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Auxiliary brightener: effect on bright nickel plating solution and additives

发布时间:2019-11-27 16:46:00 点击率: Catalog: Anhao Dynamic Release time: 2019-11-27 16:46:00 Click rate:

镀镍 光亮剂。 In the past, only one primary brightener and one secondary brightener were combined to form a group of nickel-plated brighteners. Such as saccharin with butynediol is a typical example. But things are constantly evolving and will never stop at one level. With the improvement of the quality requirements of electroplated parts, higher requirements have been put forward on the performance of the plating solution. In addition to the primary brightener and secondary brighteners to obtain bright coatings, auxiliary brighteners are needed to help, so that better performance can be obtained. This is the role of the auxiliary brightener. Common auxiliary brighteners are: sodium propyne sulfonate (PS), sodium propenyl sulfonate (ALS), sodium vinyl sulfonate (VS), ATP (a white or light yellow solid, composed of thiourea and sulfonate It is derived from the reaction of lactone. It is a sulfur- and nitrogen-containing compound, a deep plating agent and an impurity masking agent for nickel plating solution), carboxyethylthiourea betaine (ATPN), and LCDA (a light yellow Sulphur-containing compounds, which have a strong offset effect and a bright effect in the low current region).

Impurity remover

In working nickel plating bath, it is inevitable that there will be contamination by foreign metal impurities. For nickel plating solutions, they are often contaminated by copper and iron ions; because the bath is in contact with conductive copper rods and copper hooks, and plating parts fall into the bath to cause chemical or electrochemical dissolution, no matter how purified As long as the bath is working, these two kinds of foreign metal impurities are almost always present. The amount of these foreign metal impurities is not enough to affect the quality of the coating, but if it exceeds the allowable amount, it will have a deleterious effect on the nickel plating; In the past, the method for removing foreign metal impurities was electrolytic method under low current density conditions, or the pH value of the plating solution was increased to 6.2, so that copper, iron, zinc and other metal impurities were in the form of hydroxide Me (OH) n. The precipitate was removed by filtration. Although this can effectively remove foreign metal impurities, it is labor-intensive and time-consuming, and the processing cost is high. These heterometallic impurities can now be easily removed with some * impurity removal agents.

There are also two types of impurity removing agents. One is a selective chemical precipitant that forms larger particles with impurity metal ions to cause precipitation; the other is a selective chelating agent that forms chelation with metal impurities. And co-deposited with nickel in the coating. Most of these chelates are organic compounds with aromatic or heterocyclic structures, which will not adversely affect the nickel plating layer. Since these chelating agents form ions with the dissimilar metal impurities in the nickel plating solution, the electrode potential of these dissimilar metals can be changed so that their discharge potential approaches that of nickel ions. In this way, the plated layer will not be rough, nor will it Bring other harmful effects. Due to the eutectoid of the dissimilar metal impurities and nickel ions, the metal impurities in the bath solution do not accumulate too much. This method does not require filtration, is simple, low cost, and is the most effective and effective way to remove impurities from nickel plating solutions today. Of course, it is also necessary to choose a good performance impurity remover, especially it should be noted that it will not bring harmful effects to the nickel plating layer.

(1) QT copper remover

The main ingredients are ferrocyanide, such as potassium ferrocyanide commonly known as yellow blood salt potassium, K4 [Fe (CN) 6] · 3H20 and sodium ferrocyanide called yellow blood salt sodium, Na4 [Fe (CN) 6] · 10H20. Ferrocyanide can form copper ferrocyanide with copper in weakly acidic solution:

2Cu2 ++ [Fe (CN) 6] 4 → Cu2 [Fe (CN)] 6 ↓

Copper ferrocyanide is a kind of extremely fine particles with insoluble particles in the nickel plating solution. It is difficult to filter it out by conventional methods. For this reason, precise filtration is required to remove copper ferrocyanide. This method is much more economical than the chemical precipitation method in which the pH is increased to make heavy metals into hydroxides, because a large amount of nickel hydroxide can be prevented from precipitating at the same time; but the solution needs to be filtered, which is also inconvenient. As mentioned earlier, because the particles formed by copper ferrocyanide are small and suspended in a sol-like form in the plating solution, it is more difficult to filter. Therefore, this method has been used in recent years.

Chelating impurity removers have been developed over the last ten years. 上海永生助剂厂 的综合除杂剂、高效镀镍溶液除铜剂和高效除锌剂,西南化工研究院的AD871镀镍液除杂剂,武汉大学的FeZac-881除杂剂等。 These products include comprehensive impurity remover, high-efficiency nickel plating solution copper remover and high-efficiency zinc remover from Shanghai Yongsheng Auxiliary Factory , AD871 nickel plating liquid impurity remover from Southwest Chemical Research Institute, and FeZac-881 impurity remover from Wuhan University. .

In the case that the nickel plating solution is not too contaminated, usually only 1-2 mL / L of the above-mentioned selective impurity removing agent can be added. Because in the usual nickel plating solution, there is often a small amount of copper and iron pollution. 腐蚀 而来的。 Most of the copper comes from the patina produced on the copper rods and anode hooks, and the iron comes from the iron because the iron pieces fell into the plating tank and were not salvaged in time, resulting in iron corrosion . Copper and iron impurities caused by these two factors accumulate slowly in the bath, so it is only necessary to add a comprehensive impurity removing agent. The addition of a comprehensive impurity remover forms a chelate with copper and iron ions, which changes the precipitation potential of these two metals, which can be precipitated on the cathode at the same time as nickel, and the coating will not generate burrs. In this way, the copper and iron impurities in the bath solution will not be accumulated in large quantities, and the bath solution can be kept stable. If the base material of the electroplated product is copper or brass, copper impurities in the plating solution can easily accumulate, and a high-efficiency copper remover can be more effective. Accumulation of zinc ions in nickel tanks is unavoidable for nickel plating baths of electroplated zinc die castings, especially zinc die castings such as barrel-plated garment pull heads, because zinc is easily corroded in acid nickel plating baths. Such a barrel nickel plating tank generally needs to be treated once a week, and in severe cases, it needs to be treated once every other day. This seems to be time-consuming and wasteful. Now just adding high-efficiency zinc remover can solve this big problem.

There are also some other metal impurity removal agents, which can also be included in the list of auxiliary additives, because they can ensure that a good nickel plating is obtained, and also play a supporting role. Some of these heterometallic impurity removers are monomers, and some are compounds. Most of them have not been disclosed because they are product secrets. Therefore, they can be attributed to intermediates of auxiliary additives or introduced as commodities. The following are commonly used.

(2) Plating bath comprehensive impurity removing agent This is a commodity. It is a light yellow liquid. It has the function of removing various foreign metal impurities in the nickel plating solution. Each milliliter of impurity removes the effects of the following quantities of impurities:

Cu2 + 20mgAl3 + 30mg

Zn2 + 15mgCr3 + 20mg

Fe2 ++ Fe3 + 40mg

This comprehensive impurity removal agent can chelate with the above-mentioned metal impurities instead of generating a precipitate, so no filtration is required. After chelation, the electrode potential of the impurities is close to nickel ions, so that metal impurities can be deposited and precipitated on the cathode together, so that the foreign metal impurities in the plating solution will not be accumulated too much. Even if this impurity is added in excess, it will not have a harmful effect on the nickel plating layer, so it is safer. 经济 效益好。 This method is simple, convenient, safe and reliable, and has good economic benefits . If it is only the influence of foreign metal impurities, this method can be used to solve it, which can greatly reduce the processing cost than the chemical alkalinization method. It is estimated that every 10,000 liters of nickel plating solution can reduce the large processing cost by 20,000 ~ 40,000 yuan per year.

According to the empirical data of most plants, each time the alkaline treatment method is used, the average loss of nickel sulfate is 30 g / L, and the 1 × 104L tank solution will lose 300 kg of nickel sulfate. It also needs to add hydrogen peroxide and activated carbon and stop production, so the losses are considerable. A careful calculation can lead to a conclusion.

三价铬 ,然后加入综合除杂剂才会有效;这是因为六价铬是阴离子的缘故。 For nickel plating solution contaminated by a small amount of hexavalent chromium, hexavalent chromium should be reduced to trivalent chromium first with insurance powder or sodium bisulfite , and then it is effective to add a comprehensive impurity remover; this is because hexavalent chromium is an anion Sake.

(3) Copper removal agent for nickel plating solution

This is an additive designed to remove copper impurities from nickel plating solutions. It has a significant effect on the copper impurities. Each milliliter of copper remover can eliminate the effect of 50mg of copper impurities, and it is not as effective as a comprehensive impurity remover for other impurities.

(4) Nickel plating bath zinc remover This is a special additive to remove zinc impurities in nickel plating solution. Each milliliter of zinc remover can eliminate the effect of 100mg of zinc impurities, and its effect on other impurities is not as good as a comprehensive impurity remover.

The different units and different grades of nickel plating impurity removal agents introduced above all have a specific chelation relationship with the metal impurities in the plating solution, so that these foreign metal impurities can be electrodeposited and deposited on the cathode. There will be less and less metallic impurities. Since the impurities and the impurity remover do not form hydroxides, no filtering is required. 过滤机 进行定期间隙性的过滤,以除掉部分积累起来的有机杂质;平时则用一般过滤机进行循环过滤,这样镀镍槽液几乎不必进行定期大处理。 For example, the nickel plating brightener has fewer decomposition products, and the bath can be treated for a long period of time. Or it can be filtered periodically with an activated carbon filter to remove some of the accumulated organic impurities. Usually, it is circulated with a general filter. Filtration, so that the nickel plating bath almost does not need to be regularly treated. If you do this, you can increase the pH value by using alkali, add activated carbon, stir and warm, filter, remove the tank, adjust the pH value, and low-current dense electrolytic treatment, which can save a lot of labor and costs. Economic benefits should be said Is very significant.

2. Wetting agent

As wetting agents for nickel plating solutions are some surfactants, there are two types of anionic, non-ionic, the following will be introduced item by item.

(1) Sodium lauryl sulfate This is the most widely used anionic surfactant in nickel plating solution. It is obtained by esterifying dodecyl alcohol with chlorosulfonic acid. Sodium lauryl sulfate is a white powdery product that is mainly used as a detergent and foam generator for toothpaste. Its addition can reduce the surface tension of the plating solution, make the hydrogen bubbles adsorbed on the cathode easily escape, and eliminate the pinhole pits of the nickel plating layer. Sodium lauryl sulfate can also make the coating crystals finer, which may be related to the fact that hydrogen on the surface of the plating is not easy to stay.

The quality of sodium lauryl sulfate and the method of adding it will have a certain effect on the nickel plating layer, which requires attention. If the esterification is not complete, there is still un-esterified dodecanol in the finished product. Such a solution of sodium dodecyl sulfate is turbid, and the nickel plating layer will be foggy and blooming after being added. . So it is a very important job to choose good quality sodium lauryl sulfate. It is also very particular about the method of adding. Insufficient dissolution will cause flowering, fog or pitting of the coating. Do not directly heat on an electric furnace or other open flames, or the bottom will burn and become insoluble particles. If such a solution is added to the plating tank without filtering, pitting will occur once it is adsorbed on the surface of the plated part. The correct method is to first wet the powdery sodium lauryl sulfate with a small amount of water, and then wash it with boiling water, or heat it with a spacer. The solution should not be made too concentrated, generally it is appropriate to prepare a concentration of about 5%. Below we take a preparation of 1000mL

5% concentration of sodium dodecyl sulfate is taken as an example for readers' reference.

In a 1000 mL glass beaker, weigh 50 g of sodium lauryl sulfate, add 20 mL of cold water and mix thoroughly with a glass rod to make it fully wet. Then rinse with boiling water to a volume of about 800mL, stir with a glass rod to make a completely transparent solution, and then add cold water to 1000mL. If the solution is turbid, heat it with water to make it transparent; if the solution is transparent, but there are suspended matter, filter it with filter paper before using it.

Add 1mL of this solution to the nickel plating solution, that is, 0.05g / L. The general amount of nickel plating bath is 1-2mL / L, which contains 0.05-0.1g / L sodium lauryl sulfate.

Sodium lauryl sulfate has multiple bubbles, so it is only suitable for the plating solution of the cathode moving device. Modern nickel plating tanks are often used for circulating filtration and air agitation. However, they cannot be used because they have too much foam.

(2) Ethylhexyl sulfate This is an esterification product of isooctanol and chlorosulfonic acid. The production method is basically the same as that of sodium dodecyl sulfate. Because of its short carbon chain and branched structure, it has less foam. It can be used in nickel plating tanks for cathode movement and nickel plating tanks for air stirring and circulating filtration. The addition amount is 1 to 2 mL / L for rack plating, and 0.5 to 1 mL / L for barrel plating.

(3) LB low foam wetting agent This is a low carbon chain sulfonated product with a double bond structure. It is an anionic surfactant and penetrant. Because it is a sulfonated product, it is more effective than sodium ethylhexyl sulfate. Stable, with extremely good surface tension and penetration reduction, can be called surface wetting agent *. When added to the nickel plating solution, it has better wetting effect than sodium lauryl sulfate and sodium ethylhexyl sulfate, and almost does not generate foam. Like sodium ethylhexyl sulfate, it can be used for cathode mobile plating Nickel tank, nickel plating tank for air stirring and circulating filtration. Another advantage is that because it is a sulfonated product, it is not easy to decompose in the nickel plating solution and is very stable. There is no fogging or blooming on the coating. The addition amount is 1-2 mL / I. , Barrel plating 0.5 ~ 1mL / L.

(4) Polyethylene glycol Polyethylene glycol is a non-ionic surfactant with a molecular formula of H [OCH2CH2] nOH, which is obtained by condensation of ethylene glycol. It is stable in nickel plating solution, does not hydrolyze, and does not deteriorate. Small molecular weight polyethylene glycol (M below 600) is a good wetting agent for nickel plating solutions. As early as the early 1960s, the Great Leap Forward was made by the rough and rough flow. At that time, the quality of sodium lauryl sulfate was very poor. After the addition, the coating was blooming or fogging. Sometimes the pinhole pits increased. Glycols are not completely related to esterification. Because this raw material problem could not be solved for a while, I was forced to seek other ways. After several tests, low molecular weight polyethylene glycol has a better effect. The relative molecular weights are 200, 400 and 600. These three types of polyethylene glycols are slightly viscous liquids and can be used. After our tests, relative molecular weights higher than 600 will make the coating brittle, so it cannot be used. . According to the situation at the time, the quality of domestic production was not good, it was brittle, and imported from Germany was not brittle; now China's basic chemical industry has improved. What is the quality of domestic low molecular weight polyethylene glycol, can it be used in nickel plating tanks It has to be further verified. The low molecular weight polyethylene glycol is added in an amount of 0.01 to 0.1 mL / L.

(5) Sulfonated product of OP emulsifier It is reported that sulfonated OP emulsifier is an anionic surfactant which is a * wetting agent for nickel plating solution. OP emulsifier is a non-ionic surfactant, which is obtained by polycondensation of nonylphenol or octylphenol with ethylene oxide. The current TX-10 is formed by the addition polymerization of nonylphenol and ethylene oxide. The chemical formula is: From the chemical structural formula, because of its longer hydrophobic group, it can be seen that its surface activity is greater than sodium lauryl sulfate and polyethylene glycol. After sulfonation addition, it becomes an anionic surfactant with the following structure, which is more hydrophilic. It is said that this wetting agent will not cause the nickel plating layer to bloom, but also has a certain brightening effect.

(6) Fatty alcohol polyoxyethylene ether sulfate sodium salt (AES) Fatty alcohol polyoxyethylene ether sulfate sodium salt is a nonionic surfactant fatty alcohol polyoxyethylene ether RO- [OCH2CH2] nH and sulfonate, and then Product neutralized with sodium hydroxide. After esterification, it becomes an anionic surfactant. Its surface activity is also large. AES with a suitable structure is a good wetting agent for nickel plating baths. The added amount is generally 0.2 to 0.8 mg / L.

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