Platinum electrolytic plating bath and platinum plated product

Abstract

To provide an extremely stable, high purity platinum electrolytic plating solution with long bath life and low accumulation of impurities, and a platinum plated product with a high purity platinum plating film with good corrosion resistance and thick plating capability.SOLUTION: There is provided a platinum electrolytic platin bath, in which 11 g / L of DNS as platinum, 160 g / L of sulfuric acid and sulfamic acid in equal parts in total, and 60 mg / L of sodium lauryl sulfate are added, and the pH is adjusted to 0.4.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an acidic platinum electrolytic plating bath and a low-stress platinum electrodeposit electroplated from the plating bath.

Background Art

[0002] Divalent platinum (II) complexes are basically synthesized from chloroplatinic acid salts as raw materials into various compounds. Inorganic platinum complexes include compounds such as hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid. Representative ones include platinum chloride (PtCl2), platinum nitrate (Pt(NO3)2), diaminedichloroplatinum (Pt(NH3)2Cl2, trichloroamineplatinic acid (HPtCl3(NH3)) or its salt (MPtCl3(NH3)), tetrachloroplatinic acid (H2PtCl4) or its salt (M2PtCl4), tetranitroplatinic acid (H2Pt(NO2)4) or its salt (M2Pt(NO2)4), tetrasulfoplatonic acid (H6Pt(SO3)4) or its salt (M6Pt(SO3)4), hexahydroxoplatinic acid (H2Pt(OH)6) or its salt (M2Pt(OH)6), etc. Here, M represents an alkali metal, alkaline earth Class metal (hereinafter abbreviated as "alkaline earth metal") or ammonium.

[0003] Divalent platinum (II) complexes preferably used in electrolytic plating baths include dinitrodiammineplatinum (Pt(NH3)2(NO2)2, so-called p-salt), dinitrodiaquadiammineplatinum (Pt(NH3)2(H2O)2(NO2)2), nitratohydroxoaquadiammineplatinum (Pt(NH3)2(H2O)(OH)(NO2)), nitratohydroxodiammineplatinum (Pt(NH3)2(OH)(NO2)), dinitratodiammineplatinum (Pt(NH3)2(NO3)2), dinitrosulfideplatinum (Pt(SO4)(NO2)2, so-called DNS salt), dichlorotetraammineplatinum (Pt(NH3)4Cl2), dichlorodiammineplatinum (Pt(NH3)2Cl2), tetraammineplatinum hydrogen phosphate (Pt(NH3)4(HPO4), so-called Q-salt), etc.

[0004] Platinum electrolytic plating baths using these divalent platinum(II) complexes have been known for a long time. For example, dinitrodiaminoplatinum(II) (Pt(NH3)2(NO2)2) (p-salt) and dinitrosulfatoplatinum(II) [Pt(NO2)2(SO4)]2 - (DNS) are used in platinum electrolytic plating baths as follows.

[0005] For example, Japanese Patent Publication No. 36-19658 (Patent Document 1 described later) discloses an invention of an electrolytic solution for platinum plating "comprising an aqueous solution containing a composition obtained by heating platinum diammonium dinitrite in an aqueous solution of sulfamic acid". This specification describes that "it has been discovered that P salt [Pt(NH3)2(NO3)2] dissolves when heated in an aqueous solution of sulfamic acid, and that a solution obtained by heating P salt together with sulfamic acid can electroplate stress-free platinum when diluted".

[0006] However, when using this platinum electrolytic plating bath for electroplating operations at a temperature of 70 to 80 °C, there is a drawback that sulfamic acid decomposes and platinum salts precipitate. Also, Japanese Patent Publication No. 36-19812 (Patent Document 2 described later) discloses an invention of an electrolytic solution for platinum plating "comprising a solution obtained by heating a composition containing 10 to 40 g of platinum diammonium dinitrite per liter in an approximately 200 cc aqueous solution mixture of 10 to 100 cc of concentrated sulfuric acid and 10 to 100 cc of concentrated phosphoric acid and water". The specification states that "the object of this invention is to provide a platinum-containing electrolytic solution suitable for plating relatively thick and shiny platinum".

[0007] However, this electrolytic solution for platinum plating has the drawback that phosphoric acid accumulates in the electrolytic solution, inhibiting the recovery of platinum. Also, it was difficult to reliably obtain a plating of 5 μm or more with strong adhesion in a single plating operation. Subsequently, Japanese Patent Publication No. 49-21018 (Patent Document 3 described later) discloses the invention of an electrolytic platinum plating bath obtained by dissolving diamminedinitroplatinum in a solution containing 0.05 to 2 mol / L of a specific ammonium salt and 0.06 to 1 mol / L of sulfuric acid. This specification states that "(1) The bath has high stability... (3) The bath has a long life and other characteristics of an industrial plating bath."

[0008] Also, Japanese Unexamined Patent Application Publication No. 08-319595 (Patent Document 4 described later) discloses a platinum plating bath for electroplating containing 5 to 30 g / l of platinum as an amminesulfato-complex derived from the reaction of 1 mol of diaminodinitritoplatinum(II) and 4 to 6 mol of amidosulfuric acid, and having a pH value of less than 1. The electrolytic solution contains at most 5 g / l of free amidosulfuric acid and 20 to 400 g / l of sulfuric acid having a pH value of less than 1, and 0.01 to 0.2 g / l of a fluorine surfactant as a wetting agent. The invention is disclosed in Claim 4. This invention is described in the specification as being able to deposit smoothly, glossily, and without cracks even at a layer thickness exceeding 100 μm, and being stable even when not in use. Note that "amidosulfuric acid" is another name for sulfamic acid.

[0009] Also, U.S. Patent No. 3206382 (Patent Document 5 described later) discloses a method of electrodepositing platinum, which is a method of electrolyzing an electrolyte essentially consisting of an aqueous solution of a predetermined nitrito compound complex of platinum with a pH value of less than 2. Example 1 of this discloses a method of reacting potassium tetranitroplatinate(II) with sulfuric acid to prepare potassium dinitrosulfatoplatinate(II) (DNS salt) according to the following formula. K2Pt(NO2)4 + H2SO4 → Pt(NO2)2SO4

[0010] It is known that when thick plating is carried out with an alkaline platinum electrolytic plating solution containing free phosphoric acid, a shiny, dense, and high-purity platinum deposit can be obtained (Japanese Patent Laid-Open No. 02-107794). This invention is an alkaline platinum electroplating bath having a pH value generally greater than 8.5, "containing an alkaline aqueous solution of a platinum(II) complex salt, wherein the anion component of the complex salt is one or more groups or radicals derived from an inorganic acid other than an organic acid or a hydrohalic acid."

[0011] This anion component is selected such that it does not interfere with the plating process by chemical attack on metallic platinum, and examples thereof include lactate, benzoate, citrate, and tartrate. That is, the platinum ions electrochemically deposited are affected by the action of phosphorus near the cathode and become nuclei of new platinum particles. For this reason, it is presumed that a large number of fine platinum particles are electrochemically deposited, solving the problem of increased stress in the platinum coating.

[0012] Since this alkaline platinum electroplating bath is also used at high temperatures, free phosphoric acid and the like are concentrated in the plating bath. For this reason, there are still problems such as fluctuations in plating conditions and defects in platinum-plated products. In addition, it has been found that platinum electrodeposits electroplated with this alkaline plating solution have a large porosity value and poor corrosion resistance. Also, when an acidic electrolytic plating bath is used for a base of nickel, copper, palladium, etc., an acidic platinum plating solution is also used as the platinum electrolytic plating bath.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0014] As described above, since the acidic platinum electrolytic plating solution is used at high temperatures, the evaporation loss of the plating solution increases, and non-electrolytes and impurities are likely to be concentrated in the high-purity platinum plating solution. In addition, ligands coordinated to platinum by electroplating are released into the high-temperature acidic bath, and these ligands are also concentrated in the platinum plating solution. When electrical energy is externally applied to such an acidic platinum electrolytic plating solution, unstable compounds such as new nitrogen oxide (NOx) ions and sulfur oxide (SOx) ions can be released from the concentrated ligands and water molecules.

[0015] For example, tetranitroplatinic acid (H2Pt(NO2)4) forms complexes such as Pt(NO2)3(H2O) - , Pt(NO2)2(H2O)2, Pt(NO2)(H2O)3 + , Pt(H2O)4 2+ in an aqueous solution. In addition, the nitro group has a property of easily forming complex compounds of nitrogen and oxygen such as [Pt(NH3)2(NO3)2] in addition to the above compounds in an aqueous solution. In addition, when halogen ions coexist, the tendency for platinum ions to adhere to the already deposited platinum particles is enhanced. In the acidic platinum electrolytic plating solution, platinum ions electroplated near the cathode are affected by these complex compounds and ligands in various ways, and the formation of nuclei of new platinum particles and their deposition are hindered.

[0016] As a result, high-purity platinum electroplated deposits electroplated from these acidic platinum electrolytic plating solutions tend to have high tensile stress, and there are problems in that the porosity value is high and the corrosion resistance is poor in an alkaline plating bath. In addition, in the acidic platinum electrolytic plating solution, the plating conditions often vary during the electroplating operation, and the plating quality of the plated product often becomes unstable. In addition, it has been found that when organic substances and impurities accumulate in the solution, the plating conditions change and defects in the plated product occur.

[0017] In summary, in an acidic platinum electrolytic plating solution, since the electroplating conditions are likely to vary and new platinum particle nucleation cannot be obtained, there has been a problem that the electroplated deposit has high stress and only platinum plating products with many cracks and pinholes can be obtained. One of the causes of this was considered to be a silicon compound. Also, in an acidic platinum electrolytic plating solution, it was considered that a platinum(II) complex containing a ligand such as a nitro group was easily decomposed and the electroplating was often unstable, which was also the cause of these problems.

[0018] The present invention has been made in view of the above problems, and an object thereof is to provide an acidic platinum electrolytic plating bath that is extremely stable and has a long bath life. Another object of the present invention is to provide a high-purity platinum electrolytic plating bath that does not contain silicon. In particular, even in an acidic platinum electrolytic plating solution of a platinum(II) complex containing a ligand that is easily decomposed such as a nitro group, it is to provide a platinum electrolytic plating bath capable of obtaining an amorphous platinum deposit.

[0019] On the other hand, an object of the present invention is to provide a platinum plating product having a platinum film with little stress and no grain boundaries of platinum particles observed by a scanning electron microscope. Another object of the present invention is to provide a platinum plating product having an amorphous platinum film whose crystal orientation is not observed by X-ray diffraction. Another object of the present invention is to provide a platinum plating product having a thick, high-purity platinum film that does not contain silicon. In particular, it is to provide a platinum plating product having good corrosion resistance and little mechanical wear.

Means for Solving the Problems

[0020] When the present inventors examined the defects of the plating product, they found that silicon as an impurity was obscuring the problem. That is, when silicon is contained as an impurity in a conventional acidic platinum electrolytic plating bath, intermetallic compounds or the like may be formed irregularly in the deposit. Such foreign substances of silicon may have an adverse effect on the electrical properties of the platinum electroplated deposit.

[0021] Therefore, when examining the source of silicon contained in the platinum electrolytic plating bath, it was found that even platinum ingots with a nominal purity of 99.9% or more may contain silicon as an impurity on the order of several tens of ppm. It was also found that silicon is contained in distilled water. For this reason, it was found that silicon accumulates when building the platinum plating bath or replenishing the evaporated water. Furthermore, it was found that silicon is also contained in gold plating baths, palladium plating baths, nickel plating baths, etc. used as pretreatment plating solutions.

[0022] The inventor of the present invention removed silicon and variously examined various acidic platinum electrolytic plating baths. The inventor examined various additives using the sulfates or sulfamates of conventional divalent platinum (II) complexes and free sulfuric acid or sulfamic acid as the basic solution. As a result, it was found that in an acidic platinum electrolytic plating bath, when the crystal grains of high-purity platinum deposits are large, the sweat resistance deteriorates.

[0023] The inventor of the present invention focused on the property that a surfactant has both a hydrophilic group and a hydrophobic group in one molecule and reduces the surface tension of a metal. And it was found that when an anionic surfactant is added to an acidic platinum electrolytic plating solution, the shape of the platinum particles deposited on the cathode becomes uniform. That is, in the case of a platinum complex, the anionic surfactant carries the platinum complex to the cathode surface while surrounding the periphery of the divalent platinum ion and the ligand. And since the anionic surfactant surrounds the periphery of the crystal particles precipitated in the aqueous solution on the cathode surface, it was noticed that the adhesion of platinum ions in the aqueous solution to the crystal particles and the growth of crystal grains are inhibited.

[0024] This operation will be described with reference to Fig. 1. Fig. 1 is a schematic diagram of an acidic platinum electrolytic plating bath of p-salt with sodium lauryl sulfate added as an anionic surfactant. For convenience, the ligand of platinum ions is made sulfate ions. In the electrolytic plating solution, as shown in the upper left figure, the sodium lauryl sulfate of the anionic surfactant surrounds the platinum(II) sulfate complex. As shown in the lower left figure, the divalent platinum complex carried to the cathode surface receives one electron from the cathode to form a monovalent platinum complex, and the anionic surfactant surrounds it.

[0025] Subsequently, this monovalent platinum complex receives one more electron from the cathode to become zero-valent platinum shown in the central figure, that is, a metal atom of platinum. On the aqueous solution side, the anionic surfactant surrounds the platinum atom. On the other hand, individual platinum atoms on the cathode surface can spontaneously form an atomic group of platinum with a face-centered cubic structure on the cathode surface due to the cohesive force, as shown in the right figure. Thus, an atomic group of platinum fine particles is deposited on the cathode. The atomic group of platinum particles deposited in this way comes to form a part of the cathode surface by thermal energy.

[0026] On the other hand, the anionic surfactant still surrounds the periphery of the platinum atomic group. Also, the anionic surfactant surrounds the periphery of the divalent platinum complex. These anionic surfactants electrically insulate the atomic group of platinum fine particles and the platinum complex more, and suppress the interaction between the platinum atomic group and the platinum complex. Therefore, it is possible to prevent new platinum ions from adhering to this platinum fine particle until the atomic group of platinum fine particles becomes a part of the cathode surface. Further, since the working temperature of the platinum electrolytic plating bath is high, the deposition reaction of the platinum particles exemplified in Fig. 1 proceeds continuously. When the crystal particles homogenized on the cathode surface are stacked in this way, a plating film is formed without gaps, so the electroplated platinum product has a dense and amorphous crystal structure.

[0027] The gist of the platinum electrolytic plating bath of the present invention that can solve the above problems is that it contains an anionic surfactant in an acidic platinum plating bath composed of a divalent platinum(II) complex and free sulfuric acid or sulfamic acid.

[0028] Also, the platinum electrolytic plating bath of the present invention capable of solving the above problems is characterized in that in an acidic platinum plating bath composed of a divalent platinum (II) complex and free sulfuric acid or sulfamic acid, it contains an anionic surfactant, a metal salt of an alkaline earth metal, or a metal salt of an alkali metal.

[0029] The platinum electrolytic deposit of the present invention capable of solving the above problems Platinum-plated product containing the same, wherein the platinum electrodeposit has a platinum purity of 99% by weight or more is in an amorphous state and a Vickers hardness of 450 - 500 Hv, a stress of 100 Mpa or less, and a porosity of 30% or less.

[0030] In the platinum electrolytic plating bath of the present invention, the pH is preferably 2 or less, more preferably 1.5 or less. This is because it contains an anionic surfactant. Also, it is because the sulfate or sulfamate of the divalent platinum (II) complex is stable during the electroplating operation. The normal pH range is 0.2 - 1.0. A pH buffer can be used to control the pH within a predetermined range. The pH buffer may be used alone or in combination of two or more.

[0031] In the platinum electrolytic plating bath of the present invention, as the divalent platinum (II) complex, the divalent platinum (II) complex preferably used in conventional electrolytic plating baths can be used. Inorganic platinum complexes in which the divalent platinum (II) complex has at least one ligand among nitro group (NO2), nitrate group (NO3), sulfate group (SO4) 、 sulfonic acid group (SO3), ammine group (NH3), aquo group (H2O), or hydroxyl group (OH) are preferred. Examples of the divalent platinum (II) complex particularly preferably used in the electrolytic plating bath include p-salt, DNS salt, Q-salt, etc. These platinum (II) complexes may be used alone or in combination of two or more.

[0032] In the platinum electrolytic plating bath of the present invention, an aqueous solution in which a divalent platinum (II) complex is dissolved in free sulfuric acid or sulfamic acid is used. For example, when a divalent platinum complex powder such as p-salt or DNS salt is dissolved in a heated concentrated sulfuric acid solution or a heated concentrated sulfamic acid solution, a brown or pale yellow liquid is obtained. An aqueous solution obtained by adding sulfuric acid or sulfamic acid to this dissolved solution of divalent platinum is used as a concentrated solution. The platinum electrolytic plating bath of the present invention may use this concentrated solution as it is, or it can also be diluted for use.

[0033] In the platinum electrolytic plating bath of the present invention, since the metal salts of alkaline earth metals or the metal salts of alkali metals have a large ionization tendency, these metal salts do not precipitate even during electroplating. In addition, it has been found that when these metal salts are present, the content of the anionic surfactant can be reduced. However, these metal ions do not have an effect of inhibiting the growth of platinum particles like anionic surfactants.

[0034] The metal salts of alkaline earth metals or the metal salts of alkali metals do not contain halogen elements. This is because halogen elements have an adverse effect on platinum electrolytic deposits. In addition, these metal salts do not contain phosphates. This is because a platinum electrolytic plating bath containing a large amount of phosphates deteriorates the sweat resistance of platinum electrolytic deposits. Although phosphorus has an effect of densifying platinum deposits, since phosphates are difficult to evaporate, if they are used in metal salts of alkaline earth metals or metal salts of alkali metals, there is a risk of being concentrated and having an adverse effect on platinum electrolytic deposits.

[0035] In addition, when the metal salts of alkaline earth metals or the metal salts of alkali metals are present, even if the platinum concentration of the platinum electrolytic plating bath becomes low, more stable electroplating can be performed. Since the platinum electrolytic plating bath contains free sulfuric acid or sulfamic acid, generally inexpensive metal sulfates are used as the metal salts of alkaline earth metals or the metal salts of alkali metals.

[0036] Here, the preferable range of the concentration (g / L) of the metal salt of an alkaline earth metal or the metal salt of an alkali metal with respect to the platinum concentration (g / L), that is, the percentage of (metal salt concentration / platinum concentration) is 1% to 30%. The lower limit is more preferably 2.5% or more, and particularly preferably 5% or more. The upper limit is more preferably 20% or less, and particularly preferably 15% or less.

[0037] Also, the preferable range of the metal salt concentration (g / L) with respect to the concentration (mg / L) of the anionic surfactant, that is, (metal salt concentration / anionic surfactant concentration) is 10 to 500. The lower limit is more preferably 10 or more, and particularly preferably 25 or more. The upper limit is more preferably 300 or less, and particularly preferably 200 or less.

[0038] Among the metal salts of alkaline earth metals or the metal salts of alkali metals, magnesium salts are particularly preferable. Examples of magnesium salts include magnesium sulfate, magnesium oxide, magnesium hydroxide, magnesium sulfite, magnesium nitrate, and hydrates of these magnesium salts. Magnesium acetate, magnesium citrate, magnesium lactate, magnesium stearate, etc. can also be used.

[0039] The above anionic surfactant is preferably stearic acid or its salt, sulfonic acid or its salt, sulfamic acid or its salt, or sulfuric acid or its salt. This is because it dissolves in the sulfate or sulfamate of the divalent platinum (II) complex and makes the electrodeposit dense. Particularly, alkyl sulfate or its salt and alkylbenzene sulfonic acid or its salt are more preferable. Examples of alkyl sulfates include alkali metal salts, alkaline earth metal salts, and ammonium salts of lauryl sulfate. It is desirable that the anionic surfactant does not foam in order to circulate the plating solution with a pump.

[0040] Scanning electron microscope images of the surface and cross-section of the platinum electrodeposit of the present invention are shown in Fig. 2. This figure shows the surface (upper part of the photograph separated by a white horizontal line) of a platinum electrodeposit with a purity of 99% or more and a cross-section with a thickness of 4 μm (lower part of the same photograph), taken obliquely upward at an angle of 45 degrees. It can be seen from this figure that the crystal grains of the platinum electrodeposit are dense as if in an amorphous state.

Advantages of the Invention

[0041] The platinum electroplating bath of the present invention has the effect that even in an acidic platinum electroplating bath containing an anionic surfactant, an amorphous platinum electrodeposit can be obtained. That is, this platinum electrodeposit has the characteristics of being shiny, hard and dense, yet having extremely low stress. Also, in this platinum electrodeposit, no crystal orientation in a specific direction was observed, and even after heat treatment at 300 °C for 180 minutes, no crystal orientation of metallic platinum was observed.

[0042] The platinum electroplating bath of the present invention has the effect that by containing an anionic surfactant and a salt of an alkali metal or alkaline earth metal, the content of the anionic surfactant can be reduced. That is, since the amount of the anionic surfactant used can be reduced, the platinum electroplating bath of the present invention can be continuously operated for a long period even if the anionic surfactant deteriorates.

[0043] Also, according to the platinum electroplating bath of the present invention, even a thin plating film of 1 μm or less is amorphous, so a plating film with low porosity and excellent corrosion resistance can be obtained. Furthermore, the purity of platinum in this platinum electrodeposit is 99% or more and silicon can be made 1 ppm or less, so the quality of the platinum film is stable. Also, in the platinum electroplating bath of the present invention, an anionic surfactant can be appropriately selected according to the type of the divalent platinum (II) complex. Also, since the content of the anionic surfactant is small, the anionic surfactant does not accumulate even when electroplating is continuously performed for a long time.

[0044] In addition, the platinum electrolytic plating bath of the present invention has the effect of being able to set the bath temperature to a relatively low temperature. Lowering the bath temperature of the platinum electrolytic plating bath has the effect of facilitating the management of the plating solution. Further, since there is no accumulation of impurities in the platinum electrolytic plating bath of the present invention, there is an effect that it is not necessary to provide expensive equipment such as filtration and separation of the plating solution.

[0045] The platinum-plated product of the present invention has an excellent sweat resistance effect because the crystal grains of the platinum film are dense like an amorphous state. In particular, there is an effect that a platinum-plated product with high sweat resistance can be obtained even with a thin plating of 1 μm or less. Further, the platinum-plated product of the present invention is hard and dense, so it can withstand the insertion and extraction durability of connectors and the like and has an excellent mechanical wear resistance effect. Further, since the stress of this platinum film is small, there is an effect that this film does not peel off or crack.

[0046] In addition, although the purity of platinum is 99% or more, the silicon can be 1 ppm or less, so the resistance temperature coefficient is stable, and the platinum-plated product of the present invention has an effect of obtaining a uniform electrical resistance value. Further, the platinum-plated product of the present invention has a low stress, so it has an effect of strong adhesion to the metal substrate. Further, the platinum-plated product of the present invention is a high-purity platinum electrolytic deposit, so it can be used for ornaments such as bracelets and earrings.

Brief Description of the Drawings

[0047] [Fig. 1] FIG. 1 is a diagram for explaining the principle of the platinum plating bath of the present invention. [Fig. 2] FIG. 2 is a scanning electron micrograph of the platinum electrolytic deposit of the present invention.

Embodiments for Carrying Out the Invention

[0048] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments and can be arbitrarily modified and implemented. In the platinum electrolytic plating bath of the present invention, the divalent platinum (II) preferably uses a basic solution obtained by dissolving p-salt in hot concentrated sulfuric acid solution or hot concentrated sulfamic acid solution. The concentration of platinum (when using two or more kinds of platinum salts in combination, the total content) is preferably 1 to 20 g / L as the platinum (Pt) content, and more preferably 2.5 to 15 g / L.

[0049] When the platinum concentration is less than 1 g / L, the deposition rate may be slow, but the presence of metal salts can alleviate the delay in the deposition rate. Also, when observed visually, abnormal deposition such as burns and unevenness may be recognized in the plating film. On the other hand, even when the platinum concentration exceeds 20 g / L, the effect of platinum electrolytic plating hardly changes. Therefore, when the concentration of platinum (II) ions exceeds 20 g / L, the base metal cost increases. When the platinum concentration is within the range of 2.5 to 15 g / L, continuous plating can be stably performed.

[0050] In the platinum electrolytic plating bath of the present invention, free sulfuric acid or sulfamic acid, when two or more kinds are used in combination, the total content is preferably 30 to 600 g / L, and more preferably 50 to 400 g / L.

[0051] When the total content of free sulfuric acid or sulfamic acid is less than 30 g / L, depending on the content of other auxiliary conductive salts, etc., abnormal deposition such as burns and unevenness may be recognized in the plating film. On the other hand, when the total content of free sulfuric acid or sulfamic acid exceeds 600 g / L, due to the evaporation loss of moisture during the plating operation, the concentration of free sulfate becomes too high, risking disrupting the balance of the platinum electrolytic plating solution.

[0052] In the platinum electrolytic plating bath of the present invention, it is preferable to contain an anionic surfactant at 5 to 500 mg / L. The anionic surfactant acts on the platinum electrolytic deposit in a small amount to make the crystal grains amorphous. Also, since the anionic surfactant is difficult to evaporate from the platinum electrolytic plating bath, it stably acts on the platinum electrolytic deposit in the platinum electrolytic plating bath for a long time. The use of the anionic surfactant is not limited to one kind, and two or more kinds can also be used in combination.

[0053] When the content of the anionic surfactant is less than 5 mg / L, the stress of the platinum electrolytic deposit becomes high, and the effect of improving corrosion resistance cannot often be exerted. The lower limit of the total amount of the anionic surfactant is preferably 20 mg / L, and more preferably 50 mg / L. When a salt of an alkali metal or an alkaline earth metal is included, 50 mg / L can be lowered to less than 15 mg / L. When a salt of an alkali metal or an alkaline earth metal is included, 5 mg / L can be lowered to less than 3 mg / L. On the other hand, when the content of the anionic surfactant exceeds 500 mg / L, abnormal precipitation such as burning and unevenness is often observed in the plating film when visually observed. The upper limit is preferably 300 mg / L, and more preferably 200 mg / L.

[0054] Known auxiliary conductive salts can be used in the platinum electrolytic plating bath of the present invention. The auxiliary conductive salt of the present invention may overlap with the above-described metal salt. Specific examples of the auxiliary conductive salt include sulfates, nitrates, sulfites, acetates, carbonates, and the like. These are not limited to the use of one kind, and two or more kinds can be used in combination. Among the auxiliary conductive salts, it is particularly preferable to contain a magnesium salt.

[0055] In addition, well-known additives such as a pH buffer can be used in the platinum electrolytic plating bath of the present invention. The pH buffer is not particularly limited as long as it is a known pH buffer. Preferred examples include inorganic salts such as potassium hydroxide, sodium hydroxide, magnesium hydroxide, and calcium hydroxide, or acetic acid, boric acid, tetraboric acid, citric acid, malic acid, succinic acid, malonic acid, maleic acid, fumaric acid, glycine, or compounds thereof (potassium salt, sodium salt, ammonium salt, etc.). These pH buffers can be added in a concentration range of 0.1 to 100 g / L.

[0056] Furthermore, functional additives such as a complexing agent, a bath stabilizer, a rate adjuster, a leveling agent, a crystal adjuster, a stress relaxant, and a physical property improver may be included as necessary. However, functional additives that prevent the platinum electrolytic deposit from maintaining a high purity of 99% or more and functional additives that deteriorate the porosity are excluded.

[0057] The temperature of the platinum electrolytic plating bath according to the present invention can be appropriately determined according to the ambient environment of the plating operation. Preferably, it is in the range of 30 to 90°C, more preferably in the range of 35 to 70°C, and even more preferably in the range of 40 to 60°C. The higher the bath temperature, the faster the deposition rate of the platinum electrolytic deposit, but the evaporation amount of the plating solution increases. It can be appropriately determined according to the metal substrate used and the application of the platinum product.

[0058] The cathodic current density of the platinum electrolytic plating bath according to the present invention has a wide range of applications, and an optimal current density can be selected according to conditions such as the plating area of the metal substrate, the selection of dipping / spray plating equipment, and the flow rate of the plating solution.

[0059] The platinum electrolytic plating bath of the present invention is applied to a metal substrate. The metal substrate is not limited as long as platinum electroplating of the present invention can be performed on its surface. The metal or alloy is appropriately selected for the metal substrate according to its application. In the applications of electrical and electronic components such as connectors, usually, in addition to copper metal and copper alloys, metals such as iron, nickel, chromium, and their alloys are used. Furthermore, electroless plating or electroplating with nickel, palladium, gold, etc. can also be used for the metal substrate.

[0060] In addition, refractory metals such as titanium and tantalum are used for the electrodes. For applications such as jewelry and ornaments, metals such as stainless steel, nickel, silver alloy, and gold alloy are used. Also, the thick platinum electrolytic deposit can be used for ornaments and figurines.

[0061] Since the platinum electrodeposit of the present invention has low internal stress, thick plating with a thickness of 10 μm or more can be achieved. Further, the platinum electrodeposit of the present invention has low internal stress and shows no warping or curling after being peeled off from the metal substrate. Further, the platinum electrodeposit of the present invention is dense and shows no cracks or pinholes. Further, the platinum electrodeposit of the present invention was subjected to a porosity test, which is a kind of sweat resistance test as shown in the examples. This is because it is difficult to evaluate the difference in corrosion even when an artificial sweat test (JIS B7285) or an accelerated corrosion test (JIS H 8502) is performed. Further, the platinum electrodeposit of the present invention has low internal stress and shows no warping or curling after being peeled off from the metal substrate.

[0062] In the platinum plating product of the present invention, it is preferable that it has a two-layer structure of a metal substrate and a platinum electrodeposit. This is because expensive platinum ingots can be saved. As described above, the metal substrate is appropriately selected depending on the application. The metal substrate may be a single metal or a laminated metal. The single metal and the laminated metal include metals coated with plastics, ceramics, etc.

[0063] The platinum plating product with a thin plating film of the present invention is more preferably a connector. The platinum electrodeposit of the present invention is in an amorphous state, has a low porosity, a high hardness, and corrosion resistance. Therefore, it does not corrode even when the surface of the thin platinum electrodeposit is touched with bare hands. The porosity is preferably 25% or less, more preferably 20% or less, although it also depends on the film thickness of the plating film.

[0064] Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples as long as the gist thereof is not exceeded. (Examples) (Example 1)

[0065] The platinum stock solution of Example 1 is a sulfuric acid solution containing 11 g / L of DNS as platinum. Sulfuric acid and sulfamic acid were added to this platinum stock solution in equal amounts, totaling 160 g / L, to form a basic bath. Sodium lauryl sulfate (manufactured by Kao Corporation, "Emal (registered trademark of the company) 0") was added to this basic bath at 60 mg / L as an anionic surfactant, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 2)

[0066] The platinum stock solution of Example 2 is a sulfamic acid solution containing 15 g / L of p-salt as platinum. 70 g / L of sulfuric acid was added to this platinum stock solution to form a basic bath. Sodium dodecylbenzenesulfonate (manufactured by Kao Corporation, "Neoperex (registered trademark of the company) G-15") was added to this basic bath at 70 mg / L, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 3)

[0067] The platinum stock solution of Example 3 is a sulfamic acid solution containing 17 g / L of DNS as platinum. Sulfuric acid and sulfamic acid were added to this platinum stock solution in equal amounts, totaling 150 g / L, to form a basic bath. Sodium N-lauroylsarcosinate (purity 95.5% or higher) was added to this basic bath at 180 mg / L, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 4)

[0068] The platinum stock solution of Example 4 is a mixed solution of sulfuric acid and sulfamic acid containing 16 g / L of DNS as platinum. 60 g / L of sulfamic acid was added to this platinum stock solution to form a basic bath. Alkyl allyl sulfonate·alkyl ammonium salt (manufactured by Kao Corporation, "Biscotop (registered trademark of the company) 200LS-2") was added to this basic bath at 400 mg / L, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 5)

[0069] The platinum stock solution of Example 5 is a mixed solution of sulfuric acid and sulfamic acid containing 5 g / L of DNS as platinum. 80 g / L of sulfuric acid was added to this platinum stock solution to form a basic bath. 10 mg / L of ammonium lauryl sulfate (“Emal (the company's registered trademark) AD-25R” manufactured by Kao Corporation) and 15 g / L of magnesium sulfate were added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 6)

[0070] The platinum stock solution of Example 6 is a sulfamic acid solution containing 3 g / L of DNS as platinum. 180 g / L of sulfamic acid was added to this platinum stock solution to form a basic bath. 90 mg / L of sodium stearate was added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 7)

[0071] The platinum stock solution of Example 7 is a sulfuric acid solution containing 13 g / L of p-salt as platinum. 110 g / L of sulfamic acid was added to this platinum stock solution to form a basic bath. 160 mg / L of sodium linear alkylbenzene sulfonate (“Newrex (the company's registered trademark) Soft Type 30” manufactured by NOF Corporation) was added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 8)

[0072] The platinum stock solution of Example 8 is a mixed solution of sulfuric acid and sulfamic acid containing 1 g / L of DNS as platinum. A total of 80 g / L of sulfuric acid and sulfamic acid were added in equal amounts to this platinum stock solution to form a basic bath. 500 mg / L of ammonium lauryl sulfate (“Emal (the company's registered trademark) AD-25R” manufactured by Kao Corporation) was added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 9)

[0073] The platinum stock solution of Example 9 is a sulfamic acid solution containing 18 g / L of p-salt as platinum. 190 g / L of sulfamic acid was added to this platinum stock solution to obtain a basic bath. 140 mg / L of potassium lauryl sulfate manufactured by Tokyo Chemical Industry Co., Ltd. and 6 g / L of magnesium sulfate were added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 10)

[0074] The platinum stock solution of Example 10 is a sulfuric acid solution containing 8 g / L of DNS as platinum. 130 g / L of sulfuric acid was added to this platinum stock solution to obtain a basic bath. 200 mg / L of sodium linear alkylbenzene sulfonate (“Neogen (registered trademark of the company) AS-20” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 2 g / L of magnesium sulfate were added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 11)

[0075] The platinum stock solution of Example 11 is a mixed solution of sulfuric acid and sulfamic acid containing 14 g / L of p-salt as platinum. 200 g / L of sulfuric acid was added to this platinum stock solution to obtain a basic bath. 300 mg / L of sodium stearate and 4 g / L of calcium sulfate were added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 12)

[0076] The platinum stock solution of Example 12 is a mixed solution of sulfuric acid and sulfamic acid containing 6 g / L of DNS as platinum. A total of 140 g / L of sulfuric acid and sulfamic acid were added to this platinum stock solution in equal amounts to obtain a basic bath. 80 mg / L of “sodium 1-octadecanesulfonate” manufactured by Tokyo Chemical Industry Co., Ltd. and 20 g / L of magnesium sulfate were added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath. (Example 13)

[0077] The platinum stock solution of Example 13 is a sulfamic acid solution containing 7 g / L of DNS as platinum. 120 g / L of sulfuric acid was added to this platinum stock solution to form a basic bath. 5 mg / L of "dimethylsodium 5-sulfoisophthalate" manufactured by Tokyo Chemical Industry Co., Ltd. and 1 g / L of sodium sulfate were added to this basic bath, and the pH was adjusted to 0.4 to obtain a platinum electrolytic plating bath.

[0078] For the platinum electrolytic plating baths of Examples 1 to 13 above, p-salt or DNS was dissolved in a sulfuric acid solution or a sulfamic acid solution to prepare a platinum concentrate containing a divalent platinum complex. Then, a sulfuric acid solution, a sulfamic acid solution, or a mixed solution thereof was added to this platinum concentrate to form a basic bath of platinum. And, a predetermined surfactant was added to this basic bath to obtain the platinum electrolytic plating baths of Examples 1 to 13. Also, common metal sulfates as metal salts were added to the platinum electrolytic plating baths of Examples 8 to 13.

[0079] The compositions of the platinum electrolytic plating baths of these Examples 1 to 13 are excerpted and shown in Table 1. Note that silicon as an impurity is 0.1 ppm or less in any of the platinum electrolytic plating baths.

[0080]

Table 1

[0081] For the metal substrates to be electroplated, the same copper test piece (a thin sheet of 20 mm × 40 mm × 0.1 mm thickness with a lead wire welded thereto) was used. This test piece was pretreated by degreasing and pickling. Then, using the platinum electrolytic plating baths of Examples 1 to 13, a current was passed through the pretreated test piece at a bath temperature of 55°C, and platinum electrolytic plating was directly performed on this test piece from each platinum electrolytic plating bath.

[0082] In this way, platinum electrolytic deposits were deposited to a thickness of 0.8 μm from the platinum electrolytic plating baths of Examples 1 to 13. The purity of platinum in the platinum electrolytic deposits of Examples 1 to 13 was all 99%, and all of these platinum electrolytic deposits had luster. Furthermore, the porosity of the platinum electrolytic deposits of Examples 1 to 13 was measured, and the hardness and internal stress were also measured. The results are shown in Table 2.

[0083]

Table 2

[0084] Here, the porosity test is a test adopted because the platinum electrolytic deposit does not corrode in a normal corrosion test. In this porosity test, a low voltage of 0.74 V was applied to a 5% sulfuric acid electrolyte at 50 °C, and the test article was used as the anode for electrolysis for 20 minutes. The area of copper ions exposed on the platinum electrolytic deposit was measured with the current value of the rectifier, and the ratio of the copper area to the entire platinum electrolytic deposit was shown as a percentage and taken as the porosity. That is, a porosity of 100% means that the entire surface of the platinum electrolytic deposit is covered with copper.

[0085] As is clear from the above test results, the platinum electrolytic deposits of Test Articles 01 to 13 of the present invention have luster despite being as thin as 0.8 μm in film thickness. Also, the platinum electrolytic deposits of Test Articles 01 to 13 of the present invention are hard with a Vickers hardness of 450 to 480 Hv, and the porosity is also in the range of 8.5 to 13.5%, indicating excellent sweat resistance. Moreover, the purity of platinum is 99% in all cases. Also, it can be seen that the internal stress of Test Articles 01 to 13 of the present invention is in the range of 20 to 80 Mpa, which is extremely low.

[0086] When comparing the stress of the platinum electrolytic deposit of Product 09 and Product 02 of the present invention, the former is 20 Mpa, while the latter is 70 Mpa. Also, when comparing the stress of the platinum electrolytic deposit of Product 10 and Product 01 of the present invention, the former is 20 Mpa, while the latter is 40 Mpa. That is, regardless of the type of platinum compound, it can be seen that the stress of the platinum electrolytic deposit obtained from the plating bath containing the metal sulfate is lower than that from the plating bath not containing the metal sulfate. Moreover, when comparing the effectiveness of the platinum electrolytic deposit of Product 09 and Product 02 of the present invention, the former is 9.5%, while the latter is 10.5%. It can be seen that due to the effect of the magnesium salt, the numerical value of the effectiveness of the platinum electrolytic deposit becomes lower and the sweat resistance becomes higher.

[0087] On the other hand, a scanning electron micrograph of a platinum electrolytic deposit of 4 μm deposited from the platinum electrolytic plating bath of Example 1 is shown in FIG. 2 as shown in FIG. 2 As is clear from the photograph of FIG.

[0088] The platinum stock solution of Example 14 is a sulfuric acid solution containing 4 g / L of Q-salt as platinum. Sulfuric acid was added to this platinum stock solution at 70 g / L to form a basic bath. To this basic bath, 250 mg / L of N-lauroyl-N-methyl-β-alanine ("Alanon ALA" manufactured by Kawaken Fine Chemical Co., Ltd.) was added as an anionic surfactant, 5 g / L of magnesium sulfate was added, and the pH was adjusted to 0.5 to obtain a platinum electrolytic plating bath. (Example 15)

[0089] The platinum stock solution of Example 15 is a sulfuric acid solution containing 8 g / L of Q salt as platinum. 70 g / L of sulfamic acid was added to this platinum stock solution to obtain a basic bath. 70 mg / L of polycarboxylate (Carboxyl L-400 manufactured by Sanyo Chemical Industries, Ltd.) as an anionic surfactant was added to this basic bath, and the pH was adjusted to 1.5 to obtain a platinum electrolytic plating bath. (Example 16)

[0090] The platinum stock solution of Example 16 is a sulfuric acid solution containing 10 g / L of Q salt as platinum. 50 g / L of sulfamic acid was added to this platinum stock solution to obtain a basic bath. 100 mg / L of sodium dialkyl sulfosuccinate (Perlex OT-P manufactured by Kao Corporation) as an anionic surfactant was added to this basic bath, and the pH was adjusted to 1.5 to obtain a platinum electrolytic plating bath.

[0091] The compositions of the platinum electrolytic plating baths of Examples 14 to 16 are extracted and shown in Table 3. Note that silicon as an impurity is 0.1 ppm or less in any of the platinum electrolytic plating baths.

[0092]

Table 3

[0093] In the same manner as in Example 1, the same copper test piece (a thin plate of 20 mm × 40 mm × 0.1 mm thickness with a lead wire welded thereto) was used, and 0.8 μm of platinum electrolytic deposit was deposited. The purity of platinum in the platinum electrolytic deposits of Examples 14 to 16 was all 99%, and all of these platinum electrolytic deposits had luster. Further, the porosity of the platinum electrolytic deposits of Examples 14 to 16 was measured, and the hardness and internal stress were measured together.

[0094] The porosity, hardness, and internal stress of Example 14 were 11.5%, 470 Hv, and 40 Mpa, respectively. Also, the porosity, hardness, and internal stress of Example 15 were 13.8%, 465 Hv, and 80 Mpa, respectively. Also, the porosity, hardness, and internal stress of Example 16 were 10.2%, 480 Hv, and 20 Mpa, respectively. The results are shown in Table 4.

[0095]

Table 4

[0096] Comparative Example 1 was a platinum electrolytic plating bath that contained 11 g / L of DNS as platinum, and a total of 160 g / L of sulfuric acid and sulfamic acid added in equal amounts, prepared in the same manner as Example 1 except that it did not contain an anionic surfactant. (Comparative Example 2)

[0097] Comparative Example 2 was a platinum electrolytic plating bath prepared by adding 5 g / L of tetraamineplatinum(II) hydrogen phosphate (5 g / L as platinum) and 5 g / L of disodium hydrogen phosphate dihydrate, and adjusting the pH to 10.5 with a sodium hydroxide solution. (Comparative Example 3)

[0098] Comparative Example 3 was a platinum electrolytic plating bath identical to Example 1 except that 600 mg / L of sodium lauryl sulfate (manufactured by Kao Corporation, "Emal (registered trademark of the company) 0") was added.

[0099] In the same manner as in Example 1, the same copper test piece (a thin sheet of 20 mm × 40 mm × 0.1 mm thickness with a lead wire welded thereto) was used, and 0.8 μm of platinum electrolytic deposit was deposited. The purity of platinum in the platinum electrolytic deposits of Comparative Products 01 to 03 was all 99%, and all of these platinum electrolytic deposits had luster. Further, the porosity of the platinum electrolytic deposits of Comparative Products 01 to 03 was measured, and the hardness and internal stress were also measured.

[0100] The porosity, hardness, and internal stress of Comparative Product 01 were 30.6%, 400 Hv, and 450 Mpa, respectively. Also, the porosity, hardness, and internal stress of Comparative Product 02 were 35.1%, 420 Hv, and 550 Mpa, respectively. Also, the porosity, hardness, and internal stress of Comparative Product 03 were 33.5%, 410 Hv, and 510 Mpa, respectively. The results are shown in Table 3.

[0101] As is clear from the above test results, the platinum electrodeposits of the products 14 to 15 of the present invention have luster despite the fact that the film thickness is as thin as 0.8 μm. Further, it can be seen that the platinum electrodeposits of the products 14 to 15 of the present invention are hard with a Vickers hardness of 400 to 500 Hv, the porosity is also in the range of 10 to 15%, and the sweat resistance is excellent. Moreover, the purity of platinum is 99% in each case. Also, it can be seen that the internal stress of the products 14 to 16 of the present invention is in the range of 10 to 100 Mpa and is extremely low.

[0102] On the other hand, it can be seen that the platinum electroplating bath of the comparative product 01 has an extremely high porosity of 30%. Also, it can be seen that the platinum electroplating bath of the comparative product 02 also has a high porosity of 35%. Also, it can be seen that the platinum electroplating bath of the comparative product 03 also has a high porosity of 34%. Also, it was found that the internal stress of the platinum electrodeposits of the comparative products 01 to 03 is extremely high. On the other hand, a Hull cell test was conducted on the platinum electroplating bath of Comparative Example 3 and the platinum electroplating bath of Example 1. When the amorphous plated region of the Hull cell test piece was observed, the platinum electroplating bath of Comparative Example 3 was about 50% inferior on the high current density side compared to the platinum electroplating bath of Example 1.

[0103] As described above, it can be seen that the platinum electroplating bath of the present invention has excellent porosity and corrosion resistance despite being able to obtain a high-purity platinum film. Also, since the platinum-plated product of the present invention is dense, has low stress, and has luster, it can be applied to a wide range of uses such as electrical components such as connectors and printed circuit boards, seawater electrolysis electrodes, insoluble anodes for electroplating, and jewelry.

Claims

1. An acidic platinum plating bath comprising a divalent platinum (II) complex and one or both of the following free acids: (a) free sulfuric acid, (b) free sulfamic acid, containing 5 to 500 mg / L of an anionic surfactant, and further characterized in that silicon as an impurity is 1 ppm or less.

2. An acidic platinum plating bath comprising a divalent platinum (II) complex and one or both of the following free acids: (a) free sulfuric acid, (b) free sulfamic acid, containing 5 to 500 mg / L of an anionic surfactant and one or both of the following metal salts: (c) a metal salt of an alkaline earth metal, (d) a metal salt of an alkali metal, and further characterized in that silicon as an impurity is 1 ppm or less.

3. The platinum electrolytic plating bath according to Claim 1 or Claim 2, wherein the pH of the platinum electrolytic plating bath is 2 or less.

4. The platinum electrolytic plating bath according to Claim 1 or Claim 2, wherein the divalent platinum (II) complex has at least one ligand selected from nitro group (NO2), nitrate group (NO3), sulfate group (SO4), sulfonate group (SO3), ammine group (NH3), aquo group (H2O), or hydroxyl group (OH).

5. The platinum electrolytic plating bath according to Claim 1 or Claim 2, wherein the anionic surfactant is at least one compound selected from stearic acid or its salt, sulfonic acid or its salt, sulfamic acid or its salt, or sulfuric acid or its salt.

6. The platinum electrolytic plating bath according to Claim 1 or Claim 2, wherein the anionic surfactant is at least one compound selected from alkyl sulfuric acid or its salt, or alkyl benzene sulfonic acid or its salt.

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