Method for manufacturing substrate with thin silver film, substrate with thin silver film, and method for manufacturing thin silver film

Abstract

To provide a production method of a substrate with a thin silver film capable of forming a thin silver film in a shorter time than conventionally done; a substrate with a thin silver film having better binding property with a substrate and corrosion resistance than conventional ones; and a production method of a thin silver film capable of formation in a short time.SOLUTION: A production method of a substrate with a thin silver film includes, in this order, a pretreatment step of pretreating powdery silver oxide, a mixing step of mixing the pretreated silver oxide with a reducer to form a mixture, an application step of applying the mixture onto a substrate, and a heating step of heating, at a first heating temperature, the substrate with the mixture applied thereon. The pretreatment step adopts a method that immerses the silver oxide into a pretreatment solvent having a boiling point lower than the first heating temperature.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for producing a substrate with a thin silver film, a substrate with a thin silver film, and a method for producing a thin silver film layer. [Background technology]

[0002] Conventionally, a vacuum deposition method has been used as a method for forming a thin silver layer (for example, Patent Document 1). Generally, when a thin silver film layer is formed using a vacuum deposition apparatus, silver from the deposition source is evaporated into a gaseous state in an evaporation chamber or film-forming chamber, and the gaseous silver is deposited on the surface of a glass substrate from a nozzle facing the substrate in the film-forming chamber, thereby forming a thin silver film layer on the substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-180351 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a thin silver film layer is formed by using a vacuum deposition method, the pressure inside the film formation chamber must be reduced to a vacuum state every time the substrate is replaced, which results in a problem that film formation takes a long time. Furthermore, the thin silver layer formed by the vacuum deposition method has a problem in that it easily peels off from the substrate due to its poor adhesion to the substrate and its low strength. Furthermore, the thin silver layer formed by the vacuum deposition method is easily oxidized by light and heat, and is prone to corrosion and discoloration.

[0005] Therefore, an object of the present invention is to provide a method for producing a substrate with a thin silver film, which enables a thin silver film to be formed in a shorter time than conventional methods, a substrate with a thin silver film that is superior in adhesion to a substrate and corrosion resistance to conventional methods, and a method for producing a thin silver film that enables a thin silver film to be formed in a shorter time than conventional methods. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors conceived that by mixing silver oxide with a reducing agent, heating the mixture, and directly reducing the silver oxide to silver, it would be possible to form a film in a shorter time than by vacuum deposition methods, and the density of the silver thin film layer would be improved, thereby improving the film strength. As a result of extensive research by the present inventors into methods for reducing silver oxide, they discovered that by subjecting silver oxide to a specific pretreatment, the rate of the reduction reaction can be increased compared to when silver oxide is simply mixed with a reducing agent and heated.

[0007] One aspect of the present invention derived from the above discovery is a method for producing a substrate with a thin silver film, which comprises, in this order, a pretreatment step of pretreating powdered silver oxide, a mixing step of mixing the pretreated silver oxide with a reducing agent to form a mixture, a coating step of coating the mixture onto the substrate, and a heating step of heating the substrate to which the mixture has been coated at a first heating temperature, wherein in the pretreatment step, the silver oxide is exposed to a pretreatment solvent having a boiling point lower than the first heating temperature.

[0008] According to this aspect, a thin silver film layer is formed by mixing silver oxide and a reducing agent and heating the resulting mixture, thereby reducing the silver oxide. This makes it possible to form a thin silver film layer more easily and without the need for complicated equipment, as compared to forming a thin silver film layer by a vacuum deposition method. According to this aspect, in the pretreatment step, the silver oxide is exposed to a pretreatment solvent whose boiling point is lower than the first heating temperature. Therefore, compared to the case where the pretreatment step is not performed, a thin silver film can be formed in a shorter time, and solvent residue is less likely to remain during the heating step.

[0009] In a preferred aspect, the pretreatment step includes an immersion step of immersing the silver oxide in the pretreatment solvent, and a removal step of removing a part or all of the pretreatment solvent.

[0010] According to this aspect, even if the viscosity of the pretreatment solvent is low or the pretreatment solvent separates from the reducing agent, the pretreatment solvent is removed, so that the presence of the pretreatment solvent is less likely to interfere with the application of the mixture to the substrate, making it easier to apply the mixture to the substrate.

[0011] In a preferred aspect, the pretreatment solvent is a volatile organic solvent.

[0012] According to this aspect, the pretreatment solvent can be removed even at room temperature, and the reaction time can be further shortened.

[0013] In a preferred aspect, the pretreatment solvent is at least one solvent selected from the group consisting of acetone, toluene, ethanol, acetonitrile, and water.

[0014] According to this aspect, residues of the pretreatment solvent are less likely to remain in the heating step.

[0015] In a preferred aspect, the reducing agent is a hindered amine light stabilizer.

[0016] According to this aspect, it is possible to provide the thin silver film with a greater surface corrosion suppression effect than in the past.

[0017] In a preferred aspect, the reducing agent includes a hindered amine compound having two or more of at least one of 1,2,2,6,6-pentaalkylpiperidinyl groups and 2,2,6,6-tetraalkylpiperidinyl groups and having a molecular weight of 700 or less.

[0018] According to this aspect, a thin silver layer can be formed at a lower temperature than in the past.

[0019] Here, the decomposition temperature of ordinary silver oxide is said to be about 200°C, and it is known that silver oxide does not decompose easily at temperatures below 200°C.

[0020] Therefore, in a more preferred aspect, the first heating temperature is less than 200°C.

[0021] According to this aspect, a thin silver layer can be formed at a temperature lower than the decomposition temperature of ordinary silver oxide.

[0022] In a preferred aspect, in the heating step, the silver oxide is reduced by the reducing agent to form the silver thin film layer on the substrate, and the surface of the silver thin film layer is further covered with a protective layer formed from a component derived from the reducing agent.

[0023] The "components derived from the reducing agent" referred to here include not only reaction products generated when silver oxide is reduced by the reducing agent, but also unreacted components of the reducing agent.

[0024] According to this aspect, during the heating process, residues of the reducing agent bleed out on the surface of the thin silver film layer, forming a protective layer containing components derived from the reducing agent that covers the thin silver film layer. This reinforces the strength of the layer, making it less likely to peel off from the substrate.

[0025] One aspect of the present invention is a substrate with a thin silver film, comprising a substrate having a thin silver film layer and a protective layer on the substrate, the protective layer having a cross-sectional structure covering a surface of the thin silver film layer, and the protective layer containing a compound having at least one of a 2,2,6,6-tetraalkylpiperidinyl group and a 1,2,2,6,6-pentaalkylpiperidinyl group.

[0026] According to this aspect, since the surface of the silver thin film layer is covered with the protective layer, the strength of the layer is reinforced, and the silver thin film layer is less likely to peel off from the substrate. According to this aspect, the surface of the silver thin film layer is covered with a protective layer containing a compound having a 2,2,6,6-tetraalkylpiperidinyl group or a 1,2,2,6,6-pentaalkylpiperidinyl group, thereby providing a surface corrosion inhibition effect and superior corrosion resistance compared to when the silver thin film layer is exposed.

[0027] In a preferred aspect, the thin silver film layer further comprises silver particles having an average particle size larger than the average film thickness of the thin silver film layer.

[0028] In a preferred aspect, the average thickness of the silver thin film layer is 500 nm or less.

[0029] According to this aspect, it is easy to use for wiring and the like.

[0030] One aspect of the present invention is a method for producing a thin silver film layer formed on a surface to be coated, the method comprising: a pretreatment step of pretreating powdered silver oxide; a mixing step of mixing the pretreated silver oxide with a reducing agent to form a mixture; a coating step of coating the mixture on the surface to be coated; and a heating step of heating the mixture coated on the surface to be coated at a first heating temperature, wherein in the pretreatment step, the silver oxide is exposed to a pretreatment solvent having a boiling point lower than the first heating temperature.

[0031] According to this aspect, the silver oxide is reduced by mixing silver oxide with a reducing agent and heating the resulting mixture. This makes it easier to form the silver thin film layer than by forming a thin silver film layer by vacuum deposition, without requiring complex equipment. According to this aspect, in the pretreatment step, the silver oxide is exposed to a pretreatment solvent having a boiling point lower than the first heating temperature, so that the silver oxide can be formed in a short time and solvent residue is less likely to remain in the heating step. Effect of the Invention

[0032] According to the method for producing a substrate with a thin silver film of the present invention, a thin silver film can be formed in a shorter time than in the past. The substrate with a thin silver film of the present invention has superior corrosion resistance compared to conventional substrates. According to the method for producing a thin silver layer of the present invention, the layer can be formed in a shorter time than in the past. [Brief description of the drawings]

[0033] [Figure 1] FIG. 1 is a perspective view of a substrate with a thin silver film according to a first embodiment of the present invention. [Diagram 2] 2 is an explanatory diagram of the substrate with a thin silver film in FIG. 1, where (a) is a cross-sectional view taken along line AA in FIG. 1, and (b) is a cross-sectional view taken along line BB in FIG. [Diagram 3]1 shows the results of SEM observation of Experimental Example 1, where (a) is an SEM image of Experimental Example 1 and (b) is a traced drawing of (a). [Figure 4] 1 is a graph of resistance and temperature versus reaction time for Experimental Examples 1, 3, and 4. [Diagram 5] 1 shows the results of STEM observation of Experimental Example 5, where (a) is a transmission electron image of Experimental Example 1, and (b) is a trace of (a). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] Hereinafter, an embodiment of the present invention will be described in detail.

[0035] The substrate 1 with a thin silver film according to the first embodiment of the present invention is suitable for use as a reflective film for organic EL displays, liquid crystal displays and the like, conductive materials such as wiring and electrodes, decorative materials, recording materials, antibacterial materials and the like. As shown in FIG. 1, the substrate 1 with a thin silver film has a thin silver layer 3 laminated on a substrate 2, and a silver particle layer 5 is locally formed. Furthermore, as shown in FIG. 2 , the substrate 1 with a thin silver film has a cross-sectional structure in which a protective layer 6 covers the surface of the thin silver film layer 3, and the protective layer 6 extends from the surface of the thin silver film layer 3 to the surface of the silver particle layer 5 laminated on the thin silver film layer 3, and covers the surfaces of the silver particles 10 that constitute the silver particle layer 5.

[0036] The substrate 2 is a supporting substrate that extends in a planar shape and supports the silver thin film layer 3 as shown in FIG. The substrate 2 is in the form of a plate or film, and has a first main surface (a surface on which a film is to be formed) and a second main surface. The substrate 2 is not particularly limited, and may be an insulating substrate such as a glass substrate or a polyimide film, or a conductive substrate such as a metal substrate or a metal film made of copper or the like.

[0037] The silver thin film layer 3 is a thin film layer made of silver. The average thickness of the silver thin film layer 3 is 1 μm or less, and from the viewpoint of ensuring sufficient electrical conductivity, it is preferably 50 nm or more and 500 nm or less, and more preferably 150 nm or more and 300 nm or less. The average film thickness of the thin silver film layer 3 can be determined, for example, by observing a cross-section of the thin silver film layer 3 with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and calculating the arithmetic average value at any three points.

[0038] The silver particle layer 5 is a particle deposition layer in which silver particles 10 are deposited. In the silver particle layer 5, the silver particles 10 undergo crystal growth in a direction intersecting with the substrate 2, and the silver particles 10 are three-dimensionally stacked. The average particle size of the silver particles 10 constituting the silver particle layer 5 is larger than the average film thickness of the thin silver layer 3, and is preferably 10 μm or less. The average particle size refers to the number average particle size of secondary particles formed by agglomeration of primary particles, and refers to the primary particles when secondary particles formed by agglomeration of primary particles do not exist. The average particle size of the silver particles 10 can be calculated, for example, by observing the particles in an SEM image or a TEM image and calculating the arithmetic average of the particle sizes of any 10 or more silver particles that appear in the SEM image or the TEM image. The particle size of the silver particles refers to the diameter of the smallest encompassing circle that encompasses the silver particles 10 in the SEM image or the TEM image.

[0039] The protective layer 6 is a layer that has light stability and heat stability and protects the silver thin film layer 3 . The protective layer 6 in this embodiment is a layer derived from the reducing agent used to form the thin silver layer 3 in the method for producing the substrate 1 with a thin silver film, which will be described later, and is composed of a product of the reducing agent reacting with an oxidizing agent or unreacted reducing agent. The protective layer 6 of this embodiment contains a compound having at least one of a 2,2,6,6-tetraalkylpiperidinyl group and a 1,2,2,6,6-pentaalkylpiperidinyl group. The number of 1,2,2,6,6-pentaalkylpiperidinyl groups and 2,2,6,6-tetraalkylpiperidinyl groups in this compound is not particularly limited. In addition, the number of carbon atoms in the alkyl group in the 1,2,2,6,6-pentaalkylpiperidinyl group and the 2,2,6,6-tetraalkylpiperidinyl group constituting this compound is preferably 1 to 4, each independently.

[0040] The average thickness of the protective layer 6 is preferably 1 nm or more and 20 nm or less. The average film thickness of the protective layer 6 can be obtained, for example, by observing a cross section of the protective layer 6 with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and calculating the arithmetic average value at any three points.

[0041] Next, a method for producing the substrate 1 with a thin silver film of this embodiment will be described.

[0042] First, a pretreatment step is carried out in which silver oxide is pretreated with a pretreatment solvent. The pretreatment step is carried out by carrying out an immersion step and a removal step in this order. In the immersion process, powdered silver oxide and a pretreatment solvent are placed in a sealed container, and the silver oxide is immersed in the pretreatment solvent and stirred.

[0043] At this time, the maximum particle size of the silver oxide introduced into the closed vessel is preferably 0.5 μm or more and 10 μm or less. The maximum particle size of silver oxide can be determined by sieving it through a sieve with known openings to exclude particles larger than the opening size. The pretreatment solvent is not particularly limited as long as it has a boiling point lower than the first heating temperature in the heating step described below. By using a pretreatment solvent having a boiling point lower than the first heating temperature, even if the pretreatment solvent cannot be sufficiently removed in the removal step, it can be vaporized in the heating step, and the solvent is less likely to remain in the thin silver film layer 3. The pretreatment solvent may be, for example, at least one solvent selected from the group consisting of acetone, toluene, ethanol, acetonitrile, and water. The pretreatment solvent preferably has a boiling point of 50°C or higher and 120°C or lower. In addition, the pretreatment solvent is preferably volatile at room temperature. By using an organic solvent that is volatile at room temperature, it is possible to dry the pretreatment solvent by natural drying in the removal step described below.

[0044] Next, most of the pretreatment solvent is separated and removed from the silver oxide immersed in the pretreatment solvent in the sealed container (removal step). In this embodiment, the pretreatment solvent is removed by one or more decantation steps, and then the pretreatment solvent is substantially removed by drying in a dryer at a predetermined drying temperature.

[0045] The drying temperature at this time is not particularly limited as long as it is a temperature at which the pretreatment solvent volatilizes, but is preferably 100° C. or lower from the viewpoint of suppressing aggregation of silver oxide.

[0046] When the pretreatment step is performed and the pretreatment of the silver oxide is completed, the pretreated silver oxide is mixed with a reducing agent to form a mixture (mixing step).

[0047] In this case, the reducing agent is an amine-based reducing agent, and is preferably a hindered amine-based light stabilizer having at least one of a 1,2,2,6,6-pentaalkylpiperidinyl group and a 2,2,6,6-tetraalkylpiperidinyl group, and more preferably an N-CH3-type or NH-type hindered amine-based light stabilizer. As the N-CH3 type hindered amine light stabilizer, Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate or the like can be used. Examples of the NH-type hindered amine light stabilizer that can be used include Tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate, Tetrakis(2,2,6,6-tetramethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate, and Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate. From another viewpoint, the reducing agent preferably contains a hindered amine compound having two or more of at least one of 2,2,6,6-tetraalkylpiperidinyl groups and 1,2,2,6,6-pentaalkylpiperidinyl groups and having a molecular weight of 700 or less. In this hindered amine compound, the carbon at the 4-position of the piperidine ring of the 1,2,2,6,6-pentaalkylpiperidinyl group or 2,2,6,6-tetraalkylpiperidinyl group preferably forms an ester bond with a carboxylic acid. The number of 1,2,2,6,6-pentaalkylpiperidinyl groups and 2,2,6,6-tetraalkylpiperidinyl groups in this hindered amine compound is not particularly limited. In addition, it is preferable that the alkyl groups in the 1,2,2,6,6-pentaalkylpiperidinyl group and the 2,2,6,6-tetraalkylpiperidinyl group each independently have 1 to 4 carbon atoms. The reducing agent may be solid or liquid at room temperature, but it preferably has a melting point lower than the first heating temperature in the heating step described below. If the melting point of these amine compounds is lower than the first heating temperature, when the reducing agent is heated together with silver oxide in the heating step described below, even if the reducing agent is solid, the reducing agent melts and becomes liquid before the first heating temperature is reached, so that the contact area with the silver oxide is increased and the reduction of the silver oxide can be performed efficiently. In this embodiment, the reducing agent contains an amine compound having the following structural formula (1).

[0048] [ka]

[0049] In the above structural formula (1), R 1 and R 2 each independently represents a hydrogen atom or a methyl group, and p is a positive integer of 1 or more and 18 or less.

[0050] Subsequently, the mixture obtained through the mixing step is applied to a desired area on the first main surface of the substrate 2 (application step).

[0051] The coating method is not particularly limited, and examples thereof include casting, roll coating, bar coating, die coating, spin coating, spray coating, and dip coating.

[0052] Subsequently, the substrate 2 on which the mixture has been applied is placed in a heating device and heated at a first heating temperature, and the silver oxide is reduced with a reducing agent to form a thin silver layer 3 on the substrate 2 (heating step).

[0053] The first heating temperature in this case is not particularly limited as long as it is a temperature at which the reaction between the silver oxide and the reducing agent proceeds, but from the viewpoint of reducing the silver oxide in a short period of time, it is preferably 100°C or higher and lower than 200°C, and more preferably 120°C or higher and 180°C or lower.

[0054] The substrate 2 on which the thin silver layer 3 has been formed is washed with a washing solvent (washing step).

[0055] The cleaning solvent used in this case is not particularly limited as long as it does not substantially react with silver, and for example, a volatile organic solvent such as acetone can be used.

[0056] According to the method for manufacturing the substrate 1 with a thin silver film of this embodiment, silver oxide is mixed with a reducing agent and then heated to reduce the silver oxide to form the thin silver film layer 3. Therefore, compared to the case of forming a thin silver film layer by a vacuum deposition method, the apparatus is not complicated and the thin silver film layer 3 can be formed easily. According to the manufacturing method of the substrate 1 with a thin silver film of this embodiment, in the pretreatment step, the silver oxide is immersed in a pretreatment solvent whose boiling point is lower than the first heating temperature. Therefore, compared to the case where the pretreatment step is not performed, the thin silver film layer 3 can be formed in a short time and solvent residue is less likely to remain in the heating step.

[0057] According to the manufacturing method of the substrate 1 with a thin silver film of the present embodiment, the pretreatment step includes an immersion step of immersing the silver oxide in a pretreatment solvent, and a removal step of removing a part or all of the pretreatment solvent. Therefore, even if the viscosity of the pretreatment solvent is low or the pretreatment solvent separates from the reducing agent, the pretreatment solvent is removed, so that the presence of the pretreatment solvent is unlikely to interfere with the application of the mixture to the substrate 2, and the mixture can be easily applied to the substrate 2.

[0058] In the substrate 1 with a thin silver film of this embodiment, the surface of the thin silver film layer 3 is covered with a protective layer 6, which reinforces the strength of the layer and improves the adhesion to the substrate 2, making the thin silver film layer 3 less likely to peel off from the substrate 2. In the substrate 1 with a thin silver film of this embodiment, the surface of the thin silver film layer 3 is covered with the protective layer 6 containing a compound having a 2,2,6,6-tetraalkylpiperidinyl group or a 1,2,2,6,6-pentaalkylpiperidinyl group, and therefore has a surface corrosion-inhibiting effect against heat and light and is excellent in corrosion resistance, compared to a case in which the thin silver film layer 3 is exposed.

[0059] In the above-described embodiment, a plate-like or film-like body is used as the substrate 2, and the silver thin film layer 3 is formed on the first main surface of the substrate 2, but the present invention is not limited to this. The silver thin film layer 3 may be formed on a surface to be coated, such as the surface of a housing for a personal computer or the like.

[0060] In the above embodiment, the silver thin film layer 3 is formed on the first main surface of the substrate 2, but the present invention is not limited to this. The silver thin film layer 3 may be formed on both sides of the substrate 2. That is, the silver thin film layer 3 may be formed on both the first and second main surfaces of the substrate 2.

[0061] In the above embodiment, most of the pretreatment solvent is removed by decantation in the removal step, and then the pretreatment solvent is substantially removed by drying with a dryer, but the present invention is not limited to this. The method for removing the pretreatment solvent is not particularly limited. For example, if the pretreatment solvent is a volatile solvent, it may be removed by only drying with a dryer, or it may be removed by volatilizing it in the air or in a vacuum chamber at room temperature.

[0062] In the above embodiment, the silver oxide is exposed to the pretreatment solvent by immersing the silver oxide in the pretreatment solvent and stirring it, but the present invention is not limited to this, and the method of exposing the silver oxide to the pretreatment solvent is not particularly limited. For example, the silver oxide may be exposed to the pretreatment solvent by spraying the pretreatment solvent onto the silver oxide.

[0063] In the above-described embodiments, each component may be freely substituted or added between the respective embodiments as long as it falls within the technical scope of the present invention. EXAMPLES

[0064] The present invention will be specifically described below with reference to various experimental examples as examples, but the present invention is not limited to these experimental examples.

[0065] (Experimental Example 1) In Experimental Example 1, as a pretreatment step, toluene (Wako Co., Ltd., ultra-dehydrated) and silver oxide powder (Fujifilm Wako Pure Chemical Industries, Ltd., silver oxide special grade, maximum particle size 10 μm) were placed in a sealed container and stirred. Thereafter, decantation was performed three times to extract the toluene, and then the silver oxide was dried at 100° C. in a dryer to volatilize and substantially remove the toluene. Next, 100 parts by weight of silver oxide from which the toluene had been removed and 100 parts by mass of liquid bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (ADEKA CORPORATION, Adeka STAB LA-72) were mixed to obtain a paste-like mixture. The mixture obtained was applied to an area of ​​5 cm x 5 cm on a glass substrate and held at 150° C. for 60 minutes. The surface of the mixture on the substrate was then washed with acetone to obtain a silver film adhered to the substrate. The substrate with the thin silver film thus obtained was used as Experimental Example 1.

[0066] (Experimental Example 2) Experimental Example 2 was conducted in the same manner as in Experimental Example 1, except that solid bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (ADEKA CORPORATION, Adeka STAB LA-77Y, melting point 82° C. to 87° C.) was used as the reducing agent.

[0067] (SEM observation) The cross-sections of the substrates with the thin silver film of Experimental Examples 1 and 2 were subjected to SEM observation using a field emission scanning electron microscope (FE-SEM) (JSM6700F, manufactured by JEOL Ltd.).

[0068] FIG. 3(a) shows an SEM image in Experimental Example 1, and FIG. 3(b) shows a trace of the SEM image in FIG. 3(a). In Experimental Example 1, as shown in FIG. 3, a uniform thin silver layer of about 220 nm to 280 nm was confirmed, and a silver particle layer in which silver particles of about several μm were locally deposited was also confirmed. Similarly, in Experimental Example 2, SEM observation was performed, and a thin silver film layer was confirmed, as well as a silver particle layer in which silver particles of about several μm were locally deposited. These results confirm that the use of an N-CH3 type hindered amine light stabilizer or an NH type hindered amine light stabilizer as a reducing agent makes it possible to reduce silver oxide on a glass substrate and form a nano-order thin silver layer. In addition, a silver particle layer consisting of localized accumulations of silver particles of several μm in size was confirmed, suggesting that silver oxide particles larger than a certain particle size do not melt and become a thin silver layer, but are reduced to silver while maintaining their shape, causing crystal growth.

[0069] (Experimental Example 3) This was designated as Experimental Example 3, and was conducted in the same manner as in Experimental Example 1, except that distilled water was used as the pretreatment solvent.

[0070] (Experimental Example 4) This was used as Experimental Example 4 in the same manner as Experimental Example 1, except that the pretreatment step was not carried out.

[0071] (Reaction time test) In Experimental Examples 1, 3, and 4, the temperature change and resistance change during the heating process were measured, and the reaction time from the start of heating and the change in the resistance value were observed. The resistance change was measured using a Mitsubishi Chemical Analytech Loresta GP (MCP-T610) with a four-terminal four-needle method.

[0072] The results of the reaction time test are shown in FIG. In Experimental Example 1, the resistance value became nearly 0 after a reaction time of about 1090 seconds, suggesting that the silver oxide decomposed and a thin silver film layer was formed, as shown in Figure 4. Also, in Experimental Example 1, it was suggested that a thin silver film layer was formed at the stage when the heating temperature rose to about 143°C. In Experimental Example 3, the resistance value became nearly 0 after a reaction time of about 1680 seconds, suggesting that the silver oxide had decomposed and a thin silver layer had been formed. In Experimental Example 4, the resistance value became nearly 0 after a reaction time of about 1760 seconds, suggesting that the silver oxide had decomposed and a thin silver layer had been formed. In Experimental Example 1, in which pretreatment was performed with an organic solvent, the time until the silver thin film layer was formed was shortened by approximately 38% compared to Experimental Example 4, in which pretreatment was not performed, and in Experimental Example 3, in which pretreatment was performed with water, the time until the silver thin film layer was formed was shortened by approximately 5% compared to Experimental Example 4, in which pretreatment was not performed. In addition, in Experimental Example 1, in which pretreatment was performed with an organic solvent, the time required for the formation of a thin silver layer was shortened by approximately 35% compared to Experimental Example 3, in which pretreatment was performed with water. From these findings, it was found that by immersing silver oxide in a pretreatment solvent, impurities on the surface of the silver oxide are removed, the time when silver particles start to grow is brought forward compared to when the silver oxide is not pretreated, and the overall speed at which the silver thin film layer is formed is improved. In particular, it was found that the speed at which the silver thin film layer is formed is dramatically improved by using an organic solvent as the pretreatment solvent. It was also suggested that the use of an organic solvent as a pretreatment solvent would enable the formation of a thin silver layer at a lower heating temperature.

[0073] (Experimental Example 5) Experimental Example 5 was conducted in the same manner as in Experimental Example 1, except that a copper substrate was used as the base material instead of the glass substrate.

[0074] (STEM observation) Cross-sections were processed using a focused ion beam (FIB), and the cross-sections were observed using a scanning transmission electron microscope (STEM) (Hitachi High-Technologies Corporation, HD-2700) and analyzed by energy dispersive X-ray analysis (EDX).

[0075] FIG. 5(a) shows a transmission electron image (hereinafter also referred to as a TE image) by STEM in Experimental Example 5, and FIG. 5(b) shows a trace of the TE image of FIG. 5(a). In Experimental Example 5, when a high-magnification TE image was observed as in Figure 5, a silver-copper alloy layer was confirmed between the copper substrate and the silver thin film layer, and a protective layer of several nm to several tens of nm originating from the reducing agent was confirmed on the surface of the silver thin film layer. In addition, a light element layer was confirmed between the alloy layer and the silver thin film layer. Elemental analysis by EDX was performed at measurement points 1 to 3 shown in Fig. 5(b), and a silver peak was detected at measurement point 2, which corresponds to the position of the silver thin film layer, but no nitrogen peak was detected, whereas not only a silver peak but also carbon and nitrogen peaks were detected at measurement point 1, which corresponds to the position of the protective layer. Moreover, at measurement point 3, which corresponds to the alloy layer, silver and copper peaks were detected but no nitrogen peak was detected. Since a nitrogen peak and a carbon peak were detected in the results of measurement point 1, it was presumed that heating caused the reducing agent residue to bleed out on the surface of the thin silver film layer, forming a protective layer containing 1,2,2,6,6-pentaalkylpiperidinyl groups derived from the reducing agent on the thin silver film layer.

[0076] (Experimental Example 6) Vacuum degree 1×10 -4 Silver was evaporated onto the glass substrate at a deposition rate of about 0.1 to 0.3 nm / sec under reduced pressure of 0.1 Pa or more to form a thin silver layer. The substrate with the thin silver film thus obtained was used as Experimental Example 6.

[0077] (Corrosion resistance test) Experimental Examples 1 and 6 were heated in air at 190° C. for 1 hour, and the changes before and after were confirmed.

[0078] Discoloration was observed at the edge in Experimental Example 6, whereas no discoloration was observed in Experimental Example 1. From this, it is considered that in Experimental Example 1, surface corrosion was suppressed due to the presence of a protective layer having 1,2,2,6,6-pentaalkylpiperidinyl groups derived from the reducing agent. In addition, when the substrate with the thin silver film of Experimental Example 6 was scraped with a fingernail, the thin silver film was easily peeled off from the glass substrate, whereas when the substrate with the thin silver film of Experimental Example 1 was scraped with a fingernail with the same amount of force, the thin silver film did not peel off from the glass substrate. From this, it is considered that the presence of the protective layer improved the adhesion between the silver thin film layer and the glass substrate and also improved the layer strength of the silver thin film layer.

[0079] To summarise the above, the results are as follows: (1) From the results of SEM observation, it was found that by using an N-CH3-type hindered amine light stabilizer having a 1,2,2,6,6-pentaalkylpiperidinyl group or an NH-type hindered amine light stabilizer having a 2,2,6,6-tetraalkylpiperidinyl group as a reducing agent, it is possible to reduce silver oxide on a glass substrate and form a nano-order silver thin film layer. (2) The results of the reaction time test showed that the reaction time for forming the silver thin film layer was shortened by performing pretreatment with a pretreatment solvent before the heating step. In particular, it was found that the reaction time was significantly shortened by using an organic solvent as the pretreatment solvent. (3) The results of STEM observation confirmed that the use of a hindered amine light stabilizer as a reducing agent can reduce silver oxide on a glass substrate to form a thin silver film layer, and also that a protective layer is formed on the surface of the thin silver film layer. The results of EDX analysis suggested that the protective layer on the surface of the thin silver film layer is derived from the reducing agent. (4) The results of the corrosion resistance test showed that the use of a hindered amine light stabilizer as a reducing agent formed a silver thin film that was more corrosion resistant than a silver thin film layer formed by vacuum deposition. [Explanation of symbols]

[0080] 1. Substrate with thin silver film 2 Base material 3. Silver thin film layer 5 Silver particle layer 6 Protective layer 10 Silver particles

Claims

1. A method for producing a substrate with a thin silver film, comprising the steps of: forming a thin silver film layer on a substrate, A pretreatment step of pretreating powdered silver oxide; mixing the pretreated silver oxide with a reducing agent to form a mixture; a coating step of coating the mixture onto the substrate; a heating step of heating the base material coated with the mixture at a first heating temperature, The reducing agent is a hindered amine light stabilizer, The pretreatment step includes a soaking step of soaking the silver oxide in a pretreatment solvent, the pretreatment solvent being an organic solvent having a boiling point lower than the first heating temperature, and a removal step of removing a part or all of the pretreatment solvent, In the heating step, the silver oxide is reduced by the reducing agent to form the thin silver film layer on the substrate, and the surface of the thin silver film layer is further covered with a protective layer formed from a component derived from the reducing agent.

2. The method for producing a substrate having a thin silver film according to claim 1 , wherein the pretreatment solvent is a volatile organic solvent.

3. 3. The method for producing a substrate having a thin silver film according to claim 1, wherein the pretreatment solvent is at least one solvent selected from the group consisting of acetone, toluene, ethanol, and acetonitrile.

4. The method for producing a substrate with a thin silver film according to any one of claims 1 to 3, wherein the reducing agent contains a hindered amine compound having two or more of at least one of a 1,2,2,6,6-pentaalkylpiperidinyl group and a 2,2,6,6-tetraalkylpiperidinyl group and having a molecular weight of 700 or less.

5. The method for producing a substrate with a thin silver film according to any one of claims 1 to 4, wherein the first heating temperature is less than 200°C.

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