JP2019065338A - Surface treatment method - Google Patents

Abstract

To provide: a simple surface treatment method capable of preventing silver from changing color; and a silver surface treatment method capable of, when a topcoat layer is disposed on a surface of silver, realizing high adhesion between the silver and the topcoat layer while preventing the silver from changing color.SOLUTION: The surface of the silver is treated with a treatment liquid containing a compound represented by the general formula (1) in the figure or a salt thereof.SELECTED DRAWING: None

Description

  The present invention relates to a surface treatment method for preventing silver discoloration.

  Silver is widely used in various fields such as electronic materials and lighting equipment as well as design materials due to its excellent optical properties and electrochemical properties.

  However, since silver forms sulfides and oxides on the surface when it is left in the air, and turns yellow, brown or black, its prevention is a major issue. In addition, such discoloration of silver is accelerated by ultraviolet light and moisture, which causes a further problem when used outdoors.

  From such background, many methods have been proposed to prevent the color change of silver. As one of them, a method of treating the surface of silver with a compound that inactivates silver is known. As a compound which inactivates silver, a compound having a mercapto group is known, and for example, aliphatic mercaptan is used in Japanese Patent Application Laid-Open Nos. 04-110474 (patent document 1) and 05-78866. There is disclosed a method of preventing corrosion or discoloration of silver by Further, in JP-A-09-249977 (Patent Document 2) and JP-A-2015-172214 (Patent Document 3), a specific mercaptobenzothiazole compound or a specific mercapto compound as a compound for inactivating silver is disclosed. A method is disclosed that uses a triazine compound to prevent the color change of silver.

  In these methods, although the effect of suppressing the discoloration of silver due to sulfurization is observed, the effect is not sufficiently satisfactory. In particular, the resistance to ultraviolet light is insufficient and further improvement is required.

  Japanese Patent Application Laid-Open Nos. 05-311492, 09-249991 (Patent Document 4), 2011-241409, etc. disclose a method of electrolytic treatment in the presence of a compound that inactivates silver. There is. Since it is believed that this method makes it possible to cause the silver surface to be more strongly affected by a compound that inactivates silver, it is considered that the color change preventing effect is also higher. However, there is a need for a simpler and more complicated process.

  In addition, in JP-A-2004-169157 (Patent Document 5), JP-A-2011-202239, JP-A-2011-202239, etc., in addition to the above-mentioned compounds that inactivate silver, halogen compounds are disclosed. And a method of causing a silver oxidizing agent to act on the silver surface. Although this method can make silver inactivating compounds more effective, halogen compounds and oxidizing agents may promote discoloration because they cause defects on the silver surface, and control of processing steps There was a problem that was very difficult.

  On the other hand, although chromium plating has been conventionally performed as a method of decorating the surface of a plastic in metal tone, an alternative method has been studied due to environmental problems, and one of them is no surface of a plastic substrate A method of performing electrolytic silver plating has been attempted. In this case, a method of applying a clear coat agent on the electroless silver plating layer to provide a top coat layer is known for the two purposes of preventing silver discoloration and preventing physical damage. For example, JP-A-2000-129448, JP-A-2003-155580, and JP-A-2004-203014 disclose a method of providing a top coat layer on an electroless silver plating layer.

  By providing the top coat layer on the silver surface, the contact between the corrosive substance such as hydrogen sulfide and silver can be prevented, so that the effect of preventing the color change of silver can be obtained. However, it is not easy to prevent the color change of silver over a long period of time, especially in the outdoor use exposed to ultraviolet light by such a method, and the color change prevention of silver is still a major issue. In addition, there is also a problem in that peeling occurs between silver and the top coat layer, and there is also a problem in which the adhesion between the top coat layer and silver is improved.

Unexamined-Japanese-Patent No. 04-110474 Japanese Patent Application Laid-Open No. 09-249977 JP, 2015-172214, A Unexamined-Japanese-Patent No. 09-249991 JP 2004-169157 A

  The first object of the present invention is to provide a simple surface treatment method capable of preventing the color change of silver. A second object of the present invention is to provide a silver surface treatment method capable of preventing the color change of silver and achieving high adhesion between silver and the top coat layer when the top coat layer is provided on the surface of silver. It is to be.

The above object of the present invention is achieved by the invention described below.
(1) A surface treatment method of treating the surface of silver with a treatment liquid containing a compound represented by the following general formula (1) or a salt thereof.

Wherein _R 1, _{R 2,} and _{R 3} represents a linking _group, R 1, _{R 2,} and _{R 3} may be different even in the same, respectively.

  The present invention can provide a simple surface treatment method capable of preventing the color change of silver. Furthermore, when the top coat layer is provided on the surface of silver, it is possible to provide a silver surface treatment method that can prevent the color change of silver and realize high adhesion between silver and the top coat layer.

  The present invention will be described in detail below.

  The surface treatment method of silver of the present invention can be carried out by a treatment liquid containing a compound represented by the following general formula (1) or a salt thereof (hereinafter also described as a treatment liquid of the present invention or a surface treatment liquid). Process

Wherein _R 1, _{R 2,} and _{R 3} represents a linking _group, R 1, _{R 2,} and _{R 3} may be different even in the same, respectively. As R ₁ , R ₂ and R ₃ , an alkylene group or a linking group in which two alkylene groups are linked by an ester group is exemplified. When R ₁ , R ₂ and R ₃ are alkylene groups, the number of carbon atoms of the alkylene group is preferably 4 or more and 7 or less. When R ₁ , R ₂ and R ₃ each represent a linking group in which two alkylene groups are linked by an ester group, the total carbon number of the two alkylene groups is preferably 4 or more and 7 or less. Although the specific example of a compound or its salt represented with General formula (1) used for this invention below is shown, this invention is not limited to this.

  The amount of the compound of the general formula (1) added to the treatment liquid of the present invention is preferably 0.1 mmol or more, more preferably 0.35 mmol or more, per liter of the treatment liquid. When the amount of the compound of the general formula (1) added is large, the effect of preventing discoloration is enhanced, but when the amount is more than a certain level, the effect becomes flatter and the addition efficiency becomes worse. Therefore, it is preferable that it is 10 millimoles or less per liter of processing solution.

  The solvent of the surface treatment liquid containing the above-mentioned compound is not particularly limited, but water or a water-soluble organic solvent or a mixture of water and a water-soluble organic solvent is preferable because the surface treatment process can be simplified. Examples of water-soluble organic solvents include alcohols such as methanol, ethanol and isopropanol, glycols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,3-butylene glycol and hexylene glycol, and the like. Mention may be made of alkyl ethers of glycols such as methyl, ethyl, propyl and butyl.

  When the treatment liquid of the present invention contains water, the pH of the treatment liquid is preferably 5 or more, more preferably in the range of 7 to 11. The treatment solution may also contain a buffer component to keep the pH constant. Examples of pH buffer components include phosphates, carbonates, and alkanolamines such as triethanolamine and diethanolamine.

  The treatment liquid of the present invention preferably contains an antioxidant. Examples of the antioxidant include sulfites, ascorbic acid or salts thereof, isoascorbic acid or salts thereof, benzenesulfinic acid or salts thereof, p-toluenesulfinic acid or salts thereof, and the like.

  The treatment liquid of the present invention may contain an inactivating agent for silver in addition to the compound of the general formula (1). Examples of the deactivator include benzotriazoles such as 1,2,3-benzotriazole and 5-methyl-1,2,3-benzotriazole. Furthermore, if necessary, a chelating agent such as iminotriacetic acid or ethylenediaminetetraacetic acid, an alkali agent such as potassium hydroxide or sodium hydroxide, a surfactant, or a preservative may be contained.

  Examples of the method of treating silver with the surface treatment liquid of the present invention include a method of immersion in the surface treatment liquid, a method of spraying the surface treatment liquid on the surface of silver, and the like. After the treatment, the silver surface is preferably washed with deionized water and dried.

  The surface of silver to be treated according to the present invention is a surface of bulk silver formed by casting or forging, a surface of silver formed by dry plating such as vapor deposition method or sputtering method, or electrolytic plating or electroless plating Any of silver surfaces formed by wet plating such as The elemental composition of the surface may contain a small amount of atoms other than silver. A small amount said here shows 10 mass% or less in general.

  The surface treatment method of the present invention can be applied to the surface treatment of electroless silver plating performed as a design application. In electroless silver plating in design applications, an undercoat layer is usually provided on a substrate, and a silver plating layer is provided thereon by a silver mirror reaction. In addition, although a top coat layer is preferably provided on the silver plating layer, in such a case, the present invention works particularly effectively because high adhesion with the top coat layer is obtained.

  The above-mentioned undercoat layer preferably has high adhesion to silver obtained by electroless silver plating. For example, in addition to the undercoat layers described in JP-A-10-309774 and JP-A-2002-256455, polymers or oligomers having terminal hydroxyl groups such as alkyd polyols, polyester polyols, acrylic polyols, etc., as a curing agent Examples thereof include a urethane-based coating composition in which an isocyanate compound is mixed, and an undercoat layer obtained by applying an epoxy-based coating composition in which an amine compound is mixed with an epoxy resin as a curing agent. These can be appropriately selected and used based on the properties required as a substrate and a coated body.

  When an electroless silver plating layer is formed on the undercoat layer, the surface of the undercoat layer is treated with an activation treatment solution containing tin (II) chloride to support tin (II) ions on the surface of the undercoat layer It is preferable to form an electroless silver plating layer on the activated undercoat layer by silver mirror reaction.

  As a treatment method for treating with an active treatment solution containing tin (II) chloride, a method of immersing the surface of the undercoat layer in the active treatment solution, an activation treatment containing tin (II) chloride etc. on the surface of the undercoat layer There is a method of applying a solution or the like. As a coating method, spray coating which does not choose the shape of the substrate is preferable. Furthermore, it is preferable to wash the activation treatment solution that has been excessively attached to the surface with deionized water.

  After the step of treating with the above-mentioned active treatment solution, it is preferable to provide a step of activating treatment with silver ions. The activation treatment with silver ions can be, for example, treatment with an aqueous solution of silver nitrate. The concentration of the aqueous silver nitrate solution used here is preferably 0.1 mol or less per liter, and this solution is brought into contact with the tin (II) chloride-treated undercoat layer. As the method of this activation treatment, a method of immersing an undercoat layer treated with tin (II) chloride in the above-mentioned treatment solution or a method of spray coating can be mentioned.

  The formation of the electroless silver plating layer may be carried out, for example, on the surface of the undercoat layer which has been subjected to the above-mentioned activation treatment, two solutions of an ammoniacal silver nitrate solution containing silver nitrate and ammonia and a reducing agent solution containing a reducing agent and a strong alkali component. It becomes possible by applying so that it may be mixed. As a result, a redox reaction occurs to precipitate metallic silver, and an electroless silver plating layer is obtained.

  Examples of the reducing agent solution include an aqueous solution containing an aldehyde compound such as glucose and glyoxal, and an aqueous solution containing a hydrazine compound such as hydrazine sulfate, hydrazine carbonate or hydrazine hydrate.

  Several additives can also be added to the ammoniacal silver nitrate aqueous solution in order to form a good silver. For example, monoethanolamine, tris (hydroxymethyl) aminomethane, 2-amino-2-hydroxymethyl-1,3-propanediol, 1-amino-2-propanol, 2-amino-1-propanol, diethanolamine, diisopropanol Examples thereof include amino alcohol compounds such as amines, triethanolamine and triisopropanolamine, and amino acids such as glycine, alanine and glycine sodium or salts thereof, but are not particularly limited.

  As a method of applying the two solutions of the ammoniacal silver nitrate solution and the reducing agent solution so that they are mixed on the surface on which the electroless silver plating layer is to be formed, two aqueous solutions are mixed in advance, and this mixed solution is sprayed Method of spraying on the surface of the undercoat layer using a gun etc. Method of spraying using a concentric spray gun having a structure in which two aqueous solutions are mixed and immediately discharged in the head of the spray gun, Two aqueous solutions are used two There are a method of spraying and discharging each from a double head spray gun having a spray nozzle, a method of spraying two aqueous solutions simultaneously using two separate spray guns, and the like. These can be chosen arbitrarily according to the situation.

  Subsequently, the surface of the electroless silver plating layer is preferably washed with deionized water to remove the solution after the silver mirror reaction remaining on the surface. Thereafter, it is preferable to carry out the surface treatment of the present invention subsequently. After the treatment, the silver surface is preferably washed with deionized water and dried.

  As described above, when the surface treatment method of the present invention is applied to the surface treatment of electroless silver plating, it is preferable to provide a top coat layer on the silver plating layer. The top coat layer used in this case is preferably formed of a coating composition containing a thermosetting resin.

  As the thermosetting resin, for example, liquid epoxy resin, unsaturated polyester resin, fluorine resin, acrylic resin, melamine resin and silicone resin described in JP-A-2000-129448, JP-A-2003-155580 And a two-component curable polyurethane resin or an acrylic-modified silicone resin described in JP-A-2002-256445. Moreover, as a thermosetting resin generally marketed, for example, "PTC-02UH (10B)" (silicon acrylic paint) manufactured by Fujikura Kasei Co., Ltd. or "Originzuk (registered trademark) # 100" manufactured by Origin Electric Co., Ltd. Acrylic silicone based paint), "Polar (registered trademark) No. 800 (N)" (acrylic urethane based paint) manufactured by Ohashi Chemical Industry Co., Ltd., "Omac (registered trademark) No. 100 (E) clear FV" (acrylic) Silicone based paints), "Neohard Clear H" (acrylic melamine based paints), etc. are preferably used.

  The coating composition containing the above-mentioned thermosetting resin may be applied according to a conventionally known application method, for example, gravure roll method, reverse roll method, dip roll method, bar coater method, knife coater method, air Any method such as a spray method, an airless spray method, or a dip method can be used.

  Hereinafter, the present invention will be described using examples, but of course the present invention is not limited by this description. In the following description,% as a unit is on a mass basis unless otherwise specified.

Example 1
The surface of the ABS resin plate is washed with isopropanol and dried, and then an acrylic polyol-based undercoat resin (Raster clear MS for gun plating made by Ohashi Chemical Industry Co., Ltd.) and an isocyanate curing agent (Raster under hardener N for gun plating resin manufactured by Ohashi Chemical Industry) ) And thinner (mixture of methyl ethyl ketone and butyl cellosolve in a ratio of 1: 1) in a mass ratio of 10: 2: 10, respectively, to obtain a coating composition for an undercoat layer. The coating composition was spray-coated using a spray gun and dried by heating at 80 ° C. for 1 hour to form an undercoat layer having a thickness of 20 μm.

  The undercoat layer is sprayed with an activation treatment solution containing 0.1 mol of hydrochloric acid and 0.1 mol of stannous chloride per 1000 g of water with a spray gun to perform activation treatment, and then deionized water is used. Was washed. Subsequently, 0.05 mol of silver nitrate was dissolved in deionized water to make 1000 g, this solution was sprayed with a spray gun to perform activation treatment with silver ions, and then washed with deionized water.

  Next, when forming an electroless plating layer, separately prepare a silver nitrate solution in which 20 g of silver nitrate is dissolved in 1000 g of deionized water, and separately dissolve 100 g of 28% ammonia aqueous solution in 1000 g of deionized water and 5 g of monoethanolamine to adjust the ammonia solution. Liquid. Before use, the silver nitrate solution and the ammonia solution were mixed 1: 1 to obtain an ammoniacal silver nitrate solution. Next, 10 g of hydrazine sulfate, 5 g of monoethanolamine and 10 g of sodium hydroxide were dissolved in 1000 g of deionized water to prepare a reducing agent solution. The ammoniacal silver nitrate solution thus obtained and the reducing agent solution are simultaneously sprayed onto the ABS resin plate after the above activation treatment using a dual-head spray gun to form an electroless plating layer, and deionized water Washed with

  Subsequently, the following surface treatment solutions (1) to (11) are respectively sprayed on the electroless plating layer for 20 seconds with a spray gun and then washed with deionized water to sufficiently remove surface water at 45 ° C. It was made to dry for 30 minutes, and it was set as the silver plating sample. In addition, the sample which did not perform the surface treatment of silver was also produced for the comparison.

<Surface treatment solution (1)>
Potassium hydroxide 2g
Potassium sulfite 2g
Make up to 1 liter with deionized water and adjust the pH to 9.0 with sulfuric acid.

<Surface treatment liquid (2)>
1 g of potassium hydroxide
1 g of potassium sulfite
5 g of triethanolamine
Compound T-1 0.5 mmole deionized water to 1 liter and pH adjusted to 9.0 with sulfuric acid.

<Surface treatment liquid (3)>
The addition amount of compound T-1 in the surface treatment liquid (2) was changed to 0.2 mmol.

<Surface treatment liquid (4)>
The addition amount of compound T-1 in the surface treatment liquid (2) was changed to 1.0 mmol.

<Surface treatment solution (5)>
The addition amount of compound T-1 in the surface treatment liquid (2) was changed to 2.0 mmol.

<Surface treatment solution (6)>
In place of the compound T-1 of the surface treatment liquid (2), 0.5 mmol of a compound T-12 was added.

<Surface treatment solution (7)>
In place of the compound T-1 of the surface treatment liquid (2), 0.5 mmol of a compound T-2 was added.

<Surface treatment solution (8)>
In place of the compound T-1 of the surface treatment liquid (2), 0.5 mmol of a compound T-5 was added.

<Surface treatment solution (9)>
In place of the compound T-1 of the surface treatment liquid (2), 1.0 millimole of 2-mercaptobenzothiazole was added.

<Surface treatment solution (10)>
In place of the compound T-1 of the surface treatment liquid (2), 1.0 millimole of 1,3,5-triazine-2,4,6-trithiol was added.

<Surface treatment solution (11)>
In place of the compound T-1 of the surface treatment liquid (2), 1.0 millimole of 6-butylamino-1,3,5-triazine-2,4-dithiol was added.

  The prepared silver-plated sample is cut into a square of 10 cm on one side, and left outdoors for two months from June to July, using a spectrophotometer CM-2500 d manufactured by Konica Minolta Optics Co., Ltd. The color difference ΔE before and after being left outdoors was measured at 10 points for one sample, and evaluated based on the average value according to the following criteria. The results are shown in Table 1.

(Degree of discoloration)
○: no color change is observed (average ΔE ≦ 1.5).
△; slightly discolored (average value of 1.5 <ΔE ≦ 2.5).
Δ: Discolored (average value of 2.5 <ΔE ≦ 5.0).
X: remarkable discoloration (average value of 5.0 <ΔE).

  As apparent from Table 1, it can be seen that the present invention can prevent the color change of silver.

(Example 2)
For each of the silver plating samples prepared in Example 1, a top coat layer was provided on the electroless plating layer. Acrylic silicone top coat paint (Omak No. 100 (E) clear FV made by Ohashi Chemical Co., Ltd.), silicone hardener (hardener W made by Ohashi Chemical Co., Ltd.), thinner (methyl ethyl ketone and butyl cellsolve in a ratio of 1: 1 The mixture was mixed at a mass ratio of 6: 1: 6 to obtain a top coat paint. The top coat was spray-coated on the electroless plating layer using a spray gun, and then dried by heating at 80 ° C. for 60 minutes to form a top coat layer with a thickness of 15 μm.

The silver plating sample provided with the top coat layer described above was subjected to an irradiation intensity of 60 W / m ² , a black panel temperature of 63 ° C., and a humidity using an accelerated weathering tester (Suga Test Instruments Co., Ltd., xenon weather meter NX25 type) A weathering test is performed for 1500 hours under conditions including 50% RH, an in-tank temperature of 38 ° C., and a rainfall of 12 minutes in 60 minutes, and a color difference before and after the test using a Konica Minolta Optics Co., Ltd. manufactured spectral colorimeter CM-2500d. The ΔE was measured at 10 points for one sample, and based on the average value, the degree of discoloration was evaluated in the same manner as in Example 1.

  Furthermore, in order to evaluate the adhesiveness of an electroless-plating layer and a topcoat layer, the salt spray test was done with respect to the silver plating sample which provided said topcoat layer. That is, the cross was scratched with a cutter so as to reach the ABS substrate from the top coat layer surface. These samples were sprayed with a 5% saline solution at 35 ° C. for 10 days in a salt spray tester (type STP-90) manufactured by Suga Test Co., Ltd. The sample after salt spray is washed with water, dried, strongly pasted the cellophane tape from above the scratched part of the cross, then the tape is peeled off, and it is judged from the peeling condition of the top coat layer based on the following criteria did. The results are shown in Table 2.

○: The width of the widest part of paint peeling is less than 1 mm from the center of the cut line ○ △; The width of the widest part of paint peeling is 1 mm or more and less than 2 mm from the center of the cut line The width of the wide part is 2 mm or more and less than 4 mm from the center of the cut line ×; The width of the widest part of the paint peeling is 4 mm or more from the center of the cut line

  As apparent from Table 2, according to the present invention, in the case where the top coat layer is provided on the surface of silver, it is understood that the color change of silver can be prevented and high adhesion between silver and the top coat layer can be realized.

Claims (1)

The surface treatment method which processes the surface of silver with the process liquid containing the compound or its salt represented by following General formula (1).
(Wherein, R ₁ , R ₂ and R ₃ represent a linking group, and R ₁ , R ₂ and R ₃ may be the same or different)