In the same year, Siemens Halske Company of Germany proposed to use xanthate as brightener for silver plating in German patents 73 1 and 96 1. Later Durrwachter found that formaldehyde and peptone could be used as brighteners for lactic acid silver plating. Indian Rama Char suggested that adding 5 ~ 20g/L of ammonium sulfamate or 1g/L of sodium thiosulfate can significantly improve the brightness of silver iodide coating.
During the period of 1953 ~ 1957, the condensation products of carbon disulfide and ketone were proposed as brighteners for cyanide silver plating in American, French and Swiss patents. The former West Germany Schering Company used selenium or telluride as brightener for cyanide silver plating.
In the same year, Sel- Rex used antimony and bismuth compounds as brighteners for cyanide silver plating. In the original patent of West Germany, it was proposed that a hard and bright silver coating could be obtained by using polyethyleneimine with a relative molecular weight greater than 1000 as a brightener for thiosulfate silver plating.
In 1976, the British patent holds that the brightener for cyanide-free silver plating should contain the following five components: ① sulfonic acid anionic surfactant, such as Turkish red oil. ② Nitrogen-containing carboxylic acid or sulfonic acid amphoteric surfactant. ③ Cationic or nonionic surfactant. ④ Soluble aldehydes (such as furfural). ⑤ Compounds containing tautomers of C-SH or C=S, such as methoxymetallocene mercaptan.
In 1976, two additives are proposed in the U.S. patent as brighteners for cyanide-free silver plating with thiosulfate. The first category is polymer polyamine compounds, including polyethyleneimine with a relative molecular weight of 500-20000 and soluble polyazo compounds formed by the reaction of ammonia and olefins such as ethylenediamine, tetraethylenepentamine and N, N- bis (4- hydroxybutyryl) dipropyltriamine with epichlorohydrin. Another additive that can obtain a bright and tough silver layer is some compounds containing sulfur or selenium. Their structural formulas and names are shown in table 12- 13.
In 1976, Technic Company of the United States proposed a polyimide compound with a relative molecular weight of 100 ~ 60000 as a brightener for cyanide-free silver plating of succinimide, and its dosage was 0.001~1.0g/L. The polyimide used included polyethyleneimine, polypropylene imine and polyhydroxyethylenimine.
In 1977, the relationship between the half-wave potential of 25 sulfur-containing organic compounds and the brightness of the coating obtained in cyanide-based plating solution was studied by Colovbev system. It is found that the half-wave potential of additives that can obtain mirror brightness falls between 0.6 and 0.9 V, and when it is larger or smaller than this range, the brightness of the coating decreases. In order to obtain a long-lasting brightener, the half-wave potential of brightener hydrolysate should also be between 0.6 and 0.9 V.
1978 us patent put forward the patent of cyanide-free sodium thiosulfate silver plating. The brightener used consists of two parts, one is surfactant, which can be sulfonic acid anionic surfactant, or nitrogen-containing carboxylic acid or nitrogen-containing sulfonic acid amphoteric surfactant, or cationic or nonionic surfactant. Another brightener is soluble aldehyde, which can be easily reduced by electrodes and compounds containing C=S or their isomers. The dosage of aldehydes is about 1. 1g/L, and the dosage of C=S compound is about 0.03g/l. Typical aldehydes are furfural, anisaldehyde, cinnamaldehyde, glutaraldehyde, benzaldehyde or dimethylaminobenzaldehyde. The typical compound containing C=S is methyl imidazole mercaptan or disulfide brown. When the solution is stirred electroplating, the coating is as bright as a mirror, with low pinhole rate and much slower discoloration speed than ordinary silver layer.
In the British patent GB l534429 of 1978, a composite silver-graphite electroplating solution with Turkish red oil, sodium dodecyl sulfonate and sodium dibutylnaphthalene sulfonate as wetting agents and various sulfides or selenides as brighteners was proposed. Sulfides and selenides used are sodium xanthate, dithiocarbamates, thiosulfate (sodium or ammonium), thiothiazole and sodium selenite.
1979, A. Fletcher and W. L. Moriorty used negative divalent selenides as low cyanide (free cyanide
In 1980, the original West German patent used antimony tartrate, glycerol, alkylamine or other polycarboxylic acid complexes as brighteners for thiocyanate silver plating. In the early days, the solution obtained by boiling antimony trioxide, glycerol and sodium hydroxide together was used as brightener for cyanide silver plating.
1980, three engineers, Cen Qicheng, Liu and Yi Yueqin, from Guangzhou Electric Apparatus Research Institute in China, successfully studied a new silver plating process with SL-80 as brightener, and passed the technical appraisal in 1982+0 1 year. The current density is higher than other cyanide-free silver plating, and the coating is bright and fine, and the discoloration resistance is better than cyanide silver plating.
In Japanese patent 198 1, halogen negative ions (Br-I, L-I) and SeCN-I are combined as brighteners for silver thiocyanate electroplating. In the same year, in the Canadian patent, aldehydes and compounds containing C=S were used as brighteners, and anionic sulfonic acid and amphoteric nitrogen-containing carboxylic acid or sulfonic acid surfactants were used as grain refiners.
198 1 T.V.Novey proposed a brightener consisting of pyridine monocarboxylic acid or amide and a dye in the U.S. patent for sulfamic acid silver plating. The dosage of pyridine derivative is 0.5 ~ 10g/L, and the dosage of dye is 0.01~ 2.0g/L. The dye used can be any one of azo dye, acid anthracene dye and aromatic amine dye.
Australian patent 1982 proposed a silver sulfamate brightener with similar composition. Pyridine derivatives are the same as American patents. In addition to azo and anthracene dioxide, thiazine dyes are also added to the dyes. In a specific example, 3g/L nicotinic acid and 0.05g/L 3- bromo -4- aminodioxane-1- sulfonic acid are used.
Japanese patent 1982 proposes to use aromatic or heterocyclic thio compounds as brighteners for cyanide-based coatings.
In 1982, formaldehyde condensate of naphthalene sulfonic acid and disulfide condensate of ketone alkalization were used as brighteners for cyanide silver plating in Taiwan Province province, China. The dosage of the former is 50g/L and the latter is 0.2g/L. ..
1982 Japanese patent 57- 13 1382 found that dithiocarbamates or thiosemicarbazone is an effective additive for low cyanide silver plating solution, which can prevent the formation of replacement silver layer.
1984 U.S. Pat.No. 4.478.692 points out that silver alkyl sulfonate solution is a good solution for cyanide-free silver plating and silver alloy (such as Ag-Pd).
1986 us patent. No.4.6 14.568 found that cyclic thiourea-based compounds are also effective additives to prevent the formation of replacement silver layer in low cyanide or cyanide-free silver plating bath, and the plating bath also contains organic carboxylic acid.
199 1 Japanese patent 03-06 1393 invented a cyanide-free silver plating solution with thiocarbonyl compound as brightener. exist
In the Handbook of Metal Finishing published by 199 1, Kond0 et al. introduced a cyanide-free silver plating solution consisting of silver methanesulfonate, potassium iodide and N-(3- hydroxybutene) aminobenzenesulfonic acid.
1996 Japanese patent 96-4 1676 proposes that using nonionic surfactant as grain refiner in silver alkyl sulfonate bath can obtain a coating with the same density as cyanide bath.
In 200 1 U.S. Pat. No.625 1249, it is proposed to use organic sulfides and organic carboxylic acids as additives in the silver plating bath of alkyl sulfonic acid, alkyl sulfonamide or alkyl sulfonimide. Useful sulfides include mercaptoacetic acid, 2-mercaptopropionic acid, 2- mercaptonicotinic acid, cystine, 2- mercaptothiazoline, 1- mercaptoglycerol, thiosalicylic acid, thiodiglycol and thiodiglycolic acid. The carboxylic acids used include formic acid, acetic acid, propionic acid, benzoic acid, citric acid, nitrilotriacetic acid, sulfoacetic acid, oxalic acid, EDTA, succinic acid, tartaric acid, α -amino acids and polycarboxylic acids.
In the French patent FR282572 1 in 2002, it was proposed to use the mixture of dithiocarbamoyl dithiocarbamate and xanthate, that is, the reaction product of thiosemicarbazone and carbon disulfide, as a brightener for bright silver plating.
In 2003, American patent. US456620304 proposed an environment-friendly bright silver plating solution without cyanide and harmful substances. The silver salt is silver mesylate, the complexing agent is amino acid or protein, such as glycine, alanine, cystine, methionine and B vitamins, such as nicotinamide, and the stabilizer of the plating solution is mononitrophthalic acid, 4- nitrophthalic acid, m-nitrobenzenesulfonic acid, etc. The pH buffer is borax or phosphate. The surfactant is a commercial product, such as Tegotain485. The pH of the plating solution is 9.5 ~ 10.5, and the temperature is 25 ~ 30℃. The cathode current density is 1A/dm.