form of a white loose solid with a crystalline form; by weighing and calculation, the product yield was 85% and the purity was 86%.

[0089] The product obtained in Example 3 is relatively loose, easy to transfer, and has a uniform texture, indicating that when pyridine is used as the reaction solvent, part of the reaction heat can be taken away, the heat release lasts for a longer period of time, and the safety is improved; the reaction produces very little foam, very few side reactions, and the utilization rate of raw materials is high, so that the scaled-up reaction can be carried out; but since the product is not washed and purified, the purity is slightly low, and there is a certain amount of reaction solvent residue on the surface of the product; in addition, pyridine has a strong smell and is toxic to a certain extent, so the scaled-up reaction has certain limitations.

[0090] Example 4

[0091] (1) In a 5-liter three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a thermometer, add 97.1 g of aminosulfonic acid (1 mol), 114.1 g of ammonium aminosulfonate (1 mol), and 1000 ml of dimethyl sulfoxide, and mix well;

[0092] (2) using an electric heating pack to heat the mixed solution obtained in step (1) to 75°C for 20 minutes, reacting and causing self-heating. The heating rate was controlled to increase the temperature to 140°C for another 30 minutes and reflux. The temperature was maintained at 140°C for 50 minutes, and the heating was stopped.

[0093] (3) The reaction system was cooled, solidified, cooled, and filtered to obtain a crude product of 4-iminodisulfonic acid ammonium in the form of a white loose solid with a crystalline form; by weighing and calculation, the product yield was 91.6% and the purity was 87%.

[0094] The product obtained in Example 4 is loose, uniform in texture, in powder form, and easy to transfer out, indicating that using dimethyl sulfoxide as a solvent for the reaction can also take away the heat released in the reaction, the heat release is relatively mild, the heat release lasts for a long time, and the safety is high; a small amount of foam is generated during the reaction, which can avoid the risk of material impact, there are few side reactions, the raw material utilization rate is high, and the scaled-up reaction production can be carried out; since the product is not washed and purified, the purity is slightly low, and the product has a certain amount of reaction solvent residue.

[0095] Example 5

[0096] (1) In a 5-liter three-necked flask equipped with a mechanical stirrer, a reflux condenser, and a thermometer, add 97.1 g of aminosulfonic acid (1 mol), 114.1 g of ammonium aminosulfonate (1 mol), and 1000 ml of N,N-dimethylformamide (DMF), and mix well;

[0097] (2) using an electric heating pack to heat the mixed solution obtained in step (1) to 75°C for 20 minutes, reacting and causing self-heating. The heating rate was controlled, and the temperature was raised to 130°C for another 20 minutes and slightly refluxed. The temperature was maintained at 130°C for 1 hour, and the heating was stopped.

[0098] (3) The reaction system was cooled, solidified, cooled, and filtered to obtain a crude product of 5-iminodisulfonic acid ammonium in the form of a white loose solid having a crystalline form; by weighing and calculation, the product yield was 97.5% and the purity was 91.3%.

[0099] The product obtained in Example 5 is loose, uniform in texture, in powder form, and easy to transfer out, indicating that using DMF as solvent for the reaction can take away the heat released in the reaction, the heat release is relatively mild, the heat release lasts for a certain period of time, and the safety is high; no foam is generated during the reaction, indicating that there is no decomposition of the raw materials, no risk of material impact, high raw material utilization rate, and can be scaled up for reaction production; since the product is not washed and purified, the purity is slightly low, and the product has a certain amount of reaction solvent residue.

[0100] It can be seen from the above Examples 1-5 and Comparative Example 1 that in Examples 1 and 2, although the use of organic solvents diethylene glycol dimethyl ether and xylene improves the properties of the product, there are still problems of concentrated heat release and material rushing; it can be seen from Examples 3, 4 and 5 that the addition of organic solvents pyridine, dimethyl sulfoxide or DMF can solve the concentrated heat release in the melting reaction of aminosulfonic acid and ammonium aminosulfonate, and the safety problem of a large number of bubbles being generated, thereby causing reaction material rushing, and at the same time, a powdery solid with uniform texture can be obtained, which is beneficial to subsequent applications.

[0101] The following examples will study the improvement of product purity and yield of the product obtained in Example 5.

[0102] Example 6

[0103] The white loose solid 5 crude product obtained in step (3) of Example 5 was washed once with 100 ml of organic solvent B acetone, and vacuum dried at 60 degrees to obtain the purified product 5 ammonium iminodisulfonate with a yield of 90.1% and a purity of 94.5%.

[0104] Example 7

[0105] The same method as in Example 6 was used, except that the organic solvent B in S2 was replaced with ethyl acetate, and the product 7-iminodisulfonic acid ammonium was obtained by vacuum drying at 60° C. with a yield of 91% and a purity of 95.4%.

[0106] Example 8

[0107] The same method as Example 6 was used, except that the organic solvent B in S2 was replaced by methanol, and the purified product 8-iminodisulfonic acid ammonium was obtained by vacuum drying at 60° C. with a yield of 87.4% and a purity greater than 99.0%.

[0108] Example 9

[0109] The same method as Example 8 was used, except that the amount of methanol, the organic solvent B, in S2 was reduced to 80 mL, and the product was dried under vacuum at 60° C. to obtain the purified product 8-iminodisulfonic acid ammonium with a yield of 90% and a purity greater than 99%.

[0110] Example 10

[0111] The same preparation method as in Example 5 was adopted, except that the amount of DMF used as the reaction solvent in step (1) was reduced to 600 mL, and finally a crystalline white loose solid 6-iminodisulfonic acid crude product was obtained.

[0112] The white loose solid crude product was purified by the same method as in Example 9 and dried under vacuum at 60° C. to obtain the product 10-ammonium iminodisulfonate with a yield of 92.4% and a purity greater than 99%.

[0113] As can be seen from Example 10, when avoiding concentrated heat release and improving product properties, the amount of DMF was reduced from 1000ml to 600ml, and the product yield was increased from 90% in Example 9 to 92.4%, indicating that excessive reaction solvent causes the product to have dissolved residues, reducing the yield. Therefore, appropriately reducing the amount of reaction solvent DMF can improve the yield.

[0114] In order to further improve the yield, the present invention uses the reaction solvent in a recycling manner. For example, the filtrate obtained after the filtration in step (3) of Example 5 is used as the reaction solvent and returned to step (1) of Example 5 for recycling. The technical effect brought about by recycling the reaction solvent can be verified from the following Example 11.

[0115] Embodiment 11

[0116] The same preparation method as in Example 10 was adopted, except that the reaction solvent in step (1) was replaced by the recovered DMF-containing filtrate (the third recycling), and finally a crystalline white loose solid 11-iminodisulfonic acid ammonium was obtained with a yield of 97.2% and a purity greater than 99%.

[0117] After the solvent was applied, it was found that the product yield increased significantly, indicating that the product in the recovered organic solvent A was saturated, thereby reducing the dissolution loss of the product. After the application, the quality of the product did not decrease, the purity was still greater than 99%, and the product was still a powdery solid with uniform texture. In addition, reducing the amount of solvent can save costs.

[0118] Example 12

[0119] Scale-up reaction production, pilot reaction, specific steps include:

[0120] (1) In a 100-liter double-layer glass reactor equipped with a mechanical stirrer, a reflux condenser, and a thermometer, add 4855 g of aminosulfonic acid (50 mol), 5705 g of ammonium aminosulfonate (50 mol), and 30 liters of DMF recycled from the third time, and mix well;

[0121] (2) using an electric heating pack to heat the mixed solution obtained in step (1), slowly heating it to 75°C over 20 minutes, reacting, and self-exothermic temperature rise phenomenon occurs. Control the heating rate, raise the temperature to 130°C after 20 minutes and reflux, maintain the temperature at 130°C for 1 hour, and stop heating;

[0122] (3) cooling the reaction system, solidifying, cooling, and filtering to obtain a crystalline white loose solid 1,2-iminodisulfonic acid ammonium;

[0123] (4) The white loose solid product 12 obtained in step (3) was washed with 4 L of organic solvent B methanol and dried under vacuum at 60 degrees to obtain a purified product with a yield of 97.6% and a purity greater than 99%.

[0124] Example 13

[0125] The NS products in Examples 5, 6, 9, 11, 12 and Comparative Example 1 were used as the main ligand in a cyanide-free silver plating system according to conventional methods in the art to conduct experiments.

[0126] The composition of the cyanide-free silver plating solution system: AgNO3 30g / L; NS 90g / L; (NH4)2SO4 85g / L; pH 9.0.

[0127] Coating performance test method:

[0128] (1) Plating solution stability test

[0129] The copper foil replacement experiment is used to examine the stability of the complex formed by the main ligand NS and silver to indicate the stability of the plating solution. The specific operation is as follows: put the test piece into the aqueduct of the above-mentioned electroplating system, the electroplating temperature is 35°C, stir it thoroughly, and observe the changes on the surface of the test piece. If attachments appear on the surface of the test piece, it means that the plating solution can no longer withstand the replacement experiment.

[0130] (2) Coating appearance performance test

[0131] The appearance and covering ability of the coating are characterized by visual inspection and coating gloss measurement. The roughness and morphology of the coating are visually inspected to characterize the coating appearance; the glossiness of the coating is measured using a gloss meter.

[0132] (3) Test of corrosion resistance of coating

[0133] The corrosion resistance of the coating was investigated through the classic K2S immersion test.

[0134] The silver coating is in contact with sulfides, sulfur oxides, etc. in the air, which easily generates insoluble substances such as silver halide, Ag2SO4, Ag2S, etc., causing the silver coating to change color from yellow to brown and dark brown. These three colors represent the degree of corrosion of the coating, which increases in turn. After the coating is corroded, it will not only affect the appearance, but also reduce the performance of electrical conductivity, thermal conductivity and welding. The silver-plated test pieces obtained by using Examples 5, 6, 9, 11, 12 and Comparative Example 1 as the main complexing agent were immersed in 0.1 mol / L potassium sulfide solution, and the color change of the test pieces during immersion was recorded.

[0135] Table 1 shows the test results of the coating properties of the NS products obtained in Examples 5, 6, 9, 11, 12 and Comparative Example 1 after electroplating.

[0136] Table 1

[0137]

[0138] It can be seen from Table 1 that the NS synthesized by the melting method of Comparative Example 1 is used as the main complexing agent for electroplating, and the obtained plating solution has poor stability, rough and uneven coating, obvious granular substances, and low corrosion resistance of the coating. This is because the NS product synthesized by the melting method is not subjected to cumbersome subsequent purification and desulfurization treatments, and has low purity, contains many impurities, poor properties, and is uneven, which affects the complexation with silver ions, resulting in uneven and dense coating. When the selected solvent A is used, the NS product obtained in Example 5 is electroplated, and the stability of the plating solution is improved and the corrosion resistance is enhanced. This is because the product is in powder form, and the performance and texture are improved. However, since it has not been washed, the product purity is low (purity 91.3%), so the coating appearance is still slightly rough, uneven, and has low gloss, resulting in poor coating performance. After washing with the selected solvent B, the purity of the product in Example 6 reaches 94.5%, the coating performance is significantly improved, the coating appearance is smooth and uniform, and the plating solution stability can reach 4min. After replacing solvent B for washing, the purity of the product obtained in Example 9 is increased by more than 99%, the obtained plating solution is stable, the coating has excellent properties, good gloss, and strong corrosion resistance, but the yield is low. By applying the reaction solvent DMF 3 times, the dissolution of the product in pyridine is saturated, so that the product generated by the reaction is no longer insoluble in DMF, and the product yield of Example 11 is increased to 97.2%, but the purity is still greater than 99%, the product quality is high, uniform, fine, the coating performance is good, the corrosion resistance is strong, and the gloss is increased to 178.8Gu. Example 12 is the process pilot of Example 11, and the NS product obtained has stable properties, and the purity is still greater than 99%. It is used in the plating solution, and the coating performance obtained is high, corrosion-resistant, good gloss, and the plating solution is stable. It shows that the product quality is stable and can be used for industrial production. The product can be especially applied to cyanide-free silver plating to obtain an excellent coating.

[0139] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for synthesizing ammonium iminodisulfonate by a solvent process, characterized in that: The method comprises: (1) adding ammonium sulfamate and sulfamic acid to a reaction solvent A, heating, reacting, cooling, filtering, and obtaining a crude product of ammonium iminodisulfonate and a filtrate; wherein the amount of the reaction solvent A is 100-1000 mL / 1 mol of ammonium sulfamate; The heating temperature is 60-115°C; the reaction time is 1-3h; The boiling point of the reaction solvent A is greater than the heating temperature, and the reaction solvent A is at least one of pyridine, diethylene glycol dimethyl ether, ethanol, isopropanol, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and anisole.

2. The method according to claim 1, characterized in that The reaction solvent A is at least one of pyridine, diethylene glycol dimethyl ether, N,N-dimethylformamide and dimethyl sulfoxide.

3. The method according to claim 1, characterized in that The molar ratio of the ammonium sulfamate to the aminosulfonic acid is 1:

1.

4. The method according to claim 1, characterized in that: The heating time is 0-1h.

5. The method according to claim 1, characterized in that The method further comprises: (2) The filtrate obtained in step (1) is used as a reaction solvent and returned to step (1) for recycling.

6. The method according to claim 5, characterized in that The number of times of recycling is 2-5.

7. The method according to claim 1, characterized in that The method further comprises: (3) Wash the crude product obtained by filtration in step (2) with solvent B and dry it in vacuo.

8. The method according to claim 7, characterized in that The solvent B is one or two of chloroform, methanol, ethanol, acetone, isopropanol, acetonitrile, triethylamine, toluene, ethyl acetate, cyclohexane, and n-hexane; And / or, the amount of the solvent B is 25-100 mL / 100 g of ammonium iminodisulfonate.

9. Ammonium iminodisulfonate prepared by the method according to any one of claims 1 to 8, characterized in that: The ammonium iminodisulfonate is a white powder.

10. Use of ammonium iminodisulfonate prepared by the method according to any one of claims 1 to 8 in cyanide-free silver plating, characterized in that: The ammonium iminodisulfonate is used as a main complexing agent in cyanide-free silver plating.

Images